Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 221105

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
605 AM CDT MON AUG 22 2016

244 AM CDT

Through tonight...

Today through tonight:
Early this morning skies remain mostly clear, as high pressure
centered over Missouri begins to push east. The influence has
produced near calm winds over Northern Illinois/Northwest Indiana,
with minimal T/Td spread resulting in some patchy fog this morning.
Expect the bulk of the morning fog to be shallow and lift shortly
after sunrise. Temperatures will continue to radiate prior to
daybreak into the lower 50s and could see a few sites in the
west/northwest forecast area fall into the upper 40s.

The remainder of the day will still be influenced by the surface
ridge with southwest flow increasing by afternoon, and temps
bouncing back to around 80 by mid-afternoon with abundant sunshine.

Tonight mid-lvl heights will begin to rise with continued surface
anti-cyclonic flow maintaining a dry surface overnight. But with the
southerly flow persistent through the night, lows tonight will be
several degrees warmer in the upper 50s to around 60.



244 AM CDT

Tuesday through Sunday...

Tuesday through Wednesday: Mid-lvl ridging will persist into Tue,
with another strong diffluent setup keeping dry conds in place.
Southwesterly flow will continue and help to push temps a few
degrees warmer into the lower 80s. Ridging shifts east in the
afternoon hours, allowing steady increase in cloud cover associated
with return flow moisture streaming north through the Ozarks and
eventually into Northern Illinois/Northwest Indiana late Tue/early
Wed. Late Tue ngt guidance continues to show a leading wave and mid-
lvl vorticity lifting northeast towards the forecast area, which
coupled with increased llvl moisture will lead to increasing chances
for showers and thunderstorms.

Moist channel will become oriented from the Southern Plains
northeast through the Great Lakes region, with guidance developing a
weak mid-lvl trough ahead of the much stronger trough axis displaced
to the northwest across the Northern Plains. Cloud cover will hold
sfc temps in the mid/upr 60s. Precip/Convective chances steadily
increase Wed eve, with PWAT values approaching 2" within the moist
axis from the Southern Plains stretching through Northern Illinois
and then into Lower Michigan. So if any convection can develop, the
setup looks favorable for some of thunderstorms to easily produce
brief heavy downpours, and could result in hydro concerns. Have
adjusted POPs up accordingly to account for the higher confidence
given minimal spread amongst guidance for Wed eve.

Thursday through Monday: For the longer term ensembles continue to
show the downstream mid-lvl ridge parked over the Southeast CONUS as
the upper level trough pivots east across the Upper Midwest/Northern
Great Lakes region Thur/Fri. Surface ridging will help to push the
quasi-stationary boundary further south/southeast Thur evening;
however, the surface ridge will become influenced by a faster flow
in the mid-levels and quickly slide east and allow the boundary to
lift north with precip chances returning late in the week into the
weekend. Temps will also start out in the mid/upr 70s Fri, then
steadily warm into the mid 80s by the second half of the weekend.



For the 12Z TAFs...

A surface ridge of high pressure will continue to result in light
and variable winds early this morning. However, the winds should
settle into a south-southwesterly direction by this afternoon as
the surface high shifts to the east. Wind speeds will still likely
remain fairly light (under 10 KT), and this could result in the
development of a lake breeze this afternoon. However, at this time
it appears unlikely that this would impact the main terminals.



144 AM CDT

A surface ridge of high pressure will shift eastward towards the
Atlantic coast later today and tonight. Meanwhile another storm
system will be taking shape over the Dakotas. This storm system
is then expected to gradually shift east-northeastward towards
the upper Great Lakes and southern Ontario by midweek. Overall,
this will result in the development of a stout south-southwesterly
wind over the lake later today through Wednesday. Wind speeds
will likely be the strongest over the northern half of the lake,
where speeds up to 30 KT are likely.

A period or two of thunderstorms also appear probable on
Wednesday as a cold front approaches the lake. Winds will then
turn northerly later in the week following this cold front and in
advance of another surface ridge of high pressure expected to
build over the Plains.






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