Great Basin National Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Great Basin National Park clear sky chart from 2005-11-06 to 2026-10-29.

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	2 3 1 4 3 4 5% 4 6% 8% 60%	159061
	Night	2 3 1 4 3 4 4 4 6% 8% 61%	150630
Transparency	Day	18% 6% 8% 19% 27% 21%	153899
	Night	19% 5% 9% 21% 28% 18%	146790
Seeing	Day	9% 16% 30% 27% 14% 4	17725
	Night	7% 9% 26% 33% 20% 5%	27284

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	3 2 4 3 4 5% 6% 9% 14% 50%	5318
	11th to 20th	Day	2 1 3 3 3 3 3 6% 7% 67%	5340
	21st to end	Day	1 5% 2 6% 3 4 5% 4 6% 9% 54%	5844
February	1st to 10th	Day	1 5% 2 6% 4 4 4 5% 7% 10% 51%	1974
	11th to 20th	Day	2 7% 1 6% 4 4 5% 5% 8% 9% 48%	2050
	21st to end	Day	1 7% 3 4 4 4 4 4 6% 9% 54%	1730
March	1st to 10th	Day	1 9% 3 7% 6% 5% 5% 4 6% 7% 48%	4680
	11th to 20th	Day	1 9% 2 5% 4 5% 5% 5% 6% 8% 50%	5110
	21st to end	Day	1 6% 2 5% 4 5% 7% 6% 9% 11% 44%	5607
April	1st to 10th	Day	2 5% 2 5% 5% 5% 4 6% 7% 8% 52%	2437
	11th to 20th	Day	2 6% 2 4 5% 5% 4 4 6% 8% 54%	2555
	21st to end	Day	3 6% 2 5% 4 5% 5% 4 6% 8% 52%	2730
May	1st to 10th	Day	3 4 1 4 4 4 4 4 6% 6% 59%	7626
	11th to 20th	Day	2 4 1 4 3 4 5% 4 5% 7% 60%	7596
	21st to end	Day	2 3 1 4 4 4 6% 4 7% 9% 56%	8370
June	1st to 10th	Day	1 3 1 4 5% 4 5% 5% 7% 8% 58%	2730
	11th to 20th	Day	2 3 1 3 3 3 3 3 4 6% 69%	2868
	21st to end	Day	2 2 1 3 4 3 4 3 6% 5% 68%	2940
July	1st to 10th	Day	1 1 1 3 2 3 3 3 4 4 76%	8219
	11th to 20th	Day	2 2 1 4 4 5% 7% 6% 8% 9% 51%	7766
	21st to end	Day	2 2 1 3 3 4 5% 4 5% 6% 66%	8304
August	1st to 10th	Day	1 1 2 2 3 3 3 5% 7% 73%	7549
	11th to 20th	Day	1 1 1 2 3 3 3 3 4 6% 72%	7565
	21st to end	Day	1 2 1 3 3 4 5% 4 7% 9% 61%	7816
September	1st to 10th	Day	3 3 1 4 3 3 3 3 4 5% 67%	2396
	11th to 20th	Day	1 3 1 3 2 3 4 2 4 6% 71%	2310
	21st to end	Day	2 3 3 3 2 3 2 4 5% 72%	2310
October	1st to 10th	Day	2 2 1 3 2 3 4 3 4 6% 69%	3710
	11th to 20th	Day	2 3 1 2 2 3 4 3 5% 6% 70%	3419
	21st to end	Day	1 2 1 2 2 2 4 4 4 5% 72%	3410
November	1st to 10th	Day	1 4 1 3 3 4 4 3 6% 9% 62%	1854
	11th to 20th	Day	1 3 1 4 3 3 5% 5% 7% 8% 62%	1890
	21st to end	Day	2 4 2 5% 3 4 5% 5% 5% 7% 58%	1890
December	1st to 10th	Day	1 3 1 3 3 3 3 3 6% 9% 66%	3040
	11th to 20th	Day	1 5% 2 5% 4 3 4 4 8% 12% 52%	3499
	21st to end	Day	3 2 6% 6% 6% 7% 6% 8% 11% 45%	4609
January	1st to 10th	Night	4 2 4 4 4 5% 9% 8% 10% 53%	7605
	11th to 20th	Night	2 1 3 2 3 4 4 7% 9% 66%	7650
	21st to end	Night	1 5% 2 6% 4 3 4 3 5% 8% 59%	8370
February	1st to 10th	Night	1 4 2 5% 4 4 4 4 7% 10% 57%	2641
	11th to 20th	Night	1 5% 2 5% 3 5% 6% 5% 7% 9% 51%	2458
	21st to end	Night	1 4 2 5% 4 4 5% 4 6% 9% 56%	2076
March	1st to 10th	Night	1 6% 3 6% 4 5% 6% 5% 5% 6% 53%	5419
	11th to 20th	Night	3 8% 3 6% 4 4 4 7% 7% 9% 46%	5110
