Extended Forecast Discussion NWS Weather Prediction Center College Park MD 256 PM EDT Thu Mar 31 2022 Valid 12Z Sun Apr 3 2022 - 12Z Thu Apr 7 2022 ...Heavy rainfall/convection and runoff threat to focus across the South next week... ...Pacific Northwest heavy rains and terrain/mountain heavy snow threat inland to the northern Rockies... 19Z Update: The 12Z model guidance suite is in very good agreement on the quasi-zonal flow pattern across the continental U.S. for the Sunday-Monday time period, although the ECMWF is slightly more amplified with the upper trough over the Midwest on Monday and the CMC a bit stronger with the shortwave exiting New England. By Tuesday and through midweek, the GFS and to a lesser extent its ensemble mean, are more progressive with the southern stream shortwave crossing the Gulf Coast region, with a GFS/ECMWF compromise sufficing as a starting point here with some additional weighting from the ECENS mean. By the end of the forecast period next Thursday, the GFS/GEFS is also more progressive with the main closed low over the Great Lakes region, with the ECENS serving as an excellent middle ground solution. In terms of the QPF forecast, the axis of heaviest rainfall is slightly farther south across the Gulf Coast states compared to continuity, with aerial averages on the order of 1 to 3 inches likely from Louisiana to Georgia. The previous forecast discussion follows below. /Hamrick ----------------- ...Guidance Evaluation/Predictability Assessment... The WPC medium range product suite was mainly derived from a blend of well clustered guidance from the 18 UTC GFS/GEFS mean, the 12 UTC ECMWF/UKMET/Canadian/ECMWF ensemble mean and the 01 UTC National Blend of Models along with WPC continuity days 3-7 (Sun-next Thu). Embedded smaller scale system differences and run to run continuity variances have become less problematic with the 18 UTC GFS/GEFS trending more in line than earlier runs, especially into later period over the Pacific/Northwest. Newer 00 UTC guidance remains in close alignment. Overall, this seems to bolster medium range forecast confidence to above normal levels, albeit with the caveat that the energetic multi-system pattern is also transitioning to higher amplitude/convective potential over time that will likely vary the local threat focus. ...Overview and Weather Highlights/Threats... Highly energetic Pacific flow will work increasingly inland from the Northwest to the Rockies into early next week. This will act to transport some deeper moisture in support of an emerging heavy precipitation focus with rainfall over coastal and favored terrain of the Pacific Northwest. The pattern also favors periods with terrain/mountain heavy snows from the Northwest to the northern Intermountain West/Rockies prior to amplified upper ridge building slated to build eastward over the West starting midweek. Downstream progression and systems out from the West and increasing northern stream phasing potential over time will combine to support cyclogenesis/frontogenesis over the central and eastern states next week. There is a growing guidance signal for development of a building area of enhanced rainfall and some threat to monitor for some severe convection across the east-central U.S. (both especially across a more unstable/convective South) early-mid next week as deeper Gulf moisture returns and interacts with the complex series of wavy fronts and a stalled lead front. Accordingly and considering antecedent rainfall, WPC shows a "slight" risk on the newly experimental medium range excessive rainfall outlook into Day 5 (ERO linked below). Guidance consensus has improved at longer time frames with a well developed closed upper low forming over the north-central U.S. by midweek as the pattern becomes amplified downstream of the aforementioned building upper ridge over the West. There is some potential then for some wrapping/overrunning April snows from the Upper Great Lakes to the northern tier of the Northeast. Hamrick/Schichtel Hazards: - Heavy precipitation across portions of the Pacific Northwest and the Northern Great Basin, Sun-Mon, Apr 3-Apr 4. - Heavy rain across portions of the Central Plains, the Lower Mississippi Valley, the Tennessee Valley, the Middle Mississippi Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, and the Southern Plains, Mon-Tue, Apr 4-Apr 5. - Heavy rain across portions of the Southeast, the Mid-Atlantic, and the Southern Appalachians, Tue-Wed, Apr 5-Apr 6. - Flooding possible across portions of the Middle Mississippi Valley, the Great Lakes, the Upper Mississippi Valley, the Northern Plains, and the Ohio Valley. - Flooding occurring or imminent across portions of the Upper Mississippi Valley and the Northern Plains. - Flooding likely across portions of the Lower Mississippi Valley. - High winds across portions of the Central Plains, the Central Great Basin, the Northern Plains, the Northern Rockies, the Central Rockies, the Northern Great Basin, and the Pacific Northwest, Mon-Wed, Apr 4-Apr 6. 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, experimental excessive rainfall outlook, 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml