Casper
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Casper clear sky chart from 2005-11-06 to 2025-09-04.

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	5% 5% 2 5% 3 4 4 4 6% 8% 56%	135334
	Night	5% 6% 2 5% 4 4 4 4 6% 7% 53%	130879
Transparency	Day	25% 7% 13% 25% 20% 9%	130190
	Night	28% 8% 15% 26% 18% 6%	127031
Seeing	Day	9% 13% 31% 27% 16% 4	16968
	Night	8% 12% 35% 33% 11% 1	26930

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 5% 3 10% 5% 5% 5% 4 5% 7% 48%	3638
	11th to 20th	Day	2 9% 3 6% 6% 6% 6% 5% 5% 8% 43%	3640
	21st to end	Day	2 5% 2 6% 3 3 3 3 4 7% 63%	4487
February	1st to 10th	Day	2 10% 4 8% 5% 4 5% 4 5% 8% 45%	1800
	11th to 20th	Day	4 10% 3 7% 5% 3 5% 3 6% 8% 46%	1784
	21st to end	Day	3 8% 3 6% 4 4 4 3 5% 8% 53%	1650
March	1st to 10th	Day	3 9% 2 4 3 3 3 3 4 7% 60%	4584
	11th to 20th	Day	5% 9% 2 4 3 3 3 3 5% 8% 55%	5000
	21st to end	Day	5% 9% 3 6% 4 4 5% 4 6% 9% 44%	5705
April	1st to 10th	Day	7% 9% 3 5% 3 3 5% 3 7% 8% 47%	2400
	11th to 20th	Day	10% 10% 2 6% 4 4 5% 4 7% 6% 41%	2371
	21st to end	Day	12% 9% 2 6% 4 4 5% 4 6% 8% 41%	2415
May	1st to 10th	Day	12% 10% 2 6% 4 5% 4 3 5% 7% 42%	6238
	11th to 20th	Day	10% 5% 2 4 3 4 4 4 7% 9% 48%	6298
	21st to end	Day	8% 5% 2 5% 4 4 5% 4 6% 8% 50%	6925
June	1st to 10th	Day	5% 4 1 4 4 4 4 5% 6% 9% 53%	2800
	11th to 20th	Day	5% 3 1 3 3 4 4 4 6% 8% 58%	2800
	21st to end	Day	3 2 1 3 2 3 4 4 6% 8% 65%	2800
July	1st to 10th	Day	3 2 1 3 2 2 3 3 5% 8% 67%	6339
	11th to 20th	Day	3 1 1 3 3 4 4 4 7% 10% 60%	6340
	21st to end	Day	2 2 1 3 3 3 4 4 7% 8% 63%	6903
August	1st to 10th	Day	3 3 1 4 3 4 5% 4 6% 7% 61%	5786
	11th to 20th	Day	2 2 1 3 3 4 5% 4 6% 7% 64%	5695
	21st to end	Day	3 2 1 4 3 3 4 4 6% 9% 60%	5981
September	1st to 10th	Day	5% 3 1 3 2 2 3 3 5% 7% 65%	2317
	11th to 20th	Day	5% 3 1 4 2 3 3 2 5% 8% 64%	2280
	21st to end	Day	7% 3 1 4 2 2 3 3 4 5% 66%	2038
October	1st to 10th	Day	5% 3 1 3 2 2 2 2 3 4 74%	3170
	11th to 20th	Day	8% 4 1 4 3 3 4 2 4 5% 62%	3150
	21st to end	Day	7% 7% 2 4 2 3 3 3 5% 9% 54%	3314
November	1st to 10th	Day	6% 5% 2 5% 4 4 5% 3 5% 8% 53%	1763
	11th to 20th	Day	3 5% 2 5% 3 4 4 3 6% 8% 57%	1673
	21st to end	Day	3 6% 2 5% 4 4 4 3 6% 6% 56%	1600
December	1st to 10th	Day	1 6% 2 6% 3 2 3 2 4 5% 66%	2620
	11th to 20th	Day	2 5% 2 4 4 3 4 3 7% 9% 58%	3026
	21st to end	Day	3 7% 3 7% 4 5% 6% 4 7% 8% 46%	4004
January	1st to 10th	Night	2 9% 4 9% 5% 4 5% 4 7% 8% 43%	6327
	11th to 20th	Night	1 8% 4 10% 6% 5% 5% 5% 6% 7% 43%	6340
	21st to end	Night	2 6% 2 7% 4 3 3 3 5% 6% 60%	6532
February	1st to 10th	Night	3 9% 4 8% 5% 4 5% 3 6% 8% 45%	2600
	11th to 20th	Night	4 9% 3 7% 5% 5% 5% 5% 6% 8% 43%	2502
	21st to end	Night	2 7% 3 8% 4 4 4 4 6% 7% 50%	1980
March	1st to 10th	Night	5% 8% 2 4 3 3 4 3 5% 6% 57%	5291
