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 2024-11-04.

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 4 3 4 4 4 6% 8% 56%	105376
	Night	5% 6% 2 5% 4 4 4 4 6% 8% 53%	102373
Transparency	Day	26% 8% 14% 25% 19% 9%	105119
	Night	28% 8% 15% 25% 17% 7%	102220
Seeing	Day	8% 12% 31% 28% 17% 4	15786
	Night	8% 12% 35% 33% 11% 1	25799

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 5% 2 7% 5% 4 4 4 5% 7% 54%	2538
	11th to 20th	Day	2 9% 3 6% 6% 6% 6% 5% 5% 9% 43%	2540
	21st to end	Day	2 5% 2 3 3 3 3 3 4 7% 63%	3123
February	1st to 10th	Day	3 11% 4 8% 5% 4 5% 4 5% 8% 44%	1710
	11th to 20th	Day	4 10% 3 7% 5% 3 5% 3 6% 8% 47%	1692
	21st to end	Day	3 8% 3 6% 4 4 4 3 5% 8% 52%	1570
March	1st to 10th	Day	2 5% 2 5% 4 4 3 3 5% 8% 59%	3186
	11th to 20th	Day	5% 8% 2 4 3 3 4 4 6% 8% 52%	3490
	21st to end	Day	6% 10% 3 7% 5% 5% 5% 4 6% 8% 41%	3979
April	1st to 10th	Day	7% 9% 3 5% 3 3 4 3 7% 8% 47%	2280
	11th to 20th	Day	10% 10% 2 6% 4 4 5% 4 7% 6% 41%	2251
	21st to end	Day	12% 8% 2 6% 4 4 5% 4 6% 8% 42%	2294
May	1st to 10th	Day	13% 12% 3 7% 5% 5% 5% 4 6% 7% 33%	4356
	11th to 20th	Day	11% 5% 2 4 3 4 4 4 6% 9% 47%	4388
	21st to end	Day	8% 5% 2 5% 4 4 5% 5% 6% 8% 48%	4825
June	1st to 10th	Day	5% 4 1 4 4 4 4 5% 6% 9% 53%	2660
	11th to 20th	Day	6% 3 1 3 3 4 4 4 6% 8% 58%	2660
	21st to end	Day	3 2 1 3 2 3 4 4 6% 8% 65%	2660
July	1st to 10th	Day	2 1 1 2 2 2 3 3 5% 8% 69%	4430
	11th to 20th	Day	2 1 1 3 3 4 4 4 7% 10% 63%	4430
	21st to end	Day	2 2 1 3 3 3 4 4 7% 8% 63%	4802
August	1st to 10th	Day	4 3 1 4 4 4 5% 4 6% 7% 59%	4099
	11th to 20th	Day	3 2 1 4 3 4 5% 4 5% 6% 63%	3951
	21st to end	Day	2 1 1 2 2 3 3 3 5% 7% 70%	4180
September	1st to 10th	Day	5% 3 1 3 3 3 3 3 5% 7% 65%	2280
	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	5% 5% 2 5% 3 4 5% 4 5% 9% 54%	1700
	11th to 20th	Day	3 5% 2 4 3 4 4 4 7% 9% 56%	1590
	21st to end	Day	3 6% 2 5% 4 4 4 3 6% 6% 56%	1520
December	1st to 10th	Day	2 8% 3 9% 5% 3 4 3 6% 7% 49%	1520
	11th to 20th	Day	3 6% 2 3 4 3 4 3 5% 9% 59%	1926
	21st to end	Day	3 9% 3 7% 4 5% 4 3 5% 7% 50%	2794
January	1st to 10th	Night	2 8% 4 8% 4 4 5% 4 7% 9% 45%	4417
	11th to 20th	Night	2 8% 3 9% 5% 4 4 4 6% 9% 45%	4430
	21st to end	Night	3 7% 2 5% 3 3 3 3 5% 7% 58%	4571
February	1st to 10th	Night	3 9% 4 8% 5% 4 5% 3 6% 8% 45%	2470
	11th to 20th	Night	4 9% 3 6% 5% 5% 5% 5% 6% 8% 45%	2374
	21st to end	Night	3 7% 3 8% 5% 4 4 4 7% 7% 48%	1884
