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 2024-12-09.

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% 3 7% 5% 4 4 4 6% 7% 33%	101200
	Night	17% 11% 4 8% 5% 4 4 3 5% 6% 34%	98517
Transparency	Day	48% 6% 11% 21% 13% 2	104862
	Night	49% 6% 10% 21% 13% 2	102981
Seeing	Day	23% 13% 26% 21% 12% 4	14892
	Night	22% 11% 25% 27% 13% 1	24907

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	20% 20% 7% 11% 4 3 3 2 4 5% 21%	2836
	11th to 20th	Day	15% 23% 8% 13% 8% 4 3 2 3 4 17%	2840
	21st to end	Day	24% 22% 7% 10% 5% 4 4 3 3 3 15%	3124
February	1st to 10th	Day	22% 16% 4 8% 5% 4 4 2 4 5% 25%	1710
	11th to 20th	Day	18% 14% 4 12% 6% 4 3 3 4 6% 25%	1701
	21st to end	Day	21% 15% 4 9% 5% 3 4 3 5% 5% 28%	1575
March	1st to 10th	Day	21% 16% 5% 8% 4 3 3 3 4 5% 29%	3435
	11th to 20th	Day	15% 9% 4 7% 5% 4 5% 4 5% 6% 37%	3480
	21st to end	Day	21% 9% 3 7% 5% 4 4 4 6% 7% 30%	3815
April	1st to 10th	Day	16% 12% 3 8% 5% 4 5% 4 5% 6% 31%	2147
	11th to 20th	Day	17% 10% 2 7% 5% 4 4 4 5% 6% 36%	2316
	21st to end	Day	20% 9% 3 6% 4 4 4 4 6% 7% 33%	2470
May	1st to 10th	Day	22% 10% 3 7% 5% 4 5% 4 5% 7% 28%	4082
	11th to 20th	Day	19% 9% 3 7% 5% 4 5% 3 5% 7% 32%	4081
	21st to end	Day	12% 6% 3 6% 5% 5% 5% 5% 7% 10% 35%	4476
June	1st to 10th	Day	14% 6% 3 6% 5% 5% 5% 4 7% 9% 37%	2603
	11th to 20th	Day	13% 6% 2 6% 5% 6% 5% 4 7% 9% 35%	2660
	21st to end	Day	13% 6% 2 6% 5% 5% 6% 4 8% 10% 35%	2539
July	1st to 10th	Day	9% 6% 3 6% 5% 6% 5% 4 7% 9% 39%	4120
	11th to 20th	Day	11% 6% 2 6% 4 5% 5% 4 6% 9% 41%	4120
	21st to end	Day	15% 9% 3 7% 5% 5% 5% 5% 6% 8% 33%	4466
August	1st to 10th	Day	11% 7% 3 8% 5% 5% 6% 5% 7% 9% 34%	4104
	11th to 20th	Day	10% 6% 2 7% 5% 5% 6% 5% 7% 9% 38%	4044
	21st to end	Day	7% 4 1 5% 4 5% 5% 5% 7% 9% 46%	4350
September	1st to 10th	Day	16% 5% 2 5% 4 3 3 3 6% 7% 47%	2215
	11th to 20th	Day	11% 6% 2 5% 4 4 4 3 6% 8% 46%	2090
	21st to end	Day	20% 8% 3 7% 4 4 3 3 4 7% 38%	2090
October	1st to 10th	Day	14% 7% 3 6% 4 5% 4 3 6% 7% 42%	1936
	11th to 20th	Day	16% 8% 3 7% 4 5% 5% 3 5% 5% 39%	1900
	21st to end	Day	22% 9% 3 6% 3 3 3 3 4 6% 38%	2090
November	1st to 10th	Day	12% 9% 2 5% 4 4 3 4 4 5% 47%	1857
	11th to 20th	Day	17% 15% 3 7% 4 2 4 3 6% 6% 34%	1800
	21st to end	Day	19% 14% 5% 8% 4 4 4 3 5% 6% 30%	1608
December	1st to 10th	Day	23% 15% 7% 9% 5% 4 3 3 4 5% 21%	1584
	11th to 20th	Day	21% 17% 6% 9% 4 3 3 3 5% 5% 24%	1910
	21st to end	Day	24% 19% 4 10% 5% 4 4 3 5% 6% 16%	3026
January	1st to 10th	Night	17% 21% 8% 11% 6% 4 3 3 4 4 20%	4109
	11th to 20th	Night	19% 19% 7% 13% 5% 6% 4 2 3 4 18%	4120
	21st to end	Night	27% 18% 6% 13% 4 3 3 2 2 4 19%	4532
February	1st to 10th	Night	21% 14% 4 10% 5% 5% 4 3 4 5% 27%	2470
	11th to 20th	Night	22% 14% 3 10% 5% 5% 4 3 5% 4 26%	2361
