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 2024-06-30.

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 3 3 3 3 5% 7% 64%	89618
	Night	5% 3 1 3 3 3 3 3 5% 7% 64%	89632
Transparency	Day	9% 54% 4 8% 12% 13%	89357
	Night	9% 53% 4 8% 13% 13%	89416
Seeing	Day	6% 9% 22% 31% 24% 8%	14326
	Night	6% 7% 26% 38% 21% 2	24471

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	3 3 2 4 1 2 2 2 3 6% 71%	2858
	11th to 20th	Day	2 2 1 3 2 2 3 2 4 5% 73%	2860
	21st to end	Day	3 5% 2 5% 4 3 3 3 5% 7% 61%	3438
February	1st to 10th	Day	3 3 1 4 2 3 3 3 4 6% 69%	1900
	11th to 20th	Day	3 6% 2 5% 3 3 3 2 6% 6% 62%	1849
	21st to end	Day	2 4 1 4 3 3 3 3 3 4 70%	1570
March	1st to 10th	Day	3 4 2 5% 3 3 4 3 5% 7% 61%	3130
	11th to 20th	Day	12% 6% 1 4 3 3 3 2 5% 7% 53%	3455
	21st to end	Day	2 3 2 4 3 4 4 4 7% 8% 59%	4089
April	1st to 10th	Day	3 3 1 2 2 2 3 4 5% 6% 69%	2280
	11th to 20th	Day	5% 3 1 3 2 3 3 2 4 4 72%	2251
	21st to end	Day	2 2 1 2 2 2 2 3 3 5% 76%	2280
May	1st to 10th	Day	4 2 1 2 2 1 2 2 3 4 78%	3800
	11th to 20th	Day	6% 2 1 2 2 3 3 3 5% 6% 68%	3780
	21st to end	Day	3 2 1 3 2 2 2 2 4 5% 74%	4489
June	1st to 10th	Day	2 2 1 2 2 3 3 4 7% 9% 66%	2490
	11th to 20th	Day	2 2 1 2 2 2 3 4 6% 7% 68%	2660
	21st to end	Day	5% 3 1 3 3 4 4 4 6% 8% 58%	2647
July	1st to 10th	Day	5% 3 2 4 4 5% 5% 5% 10% 12% 46%	2416
	11th to 20th	Day	5% 2 1 3 4 4 5% 5% 7% 11% 54%	2340
	21st to end	Day	5% 3 1 3 3 4 4 4 7% 11% 54%	2349
August	1st to 10th	Day	4 2 3 4 4 5% 5% 8% 11% 56%	2149
	11th to 20th	Day	4 4 1 5% 5% 5% 4 6% 10% 12% 44%	2123
	21st to end	Day	6% 3 1 5% 4 4 5% 6% 8% 11% 47%	2376
September	1st to 10th	Day	8% 3 1 4 4 4 4 4 6% 9% 52%	2160
	11th to 20th	Day	9% 5% 1 4 4 4 5% 4 6% 8% 49%	2089
	21st to end	Day	8% 2 1 2 2 2 3 3 5% 5% 66%	1980
October	1st to 10th	Day	6% 3 1 2 3 3 3 3 5% 7% 64%	1953
	11th to 20th	Day	5% 4 1 3 2 2 2 2 2 4 72%	1800
	21st to end	Day	4 3 1 3 2 2 2 2 2 4 76%	1980
November	1st to 10th	Day	6% 3 1 2 2 2 2 2 3 5% 72%	1788
	11th to 20th	Day	2 3 1 4 2 2 3 2 5% 5% 69%	1710
	21st to end	Day	5% 4 1 2 2 4 3 3 5% 5% 65%	1710
December	1st to 10th	Day	6% 5% 2 4 2 3 3 4 5% 6% 61%	1710
	11th to 20th	Day	2 3 1 4 2 4 4 4 7% 8% 61%	2161
	21st to end	Day	3 4 1 3 2 2 3 3 4 6% 71%	2998
January	1st to 10th	Night	3 3 1 4 3 3 3 3 4 6% 67%	4097
	11th to 20th	Night	3 3 1 3 2 2 3 3 4 7% 69%	4110
	21st to end	Night	4 5% 2 4 3 3 3 3 5% 8% 59%	4211
February	1st to 10th	Night	3 4 1 3 2 2 3 2 5% 6% 69%	2280
	11th to 20th	Night	5% 3 2 4 2 3 3 3 5% 6% 64%	2218
	21st to end	Night	4 4 2 3 2 2 3 3 4 6% 67%	1884
March	1st to 10th	Night	4 4 2 3 3 2 3 3 4 6% 66%	3734
	11th to 20th	Night	16% 4 1 5% 3 3 4 4 5% 5% 51%	3505
