Woodstock
Clear Sky Chart
History

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

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	14% 11% 4 10% 5% 5% 5% 4 6% 7% 30%	114545
	Night	14% 11% 4 9% 5% 5% 5% 4 5% 7% 32%	114383
Transparency	Day	52% 6% 12% 19% 10% 1	118171
	Night	50% 5% 12% 19% 12% 1	118908
Seeing	Day	19% 12% 28% 23% 13% 5%	15489
	Night	19% 11% 29% 29% 11% 1	24691

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	12% 16% 6% 20% 7% 5% 5% 3 3 5% 18%	3779
	11th to 20th	Day	10% 20% 8% 23% 8% 6% 4 3 4 5% 9%	4026
	21st to end	Day	18% 17% 6% 16% 7% 5% 5% 3 4 4 14%	4466
February	1st to 10th	Day	14% 18% 5% 13% 8% 6% 6% 4 4 5% 17%	1800
	11th to 20th	Day	13% 15% 6% 14% 9% 5% 5% 4 4 6% 20%	1753
	21st to end	Day	16% 14% 6% 13% 7% 6% 5% 4 4 5% 22%	1615
March	1st to 10th	Day	17% 12% 5% 12% 8% 4 4 3 4 5% 26%	4860
	11th to 20th	Day	11% 13% 5% 10% 5% 5% 5% 4 5% 8% 30%	4980
	21st to end	Day	17% 12% 5% 11% 6% 5% 4 3 4 5% 29%	5465
April	1st to 10th	Day	16% 14% 4 8% 5% 4 4 4 5% 7% 28%	2298
	11th to 20th	Day	17% 11% 3 8% 4 4 5% 3 5% 7% 32%	2522
	21st to end	Day	20% 10% 3 8% 4 4 4 3 3 6% 33%	2600
May	1st to 10th	Day	18% 9% 3 7% 4 4 4 4 6% 8% 33%	4238
	11th to 20th	Day	15% 10% 3 8% 5% 4 4 4 7% 9% 30%	4166
	21st to end	Day	12% 5% 2 5% 4 4 5% 4 6% 8% 45%	4837
June	1st to 10th	Day	13% 6% 3 7% 5% 5% 5% 4 7% 8% 38%	2660
	11th to 20th	Day	10% 6% 3 7% 5% 5% 6% 4 8% 10% 38%	2766
	21st to end	Day	12% 6% 2 6% 4 5% 5% 5% 7% 9% 39%	2850
July	1st to 10th	Day	10% 5% 3 6% 5% 5% 6% 5% 7% 9% 39%	4737
	11th to 20th	Day	9% 5% 2 5% 5% 5% 5% 5% 8% 10% 39%	4226
	21st to end	Day	7% 6% 3 7% 5% 6% 6% 5% 7% 8% 40%	4466
August	1st to 10th	Day	15% 7% 2 6% 4 5% 5% 5% 7% 8% 35%	4104
	11th to 20th	Day	10% 7% 3 7% 5% 5% 6% 5% 7% 10% 35%	4044
	21st to end	Day	8% 6% 2 7% 5% 5% 6% 4 7% 9% 39%	4441
September	1st to 10th	Day	12% 6% 2 7% 5% 5% 6% 5% 6% 8% 39%	2264
	11th to 20th	Day	11% 5% 2 6% 5% 4 6% 4 6% 7% 45%	2090
	21st to end	Day	14% 7% 2 8% 5% 5% 4 5% 6% 8% 35%	2090
October	1st to 10th	Day	16% 9% 4 7% 5% 5% 4 3 5% 7% 36%	1918
	11th to 20th	Day	19% 11% 3 7% 5% 5% 5% 3 6% 7% 30%	1900
	21st to end	Day	22% 12% 4 8% 6% 4 6% 5% 5% 7% 22%	2081
November	1st to 10th	Day	13% 10% 4 9% 6% 4 4 4 6% 8% 32%	1757
	11th to 20th	Day	15% 14% 4 8% 6% 5% 6% 4 7% 8% 25%	1600
	21st to end	Day	17% 17% 7% 10% 6% 5% 5% 3 6% 6% 18%	1600
December	1st to 10th	Day	17% 19% 7% 13% 7% 6% 6% 5% 5% 4 12%	2600
	11th to 20th	Day	20% 20% 6% 11% 4 4 4 4 4 5% 18%	2986
	21st to end	Day	26% 19% 7% 14% 5% 4 4 3 4 4 10%	3960
