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 2025-01-22.

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% 4 3 5% 6% 27%	104832
	Night	19% 14% 4 10% 5% 4 4 3 4 5% 27%	104542
Transparency	Day	57% 5% 12% 18% 7% 1	108306
	Night	60% 5% 11% 17% 7% 1	109158
Seeing	Day	28% 17% 28% 18% 7% 2	14829
	Night	27% 14% 27% 23% 8% 1	23925

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	18% 21% 7% 19% 6% 5% 3 2 3 3 13%	2597
	11th to 20th	Day	12% 16% 8% 22% 11% 4 3 2 2 2 17%	2600
	21st to end	Day	13% 21% 6% 14% 7% 6% 6% 4 4 4 16%	2780
February	1st to 10th	Day	16% 19% 7% 13% 7% 5% 4 3 4 4 18%	1567
	11th to 20th	Day	15% 21% 8% 12% 8% 5% 4 3 3 4 18%	1841
	21st to end	Day	14% 19% 5% 11% 7% 6% 4 3 4 5% 22%	1570
March	1st to 10th	Day	20% 15% 4 11% 6% 4 4 3 4 5% 24%	3116
	11th to 20th	Day	16% 23% 6% 11% 5% 4 4 2 3 4 21%	3280
	21st to end	Day	18% 15% 5% 10% 4 4 3 3 3 4 33%	4118
April	1st to 10th	Day	23% 16% 4 10% 5% 4 4 3 4 3 25%	2280
	11th to 20th	Day	22% 12% 3 6% 5% 3 4 2 4 5% 33%	2300
	21st to end	Day	25% 12% 4 7% 4 3 4 3 4 6% 28%	2470
May	1st to 10th	Day	25% 9% 3 8% 6% 4 4 3 5% 6% 28%	4197
	11th to 20th	Day	18% 8% 3 7% 6% 5% 5% 4 6% 8% 29%	4398
	21st to end	Day	16% 8% 3 7% 5% 6% 5% 5% 6% 7% 31%	4837
June	1st to 10th	Day	26% 8% 3 7% 4 4 4 4 6% 7% 28%	2660
	11th to 20th	Day	19% 7% 2 6% 4 5% 5% 4 6% 8% 34%	2660
	21st to end	Day	24% 9% 3 8% 5% 5% 5% 3 5% 7% 27%	2660
July	1st to 10th	Day	16% 7% 3 7% 5% 5% 6% 5% 7% 8% 30%	4440
	11th to 20th	Day	16% 7% 3 7% 5% 6% 6% 4 7% 8% 30%	4440
	21st to end	Day	16% 7% 2 6% 4 4 5% 3 6% 8% 41%	4814
August	1st to 10th	Day	20% 7% 3 8% 4 5% 6% 5% 6% 9% 27%	4402
	11th to 20th	Day	19% 6% 3 7% 6% 5% 4 4 7% 10% 28%	4045
	21st to end	Day	22% 7% 2 6% 4 4 4 4 6% 7% 36%	4222
September	1st to 10th	Day	17% 6% 2 7% 4 4 4 3 6% 8% 39%	2280
	11th to 20th	Day	20% 5% 2 4 3 4 3 4 6% 6% 42%	2131
	21st to end	Day	22% 7% 2 5% 4 4 4 3 7% 8% 34%	2090
October	1st to 10th	Day	24% 9% 2 6% 4 5% 4 3 5% 8% 29%	2064
	11th to 20th	Day	24% 13% 3 7% 4 5% 4 4 5% 6% 26%	1777
	21st to end	Day	27% 17% 3 7% 4 3 4 3 3 5% 23%	1881
November	1st to 10th	Day	22% 15% 3 7% 5% 3 4 3 4 5% 29%	1761
	11th to 20th	Day	20% 19% 6% 9% 5% 3 3 3 4 6% 23%	1800
	21st to end	Day	21% 23% 5% 9% 4 4 3 4 4 4 18%	1615
December	1st to 10th	Day	19% 22% 7% 15% 7% 4 4 2 3 4 12%	2377
	11th to 20th	Day	21% 18% 8% 10% 5% 5% 3 2 3 3 22%	2802
	21st to end	Day	21% 18% 6% 12% 5% 5% 4 3 4 4 19%	3960
January	1st to 10th	Night	17% 22% 7% 15% 5% 4 4 2 3 4 16%	4569
	11th to 20th	Night	13% 19% 7% 19% 7% 6% 4 3 3 3 15%	4580
	21st to end	Night	13% 21% 6% 14% 7% 5% 4 3 4 3 20%	4899
February	1st to 10th	Night	15% 17% 6% 13% 8% 6% 4 2 4 5% 21%	2608
	11th to 20th	Night	14% 20% 5% 14% 7% 6% 4 3 3 4 20%	2223
	21st to end	Night	16% 17% 5% 10% 6% 5% 4 3 4 4 26%	1884
