Telescope Array Black Rock Mesa FD
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Telescope Array Black Rock Mesa FD clear sky chart from 2005-11-06 to 2025-06-10.

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	4 5% 2 5% 4 4 4 4 6% 7% 55%	124016
	Night	5% 6% 2 6% 4 4 4 4 6% 8% 51%	123176
Transparency	Day	25% 6% 10% 19% 23% 18%	123784
	Night	28% 6% 11% 20% 21% 15%	122996
Seeing	Day	7% 6% 16% 27% 26% 19%	15647
	Night	8% 4 18% 41% 26% 3	25851

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	3 11% 6% 10% 6% 6% 7% 4 8% 9% 31%	4098
	11th to 20th	Day	4 8% 4 11% 7% 6% 7% 5% 7% 8% 34%	4100
	21st to end	Day	6% 10% 3 8% 6% 6% 5% 4 6% 8% 39%	4510
February	1st to 10th	Day	5% 9% 3 8% 6% 5% 5% 5% 6% 11% 37%	1800
	11th to 20th	Day	6% 9% 4 8% 5% 5% 5% 5% 6% 6% 43%	1920
	21st to end	Day	4 10% 3 6% 5% 4 3 3 7% 8% 47%	1650
March	1st to 10th	Day	4 9% 3 7% 5% 5% 5% 4 5% 8% 46%	4768
	11th to 20th	Day	4 10% 3 8% 5% 5% 5% 4 6% 7% 44%	5000
	21st to end	Day	4 9% 3 9% 6% 6% 6% 5% 7% 7% 37%	5486
April	1st to 10th	Day	4 5% 2 6% 4 4 4 4 6% 8% 55%	2200
	11th to 20th	Day	5% 6% 2 7% 4 4 4 3 4 7% 54%	2517
	21st to end	Day	6% 5% 2 5% 4 3 4 3 5% 6% 57%	2600
May	1st to 10th	Day	5% 4 1 5% 4 4 5% 4 6% 7% 54%	5880
	11th to 20th	Day	4 4 2 4 3 4 4 4 6% 9% 55%	5841
	21st to end	Day	3 4 1 3 3 3 3 3 5% 7% 66%	6423
June	1st to 10th	Day	2 3 1 3 3 3 4 3 7% 8% 65%	2589
	11th to 20th	Day	3 3 1 2 2 2 2 3 4 5% 72%	2470
	21st to end	Day	2 2 2 1 2 2 3 4 6% 76%	2470
July	1st to 10th	Day	1 1 1 1 2 2 2 3 4 81%	4110
	11th to 20th	Day	2 2 1 4 3 4 6% 5% 7% 8% 59%	4110
	21st to end	Day	1 2 1 3 3 4 4 4 6% 9% 64%	4454
August	1st to 10th	Day	1 2 1 3 2 4 4 4 6% 8% 65%	4092
	11th to 20th	Day	1 1 1 3 3 4 4 4 5% 7% 68%	4028
	21st to end	Day	2 1 1 3 1 2 2 3 4 5% 75%	4438
September	1st to 10th	Day	2 2 1 2 2 3 2 2 5% 6% 73%	2095
	11th to 20th	Day	2 3 1 3 2 2 2 3 4 6% 72%	2090
	21st to end	Day	2 2 1 3 2 2 3 3 3 4 76%	2090
October	1st to 10th	Day	3 3 1 3 1 2 3 2 3 5% 73%	3412
	11th to 20th	Day	5% 3 1 4 2 3 4 4 5% 7% 63%	3150
	21st to end	Day	5% 5% 2 3 2 2 2 2 3 5% 68%	3392
November	1st to 10th	Day	6% 5% 1 5% 5% 4 4 3 6% 9% 53%	1764
	11th to 20th	Day	6% 4 2 5% 4 3 4 4 7% 9% 53%	1800
	21st to end	Day	6% 7% 3 8% 4 5% 5% 4 5% 7% 46%	1800
December	1st to 10th	Day	4 5% 3 5% 8% 7% 6% 4 6% 7% 45%	2950
	11th to 20th	Day	4 7% 3 8% 5% 5% 5% 5% 7% 11% 39%	3409
	21st to end	Day	6% 8% 4 10% 7% 7% 8% 5% 7% 8% 30%	4510
January	1st to 10th	Night	4 12% 4 9% 5% 5% 5% 4 7% 11% 35%	5867
	11th to 20th	Night	4 9% 3 10% 5% 5% 6% 4 8% 10% 36%	5880
	21st to end	Night	5% 9% 4 8% 4 5% 5% 4 7% 10% 39%	6468
February	1st to 10th	Night	5% 9% 3 8% 5% 5% 4 4 6% 9% 42%	2600
	11th to 20th	Night	6% 9% 3 7% 5% 4 3 4 5% 7% 45%	2365
	21st to end	Night	4 8% 3 7% 5% 4 5% 4 7% 7% 46%	1980
March	1st to 10th	Night	6% 13% 3 7% 3 3 4 3 4 7% 48%	5124
