Ester Dome Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ester Dome Observatory clear sky chart from 2005-11-06 to 2026-01-17.

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	11% 11% 4 11% 7% 6% 6% 5% 6% 7% 26%	132328
	Night	7% 12% 5% 12% 7% 6% 6% 4 6% 7% 28%	128151
Transparency	Day	54% 9% 15% 16% 5% 1	131927
	Night	53% 7% 14% 16% 8% 2	128130
Seeing	Day	15% 6% 19% 27% 24% 9%	20209
	Night	13% 5% 18% 32% 26% 7%	24557

By Month

Percentage Cloud Cover NW (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	4 10% 4 13% 6% 5% 5% 4 5% 6% 39%	1305
	11th to 20th	Day	3 13% 6% 14% 9% 6% 5% 3 6% 7% 29%	1832
	21st to end	Day	5% 9% 5% 15% 11% 8% 6% 5% 9% 6% 22%	2454
February	1st to 10th	Day	2 14% 4 10% 7% 4 5% 5% 6% 4 38%	1200
	11th to 20th	Day	3 12% 6% 16% 9% 7% 5% 6% 7% 8% 22%	1473
	21st to end	Day	4 12% 7% 14% 9% 7% 5% 5% 6% 5% 27%	1320
March	1st to 10th	Day	2 14% 8% 17% 7% 6% 4 3 5% 6% 27%	4375
	11th to 20th	Day	2 9% 5% 14% 8% 6% 6% 5% 6% 7% 30%	4622
	21st to end	Day	4 14% 6% 11% 7% 5% 5% 4 6% 7% 31%	5969
April	1st to 10th	Day	5% 15% 5% 12% 8% 6% 5% 5% 7% 7% 24%	2561
	11th to 20th	Day	4 11% 4 10% 6% 6% 5% 4 5% 6% 38%	2766
	21st to end	Day	4 9% 3 9% 6% 6% 7% 5% 7% 7% 38%	3054
May	1st to 10th	Day	9% 14% 5% 13% 8% 6% 6% 4 6% 6% 22%	7381
	11th to 20th	Day	5% 8% 3 9% 7% 6% 6% 5% 6% 6% 40%	7909
	21st to end	Day	10% 10% 4 11% 8% 7% 8% 6% 9% 7% 20%	9139
June	1st to 10th	Day	10% 10% 4 10% 8% 7% 7% 6% 7% 8% 24%	3950
	11th to 20th	Day	11% 8% 3 8% 7% 6% 7% 5% 7% 9% 28%	4000
	21st to end	Day	13% 7% 3 8% 6% 6% 6% 6% 7% 9% 28%	4000
July	1st to 10th	Day	20% 10% 3 8% 5% 5% 5% 4 5% 6% 29%	9060
	11th to 20th	Day	12% 9% 3 9% 6% 7% 7% 6% 9% 10% 21%	8334
	21st to end	Day	19% 10% 4 8% 6% 6% 6% 5% 7% 8% 23%	8861
August	1st to 10th	Day	23% 13% 4 9% 5% 5% 5% 4 5% 6% 20%	5212
	11th to 20th	Day	20% 13% 4 11% 6% 6% 5% 4 7% 7% 17%	4968
	21st to end	Day	21% 14% 5% 11% 6% 6% 6% 5% 6% 6% 15%	5038
September	1st to 10th	Day	17% 12% 4 9% 7% 6% 5% 4 7% 6% 22%	2601
	11th to 20th	Day	20% 16% 5% 12% 6% 4 5% 3 5% 5% 19%	2376
	21st to end	Day	19% 15% 6% 10% 5% 5% 5% 3 4 5% 24%	2155
October	1st to 10th	Day	10% 17% 6% 11% 5% 5% 4 3 4 5% 28%	3105
	11th to 20th	Day	7% 15% 7% 18% 7% 5% 5% 3 5% 5% 23%	2830
	21st to end	Day	10% 15% 7% 17% 8% 6% 5% 4 6% 5% 18%	2532
