North Sterling State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the North Sterling State Park 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	6% 5% 2 5% 3 3 4 3 5% 7% 56%	135094
	Night	7% 6% 2 6% 4 4 4 3 5% 7% 52%	131721
Transparency	Day	26% 5% 11% 27% 23% 7%	129998
	Night	30% 5% 12% 26% 21% 6%	127836
Seeing	Day	10% 6% 23% 32% 22% 7%	16997
	Night	10% 5% 29% 43% 13% 1	26880

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	4 9% 2 8% 4 3 3 3 4 5% 54%	3638
	11th to 20th	Day	3 8% 3 7% 5% 5% 4 4 5% 6% 49%	3640
	21st to end	Day	2 5% 2 6% 3 3 3 3 5% 7% 62%	4250
February	1st to 10th	Day	4 8% 3 8% 5% 4 5% 3 5% 7% 47%	1866
	11th to 20th	Day	3 7% 3 7% 5% 4 4 3 6% 7% 49%	1949
	21st to end	Day	4 7% 3 6% 4 4 3 3 4 7% 54%	1650
March	1st to 10th	Day	6% 8% 2 6% 3 3 3 3 5% 6% 55%	4500
	11th to 20th	Day	8% 5% 1 4 3 3 3 3 4 7% 59%	4665
	21st to end	Day	6% 6% 2 6% 4 4 5% 4 6% 8% 48%	5969
April	1st to 10th	Day	8% 8% 2 5% 4 4 4 4 6% 6% 52%	2400
	11th to 20th	Day	13% 8% 2 5% 4 3 4 3 6% 7% 45%	2371
	21st to end	Day	11% 6% 3 5% 4 4 4 4 6% 8% 46%	2471
May	1st to 10th	Day	8% 5% 2 6% 5% 4 5% 4 5% 6% 50%	5900
	11th to 20th	Day	7% 4 2 5% 3 4 4 4 6% 9% 51%	6072
	21st to end	Day	15% 5% 2 4 3 3 4 3 5% 7% 48%	6925
June	1st to 10th	Day	6% 3 1 3 3 3 5% 4 8% 9% 55%	2800
	11th to 20th	Day	6% 4 1 3 4 3 4 3 6% 9% 57%	2800
	21st to end	Day	3 3 1 4 3 3 4 4 7% 8% 60%	2800
July	1st to 10th	Day	5% 4 1 4 3 3 4 4 5% 8% 58%	6339
	11th to 20th	Day	4 2 1 4 3 4 4 4 7% 10% 57%	6340
	21st to end	Day	5% 3 1 4 3 4 4 4 8% 10% 53%	6903
August	1st to 10th	Day	9% 3 1 3 3 3 4 3 6% 10% 54%	5926
	11th to 20th	Day	4 3 1 3 3 3 4 3 6% 9% 60%	5366
	21st to end	Day	8% 4 2 5% 4 4 5% 4 5% 7% 51%	5984
September	1st to 10th	Day	6% 3 1 3 3 3 3 3 4 6% 63%	2400
	11th to 20th	Day	6% 2 1 4 3 3 4 3 5% 6% 62%	2295
	21st to end	Day	8% 4 1 3 2 2 2 2 4 6% 66%	2200
October	1st to 10th	Day	6% 3 1 2 2 1 2 2 3 3 76%	3429
	11th to 20th	Day	5% 3 1 5% 3 2 3 3 4 6% 64%	3150
	21st to end	Day	8% 5% 2 4 3 2 3 3 4 7% 60%	3105
November	1st to 10th	Day	4 5% 1 4 2 3 3 3 5% 7% 62%	1763
	11th to 20th	Day	3 5% 2 4 3 3 4 3 4 7% 63%	1800
	21st to end	Day	3 6% 2 4 3 3 3 3 4 6% 61%	1778
December	1st to 10th	Day	3 4 2 5% 2 2 2 2 4 5% 69%	2620
	11th to 20th	Day	3 5% 2 5% 3 3 4 3 5% 7% 61%	3026
	21st to end	Day	5% 8% 3 6% 4 4 4 3 5% 8% 50%	4004
January	1st to 10th	Night	5% 9% 3 7% 4 3 2 2 4 6% 53%	6327
	11th to 20th	Night	2 7% 3 8% 6% 4 4 4 5% 6% 51%	6340
	21st to end	Night	2 6% 2 6% 5% 4 4 3 4 6% 56%	6772
February	1st to 10th	Night	5% 9% 3 8% 6% 4 5% 4 5% 6% 46%	2532
	11th to 20th	Night	3 9% 3 7% 5% 4 4 3 6% 7% 47%	2338
	21st to end	Night	3 7% 3 7% 3 4 3 3 4 7% 56%	1980
March	1st to 10th	Night	6% 9% 3 6% 3 3 3 2 4 5% 55%	5374
	11th to 20th	Night	7% 9% 2 6% 3 3 4 3 4 5% 53%	5314
