Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

142
FXUS63 KLSX 151744
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1244 PM CDT Fri May 15 2026

.KEY MESSAGES...

- Expect increasingly warm and humid conditions today through
  early next week with a few opportunities for showers and
  thunderstorms. The risk for severe weather remains low through
  the weekend.

- A greater severe weather threat is possible as a cold front
  moves through the region sometime between Monday and Wednesday,
  with the exact timing and strength of this front remaining
  uncertain.


&&

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 351 AM CDT Fri May 15 2026

Recent radar imagery reveals a region of ongoing convection from
central MO stretching northeastward into northeast MO/west-central
IL. This activity fired around 06z and has quickly grown in coverage
thanks to a 40-50kt nocturnal LLJ nearby, coupled with around 1,000
J/kg of MUCAPE according to the latest SPC Mesoscale Analysis.
Analysis of nearby soundings shows that a surface-800mb temperature
inversion is in place meaning that this convection is elevated well
above the surface. As a result, the main threat with this
thunderstorm activity is expected to be the potential for hail up to
1", with a lesser threat for damaging winds gusts. The greatest
coverage of convection has been across northeast MO/west-central IL,
which is near the nose of the LLJ and also along the MUCAPE
instability gradient. CAMs resolve this convection persisting into
the morning with southeastward movement along the instability
gradient pushing convection into central/south-central IL by the 12-
15z timeframe. Near the same time, the nocturnal LLJ will be fading
in magnitude, which should also work to limit the coverage and
persistence of this convection past 15z today.

With the favorable ingredients (low/mid-level forcing/moisture
transport) to maintain convection waning into the day today, a
majority of the area is forecast to remain dry from late this
morning into tonight. The exception to this would be if the ongoing
convection is able to produce any sufficient outflow boundaries that
linger today. Any outlflow`s that linger may serve as localized
areas of enhanced surface convergence, which could help to initiate
additional thunderstorm development as daytime instability increases
Friday afternoon/evening. High-resolution guidance reveals that
1,500-2,000 J/kg of SBCAPE may exist for some locations by this
evening, which is highly dependent on the amount of solar insolation
that is realized. Regardless, this indicates sufficient instability
may be in place to support an isolated thunderstorm, with the main
hazard once again being hail. Confidence in a scenario like that
unfolding is low, but will continue to be monitored throughout the
morning as mesoscale results from the ongoing convection become more
clear. Low-level WAA is forecast to continue today, leading to
temperatures in the mid/upper 80s across the area, except for some
locations across IL, where lingering morning convection/cloud cover
may limit daytime heating.

Similar to early this morning, the nocturnal LLJ ramps up to 50kts
again tonight, in a similar location and orientation. The most
recent CAMs unveil convection firing across southeast NE/western IA
late this evening along and ahead of a cold front stretching from
southern Ontario into northern IA. Rapid upscale growth of this
convection is expected with the remnants of this activity forecast
to reach northeast MO/central MO early on Saturday morning. At that
time, deep layer wind shear should be around 20kts (10-15kts weaker
than now), with greater instability. That environment may result in
a messier setup than the ongoing convection, with less organized
more pulse like multicellular convection. If that convective mode is
realized, it may also enhance the damaging wind threat as storms
collapse, potentially leading to the occurrence of microbursts.
Confidence in the coverage and timing of any shower/t-storm chances
on Saturday remains low as perturbations propagate within the quasi-
zonal flow aloft. Any one of these subtle features aloft may be
capable of triggering scattered showers/t-storms given the
warm/moist airmass that will be in place. This also results in a low
confidence temperature forecast with current LREF IQRs ranging from
the mid 70s (25th) to mid 80s (75th) for high temperatures across
the area on Saturday afternoon.

Peine

&&

.LONG TERM... (Saturday Night through Next Friday)
Issued at 351 AM CDT Fri May 15 2026

At the start of the extended, the large-scale pattern begins to
shift with a mid/upper-level trough amplifying across the western
CONUS, placing the area in deep southwesterly flow. The
intensification of this trough Saturday night into Sunday leads to
height rises aloft and also works to push the active LLJ northward
further away from the area. The evolution of these features should
lead to a stretch of dry weather that will be centered on Sunday.
This, along with abundant solar insolation and continued low-level
WAA, will work to boost afternoon temperatures into the mid/upper
80s, with some locations nearing the lower 90s on Sunday.

By Monday, the aforementioned trough begins to shift eastward as
weak shortwaves propagate out ahead of it within the southwesterly
flow. As these features near the region and interact with our
warm/moist airmass, chances for more widespread showers and
thunderstorms increase, with LREF probabilities for measurable
precipitation reaching 60-80% areawide by Monday afternoon. Long-
range guidance is keying in on a more distinct shortwave propagating
into the Great Plains Monday night, triggering lee-side surface
cyclogenesis. This surface low is modeled to lift northeast into the
Upper Midwest, with a trailing cold front swinging southward towards
the region and moving through sometime between Monday and Wednesday.
The exact timing of this cold front remains uncertain and will be
key when it comes to the severe weather threat that is realized
across the area. For example, a FROPA favoring the diurnal
instability maximum would also favor a greater severe threat, while
a nocturnal FROPA may limit the severe weather potential. This key
detail will continue to be refined as long-range guidance hones in
on a general solution. Currently, the key takeaway is that multiple
chances for showers and thunderstorms exist Monday into Wednesday
with the best chance for a more widespread severe weather threat
existing when the cold front arrives, which will be fine tuned with
future forecasts.

Model guidance varies greatly beyond the mid-week timeframe
regarding certain large-scale features. Given the variance of these
features within long-range guidance, low chances for precipitation
remain across the area through the end of the week, but plenty of
dry time is currently expected Wednesday through next Friday. The
general consensus regarding temperatures, revealed by the LREF
temperature IQRs, is cooler conditions will prevail with IQRs
centered near temperatures that are slightly below climatological
normals.

Peine

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1233 PM CDT Fri May 15 2026

VFR flight conditions are expected to prevail across most of the
area through this evening. The exception will be across the
eastern Ozarks where isolated showers and thunderstorms may reduce
the visibility to 3 miles or less. Thunderstorms are expected to
move into northeast Missouri between 05-07Z tonight, and continue
moving southeast into Saturday morning. The strongest storms will
be capable of producing IFR visibilities in heavy rain, as well as
isolated wind gusts to 45-50kts and hail up to 1 inch in diameter
across northeast Missouri and west central Illinois. Storms will
weaken as they continue moving to the southeast. While current
indications are that most of the storms will dissipate/move out of
the region by 14-16Z, some isolated to widely scattered
convection probably continue into the afternoon.

Carney

&&

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

$$

WFO LSX