Extended Forecast Discussion NWS Weather Prediction Center College Park MD 250 AM EDT Thu May 05 2022 Valid 12Z Sun May 08 2022 - 12Z Thu May 12 2022 ...Heavy snow threat over a cold north-central Great Basin/Rockies to contrast north-central U.S. convection and south-central U.S to Midwest record heat as part of Omega-style block development over the lower 48 and adjoining oceans this weekend into next week... ...Pattern Overview and Guidance Evaluation... 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 Sunday into Monday. The GFS/ECMWF and GEFS/ECMWF ensemble means remain best clustered and in line with WPC continuity and the NBM Tuesday-next Thursday. Despite better similarities, recent run-run guidance continuity issues still suggests some caution with embedded feature details, especially days 5-7. Most of the newer 00 UTC guidance maintain similar trends from earlier guidance, with the Canadian remaining the most out of phase with other guidance with the timing/emphasis on systems digging into the western U.S.upper trough. ...Weather/Threat Highlights... A closed upper trough and well organized surface low/frontal system will track off the Mid-Atlantic Sunday. The low stalls and retrogrades over the western Atlantic back toward the Southeast coast mid-later next week with wrapping rains within a developing Omega-style block. Robust digging of a series of dynamic upper systems will lead to a dramatic change over much of the West later this weekend 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. 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 and adjoining oceans will trap a slow moving and wavy frontal zone over the north-central U.S. to support an emerging but uncertain 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 temperatures 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