Cherry Grove
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cherry Grove clear sky chart from 2005-11-06 to 2025-08-05.

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% 8% 3 8% 5% 4 5% 4 6% 7% 37%	126260
	Night	12% 9% 3 9% 5% 4 4 4 5% 6% 38%	122091
Transparency	Day	45% 4 12% 26% 12% 1	129825
	Night	46% 3 12% 25% 14% 2	126603
Seeing	Day	17% 9% 31% 26% 13% 4	17039
	Night	16% 9% 33% 30% 10% 1	26884

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	6% 13% 6% 19% 10% 7% 6% 4 6% 5% 17%	3617
	11th to 20th	Day	6% 11% 6% 12% 8% 7% 7% 8% 12% 7% 17%	3684
	21st to end	Day	8% 14% 7% 14% 7% 4 5% 3 5% 6% 27%	4488
February	1st to 10th	Day	9% 12% 4 12% 8% 6% 6% 5% 7% 7% 25%	1800
	11th to 20th	Day	9% 12% 5% 10% 6% 6% 5% 4 6% 6% 31%	1754
	21st to end	Day	13% 10% 4 11% 5% 6% 4 5% 5% 7% 31%	1575
March	1st to 10th	Day	13% 7% 3 6% 4 3 3 3 5% 7% 46%	4797
	11th to 20th	Day	11% 8% 3 7% 4 3 4 4 6% 8% 42%	4980
	21st to end	Day	23% 11% 4 10% 5% 5% 4 3 4 5% 26%	5549
April	1st to 10th	Day	17% 12% 4 8% 5% 4 4 3 5% 7% 31%	2400
	11th to 20th	Day	19% 12% 4 7% 4 4 5% 4 5% 5% 31%	2374
	21st to end	Day	20% 12% 3 7% 5% 4 4 4 5% 6% 29%	2564
May	1st to 10th	Day	14% 6% 2 5% 4 4 4 3 5% 7% 47%	6109
	11th to 20th	Day	14% 8% 2 6% 4 4 4 4 6% 7% 43%	6319
	21st to end	Day	19% 7% 2 6% 4 4 4 4 5% 6% 38%	6935
June	1st to 10th	Day	11% 5% 2 5% 5% 4 4 4 6% 7% 46%	2800
	11th to 20th	Day	13% 7% 2 7% 5% 4 4 5% 7% 9% 37%	2800
	21st to end	Day	13% 6% 2 6% 5% 5% 5% 4 6% 9% 39%	2800
July	1st to 10th	Day	8% 5% 2 6% 4 5% 6% 5% 7% 9% 43%	6360
	11th to 20th	Day	7% 4 2 5% 4 3 4 3 5% 8% 55%	6360
	21st to end	Day	7% 5% 2 6% 5% 4 5% 4 7% 9% 45%	6820
August	1st to 10th	Day	11% 6% 2 6% 4 5% 6% 4 6% 7% 42%	4157
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 6% 9% 43%	4041
	21st to end	Day	8% 6% 2 6% 4 5% 4 5% 5% 8% 47%	4281
September	1st to 10th	Day	13% 5% 2 5% 4 3 4 4 5% 8% 47%	2280
	11th to 20th	Day	11% 6% 2 7% 4 4 4 4 6% 6% 48%	2275
	21st to end	Day	12% 7% 3 7% 4 4 4 4 4 8% 43%	1983
October	1st to 10th	Day	15% 8% 2 5% 4 3 4 4 5% 6% 45%	1900
	11th to 20th	Day	14% 10% 2 6% 4 4 4 3 5% 6% 42%	1900
	21st to end	Day	17% 11% 4 7% 3 3 4 3 5% 6% 36%	2066
November	1st to 10th	Day	11% 10% 4 8% 3 4 4 4 6% 7% 39%	1692
	11th to 20th	Day	12% 13% 6% 11% 6% 4 4 4 5% 6% 29%	1600
	21st to end	Day	11% 12% 5% 8% 6% 5% 3 3 4 7% 35%	1600
December	1st to 10th	Day	7% 7% 4 13% 11% 8% 6% 5% 5% 7% 27%	2610
	11th to 20th	Day	11% 15% 6% 12% 8% 9% 5% 4 5% 6% 21%	3008
	21st to end	Day	17% 19% 7% 20% 5% 3 4 2 4 4 13%	3982
January	1st to 10th	Night	7% 12% 5% 17% 7% 8% 5% 4 5% 5% 25%	6348
	11th to 20th	Night	7% 10% 4 12% 8% 7% 9% 8% 10% 5% 19%	6291
	21st to end	Night	9% 12% 6% 11% 6% 5% 5% 3 5% 6% 32%	6490
February	1st to 10th	Night	7% 13% 5% 11% 6% 7% 5% 4 5% 6% 33%	2600
	11th to 20th	Night	7% 10% 4 10% 6% 6% 5% 4 6% 6% 37%	2533
