Wild Horse Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wild Horse Observatory clear sky chart from 2005-11-06 to 2026-04-02.

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 5% 2 7% 5% 5% 5% 4 6% 7% 52%	139694
	Night	2 5% 2 7% 5% 5% 5% 4 6% 7% 51%	139496
Transparency	Day	28% 7% 9% 18% 22% 16%	134538
	Night	28% 8% 10% 19% 22% 13%	135645
Seeing	Day	8% 15% 29% 27% 16% 5%	16368
	Night	6% 9% 21% 36% 23% 4	25921

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 9% 4 11% 7% 8% 9% 7% 9% 9% 25%	4722
	11th to 20th	Day	1 4 3 10% 6% 6% 6% 4 5% 9% 47%	4740
	21st to end	Day	1 6% 4 10% 7% 6% 7% 5% 6% 9% 38%	5246
February	1st to 10th	Day	2 6% 3 10% 7% 7% 7% 5% 9% 10% 32%	1993
	11th to 20th	Day	1 8% 3 12% 7% 7% 6% 5% 9% 9% 32%	2050
	21st to end	Day	1 7% 3 11% 7% 8% 6% 5% 8% 9% 36%	1730
March	1st to 10th	Day	1 10% 6% 13% 7% 7% 6% 5% 6% 7% 32%	4618
	11th to 20th	Day	1 8% 3 9% 6% 5% 5% 5% 6% 9% 43%	4970
	21st to end	Day	2 7% 4 10% 8% 8% 8% 6% 8% 8% 30%	5775
April	1st to 10th	Day	2 8% 4 10% 6% 6% 7% 5% 7% 9% 36%	2413
	11th to 20th	Day	3 7% 2 9% 6% 5% 5% 5% 7% 8% 44%	2399
	21st to end	Day	4 8% 3 7% 6% 4 5% 4 6% 7% 48%	2600
May	1st to 10th	Day	3 6% 3 8% 5% 5% 5% 3 5% 7% 50%	5880
	11th to 20th	Day	4 6% 3 6% 4 4 5% 3 4 6% 56%	5841
	21st to end	Day	3 4 1 5% 4 5% 5% 4 6% 7% 56%	6764
June	1st to 10th	Day	5% 6% 2 6% 4 4 5% 4 6% 8% 49%	2800
	11th to 20th	Day	4 4 2 4 4 4 3 3 6% 6% 61%	2800
	21st to end	Day	2 3 1 4 3 3 4 3 5% 6% 67%	2800
July	1st to 10th	Day	1 2 1 2 2 3 3 3 4 4 75%	6319
	11th to 20th	Day	2 2 1 3 3 3 4 3 5% 6% 68%	6320
	21st to end	Day	3 3 1 4 3 4 4 4 6% 8% 60%	6823
August	1st to 10th	Day	3 2 1 4 3 3 3 3 4 7% 67%	5779
	11th to 20th	Day	2 1 1 3 2 3 3 3 5% 6% 71%	5756
	21st to end	Day	5% 4 2 5% 3 3 3 3 4 5% 64%	5984
September	1st to 10th	Day	2 3 1 5% 3 3 3 3 4 5% 68%	2383
	11th to 20th	Day	3 4 2 5% 4 3 4 3 5% 5% 63%	2200
	21st to end	Day	3 4 1 5% 3 3 3 3 3 6% 66%	2200
October	1st to 10th	Day	3 4 2 4 4 4 3 3 4 6% 64%	3600
	11th to 20th	Day	2 6% 2 4 3 3 3 3 5% 6% 63%	3246
	21st to end	Day	2 4 3 6% 4 4 5% 4 6% 10% 53%	3200
November	1st to 10th	Day	3 8% 3 8% 6% 5% 5% 4 7% 7% 44%	1854
	11th to 20th	Day	3 7% 2 7% 6% 5% 5% 6% 8% 11% 40%	1890
	21st to end	Day	2 7% 3 11% 6% 6% 6% 4 5% 8% 41%	1890
December	1st to 10th	Day	1 4 2 6% 4 4 5% 4 6% 8% 55%	2909
	11th to 20th	Day	2 11% 4 10% 7% 6% 6% 5% 7% 8% 32%	3108
	21st to end	Day	2 9% 5% 12% 7% 8% 8% 6% 8% 8% 27%	4092
January	1st to 10th	Night	2 10% 5% 12% 7% 7% 8% 6% 9% 8% 27%	8172
	11th to 20th	Night	1 5% 2 10% 6% 6% 6% 5% 6% 7% 47%	8220
	21st to end	Night	2 7% 3 9% 5% 5% 6% 5% 6% 9% 44%	8924
February	1st to 10th	Night	2 7% 3 9% 6% 6% 6% 6% 8% 10% 37%	2625
	11th to 20th	Night	1 7% 3 9% 7% 6% 6% 6% 8% 8% 38%	2458
	21st to end	Night	1 7% 3 8% 7% 6% 8% 6% 9% 9% 36%	2076
March	1st to 10th	Night	1 8% 5% 12% 7% 6% 5% 5% 5% 7% 38%	5496
