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 2026-04-02.

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	16% 10% 4 8% 5% 5% 5% 4 6% 7% 32%	131019
	Night	17% 11% 4 9% 5% 4 4 3 5% 6% 32%	130786
Transparency	Day	50% 6% 10% 21% 12% 2	134637
	Night	51% 5% 10% 20% 12% 2	135225
Seeing	Day	24% 14% 26% 21% 11% 4	16563
	Night	22% 11% 25% 27% 13% 1	26668

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% 19% 7% 17% 4 3 3 2 4 5% 18%	5258
	11th to 20th	Day	13% 21% 7% 15% 10% 5% 4 2 2 3 17%	5280
	21st to end	Day	18% 17% 6% 11% 7% 6% 5% 4 4 4 18%	5780
February	1st to 10th	Day	22% 15% 4 8% 5% 5% 4 3 4 5% 26%	1890
	11th to 20th	Day	19% 14% 5% 12% 5% 4 3 3 4 6% 24%	1886
	21st to end	Day	20% 15% 4 9% 5% 3 4 3 5% 5% 29%	1735
March	1st to 10th	Day	18% 16% 5% 7% 4 3 3 3 4 5% 32%	5045
	11th to 20th	Day	14% 8% 3 6% 5% 4 4 3 5% 7% 40%	5090
	21st to end	Day	19% 9% 3 8% 5% 4 5% 4 6% 7% 30%	5586
April	1st to 10th	Day	18% 12% 3 8% 5% 4 5% 4 5% 6% 31%	2271
	11th to 20th	Day	16% 10% 2 7% 5% 4 5% 4 5% 6% 35%	2440
	21st to end	Day	20% 9% 3 6% 4 4 4 4 6% 7% 33%	2600
May	1st to 10th	Day	19% 9% 3 8% 6% 5% 5% 4 6% 7% 26%	5862
	11th to 20th	Day	18% 9% 3 7% 5% 5% 5% 4 6% 8% 29%	5861
	21st to end	Day	18% 7% 3 6% 5% 5% 5% 4 7% 9% 31%	6433
June	1st to 10th	Day	13% 6% 3 6% 5% 5% 5% 4 7% 9% 37%	2740
	11th to 20th	Day	14% 6% 3 7% 5% 6% 5% 4 7% 9% 35%	2800
	21st to end	Day	13% 6% 2 6% 5% 5% 6% 4 7% 10% 36%	2672
July	1st to 10th	Day	9% 6% 3 7% 5% 6% 5% 4 6% 9% 41%	5900
	11th to 20th	Day	13% 7% 3 7% 5% 6% 6% 5% 7% 9% 33%	5900
	21st to end	Day	13% 8% 3 7% 5% 5% 5% 5% 6% 8% 36%	6424
August	1st to 10th	Day	11% 7% 3 8% 5% 5% 6% 5% 7% 9% 34%	4234
	11th to 20th	Day	10% 6% 2 7% 5% 5% 6% 5% 7% 9% 38%	4174
	21st to end	Day	7% 4 1 5% 4 5% 5% 5% 8% 9% 46%	4487
September	1st to 10th	Day	16% 5% 2 5% 4 3 3 3 6% 7% 47%	2331
	11th to 20th	Day	10% 6% 2 5% 4 4 4 3 6% 8% 47%	2200
	21st to end	Day	20% 8% 3 7% 4 4 4 3 4 6% 37%	2200
October	1st to 10th	Day	14% 6% 2 5% 4 5% 3 3 6% 7% 44%	2038
	11th to 20th	Day	16% 8% 3 7% 4 5% 5% 3 5% 5% 40%	2000
	21st to end	Day	22% 9% 3 6% 4 3 3 3 4 6% 37%	2200
November	1st to 10th	Day	12% 10% 2 5% 4 4 4 3 4 5% 47%	1952
	11th to 20th	Day	17% 14% 3 7% 4 2 4 3 6% 6% 34%	1890
	21st to end	Day	19% 14% 5% 8% 5% 4 4 3 5% 5% 29%	1688
December	1st to 10th	Day	21% 12% 6% 15% 5% 4 3 2 4 5% 23%	2680
	11th to 20th	Day	25% 16% 5% 9% 4 3 3 2 4 5% 22%	3070
	21st to end	Day	23% 18% 4 11% 5% 4 5% 3 4 5% 17%	4422
January	1st to 10th	Night	17% 17% 8% 17% 6% 4 4 3 4 4 17%	7635
	11th to 20th	Night	16% 18% 8% 14% 7% 5% 4 2 3 3 19%	7680
	21st to end	Night	19% 14% 5% 12% 6% 7% 3 2 3 4 25%	8401
February	1st to 10th	Night	20% 14% 4 10% 5% 5% 4 3 3 6% 27%	2730
	11th to 20th	Night	22% 14% 4 10% 5% 5% 4 3 5% 4 25%	2616
	21st to end	Night	21% 15% 5% 8% 4 4 4 3 4 4 28%	2071