	21st to end	Night	22% 15% 5% 7% 4 4 4 3 4 4 27%	1879
March	1st to 10th	Night	23% 12% 3 7% 4 4 3 3 5% 6% 32%	3418
	11th to 20th	Night	15% 12% 5% 7% 5% 3 3 3 5% 6% 36%	3480
	21st to end	Night	17% 9% 3 7% 4 4 4 2 5% 5% 40%	3817
April	1st to 10th	Night	19% 12% 3 6% 4 3 4 3 4 7% 34%	2033
	11th to 20th	Night	17% 8% 2 5% 4 4 4 4 6% 8% 38%	1829
	21st to end	Night	16% 8% 3 8% 4 4 4 3 5% 7% 38%	1710
May	1st to 10th	Night	27% 11% 3 6% 5% 4 4 4 4 7% 25%	2813
	11th to 20th	Night	17% 10% 3 7% 5% 4 4 3 5% 6% 39%	2812
	21st to end	Night	12% 7% 2 7% 4 4 4 4 7% 9% 39%	3079
June	1st to 10th	Night	10% 7% 2 7% 4 4 4 4 5% 8% 45%	1568
	11th to 20th	Night	10% 6% 2 6% 5% 6% 5% 3 7% 11% 39%	1520
	21st to end	Night	12% 5% 1 5% 4 3 5% 4 8% 9% 43%	1632
July	1st to 10th	Night	10% 7% 3 7% 4 5% 5% 4 7% 8% 41%	2840
	11th to 20th	Night	10% 6% 2 7% 5% 4 5% 4 6% 8% 43%	2840
	21st to end	Night	11% 7% 2 7% 5% 4 5% 4 6% 8% 40%	3087
August	1st to 10th	Night	11% 8% 3 8% 5% 5% 5% 4 7% 9% 34%	2825
	11th to 20th	Night	13% 6% 2 8% 4 4 4 4 5% 7% 41%	2785
	21st to end	Night	6% 4 2 6% 5% 5% 5% 4 7% 9% 46%	3274
September	1st to 10th	Night	13% 5% 2 5% 4 4 4 3 4 7% 49%	1962
	11th to 20th	Night	10% 5% 2 4 3 3 3 4 5% 7% 54%	2090
	21st to end	Night	17% 7% 2 6% 4 4 4 4 5% 6% 41%	2090
October	1st to 10th	Night	14% 5% 2 7% 4 4 4 3 4 7% 46%	2242
	11th to 20th	Night	16% 7% 2 6% 4 4 3 3 6% 7% 42%	2280
	21st to end	Night	23% 7% 2 6% 3 3 4 3 3 5% 41%	2508
November	1st to 10th	Night	13% 8% 3 5% 4 3 4 2 5% 6% 47%	2436
	11th to 20th	Night	18% 12% 3 7% 4 4 5% 3 5% 6% 33%	2600
	21st to end	Night	20% 11% 4 8% 5% 4 4 3 4 5% 31%	2788
December	1st to 10th	Night	22% 16% 6% 10% 4 4 4 3 4 5% 23%	2779
	11th to 20th	Night	19% 17% 6% 8% 5% 3 4 3 4 5% 25%	3285
	21st to end	Night	23% 19% 6% 8% 5% 4 4 3 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	67% 5% 10% 13% 5%	2837
	11th to 20th	Day	73% 3 8% 11% 5%	2840
	21st to end	Day	74% 3 7% 12% 3	3124
February	1st to 10th	Day	62% 4 10% 15% 8% 1	1710
	11th to 20th	Day	61% 5% 9% 16% 9%	1710
	21st to end	Day	60% 4 9% 16% 10% 2	1575
March	1st to 10th	Day	59% 4 9% 20% 8% 1	3435
	11th to 20th	Day	45% 6% 9% 27% 11% 1	3480
	21st to end	Day	51% 5% 9% 21% 13% 1	3815
April	1st to 10th	Day	53% 5% 10% 17% 11% 3	2147
	11th to 20th	Day	48% 6% 10% 15% 18% 3	2316
	21st to end	Day	49% 6% 10% 20% 12% 2	2470
May	1st to 10th	Day	55% 7% 8% 20% 8% 1	4120
	11th to 20th	Day	50% 7% 10% 20% 11% 1	4085
	21st to end	Day	40% 10% 14% 21% 13% 3	4489
June	1st to 10th	Day	41% 8% 13% 23% 14% 1	2603
	11th to 20th	Day	43% 8% 14% 22% 13% 1	2660
	21st to end	Day	42% 8% 14% 22% 13% 1	2539
July	1st to 10th	Day	40% 8% 12% 22% 16% 3	4055
	11th to 20th	Day	37% 7% 11% 29% 16% 1	4051
	21st to end	Day	47% 6% 9% 19% 16% 2	4324
