Fort Phil Kearny Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fort Phil Kearny Observatory clear sky chart from 2005-11-06 to 2025-12-03.

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	4 5% 2 5% 4 4 5% 4 7% 9% 52%	136331
	Night	3 5% 2 5% 4 4 4 4 6% 8% 55%	131870
Transparency	Day	26% 9% 16% 25% 19% 5%	131122
	Night	23% 9% 16% 28% 18% 5%	128085
Seeing	Day	8% 12% 33% 31% 13% 3	17363
	Night	6% 10% 34% 37% 12% 1	27411

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 6% 2 6% 5% 5% 7% 5% 7% 9% 45%	3638
	11th to 20th	Day	1 2 5% 3 5% 6% 6% 10% 11% 51%	3640
	21st to end	Day	1 2 1 3 3 3 4 5% 6% 8% 64%	4395
February	1st to 10th	Day	1 6% 3 9% 7% 6% 7% 4 7% 8% 41%	1800
	11th to 20th	Day	1 6% 4 8% 6% 5% 5% 5% 6% 8% 46%	1755
	21st to end	Day	2 5% 2 8% 5% 5% 5% 6% 7% 9% 46%	1621
March	1st to 10th	Day	1 6% 3 5% 3 4 4 4 6% 8% 56%	4628
	11th to 20th	Day	3 8% 3 6% 4 5% 5% 4 6% 8% 48%	5000
	21st to end	Day	7% 13% 4 8% 5% 4 4 4 7% 10% 34%	5678
April	1st to 10th	Day	6% 11% 3 6% 5% 5% 5% 5% 7% 8% 41%	2400
	11th to 20th	Day	6% 9% 4 9% 4 5% 4 4 7% 8% 39%	2371
	21st to end	Day	11% 10% 2 7% 4 4 5% 4 6% 10% 37%	2507
May	1st to 10th	Day	10% 9% 2 6% 4 4 4 4 6% 8% 43%	6289
	11th to 20th	Day	7% 6% 2 6% 4 5% 5% 5% 7% 10% 43%	6298
	21st to end	Day	9% 6% 2 5% 4 4 4 5% 7% 9% 47%	6925
June	1st to 10th	Day	7% 5% 2 4 3 4 6% 6% 9% 9% 44%	2800
	11th to 20th	Day	5% 4 1 4 4 5% 5% 5% 9% 10% 47%	2800
	21st to end	Day	3 2 1 3 3 4 5% 5% 8% 9% 58%	2800
July	1st to 10th	Day	4 3 1 3 4 4 5% 5% 7% 9% 55%	6339
	11th to 20th	Day	4 2 1 3 3 3 5% 5% 8% 8% 57%	6340
	21st to end	Day	3 2 1 4 3 4 6% 5% 8% 10% 54%	6903
August	1st to 10th	Day	5% 3 1 4 4 4 6% 5% 9% 9% 50%	5881
	11th to 20th	Day	3 2 1 4 3 4 5% 5% 8% 10% 56%	5798
	21st to end	Day	3 3 2 5% 4 5% 4 3 6% 7% 58%	6028
September	1st to 10th	Day	6% 2 1 4 3 3 3 3 6% 7% 62%	2400
	11th to 20th	Day	5% 4 2 3 4 3 3 3 5% 7% 61%	2400
	21st to end	Day	6% 4 1 4 3 3 3 3 5% 6% 62%	2127
October	1st to 10th	Day	5% 4 1 3 2 2 2 2 3 4 70%	3270
	11th to 20th	Day	8% 5% 2 4 2 2 3 3 4 5% 63%	3250
	21st to end	Day	5% 6% 2 7% 4 3 3 3 5% 8% 55%	3395
November	1st to 10th	Day	2 5% 2 5% 4 5% 5% 4 7% 8% 55%	1829
	11th to 20th	Day	2 4 3 3 4 5% 5% 4 7% 9% 55%	1680
	21st to end	Day	3 5% 1 4 4 4 4 5% 7% 10% 53%	1680
December	1st to 10th	Day	1 3 2 4 3 3 3 5% 8% 7% 62%	2636
	11th to 20th	Day	1 2 1 3 3 4 4 4 7% 9% 61%	3026
	21st to end	Day	2 5% 2 6% 4 5% 5% 5% 7% 9% 51%	4004
January	1st to 10th	Night	1 4 3 9% 6% 6% 6% 5% 6% 8% 47%	6327
	11th to 20th	Night	1 2 2 7% 5% 6% 7% 6% 9% 9% 47%	6340
	21st to end	Night	1 3 1 4 3 3 4 4 7% 8% 62%	6626
February	1st to 10th	Night	1 5% 2 10% 6% 6% 6% 5% 7% 10% 43%	2600
	11th to 20th	Night	1 7% 3 9% 6% 5% 5% 5% 7% 8% 44%	2532
	21st to end	Night	1 5% 2 7% 5% 5% 5% 5% 7% 8% 52%	2007
March	1st to 10th	Night	1 7% 3 6% 4 4 4 4 6% 8% 53%	5251
