Vince_Condella's Blog

That's one of the most common questions I get from viewers.  The old "cooler near the lake" is a spring and summer mantra in this part of Wisconsin.  Typically you will hear a forecast with two temperature numbers for daytime highs:  lakeside and inland.  But rarely do forecasters tell you where "inland" is located.

The distance to "inland" depends on the wind speed and, to a lesser extent, the direction of the wind.  It makes sense that a faster wind speed will carry cool air from the lake a farther distance inland than a lighter wind speed.  A wind over 15 m.p.h. will usually take the cool air all the way to Highway 45 in western Milwaukee County.  It may take a few hours for the cool air to move inland from the lakeshore to Wauwatosa, but typically it arrives by 10 a.m. or 11 a.m.

Slower wind speeds mean very little distance to "inland".  In fact, when the average wind speed is less than 10 m.p.h., cool air from the lake may not make it very far past the I-43/I-94 north-south corridor.  On a light wind, warm, sunny day, Milwaukee's lakefront in May could be 55 degrees but downtown West Allis may be 70 degrees or higher.

Wind direction dictates the coolness of the air more than the distance it travels inland.  A north-northeast wind travels nearly the entire length of Lake Michigan simply because the lake is oriented north-south.  A northeast trajectory of an air parcel means it gets to spend a long time travelling over the chilly waters of the lake.  On the other hand, an east or southeast wind has a lesser trajectory and may not pick up as much cold air over the lake surface.

As a forecaster, I tend to keep the lakeside-inland temperature difference greatest with a northeast wind, slightly less for an east wind, and even less for a southeast breeze.  I will check the lake surface temperature from the mid-lake buoy as well as the harbor water temperature reports near the lakeshore.

Meteorologists also need to make it clear in their forecasts where "inland" is located.  It's impossible to list the forecasted temperature for every town and city in the viewing area, but at least a couple of locations should be referenced, e.g. today's high will be 55 at the lakefront and 75 in Waukesha, or 75 west of Highway 45, etc.

It's the little attention to detail that makes a forecast usable for everybody.  And of course we all know that if going to the lakeshore this time of year doesn't cool you off enough, you can always jump into the lake.  Come to think of it, I've had a few people tell me to do that on occasion!