Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 102357

Area Forecast Discussion
National Weather Service Lincoln IL
657 PM CDT Thu Jul 10 2014

ISSUED 300 PM CDT Thu Jul 10 2014

An airmass change will highlight the end of the week and weekend
as storms return to the forecast. However, the warmth and humidity
will be short-lived, as the next cool-snap will follow beginning
on Tuesday of next week and linger through late week.

SHORT TERM...Tonight through Sunday night.

Surface high pressure centered over the Great Lakes will slide
east tonight and tomorrow in response to low pressure progressing
eastward across southern Canada. We will still see one more night
of comfortable conditions as dewpoints remain in the upper 50s and
lows drop to around 60.

The influences of the high pressure will linger into Friday, which
will delay the onset of showers/storms. We removed any precip
chances from Fri morning, and diminished the coverage of chance
PoPs Fri afternoon to NW of the IL river. An organized MCS is
projected to roll into northern IL later Friday night, with the
highest chances of storms coming after midnight for areas N of
I-74. The storm complex could linger into Saturday morning from
Champaign to Danville before departing into Indiana.

Upper level ridging and increasing southerly flow on Saturday will
bring increasing moisture and warm air. Any breaks in the cloud
cover behind the departing MCS will help to push high temps into
the upper 80s across most of central/SE IL. Some low 90s will be
possible across the south from Jacksonville to Lawrenceville.
Dewpoints will climb toward the mid 70s, which will push heat
index readings into the mid-upper 90s.

A potential break in the storms Sat afternoon and early evening
will be followed by another strong MCS moving from Iowa across
northern-NC IL Sat night as a cold front moves ESE into the area.
SPC day 3 outlook has Slight Risk north of I-70, with damaging
winds the primary threat. Instability params look favorable for
vigorous updrafts and shear profiles look to support a progressive
MCS with bowing segments. That complex of storms should depart
into Indiana by Sunday morning, but the cold front will stall out
across IL for Sunday. Convective initiation will be focused along
that boundary and any outflows that linger from the overnight
storms. As a result, chance PoPs were left in the forecast through
Sunday night.

LONG TERM...Monday through Thursday.

The Canadian Global, ECMWF and GFS have some indications that
another nocturnal MCS may affect C IL later Sunday night into
Monday morning, but the signals are more subtle in the meso-scale
features. The GFS indicates a much stronger storm complex will
develop Monday afternoon in Iowa and move across C IL Monday
night. The ECMWF and Canadian do not have that feature, and just
progress the strong cold front SE of the area by 12z/7am Tuesday.
We kept chance PoPs through Mon night to account for possible
stormy conditions per the GFS.

Much colder air will return for Tuesday as 850 mb temps drop to
6-8C, correlating to highs in the low to mid 70s. A few
instability showers can not be ruled out for Tues afternoon, but
for now we kept the forecast dry. The airmass will only slightly
modify warmer on Wed and Thursday, as the upper level trough
becomes entrenched across the Upper Midwest and Great Lakes.
Various shortwaves rotating around the upper trough Wed and
Thurs could trigger a few showers those days as well. Once again,
the forecast was left dry for now. High temps will climb a few
degrees each day, with Wed in the mid 70s and Thur in the upper



ISSUED 657 PM CDT Thu Jul 10 2014

Scattered shallow cumulus cloud cover around 5 kft AGL will
rapidly dissipate this evening as daytime heating ends. High
clouds will spread into central IL from the northwest and thicken
overnight. From around 14-18Z Friday, scattered cloud cover
around 4-5 kft MSL will develop again due to increased low level
moisture. Light easterly winds will gradually trend southeast to
south over the next 18 hours as a storm system develops over the
central Plains and high pressure moves off to the east.




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