Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
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 231800

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
100 PM CDT Wed May 23 2018

234 AM CDT

Through tonight...

Main forecast concerns/challenges are with fog trends this
morning across much of the area, with an area of dense fog
situated across far northwest Indiana.

High pressure overhead early this morning supporting another
night/morning of fog development across the CWA. An area of dense
fog has developed across the northern portions of Lake and Porter
counties in IN, and at this time, it has remained fairly
stationary. Given how dense this fog was and that it wasn`t likely
going to dissipate, went ahead and issued a Dense Fog Advisory.
Guidance does continue to indicate this fog will expand into
remaining areas of northwest IN while other areas of dense fog
develop across portions of northern IL. Have already seen fog
development this morning, with any other areas of dense fog
remaining isolated. Overall pattern along with low dewpoint
depressions would support continued fog development, some of which
could be dense this morning. Have continued the forecast of
areas/widespread fog over much of northern IL and northwest IN
through this morning, and will continue to monitor for more
widespread dense fog and the possibility of including other areas
in the Advisory. The fog/any low clouds should scatter out through
mid morning, with partly cloudy to sunny skies expected today.
Warmer temps around 80 expected today, while locations near the
lake observe onshore flow and cooler temps in the 60s.



234 AM CDT

Thursday through Tuesday...

Overall trend into the end of the work week will be upper level
ridging with a continued warming trend. Any guidance that
indicated the possibility for some weak mid level energy to ride
along this ridge into Thursday morning is now consistent with
keeping this energy and any precip chances to the north/northwest
of the area. Dry conditions for the entire area expected through
early Friday. By late Friday into the start of the weekend, the
ridge breaks down as upstream energy dips down across the region.
This will coincide with increasing moisture, and while instability
shifts overhead. While higher focus for thunderstorm development
should stay to the north, guidance indicating the possibility for
sagging development into at least the northern half of the CWA
late Friday/Friday night. Although confidence is not overly high,
its enough to keep slight chance to low chance mention of thunder
Friday night.

Pattern going into the weekend will support a continued warming
trend with temps well above normal. Temp forecasts in the upper
80s still seem reasonable including near the lake, with some
locations possibly climbing more to around 90 this weekend. Have
not trended this way quite yet given the continued possibility for
periodic and scattered shower and thunderstorm development that
could limit some heating. Given the summer like pattern, this
thunderstorm development still seems reasonable at this time.



For the 18Z TAFs...

Concern this afternoon is lake breeze timing/speed, then maybe
some fog overnight.

The lake breeze boundary is noticeable on KLOT, still somewhat
diffuse but making inland progress. Winds will remain light and
variable ahead of the lake breeze, with an increase once it moves
inland. Confidence on an increase in speeds to above 9 kt is
fairly low, but still possible, but would likely not last too long
given the generally weak speeds at the lake and on observations
on the east side of the boundary.

Winds ease and go variable tonight, with some fog possible closer
to shore and possibly some light MVFR fog at ORD/MDW/DPA and the
best bet at GYY and any river valley locations.



300 AM CDT

High pressure over Lake Michigan early this morning will provide
light winds across the lake today and tomorrow in addition to
foggy conditions. Dense fog will continue over portions of the
lake through at least mid morning today. Beyond that confidence
decreases in how much improvement there will be, if any, but
suspect there will at least be patchy fog in place through the day
and tonight. It`s possible the dense fog advisory may need to be
extended or a new one issued for tonight. Low pressure will move
into Manitoba late Thursday and slowly dig into the Upper Midwest
Friday and Saturday. Southwest flow will increase in response,
peaking at 15 to 25 kt over northern Lake Michigan. Winds drop off
again over the weekend as the low slowly moves east across the
western Great Lakes.






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