Star Hoppers Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Star Hoppers 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	14% 11% 4 9% 5% 5% 5% 4 5% 7% 32%	108431
	Night	14% 12% 4 9% 5% 4 4 3 5% 6% 33%	110985
Transparency	Day	49% 7% 12% 20% 11% 1	112031
	Night	50% 6% 12% 20% 11% 1	115513
Seeing	Day	18% 13% 29% 22% 12% 5%	15896
	Night	19% 11% 30% 28% 10% 1	25883

By Month

Percentage Cloud Cover SE (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% 19% 7% 19% 5% 4 4 2 3 4 22%	3617
	11th to 20th	Day	13% 18% 7% 19% 10% 9% 5% 3 4 4 9%	3620
	21st to end	Day	21% 19% 7% 13% 6% 4 5% 2 3 4 15%	4310
February	1st to 10th	Day	13% 15% 6% 13% 9% 5% 5% 4 3 6% 21%	1800
	11th to 20th	Day	14% 15% 6% 13% 9% 6% 4 3 4 4 23%	1896
	21st to end	Day	12% 18% 6% 13% 7% 4 4 3 4 5% 25%	1650
March	1st to 10th	Day	16% 15% 5% 9% 5% 4 4 3 4 6% 28%	3278
	11th to 20th	Day	12% 12% 6% 10% 6% 5% 4 3 5% 7% 30%	3590
	21st to end	Day	18% 14% 4 9% 6% 4 4 3 4 5% 29%	3881
April	1st to 10th	Day	16% 13% 4 9% 6% 5% 4 3 5% 5% 30%	2228
	11th to 20th	Day	17% 12% 3 7% 4 4 4 4 6% 6% 35%	2402
	21st to end	Day	17% 8% 3 9% 5% 4 4 3 5% 7% 34%	2470
May	1st to 10th	Day	18% 9% 3 7% 4 4 5% 4 5% 6% 34%	4082
	11th to 20th	Day	16% 8% 3 6% 5% 4 5% 4 6% 9% 36%	4081
	21st to end	Day	11% 6% 3 6% 4 4 4 3 5% 9% 45%	4530
June	1st to 10th	Day	10% 6% 2 7% 5% 5% 5% 4 7% 8% 40%	2707
	11th to 20th	Day	10% 7% 2 7% 5% 4 5% 4 5% 9% 41%	2850
	21st to end	Day	12% 6% 2 6% 6% 6% 5% 5% 8% 10% 36%	2672
July	1st to 10th	Day	11% 6% 3 7% 5% 6% 5% 5% 8% 9% 36%	4440
	11th to 20th	Day	8% 5% 2 5% 4 4 5% 5% 7% 10% 47%	4440
	21st to end	Day	8% 5% 2 6% 6% 6% 6% 5% 7% 9% 40%	4597
August	1st to 10th	Day	12% 5% 2 6% 5% 6% 5% 5% 6% 8% 40%	4104
	11th to 20th	Day	11% 7% 2 6% 4 5% 5% 5% 7% 9% 39%	4044
	21st to end	Day	8% 6% 3 8% 5% 5% 6% 4 7% 9% 40%	4472
September	1st to 10th	Day	11% 7% 2 8% 5% 5% 5% 4 6% 8% 39%	2160
	11th to 20th	Day	10% 6% 2 5% 3 3 5% 3 7% 8% 47%	2090
	21st to end	Day	15% 7% 2 7% 4 4 6% 5% 6% 8% 35%	2090
October	1st to 10th	Day	13% 7% 3 7% 4 4 5% 3 5% 7% 41%	2045
	11th to 20th	Day	18% 11% 3 8% 5% 5% 5% 4 4 7% 32%	1900
	21st to end	Day	20% 13% 3 7% 5% 4 4 3 6% 7% 28%	1916
November	1st to 10th	Day	12% 11% 4 8% 5% 4 4 4 6% 7% 36%	1762
	11th to 20th	Day	14% 14% 5% 9% 5% 6% 4 4 5% 6% 28%	1800
	21st to end	Day	18% 16% 6% 9% 5% 5% 4 3 4 6% 25%	1700
December	1st to 10th	Day	14% 15% 9% 13% 7% 5% 4 3 5% 6% 20%	2600
	11th to 20th	Day	17% 21% 8% 10% 6% 4 4 4 4 4 18%	2689
	21st to end	Day	23% 23% 6% 13% 5% 3 3 3 3 5% 13%	3918
January	1st to 10th	Night	13% 14% 6% 14% 6% 5% 4 3 4 5% 24%	6348
	11th to 20th	Night	11% 16% 8% 16% 9% 7% 5% 4 4 4 13%	6360
	21st to end	Night	17% 17% 9% 10% 6% 5% 5% 3 4 5% 20%	6651
February	1st to 10th	Night	16% 16% 5% 11% 7% 6% 5% 4 4 4 23%	2600
	11th to 20th	Night	13% 15% 6% 11% 8% 5% 4 3 4 5% 26%	2388
