Crestview
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Crestview clear sky chart from 2005-11-06 to 2025-07-06.

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	1 3 1 4 3 3 3 3 5% 7% 68%	123660
	Night	1 3 1 3 2 3 3 3 5% 7% 70%	124020
Transparency	Day	17% 4 7% 21% 29% 22%	123405
	Night	15% 4 9% 24% 31% 18%	123863
Seeing	Day	6% 17% 29% 27% 16% 5%	15999
	Night	3 9% 27% 34% 22% 5%	25498

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	2 2 3 2 2 2 3 5% 11% 68%	3639
	11th to 20th	Day	2 1 3 3 4 3 4 5% 7% 67%	3748
	21st to end	Day	1 5% 3 7% 4 4 4 4 6% 9% 55%	4510
February	1st to 10th	Day	1 3 2 4 2 4 3 3 6% 8% 65%	1923
	11th to 20th	Day	3 2 5% 4 3 4 4 6% 10% 59%	1950
	21st to end	Day	3 2 5% 4 3 4 4 6% 8% 62%	1650
March	1st to 10th	Day	5% 3 8% 5% 5% 5% 4 8% 9% 48%	4518
	11th to 20th	Day	5% 3 6% 3 3 4 3 5% 10% 58%	4775
	21st to end	Day	1 5% 2 5% 3 3 4 3 6% 8% 60%	5939
April	1st to 10th	Day	1 4 2 5% 3 4 4 4 6% 8% 60%	2400
	11th to 20th	Day	1 4 1 4 3 3 4 3 5% 7% 64%	2369
	21st to end	Day	1 6% 2 3 3 3 3 3 6% 7% 64%	2400
May	1st to 10th	Day	2 4 1 3 3 3 3 3 4 5% 69%	5743
	11th to 20th	Day	2 4 1 4 3 4 3 3 3 5% 68%	5841
	21st to end	Day	2 4 1 3 3 3 3 3 4 6% 69%	6889
June	1st to 10th	Day	4 3 1 4 3 3 3 4 5% 7% 62%	2800
	11th to 20th	Day	2 2 2 2 2 2 1 3 4 79%	2800
	21st to end	Day	3 3 1 3 2 2 3 3 3 4 74%	2800
July	1st to 10th	Day	1 1 1 2 2 2 2 2 3 4 79%	4491
	11th to 20th	Day	3 3 1 5% 4 4 4 3 5% 6% 62%	4420
	21st to end	Day	4 3 1 3 3 3 3 3 4 4 70%	4702
August	1st to 10th	Day	3 2 1 4 3 3 3 3 4 5% 69%	3854
	11th to 20th	Day	2 1 1 1 2 2 2 2 2 3 83%	3724
	21st to end	Day	2 1 1 2 1 1 2 1 2 3 84%	4180
September	1st to 10th	Day	3 2 1 2 2 2 3 2 3 4 75%	2280
	11th to 20th	Day	3 3 1 3 2 2 2 2 3 4 75%	2199
	21st to end	Day	1 2 1 2 2 2 2 2 3 5% 78%	2090
October	1st to 10th	Day	3 3 1 3 2 2 3 3 4 7% 70%	3376
	11th to 20th	Day	1 1 1 3 2 2 2 1 3 4 80%	3161
	21st to end	Day	1 1 3 2 2 2 2 4 7% 74%	3326
November	1st to 10th	Day	1 2 1 3 3 2 2 3 5% 8% 69%	1764
	11th to 20th	Day	1 1 2 1 2 2 3 5% 9% 73%	1800
	21st to end	Day	1 3 1 3 2 2 2 3 5% 9% 70%	1800
December	1st to 10th	Day	1 2 1 2 2 2 3 3 4 9% 72%	2767
	11th to 20th	Day	3 1 4 4 4 4 4 7% 8% 61%	3028
	21st to end	Day	5% 2 5% 3 3 5% 4 8% 12% 53%	4004
January	1st to 10th	Night	2 2 5% 3 2 3 3 4 8% 67%	6306
	11th to 20th	Night	1 1 3 3 3 3 3 6% 9% 68%	6215
	21st to end	Night	4 2 6% 4 4 3 3 5% 8% 60%	6468
February	1st to 10th	Night	3 2 5% 4 3 3 4 5% 8% 64%	2475
	11th to 20th	Night	4 2 4 2 3 4 3 5% 9% 64%	2338
	21st to end	Night	2 1 4 3 2 3 3 5% 8% 66%	1980
March	1st to 10th	Night	3 3 6% 4 4 5% 4 6% 9% 56%	5376
	11th to 20th	Night	6% 3 6% 3 3 3 4 5% 7% 61%	5221
	21st to end	Night	4 2 4 3 3 4 3 5% 9% 63%	5034
