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 2024-01-16.

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% 3 6% 6% 4 5% 5% 6% 8% 48%	74892
	Night	3 5% 3 6% 6% 4 6% 6% 6% 8% 48%	74933
Transparency	Day	32% 7% 11% 17% 20% 13%	74598
	Night	31% 8% 12% 19% 19% 11%	74749
Seeing	Day	8% 15% 29% 28% 16% 4	13513
	Night	6% 9% 21% 36% 23% 4	23079

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	2 8% 4 9% 9% 6% 7% 8% 9% 10% 27%	1519
	11th to 20th	Day	2 5% 4 8% 9% 5% 8% 8% 8% 8% 36%	1480
	21st to end	Day	2 7% 4 10% 8% 4 8% 7% 7% 8% 34%	1601
February	1st to 10th	Day	2 5% 3 9% 8% 5% 8% 7% 9% 11% 33%	1708
	11th to 20th	Day	1 7% 4 10% 8% 5% 6% 5% 9% 9% 34%	1750
	21st to end	Day	1 7% 4 10% 8% 6% 7% 7% 8% 9% 33%	1480
March	1st to 10th	Day	2 8% 5% 12% 8% 4 7% 8% 7% 9% 30%	1800
	11th to 20th	Day	3 8% 4 7% 8% 4 6% 7% 7% 9% 37%	1921
	21st to end	Day	4 8% 4 8% 8% 6% 9% 8% 7% 8% 30%	2240
April	1st to 10th	Day	3 7% 5% 9% 8% 5% 7% 6% 7% 9% 34%	2160
	11th to 20th	Day	3 6% 3 9% 7% 3 6% 6% 6% 8% 42%	2155
	21st to end	Day	4 7% 3 6% 6% 3 5% 5% 6% 7% 49%	2340
May	1st to 10th	Day	4 6% 3 6% 6% 3 6% 6% 6% 9% 45%	2340
	11th to 20th	Day	5% 7% 3 7% 6% 4 5% 6% 6% 8% 44%	2301
	21st to end	Day	6% 9% 3 7% 7% 5% 6% 6% 7% 8% 36%	2663
June	1st to 10th	Day	6% 5% 3 6% 5% 3 5% 5% 6% 8% 48%	2520
	11th to 20th	Day	4 4 2 4 4 3 4 4 5% 6% 60%	2520
	21st to end	Day	2 2 1 3 3 2 4 4 5% 6% 68%	2520
July	1st to 10th	Day	2 2 1 3 4 3 5% 5% 5% 6% 63%	2520
	11th to 20th	Day	2 3 2 3 3 2 4 3 3 6% 70%	2520
	21st to end	Day	4 3 2 4 4 3 4 4 4 6% 62%	2721
August	1st to 10th	Day	5% 4 2 4 4 3 5% 4 5% 6% 58%	2328
	11th to 20th	Day	3 2 1 3 4 2 3 4 5% 7% 67%	2283
	21st to end	Day	2 2 1 3 3 2 3 3 4 6% 70%	2376
September	1st to 10th	Day	2 3 1 4 3 2 4 3 4 4 70%	2145
	11th to 20th	Day	3 4 2 4 4 3 3 4 4 5% 64%	1980
	21st to end	Day	3 4 1 4 4 3 3 3 3 7% 64%	1980
October	1st to 10th	Day	5% 6% 3 5% 5% 3 5% 4 3 7% 54%	1980
	11th to 20th	Day	2 7% 3 3 4 2 3 4 5% 7% 59%	1804
	21st to end	Day	3 4 2 5% 5% 3 5% 5% 6% 10% 52%	1782
November	1st to 10th	Day	3 8% 4 7% 7% 3 5% 5% 7% 8% 43%	1674
	11th to 20th	Day	3 6% 3 5% 7% 3 6% 6% 8% 10% 42%	1710
	21st to end	Day	2 6% 4 10% 9% 4 6% 5% 6% 8% 39%	1710
December	1st to 10th	Day	2 6% 4 9% 9% 5% 8% 7% 7% 9% 35%	1639
	11th to 20th	Day	3 9% 5% 11% 10% 6% 6% 7% 6% 9% 28%	1928
	21st to end	Day	2 6% 4 10% 9% 6% 9% 8% 8% 9% 28%	2794
January	1st to 10th	Night	2 7% 4 8% 9% 5% 8% 7% 9% 8% 32%	2646
	11th to 20th	Night	1 7% 4 6% 8% 6% 8% 8% 8% 9% 36%	2602
	21st to end	Night	2 8% 4 10% 8% 6% 6% 6% 6% 8% 35%	2754
February	1st to 10th	Night	2 5% 3 8% 7% 5% 6% 8% 8% 10% 38%	2250
	11th to 20th	Night	2 5% 4 8% 6% 4 6% 8% 8% 9% 41%	2098
	21st to end	Night	1 6% 4 7% 9% 5% 9% 7% 9% 9% 33%	1776
