Starry Kingdom Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starry Kingdom Observatory clear sky chart from 2005-11-06 to 2024-01-17.

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	12% 5% 2 4 3 2 3 3 4 6% 57%	74712
	Night	13% 6% 2 4 4 2 3 3 4 6% 53%	75125
Transparency	Day	30% 4 9% 21% 22% 14%	74431
	Night	34% 4 9% 19% 21% 13%	74928
Seeing	Day	15% 10% 24% 28% 17% 6%	14163
	Night	16% 5% 14% 29% 28% 8%	23437

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	25% 8% 4 7% 5% 3 5% 5% 5% 6% 28%	1610
	11th to 20th	Day	24% 7% 2 4 3 2 3 2 4 6% 42%	1675
	21st to end	Day	19% 9% 3 5% 5% 2 3 3 5% 7% 38%	1782
February	1st to 10th	Day	21% 8% 2 5% 5% 3 4 3 4 6% 41%	1620
	11th to 20th	Day	17% 8% 3 5% 5% 2 3 4 5% 7% 40%	1575
	21st to end	Day	21% 10% 3 4 4 3 3 3 5% 5% 38%	1474
March	1st to 10th	Day	25% 12% 3 6% 4 2 4 3 4 7% 30%	1980
	11th to 20th	Day	22% 9% 3 6% 5% 3 3 4 4 7% 34%	1980
	21st to end	Day	22% 8% 3 5% 4 3 5% 6% 4 7% 34%	2178
April	1st to 10th	Day	19% 8% 3 5% 5% 3 4 5% 6% 9% 32%	2142
	11th to 20th	Day	17% 7% 2 4 4 3 3 4 5% 7% 45%	2129
	21st to end	Day	9% 7% 2 4 3 2 4 3 6% 8% 52%	2219
May	1st to 10th	Day	8% 5% 2 4 3 2 3 3 4 8% 58%	2340
	11th to 20th	Day	8% 5% 2 4 4 3 3 4 5% 7% 54%	2339
	21st to end	Day	9% 4 2 4 4 2 3 4 5% 7% 57%	2723
June	1st to 10th	Day	8% 4 2 4 3 2 4 5% 6% 7% 57%	2520
	11th to 20th	Day	3 2 1 2 2 1 2 3 4 5% 76%	2520
	21st to end	Day	4 2 1 1 1 1 2 2 2 4 80%	2520
July	1st to 10th	Day	1 2 1 2 2 1 2 2 2 3 83%	2520
	11th to 20th	Day	2 1 1 1 1 1 2 2 5% 83%	2364
	21st to end	Day	1 1 1 1 1 2 1 2 3 87%	2546
August	1st to 10th	Day	1 1 2 2 1 2 2 3 4 83%	2328
	11th to 20th	Day	1 1 1 1 1 1 2 2 4 86%	2298
	21st to end	Day	1 1 1 2 1 2 2 2 4 83%	2379
September	1st to 10th	Day	1 1 1 1 1 2 2 2 4 84%	2160
	11th to 20th	Day	3 3 1 3 2 2 3 4 4 6% 69%	2097
	21st to end	Day	4 2 1 3 2 1 2 2 3 6% 74%	1928
October	1st to 10th	Day	7% 3 2 2 2 2 2 2 3 5% 70%	1800
	11th to 20th	Day	9% 4 1 3 3 2 4 4 4 7% 59%	1800
	21st to end	Day	11% 4 1 5% 4 2 2 3 4 6% 58%	1980
November	1st to 10th	Day	14% 6% 3 5% 4 3 4 3 5% 7% 45%	1850
	11th to 20th	Day	17% 6% 2 6% 5% 3 4 4 5% 8% 40%	1574
	21st to end	Day	15% 5% 2 5% 5% 3 4 4 5% 7% 46%	1520
December	1st to 10th	Day	20% 8% 2 5% 4 2 3 3 5% 5% 42%	1520
	11th to 20th	Day	32% 10% 3 7% 5% 2 4 4 4 6% 24%	1928
	21st to end	Day	24% 10% 3 6% 6% 3 4 4 6% 6% 29%	2794
January	1st to 10th	Night	23% 10% 3 5% 5% 2 5% 5% 5% 8% 29%	2551
	11th to 20th	Night	22% 8% 3 6% 4 3 4 3 4 6% 38%	2429
	21st to end	Night	19% 7% 2 5% 5% 3 3 4 5% 7% 40%	2574
February	1st to 10th	Night	18% 7% 3 5% 5% 2 4 4 4 6% 42%	2340
	11th to 20th	Night	17% 8% 3 5% 6% 3 5% 4 5% 6% 39%	2272
	21st to end	Night	19% 7% 2 5% 4 2 3 4 5% 7% 42%	1777
March	1st to 10th	Night	25% 12% 3 4 4 2 4 4 3 6% 32%	1980
