Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 130816

Area Forecast Discussion
National Weather Service Lincoln IL
316 AM CDT Fri Oct 13 2017

.SHORT TERM...(Today and tonight)
ISSUED AT 316 AM CDT Fri Oct 13 2017

Low clouds that have plagued central Illinois for the past two
days continue to dissipate early this morning: however, mid-level
clouds associated with a 30-35kt 850mb jet streak are expanding
E/SE from Iowa and will overspread the western half of the KILX
CWA by dawn. Forecast soundings suggest most locations will start
the day mostly cloudy, with skies becoming partly to mostly sunny
by afternoon. Despite afternoon sunshine and a S/SE breeze,
shallow mixing up to only 950mb will keep temperatures slightly
cooler than previously forecast...with highs mainly in the lower
to middle 70s.

A slow-moving cold front currently extending from Minnesota W/SW
to Colorado will begin to approach from the northwest tonight.
Model QPF fields vary slightly, but consensus keeps the
precipitation N/NW of the area this evening...then focuses on
locations along/north of a Rushville to Bloomington line after
midnight. With NAM MUCAPE values increasing to 1000-1200J/kg, have
included thunder in the forecast as well. Overnight lows will
range from the middle 50s near the Indiana border where clear
skies will linger the lower 60s along/west of I-55.


.LONG TERM...(Saturday through Thursday)
ISSUED AT 316 AM CDT Fri Oct 13 2017

Frontal boundary will temporarily stall from southern Lake
Michigan W/SW to northern Missouri late tonight into Saturday
morning...then will shift slightly northward during the day
Saturday as low pressure approaches from the southwest. Given the
expected frontal position, showers and thunderstorms will be
ongoing across the far northern CWA, while locations along/south
of I-72 remain largely dry. High temperatures will range from the
upper 70s far north around Galesburg and the middle 80s
along/south of I-72.

Strong to potentially severe convection will develop ahead of the
approaching low Saturday afternoon, particularly in a corridor
from Kansas City northeastward to Des Moines. SBCAPEs in excess of
2000J/kg and 0-6km bulk shear of 50-60kt will support vigorous
convection capable of producing damaging winds and large hail west
of the Mississippi River Saturday afternoon into the early
evening...with the storms gradually progressing eastward into
west-central Illinois by mid to late evening. While daytime
instability will be waning after sunset, shear/dynamics will be
sufficient to sustain convection as it comes into the area. Latest
SPC Day 2 Outlook continues to highlight areas along/west of I-55
for a Marginal Risk for severe weather Saturday evening. The
storms will tend to weaken with time, with little or no threat for
severe expected across east-central and southeast Illinois by the
time the storms arrive there after midnight.

00z Oct 13 models have come into excellent agreement regarding
timing of FROPA on Sunday, with all solutions pushing any
lingering showers out of the CWA by midday. Strong W/NW winds
gusting to 25-30mph will bring much cooler/drier air into the
region on Sunday. As high pressure builds in Sunday night, winds
will diminish and good radiational cooling condtions will develop.
Overnight low temperatures will drop into the upper 30s...potentially
allowing patchy frost formation in some favored low-lying areas.
Once the high shifts off to the east, a warming trend will get
underway for the remainder of next week. After a cool day with
highs in the lower 60s on Monday...temperatures will return to the
lower to middle 70s by Wednesday and Thursday.


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1147 PM CDT Thu Oct 12 2017

The extensive area of low cloudiness that was in place over
central IL the past few days is rapidly dissipating as drier
southerly flow pushes into the area. This may provide a brief
period of VFR conditions after removing the MVFR cigs, however
fog will likely form afterward, resulting in IFR-MVFR vsby. Think
most of the fog will not be dense due to continuing light
southerly winds. Fog should dissipate by 15Z, with scattered cloud
cover lifting to around 5000 feet AGL by afternoon.




LONG TERM...Barnes
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