Extended Forecast Discussion NWS Weather Prediction Center College Park MD 156 AM 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 is expected to fuel the development of 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 of the country will have near or above normal temperatures through the period, until early next week when an Arctic airmass settles across the Northern Plains and Midwest behind a strong cold front. ...Guidance/Predictability Assessment... The 18/00Z model guidance suite is in good synoptic scale agreement across the country for the end of the week. However there were some more timing differences observed with the CMC and UKMET solutions, so the model blend was weighted more towards the GFS/ECMWF to start. Given the transition to a more zonal flow pattern aloft by Sunday, the guidance differs more with timing and magnitude of features in the northern stream flow, and the arrival of the arctic front across the Northern Plains. The forecast blend transitioned to about 50% ensemble means by early next week to account for the increasing model uncertainty. ...Weather/Hazards Highlights... An occluded low pressure system is forecast to move 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 strong forcing aloft will create a favorable environment for heavy rainfall from the Panhandle of Florida to the southern Appalachians. There will likely be a corridor of rainfall totals approaching one inch across portions of this region, and there could be the potential for some training/repeated convection ahead of the trailing cold front, albeit less intense than what is expected on Thursday. The new Day 4 outlook has a smaller Marginal Risk area compared to the previous Day 5 outlook owing to a faster storm system, and if QPF trends lower in future forecasts, it's possible this risk area may eventually be dropped. Meanwhile with this system, precipitation will likely be in the form of snow or a wintry mix on the northern edge. 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 with a clipper type system. Moist inflow is forecast 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 will be valid for the coastal ranges and the foothills of the Oregon Cascades, and a Day 5 Marginal a little farther to the south to include more of northern California and extending into southwestern Oregon, with the heaviest rainfall likely to fall on Saturday. There is the potential that a Slight Risk may eventually be needed in future outlooks for portions of northwestern California. Temperatures are expected to be above average to close out the week for this time of year across much of the central and eastern U.S., with highs running about 5-15 degrees above average in most cases. This also holds true going into the weekend, although New England and the Mid-Atlantic region likely remain 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 degree below average in many cases. Colder weather then encompasses more of the central and northern U.S. going into Tuesday. 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