March	1st to 10th	Night	1 6% 4 7% 9% 5% 7% 7% 7% 11% 35%	2160
	11th to 20th	Night	2 6% 4 7% 6% 4 6% 6% 7% 11% 42%	2038
	21st to end	Night	4 8% 3 6% 7% 5% 6% 6% 7% 10% 40%	2111
April	1st to 10th	Night	4 6% 3 6% 6% 4 6% 6% 6% 9% 46%	1800
	11th to 20th	Night	4 6% 2 7% 6% 3 6% 6% 7% 7% 46%	1753
	21st to end	Night	4 6% 2 6% 4 4 5% 5% 6% 8% 50%	1620
May	1st to 10th	Night	4 4 2 5% 5% 3 5% 5% 6% 8% 52%	1620
	11th to 20th	Night	7% 6% 3 5% 5% 3 5% 5% 6% 9% 47%	1594
	21st to end	Night	4 7% 3 6% 6% 3 5% 6% 7% 8% 45%	1608
June	1st to 10th	Night	5% 4 2 5% 5% 3 5% 4 6% 7% 55%	1440
	11th to 20th	Night	5% 4 2 4 4 2 4 4 4 7% 60%	1440
	21st to end	Night	2 2 1 2 3 2 3 4 4 6% 69%	1440
July	1st to 10th	Night	2 2 1 4 4 3 4 6% 5% 7% 63%	1440
	11th to 20th	Night	2 2 1 3 2 2 4 3 5% 6% 71%	1440
	21st to end	Night	3 3 2 4 4 3 5% 5% 6% 7% 58%	1594
August	1st to 10th	Night	4 4 1 3 4 2 5% 5% 6% 6% 59%	1611
	11th to 20th	Night	1 2 1 3 3 3 4 4 5% 6% 69%	1614
	21st to end	Night	2 2 1 3 2 2 3 3 5% 6% 72%	1980
September	1st to 10th	Night	3 2 1 3 3 2 3 3 4 5% 71%	1814
	11th to 20th	Night	4 2 2 3 3 1 4 4 4 6% 67%	1980
	21st to end	Night	3 2 2 3 4 2 3 3 4 6% 69%	1980
October	1st to 10th	Night	5% 5% 2 4 4 2 4 3 5% 5% 61%	1980
	11th to 20th	Night	3 4 2 4 4 2 5% 5% 5% 6% 60%	2154
	21st to end	Night	2 3 2 4 5% 3 4 5% 6% 8% 58%	2574
November	1st to 10th	Night	5% 7% 2 5% 4 4 6% 6% 7% 8% 45%	2405
	11th to 20th	Night	2 5% 2 5% 6% 4 7% 6% 8% 9% 46%	2470
	21st to end	Night	1 6% 2 6% 7% 4 6% 6% 10% 9% 42%	2470
December	1st to 10th	Night	3 5% 3 9% 9% 4 6% 7% 7% 9% 37%	2539
	11th to 20th	Night	3 9% 4 10% 9% 6% 6% 7% 7% 10% 29%	3276
	21st to end	Night	3 6% 4 10% 11% 6% 9% 9% 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	48% 11% 16% 18% 5% 2	1519
	11th to 20th	Day	40% 13% 15% 15% 12% 5%	1480
	21st to end	Day	44% 10% 14% 19% 9% 5%	1601
February	1st to 10th	Day	39% 14% 12% 19% 12% 3	1708
	11th to 20th	Day	41% 10% 13% 18% 13% 4	1760
	21st to end	Day	44% 10% 13% 20% 9% 4	1480
March	1st to 10th	Day	47% 12% 14% 17% 9% 2	1800
	11th to 20th	Day	39% 11% 14% 20% 13% 3	1921
	21st to end	Day	46% 13% 15% 15% 8% 3	2240
April	1st to 10th	Day	43% 11% 13% 17% 11% 5%	2160
	11th to 20th	Day	37% 9% 13% 21% 17% 3	2158
	21st to end	Day	33% 8% 13% 25% 19% 2	2340
May	1st to 10th	Day	31% 9% 11% 23% 23% 3	2340
	11th to 20th	Day	37% 8% 11% 26% 15% 4	2304
	21st to end	Day	42% 10% 12% 20% 15% 1	2663
June	1st to 10th	Day	32% 8% 11% 21% 24% 4	2520
	11th to 20th	Day	25% 4 8% 19% 29% 15%	2520
	21st to end	Day	17% 3 6% 16% 34% 24%	2520
July	1st to 10th	Day	20% 4 7% 11% 26% 32%	2451
	11th to 20th	Day	17% 2 5% 7% 25% 44%	2445
	21st to end	Day	22% 3 6% 9% 23% 37%	2570
August	1st to 10th	Day	24% 4 6% 10% 24% 32%	2313
