SkyWatcher Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the SkyWatcher Observatory clear sky chart from 2005-11-06 to 2024-11-04.

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	7% 7% 2 6% 4 4 4 3 5% 6% 50%	105359
	Night	8% 8% 3 7% 5% 4 4 4 5% 6% 46%	102314
Transparency	Day	33% 7% 12% 22% 17% 9%	105102
	Night	37% 8% 14% 22% 14% 6%	102160
Seeing	Day	11% 14% 26% 27% 17% 4	14559
	Night	11% 8% 21% 37% 20% 2	23556

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	14% 17% 6% 12% 7% 6% 6% 4 6% 7% 14%	2539
	11th to 20th	Day	21% 17% 4 9% 5% 6% 6% 4 5% 5% 18%	2540
	21st to end	Day	16% 14% 4 11% 7% 6% 6% 5% 6% 6% 18%	2904
February	1st to 10th	Day	13% 13% 3 9% 7% 5% 5% 5% 5% 7% 28%	1710
	11th to 20th	Day	11% 11% 3 9% 6% 5% 7% 4 6% 8% 31%	1665
	21st to end	Day	8% 13% 4 8% 7% 6% 6% 5% 7% 7% 29%	1570
March	1st to 10th	Day	7% 10% 3 9% 5% 6% 6% 5% 9% 9% 32%	3138
	11th to 20th	Day	6% 9% 3 6% 4 4 4 4 5% 6% 48%	3485
	21st to end	Day	8% 11% 4 11% 7% 7% 7% 5% 7% 8% 27%	4025
April	1st to 10th	Day	10% 11% 3 7% 6% 5% 6% 5% 7% 8% 32%	2280
	11th to 20th	Day	8% 10% 2 6% 7% 5% 5% 4 6% 7% 40%	2249
	21st to end	Day	7% 7% 2 6% 5% 5% 5% 4 7% 9% 43%	2395
May	1st to 10th	Day	10% 7% 2 5% 4 4 4 3 5% 6% 50%	4420
	11th to 20th	Day	5% 4 1 4 3 2 3 3 4 7% 65%	4377
	21st to end	Day	10% 7% 2 6% 5% 5% 5% 4 6% 7% 43%	4813
June	1st to 10th	Day	10% 7% 3 6% 5% 4 4 4 5% 7% 46%	2660
	11th to 20th	Day	7% 5% 2 6% 5% 5% 5% 3 5% 7% 52%	2660
	21st to end	Day	3 2 1 3 3 3 3 3 5% 6% 68%	2660
July	1st to 10th	Day	1 1 2 1 1 2 2 2 4 85%	4420
	11th to 20th	Day	2 1 1 1 2 1 1 2 3 84%	4420
	21st to end	Day	1 1 1 2 1 2 1 2 3 4 82%	4790
August	1st to 10th	Day	3 2 1 3 2 2 2 2 4 5% 75%	4294
	11th to 20th	Day	2 1 1 3 2 3 3 3 5% 6% 72%	4010
	21st to end	Day	3 3 1 3 2 2 3 2 3 6% 71%	4180
September	1st to 10th	Day	2 1 1 2 2 2 3 2 3 6% 76%	2280
	11th to 20th	Day	4 4 2 4 4 4 5% 4 5% 6% 59%	2280
	21st to end	Day	8% 5% 1 4 4 3 4 3 4 6% 58%	2038
October	1st to 10th	Day	6% 4 1 4 3 3 4 4 6% 6% 60%	3180
	11th to 20th	Day	6% 4 2 7% 4 6% 6% 5% 7% 9% 45%	3161
	21st to end	Day	9% 8% 3 9% 4 5% 6% 4 7% 8% 36%	3237
November	1st to 10th	Day	12% 12% 3 7% 6% 6% 6% 4 7% 8% 29%	1697
	11th to 20th	Day	11% 14% 4 11% 7% 7% 6% 5% 7% 6% 22%	1520
	21st to end	Day	10% 14% 4 9% 5% 6% 5% 4 6% 7% 29%	1520
December	1st to 10th	Day	12% 13% 3 9% 7% 6% 6% 4 6% 5% 28%	1520
	11th to 20th	Day	11% 16% 6% 11% 7% 6% 6% 6% 8% 7% 17%	1928
	21st to end	Day	14% 16% 6% 14% 8% 6% 5% 4 5% 5% 18%	2794
January	1st to 10th	Night	12% 17% 6% 14% 7% 6% 6% 5% 6% 6% 15%	4406
	11th to 20th	Night	21% 18% 4 8% 6% 4 3 4 4 6% 21%	4420
	21st to end	Night	17% 14% 5% 11% 7% 6% 6% 4 5% 6% 19%	4740
February	1st to 10th	Night	13% 12% 4 8% 5% 5% 5% 4 6% 7% 31%	2470
	11th to 20th	Night	10% 11% 3 9% 5% 4 5% 4 5% 7% 37%	2402
	21st to end	Night	9% 14% 3 8% 7% 6% 5% 4 6% 8% 31%	1884
