Whispering Pines Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Whispering Pines Observatory clear sky chart from 2005-11-06 to 2026-01-17.

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	9% 5% 2 7% 5% 5% 5% 5% 7% 9% 41%	127127
	Night	10% 6% 2 6% 4 4 5% 4 6% 9% 45%	124555
Transparency	Day	37% 8% 13% 18% 17% 8%	131005
	Night	34% 7% 14% 18% 18% 9%	128747
Seeing	Day	12% 8% 21% 25% 21% 14%	16408
	Night	11% 6% 21% 32% 25% 6%	26408

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	11% 5% 2 5% 4 3 4 3 4 6% 54%	4146
	11th to 20th	Day	14% 6% 2 5% 3 3 3 3 5% 8% 48%	4327
	21st to end	Day	13% 6% 3 6% 5% 4 4 4 6% 8% 41%	4972
February	1st to 10th	Day	14% 7% 3 7% 4 4 4 3 5% 7% 42%	2000
	11th to 20th	Day	15% 6% 2 5% 4 3 3 3 5% 8% 46%	1948
	21st to end	Day	15% 6% 2 6% 4 5% 4 4 5% 6% 43%	1650
March	1st to 10th	Day	18% 7% 2 6% 3 4 4 4 5% 7% 40%	4518
	11th to 20th	Day	7% 5% 2 5% 4 4 4 3 6% 8% 52%	4980
	21st to end	Day	12% 6% 2 6% 3 4 4 3 5% 7% 47%	5465
April	1st to 10th	Day	11% 6% 2 5% 5% 4 5% 3 6% 7% 46%	2313
	11th to 20th	Day	9% 6% 2 7% 3 5% 5% 4 5% 6% 48%	2374
	21st to end	Day	6% 4 2 5% 5% 4 5% 4 5% 8% 52%	2400
May	1st to 10th	Day	10% 7% 3 7% 5% 5% 5% 5% 6% 8% 39%	5832
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 4 6% 10% 42%	5861
	21st to end	Day	5% 4 2 6% 5% 5% 6% 5% 8% 11% 44%	6433
June	1st to 10th	Day	8% 8% 3 9% 7% 7% 7% 6% 7% 11% 28%	2600
	11th to 20th	Day	5% 4 2 7% 8% 8% 8% 8% 9% 11% 30%	2600
	21st to end	Day	8% 6% 3 9% 6% 7% 6% 7% 9% 10% 29%	2600
July	1st to 10th	Day	6% 6% 3 9% 8% 9% 10% 8% 10% 12% 20%	5900
	11th to 20th	Day	4 4 2 7% 6% 8% 9% 6% 10% 13% 31%	5900
	21st to end	Day	4 4 2 9% 8% 8% 9% 8% 11% 13% 25%	6273
August	1st to 10th	Day	6% 5% 3 8% 6% 7% 8% 6% 10% 13% 28%	3905
	11th to 20th	Day	6% 5% 2 6% 5% 6% 6% 5% 8% 11% 41%	3849
	21st to end	Day	6% 5% 2 8% 7% 7% 9% 7% 9% 11% 28%	4312
September	1st to 10th	Day	9% 6% 3 9% 6% 7% 7% 6% 8% 9% 30%	2231
	11th to 20th	Day	12% 6% 3 8% 6% 5% 7% 5% 6% 8% 35%	2200
	21st to end	Day	10% 5% 2 6% 4 4 5% 5% 6% 9% 47%	2200
October	1st to 10th	Day	9% 6% 3 6% 5% 4 4 5% 5% 7% 46%	2200
	11th to 20th	Day	7% 3 2 4 3 3 3 3 5% 7% 61%	2200
	21st to end	Day	9% 4 2 5% 4 4 3 3 5% 6% 56%	2223
November	1st to 10th	Day	9% 5% 2 4 3 3 4 3 5% 6% 57%	1887
	11th to 20th	Day	10% 6% 1 4 4 3 3 3 5% 6% 56%	1890
	21st to end	Day	10% 5% 2 6% 5% 4 4 3 5% 8% 48%	1890
December	1st to 10th	Day	13% 6% 2 5% 4 3 3 2 5% 6% 52%	3020
	11th to 20th	Day	12% 6% 2 6% 4 4 4 3 4 5% 51%	3463
	21st to end	Day	15% 7% 2 7% 4 3 3 3 5% 5% 45%	4565
January	1st to 10th	Night	12% 5% 2 6% 4 4 4 3 5% 6% 50%	6019
	11th to 20th	Night	14% 7% 3 7% 4 5% 4 4 5% 7% 41%	5748
	21st to end	Night	16% 8% 3 6% 3 3 4 4 5% 8% 40%	5984
February	1st to 10th	Night	13% 8% 3 6% 4 3 3 4 5% 6% 44%	2400
	11th to 20th	Night	15% 8% 3 6% 4 3 3 3 5% 6% 45%	2338
	21st to end	Night	13% 6% 2 6% 4 5% 4 3 5% 6% 46%	1980
