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 2025-02-21.

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% 4 2 4 3 3 3 3 5% 7% 60%	112647
	Night	8% 5% 2 5% 4 4 4 3 5% 7% 53%	114744
Transparency	Day	24% 5% 8% 18% 24% 21%	112406
	Night	29% 6% 11% 17% 20% 17%	114575
Seeing	Day	9% 10% 28% 34% 16% 3	15672
	Night	11% 5% 19% 37% 25% 4	25109

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	12% 6% 2 6% 4 4 4 4 6% 8% 43%	3849
	11th to 20th	Day	10% 7% 3 7% 4 3 3 3 3 5% 51%	4100
	21st to end	Day	15% 8% 4 8% 4 4 4 3 4 6% 41%	4510
February	1st to 10th	Day	16% 7% 2 6% 4 3 4 3 5% 6% 45%	1800
	11th to 20th	Day	12% 8% 2 6% 5% 4 4 3 7% 7% 41%	1833
	21st to end	Day	12% 7% 2 6% 4 4 3 2 4 6% 49%	1571
March	1st to 10th	Day	11% 8% 4 11% 7% 6% 5% 4 6% 7% 31%	3384
	11th to 20th	Day	8% 5% 2 5% 4 3 3 3 5% 6% 56%	3490
	21st to end	Day	10% 7% 3 6% 5% 5% 6% 4 7% 8% 38%	3877
April	1st to 10th	Day	11% 7% 2 6% 4 4 4 4 6% 8% 45%	2280
	11th to 20th	Day	8% 5% 2 4 3 3 4 3 5% 7% 57%	2249
	21st to end	Day	4 4 1 3 4 3 3 3 5% 10% 60%	2280
May	1st to 10th	Day	5% 3 1 2 2 2 2 2 3 5% 73%	3952
	11th to 20th	Day	3 2 1 2 2 2 2 2 4 7% 75%	4183
	21st to end	Day	2 2 1 3 2 2 3 2 3 6% 74%	4813
June	1st to 10th	Day	4 4 1 4 3 3 3 3 5% 7% 63%	2660
	11th to 20th	Day	1 1 1 2 2 2 3 3 5% 8% 74%	2660
	21st to end	Day	2 2 1 3 2 2 3 2 4 6% 75%	2660
July	1st to 10th	Day	1 1 1 2 2 2 2 2 5% 83%	4420
	11th to 20th	Day	1 1 3 2 2 2 2 5% 7% 75%	4154
	21st to end	Day	1 2 2 2 2 2 3 6% 78%	4455
August	1st to 10th	Day	1 1 1 3 2 3 4 4 6% 9% 66%	4091
	11th to 20th	Day	1 1 2 2 2 2 2 4 6% 79%	3850
	21st to end	Day	1 2 1 2 2 2 2 2 4 7% 74%	4180
September	1st to 10th	Day	1 2 1 3 2 2 2 2 3 7% 76%	2280
	11th to 20th	Day	2 4 2 4 3 3 3 3 4 6% 66%	2280
	21st to end	Day	2 2 1 2 2 2 2 2 3 6% 76%	2011
October	1st to 10th	Day	2 2 2 4 2 2 3 2 5% 6% 72%	3180
	11th to 20th	Day	4 3 2 4 3 3 3 3 5% 6% 66%	3161
	21st to end	Day	4 3 2 5% 3 4 3 4 6% 8% 59%	3448
November	1st to 10th	Day	7% 5% 1 4 4 3 3 3 5% 8% 58%	1914
	11th to 20th	Day	9% 7% 3 7% 5% 4 4 3 6% 7% 47%	1800
	21st to end	Day	10% 7% 1 4 3 3 3 4 6% 6% 52%	1620
December	1st to 10th	Day	7% 5% 2 4 3 2 4 3 6% 10% 53%	2620
	11th to 20th	Day	18% 10% 3 8% 5% 5% 7% 6% 6% 7% 25%	3028
	21st to end	Day	17% 11% 4 10% 6% 4 4 4 5% 8% 28%	4004
January	1st to 10th	Night	9% 6% 3 6% 4 4 4 4 6% 9% 46%	6089
	11th to 20th	Night	11% 6% 3 7% 5% 4 4 3 4 5% 48%	5880
	21st to end	Night	14% 8% 3 7% 4 4 4 3 4 6% 43%	6468
February	1st to 10th	Night	14% 7% 3 5% 4 3 3 3 5% 5% 48%	2600
	11th to 20th	Night	11% 6% 3 7% 4 3 4 4 5% 8% 46%	2452
	21st to end	Night	11% 6% 2 5% 4 4 5% 3 5% 6% 52%	1884
March	1st to 10th	Night	13% 9% 3 9% 5% 4 5% 4 5% 6% 38%	3476
	11th to 20th	Night	11% 5% 2 4 3 3 4 3 4 6% 56%	3490
	21st to end	Night	11% 10% 3 8% 5% 4 4 3 4 6% 42%	3774
