DeepSkyEye Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the DeepSkyEye Observatory clear sky chart from 2005-11-06 to 2025-03-27.

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	23% 12% 4 9% 5% 4 4 3 4 6% 28%	109225
	Night	21% 13% 4 10% 5% 4 4 3 4 5% 25%	110134
Transparency	Day	33% 44% 6% 10% 6% 1	112831
	Night	36% 42% 6% 10% 6%	114692
Seeing	Day	31% 18% 30% 15% 5% 1	17215
	Night	29% 15% 29% 21% 6%	25169

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% 22% 7% 21% 7% 3 3 2 3 3 11%	3225
	11th to 20th	Day	16% 21% 9% 21% 6% 4 3 2 3 3 10%	4005
	21st to end	Day	18% 17% 7% 18% 9% 4 3 2 3 4 15%	4466
February	1st to 10th	Day	20% 20% 6% 13% 8% 5% 3 3 4 5% 14%	1800
	11th to 20th	Day	18% 16% 6% 17% 9% 4 3 3 3 4 17%	1753
	21st to end	Day	13% 17% 7% 11% 7% 4 4 3 4 5% 25%	1600
March	1st to 10th	Day	28% 14% 5% 9% 6% 3 3 2 4 4 22%	3471
	11th to 20th	Day	18% 20% 4 7% 5% 4 4 3 4 6% 26%	3590
	21st to end	Day	31% 13% 6% 10% 4 4 3 2 3 4 21%	3882
April	1st to 10th	Day	25% 15% 4 6% 4 4 3 2 4 4 29%	2187
	11th to 20th	Day	22% 10% 2 6% 3 3 4 3 5% 6% 36%	2413
	21st to end	Day	24% 11% 2 6% 3 3 3 3 5% 6% 35%	2470
May	1st to 10th	Day	24% 11% 3 7% 4 4 4 3 5% 6% 28%	4106
	11th to 20th	Day	21% 10% 3 7% 4 4 4 3 5% 7% 31%	4229
	21st to end	Day	21% 8% 3 6% 4 4 4 4 5% 8% 33%	4836
June	1st to 10th	Day	27% 9% 2 6% 4 4 3 3 4 6% 33%	2704
	11th to 20th	Day	22% 8% 2 6% 4 4 4 3 4 7% 37%	2850
	21st to end	Day	28% 8% 2 6% 4 3 4 4 5% 6% 30%	2850
July	1st to 10th	Day	27% 9% 3 5% 3 4 3 3 5% 6% 31%	4760
	11th to 20th	Day	34% 7% 2 5% 3 3 3 3 5% 7% 28%	4423
	21st to end	Day	20% 8% 3 6% 4 4 4 3 5% 8% 34%	4467
August	1st to 10th	Day	32% 10% 3 6% 3 3 4 3 4 6% 28%	4105
	11th to 20th	Day	19% 6% 3 8% 5% 5% 5% 4 4 7% 35%	4045
	21st to end	Day	14% 5% 2 5% 4 3 3 3 5% 8% 48%	4454
September	1st to 10th	Day	18% 6% 2 5% 3 4 3 3 5% 6% 46%	2271
	11th to 20th	Day	17% 6% 2 5% 4 4 3 2 4 6% 46%	2090
	21st to end	Day	21% 8% 2 5% 3 3 3 3 5% 6% 41%	2090
October	1st to 10th	Day	21% 7% 2 6% 3 4 4 3 5% 8% 37%	1916
	11th to 20th	Day	21% 8% 2 6% 4 5% 5% 3 5% 6% 34%	1900
	21st to end	Day	22% 10% 3 7% 5% 5% 4 3 5% 6% 30%	2057
November	1st to 10th	Day	23% 9% 3 7% 5% 4 3 4 4 5% 33%	1726
	11th to 20th	Day	21% 16% 5% 9% 5% 4 4 3 5% 6% 22%	1600
	21st to end	Day	21% 20% 5% 10% 6% 4 4 3 3 6% 18%	1600
December	1st to 10th	Day	25% 16% 6% 13% 5% 4 4 3 4 6% 13%	2610
	11th to 20th	Day	28% 14% 5% 11% 6% 4 4 3 4 5% 17%	2996
	21st to end	Day	21% 16% 7% 12% 5% 4 3 3 3 4 22%	3678
January	1st to 10th	Night	14% 21% 9% 23% 6% 4 4 2 3 2 11%	6734
	11th to 20th	Night	18% 16% 9% 18% 7% 5% 4 3 4 4 13%	5860
	21st to end	Night	14% 16% 6% 19% 8% 6% 5% 3 4 4 15%	6490
February	1st to 10th	Night	20% 18% 5% 13% 8% 5% 4 4 4 4 15%	2600
	11th to 20th	Night	18% 14% 5% 14% 8% 6% 5% 3 5% 5% 17%	2533
