C.O.A.M.N.D.
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the C.O.A.M.N.D. clear sky chart from 2005-11-06 to 2024-11-04.

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% 13% 4 10% 6% 5% 4 3 5% 6% 26%	101394
	Night	18% 14% 5% 10% 6% 4 4 3 4 5% 27%	97622
Transparency	Day	58% 6% 11% 17% 7% 1	104880
	Night	58% 6% 11% 17% 7% 1	102226
Seeing	Day	28% 20% 28% 16% 6% 1	15401
	Night	26% 17% 27% 22% 7% 1	23777

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	11% 19% 8% 17% 12% 6% 6% 3 4 3 12%	2517
	11th to 20th	Day	10% 15% 6% 21% 12% 9% 3 2 2 2 18%	2520
	21st to end	Day	9% 12% 8% 20% 8% 7% 5% 3 4 4 21%	2772
February	1st to 10th	Day	12% 18% 7% 14% 9% 7% 5% 3 3 4 17%	1562
	11th to 20th	Day	13% 18% 9% 15% 6% 5% 6% 3 4 3 18%	1805
	21st to end	Day	12% 17% 6% 14% 7% 4 5% 3 4 5% 22%	1570
March	1st to 10th	Day	16% 18% 5% 11% 6% 5% 4 3 4 5% 24%	3116
	11th to 20th	Day	15% 26% 7% 12% 5% 4 3 3 3 3 20%	3372
	21st to end	Day	17% 16% 5% 11% 5% 3 4 2 3 4 30%	3992
April	1st to 10th	Day	22% 18% 4 10% 4 3 3 2 4 5% 24%	2280
	11th to 20th	Day	19% 15% 4 6% 4 4 3 3 4 5% 33%	2371
	21st to end	Day	22% 12% 4 9% 4 4 4 3 4 6% 28%	2470
May	1st to 10th	Day	21% 10% 3 9% 5% 5% 5% 3 5% 5% 28%	4120
	11th to 20th	Day	21% 9% 3 8% 5% 5% 5% 5% 6% 8% 25%	4398
	21st to end	Day	20% 8% 3 8% 6% 5% 5% 4 5% 7% 29%	4979
June	1st to 10th	Day	25% 10% 3 7% 5% 5% 5% 3 7% 7% 24%	2850
	11th to 20th	Day	22% 7% 2 6% 4 6% 5% 5% 6% 7% 30%	2850
	21st to end	Day	26% 11% 4 8% 6% 4 4 4 4 4 24%	2850
July	1st to 10th	Day	19% 9% 3 9% 6% 5% 5% 4 6% 8% 27%	4581
	11th to 20th	Day	19% 9% 3 8% 6% 5% 6% 5% 6% 7% 27%	4440
	21st to end	Day	18% 7% 2 6% 4 4 5% 4 6% 8% 37%	4814
August	1st to 10th	Day	21% 7% 3 8% 5% 6% 5% 5% 6% 8% 26%	4330
	11th to 20th	Day	21% 9% 3 9% 5% 6% 7% 5% 6% 6% 22%	4045
	21st to end	Day	22% 9% 2 7% 4 4 4 4 5% 6% 33%	4390
September	1st to 10th	Day	22% 8% 3 6% 4 3 5% 4 5% 7% 34%	2271
	11th to 20th	Day	21% 7% 2 4 5% 4 3 3 4 5% 41%	2090
	21st to end	Day	23% 9% 3 6% 3 4 4 4 5% 7% 35%	2090
October	1st to 10th	Day	23% 12% 3 7% 4 4 4 3 4 6% 31%	2090
	11th to 20th	Day	24% 19% 3 7% 4 4 4 3 3 5% 23%	1752
	21st to end	Day	26% 19% 4 9% 4 3 4 3 4 4 20%	1881
November	1st to 10th	Day	20% 20% 5% 8% 4 3 3 2 3 4 26%	1698
	11th to 20th	Day	20% 18% 8% 10% 5% 5% 3 2 4 4 20%	1700
	21st to end	Day	19% 22% 6% 13% 6% 3 3 3 3 3 18%	1385
December	1st to 10th	Day	22% 23% 6% 13% 7% 2 4 3 3 3 14%	1330
	11th to 20th	Day	18% 21% 6% 12% 6% 5% 3 2 3 3 21%	1668
	21st to end	Day	23% 17% 6% 13% 8% 4 4 3 3 3 17%	2445
January	1st to 10th	Night	14% 18% 9% 16% 11% 4 4 3 4 3 15%	4429
	11th to 20th	Night	11% 18% 7% 18% 12% 6% 4 2 3 3 17%	4440
	21st to end	Night	8% 14% 8% 15% 8% 7% 5% 5% 6% 5% 20%	4884
February	1st to 10th	Night	11% 17% 6% 13% 10% 6% 5% 3 4 4 21%	2618
	11th to 20th	Night	11% 19% 6% 15% 8% 7% 5% 2 4 3 20%	2256
