Area Forecast Discussion
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FXUS63 KILX 010756

Area Forecast Discussion
256 AM CDT Sat Nov 1 2014

.SHORT TERM...(Today)

07z/2am water vapor imagery shows potent upper low diving southward
into the southern Appalachians, while deep-layer northerly flow
prevails across the Great Lakes/Midwest.  While much of the
precipitation associated with this feature has now passed well east
and south of Illinois, plenty of lake-enhanced cloud cover continues
to stream southward from Lake Michigan.  Latest IR satellite imagery
shows partly to mostly cloudy skies along/east of a Bloomington to
Shelbyville line with clear skies further west across the remainder
of the KILX CWA.  Most model guidance suggests clouds will rapidly
dissipate by mid-morning: however, think this is too fast given
current synoptic set-up.  Continued N/NE flow within the
surface-925mb layer will likely lead to a persistent lake-enhanced
cloud band from the Chicago area southward into the far eastern CWA
through midday.  Clouds will eventually scatter during the afternoon
as subsidence increases upon approach of surface ridge axis.  End
result will be partly sunny skies along/east of I-57 and mostly
sunny conditions further west.  Will be another unseasonably cool
day as well, with afternoon highs once again remaining in the 40s.
Winds will be lighter than yesterday, but may still gust to between
20 and 25mph at times across the east before pressure gradient eases
later in the day.


.LONG TERM...(Tonight through Friday)

High pressure will slide eastward across central Illinois tonight,
resulting in clear and cold conditions.  Model consensus places
surface ridge axis from southern Lake Michigan to the lower Ohio
River Valley by 12z Sun, so lightest winds and maximum radiational
cooling will be focused across the E/SE CWA.  Further west, light
S/SE return flow on the back side of the high overnight will lead
to slightly warmer temps.  Low temperatures will range from the
lower 20s near the Indiana border to around 30 degrees in the
Illinois River Valley.

Once high tracks further eastward, warm advection will begin in
earnest on Sunday.  Both the NAM and GFS indicate a band of
mid-level moisture lifting through the area, producing partly sunny
skies.  Despite cloud cover, increasing southerly winds and rapidly
rising upper heights will help temps recover into the upper 40s and
lower 50s.  As pressure gradient tightens, southerly winds will gust
to around 25mph on Monday, helping bring even warmer air into the
region.  This will lead to the warmest day of the forecast period
with highs topping out in the lower to middle 60s.

Highly amplified upper pattern will begin to break down early next
week, as a vigorous wave currently over California flattens central
CONUS ridge.  One piece of energy from this wave will track
northeastward into the Great Lakes by Tuesday, while a second piece
will cut-off from the main flow across the Desert Southwest.  The
Great Lakes wave will flatten the prevailing ridge and drive a cold
front into Illinois Monday night into Tuesday.  00z Nov 1 models
have trended slower with the pattern break down and the arrival of
the front, so have pulled PoPs across the west Monday afternoon.
Have also delayed rain chances Monday night, with areas east of I-55
remaining dry until after midnight. Atmosphere will initially be
quite dry, so rain will be slow to develop.  Forecast soundings
gradually moisten from the top-down and saturate sufficiently for
precip overnight everywhere except the far E/SE. Best rain
chances will take place on Tuesday as front slowly pushes through
the area.  Will carry likely PoPs across the board, with rainfall
amounts between 0.25 and 0.50.

Still some disagreement concerning speed of FROPA, with the ECMWF
being faster than the GFS.  Given amplified pattern initially, will
trend toward the slower GFS, which results in continued shower
chances along/south of I-70 into Wednesday.  Once front pushes
further southeast, cool/dry weather will be on tap through Friday.
After that, model agreement remains poor as ECMWF takes Desert
Southwest cut-off low and pushes it northeastward into the Midwest
on Saturday, while the GFS keeps it much further south along the
Gulf Coast.  Given discrepancies, will only mention low chance PoPs
Friday night into Saturday.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)

VFR conditions are expected across most of the area this forecast
period. Will need to keep an eye on KCMI as forecast soundings
indicate they will be on the edge of some low VFR cigs with some
tempo MVFR cigs streaming south off of Lake Michigan thru sunrise
Saturday. 250 meter winds off local VAD wind profilers continues
to show a north to northeast flow off of Lake Michigan so the
bands of clouds tracking S-SW will occasionally get into parts
of our area, mainly along and east of the I-55 corridor. Once
the large area of high pressure to our northwest settles closer
to our area, boundary layer winds will shift enough to shunt the
lake moisture more into Indiana Saturday morning. Northerly
surface winds have been slowly decreasing this evening and expect
that trend to continue overnight. With the area of high pressure
pushing into central Illinois later Saturday, winds will be much
lighter from a north to northeast direction, but still average
from 10 to 15 kts with a few afternoon gusts up to 20 kts,
especially across the east.


FREEZE WARNING until 9 AM CDT this morning FOR ILZ027>031-



LONG TERM...Barnes
AVIATION...Smith is the U.S. government's official web portal to all federal, state and local government web resources and services.