Cygnus Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cygnus Hill Observatory clear sky chart from 2005-11-06 to 2024-07-31.

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	17% 10% 3 8% 5% 5% 4 4 5% 6% 32%	90057
	Night	17% 11% 4 8% 5% 5% 4 3 5% 6% 32%	89781
Transparency	Day	50% 8% 12% 19% 10% 1	89776
	Night	52% 8% 12% 18% 10% 1	89616
Seeing	Day	23% 17% 31% 18% 8% 2	14113
	Night	22% 15% 31% 23% 8% 1	23257

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	14% 16% 6% 12% 6% 5% 5% 3 4 4 24%	2517
	11th to 20th	Day	13% 17% 7% 13% 7% 5% 5% 3 4 4 22%	2520
	21st to end	Day	18% 19% 7% 13% 6% 5% 3 3 3 3 18%	2995
February	1st to 10th	Day	15% 15% 4 12% 7% 5% 5% 4 5% 5% 23%	1710
	11th to 20th	Day	12% 15% 5% 10% 7% 5% 5% 3 4 5% 28%	1663
	21st to end	Day	20% 14% 5% 9% 7% 5% 5% 3 5% 4 24%	1551
March	1st to 10th	Day	21% 14% 4 9% 6% 4 3 3 3 5% 29%	3198
	11th to 20th	Day	11% 16% 5% 8% 6% 5% 5% 3 4 6% 30%	3480
	21st to end	Day	12% 11% 4 7% 4 4 4 3 4 6% 42%	3971
April	1st to 10th	Day	21% 13% 3 8% 4 4 3 3 4 6% 32%	2280
	11th to 20th	Day	22% 9% 3 7% 4 3 4 3 4 5% 37%	2254
	21st to end	Day	22% 11% 3 7% 5% 4 4 3 5% 5% 32%	2388
May	1st to 10th	Day	20% 8% 3 8% 5% 4 5% 3 5% 6% 33%	4426
	11th to 20th	Day	16% 9% 3 8% 5% 5% 4 3 5% 8% 33%	4398
	21st to end	Day	13% 6% 2 6% 5% 4 5% 4 6% 8% 40%	4837
June	1st to 10th	Day	20% 9% 3 7% 4 5% 5% 4 6% 6% 30%	2660
	11th to 20th	Day	14% 6% 3 6% 5% 5% 5% 4 7% 9% 36%	2660
	21st to end	Day	17% 8% 3 7% 6% 5% 6% 4 6% 7% 33%	2660
July	1st to 10th	Day	11% 5% 2 6% 5% 6% 4 5% 6% 8% 40%	2660
	11th to 20th	Day	12% 6% 3 6% 4 5% 5% 4 7% 9% 38%	2660
	21st to end	Day	11% 6% 2 6% 4 5% 7% 5% 8% 8% 37%	2887
August	1st to 10th	Day	12% 6% 2 7% 5% 5% 5% 4 6% 8% 38%	2405
	11th to 20th	Day	12% 6% 3 6% 5% 4 5% 5% 7% 9% 38%	2298
	21st to end	Day	14% 6% 2 7% 4 5% 4 4 7% 9% 39%	2376
September	1st to 10th	Day	13% 6% 2 6% 4 5% 5% 4 5% 8% 41%	2160
	11th to 20th	Day	13% 6% 2 5% 4 4 4 3 5% 7% 47%	2160
	21st to end	Day	18% 6% 2 7% 5% 4 4 4 5% 7% 39%	1909
October	1st to 10th	Day	21% 9% 2 7% 4 3 3 3 5% 6% 36%	1800
	11th to 20th	Day	21% 9% 3 8% 6% 5% 5% 3 6% 7% 28%	1800
	21st to end	Day	26% 10% 4 9% 5% 5% 4 3 4 5% 25%	1878
November	1st to 10th	Day	15% 10% 3 8% 5% 5% 5% 4 6% 7% 34%	1658
	11th to 20th	Day	17% 14% 4 8% 5% 5% 4 3 4 6% 29%	1520
	21st to end	Day	19% 16% 5% 10% 6% 5% 5% 4 5% 4 22%	1520
December	1st to 10th	Day	22% 17% 4 12% 6% 5% 4 4 4 6% 17%	1520
	11th to 20th	Day	21% 13% 5% 9% 6% 4 4 3 5% 4 25%	1906
	21st to end	Day	28% 16% 6% 12% 4 3 3 2 2 3 20%	2772
January	1st to 10th	Night	17% 14% 7% 12% 6% 5% 5% 3 5% 5% 20%	4429
	11th to 20th	Night	13% 15% 5% 14% 8% 6% 5% 4 4 6% 20%	4440
	21st to end	Night	19% 18% 6% 12% 6% 6% 4 3 3 3 20%	4660
February	1st to 10th	Night	14% 17% 5% 9% 7% 5% 4 4 7% 6% 23%	2470
	11th to 20th	Night	12% 15% 6% 10% 5% 5% 4 3 5% 5% 30%	2403
