563
FXUS21 KWNC 271842
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT June 27 2025

SYNOPSIS: Mid-level high pressure forecast across the south-central contiguous
U.S. (CONUS) favors increased chances for extreme heat across the region during
week-2. Dynamical models depict this feature shifting westward and amplifying
throughout the period, increasing concerns for extreme heat conditions
developing across the western CONUS by the second half of the period. While
monsoon activity is predicted to diminish across the Southwest heading into
week-2, daytime convection remains possible resulting in lingering heavy
precipitation and flooding concerns.

HAZARDS

Slight risk of heavy precipitation for parts of the Desert Southwest, Rockies,
and Great Basin, Sat-Mon, Jul 5-7.

Slight risk of extreme heat over parts of the Southern Plains and Lower
Mississippi Valley, Sat-Fri, Jul 5-11.

Slight risk of extreme heat over interior parts of California, the Southwest,
the Great Basin, and portions of the Northern Rockies, Tue-Fri, Jul 8-11.

Slight risk of high winds along most of the immediate West Coast, Sat-Tue, Jul
5-8.

Flooding possible over portions of Arizona and New Mexico.

DETAILED SUMMARY

FOR MONDAY JUNE 30 - FRIDAY JULY 04:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR SATURDAY JULY 05 - FRIDAY JULY 11: Monsoon activity is forecast to diminish
at the start of week-2 across the Southwest, with the strongest signals for
enhanced precipitation now appearing in the late week-1 timeframe. This is
reflected in the GEFS and ECENS Probabilistic Extremes Tools (PETs) which show
reduced probabilities for hazardous precipitation totals compared to yesterday.
Therefore, the moderate risk of heavy precipitation has been discontinued. A
slight risk for heavy precipitation remains posted through Jul 7 given the
continued likelihood of enhanced daytime convection. Due to locally heavy
precipitation received over portions of New Mexico, any additional
precipitation during week-2 is likely to worsen saturated ground conditions and
possibly trigger additional flooding in the region. A flooding possible hazard
remains issued and includes many parts of Arizona where locally heavy
precipitation may also trigger flash flooding and debris flows near recently
burned areas. In addition to flash flooding, thunderstorm impacts may include
lightning, gusty winds and blowing dust. However, in spite of these potentially
adverse but localized impacts, some areas experiencing moderate to exceptional
drought conditions and wildfires will benefit from the enhanced rainfall.



Dynamical models, particularly the 0z ECENS, continue to depict a strengthening
subtropical ridge across the southern U.S. The PETs are fairly modest with
probabilities for temperatures exceeding the 85th climatological percentile at
the start of the period across the south-central states, but humidity is likely
to result in higher heat index values. As the ridge axis amplifies and expands
westward, heat signals increase. By the end of the period, both the
uncalibrated 0z ECENS and GEFS depict actual temperatures above 100 deg F over
portions of Texas and Oklahoma, with a corresponding uptick in the
probabilities in the PETs. The calibrated skill weighted heat tool depicts
probabilities of 40-70 percent for heat index values exceeding the 95th
climatological percentile across the region, with some areas potentially having
heat index values above 110 deg F. As a result of these enhanced signals, the
slight risk for extreme heat is posted for all of week-2 across portions of the
Southern Plains and Lower Mississippi Valley. Due to the stronger signals
emerging later in the period, a moderate risk may be considered next week if
trends continue.



Extreme heat concerns may expand into the West later in the period, with the 0z
ECENS depicting a 597-dm ridge axis moving over the Four Corners Region. The 0z
GEFS and CMCE also show this feature, but a bit weaker in magnitude. For now, a
broad slight risk of extreme heat is posted from the Southwest, across the
Great Basin to the Northern Rockies Jul 8-11 where the GEFS and ECENS PETs
depict expanding coverage of probabilities for maximum temperatures exceeding
the 85th climatological percentile initially across the Great Basin and then
reaching the Desert Southwest and California Central Valley by the end of the
period. Predicted temperatures range from the mid-90s deg F across the northern
Great Basin to possibly above 110 deg F across the Desert Southwest. Another
complicating factor is the potential for renewed enhancement of the Southwest
monsoon given the ridge axis placement becoming more favorable. This could
result in some areas of the Southwest having relatively lower temperatures, as
well as further prolonging the heavy precipitation and flooding risks discussed
earlier.



A more variable summer-like pattern is predicted across the East. While the
PETs depict an elevated signal for temperatures exceeding the 85th
climatological percentile across the Ohio Valley and Mid-Atlantic early in the
period, the actual temperatures in the uncalibrated guidance are not extreme by
July standards (generally upper 80s to low 90s deg F) precluding a related
extreme heat hazard. The ECENS PET continues to depict an enhanced
precipitation signal extending across the Midwest and Northeast Jul 5-7, with
some areas having probabilities of at least 20 percent for precipitation totals
exceeding the 85th climatological percentile and 1-inch. This could be
indicative of a frontal system propagating around the ridge axis across the
southern and western states. The GEFS PET is not as robust with these
probabilities, although the uncalibrated 0z GEFS depicts the same frontal
feature, but just to a lesser extent than the ECENS. No related precipitation
hazard is posted given the system looks to be progressive, and precipitation
totals would be in line with expectations for the time of year.



Surface high pressure over the northeastern Pacific adjacent to mean surface
low pressure over the Interior West may lead to tight pressure gradients along
much of the West Coast. As a result, a slight risk of high winds remains posted
along most of the immediate West Coast Jul 5-8 where the ECENS PET also
indicates increased chances for wind speeds exceeding the 85th climatological
percentile. The aforementioned ridging predicted to build over the West may
help to reduce pressure gradients along the coast by the second half of the
period.



Shortwave troughing forecast to move into western Alaska favors enhanced
chances for above-normal precipitation across most of the state along with
relatively cooler temperatures. This may provide some wildfire relief during
the week-2 period. However, the smoke generated by these fires is forecast to
continue to meander around the state, following low-level wind currents. As a
result, periods of very poor air quality and low visibility may occur,
especially over Interior areas of Mainland Alaska that do not receive as much
precipitation.

FORECASTER: Thomas Collow

$$