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Area forecast discussion 
National Weather Service Lincoln Illinois
1145 PM CDT sun Aug 2 2015

issued at 908 PM CDT sun Aug 2 2015

A cold frontal boundary pushing into the southeast corner of Iowa
this evening has triggered some strong thunderstorms ahead of
it...approaching areas from around Galesburg-Lacon northward. With
strong instability and bulk effective shear to around 35-40 kts
associated with these storms...Knox...Stark...and Marshall County
have been included in a Severe Thunderstorm Watch until 2 a.M.
Storms approaching the area have been producing localized hail
ranging close to one inch and severe wind gusts to 60 mph+ will
also be possible. Otherwise...areas to the south in central Illinois may
see some showers and storms spread southeastward to around I-70
overnight...but not likely to be severe that far south as
nocturnal cooling and lack of significant lift expected to play a
role. Have updated for trends on convective location...and
further updates likely this evening.


Short term...(tonight)
issued at 301 PM CDT sun Aug 2 2015

19z/2pm surface analysis shows cold front extending from the Upper
Peninsula of Michigan to northern Iowa. The most active part of the
front has thus far been across central/northern Wisconsin into
Michigan...with very little convection further west along the
boundary. Think this will continue to be the case through early vigorous short-wave trough evident on latest water
vapor imagery over northern Minnesota tracks east/southeast into the northern
Great Lakes. With strongest lift remaining well north/NE of central not expecting much convection across the kilx County Warning Area
tonight. Latest visible satellite imagery is showing a cumulus-field
beginning to develop between the Illinois River and I-55. This may
be in conjunction with a subtle short-wave tracking out of Iowa. As
this area of lift shifts slowly eastward...isolated convection will
develop between I-55 and I-57 late this afternoon into the early
evening much like the rapid refresh is advertising. Any storms that
develop will quickly dissipate after sunset. Meanwhile...cold front
will gradually settle southward later this evening...with model
consensus focusing the most widespread precipitation further northeast
across Michigan into northern Indiana. Have introduced chance probability of precipitation
along/north of a Rushville to Champaign-Urbana line from middle-evening
into the first part of the overnight hours. Once daytime
instability wanes and Minnesota short-wave tracks further
eastward...any storms along the front will dissipate toward dawn

Long term...(monday through sunday)
issued at 301 PM CDT sun Aug 2 2015

Morning upper air shows northwest flow at 300mb over region with a
series of weak short waves visible in moisture channel imagery.
First wave moving across northern Illinois this afternoon and triggering
few storms. Main wave over Minnesota moving southeast. Morning soundings
show some weak moisture advection in low levels from the southwest,
but it is limited as the surface ridge in southern states has deep
moisture cutoff from moving northweard through MS valley. Edge of
850mb moisture at 12z over central IL, has apparently moved its way
to east during day, and is minor trigger for minor area of storms
moving through DeWitt County at 19z. Surface data shows main front
inot northwest IA, pushed to southeast by Minnesota wave.

Front to continue to move southeast overnight. After the boundary
reaches central Illinois late tonight, weak support for development over
southern areas on Monday, so mainly dry in County Warning Area.

Stalled boundary over south central Illinois then becomes the lingering
focus of possible scattered storms. Models similar in development
Monday night and increasing probability of precipitation into Tuesday as return moisture flow
moves back into region. Best precipitation chances are Tuesday night, Wed, and
Wednesday night as all GFS, eur, Canadian models pick up on minor
shortwave moving through. With lingering front and the wave support,
should be enough for best precipitation chances. By thur, the upper flow
appears to go back to northwest and models start high pressure to
build in from north, drying things out by Friday. Friday to sun appear to
be cool and dry with high pressure in area.


Aviation...(for the 06z tafs through 06z Monday night)
issued at 1145 PM CDT sun Aug 2 2015

A cold front currently oriented from near Chicago to southeast
Iowa will cross the central Illinois terminals from around 09-12z. Ahead
of the front...a low possibility of thunderstorms will
continue...with the best chances affecting kcmi. Have included
thunderstorms in the vicinity in kcmi taf from 08-12z...but otherwise chances too low for
mention at this time as general subsidence aloft and nocturnal
cooling are limiting thunderstorm activity in the vicinity of the
front. After the frontal passage...scattered cloud cover will
gradually dissipate...becoming clear by late afternoon Monday.
Winds SW 7-12 kts ahead of the front...becoming northwest 8-10 kts behind
the front. Winds decreasing after 00z Tuesday.


Ilx watches/warnings/advisories...



short term...Barnes
long term...goetsch

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