589
FXUS63 KILX 140804
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
304 AM CDT Tue May 14 2024

.KEY MESSAGES...

- The majority of central Illinois is forecast to see greater than
  a half inch of rain through Wednesday morning. Localized areas
  (10 percent or less) could see 2 to 3 inches of rain or more,
  with runoff causing further rises in rivers and streams.

- More rain is forecast from Thursday into Friday. Though the
  chance of over 1 inch is only about 20-40% for any particular
  location, wet soils will result in much of the rainfall being
  converted to runoff.

&&

.DISCUSSION...
Issued at 304 AM CDT Tue May 14 2024

Early morning water vapor imagery reveals a low pressure center
over northern Missouri, with modest southerly flow ahead of the
low working to slowly pull moisture northward. The latest analyzed
precipitable water values range from 1.2 to 1.4 inches, with
modest MUCAPE values of no more than a few hundred J/kg. Forecast
soundings display an ideal saturated profile through much of their
depth although with a bit of drying in the mid levels, with the
minimal CAPE distributed in a "long, skinny" fashion. Combined
with the continued approach of the upper low as well as daytime
heating, this should yield an opportunity for showers and
thunderstorms producing rain at moderate to heavy rates.

Initially, look for showers bubbling up near and west of the
Illinois River near and north of a zone of deep moist convergence
where 100-200 J/kg of MLCAPE resides with little cap. In addition,
the cluster of showers and thunderstorms moving into southern
Illinois from southeastern Missouri may clip southeastern portions
of the ILX CWA beginning within the next 2-3 hours. During the
daytime, coverage of showers and storms is forecast to be greatest
south of I-74 with coverage decreasing from north to south
beginning about 3-4 pm. Coverage of the moderate to heavy showers
will be spotty. Though most will measure at least a half inch of
rain between now and Wednesday morning, about 25% of locations
will probably measure less than that. Localized swaths could
receive 2-3 inches of rain or more. The rainfall, especially where
heavy, could result in further rises on area rivers and streams.

Precip chances have been extended into tonight and Wednesday near
the Indiana state line, as CAMs and deterministic global models
are fairly consistently showing continuation of at least light
precip to the west of the low slowly departing along the Ohio
River valley. After a brief dry period Wednesday evening and
perhaps early Thursday morning, notable precip chances return for
Thursday and Friday as another fairly weak short wave trough makes
its way across the Plains toward the Midwest. The joint
probability of SBCAPE > 250 J/kg and sfc-500mb shear > 30 kt is
only around 10-15%, but that is a bit more than for the present
system. Still, severe weather probabilities are low for the
Thursday-Friday event as well. Fortunately, the rainfall threshold
probabilities are also lower than for the current system. The
probability of an inch of rain during the entire 48 hour period
from Thursday morning to Saturday morning is around 20-40%. Even
so, each successive rain event serves to add to the saturation of
soils and result in quicker runoff.

The 00z GFS shows a closed low moving out of Missouri Friday
evening with rain continuing most of the day Saturday. This
solution appears to be a bit of an outlier, though it`s not the
only solution with rain continuing so low precip chances are
included for Saturday via the NBM. Low precip chances continue
through the Sunday-Tuesday period as well, with uncertainty
regarding timing of fast moving short-wave troughs in the presence
of at least some instability for shower and storm development.
It`s unlikely that this entire period will be wet, but it`s
difficult to nail down exactly when the rainy periods will be.

AAT

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1136 PM CDT Mon May 13 2024

Initial challenge will be timing of low MVFR or IFR ceilings. Most
thus far have been associated with the lingering showers near
KBMI/KCMI and these are lifting northward, but some breaks in the
clouds further south have quickly filled in with stratocumulus.
Evening HREF guidance shows a 60-80% chance of ceilings below
3,000 feet overspreading the terminal sites between 06-09Z, and
ceilings dropping to IFR within an hour or two afterward. Slow
improvement is expected Tuesday afternoon, with best chances of
rising back above 2,000 feet at KPIA/KBMI in the evening.

Showers will become widespread again in the 12-18Z time frame and
continue through late afternoon, before diminishing to scattered
showers. Any of the showers from late morning through afternoon
will be capable of a few lightning strikes, but confidence is too
low/sparse to pin down a specific time frame for inclusion.

Geelhart

&&

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

$$