Ash Missouri Weather Forecast Discussion

842
FXUS63 KLSX 062332
AFDLSX
Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
632 PM CDT Mon Oct 6 2025
.UPDATE...
Issued at 628 PM CDT Mon Oct 6 2025
The area of rain associated with tropical moisture and a weak
disturbance rotating around the western periphery of the ridge is
now fairly clearly going to miss our forecast area. As a result,
our rain chances have been lowered significantly. Our primary
source of rain is the front pushing down from the north tonight.
It is likely to form some scattered showers and storms across
northern MO into central IL this evening, but these will gradually
decrease in coverage as the front pushes further south overnight.
Most areas will not see rainfall with this frontal passage. Even
redevelopment along the front tomorrow afternoon looks to occur
just south of our forecast area. The main impact for most will be
an increase in clouds and cooler temperatures tomorrow.
Kimble
&&
.KEY MESSAGES...
- A cold front brings a shift toward cooler weather starting
  tomorrow. Rainfall with this front will be spotty at best.
- More seasonable temperatures last for a few days before
  temperatures begin warming again late in the week.
&&
.SHORT TERM...  (Through Late Tuesday Night)
Issued at 247 PM CDT Mon Oct 6 2025
A couple of features embedded in the regional synoptic pattern
will bring chances of rain and isolated thunderstorms today and
Tuesday. Unfortunately, trends continue to indicate a lack of
widespread, beneficial rainfall.
The two items to watch today will a surface low moving through the
Missouri Bootheel and the cold front that extends from the northern
Great Lakes into the central Plains. As the system passes to our
south, the northward push ahead of the system will gradually draw
additional moisture into southeast Missouri and southern Illinois.
RAP guidance shows some locations may even flirt with dewpoints near
70 degrees this evening, which is notable considering the recent
dryness that helped make anomalous warmth more bearable.
Satellite imagery shows cloud cover more prevalent around the
system to the south and the cold front to north, while diurnal
cloud development begins to impede the clearing in between as
moisture increases from the south.
Rain chances (30-50%) will initially be highest around the system
to the south this afternoon through early evening. The northward
extent will be limited to areas along and south of I-44/I-64,
becoming more isolated between the system and the approaching cold
front. Much of what develops during the daylight hours will be
driven by modest mid-level lift in a region of southerly flow
that runs over top marginal surface instability. SPC mesoanalysis
show SBCAPE nearing 1000 J/kg early this afternoon with 20-25
knots of 0-6km shear over much of the region, closing in on 30
knots near the front to the north. Mid- level lapse rates tuck
under 6C with model soundings showing narrow CAPE profiles. This
isn`t much of an argument for more than showers and occasional
thunder through diurnal peak with weakening trends thereafter.
While severe weather is not expected, PWAT values around 1.6"
indicate that where isolated thunderstorms develop, brief,
localized episodes of heavy rainfall are possible. Even that will
be hard to come by with the lack of stronger forcing and scattered
nature of precipitation. PMM 6-hourly QPF shows isolated
0.25-0.50" values through 00z, mainly south of St. Louis, further
highlighting the lack of widespread beneficial rainfall.
Showers and thunderstorms develop along the cold front
(Iowa/Illinois) to the north this afternoon, as well. However, the
slow progression of the front brings it into northeast Missouri and
west-central Illinois as instability wanes this evening. Initial
development is expected in the warm sector, but gradually becomes
post-frontal tonight. Thunderstorms along the front weaken to
scattered showers overnight and trends toward less coverage
through early Tuesday morning. Meanwhile, additional precipitation
develops along and south of the front Tuesday afternoon. With the
departure of the southern system, the the front is pulled
southward and brings it into the southern sections of the CWA
Tuesday late morning. Additional precipitation develops along the
front Tuesday afternoon, but should be far enough south that
rainfall gradually shift south of the CWA. The bigger story will
be the cooler temperatures that work into the region as surface
ridging builds in from the north. Cloud cover holds through much
of the day, making it feel and look more like fall with steady or
slowly falling temperatures.
Maples
&&
.LONG TERM...  (Wednesday through Next Monday)
Issued at 247 PM CDT Mon Oct 6 2025
The long range pattern holds little promise for beneficial rainfall
with the lack of any organized systems in the Midwest.
Surface high pressure builds east-southeastward from the northern
Plains Tuesday night into Wednesday as mean upper level flow briefly
turns quasi-zonal through the midweek period. A bulk of the colder
air remains over the Great Lakes Region and northward. However, some
of the cooler air is pulled southward on north-northeasterly flow
around the eastern side of the ridge with 850mb temperatures running
between 3-5C. Despite ample sunshine under mostly clear skies,
temperatures will be more representative of typical fall weather for
October. This is especially true for Wednesday night into Thursday
morning as the surface ridge centers overhead. Clear skies and
calm/light surface winds result in efficient radiational cooling
with lows dipping into the 40s areawide. There is a slight chance
(10-20%) that a couple of outlying rural locations touch the upper
30s Thursday morning. After a cool start in the morning,
temperatures rise back into the 70s Thursday.
NBM data remains fairly well-clustered through the end of the period
with a gradual moderating trend in temperatures late this week into
the weekend. The midweek surface high moves into the Great
Lakes/northeastern U.S. through the day Thursday with surface flow
turning southerly late Thursday. Mid-level temperatures climb by 10-
15C from west to east Friday as a cold front begins to wash out to
our north. The front would have been the only shot at rainfall, as
small as it may have been. Trends no long favor this either, as
upper level ridging amplifies over the southern and central Plains
and surface ridging maintains dry conditions. Both long range
ensemble solutions (GFS/ECM) look rather concerning with the highest
outliers indicating less than 1.75" of QPF through the next 7-10
days. The end of the period is favored to end dry and warmer than
normal with temperatures returning to the 80s.
Maples
&&
.AVIATION...  (For the 00z TAFs through 00z Tuesday Evening)
Issued at 619 PM CDT Mon Oct 6 2025
VFR conditions this evening will gradually give way to more cloud
cover from north to south by morning as a cold front gradually
moves southward. Winds shift from light southerly to moderate
northerly behind the front with ceilings lowering to MVFR or
perhaps IFR at times behind the front on Tuesday. Some
thunderstorms are possible along the front this evening as it`s
inching its way through Quincy. This is the only terminal that has
a significant chance of observing TS this evening and thus the
only one in which it is included in the going forecast. Showers
and storms decrease in coverage as the front moves south after
midnight, so rain impacts at other terminals are much less likely.
MVFR ceilings are likely to last most if not the entire day on
Tuesday, with some improvement to VFR possible late in the day.
Kimble
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&
$$
WFO LSX

NWS LSX Office Area Forecast Discussion