Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 281712
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1212 PM CDT WED SEP 28 2016

.UPDATE...
Issued at 942 AM CDT Wed Sep 28 2016

Upper low currently spinning over the southern tip of Lake
Michigan. Initial batch of showers mainly now east of I-57 and
continuing to move east, with a couple lightning strikes even
observed southeast of Champaign within the last hour. Some
additional showers should form this afternoon with the next
trough rotating around the low, which will only make it to central
Indiana by sunset.

Main changes to the forecast were to adjust the PoP trends through
tonight. Little change needed to the temperatures, which still
were only in the lower 50s across the northern CWA as of 9 am.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 321 AM CDT Wed Sep 28 2016

Latest upper air analysis shows a 553dm 500mb low centered over
southern Lake Michigan, with a well-defined short-wave trough
rotating around the low into central Illinois.  At the surface...a
cold front is dropping southward toward the I-72 corridor.  Despite
an initially dry environment ahead of the front, a few light showers
have been observed across the N/NE KILX CWA early this morning. The
upper low and its associated surface front will gradually sink
southward today, resulting in mostly cloudy and cool conditions.
Upper cold pocket directly beneath the low will remain just east of
the area across Indiana, where resulting instability parameters will
support isolated thunder.  Further west into central Illinois, lapse
rates will be weaker...so am only expecting isolated to widely
scattered showers.  High temperatures will range from the lower 60s
far north around Galesburg and Lacon...to the upper 60s south of the
I-70 corridor. The showers will be diurnally driven, so have dropped
PoPs everywhere except the far NE CWA for tonight as low
temperatures settle into the lower 50s.

.LONG TERM...(Thursday through Tuesday)
ISSUED AT 321 AM CDT Wed Sep 28 2016

Deep upper low will be the dominant weather-maker for the next
several days, as it remains cut off from the main flow and wobbles
across the Ohio River Valley.  With this feature remaining in the
vicinity, scattered showers will continue to be a possibility
Thursday through Saturday.  While the low will generally remain east
of Illinois, it will come close enough to support isolated thunder
along/east of I-57 both Thursday and Friday afternoons when GFS
MUCAPE values reach the 200-400J/kg range.  Will continue to focus
highest PoPs across the eastern half of the CWA, particularly on
Friday when the low makes its closest pass.

All models are showing a substantial upper trough digging across the
western CONUS this weekend that will eventually give the persistent
upper low a shove northeastward by Sunday.  Ridging in its wake will
lead to a period of warm/dry weather early next week with
temperatures climbing well into the 70s and perhaps into the lower
80s by Tuesday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1212 PM CDT Wed Sep 28 2016

Extensive MVFR cloud deck associated with upper low over northwest
corner of Indiana has started to lift some, and central Illinois
TAF sites should be in VFR territory by 20-21Z. Clouds expected to
erode some with loss of daytime heating, but another deck of
ceilings at or below 2000 feet expected to push westward later
tonight, as the low will only drift across Indiana. Some
uncertainty as to how far west this will reach. Have only
mentioned TEMPO periods of MVFR ceilings at KPIA/KSPI, but sites
further east should see the lower ceilings moving in during the
09-11Z time frame, sticking around the remainder of the morning.
Gusty winds today will settle a bit late in the afternoon and
gradually turn more northerly overnight.

&&

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

$$

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


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