METEO 3 Lesson 7 Images

Lesson 7: Mid-Latitude Weather Systems

 

Upper-Air Patterns

balloon experiment

Side-by-side images of a bottle with a red balloon, initially deflated and then inflated, in a pot on a stovetop.
balloon experiment
Text description of the balloon experiment image.

The image is split into two sections showing an experiment with a green glass bottle placed in a metal pot on a stovetop. In both sections, the pot is positioned on a coil burner. On the left side, a deflated red balloon is attached to the bottle's neck. The background consists of a stove's control panel with black dials and a striped wall. On the right side, the same setup is shown, but the red balloon is now inflated, standing upright from the bottle's neck. The burner beneath the pot appears to be on and glowing faintly. The stovetop's surface is white, and the control panel is consistent across both sections.

Credit: David Babb @ Penn State is licensed under CC BY-NC 4.0(opens in a new window)

pressure at the same altitude

Diagram showing three columns of air: warmer, standard, and colder, with pressure lines.
pressure at the same altitude
Text description of the pressure at the same altitude image.

The image depicts three vertical columns against a gradient blue background that simulates the sky. Each column is filled with white dots representing air molecules. The left column has a red tint and the dots are spread out, indicating warmer air. The center column is labeled "Standard column" in yellow, with evenly distributed dots. The right column has a blue tint and tightly packed dots, representing colder air. A horizontal black line crosses through all columns, labeled "Pressure less than 500 mb." A yellow dashed line curves through the columns, labeled "500 mb," rising in the warmer column and dipping in the colder column. The bottom of the image features a green band depicting the ground.

Credit: David Babb @ Penn State is licensed under CC BY-NC 4.0(opens in a new window)

map of approximate yearly average pressure near 20,000 feet

World map showing yearly average atmospheric pressure near 20,000 feet, using a purple to red color gradient.
map of approximate yearly average pressure near 20,000 feet
Text description of the map of approximate yearly average pressure near 20,000 feet image.

The image shows a world map displaying yearly average atmospheric pressure near 20,000 feet. The map features geographical outlines of continents on a grid background. Atmospheric pressure variations are represented using a color gradient ranging from purple, indicating lower pressures, to red, indicating higher pressures. The colors transition through blue, green, yellow, and orange. The highest pressure regions are central and extending towards the equator, while lower pressure regions appear towards the poles. Beneath the map is a legend illustrating the pressure gradient from "Lower pressures" with purple to "Higher pressures" with red.

Credit: Earth System Research Laboratory

zoomed-out version of the model analysis of upper-level winds above

Weather map of 300 mb height and wind speeds over North America with contour lines and colors indicating wind speed variations.
zoomed-out version of the model analysis of upper-level winds above
Text description of the zoomed-out version of the model analysis of upper-level winds above image.

The image is a weather map illustrating the 300 mb height and wind speed in knots over North America. It features contour lines and colors indicating varying wind speeds. The contours represent pressure levels, shown by numbers ranging from 852 to 966. The map is overlaid with bright colors: dark red and yellow signify the highest wind speeds, primarily over the Pacific Northwest, while purples and blues cover most of North America. The jet stream is visible, curving from the west coast of the United States, dipping across the central states, and moving northeastward into the Atlantic. The map includes landmass outlines, borders, and coastal lines for geographical reference.

Credit: Pivotal Weather

 

Highs, Lows, and Weight Management

 

 

Cooking Up a Mid-Latitude Cyclone

fronts mark boundaries between contrasting air masses

Weather map with high-pressure systems, cold and warm air masses, and a frontal boundary.
fronts mark boundaries between contrasting air masses
Text description of the fronts mark boundaries between contrasting air masses image.

The image is a weather map divided into two sections. The left section illustrates a large area of the United States, highlighting high-pressure systems using the letter "H". A blue shaded region indicates cooler air, while a red shaded region denotes warmer air. Yellow arrows depict wind patterns moving within these air masses, with a series of red semicircles and blue triangles marking a frontal boundary between them.

The right section is a zoomed-in view of the weather front, showing more detailed wind and pressure patterns. It also includes the notation "Frontal Zone" in a gray curved area, accompanied by red semicircles and blue triangles indicating the front's line.

Credit: David Babb @ Penn State is licensed under CC BY-NC 4.0(opens in a new window)

idealized stationary front

Diagram of cold and warm fronts with arrows showing air movement.
idealized stationary front
Text description of the idealized stationary front image.

The image is a diagram illustrating a weather front. It features a three-dimensional view of a grassy plane transitioning into a cold front and a warm front. The background shows an angled, translucent surface indicating the interface between cold and warm air masses. The cold air, labeled "Cold," is represented by blue arrows pointing toward the warm front. The warm air, labeled "Warm," is represented by red arrows pointing towards the cold front. The cold section is shaded blue, while the warm section is shaded red, symbolizing temperature differences. The ground appears in green, with the edges of the diagram framed in brown.

Credit: National Weather Service

area ahead of the cold front and south of the warm front

Weather surface analysis map of the United States showing pressure systems, fronts, and a labeled warm sector.
area ahead of the cold front and south of the warm front
Text description of the area ahead of the cold front and south of the warm front image.

