Picketwire Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Picketwire Observatory clear sky chart from 2005-11-06 to 2025-10-04.

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	3 4 2 5% 3 4 5% 4 6% 8% 56%	134862
	Night	2 4 2 4 3 3 4 3 5% 7% 63%	131956
Transparency	Day	22% 7% 10% 20% 26% 15%	129877
	Night	19% 6% 10% 22% 28% 15%	127945
Seeing	Day	14% 19% 30% 23% 11% 3	16647
	Night	10% 16% 34% 27% 12% 2	26601

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	4 2 6% 2 2 2 3 5% 9% 63%	3638
	11th to 20th	Day	3 2 5% 3 3 3 3 4 6% 68%	4008
	21st to end	Day	1 9% 2 5% 3 3 3 3 5% 6% 63%	4510
February	1st to 10th	Day	1 3 2 5% 4 2 3 3 4 8% 64%	1860
	11th to 20th	Day	1 3 2 4 2 3 3 3 6% 8% 66%	1949
	21st to end	Day	4 3 5% 3 3 3 3 5% 6% 64%	1650
March	1st to 10th	Day	1 6% 3 4 3 2 3 2 4 6% 66%	4500
	11th to 20th	Day	2 10% 4 7% 4 4 4 4 6% 7% 49%	4954
	21st to end	Day	1 5% 2 4 3 3 3 3 5% 9% 62%	5827
April	1st to 10th	Day	2 6% 1 4 3 3 4 4 6% 9% 58%	2400
	11th to 20th	Day	5% 6% 1 4 4 3 4 3 6% 8% 56%	2371
	21st to end	Day	4 7% 1 5% 4 4 4 3 7% 9% 52%	2400
May	1st to 10th	Day	7% 7% 2 5% 3 4 4 4 6% 7% 52%	5532
	11th to 20th	Day	4 4 1 4 3 4 5% 5% 6% 6% 56%	5984
	21st to end	Day	3 3 1 4 3 3 4 5% 7% 9% 58%	6925
June	1st to 10th	Day	3 3 1 4 4 5% 6% 6% 8% 10% 51%	2800
	11th to 20th	Day	3 3 1 3 3 3 5% 5% 7% 9% 60%	2800
	21st to end	Day	4 4 1 5% 4 5% 6% 6% 9% 9% 46%	2800
July	1st to 10th	Day	3 3 1 3 4 5% 6% 5% 8% 10% 52%	6339
	11th to 20th	Day	2 2 1 5% 5% 7% 9% 8% 11% 10% 40%	6340
	21st to end	Day	4 4 2 7% 7% 7% 8% 6% 9% 9% 37%	6474
August	1st to 10th	Day	4 3 1 5% 4 6% 7% 7% 9% 12% 44%	5573
	11th to 20th	Day	3 3 1 5% 4 5% 7% 7% 9% 11% 44%	5366
	21st to end	Day	5% 4 2 7% 5% 6% 7% 6% 9% 11% 39%	5984
September	1st to 10th	Day	6% 5% 2 6% 4 5% 5% 5% 7% 8% 49%	2400
	11th to 20th	Day	5% 3 1 4 3 4 5% 4 5% 8% 59%	2365
	21st to end	Day	5% 4 1 4 4 3 3 3 4 6% 62%	2200
October	1st to 10th	Day	4 3 1 3 2 3 2 3 4 5% 70%	3274
	11th to 20th	Day	4 3 1 3 2 2 4 3 6% 8% 62%	3150
	21st to end	Day	3 3 1 3 2 1 2 2 3 4 76%	3412
November	1st to 10th	Day	1 3 1 3 1 2 2 3 4 7% 71%	1763
	11th to 20th	Day	1 2 1 4 2 3 3 3 5% 7% 69%	1800
	21st to end	Day	1 5% 2 5% 2 2 2 3 5% 7% 66%	1800
December	1st to 10th	Day	2 1 3 1 1 2 2 3 5% 80%	2684
	11th to 20th	Day	1 3 1 3 2 3 3 3 5% 8% 70%	3026
	21st to end	Day	3 2 5% 3 3 3 2 4 6% 68%	4004
January	1st to 10th	Night	2 3 6% 3 3 4 3 5% 7% 63%	6327
	11th to 20th	Night	2 1 4 3 3 4 3 4 6% 68%	6000
	21st to end	Night	5% 2 4 3 3 3 3 4 6% 67%	6468
February	1st to 10th	Night	1 4 2 5% 3 3 3 3 4 6% 66%	2537
	11th to 20th	Night	1 4 2 5% 3 3 3 3 5% 6% 65%	2338
	21st to end	Night	4 2 4 3 2 3 2 4 5% 71%	1980
March	1st to 10th	Night	1 7% 2 3 2 2 3 2 4 6% 69%	5374
	11th to 20th	Night	2 9% 2 4 3 3 3 3 5% 7% 57%	5028
