Tehachapi Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tehachapi Mountain Observatory clear sky chart from 2005-11-06 to 2024-01-12.

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 2 3 4 2 3 4 4 6% 66%	74839
	Night	2 4 2 4 5% 3 4 4 4 6% 62%	74878
Transparency	Day	18% 4 7% 16% 27% 28%	74558
	Night	20% 5% 7% 16% 27% 25%	74681
Seeing	Day	7% 17% 34% 29% 11% 2	14301
	Night	5% 12% 25% 35% 19% 4	24126

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 5% 2 6% 7% 4 5% 5% 5% 8% 50%	1519
	11th to 20th	Day	5% 4 2 5% 4 3 4 4 5% 7% 56%	1565
	21st to end	Day	6% 7% 3 8% 6% 4 4 5% 3 7% 47%	1876
February	1st to 10th	Day	3 5% 2 6% 6% 2 4 5% 4 6% 56%	1800
	11th to 20th	Day	4 4 2 4 6% 4 4 5% 6% 8% 52%	1750
	21st to end	Day	4 5% 4 6% 6% 5% 4 4 6% 7% 50%	1480
March	1st to 10th	Day	4 7% 4 7% 6% 6% 6% 6% 5% 8% 42%	1800
	11th to 20th	Day	3 6% 3 5% 5% 3 6% 4 6% 10% 47%	1859
	21st to end	Day	3 5% 2 7% 5% 4 5% 5% 6% 7% 51%	2376
April	1st to 10th	Day	4 4 3 4 5% 4 4 4 5% 8% 55%	2160
	11th to 20th	Day	3 3 2 3 4 2 4 4 5% 6% 63%	2129
	21st to end	Day	1 3 2 4 3 2 3 3 5% 9% 64%	2160
May	1st to 10th	Day	2 3 1 3 4 2 4 4 4 7% 66%	2227
	11th to 20th	Day	2 2 2 2 3 2 3 4 5% 7% 69%	2301
	21st to end	Day	2 3 2 3 4 3 4 3 4 6% 67%	2530
June	1st to 10th	Day	1 2 1 2 2 2 3 3 4 8% 72%	2486
	11th to 20th	Day	1 1 1 1 1 2 3 3 88%	2520
	21st to end	Day	1 1 2 1 2 1 3 3 86%	2520
July	1st to 10th	Day	1 1 1 1 1 2 3 3 5% 83%	2520
	11th to 20th	Day	2 2 1 2 2 1 2 2 2 5% 78%	2520
	21st to end	Day	2 2 1 2 2 1 3 3 4 6% 75%	2480
August	1st to 10th	Day	1 1 1 2 1 1 2 3 3 3 82%	2149
	11th to 20th	Day	1 1 1 2 1 2 2 3 4 84%	2122
	21st to end	Day	1 1 1 2 2 2 2 3 4 83%	2376
September	1st to 10th	Day	1 1 2 1 1 2 3 3 5% 82%	2160
	11th to 20th	Day	1 2 1 1 2 2 3 87%	2050
	21st to end	Day	1 1 2 2 2 2 2 3 4 82%	1980
October	1st to 10th	Day	2 3 1 3 3 2 3 4 4 6% 69%	1980
	11th to 20th	Day	2 2 1 3 3 2 3 2 3 5% 76%	1815
	21st to end	Day	2 2 1 3 3 2 3 3 4 6% 72%	1940
November	1st to 10th	Day	1 4 2 4 5% 3 3 4 5% 7% 63%	1674
	11th to 20th	Day	2 2 1 3 5% 3 4 4 4 7% 65%	1710
	21st to end	Day	3 4 3 5% 6% 3 4 4 5% 7% 58%	1710
December	1st to 10th	Day	3 5% 2 4 5% 2 5% 5% 6% 7% 56%	1710
	11th to 20th	Day	7% 7% 3 6% 7% 4 6% 6% 6% 7% 42%	2091
	21st to end	Day	4 8% 4 7% 7% 5% 6% 5% 7% 7% 39%	2794
January	1st to 10th	Night	5% 5% 3 6% 7% 4 5% 5% 6% 8% 45%	2646
	11th to 20th	Night	2 3 3 5% 6% 4 5% 5% 6% 8% 52%	2412
	21st to end	Night	5% 7% 4 7% 7% 4 4 4 4 7% 48%	2476
February	1st to 10th	Night	3 6% 4 6% 7% 3 4 4 4 6% 51%	2160
	11th to 20th	Night	3 5% 3 5% 7% 3 4 4 6% 7% 52%	2098
	21st to end	Night	5% 4 4 7% 6% 6% 5% 5% 5% 6% 48%	1776
March	1st to 10th	Night	4 6% 4 6% 8% 4 5% 6% 6% 9% 42%	2160
	11th to 20th	Night	2 6% 3 8% 9% 5% 5% 5% 5% 7% 44%	2096
