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 2024-04-25.

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% 5% 8% 7% 4 5% 5% 5% 6% 30%	83614
	Night	13% 12% 5% 9% 7% 4 5% 5% 5% 6% 28%	85547
Transparency	Day	54% 5% 11% 20% 9% 1	83316
	Night	57% 5% 11% 18% 8% 1	85379
Seeing	Day	20% 18% 34% 19% 7% 2	15328
	Night	19% 15% 34% 24% 8% 1	25438

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	8% 14% 7% 14% 13% 5% 6% 6% 5% 6% 16%	2527
	11th to 20th	Day	6% 10% 5% 14% 13% 6% 7% 9% 7% 5% 17%	2530
	21st to end	Day	8% 16% 13% 16% 10% 4 5% 6% 5% 5% 11%	2783
February	1st to 10th	Day	7% 11% 7% 11% 7% 4 9% 8% 7% 6% 23%	1690
	11th to 20th	Day	8% 10% 5% 11% 10% 5% 6% 5% 6% 6% 28%	1664
	21st to end	Day	8% 13% 8% 11% 8% 4 4 5% 4 7% 29%	1522
March	1st to 10th	Day	8% 11% 4 7% 7% 4 5% 4 5% 6% 39%	3118
	11th to 20th	Day	6% 12% 9% 10% 7% 4 5% 4 4 6% 33%	3466
	21st to end	Day	16% 16% 5% 11% 6% 3 3 3 4 5% 27%	4032
April	1st to 10th	Day	14% 13% 5% 10% 7% 4 5% 5% 5% 6% 28%	2280
	11th to 20th	Day	18% 13% 4 8% 5% 3 4 4 5% 6% 30%	2254
	21st to end	Day	18% 11% 4 8% 6% 4 4 4 4 5% 33%	2469
May	1st to 10th	Day	16% 12% 4 7% 7% 3 4 4 4 6% 32%	2520
	11th to 20th	Day	17% 9% 4 6% 5% 3 5% 6% 6% 8% 32%	2479
	21st to end	Day	18% 7% 2 5% 4 3 4 4 6% 8% 37%	2725
June	1st to 10th	Day	16% 6% 3 5% 6% 3 5% 5% 6% 8% 38%	2520
	11th to 20th	Day	16% 6% 3 5% 5% 3 5% 5% 7% 8% 36%	2652
	21st to end	Day	18% 7% 2 5% 5% 3 4 6% 7% 9% 35%	2700
July	1st to 10th	Day	9% 5% 2 4 6% 4 5% 6% 6% 9% 46%	2678
	11th to 20th	Day	14% 6% 3 5% 5% 3 5% 6% 6% 10% 37%	2520
	21st to end	Day	13% 4 2 5% 5% 4 5% 6% 6% 8% 43%	2743
August	1st to 10th	Day	10% 6% 2 5% 6% 4 6% 6% 6% 9% 39%	2507
	11th to 20th	Day	13% 6% 3 5% 5% 3 5% 5% 6% 9% 41%	2354
	21st to end	Day	13% 5% 3 5% 5% 3 4 5% 6% 9% 42%	2426
September	1st to 10th	Day	16% 6% 2 5% 6% 4 4 4 6% 6% 41%	2160
	11th to 20th	Day	16% 8% 3 6% 5% 3 4 4 5% 8% 38%	2160
	21st to end	Day	20% 10% 4 6% 6% 3 4 4 4 6% 33%	1913
October	1st to 10th	Day	18% 14% 3 7% 5% 3 5% 5% 6% 7% 28%	1800
	11th to 20th	Day	19% 18% 6% 7% 6% 3 5% 4 4 6% 23%	1800
	21st to end	Day	19% 21% 5% 8% 5% 2 2 3 3 4 26%	1788
November	1st to 10th	Day	14% 18% 7% 10% 6% 4 5% 4 4 6% 23%	1577
	11th to 20th	Day	15% 16% 8% 13% 10% 4 5% 3 4 4 18%	1520
	21st to end	Day	15% 16% 6% 14% 9% 5% 6% 4 4 4 17%	1520
December	1st to 10th	Day	8% 14% 7% 14% 13% 7% 8% 4 5% 5% 15%	1520
	11th to 20th	Day	10% 16% 9% 13% 8% 5% 6% 6% 5% 4 19%	1914
	21st to end	Day	20% 21% 8% 11% 10% 4 3 3 3 3 14%	2783
January	1st to 10th	Night	9% 15% 7% 13% 9% 4 6% 6% 6% 5% 20%	4428
	11th to 20th	Night	6% 9% 6% 15% 13% 8% 9% 9% 5% 4 13%	4440
	21st to end	Night	7% 17% 13% 16% 9% 4 5% 6% 5% 5% 13%	4884
February	1st to 10th	Night	7% 10% 7% 10% 9% 6% 9% 7% 7% 6% 22%	2489
	11th to 20th	Night	8% 10% 5% 10% 8% 5% 8% 7% 5% 6% 28%	2403
