Area Forecast Discussion
Issued by NWS Chicago, IL

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

FXUS63 KLOT 210801

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
301 AM CDT Sat Jul 21 2018

301 AM CDT

Through tonight...

Main focus for the short term forecast period will continue to be
impacts of an unseasonable upper low slowly tracking across the
Great Lakes region.

Early this morning, the center of the vertically stacked low
pressure system was located over southern Lake Michigan.  As the
system slowly tracks eastward, winds will gradually veer to
northerly and strengthen through the day, becoming rather breezy by
late morning.  The strengthening north winds will cause building
waves along the Lake Michigan shore, bringing the potential for
dangerous rip currents to northeastern Illinois and northwestern
Indiana beaches through Sunday afternoon.  As weak vort maxs rotate
around the swrn/srn periphery of the upper low, there will be
periodic chances for showers, with some isolated thunderstorms
possible durg the afternoon hours.  While this type of system is
relatively uncommon for July, deep layer moisture levels are fairly
typical, with pwats arnd 1.7 inches over the region.  The relatively
high pwats would allow for some of the stronger showers and storms
to produce brief heavy downpours.  Temperatures will be well below
normal again today, with highs only in the lower 70s along the
lakefront and the middle to upper 70s inland.  There will be a
continued chance for showers overnight tonight with lows in the
middle to upper 60s.


301 AM CDT

Sunday through Friday...

The unseasonably cool and cloudy conditions will continue through
Sunday as the upper low very slowly tracks ewd.  The longer range
guidance is in relatively good agreement on the general track and
ewd progression of the system.  As the upper low tracks east, upper
level flow will be northerly into early next week as the upper low
settles over the Upper Ohio Valley from Sunday afternoon through
Monday.  A warming trend will begin on Monday as the upper pattern
trends to slowly progressive with increasing amplitude.  A series of
shortwaves will re-enforce the upper low, carving out a longwave
trough that will sit over the Appalachians while broad upper ridging
builds across the Mississippi Valley.  For much of next week,
conditions over the area should be generally dry with seasonable


For the 06Z TAFs...

Low pressure over southern Lake Michigan late this evening will
very slowly shift into northern Indiana through the day today. The
greatest precipitation coverage is expected to shift east of the
terminals, but widely scattered showers and an isolated
thunderstorm or two will continue to be possible farther west
through the period. Visibility may drop to between 1-4SM in the
heaviest showers. West winds in place late this evening will veer
to the north by early Saturday behind the departing low. North
winds will be gusty to around 20 kt from the late morning into the
evening Saturday. Finally, low MVFR and IFR ceilings have
developed in the vicinity of the low across the Chicago area
terminals. Low ceilings will likely continue overnight, though any
IFR should trend up to MVFR by late Saturday morning or early



258 AM CDT

Low pressure is over southern Lake Michigan early this morning
and will gradually shift into northern Indiana today. Counter-
clockwise flow around the low center this morning will give way to
moderately strong north to northeast winds across the lake today.
Winds are expected to increase into the 20 to 30 kt range much of
today and tonight. A Small Craft Advisory will go in effect for
the Illinois nearshore zone starting mid morning and the Indiana
nearshore zones by early this afternoon and continue through
Sunday afternoon. Scattered showers and possibly a thunderstorm or
two will continue today and tonight. Conditions remain favorable
for a waterspouts as well through Sunday morning, particularly
over the southern half of the lake. Winds will begin to gradually
diminish through the day Sunday as high pressure builds into the
Upper Midwest. Winds will become light Monday and Tuesday as the
high shifts into the western Great Lakes.



IL...Beach Hazards Statement...ILZ006-ILZ014...9 AM Saturday to 5 PM

IN...Beach Hazards Statement...INZ001-INZ002...1 PM Saturday to 5 PM

LM...Small Craft Advisory...LMZ740-LMZ741-LMZ742...9 AM Saturday to 5
     PM Sunday.

     Small Craft Advisory...LMZ743-LMZ744-LMZ745...1 PM Saturday to 5
     PM Sunday.




WWW.YOUTUBE.COM/NWSCHICAGO is the U.S. government's official web portal to all federal, state and local government web resources and services.