November	1st to 10th	Day	9% 18% 5% 13% 7% 5% 5% 4 6% 6% 21%	1274
	11th to 20th	Day	7% 10% 6% 15% 8% 8% 5% 4 5% 5% 28%	1050
	21st to end	Day	8% 16% 6% 14% 6% 5% 6% 4 6% 5% 22%	785
December	1st to 10th	Day	8% 13% 4 9% 7% 6% 6% 4 5% 8% 31%	1010
	11th to 20th	Day	3 13% 7% 15% 6% 5% 6% 5% 6% 6% 28%	793
	21st to end	Day	2 12% 4 12% 6% 6% 7% 6% 7% 9% 31%	1034
January	1st to 10th	Night	3 10% 5% 11% 6% 5% 4 3 5% 6% 43%	8924
	11th to 20th	Night	3 12% 5% 12% 7% 6% 5% 5% 8% 8% 30%	8218
	21st to end	Night	5% 11% 5% 13% 9% 6% 6% 5% 8% 6% 25%	8528
February	1st to 10th	Night	3 12% 6% 12% 7% 4 4 4 5% 6% 38%	3200
	11th to 20th	Night	3 11% 5% 12% 8% 7% 6% 5% 7% 8% 30%	2813
	21st to end	Night	4 13% 7% 14% 8% 7% 5% 4 6% 7% 26%	2310
March	1st to 10th	Night	2 12% 7% 17% 7% 6% 5% 4 5% 5% 29%	5479
	11th to 20th	Night	4 10% 5% 13% 9% 6% 7% 4 6% 8% 29%	5333
	21st to end	Night	6% 13% 4 10% 5% 5% 5% 4 6% 9% 32%	4962
April	1st to 10th	Night	4 16% 6% 11% 7% 7% 6% 5% 6% 6% 26%	1837
	11th to 20th	Night	5% 10% 3 9% 7% 6% 5% 5% 7% 8% 34%	1583
	21st to end	Night	6% 8% 4 9% 6% 5% 6% 5% 6% 8% 38%	1343
May	1st to 10th	Night	8% 8% 3 9% 8% 8% 7% 6% 8% 11% 23%	2593
	11th to 20th	Night	7% 8% 3 7% 5% 5% 5% 5% 7% 7% 42%	1995
	21st to end	Night	13% 11% 4 10% 7% 6% 7% 4 7% 7% 23%	1758
June	1st to 10th	Night	9% 10% 3 12% 8% 6% 5% 6% 9% 8% 24%	448
	11th to 20th	Night	12% 10% 3 11% 6% 3 6% 6% 6% 9% 29%	400
	21st to end	Night	12% 7% 1 10% 9% 5% 6% 7% 8% 9% 28%	400
July	1st to 10th	Night	19% 13% 5% 11% 6% 4 3 3 4 7% 27%	920
	11th to 20th	Night	13% 10% 4 11% 6% 6% 6% 5% 6% 8% 25%	1644
	21st to end	Night	17% 11% 3 8% 6% 6% 5% 5% 7% 8% 25%	2002
August	1st to 10th	Night	20% 13% 5% 10% 6% 6% 5% 3 6% 7% 19%	1945
	11th to 20th	Night	26% 16% 4 10% 4 4 5% 3 4 5% 18%	2077
	21st to end	Night	19% 13% 4 11% 6% 6% 6% 4 5% 7% 19%	2871
September	1st to 10th	Night	15% 11% 4 10% 6% 6% 5% 5% 6% 7% 24%	1796
	11th to 20th	Night	16% 14% 5% 11% 7% 6% 5% 4 6% 6% 19%	2024
	21st to end	Night	18% 13% 5% 10% 6% 6% 6% 4 5% 5% 23%	2243
October	1st to 10th	Night	9% 16% 5% 9% 5% 6% 6% 5% 6% 6% 28%	4080
	11th to 20th	Night	9% 14% 5% 12% 7% 7% 6% 4 6% 7% 23%	4316
	21st to end	Night	8% 16% 8% 17% 9% 6% 6% 3 4 5% 18%	5269
November	1st to 10th	Night	8% 19% 6% 12% 6% 5% 5% 4 5% 7% 23%	3244
	11th to 20th	Night	8% 13% 6% 14% 7% 6% 5% 3 6% 7% 26%	3570
