Chain Lake Provincial Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chain Lake Provincial Park clear sky chart from 2005-11-06 to 2025-09-19.

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	7% 8% 3 7% 5% 5% 5% 4 6% 8% 42%	130527
	Night	5% 8% 3 8% 5% 5% 5% 4 6% 8% 43%	127259
Transparency	Day	38% 8% 15% 23% 13% 3	130234
	Night	37% 8% 16% 23% 13% 3	127129
Seeing	Day	14% 18% 31% 23% 11% 3	16482
	Night	11% 17% 32% 28% 11% 2	25483

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	1 6% 6% 11% 7% 7% 6% 5% 6% 7% 38%	3179
	11th to 20th	Day	2 6% 3 9% 8% 7% 6% 5% 7% 9% 39%	3360
	21st to end	Day	1 6% 3 8% 4 4 4 3 7% 10% 49%	4004
February	1st to 10th	Day	2 7% 3 9% 8% 6% 6% 5% 8% 9% 36%	1605
	11th to 20th	Day	2 10% 4 9% 7% 6% 7% 5% 6% 10% 35%	1755
	21st to end	Day	2 10% 5% 11% 6% 5% 6% 4 7% 9% 36%	1635
March	1st to 10th	Day	2 7% 4 9% 5% 4 5% 4 7% 11% 42%	4518
	11th to 20th	Day	2 8% 3 8% 6% 5% 5% 5% 6% 8% 44%	4945
	21st to end	Day	4 17% 7% 14% 5% 5% 4 3 5% 8% 28%	5571
April	1st to 10th	Day	7% 14% 4 10% 5% 6% 4 5% 7% 8% 32%	2435
	11th to 20th	Day	7% 16% 5% 9% 5% 5% 5% 4 6% 8% 30%	2570
	21st to end	Day	9% 14% 4 8% 6% 4 5% 4 7% 7% 33%	2600
May	1st to 10th	Day	12% 14% 3 6% 4 3 3 3 4 7% 40%	6045
	11th to 20th	Day	11% 10% 3 10% 6% 6% 6% 5% 7% 8% 27%	6727
	21st to end	Day	11% 8% 2 7% 5% 5% 5% 4 7% 7% 38%	7405
June	1st to 10th	Day	15% 9% 3 7% 6% 5% 5% 5% 6% 7% 32%	3000
	11th to 20th	Day	20% 8% 3 7% 6% 6% 5% 5% 6% 7% 28%	3000
	21st to end	Day	9% 5% 2 5% 6% 5% 6% 6% 7% 8% 41%	3000
July	1st to 10th	Day	7% 4 2 5% 4 5% 5% 4 7% 9% 49%	6780
	11th to 20th	Day	9% 4 2 5% 3 4 5% 5% 7% 8% 47%	6780
	21st to end	Day	8% 5% 1 5% 3 4 4 4 6% 8% 54%	7062
August	1st to 10th	Day	9% 5% 2 5% 4 4 6% 6% 8% 9% 42%	4541
	11th to 20th	Day	7% 4 2 5% 4 4 6% 5% 6% 9% 48%	4170
	21st to end	Day	8% 3 1 4 3 4 4 4 6% 7% 56%	4664
September	1st to 10th	Day	11% 6% 2 5% 4 3 4 3 4 7% 51%	2455
	11th to 20th	Day	11% 5% 2 5% 5% 4 4 4 4 7% 48%	2179
	21st to end	Day	9% 8% 2 4 3 3 5% 4 5% 8% 49%	2090
October	1st to 10th	Day	6% 6% 2 6% 4 4 5% 4 6% 11% 47%	3372
	11th to 20th	Day	3 7% 2 6% 4 4 4 4 8% 12% 47%	2916
	21st to end	Day	4 8% 3 7% 5% 4 5% 4 6% 8% 47%	3101
November	1st to 10th	Day	5% 13% 4 8% 6% 4 4 5% 6% 6% 39%	1679
	11th to 20th	Day	3 8% 4 8% 5% 5% 4 4 6% 9% 46%	1554
	21st to end	Day	3 12% 4 10% 5% 5% 5% 4 6% 8% 40%	1400
December	1st to 10th	Day	1 5% 3 9% 6% 4 5% 5% 6% 12% 45%	2290
	11th to 20th	Day	2 7% 3 9% 7% 5% 5% 4 8% 9% 41%	2642
	21st to end	Day	2 7% 4 10% 6% 6% 5% 4 5% 8% 43%	3498
January	1st to 10th	Night	2 9% 5% 11% 7% 7% 6% 5% 7% 8% 33%	6766
	11th to 20th	Night	1 6% 3 11% 8% 7% 6% 6% 8% 9% 36%	6580
	21st to end	Night	1 7% 3 10% 6% 5% 5% 4 7% 9% 44%	6952
February	1st to 10th	Night	2 7% 4 12% 6% 6% 5% 5% 7% 9% 38%	2795
	11th to 20th	Night	1 10% 5% 11% 7% 5% 6% 5% 6% 8% 36%	2532
	21st to end	Night	2 8% 5% 11% 7% 7% 6% 4 6% 6% 39%	1995
