Starry Knoll
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starry Knoll clear sky chart from 2005-11-06 to 2026-07-16.

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	14% 12% 5% 11% 6% 5% 5% 4 5% 6% 28%	138392
	Night	13% 13% 5% 12% 7% 5% 5% 4 5% 6% 26%	134260
Transparency	Day	55% 7% 10% 18% 9% 1	141985
	Night	58% 7% 10% 16% 8% 1	138754
Seeing	Day	25% 20% 29% 16% 8% 3	16733
	Night	24% 19% 28% 20% 8% 1	26097

By Month

Percentage Cloud Cover NE (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	12% 19% 10% 24% 7% 4 3 2 4 3 12%	4661
	11th to 20th	Day	6% 20% 9% 24% 9% 8% 4 3 3 3 10%	5046
	21st to end	Day	12% 13% 7% 15% 11% 10% 7% 4 5% 5% 11%	5780
February	1st to 10th	Day	13% 18% 6% 17% 9% 6% 5% 3 4 4 16%	1890
	11th to 20th	Day	10% 16% 9% 19% 8% 5% 4 3 3 4 18%	1843
	21st to end	Day	14% 18% 5% 14% 8% 4 4 3 5% 4 21%	1665
March	1st to 10th	Day	15% 13% 9% 11% 5% 4 3 3 4 5% 29%	4996
	11th to 20th	Day	10% 17% 7% 9% 4 4 3 3 4 6% 32%	5090
	21st to end	Day	13% 14% 6% 13% 6% 5% 4 3 5% 5% 26%	5622
April	1st to 10th	Day	15% 18% 5% 9% 4 3 4 4 5% 6% 27%	2520
	11th to 20th	Day	16% 15% 4 7% 4 5% 4 3 5% 6% 31%	2494
	21st to end	Day	19% 11% 4 8% 6% 4 3 3 4 5% 32%	2677
May	1st to 10th	Day	22% 10% 3 8% 5% 5% 5% 4 5% 6% 29%	7691
	11th to 20th	Day	16% 11% 4 8% 5% 5% 4 4 6% 7% 30%	8221
	21st to end	Day	17% 7% 3 7% 6% 5% 6% 5% 6% 7% 32%	9060
June	1st to 10th	Day	16% 7% 3 7% 5% 4 5% 4 6% 8% 36%	2940
	11th to 20th	Day	13% 7% 3 8% 6% 6% 5% 5% 6% 8% 33%	2940
	21st to end	Day	14% 6% 3 6% 5% 5% 5% 4 6% 8% 37%	2940
July	1st to 10th	Day	9% 6% 2 7% 5% 6% 6% 5% 7% 9% 38%	6500
	11th to 20th	Day	8% 6% 3 8% 6% 5% 7% 5% 7% 10% 35%	6430
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 4 6% 8% 41%	6527
August	1st to 10th	Day	18% 6% 3 7% 5% 5% 5% 4 6% 8% 34%	4234
	11th to 20th	Day	14% 7% 3 9% 7% 7% 8% 6% 7% 9% 24%	4174
	21st to end	Day	13% 6% 3 8% 5% 5% 5% 4 6% 10% 36%	4350
September	1st to 10th	Day	15% 8% 3 7% 4 5% 4 3 5% 8% 38%	2400
	11th to 20th	Day	13% 6% 2 7% 4 5% 4 4 6% 7% 42%	2370
	21st to end	Day	18% 8% 3 8% 5% 5% 6% 4 6% 6% 31%	2105
October	1st to 10th	Day	18% 8% 3 8% 5% 5% 4 4 5% 7% 34%	2000
	11th to 20th	Day	20% 13% 3 8% 5% 4 4 4 4 6% 29%	2000
	21st to end	Day	21% 17% 4 9% 4 4 4 3 5% 7% 23%	2200
November	1st to 10th	Day	13% 14% 4 9% 6% 5% 5% 4 5% 4 31%	1872
	11th to 20th	Day	13% 23% 6% 9% 6% 5% 3 3 5% 6% 22%	1680
	21st to end	Day	14% 24% 8% 12% 6% 4 4 3 4 5% 18%	1680
December	1st to 10th	Day	14% 24% 12% 19% 6% 4 3 3 3 3 9%	2680
	11th to 20th	Day	15% 19% 8% 17% 8% 4 4 3 4 4 15%	3066
	21st to end	Day	16% 23% 7% 15% 8% 4 3 3 4 5% 12%	4048
January	1st to 10th	Night	11% 17% 9% 25% 11% 5% 4 2 3 3 9%	8234
	11th to 20th	Night	7% 17% 9% 24% 11% 8% 6% 4 4 4 8%	7837
	21st to end	Night	9% 14% 7% 16% 11% 8% 8% 4 5% 5% 14%	8401
February	1st to 10th	Night	11% 17% 6% 16% 11% 7% 5% 2 4 5% 15%	2730
