Updated: October 01, 2020 09:59 AM
Created: October 01, 2020 08:25 AM
Weather observations are most commonly taken by weather balloons that are launched by the National Weather Service (NWS). These balloons collect critical upper-air weather information such as atmospheric pressure, temperature, wind speed and direction, and humidity, with an instrument called a radiosonde. They are launched twice a day at the same time all across the United States. The first one is launched at 12Z (Zulu time). This corresponds to 8AM EST (during daylight saving time) and 7AM EST (not during daylight savings time.) The second balloon is launched at 00Z and this corresponds to 8 PM EST (daylight savings time) and 7AM EST (not daylight savings time).
The reason forecasters use Zulu time is so that we are all under the same period. For example, if you were told to go outside at 6pm, you would go outside when it was 6pm in your time zone. When all locations around the globe are following the same time zone (i.e. Zulu Time), then everyone goes outside at the exact same time.
The information collected from these weather balloons is used in forecast models all across the globe. In the United States, 92 different locations launch weather balloons. When impending weather is approaching, some stations may launch one or two extra weather balloons so that they have a better understanding of what is going on in the atmosphere.
Global Forecast System (GFS)
European Center of Midrange Weather Forecasting (ECMWF)
With broad resolutions, this makes pin pointing the exact location of a storm a bit tricky. Both of these models forecast for a long period of time. The accuracies of the forecast after 7-day starts to decrease, but comparing and contrasting the differences between these two models (after 7 days) allows forecasters to get a good understanding of incoming weather. Most of the time these models over-estimate the amount of rain or snow for a given location.
Rapid Precision Model (RPM)
High Resolution Rapid Refresh (HRRR)
Global High-Resolution Atmospheric Forecasting System by IBM (IBM GRAF)
Note that this is a global forecast, but the resolution and short forecast period make it resemble a mesoscale/regional forecast model.
In the summertime, these models are used to help pin point the exact location of severe weather or rain showers. In the wintertime, these models help forecasters determine where the freezing line is, and where or how much snow could occur at any given location.
All of these models receive new weather data every 12 hours, unless there are more than two balloon launches in one day. When this happens, weather models are updated with the most recent weather data to help create the most accurate forecasts. Lastly, it is unlikely that one model will get the entire forecast correct, so forecasters use a combination of different models to help accurately forecast the weather.
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