What Is A Wake Low?

It was an interesting weather day across the state.  It started off beautiful with plenty of sunshine this morning, but a squall line (line of strong storms) moved out of Minnesota into Wisconsin. This led to an interesting weather phenomenon. The storms were never severe in Wisconsin, but after the rain moved through the wind gusted over 60 miles per hour. This did not happen across the state, but numerous areas reported strong to damaging winds.

The picture above is from Ron and Jan Nyhus on Lake Wissota just east of Chippewa Falls. The Nyhus’ lost a dock as the strong winds created huge waves. Winds gusted to 61 miles per hour at Wausau and did a lot of tree damage and knocked power out to thousands. Here are the observations from Wausau this afternoon:

D
a
t
e
Time
(cdt)
Wind
(mph)
Vis.
(mi.)
Weather Sky Cond. Temperature (ºF) Pressure Precipitation (in.)
Air Dwpt 6 hour altimeter
(in.)
sea level
(mb)
1 hr 3 hr 6 hr
Max. Min.
09 18:54 E 12 10.00 Fair CLR 49 45 54 49 29.77 1008.8 0.01   0.48
09 17:54 SE 12 9.00 Light Rain FEW021 BKN033 BKN044 49 45     29.83 1010.9 0.03    
09 16:54 SE 21 G 37 10.00 Light Rain and Breezy SCT060 BKN110 50 42     29.85 1011.5      
09 15:54 E 22 G 38 10.00 Partly Cloudy and Breezy SCT120 51 41     29.79 1009.6   0.44  
09 14:54 SE 28 G 45 10.00 Fair and Windy CLR 51 42     29.78 1009.1 0.17    
09 13:54 SE 21 2.50 Heavy Rain and Breezy OVC030 50 44     29.95 1015.0 0.27    
09 12:54 S 9 9.00 Light Rain BKN075 OVC090 54 44 61 52 30.02 1017.1 0.02   0.02

I want to draw your eye to the pressure readings. In one hour, the pressure dropped from 29.95″ of mercury to 29.78″. This is a substantial drop.

So what in the world or atmosphere created these strong winds? It is something called a “wake low”. A wake low occurs after a squall line moves through. There is a stratiform deck of clouds and then usually a sharp cutoff where the skies clear. This is where strong subsidence is occurring. Take a look at the diagram of a wake low from Johnson and Hamilton done in 1988.

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3 Responses

  1. Hi Mark,

    Think there’s a formatting or so other type of error for this blog entry. Chart is cut off at 1st diget of temp and thus can’t see the pressure values you were pointing out. Also, it seems the blog isn’t complete as it ends only two paragraphs after the chart. Would have posted earlier, but I figured someone else perhaps already had.

    Tony (Pl. Prairie)

    • Yikes, I don’t know what happened. I will try to repost. Thanks for letting me know.

      Mark

      • Hello, everyone. Sorry about the post. I can’t get it to work properly. Something is wrong with wordpress.

        Mark

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