April	1st to 10th	Night	1 4 2 4 2 3 3 4 4 7% 65%	2000
	11th to 20th	Night	1 3 2 3 3 2 3 3 5% 7% 68%	1979
	21st to end	Night	1 5% 2 3 2 3 3 3 5% 5% 70%	2000
May	1st to 10th	Night	2 4 1 3 2 1 2 1 3 5% 75%	4243
	11th to 20th	Night	1 2 1 2 2 3 3 2 4 5% 75%	4074
	21st to end	Night	2 3 1 2 1 2 2 2 3 5% 79%	3981
June	1st to 10th	Night	2 2 1 3 3 3 3 4 6% 7% 67%	1600
	11th to 20th	Night	2 1 2 1 1 1 2 3 4 83%	1600
	21st to end	Night	1 2 1 2 2 1 1 1 3 3 83%	1600
July	1st to 10th	Night	1 1 1 1 1 1 2 3 89%	2580
	11th to 20th	Night	2 3 1 4 3 3 3 3 5% 5% 67%	2540
	21st to end	Night	2 2 1 2 2 2 2 3 4 79%	2848
August	1st to 10th	Night	2 1 1 2 2 2 2 2 3 6% 77%	3091
	11th to 20th	Night	1 1 2 1 2 2 1 2 3 85%	3126
	21st to end	Night	1 1 1 1 1 1 2 3 89%	3498
September	1st to 10th	Night	1 1 1 1 1 1 1 2 2 88%	1900
	11th to 20th	Night	1 2 1 2 1 2 2 2 3 4 80%	1980
	21st to end	Night	1 2 2 1 2 2 1 3 4 82%	2090
October	1st to 10th	Night	2 2 1 2 1 1 2 2 3 4 80%	3600
	11th to 20th	Night	1 1 1 2 1 2 2 2 4 4 80%	3777
	21st to end	Night	2 1 3 2 2 2 2 3 5% 78%	4237
November	1st to 10th	Night	1 2 1 2 2 2 3 2 4 7% 75%	2535
	11th to 20th	Night	2 1 2 2 2 2 3 4 8% 74%	2600
	21st to end	Night	3 1 3 2 3 3 3 4 7% 70%	2600
December	1st to 10th	Night	1 1 3 2 2 3 2 5% 7% 72%	4400
	11th to 20th	Night	2 1 3 3 3 4 4 8% 13% 59%	5176
	21st to end	Night	1 5% 2 6% 4 4 5% 5% 9% 12% 46%	6952

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	13% 5% 18% 29% 30% 5%	3639
	11th to 20th	Day	18% 3 13% 18% 27% 21%	3748
	21st to end	Day	26% 5% 11% 18% 27% 12%	4510
February	1st to 10th	Day	19% 5% 12% 22% 27% 15%	1923
	11th to 20th	Day	21% 5% 9% 25% 30% 10%	1960
	21st to end	Day	21% 9% 10% 24% 27% 9%	1650
March	1st to 10th	Day	31% 5% 6% 21% 28% 10%	4518
	11th to 20th	Day	22% 6% 12% 38% 18% 5%	4775
	21st to end	Day	22% 6% 12% 29% 26% 5%	5939
April	1st to 10th	Day	22% 6% 13% 29% 20% 9%	2400
	11th to 20th	Day	21% 5% 12% 29% 24% 10%	2372
	21st to end	Day	20% 5% 13% 33% 25% 5%	2400
May	1st to 10th	Day	17% 5% 7% 29% 31% 11%	5743
	11th to 20th	Day	17% 4 5% 26% 37% 11%	5844
	21st to end	Day	16% 3 4 23% 45% 8%	6891
June	1st to 10th	Day	22% 4 9% 23% 32% 11%	2800
	11th to 20th	Day	12% 1 6% 17% 37% 28%	2800
	21st to end	Day	14% 3 2 11% 33% 36%	2800
July	1st to 10th	Day	10% 2 2 6% 15% 65%	4422
	11th to 20th	Day	20% 4 3 9% 20% 44%	4345
	21st to end	Day	17% 2 4 13% 19% 45%	4553
August	1st to 10th	Day	16% 2 2 10% 26% 44%	3839
	11th to 20th	Day	8% 2 1 6% 20% 62%	3760
	21st to end	Day	8% 1 2 8% 29% 52%	4179
September	1st to 10th	Day	14% 2 3 10% 29% 43%	2280
	11th to 20th	Day	14% 3 2 18% 31% 30%	2199
	21st to end	Day	12% 2 2 18% 36% 31%	2090
October	1st to 10th	Day	14% 3 3 15% 34% 32%	3376
	11th to 20th	Day	11% 2 2 12% 44% 28%	3161
