108
FXUS21 KWNC 171824
PMDTHR
US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT July 17 2026

SYNOPSIS: A westward shifting and strengthening area of mid-level high pressure
is expected to bring an elevated risk of extreme heat over portions of the
southwestern and southcentral contiguous U.S. (CONUS) through the middle of the
period, with increasing chances for extreme heat and a rapid onset drought risk
also favored for the northcentral CONUS. A more suppressed monsoonal
circulation is expected to limit chances for heavy precipitation with drier
conditions favored for the lower Four Corners.  However, stalled frontal
activity favored over the southeastern CONUS supports a heavy precipitation
risk over the Southeast and lower Mid-Atlantic early in the period.

HAZARDS

Moderate risk of extreme heat for parts of the Southern and Central Plains,
adjacent parts of the Lower Mississippi Valley, and Desert Southwest, Sat-Tue,
Jul 25-28.

Slight risk of extreme heat for the California Valley, Desert Southwest, Great
Basin, Rockies, Great Plains, Lower Mississippi Valley, and Southeast, Sat-Fri,
Jul 25-31.

Slight risk of heavy precipitation for parts of the lower Mid-Atlantic and
Southeast, Sat-Mon, Jul 25-27.

Rapid onset drought (ROD) possible for portions of the Dakotas.

DETAILED SUMMARY

FOR MONDAY JULY 20 - FRIDAY JULY 24:
https://www.wpc.ncep.noaa.gov/threats/threats.php

FOR SATURDAY JULY 25 - FRIDAY JULY 31: Heading into the start of week-2,
dynamical models are in good agreement featuring anomalous 500-hPa ridging
centered over portions of the Interior West and Great Plains, bookended by a
pair of mean longwave troughs, with one over the northeastern Pacific, and the
other overspreading much of eastern North America. Over time, both the GEFS and
ECMWF ensembles continue to favor an amplification of the ridging over the
CONUS, as well as a shift of the anomalous ridging that becomes more positively
tilted towards the middle of the period. Consequently, stronger mid-level
positive height departures are featured along an axis from the north-central to
southwestern CONUS, with the ECMWF in particular, featuring the emergence of a
mean 597-dm contour center over the lower Four Corners early in the period,
translating to over 2 standard deviations above peak summer climatology. The
rising 500-hPa heights favored are anticipated to bring a higher risk of
extreme heat across the western and central CONUS, while keeping this risk at
bay for many areas downstream east of the Mississippi where more troughing and
accompanying northwesterly flow is forecast.



Underneath the stronger ridging aloft, an elevated potential for heat risk
continues to be supported by a number of temperature and heat tools for many
parts of the southern tier of the U.S during the week-2 period.  With high
dewpoints remaining favored east of the Rockies to help drive high heat index
values, a moderate risk of extreme heat remains posted over the Southern Plains
for Jul 25-28, with coverage adjusted to include (exclude) more the Southern
and Central Plains and Desert Southwest (Lower Mississippi Valley). These
adjustments are mainly based on the evolving ridge pattern and the associated
changes favored in the temperature anomalies and probabilities in both the raw
and calibrated tools.  Within the highlighted moderate risk area, there are
increased chances for heat index values exceeding 110 (105) deg F across the
Southern Plains and parts of the Lower Mississippi Valley (Central Plains),
with daytime maximum temperatures above 110 deg F over the lower elevations of
the Desert Southwest. Surrounding the moderate risk area, a slight risk of
extreme heat remains posted with its coverage likewise expanded to include
portions of the California Valley, Interior West, and Great Plains. Ensembles
show the greatest warming trend in proximity to the strongest mid-level height
anomalies in the Northern Plains (with 50-60% chances for double digit positive
temperature departures) supportive of this expansion over northcentral CONUS,
however heat tools show fairly low chances of heat index values exceeding the
90th climatological percentile. Although this part of the country is less
likely to reach hazardous heat criteria, the combination of antecedent dryness,
anomalous warmth and dryness during week-1, with near to slightly above normal
precipitation favored during week-2, supports an enhanced risk of Rapid Onset
Drought (ROD) across portions of the Northern Plains. The slight risk area of
extreme heat also remains extended through portions of the Southeast and into
the Florida Peninsula where enhanced subtropical ridging may linger and
anomalously warm SSTs are registered in the Gulf to support continued anomalous
warmth.



Despite the stronger mid-level ridging favored over the southwestern CONUS, the
mean ridge center looks to be in a less favorable position for the broad scale
advection of monsoonal moisture.  This is supported in both the raw and
calibrated precipitation guidance which has favored a drying trend over the
past day or so, with Probabilistic Extreme Tools (PETs) now indicating limited
chances of 3-day precipitation amounts exceeding the 85th percentile over the
lower Four Corners. Therefore, the slight risk of heavy precipitation is
discontinued in the updated outlook. However, scattered thunderstorm activity
across the region cannot be ruled out, and any upticks in monsoonal moisture
can also produce dry lightning, resulting in increased wildfire risk where
precipitation does not fall.



Tied to the mid-level troughing favored over the eastern U.S., a slight risk of
heavy precipitation remains posted for parts of the Southeast and lower
Mid-Atlantic for Jul 25-27, with an increase in coverage over the Southeast and
Florida Panhandle in the updated outlooks. Ensembles continue to point to
stalled frontal activity to maintain this increased risk early in week-2.  Both
the PETs and uncalibrated guidance bring at least 20% chances for three day
precipitation amounts to exceed the 85th climatological percentile and 1 inch,
with raw tools showing increased wet signals over the Florida Panhandle and
eastern Gulf relative to yesterday.

FORECASTER: Nick Novella

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