818 FXUS02 KWNH 200745 PREEPD Preliminary Extended Forecast Discussion NWS Weather Prediction Center College Park MD 344 AM EDT Wed May 20 2026 Valid 12Z Sat May 23 2026 - 12Z Wed May 27 2026 ***Heavy rain and thunderstorms expected to continue across eastern Texas into the lower Mississippi River valley*** ...General Overview... An active weather pattern will continue to remain in place across the south-central U.S. going into the upcoming weekend, with multiple shortwave disturbances and a weak frontal boundary producing multiple rounds of heavy rain and storms. An upper trough over the Dakotas should reach the northern Great Lakes by Monday, with widespread rain likely from the Ohio Valley to the Northeast ahead of this feature. Looking ahead to early next week, a more amplified level pattern starts to emerge as a stronger upper trough and then closed low enter the Pacific Northwest and enveloping more of the Intermountain West by next Wednesday, and a downstream upper ridge develops over the Ohio Valley and western Great Lakes. ...Guidance/Predictability Assessment... The 00Z model guidance suite has come into better overall synoptic scale agreement compared to the past couple of days, and this includes a more solidified depiction of the amplifying trough across the West late in the period. Recent runs of the GFS have trended more in line with the non-NCEP consensus in contrast to its more progressive runs yesterday, and forecast confidence has increased in this pattern change evolving. Across the southern tier states, the ECMWF and GFS have trended to a closed southern stream low over Texas and Oklahoma, whereas the CMC portrays more of an open trough aloft. The NBM is likely too warm with temperatures across the northwestern quadrant of the country going into the first half of next week, so the WPC forecast reflects a colder scenario more in line with the latest deterministic guidance, and also an increase in QPF across this same general region given better ascent. The ensemble means were increased to about 40% by next Wednesday for fronts and pressures. ...Weather/Hazards Highlights... Heavy rain will continue to make weather headlines going into the Memorial Day weekend across much of the south-central U.S. as multiple mesoscale convective systems develop. These will be in response to enhanced ascent from an upper trough coupled with a weak front in the region and plenty of moisture and instability. A Slight Risk for excessive rainfall will be valid both Saturday and Sunday from south-central Texas to western Louisiana, where the potential exists for several inches of rainfall over this time period over soils that will be becoming increasingly saturated. Another corridor of moderate to heavy rainfall is expected across northern portions of the Mid-Atlantic on Saturday, where a Marginal Risk remains valid, with the potential for some one inch plus totals within the axis of heaviest rainfall. Elsewhere across the country, scattered showers and thunderstorms are likely to develop across portions of the Carolinas this weekend, and some of these could be locally heavy. More precipitation returns to the Pacific Northwest to start next week with a cold front moving in and a building upper level trough. Lingering cloud cover and rainfall with residual cold air damming across portions of the Mid-Atlantic and Northeast should continue to keep temperatures on the cool side on Saturday, with highs running 10-20 degree below average before a gradual moderation trend ensues by early next week. It should also be slightly below average across Texas given the widespread rainfall that is expected through the weekend. With the upper low developing over the northwestern U.S., a return to colder conditions is also likely here going into Tuesday and Wednesday, with some higher elevation snow likely for portions of the northern Rockies. The greatest positive anomalies will likely be over the northern Plains and Upper Midwest with the upper ridge axis Monday through Wednesday, with readings up to 20 degrees above average. 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 $$