Asbestos
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Asbestos clear sky chart from 2005-11-06 to 2026-05-17.

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	19% 12% 4 9% 5% 5% 5% 3 5% 6% 26%	131430
	Night	18% 15% 5% 11% 6% 5% 4 3 4 5% 25%	131402
Transparency	Day	58% 5% 11% 18% 7% 1	134886
	Night	61% 4 10% 16% 7% 1	136034
Seeing	Day	28% 17% 29% 18% 7% 2	16514
	Night	27% 14% 27% 23% 8% 1	25599

By Month

Percentage Cloud Cover NE (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	15% 20% 8% 18% 6% 7% 5% 2 3 3 13%	4661
	11th to 20th	Day	10% 19% 8% 24% 11% 5% 4 2 2 2 11%	4650
	21st to end	Day	8% 17% 7% 15% 10% 11% 7% 4 4 4 14%	5124
February	1st to 10th	Day	15% 18% 6% 14% 8% 5% 4 3 4 4 18%	1733
	11th to 20th	Day	14% 20% 8% 13% 7% 5% 4 3 3 4 19%	2041
	21st to end	Day	14% 18% 6% 12% 8% 6% 4 3 3 4 22%	1730
March	1st to 10th	Day	19% 17% 6% 13% 6% 4 5% 3 3 4 20%	4576
	11th to 20th	Day	15% 18% 5% 10% 5% 4 5% 3 4 6% 27%	4800
	21st to end	Day	22% 16% 4 10% 4 4 3 2 4 4 28%	6024
April	1st to 10th	Day	23% 16% 4 10% 5% 4 4 3 4 3 25%	2520
	11th to 20th	Day	22% 13% 3 6% 5% 3 3 2 4 5% 32%	2545
	21st to end	Day	24% 12% 4 7% 4 4 4 3 4 6% 27%	2730
May	1st to 10th	Day	28% 10% 3 9% 6% 5% 4 3 5% 5% 21%	6152
	11th to 20th	Day	20% 8% 3 8% 5% 5% 5% 4 5% 7% 29%	6402
	21st to end	Day	20% 10% 3 7% 5% 5% 5% 4 5% 6% 29%	6949
June	1st to 10th	Day	25% 8% 3 7% 4 4 4 4 6% 7% 28%	2800
	11th to 20th	Day	19% 7% 2 6% 4 5% 5% 4 6% 8% 34%	2800
	21st to end	Day	24% 9% 3 8% 5% 5% 5% 4 5% 7% 27%	2800
July	1st to 10th	Day	17% 8% 3 8% 6% 6% 6% 5% 8% 9% 25%	6360
	11th to 20th	Day	15% 7% 3 7% 5% 5% 6% 4 7% 9% 34%	6360
	21st to end	Day	15% 6% 2 5% 4 4 4 4 6% 9% 41%	6926
August	1st to 10th	Day	19% 7% 3 8% 4 5% 6% 5% 6% 9% 29%	4541
	11th to 20th	Day	19% 6% 3 7% 6% 5% 4 4 7% 10% 29%	4175
	21st to end	Day	21% 7% 2 6% 4 4 4 4 6% 7% 36%	4355
September	1st to 10th	Day	17% 6% 2 7% 4 4 4 3 5% 8% 39%	2400
	11th to 20th	Day	19% 5% 2 4 3 4 3 4 6% 6% 43%	2243
	21st to end	Day	21% 7% 2 5% 4 4 4 3 6% 8% 35%	2200
October	1st to 10th	Day	23% 9% 2 6% 4 5% 4 3 5% 8% 32%	2172
	11th to 20th	Day	23% 13% 3 7% 4 5% 4 4 5% 6% 26%	1870
	21st to end	Day	27% 18% 3 7% 4 3 4 3 3 6% 23%	1980
November	1st to 10th	Day	22% 17% 4 7% 5% 3 4 3 4 5% 28%	1851
	11th to 20th	Day	19% 20% 6% 9% 5% 3 3 2 4 6% 22%	1890
