782
FXUS63 KLSX 161101
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
601 AM CDT Thu Oct 16 2025

.KEY MESSAGES...

-Warm and dry conditions continue through Friday.

-Widespread showers and thunderstorms will impact the area
 Saturday, with a low and conditional risk for severe
 thunderstorms.


&&

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 400 AM CDT Thu Oct 16 2025

Morning mid-level water vapor imagery shows the ridge over the mid-
Mississippi Valley, which is keeping the area dry and largely cloud
free. Over the course of the day the ridge will start to weaken and
shift eastward. Despite this, confidence is high that another dry
and warm day is on tap. Temperatures will peak in the low to mid
80s, similar to yesterday.

While the mid-level ridge weakens and shifts eastward, a mid-level
trough will push into the region in its wake. The center of this
trough will slide northeast from the Central Plains into the Upper
mississippi Valley overnight Thursday into Friday, but another
shortwave will surge south within the broader trough from the
Pacific Northwest during the day. It is this feature that will
progress the broader trough eastward into the weekend and generate
this weekend`s rainfall. Ahead of this system however, southerly
flow will prevail on Friday and temperatures will once again peak in
the low to mid 80s.


Delia

&&

.LONG TERM...  (Friday Night through Wednesday)
Issued at 400 AM CDT Thu Oct 16 2025

Focus now turns to Saturday and the low risk for severe
thunderstorms. As the mid-level trough strengthens and pushes
eastward into Saturday a surface low will form in response along the
US-Canada border. The associated cold front will drape through the
Central Plains and slowly approach the mid-Mississippi Valley
Saturday. Guidance has come into better agreement over the last 24
hours that this front will move through the forecast area much
slower than previous solutions were suggesting. Ahead of the front a
strong low-level jet will pump warm, moist air to the region. The
low-level jet will combine with the upper level jet exit to support
showers and thunderstorms developing ahead of the front Saturday
along low-level moisture convergence. Cooling aloft associated with
the approach of this system will help to generate some instability
across the region, with deterministic models generating 600-1500
J/kg of MLCAPE. The higher end of this range could be realized if
breaks in the clouds and ongoing showers and thunderstorms can
produce adequate surface heating and boundary layer mixing. If this
were to happen, thunderstorms will be able to take advantage of the
40-60 kts of 0-6km shear and become severe during the afternoon and
evening. Deep mixing in this scenario will result in high LCLs and
inverted V soundings that would favor hail and damaging winds. The
best location for severe thunderstorms development in this scenario
is across southeastern Missouri and southern Illinois, further away
from the best moisture convergence.

However, if instability is lower from widespread cloud cover and
rain, the shear will be too strong for thunderstorm maintenance and
strong to severe thunderstorms would be significantly less
likely. While the slower front does open the region up to a
slightly higher potential for severe weather, widespread rain and
limited severe threat is still favored. This is still the most
likely scenario as the upper-level jet and mid-level vorticity
advection are anticipated to produce widespread showers and
thunderstorms admits the abundant moisture across the forecast
area. The lack of surface heating would keep instability elevated
and limit the severe potential significantly. This would shunt the
risk for severe weather to our south where more heating and
instability would generate a more favorable environment.

Regardless of the severe potential, this system will bring much
needed rain to the entire forecast area. Strong moisture return
ahead of the system result in PWAT values between 1.3-1.6". Global
ensembles indicate a 65% chance for at least 0.50" of rain area
wide, and a 20-30% chance for at least 1.00" of rain. While this
won`t be enough to completely relieve the ongoing drought
conditions, it will certainly benefit our most drought impacted
areas, including southeast Missouri and southern Illinois.

The cold front will push through the area Saturday evening, bringing
an end to showers and thunderstorms. Cool, dry air will flow into
the region overnight as the 850 mb front passes overhead and the mid-
level trough exits the region. Temperatures on Sunday will be nearly
20 degrees cooler than recent days with highs reaching only the mid
to upper 60s despite the clear sky. A mid-level shortwave ridge will
pass over the mid-Mississippi Valley Monday, allowing for a brief
and relative warm up into the 70s before another mid-level trough
and surface cold front push through the region Monday into Tuesday.
Temperatures in the wake of this system are expected to cool to near
normal, though there is disagreement in the mid-level pattern beyond
Tuesday.

Delia

&&

.AVIATION...  (For the 12z TAFs through 12z Friday Morning)
Issued at 559 AM CDT Thu Oct 16 2025

Isolated light showers/sprinkles are moving southeast from Iowa
early this morning. Confidence is low that this will impact the
KUIN terminal, so have left a mention out of the TAF. If a shower
does move through it will have little to no impact on the flight
category and will quickly exit.

Otherwise, dry and VFR flight conditions are expected today under
east to southeasterly winds.

Delia

&&

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

$$

WFO LSX