821 FXUS02 KWBC 171912 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 312 PM EDT Sun May 17 2026 Valid 12Z Wed May 20 2026 - 12Z Sun May 24 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... Models are in reasonably good agreement on the overall synoptic pattern evolution across the lower 48 during the medium range period. There's some uncertainty regarding the existence and timing of small shortwave purtubations rotating through the Southern Plains and Lower Mississippi Valley beginning mid-week. This translates to QPF uncertainty over these same areas since the mode of precip will likely be convective in nature. The GFS is also notably more progressive than the other models when it comes to the propagation of a closed mid-level low through the North-Central U.S. this week. A general model blend consisting of the available deterministic and Euro Ai guidance was used through day 4. The UKMET and Canadian models were removed from the blend on day 5 for diverging from consensus. The ensemble means are introduced to the blend on day 5 and gradually increased in weighting preference through day 7. ...Weather/Hazards Highlights... Heavy rainfall is expected to make weather headlines going into the latter half of the work week from western Texas to the Tennessee River Valley. The highest QPF should be across central Texas where multiple mesoscale convective systems will develop and affect the same areas on multiple days. For the Day 4/Wednesday-Wednesday night time period, a Slight Risk will be valid from near Del Rio to Longview, Texas where 1-3 inches of rainfall is likely with storms producing high rainfall rates. This lingers going into Thursday as well with a broad Marginal Risk extending from the Rio Grande to Mississippi, with possible upgrades to Slight Risk in future outlooks as timing and placement become clearer. Lighter precipitation is expected farther to the east across the Carolinas into Virginia with the cold front dropping south, and also for portions of the Ohio Valley. Valley showers and mountain snow are likely for portions of Montana and Wyoming on Wednesday before a drier weather pattern ensues by the end of the week. In terms of temperatures, expect another day of hot weather across the East Coast region on Wednesday with highs reaching the lower to middle 90s from the Carolinas to southern New England, with the hottest readings likely to be over Virginia. Some daily record highs are likely given the potential for some 20 degree above average anomalies. A welcomed relief is expected to arrive on Thursday as a strong cold front reaches the Mid-Atlantic by this time, and probably lasting into Friday and Saturday as well. A cold air damming type event may become established east of the Appalachians with overcast skies and periods of mainly light rain at times. The front likely stalls over the Southeast with 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. Kebede/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 $$