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 2026-01-17.

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% 5% 2 6% 5% 5% 5% 5% 7% 9% 42%	126918
	Night	11% 6% 2 6% 4 4 4 4 6% 8% 45%	124814
Transparency	Day	37% 6% 13% 18% 17% 8%	130810
	Night	35% 5% 13% 18% 19% 9%	128995
Seeing	Day	12% 9% 21% 25% 20% 13%	16196
	Night	12% 6% 21% 30% 24% 6%	26169

By Month

Percentage Cloud Cover SE (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	12% 5% 1 4 3 3 4 3 5% 7% 53%	4164
	11th to 20th	Day	14% 5% 2 4 3 3 3 4 5% 7% 50%	4580
	21st to end	Day	18% 7% 2 6% 3 5% 4 3 5% 7% 39%	4972
February	1st to 10th	Day	16% 7% 3 6% 4 4 4 3 5% 6% 42%	2000
	11th to 20th	Day	16% 6% 2 6% 3 4 3 4 5% 7% 43%	1948
	21st to end	Day	15% 7% 2 6% 5% 5% 4 4 5% 6% 40%	1650
March	1st to 10th	Day	17% 7% 3 6% 4 4 4 3 6% 7% 40%	4480
	11th to 20th	Day	8% 5% 2 5% 4 4 4 3 5% 7% 52%	4832
	21st to end	Day	16% 6% 2 5% 4 4 4 4 5% 6% 44%	5636
April	1st to 10th	Day	13% 6% 2 6% 5% 3 4 4 5% 6% 46%	2400
	11th to 20th	Day	11% 6% 2 6% 5% 5% 4 3 5% 7% 47%	2374
	21st to end	Day	7% 4 2 5% 5% 4 4 3 5% 7% 55%	2400
May	1st to 10th	Day	13% 6% 3 7% 4 5% 4 4 6% 8% 40%	5579
	11th to 20th	Day	12% 5% 2 5% 4 5% 5% 4 7% 9% 43%	5861
	21st to end	Day	6% 4 2 6% 5% 5% 6% 5% 7% 11% 44%	6433
June	1st to 10th	Day	8% 7% 3 9% 7% 7% 6% 6% 8% 10% 29%	2600
	11th to 20th	Day	5% 4 2 6% 6% 7% 9% 7% 9% 12% 35%	2600
	21st to end	Day	6% 6% 2 8% 7% 8% 9% 6% 9% 10% 29%	2600
July	1st to 10th	Day	6% 5% 3 9% 7% 8% 8% 7% 11% 14% 24%	5900
	11th to 20th	Day	4 4 2 6% 7% 7% 9% 7% 10% 15% 29%	5900
	21st to end	Day	5% 5% 2 8% 7% 8% 9% 8% 10% 14% 24%	5924
August	1st to 10th	Day	5% 4 2 6% 5% 6% 7% 6% 9% 13% 36%	3905
	11th to 20th	Day	6% 5% 2 6% 5% 6% 6% 6% 8% 9% 42%	3849
	21st to end	Day	7% 5% 3 8% 6% 7% 7% 6% 8% 11% 33%	4312
September	1st to 10th	Day	10% 7% 3 8% 6% 7% 6% 5% 7% 8% 33%	2314
	11th to 20th	Day	12% 7% 3 8% 6% 6% 4 4 6% 7% 38%	2200
	21st to end	Day	7% 5% 2 7% 5% 5% 5% 5% 5% 6% 49%	2200
October	1st to 10th	Day	9% 5% 2 6% 4 4 4 3 5% 6% 50%	2200
	11th to 20th	Day	8% 3 1 3 3 3 4 3 5% 7% 60%	2200
	21st to end	Day	8% 4 2 6% 4 3 3 3 4 6% 57%	2225
November	1st to 10th	Day	8% 5% 2 5% 3 3 3 3 6% 6% 56%	1852
	11th to 20th	Day	9% 5% 2 5% 3 3 3 3 5% 7% 55%	1890
	21st to end	Day	12% 4 2 5% 4 4 4 4 5% 7% 49%	1890
