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 2024-11-02.

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	23% 9% 3 7% 4 4 4 3 4 6% 34%	101669
	Night	28% 10% 3 6% 4 4 3 3 4 5% 31%	97370
Transparency	Day	28% 47% 7% 11% 6% 1	101420
	Night	31% 47% 6% 10% 5% 1	97265
Seeing	Day	29% 8% 21% 24% 13% 5%	15265
	Night	35% 5% 14% 24% 18% 3	23483

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	43% 14% 3 7% 4 4 4 2 4 4 11%	2219
	11th to 20th	Day	30% 12% 4 8% 4 4 3 2 3 5% 26%	2264
	21st to end	Day	53% 12% 3 7% 3 3 2 2 3 3 11%	2798
February	1st to 10th	Day	35% 11% 4 8% 5% 4 4 3 4 5% 17%	1710
	11th to 20th	Day	32% 11% 4 8% 5% 5% 4 2 4 5% 22%	1665
	21st to end	Day	27% 17% 4 8% 5% 5% 4 3 5% 4 21%	1451
March	1st to 10th	Day	25% 17% 4 8% 5% 4 4 3 5% 6% 18%	3213
	11th to 20th	Day	22% 11% 3 7% 4 4 4 3 4 6% 33%	3490
	21st to end	Day	28% 12% 3 8% 5% 4 5% 4 4 5% 21%	3948
April	1st to 10th	Day	28% 12% 3 9% 6% 4 5% 4 5% 6% 18%	2280
	11th to 20th	Day	22% 11% 3 10% 6% 5% 5% 3 6% 5% 23%	2315
	21st to end	Day	26% 10% 3 9% 6% 3 4 4 6% 5% 24%	2541
May	1st to 10th	Day	18% 8% 2 6% 4 4 4 3 5% 5% 40%	4420
	11th to 20th	Day	15% 7% 2 7% 4 4 5% 4 6% 8% 38%	4377
	21st to end	Day	30% 10% 4 7% 5% 4 4 3 5% 6% 22%	4813
June	1st to 10th	Day	24% 8% 3 8% 5% 5% 4 3 5% 7% 28%	2850
	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	23% 9% 2 8% 3 4 4 3 4 6% 33%	1900
	11th to 20th	Day	32% 9% 3 7% 5% 3 4 3 4 6% 24%	1900
	21st to end	Day	35% 9% 3 6% 4 4 4 3 4 6% 23%	1946
November	1st to 10th	Day	40% 9% 4 6% 4 5% 4 3 4 4 17%	1496
	11th to 20th	Day	37% 12% 2 6% 4 4 3 3 4 4 21%	1520
	21st to end	Day	38% 13% 3 7% 3 3 3 3 4 4 18%	1520
December	1st to 10th	Day	34% 13% 3 6% 4 3 3 3 3 3 25%	1520
	11th to 20th	Day	35% 15% 3 8% 4 4 3 4 4 5% 14%	1725
	21st to end	Day	39% 14% 5% 9% 5% 3 3 3 3 4 11%	2442
January	1st to 10th	Night	42% 14% 4 8% 5% 4 3 2 3 3 13%	4726
	11th to 20th	Night	32% 9% 2 5% 3 3 3 3 5% 8% 27%	4631
	21st to end	Night	50% 13% 3 6% 3 3 2 2 2 3 13%	4853
February	1st to 10th	Night	37% 11% 3 7% 5% 4 3 3 3 4 20%	2470
	11th to 20th	Night	31% 13% 3 8% 5% 3 3 2 3 4 24%	2402
	21st to end	Night	30% 13% 3 6% 4 4 4 3 3 5% 25%	2003
March	1st to 10th	Night	26% 16% 3 7% 4 4 4 3 4 5% 22%	3657
	11th to 20th	Night	25% 8% 2 6% 4 4 4 3 5% 7% 32%	3489
	21st to end	Night	34% 14% 4 8% 4 4 3 2 4 3 20%	3705
April	1st to 10th	Night	29% 11% 3 8% 5% 4 4 3 5% 5% 22%	1900
	11th to 20th	Night	23% 11% 2 8% 6% 5% 5% 4 4 6% 27%	1814
	21st to end	Night	28% 10% 4 8% 5% 4 5% 4 5% 5% 23%	1638
May	1st to 10th	Night	18% 10% 2 6% 4 3 3 3 3 4 44%	2540
	11th to 20th	Night	13% 6% 3 6% 4 4 4 4 5% 7% 45%	2516
	21st to end	Night	25% 11% 4 8% 5% 5% 5% 2 5% 5% 25%	2745
June	1st to 10th	Night	22% 7% 2 8% 4 5% 5% 5% 4 6% 31%	1330
	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	22% 7% 3 6% 5% 5% 4 3 4 5% 37%	2280
	11th to 20th	Night	31% 7% 3 6% 3 4 4 3 4 6% 30%	2280
	21st to end	Night	33% 8% 2 7% 3 3 4 3 4 5% 28%	2650
November	1st to 10th	Night	40% 10% 3 6% 4 4 4 3 4 4 18%	2616
	11th to 20th	Night	39% 9% 3 6% 5% 3 3 2 3 3 23%	2660
	21st to end	Night	38% 11% 4 7% 5% 4 4 2 4 4 18%	2660
December	1st to 10th	Night	32% 10% 3 6% 4 4 4 3 5% 5% 25%	2660
	11th to 20th	Night	43% 13% 4 8% 4 4 3 2 3 3 13%	3477
	21st to end	Night	40% 14% 4 8% 4 3 3 2 3 3 15%	5214

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	52% 35% 5% 5% 2 1	2219
	11th to 20th	Day	40% 35% 4 11% 7% 4	2285
	21st to end	Day	56% 38% 3 3	2798
February	1st to 10th	Day	27% 63% 2 2 4 2	1710
	11th to 20th	Day	26% 63% 3 4 3 1	1674
	21st to end	Day	24% 63% 4 5% 3 2	1451
March	1st to 10th	Day	41% 39% 6% 10% 4	3213
	11th to 20th	Day	29% 40% 8% 21% 2	3490
	21st to end	Day	41% 39% 10% 7% 3 1	3948
April	1st to 10th	Day	24% 65% 4 6% 1	2280
	11th to 20th	Day	23% 65% 4 5% 2 1	2315
	21st to end	Day	23% 65% 4 5% 3 1	2541
May	1st to 10th	Day	27% 39% 8% 18% 8% 1	4420
	11th to 20th	Day	26% 40% 17% 15% 2	4380
	21st to end	Day	43% 39% 12% 6% 1	4814
June	1st to 10th	Day	20% 64% 6% 8% 2	2850
	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	23% 59% 6% 9% 3	1900
	11th to 20th	Day	28% 59% 4 6% 3	1900
	21st to end	Day	26% 59% 3 6% 5%	1946
November	1st to 10th	Day	30% 57% 5% 7% 1	1496
	11th to 20th	Day	26% 59% 3 7% 3 2	1520
	21st to end	Day	25% 59% 4 7% 5% 1	1520
December	1st to 10th	Day	27% 59% 3 6% 5% 1	1520
	11th to 20th	Day	38% 47% 4 7% 2 1	1728
	21st to end	Day	52% 35% 6% 4 2 1	2442
January	1st to 10th	Night	52% 35% 3 8% 2	4726
	11th to 20th	Night	34% 36% 5% 12% 8% 5%	4672
	21st to end	Night	55% 38% 3 4	4853
February	1st to 10th	Night	25% 64% 2 3 3 2	2470
	11th to 20th	Night	27% 63% 3 4 3 1	2404
	21st to end	Night	20% 64% 4 7% 4 1	2003
March	1st to 10th	Night	41% 39% 4 10% 6%	3657
	11th to 20th	Night	26% 40% 11% 21% 2	3490
	21st to end	Night	45% 39% 9% 6% 1	3705
April	1st to 10th	Night	23% 65% 4 7% 1	1900
	11th to 20th	Night	22% 64% 4 6% 2 1	1814
	21st to end	Night	23% 64% 3 6% 3	1638
May	1st to 10th	Night	27% 39% 6% 20% 8% 1	2540
	11th to 20th	Night	24% 40% 18% 14% 3	2516
	21st to end	Night	42% 38% 11% 8% 1	2745
June	1st to 10th	Night	18% 64% 6% 10% 2 1	1330
	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	22% 59% 6% 9% 4	2280
	11th to 20th	Night	26% 59% 5% 7% 3	2280
	21st to end	Night	25% 58% 4 8% 4	2650
November	1st to 10th	Night	31% 57% 6% 5% 1	2616
	11th to 20th	Night	26% 59% 4 5% 4 2	2660
	21st to end	Night	28% 58% 2 4 5% 1	2660
December	1st to 10th	Night	26% 59% 3 6% 5%	2660
	11th to 20th	Night	43% 48% 4 3 2 1	3473
	21st to end	Night	50% 35% 4 7% 2	5214

