341
FXUS21 KWNC 091915
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT September 09 2025

SYNOPSIS: Favored development of strong mid-level high pressure across central
North America next week is anticipated to result in a pattern change from
week-1, with widespread above-normal temperatures and possible extreme heat
conditions emerging for a large fraction of the east-central Contiguous U.S.
(CONUS) during week-2. The abnormally warm temperatures, combined with
antecedent dryness and below normal precipitation favored during the next two
weeks support a Rapid Onset Drought (ROD) risk over parts of the East.
Lingering mid-level low pressure forecast over the western third of the CONUS
early in the period favors increased chances for episodes of high winds over
parts of the West Coast. A stalled frontal boundary remains forecast across the
southeastern U.S. bringing an increased likelihood for enhanced precipitation
and high winds to the region. Early in week-2, tropical moisture associated
with an eastern Pacific tropical cyclone enhances the risk for heavy
precipitation across portions of the Southwest. Surface low pressure is
forecast to bring increased chances of heavy precipitation to southern and
southeastern coastal Alaska.

HAZARDS

Slight risk of high winds over coastal Northern California and coastal Oregon,
Wed-Sun, Sep 17-21.



Slight risk of heavy precipitation over the Southwest, Wed-Sun, Sep 17-21.



Slight risk of extreme heat across eastern parts of the Southern Plains, the
lower half of the Mississippi Valley, Ohio and Tennessee Valleys, and much of
Alabama, Wed-Fri, Sep 17-19.



Slight risk of heavy precipitation across the Florida Peninsula and coastal
Southeast, and far southeastern Louisiana, Wed-Sun, Sep 17-21.



Slight risk of heavy precipitation across south-central and Southeast Alaska,
Wed-Sun, Sep 17-21.



Slight risk of high winds near the Gulf Coast from Louisiana to the Georgia
coast, Wed-Sun, Sep 17-21.



Rapid Onset Drought (ROD) risk across interior portions of the deep South,
Lower and Middle Mississippi Valley, western Tennessee and much of the Ohio
Valley, West Virginia, and small parts of adjacent states.

DETAILED SUMMARY

FOR FRIDAY SEPTEMBER 12 - TUESDAY SEPTEMBER 16:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR WEDNESDAY SEPTEMBER 17 - TUESDAY SEPTEMBER 23: Mean 500-hPa height anomaly
forecasts from the 0z GEFS and ECMWF ensembles show the week-2 period starting
off with an amplified ridge center over central Canada which extends southward
over the Midwest, bookended by a pair of troughs over the eastern Bering
Sea/western Alaska and well east of the Canadian Maritimes. The latter feature
is predicted by the ECENS and CMCE models to extend southwestward near and
along the U.S. Atlantic Seaboard. Weak troughing is also indicated over the
western CONUS during the first few days of the period. Warm temperatures are
forecast for much of the CONUS heading towards the autumnal equinox. Further
north though, stronger mean troughing predicted in the dynamical models over
the eastern Bering Sea and western Alaska would favor more unsettled weather
over the southern portion of Alaska during week-2.



In response to the mid-level ridge axis extending from central Canada into the
Midwest late next week, both raw and calibrated temperature tools continue to
highlight elevated chances for above-normal temperatures focused over the
vicinity of the Middle and Lower Mississippi, Tennessee, and Ohio Valleys
during the first several days of the forecast period. Probabilistic Extreme
Tools (PETs) from the GEFS and ECENS depict at least 20% chances for daytime
temperatures exceeding the 90th percentile and 90-95 degrees F, supporting the
continuation of a slight risk of extreme heat, remaining valid through Sep 19.
The GEFS favors the core of the heat signal to be located over the Mid-South
(i.e. within about 500 miles of Memphis, TN), while the ECENS favors this heat
signal to be centered a bit farther south near/along the Central Gulf Coast.
The combination of longer-term precipitation deficits, above-normal
temperatures and below-normal precipitation forecast during the next two weeks
also supports a Rapid Onset Drought (ROD) risk posted in an arc that extends
from the interior deep South northward into the Middle Mississippi Valley, then
eastward across much of the Ohio Valley and Central Appalachians.



There are enhanced chances for heavy precipitation over three areas of the
United States during this Hazards period. The first area is along the Southeast
coast, including most of Florida, and perhaps far southeastern Louisiana, Sep
17-21. This is related to a predicted stalled frontal boundary over this
region, and a weak mid-level trough. The ECENS and GEFS Probabilistic Extremes
Tools (PETs) indicate increased chances of precipitation amounts in excess of
the 85th historical percentile and also in excess of 1-inch. The second area of
favored heavy precipitation is over the Southwest, Sep 17-21, where tropical
moisture may stream into this region from the Gulf of California, in relation
to a passing tropical cyclone over the eastern Pacific. Precipitation amounts
of 0.75-1.00 inch are considered reasonable, essentially splitting the
difference between a wetter ECENS PET and drier GEFS PET. While low-level flow
and moisture input looks favorable for heavy rainfall, the mid-level flow is
supportive of a drier pattern, which results in only a slight risk being posted
today. The influx of tropical moisture from passing tropical cyclones over the
eastern Pacific along with triggered gulf surges, are commonly accompanied by
flash and/or urban flooding, and this possibility should be monitored closely.
The third area of favored heavy precipitation is along the southern coast of
Alaska, from about the eastern Kenai Peninsula eastward to Ketchikan, thereby
including all of Southeast Alaska. With a mid-level trough predicted upstream
over the eastern Bering Sea and western Alaska, and surface low pressure near
the Alaska Peninsula, southerly onshore flow is expected to prevail across the
aforementioned portion of the Alaska coast, Sep 17-21. The GEFS and ECENS PETs
support precipitation amounts exceeding the 85th historical percentile, and at
least 2 inches.



There is a slight risk of high winds (wind speeds in excess of the 85th
climatological percentile and 20-25 mph) for two regions in the CONUS. One is
along the Pacific coast of Oregon and Northern California, Sep 17-21,
associated with a mid-level trough passing through the area and an enhanced
surface pressure gradient between high pressure over the eastern Pacific and
low pressure over the interior of the West Coast states. The other region is
from coastal Louisiana to the Florida Panhandle and coastal Georgia, Sep 17-21.
This slight risk is associated with a slowly meandering baroclinic zone
predicted across the Southeast, in addition to a weak mid-level trough close to
the Southeast coast.



At this time, no tropical cyclone activity is foreseen for the Gulf Coast or
East Coast states for the next two weeks. However, this outlook period (Sep
17-23) falls just past the peak of the Atlantic Hurricane Season (Sep 10), and
hurricane season is far from over.

FORECASTER: Anthony Artusa

$$