Extended Forecast Discussion NWS Weather Prediction Center College Park MD 314 AM EDT Sun Oct 27 2024 Valid 12Z Wed Oct 30 2024 - 12Z Sun Nov 03 2024 ...Mid-later week Mississippi Valley Heavy Rain/Runoff Threat... ...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 sharp front through the mid-section of the country where a moderately heavy rain event is forecast from the eastern Plains through the Mississippi Valley and Midwest mid-later this week. The trailing portion of the front is forecast to slow and retreat into next weekend in response to robust renewed trough energy digging into an unsettled the West. This will lead to a resurgence of moderate/heavy rain for the south-central U.S. late week/weekend. ...Guidance/Predictability Assessment... Model solutions seemed reasonably clustered Wednesday into early Friday across much of the nation and were in line with the National Blend of Models, ensembles and WPC continuity in pattern with above normal predictability. A composite was used in production of the WPC product suite for that timeframe. Forecast spread increased quickly later Friday into next weekend, with the 18 UTC GFS showing less than stellar run to run consistency by becoming a noteable outlier from 12 UTC models and ensembles in showing much less digging of upper trough to closed low energy down the West Coast. The presence of an amplified upstream ridge over the eastern Pacific and guidance from the machine learning AIFS run of the ECMWF did not support the 18 UTC GFS run and it was discounted. The newer 00 UTC GFS has trended back into the fold and overall latest 00 UTC model forecast spread has decreased at these longer time frames, hopefully portending improved forecast confidence. ...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 threat of heavy rain from the central/southern Plains through the Mississippi Valley and into the Midwest with embedded thunderstorms midweek. Cooling temps may lead to frost/freeze 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 flow over the lower 48 and vicinity. The WPC Day4 Wednesday Excessive Rainfall Outlook maintained a Marginal Risk area given potential for training and favorable up/Thursday per trough and right entrance region jet dynamics. The Day 5 ERO depicts a Marginal Risk area centered over the lower Mississippi Valley with frontal/convection and upper support progression. In the meantime, precipitation associated with the next Pacific system and long- fetch moisture is forecast to re- focus moderate precipitation into the West Coast later week/weekend, with high- elevation snow reaching into the northern Rockies and modest rains reaching down through California with a cold frontal surge and possible closed low development at the southern base of the main upper trough. Upper ridging together with a pre-frontal long fetch of strong and gusty southerly winds will transport warmth from the south through the Northeast through middle to late week. High temperatures will threaten new daily record high temperatures 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 ody.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