Extended Forecast Discussion NWS Weather Prediction Center College Park MD 400 PM EDT Sat Oct 4 2025 Valid 12Z Tue Oct 07 2025 - 12Z Sat Oct 11 2025 ...General Overview... A slowly amplifying trough-ridge-trough synoptic pattern across the mainland U.S. is forecast to be sandwiched between a subtropical High traveling westward along the Gulf Coast, and progressive baroclinic troughs in the westerlies across Canada through next week. An upper trough that digs down western Canada midweek next week will likely develop into a closed low along/off the Pacific Northwest coast for to latter half of next week. In addition, tropical moisture well ahead of what likely to be the next tropical cyclone in the eastern Pacific is forecast to be drawn northward through the Southwest and the Intermountain region late next week. ...Guidance/Predictability Assessment... The main synoptic system in the forecast period will be a digging trough across BC Tuesday that closes into an upper low off the Pacific Northwest coast on Wednesday and then persists/drifts off/along the coast into the weekend as a cutoff. The general consensus of the past couple of days has been for the upper low to close off farther off the coast of the Pacific Northwest by next Thursday, resulting in a trend toward a more amplified upper- level pattern to set up just off the West Coast late next week. Meanwhile, the next tropical cyclone is forecast to develop in the eastern Pacific and generally track northwestward to a position west of the southern Baja Peninsula late next week. The amplitude and placement of the upper low off the West Coast in relation to how far north the tropical cyclone ultimately tracks will influence how much and how fast tropical moisture will be drawn northward into the Southwest by late next week. The ECMWF cluster remains on the fastest side of the guidance in bringing the tropical cyclone closer to Mexico and therefore more abundant flow of moisture into the Southwest. Meanwhile, the GFS cluster keeps the tropical cyclone farther offshore and thus less moisture reaching into the U.S. Despite the uncertainty on exactly how these two systems will ultimately interact one another, it appears that the presence of the upper low off the West Coast alone will bring a good chance of terrain-enhanced precipitation northward across the Southwest and then through the Intermountain West late next week. Elsewhere, there is a trend toward bringing more tropical moisture into the east coast of southern Florida early next week with a better-defined low pressure center tracking onshore along a weakening or dissipating frontal boundary. The Icon model has been the most aggressive and consistent guidance in this regard. The WPC medium-range forecasts were based on the consensus of 40% from the 00Z EC/EC mean, 40% from the 06Z GFS/GEFS, and 20% from the 00Z CMC/CMC mean, with mainly the consensus of the ensemble means for Days 6 to 7. This blend agrees reasonably well with the previously WPC forecast package. ...Weather/Hazards Highlights... A cold front ahead of a powerful trough shifts from the Midwest through the central Appalachians Tuesday/Tuesday night. Despite the generally progressive nature of this pre-frontal activity, sufficient moisture (PW two sigma above normal) warrants a Day 4 Marginal Risk over the middle/upper Ohio Valley to the crest of the central Appalachians and interior New England. GFS shows a wave of low pressure developing on the front over New England which would enhance rainfall in New England on Wednesday. This scenario is considered an outlier at this point. Moisture anomalies increase over New Mexico Tuesday from continued surges of moisture from the western Gulf onto a frontal wave that is stalled over northern NM. Maintain the Marginal Risk now for Day 4 with some further expansion over NM. An influx of tropical moisture from the eastern Pacific into the Desert Southwest looks to still occur, but possible not until Friday. An upper-low lingering off the West Coast through this time would allow the tropical moisture to surge over much of the western U.S. by next weekend. Cool conditions shift east with a cold front from the Northern Plains Tuesday, the Midwest Wednesday, and the Eastern Seaboard for Thursday/Friday. Meanwhile, ridging drifting over the Gulf Coast through Texas will maintain above normal temperatures over The South through next week. Kong/Jackson 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 (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: 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