358
FXUS63 KLSX 171753
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1253 PM CDT Sun May 17 2026

.KEY MESSAGES...

- Isolated showers and thunderstorms are possible early this
  morning for parts of northeast MO/west-central IL with the
  strongest storms capable of strong wind gusts.

- Additional thunderstorm chances return early this week with a
  more widespread severe weather threat possible along a slow
  moving cold front Monday night into Tuesday.


&&

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 251 AM CDT Sun May 17 2026

For a majority of the area, conditions have been tranquil this
Saturday night with light easterly/southerly flow maintaining
temperatures in the upper 60s/lower 70s across the region. Further
to the north and west, across far northern MO/southern IA and points
west, several clusters of intense convection have been persisting
through the night. Across northern portions of our CWA, near
northern MO/west-central IL, this activity has been limited to
mostly stratiform rain showers along with occasional lightning as
the more intense convection has lifted into southeast IA. All of
this convection has continued to feed off a robust and broad 40-60kt
southerly LLJ that is centered across western MO and KS along with a
weak passing mid/upper level shortwave. One specific cluster of
convection that has the best chance of making into the area, is now
across northwestern MO. With it`s current trajectory, it would be
nearing northeast MO/west-central IL around 10z this morning.
However, with the greatest deep-layer shear displaced to the
northwest and the passing mid/upper level shortwave also lifting
northeastward away from the region, this convection is forecast to
quickly weaken as it moves eastward. A low chance (20%) exists that
remnant convection makes it into northeast MO/west-central IL
between 10-14z this morning. Any remaining stronger thunderstorms
would be capable of scattered wind gusts up to 40-50mph and frequent
lightning.

Aside from the low chance for scattered showers and thunderstorms to
the north early this morning, dry conditions are forecast for the
entire area today. The large-scale pattern features amplification of
the mid/upper-level flow today as a trough builds out west and a
ridge to the east, leading to rising heights aloft, which should
result in mostly sunny conditions. At the surface, the pressure
gradient tightens today resulting in strong southerly winds gusting
to near 30mph by this afternoon. All of these elements will aid in a
substantial warmup today, with highs forecast to reach the upper
80s/lower 90s this afternoon.

A baroclinic zone is progged by guidance to generally be positioned
near central KS northeastward into WI Monday into Tuesday, with
warm/moist flow on the equatorward side and cool/drier flow on the
poleward side. Similar to yesterday, convection is modeled by high
resolution guidance to initiate along this boundary out west both
this evening and Monday evening. By tonight, quick upscale growth
and eastward progression of this convection is forecast with CAMs
indicating this activity may be nearing central/northeast MO just
after midnight (06z Monday). Convection that approaches the area
later tonight will be outrunning a more favorable deep-layer shear
environment, along with decreasing instability, which should induce
weakening with eastward extent. Most of the CAMs indicate a decaying
convective system pushing into the area early Monday morning with
potentially widespread showers and scattered thunderstorms lingering
into the day. If instability is able to recover across portions of
the area Monday afternoon/evening, then any lingering activity may
be able to intensify. With uncertainty regarding the evolution of
lingering showers/storms on Monday, confidence is low regarding the
extent of severe weather that may be realized across the area on
Monday.

Peine

&&

.LONG TERM... (Monday Evening through Saturday)
Issued at 251 AM CDT Sun May 17 2026

By late Monday evening, a shortwave embedded within the longwave
trough ejects into the Great Plains, which once again leads to
convective initiation along the baroclinic zone across KS/NE.
Additionally, this mid-level feature triggers lee-side surface
cyclogenesis across the Central Plains/Midwest. This surface low is
modeled to lift northeast into the Midwest on Tuesday, which begins
to slowly shift the quasi-stationary baroclinic zone southeastward
as a cold front. As of now, it is unclear if the convection across
KS/NE stays rooted to this slow moving cold front early on Tuesday
or if it quickly outruns it to the southeast. If this convection
remains tied to the cold front, with better forcing for ascent and
moisture convergence, storms would be able to stay strong/severe for
a longer duration as they approach the area early on Tuesday.
Regardless, large hail, damaging winds, and tornadoes all remain
possible on Monday and Tuesday while this slow moving cold front
interacts with our unstable airmass as it pushes through the area.

Cooler conditions filter in behind the cold front thanks to modest
low-level CAA as a surface high slides southward out of Canada. In
fact, LREF IQRs on Wednesday lower to values centered on
temperatures 15 degrees cooler than Tuesday, with highs across the
area largely in the upper 60s. Quasi-zonal flow aloft envelops the
region Wednesday into the weekend with long-range guidance unveiling
potential mid-level shortwaves propagating across the area. Without
any large-scale systems forecast, moisture return from the Gulf
remains limited, which should allow for prevailing dry conditions.
By the end of the week, the general trend of LREF temperature IQRs
is a gradual warmup to near average temperatures by next weekend.

Peine

&&

.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1240 PM CDT Sun May 17 2026

VFR flight conditions and gusty southerly flow is expected to
prevail across the area through the evening. A line of
thunderstorms will develop over Kansas and Nebraska this evening
and move east through the night. It will eventually move into
central and northwest Missouri late tonight into Monday morning.
Guidance varies on the speed of the line, and therefore the
arrival time into our area. However the general consensus is that
the line will be moving into central and northeast Missouri
between 08Z and 12Z. The line will continue moving east into our
area through the morning. Gusty winds and IFR visibilities in
heavy rain will be possible.

Carney

&&

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

$$

WFO LSX