Gale Warning 15, NWS Chicago, IL

307 
WHUS73 KLOT 240213
MWWLOT

URGENT - MARINE WEATHER MESSAGE
National Weather Service Chicago IL
913 PM CDT Sat Oct 23 2021

LMZ740>743-241015-
/O.CON.KLOT.GL.W.0015.211024T2200Z-211026T0200Z/
Winthrop Harbor to Wilmette Harbor IL-
Wilmette Harbor to Northerly Island IL-
Northerly Island to Calumet Harbor IL-
Calumet Harbor IL to Gary IN-
913 PM CDT Sat Oct 23 2021

...GALE WARNING REMAINS IN EFFECT FROM 5 PM SUNDAY TO 9 PM CDT
MONDAY...

* WHAT...East gales of 40 to 45 kt. Significant waves up to 11 ft
  and occasional waves up to 14 ft.

* WHERE...Winthrop Harbor to Gary IN.

* WHEN...From 5 PM Sunday to 9 PM CDT Monday.

* IMPACTS...Strong winds will cause hazardous waves which could 
  capsize or damage vessels and reduce visibility.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Mariners should alter plans to avoid these hazardous conditions.
Remain in port, seek safe harbor, alter course, and/or secure the
vessel for severe conditions.

&&

$$

LMZ744-745-241015-
/O.CON.KLOT.GL.W.0015.211025T0100Z-211026T0200Z/
Gary to Burns Harbor IN-Burns Harbor to Michigan City IN-
913 PM CDT Sat Oct 23 2021

...GALE WARNING REMAINS IN EFFECT FROM 8 PM SUNDAY TO 9 PM CDT
MONDAY...

* WHAT...East gale force gusts to 35 kt Sunday night and 40 kt
  gales Monday. Significant waves up to 9 ft and occasional waves
  up to 12 ft.

* WHERE...Gary to Michigan City IN.

* WHEN...From 8 PM Sunday to 9 PM CDT Monday.

* IMPACTS...Strong winds will cause hazardous waves which could 
  capsize or damage vessels and reduce visibility.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Mariners should alter plans to avoid these hazardous conditions.
Remain in port, seek safe harbor, alter course, and/or secure the
vessel for severe conditions.

&&

$$

371 
WHUS73 KLOT 240816
MWWLOT

URGENT - MARINE WEATHER MESSAGE
National Weather Service Chicago IL
316 AM CDT Sun Oct 24 2021

LMZ740>743-241630-
/O.CON.KLOT.GL.W.0015.211024T2200Z-211026T0200Z/
Winthrop Harbor to Wilmette Harbor IL-
Wilmette Harbor to Northerly Island IL-
Northerly Island to Calumet Harbor IL-
Calumet Harbor IL to Gary IN-
316 AM CDT Sun Oct 24 2021

...GALE WARNING REMAINS IN EFFECT FROM 5 PM THIS AFTERNOON TO
9 PM CDT MONDAY...

* WHAT...East gales to 45 kt. Significant waves up to 18 ft and 
  occasional waves up to 21 ft.

* WHERE...Winthrop Harbor to Gary IN.

* WHEN...From 5 PM Sunday to 9 PM CDT Monday.

* IMPACTS...Strong winds will cause hazardous waves which could
  capsize or damage vessels and reduce visibility.


PRECAUTIONARY/PREPAREDNESS ACTIONS...

Mariners should alter plans to avoid these hazardous conditions.
Remain in port, seek safe harbor, alter course, and/or secure the
vessel for severe conditions.

&&

$$

LMZ744-745-241630-
/O.CON.KLOT.GL.W.0015.211025T0100Z-211026T0200Z/
Gary to Burns Harbor IN-Burns Harbor to Michigan City IN-
316 AM CDT Sun Oct 24 2021

...GALE WARNING REMAINS IN EFFECT FROM 8 PM THIS EVENING TO 9 PM
CDT MONDAY...

* WHAT...East gale force gusts to 35 kt Sunday night and north
  gales to 40 kt on Monday. Significant waves up to 14 ft and
  occasional waves up to 18 ft.

* WHERE...Gary to Michigan City IN.

* WHEN...From 8 PM Sunday to 9 PM CDT Monday.

* IMPACTS...Strong winds will cause hazardous waves which could 
  capsize or damage vessels and reduce visibility.


PRECAUTIONARY/PREPAREDNESS ACTIONS...

Mariners should alter plans to avoid these hazardous conditions.
Remain in port, seek safe harbor, alter course, and/or secure the
vessel for severe conditions.

&&

$$

Borchardt

226 
WHUS73 KLOT 241455
MWWLOT

URGENT - MARINE WEATHER MESSAGE
National Weather Service Chicago IL
955 AM CDT Sun Oct 24 2021

LMZ740>743-242300-
/O.CON.KLOT.GL.W.0015.211024T2200Z-211026T0200Z/
Winthrop Harbor to Wilmette Harbor IL-
Wilmette Harbor to Northerly Island IL-
Northerly Island to Calumet Harbor IL-
Calumet Harbor IL to Gary IN-
955 AM CDT Sun Oct 24 2021

...GALE WARNING REMAINS IN EFFECT FROM 5 PM THIS AFTERNOON TO
9 PM CDT MONDAY...

* WHAT...East gales to 45 kt. Significant waves up to 16 ft and 
  occasional waves up to 21 ft.

* WHERE...Winthrop Harbor to Gary IN.

* WHEN...From 5 PM Sunday to 9 PM CDT Monday.

* IMPACTS...Strong winds will cause hazardous waves which could 
  capsize or damage vessels and reduce visibility.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Mariners should alter plans to avoid these hazardous conditions.
Remain in port, seek safe harbor, alter course, and/or secure the
vessel for severe conditions.

&&

$$

LMZ744-745-242300-
/O.CON.KLOT.GL.W.0015.211025T0100Z-211026T0200Z/
Gary to Burns Harbor IN-Burns Harbor to Michigan City IN-
955 AM CDT Sun Oct 24 2021

...GALE WARNING REMAINS IN EFFECT FROM 8 PM THIS EVENING TO 9 PM
CDT MONDAY...

* WHAT...East gale force gusts to 35 kt Sunday night and north
  gales to 40 kt on Monday. Significant waves up to 14 ft and
  occasional waves up to 18 ft.

* WHERE...Gary to Michigan City IN.

* WHEN...From 8 PM Sunday to 9 PM CDT Monday.

* IMPACTS...Strong winds will cause hazardous waves which could 
  capsize or damage vessels and reduce visibility.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Mariners should alter plans to avoid these hazardous conditions.
Remain in port, seek safe harbor, alter course, and/or secure the
vessel for severe conditions.

&&

$$

- Izzi

424 
WHUS73 KLOT 242041
MWWLOT

URGENT - MARINE WEATHER MESSAGE
National Weather Service Chicago IL
341 PM CDT Sun Oct 24 2021

LMZ740>743-250445-
/O.CON.KLOT.GL.W.0015.211024T2200Z-211026T0200Z/
Winthrop Harbor to Wilmette Harbor IL-
Wilmette Harbor to Northerly Island IL-
Northerly Island to Calumet Harbor IL-
Calumet Harbor IL to Gary IN-
341 PM CDT Sun Oct 24 2021

...GALE WARNING REMAINS IN EFFECT UNTIL 9 PM CDT MONDAY...

* WHAT...Gales up to 45 kt and significant waves to 16 ft 
  expected.

* WHERE...Winthrop Harbor IL to Gary IN.

* WHEN...Until 9 PM CDT Monday.

* IMPACTS...Strong winds will cause hazardous waves which could 
  capsize or damage vessels and reduce visibility.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Mariners should alter plans to avoid these hazardous conditions.
Remain in port, seek safe harbor, alter course, and/or secure the
vessel for severe conditions.

&&

$$

LMZ744-745-250445-
/O.CON.KLOT.GL.W.0015.211025T0100Z-211026T0200Z/
Gary to Burns Harbor IN-Burns Harbor to Michigan City IN-
341 PM CDT Sun Oct 24 2021

...GALE WARNING REMAINS IN EFFECT FROM 8 PM THIS EVENING TO 9 PM
CDT MONDAY...

* WHAT...Gales up to 40 kt and significant waves to 14 ft 
  expected.

* WHERE...Gary to Michigan City IN.

* WHEN...From 8 PM this evening to 9 PM CDT Monday.

* IMPACTS...Strong winds will cause hazardous waves which could 
  capsize or damage vessels and reduce visibility.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Mariners should alter plans to avoid these hazardous conditions.
Remain in port, seek safe harbor, alter course, and/or secure the
vessel for severe conditions.

&&

$$

- Izzi

378 
WHUS73 KLOT 250315
MWWLOT

URGENT - MARINE WEATHER MESSAGE
National Weather Service Chicago IL
1015 PM CDT Sun Oct 24 2021

LMZ740>742-251115-
/O.CON.KLOT.GL.W.0015.000000T0000Z-211026T0200Z/
Winthrop Harbor to Wilmette Harbor IL-
Wilmette Harbor to Northerly Island IL-
Northerly Island to Calumet Harbor IL-
1015 PM CDT Sun Oct 24 2021

...GALE WARNING REMAINS IN EFFECT UNTIL 9 PM CDT MONDAY...

* WHAT...East to northeast gales to 45 kt. Significant waves to 
  12 to 16 ft occasionally to 21 ft.

* WHERE...Illinois nearshore.

* WHEN...Until 9 PM CDT Monday.

* IMPACTS...Strong winds will cause hazardous waves which could 
  capsize or damage vessels and reduce visibility.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Mariners should alter plans to avoid these hazardous conditions.
Remain in port, seek safe harbor, alter course, and/or secure the
vessel for severe conditions.

&&

$$

LMZ743>745-251115-
/O.CON.KLOT.GL.W.0015.000000T0000Z-211026T0200Z/
Calumet Harbor IL to Gary IN-Gary to Burns Harbor IN-
Burns Harbor to Michigan City IN-
1015 PM CDT Sun Oct 24 2021

...GALE WARNING REMAINS IN EFFECT UNTIL 9 PM CDT MONDAY...

* WHAT...East to northeast gales to 40 kt. Significant waves to 10
  to 14 ft occasionally to 18 ft. Briefly lower winds may occur
  late this evening before increasing again overnight. 

* WHERE...Indiana nearshore.

* WHEN...Until 9 PM CDT Monday.

* IMPACTS...Strong winds will cause hazardous waves which could 
  capsize or damage vessels and reduce visibility.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Mariners should alter plans to avoid these hazardous conditions.
Remain in port, seek safe harbor, alter course, and/or secure the
vessel for severe conditions.

&&

$$

573 
WHUS73 KLOT 250828
MWWLOT

URGENT - MARINE WEATHER MESSAGE
National Weather Service Chicago IL
328 AM CDT Mon Oct 25 2021

LMZ740>742-251700-
/O.CON.KLOT.GL.W.0015.000000T0000Z-211026T0200Z/
Winthrop Harbor to Wilmette Harbor IL-
Wilmette Harbor to Northerly Island IL-
Northerly Island to Calumet Harbor IL-
328 AM CDT Mon Oct 25 2021

...GALE WARNING REMAINS IN EFFECT UNTIL 9 PM CDT THIS EVENING...

* WHAT...Northeast gales to 45 kt. A few storm force gusts to 50
  kt are possible this morning. Significant waves to 12 to 16 ft 
  occasionally to 21 ft.

* WHERE...Illinois nearshore.

* WHEN...Until 9 PM CDT this evening.

* IMPACTS...Strong winds will cause hazardous waves which could
  capsize or damage vessels and reduce visibility.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Mariners should alter plans to avoid these hazardous conditions.
Remain in port, seek safe harbor, alter course, and/or secure the
vessel for severe conditions.

&&

$$

LMZ743>745-251700-
/O.CON.KLOT.GL.W.0015.000000T0000Z-211026T0200Z/
Calumet Harbor IL to Gary IN-Gary to Burns Harbor IN-
Burns Harbor to Michigan City IN-
328 AM CDT Mon Oct 25 2021

...GALE WARNING REMAINS IN EFFECT UNTIL 9 PM CDT THIS EVENING...

* WHAT...Northeast gales to 35 kt early, increasing to 45 kt
  through the morning. Significant waves to 12 to 16 ft,
  occasionally to 21 ft this afternoon.  

* WHERE...Indiana nearshore.

* WHEN...Until 9 PM CDT this evening.

* IMPACTS...Strong winds will cause hazardous waves which could 
  capsize or damage vessels and reduce visibility.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Mariners should alter plans to avoid these hazardous conditions.
Remain in port, seek safe harbor, alter course, and/or secure the
vessel for severe conditions.