	11th to 20th	Night	4 8% 2 5% 3 3 3 3 5% 8% 55%	5000
	21st to end	Night	5% 10% 4 8% 5% 4 5% 5% 6% 9% 38%	5260
April	1st to 10th	Night	8% 9% 3 5% 4 3 3 3 6% 8% 48%	2000
	11th to 20th	Night	10% 10% 3 6% 4 5% 5% 4 5% 6% 40%	1977
	21st to end	Night	11% 8% 2 6% 4 4 4 4 6% 8% 44%	1981
May	1st to 10th	Night	14% 9% 2 6% 4 4 3 3 4 6% 46%	3739
	11th to 20th	Night	12% 5% 1 5% 3 4 4 4 6% 8% 47%	3617
	21st to end	Night	10% 5% 2 5% 4 5% 4 4 6% 8% 48%	3972
June	1st to 10th	Night	5% 3 2 5% 3 4 5% 4 8% 9% 53%	1600
	11th to 20th	Night	6% 2 1 4 3 3 4 3 6% 7% 61%	1600
	21st to end	Night	4 2 1 3 3 2 4 3 5% 7% 66%	1600
July	1st to 10th	Night	4 4 1 5% 3 4 5% 3 7% 8% 56%	3640
	11th to 20th	Night	2 2 1 4 3 4 4 4 7% 9% 61%	3640
	21st to end	Night	2 2 1 4 3 4 5% 5% 7% 9% 58%	3970
August	1st to 10th	Night	5% 3 1 3 2 4 4 4 6% 9% 59%	4023
	11th to 20th	Night	3 2 1 4 3 5% 6% 5% 7% 8% 57%	4152
	21st to end	Night	5% 4 2 5% 3 4 5% 5% 7% 8% 53%	4993
September	1st to 10th	Night	6% 3 1 3 2 3 3 3 4 7% 67%	1930
	11th to 20th	Night	6% 2 1 4 3 2 3 3 5% 7% 65%	1900
	21st to end	Night	8% 3 1 3 2 2 2 2 3 5% 68%	2138
October	1st to 10th	Night	5% 4 1 2 2 2 1 2 3 4 74%	3800
	11th to 20th	Night	7% 6% 2 4 3 3 3 3 5% 6% 58%	3778
	21st to end	Night	6% 6% 2 3 2 3 4 4 6% 7% 57%	4212
November	1st to 10th	Night	5% 7% 2 5% 4 3 3 3 6% 8% 54%	2535
	11th to 20th	Night	5% 7% 2 6% 4 3 4 4 6% 7% 52%	2725
	21st to end	Night	4 7% 2 3 3 3 4 4 6% 7% 57%	2800
December	1st to 10th	Night	2 5% 2 5% 4 3 3 3 5% 6% 62%	4570
	11th to 20th	Night	2 5% 2 4 3 4 5% 5% 7% 9% 55%	5181
	21st to end	Night	3 9% 3 6% 4 5% 5% 4 7% 9% 45%	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	34% 10% 16% 26% 13% 1	3639
	11th to 20th	Day	37% 10% 17% 21% 14%	3640
	21st to end	Day	22% 6% 22% 27% 19% 3	4487
February	1st to 10th	Day	38% 8% 19% 25% 8% 2	1800
	11th to 20th	Day	37% 10% 17% 23% 12% 3	1793
	21st to end	Day	30% 8% 19% 26% 14% 3	1650
March	1st to 10th	Day	24% 6% 11% 35% 15% 7%	4584
	11th to 20th	Day	26% 8% 16% 32% 17% 1	5000
	21st to end	Day	34% 10% 19% 27% 10%	5705
April	1st to 10th	Day	35% 8% 19% 22% 14% 2	2400
	11th to 20th	Day	41% 8% 14% 21% 14% 2	2374
	21st to end	Day	40% 9% 14% 25% 12%	2415
May	1st to 10th	Day	38% 10% 10% 23% 17% 2	6238
	11th to 20th	Day	29% 9% 13% 27% 18% 5%	6302
	21st to end	Day	26% 10% 14% 30% 18% 2	6926
June	1st to 10th	Day	27% 9% 16% 26% 18% 5%	2800
	11th to 20th	Day	22% 8% 12% 23% 22% 13%	2800
	21st to end	Day	16% 6% 10% 24% 29% 16%	2800
July	1st to 10th	Day	14% 5% 7% 20% 32% 22%	6271
	11th to 20th	Day	15% 6% 11% 20% 28% 19%	6265
	21st to end	Day	15% 7% 11% 16% 25% 26%	6705
August	1st to 10th	Day	20% 8% 10% 23% 20% 19%	4214
	11th to 20th	Day	20% 6% 8% 20% 29% 17%	4118
	21st to end	Day	13% 5% 9% 19% 29% 24%	4311
September	1st to 10th	Day	19% 5% 8% 19% 30% 19%	2317
