High Plains Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the High Plains Observatory clear sky chart from 2005-11-06 to 2026-02-01.

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	5% 5% 2 5% 4 4 4 4 6% 8% 53%	136313
	Night	5% 6% 2 5% 3 3 4 3 5% 7% 55%	133182
Transparency	Day	29% 3 8% 25% 25% 11%	131261
	Night	29% 3 9% 26% 25% 9%	129239
Seeing	Day	8% 5% 19% 33% 24% 10%	17261
	Night	7% 3 23% 47% 18% 1	27395

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	1 8% 3 7% 4 4 3 3 5% 7% 55%	3718
	11th to 20th	Day	1 5% 3 8% 6% 5% 4 3 6% 7% 52%	3783
	21st to end	Day	1 6% 3 5% 3 4 3 4 6% 7% 59%	4609
February	1st to 10th	Day	3 7% 3 7% 3 4 5% 4 7% 7% 51%	1800
	11th to 20th	Day	1 6% 3 6% 4 4 4 3 6% 8% 55%	1924
	21st to end	Day	3 6% 2 6% 4 3 3 4 5% 7% 58%	1650
March	1st to 10th	Day	4 8% 2 4 3 3 4 3 5% 8% 58%	4500
	11th to 20th	Day	5% 7% 3 7% 4 4 4 4 6% 8% 49%	4904
	21st to end	Day	4 6% 2 6% 4 4 4 5% 7% 9% 49%	5833
April	1st to 10th	Day	6% 7% 2 5% 4 3 4 3 6% 8% 53%	2400
	11th to 20th	Day	10% 8% 2 6% 4 5% 4 3 5% 7% 46%	2371
	21st to end	Day	9% 8% 2 5% 5% 4 5% 3 7% 9% 44%	2400
May	1st to 10th	Day	10% 7% 3 6% 4 5% 5% 4 5% 7% 45%	5795
	11th to 20th	Day	7% 6% 2 6% 4 4 5% 4 7% 9% 45%	6294
	21st to end	Day	8% 5% 2 5% 4 4 5% 4 7% 9% 46%	6925
June	1st to 10th	Day	5% 4 1 5% 4 4 5% 5% 8% 10% 49%	2800
	11th to 20th	Day	5% 3 2 5% 3 4 6% 5% 7% 9% 51%	2800
	21st to end	Day	4 3 1 4 3 5% 5% 5% 9% 10% 51%	2800
July	1st to 10th	Day	4 3 1 4 3 3 5% 4 6% 9% 58%	6339
	11th to 20th	Day	3 3 1 5% 5% 6% 7% 6% 10% 11% 45%	6340
	21st to end	Day	4 4 2 7% 4 5% 5% 4 7% 8% 49%	6859
August	1st to 10th	Day	7% 4 2 5% 5% 6% 7% 5% 8% 10% 42%	5779
	11th to 20th	Day	2 3 1 4 3 4 5% 5% 7% 10% 56%	5370
	21st to end	Day	6% 5% 2 6% 5% 5% 5% 4 6% 8% 46%	5984
September	1st to 10th	Day	5% 3 1 4 3 3 3 4 5% 9% 60%	2400
	11th to 20th	Day	5% 3 1 4 3 4 4 3 6% 7% 60%	2370
	21st to end	Day	6% 5% 1 3 2 3 3 3 3 6% 64%	2200
October	1st to 10th	Day	4 3 1 3 2 2 2 2 3 4 74%	3307
	11th to 20th	Day	5% 4 1 5% 3 3 3 3 5% 7% 61%	3250
	21st to end	Day	5% 6% 2 4 2 2 3 2 5% 7% 62%	3394
November	1st to 10th	Day	3 5% 1 4 3 3 3 3 5% 8% 62%	1853
	11th to 20th	Day	2 6% 2 4 3 3 4 3 5% 7% 62%	1890
	21st to end	Day	3 6% 2 5% 3 3 3 3 6% 7% 58%	1774
December	1st to 10th	Day	1 4 2 5% 3 3 2 2 4 6% 67%	2700
	11th to 20th	Day	2 4 1 3 2 3 3 2 4 6% 69%	3106
	21st to end	Day	4 7% 3 7% 4 3 4 4 6% 7% 51%	4092
January	1st to 10th	Night	3 10% 3 7% 3 3 3 3 4 8% 53%	6467
	11th to 20th	Night	1 5% 3 10% 4 3 3 3 4 6% 56%	6462
	21st to end	Night	2 6% 3 7% 4 4 4 3 4 5% 58%	6611
February	1st to 10th	Night	2 9% 4 6% 3 4 4 3 4 7% 54%	2600
	11th to 20th	Night	2 8% 4 7% 5% 5% 4 3 5% 7% 49%	2362
	21st to end	Night	3 10% 3 6% 3 4 3 3 5% 6% 55%	1980
March	1st to 10th	Night	5% 9% 3 5% 4 3 4 3 4 6% 53%	5374