	21st to end	Night	3 6% 3 6% 8% 5% 5% 6% 5% 6% 47%	1980
April	1st to 10th	Night	3 4 3 5% 6% 3 5% 5% 5% 8% 52%	1800
	11th to 20th	Night	2 3 2 4 4 4 4 5% 5% 6% 61%	1779
	21st to end	Night	2 3 3 4 3 3 4 4 4 7% 64%	1800
May	1st to 10th	Night	1 3 1 3 5% 2 3 5% 4 8% 65%	1732
	11th to 20th	Night	2 2 2 2 3 2 3 3 4 5% 72%	1594
	21st to end	Night	1 2 1 3 5% 2 2 2 4 7% 71%	1746
June	1st to 10th	Night	1 2 1 2 3 2 4 3 4 6% 73%	1469
	11th to 20th	Night	1 2 1 2 1 2 4 86%	1440
	21st to end	Night	1 1 1 1 1 2 2 4 87%	1440
July	1st to 10th	Night	1 1 1 1 2 2 2 3 4 83%	1440
	11th to 20th	Night	1 1 2 1 1 3 2 4 4 80%	1440
	21st to end	Night	2 1 1 2 2 1 2 2 2 6% 77%	1831
August	1st to 10th	Night	2 2 1 1 2 1 1 2 3 4 82%	1790
	11th to 20th	Night	1 1 1 1 2 2 2 3 3 86%	1780
	21st to end	Night	1 1 1 1 2 1 2 2 2 4 85%	1980
September	1st to 10th	Night	1 1 1 1 1 1 1 2 3 87%	1800
	11th to 20th	Night	1 1 1 2 2 3 4 84%	1908
	21st to end	Night	1 1 1 2 1 2 3 2 3 83%	1980
October	1st to 10th	Night	2 2 2 2 3 2 3 3 3 6% 71%	1980
	11th to 20th	Night	2 2 1 3 4 3 3 3 4 5% 71%	2142
	21st to end	Night	1 3 1 3 3 2 3 3 3 5% 73%	2414
November	1st to 10th	Night	1 4 1 5% 5% 3 4 4 5% 8% 60%	2405
	11th to 20th	Night	2 3 2 5% 4 3 3 3 5% 7% 63%	2470
	21st to end	Night	3 4 4 6% 6% 4 5% 4 6% 7% 53%	2470
December	1st to 10th	Night	3 5% 3 6% 6% 4 5% 4 5% 7% 53%	2470
	11th to 20th	Night	6% 6% 4 6% 7% 4 5% 6% 6% 9% 40%	3112
	21st to end	Night	4 9% 4 7% 8% 5% 7% 7% 6% 7% 35%	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	30% 7% 8% 22% 22% 11%	1519
	11th to 20th	Day	26% 5% 9% 19% 24% 16%	1565
	21st to end	Day	36% 5% 8% 15% 20% 17%	1876
February	1st to 10th	Day	27% 6% 6% 19% 23% 19%	1800
	11th to 20th	Day	24% 7% 8% 20% 26% 15%	1760
	21st to end	Day	29% 7% 10% 20% 27% 8%	1480
March	1st to 10th	Day	33% 7% 12% 17% 19% 13%	1800
	11th to 20th	Day	27% 7% 12% 19% 21% 13%	1859
	21st to end	Day	26% 6% 12% 28% 19% 9%	2376
April	1st to 10th	Day	25% 5% 11% 24% 23% 12%	2160
	11th to 20th	Day	18% 4 10% 27% 26% 14%	2132
	21st to end	Day	16% 4 13% 25% 33% 9%	2160
May	1st to 10th	Day	15% 4 9% 22% 35% 14%	2227
	11th to 20th	Day	14% 4 7% 24% 35% 16%	2304
	21st to end	Day	18% 3 7% 24% 36% 12%	2530
June	1st to 10th	Day	12% 5% 6% 19% 32% 26%	2486
	11th to 20th	Day	4 2 5% 13% 30% 46%	2520
	21st to end	Day	6% 1 3 6% 26% 57%	2520
July	1st to 10th	Day	6% 2 3 8% 20% 62%	2451
	11th to 20th	Day	11% 2 3 10% 27% 46%	2445
	21st to end	Day	11% 3 5% 15% 32% 34%	2342
August	1st to 10th	Day	9% 2 2 8% 22% 56%	2135
	11th to 20th	Day	6% 2 3 8% 29% 52%	2122
	21st to end	Day	7% 2 2 6% 33% 51%	2376
September	1st to 10th	Day	7% 2 3 6% 27% 54%	2160
	11th to 20th	Day	5% 1 2 11% 33% 48%	2050
	21st to end	Day	8% 1 3 10% 37% 40%	1980
