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Area forecast discussion 
National Weather Service Lincoln Illinois
842 PM CDT sun Sep 21 2014

issued at 842 PM CDT sun Sep 21 2014

High amplitude 500 mb high pressure ridge over the Rocky Mountains
and a deep 500 mb trough over the eastern Great Lakes this
evening with a weak shortwave trough digging down the back side
of the trough. Subsidence behind the shortwave along with
nighttime cooling and stabilization is bringing rapid clearing to
central Illinois this evening. Dry northerly flow behind the shortwave
will result in an atmospheric profile unfavorable for fog
formation overnight with mixing ratios decreasing with height off
the surface. In addition...steady light northerly winds will
promote boundary layer mixing to help prevent fog. Temperatures
should reach into the mid 40s at most central Illinois locations in this
cool dry air mass overnight. Made minor updates to lower
temperatures overnight...but otherwise no updates necessary.


Short term...(tonight)
issued at 244 PM CDT sun Sep 21 2014

Strong 555 dm 500 mb low over Lake Huron will pull eastward across the
eastern Great Lakes region tonight. Meanwhile at the surface, 998 mb
low pressure over southeast Ontario to lift NE into the Saint
Lawrence Seaway by Monday morning, while 1027 mb high pressure over
the western Dakotas and western Nebraska to settle into the Midwest.
Broken to overcast cumulus/stratocumulus clouds from I-74 northeast
and scattered clouds to the SW to gradually diminish during the
evening after sunset and linger longest from bmi and cmi
northeast. Breezy northwest winds 10-20 mph and gusts of 20 to 35
mph during mid/late afternoon to diminish to less than 10 mph
around sunset and turn more northerly during the night. Despite
clearing skies and winds diminishing, do not think fog will be an
issue tonight due to drier air advecting into central/se Illinois. Lows
tonight in the mid 40s central Illinois and upper 40s in southeast Illinois.


Long term...(monday through sunday)
issued at 244 PM CDT sun Sep 21 2014

An extended period of dry weather, with gradually warming
temperatures can be expected in central and southeast Illinois for
the next 7 days.

The medium and long range models indicate that a complex upper level
pattern will evolve the next several days. The week will begin with
a northwest upper level flow and a surface ridge of high pressure in
control through Tuesday. This will give US cooler than normal
temperatures and plenty of sunshine. By midweek, the departing upper
level trough in the northern stream will allow ridging aloft to
build across the Midwest. This will produce a warming trend with a
dry east-southeast low level flow and rain-free weather through the
end of the week.

Model differences become apparent very late in the forecast period
for next weekend. The GFS model pushes the upper level ridge axis
much farther east than the European and Canadian models by Saturday.
This allows a return flow to develop, with tropical moisture surging
northward, resulting in the potential for rain late Saturday-Sunday.
For the upper ridge to move toward the Appalachians by Saturday, an
upper low in the southwestern U.S. Would need to kick out much
quicker. It seems that the GFS is too fast moving this feature out
considering the overall expected flow pattern in the Pacific and
rockies. Thus, will keep the forecast dry through next weekend.


Aviation...(for the 00z tafs through 00z Monday evening)
issued at 626 PM CDT sun Sep 21 2014

VFR conditions are expected for the next 24 hours. At
cover scattered-bkn040-060 across central/southeast Illinois. Dry northerly
flow and subsidence following a weak shortwave trough passage this
evening should produce decreasing cloud cover overnight followed
by clear mostly skies Monday. Winds north-northwest 7-12 kts at 00z
decreasing to less than 7 kts by 05z. No fog expected overnight
due to drier air moving over the region in north-northwest winds.


Ilx watches/warnings/advisories...



short term...07
long term...Miller

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