746 FXUS21 KWNC 201818 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT October 20 2026 SYNOPSIS: Today's model ensembles predict a mid-level trough near the West Coast and a highly anomalous mid-level ridge over the western Gulf of Alaska during week-2. In addition, a less amplified ridge over the Central Contiguous U.S. (CONUS) is predicted to deamplify as it migrates eastward across the Great Lakes and Northeast. Slight risk areas of heavy precipitation are favored across much of the West Coast and 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 trough also promotes a slight risk of heavy snow for the Klamath and Sierra Mountain Ranges in California. Surface high pressure approaching the Mid-Atlantic coast early in the period, and a developing storm off the Southeast coast, are forecast to result in a strengthened pressure gradient and a risk of high winds for the East Coast states. As the surface high moves out over the western Atlantic later in the period, southerly return flow is forecast to bring a slight risk of heavy precipitation for the southern half of the Mississippi Valley and portions of neighboring states. HAZARDS Moderate risk of heavy precipitation for portions of Arizona, Fri-Sun, Oct 30-Nov 1. Slight risk of heavy precipitation for southern portions of the Four Corners and western Texas, Fri-Sun, Oct 30-Nov 1. Slight risk of heavy snow for parts of the Northern and Central Rockies, Fri-Tue, Oct 30-Nov 3. Slight risk of heavy precipitation for portions of Oregon and California, Fri-Tue, Oct 30-Nov 3. Slight risk of heavy snow for the Klamath and Sierra Mountain Ranges, Fri-Tue, Oct 30-Nov 3. Slight risk of heavy precipitation for parts of the Lower Mississippi Valley and Southern Plains, Fri-Tue, Oct 30-Nov 3. Slight risk of high winds for portions of the East Coast, Wed-Fri, Oct 28-30. Moderate risk of high winds for parts of western Alaska, Wed-Fri, Oct 28-30. Slight risk of high winds for parts of western Alaska, the Alaska Peninsula, and Aleutians, Wed-Fri, Oct 28-30. DETAILED SUMMARY FOR FRIDAY OCTOBER 23 - TUESDAY OCTOBER 27: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR WEDNESDAY OCTOBER 28 - TUESDAY NOVEMBER 03: A mid-level trough near the West Coast is forecast to bring enhanced onshore flow to much of the West by the middle of week-2. A slight risk (20-40% chance) for periods of heavy precipitation is designated for portions of Northern and Central California and western Oregon, Oct 30-Nov 3, where the GEFS, ECENS, and CMCE Probabilistic Extremes Tools (PETs) indicate at least a 20% chance of 3-day precipitation totals exceeding the 85th percentile climatologically and 0.75 to 1 inch. ECENS indicates greater than 40% chances for these thresholds across central California. A slight risk of heavy snow is maintained for the Klamath and Sierra Mountain Ranges of California for the same valid period where uncalibrated model guidance indicates 3-day snowfall totals reaching or exceeding 4 inches (6 inches locally). Enhanced moist flow in addition to possible tropical moisture from the eastern Pacific which has been very active this season, supports continued enhanced risk of heavy precipitation for parts of the southwestern CONUS. A moderate risk (40-60% chance) of heavy precipitation is delineated for parts of Arizona, Oct 30-Nov 1, where PETs indicate at least a 30-40% chance of 3-day accumulated precipitation exceeds the 85th percentile and 0.5 inches, further supported by uncalibrated guidance. A broader area of slight risk (20-40% chance) of heavy precipitation is highlighted across southern portions of the Four Corners and western Texas for the same period. Localized flooding is possible in these areas, but a brief respite of possible flooding is anticipated by end of week-1 heading into week-2 so no flooding hazard is designated at this time. Further north, a slight risk of periodic heavy snow is posted for parts of the Northern and Central Rockies Oct 30-Nov 3. Some areas may receive greater than 4 inches of snowfall in a 3-day period. Surface high pressure over the eastern Corn Belt and Mid-Atlantic, and a developing storm system off the Southeast Coast and front further north, are expected to result in a strengthening of the regional pressure gradient, resulting in increased likelihood of high winds across parts of the East Coast. A broad area is highlighted across much of the East Coast with a slight risk of high winds due to uncertainty of where enhanced winds are most likely, Oct 28-30. Ensembles indicate increased potential for 10 m wind gusts exceeding 20 knots (about 23 mph) across the risk area. During the second half of week-2, surface high pressure moving off the Mid-Atlantic coast supports an increase in moist, southerly flow from the western Gulf northward across much of the Lower Mississippi Valley and eastern Southern Plains. A slight risk of episodic heavy precipitation is posted for parts of the Lower Mississippi Valley and Southern Plains, Oct 30-Nov 3 where there is good agreement among the PETs indicating at least a 20% chance of 3-day precipitation totals exceeding the 85th percentile and 1 inch. Mid-level troughing is forecast to develop off the west coast of mainland Alaska, along with a series of possibly strong storms tracking across the Bering Sea at the beginning of week-2. These storms may result in episodic high winds for western portions of Alaska. A moderate risk of high winds is designated for parts of western Alaska, Oct 28-30, where the ECENS (GEFS) indicates at least a 40% (30%) chance of wind speeds exceeding the 85th percentile and 40 mph, further supported by ensemble guidance showing enhanced chances of wind gusts exceeding these values. A broader area is highlighted with a slight risk (greater than 20% chance) of high winds across parts of western Alaska, the Alaska Peninsula, and Aleutians for the same duration. Anticipated strong low-level westerly wind anomalies branching off from the tropics, eastward up through Hawaii may bring enhanced moisture to the state. Additionally, a series of surface lows approaching or over Hawaii may lead to increased likelihood of enhanced rainfall across some parts of Hawaii during week-2. FORECASTER: Melissa Ou $$