Area Forecast Discussion
Issued by NWS Central Illinois

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399
FXUS63 KILX 292004
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
304 PM CDT Wed Mar 29 2017

.SHORT TERM...(This evening through Thursday)
ISSUED AT 300 PM CDT Wed Mar 29 2017

19z/2pm surface analysis shows 1002mb low over southeast Kansas,
with warm front extending eastward into the Tennessee River Valley.
As the low tracks northeastward into the Kansas City area by 00z, a
strengthening low-level jet ahead of the system will trigger
widespread showers and thunderstorms across central/eastern Missouri
into Iowa.  This precipitation will then gradually shift E/NE into
the Illinois River Valley by mid to late evening...then further east
across the remainder of the area overnight.  With central Illinois
remaining north of the warm front, surface-based instability will be
negligible: however, forecast soundings show modest elevated
instability developing with GFS MUCAPE values reaching 200-400J/kg
late.  As a result, have carried likely to categorical PoPs across
the board after midnight...and have mentioned a chance of thunder.

Some model differences still exist concerning the exact track of the
low, with the 12z NAM remaining slightly further south than the GFS.
The GFS has been the most consistent model from run to run, so have
leaned toward its solution in the short-term.  As such, am expecting
the low to track across central Illinois Thursday afternoon, then
into the southern Great Lakes Thursday night.  Warm advection
showers and isolated thunderstorms will be ongoing early in the
morning, with a lull in the precip likely from mid-morning into the
early afternoon hours.  As the warm front lifts northward, the
atmosphere will become moderately unstable during the afternoon,
with MUCAPEs climbing into the 1000-1500J/kg range everywhere east
of the Illinois River.  SPC continues to highlight this area for a
slight risk of severe, with greater severe probabilities focused
further south from southern Illinois southward to Mississippi where
instability will be greater and low-level shear will be stronger.
For central Illinois, it appears the severe weather risk will
primarily occur along/south of I-72 between noon and 6pm. Damaging
wind gusts and large hail will be the main threats from the storms.
Have gone with occasional showers and thunderstorms throughout the
day, with afternoon highs ranging from the upper 50s north of the
low track from Peoria northward...to the lower 70s well into the
warm sector south of the I-70 corridor.

&&

.LONG TERM...(Thursday night through Wednesday)
ISSUED AT 300 PM CDT Wed Mar 29 2017

Moisture channel imagery shows closed off low in central KS today.
Series of waves seen in models and in satellite rotating around low,
as it wobbles to the east across MO to IL through Thursday. Result
will be showers and storms tonight through day Thursday. Will need
to watch possible severe development Thursday, as mentioned above.

Next system approachs area late Saturday night, with models in
agreement on wave and pcpn timing. Best instability south of area,
and so have added slight chc Tstms for southern 1/2 CWA in aftn/eve.
System is slow to track south of area, so chance aftn/eve tstms
again on Monday.

Final system approahs area for Wednesday. This system is stronger
and so will need to be watched, as it also progged to move directly
over central IL. There are some prog differences though in the
track, to also watch for.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1256 PM CDT Wed Mar 29 2017

Band of showers continues to work its way across central Illinois
early this afternoon...with latest radar imagery showing it
generally along and just west of I-55. The showers will lift
northeastward out of the area over the next couple of hours, with
Rapid Refresh forecast soundings showing any residual MVFR
ceilings rising to VFR by mid to late afternoon. After a lull in
the precip chances, the next more significant wave of showers will
arrive late this evening through the overnight hours. Based on NAM
data, have introduced predominant rain at KPIA by 03z...then
further east to KCMI by around 07z. Ceilings will initially lower
to MVFR, but some high-res models are suggesting IFR ceilings will
develop late tonight into Thursday morning. Winds will be
strong/gusty from the E/SE this afternoon through tonight, then
will slowly decrease toward midday Thursday.


&&

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

$$

SHORT TERM...Barnes
LONG TERM...Goetsch
AVIATION...Barnes



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