March	1st to 10th	Night	6% 9% 3 8% 6% 6% 6% 5% 8% 9% 34%	3736
	11th to 20th	Night	5% 7% 2 5% 4 4 4 4 5% 6% 52%	3494
	21st to end	Night	8% 9% 3 9% 7% 7% 7% 6% 7% 9% 28%	3627
April	1st to 10th	Night	11% 8% 3 6% 5% 4 4 5% 7% 8% 38%	1900
	11th to 20th	Night	7% 7% 3 5% 6% 4 6% 3 6% 7% 45%	1879
	21st to end	Night	8% 6% 2 5% 4 4 5% 4 7% 8% 47%	1780
May	1st to 10th	Night	10% 7% 2 5% 4 4 3 3 5% 6% 52%	2540
	11th to 20th	Night	5% 3 1 3 3 2 3 3 5% 6% 66%	2516
	21st to end	Night	6% 6% 2 5% 4 4 4 3 6% 8% 53%	2762
June	1st to 10th	Night	10% 5% 2 6% 4 4 4 3 5% 7% 49%	1520
	11th to 20th	Night	7% 5% 2 4 3 4 3 4 5% 7% 59%	1520
	21st to end	Night	4 3 1 3 2 3 4 3 4 4 70%	1520
July	1st to 10th	Night	1 1 1 1 1 1 1 2 3 87%	2540
	11th to 20th	Night	1 1 1 2 1 1 2 2 3 4 82%	2540
	21st to end	Night	1 1 1 1 1 1 1 1 2 3 86%	2761
August	1st to 10th	Night	2 2 1 3 3 2 3 3 4 5% 74%	2623
	11th to 20th	Night	1 2 1 2 2 3 3 3 4 4 76%	2828
	21st to end	Night	2 2 1 3 2 2 2 2 4 5% 76%	3498
September	1st to 10th	Night	2 2 1 2 1 2 2 3 4 5% 77%	1900
	11th to 20th	Night	5% 3 1 3 3 4 4 3 5% 6% 63%	1900
	21st to end	Night	6% 4 1 4 3 3 3 3 5% 6% 61%	2138
October	1st to 10th	Night	5% 2 2 3 3 3 3 2 4 6% 67%	3800
	11th to 20th	Night	6% 4 2 6% 4 5% 5% 4 7% 8% 49%	3777
	21st to end	Night	10% 7% 2 7% 4 6% 6% 5% 7% 7% 39%	4325
November	1st to 10th	Night	12% 9% 2 8% 6% 5% 5% 4 6% 8% 34%	2450
	11th to 20th	Night	13% 12% 4 9% 6% 5% 5% 5% 6% 6% 29%	2660
	21st to end	Night	10% 10% 3 8% 5% 4 5% 5% 5% 8% 36%	2660
December	1st to 10th	Night	12% 12% 5% 10% 7% 7% 5% 4 6% 6% 27%	2660
	11th to 20th	Night	13% 15% 5% 11% 8% 6% 6% 5% 6% 6% 19%	3276
	21st to end	Night	13% 13% 6% 13% 8% 6% 6% 4 5% 6% 21%	4862

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	62% 14% 12% 10% 2	2539
	11th to 20th	Day	64% 11% 11% 11% 2 1	2540
	21st to end	Day	60% 12% 12% 11% 4	2904
February	1st to 10th	Day	54% 8% 17% 16% 4 1	1710
	11th to 20th	Day	47% 12% 15% 18% 7%	1674
	21st to end	Day	50% 11% 17% 14% 8%	1570
March	1st to 10th	Day	41% 7% 15% 26% 11%	3138
	11th to 20th	Day	35% 6% 14% 33% 11%	3485
	21st to end	Day	49% 12% 16% 18% 5%	4025
April	1st to 10th	Day	47% 10% 17% 17% 9%	2280
	11th to 20th	Day	42% 9% 16% 17% 13% 3	2252
	21st to end	Day	36% 9% 16% 26% 11% 2	2395
May	1st to 10th	Day	33% 7% 14% 26% 20%	4420
	11th to 20th	Day	21% 5% 10% 31% 30% 4	4380
	21st to end	Day	35% 9% 21% 25% 8% 1	4814
June	1st to 10th	Day	37% 7% 13% 27% 13% 2	2660
	11th to 20th	Day	30% 7% 13% 32% 14% 3	2660
	21st to end	Day	17% 5% 11% 34% 24% 9%	2660
July	1st to 10th	Day	7% 2 5% 15% 25% 46%	4351
	11th to 20th	Day	8% 2 5% 10% 24% 51%	4345
	21st to end	Day	8% 2 7% 19% 36% 27%	4639
August	1st to 10th	Day	13% 3 5% 17% 35% 26%	4278
	11th to 20th	Day	14% 4 10% 35% 28% 9%	4049
	21st to end	Day	17% 3 11% 28% 30% 11%	4179
September	1st to 10th	Day	12% 3 9% 30% 30% 16%	2280