	11th to 20th	Night	22% 9% 3 5% 5% 3 4 4 4 8% 35%	1980
	21st to end	Night	20% 9% 3 5% 4 3 4 4 5% 5% 40%	2178
April	1st to 10th	Night	16% 10% 3 6% 5% 3 4 5% 4 6% 37%	1818
	11th to 20th	Night	11% 8% 4 6% 4 2 3 4 4 8% 46%	1779
	21st to end	Night	9% 4 2 3 3 2 4 4 6% 7% 56%	1738
May	1st to 10th	Night	7% 5% 2 4 4 2 3 2 4 6% 62%	1620
	11th to 20th	Night	6% 4 2 4 4 3 4 3 5% 9% 57%	1550
	21st to end	Night	7% 4 1 4 4 2 3 4 4 8% 60%	1552
June	1st to 10th	Night	6% 5% 2 4 4 2 3 4 5% 8% 58%	1440
	11th to 20th	Night	4 2 1 2 2 1 1 2 3 4 78%	1440
	21st to end	Night	3 2 1 1 2 1 2 2 3 4 79%	1440
July	1st to 10th	Night	1 2 2 1 1 1 1 2 4 85%	1440
	11th to 20th	Night	1 1 1 2 2 1 1 1 2 3 86%	1592
	21st to end	Night	1 1 1 1 1 2 3 3 88%	1773
August	1st to 10th	Night	1 1 1 1 1 2 1 3 4 85%	1611
	11th to 20th	Night	1 1 1 1 1 2 2 2 3 86%	1602
	21st to end	Night	1 1 1 1 1 1 1 2 4 86%	1975
September	1st to 10th	Night	1 1 1 1 1 1 1 3 4 86%	1800
	11th to 20th	Night	4 3 1 2 2 2 2 3 4 6% 71%	1860
	21st to end	Night	4 3 1 3 3 2 2 2 4 5% 73%	2030
October	1st to 10th	Night	6% 4 2 3 2 2 2 2 3 5% 70%	2160
	11th to 20th	Night	8% 3 1 5% 4 3 3 4 4 4 61%	2160
	21st to end	Night	10% 4 1 4 4 2 3 3 4 6% 58%	2376
November	1st to 10th	Night	14% 6% 3 5% 6% 3 4 4 5% 7% 44%	2227
	11th to 20th	Night	15% 6% 3 6% 5% 3 5% 5% 6% 7% 38%	2603
	21st to end	Night	13% 6% 3 5% 5% 2 4 4 4 7% 46%	2660
December	1st to 10th	Night	23% 5% 3 5% 4 2 3 4 5% 7% 39%	2660
	11th to 20th	Night	34% 9% 3 5% 3 2 3 4 5% 6% 26%	3276
	21st to end	Night	25% 10% 3 7% 5% 3 4 4 4 6% 28%	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	56% 5% 9% 16% 8% 6%	1610
	11th to 20th	Day	45% 3 11% 12% 15% 14%	1675
	21st to end	Day	47% 3 7% 14% 18% 10%	1782
February	1st to 10th	Day	46% 3 9% 16% 17% 9%	1620
	11th to 20th	Day	42% 5% 8% 20% 21% 5%	1584
	21st to end	Day	47% 4 11% 19% 14% 5%	1474
March	1st to 10th	Day	56% 5% 9% 14% 13% 3	1980
	11th to 20th	Day	50% 4 11% 17% 14% 4	1980
	21st to end	Day	50% 6% 11% 18% 13% 3	2178
April	1st to 10th	Day	48% 5% 12% 20% 13% 2	2142
	11th to 20th	Day	39% 6% 14% 22% 15% 5%	2132
	21st to end	Day	31% 4 16% 26% 18% 4	2219
May	1st to 10th	Day	25% 4 14% 32% 19% 7%	2340
	11th to 20th	Day	29% 5% 12% 30% 18% 6%	2342
	21st to end	Day	28% 5% 15% 36% 14% 2	2724
June	1st to 10th	Day	27% 6% 13% 27% 23% 5%	2520
	11th to 20th	Day	12% 3 12% 27% 33% 14%	2520
	21st to end	Day	12% 2 5% 23% 37% 21%	2520
July	1st to 10th	Day	9% 2 4 18% 34% 33%	2451
	11th to 20th	Day	8% 2 6% 18% 30% 36%	2293
	21st to end	Day	6% 2 3 14% 36% 40%	2405
August	1st to 10th	Day	9% 2 5% 25% 34% 25%	2312
	11th to 20th	Day	6% 2 4 20% 40% 28%	2298
	21st to end	Day	7% 2 6% 22% 36% 27%	2379
September	1st to 10th	Day	7% 1 4 16% 32% 39%	2160
	11th to 20th	Day	17% 3 9% 27% 33% 12%	2097
