Mount Sterling
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mount Sterling clear sky chart from 2005-11-06 to 2026-01-17.

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	13% 8% 3 8% 5% 4 4 4 6% 7% 38%	127900
	Night	13% 9% 4 8% 5% 4 4 3 5% 6% 38%	124074
Transparency	Day	44% 5% 12% 25% 12% 1	131412
	Night	46% 5% 12% 23% 14% 1	128635
Seeing	Day	18% 12% 30% 24% 12% 3	17544
	Night	17% 10% 31% 30% 11% 1	27488

By Month

Percentage Cloud Cover SE (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	6% 11% 7% 18% 8% 7% 5% 3 4 5% 26%	3697
	11th to 20th	Day	6% 10% 7% 13% 6% 4 5% 8% 9% 7% 25%	3668
	21st to end	Day	11% 15% 7% 9% 5% 3 3 3 4 6% 33%	4369
February	1st to 10th	Day	11% 12% 6% 10% 5% 5% 4 4 6% 7% 31%	1800
	11th to 20th	Day	12% 11% 4 8% 5% 4 5% 4 5% 7% 35%	1794
	21st to end	Day	12% 11% 3 10% 6% 5% 4 3 5% 7% 34%	1650
March	1st to 10th	Day	15% 8% 3 5% 3 3 3 3 4 6% 48%	4540
	11th to 20th	Day	11% 6% 2 7% 4 3 4 4 6% 9% 44%	4980
	21st to end	Day	24% 12% 4 8% 4 3 4 3 4 5% 30%	5736
April	1st to 10th	Day	19% 12% 4 8% 4 4 4 3 5% 6% 31%	2400
	11th to 20th	Day	18% 12% 4 7% 6% 4 4 3 5% 5% 32%	2374
	21st to end	Day	20% 10% 3 7% 4 4 4 4 5% 7% 32%	2405
May	1st to 10th	Day	15% 7% 2 6% 4 4 4 4 5% 6% 41%	6307
	11th to 20th	Day	13% 7% 2 6% 4 4 4 4 6% 8% 42%	6319
	21st to end	Day	18% 6% 2 5% 4 4 4 4 6% 8% 38%	6935
June	1st to 10th	Day	12% 5% 2 7% 4 4 4 3 6% 9% 44%	2800
	11th to 20th	Day	13% 5% 2 6% 5% 5% 4 4 6% 8% 41%	2800
	21st to end	Day	14% 6% 2 6% 6% 4 4 4 7% 8% 39%	2800
July	1st to 10th	Day	8% 6% 2 7% 5% 5% 5% 5% 7% 10% 40%	6360
	11th to 20th	Day	8% 6% 2 5% 4 5% 5% 4 6% 8% 48%	6360
	21st to end	Day	10% 6% 3 8% 5% 5% 5% 4 6% 9% 40%	6924
August	1st to 10th	Day	9% 6% 2 7% 6% 5% 6% 5% 7% 8% 40%	4319
	11th to 20th	Day	13% 6% 2 6% 4 4 5% 4 6% 7% 45%	4082
	21st to end	Day	9% 6% 2 6% 4 4 5% 4 6% 8% 46%	4312
September	1st to 10th	Day	14% 5% 2 5% 4 4 4 4 6% 7% 46%	2400
	11th to 20th	Day	12% 6% 2 6% 3 4 5% 3 6% 8% 45%	2400
	21st to end	Day	12% 7% 2 6% 4 4 4 3 5% 7% 45%	2135
October	1st to 10th	Day	14% 6% 2 6% 4 4 4 3 5% 5% 48%	2000
	11th to 20th	Day	18% 9% 3 7% 4 3 5% 4 4 6% 38%	2000
	21st to end	Day	17% 10% 3 7% 5% 3 3 2 4 6% 39%	2090
November	1st to 10th	Day	13% 8% 3 8% 4 4 4 3 4 7% 42%	1852
	11th to 20th	Day	14% 13% 4 10% 5% 4 4 3 5% 6% 32%	1764
