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 2025-05-26.

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	14% 12% 5% 10% 5% 4 4 3 5% 6% 32%	113318
	Night	15% 15% 6% 13% 7% 4 4 3 4 5% 25%	116075
Transparency	Day	33% 42% 6% 12% 6%	116859
	Night	38% 41% 6% 10% 5%	120697
Seeing	Day	19% 13% 28% 25% 12% 3	16345
	Night	21% 12% 28% 28% 11% 1	26153

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	9% 22% 13% 29% 7% 4 3 2 2 2 6%	3617
	11th to 20th	Day	11% 19% 8% 27% 15% 9% 3 2 3 2 3	3589
	21st to end	Day	12% 19% 10% 23% 8% 6% 5% 2 3 3 9%	3982
February	1st to 10th	Day	9% 18% 8% 16% 14% 8% 3 3 4 4 13%	1706
	11th to 20th	Day	13% 15% 7% 16% 10% 6% 5% 3 4 3 18%	1925
	21st to end	Day	12% 16% 6% 13% 8% 5% 5% 3 4 4 23%	1650
March	1st to 10th	Day	13% 10% 3 11% 6% 5% 4 4 5% 7% 32%	4478
	11th to 20th	Day	11% 13% 5% 11% 5% 6% 5% 4 6% 7% 28%	4860
	21st to end	Day	21% 10% 7% 14% 6% 5% 4 3 3 4 22%	5647
April	1st to 10th	Day	19% 13% 4 9% 4 4 4 3 4 6% 29%	2400
	11th to 20th	Day	20% 11% 4 6% 4 3 3 3 5% 5% 36%	2490
	21st to end	Day	15% 10% 4 8% 4 5% 5% 4 5% 6% 35%	2600
May	1st to 10th	Day	14% 8% 2 6% 4 4 4 3 5% 7% 43%	4238
	11th to 20th	Day	11% 6% 3 6% 4 4 4 3 4 6% 47%	4372
	21st to end	Day	12% 6% 2 5% 4 4 4 4 6% 8% 44%	4908
June	1st to 10th	Day	13% 5% 2 6% 4 4 4 4 6% 9% 44%	2817
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 6% 9% 42%	2850
	21st to end	Day	15% 7% 2 5% 4 4 3 4 6% 8% 43%	2808
July	1st to 10th	Day	18% 8% 2 5% 3 3 4 3 5% 8% 42%	4440
	11th to 20th	Day	9% 4 2 4 3 4 4 3 6% 8% 54%	4440
	21st to end	Day	9% 5% 2 4 4 4 4 3 6% 9% 50%	4814
August	1st to 10th	Day	8% 6% 2 6% 5% 5% 5% 5% 7% 8% 44%	4247
	11th to 20th	Day	14% 5% 2 5% 3 3 4 3 5% 7% 48%	4044
	21st to end	Day	13% 6% 2 6% 4 4 4 3 5% 6% 46%	4377
September	1st to 10th	Day	15% 6% 2 5% 4 4 3 3 6% 7% 45%	2252
	11th to 20th	Day	14% 5% 2 6% 4 3 4 3 5% 7% 46%	2090
	21st to end	Day	18% 7% 3 5% 4 4 5% 3 6% 8% 37%	2090
October	1st to 10th	Day	20% 9% 3 7% 4 4 3 3 5% 8% 34%	2090
	11th to 20th	Day	25% 15% 5% 10% 5% 5% 4 3 3 5% 19%	1790
	21st to end	Day	24% 18% 5% 9% 6% 5% 3 3 5% 5% 16%	1881
November	1st to 10th	Day	18% 20% 4 8% 4 4 3 3 4 6% 24%	1762
	11th to 20th	Day	14% 26% 8% 13% 6% 4 4 3 4 4 15%	1800
	21st to end	Day	18% 25% 10% 14% 5% 4 3 2 3 3 12%	1612
December	1st to 10th	Day	12% 33% 13% 18% 5% 3 3 2 2 2 5%	2280
	11th to 20th	Day	12% 28% 9% 23% 9% 5% 3 2 2 2 5%	2621
	21st to end	Day	20% 24% 9% 15% 7% 4 4 3 4 4 6%	3751
January	1st to 10th	Night	10% 19% 9% 32% 9% 4 3 2 2 2 7%	6348
	11th to 20th	Night	11% 17% 9% 27% 17% 6% 3 2 2 1 5%	6316
	21st to end	Night	12% 20% 10% 21% 9% 8% 4 2 3 3 9%	6996
February	1st to 10th	Night	11% 19% 7% 18% 13% 6% 4 3 3 3 13%	2693
	11th to 20th	Night	12% 16% 7% 16% 10% 6% 4 3 4 4 17%	2358
