Rattle Snake Springs
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rattle Snake Springs clear sky chart from 2005-11-06 to 2026-02-01.

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	4 3 1 3 2 3 3 3 5% 7% 65%	135508
	Night	4 3 1 3 2 3 3 3 5% 7% 65%	133911
Transparency	Day	11% 37% 5% 11% 17% 18%	130609
	Night	12% 37% 5% 11% 17% 19%	129814
Seeing	Day	6% 8% 22% 31% 24% 8%	16386
	Night	6% 7% 26% 38% 21% 2	26601

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 4 2 4 3 3 3 3 4 5% 66%	4188
	11th to 20th	Day	2 2 1 3 2 2 3 2 4 6% 74%	4190
	21st to end	Day	3 4 2 4 3 3 3 3 4 6% 66%	5041
February	1st to 10th	Day	3 3 1 4 2 3 3 3 4 6% 70%	2000
	11th to 20th	Day	3 5% 2 5% 3 3 3 2 6% 6% 62%	1949
	21st to end	Day	2 4 2 4 3 3 3 2 3 4 70%	1650
March	1st to 10th	Day	2 3 2 4 3 3 3 3 4 6% 67%	4500
	11th to 20th	Day	9% 4 1 3 3 3 3 2 5% 6% 61%	4951
	21st to end	Day	2 3 2 4 3 3 3 3 6% 7% 63%	5854
April	1st to 10th	Day	3 3 1 2 2 2 3 3 5% 6% 69%	2400
	11th to 20th	Day	4 3 1 3 2 3 3 2 4 4 72%	2371
	21st to end	Day	2 2 1 2 2 2 2 2 3 5% 76%	2400
May	1st to 10th	Day	4 2 1 2 2 2 2 2 3 5% 75%	5440
	11th to 20th	Day	4 2 1 2 2 2 2 3 4 6% 72%	5420
	21st to end	Day	4 2 1 2 2 2 3 2 4 6% 71%	6446
June	1st to 10th	Day	2 2 1 3 2 3 3 4 6% 9% 66%	2621
	11th to 20th	Day	2 2 1 2 2 2 3 3 5% 7% 69%	2800
	21st to end	Day	6% 3 1 4 3 4 4 4 6% 8% 57%	2800
July	1st to 10th	Day	8% 3 1 4 4 4 5% 5% 8% 10% 48%	6067
	11th to 20th	Day	3 2 1 3 2 3 4 4 6% 11% 62%	5880
	21st to end	Day	4 2 1 4 3 3 4 4 8% 13% 53%	5922
August	1st to 10th	Day	2 1 2 2 3 3 3 6% 9% 68%	5348
	11th to 20th	Day	2 2 1 4 4 4 5% 5% 10% 12% 52%	5366
	21st to end	Day	4 2 1 3 3 3 4 4 7% 9% 59%	5984
September	1st to 10th	Day	9% 4 1 4 4 4 4 4 6% 9% 51%	2400
	11th to 20th	Day	8% 5% 1 4 4 4 5% 4 7% 8% 50%	2321
	21st to end	Day	7% 2 1 3 2 3 3 3 5% 5% 66%	2200
October	1st to 10th	Day	3 2 1 1 2 2 2 2 3 5% 78%	3535
	11th to 20th	Day	3 2 1 2 1 2 2 2 4 6% 76%	3250
	21st to end	Day	2 2 1 2 2 1 2 1 2 4 81%	3548
November	1st to 10th	Day	5% 2 1 2 2 2 2 2 3 5% 74%	1980
	11th to 20th	Day	2 3 1 4 2 2 3 2 5% 5% 70%	1890
	21st to end	Day	5% 3 1 2 2 3 3 3 5% 6% 65%	1890
December	1st to 10th	Day	11% 9% 2 5% 2 2 2 3 3 4 56%	3030
	11th to 20th	Day	2 2 1 3 2 3 4 3 6% 6% 67%	3481
	21st to end	Day	2 3 1 2 2 2 2 2 4 6% 76%	4395
January	1st to 10th	Night	4 5% 1 4 3 3 3 3 4 6% 64%	5997
	11th to 20th	Night	2 3 1 3 2 2 3 3 4 6% 72%	6010
	21st to end	Night	3 4 2 4 3 3 3 3 5% 7% 63%	6148
February	1st to 10th	Night	3 4 1 3 2 2 3 2 5% 6% 70%	2400
	11th to 20th	Night	5% 3 1 4 2 3 3 3 5% 6% 64%	2338
	21st to end	Night	4 4 2 3 2 2 3 3 4 6% 67%	1980
March	1st to 10th	Night	2 3 1 3 3 2 3 3 4 6% 69%	5374
	11th to 20th	Night	11% 3 1 4 2 3 3 3 4 5% 62%	5028
