Beaver River Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Beaver River Observatory clear sky chart from 2005-11-06 to 2025-11-18.

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	14% 12% 5% 11% 6% 5% 4 3 5% 6% 29%	127276
	Night	13% 14% 6% 13% 6% 5% 4 3 4 5% 26%	123114
Transparency	Day	55% 6% 10% 18% 10% 1	130838
	Night	57% 6% 10% 16% 9% 1	127640
Seeing	Day	20% 17% 30% 21% 9% 3	16389
	Night	20% 16% 30% 24% 9% 1	25463

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	10% 16% 10% 23% 12% 7% 4 3 3 3 7%	3158
	11th to 20th	Day	7% 18% 11% 28% 11% 9% 5% 2 2 2 4	3926
	21st to end	Day	11% 19% 8% 23% 10% 7% 5% 3 3 3 9%	4466
February	1st to 10th	Day	11% 18% 9% 20% 11% 6% 4 3 4 4 10%	1800
	11th to 20th	Day	12% 14% 9% 20% 12% 6% 4 3 4 4 13%	1753
	21st to end	Day	12% 21% 6% 14% 9% 7% 4 4 4 5% 15%	1575
March	1st to 10th	Day	13% 14% 6% 14% 8% 6% 4 3 4 5% 25%	4856
	11th to 20th	Day	9% 14% 11% 14% 5% 4 4 4 6% 6% 24%	4980
	21st to end	Day	15% 17% 8% 11% 5% 4 3 3 4 5% 26%	5465
April	1st to 10th	Day	16% 17% 5% 10% 5% 5% 4 3 4 6% 25%	2320
	11th to 20th	Day	17% 14% 4 7% 4 4 3 3 5% 5% 35%	2536
	21st to end	Day	19% 13% 4 8% 4 3 3 3 5% 6% 31%	2600
May	1st to 10th	Day	15% 11% 3 7% 5% 4 4 3 5% 7% 35%	5888
	11th to 20th	Day	14% 11% 4 8% 5% 4 4 4 5% 6% 35%	6178
	21st to end	Day	20% 9% 2 6% 4 4 4 3 5% 6% 37%	6949
June	1st to 10th	Day	16% 8% 2 7% 4 4 5% 4 6% 8% 35%	2850
	11th to 20th	Day	13% 7% 2 5% 5% 5% 5% 5% 7% 9% 38%	3000
	21st to end	Day	17% 7% 2 6% 4 4 4 4 6% 7% 37%	3000
July	1st to 10th	Day	14% 6% 2 7% 5% 5% 6% 4 6% 8% 36%	6819
	11th to 20th	Day	12% 6% 2 5% 4 4 4 4 6% 8% 45%	6552
	21st to end	Day	10% 6% 2 6% 4 4 4 3 6% 8% 48%	6424
August	1st to 10th	Day	14% 7% 2 7% 4 5% 6% 4 6% 7% 36%	4234
	11th to 20th	Day	15% 8% 3 7% 5% 5% 6% 5% 6% 8% 33%	4174
	21st to end	Day	12% 6% 3 6% 5% 4 4 4 6% 9% 41%	4588
September	1st to 10th	Day	16% 8% 2 7% 5% 4 5% 4 5% 6% 37%	2400
	11th to 20th	Day	14% 6% 2 6% 4 4 4 3 5% 8% 43%	2213
	21st to end	Day	17% 8% 3 8% 5% 5% 5% 4 5% 6% 34%	2200
October	1st to 10th	Day	20% 11% 3 7% 4 4 4 3 5% 7% 33%	2003
	11th to 20th	Day	21% 14% 4 9% 6% 5% 4 3 5% 6% 22%	2000
	21st to end	Day	25% 21% 3 9% 4 5% 3 3 5% 6% 18%	2165
November	1st to 10th	Day	16% 21% 5% 9% 6% 4 5% 4 3 6% 23%	1776
	11th to 20th	Day	14% 20% 7% 12% 6% 5% 5% 3 5% 7% 16%	1656
	21st to end	Day	15% 25% 8% 13% 7% 4 4 4 4 5% 11%	1600
December	1st to 10th	Day	14% 26% 13% 18% 5% 4 4 3 4 4 7%	2600
	11th to 20th	Day	16% 24% 9% 19% 6% 3 3 2 3 3 13%	2986
	21st to end	Day	19% 19% 8% 17% 8% 5% 3 3 4 4 11%	3586
January	1st to 10th	Night	10% 17% 10% 24% 13% 6% 4 3 3 3 7%	6808
	11th to 20th	Night	9% 15% 10% 27% 13% 9% 5% 2 3 3 5%	5952
	21st to end	Night	11% 15% 9% 22% 9% 7% 5% 3 4 4 11%	6490
February	1st to 10th	Night	10% 19% 8% 17% 11% 7% 6% 3 4 3 12%	2600
