308
FXUS63 KLSX 011920
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
220 PM CDT Tue Jul 1 2025

.KEY MESSAGES...

- Seasonable temperatures and dry conditions will persist through
  Thursday with warmer and more humid conditions returning on the
  4th of July into the holiday weekend.

- Dry conditions are expected through the 4th of July, but
  opportunities for showers and thunderstorms will be present over
  the holiday weekend into early next week.


&&

.SHORT TERM...  (Through Late Wednesday Night)
Issued at 219 PM CDT Tue Jul 1 2025

In the wake of Monday`s upper-level trough and cold front, deep,
northwesterly flow has filtered a drier and more seasonable airmass
into the region translating to temperatures in the 80s and dewpoints
in the upper 50s to mid-60s F across the CWA under large-scale
subsidence with only fair diurnal cumulus. As surface anticyclone
arrives tonight, conditions will be favorable for efficient
radiational cooling to near today`s dewpoints resulting in low
temperatures in the 60s F, upper 50s F in a few sheltered/low-lying
locations, as well as patchy river valley fog Wednesday morning
aided by increasing air-water temperature disparity.

On Wednesday conditions will be very similar today, with the only
difference being temperatures a degree or two warmer as low-level
flow becomes weakly westerly as the anticyclone very slow migrates
just south of the CWA. Patchy river valley fog will be possible
again late Wednesday night/early Thursday morning but conditions
will not be quite as favorable with repeated days of deeper BL
mixing.

Pfahler

&&

.LONG TERM...  (Thursday through Next Tuesday)
Issued at 219 PM CDT Tue Jul 1 2025

Thursday through Friday/4th of July, upper-level northwesterly flow
will give way to an amplifying ridge traversing the Upper/Mid-
Mississippi River Valley on Friday. Model guidance indicate that a
series of mid-level perturbations in conjunction with nocturnal LLJs
could result in some showers and thunderstorms across the Upper
Midwest early Thursday morning and again early Friday morning but 90
percent of ensemble model membership dissipates precipitation before
its able to reach northeastern MO/west-central IL. Largely dry
conditions will be accompanied by a continued warming trend as low-
level flow becomes more southerly. In response, high temperatures in
the 90s will become common by Friday with heat index values in the
mid-90s to near 100 F as dewpoints also rise into the upper 60s to
low-70s F.

Global model guidance is coming into better agreement that the upper-
level ridge will migrate into the Great Lakes and allow a series of
upper-level troughs or shortwave troughs to enter the Mid-
Mississippi River Valley over the weekend into next week with a cold
front arriving around Sunday and potentially lingering in the
vicinity of the region into next week. This evolution will lead to
opportunities for showers and thunderstorms at times from Saturday
onward with ensemble model membership with measurable precipitation
varying between 30 and 60 percent. As a result, there is also
decreasing confidence in temperatures through that time with the NBM
75th percentile only slightly cooling but the 25th percentile
cooling closer to average into early next week.

Pfahler

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1227 PM CDT Tue Jul 1 2025

Dry and VFR flight conditions are expected through most of the TAF
period with the exception of patchy river valley fog early Wednesday
morning, most likely impacting KSUS and KJEF. Winds will be light
and transition from north-northwesterly this afternoon to west-
northwesterly upon arrival of a surface high pressure center.

Pfahler

&&

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

$$

WFO LSX