Lake Granby (North Shore)
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Granby (North Shore) clear sky chart from 2005-11-06 to 2025-10-04.

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	4 10% 4 10% 5% 5% 5% 4 6% 7% 42%	135375
	Night	3 10% 5% 10% 5% 4 3 3 5% 6% 47%	131485
Transparency	Day	37% 7% 12% 22% 16% 5%	130293
	Night	35% 7% 13% 25% 16% 4	127571
Seeing	Day	14% 20% 33% 23% 9% 2	16875
	Night	11% 14% 37% 27% 11% 1	26838

By Month

Percentage Cloud Cover SW (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	1 9% 7% 21% 11% 4 4 2 4 5% 33%	3638
	11th to 20th	Day	1 12% 8% 18% 13% 9% 4 3 4 4 25%	3842
	21st to end	Day	1 11% 10% 16% 8% 5% 2 2 3 4 39%	4510
February	1st to 10th	Day	1 20% 8% 17% 7% 4 3 2 4 5% 29%	1800
	11th to 20th	Day	1 16% 8% 17% 6% 5% 3 3 3 4 33%	1866
	21st to end	Day	13% 9% 18% 10% 4 2 3 3 5% 33%	1650
March	1st to 10th	Day	1 11% 8% 14% 6% 3 4 3 4 5% 42%	4578
	11th to 20th	Day	1 12% 7% 14% 4 3 4 2 5% 8% 40%	5000
	21st to end	Day	2 19% 8% 16% 6% 4 4 3 5% 6% 28%	5739
April	1st to 10th	Day	4 14% 5% 10% 5% 5% 4 3 5% 7% 38%	2400
	11th to 20th	Day	5% 17% 5% 11% 6% 4 4 3 6% 6% 32%	2371
	21st to end	Day	5% 18% 6% 9% 4 4 5% 5% 6% 6% 32%	2400
May	1st to 10th	Day	5% 15% 7% 9% 6% 5% 6% 5% 7% 7% 29%	5814
	11th to 20th	Day	6% 14% 3 8% 5% 6% 6% 5% 7% 7% 33%	6298
	21st to end	Day	4 10% 2 7% 5% 5% 6% 5% 7% 8% 41%	6925
June	1st to 10th	Day	6% 6% 2 5% 4 5% 5% 5% 7% 9% 47%	2800
	11th to 20th	Day	6% 4 2 5% 4 3 5% 4 6% 8% 53%	2800
	21st to end	Day	4 4 2 5% 4 5% 5% 5% 6% 7% 54%	2800
July	1st to 10th	Day	5% 4 1 5% 3 5% 5% 4 7% 8% 52%	6339
	11th to 20th	Day	3 3 1 6% 6% 7% 8% 6% 9% 9% 43%	6340
	21st to end	Day	4 4 2 7% 6% 6% 7% 5% 8% 8% 43%	6678
August	1st to 10th	Day	5% 5% 2 6% 5% 6% 6% 5% 7% 9% 45%	5779
	11th to 20th	Day	6% 4 2 6% 5% 5% 5% 5% 8% 8% 47%	5497
	21st to end	Day	7% 6% 3 8% 6% 6% 6% 5% 7% 8% 39%	5984
September	1st to 10th	Day	6% 4 2 5% 4 4 4 3 6% 7% 56%	2400
	11th to 20th	Day	7% 6% 1 6% 3 3 4 3 5% 7% 54%	2400
	21st to end	Day	7% 6% 2 4 2 2 3 3 4 6% 61%	2165
October	1st to 10th	Day	3 6% 2 4 2 2 2 2 3 4 70%	3200
	11th to 20th	Day	4 7% 2 5% 4 4 5% 3 6% 7% 53%	3150
	21st to end	Day	6% 12% 3 5% 2 3 3 3 3 7% 53%	3380
November	1st to 10th	Day	2 13% 4 8% 3 2 3 2 5% 6% 53%	1763
