Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 300617

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
117 AM CDT MON MAY 30 2016

232 PM CDT

Through Monday...

Hi-res models hint at light rain showers west of I-55 this afternoon
and tonight, but thinking we will continue to see dry conditions.
Scattered storms are forming over northern Iowa and southern WI.
Scattered convection has a better chance of forming north of the
vort max currently over Iowa and thus north of the CWA. If any
convection does get going, thinking locations will only see
sprinkles given dewpoint depressions around 20 degrees.

Clouds clear tonight and winds diminish.  Lows will be in the lower
60s.  A few clouds are expected tomorrow with lighter winds and
highs in the low to mid 80s. Limited highs south of I-80 where there
may be more cloud cover, but if cloud cover is less than forecast,
could see high temps above 85.  The weak surface flow allows a lake
breeze to form in the afternoon.  The lake breeze looks like it will
push onshore later than normal so thinking lake side locations have
a good chance of seeing 80. Models suggest precip will spread west
of I-39 late Monday afternoon, but thinking the precip will hold off
til Monday evening when the vort max gets closer to the CWA.  Did
include a slight chance of showers and storms east of I-39 late
Monday aftn in the off chance precip does form.



246 PM CDT

Monday night through Sunday...

Monday night through Wednesday night:
Mid-lev diffluence will begin to shift East slightly Monday evening;
however, some guidance members continue to indicate enough
ridging/diffluence will hold through Monday evening to hold precip
to the West of the area. Have adjusted POPs to account for better
chance for POPs not arriving until closer to daybreak Tue. Upper
level trough will remain well West through Mon ngt, meanwhile a
displaced surface wave will be trying to develop over the Central
Plains late Monday. This may be strong enough to send a lobe of
vorticity Northeast towards the western Illinois area. Low level
feed of moisture will steadily increase Monday night, helping to
bring dew points back into the lower 60s across Northern Illinois by
Tuesday. With a continued feed of moisture Tuesday, and steady
growth of instability, the periodic chances for
showers/thunderstorms will likely continue Tuesday. Temps Tue will
return to the lower to perhaps middle 80s across much of Northern
Illinois and Northwest Indiana.

Heading into tuesday night, the 500mb trough axis will begin to
pivot east of the Rockies and increasing the forcing along the lee-
side through the Plains. This should likely increase POPs chances
through the mid-sections of the CONUS towards the Western Great
Lakes late Tue into Wed. With the trough axis being slow to arrive
over the forecast area Wed eve, a persistent chance of
showers/thunderstorms is possible. Then the frontal boundary
continues to be progged to arrive late Wed, which will usher in
drier air and bring an end to the precip chances for later in the

Thursday through Saturday: Ensembles continue to point towards a
ridge developing along the western CONUS late in the week into next
weekend. Thursday through Friday look to remain dry with weak
surface ridging arriving, then with the upstream ridge progged to
develop this will likely usher in a quasi-northwest flow for the
upcoming weekend and a return to periodic showers/thunderstorms.
Temps for late week through next weekend will return to the middle
to upper 70s, with overnight lows in the 50s.



For the 06Z TAFs...

The only aviation weather concern today will be the timing of a lake
breeze boundary this afternoon...otherwise VFR conditions are
expected. Light westerly winds will start out the day. However...a
lake breeze is likely to develop by midday...then shift inland over
the area through the afternoon. Currently it appears that it could
reach ORD and MDW as early as 20-21 UTC...with an associated
easterly wind shift expected. Wind speeds could be up around 10KT
for a period with the passage of the boundary...but should
gradually abate into the evening.



116 AM CDT

South to southwest winds will continue over the northern half of
the lake today. However...a surface ridge of high pressure setting
up over the southern half of the lake today will allow for lake
breeze development...and onshore flow across the southern end of
the lake this afternoon. Expect the winds to become east-
southeast and begin to increase on Tuesday as a storm system
begins to approach upper Midwest. It appears that winds up around
20 KT will occur late Tuesday into early Wednesday in response to
this storm system...which is forecast to shift eastward into
southern Ontario by late Wednesday. This will push a cold front
over the lake Wednesday night. A period of thunderstorms looks
likely Wednesday into Wednesday evening as this front approaches.
Following the frontal passage expect lighter westerly flow to set
up for Thursday.

Late in the period...eighter late Friday or Saturday another storm
system could impact the western Great Lakes region with another
possible period of storms and higher winds. However...confidence
with the timing and track of this system is low at this time.






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