	11th to 20th	Day	16% 2 9% 9% 36% 28%	2283
	21st to end	Day	15% 2 5% 12% 30% 35%	2376
September	1st to 10th	Day	17% 2 6% 11% 28% 36%	2145
	11th to 20th	Day	21% 4 8% 15% 30% 22%	1980
	21st to end	Day	21% 3 7% 17% 34% 18%	1980
October	1st to 10th	Day	30% 4 9% 19% 27% 11%	1980
	11th to 20th	Day	25% 5% 8% 25% 29% 8%	1804
	21st to end	Day	26% 7% 14% 26% 22% 5%	1782
November	1st to 10th	Day	38% 9% 11% 19% 19% 5%	1674
	11th to 20th	Day	33% 9% 13% 26% 16% 3	1710
	21st to end	Day	39% 8% 13% 18% 15% 7%	1710
December	1st to 10th	Day	42% 11% 14% 18% 10% 5%	1639
	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	44% 11% 17% 18% 7% 2	2646
	11th to 20th	Night	40% 12% 14% 16% 12% 6%	2602
	21st to end	Night	43% 10% 11% 18% 12% 6%	2754
February	1st to 10th	Night	36% 13% 14% 24% 11% 3	2250
	11th to 20th	Night	34% 11% 15% 20% 14% 6%	2099
	21st to end	Night	41% 11% 15% 20% 9% 5%	1776
March	1st to 10th	Night	39% 10% 14% 23% 10% 3	2160
	11th to 20th	Night	34% 10% 14% 22% 17% 4	2038
	21st to end	Night	37% 12% 17% 22% 10% 2	2111
April	1st to 10th	Night	34% 11% 13% 23% 14% 4	1800
	11th to 20th	Night	34% 10% 13% 22% 19% 3	1753
	21st to end	Night	29% 9% 15% 23% 23% 1	1620
May	1st to 10th	Night	28% 6% 12% 22% 27% 3	1620
	11th to 20th	Night	33% 8% 10% 28% 17% 3	1595
	21st to end	Night	34% 9% 13% 25% 17% 2	1608
June	1st to 10th	Night	27% 6% 14% 26% 24% 2	1440
	11th to 20th	Night	23% 5% 10% 20% 27% 15%	1440
	21st to end	Night	16% 4 6% 16% 33% 25%	1440
July	1st to 10th	Night	20% 3 8% 13% 25% 32%	1400
	11th to 20th	Night	15% 2 5% 9% 24% 45%	1392
	21st to end	Night	21% 4 7% 8% 25% 36%	1505
August	1st to 10th	Night	23% 4 7% 13% 23% 31%	1602
	11th to 20th	Night	16% 4 6% 10% 36% 29%	1614
	21st to end	Night	14% 3 6% 12% 29% 36%	1980
September	1st to 10th	Night	17% 3 5% 11% 29% 35%	1814
	11th to 20th	Night	18% 4 8% 17% 28% 26%	1980
	21st to end	Night	17% 3 7% 16% 35% 22%	1980
October	1st to 10th	Night	25% 5% 7% 21% 28% 14%	1980
	11th to 20th	Night	24% 7% 8% 23% 31% 9%	2154
	21st to end	Night	23% 6% 13% 28% 25% 6%	2574
November	1st to 10th	Night	34% 9% 11% 19% 21% 7%	2405
	11th to 20th	Night	30% 11% 13% 24% 20% 3	2470
	21st to end	Night	33% 10% 12% 21% 18% 6%	2470
December	1st to 10th	Night	39% 10% 15% 21% 9% 6%	2539
	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% 19% 32% 18% 15% 8%	170
	21st to end	Day	4 15% 30% 29% 15% 7%	184
February	1st to 10th	Day	6% 29% 27% 23% 12% 3	328
	11th to 20th	Day	8% 22% 34% 23% 12% 1	415
	21st to end	Day	8% 25% 31% 27% 8% 1	346
March	1st to 10th	Day	8% 19% 35% 29% 9%	420
	11th to 20th	Day	6% 20% 31% 28% 12% 2	420
	21st to end	Day	11% 23% 38% 22% 6% 1	462
April	1st to 10th	Day	9% 26% 26% 23% 15% 1	420
	11th to 20th	Day	8% 27% 35% 18% 9% 4	412