	11th to 20th	Day	2 18% 4 9% 4 2 2 2 3 8% 47%	1800
	21st to end	Day	2 12% 5% 11% 4 3 2 2 5% 6% 49%	1619
December	1st to 10th	Day	10% 4 13% 7% 4 3 1 2 4 52%	2620
	11th to 20th	Day	1 13% 7% 10% 4 2 2 1 4 8% 47%	3026
	21st to end	Day	1 16% 7% 18% 7% 5% 4 3 4 5% 30%	4004
January	1st to 10th	Night	9% 9% 20% 8% 6% 4 3 4 5% 32%	6327
	11th to 20th	Night	10% 10% 20% 8% 10% 3 2 3 4 31%	6182
	21st to end	Night	1 11% 8% 17% 8% 5% 3 2 3 3 40%	6468
February	1st to 10th	Night	1 17% 8% 18% 7% 5% 3 3 4 6% 29%	2600
	11th to 20th	Night	2 14% 8% 18% 5% 4 3 2 4 5% 34%	2420
	21st to end	Night	1 13% 8% 18% 7% 3 3 2 4 4 35%	1980
March	1st to 10th	Night	1 13% 12% 12% 5% 3 3 2 3 4 41%	5296
	11th to 20th	Night	1 10% 5% 11% 4 4 3 2 4 6% 48%	5000
	21st to end	Night	3 20% 8% 12% 5% 4 3 3 5% 5% 32%	5222
April	1st to 10th	Night	4 13% 4 8% 5% 4 4 3 5% 6% 45%	2000
	11th to 20th	Night	3 13% 4 9% 6% 4 4 4 5% 6% 42%	1977
	21st to end	Night	5% 14% 3 7% 4 3 3 3 5% 7% 47%	2000
May	1st to 10th	Night	4 12% 4 8% 4 4 5% 4 6% 9% 41%	4146
	11th to 20th	Night	6% 10% 2 5% 4 5% 5% 5% 6% 9% 43%	3617
	21st to end	Night	4 9% 2 4 3 3 4 3 5% 7% 56%	3972
June	1st to 10th	Night	5% 3 1 4 3 3 3 4 6% 9% 59%	1600
	11th to 20th	Night	5% 3 1 3 3 2 3 3 5% 6% 65%	1600
	21st to end	Night	3 4 1 4 3 3 3 4 7% 8% 61%	1600
July	1st to 10th	Night	5% 3 1 4 4 4 4 4 6% 8% 58%	3640
	11th to 20th	Night	2 2 1 3 4 4 5% 6% 9% 10% 55%	3640
	21st to end	Night	2 3 1 4 4 4 5% 5% 8% 9% 54%	4190
August	1st to 10th	Night	4 3 1 5% 4 4 6% 5% 7% 10% 52%	4033
	11th to 20th	Night	2 3 1 4 4 4 6% 5% 7% 9% 56%	4352
	21st to end	Night	6% 5% 2 6% 5% 5% 5% 5% 7% 8% 46%	4993
September	1st to 10th	Night	4 4 2 3 3 4 4 3 6% 7% 60%	2000
	11th to 20th	Night	5% 5% 1 4 3 3 3 3 5% 8% 61%	2000
	21st to end	Night	5% 5% 2 3 3 3 2 3 5% 6% 62%	2231
October	1st to 10th	Night	3 5% 2 3 1 2 2 2 3 4 73%	3836
	11th to 20th	Night	3 7% 2 4 3 3 3 3 5% 8% 60%	3778
	21st to end	Night	4 9% 3 7% 2 2 2 2 4 6% 59%	4146
November	1st to 10th	Night	2 13% 4 6% 3 2 2 2 4 6% 56%	2535
	11th to 20th	Night	2 17% 4 9% 4 2 2 1 4 6% 50%	2600
	21st to end	Night	2 11% 5% 10% 5% 3 3 3 4 7% 48%	2779
December	1st to 10th	Night	1 11% 5% 11% 6% 3 2 1 2 4 54%	4570
	11th to 20th	Night	1 11% 6% 16% 4 3 3 3 5% 7% 41%	5181
	21st to end	Night	1 20% 9% 14% 6% 5% 4 3 5% 6% 28%	6974