March	1st to 10th	Night	1 8% 3 10% 8% 7% 5% 4 7% 9% 39%	5376
	11th to 20th	Night	2 7% 3 8% 5% 5% 5% 4 6% 9% 45%	5054
	21st to end	Night	5% 16% 6% 11% 5% 4 5% 4 6% 9% 28%	5402
April	1st to 10th	Night	6% 13% 4 9% 5% 4 3 4 5% 7% 40%	1964
	11th to 20th	Night	8% 13% 4 9% 4 4 5% 4 6% 7% 35%	1781
	21st to end	Night	7% 12% 4 10% 5% 4 5% 4 5% 7% 37%	1800
May	1st to 10th	Night	11% 13% 3 7% 4 3 3 4 4 7% 42%	3926
	11th to 20th	Night	12% 9% 3 9% 6% 5% 5% 4 6% 8% 34%	3164
	21st to end	Night	11% 6% 2 7% 4 5% 5% 4 5% 7% 44%	3470
June	1st to 10th	Night	14% 7% 3 6% 5% 5% 4 4 7% 5% 41%	1400
	11th to 20th	Night	18% 8% 2 6% 5% 5% 4 3 5% 8% 36%	1400
	21st to end	Night	7% 4 2 4 4 4 5% 5% 6% 8% 51%	1400
July	1st to 10th	Night	6% 4 1 4 3 4 5% 4 7% 9% 54%	3180
	11th to 20th	Night	7% 5% 2 5% 4 3 4 3 6% 7% 54%	3180
	21st to end	Night	9% 5% 2 4 3 3 3 2 4 6% 57%	3777
August	1st to 10th	Night	10% 6% 2 5% 4 3 4 3 5% 8% 49%	2609
	11th to 20th	Night	6% 4 2 5% 4 5% 6% 4 7% 9% 48%	2887
	21st to end	Night	6% 3 1 5% 3 4 4 4 5% 8% 57%	3245
September	1st to 10th	Night	10% 4 1 4 3 3 4 3 5% 7% 56%	1942
	11th to 20th	Night	11% 8% 2 3 2 3 3 3 6% 7% 53%	2178
	21st to end	Night	9% 7% 2 4 3 3 3 3 6% 8% 52%	2090
October	1st to 10th	Night	5% 6% 2 4 3 3 4 4 5% 7% 57%	3604
	11th to 20th	Night	3 6% 2 4 3 3 4 5% 8% 10% 52%	4010
	21st to end	Night	3 8% 3 6% 4 4 4 4 6% 7% 51%	4457
November	1st to 10th	Night	5% 12% 5% 8% 5% 4 5% 4 7% 7% 39%	2600
	11th to 20th	Night	2 8% 3 7% 6% 5% 5% 4 7% 9% 46%	2845
	21st to end	Night	2 9% 3 9% 5% 6% 4 3 7% 9% 42%	3000
December	1st to 10th	Night	1 6% 3 7% 5% 5% 5% 5% 7% 10% 45%	4890
	11th to 20th	Night	1 9% 4 11% 6% 5% 6% 5% 8% 10% 37%	5550
	21st to end	Night	2 10% 4 10% 5% 4 5% 4 6% 7% 42%	7458

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	44% 7% 12% 21% 13% 3	3179
	11th to 20th	Day	42% 6% 14% 19% 16% 4	3382
	21st to end	Day	28% 10% 14% 32% 14% 1	4004
February	1st to 10th	Day	42% 12% 14% 18% 10% 2	1605
	11th to 20th	Day	43% 10% 16% 20% 9% 3	1764
	21st to end	Day	45% 8% 15% 18% 12% 2	1635
March	1st to 10th	Day	32% 9% 16% 21% 21% 1	4518
	11th to 20th	Day	36% 6% 17% 24% 16% 1	4946
	21st to end	Day	53% 8% 15% 16% 7% 1	5571
April	1st to 10th	Day	49% 9% 16% 17% 8% 1	2435
	11th to 20th	Day	51% 8% 14% 17% 9% 1	2570
	21st to end	Day	47% 9% 15% 18% 9% 1	2600
May	1st to 10th	Day	46% 5% 10% 20% 17% 2	6045
	11th to 20th	Day	49% 11% 13% 20% 6%	6731
	21st to end	Day	40% 10% 18% 19% 13% 1	7406
June	1st to 10th	Day	48% 10% 15% 17% 10% 1	3000
	11th to 20th	Day	53% 9% 11% 15% 10% 1	3000
	21st to end	Day	35% 11% 16% 24% 12% 2	3000
July	1st to 10th	Day	29% 7% 15% 24% 20% 5%	6706
	11th to 20th	Day	31% 7% 16% 29% 14% 3	6699
	21st to end	Day	28% 5% 13% 26% 17% 11%	6864
August	1st to 10th	Day	33% 10% 16% 27% 12% 2	4524
	11th to 20th	Day	29% 9% 21% 30% 10% 2	4209
