Cottontail Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cottontail Observatory clear sky chart from 2005-11-06 to 2024-11-02.

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	2 5% 2 5% 3 3 4 3 5% 6% 61%	101131
	Night	1 4 2 5% 3 3 3 3 5% 7% 64%	98037
Transparency	Day	22% 5% 7% 19% 25% 21%	100876
	Night	20% 4 9% 23% 26% 18%	97882
Seeing	Day	9% 22% 30% 25% 12% 3	15094
	Night	4 12% 27% 34% 19% 5%	24490

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	1 6% 2 5% 4 4 5% 5% 7% 10% 52%	2539
	11th to 20th	Day	1 5% 3 6% 4 5% 5% 6% 8% 9% 48%	2604
	21st to end	Day	3 10% 4 8% 4 5% 4 4 7% 8% 43%	3146
February	1st to 10th	Day	1 6% 3 6% 3 3 3 4 6% 10% 56%	1765
	11th to 20th	Day	1 6% 3 7% 4 3 4 4 6% 11% 51%	1850
	21st to end	Day	1 4 2 8% 4 4 5% 3 6% 7% 56%	1570
March	1st to 10th	Day	1 7% 4 11% 5% 5% 5% 5% 7% 8% 41%	3138
	11th to 20th	Day	4 3 6% 3 3 4 4 5% 8% 60%	3387
	21st to end	Day	1 11% 3 7% 3 4 5% 5% 7% 7% 48%	4103
April	1st to 10th	Day	3 5% 2 6% 4 4 4 3 6% 8% 54%	2280
	11th to 20th	Day	2 6% 2 4 3 4 3 4 6% 7% 58%	2249
	21st to end	Day	3 6% 2 5% 4 3 3 4 5% 7% 59%	2280
May	1st to 10th	Day	3 4 1 4 3 3 3 3 4 6% 67%	4004
	11th to 20th	Day	3 5% 2 4 3 3 3 3 5% 5% 65%	4188
	21st to end	Day	4 6% 2 5% 4 4 4 3 5% 6% 59%	4813
June	1st to 10th	Day	4 4 2 5% 4 4 3 4 6% 7% 57%	2660
	11th to 20th	Day	2 2 1 3 3 2 3 3 5% 5% 73%	2660
	21st to end	Day	2 3 1 4 3 3 3 3 4 4 70%	2660
July	1st to 10th	Day	1 1 1 2 1 2 2 2 3 4 79%	4420
	11th to 20th	Day	4 5% 2 7% 5% 4 5% 3 5% 5% 54%	4420
	21st to end	Day	3 3 1 4 4 4 4 3 4 6% 64%	4687
August	1st to 10th	Day	2 3 2 5% 3 5% 4 3 5% 5% 62%	3951
	11th to 20th	Day	2 2 1 3 2 2 2 2 3 3 78%	3724
	21st to end	Day	1 3 2 3 2 2 2 2 2 3 79%	4180
September	1st to 10th	Day	2 2 1 3 3 3 3 3 3 4 73%	2280
	11th to 20th	Day	3 3 1 4 3 3 3 3 4 5% 69%	2224
	21st to end	Day	2 3 1 3 2 2 2 2 3 5% 76%	2090
October	1st to 10th	Day	4 6% 2 4 2 3 2 3 3 4 68%	1976
	11th to 20th	Day	2 3 1 3 2 2 3 2 3 5% 74%	1900
	21st to end	Day	1 3 1 3 2 2 3 3 4 7% 71%	2028
November	1st to 10th	Day	1 5% 2 4 3 3 4 4 5% 7% 62%	1683
	11th to 20th	Day	1 2 1 4 2 4 4 3 7% 7% 65%	1710
	21st to end	Day	1 4 1 4 3 3 4 3 6% 11% 61%	1710
December	1st to 10th	Day	1 5% 2 3 2 3 4 4 5% 9% 59%	1530
	11th to 20th	Day	3 6% 4 8% 5% 6% 7% 5% 7% 9% 41%	1928
	21st to end	Day	1 6% 3 8% 4 3 6% 5% 8% 11% 44%	2794
January	1st to 10th	Night	1 5% 4 8% 4 4 4 3 6% 8% 52%	4406
	11th to 20th	Night	1 6% 3 8% 5% 4 5% 5% 8% 9% 47%	4354
	21st to end	Night	2 9% 3 7% 4 4 5% 5% 7% 8% 46%	4521
February	1st to 10th	Night	1 4 3 7% 4 4 5% 5% 6% 7% 55%	2413
	11th to 20th	Night	6% 2 5% 4 3 4 3 7% 10% 55%	2218
	21st to end	Night	1 4 2 6% 3 3 4 3 7% 8% 59%	1884
March	1st to 10th	Night	1 6% 4 8% 4 4 5% 4 7% 7% 50%	3736
	11th to 20th	Night	6% 3 7% 3 3 3 3 5% 7% 59%	3590
