407
FXUS63 KILX 161815
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
115 PM CDT Thu May 16 2024

.KEY MESSAGES...

- Severe weather potential remains low both Thursday and Friday,
  with the probability of greater than one inch of rainfall in the
  10-20% range south of I-70.

- Prepare for warming temperatures this weekend, with a 40-80%
  chance of high temperatures above 85 F. The greatest chances for
  temperatures in excess of 85 F are south of I-70.

&&

.UPDATE...
Issued at 944 AM CDT Thu May 16 2024

Rain showers continue to progress northeast towards the area, with
the main precipitation shield lifting through the MS River Valley
in SW IL. A few isolated showers have popped up across west-
central IL in advance of this precip shield. Made updates to the
PoPs based on recent radar trends and the latest CAMs, but the
overall message remains the same - which is that precip coverage
will increase by late morning/early afternoon, eventually becoming
more widely scattered by the evening. Organized severe wx
continues to look unlikely across central IL - owing to a
combination of weak instability, unimpressive mid-level lapse
rates, and marginal shear.

Erwin

&&

.DISCUSSION...
Issued at 322 AM CDT Thu May 16 2024

With light winds and some areas of clear sky apparent on satellite
particularly in eastern Illinois in an environment with minimal
dew point depressions, we`ve seen some areas of fog start to
develop. Visibility has locally been reported as low as a half
mile. With clouds gradually moving in from the west, we expect any
dense fog to remain transitory and localized. Look for most of the
fog to dissipate by shortly after sunrise.

Radar shows the first shower activity moving out of eastern
Missouri in an environment with a few hundred J/kg of MUCAPE but
minimal shear. Shower and thunderstorm activity is forecast to
increase from the southwest through the morning ahead of an
eastward-advancing thunderstorm complex coming out of southeastern
Kansas. HREF probabilities depict shower and storm initiation west
of I-55 in the 10-11 am time range, with storms moving
east/northeastward through the late morning and afternoon. The
same HREF probabilities show activity backing off across
southern/southwestern portions of the ILX CWA in the 3-5 pm range,
with showers ending from southwest to northeast. A few members
keep convective activity going east of I-55 well into the evening.
Though MUCAPEs reach around 1000 J/kg, shear is forecast to be on
the low side this afternoon/evening except perhaps locally south
of I-70 so severe weather probabilities are low. Rainfall will be
highly variable, with many areas receiving little or none and a
few receiving an inch or more.

Model forecasts have trended a bit southward with the low track
for Friday, and portions of the ILX CWA receiving precip Friday
may be limited. A weak boundary with little temperature or
moisture contrast across it is depicted in model forecasts,
lifting northward on Friday to various degrees. Precip chances are
greatest south of I-70, with a noticeable drop-off from southeast
to northwest. In reality many north of I-72 may not receive any
rain at all on Friday, but felt it wise to include some precip
chances in the afternoon as some ensemble members show storm
initiation occurring along the convergence boundary and the
position is uncertain.

With enough members such as the deterministic 00z GFS showing a
slower wave on Saturday, keeping precip going particularly in the
southeast, 20-40% precip chances persist though precip amounts are
not forecast to be much. Behind the low, a short wave ridge pushes
in and temperatures begin to warm. Starting on Sunday and
continuing through Tuesday, the probability of high temperatures
greater than 85 F goes up into the 40-80% range. The greatest
probability for these very warm temperatures will be south of
I-70. In addition to the warm temperatures, severe storm
ingredients will return with increasing instability, increasing
shear in southwest flow, and multiple waves forecast to move
through the flow. Though it`s difficult to time or place the
individual waves at this point, the most likely date for active
weather in the vicinity of central Illinois is Tuesday.

AAT

&&

.AVIATION...  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 114 PM CDT Thu May 16 2024

Sct -SHRA with isold TSRA expected until 23Z-01Z as a shortwave
disturbance moves through the area. MVFR cigs/vsbys will be
occasional. A weak frontal zone will move through overnight
allowing for a few continued showers, but too low probability for
mention in TAFs. Nevertheless, light winds along the frontal zone
and recent precipitation will allow for fog development which
could bring IFR or worse vsbys approximately 10Z-15Z. Surface
winds SW 8-14 kts until 00Z, then decreasing to light and
variable by 06Z.

37

&&

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

$$