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 2024-11-28.

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	10% 6% 2 7% 5% 5% 6% 5% 7% 9% 40%	101053
	Night	10% 6% 2 6% 4 4 5% 4 6% 9% 44%	98417
Transparency	Day	37% 8% 13% 17% 17% 8%	104974
	Night	35% 8% 14% 17% 18% 9%	102635
Seeing	Day	12% 7% 20% 25% 22% 15%	14925
	Night	11% 5% 21% 32% 25% 6%	24898

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	13% 6% 2 6% 4 4 5% 3 5% 7% 45%	2836
	11th to 20th	Day	12% 6% 2 4 3 3 3 3 5% 9% 50%	2982
	21st to end	Day	17% 8% 3 6% 4 4 4 3 5% 7% 37%	3476
February	1st to 10th	Day	15% 7% 3 7% 4 4 4 3 5% 7% 42%	1900
	11th to 20th	Day	15% 6% 2 5% 3 3 3 3 5% 7% 47%	1848
	21st to end	Day	15% 6% 2 6% 4 5% 5% 4 6% 6% 42%	1570
March	1st to 10th	Day	17% 8% 3 8% 4 4 4 4 5% 6% 36%	3144
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 4 6% 10% 44%	3480
	21st to end	Day	12% 6% 2 6% 3 4 5% 3 6% 7% 46%	3815
April	1st to 10th	Day	11% 6% 2 5% 5% 4 5% 3 6% 6% 45%	2197
	11th to 20th	Day	10% 6% 3 7% 3 5% 5% 4 5% 7% 46%	2254
	21st to end	Day	6% 4 2 5% 5% 4 5% 3 5% 7% 53%	2280
May	1st to 10th	Day	7% 5% 3 6% 5% 5% 5% 4 6% 8% 45%	4066
	11th to 20th	Day	13% 6% 3 7% 5% 5% 5% 4 6% 8% 39%	4081
	21st to end	Day	5% 4 2 5% 5% 5% 6% 5% 8% 10% 45%	4476
June	1st to 10th	Day	8% 8% 3 9% 7% 7% 7% 5% 7% 10% 28%	2470
	11th to 20th	Day	6% 4 2 7% 8% 8% 8% 8% 9% 11% 30%	2470
	21st to end	Day	8% 6% 3 9% 6% 7% 6% 7% 9% 10% 29%	2470
July	1st to 10th	Day	7% 6% 3 8% 8% 9% 10% 7% 10% 12% 20%	4120
	11th to 20th	Day	5% 4 2 8% 6% 8% 8% 6% 10% 12% 31%	4120
	21st to end	Day	4 5% 2 9% 9% 8% 10% 8% 11% 13% 20%	4357
August	1st to 10th	Day	6% 5% 3 7% 6% 7% 8% 6% 10% 13% 28%	3785
	11th to 20th	Day	6% 5% 2 6% 5% 6% 6% 5% 8% 11% 41%	3729
	21st to end	Day	6% 5% 2 8% 7% 7% 9% 7% 9% 11% 28%	4180
September	1st to 10th	Day	9% 6% 3 9% 7% 7% 7% 6% 8% 9% 29%	2120
	11th to 20th	Day	13% 6% 3 8% 6% 6% 7% 5% 6% 8% 33%	2090
	21st to end	Day	10% 5% 2 5% 4 4 5% 4 6% 9% 47%	2090
October	1st to 10th	Day	9% 6% 3 6% 5% 4 4 4 5% 7% 48%	2090
	11th to 20th	Day	7% 3 2 4 3 2 3 4 5% 8% 61%	2090
	21st to end	Day	8% 4 2 5% 4 4 3 3 5% 7% 56%	2112
November	1st to 10th	Day	9% 6% 2 4 3 3 4 3 5% 6% 56%	1795
	11th to 20th	Day	11% 6% 2 4 4 3 3 3 5% 6% 54%	1800
	21st to end	Day	10% 5% 2 6% 4 4 3 3 5% 8% 48%	1773
December	1st to 10th	Day	12% 6% 1 5% 5% 5% 4 3 5% 6% 47%	1710
	11th to 20th	Day	16% 7% 3 6% 4 4 4 3 5% 5% 42%	2153
	21st to end	Day	17% 8% 3 8% 4 3 3 3 4 5% 43%	3124
January	1st to 10th	Night	15% 6% 2 6% 4 4 4 3 4 6% 44%	4109
	11th to 20th	Night	9% 6% 2 7% 4 5% 5% 3 5% 7% 46%	3960
	21st to end	Night	19% 10% 3 6% 3 3 4 3 4 6% 39%	4180
February	1st to 10th	Night	13% 8% 3 6% 4 3 3 4 4 6% 45%	2280
	11th to 20th	Night	15% 8% 3 5% 4 3 3 3 5% 5% 47%	2218
	21st to end	Night	13% 6% 2 6% 4 4 4 3 5% 6% 46%	1884