	21st to end	Night	12% 9% 4 9% 5% 6% 4 3 5% 6% 36%	2054
March	1st to 10th	Night	11% 7% 3 7% 4 3 4 3 4 6% 48%	5099
	11th to 20th	Night	9% 7% 2 7% 5% 4 5% 3 7% 9% 42%	4980
	21st to end	Night	24% 11% 4 10% 4 3 3 3 4 5% 28%	5378
April	1st to 10th	Night	14% 12% 3 7% 5% 4 4 4 5% 6% 37%	2000
	11th to 20th	Night	18% 11% 3 7% 4 3 3 3 5% 6% 36%	1975
	21st to end	Night	19% 10% 3 7% 5% 4 3 3 5% 5% 37%	1833
May	1st to 10th	Night	13% 6% 2 5% 4 3 4 3 4 6% 49%	3805
	11th to 20th	Night	13% 6% 2 4 3 3 3 4 6% 7% 50%	3596
	21st to end	Night	15% 8% 3 8% 5% 4 4 3 5% 6% 40%	3942
June	1st to 10th	Night	9% 4 2 5% 4 4 5% 5% 6% 8% 49%	1600
	11th to 20th	Night	11% 6% 2 7% 5% 5% 4 4 6% 9% 43%	1600
	21st to end	Night	9% 4 2 5% 3 4 4 4 5% 7% 53%	1600
July	1st to 10th	Night	7% 4 2 5% 3 4 5% 5% 7% 10% 48%	3618
	11th to 20th	Night	6% 5% 1 4 3 4 4 4 6% 9% 54%	3617
	21st to end	Night	9% 5% 2 5% 3 4 4 3 6% 9% 50%	4036
August	1st to 10th	Night	11% 6% 2 6% 4 4 4 3 5% 7% 47%	2872
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 5% 6% 52%	2798
	21st to end	Night	8% 6% 3 6% 4 4 4 3 5% 7% 50%	3378
September	1st to 10th	Night	8% 4 2 5% 3 3 3 3 5% 6% 57%	1900
	11th to 20th	Night	11% 5% 2 5% 3 3 4 3 5% 7% 53%	1900
	21st to end	Night	12% 6% 1 5% 3 3 3 3 5% 6% 53%	2177
October	1st to 10th	Night	14% 6% 2 5% 3 3 3 3 5% 6% 50%	2280
	11th to 20th	Night	15% 7% 2 5% 4 4 4 3 5% 8% 43%	2280
	21st to end	Night	16% 10% 3 7% 4 4 4 3 5% 6% 38%	2532
November	1st to 10th	Night	11% 9% 3 7% 4 3 4 3 5% 6% 43%	2604
	11th to 20th	Night	11% 11% 4 10% 5% 5% 4 3 5% 6% 36%	2800
	21st to end	Night	13% 10% 4 8% 6% 4 4 3 5% 6% 37%	2800
December	1st to 10th	Night	6% 7% 4 14% 8% 8% 5% 4 6% 8% 30%	4580
	11th to 20th	Night	11% 14% 7% 14% 7% 5% 5% 4 4 5% 25%	5199
	21st to end	Night	20% 16% 6% 18% 6% 4 4 3 4 4 15%	6996

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% 2 8% 17% 5%	3618
	11th to 20th	Day	60% 2 8% 17% 13%	3684
	21st to end	Day	59% 3 14% 16% 9%	4488
February	1st to 10th	Day	57% 3 12% 17% 10% 1	1800
	11th to 20th	Day	53% 3 11% 25% 7% 1	1763
	21st to end	Day	53% 3 12% 20% 11% 1	1575
March	1st to 10th	Day	39% 2 16% 28% 13% 2	4797
	11th to 20th	Day	40% 3 13% 31% 11% 1	4980
	21st to end	Day	62% 2 10% 17% 8% 1	5551
April	1st to 10th	Day	53% 3 10% 22% 11% 1	2400
	11th to 20th	Day	55% 4 10% 20% 11% 1	2374
	21st to end	Day	55% 3 12% 20% 9% 1	2564
May	1st to 10th	Day	38% 3 10% 31% 17% 2	6147
	11th to 20th	Day	40% 3 9% 29% 15% 4	6323
	21st to end	Day	47% 2 9% 31% 10% 1	6949
June	1st to 10th	Day	36% 4 13% 31% 14% 1	2800
	11th to 20th	Day	42% 5% 14% 23% 15% 1	2800
	21st to end	Day	40% 4 16% 26% 11% 2	2800
July	1st to 10th	Day	36% 6% 16% 33% 9%	6291
	11th to 20th	Day	28% 4 15% 36% 16% 1	6285
	21st to end	Day	35% 6% 14% 30% 15% 1	6626
August	1st to 10th	Day	40% 4 11% 29% 13% 2	4143
	11th to 20th	Day	37% 5% 13% 33% 11%	4080
