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000
FXUS63 KILX 292338
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
538 PM CST Fri Nov 29 2013

.DISCUSSION...
ISSUED 246 PM CST Fri Nov 29 2013

A ridge of high pressure has drifted just east of Illinois this
afternoon, allowing southerly return flow to develop on its back
side. Upstream, a weak clipper system is pushing into the northern
Plains. This clipper is expected to move through the forecast area
Saturday night, but will bring little more to the area than cloud
cover and a wind shift. Generally quiet weather and seasonable
temperatures are still expected into the middle of next week,
although dry conditions are not quite a slam dunk for Monday and
Tuesday. The next stronger system, a slow mover, is still on track
for later Wednesday into Friday, bringing the next widespread
chance of precipitation to the area.

SHORT TERM...Tonight through Monday night: Neutral upper level flow
and southerly low level return flow are expected across the area
through Saturday in advance of the approaching clipper, supporting
quiet and milder conditions. The clipper system should move
through Illinois, mostly during Saturday night, and should come
through dry locally.

Behind the clipper, a surface high will build back into the area,
accompanied by more neutral yet still slightly troffy upper level
flow. The lingering troffy/northwest upper level flow is a subtle
shift from the zonal flow advertised in recent days. This places
the forecast area more in the track of some weak disturbances
rippling through the flow, especially Monday night. Still expect
the bulk of the disturbances to come through dry, but it is not
out of the question, especially Monday night, that some light rain
or snow will occur. However, the local airmass is still expected
to be too dry with the passage of these waves to go above a slight
chance mention at this time.

LONG TERM...Tuesday through Friday: Upper level heights rise
rapidly on Tuesday over the eastern U.S. as a vigorous trof digs
over the western states. These rising heights and southerly low
level flow will push temperatures warmer than normal until the
remnants of the western trof arrive by late in the week.

The models have been fairly consistent that the system will arrive
by later Wednesday into Thursday, and conditions will certainly be
warm enough for rain as it arrives. However, the front is progged
to become mostly parallel to the upper level flow on Thursday and
will be slow to depart as a result. To varying degrees, the model
progs develop additional waves along the nearly stalled frontal
boundary, while the vertical temperature profile across the region
continues to cool. So, we could end up with some precipitation
type problems before the system finally leaves the area late in
the week. However, there is too much uncertainty/model variability
in the details to be very specific at this time. For now, have
simply gone with a chance of rain or snow Thursday night and
Friday. This will most certainly need fine tuning as the system
draws closer.

Bak
&&

.AVIATION...
ISSUED 538 PM CST Fri Nov 29 2013

VFR conditions will continue at all TAF sites next 24hrs. Broken
high cirrus is over the area currently and will continue
overnight, but then will become clear during the early morning
hours. Then clear skies will prevail through remainder of the TAF
period. Winds will be southeasterly and then become southerly tomorrow.

Auten
&&

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

$$