Lake effect in the summer?

Posted at 5:54 PM, Jul 13, 2014
and last updated 2014-07-15 13:20:58-04

GRAND RAPIDS, Mich. — It’s true most of us only hear about lake-effect precipitation (usually snow) in the winter. But lake-effect rain and lake-effect clouds will be a good bet on Tuesday this week. While the cooler temperatures, clouds, and scattered rain showers will not be all compliments of Lake Michigan, there will certainly be some lake enhancement.

So how is lake anything possible (especially this time of year)? It’s easy to understand. The fact that Lake Michigan contributes to our overall weather here on the west side of the state is no secret. It doesn’t matter what time of the year it is, it just favors the late fall and early winter months more (precipitation wise). That said, we all know the colder lake temperatures have been known to knock down and skew storms coming across the water from time to time too.

There is one main rule for generating lake-effect clouds, precipitation (rain or snow), or lake-enhanced of both. At minimum, there needs to be at least a 13 degree temperature difference between the air coming across the lake (about 5,000 feet above the surface) and the actual water temperature itself. Yes…there are other factors too, but the temperature difference (or Delta T if you prefer) is the real starting point.

It’s much easier to get the temperature difference with cold air outbreaks in the winter months, but it can/does happen all year round (we just never hear much about the warmer season outbreaks). While Lake Michigan water temperatures are currently in the mid/upper 60s, even near 70 (that’s about 20 degrees Celsius), air aloft coming across the lake on Tuesday will be about four to six degrees Celsius. (My apologies…upper level temperature maps for meteorologists are in Celsius, not Fahrenheit). No matter, the temperature difference is at least 15 degrees between the two…enough to help generate lake-effect and/or lake-enhanced clouds and precipitation.

The instability will be heavily aided by a strong upper level low pressure system rotating through the Great Lakes too. The combination will keep highs on Tuesday locked in the 60s with extensive cloudiness and scattered showers (perhaps a thundershower). Take a look at the atmosphere at 18,000 feet (or 500 millibars) below. We use this level to identify upper level disturbances and the trough/ridge pattern. Note the “low” over Michigan and the energy rotating around it (the dip or trough). This forecast snapshot (GFS model) is valid for Tuesday morning.

500 mb

Once the low and associated cooler pool of air lift out of the region, high pressure will take command and clear our skies (gradually). Temperatures will slowly increase through the week and we should be back in the low 80s by the weekend.

It is true the lake can actually stabilize the atmosphere in the spring and summer when slightly cooler air aloft comes in. The sun heats up the land and mostly sunny skies persist downwind several miles from the shore, while interior locations stay mainly cloudy. That’s the stable marine layer we see, especially in the late winter/spring. Unfortunately, the air this time will be too cold aloft to have that effect.

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