Area Forecast Discussion
Issued by NWS Central Illinois

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683
FXUS63 KILX 220923
AFDILX

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

.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 06Z TAFS through 06Z Monday night)
Issued at 1145 PM CST Sun Jan 21 2018

The warm front has finally shifted north of all the terminal sites
as of 0530Z. Dense fog still lingers at PIA at 05Z, but should
improve shortly based on HRRR output and upstream observations.
The next concern turns to potential for some isolated thunder with
this initial wave of showers the rest of the night. Instability
remains less than 100 J/Kg, but wind shear looks favorable enough
for thunder. Lightning strikes have been detected into Illinois in
the last 30 mins, and that trend should continue as the north-
south axis of forcing progresses into central Illinois. Have kept
the VCTS in all TAFs for 3-4 hours later tonight.

A dry slot closely trailing the back edge of precip will push
across IL this morning, with the showers/storms departing into
Indiana by 16z or so. That will leave an 3-5 hours of dry
conditions, before the afternoon instability and wind shear
combine with a shortwave to produce a line of convection between
20z-24z. Some of those storms could contain strong winds. The
afternoon LLJ is forecast to peak at 40kt or so, while the LLJ
late tonight looks to reach 60KT.

Forecast soundings indicate that ceilings may improve to MVFR
with the line of showers, while IFR conditions remain scattered
across the area. Overall conditions look MVFR tomorrow and
possibly even VFR in the dry slot, before showers/storms develop
again.


&&

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

$$

SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Shimon



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