March	1st to 10th	Night	19% 11% 3 8% 5% 4 4 3 4 6% 33%	3707
	11th to 20th	Night	10% 6% 2 5% 4 4 4 4 7% 9% 46%	3480
	21st to end	Night	14% 7% 2 5% 4 3 4 3 5% 7% 45%	3817
April	1st to 10th	Night	9% 5% 2 6% 4 4 4 4 6% 8% 47%	1996
	11th to 20th	Night	9% 5% 2 7% 4 5% 6% 3 6% 6% 47%	1875
	21st to end	Night	6% 4 1 4 3 4 4 3 6% 8% 58%	1900
May	1st to 10th	Night	7% 5% 2 7% 4 4 4 4 6% 10% 47%	2827
	11th to 20th	Night	12% 5% 2 6% 5% 5% 5% 4 5% 8% 43%	2812
	21st to end	Night	4 4 2 5% 5% 4 4 4 6% 11% 52%	3079
June	1st to 10th	Night	6% 4 2 6% 6% 5% 6% 5% 9% 10% 39%	1710
	11th to 20th	Night	3 4 2 5% 5% 4 7% 6% 11% 13% 41%	1710
	21st to end	Night	5% 4 3 7% 6% 4 7% 6% 8% 11% 39%	1710
July	1st to 10th	Night	5% 6% 3 9% 6% 7% 7% 7% 11% 15% 25%	2840
	11th to 20th	Night	2 3 2 4 5% 5% 6% 5% 9% 14% 46%	2840
	21st to end	Night	3 4 2 7% 7% 6% 7% 6% 11% 15% 32%	3177
August	1st to 10th	Night	6% 3 2 5% 4 5% 6% 5% 9% 14% 40%	3144
	11th to 20th	Night	4 4 1 6% 4 5% 6% 5% 9% 13% 42%	3100
	21st to end	Night	6% 5% 2 7% 6% 6% 7% 7% 10% 12% 32%	3476
September	1st to 10th	Night	9% 6% 3 8% 5% 6% 6% 6% 8% 12% 31%	2038
	11th to 20th	Night	10% 7% 2 6% 6% 6% 6% 5% 7% 9% 37%	2090
	21st to end	Night	8% 5% 2 6% 4 4 5% 4 6% 9% 48%	2090
October	1st to 10th	Night	6% 4 1 7% 4 4 5% 4 5% 7% 52%	2090
	11th to 20th	Night	7% 4 2 3 3 3 4 2 4 6% 62%	2090
	21st to end	Night	8% 5% 2 6% 3 3 4 3 4 6% 56%	2484
November	1st to 10th	Night	7% 4 2 5% 5% 3 4 3 5% 6% 55%	2498
	11th to 20th	Night	10% 5% 2 5% 4 4 3 3 5% 7% 54%	2600
	21st to end	Night	11% 7% 2 5% 3 4 4 4 5% 6% 49%	2562
December	1st to 10th	Night	12% 7% 2 5% 4 4 4 4 5% 7% 46%	2470
	11th to 20th	Night	13% 7% 2 6% 4 4 4 3 5% 6% 47%	3042
	21st to end	Night	17% 9% 3 6% 4 4 3 3 4 5% 40%	4532

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	39% 4 5% 16% 23% 12%	2837
	11th to 20th	Day	32% 3 7% 18% 25% 15%	2982
	21st to end	Day	45% 4 7% 13% 20% 11%	3476
February	1st to 10th	Day	43% 3 7% 16% 21% 10%	1900
	11th to 20th	Day	37% 4 6% 17% 24% 13%	1858
	21st to end	Day	40% 6% 9% 16% 18% 10%	1570
March	1st to 10th	Day	46% 6% 7% 19% 16% 6%	3144
	11th to 20th	Day	34% 6% 13% 15% 20% 12%	3480
	21st to end	Day	35% 6% 11% 21% 15% 11%	3815
April	1st to 10th	Day	37% 6% 9% 18% 16% 13%	2197
	11th to 20th	Day	37% 6% 7% 17% 21% 11%	2254
	21st to end	Day	29% 6% 8% 23% 23% 11%	2280
May	1st to 10th	Day	33% 9% 10% 21% 21% 7%	4104
	11th to 20th	Day	41% 8% 11% 21% 16% 3	4085
	21st to end	Day	28% 11% 15% 25% 20% 2	4489
June	1st to 10th	Day	47% 10% 14% 19% 8% 1	2470
	11th to 20th	Day	40% 12% 17% 20% 10% 1	2470
	21st to end	Day	44% 13% 18% 15% 8% 2	2470
July	1st to 10th	Day	48% 16% 27% 8% 1	4055
	11th to 20th	Day	39% 15% 32% 11% 2	4051
	21st to end	Day	45% 19% 23% 11% 2	4218
August	1st to 10th	Day	40% 12% 19% 17% 10% 1	3773
	11th to 20th	Day	32% 11% 17% 24% 15% 1	3765
	21st to end	Day	42% 12% 23% 15% 7% 1	4179
