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 2024-11-01.

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	20% 11% 3 8% 5% 4 4 3 5% 6% 30%	101748
	Night	23% 13% 4 8% 5% 4 4 3 4 5% 26%	97292
Transparency	Day	55% 7% 13% 16% 8% 1	101490
	Night	58% 7% 13% 15% 6% 1	97196
Seeing	Day	25% 12% 23% 24% 12% 4	15710
	Night	28% 7% 20% 26% 16% 2	23658

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	34% 19% 7% 11% 4 3 3 2 3 4 10%	2219
	11th to 20th	Day	30% 12% 3 11% 9% 5% 4 3 5% 6% 11%	2199
	21st to end	Day	49% 19% 5% 7% 4 3 2 2 2 3 6%	2731
February	1st to 10th	Day	29% 17% 5% 10% 6% 4 4 4 4 6% 11%	1710
	11th to 20th	Day	26% 17% 5% 10% 5% 5% 4 3 4 5% 18%	1665
	21st to end	Day	23% 18% 3 9% 6% 5% 4 4 5% 5% 17%	1413
March	1st to 10th	Day	17% 22% 5% 11% 7% 6% 6% 3 4 5% 15%	3304
	11th to 20th	Day	20% 15% 3 10% 6% 4 4 3 5% 6% 25%	3490
	21st to end	Day	27% 17% 4 9% 6% 5% 4 3 5% 5% 15%	3825
April	1st to 10th	Day	26% 17% 4 9% 6% 5% 5% 4 4 4 16%	2274
	11th to 20th	Day	22% 16% 4 11% 5% 4 4 3 4 5% 21%	2438
	21st to end	Day	23% 14% 4 10% 5% 5% 6% 4 4 5% 20%	2470
May	1st to 10th	Day	16% 10% 3 8% 6% 6% 5% 3 5% 6% 31%	4379
	11th to 20th	Day	12% 9% 3 8% 6% 5% 5% 5% 7% 9% 31%	4377
	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	24% 11% 3 8% 5% 4 5% 3 4 5% 28%	1900
	11th to 20th	Day	31% 10% 4 9% 5% 4 5% 3 5% 6% 18%	1900
	21st to end	Day	31% 12% 3 8% 5% 5% 4 3 5% 6% 20%	1921
November	1st to 10th	Day	35% 17% 6% 11% 6% 4 4 2 3 3 11%	1488
	11th to 20th	Day	34% 15% 3 8% 5% 4 4 3 4 5% 14%	1520
	21st to end	Day	34% 14% 5% 9% 6% 4 4 2 4 4 14%	1520
December	1st to 10th	Day	28% 18% 5% 11% 5% 5% 5% 3 4 4 14%	1367
	11th to 20th	Day	37% 20% 7% 12% 5% 3 2 2 3 2 6%	1685
	21st to end	Day	40% 18% 5% 9% 5% 4 3 2 2 2 9%	2442
January	1st to 10th	Night	35% 20% 5% 11% 6% 5% 4 3 3 3 6%	4726
	11th to 20th	Night	30% 14% 5% 9% 5% 5% 4 4 4 5% 16%	4699
	21st to end	Night	47% 22% 4 6% 3 2 2 2 2 3 7%	4928
February	1st to 10th	Night	29% 19% 4 8% 5% 4 4 3 4 5% 16%	2470
	11th to 20th	Night	24% 16% 4 8% 4 4 4 2 4 5% 24%	2402
	21st to end	Night	22% 16% 3 9% 5% 5% 4 3 5% 5% 23%	2041
March	1st to 10th	Night	18% 22% 5% 8% 5% 4 5% 4 4 5% 18%	3565
	11th to 20th	Night	15% 13% 4 8% 6% 6% 6% 4 6% 6% 26%	3489
	21st to end	Night	25% 19% 5% 8% 6% 5% 5% 3 4 5% 15%	3828
April	1st to 10th	Night	23% 12% 4 9% 5% 5% 5% 4 5% 7% 22%	1902
	11th to 20th	Night	18% 13% 4 9% 5% 6% 4 3 6% 6% 25%	1691
	21st to end	Night	24% 12% 3 8% 5% 6% 5% 3 6% 5% 23%	1710
