One Year Since A Powerful Autumn Storm Brought 20-25 Foot Waves

A potent early autumn storm passed across the Great Lakes region one year ago on September 30th, bringing very impressive waves on Lake Michigan. The combination of winds occasionally gusting as high as 60 mph, and a long north-northwest fetch of up to 200 miles, resulted in waves building into the 20 to 25 foot range (trough to crest) on southern Lake Michigan. The NOAA south Lake Michigan buoy, around 50 miles east-southeast of Milwaukee, measured waves as high 23 feet at 4 am CDT September 30, 2011, The buoy sporadically lost wave height data during the period of maximum waves, possibly because of the extreme conditions. A tug captain at Burns Harbor Indiana estimated waves crashing over the break wall to be in the 25 foot range! The graphic below is a rough estimation of the peak wave heights during the storm.

Graphical depiction of estimated wave heights

NASA's AQUA MODIS Satellite imagery. For full and unannotated view - click here

Lake Effect Cloud Processes

Indiana Department of Natural Resources - Doug Stukey - Estimated 20-30 foot waves

Indiana Department of Natural Resources - Doug Stukey - Two subjects for comparison of number and size of waves. They would be standing in middle of beach if this were on a normal day.

Indiana Department of Natural Resources - Doug Stukey - From Pavilion parking lot. Big wave or sea maybe, with Willis tower 32 miles away in background.

Indiana Department of Natural Resources - Doug Stukey - Huge sea swell with big waves on top of Aon, Trump and Hancock towers left to right 34 miles away.

NASA's TERRA MODIS Satellite imagery from O3 OCT 2011.

(Click the graphic to enlarge)

Though the storm had moved well off to the east of Lake Michigan on October 1st, the water remained rather churned up as the long north fetch and slowly diminishing winds continued to produce relatively high waves on the south end of the lake. The water was also more of a tannish brown color than the usual more bluish hue. This was due to the sediment dredged up by the high waves of the previous few days. In fact, this change in the lake color from the sediment could even be seen from space!

High resolution, true-color imagery from NASA's polar-orbiting AQUA-MODIS satellite, clearly shows the discoloration of the water in this image of Lake Michigan from Saturday afternoon. This is a 250 meter resolution image (each pixel is 250 meters square or 820 feet) taken from an orbit of approximately 438 miles above the earth's surface.

(Click the graphic to enlarge) Animated Image

In addition to the discoloration of the lake due to the wave-churned sediment, the AQUA-MODIS image also clearly depicts stratocumulus clouds over and downwind of the lake. These clouds, which unfortunately become quite common across the lake in the cool season, form due to the advection of colder air over the still relatively mild lake waters. This results in an unstable thermodynamic profile, which leads to convective updrafts as the cold air traverses the warmer lake waters. Heat and moisture are transported upward from the surface of the lake by these updrafts, which develop into stratocumulus clouds as the moisture cools and condenses. If the cold air is sufficiently deep, these stratocumulus clouds may even produce lake-induced rain or snow showers. These clouds (or showers) typically align with the direction of the mean wind flow across the lake, and may extend well inland from the downwind shore. This is the "Lake Effect" of which residents of the Great Lakes region are so familiar with during the cold season. The following cross-sectional image depicts this process.

(Click the graphic to enlarge)

The sediment, and lake effect clouds from Saturday, can also be seen in 1 km resolution GOES weather satellite imagery. The following java loop from the visible channel of the GOES imager shows these processes in motion. Note that the clouds tend to follow the observed surface winds, which are indicated by the green barbs in the plotted observations. Warming temperatures aloft resulted in decreased lake-induced instability, and therefore shallower cloud depth and gradual dissipation of clouds during the course of the afternoon.

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Ratzer/Shea - 01 October 2011

Maximum Wind Gusts

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE CHICAGO IL
1209 PM CDT FRI SEP 30 2011 /109 PM EDT FRI SEP 30 2011/

...STRONG WINDS OVER NORTHERN ILLINOIS...NORTHWEST INDIANA...
   AND LAKE MICHIGAN...

PEAK WIND REPORTS OVER LAST 24 HOURS...

ILLINOIS                             PEAK WIND
LOCATION (COUNTY):                  SPEED (MPH)

ROCKFORD (WINNEBAGO).....................58
ROCHELLE (OGLE)..........................46
DIXON (LEE)..............................47
PERU (LA SALLE)..........................43
PONTIAC (LIVINGSTON).....................41
DE KALB (DE KALB)........................45
AURORA (KANE)............................46
WAUKEGAN (LAKE)..........................40
DUPAGE (DUPAGE)..........................49
WHEELING (COOK)..........................43
MIDWAY (COOK)............................45
O`HARE(COOK).............................46
MORRIS (GRUNDY)..........................45
ROMEOVILLE (WILL)........................41
JOLIET (WILL)............................46
KANKAKEE (KANKAKEE)......................45

INDIANA                              PEAK WIND
LOCATION (COUNTY):                  SPEED (MPH)

GARY (LAKE)..............................48
VALPARAISO (PORTER)......................37
RENSSELAER (JASPER)......................43

LAKE                                 PEAK WIND
MICHIGAN                            SPEED (MPH)

WAUKEGAN HARBOR (IL).....................44
CHICAGO CRIB (IL)........................55
CALUMET HARBOR (IL)......................37
BURNS HARBOR (IN)........................53
MICHIGAN CITY (IN).......................60
KENOSHA (WI).............................46
MILWAUKEE (WI)...........................39
PORT WASHINGTON (WI).....................45
SHEBOYGAN (WI)...........................51
KEWAUNEE (WI)............................53
ALGOMA CITY (WI).........................60
GREEN BAY ENTRANCE LIGHTHOUSE (WI).......71
CHAMBERS ISLAND (WI).....................68
DEATHS DOOR (WI).........................64
FAIRPORT (MI)............................39
PORT INLAND (MI).........................37
NAUBINWAY (MI)...........................39
MACKINAW CITY (MI).......................45
GRAND TRAVERSE (MI)......................51
MANISTEE HARBOR (MI).....................64
BIG SABLE POINT (MI).....................61
LUDINGTON (MI)...........................38
MUSKEGON (MI)............................41
HOLLAND (MI).............................54
SOUTH HAVEN (MI).........................55
ST JOSEPH (MI)...........................55
SOUTH BUOY...............................54
NORTH BUOY...............................56

The original article published one year ago can be found at this link. Also see our latest newsletter, Weather Currents, for more about this event.

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One Year Since A Powerful Autumn Storm Brought 20-25 Foot Waves