Station Model Review

Let’s take a tour of a complete station model using our interactive station model tool. I’ve set it up with data from a real weather observation in the midst of blizzard conditions occurring at Findlay, Ohio on a December day at 1240Z. Ohio is in the Eastern Time Zone, so to get local standard time, we subtract 5 hours, meaning that this was an observation from 7:40 AM Eastern Standard Time on this date. And, the conditions at this time were brutal. The temperature, which is the number in the upper-left corner of the station model, was -6 degrees Fahrenheit. The dew point, was -9 degrees Fahrenheit. So, this was bitterly cold, dry air in place. Winds were whipping from the west-southwest, or 250 degrees, at 35 knots. To get the speed, we just add the 3 long barbs at 10 knots a piece, and the one short barb, which is 5 knots. The four asterisks, or snow flakes, indicate that heavy snow was falling, and the combination of heavy snow and fierce winds had reduced visibility to ¼ of a mile, which is indicated by the number on the far left. Sky coverage is depicted in the circle, and the “X” here indicates that the sky was obscured, meaning that the state of the sky could not observed. Given that heavy snow was occurring, we can guess that it was probably overcast, but since the state of the sky couldn’t be observed due to the wind driven, heavy snow, the official observation is obscured. Finally our sea-level pressure is indicated by these three digits at the top right – 7-5-3. But, that doesn’t indicate a pressure of 753 millibars. That would be much lower than any sea-level pressure ever observed. This is expressed in tenths of a millibar, and we have to put either a 9 or a 10 in front to get the proper sea-level pressure. Since our number here is greater than 500, we’ll put a 9 in front, and when we place a decimal in front of the 3, that gives us a pressure of 975.3 millibars – a pressure consistent with what we might find in a strong winter storm. Putting a 10 in front wouldn’t have made sense because it would have given us a pressure of 1075.3 millibars, which would be one of the highest values ever recorded. Remember that the vast majority of sea-level pressure values fall between 950 and 1050 millibars, with very intense hurricanes and extremely strong high pressure systems being exceptions.

Now we’ll look at an example from a warmer time in Tallahassee, Florida as the center of a hurricane passed about 50 miles to its east. This observation was taken at 1353Z on an August day, so Daylight Saving Time was in effect. Tallahassee is in the Eastern Time Zone, so to convert to Eastern Daylight Time, we subtract 4 hours instead of 5 like we would if standard time was in effect. 1353Z – 4 hours gives us 9:53 AM Eastern Daylight Time. The temperature is 76 degrees Fahrenheit, marked in the upper-left, and the dew point is 73 degrees Fahrenheit, marked in the bottom left. The present weather is marked by these 3 dots, which indicate moderate rain, and the visibility was 7 miles at this time. Winds were blowing from the northwest, or 330 degrees, and the speed was approximately 25 knots, which we can get by adding the two long wind barbs, which indicate 10 knots each, and the short wind barb, which is 5 knots. Moving on to sea-level pressure, we see “958” in the upper-right of the station model. Remember that’s in tenths of a millibar and we have to choose either a 9 or a 10 to put on the front of the number. Since the number is greater than 500, we’ll choose a 9, for a pressure of 995.8 millibars after placing a decimal in front of the 8. Had we chosen a 10, that would have given us 1095.8 millibars, which would be higher than any sea-level pressure ever recorded on earth, so that wouldn’t make sense. Only a 9 makes sense to give us a number that falls within our typical range of pressures. And, even though this was a hurricane case, the pressure was still within the typical range because only the most intense hurricanes have sea-level pressures that fall outside of the typical range, and Tallahassee didn’t experience the lowest pressures near the center of this hurricane anyway.