	21st to end	Night	16% 13% 4 10% 5% 5% 4 3 5% 6% 27%	1980
March	1st to 10th	Night	15% 13% 4 9% 4 4 3 3 5% 6% 34%	3795
	11th to 20th	Night	9% 10% 4 7% 5% 4 5% 4 5% 7% 41%	3590
	21st to end	Night	16% 10% 3 9% 5% 4 4 3 5% 5% 35%	3890
April	1st to 10th	Night	16% 13% 3 6% 5% 4 4 3 5% 6% 35%	1969
	11th to 20th	Night	18% 10% 3 6% 5% 4 3 3 6% 7% 36%	1725
	21st to end	Night	17% 8% 2 6% 4 4 4 3 6% 6% 38%	1710
May	1st to 10th	Night	15% 9% 3 6% 5% 4 3 4 6% 8% 37%	2813
	11th to 20th	Night	15% 7% 3 7% 4 3 3 3 5% 7% 43%	2812
	21st to end	Night	10% 6% 2 5% 5% 4 4 4 6% 7% 48%	3022
June	1st to 10th	Night	11% 6% 2 5% 4 3 4 3 6% 10% 46%	1463
	11th to 20th	Night	9% 6% 2 6% 4 4 4 5% 7% 8% 45%	1330
	21st to end	Night	10% 6% 2 6% 4 4 3 3 5% 9% 47%	1494
July	1st to 10th	Night	8% 5% 1 5% 4 4 4 5% 7% 10% 46%	2530
	11th to 20th	Night	10% 4 2 4 3 3 4 4 6% 7% 54%	2530
	21st to end	Night	5% 6% 2 5% 5% 5% 5% 5% 6% 10% 47%	2958
August	1st to 10th	Night	11% 5% 2 5% 4 4 4 3 6% 8% 47%	2825
	11th to 20th	Night	10% 7% 2 5% 3 4 5% 3 5% 8% 48%	2785
	21st to end	Night	7% 6% 3 7% 5% 4 4 3 5% 8% 49%	3180
September	1st to 10th	Night	10% 7% 2 6% 4 4 4 3 5% 7% 48%	2000
	11th to 20th	Night	10% 5% 2 4 4 3 4 3 5% 7% 54%	2090
	21st to end	Night	15% 8% 2 7% 4 3 5% 3 5% 7% 42%	2090
October	1st to 10th	Night	14% 7% 3 7% 4 4 3 3 4 6% 45%	2134
	11th to 20th	Night	19% 11% 3 8% 4 4 5% 3 5% 5% 34%	2280
	21st to end	Night	20% 11% 3 7% 5% 5% 5% 4 4 5% 31%	2679
November	1st to 10th	Night	13% 10% 3 6% 5% 4 4 3 5% 6% 41%	2536
	11th to 20th	Night	15% 12% 4 9% 5% 5% 5% 4 5% 6% 29%	2600
	21st to end	Night	19% 16% 4 8% 5% 4 4 3 4 6% 26%	2695
December	1st to 10th	Night	12% 16% 7% 15% 6% 5% 5% 3 5% 6% 21%	4580
	11th to 20th	Night	14% 22% 7% 13% 7% 4 3 3 4 5% 18%	5511
	21st to end	Night	22% 24% 8% 11% 5% 3 3 3 3 4 15%	7042

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	65% 5% 11% 13% 5% 1	3618
	11th to 20th	Day	77% 6% 9% 5% 3	3620
	21st to end	Day	74% 5% 10% 8% 4	4310
February	1st to 10th	Day	63% 6% 9% 14% 7%	1800
	11th to 20th	Day	64% 4 9% 14% 8% 1	1906
	21st to end	Day	61% 5% 11% 14% 6% 2	1650
March	1st to 10th	Day	57% 6% 12% 19% 6% 1	3278
	11th to 20th	Day	52% 6% 14% 19% 8% 1	3590
	21st to end	Day	57% 6% 12% 14% 10% 2	3881
April	1st to 10th	Day	54% 5% 11% 19% 11%	2228
	11th to 20th	Day	48% 6% 12% 20% 12% 2	2402
	21st to end	Day	49% 6% 13% 17% 14% 1	2470
May	1st to 10th	Day	46% 7% 12% 21% 11% 2	4120
	11th to 20th	Day	42% 9% 14% 24% 9% 1	4085
	21st to end	Day	36% 7% 12% 18% 24% 4	4543
June	1st to 10th	Day	38% 7% 13% 26% 14% 2	2707
	11th to 20th	Day	39% 8% 12% 23% 16% 2	2850
	21st to end	Day	39% 9% 14% 22% 15% 1	2672
July	1st to 10th	Day	41% 9% 14% 19% 16% 2	4371
	11th to 20th	Day	29% 7% 14% 33% 15% 1	4365
	21st to end	Day	36% 9% 14% 18% 21% 2	4451
August	1st to 10th	Day	38% 9% 13% 23% 16% 1	4091
	11th to 20th	Day	37% 9% 11% 30% 11% 1	4083
