895
FXUS63 KLSX 130725
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
225 AM CDT Mon Jul 13 2026

.KEY MESSAGES...

- Seasonable summer heat and humidity is expected for several
  days with highs returning to the 90s. Heat index values
  approach 100-105 Thursday through Saturday.

- Most locations will remain dry with precipitation chances
  limited to the southern sections of the forecast area.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 224 AM CDT Mon Jul 13 2026

An unprecedented upper level ridge is building over the Upper
Midwest today with 500mb heights reaching around 600 dam. This ridge
draws many parallels to the July 1995 heat wave with record
temperatures possible across the northern U.S. While this brings
attention to the northern U.S., 500mb heights reach the 90th
percentile along the I-70 corridor and near the 99th percentile
around KUIN. The upper ridge is vertically stacked over mid-level
heights of similar percentiles, resulting in persistent,
unidirectional easterly flow.

Fortunately, in this scenario, the ridge is displaced further north
than the July 1995 event. With the local region on the southern
cusp of the ridge, easterly flow will help stave off higher
dewpoints more typical with a southwesterly flow component. Deep
subsidence is expected to secure a dry and warm start to the week.
Today`s dewpoints in the mid to upper 60s aren`t necessarily
considered a dry heat, but more manageable than 70s. Highs in the
mid to upper 80s will barely register a heat index for a relatively
comfortable afternoon by mid-summer standards.

On Tuesday, a cutoff upper level disturbance retrogrades west-
northwest over the Gulf States, placing the area at its northern
fringes. This pulls dewpoints back into the 70s from east to west
with a slight increase in temperatures. Tuesday feels a little less
comfortable than today and while global guidance differs slightly on
the northward extent of the system and resulting precipitation
chances, the dry lean in the hi-res guidance makes more sense given
the subsidence that would have to be overcome to produce any
sensible precipitation potential.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Issued at 224 AM CDT Mon Jul 13 2026

The long range pattern is one of persistence and comparison to
climatological means with subtle details having an increasing
influence on local conditions. The period will generally be
characterized by increasing moisture and small step increases in
temperatures each day through the end of the period. The best
chances for rain (20-40%) come Wednesday afternoon over southeast
Missouri, but this may be overdone.

Global guidance is in decent agreement with weakening the northern
ridge from its record-level heights over the second half of the week
as it takes on a southeast to northwest orientation through the
Midwest. NBM data shows small IQR spread (<5 degrees) through
Saturday before increasing slightly Sunday. Multiple vort features
rotate around the southwestern edge of the upper ridge, while some
semblance of mid-level ridging remains. The difference comes in the
late week period when the northern mid-level ridging breaks down and
gives way to a strengthening mid-level ridge over the Gulf. Easterly
flow veers out of the south/southwest, drawing moisture in from the
western Gulf. Temperatures in the 90s, combined with dewpoints in
the 70s will make conditions a little less comfortable with
afternoon heat index values approaching 100 degrees along and east
of the Mississippi River Wednesday. This trends continues through
the week with an expansion of highs in the 90s and heat index values
in the 100-105 range by the end of the week. This may approach heat
advisory criteria using the 4 day rule of 100+ heat indices. The
limiting factor is both Wednesday and Sunday, when HI values are
rather limited coverage and marginal compared to Thursday through
Saturday.

&&

.AVIATION /00Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1024 PM CDT Sun Jul 12 2026

Dry and VFR conditions are expected through the period with
light winds. The only exception will be patchy river fog that
will affect SUS between 08-12Z.

&&

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

&&

$$

SHORT TERM...Maples
LONG TERM...Maples
AVIATION...Britt