Maple Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Maple Ridge Observatory clear sky chart from 2005-11-06 to 2025-08-05.

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% 11% 4 9% 5% 5% 4 4 5% 7% 33%	125370
	Night	14% 12% 4 10% 6% 5% 4 4 5% 6% 30%	122841
Transparency	Day	50% 6% 11% 21% 11% 1	128874
	Night	52% 6% 12% 19% 10% 1	127425
Seeing	Day	20% 16% 33% 21% 8% 2	16486
	Night	20% 13% 32% 25% 9% 1	25895

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% 15% 7% 20% 9% 5% 5% 3 4 5% 16%	3543
	11th to 20th	Day	11% 17% 7% 21% 10% 6% 4 4 4 5% 11%	3589
	21st to end	Day	14% 19% 6% 15% 7% 6% 5% 3 5% 5% 15%	4026
February	1st to 10th	Day	11% 17% 6% 13% 9% 7% 6% 3 5% 5% 19%	1800
	11th to 20th	Day	11% 15% 6% 13% 8% 7% 5% 4 5% 5% 22%	1840
	21st to end	Day	10% 18% 6% 13% 8% 6% 4 4 4 5% 22%	1650
March	1st to 10th	Day	12% 11% 3 11% 5% 6% 4 4 5% 6% 32%	4519
	11th to 20th	Day	11% 13% 6% 10% 6% 5% 5% 4 7% 6% 26%	4980
	21st to end	Day	20% 12% 5% 10% 5% 4 4 3 5% 5% 25%	5465
April	1st to 10th	Day	18% 15% 4 8% 5% 4 4 3 4 6% 28%	2374
	11th to 20th	Day	18% 12% 3 7% 4 3 3 4 6% 5% 34%	2563
	21st to end	Day	16% 11% 3 7% 4 5% 4 3 5% 7% 35%	2600
May	1st to 10th	Day	18% 10% 3 6% 4 4 4 3 5% 6% 38%	5888
	11th to 20th	Day	12% 8% 3 7% 4 4 4 3 5% 7% 43%	5861
	21st to end	Day	14% 7% 2 6% 4 4 4 3 5% 7% 44%	7257
June	1st to 10th	Day	12% 6% 2 5% 5% 5% 4 4 6% 8% 41%	3000
	11th to 20th	Day	12% 7% 2 6% 5% 4 5% 5% 6% 8% 41%	3000
	21st to end	Day	14% 6% 2 7% 5% 5% 5% 4 5% 8% 40%	3000
July	1st to 10th	Day	14% 6% 2 6% 4 4 4 3 6% 8% 42%	6712
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 4 6% 9% 45%	6360
	21st to end	Day	8% 5% 2 5% 4 4 4 3 6% 10% 49%	6891
August	1st to 10th	Day	10% 5% 2 6% 4 5% 6% 5% 7% 9% 42%	4156
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 6% 9% 43%	4044
	21st to end	Day	12% 7% 3 7% 5% 5% 5% 4 6% 7% 40%	4532
September	1st to 10th	Day	12% 7% 2 7% 4 5% 5% 4 6% 7% 42%	2196
	11th to 20th	Day	13% 5% 1 6% 4 4 4 4 6% 7% 45%	2090
	21st to end	Day	17% 8% 2 8% 5% 4 4 4 6% 7% 35%	2090
October	1st to 10th	Day	17% 9% 3 7% 5% 4 4 3 5% 7% 36%	2024
	11th to 20th	Day	20% 12% 4 9% 6% 4 5% 4 4 6% 25%	1884
	21st to end	Day	21% 17% 4 9% 6% 5% 4 5% 5% 5% 18%	1881
November	1st to 10th	Day	14% 15% 5% 8% 6% 5% 4 4 6% 6% 27%	1762
	11th to 20th	Day	13% 14% 5% 12% 7% 6% 5% 4 5% 7% 21%	1715
	21st to end	Day	18% 19% 6% 10% 7% 4 4 4 5% 5% 18%	1600
December	1st to 10th	Day	13% 19% 8% 16% 7% 6% 5% 4 6% 5% 10%	2381
	11th to 20th	Day	17% 21% 6% 12% 8% 6% 5% 4 4 5% 14%	2621
	21st to end	Day	24% 23% 10% 14% 5% 7% 3 3 3 3 7%	3476
January	1st to 10th	Night	12% 12% 5% 21% 9% 6% 5% 4 6% 5% 16%	6417
	11th to 20th	Night	11% 14% 6% 18% 9% 7% 5% 4 5% 6% 14%	6316
	21st to end	Night	9% 16% 7% 15% 8% 6% 5% 4 5% 5% 19%	6936
February	1st to 10th	Night	10% 17% 5% 11% 8% 7% 5% 4 5% 6% 21%	2600
