422
FXUS63 KILX 070841
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
241 AM CST Thu Nov 7 2024

.KEY MESSAGES...

-  There is a greater than 90 percent chance for rain across most
   of central Illinois this weekend. The system has trended south
   resulting in a lower precip forecast compared to previous
   forecasts. 50th percentile precip amounts from the NBM now
   range from around a quarter inch to three quarters of an inch
   north to south across central Illinois.

&&

.DISCUSSION...
Issued at 235 AM CST Thu Nov 7 2024

High pressure extends from Pacific Northwest into the Midwest this
morning providing light winds and fair weather condtions, albeit
cloudy for much of the area. 00Z ILX sounding showed a sharp
inversion based around 900mb was in place which continues to lock
low level moisture over central Illinois resulting in the low
stratus. Clouds will likely linger at least through the rest of
the morning into the early afternoon, but will slowly get shunted
southward as drier air filters in from the north and daytime
mixing helps to erode the stratus deck. Expect highs in the mid to
upper 50s north of I-70 and lower 60s south. Similar conditions
are expected across central Illinois Friday except there should be
less cloud cover across the area.

Meanwhile, an upper low over the Desert Southwest this morning
will lift across the Great Plains to the Upper Midwest this
weekend. Mid level warm air advection will overspread central
Illinois through the day Saturday driving showers and storms
across the region. Instability appears weak across central
Illinois with MUCAPE values of less than 100 J/kg advertised by
the GFS and only pockets of a few hundred J/kg per the ECMWF.
Soundings show this instability is rooted around 800mb or so with
a strong inversion atop a shallow PBL. Any storms will be elevated
as a result greatly limiting the threat for any severe weather
with this system. There has been a slight southward trend in the
upper low track and precip amounts have trended down across
central Illinois as a result of the QPF axis also shifting south.
NBM probs for exceeding a third of an inch of rain now range from
20-40 percent north of I-72 while the 70-90 percent probs we saw
from yesterday`s guidance have shifted south of I-70. The
probability for one inch of rain has also come down quite
drastically, and is less than 10 percent north of I-70 and only up
to around 30 percent near Lawrenceville. Would not be suprised to
see some continued variability from model guidance given the
typically hard to predict cut-off upper low.

Dry weather returns to the forecast behind a cold front for the
latter part of the day Sunday through Tuesday, then a vigorous
shortwave trough is progged to move quickly across the region
around midweek. While some of the details remain unsure at this
distance, favorable low level trajectories from the Gulf of
Mexico will allow dew points to build back into the mid 50s across
central Illinois contributing to some potential for surface based
instability. NBM indicates around a 60 percent chance for at
least 100 J/kg of SBCAPE while deep layer shear values will be
seasonably strong. Depending on timing of the system, cannot rule
out a severe weather threat, if not across central Illinois then
somewhere nearby in the region. This period bears watching as the
details come into better focus over the next few days.

Deubelbeiss

&&

.AVIATION...  (For the 06z TAFs through 06z Thursday Night)
Issued at 1133 PM CST Wed Nov 6 2024

MVFR conditions will prevail at all TAF sites overnight and into
the morning hours. Cig heights are either right at 2kft or just
above. Some cigs could drop to below 2kft, but not seeing many
reports that low. Cigs should remain above 2kft tomorrow. Clouds
should then become more scattered during the afternoon hours and
then the lower clouds will dissipate and only cirrus is expected
tomorrow evening. Winds will be northerly through the period with
speeds of 8-7kts or less.

Auten

&&

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

$$