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 2024-03-28.

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	20% 12% 5% 8% 7% 4 5% 4 4 5% 26%	78336
	Night	18% 13% 5% 9% 7% 3 4 4 4 5% 26%	81642
Transparency	Day	60% 6% 10% 17% 7% 1	78041
	Night	60% 6% 10% 16% 8% 1	81472
Seeing	Day	28% 20% 28% 16% 7% 1	14502
	Night	26% 18% 27% 22% 7% 1	23117

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% 18% 9% 15% 13% 5% 6% 4 4 3 12%	2517
	11th to 20th	Day	10% 14% 7% 18% 14% 8% 3 3 2 2 18%	2520
	21st to end	Day	9% 12% 8% 18% 10% 5% 5% 4 4 4 21%	2772
February	1st to 10th	Day	12% 17% 8% 12% 10% 6% 6% 4 3 4 17%	1562
	11th to 20th	Day	14% 17% 10% 14% 7% 3 6% 4 4 3 19%	1805
	21st to end	Day	12% 15% 6% 13% 8% 4 6% 4 4 5% 22%	1570
March	1st to 10th	Day	15% 15% 7% 11% 7% 4 4 4 4 5% 24%	1897
	11th to 20th	Day	16% 18% 7% 8% 7% 3 5% 5% 3 4 25%	2021
	21st to end	Day	16% 15% 6% 9% 7% 3 4 4 4 4 28%	2351
April	1st to 10th	Day	23% 17% 4 9% 6% 3 3 3 3 6% 23%	2160
	11th to 20th	Day	19% 15% 4 6% 5% 2 3 3 4 5% 34%	2244
	21st to end	Day	23% 11% 5% 8% 5% 3 4 4 4 6% 27%	2340
May	1st to 10th	Day	23% 11% 4 6% 5% 3 5% 3 4 5% 31%	2340
	11th to 20th	Day	22% 9% 4 6% 5% 4 5% 5% 4 7% 30%	2478
	21st to end	Day	23% 7% 4 6% 6% 3 5% 4 5% 7% 29%	2797
June	1st to 10th	Day	25% 9% 3 6% 6% 3 6% 4 6% 7% 24%	2700
	11th to 20th	Day	23% 7% 3 5% 5% 4 5% 6% 6% 7% 30%	2700
	21st to end	Day	26% 10% 4 7% 6% 3 5% 5% 5% 4 25%	2700
July	1st to 10th	Day	21% 7% 3 6% 6% 4 6% 5% 5% 8% 28%	2605
	11th to 20th	Day	20% 8% 3 6% 6% 4 5% 6% 7% 8% 27%	2520
	21st to end	Day	22% 8% 3 6% 5% 3 6% 5% 6% 8% 27%	2744
August	1st to 10th	Day	24% 7% 3 7% 7% 4 5% 6% 5% 8% 24%	2454
	11th to 20th	Day	20% 9% 3 6% 7% 4 5% 5% 5% 6% 30%	2304
	21st to end	Day	22% 7% 3 6% 5% 3 4 6% 5% 7% 32%	2502
September	1st to 10th	Day	23% 7% 3 5% 4 2 4 5% 5% 7% 33%	2152
	11th to 20th	Day	23% 7% 2 4 5% 3 3 4 4 5% 40%	1980
	21st to end	Day	23% 9% 2 4 4 3 4 4 4 7% 36%	1980
October	1st to 10th	Day	23% 12% 3 5% 4 3 4 4 4 6% 31%	1980
	11th to 20th	Day	25% 18% 4 6% 5% 4 4 5% 3 5% 22%	1660
	21st to end	Day	27% 19% 4 8% 5% 3 3 4 4 4 19%	1782
November	1st to 10th	Day	21% 18% 6% 7% 5% 3 3 3 4 4 26%	1671
	11th to 20th	Day	22% 17% 8% 9% 6% 3 4 3 4 4 20%	1700
	21st to end	Day	20% 21% 6% 11% 8% 3 3 4 3 3 19%	1385
December	1st to 10th	Day	23% 21% 7% 12% 8% 2 4 4 3 3 15%	1330
	11th to 20th	Day	19% 19% 7% 11% 7% 4 4 3 3 3 21%	1668
	21st to end	Day	23% 15% 7% 11% 9% 3 5% 4 3 3 17%	2445
January	1st to 10th	Night	14% 17% 10% 13% 13% 3 4 4 3 3 15%	4429
	11th to 20th	Night	11% 17% 7% 15% 15% 5% 4 3 3 3 17%	4440
	21st to end	Night	9% 14% 8% 13% 10% 5% 5% 6% 6% 5% 20%	4884
February	1st to 10th	Night	11% 16% 6% 11% 11% 5% 6% 5% 4 4 21%	2618
	11th to 20th	Night	12% 18% 8% 14% 9% 5% 6% 3 3 4 20%	2256
	21st to end	Night	13% 16% 6% 11% 8% 3 5% 3 4 4 27%	1884
March	1st to 10th	Night	14% 14% 7% 9% 7% 3 5% 4 4 5% 28%	2270
	11th to 20th	Night	16% 16% 5% 9% 6% 4 5% 4 5% 4 27%	2157
	21st to end	Night	17% 12% 6% 9% 6% 3 4 4 3 4 31%	2159
April	1st to 10th	Night	22% 16% 6% 7% 4 3 4 3 4 5% 25%	1800