	11th to 20th	Night	5% 11% 4 7% 4 4 4 4 6% 7% 45%	5000
	21st to end	Night	7% 9% 3 7% 4 4 4 4 6% 6% 46%	5489
April	1st to 10th	Night	7% 7% 2 6% 5% 4 4 4 5% 7% 51%	2199
	11th to 20th	Night	6% 6% 2 7% 5% 4 4 4 5% 7% 51%	1827
	21st to end	Night	8% 5% 2 6% 3 4 4 4 6% 8% 52%	1800
May	1st to 10th	Night	8% 7% 3 6% 5% 5% 4 3 5% 6% 48%	4100
	11th to 20th	Night	5% 4 2 6% 4 4 5% 4 6% 6% 54%	4074
	21st to end	Night	4 4 2 5% 4 3 4 3 6% 7% 59%	4474
June	1st to 10th	Night	3 4 1 4 4 4 4 4 5% 8% 60%	1795
	11th to 20th	Night	3 3 1 4 3 3 3 3 5% 4 70%	1710
	21st to end	Night	2 2 1 3 3 3 4 3 5% 5% 69%	1710
July	1st to 10th	Night	1 2 1 3 3 2 3 3 3 4 76%	2860
	11th to 20th	Night	2 4 2 7% 5% 6% 7% 6% 8% 10% 42%	2860
	21st to end	Night	2 3 2 6% 5% 5% 5% 4 7% 9% 54%	3109
August	1st to 10th	Night	2 4 1 6% 4 4 6% 4 6% 9% 52%	2847
	11th to 20th	Night	1 2 1 3 3 3 4 4 6% 6% 66%	2811
	21st to end	Night	3 3 1 3 2 2 2 3 3 5% 73%	3228
September	1st to 10th	Night	3 2 1 2 2 2 3 3 5% 7% 70%	2085
	11th to 20th	Night	2 2 1 4 3 2 4 2 4 6% 69%	2090
	21st to end	Night	4 2 1 3 2 2 3 2 3 5% 72%	2090
October	1st to 10th	Night	3 3 1 3 2 2 3 3 4 5% 71%	3552
	11th to 20th	Night	6% 4 1 4 3 3 3 3 5% 7% 61%	3778
	21st to end	Night	5% 4 1 3 2 3 3 3 5% 8% 64%	4150
November	1st to 10th	Night	4 5% 2 5% 3 3 3 2 5% 7% 61%	2535
	11th to 20th	Night	5% 5% 2 5% 3 3 4 3 6% 8% 57%	2600
	21st to end	Night	7% 8% 2 5% 4 3 3 3 6% 10% 48%	2600
December	1st to 10th	Night	4 6% 2 5% 4 6% 7% 8% 8% 9% 43%	4240
	11th to 20th	Night	6% 7% 3 5% 4 4 5% 4 7% 11% 44%	4811
	21st to end	Night	5% 9% 3 10% 6% 6% 6% 5% 7% 10% 33%	6468

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	41% 10% 22% 17% 9%	4099
	11th to 20th	Day	41% 10% 16% 18% 12% 3	4100
	21st to end	Day	38% 11% 14% 19% 16% 2	4510
February	1st to 10th	Day	38% 10% 18% 20% 12% 3	1800
	11th to 20th	Day	38% 6% 15% 24% 14% 2	1930
	21st to end	Day	31% 7% 11% 29% 18% 4	1650
March	1st to 10th	Day	32% 7% 10% 25% 21% 4	4768
	11th to 20th	Day	34% 7% 11% 27% 17% 5%	5000
	21st to end	Day	36% 9% 14% 22% 15% 3	5486
April	1st to 10th	Day	26% 6% 10% 27% 22% 10%	2200
	11th to 20th	Day	29% 4 10% 22% 24% 11%	2520
	21st to end	Day	26% 5% 9% 22% 29% 9%	2600
May	1st to 10th	Day	23% 7% 10% 20% 29% 10%	5880
	11th to 20th	Day	21% 6% 7% 18% 35% 13%	5844
	21st to end	Day	16% 5% 6% 16% 37% 20%	6424
June	1st to 10th	Day	15% 5% 7% 15% 30% 28%	2589
	11th to 20th	Day	14% 3 6% 10% 27% 40%	2470
	21st to end	Day	10% 2 4 8% 23% 53%	2470
July	1st to 10th	Day	9% 2 4 6% 9% 71%	4046
	11th to 20th	Day	19% 4 7% 10% 23% 38%	4041
	21st to end	Day	15% 4 8% 14% 22% 36%	4314
August	1st to 10th	Day	15% 3 7% 13% 33% 28%	4078
	11th to 20th	Day	14% 5% 6% 12% 25% 38%	4067
	21st to end	Day	11% 3 4 11% 24% 47%	4437
September	1st to 10th	Day	13% 3 6% 11% 27% 41%	2095
