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 2026-07-31.

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 9% 5% 5% 5% 4 5% 7% 33%	137197
	Night	13% 12% 4 9% 5% 4 4 3 5% 6% 33%	135926
Transparency	Day	48% 6% 12% 20% 12% 1	140753
	Night	50% 6% 11% 20% 12% 1	140431
Seeing	Day	19% 14% 29% 22% 12% 5%	17808
	Night	19% 11% 30% 28% 10% 1	27586

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	12% 19% 8% 17% 6% 4 4 2 3 4 20%	4691
	11th to 20th	Day	12% 18% 8% 20% 10% 10% 4 2 3 3 10%	4710
	21st to end	Day	17% 17% 6% 12% 11% 5% 6% 3 3 4 15%	5585
February	1st to 10th	Day	13% 15% 6% 13% 9% 5% 5% 4 3 6% 22%	1890
	11th to 20th	Day	13% 15% 5% 13% 9% 6% 4 3 4 5% 23%	1994
	21st to end	Day	12% 18% 6% 13% 7% 4 4 3 4 5% 24%	1730
March	1st to 10th	Day	14% 13% 5% 10% 6% 4 4 3 4 6% 31%	4666
	11th to 20th	Day	12% 13% 5% 9% 5% 4 4 3 5% 8% 32%	5090
	21st to end	Day	18% 16% 5% 9% 5% 4 4 2 4 5% 28%	5586
April	1st to 10th	Day	17% 14% 4 9% 6% 4 4 3 5% 5% 30%	2462
	11th to 20th	Day	16% 12% 3 7% 4 4 4 4 5% 6% 35%	2658
	21st to end	Day	16% 9% 3 8% 5% 4 5% 4 5% 7% 34%	2730
May	1st to 10th	Day	16% 9% 3 8% 5% 5% 5% 4 6% 6% 34%	7616
	11th to 20th	Day	13% 9% 3 7% 5% 4 5% 4 6% 8% 35%	7626
	21st to end	Day	14% 7% 3 6% 4 4 4 3 5% 7% 44%	8487
June	1st to 10th	Day	10% 6% 2 7% 5% 4 5% 4 7% 9% 41%	2992
	11th to 20th	Day	10% 7% 2 7% 5% 4 5% 5% 6% 9% 39%	3150
	21st to end	Day	11% 6% 2 6% 6% 6% 5% 5% 8% 10% 37%	2953
July	1st to 10th	Day	9% 6% 2 6% 5% 5% 5% 5% 8% 10% 38%	6500
	11th to 20th	Day	8% 5% 2 5% 4 4 5% 4 6% 9% 46%	6500
	21st to end	Day	8% 5% 2 5% 5% 5% 5% 4 6% 9% 45%	6745
August	1st to 10th	Day	12% 5% 2 6% 5% 6% 5% 5% 6% 8% 40%	4234
	11th to 20th	Day	12% 6% 2 6% 4 5% 5% 5% 7% 9% 38%	4174
	21st to end	Day	8% 6% 3 8% 5% 5% 6% 4 7% 9% 40%	4613
September	1st to 10th	Day	10% 6% 2 7% 5% 5% 5% 4 6% 8% 40%	2273
	11th to 20th	Day	10% 6% 2 5% 3 3 5% 3 7% 8% 48%	2200
	21st to end	Day	15% 8% 2 7% 4 4 5% 5% 6% 8% 35%	2200
October	1st to 10th	Day	13% 7% 3 7% 4 4 5% 3 5% 7% 43%	2152
	11th to 20th	Day	18% 10% 3 8% 5% 5% 5% 4 4 7% 33%	2000
	21st to end	Day	19% 12% 3 7% 5% 5% 4 3 6% 7% 29%	2017
November	1st to 10th	Day	12% 11% 4 8% 5% 4 4 4 6% 7% 36%	1852
	11th to 20th	Day	14% 14% 5% 9% 5% 6% 4 3 5% 6% 28%	1890
	21st to end	Day	18% 16% 6% 9% 5% 5% 4 3 4 6% 25%	1785
December	1st to 10th	Day	13% 15% 9% 13% 7% 5% 4 3 5% 6% 20%	2680
	11th to 20th	Day	16% 21% 8% 10% 6% 4 4 4 4 4 18%	2761
	21st to end	Day	23% 23% 6% 13% 5% 3 3 3 3 5% 13%	4005
January	1st to 10th	Night	13% 15% 7% 15% 6% 5% 4 3 4 5% 23%	8232
	11th to 20th	Night	9% 18% 9% 17% 9% 9% 5% 3 4 4 13%	8280
	21st to end	Night	14% 16% 8% 12% 6% 6% 6% 3 5% 5% 20%	8604
February	1st to 10th	Night	15% 16% 5% 11% 7% 6% 5% 4 4 4 23%	2730
	11th to 20th	Night	13% 15% 6% 11% 8% 5% 4 3 4 5% 26%	2510
	21st to end	Night	16% 14% 5% 10% 5% 5% 4 3 5% 6% 27%	2076
