Shooting Star Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shooting Star Observatory clear sky chart from 2005-11-06 to 2024-12-02.

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	4 9% 4 9% 5% 5% 5% 4 5% 7% 44%	105948
	Night	3 10% 4 9% 5% 4 4 4 5% 7% 45%	102361
Transparency	Day	38% 8% 11% 19% 17% 7%	105694
	Night	38% 8% 12% 21% 15% 5%	102203
Seeing	Day	11% 18% 32% 26% 11% 2	15659
	Night	10% 10% 26% 37% 16% 1	25318

By Month

Percentage Cloud Cover SW (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	1 14% 7% 22% 9% 6% 5% 3 5% 5% 24%	2412
	11th to 20th	Day	2 14% 7% 17% 7% 6% 4 4 5% 5% 29%	2860
	21st to end	Day	1 21% 8% 15% 7% 5% 4 3 4 5% 27%	3146
February	1st to 10th	Day	2 18% 8% 16% 8% 6% 5% 3 6% 6% 22%	1710
	11th to 20th	Day	2 18% 9% 13% 8% 6% 5% 3 5% 5% 26%	1665
	21st to end	Day	2 19% 7% 18% 8% 5% 5% 4 4 5% 21%	1514
March	1st to 10th	Day	1 15% 7% 17% 7% 5% 4 3 5% 5% 31%	3383
	11th to 20th	Day	2 11% 4 9% 6% 4 4 3 5% 6% 46%	3490
	21st to end	Day	3 21% 8% 15% 8% 7% 7% 5% 5% 6% 15%	3825
April	1st to 10th	Day	6% 17% 5% 10% 7% 6% 5% 4 6% 6% 27%	2185
	11th to 20th	Day	6% 13% 5% 13% 7% 6% 5% 4 5% 6% 29%	2388
	21st to end	Day	6% 14% 5% 11% 5% 5% 6% 5% 6% 8% 29%	2470
May	1st to 10th	Day	7% 14% 4 10% 5% 6% 6% 5% 6% 6% 30%	4110
	11th to 20th	Day	5% 5% 2 6% 5% 5% 5% 5% 7% 8% 48%	4190
	21st to end	Day	7% 12% 5% 10% 5% 6% 5% 4 5% 6% 35%	4825
June	1st to 10th	Day	9% 7% 3 7% 5% 5% 5% 4 7% 8% 41%	2660
	11th to 20th	Day	8% 7% 2 7% 4 4 5% 3 7% 7% 44%	2841
	21st to end	Day	2 2 1 3 3 4 4 3 5% 7% 65%	2850
July	1st to 10th	Day	1 1 1 2 2 3 4 3 6% 8% 69%	4740
	11th to 20th	Day	1 2 1 3 3 3 5% 4 6% 8% 63%	4328
	21st to end	Day	2 2 1 4 4 4 5% 4 6% 9% 58%	4454
August	1st to 10th	Day	3 3 1 4 3 5% 5% 5% 7% 9% 56%	4092
	11th to 20th	Day	2 2 1 3 4 4 4 4 6% 7% 63%	4028
	21st to end	Day	3 2 1 4 3 3 3 3 5% 7% 67%	4471
September	1st to 10th	Day	4 4 1 5% 4 4 3 3 5% 6% 61%	2261
	11th to 20th	Day	6% 5% 2 6% 3 5% 4 3 5% 7% 54%	2090
	21st to end	Day	6% 5% 1 5% 4 3 3 3 3 6% 60%	2090
October	1st to 10th	Day	5% 6% 2 4 3 3 4 3 4 4 63%	3219
	11th to 20th	Day	4 6% 2 6% 4 3 4 2 4 5% 59%	3150
	21st to end	Day	4 8% 3 7% 5% 5% 5% 4 7% 9% 43%	3388
November	1st to 10th	Day	8% 13% 4 9% 5% 4 4 4 5% 7% 38%	1744
	11th to 20th	Day	4 15% 4 11% 5% 6% 4 3 5% 7% 35%	1600
	21st to end	Day	1 13% 5% 13% 6% 5% 4 4 5% 6% 39%	1600
December	1st to 10th	Day	3 15% 6% 12% 9% 8% 5% 4 3 6% 29%	1528
	11th to 20th	Day	4 17% 7% 15% 7% 5% 6% 4 5% 7% 23%	1926
	21st to end	Day	2 15% 4 13% 6% 6% 6% 3 5% 7% 33%	2715
January	1st to 10th	Night	1 10% 7% 20% 9% 6% 5% 4 5% 7% 26%	4538
	11th to 20th	Night	2 14% 8% 20% 9% 6% 4 3 4 5% 26%	4110
	21st to end	Night	1 23% 8% 16% 7% 5% 4 2 5% 5% 25%	4521
February	1st to 10th	Night	2 15% 7% 16% 7% 6% 6% 4 5% 7% 24%	2470
	11th to 20th	Night	3 15% 8% 13% 8% 6% 5% 2 5% 6% 31%	2402
