Sproat Lake (east)
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sproat Lake (east) clear sky chart from 2005-11-06 to 2025-05-11.

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	19% 12% 4 9% 5% 5% 5% 3 5% 6% 28%	117270
	Night	22% 14% 4 9% 5% 4 4 3 4 5% 25%	120398
Transparency	Day	56% 8% 13% 15% 7% 1	117012
	Night	59% 8% 12% 14% 6% 1	120302
Seeing	Day	25% 12% 23% 24% 12% 4	16266
	Night	28% 7% 20% 26% 16% 2	24437

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	32% 20% 8% 11% 5% 4 4 2 3 3 9%	3179
	11th to 20th	Day	21% 9% 3 10% 8% 6% 6% 4 7% 8% 18%	3159
	21st to end	Day	36% 16% 4 6% 3 3 3 2 2 3 20%	3927
February	1st to 10th	Day	27% 17% 5% 10% 6% 5% 4 4 5% 5% 11%	1800
	11th to 20th	Day	26% 16% 5% 10% 5% 5% 4 3 4 5% 18%	1755
	21st to end	Day	23% 18% 3 9% 6% 5% 4 4 5% 5% 17%	1485
March	1st to 10th	Day	19% 20% 5% 12% 7% 6% 5% 3 4 4 14%	4746
	11th to 20th	Day	17% 16% 5% 11% 7% 6% 6% 4 5% 6% 19%	5000
	21st to end	Day	24% 18% 5% 12% 7% 6% 5% 4 5% 5% 11%	5486
April	1st to 10th	Day	26% 16% 4 10% 6% 6% 5% 4 4 4 16%	2395
	11th to 20th	Day	21% 15% 4 11% 6% 4 5% 3 4 5% 22%	2568
	21st to end	Day	23% 13% 4 10% 5% 5% 6% 4 4 5% 22%	2600
May	1st to 10th	Day	16% 10% 3 8% 6% 6% 5% 3 5% 6% 31%	4518
	11th to 20th	Day	12% 9% 3 8% 6% 5% 5% 5% 7% 9% 31%	4380
	21st to end	Day	18% 13% 4 11% 7% 6% 6% 4 5% 5% 20%	5126
June	1st to 10th	Day	23% 11% 4 9% 6% 5% 5% 3 6% 6% 22%	2850
	11th to 20th	Day	18% 10% 4 10% 7% 5% 6% 6% 6% 7% 21%	2850
	21st to end	Day	16% 9% 3 10% 5% 5% 5% 4 6% 6% 31%	2850
July	1st to 10th	Day	7% 5% 2 5% 3 3 3 2 4 5% 63%	4740
	11th to 20th	Day	5% 3 1 3 3 2 2 3 4 6% 68%	4740
	21st to end	Day	6% 5% 2 5% 4 4 4 4 7% 8% 50%	5079
August	1st to 10th	Day	6% 3 2 3 3 2 3 2 5% 7% 64%	4192
	11th to 20th	Day	9% 7% 3 8% 5% 5% 6% 5% 8% 9% 36%	4026
	21st to end	Day	12% 7% 3 6% 4 4 4 4 6% 9% 40%	4521
September	1st to 10th	Day	12% 7% 2 6% 4 4 4 4 6% 7% 44%	2294
	11th to 20th	Day	18% 11% 3 7% 4 4 4 3 4 5% 36%	2176
	21st to end	Day	21% 8% 3 8% 5% 4 4 3 4 6% 32%	2067
October	1st to 10th	Day	18% 12% 4 10% 6% 5% 6% 5% 6% 7% 22%	3180
	11th to 20th	Day	29% 9% 4 9% 6% 5% 5% 3 5% 6% 21%	3161
	21st to end	Day	25% 12% 4 11% 6% 6% 6% 4 6% 5% 16%	3168
November	1st to 10th	Day	35% 16% 5% 11% 6% 4 4 2 3 3 11%	1568
	11th to 20th	Day	33% 15% 3 8% 5% 4 4 3 4 5% 14%	1600
	21st to end	Day	33% 14% 5% 10% 6% 5% 4 2 4 4 14%	1600
December	1st to 10th	Day	21% 16% 7% 12% 6% 5% 6% 4 4 4 15%	2341
	11th to 20th	Day	38% 20% 6% 11% 5% 4 2 2 3 3 6%	2645
	21st to end	Day	36% 19% 5% 10% 7% 5% 4 2 3 2 7%	3498
January	1st to 10th	Night	31% 24% 6% 11% 6% 5% 4 3 3 3 5%	6766
	11th to 20th	Night	21% 11% 4 9% 5% 5% 5% 5% 6% 6% 22%	6739
	21st to end	Night	33% 18% 4 6% 3 3 4 2 4 3 20%	7038
February	1st to 10th	Night	27% 18% 4 9% 5% 4 4 4 4 5% 17%	2600
	11th to 20th	Night	24% 16% 4 8% 4 4 4 2 4 6% 24%	2532