&&

$$

Carlaw

404 
WHUS73 KLOT 251434
MWWLOT

URGENT - MARINE WEATHER MESSAGE
National Weather Service Chicago IL
934 AM CDT Mon Oct 25 2021

LMZ740>742-252245-
/O.CON.KLOT.GL.W.0015.000000T0000Z-211026T0200Z/
Winthrop Harbor to Wilmette Harbor IL-
Wilmette Harbor to Northerly Island IL-
Northerly Island to Calumet Harbor IL-
934 AM CDT Mon Oct 25 2021

...GALE WARNING REMAINS IN EFFECT UNTIL 9 PM CDT THIS EVENING...

* WHAT...Northeast gales to 45 kt. A few storm force gusts to 50
  kt are possible this morning. Significant waves to 16 ft, with
  occasional waves to 21 ft.

* WHERE...Illinois nearshore.

* WHEN...Until 9 PM CDT this evening.

* IMPACTS...Strong winds will cause hazardous waves which could 
  capsize or damage vessels and reduce visibility.


PRECAUTIONARY/PREPAREDNESS ACTIONS...

Mariners should alter plans to avoid these hazardous conditions.
Remain in port, seek safe harbor, alter course, and/or secure the
vessel for severe conditions.

&&

$$

LMZ743>745-252245-
/O.CON.KLOT.GL.W.0015.000000T0000Z-211026T0200Z/
Calumet Harbor IL to Gary IN-Gary to Burns Harbor IN-
Burns Harbor to Michigan City IN-
934 AM CDT Mon Oct 25 2021

...GALE WARNING REMAINS IN EFFECT UNTIL 9 PM CDT THIS EVENING...

* WHAT...Northeast gales to 45 kt. Significant waves to 16 ft,
  with occasional waves to 21 ft.

* WHERE...Indiana nearshore.

* WHEN...Until 9 PM CDT this evening.

* IMPACTS...Strong winds will cause hazardous waves which could 
  capsize or damage vessels and reduce visibility.


PRECAUTIONARY/PREPAREDNESS ACTIONS...

Mariners should alter plans to avoid these hazardous conditions.
Remain in port, seek safe harbor, alter course, and/or secure the
vessel for severe conditions.

&&

$$

357 
WHUS73 KLOT 251956
MWWLOT

URGENT - MARINE WEATHER MESSAGE
National Weather Service Chicago IL
256 PM CDT Mon Oct 25 2021

LMZ740>742-260200-
/O.CON.KLOT.GL.W.0015.000000T0000Z-211026T0200Z/
Winthrop Harbor to Wilmette Harbor IL-
Wilmette Harbor to Northerly Island IL-
Northerly Island to Calumet Harbor IL-
256 PM CDT Mon Oct 25 2021

...GALE WARNING REMAINS IN EFFECT UNTIL 9 PM CDT THIS EVENING...

* WHAT...North gales to 35 kt and waves to 12 ft.

* WHERE...Northerly Island to Calumet Harbor IL, Winthrop Harbor 
  to Wilmette Harbor IL and Wilmette Harbor to Northerly Island 
  IL.

* WHEN...Until 9 PM CDT this evening.

* IMPACTS...Strong winds will cause hazardous waves which could 
  capsize or damage vessels and reduce visibility.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Mariners should alter plans to avoid these hazardous conditions.
Remain in port, seek safe harbor, alter course, and/or secure the
vessel for severe conditions.

&&

$$

LMZ743>745-260200-
/O.CON.KLOT.GL.W.0015.000000T0000Z-211026T0200Z/
Calumet Harbor IL to Gary IN-Gary to Burns Harbor IN-
Burns Harbor to Michigan City IN-
256 PM CDT Mon Oct 25 2021

...GALE WARNING REMAINS IN EFFECT UNTIL 9 PM CDT THIS EVENING...

* WHAT...North gales to 35 kt and waves 14 ft.

* WHERE...Gary to Burns Harbor IN, Burns Harbor to Michigan City 
  IN and Calumet Harbor IL to Gary IN.

* WHEN...Until 9 PM CDT this evening.

* IMPACTS...Strong winds will cause hazardous waves which could 
  capsize or damage vessels and reduce visibility.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Mariners should alter plans to avoid these hazardous conditions.
Remain in port, seek safe harbor, alter course, and/or secure the
vessel for severe conditions.

&&

$$

946 
WHUS73 KLOT 252356
MWWLOT

URGENT - MARINE WEATHER MESSAGE
National Weather Service Chicago IL
656 PM CDT Mon Oct 25 2021

LMZ740>742-260800-
/O.CAN.KLOT.GL.W.0015.000000T0000Z-211026T0200Z/
/O.NEW.KLOT.SC.Y.0083.211025T2356Z-211026T2100Z/
Winthrop Harbor to Wilmette Harbor IL-
Wilmette Harbor to Northerly Island IL-
Northerly Island to Calumet Harbor IL-
656 PM CDT Mon Oct 25 2021

...SMALL CRAFT ADVISORY IN EFFECT UNTIL 4 PM CDT TUESDAY...
...GALE WARNING IS CANCELLED...

* WHAT...North winds to 25 kt tonight and to 20 kt Tuesday. 
  Significant waves to 9 ft occasionally to 12 ft tonight and 7 ft
  occasionally to 9 ft Tuesday.

* WHERE...Winthrop Harbor to Calumet Harbor IL.

* WHEN...Until 4 PM CDT Tuesday.

* IMPACTS...Conditions will be hazardous to small craft.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Inexperienced mariners, especially those operating smaller
vessels, should avoid navigating in hazardous conditions.

&&

$$

LMZ743>745-260800-
/O.CAN.KLOT.GL.W.0015.000000T0000Z-211026T0200Z/
/O.NEW.KLOT.SC.Y.0083.211025T2356Z-211027T0200Z/
Calumet Harbor IL to Gary IN-Gary to Burns Harbor IN-
Burns Harbor to Michigan City IN-
656 PM CDT Mon Oct 25 2021

...SMALL CRAFT ADVISORY IN EFFECT UNTIL 9 PM CDT TUESDAY...
...GALE WARNING IS CANCELLED...

* WHAT...North winds to 25 kt tonight and to 20 kt Tuesday. 
  Significant waves to 9 ft occasionally to 12 ft tonight and 7 ft
  occasionally to 9 ft Tuesday.

* WHERE...Calumet Harbor IL to Michigan City IN.

* WHEN...Until 9 PM CDT Tuesday.

* IMPACTS...Conditions will be hazardous to small craft.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Inexperienced mariners, especially those operating smaller
vessels, should avoid navigating in hazardous conditions.

&&

$$

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
235 PM CDT Sat Oct 23 2021

.SHORT TERM...
235 PM CDT

Through Monday...

Synopsis:

A powerful autumn storm system will take shape over the next 24
hours and eventually bring a multitude of inclement and
potentially hazardous weather to the area Sunday into Monday.
Water vapor imagery early this afternoon depicts a powerful
Pacific jet stream beginning to crash onshore the west coast. This
strong jet stream (130-150kt at 250mb) will translate eastward
into the central Plains tonight resulting lee cyclogenesis in the
left exit region of this jet. This cyclone will intensify and
close off a mid-upper level circulation as it moves east toward
the mid Mississippi Valley Sunday night into early Monday.

Southerly winds are already transporting moisture northward from
the Gulf of Mexico north into the southern and getting into the
central Plains. Strong low level jet (>50kt @ 850mb) will develop
tonight in response to the developing lee cyclone and help
accelerate the northward transport of moisture in advance of the
system.

Early this afternoon, a warm front at the surface extends from
central Kansas east to downstate IL. As the cyclone develops
tonight, look for warm front to begin lifting northward with
strengthening low level jet resulting in significant low level
theta-e advection into strengthen low-mid level frontal system.
The strengthening low-mid level frontogenesis combined with the
strong theta-e advection should result in a blossoming area of
showers and thunderstorms to the north of the sfc warm front.
This activity will lift north into the our CWA late tonight into
tomorrow morning, with this likely to be the first of multiple
rounds of showers and some thunderstorms as the system moves
rather slowly eastward across the region.

Hydrology:

Models continue to advertise near record levels of moisture
availability with precipitable water values near or above 1.5
inches pooling near and north of the quasi-stationary boundary.
The slow moving nature of the east west boundary combined with at
least waves of strong forcing, at first via theta-e advection and
frontogenesis and eventually from the DCVA with the cyclone
itself, should be quite effective at translating this abnormally
moist atmosphere into effective heavy rainfall production.

Higher resolution models continue to advertise narrower swaths of
well over 4" inches of rain in spots mainly south of I-80. Even
the lower resolution guidance has widespread 2-3"+ rainfall
amounts south of I-80 and one inch plus over most of the CWA.
While exact locations in the various models vary, the idea of
swaths of >4" of rain is a pretty consistent and concerning
signal in the convective allowing guidance. SREF probabilities of
2" of rain in 6 hours are in the 30-80% range over a sizable
portion of our southern CWA Sunday evening, which is close to the
6 hourly flash flood guidance (which isn't taking into account
antecedent rainfall during the day Sunday).

A preponderance of the evidence supports issuing a flash flood
watch for our southern CWA. Not uncommon for warm sector
convection to our south to sometime retard the northward moisture
transport in these strong systems, reducing rainfall totals to the
north. In this case, round one of will occur tonight and into
Sunday, prior to any meaningful convection in the warm sector.
Widespread convection is expected to develop tomorrow
afternoon/evening across Missouri, however backing low-mid level
flow owing to the closing off of the mid-level low should actually
drive the weakening remnants of the Missouri convection north
into our CWA.

Latest runs suggest the rainfall with the trowel on the back side
of this system later Sunday night into Monday will probably be
mostly north of the areas most likely to see heavy and potentially
flooding rainfall on the "front" side of the storm. However,
thermodynamics would suggest a potential for a lake enhancement to
the rainfall over northeast Illinois Sunday night into Monday. So
while during and intensity of the rain stands a lower probability
of producing substantial flooding in northeast IL north of I-80,
could still see problems with standing water, particularly in poor
drainage areas. Probably a flood advisory type situation, if
anything.

Convection:

Some thunderstorms are likely very late tonight into Sunday
morning in the warm air advection regime over mainly our southern
CWA, though weak instability should result in mainly a heavy
rainfall threat. It appears very likely that our CWA will remain
safely north of the warm front with minimal severe weather threat
in our area. As the sfc low track east near I-80 the warm sector
could briefly make it into the southern portions of our CWA later
Sunday night, but instability is likely to be too weak that time
of day for a meaningful severe weather threat. However, could see
a bit of an uptick in lightning activity later Sunday night as
upper low approaches and we briefly poke into the warm sector.

Winds/Waves/Lakeshore Flooding:

Tightening pressure gradient in advance of the surface low will
result in gradually increasing easterly winds, particularly
starting late Sunday afternoon into Sunday evening. Over land,
mixing is not expected to be particularly efficient in the
easterly flow, but given the strong pressure falls and tightening
gradient it should be breezy/windy Sunday night over northern IL.

Of greater concern, relatively chilly air mass in place north of
the warm front flowing over the record warm Lake Michigan water
will result in very efficient mixing of the higher momentum air to
the surface over the lake and along western shores of the lake.
Bufkit forecast soundings from most models suggest sustained winds
over the lake of around 30kt Sunday night into Monday morning with
deep mixing in the marine boundary layer likely to transport down
gusts of 40-45kt.

These strong easterly winds will should result in large battering
waves along the Illinois shore Sunday night into Monday. While the
wind direction initially will not be favorable for a big storm
surge, the magnitude of the winds should result in some response
in lake levels which combined with the large waves will result in
a lakeshore flood threat. Winds will back to northerly and begin
to slowly ease, but likely continue at gale force until later
Monday afternoon. So while the winds may begin to ease slowly
Monday, the wind direction will result in a more favorable fetch
probably continuing the lakeshore flood threat. Will be hoisting
a lakeshore flood advisory for this time frame.

- Izzi

&&

.LONG TERM...
329 AM CDT

Sunday through Monday Night...

The main forecast concerns remain around a period of steady, soaking
rain and blustery winds from Sunday afternoon through Monday morning
across much if not most of our area.

As an elongated 180-200kt jet streak currently stretching from the
Kamchatka Peninsula of Russia to the northern California coast
propagates eastward over the Rocky Mountains this afternoon, a low
pressure system will develop in southern Colorado and rapidly deepen
overnight thanks to favorably "coupled" diffluent upper-level flow.
Ensemble model guidance is in fair agreement the low will track from
near Wichita, Kansas to Kansas City, Missouri by midday Sunday, and
pass through central Illinois overnight Sunday into Monday.

