Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 241747

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1247 PM 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 18Z TAFs...

1247 pm...Only concern this period are winds. South/southwesterly
winds increased to 10 kts or so late this morning with some higher
gusts at times...especially across northwest IL and at rfd. These
winds will remain southerly through sunset and then diminish to
5kts or less. A lake breeze is slowly moving inland and should
move west of ord/mdw but only medium confidence on timing. Winds
will shift easterly behind the lake breeze. Confidence at gyy is
low as the lake breeze may stay right near the shoreline in
northwest Indiana. Winds will turn south/southwest again Monday
morning and speeds may end up being a bit stronger than guidance
is showing. Another lake breeze is expected Monday afternoon and
it should reach ord/mdw but confidence on timing is low.

Few/sct cu this afternoon along with sct/bkn cu Monday afternoon
and there is a chance of isolated showers...possibly an isolated
thunderstorm generally west of a dpa/c09/pnt line later Monday
afternoon into Monday evening. Patchy fog is possible again early
Monday morning but signals are weak and if any developed...expect
3-5sm in the usual/favored areas. cms


356 AM CDT

Southerly winds in place across the lake as high pressure is
still situated to the east, and while a trough of low pressure is
to the northwest. Not much change in this pattern expected through
the early part of the week, helping to maintain a southerly
direction. This will finally begin to change by the middle part of
the week, as this trough pushes through the region. This will
bring a period of more northerly winds to the lake, likely lasting
through late in the work week. Throughout this time, will likely
see speeds and waves increase/build.






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