Deep Woods Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Deep Woods Observatory clear sky chart from 2005-11-06 to 2026-09-29.

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% 5% 5% 4 6% 7% 35%	149874
	Night	12% 10% 4 9% 5% 5% 4 4 5% 7% 35%	141914
Transparency	Day	45% 7% 12% 23% 12% 1	153318
	Night	46% 7% 13% 22% 11% 1	146556
Seeing	Day	21% 17% 33% 19% 8% 2	18724
	Night	20% 14% 33% 25% 8% 1	28499

By Month

Percentage Cloud Cover NE (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	8% 13% 5% 13% 8% 7% 5% 4 6% 7% 24%	4691
	11th to 20th	Day	8% 14% 6% 12% 8% 6% 8% 5% 6% 6% 21%	4679
	21st to end	Day	8% 12% 6% 13% 5% 5% 5% 4 6% 7% 28%	5156
February	1st to 10th	Day	9% 13% 5% 11% 6% 5% 5% 4 6% 6% 31%	1821
	11th to 20th	Day	10% 12% 3 10% 6% 5% 4 5% 5% 7% 32%	1963
	21st to end	Day	12% 15% 5% 10% 6% 5% 4 3 5% 8% 27%	1730
March	1st to 10th	Day	13% 10% 2 7% 4 4 4 3 6% 6% 42%	4578
	11th to 20th	Day	11% 11% 4 10% 7% 6% 5% 4 6% 7% 30%	4792
	21st to end	Day	22% 13% 5% 12% 5% 4 3 3 3 4 25%	6101
April	1st to 10th	Day	16% 15% 5% 9% 6% 4 4 3 6% 7% 26%	2520
	11th to 20th	Day	19% 12% 5% 9% 5% 4 4 4 5% 5% 30%	2494
	21st to end	Day	17% 12% 4 8% 4 5% 5% 4 5% 6% 30%	2709
May	1st to 10th	Day	11% 7% 2 7% 5% 5% 5% 4 5% 7% 42%	8037
	11th to 20th	Day	12% 8% 3 7% 5% 5% 4 3 5% 6% 41%	8222
	21st to end	Day	12% 8% 2 7% 5% 4 5% 3 6% 7% 40%	9061
June	1st to 10th	Day	13% 7% 3 6% 5% 4 5% 4 6% 8% 40%	2940
	11th to 20th	Day	15% 7% 2 7% 5% 5% 5% 4 7% 8% 35%	2940
	21st to end	Day	14% 6% 3 8% 5% 5% 5% 4 7% 9% 34%	2940
July	1st to 10th	Day	11% 5% 2 6% 5% 5% 5% 4 7% 10% 40%	8279
	11th to 20th	Day	7% 4 2 5% 4 4 5% 4 6% 10% 49%	8280
	21st to end	Day	10% 6% 2 7% 4 4 5% 4 6% 8% 44%	8992
August	1st to 10th	Day	9% 6% 2 6% 5% 5% 5% 4 6% 9% 42%	6483
	11th to 20th	Day	12% 5% 2 6% 4 5% 5% 4 6% 8% 44%	5972
	21st to end	Day	15% 7% 3 6% 4 4 5% 4 6% 8% 37%	6080
September	1st to 10th	Day	13% 6% 2 7% 5% 5% 5% 3 5% 6% 43%	2520
	11th to 20th	Day	13% 7% 2 7% 4 5% 5% 4 6% 8% 39%	2418
	21st to end	Day	13% 8% 4 8% 5% 5% 5% 3 5% 8% 36%	2288
October	1st to 10th	Day	17% 8% 3 7% 4 4 4 4 5% 7% 37%	2080
	11th to 20th	Day	20% 12% 4 9% 6% 5% 5% 4 6% 6% 25%	1938
	21st to end	Day	20% 14% 4 9% 4 3 4 3 5% 6% 27%	1980
November	1st to 10th	Day	15% 10% 4 8% 5% 5% 5% 4 5% 7% 32%	1852
	11th to 20th	Day	15% 16% 6% 10% 6% 4 4 3 5% 6% 25%	1814
	21st to end	Day	15% 15% 5% 11% 6% 6% 4 4 6% 7% 22%	1680
December	1st to 10th	Day	9% 14% 6% 20% 9% 6% 5% 5% 5% 4 18%	2690
	11th to 20th	Day	11% 20% 5% 13% 6% 5% 4 3 4 5% 24%	3084
	21st to end	Day	21% 22% 7% 10% 4 4 3 2 3 4 20%	4070
January	1st to 10th	Night	11% 13% 5% 13% 7% 6% 5% 4 5% 7% 24%	8233
	11th to 20th	Night	7% 15% 6% 15% 9% 6% 6% 4 5% 6% 20%	8236
	21st to end	Night	6% 11% 6% 14% 7% 5% 5% 4 6% 6% 29%	9058
February	1st to 10th	Night	11% 12% 5% 10% 6% 4 6% 4 6% 7% 30%	2798
