901
FXUS63 KILX 131525
AFDILX

Area Forecast Discussion...Updated
National Weather Service Lincoln IL
1025 AM CDT Mon May 13 2024

.KEY MESSAGES...

- Showers and storms are expected (70-90% chance) mainly this
  afternoon through Tuesday afternoon. Coverage/potential of >1.0"
  rainfall is lowering. There is a 20-40% chance for more than an
  inch of rainfall in any one location. The widespread amounts now
  look to be in the 0.50-0.75 inch range.

- Another system will bring rain to the area Thursday into Friday,
  with a 40-50% chance of rainfall amounts up to a half inch south
  of I-72.

&&

.UPDATE...
Issued at 1025 AM CDT Mon May 13 2024

The forecast is looking on track this morning as showers
are beginning to move into central IL. The upper level low over KS
will continue to approach from the WSW today, with the state
experiencing broad warm air/moisture advection in the 850-700 mb
layer currently. Expect shower and thunderstorm coverage to
increase over the next several hours, peaking in the late
afternoon/early evening hours. The NAM Nest has MLCAPE as high as
1500 J/kg this afternoon, but the HREF ensemble mean is closer to
500-1000 J/kg. Deep shear continues to look is rather weak today
at 10-20 kts. Given these two key ingredients being rather low,
severe storms are unlikely today. The SPC continues to have all of
IL in general thunder today, with severe storms possible in the
states further south and west.

Knutsvig

&&

.DISCUSSION...
Issued at 325 AM CDT Mon May 13 2024

IR satellite loops are showing the upper level low over western
Kansas and progressing slowly eastward. Synoptic scale lift is
gradually increasing ahead of low as far east as north-central
Missouri/south-central Iowa, where showers and a few storms are
expanding in coverage. Southerly flow today will encourage modest
low level moisture advection, to help overcome the dry sub-700mb
airmass in place early this morning. Due to the dry antecedent
air, the development of more widespread showers in central IL
looks to begin this afternoon, when instability params indicate
narrow MLCAPE as high as 1500 J/kg in the RAP soundings. Shear
profiles remain marginal for strong storms, with 0-6km bulk shear
at 25kts. However, a few supercells may develop per the
elongation of straight hodographs with time this afternoon.
Isolated hail and strong wind gusts could develop, but overall
potential of severe weather is low. Given the patchy nature of the
storm coverage, a few locations could see over 1.5" and others
less than 0.5".

The best chances of widespread showers looks to be this afternoon
into evening, with that area shifting to south of I-72 on Tuesday
afternoon.

The consensus of ensemble guidance is still indicating a break in
the rain mid-week in response to ridging at the surface and aloft
across Illinois. That break will coincide with some cooler temps,
with Wed morning lows in the upper 40s north of I-72.

Showers and isolated storms return Thursday through Friday, with
the highest potential (50-65% chance) Thursday afternoon into
evening. Instability looks marginal with 500 J/kg MUCAPE amidst
0-6km shear up to 25kts. Potential of severe weather is quite low.

A bright spot in the extended is for high temps to return to the
lower 80s Saturday and Sunday, despite 20-30% chance for showers
to bubble up each day.

Shimon

&&

.AVIATION...  (For the 12z TAFs through 12z Tuesday Morning)
Issued at 527 AM CDT Mon May 13 2024

VFR conditions will prevail this morning although ceilings will
be steadily lowering as a storm system approaches. While a few
showers are possible as early as 15Z, dry air in the lower levels
will likely delay rain in most areas until the afternoon and
evening. Main period for potential thunder appears during the mid
to late afternoon. A few storms may linger into early evening from
KPIA-KCMI, though this is less certain, and will not be mentioned
at this time.

A rapid expanse of lower ceilings is expected in the afternoon,
and most sites should be MVFR by about 21-23Z. Ensemble guidance
suggests ceilings may dip below 1,000 feet later this evening and
linger through 12z as visibility drops to MVFR in light fog or
drizzle.

Shimon

&&

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

$$