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Sugar Grove Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sugar Grove Observatory clear sky chart from 2005-11-06 to 2025-11-03.

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	13% 9% 3 8% 5% 4 5% 4 6% 7% 37%	126856
	Night	14% 9% 3 8% 4 4 4 3 5% 6% 39%	123444
Transparency	Day	44% 6% 11% 23% 14% 2	130389
	Night	44% 5% 10% 23% 15% 2	127985
Seeing	Day	15% 11% 28% 25% 16% 5%	17102
	Night	17% 10% 31% 30% 12% 1	26886

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	14% 12% 6% 14% 7% 6% 5% 4 5% 6% 22%	3617
	11th to 20th	Day	10% 10% 5% 14% 8% 7% 8% 4 6% 5% 21%	3620
	21st to end	Day	17% 16% 7% 11% 7% 4 3 3 4 5% 24%	4393
February	1st to 10th	Day	15% 13% 6% 11% 5% 6% 3 3 4 6% 29%	1820
	11th to 20th	Day	13% 11% 4 10% 7% 6% 4 3 5% 6% 32%	1948
	21st to end	Day	14% 14% 4 10% 5% 4 4 4 4 6% 32%	1650
March	1st to 10th	Day	19% 13% 4 6% 3 3 3 3 3 4 40%	4480
	11th to 20th	Day	7% 9% 3 6% 4 4 5% 4 6% 8% 43%	4791
	21st to end	Day	18% 11% 4 10% 5% 5% 5% 4 5% 7% 28%	5916
April	1st to 10th	Day	16% 11% 3 8% 4 4 5% 3 5% 6% 35%	2400
	11th to 20th	Day	15% 10% 3 7% 5% 4 4 2 6% 6% 38%	2374
	21st to end	Day	19% 7% 3 7% 4 4 4 4 6% 7% 35%	2405
May	1st to 10th	Day	18% 8% 3 7% 4 4 5% 4 6% 8% 32%	5862
	11th to 20th	Day	16% 7% 2 7% 4 4 4 3 5% 8% 40%	6195
	21st to end	Day	13% 7% 2 7% 4 5% 5% 4 6% 8% 38%	6935
June	1st to 10th	Day	9% 5% 2 6% 5% 4 4 5% 7% 9% 45%	2800
	11th to 20th	Day	8% 5% 2 5% 5% 4 5% 4 6% 8% 48%	2800
	21st to end	Day	9% 6% 2 6% 5% 5% 5% 4 7% 9% 42%	2800
July	1st to 10th	Day	10% 5% 2 6% 4 4 5% 5% 7% 11% 41%	6360
	11th to 20th	Day	10% 6% 3 7% 5% 5% 5% 5% 7% 10% 37%	6360
	21st to end	Day	11% 6% 3 6% 5% 5% 5% 5% 7% 10% 38%	6924
August	1st to 10th	Day	7% 4 2 6% 4 4 5% 4 7% 10% 49%	4270
	11th to 20th	Day	9% 5% 2 6% 4 4 6% 4 7% 10% 42%	3849
	21st to end	Day	5% 4 1 6% 4 5% 6% 4 7% 10% 48%	4312
September	1st to 10th	Day	11% 5% 2 6% 4 4 4 3 5% 7% 49%	2400
	11th to 20th	Day	9% 4 2 5% 4 4 4 3 5% 7% 53%	2315
	21st to end	Day	10% 6% 2 6% 4 4 3 5% 6% 7% 47%	2200
October	1st to 10th	Day	11% 5% 2 6% 4 4 4 4 5% 5% 50%	2088
	11th to 20th	Day	16% 8% 3 6% 4 4 4 3 5% 5% 44%	2000
	21st to end	Day	17% 9% 3 6% 4 4 3 3 5% 6% 38%	2055
November	1st to 10th	Day	11% 7% 2 5% 4 3 3 3 5% 7% 49%	1780
	11th to 20th	Day	16% 11% 3 7% 4 3 4 3 5% 6% 39%	1800
	21st to end	Day	17% 12% 3 9% 4 4 4 3 4 5% 36%	1737
December	1st to 10th	Day	8% 10% 4 8% 4 4 4 3 5% 6% 44%	2610
	11th to 20th	Day	14% 16% 6% 10% 5% 5% 5% 4 5% 6% 24%	3008
	21st to end	Day	26% 19% 6% 13% 5% 4 3 2 3 4 14%	3982
January	1st to 10th	Night	14% 15% 6% 12% 4 4 3 3 4 5% 30%	6348
	11th to 20th	Night	11% 15% 6% 13% 7% 6% 6% 4 4 4 24%	6360
	21st to end	Night	18% 14% 6% 9% 4 4 4 3 4 5% 30%	6582
February	1st to 10th	Night	16% 12% 6% 9% 5% 4 4 4 4 6% 30%	2578