	11th to 20th	Night	9% 12% 3 10% 7% 7% 5% 4 5% 7% 31%	2542
	21st to end	Night	13% 16% 4 9% 6% 5% 4 3 5% 7% 29%	2076
March	1st to 10th	Night	11% 8% 3 8% 4 4 4 3 5% 8% 41%	5482
	11th to 20th	Night	11% 11% 4 11% 5% 5% 4 4 5% 9% 30%	5431
	21st to end	Night	20% 12% 5% 9% 5% 4 4 3 5% 6% 27%	5072
April	1st to 10th	Night	19% 13% 4 9% 4 4 4 3 4 7% 30%	2100
	11th to 20th	Night	22% 10% 4 6% 4 4 3 4 4 5% 35%	2075
	21st to end	Night	17% 8% 4 8% 6% 4 5% 3 6% 5% 35%	1909
May	1st to 10th	Night	11% 8% 3 6% 4 3 4 3 6% 7% 45%	4867
	11th to 20th	Night	13% 9% 3 8% 4 3 4 3 5% 6% 40%	4670
	21st to end	Night	13% 7% 3 6% 4 4 4 3 5% 6% 44%	5148
June	1st to 10th	Night	11% 6% 3 5% 5% 5% 4 4 5% 8% 44%	1680
	11th to 20th	Night	14% 8% 3 6% 5% 4 5% 4 5% 6% 38%	1680
	21st to end	Night	14% 6% 2 5% 4 5% 5% 4 7% 8% 40%	1680
July	1st to 10th	Night	12% 5% 2 5% 4 4 5% 4 6% 11% 42%	4710
	11th to 20th	Night	8% 4 1 5% 3 3 4 3 6% 9% 54%	4710
	21st to end	Night	7% 5% 2 5% 4 4 4 4 5% 8% 52%	5118
August	1st to 10th	Night	10% 7% 2 7% 4 4 4 4 5% 8% 45%	3687
	11th to 20th	Night	11% 5% 2 6% 4 4 4 4 5% 7% 47%	4077
	21st to end	Night	14% 7% 2 7% 4 4 4 3 5% 6% 44%	5046
September	1st to 10th	Night	10% 7% 3 6% 4 3 3 3 6% 6% 51%	2100
	11th to 20th	Night	12% 6% 3 5% 4 4 4 4 5% 7% 47%	2180
	21st to end	Night	14% 7% 3 6% 4 4 4 3 4 6% 43%	2289
October	1st to 10th	Night	14% 9% 2 5% 4 4 4 3 4 6% 43%	2316
	11th to 20th	Night	17% 12% 4 7% 4 5% 4 3 6% 6% 33%	2461
	21st to end	Night	19% 14% 3 8% 5% 4 4 3 5% 7% 28%	2860
November	1st to 10th	Night	15% 11% 3 8% 4 5% 4 4 5% 7% 35%	2666
	11th to 20th	Night	15% 12% 4 9% 5% 6% 4 4 5% 6% 30%	2804
	21st to end	Night	15% 13% 4 10% 6% 5% 5% 4 5% 6% 25%	2940
December	1st to 10th	Night	13% 11% 4 11% 8% 6% 5% 4 7% 8% 23%	4720
	11th to 20th	Night	11% 16% 8% 13% 7% 5% 4 3 4 5% 24%	5343
	21st to end	Night	20% 19% 7% 10% 5% 4 3 3 4 5% 21%	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	55% 7% 14% 16% 8%	4692
	11th to 20th	Day	59% 7% 10% 16% 6% 1	4710
	21st to end	Day	52% 6% 11% 18% 12% 1	5156
February	1st to 10th	Day	50% 6% 13% 19% 11% 1	1821
	11th to 20th	Day	49% 7% 12% 22% 9% 1	1972
	21st to end	Day	54% 6% 11% 17% 11% 1	1730
March	1st to 10th	Day	41% 5% 15% 18% 18% 4	4580
	11th to 20th	Day	50% 8% 13% 18% 10% 1	4792
	21st to end	Day	62% 6% 8% 13% 11%	6101
April	1st to 10th	Day	55% 7% 12% 17% 9% 1	2520
	11th to 20th	Day	54% 6% 9% 20% 10% 1	2494
	21st to end	Day	52% 7% 9% 18% 12% 2	2709
May	1st to 10th	Day	39% 7% 10% 24% 18% 2	8046
	11th to 20th	Day	41% 7% 10% 25% 15% 2	8226
	21st to end	Day	41% 6% 9% 20% 21% 3	9061
June	1st to 10th	Day	40% 8% 13% 24% 15% 1	2940
	11th to 20th	Day	45% 8% 14% 19% 14% 1	2940
	21st to end	Day	44% 8% 14% 23% 10% 1	2940
July	1st to 10th	Day	37% 7% 17% 30% 9% 1	8211
	11th to 20th	Day	28% 6% 15% 35% 14% 1	8205
	21st to end	Day	37% 6% 11% 31% 15%	8794
August	1st to 10th	Day	36% 8% 15% 29% 10% 1	6468