March	1st to 10th	Night	23% 14% 4 8% 4 3 4 2 3 4 30%	3724
	11th to 20th	Night	18% 22% 6% 10% 5% 4 3 2 3 4 22%	3678
	21st to end	Night	16% 17% 5% 11% 5% 4 3 3 3 3 29%	3512
April	1st to 10th	Night	25% 13% 4 8% 4 4 4 3 4 4 28%	1900
	11th to 20th	Night	23% 11% 3 7% 4 4 3 3 4 6% 32%	1829
	21st to end	Night	25% 11% 3 7% 3 4 3 3 5% 5% 31%	1710
May	1st to 10th	Night	25% 9% 3 8% 5% 4 5% 3 4 6% 27%	2772
	11th to 20th	Night	21% 10% 3 5% 4 3 3 4 6% 7% 33%	2495
	21st to end	Night	19% 6% 2 5% 4 4 5% 4 6% 7% 36%	2738
June	1st to 10th	Night	26% 7% 2 6% 5% 3 5% 4 7% 7% 28%	1520
	11th to 20th	Night	21% 6% 2 5% 4 4 4 4 7% 7% 36%	1520
	21st to end	Night	21% 8% 2 7% 5% 4 6% 5% 5% 7% 30%	1520
July	1st to 10th	Night	15% 8% 3 7% 7% 5% 5% 4 6% 9% 31%	2520
	11th to 20th	Night	18% 7% 2 7% 5% 4 5% 3 6% 7% 35%	2520
	21st to end	Night	16% 6% 2 7% 4 4 4 4 7% 7% 39%	2739
August	1st to 10th	Night	23% 8% 3 8% 4 4 4 3 6% 6% 32%	2506
	11th to 20th	Night	19% 8% 2 8% 5% 5% 5% 4 5% 7% 31%	2773
	21st to end	Night	20% 8% 3 6% 3 4 4 3 5% 7% 37%	3431
September	1st to 10th	Night	20% 7% 2 7% 4 4 3 3 4 6% 40%	1900
	11th to 20th	Night	18% 6% 2 5% 2 3 3 3 5% 7% 46%	2048
	21st to end	Night	21% 7% 2 5% 4 4 3 3 4 7% 40%	2090
October	1st to 10th	Night	22% 8% 3 6% 4 4 4 3 5% 6% 36%	2114
	11th to 20th	Night	24% 12% 3 7% 4 4 4 3 4 6% 29%	2402
	21st to end	Night	27% 13% 3 7% 4 3 4 3 4 5% 27%	2717
November	1st to 10th	Night	22% 16% 3 9% 4 4 4 3 4 5% 27%	2537
	11th to 20th	Night	20% 15% 5% 8% 4 3 4 3 4 4 28%	2600
	21st to end	Night	22% 19% 6% 9% 5% 4 3 2 4 4 22%	2784
December	1st to 10th	Night	18% 24% 11% 15% 6% 4 4 2 3 3 11%	4800
	11th to 20th	Night	21% 21% 5% 13% 5% 4 3 2 3 4 19%	5384
	21st to end	Night	21% 20% 5% 10% 5% 4 3 2 3 4 23%	6996

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% 4 8% 9% 1	2598
	11th to 20th	Day	76% 3 6% 12% 3 1	2600
	21st to end	Day	71% 6% 8% 11% 4	2780
February	1st to 10th	Day	72% 4 7% 11% 5% 1	1567
	11th to 20th	Day	72% 4 8% 10% 5% 1	1850
	21st to end	Day	66% 5% 8% 14% 6% 1	1570
March	1st to 10th	Day	63% 4 8% 15% 8% 2	3119
	11th to 20th	Day	67% 4 9% 11% 8% 1	3280
	21st to end	Day	58% 3 7% 17% 14% 2	4118
April	1st to 10th	Day	64% 4 7% 15% 8% 2	2280
	11th to 20th	Day	54% 4 8% 20% 13% 1	2300
	21st to end	Day	59% 4 8% 16% 10% 2	2470
May	1st to 10th	Day	57% 5% 10% 19% 8% 1	4211
	11th to 20th	Day	51% 8% 19% 15% 6% 1	4402
	21st to end	Day	48% 8% 11% 21% 12%	4837
June	1st to 10th	Day	55% 6% 11% 20% 7% 1	2660
	11th to 20th	Day	47% 7% 14% 22% 10% 1	2660
	21st to end	Day	58% 5% 11% 18% 8%	2660
July	1st to 10th	Day	49% 6% 15% 24% 6%	4370
	11th to 20th	Day	49% 6% 17% 24% 4	4365
	21st to end	Day	42% 7% 15% 30% 6%	4661
August	1st to 10th	Day	52% 6% 18% 20% 4	4388
	11th to 20th	Day	50% 7% 20% 18% 4	4084
