529
FXUS63 KLSX 161745
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1245 PM CDT Wed Apr 16 2025

.KEY MESSAGES...

-Elevated fire danger is expected across portions of central and
northeast Missouri this afternoon.

-Multiple rounds of showers and thunderstorms will kick off
 Wednesday night and continue through Monday. A few may become
 strong to severe thunderstorms Thursday night and Friday night,
 and locally heavy rainfall possible through Monday.


&&

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 226 AM CDT Wed Apr 16 2025

A surface high is moving across Arkansas this morning and winds have
become light and variable. As the surface high shifts eastward today
winds will become southerly and increase in speed, particularly
across central Missouri where the pressure gradient will tighten as
a surface low forms over the Front Range. The southerly flow will
advect warm air into the region and high temperatures will be
roughly 10 degrees warmer than yesterday. Moisture return along the
southerly flow will initially be weak, and combined with warmer
temperatures will result in elevated fire danger conditions again
today across portions of central and northeast Missouri.

By the evening, warm air advection and a mid-level disturbance along
the axis of the passing ridge will be able to produce isolated
showers and perhaps a thunderstorm. Chances will increase overnight
as the east-west low-level jet ramps up. By late Thursday morning
any showers and thunderstorms that are lingering across the area
will move eastward out of the forecast area as the nose of the low-
level jet and mid-level disturbance exit the region. The surface
pressure gradient will continue to tighten through the day and deep
mixing will result in elevated winds sustained 15-25 mph and gusting
up to 35 mph.

The low-level jet will ramp up again overnight and combined with mid-
level disturbances could produce isolated to scattered convection
mainly across central and northeast Missouri. Sufficient shear (40-
50kts) will be able to organize a few thunderstorms in the 500-1000
J/kg of MUCAPE, which will be capable of small to marginally severe
hail. Uncertainty in the location of thunderstorm development and
how much instability will be available are keeping confidence in
severe thunderstorm development low at the moment.

Delia

&&

.LONG TERM...  (Thursday Night through Tuesday)
Issued at 226 AM CDT Wed Apr 16 2025

Thunderstorms, a few strong, will linger into the early morning
hours Friday before moving out of the forecast area with the mid-
level disturbance. Southwesterly flow will establish ahead of a cold
front, pushing high temperatures on Friday into the upper 70s to mid
80s across the area. The southwest to northeast cold front will push
through the forecast area during the afternoon and into the
overnight period, while mid-level disturbances and the low-level jet
will be able to produce showers and thunderstorms ahead of and along
the front. Upper 50 to low 60 degree dewpoints, MUCAPE values 1000-
2500 J/kg, and 40-55 kts of 0-6 km shear ahead of the cold front
will be a favorable environment for severe thunderstorm organization
and maintenance. However, most guidance continues to show evidence
of a moderate to strong cap in place from low-level warming. Some
guidance is starting to show that cap eroding ahead of the front, so
the possibility of surface-based convection remains on the table but
not guaranteed. Additionally, deep layer shear is parallel to the
front, which would favor lines of convection over
isolated/multicell clusters. Elevated storms would generate a
large hail threat while surface based convection would favor
damaging winds and weak tornadoes.

As mentioned in the previous forecast, guidance is currently
stalling the cold front further north, closer to I-44 (MO) and I-70
(IL). Additional mid-level disturbances along the established
southwesterly flow will focus several rounds of rain along the front
through Monday. Confidence is increasing that some instability will
be available Saturday for thunderstorm development along the front
as well. From Friday night through Monday ensemble guidance is
indicating a 50% chance of at least 2 inches of rain along the
front. Guidance continues to show only a 15-20% chance of greater
than 4 inches of rain, and remains the worst case scenario for this
rainfall event. Where thunderstorms develop and linger higher
rainfall rates are expected. If the front waivers at all over the
weekend it could cut down on rainfall amounts in any one particular
area, but some areas across southern Missouri and Illinois will see
rainfall capable of, at a minimum, producing rises on small creeks
and streams, and mainstem rivers such as the Black and Kaskaskia.

A surface low will push across the forecast area Monday, driven
aloft by a mid-level trough that will move northeastward across the
region. A surface high will move into the region Tuesday behind the
low, helping to bring a brief pause in the seemingly endless march
of rain. The surface high will be a brief reprieve in the active
pattern and with continued mid-level disturbances moving across the
central CONUS during the first part of next week, rain chances
remain in the forecast.

Delia

&&

.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1238 PM CDT Wed Apr 16 2025

VFR flight conditions are expected this afternoon into early
evening. Beginning later this evening, after 05z, the chances of
precipitation will begin to increase. First in the roughly 05-09z
period at KUIN and the St. Louis metro terminals when showers will
be possible. A second wave of showers and some embedded
thunderstorms will move into central MO around 10z or so impacting
KJEF/KCOU, and then several hours later impacting the remainder
of the terminals as it progresses east. Outside of any
precipitation, Flight conditions should be VFR while there is
potential for brief reductions to MVFR during the
showers/thunderstorms on Thursday morning. South-southeast winds
will also increase and become gusty on Thursday morning.

Glass

&&

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

$$

WFO LSX