	21st to end	Night	23% 16% 3 9% 5% 5% 4 3 5% 5% 22%	2145
March	1st to 10th	Night	18% 22% 5% 9% 5% 4 5% 4 5% 6% 18%	5140
	11th to 20th	Night	13% 15% 5% 9% 6% 6% 6% 5% 6% 6% 22%	4999
	21st to end	Night	25% 20% 5% 11% 6% 5% 5% 3 4 4 12%	5489
April	1st to 10th	Night	22% 12% 4 9% 5% 5% 5% 4 5% 7% 22%	2001
	11th to 20th	Night	18% 12% 4 9% 6% 6% 4 3 6% 6% 27%	1781
	21st to end	Night	23% 11% 3 8% 5% 5% 5% 3 6% 6% 24%	1800
May	1st to 10th	Night	12% 9% 3 7% 5% 4 4 3 4 6% 43%	2663
	11th to 20th	Night	11% 7% 3 7% 5% 4 6% 5% 7% 9% 37%	2519
	21st to end	Night	20% 14% 3 8% 5% 5% 5% 4 5% 6% 26%	2446
June	1st to 10th	Night	18% 11% 3 9% 5% 5% 5% 3 4 7% 29%	1330
	11th to 20th	Night	13% 9% 3 9% 6% 9% 6% 4 5% 8% 28%	1330
	21st to end	Night	10% 7% 2 8% 6% 5% 4 5% 7% 9% 37%	1330
July	1st to 10th	Night	7% 3 1 4 3 3 3 3 4 6% 63%	2220
	11th to 20th	Night	4 3 1 2 3 2 2 3 4 7% 70%	2220
	21st to end	Night	7% 4 1 3 3 3 4 4 6% 8% 56%	2471
August	1st to 10th	Night	4 3 1 3 3 2 2 2 4 6% 71%	2742
	11th to 20th	Night	10% 5% 2 6% 4 5% 5% 3 6% 9% 45%	2812
	21st to end	Night	11% 6% 2 6% 4 4 5% 4 6% 7% 45%	3146
September	1st to 10th	Night	9% 4 2 5% 4 3 4 4 5% 8% 51%	1886
	11th to 20th	Night	16% 9% 3 8% 5% 4 5% 4 5% 5% 36%	2002
	21st to end	Night	21% 9% 3 7% 5% 4 3 3 4 5% 36%	2112
October	1st to 10th	Night	16% 11% 5% 11% 6% 5% 5% 3 4 6% 28%	3800
	11th to 20th	Night	25% 11% 3 10% 5% 4 6% 4 5% 5% 21%	3777
	21st to end	Night	26% 12% 4 10% 6% 5% 5% 3 4 4 19%	4390
November	1st to 10th	Night	34% 14% 4 11% 5% 4 4 3 4 4 13%	2730
	11th to 20th	Night	32% 15% 4 8% 5% 5% 5% 3 4 4 14%	2800
	21st to end	Night	32% 12% 3 11% 6% 4 5% 3 4 5% 15%	2800
December	1st to 10th	Night	20% 16% 8% 15% 6% 5% 6% 3 4 4 13%	4824
	11th to 20th	Night	37% 21% 6% 11% 4 3 4 2 3 3 6%	5560
	21st to end	Night	36% 19% 5% 11% 5% 4 4 3 3 3 7%	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	78% 8% 6% 7% 2	3179
	11th to 20th	Day	52% 18% 14% 13% 3 1	3180
	21st to end	Day	70% 4 8% 12% 5%	3927
February	1st to 10th	Day	72% 8% 7% 7% 5% 1	1800
	11th to 20th	Day	69% 6% 9% 12% 5% 1	1764
	21st to end	Day	67% 8% 9% 10% 4 1	1485
March	1st to 10th	Day	69% 8% 10% 10% 4	4746
	11th to 20th	Day	63% 8% 10% 15% 4	5000
	21st to end	Day	73% 8% 11% 6% 1	5486
April	1st to 10th	Day	71% 8% 10% 9% 3	2395
	11th to 20th	Day	64% 6% 10% 11% 7% 1	2568
	21st to end	Day	65% 5% 12% 13% 5%	2600
May	1st to 10th	Day	52% 8% 17% 16% 7%	4518
	11th to 20th	Day	46% 11% 24% 16% 4	4383
	21st to end	Day	65% 8% 11% 10% 5%	5127
June	1st to 10th	Day	63% 7% 13% 10% 6% 1	2850
	11th to 20th	Day	60% 10% 16% 10% 3	2850
	21st to end	Day	51% 8% 17% 17% 7%	2850
July	1st to 10th	Day	25% 5% 10% 27% 22% 10%	4666
	11th to 20th	Day	19% 5% 14% 41% 21%	4659
	21st to end	Day	28% 10% 22% 24% 15% 2	4918
August	1st to 10th	Day	20% 5% 14% 40% 20% 1	4175
	11th to 20th	Day	38% 14% 22% 17% 8% 1	4065
