FXUS02 KWBC 160700 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Fri May 16 2025 Valid 12Z Mon May 19 2025 - 12Z Fri May 23 2025 ...Severe weather and flash flooding forecast for parts of the central U.S. Monday-Tuesday... ...Hazardous and record heat could continue especially across Texas and Florida into mid-next week... ...Overview... The primary weather feature next week will be an upper trough/low over the Rockies Monday that tracks east as the week progresses along with its associated surface low pressure/frontal system. This pattern will provide ample lift and instability for rain and thunderstorms in the Plains, Mississippi Valley, and Ohio Valley early week and spreading into the East for midweek and beyond. Meanwhile a subtropical upper ridge will continue to cause hot conditions to areas of the Southeast, particularly into southern Texas and Florida, where the heat could be hazardous and/or record setting. ...Guidance/Predictability Assessment... Model guidance begins the medium range period Monday in reasonably good agreement with the primary upper trough and embedded upper low(s) in the Interior West and spinning up a surface low in the central Plains. Models diverge rather quickly with the details of the energy aloft, leading to differences in this surface low track and another low developing over the southern Plains by Tuesday. Dynamical and ML models alike show a variety of solutions regarding if the upper low switches to be part of a northeastern trough by Tuesday/Wednesday, which depends on how much energy lingers atop Ontario/Quebec on the back end of an upper low ejecting east. 12/18Z GFS runs showed this type of pattern, where the initially western energy quickly combines with the eastern energy, which leads to low pressure tracking eastward much faster than slower guidance like the ECMWF. Despite the variety in solutions even with the AI/ML guidance, the primary result was that in general they were not as fast with the low track as the GFS runs. Thus for a favored middle ground WPC forecast, removed any inclusion of the GFS from the model blend, with some ECMWF inclusion but favoring the ensemble means in particular. This was pretty agreeable with the previous forecast's timing. The newer 00Z GFS is slower than the 12Z and 18Z runs with the low, and the 00Z ECMWF tracked faster, so there is some convergence in those solutions. The 00Z GEFS mean may align well with the preferred timing (after the 12Z and 18Z GEFS means were a little fast, in the vein of the GFS). However, the new 00Z CMC digs the upper low farther southwest into the Great Basin even by Monday to end up with a much slower low track. ...Weather/Hazards Highlights... The notable surface low pressure system consolidated over the central Plains by Monday will draw in above average moisture (with precipitable water values around the 90th percentile for this time of year) and ample instability ahead of its associated cold front. The upper low spinning aloft will provide good dynamical lift, and this combination of ingredients will lead to widespread rain and thunderstorms and mesoscale convective systems, with best chances slowly progressing east from the central to east-central to eastern U.S. as next week progresses. The greatest chances for heavy rain causing flash flooding look to be across the Mid-Mississippi and western Ohio Valleys Monday and Tuesday, as moisture and instability pool near a warm front stretching west-east that could promote training storms. Thus Slight Risks are in place for the Day 4/Monday and Day 5/Tuesday ERO over pretty similar areas before the upper/surface lows eject eastward. Broad Marginal Risks surround the Slights to the south and east where convection may be more scattered, and on Monday a Marginal curls back west closer to the ow track. Severe weather is also possible per the Storm Prediction Center, as they delineate possible severe areas on Monday for the south-central Plains toward the Lower/Middle Mississippi Valley on Tuesday. Rain and thunderstorm potential should press toward the Eastern Seaboard by mid to late week. Some precipitation is forecast in the Intermountain West under the upper trough/low for the first half of next week. The cool temperatures aloft could lead to May snow in higher elevations of the Rockies particularly Monday. Convective showers are possible near the Four Corners region. Meanwhile rounds of modest precipitation may be possible in the Northwest. Light rain may linger in the Northeast early next week under the influence of a northern trough. Warm to hot temperatures are likely across the southeastern U.S. as the subtropical upper ridge reaches the region. Southern Texas in particular will remain hot, with temperatures well into the 100s leading to Major to Extreme HeatRisk. The Florida Peninsula should see warm temperatures in the mid to upper 90s. Both areas could see record or near record warm lows and highs. Meanwhile the trough aloft will promote below normal temperatures, especially for highs, across the Interior West Monday and into the northern Plains Tuesday. Below average highs by around 10 degrees are also possible in the northern tier. As the trough tracks east, cooler than average temperatures should shift into the eastern third of the country under it. This may also moderate the temperatures somewhat in the South. But upper ridging poking into the West will raise temperatures to above normal there by later week, bringing highs well into the 100s for the Desert Southwest. 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 (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 $$