	11th to 20th	Day	36% 7% 19% 29% 9%	6014
	21st to end	Day	42% 7% 15% 25% 10% 1	6079
September	1st to 10th	Day	40% 7% 13% 28% 12%	2520
	11th to 20th	Day	41% 8% 17% 27% 7%	2418
	21st to end	Day	44% 7% 12% 25% 11%	2288
October	1st to 10th	Day	33% 5% 13% 29% 20%	3392
	11th to 20th	Day	52% 5% 11% 19% 12%	3128
	21st to end	Day	53% 6% 16% 21% 5%	3180
November	1st to 10th	Day	48% 7% 13% 21% 10% 1	1852
	11th to 20th	Day	58% 8% 12% 14% 7% 1	1814
	21st to end	Day	59% 10% 13% 15% 3 1	1680
December	1st to 10th	Day	62% 9% 11% 14% 4	2690
	11th to 20th	Day	62% 6% 9% 12% 11%	3085
	21st to end	Day	67% 5% 6% 14% 7%	4070
January	1st to 10th	Night	55% 7% 10% 20% 6%	8233
	11th to 20th	Night	61% 7% 11% 13% 8% 1	8280
	21st to end	Night	50% 7% 10% 20% 12%	9058
February	1st to 10th	Night	51% 6% 10% 19% 11% 2	2798
	11th to 20th	Night	49% 7% 13% 20% 10% 2	2543
	21st to end	Night	54% 5% 13% 19% 9% 1	2076
March	1st to 10th	Night	40% 5% 19% 20% 14% 1	5493
	11th to 20th	Night	48% 7% 16% 19% 9% 1	5432
	21st to end	Night	56% 7% 11% 14% 11% 1	5072
April	1st to 10th	Night	53% 6% 11% 15% 14% 1	2100
	11th to 20th	Night	51% 6% 9% 21% 11% 3	2075
	21st to end	Night	48% 7% 11% 19% 14% 1	1909
May	1st to 10th	Night	37% 6% 12% 29% 15% 2	4874
	11th to 20th	Night	41% 9% 10% 22% 17% 1	4671
	21st to end	Night	40% 6% 11% 23% 16% 4	5149
June	1st to 10th	Night	35% 8% 14% 27% 15% 2	1680
	11th to 20th	Night	44% 8% 12% 22% 14% 1	1680
	21st to end	Night	38% 9% 15% 27% 10% 2	1680
July	1st to 10th	Night	36% 7% 20% 27% 9% 2	4670
	11th to 20th	Night	25% 6% 17% 37% 13% 1	4662
	21st to end	Night	30% 6% 16% 27% 21% 1	5002
August	1st to 10th	Night	35% 8% 16% 24% 16% 1	3678
	11th to 20th	Night	34% 8% 17% 28% 11% 2	4101
	21st to end	Night	41% 7% 13% 26% 12% 1	5046
September	1st to 10th	Night	33% 7% 15% 31% 13% 1	2100
	11th to 20th	Night	35% 8% 15% 32% 10%	2180
	21st to end	Night	40% 8% 15% 26% 10% 2	2289
October	1st to 10th	Night	33% 5% 9% 36% 15% 2	3784
	11th to 20th	Night	42% 6% 11% 26% 14%	4010
	21st to end	Night	52% 5% 12% 22% 8%	4610
November	1st to 10th	Night	48% 6% 12% 22% 11% 1	2666
	11th to 20th	Night	52% 8% 13% 17% 9% 1	2804
	21st to end	Night	55% 9% 14% 17% 4 1	2940
December	1st to 10th	Night	52% 9% 20% 16% 3	4720
	11th to 20th	Night	61% 6% 9% 15% 9%	5341
	21st to end	Night	64% 5% 7% 16% 9%	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	22% 15% 37% 19% 5% 1	330
	11th to 20th	Day	28% 20% 34% 16% 3	330
	21st to end	Day	23% 19% 42% 14% 2	363
February	1st to 10th	Day	17% 32% 37% 10% 3 1	330
	11th to 20th	Day	24% 29% 33% 12% 2 1	330
	21st to end	Day	30% 26% 36% 7% 1	273
March	1st to 10th	Day	25% 26% 39% 10% 1	330
	11th to 20th	Day	28% 24% 33% 11% 4	341
	21st to end	Day	29% 21% 29% 14% 6% 1	594
April	1st to 10th	Day	30% 19% 31% 15% 3	540
	11th to 20th	Day	31% 20% 28% 15% 5% 1	532
	21st to end	Day	30% 17% 29% 16% 6% 1	540