	21st to end	Day	10% 20% 30% 26% 12% 2	420
May	1st to 10th	Day	6% 20% 32% 27% 12% 3	423
	11th to 20th	Day	17% 12% 29% 27% 13% 3	448
	21st to end	Day	11% 14% 21% 28% 19% 7%	485
June	1st to 10th	Day	9% 15% 24% 28% 18% 6%	450
	11th to 20th	Day	10% 18% 33% 24% 14% 2	450
	21st to end	Day	3 8% 36% 31% 18% 5%	450
July	1st to 10th	Day	3 8% 30% 36% 18% 5%	446
	11th to 20th	Day	3 6% 32% 38% 19% 3	444
	21st to end	Day	6% 4 30% 34% 20% 6%	487
August	1st to 10th	Day	7% 8% 26% 36% 17% 6%	447
	11th to 20th	Day	5% 5% 26% 35% 21% 9%	437
	21st to end	Day	2 8% 29% 32% 19% 9%	495
September	1st to 10th	Day	4 8% 28% 30% 19% 11%	450
	11th to 20th	Day	5% 13% 27% 26% 22% 7%	450
	21st to end	Day	8% 10% 30% 25% 23% 4	450
October	1st to 10th	Day	7% 15% 24% 24% 24% 6%	450
	11th to 20th	Day	9% 17% 22% 22% 24% 6%	352
	21st to end	Day	8% 17% 28% 27% 16% 3	297
November	1st to 10th	Day	13% 16% 25% 24% 21% 1	270
	11th to 20th	Day	8% 16% 22% 31% 18% 4	270
	21st to end	Day	9% 14% 24% 29% 19% 4	270
December	1st to 10th	Day	8% 17% 26% 31% 13% 5%	237
	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	5% 15% 21% 32% 21% 5%	744
	21st to end	Night	9% 11% 20% 32% 21% 7%	792
February	1st to 10th	Night	6% 14% 29% 28% 19% 4	720
	11th to 20th	Night	5% 12% 24% 39% 17% 2	704
	21st to end	Night	4 15% 29% 33% 17% 3	592
March	1st to 10th	Night	5% 11% 30% 35% 15% 3	720
	11th to 20th	Night	6% 8% 27% 35% 22% 2	720
	21st to end	Night	8% 16% 27% 32% 16% 1	792
April	1st to 10th	Night	9% 10% 28% 32% 18% 3	720
	11th to 20th	Night	7% 14% 28% 32% 15% 4	685
	21st to end	Night	8% 9% 29% 31% 20% 3	540
May	1st to 10th	Night	7% 11% 25% 35% 21% 2	540
	11th to 20th	Night	11% 7% 21% 31% 26% 4	531
	21st to end	Night	8% 7% 22% 32% 27% 4	446
June	1st to 10th	Night	6% 4 20% 37% 29% 5%	360
	11th to 20th	Night	7% 4 19% 44% 26%	360
	21st to end	Night	2 3 15% 49% 28% 3	360
July	1st to 10th	Night	3 1 10% 49% 31% 5%	350
	11th to 20th	Night	3 1 13% 52% 29% 2	348
	21st to end	Night	4 1 8% 45% 39% 3	412
August	1st to 10th	Night	6% 2 14% 45% 30% 3	537
	11th to 20th	Night	2 2 11% 47% 35% 4	546
	21st to end	Night	4 1 12% 44% 34% 5%	792
September	1st to 10th	Night	5% 2 11% 40% 35% 7%	720
	11th to 20th	Night	5% 3 11% 34% 35% 11%	720
	21st to end	Night	5% 6% 13% 34% 31% 11%	720
October	1st to 10th	Night	8% 5% 19% 35% 28% 6%	720
	11th to 20th	Night	6% 9% 16% 33% 30% 6%	720
	21st to end	Night	4 10% 19% 36% 24% 7%	792
November	1st to 10th	Night	9% 9% 20% 33% 24% 6%	740
	11th to 20th	Night	8% 9% 25% 36% 18% 4	760
	21st to end	Night	5% 11% 24% 31% 24% 6%	760
December	1st to 10th	Night	7% 12% 26% 34% 18% 4	760
	11th to 20th	Night	9% 11% 24% 35% 15% 4	760
	21st to end	Night	12% 15% 28% 33% 11% 2	836

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