March	1st to 10th	Night	3 7% 2 5% 4 3 4 3 6% 7% 56%	3677
	11th to 20th	Night	5% 8% 2 6% 4 4 3 3 5% 8% 52%	3490
	21st to end	Night	5% 10% 4 9% 6% 5% 6% 5% 7% 9% 35%	3669
April	1st to 10th	Night	8% 10% 3 5% 4 3 3 3 6% 8% 48%	1900
	11th to 20th	Night	11% 10% 3 7% 4 5% 5% 4 5% 6% 39%	1877
	21st to end	Night	11% 8% 2 6% 4 4 4 4 6% 8% 43%	1882
May	1st to 10th	Night	12% 11% 3 8% 5% 5% 4 4 5% 6% 39%	2611
	11th to 20th	Night	12% 4 1 4 2 3 4 3 5% 8% 52%	2517
	21st to end	Night	10% 5% 2 4 4 4 5% 4 6% 10% 46%	2762
June	1st to 10th	Night	4 3 2 5% 3 4 5% 4 8% 10% 53%	1520
	11th to 20th	Night	7% 2 1 4 3 3 4 3 5% 7% 61%	1520
	21st to end	Night	4 2 1 3 3 2 4 3 5% 8% 65%	1520
July	1st to 10th	Night	4 3 1 4 3 4 4 3 7% 8% 59%	2540
	11th to 20th	Night	1 2 1 3 3 3 3 4 7% 10% 62%	2540
	21st to end	Night	2 1 1 3 3 4 5% 5% 7% 9% 60%	2761
August	1st to 10th	Night	7% 4 1 3 3 4 4 4 6% 9% 56%	2837
	11th to 20th	Night	4 2 1 5% 4 5% 7% 5% 7% 8% 53%	2886
	21st to end	Night	2 2 1 3 2 3 5% 5% 7% 9% 63%	3487
September	1st to 10th	Night	6% 3 1 3 2 3 3 3 4 7% 66%	1900
	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%	2451
	11th to 20th	Night	5% 7% 2 6% 4 4 5% 4 6% 7% 51%	2588
	21st to end	Night	4 8% 2 3 3 3 4 3 5% 7% 57%	2660
December	1st to 10th	Night	4 7% 3 7% 5% 4 4 3 5% 7% 51%	2660
	11th to 20th	Night	2 7% 2 4 3 3 4 4 6% 9% 55%	3271
	21st to end	Night	4 10% 3 6% 4 4 5% 4 6% 8% 46%	4873

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	30% 12% 17% 27% 13% 1	2539
	11th to 20th	Day	36% 12% 19% 20% 12% 1	2540
	21st to end	Day	22% 7% 29% 29% 12% 1	3123
February	1st to 10th	Day	40% 8% 18% 26% 7% 1	1710
	11th to 20th	Day	36% 10% 17% 23% 12% 3	1701
	21st to end	Day	31% 8% 19% 25% 14% 2	1570
March	1st to 10th	Day	22% 8% 16% 34% 17% 3	3186
	11th to 20th	Day	28% 10% 21% 32% 9% 1	3490
	21st to end	Day	39% 11% 18% 26% 5% 1	3979
April	1st to 10th	Day	35% 8% 20% 22% 13% 2	2280
	11th to 20th	Day	42% 8% 14% 22% 13% 2	2254
	21st to end	Day	40% 8% 15% 25% 12% 1	2294
May	1st to 10th	Day	46% 11% 11% 18% 12% 3	4356
	11th to 20th	Day	31% 10% 13% 29% 13% 4	4392
	21st to end	Day	28% 12% 14% 27% 16% 3	4825
June	1st to 10th	Day	27% 9% 16% 25% 18% 5%	2660
	11th to 20th	Day	23% 7% 12% 23% 21% 13%	2660
	21st to end	Day	16% 6% 11% 23% 28% 16%	2660
July	1st to 10th	Day	13% 5% 7% 22% 34% 19%	4361
	11th to 20th	Day	14% 5% 9% 20% 30% 22%	4355
	21st to end	Day	15% 6% 9% 16% 29% 24%	4651
August	1st to 10th	Day	21% 8% 10% 23% 20% 19%	4084
