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 2024-11-30.

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	10% 4 1 3 2 2 2 2 4 5% 65%	105506
	Night	12% 4 1 4 3 2 3 2 4 5% 59%	102822
Transparency	Day	23% 4 7% 17% 24% 26%	105260
	Night	27% 5% 8% 18% 22% 20%	102657
Seeing	Day	11% 8% 18% 29% 24% 10%	15165
	Night	13% 5% 17% 36% 26% 3	24357

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	22% 8% 2 5% 4 3 3 3 5% 8% 37%	2539
	11th to 20th	Day	30% 10% 3 6% 3 3 2 2 3 4 35%	2794
	21st to end	Day	27% 9% 3 6% 3 3 3 2 4 6% 33%	3146
February	1st to 10th	Day	17% 5% 1 5% 4 3 4 4 5% 6% 47%	1710
	11th to 20th	Day	17% 5% 2 5% 3 3 3 3 4 6% 50%	1688
	21st to end	Day	17% 5% 2 4 3 3 4 3 4 8% 48%	1570
March	1st to 10th	Day	26% 10% 3 6% 4 4 4 3 4 5% 31%	3343
	11th to 20th	Day	12% 5% 2 4 3 2 2 2 3 6% 59%	3490
	21st to end	Day	17% 9% 3 6% 4 4 4 3 5% 6% 38%	3902
April	1st to 10th	Day	13% 7% 2 4 4 3 4 3 4 7% 48%	2280
	11th to 20th	Day	13% 4 2 4 2 3 3 3 4 7% 56%	2249
	21st to end	Day	5% 3 1 3 3 3 3 3 5% 7% 63%	2280
May	1st to 10th	Day	6% 3 1 3 2 2 2 2 3 5% 70%	4107
	11th to 20th	Day	3 2 1 2 1 2 2 2 3 5% 78%	4367
	21st to end	Day	3 1 2 2 2 2 2 4 6% 75%	4813
June	1st to 10th	Day	6% 3 1 4 2 3 4 3 4 8% 62%	2660
	11th to 20th	Day	2 1 1 1 2 2 2 2 4 5% 80%	2660
	21st to end	Day	3 1 1 2 1 1 2 2 3 3 81%	2660
July	1st to 10th	Day	1 1 1 1 2 2 92%	4420
	11th to 20th	Day	2 1 2 1 1 1 1 3 3 85%	4420
	21st to end	Day	1 1 1 1 1 1 1 2 2 90%	4458
August	1st to 10th	Day	2 2 1 2 1 1 2 2 3 5% 79%	4091
	11th to 20th	Day	1 1 1 1 1 1 1 2 90%	3943
	21st to end	Day	2 1 1 1 1 1 1 1 1 3 87%	4180
September	1st to 10th	Day	1 1 1 1 1 1 1 3 3 88%	2280
	11th to 20th	Day	3 2 1 2 2 2 2 2 3 6% 75%	2280
	21st to end	Day	2 1 1 3 2 1 2 1 3 4 81%	2009
October	1st to 10th	Day	3 1 1 2 1 1 2 2 3 4 81%	3180
	11th to 20th	Day	6% 2 1 3 1 2 3 3 5% 6% 69%	3161
	21st to end	Day	9% 4 1 4 3 4 4 3 5% 7% 56%	3448
November	1st to 10th	Day	14% 4 1 3 3 2 3 3 5% 7% 53%	1831
	11th to 20th	Day	16% 5% 1 4 3 4 3 4 6% 8% 48%	1710
	21st to end	Day	13% 5% 2 3 2 4 4 3 4 7% 54%	1595
December	1st to 10th	Day	23% 5% 1 3 2 2 2 3 3 5% 50%	1520
	11th to 20th	Day	30% 7% 3 6% 4 3 3 3 6% 5% 31%	1928
	21st to end	Day	27% 6% 2 5% 3 3 3 3 5% 6% 36%	2794
January	1st to 10th	Night	19% 7% 3 6% 4 4 4 4 6% 8% 35%	4406
	11th to 20th	Night	28% 7% 3 6% 3 3 4 3 4 6% 33%	4172
	21st to end	Night	28% 10% 3 7% 4 3 3 3 4 4 29%	4521
February	1st to 10th	Night	17% 6% 2 4 3 4 3 2 5% 6% 48%	2470
	11th to 20th	Night	18% 5% 1 4 4 3 3 3 4 6% 48%	2379
	21st to end	Night	15% 6% 2 4 4 3 3 3 4 6% 49%	1884
