905
FXUS63 KILX 111710
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1210 PM CDT Tue Jun 11 2024

.KEY MESSAGES...

- An upper disturbance may spark a few isolated showers late this
  afternoon through tonight. Chances remain pretty low (<15%) with
  most expected to stay dry.

- Temperatures become unseasonably warm Wednesday onward with
  highs peaking in the upper 80s to middle 90s. This paired with
  a more humid airmass will send heat indices near 100 as early as
  Thursday.

- There is a 30-50% chance for showers and storms Thursday afternoon
  into night as a cold front drops through the area. A few of
  these storms could be severe north of I-70.

&&

.UPDATE...
Issued at 949 AM CDT Tue Jun 11 2024

It was a crisp, sunny start to the day across central IL, with
lows in the mid 40s making it feel more like late April than mid-
June. A warming trend begins today, as 850mb temps rise from
around +6 or +7 degC yesterday to near +15 degC today, which will
translate to high temps near 80F. A weak cold front is currently
draped across central IA and will result in mid-level cloud cover
pushing in from west to east this afternoon.

Erwin

&&

.DISCUSSION...
Issued at 334 AM CDT Tue Jun 11 2024

An expansive area of ~1017 mb surface high pressure currently covers
a large portion of the country`s midsection, spanning from the
Missouri Valley northward into the Great Lakes Region. Another day
of deep mixing yesterday brought down much lower dewpoints,
especially over eastern parts of the state where upper 30s to low
40s dewpoints are noted as of 3 am. Temperatures have steadily
fallen overnight with most areas in the upper 40s to low 50s. Light
winds and mostly clear skies aside from a few cirrus will support
efficient radiational cooling through the remainder of the morning,
with lows expected to wiggle down a couple more degrees, possibly
putting some sites in eastern Illinois within a few degrees of their
low temperature records.

Surface ridging spills eastward later today as upper ridging from
the western CONUS inches closer. Flow aloft will transition to more
zonal, with mid-level heights quickly rising. Southerly surface flow
will bring in warmer temperatures today with values expected to
approach our seasonal norms. A few disturbances will ride the upper
ridge and track through the Great Lakes Region tonight and again
Wednesday night. Moisture with the wave tonight will be more so
focused in the mid to upper levels with better low-level moisture
staying well north of here. Lapse rates will steepen as the upper
wave approaches, potentially sparking a few isolated showers (<15%
chance) or virga showers. Added the mention of isolated sprinkles
from late this afternoon into tonight to account for this, but
most will stay dry.

Somewhat better chances (30-50%) for precipitation are possible
Thursday afternoon into evening as a cold front drops south through
the area. A warm, moist airmass ahead of the front characterized by
dewpoints in the upper 60s to low 70s should lead to moderately
strong instability by late Thursday afternoon. A 60-70 kt mid-level
jet will stretch from the northern Plains into the Lower Great Lakes
Region by evening, increasing shear as the cold front approaches.
Conditions look favorable for storms to develop within a largely
uncapped environment by late Thursday afternoon or evening. A few of
these storms could become severe north of I-70, posing a threat for
damaging wind gusts. Climatologically high PWATs exceeding 2 inches
and deep warm cloud layers will bring the threat for heavy rainfall
as well. Despite this, the threat for flooding still looks pretty
marginal due to the lack of appreciable recent rain and the swift
progression of the front.

Another big forecast concern going forward is the long duration heat
beginning midweek onward. Temperatures will quickly climb into the
upper 80s to middle 90s by Wednesday with similar values sticking
around through much of next week/weekend. Dewpoints will climb back
to more uncomfortable levels ahead of storms on Thursday, sending
heat indices into the 90s to near 100. Drier air behind the front
will bring a brief "break" in oppressive dewpoints Friday and
Saturday, but air temperatures will remain unseasonably hot.
Dewpoints return back to the upper 60s to low 70s Sunday onward as
southerly return flow is reinforced underneath amplified upper
ridging. Heat indices will once again approach 100 Sunday through
early next week, creating near-dangerous conditions for outdoor
activities and vulnerable individuals. A new experimental heat risk
product which is essentially a heat stress index geared toward those
actively exposed to direct sunlight in the heat approaches
moderate to major categories (level 2 to 3 out of 4) Sunday
through Tuesday of next week. This is somewhat different from heat
index (measured in shade) because the stress on your body can
occur much quicker when working or exercising in direct sunlight
during the heat.

NMA

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1209 PM CDT Tue Jun 11 2024

VFR conditions prevail through the period. Southwesterly winds
today will shift to southerly overnight, then back to
southwesterly after sunrise on Wednesday. Wind speeds will be
light, generally below 10 knots. A weak front will result in
broken mid-level cloud cover moving in from west to east this
evening. This front could produce a stray sprinkle and perhaps
some virga, but overall, precipitation is unlikely.

Erwin

&&

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

$$