	21st to end	Day	13% 3 7% 24% 29% 25%	1928
October	1st to 10th	Day	20% 3 5% 24% 26% 23%	1800
	11th to 20th	Day	27% 4 8% 17% 26% 19%	1800
	21st to end	Day	29% 3 8% 21% 23% 16%	1980
November	1st to 10th	Day	38% 5% 9% 22% 17% 9%	1850
	11th to 20th	Day	41% 5% 11% 16% 17% 9%	1574
	21st to end	Day	37% 4 11% 16% 19% 13%	1520
December	1st to 10th	Day	44% 4 7% 17% 15% 13%	1520
	11th to 20th	Day	63% 3 6% 12% 12% 4	1928
	21st to end	Day	55% 5% 8% 19% 9% 4	2794
January	1st to 10th	Night	54% 5% 12% 15% 9% 6%	2551
	11th to 20th	Night	48% 5% 9% 13% 12% 13%	2429
	21st to end	Night	45% 5% 8% 14% 19% 10%	2574
February	1st to 10th	Night	44% 3 8% 18% 18% 10%	2340
	11th to 20th	Night	46% 4 8% 18% 17% 6%	2274
	21st to end	Night	41% 5% 13% 20% 16% 4	1777
March	1st to 10th	Night	55% 5% 8% 16% 14% 2	1980
	11th to 20th	Night	49% 4 10% 19% 14% 5%	1980
	21st to end	Night	46% 5% 16% 19% 11% 3	2178
April	1st to 10th	Night	46% 6% 13% 21% 11% 4	1818
	11th to 20th	Night	36% 5% 15% 23% 17% 5%	1779
	21st to end	Night	26% 5% 16% 30% 19% 3	1738
May	1st to 10th	Night	24% 3 12% 27% 27% 6%	1620
	11th to 20th	Night	26% 4 15% 29% 19% 6%	1551
	21st to end	Night	25% 5% 18% 34% 17% 2	1552
June	1st to 10th	Night	26% 6% 14% 27% 21% 5%	1440
	11th to 20th	Night	12% 2 10% 26% 34% 16%	1440
	21st to end	Night	13% 1 7% 18% 37% 24%	1440
July	1st to 10th	Night	7% 1 4 16% 38% 33%	1400
	11th to 20th	Night	7% 2 5% 14% 33% 38%	1540
	21st to end	Night	5% 1 4 14% 33% 43%	1674
August	1st to 10th	Night	7% 2 6% 23% 37% 25%	1602
	11th to 20th	Night	6% 2 4 22% 31% 35%	1602
	21st to end	Night	7% 1 5% 24% 30% 32%	1975
September	1st to 10th	Night	6% 1 3 18% 33% 38%	1800
	11th to 20th	Night	16% 3 7% 27% 38% 10%	1860
	21st to end	Night	16% 2 8% 20% 29% 25%	2030
October	1st to 10th	Night	20% 3 6% 23% 24% 25%	2160
	11th to 20th	Night	26% 4 6% 18% 31% 14%	2160
	21st to end	Night	28% 4 8% 23% 20% 17%	2376
November	1st to 10th	Night	40% 5% 11% 16% 17% 10%	2227
	11th to 20th	Night	42% 6% 13% 16% 17% 6%	2603
	21st to end	Night	38% 4 10% 17% 20% 12%	2660
December	1st to 10th	Night	45% 4 8% 16% 18% 9%	2660
	11th to 20th	Night	59% 4 7% 13% 13% 5%	3276
	21st to end	Night	56% 5% 9% 17% 9% 3	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	37% 15% 21% 17% 9% 1	271
	11th to 20th	Day	31% 9% 24% 18% 15% 3	359
	21st to end	Day	25% 11% 20% 24% 16% 4	374
February	1st to 10th	Day	25% 12% 21% 23% 16% 4	340
	11th to 20th	Day	30% 15% 22% 22% 10% 1	335
	21st to end	Day	27% 13% 29% 21% 8% 2	334
March	1st to 10th	Day	37% 15% 26% 14% 6% 1	420
	11th to 20th	Day	30% 14% 27% 19% 8% 2	420
	21st to end	Day	28% 18% 27% 18% 8% 1	462
April	1st to 10th	Day	25% 19% 28% 19% 6% 2	420
	11th to 20th	Day	26% 14% 28% 21% 9% 2	412
	21st to end	Day	14% 22% 30% 21% 9% 4	420
May	1st to 10th	Day	15% 18% 27% 26% 11% 4	423
