Extended Forecast Discussion NWS Weather Prediction Center College Park MD 252 PM EDT Thu Mar 25 2021 Valid 12Z Sun Mar 28 2021 - 12Z Thu Apr 01 2021 ...Overview... Guidance overall agrees in showing an amplified but generally progressive upper level pattern during the medium range period, bolstering forecast confidence and WPC forecast continuity. This should be especially evident with two main northern stream systems. The first, a vigorous shortwave trough, will send another deep surface low through the Great Lakes and Northeast Sunday and Monday, with a trailing cold front exiting the East Coast. This sets the stage for continued unsettled weather from the Southern Plains to the Northeast, with some snowfall possible across the northern tier of the Northeast to end the weekend. Meanwhile, the next system enters the Western U.S. on Sunday, driving a well developed system and cold front eastward coast to coast through the remainder of the extended range. Meanwhile, a separated southern stream flow may initially be slower to progress out through the southern Rockies/Plains Sun/Mon before shearing with continued uncertainty over the east-central U.S.. ...Model Guidance/Predictability Assessment... Models and ensembles continue to show very good agreement on the overall synoptic pattern through the medium range, with typical questions in the details. A cutoff upper low over the Southwest Sunday continues to show some uncertainty regarding timing and ejection eastward early next week/interactions with approaching Western U.S. troughing. The GFS continues to struggle run to run with handling of this energy, so a less progressive non-GFS consensus was preferred for this system. This solution seems better supported by ensembles and initial separated flow nature. The 12 UTC ECMWF/Canadian and GEFS ensemble mean remain less progressive compared to the GFS with this system. Elsewhere, the deterministic models show good agreement. The WPC medium range product suite was primarily derived from a composite blend of the 00 UTC ECMWF/UKMET/Canadian days 3-5 (Sun-Tue). Used a composite of the 06 UTC GFS/GEFS, 00 UTC ECMWF/Canadian/ECENS mean and the 13 UTC National Blend of Models for days 7/8 (next Wed/Thu). This maintains good WPC product continuity and is consistent with the bulk of newer 12 UTC guidance. ...Weather/Threats Highlights... It remains the case that widespread showers and thunderstorms are likely ahead of the cold front on Sunday from the Southeast into the Mid-Atlantic, with moderate to locally heavy rainfall possible in spots. Given heavy rainfall also expected over the Southeast/Tennessee Valley during the short range, this may enhance a possible flooding threat for some areas. Expect some showers farther west into Texas as well along the trailing frontal boundary. The associated deepening surface low into the Northeast Sunday-Monday should result in accumulating snowfall across portions of northern New England, as well as gusty winds across much of the Northeast. The next system into the West will bring another round of rain and mountain snow to the region early next week. As the cold front enters the Central U.S. by Monday/Tuesday, it should tap into Gulf of Mexico moisture to produce showers and storms ahead of it initially across Texas and expanding northeastward into the Tennessee and Ohio Valleys by the middle of next week. Locally heavy rainfall is possible, but the details on this are dependent on intensity and timing of the Southwest U.S. closed low and interactions with the Western-Central U.S. trough. East Coast states begin above average on Sunday, through trend back towards normal Monday/Tuesday following the passage of the cold front. Above normal temperatures will also steadily progress eastward from the West to the Plains and the Midwest/parts of the East by middle of next week underneath of upper level ridging. The greatest anomalies are expected across the Northern Plains where daytime highs 15-25 degrees above normal are possible Sunday and Monday. The upper level trough into the Pacific Northwest will bring temperatures back down towards normal or below normal in the same regions by early to mid next week. 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