March	1st to 10th	Night	18% 10% 3 7% 4 4 4 3 4 6% 37%	5333
	11th to 20th	Night	10% 6% 2 5% 3 3 4 3 6% 8% 51%	4980
	21st to end	Night	12% 6% 2 6% 4 4 4 3 5% 7% 48%	5467
April	1st to 10th	Night	9% 5% 2 6% 4 4 4 4 6% 8% 48%	2101
	11th to 20th	Night	9% 5% 2 6% 4 4 6% 3 6% 6% 49%	1975
	21st to end	Night	6% 4 2 4 3 4 4 3 6% 9% 57%	2000
May	1st to 10th	Night	10% 6% 2 7% 4 4 4 4 6% 10% 44%	4061
	11th to 20th	Night	12% 6% 2 6% 4 4 4 4 5% 9% 43%	4032
	21st to end	Night	4 4 2 6% 4 4 4 4 6% 12% 50%	4421
June	1st to 10th	Night	6% 4 3 6% 6% 5% 6% 6% 9% 11% 38%	1800
	11th to 20th	Night	3 3 2 5% 5% 4 7% 6% 11% 13% 42%	1800
	21st to end	Night	5% 4 3 7% 6% 4 7% 6% 8% 12% 40%	1800
July	1st to 10th	Night	5% 6% 3 9% 7% 7% 8% 7% 11% 14% 23%	4058
	11th to 20th	Night	1 2 1 4 4 5% 7% 6% 10% 17% 41%	4057
	21st to end	Night	3 4 2 7% 7% 5% 7% 6% 10% 15% 34%	4559
August	1st to 10th	Night	6% 4 2 5% 5% 6% 6% 5% 10% 14% 39%	3244
	11th to 20th	Night	4 4 1 6% 4 5% 6% 5% 9% 13% 42%	3200
	21st to end	Night	6% 5% 2 7% 6% 6% 7% 7% 10% 12% 32%	3586
September	1st to 10th	Night	9% 6% 2 7% 5% 6% 6% 6% 8% 12% 32%	2146
	11th to 20th	Night	9% 7% 2 6% 5% 6% 6% 4 7% 9% 38%	2200
	21st to end	Night	7% 5% 2 6% 4 4 5% 4 6% 9% 49%	2200
October	1st to 10th	Night	6% 4 1 7% 5% 4 5% 4 6% 7% 52%	2200
	11th to 20th	Night	7% 4 2 3 3 3 4 3 4 6% 63%	2200
	21st to end	Night	8% 5% 2 6% 3 3 4 3 4 6% 56%	2615
November	1st to 10th	Night	7% 4 2 5% 4 4 3 3 5% 6% 56%	2626
	11th to 20th	Night	9% 5% 2 5% 4 4 3 3 5% 7% 55%	2730
	21st to end	Night	10% 7% 2 5% 3 4 5% 4 6% 6% 49%	2730
December	1st to 10th	Night	12% 6% 2 5% 4 3 3 3 4 7% 52%	4380
	11th to 20th	Night	11% 5% 2 4 3 3 4 3 4 5% 55%	4952
	21st to end	Night	15% 8% 3 6% 4 3 3 3 4 5% 46%	6633

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	33% 4 5% 15% 33% 10%	4147
	11th to 20th	Day	36% 3 5% 15% 28% 12%	4327
	21st to end	Day	40% 4 9% 16% 18% 12%	4972
February	1st to 10th	Day	42% 3 7% 16% 22% 10%	2000
	11th to 20th	Day	37% 4 6% 17% 23% 12%	1958
	21st to end	Day	40% 6% 9% 16% 19% 11%	1650
March	1st to 10th	Day	42% 5% 7% 16% 18% 11%	4518
	11th to 20th	Day	28% 5% 10% 14% 21% 22%	4980
	21st to end	Day	36% 5% 10% 22% 16% 12%	5465
April	1st to 10th	Day	36% 6% 9% 18% 16% 14%	2313
	11th to 20th	Day	36% 5% 7% 18% 22% 12%	2374
	21st to end	Day	29% 7% 9% 23% 22% 10%	2400
May	1st to 10th	Day	41% 8% 10% 20% 16% 5%	5868
	11th to 20th	Day	35% 7% 15% 28% 13% 2	5865
	21st to end	Day	29% 10% 16% 24% 19% 2	6447
June	1st to 10th	Day	46% 11% 15% 19% 8% 1	2600
	11th to 20th	Day	41% 12% 18% 19% 9% 1	2600
	21st to end	Day	44% 13% 17% 16% 8% 2	2600
July	1st to 10th	Day	47% 16% 26% 9% 1	5835
	11th to 20th	Day	37% 15% 33% 13% 2	5831
	21st to end	Day	42% 17% 23% 17% 2	6092
August	1st to 10th	Day	41% 12% 19% 17% 10% 1	3893
	11th to 20th	Day	32% 11% 18% 24% 15% 1	3885
