High Desert Astronomy
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the High Desert Astronomy clear sky chart from 2005-11-06 to 2026-09-29.

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 2 1 2 2 2 2 2 4 5% 77%	158338
	Night	3 2 1 2 2 2 2 2 4 5% 75%	150759
Transparency	Day	11% 2 5% 12% 27% 43%	153341
	Night	13% 2 5% 14% 27% 39%	146753
Seeing	Day	4 10% 24% 32% 21% 9%	18008
	Night	4 5% 19% 36% 29% 6%	27712

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 3 1 3 2 3 3 3 5% 7% 67%	5318
	11th to 20th	Day	2 1 1 2 2 1 2 2 3 5% 78%	5340
	21st to end	Day	5% 4 1 4 3 3 3 3 5% 6% 61%	6178
February	1st to 10th	Day	7% 3 1 3 2 2 2 3 5% 6% 67%	2100
	11th to 20th	Day	6% 3 2 2 3 4 3 4 7% 65%	2050
	21st to end	Day	5% 3 1 3 2 3 2 3 4 7% 65%	1730
March	1st to 10th	Day	6% 4 1 4 3 2 3 3 5% 6% 63%	4618
	11th to 20th	Day	4 3 1 3 3 3 3 3 5% 7% 64%	4991
	21st to end	Day	4 2 1 3 2 3 4 3 6% 8% 65%	5726
April	1st to 10th	Day	2 3 1 3 2 3 3 3 4 6% 71%	2520
	11th to 20th	Day	2 2 1 2 2 2 3 2 4 6% 75%	2489
	21st to end	Day	2 2 2 2 2 3 3 4 5% 77%	2620
May	1st to 10th	Day	1 2 1 2 2 2 2 2 3 4 78%	7626
	11th to 20th	Day	1 1 1 1 1 2 2 3 5% 83%	7596
	21st to end	Day	1 1 1 1 1 1 2 3 4 85%	8370
June	1st to 10th	Day	1 1 1 2 2 1 2 2 3 5% 81%	2730
	11th to 20th	Day	1 1 1 1 1 2 3 88%	2807
	21st to end	Day	1 1 1 1 1 2 1 2 3 86%	2940
July	1st to 10th	Day	1 1 1 1 1 1 2 3 88%	8219
	11th to 20th	Day	2 1 1 2 2 2 3 2 5% 6% 75%	7690
	21st to end	Day	1 1 1 1 1 1 1 2 4 85%	8304
August	1st to 10th	Day	1 1 1 1 1 1 1 3 4 85%	7408
	11th to 20th	Day	1 1 1 1 2 1 2 4 86%	7001
	21st to end	Day	1 2 1 2 1 2 2 2 3 4 80%	7750
September	1st to 10th	Day	2 2 1 2 2 2 2 2 3 4 78%	2468
	11th to 20th	Day	1 1 1 1 1 2 1 2 3 86%	2310
	21st to end	Day	1 1 2 1 1 2 2 3 4 85%	2289
October	1st to 10th	Day	1 1 1 1 1 1 1 3 3 86%	3600
	11th to 20th	Day	1 1 1 2 1 1 1 1 2 4 85%	3552
	21st to end	Day	1 1 2 1 1 2 2 3 5% 82%	3216
November	1st to 10th	Day	2 3 1 1 2 2 1 2 4 6% 78%	1854
	11th to 20th	Day	3 2 1 2 1 2 2 2 3 5% 76%	1890
	21st to end	Day	4 2 1 3 2 2 2 3 4 6% 71%	1890
December	1st to 10th	Day	2 1 1 2 2 2 3 3 6% 6% 70%	3040
	11th to 20th	Day	5% 3 1 3 3 3 4 3 6% 10% 59%	3499
	21st to end	Day	4 3 1 4 3 3 5% 5% 7% 9% 57%	4609
January	1st to 10th	Night	7% 4 1 3 2 2 2 2 4 5% 66%	7605
	11th to 20th	Night	2 1 1 2 2 2 2 2 3 5% 80%	7650
	21st to end	Night	7% 3 1 3 2 3 3 3 5% 7% 62%	8051
February	1st to 10th	Night	6% 4 1 3 3 2 2 3 4 5% 65%	2520
	11th to 20th	Night	5% 3 1 4 3 3 3 3 4 7% 65%	2458
	21st to end	Night	5% 3 1 3 3 2 2 2 5% 7% 67%	2076
March	1st to 10th	Night	6% 4 1 2 2 2 3 3 5% 7% 65%	5496
	11th to 20th	Night	4 3 1 3 3 4 4 4 6% 8% 61%	5228
	21st to end	Night	4 2 1 2 2 3 3 3 4 6% 70%	5487
