Bow Island
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bow Island clear sky chart from 2005-11-06 to 2026-07-01.

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	8% 7% 3 7% 5% 4 5% 4 6% 8% 44%	146969
	Night	7% 8% 3 8% 5% 5% 5% 4 6% 8% 41%	142666
Transparency	Day	37% 6% 14% 27% 14% 2	141604
	Night	39% 6% 16% 25% 12% 2	139054
Seeing	Day	13% 11% 30% 29% 14% 3	17668
	Night	12% 11% 35% 30% 11% 1	26883

By Month

Percentage Cloud Cover SW (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	4 13% 6% 12% 7% 6% 6% 4 7% 9% 27%	4124
	11th to 20th	Day	4 10% 5% 10% 5% 5% 8% 6% 6% 7% 34%	4140
	21st to end	Day	3 7% 5% 10% 6% 5% 4 3 5% 7% 45%	5067
February	1st to 10th	Day	8% 13% 5% 11% 7% 6% 5% 4 7% 7% 28%	1843
	11th to 20th	Day	7% 11% 5% 11% 7% 5% 5% 6% 7% 8% 28%	1845
	21st to end	Day	5% 11% 5% 11% 8% 6% 5% 4 6% 7% 32%	1580
March	1st to 10th	Day	5% 9% 3 9% 6% 6% 5% 4 5% 8% 41%	4794
	11th to 20th	Day	6% 7% 3 9% 6% 5% 5% 4 6% 9% 39%	5110
	21st to end	Day	9% 15% 5% 11% 6% 6% 5% 5% 7% 8% 24%	5607
April	1st to 10th	Day	9% 11% 3 8% 6% 5% 5% 5% 6% 7% 35%	2550
	11th to 20th	Day	10% 12% 4 9% 6% 5% 4 3 6% 7% 34%	2697
	21st to end	Day	10% 10% 3 8% 6% 4 4 4 6% 7% 38%	2730
May	1st to 10th	Day	11% 8% 3 6% 4 4 4 4 7% 7% 43%	7984
	11th to 20th	Day	11% 8% 3 7% 6% 6% 6% 5% 8% 9% 33%	8468
	21st to end	Day	11% 6% 2 6% 4 5% 5% 4 6% 9% 44%	9648
June	1st to 10th	Day	14% 6% 2 6% 5% 4 5% 4 7% 8% 39%	3150
	11th to 20th	Day	15% 6% 3 6% 5% 6% 6% 5% 7% 8% 34%	3150
	21st to end	Day	8% 4 2 4 3 5% 4 4 7% 9% 50%	3150
July	1st to 10th	Day	6% 3 2 4 3 3 4 3 6% 7% 58%	6780
	11th to 20th	Day	7% 4 2 4 3 3 4 3 6% 7% 56%	6780
	21st to end	Day	6% 4 1 3 2 2 3 2 4 7% 66%	7382
August	1st to 10th	Day	8% 5% 2 6% 4 4 4 4 6% 9% 48%	5931
	11th to 20th	Day	4 3 1 5% 3 4 5% 4 7% 9% 53%	5798
	21st to end	Day	7% 3 1 3 2 2 3 2 4 7% 65%	6468
September	1st to 10th	Day	10% 5% 1 4 3 3 3 2 4 7% 56%	2477
	11th to 20th	Day	13% 5% 2 5% 3 3 4 3 5% 8% 49%	2217
	21st to end	Day	8% 5% 2 6% 4 3 4 3 5% 8% 52%	2200
October	1st to 10th	Day	7% 5% 2 6% 3 4 5% 4 7% 9% 47%	3312
	11th to 20th	Day	4 5% 2 6% 5% 4 4 3 6% 7% 53%	3238
	21st to end	Day	7% 7% 3 7% 3 3 5% 4 5% 6% 50%	3178
November	1st to 10th	Day	12% 12% 4 8% 6% 4 4 3 6% 6% 33%	1648
	11th to 20th	Day	6% 9% 3 10% 7% 6% 4 4 5% 8% 38%	1680
