Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 221702
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1102 AM CST Mon Jan 22 2018

.UPDATE...
Issued at 1055 AM CST Mon Jan 22 2018
Line of showers and thunderstorms from this morning has moved
eastward into IN. Some persistent low stratus remains over the
eastern half of the state on vis sat imagery. Significant clear
slot around the approaching storm system moving into IL. Enough
llvl moisture in place to result in some low stratocu development.
How quickly the clear slot clouds over as well as how dense will
likely impact the extent of minimal instability that develops.
Cooler air is wrapping around the system, if not the larger cold
airmass back to the NW, countering the attempted warm air
advection with the southerly winds. Likely to remain gusty through
the afternoon. Minor updates to the forecast will continue, but
leaving the afternoon chances for showers and thunderstorms.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 323 AM CST Mon Jan 22 2018

08z/2am surface analysis shows 1000mb low over northeast
Kansas...with warm front extending E/NE to southern Lake Michigan.
A band of showers with a few embedded thunderstorms has developed
within the warm sector of the system well ahead of an approaching
cold front. Latest radar imagery shows widespread showers/thunder
along and west of the I-55 corridor...with the convection tracking
N/NE. Based on radar timing tools, it appears most of the precip
will be east of I-55 by 12z, then will exit into Indiana between
15z and 18z. Once this initial band departs, a pronounced mid-
level dry slot will bring partial clearing and a period of dry
weather from late morning through mid-afternoon. After that, the
big question will be if any additional convection will develop
along the advancing cold front late this afternoon. Due to partial
sunshine and surface dewpoints in the middle to upper 50s,
SBCAPEs will reach 400-600J/kg...while 0-6km bulk shear values
range from 50-70kt. Despite this high shear/moderate instability
environment, the main mitigating factor for convection later
today will be a lack of deep-layer moisture. Some high-res models
such as the NAM12, HRRR, and WRF-NMM suggest widely scattered
showers/storms will develop along the front across the Illinois
River Valley after 21z...then will quickly track E/NE late this
afternoon into the early evening. Meanwhile, other models such as
the WRF-ARW and GFS show virtually no precip. At this point, will
focus highest PoPs during the morning hours as the main band of
precip passes, then will include low chance late this afternoon as
the cold front approaches. Any storms that fire this afternoon could
potentially produce gusty winds and small hail. High temperatures
today will climb well into the 50s.

The cold front will sweep through central Illinois this evening,
followed by a return to colder conditions overnight. Overnight low
temperatures will bottom out in the lower to middle 30s.
Meanwhile, wrap around moisture associated with surface low
pressure tracking into the Great Lakes will spill into west-
central Illinois this evening...then will spread E/NE to the
Indiana border toward midnight. The thermal profile will initially
be warm enough to support rain through the evening, then will cool
sufficiently to produce a rain/snow mix overnight. Any snow
accumulation will be quite minor, amounting to little more than a
couple tenths of an inch along/north of a Rushville to Bloomington
line.

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 323 AM CST Mon Jan 22 2018

A few rain/snow showers will linger across the NE KILX CWA Tuesday
morning, followed by cool/dry weather by afternoon. Forecast
soundings suggest clearing will be slow and will likely not occur
until Tuesday night. Main weather story will be the windy and
colder conditions as temperatures hover in the 30s and brisk
northwesterly winds gusting 25-30mph create wind-chills in the
20s. Winds will gradually subside by Wednesday, but the cool
conditions will continue as highs remain mostly in the 30s.

After a short-wave trough passes on Wednesday, upper heights will
begin to rise as another wave coming onshore across California
induces downstream ridging over the Midwest. End result will be a
marked warming trend for central Illinois, with highs returning
to the 50s by Friday. 00z Jan 22 models have all quickened the
arrival of the late week system, with FROPA occurring on Saturday.
ECMWF no longer develops a substantial wave along the departing
front on Sunday, so its solution is more progressive...like the
previous runs of the GFS/GEM. As a result, PoPs will be largely
confined to the Friday night through Saturday time-frame...with
Sunday now appearing cool/dry.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 557 AM CST Mon Jan 22 2018

Band of convection is rapidly pushing E/NE across central Illinois
early this morning...with 1130z/530am radar imagery showing most
of the precip along/east of a KPIA to KTAZ line. Based on radar
timing tools, will drop mention of showers eastward to KCMI by
14z. Ceilings will generally drop to MVFR once the rain ends,
although a band of IFR ceilings will likely impact KPIA for a few
hours. Clearing is already noted immediately upstream across
Missouri and will quickly spread across the area from SW to NE by
mid to late morning. Have scattered ceilings at KSPI by 15z...then
further northeast to KCMI by 18z. Models continue to suggest
scattered showers/thunder along an advancing cold front late this
afternoon...so have included VCTS at the terminals between 21z and
03z. Once this activity departs, light rain will move into the
region from the west this evening...then will mix with and/or
change to snow overnight. Winds will initially be strong/gusty
from the south today...with gusts reaching 25-30kt at times. Winds
will then veer to the W/SW after FROPA tonight.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...HJS
SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Barnes



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