Nebraska Star Party
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Nebraska Star Party 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	8% 6% 2 5% 4 4 4 3 5% 7% 51%	134700
	Night	7% 7% 2 7% 4 4 4 3 5% 7% 49%	131384
Transparency	Day	32% 6% 13% 27% 19% 4	129500
	Night	33% 6% 13% 26% 19% 3	127594
Seeing	Day	11% 9% 32% 31% 14% 3	17054
	Night	11% 9% 38% 34% 8%	26898

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 12% 5% 12% 8% 4 3 3 3 5% 42%	3638
	11th to 20th	Day	5% 8% 3 8% 5% 5% 5% 5% 6% 8% 42%	3640
	21st to end	Day	3 5% 2 8% 3 4 4 3 5% 7% 55%	4004
February	1st to 10th	Day	7% 13% 4 8% 6% 5% 4 3 5% 6% 38%	1859
	11th to 20th	Day	5% 11% 4 7% 4 5% 3 3 5% 7% 46%	1949
	21st to end	Day	7% 8% 3 5% 4 3 3 3 4 7% 52%	1650
March	1st to 10th	Day	9% 9% 2 5% 3 2 2 2 4 5% 56%	4500
	11th to 20th	Day	7% 6% 2 5% 3 3 3 3 5% 7% 57%	4837
	21st to end	Day	14% 12% 4 6% 4 3 4 4 6% 6% 38%	5661
April	1st to 10th	Day	12% 9% 2 5% 4 3 3 3 6% 7% 46%	2400
	11th to 20th	Day	13% 10% 2 6% 4 4 4 3 5% 7% 41%	2413
	21st to end	Day	15% 8% 2 5% 4 4 4 3 4 6% 45%	2600
May	1st to 10th	Day	9% 5% 2 5% 4 4 5% 4 6% 7% 48%	5900
	11th to 20th	Day	11% 6% 2 5% 4 4 4 3 5% 7% 49%	5862
	21st to end	Day	18% 6% 2 5% 4 4 4 3 5% 6% 43%	6924
June	1st to 10th	Day	7% 5% 2 4 3 4 4 3 6% 9% 52%	2800
	11th to 20th	Day	9% 4 2 5% 4 4 4 3 5% 8% 51%	2800
	21st to end	Day	6% 3 1 3 3 3 4 4 6% 8% 59%	2800
July	1st to 10th	Day	8% 5% 2 5% 4 4 4 3 5% 7% 52%	6339
	11th to 20th	Day	8% 4 2 5% 3 4 4 4 6% 8% 52%	6340
	21st to end	Day	7% 4 1 4 3 4 5% 4 6% 9% 53%	6903
August	1st to 10th	Day	6% 4 2 5% 4 5% 4 4 6% 8% 51%	5852
	11th to 20th	Day	5% 5% 2 5% 4 4 4 4 6% 8% 55%	5821
	21st to end	Day	8% 5% 2 6% 5% 4 4 3 6% 7% 50%	5989
September	1st to 10th	Day	8% 3 2 4 3 3 3 3 4 6% 62%	2312
	11th to 20th	Day	6% 3 1 3 3 3 3 3 4 6% 64%	2090
	21st to end	Day	9% 4 1 4 3 3 3 3 5% 5% 62%	2090
October	1st to 10th	Day	8% 3 1 3 2 1 2 2 2 4 72%	3480
	11th to 20th	Day	6% 5% 2 4 3 3 3 3 4 7% 60%	3064
	21st to end	Day	8% 6% 2 5% 4 4 4 4 5% 7% 51%	3091
November	1st to 10th	Day	6% 7% 2 6% 3 4 4 3 5% 6% 55%	1763
	11th to 20th	Day	5% 7% 2 6% 4 3 4 3 5% 7% 54%	1800
	21st to end	Day	6% 8% 2 5% 4 3 4 2 5% 9% 53%	1800
December	1st to 10th	Day	4 8% 3 6% 4 4 4 4 6% 6% 53%	2699
	11th to 20th	Day	3 4 2 5% 3 4 5% 4 6% 8% 54%	3026
	21st to end	Day	7% 12% 4 6% 4 4 4 3 5% 6% 45%	4004
January	1st to 10th	Night	5% 11% 5% 14% 9% 4 4 3 4 5% 37%	6327
	11th to 20th	Night	3 9% 4 10% 5% 5% 5% 4 5% 6% 45%	6340
	21st to end	Night	2 4 2 7% 5% 5% 4 3 5% 7% 55%	6974
February	1st to 10th	Night	10% 10% 4 8% 5% 4 4 3 5% 8% 40%	2555
	11th to 20th	Night	6% 9% 3 9% 5% 4 4 4 5% 7% 43%	2338
	21st to end	Night	6% 7% 2 7% 3 4 4 3 6% 7% 50%	1980
March	1st to 10th	Night	10% 10% 3 6% 3 3 3 3 5% 5% 50%	5374
