Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Tue Jan 21 2025 Valid 12Z Fri Jan 24 2025 - 12Z Tue Jan 28 2025 ...Overview... Mean troughing over the east-Central U.S. on Friday will progress eastward and cross the East Coast by the weekend. Behind this, weak ridging and more zonal flow will develop, finally helping to moderate the bitterly cold temperatures in the South and East. A shortwave dropping into the northern Rockies late this week will split, sending northern stream energy across the northern tier of the nation while trailing energy dives south to form a closed low over the Southwest that will linger through early next week. The upper low will likely bring beneficial precipitation to parts of southern California that have been dealing with devastating wildfires. Precipitation will also be enhanced across the Lower Mississippi Valley Sunday and Monday as a slow moving frontal boundary moves through the region. ...Guidance/Predictability Assessment... Model guidance is in good agreement on the overall weather pattern through the medium range period. Uncertainty surrounding a potential upper low closing off over the Southwest this weekend into early next week is gradually decreasing. The ECMWF has shown the highest run-to-run consistency with this feature, depicting the low closing off over the Southwest on Sunday and slowly drifting east-southeast through early next week, and this is consistent with the ensemble means from the GEFS/ECENS/CMCE. The 00Z GFS and CMC kept the upper low further west, but the 06Z and 12Z runs have shifted eastwards, closer to the ECMWF solution. The CMC still remains the outlier with the low placement farther west than the general consensus. There is a bit more uncertainty late in the period as a potential shortwave drops into the northern Plains or Upper Midwest on Monday and progresses east across the Great Lakes or Northeast on Tuesday. There is a significant amount of model spread in placement and strength of this feature, which could impact the sensible weather across the northern tier Monday and Tuesday. Given good model agreement, a near even blend of the 06Z GFS and 00Z ECMWF/CMC/UKMET was used for days 3-5 (Friday through Sunday). For days 6 and 7, the weight placed on the CMC and UKMET were decreased and ensemble means from the GEFS and ECENS were added, resulting in a good middle of the road forecast that falls close to the means and general consensus. This blend kept good continuity with WPC's previous forecast as well. ...Weather/Hazards Highlights... Colder than normal temperatures will linger through Friday in the East and through Saturday in the South and Southeast. The coldest anomalies will be focused along the Gulf Coast where cold could be hazardous at night when lows dip below freezing. Temperatures will gradually moderate, returning to near normal Sunday through early next week. Anomalously cold temperatures will also develop in the High Plains, Rockies, and much of the West this weekend under the influence of upper troughing. The coldest anomalies will be in the High Plains and Rockies where high temperatures could be 10-20 degrees below normal. Precipitation wise, a couple clipper systems may produce some light scattered precipitation from the Northern Plains to the Midwest, Great Lakes, Ohio Valley, and Northeast. More widespread rain and mountain snows will move into the West by the end of the week as a frontal system drops south across the region, which will likely provide beneficial rain to Southern California over the weekend. A tight gradient behind the cold front dropping south may produce an episode of strong winds along parts of the Rockies late this week and over California and Nevada on Saturday. Farther east, some Gulf moisture will likely interact with a front approaching the Lower Mississippi Valley to Tennessee and Ohio Valleys by this coming weekend/early next week. Latest guidance continues to trend heavier with enhanced rainfall over parts of the southern U.S., with the potential for heavy rain and thunderstorms on Sunday across the Lower Mississippi Valley. Snow will be possible farther north across the Great Lakes, with a wintry mix possible across the Ohio Valley, central Appalachians, and potentially the Tennessee Valley as well. Precipitation may spread towards the East Coast early next week as the frontal system progresses. Dolan/Santorelli 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