Cottonwood
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cottonwood clear sky chart from 2005-11-06 to 2024-01-15.

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	10% 3 1 3 3 2 3 3 4 6% 64%	74739
	Night	13% 4 1 3 3 2 3 3 4 6% 58%	75047
Transparency	Day	24% 4 8% 18% 24% 23%	74453
	Night	28% 5% 9% 19% 22% 18%	74854
Seeing	Day	11% 8% 18% 29% 24% 10%	13961
	Night	13% 5% 17% 36% 26% 3	23254

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	23% 6% 2 4 3 2 4 3 5% 9% 37%	1519
	11th to 20th	Day	23% 5% 2 3 3 2 3 3 4 6% 47%	1617
	21st to end	Day	19% 6% 2 4 4 2 3 3 4 6% 46%	1782
February	1st to 10th	Day	17% 5% 1 4 4 2 3 4 5% 6% 48%	1620
	11th to 20th	Day	16% 4 2 3 4 2 3 3 4 7% 52%	1597
	21st to end	Day	18% 5% 2 4 3 2 4 3 4 8% 49%	1480
March	1st to 10th	Day	21% 7% 2 5% 4 3 4 4 4 7% 37%	1915
	11th to 20th	Day	17% 6% 2 4 4 2 3 4 4 8% 45%	1980
	21st to end	Day	17% 5% 2 4 4 2 4 4 5% 8% 46%	2217
April	1st to 10th	Day	14% 6% 2 4 5% 2 5% 4 4 8% 47%	2160
	11th to 20th	Day	13% 4 2 3 3 2 3 3 4 7% 56%	2129
	21st to end	Day	5% 3 1 2 4 2 3 4 5% 7% 64%	2160
May	1st to 10th	Day	6% 4 1 3 3 2 3 3 4 7% 66%	2337
	11th to 20th	Day	5% 3 1 3 3 2 3 4 5% 7% 63%	2467
	21st to end	Day	6% 2 1 3 3 2 3 3 5% 6% 66%	2723
June	1st to 10th	Day	6% 3 2 3 3 2 4 4 4 8% 63%	2520
	11th to 20th	Day	2 1 1 1 2 1 2 2 4 5% 80%	2520
	21st to end	Day	3 1 1 2 1 1 1 2 2 3 81%	2520
July	1st to 10th	Day	1 1 1 2 1 1 3 3 87%	2520
	11th to 20th	Day	2 1 1 1 1 1 1 2 3 87%	2520
	21st to end	Day	1 1 1 1 1 1 2 3 3 86%	2549
August	1st to 10th	Day	2 1 1 1 1 1 2 3 5% 83%	2328
	11th to 20th	Day	1 1 1 1 1 1 1 1 2 90%	2254
	21st to end	Day	1 1 1 1 1 1 1 1 3 89%	2376
September	1st to 10th	Day	1 1 1 1 1 1 1 2 3 88%	2160
	11th to 20th	Day	3 2 1 2 2 1 2 2 3 6% 76%	2160
	21st to end	Day	3 1 1 2 2 1 2 2 3 4 80%	1904
October	1st to 10th	Day	5% 2 1 2 2 1 2 2 3 4 76%	1800
	11th to 20th	Day	8% 3 1 2 2 2 2 3 4 5% 69%	1800
	21st to end	Day	11% 3 1 3 2 1 2 3 3 6% 65%	1980
November	1st to 10th	Day	15% 4 1 3 4 2 3 4 5% 7% 53%	1738
	11th to 20th	Day	14% 5% 1 3 4 2 3 4 6% 8% 49%	1625
	21st to end	Day	12% 5% 2 3 3 3 4 4 4 7% 54%	1520
December	1st to 10th	Day	23% 4 1 3 3 2 2 3 4 5% 51%	1520
	11th to 20th	Day	30% 7% 3 5% 4 2 3 4 5% 5% 31%	1928
	21st to end	Day	27% 6% 2 4 4 2 3 4 5% 6% 36%	2794
January	1st to 10th	Night	22% 6% 2 4 4 3 3 4 5% 7% 40%	2646
	11th to 20th	Night	20% 5% 2 4 3 2 4 3 4 7% 45%	2430
	21st to end	Night	20% 5% 2 4 5% 2 4 3 3 5% 47%	2574
February	1st to 10th	Night	17% 5% 2 3 3 3 3 3 4 7% 50%	2340
	11th to 20th	Night	18% 4 1 3 4 2 3 3 4 7% 50%	2250
	21st to end	Night	16% 5% 2 4 4 2 4 3 4 6% 49%	1776
March	1st to 10th	Night	22% 7% 3 5% 5% 2 4 4 4 6% 39%	2043
	11th to 20th	Night	17% 6% 2 4 4 3 3 4 5% 10% 42%	1980