The image is a weather surface analysis map of the United States, showing various meteorological features. The map is overlaid with isobars, which are thin, red contour lines indicating areas of equal atmospheric pressure. The isobars form circular patterns, particularly prominent in the northeastern region where they surround a low-pressure area marked with an "L" and a central pressure value of 994 mb. Several blue and red fronts are depicted—blue for cold fronts and red for warm fronts. The cold fronts are marked with triangular symbols, while the warm fronts have semicircular markers. Two high-pressure areas are noted, marked with "H" and pressure values like 1025 mb. The words "Warm Sector" are labeled in red to highlight a specific region. These features are dispersed across the map in relation to the geographical distribution of the United States, including key known states.

Credit: Weather Prediction Center

schematic of the occluded stage

Weather diagram showing the occluded stage with cold and warm air fronts and a low-pressure zone.
schematic of the occluded stage
Text description of the schematic of the occluded stage image.

The image depicts a weather diagram illustrating the occluded stage of a front. It features a swirling pattern of arrows overlaid on a color-coded map. On the left, broad purple shading represents the area of occlusion, with dark blue arrows curving inward, suggesting the movement of cold air. A bold red "L" is placed centrally within this area, indicating a low-pressure zone. Adjacent to this, a yellow section on the right signifies warmer air, marked by upward-curving red arrows, indicating rising warm air. A horizontal boundary separates the purple and yellow sections, marked by alternating blue triangles and red semicircles. Above this boundary, blue arrows are labeled as "Retreating stale cool air."

Credit: National Weather Service

as it was earlier in the low's life

Diagram of a cold front with advancing cold air and retreating warm air.
as it was earlier in the low's life
Text description of the as it was earlier in the low's life image.

The image is a meteorological diagram illustrating a cold front. On the left, a mass of blue-colored cold air is shown advancing towards a mass of warm air on the right. The blue area is labeled "Advancing fresh cold air" and features blue arrows pointing right to indicate the movement of the cold air mass. The boundary between the blue and yellow areas is marked by a jagged blue line symbolizing the cold front. To the right, a yellow region represents the warm air mass, with orange arrows curving upwards and to the left, indicating the uplift of this air. A red curved line with semi-circles on top denotes the warm front. Above these sections, a red letter "L" marks the location of the low-pressure system. The background features a gradient blend of blue and yellow hues.

Credit: National Weather Service

dumped more than 30 inches of snow

Map of eastern USA showing snowfall from January 22-24, 2016, with color-coded accumulation levels.
dumped more than 30 inches of snow
Text description of the dumped more than 30 inches of snow image.

The image is a map showing snowfall accumulation from January 22-24, 2016, across the eastern United States. The map is color-coded to indicate different levels of snowfall in inches. Regions with snowfall between 1-4 inches are shaded in light gray, 4-10 inches in light blue, 10-20 inches in blue, 20-30 inches in dark blue, and over 30 inches in red. The most significant snowfall, shown in red, is concentrated in areas of West Virginia, Virginia, Maryland, and Pennsylvania. A legend on the map's right side explains the color scale. The map also includes topographical details like state boundaries and mountain ranges. Text indicates the dates of the snowfall and provides a NESIS (Northeast Snowfall Impact Scale) value of 7.66, indicating a Category 4 event. A NOAA logo is positioned in the bottom right corner.

Credit: NOAA

animation of surface maps spanning the life of the Blizzard of 2016 (0:16)

animation of surface maps spanning the life of the Blizzard of 2016
Text description of the animation of surface maps spanning the life of the Blizzard of 2016 (0:14)

The animation is a weather map showing a surface analysis of the United States on January 21, 2016. It includes various meteorological symbols and data. High-pressure areas are marked with blue "H" symbols, while low-pressure areas are marked with red "L" symbols. Isobars, represented by thin brown lines, curve across the map, indicating areas of equal atmospheric pressure. The map also shows weather fronts: blue lines with triangles signify cold fronts, and red lines with semicircles denote warm fronts. Text annotations highlight specific weather conditions, such as a 1009 mb low labeled as "Baby" in the Southern U.S., regions experiencing much colder temperatures, and areas with temperatures in the 60s and 70s in the southeastern states. Temperature values in various colors and precipitation indicators are scattered across the map.

Credit: Weather Prediction Center

 

Cold Fronts

chain of blue triangles

String of blue triangular flags on a curved line.
chain of blue triangles
Text description of the chain of blue triangles image.

The image is of a cold front on a white background, the front is a series of small, triangular pennant flags strung along a curving blue line. The line resembles a string or a cable, with each of the blue flags hanging downward at intervals along the line. The flags are evenly spaced and all point in the same direction.

Credit: Weather Prediction Center

surface convergence promotes rising currents of air

Diagram with a black dashed arrow pointing upward and two red arrows pointing toward each other beneath a blue sky.
surface convergence promotes rising currents of air
Text description of the surface convergence promotes rising currents of air image.

