US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 325 PM EST Thu Mar 04 2021 Valid Sunday March 07 2021 - Thursday March 11 2021 Hazards: - Heavy snow across portions of California and the Pacific Northwest, Mon-Wed, Mar 8-Mar 10. - Heavy rain across portions of the Middle Mississippi Valley, the Northern Appalachians, and the Ohio Valley, Thu, Mar 11. - Flooding occurring or imminent across portions of the Southeast, the Lower Mississippi Valley, and the Ohio Valley. - Flooding likely across portions of the Southeast and the Ohio Valley. - Heavy precipitation across portions of mainland Alaska, Mon, Mar 8. - High winds across portions of mainland Alaska, Sun-Mon, Mar 7-Mar 8. Detailed Summary: During the medium range period (Sunday, March 7th - Thursday, March 11th) persistent upper-level troughing will set the stage for multiple rounds of precipitation west of the Rockies before propagating east, breaking a ridging pattern aloft and bringing active weather to the Midwest. On Sunday, relatively dry and quiet conditions will precede a low pressure/frontal system moving onshore from the northeast Pacific. As it propagates east, the system is forecast to bring moderate rain to coastal California and southern Oregon as well as heavy snow to the mountain ranges of northern California and the Sierra Nevada on Monday. A shortwave sweeping through the Northwest quadrant on the heels of the low pressure/frontal system will serve to prolong the precipitation near and along the coast into Tuesday and the heavy snow in the California mountains through Wednesday. After passing through and bringing moderate snowfall to the high elevation Northern and Central Rockies on Tuesday, the system is expected to generate 35+ mph wind gusts on the lee side of the mountains before advancing into the Great Plains. Current model guidance suggests the potential for mixed precipitation in the Northern Plains and Upper Midwest on Wednesday, the heaviest of which may fall along the Minnesota/Wisconsin border and the western half of the Michigan Upper Peninsula. As the storm system is ushered quickly to the northeast by a lifting upper-level trough on Thursday, its associated cold front is forecast to drape from the Middle Mississippi Valley to the Lower Great Lakes. Aided by a massive influx of moisture from the Gulf of Mexico and strong frontogentical forcing at the surface, heavy rain with accumulations reaching or exceeding 2-3 inches in 24 hours is expected along the front. Areas subject to these heavy rainfall totals will be at risk for flash, urban, and local flooding. For the entire length of the medium range period, minimum and maximum daily temperatures are forecast to sit 10 to 20 degrees above normal for the Northern/Central Plains, the Upper Mississippi Valley, and around the Upper Great Lakes. These temperature departures translate into highs that will reach the 50s and 60s, while lows will generally remain above freezing through Wednesday. This is particularity significant as states in the Upper Midwest still possess a snowpack and these high temperatures combined with a prolonged lack of re-freezing will lead to widespread, though gradual, snow melt. Along the East Coast both maximum and minimum daily temperatures are forecast to start slightly below normal before moderating and reaching double digits above normal by mid-week, aiding with snow melt in the Northeast. Out West, maximum daily temperatures are expected to take a marginal drop below normal throughout the period. In Alaska, a strong storm system is forecast to pass through the Bering Sea at the beginning of the period. A tight pressure gradient is expected to set up ahead of this strong system system, generating hazardous wind gusts over the western mainland Sunday into Monday. While high winds are also possible along the Aleutians during the same time frame, they are not expected to reach hazardous levels. As this system makes its way onshore it is expected to bring heavy precipitation to portions of the western and southern mainland Monday into Tuesday morning. Presently, guidance points towards the potential for a second heavy precipitation event along the southern mainland Wednesday into Thursday, however, a high degree of uncertainty exists because the models disagree on whether or not the low pressure/frontal system that could generate this heavy precipitation event will pass near the mainland or remain far offshore. As such, no hazard area will be drawn yet and the region will be monitored over the coming days. Above normal maximum and minimum temperatures are forecast to affect portions of the Far North and Southwestern mainland Sunday through Tuesday, with the highest temperatures expected to occur on Monday. Though warmer than usual, actual temperatures in the region will still remain well below or near freezing and are thus expected to be non-hazardous. Zavadoff