Wilderness Skies Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wilderness Skies Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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	17% 10% 4 6% 6% 3 5% 4 5% 7% 33%	74603
	Night	17% 10% 4 6% 5% 3 4 4 5% 7% 35%	75197
Transparency	Day	50% 6% 11% 20% 12% 2	74324
	Night	50% 6% 11% 20% 12% 2	74995
Seeing	Day	24% 13% 26% 21% 12% 4	13677
	Night	22% 11% 25% 27% 13% 2	23749

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	19% 15% 7% 11% 7% 3 4 4 4 5% 22%	1706
	11th to 20th	Day	20% 19% 6% 10% 6% 4 4 3 4 5% 18%	1671
	21st to end	Day	20% 19% 8% 9% 6% 3 3 4 4 4 21%	1782
February	1st to 10th	Day	24% 15% 5% 8% 6% 3 4 3 4 5% 23%	1620
	11th to 20th	Day	19% 13% 5% 12% 7% 3 3 4 4 7% 24%	1609
	21st to end	Day	21% 14% 5% 8% 6% 2 3 4 5% 5% 27%	1484
March	1st to 10th	Day	17% 11% 5% 7% 5% 3 3 4 5% 5% 35%	1980
	11th to 20th	Day	20% 12% 4 7% 6% 3 4 5% 5% 5% 30%	1980
	21st to end	Day	22% 10% 4 7% 6% 3 4 4 5% 6% 29%	2178
April	1st to 10th	Day	16% 11% 4 7% 6% 3 5% 5% 5% 6% 33%	2034
	11th to 20th	Day	17% 9% 2 6% 6% 3 4 5% 5% 7% 35%	2192
	21st to end	Day	21% 9% 4 5% 5% 3 4 4 6% 7% 32%	2340
May	1st to 10th	Day	19% 8% 3 6% 6% 4 5% 5% 5% 7% 31%	2340
	11th to 20th	Day	21% 8% 3 6% 6% 4 5% 4 6% 7% 30%	2301
	21st to end	Day	12% 6% 2 5% 6% 4 6% 6% 6% 10% 37%	2531
June	1st to 10th	Day	14% 6% 3 5% 6% 4 5% 5% 7% 8% 38%	2466
	11th to 20th	Day	14% 6% 3 5% 6% 4 6% 5% 7% 9% 35%	2520
	21st to end	Day	14% 5% 3 5% 6% 4 6% 5% 7% 10% 35%	2406
July	1st to 10th	Day	12% 6% 3 5% 6% 4 6% 5% 7% 9% 36%	2340
	11th to 20th	Day	12% 6% 3 5% 5% 4 7% 5% 6% 9% 38%	2340
	21st to end	Day	14% 6% 3 5% 5% 4 6% 6% 7% 8% 35%	2547
August	1st to 10th	Day	11% 6% 3 6% 6% 5% 6% 7% 8% 11% 33%	2327
	11th to 20th	Day	11% 6% 2 6% 6% 4 6% 6% 7% 10% 34%	2303
	21st to end	Day	12% 5% 2 5% 5% 3 5% 6% 7% 9% 41%	2476
September	1st to 10th	Day	17% 5% 2 4 5% 2 4 3 6% 7% 45%	2099
	11th to 20th	Day	11% 5% 3 4 4 3 5% 4 6% 8% 46%	1980
	21st to end	Day	19% 7% 3 6% 5% 3 4 4 4 7% 39%	1980
October	1st to 10th	Day	15% 7% 3 5% 5% 4 4 4 6% 8% 40%	1835
	11th to 20th	Day	17% 8% 3 6% 5% 4 5% 4 5% 5% 39%	1800
	21st to end	Day	24% 9% 3 5% 4 2 3 4 4 6% 36%	1980
November	1st to 10th	Day	12% 9% 3 5% 4 4 4 4 4 5% 47%	1762
	11th to 20th	Day	17% 13% 4 6% 4 2 4 3 5% 6% 34%	1710
	21st to end	Day	19% 12% 5% 6% 6% 2 5% 4 4 6% 31%	1528
December	1st to 10th	Day	24% 14% 8% 8% 5% 3 4 3 4 6% 20%	1520
	11th to 20th	Day	21% 16% 6% 8% 5% 2 3 3 5% 5% 24%	1910
	21st to end	Day	25% 19% 5% 9% 6% 3 4 4 4 6% 16%	3026
January	1st to 10th	Night	19% 15% 7% 8% 7% 4 4 4 4 4 23%	2459
	11th to 20th	Night	23% 16% 6% 10% 6% 4 5% 4 3 4 20%	2417
	21st to end	Night	19% 15% 6% 11% 7% 3 4 3 3 5% 24%	2574
February	1st to 10th	Night	22% 13% 4 9% 6% 4 4 4 3 5% 25%	2340
	11th to 20th	Night	23% 12% 4 9% 6% 4 4 4 5% 4 25%	2233