December	1st to 10th	Day	16% 5% 2 5% 3 3 3 2 4 6% 50%	3020
	11th to 20th	Day	11% 6% 2 5% 4 3 4 3 4 5% 53%	3463
	21st to end	Day	17% 8% 2 6% 3 3 3 2 4 5% 46%	4565
January	1st to 10th	Night	13% 5% 2 5% 4 4 4 3 5% 5% 48%	5996
	11th to 20th	Night	16% 8% 3 7% 4 4 3 3 4 6% 44%	5513
	21st to end	Night	18% 8% 2 5% 4 4 4 3 6% 7% 40%	5984
February	1st to 10th	Night	14% 8% 3 7% 4 4 3 3 5% 6% 44%	2400
	11th to 20th	Night	19% 7% 2 5% 4 3 3 3 5% 5% 44%	2338
	21st to end	Night	15% 9% 2 6% 5% 3 4 3 5% 5% 42%	1980
March	1st to 10th	Night	21% 11% 3 7% 4 3 3 3 4 6% 36%	5373
	11th to 20th	Night	11% 7% 2 5% 4 3 4 3 5% 7% 49%	5128
	21st to end	Night	13% 7% 3 6% 4 4 4 2 4 7% 47%	5333
April	1st to 10th	Night	12% 8% 3 6% 5% 3 4 4 6% 7% 44%	2000
	11th to 20th	Night	12% 6% 2 6% 3 3 4 3 6% 7% 48%	1975
	21st to end	Night	5% 4 2 5% 3 4 4 3 5% 7% 58%	2000
May	1st to 10th	Night	12% 7% 3 6% 4 5% 5% 4 6% 9% 40%	4311
	11th to 20th	Night	13% 6% 2 6% 4 4 4 4 5% 9% 43%	4032
	21st to end	Night	5% 4 2 5% 4 4 5% 4 8% 12% 47%	4421
June	1st to 10th	Night	7% 5% 3 6% 6% 6% 5% 6% 8% 12% 36%	1800
	11th to 20th	Night	4 4 1 4 5% 5% 6% 6% 10% 13% 42%	1800
	21st to end	Night	5% 4 2 5% 6% 5% 6% 6% 9% 13% 40%	1800
July	1st to 10th	Night	4 4 2 6% 6% 6% 8% 7% 11% 16% 29%	4058
	11th to 20th	Night	2 3 1 5% 5% 5% 6% 5% 10% 16% 41%	4057
	21st to end	Night	3 3 2 6% 6% 7% 7% 8% 10% 15% 32%	4921
August	1st to 10th	Night	4 4 1 5% 5% 5% 6% 5% 9% 13% 43%	3244
	11th to 20th	Night	3 3 2 5% 4 5% 5% 5% 8% 12% 48%	3200
	21st to end	Night	5% 5% 2 8% 6% 6% 8% 6% 8% 11% 35%	3586
September	1st to 10th	Night	9% 6% 2 7% 4 5% 6% 6% 8% 11% 37%	2065
	11th to 20th	Night	9% 6% 2 6% 5% 5% 5% 5% 7% 8% 43%	2200
	21st to end	Night	8% 5% 1 6% 4 4 4 4 5% 8% 52%	2200
October	1st to 10th	Night	7% 4 2 5% 4 3 3 5% 7% 8% 51%	2200
	11th to 20th	Night	6% 5% 2 3 3 2 3 2 5% 6% 64%	2200
	21st to end	Night	9% 5% 2 5% 3 3 3 3 4 5% 56%	2608
November	1st to 10th	Night	7% 5% 2 5% 3 2 3 3 5% 7% 58%	2666
	11th to 20th	Night	10% 5% 2 5% 4 3 3 2 5% 6% 55%	2730
	21st to end	Night	11% 6% 2 5% 4 4 5% 3 5% 7% 49%	2730
December	1st to 10th	Night	14% 6% 2 6% 3 3 3 3 5% 7% 49%	4380
	11th to 20th	Night	13% 5% 2 5% 4 3 3 3 4 6% 53%	4952
	21st to end	Night	18% 8% 2 6% 3 3 3 2 4 4 47%	6633

