Area Forecast Discussion

931
FXUS63 KLSX 031837
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
1237 PM CST Tue Nov 3 2026

.KEY MESSAGES...

- Widespread showers and isolated thunderstorms along with
  breezy southerly winds (gusting 30-40 mph) are expected across
  the area today ahead of a cold front.

- A marginal (level 1/5) severe weather threat exists today,
  though storm development remains conditional. If severe storms
  manage to form, the main threats will be damaging wind gusts
  and a brief tornado.

- Temperatures closer to seasonable normals are forecast by the
  end of the week.

&&

.UPDATE...
Issued at 1237 PM CST Tue Nov 3 2026

As of 18z, a nearly stacked cyclone was centered over northwestern
Missouri. The primary cold front associated with this low extended
to the southwest into extreme SE KS and NE OK, with a secondary cold
front reaching south/southeast of the low into south-central MO
along the leading edge of the dry slot. The atmosphere ahead of the
secondary front is characterized by relatively high dewpoints and
SSE surface winds. Accordingly, there is 250-500 J/kg of MLCAPE
across eastern MO and western IL. With effective bulk shear in
excess of 50 kts and 0-1km shear in the 30-40 kt range, the
atmosphere remains at least marginally supportive for severe storms
capable of producing damaging winds or a tornado or two. However, up
to this point, areas ahead of the secondary front have remained
capped, significantly limiting the ability for these showers to
develop into thunderstorms.

Between the fronts mentioned above, the atmosphere is less capped,
but dewpoints are lower, surface winds are out of the SSW, and the
low level jet is weaker. This points to an atmosphere less favorable
for severe storms, especially those capable of producing tornadoes.
While we still may see a few thunderstorms develop in these areas
given strong forcing associated with the approach of the primary
front and vorticity advection associated with the upper low, my
confidence in severe storms occurring is low given the above
limiting factors.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 310 AM CST Tue Nov 3 2026

Recent mid-level water vapor imagery reveals broad southerly flow
enveloping the region early this morning as a rather amplified
mid/upper-level trough axis swings into the Great Plains. The
surface reflected cyclone is across eastern KS with a swath of
ongoing showers and thunderstorms across eastern OK and KS as of 07z
this morning. As all of these features lift northeastward,
widespread showers along with isolated thunderstorms gradually make
their way through the area today. A strong surface pressure gradient
will result in peak sustained winds of 15-20mph (gusting ~35mph)
early this morning through the early afternoon timeframe. By later
this evening, winds should slightly lower to sustained values of 10-
15mph (gusts ~20-25mph). With strong (40kt) winds just above the
surface today, any showers/weak storms or breaks in cloud cover
could allow these gusts to briefly mix down resulting in isolated
non-convective wind gusts over 40mph through this afternoon.

Model guidance is in good agreement that the eastward motion of the
mid-level trough continues to slow through the day as it begins to
lift northward and phase with the northern stream. As a result,
height falls aloft will be gradual and fairly weak over the area,
leading to a scenario that does not favor the development or support
for strong to severe thunderstorms. On the other hand, wind shear
will not be in short order, with 30-40kts of 0-6km bulk shear
accompanying pockets of 200-330 m^2/s^2 of 0-1km SRH. The limiting
factor with this setup still appears to be the lack of instability,
with both the HREF/RRFS indicating SBCAPE values of only 250-350
J/kg, which is has gone up slightly over the last 24 hours.
Regardless, with the abundant shear in place, this little amount of
instability may not be enough to produce organized or sustained
updrafts as convective attempts might tend to get sheared apart.
However, low-level curvature in hodographs signals that if some
convection becomes organized/sustained for even a brief window, a
weak tornado or two is possible. Along with that, a threat for
damaging winds could accompany a few of the stronger storms given
the 40kt+ winds just above the surface. As of now, the best overlap
of sufficient shear and better instability looks to be this
afternoon across central/northeast MO, just ahead of the approaching
cold front. The favorable overlap of these two parameters should
fade with eastward extent/later in the evening, when instability
lowers even further after sunset.

The cold front extending to the SSW from the surface cyclone pushes
through the area this evening and exits tonight, veering winds from
southerly to westerly. Low-level winds behind this boundary will be
blowing nearly parallel with the thermal gradient, resulting in very
little CAA. In addition, an upstream trough currently across CA,
will quickly move eastward and slide in right behind the slowly
departing trough that is currently over the area. This leads to
continued southwesterly flow aloft through at least Thursday, which
does not support the advection of any colder air. However, even
without much low-level CAA behind tonight`s front, Wednesday will
feature highs that are about 5-10 degrees cooler than today, which
is closer to seasonable normals.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
Issued at 310 AM CST Tue Nov 3 2026

Cloud cover is forecast to be slow to clear with continued cyclonic
flow aloft across the area resulting in wrap around moisture into
Wednesday night. There is some signal for clearing, from south to
north by Thursday, which may work to boost afternoon highs about 5
degrees warmer than Wednesday. That would result in highs ranging
from the low 60s to low 70s across the area by the afternoon.

By Friday, the mid-level trough that is currently across CA finally
traverses across the region, bringing an increase in cloud cover and
a 20-30% chance for more rain, along with another cold front. This
front appears to actually shift low to mid-level winds out of the
north, advecting in some cooler more seasonable air. Analysis of
LREF IQRs indicates good agreement that temperatures behind this
front would be about 10 degrees cooler. This would bring areawide
highs into the upper 50s/lower 60s, with lows in the lower 40s/upper
30s. In fact, NBM probabilities for lows 

NWS LSX Office Area Forecast Discussion