Preliminary Forecasts
Issued by NWS
Issued by NWS
587 FXUS02 KWNH 200730 PREEPD Preliminary Extended Forecast Discussion NWS Weather Prediction Center College Park MD 329 AM EDT Sun Sep 20 2026 Valid 12Z Wed Sep 23 2026 - 12Z Sun Sep 27 2026 ...Monsoon flooding threat for the Southern High Plains/Rockies... ...Mid-Atlantic/Northeast Closed Upper Low/Coastal Storm Threat... ...Pattern Overview and Guidance/Predictability Assessment... Guidance forecast spread has improved to bolster confidence. The pattern evolution into Autumn will be quite amplified/blocky as highlighted by cooling/unsetting/wet upper troughs and surface systems over the Northwest and especially the East that sandwich a southern tier/central U.S. mean upper ridge. A multi- model and ensemble mean/machine learning guidance composite blend seems to provide a good forecast basis for consistent threat messaging, mainly in line with weather parameter forecasts of the National Blend of Models. WPC product continuity is well maintained. ...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 this week. Generally the Appalachians to Mid-Atlantic could see heavy rain through midweek, transitioning to the Northeast late week with slowed coastal storm northward track. A WPC Excessive Rainfall Outlook (linked below) Marginal Risk area is depicted over the central Appalachians/Mid-Atlantic Wednesday. 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 Wednesday- Thursday. This pattern supports strong/gusty onshore winds and a concern for coastal flooding for the Northeast and Mid-Atlantic. Pacific (including potential tropical moisture connection) and Gulf moisture are forecast to combine into the Southwest next week. Rain amounts may become heavy in New Mexico in particular, and flooding will be possible. A Marginal Risk area ERO is in place Wednesday and Thursday along with an embedded Slight Risk area Wednesday. Rain chances will extend north across the Rockies to the High Plains and into the Plains Wednesday-Friday. Elsewhere, a wet pattern will remain in place across Florida through the period, particularly for southern portions of the peninsula and the Keys. Meanwhile, hazardous heat is forecast to linger across Texas/West Gulf Coast through next midweek, but then gradually moderate as the week progresses. Meanwhile, increasingly blocky/amplified flow over/near the lower 48 will include development of a unsettling/wet Northwest U.S. mean upper trough. Schichtel 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 $$