Extended Forecast Discussion NWS Weather Prediction Center College Park MD 150 PM EST Sun Feb 20 2022 Valid 12Z Wed Feb 23 2022 - 12Z Sun Feb 27 2022 ...Heavy to excessive rainfall threat from the Lower Mississippi/Tennessee Valleys to the Mid-Atlantic along with a heavy snow/ice threat from the southern Plains to the Northeast Wednesday-Friday... ...Pattern Overview... Expect an active mid-winter pattern this week as cold Canadian high pressure digs across much of the lower 48 states. Upper level troughs will dig through the West, with ejecting energies and induced frontal waves progressing downstream then overtop a warming Southeast/East upper ridge. The main upper trough should shift eastward into the Central Plains and Midwest by later week as amplified ridging builds from the East Pacific into the West Coast. This amplified pattern favors a heavy to excessive rainfall threat from the Lower Mississippi/Tennessee Valleys to the Mid-Atlantic along with a heavy snow and ice threat from the southern Plains to the Northeast Wednesday into Friday. ...Guidance Evaluation/Predictability Assessment... The latest suite of models and ensembles continue to offer a similar large scale flow evolution through at least day 5. As such, a composite blend of the 06z GFS and 00z ECMWF/UKMET/CMC were used. After day 5/next weekend, there remains questions on how quickly the pattern will deamplify and the upper trough energy weakens and shifts east. The 00z ECMWF is notably stronger with this energy and slower, with the 06z/12z GFS trending much faster. The 00z/12z CMC actually provides a decent middle ground solution, along with the ensemble means. These differences contribute to frontal placement uncertainties across the South on day 7 and some rather significant QPF differences too. For days 6-7, prefer a solution more amplified than the GFS, but maybe not quite as robust as the ECMWF. The WPC blend used smaller portions of the CMC/ECMWF blended with the enesmble means, which also kept good continuity with the previous WPC forecast. ...Weather Highlights/Threats... Moderate to heavy mountain snows are likely midweek for the south-central Great Basin/Rockies with the approach/passage of potent upper trough energy and as enhanced by upslope fetch. Ample upper energies working downstream from the West will also act to induce waves along a lead front and tap deepening moisture from the Gulf of Mexico. This is expected to fuel a heavy to excessive rainfall and convection threat from the Lower Mississippi/Tennessee Valleys to the Mid-Atlantic, mainly Wednesday/Thursday. Some parts of especially the Tennessee Valley may receive additional heavy rainfall during this time, after an initial round in the short range period, which could lead to an increased threat for flooding and/or flash flooding. Wave organization and redevelopment should also support the spread of a potentially significant heavy snow/ice threat from parts of the southern plains and Mid-Mississippi/Ohio Valleys to a cold air dammed northern Mid-Atlantic and Northeast Wednesday-Friday. Strong ridging building over the Western U.S. mid to late period should result in a very dry period across much of the West, though some rain/mountain snow may try to move back into the Pacific northwest next weekend associated with northeast Pacific shortwave energy. Across the South, significant uncertainty concerning amplitude/speed of the Western trough results in large differences in potential QPF across the mid-south, especially the lower Mississippi Valley to Tennessee Valley. Generally light to moderate return flow moisture into the region is expected, although there are some model solutions suggesting a heavier event could materialize resulting in another round of heavy rainfall for an already water logged region. The cold high pressure surge will spread much below temperatures across much of the western and central U.S. by mid-late week to include widespread record cold values, especially frigid from the northern High Plains to the Northern/Central Plains where daytime highs and overnight lows could be 30-40+ degrees below normal. This very cold air will spread, but gradually modify later week across the Midwest/East. Meanwhile, much above normal pre-frontal temperatures are expected across the Southeast/East with some record warmth likely, especially overnight mins with upper level ridging and enhanced pre-frontal moisture into the region. Santorelli/Schichtel 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