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 2024-12-09.

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	3 5% 2 7% 5% 5% 5% 4 6% 7% 51%	105331
	Night	3 6% 2 7% 5% 5% 5% 4 6% 7% 50%	103145
Transparency	Day	30% 7% 9% 17% 20% 17%	105077
	Night	31% 7% 10% 18% 20% 14%	102989
Seeing	Day	8% 15% 29% 28% 16% 5%	14732
	Night	6% 9% 21% 36% 23% 4	24198

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 8% 3 11% 8% 9% 8% 8% 10% 11% 23%	2539
	11th to 20th	Day	1 7% 5% 12% 9% 9% 10% 6% 7% 6% 28%	2540
	21st to end	Day	3 10% 5% 14% 7% 7% 7% 5% 6% 8% 26%	2825
February	1st to 10th	Day	2 6% 3 11% 7% 7% 8% 5% 9% 10% 31%	1803
	11th to 20th	Day	2 8% 3 12% 7% 7% 6% 4 9% 10% 33%	1850
	21st to end	Day	1 7% 3 11% 8% 8% 6% 5% 8% 9% 34%	1570
March	1st to 10th	Day	1 8% 4 12% 9% 8% 8% 7% 8% 8% 27%	3138
	11th to 20th	Day	2 6% 2 7% 6% 5% 4 5% 5% 9% 50%	3392
	21st to end	Day	3 9% 5% 11% 8% 9% 8% 7% 8% 8% 26%	3938
April	1st to 10th	Day	3 8% 4 10% 6% 6% 7% 5% 7% 9% 35%	2280
	11th to 20th	Day	3 7% 2 9% 6% 5% 5% 5% 6% 8% 43%	2277
	21st to end	Day	4 8% 3 7% 5% 4 5% 4 6% 7% 48%	2470
May	1st to 10th	Day	2 8% 3 9% 6% 6% 6% 4 6% 8% 41%	4110
	11th to 20th	Day	3 4 2 5% 4 3 4 3 4 6% 62%	4071
	21st to end	Day	4 6% 2 6% 4 5% 5% 4 6% 7% 52%	4714
June	1st to 10th	Day	5% 6% 2 7% 5% 4 5% 4 6% 8% 48%	2660
	11th to 20th	Day	4 5% 2 5% 4 4 3 3 5% 6% 60%	2660
	21st to end	Day	2 2 1 4 3 3 4 3 5% 6% 68%	2660
July	1st to 10th	Day	1 2 1 2 2 3 3 2 3 4 77%	4420
	11th to 20th	Day	2 2 1 4 3 4 5% 4 6% 6% 62%	4420
	21st to end	Day	4 3 1 5% 4 4 4 4 6% 7% 59%	4746
August	1st to 10th	Day	4 3 2 5% 3 3 4 3 4 7% 63%	4092
	11th to 20th	Day	2 2 1 3 3 2 2 3 4 6% 72%	3999
	21st to end	Day	2 3 1 3 2 2 2 2 3 4 75%	4180
September	1st to 10th	Day	2 3 1 4 3 3 3 3 4 5% 70%	2264
	11th to 20th	Day	3 4 2 5% 4 3 4 3 4 5% 63%	2090
	21st to end	Day	3 4 1 5% 3 3 3 3 3 7% 66%	2090
October	1st to 10th	Day	3 4 2 4 3 4 3 3 4 6% 64%	3490
	11th to 20th	Day	2 6% 2 4 3 3 3 3 5% 6% 63%	3147
	21st to end	Day	2 4 3 6% 4 4 5% 4 6% 10% 53%	3101
November	1st to 10th	Day	3 8% 3 9% 6% 5% 5% 4 7% 8% 43%	1764
	11th to 20th	Day	3 7% 3 7% 6% 5% 5% 6% 8% 11% 40%	1800
	21st to end	Day	2 7% 4 12% 6% 6% 6% 4 5% 8% 40%	1800
December	1st to 10th	Day	2 6% 4 10% 7% 6% 7% 5% 7% 9% 37%	1709
	11th to 20th	Day	3 10% 5% 12% 9% 8% 6% 6% 6% 9% 28%	1928
	21st to end	Day	2 7% 4 12% 8% 9% 9% 6% 8% 8% 28%	2794
January	1st to 10th	Night	2 7% 5% 13% 8% 7% 8% 6% 9% 7% 29%	4406
	11th to 20th	Night	1 9% 4 12% 9% 9% 8% 6% 7% 8% 27%	4420
	21st to end	Night	3 12% 5% 15% 8% 7% 6% 4 6% 6% 28%	4831
February	1st to 10th	Night	2 7% 3 9% 7% 6% 6% 6% 8% 10% 37%	2375
	11th to 20th	Night	1 6% 3 8% 6% 6% 6% 6% 8% 9% 40%	2218
	21st to end	Night	1 7% 3 9% 8% 6% 8% 6% 9% 9% 34%	1884
March	1st to 10th	Night	1 7% 4 11% 8% 7% 6% 6% 7% 8% 35%	3736
