Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM 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 on the cooled northern periphery of the expanding precipitation shield with the tapping of deeper moisture from the Gulf of Mexico and eventually to a lesser extent from the western Atlantic. ...Guidance Evaluation/Predictability Assessment... Models and ensembles offer similar mid-larger scale flow evolutions in a pattern with above normal overall predictability. A composite of the 18 UTC GFS and 12 UTC ECMWF/UKMET/Canadian along with the 01 UTC National Blend of Models (NBM) seems to provide a good forecast basis for days 3-5 (Wednesday-Friday). Composite blending of these decently clustered models tends to mitigate smaller scale system variances consistent with predictability. This solution is supported by a composite of 00 UTC guidance, GEFS/NAEFS/ECMWF ensembles and maintains good WPC product continuity. The WPC product suite into days 6/7 (next weekend) was mainly derived from the 12 UTC ECMWF ensemble mean that more consistently maintains the likely slow to de-amplfy upper flow pattern. ...Weather Highlights/Threats... Moderate to heavy mountain snows are likely midweek for the south-central Great Basin/Rockies with 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. 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. 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. 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