Shawnigan Lake School Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shawnigan Lake School Observatory clear sky chart from 2005-11-06 to 2024-03-06.

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	16% 11% 4 8% 7% 4 5% 5% 5% 6% 29%	78101
	Night	17% 10% 4 7% 6% 4 5% 5% 5% 6% 32%	81369
Transparency	Day	37% 36% 10% 12% 5% 1	77810
	Night	38% 34% 10% 12% 5% 1	81240
Seeing	Day	19% 12% 25% 25% 15% 4	14457
	Night	21% 10% 17% 27% 20% 4	22861

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	24% 17% 6% 9% 8% 4 4 4 5% 5% 14%	2219
	11th to 20th	Day	20% 14% 4 7% 6% 4 5% 5% 6% 6% 23%	2199
	21st to end	Day	29% 19% 6% 10% 7% 4 5% 4 4 4 9%	2866
February	1st to 10th	Day	21% 16% 4 10% 7% 4 6% 5% 5% 7% 16%	1710
	11th to 20th	Day	18% 17% 6% 8% 7% 4 4 5% 5% 6% 21%	1665
	21st to end	Day	15% 15% 5% 9% 9% 4 6% 5% 7% 7% 17%	1413
March	1st to 10th	Day	15% 15% 5% 10% 9% 5% 5% 6% 7% 6% 17%	1943
	11th to 20th	Day	21% 15% 5% 9% 8% 4 6% 4 5% 5% 18%	1980
	21st to end	Day	21% 15% 5% 9% 8% 5% 7% 5% 5% 5% 16%	2207
April	1st to 10th	Day	19% 14% 5% 9% 8% 4 6% 5% 5% 6% 17%	2160
	11th to 20th	Day	18% 11% 5% 10% 8% 5% 6% 6% 6% 5% 21%	2241
	21st to end	Day	18% 14% 4 9% 6% 5% 5% 5% 5% 6% 24%	2349
May	1st to 10th	Day	14% 10% 4 8% 8% 5% 6% 6% 6% 7% 28%	2520
	11th to 20th	Day	14% 10% 4 7% 8% 4 6% 5% 6% 8% 28%	2477
	21st to end	Day	16% 9% 4 8% 7% 4 6% 6% 5% 7% 28%	2778
June	1st to 10th	Day	17% 10% 3 7% 7% 4 6% 6% 6% 8% 26%	2700
	11th to 20th	Day	13% 9% 4 9% 9% 5% 7% 6% 7% 7% 24%	2700
	21st to end	Day	11% 7% 3 7% 6% 4 5% 6% 7% 7% 38%	2700
July	1st to 10th	Day	9% 6% 3 5% 6% 4 5% 5% 4 7% 46%	2700
	11th to 20th	Day	8% 4 3 4 5% 3 4 5% 6% 7% 52%	2700
	21st to end	Day	5% 3 2 3 3 2 4 4 5% 7% 61%	2800
August	1st to 10th	Day	7% 5% 2 5% 5% 3 4 5% 6% 7% 53%	2433
	11th to 20th	Day	7% 5% 2 5% 5% 2 5% 4 6% 8% 52%	2298
	21st to end	Day	8% 5% 2 6% 7% 4 5% 5% 7% 9% 43%	2534
September	1st to 10th	Day	8% 6% 2 5% 5% 3 4 5% 6% 8% 48%	2160
	11th to 20th	Day	12% 8% 3 7% 6% 4 4 4 5% 6% 42%	2124
	21st to end	Day	17% 7% 3 6% 6% 3 4 4 6% 7% 38%	1918
October	1st to 10th	Day	18% 8% 2 6% 5% 3 5% 5% 5% 7% 35%	1800
	11th to 20th	Day	19% 10% 3 6% 8% 4 5% 5% 6% 8% 26%	1800
	21st to end	Day	21% 10% 4 8% 6% 3 5% 5% 5% 7% 27%	1855
November	1st to 10th	Day	25% 11% 6% 11% 7% 5% 5% 5% 6% 4 16%	1488
	11th to 20th	Day	22% 12% 4 9% 6% 3 5% 6% 4 5% 23%	1520
	21st to end	Day	23% 12% 5% 8% 6% 4 6% 5% 6% 5% 21%	1520
December	1st to 10th	Day	19% 14% 6% 9% 8% 4 4 4 5% 5% 23%	1497
	11th to 20th	Day	24% 17% 5% 9% 6% 4 5% 5% 4 6% 16%	1685
	21st to end	Day	22% 18% 6% 9% 7% 4 6% 5% 4 5% 14%	2442
January	1st to 10th	Night	22% 14% 6% 10% 9% 5% 7% 4 5% 4 14%	4726
	11th to 20th	Night	22% 12% 4 7% 5% 3 5% 5% 5% 7% 25%	4699
	21st to end	Night	27% 15% 4 9% 8% 4 6% 4 4 5% 14%	4791
February	1st to 10th	Night	21% 13% 5% 8% 8% 5% 5% 5% 5% 6% 21%	2470