	11th to 20th	Night	1 6% 3 8% 5% 5% 6% 4 6% 8% 49%	5249
	21st to end	Night	2 7% 2 6% 5% 5% 5% 4 7% 10% 46%	5436
April	1st to 10th	Night	3 7% 3 7% 5% 5% 6% 4 6% 8% 45%	2010
	11th to 20th	Night	3 6% 2 7% 5% 4 5% 5% 7% 7% 49%	1949
	21st to end	Night	4 6% 2 6% 4 5% 5% 4 6% 8% 50%	1800
May	1st to 10th	Night	4 5% 2 5% 4 3 4 3 5% 8% 59%	4100
	11th to 20th	Night	4 7% 2 5% 3 4 4 3 5% 7% 57%	4074
	21st to end	Night	2 4 2 4 3 3 4 3 5% 7% 63%	4112
June	1st to 10th	Night	5% 4 1 5% 5% 4 4 4 6% 7% 55%	1600
	11th to 20th	Night	4 4 2 4 3 3 4 3 5% 7% 61%	1600
	21st to end	Night	2 2 1 3 3 3 4 4 4 6% 70%	1600
July	1st to 10th	Night	2 2 1 3 2 2 3 4 4 4 73%	3640
	11th to 20th	Night	1 2 1 4 3 3 3 3 4 6% 69%	3640
	21st to end	Night	2 2 1 3 3 4 4 4 7% 8% 61%	4015
August	1st to 10th	Night	2 2 1 4 3 3 4 3 5% 6% 69%	4033
	11th to 20th	Night	2 2 1 3 2 3 3 3 4 5% 71%	4091
	21st to end	Night	4 4 2 5% 3 3 3 3 4 5% 66%	5015
September	1st to 10th	Night	3 2 1 4 2 3 3 3 4 6% 68%	2016
	11th to 20th	Night	4 2 2 3 2 3 3 3 4 6% 66%	2200
	21st to end	Night	3 2 2 3 3 2 3 2 4 5% 70%	2200
October	1st to 10th	Night	3 3 1 3 2 3 2 2 4 4 72%	3600
	11th to 20th	Night	4 5% 2 5% 3 4 4 4 4 5% 60%	3903
	21st to end	Night	2 4 2 6% 4 4 5% 4 6% 8% 57%	4600
November	1st to 10th	Night	5% 8% 2 5% 4 5% 6% 5% 8% 8% 45%	2665
	11th to 20th	Night	2 6% 2 6% 5% 5% 6% 5% 9% 9% 45%	2730
	21st to end	Night	1 6% 2 7% 6% 6% 6% 5% 10% 10% 42%	2730
December	1st to 10th	Night	2 4 2 6% 5% 4 5% 4 5% 9% 54%	4495
	11th to 20th	Night	2 9% 4 10% 7% 7% 7% 6% 7% 10% 31%	5316
	21st to end	Night	3 9% 4 12% 9% 8% 9% 6% 8% 8% 24%	7106

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	44% 14% 18% 15% 9% 1	4723
	11th to 20th	Day	33% 8% 8% 20% 26% 6%	4740
	21st to end	Day	37% 9% 9% 19% 19% 7%	5246
February	1st to 10th	Day	40% 13% 12% 20% 12% 4	1993
	11th to 20th	Day	42% 10% 13% 17% 13% 4	2060
	21st to end	Day	42% 10% 13% 20% 11% 5%	1730
March	1st to 10th	Day	46% 10% 9% 16% 14% 6%	4618
	11th to 20th	Day	33% 10% 13% 29% 15% 2	4970
	21st to end	Day	44% 13% 16% 18% 8% 2	5775
April	1st to 10th	Day	40% 12% 13% 19% 11% 5%	2413
	11th to 20th	Day	35% 9% 12% 22% 18% 4	2402
	21st to end	Day	34% 8% 12% 26% 19% 2	2600
May	1st to 10th	Day	30% 7% 10% 23% 26% 4	5880
	11th to 20th	Day	26% 7% 7% 25% 29% 6%	5844
	21st to end	Day	23% 7% 9% 27% 30% 5%	6765
June	1st to 10th	Day	31% 8% 11% 22% 25% 4	2800
	11th to 20th	Day	23% 4 8% 18% 31% 17%	2800
	21st to end	Day	17% 3 6% 16% 34% 24%	2800
July	1st to 10th	Day	12% 3 4 6% 20% 55%	6251
	11th to 20th	Day	15% 4 4 4 23% 50%	6245
	21st to end	Day	17% 5% 5% 9% 30% 35%	6625
August	1st to 10th	Day	20% 3 4 9% 23% 42%	4208
	11th to 20th	Day	13% 2 6% 6% 27% 46%	4167
	21st to end	Day	15% 2 4 10% 28% 41%	4311
September	1st to 10th	Day	18% 3 6% 10% 29% 34%	2383
	11th to 20th	Day	21% 4 8% 15% 30% 21%	2200
