Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 020758

Area Forecast Discussion
National Weather Service Lincoln IL
258 AM CDT Sat Aug 2 2014

ISSUED 258 AM CDT Sat Aug 2 2014

SHORT TERM...Today through Monday

07z/2am radar imagery shows a few lingering showers and thunderstorms
across the southeast KILX CWA, with dry conditions elsewhere around
central Illinois. Upper trough responsible for the convection is
slowly sliding eastward and will be positioned over eastern Indiana
by midday. As a result, strongest synoptic lift will be focused
further east across the Ohio River Valley today. Despite an
uncapped airmass featuring CAPE values of around 1500J/kg, think
slightly warmer temps aloft and subsidence on the back side of the
trough will prevent precip development later today. Most model
guidance agrees, with only the 4km WRF-NMM showing widely
scattered convection developing across north-central Illinois late
this afternoon. Given good model agreement, have opted to remove
slight chance PoPs and go with a dry forecast.

Surface high pressure will control the weather on Sunday, leading
to a warm/dry day with highs climbing into the lower to middle
80s. Once the high slides off to the east, an approaching
short-wave and associated frontal boundary will begin to increase
rain chances early next week. Monday appears to be the last
completely dry day of the forecast period, with forcing remaining
N/NW of central Illinois.

LONG TERM...Tuesday through Friday

Cold front will sag southward and become nearly stationary across
central Illinois beginning on Tuesday. Several upper short-waves
are expected to ride along the boundary, producing periodic
showers/thunder throughout the week. It is difficult to pinpoint
the exact timing and track of these subtle features this far in
advance, so chance PoPs will be included in the forecast from
Tuesday through Friday. As timing becomes a little more clear, may
be able to pin down a period or two where PoPs will be higher and
other times where conditions will remain dry. As it stands now, a
warm and somewhat unsettled week is unfolding. Most model
solutions gradually drop the boundary southward into the Ohio
River Valley by the end of the week, so rain chances will likely
diminish from north to south by Friday/Saturday.


ISSUED 1143 PM CDT Fri Aug 1 2014

Main concern for the upcoming TAF set is with visibilities through
early morning. Although convection has ended, skies still mostly
cloudy as of late evening. Satellite imagery showing this will be
eroding from KBMI/KDEC westward over the next few hours, but may
persist at KCMI a good part of the night. Already seeing some
patchy MVFR visibility around 5SM, and am expecting this to become
more widespread. Have introduced a period of lower visibilities of
2 to 3SM from about 10-13Z with the winds nearly calm and recent
rainfall. Heaviest rain on Friday occurred near KSPI and KDEC, and
went with lower visibilities around 2SM there. RAP model soundings
showing the fog should be rather shallow. After that, some
scattered diurnal cumulus expected to develop around 4000 feet,
but the threat of rain should be further east.



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