	11th to 20th	Night	13% 11% 4 9% 6% 4 4 3 5% 6% 35%	2338
	21st to end	Night	16% 12% 4 7% 4 3 4 3 5% 5% 37%	1980
March	1st to 10th	Night	18% 13% 3 6% 3 3 3 2 4 5% 39%	5373
	11th to 20th	Night	11% 7% 3 6% 4 4 3 3 4 6% 48%	5212
	21st to end	Night	18% 9% 3 9% 6% 5% 4 4 5% 6% 30%	5012
April	1st to 10th	Night	13% 9% 3 6% 5% 4 4 3 6% 7% 41%	2000
	11th to 20th	Night	16% 8% 2 6% 4 5% 4 3 5% 6% 42%	1975
	21st to end	Night	19% 7% 2 7% 5% 4 5% 3 4 6% 37%	1993
May	1st to 10th	Night	19% 9% 3 7% 5% 4 4 3 5% 7% 34%	4033
	11th to 20th	Night	14% 5% 2 7% 4 3 4 3 7% 10% 41%	3711
	21st to end	Night	13% 8% 3 7% 5% 4 4 3 5% 8% 40%	3942
June	1st to 10th	Night	9% 5% 2 4 4 4 5% 4 6% 9% 49%	1600
	11th to 20th	Night	8% 5% 2 7% 4 4 4 3 7% 7% 49%	1600
	21st to end	Night	7% 5% 2 6% 5% 5% 5% 5% 7% 8% 45%	1600
July	1st to 10th	Night	10% 6% 2 6% 4 5% 4 4 6% 10% 43%	3618
	11th to 20th	Night	6% 5% 2 6% 5% 5% 5% 4 7% 9% 47%	3617
	21st to end	Night	9% 7% 3 7% 5% 5% 5% 3 6% 9% 43%	3947
August	1st to 10th	Night	6% 3 1 5% 4 4 4 4 7% 9% 53%	2881
	11th to 20th	Night	7% 4 2 5% 4 4 4 4 6% 8% 51%	3200
	21st to end	Night	6% 4 1 5% 4 4 4 4 6% 9% 55%	3586
September	1st to 10th	Night	11% 4 2 5% 3 3 3 3 4 7% 55%	2000
	11th to 20th	Night	8% 3 2 5% 3 3 4 3 6% 8% 56%	2065
	21st to end	Night	8% 6% 2 6% 4 4 5% 4 5% 6% 51%	2200
October	1st to 10th	Night	11% 4 2 5% 4 4 4 3 4 6% 55%	2310
	11th to 20th	Night	15% 6% 2 4 3 3 3 2 5% 6% 51%	2400
	21st to end	Night	18% 9% 2 6% 4 4 4 3 5% 6% 40%	2785
November	1st to 10th	Night	11% 7% 1 6% 4 4 4 3 4 5% 50%	2563
	11th to 20th	Night	13% 8% 3 7% 4 4 4 4 4 7% 42%	2600
	21st to end	Night	17% 10% 4 7% 5% 4 4 3 5% 6% 37%	2660
December	1st to 10th	Night	12% 9% 3 8% 4 4 3 3 4 5% 45%	4580
	11th to 20th	Night	17% 11% 5% 10% 5% 4 3 3 4 5% 33%	5199
	21st to end	Night	25% 19% 6% 10% 5% 4 4 3 4 4 16%	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	62% 5% 9% 17% 6% 1	3618
	11th to 20th	Day	63% 6% 8% 11% 10% 2	3620
	21st to end	Day	65% 3 9% 16% 7%	4393
February	1st to 10th	Day	58% 4 11% 18% 8% 2	1820
	11th to 20th	Day	54% 5% 10% 20% 11% 1	1958
	21st to end	Day	54% 6% 8% 20% 10% 2	1650
March	1st to 10th	Day	50% 4 6% 21% 17% 2	4480
	11th to 20th	Day	37% 6% 10% 31% 15% 1	4791
	21st to end	Day	55% 6% 13% 18% 6% 1	5918
April	1st to 10th	Day	49% 5% 11% 22% 12%	2400
	11th to 20th	Day	47% 5% 9% 24% 12% 3	2374
	21st to end	Day	48% 6% 13% 20% 11% 2	2405
May	1st to 10th	Day	47% 8% 10% 22% 11% 1	5897
	11th to 20th	Day	43% 7% 10% 26% 11% 3	6199
	21st to end	Day	41% 8% 11% 22% 17% 2	6949
June	1st to 10th	Day	34% 9% 12% 27% 15% 3	2800
	11th to 20th	Day	33% 7% 11% 25% 21% 3	2800
	21st to end	Day	37% 8% 14% 22% 17% 3	2800
July	1st to 10th	Day	35% 6% 13% 29% 15% 2	6291
	11th to 20th	Day	39% 9% 15% 23% 14% 1	6285
	21st to end	Day	38% 10% 17% 22% 11% 1	6728
August	1st to 10th	Day	28% 8% 19% 32% 13% 1	4255