March	1st to 10th	Night	14% 12% 4 9% 4 4 4 3 5% 7% 34%	5407
	11th to 20th	Night	10% 10% 4 7% 4 4 4 4 6% 8% 40%	5090
	21st to end	Night	16% 11% 3 9% 5% 4 4 3 4 5% 36%	5588
April	1st to 10th	Night	16% 13% 3 6% 5% 5% 4 3 5% 6% 34%	2176
	11th to 20th	Night	17% 9% 3 7% 5% 4 4 4 6% 7% 35%	1909
	21st to end	Night	17% 8% 2 7% 4 4 4 3 6% 6% 39%	1890
May	1st to 10th	Night	17% 10% 3 7% 5% 4 4 3 5% 7% 34%	5237
	11th to 20th	Night	15% 9% 3 7% 4 4 3 3 5% 7% 41%	5234
	21st to end	Night	14% 7% 2 6% 5% 3 4 4 5% 7% 44%	5652
June	1st to 10th	Night	11% 6% 2 5% 4 3 4 3 5% 10% 47%	1617
	11th to 20th	Night	10% 6% 3 6% 4 4 4 5% 7% 8% 44%	1470
	21st to end	Night	10% 6% 2 6% 4 4 3 3 5% 9% 48%	1652
July	1st to 10th	Night	8% 5% 2 5% 4 4 4 4 7% 11% 46%	3698
	11th to 20th	Night	9% 5% 2 5% 4 4 4 4 6% 8% 50%	3697
	21st to end	Night	9% 6% 2 5% 4 4 4 4 5% 8% 49%	4332
August	1st to 10th	Night	11% 5% 2 5% 4 4 4 3 6% 8% 48%	2915
	11th to 20th	Night	10% 7% 2 5% 3 4 4 3 5% 8% 48%	2875
	21st to end	Night	7% 6% 3 7% 5% 4 4 3 5% 8% 49%	3281
September	1st to 10th	Night	10% 6% 2 6% 4 4 4 3 5% 7% 49%	2105
	11th to 20th	Night	9% 4 2 4 4 3 4 3 5% 7% 55%	2200
	21st to end	Night	14% 8% 3 7% 4 3 5% 3 5% 7% 42%	2200
October	1st to 10th	Night	14% 6% 3 7% 4 3 3 4 4 6% 47%	2247
	11th to 20th	Night	19% 11% 3 8% 4 3 4 3 4 5% 35%	2400
	21st to end	Night	20% 11% 3 7% 5% 4 5% 3 4 5% 33%	2820
November	1st to 10th	Night	13% 10% 3 6% 5% 4 4 4 5% 6% 40%	2666
	11th to 20th	Night	15% 12% 4 9% 5% 5% 5% 4 5% 6% 30%	2730
	21st to end	Night	19% 17% 4 8% 5% 4 4 3 4 6% 26%	2830
December	1st to 10th	Night	12% 16% 7% 15% 6% 5% 5% 3 4 6% 21%	4720
	11th to 20th	Night	14% 21% 7% 13% 7% 4 3 3 4 5% 18%	5659
	21st to end	Night	22% 23% 8% 11% 5% 3 3 2 3 4 15%	7197

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	67% 5% 10% 13% 4 1	4692
	11th to 20th	Day	78% 5% 7% 5% 4	4710
	21st to end	Day	73% 4 9% 9% 5%	5585
February	1st to 10th	Day	63% 6% 9% 15% 7%	1890
	11th to 20th	Day	63% 4 9% 14% 8% 1	2004
	21st to end	Day	61% 5% 11% 15% 6% 2	1730
March	1st to 10th	Day	53% 5% 13% 18% 8% 2	4666
	11th to 20th	Day	49% 5% 16% 20% 8% 1	5090
	21st to end	Day	58% 6% 10% 15% 10% 1	5586
April	1st to 10th	Day	55% 5% 11% 18% 10% 1	2462
	11th to 20th	Day	49% 6% 11% 20% 12% 2	2658
	21st to end	Day	48% 7% 13% 19% 13% 1	2730
May	1st to 10th	Day	47% 7% 11% 21% 11% 3	7651
	11th to 20th	Day	45% 7% 12% 21% 14% 1	7630
	21st to end	Day	38% 5% 9% 20% 24% 3	8501
June	1st to 10th	Day	37% 7% 13% 26% 15% 2	2992
	11th to 20th	Day	39% 8% 13% 23% 16% 2	3150
	21st to end	Day	39% 9% 14% 23% 15% 1	2953
July	1st to 10th	Day	37% 9% 14% 24% 15% 1	6431
	11th to 20th	Day	31% 7% 13% 29% 18% 1	6425
	21st to end	Day	33% 8% 14% 23% 21% 1	6557
August	1st to 10th	Day	37% 9% 13% 23% 16% 1	4221
	11th to 20th	Day	37% 9% 12% 30% 11% 1	4213
