933 FXUS02 KWBC 240732 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 332 AM EDT Thu Sep 24 2026 Valid 12Z Sun Sep 27 2026 - 12Z Thu Oct 01 2026 ...Impactful coastal storm meanders near the northern Mid- Atlantic/Northeast into early next week... ...Widespread precipitation likely in the Four Corners states and reaching the Plains/Mississippi Valley early to mid-next week... ...Overview... The western Atlantic surface low will still be lingering near the Northeast Sunday-Monday before exiting eastward. Though the low should be weakening, additional strong/gusty winds with potential for coastal flooding, beach erosion, and rip currents are possible, along with heavy rain in coastal New England. Meanwhile, an amplified upper trough will enter the West early next week and move east as the week progresses. Precipitation will be widespread ahead of this trough, for potentially multiple days of rain/storms and mountain snow in the Interior West/Four Corners states, and spreading into the Plains and Mississippi Valley as the week progresses. ...Guidance/Predictability Assessment... At the start of the period Sunday, the primary model diagnostics concern continues to be the western Atlantic coastal low position, as relatively minor differences in position could cause significantly different sensible weather impacts like wind speed and direction. There is general agreement for the low to meander south or southeast of Long Island on Sunday and Sunday night. The 00Z ECMWF seems (hopefully) like an outlier with its trend toward a stronger low in the 980s and farther west closer to the New Jersey coast. There is some support from the AIFS/some AIFS ensemble members for a position like that, but weaker. For now, will prefer a blend of the slightly farther east guidance like the GFS and 12Z EC mean. The AI-GFS has been persistently farther northeast with the low. The upper and surface lows should weaken and move northeast by Tuesday-Wednesday. After the trough comes into the West Coast Sunday, models have struggled with how to handle its progression eastward. The 12/18Z dynamical model guidance kept the trough mostly phased for a steady progression east into the central U.S., while the EC-AIFS and AIGFS instead agreed upon a split flow pattern where a southern stream upper low formed with slower movement through the Southwest and the northern stream trough progressed quickly eastward. Now with the recent 00Z guidance, the ECMWF and CMC have transitioned to show a split flow pattern as well, and the GFS is the only primary model that keeps the trough phased. Even the 00Z ECens and CMCe means seem to pull some southern stream energy southwest now. The pattern will have an impact on Hurricane Polo's track, and the slower moving upper low in the Four Corners states could pull energy and moisture from Polo north into it. See NHC for Polo's official forecast track. The WPC gridded forecast was based on the 01Z NBM with some edits, which uses the 12/18Z model cycle. But the fronts/pressures forecast used the 00Z guidance, mostly leaning away from the ECMWF with the Atlantic low early, and leaning away from the GFS later since the bulk of guidance now shows split flow. Expect more changes to continuity than normal with this large model change. ...Weather/Hazards Highlights... The meandering surface low in the western Atlantic will lead to broad onshore flow across the Mid-Atlantic and Northeast continuing into early next week. The persistent pattern could lead to coastal flooding and beach erosion, as well as marine hazards like rip currents and high surf. Heavy rain could cause inland flooding across southeastern New England into Sunday. See WPC's Key Messages regarding this coastal low for further information. Some light to moderate rain is possible in the Dakotas and parts of the Lower/Middle Mississippi Valley on Sunday. More broadly, Pacific moisture should make a return ahead of the large-scale trough in the West, bringing some rain to the Four Corners states northward Sunday-Monday. After that, uncertainty in the pattern makes rainfall placement and amounts uncertain. The current forecast shows moderate to heavy rain spreading across the Plains and Upper Midwest Monday and tracking east to reach the Mississippi Valley on Tuesday and Wednesday. But given the model trends, this may need to transition to a wetter pattern in the Four Corners states with a lingering upper low and potential Hurricane Polo influence, while rain chances are more progressive in the north- central U.S. Stay tuned for forecast updates in this uncertain pattern. Some snow is possible in the higher peaks of the Intermountain West/Rockies with the precipitation, as the trough aloft helps to cool temperatures. Warmer than average temperatures will persist in the south-central U.S. into early next week under an upper ridge, and highs in the 90s are forecast through the southern Plains and Lower Mississippi Valley. On the other hand, cooler than average temperatures (especially for highs) are forecast for the West under troughing aloft, gradually spreading eastward early next week and helping to moderate temperatures in the Plains by midweek. Temperatures could reach around 10 degrees above normal in the East ahead of the trough Wednesday-Thursday. 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 $$