Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Tue Feb 23 2021 Valid 12Z Fri Feb 26 2021 - 12Z Tue Mar 02 2021 ...Potential heavy rainfall from the southern Plains to the Tennessee Valley this weekend into early next week... ...Overview and Guidance Evaluation... A general synoptic pattern that features upper-level energies lifting across the Southwest together with a subtropical ridge anchored over the southern Gulf of Mexico will prevail during the medium range period. The resulting southwesterly flow in between will likely lift Gulf moisture across the southern U.S. and into portions of the eastern U.S. this weekend into early next week. Waves of low pressure developing along a slow-moving front would provide the focus for a multi-day heavy rainfall event across the interior southern U.S. and into the Tennessee Valley. Since yesterday, models have settled into the idea of ejecting more upper-level energy from the Southwest into the central Plains this weekend, lending more confidence for the initial bout of potentially heavy rainfall to extend across the interior Deep South into the weekend. The GFS/GEFS solutions place the rain axis farther to the south into the interior Southeast. Preference was given to the EC and CMC means for an axis farther inland across the Tennessee Valley. The extra upper-level energy is then carried downstream to promote upper-level troughing and a decent signal for a low pressure system to move across the Great Lakes on Saturday. Meanwhile, moisture ahead of the developing system will likely move up the East Coast on Saturday ahead of a warm front lifting across the Southeast into the Mid-Atlantic. Some wintry precipitation is possible across the central Appalachians Friday night into early Saturday. As the system exits New England on Sunday, model guidance continues to be quite consistent in a resurgence of moisture from the Gulf to prolong the heavy rain potential across the Mid-South into the Tennessee Valley and towards the Appalachians. Another upper-level trough that gradually digs down into the Southwest this weekend will then send additional upper-level energy into the southern Plains. When combining with broad troughing associated with a cold air mass settling into the northern tier states, the synoptic pattern will help sustain the slow-moving axis of heavy rainfall across Mid-South into early next week, although the details are yet to be determined. It is possible that the heavy rain event will gradually diminish in the Deep South by next Tuesday as the bulk of the moisture begins to shift eastward into the Southeast. The WPC morning package was derived based on the consensus of the 00Z ECMWF/00Z EC mean, the 00Z & 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... The Pacific Northwest to northern Rockies will see a couple days of widespread precipitation late this week, with the higher elevations of the Cascades, northern Rockies, and Bitterroots expected to receive heavy snow. The associated upper trough will then drop into the Southwest U.S. and gradually opens up over the Plains. A favorable setup for a prolonged period of Gulf moisture to interact with the wavy boundary in place is likely to set up a period of active weather including heavy rainfall and possibly thunderstorms for portions of the Southern Plains to the Tennessee Valley and southern Appalachians beginning late this week into early next week. 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 on Monday. Below normal temperatures are forecast predominately across the Rockies during the period and then in the wake of the late weekend and early next week system. Those below normal readings could spill into the Plains. Departures of 10F to as much as 20F are possible. Nighttime lows are forecast to be well above normal (10 to 15F) 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