Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 280111
AFDILX

Area Forecast Discussion...Updated
National Weather Service Lincoln IL
811 PM CDT Wed Mar 27 2024

.KEY MESSAGES...

-  A freeze is likely area-wide tonight (greater than 60%
   chance), which could harm any sensitive vegetation.

 - Periods of showers and storms are possible Friday evening
   through early next week. The threat of severe thunderstorms is
   low on Friday and Saturday (less than 5%), but the severe
   potential will need to be monitored for Sunday and Monday.

&&

.UPDATE...
Issued at 810 PM CDT Wed Mar 27 2024

This evening, ridge of high pressure stretches from near Omaha to
St Louis and will provide fair weather conditions across central
Illinois overnight with light winds and only some passing mid
clouds. Cloud cover is a bit of a wild card in terms of how
efficient radiational cooling will be overnight, but still
anticipate most of central Illinois to fall below freezing.
Upstream cloud cover moving into the Illinois River Valley should
continue to dissipate as it encounters dry air (0.25 PWat as
sampled by 00z ILX sounding). Some spots along the I-74 corridor
could dip into the mid 20s close to current dew points assuming
clear skies prevail.

Deubelbeiss

&&

.DISCUSSION...
Issued at 217 PM CDT Wed Mar 27 2024

Relatively benign weather conditions will exist through Thursday.
As weak sfc high pressure shifts closer to the area tonight, the
main concern is freezing temps that could impact any early-
growing, sensitive vegetation.

Skies should be mostly clear and winds will be light, which are
favorable conditions for radiational cooling. Some guidance
suggests cloud cover across western IL, though, which complicates
the low temp forecast. The forecast dewpoints for overnight (in
the mid/upper 20s) provide a lower bound to the potential low
temps. From a probabilistic viewpoint, the latest NBM has a 60-80%
chance of sub-freezing low temps south of I-70, and a 80-100%
chance north of I-70. A hard freeze isn`t out of the question
given the forecast dewpoints, and the probabilistic guidance has a
30-60% of sub-28F temps (with probabilities increasing with
northward extent). These conditions aren`t necessarily unusual, as
we often see hard freezes during the first week or two of April.
However, data from the National Phenology Network shows that leaf
development occurred 2-3 weeks earlier than normal this year,
hence the concerns that there may already be some sensitive
vegetation out there.

After tonight, a warming trend begins as a warm front develops
across the northern parts of the CWA. High temps climb into the
upper 50s on Thurs, then the mid/upper 60s for Fri. After tonight,
freezing temps are not expected through at least this weekend.

Beginning Friday, the pattern becomes more active across the
central Plains/Midwest, resulting in periods of showers/storms
across the ILX CWA through early next week. The first wave is
expected to result in a sfc low tracking across IA/northern IL Fri
night, with local precip chances increasing Fri eve into Fri
night. Scattered precip could linger into Sat, but generally
precip chances trend downward during the daytime hours on Sat.
Through Saturday, severe potential with any precip activity looks
low owing to marginal instability (MUCAPEs generally less than 500
J/kg). However, continued moisture return is expected to result
in increasing instability Sun-Mon, with the latest GEFS showing a
60-80% chance of SBCAPE over 500 J/kg by Monday. During that
timeframe, a frontal boundary is progged to be draped east-west
across the ILX CWA. The details of any severe storm threat remain
foggy at this range, but at this stage we can at least say the
potential for severe storms is higher on Sun/Mon than it is on
Fri/Sat. The latest CSU machine learning guidance (which was based
on models from 00z Wednesday) had a 15% risk area across central
IL both Sun and Mon. In terms of total rainfall, amounts don`t
appear particularly concerning at this stage, with the NBM
depicting a 30-40% chance of exceeding 1" of rainfall by Tuesday
morning.

Erwin

&&

.AVIATION...  (For the 00z TAFs through 00z Thursday Evening)
Issued at 630 PM CDT Wed Mar 27 2024

High pressure will settle south of the terminals resulting in a
modest west to southwest breeze and VFR conditions through the
period. Winds will diminish during the overnight hours and may be
a bit variable at times, then will pick up into the 9-12kt range
during the day Thursday.

Deubelbeiss

&&

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

$$


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