	11th to 20th	Night	20% 12% 3 6% 5% 3 4 4 5% 6% 32%	1665
	21st to end	Night	20% 13% 4 7% 6% 3 4 4 4 5% 30%	1620
May	1st to 10th	Night	24% 10% 3 7% 6% 3 4 4 4 5% 30%	1620
	11th to 20th	Night	22% 8% 3 6% 5% 3 5% 4 4 6% 35%	1429
	21st to end	Night	23% 6% 3 7% 4 3 4 5% 4 7% 35%	1474
June	1st to 10th	Night	25% 8% 3 6% 6% 4 6% 4 6% 5% 26%	1260
	11th to 20th	Night	20% 8% 2 7% 4 3 6% 5% 4 6% 35%	1260
	21st to end	Night	22% 9% 3 6% 5% 4 5% 5% 5% 6% 30%	1260
July	1st to 10th	Night	17% 7% 4 7% 5% 3 4 5% 6% 7% 36%	1350
	11th to 20th	Night	19% 6% 3 7% 7% 4 5% 5% 5% 7% 33%	1440
	21st to end	Night	19% 8% 4 6% 6% 3 5% 5% 5% 7% 34%	1574
August	1st to 10th	Night	18% 5% 2 4 6% 3 5% 5% 6% 10% 35%	1465
	11th to 20th	Night	21% 8% 3 6% 4 4 5% 5% 5% 7% 33%	1596
	21st to end	Night	19% 7% 2 4 5% 3 4 4 5% 7% 39%	1852
September	1st to 10th	Night	21% 7% 2 6% 5% 3 4 4 4 6% 38%	1807
	11th to 20th	Night	22% 8% 2 5% 4 2 4 3 3 6% 41%	1980
	21st to end	Night	22% 7% 2 4 5% 3 3 4 5% 6% 40%	1980
October	1st to 10th	Night	23% 9% 3 4 4 3 5% 4 5% 5% 36%	1980
	11th to 20th	Night	25% 14% 3 6% 6% 3 4 4 4 4 27%	2296
	21st to end	Night	26% 16% 4 7% 5% 3 4 4 4 4 24%	2574
November	1st to 10th	Night	21% 16% 5% 7% 6% 3 4 4 3 5% 25%	2407
	11th to 20th	Night	19% 14% 6% 9% 6% 3 4 4 3 4 26%	2478
	21st to end	Night	19% 18% 8% 11% 7% 4 4 3 4 3 20%	2793
December	1st to 10th	Night	22% 18% 8% 12% 7% 3 5% 3 3 3 14%	2850
	11th to 20th	Night	19% 17% 8% 14% 8% 4 4 3 3 4 17%	3531
	21st to end	Night	21% 20% 6% 11% 6% 3 3 3 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	62% 4 8% 14% 11% 2	1900
	11th to 20th	Day	63% 5% 7% 14% 11% 1	2021
	21st to end	Day	59% 5% 9% 16% 9% 2	2351
April	1st to 10th	Day	64% 4 9% 12% 9% 2	2160
	11th to 20th	Day	54% 5% 8% 20% 11% 2	2244
	21st to end	Day	59% 4 8% 16% 10% 2	2340
May	1st to 10th	Day	56% 3 10% 17% 12% 2	2340
	11th to 20th	Day	53% 5% 12% 20% 8% 1	2482
	21st to end	Day	54% 7% 11% 19% 9%	2797
June	1st to 10th	Day	58% 7% 9% 19% 5% 1	2700
	11th to 20th	Day	51% 7% 13% 20% 9% 1	2700
	21st to end	Day	62% 5% 11% 15% 7%	2700
July	1st to 10th	Day	53% 7% 16% 19% 6%	2535
	11th to 20th	Day	53% 7% 15% 19% 6%	2445
	21st to end	Day	55% 8% 13% 19% 5% 1	2591
August	1st to 10th	Day	56% 9% 16% 17% 3	2440
	11th to 20th	Day	52% 7% 15% 18% 7%	2304
	21st to end	Day	50% 5% 15% 22% 7%	2502
September	1st to 10th	Day	48% 7% 14% 20% 10%	2152
	11th to 20th	Day	46% 5% 12% 26% 11%	1980
	21st to end	Day	48% 5% 13% 23% 9%	1980
October	1st to 10th	Day	55% 4 10% 23% 8%	1980
	11th to 20th	Day	65% 5% 13% 15% 2	1660
	21st to end	Day	69% 5% 7% 14% 4 1	1782
November	1st to 10th	Day	62% 5% 11% 16% 6%	1671
	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	59% 5% 8% 17% 9% 1	2280
	11th to 20th	Night	58% 7% 9% 14% 10% 2	2158
	21st to end	Night	57% 5% 8% 19% 10% 3	2159
April	1st to 10th	Night	61% 5% 7% 13% 11% 3	1800
	11th to 20th	Night	51% 6% 8% 21% 12% 1	1665
	21st to end	Night	58% 6% 7% 15% 11% 2	1620
May	1st to 10th	Night	55% 6% 8% 16% 13% 1	1620
	11th to 20th	Night	51% 6% 11% 19% 13% 1	1430
