Campbell Valley Regional Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Campbell Valley Regional Park clear sky chart from 2005-11-06 to 2026-01-02.

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	21% 9% 3 7% 4 4 4 3 5% 6% 35%	131347
	Night	26% 9% 3 7% 4 4 4 3 4 5% 31%	128719
Transparency	Day	32% 40% 10% 12% 5% 1	131056
	Night	36% 39% 9% 11% 5% 1	128588
Seeing	Day	22% 7% 19% 26% 20% 6%	16723
	Night	29% 8% 16% 24% 20% 5%	25018

By Month

Percentage Cloud Cover NW (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	40% 12% 4 9% 5% 4 5% 3 4 4 11%	3186
	11th to 20th	Day	21% 11% 3 7% 5% 3 3 3 4 7% 32%	3223
	21st to end	Day	41% 11% 3 6% 3 3 2 2 2 3 24%	4032
February	1st to 10th	Day	33% 12% 3 9% 5% 5% 4 3 4 6% 18%	1800
	11th to 20th	Day	31% 11% 3 8% 5% 4 5% 3 5% 5% 22%	1755
	21st to end	Day	28% 15% 3 8% 5% 4 4 3 5% 5% 21%	1517
March	1st to 10th	Day	26% 14% 3 9% 5% 5% 4 4 5% 6% 19%	4640
	11th to 20th	Day	22% 12% 3 8% 6% 5% 5% 3 5% 6% 25%	5000
	21st to end	Day	27% 12% 4 9% 6% 5% 4 4 5% 6% 18%	5655
April	1st to 10th	Day	27% 11% 4 9% 5% 5% 5% 4 5% 7% 21%	2400
	11th to 20th	Day	21% 11% 3 6% 6% 5% 4 4 6% 6% 28%	2448
	21st to end	Day	24% 9% 3 7% 4 4 4 5% 6% 6% 29%	2669
May	1st to 10th	Day	14% 8% 3 7% 3 3 3 3 5% 6% 44%	6320
	11th to 20th	Day	18% 10% 3 7% 5% 4 4 4 6% 8% 31%	6277
	21st to end	Day	21% 8% 3 6% 4 4 5% 4 6% 8% 30%	6943
June	1st to 10th	Day	21% 6% 2 7% 5% 5% 4 4 6% 7% 33%	3000
	11th to 20th	Day	22% 8% 2 8% 5% 5% 5% 4 5% 8% 29%	3000
	21st to end	Day	14% 7% 2 6% 5% 5% 5% 4 6% 7% 39%	3000
July	1st to 10th	Day	9% 3 1 4 3 3 3 3 4 6% 62%	6780
	11th to 20th	Day	5% 3 1 3 2 2 3 2 3 6% 72%	6780
	21st to end	Day	9% 4 1 3 3 3 3 3 5% 6% 61%	6920
August	1st to 10th	Day	6% 3 1 3 3 2 3 2 4 6% 68%	4519
	11th to 20th	Day	11% 6% 2 6% 4 4 4 3 5% 7% 48%	4156
	21st to end	Day	16% 7% 3 6% 4 4 4 4 5% 7% 42%	4536
September	1st to 10th	Day	13% 6% 2 6% 4 3 4 3 4 7% 48%	2400
	11th to 20th	Day	17% 7% 3 7% 5% 3 3 3 4 7% 40%	2400
	21st to end	Day	24% 6% 2 7% 4 3 4 4 5% 5% 36%	2106
October	1st to 10th	Day	21% 6% 2 7% 5% 6% 5% 4 6% 8% 31%	3280
	11th to 20th	Day	35% 7% 3 7% 3 4 3 3 5% 6% 24%	3261
	21st to end	Day	30% 12% 4 9% 5% 4 5% 4 6% 6% 16%	3307
November	1st to 10th	Day	38% 9% 2 6% 6% 5% 3 3 5% 5% 17%	1648
	11th to 20th	Day	36% 12% 3 6% 5% 3 3 3 4 4 21%	1680
	21st to end	Day	36% 12% 4 7% 5% 4 3 3 5% 5% 17%	1680
December	1st to 10th	Day	26% 10% 3 8% 5% 4 5% 3 5% 6% 24%	2700
	11th to 20th	Day	40% 14% 4 7% 5% 3 4 3 4 4 12%	2754
	21st to end	Day	36% 15% 4 10% 5% 5% 4 3 4 4 11%	3575
January	1st to 10th	Night	39% 13% 4 9% 4 4 4 3 3 4 14%	6781
	11th to 20th	Night	23% 8% 2 6% 4 4 4 4 6% 9% 31%	6672
	21st to end	Night	38% 10% 3 6% 3 3 2 2 3 4 27%	6910
February	1st to 10th	Night	35% 12% 3 7% 4 4 4 2 4 5% 20%	2600
	11th to 20th	Night	31% 11% 3 8% 5% 4 3 2 4 4 25%	2532
