Extended Forecast Discussion NWS Weather Prediction Center College Park MD 257 PM EDT Sun Oct 27 2024 Valid 12Z Wed Oct 30 2024 - 12Z Sun Nov 03 2024 ...Severe weather possible Wednesday with an isolated heavy rain threat over parts of the central/southern Plains into the mid- Mississippi Valley... ...General Overview... An amplified upper trough will eject over the central U.S. midweek before lifting into/overtop a warm ambient upper ridge over the eastern-southeastern U.S.. This will result in a wavy and sharp front through the mid-section of the country where a couple rounds of moderately heavy rain are forecast from the eastern Plains through the Mississippi Valley and Midwest mid-later this week and into next weekend. The trailing portion of the front is forecast to slow/dissipate in response to robust renewed trough energy digging out of the northeast Pacific and into the West/Southwest. Subtropical ridging over the Southeast will maintain mild/warm temperatures for much of the Lower 48 east of the Rockies. ...Guidance/Predictability Assessment... Latest models/ensembles showed good agreement through most of the forecast period though the 00Z Canadian/UKMET were displaced from the better clustering of the 06Z GFS/00Z ECMWF with their ensemble means (and 00Z NAEFS mean). Used a blend of the GFS/ECMWF for much of the forecast period which maintained good continuity. By next weekend, the flow over the Pacific and into the West remains quite uncertain due to some vigorous features in the mid-latitudes as well as the likely future extratropical transition of what is currently Tropical Storm 23W (Kong-Rey). Though not every recurving W Pac tropical system amplifies the downstream flow into NOAM, the overall pattern seems quite active and the machine learning models have generally favored a more amplified and slower pattern by next weekend into the Southwest. Though certainly possible, stuck with a fully ensemble mean-driven solution for next Sunday that was just a bit quicker than the ensemble means but curiously slower than the deterministic models (which are not typically faster than the ensemble means in these cases). ...Weather/Hazards Highlights... Ahead of a sharpening front, a long fetch of return flow from the Gulf of Mexico appears to initiate and support an isolated and low- end threat of moderate to perhaps heavy rain from the central/southern Plains through the Mississippi Valley amid a severe weather threat Wednesday and perhaps into Thursday. Maintained the Marginal Risk in the ERO for these areas though the antecedent conditions are quite dry and most of the rain will be beneficial. Cooling temps may lead to new areas of frost/freeze potential back in the post-frontal airmass into midweek. 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 the ECMWF AIFS) 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. Upper ridging together with a pre-frontal long fetch of strong and gusty southerly winds will transport warmth from the South through the Northeast this period. High temperatures will threaten new daily record high temperatures Wed/Thu from TX northeastward before moderating. Fracasso/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