The image shows a simple diagram against a gradient blue sky transitioning into a green and brown landscape at the bottom. Three white clouds are spaced across the middle of the image. A black dashed arrow points upward from the ground, centered through the middle of the three clouds. Two solid red arrows, also positioned at the bottom, point towards each other horizontally from the left and right sides of the image, converging on the dashed arrow.

Credit: David Babb @ Penn State is licensed under CC BY-NC 4.0(opens in a new window)

Thus, showers and/or thunderstorms often precede the passage of a cold front (0:02)

Thus, showers and/or thunderstorms
Transcript: Thus, showers and/or thunderstorms (0:02)

The animation is a series of satellite images showing cloud cover overlaid with a blue cold front line. The background features a grayscale satellite view of the central United States, with clouds appearing in white and the land in shades of gray. The cold front is represented by a blue line with triangular points, extending from the top right to the bottom left of the image, indicating the boundary between different air masses. The clouds are concentrated along and ahead of the front. State boundaries are faintly visible in black in the background.

Credit: NOAA / David Babb

surface analysis on January 13, 2007

Surface weather map showing pressure systems, fronts, and precipitation areas in the U.S.
surface analysis on January 13, 2007
Text description of the surface analysis on January 13, 2007 image.

The image is an analyzed surface weather map  across a portion of the United States. Isobars are drawn across the map in dark red and labeled every 4 mb between 1024-1036. Prominent elements include areas marked "HIGH" denoting high-pressure regions, located near the Great Lakes and over the western Atlantic and southeast coast. Green shaded areas indicate precipitation. Blue lines with triangles indicate cold fronts, and red lines with semicircles show warm fronts. The background is a light beige with state borders, and water bodies are depicted in cyan.

Credit: Weather Prediction Center

eddies to form

Diagram showing wind speed increasing with height and turbulent eddies near the ground.
eddies to form
Text description of the eddies to form image.

The image illustrates the concept of wind speed increasing with height and the formation of turbulent eddies. The background is a gradient of light blue, representing the sky. On the left side, four white arrows of varying lengths point to the right, stacked vertically. The shortest arrow at the bottom, gradually increasing in length as they ascend, suggests increasing wind speed with height. Annotations next to the arrows read "Wind speed increasing with height." Below these arrows, four red circular arrows, indicating turbulent eddies, are displayed in a horizontal line. The grass-green band at the bottom represents the ground. The text "Turbulent Eddies" is written in red above the circular arrows.

Credit: David Babb @ Penn State is licensed under CC BY-NC 4.0(opens in a new window)

 

Warm Fronts and Stationary Fronts

chain of red semicircle

Five red circles on a curved red arc against a white background.
chain of red semicircle
Text description of the chain of red semicircle image.

The image features a simple design of a warm front with five red semicircles arranged along a red arc. The semicircles are evenly spaced along the line and the line curves slightly in the middle, creating a smooth, arch pattern.

Credit: Weather Prediction Center

a chain of alternating blue triangles and red semicircles

Graphic of red semi-circles and blue triangles on a wavy red line.
a chain of alternating blue triangles and red semicircles
Text description of the a chain of alternating blue triangles and red semicircles image.

The image depicts a simple graphic of a stationary front with red semi-circles and blue triangles. The graphic is composed of a wavy red and blue line with two red semi-circles positioned on the peaks. Below this line are two blue triangles located in the troughs, pointing downward. The stationary front is drawn on a plain white background.

Credit: Weather Prediction Center

typically become warm fronts

Two panels showing cross-sectional views of cold and warm air interactions.
typically become warm fronts
Text description of the typically become warm fronts image.

The image is divided into two side-by-side panels depicting meteorological phenomena involving air masses and how fronts develop around a low. Both panels illustrate interactions between cold and warm air.

On the left panel, an angled 3D cross-section shows a green ground surface with a blue-tinted overlay representing a cold air mass and an orange-tinted overlay for a warm air mass. Blue arrows indicate cold air moving towards the warm region, while red arrows show warm air interacting above the cold layer.

The right panel also displays a similar cross-section, with the cold air depicted in blue pushing into the warm air zone, creating an upward red arrow pattern representing warm air rising. The cold air seems to undercut the warm air, pushing it upwards.

Credit: National Weather Service

forced up the incline created by the cold-air wedge

Diagram of air movement over a frontal zone, showing a sloped warm front with labeled measurements.
forced up the incline created by the cold-air wedge
Text description of the forced up the incline created by the cold-air wedge image.

The image is an illustrative cross-section showing the movement of air along a surface warm front. The bottom of the image is a green band labeled "Surface warm front", with an arrow pointing upward toward a  thin purple line labeled "frontal zone". Above the frontal zone, a pink shaded region captioned "Air glides up the frontal zone" follows a black dotted arrow along the slope of the purple area. A horizontal distance of "300 km" is marked beneath the slope, alongside a vertical measurement of "1 km," indicating the height. The slope is described as "Slope = 1/300," which is positioned within the blue area, depicting the colder air ahead of the warm front.

Credit: David Babb @ Penn State is licensed under CC BY-NC 4.0(opens in a new window)

cirrostratus

Silhouette of a tall rectangular structure against a cloudy blue sky with sunlight creating a halo effect.
cirrostratus
Text description of the cirrostratus image.

