149
FXUS63 KLSX 221729
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1229 PM CDT Tue Apr 22 2025

.KEY MESSAGES...

- Warm weather returns today and lasts through the week. Rain
  chances return as early as Thursday.


&&

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 230 AM CDT Tue Apr 22 2025

Surface high pressure currently over the Ohio Valley will gradually
move east today while ridging slowly builds aloft over the central
and southern US. Surface winds turn southerly and we warm up about
10 degrees compared to yesterday, peaking near 80 degrees this
afternoon under a mostly clear sky. A front associated with a
northern stream wave stalls over southern Iowa this evening. As it
attempts to gradually lift northward overnight it may serve as a
focus for some thunderstorms tonight, but there`s good agreement
that this stays north of our forecast area. Building heights aloft
and moisture return occurring well to our west keeps things dry for
another day on Wednesday with temperatures once again peaking around
80 degrees.

Kimble

&&

.LONG TERM...  (Wednesday Night through Monday)
Issued at 230 AM CDT Tue Apr 22 2025

For much of this week, moisture return is limited to the western
Plains, but we`ll see this moisture gradually expanding later in the
week. While convective initiation remains unlikely in our area
during the day on Thursday due to a lingering capping inversion,
thunderstorms are more likely to develop to our west where a weak
shortwave trough helps to erode the cap. Convective complexes
developing to our west may drift into our area late in the day, but
additional development becomes increasingly likely overnight as the
low level jet begins to pull more moisture into our area. The
shortwave trough continues to move east and crosses through the
Mississippi Valley on Friday with more widespread showers and
thunderstorms ahead of a cold front arriving from the northwest.
There`s still a fair amount of variation in guidance on all of these
details, but the general trend is for increasing chances for
thunderstorms late Thursday through Friday. While instability
increases through this period, wind shear will be fairly limited
compared to our more recent severe weather episodes owing to weaker
flow aloft. So at the moment we are not expecting significant severe
weather. Although if storms can organize into clusters they may pose
a limited wind threat.

Ridging builds back quickly in the wake of Friday`s trough. The cold
front slips south through our area leading to a cooler and drier day
on Saturday. But this front stalls just to our south before washing
out or lifting back north on Sunday with the amplification of the
ridge. Rain chances return to the forecast on Sunday as the front
lifting through the region may spark another round of thunderstorms.
However, not all guidance produces rainfall. Some guidance washes
the front out with a more gradual shift back toward southerly flow
and less focus for another round of convection. About 50 percent of
ensemble guidance produces rainfall in our area on Sunday.

With the ridge amplifying across the center of the country and low
level flow becoming southerly, we`ll see a return of the warm
conditions. It will be even warmer this time with a more amplified
ridge. Current NBM forecast has temperatures warming into the mid
80s, but the interquartile range shows that on the upper end some
low 90s are within range. If these higher end temperatures occur
we`ll be close to record highs for late April.

While guidance is in good agreement on the development of the high
amplitude ridge in the central US early in the week and a trough in
the West, there`s more variation in how quickly the ridge breaks
down. As a result, the going forecast maintains some rain chances
just about every forecast period, but the more likely scenario is
one primary round of thunderstorms as the trough moves in from the
west and the next cold front arrives Tuesday or Wednesday. There`s a
better chance of stronger shear available when this occurs, so this
may represent our next best chance for severe thunderstorms. But at
the moment there`s still a lot of variation in guidance on when and
how this will occur.

Kimble

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1224 PM CDT Tue Apr 22 2025

VFR flight conditions and light southerly flow are expected to
prevail through the period. There is a small chance that a stray
shower or weak thunderstorm could move through far northeast
Missouri or west central Illinois late this afternoon or evening,
but the chance for rain is too low to mention in the KUIN TAF.

Carney

&&

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

$$

WFO LSX