	21st to end	Night	16% 5% 2 4 4 2 3 4 5% 7% 47%	2138
April	1st to 10th	Night	14% 5% 2 5% 4 3 4 4 5% 6% 49%	1800
	11th to 20th	Night	10% 5% 2 4 4 2 3 3 4 8% 56%	1779
	21st to end	Night	8% 4 1 3 2 1 3 3 5% 8% 62%	1800
May	1st to 10th	Night	8% 3 1 3 2 1 2 3 5% 7% 64%	1620
	11th to 20th	Night	5% 4 2 4 3 3 4 3 5% 7% 59%	1425
	21st to end	Night	6% 4 2 4 4 3 3 4 5% 6% 60%	1552
June	1st to 10th	Night	7% 4 1 3 3 2 3 4 7% 9% 57%	1440
	11th to 20th	Night	3 3 1 2 2 2 2 3 4 6% 74%	1440
	21st to end	Night	2 1 2 2 2 2 3 3 2 81%	1440
July	1st to 10th	Night	1 1 1 2 1 2 2 2 4 84%	1440
	11th to 20th	Night	1 1 1 2 2 1 1 2 3 3 83%	1440
	21st to end	Night	1 1 1 1 1 1 1 2 4 87%	1766
August	1st to 10th	Night	2 1 1 1 2 1 1 2 3 4 83%	1611
	11th to 20th	Night	1 1 1 1 1 3 3 3 85%	1644
	21st to end	Night	1 1 1 1 1 1 1 2 3 89%	1980
September	1st to 10th	Night	2 1 1 1 1 1 2 2 3 87%	1800
	11th to 20th	Night	4 1 1 1 1 1 2 2 3 5% 78%	1800
	21st to end	Night	3 1 2 1 1 2 3 4 4 77%	2051
October	1st to 10th	Night	6% 2 1 2 2 1 2 3 3 4 74%	2160
	11th to 20th	Night	6% 2 1 3 2 1 3 2 3 5% 73%	2160
	21st to end	Night	9% 2 1 2 3 1 3 3 4 6% 66%	2376
November	1st to 10th	Night	13% 4 2 3 3 2 4 4 5% 7% 52%	2338
	11th to 20th	Night	14% 4 1 4 3 2 4 4 5% 8% 50%	2550
	21st to end	Night	14% 4 2 3 4 2 2 3 4 7% 56%	2660
December	1st to 10th	Night	22% 4 1 3 2 2 3 3 4 8% 47%	2660
	11th to 20th	Night	32% 7% 2 4 3 2 3 3 5% 6% 33%	3276
	21st to end	Night	26% 7% 2 5% 4 3 4 4 5% 7% 34%	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	46% 7% 13% 22% 8% 5%	1519
	11th to 20th	Day	41% 4 9% 16% 17% 13%	1617
	21st to end	Day	41% 4 8% 17% 22% 9%	1782
February	1st to 10th	Day	36% 6% 11% 18% 20% 9%	1620
	11th to 20th	Day	34% 5% 9% 20% 25% 7%	1606
	21st to end	Day	36% 4 9% 24% 20% 8%	1480
March	1st to 10th	Day	45% 6% 10% 17% 15% 7%	1915
	11th to 20th	Day	38% 5% 9% 22% 20% 6%	1980
	21st to end	Day	37% 7% 12% 20% 18% 6%	2217
April	1st to 10th	Day	36% 6% 11% 20% 20% 6%	2160
	11th to 20th	Day	29% 6% 11% 20% 23% 12%	2132
	21st to end	Day	21% 5% 12% 26% 25% 11%	2160
May	1st to 10th	Day	21% 4 8% 20% 30% 17%	2337
	11th to 20th	Day	20% 5% 10% 22% 28% 16%	2470
	21st to end	Day	19% 6% 11% 27% 26% 11%	2724
June	1st to 10th	Day	22% 5% 10% 21% 26% 17%	2520
	11th to 20th	Day	9% 3 8% 18% 33% 29%	2520
	21st to end	Day	10% 1 5% 13% 29% 42%	2520
July	1st to 10th	Day	6% 1 4 12% 27% 50%	2451
	11th to 20th	Day	6% 2 3 11% 26% 51%	2445
	21st to end	Day	6% 2 4 9% 24% 56%	2407
August	1st to 10th	Day	7% 2 4 14% 31% 42%	2312
	11th to 20th	Day	5% 1 3 10% 32% 49%	2254
	21st to end	Day	5% 1 3 13% 33% 46%	2376
September	1st to 10th	Day	5% 1 3 9% 24% 58%	2160
	11th to 20th	Day	12% 3 6% 19% 36% 25%	2160
	21st to end	Day	11% 2 7% 16% 31% 33%	1904
October	1st to 10th	Day	15% 3 6% 18% 29% 29%	1800
