Hercules Stargazers Alternate Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hercules Stargazers Alternate Site clear sky chart from 2005-11-06 to 2026-06-16.

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	5% 4 2 4 3 3 3 3 5% 7% 62%	146254
	Night	7% 5% 2 5% 4 4 4 3 5% 7% 54%	143232
Transparency	Day	23% 4 7% 20% 25% 20%	141175
	Night	28% 5% 10% 18% 22% 17%	139301
Seeing	Day	9% 10% 29% 34% 15% 3	17447
	Night	11% 5% 19% 37% 24% 4	26800

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	13% 7% 2 6% 4 4 5% 4 6% 8% 41%	5002
	11th to 20th	Day	8% 6% 3 6% 4 3 3 3 4 7% 55%	5340
	21st to end	Day	13% 8% 3 8% 5% 5% 4 4 5% 7% 39%	5843
February	1st to 10th	Day	15% 7% 2 6% 4 3 4 3 5% 6% 45%	1890
	11th to 20th	Day	12% 8% 2 6% 6% 5% 3 3 6% 8% 40%	1927
	21st to end	Day	12% 7% 2 6% 5% 4 4 3 4 7% 46%	1730
March	1st to 10th	Day	10% 7% 3 9% 6% 5% 5% 4 6% 7% 38%	4976
	11th to 20th	Day	8% 5% 2 6% 4 4 4 3 5% 8% 50%	5110
	21st to end	Day	9% 6% 2 6% 5% 5% 6% 5% 8% 9% 38%	5687
April	1st to 10th	Day	11% 7% 2 6% 4 4 4 4 5% 8% 46%	2520
	11th to 20th	Day	8% 5% 2 4 4 3 4 3 5% 7% 56%	2489
	21st to end	Day	4 5% 1 4 4 3 3 3 5% 10% 59%	2520
May	1st to 10th	Day	4 4 2 4 2 2 2 2 4 5% 70%	7339
	11th to 20th	Day	2 1 2 1 2 1 2 3 7% 79%	7798
	21st to end	Day	1 2 1 2 2 2 3 2 4 7% 76%	8992
June	1st to 10th	Day	3 3 1 3 3 3 3 3 5% 7% 64%	2940
	11th to 20th	Day	1 1 1 2 2 2 2 3 5% 7% 75%	2871
	21st to end	Day	2 2 1 2 2 2 2 2 4 6% 76%	2800
July	1st to 10th	Day	1 1 1 2 1 2 2 3 5% 83%	6319
	11th to 20th	Day	1 1 2 2 2 3 2 4 7% 76%	5937
	21st to end	Day	1 1 3 3 3 3 3 3 6% 74%	6402
August	1st to 10th	Day	1 1 1 2 2 2 3 3 5% 7% 75%	5777
	11th to 20th	Day	1 1 2 2 2 2 2 3 5% 81%	5542
	21st to end	Day	1 2 1 2 2 2 3 3 4 7% 74%	5984
September	1st to 10th	Day	1 2 1 3 2 2 2 2 3 7% 75%	2400
	11th to 20th	Day	2 4 2 4 3 3 3 3 4 6% 66%	2400
	21st to end	Day	3 3 1 2 2 2 2 2 3 6% 75%	2117
October	1st to 10th	Day	2 2 2 4 2 2 3 2 5% 6% 72%	3280
	11th to 20th	Day	4 3 2 4 3 3 3 2 5% 6% 66%	3261
	21st to end	Day	4 3 2 5% 3 4 3 4 6% 8% 59%	3558
November	1st to 10th	Day	7% 5% 1 4 4 3 3 3 5% 8% 58%	2012
	11th to 20th	Day	9% 7% 3 7% 5% 4 4 3 6% 7% 45%	1890
	21st to end	Day	10% 6% 2 4 3 3 4 4 6% 6% 52%	1701
December	1st to 10th	Day	7% 5% 2 4 3 2 4 3 6% 10% 53%	2700
	11th to 20th	Day	18% 9% 3 8% 5% 5% 7% 6% 6% 7% 24%	3108
	21st to end	Day	17% 11% 4 10% 6% 4 4 4 5% 8% 28%	4092
January	1st to 10th	Night	13% 6% 3 6% 4 4 4 4 6% 8% 42%	7890
	11th to 20th	Night	8% 5% 3 6% 4 3 3 3 4 7% 54%	7650
	21st to end	Night	12% 8% 3 8% 4 4 4 3 4 7% 41%	8371
February	1st to 10th	Night	14% 7% 3 5% 4 3 3 3 5% 5% 48%	2730
	11th to 20th	Night	11% 6% 3 7% 4 3 4 4 5% 8% 45%	2578
	21st to end	Night	10% 6% 2 5% 4 4 4 3 5% 7% 51%	2076
March	1st to 10th	Night	11% 8% 3 8% 5% 4 5% 3 5% 7% 41%	5124