	11th to 20th	Night	7% 7% 2 5% 3 3 4 3 5% 9% 52%	5128
	21st to end	Night	11% 10% 4 9% 5% 4 4 4 6% 8% 34%	5275
April	1st to 10th	Night	12% 8% 3 6% 4 4 5% 4 5% 9% 40%	2000
	11th to 20th	Night	14% 8% 2 5% 4 3 4 3 6% 5% 46%	1933
	21st to end	Night	15% 8% 2 6% 4 4 4 3 6% 7% 42%	1800
May	1st to 10th	Night	10% 6% 2 6% 4 4 5% 3 5% 7% 47%	4080
	11th to 20th	Night	10% 5% 2 5% 3 3 4 3 6% 7% 52%	4040
	21st to end	Night	18% 6% 2 6% 4 3 4 3 5% 6% 42%	3972
June	1st to 10th	Night	10% 5% 1 3 3 3 4 4 5% 9% 53%	1600
	11th to 20th	Night	12% 4 2 4 3 4 5% 4 7% 8% 47%	1600
	21st to end	Night	5% 4 2 5% 4 4 5% 4 7% 10% 50%	1600
July	1st to 10th	Night	5% 3 2 4 3 3 4 4 6% 10% 56%	3640
	11th to 20th	Night	8% 4 2 6% 4 4 4 4 7% 10% 47%	3640
	21st to end	Night	6% 5% 2 6% 4 5% 5% 4 6% 8% 49%	3970
August	1st to 10th	Night	6% 4 2 8% 5% 6% 6% 5% 8% 10% 41%	3958
	11th to 20th	Night	5% 5% 2 5% 5% 5% 5% 5% 8% 9% 47%	4028
	21st to end	Night	8% 5% 2 7% 5% 5% 5% 5% 6% 8% 45%	4982
September	1st to 10th	Night	9% 2 1 4 3 3 4 3 5% 6% 60%	1935
	11th to 20th	Night	8% 3 1 3 3 3 3 3 5% 7% 61%	2090
	21st to end	Night	10% 4 1 3 3 4 3 3 4 5% 61%	2090
October	1st to 10th	Night	7% 3 1 3 2 2 2 2 3 4 72%	3480
	11th to 20th	Night	9% 4 1 3 2 2 2 3 4 7% 64%	3824
	21st to end	Night	7% 7% 2 6% 4 3 4 3 5% 6% 52%	4467
November	1st to 10th	Night	9% 6% 2 4 4 3 4 3 6% 7% 53%	2535
	11th to 20th	Night	5% 6% 2 5% 4 4 4 3 6% 7% 54%	2600
	21st to end	Night	5% 6% 3 6% 3 3 4 3 6% 8% 53%	2600
December	1st to 10th	Night	4 5% 2 6% 4 3 4 3 5% 6% 57%	4474
	11th to 20th	Night	3 6% 3 7% 5% 5% 5% 3 6% 7% 50%	5181
	21st to end	Night	10% 11% 3 7% 4 4 4 3 5% 6% 43%	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	45% 5% 9% 29% 12% 1	3639
	11th to 20th	Day	39% 7% 14% 21% 17% 3	3640
	21st to end	Day	28% 5% 17% 29% 17% 4	4004
February	1st to 10th	Day	45% 6% 13% 20% 12% 2	1859
	11th to 20th	Day	39% 5% 14% 22% 16% 5%	1959
	21st to end	Day	33% 4 15% 27% 17% 5%	1650
March	1st to 10th	Day	32% 4 8% 26% 27% 4	4500
	11th to 20th	Day	27% 4 12% 29% 26% 1	4837
	21st to end	Day	45% 7% 15% 23% 9% 1	5661
April	1st to 10th	Day	37% 7% 16% 25% 13% 3	2400
	11th to 20th	Day	41% 7% 12% 22% 15% 2	2416
	21st to end	Day	39% 6% 14% 28% 12% 1	2600
May	1st to 10th	Day	31% 7% 13% 27% 20% 2	5900
	11th to 20th	Day	34% 7% 14% 26% 17% 3	5866
	21st to end	Day	40% 8% 13% 25% 13% 2	6925
June	1st to 10th	Day	28% 9% 19% 30% 14% 2	2800
	11th to 20th	Day	30% 7% 16% 28% 16% 4	2800
	21st to end	Day	20% 9% 16% 30% 21% 5%	2800
July	1st to 10th	Day	31% 6% 9% 29% 23% 2	6271
	11th to 20th	Day	28% 6% 14% 29% 19% 4	6265
	21st to end	Day	26% 7% 14% 22% 22% 7%	6705
August	1st to 10th	Day	29% 8% 16% 23% 21% 3	4257
	11th to 20th	Day	32% 7% 13% 27% 18% 3	4210
	21st to end	Day	22% 6% 16% 23% 23% 10%	4319
September	1st to 10th	Day	23% 5% 11% 27% 23% 10%	2312