	21st to end	Day	37% 8% 15% 27% 12% 1	4612
September	1st to 10th	Day	39% 8% 14% 26% 12% 2	2273
	11th to 20th	Day	31% 8% 14% 31% 15% 1	2200
	21st to end	Day	44% 7% 13% 23% 13%	2200
October	1st to 10th	Day	32% 5% 10% 32% 20% 1	3503
	11th to 20th	Day	41% 5% 11% 25% 17%	3240
	21st to end	Day	46% 5% 14% 23% 11% 1	3229
November	1st to 10th	Day	46% 6% 14% 23% 11% 1	1852
	11th to 20th	Day	55% 5% 13% 18% 8% 1	1890
	21st to end	Day	60% 5% 12% 16% 6% 1	1785
December	1st to 10th	Day	65% 5% 16% 10% 3	2680
	11th to 20th	Day	70% 4 10% 12% 5%	2757
	21st to end	Day	76% 4 8% 8% 4	4005
January	1st to 10th	Night	62% 6% 10% 15% 6% 1	8233
	11th to 20th	Night	71% 6% 9% 8% 4	8280
	21st to end	Night	65% 5% 10% 15% 5%	8604
February	1st to 10th	Night	63% 6% 10% 14% 6% 1	2730
	11th to 20th	Night	59% 5% 9% 18% 8% 1	2511
	21st to end	Night	57% 5% 12% 16% 8% 1	2076
March	1st to 10th	Night	49% 5% 14% 22% 9% 1	5407
	11th to 20th	Night	40% 6% 16% 24% 14% 1	5090
	21st to end	Night	49% 6% 12% 19% 13% 2	5588
April	1st to 10th	Night	50% 6% 9% 20% 13% 2	2176
	11th to 20th	Night	46% 6% 11% 17% 17% 2	1909
	21st to end	Night	45% 7% 11% 20% 15% 2	1890
May	1st to 10th	Night	48% 7% 11% 17% 14% 4	5264
	11th to 20th	Night	43% 6% 10% 26% 13% 3	5235
	21st to end	Night	39% 6% 10% 21% 19% 5%	5662
June	1st to 10th	Night	34% 6% 10% 28% 21% 2	1617
	11th to 20th	Night	35% 7% 14% 24% 18% 2	1470
	21st to end	Night	33% 7% 13% 26% 19% 1	1652
July	1st to 10th	Night	31% 7% 15% 27% 17% 4	3660
	11th to 20th	Night	30% 7% 13% 28% 20% 1	3652
	21st to end	Night	32% 8% 13% 21% 23% 2	4207
August	1st to 10th	Night	33% 7% 15% 27% 17% 1	2904
	11th to 20th	Night	33% 7% 11% 36% 11% 2	2902
	21st to end	Night	33% 7% 12% 32% 14% 1	3281
September	1st to 10th	Night	34% 7% 12% 29% 16% 2	2105
	11th to 20th	Night	29% 6% 12% 30% 21% 2	2200
	21st to end	Night	40% 6% 13% 27% 14% 1	2200
October	1st to 10th	Night	26% 4 10% 33% 26% 1	3676
	11th to 20th	Night	44% 5% 10% 22% 18%	3899
	21st to end	Night	41% 5% 12% 29% 12% 1	4546
November	1st to 10th	Night	43% 6% 11% 26% 14% 1	2666
	11th to 20th	Night	52% 7% 13% 19% 8% 1	2730
	21st to end	Night	58% 5% 12% 18% 6%	2830
December	1st to 10th	Night	64% 6% 13% 13% 3	4720
	11th to 20th	Night	67% 6% 9% 12% 5%	5662
	21st to end	Night	74% 5% 8% 7% 6%	7197

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	23% 20% 38% 13% 5%	330
	11th to 20th	Day	25% 19% 42% 12% 2 1	330
	21st to end	Day	31% 20% 29% 16% 4 1	363
February	1st to 10th	Day	26% 21% 36% 14% 2 1	330
	11th to 20th	Day	26% 22% 37% 13% 1	330
	21st to end	Day	27% 29% 35% 8% 1	273
March	1st to 10th	Day	26% 23% 37% 10% 3	364
	11th to 20th	Day	26% 15% 32% 21% 5% 1	540
	21st to end	Day	28% 17% 32% 17% 4 1	594
April	1st to 10th	Day	23% 19% 32% 19% 6% 1	540
	11th to 20th	Day	27% 17% 32% 14% 5% 4	532
	21st to end	Day	24% 15% 30% 20% 9% 2	540
