262 FXUS21 KWNC 171834 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT September 17 2025 SYNOPSIS: Mid-level high pressure across much of the western contiguous U.S. (CONUS) may bring a brief shot of extreme heat to the Desert Southwest at the beginning of week-2. Mid-level low pressure is anticipated to quickly follow behind, shifting eastward, potentially bringing the first heavy snow of the season to northern portions of the Cascades and Rockies. Meanwhile, surface high pressure over the North Pacific adjacent to surface low pressure over the western CONUS could bring periods of high winds to much of coastal California for all of week-2. Rapid Onset Drought remains a risk for parts of the Southeast where above-normal temperatures and limited week-1 precipitation are forecast. HAZARDS Slight risk of extreme heat for the Desert Southwest, Thu, Sep 25. Slight risk of heavy snow across parts of the northern Cascades and Northern Rockies, Fri-Mon, Sep 26-29. Slight risk of episodic high winds for coastal portions of California south of Point Mendocino, Thu-Wed, Sep 25-Oct 1. Rapid Onset Drought (ROD) risk for portions of Mississippi, Alabama, and Georgia. DETAILED SUMMARY FOR SATURDAY SEPTEMBER 20 - WEDNESDAY SEPTEMBER 24: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR THURSDAY SEPTEMBER 25 - WEDNESDAY OCTOBER 01: At the beginning of week-2, amplified mid-level ridging is anticipated to build across much of the western two-thirds of the CONUS, with upstream mid-level troughing over the Northeast Pacific. This ridge is fairly short-lived with the pattern shifting eastward resulting in a transition to mid-level troughing across the Northwest and ridging over the eastern CONUS by the latter part of the period. Positive 500-hPa height anomalies are anticipated over the Desert Southwest at the beginning of the period associated with an amplified mid-level ridge situated over the north-central CONUS, resulting in the potential for a late-season heat wave for the region. Multiple Probabilistic Extremes Tools (PETs) indicate at least a 20% chance of maximum temperatures exceeding the 90th percentile climatologically and 105 deg F, further supported by other guidance tools showing increasing signals for extreme heat. Additionally, enhanced dewpoint temperatures could result in higher heat index values. Therefore a slight risk (20-40% chance) of extreme heat is posted for parts of the Desert Southwest, Sep 25. This heat feature is likely to be fairly short-lived due to an anticipated progressive pattern. Upstream, amplified mid-level troughing is anticipated to form over the Northeastern Pacific and shift eastward into the western CONUS throughout the beginning of week-2. This pattern in addition to predicted surface high pressure near the West Coast and adjacent surface low pressure over West Coast states may result in a tight pressure gradient at the surface and increased likelihood for high winds across the West Coast. A slight risk of episodic high winds is highlighted for coastal portions of California south of Point Mendocino for Sep 25-Oct 1, where PETs indicate at least a 20% chance of wind speeds exceeding the 85th percentile and 25 mph. In addition to enhanced winds, models depict significant moisture transport into the Pacific Northwest as this trough moves into the Interior West. This is likely to result in periods of enhanced precipitation for much of the northwestern CONUS through the middle of week-2. While low elevation accumulations (i.e. rain) are not likely to reach hazardous thresholds, there is an increased likelihood of heavy snow across high elevation areas of the northern Cascades and Rockies as a colder airmass moves in with the trough, potentially dropping temperatures sufficiently to allow for snow in the mountains. A slight risk of heavy snow is highlighted for the Northern Cascades, and portions of the Northern and Central Rockies, Sep 26-29. The GEFS PET shows at least a 20% chance of 3-day accumulations exceeding the 85th percentile for portions of the Central Rockies, and uncalibrated ensemble solutions from both the GEFS and ECMWF indicate at least a 20% chance of some localized areas exceeding 4 inches. While indicated snow accumulations are not particularly large, this would be unusually early to receive the first significant snows of the season for the region. There continues to be an increased likelihood of above normal temperatures across much of the CONUS. The combination of above-normal temperatures, 30 to 60-day precipitation deficits, and limited precipitation forecast during the next week supports a Rapid Onset Drought (ROD) risk across Mississippi, Alabama, and Georgia. Dry vegetative fuels in this area typically means increased risk of wildfires. There are some indications that a weakness in the subtropical ridge may begin to bring more precipitation to the region by week-2. However, the chances for above-normal precipitation are quite low at this time but will be monitored going forward. FORECASTER: Danny Barandiaran $$