452
FXUS63 KLSX 022055
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
255 PM CST Mon Mar 2 2026

.KEY MESSAGES...

- Spring-like weather is expected this week with mild temperatures
  and frequent rounds of showers and thunderstorms.

- Though limited, the best chances for more organized
  thunderstorms in our area are on Wednesday and again Friday or
  Saturday.

&&

.SHORT TERM...  (Through Late Tuesday Night)
Issued at 253 PM CST Mon Mar 2 2026

A pattern change has already begun across North America and we`re
entering into a much wetter pattern than we`ve seen in 6 months or
more. Aloft we see split flow across the western US where a northern
stream ridge remains where it has been for most of the winter, while
a southern stream trough is progressing slowly through the Great
Basin. It`s this trough, and subtle waves progressing eastward ahead
of it, that bring our next rain chances tonight through Thursday.
Looking at visible satellite, or just looking out the window, we see
that plenty of low level moisture remains in place across the region
in the wake of yesterday`s wave. This is all within a diffuse
frontal zone which is expected to sharpen overnight into a warm
front as southerly flow to the south of it ramps up. This front
remains stationary or wobbles back and forth across our area over
the next several days serving as the primary focus for showers and
thunderstorms.

Our first round begins overnight tonight as low level moist
advection intersects with the developing warm front. Instability
remains limited and elevated, so although a few lightning strikes
are possible we do not expect severe weather. But this opening salvo
will begin to dampen soils ahead of the next several rounds of rain.
Although showers and storms push ENE across the region on Tuesday,
we may not see a full break in the rain along the front before the
next round begins Tuesday night. Southerly flow increasing to the
south of the front keeps that moist low level flow going and helps
to slide the front ever so slightly northward. This focuses Tuesday
night`s round of showers and thunderstorms further north across
northern Missouri into Illinois. With another day`s worth of low
level moisture transport, there will be more instability available
for thunderstorms. However, convection will be elevated north of the
warm front limiting the severe weather potential. If multiple rounds
of storms are able to develop there will be a better potential for
training to produce heavy rainfall with this round as the mid level
steering flow is roughly parallel to the initiating boundary.
However confidence remains fairly low in any flash flood potential
as the boundary itself will likely be drifting northward with time.

Temperatures over the next several days will be highly dependent on
the position of the frontal boundary. North of the front conditions
remain cool and humid with constant cloud cover and periods of rain.
Here temperatures max out in the upper 40s to low 50s. South of the
front, though, much warmer air is available as 60s will be far more
common. In fact, if some breaks in the clouds occur then some 70s
may be observed as early as Tuesday. NBM probability of 70 degrees
shows a sharp gradient south of I-70 on Tuesday where the
probability ramps up from 10 percent to 80 percent over just about
50 miles reflecting the uncertainty in the frontal location and
cloud cover.

Kimble

&&

.LONG TERM...  (Wednesday through Next Monday)
Issued at 253 PM CST Mon Mar 2 2026

On Wednesday the western trough finally moves out through the Plains
in response to a much deeper trough digging into the West Coast. As
it does so we`ll have one more solid push of moist advection in
advance of a developing surface low tracking in or near our forecast
area. This most likely plays out as another band of thunderstorms
along and north of the warm front with the potential for additional
development in the warm sector south of the warm front and ahead of
a cold front. With the warm frontal activity, storms will again be
elevated and only have a threat for marginally severe hail. In the
warm sector to the south, though, surface based instability will
become available in an environment characterized by moderate speed
and directional wind shear. This would offer up the best potential
for severe thunderstorms in our area this week. However, that all
depends on where this warm sector develops and how much surface
based instability can develop. There`s no doubt there will be plenty
of moisture as we will have had days of flow off the Gulf to advect
moisture northward. But there`s a lot of uncertainty on how far
north the warm front gets and how much cloud cover could exist to
prevent strong destabilization. Among the 12Z low resolution
ensemble guidance, generally 20 to 40 percent of members produce
surface CAPE of 500 or more Wednesday afternoon which has come down
10 to 20 percent from last night`s 00Z guidance. So while Wednesday
does look like the next best chance for severe weather, confidence
in it occurring in our forecast area is decreasing.

The upper wave and surface low are somewhat slow to move out on
Thursday, so we still have some rain chances in through the first
half of the day on Thursday. But we will eventually get at least a
brief period of dry weather in the wake of that trough and behind
the surface cold front. But it really does not last very long. The
next larger trough developing over the western US causes
southwesterly flow to quickly redevelop over the Plains Thursday
into Friday. Guidance is in good agreement on an initial shortwave
trough pushing out across the Plains Friday into Saturday. This
initiates another surge of moisture northward ahead of the trough.
The surface front which only barely made it through our area on
Thursday quickly begins lifting back north as a warm front on
Friday. Once again, showers and thunderstorms are possible in the
vicinity of this front as it lifts northward. While there is strong
confidence that we will eventually get into the warm sector ahead of
this wave, there is uncertainty on the timing of the trough and
associated cold front that eventually makes its way southeast
through our region. Latest guidance favors this front arriving too
late on Friday to take advantage of diurnally maximized surface
based instability, but also too early on Saturday for that
instability to redevelop. A Friday night frontal passage would have
much more limited surface based instability locally. The severe
weather threat on Friday therefore is greater to our west closer to
this cold front`s position during peak heating. This could change of
course if the speed of the front changes.

As far as temperatures go, the location of the surface frontal
boundary and associated cloud cover are the biggest factors at play.
South of the front in the warm sector will exist an increasingly
warm and humid environment with daytime temperatures in the 70s or
even 80s and dewpoints well into the 50s or even 60s. Friday is the
most likely day that our region will be fully in the warm sector and
able to feel the full extent of this warmth, but Saturday has the
potential to be just as warm if the front slows down just a bit.
While NBM interquartile range (IQR) is quite small on Friday, it may
not be fully capturing the potential for clouds and showers on the
front to prevent full heating. The IQR is much higher on Saturday
due to the timing of the cold front, but the higher end values on
Saturday are just as high as those on Friday indicating that it
would be another warm day if the front slows down.

While there`s strong confidence that the cold front will eventually
move through our region and bring a break from the warmth and
frequent rainfall, the front doesn`t make it far enough south to
fully keep the Gulf moisture at bay. Guidance varies later this
weekend into early next week on how quickly to push this moisture
back north again, but with the front stalled not far to our south we
can`t rule out additional rounds of rain all the way through the
middle of next week.

Kimble

&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1128 AM CST Mon Mar 2 2026

IFR flight conditions will persist through the TAF period due to
persistent low ceilings. Drizzle is forecast to shut off early
this afternoon, and winds will become variable tonight. After
midnight, rain will move into the region impacting all terminals
and potentially dropping conditions to LIFR at times. Rain is
expected to exit in the middle of the morning with a chance of
rain persisting through 18z. Ceiling improvement to MVFR and
additional rain are forecast just outside of the period.

Jaja

&&

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

$$

WFO LSX