Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 181752
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1152 AM CST Sat Nov 18 2017

.UPDATE...
Issued at 1032 AM CST Sat Nov 18 2017

Storm system working through Central IL this morning, with
widespread showers and a line of thunderstorms moving out to the
southeast with the cold front associated with the system. For now,
forecast is doing well and plenty of rain and cooler air still
out there behind the boundary. Keeping an eye on storms as they
move through the southeast with good shear in the low and mid
levels, if minimal instability. Still a concern with strong winds
with and behind the front through the afternoon and keeping
advisory. Temps cooling into the afternoon and the potential to
see some snow mix into the northwest after midday. No
accumulations are anticipated as mixed with rain. Only minor
adjustments to the forecast made at this time.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 345 AM CST Sat Nov 18 2017

09Z/3 am surface map shows a 993 mb low pressure deepening along
the KS/MO border with a frontal boundary extending ne across the
IL river valley. An area of showers and isolated thunderstorms was
north of I-72 and lifting ENE. Temperatures ranged from around 50F
along and nw of the IL river, to the lower 60s in southeast IL
from Pittsfield to Effingham to Lawrenceville south. Breezy south
winds se of I-55 were gusting in the 20s and bringing in the
milder/moist air mass with dewpoints in the low to mid 50s.

Will expand the wind advisory another row of counties northward
today with sustained winds of 25-30 mph and gusts of 40-45 mph
expected with strongest winds (nw) behind the cold front from 11
am to 5 pm. Wind advisory is in effect from 8 am to 9 pm today,
though strongest winds will be from late morning through sunset.
Models deepen surface low pressure ENE to 989 mb over ne IN by
18Z/noon, and 985 mb over Lake Erie by 00Z/6 pm and pulls cold
front from the IL river southeast through Lawrenceville early
this afternoon. Showers will continue to become more widespread as
deepening low pressure moves across area during this morning,
with thunderstorms also possible. SPC day1 outlook has marginal
risk se of Knox, Stark and Marshall counties, with a slight risk
of severe storms from Terre Haute to Flora se mainly during late
morning into early afternoon with passage of cold front. There is
a 5% risk of large hail and damaging winds gusts in marginal risk
area, while slight risk area in southeast IL has 15% risk of
damaging wind gusts and 2% risk of tornadoes. Rainfall amounts
average from a half to 1 inch today with highest amounts ne CWA.
Highs today range from around 50F from IL river nw early this
morning, to the mid to upper 60s in southeast IL from I-70 south.
Temperatures will fall behind the cold front, reaching 35-45F from
nw to se by sunset.

Will see rain mix with or change to light snow showers during the
afternoon northern CWA but no accumulations expected. Shower
chances linger east of I-57 early this evening, then dry rest of
the night as nw winds remain gusty through the night, strongest
during the 1st part of the evening when wind advisory is still in
effect. Much colder lows in the mid to upper 20s overnight, with
Lawrenceville near 30F.

.LONG TERM...(Sunday through Friday)
ISSUED AT 345 AM CST Sat Nov 18 2017

A quiet weather pattern expected during this time frame as dry
conditions return. Strong 980 mb surface low pressure will lift
over the St Lawrence Seaway during Sunday, while 1028 mb high
pressure settles into Texas and ridges into IL by Sunday
afternoon. This should lighten WNW winds to around 10 mph during
Sunday with return of sunshine as skies clear during overnight.
Highs Sunday only 35-40F and lows Sunday night of 25-30F.

Surface ridge over Texas settles over the TN river valley by
Monday morning and return ssw winds to moderate temperatures to
50-55F on Monday with mostly sunny skies. A dry cold front moves
se across CWA on Tue and starts to bring in cooler air especially
over the IL river valley where highs in the mid to upper 40s.
Milder 50-55F from Lincoln southeast. Lows back in the low to mid
20s on Tue and Wed night with highs on Wed in the mid to upper
30s as another area of high pressure settles over IL by sunset Wed.
A weather system moves into the upper Midwest and Great Lakes
region on Friday keeping its precipitation north of central IL
then. Highs in the lower 40s Thu moderate back to the upper 40s
and lower 50s on Friday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1134 AM CST Sat Nov 18 2017

Active weather situation across Central IL with precip continuing
behind the cold front, now through ILX terminals. Other than rain
showers, and some flakes of snow possibly mixed in briefly this
afternoon for PIA and BMI...major aviation concern is the wind.
Strong winds out of the NW, gusting at the surface to 35-40kts
behind the front. Models improve ceilings in the evening hours to
VFR after 00z, going to go with that trend although the dry air is
well back to the NW, based on the speed of the wave aloft in
general. Gusty NW winds will continue into the early evening
hours, gusting to 20-25kts well after midnight.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 9 PM CST this evening for ILZ040>057-061>063-
066>068-071>073.

&&

$$

UPDATE...HJS
SHORT TERM...07
LONG TERM...07
AVIATION...HJS



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