	21st to end	Night	1 6% 3 8% 5% 4 4 4 7% 9% 50%	3550
April	1st to 10th	Night	3 5% 2 5% 3 2 5% 4 6% 8% 57%	1900
	11th to 20th	Night	1 7% 2 4 3 3 3 3 5% 6% 63%	1879
	21st to end	Night	3 6% 2 3 3 3 3 3 4 5% 65%	1900
May	1st to 10th	Night	2 3 1 3 2 2 2 2 3 6% 74%	2966
	11th to 20th	Night	3 4 2 3 2 1 2 2 3 5% 73%	2708
	21st to end	Night	3 3 1 4 2 2 3 2 4 5% 70%	2762
June	1st to 10th	Night	5% 4 1 2 3 2 3 3 5% 6% 66%	1520
	11th to 20th	Night	1 1 1 2 1 2 2 1 4 5% 80%	1520
	21st to end	Night	3 1 1 2 2 1 2 3 3 3 80%	1520
July	1st to 10th	Night	1 1 1 1 1 2 3 89%	2540
	11th to 20th	Night	2 2 1 4 3 3 4 3 5% 6% 67%	2540
	21st to end	Night	2 2 2 2 3 3 3 4 4 76%	2850
August	1st to 10th	Night	2 1 1 3 2 3 2 2 5% 5% 76%	2990
	11th to 20th	Night	1 1 1 1 2 2 2 3 3 85%	3126
	21st to end	Night	1 1 1 1 1 1 1 1 2 3 87%	3498
September	1st to 10th	Night	1 1 1 2 1 1 2 2 2 4 85%	1900
	11th to 20th	Night	2 3 1 2 2 2 2 2 3 4 78%	1954
	21st to end	Night	2 2 1 3 2 2 2 2 4 4 76%	2090
October	1st to 10th	Night	4 4 1 3 2 1 3 2 4 5% 72%	2199
	11th to 20th	Night	1 2 2 3 1 2 2 1 4 5% 76%	2280
	21st to end	Night	1 2 1 2 2 2 2 2 4 6% 74%	2570
November	1st to 10th	Night	1 3 1 4 2 3 3 4 5% 8% 66%	2430
	11th to 20th	Night	1 4 2 2 3 3 4 3 5% 9% 65%	2470
	21st to end	Night	1 3 2 5% 3 3 3 3 6% 8% 64%	2470
December	1st to 10th	Night	2 3 2 4 3 3 4 4 6% 8% 60%	2645
	11th to 20th	Night	2 5% 3 6% 4 4 5% 4 9% 11% 46%	3276
	21st to end	Night	1 6% 4 9% 5% 5% 5% 5% 9% 9% 41%	4862

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	24% 6% 15% 29% 21% 4	2539
	11th to 20th	Day	29% 4 15% 24% 20% 8%	2604
	21st to end	Day	38% 5% 9% 24% 20% 4	3146
February	1st to 10th	Day	23% 6% 11% 24% 25% 10%	1765
	11th to 20th	Day	27% 4 10% 24% 26% 8%	1860
	21st to end	Day	27% 6% 10% 25% 25% 6%	1570
March	1st to 10th	Day	37% 7% 8% 23% 16% 8%	3138
	11th to 20th	Day	20% 8% 11% 36% 21% 4	3387
	21st to end	Day	31% 6% 13% 25% 21% 3	4103
April	1st to 10th	Day	28% 6% 12% 27% 19% 8%	2280
	11th to 20th	Day	25% 6% 10% 27% 23% 9%	2252
	21st to end	Day	25% 6% 13% 29% 22% 5%	2280
May	1st to 10th	Day	17% 4 10% 24% 33% 12%	4004
	11th to 20th	Day	19% 7% 5% 23% 35% 10%	4191
	21st to end	Day	24% 7% 6% 24% 35% 4	4814
June	1st to 10th	Day	25% 5% 8% 22% 29% 11%	2660
	11th to 20th	Day	14% 3 5% 21% 36% 21%	2660
	21st to end	Day	19% 3 3 10% 32% 33%	2660
July	1st to 10th	Day	9% 2 2 5% 14% 67%	4351
	11th to 20th	Day	27% 7% 3 8% 13% 42%	4345
	21st to end	Day	19% 5% 4 11% 19% 43%	4539
August	1st to 10th	Day	20% 6% 3 8% 21% 42%	3936
	11th to 20th	Day	12% 2 1 5% 16% 63%	3760
	21st to end	Day	12% 3 1 6% 34% 44%	4179
September	1st to 10th	Day	15% 3 3 9% 31% 38%	2280
	11th to 20th	Day	18% 3 3 18% 33% 24%	2224
	21st to end	Day	14% 3 2 18% 36% 27%	2090
