327 FXUS21 KWNC 211907 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT October 21 2026 SYNOPSIS: Today's model ensembles predict a mid-level low pressure near the West Coast and a highly anomalous mid-level high pressure over the western Gulf of Alaska during week-2. In addition, a weak high pressure is forecast to flatten and move across the Great Lakes and Northeast, before reamplifying towards the end of the period near Nova Scotia. Heavy precipitation is favored across much of the West Coast and Lower Four Corners region in association with the western trough, and possibly an influx of moisture from the eastern tropical Pacific. Enhanced onshore flow accompanying the western mid-level low also promotes a slight risk of heavy snow for the Klamath and Sierra Nevada Mountain Ranges in California, and portions of the Rockies. Surface high pressure approaching the Northeast or upper Mid-Atlantic coast early in the period and low pressure off the Carolina coast are forecast to result in a strengthened pressure gradient and an increased risk of high winds for the Southeast coastal plain. As the surface high moves out over the western Atlantic during mid-period, southerly return flow is anticipated to bring a slight risk of heavy precipitation for eastern portions of the Southern Plains, the Middle and Lower Mississippi Valley, and western sections of Kentucky and Ohio. A stormy period is forecast for western Alaska, as a series of strong cyclonic systems approach the state from the Bering Sea and the biggest impact of concern would be high winds across western portions of the state. HAZARDS Moderate risk of heavy precipitation for portions of Arizona, Sat-Mon, Oct 31-Nov 2. Slight risk of heavy precipitation for portions of Oregon and California, Sat-Wed, Oct 31-Nov 4. Slight risk of heavy precipitation for the southern California coast, Sat-Mon, Oct 31-Nov 2. Slight risk of heavy precipitation for the Lower Four Corners region, Sat-Mon, Oct 31-Nov 2. Slight risk of heavy precipitation from eastern portions of the Southern Plains and the Lower Mississippi Valley northeastward into the Lower Ohio Valley, Sat-Wed, Oct 31-Nov 4. Slight risk of heavy snow for the Klamath and Sierra Nevada Mountain Ranges, Sat-Wed, Oct 31-Nov 4. Slight risk of heavy snow for portions of the Rockies, Sat-Wed, Oct 31-Nov 4. Slight risk of high winds for the Southeast coastal plain and most of Florida, Thu-Sat, Oct 29-31. Moderate risk of high winds for portions of southwestern Mainland Alaska and the Alaska Peninsula, Fri-Sat, Oct 30-31. Slight risk of high winds for southwestern Mainland Alaska, the Alaska Peninsula, Kodiak Island, and the Aleutians, Fri-Sat, Oct 30-31. DETAILED SUMMARY FOR SATURDAY OCTOBER 24 - WEDNESDAY OCTOBER 28: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR THURSDAY OCTOBER 29 - WEDNESDAY NOVEMBER 04: A mid-level trough near the West Coast is forecast to bring enhanced onshore flow to much of western Oregon and California during week-2. Uncalibrated ECENS guidance shows the bulk of the precipitation occurring during the middle and latter portions of the period, with a southward extension across the southern California coast during mid-period. A 20-30% chance of heavy precipitation is generally favored across this part of the CONUS, with a 30-40% chance along the California coast, and the Klamath and Sierra Nevada Mountain Ranges. The uncalibrated GEFS is slightly weaker compared to the ECENS. There is support from the GEFS and ECENS Probabilistic Extremes Tools (PET), which favor at least a 20-30% chance of 3-day precipitation amounts exceeding the 85th percentile and 1-inch. A slight risk for periods of heavy precipitation is therefore posted for parts of western Oregon and northern and central California from Oct 31-Nov 4, as well as a slight risk of heavy snow for the Klamath and Sierra Nevada Mountain Ranges in California. Uncalibrated ECENS guidance shows amounts on the order of 4-6 inches of snow or greater in the highlighted risk area. The slight risk of heavy precipitation extends southward across the southern California coast from Oct 31-Nov 2. Over the Lower Four Corners region, a slight risk of heavy precipitation is posted from Oct 31 - Nov 2. This is associated with a combination of shortwave energy accompanying the mean trough, and also possible tropical moisture from the eastern Pacific which has been very active this season. Precipitation amounts of 0.50-0.75 inches are predicted by the uncalibrated GEFS and ECENS precipitation tools over this region, with the ECENS solution remaining a bit more robust than the GEFS. An embedded moderate risk (40-60% chance) of heavy precipitation is depicted over portions of primarily the higher terrain of Arizona for the same period. The potential for flash flooding continues to be monitored across Arizona, and if warranted a flood shape may be introduced tomorrow. Raw snow totals from the uncalibrated ensemble means range from 4-6 inches, with locally greater amounts possible over portions of the Rockies. A slight risk of heavy snow therefore includes western Wyoming and western Colorado, from Oct 31-Nov 4. Along the East Coast, a surface ridge axis of high pressure is predicted to extend from about the New England coast to the southern Appalachians during the first few days of week-2. A slight risk of high winds (20-25 mph) is forecast from Oct 29-31. However, according to the 6z deterministic GFS run, the most likely day appears to be October 31st. This is due to a strengthening high pressure system moving across Ontario and Quebec, funneling cooler air southward across the Atlantic coastal plain and tightening the pressure gradient. During the middle and latter portions of week-2, surface high pressure moving off the Northeast or upper Mid-Atlantic coast supports an increase in moist, southerly flow from the western Gulf northward across eastern portions of the southern Plains, the Lower and Middle Mississippi Valley, and western parts of Kentucky and Tennessee. Accordingly, a slight risk of heavy precipitation is delineated for this region from Oct 31-Nov 4. The ECENS and GEFS PETs are supportive of this wet signal, as are the uncalibrated tools, with a 20-40 percent chance of 3-day precipitation amounts exceeding the 85th climatological percentile and totals of about an inch. The spatial extent of the slight risk area represents a splitting of the difference between the calibrated and uncalibrated precipitation tools; the calibrated tools concentrates the heavy rain risk over the southern Plains and Lower Mississippi Valley, with the uncalibrated tools expanding the slight risk area well into the Ohio Valley. In Alaska, the strong mid-level ridge predicted over the western Gulf of Alaska is forecast to extend northward across much of Alaska for at least the first half of week-2. Several deep low pressure areas from the vicinity of the Kamchatka Peninsula are forecast to move eastward across the Bering Sea and western Alaska. These cyclonic systems are predicted to bring high winds (at least 40 mph winds and greater than the 85th climatological percentile) to the southwestern coast of Alaska. The 0z deterministic European model forecasts 10 meter wind speed gusts over Bristol Bay in excess of 60 mph, though this is one single model run. A slight risk of high winds is depicted over portions of the southwestern Mainland, the Alaska Peninsula, Kodiak Island, and the Aleutians from Oct 30-31. A moderate risk of high winds is depicted within a smaller portion of this region, namely the southwestern coastal areas and the Alaska Peninsula, also from Oct 30-31. FORECASTER: Anthony Artusa $$