	11th to 20th	Night	3 7% 2 5% 3 3 3 3 5% 9% 56%	5000
	21st to end	Night	5% 10% 4 10% 6% 5% 5% 4 5% 8% 39%	5288
April	1st to 10th	Night	6% 9% 2 6% 4 4 5% 4 6% 8% 47%	2000
	11th to 20th	Night	5% 8% 4 6% 5% 4 5% 5% 6% 8% 45%	1977
	21st to end	Night	6% 8% 2 6% 3 3 4 4 7% 9% 48%	1890
May	1st to 10th	Night	10% 8% 2 4 2 3 3 3 4 7% 53%	3690
	11th to 20th	Night	9% 7% 2 7% 4 4 5% 4 6% 10% 42%	3617
	21st to end	Night	7% 4 1 4 3 4 3 3 6% 9% 54%	3972
June	1st to 10th	Night	7% 4 2 4 4 4 3 5% 6% 9% 51%	1600
	11th to 20th	Night	7% 4 1 3 3 4 4 4 6% 8% 56%	1600
	21st to end	Night	4 3 1 3 2 2 3 3 6% 9% 64%	1600
July	1st to 10th	Night	2 2 1 3 2 3 4 4 7% 10% 62%	3640
	11th to 20th	Night	4 2 1 2 3 3 5% 4 7% 9% 61%	3640
	21st to end	Night	4 3 1 4 3 3 5% 4 6% 10% 59%	3970
August	1st to 10th	Night	4 2 1 4 3 4 5% 5% 6% 10% 56%	3928
	11th to 20th	Night	2 2 1 3 4 3 5% 5% 8% 10% 57%	4051
	21st to end	Night	4 4 2 4 3 3 3 3 6% 9% 60%	4948
September	1st to 10th	Night	4 4 1 3 2 2 3 2 4 7% 68%	2000
	11th to 20th	Night	5% 3 1 3 3 3 3 4 5% 7% 63%	2000
	21st to end	Night	5% 4 1 3 3 2 3 2 3 6% 66%	2267
October	1st to 10th	Night	5% 5% 1 3 2 2 2 2 2 5% 72%	3920
	11th to 20th	Night	7% 4 1 4 3 2 3 3 4 6% 63%	3898
	21st to end	Night	2 5% 2 5% 3 4 4 3 5% 8% 59%	4371
November	1st to 10th	Night	2 5% 2 5% 4 4 4 4 6% 9% 53%	2686
	11th to 20th	Night	2 5% 2 5% 4 4 4 4 6% 8% 55%	2940
	21st to end	Night	3 6% 2 5% 3 4 4 4 5% 7% 57%	2940
December	1st to 10th	Night	1 3 1 4 3 4 4 4 7% 9% 60%	4599
	11th to 20th	Night	1 3 1 4 3 3 4 5% 8% 10% 59%	5181
	21st to end	Night	2 6% 2 6% 4 4 5% 4 7% 9% 51%	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	28% 13% 15% 27% 15% 1	3639
	11th to 20th	Day	20% 12% 24% 24% 18% 2	3640
	21st to end	Day	15% 8% 16% 35% 22% 4	4395
February	1st to 10th	Day	37% 10% 17% 22% 10% 3	1800
	11th to 20th	Day	32% 11% 18% 22% 13% 4	1764
	21st to end	Day	30% 11% 17% 21% 15% 6%	1621
March	1st to 10th	Day	21% 7% 13% 25% 29% 5%	4628
	11th to 20th	Day	29% 11% 20% 26% 13% 1	5000
	21st to end	Day	40% 14% 18% 22% 5%	5678
April	1st to 10th	Day	39% 10% 18% 21% 10% 2	2400
	11th to 20th	Day	40% 9% 20% 19% 11% 1	2374
	21st to end	Day	42% 10% 18% 20% 8% 1	2507
May	1st to 10th	Day	37% 7% 17% 24% 14% 2	6289
	11th to 20th	Day	32% 10% 19% 23% 14% 2	6302
	21st to end	Day	29% 10% 18% 33% 9%	6926
June	1st to 10th	Day	29% 13% 22% 22% 12% 2	2800
	11th to 20th	Day	27% 12% 20% 19% 19% 3	2800
	21st to end	Day	17% 11% 16% 27% 20% 8%	2800
July	1st to 10th	Day	20% 8% 11% 27% 24% 10%	6271
	11th to 20th	Day	19% 7% 10% 24% 27% 12%	6265
	21st to end	Day	19% 9% 14% 21% 25% 11%	6705
August	1st to 10th	Day	28% 9% 13% 21% 19% 9%	4283
	11th to 20th	Day	21% 9% 12% 26% 25% 7%	4197
	21st to end	Day	16% 6% 11% 23% 34% 11%	4343
September	1st to 10th	Day	21% 6% 10% 23% 28% 13%	2400