	21st to end	Night	1 4 2 3 2 2 3 3 4 6% 69%	5132
April	1st to 10th	Night	2 5% 1 3 2 3 3 3 5% 6% 68%	2000
	11th to 20th	Night	3 5% 1 5% 3 3 3 3 4 7% 65%	1977
	21st to end	Night	4 6% 2 3 3 3 4 4 5% 6% 61%	2000
May	1st to 10th	Night	7% 6% 2 3 3 3 3 3 5% 6% 59%	4448
	11th to 20th	Night	6% 4 1 3 2 3 3 2 5% 7% 64%	3927
	21st to end	Night	3 4 1 4 3 3 4 3 5% 7% 63%	3972
June	1st to 10th	Night	3 4 1 3 3 4 4 4 7% 9% 59%	1600
	11th to 20th	Night	2 3 1 2 2 4 3 4 5% 8% 66%	1600
	21st to end	Night	5% 4 1 3 3 5% 4 5% 8% 10% 52%	1600
July	1st to 10th	Night	5% 3 1 3 3 4 5% 4 7% 9% 54%	3640
	11th to 20th	Night	2 2 1 4 4 5% 7% 6% 9% 11% 49%	3640
	21st to end	Night	4 3 2 5% 4 5% 6% 6% 10% 11% 44%	4381
August	1st to 10th	Night	3 3 1 5% 4 6% 6% 5% 7% 9% 51%	4237
	11th to 20th	Night	3 2 1 4 3 4 5% 5% 10% 15% 48%	4483
	21st to end	Night	5% 5% 2 6% 4 5% 6% 6% 9% 13% 40%	4993
September	1st to 10th	Night	6% 3 1 3 3 3 4 4 7% 10% 56%	2000
	11th to 20th	Night	5% 3 1 2 3 2 3 2 5% 8% 66%	2035
	21st to end	Night	4 4 1 3 2 2 2 3 4 6% 69%	2200
October	1st to 10th	Night	3 3 1 2 2 1 3 2 3 5% 74%	3756
	11th to 20th	Night	5% 3 1 2 2 2 3 3 4 6% 68%	3778
	21st to end	Night	2 3 2 4 2 2 2 2 2 3 76%	4120
November	1st to 10th	Night	1 3 1 3 2 2 2 3 4 5% 74%	2529
	11th to 20th	Night	1 2 1 4 2 2 2 2 3 5% 76%	2600
	21st to end	Night	1 4 1 3 3 2 3 3 5% 6% 69%	2600
December	1st to 10th	Night	2 1 4 2 2 2 2 4 6% 75%	4501
	11th to 20th	Night	1 2 1 4 2 2 2 2 4 9% 71%	5181
	21st to end	Night	1 4 2 5% 3 3 3 3 4 7% 66%	6974

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	17% 4 7% 25% 33% 14%	3639
	11th to 20th	Day	17% 5% 6% 19% 36% 18%	4008
	21st to end	Day	21% 5% 7% 20% 32% 16%	4510
February	1st to 10th	Day	20% 3 9% 25% 28% 16%	1860
	11th to 20th	Day	16% 4 8% 26% 31% 15%	1959
	21st to end	Day	19% 4 6% 15% 30% 25%	1650
March	1st to 10th	Day	19% 3 4 12% 35% 26%	4500
	11th to 20th	Day	31% 4 7% 17% 30% 12%	4954
	21st to end	Day	19% 4 7% 34% 29% 6%	5827
April	1st to 10th	Day	21% 5% 8% 24% 25% 17%	2400
	11th to 20th	Day	25% 6% 7% 23% 22% 17%	2374
	21st to end	Day	26% 7% 11% 21% 27% 9%	2400
May	1st to 10th	Day	28% 8% 10% 20% 19% 16%	5532
	11th to 20th	Day	23% 7% 10% 13% 25% 22%	5988
	21st to end	Day	19% 8% 11% 20% 20% 22%	6926
June	1st to 10th	Day	24% 10% 13% 22% 19% 13%	2800
	11th to 20th	Day	18% 7% 11% 17% 21% 26%	2800
	21st to end	Day	27% 9% 13% 18% 18% 14%	2800
July	1st to 10th	Day	21% 10% 13% 16% 24% 16%	6271
	11th to 20th	Day	27% 13% 18% 26% 13% 3	6265
	21st to end	Day	35% 13% 14% 18% 16% 4	6288
August	1st to 10th	Day	34% 14% 19% 18% 9% 5%	4057
	11th to 20th	Day	24% 12% 16% 20% 16% 13%	3882
	21st to end	Day	30% 13% 15% 21% 17% 4	4311
September	1st to 10th	Day	29% 8% 10% 22% 20% 10%	2400
	11th to 20th	Day	21% 7% 10% 17% 27% 17%	2365
