Boundary Waters Canoe Area Wilderness
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Boundary Waters Canoe Area Wilderness clear sky chart from 2005-11-06 to 2025-10-04.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	13% 11% 4 9% 5% 5% 5% 4 6% 7% 32%	127697
	Night	12% 12% 5% 11% 6% 5% 5% 4 5% 6% 29%	121941
Transparency	Day	32% 39% 8% 14% 7% 1	131135
	Night	35% 38% 7% 12% 6% 1	126589
Seeing	Day	20% 18% 34% 19% 7% 2	17490
	Night	19% 15% 34% 24% 8% 1	27309

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	6% 12% 6% 19% 9% 7% 6% 4 5% 6% 20%	3617
	11th to 20th	Day	5% 12% 5% 19% 9% 7% 9% 6% 10% 5% 13%	3589
	21st to end	Day	6% 16% 13% 18% 8% 5% 5% 4 5% 5% 14%	3982
February	1st to 10th	Day	7% 12% 6% 12% 7% 6% 9% 6% 7% 5% 23%	1779
	11th to 20th	Day	7% 11% 4 12% 8% 7% 6% 4 7% 6% 28%	1754
	21st to end	Day	7% 16% 6% 12% 7% 5% 4 3 4 7% 28%	1600
March	1st to 10th	Day	9% 11% 4 10% 6% 5% 4 3 4 6% 37%	4478
	11th to 20th	Day	7% 13% 7% 11% 6% 6% 5% 4 5% 6% 30%	4952
	21st to end	Day	17% 15% 5% 11% 4 4 3 3 4 4 29%	5780
April	1st to 10th	Day	13% 14% 4 12% 6% 5% 5% 4 5% 5% 28%	2400
	11th to 20th	Day	18% 14% 4 9% 5% 4 4 3 5% 6% 29%	2374
	21st to end	Day	18% 12% 5% 8% 5% 5% 4 3 4 5% 31%	2684
May	1st to 10th	Day	15% 9% 2 6% 3 3 3 3 4 5% 47%	6348
	11th to 20th	Day	16% 9% 3 6% 4 4 4 4 6% 8% 38%	6319
	21st to end	Day	14% 7% 2 6% 4 5% 4 4 6% 7% 41%	6949
June	1st to 10th	Day	16% 7% 2 6% 5% 4 5% 4 6% 7% 39%	2800
	11th to 20th	Day	16% 6% 3 6% 4 5% 5% 4 7% 9% 34%	2948
	21st to end	Day	18% 7% 2 6% 5% 4 4 5% 7% 8% 34%	3000
July	1st to 10th	Day	9% 6% 3 7% 5% 5% 6% 5% 8% 9% 37%	6738
	11th to 20th	Day	15% 6% 2 5% 4 4 4 4 7% 10% 40%	6360
	21st to end	Day	10% 6% 2 6% 5% 4 5% 4 6% 9% 41%	6926
August	1st to 10th	Day	14% 7% 3 7% 5% 5% 6% 5% 6% 8% 35%	4563
	11th to 20th	Day	14% 4 2 4 3 3 5% 4 7% 9% 45%	4266
	21st to end	Day	12% 7% 2 6% 4 4 4 4 7% 9% 40%	4393
September	1st to 10th	Day	15% 6% 2 7% 5% 5% 4 3 6% 7% 40%	2400
	11th to 20th	Day	15% 8% 3 7% 5% 3 4 4 5% 8% 39%	2400
	21st to end	Day	19% 10% 4 7% 4 4 4 3 4 6% 35%	2124
October	1st to 10th	Day	17% 14% 3 7% 5% 4 4 4 6% 7% 30%	1930
	11th to 20th	Day	18% 19% 5% 8% 5% 4 5% 3 4 6% 24%	1900
	21st to end	Day	19% 21% 5% 9% 4 3 2 3 4 4 27%	1887
November	1st to 10th	Day	14% 20% 6% 11% 5% 5% 4 3 4 6% 22%	1661
	11th to 20th	Day	14% 19% 6% 14% 8% 5% 4 3 5% 4 18%	1600
	21st to end	Day	15% 17% 6% 17% 7% 6% 5% 3 4 4 16%	1600
December	1st to 10th	Day	9% 19% 6% 22% 14% 6% 4 2 3 4 11%	2610
	11th to 20th	Day	6% 16% 8% 16% 6% 8% 6% 4 5% 4 21%	3004
	21st to end	Day	16% 19% 6% 17% 9% 5% 4 3 4 3 14%	3982
January	1st to 10th	Night	6% 12% 6% 20% 8% 6% 6% 4 5% 4 22%	6348
	11th to 20th	Night	6% 11% 7% 17% 11% 9% 8% 7% 8% 3 12%	6316
	21st to end	Night	6% 15% 10% 19% 8% 6% 5% 4 5% 6% 15%	6996
February	1st to 10th	Night	7% 11% 6% 11% 8% 8% 10% 6% 6% 6% 21%	2620
