


Prognostic Meteorological Discussion
Issued by NWS
Issued by NWS
541 FXUS02 KWBC 171951 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 351 PM EDT Fri Oct 17 2025 Valid 12Z Mon Oct 20 2025 - 12Z Fri Oct 24 2025 ...Overview... A couple of progressive upper troughs are forecast to move through the eastern two-thirds of the country through the medium range period, with a tendency for them to close off into upper lows as they near the New England coast. Meanwhile, an upper low is forecast to push onshore into the Southwest amid general ridging across the Northwest before ridging takes over late next week while progressing east into the northern High Plains. Precipitation chances look to increase late next week across the Pacific Northwest as an upper-trough/potential Atmospheric River approaches, with heavy rain possible. ...Guidance/Predictability Assessment... The medium range period beings Monday (Oct 20) with good consensus in most of the guidance on a continued progressive pattern featuring a couple upper-troughs over the eastern/central U.S., another upper-trough upstream over the northeastern Pacific, and a southern stream upper-low off the coast of California. Most guidance also remains in good agreement through at least the middle part of the period, with the progression of both of the upper- troughs/potential closed lows over the Great Lakes/Northeast followed by the upper- trough over the northeastern Pacific dropping southeastward across southwestern Canada and into the north-central U.S., as well as with the upper-low moving eastward over California. Guidance begins to diverge by later next week with regards to the upper-low and the amplification of the overall pattern, specifically indications that an upper-ridge will build over the western/central U.S. Both the latest GFS and ECMWF, and to a lesser degree the ECens mean, are relatively similar in bringing the upper-low east, possibly as an open wave, over the southwestern to south- central U.S. under the amplifying ridge, while the CMC brings the wave east a bit faster and shows that it merges with the northern stream upper- trough dropping southeastward. The last several runs of the ECMWF/GFS also show large run-to-run variability on timing. This will have implications on the coverage and amount of potential rainfall over the south- central U.S. For now, the agreement on this feature from the GFS/ECMWF this run cycle, as well as the presence of this feature regardless of exact timing in previous run cycles, at least signals an increasing chance of precipitation from the central Rockies east through the south- central U.S. Further upstream, some uncertainty exists on the timing and coverage of precipitation across the Pacific Northwest associated with another upper- trough/potential atmospheric river depending on the amplification of the upper-ridge downstream, but all guidance does reflect a significant increase in precipitation chances by late next week. The updated WPC forecast used a blend of the 00Z ECMWF/06Z GFS with a component of the 00Z CMC through mid- period, with the CMC removed and a contribution from the ECens and then GEFS means ramped up to 50% of the blend by the end of the period as uncertainty with respect to the evolution of the upper- low into the southwest/south-central U.S. grows. ...Weather/Hazards Highlights... The medium range period should begin with moderate to locally heavy rain possibly with embedded thunderstorms across northern New England ahead of the first trough that could develop into a closed low. A marginal risk of flash flooding has been maintained for this area. Meanwhile, another upper trough may develop into a closed low over the Great Lakes on Tuesday but with modest amounts of rainfall. The progressive pattern with consistent post-frontal northwesterly flow over the Great Lakes will also bring the chance of lake-effect showers through much of next week. Out West, increasing chance of moderate to heavy precipitation is seen near the Pacific Northwest coast toward the end of next week ahead of an approaching upper trough and potential atmospheric river. Meanwhile, there are increasing model signals for an expanding area of rain across the south-central U.S. later next week but with a fair amount of uncertainty in the amounts and placement at this point in time. There is also a signal for some precipitation in the Four Corners region/central Rockies vicinity, with higher elevation snow possible. High temperatures across the south-central U.S. look to remain persistently above average next week, especially for Texas where highs into the 90s may tie/break a few daily high temperature records. There may be some periods of below average temperatures for the Midwest/Northeast following cold frontal passages, though highs in general look to remain near Fall averages through much of next week. Highs across the northern- tier from the Rockies east to the Plains will initially be below average before an amplifying upper-ridge brings well above average highs by late next week. Putnam/Kong 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 $$