	11th to 20th	Night	7% 9% 2 5% 3 4 3 3 4 6% 53%	5088
	21st to end	Night	8% 8% 3 6% 4 4 4 4 5% 8% 47%	5124
April	1st to 10th	Night	6% 7% 3 5% 4 4 4 3 5% 6% 54%	2000
	11th to 20th	Night	11% 7% 2 5% 4 3 3 5% 5% 7% 47%	1977
	21st to end	Night	13% 8% 3 5% 4 3 3 4 5% 8% 45%	2000
May	1st to 10th	Night	12% 7% 2 6% 4 4 4 4 6% 7% 44%	4182
	11th to 20th	Night	9% 7% 2 7% 4 4 4 3 6% 8% 45%	3617
	21st to end	Night	11% 7% 2 5% 3 3 3 3 5% 7% 52%	3972
June	1st to 10th	Night	6% 3 1 4 4 4 3 4 6% 10% 56%	1600
	11th to 20th	Night	5% 3 1 4 4 4 3 4 5% 7% 60%	1600
	21st to end	Night	4 3 1 4 4 3 3 4 7% 8% 57%	1600
July	1st to 10th	Night	3 3 1 4 3 3 4 3 5% 9% 60%	3640
	11th to 20th	Night	4 3 1 4 3 4 5% 5% 8% 12% 51%	3640
	21st to end	Night	4 4 2 5% 4 4 6% 5% 7% 10% 50%	4010
August	1st to 10th	Night	7% 5% 1 5% 4 4 4 5% 7% 9% 48%	4033
	11th to 20th	Night	3 2 1 5% 4 4 5% 4 7% 10% 54%	4478
	21st to end	Night	7% 6% 2 7% 4 4 5% 4 6% 9% 45%	4993
September	1st to 10th	Night	6% 3 1 3 4 4 4 3 6% 7% 58%	2000
	11th to 20th	Night	6% 3 1 4 3 3 3 4 5% 7% 61%	2029
	21st to end	Night	7% 3 2 4 3 3 3 2 4 7% 63%	2200
October	1st to 10th	Night	5% 4 1 3 2 2 2 1 3 4 72%	3877
	11th to 20th	Night	6% 5% 2 5% 3 3 3 3 5% 7% 59%	3898
	21st to end	Night	6% 5% 2 4 2 3 3 2 3 6% 63%	4372
November	1st to 10th	Night	4 4 2 4 3 2 3 3 4 6% 64%	2665
	11th to 20th	Night	4 5% 2 5% 3 3 3 3 5% 6% 62%	2730
	21st to end	Night	4 7% 2 4 3 2 3 3 5% 7% 59%	2842
December	1st to 10th	Night	2 4 2 4 2 3 2 2 4 5% 70%	4710
	11th to 20th	Night	1 5% 2 4 3 2 3 2 5% 8% 64%	5321
	21st to end	Night	5% 10% 3 6% 4 3 3 3 5% 6% 51%	7128

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	32% 1 6% 34% 19% 8%	3719
	11th to 20th	Day	32% 2 8% 25% 25% 9%	3783
	21st to end	Day	26% 2 8% 29% 26% 11%	4609
February	1st to 10th	Day	32% 3 10% 28% 21% 6%	1800
	11th to 20th	Day	27% 3 7% 31% 27% 5%	1934
	21st to end	Day	28% 2 6% 27% 27% 12%	1650
March	1st to 10th	Day	27% 2 5% 20% 33% 14%	4500
	11th to 20th	Day	33% 3 9% 25% 25% 6%	4904
	21st to end	Day	32% 2 9% 38% 17% 2	5833
April	1st to 10th	Day	30% 3 9% 25% 24% 9%	2400
	11th to 20th	Day	38% 3 7% 23% 21% 9%	2374
	21st to end	Day	37% 4 7% 28% 22% 3	2400
May	1st to 10th	Day	39% 2 8% 27% 18% 6%	5795
	11th to 20th	Day	35% 3 8% 22% 23% 9%	6298
	21st to end	Day	34% 3 11% 26% 20% 5%	6926
June	1st to 10th	Day	29% 4 15% 25% 19% 8%	2800
	11th to 20th	Day	28% 4 9% 19% 25% 14%	2800
	21st to end	Day	24% 4 8% 25% 26% 13%	2800
July	1st to 10th	Day	22% 4 5% 19% 30% 20%	6271
	11th to 20th	Day	28% 5% 11% 26% 19% 11%	6265
	21st to end	Day	31% 4 9% 19% 20% 17%	6661
August	1st to 10th	Day	38% 4 13% 21% 16% 9%	4208
	11th to 20th	Day	26% 4 11% 21% 22% 16%	3886
	21st to end	Day	27% 4 7% 20% 26% 15%	4311
September	1st to 10th	Day	22% 3 6% 23% 27% 19%	2400