	21st to end	Night	7% 13% 7% 12% 9% 5% 6% 6% 5% 6% 25%	1931
March	1st to 10th	Night	10% 11% 4 8% 8% 5% 5% 5% 4 6% 34%	3722
	11th to 20th	Night	8% 13% 5% 11% 9% 5% 5% 4 4 6% 29%	3523
	21st to end	Night	17% 14% 4 11% 7% 3 4 4 5% 6% 25%	3599
April	1st to 10th	Night	15% 12% 4 7% 6% 3 5% 6% 5% 6% 30%	1900
	11th to 20th	Night	16% 12% 4 6% 6% 3 5% 5% 6% 6% 32%	1875
	21st to end	Night	18% 11% 4 7% 6% 3 4 5% 5% 5% 32%	1585
May	1st to 10th	Night	17% 11% 4 6% 5% 3 4 6% 5% 7% 33%	1440
	11th to 20th	Night	16% 8% 3 5% 5% 3 5% 5% 6% 7% 38%	1416
	21st to end	Night	17% 6% 3 5% 4 2 4 5% 6% 7% 39%	1551
June	1st to 10th	Night	17% 8% 3 5% 5% 2 4 4 5% 8% 38%	1440
	11th to 20th	Night	13% 5% 3 5% 5% 3 4 5% 7% 8% 41%	1303
	21st to end	Night	14% 6% 2 4 4 3 5% 6% 7% 8% 41%	1260
July	1st to 10th	Night	9% 4 2 4 4 3 4 5% 6% 9% 51%	1278
	11th to 20th	Night	11% 5% 2 5% 5% 4 4 5% 6% 7% 45%	1440
	21st to end	Night	8% 4 2 4 4 3 4 5% 5% 9% 51%	1575
August	1st to 10th	Night	8% 5% 2 5% 5% 4 4 5% 7% 9% 47%	1432
	11th to 20th	Night	13% 6% 3 4 4 3 3 4 5% 7% 48%	1543
	21st to end	Night	13% 7% 3 5% 4 2 4 4 6% 8% 45%	1930
September	1st to 10th	Night	14% 6% 2 5% 4 3 5% 4 5% 7% 45%	1800
	11th to 20th	Night	15% 7% 2 4 5% 2 4 4 5% 7% 47%	1800
	21st to end	Night	22% 10% 2 6% 5% 3 3 3 4 6% 36%	2025
October	1st to 10th	Night	19% 12% 3 5% 5% 3 5% 4 4 7% 33%	2160
	11th to 20th	Night	17% 18% 4 7% 5% 3 4 4 4 6% 29%	2160
	21st to end	Night	20% 16% 4 8% 5% 2 4 4 5% 6% 25%	2567
November	1st to 10th	Night	14% 17% 7% 9% 6% 3 5% 4 5% 7% 23%	2501
	11th to 20th	Night	15% 15% 8% 13% 9% 4 5% 4 4 5% 18%	2660
	21st to end	Night	12% 14% 7% 15% 11% 5% 5% 4 4 5% 18%	2660
December	1st to 10th	Night	10% 16% 7% 15% 12% 5% 6% 5% 5% 4 15%	2660
	11th to 20th	Night	9% 14% 7% 12% 10% 6% 6% 8% 5% 5% 17%	3283
	21st to end	Night	20% 22% 8% 12% 8% 3 4 3 4 3 13%	4884

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	68% 3 7% 14% 7%	2528
	11th to 20th	Day	67% 3 7% 19% 4	2530
	21st to end	Day	74% 4 7% 11% 5%	2783
February	1st to 10th	Day	58% 4 10% 15% 12% 1	1690
	11th to 20th	Day	55% 4 10% 21% 10% 1	1673
	21st to end	Day	56% 4 10% 15% 14% 2	1522
March	1st to 10th	Day	46% 5% 11% 21% 15% 1	3120
	11th to 20th	Day	54% 4 11% 20% 11%	3466
	21st to end	Day	61% 3 7% 15% 11% 2	4032
April	1st to 10th	Day	57% 6% 6% 16% 14% 2	2280
	11th to 20th	Day	55% 5% 10% 19% 11% 1	2254
	21st to end	Day	55% 4 8% 18% 13% 2	2469
May	1st to 10th	Day	53% 5% 11% 21% 9% 1	2520
	11th to 20th	Day	49% 6% 13% 22% 9% 1	2483
	21st to end	Day	45% 7% 13% 22% 12% 1	2725
June	1st to 10th	Day	44% 6% 14% 24% 11% 1	2520
	11th to 20th	Day	44% 7% 12% 23% 14% 1	2652
	21st to end	Day	45% 8% 14% 25% 8%	2700
July	1st to 10th	Day	35% 6% 13% 30% 15% 1	2605
	11th to 20th	Day	41% 7% 13% 29% 10%	2445
	21st to end	Day	39% 7% 14% 30% 10% 1	2591