	11th to 20th	Day	19% 4 8% 16% 25% 28%	1800
	21st to end	Day	23% 4 8% 17% 25% 23%	1980
November	1st to 10th	Day	31% 5% 8% 25% 18% 13%	1738
	11th to 20th	Day	33% 6% 12% 22% 17% 10%	1625
	21st to end	Day	31% 5% 9% 20% 23% 12%	1520
December	1st to 10th	Day	37% 5% 7% 19% 22% 11%	1520
	11th to 20th	Day	55% 6% 8% 13% 14% 4	1928
	21st to end	Day	48% 7% 11% 19% 12% 3	2794
January	1st to 10th	Night	42% 7% 14% 21% 10% 5%	2646
	11th to 20th	Night	40% 6% 9% 17% 16% 12%	2430
	21st to end	Night	41% 4 7% 16% 22% 9%	2574
February	1st to 10th	Night	36% 5% 7% 23% 20% 10%	2340
	11th to 20th	Night	35% 5% 10% 19% 25% 8%	2252
	21st to end	Night	36% 4 11% 21% 20% 7%	1776
March	1st to 10th	Night	47% 6% 12% 14% 15% 6%	2043
	11th to 20th	Night	38% 5% 12% 21% 16% 8%	1980
	21st to end	Night	35% 8% 12% 23% 17% 5%	2138
April	1st to 10th	Night	34% 6% 14% 21% 17% 8%	1800
	11th to 20th	Night	29% 5% 12% 23% 20% 11%	1779
	21st to end	Night	21% 6% 13% 27% 26% 7%	1800
May	1st to 10th	Night	21% 4 10% 20% 32% 12%	1620
	11th to 20th	Night	23% 7% 9% 25% 25% 12%	1425
	21st to end	Night	24% 7% 11% 29% 21% 8%	1552
June	1st to 10th	Night	24% 5% 10% 23% 28% 10%	1440
	11th to 20th	Night	14% 3 8% 19% 31% 26%	1440
	21st to end	Night	10% 3 4 13% 33% 36%	1440
July	1st to 10th	Night	7% 2 2 12% 32% 45%	1400
	11th to 20th	Night	8% 1 4 9% 22% 55%	1392
	21st to end	Night	5% 1 4 9% 25% 56%	1668
August	1st to 10th	Night	9% 1 2 16% 33% 38%	1602
	11th to 20th	Night	5% 1 4 15% 29% 45%	1644
	21st to end	Night	5% 1 2 15% 34% 43%	1980
September	1st to 10th	Night	5% 1 3 8% 26% 57%	1800
	11th to 20th	Night	11% 3 5% 20% 35% 27%	1800
	21st to end	Night	11% 2 7% 16% 28% 36%	2051
October	1st to 10th	Night	16% 4 6% 15% 30% 30%	2160
	11th to 20th	Night	17% 3 6% 21% 24% 29%	2160
	21st to end	Night	20% 4 7% 20% 25% 24%	2376
November	1st to 10th	Night	30% 6% 11% 22% 17% 13%	2338
	11th to 20th	Night	32% 6% 13% 22% 17% 10%	2550
	21st to end	Night	30% 5% 10% 21% 22% 13%	2660
December	1st to 10th	Night	37% 5% 9% 18% 21% 11%	2660
	11th to 20th	Night	52% 4 8% 14% 18% 3	3276
	21st to end	Night	48% 7% 10% 18% 13% 3	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	38% 11% 13% 24% 11% 3	180
	11th to 20th	Day	27% 8% 19% 23% 17% 6%	313
	21st to end	Day	22% 9% 20% 21% 18% 10%	374
February	1st to 10th	Day	20% 11% 19% 24% 21% 5%	340
	11th to 20th	Day	19% 14% 22% 28% 14% 3	345
	21st to end	Day	17% 12% 23% 31% 14% 3	346
March	1st to 10th	Day	30% 11% 25% 21% 8% 5%	420
	11th to 20th	Day	24% 9% 21% 26% 16% 4	420
	21st to end	Day	20% 12% 27% 23% 16% 2	462
April	1st to 10th	Day	18% 15% 27% 21% 15% 2	420
	11th to 20th	Day	15% 17% 21% 29% 13% 6%	412
	21st to end	Day	7% 11% 26% 28% 18% 8%	420
May	1st to 10th	Day	6% 15% 29% 25% 18% 6%	423
	11th to 20th	Day	10% 8% 25% 27% 20% 10%	448
