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FXUS63 KILX 101139 AFDILX

Area Forecast Discussion...Updated Aviation National Weather Service Lincoln IL 539 AM CST Sun Dec 10 2023

SHORT TERM
(Today through Monday)
Issued at 315 AM CST Sun Dec 10 2023

An upper trough over the Upper Midwest/Great Lakes will dominate the weather across central Illinois today. A large area of low clouds associated with this feature blankets much of the region early this morning, with 08z/2am satellite imagery showing the back edge of the clouds extending from far eastern South Dakota
to central Iowa
to eastern Missouri. With boundary layer winds expected to remain northwesterly, the clearing line will make only slow progress eastward. This process will be further complicated by a short-wave pivoting southward around the parent trough across Minnesota. This will bring additional clouds southward and thus slow the clearing. Models disagree on how fast clearing will occur later today, with NAM/GFS soundings suggesting at least partial clearing along/west of I-55 by midday. Meanwhile the RAP/HRRR are much slower and tend to keep clouds across much of the KILX CWA through the afternoon and even into the evening.
Based on current synoptic set-up, think the slower RAP/HRRR is the prudent solution. As a result, am going with overcast conditions across most of central Illinois through the entire day. The exception will be along/southwest of a Rushville...to Jacksonville...to Flora line where a few peeks of sunshine will be possible late this afternoon. Given extensive cloud cover and continued northwesterly winds, chilly high temperatures in the middle to upper 30s are anticipated.

Low clouds will gradually clear from southwest to northeast across the area this evening, but may not depart the E/NE around Champaign/Danville until midnight. Even after the low clouds are gone, NAM/RAP layer RH profiles indicate high clouds streaming across the area overnight. Despite high pressure building overhead and winds becoming light/variable, at least partial cloud cover will help mitigate optimal radiational cooling. It will still be a cold night with lows in the lower 20s, but do not think readings will drop quite as far as they could under completely clear skies.
After a period of high clouds during the morning, skies will become sunny across the board by Monday afternoon as highs rebound into the lower to middle 40s.

Barnes

LONG TERM
(Tuesday through Saturday)
Issued at 315 AM CST Sun Dec 10 2023

Quiet weather will prevail through the extended. A weak cold front will sag southward into central Illinois on Tuesday: however, it will be devoid of moisture and will produce little more than a few clouds and a shift in the wind as it passes. Temperatures will remain near normal for this time of year in the lower to middle 40s through Wednesday, then will climb into the upper 40s and lower 50s by the end of the week as the polar jet stream retreats well to the north across central/northern Canada. Meanwhile a cut- off upper low progged to develop over the Great Basin on Wednesday will slowly meander eastward late in the period. 00z Dec 10 models have shifted its track much further south across the Gulf Coast in response to a weak northern-stream wave rippling eastward along the U.S./Canada border. If this solution pans out, any precip associated with the low will stay well south of Illinois and a mild/dry weekend will be on tap. At this point, will still carry slight chance PoPs Friday night into Saturday as the northern feature passes to the north.

Barnes

AVIATION
(For the 12z TAFs through 12z Monday Morning)
Issued at 539 AM CST Sun Dec 10 2023

MVFR ceilings will prevail at the central Illinois terminals through this afternoon before gradually scattering from southwest to northeast during the evening. While the back edge of the overcast is currently just west of the Mississippi River, it will make only very slow progress eastward today. In fact, the last few runs of the HRRR have continued to delay the clearing. Based on latest satellite trends and model guidance, have scattered the MVFR ceilings at KSPI by 01z...then further northeast to KBMI/KCMI by 06z. Winds will initially be NW with gusts of 15-20kt early this morning, then will decrease as the day progresses...eventually becoming light/variable after sunset as high pressure builds overhead.

Barnes

ILX WATCHES/WARNINGS/ADVISORIES
None.

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