	11th to 20th	Night	10% 14% 7% 19% 9% 7% 6% 4 5% 5% 16%	2663
	21st to end	Night	13% 15% 6% 18% 9% 4 4 4 4 4 19%	2140
March	1st to 10th	Night	13% 12% 6% 12% 9% 5% 4 3 4 5% 25%	5051
	11th to 20th	Night	12% 15% 7% 10% 5% 4 4 3 4 6% 31%	5089
	21st to end	Night	12% 12% 5% 12% 6% 5% 5% 3 5% 6% 29%	5551
April	1st to 10th	Night	15% 15% 5% 9% 5% 5% 5% 3 4 5% 28%	2100
	11th to 20th	Night	16% 15% 2 7% 4 4 5% 3 4 6% 34%	2075
	21st to end	Night	14% 13% 3 8% 4 4 4 4 5% 8% 33%	1959
May	1st to 10th	Night	24% 8% 4 8% 5% 5% 4 3 5% 6% 28%	5205
	11th to 20th	Night	16% 10% 3 7% 5% 5% 5% 4 5% 7% 33%	4639
	21st to end	Night	17% 9% 3 7% 4 4 4 4 6% 7% 36%	5114
June	1st to 10th	Night	13% 6% 2 6% 5% 5% 5% 5% 7% 9% 37%	1680
	11th to 20th	Night	11% 6% 2 7% 4 4 5% 5% 6% 10% 39%	1680
	21st to end	Night	10% 7% 3 6% 5% 5% 5% 5% 5% 7% 42%	1680
July	1st to 10th	Night	8% 7% 3 9% 5% 4 4 3 7% 10% 39%	3680
	11th to 20th	Night	7% 5% 2 7% 5% 5% 5% 5% 7% 9% 43%	3640
	21st to end	Night	10% 5% 2 6% 4 4 5% 4 6% 8% 47%	4308
August	1st to 10th	Night	13% 8% 3 7% 5% 5% 4 5% 6% 8% 37%	2915
	11th to 20th	Night	14% 8% 3 8% 5% 4 5% 4 6% 8% 35%	2875
	21st to end	Night	10% 5% 2 6% 4 5% 5% 4 6% 9% 44%	3514
September	1st to 10th	Night	15% 6% 2 5% 4 4 3 3 6% 7% 45%	2000
	11th to 20th	Night	13% 7% 2 5% 4 3 3 4 5% 7% 48%	2028
	21st to end	Night	17% 9% 3 6% 5% 4 4 5% 5% 7% 34%	2295
October	1st to 10th	Night	16% 8% 2 7% 5% 4 3 4 6% 7% 39%	2400
	11th to 20th	Night	17% 11% 4 7% 5% 4 4 3 5% 7% 31%	2400
	21st to end	Night	23% 12% 4 7% 5% 4 4 4 5% 6% 26%	2640
November	1st to 10th	Night	12% 15% 3 9% 4 4 4 3 5% 5% 34%	2639
	11th to 20th	Night	13% 18% 5% 10% 6% 5% 5% 4 6% 6% 23%	2940
	21st to end	Night	12% 20% 8% 13% 7% 4 4 3 4 5% 19%	2940
December	1st to 10th	Night	9% 19% 10% 20% 8% 7% 6% 4 4 4 9%	4720
	11th to 20th	Night	15% 20% 9% 15% 7% 4 4 3 4 4 14%	5348
	21st to end	Night	16% 19% 8% 15% 8% 6% 4 3 5% 4 12%	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	78% 4 6% 8% 4	4662
	11th to 20th	Day	80% 4 5% 7% 4	5080
	21st to end	Day	75% 6% 8% 8% 3	5780
February	1st to 10th	Day	73% 6% 7% 10% 4	1890
	11th to 20th	Day	70% 5% 6% 13% 6%	1852
	21st to end	Day	65% 5% 10% 14% 5% 1	1665
March	1st to 10th	Day	59% 5% 10% 18% 8%	4999
	11th to 20th	Day	53% 6% 16% 16% 7% 2	5090
	21st to end	Day	58% 7% 6% 18% 9% 1	5622
April	1st to 10th	Day	58% 6% 9% 16% 10% 1	2520
	11th to 20th	Day	53% 7% 10% 17% 11% 1	2494
	21st to end	Day	54% 6% 9% 18% 12% 1	2677
May	1st to 10th	Day	55% 6% 9% 19% 9% 2	7700
	11th to 20th	Day	52% 8% 9% 21% 10%	8225
	21st to end	Day	49% 7% 10% 21% 11% 1	9061
June	1st to 10th	Day	45% 8% 12% 20% 14% 1	2940
	11th to 20th	Day	46% 8% 14% 20% 11% 1	2940
	21st to end	Day	43% 9% 13% 23% 12%	2940
July	1st to 10th	Day	39% 8% 13% 26% 13% 1	6430
	11th to 20th	Day	41% 8% 14% 20% 15% 1	6355
	21st to end	Day	39% 8% 11% 25% 16%	6340