	21st to end	Night	1 3 1 4 3 4 4 4 6% 7% 64%	3555
April	1st to 10th	Night	3 3 1 4 3 3 4 3 4 5% 68%	1900
	11th to 20th	Night	5% 3 1 3 2 2 3 3 4 6% 69%	1877
	21st to end	Night	2 2 1 3 2 2 2 2 3 5% 76%	1900
May	1st to 10th	Night	5% 2 1 2 2 2 2 2 2 4 76%	3170
	11th to 20th	Night	8% 2 1 3 2 3 3 2 5% 6% 66%	3122
	21st to end	Night	3 2 1 2 2 2 2 2 4 5% 76%	3098
June	1st to 10th	Night	2 2 1 3 3 3 5% 4 8% 10% 59%	1683
	11th to 20th	Night	2 2 1 3 2 2 3 3 6% 7% 69%	1520
	21st to end	Night	4 2 1 3 3 4 4 4 7% 11% 58%	1512
July	1st to 10th	Night	5% 2 1 4 3 3 4 4 10% 11% 51%	1537
	11th to 20th	Night	3 2 2 3 4 4 5% 4 8% 12% 53%	1620
	21st to end	Night	4 3 1 4 4 4 5% 5% 7% 12% 50%	1964
August	1st to 10th	Night	3 2 1 4 4 5% 4 4 8% 13% 52%	1790
	11th to 20th	Night	4 3 1 4 4 5% 5% 5% 9% 13% 48%	1778
	21st to end	Night	4 3 2 4 4 5% 5% 5% 9% 12% 47%	1980
September	1st to 10th	Night	7% 4 2 3 3 4 4 4 6% 8% 55%	1800
	11th to 20th	Night	8% 4 1 4 3 4 4 3 6% 9% 53%	1868
	21st to end	Night	7% 3 1 4 3 3 3 3 5% 7% 61%	1980
October	1st to 10th	Night	7% 3 1 3 2 2 3 3 4 6% 65%	2003
	11th to 20th	Night	7% 3 1 2 2 2 2 1 3 4 72%	2160
	21st to end	Night	5% 3 1 3 2 2 2 2 3 4 73%	2376
November	1st to 10th	Night	6% 2 2 1 2 2 2 4 5% 74%	2267
	11th to 20th	Night	2 3 1 3 2 3 3 3 5% 5% 71%	2470
	21st to end	Night	6% 4 1 2 2 3 3 3 4 5% 68%	2470
December	1st to 10th	Night	7% 4 1 3 3 3 3 3 5% 8% 61%	2470
	11th to 20th	Night	3 3 1 4 4 3 3 3 4 7% 64%	3036
	21st to end	Night	2 3 1 3 2 2 3 2 4 5% 73%	4687

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	9% 36% 4 6% 23% 21%	2859
	11th to 20th	Day	7% 37% 4 9% 27% 16%	2860
	21st to end	Day	13% 41% 5% 17% 16% 8%	3438
February	1st to 10th	Day	7% 65% 2 6% 9% 11%	1900
	11th to 20th	Day	8% 64% 3 6% 8% 10%	1859
	21st to end	Day	10% 65% 2 3 7% 14%	1570
March	1st to 10th	Day	12% 41% 5% 6% 17% 21%	3130
	11th to 20th	Day	21% 42% 4 9% 16% 9%	3455
	21st to end	Day	10% 42% 7% 7% 18% 17%	4089
April	1st to 10th	Day	5% 64% 2 5% 12% 11%	2280
	11th to 20th	Day	8% 65% 2 4 10% 11%	2254
	21st to end	Day	5% 64% 3 5% 11% 12%	2280
May	1st to 10th	Day	5% 40% 2 5% 8% 40%	3800
	11th to 20th	Day	6% 41% 5% 9% 16% 23%	3783
	21st to end	Day	7% 39% 3 6% 8% 37%	4489
June	1st to 10th	Day	7% 66% 5% 9% 7% 6%	2490
	11th to 20th	Day	4 65% 3 7% 8% 13%	2660
	21st to end	Day	7% 63% 4 9% 8% 9%	2647
July	1st to 10th	Day	8% 64% 8% 9% 9% 2	2352
	11th to 20th	Day	7% 63% 6% 10% 9% 5%	2271
	21st to end	Day	5% 63% 6% 13% 11% 2	2219
August	1st to 10th	Day	8% 66% 6% 12% 7% 1	2136
	11th to 20th	Day	8% 66% 8% 10% 6% 3	2123
	21st to end	Day	8% 66% 8% 9% 6% 3	2376
September	1st to 10th	Day	9% 64% 7% 8% 6% 6%	2160
	11th to 20th	Day	12% 64% 4 9% 8% 3	2089
	21st to end	Day	11% 64% 4 8% 10% 3	1980