	21st to end	Day	9% 4 3 20% 45% 20%	3326
November	1st to 10th	Day	14% 3 9% 25% 33% 16%	1764
	11th to 20th	Day	10% 4 11% 28% 34% 14%	1800
	21st to end	Day	14% 4 11% 24% 32% 15%	1800
December	1st to 10th	Day	13% 4 8% 28% 32% 15%	2767
	11th to 20th	Day	17% 5% 19% 28% 22% 9%	3028
	21st to end	Day	22% 5% 16% 28% 21% 8%	4004
January	1st to 10th	Night	16% 4 15% 29% 30% 6%	6306
	11th to 20th	Night	15% 3 12% 24% 33% 13%	6215
	21st to end	Night	22% 5% 10% 22% 29% 12%	6468
February	1st to 10th	Night	20% 5% 11% 25% 23% 15%	2475
	11th to 20th	Night	19% 5% 10% 25% 28% 12%	2339
	21st to end	Night	18% 7% 10% 29% 27% 10%	1980
March	1st to 10th	Night	23% 5% 7% 26% 28% 10%	5376
	11th to 20th	Night	21% 5% 10% 37% 20% 6%	5221
	21st to end	Night	19% 5% 19% 31% 22% 4	5034
April	1st to 10th	Night	21% 5% 13% 31% 22% 7%	2000
	11th to 20th	Night	18% 5% 12% 29% 26% 10%	1979
	21st to end	Night	18% 4 16% 38% 21% 4	2000
May	1st to 10th	Night	16% 3 7% 38% 31% 5%	4240
	11th to 20th	Night	12% 2 9% 32% 38% 6%	4075
	21st to end	Night	11% 2 5% 28% 48% 5%	3981
June	1st to 10th	Night	16% 4 9% 32% 32% 7%	1600
	11th to 20th	Night	8% 2 8% 21% 37% 24%	1600
	21st to end	Night	9% 1 3 14% 38% 35%	1600
July	1st to 10th	Night	4 1 2 7% 19% 68%	2540
	11th to 20th	Night	17% 3 2 12% 28% 38%	2492
	21st to end	Night	10% 2 4 19% 24% 42%	2759
August	1st to 10th	Night	10% 1 4 13% 32% 39%	3082
	11th to 20th	Night	7% 2 1 10% 22% 58%	3156
	21st to end	Night	4 2 2 11% 40% 42%	3498
September	1st to 10th	Night	6% 1 2 13% 40% 38%	1900
	11th to 20th	Night	10% 2 5% 19% 40% 23%	1980
	21st to end	Night	9% 2 3 23% 38% 25%	2090
October	1st to 10th	Night	10% 2 4 16% 42% 27%	3600
	11th to 20th	Night	8% 4 3 16% 44% 25%	3777
	21st to end	Night	10% 2 4 19% 43% 20%	4237
November	1st to 10th	Night	11% 6% 10% 26% 33% 15%	2535
	11th to 20th	Night	11% 4 10% 27% 35% 13%	2600
	21st to end	Night	15% 5% 11% 25% 31% 13%	2600
December	1st to 10th	Night	12% 4 13% 25% 30% 16%	4400
	11th to 20th	Night	14% 6% 20% 29% 25% 6%	5176
	21st to end	Night	27% 5% 16% 21% 21% 11%	6952

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	7% 25% 32% 23% 10% 4	200
	11th to 20th	Day	3 23% 28% 23% 17% 6%	243
	21st to end	Day	3 18% 29% 30% 16% 5%	440
February	1st to 10th	Day	8% 24% 30% 21% 13% 5%	463
	11th to 20th	Day	6% 21% 33% 26% 13% 1	495
	21st to end	Day	6% 23% 33% 26% 12%	414
March	1st to 10th	Day	6% 25% 34% 25% 7% 2	500
	11th to 20th	Day	10% 26% 27% 21% 13% 3	500
	21st to end	Day	9% 26% 33% 23% 9%	550
April	1st to 10th	Day	8% 23% 33% 23% 11% 3	500
	11th to 20th	Day	11% 24% 32% 21% 10% 2	492
	21st to end	Day	8% 21% 30% 24% 12% 5%	500
May	1st to 10th	Day	10% 21% 31% 22% 11% 5%	503
	11th to 20th	Day	11% 21% 28% 22% 12% 6%	528
	21st to end	Day	8% 18% 25% 24% 18% 6%	573
