Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 171145

Area Forecast Discussion
National Weather Service Lincoln IL
645 AM CDT Tue Apr 17 2018

.SHORT TERM...(Today and tonight)
ISSUED AT 345 AM CDT Tue Apr 17 2018

Continued the freeze warning for our 8 southeast IL counties along
and south of I-70 through 9 am cdt this morning. Temps in
southeast IL are currently in the lower 30s, and will slip into
the 28-30F range by sunrise, before rising back above freezing
toward 9 am.

09Z/3 am surface map shows elongated 998 mb low pressure along he
southern Quebec/Ontario province line and into New Hampshire,
while 1028 mb Canadian high pressure along the Manitoba/Ontario
province line was ridging southward over western MN/IA into
central MO and mid MS river valley. A band of stratocumulus clouds
lingered from I-74 south to a Springfield to Paris line and was
drifting southeast. Another patch of stratocu was moving se into
northeast Knox, Stark and western Marshall counties. Temps had
cooled into the lower 30s across much of CWA, with upper 20s west
of a Macomb to Springfield line where low clouds cleared out
earlier in the evening. Aloft a strong 532 dm 500 mb low was over
eastern tip of upper MI and another 535 dm 500 mb low in ne PA.
Upper level ridge over the great plains putting IL in a cool and
dry nw upper level flow.

Some patches of stratocumulus clouds will continue this morning
over mainly ne half of CWA, but skies should trend mostly sunny
across area toward midday as high pressure ridge edges closer to
central IL. High clouds will increase from the west during the
afternoon, but overall a mostly sunny afternoon. Highs today range
from lower 50s from I-74 ne to the mid to upper 50s sw CWA. NW
winds 10-15 mph this morning to diminish to near 10 mph or less
during mid and late afternoon as high pressure moves in.

Clouds to increase from sw to ne during tonight and not as cold
tonight, with lows in the upper 30s and lower 40s, except mid 30s
north of Peoria. Have a slight chance of light rain showers across
the IL river valley late tonight as 990 mb surface low movings
into western KS by sunset and weakens to 999 mb as it moves into
ne MO by 12z/7 am Wed. Brunt of its precipitation including
isolated thunderstorms will be over IA and northern MO overnight.

.LONG TERM...(Wednesday through Monday)
ISSUED AT 345 AM CDT Tue Apr 17 2018

00Z models bring 1000 mb surface low pressure to near Peoria by
18Z/Wed and into west central Ohio by sunset Wed. Models have
continued to trend further south with this system, and have
expanded chances of showers Wed further south to include central
and northern CWA, with highest pops still along and north of I-74
where chance of thunderstorms Wed morning. Temps are tricky on Wed
as MET is 8-12F colder than the MAV for Wed highs. Leaned toward
the warmer MAV guidance which has upper 40s to near 50F from
Peoria north to the 65-70F in southeast IL which gets into the
warm sector. Areas south of Peoria will have stronger/gustier
winds on Wed with gusts 30-35 mph. Chance of showers Wed evening
over ne half of CWA, and mixing with and changing to light snow
showers. Light snow accumulations still appear to be confined to
areas north of CWA Wed night. Lows Wed night in the lower 30s
northern CWA, and upper 30s in southeast IL.

Surface low pressure tracks into southern New England by midday
Thu, while large upper level trof shifts over the eastern states
Thu. Cool highs Thu in the lower 50s, with some upper 40s ne of
I-74 as skies become mostly sunny Thu afternoon. Lows Thu night
in the lower 30s, and southeast 8 counties may need another
frost/freeze headline overnight Thu night.

Upper level ridge shifts east into the MS river valley by sunset
Friday while large cutoff upper level low moves into the 4
corners in the southern Rockies. A fair amount of sunshine Friday
with highs in the mid to upper 50s, which is still about 10
degrees cooler than normal.

Extended models are in agreement with keeping upper level low
further south as it tracks into the Red river valley along TX/OK
border Sat night and into the lower MS river valley Sunday night.
Models keep qpf sw and south of our CWA through Monday evening and
trended forecast in that direction. Highs in the upper 50s in
central IL Sat and lower 60s in southeast IL. Highs mostly in the
lower 60s Sunday and modify slowly into the mid 60s Monday and Tue.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 644 AM CDT Tue Apr 17 2018

Dry high pressure will advance into Illinois today, which should
point toward minimal cloud cover today. However, some moisture
trapped in the lower levels could lead toward cumulus
redevelopment near our NE terminals. The HRRR is more pessimistic,
with MVFR clouds developing by 15Z across PIA, BMI, CMI, and
remaining across that area until late afternoon. The NAM and GFS
are showing a brief period of clouds around 3K FT in the mid-
morning time frame, then mixing of dry air clearing out the
clouds. To trend towards HRRR somewhat, VFR clouds were included
across the northern TAF sites in the daytime period, at 3.5K FT.
After some clearing this afternoon, VFR to borderline MVFR clouds
will advance into central IL from the SW overnight.

Winds will start out W-NW in the 8-12KT range, then shift through
N to the NE late this afternoon and evening. After midnight, winds
should become E-SE and increase to 10-13kt.


Freeze Warning until 9 AM CDT this morning for ILZ062-063-



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