	21st to end	Night	14% 13% 5% 10% 7% 6% 6% 4 5% 6% 24%	2025
March	1st to 10th	Night	25% 13% 4 9% 8% 5% 3 2 3 4 24%	3587
	11th to 20th	Night	17% 17% 5% 9% 5% 5% 4 4 5% 6% 23%	3589
	21st to end	Night	32% 12% 4 9% 4 3 2 2 3 4 26%	3889
April	1st to 10th	Night	23% 14% 3 6% 4 4 4 3 5% 6% 28%	1991
	11th to 20th	Night	24% 9% 3 5% 4 3 5% 3 5% 7% 32%	1713
	21st to end	Night	25% 10% 2 6% 4 3 4 4 5% 6% 32%	1710
May	1st to 10th	Night	22% 13% 4 6% 5% 4 4 3 5% 7% 28%	2834
	11th to 20th	Night	22% 12% 3 8% 5% 4 3 4 4 6% 29%	2666
	21st to end	Night	21% 12% 3 8% 4 3 4 2 5% 6% 32%	2749
June	1st to 10th	Night	28% 9% 3 5% 3 4 4 3 5% 6% 29%	1490
	11th to 20th	Night	20% 10% 3 7% 4 3 4 3 5% 6% 34%	1330
	21st to end	Night	29% 11% 3 6% 4 3 5% 3 5% 5% 26%	1330
July	1st to 10th	Night	33% 12% 3 5% 4 3 3 4 6% 6% 22%	2210
	11th to 20th	Night	35% 11% 2 5% 4 3 4 3 5% 5% 23%	2503
	21st to end	Night	19% 8% 3 8% 5% 4 4 4 5% 7% 31%	3087
August	1st to 10th	Night	35% 10% 3 6% 3 3 2 2 4 6% 27%	2825
	11th to 20th	Night	21% 12% 4 9% 4 4 3 3 4 6% 30%	2782
	21st to end	Night	14% 9% 2 6% 3 3 3 3 5% 6% 45%	3188
September	1st to 10th	Night	19% 7% 2 4 3 4 4 3 6% 7% 41%	1907
	11th to 20th	Night	20% 6% 2 5% 3 3 3 3 5% 7% 43%	2090
	21st to end	Night	23% 8% 2 5% 4 3 4 3 4 7% 37%	2090
October	1st to 10th	Night	22% 6% 2 6% 3 5% 3 3 5% 5% 39%	2262
	11th to 20th	Night	18% 9% 2 5% 4 3 3 3 5% 7% 41%	2280
	21st to end	Night	25% 10% 3 6% 4 4 4 3 4 6% 32%	2538
November	1st to 10th	Night	19% 9% 3 7% 4 4 4 4 5% 6% 34%	2569
	11th to 20th	Night	20% 15% 4 9% 6% 4 4 4 6% 6% 23%	2800
	21st to end	Night	20% 16% 5% 8% 6% 5% 4 3 5% 6% 24%	2800
December	1st to 10th	Night	18% 17% 6% 15% 6% 5% 4 4 5% 6% 16%	4580
	11th to 20th	Night	23% 14% 4 10% 5% 5% 5% 4 6% 6% 19%	5213
	21st to end	Night	23% 16% 5% 11% 5% 3 3 2 3 3 24%	7290

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	60% 28% 8% 5%	3226
	11th to 20th	Day	59% 29% 5% 5% 2	4038
	21st to end	Day	55% 28% 5% 5% 7%	4466
February	1st to 10th	Day	28% 62% 3 4 3	1800
	11th to 20th	Day	27% 61% 3 6% 3	1761
	21st to end	Day	21% 63% 4 7% 4 1	1600
March	1st to 10th	Day	42% 39% 5% 9% 3 1	3475
	11th to 20th	Day	38% 42% 6% 9% 4	3590
	21st to end	Day	47% 40% 3 5% 5% 1	3882
April	1st to 10th	Day	23% 64% 3 6% 4	2187
	11th to 20th	Day	16% 66% 5% 8% 4	2413
	21st to end	Day	18% 64% 3 7% 7% 1	2470
May	1st to 10th	Day	32% 44% 6% 15% 3	4120
	11th to 20th	Day	34% 43% 8% 12% 3	4233
	21st to end	Day	29% 46% 8% 7% 9% 1	4836
June	1st to 10th	Day	17% 66% 3 9% 5%	2704
	11th to 20th	Day	16% 65% 5% 8% 6% 1	2850
	21st to end	Day	19% 64% 4 8% 5% 1	2850
July	1st to 10th	Day	37% 37% 5% 11% 8% 1	4685
	11th to 20th	Day	39% 37% 5% 13% 6%	4343
	21st to end	Day	32% 38% 7% 14% 8% 1	4325
August	1st to 10th	Day	41% 38% 5% 10% 6%	4092
