US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 313 PM EST Fri Feb 12 2021 Valid Monday February 15 2021 - Friday February 19 2021 Hazards: - Heavy precipitation across portions of California and the Pacific Northwest, Mon-Tue, Feb 15-Feb 16 and Thu-Fri, Feb 18-Feb 19. - Heavy snow across portions of the Northern Rockies and the Northern Great Basin, Mon-Tue, Feb 15-Feb 16 and Thu-Fri, Feb 18-Feb 19. - Heavy snow across portions of the Northern Rockies, Mon, Feb 15 and Thu, Feb 18. - Heavy snow across portions of the Central Rockies, Mon, Feb 15 - Heavy snow across portions of the Central Great Basin, Mon-Tue, Feb 15-Feb 16. - Heavy snow across portions of the Southern Rockies and the Southwest, Tue, Feb 16. - Heavy snow across portions of the Middle/Lower Mississippi Valley, the Tennessee Valley, the Ohio Valley, the Great Lakes, and the Central Appalachians, Mon, Feb 15. - Heavy snow across portions of the Northeast, and the Great Lakes, Tue, Feb 16. - Heavy precipitation across portions of the Lower Mississippi Valley, the Tennessee Valley, the Ohio Valley, the Central Appalachians, the Mid-Atlantic, and the Northeast, Mon-Tue, Feb 15-Feb 16. - Heavy rain across portions of the Southern Appalachians and the Mid-Atlantic, Mon-Tue, Feb 15-Feb 16. - Heavy precipitation across portions of the Lower Mississippi Valley, the Tennessee Valley, the Ohio Valley, the Central Appalachians, the Great Lakes, the Mid-Atlantic, and the Northeast, Wed-Fri, Feb 17-Feb 19. - Heavy rain across portions of the Lower Mississippi Valley, the Central/Southern Appalachians, the Tennessee Valley, the Mid-Atlantic, and the Southeast, Wed-Fri, Feb 17-Feb 19. - Much below normal temperatures across portions of the Northern/Central/Southern Rockies, the Northern/Central Plains, and the Southwest, Mon-Tue, Feb 15-Feb 16. - Much below normal temperatures across portions of the Northern/Central/Southern Plains, the Upper/Middle/Lower Mississippi Valley, the Tennessee Valley, the Ohio Valley, and the Great Lakes, Mon-Fri, Feb 15-Feb 19. - Heavy precipitation across portions of mainland Alaska, Wed-Thu, Feb 17-Feb 18. Detailed Summary: During the medium range period (Monday, February 15th - Friday, February 19th) upper-level troughing over the central U.S. will act as a double whammy for the CONUS with respect to frigid temperatures and very active weather all across the country. On Monday, a moisture-rich low pressure/frontal system moving onshore from the eastern Pacific will serve as the impetus for heavy snowfall in the higher elevation Cascade and Olympic Mountains and heavy rain along coastal northern California, Oregon and Washington through Tuesday. As the low pressure/frontal system progresses southeast through the western terrain Monday into Tuesday it will leave behind a trail of snow extending from the Northern Great Basin and Rockies through the Southwest, the heaviest of which is expected to fall in the higher elevation mountain ranges. A few days later another low pressure/frontal system is forecast to move onshore from the eastern Pacific, bringing a second round of heavy rainfall to the low lying coastal regions as well as heavy snowfall to the high elevation mountain ranges of the Pacific Northwest, the Northern Great Basin, and the Northern Rockies Thursday into Friday. Shifting focus further east, a major winter storm that is forecast to develop over the Southern Plains Sunday will begin moving northeast early Monday, guided by a packet of upper-level shortwave energy. With frigid temperatures permeating much of the country, significant amounts of snow, sleet, and freezing rain will accompany system. On Monday, heavy snow will be possible from the Lower Mississippi Valley to the Central Appalachians, with the greatest potential for 6+" of snow expected in the Ohio Valley, while portions of the Lower Mississippi and Tennessee Valleys will carry the highest risk for icy conditions. As the storm system continues on its northeastern trajectory it will give one final push on Tuesday, likely bringing heavy snow to the Northeast, inundating the I-95 corridor with mixed precipitation, and soaking portions of the Southern Appalachians and Mid-Atlantic with heavy rain. Though only a few days out, forecast uncertainty still remains in regards to the exact path of the storm track as well as the location of the rain/snow line and heaviest snowfall. Even a small shift in the storm track can produce significant changes, however, the fact still remains that this multi-day storm will affect a large portion of the country and produce significant hazards that have the potential to impact travel, produce power outages, and threaten personal safety. As if one far reaching storm system in the medium range wasn't enough, a second system is expected to develop on Wednesday, following an almost identical track to the first. As two low pressure/frontal systems coalesce into one over Texas, shortwave energy over the Southern Plains and a warm front moving towards the Southeast are forecast to begin producing snow and rain, respectively. Guided by a strong upper-level shortwave, the newly formed low pressure/frontal system will propagate from the Southeast to the Northeast Wednesday through Friday, bringing snow, mixed precipitation and rain to many of the same areas hit a few days prior. While the models are currently in general agreement that the heaviest rain will likely fall over the southern states and Mid-Atlantic, there is still a significant disparity in the storm track in the guidance that areas of snow and mixed precipitation cannot confidently be distinguished. Therefore, the remaining area impacted by this second system is marked as heavy precipitation. As with the first storm, this system will also carry the potential to produce significant hazards and will continue to be watched over the coming days. Throughout the period, high pressure at the surface will continue its reign of forcing bitter cold temperatures over the central U.S. While much of the eastern Rockies and western Great Plains will feel some relief after Tuesday, temperatures well below normal will keep their tightest grip over the Central/Eastern Plains and Mississippi Valley. On Monday and Tuesday, the most anomalously cold air is expected to settle in the Central and Southern Plains and break over 40 daily low record temperatures, as low temperatures dip to between 30 and 40 degrees below normal. By mid-week temperatures are expected to become slightly more moderate throughout the central U.S., with daily low temperatures in most places reaching closer to or above zero and plateauing at approximately 10 to 25 degrees below normal. Conversely, the Ohio Valley will cool down briefly on Wednesday as the high pressure system settles over the region, dropping daily low temperatures approximately 20 degrees below normal. These widespread anomalously low temperatures can pose a threat to health and safety and should be taken seriously in all affected locations, particularly in the North/Central Plains and Upper Mississippi Valley where low temperatures in the negative teens and 20s could cause frostbite on exposed areas of skin in a matter of minutes. Over Alaska, a series of deep low pressure/frontal systems are forecast to pass over the Aleutians early in the week, bringing some moderate rain to the region. In the latter half of the week, multiple weaker systems will make their way through the Gulf of Alaska, bringing precipitation to the Southern Mainland and Panhandle as they move onshore. While precipitation over the Panhandle is expected to be moderate, recent model guidance has significantly increased the amount of precipitation expected to fall over the Southern Mainland Wednesday and Thursday, suggesting hazardous levels could be reached or exceeded for the region. Additionally, below normal low temperatures are forecast for portions of the eastern Interior Monday and Tuesday, however, they are not anticipated to be low enough to be hazardous. Zavadoff