August	1st to 10th	Day	44% 8% 12% 25% 10%	4091
	11th to 20th	Day	39% 7% 11% 29% 13%	4083
	21st to end	Day	32% 7% 15% 27% 17% 2	4350
September	1st to 10th	Day	37% 5% 10% 22% 22% 4	2215
	11th to 20th	Day	34% 6% 12% 29% 16% 3	2090
	21st to end	Day	48% 5% 9% 21% 17% 1	2090
October	1st to 10th	Day	30% 5% 9% 28% 25% 3	3209
	11th to 20th	Day	40% 5% 12% 23% 15% 6%	3140
	21st to end	Day	34% 3 12% 29% 20% 2	3428
November	1st to 10th	Day	39% 5% 9% 26% 17% 4	1857
	11th to 20th	Day	50% 4 10% 20% 14% 3	1800
	21st to end	Day	57% 4 10% 18% 10% 1	1608
December	1st to 10th	Day	66% 4 10% 15% 5% 1	1584
	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	68% 4 9% 13% 6%	4109
	11th to 20th	Night	71% 4 9% 11% 3	4120
	21st to end	Night	72% 3 6% 14% 4 1	4532
February	1st to 10th	Night	61% 4 10% 17% 8%	2470
	11th to 20th	Night	62% 4 8% 16% 9%	2363
	21st to end	Night	60% 5% 9% 16% 8% 3	1879
March	1st to 10th	Night	54% 4 7% 23% 11% 1	3418
	11th to 20th	Night	48% 7% 8% 28% 9% 1	3480
	21st to end	Night	46% 5% 7% 27% 14% 2	3817
April	1st to 10th	Night	49% 5% 9% 19% 15% 2	2033
	11th to 20th	Night	44% 5% 12% 19% 16% 5%	1829
	21st to end	Night	45% 5% 11% 20% 16% 2	1710
May	1st to 10th	Night	58% 7% 9% 15% 9% 2	2840
	11th to 20th	Night	46% 8% 10% 23% 11% 2	2813
	21st to end	Night	38% 10% 13% 23% 12% 5%	3087
June	1st to 10th	Night	37% 8% 10% 24% 18% 2	1568
	11th to 20th	Night	37% 9% 13% 23% 15% 3	1520
	21st to end	Night	35% 9% 15% 22% 17% 2	1632
July	1st to 10th	Night	40% 7% 10% 23% 17% 4	2795
	11th to 20th	Night	37% 7% 12% 27% 15% 2	2786
	21st to end	Night	40% 9% 10% 19% 18% 4	2988
August	1st to 10th	Night	43% 9% 15% 24% 9%	2814
	11th to 20th	Night	41% 7% 9% 23% 20% 1	2812
	21st to end	Night	32% 7% 12% 31% 15% 3	3274
September	1st to 10th	Night	35% 6% 12% 19% 21% 6%	1962
	11th to 20th	Night	29% 6% 13% 25% 25% 2	2090
	21st to end	Night	43% 6% 10% 21% 19% 2	2090
October	1st to 10th	Night	32% 5% 8% 28% 23% 4	3736
	11th to 20th	Night	34% 4 12% 23% 19% 9%	3779
	21st to end	Night	34% 3 7% 27% 25% 4	4120
November	1st to 10th	Night	39% 4 10% 23% 20% 4	2436
	11th to 20th	Night	52% 4 8% 20% 13% 3	2600
	21st to end	Night	55% 5% 10% 19% 10% 1	2788
December	1st to 10th	Night	64% 4 9% 17% 5% 1	2779
	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	40% 24% 27% 9%	270
	21st to end	Day	36% 29% 26% 6% 1 1	297
February	1st to 10th	Day	39% 20% 30% 9% 1	270
	11th to 20th	Day	40% 28% 26% 4 1	270
	21st to end	Day	39% 22% 33% 6%	230
March	1st to 10th	Day	31% 22% 28% 15% 4	460
	11th to 20th	Day	34% 18% 31% 11% 5% 1	460
	21st to end	Day	32% 18% 30% 16% 4	506
April	1st to 10th	Day	28% 20% 27% 18% 6% 1	460
	11th to 20th	Day	25% 21% 27% 15% 8% 3	452
	21st to end	Day	30% 17% 29% 17% 5% 2	460
