Hartford, Illinois Weather Forecast Discussion

373
FXUS63 KLSX 200401
AFDLSX
Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1101 PM CDT Fri Sep 19 2025
.KEY MESSAGES...
-Isolated afternoon thunderstorms are expected today and Saturday
with 50 mph gusts expected with the strongest thunderstorms.
-There are multiple chances for rain Sunday through mid-week, with
 cooling temperatures near normal by mid-week.
&&
.SHORT TERM...  (Through Late Saturday Night)
Issued at 223 PM CDT Fri Sep 19 2025
A weak surface boundary is currently stretched north to south across
mid-Missouri and is making progress eastward this afternoon. Ahead
of and along the boundary, cumulus has developed nicely and a few
showers and thunderstorms have popped up in central Missouri. As a
mid-level shortwave associated with a larger trough continues to
swing through the forecast area this afternoon into evening it will
produce isolated to scattered showers and thunderstorms across the
area. The best time for these to develop will be during the late
afternoon to early evening, when instability will reach its maximum
around 1500 J/kg (MUCAPE) with little to no cap in place where
sunshine has persisted today. Along and east of the Mississippi
River high level clouds have persisted, keeping the area cooler with
more stability. Thunderstorm development will be limited in this
area.
Any thunderstorms that develop will be able to take advantage of the
steep low-level lapse rates and send cores up quickly. But in an
environment with weak mid-level lapse rates and 0-6 km shear, these
storms are unlikely to become severe. It`s more likely that they
will drop their cores quickly into the low level dry air and produce
brief periods of up to 50 mph wind gusts. Thunderstorm development
will largely wane with sun set, but I cannot rule out a few showers
and thunderstorms popping up across the area overnight as additional
mid-level shortwaves traverse the area.
Overnight an MCS (stemming from convection currently across central
Nebraska), will march through the region. Most guidance is
indicating it will slide across Iowa and portions of far northern
Missouri overnight and into the early morning hours, decaying as it
gets closer to the Mississippi River. CAM guidance is also hinting
at an area of convection developing in Kansas tonight and quickly
tracking eastward across southern Missouri into the morning hours,
though there is less confidence in the development of this system.
The timing and position of these systems, combined with the strength
of the outflow boundaries and persistence of cloud shields will
determine Saturday`s thunderstorm potential. A weaker system and
outflow boundary, or thinner cloud shield will allow the area to
destabilize tomorrow afternoon. A stronger system and outflow
boundary, or thicker cloud shield may be able to keep portions of
the area stable through the afternoon, reducing the thunderstorm
chances across portions of the area.
Where instability is able to form, around 1000 J/kg of MLCAPE is
expected with little cap and strong low-level lapse rates. Just like
today, this will allow cells to develop quickly. Despite a
continuation of the weak mid-level lapse rates tomorrow, 0-6km shear
will be stronger, near 20-30 kts, and will be better able to
organize a few strong storms capable of 50 mph wind gusts. The best
chance for these thunderstorms will be during the afternoon when
instability is maximized.
Delia
&&
.LONG TERM...  (Sunday through Next Friday)
Issued at 223 PM CDT Fri Sep 19 2025
Additional chances for showers and thunderstorms persists through
the forecast period. The mid-level trough sitting in the Upper-
Mississippi River Valley will send additional shortwaves through the
area Sunday. The best chance for rain will be during the afternoon
when around 1000 J/kg of MLCAPE can form. Sunday`s thunderstorm
conditions will be wildly similar to today, resulting in a strong
storm or two that produce 40-50 mph winds.
The mid-level trough exits the area overnight Sunday into Monday
morning, leaving largely quasi-zonal flow in its wake until another
mid-level low moves into the region from the west. All the ensemble
guidance shows a mid-level low moving into the mid-Mississippi
Valley mid-week, though there is still some disagreement on the
specifics of how and when. 75% of ensemble members show the low
stalling over the region through Thursday, which if this comes to
fruition, would result in beneficial rain across the area. The other
25% show a weakening and more progressive low that would result in
less rain.
Regardless of how the specifics of our rain chances shake out,
confidence is growing in a "cool down" to at least near normal
temperatures by mid-week as these mid-level troughs kick through the
area. By Wednesday the 75th percentile for high temperatures will be
at normal, and if cloud cover and rain persist with a stalled mid-
level low, temperatures will come in much cooler than that.
Delia
&&
.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1049 PM CDT Fri Sep 19 2025
Isolated showers have developed late this evening with little
indication that thunder is or will accompany this activity as
much of the daytime surface instability has faded. What is
occurring has been difficult for guidance to grasp given the small
scale features leading to what has developed. Additionally, there
isn`t much support for showers to become anything more than a
short-lived nuisance. Considering their low impact and uncertainty
in direct hit the terminals, prevailing -SHRA is not justified and
chance don`t quite rise to the PROB30 threshold. VCSH was recently
added to KSUS but left out of KSTL with the showers moving just
north of the terminal. Most areas will remain dry and VFR with any
shower activity lasting a mere few minutes if showers do impact
any of the terminals.
There is virtually no change to Saturday`s precipitation potential
with isolated to widely scattered showers and isolated
thunderstorms relying on upstream trends in convection over the
central Plains. Outside of thunderstorms, VFR is favored.
Maples
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&
$$
WFO LSX

NWS LSX Office Area Forecast Discussion