	11th to 20th	Night	1 6% 3 7% 4 4 4 4 5% 7% 53%	3587
	21st to end	Night	3 9% 3 7% 6% 5% 5% 5% 7% 10% 40%	3710
April	1st to 10th	Night	3 7% 3 7% 5% 5% 6% 4 6% 8% 46%	1900
	11th to 20th	Night	3 7% 2 7% 5% 4 5% 5% 7% 7% 48%	1851
	21st to end	Night	4 6% 2 6% 4 5% 5% 4 6% 8% 50%	1710
May	1st to 10th	Night	4 6% 2 6% 5% 4 5% 4 6% 8% 51%	2860
	11th to 20th	Night	4 4 2 4 2 3 3 3 5% 6% 66%	2834
	21st to end	Night	3 5% 2 6% 4 4 4 4 6% 7% 56%	2860
June	1st to 10th	Night	5% 4 1 5% 5% 4 4 4 6% 7% 55%	1520
	11th to 20th	Night	4 4 2 4 3 3 4 3 5% 7% 61%	1520
	21st to end	Night	2 2 1 3 3 3 4 4 4 6% 69%	1520
July	1st to 10th	Night	1 1 1 2 2 2 2 3 3 4 78%	2540
	11th to 20th	Night	2 3 1 5% 3 4 5% 4 5% 7% 62%	2540
	21st to end	Night	2 3 1 4 4 4 4 4 7% 8% 58%	2792
August	1st to 10th	Night	3 3 1 4 3 4 4 3 5% 6% 63%	2847
	11th to 20th	Night	3 2 1 4 2 3 3 3 4 5% 72%	2837
	21st to end	Night	4 3 1 3 1 2 2 2 3 3 76%	3498
September	1st to 10th	Night	3 2 1 4 2 3 3 3 4 5% 71%	1915
	11th to 20th	Night	4 2 2 3 2 3 3 3 4 6% 67%	2090
	21st to end	Night	3 2 2 3 3 2 2 2 4 5% 71%	2090
October	1st to 10th	Night	3 3 1 3 2 3 2 2 4 4 72%	3490
	11th to 20th	Night	4 5% 2 5% 3 4 4 4 4 5% 60%	3783
	21st to end	Night	2 4 2 6% 4 4 5% 4 6% 8% 57%	4457
November	1st to 10th	Night	5% 8% 2 6% 4 5% 6% 5% 7% 8% 45%	2535
	11th to 20th	Night	2 6% 2 6% 5% 5% 7% 5% 8% 9% 45%	2600
	21st to end	Night	1 7% 2 7% 6% 6% 5% 5% 10% 9% 42%	2600
December	1st to 10th	Night	3 6% 3 10% 7% 6% 6% 6% 7% 9% 39%	2651
	11th to 20th	Night	3 10% 4 12% 7% 7% 7% 6% 7% 10% 29%	3276
	21st to end	Night	3 7% 3 12% 10% 8% 9% 7% 7% 8% 27%	4862

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	51% 10% 13% 17% 7% 1	2539
	11th to 20th	Day	55% 10% 11% 14% 7% 3	2540
	21st to end	Day	50% 10% 12% 19% 7% 3	2825
February	1st to 10th	Day	41% 14% 12% 19% 11% 3	1803
	11th to 20th	Day	41% 10% 13% 18% 13% 4	1860
	21st to end	Day	43% 10% 13% 20% 10% 4	1570
March	1st to 10th	Day	49% 10% 11% 12% 14% 3	3138
	11th to 20th	Day	30% 7% 14% 32% 15% 2	3392
	21st to end	Day	50% 15% 12% 16% 6% 1	3938
April	1st to 10th	Day	41% 12% 14% 19% 10% 5%	2280
	11th to 20th	Day	36% 9% 13% 22% 18% 3	2280
	21st to end	Day	34% 8% 12% 26% 19% 2	2470
May	1st to 10th	Day	36% 8% 12% 22% 17% 6%	4110
	11th to 20th	Day	22% 5% 9% 24% 31% 9%	4074
	21st to end	Day	28% 7% 11% 28% 25% 1	4714
June	1st to 10th	Day	32% 8% 11% 22% 23% 4	2660
	11th to 20th	Day	24% 4 8% 18% 30% 15%	2660
	21st to end	Day	17% 3 6% 16% 33% 25%	2660
July	1st to 10th	Day	12% 3 4 6% 15% 60%	4351
	11th to 20th	Day	18% 4 4 5% 21% 47%	4345
	21st to end	Day	21% 5% 5% 8% 27% 33%	4596
August	1st to 10th	Day	20% 3 4 8% 22% 43%	4078
	11th to 20th	Day	13% 2 6% 6% 27% 46%	4038
	21st to end	Day	14% 2 4 10% 28% 42%	4179
September	1st to 10th	Day	17% 2 6% 10% 29% 35%	2264
	11th to 20th	Day	21% 4 8% 16% 30% 21%	2090
