Early Monarch in Ontario: Weather Backtracking Tells a Story

Monarch Butterflies

Early Monarch in Ontario: Weather Backtracking Tells a Story

Update your records because the first Canadian sighting was not on May 8th as we reported previously but on April 27th according to an observer in Port Glascow, Ontario. Let's look at the weather conditions that occurred before the monarch appeared in Ontario through a process called "weather backtracking."

Weather Backtracking: Conditions Before the April 27th Sighting...
	Many days of warm temperatures There were 10 days of unusually warm weather in the eastern region before the day of the sighting. This map shows that from April 20-26th it was at least 9 degrees above normal in the east.
	A warm air mass stretching into Canada This temperature map shows how far north the warm air mass extended on April 25th, a typical day during the warm spell. Notice how much warmer it is in the east than in the west at the same latitude.
	Strong south winds South winds are common when weather systems like this are in place. This map shows the conditions on April 25th.
	Milkweed emerging Milkweed grew quickly due to the warm spell. As you watch the animation, focus on the changes that occurred between April 18th and 25th.
	Other early monarch sightings Other unusually early monarchs were also reported during this time, in South Dakota (April 22), Michigan (April 28) and Minnesota (April 29). These early monarchs either rode or got caught in the strong south winds associated with the warm air mass. They travelled far beyond the northern limit of milkweed at the time.