The image portrays a silhouette of a tall, rectangular structure prominently displayed on the left side of the image, against a backdrop of a sky filled with thin, wispy clouds. The sky has a gradient of blue hues, gradually lightening toward the horizon, and thin clouds stretch horizontally across the frame. The sun is positioned behind the structure, creating a bright halo effect and casting the structure into shadow.

Credit: David Babb @ Penn State is licensed under CC BY-NC 4.0(opens in a new window)

22-degree halo

Silhouette of a basketball hoop against the sky with a sun halo and wispy clouds.
22-degree halo
Text description of the 22-degree halo image.

The image features a silhouette of a basketball hoop centered in the lower half, with a distinct halo effect encircling the bright sun behind it. The sky is filled with thin, wispy clouds, and the halo appears as a faint, semi-circular rainbow. Leafless trees occupy the lower edges, stretching up towards the sky and framing the silhouette of the hoop.

Credit: David Babb @ Penn State is licensed under CC BY-NC 4.0(opens in a new window)

altostratus

Overcast sky with a bright sun above a suburban landscape.
altostratus
Text description of the altostratus image.

The image shows an overcast sky with the sun obscured by clouds, appearing fainter, situated in the upper part of the image. Below, a suburban landscape is visible, populated with a mix of residential and commercial buildings. The buildings are primarily low-rise with varied roofing styles and colors, set among sparse greenery. In the distance, a range of low hills or mountains can be seen, providing a faint backdrop to the scene.

Credit: David Babb @ Penn State is licensed under CC BY-NC 4.0(opens in a new window)

surface analysis on April 25, 2010

Surface weather analysis map of the U.S. showing fronts and pressure systems on April 25, 2010.
surface analysis on April 25, 2010
Text description of the surface analysis on April 25, 2010 image.

The image is a surface analysis weather map of the United States. Isobars, lines of constant pressure, are drawn in dark red and labeled every 4 millibars between 984 - 1020. A low-pressure system is prominently located over western Illinois, with concentric isobars indicating decreasing pressure towards the center, labeled as 984 within the lowest circle. Blue lines with triangles indicate cold fronts, while red lines with semicircles represent warm fronts. A mix of blue and red symbols on lines marks stationary fronts, and a purple occluded front is analyzed near the main area of low pressure. Areas of high and low pressure are denoted by blue "H" and red "L" respectively, situated across various regions. The weather map includes time and date details, with additional data and annotations along the bottom and sides.

Credit: Weather Prediction Center

upper-level disturbance creates strong divergence aloft

Illustration of a cumulonimbus cloud with divergence and airflow indicators.
upper-level disturbance creates strong divergence aloft
Text description of the upper-level disturbance creates strong divergence aloft image.

The image depicts a cross-section of a thunderstorm system against a pink and blue gradient sky. At the center, there is a towering white cumulonimbus cloud extending upwards from a base of flatter, spread-out clouds. Above the cloud, in the pink sky area, there is an oval shape labeled "Strong Divergence" with arrows pointing left and right, indicating the outward flow of air. A thick red arrow runs vertically through the cumulonimbus cloud, and another red arrow extends diagonally from the left side of the cloud, pointing up and to the right. Below the clouds, the foreground shows a green horizontal band representing the ground. Blue shaded regions directly below the cloud base indicate areas of rainfall, small lightning bolts can also be see underneath the clouds.

Credit: David Babb @ Penn State is licensed under CC BY-NC 4.0(opens in a new window)

 

Conveyor Belts

cloud structure of an infant low often resembles a leaf on a tree

Satellite image of a weather system with vibrant colors indicating cloud patterns and intensities.
cloud structure of an infant low often resembles a leaf on a tree
Text description of the cloud structure of an infant low often resembles a leaf on a tree image.

The image is a satellite view of a weather system captured from above. It displays a region of cloud cover in various colors indicative of different temperatures. In the center, there is a prominent area of turquoise blue, surrounded by irregular patterns of bright magenta, red, and yellow, indicating the presence and intensity of clouds. The background consists of a gradient of gray, representing the Earth's surface or ocean beneath the clouds. The upper portion of the image has a black space indicating the edge of the visible atmosphere and space. Portions of the Pacific northwest coast are outlined in pink.

Credit: NOAA

Short Video Mid-Latittude Cyclone Conveyor Belts

Mid-Latittude Cyclone Conveyor Belts (3:00)
Transcript of the Mid-Latittude Cyclone Conveyor Belts video

Let’s use this schematic to get a feel for the spatial orientation of the conveyor belts associated with a mature mid-latitude low-pressure system. The warm conveyor belt is marked in orange. The cold conveyor belt is marked in blue, and the dry conveyor belt is marked in yellow. They’ve been drawn over this satellite image of a mature mid-latitude cyclone. There surface fronts are drawn in, too, so you can get your bearings.

Let’s start with the warm conveyor belt, which transports warm, moist air northward through the warm sector. The warm conveyor belt gradually rises during its northward trek, and notably overruns the cold air north of the warm front, which creates stratiform clouds and precipitation. The western edge of the warm conveyor belt gets drawn a bit westward by the upper-level disturbance that helps spur the low-pressure system, but as it rises to altitudes near 30,000 feet, it usually encounters high-altitude winds from the west, and, in response, turns eastward.

