Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 271719
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1219 PM CDT TUE SEP 27 2016

.UPDATE...
Issued at 945 AM CDT Tue Sep 27 2016

Forecast largely on track and did not require much update. Main
issue was with the amount of dry air in place across the northern
CWA this afternoon. Have backed off on the timing of the minor
rain chances associated with the cold front to our north, and have
largely gone dry this evening except for some isolated showers in
the extreme northern CWA late this evening. Other concerns
addressed in the Fire Weather section below.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 335 AM CDT Tue Sep 27 2016

Flow across central and southeast Illinois will become more cyclonic
into this evening as a surface low pressure area and associated
cutoff upper level low drops south through the Great Lakes region.
Today`s weather should be a repeat of yesterday`s, with mostly sunny
skies, westerly winds gusting up to 25 mph at times, and temps
rising into the lower to middle 70s by this afternoon. As the cutoff
low drops toward the area, clouds will begin to increase this
evening in the north and northeast parts of the CWA. Short term
models also bring a short wave around the back side of the low
pressure area tonight. So will need to add a slight chance of
showers along and north of I-74 for tonight.

.LONG TERM...(Wednesday through Monday)
ISSUED AT 335 AM CDT Tue Sep 27 2016

Cooler than normal temperatures, diurnal cloudiness and a few
periods of light rain showers - mainly in eastern Illinois - will be
the main weather features from mid-week into the weekend. The medium
range models are in slightly better agreement on the position of the
main weather maker, an upper low expected to settle into parts of
the Midwest through the end of the week.

The latest 00z model runs show excellent agreement in dropping an
upper low from Lake Superior to southern Lake Michigan Wednesday,
and then just south of the lower Ohio Valley Thursday. This will
bring a reinforcing cold front and strong low level cold advection
into Illinois. The result will be unseasonably chilly temperatures
for Wednesday with highs struggling to reach the mid 60s. Plenty of
diurnal cloudiness will also develop with the cold air aloft. Will
continue with low chance PoPs for scattered showers in extreme east
central IL/Danville area, with isolated showers/slight chance PoPs
from Galesburg-Lincoln-Mattoon-Lawrenceville and eastward for
Wednesday.

Increased the chance for light rain showers in most of east central
Illinois for Thursday as diurnal cloudiness increases and spokes of
energy rotating around the upper low in central KY provide upper
support. This will also keep temperatures in the upper 60s in
eastern IL, with somewhat warmer readings closer to the IL River
Valley.

Model solutions begin to diverge on the specifics of the upper low
center for Friday and Saturday, with the European continuing to be
further to the west. However, each run of the GFS is also a bit more
to the west. Thus, there is more confidence that eastern IL will
have scattered showers and continued cool temperatures through
Friday. Despite the differences in model solutions for the position
of the upper low, they are also starting to agree that the low will
pull out toward the eastern Great Lakes during the day Saturday.
This should result in only spotty showers late Friday into early
Saturday in eastern IL, followed by a decreasing cloud trend and
gradually warmer temperatures the rest of the weekend. By early next
week, upper level ridging and a southerly low level flow will bounce
us right back into warmer than normal temperatures for the first
full week of October.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1219 PM CDT Tue Sep 27 2016

West winds gusting from 20-25 knots this afternoon will subside
before 23Z with loss of daytime heating. Main issue past that will
be associated with an area of low pressure dropping southward from
Lake Superior. Cloud heights will be steadily lowering after 06Z,
and MVFR conditions likely to reach KPIA/KBMI toward 12Z.
Some possibility of it pushing further south of there as the low
reaches southern Lake Michigan, but this is more uncertain and
will keep ceilings in the low VFR range from KSPI-KCMI. Winds
expected to pick up again and shift northwest after a front
passes through in the 09-12Z time frame.

&&

.FIRE WEATHER...
Issued at 945 AM CDT Tue Sep 27 2016

Some concerns with the amount of dry air expected across the
northern half of the CWA this afternoon. Forecast soundings off
the RAP model suggest mixing down from around 850 mb, where dew
points are expected to be in the teens. Large part of the area
yesterday saw surface dew points drop into the 30s. Latest HRRR
guidance shows dew points in the mid-upper 20s north of I-72 which
seems a bit too low, but forecast dew point grids have been
updated to bring a more widespread mid-upper 30s as far south as
Taylorville. 10-hour dead fuel levels still somewhat elevated down
toward the I-72 corridor but are closer to 9-10% across the
northern CWA. Gusts in that area will be close to 30 mph at times
this afternoon. While the fuels do not meet the local red flag
criteria, the dry crops being harvested do pose a risk should any
sparks be triggered by farming equipment. This will be addressed
in the upcoming Hazardous Weather Outlook product.

&&

.ILX Watches/Warnings/Advisories...
NONE.
&&

$$

UPDATE...Geelhart
SHORT TERM...Auten
LONG TERM...Miller
AVIATION...Geelhart
FIRE WEATHER...Geelhart



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