Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 180510

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1210 AM CDT Wed Oct 18 2017

914 PM CDT

Only change to going forecast was to bump up high temperatures
slightly on Wednesday. Highs in the low 70s were widespread today.
Tomorrow will be nearly a carbon copy synoptically to today along
with similar 850/925 mb temperatures. Thus, high temperatures
tomorrow should be similar if not a degree or so warmer in spots,
with an isolated mid 70s reading probable.




Through Wednesday...

154 pm...Only forecast concern are the winds Wednesday afternoon.
Under sunny skies with gusty southwesterly winds...temps are
currently pushing 70 in many areas. Wednesday will be a carbon
copy of today with temps maybe a degree or two the
lower 70s. Winds will once again steadily increase during the
morning and should be similar to today through midday. But by
afternoon...winds are bit stronger in the low levels and how much
of this is able to make it to the surface will depend on how deep
the low levels will mix. Its possible wind gusts may approach
35-40 mph by mid/late afternoon...especially across the northern
cwa...but confidence is low and trends will need to be monitored.
Temps will quickly cool through the 50s early this evening with
lows likely in the lower/mid 40s with perhaps a few/usual cooler
spots. cms


154 PM CDT

Wednesday night through Tuesday...

With the large dome of high pressure parked across the southeast
CONUS continuing to block Gulf moisture return, the stretch of
nearly identical days continues Thursday except with a small bubble
of high pressure moving overhead and supporting considerably less
wind than is expected Wednesday afternoon. Morning lows Thursday
also will be just a bit warmer than on Wednesday morning, though
afternoon highs in the upper 60s north to lower 70s south will be
similar to the pattern on Wednesday.

Friday also looks very similar to the going trends except for a few
degrees more warmth in the afternoon.  Highs should reach the 70s
across the area.

Moisture and associated cloudiness begin to increase Friday night
and will not allow lows Saturday morning to be quite as cool as seen
so far this week.  A start in the mid 50s areawide will yield to mid
70s by afternoon and rain chances will be on the increase.
Deterministic models agree on bringing a cold front across the area
during the weekend, but disagree on the timing of its passage and
the strength of the associated trough.  Current guidance does agree
on the possibility of some prefrontal showers Saturday morning in
western portions of the area, so latest forecast update has included
chance POPs to account for this.  The best chance for widespread
activity would appear to be late Saturday into early Sunday, and
periodic showers could linger through Tuesday under the postfrontal
upper trough and vort maxes.

Saturday easily looks like the warmer of the two days this weekend,
with Sunday and Monday cooling back into the 60s, followed by even
cooler air in the 50s for Tuesday as the deepest part of the upper
trough settles overhead.



For the 06Z TAFs...

Winds will be the only aviation concern today as the surface
gradient continues to support gusty south-southwesterly winds.
Expect winds to become gusty again up into the lower 20 KT range
by mid morning, then up around 25 KT during the afternoon.
Otherwise, similar to Tuesday, expect these gusty winds to ease
with sunset.

VFR conditions continue to be expected through the period.



212 PM CDT

A decent October gale event for the north half of the lake appears
on track to develop Wednesday morning and persist into the overnight
hours. Small craft conditions are possible for the southern
nearshore, and there could also be a period of gale force gusts in
portions of the south half late Wednesday. This strong south to
southwest flow also will support considerable wave growth at the
north end of the lake. Winds relax Thursday and Thursday night,
especially toward the south end, before the gradient increases again
and remains strong through the first half of the weekend ahead of an
approaching cold front. Behind the front the southwest flow will
veer westerly by late in the weekend into early next week.



LM...Small Craft Advisory...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...9 AM Wednesday to 3 AM Thursday.




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