	21st to end	Day	20% 3 7% 17% 33% 20%	2090
October	1st to 10th	Day	22% 3 6% 14% 31% 23%	3490
	11th to 20th	Day	22% 4 5% 24% 31% 14%	3147
	21st to end	Day	22% 8% 10% 29% 22% 8%	3101
November	1st to 10th	Day	37% 9% 11% 20% 19% 5%	1764
	11th to 20th	Day	34% 9% 13% 26% 16% 2	1800
	21st to end	Day	38% 8% 12% 18% 17% 6%	1800
December	1st to 10th	Day	40% 10% 14% 19% 12% 5%	1709
	11th to 20th	Day	49% 9% 13% 14% 11% 3	1928
	21st to end	Day	43% 9% 16% 15% 13% 3	2794
January	1st to 10th	Night	47% 11% 13% 18% 9% 1	4406
	11th to 20th	Night	55% 9% 11% 13% 8% 4	4420
	21st to end	Night	50% 9% 12% 18% 9% 3	4831
February	1st to 10th	Night	37% 13% 14% 23% 10% 3	2375
	11th to 20th	Night	35% 10% 14% 21% 14% 6%	2219
	21st to end	Night	40% 11% 14% 21% 10% 5%	1884
March	1st to 10th	Night	45% 8% 12% 17% 10% 7%	3736
	11th to 20th	Night	29% 6% 13% 28% 22% 3	3587
	21st to end	Night	38% 12% 15% 24% 10% 1	3710
April	1st to 10th	Night	34% 11% 13% 24% 14% 4	1900
	11th to 20th	Night	32% 9% 12% 23% 20% 3	1851
	21st to end	Night	30% 9% 14% 23% 23% 1	1710
May	1st to 10th	Night	29% 6% 12% 23% 25% 5%	2860
	11th to 20th	Night	20% 5% 7% 27% 33% 7%	2835
	21st to end	Night	26% 6% 10% 32% 25% 2	2860
June	1st to 10th	Night	27% 6% 14% 26% 24% 2	1520
	11th to 20th	Night	22% 5% 9% 20% 28% 16%	1520
	21st to end	Night	16% 3 6% 15% 33% 26%	1520
July	1st to 10th	Night	11% 2 4 7% 17% 59%	2500
	11th to 20th	Night	19% 4 5% 6% 18% 47%	2492
	21st to end	Night	19% 5% 5% 10% 25% 36%	2704
August	1st to 10th	Night	20% 4 4 10% 21% 40%	2838
	11th to 20th	Night	16% 3 4 7% 30% 40%	2864
	21st to end	Night	15% 2 4 10% 24% 46%	3498
September	1st to 10th	Night	17% 3 5% 11% 30% 35%	1915
	11th to 20th	Night	18% 4 8% 17% 29% 25%	2090
	21st to end	Night	16% 3 6% 17% 35% 23%	2090
October	1st to 10th	Night	16% 4 4 14% 35% 26%	3490
	11th to 20th	Night	23% 7% 6% 19% 33% 12%	3783
	21st to end	Night	22% 7% 9% 28% 28% 6%	4457
November	1st to 10th	Night	33% 9% 11% 19% 21% 6%	2535
	11th to 20th	Night	30% 11% 13% 24% 20% 3	2600
	21st to end	Night	32% 10% 12% 21% 19% 5%	2600
December	1st to 10th	Night	38% 9% 15% 22% 11% 5%	2651
	11th to 20th	Night	47% 8% 13% 16% 12% 5%	3276
	21st to end	Night	44% 8% 16% 15% 12% 4	4862

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	13% 22% 26% 23% 14% 1	180
	11th to 20th	Day	8% 18% 33% 18% 16% 7%	180
	21st to end	Day	5% 14% 29% 30% 14% 7%	207
February	1st to 10th	Day	8% 29% 27% 23% 11% 2	363
	11th to 20th	Day	8% 22% 34% 23% 11% 1	455
	21st to end	Day	8% 24% 31% 27% 9% 1	382
March	1st to 10th	Day	9% 20% 35% 27% 8%	460
	11th to 20th	Day	6% 21% 30% 28% 12% 2	460
	21st to end	Day	11% 23% 37% 22% 6% 1	506
April	1st to 10th	Day	8% 26% 27% 24% 15% 1	460
	11th to 20th	Day	7% 26% 34% 20% 10% 4	452
	21st to end	Day	10% 20% 30% 27% 11% 2	460
May	1st to 10th	Day	7% 22% 32% 25% 11% 3	463
