US Day 3-7 Hazards Outlook NWS Weather Prediction Center College Park MD 305 PM EST Tue Mar 02 2021 Valid Friday March 05 2021 - Tuesday March 09 2021 Hazards: - Heavy precipitation across portions of the Pacific Northwest, Fri, Mar 5. - Heavy precipitation across portions of California and the Pacific Northwest, Fri, Mar 5 and Mon-Tue, Mar 8-Mar 9. - Heavy snow across portions of California, Mon-Tue, Mar 8-Mar 9. - Flooding possible across portions of the Southeast. - Flooding occurring or imminent across portions of the Southeast, the Lower Mississippi Valley, the Central Appalachians, and the Ohio Valley. - Flooding likely across portions of the Central Appalachians and the Ohio Valley. - High winds across portions of the Aleutians, Fri, Mar 5. - Heavy precipitation across portions of mainland Alaska, Fri-Sat, Mar 5-Mar 6 and 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 (Friday, March 5th - Tuesday, March 9th) 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. On Friday a moisture-rich cold front is forecast to move onshore, bringing heavy rain to the low-lying coastal regions of northern California and the Pacific Northwest, while heavy snow is expected to fall in the Olympic and Kalamath Mountains. Moderate precipitation along the northern California/Oregon border will likely linger into Saturday, as the frontal boundary is anticipated to stall over the region before continuing its eastward propagation late Saturday into Sunday. As the system passes through eastern California, moderate to heavy snowfall will be possible over the higher elevations of the Sierra Nevada. Early next week a second system will make its way onshore along an almost identical path as the first, however, the greatest influx of moisture will occur along the northern California/Oregon border, where a mix of heavy coastal rain and mountain snow, particularly in the Sierra Nevada, is forecast Monday into Tuesday. Elsewhere, an upper-level low working in tandem with a low pressure/frontal system at the surface is forecast to bring moderate rain to the Southern Plains on Friday. Current model guidance suggests 24 hour rainfall totals exceeding an inch will be possible in some isolated areas of Kansas and Oklahoma, however, there is stark disagreement on how much, when, and where this will occur. Given the uncertainty and the fact that the system will be fast moving with minimal flooding concerns, no hazard area has been drawn. After exiting the Southern Plains this system will progress eastward, passing through the Gulf of Mexico and gathering a significant amount of moisture on its path to Florida. As this system progresses eastward, it is forecast to move through the Gulf of Mexico, where it will gather a significant amount of moisture, before quickly passing through Florida on Saturday. Similarly to the situation in the Southern Plains model guidance indicates there is potential for this system to produce heavy rainfall with totals of 1-2 inches in 24 hours, however, there is disagreement on whether this will occur onshore along northeast/central Florida or completely offshore. This uncertainty, combined with the fact that the soils in northeast/central Florida are abnormally dry thus minimizing flooding concerns, has led to the decision to omit a hazard area at present. However, the area will be closely monitored over the coming days. 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 Plains, the Upper Mississippi Valley, and around the Upper Great Lakes. These temperature departures translate into highs will reach into the 50s and 60s, while lows on will remain above freezing starting Saturday. This is particularity significant as many states in these regions still possess a snowpack and these high temperatures combined with a prolonged lack of re-freezing will lead to widespread 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. 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 Aleutians on Friday and the western Mainland Sunday into Monday. As some of these systems propagate southeast towards and into the Gulf of Alaska, their onshore flow is expected to bring a virtually continuous influx of heavy precipitation to the southern Mainland, save for a reprieve on Sunday. Above normal maximum and minimum temperatures are forecast to affect portions of the Far North 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 freezing and are thus expected to be non-hazardous. Zavadoff