Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 090212

Area Forecast Discussion
National Weather Service Lincoln IL
912 PM CDT Tue Jul 8 2014

ISSUED 912 PM CDT Tue Jul 8 2014

Dry and stable WNW flow over central and southeast IL this evening
as an upper level trough remains centered north of the Great
Lakes. This will allow clouds to continue to dissipate overnight.
With little cloud cover expected overnight, temperatures will drop
into the upper 50s and lower 60s bringing some possibility of fog
formation as dewpoints remain generally in the low 60s...however
surface pressure gradients indicate winds will remain around 5 mph
which should tend to inhibit fog formation through mixing. For
Wednesday, surface high pressure will cross the state bringing
light winds. Enough moisture will remain at low levels for
scattered shallow convective clouds during the daytime but no
significant chance for precipitation. Current forecast package
incorporates these features well, and no updates are planned this


ISSUED 609 PM CDT Tue Jul 8 2014

VFR conditions will continue across central and southeast IL
through late evening as scattered cumulus cloud cover dissipates
with winds WNW 10-15 kts. WNW surface winds will weaken overnight.
Higher dewpoints from around KTAZ-KCMI eastward in east-central
and southeast IL indicate the potential for fog development in
this region, and areas of IFR/MVFR visibilities will be possible
from around 06Z-14Z. After 14Z...expect VFR conditions again with
cloud cover SCT040-050 and winds NW5-10 kts.


ISSUED 243 PM CDT Tue Jul 8 2014

SHORT TERM...Tonight through Friday

19z/2pm surface analysis shows cold front extending from eastern
Michigan southwestward to the Ozarks. Very warm/humid airmass
remains in place ahead of the front, while cooler/drier air is
slowly filtering southward behind it. Current dewpoints have
dropped into the upper 50s/lower 60s across the far northern KILX
CWA, but remain around 70 degrees south of I-70. Will need to
monitor satellite/radar trends over the next couple of hours, as
widely scattered showers may develop near the boundary late this
afternoon. Any precip that occurs will dissipate/drop south of the
CWA this evening, followed by mostly clear and cooler conditions.
Overnight lows will mainly be in the upper 50s and lower 60s.

Upper-level troughing will remain in place over the Great Lakes
through Wednesday before gradually retreating northward into
Canada by the end of the week. With northwesterly flow aloft and
surface high pressure building into the region, expect abundant
sunshine and below normal temps through Thursday. Afternoon highs
will remain in the upper 70s and lower 80s, while nighttime lows
dip into the upper 50s and lower 60s.

Upper heights will rise significantly by Friday as a ridge tries
to build over the central U.S. As has been the case throughout the
spring and early summer, the main ridge axis will remain further
west along/west of the Rockies while a zonal or weak northwest
flow persists downstream across the Midwest. The end result will
be a return to warmer weather with periodic thunderstorm chances
as upper waves track through the flow pattern. The first short-wave
trough is expected to arrive on Friday, with all model solutions
keeping any associated precip west of central Illinois until
Friday morning at the earliest. Given dry airmass initially in
place, have slowed onset of precip by about 6 to 12 hours. As a
result, have kept Thursday night dry across the board and only
introduced low chance POPs across the E/SE CWA by Friday

LONG TERM...Saturday through Tuesday

Zonal flow pattern will persist through the weekend, resulting in
warm and occasionally wet weather. With a weak baroclinic zone
stationary across the region and upper waves tracking southeastward
out of the Northern Plains, scattered showers and thunderstorms
will be possible Friday night through Sunday. Model solutions
generally show a stronger wave approaching by late in the weekend
that will eventually push the front south of central Illinois by
Monday. GFS is most aggressive in driving the front southward,
while ECMWF is a bit slower. Have trended the forecast drier by
Monday, with chance POPs confined to only the far SE. After that,
models are in good agreement that another appreciable chunk of
cooler/less humid air will settle into the Midwest by the middle
of next week with temperatures once again dropping into the 70s by




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