	11th to 20th	Night	11% 16% 8% 18% 9% 6% 5% 4 4 5% 15%	2533
	21st to end	Night	11% 16% 6% 14% 9% 6% 5% 4 4 5% 19%	2050
March	1st to 10th	Night	12% 14% 6% 12% 6% 5% 5% 4 5% 7% 25%	4983
	11th to 20th	Night	7% 13% 7% 10% 5% 5% 6% 4 7% 6% 29%	4979
	21st to end	Night	15% 13% 5% 12% 5% 4 4 3 5% 4 29%	5467
April	1st to 10th	Night	17% 15% 4 9% 5% 4 4 4 5% 5% 28%	2080
	11th to 20th	Night	16% 13% 3 7% 4 4 4 2 3 7% 36%	1830
	21st to end	Night	16% 14% 5% 8% 5% 4 4 3 4 6% 31%	1800
May	1st to 10th	Night	15% 9% 3 7% 4 4 5% 3 5% 7% 37%	4053
	11th to 20th	Night	12% 8% 2 6% 4 4 4 3 6% 7% 44%	3713
	21st to end	Night	18% 9% 2 6% 3 3 3 3 5% 6% 42%	3926
June	1st to 10th	Night	14% 8% 3 6% 5% 5% 5% 3 6% 7% 39%	1545
	11th to 20th	Night	11% 5% 2 7% 5% 5% 5% 4 7% 9% 41%	1400
	21st to end	Night	14% 7% 2 5% 4 4 3 4 5% 7% 42%	1400
July	1st to 10th	Night	13% 8% 3 5% 4 3 4 3 5% 9% 44%	3160
	11th to 20th	Night	14% 7% 1 5% 4 3 3 3 5% 7% 49%	3411
	21st to end	Night	9% 7% 2 5% 3 4 4 4 6% 8% 49%	4428
August	1st to 10th	Night	10% 7% 2 6% 5% 3 4 4 6% 7% 44%	2915
	11th to 20th	Night	14% 7% 3 7% 5% 4 4 4 5% 7% 41%	2875
	21st to end	Night	13% 6% 2 6% 4 4 5% 3 5% 7% 45%	3275
September	1st to 10th	Night	12% 6% 2 6% 4 3 4 4 5% 7% 47%	2000
	11th to 20th	Night	12% 6% 2 4 3 3 4 3 5% 7% 51%	2184
	21st to end	Night	18% 9% 2 7% 4 4 5% 4 5% 6% 36%	2200
October	1st to 10th	Night	18% 9% 3 6% 4 4 4 3 5% 7% 36%	2396
	11th to 20th	Night	21% 15% 4 8% 4 5% 4 3 5% 6% 26%	2400
	21st to end	Night	21% 18% 4 8% 6% 4 4 4 4 5% 22%	2670
November	1st to 10th	Night	16% 19% 5% 9% 5% 5% 4 3 4 5% 25%	2740
	11th to 20th	Night	14% 19% 6% 12% 6% 5% 5% 3 5% 6% 19%	2899
	21st to end	Night	16% 21% 9% 13% 6% 4 5% 3 4 5% 14%	2800
December	1st to 10th	Night	13% 25% 10% 18% 5% 4 4 3 4 4 9%	4580
	11th to 20th	Night	9% 22% 10% 21% 8% 5% 4 3 3 3 11%	5208
	21st to end	Night	16% 21% 8% 20% 7% 7% 4 3 3 3 8%	7364

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	82% 6% 6% 5% 1	3159
	11th to 20th	Day	86% 6% 4 3 2	3960
	21st to end	Day	77% 7% 7% 6% 3	4466
February	1st to 10th	Day	76% 7% 7% 8% 1	1800
	11th to 20th	Day	74% 6% 7% 8% 4 1	1762
	21st to end	Day	71% 6% 7% 10% 4	1575
March	1st to 10th	Day	62% 5% 12% 11% 9%	4859
	11th to 20th	Day	60% 5% 10% 17% 5% 2	4980
	21st to end	Day	60% 5% 9% 17% 8% 1	5465
April	1st to 10th	Day	60% 5% 9% 17% 8% 1	2320
	11th to 20th	Day	51% 5% 8% 20% 14% 1	2536
	21st to end	Day	53% 6% 10% 17% 12% 2	2600
May	1st to 10th	Day	47% 5% 12% 18% 12% 5%	5897
	11th to 20th	Day	48% 8% 10% 16% 17% 1	6182
	21st to end	Day	47% 5% 10% 19% 15% 4	6949
June	1st to 10th	Day	44% 8% 11% 21% 15% 1	2850
	11th to 20th	Day	39% 8% 12% 23% 16% 1	3000
	21st to end	Day	44% 7% 13% 22% 13% 1	3000
July	1st to 10th	Day	44% 5% 13% 23% 14% 1	6746
	11th to 20th	Day	36% 5% 10% 33% 15%	6471
	21st to end	Day	34% 5% 12% 32% 17% 1	6240
August	1st to 10th	Day	43% 7% 13% 23% 13% 1	4221