	21st to end	Day	6% 11% 5% 9% 6% 6% 4 3 6% 9% 34%	1593
December	1st to 10th	Day	7% 14% 4 10% 7% 5% 5% 3 5% 7% 33%	2360
	11th to 20th	Day	5% 11% 4 10% 8% 7% 6% 5% 6% 6% 31%	2715
	21st to end	Day	3 9% 4 8% 5% 5% 5% 4 6% 7% 44%	3575
January	1st to 10th	Night	3 11% 4 11% 6% 6% 6% 5% 6% 9% 34%	8768
	11th to 20th	Night	3 11% 4 10% 5% 4 5% 4 6% 9% 38%	8820
	21st to end	Night	2 8% 4 9% 6% 5% 6% 5% 7% 8% 40%	9158
February	1st to 10th	Night	8% 12% 4 9% 7% 6% 6% 4 7% 7% 31%	2776
	11th to 20th	Night	5% 12% 4 9% 5% 7% 7% 6% 7% 8% 31%	2662
	21st to end	Night	5% 12% 4 10% 6% 5% 6% 4 6% 9% 35%	2223
March	1st to 10th	Night	4 8% 4 11% 5% 5% 5% 4 7% 9% 38%	5319
	11th to 20th	Night	6% 7% 3 8% 5% 6% 6% 5% 7% 9% 39%	5110
	21st to end	Night	10% 16% 5% 11% 5% 5% 5% 5% 7% 8% 24%	5610
April	1st to 10th	Night	9% 11% 4 8% 5% 5% 4 3 6% 9% 35%	2065
	11th to 20th	Night	10% 10% 4 8% 5% 5% 5% 4 6% 8% 35%	1871
	21st to end	Night	12% 9% 4 8% 5% 5% 5% 4 7% 6% 36%	1890
May	1st to 10th	Night	15% 9% 3 6% 4 4 3 3 5% 7% 42%	4948
	11th to 20th	Night	9% 8% 4 9% 6% 6% 6% 5% 7% 9% 31%	4404
	21st to end	Night	12% 6% 2 8% 5% 5% 6% 4 6% 8% 37%	4525
June	1st to 10th	Night	16% 6% 2 6% 4 4 5% 4 7% 9% 36%	1470
	11th to 20th	Night	12% 5% 2 6% 5% 4 7% 5% 7% 9% 38%	1470
	21st to end	Night	8% 3 1 4 4 4 5% 3 7% 9% 52%	1470
July	1st to 10th	Night	6% 3 1 4 3 4 4 4 6% 8% 58%	3180
	11th to 20th	Night	7% 5% 1 5% 2 3 4 4 6% 10% 52%	3180
	21st to end	Night	6% 3 1 4 3 3 3 3 5% 8% 61%	3468
August	1st to 10th	Night	10% 5% 2 5% 3 4 4 4 7% 9% 46%	3858
	11th to 20th	Night	5% 3 2 5% 4 4 5% 5% 8% 11% 48%	4051
	21st to end	Night	8% 4 1 4 3 2 3 3 4 7% 62%	4509
September	1st to 10th	Night	10% 4 2 5% 3 4 4 3 5% 7% 53%	1922
	11th to 20th	Night	11% 6% 2 5% 3 4 4 3 5% 7% 50%	2180
	21st to end	Night	6% 6% 1 4 4 4 4 4 7% 8% 51%	2200
October	1st to 10th	Night	7% 5% 2 5% 3 4 4 4 6% 8% 51%	3878
	11th to 20th	Night	5% 6% 2 6% 4 4 4 3 6% 9% 50%	3898
	21st to end	Night	6% 8% 3 7% 4 4 5% 4 6% 7% 47%	4600
November	1st to 10th	Night	11% 12% 4 7% 5% 4 4 3 5% 8% 36%	2860
	11th to 20th	Night	6% 10% 3 8% 7% 5% 5% 4 6% 7% 39%	2940
	21st to end	Night	5% 11% 4 9% 6% 5% 4 4 7% 8% 37%	3024
December	1st to 10th	Night	4 12% 5% 11% 7% 6% 6% 5% 6% 7% 32%	5040
	11th to 20th	Night	6% 12% 5% 10% 5% 6% 6% 5% 6% 9% 30%	5696
	21st to end	Night	4 8% 3 8% 5% 4 5% 4 6% 7% 45%	7623