September	1st to 10th	Day	47% 10% 15% 16% 10% 3	2120
	11th to 20th	Day	46% 9% 12% 16% 12% 5%	2090
	21st to end	Day	33% 7% 12% 20% 20% 9%	2090
October	1st to 10th	Day	40% 5% 6% 11% 17% 21%	3480
	11th to 20th	Day	15% 3 5% 18% 25% 33%	3458
	21st to end	Day	19% 3 4 15% 40% 19%	3462
November	1st to 10th	Day	30% 4 7% 21% 23% 16%	1795
	11th to 20th	Day	31% 4 6% 17% 27% 15%	1800
	21st to end	Day	34% 5% 6% 22% 22% 11%	1773
December	1st to 10th	Day	37% 4 12% 17% 22% 8%	1710
	11th to 20th	Day	44% 4 6% 15% 23% 9%	2150
	21st to end	Day	44% 4 6% 18% 22% 7%	3124
January	1st to 10th	Night	41% 4 7% 10% 22% 16%	4109
	11th to 20th	Night	37% 4 6% 13% 28% 12%	3960
	21st to end	Night	46% 4 7% 14% 21% 8%	4180
February	1st to 10th	Night	40% 4 7% 14% 22% 13%	2280
	11th to 20th	Night	40% 4 7% 13% 20% 16%	2219
	21st to end	Night	39% 5% 7% 17% 18% 14%	1884
March	1st to 10th	Night	52% 6% 7% 14% 14% 7%	3707
	11th to 20th	Night	33% 6% 12% 18% 20% 11%	3480
	21st to end	Night	38% 4 10% 19% 18% 11%	3817
April	1st to 10th	Night	33% 6% 13% 16% 17% 14%	1996
	11th to 20th	Night	36% 5% 8% 18% 24% 10%	1875
	21st to end	Night	23% 5% 9% 29% 23% 10%	1900
May	1st to 10th	Night	30% 9% 17% 20% 18% 6%	2854
	11th to 20th	Night	37% 8% 14% 22% 16% 3	2813
	21st to end	Night	23% 10% 17% 32% 16% 3	3087
June	1st to 10th	Night	34% 11% 21% 24% 8% 2	1710
	11th to 20th	Night	27% 13% 23% 26% 8% 3	1710
	21st to end	Night	33% 12% 28% 16% 10% 2	1710
July	1st to 10th	Night	43% 16% 29% 10% 2	2795
	11th to 20th	Night	24% 16% 44% 13% 2	2786
	21st to end	Night	35% 20% 29% 13% 2	3076
August	1st to 10th	Night	30% 12% 23% 24% 9% 1	3132
	11th to 20th	Night	27% 14% 24% 25% 9% 1	3130
	21st to end	Night	37% 14% 27% 14% 7% 1	3476
September	1st to 10th	Night	41% 13% 19% 14% 10% 3	2038
	11th to 20th	Night	40% 11% 15% 16% 14% 3	2090
	21st to end	Night	30% 8% 15% 20% 19% 8%	2090
October	1st to 10th	Night	36% 5% 9% 12% 20% 18%	3480
	11th to 20th	Night	14% 3 5% 17% 30% 32%	3461
	21st to end	Night	20% 3 5% 13% 39% 19%	4084
November	1st to 10th	Night	29% 4 7% 20% 23% 17%	2498
	11th to 20th	Night	32% 3 6% 15% 28% 15%	2600
	21st to end	Night	34% 6% 8% 17% 21% 14%	2562
December	1st to 10th	Night	37% 5% 11% 17% 22% 7%	2470
	11th to 20th	Night	39% 4 7% 14% 24% 13%	3044
	21st to end	Night	46% 5% 6% 18% 22% 5%	4532

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	14% 14% 43% 23% 5%	270
	11th to 20th	Day	10% 19% 33% 25% 11% 2	270
	21st to end	Day	22% 20% 40% 13% 4	297
February	1st to 10th	Day	20% 16% 37% 20% 6%	270
	11th to 20th	Day	21% 16% 36% 20% 7%	270
	21st to end	Day	13% 21% 41% 19% 5%	225
March	1st to 10th	Day	12% 18% 42% 18% 9%	281
	11th to 20th	Day	13% 13% 34% 25% 12% 2	460
	21st to end	Day	13% 14% 32% 27% 12% 1	506
April	1st to 10th	Day	16% 14% 26% 26% 15% 2	460
	11th to 20th	Day	14% 10% 29% 25% 17% 4	452