	21st to end	Night	2 4 1 4 3 4 5% 5% 6% 10% 57%	5610
April	1st to 10th	Night	3 3 2 4 5% 5% 5% 5% 6% 8% 56%	2179
	11th to 20th	Night	3 6% 2 3 3 4 5% 4 6% 8% 58%	2012
	21st to end	Night	4 4 1 3 3 5% 5% 5% 6% 8% 57%	1890
May	1st to 10th	Night	4 5% 1 4 3 3 4 4 5% 8% 58%	5321
	11th to 20th	Night	3 4 1 4 3 3 3 3 5% 6% 64%	5296
	21st to end	Night	2 3 1 4 3 4 5% 4 6% 8% 60%	5837
June	1st to 10th	Night	3 4 1 3 4 4 4 4 5% 9% 60%	1890
	11th to 20th	Night	2 3 1 4 3 3 3 2 4 6% 69%	1743
	21st to end	Night	2 2 1 4 3 2 3 2 6% 7% 68%	1680
July	1st to 10th	Night	1 1 1 2 2 3 3 3 3 4 79%	4740
	11th to 20th	Night	3 3 2 6% 5% 6% 6% 6% 8% 9% 46%	5210
	21st to end	Night	2 2 1 3 4 5% 5% 4 6% 6% 63%	5805
August	1st to 10th	Night	2 2 1 4 2 3 3 3 4 6% 69%	5273
	11th to 20th	Night	1 1 2 2 3 3 2 4 6% 75%	5291
	21st to end	Night	1 1 1 3 3 4 4 3 6% 8% 65%	6414
September	1st to 10th	Night	3 3 1 3 3 2 4 3 5% 5% 70%	2222
	11th to 20th	Night	2 3 1 3 2 3 4 3 5% 6% 70%	2310
	21st to end	Night	2 2 1 2 2 2 3 2 3 5% 77%	2310
October	1st to 10th	Night	3 2 1 2 2 2 2 2 3 5% 74%	3710
	11th to 20th	Night	3 3 1 3 3 3 3 3 4 6% 68%	3949
	21st to end	Night	2 3 1 3 2 4 3 3 5% 5% 69%	4562
November	1st to 10th	Night	1 4 1 3 2 3 2 3 6% 8% 66%	2665
	11th to 20th	Night	2 3 1 3 2 3 4 3 6% 8% 66%	2730
	21st to end	Night	2 4 1 4 3 3 5% 4 6% 9% 58%	2730
December	1st to 10th	Night	1 2 1 3 2 3 4 3 4 7% 69%	4370
	11th to 20th	Night	1 3 2 4 3 3 4 3 6% 11% 60%	4941
	21st to end	Night	1 4 2 6% 5% 5% 5% 5% 8% 11% 47%	6611

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	18% 6% 25% 34% 16% 2	5321
	11th to 20th	Day	17% 6% 11% 23% 34% 10%	5340
	21st to end	Day	24% 5% 14% 24% 28% 5%	5844
February	1st to 10th	Day	27% 9% 14% 25% 17% 7%	1974
	11th to 20th	Day	28% 8% 13% 22% 22% 7%	2060
	21st to end	Day	25% 8% 15% 25% 21% 6%	1730
March	1st to 10th	Day	31% 9% 6% 21% 20% 14%	4680
	11th to 20th	Day	25% 6% 8% 30% 22% 9%	5110
	21st to end	Day	25% 9% 14% 28% 21% 3	5607
April	1st to 10th	Day	26% 9% 11% 24% 22% 8%	2437
	11th to 20th	Day	25% 8% 9% 24% 26% 8%	2558
	21st to end	Day	25% 8% 9% 24% 29% 5%	2730
May	1st to 10th	Day	19% 5% 7% 24% 35% 10%	7626
	11th to 20th	Day	18% 6% 6% 15% 39% 17%	7599
	21st to end	Day	18% 7% 5% 17% 44% 10%	8371
June	1st to 10th	Day	19% 7% 9% 16% 34% 16%	2730
	11th to 20th	Day	16% 5% 5% 12% 29% 34%	2868
	21st to end	Day	14% 5% 5% 10% 25% 40%	2940
July	1st to 10th	Day	11% 3 2 3 14% 67%	8151
	11th to 20th	Day	20% 5% 6% 12% 18% 38%	7694
	21st to end	Day	14% 4 6% 11% 19% 46%	8120
August	1st to 10th	Day	11% 4 4 11% 28% 42%	5978
	11th to 20th	Day	14% 3 7% 22% 20% 34%	5964
	21st to end	Day	13% 3 5% 16% 32% 31%	6131
September	1st to 10th	Day	18% 5% 5% 10% 29% 33%	2396
	11th to 20th	Day	14% 5% 5% 16% 31% 29%	2310
	21st to end	Day	14% 4 5% 17% 33% 27%	2310
