University City, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

561
FXUS63 KLSX 170947
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
447 AM CDT Thu Apr 17 2025

.KEY MESSAGES...

-There is a low threat for severe thunderstorms across the area
Friday afternoon and evening, with large hail, and to a lesser
extent damaging winds, the main hazards.

-The heavy rainfall and flooding threat continues to increase near
and along I-44 (MO) and I-70 (IL), with 3-5" of rain possible
through Monday morning.

-There remains a conditional chance for a strong to severe
thunderstorm or two across southeastern missouri and southern
Illinois Sunday.


&&

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 327 AM CDT Thu Apr 17 2025

Showers and a few thunderstorms will exit the forecast area this
morning as the upper level jet entrance and low-level jet forcing
this precipitation shift east/northeastward out of the CWA. The
remainder of the day will be warm and dry with low-level southerly
flow helping temperatures warm an additional few degrees from
yesterday, with some portions of central Missouri touching 80 for
their high.

Southwesterly flow will dominate the mid-level pattern by this
evening. Overnight a mid-level disturbance will combine with the
ramp up of the low-level jet in the vicinity of a surface
low/triple point to spawn showers and thunderstorms northwest of
the forecast area over Iowa. Convection is expected to form and
track northeast to east with the deep layer shear, missing our
forecast area all together, so we have pulled the threat of strong
to severe thunderstorms from our messaging. The surface low will
be positioned across the intersection of NE-IA-MO-KS overnight,
but will gradually track to the northeast through Iowa during the
day, helping to advance a cold front into the forecast area by the
afternoon. Southwesterly flow ahead of the approaching cold front
will pull warm, moist air into the region, pushing dewpoints into
the 60s and high temperatures into the 80s areawide. Convection
will form ahead of and along the front during the late afternoon
and evening, driven by surface convergence and mid-level
disturbances.

Instability will form ahead of the front, with the HREF and
deterministic models indicating 1000-2000 J/kg of SBCAPE available
across the forecast area. Strong 0-6 km shear (50+ kts) will also be
available ahead of and along the front to organize any severe
thunderstorms that form. Most guidance also continues to show a
strong low-level warm nose inhibiting surface based convection ahead
of the cold front during the afternoon, although a few sources do
show CIN eroding during the afternoon. If surface based convection
is able to form, large hail and damaging winds would be favored
threats while the tornado risk would remain very low due to veered
(and therefore unfavorable) 0-1 km shear. Elevated convection, which
is more favored at the moment, would result in large hail as the
main threat.

Delia

&&

.LONG TERM...  (Friday Night through Wednesday)
Issued at 327 AM CDT Thu Apr 17 2025

The front will stall out and remain quasi-stationary across
southern Missouri/Illinois over the weekend, focusing numerous
rounds of showers and thunderstorms that will move through the
region. These rounds will be driven by the almost continuous
stream of mid-level disturbances along the southwesterly flow.
Guidance continues to hone in on I-44 (MO) and I-70 (IL) as the
location for the axis of heaviest rainfall as the surface and
elevated fronts waggle north and south slightly with each passing
wave. A few thunderstorms will mix in during Saturday morning as
SREF guidance shows a 50-70% chance of at least 250 J/kg of MUCAPE
along the axis of heavy rainfall. These thunderstorms will
locally enhance rainfall amounts. Currently, a swath of 40-50%
chance for at least 3" of rain through 7 AM Monday exists across
the axis, with a 10-20% chance for exceeding 4.5" of rain. In
areas where thunderstorms linger Friday night into Saturday
morning, rainfall amounts closer to 4.5" are expected.

The bulk of the rainfall (2-3") will fall from early Saturday
morning through Saturday night, and is expected to fall on soil
primed from convection Friday afternoon and evening. Flooding of low
lying areas is possible, particularly where thunderstorms linger.
Additionally, at least minor flooding is expected along the Meramec,
Big, Bourbeuse, and Black rivers and more significant rises along
the creeks and streams in those basins.

Through the weekend the mid-level flow will remain southwesterly as
a trough swings from the Four Corners region into the mid-
Mississippi Valley. At the surface a low will move northeast from
Texas into the forecast area late Sunday into early Monday, bringing
one more shot of rainfall to the entire forecast area. Despite the
strong forcing, instability will be the limiting factor for strong
to severe thunderstorm development with only a 50% chance for MUCAPE
greater than 500 J/kg, 0-6 km shear greater than 30 kts, and CIN
less than -25 J/kg. I cannot rule out a strong to severe
thunderstorm, but confidence in this developing remains low, and we
are not publicly messaging this potential. The system will exit
the area Monday, and an advancing surface high will help to clear
out any remaining light precipitation. The surface high will also
help keep the region dry through a portion of Tuesday before
chances for precipitation return to the forecast, driven by
multiple disturbances passing through the quasi-zonal mid-level
flow.

Delia

&&

.AVIATION...  (For the 12z TAFs through 12z Friday Morning)
Issued at 438 AM CDT Thu Apr 17 2025

Showers and thunderstorms are moving east from western Missouri
into central Missouri and will eventually make it into the St.
Louis metro terminals even as they weaken. MVFR visibilities will
accompany the heaviest thunderstorms but will improve once the
thunderstorms exit the terminal.

Otherwise, VFR flight conditions will prevail through the TAF
period. Winds will start as southeasterly and become southerly
through the day. Sustained winds will be strong, in the upper
teens, and gust into the upper 20s during the day. Gusts should
largely diminish overnight but I can`t rule out a stray gust or
two after 01Z.

Delia

&&

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

$$

WFO LSX