Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 200429

Area Forecast Discussion
National Weather Service Lincoln IL
1129 PM CDT WED OCT 19 2016

Issued at 912 PM CDT Wed Oct 19 2016

Forecast generally on track as low pressure passes across
southeast Illinois the rest of the evening. Instability params are
showing thunderstorm potential continuing south of I-72 through
midnight, with chances more confined to S of I-70 from midnight to
sunrise Thursday. While the low pressure center is expected to progress
into western Ohio by 12z Thurs, shower chances will continue behind
the low well into Thursday for areas east of I-55. Minor updates
were done to weather/PoP grids this evening. Otherwise, no major
changes done this evening.


.SHORT TERM...(This evening through Thursday)
ISSUED AT 250 PM CDT Wed Oct 19 2016

19z/2pm surface analysis shows stationary frontal boundary extending
from southern Indiana southwestward into the Ozarks.  Several
clusters of thunderstorms have developed along/north of the boundary
this afternoon, with the first cluster currently tracking across the
SE KILX CWA.  Additional storms are noted further upstream around
St. Louis and across southwest Missouri.  This convection will track
E/NE along the front and continue to impact mainly the southeast
half of the CWA tonight.  Given a frontal position slightly further
north than previously forecast, have expanded higher PoPs further
northward as well.  While minimal elevated instability exists across
all of central Illinois tonight, the highest values remain focused
closer to the baroclinic zone.  As a result, have limited likely to
categorical PoPs and thunder mention to locations along and
southeast of a Springfield to Champaign line.  Further northwest,
have only gone with chance PoPs for showers.  Overnight lows will
range from the upper 40s far northwest around Galesburg to the upper
50s south of I-70.

As low pressure tracks along the frontal boundary into the Ohio
River Valley, precip chances will gradually decrease from west to
east across the region on Thursday.  Will continue likely to
categorical PoPs along/east of I-57 through the morning, then will
decrease to just chance by afternoon before the showers taper off
and completely come to an end by evening.  Total rainfall with this
system will be heaviest along the I-70 corridor where amounts of
1.50 to 1.75 will be common.  Amounts will steadily drop off further
northwest, with just a couple hundredths of an inch expected from
the Peoria area northward.  Skies will initially be overcast
Thursday morning, then will become mostly sunny along/west of I-55
by afternoon.  Highs will generally be in the lower 60s, with cooler
upper 50s noted near the Indiana border where clouds/showers will
prevail throughout the day.

.LONG TERM...(Thursday night through Wednesday)
ISSUED AT 250 PM CDT Wed Oct 19 2016

The upper level trough axis is forecast by all models to progress
east of the central/SE Illinois forecast area by Thursday evening
with subsidence and high pressure building into the area
subsequently. Northwesterly flow behind the departing trough will
bring in much cooler air...but also will keep a light breeze in
place through Thursday night. The lightest winds should be northwest
of the Illinois River nearest the approaching surface high pressure
center. As a result...patchy frost may develop by Friday morning
roughly northwest of a Havana to Bloomington line as temperatures
reach the mid 30s. Elsewhere...lows are expected to reach the upper
30s to lower 40s. Otherwise...slightly warmer temperatures and light
wind should prevent frost.

For Friday, clear skies, light winds, and cool temperatures are
expected as high pressure moves into the central IL area. Expect
highs in the mid to upper 50s, and lows Friday night near 40.

Fair weather will continue into early next week as high pressure
slowly slips into the southeastern U.S., upper level ridging builds
into the central U.S., and a warmer air mass begins to edge eastward
into the central IL area. Expect highs in the low to mid 60s
Saturday, and upper 60s to lower 70s Sunday through Tuesday...above
normal. Lows generally in the 40s to around 50...also slightly above

The next storm system to potentially impact the area looks to be
midweek according to a consensus of 12Z models. However...GFS and
ECMWF disagree on the amplitude of the responsible upper level wave
and therefore the speed of it`s progression. GFS ensembles also
break down consistency by the middle of next week implying low
predictability. Therefore...have slowly spread chance PoPs into
forecast through the day Wednesday and kept the higher Pops toward
areas west of the Illinois River.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1128 PM CDT Wed Oct 19 2016

Showers have begun to diminish west of PIA to SPI, and that trend
will continue slowly to the east. Low pressure is making its
closest approach to our southeast counties from now through 06z,
then will advance east of Illinois the rest of the night. However,
rain chances for the eastern terminals will continue through
Thursday morning in the wake of the low, as we experience
continued lift in the mid-upper levels ahead of the upper trough
axis. CMI could even see stray showers linger Thursday afternoon.

Instability parameters show low potential for thunderstorms near
any TAF site through tomorrow, so no thunder was included this
TAF issuance.

VFR conditions are expected to prevail throughout the next 24
hours, with brief MVFR cloud conditions possible for DEC and CMI
the rest of the night, per the latest HRRR. Have not included any
MVFR conditions in the 06z TAFs.

Winds will increase toward sunrise from the northeast, into the
10-13kt range. Gusts are expected tomorrow from the north at
12g18kt at times, especially near our eastern terminals. Winds
will subside with sunset tomorrow, as clouds decrease from west to


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