	21st to end	Day	48% 6% 15% 18% 12% 1	4222
September	1st to 10th	Day	44% 6% 16% 24% 9% 1	2280
	11th to 20th	Day	42% 5% 13% 29% 11%	2131
	21st to end	Day	47% 7% 13% 24% 9%	2090
October	1st to 10th	Day	51% 5% 16% 23% 6%	3428
	11th to 20th	Day	56% 4 14% 24% 2	2928
	21st to end	Day	56% 4 16% 18% 6% 1	3081
November	1st to 10th	Day	59% 4 12% 18% 7%	1761
	11th to 20th	Day	64% 4 10% 13% 8% 1	1800
	21st to end	Day	70% 5% 12% 11% 2	1615
December	1st to 10th	Day	78% 3 9% 7% 3	2377
	11th to 20th	Day	69% 3 6% 15% 6%	2803
	21st to end	Day	70% 3 7% 11% 9%	3960
January	1st to 10th	Night	73% 6% 11% 8% 2	4569
	11th to 20th	Night	75% 4 8% 9% 2	4580
	21st to end	Night	69% 5% 10% 11% 4 1	4899
February	1st to 10th	Night	67% 4 9% 13% 6% 1	2608
	11th to 20th	Night	69% 4 8% 12% 7%	2225
	21st to end	Night	62% 4 9% 15% 10% 1	1884
March	1st to 10th	Night	60% 4 10% 15% 9% 2	3734
	11th to 20th	Night	68% 4 7% 12% 8% 1	3679
	21st to end	Night	61% 3 7% 18% 9% 2	3512
April	1st to 10th	Night	60% 4 7% 16% 11% 1	1900
	11th to 20th	Night	54% 4 8% 21% 12% 2	1829
	21st to end	Night	55% 5% 10% 17% 11% 2	1710
May	1st to 10th	Night	56% 6% 11% 17% 8% 1	2778
	11th to 20th	Night	47% 9% 14% 19% 9% 1	2496
	21st to end	Night	45% 7% 12% 18% 17% 1	2739
June	1st to 10th	Night	53% 7% 11% 19% 9% 1	1520
	11th to 20th	Night	45% 7% 11% 23% 13% 2	1520
	21st to end	Night	53% 7% 12% 18% 10% 1	1520
July	1st to 10th	Night	49% 6% 17% 19% 9%	2480
	11th to 20th	Night	47% 6% 20% 21% 7%	2472
	21st to end	Night	43% 7% 18% 25% 7%	2651
August	1st to 10th	Night	52% 5% 15% 23% 4	2496
	11th to 20th	Night	53% 7% 16% 19% 6%	2800
	21st to end	Night	47% 5% 12% 22% 13%	3431
September	1st to 10th	Night	45% 6% 14% 24% 11% 1	1900
	11th to 20th	Night	38% 4 16% 30% 10% 1	2048
	21st to end	Night	45% 6% 12% 25% 12% 1	2090
October	1st to 10th	Night	51% 5% 12% 23% 9%	3530
	11th to 20th	Night	54% 5% 12% 24% 4	3990
	21st to end	Night	53% 5% 14% 19% 7% 2	4467
November	1st to 10th	Night	59% 6% 12% 17% 6% 1	2537
	11th to 20th	Night	61% 4 11% 15% 8% 2	2600
	21st to end	Night	67% 4 11% 14% 4	2784
December	1st to 10th	Night	81% 3 8% 7% 2	4800
	11th to 20th	Night	72% 3 7% 13% 6%	5384
	21st to end	Night	67% 3 8% 14% 8%	6996

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	32% 25% 30% 12% 2	200
	11th to 20th	Day	30% 24% 32% 13% 3	200
	21st to end	Day	26% 23% 34% 13% 4 1	200
February	1st to 10th	Day	42% 27% 24% 7% 1	202
	11th to 20th	Day	31% 26% 32% 9% 2	449
	21st to end	Day	30% 27% 27% 13% 2	382
March	1st to 10th	Day	29% 22% 28% 16% 4	460
	11th to 20th	Day	30% 23% 28% 14% 4 1	460
	21st to end	Day	30% 23% 26% 13% 6% 2	506
April	1st to 10th	Day	36% 18% 26% 14% 7%	460
	11th to 20th	Day	35% 19% 25% 14% 5% 2	452
	21st to end	Day	33% 22% 29% 12% 4 1	460
May	1st to 10th	Day	31% 21% 27% 15% 5% 1	463