Increasing warm-air advection early Sunday morning will lead to the
burgeoning of showers and thunderstorms along an axis from northern
Missouri to southern Illinois along a developing 850mb warm front.
As the surface low approaches Sunday afternoon, the 850mb front will
tighten and frontogenetical forcing will increase leading to the
development of waves of steady rain across our area (e.g. the
morning hours may end up mostly dry). Sunday evening, the surface
low will track through central Illinois potentially lifting the
surface warm front as far north as Livingston, Ford, and Iroquois
counties. Should the front indeed make it so far north, at least
some threat for surface-based severe storms cannot be ruled out with
an associated threat for all severe hazards. However, it currently
appears more likely that the surface front will remain south,
and the approach of the surface low will "merely" allow the zone
of active thunderstorms (with effective inflow above the boundary
layer) to lift northward into our area but south of I-80. Behind
the center of the low, steady rain will continue overnight into
Monday thanks to a healthy TROWAL and impressive low-level
moisture convergence aided by an easterly 40-50kt 950mb low-level
jet. Rain should taper from west to east through morning on
Monday, with all areas expected to be dry by afternoon.

Pinpointing where and how much rain will fall can sometimes be
tricky whenever warm-season moisture (PWATs of 1.25 to 1.5")
overlaps with cool-season synoptic-scale forcing, especially when
convection is involved. However, it appears most of our area has a
good shot at seeing at least 1" of rain by Monday morning (EPS
probabilities are 80-100% chance areawide), with the heaviest totals
exceeding 2" increasingly likely as one heads downstate (especially
south of I-80). Depending on whether the zone of active convection
works as far north as our area (again, looking at Livingston, Ford,
and Iroquois counties) rainfall totals may easily get out of hand
leading to a narrow, localized west to east zone where flooding of
roads, farm fields, and low-lying areas would become likely. Our
feeling at this point is that the zone of most active convection
should remain just to our south, but trends will need to be
monitored closely. Regardless of how much rain falls, confidence is
high that Sunday afternoon through Monday morning will be wet and
that river and stream levels will increase toward bankfull.

Increasing easterly low-level flow north of the center of the low
will lead to blustery winds particularly Sunday night through at
least daybreak Monday but possibly as late as Monday afternoon.
EPS mean ensemble wind gusts peak between 35-40 mph north of I-88
during the overnight hours, which is right on the cusp of strong
enough to blow around twigs, lawn furniture, and even down a few
small tree branches. The strongest wind gusts are likely along the
immediate Illinois shoreline of Lake Michigan, where EPS mean
ensemble peak wind gusts approach 50 mph. With such strong winds
over the lake, waves heights are likely to build greater than 8
feet (highest toward daybreak Monday) which will splash up on
lakeshore trails, parks, and low-lying spots. Meanwhile, winds
south of I-80 may end up rather light as the low tracks overhead.

In all, Sunday afternoon through Monday morning will be raw,
blustery, and wet, especially considering temperatures will be
somewhat stagnant near 50 degrees. The Monday morning commute in
particular may be gnarly with steady rain and blustery winds. The
best way to get through these fall storms is with a comfy sweater
and a good book (or sturdy rain gear if heading outdoors is
inevitable).

Borchardt

Tuesday through Saturday...

Tranquil weather conditions make a very brief return to the region
on Tuesday in the wake of the Sunday/Monday soaker. As high
pressure noses into the region, lingering north winds will trend
northeasterly off the lake through the afternoon yielding fairly
seasonable temperatures with highs in the upper 50s. With
relatively light winds expected to prevail through most of the
overnight hours, temperatures look set to drop back into the mid
and upper 30s across most of the forecast area away from the
immediate lakeshore, and pockets of near-freezing temperatures
seem to be in play based on the latest statistical guidance.

As has been the case the past few nights, noting quite a bit of
model disparity and run-to-run continuity issues as we head
towards the end of the week as our next potent PV-anomaly
translates across the Great Basin and out across the Continental
Divide. Latest EPS shows tremendous spread in surface low centers
with this next system from as far north as about Wisconsin to the
northern Gulf, and this amount of spread is seen across the rest
of the ensemble model suite. The main change for this forecast
package was to trend PoPs downwards and a bit slower heading into
Wednesday, but no significant alterations to the blended offering
were made Wednesday night and beyond given the aforementioned
guidance spread.

