Wild Apple Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wild Apple Observatory clear sky chart from 2005-11-06 to 2026-04-17.

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	12% 9% 3 8% 5% 4 4 4 6% 7% 38%	131823
	Night	12% 9% 4 8% 5% 4 4 3 5% 6% 39%	130635
Transparency	Day	44% 5% 12% 25% 13% 1	135293
	Night	45% 4 11% 23% 15% 2	135226
Seeing	Day	16% 11% 30% 25% 14% 4	17802
	Night	17% 10% 31% 29% 11% 1	27801

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	9% 11% 7% 16% 6% 6% 6% 3 5% 5% 26%	4691
	11th to 20th	Day	6% 10% 6% 11% 5% 4 5% 7% 7% 7% 32%	4710
	21st to end	Day	9% 12% 6% 9% 6% 4 5% 3 4 6% 38%	5496
February	1st to 10th	Day	12% 13% 5% 10% 6% 4 4 4 5% 7% 31%	1890
	11th to 20th	Day	12% 12% 4 8% 5% 3 5% 3 6% 7% 36%	1957
	21st to end	Day	12% 14% 4 10% 6% 5% 4 3 4 6% 33%	1730
March	1st to 10th	Day	15% 8% 3 6% 3 3 3 3 4 7% 46%	4580
	11th to 20th	Day	12% 6% 2 8% 4 4 4 3 6% 8% 44%	4986
	21st to end	Day	22% 12% 3 9% 5% 4 4 3 4 5% 29%	5991
April	1st to 10th	Day	17% 13% 4 7% 6% 4 4 3 5% 6% 31%	2520
	11th to 20th	Day	18% 11% 3 8% 5% 4 4 3 6% 6% 33%	2446
	21st to end	Day	18% 10% 3 8% 5% 4 5% 3 5% 5% 33%	2440
May	1st to 10th	Day	14% 8% 3 6% 5% 4 4 4 6% 7% 40%	6128
	11th to 20th	Day	13% 6% 3 6% 5% 4 4 4 5% 8% 42%	6319
	21st to end	Day	15% 7% 2 6% 4 4 4 4 6% 9% 38%	6935
June	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 4 7% 8% 44%	2800
	11th to 20th	Day	12% 5% 2 6% 5% 4 5% 4 7% 8% 41%	2800
	21st to end	Day	12% 6% 3 6% 6% 4 5% 4 7% 7% 40%	2800
July	1st to 10th	Day	9% 6% 2 7% 5% 5% 6% 4 8% 9% 39%	6360
	11th to 20th	Day	8% 6% 2 6% 4 5% 5% 4 6% 8% 47%	6360
	21st to end	Day	10% 6% 3 7% 5% 5% 6% 4 7% 9% 38%	6924
August	1st to 10th	Day	10% 6% 2 6% 5% 5% 6% 5% 6% 9% 41%	4437
	11th to 20th	Day	11% 4 2 6% 4 4 5% 4 5% 7% 47%	3974
	21st to end	Day	9% 6% 2 6% 4 4 4 4 7% 9% 45%	4312
September	1st to 10th	Day	13% 5% 2 6% 5% 6% 4 3 6% 7% 44%	2400
	11th to 20th	Day	12% 5% 2 4 3 4 4 3 6% 8% 50%	2354
	21st to end	Day	12% 7% 2 7% 4 5% 3 3 5% 7% 45%	2200
October	1st to 10th	Day	12% 6% 2 6% 4 4 4 3 4 6% 49%	2011
	11th to 20th	Day	18% 10% 2 7% 4 4 4 3 5% 5% 38%	2000
	21st to end	Day	17% 11% 3 6% 4 3 3 3 3 6% 41%	2039
November	1st to 10th	Day	11% 8% 2 8% 4 5% 4 3 4 6% 44%	1852
	11th to 20th	Day	15% 12% 4 9% 5% 5% 4 3 5% 6% 34%	1853
	21st to end	Day	13% 13% 4 10% 5% 4 3 3 4 6% 35%	1680
December	1st to 10th	Day	8% 10% 4 9% 5% 5% 4 4 6% 8% 38%	2690
	11th to 20th	Day	13% 15% 5% 11% 6% 5% 5% 4 6% 7% 24%	3088
	21st to end	Day	17% 23% 9% 12% 4 4 4 4 5% 4 14%	4070
January	1st to 10th	Night	10% 11% 7% 13% 7% 4 4 3 4 5% 32%	8232
	11th to 20th	Night	8% 12% 6% 14% 7% 6% 5% 5% 6% 6% 24%	8280
	21st to end	Night	9% 12% 7% 10% 6% 5% 4 4 4 6% 34%	8700
February	1st to 10th	Night	10% 13% 5% 10% 6% 5% 4 4 5% 5% 33%	2730
	11th to 20th	Night	12% 9% 3 7% 6% 5% 5% 3 4 6% 39%	2549