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	48% 10% 11% 20% 11% 1	3639
	11th to 20th	Day	57% 9% 10% 13% 9% 2	3842
	21st to end	Day	42% 10% 10% 18% 13% 6%	4510
February	1st to 10th	Day	57% 4 12% 15% 10% 2	1800
	11th to 20th	Day	52% 6% 9% 21% 10% 2	1875
	21st to end	Day	52% 5% 10% 14% 16% 2	1650
March	1st to 10th	Day	41% 4 9% 24% 16% 5%	4578
	11th to 20th	Day	40% 7% 14% 29% 9% 1	5000
	21st to end	Day	48% 10% 13% 22% 5% 1	5739
April	1st to 10th	Day	41% 7% 13% 21% 15% 4	2400
	11th to 20th	Day	48% 8% 11% 16% 15% 2	2374
	21st to end	Day	46% 7% 13% 24% 9% 1	2400
May	1st to 10th	Day	43% 11% 13% 18% 14% 1	5814
	11th to 20th	Day	40% 11% 11% 22% 14% 2	6302
	21st to end	Day	31% 10% 11% 25% 21% 2	6926
June	1st to 10th	Day	29% 8% 16% 23% 17% 6%	2800
	11th to 20th	Day	26% 7% 11% 19% 24% 13%	2800
	21st to end	Day	25% 6% 11% 21% 24% 12%	2800
July	1st to 10th	Day	24% 6% 8% 17% 24% 22%	6271
	11th to 20th	Day	30% 8% 12% 27% 17% 7%	6265
	21st to end	Day	33% 7% 13% 18% 19% 11%	6485
August	1st to 10th	Day	37% 7% 16% 17% 14% 8%	4208
	11th to 20th	Day	35% 8% 13% 17% 21% 6%	3979
	21st to end	Day	32% 6% 12% 17% 22% 9%	4311
September	1st to 10th	Day	26% 4 10% 22% 26% 12%	2400
	11th to 20th	Day	28% 6% 11% 23% 24% 9%	2400
	21st to end	Day	25% 3 9% 29% 28% 5%	2165
October	1st to 10th	Day	19% 4 7% 25% 34% 11%	3200
	11th to 20th	Day	27% 4 11% 36% 19% 2	3150
	21st to end	Day	30% 5% 9% 39% 15% 2	3380
November	1st to 10th	Day	31% 6% 13% 27% 21% 2	1763
	11th to 20th	Day	37% 5% 13% 24% 17% 3	1800
	21st to end	Day	35% 5% 15% 29% 14% 3	1619
December	1st to 10th	Day	37% 4 14% 33% 11% 1	2620
	11th to 20th	Day	36% 4 17% 34% 8%	3024
	21st to end	Day	50% 9% 11% 19% 10% 1	4004
January	1st to 10th	Night	49% 10% 11% 19% 9% 3	6327
	11th to 20th	Night	52% 10% 10% 15% 10% 2	6182
	21st to end	Night	44% 10% 10% 15% 17% 4	6468
February	1st to 10th	Night	55% 7% 11% 16% 9% 1	2600
	11th to 20th	Night	50% 6% 10% 23% 10% 1	2421
	21st to end	Night	49% 6% 9% 17% 16% 3	1980
March	1st to 10th	Night	41% 7% 6% 24% 18% 3	5296
	11th to 20th	Night	32% 9% 12% 29% 16% 1	5000
	21st to end	Night	45% 10% 14% 26% 4 1	5222
April	1st to 10th	Night	37% 8% 13% 24% 15% 3	2000
	11th to 20th	Night	41% 7% 11% 25% 14% 2	1977
	21st to end	Night	37% 6% 15% 27% 15%	2000
May	1st to 10th	Night	34% 10% 15% 28% 12% 1	4143
	11th to 20th	Night	31% 12% 15% 28% 13%	3618
	21st to end	Night	23% 9% 14% 30% 22% 2	3972
June	1st to 10th	Night	19% 11% 20% 28% 17% 5%	1600
	11th to 20th	Night	19% 7% 11% 23% 25% 16%	1600
	21st to end	Night	18% 5% 13% 26% 25% 14%	1600
July	1st to 10th	Night	21% 7% 9% 17% 24% 21%	3600
	11th to 20th	Night	20% 6% 22% 30% 17% 6%	3592
	21st to end	Night	22% 6% 20% 25% 16% 11%	4071
August	1st to 10th	Night	27% 7% 23% 19% 19% 5%	2928
	11th to 20th	Night	26% 11% 20% 17% 17% 9%	3146
	21st to end	Night	28% 7% 13% 20% 26% 5%	3597
September	1st to 10th	Night	23% 7% 13% 20% 26% 11%	2000
	11th to 20th	Night	21% 6% 12% 28% 23% 11%	2000
	21st to end	Night	22% 5% 10% 31% 27% 6%	2231
October	1st to 10th	Night	17% 4 6% 26% 37% 9%	3836
	11th to 20th	Night	22% 3 14% 38% 19% 3	3778
	21st to end	Night	26% 5% 11% 37% 19% 2	4146
November	1st to 10th	Night	29% 5% 12% 28% 23% 3	2535
	11th to 20th	Night	36% 5% 13% 27% 17% 3	2600
	21st to end	Night	35% 6% 12% 30% 14% 2	2779
December	1st to 10th	Night	35% 4 13% 36% 10% 1	4570
	11th to 20th	Night	40% 6% 15% 32% 6%	5182
	21st to end	Night	54% 7% 9% 20% 10% 1	6974