	21st to end	Day	21% 5% 9% 19% 33% 14%	2200
October	1st to 10th	Day	17% 4 6% 19% 36% 19%	3274
	11th to 20th	Day	16% 6% 8% 24% 31% 14%	3150
	21st to end	Day	13% 3 4 16% 40% 25%	3412
November	1st to 10th	Day	13% 4 5% 22% 35% 21%	1763
	11th to 20th	Day	15% 3 7% 25% 35% 16%	1800
	21st to end	Day	19% 3 5% 18% 34% 21%	1800
December	1st to 10th	Day	9% 2 6% 24% 43% 14%	2684
	11th to 20th	Day	14% 3 7% 22% 37% 17%	3024
	21st to end	Day	16% 3 8% 24% 34% 16%	4004
January	1st to 10th	Night	20% 5% 7% 21% 36% 11%	6327
	11th to 20th	Night	17% 4 6% 22% 34% 17%	6000
	21st to end	Night	18% 5% 7% 22% 31% 17%	6468
February	1st to 10th	Night	20% 4 7% 26% 27% 16%	2537
	11th to 20th	Night	19% 4 10% 26% 28% 13%	2338
	21st to end	Night	17% 3 5% 19% 36% 21%	1980
March	1st to 10th	Night	18% 3 5% 11% 38% 26%	5374
	11th to 20th	Night	25% 6% 8% 15% 28% 18%	5028
	21st to end	Night	17% 4 6% 35% 31% 7%	5132
April	1st to 10th	Night	17% 4 7% 28% 29% 15%	2000
	11th to 20th	Night	21% 4 9% 25% 27% 15%	1977
	21st to end	Night	23% 7% 12% 25% 25% 9%	2000
May	1st to 10th	Night	26% 6% 10% 22% 19% 17%	4445
	11th to 20th	Night	20% 5% 9% 20% 27% 18%	3928
	21st to end	Night	20% 8% 11% 15% 22% 23%	3972
June	1st to 10th	Night	19% 9% 14% 23% 19% 16%	1600
	11th to 20th	Night	16% 6% 10% 18% 26% 25%	1600
	21st to end	Night	23% 10% 12% 18% 22% 14%	1600
July	1st to 10th	Night	23% 11% 17% 18% 18% 14%	3600
	11th to 20th	Night	24% 12% 23% 29% 10% 3	3592
	21st to end	Night	28% 13% 18% 22% 14% 6%	4255
August	1st to 10th	Night	35% 14% 21% 16% 9% 5%	3077
	11th to 20th	Night	21% 11% 24% 22% 15% 7%	3243
	21st to end	Night	28% 12% 20% 24% 13% 3	3597
September	1st to 10th	Night	22% 8% 14% 27% 22% 8%	2000
	11th to 20th	Night	17% 5% 12% 19% 29% 17%	2035
	21st to end	Night	17% 5% 9% 23% 33% 13%	2200
October	1st to 10th	Night	14% 4 7% 18% 35% 21%	3756
	11th to 20th	Night	16% 5% 8% 23% 33% 13%	3778
	21st to end	Night	16% 3 4 19% 37% 22%	4120
November	1st to 10th	Night	13% 2 6% 22% 36% 21%	2529
	11th to 20th	Night	13% 2 5% 26% 35% 19%	2600
	21st to end	Night	16% 3 7% 22% 31% 20%	2600
December	1st to 10th	Night	13% 3 6% 27% 38% 14%	4501
	11th to 20th	Night	13% 3 6% 20% 38% 20%	5182
	21st to end	Night	18% 4 8% 24% 30% 16%	6974

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	21% 20% 32% 16% 11%	300
	11th to 20th	Day	20% 27% 30% 18% 3 1	300
	21st to end	Day	12% 23% 36% 19% 9%	330
February	1st to 10th	Day	22% 30% 34% 11% 3 1	300
	11th to 20th	Day	22% 28% 33% 14% 4	300
	21st to end	Day	29% 28% 31% 11%	249
March	1st to 10th	Day	23% 27% 27% 20% 3	300
	11th to 20th	Day	22% 27% 31% 15% 5% 1	480
	21st to end	Day	28% 34% 25% 10% 3	550
April	1st to 10th	Day	22% 34% 31% 9% 4 1	500
	11th to 20th	Day	26% 34% 28% 10% 2	492
	21st to end	Day	21% 34% 30% 13% 2	500
