Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 229 AM EST Sun Feb 22 2015 Valid 12Z Sun Feb 22 2015 - 12Z Tue Feb 24 2015 ***Active weather pattern across the southern U.S.*** ***Cold front brings more frigid temperatures to northern U.S.*** ***Significant snow expected for the Rocky Mountains*** After a lengthy period of upper-level ridging with warm and dry conditions over the western U.S., things are forecast to change starting Sunday and lasting into the beginning of the work week. A strong shortwave rotating around the eastern U.S. trough axis is expected to drop southward over the Intermountain West and then towards the Desert Southwest. At the surface, a cold front will slowly move southward over this region and bring showers and mountain snow from eastern California to the southern Rockies. Upslope flow on the western side of a large surface high over the Plains will tend to enhance snowfall from northern New Mexico to Colorado, where amounts in excess of six inches are likely. The wintry weather is forecast to extend eastward across the southern Plains and into parts of the Deep South as moisture overrides a cold front situated over the northern Gulf of Mexico. A layer of warmer air over-running a shallow layer of sub-freezing temperatures in the lowest parts of the atmosphere will result in sleet and freezing rain for many of those areas. Light snow will be possible on the northern edge of the precipitation shield from Oklahoma to Tennessee. Another arctic boundary that has dropped south from northern Canada will reinforce the frigid temperatures for the north central U.S. over the next few days. The persistent upper level trough over eastern North America, along with the widespread snow cover, is allowing these arctic air masses to arrive in the northern and eastern U.S. unabated. Hamrick Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php