May	1st to 10th	Day	23% 18% 28% 20% 9% 2	543
	11th to 20th	Day	18% 13% 31% 23% 11% 5%	567
	21st to end	Day	18% 10% 24% 27% 15% 6%	648
June	1st to 10th	Day	12% 10% 31% 29% 14% 3	780
	11th to 20th	Day	14% 12% 31% 24% 15% 3	780
	21st to end	Day	12% 9% 31% 30% 14% 4	780
July	1st to 10th	Day	10% 6% 24% 31% 20% 9%	771
	11th to 20th	Day	11% 7% 29% 29% 18% 7%	768
	21st to end	Day	8% 6% 26% 31% 21% 8%	703
August	1st to 10th	Day	9% 6% 21% 27% 23% 14%	526
	11th to 20th	Day	14% 4 20% 28% 23% 11%	519
	21st to end	Day	11% 6% 23% 28% 21% 11%	583
September	1st to 10th	Day	13% 8% 24% 24% 20% 11%	530
	11th to 20th	Day	10% 4 19% 23% 29% 15%	530
	21st to end	Day	18% 13% 21% 24% 18% 7%	530
October	1st to 10th	Day	17% 10% 28% 21% 18% 6%	530
	11th to 20th	Day	20% 17% 28% 27% 6% 1	530
	21st to end	Day	29% 18% 35% 15% 3	400
November	1st to 10th	Day	21% 22% 34% 17% 5% 2	330
	11th to 20th	Day	25% 23% 32% 14% 5% 1	330
	21st to end	Day	29% 22% 35% 11% 3	275
December	1st to 10th	Day	26% 22% 31% 14% 7%	220
	11th to 20th	Day	28% 25% 37% 7% 2	220
	21st to end	Day	28% 28% 31% 12% 1	349
January	1st to 10th	Night	21% 18% 37% 19% 5% 1	1050
	11th to 20th	Night	25% 16% 35% 20% 3 1	1050
	21st to end	Night	21% 14% 35% 24% 5%	997
February	1st to 10th	Night	25% 14% 36% 23% 2	840
	11th to 20th	Night	22% 17% 34% 22% 4	823
	21st to end	Night	27% 17% 35% 18% 3	692
March	1st to 10th	Night	22% 15% 35% 22% 6%	840
	11th to 20th	Night	20% 16% 35% 23% 5% 1	840
	21st to end	Night	23% 14% 31% 26% 6% 1	924
April	1st to 10th	Night	22% 16% 36% 21% 3 1	706
	11th to 20th	Night	22% 14% 34% 22% 7% 2	623
	21st to end	Night	21% 10% 32% 30% 7%	630
May	1st to 10th	Night	20% 9% 33% 31% 7% 1	630
	11th to 20th	Night	21% 5% 31% 32% 10%	621
	21st to end	Night	12% 5% 27% 38% 16% 1	683
June	1st to 10th	Night	12% 7% 25% 44% 13%	567
	11th to 20th	Night	12% 6% 31% 40% 11%	420
	21st to end	Night	11% 5% 24% 42% 16% 1	602
July	1st to 10th	Night	10% 2 19% 40% 26% 3	615
	11th to 20th	Night	10% 2 22% 42% 20% 3	612
	21st to end	Night	6% 3 20% 49% 20% 2	687
August	1st to 10th	Night	9% 2 17% 43% 27% 2	597
	11th to 20th	Night	10% 2 21% 36% 27% 4	594
	21st to end	Night	10% 4 20% 37% 27% 3	660
September	1st to 10th	Night	11% 5% 23% 33% 24% 4	705
	11th to 20th	Night	12% 4 18% 35% 28% 4	800
	21st to end	Night	16% 6% 23% 31% 19% 4	800
October	1st to 10th	Night	18% 7% 26% 31% 17% 1	800
	11th to 20th	Night	26% 13% 27% 26% 8% 1	800
	21st to end	Night	26% 12% 34% 24% 4	880
November	1st to 10th	Night	20% 14% 30% 26% 9% 1	820
	11th to 20th	Night	22% 18% 32% 20% 7% 1	840
	21st to end	Night	28% 15% 34% 19% 4	840
December	1st to 10th	Night	23% 18% 35% 20% 5%	840
	11th to 20th	Night	23% 16% 39% 19% 2	1003
	21st to end	Night	30% 15% 37% 16% 1	1155

Page generated at 2026-07-28 03:25:27. Version ac07

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