Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 240828

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
328 AM CDT Sun Sep 24 2017

326 AM CDT

Through tonight...

Main forecast concerns/challenges are with continued warmth and
near to record breaking heat.

Pattern/air mass will once again be supportive of another day of
near to record breaking heat across the area today. Latest trends
and guidance in line with the previous forecast update to today`s
high temps, and have made little additional changes. Low 90s
appear likely, with mid 90s definitely not out of the question.
These temps with similar dewpoint temps will once again provide
heat index values in the low to mid 90s. Not anticipating any
precip this period, with any stray convection this afternoon
remaining west of the area.



326 AM CDT

Monday through Saturday...

The heat will once again be the main focus at the start of the
period, with an additional day of 90 degree temps appearing
possible on Monday. Given setup, guidance did appear too low and
made some minor changes to have highs around 90. Similar lake
cooling expected for locations near the lake, with highs staying
in the 80s. Pattern begins to change across the region as upper
level ridge shifts to the east and with large trough pushing
through the central CONUS. Energetic flow and resultant active
weather will try to inch its way east towards the area through the
early part of the work week, however, focus looks to remain just
west of the CWA through Monday night.

Tuesday will likely be another warm day with some 90 degree temps
possible, but with approaching cloud cover and possible precip,
confidence does lower with high temps. Tuesday into Tuesday night
will have the highest chances for precip for the area, but this
does not appear to be overly great. Upper level trough will
continue east but likely lift more into Canada, as surface trough
and front push east through the Midwest Tuesday. With this
occurring, large scale lift will likely depart as the front
approaches northern Illinois. So could see a scenario with
scattered convection developing along the front just west of the
CWA Tuesday, and then diminishing through the evening as it tries
to push east. This would keep most locations dry, with latest
updates to pops reflecting this trend. Front will push through
Tuesday night with high pressure then expected to build across the
region. Dry, but cooler, weather is then expected. This cooler
weather will remain into next weekend, but it does appear as some
showery development will be possible as a large upper level trough
settles in. However, guidance highly variable to the extent of
this trough at this time.



For the 06Z TAFs...

VFR conditions to persist across the terminals, outside of patchy
MVFR/fog early this morning. Should be limited, and mainly
confined to the DPA area though. Light southeast winds will
prevail through the period, outside of lake breeze interaction
which will shift the winds to more of an easterly direction this
afternoon, while at or above 10 KT. Current forecast time of wind
shift still appears reasonable.




215 pm...A series of weak low pressures will move from the north
central plains into Ontario and Quebec through midweek with with
the last low dragging a cold front across Lake Michigan Tuesday
night. Southerly winds will continue until this front arrives and
then winds will shift northwest and increase to 15-25kts with a
a short period or some gusts to 30 kts possible. Winds will
diminish by Wednesday night...turn southwesterly Thursday and then
another stronger cold front will move across the region Thursday
night...shifting winds back northwesterly with speeds likely
increasing to 30kts with a period of gales possible Friday
afternoon/evening. cms





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