March	1st to 10th	Night	21% 12% 3 7% 4 4 3 2 4 5% 34%	5028
	11th to 20th	Night	12% 10% 4 7% 5% 3 3 4 5% 7% 41%	5090
	21st to end	Night	17% 9% 3 8% 5% 5% 5% 3 5% 5% 35%	5588
April	1st to 10th	Night	19% 12% 3 6% 4 3 4 3 4 7% 33%	2152
	11th to 20th	Night	17% 9% 2 5% 4 5% 4 4 6% 8% 37%	1926
	21st to end	Night	16% 8% 3 8% 4 4 4 3 5% 7% 38%	1800
May	1st to 10th	Night	26% 11% 3 7% 5% 4 4 4 5% 7% 24%	4033
	11th to 20th	Night	16% 8% 3 7% 4 4 4 4 6% 9% 36%	4032
	21st to end	Night	19% 9% 3 8% 4 4 4 3 6% 8% 33%	4421
June	1st to 10th	Night	10% 8% 2 7% 4 4 4 3 5% 8% 45%	1650
	11th to 20th	Night	11% 6% 2 6% 5% 6% 5% 3 7% 11% 39%	1600
	21st to end	Night	12% 5% 2 5% 4 4 5% 4 7% 9% 43%	1718
July	1st to 10th	Night	11% 7% 3 7% 4 4 4 4 7% 8% 41%	4058
	11th to 20th	Night	14% 7% 3 7% 5% 5% 5% 4 6% 9% 36%	4057
	21st to end	Night	10% 7% 2 7% 5% 4 5% 5% 6% 9% 40%	4427
August	1st to 10th	Night	10% 8% 3 8% 5% 5% 5% 4 7% 9% 35%	2915
	11th to 20th	Night	13% 6% 2 7% 4 4 5% 3 5% 7% 42%	2875
	21st to end	Night	6% 4 2 6% 5% 5% 6% 4 7% 9% 46%	3378
September	1st to 10th	Night	13% 5% 2 5% 4 4 4 3 4 7% 49%	2065
	11th to 20th	Night	9% 5% 2 4 3 3 3 3 5% 7% 54%	2200
	21st to end	Night	17% 7% 3 6% 4 4 4 4 5% 6% 40%	2200
October	1st to 10th	Night	14% 5% 2 7% 4 4 4 3 4 7% 47%	2360
	11th to 20th	Night	16% 7% 2 6% 4 4 3 3 6% 7% 43%	2400
	21st to end	Night	23% 7% 2 6% 3 3 4 3 4 5% 41%	2640
November	1st to 10th	Night	13% 8% 2 5% 4 3 4 2 5% 6% 47%	2561
	11th to 20th	Night	18% 12% 3 7% 4 4 4 3 5% 6% 33%	2730
	21st to end	Night	21% 12% 4 8% 5% 4 4 3 4 5% 30%	2928
December	1st to 10th	Night	20% 14% 6% 16% 4 4 4 3 4 5% 21%	4720
	11th to 20th	Night	20% 17% 7% 9% 4 3 4 3 4 5% 23%	5345
	21st to end	Night	21% 17% 5% 9% 5% 5% 5% 3 4 6% 20%	6756

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	71% 3 11% 11% 3	5259
	11th to 20th	Day	74% 3 7% 8% 7% 1	5280
	21st to end	Day	69% 3 8% 14% 6%	5780
February	1st to 10th	Day	61% 4 10% 16% 8% 1	1890
	11th to 20th	Day	62% 4 9% 15% 9%	1895
	21st to end	Day	59% 3 10% 17% 10% 1	1735
March	1st to 10th	Day	55% 4 7% 22% 9% 3	5045
	11th to 20th	Day	42% 5% 9% 29% 12% 2	5090
	21st to end	Day	52% 5% 8% 21% 13% 2	5586
April	1st to 10th	Day	54% 5% 10% 17% 11% 3	2271
	11th to 20th	Day	48% 6% 10% 15% 18% 3	2440
	21st to end	Day	49% 6% 10% 21% 13% 2	2600
May	1st to 10th	Day	54% 7% 10% 18% 9% 3	5897
	11th to 20th	Day	51% 7% 10% 21% 10% 1	5865
	21st to end	Day	46% 8% 12% 20% 12% 2	6447
June	1st to 10th	Day	41% 9% 13% 22% 14% 1	2740
	11th to 20th	Day	44% 8% 13% 21% 13% 1	2800
	21st to end	Day	41% 8% 14% 22% 14% 1	2672
July	1st to 10th	Day	39% 7% 10% 24% 17% 2	5835
	11th to 20th	Day	45% 8% 12% 23% 11% 1	5831
	21st to end	Day	44% 6% 10% 20% 18% 1	6240
August	1st to 10th	Day	44% 8% 12% 26% 10%	4221
	11th to 20th	Day	39% 7% 11% 30% 13%	4213
