Prognostic Meteorological Discussion
Issued by NWS
Issued by NWS
878 FXUS02 KWBC 151855 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 255 PM EDT Tue Sep 15 2026 Valid 12Z Fri Sep 18 2026 - 12Z Tue Sep 22 2026 ...Hazardous Heat subsides over the South-Central U.S. late week as heavy rain/strong thunderstorms threaten the Northern/Central Plains, Upper Midwest/Great Lakes, Southwest and Southern Rockies... ...Overview... An anomalous ridge which supported a heat wave in the Southern Plains and Lower Mississippi Valley will weaken considerably under the influence of an amplifying upstream trough as well as a closed mid-level disturbance moving into the northeast Gulf later this week. The upstream trough will produce heavy rainfall across portions of the Northern Plains, Upper Midwest/Great Lakes and Northeast this weekend. Meanwhile, the passage of the Central U.S. trough should reduce heavy rainfall concerns over the Southwest/Southern Plains this weekend before an East Pacific disturbance renews monsoonal storms across the region early next week. ...Guidance/Predictability Assessment... Latest guidance is in fairly good agreement on the large scale pattern evolution through the period, but with some notable differences in the details of various systems. The large upper low moving across Florida and into the Gulf this weekend shows some uncertainty in strength and how long it lingers across the northeast Gulf before weakening. The main outlier with the shortwave into the Upper Midwest this weekend is the CMC which becomes out of phase with the consensus by early next week as energy gets leftover across the West and entrained in another system across the West. A deeper trough moving towards the Northwest late period shows ok agreement, with the exception of the GFS which was quite a bit faster. The WPC forecast today used a blend of the deterministic guidance, more heavily weighted towards the ECMWF and EC-AIFS early period, before transitioning to a 50/50 blend of the EC/EC-AIFS with the ensemble means. ...Weather/Hazards Highlights... A potent low pressure system will bring rounds of thunderstorms and heavy rainfall to portions of the Central U.S. later this week. Scattered showers and thunderstorms are expected to redevelop over parts of the Upper Midwest, where a slight risk (at least 15 percent chance) of excessive rainfall is in effect on Friday. Thunderstorms and heavy rainfall focus should spread across the Great Lakes, Ohio Valley and Northeast over the weekend, before dropping south into the Mid- Atlantic early next week. Shortwave disturbances streaming north through the Southwest/Southern Plains will generate a little bit more convection over New Mexico on Friday before an amplifying trough shifts the unsettled weather into the Central/Southern Plains this weekend. An East Pacific trough moving into the Southwest should reignite monsoonal moisture across New Mexico by early next week. Slot canyons and dry washes are especially susceptible to flash flooding from any storms that develop. Hazardous heat will continue to be a concern across parts of the South and Lower Mississippi Valley/Tennessee Valley late this week and into the weekend with major to extreme HeatRisk and some record high temperatures. The heatwave across this region should finally moderate by Sunday and especially next week as the upper level ridge weakens. Santorelli/Kebede 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 $$