	21st to end	Night	10% 9% 3 7% 4 5% 4 3 6% 8% 41%	4984
April	1st to 10th	Night	9% 7% 3 6% 5% 3 4 4 5% 6% 49%	2000
	11th to 20th	Night	13% 7% 3 6% 3 4 4 3 5% 6% 48%	1977
	21st to end	Night	15% 7% 2 6% 4 4 4 3 5% 7% 43%	1927
May	1st to 10th	Night	12% 6% 2 5% 4 4 4 4 6% 8% 45%	4080
	11th to 20th	Night	9% 5% 2 5% 4 3 5% 4 6% 9% 48%	3839
	21st to end	Night	18% 7% 2 6% 4 4 4 3 6% 7% 40%	3972
June	1st to 10th	Night	6% 4 1 5% 3 4 5% 4 7% 11% 50%	1600
	11th to 20th	Night	8% 4 1 4 3 4 5% 5% 6% 9% 53%	1600
	21st to end	Night	5% 3 2 6% 5% 5% 4 5% 7% 10% 48%	1600
July	1st to 10th	Night	4 3 1 4 4 4 5% 5% 7% 9% 54%	3640
	11th to 20th	Night	6% 3 1 4 3 4 5% 5% 7% 11% 50%	3640
	21st to end	Night	6% 5% 2 6% 5% 4 5% 4 7% 10% 47%	3970
August	1st to 10th	Night	11% 5% 2 6% 6% 6% 6% 5% 6% 9% 40%	3856
	11th to 20th	Night	6% 4 2 6% 4 5% 5% 5% 6% 9% 49%	4483
	21st to end	Night	9% 5% 2 6% 4 5% 5% 4 6% 9% 45%	4993
September	1st to 10th	Night	5% 4 1 4 3 3 5% 4 6% 7% 57%	2000
	11th to 20th	Night	6% 3 2 4 4 3 4 3 5% 7% 60%	2105
	21st to end	Night	7% 4 1 4 3 2 3 3 5% 6% 63%	2200
October	1st to 10th	Night	7% 2 1 2 2 2 2 2 3 4 73%	3598
	11th to 20th	Night	8% 4 1 3 2 2 3 2 5% 7% 63%	3778
	21st to end	Night	5% 5% 2 4 3 3 3 3 4 5% 62%	4422
November	1st to 10th	Night	5% 4 2 4 3 3 3 3 6% 7% 60%	2535
	11th to 20th	Night	5% 5% 2 5% 4 4 4 3 5% 6% 59%	2600
	21st to end	Night	5% 7% 1 5% 3 4 3 3 5% 6% 58%	2620
December	1st to 10th	Night	2 4 2 4 3 3 3 3 4 5% 66%	4570
	11th to 20th	Night	3 6% 2 5% 3 3 4 3 5% 8% 59%	5181
	21st to end	Night	7% 9% 3 6% 4 5% 4 4 5% 7% 46%	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	33% 4 11% 30% 19% 3	3639
	11th to 20th	Day	34% 5% 13% 24% 21% 4	3640
	21st to end	Day	23% 5% 15% 28% 24% 5%	4250
February	1st to 10th	Day	37% 5% 12% 25% 16% 4	1866
	11th to 20th	Day	34% 5% 10% 28% 19% 4	1959
	21st to end	Day	30% 5% 10% 26% 22% 7%	1650
March	1st to 10th	Day	30% 3 7% 21% 31% 7%	4500
	11th to 20th	Day	25% 5% 10% 25% 32% 4	4665
	21st to end	Day	31% 8% 16% 32% 12% 1	5969
April	1st to 10th	Day	32% 6% 11% 26% 18% 7%	2400
	11th to 20th	Day	36% 5% 13% 23% 17% 6%	2374
	21st to end	Day	34% 5% 12% 29% 18% 2	2471
May	1st to 10th	Day	32% 6% 12% 29% 17% 4	5900
	11th to 20th	Day	28% 6% 12% 26% 24% 4	6076
	21st to end	Day	34% 6% 13% 26% 18% 2	6926
June	1st to 10th	Day	23% 7% 19% 30% 16% 5%	2800
	11th to 20th	Day	23% 6% 12% 26% 23% 10%	2800
	21st to end	Day	19% 6% 11% 27% 27% 10%	2800
July	1st to 10th	Day	23% 6% 9% 21% 32% 10%	6271
	11th to 20th	Day	20% 6% 14% 30% 21% 9%	6265
	21st to end	Day	24% 7% 13% 22% 19% 15%	6705
August	1st to 10th	Day	27% 6% 15% 30% 17% 6%	4311
	11th to 20th	Day	23% 8% 13% 23% 25% 8%	3882
	21st to end	Day	22% 5% 11% 21% 26% 14%	4311
September	1st to 10th	Day	21% 4 7% 27% 25% 15%	2400
