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Forecast Models

Meteorology uses pressure as the vertical coordinate and not height. This works out better for thermodynamic computations that are done on a regular basis. Pressure decreases in the atmosphere exponentially as height increases reaching zero pressure in space. The standard unit of pressure is millibars (mb or hectopascals-hPa) of which sea level is around 1013 mb. Standard pressure levels and approximate heights:

Pressure Approximate Height Approximate Temp
Sea level 0 m 0 ft 15oC 59oF
1000 mb 100 m 300 ft 15oC 59oF
850 mb 1,500 m 5,000 ft 5oC 41oF
700 mb 3,000 m 10,000 ft -5oC 23oF
500 mb 5,000 m 18,000 ft -20oC -4oF
300 mb 9,000 m 30,000 ft -45oC -49oF
200 mb 12,000 m 40,000 ft -55oC -67oF
100 mb 16,000 m 53,000 ft -56oC -69oF

The the primary difference between the models is their resolution or grid boxes. The smaller the grid box, the higher the resolution so little nuances in the atmosphere are more easily identified. Below are some of the models used by the National Weather Service.

Model Data Servers

NAM Forecast Model

This table contains contour plots of data from the NAM forecast model. This model gives forecast information out to 84 hours and are updated once every 6 hours at roughly 02:00 PST and 08:00 PST.

NAM North America Forecasts
NAM North Pacific Forecasts

NAM MOS Numerical Guidance:

GFS (Global Forecast System) Forecast Model

This is a global model run by NCEP whereas the NAM is a regional model. As a result, the grids from this model are somewhat coarser than the grids from those models and lack some products. This model replaced the AVN and MRF models and gives forecast information out to 384 hours, and are updated once every 6 hours by roughly 04:00 and 10:00 PST.

GFS North America Forecasts
GFS North Pacific Forecasts

GFS Short Range Numerical Guidance: GFS Medium Range Numerical Guidance:

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National Oceanic and Atmospheric Administration
National Weather Service
San Joaquin Valley Weather Forecast Office
900 Foggy Bottom Road
Hanford, CA 93230-5236

Tel: (559) 584-3752

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