April	1st to 10th	Night	8% 7% 2 6% 4 3 4 4 5% 7% 50%	1900
	11th to 20th	Night	7% 5% 2 5% 3 3 3 3 5% 6% 58%	1879
	21st to end	Night	4 3 1 3 4 3 3 4 6% 8% 61%	1900
May	1st to 10th	Night	3 3 1 3 3 2 2 2 4 5% 72%	3006
	11th to 20th	Night	2 2 1 3 3 4 6% 3 5% 8% 64%	2716
	21st to end	Night	2 2 1 3 2 3 3 3 3 6% 72%	2762
June	1st to 10th	Night	3 3 2 5% 3 4 4 4 7% 11% 55%	1520
	11th to 20th	Night	1 2 1 3 2 3 3 3 6% 9% 67%	1520
	21st to end	Night	1 3 1 3 3 3 4 3 5% 8% 66%	1520
July	1st to 10th	Night	1 2 2 3 4 2 3 5% 76%	2540
	11th to 20th	Night	1 2 2 4 3 5% 4 3 5% 7% 63%	2811
	21st to end	Night	1 2 1 4 5% 7% 9% 5% 7% 9% 50%	3109
August	1st to 10th	Night	3 3 1 4 3 5% 6% 5% 8% 12% 49%	2848
	11th to 20th	Night	1 1 3 3 3 4 4 5% 8% 67%	2994
	21st to end	Night	1 3 1 4 3 4 5% 4 4 8% 63%	3498
September	1st to 10th	Night	3 1 3 3 3 4 3 5% 8% 69%	1900
	11th to 20th	Night	3 5% 1 5% 3 4 4 3 5% 8% 58%	1900
	21st to end	Night	1 3 1 4 3 3 3 3 3 7% 69%	2163
October	1st to 10th	Night	3 2 1 3 3 2 3 2 4 6% 70%	3800
	11th to 20th	Night	3 6% 2 4 3 5% 5% 3 4 6% 60%	3777
	21st to end	Night	4 3 1 5% 3 3 4 4 5% 7% 60%	4121
November	1st to 10th	Night	6% 6% 1 5% 4 4 4 3 4 8% 56%	2381
	11th to 20th	Night	9% 6% 2 5% 3 3 3 4 5% 8% 52%	2600
	21st to end	Night	9% 5% 1 4 4 3 3 3 5% 6% 56%	2778
December	1st to 10th	Night	8% 4 2 5% 3 3 4 3 4 6% 57%	4560
	11th to 20th	Night	18% 10% 3 8% 5% 5% 5% 4 7% 8% 27%	5176
	21st to end	Night	19% 9% 3 9% 5% 5% 5% 4 5% 5% 32%	6952

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	39% 7% 16% 20% 15% 4	3849
	11th to 20th	Day	38% 4 7% 15% 21% 14%	4100
	21st to end	Day	45% 6% 6% 12% 14% 17%	4510
February	1st to 10th	Day	40% 6% 7% 19% 20% 8%	1800
	11th to 20th	Day	39% 7% 9% 19% 21% 6%	1842
	21st to end	Day	37% 4 9% 23% 20% 7%	1571
March	1st to 10th	Day	51% 9% 10% 15% 13% 2	3384
	11th to 20th	Day	29% 6% 11% 29% 13% 11%	3490
	21st to end	Day	40% 11% 14% 21% 11% 2	3877
April	1st to 10th	Day	37% 6% 13% 20% 19% 4	2280
	11th to 20th	Day	28% 6% 14% 24% 21% 6%	2252
	21st to end	Day	20% 7% 13% 30% 26% 4	2280
May	1st to 10th	Day	15% 4 11% 30% 24% 16%	3952
	11th to 20th	Day	12% 4 8% 25% 39% 13%	4186
	21st to end	Day	13% 9% 10% 32% 33% 4	4814
June	1st to 10th	Day	20% 7% 11% 27% 26% 8%	2660
	11th to 20th	Day	9% 6% 9% 22% 37% 17%	2660
	21st to end	Day	11% 4 7% 13% 32% 33%	2660
July	1st to 10th	Day	6% 2 4 6% 13% 68%	4351
	11th to 20th	Day	9% 3 5% 6% 15% 61%	4083
	21st to end	Day	7% 2 4 6% 27% 54%	4315
August	1st to 10th	Day	13% 3 4 9% 25% 46%	4076
	11th to 20th	Day	7% 2 4 9% 41% 37%	3889
	21st to end	Day	10% 2 5% 13% 35% 35%	4179
September	1st to 10th	Day	10% 3 4 9% 31% 43%	2280
	11th to 20th	Day	19% 6% 6% 21% 32% 16%	2280
	21st to end	Day	13% 3 5% 21% 34% 25%	2011