	11th to 20th	Day	14% 4 7% 16% 26% 34%	2090
	21st to end	Day	13% 3 5% 15% 34% 30%	2090
October	1st to 10th	Day	14% 3 5% 12% 33% 34%	3412
	11th to 20th	Day	19% 4 7% 20% 34% 16%	3150
	21st to end	Day	19% 3 8% 28% 33% 9%	3392
November	1st to 10th	Day	26% 6% 14% 26% 23% 5%	1764
	11th to 20th	Day	26% 6% 12% 33% 21% 3	1800
	21st to end	Day	33% 6% 15% 25% 19% 2	1800
December	1st to 10th	Day	34% 7% 14% 31% 12% 2	2950
	11th to 20th	Day	33% 8% 16% 30% 12%	3408
	21st to end	Day	43% 10% 15% 21% 10% 1	4510
January	1st to 10th	Night	38% 10% 20% 21% 10% 1	5867
	11th to 20th	Night	38% 9% 19% 20% 12% 2	5880
	21st to end	Night	35% 10% 18% 21% 16% 1	6468
February	1st to 10th	Night	37% 7% 16% 25% 12% 3	2600
	11th to 20th	Night	35% 6% 13% 22% 21% 3	2366
	21st to end	Night	34% 6% 10% 25% 20% 4	1980
March	1st to 10th	Night	35% 5% 10% 23% 19% 8%	5124
	11th to 20th	Night	34% 7% 10% 25% 19% 5%	5000
	21st to end	Night	34% 7% 10% 24% 21% 4	5489
April	1st to 10th	Night	31% 5% 8% 24% 20% 11%	2199
	11th to 20th	Night	31% 5% 8% 21% 23% 12%	1827
	21st to end	Night	27% 6% 11% 21% 27% 7%	1800
May	1st to 10th	Night	31% 8% 9% 14% 28% 10%	4097
	11th to 20th	Night	25% 7% 8% 16% 32% 12%	4075
	21st to end	Night	20% 5% 7% 17% 36% 15%	4474
June	1st to 10th	Night	17% 7% 9% 14% 28% 26%	1795
	11th to 20th	Night	16% 4 6% 8% 24% 41%	1710
	21st to end	Night	14% 3 5% 7% 18% 52%	1710
July	1st to 10th	Night	12% 3 4 5% 7% 69%	2815
	11th to 20th	Night	30% 4 8% 10% 20% 28%	2806
	21st to end	Night	24% 6% 8% 13% 18% 31%	3011
August	1st to 10th	Night	25% 5% 8% 14% 22% 26%	2838
	11th to 20th	Night	16% 4 8% 14% 18% 40%	2838
	21st to end	Night	14% 3 4 11% 18% 50%	3228
September	1st to 10th	Night	13% 4 7% 12% 22% 42%	2085
	11th to 20th	Night	16% 3 7% 15% 22% 36%	2090
	21st to end	Night	16% 3 5% 12% 29% 35%	2090
October	1st to 10th	Night	15% 3 5% 9% 29% 39%	3552
	11th to 20th	Night	22% 3 6% 16% 36% 17%	3778
	21st to end	Night	19% 2 6% 23% 41% 9%	4150
November	1st to 10th	Night	23% 4 9% 25% 30% 9%	2535
	11th to 20th	Night	23% 5% 11% 32% 25% 5%	2600
	21st to end	Night	31% 4 10% 29% 23% 2	2600
December	1st to 10th	Night	29% 9% 20% 27% 14% 2	4240
	11th to 20th	Night	30% 8% 18% 33% 10%	4811
	21st to end	Night	40% 10% 15% 24% 11%	6468

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	15% 4 14% 33% 24% 9%	300
	11th to 20th	Day	11% 5% 17% 32% 24% 10%	300
	21st to end	Day	13% 3 12% 31% 27% 15%	330
February	1st to 10th	Day	7% 10% 19% 34% 17% 12%	300
	11th to 20th	Day	10% 7% 19% 31% 25% 8%	465
	21st to end	Day	7% 8% 22% 31% 23% 8%	414
March	1st to 10th	Day	12% 9% 20% 27% 25% 7%	500
	11th to 20th	Day	8% 9% 20% 31% 21% 11%	500
	21st to end	Day	13% 12% 26% 24% 18% 7%	550
April	1st to 10th	Day	9% 9% 19% 25% 24% 13%	500
	11th to 20th	Day	9% 14% 22% 27% 21% 8%	492
	21st to end	Day	9% 11% 20% 24% 21% 15%	500
