Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 232 PM EST Fri Nov 30 2018 Valid 00Z Sat Dec 01 2018 - 00Z Mon Dec 03 2018 ...Severe thunderstorms and heavy rainfall are likely across portions of the southern Plains, lower Mississippi Valley and Gulf Coast states... ...Major winter storm to impact the Great Plains this weekend... ...Unsettled weather will continue across much of the Western U.S. with locally heavy rain and high elevation snowfall... A very active and wet pattern is anticipated this weekend over a large portion of the nation as a series of storm systems crossing the Western U.S. advance downstream across the Plains, Midwest and gradually toward the Eastern Seaboard. The concern for tonight and Saturday will be severe weather and heavy rainfall which is expected to impact areas of the southern Plains, lower Mississippi Valley and Gulf Coast states as deepening low pressure near the Oklahoma and Texas panhandles ejects off to the east overnight and then toward the Midwest on Saturday. The low center and supporting upper trough aloft will interact with an increasingly moist and unstable airmass pooling north from the Gulf of Mexico and along a quasi-stationary front draped across the Ohio Valley southwestward to the lower Mississippi Valley. Widespread showers and thunderstorms will develop along and south of this front overnight, and conditions are expected to be conducive for severe weather and locally heavy rainfall amounts. In fact, the Storm Prediction Center has highlighted an Enhanced Risk of severe thunderstorms for the Arklatex region including adjacent areas of the southern Plains and lower Mississippi Valley for tonight. The hazards will tornadoes, damaging winds and large hail. On Saturday, the heavy rainfall and severe weather threat will shift east to include the remainder of the central and eastern Gulf Coast states as a cold front gradually approaches from the west. Farther north, around the northwest side of the same low pressure center causing the heavy rain and severe weather concerns, will be a major winter storm which is expected to hit areas of the Great Plains on Saturday including a large area of the northern and central Plains. Heavy snow and strong winds are expected across these areas, and especially over southern South Dakota and north-central Nebraska where snowfall totals of as much as 12 to 18 inches are expected. A period of sleet and freezing rain is expected locally as well before a changeover to all snow occurs. Thus, the combination of heavy snow and ice will result in hazardous travel conditions. By Sunday, the snow will begin to advance northeast across areas of the upper Midwest and the upper Great Lakes. Numerous winter storm warnings, watches and advisories are in effect across these areas in anticipation of this next major winter storm. Some snow and even areas of sleet and freezing rain will also be possible across the far northern and interior sections of the Northeast as moisture ahead of this system arrives on Sunday with a marginally cold airmass for winter weather. Rain and some thunderstorms will be expected farther south along the Eastern Seaboard by Sunday as a cold front arrives from the west and with much warmer temperatures in place as well. Across the Western U.S., a new storm system will arrive across the Pacific Northwest which will bring another round of heavier precipitation to especially southwest Oregon and northern California tonight and Saturday. This will bring a new round of heavy snowfall for the Sierra-Nevada and also portions of the Cascades. In fact, additional snowfall totals of 1 to 2 feet can be expected going through Saturday. By Sunday, all of this Pacific moisture and energy will traverse the Great Basin and the central and southern Rockies. The result will be locally heavy snowfall over the higher terrain. Areas likely to see the heaviest amounts will be the Wasatch of Utah and the San Juan mountains of southwest Colorado where over 1 foot of new snow is possible. Regarding temperatures, there will be notably milder temperatures gradually shifting from the Midwest to the Eastern U.S. this weekend, with temperatures locally over 20 degrees above normal from the Ohio Valley down to the lower Mississippi Valley region. Meanwhile, all of the unsettled weather moving through the West will keep temperatures here much colder and especially over the Rockies by Sunday where temperatures will be as much as 15 degrees below normal. Orrison Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php