797
FXUS21 KWNC 051802
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT August 05 2025

SYNOPSIS: Broad mid-level high pressure supports an increased chance of
above-normal temperatures throughout much of the contiguous U.S. (CONUS) during
mid-August. The most likely areas to be affected by extreme heat include the
Northeast early in week-2 and then the Midwest, beginning on August 15.
Following a heat wave this week, an enhanced monsoon is expected across the
Desert Southwest from August 13 to 17. The tropics in the Atlantic basin are
becoming more active and will be closely monitored in the weeks ahead.

HAZARDS

Moderate risk of extreme heat for the Northeast, Wed, Aug 13.

Slight risk of extreme heat for the Northeast and mid-Atlantic, Wed-Sun, Aug
13-17.

Slight risk of extreme heat for parts of the western U.S., Wed, Aug 13.

Slight risk of extreme heat for parts of the central U.S., Fri-Tue, Aug 15-19.

Slight risk of heavy precipitation for the Southwest, Wed-Sun, Aug 13-17.

Slight risk of heavy precipitation for southeastern Alaska, Wed-Thu, Aug 13-14.

DETAILED SUMMARY

FOR FRIDAY AUGUST 08 - TUESDAY AUGUST 12:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR WEDNESDAY AUGUST 13 - TUESDAY AUGUST 19: The GEFS and ECENS are in good
agreement and remain consistent that anomalous 500-hPa ridging becomes anchored
over the mid to higher latitudes of eastern North America during mid-August. A
moderate risk of extreme heat is maintained for portions of the Northeast on
August 13 and extends south to include Philadelphia. The ECENS model is running
a few degrees warmer (low to middle 90s) for the I-95 corridor of the Northeast
than the GEFS. In addition, the ECENS Probabilistic Extremes Tool (PET) has a
50 to 70 percent chance that maximum temperatures exceed the 90th percentile on
August 13 while the GEFS has probabilities less than 30 percent. Given the
persistence of the anomalous 500-hPa ridging during week-2 and guidance from
the ECENS and GEFS PETs, a slight risk of extreme heat for the Northeast is
valid through August 17th. Extreme heat thresholds during mid-August generally
range from heat index values of 105F in the mid-Atlantic to near 90F for
northern New England.



Although temperatures are forecast to moderate over the West during week-2, a
slight risk of extreme heat was maintained for portions of the interior Pacific
Northwest, Great Basin, and northern California through August 13th. This is
supported by the GEFS and ECENS PETs (20 percent chance of maximum temperatures
reaching the 85th percentile and heat advisory thresholds) and also considering
the anomalous heat prior to week-2.



Beginning on August 15, the strong mid-level ridge initially centered over
eastern Canada and the northeastern CONUS is favored to expand westward with
500-hPa heights rising over the Midwest and Central Great Plains. Even out
through the end of week-2, the GEFS and ECENS depict daily positive 500-hPa
height anomalies of 60 meters or more across the north-central CONUS. Based on
this evolving 500-hPa height pattern and the calibrated ECMWF model having more
than a 20 percent chance of heat index values exceeding the 90th percentile, a
slight risk of extreme heat (August 15-19) was added to portions of the
Mississippi Valley and more humid areas of the Great Plains. Within this slight
risk area, there is a 20 percent chance of heat index values to exceed 100F as
far north as Chicago and Minneapolis.



As the 500-hPa ridge axis shifts north towards the Four Corners region and
consistent with days following a heat wave, an enhanced monsoon is expected to
resume across the Southwest during week-2. Based on the preferred ECMWF PET (20
percent chance of 3-day amounts exceeding the 85th percentile and 0.5 inches),
a slight risk of heavy precipitation is posted for this region from August
13-17. Any heavy rainfall in a short period of time could trigger flash
flooding with burn scar areas being the most vulnerable.



The National Hurricane Center is monitoring a tropical wave across the eastern
Atlantic and states that this wave has a 50 percent chance of tropical cyclone
(TC) development during the next week. The deterministic ECMWF model and its
ensemble members favor a northward track of this potential TC, while the GEFS
has a more westward track into the southwestern Atlantic. Future model runs
will be closely monitored. With the Madden-Julian Oscillation (MJO) forecast to
propagate eastward over Africa to the Indian Ocean during the next two weeks,
the large scale environment is expected to remain favorable for TC genesis
across the Main Development Region of the tropical Atlantic through late
August.



A broad 500-hPa trough is forecast to persist over Alaska through mid-August
which favors a cool, wet pattern for much of the state. Enhanced onshore flow
along with support from the ECMWF PET, a slight risk of heavy precipitation is
posted for southeastern Alaska on August 13 and 14. Given the
colder-than-normal temperatures, periods of snow are expected to affect the
Brooks Range.

FORECASTER: Brad Pugh

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