	11th to 20th	Day	23% 7% 11% 27% 24% 8%	2400
	21st to end	Day	23% 6% 13% 27% 26% 6%	2127
October	1st to 10th	Day	20% 4 9% 18% 34% 14%	3270
	11th to 20th	Day	25% 5% 12% 26% 25% 7%	3250
	21st to end	Day	26% 8% 14% 33% 14% 4	3395
November	1st to 10th	Day	24% 12% 17% 23% 20% 4	1829
	11th to 20th	Day	24% 10% 19% 26% 18% 4	1680
	21st to end	Day	25% 8% 21% 26% 16% 3	1680
December	1st to 10th	Day	18% 9% 21% 32% 18% 2	2636
	11th to 20th	Day	17% 9% 23% 36% 14% 1	3024
	21st to end	Day	26% 9% 14% 32% 16% 5%	4004
January	1st to 10th	Night	29% 13% 15% 29% 12% 1	6327
	11th to 20th	Night	22% 10% 25% 25% 15% 3	6340
	21st to end	Night	17% 10% 15% 31% 23% 4	6626
February	1st to 10th	Night	32% 13% 18% 23% 11% 3	2600
	11th to 20th	Night	32% 12% 19% 20% 14% 3	2533
	21st to end	Night	27% 10% 16% 22% 18% 6%	2007
March	1st to 10th	Night	23% 9% 15% 26% 23% 6%	5251
	11th to 20th	Night	24% 9% 20% 24% 19% 3	5000
	21st to end	Night	34% 17% 22% 19% 8%	5288
April	1st to 10th	Night	33% 11% 18% 23% 12% 3	2000
	11th to 20th	Night	33% 11% 18% 26% 12% 1	1977
	21st to end	Night	30% 12% 19% 28% 11% 1	1890
May	1st to 10th	Night	30% 7% 13% 32% 18% 1	3689
	11th to 20th	Night	35% 10% 18% 24% 11% 2	3618
	21st to end	Night	23% 11% 21% 37% 8%	3972
June	1st to 10th	Night	28% 11% 24% 22% 15% 1	1600
	11th to 20th	Night	22% 12% 21% 24% 17% 4	1600
	21st to end	Night	16% 9% 16% 32% 22% 5%	1600
July	1st to 10th	Night	16% 7% 13% 33% 23% 8%	3600
	11th to 20th	Night	16% 8% 12% 27% 30% 7%	3592
	21st to end	Night	19% 8% 12% 21% 28% 12%	3856
August	1st to 10th	Night	21% 9% 16% 23% 20% 10%	2850
	11th to 20th	Night	20% 7% 13% 32% 19% 9%	2928
	21st to end	Night	14% 5% 10% 27% 27% 17%	3564
September	1st to 10th	Night	17% 5% 10% 25% 30% 13%	2000
	11th to 20th	Night	22% 7% 12% 27% 24% 9%	2000
	21st to end	Night	20% 6% 11% 28% 27% 8%	2267
October	1st to 10th	Night	19% 4 10% 22% 27% 17%	3920
	11th to 20th	Night	22% 5% 12% 29% 23% 9%	3898
	21st to end	Night	22% 7% 15% 31% 16% 8%	4371
November	1st to 10th	Night	25% 11% 18% 24% 18% 5%	2686
	11th to 20th	Night	23% 10% 16% 29% 17% 4	2940
	21st to end	Night	25% 8% 19% 26% 16% 5%	2940
December	1st to 10th	Night	18% 10% 20% 30% 20% 3	4599
	11th to 20th	Night	17% 10% 22% 38% 12% 2	5182
	21st to end	Night	26% 8% 13% 33% 15% 5%	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	5% 10% 34% 32% 14% 4	300
	11th to 20th	Day	8% 15% 38% 23% 12% 4	300
	21st to end	Day	5% 19% 41% 24% 7% 3	330
February	1st to 10th	Day	6% 16% 56% 20% 2	300
	11th to 20th	Day	5% 16% 42% 33% 5%	300
	21st to end	Day	5% 18% 42% 27% 7% 1	249
March	1st to 10th	Day	4 21% 40% 28% 6% 1	350
	11th to 20th	Day	8% 19% 38% 25% 8% 2	500
	21st to end	Day	13% 17% 39% 22% 8% 1	550
April	1st to 10th	Day	15% 19% 39% 22% 5% 1	500
	11th to 20th	Day	14% 27% 34% 20% 4	492
	21st to end	Day	17% 16% 34% 24% 7% 1	500