	21st to end	Day	12% 13% 5% 8% 5% 3 4 3 4 6% 37%	1680
December	1st to 10th	Day	8% 9% 4 12% 7% 6% 5% 4 5% 7% 34%	2690
	11th to 20th	Day	13% 14% 5% 12% 7% 7% 4 4 5% 6% 23%	3088
	21st to end	Day	18% 21% 9% 13% 5% 4 4 3 4 4 14%	4070
January	1st to 10th	Night	7% 11% 7% 15% 7% 6% 5% 3 5% 5% 30%	6488
	11th to 20th	Night	10% 12% 6% 15% 6% 5% 5% 6% 8% 6% 22%	6445
	21st to end	Night	10% 13% 7% 11% 5% 5% 4 3 5% 5% 31%	6605
February	1st to 10th	Night	9% 14% 5% 11% 5% 5% 4 4 4 5% 32%	2600
	11th to 20th	Night	10% 10% 3 8% 6% 5% 5% 3 4 6% 39%	2493
	21st to end	Night	14% 11% 3 9% 5% 5% 5% 3 5% 5% 36%	1980
March	1st to 10th	Night	14% 8% 4 7% 4 4 4 3 4 5% 43%	5355
	11th to 20th	Night	10% 8% 3 7% 4 4 4 3 5% 8% 46%	4980
	21st to end	Night	24% 12% 4 10% 5% 4 3 2 4 4 28%	5192
April	1st to 10th	Night	16% 10% 3 7% 5% 4 4 3 4 6% 38%	2000
	11th to 20th	Night	19% 8% 2 6% 4 4 4 4 5% 7% 38%	1975
	21st to end	Night	20% 7% 3 7% 4 4 4 4 6% 6% 36%	1992
May	1st to 10th	Night	16% 7% 3 7% 3 3 3 3 5% 7% 43%	3606
	11th to 20th	Night	11% 6% 2 5% 4 4 4 4 5% 7% 49%	3596
	21st to end	Night	16% 7% 2 6% 4 4 5% 4 5% 6% 41%	3942
June	1st to 10th	Night	10% 5% 2 6% 5% 4 4 4 6% 8% 45%	1600
	11th to 20th	Night	11% 7% 2 5% 4 3 5% 4 5% 9% 45%	1600
	21st to end	Night	10% 7% 3 5% 4 3 4 4 5% 8% 49%	1600
July	1st to 10th	Night	11% 6% 2 6% 4 4 4 4 6% 9% 44%	3618
	11th to 20th	Night	6% 6% 2 4 3 4 4 3 7% 9% 52%	3617
	21st to end	Night	7% 5% 2 6% 4 4 4 4 7% 9% 48%	3947
August	1st to 10th	Night	10% 4 2 5% 5% 4 4 4 5% 7% 49%	2824
	11th to 20th	Night	10% 6% 2 5% 4 3 4 3 5% 7% 50%	2974
	21st to end	Night	10% 5% 2 5% 3 3 5% 4 5% 7% 50%	3586
September	1st to 10th	Night	10% 5% 2 5% 3 3 3 3 6% 7% 53%	2000
	11th to 20th	Night	12% 4 2 5% 4 4 4 3 5% 7% 51%	2000
	21st to end	Night	10% 5% 2 5% 4 4 3 3 5% 7% 53%	2240
October	1st to 10th	Night	12% 7% 2 5% 4 3 3 3 5% 5% 52%	2400
	11th to 20th	Night	16% 7% 2 6% 4 4 4 4 5% 7% 42%	2400
	21st to end	Night	16% 10% 3 7% 4 4 4 4 6% 6% 37%	2750
November	1st to 10th	Night	14% 8% 3 6% 4 4 4 3 5% 6% 44%	2666
	11th to 20th	Night	14% 12% 5% 9% 6% 4 4 3 5% 7% 32%	2854
	21st to end	Night	16% 11% 4 9% 5% 4 3 3 4 5% 36%	2940
December	1st to 10th	Night	7% 9% 3 10% 7% 6% 6% 4 6% 8% 36%	4720
	11th to 20th	Night	13% 17% 6% 12% 5% 5% 4 3 5% 5% 25%	5339
	21st to end	Night	21% 18% 7% 14% 6% 5% 4 3 4 4 16%	7150

