Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 250705
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
205 AM CDT MON JUL 25 2016

.SHORT TERM...
230 PM CDT

Through tonight...

Convective trends remain the main focus and the main challenge
through the rest of the afternoon. The cool front continues to
advance east and southeast across southwest WI and eastern IA with
the stratus of earlier now more of an open cell cu field. Ahead of
that, another corridor of low level and mid level convergence
generating mid level accas along with newly developing cumulus. A
few echoes have developed with this area across southeast WI, with
more substantial cell moving toward Milwaukee at 1915z. Additional
outflows from morning storms over the lake are likely meandering
across southern Lake Michigan with some indication of one such
boundary oriented from northwest to southeast from offshore of
Waukegan into central Berrien County, MI. Tough to say if this is
the case though. Instability is extreme and maximized over the
forecast area but recent aircraft soundings still show some
capping in place which may be accounting for the rather slow
increase in cell development.

Expect that the cap will erode and isolated-scattered cells will
continue to develop in the cu/accas field across the northwest
third of the area in the next 1-2 hours. High res convective
allowing models have been little help by showing a range of
possibilities from little if anything to aggressive development
and a substantial line of storms moving through. Will continue
with earlier thinking of scattered coverage with potential for
several clusters working east and southeast. With potential for
more complex storm interaction among several boundaries, and being
co-located with the instability gradient, areas from the northern
Chicago metro southward into NW IN may see the greatest coverage,
with more scattered coverage to the south and west. Storm
progression should be more steady than yesterday. Torrential rain
will be one of the primary concerns, along with damaging wind, but
storm progression may help mitigate max rainfall potential.

Convective coverage will translate southeastward as the front
moves through into the evening. The front may slow as it moves
further south and away from the parent surface low over western
Ontario. This may keep pops lingering in the south but suspect
that may be too high with pops overnight in our southern counties.
Relatively drier air/lower dewpoints will steadily spread in from
the northwest overnight but it will still remain mild with lows
around 70 with lower 70s in the Chicago metro.

MDB

&&

.LONG TERM...
230 PM CDT

Monday through Saturday...

A less oppressive air mass that is probably welcome by many
(including us) will move into the area Monday. Dew points are
still forecast to be in the mid to upper 60s but that will
certainly feel less humid. A small chance for a lingering shower
in the southern CWA during mainly Monday morning, but dry
advection aloft will shunt that chance southward by late morning
or early afternoon with a mainly sunny sky to follow. Surface high
pressure will settle in through Monday night with lows in the mid
60s in most areas.

The upper ridge will deamplify though upper level heights will
not substantially drop through Wednesday. Warm and slightly humid
weather should prevail during that stretch, with temperatures a
few degrees above normal. Lake breeze development will be favored
each day.

A buckle in the northern stream jet will occur in the middle of
the U.S. during Wednesday into Thursday. This will cause low
pressure development in the general mid-Mississippi Valley region,
though there is model differences on when and just how fast. Tend
to prefer the slower 24.12Z EC in this situation than the GFS.
Not seeing a signal for any pronounced severe weather setup over
our area with this system at this time. Behind this system
northerly winds look to prevail into the start to next weekend
with temperatures around late July normals.

MTF

&&

.AVIATION...
For the 06Z TAFs...

Welcome to quieter weather! Winds will become northwest behind the
cold front pushing southeast through the terminals early this
morning. The cirrus shield from the convection south of the
terminals will dissipate through the day. A lake breeze will
likely form but thinking it will struggle to push on shore. Have
the lake breeze impacting GYY only for now, but there is a chance
it may reach MDW. Have low confidence in the lake breeze reaching
ORD. With high pressure overhead, winds become variable this
evening under clear skies. Given all of the recent rain, fog could
develop tonight, but thinking it will form outside of the metro
and only have low to medium confidence at this time.

JEE

&&

.MARINE...
205 AM CDT

The cold front associated with the low over Ontario shifts southeast
of the lake early this morning.  West to northwest winds diminish as
the gradient weakens today and a lake breeze is expected.  High
pressure moves over the lake early Tuesday morning. Winds become
light and variable over the southern end of the lake and southwest
10-20 kt over the northern half.  Winds will be light and variable
Wednesday, but then become north to northeast Wednesday night as the
high shifts east.  Winds remain northeast through the end of the
week as a weak low moves over northern IL Thursday night.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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