	11th to 20th	Day	20% 5% 9% 23% 29% 15%	2280
	21st to end	Day	21% 5% 10% 27% 29% 8%	2038
October	1st to 10th	Day	17% 3 8% 18% 31% 22%	3170
	11th to 20th	Day	25% 5% 10% 28% 27% 5%	3150
	21st to end	Day	27% 6% 12% 32% 20% 3	3314
November	1st to 10th	Day	29% 7% 16% 27% 17% 3	1763
	11th to 20th	Day	24% 8% 17% 31% 16% 4	1673
	21st to end	Day	28% 7% 17% 28% 17% 2	1600
December	1st to 10th	Day	22% 5% 14% 37% 20% 1	2620
	11th to 20th	Day	23% 7% 26% 33% 11%	3024
	21st to end	Day	33% 9% 13% 30% 13% 1	4004
January	1st to 10th	Night	36% 10% 17% 24% 11% 1	6327
	11th to 20th	Night	37% 9% 18% 22% 12% 2	6340
	21st to end	Night	27% 5% 23% 26% 16% 3	6532
February	1st to 10th	Night	36% 9% 19% 24% 10% 2	2600
	11th to 20th	Night	36% 10% 17% 23% 12% 3	2503
	21st to end	Night	33% 8% 18% 23% 16% 3	1980
March	1st to 10th	Night	26% 7% 12% 29% 20% 6%	5291
	11th to 20th	Night	26% 7% 15% 32% 18% 1	5000
	21st to end	Night	38% 12% 19% 22% 8%	5260
April	1st to 10th	Night	35% 8% 16% 24% 14% 3	2000
	11th to 20th	Night	42% 9% 14% 17% 16% 2	1977
	21st to end	Night	36% 10% 13% 26% 14% 1	1981
May	1st to 10th	Night	35% 9% 10% 27% 18% 1	3737
	11th to 20th	Night	31% 8% 14% 29% 14% 4	3618
	21st to end	Night	29% 10% 15% 32% 13% 1	3972
June	1st to 10th	Night	25% 9% 19% 27% 17% 4	1600
	11th to 20th	Night	22% 5% 14% 24% 21% 13%	1600
	21st to end	Night	17% 5% 10% 24% 28% 16%	1600
July	1st to 10th	Night	22% 7% 10% 23% 22% 16%	3600
	11th to 20th	Night	16% 7% 10% 24% 28% 15%	3592
	21st to end	Night	18% 8% 12% 18% 25% 19%	3856
August	1st to 10th	Night	24% 6% 10% 25% 19% 16%	2919
	11th to 20th	Night	25% 8% 9% 22% 22% 14%	3005
	21st to end	Night	17% 6% 11% 17% 27% 22%	3597
September	1st to 10th	Night	18% 5% 9% 22% 29% 17%	1930
	11th to 20th	Night	19% 6% 10% 23% 27% 14%	1900
	21st to end	Night	21% 3 9% 26% 29% 12%	2138
October	1st to 10th	Night	17% 4 8% 18% 31% 23%	3800
	11th to 20th	Night	27% 5% 11% 26% 25% 6%	3778
	21st to end	Night	25% 6% 13% 30% 19% 7%	4212
November	1st to 10th	Night	27% 7% 16% 27% 19% 3	2535
	11th to 20th	Night	30% 8% 14% 29% 15% 3	2725
	21st to end	Night	26% 7% 16% 31% 18% 2	2800
December	1st to 10th	Night	24% 6% 16% 34% 19% 1	4570
	11th to 20th	Night	21% 10% 22% 38% 8% 1	5182
	21st to end	Night	33% 8% 16% 29% 12% 2	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	9% 20% 39% 23% 9% 1	300
	11th to 20th	Day	9% 21% 47% 20% 4	300
	21st to end	Day	7% 16% 50% 20% 7% 1	330
February	1st to 10th	Day	9% 26% 49% 12% 3 1	300
	11th to 20th	Day	10% 22% 50% 12% 6%	300
	21st to end	Day	14% 20% 41% 20% 5%	249
March	1st to 10th	Day	8% 24% 40% 20% 7%	332
	11th to 20th	Day	12% 19% 36% 27% 5% 1	500
	21st to end	Day	14% 21% 33% 23% 8% 1	550
April	1st to 10th	Day	14% 19% 40% 23% 4	500
	11th to 20th	Day	14% 17% 40% 23% 5%	492
