Extended Forecast Discussion NWS Weather Prediction Center College Park MD 221 AM EDT Thu Mar 17 2022 Valid 12Z Sun Mar 20 2022 - 12Z Thu Mar 24 2022 ***Strong low pressure system will likely produce heavy rain and severe storms across portions of the southern U.S. by early next week*** ...Overview... A rather active weather pattern will be developing across much of the nation beginning this weekend, and particularly into the beginning of next week as a deep upper level trough develops over the Intermountain West as Pacific shortwave energy moves inland. This will likely evolve into a closed upper low by Monday along with an intensifying surface low over the central/southern Plains that will eventually result in heavy rain and severe storms from Texas to the Deep South by the middle of the week. There will also be a well organized storm system exiting the Northeast U.S. Sunday ahead of the central U.S. event. ...Guidance Evaluation/Predictability Assessment... The 00Z model guidance suite is generally in above average agreement through Monday night with the overall synoptic scale pattern and the evolution of the main upper level trough/closed low over the Rockies and Southern Plains. Model differences become more apparent as the upper low begins lifting out and evolving into a positively tilted open wave feature by the middle of the week, with the CMC considerably slower and keeps the trough axis in place longer across the Plains, whereas the GFS and ECMWF indicate a northern stream shortwave amplifying the trough over the Great Lakes and Ohio Valley region by Thursday. The models are still struggling with the arrival of shortwave energy crossing the northern periphery of the upper ridge over the West Coast later in the period that would affect the Pacific Northwest, with the past few runs of the GFS differing the most from the model consensus. Taking these factors into account, the WPC forecast was primarily based on a multi-deterministic model blend as a starting point through Tuesday morning, and then incorporated more of the ensemble means whilst still maintaining smaller contributions from the ECMWF/GFS/CMC going forward through Thursday. ...Weather Highlights/Threats... The surface low over the Northeast on Sunday will likely be accompanied by some lingering snow showers across northern portions of New England, and then drier weather commences for this region in time for the beginning of the work week. Attention then turns to the Plains and Gulf Coast region as a surface low becomes better organized by late Monday over northern Texas/Oklahoma and taps into a surge of Gulf moisture across Texas and the central Gulf Coast region. There is a strong model signal for episodes of heavy rainfall that could result in instances of flash flooding, mainly later in the day Monday and especially into Tuesday and persisting into early Wednesday. The best prospects for this would be from the ArkLaTex region to the southern Appalachians. There is also an increasing threat of severe thunderstorms with favorable dynamics and instability parameters in place, mainly across eastern Texas and the lower Mississippi River valley. The Storm Prediction Center has additional information pertaining to the severe weather potential. In terms of temperatures, highs are expected to be well above average across most of the central and northern Plains and Midwest, with highs up to 25 degrees above average on Sunday. There will also be a surge of humidity across the Gulf Coast region ahead of the cold front from the central U.S. low. Warm weather returns to the West Coast region for the Tuesday through Thursday time period as an upper ridge builds in behind the departing trough. Some below average readings are likely across the Rockies and western High Plains for early in the week in association with the upper trough, but no major surges of arctic air are expected. 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