Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 222357
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
657 PM CDT Sat Jul 22 2017

.SHORT TERM...
150 PM CDT

Through Sunday...

Quieter weather is in place with surface high pressure overhead.
The surface boundary is anchored along our southern counties.
Southerly flow ahead of the boundary and some cloud breaks should
lead to destabilization across the area. Hi resolution guidance
does still attempt to break out some convective activity in the
WAA atop this boundary but it would fairly limited in coverage at
least in our area and more likely confined across Central and
southern IL/IN. DCAPE and high PWATs suggest a wind and heavy rain
threat.

A fairly broad mid-upper level trough will push southeast through
the Great Lakes on Sunday. Ahead of this trough, convection is
expected across the Upper Midwest this evening, with the majority
shorter term guidance weakening this activity as it nears IL,
though some sprinkles or isolated showers would not be unheard of.

The associated cold front will pass through the area during the
morning into early afternoon. Convective coverage is still a bit
uncertain at this time, given the main upper forcing is north in
the less unstable air, and the cold front will largely be through
a good portion of the area in the afternoon. Some convection
remains plausible both north and ahead of the wave, so held onto
some lower chances at this time. Areas east and south stand the
best chance for isolated severe storms later in the day. Generally
speaking most times will be dry, and it will be at least a little
less muggy with dewpoints in the 60s instead of 70s.

KMD

&&

.LONG TERM...
217 PM CDT

Sunday night through Saturday...

Looking at a cooler and drier upcoming week.

An upper level wave swings overhead Sunday, and we may have
lingering showers and storms mainly along and east of I-55 Sunday
night.

Northerly winds set up Monday bringing in cooler and less humid air.
Highs Monday are forecast to be in the low 70s along the lake to
around 80 south of I-80.  High pressure moves over the lake Monday
night leading to dry conditions through Wednesday morning.
Temperatures slowly climb back into the mid to upper 80s by
Wednesday.

The next chance of precip arrives Wednesday afternoon and evening in
advance of a weak low and cold front. Showers and storms linger into
Thursday.  Cooler air moves in behind the cold front with highs in
the low 80s away from the lake Thursday.  Another high moves over
the midwest late next week.

JEE

&&

.AVIATION...
For the 00Z TAFs...

No significant weather related aviation concerns through the TAF
cycle. There is a very small chance of a shower or storm Sunday,
but the threat is far too low to include in the TAF. Also, some
models suggest that a lake breeze could develop and move through
ORD/MDW Sunday afternoon, but given the forecast synoptic wind
direction and increasingly warm lake, opted to keep a lake breeze
wind shift out of MDW and ORD Sunday afternoon.

- Izzi

&&

.MARINE...
217 PM CDT

A baggy pressure field will lead to a light and variable wind field
today. The low pressure system over Minnesota will pass over the
northern end of the lake early Sunday morning before reaching the
eastern Great Lakes Sunday night. Winds become north behind the low
and increase to 15-25 kt Sunday night into Monday morning.

High pressure builds over the lake Monday evening and continues east
Tuesday. Winds become south behind the high and 15-25 kt winds are
possible over the northern end of the lake Tuesday night.

Another weak low and cold front swing down the lake Wednesday night
with winds becoming north behind the front.

JEE

&&

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

$$

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