Kolapore Uplands: Lake Effect

Predicting Lake Effect Snow

I haven't been able to find a good source for maps of predicted lake effect snowfall, which is the largest contributor to the snowpack at Kolapore. I did however find a do-it-yerself guide using skew-T charts which was fairly easy to follow. The meteorologist's skew-T chart has more information packed into it than I'd like, but beggars cannot be choosers. With the skew-T (KAPX, Gaylord MI) in combination with the image of water temperature on the right, you'll know right away what the situation is.

What's a skew-T?

Skew-T Tutorial In simple terms, the skew-T is a graph of air temperature and windspeed versus height above ground.

The height scale is labelled in metres on the left, in white.
The temperature scale is labelled in blue along the bottom.
Of the two somewhat jagged white lines, temperature data are on the RIGHT.
Windspeed data are shown by the wind bar icons on the far right.

Now consider the example below. There are four places in the chart to consult.

. . .

1	In region 1, look at the wind bar icons in the band of elevations close to surface (typically 1 to 3 km in thickness). You need winds with a direction of anywhere from WNW to N (ie coming in across the lake), but the key is that direction must be quite constant throughout the lower band of elevation ; if there is a shear, or rotation, in the direction with height, it's no good. Get the direction from the main 'flagstaff' part of the icon. Think of a compass with N at the top, W on the left, and so on. Furthermore, the wind speeds must average between 10-45 miles per hour in this band of 1-3 km above surface. Get the speed from the number of 'flag' bars sticking off the 'flagstaff'. Each thin bar counts 10 mph, and a solid triangle is 50 mph. Add up the bars for the total. In this example the range is 15-40 mph from the NW, which is good.	2	What is the temperature at the 850 millibar height? The millibar scale is on the far left in blue, paralleling the height scale. In this example, that temperature looks like -13, but it's actually -20. You see, skew-T means that the temperature is plotted at a 45 degree angle! Now, this temperature should be at least 13 degrees less than the average lake water temperature. So, -20 easily qualifies.
3	Region 3 is the average temperature in the lower band of 1-3 km above surface. In addition to requirement 2 above, the average temperature throughout this band must be below freezing. In this example, it looks to be about -25, which is choice.	4	Finally, consider the temperatures in the upper band. You need to see an inversion here, whereby the temperatures actually get slightly warmer at high elevations. That is basically telling you that there is a wicked mass of heavy Arctic air down low. In this example, you can see the inversion starting just to the above the '3', where the temperature increases from -40 to -30.

Now put it all together. Did you see:

1. NW winds of 10-45 mph?
temperature at least 13 below lake water at 850 mb height?
average temp less than 0 through the lower band?

temperature inversion in the upper band?

If so, then yeehaw! Lake effect snow could be on the way. The example above was taken on Nov 24, 2005 when moderate lake effect snowfall occurred over southern Ontario, including 8 cm reported near Collingwood. Skew-t graphs are updated twice per day. Check this page, and look for the pattern you see described here. Note that once the lake freezes over, no more lake effect snow is possible! The source of this material is the website of Jeff Haby, a meteorologist in Texas.