	21st to end	Night	14% 18% 6% 12% 7% 5% 5% 3 4 5% 21%	1980
March	1st to 10th	Night	16% 10% 4 8% 6% 4 3 3 4 6% 36%	5362
	11th to 20th	Night	11% 14% 5% 10% 5% 4 5% 4 6% 7% 31%	5099
	21st to end	Night	20% 12% 5% 10% 5% 4 4 3 5% 5% 27%	5315
April	1st to 10th	Night	20% 12% 4 9% 4 5% 4 4 4 5% 29%	2000
	11th to 20th	Night	19% 10% 4 8% 5% 4 3 3 5% 4 34%	1858
	21st to end	Night	17% 10% 3 7% 6% 4 4 3 5% 6% 35%	1800
May	1st to 10th	Night	15% 8% 2 8% 4 4 5% 4 5% 5% 40%	2923
	11th to 20th	Night	12% 9% 3 7% 5% 5% 5% 3 6% 6% 40%	2733
	21st to end	Night	18% 7% 3 5% 4 3 3 3 5% 7% 41%	2795
June	1st to 10th	Night	14% 7% 2 7% 6% 4 5% 3 5% 8% 40%	1359
	11th to 20th	Night	11% 6% 2 7% 5% 4 5% 4 6% 8% 41%	1330
	21st to end	Night	12% 7% 2 6% 5% 4 4 3 4 7% 45%	1365
July	1st to 10th	Night	14% 7% 2 7% 4 3 4 3 6% 7% 41%	2530
	11th to 20th	Night	8% 6% 2 6% 4 3 5% 4 6% 7% 51%	2530
	21st to end	Night	8% 6% 2 6% 4 4 4 4 6% 8% 48%	2750
August	1st to 10th	Night	11% 6% 3 7% 4 4 5% 3 5% 8% 42%	2671
	11th to 20th	Night	14% 5% 2 5% 3 4 3 3 5% 7% 48%	2785
	21st to end	Night	11% 6% 2 6% 4 4 4 4 5% 6% 47%	3276
September	1st to 10th	Night	13% 6% 3 6% 5% 4 4 3 5% 6% 47%	1909
	11th to 20th	Night	16% 6% 2 6% 3 3 3 3 5% 7% 44%	2090
	21st to end	Night	19% 6% 3 8% 4 5% 4 3 6% 7% 37%	2090
October	1st to 10th	Night	19% 10% 3 6% 4 4 4 3 5% 5% 37%	2090
	11th to 20th	Night	23% 14% 4 10% 5% 4 4 4 4 5% 23%	2384
	21st to end	Night	27% 16% 3 9% 5% 4 4 3 4 4 20%	2717
November	1st to 10th	Night	19% 18% 4 9% 5% 4 3 2 4 5% 26%	2536
	11th to 20th	Night	16% 25% 6% 12% 6% 4 3 3 3 4 17%	2600
	21st to end	Night	18% 27% 9% 13% 6% 4 3 3 3 3 12%	2783
December	1st to 10th	Night	12% 30% 12% 17% 7% 4 4 2 2 2 7%	4910
	11th to 20th	Night	13% 24% 9% 24% 7% 4 3 2 3 3 9%	5586
	21st to end	Night	22% 21% 10% 15% 7% 4 4 3 3 3 9%	7208

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	66% 27% 3 5% 1	3618
	11th to 20th	Day	68% 27% 2 2 1	3620
	21st to end	Day	58% 30% 7% 4 1	3982
February	1st to 10th	Day	31% 62% 2 4 1	1706
	11th to 20th	Day	27% 61% 4 5% 4	1935
	21st to end	Day	24% 62% 4 6% 3	1650
March	1st to 10th	Day	36% 31% 12% 12% 8% 2	4480
	11th to 20th	Day	42% 30% 10% 12% 5% 1	4860
	21st to end	Day	52% 30% 4 9% 5%	5647
April	1st to 10th	Day	24% 62% 3 9% 3	2400
	11th to 20th	Day	19% 62% 3 9% 6% 1	2490
	21st to end	Day	19% 62% 5% 8% 7%	2600
May	1st to 10th	Day	24% 41% 6% 15% 14% 1	4250
	11th to 20th	Day	22% 39% 6% 22% 10%	4376
	21st to end	Day	23% 41% 7% 14% 14% 1	4908
June	1st to 10th	Day	15% 64% 4 10% 5% 1	2817
	11th to 20th	Day	16% 64% 5% 8% 5% 1	2850
	21st to end	Day	15% 63% 4 12% 5%	2808
July	1st to 10th	Day	31% 36% 10% 16% 6% 1	4371
	11th to 20th	Day	16% 37% 11% 27% 7% 1	4365
	21st to end	Day	19% 37% 8% 22% 13%	4662
August	1st to 10th	Day	22% 40% 8% 21% 9%	4232
	11th to 20th	Day	26% 38% 7% 22% 7%	4083
