Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 301942

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
242 PM CDT MON MAY 30 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 18Z TAFs...

Main question for this afternoon is timing of lake breeze. Winds
from the west have picked up a bit which may prompt additional
tweaks but timing generally looks on track from previous TAFs.
At MDW it could push through a little sooner than shown...closer
to 1930 UTC...and at ORD it could be a little later than
shown...perhaps 2130 UTC. Overnight the easterly direction should
prevail except in locations that go light and variable. Tomorrow
brings southeast flow and an increasing chance of TSRA by
afternoon...especially toward the RFD area.



226 PM CDT

Relatively light winds will continue across the lake at least
through midweek.  Increasing southerly winds on Wednesday do not
look strong enough to prompt concerns for small craft...and the
offshore direction will also limit wave heights along the south end.
The only concern would be periods of thunderstorms tomorrow and
more so Wednesday and Wednesday evening. The increasing winds
and thunderstorm activity Wednesday are ahead of an approaching
cold front which will veer winds westerly on Wednesday night.






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