655 FXUS02 KWBC 191930 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 330 PM EDT Sat Sep 19 2026 Valid 12Z Tue Sep 22 2026 - 12Z Sat Sep 26 2026 ...Wet pattern with possible flooding threat in the Southern High Plains/Rockies next week... ...Overview... During this period an upper trough/low will advance through the Great Lakes region ushering a frontal system through the East with a cold air damming wedge of high pressure behind it, while coastal low development becomes likely. This pattern will be favorable 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... The latest suite of guidance has overall decent agreement on the larger pattern with continued variances on smaller scale features. Across the East, models depict an upper low tracking east across the Upper Midwest into the Great Lakes midweek, while Gulf energy shears northward tracking across the East. These combining features allow for the upper low/trough to slowly track atop the East late week, with differences in how broad and far south it gets. A surface low will spin up over the western Atlantic and lift northward toward the later part of the extended period. There continues to be notable differences with its placement, strength and track that will impacts QPF and winds/wind gusts particularly for the Mid-Atlantic and Northeast coastal areas. The 00Z GFS, AI- GFS, and CMC show the low quite close to the coast and a bit faster to track north, while the ECMWF, EC- AIFS, and UKMET are farther offshore and slower. Ensemble members continue to show ample spread too, so confidence in any particular solution is low. Followed persistence by leaning away from the farthest west/wetter solutions. Multiple cycles have struggled with the details of southern stream troughing in the Southwest by Wednesday-Thursday as some energy tracks north and some stays behind. However consensus has started to improve with the shortwave tracking north/northeast, reaching the Dakotas by early Thursday. This in turn will briefly disrupt the ridge, then feeding into the eastern trough by Friday. By the end of the week guidance has differences with the troughing over the West on whether streams will separate. The AIFS and AIGFS leave some southern stream troughing behind and track the northern stream more quickly eastward across central Canada by next Saturday, with ridging in the West. The GFS and CMC keep a phased positively tilted trough moving into the West while the ECMWF seems to be a middle ground depiction, with some separation of the streams but not as aggressive as the AIs. The WPC forecast was based on a multi-model blend early before transitioning to a heaviest weighting of the ensemble means to account for the increasing model differences. ...Weather/Hazards Highlights... Upper-level support and a surface frontal system with a developing coastal low will lead to multiple rounds of moderate to heavy rain in the East next week. Generally the Appalachians to Mid-Atlantic could see heavy rain through midweek, potentially transitioning to the Northeast by late week if and when the coastal low tracks north. 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-Thursday. This pattern will also allow for onshore winds and potentially some concern for coastal flooding for portions of the Northeast and Mid-Atlantic. Pacific (including a potential tropical connection) and Gulf moisture are forecast to combine as they stream into the Interior West, increasing by Tuesday and persisting through at least Friday. 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- Friday. Meanwhile, a wet pattern will be in place across Florida through the period, particularly for southern portions of the peninsula and the Keys. Above average temperatures well into the 90s are forecast to linger across Texas into the Southeast through Tuesday, but gradually reduce in scope and magnitude as the week progresses. Campbell/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 $$