	21st to end	Day	20% 3 7% 17% 34% 20%	2200
October	1st to 10th	Day	22% 3 6% 15% 31% 23%	3600
	11th to 20th	Day	22% 4 5% 24% 31% 14%	3246
	21st to end	Day	22% 8% 10% 30% 23% 8%	3200
November	1st to 10th	Day	36% 9% 11% 21% 20% 4	1854
	11th to 20th	Day	33% 9% 13% 27% 15% 2	1890
	21st to end	Day	37% 8% 13% 19% 17% 6%	1890
December	1st to 10th	Day	25% 7% 9% 26% 29% 4	2909
	11th to 20th	Day	43% 10% 14% 20% 9% 2	3108
	21st to end	Day	42% 12% 15% 19% 11% 2	4092
January	1st to 10th	Night	43% 15% 15% 17% 10% 1	8172
	11th to 20th	Night	34% 8% 8% 18% 24% 8%	8220
	21st to end	Night	32% 7% 10% 19% 26% 6%	8924
February	1st to 10th	Night	36% 12% 13% 24% 12% 3	2625
	11th to 20th	Night	36% 11% 14% 20% 13% 6%	2459
	21st to end	Night	37% 11% 14% 22% 10% 6%	2076
March	1st to 10th	Night	42% 9% 9% 17% 13% 10%	5496
	11th to 20th	Night	28% 9% 11% 25% 24% 2	5249
	21st to end	Night	30% 11% 19% 26% 11% 2	5436
April	1st to 10th	Night	33% 11% 14% 24% 15% 4	2010
	11th to 20th	Night	31% 9% 12% 22% 21% 4	1949
	21st to end	Night	29% 9% 14% 24% 23% 1	1800
May	1st to 10th	Night	24% 5% 11% 24% 32% 4	4097
	11th to 20th	Night	25% 7% 7% 28% 29% 5%	4075
	21st to end	Night	20% 5% 8% 31% 31% 4	4112
June	1st to 10th	Night	26% 6% 14% 26% 25% 3	1600
	11th to 20th	Night	22% 5% 9% 19% 28% 17%	1600
	21st to end	Night	16% 3 6% 15% 35% 25%	1600
July	1st to 10th	Night	15% 3 4 7% 20% 52%	3600
	11th to 20th	Night	15% 3 4 5% 21% 52%	3592
	21st to end	Night	16% 5% 4 12% 28% 35%	3901
August	1st to 10th	Night	20% 4 4 10% 22% 40%	2928
	11th to 20th	Night	15% 3 4 7% 31% 40%	2955
	21st to end	Night	15% 2 4 10% 24% 45%	3608
September	1st to 10th	Night	18% 3 5% 11% 30% 33%	2016
	11th to 20th	Night	18% 4 8% 17% 29% 24%	2200
	21st to end	Night	17% 3 6% 16% 34% 23%	2200
October	1st to 10th	Night	16% 4 4 14% 35% 26%	3600
	11th to 20th	Night	23% 7% 6% 19% 33% 12%	3903
	21st to end	Night	22% 7% 9% 28% 29% 6%	4600
November	1st to 10th	Night	32% 9% 12% 20% 21% 6%	2665
	11th to 20th	Night	29% 10% 14% 24% 19% 3	2730
	21st to end	Night	31% 10% 13% 21% 19% 5%	2730
December	1st to 10th	Night	24% 7% 11% 27% 28% 3	4495
	11th to 20th	Night	40% 12% 14% 17% 13% 3	5316
	21st to end	Night	45% 10% 16% 16% 11% 3	7106

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	12% 20% 29% 25% 13% 2	220
	11th to 20th	Day	6% 16% 30% 21% 16% 10%	220
	21st to end	Day	4 13% 30% 30% 17% 7%	253
February	1st to 10th	Day	8% 27% 27% 22% 12% 3	433
	11th to 20th	Day	8% 21% 35% 24% 10% 1	535
	21st to end	Day	9% 22% 31% 28% 9% 1	446
March	1st to 10th	Day	11% 19% 34% 27% 9% 1	540
	11th to 20th	Day	7% 21% 32% 26% 12% 2	540
	21st to end	Day	10% 21% 38% 21% 8% 1	594
April	1st to 10th	Day	8% 25% 27% 24% 15% 2	505
	11th to 20th	Day	7% 25% 35% 20% 10% 4	492
	21st to end	Day	9% 19% 29% 28% 12% 2	500
May	1st to 10th	Day	7% 21% 32% 24% 12% 5%	503