	11th to 20th	Night	12% 14% 5% 11% 8% 5% 5% 4 5% 6% 24%	2443
	21st to end	Night	15% 14% 5% 11% 6% 5% 5% 4 5% 6% 24%	1980
March	1st to 10th	Night	14% 10% 3 9% 6% 5% 5% 3 5% 6% 35%	5318
	11th to 20th	Night	10% 11% 4 9% 4 4 5% 4 6% 8% 34%	4979
	21st to end	Night	19% 13% 5% 10% 5% 3 3 3 4 5% 30%	5467
April	1st to 10th	Night	18% 12% 3 7% 4 4 5% 4 5% 6% 32%	2044
	11th to 20th	Night	18% 9% 3 7% 4 4 4 4 5% 6% 36%	1785
	21st to end	Night	16% 10% 3 9% 4 3 5% 4 5% 7% 34%	1800
May	1st to 10th	Night	14% 8% 3 7% 5% 5% 5% 4 5% 7% 36%	4053
	11th to 20th	Night	13% 8% 3 7% 4 4 5% 3 6% 7% 39%	4032
	21st to end	Night	20% 8% 3 5% 3 3 3 3 4 6% 41%	3633
June	1st to 10th	Night	13% 6% 2 6% 5% 5% 4 4 5% 8% 44%	1400
	11th to 20th	Night	9% 5% 2 7% 5% 4 5% 5% 8% 8% 41%	1400
	21st to end	Night	14% 6% 2 6% 4 4 4 4 5% 7% 44%	1400
July	1st to 10th	Night	10% 6% 2 6% 4 4 5% 4 5% 8% 46%	3249
	11th to 20th	Night	9% 6% 2 5% 4 4 4 4 5% 7% 51%	3620
	21st to end	Night	7% 5% 2 5% 4 4 4 4 6% 8% 52%	3980
August	1st to 10th	Night	9% 5% 2 6% 5% 4 4 3 5% 8% 48%	2861
	11th to 20th	Night	15% 5% 2 4 3 3 3 3 5% 8% 49%	2785
	21st to end	Night	10% 5% 2 5% 4 4 4 3 5% 8% 50%	3124
September	1st to 10th	Night	11% 5% 2 5% 4 4 4 4 5% 7% 48%	1962
	11th to 20th	Night	12% 4 2 5% 3 4 3 4 5% 7% 50%	2090
	21st to end	Night	17% 7% 2 7% 3 4 5% 3 5% 7% 40%	2090
October	1st to 10th	Night	15% 7% 3 7% 4 4 4 3 4 7% 42%	2155
	11th to 20th	Night	18% 12% 3 8% 5% 4 4 3 5% 7% 30%	2294
	21st to end	Night	24% 13% 3 8% 5% 4 5% 3 4 5% 25%	2717
November	1st to 10th	Night	13% 13% 4 7% 6% 4 4 4 5% 7% 32%	2536
	11th to 20th	Night	15% 15% 4 9% 5% 6% 5% 5% 5% 7% 23%	2685
	21st to end	Night	19% 17% 5% 10% 6% 4 4 3 6% 6% 20%	2800
December	1st to 10th	Night	13% 15% 7% 12% 6% 6% 5% 4 6% 7% 18%	4802
	11th to 20th	Night	12% 21% 7% 15% 7% 5% 4 3 4 5% 16%	5586
	21st to end	Night	23% 22% 9% 13% 6% 5% 4 2 4 3 8%	7502

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	69% 7% 9% 10% 3 1	3544
	11th to 20th	Day	75% 6% 6% 10% 4	3620
	21st to end	Day	70% 6% 11% 8% 5%	4026
February	1st to 10th	Day	65% 6% 10% 15% 4	1800
	11th to 20th	Day	62% 6% 11% 13% 8%	1849
	21st to end	Day	63% 6% 9% 15% 6%	1650
March	1st to 10th	Day	52% 5% 15% 17% 10% 2	4522
	11th to 20th	Day	56% 5% 14% 17% 7% 1	4980
	21st to end	Day	61% 5% 10% 17% 7% 1	5465
April	1st to 10th	Day	57% 5% 9% 18% 9% 1	2374
	11th to 20th	Day	49% 5% 10% 19% 16% 2	2563
	21st to end	Day	49% 5% 12% 17% 14% 3	2600
May	1st to 10th	Day	44% 6% 10% 20% 18% 2	5897
	11th to 20th	Day	40% 7% 12% 21% 18% 2	5865
	21st to end	Day	39% 6% 10% 20% 19% 5%	7257
June	1st to 10th	Day	38% 7% 11% 27% 14% 3	3000
	11th to 20th	Day	39% 7% 12% 24% 16% 2	3000
	21st to end	Day	41% 6% 12% 25% 13% 2	3000
July	1st to 10th	Day	40% 4 13% 28% 14% 1	6641
	11th to 20th	Day	34% 5% 12% 37% 11% 1	6285
	21st to end	Day	32% 4 12% 32% 18% 1	6693
