559 FXUS02 KWBC 181735 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 135 PM EDT Mon May 18 2026 Valid 12Z Thu May 21 2026 - 12Z Mon May 25 2026 ***Multiple rounds of heavy rain and severe storms expected for the southern Plains, and early season heatwave ends for the East Coast states*** ...General Overview... A moderately amplified upper level pattern over the country during the middle of the week is expected to become more quasi-zonal by next weekend, as the trough lifts out from the Rockies and the northern Plains, and the eastern U.S. ridge gets flattened with a return to more typical temperatures for the month of May, with relief from the early season heat wave. A stalling frontal boundary with shortwave impulses aloft will fuel the development of multiple thunderstorm complexes from Texas to the Deep South, with episodes of heavy rainfall and strong/severe storms. Mainly dry conditions are expected for most of the western U.S. ...Guidance/Predictability Assessment... Overall model agreement continues for the large scale features of the quasi-stationary flow through much of CONUS and a trough over western U.S. through the first portion of the period. Models begin to diverge towards the weekend in regard to the shortwave features along the south-southwest, especially with CMC where the trough over the southwest is slower compared to the GFS and ECMWF. In addition, the GFS begin to show amplitude differences towards Sunday. The ensemble means seem to smooth some of these differences, but the GEFS continues as an outlier in regard to features over the West early next week. ECMWF shows a trough entering the West Coast by Monday, while the GFS and CMC shows slower solutions in terms of timing. Therefore, the WPC forecast encompassed a blend of the CMC/GFS/ECMWF/UKMET/EC- AIFS for the first portion of the period, while incorporating the ensemble means for the remainder of the timeframe. ...Weather/Hazards Highlights... Heavy rainfall is expected to make weather headlines going into the latter half of the work week from central Texas to the Tennessee River Valley. The highest QPF should be across east-central Texas where multiple mesoscale convective systems will develop and affect the same areas on multiple days. For the Day 4/Thursday ERO, a Slight Risk will remain valid from near San Antonio to northeast Texas where 1-3 inches of rainfall is likely with storms producing high rainfall rates. This lingers going into Friday as well with a broad Marginal Risk for the Day 5/Friday ERO, extending from the Rio Grande to Ohio, with possible upgrades to Slight Risk in future outlooks as timing and placement become clearer. Elsewhere across the country, lighter precipitation is expected farther to the east across the Carolinas into Virginia with overrunning flow north of the frontal boundary. There should also be corridors of moderate rainfall across portions of the central/northern Plains to the Midwest states through Friday. The potential exists for this region to see an upward trend in rainfall totals in future forecasts. Mountain snow across the northern Rockies on Thursday should abate in intensity before a drier weather pattern ensues by Friday. In terms of temperatures, a welcomed relief from the heat wave across the eastern U.S. is expected to arrive on Thursday as a strong cold front reaches the Mid-Atlantic, and then drops south across North Carolina going into Friday before stalling. A cold air damming type event will likely become established east of the Appalachians with overcast skies and periods of mainly light rain at times, and warm and humid conditions continuing south of the boundary. Elsewhere, relatively cool conditions across the central/northern Plains are expected to gradually warm through the forecast period. Oudit/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, 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 $$