EyeScope Star Shack
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the EyeScope Star Shack clear sky chart from 2005-11-06 to 2026-09-29.

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	13% 11% 4 10% 5% 5% 4 3 5% 6% 34%	148804
	Night	14% 14% 5% 13% 7% 5% 4 3 4 5% 27%	142868
Transparency	Day	35% 34% 7% 16% 8% 1	152297
	Night	40% 34% 7% 12% 6% 1	147462
Seeing	Day	19% 13% 28% 25% 11% 3	18280
	Night	21% 12% 28% 28% 11% 1	27859

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% 23% 13% 29% 7% 3 3 1 2 2 5%	4691
	11th to 20th	Day	9% 21% 9% 26% 15% 10% 3 1 2 1 3	4679
	21st to end	Day	9% 16% 8% 21% 11% 10% 6% 3 3 3 11%	5156
February	1st to 10th	Day	9% 18% 8% 16% 14% 8% 3 3 4 4 12%	1792
	11th to 20th	Day	13% 15% 7% 16% 9% 6% 5% 3 4 4 19%	2024
	21st to end	Day	12% 16% 6% 13% 8% 5% 5% 3 4 4 22%	1730
March	1st to 10th	Day	14% 10% 3 11% 6% 5% 4 4 5% 6% 32%	4578
	11th to 20th	Day	11% 13% 4 11% 5% 6% 5% 4 6% 7% 28%	4967
	21st to end	Day	21% 10% 7% 14% 6% 5% 4 3 3 4 22%	5772
April	1st to 10th	Day	19% 13% 4 9% 4 4 4 3 4 6% 29%	2520
	11th to 20th	Day	20% 12% 4 6% 4 3 3 3 5% 5% 36%	2616
	21st to end	Day	15% 10% 4 8% 5% 5% 5% 4 5% 6% 34%	2730
May	1st to 10th	Day	12% 8% 3 5% 4 4 4 3 5% 7% 44%	7642
	11th to 20th	Day	13% 8% 3 7% 4 4 4 3 4 6% 42%	7922
	21st to end	Day	11% 7% 3 6% 3 4 3 3 5% 7% 48%	9061
June	1st to 10th	Day	12% 5% 2 6% 5% 4 4 4 6% 9% 44%	3113
	11th to 20th	Day	13% 6% 2 6% 4 5% 5% 4 6% 9% 41%	3150
	21st to end	Day	15% 7% 2 5% 5% 4 4 4 5% 8% 42%	3104
July	1st to 10th	Day	15% 7% 2 5% 3 3 4 3 6% 9% 44%	8279
	11th to 20th	Day	9% 5% 2 4 3 4 4 4 6% 8% 51%	8280
	21st to end	Day	10% 6% 2 5% 4 3 4 3 6% 9% 49%	8992
August	1st to 10th	Day	9% 6% 2 6% 4 4 4 4 6% 9% 45%	6232
	11th to 20th	Day	13% 5% 2 5% 3 3 4 3 5% 7% 48%	5951
	21st to end	Day	14% 7% 3 7% 5% 5% 5% 4 5% 6% 40%	6364
September	1st to 10th	Day	15% 6% 2 5% 4 4 3 3 6% 7% 44%	2488
	11th to 20th	Day	13% 5% 2 6% 4 4 4 3 5% 8% 46%	2310
	21st to end	Day	17% 7% 3 6% 4 4 5% 3 6% 8% 38%	2288
October	1st to 10th	Day	19% 9% 3 7% 4 4 3 3 5% 8% 35%	2200
	11th to 20th	Day	24% 15% 4 10% 5% 5% 4 3 4 5% 19%	1884
	21st to end	Day	23% 17% 5% 9% 6% 6% 4 3 5% 5% 18%	1980
November	1st to 10th	Day	18% 20% 5% 9% 4 4 3 3 4 6% 24%	1852
	11th to 20th	Day	14% 26% 8% 13% 5% 4 4 3 4 4 15%	1890
	21st to end	Day	18% 26% 10% 14% 5% 4 3 2 3 3 12%	1692
December	1st to 10th	Day	12% 33% 13% 19% 6% 3 3 2 2 2 5%	2350
	11th to 20th	Day	12% 27% 9% 23% 9% 5% 3 2 2 2 5%	2691
	21st to end	Day	20% 24% 9% 15% 7% 4 4 3 4 4 6%	3834
January	1st to 10th	Night	12% 20% 9% 31% 9% 4 3 2 2 2 6%	8233
	11th to 20th	Night	10% 19% 10% 26% 16% 8% 3 2 1 1 5%	8236
	21st to end	Night	9% 16% 8% 21% 12% 10% 6% 3 3 3 10%	9058
February	1st to 10th	Night	11% 18% 7% 18% 13% 6% 4 3 3 4 13%	2827
	11th to 20th	Night	11% 15% 6% 15% 10% 6% 5% 3 4 5% 18%	2479
