Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 170523
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1123 PM CST Sat Dec 16 2017

.UPDATE...
Issued at 826 PM CST Sat Dec 16 2017

High clouds are moving in from the southwest a bit quicker than
expected, ahead of the developing storm system over the southern
Plains. Have made some adjustments to the sky trends through the
midnight hour, with mostly cloudy conditions still expected after
midnight. With the southerly winds, temperatures should hold up in
most areas, with sub-freezing conditions only expected in the far
northern CWA, closer to the boundary located near I-80. That
aspect of the forecast needed only minor adjustments.

Have updated PoP trends for Sunday. Quite a bit of dry air evident
below 10,000 feet early in the day, though this moistens up
fairly quickly. Still kept the highest PoP`s during the late
morning through about midday, before the system quickly lifts
northeast. With the dry air, can`t rule out some patches of sleet
initially as the precip develops, though rain will be the
prevailing weather type. This change was more of an impact on the
gridded forecast, with little change needed in the coarser zone
forecasts.

&&

.SHORT TERM...(This evening through Sunday)
ISSUED AT 315 PM CST Sat Dec 16 2017

A sunny and pleasant day across central and southeast IL with
breezy sw winds 10-20 mph and gusts of 20-25 mph giving milder
temps in the low to mid 50s, even upper 50s from Springfield and
Jacksonville sw. 1025 mb high pressure over GA and sprawled across
the southeast states while a cold front extended from central IA
thru nw KS to deepening 1000 mb low pressure over se CO. Low
pressure is forecast to weaken as it ejects into the central
plains by dawn Sunday and eject ne over nw IL by Sunday afternoon.
Tonight should stay dry with mid/high clouds increasing from the
ssw overnight. Lows ranging from around 30F from i-74 ne and mid
30s from Springfield and Effingham sw.

12Z forecast models remain fairly consistent in spreading qpf ne
across CWA during Sunday morning, though likely not getting to
I-74 and ne until between 15-18Z Sunday. Could see a very brief
period of light snow/sleet mix at the onset of the precipitation
over central IL as initially dry low levels give evaporative
cooling. Rain to diminish from sw to ne during mid/late Sunday
afternoon and total rainfall amounts only near a tenth inch or
less. Highs in the low to mid 40s Sunday with ssw winds 5-10 mph,
temperature rise held back by overcast skies and light rain.

.LONG TERM...(Sunday night through Saturday)
ISSUED AT 315 PM CST Sat Dec 16 2017

A split upper level pattern takes shape early in the work week
with central IL staying in a quiet and mild wx pattern. Storm
tracks stay over the northern tier states and over the southeast
states from Monday thru Wed night. Some fog and drizzle looks to
develop later Sunday evening into mid Monday morning especially
north of I-72 with light sw winds and lingering low level
moisture/clouds. Lows Sunday night in the mid to upper 30s. Low
clouds to decrease from the west during Monday afternoon, though
eastern IL may not see much sunshine most of the day. SW winds
keep mild temps around with highs Monday mostly in the lower 50s,
with some upper 40s ne of I-74. More sunshine on Tue to warm temps
a bit more, into the low to mid 50s, with upper 40s by Galesburg.

A weak cold front passes through area late Tue and turning cooler
about 10F cooler for Wed with highs in the low to mid 40s. A
southern stream storm system still appears to pass far enough
south of IL on Wed to keep our area dry, though could see more
cloud cover over southeast IL. Have partly to mostly sunny skies
Wed.

A strong upper level trof digging over the Rockies Wed night to
eject low pressure into the central plains Thu morning with a
frontal boundary extending from se KS into nw IL. Still have small
chances of light rain showers developing nw of IL river during Thu
afternoon, especially late. Highs Thu mostly in the mid to upper
40s, but range from lower 40s nw by Galesburg to 50F far se IL at
Lawrenceville. Precipitation chances spread se across the CWA
during thu night and as colder air arrives, the rain chances to
turn to snow chances in central IL. Kept it all rain se of I-70
overnight Thu night where lows above freezing. Surface low
pressure ejects ne into the central Great Lakes by midday Friday
with some light snow showers Fri morning over area especially ne
CWA. Colder highs Fri range from lower 30s nw of IL river to lower
40s se of I-70. Highs Sat mostly in the low to mid 30s which is
closer to normal levels. A deepening upper level trof over the
nations midsection next weekend to keep seasonably cold temps
around. A low pressure lifting ne from lower MS river valley into
eastern ohio river valley Fri night could bring more snow showers
to eastern/se IL Fri night. Still some differences with models
with how far north southern stream storm track gets next weekend,
and most keep our area dry yet on Saturday and Sat night.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1123 PM CST Sat Dec 16 2017

Ceilings will be steadily lowering through the night, but anything
below 10,000 feet should hold off until Sunday morning. As areas
of rain spread northeast across central Illinois, moistening of
the lower levels will result in continued lowering of ceiling
heights. MVFR conditions will overspread the area during the
afternoon. By evening, there are some indications of potential
ceilings below 1,000 feet. Have included IFR conditions from
KPIA-KCMI late in the period as a result.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Geelhart
SHORT TERM...07
LONG TERM...07
AVIATION...Geelhart



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