	21st to end	Day	21% 23% 6% 9% 4 4 3 4 4 4 17%	1696
December	1st to 10th	Day	19% 21% 7% 15% 7% 4 4 2 3 4 12%	2450
	11th to 20th	Day	21% 18% 8% 11% 5% 4 3 2 3 3 22%	2876
	21st to end	Day	21% 18% 6% 12% 5% 5% 4 2 4 4 19%	4048
January	1st to 10th	Night	13% 21% 8% 17% 7% 4 4 3 3 4 15%	8234
	11th to 20th	Night	12% 23% 8% 22% 8% 6% 4 3 2 3 10%	8235
	21st to end	Night	8% 16% 6% 16% 11% 8% 5% 4 4 5% 19%	9057
February	1st to 10th	Night	14% 17% 6% 13% 7% 6% 4 2 4 5% 21%	2882
	11th to 20th	Night	14% 20% 5% 14% 7% 6% 4 3 3 4 21%	2463
	21st to end	Night	15% 18% 5% 10% 6% 5% 4 3 4 4 26%	2076
March	1st to 10th	Night	20% 15% 6% 11% 5% 5% 4 3 3 4 24%	5484
	11th to 20th	Night	16% 17% 6% 10% 5% 5% 4 3 4 6% 24%	5378
	21st to end	Night	17% 18% 5% 11% 5% 4 3 3 4 4 26%	5148
April	1st to 10th	Night	25% 13% 4 8% 4 4 4 3 4 4 28%	2100
	11th to 20th	Night	23% 12% 3 7% 4 4 3 3 4 6% 31%	2023
	21st to end	Night	25% 11% 3 7% 3 4 3 3 5% 4 32%	1890
May	1st to 10th	Night	27% 11% 3 9% 5% 4 5% 3 4 5% 23%	4052
	11th to 20th	Night	24% 10% 3 5% 5% 4 4 4 5% 7% 30%	3623
	21st to end	Night	20% 9% 3 6% 5% 4 5% 4 5% 7% 32%	3926
June	1st to 10th	Night	26% 7% 2 6% 5% 3 5% 4 7% 7% 28%	1600
	11th to 20th	Night	21% 6% 2 5% 4 4 4 5% 7% 7% 35%	1600
	21st to end	Night	21% 8% 2 7% 5% 4 6% 5% 5% 7% 31%	1600
July	1st to 10th	Night	17% 8% 3 7% 6% 6% 5% 4 7% 9% 29%	3600
	11th to 20th	Night	20% 6% 2 6% 4 4 4 3 6% 7% 36%	3600
	21st to end	Night	14% 6% 2 7% 5% 4 5% 4 7% 8% 38%	3926
August	1st to 10th	Night	22% 8% 3 8% 4 4 4 3 6% 6% 33%	2586
	11th to 20th	Night	19% 8% 2 8% 5% 5% 5% 4 5% 7% 32%	2863
	21st to end	Night	20% 8% 3 6% 3 4 4 3 5% 7% 37%	3540
September	1st to 10th	Night	19% 6% 2 7% 4 4 3 3 5% 6% 41%	2000
	11th to 20th	Night	17% 5% 2 6% 2 3 3 3 5% 6% 47%	2156
	21st to end	Night	21% 7% 2 5% 4 4 3 3 4 7% 40%	2200
October	1st to 10th	Night	21% 8% 3 6% 4 4 4 3 5% 6% 38%	2225
	11th to 20th	Night	23% 12% 3 7% 4 4 4 3 5% 6% 30%	2529
	21st to end	Night	26% 13% 3 7% 4 4 4 3 4 5% 27%	2860
November	1st to 10th	Night	22% 16% 3 8% 4 4 4 3 4 4 26%	2667
	11th to 20th	Night	20% 17% 5% 9% 4 3 4 3 4 4 27%	2730
	21st to end	Night	22% 19% 6% 10% 5% 4 3 3 4 4 21%	2923
December	1st to 10th	Night	18% 24% 11% 15% 6% 4 4 2 3 3 11%	4947
	11th to 20th	Night	20% 20% 5% 13% 5% 4 4 2 3 4 19%	5529
	21st to end	Night	20% 20% 5% 11% 5% 4 3 2 3 4 22%	7150