May	1st to 10th	Night	13% 9% 3 7% 5% 4 4 3 4 5% 43%	2582
	11th to 20th	Night	11% 7% 3 7% 5% 4 6% 5% 7% 9% 37%	2516
	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	20% 9% 4 7% 4 4 5% 3 4 7% 34%	2280
	11th to 20th	Night	28% 12% 3 9% 5% 3 5% 4 4 5% 23%	2280
	21st to end	Night	31% 11% 4 8% 5% 4 4 3 5% 5% 22%	2674
November	1st to 10th	Night	34% 13% 4 10% 5% 4 4 3 4 5% 14%	2596
	11th to 20th	Night	33% 15% 4 8% 5% 5% 4 3 4 4 14%	2660
	21st to end	Night	33% 11% 3 11% 6% 4 5% 3 4 5% 15%	2660
December	1st to 10th	Night	26% 16% 5% 10% 5% 5% 6% 4 4 4 15%	2812
	11th to 20th	Night	38% 19% 6% 11% 4 3 3 2 3 4 7%	3520
	21st to end	Night	39% 19% 5% 10% 4 3 3 2 3 3 10%	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	78% 6% 6% 7% 2	2219
	11th to 20th	Day	66% 13% 10% 8% 3 1	2220
	21st to end	Day	86% 4 4 4 2	2731
February	1st to 10th	Day	73% 8% 7% 7% 5% 1	1710
	11th to 20th	Day	69% 6% 9% 11% 5% 1	1674
	21st to end	Day	66% 8% 9% 11% 4 2	1413
March	1st to 10th	Day	68% 7% 11% 9% 5%	3304
	11th to 20th	Day	59% 7% 11% 19% 4	3490
	21st to end	Day	69% 7% 14% 8% 2	3825
April	1st to 10th	Day	72% 7% 9% 9% 3	2274
	11th to 20th	Day	66% 6% 9% 10% 7% 1	2438
	21st to end	Day	67% 5% 11% 12% 5%	2470
May	1st to 10th	Day	52% 8% 17% 16% 7%	4379
	11th to 20th	Day	46% 11% 24% 16% 4	4380
	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% 7% 14% 12% 9%	1900
	11th to 20th	Day	66% 7% 11% 12% 3	1900
	21st to end	Day	66% 6% 10% 11% 7%	1921
November	1st to 10th	Day	80% 4 7% 5% 4 1	1488
	11th to 20th	Day	72% 6% 9% 7% 6% 1	1520
	21st to end	Day	72% 8% 7% 7% 5% 1	1520
December	1st to 10th	Day	74% 5% 7% 8% 5% 1	1367
	11th to 20th	Day	81% 9% 5% 3 2 1	1688
	21st to end	Day	80% 5% 6% 6% 2 1	2442
January	1st to 10th	Night	79% 9% 6% 4 2	4726
	11th to 20th	Night	63% 12% 9% 11% 4 1	4740
	21st to end	Night	86% 3 4 5% 3	4928
February	1st to 10th	Night	71% 6% 7% 9% 5% 1	2470
	11th to 20th	Night	63% 6% 11% 12% 7% 1	2404
	21st to end	Night	64% 6% 10% 15% 5% 1	2041
March	1st to 10th	Night	62% 7% 13% 13% 4	3565
	11th to 20th	Night	55% 8% 13% 20% 4 1	3490
	21st to end	Night	69% 8% 10% 10% 2	3828
April	1st to 10th	Night	62% 8% 12% 13% 5%	1902
	11th to 20th	Night	57% 7% 13% 13% 8% 1	1691
	21st to end	Night	61% 8% 10% 13% 6% 1	1710
May	1st to 10th	Night	42% 7% 18% 25% 7%	2582
	11th to 20th	Night	40% 13% 25% 16% 4 1	2516
	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	50% 7% 15% 15% 11% 1	2280
	11th to 20th	Night	62% 6% 12% 14% 5%	2280
