Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 202003

Area Forecast Discussion
National Weather Service Lincoln IL
303 PM CDT THU OCT 20 2016

.SHORT TERM...(This evening through Friday)
ISSUED AT 303 PM CDT Thu Oct 20 2016

A vigorous short-wave trough evident on 19z/2pm water vapor imagery
over southern Iowa/northern Missouri will continue to track eastward
across the area this afternoon and evening.  Enough synoptic lift is
being generated by this feature that weak radar returns are showing
up, suggesting the possibility of a few light showers or sprinkles.
Both the NAM and GFS show measurable precip developing across the
E/SE KILX CWA this evening as the wave passes through.  Think this
may be a bit too aggressive, but will mention isolated showers
along/east of the I-57 based on current radar trends.  Clouds will
hold firm into the early evening hours before gradually clearing
from west to east overnight.  HRRR has been handling cloud trends
quite well, so have followed its solution closely.  Skies will clear
to the I-55 corridor by midnight, then to the Indiana border by dawn
Friday.  With skies clearing and a cool/dry airmass flowing into the
region, overnight lows will dip into the middle to upper 30s across
the western CWA.  Think winds will decrease enough to allow the
formation of frost across the Illinois River Valley toward dawn.
Have therefore issued a Frost Advisory for all counties along and
west of the Illinois River.  Further east, clouds will hold on long
enough to keep lows in the lower 40s.  High pressure will slide
overhead on Friday, resulting in sunny skies and cool high
temperatures in the middle to upper 50s.


.LONG TERM...(Friday night through Thursday)
ISSUED AT 303 PM CDT Thu Oct 20 2016

High pressure ridge will sit right over the CWA Friday night, and
with clear skies and light winds, frost will be a concern. Based on
the forecasted ridge axis, believe the best area for frost will be
in the eastern half of the CWA. Will probably need an advisory for
Fri night, but will wait til tomorrow to issue. High pressure will
dominate the area with dry weather through most of the weekend. A
frontal system will slide across northern half of the CWA on Sunday,
but there will be a lack of moisture, so no precip is expected when
this moves through. Behind this weak front, cooler high pressure
will move into the area for the first couple of days of the week.
Dry weather will continue as well. The next real chance of precip
will be beginning Tue night after midnight and then continuing into
Wed night. Earlier model runs differed on timing and location of the
precip; however, now models in better agreement. This system is
expected to move through quickly, so Thursday of next week should be

Besides the cool temps Fri night, seasonable temps will continue for
Sat and Sat night. Temps will then warm to above normal for Sunday,
before becoming seasonable again after the second high pressure area
moves in for next week.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1253 PM CDT Thu Oct 20 2016

While the main area of rain from earlier this morning has now
shifted east of the terminals, a trailing upper-level wave may
bring a few light showers or sprinkles through the afternoon, so
have included VCSH at all sites. The main aviation forecast
concern will be the approach/timing of MVFR ceilings currently
spilling southward out of northern Illinois. Latest satellite
imagery shows the leading edge of the lower clouds along the I-74
corridor. HRRR seems to have a good handle on the clouds, so have
followed its solution closely. As a result, have initially started
with MVFR ceilings at the I-74 terminals...then have spread them
into KSPI/KDEC by 19-20z. With ridge of high pressure approaching
from the west, skies will gradually clear from west to east across
the area tonight. Based on forecast soundings, have scattered the
ceiling at KPIA by 02z...then further southeast to KCMI and KDEC
by 06z. Winds will initially be gusty from the N/NW this
afternoon, then will decrease to less than 10kt overnight into
Friday morning.


.ILX Watches/Warnings/Advisories...
Frost Advisory from 4 AM to 8 AM CDT Friday for ILZ027>031-036-



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