	21st to end	Night	14% 14% 5% 8% 6% 4 5% 3 5% 6% 29%	1903
March	1st to 10th	Night	19% 12% 4 9% 5% 4 4 2 4 4 32%	3639
	11th to 20th	Night	17% 16% 4 8% 5% 4 4 4 5% 6% 26%	3479
	21st to end	Night	15% 10% 3 8% 4 4 3 3 4 6% 41%	3659
April	1st to 10th	Night	20% 10% 3 8% 4 4 4 3 4 5% 35%	1900
	11th to 20th	Night	20% 9% 2 7% 4 5% 4 3 5% 5% 37%	1875
	21st to end	Night	19% 11% 3 8% 4 4 4 3 5% 6% 33%	1809
May	1st to 10th	Night	21% 9% 3 7% 4 4 4 4 5% 6% 31%	2514
	11th to 20th	Night	19% 9% 2 6% 4 4 4 3 5% 6% 38%	2495
	21st to end	Night	13% 6% 3 6% 4 4 4 4 6% 7% 42%	2738
June	1st to 10th	Night	15% 8% 2 7% 6% 5% 5% 5% 6% 8% 33%	1520
	11th to 20th	Night	13% 6% 3 6% 4 5% 4 3 7% 7% 42%	1520
	21st to end	Night	17% 7% 2 7% 5% 5% 5% 4 6% 8% 35%	1520
July	1st to 10th	Night	9% 5% 2 6% 5% 5% 5% 3 6% 8% 45%	1520
	11th to 20th	Night	11% 6% 2 7% 4 4 4 4 6% 8% 44%	1520
	21st to end	Night	9% 6% 2 4 4 5% 5% 4 7% 8% 46%	1662
August	1st to 10th	Night	10% 6% 2 6% 4 5% 4 4 6% 7% 44%	1529
	11th to 20th	Night	9% 7% 3 7% 5% 5% 5% 4 6% 8% 44%	1598
	21st to end	Night	11% 6% 2 6% 5% 4 4 4 6% 8% 45%	1966
September	1st to 10th	Night	11% 6% 2 6% 4 4 4 4 5% 8% 45%	1800
	11th to 20th	Night	13% 5% 2 4 3 4 4 4 5% 7% 50%	1800
	21st to end	Night	17% 6% 2 6% 4 4 4 3 5% 6% 44%	2049
October	1st to 10th	Night	18% 7% 3 7% 5% 5% 4 3 4 7% 37%	2160
	11th to 20th	Night	21% 10% 2 7% 5% 4 5% 3 5% 6% 31%	2160
	21st to end	Night	23% 11% 3 8% 5% 4 4 3 5% 5% 29%	2476
November	1st to 10th	Night	17% 11% 3 6% 5% 4 4 3 5% 6% 36%	2416
	11th to 20th	Night	17% 12% 3 7% 5% 4 5% 3 5% 6% 32%	2660
	21st to end	Night	21% 13% 3 9% 5% 5% 5% 3 5% 7% 24%	2660
December	1st to 10th	Night	20% 17% 5% 11% 7% 5% 4 3 4 5% 19%	2660
	11th to 20th	Night	20% 16% 4 9% 5% 4 3 3 4 4 28%	3288
	21st to end	Night	29% 17% 4 11% 5% 4 4 3 3 4 16%	4884

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	59% 11% 13% 11% 6% 2	2518
	11th to 20th	Day	63% 8% 10% 11% 7%	2520
	21st to end	Day	72% 6% 8% 9% 5% 1	2995
February	1st to 10th	Day	61% 7% 10% 16% 5% 1	1710
	11th to 20th	Day	58% 6% 11% 15% 9% 1	1672
	21st to end	Day	62% 5% 10% 12% 10% 1	1551
March	1st to 10th	Day	58% 6% 10% 16% 9% 1	3201
	11th to 20th	Day	52% 9% 13% 15% 10% 2	3480
	21st to end	Day	41% 6% 8% 24% 16% 4	3971
April	1st to 10th	Day	54% 5% 8% 18% 12% 3	2280
	11th to 20th	Day	49% 6% 7% 21% 15% 2	2254
	21st to end	Day	54% 6% 9% 15% 14% 4	2388
May	1st to 10th	Day	49% 8% 10% 20% 11% 2	4440
	11th to 20th	Day	47% 9% 13% 20% 9% 1	4402
	21st to end	Day	39% 9% 12% 23% 15% 2	4837
June	1st to 10th	Day	51% 8% 10% 18% 12% 1	2660
	11th to 20th	Day	41% 8% 11% 25% 13% 2	2660
	21st to end	Day	48% 9% 12% 19% 11% 1	2660
July	1st to 10th	Day	38% 8% 12% 26% 14% 1	2590
	11th to 20th	Day	38% 10% 16% 26% 10%	2585
	21st to end	Day	40% 11% 15% 24% 10%	2734
August	1st to 10th	Day	41% 9% 14% 24% 11%	2391
