University City, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

755
FXUS63 KLSX 261955
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
255 PM CDT Sat Jul 26 2025

.KEY MESSAGES...

- Dangerous heat and humidity is expected to expand northward on
  Sunday, peaking across the area on Monday and Tuesday.
  Widespread relief from the heat is expected between Wednesday
  and Thursday.

- Mainly scattered thunderstorms are forecast tonight through
  Sunday. A few of the strongest storms may have gusty winds with
  locally heavy rainfall also possible.


&&

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 235 PM CDT Sat Jul 26 2025

Widespread showers and thunderstorms in northeast Missouri
weakened late this morning, but an outflow boundary further to
the east has been a focus for showers and thunderstorms so far
this afternoon. This southwest-northeast axis in the vicinity of
the outflow boundary is where the best chances (40-60%) are
through mid/late evening, roughly from KJEF to southeast of KPPQ.
Further southeast, there has been more purely diurnally-driven
convection with a focus across portions of southeast Missouri and
southwest Illinois. The latest SPC mesoanalysis shows a very
unstable environment (>3000 J/kg MLCAPE), but deep- layer shear
has decreased to around 25-30 knots behind the MCV moving into the
southern Great Lakes. These values will continue to drop over the
next few hours. RAP soundings show some dry air at midlevels and
moderately high low- level lapse rates (~ 7 C/km), indicating a
low threat for isolated microbursts. This threat should gradually
wane after dusk as diurnal instability abates and low-level lapse
rates weaken.

Overnight tonight, low-level moisture convergence increases on the
nose of a ~20 kt low-level jet. At least scattered showers and
thunderstorms are expected along/north of the composite outflow
boundary from this afternoon/evening`s convection. The low-level
moisture convergence is not particularly strong. Therefore, would
not expect too much in the way of organization of the convection
late tonight. That being said, there may be some training of storms
in an environment characterized by deep warm cloud depths and
precipitable water values around 2.00" (>95th percentile of
climatology). The 12Z HREF hints at this threat as well, showing
some isolated pockets of 2-4" of rain. Given that this rain should
focus southeast of where it fell last night/this morning and the
fact that the low-level forcing for ascent is not particularly
strong, did not elect to go with a flash flood watch and think that
flash flooding, if any were to occur, would be very isolated in
nature. Exactly where in the CWA this activity will focus is
uncertain, mainly due to the fact we will not know where the
composite outflow boundary will be later this evening. The best
guess is that it may get as far southeast as the I-44/I-70 corridors
in Missouri/Illinois respectively. That would mean that the best
chances (40-60%) of showers and thunderstorms tonight would tend to
want to focus from central Missouri east/northeast into south-
central Illinois.

While there is some variability in CAMs with how things evolve on
Sunday, the nocturnal low-level jet does not fade very quickly. This
would suggest that isolated to scattered showers and thunderstorms
may keep going through the morning hours, before there is at least a
slight uptick in coverage by early afternoon as diurnal instability
increases. The best chances by Sunday afternoon (30-50%) should
shift southeast, more across east central and southeast Missouri as
well as southwest Illinois. The threat for any microbursts should be
lower than today, mainly due to poorer low-level lapse rates.

In terms of the heat, an expansion to the north still appears
likely. Even with highs around 90 degrees in northeast Missouri and
west-central Illinois, dewpoints in the upper 70s are expected.
Therefore, expanded the heat advisory for the remainder of the CWA
as peak heat index values of around 105 degrees are expected
Sunday afternoon. Further southeast, there actually is a bit more
uncertainty with respect to temperatures and associated heat
index values given the better chances for showers and
thunderstorms Sunday morning/afternoon. However, given that the
convection is not expected to be too widespread nor organized,
temperatures should be able to get at least to around 90 degrees.
With the very high humidity/dewpoints, that should be enough to
see maximum heat index values of 100-105F+. That being said, there
may be some pockets that stay cooler tomorrow afternoon due to
thunderstorms, but confidence in widespread cooler temperatures is
definitely not high enough to make any changes with the ongoing
heat advisory/extreme heat warning.

Gosselin

&&

.LONG TERM...  (Sunday Night through Next Saturday)
Issued at 235 PM CDT Sat Jul 26 2025

(Sunday Night - Tuesday Night)

There may be some lingering showers and thunderstorms Sunday evening
across parts of southeast Missouri and southwest Illinois, but this
activity should diminish with loss of daytime heating. It appears we
may finally get a dry overnight period as the mid-Mississippi Valley
begins to feel more direct influences from the amplifying mid/upper
level anticyclone just to our south. This should help steer Sunday
night/Monday morning`s round of storms further to the north and
east. Dry weather is then forecast through Tuesday night.

