US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 445 PM EDT Thu Mar 18 2021 Valid Sunday March 21 2021 - Thursday March 25 2021 Hazards: - Heavy rain across portions of the Plains, and the Upper/Middle Mississippi Valley, Mon, Mar 22. - Heavy rain across portions of the Middle/Lower Mississippi Valley, the Tennessee Valley, the Southern Appalachians, the Southeast, the Southern Plains, and the Ohio Valley, Tue-Thu, Mar 23-Mar 25. - Heavy snow across portions of the Pacific Northwest and the Northern Great Basin, Sun, Mar 21 and Wed, Mar 24. - Heavy snow across portions of the Northern Rockies and the Northern Great Basin, Mon, Mar 22. - Heavy snow across portions of the Central Rockies and the Central Plains, Sun, Mar 21. - Flooding possible across portions of the Central Plains, the Middle Mississippi Valley, the Great Lakes, the Ohio Valley, and the Upper Mississippi Valley. - Flooding occurring or imminent across portions of the Central Plains and the Middle Mississippi Valley. - Flooding likely across portions of the Central Plains, the Middle Mississippi Valley, and the Southern Plains. Detailed Summary: The medium-range forecast period (Sunday, March 21st to Thursday, March 25th) features an area of low pressure off the southeastern tip of Florida and an area of strong high pressure over the Northeast on Sunday. The pressure gradient between the high and low will be slowly weakened along the Mid-Atlantic and the Southeast Coast on Sunday; therefore, the wind will slowly weaken below the criteria, and an area of high wind was not depicted on the Hazards Chart. Meanwhile, upper-level energy and weak onshore flow help produce heavy snow over parts of the Cascades and parts of the Bitterroot Range/Salmon Range on Sunday into Monday. The onshore flow will become stronger on Wednesday, so heavy snow will return to the Cascades on Wednesday. A front extending from the Upper Midwest to the Central/Southern High Plains on Sunday, with a low-pressure wave over the Central High Plains, will deepen and move to the Upper Great Lakes by Wednesday. The front and an associated wave of low pressure will help produce an area of heavy snow over parts of the Central Rockies on Sunday. Ahead of the front, temperatures will be about 12 degrees above average over the Upper Midwest on Sunday into Tuesday and expand into parts of the Northeast/Ohio Valley by Wednesday. Moisture pooling over the Middle Missouri Valley/Central Plains helps develop heavy rain along the boundary on Monday. As the southern end of the front moves southeastward and becomes quasi-stationary over the Lower Mississippi/Tennessee Valleys, the rain will develop over parts of the Lower Mississippi Valley and Southern Plains on Tuesday. The rain's uncertainty has decreased, so an area of heavy rain will be depicted on the Hazards Chart. The heavy rain will expand into parts of the Tennessee Valley and Southeast on Wednesday and Thursday. For Alaska, low pressure over the Bering Sea will weaken as low pressure moves into the Gulf of Alaska on Sunday. The low will move into the Alaska Panhandle and dissipate by Monday. The system will then produce light precipitation over the Alaska Panhandle on Sunday. A second area of low pressure will develop over the North Pacific on Sunday, strengthening on Monday. The low will move into the Gulf of Alaska on Tuesday. The associated plume of moisture will be weaker and steer more into British Columbia. However, an area of precipitation will develop over parts of the panhandle on Tuesday. A third area of low pressure will move eastward from the Eurasian continent and into the Bering Sea on Wednesday and the mainland on Thursday. There will be an area of strong wind associated with the low over parts of the Western Mainland on Wednesday. The system will produce snow over the Western Mainland on Wednesday as well, extending into parts of the Alaska Range's western end. Ziegenfelder