Next, let’s look at the cold conveyor belt, here in blue. The cold conveyor belt is responsible for the westward transport of cool, moist air north of the warm front and back into the cold air west of the low. The cold conveyor belt actually travels under the warm conveyor belt north of a low’s warm front, much like traffic moving under an overpass. As the cold conveyor travels under the warm conveyor belt, it gains some moisture as precipitation evaporates into its westward moving stream of cold air.

The increasingly moist cold conveyor belt starts to rise as it enters the general pattern of strong upward motion around the periphery of the low’s center. This strong ascent continues until the cold conveyor belt reaches the northwest flank of the low, where it often contributes to a swath of heavy precipitation. After reaching the northwest flank of a mature low, the cold conveyor splits into two tributaries. One branch turns clockwise and then heads eastward, while the other branch turns cyclonically as it heads southward, creating the clouds in the comma head of the mature low.

Finally, we have the dry conveyor belt, marked here in yellow. The dry conveyor belt is formed by dry air near the tropopause sinking west of the low’s center It starts to wrap counterclockwise around the low’s periphery, helping to scour out clouds and create the dry slot, west of the cold front, which puts the finishing touches on the overall comma shape of the mass of clouds associated with mature mid-latitude cyclone.

Credit: @ Penn State is licensed under CC BY-NC 4.0(opens in a new window)

resemble the shape of a comma on satellite

Infrared satellite weather map of the United States with a black curved line highlighting a weather system.
resemble the shape of a comma on satellite
Text description of the resemble the shape of a comma on satellite image.

The image is a colorful infrared satellite weather map showing a large part of the United States. It displays states in various colors indicating different temperatures of cloud tops or the surface. A comma shaped cloud pattern with cooler colors, such as blue and green, is visible over the north central United States, indicating clouds and an area of low pressure. The warmer colors, orange and red, cover the southern and some eastern parts, indicating the warmer temperatures of shallower clouds or even the surface. A prominent black curved line is drawn across the map, starting in the northern central U.S. and curving southeastward, highlighting the comma shape of this low pressure system. State borders and geographic outlines are visible in white beneath the color overlay.

Credit: NCAR

radar imagery

Radar map of the U.S. showing a significant weather front from southwest to northeast in the central region.
radar imagery
Text description of the radar imagery image.

The image is a radar map of the United States, showing composite radar reflectivity across the country. The map highlights precipitation using various colors, ranging from green to red, indicating intensity. A large, curved band of intense reflectivity values stretch from Arkansas to Indiana and north into Michigan and Wisconsin, suggesting a significant frontal passage. Lighter areas of precipitation are visible sporadically in the northwestern and eastern United States. A color scale on the right side shows levels from 10 to 70. The image is framed with state boundaries and major roadways marked with blue and green lines.

Credit: College of DuPage

warm conveyor belt

Weather map of the northeastern U.S. showing cold and warm fronts with wind patterns.
warm conveyor belt
Text description of the warm conveyor belt image.

The image depicts a map showing a portion of the United States with overlaying weather fronts and cloud patterns. An  area of low presure is analyzed over Michigan with a purple occluded front attached to the eastern side of the low. Connected to the occluded front, a blue line with triangular spikes indicates a cold front is drawn to the south and a red line with semicircles, representing a warm front, is drawn to the east. An orange arrow above the map suggest the movement of warm air, called the warm conveyor belt, through this region. The entire scene has an overlay of a light blue hue, adding contrast to the white clouds and dark land below.

Credit: David Babb @ Penn State is licensed under CC BY-NC 4.0(opens in a new window)

S-shape

Weather map showing cold, warm, and occluded fronts over the Northeastern U.S.
S-shape
Text description of the S-shape image.

The image is a detailed graphical representation of a satellite image depicting an area of low pressure over a the eastern Pacific, off the coast of California and Oregon. Superimposed over the map is an orange line, drawn in an S shape on the eastern side of the low, indicating a warm conveyor belt. The west coast of the United States and Canada can be seen and is drawn in thin blue lines.

Credit: NOAA

dry slot

Side-by-side infrared satellite images of a weather system over the eastern U.S., highlighting a “Dry Slot.”
dry slot
Text description of the dry slot image.

The image is divided into two sections, each showing a weather satellite infrared image of the eastern United States. Both sections depict significant cloud coverage associated with a large area of low pressure, along with a notable clear area labeled "Dry Slot". In the left image, the dry slot appears as a lighter region cutting into the cloud formation, while in the right image, it appears darker, contrasting with the surrounding lighter clouds. The images highlight the contrast in visible satellite imagery at daytime versus nighttime.

Credit: NOAA

dry conveyor belt

3D weather map with red, blue, and purple lines indicating weather fronts, and a yellow arrow showing wind direction over a cloudy satellite image.
dry conveyor belt
Text description of the dry conveyor belt image.