	21st to end	Night	30% 12% 3 6% 5% 4 3 3 4 5% 24%	2112
March	1st to 10th	Night	23% 15% 3 7% 5% 5% 4 3 5% 7% 22%	5250
	11th to 20th	Night	26% 11% 3 7% 4 4 5% 3 5% 6% 27%	4999
	21st to end	Night	36% 15% 4 8% 4 3 3 3 4 4 16%	5319
April	1st to 10th	Night	28% 11% 3 8% 5% 4 4 3 6% 6% 22%	2000
	11th to 20th	Night	22% 10% 3 8% 5% 4 4 4 5% 5% 30%	1900
	21st to end	Night	26% 9% 3 8% 5% 4 4 3 5% 6% 27%	1730
May	1st to 10th	Night	16% 9% 3 6% 4 3 3 2 3 4 46%	3640
	11th to 20th	Night	18% 8% 3 7% 5% 4 4 3 5% 6% 36%	3616
	21st to end	Night	17% 9% 4 9% 6% 6% 5% 4 5% 6% 29%	3928
June	1st to 10th	Night	20% 8% 2 7% 5% 4 5% 4 6% 6% 34%	1400
	11th to 20th	Night	19% 9% 4 8% 6% 5% 5% 4 5% 6% 29%	1400
	21st to end	Night	15% 6% 2 6% 5% 5% 3 4 6% 7% 42%	1400
July	1st to 10th	Night	8% 3 1 5% 3 2 3 2 4 5% 62%	3180
	11th to 20th	Night	4 2 1 2 2 1 2 2 3 4 78%	3180
	21st to end	Night	6% 4 1 4 3 3 3 3 4 6% 64%	3922
August	1st to 10th	Night	5% 2 1 2 2 2 2 3 4 7% 70%	2630
	11th to 20th	Night	10% 5% 3 6% 4 3 3 3 5% 8% 50%	2902
	21st to end	Night	12% 6% 2 6% 5% 4 5% 4 7% 9% 42%	3377
September	1st to 10th	Night	9% 3 2 4 3 3 4 3 6% 7% 56%	2000
	11th to 20th	Night	19% 6% 2 6% 4 4 4 3 4 6% 43%	2000
	21st to end	Night	21% 6% 3 7% 4 3 4 3 4 6% 39%	2289
October	1st to 10th	Night	20% 7% 2 7% 6% 5% 5% 4 5% 6% 32%	3920
	11th to 20th	Night	30% 7% 2 6% 4 3 4 4 4 6% 29%	3897
	21st to end	Night	30% 10% 3 8% 4 4 4 3 4 5% 25%	4494
November	1st to 10th	Night	39% 9% 3 7% 5% 4 5% 3 4 4 18%	2870
	11th to 20th	Night	38% 10% 3 6% 4 4 3 3 4 4 22%	2940
	21st to end	Night	37% 11% 3 8% 5% 4 4 3 4 4 18%	2940
December	1st to 10th	Night	27% 9% 3 7% 5% 5% 6% 5% 6% 7% 21%	4700
	11th to 20th	Night	42% 14% 4 8% 4 4 3 2 3 4 12%	5666
	21st to end	Night	36% 14% 4 10% 5% 4 4 3 3 4 14%	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	58% 29% 6% 6% 1 1	3186
	11th to 20th	Day	35% 28% 7% 19% 8% 3	3244
	21st to end	Day	50% 28% 4 13% 5%	4032
February	1st to 10th	Day	28% 61% 2 3 3 2	1800
	11th to 20th	Day	27% 62% 3 5% 3 1	1764
	21st to end	Day	25% 62% 4 5% 2 1	1517
March	1st to 10th	Day	46% 32% 9% 10% 3	4640
	11th to 20th	Day	44% 31% 8% 15% 2	5000
	21st to end	Day	50% 33% 9% 6% 2	5655
April	1st to 10th	Day	25% 64% 5% 5% 1	2400
	11th to 20th	Day	23% 63% 5% 7% 2 1	2448
	21st to end	Day	23% 63% 4 7% 3	2669
May	1st to 10th	Day	29% 32% 11% 20% 8%	6320
	11th to 20th	Day	39% 34% 16% 11% 1	6280
	21st to end	Day	36% 35% 15% 12% 2	6944
June	1st to 10th	Day	18% 63% 8% 8% 3	3000
	11th to 20th	Day	21% 63% 6% 7% 3	3000
	21st to end	Day	19% 62% 8% 9% 3	3000
July	1st to 10th	Day	19% 27% 14% 16% 16% 7%	6706
	11th to 20th	Day	10% 26% 16% 26% 19% 2	6699
	21st to end	Day	21% 28% 24% 21% 6% 1	6726
August	1st to 10th	Day	11% 37% 8% 29% 14% 1	4502
	11th to 20th	Day	30% 39% 16% 11% 3 1	4195