August	1st to 10th	Day	47% 8% 13% 20% 12%	4221
	11th to 20th	Day	51% 10% 13% 20% 6%	4213
	21st to end	Day	43% 7% 11% 29% 8% 1	4350
September	1st to 10th	Day	43% 8% 11% 26% 11% 2	2400
	11th to 20th	Day	40% 7% 12% 27% 14% 1	2370
	21st to end	Day	51% 8% 10% 20% 11% 1	2105
October	1st to 10th	Day	43% 7% 11% 23% 15% 1	3260
	11th to 20th	Day	49% 5% 14% 15% 15% 3	3240
	21st to end	Day	49% 5% 14% 22% 8% 1	3538
November	1st to 10th	Day	53% 8% 12% 15% 11% 2	1872
	11th to 20th	Day	62% 6% 10% 14% 5% 2	1680
	21st to end	Day	70% 5% 10% 11% 4 1	1680
December	1st to 10th	Day	80% 5% 5% 8% 2	2680
	11th to 20th	Day	73% 5% 9% 9% 3	3066
	21st to end	Day	75% 5% 9% 8% 4	4048
January	1st to 10th	Night	79% 6% 6% 6% 3	8234
	11th to 20th	Night	79% 6% 7% 5% 2	7878
	21st to end	Night	74% 5% 6% 9% 5% 1	8401
February	1st to 10th	Night	72% 5% 9% 10% 4	2730
	11th to 20th	Night	70% 6% 9% 10% 4	2665
	21st to end	Night	68% 6% 8% 11% 7% 1	2140
March	1st to 10th	Night	61% 6% 13% 15% 5%	5061
	11th to 20th	Night	54% 6% 14% 17% 5% 3	5090
	21st to end	Night	54% 7% 8% 16% 13% 2	5551
April	1st to 10th	Night	58% 6% 10% 17% 9% 1	2100
	11th to 20th	Night	52% 6% 12% 17% 12% 1	2075
	21st to end	Night	49% 7% 11% 20% 11% 2	1959
May	1st to 10th	Night	57% 7% 8% 17% 9% 2	5212
	11th to 20th	Night	50% 8% 12% 19% 10%	4640
	21st to end	Night	47% 8% 11% 21% 12% 2	5115
June	1st to 10th	Night	41% 8% 11% 25% 14% 1	1680
	11th to 20th	Night	39% 9% 15% 23% 13% 1	1680
	21st to end	Night	40% 10% 13% 24% 12% 1	1680
July	1st to 10th	Night	41% 7% 14% 23% 13% 1	3640
	11th to 20th	Night	37% 9% 15% 25% 13% 1	3592
	21st to end	Night	35% 7% 13% 25% 19% 2	4180
August	1st to 10th	Night	44% 7% 15% 24% 8% 1	2904
	11th to 20th	Night	45% 9% 14% 25% 8%	2902
	21st to end	Night	36% 9% 14% 33% 8% 1	3514
September	1st to 10th	Night	37% 7% 13% 28% 12% 2	2000
	11th to 20th	Night	35% 6% 14% 28% 15% 1	2028
	21st to end	Night	48% 8% 14% 18% 11% 1	2295
October	1st to 10th	Night	43% 7% 10% 24% 16% 1	3920
	11th to 20th	Night	46% 6% 12% 19% 14% 3	3899
	21st to end	Night	46% 5% 15% 24% 9% 1	4252
November	1st to 10th	Night	50% 6% 11% 20% 10% 2	2639
	11th to 20th	Night	60% 8% 11% 13% 6% 2	2940
	21st to end	Night	66% 7% 11% 12% 3	2940
December	1st to 10th	Night	78% 7% 8% 6% 1	4720
	11th to 20th	Night	74% 5% 8% 9% 4	5348
	21st to end	Night	75% 7% 7% 8% 3	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	31% 34% 26% 6% 3	220
	11th to 20th	Day	31% 37% 26% 4 1 1	294
	21st to end	Day	32% 31% 27% 7% 2	363
February	1st to 10th	Day	38% 29% 24% 7% 1	330
	11th to 20th	Day	36% 31% 30% 2 1	330
	21st to end	Day	40% 29% 26% 5%	381
March	1st to 10th	Day	33% 26% 27% 11% 3	540
	11th to 20th	Day	34% 26% 27% 9% 4	540
	21st to end	Day	36% 24% 26% 10% 3 1	594
April	1st to 10th	Day	35% 25% 25% 10% 5% 1	540
	11th to 20th	Day	32% 26% 24% 10% 5% 2	532
