Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 150124
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
824 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 00Z TAFS through 00Z Monday evening)
ISSUED AT 600 PM CDT SUN SEP 14 2014

Water Vapor Imagery showing short wave now moving into high plains
rotating through broad long-wave trough over much of the nothern
U.S. Surface reflection begining to develop over northeast
Colorado is expected to push east quickly with the wave.

Gradual increase in VFR clouds overnight will eventually give way
to lower cigs around 12z in western terminals. Still some question
of how low bases will become as it should take some time to
saturate low levels. For now will keep vfr through 17z until have a
better handle on evolution. Showers should overspread all central
Illinois terminals during the morning. Will mention VCTS at KSPI
and KDEC as NAM indicates elevated instability during the morning.
Cold front will push quickly southeast with the best chance of
precip and mvfr conds after 18z once the wave moves by and should
end precip chances by 00z.



&&

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

$$

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






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