	21st to end	Night	13% 17% 6% 12% 7% 5% 4 2 4 4 27%	1884
March	1st to 10th	Night	18% 18% 4 8% 5% 3 6% 3 3 5% 27%	3724
	11th to 20th	Night	13% 20% 6% 13% 5% 5% 4 3 4 4 22%	3586
	21st to end	Night	18% 16% 5% 10% 6% 4 4 2 3 4 29%	3639
April	1st to 10th	Night	20% 17% 5% 8% 4 4 4 3 3 4 27%	1900
	11th to 20th	Night	20% 14% 3 8% 4 4 4 3 5% 6% 30%	1758
	21st to end	Night	20% 14% 4 7% 5% 4 4 3 5% 4 30%	1710
May	1st to 10th	Night	23% 9% 3 7% 5% 4 5% 3 4 7% 30%	2834
	11th to 20th	Night	20% 11% 2 8% 5% 4 4 3 4 6% 33%	2509
	21st to end	Night	19% 6% 2 6% 4 4 5% 4 5% 9% 35%	2597
June	1st to 10th	Night	24% 9% 3 7% 6% 5% 5% 4 6% 5% 26%	1330
	11th to 20th	Night	19% 8% 2 8% 4 5% 6% 4 5% 6% 35%	1330
	21st to end	Night	23% 11% 3 7% 5% 5% 5% 4 5% 6% 29%	1330
July	1st to 10th	Night	16% 9% 4 10% 5% 4 4 4 6% 7% 31%	2378
	11th to 20th	Night	25% 9% 3 8% 5% 4 4 3 4 5% 30%	2520
	21st to end	Night	17% 8% 2 6% 4 3 4 3 5% 7% 41%	2739
August	1st to 10th	Night	23% 7% 3 6% 5% 5% 5% 4 5% 8% 30%	2567
	11th to 20th	Night	21% 11% 3 9% 5% 5% 5% 4 4 6% 27%	2782
	21st to end	Night	18% 8% 3 8% 4 4 4 3 5% 7% 36%	3250
September	1st to 10th	Night	22% 7% 2 6% 4 4 4 3 4 6% 38%	1908
	11th to 20th	Night	20% 8% 2 6% 3 3 4 2 4 6% 42%	2090
	21st to end	Night	21% 8% 2 5% 4 4 4 3 5% 6% 39%	2090
October	1st to 10th	Night	22% 10% 3 5% 4 4 5% 3 5% 5% 36%	2090
	11th to 20th	Night	25% 14% 3 7% 5% 4 4 2 4 4 28%	2424
	21st to end	Night	25% 16% 3 8% 4 4 4 3 4 4 25%	2717
November	1st to 10th	Night	20% 17% 5% 8% 5% 4 4 3 3 5% 25%	2453
	11th to 20th	Night	19% 16% 5% 11% 5% 4 4 3 3 4 26%	2478
	21st to end	Night	18% 20% 7% 12% 5% 5% 4 2 4 3 20%	2793
December	1st to 10th	Night	21% 20% 8% 13% 6% 4 5% 2 3 3 14%	2850
	11th to 20th	Night	19% 18% 7% 15% 6% 5% 4 2 3 3 17%	3531
	21st to end	Night	21% 21% 6% 12% 5% 3 3 2 2 3 23%	5204

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	75% 6% 6% 10% 3	2518
	11th to 20th	Day	73% 5% 3 13% 5% 1	2520
	21st to end	Day	64% 8% 6% 12% 10% 1	2772
February	1st to 10th	Day	71% 4 6% 10% 7% 1	1562
	11th to 20th	Day	71% 4 7% 10% 7% 1	1814
	21st to end	Day	64% 5% 7% 16% 6% 2	1570
March	1st to 10th	Day	64% 3 9% 13% 10% 2	3119
	11th to 20th	Day	69% 5% 8% 11% 6%	3372
	21st to end	Day	57% 5% 7% 16% 12% 3	3992
April	1st to 10th	Day	64% 4 9% 13% 9% 2	2280
	11th to 20th	Day	54% 5% 8% 20% 11% 2	2371
	21st to end	Day	58% 5% 8% 17% 10% 2	2470
May	1st to 10th	Day	56% 6% 9% 18% 10% 1	4134
	11th to 20th	Day	54% 6% 17% 16% 5%	4402
	21st to end	Day	52% 8% 11% 20% 9%	4979
June	1st to 10th	Day	57% 7% 9% 20% 5% 1	2850
	11th to 20th	Day	50% 7% 14% 20% 8% 1	2850
	21st to end	Day	63% 5% 10% 15% 7%	2850
July	1st to 10th	Day	54% 7% 14% 18% 7%	4511
	11th to 20th	Day	53% 7% 17% 21% 3	4365
	21st to end	Day	46% 7% 13% 26% 7%	4661
August	1st to 10th	Day	53% 8% 16% 18% 4	4316