	11th to 20th	Day	25% 15% 32% 21% 6% 2	487
	21st to end	Day	23% 22% 31% 18% 5% 1	529
June	1st to 10th	Day	28% 17% 29% 18% 6% 1	490
	11th to 20th	Day	22% 19% 29% 21% 9% 1	490
	21st to end	Day	29% 13% 32% 17% 7% 2	490
July	1st to 10th	Day	20% 10% 34% 25% 9%	485
	11th to 20th	Day	18% 12% 36% 26% 7% 1	484
	21st to end	Day	22% 8% 35% 27% 7% 1	532
August	1st to 10th	Day	22% 11% 27% 27% 12% 2	486
	11th to 20th	Day	20% 8% 30% 25% 15% 2	479
	21st to end	Day	23% 14% 23% 22% 12% 6%	539
September	1st to 10th	Day	20% 12% 32% 21% 11% 5%	490
	11th to 20th	Day	20% 10% 22% 25% 16% 7%	490
	21st to end	Day	21% 13% 25% 26% 10% 5%	490
October	1st to 10th	Day	26% 15% 26% 20% 10% 3	490
	11th to 20th	Day	35% 16% 24% 15% 9% 1	425
	21st to end	Day	40% 16% 24% 16% 4	429
November	1st to 10th	Day	36% 15% 28% 18% 3	395
	11th to 20th	Day	32% 20% 27% 16% 4 1	400
	21st to end	Day	35% 21% 30% 11% 3	215
December	1st to 10th	Day	36% 16% 29% 13% 5% 1	200
	11th to 20th	Day	38% 21% 30% 10% 1 1	200
	21st to end	Day	37% 25% 23% 10% 3 1	220
January	1st to 10th	Night	31% 20% 31% 16% 3	800
	11th to 20th	Night	28% 22% 30% 17% 4	800
	21st to end	Night	22% 20% 30% 23% 5%	841
February	1st to 10th	Night	25% 21% 31% 20% 4	760
	11th to 20th	Night	26% 23% 31% 17% 3	743
	21st to end	Night	26% 17% 33% 21% 3	628
March	1st to 10th	Night	29% 15% 33% 20% 3	760
	11th to 20th	Night	31% 18% 27% 19% 5%	760
	21st to end	Night	26% 17% 27% 23% 7% 1	836
April	1st to 10th	Night	33% 15% 25% 23% 4	760
	11th to 20th	Night	30% 16% 27% 21% 6%	705
	21st to end	Night	32% 18% 27% 17% 6%	570
May	1st to 10th	Night	29% 10% 32% 21% 8% 1	534
	11th to 20th	Night	24% 11% 29% 29% 6% 1	374
	21st to end	Night	23% 12% 29% 27% 8%	411
June	1st to 10th	Night	28% 7% 27% 30% 8%	380
	11th to 20th	Night	21% 8% 26% 34% 12%	380
	21st to end	Night	23% 7% 27% 33% 10%	380
July	1st to 10th	Night	18% 5% 28% 36% 13% 1	370
	11th to 20th	Night	16% 5% 27% 36% 14% 2	368
	21st to end	Night	17% 5% 25% 39% 14%	416
August	1st to 10th	Night	18% 6% 16% 41% 18% 1	378
	11th to 20th	Night	19% 5% 21% 37% 18% 1	553
	21st to end	Night	21% 6% 22% 33% 16% 2	804
September	1st to 10th	Night	23% 7% 25% 33% 12% 2	760
	11th to 20th	Night	21% 6% 20% 30% 20% 2	760
	21st to end	Night	24% 9% 25% 25% 15% 1	760
October	1st to 10th	Night	26% 12% 24% 28% 10% 1	760
	11th to 20th	Night	30% 12% 25% 24% 7% 2	760
	21st to end	Night	34% 15% 28% 20% 4	836
November	1st to 10th	Night	31% 17% 26% 21% 5% 1	780
	11th to 20th	Night	28% 19% 28% 17% 9% 1	800
	21st to end	Night	35% 19% 24% 17% 5% 1	800
December	1st to 10th	Night	37% 18% 26% 15% 4	865
	11th to 20th	Night	33% 19% 26% 16% 5% 1	853
	21st to end	Night	36% 19% 25% 16% 4	880

Page generated at 2025-01-19 03:06:49. Version ac07

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