October	1st to 10th	Day	14% 3 4 11% 28% 40%	3180
	11th to 20th	Day	18% 3 6% 25% 29% 19%	3161
	21st to end	Day	23% 3 6% 25% 30% 14%	3448
November	1st to 10th	Day	26% 4 10% 27% 21% 12%	1914
	11th to 20th	Day	36% 6% 9% 22% 21% 6%	1800
	21st to end	Day	31% 4 11% 19% 24% 11%	1620
December	1st to 10th	Day	27% 3 7% 31% 26% 6%	2620
	11th to 20th	Day	58% 5% 8% 14% 12% 3	3028
	21st to end	Day	54% 6% 12% 18% 9% 2	4004
January	1st to 10th	Night	34% 7% 21% 20% 14% 4	6089
	11th to 20th	Night	38% 6% 8% 16% 20% 12%	5880
	21st to end	Night	43% 5% 7% 11% 19% 15%	6468
February	1st to 10th	Night	38% 5% 8% 19% 20% 10%	2600
	11th to 20th	Night	37% 6% 11% 18% 20% 8%	2454
	21st to end	Night	33% 6% 11% 27% 19% 5%	1884
March	1st to 10th	Night	45% 12% 12% 14% 14% 3	3476
	11th to 20th	Night	30% 9% 10% 22% 18% 11%	3490
	21st to end	Night	42% 10% 14% 20% 11% 3	3774
April	1st to 10th	Night	33% 6% 14% 21% 20% 5%	1900
	11th to 20th	Night	27% 7% 13% 26% 18% 9%	1879
	21st to end	Night	20% 7% 14% 30% 24% 6%	1900
May	1st to 10th	Night	15% 5% 12% 26% 28% 14%	3006
	11th to 20th	Night	16% 5% 23% 15% 26% 14%	2717
	21st to end	Night	12% 9% 19% 29% 28% 3	2762
June	1st to 10th	Night	21% 10% 13% 22% 25% 9%	1520
	11th to 20th	Night	12% 7% 9% 20% 34% 18%	1520
	21st to end	Night	13% 4 12% 14% 27% 29%	1520
July	1st to 10th	Night	7% 3 6% 5% 12% 66%	2500
	11th to 20th	Night	15% 4 8% 7% 10% 57%	2759
	21st to end	Night	14% 4 8% 7% 23% 46%	3011
August	1st to 10th	Night	20% 3 7% 8% 22% 40%	2839
	11th to 20th	Night	10% 4 8% 6% 36% 35%	3021
	21st to end	Night	13% 4 8% 11% 32% 32%	3498
September	1st to 10th	Night	12% 3 9% 9% 25% 42%	1900
	11th to 20th	Night	22% 7% 11% 19% 26% 16%	1900
	21st to end	Night	14% 3 8% 19% 29% 27%	2163
October	1st to 10th	Night	16% 3 6% 10% 18% 48%	3800
	11th to 20th	Night	21% 3 7% 26% 21% 22%	3777
	21st to end	Night	23% 3 6% 23% 25% 20%	4121
November	1st to 10th	Night	27% 6% 11% 25% 17% 14%	2381
	11th to 20th	Night	31% 5% 12% 24% 20% 8%	2600
	21st to end	Night	29% 5% 11% 19% 23% 13%	2778
December	1st to 10th	Night	29% 4 6% 24% 27% 10%	4560
	11th to 20th	Night	54% 4 9% 15% 15% 2	5176
	21st to end	Night	53% 7% 12% 16% 9% 3	6952

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% 10% 30% 20% 14% 2	293
	11th to 20th	Day	18% 11% 23% 33% 13% 2	400
	21st to end	Day	14% 9% 28% 32% 16% 2	440
February	1st to 10th	Day	23% 11% 19% 29% 17% 2	400
	11th to 20th	Day	19% 17% 26% 24% 13% 1	435
	21st to end	Day	12% 16% 26% 29% 15% 2	383
March	1st to 10th	Day	21% 17% 30% 20% 10% 3	460
	11th to 20th	Day	17% 17% 27% 21% 15% 4	460
	21st to end	Day	13% 19% 32% 26% 9% 1	506
April	1st to 10th	Day	17% 14% 32% 24% 10% 3	460
	11th to 20th	Day	13% 17% 31% 24% 9% 5%	452
	21st to end	Day	7% 20% 30% 28% 11% 5%	460
May	1st to 10th	Day	9% 16% 31% 32% 11% 1	463
