118 FXUS02 KWBC 220734 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 334 AM EDT Tue Sep 22 2026 Valid 12Z Fri Sep 25 2026 - 12Z Tue Sep 29 2026 ...Impactful coastal storm meanders near the Mid-Atlantic and Northeast late week/weekend... ...Overview... An upper low will stall atop the Mid-Atlantic and Northeast late week into the weekend, supporting a meandering coastal surface low. This pattern will lead to strong/gusty onshore winds for multiple days, leading to coastal flooding, rip currents and high surf, and potential beach erosion. An upper ridge persisting in the south- central U.S. will promote warm temperatures, while a couple of upper troughs come into the northwestern and north-central U.S. through the period and bring rounds of precipitation to those regions. ...Guidance/Predictability Assessment... Models continue to agree that a coastal low will be in the western Atlantic Friday into the weekend underneath a stalling upper low. The surface low should be rather deep, reaching the 980s or at least 990s (mb) around Saturday. The low will likely be pretty stacked and seems to be warm core per phase space diagrams, indicating there could be a warm seclusion and/or have some subtropical characteristics. Its position from day to day at it meanders is much more uncertain. The EC and UKMET develop the low farther south in the Atlantic Friday-Saturday and reach near Long Island by Sunday, compared to the farther northeast GFS/AIGFS/CMC, with the EC-AIFS looking like a reasonable middle ground like the EC mean. By Monday-Tuesday the low should be weaker but with remaining questions on when it pulls away. All in all there is still ample spread with the details, which could have sensible weather impacts like wind speed/direction and how much rain falls onshore or offshore. Elsewhere, guidance shows good consensus on the upper ridge in the south-central U.S., though varying positions of weak fronts and precipitation potential cause uncertainties in the temperatures. The ridge looks to extend north and traverse the Midwest/Great Lakes Friday and over the weekend, contributing to the blocky pattern as it stretches into southeast Canada north of the Atlantic upper low. Meanwhile a couple of trough axes will track across the northwestern to north-central U.S. with typical spread in their timing and depth. Guidance generally shows one crossing the Pacific Northwest at the start of the period Friday, tracking across the northern tier and lifting into central Canada on Sunday. Then an upstream trough is forecast to move into the West Coast Sunday and continue tracking east. By Monday into Tuesday models show varying degrees of stream separation that affects the trough's timing. Will also mention that Hurricane Polo in the eastern Pacific still has some model spread in its track, but number of models/ensemble members are decreasing for having it curve into Baja California. Polo's track will affect potential moisture inflow into the Southwest. The WPC forecast used a model and ensemble blend even early in the forecast period, given the spread with the eastern low. Increased the proportion of ensemble means to well over half by Days 6-7 to mitigate the individual model differences in the details of the pattern. ...Weather/Hazards Highlights... The surface low in the western Atlantic meandering will lead to broad onshore flow across the Mid-Atlantic and Northeast for multiple days. This persistent pattern could lead to coastal flooding and beach erosion concerns, especially when combined with high astronomical tides. Exact placement of the surface low from day to day and thus any heavy rain is more uncertain. The current forecast supports that coastal New England may see heavy rainfall on Friday into the weekend. However, stay tuned for forecast updates, as small shifts in the low track would lead to significant forecast shifts in rainfall amounts. See WPC's Key Messages for this coastal low for further information. Pacific moisture is forecast to advect around the western side of the south-central U.S. upper ridge and lead to some rain across parts of the central U.S. on Friday. If/where additional rain falls in New Mexico, there could be flooding concerns after the forecast heavy rainfall event in the short range causes very wet antecedent conditions. Meanwhile farther east and northeast into the Plains, moderate to locally heavy rainfall may be possible, but on less sensitive ground. Rain chances persist in the Upper/Middle Mississippi Valley into Saturday. Meanwhile, upper troughing will bring precipitation to the Pacific Northwest and northern Rockies, including higher elevation snow chances, on Friday. Scattered showers and thunderstorms are again possible in parts of the Plains/Mississippi Valley on Sunday, but a more widespread rainy pattern with potentially heavier amounts is possible by Monday as Pacific and Gulf moisture combine and stream into the central U.S. ahead of troughing in the West. Temperatures are forecast to remain cooler than average by 5-10 degrees in the Mid-Atlantic and Northeast into the weekend underneath the upper low, and highs will generally be in the 60s. On the other hand, broad upper ridging over the south-central U.S. could maintain highs in the 90s for the southern Plains and Lower Mississippi Valley. Cooler than normal temperatures are likely in the Northwest given troughing aloft, which should push into the northern Rockies/High Plains after a warmer than average period into Friday. 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 $$