	21st to end	Day	39% 9% 22% 22% 7%	4520
September	1st to 10th	Day	38% 7% 16% 25% 11% 2	2294
	11th to 20th	Day	49% 7% 13% 16% 14% 1	2176
	21st to end	Day	53% 7% 13% 16% 10% 1	2067
October	1st to 10th	Day	57% 10% 14% 12% 6%	3180
	11th to 20th	Day	63% 7% 11% 16% 3	3161
	21st to end	Day	64% 10% 10% 11% 5%	3168
November	1st to 10th	Day	80% 4 6% 5% 4 1	1568
	11th to 20th	Day	71% 7% 9% 7% 5% 1	1600
	21st to end	Day	73% 8% 7% 6% 5% 1	1600
December	1st to 10th	Day	68% 9% 9% 10% 4 1	2341
	11th to 20th	Day	81% 9% 6% 3 1 1	2648
	21st to end	Day	80% 8% 5% 4 2	3498
January	1st to 10th	Night	80% 9% 6% 4 1	6766
	11th to 20th	Night	52% 15% 13% 15% 4 1	6780
	21st to end	Night	68% 6% 9% 12% 5%	7038
February	1st to 10th	Night	69% 7% 8% 9% 5% 1	2600
	11th to 20th	Night	63% 6% 11% 12% 7% 1	2534
	21st to end	Night	64% 6% 9% 15% 4 1	2145
March	1st to 10th	Night	62% 8% 13% 13% 4	5140
	11th to 20th	Night	57% 10% 13% 17% 3	5000
	21st to end	Night	72% 8% 9% 8% 2	5489
April	1st to 10th	Night	62% 8% 13% 12% 4	2001
	11th to 20th	Night	56% 7% 13% 15% 7% 1	1781
	21st to end	Night	60% 8% 12% 14% 6% 1	1800
May	1st to 10th	Night	42% 7% 18% 25% 7%	2663
	11th to 20th	Night	40% 13% 25% 16% 4 1	2519
	21st to end	Night	56% 10% 16% 15% 2	2446
June	1st to 10th	Night	54% 6% 22% 11% 5% 2	1330
	11th to 20th	Night	53% 9% 22% 12% 4	1330
	21st to end	Night	42% 11% 22% 17% 7% 1	1330
July	1st to 10th	Night	24% 6% 12% 28% 23% 7%	2185
	11th to 20th	Night	16% 5% 16% 46% 16% 1	2178
	21st to end	Night	23% 9% 24% 31% 12% 1	2393
August	1st to 10th	Night	17% 5% 13% 42% 22% 1	2734
	11th to 20th	Night	35% 12% 29% 15% 8% 2	2839
	21st to end	Night	36% 11% 24% 23% 6%	3146
September	1st to 10th	Night	30% 8% 19% 28% 13% 2	1886
	11th to 20th	Night	50% 7% 11% 16% 14% 3	2002
	21st to end	Night	50% 7% 14% 17% 10% 2	2112
October	1st to 10th	Night	55% 9% 14% 13% 7%	3800
	11th to 20th	Night	63% 7% 12% 15% 3	3777
	21st to end	Night	63% 11% 11% 10% 4 1	4390
November	1st to 10th	Night	74% 5% 8% 8% 4 1	2730
	11th to 20th	Night	72% 7% 10% 6% 4 2	2800
	21st to end	Night	69% 8% 9% 8% 5% 1	2800
December	1st to 10th	Night	68% 10% 9% 9% 2	4824
	11th to 20th	Night	82% 7% 5% 4 2	5556
	21st to end	Night	80% 6% 7% 5% 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	42% 10% 20% 19% 7% 4	200
	11th to 20th	Day	39% 12% 13% 23% 13% 2	200
	21st to end	Day	37% 11% 18% 19% 11% 4	337
February	1st to 10th	Day	36% 12% 27% 17% 7% 1	400
	11th to 20th	Day	35% 12% 24% 21% 7% 2	395
	21st to end	Day	35% 20% 23% 15% 6% 2	331
March	1st to 10th	Day	31% 15% 19% 21% 11% 2	470
	11th to 20th	Day	32% 16% 19% 20% 10% 4	500
	21st to end	Day	34% 16% 25% 17% 6% 3	550
April	1st to 10th	Day	37% 14% 23% 17% 8% 1	500
	11th to 20th	Day	27% 16% 26% 16% 11% 4	492
	21st to end	Day	32% 15% 23% 17% 9% 4	500
May	1st to 10th	Day	19% 15% 24% 30% 10% 3	503
