493 FXUS02 KWBC 212029 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 429 PM EDT Thu May 21 2026 Valid 12Z Sun May 24 2026 - 12Z Thu May 28 2026 ...Heavy rain and thunderstorms expected to continue across eastern Texas into the Lower Mississippi Valley... ...Overview... A couple of southern stream upper troughs will pass through the southwestern and south-central U.S. next week, providing lift for widespread rain and thunderstorms in a moist and unstable airmass. The heaviest rain should generally affect the Lower Mississippi Valley and Southeast Sunday-Monday, and potentially get renewed in Texas and vicinity into the workweek over areas that will already have wet antecedent conditions. An upper trough over the Great Lakes this weekend should reach northern New England by Monday night, with widespread showers from the Ohio Valley to the Northeast ahead of this feature. Out West, a more amplified level pattern starts to emerge as a stronger upper trough likely becoming a closed low enters the Pacific Northwest and envelops more of the Intermountain West by the middle of the week, yielding cooler temperatures and precipitation. An upper ridge should develop downstream in the east-central U.S., reaching into the Upper Midwest/Great Lakes and bringing above average temperatures. ...Guidance/Predictability Assessment... Recent model guidance indicates reasonable agreement with the initial pattern, including the trough tracking through the northern tier. The first southern stream trough across Texas shows mostly good consensus, aside from the CMC a bit fast/farther northeast. In general that feature has trended a bit farther east over the past couple days, allowing for a shift eastward in the placement of heaviest QPF. The northern stream trough will shift across southeastern Canada Monday-Tuesday while the southern stream trough erodes during that time. Meanwhile the primary larger scale model variations are with the upper trough moving toward and into the Northwest early to mid-next week. The last few model cycles have shown a marked difference between the GFS/GEFS being weaker with the trough and moving it east more quickly, compared to the other dynamical and AI models/ensembles. Even the GFS-based AI models are slower and more closed off than the dynamical GFS/GEFS. This gives more confidence to eliminate the GFS and GEFS from the model blend, adjusting toward the non-NCEP guidance from the NBM starting point as necessary in the gridded forecast as well (cooler temperatures and slower movement of QPF through the Northwest). ...Weather/Hazards Highlights... Heavy rain will continue to be a threat across the south-central to southeastern U.S. into Sunday and Monday, with multiple mesoscale convective systems developing. These will be in response to enhanced ascent from a weak upper trough in the southern stream flow, coupled with a weak front in the region and plenty of moisture and instability. A Slight Risk of excessive rainfall still looks reasonable for Sunday from far southeast Texas into much of Louisiana. Fortunately this is mostly shifted a bit east of the heaviest rains during the short term forecast, but there may still be somewhat wet antecedent conditions there. The surrounding Marginal Risk in the Day 4 ERO was trimmed on the western side as models consolidate to the east. Then by Day 5/Friday, there is lessening support aloft for particularly heavy rainfall amounts, though widespread rain and thunderstorms could continue in the moist and unstable air. A Marginal Risk stretching across much of the Lower Mississippi Valley to Southeast and Mid-South remains in place for Day 5/Memorial Day. Meanwhile, the northern stream trough will push through the northeastern quadrant of the country and spread rain there Sunday, with lessening coverage through Monday and Tuesday. Convection also looks to spark in the Four Corners region on Monday in response to the next southern stream trough aloft. That system could renew heavy rain potential in Texas and vicinity for Tuesday and Wednesday potentially in areas that will be quite saturated from the near term and short range rain, which bears watching. Showers and storms are possible across the Mid-Mississippi and Ohio Valleys as well. Upper troughing moving into the Northwest early next week and a frontal system ahead of it will allow for increased precipitation reaching the Pacific Northwest Sunday and spreading southeast on Monday and into the workweek. Snow is possible at the highest elevations of the Cascades to Rockies. Cooler than average temperatures may persist in the Northeast and northern Mid-Atlantic on Sunday, but should see a gradual warm-up after that. Meanwhile the West can expect gradual cooling as the week progresses with the trough overhead. On the other hand, the upper ridge to its east will allow for warmer than average temperatures across the north-central U.S. through much of next week. Tate 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 $$