Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 301756

Area Forecast Discussion
National Weather Service Lincoln IL
1256 PM CDT MON MAY 30 2016

Issued at 1050 AM CDT Mon May 30 2016

Update forecast to expand chances of showers and thunderstorms
further east over central IL this afternoon. Most of CWA will have
20% chance of showers and thunderstorms this afternoon with 30-40%
chances nw of the IL river. Already had some isolated convection
affect southwest fringe of CWA earlier this morning. More isolated
to scattered showers/thunderstorms were just nw of Knox county
extending into eastern IA and tracking eastward. CAPES have
increased to 1-2k J/kg west of I-57 by late morning and this to
support isolated convection as a weak short wave over sw IL lifts
ne and to exit area by 00Z/7 pm today. 0-6 km bulk shear is quite
weak today, less than 20 kts, hence SPC just keeps our area in a
general risk of thunderstorms today. But isolated strong
thunderstorms could develop during afternoon nw of IL river with
brief period of pea size hail and gusty winds possible (pulse type
variety). HRRR and RAP models appear a bit too widespread with
coverage of convection today along and nw of I-70. Meanwhile NAM
model is dry today over CWA and that seems too dry with
instability returning today especially west of I-57. Another very
warm day in the mid to upper 80s this afternoon with dewpoints in
the upper 50s/lower 60s.


.SHORT TERM...(Today)
ISSUED AT 337 AM CDT Mon May 30 2016

08z/3am surface analysis shows a weak bubble of high pressure
over central Illinois, while a stationary frontal boundary remains
poised just to the west from southern Iowa into eastern Missouri.
Widely scattered convection continues to develop and move
southeastward along the boundary, with most of the activity thus far
remaining west of the Mississippi River.  Will need to keep an eye
on radar trends, as a few showers could potentially reach the far
W/SW KILX CWA from Rushville to Jacksonville southwestward over the
next couple of hours.  Airmass across central Illinois is drier than
it has been over the past few days, as evidenced by precipitable
water values on the 00z KILX upper air sounding of only 0.86.  This
dry air should keep most of the showers west of the area, similar to
latest HRRR forecast.  Have therefore maintained a dry forecast
through the morning, then have introduced slight chance PoPs across
the Illinois River Valley this afternoon as the airmass slowly
moistens and the stationary front begins to shift northward.
Elsewhere around the area...mostly sunny and dry conditions will
prevail with high temperatures reaching the middle 80s.

.LONG TERM...(Tonight through Sunday)
ISSUED AT 337 AM CDT Mon May 30 2016

Forecast still showery with thunderstorm activity off and on through
the middle of the week until another upper low digs in over the
Plains and drags a front through the region. Although the models are
showing some consistency...timing confidence remains problematic.
Temperatures in the forecast stay summer-like through the first
couple of days this week...several degrees above normal.  A few
degrees cooler behind the boundary, but not by much and not for southerly flow at the sfc reestablishes and sets up WAA
briefly going into next weekend. That being said, Tue/Wed high
temperatures will fall prey to any shower/cloud activity that could
dampen the diurnal curve.

Quasi-zonal flow sets up over the Midwest today and a weak flow
pattern aloft setting up as the next low digs in over the northern
Rockies. Main concern with the forecast surrounds the progression of
the low with the performance of the models lately with timing. Not a
distinct kicker on the horizon and yet the models steadily push that
wave across the country through the first half of the week. Would
prefer a slightly slower solution...and grids reflecting that for
now. GFS/ECMWF still together with the clearing of the frontal
boundary and associated rain by Thursday morning...with the possible
exceptions of the far east/SE. Until then...showery activity in the
forecast more often than not.  Dry on the other side of the front at
least for Friday...with warm weather lasting into next weekend.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1255 PM CDT Mon May 30 2016

Isolated showers and thunderstorms will continue to develop across
central and nw IL during the afternoon in unstable airmass with
CAPES of 1-2k J/kg west of I-57. A short wave moving ne into
central IL by mid afternoon ahead of upper level trof near the
KS/MO and OK/AR border will help support isolated convection this
afternoon and then dissipate by sunset. Scattered to broken
cumulus clouds 5-8k ft so VFR conditions expected with sky cover.
Weak high pressure of 1018 mb over southern IL, sw IN and western
KY to keep wind fields fairly light (less than 10 kts) next 24
hours as high pressure drifts over the Ohio river valley. Some
light fog/haze possible from 09Z-13Z where vsbys could lower to
4-6 miles.


.ILX Watches/Warnings/Advisories...



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