I’m sure most have heard the term “Lake Breeze”.   Or, in the forecast, “cooler near the lake”.

Posting this today because yesterday was a classic set up for a lake breeze to develop, especially along the south shore of Lake Ontario.  For example, at one point yesterday, April 27 , 2017 Vineland station was reporting a temperature of 10C, while inland towards Niagara Falls, their station was reporting a temperature of 30C!

Living in close proximity to Lake Ontario in the Niagara region, every spring has its share of breezes that form off the lake and aim towards the closest shoreline.  If you are a lover of the heat, then this breeze can significantly alter the forecast highs for the day and can damper your mood!

But why does it occur?

In the spring, the lakes are quite cold from the previous winter.  The heat capacity of water is significantly greater than land, so land is able to warm much quicker than water.  As the land warms with the advancing season, the huge differences in temperatures can create a lake breeze circulation.

The atmosphere is continually trying to balance itself.  Since warm air (over land) is less dense it is able to expand and rise, this creates a lower pressure over land.  Cooler air is more dense so it contracts and sinks.  At the surface, considering that balance I previously mentioned, the cooler air wants to flow towards the void of the rising air over land.

To keep things simple, air flows from high to low pressure.  In this case, high pressure over water and low pressure over land.  Air begins to flow from its colder origin towards low pressure.  Again, the origin is over colder water therefore carrying in this colder environment towards the land.  Image below.

Eventually at a distance, the cooler air will be overcome by the advecting (advancing) warmer air.

Then why even near the lakeshore, the temperatures can still get pretty high in the spring?

The synoptic (greater scale)winds, if strong enough can overpower and simply shut down the lake breeze so it can become non-existent.   In my studies, typically its told that a synoptic flow over 15km/h can shut down a lake breeze.  However in my experience, and my location under the Niagara escarpment, synoptic flow of at least 20km/h with higher gusts is needed to diminish the breeze.

Can this effect or enhance precipitation?

Simply, occasionally yes.  In the great lakes, imagine all the lake breezes occurring at the same time.  Eventually the lake breezes can and will converge since there are so many lakes!  Where they come together is called a lake breeze convergence zone.  When these breezes collide with one another, they are forced to rise, cool and condense into the atmosphere creating convection.  This eventually can produce precipitation.  More on that in a future post.

To close, the fascination I have is quite considerable.  If unfamiliar with the lake breeze, it’s quite something to be along the lake shore and notice the almost bone chilling cold marine layer, then to drive 3km away up the escarpment where the temperature can be upwards of 20 degrees C difference!  Amazing!