October	1st to 10th	Day	21% 4 4 16% 30% 25%	1976
	11th to 20th	Day	15% 3 4 21% 36% 21%	1900
	21st to end	Day	13% 4 6% 25% 35% 17%	2028
November	1st to 10th	Day	20% 6% 9% 23% 28% 14%	1683
	11th to 20th	Day	15% 4 13% 23% 32% 12%	1710
	21st to end	Day	18% 5% 10% 26% 27% 14%	1710
December	1st to 10th	Day	20% 6% 13% 26% 25% 9%	1530
	11th to 20th	Day	37% 6% 12% 21% 17% 7%	1928
	21st to end	Day	30% 5% 16% 21% 22% 5%	2794
January	1st to 10th	Night	29% 4 13% 29% 20% 4	4406
	11th to 20th	Night	30% 4 16% 25% 18% 6%	4354
	21st to end	Night	34% 5% 12% 26% 19% 6%	4521
February	1st to 10th	Night	25% 6% 11% 25% 21% 12%	2413
	11th to 20th	Night	24% 4 10% 27% 26% 10%	2219
	21st to end	Night	22% 6% 12% 28% 24% 7%	1884
March	1st to 10th	Night	30% 7% 9% 24% 21% 8%	3736
	11th to 20th	Night	23% 5% 12% 38% 18% 4	3590
	21st to end	Night	27% 9% 14% 25% 22% 3	3550
April	1st to 10th	Night	23% 7% 14% 30% 19% 7%	1900
	11th to 20th	Night	22% 5% 14% 27% 23% 10%	1879
	21st to end	Night	21% 4 16% 33% 24% 3	1900
May	1st to 10th	Night	14% 3 7% 33% 35% 8%	2966
	11th to 20th	Night	16% 2 7% 25% 40% 10%	2708
	21st to end	Night	18% 3 7% 32% 36% 4	2762
June	1st to 10th	Night	19% 4 11% 26% 32% 8%	1520
	11th to 20th	Night	9% 2 8% 21% 39% 21%	1520
	21st to end	Night	11% 3 3 16% 31% 35%	1520
July	1st to 10th	Night	4 1 2 7% 19% 68%	2500
	11th to 20th	Night	15% 5% 2 7% 20% 50%	2492
	21st to end	Night	12% 3 2 14% 23% 46%	2761
August	1st to 10th	Night	11% 2 3 11% 32% 40%	2981
	11th to 20th	Night	7% 2 1 9% 20% 62%	3156
	21st to end	Night	6% 2 2 12% 36% 43%	3498
September	1st to 10th	Night	6% 2 1 14% 38% 39%	1900
	11th to 20th	Night	12% 2 5% 20% 36% 25%	1954
	21st to end	Night	13% 3 2 20% 37% 25%	2090
October	1st to 10th	Night	17% 2 7% 20% 34% 20%	2199
	11th to 20th	Night	13% 3 5% 23% 36% 21%	2280
	21st to end	Night	12% 2 7% 24% 36% 18%	2570
November	1st to 10th	Night	16% 5% 8% 28% 28% 14%	2430
	11th to 20th	Night	16% 5% 9% 27% 32% 11%	2470
	21st to end	Night	19% 4 11% 24% 29% 12%	2470
December	1st to 10th	Night	20% 7% 14% 23% 25% 10%	2645
	11th to 20th	Night	29% 6% 13% 25% 20% 6%	3276
	21st to end	Night	35% 6% 12% 20% 20% 8%	4862

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	13% 29% 28% 21% 9% 1	180
	11th to 20th	Day	10% 25% 28% 22% 12% 2	218
	21st to end	Day	7% 21% 31% 28% 9% 3	407
February	1st to 10th	Day	8% 28% 31% 21% 10% 2	397
	11th to 20th	Day	9% 29% 31% 21% 9% 1	455
	21st to end	Day	13% 26% 33% 23% 6%	382
March	1st to 10th	Day	15% 29% 32% 18% 5% 1	460
	11th to 20th	Day	10% 32% 29% 18% 11%	460
	21st to end	Day	13% 30% 33% 19% 5%	506
April	1st to 10th	Day	11% 30% 31% 19% 8% 1	460
	11th to 20th	Day	16% 29% 29% 19% 7% 1	452
	21st to end	Day	13% 27% 30% 20% 9% 1	460
May	1st to 10th	Day	16% 27% 27% 20% 8% 3	463
