Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 121745
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1145 AM CST Sun Nov 12 2017

.UPDATE...
Issued at 1035 AM CST Sun Nov 12 2017

Updated the forecast earlier to add a rain/snow mix to the far
northern KILX CWA this morning...mainly along and north of a
Galesburg to Lacon line. Have not seen any automated sites
reporting snow, but did receive a report of some snow mixing in
with the rain from a COOP observer in Altona in far northern Knox
County. Upper wave responsible for the light precip is currently
tracking out of eastern Iowa into northern Illinois, with
subsequent dynamic cooling associated with this feature resulting
in rain changing to a period of snow along/north of I-80. Further
south into central Illinois, think precip will primarily stay in
the form of rain. Based on radar trends and latest HRRR forecast,
adjusted PoPs to go with likely to categorical along/north of a
Rushville...to Lincoln...to Paris line through midday...with only
chance PoPs further south across the remainder of the CWA where
precip has become much more scattered in nature.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 230 AM CST Sun Nov 12 2017

Light rain continues to spread across the forecast area early this
morning, though drier air over eastern Illinois is still holding
in place as of 2 am. Radar mosaics and short range model progs
suggest this may be the main show in our area, with a more
widespread precipitation band through midday from Iowa to northern
Indiana. However, some light rain or drizzle will linger until the
passage of the low through our area toward midday. After that, a
quick drying trend from west to east is expected.

With the extensive cloud cover and low sun angle, have leaned
temperatures a bit below the cooler MET guidance. Far northern CWA
may struggle to reach 40 degrees.

.LONG TERM...(Monday through Saturday)
ISSUED AT 230 AM CST Sun Nov 12 2017

West/southwest upper flow will prevail much of the week,
preventing any significant Arctic intrusions through Thursday. By
late in the week, the models are coming into better agreement with
a significant long wave trough digging southward from Canada,
marking the start of a cooling trend. The bulk of this cooler
weather appears to be next weekend, though, especially if the
European model verifies.

Early in the week, high pressure will keep Monday and Tuesday dry
in our area, though some WAA-type precip may start to form toward
the Mississippi River. By Tuesday night, a shortwave will be
digging across the northern Plains. The models remain in good
agreement with sweeping a cold front through our area on
Wednesday. Thus, highest PoP`s remain focused on late Tuesday
night into Wednesday morning. Have continued with the mention of
isolated thunder late Tuesday night, with a couple hundred J/kg of
MUCAPE available for some elevated convection. The rain with this
system should be out of the area by early Wednesday evening.

The late week storm system continues to be more of a challenge.
The GFS remains the stronger system, and brings WAA showers in as
early as Thursday evening. Its stronger and more northern solution
would sweep the cold front through Friday afternoon, accompanied
by thunderstorms. The European model is further south with the
low and more slow moving, with an extensive area of post-frontal
showers lingering well into Friday night. PoP`s will be high on
Friday, regardless of solution, with dry weather returning
Saturday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1145 AM CST Sun Nov 12 2017

IFR ceilings have spread across all terminals except KCMI late
this morning. Based on HRRR forecast, it appears the IFR ceilings
will not reach KCMI...instead a period of MVFR ceilings are
anticipated at that site between 19z and 03z. Further west, IFR
ceilings will persist for another couple of hours before gradually
rising to MVFR by mid to late afternoon. Regional satellite
imagery shows clearing conditions across the western half of Iowa,
but the clearing will be slow to arrive in central Illinois. In
fact, some models suggest low clouds will re-develop after sunset.
Do not see much evidence for that, so have gone with a gradual
clearing trend from west to east between 01z and 03z. With
clearing skies and diminishing winds, fog will likely develop
overnight. While temp/dewpoint spreads generally remain in the
2-3F range, all numeric guidance suggests some obscuration to
visby late tonight into Monday morning. HRRR focuses the most
widespread/densest fog west of the Mississippi River. For now,
have carried 3-4 mile visbys after 06z at all sites.

&&

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

$$

UPDATE...Barnes
SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...Barnes



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