August	1st to 10th	Day	39% 7% 17% 27% 9% 1	2492
	11th to 20th	Day	40% 7% 18% 26% 9%	2354
	21st to end	Day	39% 6% 17% 27% 12%	2426
September	1st to 10th	Day	44% 4 15% 28% 9%	2160
	11th to 20th	Day	45% 6% 21% 22% 6%	2160
	21st to end	Day	53% 5% 13% 22% 6%	1913
October	1st to 10th	Day	55% 5% 14% 20% 5%	1800
	11th to 20th	Day	64% 4 10% 17% 4 1	1800
	21st to end	Day	64% 3 8% 19% 6%	1788
November	1st to 10th	Day	64% 5% 10% 15% 6% 1	1577
	11th to 20th	Day	70% 4 9% 12% 5%	1520
	21st to end	Day	71% 5% 10% 9% 4 1	1520
December	1st to 10th	Day	70% 4 12% 11% 3 1	1520
	11th to 20th	Day	69% 3 11% 10% 7% 1	1915
	21st to end	Day	77% 1 5% 12% 4	2783
January	1st to 10th	Night	65% 3 8% 17% 6%	4428
	11th to 20th	Night	71% 3 9% 12% 4	4440
	21st to end	Night	72% 4 8% 11% 5%	4884
February	1st to 10th	Night	59% 4 10% 16% 10% 1	2489
	11th to 20th	Night	55% 4 11% 17% 11% 1	2404
	21st to end	Night	59% 4 9% 18% 9% 2	1931
March	1st to 10th	Night	50% 4 12% 15% 16% 2	3733
	11th to 20th	Night	57% 4 12% 18% 8% 1	3524
	21st to end	Night	60% 4 7% 15% 11% 2	3599
April	1st to 10th	Night	53% 6% 8% 17% 15% 1	1900
	11th to 20th	Night	53% 5% 10% 20% 11% 1	1875
	21st to end	Night	53% 5% 7% 22% 12% 2	1585
May	1st to 10th	Night	50% 7% 10% 21% 12%	1440
	11th to 20th	Night	45% 7% 12% 22% 13% 2	1417
	21st to end	Night	43% 7% 11% 24% 13% 2	1552
June	1st to 10th	Night	44% 5% 12% 25% 12% 1	1440
	11th to 20th	Night	39% 5% 14% 25% 16% 1	1303
	21st to end	Night	38% 9% 16% 25% 10% 2	1260
July	1st to 10th	Night	29% 6% 16% 33% 15% 1	1242
	11th to 20th	Night	35% 7% 13% 29% 14% 1	1392
	21st to end	Night	30% 7% 18% 30% 14% 1	1487
August	1st to 10th	Night	34% 6% 17% 30% 10% 2	1423
	11th to 20th	Night	36% 5% 16% 34% 9% 1	1543
	21st to end	Night	37% 5% 19% 26% 13%	1930
September	1st to 10th	Night	39% 7% 15% 30% 9% 1	1800
	11th to 20th	Night	38% 6% 21% 30% 5%	1800
	21st to end	Night	51% 4 14% 26% 5%	2025
October	1st to 10th	Night	53% 6% 12% 23% 6% 1	2160
	11th to 20th	Night	58% 5% 10% 22% 5%	2160
	21st to end	Night	60% 6% 11% 17% 5%	2567
November	1st to 10th	Night	63% 4 11% 16% 6%	2501
	11th to 20th	Night	70% 4 10% 11% 5%	2660
	21st to end	Night	70% 4 9% 12% 4 1	2660
December	1st to 10th	Night	72% 4 10% 10% 3	2660
	11th to 20th	Night	68% 5% 10% 12% 6%	3281
	21st to end	Night	77% 3 5% 10% 5%	4884

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	17% 20% 37% 21% 5%	270
	11th to 20th	Day	16% 18% 42% 20% 5%	270
	21st to end	Day	15% 23% 40% 18% 4	297
February	1st to 10th	Day	16% 23% 43% 12% 4 2	270
	11th to 20th	Day	19% 27% 36% 11% 6% 1	270
	21st to end	Day	19% 29% 40% 10% 2	225
March	1st to 10th	Day	14% 22% 43% 17% 4	270
	11th to 20th	Day	17% 25% 37% 14% 7% 1	270
	21st to end	Day	24% 21% 32% 14% 7% 1	425
April	1st to 10th	Day	23% 18% 34% 18% 6%	460
	11th to 20th	Day	26% 20% 28% 19% 7%	452
