Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 202012

Area Forecast Discussion
National Weather Service Lincoln IL
312 PM CDT Sun Aug 20 2017

.SHORT TERM...(This evening through Monday)
ISSUED AT 305 PM CDT Sun Aug 20 2017

Old outflow from an earlier MCS was moving east near I-57 at mid
afternoon and had an isolated thunderstorm along it in west
central Clay county. A few showers were in eastern Marshall and
Woodford counties while more widespread in northern/nw IL closer
to MCV over east central IA. More widespread thunderstorms were
over sw IA into northern/nw MO and in southern MO and ne AR. More
sunshine in eastern IL while more clouds west of I-57 behind
outflow boundary. Temps at 20Z/3 pm ranged from around 80F north
of Peoria to the lower 90s from Effingham to Lawrenceville south
where heat indices were topping 100F with muggy dewpoints in the
low to mid 70s. Dewpoints around 70F were as far north as
Galesburg and Lacon.

Latest forecast models still have varying solutions with handling
convection through Monday over IL. The MCV over east central IA is
forecast to track east toward Chicago in ne IL by late evening
with its swirl of convection mainly impacting northern half of IL.
Also have the system in northern/nw MO that tracks into sw IL
after sunset and to give southern counties some isolated
convection tonight. So have carried 20-30% pops over most of
central IL tonight with only isolated convection in southeast IL
until sunset due to old outflow boundary and very unstable
tropical airmass. SPC day1 outlook has marginal risk of severe
storms over all but sw 4 counties due to high CAPES above 1800
j/kg from IL se (as high as 3000-4000 j/kg in southeast IL) while
slight risk of severe storms was over IA. Muggy lows tonight
around 70F.

Convection chances increase to between 20-40% during the day
Monday with highest pops nw CWA over IL river valley. Another
very warm and humid day with highs in the upper 80s and lower 90s
and afternoon heat indices peaking from the mid 90s to near 100F,
highest in southeast IL by Lawrenceville. Sky cover during solar
eclipse around 18Z/1 pm Monday is 50-70% with least amount of
clouds in southeast IL and also the clouds will be higher in
southeast IL with filtered sunshine. Solar eclipse peaks in our
area around 120 pm cdt with 93-97% of sun covered by the moon.


.LONG TERM...(Monday night through Sunday)
ISSUED AT 305 PM CDT Sun Aug 20 2017

SPC day2 outlook has marginal risk of severe storms from I-72
north on Monday night with slight risk of severe storms over parts
of Knox, Stark and Marshall counties and to the nw. The marginal
risk of severe storms shifts to se CWA on Tue from Paris to
Shelbyville se while slight risk from Lawrenceville se during Tue
afternoon. A cold front will track se through central IL on Tue
likely bringing a round of showers and thunderstorms, and
lingering over southeast IL southeast of I-70 early Tue evening.
Highs Tue of 80 to 85F with warmest temps in southeast IL. One
more humid day on Tue with dewpoints in the upper 60s and lower

A nice stretch of late summer weather expected from Wednesday
through Sunday as large surface high pressure ridging from eastern
Canada southwest into IL, and upper level trof over the northeast
U.S. Expect below normal temperatures during most of this period
with highs in the upper 70s and lower 80s while fairly comfortable
dewpoints with east to ne flow around high pressure and giving
some cooler nights. 12Z extended forecast models are showing some
qpf se over the Ohio river valley next Sunday afternoon and also
some qpf with low pressure system moving into the upper Midwest,
with most of our CWA remaining dry yet on next Sunday. Some models
show temperatures warming into the mid 80s next weekend, but
stayed close to model consensus for temperatures along with dry


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1259 PM CDT Sun Aug 20 2017

A weakening leading edge of MCS was spreading a band of showers
eastward toward the IL river early this afternoon. The outflow
boundary from this MCS was approaching I-57. HRRR model is showing
isolated convection developing during mid/late afternoon over
central IL with this MCS as airmass is getting quite unstable with
CAPES rising above 2000 J/kg along and east of the IL river where
more heating occurring. Have VCSH/VCTS this afternoon especially
over northern taf sites. Then an MCV over central IA will track
east into northern IL late this evening and early overnight and
reintroduced VCTS at northern TAF sites for a few hours.
Convection Monday morning appears to be focused best by PIA. Winds
to stay under 10 kts next 24 hours (except if an isolated
thunderstorms occurs) with wind direction mainly south today, se
tonight and sw on Monday morning.




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