National Weather Service United States Department of Commerce

Severe Weather Expected for the South on Tuesday; Winter Weather Conditions for the West, Central Plains, and Upper Mississippi River Valley

Severe weather is forecast across the middle and lower Mississippi Valley Tuesday afternoon where tornadoes and damaging winds are expected. A strong cold front will track across the Intermountain West accompanied by strong winds, heavy snow and elevated fire weather conditions for portions of the western High Plains with heavy snow likely for Upper Mississippi Valley Tuesday. Read More >

The passage of a disturbance through the region on Monday will provide the support that will allow strong winds to exist across the Kern County Mountains and Deserts. As the disturbance passes on Monday, winds on the Eastern Slopes of the Tehachapi Range and across the Kern Desert will increase with gusts reaching 55 mph during the afternoon and early evening hours. Highways affected by the strong winds include 58, 178, 14 and U.S. 395. Drive safely and heed highway signs.
Here are the chances that select areas in the San Joaquin Valley hit the freezing mark Wednesday morning.
Freezing temperatures of 28 to 32 degrees will be possible across the San Joaquin Valley Wednesday morning. A Freeze Watch has been issued.
A Winter Storm Watch is in effect for the higher elevations of the Sierra Nevada from Late Wednesday night through Friday afternoon. Total snow accumulations of 20 to 30 inches of new snowfall are expected above 5000 feet with locally heavier amounts possible above 6000 feet. Winds could gust as high as 40 mph.
Widespread rain and mountain snow are expected across the area between late Wednesday night and Friday morning.


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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: