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 2026-10-14.

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	22% 9% 3 7% 4 4 4 3 5% 6% 35%	153820
	Night	26% 9% 3 7% 4 4 4 3 4 5% 31%	146655
Transparency	Day	35% 32% 11% 15% 6% 1	153530
	Night	39% 33% 10% 13% 6% 1	146527
Seeing	Day	29% 8% 21% 24% 14% 5%	17786
	Night	35% 5% 14% 25% 19% 3	25919

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	42% 15% 4 8% 4 4 4 2 3 3 10%	4125
	11th to 20th	Day	21% 9% 3 7% 4 4 4 3 4 5% 36%	4254
	21st to end	Day	39% 10% 3 7% 3 3 2 2 3 3 25%	5218
February	1st to 10th	Day	34% 11% 4 8% 5% 4 4 3 4 5% 17%	1890
	11th to 20th	Day	31% 11% 3 7% 5% 5% 4 2 4 5% 22%	1845
	21st to end	Day	28% 17% 4 8% 5% 5% 4 3 5% 4 20%	1599
March	1st to 10th	Day	27% 15% 4 9% 5% 4 4 3 5% 6% 18%	4721
	11th to 20th	Day	25% 14% 4 9% 5% 4 4 3 4 5% 24%	5110
	21st to end	Day	29% 12% 3 9% 6% 5% 5% 4 4 6% 17%	5786
April	1st to 10th	Day	28% 11% 3 9% 6% 5% 5% 4 5% 6% 19%	2520
	11th to 20th	Day	21% 10% 4 10% 6% 5% 6% 4 6% 6% 24%	2562
	21st to end	Day	24% 10% 3 8% 5% 4 4 4 5% 5% 27%	2809
May	1st to 10th	Day	13% 8% 3 7% 4 4 4 4 5% 6% 42%	8195
	11th to 20th	Day	19% 10% 3 8% 4 5% 5% 4 6% 8% 30%	8160
	21st to end	Day	22% 7% 3 7% 4 4 4 4 7% 8% 30%	8993
June	1st to 10th	Day	22% 8% 3 7% 5% 5% 4 3 5% 7% 30%	3150
	11th to 20th	Day	21% 10% 4 8% 5% 4 4 4 5% 7% 27%	3150
	21st to end	Day	15% 8% 3 7% 5% 5% 5% 4 6% 7% 35%	3150
July	1st to 10th	Day	11% 5% 2 5% 3 3 3 3 5% 6% 54%	8820
	11th to 20th	Day	6% 4 1 4 3 2 3 2 4 6% 66%	8820
	21st to end	Day	12% 4 2 4 2 3 3 3 5% 7% 54%	8921
August	1st to 10th	Day	6% 4 1 3 2 2 2 2 4 5% 68%	6441
	11th to 20th	Day	10% 6% 2 5% 3 4 4 3 5% 7% 50%	5923
	21st to end	Day	17% 8% 2 6% 4 4 4 3 5% 7% 39%	6369
September	1st to 10th	Day	15% 6% 2 6% 4 4 4 3 4 7% 46%	2520
	11th to 20th	Day	17% 7% 3 8% 5% 4 4 3 4 6% 39%	2520
	21st to end	Day	25% 6% 3 6% 4 3 4 3 5% 6% 34%	2216
October	1st to 10th	Day	21% 7% 2 8% 5% 5% 5% 4 6% 7% 30%	3380
	11th to 20th	Day	36% 7% 2 6% 4 3 4 3 4 6% 24%	3292
	21st to end	Day	32% 11% 4 8% 4 4 5% 4 5% 6% 16%	3293
November	1st to 10th	Day	39% 9% 4 7% 4 5% 4 3 4 5% 16%	1648
	11th to 20th	Day	38% 13% 3 6% 4 4 3 3 4 4 20%	1680
	21st to end	Day	38% 13% 3 7% 4 3 3 3 4 5% 17%	1680
December	1st to 10th	Day	27% 10% 4 8% 5% 3 4 4 6% 6% 25%	2700
	11th to 20th	Day	41% 15% 3 7% 4 4 3 3 4 4 12%	2785
	21st to end	Day	39% 15% 4 9% 5% 4 4 2 3 4 10%	3575
January	1st to 10th	Night	41% 15% 4 8% 4 4 3 2 3 3 12%	8770
	11th to 20th	Night	25% 8% 2 5% 3 4 4 3 5% 7% 34%	8641
	21st to end	Night	36% 9% 3 6% 3 3 3 2 3 4 29%	8959
February	1st to 10th	Night	35% 12% 3 8% 5% 4 3 3 3 4 21%	2730
	11th to 20th	Night	31% 13% 3 7% 5% 3 3 2 3 4 25%	2662
	21st to end	Night	30% 13% 3 7% 5% 4 4 3 3 5% 24%	2207
March	1st to 10th	Night	25% 16% 3 8% 4 4 4 3 5% 5% 23%	5389
	11th to 20th	Night	29% 11% 3 7% 4 4 4 3 5% 6% 24%	5109
	21st to end	Night	38% 13% 4 8% 4 3 3 2 4 4 17%	5431
April	1st to 10th	Night	29% 11% 3 7% 5% 5% 4 3 5% 5% 22%	2100
	11th to 20th	Night	22% 10% 2 8% 5% 5% 5% 4 5% 6% 27%	2006
	21st to end	Night	26% 9% 3 7% 5% 4 5% 3 5% 6% 27%	1810
May	1st to 10th	Night	13% 8% 2 6% 4 4 4 3 4 5% 46%	4724
	11th to 20th	Night	20% 9% 3 7% 5% 4 4 4 5% 6% 32%	4700
	21st to end	Night	17% 8% 3 8% 5% 5% 5% 3 6% 7% 31%	5161
June	1st to 10th	Night	21% 7% 3 9% 4 5% 5% 4 4 6% 31%	1470
	11th to 20th	Night	18% 10% 4 8% 5% 5% 4 5% 5% 6% 30%	1470
	21st to end	Night	15% 8% 2 6% 5% 4 4 3 5% 7% 42%	1470
July	1st to 10th	Night	10% 4 2 4 3 3 4 3 5% 7% 57%	4140
	11th to 20th	Night	7% 3 1 3 2 2 2 2 3 4 72%	4140
	21st to end	Night	8% 4 2 5% 3 3 3 3 5% 8% 56%	5143
August	1st to 10th	Night	4 2 1 2 2 1 2 3 4 6% 73%	3709
	11th to 20th	Night	9% 4 2 5% 3 3 3 3 6% 9% 53%	4139
	21st to end	Night	16% 6% 3 6% 4 4 4 3 5% 7% 41%	4787
September	1st to 10th	Night	10% 4 2 5% 3 4 4 4 5% 6% 54%	2100
	11th to 20th	Night	19% 6% 2 6% 4 4 3 3 4 7% 43%	2100
	21st to end	Night	22% 7% 3 6% 5% 4 4 3 4 6% 37%	2399
October	1st to 10th	Night	21% 9% 3 9% 5% 5% 5% 3 5% 5% 29%	4040
	11th to 20th	Night	32% 7% 3 5% 3 4 3 3 4 6% 29%	3933
	21st to end	Night	32% 11% 3 8% 4 4 4 3 4 5% 23%	4506
November	1st to 10th	Night	40% 10% 3 6% 4 4 4 3 4 4 18%	2870
	11th to 20th	Night	39% 10% 3 6% 5% 3 3 2 3 3 21%	2940
	21st to end	Night	37% 11% 4 8% 5% 4 4 2 4 4 18%	2940
December	1st to 10th	Night	28% 10% 3 7% 4 5% 5% 4 6% 7% 22%	4700
	11th to 20th	Night	43% 13% 4 8% 4 4 3 2 3 4 12%	5637
	21st to end	Night	39% 15% 4 9% 4 4 3 2 3 4 13%	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	67% 20% 4 6% 1	4125
	11th to 20th	Day	38% 20% 7% 22% 11% 2	4275
	21st to end	Day	53% 21% 5% 15% 5% 2	5219
February	1st to 10th	Day	30% 57% 3 2 5% 2	1890
	11th to 20th	Day	29% 57% 4 6% 3 1	1854
	21st to end	Day	29% 58% 4 5% 3 1	1599
March	1st to 10th	Day	50% 27% 6% 13% 3	4721
	11th to 20th	Day	47% 28% 6% 17% 2	5110
	21st to end	Day	52% 28% 10% 7% 2	5786
April	1st to 10th	Day	27% 59% 5% 8%	2520
	11th to 20th	Day	26% 59% 5% 7% 2 1	2562
	21st to end	Day	24% 59% 5% 8% 4	2809
May	1st to 10th	Day	33% 22% 12% 24% 9% 1	8195
	11th to 20th	Day	45% 24% 16% 14% 2	8163
	21st to end	Day	40% 23% 18% 16% 2	8994
June	1st to 10th	Day	21% 58% 7% 11% 3	3150
	11th to 20th	Day	22% 58% 5% 10% 4	3150
	21st to end	Day	21% 57% 7% 10% 3	3150
July	1st to 10th	Day	27% 20% 15% 19% 15% 5%	8746
	11th to 20th	Day	16% 20% 13% 30% 18% 3	8739
	21st to end	Day	27% 20% 23% 23% 7%	8727
August	1st to 10th	Day	14% 26% 10% 27% 20% 3	6424
	11th to 20th	Day	28% 27% 24% 18% 2 1	5962
	21st to end	Day	37% 27% 13% 16% 7%	6368
September	1st to 10th	Day	22% 54% 8% 11% 4 1	2520
