762
FXUS63 KILX 170954
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
454 AM CDT Sat Aug 17 2024

.KEY MESSAGES...

- Scattered showers possible (30% chance or less) this afternoon
  along and north of a Davenport- to- Vincennes line. There could
  even be an isolated thunderstorm or funnel cloud, but severe
  weather is not anticipated.

- Drier, cooler and otherwise low-impact weather is then forecast
  for the upcoming week.


&&

.DISCUSSION...
Issued at 1220 AM CDT Sat Aug 17 2024

Morning water vapor imagery shows an upper-level low positioned
over the Great Lakes region, with multiple shortwaves embedded
within the cyclonic flow. Short-term model guidance is in
excellent agreement that this feature hangs around through the
weekend, aiding periods of scattered showers through Sunday
afternoon as various spokes of vorticity rotate through central
IL.

The latest 00z HREF guidance suggests shower chances (20-30%)
largely remain confined along/north of a Davenport-to-Vincennes
line today, and then east of Bloomington-to-Effingham line on
Sunday as the upper-level low begins to pivot/depart eastward.

Enough residual moisture and instability exists on the back side
of the surface low for showers to be convective in nature, and
with steep low-level lapse rates and a core of colder temperatures
aloft, we could see a few funnel clouds today across the region.
This idea is loosely supported by recent RAP13 guidance, which
offers non-supercell tornado (NST) parameter values > 1 in areas
along/north of I-74, with the highest values staying across the
Chicagoland area.

Another byproduct of steep low-level lapse rates today will be
breezy conditions, as deeper boundary layer mixing helps achieve
occasional gusts between 20-25 mph.

Temperatures this afternoon will be held down by increasing
clouds, as most locations across central Illinois hover around 80
degrees, while areas south of I-70 once again surge into the mid-
to-upper 80s beneath less cloud coverage.

A strong omega block appears to evolve by next week. The net
effect will be lengthy stretch of dry and mild days across much of
the Midwest. NBM deterministic guidance is providing afternoon
highs between 76-82 degF and overnight lows between 55-60 degF
each day between Monday and Thursday, with less than a 10% chance
of rain. Eventually the anomalous ridge-axis portion of the omega
block will nose across the Mid-Mississippi Valley, turning the
heat up into the mid-to-upper 80s by late next week.

At this point, it is difficult to target the next best chance for
rain beyond the current weekend. A quick glance at the latest
global deterministic solutions (GFS, ECMWF, and CMC) paint central
Illinois beneath the core of the 594mb ridge, which would
seemingly shunt any frontal or MCS precip well north of here. On
the other hand, global ensembles such as the GEFS and EPS keep
central Illinois more along the periphery of the 594mb ridge,
perhaps offering a slightly better chance of tapping into frontal
or MCS precip by next weekend. Either way, it`s hard to ignore the
signal for an extended dry period across the Midwest, and this is
supported by CPC`s increasing probability for below normal
rainfall through August 30th.

MJA

&&

.AVIATION...  (For the 12z TAFs through 12z Sunday Morning)
Issued at 447 AM CDT Sat Aug 17 2024

Upstream observations indicate MVFR ceilings over northern
Illinois this morning. Short-term forecast guidance supports
these lower ceilings moving southward into portions of central
Illinois after 14z/9am. Both PIA and BMI have the greatest chance
of seeing these MVFR ceilings, eventually lifting and scattering
to VFR early this afternoon. Elsewhere, VFR are expected to
persist through the period.

With the passage of another weak surface front this afternoon,
winds will veer to the NW and gust to around 18-20 kts before
diminishing around sunset.

MJA

&&

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

$$