	11th to 20th	Night	7% 11% 4 11% 7% 7% 8% 5% 6% 6% 27%	2533
	21st to end	Night	6% 15% 6% 13% 8% 6% 5% 4 5% 6% 25%	2029
March	1st to 10th	Night	9% 9% 4 10% 6% 6% 5% 4 5% 6% 36%	5362
	11th to 20th	Night	8% 14% 5% 15% 8% 6% 5% 4 5% 7% 24%	5037
	21st to end	Night	18% 15% 4 11% 5% 4 4 3 4 5% 26%	5151
April	1st to 10th	Night	14% 14% 4 9% 4 5% 5% 4 6% 6% 30%	2000
	11th to 20th	Night	16% 13% 4 7% 5% 4 4 4 6% 6% 32%	1975
	21st to end	Night	19% 12% 4 8% 5% 4 4 4 5% 4 32%	1711
May	1st to 10th	Night	15% 8% 2 4 3 3 4 3 4 5% 47%	3613
	11th to 20th	Night	13% 8% 3 7% 5% 4 3 4 5% 6% 41%	3596
	21st to end	Night	15% 7% 2 6% 3 4 4 4 6% 8% 42%	3949
June	1st to 10th	Night	16% 9% 3 5% 5% 3 4 4 6% 7% 38%	1600
	11th to 20th	Night	12% 6% 3 6% 5% 4 4 4 7% 8% 41%	1447
	21st to end	Night	14% 6% 2 5% 4 4 6% 4 7% 8% 41%	1400
July	1st to 10th	Night	10% 5% 2 5% 3 4 4 4 7% 9% 47%	3224
	11th to 20th	Night	13% 6% 2 5% 4 4 4 3 5% 7% 46%	3620
	21st to end	Night	11% 6% 3 6% 4 4 4 4 5% 9% 44%	3948
August	1st to 10th	Night	16% 4 1 5% 4 4 4 4 7% 9% 42%	2597
	11th to 20th	Night	13% 5% 2 5% 4 3 4 4 6% 8% 47%	2789
	21st to end	Night	14% 7% 3 6% 4 3 4 3 5% 7% 44%	3507
September	1st to 10th	Night	14% 7% 2 5% 4 4 5% 3 5% 7% 44%	2000
	11th to 20th	Night	13% 7% 2 5% 4 4 4 3 5% 7% 46%	2000
	21st to end	Night	20% 10% 2 7% 4 3 3 2 4 6% 39%	2251
October	1st to 10th	Night	18% 12% 3 6% 4 4 4 4 4 7% 34%	2317
	11th to 20th	Night	17% 18% 4 8% 4 4 4 3 4 5% 29%	2280
	21st to end	Night	20% 16% 4 9% 5% 3 4 3 5% 6% 25%	2710
November	1st to 10th	Night	14% 19% 6% 10% 6% 4 4 3 5% 7% 23%	2636
	11th to 20th	Night	14% 17% 7% 14% 7% 5% 4 3 4 4 19%	2800
	21st to end	Night	12% 16% 7% 17% 10% 6% 5% 3 4 4 17%	2800
December	1st to 10th	Night	11% 20% 8% 23% 10% 6% 4 3 3 3 9%	4580
	11th to 20th	Night	8% 16% 6% 15% 8% 7% 6% 7% 5% 4 17%	5203
	21st to end	Night	16% 20% 6% 16% 7% 4 4 3 4 4 15%	6996

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	50% 26% 3 9% 8% 4	3618
	11th to 20th	Day	49% 27% 4 17% 3	3620
	21st to end	Day	54% 29% 5% 9% 4	3982
February	1st to 10th	Day	26% 62% 4 6% 3	1779
	11th to 20th	Day	23% 61% 3 9% 4	1763
	21st to end	Day	22% 62% 3 6% 6%	1600
March	1st to 10th	Day	34% 30% 8% 14% 11% 4	4480
	11th to 20th	Day	40% 30% 7% 14% 8%	4952
	21st to end	Day	44% 29% 3 13% 11% 1	5780
April	1st to 10th	Day	24% 61% 2 6% 6% 1	2400
	11th to 20th	Day	21% 62% 3 9% 4	2374
	21st to end	Day	22% 61% 3 8% 5% 1	2684
May	1st to 10th	Day	25% 29% 9% 19% 16% 1	6357
	11th to 20th	Day	31% 30% 9% 16% 14% 1	6323
	21st to end	Day	29% 30% 8% 19% 13% 1	6949
June	1st to 10th	Day	17% 62% 6% 8% 5% 1	2800
	11th to 20th	Day	18% 63% 5% 10% 4	2948
	21st to end	Day	20% 62% 6% 8% 4	3000
July	1st to 10th	Day	31% 32% 13% 19% 5%	6666
	11th to 20th	Day	29% 29% 16% 22% 4	6285
	21st to end	Day	27% 28% 14% 24% 7%	6728