March	1st to 10th	Night	23% 9% 3 6% 4 4 4 3 4 5% 36%	3529
	11th to 20th	Night	15% 5% 2 3 2 2 2 2 4 6% 57%	3490
	21st to end	Night	14% 8% 2 7% 5% 4 5% 4 6% 8% 38%	3750
April	1st to 10th	Night	13% 6% 2 5% 4 3 4 3 5% 6% 49%	1900
	11th to 20th	Night	10% 5% 2 4 3 3 3 2 4 8% 55%	1879
	21st to end	Night	8% 4 1 3 2 2 2 3 5% 9% 61%	1899
May	1st to 10th	Night	7% 4 1 4 3 2 2 2 4 4 67%	2860
	11th to 20th	Night	3 2 1 2 2 2 2 2 4 4 76%	2525
	21st to end	Night	4 3 1 3 3 2 3 2 4 5% 70%	2762
June	1st to 10th	Night	6% 4 2 3 3 3 4 3 7% 9% 57%	1520
	11th to 20th	Night	3 3 1 2 2 2 2 2 4 5% 75%	1520
	21st to end	Night	2 1 2 2 2 2 2 3 2 82%	1520
July	1st to 10th	Night	1 1 1 1 1 1 2 91%	2540
	11th to 20th	Night	1 2 1 2 2 1 2 1 2 3 83%	2540
	21st to end	Night	1 1 1 1 2 3 90%	3102
August	1st to 10th	Night	3 2 1 2 2 2 2 2 3 4 79%	2848
	11th to 20th	Night	1 1 1 1 1 2 3 90%	2896
	21st to end	Night	4 2 1 1 1 1 1 2 3 85%	3498
September	1st to 10th	Night	1 1 1 1 1 1 1 2 3 87%	1900
	11th to 20th	Night	4 2 1 2 1 1 2 1 3 5% 77%	1900
	21st to end	Night	3 1 2 1 2 2 2 4 4 78%	2166
October	1st to 10th	Night	3 2 1 1 1 2 2 2 3 3 80%	3800
	11th to 20th	Night	4 2 1 3 2 2 3 2 3 6% 72%	3777
	21st to end	Night	7% 2 1 3 2 2 4 3 7% 8% 61%	4121
November	1st to 10th	Night	13% 5% 2 4 3 3 3 3 6% 8% 51%	2465
	11th to 20th	Night	14% 5% 1 4 3 3 4 3 5% 8% 49%	2685
	21st to end	Night	16% 4 1 4 3 2 2 3 4 7% 54%	2800
December	1st to 10th	Night	22% 5% 1 3 2 3 3 2 4 8% 47%	2660
	11th to 20th	Night	32% 7% 2 4 3 3 3 2 5% 6% 33%	3276
	21st to end	Night	26% 7% 2 5% 3 3 4 3 5% 6% 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	44% 8% 12% 26% 7% 3	2539
	11th to 20th	Day	56% 4 8% 14% 10% 7%	2794
	21st to end	Day	53% 5% 11% 13% 12% 5%	3146
February	1st to 10th	Day	36% 6% 11% 18% 20% 9%	1710
	11th to 20th	Day	37% 5% 9% 19% 24% 7%	1697
	21st to end	Day	36% 5% 9% 24% 19% 7%	1570
March	1st to 10th	Day	53% 6% 9% 12% 16% 4	3343
	11th to 20th	Day	29% 4 7% 24% 25% 10%	3490
	21st to end	Day	43% 9% 11% 21% 13% 3	3902
April	1st to 10th	Day	36% 6% 11% 21% 20% 6%	2280
	11th to 20th	Day	29% 6% 10% 22% 22% 11%	2252
	21st to end	Day	21% 5% 12% 25% 25% 11%	2280
May	1st to 10th	Day	17% 4 9% 21% 28% 21%	4107
	11th to 20th	Day	11% 3 6% 16% 32% 32%	4370
	21st to end	Day	12% 4 11% 27% 31% 14%	4814
June	1st to 10th	Day	22% 5% 10% 21% 27% 16%	2660
	11th to 20th	Day	9% 3 8% 17% 33% 30%	2660
	21st to end	Day	9% 1 5% 13% 29% 43%	2660
July	1st to 10th	Day	3 1 2 7% 15% 72%	4351
	11th to 20th	Day	8% 1 3 7% 19% 62%	4345
	21st to end	Day	4 1 3 8% 27% 57%	4317
August	1st to 10th	Day	10% 1 3 9% 24% 53%	4076