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	33% 2 5% 16% 33% 10%	4165
	11th to 20th	Day	34% 2 6% 18% 28% 12%	4580
	21st to end	Day	46% 2 8% 14% 18% 13%	4972
February	1st to 10th	Day	44% 3 7% 16% 21% 10%	2000
	11th to 20th	Day	40% 4 5% 17% 22% 12%	1958
	21st to end	Day	42% 5% 7% 18% 16% 12%	1650
March	1st to 10th	Day	44% 3 7% 18% 17% 11%	4480
	11th to 20th	Day	32% 3 9% 16% 20% 20%	4832
	21st to end	Day	41% 3 11% 18% 17% 10%	5638
April	1st to 10th	Day	37% 4 10% 17% 20% 12%	2400
	11th to 20th	Day	37% 3 8% 19% 22% 11%	2374
	21st to end	Day	28% 4 11% 24% 23% 9%	2400
May	1st to 10th	Day	41% 4 12% 24% 15% 4	5614
	11th to 20th	Day	36% 5% 17% 28% 13% 2	5865
	21st to end	Day	32% 6% 15% 28% 17% 2	6447
June	1st to 10th	Day	46% 7% 16% 21% 9% 1	2600
	11th to 20th	Day	37% 9% 19% 23% 11% 2	2600
	21st to end	Day	42% 12% 18% 17% 9% 2	2600
July	1st to 10th	Day	41% 16% 29% 12% 2	5835
	11th to 20th	Day	36% 15% 33% 13% 1	5831
	21st to end	Day	43% 15% 24% 16% 2	5753
August	1st to 10th	Day	33% 10% 20% 22% 12% 2	3893
	11th to 20th	Day	33% 9% 19% 21% 16% 1	3885
	21st to end	Day	40% 12% 22% 16% 9% 1	4311
September	1st to 10th	Day	45% 9% 16% 14% 11% 4	2314
	11th to 20th	Day	45% 6% 11% 17% 15% 6%	2200
	21st to end	Day	34% 6% 10% 20% 21% 9%	2200
October	1st to 10th	Day	35% 3 7% 12% 16% 27%	3590
	11th to 20th	Day	17% 3 4 19% 23% 35%	3568
	21st to end	Day	21% 2 4 13% 39% 21%	3578
November	1st to 10th	Day	28% 4 9% 19% 23% 17%	1852
	11th to 20th	Day	30% 3 7% 17% 28% 15%	1890
	21st to end	Day	34% 4 7% 19% 22% 13%	1890
December	1st to 10th	Day	37% 2 8% 17% 25% 11%	3020
	11th to 20th	Day	34% 2 5% 25% 23% 11%	3460
	21st to end	Day	42% 2 5% 17% 29% 5%	4565
January	1st to 10th	Night	37% 3 5% 14% 29% 12%	5996
	11th to 20th	Night	43% 2 4 12% 29% 9%	5513
	21st to end	Night	45% 3 7% 17% 20% 9%	5984
February	1st to 10th	Night	41% 2 6% 18% 21% 11%	2400
	11th to 20th	Night	42% 3 6% 13% 21% 14%	2339
	21st to end	Night	44% 3 7% 15% 18% 13%	1980
March	1st to 10th	Night	50% 2 6% 15% 19% 8%	5373
	11th to 20th	Night	36% 3 9% 14% 21% 18%	5128
	21st to end	Night	39% 2 9% 22% 15% 12%	5333
April	1st to 10th	Night	40% 4 10% 14% 19% 13%	2000
	11th to 20th	Night	36% 4 7% 20% 22% 11%	1975
	21st to end	Night	27% 3 11% 27% 24% 9%	2000
May	1st to 10th	Night	40% 3 21% 19% 12% 4	4341
	11th to 20th	Night	38% 4 17% 25% 14% 2	4033
	21st to end	Night	27% 5% 20% 32% 14% 2	4429
June	1st to 10th	Night	37% 8% 19% 23% 11% 2	1800
	11th to 20th	Night	28% 12% 25% 23% 11% 2	1800
	21st to end	Night	32% 11% 27% 19% 9% 2	1800
July	1st to 10th	Night	36% 15% 33% 14% 2	4015
	11th to 20th	Night	25% 15% 45% 13% 2	4006
	21st to end	Night	34% 20% 26% 18% 2	4778
August	1st to 10th	Night	29% 10% 26% 23% 12% 1	3232
	11th to 20th	Night	25% 9% 28% 23% 13%	3230
	21st to end	Night	37% 12% 22% 17% 9% 2	3586
September	1st to 10th	Night	37% 9% 23% 17% 11% 4	2065
	11th to 20th	Night	36% 9% 16% 18% 17% 5%	2200
	21st to end	Night	30% 6% 13% 21% 21% 8%	2200
October	1st to 10th	Night	36% 4 8% 12% 19% 21%	3590
	11th to 20th	Night	14% 2 5% 18% 29% 33%	3571
	21st to end	Night	22% 2 4 13% 42% 18%	4205
November	1st to 10th	Night	27% 4 7% 19% 25% 18%	2666
	11th to 20th	Night	31% 3 5% 18% 28% 15%	2730
	21st to end	Night	34% 4 9% 18% 22% 13%	2730
December	1st to 10th	Night	36% 3 7% 18% 24% 13%	4380
	11th to 20th	Night	34% 3 7% 23% 23% 11%	4954
	21st to end	Night	42% 2 5% 19% 27% 5%	6633

