Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 170213

Area Forecast Discussion
National Weather Service Lincoln IL
913 PM CDT Fri Jun 16 2017

Issued at 913 PM CDT Fri Jun 16 2017

Made some adjustments to the forecast grids for the overnight time
period to slightly increase PoPs. Radar mosaics and Clean IR loop
showing several clusters of storms/MCSs from southern WI to
central IA and southeast NE. The MCS in southwest IA and NE has a
definite southeastward propagation to it, while the weaker cluster
of storms in northern IA is moving more eastward.

Many of the convective allowing models, are bringing at least a
portion of the convection into central Illinois. The HRRR, and to
a lesser extent the 00z NAM, are indicating showers and a few
thunderstorms pushing into the IL River Valley around 3 am. After
that time the convection scatters out more and weakens. Thus, went
with likely PoPs for the IL River valley and 30-50 PoPs in the
rest of central and eastern IL. Parts of southeast IL may stay
rain free overnight, with any lingering showers holding off until
Saturday morning.


.SHORT TERM...(This evening through Saturday)
ISSUED AT 313 PM CDT Fri Jun 16 2017

Partly cloudy afternoon today going into a rather stormy start to
the weekend. Some cu out there, but so far convective activity
has been limited for the bulk of Central IL. Some showers and
thunderstorms over the southern portions of the state along the
Mississippi River Valley, but otherwise quiet for the afternoon.
Expected scattered development of some convection later this
afternoon in the east. Weak pops continuing through the evening
hours, increasing after midnight, particularly in the NW.
Overnight convection will receive an assist by the LLJ ramping up
ahead of the next system. Wave of energy rippling through the
region tomorrow as well as warm advection will assist in a general
lifting of the airmass and scattered showers and thunderstorms
will be possible throughout the day. However, the chances will
increase into the afternoon/evening hours as a front draws closer
to the NW.

.LONG TERM...(Saturday night through Friday)
ISSUED AT 313 PM CDT Fri Jun 16 2017

Details for the frontal passage tomorrow night are difficult to
come by as the models are still having issue with the speed of the
system, as well as the volume of convection during the day
providing a wrench to instability parameters later in the evening.
As a whole, the forecast remains much the and muggy
until a frontal passage late Saturday night brings a different
airmass into the Midwest.

A weakened area of low pressure has remained over south central
Canada for several days now. Early Saturday an impulse moves on
the Pac NW coast, rippling into the region and digging back in
over the northern Plains and Upper Midwest, resulting in a more
amplified flow pattern. Associated surface
system develops over the Northern Plains and becomes better
defined as it moves into the Great Lakes region, dragging a cold
front behind it for Saturday night. Uncertainty still clouds how
deep the system, the time of arrival, as well as the impact of
prefrontal showers and thunderstorms for the afternoon that would
impact the development of the evening storms along the boundary.
Should the heat of the day remain largely untouched through the
day on Saturday, the convective potential will lend itself to some
severe storm development tomorrow night, with some decent sheer
into the midlevels. SPC has left much of Central IL in an Enhanced
Risk as a result.

Temperatures at 850mb drop a few degrees for a slightly cooler
wrap up to the weekend and beginning of next week. Behind Sat
night/ Sun morning storms, models dry out and cool off least until midweek. At the end of the forecast,
significant WAA pattern setting up in the midlevels resulting in a
warm up and return of pops for midweek.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 650 PM CDT Fri Jun 16 2017

Isolated convection is expected in east and southeast Illinois
early this evening, but far enough away from any of the TAF sites
to mention VCTS.

Will be watching the convective systems blossoming into western
Iowa for the potential to slide ESE into central Illinois late
tonight. The short range convective allowing models don`t have the
best handle on this, although the HRRR does show the remnants of
an MCS moving into central IL in the 07-11z time frame. For now
will mention VCTS in the TAFS after 07z and through daybreak, but
with VFR ceilings.

VFR conditions will prevail through much of Saturday. However,
with a tightening gradient and decent mixing will increase the
winds and add gusts at most location from late morning through the

Kind of tough to time the movement of t-storms toward the TAF
sites late in the afternoon due to the movement of a weak front
from the west and associated upper level forcing/shear. The best
bet is after 22-23z, so will introduce at least VCTS at the TAF
sites along and west of I-55.




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