	11th to 20th	Day	12% 26% 27% 21% 11% 3	488
	21st to end	Day	14% 18% 26% 23% 14% 5%	529
June	1st to 10th	Day	9% 21% 30% 21% 13% 5%	490
	11th to 20th	Day	10% 24% 31% 21% 11% 4	490
	21st to end	Day	5% 18% 33% 26% 12% 5%	490
July	1st to 10th	Day	3 17% 32% 28% 14% 5%	486
	11th to 20th	Day	5% 13% 25% 33% 19% 5%	484
	21st to end	Day	6% 12% 30% 30% 17% 6%	531
August	1st to 10th	Day	4 17% 29% 27% 18% 4	487
	11th to 20th	Day	7% 17% 28% 27% 17% 4	477
	21st to end	Day	5% 14% 33% 29% 16% 3	539
September	1st to 10th	Day	4 14% 30% 31% 15% 4	490
	11th to 20th	Day	8% 21% 28% 28% 13% 3	490
	21st to end	Day	6% 15% 36% 30% 11% 2	490
October	1st to 10th	Day	7% 20% 29% 29% 14% 1	490
	11th to 20th	Day	7% 17% 28% 34% 11% 3	490
	21st to end	Day	6% 18% 33% 26% 14% 4	477
November	1st to 10th	Day	8% 18% 26% 23% 19% 6%	273
	11th to 20th	Day	3 20% 27% 30% 14% 7%	270
	21st to end	Day	3 20% 29% 30% 15% 3	270
December	1st to 10th	Day	10% 23% 23% 23% 16% 5%	185
	11th to 20th	Day	5% 25% 31% 24% 11% 3	180
	21st to end	Day	15% 19% 27% 27% 10% 3	198
January	1st to 10th	Night	6% 16% 32% 24% 15% 8%	760
	11th to 20th	Night	4 15% 28% 33% 15% 5%	760
	21st to end	Night	5% 12% 32% 30% 15% 5%	836
February	1st to 10th	Night	3 15% 31% 31% 16% 3	760
	11th to 20th	Night	5% 15% 31% 29% 15% 6%	744
	21st to end	Night	5% 20% 27% 34% 11% 3	628
March	1st to 10th	Night	7% 18% 34% 27% 11% 3	760
	11th to 20th	Night	3 22% 27% 28% 16% 4	760
	21st to end	Night	4 21% 34% 27% 12% 1	836
April	1st to 10th	Night	6% 15% 31% 33% 13% 2	760
	11th to 20th	Night	6% 19% 27% 29% 14% 4	751
	21st to end	Night	6% 15% 27% 31% 17% 4	760
May	1st to 10th	Night	8% 11% 30% 31% 15% 5%	637
	11th to 20th	Night	7% 9% 24% 41% 17% 2	488
	21st to end	Night	8% 5% 22% 39% 24% 2	411
June	1st to 10th	Night	7% 8% 23% 41% 19% 3	380
	11th to 20th	Night	2 7% 28% 40% 20% 3	380
	21st to end	Night	2 6% 22% 45% 22% 3	380
July	1st to 10th	Night	1 3 20% 49% 24% 3	370
	11th to 20th	Night	2 1 24% 47% 24% 2	368
	21st to end	Night	3 3 17% 42% 30% 4	469
August	1st to 10th	Night	2 2 21% 40% 29% 5%	644
	11th to 20th	Night	2 5% 22% 40% 26% 5%	752
	21st to end	Night	3 4 19% 45% 25% 4	836
September	1st to 10th	Night	1 4 22% 37% 30% 5%	760
	11th to 20th	Night	3 8% 21% 36% 26% 6%	760
	21st to end	Night	2 8% 24% 31% 28% 7%	760
October	1st to 10th	Night	5% 8% 19% 39% 23% 6%	760
	11th to 20th	Night	3 10% 19% 39% 23% 6%	760
	21st to end	Night	3 10% 25% 30% 21% 11%	836
November	1st to 10th	Night	3 13% 23% 31% 22% 7%	748
	11th to 20th	Night	4 11% 30% 34% 15% 6%	760
	21st to end	Night	4 13% 28% 32% 18% 6%	760
December	1st to 10th	Night	5% 14% 29% 33% 14% 5%	760
	11th to 20th	Night	5% 18% 31% 28% 14% 4	760
	21st to end	Night	6% 16% 35% 29% 11% 3	836

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