Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Wed Feb 12 2025 Valid 12Z Sat Feb 15 2025 - 12Z Wed Feb 19 2025 ...Strong storm to bring heavy rain and flooding threat to the Tennessee/Ohio Valley on Saturday and heavy snow from the Midwest to Northeast this weekend... ...Overview... A deep upper trough will move east across the Central U.S. this weekend, then lift rapidly northeastward early next week. This will drive a strong storm system across the Central and Eastern U.S. that will likely bring a significant threat of heavy rain and flash flooding to the Ohio/Tennessee Valley region on Saturday. Wintry precipitation and snow is expected on the northern side of the storm system, and a swath of heavy snow will be possible from the Midwest to the Northeast this weekend. Meanwhile, the next Pacific system will approach the West Coast late Saturday into Sunday, bringing low elevation rain and mountain snow to the Pacific Northwest and Northern California. This system will push inland early next week, bringing precipitation southeastward to the Central Rockies and the Central/Southern Plains by Tuesday. Mid- next week, the system in the Plains will sink south towards the Gulf Coast and another Pacific system will move into the West Coast. Arctic high pressure will expand south and east from the north-Central U.S. through the period, resulting in well below normal temperatures for much of the eastern two-thirds of the nation. ...Guidance/Predictability Assessment... Model guidance is in good agreement on the large scale pattern through the period with an expected amount of model spread/differences in details of specific systems. The highest impact differences will be concerning the strength of the storm system in the Central/Eastern U.S. this weekend. The overall pattern and model trends favor a deeper low pressure system, which is in line with the 12Z GFS/GEFS and 00Z ECMWF/ECENS, but the CMC/CMCE and machine learning models have a weaker low. In order to depict the deeper favored solution, the WPC model blend leaned heavily into the GFS/ECMWF with smaller amounts of the CMC and UKMET. Other than the strength, there was good agreement on the overall structure and evolution of this system as is tracks northeast. Later in the period, there is some more significant model spread as an upper low/trough drops into the north-Central U.S. and another low/trough moves onshore in the Pacific Northwest. Differences in location and timing of the two troughs will likely influence the surface features and sensible weather. WPCs forecast blend favored a solution closer to the GFS/ECMWF which are in line with the ensemble mean solutions from the GEFS/ECENS/CMCE. Ensemble means from the GEFS/ECENS were added to the forecast blend in increasing amounts Monday through Wednesday, which helped smooth out model differences and create a middle of the road solution. ...Weather/Hazards Highlights... The upper trough swinging across the Central U.S. this weekend will provide support for a strong storm system moving across the eastern half of the nation this weekend. Southerly flow ahead of the system will bring up anomalous moisture from the Gulf, which will combine with Pacific moisture and allow for widespread precipitation on Saturday. A broad area of heavy precipitation is expected from the Ark-La-Tex through the Mississippi, Tennessee, and Ohio Valleys to the Central Appalachians, and a Slight Risk of Excessive Rainfall is in effect for these regions on Day 4/Saturday. There will be enough instability for thunderstorm development across the Lower Mississippi Valley, which may help enhance rainfall rates in this region as well. The heaviest precipitation is forecast to focus over Kentucky and western/central Tennessee where a Moderate Risk of Excessive Rainfall is in effect. If the forecast comes to fruition, numerous flash floods, some significant, and moderate to major river flooding will be possible. The system will quickly lift northeast on Sunday, and precipitation will push off the East Coast. The threat of heavy rainfall will decrease as the system becomes more progressive, so there are no risk areas depicted in the Day 5/Sunday Excessive Rainfall Outlook. Wintry weather on the northern side of this storm system is expected to impact areas from the Midwest to the Northeast this weekend, and a swath of heavy snow is forecast from central Michigan through New York state to the Northeast. The location of heavy snow may shift if the low pressure track changes, which would also shift the transition zone of wintry mixed precipitation. There may be a period of strong and gusty winds over parts of the East behind this system, along with some lake effect snow. In the West, a Pacific system will likely spread rain and mountain snow into the Pacific Northwest Saturday into Sunday. Precipitation amounts/rates are currently forecast to stay below the criteria for an Excessive Rainfall Outlook area, but light to moderate precipitation will still be possible. Precipitation will push east/southeast through the Rockies early next week while tapering off in the Pacific Northwest. Another system is forecast to bring precipitation back to the Northwest Tuesday into Wednesday with another round of light to moderate precipitation expected. As the upper trough crossing the West early next week heads into the Central U.S. by Wednesday, expect precipitation to develop from the Central/Southern Plains eastward. Wintry weather will be possible in the northern part of the precipitation shield with rain over the South. Temperature-wise, below normal temperatures are expected through the period for much of the Central U.S. with surges reaching the South and East late this weekend and mid-next week. The north- Central U.S. will experience persistently cold temperatures, with high temperatures as much as 20-30 degrees below average possible each day. High temperatures will drop 15-25 degrees below average for portions of the South and East Sunday into Monday in the wake of this weekend's strong storm system. Ahead of the storm system, a brief surge of warmer than average air is expected in the South and Southeast on Saturday and along the East Coast on Sunday. Another cold surge will be possible in the South on Wednesday as the Plains system drops south towards the Gulf Coast. Temperatures in the West are expected to remain near normal with small fluctuations between slightly below and slightly above average. Dolan/Rausch 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