Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 342 PM EST Mon Dec 21 2015 Valid 00Z Tue Dec 22 2015 - 00Z Thu Dec 24 2015 ...Heavy rainfall expected over the central/eastern Gulf Coast into the Southern Appalachians... ...Anomalous warmth anticipated from the Great Plains eastward... ...Lower elevation rain/mountain snow in the forecast across the western U.S... To begin the period, a broad upper trough will extend across a majority of the country with a series of embedded disturbances traversing this flow regime. Each such feature should be an impetus for precipitation with a bulk of the heaviest rainfall congregating over the central/eastern Gulf Coasts up into the Southern Appalachians. A stalled frontal boundary combined with abundant moisture lifting out of the Gulf of Mexico will help focus this heavy rainfall threat over the southern U.S. Recent forecasts suggest 3 to 6 inch amounts over the aforementioned Gulf Coast locales with an additional maxima into the Southern Appalachians where orographics will come into play. Consequently, WPC has placed a threat for excessive rainfall over these regions which may lead to areas of flash flooding through at least mid-week. Farther to the west toward the Arklatex and lower Mississippi Valley region, severe weather will be possible where the atmospheric dynamics should be stronger. As the upper flow becomes more amplified in time, broad-scale ridging sets up over the eastern U.S. While conditions are already rather mild for this time of year, forecast temperature anomalies will be quite impressive. The calendar may suggest that Winter commences on Tuesday. However, daily temperatures will rise markedly, particularly by mid-week. On Wednesday, many records may be broken as readings approach the 20 to 30 degrees Fahrenheit above normal from the Mississippi River eastward. Local forecasts indicate this equates to highs in the low/mid 60s over Chicago, Indianapolis, and Cleveland with 70 degrees as far north as Cincinnati. Expect this anomalous warmth to continue into following day as well. An amplified trough over the western U.S. will favor cool and unsettled conditions throughout the region. The lack of arctic air will ensure a majority of the wintry precipitation should reside in the higher elevations. Based on the latest WPC snowfall forecast, the heaviest snow can be expected over the Cascades, Sierra Nevada range, and into the Wasatch. 2 to 3 feet of snow is likely through Wednesday evening with isolated higher amounts of course possible. Meanwhile, 1 to 2 feet is more likely moving into ranges such as the Bitterroots, Rubys, Tetons, and the Colorado Rockies. While temperatures will be below normal, expect readings to be around 5 to 10 degrees off of climatology given the dominance of Pacific air which is milder in nature. Rubin-Oster Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_wbg.php