012
FXUS63 KILX 070635
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
135 AM CDT Sun Jul 7 2024

.KEY MESSAGES...

- There is around a 20-30% chance for thunderstorms west of the
  Illinois River this afternoon and evening, with more numerous
  showers and storms (40-50% chance) area-wide tomorrow.

- Tuesday into Wednesday, a swath of heavy rainfall is expected
  somewhere across central or southern Illinois, with the highest
  chance (10-15%) for more than 3 inches of rain south of I-70.
  There is a level 2 of 4, slight, risk for excessive rainfall
  south of the I-72 corridor.

&&

.DISCUSSION...
Issued at 127 AM CDT Sun Jul 7 2024

Quiet conditions continue this Sunday morning, as surface high
pressure dominates the region`s weather. Nighttime microphysics
satellite shows mid to high clouds streaming toward central and
northern Illinois from the west, and regional MRMS base reflectivity
shows some scattered showers beneath those clouds. The 07.00z suite
of CAMs generally agree this activity may graze our northern county
or two late morning, but by and large the area should stay dry
through early-mid afternoon. The aforementioned cloud cover may
inhibit radiational warming a little, and hence limit depth of
afternoon mixing; nevertheless, middle of the road guidance from a
blend of CAMs brings highs to the upper 80s most locations, with a
few spots touching 90.

HREF mean brings MUCAPE values to between 1000 and 1500 J/kg across
areas near and west of I-55 this afternoon, when CAMs depict various
convective scenarios unfolding near outflows from upstream
convection and a potential MCV. Although shear near an MCV could be
locally higher than blended guidance would suggest, the HREF
suggests probabilities for more than 30 kt 0-6km bulk shear are
generally less than 30% - indicating support for organized and
sustained storms is lacking. Given mid level dry air in place, can`t
rule out some localized gusty winds and brief heavy rains with
collapsing storms as various iterations of the HRRR would suggest;
however, the same model may be depicting a more impressive low-level
inverted V type sounding than reality if it`s overmixing as it did
yesterday when surface minimum afternoon dew points were about 5
degrees warmer than it suggested. Severe chances remain generally
lower than 5%.

Shear actually increases a smidgen tonight into tomorrow morning,
and with an ill-defined mid level shortwave lifting northeast
through the area ahead of its parent upper trough (in the Upper
Midwest) we`ll have some meso-a/synoptic support for a few lingering
showers and possibly a rumble of thunder. Marginal (1000 or so J/kg
SBCAPE) instability returns tomorrow for perhaps a few more storms
during the afternoon and evening, though coverage is only looking 40-
60% (highest west of I-55) at best with many locations staying dry.

Things get a little murkier as we head into the mid week time frame
with the approach of Beryl`s remnants which have the potential to
bring quite a bit of rain to parts of the area. Ensemble guidance
has been trending northward with this feature. For example, the LREF
mean PWAT Tuesday evening at arbitrarily-chosen Lawrenceville
climbed from 1.73" to 1.80" to 1.95" from the 05.12z to 06.00z to
06.12z iterations; for reference, the ILX raob 90th climatological
percentile is 1.73", while its moving average daily max is 2.09",
for 00z July 10th. Granted, there`s still a significant amount of
ensemble spread in how moist the airmass gets with the approach
of post-tropical Beryl, with the 10th to 90th percentile PWAT
range spanning 1.1 to 2.5 inches at the same location (KLWV),
where the rainiest members have over 4 inches of rain falling
while 50% of members have 24 hour precip totals somewhere between
a tenth of an inch and 1.5 inches. All three deterministic models
now have a notable surface low passing through a portion of
central or southeast Illinois late Tuesday into Wednesday, with
some corridor of heavy (i.e., 2+ inch) rain totals. And while this
would be beneficial if it fell slowly enough for the ground to
absorb it, we`re a little concerned the global models are having a
bit of a resolution issue, and that in reality there will be a
narrow corridor of 4+ inches of rain that may result in some
hydrological issues (especially if it overlaps with locations that
saw the most of the Sunday-Monday precip), while much of the area
just doesn`t get enough rain. Given how dry the area is, thinking
is we can take quite a bit of rain so the overall flooding risk
is still not particularly high, but it will certainly bear
watching. One other noteworthy mention would be potential for
gusty gradient winds which at this point aren`t looking strong
enough to do any damage, although a small subset of ENS members
depict gusts over 45 mph in our southeast Wednesday afternoon, and
with the strengthening trends in Beryl`s remnants it wouldn`t be
prudent to completely discount it. We`ll continue monitoring model
trends for both heavy rainfall and wind potential as the
potentially stormy mid-week approaches.

The eastern half of the CONUS is slated to remain troughy to close
the work week, which would suggest chances for precipitation can`t
be safely eradicated from our forecast while temps linger near to
perhaps slightly below normal (typical mid-July highs are in the mid-
upper 80s). Heading into the upcoming weekend, the trend is for the
wicked ridge of the West to expand gradually east, though how
quickly that occurs is in question. At some point next weekend into
the following week (of July 15th), we`ll find ourselves near the
east-northeast periphery of that ridge with the westerlies mainly
north of us...though maybe a little too close for comfort given
seasonably uncomfortable evapotranspiration-enhanced moisture and
attendant instability.

Bumgardner

&&

.AVIATION...  (For the 06z TAFs through 06z Sunday Night)
Issued at 1046 PM CDT Sat Jul 6 2024

VFR conditions through much of the forecast with scattered
diurnal cu redeveloping Sunday morning. High pressure will shift
over the area tonight, resulting in light to calm winds. After
the high pushes off to our east Sunday morning, winds will set up
from the south/southwest around 10 kt. A slow moving front will
bring scattered showers and a few storms to northwest IL late
tonight and Sunday morning, with a low chance of storms reaching
KPIA by late afternoon to evening where a PROB30 group will be
added.

25

&&

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

$$