	11th to 20th	Day	57% 10% 16% 13% 4	4084
	21st to end	Day	50% 6% 15% 18% 11% 1	4390
September	1st to 10th	Day	47% 7% 14% 21% 10%	2271
	11th to 20th	Day	45% 4 12% 27% 11%	2090
	21st to end	Day	49% 5% 13% 23% 9%	2090
October	1st to 10th	Day	56% 4 12% 22% 6%	3480
	11th to 20th	Day	60% 4 12% 20% 4	2890
	21st to end	Day	57% 5% 14% 16% 7%	3081
November	1st to 10th	Day	62% 5% 10% 16% 6%	1698
	11th to 20th	Day	68% 4 9% 13% 6% 1	1700
	21st to end	Day	70% 5% 9% 12% 3	1385
December	1st to 10th	Day	74% 4 6% 11% 4	1330
	11th to 20th	Day	70% 4 5% 14% 7%	1668
	21st to end	Day	72% 5% 5% 11% 6% 2	2445
January	1st to 10th	Night	74% 5% 7% 10% 3	4429
	11th to 20th	Night	71% 6% 7% 12% 4	4440
	21st to end	Night	63% 7% 8% 12% 9% 2	4884
February	1st to 10th	Night	66% 5% 8% 12% 9% 1	2618
	11th to 20th	Night	68% 6% 5% 13% 6% 1	2258
	21st to end	Night	60% 4 8% 16% 11% 1	1884
March	1st to 10th	Night	61% 5% 9% 15% 8% 1	3734
	11th to 20th	Night	63% 7% 11% 11% 6% 1	3587
	21st to end	Night	60% 4 6% 19% 10% 2	3639
April	1st to 10th	Night	60% 4 7% 14% 12% 3	1900
	11th to 20th	Night	52% 6% 8% 21% 11% 1	1758
	21st to end	Night	57% 6% 7% 16% 12% 2	1710
May	1st to 10th	Night	51% 8% 11% 20% 9% 1	2840
	11th to 20th	Night	52% 6% 14% 18% 9%	2510
	21st to end	Night	44% 7% 15% 20% 14%	2598
June	1st to 10th	Night	57% 5% 12% 20% 6%	1330
	11th to 20th	Night	47% 8% 11% 21% 11% 2	1330
	21st to end	Night	55% 7% 14% 16% 8%	1330
July	1st to 10th	Night	49% 7% 19% 18% 6%	2338
	11th to 20th	Night	53% 7% 19% 18% 4	2472
	21st to end	Night	41% 7% 21% 23% 7%	2651
August	1st to 10th	Night	52% 6% 16% 23% 3	2557
	11th to 20th	Night	54% 10% 16% 16% 4	2809
	21st to end	Night	45% 7% 15% 20% 12% 2	3250
September	1st to 10th	Night	46% 6% 13% 24% 9% 1	1908
	11th to 20th	Night	44% 5% 17% 26% 8% 1	2090
	21st to end	Night	46% 6% 12% 23% 12%	2090
October	1st to 10th	Night	48% 4 11% 27% 9%	3480
	11th to 20th	Night	57% 4 10% 23% 6%	4025
	21st to end	Night	53% 5% 17% 17% 8%	4467
November	1st to 10th	Night	60% 6% 11% 17% 5%	2453
	11th to 20th	Night	60% 7% 10% 14% 9% 1	2478
	21st to end	Night	69% 5% 9% 13% 5%	2793
December	1st to 10th	Night	74% 5% 8% 10% 3	2850
	11th to 20th	Night	72% 5% 5% 13% 6%	3532
	21st to end	Night	69% 4 7% 13% 7%	5204

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	27% 29% 34% 7% 2 1	180
	11th to 20th	Day	32% 26% 32% 7% 3	180
	21st to end	Day	18% 31% 36% 11% 3 1	198
February	1st to 10th	Day	37% 26% 25% 9% 2	222
	11th to 20th	Day	29% 26% 33% 11% 2	435
	21st to end	Day	30% 26% 28% 13% 3	382
March	1st to 10th	Day	28% 26% 30% 12% 3	460
	11th to 20th	Day	30% 25% 26% 13% 5% 1	460
	21st to end	Day	31% 25% 24% 12% 7% 2	506
April	1st to 10th	Day	37% 21% 23% 13% 5% 1	460
	11th to 20th	Day	30% 26% 25% 14% 4 1	452
	21st to end	Day	33% 20% 30% 12% 3 1	460