	11th to 20th	Day	21% 6% 12% 30% 25% 6%	2090
	21st to end	Day	24% 5% 9% 30% 27% 5%	2090
October	1st to 10th	Day	19% 3 8% 19% 34% 18%	3480
	11th to 20th	Day	24% 4 16% 33% 20% 4	3064
	21st to end	Day	33% 5% 11% 31% 15% 6%	3091
November	1st to 10th	Day	29% 5% 17% 25% 20% 5%	1763
	11th to 20th	Day	30% 5% 10% 27% 22% 6%	1800
	21st to end	Day	30% 4 15% 28% 18% 4	1800
December	1st to 10th	Day	33% 5% 15% 29% 16% 2	2699
	11th to 20th	Day	27% 6% 20% 30% 17% 1	3024
	21st to end	Day	40% 5% 8% 35% 11% 1	4004
January	1st to 10th	Night	49% 5% 10% 21% 13% 1	6327
	11th to 20th	Night	39% 6% 14% 23% 16% 2	6340
	21st to end	Night	30% 6% 15% 29% 18% 2	6974
February	1st to 10th	Night	43% 6% 14% 23% 12% 2	2555
	11th to 20th	Night	39% 6% 12% 25% 14% 3	2338
	21st to end	Night	31% 7% 15% 26% 16% 5%	1980
March	1st to 10th	Night	35% 5% 8% 25% 24% 3	5374
	11th to 20th	Night	28% 5% 11% 25% 28% 2	5128
	21st to end	Night	45% 8% 15% 20% 10% 1	5275
April	1st to 10th	Night	40% 8% 14% 21% 15% 3	2000
	11th to 20th	Night	38% 7% 11% 25% 17% 2	1933
	21st to end	Night	40% 9% 13% 25% 12% 1	1800
May	1st to 10th	Night	34% 7% 13% 26% 19% 2	4080
	11th to 20th	Night	29% 8% 15% 29% 16% 3	4041
	21st to end	Night	41% 8% 13% 23% 13% 1	3972
June	1st to 10th	Night	27% 9% 19% 26% 17% 2	1600
	11th to 20th	Night	33% 7% 18% 24% 15% 4	1600
	21st to end	Night	26% 8% 17% 29% 16% 3	1600
July	1st to 10th	Night	23% 5% 20% 31% 18% 3	3600
	11th to 20th	Night	30% 6% 16% 27% 17% 3	3592
	21st to end	Night	31% 8% 16% 22% 19% 4	3856
August	1st to 10th	Night	34% 8% 17% 22% 17% 3	2877
	11th to 20th	Night	34% 6% 16% 27% 14% 3	2915
	21st to end	Night	26% 7% 14% 23% 20% 10%	3586
September	1st to 10th	Night	24% 6% 11% 26% 25% 8%	1935
	11th to 20th	Night	23% 7% 12% 29% 25% 5%	2090
	21st to end	Night	27% 4 8% 28% 27% 6%	2090
October	1st to 10th	Night	19% 3 6% 18% 44% 10%	3480
	11th to 20th	Night	23% 3 12% 31% 25% 5%	3824
	21st to end	Night	32% 5% 12% 25% 22% 5%	4467
November	1st to 10th	Night	30% 6% 13% 24% 22% 6%	2535
	11th to 20th	Night	29% 5% 13% 24% 23% 6%	2600
	21st to end	Night	29% 6% 14% 29% 20% 4	2600
December	1st to 10th	Night	28% 4 17% 30% 18% 2	4474
	11th to 20th	Night	32% 5% 14% 34% 14% 1	5182
	21st to end	Night	41% 5% 10% 30% 13% 1	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% 13% 33% 31% 12% 2	300
	11th to 20th	Day	11% 18% 35% 28% 8% 1	300
	21st to end	Day	12% 11% 43% 24% 8% 3	330
February	1st to 10th	Day	13% 14% 46% 22% 4	300
	11th to 20th	Day	11% 14% 44% 23% 8%	300
	21st to end	Day	10% 14% 48% 24% 3	249
March	1st to 10th	Day	11% 12% 41% 23% 12% 1	300
	11th to 20th	Day	10% 12% 38% 28% 12% 1	300
	21st to end	Day	18% 14% 37% 20% 9% 2	411
April	1st to 10th	Day	17% 17% 38% 21% 7%	500
	11th to 20th	Day	18% 20% 33% 23% 5% 1	534
	21st to end	Day	19% 12% 30% 28% 10% 1	700
