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Area Forecast Discussion (AFD)

Issued by Central Illinois (ILX)

FXUS63 KILX 260143

Area Forecast Discussion
National Weather Service Lincoln IL
843 PM CDT Sun Aug 25 2019

Issued at 843 PM CDT Sun Aug 25 2019

Expect periods of showers and thunderstorms across central and 
southeast Illinois into Monday night, with locally heavy rain. 
Strong to severe thunderstorms are possible west of I-55 Monday 
night, with a few stronger storms as far east as I-57. A few 
showers and isolated thunderstorms will linger in eastern Illinois
Tuesday morning, then drier conditions are expected from Tuesday 
afternoon through Thursday night along with pleasant temperatures 
and humidity levels.


Issued at 843 PM CDT Sun Aug 25 2019

Well defined mesoscale convective vort max seen on radar imagery
across central Missouri this evening, with an increase in showers
and thunderstorms over that area. So far this far east, showers
have been lighter but have increased in number, though another
break is developing south of I-70. Between the vort max and the
extensive area of showers/storms south of the Ohio River migrating
northward, rain chances should quickly increase after midnight 
and continue into Monday morning. Thunder chances should ramp up 
as the warm front lifts north, being more of a factor after about 
3 am, as surface based CAPE's increase to around 500 J/kg. 

Forecasts have been updated to significantly increase the PoP's
into Monday morning, especially near and west of I-55. 


.SHORT TERM...(This evening through Monday)
ISSUED AT 345 PM CDT Sun Aug 25 2019

Latest radar mosaic shows light to moderate showers lifting NNE 
toward into sw CWA at mid afternoon, while isolated light showers
or sprinkles over rest of CWA. More unstable air was south of IL
over southern parts of KY/MO where some thunderstorms were. Clouds
were thickening and lowering over central and western CWA while 
mainly broken mid level clouds in eastern IL with some peaks of 
sun. Temps at 330 pm ranged from upper 60s and lower 70s in rain 
cooled area from Quincy to Pittsfield to Litchfield sw to St 
Louis, to around 80F in far eastern IL from Danville to 
Charleston/Mattoon to Lawrenceville east where more sunshine 
observed today. Dewpoints ranged from the upper 50s northern CWA, 
to the upper 60s from Pittsfield to Litchfield sw and from 
Robinson to Flora south in southeast IL.

1029 mb high pressure that provided us nice weather the past few
days, is drifting east over northeast New England and into the
eastern Canadian maritimes. An upper level short wave trof over
the eastern plains of western IA/MO into nw AR. Precipitable water
values had increase to 1.3-1.8" over CWA, highest over sw CWA and
were 1.9-2.2 inches in southern IL from I-64 south. WAA and
isentropic lift to increase chances of showers and isolated
thunderstorms NNE into central IL tonight and have trended higher
with pops as showers moving in quicker. Lows tonight in the mid
60s central IL and upper 60s in southeast IL.

The short wave trof slowly tracks east over IL by dawn Monday and 
weakens as it shifts east of IL by late Mon afternoon. Have high
chances of showers and isolated thunderstorms Mon morning over
central and eastern CWA, then diminishing from the west during 
Mon afternoon. Highs Mon in the lower 80s, with upper 70s east of
I-57 where low clouds and showers linger longer in the afternoon.
More humid Monday with dewpoints in the upper 60s/lower 70s. 

.LONG TERM...(Monday night through Sunday)
ISSUED AT 345 PM CDT Sun Aug 25 2019

A large northern stream upper level trof digs into the upper 
Midwest on Monday and pushes a cold front se toward the IL/IA
border by sunset Mon and se toward the Wabash river by dawn Tue.
Precipitable water values that rise around 2 inches tonight, could
pool even higher ahead of this cold front and supports marginal
risk of excessive rainfall with around 1 inch or more possible.
SPC day2 update has expanded marginal risk of severe storms east
to I-57 Mon night with slight risk over western CWA for mainly Mon
evening. Lows Mon night in the lower 60s far nw CWA with upper 60s
from I-55 east. 

Have a chance of showers and isolated thunderstorms in eastern/se
IL Tue morning then dry and less humid conditions to arrive Tue
afternoon into Tue night as cold front pushes further se of IL.
Return of sunshine on Tue helps warm temps into the lower 80s,
except upper 70s nw of the IL river. Cooler lows Tue night in the
upper 50s to near 60F. 

Dry conditions Tue night thru Thu night across the area with more
comfortable humidity levels/lower dewpoints and temperatures
overall during mid week with upper level trof digging over the
area on Wed and weak surface high pressure settling into the mid
MS river valley. Another cold front progged by models to sweep se
over central IL late Thu night and Fri but will have limited
moisture with gulf moisture cut off, so just 20-30% chance of 
convection on Friday and Fri night. Models show some moisture
moving east from MO valley Fri night into Sat and could linger 
chances of showers and isolated thunderstorms. Cooler highs in the
70s expected next weekend behind secondary cold frontal passage on


.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 622 PM CDT Sun Aug 25 2019

Band of showers is currently lifting northeast across central
Illinois, and will impact the TAF sites for a time early this
evening. Main threat of any steady rain will be after 06Z, as a
warm front lifts northward. Think the threat of thunder will be
with this latter feature, and have timed the mention of TSRA/VCTS
for a period beginning around 07Z from KSPI-KCMI, and around
11-12Z KPIA-KBMI. Will linger some showers late morning, before
conditions dry out.

Cloud-wise, some low MVFR conditions were located in far western
Illinois early this evening, but think the substantial cloud
lowering in central Illinois should accompany the front. Continued
with a rapid lowering to IFR conditions between 06-09Z KSPI-KCMI,
then toward 10-11Z further north. A slow improvement is expected 
once the heavier rain moves out. May see VFR conditions return by
late afternoon at KSPI, but have held off on a mention elsewhere
for this TAF set.