Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 122012

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
312 PM CDT Sat Aug 12 2017

232 PM CDT

Through Sunday...

A broad upper level trough continues to swing across the Great
Lakes this afternoon. Water vapor also shows a closed upper low
moving eastward across North Dakota which will take its` time
passing north of the area later Sunday into Monday. A shortwave
ridge is out ahead of this circulation and will pass overhead
tonight. Surface high pressure stretching from Minnesota to
Missouri will move in tonight and crest the area early Sunday.
Late afternoon clouds will dissipate into early evening and the
north to northeast breeze will diminish. Light and variable or
even calm winds will prevail overnight and radiational cooling
will ensue supporting some patchy/shallow fog development, mainly
in rural and less urban areas. Light winds will be in place Sunday
and favor a east to northeast direction early then trend
southeasterly toward evening. Expect to see less stratocu
development but high clouds will likely increase through the day
ahead of the advancing upper low to the north. Temps should warm
to levels several degrees higher than today given more sunshine
and some modest mid level warming.



251 PM CDT

Sunday night through Saturday...

An extended period of dry conditions is expected through much of
the long term period. High pressure will be parked over the Great
Lakes and upper Midwest into early next week. The weak pressure
gradient persisting across the region will allow the development
of daily lake breezes. While temperatures should trend back closer
to near seasonal normal levels, low to middle 80s through the long
term forecast period, lake breeze development will keep the
lakefront cooler than inland locations through Wednesday. The
longer range models are trending a little faster in tracking a
series of weak shortwaves passing across the middle and upper
Mississippi Valley Tuesday and Wednesday, bringing the next chance
for any pcpn to the region. The longer range guidance is also
trending stronger with a shortwave lifting out of the central
Rockies Tuesday night or early Wednesday, inducing a deepening
surface low. While the GFS and ECMWF differ in the strength of the
low, they generally agree on the track and timing, with the main
sfc low lifting to western Lake Superior Wednesday night. The low
should continue to lift northeast while dragging a cold front
across the region Thursday. Scattered showers and thunderstorms
may develop in advance of the front, but the greatest chance for
pcpn will be Wednesday into Wednesday night as the front pushes
across the area.


For the 18Z TAFs...

Scattered to broken stratocu continues across the terminals with
bases steadily rising. North to north-northeast winds have taken
over with speeds around 10 kt. Somewhat drier air should work in
off the lake through the afternoon allowing for a decrease in
cloud coverage mid to late afternoon. Winds will drop off this
evening and become light and variable or even calm. Will need to
watch out for some vsby reduction/patchy fog, mainly at RFD/DPA so
have retained MVFR vsby group overnight. It`s possible it may be
more of a shallow or patchy fog situation where the shallow/patchy
fog may be producing IFR vsby. Winds will be more erratic but
light for Sunday with high pressure moving overhead. Direction
should favor east to southeast overall.



251 PM CDT

Low pressure over southern Quebec this afternoon will continue to
lift northeast as high pressure spreads across the upper
Mississippi Valley. This will maintain brisk northerly flow
through this evening. The pressure gradient will gradually
relax from the west allowing winds to diminish overnight tonight.
Small craft advisory conditions will persist over the Indiana
nearshore waters east of Burns Harbor through this evening.

The high pressure will spread into the Great Lakes region tonight
allowing winds to diminish overnight. High pressure ridging will
remain over the the Great Lakes region into the middle of next
week. allowing for relatively light and somewhat variable winds
while the ridge of high pressure dominates the area. South flow
will increase Wednesday ahead of low pressure moving east out of
the northern Plains.


IN...Beach Hazards Statement...INZ001-INZ002 until 10 PM Saturday.

LM...Small Craft Advisory...IN nearshore waters until 10 PM Saturday.




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