Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 010859

Area Forecast Discussion
359 AM CDT Mon Sep 1 2014

.SHORT TERM...(Today and tonight)

Shortwave trough axis approaching Illinois from the west this
morning bringing a line of thunderstorms to the region. Trends this
morning are for the line splitting into to intense
grazing Knox, Peoria, Stark county and likely Marshall and Woodford
as it continues this morning. Have reports of pea-sized hail and
wind gusts 30-40 mph with the more intense storm cells. The intense
activity looks like it will have a break through central IL in the
early morning once this initial activity shifts east-northeastward.
Isolated thunderstorms will likely develop throughout the CWA during
the morning...however daytime heating will likely be necessary to
bring CAPE values up to 1500-2500 J/KG range to bring a better
chance for severe storms when combined with 30-50 kt bulk shear
values also shifting into central Illinois. Large hail and severe
wind gusts will be a threat with the stronger storms this
afternoon...and have continued mention of severe hail and heavy rain
in forecast grids beginning at 3 pm this afternoon...continuing
through around midnight. Heavy rain will continue through the night
as a potent and moist low-level jet continues to push through the
CWA...along with lift associated with the progressive trough and
cold frontal boundary.


.LONG TERM...(Tuesday through Sunday)

00Z models have trended slower with frontal boundary pushing into
southeast IL Tue especially the NAM model and have increase pops to
likely se of I-70 Tue morning. NAM model may be overdoing qpf
amounts Tue morning over southeast IL but models have trended higher
with qpf amounts with precipitable water values of 1.5-2 inches
from 12-15Z Tue and have increased qpf amounts to around a quarter
inch in southeast IL. IL river valley should be dry Tue and chances
of showers and thunderstorms will diminish from nw to se during
Tue afternoon. Highs 82-88F Tue and still rather humid especially
in southeast IL with dewpoints 70-75F while dewpoints lower into
mid 60s over IL river valley. Dry conditions return across area
Tue night with frontal boundary dropping south of area. Lows in
the low to mid 60s Tue night.

Models show frontal boundary starting to lift back north especially
over MS river valley and MO on Wed and have kept 20-30% chance of
showers and thunderstorms sw areas by Wed afternoon with ne areas
staying dry Wed. Warm highs in the mid to upper 80s Wed and model
guidance has trended upward in high temps Wed. Dewpoints elevate
during day Wed into upper 60s and lower 70s Wed afternoon.

Convection chances appear highest over northern IL Wed night closer
to short waves tracking into WI/northern IL and eventually eastward
into lower MI and northern IN. Have areas south of I-72 dry Wed

Thu and Fri still appear to be back into the heat and humidity with
highs in the upper 80s and lower 90s and dewpoints peaking in the
low to mid 70s giving afternoon heat indices of upper 90s to lower 100s
especially Thu afternoon and in southeast IL Friday afternoon. A 593
dm 500 mb high pressure ridge over the southeast states builds the
heat into central/southeast IL late this work week. Most of our area
should be dry Thu and Thu night with just slight chance of
convection Thu afternoon mainly over the Wabash river valley and
nw of IL river Thu night. Models have trended faster with cold
front dropping se through central IL Friday and thru southeast IL
Fri evening. Have increased pops Friday and also trending cooler
with temps and dewpoints during the weekend as 1025 mb high
pressure settles into the Great Lakes region.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)

Convective complex making steady progress toward central Illinois
from the west, although it has been weakening with time as
expected. Cigs will develop/thicken/lower across the terminals
overnight as the complex draws closer/pushes in, but predominantly
VFR conditions are likely aside from any heavier precipitation.
Still some uncertainty when/if the storm complex will dry up
completely, so have only included a TEMPO at KPIA overnight.
Shower/storm redevelopment is likely across central Illinois by
Monday afternoon, focusing along an outflow boundary from
tonight`s storms and/or an approaching cold front. This
precipitation is apt to be more widespread, so have included
predominant showers with VCTS beginning in the afternoon and
continuing into the evening hours Monday. At this point, only have
VSBYs falling to MVFR levels in the steadier rainfall, but the
CIGs certainly may as well.





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