Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 240439
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1139 PM CDT SAT JUL 23 2016

.UPDATE...
Issued at 830 PM CDT Sat Jul 23 2016

Strong to locally severe storms continue to track mainly to the
east over north central Illinois this evening, with the strongest
convection tied to a stalled frontal boundary over northeast Iowa
through extreme northern Illinois and southern Wisconsin. The
outflow boundary from the convection to our north looks to push
through Knox, Stark and Marshall counties over the next hour with
winds shifting into the north and gusting up to 45 mph along with
a nice temperature drop. Question becomes if the precip from the
trailing convection over extreme northwest IL will affect our far
northern counties. It still appears worthy of keeping the 25-35
POPs (scattered) wording across the far north over the next
several hours. Atmosphere in our area characterized by plenty of
instability with MUCAPEs above 5000 j/kg and Precipitable water
values of nearly 2 inches. If they are able to get in the north,
gusty winds and torrential rainfall will be the primary concerns.

Further south, another very warm night with not much help from the
wind as most areas will see wind speeds of around 5 mph. Some
patchy fog still appears most likely over our southeast which is
already addressed in the zones. Already sent out an update when
the Excessive Heat Warning expired at 7 pm, and see no reason for
any update at the present time but will continue to monitor the
track of the convection to our north for possible updates to the
ZFP over the next hour or two.

&&

.SHORT TERM...(This evening through Sunday)
ISSUED AT 305 PM CDT Sat Jul 23 2016

19z/2pm surface analysis shows stationary frontal boundary extending
from southern Lake Michigan northwestward into the Dakotas.
Widespread convection is ongoing along/north of the boundary in
advance of a well-defined short-wave trough evident on water vapor
imagery over southern Manitoba.  Latest radar mosaic shows bulk of
thunderstorms focused from Minnesota and northeast Iowa across
Wisconsin...however a few radar echoes extending southwestward into
central Illinois will have to be watched as they may impact parts of
north-central Illinois this evening.  Models are handling the
convective evolution differently...with the WRF-ARW and GFS
depicting a dry forecast across the KILX CWA tonight...and the NAM
and HRRR showing the central Iowa convection tracking into the
northwest counties around Galesburg early this evening.  Based on
current radar/satellite trends...will follow the NAM/HRRR most
closely for the immediate short-term.  As such...have brought low
chance PoPs into the Illinois River Valley from the Canton area
northward early this evening...with the PoPs spreading eastward
along/north of I-74 through the overnight hours.  Further south
across the remainder of the CWA...have gone with a mostly clear
forecast with patchy fog developing along/southeast of a Paris to
Shelbyville line where dense fog was observed last night.

Cold front currently over the western Plains will push slowly
eastward on Sunday...eventually reaching the Mississippi River by
late afternoon.  Airmass ahead of the front will remain capped...as
evidenced by 700mb temps around 12C.  As a result, most model
guidance suggests dry conditions until the cap weakens late in the
day.  Have tailored PoPs accordingly to go with 30-40 PoPs
along/west of I-57 by afternoon...with only slight chance PoPs
further east and south.  High temperatures will once again reach the
lower to middle 90s...with heat index values topping out between 100
and 110 degrees.  Will continue the current Excessive Heat Warning
along/south of a Rushville to Danville line through Sunday
evening...and may need to include the northwest CWA in a headline
as well if current trends continue.

.LONG TERM...(Sunday night through Saturday)
ISSUED AT 305 PM CDT Sat Jul 23 2016

Cold front will sink into central Illinois Sunday night...bringing
scattered showers and thunderstorms to the entire area.  Have gone
with 50 PoPs across the board accordingly.  Boundary will then drop
slowly southward into the Ohio River Valley on Monday...gradually
taking the rain chances with it.  Have gone with chance PoPs
everywhere during the morning...then only south of I-72 by
afternoon.  Temperatures behind the front will be slightly
cooler...with highs dropping back into the middle to upper 80s.

High pressure will build into the Great Lakes for Tuesday, pushing
the front into Missouri/Kentucky.  While a warm/dry day will be on
tap across all of central and southeast Illinois, the front will
quickly begin to return northward as the high departs the region.
Models have continued the trend of bringing rain chances back into
central Illinois faster, with chance PoPs now in place across nearly
the entire area by Wednesday.  After that, the boundary will become
nearly stationary across the Midwest, resulting in daily rain
chances through the end of the week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1120 PM CDT Sat Jul 23 2016

We may see some patchy MVFR vsbys in fog/hz in the 08z-12z time
frame, but mainly VFR conditions are expected this forecast
period. Convection to our north looks to remain just north of the
BMI and CMI TAF sites, but will hold on to a VCTS mention in those
locations in case the storms track a bit further southeast than
currently projected. Any fog/low vsbys should burn off quickly in
the morning, after 13z, followed by some cumulus developing by
late morning. A cold front is expected to approach the area from
the northwest tomorrow night and that appears to be the best
chance for seeing some scattered TSRA but this far out and with
coverage still very much in question, will only go with a VCTS
late tomorrow afternoon into the evening hours. Light and variable
winds tonight will pick up a bit from a southerly direction on
Sunday with speeds in the 8 to 13 kt range.

&&

.ILX Watches/Warnings/Advisories...
Excessive Heat Warning until 7 PM CDT Sunday for ILZ040>057-
061>063-066>068-071>073.

&&

$$

UPDATE...Smith
SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Smith


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