	21st to end	Day	42% 12% 22% 15% 8% 1	4311
September	1st to 10th	Day	45% 10% 16% 17% 10% 3	2231
	11th to 20th	Day	44% 9% 12% 18% 13% 5%	2200
	21st to end	Day	33% 7% 12% 21% 20% 8%	2200
October	1st to 10th	Day	40% 5% 7% 11% 17% 21%	3590
	11th to 20th	Day	15% 3 5% 18% 25% 33%	3568
	21st to end	Day	19% 3 4 14% 40% 19%	3573
November	1st to 10th	Day	29% 4 7% 21% 23% 16%	1887
	11th to 20th	Day	29% 4 5% 18% 28% 15%	1890
	21st to end	Day	34% 5% 7% 21% 22% 11%	1890
December	1st to 10th	Day	35% 3 8% 16% 28% 10%	3020
	11th to 20th	Day	36% 3 6% 21% 24% 9%	3460
	21st to end	Day	41% 4 6% 18% 26% 5%	4565
January	1st to 10th	Night	35% 4 6% 13% 29% 13%	6019
	11th to 20th	Night	43% 3 5% 13% 27% 9%	5748
	21st to end	Night	42% 4 8% 18% 19% 9%	5984
February	1st to 10th	Night	40% 4 7% 15% 21% 12%	2400
	11th to 20th	Night	41% 4 8% 13% 20% 15%	2339
	21st to end	Night	39% 5% 7% 17% 18% 14%	1980
March	1st to 10th	Night	47% 5% 6% 13% 20% 9%	5333
	11th to 20th	Night	30% 5% 10% 16% 20% 19%	4980
	21st to end	Night	36% 4 9% 21% 16% 13%	5467
April	1st to 10th	Night	33% 6% 13% 18% 17% 14%	2101
	11th to 20th	Night	34% 5% 8% 18% 24% 12%	1975
	21st to end	Night	24% 6% 11% 29% 22% 9%	2000
May	1st to 10th	Night	34% 8% 19% 21% 13% 4	4088
	11th to 20th	Night	35% 7% 16% 26% 14% 2	4033
	21st to end	Night	25% 9% 19% 32% 13% 2	4429
June	1st to 10th	Night	34% 11% 21% 24% 8% 2	1800
	11th to 20th	Night	27% 13% 25% 25% 8% 2	1800
	21st to end	Night	33% 12% 28% 17% 10% 2	1800
July	1st to 10th	Night	45% 16% 28% 9% 1	4015
	11th to 20th	Night	25% 16% 44% 13% 1	4006
	21st to end	Night	34% 17% 29% 18% 2	4427
August	1st to 10th	Night	31% 12% 23% 23% 9% 1	3232
	11th to 20th	Night	27% 13% 25% 24% 9% 1	3230
	21st to end	Night	38% 14% 27% 14% 7% 1	3586
September	1st to 10th	Night	40% 13% 19% 15% 10% 3	2146
	11th to 20th	Night	38% 11% 15% 16% 16% 3	2200
	21st to end	Night	30% 8% 15% 20% 19% 8%	2200
October	1st to 10th	Night	36% 5% 9% 12% 19% 18%	3590
	11th to 20th	Night	14% 3 5% 17% 30% 31%	3571
	21st to end	Night	21% 3 5% 13% 39% 19%	4215
November	1st to 10th	Night	28% 4 6% 20% 23% 18%	2626
	11th to 20th	Night	30% 3 6% 16% 28% 16%	2730
	21st to end	Night	34% 6% 9% 17% 21% 13%	2730
December	1st to 10th	Night	34% 4 8% 17% 24% 13%	4380
	11th to 20th	Night	32% 4 9% 21% 23% 11%	4954
	21st to end	Night	40% 4 6% 18% 26% 5%	6633

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	15% 15% 43% 22% 5%	330
	11th to 20th	Day	14% 18% 34% 22% 10% 2	318
	21st to end	Day	22% 19% 40% 14% 4	330
February	1st to 10th	Day	18% 15% 37% 22% 8% 1	300
	11th to 20th	Day	21% 19% 36% 18% 6%	300
	21st to end	Day	14% 21% 39% 20% 5%	249
March	1st to 10th	Day	14% 19% 42% 16% 8%	312
	11th to 20th	Day	14% 15% 33% 25% 11% 2	500
	21st to end	Day	14% 14% 32% 27% 12% 1	550
April	1st to 10th	Day	16% 14% 28% 25% 15% 2	500
	11th to 20th	Day	13% 10% 30% 27% 16% 4	492