	11th to 20th	Day	34% 8% 14% 27% 15% 1	3885
	21st to end	Day	29% 7% 14% 29% 16% 4	4311
September	1st to 10th	Day	34% 6% 10% 25% 21% 5%	2400
	11th to 20th	Day	31% 6% 9% 25% 24% 5%	2315
	21st to end	Day	36% 5% 8% 26% 23% 2	2200
October	1st to 10th	Day	25% 4 7% 23% 38% 4	3400
	11th to 20th	Day	30% 3 9% 21% 34% 3	3240
	21st to end	Day	40% 4 8% 24% 21% 2	3293
November	1st to 10th	Day	36% 4 14% 25% 17% 4	1780
	11th to 20th	Day	47% 3 10% 24% 13% 3	1800
	21st to end	Day	51% 4 11% 23% 11%	1737
December	1st to 10th	Day	41% 4 14% 31% 10%	2610
	11th to 20th	Day	60% 5% 10% 19% 6% 1	3005
	21st to end	Day	75% 4 8% 9% 4	3982
January	1st to 10th	Night	57% 4 9% 22% 7%	6348
	11th to 20th	Night	63% 4 8% 12% 11% 2	6360
	21st to end	Night	58% 4 8% 18% 11% 1	6582
February	1st to 10th	Night	55% 4 10% 18% 11% 2	2578
	11th to 20th	Night	50% 4 11% 21% 12% 2	2339
	21st to end	Night	49% 3 9% 23% 13% 2	1980
March	1st to 10th	Night	49% 4 8% 23% 14% 3	5373
	11th to 20th	Night	37% 5% 9% 28% 18% 3	5212
	21st to end	Night	54% 6% 10% 22% 8% 1	5012
April	1st to 10th	Night	43% 5% 11% 23% 15% 2	2000
	11th to 20th	Night	43% 5% 8% 25% 15% 5%	1975
	21st to end	Night	48% 5% 11% 21% 12% 3	1993
May	1st to 10th	Night	49% 6% 10% 20% 11% 3	4060
	11th to 20th	Night	38% 8% 12% 26% 13% 3	3712
	21st to end	Night	42% 7% 11% 21% 16% 3	3950
June	1st to 10th	Night	32% 6% 12% 28% 17% 5%	1600
	11th to 20th	Night	33% 6% 12% 23% 22% 4	1600
	21st to end	Night	34% 8% 15% 23% 17% 4	1600
July	1st to 10th	Night	35% 6% 11% 29% 16% 2	3580
	11th to 20th	Night	31% 9% 15% 25% 19% 1	3572
	21st to end	Night	37% 9% 15% 22% 14% 3	3832
August	1st to 10th	Night	25% 8% 17% 31% 17% 2	2872
	11th to 20th	Night	29% 8% 13% 32% 17% 1	3230
	21st to end	Night	26% 7% 13% 32% 17% 3	3586
September	1st to 10th	Night	30% 5% 9% 26% 23% 6%	2000
	11th to 20th	Night	27% 5% 9% 26% 28% 5%	2065
	21st to end	Night	32% 6% 9% 26% 23% 4	2200
October	1st to 10th	Night	21% 4 6% 26% 39% 4	3778
	11th to 20th	Night	25% 3 8% 25% 35% 5%	3899
	21st to end	Night	37% 4 9% 22% 23% 4	4497
November	1st to 10th	Night	36% 5% 10% 26% 19% 4	2563
	11th to 20th	Night	42% 4 12% 23% 17% 2	2600
	21st to end	Night	49% 3 10% 23% 13% 1	2660
December	1st to 10th	Night	41% 4 12% 30% 12% 1	4580
	11th to 20th	Night	54% 4 12% 20% 10% 1	5201
	21st to end	Night	72% 4 8% 11% 4	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	23% 16% 35% 21% 5%	300
	11th to 20th	Day	23% 21% 42% 12% 2	300
	21st to end	Day	20% 17% 38% 22% 3	330
February	1st to 10th	Day	24% 15% 39% 19% 2	300
	11th to 20th	Day	23% 18% 37% 17% 5%	300
	21st to end	Day	27% 16% 41% 15% 2	249
March	1st to 10th	Day	21% 23% 35% 18% 3	300
	11th to 20th	Day	22% 23% 35% 15% 5%	300
	21st to end	Day	29% 16% 34% 15% 5% 1	525
April	1st to 10th	Day	23% 15% 34% 22% 6%	500
	11th to 20th	Day	19% 21% 28% 20% 10% 2	492
	21st to end	Day	21% 16% 35% 20% 7% 1	500