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	78% 3 7% 9% 2	4662
	11th to 20th	Day	81% 2 4 8% 3	4680
	21st to end	Day	73% 4 5% 9% 8%	5124
February	1st to 10th	Day	71% 4 6% 13% 5% 1	1733
	11th to 20th	Day	71% 3 8% 12% 5% 1	2050
	21st to end	Day	67% 4 8% 14% 6% 1	1730
March	1st to 10th	Day	69% 4 6% 11% 8% 3	4579
	11th to 20th	Day	60% 4 13% 12% 9% 1	4800
	21st to end	Day	62% 3 6% 15% 13% 1	6024
April	1st to 10th	Day	64% 4 7% 16% 8% 2	2520
	11th to 20th	Day	56% 3 8% 19% 13% 1	2545
	21st to end	Day	58% 4 8% 17% 10% 2	2730
May	1st to 10th	Day	64% 5% 9% 16% 5% 1	6163
	11th to 20th	Day	53% 7% 16% 16% 7% 2	6406
	21st to end	Day	53% 6% 11% 18% 11% 1	6949
June	1st to 10th	Day	54% 6% 11% 20% 8% 1	2800
	11th to 20th	Day	47% 6% 14% 23% 10% 1	2800
	21st to end	Day	58% 5% 11% 18% 8%	2800
July	1st to 10th	Day	54% 6% 15% 20% 5%	6290
	11th to 20th	Day	45% 6% 16% 27% 6%	6285
	21st to end	Day	39% 6% 16% 32% 7%	6728
August	1st to 10th	Day	51% 6% 18% 20% 4	4527
	11th to 20th	Day	50% 7% 20% 18% 5%	4214
	21st to end	Day	48% 6% 15% 19% 12% 1	4355
September	1st to 10th	Day	43% 6% 15% 26% 9% 1	2400
	11th to 20th	Day	41% 5% 13% 30% 11%	2243
	21st to end	Day	46% 7% 13% 24% 10%	2200
October	1st to 10th	Day	50% 5% 16% 23% 6%	3536
	11th to 20th	Day	56% 4 13% 24% 3	3021
	21st to end	Day	56% 4 16% 18% 6% 1	3180
November	1st to 10th	Day	61% 4 12% 17% 6%	1851
	11th to 20th	Day	65% 4 10% 13% 7% 1	1890
	21st to end	Day	71% 4 11% 11% 2	1696
December	1st to 10th	Day	78% 3 9% 8% 3	2450
	11th to 20th	Day	70% 3 6% 15% 6%	2877
	21st to end	Day	70% 3 7% 11% 8%	4048
January	1st to 10th	Night	74% 4 8% 10% 3	8234
	11th to 20th	Night	82% 3 5% 7% 2	8280
	21st to end	Night	69% 4 7% 11% 9%	9057
February	1st to 10th	Night	67% 4 8% 14% 6% 1	2882
	11th to 20th	Night	69% 4 8% 12% 7%	2465
	21st to end	Night	62% 3 8% 16% 9% 1	2076
March	1st to 10th	Night	65% 4 7% 12% 9% 2	5494
	11th to 20th	Night	63% 4 12% 13% 7% 1	5379
	21st to end	Night	64% 3 6% 17% 9% 1	5148
April	1st to 10th	Night	60% 4 7% 16% 11% 1	2100
	11th to 20th	Night	56% 4 7% 19% 12% 2	2023
	21st to end	Night	55% 5% 10% 18% 11% 2	1890
May	1st to 10th	Night	62% 5% 10% 15% 7% 1	4058
	11th to 20th	Night	53% 7% 12% 20% 7% 1	3624
	21st to end	Night	50% 6% 13% 16% 14% 1	3927
June	1st to 10th	Night	53% 7% 11% 19% 9% 1	1600
	11th to 20th	Night	46% 7% 11% 22% 12% 2	1600
	21st to end	Night	52% 7% 12% 18% 10% 1	1600
July	1st to 10th	Night	52% 5% 19% 17% 6%	3560
	11th to 20th	Night	46% 5% 18% 23% 7%	3552
	21st to end	Night	43% 6% 17% 26% 7%	3809
August	1st to 10th	Night	51% 5% 15% 24% 5%	2576
	11th to 20th	Night	52% 7% 15% 19% 6%	2890
	21st to end	Night	47% 5% 12% 23% 13%	3540
September	1st to 10th	Night	45% 6% 14% 25% 11% 1	2000
	11th to 20th	Night	38% 4 16% 31% 10% 1	2156
	21st to end	Night	45% 5% 11% 25% 12% 1	2200
October	1st to 10th	Night	50% 4 12% 24% 10%	3641
	11th to 20th	Night	54% 5% 12% 25% 5%	4117
	21st to end	Night	54% 5% 14% 19% 8% 2	4610
November	1st to 10th	Night	60% 6% 11% 17% 5% 1	2667
	11th to 20th	Night	62% 4 11% 14% 8% 1	2730
	21st to end	Night	68% 4 11% 13% 4	2923
December	1st to 10th	Night	81% 3 8% 7% 2	4947
	11th to 20th	Night	72% 3 7% 13% 6%	5529
	21st to end	Night	68% 3 8% 14% 8%	7150