	21st to end	Night	3 14% 7% 17% 8% 6% 5% 4 6% 5% 25%	1937
March	1st to 10th	Night	1 14% 6% 19% 6% 5% 3 3 4 6% 32%	3490
	11th to 20th	Night	2 8% 4 8% 4 4 4 3 5% 7% 51%	3490
	21st to end	Night	3 15% 6% 12% 7% 6% 6% 5% 6% 6% 26%	3828
April	1st to 10th	Night	4 13% 4 9% 6% 5% 6% 4 6% 8% 35%	1995
	11th to 20th	Night	5% 11% 4 9% 6% 5% 5% 5% 6% 7% 37%	1738
	21st to end	Night	5% 10% 3 8% 5% 5% 5% 4 5% 8% 43%	1710
May	1st to 10th	Night	7% 14% 4 9% 4 4 5% 4 5% 8% 36%	2860
	11th to 20th	Night	4 4 1 5% 3 4 4 4 7% 10% 53%	2712
	21st to end	Night	6% 10% 3 6% 5% 4 5% 4 6% 7% 43%	2762
June	1st to 10th	Night	9% 5% 3 5% 4 4 4 4 8% 8% 46%	1520
	11th to 20th	Night	8% 5% 1 4 4 3 3 4 5% 9% 53%	1332
	21st to end	Night	2 1 3 2 3 4 3 5% 7% 70%	1330
July	1st to 10th	Night	1 1 1 2 2 3 4 3 6% 7% 71%	2220
	11th to 20th	Night	1 1 1 1 1 2 3 4 6% 9% 71%	2618
	21st to end	Night	1 1 1 3 2 3 4 4 7% 8% 66%	3109
August	1st to 10th	Night	2 2 1 3 3 3 4 4 7% 8% 62%	2847
	11th to 20th	Night	1 2 1 3 4 3 4 5% 6% 8% 62%	2811
	21st to end	Night	3 2 1 3 2 2 2 3 5% 5% 72%	3194
September	1st to 10th	Night	4 3 1 3 3 2 3 3 5% 6% 66%	1914
	11th to 20th	Night	4 3 2 5% 3 5% 5% 4 5% 7% 56%	2090
	21st to end	Night	8% 5% 1 3 2 3 3 1 3 5% 65%	2090
October	1st to 10th	Night	5% 5% 2 3 3 2 3 3 3 4 68%	3751
	11th to 20th	Night	5% 7% 2 4 3 4 4 3 4 6% 56%	3778
	21st to end	Night	3 8% 3 7% 4 3 4 4 6% 8% 50%	4167
November	1st to 10th	Night	7% 12% 3 9% 5% 4 3 4 5% 7% 41%	2535
	11th to 20th	Night	4 12% 4 10% 6% 5% 5% 5% 6% 6% 38%	2799
	21st to end	Night	3 12% 5% 9% 6% 4 4 3 5% 7% 41%	2800
December	1st to 10th	Night	3 15% 6% 13% 8% 7% 5% 4 4 5% 30%	2687
	11th to 20th	Night	4 15% 6% 15% 7% 6% 4 4 5% 6% 28%	3271
	21st to end	Night	2 16% 5% 13% 6% 6% 5% 4 5% 6% 31%	4935

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	61% 8% 12% 16% 3 1	2412
	11th to 20th	Day	56% 9% 14% 12% 7% 3	2860
	21st to end	Day	59% 8% 11% 13% 8% 1	3146
February	1st to 10th	Day	62% 9% 12% 12% 4 1	1710
	11th to 20th	Day	59% 9% 13% 12% 5% 2	1674
	21st to end	Day	63% 9% 8% 13% 5% 2	1514
March	1st to 10th	Day	53% 10% 9% 16% 12% 1	3383
	11th to 20th	Day	39% 9% 18% 25% 8% 1	3490
	21st to end	Day	68% 11% 10% 9% 2	3825
April	1st to 10th	Day	56% 9% 13% 14% 7% 1	2185
	11th to 20th	Day	54% 9% 11% 17% 8% 1	2391
	21st to end	Day	51% 10% 13% 21% 5%	2470
May	1st to 10th	Day	48% 11% 12% 20% 7% 1	4110
	11th to 20th	Day	30% 11% 13% 30% 13% 4	4193
	21st to end	Day	45% 11% 10% 25% 8%	4825
June	1st to 10th	Day	38% 9% 17% 24% 11% 1	2660
	11th to 20th	Day	36% 8% 10% 20% 17% 8%	2841
	21st to end	Day	17% 7% 9% 24% 32% 12%	2850
July	1st to 10th	Day	12% 4 9% 14% 37% 24%	4666
	11th to 20th	Day	16% 4 7% 14% 25% 34%	4251
	21st to end	Day	21% 6% 7% 18% 33% 15%	4314
August	1st to 10th	Day	21% 6% 8% 17% 31% 17%	4078
	11th to 20th	Day	18% 5% 8% 23% 33% 12%	4067
