Extended Forecast Discussion NWS Weather Prediction Center College Park MD 212 PM EST Mon Jan 27 2025 Valid 12Z Thu Jan 30 2025 - 12Z Mon Feb 03 2025 ...Heavy rain and strong thunderstorms expected across the Lower Mississippi Valley to Mid-South to close out the workweek... ...Overview... The forecast period begins Thursday with a cutoff upper low ejecting eastward from the Southern Rockies to the western High Plains, and this will sustain a surface low that is expected to track from Texas and eventually to the East Coast by Saturday. This is expected to fuel the development of rain and some strong/severe thunderstorms across parts of Texas through the Lower Mississippi Valley Thursday, migrating east to the Lower Ohio/Tennessee Valleys and Southeast Friday. 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 lower 48 will see near or above normal temperatures through the period, until early next week when an Arctic airmass settles across the Northern Plains behind a strong cold front. ...Guidance/Predictability Assessment... Recent model guidance remains in good agreement on the large scale through late week. Models continue to show a faster trend compared to a day or two ago with the ejection of the upper low eastward. But there are still some variations in just how fast it will move out. Through 00/06Z, the deterministic GFS/ECMWF/UKMET were faster late Friday into Saturday with the remaining shortwave compared to the CMC and ensemble means. The 12Z CMC has jumped faster. As that feature weakens, the pattern transitions to more zonal flow over the weekend with some shortwaves and surface low variations that have typical predictability issues for small scale features. The somewhat more notable model discrepancies are with an upper low/trough focused off of British Columbia by early next week. GFS runs show it oriented southwest to northeast and a bit farther south in the Northwest compared to the ECMWF/CMC, and this has implications for the position and magnitude of atmospheric river precipitation. The 12Z GFS adjusted just a bit in the direction of the non-NCEP models. The WPC forecast transitioned from a multi-model deterministic blend early in the forecast period to around half ensemble means by Days 6-7 (with the EC the main remaining deterministic model) as model spread increased. ...Weather/Hazards Highlights... An occluded low pressure system is forecast to move across the Southern Plains Thursday and into the Mid-Mississippi Valley by early Friday. 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 ArkLaTex region to the Mid-South. There will likely be a corridor of 2 to 4 inch rainfall totals across portions of this region, and there could be the potential for training/repeated convection ahead of the initially slow trailing cold front. A Slight Risk remains in place from northeast Texas to near the greater Memphis area in the Day 4/Thursday ERO. The low pressure system is forecast to move quickly eastward on Friday, but some convection with locally heavy rainfall rates along the trailing front could produce isolated flooding from the Southeast toward the Tennessee/Ohio Valleys for a low-end Marginal Risk on the Day 5 ERO. Meanwhile with this system, precipitation chances will expand to the west and north of the occluded low with potential for snow and ice. Wintry weather is anticipated to linger in the south-central Rockies to Plains Thursday and could spread into the Lower Great Lakes region to Northeast Friday. Current forecasts show potential for winter weather to linger in the northern Mid-Atlantic to Northeast Saturday, with winter precipitation perhaps reaching NYC to Boston. Another round of winter weather could track across the Great Lakes to Northeast on Sunday with a clipper 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. Maintained a low- end Marginal Risk for coastal northwest California through the Pacific Northwest for Day 5/Friday as a moderate atmospheric river event begins and could lead to some periods of heavier rainfall on Friday. This is expected to continue into the weekend as well with additional moist onshore flow. 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, and likely 20+ degrees above average across parts of the Upper Midwest on Thursday. 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 likely arrives across Montana on Sunday and extends into the Dakotas by Monday, with highs potentially 15-25 degree below average in many cases. Tate/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