	21st to end	Night	14% 18% 6% 12% 7% 5% 5% 3 4 5% 21%	2076
March	1st to 10th	Night	16% 10% 4 8% 6% 4 3 3 4 6% 36%	5482
	11th to 20th	Night	11% 14% 5% 10% 5% 4 5% 4 6% 7% 30%	5212
	21st to end	Night	20% 12% 5% 10% 5% 4 4 3 5% 5% 27%	5433
April	1st to 10th	Night	20% 12% 4 10% 5% 5% 4 4 5% 5% 28%	2100
	11th to 20th	Night	20% 10% 4 8% 5% 4 3 3 5% 4 34%	1952
	21st to end	Night	17% 10% 3 7% 6% 4 4 3 5% 6% 35%	1890
May	1st to 10th	Night	12% 7% 2 7% 5% 4 5% 4 6% 7% 41%	5257
	11th to 20th	Night	12% 9% 3 7% 4 5% 4 3 6% 7% 40%	4940
	21st to end	Night	14% 8% 3 6% 4 3 4 3 5% 6% 45%	5148
June	1st to 10th	Night	14% 7% 2 6% 6% 4 5% 3 5% 8% 41%	1502
	11th to 20th	Night	13% 6% 2 7% 5% 4 5% 4 7% 8% 39%	1470
	21st to end	Night	13% 7% 2 6% 5% 4 4 3 4 7% 44%	1509
July	1st to 10th	Night	13% 7% 3 7% 4 4 4 3 6% 8% 40%	4710
	11th to 20th	Night	8% 5% 2 6% 4 4 5% 4 5% 8% 50%	4710
	21st to end	Night	8% 6% 2 6% 3 4 4 4 6% 8% 49%	5118
August	1st to 10th	Night	14% 7% 3 7% 4 4 4 3 5% 7% 42%	3911
	11th to 20th	Night	11% 5% 2 5% 3 3 4 3 6% 9% 48%	4095
	21st to end	Night	13% 7% 3 7% 5% 4 4 4 5% 7% 42%	4759
September	1st to 10th	Night	12% 6% 3 6% 5% 4 4 3 5% 6% 45%	2110
	11th to 20th	Night	15% 5% 2 6% 3 4 4 3 6% 8% 44%	2310
	21st to end	Night	18% 6% 3 8% 4 5% 4 3 5% 7% 38%	2289
October	1st to 10th	Night	18% 9% 3 6% 4 4 4 3 5% 6% 37%	2200
	11th to 20th	Night	23% 14% 4 10% 5% 4 4 4 4 5% 23%	2510
	21st to end	Night	27% 15% 3 9% 5% 4 4 3 4 4 21%	2860
November	1st to 10th	Night	19% 18% 4 9% 5% 4 3 2 4 5% 26%	2666
	11th to 20th	Night	16% 24% 6% 12% 6% 4 4 3 3 4 17%	2730
	21st to end	Night	18% 27% 9% 13% 6% 4 3 3 3 3 11%	2923
December	1st to 10th	Night	12% 29% 12% 18% 7% 4 4 2 2 2 7%	5060
	11th to 20th	Night	13% 24% 9% 24% 8% 4 3 2 3 3 9%	5736
	21st to end	Night	22% 21% 10% 15% 7% 4 3 3 3 3 9%	7367

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	72% 21% 3 3 1	4692
	11th to 20th	Day	74% 21% 2 1 1	4710
	21st to end	Day	62% 24% 6% 6% 2	5156
February	1st to 10th	Day	33% 59% 2 4 1	1792
	11th to 20th	Day	28% 58% 4 6% 4	2034
	21st to end	Day	27% 59% 4 6% 3	1730
March	1st to 10th	Day	37% 30% 12% 12% 8% 2	4580
	11th to 20th	Day	42% 30% 9% 12% 5% 1	4967
	21st to end	Day	52% 29% 5% 9% 5%	5772
April	1st to 10th	Day	25% 59% 3 9% 3	2520
	11th to 20th	Day	21% 59% 3 9% 6% 1	2616
	21st to end	Day	20% 59% 5% 8% 7%	2730
May	1st to 10th	Day	29% 25% 7% 21% 16% 2	7651
	11th to 20th	Day	35% 24% 6% 21% 15%	7926
	21st to end	Day	29% 24% 6% 20% 17% 3	9061
June	1st to 10th	Day	17% 59% 4 12% 7% 1	3113
	11th to 20th	Day	20% 59% 6% 9% 6% 1	3150
	21st to end	Day	17% 58% 5% 14% 5%	3104
July	1st to 10th	Day	31% 23% 14% 21% 10% 1	8211
	11th to 20th	Day	24% 22% 12% 32% 9%	8205
	21st to end	Day	26% 22% 11% 29% 11%	8794
August	1st to 10th	Day	25% 28% 11% 23% 12%	6217
