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 2024-04-03.

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	9% 8% 3 6% 5% 3 5% 5% 5% 7% 45%	78764
	Night	10% 9% 3 6% 6% 3 5% 5% 5% 7% 41%	81376
Transparency	Day	38% 8% 13% 21% 15% 5%	78467
	Night	41% 9% 14% 20% 12% 4	81194
Seeing	Day	11% 14% 26% 27% 17% 4	13710
	Night	12% 8% 21% 37% 20% 2	22912

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% 16% 6% 11% 8% 5% 6% 6% 6% 7% 14%	2539
	11th to 20th	Day	21% 17% 5% 8% 6% 4 6% 5% 4 6% 18%	2540
	21st to end	Day	17% 13% 5% 10% 8% 4 6% 7% 6% 6% 18%	2904
February	1st to 10th	Day	13% 13% 3 8% 8% 4 5% 5% 5% 7% 29%	1710
	11th to 20th	Day	11% 9% 4 8% 7% 3 7% 6% 6% 8% 31%	1665
	21st to end	Day	8% 12% 5% 7% 8% 4 6% 7% 7% 7% 29%	1570
March	1st to 10th	Day	10% 11% 4 8% 6% 4 5% 6% 8% 9% 29%	1900
	11th to 20th	Day	9% 12% 5% 7% 7% 4 6% 6% 6% 7% 30%	2085
	21st to end	Day	11% 11% 4 9% 7% 4 7% 6% 6% 7% 26%	2416
April	1st to 10th	Day	10% 11% 3 7% 6% 4 5% 7% 7% 8% 32%	2185
	11th to 20th	Day	9% 9% 3 6% 7% 4 6% 5% 5% 7% 39%	2129
	21st to end	Day	7% 6% 3 5% 5% 3 5% 5% 7% 9% 45%	2268
May	1st to 10th	Day	7% 5% 2 5% 5% 3 5% 4 6% 7% 51%	2520
	11th to 20th	Day	8% 6% 2 6% 5% 3 4 5% 6% 9% 44%	2477
	21st to end	Day	11% 5% 3 5% 6% 3 4 5% 5% 8% 45%	2723
June	1st to 10th	Day	10% 6% 3 5% 6% 3 4 5% 5% 8% 46%	2520
	11th to 20th	Day	7% 4 2 5% 5% 3 5% 4 5% 7% 52%	2520
	21st to end	Day	4 2 1 3 3 2 3 3 5% 6% 69%	2520
July	1st to 10th	Day	2 1 1 2 2 2 3 3 4 5% 77%	2520
	11th to 20th	Day	3 1 1 2 2 2 3 2 3 5% 76%	2520
	21st to end	Day	2 1 1 2 1 1 2 3 4 84%	2741
August	1st to 10th	Day	2 1 2 2 2 2 3 4 6% 75%	2453
	11th to 20th	Day	2 1 1 2 2 2 2 3 3 5% 78%	2295
	21st to end	Day	2 1 1 2 2 2 3 3 3 6% 75%	2376
September	1st to 10th	Day	2 1 1 2 2 1 3 3 3 5% 77%	2160
	11th to 20th	Day	4 4 2 3 4 3 5% 5% 5% 6% 60%	2160
	21st to end	Day	8% 5% 1 4 4 3 4 4 4 6% 57%	1932
October	1st to 10th	Day	8% 5% 2 5% 6% 3 4 5% 6% 7% 50%	1800
	11th to 20th	Day	9% 4 3 5% 4 4 6% 6% 6% 7% 46%	1800
	21st to end	Day	11% 8% 3 7% 5% 4 5% 5% 5% 6% 41%	1864
November	1st to 10th	Day	12% 11% 4 6% 7% 5% 5% 5% 7% 8% 29%	1670
	11th to 20th	Day	11% 13% 5% 10% 8% 5% 7% 6% 7% 6% 22%	1520
	21st to end	Day	11% 12% 5% 8% 6% 5% 6% 5% 6% 7% 29%	1520
December	1st to 10th	Day	12% 12% 5% 8% 7% 4 7% 5% 6% 5% 29%	1520
	11th to 20th	Day	11% 15% 6% 10% 8% 5% 6% 7% 7% 8% 18%	1928
	21st to end	Day	14% 15% 6% 12% 9% 5% 6% 5% 5% 5% 18%	2794
January	1st to 10th	Night	12% 16% 6% 13% 9% 5% 6% 6% 6% 6% 15%	4406
	11th to 20th	Night	22% 17% 5% 7% 6% 3 4 5% 4 6% 22%	4420
	21st to end	Night	17% 14% 5% 9% 8% 4 6% 5% 5% 6% 19%	4740
February	1st to 10th	Night	13% 12% 4 7% 6% 4 5% 5% 6% 7% 31%	2470
	11th to 20th	Night	10% 10% 3 8% 6% 3 4 5% 5% 7% 37%	2402
	21st to end	Night	10% 13% 4 7% 7% 4 6% 5% 6% 8% 31%	1884
March	1st to 10th	Night	11% 10% 4 7% 7% 4 5% 6% 6% 9% 32%	2280
	11th to 20th	Night	8% 8% 3 5% 7% 4 6% 7% 7% 9% 37%	2094
	21st to end	Night	8% 9% 3 7% 7% 5% 7% 7% 6% 8% 33%	2181
April	1st to 10th	Night	11% 8% 3 6% 6% 3 4 6% 7% 8% 38%	1820