	11th to 20th	Night	12% 6% 2 5% 3 3 4 3 5% 6% 52%	5110
	21st to end	Night	11% 9% 2 6% 5% 4 4 3 5% 7% 44%	5528
April	1st to 10th	Night	7% 6% 2 6% 4 4 4 4 6% 7% 50%	2100
	11th to 20th	Night	6% 6% 2 5% 4 4 4 3 5% 6% 56%	2079
	21st to end	Night	4 4 1 4 4 3 3 4 7% 7% 60%	2100
May	1st to 10th	Night	4 5% 1 4 3 4 4 2 3 4 65%	5607
	11th to 20th	Night	1 2 1 3 3 3 4 3 4 6% 71%	5066
	21st to end	Night	2 2 1 3 3 3 4 2 3 5% 71%	5181
June	1st to 10th	Night	3 3 2 5% 3 4 4 4 7% 11% 56%	1680
	11th to 20th	Night	1 2 1 2 2 3 3 3 6% 8% 69%	1640
	21st to end	Night	1 3 1 3 3 3 4 3 5% 8% 67%	1600
July	1st to 10th	Night	1 2 2 4 5% 3 4 6% 73%	3640
	11th to 20th	Night	1 3 2 4 4 7% 9% 5% 5% 7% 54%	4023
	21st to end	Night	1 5% 1 6% 5% 9% 10% 5% 6% 8% 45%	4472
August	1st to 10th	Night	2 2 1 3 2 4 5% 4 6% 9% 62%	4035
	11th to 20th	Night	1 1 3 3 4 5% 3 5% 7% 69%	4318
	21st to end	Night	1 2 1 3 3 4 6% 5% 5% 8% 62%	5015
September	1st to 10th	Night	1 3 1 3 3 3 4 3 5% 8% 67%	2000
	11th to 20th	Night	3 5% 1 5% 4 4 4 3 5% 8% 58%	2000
	21st to end	Night	2 3 1 4 3 3 3 3 3 6% 69%	2277
October	1st to 10th	Night	3 2 1 3 3 2 3 2 4 6% 70%	3920
	11th to 20th	Night	3 6% 2 4 3 5% 5% 3 4 6% 60%	3897
	21st to end	Night	4 3 1 5% 3 4 4 4 5% 7% 60%	4253
November	1st to 10th	Night	5% 6% 1 5% 4 4 4 3 4 8% 55%	2503
	11th to 20th	Night	10% 7% 2 5% 4 3 3 4 5% 8% 50%	2730
	21st to end	Night	9% 5% 1 4 4 3 3 3 5% 6% 56%	2917
December	1st to 10th	Night	7% 4 1 5% 3 3 4 3 5% 6% 57%	4700
	11th to 20th	Night	18% 10% 3 8% 5% 5% 5% 4 7% 8% 27%	5316
	21st to end	Night	19% 9% 3 9% 5% 5% 4 4 5% 5% 32%	7106

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	41% 5% 15% 23% 13% 3	5003
	11th to 20th	Day	32% 4 6% 15% 25% 19%	5340
	21st to end	Day	46% 5% 6% 17% 13% 14%	5843
February	1st to 10th	Day	39% 6% 7% 19% 20% 8%	1890
	11th to 20th	Day	40% 6% 9% 18% 20% 5%	1936
	21st to end	Day	38% 4 10% 22% 19% 7%	1730
March	1st to 10th	Day	44% 6% 7% 20% 20% 2	4976
	11th to 20th	Day	32% 4 14% 28% 12% 9%	5110
	21st to end	Day	38% 8% 15% 27% 10% 2	5687
April	1st to 10th	Day	37% 6% 13% 21% 20% 5%	2520
	11th to 20th	Day	29% 6% 14% 24% 21% 7%	2492
	21st to end	Day	22% 7% 13% 31% 25% 4	2520
May	1st to 10th	Day	18% 2 6% 27% 31% 16%	7339
	11th to 20th	Day	9% 2 5% 28% 42% 14%	7801
	21st to end	Day	11% 5% 6% 30% 43% 6%	8994
June	1st to 10th	Day	19% 7% 10% 26% 29% 9%	2940
	11th to 20th	Day	8% 6% 8% 20% 37% 20%	2871
	21st to end	Day	11% 3 6% 13% 33% 34%	2800
July	1st to 10th	Day	6% 2 3 6% 23% 61%	6251
	11th to 20th	Day	8% 2 3 5% 12% 70%	5866
	21st to end	Day	11% 2 4 16% 28% 40%	6217
August	1st to 10th	Day	13% 3 4 9% 26% 45%	4206
	11th to 20th	Day	7% 2 3 9% 41% 37%	4013
	21st to end	Day	10% 2 5% 13% 36% 35%	4311
September	1st to 10th	Day	11% 3 4 11% 31% 41%	2400
	11th to 20th	Day	19% 5% 6% 21% 33% 15%	2400