	11th to 20th	Day	24% 7% 12% 25% 22% 9%	2280
	21st to end	Day	27% 6% 14% 27% 20% 6%	2038
October	1st to 10th	Day	24% 6% 8% 30% 25% 7%	3180
	11th to 20th	Day	32% 8% 18% 25% 16% 1	3161
	21st to end	Day	42% 8% 11% 27% 11% 1	3237
November	1st to 10th	Day	50% 11% 14% 18% 7% 1	1697
	11th to 20th	Day	59% 12% 13% 13% 4	1520
	21st to end	Day	54% 8% 15% 15% 8% 1	1520
December	1st to 10th	Day	56% 9% 12% 17% 6%	1520
	11th to 20th	Day	58% 12% 17% 11% 2	1928
	21st to end	Day	63% 10% 13% 12% 2	2794
January	1st to 10th	Night	65% 10% 13% 8% 3	4406
	11th to 20th	Night	62% 10% 15% 9% 3 1	4420
	21st to end	Night	60% 12% 14% 11% 3	4740
February	1st to 10th	Night	51% 10% 18% 16% 5%	2470
	11th to 20th	Night	45% 10% 17% 20% 7%	2404
	21st to end	Night	48% 11% 15% 17% 8% 1	1884
March	1st to 10th	Night	39% 8% 15% 26% 11% 1	3736
	11th to 20th	Night	28% 9% 15% 34% 13%	3494
	21st to end	Night	46% 13% 20% 17% 4	3627
April	1st to 10th	Night	41% 11% 18% 22% 7% 1	1900
	11th to 20th	Night	37% 10% 19% 20% 11% 3	1879
	21st to end	Night	34% 11% 16% 25% 11% 3	1780
May	1st to 10th	Night	31% 6% 13% 30% 20% 1	2540
	11th to 20th	Night	18% 6% 12% 38% 24% 2	2516
	21st to end	Night	25% 10% 33% 24% 6% 1	2762
June	1st to 10th	Night	35% 8% 13% 28% 13% 2	1520
	11th to 20th	Night	25% 7% 15% 38% 13% 2	1520
	21st to end	Night	19% 5% 12% 35% 23% 8%	1520
July	1st to 10th	Night	6% 2 7% 16% 28% 42%	2500
	11th to 20th	Night	10% 2 5% 13% 22% 47%	2492
	21st to end	Night	7% 1 6% 20% 38% 29%	2674
August	1st to 10th	Night	13% 3 6% 16% 37% 25%	2615
	11th to 20th	Night	12% 3 11% 39% 25% 9%	2855
	21st to end	Night	12% 3 13% 29% 31% 11%	3498
September	1st to 10th	Night	10% 4 12% 29% 29% 17%	1900
	11th to 20th	Night	22% 6% 12% 27% 21% 12%	1900
	21st to end	Night	23% 5% 12% 29% 23% 8%	2138
October	1st to 10th	Night	20% 4 11% 34% 28% 3	3800
	11th to 20th	Night	31% 7% 20% 24% 16% 2	3777
	21st to end	Night	40% 8% 14% 26% 13% 1	4325
November	1st to 10th	Night	46% 10% 13% 22% 8%	2450
	11th to 20th	Night	52% 11% 14% 18% 5%	2660
	21st to end	Night	45% 9% 17% 22% 8%	2660
December	1st to 10th	Night	56% 9% 15% 16% 5%	2660
	11th to 20th	Night	61% 10% 15% 11% 4	3276
	21st to end	Night	58% 11% 13% 13% 5%	4862

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% 18% 26% 19% 11% 3	180
	11th to 20th	Day	22% 10% 26% 27% 13% 2	180
	21st to end	Day	20% 10% 26% 28% 13% 2	269
February	1st to 10th	Day	20% 15% 25% 28% 11% 1	370
	11th to 20th	Day	17% 16% 30% 23% 13% 1	365
	21st to end	Day	16% 19% 29% 25% 9% 2	382
March	1st to 10th	Day	17% 19% 30% 25% 8% 2	460
	11th to 20th	Day	13% 22% 26% 25% 12% 2	460
	21st to end	Day	19% 17% 27% 26% 10% 1	506
April	1st to 10th	Day	22% 18% 27% 21% 8% 3	460
	11th to 20th	Day	15% 19% 35% 19% 8% 4	452
	21st to end	Day	11% 20% 30% 23% 13% 3	460
May	1st to 10th	Day	12% 17% 28% 25% 14% 3	463
