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fxus63 kilx 262343 
afdilx

Area forecast discussion
National Weather Service Lincoln Illinois
643 PM CDT Fri may 26 2017

Short term...(this evening through saturday)
issued at 259 PM CDT Fri may 26 2017

Clusters of thunderstorms along the southern periphery of an mesoscale convective vortex
will track across north-central Illinois this afternoon into the
early evening. Based on radar trends and output from the hrrr and
3km NAM, it appears locations along/north of the I-74 corridor will
be impacted through about 00z/7pm. As a result, have increased pops
to likely across this area through the remainder of the afternoon.
Once this system races into Indiana, it will drag a weak cold front
southward into central Illinois this evening. With strong warm air advection
occurring throughout the entire depth of the atmosphere, mid-level
capping will be strong enough to prevent much convection from
developing along the trailing front. Have therefore only carried
slight chance pops across the southern two-thirds of the kilx County Warning Area
from mid-evening through the overnight hours. With the boundary in
the vicinity, winds are expected to become light/variable. Given
increasing boundary layer moisture (both from advection and any
rainfall that occurs this afternoon), think fog will develop
tonight. Hrrr continues to show fog developing along the I-74
corridor by around midnight, then spreading further southward across
the remainder of the area as the night progresses. Have added
patchy fog across the board accordingly.

Frontal boundary will stall along the I-70 corridor late tonight
through Saturday and will eventually serve as a focusing mechanism
for strong to potentially severe convection late Saturday. Latest
models have continued to trend later with the next round of storms,
with most high-res solutions shifting the emphasis into the evening.
Given good consensus that Saturday will be dry, have dropped pops
until late in the afternoon across the far SW County Warning Area. Main event will
arrive Saturday evening, with models still not set on an exact
timing just yet. NAM/GFS are the fastest models, with convection
developing upstream across Kansas during the afternoon...then
tracking eastward along the boundary and arriving in west-central
Illinois by early evening. Meanwhile, other convective-allowing
models such as the WRF-nmm and WRF-arw delay the arrival of the
convection until late evening into the overnight hours. Storm Mode
by the time the system arrives will be linear, so damaging wind
gusts with an isolated tornado threat would be most probable. At
this time, have gone with likely pops across the western half of the
County Warning Area during the evening, then further east to the Indiana border
after midnight. If trends continue, the timing may eventually need
to be adjusted a bit later.

Long term...(saturday night through friday)
issued at 259 PM CDT Fri may 26 2017

Once the Saturday night wave of convection passes to the east, it
will give the stalled frontal boundary a push to the south on
Sunday. Airmass destabilizes ahead of the front by afternoon,
resulting in scattered thunderstorm development primarily along and
south of I-70. Have included 30 pops across this area, with little
or no precip expected further north across the remainder of the
area. High temperatures on Sunday will reach the middle to upper
70s.

Pronounced upper low will dig southward through Ontario into the
Great Lakes early next week, resulting in a cooling trend across
central Illinois. A weak surface trough will sink southward around
the parent low on Monday, potentially bringing a few showers.
Convergence along the boundary will be weak and with the main upper
cold core still to the north, think areal coverage of precip will
remain low. As a result, have only mentioned slight chance pops for
showers/thunder along and north of I-74 Monday afternoon. Cool/dry
conditions will prevail Monday night into Tuesday before the next
potential system spreads showers across south-central Illinois
Tuesday night. After that, mainly dry weather is expected until a
stronger system brings the next chance for rain by Friday.

&&

Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 643 PM CDT Fri may 26 2017

Main cluster of convection has now pushed into west-central
indiana:however, a trailing outflow boundary may trigger isolated
storms for the next couple of hours at the I-72 terminals. Have
carried thunderstorms in the vicinity at kspi/kdec/kcmi through 01z accordingly. Once any
early evening convection dissipates, winds will become
light/variable behind the boundary. Due to increasing low-level
moisture and rainfall across the northern counties this afternoon,
fog will develop overnight. Hrrr has been consistently showing
fog developing along the I-74 corridor around midnight, then
slowly spreading southward toward dawn. Will reduce visbys to
around 2 miles between 09z and 13z at all sites. After the morning
fog lifts, mostly sunny skies will be noted through Saturday
afternoon.

&&

Ilx watches/warnings/advisories...
none.
&&

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