248
FXUS63 KILX 300322
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1022 PM CDT Mon Apr 29 2024

.KEY MESSAGES...

- Patchy fog will develop across much of central and southeast
  Illinois tonight...with a 30-50% chance of visibilities dropping
  below 1/4 mile in spots along/south of a Danville to Taylorville
  line.

- Above normal temperatures will prevail for the remainder of the
  week.

- The next significant chance for rain will arrive Thursday into
  Friday, followed by slightly cooler conditions by next weekend.

&&

.UPDATE...
Issued at 811 PM CDT Mon Apr 29 2024

Slow moving cold front was located between I-55 and I-57 at 8 pm.
Back edge of the rain has moved into the extreme southeast CWA
near Lawrenceville and will completely exit the area over the next
1-2 hours. Behind the front, dew points fell into the upper 40s
and lower 50s. With the front washing out over the area, MSLP
gradient relaxes overnight and the dry advection will lose its
southeast push, leaving areas near and south of I-70 with dewpoint
depressions approaching zero late tonight. This combined with wet
ground from today`s rainfall should lead to the formation of fog,
some of which could become dense at times. The presence of high
clouds streaming northeast from a southern stream shortwave lowers
confidence in dense fog coverage. Latest high resolution guidance
does show areas of dense fog south of I-70 primarily between 1-7
am. Will monitor trends over the next several hours, and a dense
fog advisory may eventually be needed. Aside from this, weather
will be quiet for the remainder of the area overnight with lows
ranging from the upper 40s/lower 50s over central IL, to the upper
50s in SE IL.

25

&&

.SHORT TERM...(Tonight through Tuesday)
Issued at 302 PM CDT Mon Apr 29 2024

19z/2pm surface analysis shows a weak cold front pushing slowly
eastward through the Illinois River Valley. Low clouds persist
east of the front, with persistent showers impacting locations
along/southeast of a Paris to Effingham line. Showers will
continue across the far E/SE KILX CWA through early evening before
gradually pushing further eastward into Indiana. The cold front
will eventually exit the CWA as well, but this will not occur
until late evening. While the upstream airmass behind the boundary
is considerably drier with current dewpoints only in the 40s
across Iowa/far western Illinois, this airmass will only gradually
trickle eastward after FROPA. As a result, there will be quite a
bit of lingering boundary layer moisture. Given clearing skies and
light winds, patchy fog looks to be a good bet...especially across
the E/SE where the drier air will be slowest to arrive.
HRRR/RAP/GFSLAMP all suggest the potential for locally dense fog
in a few spots across this area. In addition, the 12z Apr 29 HREF
indicates a 30-50% chance of visibilities dropping below 1/4 mile
along/south of a Danville to Taylorville line. Am not confident
enough to issue a Dense Fog Advisory at this time, but have
included areas of fog across the E/SE accordingly. After any early
morning fog dissipates, Tuesday looks to be a mostly sunny and
pleasant spring day with high temperatures topping out in the
middle to upper 70s.

Barnes

.LONG TERM...(Wednesday through Next Monday)
Issued at 302 PM CDT Mon Apr 29 2024

A short-wave trough is progged to eject northeastward out of the
Rockies on Tuesday, then track into the Upper Midwest by Wednesday.
While the strongest lift associated with this feature will remain
well northwest of Illinois, it will drag a weak cold front into
north-central Illinois by early Wednesday. Scattered showers and
perhaps a thunderstorm will precede the front Tuesday night with
any showers dissipating before daybreak Wednesday. Despite the
lingering weak boundary in the area, short-wave ridging aloft in
the wake of the system will ensure a warm/dry day on Wednesday
with high temperatures topping out in the upper 70s/lower 80s.

A more significant short-wave will cross the Rockies into the
Plains by Thursday...and this system will bring the next
significant chance of rain to central Illinois by the end of the
week. 12z models continue to be too fast with the eastward
progression of this amplifying system, so rain chances Wednesday
night/Thursday morning will likely be removed as models come into
better focus. The main window for the strongest forcing/deepest
moisture continues to look like Thursday afternoon through Friday
morning when GFS precipitable water values increase to 1.50-1.75.
Have therefore carried likely to categorical PoPs during that
timeframe.

Once the late week system passes, slightly cooler/drier weather
can be expected Friday night into Saturday before another short-
wave trough approaches by Sunday.

Barnes

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1022 PM CDT Mon Apr 29 2024

VFR TAFs this cycle. Light northwest winds will become
variable/calm at times tonight, then increase from the south
around 10 kt by mid morning. A decaying thunderstorm complex is
forecast to approach KPIA from the northwest toward 06z Wed, and
included a PROB30 to account for this.

25

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 9 AM CDT Tuesday for ILZ062-063-066>068-
071>073.

&&

$$