	21st to end	Day	26% 6% 13% 38% 16% 2	4663
September	1st to 10th	Day	34% 6% 13% 24% 17% 6%	2455
	11th to 20th	Day	35% 8% 13% 26% 16% 2	2179
	21st to end	Day	33% 8% 14% 29% 13% 3	2090
October	1st to 10th	Day	32% 7% 16% 35% 10% 1	3372
	11th to 20th	Day	30% 6% 22% 25% 15% 3	2916
	21st to end	Day	35% 7% 14% 26% 14% 4	3101
November	1st to 10th	Day	44% 9% 14% 20% 13%	1679
	11th to 20th	Day	35% 10% 19% 22% 13% 1	1554
	21st to end	Day	41% 8% 20% 19% 9% 4	1400
December	1st to 10th	Day	33% 8% 22% 26% 9% 3	2290
	11th to 20th	Day	38% 8% 23% 23% 7% 1	2644
	21st to end	Day	38% 7% 12% 23% 17% 4	3498
January	1st to 10th	Night	45% 10% 12% 23% 8% 2	6766
	11th to 20th	Night	42% 7% 14% 18% 13% 5%	6620
	21st to end	Night	33% 9% 16% 25% 15% 2	6952
February	1st to 10th	Night	43% 9% 14% 18% 13% 3	2795
	11th to 20th	Night	44% 9% 16% 18% 11% 2	2533
	21st to end	Night	45% 7% 13% 21% 11% 3	1995
March	1st to 10th	Night	38% 8% 17% 21% 14% 3	5376
	11th to 20th	Night	34% 8% 19% 23% 16% 1	5054
	21st to end	Night	51% 8% 18% 14% 7% 1	5402
April	1st to 10th	Night	42% 8% 15% 22% 11% 1	1964
	11th to 20th	Night	46% 8% 13% 23% 9% 1	1781
	21st to end	Night	47% 8% 13% 22% 8% 2	1800
May	1st to 10th	Night	43% 6% 11% 25% 13% 2	3923
	11th to 20th	Night	42% 8% 14% 27% 7% 1	3164
	21st to end	Night	37% 9% 16% 26% 11% 1	3470
June	1st to 10th	Night	43% 8% 15% 23% 10% 1	1400
	11th to 20th	Night	46% 8% 15% 20% 10% 1	1400
	21st to end	Night	28% 9% 19% 28% 14% 2	1400
July	1st to 10th	Night	24% 6% 19% 22% 24% 5%	3145
	11th to 20th	Night	28% 7% 18% 30% 13% 4	3138
	21st to end	Night	30% 5% 14% 25% 16% 10%	3670
August	1st to 10th	Night	32% 7% 17% 24% 16% 2	2601
	11th to 20th	Night	30% 7% 20% 29% 11% 2	2914
	21st to end	Night	24% 6% 16% 34% 18% 2	3245
September	1st to 10th	Night	28% 6% 15% 30% 16% 5%	1942
	11th to 20th	Night	30% 7% 15% 28% 16% 4	2178
	21st to end	Night	30% 8% 18% 27% 14% 4	2090
October	1st to 10th	Night	26% 6% 12% 30% 24% 2	3604
	11th to 20th	Night	26% 7% 20% 26% 19% 3	4010
	21st to end	Night	32% 6% 15% 31% 16% 1	4457
November	1st to 10th	Night	42% 10% 16% 20% 11% 2	2600
	11th to 20th	Night	33% 11% 19% 21% 16% 1	2845
	21st to end	Night	37% 9% 20% 20% 11% 4	3000
December	1st to 10th	Night	33% 8% 23% 22% 11% 3	4890
	11th to 20th	Night	40% 10% 23% 18% 9%	5547
	21st to end	Night	39% 6% 13% 22% 15% 5%	7458

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	7% 23% 31% 24% 11% 6%	200
	11th to 20th	Day	8% 17% 43% 25% 7% 2	200
	21st to end	Day	7% 30% 37% 17% 5% 3	220
February	1st to 10th	Day	14% 23% 35% 20% 5% 2	203
	11th to 20th	Day	10% 19% 38% 24% 8% 1	300
	21st to end	Day	14% 22% 36% 22% 5% 1	399
March	1st to 10th	Day	12% 25% 36% 16% 8% 2	500
	11th to 20th	Day	12% 23% 32% 23% 8% 2	500
	21st to end	Day	14% 25% 33% 18% 7% 2	550
April	1st to 10th	Day	15% 26% 34% 19% 4 1	500
	11th to 20th	Day	17% 24% 31% 18% 9% 1	492