	21st to end	Day	16% 5% 7% 21% 32% 19%	4470
September	1st to 10th	Day	24% 5% 8% 17% 33% 12%	2261
	11th to 20th	Day	28% 7% 9% 23% 24% 8%	2090
	21st to end	Day	27% 5% 13% 27% 24% 5%	2090
October	1st to 10th	Day	26% 5% 7% 21% 33% 8%	3219
	11th to 20th	Day	29% 5% 10% 36% 16% 4	3150
	21st to end	Day	34% 9% 18% 28% 11% 1	3388
November	1st to 10th	Day	46% 8% 15% 21% 8% 2	1744
	11th to 20th	Day	47% 8% 19% 17% 8% 1	1600
	21st to end	Day	47% 9% 17% 19% 9% 1	1600
December	1st to 10th	Day	58% 9% 11% 11% 9% 3	1528
	11th to 20th	Day	61% 9% 12% 15% 4	1924
	21st to end	Day	49% 8% 12% 14% 9% 8%	2715
January	1st to 10th	Night	56% 10% 13% 15% 5% 1	4538
	11th to 20th	Night	62% 8% 11% 12% 6% 2	4110
	21st to end	Night	62% 7% 13% 12% 5% 1	4521
February	1st to 10th	Night	60% 11% 11% 12% 5%	2470
	11th to 20th	Night	57% 8% 11% 15% 7% 1	2403
	21st to end	Night	60% 9% 10% 14% 6% 2	1937
March	1st to 10th	Night	52% 10% 9% 18% 10%	3490
	11th to 20th	Night	31% 10% 18% 27% 11% 2	3490
	21st to end	Night	53% 15% 14% 15% 2 1	3828
April	1st to 10th	Night	45% 12% 16% 16% 9% 2	1995
	11th to 20th	Night	44% 11% 16% 20% 8% 1	1738
	21st to end	Night	37% 10% 16% 28% 8%	1710
May	1st to 10th	Night	43% 10% 14% 22% 11% 1	2860
	11th to 20th	Night	22% 9% 20% 34% 12% 3	2713
	21st to end	Night	34% 13% 13% 29% 10% 1	2762
June	1st to 10th	Night	33% 10% 19% 25% 12% 1	1520
	11th to 20th	Night	28% 7% 13% 25% 20% 8%	1332
	21st to end	Night	13% 5% 11% 24% 33% 14%	1330
July	1st to 10th	Night	11% 4 9% 16% 42% 18%	2185
	11th to 20th	Night	9% 3 6% 19% 35% 28%	2572
	21st to end	Night	12% 7% 8% 23% 33% 17%	3011
August	1st to 10th	Night	17% 5% 9% 18% 36% 15%	2838
	11th to 20th	Night	18% 6% 9% 27% 26% 14%	2838
	21st to end	Night	14% 4 7% 23% 36% 16%	3194
September	1st to 10th	Night	18% 6% 8% 19% 32% 17%	1914
	11th to 20th	Night	24% 7% 12% 23% 25% 9%	2090
	21st to end	Night	24% 4 10% 29% 28% 6%	2090
October	1st to 10th	Night	21% 3 9% 27% 34% 5%	3751
	11th to 20th	Night	29% 6% 9% 37% 17% 3	3778
	21st to end	Night	31% 9% 15% 30% 14% 1	4167
November	1st to 10th	Night	43% 9% 14% 22% 9% 2	2535
	11th to 20th	Night	44% 9% 17% 21% 7% 1	2799
	21st to end	Night	43% 9% 17% 21% 10% 2	2800
December	1st to 10th	Night	56% 9% 15% 11% 7% 2	2687
	11th to 20th	Night	58% 8% 14% 14% 5%	3272
	21st to end	Night	52% 7% 13% 15% 9% 4	4935

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	14% 20% 25% 30% 10% 1	210
	11th to 20th	Day	6% 18% 38% 25% 10% 3	270
	21st to end	Day	7% 16% 36% 30% 9% 1	297
February	1st to 10th	Day	16% 30% 36% 16% 2	270
	11th to 20th	Day	14% 27% 30% 23% 6%	270
	21st to end	Day	14% 27% 36% 17% 6%	326
March	1st to 10th	Day	15% 31% 33% 17% 3	460
	11th to 20th	Day	11% 24% 33% 24% 7%	460
	21st to end	Day	16% 27% 35% 18% 3	506
April	1st to 10th	Day	19% 27% 30% 19% 5% 1	460
	11th to 20th	Day	18% 28% 35% 14% 5% 1	452
