17.2. Operational NWP Models

There are three primary synoptic models that are used for forecasting across the United States: the Rapid Refresh (RAP), the North American Model (NAM), and the Global Forecast System (GFS) model. All three models have a slightly varying purpose and have different forecast periods, which are summarized below.

	RAP	NAM	GFS
Forecast Hours	48	84	384
Model Type	Grid Point	Grid Point	Finite Volume
Output Time	Every hour	Every three hours	Every six hours
Areal Coverage	Regional (U.S.)	Regional (NA)	Global
Runs	Every hour	00, 06, 12, 18 UTC	00, 06, 12, 18 UTC

For more information on these and other models run by governments across the world check out the Operational Models Encyclopedia.

To access forecast hours from a model file you would simply input how many hours into the future you desire into a timedelta function and add it to your date variable. If model run time is set as,

model_run_time = datetime(2020, 2, 20, 12)

Then if you wanted the six-hour forecast then,

plot_time = model_run_time + timedelta(hours=6)

or the 24-hour forecast

plot_time = model_run_time + timedelta(hours=24)

or the 120-hour forecast

plot_time = model_run_time + timedelta(hours=120)