Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 230830

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
330 AM CDT Sat Sep 23 2017

328 AM CDT

Through tonight...

Main forecast concerns/challenges are with continued warmth and
near to record breaking heat, and low potential for an isolated
shower this afternoon across north central IL.

Pattern still supportive of mainly dry/quiet conditions across
the region today, as large upper level ridge remains in place.
With this in place, focus for precip development will stay tied to
the stronger and more energetic westerlies across the central and
northern CONUS. However, similar to yesterday, there remains a
possibility for isolated convection later this afternoon. Very low
chance, but still a possibility as there will be some weak upper
level support in place. This coinciding with some possible low
level convergence and steepening low level lapse rates across
northern Illinois, can`t rule out an isolated shower or an isolate
storm. With low confidence, have excluded at this time though. In
this location, scattered CU will support partly cloudy skies in
the afternoon. However, don`t think either will limit expected
warmth today. Latest trends and guidance now supporting another
hot day today, with temps likely getting well into the 90s across
much of northern Illinois and northwest Indiana. Did raise high
temps today to reflect latest trends, and think record high temps
at both Rockford and Chicago may be reached today. Locations near
the lake will stay slightly cooler though, as lake breeze
development is likely by around midday. These temps and
anticipated dew points will support heat index values in the mid
to upper 90s.



328 AM CDT

Sunday through Friday...

Large upper level ridge and surface high will remain in place
late in the weekend, with similar conditions expected to persist.
As some slight moderation to the air mass is expected, temps will
not be as warm Sunday. Still think many locations will have a
chance at reaching the 90 degree mark though. By early next week,
upper level ridge shifts to the east while a trough moves through
the central CONUS. As this trough and surface low push east
through the region, will see precip chances returning Tuesday into
Wednesday. This will also be an end to the warmth, as a much
cooler air mass will move in behind this system.



For the 06Z TAFs...

Expect generally VFR conditions, outside of some patchy MVFR fog
early this morning, and light southerly winds this morning. Expect
these conditions to persist through midday or early afternoon,
but then expect lake breeze development to impact the terminals
today. Some possible slight time differences with the wind shift
today, however, an earlier wind shift still appears reasonable.
Dry conditions should continue but am monitoring for possible
isolated showers with a very low chance of a thunderstorm across
northern Illinois this afternoon. Very low confidence and not
worthy of including in the TAFs at this time, but will monitor
this potential later today.




205 pm...A large trough of low pressure will remain across the
plains through Monday maintaining southerly flow across Lake
Michigan. This trough/front will move across the region Tuesday
night into Wednesday. High pressure will build across southern
Canada and the northern plains late next week and as the gradient
tightens behind this front ahead of the high...a period of
15-25kts from the northwest is expected. cms





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