October	1st to 10th	Day	13% 4 5% 9% 36% 33%	3710
	11th to 20th	Day	12% 3 4 20% 38% 23%	3419
	21st to end	Day	12% 3 5% 28% 41% 11%	3410
November	1st to 10th	Day	19% 6% 12% 25% 28% 10%	1854
	11th to 20th	Day	16% 8% 10% 32% 28% 5%	1890
	21st to end	Day	24% 7% 11% 24% 25% 9%	1890
December	1st to 10th	Day	15% 6% 8% 33% 33% 5%	3040
	11th to 20th	Day	24% 6% 15% 28% 22% 5%	3498
	21st to end	Day	26% 8% 18% 24% 21% 4	4609
January	1st to 10th	Night	18% 5% 17% 34% 23% 2	7605
	11th to 20th	Night	15% 6% 12% 25% 30% 12%	7650
	21st to end	Night	23% 5% 11% 21% 32% 7%	8370
February	1st to 10th	Night	23% 8% 15% 29% 18% 7%	2641
	11th to 20th	Night	26% 7% 13% 22% 24% 8%	2459
	21st to end	Night	24% 8% 15% 23% 22% 8%	2076
March	1st to 10th	Night	27% 9% 8% 18% 22% 15%	5419
	11th to 20th	Night	26% 7% 9% 28% 24% 6%	5110
	21st to end	Night	20% 6% 13% 26% 30% 5%	5610
April	1st to 10th	Night	23% 9% 10% 26% 23% 8%	2179
	11th to 20th	Night	21% 7% 10% 27% 28% 7%	2012
	21st to end	Night	21% 7% 11% 23% 30% 7%	1890
May	1st to 10th	Night	21% 6% 7% 21% 31% 13%	5319
	11th to 20th	Night	17% 5% 5% 16% 36% 21%	5297
	21st to end	Night	18% 5% 7% 18% 42% 11%	5838
June	1st to 10th	Night	18% 7% 9% 15% 34% 16%	1890
	11th to 20th	Night	17% 4 5% 11% 28% 35%	1743
	21st to end	Night	14% 4 5% 10% 25% 41%	1680
July	1st to 10th	Night	10% 2 2 4 15% 67%	4700
	11th to 20th	Night	26% 5% 7% 11% 17% 34%	5159
	21st to end	Night	18% 3 8% 11% 17% 43%	5677
August	1st to 10th	Night	17% 4 4 10% 21% 44%	4168
	11th to 20th	Night	12% 3 7% 20% 24% 34%	4168
	21st to end	Night	11% 2 5% 17% 30% 35%	5020
September	1st to 10th	Night	16% 4 7% 12% 28% 33%	2222
	11th to 20th	Night	15% 5% 7% 15% 27% 31%	2310
	21st to end	Night	12% 3 6% 15% 35% 28%	2310
October	1st to 10th	Night	13% 3 4 10% 36% 34%	3710
	11th to 20th	Night	16% 3 4 16% 37% 23%	3949
	21st to end	Night	16% 3 4 22% 41% 14%	4562
November	1st to 10th	Night	17% 7% 10% 29% 25% 11%	2665
	11th to 20th	Night	15% 7% 11% 29% 30% 7%	2730
	21st to end	Night	21% 7% 9% 27% 29% 8%	2730
December	1st to 10th	Night	16% 5% 9% 29% 33% 7%	4370
	11th to 20th	Night	19% 6% 14% 30% 25% 5%	4941
	21st to end	Night	27% 7% 16% 25% 21% 4	6611

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	15% 18% 33% 22% 10% 1	330
	11th to 20th	Day	8% 19% 32% 22% 15% 5%	330
	21st to end	Day	7% 15% 33% 24% 16% 6%	363
February	1st to 10th	Day	12% 19% 33% 19% 14% 2	414
	11th to 20th	Day	15% 19% 33% 21% 10% 1	535
	21st to end	Day	8% 22% 40% 21% 9%	446
March	1st to 10th	Day	12% 22% 29% 24% 11% 2	540
	11th to 20th	Day	12% 21% 32% 21% 11% 3	540
	21st to end	Day	12% 25% 34% 22% 6% 1	594
April	1st to 10th	Day	10% 25% 27% 24% 11% 3	540
	11th to 20th	Day	14% 25% 33% 19% 7% 2	532
	21st to end	Day	16% 25% 29% 19% 9% 2	540
May	1st to 10th	Day	12% 23% 33% 22% 8% 1	543
	11th to 20th	Day	12% 19% 28% 25% 13% 3	568