	21st to end	Day	34% 6% 15% 29% 15% 1	4280
September	1st to 10th	Day	36% 4 12% 32% 15%	2280
	11th to 20th	Day	37% 3 15% 33% 11% 1	2275
	21st to end	Day	41% 3 10% 32% 12% 1	1983
October	1st to 10th	Day	29% 2 7% 38% 23%	3160
	11th to 20th	Day	38% 2 12% 24% 21% 2	3140
	21st to end	Day	43% 3 13% 31% 10%	3380
November	1st to 10th	Day	43% 4 14% 22% 14% 3	1692
	11th to 20th	Day	55% 4 12% 18% 10% 1	1600
	21st to end	Day	50% 3 17% 21% 8% 1	1600
December	1st to 10th	Day	58% 4 16% 15% 7% 1	2610
	11th to 20th	Day	64% 3 14% 15% 5%	3005
	21st to end	Day	77% 2 7% 10% 4	3982
January	1st to 10th	Night	61% 2 9% 20% 7%	6348
	11th to 20th	Night	60% 3 11% 14% 12% 1	6291
	21st to end	Night	53% 2 11% 23% 10% 1	6490
February	1st to 10th	Night	53% 2 11% 22% 10% 2	2600
	11th to 20th	Night	47% 3 12% 26% 10% 1	2534
	21st to end	Night	50% 2 12% 22% 13% 2	2054
March	1st to 10th	Night	38% 2 11% 31% 15% 3	5099
	11th to 20th	Night	39% 3 12% 29% 17% 1	4980
	21st to end	Night	59% 3 10% 17% 10% 2	5378
April	1st to 10th	Night	49% 3 9% 23% 15% 1	2000
	11th to 20th	Night	50% 3 9% 21% 16% 2	1975
	21st to end	Night	49% 2 9% 22% 15% 2	1833
May	1st to 10th	Night	38% 3 8% 27% 23% 1	3832
	11th to 20th	Night	35% 3 11% 25% 21% 6%	3597
	21st to end	Night	46% 3 9% 30% 12%	3950
June	1st to 10th	Night	33% 4 13% 31% 16% 2	1600
	11th to 20th	Night	38% 5% 13% 25% 17% 3	1600
	21st to end	Night	30% 4 16% 30% 18% 3	1600
July	1st to 10th	Night	30% 5% 21% 31% 12% 1	3580
	11th to 20th	Night	26% 6% 16% 37% 14% 2	3572
	21st to end	Night	31% 5% 16% 29% 17% 2	3920
August	1st to 10th	Night	37% 4 11% 30% 16% 3	2862
	11th to 20th	Night	33% 4 14% 32% 15% 1	2825
	21st to end	Night	34% 4 17% 28% 16% 2	3378
September	1st to 10th	Night	29% 4 10% 36% 20% 1	1900
	11th to 20th	Night	32% 3 15% 33% 17% 1	1900
	21st to end	Night	33% 3 12% 32% 18% 1	2177
October	1st to 10th	Night	25% 2 6% 36% 28% 4	3800
	11th to 20th	Night	30% 3 13% 28% 23% 3	3779
	21st to end	Night	44% 3 10% 27% 16% 1	4168
November	1st to 10th	Night	42% 2 13% 26% 14% 2	2604
	11th to 20th	Night	50% 3 11% 21% 13% 1	2800
	21st to end	Night	50% 3 15% 23% 8% 1	2800
December	1st to 10th	Night	53% 3 17% 20% 6% 1	4580
	11th to 20th	Night	63% 3 11% 17% 6% 1	5201
	21st to end	Night	74% 2 7% 12% 5%	6996

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	13% 14% 38% 23% 9% 3	300
	11th to 20th	Day	17% 12% 44% 22% 4 1	300
	21st to end	Day	16% 10% 41% 23% 9% 2	330
February	1st to 10th	Day	16% 16% 44% 19% 3 1	300
	11th to 20th	Day	15% 19% 41% 19% 4 1	300
	21st to end	Day	22% 14% 38% 24% 2	249
March	1st to 10th	Day	15% 14% 46% 19% 6% 1	300
	11th to 20th	Day	24% 11% 36% 21% 7% 1	300
	21st to end	Day	31% 11% 30% 20% 6% 1	366
April	1st to 10th	Day	28% 14% 33% 19% 7%	500
	11th to 20th	Day	29% 17% 23% 21% 9% 1	492
	21st to end	Day	29% 11% 28% 22% 8% 2	664
