Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 071733

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1233 PM CDT Wed Jun 7 2023

Issued at 338 AM CDT Wed Jun 7 2023

Through Thursday...

A period of cooler and dry weather is expected across the area
through the period. Skies will gradually clear from north to south
across the area this morning, setting up a mostly sunny day across
the area. However, we may end up with more of a hazy sunshine
later today as some Canadian wildfire smoke tries to shift
overhead. Expect high temperatures this afternoon to range from
the upper 70s inland, to the mid to upper 60s along the Lake
Michigan shore. Nearly identical weather conditions are expected
on Thursday.

While the weather will be otherwise rather pleasant across the
area, there is concern for the spread of wildfires this afternoon
as a very dry airmass sets up overhead. Afternoon relative
humidity values are expected to drop into the lower to middle 20s
as northeasterly winds become increasingly breezy. This in
combination with the dry antecedent conditions with the developing
drought across the area supports an enhanced threat for fire
spread today. For this reason, consider postponing any outdoor

The other concern for today into tonight is the swim risk at Lake
Michigan beaches. Breezy northerly winds overnight have resulted
in 3 to 4` waves being reported along the southern shores of the
lake early this morning. While the winds and the waves look to
abate for a period this morning, it appears winds and waves will
ramp up again this afternoon and evening, with waves potentially
topping 4` for a period into tonight. For this reason, we have
opted to issue a beach hazards statement for all southern Lake
Michigan beaches for later today into tonight for dangerous
swimming conditions.



Issued at 338 AM CDT Wed Jun 7 2023

Thursday night through Tuesday...

The long term forecast period should start off on a quiet and dry
note on Friday with the region under the influence of surface
high pressure. Ample sunshine should allow for most inland
locations to warm into the upper 70s to mid 80s during the
afternoon. Synoptic winds remaining fairly light and carrying an
onshore component over Lake Michigan will facilitate the
development of another lake breeze that should cause our lake-
adjacent locales struggle to reach 70 degrees.

Heading into this weekend, it appears that the persistent Omega
blocking pattern`s reign will finally see the beginning of its
demise with the Omega high getting distorted as it is yanked
westward on Friday. As this occurs, northwesterly flow will be
established aloft from the northern Plains down through the Midwest,
and a surface cold front will accordingly be thrusted southeastward
towards the Great Lakes on Saturday. The general trend in recent
ensemble guidance has been for this cold front, and the bulk of the
forcing support aloft, to be a little slower to arrive to our
forecast area. With this trend continuing in the 00Z GEFS and EPS,
it is looking increasingly likely that at least the morning hours on
Saturday should be dry, and it appears quite possible that a good
chunk of the CWA could even remain dry through most or all of the
afternoon too. Didn`t quite have enough confidence in that just yet
to start peeling away at the NBM`s chance PoPs for Saturday
afternoon, though. The slower cold frontal passage should allow for
Saturday`s highs to end up in the 80s pretty much area-wide,
including near the lakeshore (for once!) with surface winds likely
to be out of the west.

Eventually, the cold front will work its way through our forecast
area with at least widely scattered showers likely to develop
near/along it as favorable jet dynamics and DPVA aloft lend a
helping hand. Limited boundary layer moisture and less-than-stellar
mid-level lapse rates will both contribute to an overall lack of
instability being present as the front passes through, so it doesn`t
look like there will be a whole lot in the way of thunderstorm
coverage, especially if the front arrives after sunset, but have
maintained a slight chance thunder mention for Saturday into
Sunday for now.

Guidance is still in fair agreement that a cut-off upper-level low
will emerge somewhere over the northeastern quadrant of the CONUS
for the beginning of next week, with a slight increase in the amount
of support amongst forecast guidance for that being over the Great
Lakes versus farther to the east compared to 24 hours ago. The
NBM`s PoPs have come up a bit for Monday and Tuesday as a result,
with some chance PoPs now being advertised in our eastern counties
(primarily on Monday). Cooler temperatures would also be favored
if the upper low were to end up meandering over the Great Lakes to
start off next week, though this exact outcome is still far from
being set in stone.



For the 18Z TAFs...

No significant aviation weather concerns for this TAF period.
Winds were briefly a bit more easterly this morning but have
returned to northeast where they should generally prevail through
the TAF period. A reinforcing cold front this afternoon could
support a period of gusts to around 20 kts before winds relax
again this evening. Canadian wildfire smoke should keep skies hazy
through much of the day today but is not expected to reduce vsbys
below VFR.



IL...Beach Hazards Statement...ILZ006-ILZ103-ILZ104...4 PM Wednesday
     to 4 AM Thursday.

IN...Beach Hazards Statement...INZ001-INZ002...4 PM Wednesday to 4 AM

LM...Small Craft Advisory...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...4 PM Wednesday to 4 AM Thursday.



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