Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 310650

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
150 AM CDT TUE MAY 31 2016

242 PM CDT

Through Tuesday...

Main concern rest of this afternoon will be potential for
continued isolated thunderstorm development. Water vapor imagery
shows a weak shortwave trough moving into northwest IL, providing
some weak large scale ascent in a modestly unstable and now
uncapped air mass. Observations suggest a weak convergence zone
over our southern CWA where visible satellite imagery has shown
more impressive vertical development to the cumulus field. Already
have seen a couple isolated cells develop and see no reason that
there wont be additional isold to widely scattered showers and
storms through early this evening south of I-80. Will also need to
closely monitor the convergence zone associated with the lake
breeze which has also seen a bit of an enhancement to the cumulus
field. Outside of any isolated convection, no weather concerns for
the remainder of the holiday.

By tomorrow potential impetus for thunderstorm development looks
to be a fairly well defined shortwave over Oklahoma this
afternoon. Guidance is generally in pretty good agreement on
lifting this feature northeast and arrive in our area fairly close
to peak heating on tomorrow afternoon. Magnitude of
heating/destabilization could be hampered a bit by mid-high level
cloudiness moving in ahead of the feature, but even still models
support MLCAPE values potentially nearing 1000 j/kg. Shortwave is
forecast to be dampening out leaving wind fields and resultant
vertical shear profiles fairly weak, so really not looking at any
organized severe threat. Still think that there could be a more
appreciable coverage of convection Tuesday afternoon.



242 PM CDT

Tuesday night through Monday...

More significant trough and associated cold front will move
across the region Wednesday bringing, potentially bringing a more
substantial threat of showers and thunderstorms to the area.
Guidance varies on the forecast wind fields/shear profiles, but
generally agree in atmosphere growing modestly unstable. Even with
weak vertical wind shear, still could see some an isolated pulse
severe threat with multicellular convection. In the wake of the
front, cooler and less humid air will filter into the area
Thursday and Friday.

Another shortwave and associated cold front look to move across
the area Saturday with a threat of some showers and perhaps
t-storms, followed by a re-enforcing shot of seasonably cool air.
Temperature look to be below average Sunday into the beginning of
next week.



For the 06Z TAFs...

The main concerns during the period will be the potently for a
period of showers and thunderstorms this afternoon at the terminals.

A decent upper level disturbance...currently over
expected to shift east-northward into Illinois during the day today.
This feature looks to kick off scattered thunderstorm development
over portions of western Illinois by early afternoon...with the
focus gradually shifting eastward through the afternoon. The storms
could be on a weakening trend as they begin to approach a less
favorable environment over far northeastern Illinois late in the day.
With this possibility...I have introduced only a PROB30 for thunder
at KORD...KMDW and KGYY after 21 UTC. However...farther west at KDPA
and KRFD...I introduced a tempo for storms this afternoon where
slight better chances are forecast.

Winds through the period will remain east-southeasterly in the 5 to
10 KT range.



150 AM CDT

A cold front is currently dropping southward over northern
portions of the lake this morning...and this is setting up some
higher northerly winds up around 20 KT at times. This front will
stall out across the central portion of the lake today...with
east- southeast winds expected to the south. Tonight...the winds
will shift southeastward up around 20 KT lake-wide as a storm
system moves into the upper Midwest. This storm system is forecast
to shift eastward into southern Ontario by late Wednesday. This
will push a cold front over the lake Wednesday night...before
ending up near James Bay on Thursday. An associated cold front is
expected to move across Lake Michigan Wednesday night. It still
appears that a period of thunderstorms will occur ahead of this
front Wednesday into Wednesday evening. Following the frontal
passage expect lighter westerly flow to set up for Thursday.

In the extended period it appears that another storm system could
take aim on the western Great Lakes by Saturday. This could result
in the next chance of showers and thunderstorms along with stronger






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