	21st to end	Day	32% 7% 14% 28% 17% 2	4487
September	1st to 10th	Day	36% 5% 10% 22% 23% 3	2331
	11th to 20th	Day	33% 6% 12% 30% 16% 3	2200
	21st to end	Day	49% 5% 9% 20% 16% 1	2200
October	1st to 10th	Day	30% 5% 9% 28% 26% 3	3311
	11th to 20th	Day	39% 5% 11% 23% 15% 5%	3240
	21st to end	Day	35% 3 11% 28% 20% 2	3538
November	1st to 10th	Day	40% 5% 10% 25% 17% 3	1952
	11th to 20th	Day	50% 4 9% 20% 13% 3	1890
	21st to end	Day	57% 4 10% 18% 10% 1	1688
December	1st to 10th	Day	64% 5% 12% 15% 4	2680
	11th to 20th	Day	66% 3 10% 17% 4	3066
	21st to end	Day	68% 5% 9% 13% 5%	4422
January	1st to 10th	Night	73% 3 9% 11% 4	7636
	11th to 20th	Night	70% 3 6% 11% 8% 2	7680
	21st to end	Night	65% 3 10% 15% 6% 1	8401
February	1st to 10th	Night	60% 4 9% 17% 9%	2730
	11th to 20th	Night	63% 4 9% 16% 8%	2618
	21st to end	Night	59% 4 9% 16% 8% 2	2071
March	1st to 10th	Night	54% 4 6% 24% 11% 2	5028
	11th to 20th	Night	42% 6% 8% 30% 11% 3	5090
	21st to end	Night	50% 4 8% 21% 14% 2	5588
April	1st to 10th	Night	51% 5% 9% 18% 14% 2	2152
	11th to 20th	Night	45% 5% 11% 19% 15% 4	1926
	21st to end	Night	45% 5% 11% 21% 16% 2	1800
May	1st to 10th	Night	59% 7% 11% 12% 7% 4	4060
	11th to 20th	Night	44% 9% 10% 25% 11% 1	4033
	21st to end	Night	48% 8% 11% 22% 8% 3	4429
June	1st to 10th	Night	38% 8% 10% 24% 18% 2	1650
	11th to 20th	Night	39% 9% 13% 22% 15% 3	1600
	21st to end	Night	35% 9% 15% 21% 18% 2	1718
July	1st to 10th	Night	40% 7% 9% 24% 18% 3	4015
	11th to 20th	Night	44% 8% 16% 20% 11% 1	4006
	21st to end	Night	39% 9% 11% 19% 20% 3	4297
August	1st to 10th	Night	43% 9% 15% 24% 9%	2904
	11th to 20th	Night	40% 7% 9% 23% 20% 1	2902
	21st to end	Night	32% 7% 12% 31% 15% 3	3378
September	1st to 10th	Night	34% 6% 12% 19% 22% 6%	2065
	11th to 20th	Night	29% 6% 13% 26% 25% 2	2200
	21st to end	Night	44% 6% 10% 20% 19% 1	2200
October	1st to 10th	Night	31% 5% 8% 28% 24% 4	3854
	11th to 20th	Night	34% 4 12% 23% 19% 8%	3899
	21st to end	Night	35% 3 7% 27% 25% 4	4252
November	1st to 10th	Night	39% 4 10% 23% 20% 4	2561
	11th to 20th	Night	52% 4 8% 20% 13% 3	2730
	21st to end	Night	56% 5% 9% 19% 10% 1	2928
December	1st to 10th	Night	66% 4 10% 16% 4	4720
	11th to 20th	Night	64% 4 12% 15% 4	5348
	21st to end	Night	66% 4 10% 14% 7%	6756

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	35% 27% 24% 10% 4	330
	11th to 20th	Day	44% 25% 24% 7%	330
	21st to end	Day	38% 29% 25% 6% 1 1	363
February	1st to 10th	Day	38% 22% 29% 10% 2	330
	11th to 20th	Day	43% 26% 26% 4 1	330
	21st to end	Day	36% 24% 35% 5%	278
March	1st to 10th	Day	32% 22% 28% 15% 3	540
	11th to 20th	Day	34% 19% 30% 11% 5% 1	540
	21st to end	Day	31% 20% 31% 15% 3	594
April	1st to 10th	Day	31% 19% 27% 17% 5% 1	504
	11th to 20th	Day	25% 22% 28% 15% 8% 3	492
	21st to end	Day	29% 17% 29% 18% 6% 2	500
May	1st to 10th	Day	25% 22% 27% 15% 8% 2	503
