####018005805#### FXUS02 KWBC 240656 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 256 AM EDT Wed Apr 24 2024 Valid 12Z Sat Apr 27 2024 - 12Z Wed May 01 2024 ***Severe thunderstorms and heavy rain expected for the Plains and Midwest over the weekend*** ...General Overview... An amplified upper level flow pattern is forecast to be in place across the Continental U.S. this weekend, with a building ridge across the East and a trough across the West. Multiple shortwave ejecting across the Plains will spur surface cyclogenesis and multiple rounds of heavy rain and strong/severe thunderstorms, mainly from central Texas to Iowa/Missouri. A pronounced warming trend is expected for the eastern half of the U.S. going into the beginning of next week, and colder temperatures out West will support late season snowfall for the higher terrain of the Central and Northern Rockies. A second trough is then likely to develop along the West Coast by the middle to end of the next week. ...Guidance/Predictability Assessment... The 00Z model guidance suite features good overall agreement across the U.S. on Saturday with similar timing on both of the main shortwave troughs across the western High Plains and Upper Midwest, so a multi-deterministic model blend works well as a starting point in the forecast process. The 00Z CMC becomes a little slower with the trough ejecting east across the Central Plains by Sunday, but otherwise the guidance is close in most aspects. Recent runs of the CMC have differed more across the northwestern U.S. going into the Monday-Wednesday time period, especially with the 12Z CMC that was much faster bringing the shortwave inland compared to the model consensus, so the fronts/pressures was based on the better clustered GFS/ECMWF and their ensemble means for the latter half of the forecast period. The QPF forecast started with about 50% NBM and 1/6 each of the GFS/ECMWF/CMC through Sunday, and then trending to about 2/3 NBM and removing the CMC Monday and Tuesday. ...Weather/Hazards Highlights... The overall synoptic environment will be increasingly conducive for episodes of excessive rainfall across portions of the central/southern Plains and into portions of the Midwest states over the weekend. There will likely be multiple mesoscale convective systems that develop from central Texas to Missouri, and there is a good chance of training convection given the slow overall progression of the frontal boundary and nearly unidirectional flow through the lower to middle troposphere. For the Day 4 period Saturday, the existing Slight Risk area from the previous Day 5 will be expanded to include parts of north-central Texas where the QPF signal in the GFS/ECMWF has increased, with a MCS likely to develop. There will likely be another MCS across eastern Kansas into western Missouri, and both with rainfall rates reaching two inches per hour with some storms. The core of the heaviest rainfall should slowly progress eastward for the Day 5 period Sunday across the ArkLaTex region and into southern Missouri, where a Slight Risk area is planned with a multi-model signal for some 2-4 inch totals where storms train over the same areas. There is a good chance that portions of both outlook areas may eventually need a Moderate Risk in later forecast updates if the QPF signal continues to remain robust, so this will continue to be closely monitored. Elsewhere across the U.S., widespread moderate to locally heavy rain is expected from Minnesota to northern Michigan on Sunday as the surface low lifts northeastward, and a Marginal Risk area is planned to account for that. Another area of enhanced rainfall is also probable over northeastern Colorado and portions of adjacent states, where a Marginal Risk remains valid for Saturday. Colder temperatures moving in across the Intermountain West and the Rockies behind this storm system will likely result in several inches of snow for the higher mountain ranges. Rain and mountain snow is also likely to make a return to the Pacific Northwest for the middle of next week as the next shortwave trough arrives. Temperatures will also be making weather headlines as a major warm-up is expected for most of the country east of the Rockies. Highs are expected to rise well into the 80s from the Central/Southern Plains to the Ohio Valley and then reaching the East Coast by Monday, perhaps reaching 90 degrees in some cases. These readings are on the order of 10-20 degrees above normal for late April, and there may be some daily record highs set. The opposite holds true for the Intermountain West this weekend with readings 5-15 degrees below average, before things moderate going into early next week. Hamrick 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 $$