	21st to end	Night	1 2 1 3 2 3 4 3 5% 6% 68%	5104
April	1st to 10th	Night	3 3 1 4 3 3 3 3 4 5% 68%	2000
	11th to 20th	Night	4 2 1 3 2 2 3 3 5% 6% 69%	1977
	21st to end	Night	3 2 1 3 2 2 2 2 3 5% 76%	2000
May	1st to 10th	Night	7% 3 1 3 2 2 2 2 3 5% 71%	4540
	11th to 20th	Night	6% 3 1 3 2 2 3 3 5% 8% 63%	4478
	21st to end	Night	4 2 1 2 2 2 2 3 4 5% 73%	4451
June	1st to 10th	Night	2 2 1 3 2 3 4 4 8% 10% 60%	1771
	11th to 20th	Night	2 2 1 3 2 2 3 3 6% 7% 69%	1600
	21st to end	Night	4 2 1 4 4 4 3 4 7% 11% 56%	1600
July	1st to 10th	Night	10% 3 2 4 3 3 4 4 8% 10% 50%	3905
	11th to 20th	Night	2 2 1 3 2 3 4 4 8% 12% 60%	4100
	21st to end	Night	5% 2 1 4 4 4 5% 5% 9% 15% 46%	4946
August	1st to 10th	Night	1 1 1 2 2 3 4 4 7% 12% 62%	4464
	11th to 20th	Night	3 3 1 4 4 4 5% 5% 8% 12% 50%	4483
	21st to end	Night	5% 3 1 4 4 5% 5% 5% 8% 12% 49%	4993
September	1st to 10th	Night	8% 4 2 4 3 4 4 4 6% 8% 54%	2000
	11th to 20th	Night	8% 4 1 5% 3 4 4 3 6% 9% 53%	2076
	21st to end	Night	6% 3 1 4 3 3 3 3 5% 7% 62%	2200
October	1st to 10th	Night	4 2 1 2 1 2 2 2 3 4 78%	3643
	11th to 20th	Night	8% 3 1 2 2 2 2 1 3 4 72%	3898
	21st to end	Night	3 2 1 2 1 1 2 2 2 4 82%	4252
November	1st to 10th	Night	6% 2 2 1 2 2 2 4 5% 75%	2513
	11th to 20th	Night	2 3 1 3 2 2 3 3 5% 5% 72%	2730
	21st to end	Night	6% 4 1 2 3 3 3 3 4 5% 67%	2730
December	1st to 10th	Night	12% 6% 1 3 2 2 2 2 4 6% 60%	4380
	11th to 20th	Night	3 2 1 2 2 2 2 3 4 6% 72%	4946
	21st to end	Night	2 2 1 2 2 2 2 2 3 5% 78%	6856

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	17% 25% 4 8% 26% 20%	4189
	11th to 20th	Day	8% 26% 3 14% 28% 21%	4190
	21st to end	Day	12% 28% 4 17% 18% 20%	5041
February	1st to 10th	Day	7% 61% 2 6% 10% 14%	2000
	11th to 20th	Day	9% 61% 3 8% 8% 10%	1959
	21st to end	Day	11% 62% 2 3 8% 16%	1650
March	1st to 10th	Day	11% 28% 3 4 17% 36%	4500
	11th to 20th	Day	18% 30% 3 6% 15% 28%	4951
	21st to end	Day	12% 29% 5% 6% 18% 29%	5854
April	1st to 10th	Day	7% 61% 2 6% 13% 12%	2400
	11th to 20th	Day	8% 62% 2 5% 11% 13%	2374
	21st to end	Day	5% 61% 3 6% 12% 14%	2400
May	1st to 10th	Day	9% 28% 3 13% 15% 31%	5440
	11th to 20th	Day	7% 29% 3 8% 20% 33%	5423
	21st to end	Day	11% 28% 5% 10% 11% 36%	6447
June	1st to 10th	Day	7% 63% 5% 9% 9% 7%	2621
	11th to 20th	Day	4 62% 3 7% 10% 14%	2800
	21st to end	Day	10% 60% 5% 10% 8% 8%	2800
July	1st to 10th	Day	22% 27% 9% 20% 16% 5%	6004
	11th to 20th	Day	12% 26% 10% 27% 19% 6%	5811
	21st to end	Day	15% 26% 14% 23% 18% 3	5752
August	1st to 10th	Day	8% 36% 4 18% 25% 8%	3892
	11th to 20th	Day	8% 37% 7% 12% 24% 12%	3882
	21st to end	Day	13% 37% 12% 19% 17% 3	4311
September	1st to 10th	Day	12% 58% 7% 9% 7% 7%	2400
	11th to 20th	Day	13% 58% 4 11% 9% 5%	2321
	21st to end	Day	12% 57% 4 10% 11% 5%	2200