	11th to 20th	Day	29% 28% 11% 27% 6%	5990
	21st to end	Day	35% 30% 11% 20% 4	6363
September	1st to 10th	Day	20% 55% 8% 12% 5%	2488
	11th to 20th	Day	15% 55% 6% 16% 7%	2310
	21st to end	Day	17% 55% 6% 13% 8% 1	2288
October	1st to 10th	Day	20% 37% 6% 24% 13%	3590
	11th to 20th	Day	33% 37% 6% 15% 8%	3048
	21st to end	Day	40% 37% 8% 11% 3	3180
November	1st to 10th	Day	33% 53% 4 8% 2	1852
	11th to 20th	Day	34% 54% 5% 5% 2	1890
	21st to end	Day	39% 54% 3 3 1	1692
December	1st to 10th	Day	59% 36% 3 2	2350
	11th to 20th	Day	63% 32% 2 2 1	2691
	21st to end	Day	60% 27% 6% 5% 2	3834
January	1st to 10th	Night	68% 22% 5% 3 1	8233
	11th to 20th	Night	73% 22% 3 2	8280
	21st to end	Night	62% 24% 5% 6% 2	9058
February	1st to 10th	Night	32% 59% 3 4 2	2827
	11th to 20th	Night	26% 58% 4 9% 2	2480
	21st to end	Night	26% 59% 4 7% 4	2076
March	1st to 10th	Night	37% 29% 13% 14% 7%	5493
	11th to 20th	Night	39% 29% 14% 14% 4	5213
	21st to end	Night	45% 30% 7% 11% 7%	5433
April	1st to 10th	Night	26% 59% 2 8% 4 1	2100
	11th to 20th	Night	24% 59% 2 9% 4 2	1952
	21st to end	Night	22% 59% 4 9% 6% 1	1890
May	1st to 10th	Night	29% 26% 9% 20% 13% 2	5264
	11th to 20th	Night	32% 25% 6% 23% 13%	4941
	21st to end	Night	32% 23% 8% 18% 13% 6%	5149
June	1st to 10th	Night	17% 59% 4 10% 9% 1	1502
	11th to 20th	Night	19% 60% 5% 10% 5% 1	1470
	21st to end	Night	18% 58% 4 12% 7% 1	1509
July	1st to 10th	Night	35% 23% 11% 16% 11% 4	4670
	11th to 20th	Night	25% 24% 10% 29% 12% 1	4662
	21st to end	Night	26% 23% 12% 26% 13%	5002
August	1st to 10th	Night	33% 28% 10% 15% 13% 1	3902
	11th to 20th	Night	25% 29% 15% 25% 6%	4122
	21st to end	Night	31% 30% 11% 21% 7%	4759
September	1st to 10th	Night	17% 55% 9% 12% 7%	2110
	11th to 20th	Night	17% 55% 6% 14% 8%	2310
	21st to end	Night	20% 54% 7% 10% 8% 1	2289
October	1st to 10th	Night	26% 38% 7% 20% 9%	3590
	11th to 20th	Night	30% 37% 7% 15% 11%	4085
	21st to end	Night	37% 37% 10% 13% 3	4610
November	1st to 10th	Night	33% 53% 4 7% 3	2666
	11th to 20th	Night	32% 54% 5% 6% 3	2730
	21st to end	Night	39% 54% 4 2 1	2923
December	1st to 10th	Night	55% 38% 4 4	5060
	11th to 20th	Night	58% 33% 5% 4 1	5735
	21st to end	Night	58% 30% 6% 5% 2	7367

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	21% 18% 38% 18% 4 1	330
	11th to 20th	Day	22% 20% 38% 15% 4 1	330
	21st to end	Day	23% 17% 35% 21% 5%	363
February	1st to 10th	Day	20% 26% 35% 12% 5% 1	330
	11th to 20th	Day	19% 24% 36% 18% 3 1	330
	21st to end	Day	24% 26% 38% 10% 2	273
March	1st to 10th	Day	21% 23% 35% 19% 3	330
	11th to 20th	Day	22% 17% 34% 20% 7%	482
	21st to end	Day	29% 15% 27% 21% 7% 1	594
April	1st to 10th	Day	26% 15% 32% 19% 6% 1	540
	11th to 20th	Day	29% 15% 27% 17% 9% 2	532
	21st to end	Day	20% 15% 29% 24% 10% 2	540
May	1st to 10th	Day	20% 16% 29% 21% 11% 2	543