	21st to end	Night	14% 12% 3 9% 4 4 4 3 5% 5% 36%	2076
March	1st to 10th	Night	16% 8% 3 7% 4 4 4 3 4 4 43%	5493
	11th to 20th	Night	10% 7% 2 6% 4 4 3 3 5% 8% 47%	5236
	21st to end	Night	22% 13% 4 10% 5% 4 4 3 4 5% 27%	5179
April	1st to 10th	Night	18% 9% 3 7% 4 3 4 4 5% 6% 37%	2100
	11th to 20th	Night	19% 9% 3 7% 4 3 4 3 5% 6% 37%	2035
	21st to end	Night	18% 8% 2 5% 4 4 5% 3 6% 7% 37%	1960
May	1st to 10th	Night	17% 7% 3 6% 4 4 4 4 6% 6% 40%	3774
	11th to 20th	Night	10% 6% 2 6% 4 4 4 4 5% 8% 47%	3596
	21st to end	Night	14% 7% 3 6% 5% 4 4 4 6% 7% 40%	3942
June	1st to 10th	Night	8% 5% 2 6% 3 5% 5% 4 7% 9% 46%	1600
	11th to 20th	Night	13% 6% 2 5% 4 4 4 3 7% 9% 45%	1600
	21st to end	Night	9% 6% 2 6% 4 4 4 4 5% 7% 50%	1600
July	1st to 10th	Night	12% 6% 2 6% 4 4 4 4 6% 9% 43%	3618
	11th to 20th	Night	6% 5% 2 6% 4 4 4 4 6% 8% 52%	3617
	21st to end	Night	8% 5% 2 6% 4 4 5% 4 6% 8% 49%	3947
August	1st to 10th	Night	9% 5% 2 6% 3 4 4 4 6% 7% 50%	2719
	11th to 20th	Night	10% 5% 2 5% 3 4 4 3 6% 8% 49%	3079
	21st to end	Night	10% 4 2 5% 4 4 4 3 5% 7% 50%	3586
September	1st to 10th	Night	8% 5% 1 5% 3 3 4 3 5% 7% 55%	2000
	11th to 20th	Night	10% 5% 2 4 4 4 4 3 5% 7% 52%	2025
	21st to end	Night	9% 5% 2 6% 4 4 4 3 5% 7% 52%	2200
October	1st to 10th	Night	12% 6% 2 6% 3 4 4 3 4 6% 51%	2385
	11th to 20th	Night	16% 8% 2 6% 4 3 3 3 5% 6% 43%	2400
	21st to end	Night	17% 9% 3 6% 4 4 4 4 5% 7% 37%	2800
November	1st to 10th	Night	12% 8% 3 6% 3 4 4 3 5% 6% 47%	2666
	11th to 20th	Night	14% 10% 4 9% 5% 4 4 3 6% 6% 35%	2762
	21st to end	Night	16% 11% 4 8% 5% 4 3 3 4 5% 37%	2940
December	1st to 10th	Night	8% 8% 3 8% 5% 5% 5% 4 5% 7% 42%	4720
	11th to 20th	Night	14% 17% 5% 10% 5% 5% 5% 3 4 5% 27%	5339
	21st to end	Night	19% 19% 6% 12% 6% 5% 4 3 4 4 18%	7150

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	61% 3 13% 16% 7% 1	4692
	11th to 20th	Day	49% 3 11% 17% 18% 1	4710
	21st to end	Day	49% 3 11% 25% 11%	5496
February	1st to 10th	Day	54% 4 12% 18% 12% 1	1890
	11th to 20th	Day	48% 4 11% 25% 10% 3	1966
	21st to end	Day	54% 4 9% 21% 10% 2	1730
March	1st to 10th	Day	41% 3 11% 29% 11% 4	4580
	11th to 20th	Day	39% 3 13% 30% 13% 2	4986
	21st to end	Day	59% 3 11% 15% 10% 2	5993
April	1st to 10th	Day	54% 5% 10% 20% 11% 1	2520
	11th to 20th	Day	52% 5% 10% 20% 12% 2	2446
	21st to end	Day	52% 5% 11% 18% 12% 1	2440
May	1st to 10th	Day	43% 5% 9% 25% 18% 1	6163
	11th to 20th	Day	40% 7% 10% 28% 14%	6323
	21st to end	Day	42% 6% 11% 27% 12% 2	6949
June	1st to 10th	Day	36% 7% 15% 26% 15% 1	2800
	11th to 20th	Day	38% 7% 14% 24% 17% 1	2800
	21st to end	Day	40% 7% 13% 23% 14% 2	2800
July	1st to 10th	Day	39% 7% 14% 30% 10% 1	6291
	11th to 20th	Day	34% 6% 14% 32% 13% 1	6285
	21st to end	Day	41% 7% 14% 22% 15% 1	6728
August	1st to 10th	Day	38% 7% 14% 27% 13% 1	4422
	11th to 20th	Day	35% 6% 14% 31% 13% 1	4013