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	31% 25% 30% 12% 2	220
	11th to 20th	Day	32% 24% 31% 11% 2	220
	21st to end	Day	29% 22% 33% 13% 3	242
February	1st to 10th	Day	36% 27% 27% 8% 2	248
	11th to 20th	Day	31% 25% 32% 11% 2	529
	21st to end	Day	30% 27% 29% 13% 1	446
March	1st to 10th	Day	29% 24% 29% 15% 3	540
	11th to 20th	Day	31% 24% 27% 13% 4 1	540
	21st to end	Day	34% 22% 25% 12% 5% 1	594
April	1st to 10th	Day	38% 18% 25% 13% 6%	540
	11th to 20th	Day	38% 17% 25% 14% 4 2	532
	21st to end	Day	33% 21% 28% 12% 5% 1	540
May	1st to 10th	Day	33% 20% 28% 13% 5% 1	543
	11th to 20th	Day	26% 15% 32% 20% 6% 2	551
	21st to end	Day	24% 22% 30% 18% 6% 1	573
June	1st to 10th	Day	28% 16% 31% 18% 5% 1	530
	11th to 20th	Day	22% 18% 31% 21% 8% 1	530
	21st to end	Day	29% 14% 34% 16% 6% 2	530
July	1st to 10th	Day	21% 10% 35% 25% 9%	525
	11th to 20th	Day	18% 12% 37% 26% 7% 1	524
	21st to end	Day	22% 9% 35% 27% 7% 1	576
August	1st to 10th	Day	20% 10% 27% 28% 12% 2	526
	11th to 20th	Day	19% 8% 30% 25% 16% 2	519
	21st to end	Day	22% 15% 23% 23% 11% 6%	583
September	1st to 10th	Day	20% 11% 32% 22% 11% 5%	530
	11th to 20th	Day	19% 10% 22% 24% 17% 7%	530
	21st to end	Day	22% 13% 25% 26% 10% 4	530
October	1st to 10th	Day	25% 15% 26% 22% 10% 3	530
	11th to 20th	Day	34% 16% 25% 16% 9% 1	458
	21st to end	Day	40% 16% 25% 16% 4	462
November	1st to 10th	Day	37% 15% 28% 17% 3	425
	11th to 20th	Day	32% 20% 27% 16% 4 1	430
	21st to end	Day	36% 22% 30% 10% 3	236
December	1st to 10th	Day	35% 16% 30% 14% 5% 1	220
	11th to 20th	Day	37% 22% 30% 9% 1	220
	21st to end	Day	36% 25% 24% 11% 2 1	242
January	1st to 10th	Night	30% 20% 31% 16% 3	840
	11th to 20th	Night	28% 22% 29% 16% 4	840
	21st to end	Night	22% 19% 31% 22% 5%	924
February	1st to 10th	Night	24% 20% 31% 20% 4	840
	11th to 20th	Night	27% 22% 32% 16% 3	823
	21st to end	Night	27% 17% 34% 20% 3	692
March	1st to 10th	Night	29% 16% 33% 18% 3	840
	11th to 20th	Night	32% 19% 27% 18% 4	840
	21st to end	Night	27% 16% 28% 21% 6% 1	924
April	1st to 10th	Night	34% 15% 26% 21% 4	840
	11th to 20th	Night	31% 16% 27% 20% 6%	779
	21st to end	Night	31% 18% 28% 17% 6%	630
May	1st to 10th	Night	29% 10% 33% 21% 7% 1	590
	11th to 20th	Night	24% 10% 30% 29% 6% 1	406
	21st to end	Night	24% 12% 29% 28% 8%	433
June	1st to 10th	Night	29% 7% 27% 30% 8%	400
	11th to 20th	Night	21% 9% 25% 34% 11%	400
	21st to end	Night	22% 8% 27% 33% 10%	400
July	1st to 10th	Night	18% 6% 27% 35% 13% 1	390
	11th to 20th	Night	16% 5% 27% 37% 14% 2	388
	21st to end	Night	16% 5% 26% 39% 13%	438
August	1st to 10th	Night	17% 6% 15% 43% 18% 1	398
	11th to 20th	Night	18% 4 21% 36% 20% 1	583
	21st to end	Night	21% 6% 21% 34% 16% 2	847
September	1st to 10th	Night	22% 7% 25% 33% 12% 2	800
	11th to 20th	Night	20% 6% 20% 30% 22% 2	800
	21st to end	Night	24% 9% 26% 25% 15% 1	800
October	1st to 10th	Night	25% 11% 24% 29% 11% 1	800
	11th to 20th	Night	29% 12% 26% 24% 7% 2	800
	21st to end	Night	33% 15% 28% 21% 4	880
November	1st to 10th	Night	32% 17% 26% 20% 5%	820
	11th to 20th	Night	27% 19% 28% 17% 8% 1	840
	21st to end	Night	34% 19% 25% 17% 5% 1	840
December	1st to 10th	Night	36% 19% 26% 15% 4	912
	11th to 20th	Night	33% 20% 26% 16% 5% 1	898
	21st to end	Night	36% 19% 24% 16% 4	924

Page generated at 2026-05-14 01:58:55. Version ac07

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