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	17% 19% 40% 17% 6% 1	330
	11th to 20th	Day	13% 21% 37% 19% 9% 1	318
	21st to end	Day	20% 23% 40% 13% 4	330
February	1st to 10th	Day	18% 23% 33% 18% 7% 1	300
	11th to 20th	Day	24% 23% 34% 18% 2	300
	21st to end	Day	14% 25% 42% 16% 4	249
March	1st to 10th	Day	15% 23% 41% 16% 4	300
	11th to 20th	Day	16% 20% 33% 22% 9% 1	430
	21st to end	Day	17% 15% 34% 23% 10% 1	550
April	1st to 10th	Day	17% 17% 31% 23% 10% 2	500
	11th to 20th	Day	14% 14% 29% 27% 14% 2	492
	21st to end	Day	9% 10% 27% 30% 19% 4	500
May	1st to 10th	Day	10% 11% 24% 29% 19% 7%	503
	11th to 20th	Day	9% 6% 22% 28% 21% 13%	527
	21st to end	Day	9% 3 18% 31% 21% 18%	573
June	1st to 10th	Day	11% 4 14% 29% 25% 18%	530
	11th to 20th	Day	7% 4 10% 26% 27% 25%	530
	21st to end	Day	7% 2 11% 23% 28% 29%	530
July	1st to 10th	Day	7% 2 6% 19% 30% 37%	525
	11th to 20th	Day	5% 1 3 17% 32% 41%	524
	21st to end	Day	6% 1 7% 18% 37% 31%	576
August	1st to 10th	Day	7% 6% 18% 33% 36%	526
	11th to 20th	Day	8% 1 5% 20% 31% 34%	519
	21st to end	Day	12% 3 7% 27% 31% 22%	583
September	1st to 10th	Day	12% 3 9% 25% 29% 22%	530
	11th to 20th	Day	15% 3 9% 29% 31% 13%	530
	21st to end	Day	9% 3 10% 32% 32% 14%	530
October	1st to 10th	Day	11% 4 25% 32% 23% 5%	530
	11th to 20th	Day	8% 4 21% 34% 25% 8%	530
	21st to end	Day	10% 10% 23% 33% 20% 3	488
November	1st to 10th	Day	14% 7% 25% 36% 15% 3	330
	11th to 20th	Day	12% 12% 33% 29% 12% 2	330
	21st to end	Day	12% 13% 39% 23% 12% 2	330
December	1st to 10th	Day	20% 16% 34% 21% 8% 2	330
	11th to 20th	Day	20% 13% 37% 22% 7% 1	330
	21st to end	Day	23% 15% 28% 24% 9% 2	363
January	1st to 10th	Night	18% 10% 35% 29% 7%	840
	11th to 20th	Night	16% 12% 29% 33% 9%	825
	21st to end	Night	22% 12% 34% 28% 5%	880
February	1st to 10th	Night	16% 11% 32% 34% 6% 1	800
	11th to 20th	Night	20% 11% 36% 25% 9%	783
	21st to end	Night	18% 12% 36% 29% 4	660
March	1st to 10th	Night	15% 12% 32% 33% 8%	800
	11th to 20th	Night	13% 10% 35% 30% 11% 1	800
	21st to end	Night	13% 10% 32% 32% 12% 1	823
April	1st to 10th	Night	16% 11% 23% 37% 13% 1	600
	11th to 20th	Night	13% 7% 26% 35% 18% 1	593
	21st to end	Night	7% 6% 21% 41% 24% 2	600
May	1st to 10th	Night	11% 5% 18% 41% 21% 4	600
	11th to 20th	Night	8% 3 15% 37% 31% 5%	591
	21st to end	Night	7% 2 11% 32% 41% 7%	650
June	1st to 10th	Night	9% 3 8% 30% 41% 9%	600
	11th to 20th	Night	4 3 7% 28% 46% 13%	600
	21st to end	Night	5% 2 6% 21% 51% 16%	600
July	1st to 10th	Night	5% 1 3 20% 48% 23%	585
	11th to 20th	Night	6% 1 3 13% 48% 29%	582
	21st to end	Night	3 1 2 19% 53% 22%	657
August	1st to 10th	Night	5% 1 4 14% 50% 27%	597
	11th to 20th	Night	5% 1 3 15% 51% 25%	594
	21st to end	Night	8% 3 8% 21% 43% 17%	660
September	1st to 10th	Night	11% 2 5% 25% 40% 17%	665
	11th to 20th	Night	13% 2 10% 30% 39% 7%	800
	21st to end	Night	10% 2 11% 30% 39% 8%	800
October	1st to 10th	Night	9% 2 23% 37% 26% 3	800
	11th to 20th	Night	9% 3 21% 35% 28% 4	800
	21st to end	Night	12% 5% 22% 38% 22% 1	880
November	1st to 10th	Night	10% 6% 23% 39% 20% 2	820
	11th to 20th	Night	11% 8% 28% 36% 16% 1	840
	21st to end	Night	13% 7% 30% 34% 14% 1	840
December	1st to 10th	Night	19% 7% 29% 30% 15% 1	840
	11th to 20th	Night	16% 9% 28% 33% 14% 1	840
	21st to end	Night	23% 9% 27% 31% 10% 1	924

Page generated at 2026-01-14 01:14:31. Version ac07

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