Extended Forecast Discussion NWS Weather Prediction Center College Park MD 201 PM EST Wed Feb 24 2021 Valid 12Z Sat Feb 27 2021 - 12Z Wed Mar 03 2021 ...Heavy rain threat continues from the southern Plains to the Tennessee Valley this weekend into early next week... ...Overview and Guidance Evaluation... Models and ensembles continue to advertise a heightened chance for a heavy rain event to extend across the Mid-South as we begin the medium range period this weekend. The heavy rain area will remain sandwiched between a strong upper ridge across the southern Gulf of Mexico and broad upper-level cyclonic flow dipping into the northern tier states. This will tend to prolong the threat of heavy rain in the same general area from the southern Plains to the Tennessee Valley and towards the southern Appalachians into early next week. Models have been relatively consistent in placing the heavy rain axis through much of the event from this weekend into early next week, although there has been a tendency to extend the heavy rain farther east into the southern Appalachians. A general model compromise together with the WPC ensemble biased-corrected QPF was used to create the medium-range QPF field. As we head beyond Day 5, there is a general model signal to gradually push the moisture eastward into the Southeast as the heavy rain threat diminishes across the Deep South beginning on Tuesday. By Wednesday, much of the rain could be heading off the coast of the southeastern U.S. There is some indication for a low pressure wave to form near the central Gulf around this time frame. The ECMWF tracks this system across the East Coast. This scenario is not supported by the EC ensemble mean, the GEFS and the CMC mean however. The WPC medium-range package was derived based on the consensus of the 00Z ECMWF/00Z EC mean, the 06Z GFS/06Z GEFS, and smaller contribution from the 00Z CMC/CMC mean with more of the ensemble means on day 6-7 to account for the forecast uncertainty. This resulted in a blend that lied reasonably close to continuity. ...Weather/Threats Highlights... Precipitation spreading into portions of the central to northern Rockies could result in heavy snow for the higher elevations. Meanwhile, upper level troughing across the Four Corners region will allow Gulf moisture to lift northward as waves of low pressure rides along a slow-moving front. This setup will favor a few rounds of locally heavy rainfall this weekend into early next week across portions of the Arklatex to the TN and OH Valleys. The latest guidance shows the possibility of general rainfall totaling several inches over the period. Farther north, some wintry precipitation can be expected across the upper Great Lakes early on Saturday, across the Midwest on Sunday and Sunday night, and across northern New England Monday and Monday night. Another round of wintry weather is possible across the Midwest to the Ohio Valley Monday to Tuesday. Below normal temperatures are expected to remain primarily over the Northern Rockies to start the period with departures of 10F to as much as 20F Saturday while the eastern half of the CONUS experiences slightly above normal daytime highs. Ahead of the stationary boundary expected to be draped across portions of the South, daytime highs as much as 15F above normal are possible Sunday along the Gulf Coast as well as portions of the Northeast and New England. Nighttime lows are forecast to be well above normal (10 to 20F) for much of the central and eastern U.S. Sunday and Monday, ahead of the frontal boundary draped through the MS River Valley to Great Lakes. Kong/Taylor 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, winter weather outlook probabilities and heat indices are at: 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml