I’ve been watching Minnesota weather for more than 35 years. This is something I have never seen before.
The massive floodwaters in northwest Minnesota have created (temporary) new lakes. The flood zones are so big, that they are able to generate their own localized weather patterns.
Check out this tweet below from the Grand Forks NWS Office. The dark areas are north-south-oriented flood-created lakes. The lakes string along either side of the Red River from northwest Minnesota and eastern North Dakota northward into Canada.
Then watch the bumpy white line of cumulus clouds form east of the lake zone. Those are cumulus clouds developing along what is essentially a lake breeze frontal convergence zone.
Lake breezes and sea breezes form as the land near water bodies heats with strong sunshine like we had Tuesday. The warming air over the land rises, and cooler denser air from the lake blows inland to take its place.
The sun warms both the ground and ocean at the same rate. However, since the ground's heat remains confined to the top few inches of soil it radiates back into the atmosphere warming the air. As the air warms, its density decreases creating a weak low-pressure area called a "thermal low.”
Over the adjacent water the cooler, more dense air, being pull down by gravity, begins to spread inland.
This inland push of air from the ocean undercuts the less dense air over land forcing it to rise. A sharp boundary develops due to the large difference between the air temperature over land and over water. This boundary, called a sea breeze front, acts in the same manner as the cold front we typically experience.
These temporary flood lakes may not last long, but they are producing some highly unusual localized weather patterns in the Red River Valley.
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