	11th to 20th	Day	4 1 3 13% 38% 42%	3982
	21st to end	Day	7% 1 3 17% 33% 39%	4179
September	1st to 10th	Day	5% 1 3 8% 24% 59%	2280
	11th to 20th	Day	13% 3 6% 19% 35% 24%	2280
	21st to end	Day	10% 2 6% 16% 31% 35%	2009
October	1st to 10th	Day	11% 2 4 12% 23% 48%	3180
	11th to 20th	Day	16% 3 8% 21% 32% 19%	3161
	21st to end	Day	27% 5% 8% 19% 28% 15%	3448
November	1st to 10th	Day	30% 5% 8% 26% 18% 13%	1831
	11th to 20th	Day	35% 6% 12% 22% 17% 9%	1710
	21st to end	Day	32% 5% 9% 19% 22% 13%	1595
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% 10% 16% 21% 8% 3	4406
	11th to 20th	Night	52% 8% 9% 13% 12% 7%	4172
	21st to end	Night	57% 6% 7% 11% 13% 5%	4521
February	1st to 10th	Night	37% 5% 8% 22% 19% 10%	2470
	11th to 20th	Night	36% 5% 10% 18% 24% 7%	2381
	21st to end	Night	36% 4 12% 21% 20% 7%	1884
March	1st to 10th	Night	47% 7% 15% 14% 13% 3	3529
	11th to 20th	Night	30% 4 9% 25% 22% 10%	3490
	21st to end	Night	37% 11% 15% 24% 11% 3	3750
April	1st to 10th	Night	34% 6% 14% 22% 17% 8%	1900
	11th to 20th	Night	29% 6% 12% 24% 20% 10%	1879
	21st to end	Night	21% 6% 13% 27% 25% 7%	1899
May	1st to 10th	Night	22% 4 8% 18% 31% 17%	2860
	11th to 20th	Night	13% 4 6% 16% 35% 26%	2525
	21st to end	Night	17% 5% 11% 33% 24% 11%	2762
June	1st to 10th	Night	23% 5% 10% 24% 28% 9%	1520
	11th to 20th	Night	13% 3 8% 18% 32% 26%	1520
	21st to end	Night	10% 3 4 13% 33% 37%	1520
July	1st to 10th	Night	4 1 1 7% 18% 69%	2500
	11th to 20th	Night	9% 1 3 5% 16% 65%	2492
	21st to end	Night	4 1 3 9% 29% 55%	3005
August	1st to 10th	Night	13% 1 2 9% 25% 50%	2839
	11th to 20th	Night	3 1 2 15% 40% 39%	2923
	21st to end	Night	8% 1 2 16% 35% 37%	3498
September	1st to 10th	Night	5% 1 3 8% 25% 58%	1900
	11th to 20th	Night	12% 3 5% 20% 35% 25%	1900
	21st to end	Night	11% 2 6% 16% 28% 37%	2166
October	1st to 10th	Night	11% 3 4 10% 22% 50%	3800
	11th to 20th	Night	16% 3 6% 29% 28% 18%	3777
	21st to end	Night	19% 4 8% 25% 27% 16%	4121
November	1st to 10th	Night	30% 6% 11% 23% 17% 13%	2465
	11th to 20th	Night	33% 7% 13% 22% 17% 9%	2685
	21st to end	Night	31% 5% 10% 20% 22% 12%	2800
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% 5%	330
	21st to end	Day	23% 9% 20% 23% 17% 9%	407
February	1st to 10th	Day	21% 12% 18% 26% 20% 4	370
	11th to 20th	Day	20% 15% 22% 27% 14% 3	376
	21st to end	Day	17% 12% 23% 31% 15% 3	382
March	1st to 10th	Day	31% 12% 25% 20% 8% 4	460
	11th to 20th	Day	23% 10% 22% 24% 17% 5%	460
	21st to end	Day	20% 12% 28% 23% 15% 1	506
April	1st to 10th	Day	17% 15% 27% 21% 17% 2	460
	11th to 20th	Day	15% 16% 20% 28% 15% 7%	452