	11th to 20th	Day	23% 3 6% 22% 28% 18%	2370
	21st to end	Day	23% 2 4 21% 36% 14%	2200
October	1st to 10th	Day	16% 2 4 17% 36% 25%	3307
	11th to 20th	Day	25% 2 6% 25% 31% 10%	3250
	21st to end	Day	23% 3 4 25% 34% 11%	3394
November	1st to 10th	Day	22% 2 7% 27% 29% 13%	1853
	11th to 20th	Day	23% 2 5% 26% 35% 8%	1890
	21st to end	Day	25% 3 7% 24% 31% 10%	1774
December	1st to 10th	Day	21% 2 6% 35% 27% 10%	2700
	11th to 20th	Day	18% 2 5% 33% 35% 7%	3104
	21st to end	Day	34% 1 7% 27% 23% 8%	4092
January	1st to 10th	Night	33% 1 7% 31% 21% 7%	6467
	11th to 20th	Night	31% 3 8% 23% 23% 11%	6462
	21st to end	Night	31% 1 8% 26% 25% 9%	6611
February	1st to 10th	Night	32% 3 9% 28% 23% 6%	2600
	11th to 20th	Night	34% 2 7% 29% 21% 6%	2362
	21st to end	Night	30% 2 4 24% 27% 13%	1980
March	1st to 10th	Night	34% 2 3 17% 35% 9%	5374
	11th to 20th	Night	34% 1 8% 17% 28% 11%	5088
	21st to end	Night	38% 2 8% 34% 16% 2	5124
April	1st to 10th	Night	32% 3 8% 25% 22% 9%	2000
	11th to 20th	Night	37% 3 9% 24% 20% 7%	1977
	21st to end	Night	39% 3 7% 28% 19% 4	2000
May	1st to 10th	Night	40% 3 11% 27% 13% 6%	4180
	11th to 20th	Night	38% 3 14% 23% 17% 7%	3618
	21st to end	Night	34% 2 17% 27% 15% 4	3972
June	1st to 10th	Night	24% 4 20% 31% 14% 7%	1600
	11th to 20th	Night	25% 3 12% 22% 23% 14%	1600
	21st to end	Night	24% 4 10% 26% 28% 9%	1600
July	1st to 10th	Night	24% 3 8% 23% 33% 9%	3600
	11th to 20th	Night	24% 4 17% 28% 21% 6%	3592
	21st to end	Night	28% 4 15% 22% 21% 10%	3896
August	1st to 10th	Night	37% 5% 15% 22% 17% 5%	2928
	11th to 20th	Night	27% 6% 16% 23% 18% 11%	3238
	21st to end	Night	26% 4 13% 24% 25% 8%	3597
September	1st to 10th	Night	25% 3 8% 23% 23% 18%	2000
	11th to 20th	Night	23% 3 7% 26% 25% 17%	2029
	21st to end	Night	24% 3 6% 22% 33% 13%	2200
October	1st to 10th	Night	19% 2 6% 19% 31% 23%	3877
	11th to 20th	Night	26% 3 7% 27% 29% 9%	3898
	21st to end	Night	24% 2 4 26% 32% 12%	4372
November	1st to 10th	Night	22% 2 7% 27% 29% 13%	2665
	11th to 20th	Night	24% 2 4 30% 32% 8%	2730
	21st to end	Night	26% 2 8% 25% 30% 8%	2842
December	1st to 10th	Night	18% 2 7% 37% 29% 7%	4710
	11th to 20th	Night	21% 2 5% 36% 32% 5%	5322
	21st to end	Night	35% 2 6% 25% 27% 6%	7128

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	6% 7% 18% 43% 18% 8%	330
	11th to 20th	Day	7% 7% 22% 44% 17% 3	330
	21st to end	Day	4 3 27% 47% 15% 5%	363
February	1st to 10th	Day	6% 9% 30% 42% 10% 3	300
	11th to 20th	Day	3 4 33% 47% 9% 4	300
	21st to end	Day	6% 8% 30% 42% 12% 2	249
March	1st to 10th	Day	7% 5% 28% 36% 19% 5%	300
	11th to 20th	Day	12% 11% 25% 32% 15% 5%	456
	21st to end	Day	12% 11% 28% 33% 13% 3	550
April	1st to 10th	Day	14% 10% 26% 29% 18% 3	500
	11th to 20th	Day	16% 14% 28% 27% 10% 4	492
	21st to end	Day	14% 11% 26% 27% 18% 4	500