	21st to end	Day	30% 23% 29% 13% 5% 1	540
May	1st to 10th	Day	31% 20% 28% 13% 5% 2	543
	11th to 20th	Day	24% 18% 31% 18% 8% 1	567
	21st to end	Day	20% 17% 30% 20% 10% 3	617
June	1st to 10th	Day	19% 19% 32% 21% 7% 2	570
	11th to 20th	Day	19% 16% 31% 19% 12% 1	570
	21st to end	Day	18% 15% 37% 21% 6% 2	570
July	1st to 10th	Day	13% 12% 31% 28% 13% 4	565
	11th to 20th	Day	12% 10% 30% 30% 13% 5%	544
	21st to end	Day	13% 10% 38% 26% 10% 4	576
August	1st to 10th	Day	13% 10% 28% 26% 16% 7%	526
	11th to 20th	Day	15% 9% 30% 24% 15% 6%	519
	21st to end	Day	13% 11% 33% 23% 14% 7%	583
September	1st to 10th	Day	18% 15% 25% 20% 16% 7%	530
	11th to 20th	Day	12% 8% 25% 23% 23% 9%	530
	21st to end	Day	23% 16% 27% 18% 12% 4	530
October	1st to 10th	Day	21% 14% 29% 19% 14% 4	530
	11th to 20th	Day	30% 21% 28% 14% 5% 2	530
	21st to end	Day	34% 21% 27% 16% 2	583
November	1st to 10th	Day	27% 23% 27% 14% 7% 1	424
	11th to 20th	Day	37% 24% 26% 11% 1 1	220
	21st to end	Day	32% 33% 29% 6%	220
December	1st to 10th	Day	39% 26% 28% 4 3 1	220
	11th to 20th	Day	40% 28% 25% 6% 1	220
	21st to end	Day	38% 24% 31% 5% 2	242
January	1st to 10th	Night	29% 26% 31% 11% 2	840
	11th to 20th	Night	28% 30% 27% 13% 2	840
	21st to end	Night	24% 32% 29% 14% 2	924
February	1st to 10th	Night	27% 29% 30% 13% 1	840
	11th to 20th	Night	29% 29% 30% 11% 1	823
	21st to end	Night	30% 28% 28% 12% 1	692
March	1st to 10th	Night	27% 25% 31% 14% 2	840
	11th to 20th	Night	31% 23% 26% 16% 4	840
	21st to end	Night	25% 25% 30% 15% 4 1	924
April	1st to 10th	Night	28% 22% 30% 18% 2	840
	11th to 20th	Night	28% 18% 29% 19% 5% 1	831
	21st to end	Night	23% 14% 30% 27% 6%	699
May	1st to 10th	Night	23% 13% 26% 27% 10% 1	616
	11th to 20th	Night	17% 13% 32% 31% 7%	414
	21st to end	Night	16% 10% 29% 30% 15% 1	455
June	1st to 10th	Night	15% 10% 30% 33% 11% 1	420
	11th to 20th	Night	15% 12% 27% 35% 11%	420
	21st to end	Night	10% 7% 34% 36% 12%	420
July	1st to 10th	Night	9% 6% 25% 42% 16% 2	410
	11th to 20th	Night	9% 4 28% 38% 20% 1	398
	21st to end	Night	12% 5% 25% 36% 20% 1	602
August	1st to 10th	Night	11% 5% 25% 36% 21% 3	597
	11th to 20th	Night	13% 6% 22% 32% 25% 2	594
	21st to end	Night	12% 7% 26% 31% 22% 2	834
September	1st to 10th	Night	19% 7% 25% 28% 19% 3	800
	11th to 20th	Night	16% 7% 20% 25% 28% 4	800
	21st to end	Night	20% 14% 23% 25% 16% 3	800
October	1st to 10th	Night	21% 13% 27% 21% 17% 1	800
	11th to 20th	Night	25% 18% 31% 21% 5% 1	800
	21st to end	Night	33% 17% 29% 18% 4	880
November	1st to 10th	Night	25% 19% 29% 20% 6%	820
	11th to 20th	Night	29% 24% 27% 13% 6% 2	840
	21st to end	Night	28% 26% 28% 13% 4	840
December	1st to 10th	Night	32% 26% 28% 10% 3	840
	11th to 20th	Night	30% 27% 29% 11% 2	840
	21st to end	Night	30% 28% 31% 11% 1	924

Page generated at 2026-07-13 03:14:49. Version ac07

Copyright © 2026 Attilla Danko.