Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Sun Mar 20 2022 Valid 12Z Wed Mar 23 2022 - 12Z Sun Mar 27 2022 ...A low pressure system will likley spread moderate to heavy rain through the eastern U.S. midweek, with severe storms possible in the Southeast, and wintry weather across the northern tier... ...Overview... Active weather will likely reach the eastern U.S. by Wednesday with a tendency of decreasing rain intensity as a large occluded cyclone should gradually weaken and move across the region late this week, with initial threat of severe thunderstorms ahead of the cold front in the Southeast. Meanwhile on the cold northern side of the system, springtime snow and mixed precipitation are possible from the Great Lakes region to the interior Northeast. As a ridge builds into the West, possible record high temperatures across California will be contrasted with a cooling trend in the Great Lakes to the Northeast where an upper trough is forecast to amplify. This increase in amplitude of the upper-level pattern across the U.S. by next weekend would introduce higher uncertainty and thus lower predictability particularly across the Northeast and just off the West Coast. ...Guidance Evaluation/Predictability Assessment... The medium-range period will begin by an occluded cyclone likely near peak intensity as its center tracks across the Midwest. Model guidance/consensus continues with a subtle trend of wrapping additional precipitation around the northern side of the cyclone across the upper Midwest toward the northern Plains, while rain and thunderstorms ahead of the trailing cold front were nudged progressively faster through the eastern U.S. This trend is due to a gradual amplification of the upper trough behind the cyclone across the Plains states in the model guidance, leading to a gradual trend for the cyclone to evolve into a classical occlusion. The CMC remains to be the more enthusiastic guidance in this regard, though with noticeable run-to-run variability, and thus has been the slowest guidance in pulling the system out of the Northwest late this week. The GFS and ECMWF are mostly in agreement with one another, and not as slow as the CMC regarding this system. Toward next weekend, models are generally indicating a trend toward an increasingly amplified pattern across the U.S. as a ridge is forecast to build over the West while upper-level shortwaves are predicted to dig southeastward from central Canada toward the northeastern U.S. This increase in amplitude of the upper-level pattern would tend to introduce higher uncertainty and thus lower predictability particularly across the Northeast and just off the West Coast where another amplified trough in the Pacific appears to edge closer. Both the EC and GFS begin to diverge from their corresponding ensemble means by late week, which implies higher uncertainty with the pattern. Therefore, the WPC medium-range packaged was based mainly on the consensus of the 00Z ECMWF/EC mean and the 06Z GFS/GEFS mean, with increasing usage of the ensemble means toward the weekend. A small contribution of the 00Z CMC was included for Days 3-4 followed by a small amount from the CMC mean Days 5-7. The results are reasonably compatible with WPC continuity. ...Weather Highlights/Threats... Another rainy day is expected as the medium range period begins Wednesday as Gulf of Mexico moisture ahead of the low pressure system tracking across the central U.S. will likely begin trending downward thereafter. Storms could be severe across the Deep South down to the central/eastern Gulf Coast per the Storm Prediction Center. Furthermore, widespread rain is likely across the East, which could potentially cause some isolated flash flooding in some areas from the southern/central Appalachians eastward. North and west of the low track, snow and wintry precipitation are possible, with the highest probabilities for notable snow in the Upper Great Lakes region. Wintry mix or snow could also occur particularly in higher elevations of the interior Northeast north of a warm front on Wednesday-Thursday and as a western Atlantic low develops by early Friday. Showers could linger into late week across the East with generally light amounts expected, but perhaps with more moderate amounts as a front lingers in Florida, which could cause localized flooding issues if rain falls atop saturated soils. A mainly dry pattern is expected for the western and central U.S. for the latter part of the week, though with some Pacific Northwest and Northern Rockies light precipitation possible before a more widespread moisture surge next weekend. The strong upper ridge building into the West will lead to a broad area of highs 10-20F above normal Wednesday-Sunday with slightly higher localized anomalies possible. There is potential to reach daily record highs across California Wednesday to Friday and spreading eastward into the Intermountain West and Southwest as the ridge axis shifts east. Leading upper level troughing should support temperatures 10-20F below average across the central/southern High Plains Wednesday. The cooler air should moderate closer to normal by the latter part of next week as it progresses eastward. Ahead of the trough and cold fronts, generally warmer than normal conditions are likely across much of the eastern third of the U.S. for much of the week, transitioning to near normal temperatures by Friday and Saturday and a cooldown associated with a secondary cold front in the Great Lakes by Sunday. Isolated record highs are possible over parts of Florida Tuesday-Wednesday. Kong/Tate 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