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	18% 19% 35% 18% 9% 1	300
	11th to 20th	Day	16% 28% 33% 19% 3 1	300
	21st to end	Day	8% 26% 43% 17% 6% 1	330
February	1st to 10th	Day	25% 34% 30% 9% 1 1	300
	11th to 20th	Day	23% 32% 34% 9% 3	300
	21st to end	Day	24% 31% 32% 12% 1	249
March	1st to 10th	Day	22% 25% 34% 15% 3	326
	11th to 20th	Day	17% 29% 33% 18% 2	500
	21st to end	Day	20% 39% 28% 10% 2	550
April	1st to 10th	Day	24% 31% 33% 10% 2	500
	11th to 20th	Day	24% 35% 26% 12% 2	492
	21st to end	Day	20% 28% 31% 16% 4 1	500
May	1st to 10th	Day	21% 26% 29% 16% 6% 1	588
	11th to 20th	Day	16% 17% 34% 24% 8% 1	725
	21st to end	Day	14% 19% 29% 26% 11% 2	789
June	1st to 10th	Day	8% 14% 32% 28% 15% 4	730
	11th to 20th	Day	9% 19% 35% 24% 11% 2	730
	21st to end	Day	6% 16% 35% 26% 15% 2	730
July	1st to 10th	Day	6% 8% 27% 35% 20% 3	721
	11th to 20th	Day	5% 6% 29% 35% 19% 5%	718
	21st to end	Day	6% 8% 27% 34% 21% 4	696
August	1st to 10th	Day	11% 11% 34% 31% 11% 3	527
	11th to 20th	Day	7% 9% 33% 35% 13% 4	517
	21st to end	Day	10% 9% 34% 29% 14% 3	583
September	1st to 10th	Day	8% 13% 32% 29% 13% 4	530
	11th to 20th	Day	9% 13% 39% 27% 11% 1	530
	21st to end	Day	10% 15% 27% 32% 12% 4	345
October	1st to 10th	Day	12% 14% 31% 25% 14% 4	309
	11th to 20th	Day	16% 21% 33% 19% 10% 2	300
	21st to end	Day	24% 22% 32% 17% 5%	330
November	1st to 10th	Day	19% 25% 34% 14% 7% 1	300
	11th to 20th	Day	18% 25% 36% 15% 5% 1	300
	21st to end	Day	11% 23% 44% 18% 3 1	300
December	1st to 10th	Day	16% 24% 37% 16% 5% 2	300
	11th to 20th	Day	15% 28% 42% 12% 3	300
	21st to end	Day	20% 21% 38% 15% 4 1	330
January	1st to 10th	Night	14% 21% 39% 19% 7% 1	1000
	11th to 20th	Night	14% 24% 39% 17% 4 1	933
	21st to end	Night	10% 19% 50% 17% 4	880
February	1st to 10th	Night	15% 22% 46% 13% 4	800
	11th to 20th	Night	12% 24% 44% 17% 2	784
	21st to end	Night	14% 24% 47% 13% 3	660
March	1st to 10th	Night	13% 17% 47% 17% 6%	800
	11th to 20th	Night	8% 15% 47% 24% 6%	800
	21st to end	Night	10% 20% 46% 21% 4 1	768
April	1st to 10th	Night	12% 19% 45% 22% 2	600
	11th to 20th	Night	11% 20% 43% 20% 5% 1	593
	21st to end	Night	13% 14% 39% 25% 8% 1	600
May	1st to 10th	Night	12% 12% 41% 25% 9% 1	600
	11th to 20th	Night	10% 9% 31% 38% 11% 1	591
	21st to end	Night	10% 10% 30% 36% 13% 1	650
June	1st to 10th	Night	6% 5% 30% 37% 20% 2	600
	11th to 20th	Night	7% 9% 33% 42% 10% 1	600
	21st to end	Night	5% 5% 26% 43% 21% 1	600
July	1st to 10th	Night	5% 2 15% 44% 30% 4	585
	11th to 20th	Night	2 2 16% 45% 32% 3	582
	21st to end	Night	4 2 12% 46% 33% 4	657
August	1st to 10th	Night	6% 2 16% 48% 27% 1	597
	11th to 20th	Night	3 2 19% 50% 24% 3	594
	21st to end	Night	5% 2 16% 43% 31% 4	660
September	1st to 10th	Night	7% 4 20% 46% 21% 4	600
	11th to 20th	Night	5% 3 28% 44% 18% 3	600
	21st to end	Night	6% 5% 32% 36% 17% 3	647
October	1st to 10th	Night	11% 7% 37% 31% 12% 2	772
	11th to 20th	Night	12% 12% 38% 28% 9% 1	760
	21st to end	Night	14% 12% 45% 21% 7% 2	850
November	1st to 10th	Night	12% 16% 46% 20% 5% 1	975
	11th to 20th	Night	17% 20% 43% 16% 3 1	1000
	21st to end	Night	11% 16% 47% 22% 4	1000
December	1st to 10th	Night	15% 19% 46% 17% 4	1000
	11th to 20th	Night	15% 22% 44% 15% 4	1000
	21st to end	Night	17% 20% 42% 16% 5%	1100

Page generated at 2025-09-30 23:39:04. Version ac07

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