October	1st to 10th	Day	6% 35% 2 4 15% 38%	3535
	11th to 20th	Day	8% 35% 10% 12% 12% 23%	3250
	21st to end	Day	7% 34% 1 8% 28% 22%	3548
November	1st to 10th	Day	11% 53% 3 8% 11% 14%	1980
	11th to 20th	Day	9% 55% 4 9% 13% 10%	1890
	21st to end	Day	9% 54% 4 9% 14% 9%	1890
December	1st to 10th	Day	27% 34% 3 8% 12% 16%	3030
	11th to 20th	Day	13% 31% 3 9% 23% 22%	3479
	21st to end	Day	7% 25% 3 8% 35% 21%	4395
January	1st to 10th	Night	17% 25% 4 10% 26% 17%	5997
	11th to 20th	Night	8% 26% 5% 13% 27% 22%	6010
	21st to end	Night	15% 29% 3 18% 18% 18%	6148
February	1st to 10th	Night	4 62% 3 5% 10% 17%	2400
	11th to 20th	Night	7% 61% 4 6% 9% 12%	2338
	21st to end	Night	12% 61% 2 4 8% 13%	1980
March	1st to 10th	Night	10% 29% 2 4 18% 36%	5374
	11th to 20th	Night	17% 31% 3 5% 15% 30%	5028
	21st to end	Night	10% 30% 5% 7% 18% 30%	5104
April	1st to 10th	Night	9% 61% 2 4 10% 13%	2000
	11th to 20th	Night	6% 62% 3 6% 9% 13%	1977
	21st to end	Night	5% 61% 3 8% 11% 12%	2000
May	1st to 10th	Night	13% 28% 4 14% 8% 33%	4537
	11th to 20th	Night	13% 29% 4 7% 18% 30%	4479
	21st to end	Night	10% 28% 5% 7% 8% 42%	4452
June	1st to 10th	Night	7% 63% 4 11% 10% 5%	1771
	11th to 20th	Night	4 62% 3 6% 10% 14%	1600
	21st to end	Night	9% 60% 6% 10% 9% 7%	1600
July	1st to 10th	Night	23% 27% 11% 24% 13% 3	3860
	11th to 20th	Night	11% 26% 15% 26% 17% 4	4046
	21st to end	Night	19% 25% 13% 24% 17% 2	4804
August	1st to 10th	Night	9% 36% 5% 15% 26% 7%	3244
	11th to 20th	Night	9% 36% 8% 15% 24% 9%	3243
	21st to end	Night	16% 37% 12% 20% 13% 2	3597
September	1st to 10th	Night	12% 58% 6% 8% 7% 10%	2000
	11th to 20th	Night	13% 58% 5% 11% 8% 4	2076
	21st to end	Night	13% 57% 5% 9% 10% 5%	2200
October	1st to 10th	Night	7% 35% 2 3 15% 37%	3643
	11th to 20th	Night	13% 35% 6% 8% 10% 28%	3898
	21st to end	Night	6% 34% 2 7% 25% 25%	4252
November	1st to 10th	Night	10% 53% 3 6% 12% 15%	2513
	11th to 20th	Night	9% 54% 3 9% 12% 12%	2730
	21st to end	Night	9% 54% 3 9% 14% 11%	2730
December	1st to 10th	Night	21% 34% 3 11% 17% 14%	4380
	11th to 20th	Night	9% 30% 2 8% 21% 30%	4947
	21st to end	Night	8% 26% 2 8% 29% 27%	6856

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	9% 15% 32% 33% 11%	330
	11th to 20th	Day	9% 12% 34% 32% 12% 1	330
	21st to end	Day	4 12% 33% 38% 11% 1	363
February	1st to 10th	Day	5% 13% 34% 33% 13% 3	300
	11th to 20th	Day	11% 14% 37% 29% 9% 1	300
	21st to end	Day	8% 20% 35% 28% 7% 2	249
March	1st to 10th	Day	12% 12% 37% 31% 8% 1	300
	11th to 20th	Day	13% 17% 32% 26% 9% 2	477
	21st to end	Day	5% 24% 40% 23% 7% 1	550
April	1st to 10th	Day	8% 20% 35% 29% 7% 1	500
	11th to 20th	Day	6% 23% 37% 26% 6% 1	492
	21st to end	Day	4 16% 40% 30% 10% 1	500
May	1st to 10th	Day	5% 14% 41% 30% 10%	503