	11th to 20th	Day	21% 5% 9% 23% 27% 15%	2295
	21st to end	Day	21% 3 7% 24% 34% 11%	2200
October	1st to 10th	Day	16% 3 5% 19% 32% 25%	3429
	11th to 20th	Day	22% 4 9% 34% 23% 9%	3150
	21st to end	Day	25% 3 9% 29% 27% 7%	3105
November	1st to 10th	Day	22% 4 13% 27% 24% 9%	1763
	11th to 20th	Day	24% 4 7% 31% 29% 6%	1800
	21st to end	Day	25% 3 11% 27% 27% 7%	1778
December	1st to 10th	Day	20% 3 10% 34% 29% 5%	2620
	11th to 20th	Day	23% 4 9% 39% 23% 3	3024
	21st to end	Day	33% 4 12% 33% 15% 3	4004
January	1st to 10th	Night	33% 3 13% 30% 17% 4	6327
	11th to 20th	Night	33% 5% 10% 24% 23% 5%	6340
	21st to end	Night	28% 5% 12% 28% 22% 5%	6772
February	1st to 10th	Night	38% 5% 12% 24% 17% 4	2532
	11th to 20th	Night	35% 5% 13% 28% 16% 3	2338
	21st to end	Night	29% 4 9% 26% 24% 7%	1980
March	1st to 10th	Night	31% 4 6% 20% 32% 7%	5374
	11th to 20th	Night	33% 4 10% 18% 29% 6%	5314
	21st to end	Night	39% 7% 17% 25% 11% 1	4984
April	1st to 10th	Night	36% 5% 11% 23% 18% 6%	2000
	11th to 20th	Night	36% 5% 13% 24% 17% 4	1977
	21st to end	Night	41% 5% 10% 26% 17% 2	1927
May	1st to 10th	Night	35% 7% 15% 28% 11% 3	4080
	11th to 20th	Night	30% 8% 13% 28% 15% 5%	3840
	21st to end	Night	42% 8% 15% 22% 10% 3	3972
June	1st to 10th	Night	27% 9% 24% 25% 12% 3	1600
	11th to 20th	Night	28% 8% 15% 24% 17% 8%	1600
	21st to end	Night	27% 9% 14% 24% 22% 5%	1600
July	1st to 10th	Night	24% 7% 13% 25% 27% 4	3600
	11th to 20th	Night	26% 8% 20% 23% 18% 6%	3592
	21st to end	Night	31% 7% 15% 22% 16% 9%	3856
August	1st to 10th	Night	40% 9% 16% 19% 13% 3	2807
	11th to 20th	Night	35% 8% 13% 22% 17% 5%	3243
	21st to end	Night	25% 7% 16% 22% 19% 10%	3597
September	1st to 10th	Night	24% 6% 10% 25% 24% 12%	2000
	11th to 20th	Night	23% 5% 11% 26% 24% 12%	2105
	21st to end	Night	22% 4 8% 27% 26% 12%	2200
October	1st to 10th	Night	17% 3 6% 19% 32% 24%	3598
	11th to 20th	Night	22% 4 9% 31% 27% 8%	3778
	21st to end	Night	26% 4 9% 28% 24% 9%	4422
November	1st to 10th	Night	23% 5% 11% 26% 26% 8%	2535
	11th to 20th	Night	26% 4 10% 27% 24% 9%	2600
	21st to end	Night	28% 4 9% 27% 26% 7%	2620
December	1st to 10th	Night	21% 3 12% 33% 26% 4	4570
	11th to 20th	Night	24% 3 7% 40% 21% 4	5182
	21st to end	Night	37% 4 10% 29% 18% 2	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	8% 5% 25% 41% 17% 4	300
	11th to 20th	Day	11% 10% 32% 33% 13%	300
	21st to end	Day	9% 7% 39% 32% 9% 4	330
February	1st to 10th	Day	8% 9% 38% 35% 9%	300
	11th to 20th	Day	9% 8% 37% 35% 9% 2	300
	21st to end	Day	8% 11% 38% 33% 8% 1	249
March	1st to 10th	Day	10% 7% 28% 32% 20% 2	300
	11th to 20th	Day	12% 8% 30% 28% 19% 3	330
	21st to end	Day	15% 10% 33% 31% 11% 1	550
April	1st to 10th	Day	14% 15% 31% 24% 12% 4	500
	11th to 20th	Day	18% 13% 30% 25% 12% 3	492