April	1st to 10th	Night	3 2 1 3 3 3 3 2 3 6% 73%	2100
	11th to 20th	Night	2 2 1 2 1 2 3 3 5% 5% 75%	2079
	21st to end	Night	2 1 1 1 2 2 2 4 6% 79%	2000
May	1st to 10th	Night	2 2 1 2 1 2 2 2 3 5% 78%	5321
	11th to 20th	Night	1 1 1 1 1 1 2 3 4 85%	5296
	21st to end	Night	1 1 1 1 2 2 1 3 4 84%	5837
June	1st to 10th	Night	1 1 1 1 1 1 1 1 3 5% 83%	1890
	11th to 20th	Night	1 1 1 1 1 1 1 3 3 86%	1803
	21st to end	Night	1 1 1 1 1 1 2 3 89%	1680
July	1st to 10th	Night	1 1 1 1 1 1 2 2 89%	4740
	11th to 20th	Night	1 1 2 1 2 2 2 4 5% 79%	5275
	21st to end	Night	1 1 1 1 1 1 2 1 3 4 82%	5805
August	1st to 10th	Night	1 1 1 1 1 1 2 3 4 85%	5406
	11th to 20th	Night	1 1 1 2 2 2 3 4 84%	5886
	21st to end	Night	1 1 1 2 1 2 2 2 3 5% 79%	6499
September	1st to 10th	Night	1 2 1 2 2 2 2 2 3 4 79%	2152
	11th to 20th	Night	1 2 1 1 2 1 3 3 86%	2310
	21st to end	Night	1 1 1 1 1 2 2 2 3 86%	2288
October	1st to 10th	Night	1 1 1 1 1 1 1 2 3 86%	3600
	11th to 20th	Night	1 1 1 1 1 2 2 3 4 85%	3605
	21st to end	Night	1 1 2 1 1 2 2 4 4 82%	4569
November	1st to 10th	Night	1 2 1 2 2 2 2 1 3 5% 79%	2665
	11th to 20th	Night	3 1 1 2 2 2 2 2 4 5% 74%	2730
	21st to end	Night	3 3 1 3 2 2 3 2 4 5% 72%	2730
December	1st to 10th	Night	3 2 2 2 2 3 3 4 7% 71%	4370
	11th to 20th	Night	5% 2 1 3 2 3 2 3 5% 9% 65%	4941
	21st to end	Night	4 3 1 4 4 4 4 3 6% 10% 56%	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% 4 10% 26% 30% 12%	5321
	11th to 20th	Day	11% 3 8% 16% 30% 32%	5340
	21st to end	Day	22% 3 6% 19% 32% 18%	6178
February	1st to 10th	Day	20% 3 7% 17% 33% 21%	2100
	11th to 20th	Day	19% 3 6% 17% 34% 20%	2060
	21st to end	Day	19% 3 9% 19% 28% 22%	1730
March	1st to 10th	Day	21% 2 5% 19% 27% 25%	4618
	11th to 20th	Day	20% 4 7% 22% 29% 18%	4991
	21st to end	Day	15% 3 11% 20% 34% 18%	5726
April	1st to 10th	Day	16% 2 6% 18% 30% 28%	2520
	11th to 20th	Day	12% 3 5% 16% 30% 35%	2492
	21st to end	Day	11% 2 5% 14% 36% 31%	2620
May	1st to 10th	Day	10% 2 5% 12% 32% 39%	7626
	11th to 20th	Day	6% 1 3 7% 29% 54%	7599
	21st to end	Day	6% 1 3 8% 34% 48%	8371
June	1st to 10th	Day	9% 2 3 9% 25% 52%	2730
	11th to 20th	Day	4 1 2 6% 17% 70%	2807
	21st to end	Day	6% 1 2 4 13% 74%	2940
July	1st to 10th	Day	5% 1 2 3 9% 80%	8151
	11th to 20th	Day	11% 1 4 8% 16% 59%	7620
	21st to end	Day	6% 2 2 7% 20% 63%	8120
August	1st to 10th	Day	7% 1 2 6% 28% 56%	5871
	11th to 20th	Day	7% 1 2 10% 26% 53%	5517
	21st to end	Day	7% 1 2 5% 26% 60%	6077
September	1st to 10th	Day	11% 2 3 8% 18% 57%	2468
	11th to 20th	Day	6% 1 3 6% 26% 58%	2310
	21st to end	Day	6% 1 3 8% 27% 55%	2289
October	1st to 10th	Day	6% 2 3 6% 21% 62%	3600
	11th to 20th	Day	7% 1 2 7% 34% 49%	3552
