Isle Royale National Park Weather Page

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Isle Royale National Park Weather Information

Lake Superior weather is cool throughout the year. Dense fog in spring, sunny with temperatures rarely exceeding 80� F. Thunderstorms and rain occur throughout the season. Weather and rough seas may delay departures to and from the island. Bring plenty of warm clothing, even in August. A jacket is a must for the ferry trip to the island or if boating around the island.

Summers are cool and winters are very cold; periods of warm summer temperatures rarely exceed 2 to 3 days in length. Day to day temperature changes are strongly moderated by the surrounding waters of Lake Superior, the coldest of the Great Lakes.

Isle Royale National Park Temperature Stats - in �F

Temperature	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Annual
Normal Daily Maximum	11	20	32	45	54	62	68	69	60	52	33	18	43.7
Normal Daily Minimum	-11	-5	9	25	36	43	50	54	47	39	17	-1	25.3
Extreme High	48	53	66	70	79	87	89	86	82	72	65	57	71.2
Extreme Low	-46	-44	-38	-5	19	32	37	34	29	12	-32	-41	-3.6
Days Above 90�F	0	0	0	0	0	0	0	0	0	0	0	0	0
Days Below 32�F	31	28	30	22	8	0	0	0	1	6	28	31	185

Isle Royale National Park Precipitation Stats

Precipitation	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Normal	1.2	0.9	1.8	2.2	2.5	3.1	2.5	3.2	3.4	2.1	1.7	1.3
Maximum	4.7	2.4	5.1	5.8	7.7	8.0	8.5	10.3	6.6	7.5	5.0	3.7
Maximum 24 Hour	1.7	1.4	2.4	2.3	2.6	2.5	2.3	1.8	4.5	1.8	2.6	2.1
Maximum Snowfall	47	32	46	32	8	0	0	0	4	9	38	44
Days With Measureable Precipitation	12	10	11	11	12	13	11	11	12	10	11	12
Average Number of Thunderstorms	0	0	0	0	1	2	2	2	2	1	0	0

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by John William Uhler

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