	21st to end	Day	30% 38% 11% 11% 10% 1	4535
September	1st to 10th	Day	20% 59% 6% 10% 4 1	2400
	11th to 20th	Day	23% 58% 5% 8% 6%	2400
	21st to end	Day	22% 58% 8% 8% 4	2106
October	1st to 10th	Day	36% 38% 12% 13% 2	3280
	11th to 20th	Day	43% 36% 7% 8% 6%	3261
	21st to end	Day	46% 38% 5% 7% 3	3307
November	1st to 10th	Day	33% 55% 6% 5% 1	1648
	11th to 20th	Day	30% 56% 4 6% 3 2	1680
	21st to end	Day	29% 55% 6% 5% 5% 1	1680
December	1st to 10th	Day	38% 37% 7% 13% 5%	2700
	11th to 20th	Day	55% 32% 7% 4 1	2757
	21st to end	Day	59% 30% 7% 4 1	3575
January	1st to 10th	Night	56% 29% 6% 7% 2	6781
	11th to 20th	Night	31% 31% 12% 16% 8% 2	6713
	21st to end	Night	46% 29% 7% 13% 5%	6910
February	1st to 10th	Night	27% 61% 3 3 4 3	2600
	11th to 20th	Night	28% 61% 3 5% 2 1	2534
	21st to end	Night	22% 62% 4 7% 2 1	2112
March	1st to 10th	Night	43% 33% 9% 10% 5%	5250
	11th to 20th	Night	40% 33% 10% 16% 2	5000
	21st to end	Night	54% 31% 11% 4 1	5319
April	1st to 10th	Night	25% 63% 4 7% 1	2000
	11th to 20th	Night	22% 63% 5% 6% 3 1	1900
	21st to end	Night	22% 63% 5% 7% 3	1730
May	1st to 10th	Night	30% 29% 7% 25% 8%	3637
	11th to 20th	Night	36% 34% 18% 11% 2	3616
	21st to end	Night	41% 33% 12% 13% 1	3928
June	1st to 10th	Night	17% 63% 8% 8% 3 1	1400
	11th to 20th	Night	20% 64% 5% 9% 3	1400
	21st to end	Night	17% 61% 9% 10% 3	1400
July	1st to 10th	Night	18% 26% 12% 23% 14% 7%	3145
	11th to 20th	Night	7% 25% 15% 27% 22% 3	3138
	21st to end	Night	19% 26% 19% 23% 11% 1	3812
August	1st to 10th	Night	8% 35% 9% 29% 19% 1	2622
	11th to 20th	Night	28% 38% 17% 12% 3 1	2929
	21st to end	Night	28% 40% 11% 12% 8% 1	3377
September	1st to 10th	Night	16% 60% 9% 9% 5% 1	2000
	11th to 20th	Night	21% 59% 6% 7% 6% 1	2000
	21st to end	Night	22% 58% 6% 10% 4	2289
October	1st to 10th	Night	39% 38% 12% 9% 2	3920
	11th to 20th	Night	40% 36% 7% 11% 5%	3897
	21st to end	Night	44% 38% 7% 8% 3	4494
November	1st to 10th	Night	34% 54% 6% 5% 1	2870
	11th to 20th	Night	31% 55% 4 5% 3 2	2940
	21st to end	Night	31% 56% 4 3 5% 1	2940
December	1st to 10th	Night	40% 38% 9% 9% 3	4700
	11th to 20th	Night	55% 33% 5% 5% 1	5662
	21st to end	Night	57% 29% 6% 6% 1	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	37% 10% 24% 13% 10% 5%	202
	11th to 20th	Day	37% 13% 19% 15% 13% 5%	200
	21st to end	Day	39% 11% 19% 14% 11% 5%	235
February	1st to 10th	Day	39% 11% 21% 17% 11% 2	400
	11th to 20th	Day	35% 9% 24% 20% 12% 1	395
	21st to end	Day	32% 14% 21% 19% 11% 2	349
March	1st to 10th	Day	31% 9% 24% 20% 13% 3	500
	11th to 20th	Day	29% 12% 17% 20% 16% 6%	500
	21st to end	Day	32% 9% 23% 22% 12% 2	550
April	1st to 10th	Day	28% 11% 20% 24% 15% 2	500
	11th to 20th	Day	21% 8% 28% 25% 14% 4	492
	21st to end	Day	23% 8% 22% 29% 15% 4	500
May	1st to 10th	Day	13% 7% 22% 35% 19% 3	503