	21st to end	Day	9% 1 2 8% 35% 45%	3216
November	1st to 10th	Day	10% 1 5% 13% 42% 30%	1854
	11th to 20th	Day	14% 2 6% 15% 34% 29%	1890
	21st to end	Day	15% 2 6% 20% 33% 24%	1890
December	1st to 10th	Day	14% 3 7% 15% 36% 25%	3040
	11th to 20th	Day	20% 3 10% 24% 34% 9%	3498
	21st to end	Day	21% 6% 13% 31% 22% 7%	4609
January	1st to 10th	Night	21% 3 8% 24% 31% 13%	7605
	11th to 20th	Night	10% 2 6% 19% 31% 31%	7650
	21st to end	Night	23% 2 6% 16% 31% 22%	8051
February	1st to 10th	Night	23% 2 7% 16% 29% 22%	2520
	11th to 20th	Night	20% 3 6% 18% 28% 24%	2459
	21st to end	Night	17% 3 8% 19% 30% 22%	2076
March	1st to 10th	Night	18% 3 7% 17% 29% 26%	5496
	11th to 20th	Night	20% 5% 8% 25% 27% 16%	5228
	21st to end	Night	15% 2 7% 20% 36% 20%	5487
April	1st to 10th	Night	14% 3 5% 19% 29% 29%	2100
	11th to 20th	Night	12% 3 5% 17% 32% 32%	2079
	21st to end	Night	8% 2 5% 16% 35% 34%	2000
May	1st to 10th	Night	12% 2 4 10% 30% 42%	5319
	11th to 20th	Night	6% 1 3 7% 27% 57%	5297
	21st to end	Night	7% 1 2 5% 32% 53%	5838
June	1st to 10th	Night	6% 2 3 9% 23% 57%	1890
	11th to 20th	Night	6% 1 2 6% 16% 68%	1803
	21st to end	Night	5% 1 1 4 11% 77%	1680
July	1st to 10th	Night	5% 1 2 2 8% 82%	4700
	11th to 20th	Night	9% 1 4 10% 19% 58%	5223
	21st to end	Night	7% 1 2 8% 19% 62%	5677
August	1st to 10th	Night	8% 1 2 6% 24% 59%	4276
	11th to 20th	Night	9% 2 3 11% 26% 50%	4636
	21st to end	Night	7% 1 2 5% 25% 59%	5092
September	1st to 10th	Night	10% 2 4 8% 17% 59%	2152
	11th to 20th	Night	7% 1 3 7% 23% 59%	2310
	21st to end	Night	7% 1 2 7% 24% 59%	2288
October	1st to 10th	Night	6% 1 3 6% 16% 68%	3600
	11th to 20th	Night	6% 1 2 6% 26% 59%	3605
	21st to end	Night	8% 1 3 8% 30% 49%	4569
November	1st to 10th	Night	11% 1 4 15% 36% 33%	2665
	11th to 20th	Night	13% 2 5% 15% 33% 32%	2730
	21st to end	Night	15% 3 5% 16% 30% 30%	2730
December	1st to 10th	Night	14% 2 5% 16% 38% 24%	4370
	11th to 20th	Night	16% 3 9% 24% 37% 11%	4941
	21st to end	Night	23% 4 14% 30% 23% 7%	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	11% 12% 23% 32% 17% 5%	330
	11th to 20th	Day	9% 7% 21% 33% 22% 8%	330
	21st to end	Day	8% 10% 18% 30% 25% 9%	479
February	1st to 10th	Day	9% 16% 24% 29% 16% 6%	540
	11th to 20th	Day	10% 16% 29% 27% 15% 4	535
	21st to end	Day	9% 17% 24% 32% 15% 3	446
March	1st to 10th	Day	10% 20% 29% 23% 15% 3	540
	11th to 20th	Day	8% 15% 34% 24% 13% 6%	540
	21st to end	Day	7% 19% 33% 23% 13% 5%	594
April	1st to 10th	Day	5% 16% 27% 30% 16% 6%	540
	11th to 20th	Day	5% 23% 32% 24% 12% 4	532
	21st to end	Day	4 18% 33% 26% 15% 4	540
May	1st to 10th	Day	4 12% 34% 27% 14% 8%	543
	11th to 20th	Day	2 13% 30% 30% 18% 6%	568
	21st to end	Day	2 12% 27% 35% 17% 7%	617
