612
FXUS63 KLSX 231901
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
Issued by National Weather Service Kansas City/Pleasant Hill MO
201 PM CDT Tue Jun 23 2026

.KEY MESSAGES...

- Seasonably cool conditions will continue through the work week.

- Showers and thunderstorms are forecast (70-80%) Thursday into
  Friday with the main concern being heavy rainfall potentially
  leading to flash flooding.

- A return to warm and humid summerlike conditions is anticipated
  late this weekend into the start of next week.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 158 PM CDT Tue Jun 23 2026

Today and Tonight: Latest surface analysis revealed high
pressure centered over the Great Lakes and extending south
across eastern Missouri. PWATs this morning are less than 1.00
(or near the 25th percentile for this time of year), which has
allowed for mostly clear skies across the area. The one
exception to this is near Columbia where some cumulus have
formed and that are on the edge of the higher moisture gradient.
Expect highs today in the upper 70s to lower 80s. Tonight,
surface high pressure will slide east of the region with lows
generally in the lower 60s. No precipitation is expected.

Wednesday: Surface high pressure will be located over the Ohio
River Valley with southerly flow over Missouri and western
Illinois. At 250 mb, a weak jet streak (70 - 80kt) is forecast
to traverse Kansas and Missouri ahead of a stronger shortwave
over southern Canada. An approaching cold front from the
northwest working in tandem with the jet streak will provide
more than sufficient lift. PWATs rise to around 1.5 with
sufficient instability (MLCAPE around 1000 J/kg). The highest
instability will be across our northwestern and western zones,
or closer to the deeper moisture and better lapse rates. This is
also where the highest chance of thunderstorms (20 - 50%) exist
tomorrow, closer to Columbia, MO. Thunderstorms across the
western zones will then start to wane Wednesday night into
Thursday morning as we lose afternoon heating and the convergent
side of an upper level jet streak moves overhead.


&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Issued at 158 PM CDT Tue Jun 23 2026

Thursday and Friday: In the mid-levels of the atmosphere, a
shortwave will rotate southeast over the Great Lakes with a
surface cold front stalled across central Missouri. At 250 MB,
the 100 - 120 kt jet streak will progress eastward allowing the
region to fall in the RRQ. Simultaneously, at 500 mb a shortwave
will eject east across Kansas along the stationary front.
Widespread showers and thunderstorms (70 - 90%) are forecast
with the potential for heavy rainfall. This is due to multiple
rounds of training thunderstorms possible. Taking a look at WPC
cluster analysis, reveals that models are in fairly good
agreement that heavy rainfall will likely fall from Thursday
into Friday somewhere across the state of Missouri. A majority
of CMC/ GEPS members show the heaviest QPF over central
Missouri, while the EPS is slightly further south and the GEFS
is generally slightly further north. Storm total rainfall of 1 -
3 with locally higher amounts of precipitation is possible and
dependent upon the track of the mid-level low and stationary
front. WPC currently has the area in a slight risk for excessive
rainfall. A Flood Watch might be required.

Saturday- Monday: Precipitation will slowly come to an end from
west to east as the stationary front washes out and heads north.
Over the western United States, a deepening closed low will
allow heights to rapidly rise over the central United States. As
such, high temperatures will begin to warm on Saturday. By
Sunday into Monday, mid-level heights will rise to around 595 dm
with highs in the mid 90s. Dewpoints will also be in the 70s,
with heat index values well into the triple digits. Heat
products might be required starting Sunday and continuing into
Monday.

&&

.AVIATION /18Z TAFS THROUGH 00Z THURSDAY/...
Issued at 1233 PM CDT Tue Jun 23 2026

Surface high pressure remains centered across the Great Lakes
region south towards KSTL. The ridge will continue to slowly
move east this afternoon with winds veering from the east and
then southeast. Only some cumulus are expected at KCOU and KJEF.

Tonight, surface high pressure will be east of the terminals
with light southerly winds. A mid level cloud deck will start to
spread in from the west, but VFR conditions are expected to
continue. During the day Wednesday, moisture will return with a
widespread CU deck forecast with winds out of the southwest. A
weak cold front will then approach the terminals from the west.
For now, we have left the mention of precipitation out of the
TAFs given the uncertainty of when showers and thunderstorms
will initiate. This will likely need to be added in future TAF
issuances though.

&&

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

&&

$$

SHORT TERM...BSH
LONG TERM...BSH
AVIATION...BSH