560
FXUS21 KWNC 151750
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT August 15 2025

SYNOPSIS: Mid-level high pressure remains forecast across the western
contiguous U.S. during the first half of the week-2 period. This leads to
enhanced chances for extreme heat for portions of the West. Above-normal
temperatures across the Interior West may lead to enhanced winds along parts of
the West Coast. Farther east, hot weather may also affect parts of the Middle
and Lower Mississippi Valley and adjacent areas just downstream from the
mid-level high pressure, although humidity may be relatively low for this time
of year. In the Ohio and the Middle and Lower Mississippi Valleys, declining
soil moisture and near to below-normal precipitation over the next two weeks
increases chances for Rapid Onset Drought across the region.

HAZARDS

Slight risk of extreme heat for many parts of the Interior West, Sat-Sun, Aug
23-24.

Slight risk of extreme heat for the California Central Valley, Sat-Sun, Aug
23-24.

Slight risk of episodic high winds for coastal portions of California, Sat-Fri,
Aug 23-29.

Slight risk of extreme heat for portions of the Central Plains, the Middle and
LowerMississippi Valley, and surrounding regions for Sat-Sun, Aug 23-24.

Rapid Onset Drought risk for parts of the Central and Southern Plains, Middle
and Lower Mississippi, Ohio, and Tennessee Valleys.

DETAILED SUMMARY

FOR MONDAY AUGUST 18 - FRIDAY AUGUST 22:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR SATURDAY AUGUST 23 - FRIDAY AUGUST 29: The 0Z GEFS, ECENS, and Canadian
ensemble means predict amplified mid-level ridging over the west-central CONUS
at the beginning of week-2 which slowly deamplifies during the period. This
feature remains approximately stationary while deamplifying, and may expand
eastward slightly toward the central Contiguous United States (CONUS) later
week-2. Maximum 500-hPa heights near 595 dm are centered near the Four Corners
in all three ensemble means on day 8 (Aug 23). The Probabilistic Extremes Tool
(PET) derived from the GEFS is considerably more bullish with the potential
heat than the ECENS or Canadian ensemble PETs. The GEFS PET shows a 60% to 80%
chance for high temperatures in the top 15 percent of climatology across the
eastern Great Basin and central Rockies on Aug 23, with chances exceeding 40%
from the Cascades and Sierra Nevada eastward through most of the Rockies. The
ECENS PET has much lower odds for high temperatures in the top 15 percentile
climatologically, topping out at 30% to 40% chances in parts of the Great Basin
and northern Intermountain West. Despite this inconsistency, a slight risk of
extreme heat seems warranted across the Interior West. With the upper-level
pattern deamplifying, the heat risk will decrease with time, and the hazard is
posted for the first two days of the period (Aug 23-24). The risk area is
expanded northwestward compared to yesterday, including the valleys of
Washington, Oregon, and Idaho. Lower elevations there are forecast to approach
or exceed 100F in the 0Z operational European model run, which is several
degrees higher than yesterday. Little precipitation is expected during this
period, so humidity will remain relatively low. In addition, some guidance
indicates the possibility that wind gusts may increase later in the period
throughout this region. There is too much uncertainty to justify the posting of
any wind hazard, but the combination of heat, dryness, and gusty winds could
enhance the chances for the development and spread of wildfires. The National
Interagency Fire Center (NIFC) indicates a moderate risk for wildfires at the
end of week-1 and there are currently active wildfires across the Interior West.





A slight risk of extreme heat is also indicated over the California Central
Valley for the same time frame (Aug 23-24).  with PETs indicating at least a
slight chance of temperatures exceeding the 85th climatological percentile and
100 deg F across much of the Valley early week-2. The GEFS PET shows greater
potential for extreme heat than the others, and keeps the risk in place for one
to two additional days. In either case, the deamplifying mid-level pattern will
slowly bring down the risk for extreme heat as the period progresses. The
locations and duration of the slight extreme heat risk are identical to
yesterday. On Aug 23 (day 8), the operational GFS forecasts temperatures
approaching 110F in the northern California Valleys, and reaching as high as
117F farther south. The operational European model is about 3F to 5F cooler.
Temperatures begin a moderating trend the next day.



A thermal surface low pressure from near the California-Arizona border into the
Great Basin combined with surface high pressure off the West Coast may lead to
a tight pressure gradient along the Pacific Coast from southern Oregon through
central California. The strength of this gradient will wax and wane through
week-2, but the pattern supports a slight risk of periodic high winds for
portions of coastal California and adjacent southwestern Oregon throughout
week-2 (Aug 23-29). In conjunction with seasonable dryness, this could increase
the wildfire risk in the region, at least at times. The GEFS and ECENS PETs
both show a 20% to 30% chance for winds reaching the 85th percentile
climatologically and exceeding 25 mph.



As of 11 am EDT Aug 15, the National Hurricane Center (NHC) analyzed Hurricane
Erin over the low-latitudes of the central Atlantic. The NHC forecasts Erin to
become a Major Hurricane within the next 5 days. Todays guidance keeps the
storm track off the East Coast and moves the system a little faster, so that
Erin will be heading eastward out to sea as week-2 begins. This led to the
removal of the high wind threat along the East Coast. Later week-2, however,
the operational GFS, operational European, and EC-AIFS models all show some
sort of surface low pressure system near or off the Southeast Coast. This could
bring wet and windy weather to some part of the Southeast, but due to the high
uncertainties regarding the strength and track of any system that might develop
(if one does), no hazard is posted at this time.



An area centered over Missouri and Arkansas has seen a depletion of surface
moisture over the past 2-3 weeks despite a wet start to the summer. This area
is expected to see above normal temperatures and near or below normal
precipitation over the next two weeks. This would continue to ramp up dryness,
increasing the risk of Rapid Onset Drought, and this potential is posted on the
map.



From around the same area southward through the Lower Mississippi Valley to the
Gulf Coast, a slight risk of extreme heat is forecast for Aug 23-24. PETs show
enhanced odds (20%-40%) for maximum temperatures exceeding the 85th
climatological percentile, and skill-weighted apparent temperature guidance
shows enhanced chances for maximum apparent temperatures above the 90th
percentile on at least one day. With the mid-level pattern deamplifying, the
risk of extreme heat will decline, but some tools show the mid-level ridge
possibly expanding a bit eastward during week-2, which would imply some degree
of continued or renewed risk later week-2, but at this time there is too much
uncertainty to post a heat hazard for later week-2.

FORECASTER: Rich Tinker

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