Aldergrove Lake Regional Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Aldergrove Lake Regional Park clear sky chart from 2005-11-06 to 2025-06-10.

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	24% 9% 3 7% 4 4 4 3 5% 6% 32%	123307
	Night	28% 10% 3 7% 4 4 4 3 4 5% 29%	123621
Transparency	Day	34% 39% 8% 13% 5% 1	123058
	Night	38% 38% 8% 11% 5% 1	123513
Seeing	Day	29% 8% 21% 24% 13% 5%	15949
	Night	35% 5% 14% 24% 18% 3	24298

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	41% 13% 4 8% 5% 4 4 2 4 4 11%	3179
	11th to 20th	Day	21% 11% 3 7% 4 4 3 2 4 6% 33%	3266
	21st to end	Day	42% 10% 3 6% 3 3 2 2 2 2 25%	4022
February	1st to 10th	Day	34% 11% 5% 8% 5% 4 4 3 4 5% 17%	1800
	11th to 20th	Day	32% 11% 3 8% 5% 5% 4 2 4 5% 22%	1755
	21st to end	Day	28% 16% 4 8% 5% 5% 4 3 5% 4 20%	1525
March	1st to 10th	Day	27% 15% 4 9% 5% 4 4 3 5% 6% 18%	4619
	11th to 20th	Day	24% 14% 4 9% 5% 4 4 3 4 5% 24%	5000
	21st to end	Day	29% 12% 3 9% 6% 5% 5% 4 4 6% 17%	5661
April	1st to 10th	Day	29% 12% 3 9% 6% 5% 5% 4 5% 6% 18%	2400
	11th to 20th	Day	21% 10% 4 10% 6% 5% 5% 3 6% 6% 24%	2439
	21st to end	Day	25% 10% 3 9% 5% 3 4 4 5% 5% 26%	2675
May	1st to 10th	Day	16% 8% 3 7% 4 4 4 3 4 5% 41%	6320
	11th to 20th	Day	21% 10% 3 8% 4 4 5% 4 6% 7% 29%	6277
	21st to end	Day	24% 8% 3 7% 4 4 4 4 6% 7% 27%	6903
June	1st to 10th	Day	23% 7% 3 8% 5% 5% 4 3 5% 7% 30%	2989
	11th to 20th	Day	23% 10% 4 8% 5% 4 4 4 5% 7% 25%	2850
	21st to end	Day	14% 8% 3 7% 5% 5% 5% 4 6% 7% 36%	2850
July	1st to 10th	Day	9% 4 1 4 2 3 3 3 3 5% 63%	4740
	11th to 20th	Day	6% 3 1 2 3 2 2 2 3 5% 70%	4740
	21st to end	Day	14% 4 2 4 2 3 3 3 4 6% 56%	4795
August	1st to 10th	Day	6% 3 1 4 2 2 3 2 4 6% 66%	4401
	11th to 20th	Day	14% 7% 3 6% 3 4 4 3 5% 7% 44%	4026
	21st to end	Day	18% 7% 2 6% 4 4 4 3 5% 7% 40%	4378
September	1st to 10th	Day	15% 6% 2 7% 4 3 4 3 4 7% 47%	2280
	11th to 20th	Day	18% 7% 3 8% 5% 4 3 3 4 6% 38%	2280
	21st to end	Day	25% 7% 3 6% 4 3 4 2 5% 6% 35%	2006
October	1st to 10th	Day	22% 7% 2 8% 5% 5% 5% 4 6% 7% 30%	3180
	11th to 20th	Day	37% 7% 2 6% 4 3 4 3 4 6% 23%	3161
	21st to end	Day	32% 11% 4 8% 4 4 5% 4 5% 6% 16%	3191
November	1st to 10th	Day	40% 9% 4 7% 4 5% 4 3 4 5% 16%	1568
	11th to 20th	Day	36% 13% 3 6% 4 4 3 3 4 4 21%	1600
	21st to end	Day	37% 13% 3 7% 4 3 3 3 4 5% 18%	1600
December	1st to 10th	Day	26% 10% 4 8% 5% 3 4 4 6% 6% 25%	2620
	11th to 20th	Day	40% 15% 3 7% 4 4 3 3 4 4 12%	2713
	21st to end	Day	40% 15% 4 9% 5% 4 4 2 3 4 10%	3498
January	1st to 10th	Night	41% 14% 4 8% 5% 4 3 2 3 3 14%	6766
	11th to 20th	Night	23% 8% 2 5% 4 4 4 4 6% 9% 31%	6629
	21st to end	Night	38% 10% 3 5% 3 3 2 2 2 3 28%	6930
February	1st to 10th	Night	35% 12% 3 8% 5% 4 3 3 3 4 21%	2600
	11th to 20th	Night	31% 13% 3 7% 5% 3 3 2 3 4 24%	2532
	21st to end	Night	30% 13% 3 6% 5% 4 4 3 3 5% 24%	2105
March	1st to 10th	Night	24% 16% 3 8% 4 4 4 3 5% 5% 23%	5271
	11th to 20th	Night	28% 11% 3 7% 4 4 4 3 5% 6% 25%	4999
	21st to end	Night	38% 13% 4 8% 4 3 3 2 4 4 17%	5314
April	1st to 10th	Night	30% 11% 3 7% 5% 4 4 3 5% 5% 21%	2000
	11th to 20th	Night	23% 10% 2 8% 5% 5% 5% 4 5% 6% 28%	1910
	21st to end	Night	27% 10% 3 8% 5% 4 4 3 5% 6% 26%	1724
May	1st to 10th	Night	16% 10% 3 7% 4 3 3 2 3 4 45%	3640
	11th to 20th	Night	20% 9% 3 7% 4 4 4 3 5% 6% 35%	3616
	21st to end	Night	20% 10% 4 9% 5% 5% 6% 3 5% 6% 27%	3955
June	1st to 10th	Night	21% 7% 2 8% 4 5% 5% 4 4 6% 32%	1395
	11th to 20th	Night	20% 11% 4 8% 5% 5% 5% 5% 5% 6% 26%	1330
	21st to end	Night	14% 7% 2 6% 5% 4 4 4 5% 7% 42%	1330
July	1st to 10th	Night	6% 3 2 4 3 3 2 2 4 5% 67%	2220
	11th to 20th	Night	6% 3 1 2 2 2 2 1 2 3 75%	2220
	21st to end	Night	11% 4 2 4 2 3 3 3 4 5% 60%	2753
August	1st to 10th	Night	5% 2 1 3 2 2 2 3 5% 7% 69%	2529
	11th to 20th	Night	12% 5% 2 5% 4 3 3 3 5% 8% 49%	2809
	21st to end	Night	15% 6% 3 6% 4 5% 4 4 6% 9% 39%	3293
September	1st to 10th	Night	10% 3 2 5% 3 5% 4 4 4 6% 54%	1900
	11th to 20th	Night	20% 6% 2 6% 4 4 3 3 4 7% 42%	1900
	21st to end	Night	22% 6% 3 6% 4 4 4 3 4 5% 39%	2170
October	1st to 10th	Night	21% 9% 3 8% 5% 5% 5% 4 5% 5% 29%	3800
	11th to 20th	Night	33% 7% 3 5% 3 4 3 3 5% 6% 28%	3777
	21st to end	Night	32% 11% 3 8% 4 4 4 3 4 5% 23%	4367
November	1st to 10th	Night	40% 10% 3 6% 4 4 4 3 4 4 18%	2730
	11th to 20th	Night	39% 10% 3 6% 5% 3 3 2 3 3 22%	2800
	21st to end	Night	37% 11% 4 7% 5% 4 4 2 4 4 18%	2800
December	1st to 10th	Night	27% 9% 3 7% 4 5% 5% 4 6% 7% 23%	4560
	11th to 20th	Night	43% 13% 4 8% 4 4 3 2 3 4 13%	5489
	21st to end	Night	40% 15% 4 9% 4 4 3 2 3 4 13%	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	60% 25% 5% 8% 2	3179
	11th to 20th	Day	37% 26% 8% 18% 9% 2	3287
	21st to end	Day	50% 27% 5% 13% 5%	4022
February	1st to 10th	Day	28% 60% 2 2 5% 2	1800
	11th to 20th	Day	28% 60% 4 5% 3 1	1764
	21st to end	Day	27% 60% 4 5% 3 2	1525
March	1st to 10th	Day	50% 27% 6% 13% 4	4619
	11th to 20th	Day	46% 29% 7% 17% 2	5000
	21st to end	Day	52% 29% 10% 7% 2	5661
April	1st to 10th	Day	26% 62% 4 7% 1	2400
	11th to 20th	Day	23% 62% 5% 7% 2 1	2439
	21st to end	Day	24% 61% 4 7% 3	2675
May	1st to 10th	Day	32% 28% 10% 21% 9%	6320
	11th to 20th	Day	44% 29% 14% 12% 2	6280
	21st to end	Day	41% 28% 15% 14% 2	6904
June	1st to 10th	Day	19% 61% 7% 9% 3	2989
	11th to 20th	Day	20% 64% 5% 7% 3	2850
	21st to end	Day	18% 63% 7% 9% 3	2850
July	1st to 10th	Day	15% 35% 4 16% 21% 9%	4666
	11th to 20th	Day	8% 35% 6% 29% 20% 2	4659
	21st to end	Day	23% 35% 16% 18% 6% 1	4643
August	1st to 10th	Day	11% 36% 8% 30% 15% 1	4384
	11th to 20th	Day	32% 38% 16% 11% 3 1	4065
	21st to end	Day	32% 37% 10% 13% 9%	4377