	21st to end	Day	15% 14% 32% 26% 11% 2	500
May	1st to 10th	Day	16% 14% 26% 25% 13% 6%	653
	11th to 20th	Day	15% 8% 26% 28% 19% 3	725
	21st to end	Day	13% 11% 26% 27% 20% 4	789
June	1st to 10th	Day	5% 9% 24% 28% 26% 7%	730
	11th to 20th	Day	7% 11% 30% 32% 17% 2	730
	21st to end	Day	4 6% 27% 34% 24% 5%	730
July	1st to 10th	Day	4 5% 19% 34% 32% 6%	721
	11th to 20th	Day	3 4 19% 37% 30% 7%	718
	21st to end	Day	3 3 18% 36% 34% 6%	794
August	1st to 10th	Day	3 6% 22% 34% 28% 6%	534
	11th to 20th	Day	3 5% 21% 37% 26% 9%	517
	21st to end	Day	3 7% 25% 35% 23% 7%	583
September	1st to 10th	Day	6% 6% 23% 32% 24% 10%	503
	11th to 20th	Day	6% 10% 30% 30% 19% 5%	490
	21st to end	Day	8% 9% 28% 28% 18% 9%	338
October	1st to 10th	Day	9% 9% 25% 29% 21% 7%	300
	11th to 20th	Day	11% 12% 35% 26% 12% 3	300
	21st to end	Day	9% 18% 42% 22% 8% 1	330
November	1st to 10th	Day	10% 15% 45% 23% 6% 2	300
	11th to 20th	Day	10% 24% 40% 20% 5%	300
	21st to end	Day	11% 21% 44% 21% 3	300
December	1st to 10th	Day	9% 22% 41% 20% 7%	300
	11th to 20th	Day	12% 29% 38% 18% 2	300
	21st to end	Day	15% 20% 40% 21% 4 1	330
January	1st to 10th	Night	7% 17% 42% 27% 6% 1	1000
	11th to 20th	Night	7% 21% 48% 20% 4	1000
	21st to end	Night	9% 13% 52% 21% 4	905
February	1st to 10th	Night	8% 16% 48% 22% 5%	800
	11th to 20th	Night	7% 15% 43% 28% 7%	784
	21st to end	Night	7% 22% 43% 23% 6%	660
March	1st to 10th	Night	8% 15% 42% 28% 7%	800
	11th to 20th	Night	9% 12% 35% 34% 9%	800
	21st to end	Night	11% 14% 33% 34% 8% 1	780
April	1st to 10th	Night	15% 11% 35% 35% 4	600
	11th to 20th	Night	14% 11% 34% 35% 6%	593
	21st to end	Night	12% 10% 26% 39% 13%	600
May	1st to 10th	Night	16% 8% 26% 34% 15% 2	600
	11th to 20th	Night	15% 9% 21% 35% 19% 1	591
	21st to end	Night	10% 9% 27% 38% 16%	650
June	1st to 10th	Night	7% 5% 23% 44% 20% 2	600
	11th to 20th	Night	8% 7% 34% 41% 9%	600
	21st to end	Night	5% 4 24% 50% 17%	600
July	1st to 10th	Night	4 4 21% 45% 25% 1	585
	11th to 20th	Night	3 2 24% 50% 21%	582
	21st to end	Night	3 2 18% 54% 23%	657
August	1st to 10th	Night	4 4 19% 52% 22%	597
	11th to 20th	Night	3 3 19% 49% 25% 1	594
	21st to end	Night	4 4 23% 46% 22% 1	660
September	1st to 10th	Night	7% 3 19% 48% 22% 2	579
	11th to 20th	Night	6% 6% 26% 41% 19% 1	570
	21st to end	Night	10% 5% 24% 41% 19% 2	656
October	1st to 10th	Night	13% 9% 26% 33% 18% 1	760
	11th to 20th	Night	10% 8% 31% 39% 11% 1	760
	21st to end	Night	10% 9% 37% 33% 10% 2	892
November	1st to 10th	Night	8% 13% 42% 29% 8%	975
	11th to 20th	Night	8% 21% 45% 23% 4	1000
	21st to end	Night	7% 14% 48% 26% 5%	1000
December	1st to 10th	Night	8% 20% 44% 24% 5%	1000
	11th to 20th	Night	8% 21% 46% 22% 4	1000
	21st to end	Night	9% 24% 41% 21% 4	1100

Page generated at 2025-08-31 23:51:05. Version ac07

Copyright © 2025 Attilla Danko.