Hazelwood, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

682
FXUS63 KLSX 121928
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
228 PM CDT Tue Aug 12 2025

.KEY MESSAGES...

- Scattered storms capable of locally heavy rainfall and gusty
  winds are expected to continue across portions of the area
  through this evening.

- Potentially dangerous heat returns to the region this weekend
  into early next week.


&&

.SHORT TERM...  (Through Late Wednesday Night)
Issued at 227 PM CDT Tue Aug 12 2025

Current water vapor imagery shows upper-level troughing digging into
the Midwest with several shortwaves traversing the flow within it.
One of these shortwaves is moving through northern Missouri as of
early this afternoon, and a cold front can be seen in surface
observations moving through northeastern Missouri. Ahead of the
front, an area of surface convergence along the I-44 Missouri/I-70
Illinois corridor has led to convection developing early this
afternoon - about an hour or two earlier than anticipated. If ACARS
soundings out of KSTL are accurate, models have been overdoing
instability by about 1,000 J/kg for SBCAPE. Between this and the
slightly earlier convective initiation, updrafts may not be able to
reach their full potential later this afternoon. Effective shear is
around 20 kts across the CWA currently, leading to the poor storm
organization we have seen so far. While PWAT is around 2" and an
inverted "V" signature is noted in several soundings, the slightly
lower instability and convective debris may inhibit updrafts from
reaching a height that, when they collapse, would lead to severe-
strength winds. Even so, several downburst signatures have been
noted around the St. Louis metro area so far this afternoon, and
confidence is high that at least isolated sub-severe downburst winds
(up to 50 mph) will occur under stronger storms that collapse. The
high PWAT and slower storm motion may also lead to isolated flooding
issues, but the shorter lifespan of storms is expected to mitigate a
more notable flood threat. With instability waning with the setting
sun and convection easily becoming outflow dominant, a gradual
weakening and decrease in coverage of convection is expected this
evening.

The front will gradually pass through the rest of the CWA this
evening and tonight, clearing it to the southeast by Wednesday
morning. In its wake, high pressure will spread into the Middle
Mississippi Valley, characterized by generally northerly winds and
temperatures running at to just below climatological normals. There
is a low probability (20%) that there will be enough boundary layer
moisture behind the front to lead to isolated to scattered
convection across far southeastern Missouri and southwestern
Illinois as a shortwave and the upper-level trough axis swing
overhead during the afternoon, but most locations will remain dry.

Elmore

&&

.LONG TERM...  (Thursday through Next Tuesday)
Issued at 227 PM CDT Tue Aug 12 2025

The main focus for impactful weather in the extended forecast period
is going to be the return of above normal temperatures. While
guidance consensus is that upper-level ridging will still be
gradually building into the Midwest on Thursday, the trend has been
for it to do so more slowly. As a result, the surface high
responsible for our more seasonable weather mid-week will hang
around a little longer and inhibit southerly flow from returning to
the CWA, with conditions on Thursday being similar to those forecast
on Wednesday. However, the upper-level ridge will notably amplify on
Friday, quickly pushing the surface high eastward and deepening
southerly flow over the Middle Mississippi Valley. Temperatures at
850 mb are expected to see at least a 5 degree C jump, with values
forecast to top out in the low 20s C. This climatologically favors
surface temperatures in the mid 90s, which matches well with
ensemble means on Friday. Guidance consensus is that the ridge will
only continue to build into the region over the weekend, with
potentially dangerous levels of heat and humidity occurring. NBM-
based probabilities for high temperatures of at least 90 degrees top
out at 80-100% for nearly the entire CWA Saturday and Sunday, and 60-
80% of at least 95 degrees for locations mainly along and south of I-
70 over the same period. With dew points from the NBM and ensemble
mean hovering in the low to mid 70s, heat index values of at least
100 degrees are expected, and there is growing concern for Heat
Advisory criteria or perhaps Extreme Heat Warning criteria for
portions of the area over the weekend.

How long this heat carries into next week is uncertain. Both
deterministic guidance and ensemble clusters show the upper-level
ridge retrograding westward as troughing develops over the eastern
CONUS. However, guidance differs on the timing of this and the
amplitude of the trough, leading to the spread among the global
ensemble IQR increasing to 10 degrees next Tuesday. If the ridge is
able to hold on over the region, we may at most see temperatures
only decrease by a degree or two through the early week period
compared to the weekend. However, if the ridge moves far enough
west, the CWA will be beneath northwesterly flow aloft, allowing for
cooler air and increasing rain/cloud chances across the region early
next week. A majority of guidance favors the more stubborn ridge,
and this is reflected in the current forecast.

Elmore

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1218 PM CDT Tue Aug 12 2025

The main concern for impacts this TAF period is scattered showers
and thunderstorms along a cold front sinking southward through the
region. This showers and thunderstorms have the greatest chance of
impacting KSUS, KSTL, and KCPS, though a brief period of impacts
can`t be ruled out at KCOU and KJEF. With showers or storms that
make direct impact to terminals, heavy rainfall will reduce
visibilities, and storms in proximity to local terminals could
produce gusty, erratic winds. Behind the front tonight and
tomorrow, winds will be very light and mostly variable.

Elmore

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX