Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EST Wed Nov 20 2024 Valid 12Z Wed Nov 20 2024 - 12Z Fri Nov 22 2024 ...Back-to-back powerful Pacific storm systems to impact the West Coast through the end of this week with heavy rain, life-threatening flooding, strong winds, and higher elevation mountain snow... ...Near blizzard conditions are possible through this evening across the northern Plains... ...Heavy snow is likely throughout parts of the central Appalachians beginning on Thursday, with a separate burst of snowfall possible across northeast Pennsylvania and neighboring regions of the Northeast Thursday night into Friday... The active November weather pattern impacting CONUS is forecast to continue through the end of this week and bring hazardous rain, wind, and snow for several regions. A significant Pacific storm system and strong atmospheric river have already started pummeling the West Coast and Northwest this morning. The very deep low pressure system churning about 300 miles off the coast of Washington is responsible for high winds impacting much of northern California, Oregon, and Washington. These winds have already produced numerous power outages, reports of tree damage, and are expected to create blizzard conditions throughout the Cascades. Fortunately these winds are expected to gradually subside by midday as the low pressure system swings away from the region. However, a continuous plume of ample atmospheric moisture content entering northern California this morning is forecast to linger through the end of the week and lead to extreme rainfall totals. Over 10 inches of rainfall across the northern California coast and inland mountain ranges are likely to increase the threat of life-threatening flash flooding, rock slides, and debris flows. As this corridor of heavy rainfall lingers along a stationary boundary extending into the Pacific Ocean, a separate area of low pressure is forecast to develop and rapidly strengthen off the Northwest coast on Friday. This storm will help amplify the atmospheric river streaming into northern California through Friday morning, exacerbating the flooding threat. WPC has issued a High Risk (level 4/4) of Excessive Rainfall on Thursday in order to further highlight this concern. Additionally, another round of strong winds are anticipated from this second low pressure system throughout the Northwest to end the week. Residents and visitors residing or traveling between northern California and Washington are advised to check road conditions before venturing out, listen to advice from local officials, review emergency plans, and have multiple ways of receiving warnings. For the central U.S. the main weather story will be found throughout the northern Plains as heavy snow and gusty winds create near blizzard conditions today. These hazardous weather conditions are resulting from a slow-moving and gradually weakening low pressure system just north of the Minnesota-North Dakota border. The greatest snowfall amounts are forecast across North Dakota, eastern South Dakota, and northwest Minnesota, but with additional totals today generally under 4 inches. Wind impacts should be more widespread and extend into eastern Montana and Nebraska as maximum gusts could exceed 60 mph through tonight. This area of low pressure is anticipated to rapidly weaken tonight and lead to calmer conditions on Thursday. After an extended period of dry and tranquil weather across the Northeast, the upper level system exiting the northern Plains today will slide eastward and produce a chance for heavy precipitation in the form of both rain and snow. The evolution of surface features over the next few days are forecast to begin with a developing strong and compact low pressure system over the Great Lakes today, while a cold front quickly pushes eastward to the Mid-Atlantic by tonight. Showers and maybe a rumble of thunder may accompany this cold front as rain possibly mixes with snow spreading across the Great Lakes. By Thursday, a separate area of low pressure forming along the aforementioned cold front is expected to deepen and lift northward into the Northeast, while also leading to a blossoming precipitation shield. Rain is most likely across New England where warmer air surges from the Atlantic Ocean, but the higher elevations and area directly underneath the cold upper low pressure system may see precipitation fall as heavy snow. Probabilities for at least 4 inches of snow by Friday night are high (70-90%) across northeast Pennsylvania and the southern Catskill mountains of New York. Impactful snowfall is also likely to be experienced throughout the Allegheny mountains of West Virginia, Maryland, and Pennsylvania through the end of the week due to a longer duration favorable upslope snow setup. Total snowfall amounts in these higher elevations could add up to a foot. Elsewhere, high pressure building into the south-central U.S. will create dry conditions from the lower Mississippi Valley to much of the Plains, Rockies, and Southwest. The temperature outlook features one final day of widespread 60s and 70s along the East Coast before a strong cold front knocks afternoon highs below average through the start of the weekend. The coldest temperatures when compared to climatology over the next few days are forecast across the northern Plains (highs in the 20s) and Ohio Valley (highs in the 30s and 40s). Snell Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php