The image displays a satellite image, illustrating portions of a landmass with an overlaid satellite view depicting clouds. The map features several superimposed colored lines: a red line with semi-circles indicating a warm front, a blue line with triangles indicating a cold front, and a purple line combining both symbols, indicating an occluded front. A curved yellow arrow from the western side of the low curving around to the south side, indicates the movement of air in the dry slot region. The geographical area is mostly covered by clouds, obscuring much of the land details, but coastlines and state borders are faintly visible.

Credit: David Babb @ Penn State is licensed under CC BY-NC 4.0(opens in a new window)

cold conveyor belt

Weather map with fronts and wind patterns over the northeastern US.
cold conveyor belt
Text description of the cold conveyor belt image.

The image depicts a weather map showing parts of the northeastern United States with weather fronts overlaid. A blue cold front, marked with triangles, extends southward along the East Coast and curves slightly westward. A red warm front line, marked with semicircles, is visible above, arching eastward. An occluded front, in purple, connects the area of low pressure with the warm and cold fronts. The background shows satellite imagery of clouds covering the region. Large, light blue arrows sweep across the northern side of the image, wrapping around the low, indicating the movement of air along the cold conveyor belt. 

Credit: David Babb

infrared satellite image

Satellite image of a weather system with labeled warm and cold conveyor belts.
infrared satellite image
Text description of the infrared satellite image.

The image is a satellite view showing a low pressure system over the eastern Pacific Ocean, near the Pacific Northwest coastline. The cyclone is rotating counterclockwise, characterized by swirling cloud formations. Two main conveyor belts are indicated on the image: a yellow line labeled "Warm Conveyor Belt" arcs northeastward toward the cyclone from the coast, while a blue line labeled "Cold Conveyor Belt" extends horizontally across the northern part of the image, curving southward around the western side of the low. The outlines of the coastal regions and the US states are marked in purple. A speech bubble near the top left corner contains text describing cloud-top temperatures. A textbox is featured and reads "Note the difference in cloud-top temperatures that marks the edge of the warm conveyor belt".

Credit: NOAA

precipitation

Diagram showing warm and cold conveyor belts with clouds and directional arrows.
precipitation
Text description of the precipitation image.

The image is a diagram illustrating the interaction between a warm conveyor belt and a cold conveyor belt in the atmosphere. The background, split diagonally consists of a pink sky at the top transitioning to a light blue near the bottom, signifying the airmasses of the warm and cold conveyor belts. An orange arrow labeled "Warm Conveyor Belt" ascends diagonally from left to right, above a series of white and gray clouds. Below these clouds, a light blue bar labeled "Cold Conveyor Belt" extends horizontally. At the bottom, there is a green band with a gradient effect, labeled "S" on the left and "N" on the right, representing south and north directions.

Credit: David Babb @ Penn State is licensed under CC BY-NC 4.0(opens in a new window)

swath of snow created by a powerful mid-latitude cyclone

Satellite view of Midwest USA showing a diagonal strip of snow cover.
swath of snow created by a powerful mid-latitude cyclone
Text description of the swath of snow created by a powerful mid-latitude cyclone image.

The image is a satellite view of a large geographical area in the Midwest United States. The region is primarily covered by a significant swath of snow stretching diagonally from the southwest to northeast. Outside of the white snow covered region, the landscape is a mix of greens and browns, indicating snow-free land. The snow's coverage is extensive, contrasting sharply against the surrounding barren land. Cloud formations are also visible, primarily in the northern and eastern parts of the image, exhibiting a mix of wispy and dense clouds. Several state boundaries are outlined, and Lake Michigan can be seen at the northeastern edge, bordered by more clouds and snow.

Credit: NASA

radar image of a Midwestern blizzard

Weather radar map showing fronts and precipitation in the central U.S., with “Wrap-around Precipitation” text.
radar image of a Midwestern blizzard
Text description of the radar image of a Midwestern blizzard image.

The image is a composite radar map of the central United States, highlighting a significant weather system. The map includes state boundaries overlaid with varying colors indicating precipitation. The central part of the image is dominated by blue and green colors, representing different intensities of precipitation. Alongside these, areas in yellow suggest heavier rain and snowfall. A low-pressure "L" symbol is present, with blue and red lines indicating fronts. The blue line with triangles represents a cold front and extends from Missouri through Texas, while the red line with semi-circles represents a warm front and is analyzed from Missouri to Georgia. There is a purple line denoting an occluded front that connects the warm and cold front. Text in yellow at the top left reads "Wrap-around Precipitation."

Credit: National Weather Service

 

Types of Winter Precipitation

columns and hexagon plates

A detailed geometric pattern featuring hexagonal shapes and intersecting cylinders on a light background.
columns and hexagon plates
Text description of the columns and hexagon plates image.

The image shows a close-up view of ice crystals. The crystals showcase different cylindrical and polygon structures. The cylinders are indicative of columns and the polygons more closely resemble hexagon structures. The image is black and white with the crystals featured in an illuminated circle of the microscope. The hexagonal crystals appear lighter and more transparent while the columns appear darker and more opaque.

trees

Trees broken and covered in ice after an ice storm.
trees
Text description of the trees image.