	21st to end	Day	14% 3 5% 21% 34% 24%	2117
October	1st to 10th	Day	14% 3 4 12% 28% 39%	3280
	11th to 20th	Day	18% 2 6% 25% 30% 19%	3261
	21st to end	Day	23% 3 7% 25% 30% 14%	3558
November	1st to 10th	Day	26% 4 11% 27% 21% 11%	2012
	11th to 20th	Day	38% 6% 10% 22% 20% 6%	1890
	21st to end	Day	31% 4 11% 20% 24% 10%	1701
December	1st to 10th	Day	27% 3 7% 31% 26% 6%	2700
	11th to 20th	Day	58% 5% 8% 15% 12% 3	3108
	21st to end	Day	54% 6% 11% 18% 10% 2	4092
January	1st to 10th	Night	39% 6% 19% 20% 13% 3	7890
	11th to 20th	Night	31% 5% 6% 15% 26% 16%	7650
	21st to end	Night	44% 4 6% 15% 18% 12%	8371
February	1st to 10th	Night	38% 4 8% 19% 21% 10%	2730
	11th to 20th	Night	38% 6% 11% 19% 19% 8%	2580
	21st to end	Night	33% 5% 11% 26% 18% 6%	2076
March	1st to 10th	Night	41% 8% 9% 18% 20% 3	5124
	11th to 20th	Night	33% 6% 13% 24% 16% 8%	5110
	21st to end	Night	39% 8% 14% 24% 13% 2	5528
April	1st to 10th	Night	32% 6% 14% 22% 21% 5%	2100
	11th to 20th	Night	29% 6% 12% 25% 18% 9%	2079
	21st to end	Night	21% 6% 13% 31% 23% 6%	2100
May	1st to 10th	Night	21% 3 7% 22% 32% 16%	5605
	11th to 20th	Night	14% 3 13% 22% 33% 15%	5067
	21st to end	Night	13% 5% 12% 24% 39% 7%	5182
June	1st to 10th	Night	20% 9% 11% 22% 27% 11%	1680
	11th to 20th	Night	11% 6% 8% 19% 35% 21%	1640
	21st to end	Night	13% 4 12% 14% 28% 30%	1600
July	1st to 10th	Night	6% 2 4 5% 21% 62%	3600
	11th to 20th	Night	14% 3 6% 5% 10% 63%	3971
	21st to end	Night	19% 2 6% 14% 24% 35%	4345
August	1st to 10th	Night	19% 3 7% 8% 23% 39%	2929
	11th to 20th	Night	10% 4 8% 7% 36% 36%	3117
	21st to end	Night	13% 3 8% 11% 32% 32%	3608
September	1st to 10th	Night	12% 3 9% 11% 25% 40%	2000
	11th to 20th	Night	23% 6% 11% 19% 25% 15%	2000
	21st to end	Night	15% 3 7% 18% 29% 26%	2277
October	1st to 10th	Night	16% 3 6% 11% 18% 46%	3920
	11th to 20th	Night	21% 3 7% 26% 22% 22%	3897
	21st to end	Night	24% 3 6% 23% 25% 19%	4253
November	1st to 10th	Night	27% 6% 11% 25% 18% 13%	2503
	11th to 20th	Night	33% 5% 12% 24% 19% 7%	2730
	21st to end	Night	30% 5% 10% 20% 22% 12%	2917
December	1st to 10th	Night	29% 4 6% 25% 26% 10%	4700
	11th to 20th	Night	54% 5% 9% 15% 15% 3	5316
	21st to end	Night	53% 7% 12% 16% 9% 3	7106

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	24% 11% 31% 19% 13% 2	318
	11th to 20th	Day	17% 10% 26% 33% 12% 2	430
	21st to end	Day	14% 9% 29% 31% 15% 2	473
February	1st to 10th	Day	21% 11% 20% 29% 17% 2	430
	11th to 20th	Day	20% 17% 26% 24% 12% 1	469
	21st to end	Day	13% 15% 28% 30% 13% 2	446
March	1st to 10th	Day	19% 16% 31% 20% 10% 2	540
	11th to 20th	Day	17% 16% 26% 21% 16% 4	540
	21st to end	Day	13% 17% 32% 26% 10% 2	594
April	1st to 10th	Day	16% 13% 31% 26% 10% 3	540
	11th to 20th	Day	13% 16% 32% 25% 9% 5%	532
	21st to end	Day	7% 18% 31% 29% 11% 4	540
May	1st to 10th	Day	9% 15% 32% 31% 11% 1	543