	11th to 20th	Day	7% 10% 31% 33% 16% 3	530
	21st to end	Day	5% 6% 31% 40% 17% 1	789
June	1st to 10th	Day	3 3 17% 44% 30% 3	730
	11th to 20th	Day	2 3 19% 41% 30% 5%	730
	21st to end	Day	7% 1 11% 34% 38% 9%	730
July	1st to 10th	Day	6% 1 6% 27% 45% 16%	610
	11th to 20th	Day	3 4 28% 42% 23%	524
	21st to end	Day	2 1 3 28% 44% 23%	575
August	1st to 10th	Day	3 3 23% 47% 23%	527
	11th to 20th	Day	4 2 7% 28% 41% 18%	517
	21st to end	Day	5% 1 6% 24% 40% 25%	583
September	1st to 10th	Day	9% 1 8% 31% 36% 15%	530
	11th to 20th	Day	5% 1 8% 32% 41% 13%	451
	21st to end	Day	7% 2 11% 30% 34% 16%	330
October	1st to 10th	Day	10% 3 15% 31% 33% 9%	330
	11th to 20th	Day	7% 4 18% 37% 26% 7%	330
	21st to end	Day	6% 9% 26% 26% 24% 9%	363
November	1st to 10th	Day	11% 8% 28% 28% 20% 5%	330
	11th to 20th	Day	6% 11% 23% 32% 22% 6%	330
	21st to end	Day	9% 12% 35% 28% 12% 4	330
December	1st to 10th	Day	14% 12% 24% 35% 15% 2	330
	11th to 20th	Day	4 14% 25% 38% 16% 3	330
	21st to end	Day	7% 13% 33% 32% 12% 3	363
January	1st to 10th	Night	9% 10% 33% 36% 12% 1	840
	11th to 20th	Night	7% 9% 37% 35% 10% 2	840
	21st to end	Night	6% 9% 35% 39% 10% 1	924
February	1st to 10th	Night	5% 12% 36% 35% 12% 1	800
	11th to 20th	Night	8% 10% 38% 37% 6% 1	784
	21st to end	Night	6% 17% 43% 28% 5%	660
March	1st to 10th	Night	8% 12% 37% 35% 8% 1	800
	11th to 20th	Night	11% 13% 30% 32% 13%	800
	21st to end	Night	3 12% 44% 34% 6%	715
April	1st to 10th	Night	6% 12% 42% 35% 5%	600
	11th to 20th	Night	5% 11% 42% 36% 6%	593
	21st to end	Night	3 11% 42% 36% 8%	600
May	1st to 10th	Night	4 5% 43% 41% 7%	600
	11th to 20th	Night	7% 6% 31% 42% 13%	591
	21st to end	Night	4 4 29% 50% 12%	650
June	1st to 10th	Night	2 3 20% 55% 19% 1	600
	11th to 20th	Night	2 1 20% 57% 20%	600
	21st to end	Night	5% 1 13% 50% 31% 1	600
July	1st to 10th	Night	6% 7% 42% 42% 3	585
	11th to 20th	Night	3 4 41% 48% 3	582
	21st to end	Night	4 1 5% 32% 54% 5%	657
August	1st to 10th	Night	3 4 26% 62% 4	597
	11th to 20th	Night	4 4 28% 55% 8%	594
	21st to end	Night	6% 1 4 29% 54% 6%	660
September	1st to 10th	Night	9% 1 5% 38% 43% 5%	600
	11th to 20th	Night	8% 1 5% 42% 43% 2	600
	21st to end	Night	8% 1 9% 45% 35% 3	600
October	1st to 10th	Night	8% 2 16% 46% 27% 2	627
	11th to 20th	Night	9% 4 18% 45% 22% 3	800
	21st to end	Night	6% 7% 21% 37% 25% 5%	880
November	1st to 10th	Night	7% 4 23% 39% 24% 3	873
	11th to 20th	Night	4 6% 26% 43% 19% 2	1050
	21st to end	Night	8% 9% 29% 36% 16% 2	1050
December	1st to 10th	Night	10% 8% 31% 36% 14% 1	1050
	11th to 20th	Night	5% 10% 34% 38% 12% 1	1050
	21st to end	Night	5% 12% 35% 36% 10% 1	1149

Page generated at 2026-01-28 23:21:40. Version ac07

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