Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 191721
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1121 AM CST Thu Jan 19 2017

.UPDATE...
Issued at 1010 AM CST Thu Jan 19 2017

Initial surge of rain showers has moved into the south central CWA
this morning, approaching the Springfield and Decatur areas as of
10 am. Short range models fairly unanimous in a more widespread
area covering the CWA by early-mid afternoon, with a dry slot
starting to push into the southwest counties by early evening. The
western CWA will likely see most of the showers move out this
evening, but some drizzle will persist overnight. Have updated the
zones/grids to refine the precipitation trends through tonight.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 257 AM CST Thu Jan 19 2017

Upper low over the Central Plains will be the primary weather-maker
across central Illinois over the next 24 hours.  08z/2am water vapor
imagery shows ample Pacific and Gulf of Mexico moisture flowing
northward ahead of this feature, with the primary moisture channel
focused from eastern Texas into the Ohio River Valley.  This is
slightly further east than previous model runs had suggested, so it
appears the heaviest rainfall with this wave will occur across
Kentucky and Indiana.  NAM still shows precipitable water values
increasing to greater than 1 inch this afternoon/evening...with near
record values of around 1.25 near the Illinois/Indiana border. Given
copious deep-layer moisture and strong forcing from approaching
upper low, showers will become numerous across the area this
afternoon.  Based on HRRR forecast, will keep PoPs in the chance
category along/north of I-74 through midday...then will go with
categorical PoPs across the board this afternoon and evening.  With
MUCAPES reaching 200-400J/kg, isolated thunderstorms will be
possible as well.  The wave will lift into the southern Great Lakes
overnight, resulting in an end to the precip from south to north
across the area after midnight.  Total rainfall will generally be
around one half inch...although higher amounts will be possible
within thunderstorms.  Given the expected rainfall on the frozen or
partially frozen ground, run-off will be high.  This will likely
result in further rises and minor flooding on many area rivers.
Contemplated a Flood Watch, but decided to issue a Special Weather
Statement(SPS) instead since widespread flooding is not expected.

.LONG TERM...(Friday through Wednesday)
ISSUED AT 257 AM CST Thu Jan 19 2017

May see a few lingering showers across the E/NE KILX CWA into early
Friday morning: however, most of the day will be mild and dry.
Several models are producing light QPF across the area Friday night
as a warm front lifts through central Illinois.  Have therefore
included low chance PoPs for showers Friday night.  Once the front
lifts northward into the Great Lakes and winds become S/SW, very
warm weather will be on tap for Saturday.  850mb temps are progged
to rise into the 8-9C range, supporting highs in the upper 50s and
lower 60s.  Numeric guidance continues to hint at possible record
highs in the middle 60s, but this may be contingent upon seeing
partial sunshine during the afternoon which seems unlikely.  Will
therefore continue to undercut guidance by a couple of degrees.

The next major storm system will approach the region early next
week: however, as first predicted by the 00z Jan 18 ECMWF...the 00z
Jan 19 GFS is now keeping that system well to the south of Illinois.
Both the ECMWF and GFS now show a closed 500mb low tracking mainly
eastward across the Deep South Sunday into Monday.  This would keep
most of the rain south of Illinois across the Ohio and Tennessee
River Valleys.  Have scaled back PoPs and lowered rainfall amounts
accordingly.  Will still go with a cloudy/warm forecast with a
chance for showers from Saturday night through Monday.  Rainfall
amounts with this system will range from around one tenth of an inch
northwest of the Illinois River...to as much as three quarters of an
inch south of I-70.

Once the early week system passes, yet another upper wave will
follow close on its heels.  This particular low will likely track
W/NW of Illinois Tuesday night into Wednesday...resulting in
continued warm weather through mid-week.  Once this low lifts into
the Great Lakes, colder air will be drawn southward on its back
side...with all indications suggesting a return to near normal
temps by the end of next week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1121 AM CST Thu Jan 19 2017

Conditions will be steadily deteriorating this afternoon as rain
and low clouds continue to spread northward into central Illinois.
Widespread IFR/LIFR ceilings expected over the TAF sites by late
afternoon, which will persist the remainder of the forecast
period. The rains around KPIA/KSPI will diminish to drizzle by
mid-late evening, while remaining persistent near KCMI most of the
night. After the rains diminish, light winds and saturated lower
levels of the atmosphere will likely result in fog development
with visibility under 1SM. The fog should persist until late
morning Friday.

&&

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

$$

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



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