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	63% 3 11% 17% 7%	3698
	11th to 20th	Day	53% 6% 11% 13% 18%	3668
	21st to end	Day	53% 4 14% 18% 11%	4369
February	1st to 10th	Day	51% 6% 14% 17% 11% 1	1800
	11th to 20th	Day	48% 5% 12% 24% 9% 2	1803
	21st to end	Day	50% 7% 11% 19% 11% 2	1650
March	1st to 10th	Day	38% 4 12% 28% 13% 4	4540
	11th to 20th	Day	36% 5% 15% 31% 11% 2	4980
	21st to end	Day	57% 6% 11% 15% 10% 2	5738
April	1st to 10th	Day	53% 6% 11% 20% 10% 1	2400
	11th to 20th	Day	52% 6% 10% 20% 10% 2	2374
	21st to end	Day	51% 8% 11% 18% 11% 1	2405
May	1st to 10th	Day	41% 6% 8% 25% 16% 2	6345
	11th to 20th	Day	39% 6% 13% 28% 13% 1	6323
	21st to end	Day	43% 6% 11% 27% 12% 1	6949
June	1st to 10th	Day	35% 8% 14% 27% 14% 2	2800
	11th to 20th	Day	39% 7% 14% 22% 16% 1	2800
	21st to end	Day	41% 7% 13% 23% 13% 2	2800
July	1st to 10th	Day	39% 4 17% 32% 7% 1	6291
	11th to 20th	Day	35% 4 14% 32% 15% 1	6285
	21st to end	Day	42% 5% 13% 23% 16% 1	6728
August	1st to 10th	Day	40% 6% 14% 27% 12% 1	4304
	11th to 20th	Day	38% 5% 13% 32% 13% 1	4121
	21st to end	Day	35% 5% 14% 31% 14% 1	4311
September	1st to 10th	Day	36% 7% 13% 25% 17% 1	2400
	11th to 20th	Day	36% 6% 14% 30% 13% 1	2400
	21st to end	Day	38% 6% 11% 29% 15% 1	2135
October	1st to 10th	Day	24% 4 7% 42% 23% 1	3260
	11th to 20th	Day	38% 4 9% 26% 20% 2	3240
	21st to end	Day	43% 3 11% 29% 12% 1	3354
November	1st to 10th	Day	42% 5% 13% 24% 13% 2	1852
	11th to 20th	Day	53% 6% 11% 21% 9% 1	1764
	21st to end	Day	49% 6% 16% 22% 7%	1680
December	1st to 10th	Day	52% 5% 16% 21% 7% 1	2690
	11th to 20th	Day	62% 5% 12% 14% 6% 1	3085
	21st to end	Day	74% 4 8% 10% 4	4070
January	1st to 10th	Night	56% 4 12% 20% 7% 1	6488
	11th to 20th	Night	59% 5% 10% 12% 14%	6445
	21st to end	Night	55% 5% 11% 17% 11% 1	6605
February	1st to 10th	Night	54% 5% 12% 17% 11% 1	2600
	11th to 20th	Night	47% 5% 12% 22% 12% 1	2494
	21st to end	Night	48% 6% 12% 20% 11% 2	1980
March	1st to 10th	Night	43% 5% 11% 24% 12% 5%	5355
	11th to 20th	Night	37% 5% 12% 30% 14% 3	4980
	21st to end	Night	61% 4 9% 16% 9% 1	5192
April	1st to 10th	Night	47% 6% 10% 21% 15% 1	2000
	11th to 20th	Night	46% 5% 10% 21% 15% 3	1975
	21st to end	Night	48% 6% 11% 20% 13% 3	1992
May	1st to 10th	Night	40% 6% 10% 22% 21% 1	3630
	11th to 20th	Night	34% 7% 13% 23% 19% 4	3597
	21st to end	Night	41% 7% 10% 27% 14% 1	3950
June	1st to 10th	Night	34% 8% 13% 26% 17% 2	1600
	11th to 20th	Night	35% 7% 13% 22% 20% 2	1600
	21st to end	Night	33% 7% 14% 24% 17% 4	1600
July	1st to 10th	Night	38% 3 16% 28% 13% 2	3580
	11th to 20th	Night	30% 3 16% 33% 16% 1	3572
	21st to end	Night	33% 4 20% 22% 19% 2	3832
August	1st to 10th	Night	34% 5% 14% 28% 18% 1	2815
	11th to 20th	Night	34% 4 13% 32% 15% 1	3001
	21st to end	Night	33% 5% 13% 27% 18% 3	3586
September	1st to 10th	Night	31% 7% 10% 27% 24% 1	2000
	11th to 20th	Night	33% 5% 13% 32% 17% 1	2000
	21st to end	Night	30% 6% 10% 30% 22% 1	2240
October	1st to 10th	Night	26% 3 6% 35% 28% 2	3920
	11th to 20th	Night	31% 4 10% 25% 28% 1	3899
	21st to end	Night	46% 4 9% 26% 15% 1	4436
November	1st to 10th	Night	41% 5% 13% 23% 16% 2	2666
	11th to 20th	Night	52% 6% 13% 18% 10% 1	2854
	21st to end	Night	52% 4 13% 23% 8% 1	2940
December	1st to 10th	Night	48% 4 18% 23% 6% 1	4720
	11th to 20th	Night	61% 5% 11% 15% 7%	5341
	21st to end	Night	72% 4 8% 11% 4	7150