	21st to end	Day	27% 39% 9% 20% 5%	4376
September	1st to 10th	Day	18% 60% 6% 11% 5%	2252
	11th to 20th	Day	13% 60% 5% 14% 7% 1	2090
	21st to end	Day	16% 60% 6% 12% 5%	2090
October	1st to 10th	Day	20% 38% 5% 23% 13%	3480
	11th to 20th	Day	33% 38% 6% 14% 8%	2954
	21st to end	Day	41% 38% 8% 11% 2	3081
November	1st to 10th	Day	32% 55% 3 8% 2	1762
	11th to 20th	Day	33% 57% 5% 4 2	1800
	21st to end	Day	37% 57% 3 3 1	1612
December	1st to 10th	Day	58% 37% 3 2	2280
	11th to 20th	Day	62% 33% 3 2 1	2621
	21st to end	Day	59% 28% 5% 5% 2	3751
January	1st to 10th	Night	62% 28% 5% 3 2	6348
	11th to 20th	Night	66% 28% 3 2 1	6360
	21st to end	Night	59% 30% 5% 5% 1	6996
February	1st to 10th	Night	30% 62% 3 3 2 1	2693
	11th to 20th	Night	26% 60% 4 8% 2	2359
	21st to end	Night	24% 62% 4 6% 4	1980
March	1st to 10th	Night	37% 30% 13% 13% 7%	5373
	11th to 20th	Night	38% 30% 14% 14% 4	5100
	21st to end	Night	44% 30% 7% 11% 7%	5315
April	1st to 10th	Night	24% 62% 2 8% 4 1	2000
	11th to 20th	Night	22% 62% 2 8% 4 2	1858
	21st to end	Night	21% 61% 3 8% 6% 1	1800
May	1st to 10th	Night	26% 40% 6% 14% 12% 2	2930
	11th to 20th	Night	25% 40% 5% 20% 9%	2734
	21st to end	Night	28% 39% 9% 12% 9% 3	2796
June	1st to 10th	Night	16% 65% 4 9% 6% 1	1359
	11th to 20th	Night	15% 65% 4 9% 5% 1	1330
	21st to end	Night	15% 63% 3 11% 7% 1	1365
July	1st to 10th	Night	30% 36% 10% 13% 8% 2	2490
	11th to 20th	Night	20% 39% 10% 20% 11% 1	2482
	21st to end	Night	21% 38% 9% 16% 15%	2662
August	1st to 10th	Night	27% 39% 9% 15% 9%	2662
	11th to 20th	Night	25% 38% 10% 20% 8%	2812
	21st to end	Night	22% 39% 9% 19% 10%	3276
September	1st to 10th	Night	15% 60% 7% 11% 7%	1909
	11th to 20th	Night	15% 60% 5% 12% 8%	2090
	21st to end	Night	19% 59% 7% 10% 5%	2090
October	1st to 10th	Night	27% 39% 7% 19% 9%	3480
	11th to 20th	Night	30% 38% 7% 15% 10%	3959
	21st to end	Night	37% 38% 10% 12% 2	4467
November	1st to 10th	Night	32% 56% 4 6% 2	2536
	11th to 20th	Night	31% 56% 5% 5% 3	2600
	21st to end	Night	37% 57% 3 2 1	2783
December	1st to 10th	Night	54% 38% 4 4	4910
	11th to 20th	Night	57% 33% 5% 4 1	5585
	21st to end	Night	58% 30% 6% 4 2	7208

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	20% 17% 39% 18% 5% 1	300
	11th to 20th	Day	22% 19% 38% 16% 4 1	300
	21st to end	Day	24% 17% 33% 21% 5%	330
February	1st to 10th	Day	21% 27% 34% 11% 5% 1	300
	11th to 20th	Day	18% 26% 36% 17% 2 1	300
	21st to end	Day	24% 24% 39% 11% 2	249
March	1st to 10th	Day	20% 24% 35% 18% 3	300
	11th to 20th	Day	21% 17% 33% 21% 8%	445
	21st to end	Day	28% 15% 27% 22% 7% 1	550
April	1st to 10th	Day	26% 14% 32% 20% 7% 2	500
	11th to 20th	Day	29% 16% 26% 17% 10% 2	492
	21st to end	Day	20% 15% 29% 24% 10% 2	500
May	1st to 10th	Day	21% 15% 29% 21% 11% 2	503
	11th to 20th	Day	16% 9% 35% 28% 8% 4	623