August	1st to 10th	Day	37% 5% 15% 30% 13% 1	4143
	11th to 20th	Day	38% 5% 16% 29% 12%	4083
	21st to end	Day	41% 6% 13% 29% 9% 1	4531
September	1st to 10th	Day	39% 7% 12% 28% 13% 1	2196
	11th to 20th	Day	36% 6% 14% 30% 13% 1	2090
	21st to end	Day	46% 6% 16% 23% 9%	2090
October	1st to 10th	Day	36% 5% 10% 32% 16% 1	3362
	11th to 20th	Day	54% 4 8% 20% 14%	3112
	21st to end	Day	62% 5% 9% 18% 6%	3081
November	1st to 10th	Day	56% 6% 11% 21% 7%	1762
	11th to 20th	Day	59% 7% 14% 13% 6%	1715
	21st to end	Day	67% 6% 14% 10% 2	1600
December	1st to 10th	Day	73% 6% 12% 7% 2	2381
	11th to 20th	Day	71% 6% 8% 10% 5%	2621
	21st to end	Day	84% 4 4 6% 2	3476
January	1st to 10th	Night	66% 7% 11% 13% 3	6417
	11th to 20th	Night	69% 7% 9% 10% 4	6360
	21st to end	Night	65% 6% 9% 13% 7%	6936
February	1st to 10th	Night	62% 5% 11% 15% 6%	2600
	11th to 20th	Night	58% 7% 12% 16% 6%	2445
	21st to end	Night	59% 6% 12% 16% 6%	1980
March	1st to 10th	Night	50% 5% 15% 19% 10% 1	5328
	11th to 20th	Night	46% 5% 21% 20% 7% 1	4980
	21st to end	Night	56% 5% 10% 18% 10% 1	5467
April	1st to 10th	Night	52% 6% 9% 19% 13% 1	2044
	11th to 20th	Night	47% 4 8% 23% 16% 2	1785
	21st to end	Night	49% 6% 10% 16% 15% 3	1800
May	1st to 10th	Night	45% 8% 9% 18% 17% 3	4060
	11th to 20th	Night	42% 7% 9% 24% 18% 1	4033
	21st to end	Night	45% 6% 9% 21% 14% 5%	3634
June	1st to 10th	Night	38% 6% 11% 25% 17% 2	1400
	11th to 20th	Night	34% 8% 15% 24% 17% 2	1400
	21st to end	Night	39% 6% 12% 24% 14% 4	1400
July	1st to 10th	Night	36% 3 16% 25% 17% 2	3213
	11th to 20th	Night	33% 4 10% 34% 18% 1	3572
	21st to end	Night	30% 4 15% 32% 18% 1	3864
August	1st to 10th	Night	35% 4 14% 30% 16% 1	2850
	11th to 20th	Night	34% 5% 17% 30% 13% 2	2812
	21st to end	Night	33% 5% 15% 34% 13% 1	3124
September	1st to 10th	Night	33% 8% 13% 29% 16% 2	1962
	11th to 20th	Night	32% 6% 16% 33% 12%	2090
	21st to end	Night	43% 7% 16% 23% 11%	2090
October	1st to 10th	Night	33% 5% 12% 34% 16%	3597
	11th to 20th	Night	48% 4 11% 24% 13%	3805
	21st to end	Night	54% 4 13% 23% 5%	4467
November	1st to 10th	Night	49% 7% 14% 23% 7% 1	2536
	11th to 20th	Night	57% 9% 13% 15% 6%	2685
	21st to end	Night	64% 8% 14% 11% 3	2800
December	1st to 10th	Night	64% 6% 16% 12% 2	4802
	11th to 20th	Night	70% 7% 9% 9% 5%	5585
	21st to end	Night	81% 5% 5% 6% 3	7502

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	23% 18% 35% 20% 4	283
	11th to 20th	Day	24% 20% 39% 13% 4	300
	21st to end	Day	26% 18% 37% 13% 4 1	330
February	1st to 10th	Day	26% 25% 35% 12% 2	300
	11th to 20th	Day	22% 33% 34% 10% 1	300
	21st to end	Day	29% 31% 29% 10%	249
March	1st to 10th	Day	26% 26% 33% 13% 2 1	316
	11th to 20th	Day	24% 18% 37% 16% 5% 1	500
	21st to end	Day	31% 17% 33% 14% 5% 1	550
April	1st to 10th	Day	28% 20% 30% 16% 5% 1	500
	11th to 20th	Day	30% 19% 27% 15% 8% 2	492
	21st to end	Day	27% 18% 33% 15% 6% 1	500