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	19% 15% 37% 21% 7% 2	330
	11th to 20th	Day	19% 18% 43% 14% 5%	318
	21st to end	Day	22% 20% 34% 20% 4	330
February	1st to 10th	Day	18% 20% 43% 14% 5% 1	300
	11th to 20th	Day	19% 27% 34% 15% 5% 1	300
	21st to end	Day	20% 21% 45% 11% 2	249
March	1st to 10th	Day	20% 22% 41% 13% 4	300
	11th to 20th	Day	23% 19% 36% 15% 5% 2	300
	21st to end	Day	28% 18% 29% 17% 6% 1	449
April	1st to 10th	Day	29% 16% 33% 19% 4	500
	11th to 20th	Day	27% 18% 26% 18% 9% 1	492
	21st to end	Day	25% 16% 30% 20% 8% 2	505
May	1st to 10th	Day	20% 14% 32% 24% 7% 2	703
	11th to 20th	Day	21% 15% 25% 24% 12% 2	725
	21st to end	Day	19% 10% 29% 24% 13% 4	789
June	1st to 10th	Day	10% 8% 29% 31% 17% 4	730
	11th to 20th	Day	17% 6% 35% 24% 15% 3	730
	21st to end	Day	15% 9% 32% 28% 13% 4	730
July	1st to 10th	Day	9% 3 21% 31% 24% 11%	721
	11th to 20th	Day	10% 6% 28% 32% 19% 6%	718
	21st to end	Day	8% 3 28% 36% 18% 6%	794
August	1st to 10th	Day	8% 2 24% 34% 23% 9%	726
	11th to 20th	Day	17% 5% 19% 27% 23% 9%	665
	21st to end	Day	12% 6% 24% 31% 20% 7%	583
September	1st to 10th	Day	16% 8% 23% 29% 18% 6%	530
	11th to 20th	Day	12% 6% 21% 36% 19% 5%	530
	21st to end	Day	16% 12% 29% 23% 18% 2	461
October	1st to 10th	Day	16% 10% 33% 28% 12% 1	330
	11th to 20th	Day	29% 14% 34% 18% 5%	330
	21st to end	Day	26% 16% 32% 19% 6% 1	363
November	1st to 10th	Day	18% 17% 38% 20% 5% 2	330
	11th to 20th	Day	19% 23% 36% 15% 6% 1	330
	21st to end	Day	23% 15% 39% 18% 4	330
December	1st to 10th	Day	16% 17% 41% 18% 7% 1	330
	11th to 20th	Day	21% 18% 38% 18% 5%	330
	21st to end	Day	27% 15% 39% 15% 2 1	363
January	1st to 10th	Night	14% 15% 36% 27% 7%	1050
	11th to 20th	Night	19% 16% 36% 25% 5%	1031
	21st to end	Night	20% 12% 36% 27% 5% 1	1100
February	1st to 10th	Night	17% 15% 35% 28% 5% 1	1000
	11th to 20th	Night	17% 14% 40% 23% 5%	939
	21st to end	Night	20% 15% 37% 24% 4	660
March	1st to 10th	Night	21% 13% 36% 24% 6%	795
	11th to 20th	Night	18% 12% 34% 27% 8% 1	600
	21st to end	Night	25% 11% 30% 27% 6% 1	660
April	1st to 10th	Night	21% 14% 36% 25% 5%	600
	11th to 20th	Night	23% 13% 30% 28% 6%	593
	21st to end	Night	24% 7% 32% 29% 8% 1	600
May	1st to 10th	Night	20% 8% 32% 33% 7% 1	600
	11th to 20th	Night	19% 9% 28% 34% 10% 1	591
	21st to end	Night	16% 5% 27% 37% 13% 1	650
June	1st to 10th	Night	12% 5% 29% 40% 13% 1	600
	11th to 20th	Night	14% 4 32% 38% 12%	600
	21st to end	Night	13% 4 27% 41% 15% 1	600
July	1st to 10th	Night	8% 1 18% 40% 29% 3	585
	11th to 20th	Night	9% 2 19% 44% 23% 2	582
	21st to end	Night	8% 2 15% 48% 25% 2	657
August	1st to 10th	Night	7% 2 16% 48% 26% 1	597
	11th to 20th	Night	11% 3 16% 41% 24% 6%	594
	21st to end	Night	12% 3 17% 43% 23% 2	660
September	1st to 10th	Night	13% 4 21% 37% 20% 5%	600
	11th to 20th	Night	14% 4 20% 35% 25% 3	600
	21st to end	Night	11% 10% 25% 35% 18% 1	775
October	1st to 10th	Night	16% 7% 28% 30% 18% 2	800
	11th to 20th	Night	19% 12% 32% 28% 8%	800
	21st to end	Night	21% 13% 30% 28% 7% 1	880
November	1st to 10th	Night	19% 12% 35% 25% 9%	820
	11th to 20th	Night	19% 16% 38% 22% 5%	964
	21st to end	Night	22% 15% 33% 23% 7%	1050
December	1st to 10th	Night	18% 14% 40% 22% 5%	1050
	11th to 20th	Night	22% 14% 35% 24% 6%	1050
	21st to end	Night	27% 14% 34% 22% 3	1155

Page generated at 2026-01-14 00:14:27. Version ac07

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