	21st to end	Night	50% 6% 13% 18% 13%	1475
June	1st to 10th	Night	58% 5% 12% 18% 6%	1260
	11th to 20th	Night	47% 8% 10% 22% 11% 2	1260
	21st to end	Night	54% 7% 14% 17% 8%	1260
July	1st to 10th	Night	46% 7% 19% 21% 7%	1310
	11th to 20th	Night	47% 8% 18% 20% 7%	1392
	21st to end	Night	49% 8% 16% 20% 8%	1486
August	1st to 10th	Night	43% 8% 19% 27% 2	1455
	11th to 20th	Night	48% 8% 18% 21% 6%	1596
	21st to end	Night	42% 7% 14% 28% 8%	1852
September	1st to 10th	Night	47% 6% 13% 24% 9% 1	1807
	11th to 20th	Night	45% 5% 17% 24% 8% 1	1980
	21st to end	Night	45% 6% 12% 23% 13%	1980
October	1st to 10th	Night	48% 4 12% 23% 12%	1980
	11th to 20th	Night	59% 5% 12% 18% 5%	2296
	21st to end	Night	63% 5% 10% 14% 7% 1	2574
November	1st to 10th	Night	60% 6% 12% 17% 5%	2407
	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	30% 25% 24% 12% 7% 2	490
April	1st to 10th	Day	37% 21% 23% 13% 5% 1	420
	11th to 20th	Day	30% 25% 25% 15% 4 1	412
	21st to end	Day	34% 19% 30% 12% 4 1	420
May	1st to 10th	Day	31% 16% 37% 12% 3 1	423
	11th to 20th	Day	28% 16% 31% 19% 5%	447
	21st to end	Day	24% 22% 29% 17% 7% 1	557
June	1st to 10th	Day	30% 16% 32% 16% 6%	630
	11th to 20th	Day	24% 17% 25% 25% 10%	630
	21st to end	Day	29% 13% 28% 19% 10% 1	630
July	1st to 10th	Day	22% 15% 32% 22% 9%	530
	11th to 20th	Day	22% 16% 35% 20% 7% 1	444
	21st to end	Day	24% 14% 34% 20% 7% 1	488
August	1st to 10th	Day	24% 15% 31% 19% 11% 1	446
	11th to 20th	Day	23% 10% 30% 25% 10% 2	439
	21st to end	Day	25% 15% 24% 20% 9% 5%	495
September	1st to 10th	Day	23% 17% 25% 21% 11% 3	450
	11th to 20th	Day	25% 14% 28% 20% 10% 3	450
	21st to end	Day	25% 17% 28% 15% 12% 4	450
October	1st to 10th	Day	25% 19% 24% 19% 11% 2	450
	11th to 20th	Day	36% 19% 22% 15% 8% 1	360
	21st to end	Day	39% 22% 21% 14% 4	396
November	1st to 10th	Day	34% 20% 24% 17% 4 1	365
	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% 20% 26% 23% 7%	821
April	1st to 10th	Night	30% 20% 26% 18% 6%	720
	11th to 20th	Night	27% 15% 29% 22% 6%	601
	21st to end	Night	31% 15% 26% 20% 7% 1	540
May	1st to 10th	Night	27% 14% 28% 23% 8%	540
	11th to 20th	Night	26% 10% 27% 29% 8% 1	368
	21st to end	Night	25% 10% 27% 30% 8%	389
June	1st to 10th	Night	28% 8% 29% 26% 9%	360
	11th to 20th	Night	19% 10% 25% 31% 15%	360
	21st to end	Night	25% 10% 24% 29% 11%	360
July	1st to 10th	Night	17% 9% 31% 29% 12%	350
	11th to 20th	Night	21% 8% 20% 40% 12%	348
	21st to end	Night	19% 7% 21% 40% 13%	394
August	1st to 10th	Night	19% 4 20% 37% 19% 1	391
	11th to 20th	Night	21% 8% 21% 33% 15% 1	532
	21st to end	Night	19% 9% 24% 31% 13% 3	664
September	1st to 10th	Night	21% 9% 27% 28% 12% 2	720
	11th to 20th	Night	24% 9% 24% 28% 14% 2	720
	21st to end	Night	26% 11% 24% 26% 12% 1	720
October	1st to 10th	Night	24% 15% 23% 28% 9% 1	720
	11th to 20th	Night	29% 17% 24% 21% 8% 1	720
	21st to end	Night	35% 20% 23% 16% 6%	792
November	1st to 10th	Night	29% 19% 26% 20% 5%	740
	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 2024-03-24 23:37:00. Version ac07

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