September	1st to 10th	Day	20% 59% 6% 10% 4 1	2280
	11th to 20th	Day	24% 59% 4 7% 6% 1	2280
	21st to end	Day	21% 59% 8% 8% 5%	2006
October	1st to 10th	Day	36% 37% 11% 13% 2	3180
	11th to 20th	Day	43% 37% 6% 8% 6%	3161
	21st to end	Day	47% 37% 5% 8% 3	3191
November	1st to 10th	Day	31% 55% 6% 7% 1	1568
	11th to 20th	Day	29% 56% 3 7% 3 2	1600
	21st to end	Day	27% 56% 4 7% 4 1	1600
December	1st to 10th	Day	37% 37% 8% 13% 6%	2620
	11th to 20th	Day	56% 31% 6% 6% 1	2716
	21st to end	Day	61% 25% 7% 4 1	3498
January	1st to 10th	Night	58% 25% 4 9% 3	6766
	11th to 20th	Night	35% 29% 10% 15% 9% 3	6670
	21st to end	Night	47% 28% 8% 13% 4	6930
February	1st to 10th	Night	27% 61% 3 4 4 3	2600
	11th to 20th	Night	29% 59% 3 5% 3 1	2534
	21st to end	Night	23% 61% 4 7% 4 1	2105
March	1st to 10th	Night	47% 29% 6% 12% 6%	5271
	11th to 20th	Night	43% 29% 9% 18% 2	5000
	21st to end	Night	56% 27% 11% 5% 1	5314
April	1st to 10th	Night	26% 61% 4 8% 1	2000
	11th to 20th	Night	23% 61% 5% 6% 3 1	1910
	21st to end	Night	22% 61% 5% 7% 3	1724
May	1st to 10th	Night	31% 28% 7% 25% 8%	3637
	11th to 20th	Night	40% 29% 17% 12% 2	3616
	21st to end	Night	44% 28% 13% 13% 1	3955
June	1st to 10th	Night	18% 61% 8% 10% 3 1	1395
	11th to 20th	Night	19% 65% 5% 7% 3	1330
	21st to end	Night	16% 62% 8% 10% 3	1330
July	1st to 10th	Night	10% 34% 4 24% 19% 9%	2185
	11th to 20th	Night	8% 34% 4 30% 23% 2	2178
	21st to end	Night	22% 35% 10% 18% 14% 1	2666
August	1st to 10th	Night	7% 36% 9% 30% 17% 1	2521
	11th to 20th	Night	27% 37% 20% 12% 3 1	2836
	21st to end	Night	31% 39% 11% 12% 7%	3293
September	1st to 10th	Night	18% 60% 7% 9% 5% 1	1900
	11th to 20th	Night	22% 59% 5% 6% 5% 1	1900
	21st to end	Night	21% 59% 6% 10% 4	2170
October	1st to 10th	Night	40% 37% 12% 9% 2	3800
	11th to 20th	Night	39% 37% 7% 12% 5%	3777
	21st to end	Night	45% 36% 7% 9% 3	4367
November	1st to 10th	Night	32% 55% 6% 5% 1	2730
	11th to 20th	Night	30% 56% 4 5% 4 2	2800
	21st to end	Night	31% 56% 3 4 5% 1	2800
December	1st to 10th	Night	40% 39% 7% 9% 4	4560
	11th to 20th	Night	55% 31% 6% 7% 1 1	5485
	21st to end	Night	60% 26% 5% 8% 2	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	45% 8% 21% 14% 10% 4	200
	11th to 20th	Day	46% 9% 13% 19% 11% 4	200
	21st to end	Day	45% 7% 14% 18% 11% 5%	225
February	1st to 10th	Day	46% 11% 17% 16% 7% 3	400
	11th to 20th	Day	40% 9% 22% 18% 10% 2	395
	21st to end	Day	41% 11% 26% 13% 8% 2	351
March	1st to 10th	Day	39% 9% 20% 21% 10% 2	500
	11th to 20th	Day	37% 10% 18% 21% 11% 2	500
	21st to end	Day	41% 9% 20% 19% 9% 2	550
April	1st to 10th	Day	37% 10% 21% 20% 11% 2	500
	11th to 20th	Day	27% 13% 25% 20% 11% 4	492
	21st to end	Day	29% 11% 24% 20% 11% 5%	500
May	1st to 10th	Day	22% 10% 24% 28% 13% 3	503
	11th to 20th	Day	26% 7% 19% 28% 14% 5%	528