	11th to 20th	Day	31% 40% 7% 18% 3	4084
	21st to end	Day	19% 38% 8% 18% 15% 2	4454
September	1st to 10th	Day	16% 61% 5% 11% 7% 1	2271
	11th to 20th	Day	19% 61% 4 9% 7% 1	2090
	21st to end	Day	17% 60% 3 11% 8% 1	2090
October	1st to 10th	Day	29% 39% 6% 18% 7% 1	3176
	11th to 20th	Day	25% 38% 5% 15% 16% 1	3140
	21st to end	Day	26% 37% 8% 19% 8% 3	3371
November	1st to 10th	Day	25% 57% 6% 8% 3 1	1726
	11th to 20th	Day	29% 57% 5% 6% 3 1	1600
	21st to end	Day	31% 57% 4 6% 1	1600
December	1st to 10th	Day	45% 38% 8% 9% 1	2610
	11th to 20th	Day	48% 32% 9% 7% 4	2995
	21st to end	Day	46% 29% 11% 8% 6%	3678
January	1st to 10th	Night	60% 27% 5% 7% 1	6734
	11th to 20th	Night	55% 29% 6% 8% 3	5902
	21st to end	Night	51% 30% 7% 7% 6%	6490
February	1st to 10th	Night	29% 61% 3 3 3	2600
	11th to 20th	Night	26% 61% 3 7% 3	2536
	21st to end	Night	23% 62% 4 6% 5%	2025
March	1st to 10th	Night	42% 40% 4 6% 7% 1	3596
	11th to 20th	Night	38% 42% 8% 8% 5%	3590
	21st to end	Night	46% 39% 4 6% 5% 1	3889
April	1st to 10th	Night	21% 64% 3 6% 5% 2	1991
	11th to 20th	Night	19% 65% 3 8% 3 1	1713
	21st to end	Night	19% 66% 3 6% 5% 1	1710
May	1st to 10th	Night	34% 43% 9% 11% 3	2840
	11th to 20th	Night	36% 42% 7% 13% 3	2667
	21st to end	Night	33% 42% 7% 15% 3	2750
June	1st to 10th	Night	17% 66% 3 9% 5%	1490
	11th to 20th	Night	16% 65% 5% 10% 5%	1330
	21st to end	Night	20% 63% 3 7% 6% 1	1330
July	1st to 10th	Night	45% 37% 4 7% 7%	2175
	11th to 20th	Night	44% 36% 5% 7% 8%	2460
	21st to end	Night	33% 38% 7% 13% 8% 1	2989
August	1st to 10th	Night	41% 38% 6% 10% 4	2813
	11th to 20th	Night	34% 40% 10% 14% 1	2809
	21st to end	Night	22% 39% 7% 18% 13% 1	3187
September	1st to 10th	Night	16% 61% 3 12% 7% 1	1907
	11th to 20th	Night	19% 59% 4 11% 6% 1	2090
	21st to end	Night	18% 60% 2 12% 7%	2090
October	1st to 10th	Night	32% 38% 8% 13% 8% 1	3782
	11th to 20th	Night	19% 37% 8% 18% 18% 1	3779
	21st to end	Night	26% 37% 8% 19% 10% 1	4174
November	1st to 10th	Night	24% 57% 7% 8% 4	2569
	11th to 20th	Night	26% 57% 5% 8% 3	2800
	21st to end	Night	28% 57% 6% 6% 3	2800
December	1st to 10th	Night	42% 38% 7% 12% 2	4580
	11th to 20th	Night	42% 33% 9% 9% 6%	5215
	21st to end	Night	47% 27% 7% 11% 7% 1	7290

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	42% 23% 28% 6% 2	200
	11th to 20th	Day	37% 19% 28% 13% 3	391
	21st to end	Day	27% 25% 35% 11% 2	440
February	1st to 10th	Day	37% 20% 31% 10% 3	400
	11th to 20th	Day	39% 26% 24% 9% 2	396
	21st to end	Day	33% 22% 30% 13% 2	389
March	1st to 10th	Day	35% 23% 30% 9% 2	500
	11th to 20th	Day	37% 23% 27% 8% 4 1	500
	21st to end	Day	33% 25% 26% 11% 5% 1	530
April	1st to 10th	Day	40% 25% 25% 7% 2	460
	11th to 20th	Day	32% 23% 32% 10% 3	452
	21st to end	Day	34% 20% 29% 11% 5% 1	460
