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Area forecast discussion 
National Weather Service Lincoln Illinois
257 PM CDT Friday may 29 2015

Short term...(tonight)
issued at 257 PM CDT Friday may 29 2015

Despite a moderately unstable airmass characterized by sbcapes of
around 2000j/kg...19z/2pm radar imagery shows very little convection
across central Illinois. Very weak wind shear and an overall lack
of significant forcing appears to be keeping the storms at Bay this
afternoon. Clusters of convection are developing further south from
just east of Saint Louis into the Ozarks. This activity will slowly
lift northeastward and impact portions of the kilx County Warning Area late this
afternoon...mainly along and south of a Danville to Shelbyville
line. Overall areal coverage will remain relatively will
only go with chance probability of precipitation through early evening. Rain chances will
begin to increase tonight as stronger forcing associated with a
short-wave trough over Oklahoma/East Texas approaches from the
southwest. Models are all over the place...however consensus of
high-res solutions focuses highest probability of precipitation across the western half of
the County Warning Area from middle-evening through the overnight hours. Band of
precipitation will gradually spread into east-central Illinois toward dawn a cold front approaches from the west.


Long term...(saturday through friday)
issued at 257 PM CDT Friday may 29 2015

Models generally show a cold front reaching around I-55 by middle
morning Saturday...reaching southeastern Illinois by Saturday
evening and exiting the central Illinois forecast area. Ahead of the
front...modest surface-6km bulk shear of generally 20 kts will
prevail...increasing to around 30 kts near the front. Instability
generally around 1500-2500 j/kg are indicated ahead of the
front...depending on surface heating. These ingredients will come
together...along with an upper level shortwave...during the day
Saturday for scattered showers and thunderstorms especially from
around the Illinois River southeastward. Thunderstorm activity will
shift farther southeastward through the day and evening as the front
slips southeastward. A marginal threat for severe thunderstorms is
forecast by Storm Prediction Center with the main threat being severe wind gusts. With
the frontal boundary lingering near the southern tip of Illinois
Sunday least a slight chance of thunderstorms will
remain through Sunday south of I-70 as another upper level wave
passes through the area. Temperatures will drop off substantially
for Saturday and Sunday. Highs around 67 near Galesburg to around 80
just south of I-70 Saturday...then middle to upper 60s across the area
Sunday. Some lows north of I-72 should reach into the 40s Saturday
and Sunday night.

A building high pressure ridge should bring subsidence and dry
conditions through the early part of next work week. By middle to late
week...a cut-off upper low over the Gulf Coast could help transport
a return of moist/unstable conditions to the Midwest...with
precipitable water values around 1.5-1.75 inches possible. Models
continue to disagree on the position of the ridge/cut-off...and this
will impact the moisture return. Although a strong lifting mechanism
isnt expected at this time...daily chances for thunderstorms will be
possible mainly driven by daytime heating and convective
outflows...perhaps an mesoscale convective system over the upper Midwest. Expect a gradual
warming trend through the week with highs in the low 70s Monday
reaching the middle 80s for Thursday and Friday.


Aviation...(for the 18z tafs through 18z Saturday afternoon)
issued at 1255 PM CDT Friday may 29 2015

Showers and thunderstorms will develop across central Illinois
this afternoon in an increasingly unstable airmass...however with
no significant forcing in place...think areal coverage will
remain scattered. A short-wave trough currently evident on water
vapor imagery over Oklahoma/Texas will lift northeastward into
Illinois tonight...bringing enhanced forcing and a greater areal
coverage of precipitation. Based on rapid refresh forecast...have
introduced predominant rain with thunderstorms in the vicinity at kpia and kspi by
03z...then further east to kcmi by 08z. Will give each taf site a
10-hour period of showers...followed by vcsh by Saturday morning
as the wave tracks north of the area. Forecast soundings indicate
low VFR ceilings initially...lowering to MVFR Saturday morning
immediately ahead/along an approaching cold front. Winds will be
southwesterly through the entire 18z taf period...then will become
west/northwest behind the front by Saturday afternoon.


Ilx watches/warnings/advisories...


Short term...Barnes
long term...Onton

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