Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 420 AM EDT Thu Apr 22 2021 Valid 12Z Thu Apr 22 2021 - 12Z Sat Apr 24 2021 ...Snow lingers over northern Maine into Friday as another shot of cold air and snow moves into the northern Rockies and High Plains... ...Record cold temperatures today across the central to eastern U.S. will moderate on Friday... ...A complex low pressure system will begin to bring a threat of heavy rain and severe thunderstorms across the Deep South on Friday... ...Fire weather threat increasing across the Desert Southwest to the southern High Plains... The intensifying low pressure system that recently brought wet snow across the Ohio Valley to the interior Northeast is beginning to move into southeastern Canada. However, its forward motion is being slowed down by a blocky weather pattern across much of Canada. The system will continue to intensify over the Canadian Maritimes today as it rotates snow back toward northern Maine where a foot of accumulation is still possible near the Canadian border. The circulation of the low will also expand in size as it pulls more cold air across the Great Lakes and down into the East Coast. In fact, some lake-enhanced snow is expected today downwind of the Great Lakes. Winds will remain strong and gusty across much of the Northeast into the Mid-Atlantic today and they will be slow to subside on Friday. A large dome of unseasonably cold air will expand eastward into much of the eastern U.S. under a large area of high pressure centered over the Mid-Mississippi Valley. Freeze Warnings and Frost Advisories remain in effect across multiple states from the central Plains eastward to the Appalachians and northern Mid-Atlantic where numerous daily record low temperatures are forecast to be tied or broken. By Friday, the cold airmass will moderate as it drifts east, although low temperatures will still be around 10 degrees below normal in the Central U.S., with lows hovering in the mid-30's to 40's. In the western U.S., a low pressure system will bring lingering light snow across the central Rockies for the next few days as another dome of cold air from western Canada is poised to surge into the northern Rockies/High Plains. Temperatures will once again tumble, along with a quick burst of snow, as the associated cold front passes through much of Montana by this evening. The higher elevations will once again receive the heaviest snowfall amounts, with 6 to 12 inches possible. The snow should then move further south into Wyoming by Friday morning where 3 to 4 inches, with up to 6 in the mountains, is forecast. Meanwhile, little improvement of fire weather conditions is in store for the Desert Southwest where Critical fire weather risk is in place over the region. The main area of concern will be from far eastern Arizona through New Mexico and into the Texas Panhandle. A deepening low pressure system will couple with dry conditions to promote Critical risk of fire weather across the region into Saturday. Moreover, portions of northern Plains and interior Northwest should be on the alert for elevated to critical fire weather risk today. Attention will turn to the southern Plains Friday morning as a complex frontal low pressure system develops over the area. Widespread showers and thunderstorms are likely as a warm front lifts north. The unstable airmass will promote the development of heavy rain and severe thunderstorms which will likely expand eastward across the Deep South late Friday into early Saturday. Accordingly, a Slight risk of excessive rainfall and severe weather have been issued by the Weather Prediction Center and Storm Prediction Center, respectively. Last but not least, precipitation associated with a deepening upper low is forecast to reach the Pacific Northwest and northern California Friday night. Kong/Asherman Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php