880
FXUS63 KILX 281958
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
258 PM CDT Fri Jun 28 2024

.KEY MESSAGES...

- Numerous thunderstorms will bring beneficial rain to most of central
  Illinois tonight. The risk for severe weather remains low (only
  around 5%).

- There is only a 20-30% chance for thunderstorms Saturday. Once
  again, the severe risk is low (around 5%).

- Drier, cooler, and less humid conditions evolve Saturday night
  through Monday; ideal for outdoor activities.

- The relief from the heat and humidity will be brief as it makes
  a return by the middle of next week along with daily chances
  for rain starting Wednesday lasting into the holiday weekend.

&&

.SHORT TERM...  (Through Late Saturday Night)
Issued at 258 PM CDT Fri Jun 28 2024

At 230pm, day cloud phase distinction satellite shows scattered mid
(mostly supercooled water, as the freezing level is >14,000 ft!) and
high-level (ice) clouds across central Illinois, with scattered
convection upstream across southeast Iowa where low level moisture
transport is strong ahead of a shortwave trough. Current suite of
CAMs suggests this wave of thunderstorm activity will gradually
weaken as it becomes displaced from better instability and shear in
west central/northwest Illinois, though this forecaster wasn`t
confident enough to completely eradicate all mention from the
forecast this evening; hence, 25-50% PoPs remain northwest of I-55
this evening.

The better chance (60-80%) for precip will arrive later tonight, as
storms developing closer to the upper-level forcing drift into our
area while simultaneously weakening. It`s uncertain whether we`ll
wind up with any hydrological or convective (wind, hail) issues
tonight, but the CAMs continue to advertise the greatest
thermodynamics to our southwest where storms developing along the
northern periphery of the instability axis/LLJ across central/east
Missouri may rob our region of any appreciable CAPE. Nonetheless,
our morning sounding revealed a PWAT of 1.62 (near the
climatological 90th percentile), and given continued warm/moist
advection those values may surge to nearly 2 inches overnight -
more than enough for efficient rain producers (especially given
the depth of the warm cloud layer). NBM suggests the greatest
chance (20-35%) for rain amounts surpassing 1 inch will be
generally west of a Galesburg to Taylorville line, where some
guidance even depicts some highly- localized 2+ inch totals.
Precip loading could also contribute to downward momentum
transport fostering gusty winds in the heaviest cells, especially
if we struggle to decouple given continued mixing via the LLJ. In
general, the severe risk appears low, with SPC maintaining just a
level 1 of 5, marginal (5%), risk for severe weather.

That holds for tomorrow as well, though tomorrow the reason for the
marginal risk is slightly different. Recovery of instability (HREF
mean is 1500-2500 for SBCAPE) in our area is well forecast by the
12z CAMs, though none of them are particularly aggressive in
redevelopment of storms along/ahead of the cold front. If storms
should develop, the unstable airmass would favor severe wind/hail
with them, though at this point only about 20-30% of guidance shows
redevelopment during the afternoon. We`ll be keeping a close eye on
model trends for this activity.

Tomorrow evening, quite the impressive cold front for this time of
year will sink southward across central Illinois, bringing a quick
drop in humidity (dewpoints are forecast to drop 15+ degrees, from
mid 70s to upper 50s, in the span of 1-2 hours) and increase in wind
(northwest gusts are forecast to reach 30+ mph). By Sunday morning,
our northwest counties are likely to drop into the mid-upper 50s,
while south of I-70 some spots might still be hovering around 70.

Bumgardner

.LONG TERM...  (Sunday through Next Friday)
Issued at 258 PM CDT Fri Jun 28 2024

A brief stretch of unseasonably cool and dry weather is on tap for
Sunday and Monday as a strong mid to upper level ridge will be
building to our west over the Great Plains. Unfortunately, the
pleasant stretch of weather will be short lived as the ridge axis
passes through by Monday evening, placing us back under a southerly
flow regime once again by Tuesday. A weak mid level shortwave, that
is expected to traverse across the Upper Midwest Tuesday night into
Wednesday, may provide enough forcing aloft to support some rain.
With the depth of moisture still in question, especially east of I-
55 in Illinois, only chance PoPs remain for most of the area on
Wednesday. The 00z LREF members are in good consensus that the same
upper level ridge that will bring us our cool down Sunday and Monday
will setup over the SE CONUS, with 500mb heights of 594dm. The
current placement of this 594dm heat dome puts us under the "ring of
fire", giving us 30-50% PoPs daily from Wednesday through the end
of the extended.

With deep northwesterly flow aloft, along with rising heights,
Sunday and Monday will be dry and unseasonably cool with widespread
highs in the 70s. The coolest night in the next 7 days will be on
Sunday night when lows are expected to drop into the 50s, bringing a
springtime like chill back to the area. With southerly flow
returning by Tuesday, temps will be on the rise with highs reaching
the upper 80s to lower 90s on Tuesday and Wednesday along with
dewpoints reaching the lower 70s. The combination of heat and
humidity will result in heat indices nearing or exceeding 100
degrees in some locations on Tuesday and Wednesday, especially south
of I-70 in Illinois on Wednesday. Confidence in temps Thursday and
Friday is lower due to the uncertainty in the strength and position
of the nearby heat dome by the end of next week.

Peine

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1239 PM CDT Fri Jun 28 2024

Latest visible satellite imagery shows scattered to broken mid-
level (VFR) clouds streaming across central Illinois ahead of a
shortwave trough which has spawned showers and storms upstream
across northern Missouri and Iowa. High resolution model guidance
continues to suggest most of this activity will remain to our
north through the evening, though cannot completely rule out a
stray shower or storm - especially at BMI and PIA where the chance
is highest (around 30%). Later tonight, an additional round of
storms that fires upstream will weaken as it races across central
Illinois between 05z (midnight) and 12z (7am), bringing briefly
heavy rain and gusty winds, along with localized small hail.
Behind that wave of storms, ceilings will lower with a 30-60%
chance (highest at PIA and BMI) chance for MVFR conditions the
last few hours of the TAF period.

Bumgardner

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$