The image shows a scene of devastation following an ice storm, with numerous trees damaged and covered in ice. The ground is blanketed with a layer of snow and ice, and broken tree limbs are scattered throughout the area. Trees in the background are bent and fractured, with branches coated heavily in ice and appearing more white. On the right side of the image, a building corner with brickwork is visible, and icicles hang from the eaves. The sky is grey and overcast.

Credit: flicker.com / Tom Hapgood / CC BY-NC 2.0

freeze on all surfaces

Utility pole and power lines covered in ice, with ice-laden tree branches in the background.
freeze on all surfaces
Text description of the freeze on all surfaces image.

The image shows a utility pole and power lines heavily coated in ice, framed against a backdrop of ice-covered tree branches. The pole stands at an angle, supporting several wires and electrical boxes. The power lines stretch diagonally across the image, draped with long icicles. Tree branches, densely covered in ice, fill the space around the pole and lines. The sky in the background is overcast, casting a muted, cold light across the scene.

Credit: flickr.com / vgm8383 / CC BY-NC 2.0

general template for the distribution of wintry precipitation

Weather map showing heavy snow in the west, light snow in the north, sleet and freezing rain in the central east, rain, and thunderstorms in the south.
general template for the distribution of wintry precipitation
Text description of the general template for the distribution of wintry precipitation image.

The image is a map depicting various weather conditions along an idealized low pressure system schematic. A large, red "L" symbolizing a low-pressure system is centered over the central U.S. To the west and northwest, a deep blue area represents heavy snow. Surrounding this is a lighter blue area to the north and east, labeled "light snow". To the south of the light snow, nearing the warm front, A narrow band in purple shows sleet, running horizontally across the central eastern part of the map. Below this, a thin band in prink represents freezing rain. A green area depicting rain is situated to the south of the warm front. Further south, a green shaded area indicates thunderstorms, stretching from the Gulf of Mexico into the southeastern U.S. along the cold front. The background shows a faint outline of the United States with state borders.

Credit: David Babb @ Penn State is licensed under CC BY-NC 4.0(opens in a new window)

 

Winter Weather Safety

plot shows the number of hours of "near blizzard" conditions

Map showing hourly observations near blizzard conditions in the northeastern US on January 23-24, 2016, with a color scale indicating the number of hours.
plot shows the number of hours of "near blizzard" conditions
Text description of the plot shows the number of hours of "near blizzard" conditions image.

The image is a map of the northeastern United States displaying the number of hourly observations near blizzard conditions on January 23-24, 2016. The map highlights different states, including New York, New Jersey, Pennsylvania, and surrounding areas. Various colored dots indicate the number of hours where conditions approached blizzard status. The dots range in color from light blue to purple and yellow, corresponding to a scale on the right labeled from 1 to 9. On the left, there's a list of station codes followed by numbers, indicating the duration of blizzard-like conditions at each location. A legend at the bottom specifies that data represents observations with visibility less than or equal to 0.25 miles and wind gusts of 35 mph or more.

Credit: Greg Carbin

Weather World — Overuse of "Blizzards" (2013-02-13)

Overuse of "Blizzards" (3:18)
Transcript of Overuse of "Blizzards" video

It’s inevitable. Every time it snows hard and the wind blows, the word blizzard creeps into the conversation. Usually, it’s from non-meteorologists, but even folks in the business occasionally use the word when it’s not warranted. Last week gave us two chances to look deeper into when we should and shouldn’t say blizzard.

Now, officially a blizzard requires three consecutive hours with sustained winds or frequent gusts of 35 miles per hour or higher, accompanied by falling or blowing snow that reduces visibility to a quarter mile or less. There is no temperature requirement. I think it’s telling that by this definition, the blizzard of ’96—arguably the most famous Pennsylvania snowstorm in recent decades—wasn’t officially a blizzard anywhere in Pennsylvania, though a few stations satisfied the blizzard criteria for less than the necessary three straight hours.

Now let’s look at last week’s historic Nor’easter, already dubbed the blizzard of 2013. Here are the areas that were under blizzard warnings: New York City and Long Island, all of Connecticut and Rhode Island, and parts of five other states. And just to establish where a lot of snow fell, here’s the one-foot line. Everywhere south and east of that line got a foot of snow or more.

Now, here’s all the official observing sites that were in the blizzard warning and measure visibility, wind, and precipitation. There’s a total of 55 places from eastern Maine to northern New Jersey. So these are places where we can assess whether there really was a blizzard.

But first, we need to clarify some ambiguities in the definition. For example, what does frequent mean? Well, I’ll take a pretty lenient definition—just one gust of 35 miles per hour in an hour. Also, as long as there’s just one observation per hour with the proper combination of wind and visibility, I’ll count that hour as having a blizzard, even if other observations that hour fall below the blizzard requirement.

Now, with that fairly relaxed interpretation, here’s where blizzard conditions verified in last week’s Nor’easter: about half of the observing sites in the warnings. And that’s actually a pretty high percentage based on my experience. There were also three observing sites that had blizzard conditions but weren’t in the warnings. All three of those were in Massachusetts.