	21st to end	Day	27% 9% 25% 21% 14% 5%	573
June	1st to 10th	Day	23% 10% 25% 28% 11% 3	727
	11th to 20th	Day	27% 10% 26% 26% 8% 3	680
	21st to end	Day	20% 8% 24% 30% 15% 4	680
July	1st to 10th	Day	17% 5% 25% 34% 15% 4	671
	11th to 20th	Day	12% 6% 23% 38% 16% 6%	668
	21st to end	Day	11% 4 19% 37% 20% 9%	536
August	1st to 10th	Day	14% 4 17% 33% 21% 12%	487
	11th to 20th	Day	11% 3 16% 36% 23% 11%	477
	21st to end	Day	18% 7% 21% 29% 17% 8%	539
September	1st to 10th	Day	20% 7% 21% 26% 16% 9%	490
	11th to 20th	Day	23% 7% 17% 30% 18% 5%	490
	21st to end	Day	27% 7% 22% 22% 17% 5%	490
October	1st to 10th	Day	32% 6% 16% 21% 19% 5%	490
	11th to 20th	Day	38% 6% 14% 20% 17% 5%	490
	21st to end	Day	41% 9% 18% 18% 10% 4	397
November	1st to 10th	Day	44% 10% 20% 16% 11%	200
	11th to 20th	Day	48% 5% 17% 12% 13% 6%	200
	21st to end	Day	46% 6% 21% 9% 11% 8%	200
December	1st to 10th	Day	47% 5% 16% 11% 12% 11%	200
	11th to 20th	Day	53% 10% 13% 16% 8% 2	200
	21st to end	Day	53% 5% 17% 19% 6%	220
January	1st to 10th	Night	54% 6% 15% 17% 7% 1	900
	11th to 20th	Night	45% 7% 13% 24% 11% 1	877
	21st to end	Night	44% 6% 15% 21% 13% 1	880
February	1st to 10th	Night	44% 10% 18% 20% 7% 1	800
	11th to 20th	Night	42% 8% 17% 23% 9%	784
	21st to end	Night	40% 8% 19% 21% 10% 2	660
March	1st to 10th	Night	37% 7% 18% 23% 14% 1	800
	11th to 20th	Night	42% 4 19% 23% 12% 1	800
	21st to end	Night	43% 6% 15% 24% 10% 2	880
April	1st to 10th	Night	38% 5% 15% 27% 14% 2	800
	11th to 20th	Night	30% 6% 20% 25% 16% 3	722
	21st to end	Night	34% 4 15% 28% 16% 3	524
May	1st to 10th	Night	24% 4 13% 32% 25% 2	400
	11th to 20th	Night	22% 4 9% 28% 33% 5%	394
	21st to end	Night	23% 3 8% 34% 28% 4	433
June	1st to 10th	Night	25% 2 14% 28% 27% 4	399
	11th to 20th	Night	24% 5% 14% 32% 20% 4	380
	21st to end	Night	18% 3 9% 32% 34% 4	380
July	1st to 10th	Night	14% 2 10% 28% 42% 4	370
	11th to 20th	Night	12% 4 7% 30% 40% 8%	368
	21st to end	Night	7% 2 6% 26% 50% 9%	416
August	1st to 10th	Night	13% 1 3 21% 47% 15%	378
	11th to 20th	Night	11% 1 4 25% 45% 14%	561
	21st to end	Night	15% 3 7% 28% 39% 7%	709
September	1st to 10th	Night	15% 2 8% 38% 31% 7%	760
	11th to 20th	Night	23% 3 10% 23% 34% 8%	760
	21st to end	Night	27% 4 12% 28% 25% 3	760
October	1st to 10th	Night	28% 4 12% 28% 24% 4	760
	11th to 20th	Night	37% 4 13% 25% 17% 4	760
	21st to end	Night	41% 6% 16% 24% 11% 2	836
November	1st to 10th	Night	48% 5% 18% 23% 6% 1	780
	11th to 20th	Night	50% 5% 15% 18% 10% 2	800
	21st to end	Night	47% 7% 13% 18% 12% 3	800
December	1st to 10th	Night	39% 6% 17% 25% 13% 1	800
	11th to 20th	Night	53% 7% 18% 17% 5% 1	877
	21st to end	Night	52% 8% 20% 17% 4	990

Page generated at 2025-06-07 07:28:15. Version ac07

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