October	1st to 10th	Day	15% 3 6% 16% 24% 36%	1980
	11th to 20th	Day	12% 2 5% 13% 30% 38%	1815
	21st to end	Day	12% 3 6% 13% 28% 38%	1940
November	1st to 10th	Day	18% 5% 7% 14% 32% 23%	1674
	11th to 20th	Day	18% 4 8% 18% 26% 27%	1710
	21st to end	Day	25% 5% 8% 14% 25% 25%	1710
December	1st to 10th	Day	24% 7% 8% 18% 23% 20%	1710
	11th to 20th	Day	36% 9% 9% 16% 18% 12%	2090
	21st to end	Day	37% 9% 8% 21% 17% 8%	2794
January	1st to 10th	Night	31% 7% 8% 20% 22% 13%	2646
	11th to 20th	Night	25% 6% 9% 19% 24% 17%	2412
	21st to end	Night	33% 5% 7% 15% 21% 18%	2476
February	1st to 10th	Night	31% 5% 6% 14% 24% 21%	2160
	11th to 20th	Night	29% 5% 6% 16% 26% 19%	2099
	21st to end	Night	29% 8% 9% 19% 24% 11%	1776
March	1st to 10th	Night	32% 8% 9% 19% 19% 13%	2160
	11th to 20th	Night	31% 8% 10% 16% 22% 13%	2096
	21st to end	Night	29% 8% 12% 26% 19% 7%	1980
April	1st to 10th	Night	26% 7% 11% 25% 21% 10%	1800
	11th to 20th	Night	19% 4 12% 24% 28% 12%	1779
	21st to end	Night	18% 3 10% 31% 31% 7%	1800
May	1st to 10th	Night	15% 6% 8% 27% 34% 10%	1732
	11th to 20th	Night	14% 3 8% 24% 41% 11%	1595
	21st to end	Night	14% 3 9% 26% 38% 10%	1746
June	1st to 10th	Night	11% 4 10% 19% 35% 22%	1469
	11th to 20th	Night	5% 2 5% 15% 33% 39%	1440
	21st to end	Night	5% 2 2 7% 31% 53%	1440
July	1st to 10th	Night	6% 1 3 7% 23% 59%	1400
	11th to 20th	Night	9% 2 4 12% 26% 47%	1392
	21st to end	Night	11% 2 5% 17% 33% 33%	1730
August	1st to 10th	Night	8% 2 4 8% 26% 52%	1780
	11th to 20th	Night	5% 2 3 9% 34% 47%	1780
	21st to end	Night	7% 1 2 7% 37% 46%	1980
September	1st to 10th	Night	6% 2 3 8% 28% 53%	1800
	11th to 20th	Night	5% 2 3 10% 38% 41%	1908
	21st to end	Night	7% 2 2 12% 38% 38%	1980
October	1st to 10th	Night	13% 3 5% 17% 25% 36%	1980
	11th to 20th	Night	14% 4 5% 15% 28% 35%	2142
	21st to end	Night	13% 4 5% 12% 29% 38%	2414
November	1st to 10th	Night	19% 6% 6% 15% 30% 25%	2405
	11th to 20th	Night	19% 4 7% 14% 26% 29%	2470
	21st to end	Night	27% 5% 7% 14% 22% 25%	2470
December	1st to 10th	Night	26% 6% 7% 15% 24% 21%	2470
	11th to 20th	Night	36% 10% 8% 16% 18% 12%	3112
	21st to end	Night	35% 11% 9% 19% 17% 8%	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	16% 22% 37% 19% 6%	180
	11th to 20th	Day	16% 25% 32% 20% 8%	279
	21st to end	Day	11% 26% 36% 19% 7% 1	416
February	1st to 10th	Day	9% 25% 37% 22% 6% 2	420
	11th to 20th	Day	13% 32% 29% 20% 6% 1	415
	21st to end	Day	14% 26% 37% 18% 4	346
March	1st to 10th	Day	15% 32% 31% 17% 5%	420
	11th to 20th	Day	14% 29% 29% 20% 7% 1	420
	21st to end	Day	15% 32% 33% 15% 4	462
April	1st to 10th	Day	14% 25% 34% 18% 9% 1	420
	11th to 20th	Day	14% 28% 35% 17% 5% 1	412
	21st to end	Day	9% 26% 33% 17% 12% 3	420
May	1st to 10th	Day	9% 25% 35% 23% 8% 1	423
