Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 260839

Area Forecast Discussion
National Weather Service Lincoln IL
339 AM CDT Sat Jul 26 2014

ISSUED 312 AM CDT Sat Jul 26 2014
Unsettled weather anticipated today as low pressure and associated
fronts make their way through the Midwest. Plenty of fuel for
storms as hot and humid air pools over the region, but there is
much derision in the models as to initiation and timing and
location of waves to the west to move along the boundaries in the
region and trigger the storms/MCS that will bring the potential
for severe weather to Central Illinois. Warm front currently to
the southwest and expected to lift into the area today, leaving
ILX in the warm sector for much of the day. Depending on the speed
of the cold front expected this afternoon/evening will depend on
how much instability it taps into. Sfc dewpoints into the upper
60s and lower 70s just on the other side of the Miss River Valley
this morning are expected to shift eastward with high temps
approaching 90F. Beyond stormy today and tonight... remainder of
the forecast cooler behind the boundary slowly modifying through
next week to more seasonable temperatures ahead of the next system.

SHORT TERM...Today and tonight...
Plenty of instability for the area with a Moderate Risk in place
for just that reason. 18z forecast soundings showing 4000-4500 j/kg CAPE
as a reflection of the increasing moisture at the sfc and climbing
temps in the warm sector as the warm front lifts northward. Warm
front expected to be northeast and east by midday as the cold
front and actual low center makes its way into the region. As
similar situations have set up over the fa recently, trouble will
be fighting the cap in place for much of the day... and the
approach of the front being enough to break it. Not only the front
itself but models have persisted with a couple waves moving into
the region. Major issues with this are beginning to show their
hand this morning as the locations of the waves this morning on
sat imagery are not initializing in the same locations as many of
the models. Bottom line is... plenty of fuel for storms, and the
triggers are there, but timing and exact locations of impact are
troublesome at best. Llvl helicity better in the early evening
with the proximity of the cold front and the low itself...but
cannot ignore the impact of the warm front and its location should
it not progress further north, storms crossing the boundary could
also be impacted by the turning of the winds for the front. Once
the cap breaks, the forecast soundings/CAPE are indicative of rapid
development of storms. Once going, the very high CAPE values
remain in place well into the evening up to 06z. Best directional
shear is actually in place for the late afternoon/early evening
lending itself to supercells in the beginning of the
event...transitioning to more of a wind event with time. Large
hail will also be a threat mostly with supercells and long
sustained updrafts as the freezing levels are more than 15k ft.
Some tornadic potential early with supercells and invof both
outflows and frontal boundaries.

LONG TERM...Tomorrow through Friday...
Event coming to a close from west to east on Sunday early...but
proximity to upper trof over the Great Lakes will keep an enhanced
threat for instability showers under cyclonic flow, esp Sunday
afternoon. Cooler temps in place for Monday in particular as 850mb
temps drop to closer to 10-12C. Moderating temperatures for the
week as northwesterly flow establishes itself in the region.
Majority of waves alluded to in the models remain north of here
and forecast remains mostly dry, though subtle shifts with those
waves could easily shift the forecast. Next major system impacting
the Midwest Thurs late into Saturday with an open wave aloft and
more cyclonic flow bringing threat for instability showers yet


ISSUED 1150 PM CDT Fri Jul 25 2014

A mid level cig around 7kft has overspread the sites this evening,
but based on satellite trends, the southwest edge of the clouds is
becoming more scattered. So for SPI and DEC, will have them at
scattered with a TEMPO group for broken. PIA/BMI/CMI should stay
broken to overcast overnight but then begin to improve toward
morning and become scattered. Then scattered mid clouds will
continue, but at a higher level during the day tomorrow. As the
warm front slowly sinks into the area tomorrow afternoon, this
will become the focus for the development of thunderstorms late
afternoon and into the evening. Will start each site with VCTS and
then have a 2hr TEMPO group for when best chance of thunder on
station. This could get adjusted as the features become better
defined tomorrow afternoon. Will also keep VCTS in TAFs for
remainder forecast period, due to some uncertainty of timing.
Winds will be southeasterly overnight, but then become
southwesterly after the warm front lifts north through the area.
As the front gets pulled back south into the area during the
evening, winds will become variable. With the threat of severe
weather possible tomorrow evening, will have strong wind mentioned
with the TEMPO group.



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