	11th to 20th	Day	15% 13% 30% 27% 12% 3	528
	21st to end	Day	10% 14% 21% 28% 20% 8%	573
June	1st to 10th	Day	8% 13% 24% 30% 19% 6%	530
	11th to 20th	Day	9% 17% 34% 24% 14% 3	530
	21st to end	Day	3 7% 35% 31% 18% 5%	530
July	1st to 10th	Day	2 8% 30% 37% 17% 6%	526
	11th to 20th	Day	3 6% 31% 35% 19% 6%	524
	21st to end	Day	6% 4 29% 32% 20% 9%	575
August	1st to 10th	Day	7% 7% 26% 35% 17% 7%	527
	11th to 20th	Day	5% 6% 28% 32% 21% 9%	517
	21st to end	Day	4 8% 28% 30% 20% 10%	583
September	1st to 10th	Day	5% 8% 26% 29% 21% 12%	530
	11th to 20th	Day	5% 12% 27% 27% 21% 9%	530
	21st to end	Day	7% 10% 28% 26% 24% 5%	530
October	1st to 10th	Day	7% 14% 23% 25% 23% 8%	530
	11th to 20th	Day	9% 15% 22% 23% 24% 7%	420
	21st to end	Day	8% 15% 28% 27% 17% 4	363
November	1st to 10th	Day	12% 15% 24% 26% 20% 3	330
	11th to 20th	Day	8% 15% 25% 29% 18% 5%	330
	21st to end	Day	9% 14% 24% 29% 19% 5%	330
December	1st to 10th	Day	7% 15% 25% 29% 13% 9%	289
	11th to 20th	Day	10% 15% 32% 26% 13% 4	220
	21st to end	Day	17% 18% 21% 26% 13% 4	242
January	1st to 10th	Night	8% 14% 24% 31% 19% 5%	840
	11th to 20th	Night	5% 15% 21% 32% 22% 5%	840
	21st to end	Night	7% 10% 21% 36% 20% 6%	924
February	1st to 10th	Night	6% 15% 28% 28% 18% 4	840
	11th to 20th	Night	5% 13% 26% 38% 16% 2	824
	21st to end	Night	4 13% 30% 34% 16% 3	692
March	1st to 10th	Night	6% 12% 30% 35% 14% 3	840
	11th to 20th	Night	6% 9% 27% 35% 21% 2	840
	21st to end	Night	7% 15% 28% 33% 15% 1	924
April	1st to 10th	Night	8% 10% 28% 33% 18% 3	804
	11th to 20th	Night	6% 14% 28% 33% 15% 3	761
	21st to end	Night	8% 10% 28% 33% 19% 3	600
May	1st to 10th	Night	7% 12% 26% 34% 21% 2	600
	11th to 20th	Night	11% 7% 22% 32% 24% 3	591
	21st to end	Night	7% 6% 22% 33% 27% 4	496
June	1st to 10th	Night	5% 4 20% 37% 29% 5%	400
	11th to 20th	Night	7% 4 19% 45% 25%	400
	21st to end	Night	2 3 15% 49% 28% 3	400
July	1st to 10th	Night	3 1 10% 52% 28% 5%	390
	11th to 20th	Night	4 1 12% 51% 31% 2	388
	21st to end	Night	3 1 7% 46% 39% 3	458
August	1st to 10th	Night	5% 2 14% 47% 29% 3	597
	11th to 20th	Night	2 2 12% 47% 34% 3	608
	21st to end	Night	4 1 13% 43% 34% 5%	880
September	1st to 10th	Night	5% 2 11% 40% 36% 6%	800
	11th to 20th	Night	5% 3 11% 35% 36% 10%	800
	21st to end	Night	5% 5% 13% 35% 32% 11%	800
October	1st to 10th	Night	8% 5% 18% 34% 29% 6%	800
	11th to 20th	Night	6% 9% 17% 34% 29% 6%	800
	21st to end	Night	4 9% 19% 38% 24% 6%	880
November	1st to 10th	Night	9% 9% 20% 34% 23% 6%	820
	11th to 20th	Night	7% 9% 26% 36% 18% 4	840
	21st to end	Night	5% 10% 23% 32% 24% 6%	840
December	1st to 10th	Night	7% 11% 25% 34% 18% 5%	840
	11th to 20th	Night	9% 11% 24% 36% 16% 4	840
	21st to end	Night	12% 15% 28% 31% 11% 2	924

Page generated at 2026-03-29 23:18:40. Version ac07

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