	11th to 20th	Night	17% 13% 4 7% 6% 3 5% 4 5% 6% 29%	2402
	21st to end	Night	17% 13% 4 8% 7% 4 5% 4 5% 7% 26%	2041
March	1st to 10th	Night	16% 10% 3 6% 7% 4 6% 6% 5% 7% 29%	2129
	11th to 20th	Night	17% 10% 3 7% 7% 4 6% 6% 7% 8% 25%	1979
	21st to end	Night	16% 13% 4 9% 7% 4 6% 5% 6% 7% 23%	2148
April	1st to 10th	Night	18% 8% 3 8% 7% 4 5% 5% 5% 7% 29%	1800
	11th to 20th	Night	16% 9% 3 6% 6% 3 5% 5% 7% 7% 33%	1667
	21st to end	Night	15% 9% 3 7% 6% 4 5% 4 6% 7% 34%	1610
May	1st to 10th	Night	10% 6% 3 6% 6% 3 5% 5% 6% 7% 44%	1440
	11th to 20th	Night	11% 5% 2 6% 6% 3 6% 6% 7% 9% 39%	1416
	21st to end	Night	10% 7% 3 6% 5% 3 4 5% 6% 8% 42%	1494
June	1st to 10th	Night	12% 7% 3 6% 8% 3 5% 4 5% 7% 41%	1260
	11th to 20th	Night	11% 4 2 5% 5% 3 5% 5% 6% 10% 43%	1260
	21st to end	Night	6% 3 2 5% 4 2 5% 5% 7% 11% 51%	1260
July	1st to 10th	Night	6% 4 2 4 4 2 4 4 3 8% 59%	1260
	11th to 20th	Night	4 2 2 3 3 2 3 3 4 8% 66%	1260
	21st to end	Night	3 1 1 2 2 1 3 3 5% 6% 75%	1514
August	1st to 10th	Night	4 3 2 4 3 1 4 3 4 6% 66%	1503
	11th to 20th	Night	4 2 1 2 3 2 4 3 4 8% 68%	1602
	21st to end	Night	6% 5% 1 4 4 3 4 4 6% 9% 55%	1822
September	1st to 10th	Night	6% 2 1 3 4 2 4 4 5% 8% 61%	1800
	11th to 20th	Night	12% 5% 2 5% 5% 3 4 5% 5% 7% 48%	1834
	21st to end	Night	11% 6% 2 5% 5% 4 4 4 6% 8% 44%	2042
October	1st to 10th	Night	14% 6% 3 4 6% 3 5% 4 4 5% 44%	2160
	11th to 20th	Night	18% 8% 3 6% 6% 4 4 5% 5% 6% 34%	2160
	21st to end	Night	22% 9% 2 6% 6% 3 4 4 5% 6% 33%	2497
November	1st to 10th	Night	24% 11% 4 7% 7% 4 5% 5% 5% 6% 22%	2590
	11th to 20th	Night	22% 10% 4 7% 6% 4 5% 4 5% 6% 26%	2660
	21st to end	Night	21% 10% 4 8% 7% 4 5% 5% 5% 6% 25%	2660
December	1st to 10th	Night	18% 13% 6% 8% 7% 4 5% 5% 4 5% 25%	2679
	11th to 20th	Night	23% 14% 5% 9% 7% 5% 6% 5% 5% 5% 17%	3520
	21st to end	Night	21% 15% 5% 9% 8% 4 6% 4 5% 5% 18%	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	59% 24% 6% 9% 2	2219
	11th to 20th	Day	48% 24% 12% 11% 5%	2220
	21st to end	Day	66% 21% 6% 5% 1	2866
February	1st to 10th	Day	48% 35% 8% 7% 2	1710
	11th to 20th	Day	45% 35% 6% 8% 5%	1674
	21st to end	Day	47% 35% 8% 6% 4	1413
March	1st to 10th	Day	44% 37% 8% 8% 3 1	1943
	11th to 20th	Day	46% 36% 7% 8% 2 1	1980
	21st to end	Day	48% 36% 7% 7% 1	2207
April	1st to 10th	Day	44% 38% 8% 7% 3	2160
	11th to 20th	Day	40% 37% 6% 9% 7% 1	2241
	21st to end	Day	40% 38% 8% 10% 4	2349
May	1st to 10th	Day	37% 40% 8% 12% 3	2520
	11th to 20th	Day	32% 38% 11% 14% 4	2480
	21st to end	Day	38% 38% 11% 12% 2	2779
June	1st to 10th	Day	35% 39% 10% 10% 3 2	2700
	11th to 20th	Day	36% 39% 15% 9% 1	2700
	21st to end	Day	27% 38% 15% 13% 6% 1	2700
July	1st to 10th	Day	20% 40% 12% 20% 7% 2	2626
	11th to 20th	Day	18% 38% 15% 22% 8%	2619
	21st to end	Day	12% 39% 11% 24% 10% 3	2644
August	1st to 10th	Day	19% 37% 15% 21% 7% 1	2416
	11th to 20th	Day	19% 37% 15% 17% 11% 2	2298
