Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 210605

Area Forecast Discussion
National Weather Service Lincoln IL
105 AM CDT Fri Jul 21 2017

Issued at 907 PM CDT Thu Jul 20 2017

Convection that developed in southeast IA is either backbuilding
or quasi-stationary. However, a frontal boundary is located near
I-74 and one shower has developed in Mclean county. isolated
showers/storms are still possible along this boundary this evening
and into the overnight hours. So will be keeping some form of pops
in this area though need to make some adjustments to pops to
match current radar trends/situation. Will also be updating cloud
cover to account for large cirrus shield that has spread into
central IL.

Update out shortly.


.SHORT TERM...(This evening through Friday)
ISSUED AT 309 PM CDT Thu Jul 20 2017

Subsidence in the wake of a morning MCS that skirted central
Illinois to the northeast has prevented convective re-development
thus far this afternoon. However, latest LAPs analysis shows an
extremely unstable airmass in place...with peak CAPE values in
excess of 5000J/kg along and north of I-74.  In addition, an area
of deep-layer moisture convergence is noted across the far
northern KILX CWA from near Galesburg E/SE to Chenoa. This is
likely in proximity to a residual outflow/differential heating
boundary left behind by the morning convection. Think this will be
the area to watch over the next few hours for widely scattered
thunderstorm development. HRRR has been consistently showing a few
cells firing across the N/NE late this afternoon into the evening,
so have included low chance PoPs along/north of I-74 accordingly.
Think any storms that develop will dissipate toward midnight, with
largely dry conditions noted overnight.

A cold front currently extending from southern Lake Michigan
to central Iowa will sag southward late tonight...eventually
stalling across north-central Illinois Friday morning. With a weak
boundary in the vicinity, have included low chance PoPs across the
entire CWA on Friday. While most locations will remain dry, a few
spots may pick up locally heavy rainfall with slow-moving storms.
The main story for Friday however, will be the continuation of the
oppressive heat and humidity. High temperatures will once again
top out in the lower to middle 90s, with peak afternoon heat index
values reaching the 105 to 110 degree range.

.LONG TERM...(Friday night through Thursday)
ISSUED AT 309 PM CDT Thu Jul 20 2017

Low pressure will develop over the Dakotas on Friday, then will
track slowly eastward into Wisconsin by early Saturday. Favorable
dynamics will exist ahead of the low to trigger the development of
an MCS across Minnesota/Wisconsin Friday night. This system will
track E/SE into southern Wisconsin and far northern Illinois late
Friday night into Saturday morning. All indications suggest the
storms will remain mostly N/NE of the KILX CWA: however, have
included low chance PoPs along/north of I-74 as the system brushes
by the north. Once the low moves into the Great Lakes, it will
drag a stronger cold front southward into central Illinois by late
Saturday. Most models suggests scattered thunderstorms will
develop along/ahead of the front across the northern two-thirds of
the CWA late Saturday afternoon and evening. With CAPES once again
exceeding 4000J/kg and 0-6km bulk shear increasing to around 30kt,
a few strong to severe thunderstorms with gusty winds, large hail,
and torrential rainfall will be possible. The storms will settle
into the southern CWA by Saturday night as the front sinks toward
the I-70 corridor.

Despite FROPA Saturday night, a trailing trough axis may trigger
isolated convection Sunday/Sunday evening. After that, deep-layer
northwesterly flow will bring a cooler and less humid airmass into
the region early next week...with highs dropping into the lower to
middle 80s for Monday and Tuesday. The next chance for widespread
precipitation will likely hold off until Thursday at the earliest
as another cold front approaches from the northwest.


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 102 AM CDT Fri Jul 21 2017

Predominantly a light and variable wind overnight, with bkn
cirrus. However, convection passing to the north and northeast
will keep a VCSH in PIA and VCTS in BMI at the very least.
Another round of showers/ts possible for the afternoon hours again
in the north closer to the stalled frontal boundary.


Excessive Heat Warning until 8 PM CDT Saturday for ILZ027>029-

Heat Advisory until 8 PM CDT Saturday for ILZ030-031-038-043>046-



LONG TERM...Barnes
AVIATION...HJS is the U.S. government's official web portal to all federal, state and local government web resources and services.