May	1st to 10th	Day	22% 11% 30% 25% 10% 2	703
	11th to 20th	Day	21% 11% 26% 27% 11% 4	725
	21st to end	Day	21% 8% 26% 27% 15% 3	789
June	1st to 10th	Day	10% 8% 29% 30% 18% 5%	730
	11th to 20th	Day	15% 8% 33% 32% 10% 3	730
	21st to end	Day	15% 8% 31% 27% 15% 4	730
July	1st to 10th	Day	9% 4 23% 32% 23% 9%	721
	11th to 20th	Day	9% 5% 28% 32% 18% 8%	718
	21st to end	Day	8% 3 26% 39% 19% 6%	794
August	1st to 10th	Day	11% 2 21% 36% 22% 8%	697
	11th to 20th	Day	14% 3 18% 35% 23% 7%	665
	21st to end	Day	12% 4 27% 30% 22% 5%	601
September	1st to 10th	Day	17% 5% 27% 31% 14% 6%	490
	11th to 20th	Day	13% 3 29% 30% 20% 5%	485
	21st to end	Day	16% 12% 29% 26% 14% 3	300
October	1st to 10th	Day	18% 11% 26% 26% 15% 4	300
	11th to 20th	Day	19% 16% 39% 19% 7% 1	300
	21st to end	Day	25% 15% 35% 15% 8% 1	330
November	1st to 10th	Day	20% 13% 37% 20% 8% 1	300
	11th to 20th	Day	19% 19% 41% 16% 5%	300
	21st to end	Day	21% 13% 45% 18% 4	300
December	1st to 10th	Day	15% 10% 43% 26% 5% 1	300
	11th to 20th	Day	21% 13% 40% 18% 7% 1	300
	21st to end	Day	27% 14% 38% 18% 3 1	330
January	1st to 10th	Night	14% 13% 38% 27% 7% 1	1000
	11th to 20th	Night	18% 10% 41% 25% 5% 1	1000
	21st to end	Night	17% 12% 38% 26% 7% 1	1100
February	1st to 10th	Night	13% 14% 41% 26% 6% 1	1000
	11th to 20th	Night	13% 14% 44% 21% 6% 1	979
	21st to end	Night	18% 14% 35% 26% 6%	734
March	1st to 10th	Night	18% 13% 36% 26% 7% 1	682
	11th to 20th	Night	17% 10% 39% 26% 7% 1	600
	21st to end	Night	23% 10% 30% 26% 9% 2	660
April	1st to 10th	Night	20% 13% 37% 25% 6%	600
	11th to 20th	Night	25% 10% 31% 28% 6%	593
	21st to end	Night	24% 7% 33% 27% 9% 1	600
May	1st to 10th	Night	20% 7% 31% 33% 8% 1	600
	11th to 20th	Night	19% 6% 31% 32% 11% 2	591
	21st to end	Night	18% 5% 25% 38% 12% 1	650
June	1st to 10th	Night	10% 4 32% 39% 15% 1	600
	11th to 20th	Night	14% 4 34% 37% 11%	600
	21st to end	Night	12% 4 25% 43% 16% 1	600
July	1st to 10th	Night	8% 1 19% 41% 28% 3	585
	11th to 20th	Night	6% 4 25% 40% 23% 2	582
	21st to end	Night	7% 2 21% 49% 20% 2	657
August	1st to 10th	Night	8% 2 17% 45% 26% 2	579
	11th to 20th	Night	13% 1 18% 37% 27% 4	564
	21st to end	Night	10% 1 25% 38% 23% 3	627
September	1st to 10th	Night	11% 4 23% 41% 16% 5%	570
	11th to 20th	Night	14% 3 30% 32% 18% 2	570
	21st to end	Night	15% 8% 30% 32% 14% 1	657
October	1st to 10th	Night	17% 7% 29% 33% 13% 1	760
	11th to 20th	Night	18% 12% 35% 27% 8% 1	760
	21st to end	Night	22% 11% 31% 28% 7% 1	836
November	1st to 10th	Night	16% 13% 35% 28% 6% 1	848
	11th to 20th	Night	16% 15% 38% 24% 6%	1000
	21st to end	Night	17% 17% 36% 23% 7%	1000
December	1st to 10th	Night	16% 11% 40% 27% 6% 1	1000
	11th to 20th	Night	19% 11% 39% 24% 7% 1	1000
	21st to end	Night	26% 12% 33% 24% 5%	1100

Page generated at 2025-08-02 00:32:29. Version ac07

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