Extended Forecast Discussion NWS Weather Prediction Center College Park MD 156 AM EST Sun Jan 26 2025 Valid 12Z Wed Jan 29 2025 - 12Z Sun Feb 02 2025 ...South-Central U.S. Heavy Rainfall Threat Wednesday-Saturday... ...General Overview... A slow moving closed upper low will linger over the Southwest Wednesday and Thursday, then gradually push northeast towards the southern/central Plains and Midwest Friday and Saturday. This feature will be accompanied by an occluded low pressure system at the surface that could bring a heavy rainfall threat to the south- Central U.S. during the second half of the week. Meanwhile, a broad upper trough will swing across the north-Central and northeastern U.S. and ridging will extend north into the Pacific Northwest. By Friday, a trough will approach the West Coast and push a Pacific frontal system east across the West next weekend while an Arctic front sinks south across the north-Central U.S.. ...Guidance/Predictability Assessment... Model guidance is in good agreement on the overall pattern through the end of the week, then model spread increases for next weekend, which is typical at this time frame. Deterministic and AI guidance has trended a little faster with the closed low moving across the southern/central Plains, which is reflected in WPCs forecast. There is still some uncertainty surrounding the evolution of the occluded surface low, but there is still good agreement for heavy rainfall in the warm sector of the system over the south-Central U.S. later this week. The most uncertain features are on Day 7/Sunday when there is significant spread in the timing/location of surface features. For now, a compromise near the ensemble mean solutions was used for the WPC forecast. The WPC forecast model blend consists of a even blend of the GFS/ECMWF/CMC/UKMET for Wednesday and Thursday. For Friday onward, the weight put on the CMC was reduced as it becomes more of an outlier from the general consensus, the UKMET was removed as it is unavailable that far out, and the GEFS and ECENS means were added in increasing amounts. This blend maintains good continuity with WPC's previous forecast. ...Weather/Hazards Highlights... A slow moving occluded low pressure system is forecast to move across the southern Plains Wednesday through Friday with a cold front extending southwest into Mexico and a warm front lifting into the Lower Mississippi Valley. Warm, moist air from the Gulf will be in place across the south-Central U.S., setting the stage for a multi-day heavy rainfall event. The best chance for heavy rainfall will be in the warm sector and in the vicinity of the triple point low where moisture and instability will be maximized, and there could be potential for training convection ahead of the slow trailing cold front. Heavy rainfall could lead to flash flooding concerns across the southern Plains and Lower Mississippi Valley, especially in the Ark-La-Tex region on Thursday and Louisiana and Mississippi on Friday. For the Day 4/Wednesday Excessive Rainfall Outlook, there is a bit too much uncertainty in rainfall location to introduce any risk areas at this time, but there still could be limited potential for heavy rainfall in portions of Texas. For the Day 5/Thursday Excessive Rainfall Outlook, a broad Marginal Risk from the southern Plains to the Mid/Lower Mississippi Valley and a Slight Risk for the Ark-La-Tex will likely be needed given the strong signal for heavy rainfall. Early in the period, a clipper type low pressure system will bring a swath of wintry weather to the Great Lakes and Northeast, with some localized heavy snow potential. This system will quickly move east, and a couple days of dry weather are expected for the northern tier before precipitation associated with the occluded low reaches the area. Precipitation chances will extend well to the north of the occluded system, spreading to encompass the eastern third of the nation by Saturday, and there will be a chance for wintry weather on the northern extent of the precipitation shield given lingering cold air in place. Wintry weather is also anticipated on the backside of the low as it initially strengthens, and heavy snow will be possible in northern New Mexico and southern Colorado on Wednesday and Thursday. By Sunday, the system will be weakening and precipitation chances will be mainly limited to the Great Lakes and Northeast. In the West, precipitation chances will gradually increase across the region late this week into the weekend as a Pacific frontal system pushes inland. Widespread rain and mountain snow is expected, and heavy snowfall is forecast for the Cascades and northern/central Rockies. Temperatures will generally be near or above normal for much of the lower 48 late this week into the weekend, but there will be a few opportunities for below normal temperatures. The Southwest will likely be below normal Wednesday and Thursday under the influence of the closed upper low. The Northeast will likely be below normal Wednesday through Friday in as the clipper system moves through and colder air sinks into the region. Finally, there will be a chance for well below normal temperatures in the northern Rockies and northern High plains on Sunday as an Arctic front sinks south across the region. Dolan 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