Extended Forecast Discussion NWS Weather Prediction Center College Park MD 235 AM EDT Mon Sep 25 2023 Valid 12Z Thu Sep 28 2023 - 12Z Mon Oct 02 2023 ...Overview... The flow pattern features an eastward moving and reasonably strong mid-level height anomaly/ridge moving eastward near the 45th parallel from roughly 160W to 140W longitude. The consequence of this approaching feature is an amplifying upper trough downstream across the West with building ridging across the eastern portion of the United States. Expect rainfall to shift inland from the Pacific Northwest with high elevation snow for the northern Rockies this weekend into early next week. ...Guidance Evaluation/Predictability Assessment... The guidance shows very good agreement with the expected flow pattern with some issues with details. To deal with the detail issues, used a blend of the 12z Canadian, 12z ECMWF, 18z GFS, and 12z UKMET early before swapping out the UKMET for increasing amounts of the 12z NAEFS and 12z ECMWF ensemble mean. This led to reasonably good agreement with continuity in the pressures and fronts. The above blend was used for pressures, fronts, and QPF. The remainder of the grids were more heavily based on the 01z NBM. ...Weather/Hazards Highlights... A stalled front over the Florida should progress southward as a frontal wave forms to their east, progressing past Bermuda ahead of a progressive and positively tilted upper level trough. This should allow the Sunshine State to dry out eventually. In the meantime, for Day 4/Thursday into Friday morning, there's enough of a signal of a cool season heavy rainfall setup into northeast FL to introduce a Marginal Risk. For day 5/Friday into Saturday morning, a Marginal Risk was introduced for both cool season, post-frontal heavy rainfall off the very warm western subtropical North Atlantic and for the central and southern peninsula closer to the front, which have been a bit wetter than average this past week. A deepening western trough 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 appear needed. 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. Roth/Jackson 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