October	1st to 10th	Day	10% 63% 4 6% 9% 8%	1953
	11th to 20th	Day	8% 63% 3 5% 11% 10%	1800
	21st to end	Day	9% 61% 2 6% 12% 10%	1980
November	1st to 10th	Day	12% 59% 3 7% 10% 9%	1788
	11th to 20th	Day	9% 61% 4 9% 10% 7%	1710
	21st to end	Day	8% 60% 4 9% 12% 8%	1710
December	1st to 10th	Day	13% 60% 3 8% 9% 6%	1710
	11th to 20th	Day	12% 49% 5% 11% 12% 11%	2159
	21st to end	Day	8% 37% 3 8% 22% 21%	2998
January	1st to 10th	Night	11% 37% 5% 7% 24% 16%	4097
	11th to 20th	Night	7% 37% 7% 11% 22% 16%	4110
	21st to end	Night	15% 41% 4 15% 18% 7%	4211
February	1st to 10th	Night	5% 65% 3 5% 10% 13%	2280
	11th to 20th	Night	7% 65% 4 5% 7% 12%	2218
	21st to end	Night	11% 64% 2 4 7% 12%	1884
March	1st to 10th	Night	11% 41% 3 5% 14% 26%	3734
	11th to 20th	Night	22% 43% 5% 7% 14% 9%	3505
	21st to end	Night	9% 42% 5% 6% 22% 16%	3555
April	1st to 10th	Night	8% 65% 2 5% 9% 13%	1900
	11th to 20th	Night	6% 65% 3 6% 8% 12%	1877
	21st to end	Night	5% 64% 3 7% 10% 11%	1900
May	1st to 10th	Night	8% 39% 2 4 8% 40%	3170
	11th to 20th	Night	9% 41% 5% 7% 12% 25%	3123
	21st to end	Night	5% 39% 3 5% 8% 39%	3099
June	1st to 10th	Night	7% 66% 4 10% 9% 4	1683
	11th to 20th	Night	4 65% 3 6% 9% 14%	1520
	21st to end	Night	6% 63% 6% 9% 9% 7%	1512
July	1st to 10th	Night	7% 64% 7% 10% 9% 2	1492
	11th to 20th	Night	9% 65% 6% 7% 8% 5%	1566
	21st to end	Night	7% 62% 5% 11% 11% 3	1855
August	1st to 10th	Night	10% 65% 6% 11% 6% 2	1779
	11th to 20th	Night	8% 64% 8% 10% 6% 3	1778
	21st to end	Night	9% 65% 7% 10% 7% 3	1980
September	1st to 10th	Night	9% 64% 6% 7% 6% 9%	1800
	11th to 20th	Night	12% 64% 4 10% 6% 3	1868
	21st to end	Night	13% 64% 5% 8% 8% 3	1980
October	1st to 10th	Night	11% 64% 4 4 8% 9%	2003
	11th to 20th	Night	8% 62% 3 6% 11% 10%	2160
	21st to end	Night	9% 61% 3 5% 12% 10%	2376
November	1st to 10th	Night	10% 59% 4 6% 11% 11%	2267
	11th to 20th	Night	9% 60% 4 9% 11% 8%	2470
	21st to end	Night	8% 60% 3 8% 12% 9%	2470
December	1st to 10th	Night	11% 60% 3 9% 10% 7%	2470
	11th to 20th	Night	11% 49% 3 11% 13% 13%	3037
	21st to end	Night	9% 37% 3 7% 25% 20%	4687

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% 14% 33% 34% 10%	270
	11th to 20th	Day	10% 14% 33% 32% 11% 1	270
	21st to end	Day	3 13% 33% 37% 12% 1	297
February	1st to 10th	Day	4 14% 34% 33% 13% 2	270
	11th to 20th	Day	11% 13% 36% 30% 9% 1	270
	21st to end	Day	8% 22% 34% 28% 7% 1	225
March	1st to 10th	Day	10% 13% 37% 31% 8% 1	270
	11th to 20th	Day	13% 16% 33% 28% 9% 2	438
	21st to end	Day	6% 25% 40% 23% 6% 1	506
April	1st to 10th	Day	7% 20% 37% 29% 7% 1	460
	11th to 20th	Day	5% 24% 38% 26% 6% 1	452
	21st to end	Day	5% 16% 39% 29% 10% 1	460