May	1st to 10th	Day	5% 8% 22% 30% 21% 15%	503
	11th to 20th	Day	7% 6% 19% 25% 26% 19%	528
	21st to end	Day	7% 5% 14% 25% 24% 25%	573
June	1st to 10th	Day	3 5% 14% 27% 27% 24%	527
	11th to 20th	Day	4 8% 19% 23% 26% 20%	490
	21st to end	Day	3 4 14% 28% 32% 19%	490
July	1st to 10th	Day	3 1 13% 31% 30% 21%	486
	11th to 20th	Day	4 2 9% 27% 27% 31%	484
	21st to end	Day	2 2 6% 20% 37% 33%	531
August	1st to 10th	Day	3 1 10% 29% 32% 24%	487
	11th to 20th	Day	3 1 13% 25% 30% 29%	477
	21st to end	Day	3 4 13% 20% 31% 29%	539
September	1st to 10th	Day	3 3 11% 22% 26% 35%	490
	11th to 20th	Day	3 6% 18% 21% 28% 24%	490
	21st to end	Day	4 3 14% 20% 30% 29%	490
October	1st to 10th	Day	5% 4 16% 21% 28% 26%	451
	11th to 20th	Day	5% 3 10% 24% 27% 30%	300
	21st to end	Day	9% 3 10% 27% 32% 18%	330
November	1st to 10th	Day	9% 7% 14% 26% 22% 22%	300
	11th to 20th	Day	5% 4 13% 30% 32% 16%	300
	21st to end	Day	10% 4 11% 24% 32% 19%	300
December	1st to 10th	Day	10% 3 11% 31% 28% 16%	300
	11th to 20th	Day	9% 5% 7% 34% 34% 11%	300
	21st to end	Day	12% 8% 15% 38% 22% 6%	330
January	1st to 10th	Night	10% 5% 13% 42% 25% 6%	800
	11th to 20th	Night	10% 4 15% 41% 26% 5%	800
	21st to end	Night	11% 3 14% 44% 24% 5%	880
February	1st to 10th	Night	11% 4 20% 44% 18% 3	800
	11th to 20th	Night	11% 3 20% 45% 19% 2	784
	21st to end	Night	8% 6% 22% 47% 15% 1	660
March	1st to 10th	Night	13% 5% 21% 42% 18% 1	800
	11th to 20th	Night	7% 5% 22% 43% 22% 1	800
	21st to end	Night	10% 7% 28% 38% 16% 1	880
April	1st to 10th	Night	9% 7% 25% 40% 18% 2	800
	11th to 20th	Night	8% 8% 29% 40% 14% 1	639
	21st to end	Night	11% 7% 25% 36% 19% 2	600
May	1st to 10th	Night	13% 5% 22% 40% 18% 2	600
	11th to 20th	Night	8% 6% 19% 42% 23% 2	591
	21st to end	Night	8% 6% 21% 38% 27% 1	650
June	1st to 10th	Night	5% 5% 21% 43% 26% 1	599
	11th to 20th	Night	6% 6% 26% 40% 22%	570
	21st to end	Night	3 2 21% 47% 25% 1	570
July	1st to 10th	Night	4 1 16% 43% 35% 2	555
	11th to 20th	Night	6% 1 11% 43% 35% 3	552
	21st to end	Night	5% 1 10% 42% 40% 1	624
August	1st to 10th	Night	5% 2 16% 46% 31% 1	567
	11th to 20th	Night	3 2 14% 46% 33% 2	564
	21st to end	Night	5% 2 14% 38% 38% 3	670
September	1st to 10th	Night	4 2 11% 36% 41% 7%	760
	11th to 20th	Night	4 2 18% 35% 35% 6%	760
	21st to end	Night	5% 2 14% 34% 38% 7%	760
October	1st to 10th	Night	6% 3 17% 40% 29% 6%	760
	11th to 20th	Night	5% 3 13% 41% 33% 6%	760
	21st to end	Night	6% 3 17% 37% 32% 5%	836
November	1st to 10th	Night	6% 3 17% 38% 31% 4	780
	11th to 20th	Night	7% 3 16% 45% 25% 4	800
	21st to end	Night	11% 2 16% 38% 27% 6%	800
December	1st to 10th	Night	10% 4 14% 46% 22% 4	800
	11th to 20th	Night	10% 3 14% 44% 27% 2	800
	21st to end	Night	12% 6% 16% 44% 19% 2	880

Page generated at 2025-06-07 08:28:17. Version ac07

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