Rip Current in Illinois, August 15, 2023

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
100 AM CDT Tue Aug 15 2023

.SHORT TERM...
Issued at 212 PM CDT Mon Aug 14 2023

Through Tuesday night...

Instability continues to gradually increase as mid-level
temperatures are cooling in advance of the incoming upper low.
Through about 5 pm or so, just enough low-level shear will remain
that we can't rule out a brief/weak tornado threat. That said,
this potential should wane quickly thereafter with diminishing
low-level instability and low-level shear, and thus far, cells
have been behaving for the most part.

Farther to the west, a southward-moving frontal boundary pushing
into northern Illinois out of SW Wisconsin will serve as another
focus for scattered thunderstorm development this afternoon. While
deep layer shear decreases with farther west extent, the
combination of enhanced environmental vorticity, steepening low-
level lapse rates, and slackening mid-level winds may support a
potential for funnel clouds and possibly even a few landspout
tornadoes. This threat seems like it may sneak towards our I-39
corridor locales this afternoon. Throughout the rest of the
region, a level 1/5 threat for a few strong to possibly
marginally-severe wind gusts/hail will persist through early-
evening with any additional cells that pop.

Main concern through tonight remains on the heavy rain/flood
potential. Elected to not make any changes to the inherited flood
watch which continues to encompass the area we're most concerned
with, as this aligns with the most significant upper jet
divergence, DCVA, and low-level convergence/deformation.
Additionally, individual cell motions near/in the flood watch will
slow markedly this evening with the approach of the parent upper
low. While not consistent in the precise area, hires guidance has
repeatedly depicted swaths of isolated 5-6+" rainfall amounts
within the mid-level deformation axis. While this heaviest axis
could very well set up just out over the lake, and small wobbles
would bring this heavy rainfall axis into Chicago/NE Illinois.

We'll gradually lose large scale ascent through very late tonight
and Tuesday morning as we get into the backside of the upper low.
Sufficient near-surface convergence will remain through the
morning hours, however, to squeeze out additional scattered
showers across NE IL and NW IN. We'll eventually dry and scour
things out through the afternoon, however, with a notably more
subsident regime set to arrive into Tuesday evening and overnight.

Carlaw

&&

.LONG TERM...
Issued at 309 AM CDT Mon Aug 14 2023

Tuesday night through Sunday...

Key messages during the period:

* Quiet and pleasant weather Wednesday.

* Chance for a short period of showers/storms with a cold frontal
  passage on Thursday.

* Warming up significantly into this weekend, with a period of hot
  weather (temperatures potentially getting well into the 90s)
  looking plausible later this weekend into early next week.

The weather for the start of the period on Wednesday is looking
very nice as surface high pressure shifts eastward across the
Mid-Mississippi Valley. This will result in mainly sunny skies,
light winds and temperatures topping out around 80. Mild
conditions continue Wednesday night as surface winds ramp up from
the southwest following the eastward passage of the surface high.

Our only real shot (albeit low) at any precipitation during the
period looks to be on Thursday. This as a potent storm system
moving across Ontario is expected to drive a training cold front
southeastward into our area for Thursday. While this may result in
a short period of scattered showers/storms in our area on
Thursday, low-level moisture return in advance of the front does
not look overly impressive, so this does not appear to be a big
shower and thunderstorm producer for our area.

After this front pushes through the area anther surface high is
expected to move across the area on Friday. This should result in
another fairly nice day for the area, with temperatures again
topping out around, or a bit above 80.

Conditions look to begin to heat up in a big way into this weekend
as a large upper ridge (~600 DAM) begins to build across the the
Midwest. The magnitude of this upper ridge suggests a hot
summertime airmass will be setting up across a vast portion of
the central CONUS (including our area) this weekend into at least
early next week. Very hot temperatures will thus be likely late in
the period, with readings potentially climbing well into the 90s!

KJB

&&

.AVIATION...
For the 06Z TAFs...

Forecast concerns for the terminals...