	11th to 20th	Day	46% 7% 15% 23% 9%	4213
	21st to end	Day	38% 7% 13% 32% 10% 1	4588
September	1st to 10th	Day	45% 7% 13% 23% 10% 2	2400
	11th to 20th	Day	38% 6% 14% 29% 12%	2213
	21st to end	Day	50% 8% 11% 22% 9% 1	2200
October	1st to 10th	Day	46% 6% 11% 25% 11% 1	3263
	11th to 20th	Day	55% 5% 9% 19% 11%	3240
	21st to end	Day	63% 6% 11% 16% 5%	3479
November	1st to 10th	Day	61% 7% 10% 15% 6%	1776
	11th to 20th	Day	67% 8% 10% 9% 5%	1656
	21st to end	Day	75% 7% 9% 8% 1	1600
December	1st to 10th	Day	81% 6% 7% 5% 1	2600
	11th to 20th	Day	78% 6% 7% 7% 3	2986
	21st to end	Day	79% 5% 6% 6% 4	3586
January	1st to 10th	Night	82% 6% 5% 5% 2	6808
	11th to 20th	Night	81% 8% 5% 4 2	5993
	21st to end	Night	73% 8% 7% 6% 6%	6490
February	1st to 10th	Night	75% 7% 8% 9% 2	2600
	11th to 20th	Night	70% 7% 9% 11% 3	2535
	21st to end	Night	64% 8% 10% 12% 6%	2050
March	1st to 10th	Night	57% 7% 12% 14% 9% 1	4993
	11th to 20th	Night	51% 7% 17% 17% 8% 1	4980
	21st to end	Night	56% 6% 10% 17% 10% 1	5467
April	1st to 10th	Night	57% 4 8% 18% 11% 1	2080
	11th to 20th	Night	50% 5% 8% 19% 17% 1	1830
	21st to end	Night	54% 7% 8% 15% 16% 2	1800
May	1st to 10th	Night	46% 6% 11% 16% 15% 7%	4060
	11th to 20th	Night	38% 8% 12% 24% 16% 2	3714
	21st to end	Night	42% 7% 10% 25% 14% 2	3927
June	1st to 10th	Night	42% 7% 11% 20% 18% 2	1545
	11th to 20th	Night	38% 6% 13% 25% 17% 1	1400
	21st to end	Night	39% 7% 14% 24% 14% 2	1400
July	1st to 10th	Night	39% 4 13% 26% 16% 3	3125
	11th to 20th	Night	36% 4 11% 30% 18% 1	3369
	21st to end	Night	34% 5% 11% 33% 16% 1	4297
August	1st to 10th	Night	38% 5% 12% 27% 16% 1	2904
	11th to 20th	Night	42% 6% 16% 23% 12% 1	2902
	21st to end	Night	38% 7% 12% 30% 11% 1	3275
September	1st to 10th	Night	34% 8% 14% 29% 12% 1	2000
	11th to 20th	Night	32% 8% 14% 29% 16% 1	2184
	21st to end	Night	47% 8% 11% 23% 9% 1	2200
October	1st to 10th	Night	41% 6% 10% 25% 17% 1	3916
	11th to 20th	Night	52% 5% 12% 18% 14%	3899
	21st to end	Night	55% 6% 14% 19% 6%	4306
November	1st to 10th	Night	60% 7% 10% 16% 6% 1	2740
	11th to 20th	Night	65% 8% 13% 10% 4 1	2899
	21st to end	Night	72% 8% 11% 7% 2	2800
December	1st to 10th	Night	79% 6% 10% 4 1	4580
	11th to 20th	Night	76% 6% 7% 7% 2	5208
	21st to end	Night	82% 4 5% 7% 1	7364

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	18% 30% 34% 14% 5% 1	200
	11th to 20th	Day	18% 33% 35% 11% 3	293
	21st to end	Day	24% 24% 33% 17% 2	330
February	1st to 10th	Day	26% 31% 32% 9% 2	300
	11th to 20th	Day	24% 30% 36% 8% 2	300
	21st to end	Day	27% 30% 34% 9%	249
March	1st to 10th	Day	21% 24% 36% 14% 4	461
	11th to 20th	Day	22% 21% 36% 17% 4	500
	21st to end	Day	28% 16% 33% 17% 5%	550
April	1st to 10th	Day	25% 21% 33% 16% 5%	500
	11th to 20th	Day	29% 21% 24% 14% 8% 4	492
	21st to end	Day	28% 17% 29% 19% 6% 1	500