	11th to 20th	Day	17% 11% 34% 27% 8% 3	668
	21st to end	Day	15% 12% 29% 28% 14% 3	844
June	1st to 10th	Day	14% 9% 30% 31% 13% 2	780
	11th to 20th	Day	17% 8% 30% 31% 12% 2	780
	21st to end	Day	18% 7% 28% 30% 14% 2	780
July	1st to 10th	Day	10% 6% 26% 35% 17% 5%	771
	11th to 20th	Day	11% 9% 26% 33% 16% 5%	768
	21st to end	Day	11% 6% 26% 35% 17% 4	849
August	1st to 10th	Day	9% 5% 22% 33% 23% 8%	668
	11th to 20th	Day	15% 4 19% 34% 19% 9%	559
	21st to end	Day	18% 9% 20% 29% 18% 5%	627
September	1st to 10th	Day	17% 11% 24% 24% 19% 6%	570
	11th to 20th	Day	11% 7% 21% 31% 21% 9%	570
	21st to end	Day	17% 11% 19% 28% 19% 6%	562
October	1st to 10th	Day	23% 14% 26% 22% 14% 2	530
	11th to 20th	Day	29% 15% 29% 23% 4 1	410
	21st to end	Day	28% 18% 30% 17% 5% 1	363
November	1st to 10th	Day	31% 16% 30% 17% 6%	330
	11th to 20th	Day	25% 23% 31% 18% 3	330
	21st to end	Day	27% 29% 27% 14% 3	256
December	1st to 10th	Day	30% 23% 28% 14% 5% 1	220
	11th to 20th	Day	23% 29% 33% 14% 1	220
	21st to end	Day	33% 25% 30% 9% 2 1	308
January	1st to 10th	Night	21% 18% 33% 21% 6% 1	1050
	11th to 20th	Night	22% 18% 32% 22% 6%	1050
	21st to end	Night	20% 13% 34% 26% 6%	1155
February	1st to 10th	Night	19% 16% 34% 24% 6% 1	937
	11th to 20th	Night	19% 18% 32% 26% 5%	823
	21st to end	Night	25% 15% 32% 24% 4	692
March	1st to 10th	Night	18% 11% 35% 26% 9% 1	840
	11th to 20th	Night	19% 13% 34% 27% 6%	840
	21st to end	Night	20% 9% 30% 31% 8% 1	859
April	1st to 10th	Night	25% 11% 31% 27% 5% 1	630
	11th to 20th	Night	25% 10% 27% 27% 10% 1	623
	21st to end	Night	20% 10% 27% 33% 9% 1	630
May	1st to 10th	Night	16% 7% 28% 38% 11%	630
	11th to 20th	Night	18% 8% 26% 36% 11% 1	621
	21st to end	Night	15% 5% 24% 37% 19% 1	683
June	1st to 10th	Night	15% 4 25% 40% 14% 1	452
	11th to 20th	Night	13% 5% 24% 41% 16%	420
	21st to end	Night	15% 5% 22% 40% 16% 1	459
July	1st to 10th	Night	13% 3 17% 45% 20% 2	615
	11th to 20th	Night	10% 4 18% 39% 26% 3	612
	21st to end	Night	9% 2 21% 40% 26% 2	690
August	1st to 10th	Night	11% 3 18% 41% 26% 1	627
	11th to 20th	Night	11% 5% 15% 38% 29% 3	624
	21st to end	Night	17% 5% 17% 37% 22% 1	693
September	1st to 10th	Night	13% 5% 23% 33% 23% 3	640
	11th to 20th	Night	17% 4 20% 33% 23% 4	840
	21st to end	Night	21% 6% 18% 33% 17% 4	833
October	1st to 10th	Night	22% 11% 24% 30% 13% 1	800
	11th to 20th	Night	30% 13% 26% 24% 7% 1	800
	21st to end	Night	33% 14% 25% 22% 6% 1	880
November	1st to 10th	Night	29% 15% 28% 22% 6%	820
	11th to 20th	Night	26% 19% 30% 20% 4	840
	21st to end	Night	31% 18% 31% 17% 3	896
December	1st to 10th	Night	25% 21% 32% 18% 3	1050
	11th to 20th	Night	23% 22% 34% 16% 4 1	1050
	21st to end	Night	30% 15% 33% 18% 4	1155

Page generated at 2026-09-26 04:18:43. Version ac07

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