	11th to 20th	Day	20% 14% 24% 27% 9% 7%	448
	21st to end	Day	14% 13% 27% 27% 13% 6%	485
June	1st to 10th	Day	13% 10% 26% 30% 16% 5%	450
	11th to 20th	Day	9% 13% 31% 29% 14% 4	450
	21st to end	Day	2 6% 27% 37% 20% 9%	450
July	1st to 10th	Day	3 5% 27% 40% 19% 7%	446
	11th to 20th	Day	1 2 20% 44% 22% 10%	444
	21st to end	Day	1 1 16% 46% 24% 12%	487
August	1st to 10th	Day	2 3 22% 41% 22% 10%	447
	11th to 20th	Day	1 2 24% 38% 23% 11%	437
	21st to end	Day	1 3 21% 42% 25% 8%	495
September	1st to 10th	Day	2 6% 22% 37% 26% 8%	450
	11th to 20th	Day	5% 6% 24% 36% 23% 6%	450
	21st to end	Day	7% 9% 22% 32% 24% 6%	450
October	1st to 10th	Day	9% 9% 23% 26% 25% 8%	450
	11th to 20th	Day	11% 7% 19% 22% 30% 9%	450
	21st to end	Day	14% 9% 19% 29% 22% 7%	495
November	1st to 10th	Day	17% 11% 21% 24% 19% 8%	446
	11th to 20th	Day	16% 6% 16% 28% 24% 10%	205
	21st to end	Day	17% 6% 21% 29% 23% 4	180
December	1st to 10th	Day	27% 11% 20% 18% 14% 10%	180
	11th to 20th	Day	31% 12% 15% 22% 13% 7%	180
	21st to end	Day	25% 13% 20% 22% 17% 4	198
January	1st to 10th	Night	29% 7% 14% 27% 19% 4	760
	11th to 20th	Night	26% 5% 17% 29% 17% 7%	748
	21st to end	Night	24% 4 15% 30% 21% 5%	792
February	1st to 10th	Night	23% 7% 15% 32% 21% 3	720
	11th to 20th	Night	23% 7% 19% 25% 21% 5%	704
	21st to end	Night	24% 8% 20% 33% 13% 2	592
March	1st to 10th	Night	31% 10% 16% 28% 12% 3	720
	11th to 20th	Night	28% 6% 13% 30% 20% 3	720
	21st to end	Night	26% 10% 19% 28% 14% 3	792
April	1st to 10th	Night	22% 8% 22% 28% 17% 3	720
	11th to 20th	Night	17% 11% 21% 28% 19% 5%	711
	21st to end	Night	11% 6% 23% 31% 24% 5%	658
May	1st to 10th	Night	9% 7% 22% 26% 29% 6%	540
	11th to 20th	Night	9% 2 16% 30% 36% 8%	488
	21st to end	Night	9% 7% 17% 30% 30% 7%	389
June	1st to 10th	Night	8% 4 16% 39% 27% 6%	360
	11th to 20th	Night	3 6% 18% 38% 32% 3	360
	21st to end	Night	4 1 5% 39% 43% 8%	360
July	1st to 10th	Night	2 8% 30% 51% 9%	350
	11th to 20th	Night	2 1 3 27% 50% 17%	496
	21st to end	Night	1 2 20% 57% 21%	591
August	1st to 10th	Night	2 3 26% 52% 18%	537
	11th to 20th	Night	1 1 3 28% 50% 17%	534
	21st to end	Night	2 1 4 28% 52% 13%	787
September	1st to 10th	Night	1 2 8% 30% 46% 13%	720
	11th to 20th	Night	6% 2 10% 33% 36% 13%	720
	21st to end	Night	5% 4 13% 29% 36% 14%	720
October	1st to 10th	Night	7% 4 14% 32% 34% 9%	720
	11th to 20th	Night	11% 2 11% 29% 36% 11%	720
	21st to end	Night	14% 4 11% 30% 30% 12%	792
November	1st to 10th	Night	17% 5% 15% 26% 28% 8%	740
	11th to 20th	Night	19% 5% 14% 36% 22% 5%	760
	21st to end	Night	16% 7% 17% 33% 21% 7%	760
December	1st to 10th	Night	26% 5% 16% 29% 19% 6%	760
	11th to 20th	Night	31% 6% 14% 31% 14% 4	760
	21st to end	Night	30% 9% 17% 25% 16% 3	836

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