	21st to end	Day	7% 12% 26% 28% 20% 8%	460
May	1st to 10th	Day	6% 16% 29% 25% 17% 6%	463
	11th to 20th	Day	9% 8% 24% 27% 22% 10%	488
	21st to end	Day	5% 10% 20% 29% 25% 10%	529
June	1st to 10th	Day	4 10% 17% 30% 27% 11%	490
	11th to 20th	Day	4 11% 23% 31% 24% 7%	490
	21st to end	Day	2 3 18% 32% 33% 12%	490
July	1st to 10th	Day	1 1 14% 38% 31% 14%	486
	11th to 20th	Day	1 10% 31% 39% 18%	484
	21st to end	Day	1 6% 35% 36% 22%	531
August	1st to 10th	Day	2 1 9% 35% 32% 20%	487
	11th to 20th	Day	1 2 13% 29% 36% 19%	477
	21st to end	Day	1 3 11% 34% 33% 18%	539
September	1st to 10th	Day	1 2 15% 30% 40% 13%	490
	11th to 20th	Day	4 4 18% 31% 30% 14%	490
	21st to end	Day	2 6% 19% 32% 30% 11%	490
October	1st to 10th	Day	4 10% 16% 29% 28% 14%	490
	11th to 20th	Day	8% 5% 16% 30% 27% 13%	490
	21st to end	Day	11% 10% 19% 28% 23% 9%	539
November	1st to 10th	Day	16% 8% 20% 23% 23% 11%	367
	11th to 20th	Day	17% 4 13% 34% 24% 9%	255
	21st to end	Day	17% 6% 16% 31% 25% 7%	199
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	760
	21st to end	Night	21% 5% 19% 33% 18% 4	836
February	1st to 10th	Night	19% 5% 19% 36% 18% 3	760
	11th to 20th	Night	20% 6% 21% 33% 18% 2	744
	21st to end	Night	16% 9% 24% 37% 13% 1	628
March	1st to 10th	Night	24% 10% 23% 26% 15% 3	760
	11th to 20th	Night	19% 7% 18% 32% 23% 1	760
	21st to end	Night	18% 11% 23% 33% 14% 1	836
April	1st to 10th	Night	15% 9% 26% 32% 16% 2	760
	11th to 20th	Night	12% 9% 25% 35% 17% 3	751
	21st to end	Night	9% 5% 28% 35% 22% 2	759
May	1st to 10th	Night	9% 5% 32% 29% 23% 1	570
	11th to 20th	Night	7% 4 23% 38% 27% 1	383
	21st to end	Night	7% 8% 23% 36% 26% 1	411
June	1st to 10th	Night	5% 4 22% 42% 26% 1	380
	11th to 20th	Night	3 6% 26% 46% 19% 1	380
	21st to end	Night	3 1 14% 52% 29% 1	380
July	1st to 10th	Night	1 9% 49% 39% 1	370
	11th to 20th	Night	1 1 10% 50% 36% 2	368
	21st to end	Night	1 3 41% 50% 5%	617
August	1st to 10th	Night	2 1 6% 35% 50% 7%	567
	11th to 20th	Night	1 6% 42% 44% 6%	609
	21st to end	Night	1 1 6% 39% 49% 4	836
September	1st to 10th	Night	2 1 10% 43% 42% 3	760
	11th to 20th	Night	4 2 11% 36% 41% 7%	760
	21st to end	Night	4 3 15% 36% 34% 8%	760
October	1st to 10th	Night	6% 4 17% 35% 33% 5%	760
	11th to 20th	Night	7% 3 15% 36% 33% 6%	760
	21st to end	Night	10% 5% 15% 35% 28% 7%	836
November	1st to 10th	Night	12% 7% 15% 33% 28% 5%	780
	11th to 20th	Night	15% 3 17% 39% 23% 3	800
	21st to end	Night	19% 4 15% 35% 24% 3	800
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 2024-11-27 14:30:49. Version ac07

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