May	1st to 10th	Day	14% 12% 30% 29% 12% 3	703
	11th to 20th	Day	18% 10% 30% 26% 13% 3	725
	21st to end	Day	17% 10% 31% 27% 12% 3	789
June	1st to 10th	Day	7% 6% 30% 32% 18% 8%	730
	11th to 20th	Day	10% 8% 32% 33% 15% 3	730
	21st to end	Day	7% 6% 29% 40% 17% 2	730
July	1st to 10th	Day	6% 3 25% 38% 22% 6%	721
	11th to 20th	Day	5% 4 24% 44% 20% 3	718
	21st to end	Day	7% 3 24% 42% 22% 3	794
August	1st to 10th	Day	7% 4 24% 43% 18% 5%	726
	11th to 20th	Day	8% 4 25% 40% 20% 4	715
	21st to end	Day	4 4 24% 40% 23% 5%	591
September	1st to 10th	Day	6% 3 26% 42% 19% 4	498
	11th to 20th	Day	5% 5% 26% 30% 27% 8%	300
	21st to end	Day	12% 11% 28% 28% 16% 4	300
October	1st to 10th	Day	15% 8% 22% 31% 17% 7%	300
	11th to 20th	Day	10% 13% 40% 26% 9% 2	300
	21st to end	Day	13% 15% 32% 28% 11% 2	330
November	1st to 10th	Day	11% 11% 37% 24% 14% 3	300
	11th to 20th	Day	13% 13% 35% 28% 10% 1	300
	21st to end	Day	13% 8% 40% 25% 12% 2	300
December	1st to 10th	Day	10% 11% 46% 25% 7% 1	300
	11th to 20th	Day	11% 12% 45% 21% 10% 1	300
	21st to end	Day	14% 16% 38% 24% 5% 2	330
January	1st to 10th	Night	8% 13% 42% 29% 7% 1	1000
	11th to 20th	Night	7% 14% 43% 31% 5%	1000
	21st to end	Night	9% 9% 47% 28% 7%	1100
February	1st to 10th	Night	14% 12% 46% 24% 5%	925
	11th to 20th	Night	10% 11% 50% 24% 5%	784
	21st to end	Night	10% 10% 47% 28% 4	660
March	1st to 10th	Night	12% 11% 40% 32% 5%	800
	11th to 20th	Night	10% 9% 42% 30% 7% 1	670
	21st to end	Night	15% 11% 36% 30% 8%	660
April	1st to 10th	Night	17% 11% 41% 27% 4	600
	11th to 20th	Night	16% 13% 39% 29% 3	593
	21st to end	Night	18% 11% 32% 33% 7% 1	600
May	1st to 10th	Night	14% 8% 34% 35% 9%	600
	11th to 20th	Night	18% 8% 32% 32% 9%	591
	21st to end	Night	17% 8% 35% 33% 6% 1	650
June	1st to 10th	Night	10% 5% 29% 41% 14% 1	600
	11th to 20th	Night	12% 6% 36% 38% 8%	600
	21st to end	Night	6% 4 31% 48% 12%	600
July	1st to 10th	Night	6% 3 31% 45% 14%	585
	11th to 20th	Night	6% 3 31% 52% 9% 1	582
	21st to end	Night	4 4 30% 51% 12%	657
August	1st to 10th	Night	4 2 30% 50% 14% 1	597
	11th to 20th	Night	7% 3 30% 47% 12%	594
	21st to end	Night	5% 4 35% 43% 14%	660
September	1st to 10th	Night	8% 4 30% 46% 10% 1	579
	11th to 20th	Night	9% 4 34% 39% 15%	570
	21st to end	Night	12% 7% 32% 39% 10% 1	570
October	1st to 10th	Night	14% 8% 34% 34% 9%	570
	11th to 20th	Night	12% 9% 36% 34% 9%	781
	21st to end	Night	13% 10% 36% 32% 9%	1045
November	1st to 10th	Night	11% 7% 42% 33% 7% 1	975
	11th to 20th	Night	9% 11% 41% 31% 8%	1000
	21st to end	Night	8% 8% 42% 35% 7%	1000
December	1st to 10th	Night	9% 11% 45% 29% 6%	1000
	11th to 20th	Night	9% 9% 45% 31% 6%	1000
	21st to end	Night	15% 13% 37% 29% 6%	1100

Page generated at 2025-09-01 00:51:07. Version ac07

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