Area Forecast Discussion
Issued by NWS Central Illinois

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS63 KILX 221725
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1225 PM CDT Fri Mar 22 2024

.KEY MESSAGES...

- Gusty winds and sub-freezing temperatures will filter into the
  region this evening behind a sharpening cold front. Peak gusts
  will range between 25-35 mph, and areas north of I-72 have a
  high probability (greater than 70% chance) of overnight lows
  falling below 32 degrees.

- A powerhouse spring storm system will bring gusty winds, periods
  of rainfall, and perhaps a few thunderstorms between Sunday
  night and Tuesday. The probability for gusty winds exceeding 40
  mph is high (greater than 60%). The probability for rainfall
  exceeding 2 inches is low (less than 25%). And, the probability
  for severe storms is very low (less than 2%).

- Another brief shot of sub-freezing temperatures then appears
  likely (greater than 70% chance) by the middle of next week
  behind the departing storm system.


&&

.UPDATE...
Issued at 953 AM CDT Fri Mar 22 2024

The forecast generally remains on track today, though the sharpness
of the cold front`s arrival was highlighted by freshening up the
hourly wind and temp forecasts using a blend of highres guidance -
mainly the 12/13z iterations of the HRRR. This brings the plunge in
temperatures in up-tick in gusty surface winds (to around 35 mph) to
Galesburg around 19z/2pm and I-55 around 22z/5pm. This abrupt
frontal passage will bring a 20 degree plunge in apparent temps over
the span of about an hour at any given point across central Illinois
this afternoon, with those "feels like" temps falling from 50s/low
60s ahead of the front to the low-mid 20s by late evening.

Bumgardner

&&

.DISCUSSION...
Issued at 1229 AM CDT Fri Mar 22 2024

A couple of forecast challenges exist today across central
Illinois. Chief among them is nailing down afternoon
temperatures, though p-type could become tricky as well for a
brief time this evening before precip ends. Of more certainty is
gusty north winds spilling-in behind the cold front, as
temperatures drop sharply overnight.

An early morning loop of water vapor imagery reveals weak
shortwave energy moving across the Corn Belt, with short-term
models in excellent agreement in pushing an 850mb low along the
I-80 corridor this afternoon. As this disturbance becomes
displaced further east throughout the day, it will help drop a
sharpening baroclinic zone through central Illinois. The net
effect will be a large spread in afternoon temperatures, with
locations north of the IL River Valley peaking in the upper 40s
and locations south of I-70 topping-out in the mid 60s.

Light precip is likely (> 60% chance) this afternoon and early
evening in areas west of I-55 as a strengthening band of f-gen
(850-700mb layer) helps provide enough forcing to tap into a
narrow ribbon of moisture. QPF will be modest with this passing
disturbance, with the latest HREF LPMM output offering 0.10" (give
or take a few hundredths); though, amounts will be less in areas
east of I-55 where mid- level dry air eventually punches in.

As mentioned, there could be a brief window this evening in which
precip becomes mixed. Processes such as wet-bulbing and seeder-
feeder will occur non-uniformly across the region, resulting in
various thermal profile outcomes and p-types. Model soundings are
split, with the NAM showing partial-melting (sleet) and the
RAP/HRRR showing cold isothermal layer (rain/snow). Regardless of
the ptype, cloud ice nucleation gets lost quickly this evening as
dry air surges overtop the moist layer. This should limit the
window for wintry weather to just a few hours, and no impacts are
anticipated.

Breezy north winds will help usher in a much colder air mass
overnight as the front departs. Lows will dip into the mid-to-
upper 20s north of the IL River Valley, with low-to-mid 30s
elsewhere.  Wind chill values will fall into the teens.

After a few seasonably cold days, temperatures bounce warmer by
early next week as winds turn southerly ahead of deepening low
pressure. The deterministic NBM is offering highs in the 60s on
Monday, and we see no reason to stray given the warm advection
pattern.

As the frontal system continues to evolve next week, it may pose
multiple risks to the region including gusty winds, heavy rain,
and strong thunderstorms. Of these, gusty winds appear to be the
most likely, with blended and ensemble guidance both exhibiting
high probabilities (> 60% chance) of gusts exceeding 40 mph on
Monday. Confidence in heavy rainfall is lower, with only a 25%
chance of exceeding 2 inches in areas south of I-70. And, the
probability of severe weather on Monday is very low (< 2%
chance), with the latest LREF output shifting the threat area
slightly westward.

MJA

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1224 PM CDT Fri Mar 22 2024

A cold front will push across central Illinois this afternoon and
early evening. A narrow band of light showers is expected to
accompany the front. Behind the front, winds will turn northerly
and gust to around 20-25kt as MVFR ceilings overspread the
terminals. MVFR ceilings will persist overnight with improvement
possible mid to late Saturday morning.

Deubelbeiss

&&

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

$$


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.