Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Tue Jan 28 2025 Valid 12Z Fri Jan 31 2025 - 12Z Tue Feb 04 2025 ...General Overview... The forecast period begins Friday with a closed upper low tracking eastward from the central Plains and evolving into an open wave as it reaches the East Coast Saturday morning. This feature should produce widespread rain and some thunderstorms from the central Gulf Coast to the Mid-Atlantic and southern New England. A couple rounds of snow are possible across the northern tier through the period. Back across the Pacific Northwest, a cold front and associated moisture feed ahead of it will lead to the return of rain and mountain snow by Friday and continuing into the weekend. Most guidance develops an eastern Pacific upper trough by next Tuesday, helping to maintain the flow of moisture into the West, while guidance differs on how much troughing may exist over the East. Most of the country will have near or above normal temperatures through the period, aside from parts of the Northeast on Saturday and then Sunday-Tuesday when an Arctic airmass settles across the Northern Plains and Upper Midwest (possibly extending eastward somewhat) behind a strong cold front. ...Guidance/Predictability Assessment... The updated forecast started with a 00Z/06Z model blend on Friday, with subsequent removal of the UKMET due to its slow progression of the northern tier system/trailing cold front Saturday onward (an issue also evident in the new 12Z run) while keeping CMC weight fairly low due to being on the slow edge of the spread for the upper shortwave reaching the East Coast by early Saturday. GFS input was split between the 06Z/00Z runs as one or the other compared better to consensus than the other depending on the feature. The forecast included at least modest ensemble mean input (06Z GEFS/00Z ECens) from Saturday onward. The resulting blend yielded fairly good continuity. Models/ensemble means have trended notably faster over the past couple days with the opening Plains/Mississippi Valley upper low on Friday and reaching the East Coast by early Saturday. 00Z machine learning (ML) models still showed a fair amount of spread but the trends over recent days argue against the slow CMC/CMCens side. The new 12Z run has improved somewhat. By mid-late period, there are combined uncertainties with the eastern Pacific/West Coast evolution and leading energy that should promote a northern tier surface system/trailing cold front. Recent trends and a modest majority of ML guidance support the idea of an upper low drifting just off Vancouver Island by early next week while some ridging develops over the Interior West with troughing farther east. However some 12Z solutions including the CMC in particular and even to some degree ECMWF/GFS have backed away from meaningful eastern troughing and thus do not push the cold front as far south over the central/eastern U.S. ML models showed some spread at the surface and aloft late in the period but generally did not seem to favor the flatter side of the dynamical spread aloft or the northernmost side for the surface front. ...Weather/Hazards Highlights... An occluded low pressure system should track across Missouri and then over the Ohio Valley by Friday morning. In the warm sector of the surface low, warm air advection in combination with forcing aloft may produce some pockets of heavy rainfall from the Panhandle of Florida to the southern Appalachians, but with coverage/intensity likely to be less than on Thursday. Continued guidance trends toward faster progression of this system have lowered QPF in most guidance, with current clustering for heavy rain rates now appearing too diffuse to support a Marginal Risk area in the Day 4 Excessive Rainfall Outlook. Therefore this area has been removed in the afternoon update. Meanwhile this system will likely produce snow or a wintry mix over parts of the Northeast. Current forecasts show the potential for winter weather to linger across Upstate New York to interior New England through Saturday morning. Another round of winter weather could track across the Great Lakes to the Northeast on Sunday into Monday with a clipper type system. Expect moist inflow to return to the West Coast late this week, expanding into the northern Great Basin/Rockies, with rounds of low pressure/frontal systems tracking through the region. An atmospheric river event is becoming more likely for the Friday- Saturday time period from northern California to the Olympic Peninsula. A Day 4 Marginal Risk remains valid for the coastal ranges and the foothills of the Oregon Cascades, and a Day 5 Marginal Risk covers areas a little farther south to include more of northern California and extending into southwestern Oregon, with the heaviest rainfall likely to fall on Saturday. New 12Z guidance is continuing to show some signal for greater enhancement of rainfall around northern California around Saturday. There is still enough spread for location/magnitude to hold off introducing an embedded Slight Risk area for now, but it would not take much improvement in clustering to merit that action. The evolving upper trough forecast to evolve just off the West Coast early next week may continue the flow of moisture into the West, with highest totals likely over northern California and vicinity with snow continuing over the northern Rockies. Above average temperatures will prevail late this week across much of the central and eastern U.S., with decent coverage of plus 10-20 degree anomalies for highs and morning lows. This also holds true going into the weekend, although New England and New York State may be quite chilly on Saturday into early Sunday with the Mid-Atlantic region closer to seasonal averages. The next round of Arctic cold arrives across Montana on Sunday and extends into the Dakotas by Monday, with highs potentially 15-25 degrees below average in many cases. Colder weather then encompasses more of the central and northern U.S. going into Tuesday. However, at that time temperatures over the eastern half of the country become more uncertain as reflected in guidance spread for how much upper troughing exists over the East and position of the primary surface front. Upper ridging that develops over the West/Rockies should promote a warming trend over the southern half or so of those areas. Rausch/Hamrick 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