Extended Forecast Discussion NWS Weather Prediction Center College Park MD 159 AM EST Tue Feb 4 2025 Valid 12Z Fri Feb 07 2025 - 12Z Tue Feb 11 2025 ...Potentially heavy snow and ice across the northern Mid-Atlantic and Northeast this weekend... ...Overview... Quasi-zonal flow with embedded shortwaves across the lower 48 late week will transition to a pattern with a positively tilted mean trough setting up across the interior West this weekend into early next week, just downstream of a highly amplified Pacific through Alaska upper ridge. Precipitation is likely to spread through the West Friday before finally trending drier over the weekend. Farther east, snow across the north-central U.S. and rain centered in the Ohio Valley on Friday will consolidate into a low pressure/frontal system bringing possible locally heavy rain to the Ohio Valley/central Appalachians and possible heavy snow to the Northeast, along with some freezing rain and sleet in between, for the weekend. Precipitation looks to remain/get renewed centered over the Tennessee Valley into early next week. Temperature-wise, broad areas of well above normal temperatures late this week will shrink in scope to the Southeast early next week. Meanwhile below average temperatures in the northwestern and north-central U.S. are forecast to trend even colder into Monday-Tuesday. ...Guidance/Predictability Assessment... Tonight's models and ensembles remain fairly agreeable for the overall pattern with typical scatter for individual features and shortwave details. A quick-moving shortwave along the northern tier will draw a surface low from the south-central Plains northeastward over the weekend. By early Sunday, models show some spread with the low track, made more complicated by potential secondary low formation just offshore while the original low tracks near/over the Lower Great Lakes. The 18Z GFS favored the offshore low for a more suppressed low track. The 12Z/newer 00Z GFS runs were more agreeable with other guidance that the Great Lakes low will remain the primary low. However, a solution like the 18Z GFS cannot be completely ruled out especially because a handful of the AI/ML models were similar. The low track has implications for winter weather across the Northeast, but at least models agree in the existence of the low albeit with some track differences. The pattern of a western trough with its axis toward Hudson Bay this weekend into early next week has broad agreement, but rounds of northern and southern stream energy feeding into the trough are much more variable. These lower predictability features favor using a model/ensemble mean blend so as not to favor any particular individual solution that could easily change with its next run. The WPC forecast used a multi-model deterministic blend of the 12Z guidance early in the forecast period, and gradually increased the proportion of GEFS and EC ensemble means to near/just over half by Days 6/7 as spread in the details increased. ...Weather/Hazards Highlights... Precipitation is likely to continue in the western U.S. on Friday as a couple of low pressure/frontal systems move through. Rainfall magnitudes will finally lessen in coastal California, but farther inland snow will be possible across the Cascades/Sierra Nevada and farther east across the northern and central Rockies. By the weekend, much less precipitation is forecast for the West, with just some light amounts in the Pacific Northwest and parts of the northern/central Rockies. The central Rockies may see some high winds in the post-frontal pattern on Saturday. Farther east, some snow is forecast to spread into the Dakotas Friday and into the Upper Midwest Friday-Saturday to the north of developing low pressure in the south-central Plains. Meanwhile moisture present across the Ohio Valley and vicinity will lead to some light to moderate rain Friday. Then as the surface low tracks northeast, moderate to heavy snow is forecast to develop across the Great Lakes and the northeastern U.S. on Saturday. Probabilities of plowable snow/sleet continue to increase across the northern Mid-Atlantic into the Northeast, especially in higher elevations of the Catskills, Adirondacks, and Berkshires. Sleet and freezing rain are also a possibility across portions of the Mid-Atlantic, New York, and southern New England. To the southwest, rain is likely across the Ohio Valley and central Appalachians. Potentially heavy rain be most concerning in the central Appalachians where there are wet antecedent conditions already, plus ample rainfall in the short range period. Multiple rounds of rain are possible due to convection well ahead and then rain directly ahead of the cold front. Thus a Marginal Risk is delineated in the Day 5/Saturday ERO centered in West Virginia. The pattern will be favorable for precipitation across the southern half of the Mississippi Valley to Tennessee Valley and southern Mid-Atlantic into early next week. Some wintry weather may be possible on the northern side of the precipitation shield. Colder than average temperatures are forecast for northwestern and north-central parts of the lower 48 through the period. The cold will be especially pronounced across Montana and North Dakota, especially by early next week when another surge of cold air is likely. By Monday-Tuesday, lows are forecast to be in the -10s and -20s, along with some below zero highs. Meanwhile, areas from the Four Corners states across the South are expected to see unseasonable warmth as highs and lows that are 20-30 degrees above average become widespread. These anomalies could set daily records. Exact temperatures/anomalies vary somewhat at any particular place Friday-Saturday, but by Sunday-Monday there should be a more pronounced cooling trend across the Four Corners and south-central U.S. to the Mid-Atlantic behind a strong cold front. By Tuesday warmer than average temperatures should be limited to the central Gulf Coast to Florida. Tate Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml https://www.wpc.ncep.noaa.gov/#page=ovw