	11th to 20th	Day	20% 6% 8% 20% 29% 16%	3990
	21st to end	Day	13% 5% 9% 19% 30% 24%	4179
September	1st to 10th	Day	19% 5% 8% 18% 30% 19%	2280
	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	28% 7% 16% 27% 17% 3	1700
	11th to 20th	Day	25% 9% 18% 30% 15% 4	1590
	21st to end	Day	28% 7% 17% 28% 17% 2	1520
December	1st to 10th	Day	33% 9% 21% 23% 13% 1	1520
	11th to 20th	Day	25% 7% 25% 34% 9%	1924
	21st to end	Day	33% 8% 14% 30% 13% 2	2794
January	1st to 10th	Night	32% 12% 19% 26% 10% 1	4417
	11th to 20th	Night	34% 11% 21% 19% 12% 3	4430
	21st to end	Night	26% 6% 30% 27% 10% 1	4571
February	1st to 10th	Night	36% 9% 19% 25% 9% 1	2470
	11th to 20th	Night	36% 10% 16% 24% 12% 2	2375
	21st to end	Night	34% 9% 18% 23% 14% 3	1884
March	1st to 10th	Night	24% 10% 16% 31% 18% 1	3677
	11th to 20th	Night	29% 8% 19% 34% 8% 2	3490
	21st to end	Night	41% 14% 17% 21% 6%	3669
April	1st to 10th	Night	36% 8% 17% 23% 13% 3	1900
	11th to 20th	Night	43% 9% 14% 18% 14% 2	1877
	21st to end	Night	37% 10% 12% 26% 14% 1	1882
May	1st to 10th	Night	40% 11% 12% 20% 16% 1	2611
	11th to 20th	Night	27% 8% 15% 33% 11% 5%	2518
	21st to end	Night	29% 11% 17% 29% 13% 1	2762
June	1st to 10th	Night	24% 9% 19% 27% 16% 4	1520
	11th to 20th	Night	23% 5% 13% 24% 21% 13%	1520
	21st to end	Night	18% 6% 10% 23% 28% 16%	1520
July	1st to 10th	Night	19% 7% 10% 24% 24% 15%	2500
	11th to 20th	Night	15% 5% 10% 25% 27% 18%	2492
	21st to end	Night	17% 7% 10% 20% 30% 16%	2674
August	1st to 10th	Night	24% 6% 11% 26% 18% 16%	2829
	11th to 20th	Night	26% 8% 9% 22% 21% 13%	2913
	21st to end	Night	16% 6% 11% 16% 28% 23%	3487
September	1st to 10th	Night	19% 5% 9% 21% 29% 18%	1900
	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% 28% 19% 3	2451
	11th to 20th	Night	31% 9% 14% 29% 14% 3	2588
	21st to end	Night	27% 7% 17% 30% 18% 2	2660
December	1st to 10th	Night	33% 8% 19% 25% 14% 1	2660
	11th to 20th	Night	25% 8% 22% 35% 9% 1	3272
	21st to end	Night	34% 8% 16% 25% 14% 2	4873

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% 21% 38% 23% 9% 1	270
	11th to 20th	Day	8% 21% 47% 20% 4	270
	21st to end	Day	7% 15% 51% 20% 6% 1	297
February	1st to 10th	Day	8% 25% 50% 13% 4 1	270
	11th to 20th	Day	9% 23% 53% 11% 5%	270
	21st to end	Day	12% 20% 42% 21% 5%	225
March	1st to 10th	Day	8% 25% 41% 20% 7%	300
	11th to 20th	Day	10% 18% 37% 28% 6% 1	460
	21st to end	Day	13% 20% 34% 24% 8% 1	506
April	1st to 10th	Day	15% 18% 41% 22% 4	460