August	1st to 10th	Day	30% 39% 10% 16% 5%	4548
	11th to 20th	Day	21% 39% 16% 22% 2	4308
	21st to end	Day	27% 38% 13% 18% 3	4392
September	1st to 10th	Day	20% 58% 7% 10% 4	2400
	11th to 20th	Day	20% 58% 10% 9% 2	2400
	21st to end	Day	23% 57% 5% 10% 4 1	2124
October	1st to 10th	Day	25% 38% 12% 16% 8% 1	3190
	11th to 20th	Day	30% 37% 9% 18% 5%	3140
	21st to end	Day	39% 39% 10% 12% 1	3087
November	1st to 10th	Day	32% 56% 4 6% 2	1661
	11th to 20th	Day	29% 57% 5% 7% 2	1600
	21st to end	Day	35% 57% 2 3 3	1600
December	1st to 10th	Day	55% 35% 4 4 1	2610
	11th to 20th	Day	44% 32% 6% 7% 10% 1	3005
	21st to end	Day	55% 27% 4 11% 4	3982
January	1st to 10th	Night	50% 26% 5% 10% 9% 1	6348
	11th to 20th	Night	53% 27% 6% 10% 5%	6360
	21st to end	Night	53% 28% 5% 9% 4	6996
February	1st to 10th	Night	25% 62% 5% 5% 3	2620
	11th to 20th	Night	25% 61% 5% 6% 2 1	2534
	21st to end	Night	24% 62% 3 7% 4	2029
March	1st to 10th	Night	32% 31% 9% 8% 16% 5%	5373
	11th to 20th	Night	47% 29% 9% 10% 5%	5038
	21st to end	Night	46% 29% 3 12% 10% 1	5151
April	1st to 10th	Night	23% 62% 3 5% 6% 1	2000
	11th to 20th	Night	20% 62% 3 8% 5% 1	1975
	21st to end	Night	20% 61% 3 11% 5%	1711
May	1st to 10th	Night	25% 29% 7% 22% 14% 2	3620
	11th to 20th	Night	31% 30% 7% 16% 13% 2	3597
	21st to end	Night	27% 30% 10% 20% 11% 2	3950
June	1st to 10th	Night	17% 61% 5% 9% 6% 1	1600
	11th to 20th	Night	16% 62% 4 11% 6%	1447
	21st to end	Night	17% 62% 6% 9% 4 1	1400
July	1st to 10th	Night	25% 31% 15% 20% 8%	3188
	11th to 20th	Night	26% 29% 19% 22% 4	3572
	21st to end	Night	29% 28% 11% 25% 6%	3832
August	1st to 10th	Night	25% 38% 12% 19% 6%	2588
	11th to 20th	Night	23% 39% 14% 22% 2	2813
	21st to end	Night	27% 38% 12% 20% 3	3507
September	1st to 10th	Night	19% 58% 8% 11% 4	2000
	11th to 20th	Night	16% 59% 11% 11% 2	2000
	21st to end	Night	21% 57% 7% 12% 3	2251
October	1st to 10th	Night	21% 37% 7% 24% 11%	3837
	11th to 20th	Night	31% 38% 7% 16% 8%	3779
	21st to end	Night	40% 38% 11% 9% 2	4460
November	1st to 10th	Night	30% 56% 5% 7% 2	2636
	11th to 20th	Night	30% 57% 5% 6% 2	2800
	21st to end	Night	34% 57% 3 5% 2	2800
December	1st to 10th	Night	57% 35% 4 3 1	4580
	11th to 20th	Night	46% 32% 5% 10% 6%	5201
	21st to end	Night	54% 27% 4 10% 6%	6996

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	16% 19% 38% 21% 6%	300
	11th to 20th	Day	16% 17% 42% 20% 5%	300
	21st to end	Day	15% 23% 41% 16% 4	330
February	1st to 10th	Day	16% 24% 42% 12% 4 2	300
	11th to 20th	Day	18% 24% 39% 12% 6% 1	300
	21st to end	Day	21% 29% 38% 10% 2	249
March	1st to 10th	Day	17% 22% 40% 17% 3	300
	11th to 20th	Day	17% 25% 38% 13% 6% 1	300
	21st to end	Day	24% 22% 32% 14% 7% 1	465
April	1st to 10th	Day	24% 19% 33% 18% 6%	500
	11th to 20th	Day	27% 20% 28% 18% 7%	492
	21st to end	Day	27% 17% 30% 18% 7% 1	660
May	1st to 10th	Day	23% 20% 33% 17% 6% 2	703