	21st to end	Day	7% 9% 25% 30% 21% 8%	500
May	1st to 10th	Day	8% 8% 25% 27% 23% 10%	503
	11th to 20th	Day	9% 5% 19% 33% 19% 15%	527
	21st to end	Day	10% 2 14% 30% 22% 21%	573
June	1st to 10th	Day	14% 3 12% 25% 27% 19%	530
	11th to 20th	Day	6% 2 12% 23% 31% 27%	530
	21st to end	Day	9% 3 6% 24% 29% 28%	530
July	1st to 10th	Day	6% 3 5% 17% 31% 38%	525
	11th to 20th	Day	7% 2 2 15% 33% 40%	524
	21st to end	Day	4 1 3 21% 36% 34%	576
August	1st to 10th	Day	7% 4 6% 18% 31% 35%	526
	11th to 20th	Day	9% 2 3 17% 34% 34%	519
	21st to end	Day	10% 2 8% 25% 32% 23%	583
September	1st to 10th	Day	12% 2 9% 20% 32% 24%	530
	11th to 20th	Day	15% 4 8% 28% 28% 17%	530
	21st to end	Day	11% 2 11% 26% 32% 18%	530
October	1st to 10th	Day	11% 6% 21% 36% 20% 6%	530
	11th to 20th	Day	6% 5% 20% 33% 28% 9%	530
	21st to end	Day	10% 7% 24% 34% 21% 4	583
November	1st to 10th	Day	15% 5% 26% 30% 19% 6%	365
	11th to 20th	Day	12% 9% 35% 31% 9% 4	330
	21st to end	Day	10% 14% 36% 27% 10% 3	330
December	1st to 10th	Day	22% 15% 30% 22% 9% 3	330
	11th to 20th	Day	20% 11% 37% 22% 9% 1	330
	21st to end	Day	19% 10% 34% 23% 13% 1	363
January	1st to 10th	Night	16% 10% 36% 30% 7% 1	840
	11th to 20th	Night	13% 12% 31% 34% 10%	825
	21st to end	Night	20% 10% 36% 29% 5%	880
February	1st to 10th	Night	16% 10% 30% 36% 8% 1	800
	11th to 20th	Night	18% 12% 33% 30% 7%	783
	21st to end	Night	15% 11% 37% 32% 5%	660
March	1st to 10th	Night	17% 9% 29% 37% 8%	800
	11th to 20th	Night	14% 8% 34% 32% 12% 1	800
	21st to end	Night	12% 9% 31% 37% 11%	880
April	1st to 10th	Night	10% 8% 30% 39% 12% 1	701
	11th to 20th	Night	11% 4 29% 37% 18% 1	593
	21st to end	Night	7% 3 23% 43% 22% 2	600
May	1st to 10th	Night	7% 4 22% 41% 24% 2	600
	11th to 20th	Night	8% 3 18% 37% 30% 4	591
	21st to end	Night	6% 3 10% 38% 37% 7%	650
June	1st to 10th	Night	7% 2 7% 35% 41% 8%	600
	11th to 20th	Night	4 1 8% 28% 46% 13%	600
	21st to end	Night	7% 1 8% 26% 47% 12%	600
July	1st to 10th	Night	5% 3 4 21% 48% 20%	585
	11th to 20th	Night	5% 1 17% 50% 27%	582
	21st to end	Night	3 1 2 19% 56% 18%	657
August	1st to 10th	Night	8% 2 3 18% 45% 25%	597
	11th to 20th	Night	6% 1 2 17% 52% 22%	594
	21st to end	Night	9% 3 5% 22% 45% 16%	660
September	1st to 10th	Night	10% 3 7% 25% 41% 14%	746
	11th to 20th	Night	11% 4 9% 31% 38% 8%	800
	21st to end	Night	10% 1 13% 28% 40% 8%	800
October	1st to 10th	Night	8% 2 23% 35% 29% 4	800
	11th to 20th	Night	9% 5% 19% 32% 32% 4	800
	21st to end	Night	10% 5% 19% 41% 23% 2	880
November	1st to 10th	Night	9% 5% 24% 37% 23% 2	820
	11th to 20th	Night	12% 7% 27% 36% 17% 1	840
	21st to end	Night	15% 7% 30% 32% 16% 1	840
December	1st to 10th	Night	17% 8% 28% 32% 15% 1	840
	11th to 20th	Night	15% 6% 29% 36% 13% 1	840
	21st to end	Night	20% 8% 28% 32% 11% 1	924

Page generated at 2026-01-14 01:14:25. Version ac07

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