	11th to 20th	Day	25% 54% 5% 10% 6% 1	2520
	21st to end	Day	24% 53% 9% 8% 5%	2216
October	1st to 10th	Day	37% 35% 11% 14% 2	3380
	11th to 20th	Day	44% 35% 7% 8% 6%	3292
	21st to end	Day	48% 36% 5% 8% 3	3293
November	1st to 10th	Day	33% 53% 6% 7% 1	1648
	11th to 20th	Day	31% 54% 3 7% 3 2	1680
	21st to end	Day	30% 53% 4 7% 5% 1	1680
December	1st to 10th	Day	38% 35% 8% 12% 6%	2700
	11th to 20th	Day	56% 30% 6% 6% 1	2788
	21st to end	Day	62% 25% 7% 4 1	3575
January	1st to 10th	Night	65% 20% 5% 8% 2	8770
	11th to 20th	Night	37% 23% 9% 16% 14% 3	8682
	21st to end	Night	49% 22% 7% 15% 7%	8959
February	1st to 10th	Night	28% 58% 3 4 5% 2	2730
	11th to 20th	Night	30% 57% 3 6% 4 1	2664
	21st to end	Night	26% 58% 4 7% 4 1	2207
March	1st to 10th	Night	48% 28% 6% 12% 6%	5389
	11th to 20th	Night	44% 28% 9% 17% 2	5110
	21st to end	Night	55% 27% 11% 6% 1	5431
April	1st to 10th	Night	27% 59% 5% 9% 1	2100
	11th to 20th	Night	25% 59% 6% 6% 3 1	2006
	21st to end	Night	22% 58% 7% 8% 4	1810
May	1st to 10th	Night	32% 22% 9% 28% 8%	4721
	11th to 20th	Night	45% 24% 17% 13% 2	4700
	21st to end	Night	42% 22% 19% 15% 2	5165
June	1st to 10th	Night	20% 58% 7% 11% 3 1	1470
	11th to 20th	Night	20% 59% 5% 13% 3	1470
	21st to end	Night	19% 57% 8% 11% 4	1470
July	1st to 10th	Night	22% 19% 17% 24% 12% 5%	4105
	11th to 20th	Night	14% 19% 12% 30% 22% 2	4098
	21st to end	Night	25% 20% 20% 24% 11% 1	5032
August	1st to 10th	Night	8% 25% 13% 31% 19% 4	3701
	11th to 20th	Night	24% 26% 29% 17% 2 1	4166
	21st to end	Night	34% 29% 16% 14% 6%	4787
September	1st to 10th	Night	19% 55% 10% 11% 5% 1	2100
	11th to 20th	Night	24% 54% 6% 8% 6% 1	2100
	21st to end	Night	25% 54% 7% 11% 4	2399
October	1st to 10th	Night	41% 35% 12% 10% 2	4040
	11th to 20th	Night	40% 35% 7% 12% 6%	3933
	21st to end	Night	46% 35% 7% 9% 3	4506
November	1st to 10th	Night	34% 53% 6% 6% 1	2870
	11th to 20th	Night	32% 54% 4 5% 3 2	2940
	21st to end	Night	33% 53% 3 4 5% 1	2940
December	1st to 10th	Night	42% 38% 7% 9% 4	4700
	11th to 20th	Night	56% 30% 6% 6% 1 1	5633
	21st to end	Night	60% 25% 5% 8% 2	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	46% 8% 20% 13% 10% 3	220
	11th to 20th	Day	44% 8% 12% 20% 12% 4	220
	21st to end	Day	45% 7% 14% 17% 12% 5%	248
February	1st to 10th	Day	46% 10% 16% 17% 8% 3	430
	11th to 20th	Day	39% 10% 22% 18% 10% 2	425
	21st to end	Day	42% 11% 25% 13% 8% 2	377
March	1st to 10th	Day	39% 9% 19% 21% 10% 1	540
	11th to 20th	Day	40% 10% 17% 20% 10% 2	540
	21st to end	Day	40% 9% 21% 19% 9% 2	594
April	1st to 10th	Day	35% 10% 21% 20% 12% 3	540
	11th to 20th	Day	27% 13% 24% 21% 11% 5%	532
	21st to end	Day	28% 12% 24% 21% 10% 5%	540
May	1st to 10th	Day	21% 10% 24% 29% 12% 3	543
	11th to 20th	Day	26% 8% 19% 28% 14% 5%	568
