377
FXUS63 KLSX 052327
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
627 PM CDT Tue May 5 2026

.KEY MESSAGES...

- Rain will end from northwest to southeast tonight.

- It will be relatively cool Wednesday and Thursday, but warmer
  temperatures and a chance for showers and thunderstorms returns
  Friday.


&&

.SHORT TERM...  (Through Late Wednesday Night)
Issued at 227 PM CDT Tue May 5 2026

A cold front continues moving slowly through southeast Missouri this
afternoon.  The 850mb low associated with this system is over
northeast Oklahoma and is producing southerly flow across the Ozarks
and up the I-44 corridor into southwest and south central Illinois.
Short range RAP forecast is showing increasing low level moisture
convergence this afternoon into this evening along the 850mb front
due to this warm moist flow as it sags slowly south.  This moisture
convergence will continue to produce light to occasionally moderate
rain with a rumble or two of thunder this afternoon and evening.
Rain will taper off and end from northwest to southeast tonight as
the 850mb front finally drifts into Arkansas and Kentucky.

Cooler and drier air will filter into the area behind the front with
Wednesday morning`s lows dipping into the low to mid 40s.  Previous
forecasts were hinting at a chance for some light rain on Wednesday
as a mid-upper level trough digs into the Great Plains.  Latest runs
are showing somewhat weaker frontogenesis ahead of the trough, and
somewhat drier low levels.  LREF >0.01 QPF probs have fallen to 20%
and below for Wednesday, and all deterministic guidance shows much
less, if any QPF.  Have therefore reduced PoPs to only slight chance
(20%), and mainly in the morning.  Highs will struggle to reach 55-
60 on Wednesday due to lingering clouds and continuing weak cold
advection.  The cool start to the evening along with breaks in the
overcast and light winds will allow temperatures to cool into the
upper 30s to low 40s Wednesday night/Thursday morning.

Carney

&&

.LONG TERM...  (Thursday through Next Tuesday)
Issued at 227 PM CDT Tue May 5 2026

The weather pattern over North America for Thursday through next
Tuesday will be dominated by an upper level low over Hudson Bay, and
semi-persistent long wave ridging over the West Coast.  This results
in persistent west to northwest flow aloft over the Mid Mississippi
Valley through the period.  A few short waves will move across the
area embedded in the long wave flow, at least two of which will have
the potential to produce more rain.  The first wave on Thursday
pushes the cold front through the Lower Mississippi Valley into
the northern Gulf.  Forecast soundings show a fairly dry atmosphere
above us, so the wave should pass with little sensible weather at
the surface.  The wave will help to move the cool surface high from
the eastern Plains into the Lower Mississippi Valley by late
Thursday which will keep our afternoon highs seasonably cool in the
mid 60s.

Low level flow swings back to the southwest as the surface high
moves across the Appalachians Thursday night.  This brings some
moisture back into our region for the next short wave on Friday to
work with.  Models generate some light QPF across the area as the
wave moves through Friday afternoon, and CAPE values rise to around
1000 J/Kg ahead of the surface reflection of the wave.  This will
likely result in scattered showers and a few thunderstorms in the
afternoon.  Forecast soundings show weak lapse rates and skinny CAPE
profiles which are not conducive to strong updrafts and severe
storms.  Temperatures show a steady rise Friday into Saturday as low
level flow mostly prevails from the southwest, even after the
trough passes on Friday night.

A third, stronger short wave will dig into the Great Plains Saturday
night into Sunday morning.  This wave will push a cold front through
the area on Sunday and there should be plenty of moisture to produce
precipitation with this system.  The LREF continues to show some
variance with the timing and amplitude of the wave, and therefore
the speed of the front and strength of cold air advection behind it.
 Temperature IQRs have narrowed on this morning`s 12Z run of the
LREF, but are still 6-8 degrees both Sunday and Monday.
Deterministic NBM highs both days are in the low to mid 70s which is
around the 75th percentile for the LREF.  Another short wave is
forecast to move into the Great Plains on Tuesday with another
chance for precipitation.  However the LREF cluster analysis is
showing a lot of variance in is position, so confidence in another
round of rain is low at this time.


Carney

&&

.AVIATION...  (For the 00z TAFs through 00z Wednesday Evening)
Issued at 626 PM CDT Tue May 5 2026

Rain continues from central MO to St Louis this evening. It will
be more steady than not, but pockets of MVFR to even potentially
IFR conditions may occur within the rain. It should end from
northwest to southeast this evening giving way to VFR ceilings
lasting through tomorrow. Winds are mainly light out of the north,
though may be variable at times tonight.

Kimble

&&

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

$$

WFO LSX