	11th to 20th	Day	15% 12% 29% 28% 13% 3	488
	21st to end	Day	10% 15% 21% 28% 20% 6%	529
June	1st to 10th	Day	8% 14% 24% 30% 18% 6%	490
	11th to 20th	Day	10% 17% 33% 24% 14% 2	490
	21st to end	Day	3 8% 36% 31% 18% 4	490
July	1st to 10th	Day	2 8% 30% 35% 18% 6%	486
	11th to 20th	Day	4 6% 31% 36% 19% 5%	484
	21st to end	Day	6% 4 29% 33% 21% 8%	531
August	1st to 10th	Day	7% 7% 26% 36% 17% 7%	487
	11th to 20th	Day	5% 6% 28% 32% 20% 8%	477
	21st to end	Day	3 8% 29% 31% 19% 10%	539
September	1st to 10th	Day	4 8% 27% 29% 20% 12%	490
	11th to 20th	Day	6% 13% 27% 26% 21% 8%	490
	21st to end	Day	7% 10% 29% 25% 24% 5%	490
October	1st to 10th	Day	7% 14% 23% 26% 23% 7%	490
	11th to 20th	Day	9% 16% 22% 22% 24% 8%	386
	21st to end	Day	8% 17% 29% 26% 17% 3	330
November	1st to 10th	Day	12% 15% 25% 25% 20% 2	300
	11th to 20th	Day	8% 17% 25% 30% 16% 4	300
	21st to end	Day	10% 14% 24% 29% 18% 5%	300
December	1st to 10th	Day	7% 16% 24% 29% 14% 10%	259
	11th to 20th	Day	9% 16% 31% 29% 12% 3	180
	21st to end	Day	14% 17% 22% 31% 14% 3	198
January	1st to 10th	Night	7% 14% 22% 31% 20% 6%	760
	11th to 20th	Night	6% 16% 21% 31% 21% 5%	760
	21st to end	Night	8% 11% 21% 33% 21% 7%	836
February	1st to 10th	Night	6% 15% 29% 27% 18% 4	760
	11th to 20th	Night	5% 13% 24% 38% 17% 2	744
	21st to end	Night	4 14% 29% 34% 16% 3	628
March	1st to 10th	Night	5% 13% 30% 35% 15% 3	760
	11th to 20th	Night	6% 9% 26% 35% 22% 2	760
	21st to end	Night	8% 16% 28% 32% 15% 1	836
April	1st to 10th	Night	8% 11% 29% 32% 18% 3	760
	11th to 20th	Night	7% 14% 28% 33% 15% 4	723
	21st to end	Night	8% 10% 28% 32% 19% 3	570
May	1st to 10th	Night	7% 12% 26% 34% 20% 2	570
	11th to 20th	Night	10% 7% 22% 32% 25% 3	561
	21st to end	Night	8% 7% 22% 33% 26% 4	471
June	1st to 10th	Night	5% 4 21% 37% 28% 4	380
	11th to 20th	Night	7% 4 19% 45% 25%	380
	21st to end	Night	2 3 15% 50% 27% 3	380
July	1st to 10th	Night	2 1 10% 51% 30% 5%	370
	11th to 20th	Night	4 1 13% 51% 30% 2	368
	21st to end	Night	3 1 8% 46% 39% 3	435
August	1st to 10th	Night	5% 2 13% 46% 30% 3	567
	11th to 20th	Night	2 2 12% 47% 33% 3	577
	21st to end	Night	4 1 13% 43% 34% 5%	836
September	1st to 10th	Night	4 2 12% 40% 36% 6%	760
	11th to 20th	Night	5% 3 11% 35% 36% 11%	760
	21st to end	Night	5% 6% 13% 34% 31% 11%	760
October	1st to 10th	Night	8% 5% 18% 35% 29% 6%	760
	11th to 20th	Night	6% 9% 15% 33% 30% 6%	760
	21st to end	Night	4 10% 20% 37% 23% 6%	836
November	1st to 10th	Night	9% 9% 20% 34% 23% 6%	780
	11th to 20th	Night	8% 9% 26% 36% 18% 4	800
	21st to end	Night	5% 11% 24% 31% 24% 6%	800
December	1st to 10th	Night	6% 11% 25% 33% 19% 5%	794
	11th to 20th	Night	9% 11% 24% 35% 15% 4	760
	21st to end	Night	12% 15% 28% 33% 11% 2	836

Page generated at 2024-12-06 00:54:52. Version ac07

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