	21st to end	Night	23% 15% 5% 6% 4 3 4 4 4 4 27%	1772
March	1st to 10th	Night	17% 10% 5% 7% 5% 3 4 4 4 5% 36%	1980
	11th to 20th	Night	20% 10% 4 6% 6% 2 4 4 5% 6% 33%	1980
	21st to end	Night	21% 9% 4 7% 5% 3 4 3 4 5% 35%	2178
April	1st to 10th	Night	19% 9% 3 5% 5% 2 4 4 4 8% 36%	1926
	11th to 20th	Night	17% 8% 2 4 4 4 4 5% 5% 8% 38%	1732
	21st to end	Night	17% 8% 3 6% 5% 3 4 4 5% 7% 38%	1620
May	1st to 10th	Night	18% 8% 3 5% 6% 3 6% 6% 5% 8% 33%	1620
	11th to 20th	Night	17% 8% 3 6% 6% 3 5% 4 5% 7% 36%	1592
	21st to end	Night	10% 6% 2 6% 5% 3 4 5% 7% 10% 41%	1744
June	1st to 10th	Night	10% 6% 3 6% 5% 3 4 5% 5% 8% 46%	1486
	11th to 20th	Night	10% 6% 2 5% 5% 4 5% 5% 7% 11% 39%	1440
	21st to end	Night	13% 4 2 4 5% 2 5% 5% 7% 9% 44%	1546
July	1st to 10th	Night	10% 5% 3 6% 5% 3 5% 5% 7% 9% 41%	1620
	11th to 20th	Night	9% 5% 2 5% 6% 3 4 5% 5% 9% 46%	1620
	21st to end	Night	11% 5% 2 5% 6% 3 5% 6% 6% 9% 42%	1771
August	1st to 10th	Night	7% 6% 2 6% 6% 4 6% 7% 8% 9% 41%	1611
	11th to 20th	Night	10% 6% 3 5% 5% 3 5% 5% 6% 8% 43%	1598
	21st to end	Night	9% 5% 2 5% 5% 3 4 5% 5% 9% 48%	1862
September	1st to 10th	Night	13% 5% 2 4 5% 3 4 4 4 7% 48%	1858
	11th to 20th	Night	10% 5% 2 3 4 2 4 4 4 8% 54%	1980
	21st to end	Night	16% 6% 3 5% 4 3 5% 5% 5% 6% 42%	1980
October	1st to 10th	Night	14% 5% 2 5% 6% 3 3 5% 4 7% 45%	2124
	11th to 20th	Night	17% 7% 2 5% 5% 3 3 3 6% 7% 41%	2160
	21st to end	Night	24% 7% 3 5% 4 3 4 3 3 5% 39%	2376
November	1st to 10th	Night	13% 7% 3 5% 5% 2 4 3 5% 6% 47%	2311
	11th to 20th	Night	17% 11% 4 6% 5% 3 5% 4 5% 6% 34%	2470
	21st to end	Night	20% 10% 4 7% 6% 3 5% 4 4 5% 31%	2648
December	1st to 10th	Night	23% 14% 7% 8% 5% 3 5% 4 4 5% 23%	2660
	11th to 20th	Night	19% 17% 7% 7% 5% 3 4 3 4 6% 25%	3285
	21st to end	Night	23% 18% 6% 7% 6% 3 5% 4 4 5% 19%	4624

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	66% 6% 8% 14% 6%	1707
	11th to 20th	Day	69% 4 11% 13% 3	1671
	21st to end	Day	68% 3 9% 14% 6% 1	1782
February	1st to 10th	Day	65% 4 10% 14% 6% 1	1620
	11th to 20th	Day	62% 5% 9% 16% 8%	1618
	21st to end	Day	60% 4 9% 16% 9% 2	1484
March	1st to 10th	Day	51% 4 11% 23% 11% 1	1980
	11th to 20th	Day	55% 5% 9% 18% 11% 1	1980
	21st to end	Day	57% 4 9% 17% 12% 2	2178
April	1st to 10th	Day	52% 5% 10% 18% 12% 3	2034
	11th to 20th	Day	49% 6% 10% 14% 18% 3	2192
	21st to end	Day	50% 6% 10% 20% 12% 2	2340
May	1st to 10th	Day	52% 7% 10% 20% 10% 2	2340
	11th to 20th	Day	53% 6% 12% 16% 11% 1	2305
	21st to end	Day	41% 10% 17% 22% 10% 1	2531
June	1st to 10th	Day	41% 9% 13% 22% 13% 1	2466
	11th to 20th	Day	44% 9% 14% 21% 12% 1	2520
	21st to end	Day	42% 8% 14% 22% 12% 1	2406
July	1st to 10th	Day	44% 9% 12% 19% 14% 2	2275
	11th to 20th	Day	42% 8% 11% 22% 16% 1	2271
	21st to end	Day	43% 8% 12% 24% 12% 2	2405
August	1st to 10th	Day	42% 10% 14% 23% 11% 1	2314