	11th to 20th	Night	8% 7% 3 4 6% 3 6% 5% 6% 7% 45%	1779
	21st to end	Night	9% 6% 2 4 5% 3 5% 5% 6% 9% 46%	1688
May	1st to 10th	Night	5% 5% 2 4 4 3 4 4 7% 8% 55%	1440
	11th to 20th	Night	8% 5% 2 4 5% 2 5% 5% 6% 9% 50%	1416
	21st to end	Night	6% 5% 2 5% 5% 3 5% 4 6% 8% 50%	1552
June	1st to 10th	Night	10% 5% 2 5% 5% 3 4 4 5% 8% 49%	1440
	11th to 20th	Night	7% 5% 2 4 3 3 4 4 5% 7% 58%	1440
	21st to end	Night	4 3 1 3 3 2 4 4 3 4 70%	1440
July	1st to 10th	Night	2 1 2 2 2 2 2 3 5% 78%	1440
	11th to 20th	Night	1 1 1 2 1 1 3 3 4 6% 79%	1440
	21st to end	Night	1 1 1 2 1 2 3 2 4 84%	1576
August	1st to 10th	Night	2 2 1 2 3 2 2 4 3 5% 76%	1484
	11th to 20th	Night	2 2 1 2 3 2 3 2 3 3 79%	1604
	21st to end	Night	2 1 1 2 3 1 2 2 4 4 77%	1980
September	1st to 10th	Night	2 2 1 2 1 1 2 3 3 5% 78%	1800
	11th to 20th	Night	5% 2 1 2 4 3 4 4 5% 6% 64%	1800
	21st to end	Night	6% 4 1 3 4 2 3 4 5% 7% 61%	2025
October	1st to 10th	Night	8% 4 3 5% 4 3 3 3 5% 6% 57%	2160
	11th to 20th	Night	7% 5% 2 6% 5% 3 5% 4 6% 6% 51%	2160
	21st to end	Night	12% 8% 2 5% 4 3 4 4 5% 6% 46%	2492
November	1st to 10th	Night	13% 7% 3 7% 7% 4 5% 5% 6% 8% 35%	2405
	11th to 20th	Night	13% 10% 6% 9% 7% 4 5% 6% 6% 6% 29%	2660
	21st to end	Night	10% 8% 5% 8% 5% 3 5% 6% 5% 8% 37%	2660
December	1st to 10th	Night	13% 10% 6% 9% 8% 5% 5% 5% 6% 6% 27%	2660
	11th to 20th	Night	13% 15% 5% 10% 9% 5% 6% 6% 6% 7% 19%	3276
	21st to end	Night	13% 12% 6% 12% 9% 5% 6% 5% 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	48% 8% 17% 18% 9%	1900
	11th to 20th	Day	51% 8% 13% 24% 5%	2085
	21st to end	Day	55% 10% 15% 16% 4	2416
April	1st to 10th	Day	47% 10% 17% 17% 9%	2185
	11th to 20th	Day	43% 9% 16% 16% 12% 3	2132
	21st to end	Day	35% 9% 16% 26% 11% 2	2268
May	1st to 10th	Day	32% 7% 15% 29% 16%	2520
	11th to 20th	Day	36% 8% 13% 26% 15% 1	2480
	21st to end	Day	38% 8% 16% 26% 12% 1	2724
June	1st to 10th	Day	37% 7% 14% 27% 13% 2	2520
	11th to 20th	Day	31% 7% 14% 33% 13% 3	2520
	21st to end	Day	17% 5% 12% 33% 24% 9%	2520
July	1st to 10th	Day	12% 4 10% 25% 30% 19%	2451
	11th to 20th	Day	13% 3 8% 17% 33% 27%	2445
	21st to end	Day	8% 2 5% 19% 40% 27%	2589
August	1st to 10th	Day	12% 3 9% 26% 34% 16%	2436
	11th to 20th	Day	11% 3 8% 24% 37% 16%	2295
	21st to end	Day	12% 4 8% 32% 33% 10%	2376
September	1st to 10th	Day	12% 3 9% 30% 29% 17%	2160
	11th to 20th	Day	24% 7% 11% 25% 23% 10%	2160
	21st to end	Day	28% 6% 14% 25% 20% 6%	1932
October	1st to 10th	Day	34% 6% 11% 25% 19% 5%	1800
	11th to 20th	Day	34% 10% 15% 24% 16% 2	1800
	21st to end	Day	42% 9% 13% 24% 11% 1	1864
November	1st to 10th	Day	50% 11% 14% 18% 7% 1	1670
	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	46% 10% 14% 20% 8% 1	2280
	11th to 20th	Night	41% 11% 16% 24% 7%	2094
	21st to end	Night	46% 12% 20% 16% 5%	2181
April	1st to 10th	Night	41% 10% 18% 22% 8% 1	1820
	11th to 20th	Night	38% 10% 19% 20% 10% 3	1779
	21st to end	Night	35% 10% 15% 25% 12% 3	1688
May	1st to 10th	Night	28% 8% 16% 34% 13% 1	1440
	11th to 20th	Night	31% 10% 17% 26% 14% 2	1416
