Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 290448

Area Forecast Discussion
National Weather Service Lincoln IL
1148 PM CDT SAT MAY 28 2016

Issued at 1005 PM CDT Sat May 28 2016

Main changes to the forecast were related to convective trends for
the rest of the late evening and very early morning hours.

Numerous convective boundary interactions, low level convergence
along those boundaries and just enough mid level forcing will keep
thunderstorms going between the IL River and I-55, from about
Lincoln northward, through at least midnight. Locally heavy rain
can be expected in this area, but the ground is fairly dry and
able to absorb quite a bit of rainfall.

Areas from Springfield toward Champaign/Danville and locations
south are less likely to see rainfall overnight, with only a few
showers and isolated thunderstorms possible. The activity in the
St. Louis metro area is expected to dissipate, but we can`t rule
out a few showers/t-storms south of the I-70 corridor well after

Drier air and subsidence in the wake of the convection will yield
a partly cloudy toward daybreak in much of the forecast area.


.SHORT TERM...(Tonight)
ISSUED AT 244 PM CDT Sat May 28 2016

SPC issued a severe thunderstorm watch until 9 pm for 9 of our
northwest counties in the IL river valley. Have increased chances of
thunderstorms in this area into early evening. So far much of this
convection has been over IA and lifting NNE at 35-40 mph. But expect
this band to develop southward with time as it spreads into the IL
river valley late this afternoon and early evening until sunset.
Some sunshine helping with heating and making airmass more unstable
as CAPES are elevating to 1-2k J/kg during mid/late afternoon while
0-6 km bulk shear is 25-30 kts. This convection is developing ahead
of a frontal boundary over sw IA into central MO and expected to
track eastward across western and central IL during this evening and
eastern IL overnight. 1006 mb surface low pressure near the SD/IA
border to lift northeast into nw WI by midnight tonight helping push
the front eastward into IL this evening. Aloft a 565 dm 500 mb low
was in far southeast SD and to continue to weaken as it lifts into
western Lake Superior by dawn Sunday. Instability/CAPES to weaken
after sunset with convection also diminishing as it spreads into
eastern IL later this evening and overnight. Lows overnight mostly
in the mid 60s, with some lower 60s from Galesburg and Jacksonville
west as some drier air moves in behind the front overnight.

.LONG TERM...(Sunday through Saturday)
ISSUED AT 244 PM CDT Sat May 28 2016

Unsettled weather expected to persist across central and southeast
Illinois for much of the coming week. While the first half of the
week should still see daily highs in the 80s & daily lows in the 60s
to start the week, consensus is building that these readings will
cool to the 70s (highs) & 50s (lows) in most areas to end the week.
Main forecast concern revolves around shower/storm chances, and
looking for opportunities to remove them. Selecting dry periods is
proving difficult as the local airmass should remain fairly "juicy"
and uncapped for much of the week.

Most of Sunday is still expected to remain dry as the upper-level
low remnants, currently tracking into the upper Midwest, pushes
north/east of the area. The passage of this upper feature will push
a weak cold front through the area by early Sunday. Any stabilizing
of the atmosphere in the wake of the front will be fairly short
lived, with spotty development possible by late Monday across at
least western portions of the forecast area.

A northern stream wave and associated frontal system will impact the
area Wednesday into Thursday bringing our next chance of more
widespread showers/storms. However, scattered showers/storms are
possible as early as Tuesday areawide under pre-system WAA and
diurnal instability. Precipitation chances will lower or possibly end
for a time Friday/Saturday in the wake of the midweek system, with
temperatures trending a little cooler than normal. The operational
GFS had previously lingered precipitation chances much longer than
Thursday, but it and many of its ensemble members have trended
toward what the ECMWF & Canadian models showed yesterday.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1142 PM CDT Sat May 28 2016

The late evening convection has ended at nearly all of the central
IL TAF sites, except for BMI. Showers/T-storms with IFR/MFR
visibility and ceilings have been training through the BMI area
between 02-05Z. The mid level shortwave providing the support for
this convection will be moving out of the area around 06Z.
However, will keep a predominant VCSH group with the potential for
a brief TSRA at BMI through 07-08Z as additional convection may
develop on the tail end of the upper support and cold cloud tops.

The rest of the TAF sites can expect VFR conditions the next 24
hours as a cold front passes through the region Sunday late
morning/early afternoon. This will also result in a wind shift in
the 15-18Z time frame from SSW to west winds. The wind will drop
off considerably around dusk as the atmosphere decouples under a
clear sky.


.ILX Watches/Warnings/Advisories...


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