Extended Forecast Discussion NWS Weather Prediction Center College Park MD 301 AM EDT Wed May 04 2022 Valid 12Z Sat May 07 2022 - 12Z Wed May 11 2022 ...North-central Great Basin/Rockies cold heavy snow threat to contrast emerging north-central U.S. convection and record south-central U.S to Midwest heat pattern with Omega-style block development this weekend into next week... ...Lead Mid-Atlantic rainfall threat into Saturday with the closed low to settle over a blocked western Atlantic next week... ...Pattern Overview and Guidance Evaluation... Model and ensemble solutions still offer pesky embedded system timing and emphasis differences, but have overall converged upon a better clustered mid-larger scale pattern evolution highlighted by Omega-style block development over the lower 48 and vicinity. A composite of the 18 UTC GFS/GEFS along with the 12 UTC ECMWF/UKMET/Canadian, ECMWF ensemble mean and 01 UTC National Blend of Models seems to present a reasonable forecast basis while tending to mitigate embedded system variance consistent with a pattern with near normal predictability Saturday into Monday. The GFS/ECMWF and GEFS/ECMWF ensemble means remain best clustered and in line with WPC continuity and the NBM Monday-next Wednesday. Despite better similarities, recent run-run guidance continuity issues offers caution with embedded feature details. Most of the newer 00 UTC guidance maintain similar trends from earlier guidance, but the Canadian is not as diggy over the western Atlantic. ...Weather/Threat Highlights... A leading closed upper trough and well organized surface low/frontal system will track from the Ohio Valley through the Appalachians/Mid-Atlantic this weekend. Some strong storms and locally heavy downpours are possible considering slow system track and pooled moisture/instability. The system will then stall and retrograde over the western Atlantic next week as part of a developing Omega-style block. Robust digging of a series of dynamic upper systems will lead to a dramactic change over much of the West later this week into next week as an amplified mean upper trough and wavy frontal systems become established over the region. This will support significant cooling to include spotty record values along with a widespread precipitation focus from the Northwest/Sierra through the north-central Great Basin/Rockies. This will include a substantial and lingering threat for widespread heavy snows as further enhanced in favored terrain. Expect temperatures to range as much as 10-20 degrees below normal. Uncertain upper system ejections channeled between amplified eastern Pacific upper ridging/upper troughing over the West and amplified east-central U.S. upper ridging as part of the aforementioned Omega-style block over the lower 48 will trap a slow moving and wavy frontal zone over the north-central U.S. to support an emerging convection/rainfall pattern. This offers a runoff threat given moist ambient Northern Plains soil conditions. The Storm Prediction Center also highlights a concern for severe weather into the eastern Central Plains for at least Sunday and Monday. The pattern meanwhile favors record high tempertures over the south-central U.S., with pre-frontal warmth gradually building northeastward next week through the MS/TN Valleys/Midwest under the upper ridge, in stark contrast to the wintry conditions over the West and moderated/cooled high pressure dammed airmass to linger over the East on the backside of a difficult to dislodge western Atlantic circulation. 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, 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