January	1st to 10th	Night	13% 12% 6% 15% 7% 6% 5% 4 5% 7% 19%	6165
	11th to 20th	Night	11% 15% 7% 18% 9% 7% 6% 4 6% 5% 10%	5859
	21st to end	Night	17% 13% 7% 14% 6% 5% 4 3 5% 5% 20%	6490
February	1st to 10th	Night	15% 15% 6% 11% 8% 5% 6% 3 5% 6% 21%	2600
	11th to 20th	Night	14% 13% 5% 11% 7% 5% 5% 4 6% 7% 23%	2533
	21st to end	Night	15% 14% 4 12% 6% 5% 5% 4 5% 6% 23%	2013
March	1st to 10th	Night	12% 10% 4 9% 7% 5% 5% 4 6% 6% 33%	4980
	11th to 20th	Night	9% 8% 4 9% 5% 5% 5% 4 7% 8% 36%	4979
	21st to end	Night	18% 10% 4 8% 4 3 4 3 4 5% 37%	5467
April	1st to 10th	Night	19% 10% 3 8% 5% 4 5% 4 5% 7% 31%	2101
	11th to 20th	Night	17% 9% 3 7% 5% 5% 4 3 4 7% 35%	1842
	21st to end	Night	13% 10% 2 7% 5% 4 5% 4 7% 8% 34%	1800
May	1st to 10th	Night	18% 8% 3 7% 4 3 4 3 5% 7% 39%	2923
	11th to 20th	Night	11% 10% 3 8% 6% 5% 5% 4 6% 8% 36%	2729
	21st to end	Night	10% 4 2 5% 3 3 4 4 6% 7% 51%	2738
June	1st to 10th	Night	11% 6% 2 6% 4 4 4 4 7% 7% 45%	1520
	11th to 20th	Night	9% 6% 1 6% 4 4 5% 5% 7% 10% 44%	1406
	21st to end	Night	10% 5% 2 6% 4 5% 5% 4 6% 8% 46%	1330
July	1st to 10th	Night	6% 4 2 5% 4 4 4 3 5% 11% 52%	2227
	11th to 20th	Night	9% 4 2 5% 4 3 3 4 6% 8% 52%	2730
	21st to end	Night	5% 5% 2 5% 4 4 6% 5% 6% 8% 49%	3087
August	1st to 10th	Night	11% 5% 2 6% 4 5% 5% 4 6% 7% 45%	2825
	11th to 20th	Night	10% 6% 2 6% 3 4 4 4 5% 9% 46%	2785
	21st to end	Night	8% 5% 2 6% 4 4 4 4 7% 9% 47%	3183
September	1st to 10th	Night	10% 6% 2 7% 5% 4 4 3 5% 7% 47%	1913
	11th to 20th	Night	10% 5% 1 4 3 4 4 3 5% 7% 54%	2090
	21st to end	Night	16% 7% 3 7% 4 4 4 3 5% 7% 39%	2090
October	1st to 10th	Night	15% 8% 3 6% 4 4 4 3 5% 7% 42%	2261
	11th to 20th	Night	17% 9% 3 7% 5% 5% 4 4 5% 7% 35%	2280
	21st to end	Night	21% 9% 3 8% 5% 5% 4 4 6% 7% 29%	2514
November	1st to 10th	Night	14% 8% 3 6% 5% 4 4 4 6% 7% 37%	2539
	11th to 20th	Night	15% 12% 4 9% 5% 5% 4 4 7% 7% 27%	2800
	21st to end	Night	19% 13% 5% 9% 6% 5% 4 4 5% 7% 23%	2800
December	1st to 10th	Night	13% 16% 6% 13% 7% 8% 6% 5% 5% 5% 16%	4580
	11th to 20th	Night	14% 21% 6% 12% 5% 4 3 3 4 6% 22%	5208
	21st to end	Night	22% 19% 7% 11% 6% 4 4 3 4 5% 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	67% 7% 8% 11% 7%	3780
	11th to 20th	Day	77% 4 8% 6% 4	4060
	21st to end	Day	74% 5% 8% 7% 6%	4466
February	1st to 10th	Day	68% 6% 9% 13% 4 1	1800
	11th to 20th	Day	65% 5% 10% 13% 7%	1762
	21st to end	Day	64% 5% 10% 13% 6% 1	1615
March	1st to 10th	Day	60% 4 13% 16% 6% 1	4863
	11th to 20th	Day	51% 5% 16% 19% 7% 2	4980
	21st to end	Day	58% 4 10% 18% 10% 1	5465
April	1st to 10th	Day	56% 5% 11% 17% 11% 1	2298
