Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 191611

Area Forecast Discussion
National Weather Service Lincoln IL
1111 AM CDT WED OCT 19 2016

Issued at 1111 AM CDT Wed Oct 19 2016

16z/11am surface analysis shows stationary frontal boundary draped
along the Ohio River, while weak high pressure is in place over
northeast Illinois. An approaching short-wave trough evident on
latest water vapor imagery over the western Plains will interact
with the boundary to produce showers and a few thunderstorms
across portions of central/southeast Illinois today. Clouds have
already overspread most of the KILX CWA south of the I-74
corridor...while radar shows showers developing upstream from the
St. Louis area eastward to Effingham. Based on latest radar trends
and HRRR forecast, have updated hourly PoP trends to spread rain
chances into central Illinois faster than previously forecast.
Areal coverage will likely be limited somewhat due to dry E/NE
low-level flow: however, think many areas east of the Illinois
River will experience showers this afternoon. Have therefore gone
with high chance PoPs for scattered showers/thunder along/east of
the Illinois River...with only isolated showers further northwest
towards Galesburg. Due to the cloud cover and showers, have
lowered highs by a couple of degrees across the board. Coolest
readings in the upper 60s to around 70 will be focused across the
SW CWA from Jacksonville to Taylorville where overcast conditions
have developed soonest this morning.


.SHORT TERM...(Today and tonight)
ISSUED AT 301 AM CDT Wed Oct 19 2016

The cold front has finally slipped south of Lawrenceville as of 200
am and will continue to edge a bit further south before stalling out
over far southern Illinois into southern Indiana. To the north of
the front, temperatures and dew points have lowered considerably
from the past few mornings with temperatures in the upper 40s to
lower 50s across our northern counties to the upper 60s over the
I-70 corridor. Radar was indicating some isolated showers starting
to develop along the front from near Mount Vernon to just south of
Mount Carmel and were tracking mainly to the east.

The main challenge today will be timing of the showers back into our
area as an upper level trof moves across the Plains inducing a
surface low along the frontal boundary to our south. Most of the
guidance now was keeping the frontal boundary and surface wave just
south of the I-70 corridor late this afternoon through this evening
with the better instability axis along and just south of the front
with MUCAPEs around 1000 J/KG over extreme southeast Illinois for
a brief time late this afternoon into early this evening. Plenty of
deep layered shear as well near the frontal boundary with 0-6km
shear values around 50 kts. With the warm sector expected to remain
just south of the I-70 corridor, it appears the more organized
severe weather threat will be south of our area, however, a few of
the storms could produce some gusty winds and hail before the threat
wanes early this evening. Most areas today should be in the 70s with
a few locations in far southeast Illinois possibly approaching the
80 degree mark.

As the surface wave shifts east-northeast along the frontal boundary
tonight, widespread showers and isolated thunderstorms will occur
over far east central and especially southeast Illinois with the
potential for some significant rainfall over southeast Illinois
where up to 1.50 inches of rain may fall by later tonight into
early Thursday morning. Further north, precipitation chances start
to lower but it appears there should be enough forcing for at least
some scattered showers through the evening before the POPs begin to
decrease late tonight from northwest to southeast.

.LONG TERM...(Thursday through Tuesday)
ISSUED AT 301 AM CDT Wed Oct 19 2016

Upper trough will sharpen as it moves into the Mississippi Valley on
Thursday, helping to boot the cold front and rain off to our east.
Behind it, quiet weather will dominate into the weekend as a surface
high pressure drifts across the Midwest into the southeast states.
Some patchy frost is possible late Thursday night across the
northwest corner of the CWA around Peoria and Galesburg, as
temperatures dip into the upper 30s. However, temperatures will
recover nicely over the weekend across central Illinois, with more
of a zonal flow setting up as the trough shifts to the east.

As an upper ridge begins to build across the Plains early in the
week, the dry weather pattern will continue over our area. Latest
runs of the GFS and ECMWF models focus most of the precipitation
with the mid-week system more over the upper Mississippi Valley on
Tuesday, with more of an impact in our CWA on Wednesday, just beyond
the current forecast period.


.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 610 AM CDT Wed Oct 19 2016

VFR conditions are expected thru this forecast period. Weak high
pressure to our north will drift off to our northeast during the
day while low pressure develops to our south. Clouds will be on
the increase, at least the high and mid level clouds, as the
storm tracks along a stalled frontal boundary along the Ohio River
Valley. Rain will start to spread slowly north into south central
Illinois later this morning and possibly into our southern TAF
sites by mid to late afternoon. The better chances for rain look
to be from Decatur and Champaign east later this afternoon thru
tonight. Forecast soundings suggest cloud bases around 4000-5000
feet in Decatur and Champaign, while further to the west and
north, cig heights from 5000-8000 feet are expected later today
and thru tonight.

Surface winds will out of the northeast at 8 to 13 kts today
and increase some tonight from the northeast to between 10 and
15 kts.


.ILX Watches/Warnings/Advisories...


LONG TERM...Geelhart
AVIATION...Smith is the U.S. government's official web portal to all federal, state and local government web resources and services.