May	1st to 10th	Day	19% 27% 37% 12% 5% 1	543
	11th to 20th	Day	14% 20% 35% 22% 9% 2	725
	21st to end	Day	13% 21% 33% 22% 10% 2	789
June	1st to 10th	Day	6% 15% 30% 32% 15% 3	730
	11th to 20th	Day	7% 16% 36% 25% 13% 3	730
	21st to end	Day	6% 14% 35% 27% 13% 5%	730
July	1st to 10th	Day	6% 8% 27% 32% 22% 6%	721
	11th to 20th	Day	5% 4 17% 36% 27% 10%	718
	21st to end	Day	8% 5% 18% 36% 26% 8%	609
August	1st to 10th	Day	9% 5% 25% 35% 19% 6%	527
	11th to 20th	Day	5% 6% 29% 38% 17% 5%	517
	21st to end	Day	7% 7% 31% 35% 15% 5%	583
September	1st to 10th	Day	7% 8% 28% 34% 18% 5%	530
	11th to 20th	Day	7% 12% 35% 31% 13% 3	495
	21st to end	Day	11% 14% 30% 23% 16% 5%	330
October	1st to 10th	Day	14% 15% 26% 26% 13% 6%	309
	11th to 20th	Day	12% 21% 29% 24% 9% 4	300
	21st to end	Day	17% 18% 31% 22% 11% 2	330
November	1st to 10th	Day	17% 20% 33% 21% 10%	300
	11th to 20th	Day	12% 23% 31% 22% 10% 2	300
	21st to end	Day	16% 21% 35% 18% 9% 2	300
December	1st to 10th	Day	15% 26% 33% 19% 6% 1	300
	11th to 20th	Day	14% 26% 34% 20% 5% 1	300
	21st to end	Day	21% 29% 33% 12% 4	330
January	1st to 10th	Night	11% 20% 34% 24% 9% 2	1000
	11th to 20th	Night	14% 21% 34% 22% 8% 1	855
	21st to end	Night	6% 22% 39% 25% 8% 1	880
February	1st to 10th	Night	11% 25% 43% 19% 4	800
	11th to 20th	Night	14% 24% 42% 16% 4	784
	21st to end	Night	13% 27% 43% 15% 2	660
March	1st to 10th	Night	15% 28% 35% 19% 4 1	800
	11th to 20th	Night	11% 19% 40% 23% 7% 1	800
	21st to end	Night	16% 25% 37% 19% 3	730
April	1st to 10th	Night	13% 26% 44% 14% 3	600
	11th to 20th	Night	13% 24% 37% 21% 5%	593
	21st to end	Night	13% 21% 40% 20% 6%	600
May	1st to 10th	Night	12% 17% 38% 27% 6% 1	600
	11th to 20th	Night	13% 15% 32% 28% 10% 2	591
	21st to end	Night	10% 16% 36% 27% 9% 1	650
June	1st to 10th	Night	4 12% 31% 36% 16% 2	600
	11th to 20th	Night	3 13% 41% 34% 9% 1	600
	21st to end	Night	5% 7% 33% 34% 20% 2	600
July	1st to 10th	Night	7% 3 24% 36% 27% 3	585
	11th to 20th	Night	4 3 18% 41% 30% 5%	582
	21st to end	Night	7% 2 11% 36% 37% 7%	657
August	1st to 10th	Night	4 4 15% 40% 32% 5%	597
	11th to 20th	Night	7% 3 17% 43% 27% 3	594
	21st to end	Night	6% 4 20% 37% 28% 4	660
September	1st to 10th	Night	6% 4 22% 41% 23% 4	600
	11th to 20th	Night	7% 5% 34% 32% 18% 3	600
	21st to end	Night	7% 12% 28% 37% 15% 2	600
October	1st to 10th	Night	8% 14% 33% 30% 13% 2	718
	11th to 20th	Night	6% 16% 35% 29% 12% 3	760
	21st to end	Night	12% 16% 32% 25% 12% 3	836
November	1st to 10th	Night	11% 15% 36% 28% 10% 1	969
	11th to 20th	Night	10% 17% 39% 25% 9% 2	1000
	21st to end	Night	11% 16% 36% 27% 9% 1	1000
December	1st to 10th	Night	10% 19% 38% 25% 7% 1	1000
	11th to 20th	Night	13% 21% 36% 23% 6% 1	1000
	21st to end	Night	13% 22% 37% 23% 4 1	1100

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