	11th to 20th	Day	23% 14% 28% 20% 11% 3	527
	21st to end	Day	19% 9% 27% 25% 16% 4	573
June	1st to 10th	Day	15% 9% 27% 31% 14% 5%	530
	11th to 20th	Day	20% 8% 23% 28% 16% 4	530
	21st to end	Day	13% 9% 30% 29% 16% 4	530
July	1st to 10th	Day	15% 5% 21% 28% 19% 12%	525
	11th to 20th	Day	12% 7% 25% 28% 19% 9%	524
	21st to end	Day	18% 5% 23% 27% 20% 8%	576
August	1st to 10th	Day	12% 7% 22% 30% 20% 9%	526
	11th to 20th	Day	14% 5% 22% 29% 18% 11%	519
	21st to end	Day	11% 4 22% 30% 22% 10%	583
September	1st to 10th	Day	16% 7% 20% 27% 22% 8%	530
	11th to 20th	Day	11% 4 16% 30% 29% 10%	530
	21st to end	Day	25% 10% 24% 24% 14% 3	530
October	1st to 10th	Day	15% 9% 27% 25% 20% 4	530
	11th to 20th	Day	21% 14% 29% 24% 10% 2	530
	21st to end	Day	29% 15% 28% 18% 9% 1	583
November	1st to 10th	Day	22% 15% 33% 19% 8% 3	430
	11th to 20th	Day	33% 15% 30% 16% 4 1	330
	21st to end	Day	33% 18% 35% 13% 1	223
December	1st to 10th	Day	35% 22% 30% 9% 3 1	220
	11th to 20th	Day	34% 23% 26% 13% 4	220
	21st to end	Day	41% 21% 21% 13% 4	330
January	1st to 10th	Night	30% 22% 28% 17% 3	840
	11th to 20th	Night	34% 19% 29% 16% 2	840
	21st to end	Night	29% 20% 31% 18% 2	924
February	1st to 10th	Night	30% 16% 27% 25% 2	840
	11th to 20th	Night	33% 18% 32% 15% 1	823
	21st to end	Night	30% 20% 30% 18% 2	692
March	1st to 10th	Night	26% 18% 30% 22% 3	840
	11th to 20th	Night	30% 16% 28% 20% 6%	840
	21st to end	Night	27% 16% 33% 19% 4 1	924
April	1st to 10th	Night	28% 16% 28% 22% 5%	805
	11th to 20th	Night	22% 14% 32% 22% 9% 1	742
	21st to end	Night	19% 9% 36% 29% 7%	600
May	1st to 10th	Night	23% 10% 29% 26% 12% 1	600
	11th to 20th	Night	19% 7% 28% 31% 14% 1	591
	21st to end	Night	13% 5% 22% 34% 22% 3	650
June	1st to 10th	Night	12% 4 26% 39% 18% 1	450
	11th to 20th	Night	11% 6% 23% 38% 21% 2	400
	21st to end	Night	12% 5% 19% 39% 25% 1	518
July	1st to 10th	Night	12% 3 16% 37% 26% 5%	585
	11th to 20th	Night	9% 4 17% 33% 32% 5%	582
	21st to end	Night	12% 4 13% 36% 32% 2	657
August	1st to 10th	Night	9% 2 16% 39% 32% 3	597
	11th to 20th	Night	12% 3 13% 36% 31% 5%	594
	21st to end	Night	11% 3 16% 35% 29% 6%	750
September	1st to 10th	Night	15% 4 15% 35% 25% 5%	800
	11th to 20th	Night	11% 3 18% 32% 31% 4	800
	21st to end	Night	19% 9% 19% 32% 19% 3	800
October	1st to 10th	Night	17% 5% 21% 30% 24% 3	800
	11th to 20th	Night	22% 9% 27% 31% 12% 1	800
	21st to end	Night	25% 10% 23% 31% 10%	880
November	1st to 10th	Night	17% 9% 28% 32% 14%	820
	11th to 20th	Night	29% 13% 26% 24% 7% 1	840
	21st to end	Night	28% 13% 27% 25% 6%	840
December	1st to 10th	Night	31% 17% 28% 20% 4	840
	11th to 20th	Night	30% 17% 27% 22% 4	840
	21st to end	Night	31% 16% 29% 23% 2	924

Page generated at 2026-03-30 02:18:41. Version ac07

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