Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 270848

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
348 AM CDT WED JUL 27 2016

335 AM CDT

Through Thursday...

Satellite imagery this morning depicts quiet conditions
across the Midwest as surface high pressure is remains in
control. Several smaller scale disturbances are embedded
in west/northwest flow aloft across the Northern Plains and Upper
Midwest ahead of a more organized shortwave in the positively
tilted upper trough axis in North Dakota. The most noticeable area
of thunderstorms is a convective complex across the nation`s
heartland, near the intersection of a cold front stretch from the
Black Hills of South Dakota northeast to Lake Superior, though
this area has and will continue to weaken as evidenced by warming
IR cloud tops. Ahead of the cloud shield patchy fog has formed.

Today:  The upper trough will continue its southeastward
trajectory, while surface high pressure shifts only slightly
eastward to the southern tip of Lake Michigan. The main forcing
this afternoon will be west and north of the area, but the myriad
of small scale disturbances will pass through our region. Expect
increased high clouds and another round of afternoon cumulus
development, most notably along the lake breeze. A weakly unstable
air mass will develop ahead of this wave. Forecast soundings,
similar to upstream observed soundings depict a fairly dry column
today. Convergence other than the lake breeze is weak as is shear,
but there could be some shallow showers/storms this afternoon if
diurnal timing of any waves is favorable. If there are an that do
form, which short term guidance is not too excited about, the lake
breeze could be a trigger point, possibly favored along the IL/WI
border or northern tier of counties where several guidance sources
paint some weak QPF. High temperatures today will be similar to
Monday, mid to upper 80s inland and near 80 at the lake.

Tonight and Thursday: The coverage of storms and some storms may
increase tonight as the leading more organized shortwave moves
through, but coverage is also not certain. Guidance depicts
scattered coverage given the less than ideal forcing. The core of
the upper trough axis will move overhead on Thursday. This is the
day that models suggest would be the best chance of shower
activity, with highest chances across along a nw-se axis from
Rockford to Lansing, IL.



335 AM CDT

Friday through Tuesday...

Broad upper troughing remains in place Friday and Saturday, while
surface high pressure remains positioned north of the area with
drier northeast flow in place across WI and into IL. Have
maintained chances of precip Friday, still on the lower end.

Upper heights increase some Saturday in spite of a weak trough
lingering, and then increasing more signfiicantly on Sunday.
Cannot rule out showers a a weak theta-e ridge will be focused
into NE IL/NW IN Saturday and less so Sunday, but no washouts
either day as dry northeast low- level flow will continue.

Warm and more humid conditions will arrive to start the work week
as southwest flow increases ahead an upper ridge/hot dome that
will expand eastward. CPC has the region pegged with fairly high
probabilities of above average temperatures during this time
frame. 850-925 Temps support readings well into the 90s, while a
max of blended guidance gives temperatures in the 90-95. Dewpoints
will again be elevated in this pattern. GFS Ensemble guidance has
the highest confidence on the Tuesday-Wednesday time frame, though
of note the ECMWF keeps us more on the edge of the heat dome an in
a more favorable position for impacts from both nearby and
possibly local convection. Blended guidance keeps slight chance to
eventually chance pops M-W.



For the 06Z TAFs...

High pressure will result in light winds and vfr skies. MVFR fog
is possible at DPA and RFD, but thinking fog will develop a little
bit later this morning than previously thought. Terminals along
the lake will see light east winds develop early this afternoon
while the other two terminals will see southwest winds. VFR
conditions continue this afternoon through the night. Winds become
east at all of the eastern terminals while winds at RFD become



304 AM CDT

High pressure over northern IL weakens and shifts south today.
Northwest winds become north across the north half of the lake while
winds remain southwest on the south half. A cold front slowly shifts
down the lake today through Thursday with winds becoming north
behind it.  A weak low passes south of the lake Thursday while high
pressure builds over south central Canada. This will result in north
to northeast winds 15-25 kt Thursday afternoon and night.  Winds
remain north to northeast through Friday and then high pressure
builds over the lake.  Winds will be northeast to southeast through
the weekend.






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