	21st to end	Night	64% 6% 10% 13% 6% 1	2674
November	1st to 10th	Night	74% 5% 9% 8% 4 1	2596
	11th to 20th	Night	72% 6% 10% 6% 4 2	2660
	21st to end	Night	69% 7% 9% 8% 5% 1	2660
December	1st to 10th	Night	71% 6% 10% 8% 4 1	2812
	11th to 20th	Night	81% 7% 5% 5% 2 1	3516
	21st to end	Night	80% 4 7% 6% 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	42% 9% 19% 18% 7% 4	180
	11th to 20th	Day	43% 13% 14% 18% 11% 2	180
	21st to end	Day	40% 12% 19% 18% 10% 2	309
February	1st to 10th	Day	38% 12% 27% 15% 7% 1	370
	11th to 20th	Day	34% 13% 25% 21% 6% 1	365
	21st to end	Day	35% 20% 23% 15% 6% 2	307
March	1st to 10th	Day	31% 15% 19% 21% 11% 3	433
	11th to 20th	Day	33% 14% 19% 21% 9% 4	460
	21st to end	Day	35% 14% 24% 18% 6% 3	506
April	1st to 10th	Day	37% 14% 24% 18% 7% 1	460
	11th to 20th	Day	29% 17% 26% 15% 10% 3	452
	21st to end	Day	33% 16% 24% 16% 8% 3	460
May	1st to 10th	Day	20% 14% 24% 29% 10% 3	463
	11th to 20th	Day	20% 10% 25% 26% 14% 5%	488
	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% 12% 24% 16% 9% 4	431
November	1st to 10th	Day	41% 12% 12% 21% 12% 2	180
	11th to 20th	Day	39% 9% 14% 17% 15% 4	180
	21st to end	Day	43% 12% 16% 14% 6% 9%	180
December	1st to 10th	Day	33% 12% 19% 18% 12% 6%	180
	11th to 20th	Day	42% 7% 17% 18% 15% 2	180
	21st to end	Day	48% 8% 17% 17% 10% 1	198
January	1st to 10th	Night	45% 10% 19% 16% 8% 2	850
	11th to 20th	Night	41% 7% 18% 21% 12% 1	850
	21st to end	Night	40% 8% 20% 20% 11% 2	906
February	1st to 10th	Night	38% 8% 21% 26% 7% 1	760
	11th to 20th	Night	32% 8% 20% 28% 11%	744
	21st to end	Night	30% 8% 25% 24% 11% 2	628
March	1st to 10th	Night	27% 9% 25% 21% 15% 2	760
	11th to 20th	Night	28% 12% 23% 22% 13% 1	760
	21st to end	Night	33% 9% 20% 26% 11% 2	836
April	1st to 10th	Night	28% 8% 21% 28% 14% 1	751
	11th to 20th	Night	21% 7% 27% 32% 10% 2	563
	21st to end	Night	26% 5% 24% 31% 11% 2	570
May	1st to 10th	Night	15% 6% 18% 38% 23%	409
	11th to 20th	Night	17% 5% 18% 34% 22% 3	374
	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	34% 6% 22% 25% 11% 2	836
November	1st to 10th	Night	39% 9% 20% 25% 6%	742
	11th to 20th	Night	37% 10% 23% 18% 10% 2	760
	21st to end	Night	38% 5% 21% 22% 11% 3	760
December	1st to 10th	Night	32% 10% 19% 23% 13% 2	832
	11th to 20th	Night	42% 7% 22% 21% 7% 1	850
	21st to end	Night	41% 8% 25% 20% 6%	935

Page generated at 2024-10-29 08:20:45. Version ac07

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