	21st to end	Day	22% 39% 13% 21% 5% 1	2534
September	1st to 10th	Day	18% 37% 14% 19% 10% 3	2160
	11th to 20th	Day	26% 36% 11% 14% 12% 1	2124
	21st to end	Day	30% 38% 11% 14% 7% 1	1918
October	1st to 10th	Day	32% 37% 10% 14% 7%	1800
	11th to 20th	Day	39% 37% 12% 9% 2	1800
	21st to end	Day	37% 37% 9% 11% 5%	1855
November	1st to 10th	Day	44% 40% 6% 5% 3 1	1488
	11th to 20th	Day	44% 39% 7% 6% 4	1520
	21st to end	Day	44% 39% 6% 9% 2	1520
December	1st to 10th	Day	42% 40% 8% 6% 4	1497
	11th to 20th	Day	49% 31% 11% 7% 1 1	1688
	21st to end	Day	59% 24% 8% 6% 2	2442
January	1st to 10th	Night	60% 24% 7% 7% 2	4726
	11th to 20th	Night	46% 26% 10% 14% 4 1	4740
	21st to end	Night	62% 21% 7% 6% 3	4791
February	1st to 10th	Night	45% 35% 10% 8% 2	2470
	11th to 20th	Night	37% 36% 10% 11% 6%	2404
	21st to end	Night	44% 34% 6% 12% 4	2041
March	1st to 10th	Night	39% 37% 9% 11% 5%	2129
	11th to 20th	Night	41% 37% 9% 9% 3	1980
	21st to end	Night	42% 36% 10% 10% 2	2148
April	1st to 10th	Night	37% 37% 11% 11% 4	1800
	11th to 20th	Night	31% 38% 9% 14% 6% 1	1667
	21st to end	Night	35% 36% 11% 13% 5%	1610
May	1st to 10th	Night	29% 37% 13% 16% 5%	1440
	11th to 20th	Night	26% 37% 12% 18% 6%	1416
	21st to end	Night	32% 37% 15% 12% 4	1494
June	1st to 10th	Night	31% 36% 13% 14% 3 3	1260
	11th to 20th	Night	26% 38% 20% 15% 2	1260
	21st to end	Night	20% 36% 20% 13% 8% 3	1260
July	1st to 10th	Night	16% 37% 15% 22% 6% 4	1225
	11th to 20th	Night	13% 37% 14% 25% 10% 1	1218
	21st to end	Night	7% 38% 10% 25% 17% 3	1430
August	1st to 10th	Night	16% 37% 14% 23% 9% 2	1495
	11th to 20th	Night	11% 36% 15% 20% 10% 6%	1602
	21st to end	Night	17% 36% 14% 24% 8% 1	1822
September	1st to 10th	Night	13% 35% 12% 23% 13% 4	1800
	11th to 20th	Night	23% 36% 11% 14% 12% 4	1834
	21st to end	Night	26% 36% 13% 15% 8% 2	2042
October	1st to 10th	Night	28% 36% 12% 15% 9% 1	2160
	11th to 20th	Night	32% 37% 13% 14% 5%	2160
	21st to end	Night	34% 38% 9% 12% 7%	2497
November	1st to 10th	Night	40% 41% 6% 9% 3 1	2590
	11th to 20th	Night	40% 40% 8% 8% 4	2660
	21st to end	Night	41% 39% 9% 8% 2	2660
December	1st to 10th	Night	40% 40% 9% 8% 3	2679
	11th to 20th	Night	50% 32% 12% 5% 1	3516
	21st to end	Night	55% 25% 8% 8% 3	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	36% 19% 18% 15% 7% 5%	180
	11th to 20th	Day	41% 12% 14% 17% 13% 2	180
	21st to end	Day	33% 16% 22% 17% 10% 1	273
February	1st to 10th	Day	33% 19% 24% 18% 6% 1	370
	11th to 20th	Day	30% 19% 30% 15% 5%	365
	21st to end	Day	30% 21% 25% 17% 5% 1	307
March	1st to 10th	Day	27% 18% 25% 20% 8% 1	440
	11th to 20th	Day	25% 20% 23% 21% 9% 1	420
	21st to end	Day	28% 18% 24% 21% 7% 1	462
April	1st to 10th	Day	27% 17% 27% 17% 10% 2	420
	11th to 20th	Day	23% 15% 30% 18% 11% 3	412
	21st to end	Day	22% 17% 27% 23% 9% 2	420
May	1st to 10th	Day	14% 12% 29% 30% 12% 3	423