Carlaw

&&

.AVIATION...
For the 18Z TAFs...
1254 PM CDT

The concerns for the Chicago area TAF sites include:

* Rain developing on Sunday with CIGs deteriorating to IFR or
  possibly lower and reduced VSBY in steady to heavy rain
* Gusty east to northeast winds on Sunday

The quiet VFR conditions will continue through tonight, followed
by a long duration of aviation impacts starting Sunday morning.
Variable winds will shift to easterly this afternoon and then
start to increase late tonight. A slow moving low pressure will
approach the mid MO Valley by mid day Sunday, with rain
overspreading the local region well in advance of the system.

Expect a steady light rain to commence by the mid morning into the
Chicago area, earliest at GYY, while RFD on northern edge may see
spotty -SHRA initially. Confidence is high in a steady moderate
rain Sunday afternoon, with occasional heavier rates probable.
ORD/MDW extended TAFs indicate prevailing lower MVFR VSBY, though
IFR VSBY is certainly possible by the mid afternoon. CIGs will
deteriorate from MVFR to IFR from south to north into the early
afternoon. At least temporary LIFR CIGs are possible mid to late
Sunday afternoon. East winds will become gusty during the morning
and then shift to more east-northeast during the afternoon, with
peak gusts generally in 20-25 kt range. Even stronger winds are in
store beyond the current TAF period.

Castro

&&

.MARINE...
235 PM CDT

Upgrading the gale watch to a gale warning. The gale threat
appears most substantial in the Illinois nearshore waters, but
will be upgrading Indiana as well even though gales appear very
marginal there until Monday. Confidence is high in 40-45kt
easterly gales Sunday night into Monday morning, with a couple of
the more aggressive models even hinting at a threat of a couple
brief low end storm force gusts. Winds should begin to slowly
subiside Monday as they back to more northerly direction.

- Izzi

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Flash Flood Watch...ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-
     ILZ039-ILZ105-ILZ106-ILZ107-ILZ108...4 PM Sunday to 10 AM
     Monday.

IN...Flash Flood Watch...INZ001-INZ002-INZ010-INZ011-INZ019...4 PM
     Sunday to 10 AM Monday.

LM...Gale Watch...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...6 PM
     Sunday to 4 PM Monday.

&&

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Hazardous Weather Outlook
National Weather Service Chicago/Romeoville IL
417 AM CDT Sat Oct 23 2021

ILZ003>006-008-010>013-019>021-023-032-033-039-103>108-INZ001-002-
010-011-019-240930-
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-
417 AM CDT Sat Oct 23 2021 /517 AM EDT Sat Oct 23 2021/

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

.DAY ONE...Today and Tonight.

Weather hazards expected...

  Elevated Frost and Freeze Risk this morning.
  Limited Frost Risk for interior NW Illinois tonight.

DISCUSSION...

The threat for frost and near-freezing temperatures will continue
near and northwest of the I-55 corridor outside of Chicago this
morning. Elsewhere, patchy frost is possible away from the
lakefront.

Additional patchy frost development is possible late tonight.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

Sunday...
  Limited Flooding Risk.
  Limited Non Thunderstorm Wind Risk.
  Elevated Lakeshore Flood Risk.
Monday...
  Limited Thunderstorm Risk.
  Limited Non Thunderstorm Wind Risk.
  Elevated Lakeshore Flood Risk.
Tuesday morning...
  Limited Frost and or Freeze Risk.

DISCUSSION:

Widespread, soaking rain and strong easterly winds are becoming
increasingly likely Sunday and Monday. Winds could gust as high as
40-45 mph near the immediate lakeshore Sunday evening into Monday.
Rises in river and stream levels, some possibly significant,
will occur. Flooding may occur on roadways near leaf-clogged
sewer drains. Additionally, flooding of parks and trails
immediately along the Lake Michigan shore may occur, particularly
in Illinois, including the Chicago bike path. Finally, a few
strong thunderstorms may occur south of US-24 Sunday evening.

.SPOTTER INFORMATION STATEMENT...

  Spotter activation will not be necessary through tonight.

LMZ740>745-240930-
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-
417 AM CDT Sat Oct 23 2021

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...Today and Tonight.

  No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

Sunday and Monday...
  Gale force winds and very hazardous waves are likely.
  Limited Thunderstorm Risk.
Tuesday...
  Hazardous conditions for small craft are likely.

Doom

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