	21st to end	Day	8% 10% 25% 29% 21% 7%	460
May	1st to 10th	Day	7% 8% 23% 27% 24% 11%	463
	11th to 20th	Day	9% 4 16% 33% 21% 16%	487
	21st to end	Day	10% 2 13% 30% 23% 22%	529
June	1st to 10th	Day	14% 2 11% 24% 28% 20%	490
	11th to 20th	Day	7% 2 12% 23% 30% 27%	490
	21st to end	Day	9% 3 6% 25% 28% 29%	490
July	1st to 10th	Day	7% 3 5% 15% 30% 40%	485
	11th to 20th	Day	8% 2 2 15% 32% 41%	484
	21st to end	Day	5% 1 3 20% 36% 35%	532
August	1st to 10th	Day	7% 4 5% 17% 31% 37%	486
	11th to 20th	Day	10% 2 3 16% 33% 35%	479
	21st to end	Day	10% 1 7% 25% 33% 24%	539
September	1st to 10th	Day	13% 2 6% 19% 33% 26%	490
	11th to 20th	Day	16% 4 8% 27% 28% 17%	490
	21st to end	Day	12% 2 10% 25% 32% 19%	490
October	1st to 10th	Day	11% 6% 21% 36% 21% 6%	490
	11th to 20th	Day	7% 5% 19% 32% 27% 10%	490
	21st to end	Day	9% 7% 22% 35% 22% 4	539
November	1st to 10th	Day	15% 5% 25% 29% 20% 6%	333
	11th to 20th	Day	13% 10% 35% 31% 8% 4	300
	21st to end	Day	9% 12% 35% 29% 11% 4	291
December	1st to 10th	Day	18% 14% 30% 25% 11% 3	270
	11th to 20th	Day	23% 11% 34% 22% 9% 1	270
	21st to end	Day	20% 11% 34% 21% 13% 2	297
January	1st to 10th	Night	17% 9% 36% 29% 7% 1	760
	11th to 20th	Night	12% 12% 31% 34% 11%	760
	21st to end	Night	20% 11% 35% 29% 5%	836
February	1st to 10th	Night	16% 10% 30% 36% 8% 1	760
	11th to 20th	Night	18% 11% 32% 31% 8%	743
	21st to end	Night	15% 11% 36% 32% 5%	628
March	1st to 10th	Night	17% 8% 28% 38% 9%	760
	11th to 20th	Night	14% 8% 34% 32% 12% 1	760
	21st to end	Night	11% 9% 31% 37% 12%	836
April	1st to 10th	Night	10% 8% 30% 39% 13% 1	666
	11th to 20th	Night	11% 4 29% 37% 18% 1	563
	21st to end	Night	7% 4 24% 42% 22% 1	570
May	1st to 10th	Night	7% 4 22% 41% 25% 2	570
	11th to 20th	Night	8% 3 16% 38% 31% 5%	561
	21st to end	Night	6% 2 10% 37% 38% 7%	617
June	1st to 10th	Night	7% 1 6% 34% 42% 8%	570
	11th to 20th	Night	4 1 8% 29% 46% 12%	570
	21st to end	Night	7% 1 8% 27% 45% 12%	570
July	1st to 10th	Night	5% 3 3 20% 48% 21%	555
	11th to 20th	Night	5% 1 16% 49% 28%	552
	21st to end	Night	3 1 2 20% 56% 19%	624
August	1st to 10th	Night	7% 2 2 17% 45% 26%	567
	11th to 20th	Night	6% 1 2 17% 51% 22%	564
	21st to end	Night	9% 3 5% 20% 46% 16%	627
September	1st to 10th	Night	11% 3 6% 23% 42% 15%	708
	11th to 20th	Night	12% 4 9% 29% 38% 8%	760
	21st to end	Night	10% 1 13% 28% 40% 8%	760
October	1st to 10th	Night	8% 1 22% 35% 30% 4	760
	11th to 20th	Night	9% 5% 19% 32% 31% 4	760
	21st to end	Night	9% 5% 19% 41% 24% 2	836
November	1st to 10th	Night	9% 5% 24% 37% 23% 2	780
	11th to 20th	Night	12% 7% 28% 35% 17% 1	800
	21st to end	Night	15% 6% 28% 33% 17% 2	789
December	1st to 10th	Night	15% 7% 28% 32% 16% 2	760
	11th to 20th	Night	16% 6% 30% 35% 13% 1	760
	21st to end	Night	21% 8% 28% 32% 12% 1	836

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