	11th to 20th	Day	9% 14% 33% 31% 13% 1	568
	21st to end	Day	6% 12% 33% 35% 12% 2	617
June	1st to 10th	Day	7% 10% 36% 34% 11% 2	570
	11th to 20th	Day	4 12% 37% 36% 9% 1	551
	21st to end	Day	1 7% 35% 43% 14% 1	530
July	1st to 10th	Day	2 4 33% 47% 12% 1	526
	11th to 20th	Day	1 2 24% 54% 17% 2	524
	21st to end	Day	2 2 31% 48% 15% 2	575
August	1st to 10th	Day	2 5% 31% 46% 13% 3	527
	11th to 20th	Day	2 4 30% 44% 16% 4	517
	21st to end	Day	2 3 24% 48% 20% 4	583
September	1st to 10th	Day	2 5% 24% 44% 18% 7%	530
	11th to 20th	Day	4 11% 28% 36% 16% 6%	530
	21st to end	Day	4 9% 26% 32% 25% 5%	530
October	1st to 10th	Day	5% 7% 27% 31% 22% 8%	530
	11th to 20th	Day	7% 9% 22% 30% 26% 7%	530
	21st to end	Day	9% 7% 24% 30% 24% 6%	583
November	1st to 10th	Day	11% 9% 19% 26% 30% 6%	488
	11th to 20th	Day	10% 12% 19% 34% 21% 4	330
	21st to end	Day	13% 6% 30% 34% 15% 2	231
December	1st to 10th	Day	14% 11% 27% 30% 14% 4	220
	11th to 20th	Day	18% 13% 25% 31% 13% 1	220
	21st to end	Day	24% 11% 29% 26% 10%	242
January	1st to 10th	Night	20% 6% 16% 32% 22% 4	840
	11th to 20th	Night	13% 6% 16% 38% 22% 4	840
	21st to end	Night	17% 5% 14% 38% 23% 3	924
February	1st to 10th	Night	18% 6% 15% 37% 20% 3	840
	11th to 20th	Night	15% 9% 19% 33% 20% 4	824
	21st to end	Night	14% 8% 20% 35% 20% 2	692
March	1st to 10th	Night	18% 9% 22% 30% 18% 3	840
	11th to 20th	Night	16% 7% 20% 32% 22% 3	840
	21st to end	Night	15% 7% 26% 34% 17% 1	924
April	1st to 10th	Night	12% 8% 25% 35% 17% 2	840
	11th to 20th	Night	10% 13% 25% 31% 18% 3	831
	21st to end	Night	7% 9% 29% 33% 19% 3	840
May	1st to 10th	Night	7% 5% 28% 40% 19% 2	734
	11th to 20th	Night	5% 4 24% 41% 23% 3	548
	21st to end	Night	6% 7% 29% 40% 16% 2	455
June	1st to 10th	Night	4 3 32% 44% 16% 1	420
	11th to 20th	Night	1 4 26% 53% 15% 1	410
	21st to end	Night	3 3 23% 45% 24% 1	400
July	1st to 10th	Night	3 19% 52% 25% 1	390
	11th to 20th	Night	3 1 14% 53% 25% 4	546
	21st to end	Night	3 2 18% 45% 30% 3	657
August	1st to 10th	Night	6% 3 20% 43% 26% 3	597
	11th to 20th	Night	3 1 21% 46% 26% 4	704
	21st to end	Night	5% 1 14% 47% 29% 4	880
September	1st to 10th	Night	2 1 15% 42% 33% 7%	800
	11th to 20th	Night	6% 2 18% 41% 28% 4	800
	21st to end	Night	5% 4 16% 37% 33% 6%	800
October	1st to 10th	Night	7% 3 16% 36% 31% 7%	800
	11th to 20th	Night	8% 5% 14% 33% 33% 7%	800
	21st to end	Night	9% 4 12% 32% 34% 10%	880
November	1st to 10th	Night	8% 5% 14% 30% 35% 7%	820
	11th to 20th	Night	13% 4 15% 36% 27% 5%	840
	21st to end	Night	11% 5% 14% 40% 26% 5%	840
December	1st to 10th	Night	15% 5% 16% 35% 24% 5%	840
	11th to 20th	Night	23% 5% 16% 33% 20% 3	840
	21st to end	Night	22% 8% 22% 29% 17% 1	924

Page generated at 2026-06-12 23:31:43. Version ac07

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