468
FXUS63 KLSX 100843
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
343 AM CDT Thu Jul 10 2025

.KEY MESSAGES...

- There are multiple chances for showers and thunderstorms through the
  middle of next week. A few severe thunderstorms are possible
  Friday afternoon and evening over northeast Missouri and west
  central Illinois.

- Friday will be the warmest day of the week as heat index values
  climb to around 100 degrees for most. The St. Louis metro area
  will see values closer to 105 degrees.


&&

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 342 AM CDT Thu Jul 10 2025

The sky was mainly clear across the area this morning, though there
were some high clouds beginning to filter in from the northwest
ahead of a large MCS over Nebraska and Iowa.  Winds were light
thanks to high pressure centered over Kentucky and Tennessee. The
latest surface observations are showing some fog over the southern
parts of Illinois and Missouri, but I do not expect as much fog as
yesterday morning considering the amount of mixing that we saw
during the afternoon.  The latest CAMS are showing that the most
active part of the QLCS over the middle Missouri Valley will
continue to move east and stay north of the CWA.  The outflow from
the QLCS will move into the northern part of the CWA today where the
RAP soundings are showing some uncapped soundings this afternoon.
The HREF is focusing isolated development over the northern and
eastern part of the CWA this afternoon, so that is where I have
maintained slight chance PoPS.

A better chance for showers and thunderstorms will occur on Friday
afternoon and Friday night when an upper trough will approach the
area from the west.  There will be several boundaries associated
with the trough including a warm front over Iowa and northern
Illinois and an attendant cold front that will be entering western
Missouri on Friday night.  Showers and thunderstorms may develop
over the northern CWA as soon as Friday afternoon associated with a
residual outflow boundary from convection that will move through
Iowa tonight.  Most of the CAMS keep thunderstorms out of the CWA
tomorrow afternoon except for the FV3 and ARW.  A better chance will
wait until tomorrow evening associated with the cold front when
MLCAPES of 2000-3000+ J/kg and deep layer shear of 20-30 kts will
support a few organized severe multicell storms across the northern
CWA per the latest SWODY2.  Large hail and damaging wind gusts will
be the primary threat from any severe thunderstorms.

Highs the next two days will be in the lower to mid 90s with Friday
slightly warmer.  Dewpoints will climb into the 70s on Friday
supporting heat indexes from the mid 90s to near 105 degrees.

Britt

&&

.LONG TERM...  (Friday Night through Wednesday)
Issued at 342 AM CDT Thu Jul 10 2025

The LREF is still supporting an active pattern over the weekend
through the middle of next week with several chances for showers and
thunderstorms as several upper troughs will move through Missouri
and Illinois.  The LREF members are still producing the best chance
of rain (40-60%) on Friday night and Saturday with a lingering
chance (30-50%) across the southern half of the CWA as a front gets
stalled across the CWA and a second trough moves across the Missouri
and Illinois.  Here again, it should be pointed out that while the
weekend will not be a washout, some locally heavy rainfall could be
possible as both the GFS/NAM have PWATS AOA 2" along the front.
Additional chances for thunderstorms will be possible by early-mid
next week as all of the global models are showing yet another trough
and attendant front moving across the Midwest.

Temperatures through the weekend into next week will be close to
July normals ranging from the mid 80s to around 90 degrees.
Confidence in temperatures remains fairly high as the NBM IQR is
only 4-6 degrees.

Britt

&&

.AVIATION...  (For the 06z TAFs through 06z Thursday Night)
Issued at 1045 PM CDT Wed Jul 9 2025

VFR conditions are expected to prevail for a majority of the 06Z
TAF cycle. Clearing skies and light winds tonight may allow for
some patchy river valley fog formation. While dense fog did occur
yesterday in a few locations, much of this was likely caused by
rain earlier in the day, which did not occur today. After a day of
full sun and deep mixing, we don`t expect that coverage will be as
widespread, and confidence is low that local terminals will be
impacted again tonight. Otherwise, there is a low chance for
showers and weak thunderstorms during the day, with highest
chances (~40%) at UIN late in the afternoon. At other sites, lower
probabilities (20% or less) exist, and this remains too low to
included in the TAF at this time. Light southerly winds are also
expected to prevail from tomorrow morning onward.

BRC

&&

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

$$

WFO LSX