May	1st to 10th	Day	34% 27% 26% 10% 3 1	463
	11th to 20th	Day	27% 22% 30% 17% 4 1	570
	21st to end	Day	30% 16% 31% 18% 4 1	735
June	1st to 10th	Day	33% 17% 28% 18% 4	680
	11th to 20th	Day	24% 15% 33% 20% 6% 1	680
	21st to end	Day	35% 13% 29% 18% 5% 1	680
July	1st to 10th	Day	29% 10% 29% 22% 9% 1	670
	11th to 20th	Day	27% 10% 33% 22% 8% 1	597
	21st to end	Day	24% 12% 38% 21% 5% 1	532
August	1st to 10th	Day	24% 10% 36% 22% 7% 1	486
	11th to 20th	Day	25% 11% 35% 18% 9% 2	479
	21st to end	Day	23% 14% 30% 20% 10% 3	539
September	1st to 10th	Day	19% 15% 35% 23% 7% 1	490
	11th to 20th	Day	23% 15% 32% 18% 7% 5%	490
	21st to end	Day	23% 15% 32% 19% 7% 3	490
October	1st to 10th	Day	26% 12% 30% 19% 9% 3	397
	11th to 20th	Day	26% 16% 32% 18% 6% 2	390
	21st to end	Day	28% 22% 28% 14% 7%	429
November	1st to 10th	Day	28% 21% 30% 14% 7% 1	395
	11th to 20th	Day	38% 19% 28% 11% 4 1	400
	21st to end	Day	35% 21% 31% 9% 3 1	400
December	1st to 10th	Day	35% 22% 29% 12% 2	400
	11th to 20th	Day	43% 24% 22% 10% 2 1	400
	21st to end	Day	38% 24% 23% 10% 4 1	305
January	1st to 10th	Night	33% 22% 29% 15% 2	883
	11th to 20th	Night	35% 17% 29% 16% 3	800
	21st to end	Night	27% 23% 30% 16% 3	880
February	1st to 10th	Night	35% 18% 29% 17% 1	800
	11th to 20th	Night	33% 25% 25% 14% 2	783
	21st to end	Night	24% 21% 34% 17% 4	660
March	1st to 10th	Night	30% 20% 32% 16% 3	800
	11th to 20th	Night	27% 20% 28% 19% 6%	800
	21st to end	Night	26% 20% 32% 16% 6% 1	863
April	1st to 10th	Night	34% 17% 32% 15% 2	661
	11th to 20th	Night	28% 19% 35% 16% 3	564
	21st to end	Night	32% 14% 29% 19% 6%	570
May	1st to 10th	Night	28% 16% 36% 17% 3	570
	11th to 20th	Night	27% 13% 33% 22% 5%	562
	21st to end	Night	24% 13% 36% 23% 4 1	616
June	1st to 10th	Night	32% 9% 33% 21% 5%	540
	11th to 20th	Night	22% 8% 34% 31% 5% 1	380
	21st to end	Night	33% 4 29% 27% 7%	380
July	1st to 10th	Night	27% 4 33% 28% 8%	370
	11th to 20th	Night	24% 8% 34% 25% 9%	467
	21st to end	Night	24% 5% 35% 30% 6%	623
August	1st to 10th	Night	24% 6% 30% 32% 8% 1	568
	11th to 20th	Night	26% 6% 29% 30% 9%	562
	21st to end	Night	19% 7% 29% 32% 12% 1	627
September	1st to 10th	Night	22% 7% 30% 30% 11%	577
	11th to 20th	Night	24% 9% 26% 24% 15% 2	760
	21st to end	Night	25% 11% 26% 25% 11% 2	760
October	1st to 10th	Night	26% 10% 26% 26% 11% 1	760
	11th to 20th	Night	24% 15% 27% 24% 9% 1	760
	21st to end	Night	31% 16% 25% 22% 5%	836
November	1st to 10th	Night	27% 14% 28% 23% 8% 1	797
	11th to 20th	Night	32% 18% 25% 19% 5%	900
	21st to end	Night	32% 21% 25% 17% 5%	900
December	1st to 10th	Night	35% 18% 28% 15% 4	900
	11th to 20th	Night	36% 22% 25% 14% 3	900
	21st to end	Night	35% 21% 23% 17% 3	990

Page generated at 2025-03-24 10:04:31. Version ac07

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