Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Wed Mar 16 2022 Valid 12Z Sat Mar 19 2022 - 12Z Wed Mar 23 2022 ...Strong low pressure system will likely produce heavy rain and severe storms across large sections of the southern U.S. toward the Tennessee Valley by early next week... ...Overview... A rather active weather pattern is in store for the medium-range period as a low pressure system moving through the Northeast this weekend will give way to a deep upper level trough forecast to move quickly through the western U.S. This deep trough will likely amplify as it reaches the central/southern Plains early next week and evolves into an elongated low pressure system. A large section of the southern U.S. to the Tennessee Valley will likely be impacted by heavy rain and severe storms. Meanwhile on the back side of the system, the central Rockies to the Front Range could potentially be impacted by a winter weather event. ...Guidance Evaluation/Predictability Assessment... Model guidance this morning appears to be in rather decent agreement with the aforementioned synoptic evolution across the U.S. through the medium-range period. The deterministic solutions begin to diverge toward the middle of next week as expected but the ensemble means still show rather decent agreement on the position of the surface low pressure system forecast to form over the central Plains. The GFS continues to be on the faster side of the guidance with more aggressive downstream frontal development toward the East Coast by midweek next week. In contrast, the ECMWF has been slower with the progression of the trough by digging the upper energy farther south across the Southwest and into the southern Plains. The Canadian model has been in between these extremes. Overall, the consensus appears to trend toward the ECMWF's side although recent ECMWF runs have shown some more northern stream development. Taking these factors into account, the WPC forecast was primarily based on the consensus of 40% 00Z ECMWF/EC mean, 40% 06Z GFS/GEFS, and 20% 00Z CMC/CMC mean with increasing contributions from the ensemble means toward Day 7. Overall, very good agreement with WPC continuity was maintained for Days 3-5. A slight southward trend on the cyclone position was noted on Day 6 , leading to a south/eastward push of the heavy rain axis across the Mid-South. ...Weather Highlights/Threats... The surface low tracking from the Ohio Valley to the Northeast on Saturday will likely be accompanied by a swath of moderate to locally heavy snow across northern portions of New England, particularly central and northern Maine. Elsewhere, moderate rain is expected from the northern Mid-Atlantic to central/southern New England for the first half of the weekend. Attention then turns to the Plains and Gulf Coast region as an elongated surface low exiting the central/southern Rockies begins to intensify over the central Plains by early Monday while taping into a surge of Gulf moisture across Texas and the central Gulf Coast region. The prospects for severe weather will expand from eastern Texas to the central Gulf Coast states from Monday to Tuesday whereas the heavy rainfall threat will be farther inland from the lower to mid-Mississippi Valley northeastward to the Tennessee Valley. Flooding rain could become an issue as multiple rounds of convection develop over the same general areas. The Storm Prediction Center has additional information pertaining to the severe weather potential. On the back side of the storm, the air mass could be cold enough to support a winter weather event across the central Rockies into the Front Range on Monday and possibly into Tuesday. Some wintry precipitation could also develop over the upper Midwest/upper Great Lakes Wednesday morning as the threat of heavy rain edges toward the Appalachians. In terms of temperatures, the East Coast should continue to have above normal readings this weekend and into the middle of next week as upper level ridging develops ahead of the deep trough over the Plains. Even greater positive anomalies are likely across the central and northern Plains by Sunday ahead of the storm system, with highs up to 25 degrees above average, whereas a return to slightly below average temperatures is expected across the Rockies and the western High Plains under the upper level trough for Monday and Tuesday. No major surges of arctic air are expected. Kong/Hamrick 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 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