*Lingering showers through the night into Tuesday morning

*MVFR ceilings overnight with pockets of IFR conditions possible,
 ceilings gradually improve through Tuesday afternoon

*Breezy northerly winds tonight, but will gradually ease late
 Tuesday afternoon

An upper-level low continues to spiral over southern Lake Michigan
which will allow showers to persist through the night at the
Chicago and adjacent terminals. The low is expected to move into
southern Michigan Tuesday morning which should entrain mid-level
dry air and diminish the showers across northeastern Illinois,
however; guidance continues to show a couple of disturbances
pivoting over northwestern Indiana which may allow lake induced showers
to linger into the early afternoon hours. The low and subsequent
low-level moisture will continue to support MVFR ceilings through
the night into Tuesday morning as well. While not expected to be
widespread, periods of IFR ceilings are also possible especially
under heavier showers but given the scattered nature have foregone
a formal mention for now. Ceilings will gradually improve Tuesday
morning as the aforementioned dry air mixes down with most sites
expected to return to VFR by Tuesday afternoon.

Lastly, breezy north-northwesterly winds will persist through
Tuesday morning with gusts in the 20 to 25 kt range. Gusts are
expected to ease during the afternoon but some occasional gusts in
the 15 to 20 kt range will be possible until winds fully subside
Tuesday evening. Additionally, the Chicago terminals are expected
to see winds wobble to a slightly east of north direction Tuesday
afternoon as speeds begin to decrease.

Yack

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement...ILZ006-ILZ103-ILZ104 until 7 PM
     Tuesday.

IN...Beach Hazards Statement...INZ001-INZ002 until 7 PM Tuesday.

LM...Small Craft Advisory...nearshore waters until 7 PM Tuesday.

&&

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Hazardous Weather Outlook...UPDATED
National Weather Service Chicago/Romeoville IL
907 PM CDT Mon Aug 14 2023

ILZ003>006-008-010>013-019>021-023-032-033-039-103>108-INZ001-002-
010-011-019-160215-
Winnebago-Boone-McHenry-Lake IL-Ogle-Lee-De Kalb-Kane-DuPage-
La Salle-Kendall-Grundy-Kankakee-Livingston-Iroquois-Ford-
Northern Cook-Central Cook-Southern Cook-Northern Will-
Southern Will-Eastern Will-Lake IN-Porter-Newton-Jasper-Benton-
907 PM CDT Mon Aug 14 2023 /1007 PM EDT Mon Aug 14 2023/

This Hazardous Weather Outlook is for portions of North Central
Illinois...Northeast Illinois and Northwest Indiana.

.DAY ONE...Tonight.

Weather hazards expected...

  High Swim Risk Lake Michigan Shore.

DISCUSSION...

Large waves and high winds will result in dangerous swimming
conditions at Lake Michigan beaches tonight.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Tuesday...
  High Swim Risk Lake Michigan Shore.
Wednesday and Thursday...
  Limited Thunderstorm Risk.
Sunday...
  Limited Excessive Heat Risk.

.SPOTTER INFORMATION STATEMENT...

  Spotter activation will not be necessary through tonight.

LMZ740>745-160215-
Winthrop Harbor to Wilmette Harbor IL-
Wilmette Harbor to Northerly Island IL-
Northerly Island to Calumet Harbor IL-
Calumet Harbor IL to Gary IN-Gary to Burns Harbor IN-
Burns Harbor to Michigan City IN-
907 PM CDT Mon Aug 14 2023

This Hazardous Weather Outlook is for portions of the Illinois
nearshore waters of Lake Michigan and the Indiana nearshore
waters of Lake Michigan.

.DAY ONE...Tonight.

Weather hazards expected...

  Hazardous conditions for small craft.
  Waterspout Risk.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Tuesday...
  Hazardous conditions for small craft are likely.
  Waterspout Risk in the morning.
Wednesday...
  Hazardous conditions for small craft are likely.
Thursday...
  Hazardous conditions for small craft are likely.
  Limited Thunderstorm Risk.

- Izzi

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Preliminary Local Storm Report
National Weather Service Chicago IL
956 PM CDT Mon Aug 14 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0449 PM     Funnel Cloud     3 WNW Troy Grove        41.48N 89.14W
08/14/2023                   La Salle           IL   Public

            Possible tornado. Time estimated by radar.

&&

- Izzi