	21st to end	Day	38% 8% 15% 26% 12% 1	4471
September	1st to 10th	Day	40% 8% 14% 24% 12% 2	2160
	11th to 20th	Day	32% 8% 14% 31% 14% 1	2090
	21st to end	Day	44% 7% 13% 23% 12%	2090
October	1st to 10th	Day	32% 5% 11% 31% 20% 1	3396
	11th to 20th	Day	41% 5% 11% 25% 17%	3140
	21st to end	Day	46% 5% 13% 23% 11% 1	3128
November	1st to 10th	Day	46% 6% 14% 22% 11% 1	1762
	11th to 20th	Day	56% 5% 13% 17% 9% 1	1800
	21st to end	Day	60% 5% 12% 16% 6% 1	1700
December	1st to 10th	Day	65% 5% 16% 10% 3	2600
	11th to 20th	Day	70% 4 9% 12% 5%	2685
	21st to end	Day	76% 4 8% 8% 4	3918
January	1st to 10th	Night	61% 6% 10% 16% 5% 2	6348
	11th to 20th	Night	70% 7% 10% 8% 5%	6360
	21st to end	Night	67% 5% 11% 12% 5%	6651
February	1st to 10th	Night	64% 6% 10% 12% 7% 1	2600
	11th to 20th	Night	60% 5% 10% 17% 8%	2389
	21st to end	Night	57% 5% 13% 16% 8% 1	1980
March	1st to 10th	Night	50% 5% 13% 24% 7% 1	3795
	11th to 20th	Night	39% 6% 16% 21% 17% 1	3590
	21st to end	Night	49% 6% 12% 21% 11% 1	3890
April	1st to 10th	Night	49% 5% 10% 21% 13% 2	1969
	11th to 20th	Night	46% 6% 11% 17% 18% 2	1725
	21st to end	Night	45% 7% 11% 19% 16% 3	1710
May	1st to 10th	Night	44% 7% 12% 21% 13% 4	2840
	11th to 20th	Night	41% 6% 11% 28% 12% 2	2813
	21st to end	Night	34% 8% 12% 21% 20% 6%	3030
June	1st to 10th	Night	34% 6% 11% 29% 18% 2	1463
	11th to 20th	Night	34% 8% 14% 24% 19% 2	1330
	21st to end	Night	34% 7% 13% 26% 19% 1	1494
July	1st to 10th	Night	31% 6% 14% 27% 16% 6%	2490
	11th to 20th	Night	28% 7% 12% 31% 21% 1	2482
	21st to end	Night	30% 11% 17% 19% 22% 2	2864
August	1st to 10th	Night	34% 7% 14% 27% 16% 1	2814
	11th to 20th	Night	33% 7% 11% 36% 11% 2	2812
	21st to end	Night	34% 7% 12% 32% 14% 1	3180
September	1st to 10th	Night	34% 7% 13% 27% 17% 2	2000
	11th to 20th	Night	30% 6% 11% 29% 21% 2	2090
	21st to end	Night	41% 6% 12% 27% 14% 1	2090
October	1st to 10th	Night	26% 4 10% 33% 26% 1	3563
	11th to 20th	Night	44% 5% 11% 22% 17%	3779
	21st to end	Night	42% 5% 12% 29% 12% 1	4405
November	1st to 10th	Night	43% 6% 11% 26% 14% 1	2536
	11th to 20th	Night	54% 7% 13% 18% 9% 1	2600
	21st to end	Night	58% 5% 13% 19% 6% 1	2695
December	1st to 10th	Night	64% 6% 13% 13% 3	4580
	11th to 20th	Night	67% 6% 9% 12% 5%	5514
	21st to end	Night	74% 5% 9% 7% 6%	7042

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	22% 19% 39% 14% 6%	300
	11th to 20th	Day	22% 19% 44% 12% 2 1	300
	21st to end	Day	31% 19% 30% 16% 4 1	330
February	1st to 10th	Day	27% 22% 36% 13% 2 1	300
	11th to 20th	Day	26% 22% 37% 13% 1	300
	21st to end	Day	29% 27% 34% 9% 2	249
March	1st to 10th	Day	25% 23% 37% 11% 4	332
	11th to 20th	Day	24% 14% 34% 22% 5% 1	500
	21st to end	Day	29% 14% 34% 18% 5% 1	530
April	1st to 10th	Day	20% 19% 33% 21% 7% 1	460
	11th to 20th	Day	27% 18% 32% 14% 5% 5%	452
	21st to end	Day	24% 14% 32% 19% 10% 2	460
