Old Jamestown, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

403
FXUS63 KLSX 311140
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
640 AM CDT Tue Mar 31 2026

.KEY MESSAGES...

- Areawide near-record warmth continues today ahead of a cold
  front, and the warm, dry, and windy conditions will again
  combine to promote elevated fire danger for most of the region
  this afternoon.

- Showers and thunderstorms become more numerous this evening
  along and behind the front, primarily along and north of the
  I-70 corridor. Isolated instances of hail approaching 1.00" in
  diameter and locally-heavy rain are the predominant threats.

- Numerous rounds of showers and thunderstorms will impact the
  broader region, with a 40-60% chance for 2.00" of rain through
  Friday night across central/northeast Missouri and west-central
  Illinois.


&&

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 323 AM CDT Tue Mar 31 2026

Regional surface analysis features an extensive baroclinic zone
stretching from the northern Plains into the Great Lakes region,
with quasi-zonal flow aloft. Subtle shortwaves embedded within the
mid-level flow leading to strong to severe convection across Iowa
and northern Illinois at this hour, but the immediate forecast
area remains dry and hazard-free amidst gusty southwest surface
winds. The stout southwesterly wind and resultant warm advection
will promote another day of areawide near-record warmth,
especially south of US-36 where cloud cover and rain chances are
lowest. The surface front itself approaches and enters the
forecast area during the mid to late afternoon from the north.
While some CAMs insist on weak CI during the afternoon, model
soundings depict a strongly capped boundary layer that will likely
keep convection ahead of the front to a minimum in the absence of
mid-level ascent (of which there is very little). The warm pre-
frontal boundary layer combined with blocked/downsloped
southwesterly flow from the Ozarks will also result in elevated
fire danger across areas south of US-36/I-72 in Missouri and
Illinois. High-resolution ensemble probabilities of this danger
remain fairly high (70-90%), with low (10-20%) chances for
critical fire danger (Red Flag conditions).

The front oozes south during the early evening, while a low-level
jet simultaneously develops across western Missouri and intersects
the front. The strong LLJ stalls the front, at which point
convection blossoms at the nose of the jet largely behind the front.
At this point, rain and thunderstorm chances ramp up in the forecast
with highest values (70-90%) mostly along and north of I-70. High-
resolution guidance paints some modest elevated instability behind
the front, with -10C - -30C (hail growth zone) CAPE values in the
200-400J/kg range. While the strongest convection may be able to
approach severe hail criterion (1.00" diameter), most of the
thunderstorms will be sub-severe. As such, we are not currently
messaging the SPC Day 1 Marginal Risk for severe weather and will
monitor conditions for an increased threat.

What may be of slightly greater concern is the heavy rain threat
from these thunderstorms overnight into Wednesday morning. While
warm cloud depths are still fairly pedestrian, near-record PWATs are
still in place by this point and there is some suggestion that
training convection on the nose of the LLJ could lead to some
excessive rainfall across northern Missouri. HREF LPMM output
suggests a stripe of 1.00-2.00" (with localized amounts close to
3.00") is possible in this general area by late Wednesday morning.
While mitigating factors, like unfavorable storm vectors for
training convection, do exist, this threat will need to be monitored
closely. Outside of this, little to no impacts from the rain is
expected. The front gradually drifts back north Wednesday as a mid-
level wave approaches and a stronger surface low develops across the
Plains. The forecast is trending warmer and drier (though not
completely dry) across most of the region, except for northern
Missouri and west-central Illinois where rain chances remain fairly
high and temperatures may struggle to top 60 degrees.

MRB

&&

.LONG TERM...  (Wednesday Night through Monday)
Issued at 323 AM CDT Tue Mar 31 2026

The more potent upper-level wave and attendant surface low approach
the region Wednesday night, with a more impressive cold front
serving as a focus for convection. Most available guidance delays
the arrival of these thunderstorms until after sunrise Thursday,
keeping us largely (again not completely) dry overnight. The cold
front crosses through the region Thursday, with most guidance
supporting some meager surface-based instability developing in its
vicinity. This alone would introduce at least a low threat for
strong to severe thunderstorms under stronger mid-level ascent, but
uncertainty surrounding low-level forcing and cloud cover (which
affects instability) does exist. Many depictions of the cold front
feature lackluster convergence in the low-levels, which may keep any
threat more isolated. That, along with the instability uncertainty,
precludes us from messaging the SPC Day 3 outlook quite yet as well.
If severe weather becomes more of a threat, all hazards would be
possible.

The front is really more of a glancing blow, and by Friday morning
we`re back in a southerly low-level flow regime. Yet another strong
upper-level wave takes aim at the region late Friday into Saturday,
and probably represents the best synoptic-scale pattern for
widespread appreciable precipitation along another cold front. NBM
probabilities for 1.00" of rain on Saturday are 30-50% across the
region coincident with the front, though the actual probability of
it occurring is likely higher and owing more to timing uncertainty.
Luckily, most of this rain will fall outside of where the heavier
rain fell previously. While an axis of 3.00-4.00" with locally-
higher amounts still looks more probable than not (60-70% chance)
mainly over central and western Missouri, the rain will fall over
the course of several days. I can`t rule out a few instances of
nuisance or minor flash flooding during this time, as well as rises
to minor flood stage on smaller creeks in Missouri, but more
significant issues remain an outside possibility at best.

A well-deserved reprieve from this active pattern arrives just in
time for Easter Sunday, with dry weather and near-normal
temperatures favored through early next week. CPC Outlooks, NBM
temperature IQRs, and CIPS Extended Analogs all support a gradual
warmup above normal by the middle of next week.

MRB

&&

.AVIATION...  (For the 12z TAFs through 12z Wednesday Morning)
Issued at 623 AM CDT Tue Mar 31 2026

VFR conditions currently prevail at the regional terminals, with
LLWS waning thanks to a more unidirectional wind profile over the
last few hours. Showers and a few weak thunderstorms forced off
the nose of a LLJ currently exist along a line from Sedalia, MO to
Keokuk, IA. Thunderstorms have been transient and largely are
avoiding the central Missouri and west-central Illinois terminals,
which precluded mention of any convection at this time.

Winds will remain gusty up to 30kts out of the southwest ahead of
a slowly-approaching cold front. Most of the day will remain dry
outside of a threat for some weak showers during the afternoon,
but as the front sags south to the I-70 corridor and the nocturnal
LLJ intensifies convection will blossom and affect all terminals.
The TAF represents the current forecast timing as best as
possible, but timing is uncertain as it will hinge on the front`s
location. Eventually the focus for convection drifts north but IFR
CIGs build into the region and stop right over the St. Louis
metropolitan terminals. IFR was added for KSTL but left out of
KSUS and KCPS as they are just a bit further south and may not
quite see that restriction.

MRB

&&

.CLIMATE...
Issued at 238 AM CDT Sun Mar 29 2026

Records at Regional Long-Term Climate Sites - March 31st

             Record Highs | Record Warm Lows

St. Louis:   87F (1981)   | 63F (1917)
Columbia:    86F (1940)   | 59F (1967)
Quincy:      81F (2010)   | 58F (2010)


&&

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

$$

WFO LSX