US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 335 PM EST Mon Feb 15 2021 Valid Thursday February 18 2021 - Monday February 22 2021 Hazards: - Heavy snow across portions of the Great Lakes, the Northeast, the Central Appalachians, and the Ohio Valley, Thu-Fri, Feb 18-Feb 19. - Heavy precipitation across portions of the Mid-Atlantic, the Lower Mississippi Valley, the Central/Southern Appalachians, the Tennessee Valley, the Northeast, and the Ohio Valley, Thu-Fri, Feb 18-Feb 19. - Heavy rain across portions of the Lower Mississippi Valley, the Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, and the Southeast, Thu, Feb 18. - Severe weather across portions of the Southeast, Thu, Feb 18. - Flooding possible across portions of the Southeast, the Southern Appalachians, the Mid-Atlantic, the Central Appalachians, and the Ohio Valley. - Flooding occurring or imminent across portions of the Mid-Atlantic. - Flooding likely across portions of the Southeast and the Mid-Atlantic. - Heavy precipitation across portions of California and the Pacific Northwest, Thu-Mon, Feb 18-Feb 22. - Heavy snow across portions of the Central Great Basin and California, Fri, Feb 19. - Heavy snow across portions of the Northern Great Basin, Thu-Fri, Feb 18-Feb 19 and Sun-Mon, Feb 21-Feb 22. - Heavy snow across portions of the Northern Rockies, Fri, Feb 19 and Sun-Mon, Feb 21-Feb 22. - High winds across portions of the Pacific Northwest, Sun, Feb 21. - High winds across portions of the Northern/Central Rockies and the Northern Plains, Sun-Mon, Feb 21-Feb 22. - Much below normal temperatures across portions of the Northern/Central/Southern Plains, the Upper/Middle/Lower Mississippi Valley, the Tennessee Valley, the Great Lakes, and the Ohio Valley, Thu-Sat, Feb 18-Feb 20. - Heavy precipitation across portions of mainland Alaska, Thu, Feb 18. - Much below normal temperatures across portions of mainland Alaska, Sun-Mon, Feb 21-Feb 22. Detailed Summary: During the medium range period (Thursday, February 18th - Monday, February 22nd) strong upper-level troughing will act as the force behind below average temperatures and very active weather across the country. On Thursday all eyes will be on the East, where the second winter storm of the week is forecast to follow in it's predecessors footsteps as it makes its way from the Lower Mississippi Valley to the Northeast, bringing snow, mixed precipitation, and rain to many of the same areas hit a few days prior. The current guidance suggests that heavy rain, which could be severe at times, will impact the southern and Mid-Atlantic states, where rainfall totals up to and exceeding 2 inches in 24 hours may occur. Meanwhile, the greatest potential for heavy snowfall lies in the Ohio Valley, Central Appalachians and interior Northeast, with some locations expected to receive 6 to 8 inches of snow. Elsewhere, the storm is expected to bring a mix of snow, sleet, and freezing rain, which may result in ice accumulations up to one-tenth of an inch in the Lower Mississippi Valley and up to a quarter of an inch in the Mid-Atlantic. Along with travel being significantly impacted, areas subject to accumulating ice may also experience widespread power outages. In the West, a series of moisture-rich low pressure/frontal systems forecast to move onshore from the eastern Pacific will serve as the impetus for heavy snowfall in the higher elevation Cascade and Olympic Mountains throughout the period. Heavy rain along coastal northern California, Oregon and Washington will also accompany these systems, however, more moderate, non-hazardous amounts are expected on Friday and Monday. As the first low pressure/frontal system progresses southeast through the western terrain Thursday into Friday it will leave behind a trail of heavy snow in the high elevation mountain ranges of the Northern/Central Great Basin and Rockies as well as the Sierra Nevada. Driven by surface shortwave energy immediately followed by a cold front descending from Canada, a second round of heavy snowfall is expected for the high elevation mountain ranges throughout the Northern Great Basin and Rockies, Sunday into Monday. Concurrently, a tight pressure gradient over the northwest quadrant of the country will cause hazardous wind gusts to develop over the Pacific Northwest, Northern/Central Rockies, and the Northern Plains. Through the first half of the period, high pressure at the surface will keep temperatures well below normal over the central U.S. As opposed to the beginning of the week, by week's end temperatures are expected to become slightly more moderate, with daily low temperatures in most places reaching closer to or above zero and plateauing at approximately 10 to 20 degrees below normal. However, residents of the Central/Southern Plains and Middle/Lower Mississippi Valley will have to endure temperatures 20 to 30 degrees below normal for a few days longer. As the surface high pressure moves east through the weekend the cold air will follow suit, dropping low temperatures in the Ohio valley to 20 degrees below normal on Saturday before moderately cooling down the eastern seaboard on Sunday. 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 prolonged exposure to near-zero and negative could cause frostbite on uncovered areas of skin. Over Alaska, a busy pattern over the mainland in addition to a series of deep low pressure/frontal systems forecast to pass through the Gulf of Alaska, will bring precipitation to the Aleutians, Mainland, and Panhandle. While precipitation over the Aleutians is expected to be moderate, recent model guidance has significantly increased the amount of precipitation expected to fall over the southern Mainland Thursday, suggesting hazardous levels could be reached or exceeded for the region. Heavy precipitation may occur in the Panhandle region towards the end of the medium range period, however, there is still a significant amount of uncertainty in the precipitation forecast, so no hazard area has been drawn at this time. Additionally, daily low temperatures are expected to be much below normal for portions of the Interior Sunday and Monday. With temperatures reaching as low as -20F, extreme caution should be taken when traveling outdoors to prevent frostbite and illness. Zavadoff