118 FXUS02 KWBC 180710 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 310 AM EDT Fri Sep 18 2026 Valid 12Z Mon Sep 21 2026 - 12Z Fri Sep 25 2026 ...Wet pattern with possible flooding threat in the Southern High Plains/Rockies next week... ...Overview... An upper low hovering over the Great Lakes next week will interact with southern stream energy moving northward from the Gulf across the Eastern Seaboard. At the surface, a frontal system is forecast to push through the East with a cold air damming wedge of high pressure behind it. This setup will allow for multiple rounds of rain in the East, as well as cooler temperatures and notable onshore flow across the Northeast and Mid-Atlantic. Meanwhile, an eastern Pacific/southwestern U.S. upper trough and warm upper ridging sticking around the south-central U.S. will direct moist southerly monsoonal flow into parts of the western U.S. to the Plains. Multiple days of heavy rain are possible in the southern Rockies/High Plains in particular, which could cause flooding concerns. ...Guidance/Predictability Assessment... Model guidance begins the medium range period Monday in reasonably good agreement with the pattern described above. Upper troughing in the north-central U.S. could close off into an upper low as it moves into the Great Lakes by midweek. Weak energy in the Gulf early next week should shear north and track across the East. One issue with the northern/eastern pattern is that the 00Z GFS and CMC have a stronger shortwave in the Dakotas by Tuesday compared to other models. But in general, the upper low in the Great Lakes should slowly push into the East late week as it opens up into a trough. Southern stream troughing is forecast to hover over the eastern Pacific and slowly track into California Monday-Tuesday. After that its evolution becomes questionable as some energy may linger while some tracks northeastward across the Intermountain West. The 00Z ECMWF is on the strong side as it tracks most of the energy northeast and reaches the north-central Plains as a strong shortwave by Thursday. Other models tend to favor ridging reaching farther north into the Plains from the more agreeable south-central U.S. upper ridge, so some out of phase differences develop. Farther north, northeast Pacific troughing could reach the Northwest at times, potentially stronger by late next week. By Friday, the 00Z GFS and the EC-AIFS are on the faster side in reaching the Pacific Northwest compared to the slightly slower EC and AI-GFS, and the CMC is the slowest. Overall, the WPC forecast favored a multi-model blend of the dynamical and AI guidance early in the period, but transitioned to favor increasing proportions of ensemble means to half Day 6 and more Day 7 given the increasing model spread, especially with the smaller scale features. ...Weather/Hazards Highlights... Upper-level support and a surface frontal system will lead to multiple rounds of moderate to heavy rain in the East next week. The placement of the heaviest amounts will vary from day to day, but generally the Mid-Atlantic looks like a focus. A relatively strong surface high for September should set up over Quebec and spill a cold air damming wedge south behind the front, yielding colder than average temperatures across the Northeast/Mid-Atlantic, with highs generally in the 60s and upper 50s Tuesday-Wednesday. This pattern will also allow for onshore winds and potentially some concern for coastal flooding for portions of the Northeast and Mid-Atlantic. Pacific and Gulf moisture are forecast to combine as they stream into the Interior West, increasing by Tuesday and persisting through at least Thursday. Rain amounts may become heavy in New Mexico in particular, and flooding will be possible--see the Excessive Rainfall Outlooks for more information. Some chance of rain will extend north across the Rockies to High Plains Tuesday and into the Plains Wednesday-Thursday. Meanwhile, a wet pattern will be in place across Florida through the period, particularly for the Keys and southern portions of the peninsula. Warmer than average temperatures should stay farther north across Texas to the Southeast under an upper ridge, but gradually reducing in scope and magnitude as next week progresses. 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 $$