May	1st to 10th	Day	14% 9% 21% 33% 18% 4	650
	11th to 20th	Day	18% 5% 14% 30% 25% 8%	725
	21st to end	Day	12% 6% 19% 31% 23% 8%	789
June	1st to 10th	Day	7% 5% 14% 30% 29% 16%	730
	11th to 20th	Day	7% 4 21% 34% 26% 8%	730
	21st to end	Day	6% 5% 17% 32% 30% 11%	730
July	1st to 10th	Day	7% 2 11% 26% 37% 17%	721
	11th to 20th	Day	5% 1 12% 28% 36% 18%	718
	21st to end	Day	6% 2 10% 21% 42% 18%	775
August	1st to 10th	Day	6% 3 16% 30% 30% 14%	527
	11th to 20th	Day	3 4 15% 30% 29% 18%	517
	21st to end	Day	6% 3 13% 28% 31% 18%	583
September	1st to 10th	Day	7% 3 11% 32% 31% 18%	530
	11th to 20th	Day	5% 2 15% 33% 29% 15%	500
	21st to end	Day	6% 3 13% 27% 31% 20%	330
October	1st to 10th	Day	10% 4 14% 27% 26% 19%	330
	11th to 20th	Day	4 7% 18% 36% 27% 8%	330
	21st to end	Day	9% 4 21% 38% 22% 7%	363
November	1st to 10th	Day	9% 3 19% 42% 18% 10%	330
	11th to 20th	Day	6% 5% 24% 39% 20% 6%	330
	21st to end	Day	8% 2 22% 42% 21% 5%	330
December	1st to 10th	Day	5% 7% 23% 42% 18% 7%	330
	11th to 20th	Day	4 5% 28% 42% 19% 2	330
	21st to end	Day	6% 5% 27% 44% 13% 4	363
January	1st to 10th	Night	6% 4 29% 47% 13% 2	1050
	11th to 20th	Night	4 5% 31% 48% 11% 1	1045
	21st to end	Night	5% 1 30% 51% 11% 1	924
February	1st to 10th	Night	7% 3 35% 47% 7% 1	800
	11th to 20th	Night	5% 4 31% 49% 11%	784
	21st to end	Night	8% 4 35% 47% 5%	660
March	1st to 10th	Night	6% 3 34% 48% 10% 1	800
	11th to 20th	Night	10% 4 26% 48% 12% 1	800
	21st to end	Night	10% 5% 26% 48% 9%	722
April	1st to 10th	Night	9% 7% 32% 45% 7%	600
	11th to 20th	Night	16% 7% 26% 42% 9%	593
	21st to end	Night	17% 5% 24% 39% 15%	600
May	1st to 10th	Night	14% 6% 23% 40% 17% 1	600
	11th to 20th	Night	17% 3 15% 45% 19% 2	591
	21st to end	Night	9% 5% 20% 43% 22% 1	650
June	1st to 10th	Night	8% 2 15% 46% 26% 4	600
	11th to 20th	Night	7% 3 17% 53% 20% 1	600
	21st to end	Night	5% 3 16% 48% 28% 1	600
July	1st to 10th	Night	7% 3 12% 38% 37% 3	585
	11th to 20th	Night	5% 2 8% 44% 38% 3	582
	21st to end	Night	6% 2 8% 36% 44% 3	657
August	1st to 10th	Night	7% 2 9% 39% 40% 2	597
	11th to 20th	Night	4 2 7% 49% 36% 2	594
	21st to end	Night	6% 2 9% 45% 36% 3	660
September	1st to 10th	Night	6% 3 10% 45% 31% 5%	600
	11th to 20th	Night	7% 1 13% 48% 28% 3	600
	21st to end	Night	7% 3 14% 51% 23% 2	600
October	1st to 10th	Night	11% 4 16% 45% 22% 3	770
	11th to 20th	Night	6% 2 21% 51% 18% 2	800
	21st to end	Night	10% 2 22% 50% 14% 2	951
November	1st to 10th	Night	6% 3 25% 50% 14% 1	1025
	11th to 20th	Night	6% 5% 28% 51% 9% 1	1050
	21st to end	Night	8% 3 26% 48% 15% 1	1050
December	1st to 10th	Night	5% 3 32% 49% 11%	1050
	11th to 20th	Night	6% 4 33% 46% 10% 1	1050
	21st to end	Night	6% 4 31% 48% 9% 1	1155

Page generated at 2026-01-28 23:21:44. Version ac07

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