	11th to 20th	Day	40% 10% 16% 23% 10% 1	2298
	21st to end	Day	39% 9% 14% 25% 12% 1	2376
September	1st to 10th	Day	39% 8% 15% 26% 12% 1	2160
	11th to 20th	Day	36% 8% 12% 29% 15%	2160
	21st to end	Day	44% 8% 13% 26% 9%	1909
October	1st to 10th	Day	49% 7% 11% 22% 11% 1	1800
	11th to 20th	Day	54% 9% 13% 17% 7% 1	1800
	21st to end	Day	59% 7% 10% 16% 7% 1	1878
November	1st to 10th	Day	47% 9% 16% 19% 8% 1	1658
	11th to 20th	Day	55% 7% 11% 15% 10% 1	1520
	21st to end	Day	62% 9% 11% 9% 7%	1520
December	1st to 10th	Day	67% 8% 11% 10% 4 1	1520
	11th to 20th	Day	62% 7% 14% 13% 4	1906
	21st to end	Day	71% 5% 7% 13% 4	2772
January	1st to 10th	Night	62% 9% 13% 11% 3	4429
	11th to 20th	Night	63% 10% 13% 10% 5% 1	4440
	21st to end	Night	68% 7% 9% 9% 6% 1	4660
February	1st to 10th	Night	59% 8% 12% 15% 6% 1	2470
	11th to 20th	Night	55% 6% 11% 20% 8% 1	2405
	21st to end	Night	55% 6% 11% 17% 10% 1	1903
March	1st to 10th	Night	54% 6% 9% 21% 9% 1	3649
	11th to 20th	Night	55% 8% 14% 14% 7% 1	3480
	21st to end	Night	42% 7% 9% 24% 16% 3	3659
April	1st to 10th	Night	51% 5% 8% 20% 14% 2	1900
	11th to 20th	Night	49% 6% 7% 19% 17% 1	1875
	21st to end	Night	52% 5% 9% 16% 15% 3	1809
May	1st to 10th	Night	50% 9% 11% 18% 10% 2	2520
	11th to 20th	Night	45% 8% 13% 23% 9% 2	2496
	21st to end	Night	37% 9% 15% 20% 18% 2	2739
June	1st to 10th	Night	46% 9% 13% 19% 11% 1	1520
	11th to 20th	Night	39% 8% 13% 21% 18% 2	1520
	21st to end	Night	45% 10% 13% 18% 12% 1	1520
July	1st to 10th	Night	34% 8% 13% 24% 18% 3	1480
	11th to 20th	Night	36% 9% 12% 30% 12%	1472
	21st to end	Night	33% 8% 17% 28% 13% 1	1574
August	1st to 10th	Night	36% 8% 18% 25% 12% 1	1519
	11th to 20th	Night	36% 9% 17% 26% 12% 1	1598
	21st to end	Night	35% 9% 16% 28% 12% 1	1966
September	1st to 10th	Night	36% 9% 13% 27% 14% 1	1800
	11th to 20th	Night	32% 8% 15% 32% 12% 1	1800
	21st to end	Night	41% 7% 11% 31% 10% 1	2049
October	1st to 10th	Night	47% 7% 11% 20% 14%	2160
	11th to 20th	Night	53% 7% 14% 18% 8% 1	2160
	21st to end	Night	56% 8% 12% 15% 9%	2476
November	1st to 10th	Night	47% 7% 15% 20% 10% 1	2416
	11th to 20th	Night	52% 7% 11% 19% 10% 2	2660
	21st to end	Night	59% 8% 13% 15% 5%	2660
December	1st to 10th	Night	66% 7% 10% 13% 4	2660
	11th to 20th	Night	61% 6% 10% 15% 7% 1	3288
	21st to end	Night	71% 7% 8% 12% 3	4884

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	26% 22% 36% 13% 3 1	180
	11th to 20th	Day	34% 18% 28% 17% 2 1	180
	21st to end	Day	28% 20% 33% 16% 4	261
February	1st to 10th	Day	31% 27% 32% 9% 1	270
	11th to 20th	Day	28% 29% 39% 4	270
	21st to end	Day	34% 23% 31% 10% 2	363
March	1st to 10th	Day	26% 23% 33% 14% 4	460
	11th to 20th	Day	28% 22% 32% 13% 4	460
	21st to end	Day	32% 22% 27% 12% 5% 1	506
April	1st to 10th	Day	30% 24% 29% 12% 5%	460
	11th to 20th	Day	33% 22% 22% 14% 7% 2	452
	21st to end	Day	29% 23% 28% 12% 5% 2	460