	21st to end	Day	15% 11% 26% 30% 14% 3	760
June	1st to 10th	Day	15% 9% 30% 30% 13% 2	680
	11th to 20th	Day	16% 8% 28% 32% 13% 3	680
	21st to end	Day	18% 7% 26% 31% 15% 3	680
July	1st to 10th	Day	10% 7% 26% 33% 18% 6%	671
	11th to 20th	Day	11% 8% 25% 34% 16% 6%	668
	21st to end	Day	11% 6% 25% 35% 19% 5%	739
August	1st to 10th	Day	10% 5% 23% 32% 22% 8%	578
	11th to 20th	Day	14% 5% 18% 34% 19% 10%	479
	21st to end	Day	18% 8% 19% 30% 19% 5%	539
September	1st to 10th	Day	16% 10% 24% 23% 20% 6%	490
	11th to 20th	Day	12% 7% 21% 30% 21% 8%	490
	21st to end	Day	17% 11% 20% 28% 18% 5%	490
October	1st to 10th	Day	24% 15% 26% 20% 14% 2	490
	11th to 20th	Day	30% 16% 28% 22% 3 1	376
	21st to end	Day	31% 18% 30% 16% 4 1	330
November	1st to 10th	Day	30% 16% 31% 17% 6%	300
	11th to 20th	Day	24% 23% 32% 18% 3	300
	21st to end	Day	27% 27% 28% 14% 3	233
December	1st to 10th	Day	32% 19% 30% 14% 6% 1	200
	11th to 20th	Day	24% 27% 34% 15% 2 1	200
	21st to end	Day	33% 26% 30% 9% 2 1	280
January	1st to 10th	Night	21% 17% 34% 21% 6% 1	1000
	11th to 20th	Night	22% 18% 31% 22% 6%	1000
	21st to end	Night	21% 13% 34% 26% 6%	1100
February	1st to 10th	Night	19% 17% 33% 24% 5% 1	893
	11th to 20th	Night	19% 18% 32% 25% 5%	783
	21st to end	Night	23% 15% 32% 24% 4	660
March	1st to 10th	Night	18% 11% 35% 26% 9% 1	800
	11th to 20th	Night	19% 12% 35% 28% 6%	800
	21st to end	Night	21% 9% 29% 32% 8% 1	818
April	1st to 10th	Night	25% 11% 31% 28% 5% 1	600
	11th to 20th	Night	24% 10% 28% 27% 10% 1	593
	21st to end	Night	21% 11% 27% 32% 9% 1	600
May	1st to 10th	Night	16% 7% 28% 38% 11% 1	600
	11th to 20th	Night	18% 8% 26% 36% 11% 1	591
	21st to end	Night	16% 5% 23% 36% 19% 1	634
June	1st to 10th	Night	16% 5% 26% 38% 15%	409
	11th to 20th	Night	11% 5% 24% 43% 17% 1	380
	21st to end	Night	14% 6% 23% 38% 18% 1	415
July	1st to 10th	Night	13% 3 18% 45% 19% 3	555
	11th to 20th	Night	11% 4 19% 38% 26% 3	552
	21st to end	Night	10% 2 21% 38% 27% 2	624
August	1st to 10th	Night	11% 3 18% 41% 26% 1	567
	11th to 20th	Night	11% 5% 15% 36% 30% 3	564
	21st to end	Night	17% 6% 17% 36% 22% 1	627
September	1st to 10th	Night	14% 4 23% 33% 22% 3	579
	11th to 20th	Night	18% 4 20% 32% 22% 3	760
	21st to end	Night	22% 7% 18% 33% 16% 3	760
October	1st to 10th	Night	23% 11% 23% 29% 13% 1	760
	11th to 20th	Night	31% 12% 26% 24% 7% 1	760
	21st to end	Night	34% 14% 25% 21% 5% 1	836
November	1st to 10th	Night	28% 15% 29% 22% 6% 1	780
	11th to 20th	Night	27% 18% 31% 20% 4	800
	21st to end	Night	31% 18% 30% 17% 3	853
December	1st to 10th	Night	26% 21% 32% 18% 3	1000
	11th to 20th	Night	23% 21% 35% 16% 4 1	1000
	21st to end	Night	30% 15% 33% 18% 4	1100

Page generated at 2025-05-23 09:21:03. Version ac07

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