	11th to 20th	Day	15% 15% 24% 28% 13% 5%	488
	21st to end	Day	13% 13% 24% 27% 18% 5%	529
June	1st to 10th	Day	12% 16% 25% 26% 16% 6%	490
	11th to 20th	Day	10% 20% 28% 25% 14% 3	490
	21st to end	Day	3 13% 26% 32% 21% 5%	490
July	1st to 10th	Day	2 9% 29% 34% 22% 5%	486
	11th to 20th	Day	1 12% 26% 32% 23% 6%	484
	21st to end	Day	2 6% 26% 33% 25% 8%	531
August	1st to 10th	Day	3 9% 23% 28% 25% 12%	487
	11th to 20th	Day	2 7% 18% 31% 28% 14%	477
	21st to end	Day	4 11% 23% 28% 28% 6%	539
September	1st to 10th	Day	2 8% 24% 32% 25% 9%	490
	11th to 20th	Day	5% 9% 24% 32% 25% 4	490
	21st to end	Day	10% 12% 22% 29% 22% 6%	490
October	1st to 10th	Day	10% 10% 26% 30% 20% 4	490
	11th to 20th	Day	12% 12% 23% 26% 22% 5%	490
	21st to end	Day	15% 19% 25% 24% 13% 5%	416
November	1st to 10th	Day	17% 17% 29% 25% 11% 1	277
	11th to 20th	Day	15% 16% 28% 19% 18% 4	180
	21st to end	Day	18% 14% 22% 30% 14% 2	180
December	1st to 10th	Day	18% 8% 24% 29% 13% 7%	180
	11th to 20th	Day	21% 11% 34% 27% 8%	180
	21st to end	Day	17% 15% 30% 24% 14% 1	198
January	1st to 10th	Night	18% 13% 25% 28% 14% 2	760
	11th to 20th	Night	19% 10% 21% 29% 18% 2	760
	21st to end	Night	20% 7% 21% 35% 15% 2	836
February	1st to 10th	Night	18% 11% 23% 33% 14% 1	760
	11th to 20th	Night	15% 10% 27% 32% 14% 1	744
	21st to end	Night	17% 12% 27% 33% 11%	628
March	1st to 10th	Night	13% 12% 26% 34% 13% 1	760
	11th to 20th	Night	11% 11% 21% 40% 16% 1	760
	21st to end	Night	11% 12% 27% 36% 13% 1	836
April	1st to 10th	Night	16% 10% 23% 34% 15% 1	760
	11th to 20th	Night	11% 12% 28% 29% 17% 3	751
	21st to end	Night	11% 9% 26% 36% 17% 2	640
May	1st to 10th	Night	7% 7% 23% 39% 22% 1	380
	11th to 20th	Night	10% 5% 15% 39% 28% 2	374
	21st to end	Night	6% 6% 18% 40% 27% 3	411
June	1st to 10th	Night	11% 6% 17% 43% 22% 1	380
	11th to 20th	Night	7% 7% 24% 43% 17% 1	380
	21st to end	Night	7% 2 18% 46% 27% 1	380
July	1st to 10th	Night	2 1 11% 53% 32% 1	370
	11th to 20th	Night	1 1 13% 57% 26% 2	368
	21st to end	Night	1 1 9% 54% 32% 2	416
August	1st to 10th	Night	2 1 9% 48% 36% 5%	433
	11th to 20th	Night	2 1 7% 38% 43% 8%	567
	21st to end	Night	3 3 16% 46% 28% 5%	836
September	1st to 10th	Night	2 3 15% 44% 32% 4	760
	11th to 20th	Night	5% 2 14% 40% 34% 5%	760
	21st to end	Night	7% 4 15% 39% 30% 4	760
October	1st to 10th	Night	9% 3 19% 43% 23% 2	760
	11th to 20th	Night	8% 8% 19% 38% 24% 4	760
	21st to end	Night	14% 8% 23% 34% 17% 3	836
November	1st to 10th	Night	13% 10% 22% 39% 15% 1	754
	11th to 20th	Night	16% 14% 24% 32% 13% 2	760
	21st to end	Night	11% 10% 22% 37% 17% 3	760
December	1st to 10th	Night	16% 9% 23% 33% 16% 3	760
	11th to 20th	Night	19% 11% 24% 33% 13% 1	760
	21st to end	Night	19% 12% 27% 30% 10% 1	836

Page generated at 2024-11-01 19:47:51. Version ac07

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