185
FXUS63 KLSX 100758
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
258 AM CDT Mon Jun 10 2024

.KEY MESSAGES...

- Below normal temperatures are expected through Tuesday, with
  summer-like warmth returning to end the week.

- Much of the region will remain dry through the week.

&&

.SHORT TERM... (Through Tuesday Night)
Issued at 253 AM CDT Mon Jun 10 2024

Current water vapor imagery shows the Middle Mississippi Valley
beneath northwesterly flow on the western periphery of an upper-
level trough over the eastern CONUS. An area of high pressure at the
surface resides over the Northern Plains and Upper Midwest per
surface observations, and this high will gradually shift south-
southeastward through the day today. This surface high and deep
northwesterly flow will keep conditions calm and cooler today, with
temperatures this afternoon topping out 5-10 degrees below
climatological normals.

Tonight into Tuesday, the upper-level trough will begin to shift
eastward as subtle ridging briefly builds into the Midwest. As a
result, the surface high will shift eastward, returning southerly
low level flow to the area for Tuesday. This flow will begin
advecting warmer air into the CWA, bumping temperatures up closer to
climatological normals during the day. A weakening cold front will
approach the CWA during the afternoon and evening, and some recent
runs of CAMs show isolated, weak convection along this front near
and in the CWA. However, given the weakening nature of the front and
height rises due to a ridge building into the region from the west,
a dry forecast has been maintained for now.

Elmore

&&

.LONG TERM... (Wednesday through Sunday)
Issued at 253 AM CDT Mon Jun 10 2024

The upper-level ridge over the western CONUS will begin broadening
and expanding eastward toward the Middle Mississippi Valley on
Wednesday per guidance consensus. Between the building ridge and a
surface high positioned east of the area, southerly to southwesterly
flow will continue to advect warm air into the CWA. By Thursday,
deterministic guidance and ensemble means show 850 mb temperatures
rising to around 20 degrees C, climatologically supporting surface
temperatures in the upper 80s to mid 90s.

How long this warm up will last is uncertain, as through the day on
Thursday, a shortwave will track along the U.S.-Canada border and
push a surface low through the Great Lakes region. This low`s cold
front will slowly sag southward through the Midwest and approach the
CWA late Thursday. Guidance diverges at this point on the progress
of the front through the CWA into Friday, with a more northerly
solution stalling and dissolving the front over the CWA, while a
more southerly solution has the front clearing the CWA prior to
dissolving. Even with the more southerly solution, guidance
consensus is that the post-frontal airmass will merely take the edge
off of surface and mid-level temperatures. Warmer ensemble members
continue Thursday`s heat into Friday and through the weekend, while
cooler members show about a 5-10 degree drop in temperatures Friday
compared to Thursday. Even if temperatures are able to cool,
guidance consensus is that a warm front will lift through the region
Saturday into Sunday bringing more summer-like conditions right back
to end the weekend.

As for rain chances, convergence along Thursday night`s cold front
is weak, and the shortwave and surface low`s positioning well
northeast of the area limits upper-level support for convection.
However, there is a strong signal for convection to develop along
the front among guidance somewhere across the Midwest due to the
unstable airmass south of the front. If convection is to impact the
CWA, the best chances reside over northeastern Missouri and west-
central Illinois. However, given the spread of solutions, only a 30-
40% chance will be maintained in this area for now. Additional
rounds of rain are possible for portions of the area if disturbances
traversing the northern periphery of the ridge pass near the area.
However, there is not a clear signal for such activity through the
extended, so a mainly dry forecast has been maintained outside of
Thursday night.

Elmore

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1025 PM CDT Sun Jun 9 2024

Dry, VFR flight conditions will persist through the end of the TAF
period with diurnal cumulus developing during the day on Monday.
Surface high pressure will continue to move into the region,
favoring light north-northwesterly winds overnight. By Monday
morning, winds will become northerly.

MMG/Kimble

&&

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

$$

WFO LSX