Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 150138

Area Forecast Discussion
National Weather Service Lincoln IL
838 PM CDT Mon Aug 14 2017

Issued at 832 PM CDT Mon Aug 14 2017

The latest surface map indicates a weak cool front over east
central Iowa early this evening. This boundary is expected to
slowly edge southeast into our area but not until tomorrow
morning based on the latest HRRR model. Shower development
has been few and far between late this afternoon into early
this evening as the upper wave and forcing has shifted off
to our northeast. Latest ILX and DVN soundings indicating
rather weak mid level lapse rates and a lack of deep moisture
in the sounding profiles. Will continue to carry the isolated
wording across the north as the front settles into our area
Tuesday morning.

With the boundary in our area on Tuesday combined with some
daytime heating, isolated to widely scattered convection will be
possible in the afternoon, but again, large scale forcing will not
be present, so coverage looks to be rather limited with any
convection that does develop, and that would be tied closer to
where the front sets up tomorrow. Other than some minor tweaks
to the early evening temperatures, no other changes were made to
the grids that would require a forecast update at this time.


.SHORT TERM...(This evening through Tuesday)
ISSUED AT 250 PM CDT Mon Aug 14 2017

19z/2pm surface analysis shows 1009mb low over southeast Minnesota
with weak cold front trailing into Nebraska. As the low moves
slowly eastward over the next 12-24 hours, the frontal boundary
will sink southward and eventually stall across central Illinois
by Tuesday morning. While boundary layer moisture has been on the
increase today resulting in surface dewpoints rising into the
middle to upper 60s, deep-layer moisture will remain sparse
through the period. As a result, areal coverage of convection
associated with the boundary will be low. Based on 12z NAM and
latest HRRR, have included slight chance PoPs along/north of a
Macomb to Bloomington line tonight. The front will become
stationary near the I-72 corridor on Tuesday, with isolated to
widely scattered convection developing in its vicinity. Have
therefore carried low chance PoPs across all but the far SE KILX
CWA by Tuesday afternoon. Low temperatures tonight will be in the
middle to upper 60s, while highs on Tuesday reach the middle 80s.

.LONG TERM...(Tuesday night through Monday)
ISSUED AT 250 PM CDT Mon Aug 14 2017

A short-wave trough will cross the Rockies on Wednesday, invoking
an increasingly moist southwesterly flow downstream across the
Midwest. As a result, showers and thunderstorms will become more
prevalent across central Illinois by Wednesday afternoon, with
30-40 PoPs warranted across the board. The best rain chances of
the entire forecast period will materialize Wednesday night into
Thursday morning as the upper wave and its associated cold front
approach from the west. Thanks to deeper moisture profiles, this
system will produce widespread showers/thunder, warranting likely
PoPs everywhere Wednesday night...then just across east-central
Illinois by Thursday morning. The front will pass through the KILX
CWA by midday Thursday, resulting in rapidly diminishing rain
chances by afternoon. A slightly cooler/drier airmass will arrive
in the wake of the front Thursday night into Friday, with lows
dropping into the lower to middle 60s and highs on Friday staying
mostly in the lower 80s. After that, both the 12z GFS and ECMWF
suggest the next short-wave will arrive by Saturday. The GFS
remains more aggressive with its QPF, while the ECMWF indicates
much less precip with this feature. At this time, will increase
cloud cover and go with just a slight chance for showers/thunder
on Saturday until better model consistency is achieved.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 605 PM CDT Mon Aug 14 2017

VFR conditions through this evening then we will need to watch for
the potential for MVFR conditions (cigs & vsbys) after 09z,
especially across the north, as a frontal system slips south into
our area. Isolated showers and TSRA will be possible across our
northern TAF sites but coverage appears to be too limited to
include in the forecast. Any MVFR cigs across the north will
gradually lift after 15z on Tuesday with sct-bkn cumulus expected
during the afternoon across most of the area. Once again, with a
frontal boundary stretching across central IL, we could see an
isolated TSRA develop during the afternoon. Surface winds tonight
will be light south to southwest with winds shifting into a
northerly direction at PIA and BMI, while winds at SPI, DEC and
CMI will be westerly at 5 to 10 kts during the day.




LONG TERM...Barnes
AVIATION...Smith is the U.S. government's official web portal to all federal, state and local government web resources and services.