May	1st to 10th	Day	24% 16% 27% 21% 11% 2	463
	11th to 20th	Day	18% 11% 30% 23% 12% 6%	487
	21st to end	Day	16% 8% 22% 29% 17% 7%	557
June	1st to 10th	Day	12% 10% 30% 29% 16% 4	680
	11th to 20th	Day	13% 10% 31% 26% 17% 4	680
	21st to end	Day	12% 9% 31% 29% 15% 5%	680
July	1st to 10th	Day	10% 6% 23% 30% 21% 10%	671
	11th to 20th	Day	11% 7% 28% 28% 19% 7%	668
	21st to end	Day	9% 5% 25% 31% 21% 9%	611
August	1st to 10th	Day	9% 6% 22% 26% 22% 14%	486
	11th to 20th	Day	14% 4 20% 28% 22% 12%	479
	21st to end	Day	11% 5% 23% 28% 21% 11%	539
September	1st to 10th	Day	13% 8% 24% 24% 20% 10%	490
	11th to 20th	Day	11% 4 21% 23% 28% 13%	490
	21st to end	Day	18% 14% 21% 23% 18% 7%	490
October	1st to 10th	Day	18% 11% 28% 20% 17% 6%	490
	11th to 20th	Day	21% 18% 27% 27% 7% 1	490
	21st to end	Day	30% 17% 35% 15% 3	365
November	1st to 10th	Day	19% 22% 35% 17% 6% 2	300
	11th to 20th	Day	23% 23% 32% 15% 5% 1	300
	21st to end	Day	28% 22% 36% 12% 3	250
December	1st to 10th	Day	26% 22% 33% 14% 7%	200
	11th to 20th	Day	25% 27% 39% 8% 2 1	200
	21st to end	Day	27% 27% 32% 12% 1	317
January	1st to 10th	Night	22% 17% 37% 19% 5% 1	1000
	11th to 20th	Night	25% 15% 35% 21% 4 1	1000
	21st to end	Night	21% 13% 35% 25% 5%	950
February	1st to 10th	Night	25% 14% 36% 23% 2	800
	11th to 20th	Night	23% 16% 34% 23% 4	783
	21st to end	Night	26% 17% 35% 18% 3	660
March	1st to 10th	Night	22% 15% 35% 23% 6%	800
	11th to 20th	Night	18% 16% 36% 24% 5% 1	800
	21st to end	Night	23% 13% 30% 27% 7% 1	863
April	1st to 10th	Night	20% 16% 37% 23% 4 1	639
	11th to 20th	Night	21% 13% 35% 22% 6% 2	563
	21st to end	Night	21% 10% 33% 29% 7%	570
May	1st to 10th	Night	19% 8% 32% 33% 7% 1	570
	11th to 20th	Night	21% 4 31% 33% 11% 1	561
	21st to end	Night	12% 4 26% 39% 18% 2	617
June	1st to 10th	Night	12% 6% 25% 44% 13%	513
	11th to 20th	Night	11% 5% 30% 42% 12%	380
	21st to end	Night	12% 5% 23% 42% 17% 1	544
July	1st to 10th	Night	10% 2 20% 39% 27% 3	555
	11th to 20th	Night	11% 2 22% 42% 20% 3	552
	21st to end	Night	5% 3 20% 49% 21% 2	624
August	1st to 10th	Night	9% 2 17% 43% 27% 2	567
	11th to 20th	Night	9% 2 21% 35% 28% 4	564
	21st to end	Night	10% 4 19% 36% 28% 3	627
September	1st to 10th	Night	12% 4 23% 34% 24% 4	670
	11th to 20th	Night	12% 4 18% 35% 26% 4	760
	21st to end	Night	17% 6% 23% 31% 19% 4	760
October	1st to 10th	Night	19% 7% 26% 29% 17% 1	760
	11th to 20th	Night	26% 13% 26% 26% 8% 1	760
	21st to end	Night	26% 12% 34% 23% 4	836
November	1st to 10th	Night	21% 13% 30% 26% 10% 1	780
	11th to 20th	Night	23% 17% 33% 20% 7% 1	800
	21st to end	Night	27% 15% 35% 19% 5%	800
December	1st to 10th	Night	23% 18% 35% 20% 5%	800
	11th to 20th	Night	23% 16% 39% 20% 2	955
	21st to end	Night	30% 14% 37% 17% 1	1100

Page generated at 2025-03-24 09:04:30. Version ac07

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