	21st to end	Day	18% 24% 27% 19% 10% 2	500
May	1st to 10th	Day	19% 16% 29% 22% 11% 2	503
	11th to 20th	Day	21% 14% 23% 25% 15% 3	718
	21st to end	Day	21% 12% 22% 29% 15% 2	789
June	1st to 10th	Day	17% 19% 30% 22% 9% 2	730
	11th to 20th	Day	21% 18% 29% 21% 9% 2	730
	21st to end	Day	11% 13% 30% 27% 15% 4	730
July	1st to 10th	Day	10% 10% 31% 27% 19% 3	721
	11th to 20th	Day	12% 12% 30% 28% 15% 3	718
	21st to end	Day	8% 13% 32% 29% 15% 3	659
August	1st to 10th	Day	11% 13% 30% 31% 14% 2	527
	11th to 20th	Day	7% 14% 32% 29% 15% 3	517
	21st to end	Day	11% 14% 32% 25% 14% 4	583
September	1st to 10th	Day	14% 17% 29% 24% 11% 5%	530
	11th to 20th	Day	14% 15% 30% 24% 13% 3	523
	21st to end	Day	18% 25% 30% 19% 6% 2	490
October	1st to 10th	Day	16% 18% 30% 25% 10% 2	424
	11th to 20th	Day	15% 22% 30% 19% 11% 3	300
	21st to end	Day	17% 22% 35% 19% 4 3	330
November	1st to 10th	Day	18% 22% 32% 21% 6%	300
	11th to 20th	Day	20% 24% 37% 14% 4 1	276
	21st to end	Day	16% 23% 28% 21% 7% 7%	200
December	1st to 10th	Day	10% 21% 37% 23% 9% 2	200
	11th to 20th	Day	10% 22% 37% 22% 7% 2	200
	21st to end	Day	10% 17% 35% 25% 9% 4	220
January	1st to 10th	Night	10% 23% 40% 20% 6% 1	1000
	11th to 20th	Night	8% 21% 44% 20% 6% 1	931
	21st to end	Night	7% 22% 40% 23% 6% 1	880
February	1st to 10th	Night	8% 20% 35% 25% 9% 3	800
	11th to 20th	Night	7% 17% 38% 30% 8% 1	784
	21st to end	Night	8% 14% 38% 27% 11% 2	660
March	1st to 10th	Night	7% 20% 37% 25% 10% 2	800
	11th to 20th	Night	9% 21% 33% 29% 8% 1	800
	21st to end	Night	9% 16% 34% 30% 9% 3	880
April	1st to 10th	Night	12% 18% 32% 25% 11% 1	764
	11th to 20th	Night	15% 16% 31% 28% 10% 1	593
	21st to end	Night	12% 16% 33% 29% 10%	600
May	1st to 10th	Night	16% 12% 26% 31% 14% 1	530
	11th to 20th	Night	14% 10% 22% 33% 19% 2	394
	21st to end	Night	24% 6% 19% 30% 21% 1	433
June	1st to 10th	Night	17% 11% 28% 29% 14% 2	400
	11th to 20th	Night	21% 11% 28% 28% 13% 1	400
	21st to end	Night	10% 9% 24% 35% 22% 1	400
July	1st to 10th	Night	8% 7% 17% 45% 23%	390
	11th to 20th	Night	8% 7% 24% 41% 19% 2	388
	21st to end	Night	8% 6% 18% 45% 21% 2	438
August	1st to 10th	Night	10% 4 16% 41% 28% 2	398
	11th to 20th	Night	8% 4 24% 40% 23% 2	580
	21st to end	Night	8% 10% 25% 39% 16% 2	660
September	1st to 10th	Night	13% 9% 21% 34% 20% 4	727
	11th to 20th	Night	15% 6% 24% 31% 20% 4	792
	21st to end	Night	13% 17% 31% 24% 12% 4	760
October	1st to 10th	Night	14% 13% 27% 31% 13% 2	760
	11th to 20th	Night	11% 16% 31% 29% 10% 2	760
	21st to end	Night	12% 20% 34% 26% 7% 1	836
November	1st to 10th	Night	15% 23% 36% 19% 7%	845
	11th to 20th	Night	11% 27% 40% 18% 3 1	1000
	21st to end	Night	8% 25% 39% 20% 7% 2	1000
December	1st to 10th	Night	8% 23% 37% 23% 7% 2	1000
	11th to 20th	Night	7% 24% 38% 25% 6% 1	1000
	21st to end	Night	9% 21% 40% 21% 8% 1	1100

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