	21st to end	Night	8% 15% 6% 14% 7% 6% 5% 5% 6% 6% 24%	3812
December	1st to 10th	Night	5% 12% 5% 12% 7% 6% 6% 4 6% 7% 29%	6400
	11th to 20th	Night	4 14% 7% 12% 6% 6% 5% 5% 6% 6% 29%	7628
	21st to end	Night	3 11% 5% 12% 7% 6% 6% 5% 7% 8% 29%	10186

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	46% 5% 11% 17% 17% 3	1305
	11th to 20th	Day	53% 6% 15% 17% 6% 3	1844
	21st to end	Day	57% 5% 8% 16% 10% 5%	2454
February	1st to 10th	Day	44% 8% 7% 19% 19% 4	1200
	11th to 20th	Day	55% 9% 11% 15% 9% 1	1479
	21st to end	Day	56% 7% 10% 14% 12% 1	1320
March	1st to 10th	Day	58% 5% 8% 17% 11% 1	4375
	11th to 20th	Day	51% 7% 10% 17% 11% 4	4622
	21st to end	Day	50% 7% 14% 16% 12% 1	5969
April	1st to 10th	Day	56% 7% 13% 17% 6% 1	2561
	11th to 20th	Day	44% 7% 15% 25% 7% 2	2766
	21st to end	Day	41% 7% 14% 29% 9%	3054
May	1st to 10th	Day	57% 9% 10% 19% 5%	7381
	11th to 20th	Day	40% 8% 11% 23% 14% 4	7912
	21st to end	Day	52% 11% 15% 18% 4	9140
June	1st to 10th	Day	54% 10% 15% 18% 3	3950
	11th to 20th	Day	48% 11% 17% 21% 3	4000
	21st to end	Day	48% 12% 20% 18% 2	4000
July	1st to 10th	Day	54% 9% 18% 16% 3	8961
	11th to 20th	Day	51% 11% 23% 13% 1	8230
	21st to end	Day	56% 10% 21% 11% 3	8612
August	1st to 10th	Day	63% 8% 20% 9% 1	5192
	11th to 20th	Day	62% 10% 20% 8%	5016
	21st to end	Day	66% 10% 16% 8% 1	5037
September	1st to 10th	Day	59% 11% 19% 10% 1	2601
	11th to 20th	Day	65% 9% 15% 11%	2376
	21st to end	Day	63% 8% 14% 13% 3	2155
October	1st to 10th	Day	58% 6% 12% 20% 4	3105
	11th to 20th	Day	62% 8% 13% 16% 2	2830
	21st to end	Day	66% 8% 12% 11% 3	2532
November	1st to 10th	Day	61% 8% 15% 12% 4	1274
	11th to 20th	Day	57% 7% 12% 20% 4	1050
	21st to end	Day	60% 9% 11% 15% 5%	785
December	1st to 10th	Day	52% 7% 16% 19% 6% 1	1010
	11th to 20th	Day	54% 6% 16% 14% 4 6%	795
	21st to end	Day	46% 7% 17% 15% 14% 1	1034
January	1st to 10th	Night	41% 6% 14% 20% 14% 6%	8924
	11th to 20th	Night	47% 6% 20% 17% 9% 1	8268
	21st to end	Night	54% 5% 9% 14% 13% 5%	8528
February	1st to 10th	Night	47% 4 8% 17% 20% 4	3200
	11th to 20th	Night	49% 6% 13% 20% 11% 1	2818
	21st to end	Night	57% 6% 13% 15% 8% 1	2310
March	1st to 10th	Night	56% 5% 8% 20% 10% 1	5479
	11th to 20th	Night	52% 5% 12% 16% 13% 3	5335
	21st to end	Night	44% 9% 15% 17% 13% 2	4962
April	1st to 10th	Night	55% 7% 14% 18% 6% 1	1837
