118
FXUS63 KLSX 140809
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
309 AM CDT Sat Jun 14 2025

.KEY MESSAGES...

- Dense fog will expand across portions of central and
  northeastern MO as well as west-central IL before dissipating
  after sunrise (7 to 9 am).

- There is a potential for a few strong to severe thunderstorms
  on Wednesday, but there are unresolved details that will
  influence the risk.

- A warming trend into next week will support some high
  temperatures reaching the 90s F, threatening the long run of
  sub-90 F temperatures.


&&

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 308 AM CDT Sat Jun 14 2025

An upper-level closed low over the Mid-Mississippi River Valley this
morning is maintaining isolated showers, mainly across east-
central/southeastern MO and south-central/southwestern MO along a
low-level trough axis. To the northwest and west, clouds associated
with the closed low have cleared enough to allow development of fog
in central and northeastern MO as well as west-central IL where
radiational cooling of a very moist BL is taking place. Among this
fog, the footprint of visibilities at or below 1/4 mi have been
increasing, prompting issuance of a Dense Fog Advisory.

The closed low will shift east of the CWA through the morning but
will remain close enough to generate an uptick in the coverage of
showers and thunderstorms this afternoon. HREF membership highlights
the greatest coverage across southwestern IL with decreasing ascent
and increasing convective inhibition with westward extent as mid-
level heights begin rising. Fog will dissipate shortly after sunrise
this morning, followed by a scattering and breaking of stratus late
this morning into afternoon as it becomes more cumuliform. With
greater insolation and less precipitation than Friday, high
temperatures will be warmer and around 80 to the mid-80s F. Showers
and thunderstorms will dissipate with loss of daytime heating and
instability this evening. There is potential for additional fog
tonight into Sunday morning, but conditions may not be as favorable
for widespread dense fog since there will be more preceding daytime
mixing and less precipitation, not to mention uncertainty with night
time cloud cover.

An upper-level shortwave trough will be approaching the Mid-
Mississippi River Valley on Sunday but model guidance has slowed
down its arrival, leaving most of the daytime hours Sunday now dry
with associated showers and thunderstorms remaining to the southwest
and west of the CWA. Some upper-level clouds and diurnal cumulus
will be around on Sunday, but a slight warming trend will persist
with high temperatures more firmly in the 80s F.

Pfahler

&&

.LONG TERM...  (Sunday Night through Friday)
Issued at 308 AM CDT Sat Jun 14 2025

Sunday evening through Monday evening, the upper-level shortwave
trough is anticipated to very slowly traverse the Mid-Mississippi
River Valley along with one or more potential remnant MCVs emanating
from antecedent thunderstorms. The greatest coverage of showers and
thunderstorms influenced by these features will be on Monday when
there is coinciding diurnal instability. Exact coverage of showers
and thunderstorms is not completely clear with some differences in
the amplitude/strength of the shortwave trough and MCVs, but 40 to
60 percent of ensemble model membership have measurable rainfall
across much of the CWA at some point Monday. Modest deep-layer wind
shear of 10 to 20 kt will likely preclude much organization of
thunderstorms and keep them more pulse-like. As such, the threat of
any severe thunderstorms appears low on Monday.

Following the upper-level shortwave trough, the flow pattern over
the Mid-Mississippi River Valley will transition from northwesterly
on Tuesday to southwesterly on Wednesday ahead of a longer
wavelength trough propagating eastward. This evolution will deliver
additional opportunities for showers and thunderstorms, possibly in
the form of a decaying MCS tracking into the CWA Tuesday
night/Wednesday morning at the nose of a LLJ and a more confident
round on Wednesday with a cold front. The combination of seasonably
high instability and enhanced deep-layer wind shear of 25 to 35 kt
with an upper-level jet streak glancing the region supports a risk
of strong to severe thunderstorms on Wednesday. However, there are
still plenty of details that also need to be considered, including
trough/cold front timing and the impact of any early day remnants of
an overnight MCS.

In terms of temperatures through Tuesday and Wednesday, this
pattern will also be favorable for low-level southwesterly WAA to
further warm temperatures. The NBM remains in good agreement on
some high temperatures reaching the 90s F on Tuesday and Wednesday
along the Missouri River (90+ F probabilities 50 to 70 percent)
with the potential for downsloping of the southwesterly flow off
the Ozark Plateau. However, confidence is lower in temperatures on
Wednesday with much larger NBM high temperature interquartile
ranges (5 to 8 F) due to a greater chance of showers and
thunderstorms. Either way, these temperatures could threaten the
going long streak of sub-90 F high temperatures at KCOU and KSTL.

Following Wednesday`s upper-level trough, global model guidance are
in general consensus that flow will become northwesterly Thursday
through Friday in response to upstream ridging over the Great
Plains. This pattern will result in another warming trend as well as
a low chance (20 percent, per ensemble model guidance) of showers
and thunderstorms accompanying one or more passing shortwave
troughs somewhere in the region.

Pfahler

&&

.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1048 PM CDT Fri Jun 13 2025

Main issue for the TAFs overnight will be the potential
redevelopment of more widespread IFR ceilings. Most guidance says
this will occur, although I think this is most likely near the
slow moving surface low which will be tracking northeast through
the St Louis metro overnight. Areas that see some clearing will be
more likely to fog in. This scenario is more likely in central
Missouri. Conditions should improve area wide through the day on
Saturday. Some scattered showers and thunderstorms are expected
again during the afternoon, but should for the most part stay east
of the TAF sites.

Kimble

&&

.CLIMATE...
Issued at 620 PM CDT Wed Jun 11 2025

St Louis still hasn`t reached 90 yet in 2025. This puts 2025 in
the Top 20 all time latest dates of the first 90 degree
temperature, and the latest in at least 30 years (Jun 19, 1995).
The all time latest first 90 degrees was July 4 in both 1961 and
1912. Records began in St Louis in 1874.

Columbia has also not yet seen a 90 degree reading in 2025. The
latest date of first 90 degrees on record was July 14, 1904.
Records began in Columbia in 1890.

Quincy reached 90 degrees on May 15 of this year.

Based on the current forecast, our next best chance to see 90
degrees is around June 17.

Kimble


&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Dense Fog Advisory until 9 AM CDT this morning for Audrain MO-
     Boone MO-Callaway MO-Cole MO-Knox MO-Lewis MO-Marion MO-
     Moniteau MO-Monroe MO-Ralls MO-Shelby MO.

IL...Dense Fog Advisory until 9 AM CDT this morning for Adams IL.

&&

$$

WFO LSX