June	1st to 10th	Day	6% 15% 31% 24% 18% 7%	530
	11th to 20th	Day	6% 22% 31% 22% 13% 7%	530
	21st to end	Day	3 13% 32% 30% 14% 7%	530
July	1st to 10th	Day	3 8% 32% 30% 20% 7%	507
	11th to 20th	Day	4 6% 26% 35% 20% 9%	484
	21st to end	Day	7% 7% 26% 32% 18% 10%	531
August	1st to 10th	Day	4 10% 29% 29% 21% 7%	487
	11th to 20th	Day	4 11% 27% 29% 20% 9%	477
	21st to end	Day	4 7% 26% 35% 20% 8%	539
September	1st to 10th	Day	5% 10% 23% 33% 22% 6%	490
	11th to 20th	Day	7% 14% 26% 29% 19% 4	490
	21st to end	Day	5% 12% 25% 35% 18% 5%	490
October	1st to 10th	Day	5% 14% 29% 28% 19% 5%	490
	11th to 20th	Day	4 15% 23% 35% 18% 5%	490
	21st to end	Day	5% 16% 30% 26% 18% 6%	466
November	1st to 10th	Day	6% 16% 27% 18% 24% 9%	300
	11th to 20th	Day	4 19% 21% 31% 16% 8%	300
	21st to end	Day	4 14% 26% 29% 21% 5%	300
December	1st to 10th	Day	6% 13% 27% 26% 19% 9%	247
	11th to 20th	Day	5% 21% 29% 25% 16% 6%	200
	21st to end	Day	7% 25% 25% 27% 10% 5%	220
January	1st to 10th	Night	4 11% 35% 25% 17% 9%	800
	11th to 20th	Night	1 13% 32% 34% 15% 7%	800
	21st to end	Night	3 10% 33% 33% 16% 6%	880
February	1st to 10th	Night	3 12% 31% 32% 18% 4	800
	11th to 20th	Night	3 13% 33% 29% 17% 5%	784
	21st to end	Night	1 17% 33% 34% 11% 4	660
March	1st to 10th	Night	3 16% 36% 29% 12% 5%	800
	11th to 20th	Night	3 14% 33% 27% 18% 6%	800
	21st to end	Night	3 17% 38% 28% 13% 2	880
April	1st to 10th	Night	4 12% 35% 31% 16% 3	800
	11th to 20th	Night	3 14% 31% 32% 14% 5%	791
	21st to end	Night	4 9% 33% 32% 17% 6%	800
May	1st to 10th	Night	5% 10% 31% 34% 17% 4	665
	11th to 20th	Night	4 9% 30% 37% 18% 3	591
	21st to end	Night	6% 6% 24% 35% 24% 5%	442
June	1st to 10th	Night	2 4 22% 41% 30% 2	400
	11th to 20th	Night	3 5% 25% 42% 23% 3	400
	21st to end	Night	2 2 19% 48% 26% 2	400
July	1st to 10th	Night	1 1 14% 45% 37% 2	380
	11th to 20th	Night	2 1 14% 45% 35% 3	368
	21st to end	Night	3 8% 43% 41% 5%	467
August	1st to 10th	Night	3 2 14% 41% 34% 6%	706
	11th to 20th	Night	1 2 17% 43% 32% 5%	752
	21st to end	Night	2 2 15% 41% 34% 7%	836
September	1st to 10th	Night	2 2 15% 39% 36% 7%	760
	11th to 20th	Night	3 6% 18% 35% 31% 7%	760
	21st to end	Night	2 6% 17% 36% 31% 8%	760
October	1st to 10th	Night	4 6% 20% 36% 28% 6%	760
	11th to 20th	Night	3 8% 17% 38% 27% 8%	760
	21st to end	Night	3 6% 25% 30% 24% 12%	836
November	1st to 10th	Night	2 9% 24% 31% 25% 9%	780
	11th to 20th	Night	2 8% 32% 33% 19% 6%	800
	21st to end	Night	3 10% 28% 31% 23% 5%	800
December	1st to 10th	Night	2 11% 31% 35% 16% 6%	800
	11th to 20th	Night	3 14% 34% 31% 15% 3	800
	21st to end	Night	2 15% 38% 28% 14% 3	880

Page generated at 2025-07-02 22:30:18. Version ac07

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