How Do Meteorologists Predict Weather?

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By Joey W on April 6, 2013, 8:16am Last modified: April 8, 2013, 10:16am

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Many watch the weather on the local news, but have you ever wondered how meteorologists predict weather?  Well, you have probably heard of computer models, such as the European and the GFS, but, there are MANY other computer models that meteorologists look at.

What are isobars?
Isobars appear in computer models such as the “Thickness Charts” like the GFS 1000_850_thick.  Isobars are lines of equal pressure.  As you can see in the picture below, the isobars are very close to each other.  If this computer model was correct, there would be very strong winds over the Atlantic ocean just southeast of Long Island.  Isobars also usually face the way the wind direction is predicted to be.

then

Computer models do NOT always agree, in fact, most of the time they don’t agree.  Believe it or not, the computer models have actually gotten more uncertain in the past year, that is why sometimes when a snowstorm is 2 days away,meteorologists can not make a snowfall accumulation map.

Meteorologists do not just rely on computer models to predict their forecasts, another source they use is taking hourly observations.  If you have ever listened to NOAA weather radio, you have probably heard the hourly observations.  This is very important when predicting a storm.  During snowstorms, temperature is VERY important, especially when the temperature is right around 32F.  During storms such as hurricanes, pressure is also VERY important.  Because if the pressure is extremely low, then the storm could have catastrophic impacts.  But if the pressure is at like 1001 millibars, the hurricane will probably only have minor impacts.

What is Z or UTC time?

Z or UTC time is known as “Greenwich Mean Time”.  The whole world is on Z time, for example, it would be 06z in New Haven,CT, but it would also be 06z anywhere else across the world.  When you hear of computer models, such as the 12z GFS, that means that the GFS comes out at 12z, but, it’s not quite that simple.  The computer models usually take about 6 hours to process, so that means that the 12z GFS, wouldn’t be able to be viewed until 18z.  Then, there is an 18z GFS, and that won’t be able to be viewed until 00z.  There is a 00z GFS, and that won’t be able to be viewed until 06z.  And the 06z GFS won’t be able to be viewed until 12z.  Then the cycle repeats again.  This is the same with the NAM model, but models such as the SREF are a bit different.  Like the GFS and NAM, there are four runs of the SREF a day, but it comes out at different times.  There is a 03z SREF, a 09z SREF, a 15z SREF, and a 21z SREF.  Some computer models only come out twice a day, like the ECMWF or the European model.  There is only a 00z ECMWF, and a 12z ECMWF.  However, some computer models such as the RAP come out ever hour.

Did You Know?

Did you know, Greenwich Mean Time is also known as “Zulu” time?

Joey’s Weather Forecasting Tip:

When computer models are not agreeing, always forecast the AVERAGE forecast.  For example, if half of the computer models are forecasting 21″ of snow, and the other half are forecasting 7″ of snow, predict around 14″ of snow. ***This will involve math.***


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Joey W

Town: New Haven Area  

Reporting for WXedge since September 2012.

Articles: 106

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