US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 347 PM EST Thu Feb 18 2021 Valid Sunday February 21 2021 - Thursday February 25 2021 Hazards: - Heavy precipitation across portions of the Pacific Northwest, Sun-Mon, Feb 21-Feb 22. - Heavy snow across portions of the Pacific Northwest and the Northern Great Basin, Sun-Thu, Feb 21-Feb 25. - Heavy snow across portions of the Northern Rockies, Sun-Tue, Feb 21-Feb 23. - Heavy snow across portions of the Northeast, the Great Lakes, the Northern Plains, and the Northern Rockies, Tue, Feb 23. - Heavy snow across portions of the Upper/Middle Mississippi Valley, and the Great Lakes, Sun, Feb 21. - Heavy snow across portions of the Great Lakes, the Mid-Atlantic, the Northeast, the Central Appalachians, and the Ohio Valley, Mon, Feb 22. - Flooding possible across portions of the Southeast and the Mid-Atlantic. - Flooding occurring or imminent across portions of the Southeast and the Mid-Atlantic. - Flooding likely across portions of the Southeast and the Mid-Atlantic. - High winds across portions of the Northern/Central Rockies and the Northern/Central Plains, the Central Great Basin, Sun-Mon, Feb 21-Feb 22. - Heavy precipitation across portions of the Alaska Panhandle, Sun-Mon, Feb 21-Feb 22 and Wed, Feb 24. - Much below normal temperatures across portions of mainland Alaska, Sun-Tue, Feb 21-Feb 23. Detailed Summary: The medium-range period (Sunday, February 21st - Thursday, February 25th) is expected to be less cold and less active across the Lower 48 compared to current conditions. On Sunday, a front will move onshore over the Northwest and race eastward to the Plains by Monday. The system will produce rain and higher elevation snow over the Pacific Northwest on Sunday and Monday. Moisture will stream into the Northwest behind the front that will continue making snow over the Cascades through Thursday. A wave of low pressure will develop along the front over the Northern High Plains on Tuesday, which will allow heavy snow to continue over parts of the Northern Rockies on Sunday into Tuesday. Heavy snow will also develop over parts of northwestern Wyoming on Tuesday. One more thing, the pressure gradient will be strong from the high over the Great Basin and the deep low moving across Western Canada on Sunday and Monday. Due to this pressure gradient, an area of high wind will develop over the region on those two days. Low pressure over the Central Plains on Sunday will move eastward to the Upper Great Lakes on Monday and off the Northeast Coast on Tuesday. The storm will produce snow areas on Sunday from parts of the Middle Mississippi Valley into parts of the Great Lakes. The snow amounts that reach the criteria for heavy snow will be intermittent across the area. However, it would be significant enough to put it as one area instead of three much smaller areas. As the storm moves into the Lower Great Lakes and the Northeast, snow will develop over parts of northwestern Pennsylvania, then into parts of eastern Pennsylvania and New York State, and across parts of the Central Appalachians. The heavy snow here may not be continuous, but the coverage will be generous enough to include it on the Hazards Chart. Additionally, heavy lake enhanced snow will develop downwind from Lake Ontario on Monday and continue as heavy lake effect snow on Tuesday, thus the much smaller area. Furthermore, as the low moves across the Northeast, heavy snow will fall across parts of Northern New England. On Thursday, a front will extend from parts of the Northeast to the Southern Plains. There is uncertainty in the boundary's exact location, where the precipitation will develop, and the precipitation type. There could be heavy snow over the Ohio Valley or heavy precipitation (snow and rain) over parts of the Lower Mississippi Valley into parts of the Tennessee Valley. The current spread in the models makes for uncertainty in what will occur on Thursday. For Alaska, high pressure is nosing into the Far North on Sunday into Monday but will get disrupted by low pressure moving into the Bering Sea on Tuesday. The high pressure will help produce temperatures as low as -30F, fostering an area of much below normal on the Hazards Chart for Sunday into Tuesday. Extreme caution should be taken when traveling outdoors to prevent frostbite and illness. These temperatures will begin to slowly increase back to near normal across southwest portions of the state by Tuesday. Additionally, low pressure over the Gulf of Alaska near the Alaska Panhandle will produce heavy precipitation over the Panhandle with coastal rain and snow inland and at higher elevations on Sunday and Monday. The low over the Bering Sea will move eastward to the Gulf of Alaska and into the Alaska Panhandle on Wednesday. This will cause heavy precipitation will return to the area on Wednesday. Ziegenfelder