


Prognostic Meteorological Discussion
Issued by NWS
Issued by NWS
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059 FXUS02 KWBC 151958 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 358 PM EDT Wed Oct 15 2025 Valid 12Z Sat Oct 18 2025 - 12Z Wed Oct 22 2025 ...Guidance/Predictability Assessment... The depiction of the large scale pattern by the latest model guidance remains reasonably good to start off the medium range period, but uncertainty increases quite a bit for Day 5 and beyond. Given only minor differences of the strength and timing of an eastern U.S. ridge, central U.S. trough and western U.S. ridge, a composite blend of the 00Z EC, 00Z UKMET, 00Z CMC and 06Z GFS were utilized for the Day 3 and Day 4 forecast. By Day 5, the trough progged to push from the Pacific across the Pacific Northwest is trending to be much more progressive compared to yesterday`s package. In fact, most of yesterday`s guidance aside from the CMC was on board with a much slower and more amplified solution, with a deepening trough digging southward along the West Coast. Instead, the more progressive solution is now looking more likely, with all guidance including the latest machine learning guidance all depicting this evolution fairly similarly. The latest 00Z and 06Z runs of the GFS were slow to catch on (and thus were not used in the composite blend for Days 5-7) but the most recent 12Z run has joined consensus as well. Given the strength and amplitude of the eastern U.S. ridge at the beginning of the period, the faster and more progressive flow upstream is leading to a sharper and more negatively tilted trough pushing from the central U.S. into the eastern U.S. this weekend into early next week. As a result, a stronger and more consolidated surface low is looking more likely to track across the Great Lakes, with implications to QPF and hazards. More on that below. Given the above, the Days 5-7 forecast consisted of a blend that increasingly relied on the ensemble means of the EPS, CMCE, and GEFS, which provided more stability and less noise from individual deterministic guidance sources. ...Weather/Hazards Highlights... A sharpening upper trough/shortwave and strengthening surface low pressure pushing across the Great Lakes region this weekend will draw anomalous moisture and instability northward in advance of a cold front. PW anomalies of >200% of normal combined with instability of 500-1500 j/kg will support an axis of heavier rainfall across parts of the Upper Midwest, Ohio Valley and Mid- South on Saturday. As a result, the Day 4/Saturday Excessive Rainfall Outlook (ERO) expanded the Marginal Risk northward to include southeast Wisconsin and southwest Michigan. The recently introduced Slight Risk area centered over the Mid-South was maintained given the overlap with the greatest instability and relatively lower FFG. SPC also shows a threat for severe weather in this pattern. The slowly progressive nature of the upper-level and surface features will then spread organized rainfall eastward into the East/Northeast Sunday into early next week. This will especially be the case near and along the track of a deepening/consolidating coastal low pressure system (and more modestly into the Southeast ahead of the cold front). A Day 5/Sunday ERO Marginal Risk area was maintained and broadened to capture local runoff potential into the Appalachians and parts of the Ohio Valley. Out West, the now more progressive trough and surface low will quickly approach and push across the Pacific Northwest and northern Rockies over the weekend to produce a period of moderately heavy coastal and valley rains along with higher mountain snow. The Day 4/Saturday ERO maintains a coastal Washington Marginal Risk area given a favorable QPF signal while our Day 4-7 Winter Weather Outlook shows mountain snow potential inland from the Northwest to the Northern Rockies Sunday into Monday. Miller/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 (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 $$