May	1st to 10th	Day	20% 17% 32% 21% 8% 2	503
	11th to 20th	Day	20% 9% 30% 24% 13% 3	527
	21st to end	Day	20% 11% 27% 25% 14% 3	573
June	1st to 10th	Day	18% 15% 28% 26% 11% 1	580
	11th to 20th	Day	15% 13% 32% 28% 10% 2	730
	21st to end	Day	20% 10% 31% 26% 10% 2	730
July	1st to 10th	Day	13% 10% 28% 30% 16% 3	721
	11th to 20th	Day	13% 9% 30% 28% 13% 6%	625
	21st to end	Day	10% 8% 31% 31% 16% 4	576
August	1st to 10th	Day	12% 7% 25% 33% 16% 7%	526
	11th to 20th	Day	16% 7% 22% 30% 18% 7%	519
	21st to end	Day	14% 10% 26% 30% 16% 5%	583
September	1st to 10th	Day	16% 13% 24% 25% 15% 6%	530
	11th to 20th	Day	12% 7% 22% 27% 21% 10%	530
	21st to end	Day	15% 14% 29% 24% 14% 3	530
October	1st to 10th	Day	24% 15% 24% 22% 12% 3	530
	11th to 20th	Day	24% 25% 32% 15% 4	530
	21st to end	Day	31% 26% 26% 14% 3	548
November	1st to 10th	Day	29% 26% 28% 12% 4	289
	11th to 20th	Day	29% 28% 32% 9% 2 1	214
	21st to end	Day	25% 28% 38% 9% 1	200
December	1st to 10th	Day	22% 35% 31% 12% 1	200
	11th to 20th	Day	25% 36% 30% 9% 2	200
	21st to end	Day	28% 32% 31% 6% 3	220
January	1st to 10th	Night	19% 27% 34% 16% 4	1000
	11th to 20th	Night	22% 24% 33% 17% 3	831
	21st to end	Night	16% 19% 39% 20% 5% 1	880
February	1st to 10th	Night	19% 26% 35% 18% 2	800
	11th to 20th	Night	20% 22% 35% 20% 4	783
	21st to end	Night	21% 24% 33% 18% 3	660
March	1st to 10th	Night	18% 21% 36% 20% 5%	800
	11th to 20th	Night	18% 22% 37% 19% 4 1	800
	21st to end	Night	20% 16% 30% 26% 7% 1	880
April	1st to 10th	Night	23% 17% 33% 23% 3	800
	11th to 20th	Night	21% 15% 30% 23% 9% 1	646
	21st to end	Night	23% 14% 28% 25% 10%	600
May	1st to 10th	Night	19% 8% 27% 33% 11% 2	600
	11th to 20th	Night	17% 8% 28% 35% 11% 1	454
	21st to end	Night	15% 6% 27% 39% 14%	433
June	1st to 10th	Night	16% 10% 30% 34% 10% 1	400
	11th to 20th	Night	11% 11% 23% 40% 16%	400
	21st to end	Night	17% 6% 25% 34% 16% 1	400
July	1st to 10th	Night	10% 5% 19% 46% 19% 1	390
	11th to 20th	Night	11% 5% 28% 34% 21% 1	403
	21st to end	Night	10% 4 25% 42% 18% 1	657
August	1st to 10th	Night	12% 5% 21% 37% 24% 1	597
	11th to 20th	Night	10% 5% 20% 36% 26% 4	594
	21st to end	Night	15% 7% 23% 31% 22% 2	686
September	1st to 10th	Night	14% 9% 24% 32% 17% 5%	800
	11th to 20th	Night	15% 5% 21% 36% 19% 5%	800
	21st to end	Night	19% 11% 22% 30% 14% 4	800
October	1st to 10th	Night	23% 10% 29% 24% 13% 1	800
	11th to 20th	Night	27% 18% 26% 22% 6% 1	800
	21st to end	Night	31% 20% 28% 17% 3	880
November	1st to 10th	Night	28% 18% 31% 16% 6%	820
	11th to 20th	Night	23% 27% 28% 17% 4 1	829
	21st to end	Night	26% 24% 33% 15% 2	800
December	1st to 10th	Night	27% 25% 33% 12% 4	800
	11th to 20th	Night	21% 28% 35% 13% 2 1	800
	21st to end	Night	27% 24% 34% 13% 2	1040

Page generated at 2025-11-15 00:55:58. Version ac07

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