	11th to 20th	Day	19% 5% 17% 28% 25% 5%	528
	21st to end	Day	18% 6% 23% 29% 19% 5%	587
June	1st to 10th	Day	19% 5% 21% 32% 19% 4	730
	11th to 20th	Day	18% 7% 23% 34% 15% 3	730
	21st to end	Day	14% 4 18% 33% 26% 5%	730
July	1st to 10th	Day	12% 4 17% 34% 28% 6%	721
	11th to 20th	Day	6% 5% 16% 38% 29% 7%	718
	21st to end	Day	7% 2 13% 30% 37% 11%	595
August	1st to 10th	Day	7% 3 13% 31% 33% 13%	527
	11th to 20th	Day	6% 3 11% 36% 33% 11%	517
	21st to end	Day	13% 4 17% 30% 27% 10%	583
September	1st to 10th	Day	11% 4 19% 34% 25% 7%	530
	11th to 20th	Day	17% 5% 19% 26% 26% 7%	530
	21st to end	Day	23% 7% 18% 25% 21% 6%	530
October	1st to 10th	Day	23% 8% 21% 22% 19% 9%	530
	11th to 20th	Day	36% 6% 15% 20% 17% 6%	530
	21st to end	Day	32% 15% 19% 18% 11% 5%	439
November	1st to 10th	Day	35% 14% 22% 16% 12% 1	220
	11th to 20th	Day	39% 11% 16% 13% 12% 8%	220
	21st to end	Day	37% 11% 21% 14% 9% 8%	220
December	1st to 10th	Day	39% 13% 14% 10% 15% 9%	220
	11th to 20th	Day	45% 16% 14% 14% 10% 1	220
	21st to end	Day	42% 13% 19% 17% 7% 1	242
January	1st to 10th	Night	43% 13% 16% 16% 9% 2	905
	11th to 20th	Night	39% 8% 16% 18% 17% 2	885
	21st to end	Night	40% 7% 15% 22% 14% 3	880
February	1st to 10th	Night	38% 10% 20% 22% 7% 2	800
	11th to 20th	Night	34% 10% 19% 24% 11% 1	784
	21st to end	Night	35% 10% 20% 22% 11% 3	660
March	1st to 10th	Night	31% 9% 21% 21% 16% 2	800
	11th to 20th	Night	34% 10% 19% 19% 15% 3	800
	21st to end	Night	34% 9% 18% 24% 13% 3	880
April	1st to 10th	Night	31% 6% 18% 27% 14% 3	800
	11th to 20th	Night	24% 8% 18% 29% 17% 4	712
	21st to end	Night	27% 7% 16% 29% 17% 5%	530
May	1st to 10th	Night	18% 5% 15% 29% 30% 4	400
	11th to 20th	Night	18% 6% 10% 28% 33% 5%	394
	21st to end	Night	16% 4 13% 32% 29% 6%	433
June	1st to 10th	Night	19% 5% 17% 30% 26% 4	400
	11th to 20th	Night	18% 7% 18% 32% 22% 4	400
	21st to end	Night	15% 2 13% 31% 33% 7%	400
July	1st to 10th	Night	9% 3 12% 30% 41% 5%	390
	11th to 20th	Night	6% 4 13% 33% 37% 7%	388
	21st to end	Night	5% 3 8% 29% 45% 10%	438
August	1st to 10th	Night	8% 2 9% 24% 42% 16%	406
	11th to 20th	Night	8% 2 7% 25% 44% 14%	594
	21st to end	Night	9% 3 11% 25% 41% 10%	740
September	1st to 10th	Night	10% 2 10% 34% 36% 10%	800
	11th to 20th	Night	18% 4 13% 20% 33% 12%	800
	21st to end	Night	22% 5% 14% 25% 29% 5%	800
October	1st to 10th	Night	21% 6% 14% 27% 25% 8%	800
	11th to 20th	Night	32% 7% 15% 21% 19% 6%	800
	21st to end	Night	34% 9% 18% 24% 12% 3	880
November	1st to 10th	Night	40% 11% 17% 22% 10% 1	820
	11th to 20th	Night	41% 9% 20% 17% 11% 3	840
	21st to end	Night	39% 10% 16% 20% 11% 4	840
December	1st to 10th	Night	35% 7% 17% 24% 14% 3	840
	11th to 20th	Night	46% 13% 17% 17% 5% 1	934
	21st to end	Night	43% 12% 22% 18% 5%	1045

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