May	1st to 10th	Day	14% 18% 24% 27% 13% 3	678
	11th to 20th	Day	16% 11% 30% 26% 14% 3	725
	21st to end	Day	15% 11% 29% 27% 15% 3	789
June	1st to 10th	Day	7% 11% 25% 33% 20% 4	730
	11th to 20th	Day	7% 13% 35% 32% 12% 2	730
	21st to end	Day	4 8% 31% 38% 15% 3	730
July	1st to 10th	Day	4 4 25% 39% 25% 3	721
	11th to 20th	Day	2 4 29% 44% 19% 3	718
	21st to end	Day	3 4 26% 40% 23% 5%	794
August	1st to 10th	Day	5% 4 31% 38% 17% 4	577
	11th to 20th	Day	4 6% 26% 41% 19% 5%	517
	21st to end	Day	3 7% 31% 39% 17% 3	583
September	1st to 10th	Day	5% 8% 27% 41% 15% 5%	530
	11th to 20th	Day	8% 6% 30% 36% 16% 4	530
	21st to end	Day	11% 10% 25% 32% 16% 6%	391
October	1st to 10th	Day	11% 9% 25% 33% 15% 6%	330
	11th to 20th	Day	9% 18% 28% 28% 12% 4	330
	21st to end	Day	8% 15% 39% 26% 9% 3	363
November	1st to 10th	Day	7% 14% 39% 25% 11% 3	330
	11th to 20th	Day	8% 15% 37% 29% 10% 1	330
	21st to end	Day	7% 14% 38% 31% 8% 2	330
December	1st to 10th	Day	8% 15% 40% 24% 11% 1	306
	11th to 20th	Day	4 15% 51% 25% 5%	300
	21st to end	Day	4 17% 40% 27% 11% 1	330
January	1st to 10th	Night	3 11% 39% 34% 11% 2	1000
	11th to 20th	Night	4 18% 44% 23% 10% 2	1000
	21st to end	Night	4 15% 42% 29% 9% 1	947
February	1st to 10th	Night	3 12% 48% 28% 8% 1	800
	11th to 20th	Night	3 12% 41% 34% 8% 2	784
	21st to end	Night	4 12% 43% 30% 10% 2	660
March	1st to 10th	Night	4 11% 44% 31% 9% 2	800
	11th to 20th	Night	6% 9% 43% 30% 10% 2	800
	21st to end	Night	9% 12% 37% 30% 11% 1	795
April	1st to 10th	Night	10% 10% 40% 35% 6% 1	600
	11th to 20th	Night	9% 15% 38% 32% 6%	593
	21st to end	Night	11% 11% 30% 39% 9% 1	600
May	1st to 10th	Night	11% 9% 26% 37% 17% 1	600
	11th to 20th	Night	14% 9% 22% 36% 18% 1	591
	21st to end	Night	14% 6% 27% 39% 14%	650
June	1st to 10th	Night	8% 7% 28% 41% 15% 1	600
	11th to 20th	Night	8% 6% 36% 39% 11%	600
	21st to end	Night	4 6% 24% 49% 17% 1	600
July	1st to 10th	Night	4 2 18% 55% 19% 1	585
	11th to 20th	Night	2 2 21% 55% 18% 1	582
	21st to end	Night	2 2 17% 55% 23% 1	657
August	1st to 10th	Night	4 3 15% 55% 23% 1	597
	11th to 20th	Night	3 3 14% 51% 26% 3	594
	21st to end	Night	3 3 20% 49% 23% 2	660
September	1st to 10th	Night	5% 3 18% 50% 21% 2	600
	11th to 20th	Night	5% 6% 22% 47% 16% 4	600
	21st to end	Night	8% 6% 26% 38% 17% 4	730
October	1st to 10th	Night	12% 6% 30% 34% 15% 3	800
	11th to 20th	Night	9% 9% 33% 33% 14% 2	800
	21st to end	Night	5% 12% 36% 34% 11% 2	950
November	1st to 10th	Night	5% 12% 41% 32% 9% 1	1025
	11th to 20th	Night	5% 14% 43% 31% 7% 1	1050
	21st to end	Night	7% 12% 39% 33% 8% 1	1050
December	1st to 10th	Night	2 13% 44% 33% 7% 1	1011
	11th to 20th	Night	3 10% 46% 32% 8% 1	1000
	21st to end	Night	5% 13% 42% 31% 8% 1	1100

Page generated at 2025-11-29 23:00:52. Version ac07

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