Extended Forecast Discussion NWS Weather Prediction Center College Park MD 159 PM 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 and 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. Rainfall looks to remain/get renewed centered over the Tennessee Valley into early next week, with the potential of wintry precipitation from the Ohio Valley to Mid-Atlantic. 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... The latest deterministic guidance is in good agreement with respect to both the pattern and system progression across the CONUS to start the medium range period. Following the departure of a system over the northeastern U.S. into the Atlantic late this week, guidance shows that a progressive upper-level wave will move quickly across the CONUS from the West Coast to the Midwest/Great Lakes and eventually the Northeast this weekend. Guidance has come into better agreement with respect to the track of the accompanying surface system, following a path from the Southern Plains through the Ohio Valley and into the Mid-Atlantic, after the GFS in particular had been suggesting a more southerly path. There remains some disagreement with regards to potential secondary low development off the coast as the system reaches the Mid-Atlantic that could impact the amount and type of precipitation received in the region. Guidance differences increase in the mid- to late period upstream as various northern and southern stream energies traverse the western to central U.S. The latest 00Z/06Z GFS tended to be within the middle ground amongst the deterministic guidance, ensemble means, and various available AI models, with the CMC more progressive with northern stream energy and the ECMWF with a much slower, much more amplified pattern over western Canada and the northeastern Pacific. The means tended to fall within the middle of the solutions and the AI models depicted a similar variety of possibilities to the GFS/ECMWF/CMC. However, the general consensus is one (or more) energies will pass through the western U.S. and lead to an expanding area of precipitation from the Plains to Southeast/Mid- Atlantic early next week. The updated WPC forecast used a composite blend of the GFS/ECMWF/CMC/UKMET guidance given the noted good agreement through the upcoming weekend. The later period relied more on the 06Z GFS and a significant contribution (60% by day 7) from the GEFS/ECens/CMC means given the significant increase with respect to individual wave specifics early next week. ...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. Some gusty winds will be possible for higher elevations of the central Appalachians and northern New England as a low pressure system departs the region. 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 will 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 of and then along the cold front. Thus a Marginal Risk is delineated in the Day 5/Saturday ERO centered in West Virginia. The pattern looks to become increasingly favorable for precipitation across the southern half of the Mississippi Valley to Tennessee Valley and southern Mid- Atlantic into early next week. There is an increasing signal for the potential of local to widespread heavy rainfall from the Mississippi Valley to Tennessee Valley, and potentially disruptive wintry precipitation along the northern side of the precipitation shield from the Ohio Valley to Mid-Atlantic. 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 theFour 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. Putnam/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