823
FXUS63 KLSX 082321
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
621 PM CDT Wed Jul 8 2026

.KEY MESSAGES...

- Some thunderstorms may be strong to severe Thursday and Friday afternoons
  with damaging winds the primary threat along with locally heavy
  rainfall.

- Mostly dry weather with temperatures slightly above average are
  forecast Sunday into early next week.


&&

.SHORT TERM...  (Through Late Thursday Night)
Issued at 223 PM CDT Wed Jul 8 2026

Dry weather is forecast tonight with light winds and seasonably
warm temperatures. Widespread showers and thunderstorms are
forecast to develop across the mid-Missouri Valley and head
east/southeast late tonight into early Thursday morning. This
activity should weaken gradually with time as it enters
central/northeast Missouri due to an abating low-level jet and
lesser instability to work with. A remnant MCV is likely to remain
from this morning convection and work eastward. By early-mid
afternoon, this feature should help develop renewed convection
downstream, mostly likely along/east of the Mississippi River.
Instability will increase with time, and combined with some
enhanced (~30 knots) effective shear downstream of the
aforementioned MCV, at least a few strong to severe thunderstorms
may occur. Damaging winds will be the main threat along with
locally heavy rainfall from roughly 2 PM until 10 PM.

While the severe threat likely will wane by mid-late evening, the
low-level jet does ramp up. Enhanced low-level moisture convergence
on the nose of the jet should lead to fairly widespread showers and
thunderstorms across southeast Missouri and far southwest Illinois.
These storms may tend to train (especially if they stay elevated)
over the same areas so the threat for isolated flash flooding may
increase. Precipitable water values are expected to be high,
generally above 1.75" or closer to the 95th percentile of
climatology. Flash flood guidance though is also real high (>3"/3
hr), and the low-level jet does veer about 30 degrees from 0600
to 1200 UTC Friday. This should help shift convection equatorward
overnight, lessening the duration of accumulating rainfall.
Therefore, will hold off on a flash flood watch for now.


Gosselin

&&

.LONG TERM...  (Friday through Next Wednesday)
Issued at 223 PM CDT Wed Jul 8 2026

(Friday - Saturday Night)

Forecast uncertainty increases after Thursday night. Deterministic
model guidance is hinting at another midlevel shortwave trough (or
convectively-induced MCV) moving eastward in zonal flow aloft.
The timing/track/strength of this feature is unknown, but
additional showers and thunderstorms should develop by Friday
afternoon. Similar to Thursday afternoon, there should be plenty
of instability and just enough shear in place for the threat of
damaging wind gusts. At this early juncture, the best chances of
thunderstorms and severe weather would be across southeast
Missouri. This is where the effective frontal boundary is most
likely to be located, but the exact location will of course
depend heavily on the evolution of convection Thursday night.

Friday night into Saturday morning may have a subsequent round of
showers and thunderstorms as the low-level jet increases. Exactly
where and how organized this round will be is highly uncertain,
but I would tend to favor southeast Missouri and points south.
Each preceding round of convection may tend to shift the effective
front farther south and deterministic guidance (especially coarser
resolution) tends to be too far north with these subsequent
rounds. If parts of southeast Missouri and adjacent southwest
Illinois do end up receiving additional rounds of showers and
thunderstorms, the flash flood threat would increase though at
this time range there is too much uncertainty to say whether or
not any given location will see multiple rounds.


(Sunday - Next Wednesday)

A record-breaking mid/upper level ridge is forecast to amplify
across the northern Plains late this weekend into early next week
with deep northeasterly flow across the mid-Mississippi Valley. A
shift to dry weather along with temperatures running slightly above
normal seems likely during this period of time. There is some
uncertainty with the exact strength/placement of the mid/upper
level ridge heading into the middle of next week. One cluster of
the 500-hPa height pattern has a more elongated west-east ridge
(~25% of LREF members) over our area. If this scenario were to
occur, highs more into the mid 90s would be expected. However,
even in that scenario, surface dewpoints should tend to lower with
time and heat index values likely would stay largely below 100
degrees. On the other end of the spectrum, there is a cluster
(~10% of members) that has a much deeper trough moving across the
Great Lakes/northeast. This scenario would potentially lead to
much cooler (highs mid 80s) temperatures. The current forecast
lies between these two opposite ends of the spectrum, and more
toward the middle two clusters which comprises a large majority of
LREF members.


Gosselin

&&

.AVIATION...  (For the 00z TAFs through 00z Thursday Evening)
Issued at 619 PM CDT Wed Jul 8 2026

VFR conditions continue overnight with light winds expected. The
remnants of a thunderstorm complex to our west is expected to move
into the region tomorrow morning, but convective activity should
dissipate before it arrives. However, renewed convection is
expected to begin as it arrives near the Mississippi River
Thursday afternoon. These thunderstorms are most likely to affect
the St louis area TAF locations while other areas are unlikely to
be affected. Outside of this, conditions will remain VFR.

Kimble

&&

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

$$

WFO LSX