May	1st to 10th	Day	21% 21% 33% 17% 6% 3	503
	11th to 20th	Day	18% 15% 37% 20% 7% 3	527
	21st to end	Day	15% 13% 36% 27% 6% 3	762
June	1st to 10th	Day	15% 16% 40% 21% 7% 1	730
	11th to 20th	Day	16% 15% 38% 22% 8% 2	730
	21st to end	Day	18% 12% 38% 24% 7% 2	730
July	1st to 10th	Day	11% 10% 34% 31% 12% 2	721
	11th to 20th	Day	12% 9% 36% 29% 10% 4	718
	21st to end	Day	11% 7% 36% 30% 13% 4	784
August	1st to 10th	Day	12% 10% 26% 30% 15% 8%	502
	11th to 20th	Day	10% 8% 24% 32% 16% 9%	479
	21st to end	Day	15% 11% 29% 26% 16% 3	539
September	1st to 10th	Day	14% 9% 36% 21% 13% 7%	490
	11th to 20th	Day	13% 9% 25% 31% 15% 7%	490
	21st to end	Day	22% 12% 25% 24% 13% 5%	490
October	1st to 10th	Day	24% 15% 28% 19% 13% 1	490
	11th to 20th	Day	26% 18% 33% 18% 4 1	474
	21st to end	Day	29% 26% 32% 9% 4	330
November	1st to 10th	Day	23% 21% 35% 15% 6%	300
	11th to 20th	Day	25% 25% 31% 14% 4	257
	21st to end	Day	31% 20% 34% 15% 2	200
December	1st to 10th	Day	27% 22% 34% 14% 4 1	200
	11th to 20th	Day	26% 27% 34% 10% 4	200
	21st to end	Day	33% 21% 30% 11% 4	220
January	1st to 10th	Night	20% 17% 39% 19% 4 1	1000
	11th to 20th	Night	24% 18% 33% 20% 6%	1000
	21st to end	Night	17% 14% 38% 24% 5% 1	1079
February	1st to 10th	Night	19% 20% 38% 19% 4	800
	11th to 20th	Night	20% 19% 33% 22% 5%	783
	21st to end	Night	24% 18% 36% 19% 3	660
March	1st to 10th	Night	18% 16% 38% 22% 6% 1	800
	11th to 20th	Night	20% 17% 36% 23% 5%	800
	21st to end	Night	22% 14% 33% 25% 6%	880
April	1st to 10th	Night	24% 15% 36% 20% 5% 1	644
	11th to 20th	Night	25% 11% 31% 23% 8% 1	593
	21st to end	Night	21% 13% 33% 25% 9% 1	600
May	1st to 10th	Night	16% 9% 35% 29% 10% 2	600
	11th to 20th	Night	20% 8% 29% 32% 11% 1	591
	21st to end	Night	14% 9% 28% 35% 14% 1	495
June	1st to 10th	Night	15% 7% 34% 33% 11%	400
	11th to 20th	Night	11% 8% 34% 34% 13% 1	400
	21st to end	Night	16% 8% 29% 34% 12% 1	400
July	1st to 10th	Night	7% 3 28% 44% 17%	426
	11th to 20th	Night	11% 3 24% 40% 20% 2	582
	21st to end	Night	9% 4 28% 37% 21% 1	657
August	1st to 10th	Night	10% 2 23% 41% 22% 2	579
	11th to 20th	Night	12% 4 21% 32% 26% 5%	564
	21st to end	Night	14% 6% 24% 34% 21% 1	627
September	1st to 10th	Night	12% 7% 27% 30% 19% 4	648
	11th to 20th	Night	14% 6% 25% 33% 18% 4	760
	21st to end	Night	21% 8% 25% 28% 15% 3	760
October	1st to 10th	Night	19% 10% 31% 27% 12% 1	760
	11th to 20th	Night	24% 14% 32% 24% 6%	760
	21st to end	Night	32% 14% 29% 20% 4 1	836
November	1st to 10th	Night	21% 16% 34% 21% 8% 1	780
	11th to 20th	Night	23% 19% 34% 18% 6%	800
	21st to end	Night	29% 14% 37% 17% 3	800
December	1st to 10th	Night	22% 19% 37% 17% 5%	931
	11th to 20th	Night	24% 20% 37% 15% 4 1	1000
	21st to end	Night	28% 17% 34% 17% 4	1100

Page generated at 2025-08-02 01:32:28. Version ac07

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