May	1st to 10th	Day	31% 16% 36% 12% 3 2	463
	11th to 20th	Day	26% 16% 32% 19% 6%	487
	21st to end	Day	24% 22% 29% 17% 6% 1	606
June	1st to 10th	Day	29% 16% 31% 16% 7% 1	680
	11th to 20th	Day	24% 17% 26% 24% 9%	680
	21st to end	Day	31% 14% 27% 18% 9% 1	680
July	1st to 10th	Day	21% 16% 34% 21% 8%	574
	11th to 20th	Day	23% 17% 35% 18% 6% 1	484
	21st to end	Day	24% 14% 33% 21% 7% 1	532
August	1st to 10th	Day	24% 15% 30% 19% 10% 1	486
	11th to 20th	Day	23% 10% 30% 24% 10% 2	479
	21st to end	Day	24% 15% 26% 21% 9% 5%	539
September	1st to 10th	Day	23% 18% 26% 20% 10% 3	490
	11th to 20th	Day	23% 13% 29% 21% 11% 3	490
	21st to end	Day	25% 16% 27% 16% 12% 4	490
October	1st to 10th	Day	26% 19% 24% 18% 11% 2	490
	11th to 20th	Day	35% 20% 22% 14% 7% 1	390
	21st to end	Day	39% 23% 21% 14% 3	429
November	1st to 10th	Day	34% 20% 25% 17% 4 1	374
	11th to 20th	Day	29% 25% 22% 16% 6% 1	370
	21st to end	Day	31% 29% 27% 10% 2	235
December	1st to 10th	Day	32% 20% 27% 17% 3 1	180
	11th to 20th	Day	37% 29% 23% 10% 1 1	180
	21st to end	Day	39% 23% 24% 12% 2 1	198
January	1st to 10th	Night	26% 24% 33% 15% 2	760
	11th to 20th	Night	27% 24% 29% 16% 3	760
	21st to end	Night	19% 22% 35% 20% 4 1	836
February	1st to 10th	Night	20% 28% 33% 15% 5%	760
	11th to 20th	Night	25% 26% 31% 14% 3 1	743
	21st to end	Night	25% 21% 31% 18% 4	628
March	1st to 10th	Night	24% 20% 34% 18% 3	760
	11th to 20th	Night	24% 23% 30% 17% 5% 1	760
	21st to end	Night	23% 21% 26% 22% 7%	836
April	1st to 10th	Night	30% 19% 26% 18% 6%	760
	11th to 20th	Night	27% 16% 28% 22% 6%	634
	21st to end	Night	31% 15% 27% 20% 6% 1	570
May	1st to 10th	Night	27% 13% 29% 22% 8%	570
	11th to 20th	Night	25% 10% 27% 29% 9% 1	388
	21st to end	Night	25% 9% 28% 30% 8%	411
June	1st to 10th	Night	28% 8% 28% 27% 9%	380
	11th to 20th	Night	19% 10% 25% 31% 15%	380
	21st to end	Night	26% 10% 24% 29% 10%	380
July	1st to 10th	Night	17% 10% 31% 30% 12%	370
	11th to 20th	Night	22% 8% 20% 38% 11%	368
	21st to end	Night	20% 6% 21% 39% 13%	416
August	1st to 10th	Night	20% 5% 20% 36% 19%	413
	11th to 20th	Night	22% 9% 22% 32% 15% 1	562
	21st to end	Night	19% 9% 24% 31% 14% 3	701
September	1st to 10th	Night	22% 10% 27% 29% 12% 2	760
	11th to 20th	Night	23% 9% 24% 29% 14% 2	760
	21st to end	Night	26% 10% 23% 27% 12% 2	760
October	1st to 10th	Night	24% 15% 23% 28% 10% 1	760
	11th to 20th	Night	30% 17% 24% 20% 8% 1	760
	21st to end	Night	34% 20% 23% 16% 6%	836
November	1st to 10th	Night	29% 19% 26% 20% 5%	755
	11th to 20th	Night	27% 21% 25% 18% 8% 1	764
	21st to end	Night	29% 24% 26% 16% 4 1	850
December	1st to 10th	Night	32% 20% 29% 13% 5% 1	850
	11th to 20th	Night	30% 24% 23% 18% 5%	850
	21st to end	Night	31% 25% 25% 15% 3	926

Page generated at 2024-11-01 22:47:40. Version ac07

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