	11th to 20th	Day	42% 9% 12% 26% 11%	2303
	21st to end	Day	38% 8% 14% 22% 14% 4	2476
September	1st to 10th	Day	38% 5% 10% 21% 21% 4	2099
	11th to 20th	Day	34% 6% 13% 30% 15% 2	1980
	21st to end	Day	46% 5% 9% 21% 17% 1	1980
October	1st to 10th	Day	42% 6% 12% 22% 17% 1	1835
	11th to 20th	Day	46% 6% 10% 25% 13%	1800
	21st to end	Day	50% 4 10% 22% 14% 1	1980
November	1st to 10th	Day	40% 5% 9% 26% 17% 4	1762
	11th to 20th	Day	50% 4 10% 20% 14% 3	1710
	21st to end	Day	55% 4 10% 19% 11% 1	1528
December	1st to 10th	Day	67% 4 9% 15% 5% 1	1520
	11th to 20th	Day	63% 4 9% 19% 5%	1906
	21st to end	Day	69% 6% 10% 11% 4	3026
January	1st to 10th	Night	65% 4 8% 14% 8% 1	2459
	11th to 20th	Night	69% 4 10% 13% 3	2417
	21st to end	Night	64% 4 9% 17% 6% 1	2574
February	1st to 10th	Night	62% 4 10% 17% 7% 1	2340
	11th to 20th	Night	63% 4 8% 16% 8%	2235
	21st to end	Night	60% 5% 8% 16% 8% 3	1772
March	1st to 10th	Night	50% 4 8% 24% 13% 1	1980
	11th to 20th	Night	53% 5% 9% 22% 11% 1	1980
	21st to end	Night	53% 4 8% 19% 13% 4	2178
April	1st to 10th	Night	48% 5% 10% 20% 15% 2	1926
	11th to 20th	Night	44% 5% 11% 19% 16% 5%	1732
	21st to end	Night	46% 5% 11% 19% 15% 3	1620
May	1st to 10th	Night	48% 8% 12% 18% 11% 4	1620
	11th to 20th	Night	46% 8% 11% 19% 13% 3	1593
	21st to end	Night	37% 9% 16% 25% 11% 1	1745
June	1st to 10th	Night	37% 8% 10% 25% 17% 2	1486
	11th to 20th	Night	38% 9% 12% 23% 15% 3	1440
	21st to end	Night	35% 9% 15% 22% 17% 2	1546
July	1st to 10th	Night	38% 9% 13% 21% 17% 3	1575
	11th to 20th	Night	34% 8% 14% 22% 19% 3	1566
	21st to end	Night	35% 10% 14% 23% 16% 2	1672
August	1st to 10th	Night	35% 11% 15% 25% 14% 1	1600
	11th to 20th	Night	37% 8% 13% 24% 16% 2	1598
	21st to end	Night	33% 7% 12% 27% 16% 5%	1862
September	1st to 10th	Night	35% 7% 13% 19% 20% 6%	1858
	11th to 20th	Night	29% 6% 14% 26% 24% 2	1980
	21st to end	Night	41% 6% 10% 21% 20% 2	1980
October	1st to 10th	Night	39% 6% 11% 24% 17% 3	2124
	11th to 20th	Night	42% 4 11% 24% 17% 1	2160
	21st to end	Night	48% 4 8% 22% 15% 3	2376
November	1st to 10th	Night	39% 4 11% 23% 19% 5%	2311
	11th to 20th	Night	51% 4 9% 20% 14% 2	2470
	21st to end	Night	54% 5% 10% 20% 11% 1	2648
December	1st to 10th	Night	64% 4 9% 17% 5% 1	2660
	11th to 20th	Night	61% 5% 11% 16% 6%	3288
	21st to end	Night	68% 4 9% 13% 5%	4624

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	34% 27% 25% 10% 4	270
	11th to 20th	Day	38% 24% 28% 9%	257
	21st to end	Day	36% 30% 25% 7% 1 2	264
February	1st to 10th	Day	43% 18% 31% 6% 1	240
	11th to 20th	Day	42% 29% 25% 4	240
	21st to end	Day	39% 23% 33% 5%	202
March	1st to 10th	Day	30% 22% 30% 15% 3	420
	11th to 20th	Day	34% 18% 31% 11% 5% 1	420
	21st to end	Day	32% 18% 29% 16% 4	462
April	1st to 10th	Day	28% 19% 27% 19% 6% 1	420
	11th to 20th	Day	24% 21% 27% 16% 8% 3	412