	11th to 20th	Day	18% 9% 24% 26% 18% 5%	448
	21st to end	Day	15% 9% 27% 31% 15% 4	540
June	1st to 10th	Day	18% 10% 30% 25% 15% 2	630
	11th to 20th	Day	12% 15% 33% 25% 13% 2	630
	21st to end	Day	10% 8% 27% 33% 20% 3	630
July	1st to 10th	Day	12% 5% 19% 33% 26% 4	621
	11th to 20th	Day	6% 6% 25% 37% 21% 6%	618
	21st to end	Day	5% 4 20% 34% 29% 8%	546
August	1st to 10th	Day	8% 6% 16% 30% 30% 10%	447
	11th to 20th	Day	5% 5% 19% 35% 27% 9%	437
	21st to end	Day	10% 7% 25% 34% 16% 8%	495
September	1st to 10th	Day	11% 6% 29% 36% 14% 3	450
	11th to 20th	Day	18% 10% 22% 28% 17% 5%	450
	21st to end	Day	17% 13% 26% 26% 16% 2	450
October	1st to 10th	Day	21% 8% 25% 25% 19% 2	450
	11th to 20th	Day	25% 13% 21% 24% 14% 3	450
	21st to end	Day	26% 21% 25% 16% 10% 3	395
November	1st to 10th	Day	33% 17% 27% 17% 6% 1	180
	11th to 20th	Day	29% 17% 21% 18% 12% 4	180
	21st to end	Day	31% 18% 21% 13% 10% 8%	180
December	1st to 10th	Day	32% 16% 18% 13% 14% 7%	180
	11th to 20th	Day	33% 13% 19% 23% 9% 2	180
	21st to end	Day	35% 13% 24% 19% 7% 2	198
January	1st to 10th	Night	33% 16% 20% 17% 11% 3	850
	11th to 20th	Night	31% 11% 16% 24% 17% 2	850
	21st to end	Night	30% 10% 16% 26% 15% 3	848
February	1st to 10th	Night	31% 14% 17% 22% 13% 3	760
	11th to 20th	Night	25% 14% 19% 27% 15% 1	744
	21st to end	Night	25% 14% 21% 25% 13% 3	628
March	1st to 10th	Night	20% 15% 18% 29% 15% 2	742
	11th to 20th	Night	22% 15% 21% 26% 15% 2	720
	21st to end	Night	23% 12% 18% 28% 15% 3	792
April	1st to 10th	Night	22% 10% 21% 27% 18% 3	720
	11th to 20th	Night	18% 12% 20% 29% 18% 3	599
	21st to end	Night	19% 8% 20% 35% 16% 2	530
May	1st to 10th	Night	12% 9% 16% 38% 22% 4	360
	11th to 20th	Night	13% 5% 13% 35% 28% 6%	354
	21st to end	Night	12% 2 20% 37% 25% 4	389
June	1st to 10th	Night	15% 8% 18% 32% 25% 3	360
	11th to 20th	Night	11% 8% 23% 34% 22% 3	360
	21st to end	Night	7% 5% 19% 32% 32% 5%	360
July	1st to 10th	Night	7% 3 13% 31% 41% 6%	350
	11th to 20th	Night	4 3 13% 35% 37% 7%	348
	21st to end	Night	3 2 10% 30% 44% 11%	394
August	1st to 10th	Night	6% 2 7% 26% 44% 16%	429
	11th to 20th	Night	4 1 6% 27% 49% 13%	534
	21st to end	Night	8% 4 13% 32% 36% 7%	634
September	1st to 10th	Night	7% 3 11% 39% 31% 9%	720
	11th to 20th	Night	14% 4 14% 23% 32% 14%	720
	21st to end	Night	16% 5% 17% 29% 28% 5%	720
October	1st to 10th	Night	18% 5% 13% 32% 27% 6%	720
	11th to 20th	Night	22% 8% 17% 25% 21% 7%	720
	21st to end	Night	28% 9% 19% 26% 15% 4	792
November	1st to 10th	Night	32% 12% 17% 28% 10% 1	740
	11th to 20th	Night	29% 15% 19% 22% 13% 2	760
	21st to end	Night	27% 12% 20% 22% 15% 4	760
December	1st to 10th	Night	26% 12% 16% 26% 17% 2	769
	11th to 20th	Night	31% 12% 20% 27% 9% 1	850
	21st to end	Night	34% 15% 20% 23% 7% 1	935

Page generated at 2024-03-03 03:29:00. Version ac07

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