	21st to end	Day	17% 23% 29% 20% 10% 2	460
May	1st to 10th	Day	13% 22% 31% 25% 7% 2	463
	11th to 20th	Day	15% 16% 31% 24% 12% 2	555
	21st to end	Day	17% 13% 26% 26% 16% 3	734
June	1st to 10th	Day	9% 17% 26% 29% 16% 3	680
	11th to 20th	Day	14% 19% 33% 24% 9%	680
	21st to end	Day	6% 12% 32% 31% 17% 3	680
July	1st to 10th	Day	3 8% 31% 38% 17% 2	671
	11th to 20th	Day	4 11% 40% 31% 13% 2	569
	21st to end	Day	3 10% 32% 38% 15% 3	531
August	1st to 10th	Day	5% 10% 37% 32% 15% 2	487
	11th to 20th	Day	4 9% 35% 29% 19% 4	477
	21st to end	Day	6% 14% 31% 29% 15% 5%	539
September	1st to 10th	Day	5% 12% 33% 28% 17% 4	490
	11th to 20th	Day	12% 18% 29% 26% 12% 4	490
	21st to end	Day	9% 13% 30% 29% 15% 3	490
October	1st to 10th	Day	10% 14% 29% 25% 18% 3	336
	11th to 20th	Day	10% 18% 23% 25% 17% 7%	300
	21st to end	Day	15% 18% 32% 28% 6% 1	330
November	1st to 10th	Day	15% 22% 29% 21% 9% 3	300
	11th to 20th	Day	11% 21% 35% 22% 9% 2	300
	21st to end	Day	7% 15% 39% 29% 10% 1	300
December	1st to 10th	Day	15% 16% 31% 27% 11% 1	273
	11th to 20th	Day	17% 19% 32% 25% 7%	270
	21st to end	Day	14% 19% 32% 21% 11% 2	273
January	1st to 10th	Night	9% 14% 29% 37% 11% 1	912
	11th to 20th	Night	9% 12% 33% 33% 11% 2	760
	21st to end	Night	9% 8% 36% 35% 10% 1	836
February	1st to 10th	Night	9% 16% 35% 33% 7% 1	760
	11th to 20th	Night	10% 14% 32% 34% 9% 1	744
	21st to end	Night	10% 14% 37% 30% 8% 1	628
March	1st to 10th	Night	8% 18% 31% 33% 9% 1	760
	11th to 20th	Night	8% 11% 29% 38% 13% 1	760
	21st to end	Night	11% 12% 32% 33% 11%	836
April	1st to 10th	Night	11% 15% 30% 33% 10% 1	665
	11th to 20th	Night	12% 11% 33% 34% 10%	563
	21st to end	Night	11% 9% 26% 35% 17% 1	570
May	1st to 10th	Night	12% 11% 23% 36% 17% 1	570
	11th to 20th	Night	12% 6% 23% 36% 21% 2	561
	21st to end	Night	14% 8% 20% 38% 19% 1	617
June	1st to 10th	Night	12% 8% 22% 34% 22% 1	570
	11th to 20th	Night	10% 8% 25% 43% 14%	382
	21st to end	Night	3 1 18% 48% 29% 2	380
July	1st to 10th	Night	1 1 18% 45% 32% 2	370
	11th to 20th	Night	3 2 16% 51% 28%	498
	21st to end	Night	2 1 13% 50% 31% 2	624
August	1st to 10th	Night	5% 2 14% 47% 29% 2	567
	11th to 20th	Night	3 2 13% 49% 31% 2	564
	21st to end	Night	4 4 19% 38% 32% 3	627
September	1st to 10th	Night	6% 2 16% 44% 29% 3	584
	11th to 20th	Night	7% 4 18% 39% 28% 4	760
	21st to end	Night	11% 3 19% 38% 24% 4	760
October	1st to 10th	Night	12% 6% 23% 37% 20% 2	760
	11th to 20th	Night	13% 8% 19% 38% 20% 2	760
	21st to end	Night	9% 9% 25% 43% 11% 3	836
November	1st to 10th	Night	14% 12% 27% 35% 11% 2	780
	11th to 20th	Night	12% 14% 34% 34% 6% 1	999
	21st to end	Night	10% 11% 32% 35% 11% 2	1000
December	1st to 10th	Night	14% 12% 33% 34% 7% 1	960
	11th to 20th	Night	14% 14% 29% 36% 7%	950
	21st to end	Night	13% 15% 32% 29% 9% 2	1045

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