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	46% 7% 22% 11% 9% 4	180
	11th to 20th	Day	50% 9% 14% 16% 9% 3	180
	21st to end	Day	48% 8% 15% 17% 10% 2	202
February	1st to 10th	Day	46% 11% 17% 16% 7% 3	370
	11th to 20th	Day	40% 10% 22% 17% 9% 2	365
	21st to end	Day	41% 11% 26% 13% 8% 2	325
March	1st to 10th	Day	39% 10% 20% 20% 9% 2	460
	11th to 20th	Day	37% 10% 18% 22% 12% 3	460
	21st to end	Day	41% 10% 19% 19% 9% 2	506
April	1st to 10th	Day	37% 10% 21% 20% 10% 2	460
	11th to 20th	Day	28% 13% 25% 20% 10% 4	452
	21st to end	Day	30% 11% 25% 20% 10% 3	460
May	1st to 10th	Day	22% 9% 25% 29% 12% 3	463
	11th to 20th	Day	24% 7% 19% 29% 15% 6%	488
	21st to end	Day	27% 9% 25% 21% 13% 5%	529
June	1st to 10th	Day	25% 10% 25% 27% 11% 3	680
	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	45% 10% 19% 14% 11%	182
	11th to 20th	Day	48% 4 16% 11% 14% 7%	180
	21st to end	Day	47% 5% 21% 9% 11% 7%	180
December	1st to 10th	Day	50% 6% 17% 11% 9% 7%	180
	11th to 20th	Day	52% 9% 12% 16% 8% 2	180
	21st to end	Day	52% 5% 18% 19% 6%	198
January	1st to 10th	Night	54% 6% 14% 16% 8% 1	850
	11th to 20th	Night	47% 7% 13% 21% 11% 1	830
	21st to end	Night	46% 6% 15% 21% 12% 1	836
February	1st to 10th	Night	45% 9% 18% 20% 7% 1	760
	11th to 20th	Night	43% 8% 17% 23% 9%	744
	21st to end	Night	40% 8% 20% 21% 10% 2	628
March	1st to 10th	Night	37% 7% 19% 22% 14% 1	760
	11th to 20th	Night	42% 4 19% 22% 12% 1	760
	21st to end	Night	42% 6% 16% 24% 10% 2	836
April	1st to 10th	Night	37% 5% 16% 27% 13% 2	760
	11th to 20th	Night	31% 6% 20% 25% 16% 2	686
	21st to end	Night	35% 4 16% 29% 15% 2	498
May	1st to 10th	Night	24% 4 13% 32% 25% 2	380
	11th to 20th	Night	21% 3 8% 29% 34% 5%	374
	21st to end	Night	24% 4 7% 34% 27% 4	411
June	1st to 10th	Night	26% 2 14% 28% 26% 4	380
	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	49% 5% 18% 23% 6% 1	748
	11th to 20th	Night	48% 6% 16% 18% 10% 2	760
	21st to end	Night	48% 7% 13% 18% 12% 2	760
December	1st to 10th	Night	40% 6% 17% 25% 11% 1	760
	11th to 20th	Night	53% 7% 17% 17% 5% 1	829
	21st to end	Night	52% 8% 20% 16% 4	935

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