404
FXUS63 KLSX 021113
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
513 AM CST Mon Nov 2 2026

.KEY MESSAGES...

- A strong system brings gusty winds, widespread rain, and a few
  thunderstorms to the region tonight through Wednesday. Other
  than a few 40-50mph gusts in the afternoon, mainly along and
  east of the Mississippi River, few impacts are expected.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 302 AM CST Mon Nov 2 2026

Weak upper level ridging remains in place at this hour, trapping a
thin layer of moisture about 500-1000ft above the surface and
promoting abundant cloud cover. Some weak warm advection evident at
925mb is promoting patchy drizzle amidst these clouds, which should
continue through sunrise. Meanwhile, the axis of our much-advertised
amplified trough that will bring our first widespread rainfall in
quite some time is just now approaching the western edge of the
Rockies. Strong, broad diffluence overspreads the Front Range with
leeside cyclogenesis occurring centered across western Nebraska as a
result. This system, which will eventually be the catalyst for our
more active mid-week weather, is promoting an expansive area of
showers from the High Plains to Upper Mississippi Valley. This
activity will only glance our northern and western counties today,
keeping most of the region dry to start the work week. Temperatures
should be a little bit warmer today compared to yesterday,
especially as the surface pressure gradient tightens and warm
southerly low-level flow strengthens. The overcast low stratus will
work against this warming, though we`ll likely end up several
degrees above normal for early November.

The system gradually approaches the Mid-Mississippi Valley this
evening, at which point we would be squarely in the cyclone`s warm
sector. Some warm advection showers ahead of the front can be
expected after midnight with a stout 40-50kt low-level jet in place.
By most guidance depictions, the waves of pre-frontal showers
arrive in central Missouri between 4-6am with the cold front
lagging behind. Jet-level ascent and mid-level forcing for the
rain seems appreciable, all of this amidst near-record PWATs.
That said, instability is at a significant premium (MUCAPE
struggles to exceed 500 J/kg in the most bullish guidance, with
lower and capped MLCAPE). Model soundings also depict several
warm layers aloft that would promote negative buoyancy and
inhibit robust updrafts. While some of the shower downdrafts
could mix the strong LLJ winds to the surface, as is typical in
strong kinematic systems like this, the poor low-level lapse
rates evident in all guidance suggests that the damaging wind
potential is low (<10%) in central Missouri overnight. These
slow-moving systems with flow parallel to the front would also
normally be concerning for heavy rain and flooding, but the
antecedent dryness and inefficient rain processes preclude such
threat this time.

The strong wave and surface low continue their slow progress east
through the morning, but guidance continues to depict a
reinforcing shortwave in the cyclonic flow aloft that slows the
larger trough`s progress. It also seems to tilt its axis
negatively, pinching off the diffluent flow ahead of the wave,
weakening height falls, and occluding the surface low. All of
these impacts to the trough structure negatively affect the
potential for strong convection and damaging wind on Tuesday, as
instability really struggles to advance poleward. The showers
that develop, likely in broken lines and waves given the strong
forcing-parallel shear, will be shallow and occurring amidst
very poor lapse rates. Shallow, warm equilibrium levels will
keep thunderstorm chances pretty low. Any hope of stronger gusts
(40-50mph) from the convection would need to take advantage of
locally-steeper lapse rates if breaks of sun can develop. The
main source of the gusty winds will be thanks in large part to
the isallobaric wind component as the system intensifies,
particularly in far eastern Missouri and western Illinois.
Otherwise, strong to severe convection is not expected. As such,
we continue to not explicitly message the SPC Day 2 Marginal
(Level 1) Risk for severe thunderstorms. In the very unlikely
event that instability can develop, that damaging wind (and a
low tornado) threat would materialize.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Issued at 302 AM CST Mon Nov 2 2026

Rain largely comes to an end from west to east overnight Tuesday
into Wednesday morning, with the (likely occluded by this point)
front lagging an hour or two behind the clearing line. Some
anafrontal showers can be expected on Wednesday across the region,
though there will be plenty of dry time. Winds behind the front will
be more westerly, if not southwesterly, which won`t allow for a
drastic airmass change and significant cooling. Still, dewpoints
will fall into the 40s and temperatures will drop compared to
previous days and approach more usual values for early November.
Situations like these (dry air rushing in without significant
cooling) can lend themselves to elevated fire danger, however the
widespread wetting rain on Tuesday will tamp down any fire threat.

Aloft, amidst longwave troughing that encompasses most of the CONUS,
the closed wave affecting our weather will gradually shunt
downstream as additional reinforcing waves arrive. While largely
moisture-starved due to the longwave stunting any Gulf influence,
they should feature enough forcing to result in some light
precipitation at times (particularly on Friday, when another cold
front arrives). Exactly where and when these occur is unsure, but
LREF ensemble guidance suggests areas of light precipitation
(less than 0.05 inches) intermittently during this time.
Temperatures will be held in check as a combination of weak cold
advection and cloud cover stunt any diurnal warming. Additional
waves track through the region this weekend into early next
week, bringing more precipitation chances, but confidence in
this aspect of the forecast is quite low. It does seem likely
that, while somewhat more normal temperatures remain favored
into the end of the week, no signs of a dramatic cooldown are
evident beyond that.

&&

.AVIATION /12Z TAFS THROUGH 18Z TUESDAY/...
Issued at 504 AM CST Mon Nov 2 2026

Very low stratus continues to keep flight conditions degraded at
this hour, ranging from IFR to LIFR. Mist and drizzle that
reinforced these poor conditions overnight is largely over.
Marginal improvements are expected over the next several hours
as the weak subsidence aloft that kept the low stratus in place
erodes. A strong synoptic wave and surface low will gradually
approach from the west today, strengthening winds out of the
south. Rain eventually arrives at all terminals from west to
east late tonight into Tuesday ahead of a cold front. Flight
conditions are unlikely to improve to VFR until after this
feature passes on Wednesday.

&&

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

&&

$$

SHORT TERM...MRB
LONG TERM...MRB
AVIATION...MRB