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	52% 6% 15% 21% 5%	4125
	11th to 20th	Day	48% 5% 16% 16% 12% 2	4140
	21st to end	Day	39% 5% 18% 29% 8% 1	5067
February	1st to 10th	Day	54% 6% 14% 16% 9% 1	1843
	11th to 20th	Day	51% 6% 14% 19% 9% 1	1854
	21st to end	Day	49% 7% 12% 22% 9% 1	1580
March	1st to 10th	Day	41% 5% 13% 24% 16%	4794
	11th to 20th	Day	40% 7% 16% 25% 12%	5110
	21st to end	Day	53% 10% 17% 15% 5%	5607
April	1st to 10th	Day	46% 7% 13% 23% 9% 1	2550
	11th to 20th	Day	49% 5% 11% 25% 9% 1	2700
	21st to end	Day	44% 6% 13% 26% 10% 1	2730
May	1st to 10th	Day	38% 5% 11% 27% 14% 5%	7984
	11th to 20th	Day	42% 7% 12% 27% 11%	8472
	21st to end	Day	34% 7% 12% 31% 16%	9650
June	1st to 10th	Day	40% 7% 16% 23% 13% 2	3150
	11th to 20th	Day	45% 7% 13% 22% 12% 1	3150
	21st to end	Day	29% 7% 17% 31% 14% 3	3150
July	1st to 10th	Day	24% 6% 14% 25% 25% 7%	6707
	11th to 20th	Day	26% 6% 17% 30% 18% 4	6699
	21st to end	Day	20% 5% 13% 31% 20% 12%	7169
August	1st to 10th	Day	27% 5% 13% 31% 21% 3	4321
	11th to 20th	Day	24% 6% 15% 38% 14% 2	4197
	21st to end	Day	21% 4 12% 40% 21% 2	4663
September	1st to 10th	Day	29% 3 12% 29% 18% 8%	2477
	11th to 20th	Day	33% 6% 12% 30% 16% 3	2217
	21st to end	Day	31% 5% 14% 32% 15% 3	2200
October	1st to 10th	Day	32% 6% 13% 32% 14% 2	3312
	11th to 20th	Day	30% 5% 16% 33% 15% 1	3238
	21st to end	Day	33% 5% 10% 38% 13% 1	3178
November	1st to 10th	Day	49% 7% 15% 19% 8% 2	1648
	11th to 20th	Day	44% 6% 19% 23% 8% 1	1680
	21st to end	Day	47% 6% 19% 20% 7% 1	1593
December	1st to 10th	Day	51% 5% 18% 22% 3 1	2360
	11th to 20th	Day	51% 7% 18% 20% 3	2714
	21st to end	Day	38% 5% 15% 26% 15% 1	3575
January	1st to 10th	Night	45% 7% 18% 21% 8% 1	8769
	11th to 20th	Night	43% 5% 19% 20% 12% 1	8820
	21st to end	Night	40% 6% 19% 26% 9%	9158
February	1st to 10th	Night	50% 6% 13% 19% 10% 1	2776
	11th to 20th	Night	47% 8% 14% 18% 11% 1	2663
	21st to end	Night	45% 6% 15% 22% 9% 2	2223
March	1st to 10th	Night	40% 6% 20% 22% 12%	5319
	11th to 20th	Night	39% 6% 16% 29% 10%	5110
	21st to end	Night	54% 10% 16% 15% 5%	5610
April	1st to 10th	Night	45% 6% 15% 23% 10%	2065
	11th to 20th	Night	45% 6% 12% 23% 12% 1	1871
	21st to end	Night	45% 7% 12% 25% 10% 1	1890
May	1st to 10th	Night	42% 5% 8% 28% 13% 4	4946
	11th to 20th	Night	44% 9% 11% 23% 13%	4404
	21st to end	Night	40% 8% 12% 29% 10% 1	4526
June	1st to 10th	Night	42% 6% 15% 23% 12% 2	1470
	11th to 20th	Night	38% 9% 13% 25% 13% 2	1470
	21st to end	Night	28% 6% 15% 35% 14% 3	1470
July	1st to 10th	Night	23% 6% 17% 26% 22% 6%	3145
	11th to 20th	Night	26% 7% 15% 30% 16% 5%	3138
	21st to end	Night	22% 5% 13% 30% 20% 10%	3369
August	1st to 10th	Night	28% 6% 12% 32% 17% 5%	2807
	11th to 20th	Night	27% 8% 16% 29% 16% 3	2928
	21st to end	Night	24% 4 12% 36% 20% 4	3245
September	1st to 10th	Night	30% 5% 10% 27% 19% 8%	1922
	11th to 20th	Night	33% 5% 13% 28% 16% 5%	2180
	21st to end	Night	29% 6% 13% 32% 18% 3	2200
October	1st to 10th	Night	29% 5% 12% 35% 17% 2	3878
	11th to 20th	Night	30% 5% 15% 31% 16% 2	3898
	21st to end	Night	35% 5% 11% 35% 12% 1	4600
November	1st to 10th	Night	48% 5% 15% 22% 9% 1	2860
	11th to 20th	Night	43% 6% 19% 21% 11%	2940
	21st to end	Night	43% 6% 21% 19% 8% 1	3024
December	1st to 10th	Night	51% 6% 19% 17% 6% 1	5040
	11th to 20th	Night	49% 7% 26% 16% 3	5697
	21st to end	Night	37% 5% 13% 26% 16% 2	7623

