136
FXUS63 KLSX 071748
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1248 PM CDT Mon Jul 7 2025

.KEY MESSAGES...

- Scattered thunderstorms are possible mainly this afternoon
  across the eastern Ozarks. They are not expected to be as strong
  as Sunday`s storms.


- Another round of strong to isolated severe storms is possible on
  Tuesday. Isolated gusty winds up to 60 mph and locally heavy
  rain are the threats on Tuesday.


&&

.SHORT TERM...  (Through Late Tonight)
Issued at 407 AM CDT Mon Jul 7 2025

The "cold front" is difficult to discern in surface obs this
morning, however there is a pressure trough which lies generally
along the I-70 corridor.  Short range guidance shows it sagging
south today as a weak high pressure system moves across the Upper
Midwest and pushes somewhat drier air south into eastern Missouri
and central and southern Illinois.  The lower humidity will be
noticeable across northeast Missouri and west central/south central
Illinois, but temperatures will be very similar to Sunday`s ranging
from the mid 80s to around 90.  The lower dew point temperatures are
expected to lead to lower instability this afternoon, particularly
north of I-70 where RAP MLCAPE values are hard pressed to break 1000
J/Kg. However, 1500-2000 J/Kg MLCAPE values are forecast by the RAP
farther south across the eastern Ozarks, and this is where the
best chance for thunderstorms is today.  Most short range guidance is
not particularly bullish on developing thunderstorms this afternoon
so have limited PoPs to 30-40 percent.

Models are developing an MCS over South Dakota or Nebraska late this
afternoon or early this evening.  The MCS drops southeast into
western Iowa and northwest Missouri late in the evening into the
overnight hours.  There are speed and strength differences in how
each model handles the MCS tonight, but a few bring the dissipating
storms into central and northeast Missouri after 09Z tonight.  There
may be some gusty winds associated with the outflow boundary should
this occur, but severe gusts are not expected.

Carney

&&

.LONG TERM...  (Tuesday through Sunday)
Issued at 407 AM CDT Mon Jul 7 2025

The upper level pattern shifts slowly Tuesday and Wednesday with the
upper level ridge over the Desert Southwest and a long wave trough
drifting east through the Central U.S. into the Ohio Valley. The
trough axis is forecast to pass over Missouri and Illinois Tuesday
into Tuesday evening.  Synoptic scale lift with the trough as well
as low level moisture convergence ahead of the 850 trough will
produce another round of convection Tuesday afternoon and evening
which should be more widespread than today`s. Most guidance focuses
the convection along and east of the Mississippi River Tuesday
afternoon, which makes sense given the trough axis is forecast to be
stretching from west central Illinois into central/east central
Missouri at that time.  However, small differences in the speed of
the trough will change the position of the best forcing, which would
produce convection farther west or east than the current forecast.
The GFS continues to look like it`s contaminated by convective
feedback, but the extended RAP looks clean with MLCAPE reaching 2500-
3000 J/Kg Tuesday afternoon/evening.  This may be a higher-end value
as the LREF shows about that much CAPE at the 75th percentile.  0-
6km shear is not very impressive at ~20kts, but those levels of
instability and shear will be capable of sustaining marginally
severe clusters and inverted V forecast soundings will be conducive
to wet microbursts. Precipitable Water values will be near 2 inches,
and warm cloud depths will be in excess of 12,000ft as well, so
locally heavy rain will continue to be possible Tuesday afternoon
and evening.

Weak northwest flow aloft on Wednesday will transition to more zonal
Thursday and Friday with a series of waves moving across the Upper
Midwest.  Guidance shows the energy from these waves staying north
of the forecast area so our convection will likely be driven
primarily by daytime heating lingering outflow boundaries, and weak
overnight low level jets.  It will be tough to find a time during
that period where there is NO chance for rain, but coverage through
that period is not expected to be greater than isolated to widely
scattered (20-30%). A stronger short wave will move along the
U.S./Canada border on Saturday and Sunday, driving a surface cold
front through the Northern Plains into Iowa and northern Missouri.
The front could make it as far south as the I-70 corridor by Sunday
afternoon and be a focus for more widespread (40-50%) storms.
Guidance continues to show seasonably warm temperatures and humid
conditions, typical for early to mid July.

Carney

&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1232 PM CDT Mon Jul 7 2025

Despite the dry forecast at all but KUIN (PROB30), there are
several caveats to what is an uncertain forecast with respect to
point-specific impacts. What is essentially a washed out cold
front over southeastern MO and southwestern IL will be the primary
focus for afternoon/evening thunderstorm potential. Then, another
area in question is central MO, where isolated showers and perhaps
a thunderstorm or two is being supported by ascent from mid/upper
level vorticity.

The best potential for thunderstorms will ride along the surface
boundary south of the terminals this afternoon. The one exception
will be central MO, where trends will have to be monitored, but as
of now, showers have remained north of KCOU/KJEF with Little
indication that it will move much further south. KUIN`s PROB30
addresses the potential that isolated/widely scattered
thunderstorms impact areas of northeastern MO and west-central IL
between late morning/early afternoon Tuesday as a weakening
complex progresses southeast out of the Plains. Considering the
summer pattern, each round will dependent on the prior round,
which results in a higher degrees of uncertainty at any given
point. That said, better probabilities for thunderstorms will be
near the end or just beyond the 24 hour TAF period Tuesday, when
additional convection redevelops and present potential for broader
coverage in scattered thunderstorms. Until then, VFR is favored.

Maples

&&

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

$$

WFO LSX