	11th to 20th	Night	44% 9% 17% 22% 7% 1	1583
	21st to end	Night	42% 6% 13% 28% 10%	1343
May	1st to 10th	Night	48% 12% 15% 22% 3	2590
	11th to 20th	Night	36% 9% 12% 27% 13% 2	1995
	21st to end	Night	53% 10% 12% 19% 6%	1758
June	1st to 10th	Night	50% 15% 15% 18% 3	448
	11th to 20th	Night	50% 9% 15% 21% 5%	400
	21st to end	Night	49% 12% 21% 18% 1	400
July	1st to 10th	Night	58% 7% 15% 14% 5%	910
	11th to 20th	Night	56% 9% 20% 14% 3	1625
	21st to end	Night	56% 9% 20% 11% 4	1946
August	1st to 10th	Night	64% 9% 19% 8% 1	1940
	11th to 20th	Night	68% 8% 17% 7%	2095
	21st to end	Night	63% 9% 18% 10% 1	2871
September	1st to 10th	Night	55% 11% 20% 13% 2	1796
	11th to 20th	Night	64% 9% 14% 12% 1	2024
	21st to end	Night	62% 9% 12% 14% 3	2243
October	1st to 10th	Night	55% 7% 13% 21% 4	4080
	11th to 20th	Night	59% 8% 17% 15% 2	4316
	21st to end	Night	67% 7% 11% 13% 1	5269
November	1st to 10th	Night	60% 7% 13% 16% 4	3244
	11th to 20th	Night	58% 6% 14% 17% 4	3570
	21st to end	Night	59% 7% 9% 18% 6%	3812
December	1st to 10th	Night	52% 7% 16% 18% 7% 1	6400
	11th to 20th	Night	54% 5% 17% 14% 6% 4	7625
	21st to end	Night	49% 7% 15% 13% 14% 1	10186

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	7% 5% 19% 40% 24% 5%	110
	11th to 20th	Day	10% 6% 21% 28% 29% 6%	106
	21st to end	Day	9% 5% 16% 35% 25% 10%	230
February	1st to 10th	Day	7% 7% 14% 31% 24% 17%	300
	11th to 20th	Day	9% 7% 24% 30% 21% 9%	359
	21st to end	Day	9% 10% 25% 30% 19% 6%	331
March	1st to 10th	Day	7% 7% 26% 36% 19% 6%	400
	11th to 20th	Day	7% 8% 25% 30% 24% 7%	412
	21st to end	Day	9% 6% 24% 30% 24% 7%	660
April	1st to 10th	Day	12% 10% 25% 29% 19% 5%	660
	11th to 20th	Day	10% 8% 26% 30% 21% 5%	690
	21st to end	Day	7% 5% 15% 35% 31% 7%	700
May	1st to 10th	Day	11% 8% 21% 31% 23% 6%	703
	11th to 20th	Day	9% 8% 25% 29% 22% 7%	828
	21st to end	Day	15% 7% 19% 29% 24% 7%	1104
June	1st to 10th	Day	13% 5% 20% 27% 25% 11%	1130
	11th to 20th	Day	11% 4 14% 24% 34% 13%	1130
	21st to end	Day	14% 3 13% 25% 31% 15%	1130
July	1st to 10th	Day	16% 4 14% 26% 31% 9%	1111
	11th to 20th	Day	18% 4 15% 26% 26% 12%	964
	21st to end	Day	18% 4 15% 23% 26% 14%	1008
August	1st to 10th	Day	26% 6% 16% 23% 21% 9%	726
	11th to 20th	Day	24% 6% 18% 23% 23% 5%	715
	21st to end	Day	25% 8% 18% 20% 20% 9%	803
September	1st to 10th	Day	21% 9% 19% 21% 22% 10%	702