	21st to end	Day	26% 17% 30% 19% 7% 1	584
May	1st to 10th	Day	23% 21% 33% 17% 5% 2	603
	11th to 20th	Day	20% 17% 36% 17% 6% 3	625
	21st to end	Day	24% 15% 32% 20% 6% 2	679
June	1st to 10th	Day	21% 17% 32% 18% 9% 3	630
	11th to 20th	Day	19% 17% 38% 18% 6% 2	630
	21st to end	Day	21% 15% 32% 20% 9% 3	630
July	1st to 10th	Day	11% 11% 39% 24% 11% 4	621
	11th to 20th	Day	15% 16% 31% 23% 10% 4	618
	21st to end	Day	13% 12% 34% 23% 12% 6%	684
August	1st to 10th	Day	15% 11% 35% 24% 12% 3	626
	11th to 20th	Day	16% 11% 27% 28% 14% 4	615
	21st to end	Day	20% 13% 29% 24% 12% 2	545
September	1st to 10th	Day	19% 12% 32% 25% 11% 1	450
	11th to 20th	Day	21% 15% 32% 21% 10% 2	450
	21st to end	Day	30% 19% 25% 17% 8% 2	375
October	1st to 10th	Day	23% 18% 33% 17% 6% 3	270
	11th to 20th	Day	27% 21% 38% 10% 3	270
	21st to end	Day	33% 27% 29% 8% 2	297
November	1st to 10th	Day	27% 22% 33% 15% 3	270
	11th to 20th	Day	23% 27% 36% 10% 3 1	270
	21st to end	Day	29% 20% 36% 12% 3 1	270
December	1st to 10th	Day	20% 21% 37% 18% 3	270
	11th to 20th	Day	22% 20% 39% 17% 2	270
	21st to end	Day	21% 18% 43% 13% 3 2	297
January	1st to 10th	Night	16% 19% 42% 19% 4	950
	11th to 20th	Night	16% 20% 41% 18% 5% 1	950
	21st to end	Night	18% 17% 40% 20% 4	1045
February	1st to 10th	Night	15% 18% 39% 21% 7% 1	950
	11th to 20th	Night	15% 21% 35% 22% 7% 1	929
	21st to end	Night	16% 17% 37% 22% 7%	675
March	1st to 10th	Night	15% 18% 34% 26% 6% 1	760
	11th to 20th	Night	16% 18% 36% 23% 6%	601
	21st to end	Night	22% 11% 31% 25% 10% 2	627
April	1st to 10th	Night	21% 13% 36% 25% 6%	570
	11th to 20th	Night	22% 15% 32% 23% 7%	563
	21st to end	Night	24% 10% 31% 25% 9% 1	555
May	1st to 10th	Night	22% 14% 33% 25% 5% 1	540
	11th to 20th	Night	20% 12% 33% 26% 9% 1	531
	21st to end	Night	20% 9% 31% 30% 8% 1	584
June	1st to 10th	Night	20% 10% 30% 29% 10% 1	540
	11th to 20th	Night	16% 9% 37% 30% 8%	540
	21st to end	Night	16% 10% 29% 32% 13% 1	540
July	1st to 10th	Night	11% 5% 31% 38% 15%	525
	11th to 20th	Night	14% 8% 33% 31% 14% 1	522
	21st to end	Night	9% 6% 32% 34% 16% 2	591
August	1st to 10th	Night	11% 6% 33% 36% 13% 1	537
	11th to 20th	Night	16% 8% 22% 32% 19% 4	534
	21st to end	Night	14% 9% 29% 30% 17%	594
September	1st to 10th	Night	19% 8% 27% 31% 14% 1	540
	11th to 20th	Night	18% 9% 30% 27% 14% 1	540
	21st to end	Night	28% 11% 29% 22% 7% 2	693
October	1st to 10th	Night	26% 14% 29% 21% 8% 1	720
	11th to 20th	Night	30% 15% 31% 19% 4 1	720
	21st to end	Night	28% 14% 33% 20% 5%	792
November	1st to 10th	Night	24% 17% 32% 21% 4 1	835
	11th to 20th	Night	24% 19% 34% 17% 6% 1	950
	21st to end	Night	21% 22% 38% 15% 4	950
December	1st to 10th	Night	17% 20% 38% 20% 5%	950
	11th to 20th	Night	20% 19% 35% 19% 6% 1	950
	21st to end	Night	25% 17% 35% 17% 6%	1045

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