	21st to end	Day	33% 5% 14% 31% 15% 1	4311
September	1st to 10th	Day	38% 6% 11% 26% 17% 2	2400
	11th to 20th	Day	32% 6% 12% 32% 16% 2	2354
	21st to end	Day	39% 5% 9% 29% 18% 1	2200
October	1st to 10th	Day	25% 3 6% 40% 26% 1	3271
	11th to 20th	Day	36% 3 8% 26% 23% 3	3240
	21st to end	Day	43% 3 10% 27% 15% 3	3264
November	1st to 10th	Day	42% 4 13% 25% 14% 2	1852
	11th to 20th	Day	51% 5% 12% 21% 10% 1	1853
	21st to end	Day	51% 4 15% 22% 7% 1	1680
December	1st to 10th	Day	44% 4 20% 25% 7% 1	2690
	11th to 20th	Day	59% 3 12% 17% 7% 2	3085
	21st to end	Day	73% 4 8% 10% 6%	4070
January	1st to 10th	Night	55% 3 12% 20% 9% 1	8233
	11th to 20th	Night	59% 4 9% 12% 16% 1	8280
	21st to end	Night	52% 2 11% 22% 12%	8700
February	1st to 10th	Night	53% 4 12% 19% 12% 1	2730
	11th to 20th	Night	46% 5% 11% 24% 13% 1	2550
	21st to end	Night	49% 4 11% 22% 11% 3	2076
March	1st to 10th	Night	46% 3 11% 23% 10% 7%	5493
	11th to 20th	Night	36% 3 10% 34% 13% 4	5236
	21st to end	Night	61% 3 8% 16% 11% 1	5179
April	1st to 10th	Night	47% 6% 9% 22% 14% 2	2100
	11th to 20th	Night	48% 5% 6% 20% 18% 3	2035
	21st to end	Night	45% 6% 12% 23% 12% 2	1960
May	1st to 10th	Night	43% 6% 10% 18% 22% 2	3801
	11th to 20th	Night	36% 7% 15% 22% 19% 2	3597
	21st to end	Night	40% 6% 11% 25% 15% 2	3950
June	1st to 10th	Night	32% 6% 13% 28% 19% 1	1600
	11th to 20th	Night	35% 5% 12% 24% 22% 2	1600
	21st to end	Night	35% 6% 15% 22% 19% 3	1600
July	1st to 10th	Night	38% 6% 14% 27% 13% 2	3580
	11th to 20th	Night	30% 6% 13% 31% 19% 2	3572
	21st to end	Night	32% 6% 17% 23% 19% 3	3832
August	1st to 10th	Night	32% 5% 13% 29% 20% 1	2710
	11th to 20th	Night	33% 6% 13% 31% 17% 1	3106
	21st to end	Night	34% 5% 11% 28% 18% 3	3586
September	1st to 10th	Night	28% 6% 12% 29% 23% 2	2000
	11th to 20th	Night	31% 5% 11% 32% 18% 2	2025
	21st to end	Night	32% 5% 10% 29% 22% 1	2200
October	1st to 10th	Night	25% 4 5% 37% 28% 2	3905
	11th to 20th	Night	32% 4 10% 27% 24% 3	3899
	21st to end	Night	43% 4 9% 26% 15% 2	4512
November	1st to 10th	Night	39% 4 11% 26% 17% 2	2666
	11th to 20th	Night	50% 4 13% 21% 11% 2	2762
	21st to end	Night	50% 3 12% 23% 10% 1	2940
December	1st to 10th	Night	42% 4 17% 28% 9% 1	4720
	11th to 20th	Night	61% 3 10% 16% 9% 1	5341
	21st to end	Night	70% 4 7% 13% 5%	7150

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% 16% 35% 24% 8% 2	330
	11th to 20th	Day	18% 18% 40% 19% 4 1	330
	21st to end	Day	19% 19% 37% 21% 4	363
February	1st to 10th	Day	15% 20% 41% 18% 5% 1	330
	11th to 20th	Day	20% 22% 35% 20% 4	330
	21st to end	Day	24% 16% 45% 14% 1	273
March	1st to 10th	Day	18% 20% 41% 17% 4	330
	11th to 20th	Day	21% 20% 39% 13% 5% 2	330
	21st to end	Day	26% 16% 33% 18% 6% 1	538
April	1st to 10th	Day	25% 17% 34% 20% 4	540
	11th to 20th	Day	26% 17% 28% 17% 11% 1	516
	21st to end	Day	23% 14% 29% 23% 9% 2	500