	21st to end	Day	26% 9% 26% 21% 14% 5%	617
June	1st to 10th	Day	23% 11% 25% 26% 11% 3	780
	11th to 20th	Day	26% 10% 26% 27% 9% 3	780
	21st to end	Day	20% 8% 23% 30% 16% 4	780
July	1st to 10th	Day	17% 5% 25% 35% 14% 4	771
	11th to 20th	Day	11% 6% 25% 36% 16% 5%	768
	21st to end	Day	11% 4 19% 37% 20% 9%	624
August	1st to 10th	Day	14% 4 17% 33% 20% 12%	567
	11th to 20th	Day	11% 4 16% 35% 23% 11%	557
	21st to end	Day	17% 7% 21% 28% 17% 10%	627
September	1st to 10th	Day	19% 6% 21% 26% 17% 10%	570
	11th to 20th	Day	22% 6% 17% 29% 19% 8%	570
	21st to end	Day	28% 6% 22% 22% 17% 4	570
October	1st to 10th	Day	31% 6% 16% 22% 20% 5%	570
	11th to 20th	Day	37% 7% 14% 20% 16% 6%	543
	21st to end	Day	42% 9% 18% 17% 10% 3	433
November	1st to 10th	Day	45% 10% 20% 16% 10%	220
	11th to 20th	Day	50% 5% 15% 12% 12% 5%	220
	21st to end	Day	47% 6% 20% 9% 10% 7%	220
December	1st to 10th	Day	50% 5% 14% 10% 11% 10%	220
	11th to 20th	Day	54% 11% 12% 15% 7% 1	220
	21st to end	Day	52% 5% 17% 18% 7%	242
January	1st to 10th	Night	53% 6% 15% 17% 8% 1	950
	11th to 20th	Night	45% 6% 12% 24% 12% 1	925
	21st to end	Night	44% 6% 14% 22% 13% 1	924
February	1st to 10th	Night	44% 9% 18% 20% 7% 1	840
	11th to 20th	Night	41% 8% 17% 24% 10%	824
	21st to end	Night	41% 8% 19% 21% 9% 1	692
March	1st to 10th	Night	37% 7% 18% 23% 14% 1	840
	11th to 20th	Night	44% 4 18% 22% 11% 1	840
	21st to end	Night	41% 6% 16% 25% 10% 2	924
April	1st to 10th	Night	36% 5% 15% 27% 15% 2	840
	11th to 20th	Night	30% 6% 20% 25% 17% 3	758
	21st to end	Night	33% 4 15% 29% 16% 3	550
May	1st to 10th	Night	23% 4 12% 32% 27% 2	420
	11th to 20th	Night	23% 3 9% 28% 32% 5%	414
	21st to end	Night	22% 3 8% 34% 28% 4	455
June	1st to 10th	Night	26% 2 13% 29% 26% 4	420
	11th to 20th	Night	22% 5% 13% 34% 21% 4	420
	21st to end	Night	19% 2 9% 32% 34% 5%	420
July	1st to 10th	Night	14% 2 9% 29% 41% 4	410
	11th to 20th	Night	12% 3 7% 32% 38% 8%	408
	21st to end	Night	7% 2 6% 26% 50% 9%	460
August	1st to 10th	Night	14% 1 3 22% 47% 14%	418
	11th to 20th	Night	11% 1 4 25% 45% 14%	621
	21st to end	Night	15% 3 8% 27% 39% 8%	784
September	1st to 10th	Night	14% 2 8% 37% 30% 8%	840
	11th to 20th	Night	22% 3 10% 23% 34% 8%	840
	21st to end	Night	28% 4 12% 29% 25% 3	840
October	1st to 10th	Night	27% 4 12% 28% 24% 4	840
	11th to 20th	Night	36% 5% 13% 25% 17% 4	812
	21st to end	Night	41% 6% 16% 25% 11% 2	880
November	1st to 10th	Night	48% 5% 17% 24% 6% 1	820
	11th to 20th	Night	50% 5% 15% 19% 9% 2	840
	21st to end	Night	47% 7% 13% 19% 11% 3	840
December	1st to 10th	Night	40% 6% 16% 24% 12% 1	840
	11th to 20th	Night	54% 7% 17% 16% 5% 1	925
	21st to end	Night	51% 7% 20% 18% 4	1045

Page generated at 2026-10-11 02:06:26. Version ac07

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