	11th to 20th	Day	8% 14% 32% 32% 13% 1	488
	21st to end	Day	7% 12% 32% 35% 13% 2	529
June	1st to 10th	Day	7% 11% 34% 33% 12% 2	490
	11th to 20th	Day	3 12% 37% 36% 10% 2	490
	21st to end	Day	1 6% 36% 43% 14% 1	490
July	1st to 10th	Day	2 4 31% 49% 13% 1	486
	11th to 20th	Day	1 2 25% 54% 17% 2	484
	21st to end	Day	1 2 31% 48% 16% 2	531
August	1st to 10th	Day	2 5% 30% 47% 13% 2	487
	11th to 20th	Day	2 4 30% 44% 15% 4	477
	21st to end	Day	2 3 24% 47% 20% 4	539
September	1st to 10th	Day	2 4 23% 44% 20% 7%	490
	11th to 20th	Day	4 10% 27% 37% 16% 6%	490
	21st to end	Day	3 8% 26% 33% 26% 6%	490
October	1st to 10th	Day	4 7% 27% 32% 22% 8%	490
	11th to 20th	Day	6% 9% 22% 29% 27% 7%	490
	21st to end	Day	9% 7% 24% 29% 25% 6%	539
November	1st to 10th	Day	11% 9% 20% 24% 31% 5%	450
	11th to 20th	Day	8% 12% 18% 34% 23% 5%	300
	21st to end	Day	14% 7% 29% 32% 16% 2	210
December	1st to 10th	Day	16% 13% 25% 28% 15% 5%	200
	11th to 20th	Day	18% 13% 27% 29% 14% 1	200
	21st to end	Day	21% 10% 29% 28% 11%	220
January	1st to 10th	Night	19% 5% 16% 32% 23% 5%	800
	11th to 20th	Night	14% 6% 17% 36% 23% 4	800
	21st to end	Night	18% 5% 13% 37% 23% 4	880
February	1st to 10th	Night	19% 6% 15% 37% 21% 3	800
	11th to 20th	Night	14% 9% 18% 33% 21% 4	784
	21st to end	Night	14% 9% 20% 33% 21% 2	628
March	1st to 10th	Night	19% 9% 22% 29% 19% 3	760
	11th to 20th	Night	16% 8% 20% 31% 22% 3	760
	21st to end	Night	15% 8% 27% 32% 16% 1	836
April	1st to 10th	Night	12% 8% 26% 35% 17% 3	760
	11th to 20th	Night	10% 13% 25% 30% 19% 3	751
	21st to end	Night	6% 9% 29% 32% 20% 3	760
May	1st to 10th	Night	7% 6% 28% 38% 20% 2	664
	11th to 20th	Night	5% 2 24% 41% 24% 3	496
	21st to end	Night	5% 8% 29% 38% 18% 2	411
June	1st to 10th	Night	4 4 31% 44% 17% 1	380
	11th to 20th	Night	1 4 25% 53% 15% 1	380
	21st to end	Night	3 2 23% 45% 25% 1	380
July	1st to 10th	Night	3 18% 52% 26% 1	370
	11th to 20th	Night	3 1 14% 51% 26% 5%	518
	21st to end	Night	3 2 17% 44% 31% 3	624
August	1st to 10th	Night	6% 2 19% 43% 26% 4	567
	11th to 20th	Night	3 1 21% 45% 27% 4	668
	21st to end	Night	5% 1 14% 47% 29% 4	836
September	1st to 10th	Night	2 1 14% 41% 34% 7%	760
	11th to 20th	Night	6% 2 18% 42% 29% 4	760
	21st to end	Night	4 3 15% 37% 34% 6%	760
October	1st to 10th	Night	6% 2 16% 36% 32% 7%	760
	11th to 20th	Night	8% 5% 14% 32% 34% 7%	760
	21st to end	Night	8% 4 12% 33% 33% 10%	836
November	1st to 10th	Night	8% 5% 15% 31% 34% 7%	780
	11th to 20th	Night	12% 4 15% 36% 28% 6%	800
	21st to end	Night	11% 6% 14% 39% 26% 5%	800
December	1st to 10th	Night	15% 5% 16% 35% 24% 5%	800
	11th to 20th	Night	23% 6% 17% 32% 20% 3	800
	21st to end	Night	21% 8% 22% 30% 18% 1	880

Page generated at 2025-02-18 00:26:26. Version ac07

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