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	11% 14% 39% 23% 9% 4	220
	11th to 20th	Day	17% 12% 38% 25% 6% 1	220
	21st to end	Day	11% 13% 42% 26% 6% 2	242
February	1st to 10th	Day	18% 16% 42% 16% 6% 1	305
	11th to 20th	Day	12% 13% 42% 25% 7% 1	330
	21st to end	Day	14% 17% 31% 27% 9% 2	296
March	1st to 10th	Day	12% 18% 36% 21% 10% 2	540
	11th to 20th	Day	13% 14% 37% 24% 9% 2	540
	21st to end	Day	14% 15% 39% 20% 10% 2	594
April	1st to 10th	Day	14% 19% 32% 28% 6% 1	540
	11th to 20th	Day	15% 15% 36% 26% 8%	532
	21st to end	Day	16% 15% 25% 31% 11% 3	540
May	1st to 10th	Day	14% 11% 26% 28% 16% 4	669
	11th to 20th	Day	16% 10% 25% 29% 18% 3	775
	21st to end	Day	17% 7% 21% 30% 19% 6%	844
June	1st to 10th	Day	17% 12% 24% 30% 14% 3	780
	11th to 20th	Day	17% 13% 31% 28% 10% 1	780
	21st to end	Day	10% 9% 26% 34% 18% 3	780
July	1st to 10th	Day	6% 5% 24% 37% 22% 6%	722
	11th to 20th	Day	9% 5% 29% 37% 18% 2	718
	21st to end	Day	5% 5% 23% 38% 23% 6%	794
August	1st to 10th	Day	7% 5% 19% 39% 24% 6%	540
	11th to 20th	Day	6% 4 27% 33% 24% 7%	517
	21st to end	Day	8% 7% 26% 30% 23% 5%	583
September	1st to 10th	Day	10% 10% 27% 33% 17% 3	530
	11th to 20th	Day	15% 7% 27% 33% 16% 3	530
	21st to end	Day	13% 11% 34% 28% 10% 4	530
October	1st to 10th	Day	14% 9% 29% 27% 18% 3	359
	11th to 20th	Day	12% 14% 35% 25% 11% 2	330
	21st to end	Day	17% 18% 33% 23% 7% 1	363
November	1st to 10th	Day	22% 16% 36% 20% 5% 1	330
	11th to 20th	Day	14% 19% 41% 21% 5% 1	330
	21st to end	Day	10% 20% 39% 19% 8% 5%	283
December	1st to 10th	Day	10% 21% 41% 19% 8%	220
	11th to 20th	Day	12% 23% 40% 20% 5%	220
	21st to end	Day	15% 10% 37% 26% 8% 4	242
January	1st to 10th	Night	10% 15% 41% 24% 9% 1	1050
	11th to 20th	Night	14% 15% 38% 24% 8%	1050
	21st to end	Night	10% 15% 42% 24% 7% 1	984
February	1st to 10th	Night	15% 11% 35% 26% 11% 1	840
	11th to 20th	Night	11% 13% 38% 29% 9%	824
	21st to end	Night	12% 12% 31% 30% 13% 2	692
March	1st to 10th	Night	11% 11% 36% 31% 10% 1	840
	11th to 20th	Night	12% 13% 36% 30% 8% 1	840
	21st to end	Night	13% 13% 38% 27% 8% 1	924
April	1st to 10th	Night	14% 11% 39% 27% 8% 1	693
	11th to 20th	Night	13% 10% 39% 27% 9%	623
	21st to end	Night	17% 10% 31% 33% 9%	630
May	1st to 10th	Night	15% 7% 27% 35% 14% 1	630
	11th to 20th	Night	10% 8% 29% 34% 17% 1	520
	21st to end	Night	18% 8% 25% 31% 17% 2	455
June	1st to 10th	Night	20% 8% 30% 28% 12% 1	420
	11th to 20th	Night	15% 10% 35% 30% 9%	420
	21st to end	Night	9% 7% 29% 38% 16%	420
July	1st to 10th	Night	7% 5% 26% 42% 20%	390
	11th to 20th	Night	7% 6% 30% 44% 12% 1	388
	21st to end	Night	4 5% 25% 42% 22% 2	438
August	1st to 10th	Night	8% 4 26% 39% 22% 2	528
	11th to 20th	Night	7% 4 22% 44% 22% 1	594
	21st to end	Night	10% 5% 26% 40% 18% 1	660
September	1st to 10th	Night	12% 6% 28% 41% 13% 1	600
	11th to 20th	Night	13% 5% 25% 39% 17% 1	780
	21st to end	Night	9% 10% 35% 31% 13% 2	800
October	1st to 10th	Night	15% 8% 28% 35% 13% 1	800
	11th to 20th	Night	13% 11% 34% 31% 10% 1	800
	21st to end	Night	12% 16% 38% 28% 6%	880
November	1st to 10th	Night	18% 13% 39% 24% 6%	1015
	11th to 20th	Night	13% 17% 41% 23% 5% 1	1050
	21st to end	Night	11% 14% 41% 27% 6%	1050
December	1st to 10th	Night	13% 13% 39% 25% 9% 1	1050
	11th to 20th	Night	12% 15% 40% 25% 7% 1	1050
	21st to end	Night	13% 14% 39% 27% 6% 1	1155

Page generated at 2026-06-28 00:10:44. Version ac07

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