251
FXUS63 KLSX 092341
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
641 PM CDT Wed Jul 9 2025

.KEY MESSAGES...

- There are multiple chances for showers and thunderstorms between Thursday
  and the middle of next week. Severe weather is not expected.

- 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 Thursday Night)
Issued at 142 PM CDT Wed Jul 9 2025

Surface analysis shows a diffuse quasi-stationary front extending
from the central Plains through central Iowa. This front will creep
south into northeast Missouri/west-central Illinois through this
afternoon and will have no noticeable impact on our sensible
weather. However, the boundary has been a catalyst for convective
initiation in Nebraska and the Dakotas today. As the nocturnal
low-level jet ramps up tonight, these showers and thunderstorms
will congeal into an MCS and follow the front into northeast
Missouri. Scattered showers and thunderstorms from the MCS are
forecast to arrive in the middle to late morning tomorrow and
linger through the afternoon. The areal extent of convection will
depend on the presence of any outflow boundaries laid out by the
morning convection. Latest CAMs are keen on outflow boundaries
playing a role in upstream convection tomorrow afternoon, and I`m
not inclined to disagree given 1) that we`ll have up to 2000 J/kg
of SBCAPE and 2) that outflow has played a large role in
thunderstorm propagation this past week. Because of this and the
chaotic nature of outflow boundaries, I`ve spread slight chance
PoPs over the rest of the CWA tomorrow afternoon. With effective
shear only around 15 kts, severe weather is not expected.

Otherwise, tomorrow will be a seasonable day with lows near 70
degrees and highs around 90.

Jaja

&&

.LONG TERM...  (Friday through Next Wednesday)
Issued at 142 PM CDT Wed Jul 9 2025

A series of shortwaves will keep our weather pattern active until at
least the middle of next week. The greatest chance for rain (up to
50%) will come Friday night into Saturday as a shortwave interacts
with a stationary front in the vicinity of the CWA. Not everyone
will see rain out of this due to the scattered nature of the
convection. Those who do see rain, however, have the potential to
brief heavy rainfall since PWATs will be hovering around 1.7" during
this timeframe. This forecast is generally true through Wednesday.
The front will linger in the area through Sunday providing another
chance of showers and thunderstorms. Monday looks drier as the front
moves off, but rain chances ramp up again on Tuesday as another
shortwave triggers a cold front at the surface. A lack of sufficient
effective shear each day (only 10 - 15 kts) will keep the potential
for severe weather low.

The temperature forecast through Wednesday will generally be
seasonable with highs in the 80s to 90 degrees and lows in the 60s
and 70s. Friday is expected to be the warmest day as heat index
values climb to around 100 degrees for most and near 105 in the St.
Louis metro area. Overall, nothing uncharacteristic for July.

Jaja

&&

.AVIATION...  (For the 00z TAFs through 00z Thursday Evening)
Issued at 633 PM CDT Wed Jul 9 2025

VFR conditions are likely to prevail throughout the 00Z TAF cycle.
Afternoon VFR cumulus clouds are expected to diminish near the
start of the period, with light winds and occasional high level
clouds overnight. A few river valley locations may see some patchy
fog tonight, but confidence remains too low that this will impact
any of our local terminals like it did the prior morning.

During the day, there will be a low probability of rain showers
and thunderstorms, with best chances (~40%) during the late
afternoon at UIN. However, shower chances at other terminals
remain near 20% or less, and are too low for TAF mention at this
time. Otherwise, expect another VFR afternoon cumulus field and
light southerly winds.

BRC

&&

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

$$

WFO LSX