966
FXUS63 KLSX 281959
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
259 PM CDT Thu May 28 2026

.KEY MESSAGES...

- There is a 40 to 70 percent chance of showers with a few rumbles
  of thunder on Friday in central/southeastern MO. Lower chances
  linger through Monday, but there will be plenty of dry time.

- Temperatures will remain seasonable but variable through next
  week.


&&

.SHORT TERM...  (Through Late Friday Night)
Issued at 258 PM CDT Thu May 28 2026

An overhead upper-level ridge, part of a larger continental-scale
Omega Block, continues to keep the CWA dry along as a dissipating
back door cold front also arrives from the northeast, which will
briefly inject drier air this evening and keep ongoing showers and
thunderstorms across AR and southwestern MO from advancing northward
into CWA. Dry conditions will persist until early Friday morning as
an upper-level trough lifts northward into the Mid-Mississippi River
Valley and showers with a few rumbles of thunder reach central and
southeastern MO along a belt of low to mid-level moist isentropic
ascent. Overall forcing ebbs after Friday morning as the attendant
trough fractures and slows upon encountering the aforementioned
ridge axis, leading to more isolated to scattered coverage of
showers and thunderstorms during the afternoon along/west of the
Mississippi River where moisture will be greatest through that time.
Even outside of precipitation, widespread clouds will overspread the
CWA leading to cooler high temperatures, but exact values are
uncertain with the NBM interquartile range spread from the mid-70s
to low-80s F. These values will be sensitive to persistence of
showers and thunderstorms as well as thickness of cloud cover.

CAMs and short-term model guidance indicate another potential uptick
in showers Friday night/early Saturday morning as a lobe of
vorticity from the fracturing trough and/or MCV meanders, supported
by 30 to 50 percent of ensemble model guidance across a broader
portion of the CWA.

Pfahler

&&

.LONG TERM...  (Saturday through Next Thursday)
Issued at 258 PM CDT Thu May 28 2026

Saturday through Monday, the dissipating upper-level trough will
give way to another period of ridge amplification and rising
heights, lapsing during passages of additional potential MCVs
emanating from thunderstorms across the Central Plains. These
potential MCVs and diurnal instability will be the main drivers of
showers and thunderstorms in this time period, which leads to
uncertainty on the exact coverage and timing other than that
afternoon and evening is most preferred and there will be much more
time dry vs wet. Ensemble model guidance depicts highest
probabilities (20 to 50 percent) of measurable rainfall along and
west of the Mississippi River, tied to where moisture and
instability will be greatest. It is worth noting that these
probabilities have actually increased locally in the last 24 hours
with a trend toward less support for any back door cold fronts to
shunt moisture back southwest of the CWA. High temperatures each day
are not completely clear due to these showers/thunderstorms and
associated cloud cover, but a gradual warming trend is captured by
the NBM with overall less and less clouds each day and high
temperatures increasingly in the 80s F.

Tuesday, global model guidance is coming into better agreement that
a more prominent back door cold front will pass through the CWA
around Tuesday with subsequent low-level easterly to northeasterly
flow filtering a drier and cooler airmass into the Mid-Mississippi
River Valley. However, there is uncertainty in how much temperatures
will cool Tuesday through Wednesday due to differences in frontal
timing and strength along with how long easterly/northeasterly flow
is maintained. The range in the NBM spans from temperatures
remaining steady to cooling into the 70s F. With increasingly dry
air (below 25th climatological percentile) and a lack of strong
forcing, the probability of measurable rainfall is around 20 percent
or less across the CWA.

Pfahler

&&

.AVIATION...  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1217 PM CDT Thu May 28 2026

Dry and VFR flight conditions will continue into tonight, before
showers, maybe a rumble of thunder, and lower ceilings begin to
enter central and southeastern MO, impacting KCOU and KJEF with MVFR
flight conditions Friday morning. Across the remainder of the area,
confidence is much lower in a deviation from VFR flight conditions
through the afternoon, but a few showers cannot be ruled out.
Easterly winds will veer slightly toward southeasterly on Friday.

Pfahler

&&

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

$$

WFO LSX