	21st to end	Day	17% 11% 29% 24% 15% 4	571
May	1st to 10th	Day	15% 8% 26% 28% 18% 5%	703
	11th to 20th	Day	17% 6% 21% 29% 22% 5%	725
	21st to end	Day	15% 7% 24% 27% 22% 6%	789
June	1st to 10th	Day	8% 4 18% 32% 25% 12%	730
	11th to 20th	Day	8% 5% 23% 36% 22% 7%	730
	21st to end	Day	6% 3 22% 37% 27% 6%	730
July	1st to 10th	Day	9% 1 14% 34% 33% 10%	721
	11th to 20th	Day	5% 1 12% 33% 36% 14%	718
	21st to end	Day	5% 2 11% 33% 38% 12%	794
August	1st to 10th	Day	7% 1 12% 32% 38% 9%	681
	11th to 20th	Day	4 2 19% 31% 29% 16%	517
	21st to end	Day	6% 2 18% 32% 30% 12%	583
September	1st to 10th	Day	7% 3 16% 34% 28% 13%	530
	11th to 20th	Day	5% 3 16% 30% 32% 15%	425
	21st to end	Day	11% 3 18% 26% 29% 13%	330
October	1st to 10th	Day	13% 4 18% 26% 22% 17%	309
	11th to 20th	Day	6% 9% 29% 32% 15% 9%	300
	21st to end	Day	12% 11% 24% 30% 18% 6%	330
November	1st to 10th	Day	9% 8% 28% 32% 19% 5%	300
	11th to 20th	Day	6% 8% 28% 40% 15% 3	300
	21st to end	Day	8% 7% 27% 36% 20% 3	300
December	1st to 10th	Day	7% 12% 26% 39% 14% 2	300
	11th to 20th	Day	12% 8% 30% 40% 10%	300
	21st to end	Day	12% 9% 29% 37% 11% 2	330
January	1st to 10th	Night	7% 8% 31% 42% 12% 1	1000
	11th to 20th	Night	7% 8% 35% 41% 9% 1	1000
	21st to end	Night	7% 6% 40% 38% 9% 1	1015
February	1st to 10th	Night	10% 6% 40% 37% 7%	800
	11th to 20th	Night	8% 6% 38% 39% 8%	784
	21st to end	Night	7% 6% 43% 39% 4	660
March	1st to 10th	Night	9% 7% 33% 43% 9%	800
	11th to 20th	Night	12% 5% 34% 39% 10% 1	780
	21st to end	Night	14% 6% 35% 38% 7%	660
April	1st to 10th	Night	13% 9% 35% 37% 6%	600
	11th to 20th	Night	17% 8% 31% 39% 5%	593
	21st to end	Night	19% 9% 28% 34% 10%	600
May	1st to 10th	Night	15% 9% 28% 37% 11%	600
	11th to 20th	Night	19% 4 22% 39% 15% 1	591
	21st to end	Night	16% 4 30% 36% 15%	650
June	1st to 10th	Night	10% 3 22% 44% 20% 1	600
	11th to 20th	Night	10% 5% 26% 49% 10%	600
	21st to end	Night	7% 2 23% 51% 17% 1	600
July	1st to 10th	Night	7% 2 17% 51% 22% 1	585
	11th to 20th	Night	5% 1 16% 53% 23% 1	582
	21st to end	Night	6% 1 12% 50% 30% 1	657
August	1st to 10th	Night	7% 1 15% 51% 25% 1	597
	11th to 20th	Night	6% 2 15% 55% 22%	594
	21st to end	Night	5% 2 16% 56% 21%	660
September	1st to 10th	Night	6% 3 18% 53% 20% 1	600
	11th to 20th	Night	8% 2 20% 48% 21% 1	600
	21st to end	Night	8% 3 21% 49% 19%	600
October	1st to 10th	Night	15% 4 20% 40% 19% 2	625
	11th to 20th	Night	11% 4 29% 40% 15% 1	760
	21st to end	Night	10% 6% 27% 45% 12% 1	1012
November	1st to 10th	Night	8% 3 29% 48% 12% 1	975
	11th to 20th	Night	8% 8% 31% 44% 9%	1000
	21st to end	Night	9% 6% 30% 44% 11% 1	1000
December	1st to 10th	Night	7% 7% 37% 41% 8%	1000
	11th to 20th	Night	8% 7% 33% 44% 8%	1000
	21st to end	Night	10% 9% 31% 42% 7%	1100

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