Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Graphics & Text | 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 221918

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

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

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.



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

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

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.



For the 18Z TAFs...

Concerns center on lake breeze arrival, and on small convective

Radar shows the lake breeze confined near the shore in northern
Cook county, with some inland headway in southern Cook. Movement
has been slow and conversely short term guidance has slowed the
easterly wind shift. Confidence is only medium on arrival time,
and it could be delayed, but weak pressure pattern would support
movement inland.

Initial frontal boundary is south of the terminals in an area
currently capped but likely to lose the cap later this afternoon.
Some convection is possible but forcing is limited, and expected
to be well south. This activity may strengthen late tonight but
still remain south. There is a cold front across MN and it will
move close to the area late tonight. Some weakening showers may
impact area near the WI border overnight but chances locally are
small. The front will pass southeast through the area in the
morning. With the main upper forcing well north expected shower or
storm coverage to be limited and have kept the TAFs dry. Winds
shift to NW behind the front.



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.






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