	21st to end	Day	32% 16% 28% 16% 5% 2	420
May	1st to 10th	Day	27% 22% 25% 15% 9% 3	423
	11th to 20th	Day	23% 14% 28% 21% 11% 3	447
	21st to end	Day	16% 7% 27% 27% 18% 5%	485
June	1st to 10th	Day	14% 8% 26% 32% 15% 5%	450
	11th to 20th	Day	21% 9% 24% 26% 16% 5%	450
	21st to end	Day	14% 9% 31% 29% 14% 4	450
July	1st to 10th	Day	16% 4 20% 27% 20% 13%	445
	11th to 20th	Day	12% 6% 25% 30% 18% 10%	444
	21st to end	Day	18% 4 24% 26% 20% 8%	488
August	1st to 10th	Day	13% 6% 20% 31% 20% 10%	446
	11th to 20th	Day	15% 5% 21% 29% 19% 11%	439
	21st to end	Day	13% 4 22% 28% 21% 11%	495
September	1st to 10th	Day	17% 6% 19% 27% 21% 9%	450
	11th to 20th	Day	12% 4 16% 29% 29% 9%	450
	21st to end	Day	22% 10% 24% 25% 15% 4	450
October	1st to 10th	Day	16% 9% 27% 26% 18% 4	450
	11th to 20th	Day	22% 13% 29% 25% 9% 1	450
	21st to end	Day	31% 15% 27% 18% 8% 1	495
November	1st to 10th	Day	21% 14% 31% 21% 9% 3	360
	11th to 20th	Day	33% 15% 27% 18% 5% 1	270
	21st to end	Day	27% 19% 38% 14% 1 1	183
December	1st to 10th	Day	34% 22% 29% 10% 3 1	180
	11th to 20th	Day	34% 23% 27% 12% 4	180
	21st to end	Day	39% 23% 21% 12% 4	270
January	1st to 10th	Night	29% 22% 28% 17% 4	760
	11th to 20th	Night	35% 16% 29% 18% 3	744
	21st to end	Night	29% 19% 31% 18% 2	792
February	1st to 10th	Night	32% 17% 26% 24% 2	720
	11th to 20th	Night	33% 18% 34% 15% 1	703
	21st to end	Night	32% 20% 29% 17% 2	592
March	1st to 10th	Night	25% 18% 31% 22% 4	720
	11th to 20th	Night	28% 16% 29% 19% 7% 1	720
	21st to end	Night	27% 16% 32% 20% 5% 1	792
April	1st to 10th	Night	27% 14% 29% 24% 6%	720
	11th to 20th	Night	22% 14% 31% 22% 10% 1	668
	21st to end	Night	20% 9% 36% 28% 7%	540
May	1st to 10th	Night	22% 8% 30% 26% 13% 1	540
	11th to 20th	Night	20% 7% 28% 31% 13% 1	531
	21st to end	Night	12% 4 22% 35% 24% 4	584
June	1st to 10th	Night	12% 3 26% 40% 17% 1	406
	11th to 20th	Night	11% 6% 24% 37% 21% 2	360
	21st to end	Night	12% 5% 19% 40% 24%	466
July	1st to 10th	Night	12% 3 17% 36% 27% 6%	525
	11th to 20th	Night	8% 4 17% 34% 32% 5%	522
	21st to end	Night	13% 4 14% 35% 32% 3	591
August	1st to 10th	Night	8% 1 14% 39% 34% 3	537
	11th to 20th	Night	12% 3 13% 35% 32% 5%	534
	21st to end	Night	12% 3 16% 35% 28% 7%	674
September	1st to 10th	Night	15% 4 15% 33% 27% 6%	720
	11th to 20th	Night	12% 3 19% 31% 31% 4	720
	21st to end	Night	18% 8% 19% 32% 19% 4	720
October	1st to 10th	Night	18% 5% 22% 29% 23% 3	720
	11th to 20th	Night	23% 9% 27% 30% 11% 1	720
	21st to end	Night	27% 11% 23% 30% 9%	792
November	1st to 10th	Night	17% 9% 27% 32% 15%	740
	11th to 20th	Night	28% 13% 26% 24% 8% 1	760
	21st to end	Night	26% 14% 27% 26% 7% 1	760
December	1st to 10th	Night	33% 16% 27% 21% 4	760
	11th to 20th	Night	29% 17% 27% 23% 5%	760
	21st to end	Night	31% 15% 29% 23% 2	836

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