May	1st to 10th	Day	4 14% 40% 31% 11%	463
	11th to 20th	Day	6% 9% 31% 34% 17% 3	490
	21st to end	Day	5% 6% 30% 40% 17% 1	734
June	1st to 10th	Day	3 2 17% 44% 31% 3	680
	11th to 20th	Day	2 3 19% 41% 30% 6%	680
	21st to end	Day	5% 1 11% 34% 39% 9%	676
July	1st to 10th	Day	5% 6% 26% 45% 17%	522
	11th to 20th	Day	3 3 27% 42% 25%	444
	21st to end	Day	2 1 2 28% 44% 24%	487
August	1st to 10th	Day	3 4 21% 46% 26%	447
	11th to 20th	Day	4 2 7% 26% 42% 19%	437
	21st to end	Day	5% 1 6% 22% 40% 26%	495
September	1st to 10th	Day	8% 1 8% 30% 38% 16%	450
	11th to 20th	Day	5% 1 6% 30% 44% 15%	379
	21st to end	Day	8% 1 10% 27% 35% 18%	270
October	1st to 10th	Day	11% 3 16% 28% 34% 8%	270
	11th to 20th	Day	9% 4 17% 35% 27% 7%	270
	21st to end	Day	7% 8% 25% 27% 24% 9%	297
November	1st to 10th	Day	12% 8% 27% 29% 20% 4	270
	11th to 20th	Day	5% 11% 22% 34% 23% 5%	270
	21st to end	Day	10% 14% 33% 27% 13% 3	270
December	1st to 10th	Day	13% 13% 20% 37% 16% 2	270
	11th to 20th	Day	4 16% 26% 40% 13%	270
	21st to end	Day	7% 14% 35% 32% 10% 1	297
January	1st to 10th	Night	8% 9% 32% 37% 13% 1	760
	11th to 20th	Night	7% 9% 37% 34% 11% 2	760
	21st to end	Night	6% 10% 35% 38% 11% 1	836
February	1st to 10th	Night	5% 12% 36% 34% 12% 1	760
	11th to 20th	Night	8% 10% 37% 37% 6% 1	744
	21st to end	Night	6% 18% 43% 27% 6%	628
March	1st to 10th	Night	8% 12% 37% 35% 8% 1	760
	11th to 20th	Night	10% 13% 29% 34% 13%	760
	21st to end	Night	3 13% 44% 33% 6%	679
April	1st to 10th	Night	4 12% 43% 35% 5%	570
	11th to 20th	Night	5% 11% 43% 35% 6%	563
	21st to end	Night	3 11% 44% 34% 8%	570
May	1st to 10th	Night	4 5% 43% 40% 7%	570
	11th to 20th	Night	7% 6% 29% 43% 14%	561
	21st to end	Night	5% 4 29% 50% 12%	617
June	1st to 10th	Night	2 3 20% 55% 19% 1	570
	11th to 20th	Night	2 1 20% 56% 19%	570
	21st to end	Night	4 1 12% 51% 31% 1	567
July	1st to 10th	Night	5% 7% 42% 43% 3	525
	11th to 20th	Night	3 5% 40% 49% 3	522
	21st to end	Night	4 1 5% 32% 54% 5%	591
August	1st to 10th	Night	4 4 26% 62% 5%	537
	11th to 20th	Night	4 4 25% 58% 8%	534
	21st to end	Night	6% 1 4 29% 55% 6%	594
September	1st to 10th	Night	8% 1 5% 36% 45% 6%	540
	11th to 20th	Night	8% 1 4 40% 45% 3	540
	21st to end	Night	8% 1 9% 42% 36% 4	540
October	1st to 10th	Night	9% 2 17% 45% 25% 2	563
	11th to 20th	Night	8% 5% 18% 44% 22% 3	720
	21st to end	Night	6% 7% 21% 35% 25% 6%	792
November	1st to 10th	Night	6% 4 23% 39% 25% 3	787
	11th to 20th	Night	4 6% 25% 43% 20% 2	950
	21st to end	Night	8% 10% 28% 35% 16% 2	950
December	1st to 10th	Night	9% 8% 30% 36% 15% 1	950
	11th to 20th	Night	6% 10% 35% 36% 11% 1	950
	21st to end	Night	5% 13% 36% 36% 9% 1	1041

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