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FXUS63 KILX 241932 AFDILX

Area Forecast Discussion National Weather Service Lincoln IL 232 PM CDT Wed Apr 24 2024

KEY MESSAGES

- Temperatures will fall into the 30s across most of central Illinois tonight. There is a 60-80 percent chance of sub- freezing temps from Lacon to Bloomington Rantoul and areas north.

- There will be periodic chances for showers and thunderstorms Friday through Sunday. Some storms could be severe (5-15 percent) at times and there is potential (5-15 percent) for locally heavy rain.

DISCUSSION
Issued at 226 PM CDT Wed Apr 24 2024

Through Thursday...
High pressure will slowly drift east across the Great Lakes in the near term resulting in continued cooler but otherwise quiet weather conditions across central Illinois in the near term. Some cold air stratocu persists across much of central Illinois this afternoon, but should continue to gradually erode from the edges with mainly portions of east central Illinois holding onto cloud cover late into the evening. Temperatures will fall into the 30s across most of central Illinois overnight into Thursday morning.
While there remains some concern that a light easterly gradient or lingering clouds may mitigate frost potential tonight, have enough confidence in temps near the freezing mark to hoist a Frost Advisory for portions of the I-74 corridor Thursday morning.

Friday through the weekend...
A pair of low pressure systems are progged to lift from the central Great Plains into the Upper Midwest; the first Friday into Saturday, and the second Saturday night through Sunday night. Low level trajectories off of the Gulf of Mexico will allow dew points to rise into the 60s as the first warm front lifts across central Illinois Friday. Dew points further rise into the mid 60s this weekend accompanied by high temperatures near 80 degrees.

Increasing cloud cover is expected Friday along with scattered showers and non-severe storms as mid level warm air advection overspreads central Illinois. This will result in only modest diurnal destabilization Friday afternoon with the strongest instability progged to set up well to our west along the KS/MO state line. Storm coverage should increase to our west Friday evening as a low level jet strengthens. Storms will spread east overnight and could bring an accompanying severe weather threat as instability advects into Illinois overnight associated with a veering LLJ. Eastward extent of the severe weather threat remains uncertain but could reach portions of central Illinois.

As the first low lifts into the Upper Midwest Saturday, a broad warm sector will in in place across portions of the Mid Mississippi Valley. Forecast soundings show steep low/mid level lapse rates and minimal capping in place Saturday afternoon.
Forcing will be a bit nebulous, but shouldn't take much to kick off deep convection. LREF joint probabilities of CAPE >500 J/kg, Cin >-25 J/kg, and deep layer shear >30kt are maximized across central Illinois west of I-55 Friday afternoon around 50 percent.
If storms are able to initiate, this appears to be the time frame for highest impacts from severe storms during the Friday-Sunday time frame.

Second low begins to take shape Saturday night into Sunday over the Great Plains and will take a similar path as the first low, albeit ever so slightly further east. Similar to the first low, LLJ appears to be focused to our northwest Saturday night, and the strongest instability is also in place to our west lending some uncertainty in whether the severe threat will make it as far east as central Illinois. The trailing cold front will eventually sweep across central Illinois Sunday night into Monday morning marking the back edge of the precip chances.

All said through the weekend, mean 72-hr QPF amounts through Monday morning look to total between 1 and 2 inches for most of central Illinois with highest amounts in the west. 90th percentile amounts peak between 3-4 inches west of the Illinois River and would not be suprised to see some localized swaths of these higher end amounts.

Deubelbeiss

AVIATION
(For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1234 PM CDT Wed Apr 24 2024

High pressure will very gradually shift east across the Great Lakes tonight and Thursday resulting in NE winds slowly veering to SE across central Illinois. MVFR ceilings across the region will linger into the afternoon, longest at DEC and CMI, but should eventually scatter back to VFR. VFR conditions should then prevail the remainder of the period.

Deubelbeiss

ILX WATCHES/WARNINGS/ADVISORIES
Frost Advisory from midnight tonight to 6 AM CDT Thursday for ILZ030-031-038-043>046.

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