May	1st to 10th	Day	25% 17% 32% 18% 7% 2	463
	11th to 20th	Day	19% 16% 35% 20% 8% 2	487
	21st to end	Day	19% 15% 33% 22% 9% 3	529
June	1st to 10th	Day	22% 13% 36% 22% 6% 2	490
	11th to 20th	Day	15% 17% 34% 21% 11% 2	490
	21st to end	Day	20% 16% 30% 22% 9% 3	490
July	1st to 10th	Day	14% 10% 30% 29% 15% 3	485
	11th to 20th	Day	15% 13% 32% 22% 15% 3	484
	21st to end	Day	13% 9% 35% 28% 10% 4	529
August	1st to 10th	Day	13% 9% 33% 29% 13% 4	446
	11th to 20th	Day	14% 8% 29% 27% 16% 6%	439
	21st to end	Day	14% 12% 33% 24% 11% 7%	495
September	1st to 10th	Day	14% 15% 31% 21% 12% 7%	450
	11th to 20th	Day	13% 10% 28% 23% 16% 10%	450
	21st to end	Day	19% 12% 30% 22% 13% 4	450
October	1st to 10th	Day	27% 17% 25% 16% 12% 4	450
	11th to 20th	Day	29% 20% 30% 15% 5% 1	450
	21st to end	Day	30% 21% 27% 18% 4	444
November	1st to 10th	Day	26% 18% 28% 20% 8%	352
	11th to 20th	Day	31% 21% 29% 13% 4 2	180
	21st to end	Day	30% 24% 28% 15% 3	180
December	1st to 10th	Day	32% 20% 34% 12% 2	180
	11th to 20th	Day	34% 23% 31% 9% 2 1	180
	21st to end	Day	33% 20% 32% 11% 3 1	198
January	1st to 10th	Night	28% 19% 31% 18% 4	760
	11th to 20th	Night	29% 18% 30% 18% 4 1	760
	21st to end	Night	20% 17% 37% 22% 5%	836
February	1st to 10th	Night	23% 22% 34% 19% 2	760
	11th to 20th	Night	22% 22% 36% 16% 3	743
	21st to end	Night	25% 20% 35% 18% 3	628
March	1st to 10th	Night	25% 16% 36% 20% 3	760
	11th to 20th	Night	27% 21% 27% 21% 4 1	760
	21st to end	Night	22% 17% 34% 19% 7%	836
April	1st to 10th	Night	27% 17% 33% 20% 3	760
	11th to 20th	Night	25% 21% 29% 18% 7% 1	751
	21st to end	Night	25% 15% 29% 22% 8% 1	669
May	1st to 10th	Night	23% 12% 27% 26% 9% 2	380
	11th to 20th	Night	16% 11% 38% 28% 7%	374
	21st to end	Night	13% 10% 38% 27% 11%	411
June	1st to 10th	Night	15% 6% 36% 35% 7% 1	380
	11th to 20th	Night	14% 11% 33% 28% 13% 1	380
	21st to end	Night	18% 8% 29% 33% 12% 1	380
July	1st to 10th	Night	10% 6% 32% 37% 14% 1	370
	11th to 20th	Night	12% 4 32% 36% 15% 1	368
	21st to end	Night	11% 4 31% 42% 12%	416
August	1st to 10th	Night	12% 5% 28% 34% 20%	455
	11th to 20th	Night	11% 5% 24% 35% 22% 2	534
	21st to end	Night	12% 7% 32% 32% 15% 2	778
September	1st to 10th	Night	13% 8% 34% 27% 17% 2	720
	11th to 20th	Night	14% 9% 24% 28% 20% 4	720
	21st to end	Night	20% 11% 24% 26% 18% 2	720
October	1st to 10th	Night	22% 14% 28% 22% 13% 2	720
	11th to 20th	Night	27% 13% 32% 20% 7%	720
	21st to end	Night	30% 15% 28% 22% 5%	792
November	1st to 10th	Night	26% 14% 31% 21% 7%	740
	11th to 20th	Night	26% 17% 32% 16% 8% 1	760
	21st to end	Night	29% 19% 29% 19% 5%	760
December	1st to 10th	Night	29% 20% 31% 16% 3	760
	11th to 20th	Night	26% 19% 34% 17% 3 1	760
	21st to end	Night	34% 17% 30% 17% 1	836

Page generated at 2024-07-28 09:52:11. Version ac07

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