	11th to 20th	Day	20% 10% 25% 26% 14% 5%	489
	21st to end	Day	21% 10% 28% 27% 12% 3	712
June	1st to 10th	Day	27% 14% 28% 20% 8% 3	680
	11th to 20th	Day	19% 17% 31% 20% 9% 3	680
	21st to end	Day	18% 12% 25% 29% 13% 4	680
July	1st to 10th	Day	14% 8% 23% 36% 16% 3	671
	11th to 20th	Day	9% 10% 26% 32% 18% 5%	668
	21st to end	Day	8% 9% 24% 32% 21% 5%	704
August	1st to 10th	Day	12% 6% 18% 30% 24% 10%	487
	11th to 20th	Day	8% 7% 20% 32% 23% 10%	477
	21st to end	Day	16% 7% 25% 30% 14% 8%	539
September	1st to 10th	Day	18% 7% 24% 29% 16% 7%	490
	11th to 20th	Day	23% 9% 23% 23% 16% 5%	490
	21st to end	Day	25% 11% 25% 20% 16% 3	490
October	1st to 10th	Day	25% 12% 21% 23% 13% 6%	490
	11th to 20th	Day	34% 9% 20% 21% 11% 5%	490
	21st to end	Day	34% 13% 24% 16% 9% 4	431
November	1st to 10th	Day	41% 15% 13% 20% 11% 2	200
	11th to 20th	Day	39% 10% 14% 18% 15% 4	200
	21st to end	Day	41% 12% 15% 17% 7% 9%	200
December	1st to 10th	Day	32% 12% 19% 18% 14% 7%	200
	11th to 20th	Day	43% 9% 17% 17% 14% 2	200
	21st to end	Day	47% 11% 16% 16% 9%	220
January	1st to 10th	Night	44% 10% 19% 17% 8% 1	900
	11th to 20th	Night	38% 7% 17% 23% 13% 1	900
	21st to end	Night	38% 7% 20% 21% 12% 3	957
February	1st to 10th	Night	36% 8% 21% 26% 8% 1	800
	11th to 20th	Night	32% 9% 19% 28% 12%	784
	21st to end	Night	31% 9% 25% 23% 11% 2	660
March	1st to 10th	Night	27% 9% 25% 22% 15% 2	800
	11th to 20th	Night	28% 13% 23% 22% 13% 1	800
	21st to end	Night	33% 10% 20% 25% 11% 2	880
April	1st to 10th	Night	28% 8% 21% 27% 14% 2	790
	11th to 20th	Night	20% 7% 26% 33% 11% 2	593
	21st to end	Night	25% 6% 24% 31% 13% 2	600
May	1st to 10th	Night	15% 6% 17% 38% 23%	430
	11th to 20th	Night	17% 5% 18% 34% 22% 3	375
	21st to end	Night	17% 4 19% 39% 20% 1	411
June	1st to 10th	Night	19% 8% 22% 31% 20%	380
	11th to 20th	Night	16% 5% 24% 36% 17% 1	380
	21st to end	Night	12% 6% 23% 36% 20% 4	380
July	1st to 10th	Night	11% 3 14% 38% 32% 2	370
	11th to 20th	Night	8% 4 17% 35% 33% 2	368
	21st to end	Night	6% 4 14% 34% 38% 3	416
August	1st to 10th	Night	9% 3 9% 31% 38% 10%	500
	11th to 20th	Night	6% 3 9% 36% 37% 9%	564
	21st to end	Night	15% 3 17% 30% 31% 5%	627
September	1st to 10th	Night	12% 3 15% 35% 29% 6%	746
	11th to 20th	Night	19% 6% 16% 24% 28% 8%	760
	21st to end	Night	24% 7% 20% 26% 19% 4	760
October	1st to 10th	Night	25% 6% 16% 28% 23% 3	760
	11th to 20th	Night	32% 6% 18% 24% 16% 4	760
	21st to end	Night	35% 6% 22% 25% 11% 2	836
November	1st to 10th	Night	38% 10% 20% 25% 6%	780
	11th to 20th	Night	37% 10% 23% 18% 10% 2	800
	21st to end	Night	37% 7% 21% 21% 11% 3	800
December	1st to 10th	Night	31% 10% 19% 23% 15% 2	880
	11th to 20th	Night	42% 7% 22% 21% 7% 1	900
	21st to end	Night	41% 9% 25% 20% 6%	990

Page generated at 2025-05-08 06:34:00. Version ac07

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