Extended Forecast Discussion NWS Weather Prediction Center College Park MD 316 AM EDT Mon Oct 28 2024 Valid 12Z Thu Oct 31 2024 - 12Z Mon Nov 04 2024 ...General Overview... An initially energetic upper trough and moderate surface low will lift northeastward from the Midwest through the Northeast Thursday/Friday overtop a warm ambient upper ridge over the eastern-southeastern U.S.. An associated cold front will swing through the east-central to eastern U.S. to focus lingering showers and thunderstorms and usher in moderating post-frontal high pressure. The trailing portion of the front is forecast to slow/dissipate, but remain a convective focus to eminate out from the south-central U.S. with return flow. Meanwhile upstream, robust Pacific upper trough energy digs sharply into an unsettled West, with moderate rains and some elevation snows over the Northwest, and more spotty activity furthern inland and down the coast across California. This pattern may lead to closed trough/low development near southern California/Baja. Warm and amplified subtropical ridging over the Southeast may prove difficult to fully dislodge. ...Guidance/Predictability Assessment... A reduction of forecast spread in guidance over the past few cycles has bolstered forecast confidence through medium range time scales to above normal levels. Prefer a composite of the latest models and best clustered ensemble means over time along with the National Blend of Models to best emphasize the most predictable forecast components at the expense of the least. This solution, despite lingering associated forecast spread, does allow less certain, but reasonable weekend closed low development near southern California/Baja given favorable upstream upper ridge amplitude. Overall, WPC product continuity is well maintained. ...Weather/Hazards Highlights... Ahead of a sharpening front, a long fetch of return flow from the Gulf of Mexico appears to initiate and support a lingering threat of moderate to heavy rain over the lower the Mississippi Valley and vicinity along with a possible severe weather threat holding into Thursday. Maintained a WPC Excessive Rainfall Outlook Marginal Risk for this area, though the antecedent conditions are quite dry and most of the rain will hopefully be beneficial. The trailing portion of the front is then forecast to stall over the southern Plains where moderate to heavy rainfall could linger and then expand northeastward by next weekend as robust upper trough/closed low energy digs upstream into the West Coast to re- amplify the flow over the Lower 48 and vicinity. Precipitation associated with the next Pacific system and long-fetch moisture is forecast to re- focus into the West Coast later in the week and into next weekend, with high-elevation snow reaching into the northern Rockies and modest rains reaching down through California. Here, rainfall could be heavier (per recent ECMWF AIFS trends) should a slower/stronger solution verify. Regardless, the cold frontal surge and possible closed low development at the southern base of the main upper trough will bring in cooler temperatures to much of the West to west-central U.S.. Upper ridging together with a pre-frontal long fetch of strong and gusty southerly winds will transport warmth from the South through the Northeast before moderating. 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 forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: 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