	11th to 20th	Day	7% 21% 36% 26% 9% 1	448
	21st to end	Day	8% 22% 31% 28% 10% 1	485
June	1st to 10th	Day	4 14% 38% 29% 13% 2	450
	11th to 20th	Day	2 13% 38% 32% 14% 2	450
	21st to end	Day	2 11% 41% 29% 14% 3	450
July	1st to 10th	Day	5% 38% 39% 14% 4	446
	11th to 20th	Day	1 2 26% 46% 19% 6%	444
	21st to end	Day	1 2 31% 43% 18% 6%	487
August	1st to 10th	Day	1 6% 38% 38% 13% 4	447
	11th to 20th	Day	2 2 30% 43% 18% 5%	437
	21st to end	Day	1 3 36% 41% 15% 5%	495
September	1st to 10th	Day	1 6% 37% 38% 16% 3	450
	11th to 20th	Day	1 12% 38% 36% 10% 2	450
	21st to end	Day	3 11% 34% 35% 15% 2	450
October	1st to 10th	Day	5% 15% 34% 32% 14%	450
	11th to 20th	Day	4 15% 35% 36% 9% 1	450
	21st to end	Day	5% 17% 33% 31% 12% 2	455
November	1st to 10th	Day	8% 14% 32% 33% 12% 1	270
	11th to 20th	Day	8% 13% 38% 31% 9% 1	270
	21st to end	Day	6% 23% 35% 24% 10% 1	270
December	1st to 10th	Day	7% 20% 37% 29% 6%	270
	11th to 20th	Day	11% 19% 35% 24% 11% 1	246
	21st to end	Day	16% 30% 26% 21% 7% 1	198
January	1st to 10th	Night	11% 12% 31% 30% 12% 6%	760
	11th to 20th	Night	5% 14% 30% 35% 13% 3	724
	21st to end	Night	9% 18% 27% 31% 12% 3	792
February	1st to 10th	Night	6% 15% 33% 26% 16% 4	720
	11th to 20th	Night	9% 15% 30% 27% 15% 4	704
	21st to end	Night	9% 18% 29% 31% 11% 3	592
March	1st to 10th	Night	8% 19% 31% 30% 10% 2	720
	11th to 20th	Night	9% 17% 27% 28% 15% 4	720
	21st to end	Night	8% 23% 28% 28% 13% 1	792
April	1st to 10th	Night	7% 23% 31% 24% 12% 3	720
	11th to 20th	Night	7% 21% 30% 28% 12% 2	711
	21st to end	Night	4 24% 29% 26% 14% 3	720
May	1st to 10th	Night	4 20% 36% 28% 12% 1	652
	11th to 20th	Night	3 20% 28% 36% 13% 1	531
	21st to end	Night	5% 20% 32% 31% 12%	584
June	1st to 10th	Night	2 11% 35% 41% 11% 1	389
	11th to 20th	Night	8% 31% 44% 16% 1	360
	21st to end	Night	4 32% 44% 21%	360
July	1st to 10th	Night	1 15% 51% 32% 1	350
	11th to 20th	Night	2 7% 54% 36% 1	348
	21st to end	Night	2 1 11% 44% 37% 4	649
August	1st to 10th	Night	2 1 19% 45% 30% 3	716
	11th to 20th	Night	1 14% 44% 35% 7%	712
	21st to end	Night	1 1 11% 44% 35% 8%	792
September	1st to 10th	Night	1 3 11% 41% 37% 7%	720
	11th to 20th	Night	2 18% 43% 30% 6%	720
	21st to end	Night	1 6% 17% 39% 29% 8%	720
October	1st to 10th	Night	3 8% 21% 43% 23% 2	720
	11th to 20th	Night	3 8% 22% 37% 23% 7%	720
	21st to end	Night	3 10% 24% 33% 21% 10%	792
November	1st to 10th	Night	4 11% 24% 34% 21% 6%	740
	11th to 20th	Night	4 7% 27% 37% 20% 6%	760
	21st to end	Night	5% 14% 28% 33% 18% 4	760
December	1st to 10th	Night	7% 12% 31% 31% 16% 3	760
	11th to 20th	Night	11% 14% 30% 32% 12% 2	760
	21st to end	Night	11% 15% 29% 30% 12% 2	836

Page generated at 2024-01-08 19:31:25. Version ac07

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