May	1st to 10th	Day	20% 13% 32% 24% 9% 2	503
	11th to 20th	Day	20% 12% 25% 26% 14% 3	666
	21st to end	Day	14% 7% 33% 25% 14% 6%	789
June	1st to 10th	Day	9% 7% 27% 29% 22% 6%	730
	11th to 20th	Day	9% 6% 25% 34% 21% 5%	730
	21st to end	Day	9% 7% 32% 30% 17% 4	730
July	1st to 10th	Day	9% 3 19% 29% 25% 15%	721
	11th to 20th	Day	8% 3 21% 33% 25% 10%	718
	21st to end	Day	9% 2 16% 36% 30% 7%	794
August	1st to 10th	Day	7% 2 17% 35% 28% 10%	686
	11th to 20th	Day	8% 4 19% 27% 29% 12%	519
	21st to end	Day	7% 3 17% 30% 34% 9%	583
September	1st to 10th	Day	10% 6% 20% 29% 30% 5%	530
	11th to 20th	Day	7% 3 15% 31% 31% 13%	530
	21st to end	Day	11% 11% 23% 23% 23% 9%	530
October	1st to 10th	Day	12% 5% 27% 31% 20% 5%	418
	11th to 20th	Day	17% 19% 29% 25% 8% 2	330
	21st to end	Day	27% 15% 35% 18% 4 1	363
November	1st to 10th	Day	13% 16% 31% 26% 11% 3	306
	11th to 20th	Day	20% 18% 34% 18% 9% 1	300
	21st to end	Day	24% 12% 36% 24% 4	300
December	1st to 10th	Day	13% 19% 45% 15% 6% 3	300
	11th to 20th	Day	19% 20% 35% 23% 4	300
	21st to end	Day	26% 22% 35% 16% 2	330
January	1st to 10th	Night	18% 15% 40% 22% 5%	1000
	11th to 20th	Night	20% 16% 38% 21% 5%	1000
	21st to end	Night	21% 15% 37% 24% 3	1100
February	1st to 10th	Night	22% 13% 39% 22% 3	978
	11th to 20th	Night	21% 13% 37% 26% 3	783
	21st to end	Night	23% 16% 38% 21% 2	660
March	1st to 10th	Night	21% 13% 38% 24% 4	800
	11th to 20th	Night	19% 14% 34% 27% 5% 1	702
	21st to end	Night	24% 11% 37% 22% 5%	660
April	1st to 10th	Night	18% 15% 36% 27% 4	600
	11th to 20th	Night	18% 13% 34% 26% 9%	593
	21st to end	Night	24% 10% 33% 27% 6% 1	600
May	1st to 10th	Night	18% 9% 35% 30% 7% 1	600
	11th to 20th	Night	17% 7% 27% 37% 12% 1	591
	21st to end	Night	11% 5% 32% 31% 20% 2	650
June	1st to 10th	Night	11% 4 26% 45% 15%	600
	11th to 20th	Night	10% 4 25% 45% 16% 1	600
	21st to end	Night	8% 3 28% 39% 21% 1	600
July	1st to 10th	Night	11% 3 14% 36% 32% 5%	585
	11th to 20th	Night	7% 2 16% 44% 29% 2	582
	21st to end	Night	6% 1 15% 44% 33% 1	657
August	1st to 10th	Night	7% 2 14% 44% 29% 4	597
	11th to 20th	Night	6% 3 15% 43% 29% 5%	594
	21st to end	Night	6% 2 15% 40% 36% 2	660
September	1st to 10th	Night	12% 4 15% 37% 29% 3	600
	11th to 20th	Night	9% 2 17% 39% 29% 4	665
	21st to end	Night	11% 6% 22% 35% 24% 2	800
October	1st to 10th	Night	12% 4 27% 37% 18% 2	800
	11th to 20th	Night	17% 11% 31% 30% 10% 1	800
	21st to end	Night	24% 12% 35% 22% 7%	880
November	1st to 10th	Night	14% 11% 38% 28% 9% 1	789
	11th to 20th	Night	17% 15% 35% 27% 6%	800
	21st to end	Night	21% 13% 37% 24% 5%	860
December	1st to 10th	Night	21% 11% 40% 22% 5%	1000
	11th to 20th	Night	22% 12% 34% 27% 5%	1000
	21st to end	Night	29% 15% 33% 20% 2	1100

Page generated at 2025-10-31 01:02:40. Version ac07

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