Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 181414
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
914 AM CDT Sat Oct 18 2014

.UPDATE...
ISSUED AT 914 AM CDT SAT OCT 18 2014

Vigorous short-wave evident on 1330z water vapor imagery is
dropping southward out of Wisconsin this morning. This feature is
bringing widespread cloud cover to the Great Lakes and Upper
Midwest, with the leading edge of the clouds currently sinking
into north-central Illinois. Based on satellite timing tools and
forecast soundings, clouds will overspread much of the KILX CWA
over the next 1 to 2 hours, with areas along/south of I-70
remaining mostly sunny until early afternoon. Further north
beneath the short-wave, scattered showers are noted on radar
imagery across southern Wisconsin into northeast Illinois.
Trajectory of wave and associated precip is generally to the S/SE
into northern/central Indiana: however, think the far NE CWA
around Champaign and Danville may see a few sprinkles from midday
into mid-afternoon before the wave passes to the south. Once the
wave drops into the Ohio River Valley, subsidence on its back side
will lead to clearing skies from northwest to southeast across the
region this afternoon/evening. Despite widespread cloud cover
currently upstream, models insist that skies will become clear
across the board by early evening. Will continue to monitor
satellite over the next several hours to see if clearing trend
needs to be tempered, but for now will follow NAM/HRRR idea of
rapid clearing in the wake of the wave later today. Have adjusted
sky grids to better reflect current trends and have nudged high
temps into the lower 60s along/south of I-70 where sunshine will
prevail for a few more hours before clouds arrive. Have also
expanded the Frost Advisory to include the entire CWA tonight, as
clear skies/light winds will allow for lows in the middle 30s and
areas of frost everywhere.

&&

.SHORT TERM...(Today)
ISSUED AT 336 AM CDT SAT OCT 18 2014

Persistent/deep cyclonic northwest flow exists across central and
southeast Illinois early this morning, and it is expected to last
through the day. The low cloud deck in this flow regime has some
sizable breaks in it at the moment, with parts of the forecast area
and upstream into the upper Midwest seeing mostly clear skies for a
time. Expect one more surge of widespread overcast skies later today
as a compact/potent upper wave (currently near the U.S./Canada
border of the upper Midwest/western Great Lakes region) and
associated surface trof swing through the region. However,
upper/surface ridging building in late today should help to scour
out the cloud cover for later tonight. The persistent low level cold
advection, expected breezy conditions, and considerable cloud cover
today is expected to result in chilly highs mainly in the 50s.

&&

.LONG TERM...(Tonight through Friday)
ISSUED AT 336 AM CDT SAT OCT 18 2014

A couple items for consideration during this forecast range:

1) Frost potential tonight -- High pressure expected to settle into
the Ohio Valley late tonight, with winds dropping off to nearly
calm. Earlier cloud cover expected to be out of the area before
midnight. Most areas will be dropping into the mid 30s for lows.
About the east 1/2 of the CWA would be vulnerable for some patchy
frost, with the far southwest less likely as southwest winds already
start up by late night. After collaborating with neighboring
offices, will issue a frost advisory over most of the CWA except for
the far southwest (i.e. Rushville to Jacksonville).

2) Shower potential Sunday night/Monday -- Shortwave expected to dig
across the northern Plains on Sunday as upper ridging amplifies over
the Rockies before shifting eastward. Latest ECMWF starting to come
more toward the GFS solution with an increase in showers after
midnight Sunday night, lingering across the southeast CWA into
Monday. Have not made much change aside from splitting the PoP grids
into 6-hour periods to focus the best chances during these two time
frames.

Otherwise, fairly quiet weather expected through the period. As the
week progresses, a blocking pattern will be setting up, as the
Monday wave digs even further and develops a large closed low over
the mid-Atlantic states by mid week. This feature only slowly drifts
east late week as a large surface cyclone develops. While an upper
wave tries to drop down into the Midwest toward the end of the week,
there will not be any moisture advection, as a surface low forms
along the trailing front over the western Caribbean and forces a
northeast flow across the Gulf. Thus, will keep the forecast dry
from Monday night onward.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
ISSUED AT 645 AM CDT SAT OCT 18 2014

A large area of MVFR cigs will spread across the central Illinois
terminals early this morning from the north, and linger through
much of the daytime hours. Then, the cigs are expected to scatter
out by this evening as a ridge of high pressure builds into the
area. Northerly winds, possibly gusty at times today, will trend
light and variable for tonight.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
FROST ADVISORY from 3 AM to 8 AM CDT Sunday FOR ILZ027>031-
036>038-040>057-061>063-066>068-071>073.

&&

$$

UPDATE...Barnes
SHORT TERM...Bak
LONG TERM...Geelhart
AVIATION...Bak






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