May	1st to 10th	Day	19% 11% 32% 26% 10% 2	613
	11th to 20th	Day	19% 12% 28% 25% 11% 5%	725
	21st to end	Day	17% 10% 26% 24% 17% 6%	789
June	1st to 10th	Day	9% 7% 30% 29% 20% 5%	730
	11th to 20th	Day	14% 5% 31% 30% 15% 4	730
	21st to end	Day	13% 9% 28% 29% 16% 5%	730
July	1st to 10th	Day	7% 4 21% 29% 26% 13%	721
	11th to 20th	Day	9% 6% 25% 31% 20% 9%	718
	21st to end	Day	8% 3 27% 33% 21% 7%	794
August	1st to 10th	Day	7% 3 21% 35% 24% 11%	726
	11th to 20th	Day	14% 5% 21% 24% 25% 11%	596
	21st to end	Day	11% 6% 20% 31% 22% 9%	583
September	1st to 10th	Day	14% 8% 22% 29% 19% 8%	530
	11th to 20th	Day	10% 3 22% 30% 26% 9%	530
	21st to end	Day	12% 11% 27% 27% 17% 5%	530
October	1st to 10th	Day	15% 11% 28% 27% 15% 4	341
	11th to 20th	Day	23% 16% 36% 17% 8%	330
	21st to end	Day	24% 18% 30% 21% 5% 1	363
November	1st to 10th	Day	15% 19% 37% 19% 8% 1	330
	11th to 20th	Day	20% 20% 35% 18% 7%	330
	21st to end	Day	21% 15% 42% 18% 4	330
December	1st to 10th	Day	15% 17% 42% 17% 8% 1	330
	11th to 20th	Day	21% 15% 38% 19% 7%	330
	21st to end	Day	27% 18% 36% 17% 3	363
January	1st to 10th	Night	16% 16% 38% 23% 6% 1	1050
	11th to 20th	Night	20% 14% 39% 23% 4 1	1050
	21st to end	Night	18% 14% 38% 25% 5%	1155
February	1st to 10th	Night	18% 13% 38% 25% 6%	1050
	11th to 20th	Night	17% 15% 39% 25% 4	914
	21st to end	Night	21% 16% 39% 20% 3	692
March	1st to 10th	Night	20% 13% 38% 22% 5%	840
	11th to 20th	Night	18% 12% 36% 26% 7%	698
	21st to end	Night	22% 11% 36% 25% 5%	693
April	1st to 10th	Night	23% 14% 36% 23% 5%	630
	11th to 20th	Night	22% 13% 30% 28% 6%	611
	21st to end	Night	20% 10% 33% 28% 9% 1	600
May	1st to 10th	Night	19% 8% 34% 30% 9% 1	600
	11th to 20th	Night	18% 6% 31% 34% 11%	591
	21st to end	Night	13% 4 28% 39% 15% 1	650
June	1st to 10th	Night	11% 5% 25% 44% 15% 1	600
	11th to 20th	Night	15% 4 31% 37% 13%	600
	21st to end	Night	11% 5% 26% 41% 16% 1	600
July	1st to 10th	Night	10% 2 13% 39% 32% 4	585
	11th to 20th	Night	7% 3 22% 41% 23% 3	582
	21st to end	Night	7% 2 18% 46% 24% 2	657
August	1st to 10th	Night	6% 2 17% 45% 28% 3	597
	11th to 20th	Night	11% 3 14% 40% 26% 5%	594
	21st to end	Night	11% 2 16% 46% 23% 3	660
September	1st to 10th	Night	9% 3 24% 36% 23% 6%	600
	11th to 20th	Night	12% 4 20% 35% 25% 4	625
	21st to end	Night	11% 8% 25% 35% 20% 2	800
October	1st to 10th	Night	16% 6% 27% 34% 17% 1	800
	11th to 20th	Night	19% 12% 31% 29% 9%	800
	21st to end	Night	22% 12% 33% 27% 6% 1	880
November	1st to 10th	Night	16% 11% 39% 25% 9% 1	820
	11th to 20th	Night	19% 15% 37% 22% 6% 1	872
	21st to end	Night	22% 14% 34% 23% 6%	1050
December	1st to 10th	Night	20% 13% 39% 23% 5%	1050
	11th to 20th	Night	24% 13% 35% 24% 5%	1050
	21st to end	Night	28% 14% 33% 22% 3	1155

Page generated at 2026-04-14 01:44:23. Version ac07

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