484 FXUS02 KWBC 161917 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 317 PM EDT Wed Sep 16 2026 Valid 12Z Sat Sep 19 2026 - 12Z Wed Sep 23 2026 ...Heavy rainfall threats for the Upper Great Lakes and northern High Plains this weekend, with monsoonal moisture increasing again next week for the Southwest... ...Overview... A trough will produce heavy rainfall across portions of the Upper Midwest/Great Lakes and potentially the Northeast this weekend. Meanwhile, the passage of a Central U.S. trough will bring heavy rainfall concerns to parts of Montana but should also reduce the threat over the Southwest and Southern Plains/Rockies this weekend. An East Pacific disturbance looks to renew monsoonal storms across the region early next week. A mid- level disturbance meandering around the Florida Peninsula should generate multiple days of wet weather across southern Florida beginning this weekend. ...Guidance/Predictability Assessment... The latest guidance remains in relatively good agreement on the evolution of the pattern during the medium range period. There are lingering uncertainties/differences with various systems, but these seem well within the realm of possibilities with no true outlier solutions. Even small differences though pose impacts to sensible weather, especially across Florida as a broad upper disturbance shifts across the state. The second trough into the Southwest next week also shows some notable differences and thus impacts on heavy rainfall potential across this region. A general model blend served as a good starting point for the early half of the forecast period. Trended more towards the ECMWF and EC-AIFS solutions late period as they were closer to the ensemble means amidst growing uncertainty in the details and timing of individual systems. The ensemble means made up 60 percent of the blend by Day 7, helping to maintain overall consistency with the previous WPC forecast. ...Weather/Hazards Highlights... A low pressure system will bring rounds of thunderstorms and heavy rainfall to portions of the north-Central U.S. later this week. Scattered showers and thunderstorms are expected to spread into parts of the Upper Midwest/Great Lakes, where a slight risk (at least 15 percent chance) of excessive rainfall is in effect on Saturday. Thunderstorms and heavy rainfall focus should expand into the Ohio Valley and Northeast on Sunday, before dropping south into the Mid-Atlantic by early next week. A compact closed low/upper shortwave will shift into the north- central U.S. this weekend bringing a threat for heavy rainfall across parts of the northern High Plains on Saturday. Showers will continue along and ahead of the surface front as it shifts into the central and southern Plains. This trough will also weaken the southern U.S. ridge, providing a break in the monsoonal moisture across the Southwest. This may be short lived though as another trough into southern California early next week renews moisture with a heavy rainfall threat. Slot canyons and dry washes are especially susceptible to flash flooding from any storms that develop. The persistent and anomalous ridge over the South will break down this weekend, with temperatures beginning to moderate across many areas by later in the weekend and especially early next week. Hazardous heat threats may persist in some parts of the south- central U.S., but should not be nearly as widespread as it is this week. 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 $$