May	1st to 10th	Day	25% 22% 27% 16% 8% 3	463
	11th to 20th	Day	23% 14% 28% 20% 12% 3	487
	21st to end	Day	16% 8% 27% 26% 18% 5%	529
June	1st to 10th	Day	15% 9% 25% 31% 14% 5%	490
	11th to 20th	Day	19% 9% 23% 29% 16% 4	490
	21st to end	Day	14% 10% 32% 28% 14% 3	490
July	1st to 10th	Day	15% 6% 22% 27% 19% 12%	485
	11th to 20th	Day	11% 6% 25% 29% 18% 9%	484
	21st to end	Day	18% 5% 24% 26% 20% 8%	532
August	1st to 10th	Day	13% 6% 22% 30% 19% 9%	486
	11th to 20th	Day	14% 5% 23% 29% 18% 10%	479
	21st to end	Day	12% 4 21% 29% 22% 11%	539
September	1st to 10th	Day	16% 6% 20% 27% 21% 8%	490
	11th to 20th	Day	12% 4 17% 30% 29% 9%	490
	21st to end	Day	24% 10% 24% 23% 14% 4	490
October	1st to 10th	Day	15% 9% 28% 26% 18% 4	490
	11th to 20th	Day	22% 13% 28% 25% 10% 2	490
	21st to end	Day	28% 14% 28% 19% 9% 1	539
November	1st to 10th	Day	21% 15% 32% 20% 9% 3	395
	11th to 20th	Day	32% 15% 31% 17% 5% 1	300
	21st to end	Day	31% 19% 36% 13% 1	203
December	1st to 10th	Day	34% 21% 32% 10% 3 1	196
	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	34% 16% 29% 17% 3	760
	21st to end	Night	29% 19% 31% 18% 2	836
February	1st to 10th	Night	31% 16% 26% 25% 2	760
	11th to 20th	Night	33% 18% 33% 15% 1	743
	21st to end	Night	31% 20% 29% 18% 2	628
March	1st to 10th	Night	25% 18% 31% 23% 4	760
	11th to 20th	Night	29% 16% 29% 19% 7% 1	760
	21st to end	Night	26% 16% 33% 19% 5% 1	836
April	1st to 10th	Night	27% 16% 29% 23% 5%	760
	11th to 20th	Night	22% 14% 32% 22% 9% 1	705
	21st to end	Night	19% 9% 36% 29% 7%	570
May	1st to 10th	Night	22% 9% 29% 26% 13% 1	570
	11th to 20th	Night	19% 7% 28% 31% 14% 1	561
	21st to end	Night	12% 4 22% 35% 23% 3	617
June	1st to 10th	Night	11% 4 27% 39% 18% 1	428
	11th to 20th	Night	10% 6% 23% 38% 21% 2	380
	21st to end	Night	12% 5% 20% 39% 24%	492
July	1st to 10th	Night	12% 3 17% 36% 26% 5%	555
	11th to 20th	Night	9% 4 18% 34% 31% 5%	552
	21st to end	Night	12% 3 14% 37% 32% 2	624
August	1st to 10th	Night	9% 2 15% 39% 32% 3	567
	11th to 20th	Night	12% 3 13% 36% 31% 4	564
	21st to end	Night	11% 3 15% 35% 30% 6%	712
September	1st to 10th	Night	15% 4 15% 34% 26% 5%	760
	11th to 20th	Night	12% 3 19% 32% 31% 4	760
	21st to end	Night	19% 8% 19% 32% 19% 3	760
October	1st to 10th	Night	17% 5% 22% 30% 23% 3	760
	11th to 20th	Night	22% 8% 26% 30% 12% 1	760
	21st to end	Night	25% 10% 23% 31% 10%	836
November	1st to 10th	Night	17% 9% 28% 31% 14%	780
	11th to 20th	Night	28% 14% 26% 24% 7% 1	800
	21st to end	Night	27% 13% 27% 26% 7% 1	800
December	1st to 10th	Night	32% 16% 27% 20% 4	795
	11th to 20th	Night	29% 17% 27% 23% 5%	760
	21st to end	Night	31% 15% 29% 23% 2	836

Page generated at 2024-12-06 03:54:53. Version ac07

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