Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 290401
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1101 PM CDT Sun Sep 28 2014

.UPDATE...
ISSUED AT 825 PM CDT SUN SEP 28 2014

Quiet weather to continue through the overnight hours as high
pressure holds just north of our area this evening. Weak cold
front across far northern Wisconsin will slip south across the
lower Great Lakes Monday evening and may bring us some cooler
temperatures by Tuesday. Until then, little change is expected
with a pleasant overnight as lows dip into the 50s and another
rather large diurnal swing in temps expected on Monday with
afternoon highs soaring back into the middle 80s. Have made some
adjustments to the temperatures for Monday afternoon as
temperatures aloft will change little, so am not expecting any
significant changes in afternoon highs compared with the last two
days. Should have the update out by 845 pm.

&&

.SHORT TERM...(Tonight)
ISSUED AT 302 PM CDT SUN SEP 28 2014

The 581 dm 500mb low over central Iowa will become an open wave and
drift southeast across MO and sw IL tonight. That will just bring
scattered cirrus clouds with it to central IL, while diurnally driven
few to scattered cumulus clouds 5-7k ft dissipate around sunset. A
shallow layer of moisture below a subsidence inversion will allow
some patchy ground fog to develop again near river valleys like the
IL and Wabash rivers overnight. Any fog that develops overnight
should dissipate by 830 am Monday morning. Lows overnight will be
similar to last night lows and current dewpoints in the low to mid
50s with coolest readings over east central IL. Winds will remain
light to calm through Monday morning under a weak surface pressure
gradient as 1021 mb high pressure and ridging into WI, northern IL
and eastern IA remains in place through Monday.

&&

.LONG TERM...(Monday through Sunday)
ISSUED AT 302 PM CDT SUN SEP 28 2014

Quiet weather is still expected for the start of the work week.
Shortwave currently entering western Saskatchewan will be digging as
it approaches Lake Superior, forming a closed low over Lake Huron by
early Tuesday. This will push a cold front southward, with all
models indicating it getting into central IL before lifting back
north as a warm front on Wednesday.

Then a broad trough in the Rockies will slowly move east into the
plains. The first surface low associated with this feature will lift
northeast into the northern plains with showers and thunderstorms
trailing just ahead of a front in the plains, slowly moving east.
This first batch of pcpn will not make it into the CWA, as it will
be well away from it`s best support and it will be moving into a
strong ridge. The cold front will still be west of the area, but
will refire with showers and thunderstorms Wed night. The front will
also be moving into the area Wed night and Thur, so pcpn will become
likely through Thur night, across the CWA. A strong surge of cooler
air move into the midwest on Friday behind the front. Models differ
on timing of all this pcpn and believe the ECMWF/GEM have the best
handle on the timing of onset of the pcpn, while the GFS is too
fast. Beyond this system and into the weekend, much cooler high
pressure will build into the area for the weekend.

850 mb temperatures in the 13-15C range will keep our highs above
normal, with some cooling on Tuesday as the front moves south into
the CWA and then back north Tue night. Temps will stay above normal
for Thur ahead of the cold front and pcpn, but then cool behind this
front for the remainder of the week and into the weekend.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
ISSUED AT 1100 PM CDT SUN SEP 28 2014

Little change from previous discussion with the main forecast
concern being the potential for some patchy MVFR vsbys in fog
from 10z thru 12z, otherwise, the majority of the forecast
period will have VFR conditions. Temp-dew point spreads were
still greater than 5 degrees across the entire area late this
evening. Similar conditions are expected during the daylight
hours on Monday that we had today with some scattered high
based cumulus forming after 16z, which should dissipate by
00z. Beyond 00z Tuesday, we will be watching a cold front slip
south into northern Illinois by early evening with a band of
MVFR cigs just behind the frontal boundary. Current thinking
is that the band of lower clouds will affect our northern TAF
sites (KPIA, KBMI) first, but not until after 06z. Surface
winds will remain calm overnight and be light and variable
on Monday.

&&

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

$$

UPDATE...Smith
SHORT TERM...07
LONG TERM...Auten
AVIATION...Smith



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