|Lake and Land Breezes on Lake Erie|
and their Effect on Summertime Weather
Having lived all my life in Cleveland Ohio, and developing my love of weather here, I have often witnessed
the unique effects of our Lake Erie on our weather, both summer and winter. I will briefly describe
here some of the summertime events that occur, and why.
First of all, a brief primer on lake and land breezes. They can develop best only when the synoptic or
gradient winds are very light to non existent, and they need partly to mostly clear skies to allow
the solar heating to warm the land. During the morning the land warms up significantly and the
air above it becomes warmer, lighter and begins to rise. This causes a pressure gradient to
develop between the air over land and that over the lake, which is cooler due to the lake water
being cooler than the land. Then this cooler air begins to flow on shore to replace the warmer
lighter air. This is the lake breeze. Aloft the warmer air is flowing off shore to replace
the air over the lake that has sunk to replace the surface air that flowed onshore. This
is the cycle that keeps the atmosphere balanced. It begins to calm down later toward evening, and
then at night the opposite often takes place. As the land surface cools below the lake temperature
and the air above the lake, the air above the land becomes cooler than that over the lake and
therefore will blow off shore to replace the lighter more buoyant air residing over the
lake. Then an onshore breeze develops aloft, and the cycle begins again, in reverse.
Many times in summer there is a “lake shadow” of clouds immediately along the shore, and sometimes for a number
of miles inland, and then further south the sky is filled with cotton ball cumulus. Many times on hot
summer days with temperatures nearing the 90 degree mark, and even higher and I thought we might tie
or break an old record high, the northerly wind would kick in and temperatures would fall sharply
back into the 80’s, and the old record high would stay intact! Further south across the rest of the
state it would continue hot and oppressive all day and this is why local weather people in Cleveland
often call Lake Erie nature’s air conditioner, and millions flock to our shores
every evening and all day on weekends. Many times local TV weather and weather websites have
radar which can be put on the clear air mode, which shows this lake breeze flowing onshore similar
to a gust front ahead of a thunderstorm. This is known as a lake breeze front.
So much for warm stable weather conditions. When the atmosphere becomes unstable, things get a lot
more interesting here. I have observed on many occasions cumulus build ups and cumulonimbus on both
sides of the lake; to the south and east of Cuyahoga county, especially in the higher snowbelt
terrain, and also in the far north where the same phenomena is occurring just north of Lake
Erie in Ontario Canada. They are easily visible on satellite imagery, and are quite impressive
when viewed up close. In the distance the characteristic bright orange color on the horizon and
ivory to white on the anvil tops is easily visible due to their much higher reflectivity compared
to the dull and even gray color of weak nearby clouds silhouetted against the bright blue sky. I
have never tired of gazing at them for hours.
As is the case with air mass thunderstorms, it is sometimes difficult to predict just when and where the
lake breeze front might cause enough instability to form convective storms over land. One has to study
the same indices that are used to predict any type of convective instability that involves forced
lifting. In the case of local lake breezes, things can get quite complex. There are three ingredients
that are required for severe thunderstorms to develop: 1). Large quantities of low-level moisture,
or a high dew point, 2). A deep layer of conditional instability and 3). A significant UVV, or
upward vertical motion. If the first two conditions exist in the vicinity of a well developed
lake breeze, severe thunderstorms are a distinct possibility. Strong vertical motion can
result from the collision of two or even more lake breeze fronts. Gust fronts from
thunderstorms can interact with the lake breeze front much like with another gust front, to
enhance the development of new nearby thunderstorms. Heavy thunderstorms with intense lightning
and flash flooding rainfall can form if deep moist convection
is created along a lake breeze front.
Current research is studying the effects of synoptic pressure gradient winds on the lake breeze front, and
the resulting wind shear, as to just where the heaviest storms are likely to develop. Generally speaking,
they are most likely to strengthen when moving at or near parallel to the orientation of the
lake breeze front, allowing them to remain in the area of frontal convergence the longest. There
is a 1996 study called COMET that examined the effects of environmental wind shear reacting
with the lake breeze front to produce either weak thunderstorms, or strong ones, depending
on the direction of the wind shear.
There is even some recent research into the possibility that these lake breeze enhanced thunderstorms can
be further enhanced by wind shear to produce tornadoes. However most of the tornadoes that have been
studied in lake-enhanced thunderstorms have been of the weak to moderate varieties, F0 to F3 on the
Fujita scale, at the most.
Then last, but certainly not least, are the effects of the lake breeze on air pollution in
Cleveland, and other Great Lakes cities. The results are very similar to sea breezes effecting major
cities on the coasts of oceans. The pollutants emitted into the inflow layer get trapped in the
quasi-closed circulation pattern of lake and land breezes, and in a stagnant synoptic condition
the pollution can accumulate to dangerous levels, especially when ground level ozone develops. This
occurs when the same conditions necessary for creating the lake breeze; the strong insolation from
the sun, high temperatures near the surface, and light mixing winds also react with reactive
hydrocarbons (RHC) and nitrogen oxides (NOx) often found in pollution, producing the ground
level ozone. And it is well known that a stagnant synoptic situation can cause these
dangerous conditions to develop anywhere a lot of effluent is sent skyward, a lake or
sea breeze condition isn’t necessary, but it can enhance the effect.
The research papers I reviewed for this paper mentioned much of the research that is being done, but nothing
about what could be done to improve the forecasting of these lake breeze effects, except
to increase the research. I personally feel forecasting could be improved immediately by the installation
of more automatic weather observation systems around the Great lakes, and on more floating buoys
and on any commercial and Coast Guard ships on the lakes at any given time, much like the
constantly transmitting equipment used on aircraft. I would also like to see more private weather offices
staffed by qualified personnel who can report on actual sky and weather conditions, air quality, and
return to including actual cloud types in their station reports too. Then I would like to recommend
that all weather stations send up their radiosondes more frequently, to get soundings more often. I
haven’t heard yet why they don’t, and assume it’s either because they are an aviation hazard or
maybe too expensive, and possibly both. But these are my personal recommendations.
On the Web:
“A Lake and Land Breeze Primer” by Dr. David Sills, 1998 York University. He has an extensive list of
references for his dissertation.
“Are Thunderstorms That Form Along Lake Breezes More Intense?”
David A.R. Kristovich, (1, 2) Robert E LaPlante, (2), Neil F. Laird (3), and Will Kubina (2)
(1) Atmospheric Environment Section, Illinois State Water Survey, Champaign, IL.
(2) NOAA/National Weather Service Office, Cleveland Ohio
(3) Dept. of Atmospheric Sciences, University of Illinois at Urbana-Champaign, IL.