US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 255 PM EST Wed Mar 03 2021 Valid Saturday March 06 2021 - Wednesday March 10 2021 Hazards: - Heavy precipitation across portions of California and the Pacific Northwest, Mon-Tue, Mar 8-Mar 9. - Heavy snow across portions of California, Mon-Wed, Mar 8-Mar 10. - Flooding possible across portions of the Southeast. - Flooding occurring or imminent across portions of the Southeast, the Lower Mississippi Valley, and the Ohio Valley. - Flooding likely across portions of the Mid-Atlantic and the Ohio Valley. - Heavy precipitation across portions of mainland Alaska and the Alaskan Peninsula, Mon-Tue, Mar 8-Mar 9. - High winds across portions of mainland Alaska, Sun-Mon, Mar 7-Mar 8. Detailed Summary: During the medium range period (Saturday, March 6th - Wednesday, March 10th) much of the activity over the lower 48 will be isolated to the west of the Rockies where persistent upper-level troughing will set the stage for multiple rounds of precipitation, while ridging over the remainder of the CONUS will keep activity to a minimum. On Saturday, a moisture-rich cold front is expected to pass through California and the Great Basin, leaving a trail of light to moderate rain and high elevation snow in its wake. Dry and quiet conditions on Sunday will precede the arrival of a pair of low pressure/frontal systems that will bring a mix of heavy coastal rain and mountain snow to the northern California/Oregon border as well as the Sierra Nevada on Monday. Shortly after these systems progress further inland a shortwave is forecast to sweep through, prolonging the heavy precipitation near and along the coast into Tuesday and the heavy snow in the Sierra Nevada through Wednesday. After passing through and bringing moderate snowfall to the Northern and Central Rockies on Tuesday, the two low pressure/frontal systems will coalesce into one and continue moving eastward into the Great Plains. Current model guidance is still too uncertain at this time to make any definitive comments about the potential hazards associated with this storm system, however, the guidance does indicate the potential for heavy precipitation to develop over the Northern Great Plains and Upper Midwest. Additionally, a tight pressure gradient surrounding this system may produce high winds and wind gusts from the base of the Rockies to the Mississippi Valley. Updates will be provided in the coming days as the guidance evolves and the details come into better focus. Elsewhere, an upper-level trough working in tandem with a low pressure/frontal system at the surface is forecast to bring moderate rain to Florida's Space Coast on Saturday. Current model guidance suggests 24 hour rainfall totals reaching or exceeding an inch will be possible in some isolated areas, but most, if not all, of the significant rainfall is expected to remain offshore. For the entire length of the medium range period, minimum and maximum 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 Tuesday. 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 temperatures are forecast to be slightly below normal throughout the weekend before moderating at the beginning of next week. Out West, temperatures are expected to remain close to average until Monday when maximum temperatures are set to take a marginal drop below normal. In Alaska, a series of storm systems are expected pass through the Bering Sea, the stronger of which will occur at the beginning of the period. Tight pressure gradients associated with these strong systems are forecast to set up and generate 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 the second of these systems propagates east towards the mainland, a wave of low pressure and its fronts are expected to pass through and bring heavy precipitation to the Southwestern and Southcentral mainland Monday into Tuesday. 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