Early next week is all about the heat. The very anomalous mid/upper
level anticyclone continues to build northward through Monday
night/early Tuesday. A near 600 dm 500-hPa anticyclone centered in
the mid south would be record-breaking for that part of the country
to put this pattern in perspective. High temperatures will increase
early next week, likely peaking on Tuesday afternoon in most areas.
Highs in the mid to upper 90s are forecast each afternoon. I think
the chances of anyone actually seeing 100+ degree highs has
decreased as the 850-hPa thermal ridge is a bit more modest (+21
to +23C) compared to what it looked like 24-48 hours ago. These
values are certainly anomalously warm, but more on the order of
just above the 90th percentile of climatology and not extremely
warm for this time of year. In addition, there is a bit more
confidence in dewpoints staying well into the 70s for most
locations. This rich low-level moisture also helps with diurnal
cumulus development in the afternoon, helping to limit the
temperature rise after the cumulus forms. Regardless of the exact
air temperatures, very dangerous heat is expected both afternoons.
Peak heat index values of 105-110F+ are expected, with the
highest values within the urban heat island of metropolitan St.
Louis and adjacent portions of southwest Illinois where dewpoints
are most likely to be closer to the 80 degree mark.


(Wednesday - Next Saturday)

A significant pattern change will take place as we transition from
mid to late week as anomalous mid/upper level troughing carves
into southeast Canada. All signs continue to point toward a cold
frontal passage sometime Wednesday/Wednesday night, with
significantly cooler temperatures infiltrating the mid-Mississippi
Valley. Ensemble guidance has also trended cooler with the
strength of this air mass, with mean 850-hPa temperatures
anomalies Friday/Friday night in the -2 to -5C range. What remains
more impressive is the strength of the surface anticyclone moving
into the Upper Midwest. The latest NAEFS has a 1026+ hPa high in
Wisconsin Friday afternoon, which would be near-record breaking
for the beginning of August. High temperatures in the mid 70s to
low 80s are forecast Friday/Saturday, with lows ranging from the
upper 50s to mid 60s. Spread on the NBM remains on the low side
for 5-7 days out, with only about a 3-5 degree difference for most
locations between the 25th/75th percentiles. Even the 75th
percentile still shows high temperatures some 5+ degrees below
normal, so there remains high confidence in well-below normal
temperatures entering next weekend.

What does remain uncertain is exactly when the cold front will
move through the region. Latest trends have slowed down the front
slightly, but there is a signal for a possible MCS moving
southeast into the area Wednesday morning. This of course would
lead to much cooler temperatures due to the rain and associated
cloud cover. However, if the front is delayed enough and it stays
dry/sunny, one last day of heat/humidity would be in store at
least for parts of the area. Given the uncertainty and the fact
that Wednesday is still 4 days out, no change to the end of the
heat headlines.

The best chances of showers and thunderstorms (40-60%) are
accompanied by the cold front in the Wednesday/Wednesday night
time frame. Deterministic guidance also shows some northwest flow
disturbances behind the front, which could yield some showers and
maybe even some elevated convection Thursday/Thursday night.


Gosselin

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1210 PM CDT Sat Jul 26 2025

Chances of showers and thunderstorms are the biggest concern into
Sunday morning. The best chances this afternoon/early evening will
be at central Missouri and KUIN terminals, though metro St. Louis
is just northwest of another axis of showers and thunderstorms.
Any site that does see a direct impact from a thunderstorm could
see MVFR/IFR visibilities in heavier downpours and the potential
at least for some gusty winds. Activity should gradually shift
southeast in time, with better chances for showers and
thunderstorms for metro St. Louis late tonight/early Sunday
morning.

Gosselin

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory until 7 PM CDT Tuesday for Audrain MO-Boone MO-
     Callaway MO-Cole MO-Crawford MO-Gasconade MO-Iron MO-
     Lincoln MO-Madison MO-Moniteau MO-Monroe MO-Montgomery MO-
     Osage MO-Pike MO-Ralls MO-Reynolds MO-Saint Francois MO-
     Warren MO-Washington MO.

     Extreme Heat Warning until 7 PM CDT Tuesday for Franklin MO-
     Jefferson MO-Saint Charles MO-Saint Louis City MO-Saint
     Louis MO-Sainte Genevieve MO.

     Heat Advisory from 1 PM Sunday to 7 PM CDT Tuesday for Knox MO-
     Lewis MO-Marion MO-Shelby MO.

IL...Heat Advisory until 7 PM CDT Tuesday for Calhoun IL-Fayette IL-
     Greene IL-Jersey IL-Macoupin IL-Montgomery IL-Pike IL.

     Extreme Heat Warning until 7 PM CDT Tuesday for Bond IL-Clinton
     IL-Madison IL-Marion IL-Monroe IL-Randolph IL-Saint Clair
     IL-Washington IL.

     Heat Advisory from 1 PM Sunday to 7 PM CDT Tuesday for Adams IL-
     Brown IL.

&&

$$

WFO LSX