	11th to 20th	Day	15% 16% 40% 23% 5%	452
	21st to end	Day	15% 14% 32% 27% 11% 2	460
May	1st to 10th	Day	16% 15% 27% 26% 13% 4	605
	11th to 20th	Day	16% 7% 24% 28% 21% 3	675
	21st to end	Day	13% 10% 26% 26% 20% 4	734
June	1st to 10th	Day	5% 10% 24% 28% 26% 8%	680
	11th to 20th	Day	7% 12% 31% 31% 16% 2	680
	21st to end	Day	4 6% 28% 33% 24% 5%	680
July	1st to 10th	Day	4 5% 19% 33% 33% 6%	671
	11th to 20th	Day	3 4 19% 38% 30% 6%	668
	21st to end	Day	3 2 17% 36% 35% 6%	739
August	1st to 10th	Day	3 5% 22% 33% 30% 6%	494
	11th to 20th	Day	3 5% 21% 36% 25% 9%	477
	21st to end	Day	2 7% 25% 34% 24% 8%	539
September	1st to 10th	Day	6% 6% 23% 32% 23% 10%	490
	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% 46% 21% 6% 2	279
	11th to 20th	Day	9% 23% 41% 22% 6%	270
	21st to end	Day	10% 20% 45% 21% 3	270
December	1st to 10th	Day	10% 23% 41% 19% 7%	270
	11th to 20th	Day	11% 29% 39% 19% 3	270
	21st to end	Day	14% 20% 40% 22% 4 1	297
January	1st to 10th	Night	6% 18% 42% 26% 6% 1	950
	11th to 20th	Night	7% 21% 47% 20% 5%	950
	21st to end	Night	9% 13% 53% 20% 4	860
February	1st to 10th	Night	7% 16% 49% 22% 6%	760
	11th to 20th	Night	7% 16% 43% 27% 7%	744
	21st to end	Night	7% 21% 43% 23% 6%	628
March	1st to 10th	Night	8% 15% 42% 28% 6%	760
	11th to 20th	Night	9% 12% 34% 36% 9%	760
	21st to end	Night	11% 14% 33% 34% 8% 1	741
April	1st to 10th	Night	15% 11% 36% 35% 3	570
	11th to 20th	Night	14% 12% 33% 35% 6%	563
	21st to end	Night	12% 10% 26% 38% 13%	570
May	1st to 10th	Night	15% 8% 27% 34% 14% 2	570
	11th to 20th	Night	15% 8% 21% 35% 20% 1	561
	21st to end	Night	10% 9% 27% 38% 16%	617
June	1st to 10th	Night	6% 5% 24% 43% 20% 1	570
	11th to 20th	Night	8% 8% 35% 40% 9%	570
	21st to end	Night	5% 3 24% 50% 18%	570
July	1st to 10th	Night	4 4 21% 45% 26% 1	555
	11th to 20th	Night	3 2 25% 50% 21%	552
	21st to end	Night	3 2 17% 54% 24%	624
August	1st to 10th	Night	4 4 18% 52% 23%	567
	11th to 20th	Night	4 3 20% 49% 24% 1	564
	21st to end	Night	3 3 23% 46% 23% 1	627
September	1st to 10th	Night	7% 3 20% 47% 21% 2	570
	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% 43% 29% 8%	943
	11th to 20th	Night	7% 20% 45% 23% 4	950
	21st to end	Night	7% 14% 47% 26% 5%	950
December	1st to 10th	Night	8% 20% 44% 23% 5%	950
	11th to 20th	Night	7% 20% 47% 22% 4	950
	21st to end	Night	9% 24% 41% 21% 4	1045

Page generated at 2024-11-01 20:47:30. Version ac07

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