Now, as that Nor’easter was winding down, another powerful storm was strengthening in the Plains, and blizzard warnings were issued there for parts of four states—from northern Nebraska to western Minnesota—with about 40 observing sites in the warning area where we have enough data to evaluate the blizzard criteria. Now, in this case, just three stations officially had a blizzard. At about half the other stations, there was a period of very low visibility due to heavy snow, and there was also a time of very strong winds. The period simply did not overlap.

Now, please don’t get me wrong here. I’m not saying that these weren’t extremely disruptive storms, nor am I being critical of the Weather Service’s forecasts. My point is simply that true blizzard conditions are fairly rare and pretty darn hard to achieve.

Fred is back next with the extended forecast.

the moving air transports warm air away from our bodies faster

Illustration comparing effects of no wind and windy conditions on body temperature, highlighting heat retention and increased loss.
the moving air transports warm air away from our bodies faster
Text description of the the moving air transports warm air away from our bodies faster image.

The image is a split illustration comparing the effects of no wind vs. windy conditions on body temperature. The left side, titled "NO WIND," shows a person wearing winter clothing, including a hat with ear muffs and a jacket, standing against a backdrop of trees and a snowing sky. There are red wavy lines around the person symbolizing retained body heat, with text noting "98.6°F - Average temperature of the human body." Below, a caption explains that people lose heat through convection, with a layer of warmth maintained between the skin and surroundings.

The right side, titled "WINDY," has a similar illustration of a person, but with an added effect of a breeze depicted by diagonal lines and snowflakes. The red wavy lines suggest increased heat loss. The text notes "95°F - Hypothermia begins when our body temperature drops two to four degrees." A caption explains that wind breaks up the insulating layer of warmth, accelerating heat loss. The phrase "Heat is moved away from our bodies" is displayed in red. The NOAA logo and a website, "weather.gov/winter," are located at the bottom right.

Credit: National Weather Service

National Weather Serivice wind chill chart

Wind chill chart showing temperatures, wind speeds, and frostbite duration, with a colored gradient from light blue to dark purple.
National Weather Serivice wind chill chart
Text description of the National Weather Serivice wind chill chart image.

The image is a wind chill chart against a black background displaying how temperature and wind speed affect the perceived wind chill temperature. The chart is divided into columns representing temperatures in Fahrenheit, ranging from 40°F to -45°F, and rows for wind speeds from 5 mph to 60 mph. The chart uses a gradient of colors, from light blue to dark purple, indicating how quickly a person can get frostbite at different wind chill temmperatures. The chart contains a legend indicating frostbite times: light blue for 30 minutes, medium blue for 10 minutes, and dark purple for 5 minutes. Logos for NOAA and the National Weather Service appear at the top. The formula for calculating wind chill is Wind Chill (ºF)=35.74+0.6215T-35.75(V0.16)+0.4275T(V0.16) where T= Air Temperature (ºF) and V=Wind Speed (mph). The chart's effectiveness date is November 11, 2001.

National Weather Serivice wind chill chart
(Temperature and Wind Speed)
Calm40º35º30º25º20º15º10º-5º-10º-15º-20º-25º-30º-35º-40º-45º
5 mph363125191371-5-11-16-22-28-34-40-46-52-57-63
10 mph3427211593-4-10-16-22-28-35-41-47-53-59-66-72
15 mph3225191360-7-13-19-26-32-39-45-51-58-64-71-77
20 mph302417114-2-9-15-22-29-35-42-48-55-61-68-74-81
25 mph29231693-4-11-17-24-31-37-44-51-58-64-71-78-84
30 mph28221581-5-12-19-26-33-39-46-53-60-67-73-80-87
35 mph28211470-7-14-21-27-34-41-48-55-62-69-76-82-89
40 mph2720136-1-8-15-22-29-36-43-50-57-64-71-78-84-91
45 mph2619125-2-9-16-23-30-37-44-51-58-65-72-79-86-93
50 mph2619124-3-10-17-24-31-38-45-52-60-67-74-81-88-95
55 mph2518114-3-11-18-25-32-39-46-54-61-68-75-82-89-97
60 mph2517103-4-11-19-26-33-40-48-55-62-69-76-84-91-98
Credit: National Weather Serivice

preferably in in layers

Infographic showing how to dress for “Chilly,” “Cold,” and “Extreme Cold” weather with illustrations of layered clothing.
preferably in in layers
Text description of the preferably in in layers image.

The image is an infographic titled "Dressing for Cold Weather" divided into three sections: "Chilly," "Cold," and "Extreme Cold." Each section presents an illustrated character dressed appropriately for the specified weather condition. The background consists of varying shades of blue, suggesting different temperatures.

The "Chilly" section shows a character with dark skin and curly hair wearing 1-2 layers: a long-sleeve shirt and pants, with advice to add a waterproof outer layer for wind and rain and warm shoes.

The "Cold" section depicts a character with light skin wearing a blue hat, 2-3 layers including a jacket, gloves, boots, and a note to use an outer layer against wind and wet snow.

The "Extreme Cold" section illustrates a character with light skin in a red hat and face mask, with 3+ insulating layers, gloves, boots, and an outer layer for wind protection. Accessories like the warm hat and boots are emphasized as waterproof.

Credit: National Weather Service