	21st to end	Night	31% 11% 21% 25% 11% 1	1552
June	1st to 10th	Night	35% 9% 14% 28% 13% 2	1440
	11th to 20th	Night	26% 7% 15% 38% 12% 2	1440
	21st to end	Night	19% 5% 11% 35% 22% 8%	1440
July	1st to 10th	Night	11% 3 12% 27% 27% 21%	1400
	11th to 20th	Night	10% 4 10% 18% 31% 28%	1392
	21st to end	Night	8% 2 5% 16% 39% 30%	1488
August	1st to 10th	Night	12% 3 9% 24% 34% 17%	1476
	11th to 20th	Night	12% 3 7% 25% 36% 16%	1604
	21st to end	Night	11% 4 9% 29% 37% 10%	1980
September	1st to 10th	Night	10% 3 12% 29% 29% 17%	1800
	11th to 20th	Night	21% 6% 12% 26% 22% 13%	1800
	21st to end	Night	23% 5% 12% 28% 23% 8%	2025
October	1st to 10th	Night	29% 6% 11% 28% 22% 4	2160
	11th to 20th	Night	33% 8% 13% 24% 18% 4	2160
	21st to end	Night	38% 8% 12% 22% 18% 1	2492
November	1st to 10th	Night	45% 10% 13% 23% 8%	2405
	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% 17% 26% 22% 9% 3	429
	11th to 20th	Day	15% 19% 34% 18% 8% 5%	412
	21st to end	Day	11% 20% 30% 23% 13% 3	420
May	1st to 10th	Day	10% 18% 28% 26% 15% 3	423
	11th to 20th	Day	16% 15% 23% 28% 13% 5%	448
	21st to end	Day	13% 12% 25% 28% 18% 5%	485
June	1st to 10th	Day	11% 16% 26% 25% 17% 6%	450
	11th to 20th	Day	9% 21% 28% 26% 14% 3	450
	21st to end	Day	2 12% 27% 33% 22% 4	450
July	1st to 10th	Day	2 9% 30% 35% 22% 3	446
	11th to 20th	Day	1 12% 26% 33% 23% 4	444
	21st to end	Day	2 6% 26% 34% 25% 7%	487
August	1st to 10th	Day	2 9% 24% 29% 24% 12%	447
	11th to 20th	Day	2 7% 19% 31% 29% 12%	437
	21st to end	Day	3 10% 25% 29% 27% 6%	495
September	1st to 10th	Day	2 8% 25% 32% 25% 7%	450
	11th to 20th	Day	6% 8% 24% 33% 25% 4	450
	21st to end	Day	10% 12% 22% 30% 20% 5%	450
October	1st to 10th	Day	10% 11% 26% 31% 20% 3	450
	11th to 20th	Day	12% 12% 23% 26% 21% 5%	450
	21st to end	Day	15% 19% 26% 22% 12% 5%	379
November	1st to 10th	Day	16% 17% 29% 25% 11% 1	268
	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% 22% 34% 16% 2	728
	11th to 20th	Night	12% 13% 27% 29% 17% 3	711
	21st to end	Night	11% 9% 26% 35% 17% 2	608
May	1st to 10th	Night	7% 6% 23% 40% 23% 1	360
	11th to 20th	Night	11% 5% 14% 38% 29% 2	354
	21st to end	Night	6% 5% 18% 39% 28% 3	389
June	1st to 10th	Night	11% 6% 17% 43% 22% 1	360
	11th to 20th	Night	7% 8% 24% 43% 17% 1	360
	21st to end	Night	7% 2 18% 46% 27% 1	360
July	1st to 10th	Night	2 1 11% 52% 33% 1	350
	11th to 20th	Night	1 1 13% 57% 25% 2	348
	21st to end	Night	2 1 9% 54% 32% 2	394
August	1st to 10th	Night	2 1 9% 47% 36% 5%	410
	11th to 20th	Night	2 1 7% 38% 43% 9%	536
	21st to end	Night	3 3 16% 46% 28% 4	792
September	1st to 10th	Night	2 3 15% 45% 31% 4	720
	11th to 20th	Night	5% 2 14% 39% 34% 5%	720
	21st to end	Night	7% 4 14% 40% 30% 4	720
October	1st to 10th	Night	10% 3 20% 43% 23% 3	720
	11th to 20th	Night	8% 8% 18% 37% 24% 4	720
	21st to end	Night	15% 8% 23% 33% 18% 3	792
November	1st to 10th	Night	13% 10% 21% 39% 15% 1	740
	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 2024-03-31 03:08:51. Version ac07

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