	21st to end	Day	5% 11% 20% 28% 26% 10%	485
June	1st to 10th	Day	5% 11% 17% 29% 27% 12%	450
	11th to 20th	Day	4 11% 23% 33% 23% 6%	450
	21st to end	Day	2 4 17% 32% 33% 13%	450
July	1st to 10th	Day	2 1 14% 41% 31% 12%	446
	11th to 20th	Day	1 10% 32% 38% 18%	444
	21st to end	Day	1 6% 35% 37% 21%	487
August	1st to 10th	Day	2 1 10% 36% 32% 19%	447
	11th to 20th	Day	1 2 12% 28% 36% 21%	437
	21st to end	Day	1 2 11% 36% 34% 16%	495
September	1st to 10th	Day	1 2 14% 30% 41% 13%	450
	11th to 20th	Day	3 4 17% 31% 30% 14%	450
	21st to end	Day	3 6% 19% 32% 29% 11%	450
October	1st to 10th	Day	4 11% 17% 29% 26% 13%	450
	11th to 20th	Day	8% 5% 16% 30% 27% 14%	450
	21st to end	Day	11% 9% 18% 27% 25% 10%	495
November	1st to 10th	Day	16% 7% 19% 23% 23% 12%	334
	11th to 20th	Day	14% 3 12% 35% 26% 10%	230
	21st to end	Day	14% 5% 17% 32% 25% 7%	180
December	1st to 10th	Day	26% 7% 18% 22% 18% 10%	180
	11th to 20th	Day	27% 4 13% 28% 18% 9%	180
	21st to end	Day	21% 5% 19% 33% 18% 4	198
January	1st to 10th	Night	24% 4 17% 32% 20% 4	760
	11th to 20th	Night	23% 6% 18% 34% 16% 3	736
	21st to end	Night	20% 4 19% 34% 19% 4	792
February	1st to 10th	Night	19% 4 18% 37% 19% 3	720
	11th to 20th	Night	19% 6% 21% 34% 18% 3	704
	21st to end	Night	17% 9% 23% 38% 12% 1	592
March	1st to 10th	Night	24% 10% 23% 26% 16% 3	720
	11th to 20th	Night	19% 6% 18% 33% 23% 1	720
	21st to end	Night	18% 10% 22% 34% 15% 1	792
April	1st to 10th	Night	15% 9% 25% 32% 16% 2	720
	11th to 20th	Night	11% 9% 25% 35% 17% 3	711
	21st to end	Night	9% 5% 28% 34% 22% 2	720
May	1st to 10th	Night	9% 5% 31% 30% 24% 1	540
	11th to 20th	Night	7% 4 24% 37% 26% 1	363
	21st to end	Night	7% 8% 22% 36% 26% 1	389
June	1st to 10th	Night	6% 4 22% 42% 26% 1	360
	11th to 20th	Night	3 5% 26% 45% 19% 1	360
	21st to end	Night	3 1 14% 50% 31% 1	360
July	1st to 10th	Night	1 9% 50% 39% 1	350
	11th to 20th	Night	1 10% 49% 37% 2	348
	21st to end	Night	1 3 40% 51% 5%	584
August	1st to 10th	Night	2 1 6% 34% 50% 7%	537
	11th to 20th	Night	1 1 6% 40% 46% 6%	576
	21st to end	Night	1 1 6% 39% 49% 4	792
September	1st to 10th	Night	2 2 9% 41% 43% 3	720
	11th to 20th	Night	4 1 10% 35% 42% 7%	720
	21st to end	Night	4 3 15% 35% 34% 9%	720
October	1st to 10th	Night	6% 4 18% 34% 32% 5%	720
	11th to 20th	Night	7% 3 15% 37% 32% 6%	720
	21st to end	Night	10% 5% 14% 34% 29% 7%	792
November	1st to 10th	Night	12% 7% 14% 33% 28% 5%	740
	11th to 20th	Night	15% 3 16% 40% 24% 3	760
	21st to end	Night	17% 4 16% 36% 24% 4	760
December	1st to 10th	Night	23% 4 16% 33% 19% 5%	760
	11th to 20th	Night	30% 5% 15% 31% 18% 2	760
	21st to end	Night	25% 5% 20% 34% 15% 1	836

Page generated at 2024-01-11 19:33:46. Version ac07

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