Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 150452
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1152 PM CDT Sun Sep 14 2014

.UPDATE...
ISSUED AT 823 PM CDT SUN SEP 14 2014

Cyclogenesis occurring over central High Plains this evening in
response to a fast moving short wave moving out of the northern
Rockies. Warm advection precip is developing ahead of the wave and
should move quickly east into the Midwest late tonight. Some minor
differences between model timing of onset. Still fair amount of
dry air evident in 00z KILX sounding, but dew points are climbing
as southerly wind component develops in the boundary layer. Have
made some minor adjustment to wx/pop grids late tonight and
tomorrow to reflect a compromise between HRRR and NAM precip fields.

&&

.SHORT TERM...(Tonight)
ISSUED AT 242 PM CDT SUN SEP 14 2014

High pressure across the Midwest and into the Atlantic northeast
will keep the weather quiet in the early evening hours, but give way
to another quick disturbance moving into the region tonight. A front
moving across the area tonight associated with the disturbance will
bring the chance for showers and isolated thunder into tomorrow
morning. Models have been delaying the precip until after midnight
and have maintained that trend, with pops starting to move in NW of
the Illinois River Valley before 12z. Some of the cloud cover moving
into the region should keep the temps from bottoming out, but still
unseasonably cool with lows in the upper 40s and near 50.

&&

.LONG TERM...(Monday through Sunday)
ISSUED AT 242 PM CDT SUN SEP 14 2014

There is decent agreement in the models that the track of the best
forcing for precip on Monday looks to remain across northern
Illinois. Therefore we continued to limit the likely PoPs to areas N
of I-72, with chance PoPs south of there. Instability will be weak
at best, but a rumble of thunder could develop for SW areas from
Rushville to Jacksonville.

By Monday evening, any residual lift along a trailing trough will
diminish quickly. It`s entirely possible that all rain may come to
an end by sunset. However, with the forward progress of that trough
slowing, shower chances could linger for at least a few hours into
Monday evening, so we left chance PoPs in place toward I-70.

The widespread clouds and rain across northern areas will keep high
temps on Monday near 60, and we continued to trim numbers a few
degrees below guidance values. With rain holding off until afternoon
and some filtered sun expected south of I-70, highs should get into
the lower 70s.

The colder than normal conditions will last through at least
mid-week as high pressure extends from the Great Lakes and back into
Illinois. Dry conditions are expected, due to the deep layer of dry
air. A weather system approaches western IL on Wed, but all models
curl it to the southeast of IL as high pressure remains in control
of our region.

A stronger system moving across the northern states on Saturday will
drag a cold front across IL Sat night and Sunday. There appears to
be enough instability for a few thunderstorms as mid-level lapse
rates increase and deeper moisture arrives. Chance PoPs were
included Saturday west of I-55, and area-wide for Sat night and
Sunday associated with the frontal passage. Temperatures will warm into
the upper 70s/near 80 by Saturday, with Sunday a few degrees cooler
under clouds and showers.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
ISSUED AT 1152 PM CDT SUN SEP 14 2014

Southerly winds have developed across the central Illinois
terminals this evening. Lift ahead of fast moving short-wave over
the plains is producing some virga echoes to the northwest of the
TAF sites late this evening. Moisture will continue to develop
ahead of the wave through the remainder of the night with the
column gradually becoming saturated. there will be an increasing
chance of precip reaching the surface at KPIA and possibly KBMI
and KSPI by 12z. 15/00z NAM has slowed the progress of the system
and latest HRRR also shows a delay in the system suggesting that
the passage of the cold front associated with the wave will be a
bit slower than the previous TAF package.

Elevated instability may be sufficient for some thunder during the
day ahead of the front. Will keep current metion of VCTS in KSPI
and KDEC but push timing back into the afternoon just ahead of
frontal passage.

Winds should shift to the North during the late afternoon and
early evening behind the front. Although the boundary layer
remains saturated through the night, winds appear to be significant
enough to keep vsbys at least MVFR. Will keep MVFR CIGS in place as
well as stratus appears to be more likely.

&&

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

$$

UPDATE...BARKER
SHORT TERM...HJS
LONG TERM...SHIMON/25
AVIATION...BARKER/BAK






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