May	1st to 10th	Day	25% 19% 33% 15% 7% 1	679
	11th to 20th	Day	22% 20% 34% 17% 4 3	775
	21st to end	Day	19% 15% 35% 20% 7% 4	844
June	1st to 10th	Day	18% 16% 33% 22% 9% 3	780
	11th to 20th	Day	21% 13% 36% 19% 8% 1	780
	21st to end	Day	19% 14% 32% 22% 9% 3	780
July	1st to 10th	Day	9% 9% 36% 27% 13% 5%	771
	11th to 20th	Day	12% 11% 36% 25% 9% 6%	768
	21st to end	Day	9% 11% 37% 25% 13% 5%	849
August	1st to 10th	Day	13% 10% 31% 27% 15% 5%	776
	11th to 20th	Day	16% 7% 27% 28% 16% 6%	644
	21st to end	Day	19% 11% 27% 22% 16% 5%	627
September	1st to 10th	Day	20% 12% 26% 26% 12% 5%	570
	11th to 20th	Day	16% 10% 32% 28% 11% 3	570
	21st to end	Day	19% 13% 25% 28% 12% 3	562
October	1st to 10th	Day	21% 19% 31% 18% 10% 1	410
	11th to 20th	Day	26% 27% 32% 13% 2	330
	21st to end	Day	30% 23% 33% 12% 2	363
November	1st to 10th	Day	25% 20% 38% 13% 4 1	330
	11th to 20th	Day	28% 25% 33% 9% 3 2	330
	21st to end	Day	29% 23% 34% 10% 3	330
December	1st to 10th	Day	21% 22% 40% 13% 4 1	330
	11th to 20th	Day	27% 26% 32% 12% 2	330
	21st to end	Day	33% 20% 32% 11% 2 1	363
January	1st to 10th	Night	18% 20% 41% 19% 3 1	1050
	11th to 20th	Night	20% 18% 39% 17% 5% 1	1050
	21st to end	Night	18% 16% 41% 20% 5%	1155
February	1st to 10th	Night	20% 18% 38% 18% 6%	1050
	11th to 20th	Night	20% 22% 34% 20% 5%	907
	21st to end	Night	21% 21% 40% 17% 2	692
March	1st to 10th	Night	19% 17% 35% 23% 6%	840
	11th to 20th	Night	20% 20% 36% 19% 5%	802
	21st to end	Night	23% 12% 33% 25% 7% 1	693
April	1st to 10th	Night	27% 14% 33% 22% 4	630
	11th to 20th	Night	29% 13% 27% 25% 5%	623
	21st to end	Night	23% 13% 33% 25% 6% 1	630
May	1st to 10th	Night	22% 12% 32% 26% 7%	630
	11th to 20th	Night	22% 11% 36% 25% 6% 1	621
	21st to end	Night	15% 9% 31% 34% 10% 1	683
June	1st to 10th	Night	14% 10% 29% 34% 12%	630
	11th to 20th	Night	20% 9% 29% 34% 8% 1	630
	21st to end	Night	16% 6% 31% 33% 13% 1	630
July	1st to 10th	Night	10% 4 29% 39% 16% 1	615
	11th to 20th	Night	10% 5% 34% 33% 17% 1	612
	21st to end	Night	8% 4 32% 40% 15% 2	690
August	1st to 10th	Night	12% 4 28% 38% 17% 1	627
	11th to 20th	Night	13% 4 24% 36% 21% 2	624
	21st to end	Night	15% 6% 26% 34% 18% 1	693
September	1st to 10th	Night	14% 9% 26% 30% 19% 3	630
	11th to 20th	Night	16% 7% 29% 32% 15% 2	710
	21st to end	Night	19% 9% 29% 31% 11% 1	833
October	1st to 10th	Night	20% 13% 30% 23% 13% 1	800
	11th to 20th	Night	24% 18% 29% 23% 7%	800
	21st to end	Night	28% 12% 31% 23% 6%	880
November	1st to 10th	Night	22% 15% 38% 20% 5%	820
	11th to 20th	Night	24% 20% 33% 17% 5% 1	914
	21st to end	Night	24% 19% 32% 21% 4	1050
December	1st to 10th	Night	22% 20% 37% 16% 5% 1	1050
	11th to 20th	Night	21% 20% 34% 19% 5% 1	1050
	21st to end	Night	30% 16% 35% 16% 3	1155

Page generated at 2026-09-26 03:18:38. Version ac07

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