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 291731

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1231 PM CDT WED JUN 29 2016

147 AM CDT

Through tonight...

With surface high pressure becoming centered overhead, winds have
become light to calm across much of Northern Illinois/Northwest
Indiana. With Td`s lingering in the upper 40s to lower 50s, expect
surface temps to continue to radiate optimally into the lower 50s
prior to daybreak. There will likely be several spots inland that
fall into the upper 40s, with near cloudless skies later today,
temps are expected to quickly rebound.

The surface ridge will drift south, but the continued lack of a
gradient should allow for an onshore/lake breeze by midday/early
afternoon. Temps inland will warm into the middle/upper 70s, while
areas adjacent to Lake Michigan will only warm to around 70. A weak
mid-lvl wave across Iowa is expected to remain nearly stationary,
but could spread a thin cirrus cloud layer east towards the Great
Lakes region by midday/early afternoon. Otherwise expect a mostly
sunny day.

A weak mid-lvl vort will slide southeast across the Upper Midwest
this afternoon, arriving in the Western Great Lakes around 00z. The
surface ridge is expected to continue drifting southeast, which will
allow low-level flow to turn southerly/southwesterly. This will
allow shallow moisture to begin advecting north/northeast from
Iowa/Missouri into Northern Illinois late tonight into Thursday
morning. Expect just enough influence from the departing surface
ridge, so will maintain a dry overnight period. Temps will only fall
into the mid/upr 50s.



147 AM CDT

Thursday through Tuesday...

A frontal boundary will be steadily sliding south across
the Upper Midwest early Thursday morning, associated with a surface
low over Hudson Bay. In the mid-lvls a vort max will be nearly
phased with the surface features near Hudson Bay, with an elongated
trailing vorticity maxima into the Upper Midwest. While low-level
moisture is expected to moderate throughout the day Thursday, Td`s
will be retuning to around 60. The best timing for precip appears to
be Thur afternoon into the evening hours; however, the challenge
will be on coverage and intensity for rain/thunderstorms. There
is some concern that POPs may struggle to maintain the coverage
further south across Northern Illinois, which is highlighted with
considerable spread in the SREF members. Although with cooler air
advecting south/southeast late Thur aftn/eve, and modest
steepening to the low/mid level lapse rates, it is conceivable
that POPs could indeed become likely for a short period of time.
Expect clouds to slowly become mostly cloudy late Thur aftn, which
should allow surface temps to reach at least 80 to the lower 80s.

Thursday night expect the frontal boundary to remain progressive,
which should clear the forecast area around 6z Friday. Then winds
will quickly flip to the northwest, as yet another broad surface
ridge arrives for the first half of the weekend.

Friday through Wednesday: Ensembles are in good agreement with
keeping a quasi-northwest flow going into the weekend for the Upper
Midwest/Great Lakes regions. This should also keep the surface ridge
in place through at least Monday; however, the 500mb trough will be
pivoting northeast late Sunday. Operational guidance continues to
prog diffluent flow in the mid-levels for Sunday/Monday, although
the southern stream wave may start to become active, and could bring
some light precip to the southern counties early next week.

Temps for much of the extended will be around 80, but steadily
warming by the final few periods of the current extended into the
middle/upper 80s. Towards the Tue/Wed of next week, guidance is
indicating the heat and perhaps humidity return just after the 4th
of July.



For the 18Z TAFs...

Quiet weather continues with VFR conditions through the period.
VFR CU has sprouted across southern WI and is trying to get going
over the terminals. Winds will remain light and variable at times
under the surface high. The center of the high shifts east over
IN this evening and winds become southeast. Winds continue to
veer to southwest overnight and increase to around 10 kt mid
Thursday morning. VFR clouds will increase from west to east
Thursday ahead of the next system. Thinking precip will hold off
through the end of the 18Z TAF time frame.



415 AM CDT

High pressure building across the western Great Lakes is allowing
winds over lake Michigan to subside following the passage of a
cold front. With a weak gradient and light winds expected today,
lake breezes and onshore flow should set up this afternoon over
the nearshore waters. By Thursday, the high will sag to the
southeast setting up strong south to southwest winds ahead of
another cold front which will push across Lake Michigan during the
evening and overnight hours. Following the passage of the cold
front, strong north winds will overspread the lake Thursday night
and Friday.





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