	11th to 20th	Day	26% 9% 17% 25% 15% 8%	596
	21st to end	Day	26% 5% 19% 18% 19% 13%	420
October	1st to 10th	Day	21% 10% 23% 20% 18% 8%	420
	11th to 20th	Day	17% 6% 21% 23% 21% 11%	420
	21st to end	Day	15% 8% 15% 24% 26% 13%	462
November	1st to 10th	Day	16% 8% 14% 28% 26% 8%	318
	11th to 20th	Day	9% 3 19% 33% 19% 17%	110
	21st to end	Day	13% 6% 15% 31% 28% 6%	110
December	1st to 10th	Day	19% 5% 19% 31% 16% 9%	110
	11th to 20th	Day	8% 7% 27% 30% 22% 5%	110
	21st to end	Day	6% 11% 28% 30% 20% 6%	121
January	1st to 10th	Night	8% 2 19% 35% 27% 9%	1217
	11th to 20th	Night	11% 5% 20% 39% 20% 5%	1036
	21st to end	Night	9% 4 20% 39% 22% 6%	1060
February	1st to 10th	Night	6% 5% 21% 34% 27% 8%	900
	11th to 20th	Night	7% 5% 21% 39% 23% 4	884
	21st to end	Night	8% 6% 24% 36% 24% 2	743
March	1st to 10th	Night	8% 5% 22% 37% 25% 3	705
	11th to 20th	Night	9% 4 20% 38% 24% 6%	687
	21st to end	Night	11% 4 18% 35% 23% 8%	660
April	1st to 10th	Night	10% 8% 22% 35% 23% 3	600
	11th to 20th	Night	9% 5% 19% 38% 24% 5%	593
	21st to end	Night	9% 2 15% 30% 37% 7%	531
May	1st to 10th	Night	10% 4 14% 26% 40% 7%	351
	11th to 20th	Night	8% 6% 21% 37% 26% 1	197
	21st to end	Night	14% 6% 13% 32% 29% 6%	217
June	1st to 10th	Night	10% 4 22% 24% 32% 9%	200
	11th to 20th	Night	12% 5% 15% 25% 37% 8%	200
	21st to end	Night	15% 2 10% 27% 39% 9%	200
July	1st to 10th	Night	14% 5% 15% 27% 33% 6%	195
	11th to 20th	Night	22% 3 14% 23% 32% 5%	194
	21st to end	Night	17% 3 14% 27% 32% 7%	219
August	1st to 10th	Night	25% 2 12% 26% 29% 5%	389
	11th to 20th	Night	25% 6% 12% 21% 29% 6%	459
	21st to end	Night	26% 4 10% 22% 27% 10%	660
September	1st to 10th	Night	20% 4 16% 22% 30% 9%	600
	11th to 20th	Night	21% 5% 15% 27% 28% 4	600
	21st to end	Night	23% 4 17% 24% 28% 4	625
October	1st to 10th	Night	24% 6% 21% 22% 23% 3	805
	11th to 20th	Night	15% 5% 18% 28% 26% 8%	910
	21st to end	Night	14% 4 17% 31% 28% 7%	1001
November	1st to 10th	Night	16% 5% 19% 30% 25% 4	930
	11th to 20th	Night	14% 4 17% 28% 26% 11%	950
	21st to end	Night	14% 4 16% 31% 26% 10%	1102
December	1st to 10th	Night	15% 6% 19% 32% 20% 7%	1270
	11th to 20th	Night	11% 6% 20% 31% 26% 6%	1270
	21st to end	Night	9% 5% 20% 34% 23% 9%	1397

Page generated at 2026-01-13 21:14:27. Version ac07

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