040
FXUS63 KLSX 080837
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
337 AM CDT Tue Jul 8 2025

.KEY MESSAGES...

- There is a chance (30-60%) of showers and thunderstorms today.
  Isolated severe thunderstorms are possible capable of producing
  damaging wind gusts to 60 mph and a localized threat for heavy
  rainfall.

- There will be additional chances for showers and thunderstorms through
  the weekend with the best chance (40-60%) on Friday night and
  Saturday.

&&

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 336 AM CDT Tue Jul 8 2025

An MCS currently over northwest Missouri is expected to continue to
move east and southeast and weaken early this morning as they move
into an environment that is increasingly stable over eastern MO.
This is reflected in the latest CAMS runs which show this line
diminishing before thunderstorms regenerate over the CWA this
afternoon.  This will occur as an upper trough currently over the
middle Missouri Valley will drops southeast into the Missouri and
Illinois later today.  The outflow and potentially an MCV from the
remnant MCS may also aid in the redevelopment of thunderstorms this
afternoon.  While MLCAPES will be in the 1500-2500 J/kg range, deep
layer shear will only be in the 20-30 knot range with most of the
shear in the lower part of the hodograph.  Forecast soundings do
support the potential for isolated damaging winds to 60 mph per the
SPC marginal risk.  In addition, PWATS will be in 1.75 to 2.0"
range, so any slow moving thunderstorms could produce locally heavy
rainfall. It still appears the most likely time for any severe
weather or heavy rainfall will be between 2 and 8 pm.

The rain chances will diminish tonight with the loss of daytime
heating.  The southern end of the upper trough will linger over the
Middle Mississippi Valley on Wednesday bringing additional chances
(20-40%) of showers and thunderstorms over the southeast half of the
CWA on Wednesday afternoon.  High temperatures the next two days
will be seasonably warm in the 85 to 90 degree range as 850 mb
temperatures are in the 15-20C range.

Britt

&&

.LONG TERM...  (Wednesday Night through Monday)
Issued at 336 AM CDT Tue Jul 8 2025

The LREF is showing that the upper pattern from mid week into early
next week will be highlighted by a large high over the southwest
CONUS with Missouri and Illinois on the southern edge of the active
westerlies.   While there will be on and off chance of showers and
thunderstorms over the Midwest as troughs move through the
aforementioned westerlies, the best chance (40-60%) over our area
will be Friday night into Saturday when there is good agreement in
the global models that a upper trough and attendant cold front will
move across Missouri and Illinois.  While the weekend does not look
like a washout, I can`t rule out heavy downpours with some of the
thunderstorms given PWATS around 2".

Temperatures through the period will be close to July normals
ranging from the mid 80s to around 90 degrees.  The NBM is showing
the warmest day on Friday when most areas will see highs in the low
90s and heat indexes near 100 degrees ahead of the front.

Britt

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 934 PM CDT Mon Jul 7 2025

Dry conditions are expected for the most part overnight tonight,
though we are watching organized convection moving southward
across eastern Nebraska. The most likely scenario is for this
activity to largely or completely miss us to the west. In
addition, it should weaken with time. Additional thunderstorms are
forecast to develop by early-mid afternoon, mainly from central
Missouri east/northeast. The best chances for thunderstorms may be
at the metro terminals, largely between 2000 UTC Tuesday and 0000
UTC Wednesday. Wasn`t quite confident to add a TEMPO, as there
remains enough uncertainty on timing and where convective
development will be preferred. However, any terminal that does see
a direct impact from a thunderstorm Tuesday will be capable of
producing gusty winds and brief downpours reducing visibilities.

The other concern is for some fog tonight at the river valley
sites. The best chances look to be across southeast Missouri and
southwest Illinois, but cannot rule out a brief period of say MVFR
visibilities at KSUS, KCPS, and/or KJEF. Left this mention out of
the TAFs for now, but this will be something to monitor overnight.

Gosselin

&&

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

$$

WFO LSX