	21st to end	Day	12% 18% 27% 25% 15% 3	617
June	1st to 10th	Day	5% 13% 31% 31% 17% 4	570
	11th to 20th	Day	9% 18% 36% 24% 11% 2	570
	21st to end	Day	7% 15% 33% 29% 14% 2	570
July	1st to 10th	Day	5% 9% 32% 37% 15% 2	566
	11th to 20th	Day	5% 6% 29% 38% 17% 6%	564
	21st to end	Day	5% 7% 26% 37% 20% 5%	619
August	1st to 10th	Day	5% 8% 32% 36% 16% 4	567
	11th to 20th	Day	5% 10% 30% 31% 19% 5%	557
	21st to end	Day	5% 10% 28% 34% 18% 6%	627
September	1st to 10th	Day	7% 11% 31% 25% 18% 8%	570
	11th to 20th	Day	8% 17% 31% 24% 15% 6%	570
	21st to end	Day	6% 15% 27% 28% 18% 5%	570
October	1st to 10th	Day	7% 17% 29% 25% 15% 7%	570
	11th to 20th	Day	11% 15% 25% 27% 15% 6%	403
	21st to end	Day	12% 13% 28% 27% 16% 4	387
November	1st to 10th	Day	9% 16% 28% 22% 17% 7%	330
	11th to 20th	Day	10% 16% 27% 29% 13% 5%	330
	21st to end	Day	8% 16% 26% 26% 17% 6%	330
December	1st to 10th	Day	9% 14% 28% 32% 13% 5%	330
	11th to 20th	Day	7% 17% 31% 29% 12% 3	330
	21st to end	Day	14% 19% 28% 28% 9% 3	363
January	1st to 10th	Night	9% 10% 30% 28% 16% 7%	840
	11th to 20th	Night	3 10% 29% 31% 21% 5%	840
	21st to end	Night	6% 10% 32% 29% 16% 6%	924
February	1st to 10th	Night	8% 10% 31% 33% 13% 5%	840
	11th to 20th	Night	9% 10% 32% 32% 14% 3	824
	21st to end	Night	6% 13% 30% 35% 13% 2	692
March	1st to 10th	Night	7% 14% 29% 33% 14% 3	840
	11th to 20th	Night	8% 11% 28% 31% 19% 3	840
	21st to end	Night	6% 15% 35% 31% 13% 2	924
April	1st to 10th	Night	7% 13% 29% 33% 14% 3	840
	11th to 20th	Night	9% 15% 31% 30% 14% 2	764
	21st to end	Night	10% 13% 28% 30% 16% 3	630
May	1st to 10th	Night	9% 11% 30% 33% 15% 2	630
	11th to 20th	Night	8% 8% 24% 35% 20% 4	621
	21st to end	Night	12% 9% 26% 29% 21% 3	683
June	1st to 10th	Night	5% 11% 25% 32% 23% 4	630
	11th to 20th	Night	4 13% 29% 35% 18% 1	483
	21st to end	Night	4 8% 21% 40% 25% 3	420
July	1st to 10th	Night	4 3 18% 41% 30% 4	410
	11th to 20th	Night	7% 4 18% 40% 27% 4	563
	21st to end	Night	7% 5% 18% 37% 30% 3	690
August	1st to 10th	Night	7% 4 21% 43% 23% 2	627
	11th to 20th	Night	5% 5% 19% 38% 30% 2	624
	21st to end	Night	5% 4 18% 37% 31% 6%	889
September	1st to 10th	Night	6% 6% 15% 34% 31% 8%	840
	11th to 20th	Night	6% 9% 17% 31% 28% 9%	840
	21st to end	Night	4 5% 19% 30% 30% 11%	840
October	1st to 10th	Night	7% 8% 19% 35% 24% 7%	840
	11th to 20th	Night	9% 8% 19% 32% 24% 8%	840
	21st to end	Night	5% 8% 25% 31% 23% 8%	912
November	1st to 10th	Night	5% 11% 19% 35% 22% 8%	820
	11th to 20th	Night	6% 9% 25% 35% 18% 7%	840
	21st to end	Night	7% 9% 27% 26% 23% 8%	840
December	1st to 10th	Night	5% 9% 32% 31% 18% 6%	840
	11th to 20th	Night	5% 9% 32% 33% 17% 3	840
	21st to end	Night	8% 13% 32% 33% 11% 2	924

Page generated at 2026-10-26 01:37:46. Version ac07

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