Extended Forecast Discussion NWS Weather Prediction Center College Park MD 201 PM EDT Sun Sep 24 2023 Valid 12Z Wed Sep 27 2023 - 12Z Sun Oct 01 2023 ...Overview... The flow pattern of an upper trough spreading across the West and closed high centered over Quebec becomes increasingly amplified through the latter half of this week with ridging extending over the east-central CONUS and troughing along or just off the eastern seaboard this weekend. Expect rainfall to shift inland from the Pacific Northwest with high elevation snow for the northern Rockies this weekend. A stalled/slow moving cold front over Florida brings prolonged wet weather and a blocked low over the Midwest should bring wet weather to the Ohio Valley Wednesday to Friday. ...Guidance Evaluation/Predictability Assessment... The timing and amplitude of the digging trough from the Northwest to an either sharp trough or closed low over the Great Basin by this weekend is in decent agreement among global deterministic guidance which for the bulk of the blend Days 3-6. The GFS and CMC have been more closed with the low and farther west/into California this weekend than the ECMWF which is more open and more progressive over the Great Basin. The 06Z GEFS is also farther west with a trough/low than the ECENS, so more reliance went to the 06Z GEFS by Day 7 than the 00Z ECENS. QPF grids are a blend of the 13Z NBM with a selection of the ECMWF/GFS/CMC/UKMET through Day 5, and the ECMWF/GFS/CMC thereafter. ...Weather/Hazards Highlights... A stalled front over the Florida Peninsula through much of this week will bring periodic heavy rains. Enough guidance agreement on heavy rainfall in and near northern FL and southern GA remains to maintain a Marginal Risk there for day 4/Wednesday into Thursday morning. The latest consensus shift the heavier rainfall focus east of Florida on Thursday. A series of early season storms that dig a trough/close a low over the northern CA/NV border by this weekend will shift active weather from the Pacific Northwest through the Great Basin/northern Rockies, and northern High Plains midweek through this weekend. Rates will generally be light to moderate, so no excessive rainfall areas are needed on Days 4 or 5. Snow at higher elevation becomes increasingly favored with time across the Northern Rockies as the upper level trough strengthens. Increased ridging over the center of the country and troughing across the West, will slowly shift temperatures of 10 to 15 degrees above normal east across the Central Plains through the Great Lakes with temperatures below normal expanding from the Northwest to across the West. Below normal temperatures over the Mid-Atlantic States can be expected into Friday before moderating on approach of the ridge axis (but perhaps staying below normal under trough along the Eastern Seaboard). Jackson/Roth 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 forecast, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages 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 https://www.wpc.ncep.noaa.gov/#page=ovw