	11th to 20th	Day	20% 18% 35% 17% 6% 3	725
	21st to end	Day	23% 16% 31% 21% 7% 2	789
June	1st to 10th	Day	21% 19% 32% 18% 8% 2	730
	11th to 20th	Day	20% 18% 38% 17% 5% 2	730
	21st to end	Day	22% 16% 33% 20% 8% 2	730
July	1st to 10th	Day	11% 11% 38% 25% 12% 4	721
	11th to 20th	Day	15% 15% 32% 22% 11% 4	718
	21st to end	Day	13% 13% 34% 23% 11% 6%	794
August	1st to 10th	Day	16% 12% 33% 24% 12% 3	726
	11th to 20th	Day	16% 10% 28% 29% 14% 3	715
	21st to end	Day	19% 13% 29% 25% 12% 2	638
September	1st to 10th	Day	18% 13% 32% 25% 11% 2	530
	11th to 20th	Day	18% 15% 33% 22% 11% 1	530
	21st to end	Day	26% 17% 25% 20% 9% 3	446
October	1st to 10th	Day	25% 18% 33% 16% 5% 3	309
	11th to 20th	Day	27% 20% 39% 11% 3	300
	21st to end	Day	32% 27% 29% 9% 2	330
November	1st to 10th	Day	27% 23% 32% 15% 3 1	300
	11th to 20th	Day	23% 27% 36% 9% 3 1	300
	21st to end	Day	28% 20% 37% 12% 2 1	300
December	1st to 10th	Day	20% 22% 37% 18% 3	300
	11th to 20th	Day	20% 21% 41% 16% 3	300
	21st to end	Day	19% 17% 43% 15% 4 2	330
January	1st to 10th	Night	15% 19% 42% 20% 4	1000
	11th to 20th	Night	16% 19% 41% 18% 5% 1	1000
	21st to end	Night	18% 18% 40% 20% 4	1100
February	1st to 10th	Night	15% 19% 39% 20% 6% 1	1000
	11th to 20th	Night	14% 21% 36% 21% 7% 1	979
	21st to end	Night	17% 17% 37% 22% 7%	709
March	1st to 10th	Night	15% 18% 34% 26% 6% 1	800
	11th to 20th	Night	16% 19% 37% 22% 6%	632
	21st to end	Night	22% 11% 31% 24% 10% 2	660
April	1st to 10th	Night	21% 14% 35% 25% 5%	600
	11th to 20th	Night	22% 15% 32% 23% 7%	593
	21st to end	Night	25% 11% 31% 25% 8% 1	600
May	1st to 10th	Night	21% 13% 34% 26% 6% 1	600
	11th to 20th	Night	19% 14% 32% 26% 8% 1	591
	21st to end	Night	20% 9% 31% 30% 9% 1	650
June	1st to 10th	Night	21% 10% 30% 28% 10% 1	600
	11th to 20th	Night	15% 10% 37% 30% 7%	600
	21st to end	Night	16% 11% 29% 31% 12% 1	600
July	1st to 10th	Night	11% 6% 31% 37% 15% 1	585
	11th to 20th	Night	13% 8% 32% 32% 14% 1	582
	21st to end	Night	9% 6% 32% 35% 16% 2	657
August	1st to 10th	Night	12% 6% 32% 37% 13% 1	597
	11th to 20th	Night	15% 8% 24% 31% 19% 3	594
	21st to end	Night	14% 10% 29% 31% 16%	660
September	1st to 10th	Night	19% 8% 27% 31% 15% 2	600
	11th to 20th	Night	17% 8% 32% 28% 15% 1	600
	21st to end	Night	26% 11% 30% 24% 8% 2	771
October	1st to 10th	Night	25% 15% 30% 21% 7% 1	773
	11th to 20th	Night	30% 15% 32% 18% 4 1	760
	21st to end	Night	28% 15% 33% 20% 4	836
November	1st to 10th	Night	24% 18% 32% 21% 4 1	880
	11th to 20th	Night	24% 19% 33% 17% 6% 1	1000
	21st to end	Night	22% 22% 38% 15% 3	1000
December	1st to 10th	Night	18% 20% 37% 20% 4	1000
	11th to 20th	Night	20% 19% 36% 19% 6% 1	1000
	21st to end	Night	24% 16% 35% 17% 6%	1100

Page generated at 2025-10-01 00:39:06. Version ac07

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