June	1st to 10th	Day	2 8% 26% 35% 21% 8%	570
	11th to 20th	Day	1 8% 25% 34% 22% 9%	570
	21st to end	Day	1 8% 25% 37% 20% 10%	570
July	1st to 10th	Day	1 2 22% 40% 23% 11%	566
	11th to 20th	Day	2 1 13% 41% 28% 15%	564
	21st to end	Day	1 2 12% 47% 24% 14%	619
August	1st to 10th	Day	2 4 19% 39% 25% 13%	567
	11th to 20th	Day	2 2 17% 39% 26% 15%	557
	21st to end	Day	2 3 19% 39% 26% 12%	627
September	1st to 10th	Day	2 6% 17% 36% 27% 12%	570
	11th to 20th	Day	1 8% 23% 37% 23% 8%	570
	21st to end	Day	2 8% 21% 33% 28% 8%	563
October	1st to 10th	Day	2 9% 26% 28% 23% 12%	530
	11th to 20th	Day	2 8% 22% 30% 30% 8%	515
	21st to end	Day	3 7% 18% 30% 25% 17%	363
November	1st to 10th	Day	3 14% 18% 24% 28% 13%	330
	11th to 20th	Day	7% 8% 15% 36% 25% 10%	330
	21st to end	Day	5% 6% 18% 30% 30% 10%	330
December	1st to 10th	Day	4 5% 19% 40% 22% 10%	330
	11th to 20th	Day	4 8% 19% 32% 27% 11%	330
	21st to end	Day	9% 12% 22% 34% 19% 3	363
January	1st to 10th	Night	8% 8% 20% 33% 23% 8%	840
	11th to 20th	Night	4 5% 19% 40% 26% 6%	840
	21st to end	Night	9% 5% 23% 35% 22% 6%	924
February	1st to 10th	Night	8% 7% 24% 33% 24% 4	840
	11th to 20th	Night	7% 8% 26% 37% 17% 4	824
	21st to end	Night	7% 9% 28% 35% 17% 4	692
March	1st to 10th	Night	5% 10% 30% 36% 15% 4	840
	11th to 20th	Night	6% 8% 26% 32% 22% 7%	840
	21st to end	Night	5% 12% 25% 37% 18% 3	924
April	1st to 10th	Night	4 9% 25% 35% 23% 4	840
	11th to 20th	Night	3 11% 30% 33% 19% 4	831
	21st to end	Night	3 6% 28% 38% 20% 5%	740
May	1st to 10th	Night	4 6% 27% 40% 21% 2	630
	11th to 20th	Night	2 8% 20% 36% 30% 4	621
	21st to end	Night	2 8% 19% 39% 28% 3	683
June	1st to 10th	Night	1 5% 19% 39% 33% 3	630
	11th to 20th	Night	1 4 22% 37% 33% 3	543
	21st to end	Night	1 1 16% 40% 37% 5%	420
July	1st to 10th	Night	1 1 8% 43% 42% 6%	410
	11th to 20th	Night	2 1 7% 42% 44% 5%	588
	21st to end	Night	2 1 5% 39% 48% 3	690
August	1st to 10th	Night	1 1 10% 44% 40% 3	670
	11th to 20th	Night	1 1 6% 35% 49% 8%	832
	21st to end	Night	2 1 10% 32% 43% 11%	924
September	1st to 10th	Night	2 2 11% 31% 43% 11%	840
	11th to 20th	Night	1 1 15% 39% 38% 7%	840
	21st to end	Night	1 3 14% 35% 35% 12%	832
October	1st to 10th	Night	2 3 20% 38% 29% 7%	800
	11th to 20th	Night	2 4 17% 36% 30% 11%	800
	21st to end	Night	2 7% 17% 32% 32% 10%	880
November	1st to 10th	Night	2 5% 17% 34% 32% 10%	820
	11th to 20th	Night	3 3 17% 40% 29% 7%	840
	21st to end	Night	4 5% 21% 34% 30% 7%	840
December	1st to 10th	Night	6% 5% 17% 40% 26% 7%	840
	11th to 20th	Night	8% 4 21% 36% 24% 7%	840
	21st to end	Night	7% 11% 20% 37% 20% 4	924

Page generated at 2026-09-26 01:18:41. Version ac07

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