	11th to 20th	Day	51% 5% 11% 20% 11% 1	2522
	21st to end	Day	53% 5% 9% 19% 11% 2	2600
May	1st to 10th	Day	48% 7% 13% 19% 11% 3	4250
	11th to 20th	Day	47% 10% 14% 21% 7% 1	4170
	21st to end	Day	36% 8% 12% 20% 20% 4	4837
June	1st to 10th	Day	42% 7% 13% 24% 13% 2	2660
	11th to 20th	Day	41% 8% 12% 22% 16% 2	2766
	21st to end	Day	39% 7% 14% 24% 15%	2850
July	1st to 10th	Day	39% 5% 13% 26% 14% 2	4663
	11th to 20th	Day	37% 6% 13% 31% 12% 1	4153
	21st to end	Day	39% 6% 14% 21% 19% 1	4324
August	1st to 10th	Day	45% 6% 14% 21% 13% 1	4091
	11th to 20th	Day	43% 6% 15% 26% 9% 1	4083
	21st to end	Day	40% 5% 13% 30% 12% 1	4441
September	1st to 10th	Day	41% 7% 14% 24% 13% 1	2264
	11th to 20th	Day	36% 6% 14% 28% 16%	2090
	21st to end	Day	45% 7% 13% 24% 10% 1	2090
October	1st to 10th	Day	42% 4 13% 23% 18% 1	3178
	11th to 20th	Day	41% 4 14% 21% 20%	3140
	21st to end	Day	51% 4 15% 22% 7%	3407
November	1st to 10th	Day	49% 6% 13% 22% 8% 2	1757
	11th to 20th	Day	54% 7% 16% 14% 9% 1	1600
	21st to end	Day	64% 6% 14% 12% 4	1600
December	1st to 10th	Day	72% 5% 12% 7% 3	2600
	11th to 20th	Day	69% 4 10% 9% 8%	2986
	21st to end	Day	77% 5% 6% 8% 4	3960
January	1st to 10th	Night	61% 6% 10% 16% 6%	6165
	11th to 20th	Night	71% 6% 9% 10% 4	5900
	21st to end	Night	66% 4 8% 11% 10% 1	6490
February	1st to 10th	Night	64% 6% 10% 15% 5%	2600
	11th to 20th	Night	59% 6% 12% 15% 8%	2535
	21st to end	Night	60% 6% 11% 16% 7%	2013
March	1st to 10th	Night	50% 5% 14% 19% 11% 2	4990
	11th to 20th	Night	42% 5% 19% 22% 11% 1	4980
	21st to end	Night	49% 4 10% 19% 17% 2	5467
April	1st to 10th	Night	53% 5% 10% 18% 14% 1	2101
	11th to 20th	Night	48% 4 9% 19% 17% 2	1842
	21st to end	Night	46% 5% 11% 20% 15% 3	1800
May	1st to 10th	Night	45% 6% 11% 19% 15% 5%	2930
	11th to 20th	Night	43% 9% 14% 23% 9% 2	2730
	21st to end	Night	30% 8% 12% 23% 24% 3	2739
June	1st to 10th	Night	37% 7% 11% 26% 17% 2	1520
	11th to 20th	Night	34% 8% 13% 25% 17% 2	1406
	21st to end	Night	36% 7% 14% 23% 20% 1	1330
July	1st to 10th	Night	29% 5% 13% 27% 20% 6%	2192
	11th to 20th	Night	31% 4 14% 32% 17% 2	2680
	21st to end	Night	32% 6% 16% 24% 18% 3	2988
August	1st to 10th	Night	37% 5% 14% 26% 17% 1	2814
	11th to 20th	Night	36% 6% 16% 28% 13% 1	2812
	21st to end	Night	33% 5% 12% 32% 18% 1	3183
September	1st to 10th	Night	38% 6% 11% 26% 17% 2	1913
	11th to 20th	Night	29% 6% 12% 33% 19% 1	2090
	21st to end	Night	44% 7% 12% 25% 12% 1	2090
October	1st to 10th	Night	33% 4 7% 29% 25% 1	3768
	11th to 20th	Night	43% 4 14% 23% 16%	3779
	21st to end	Night	43% 4 14% 26% 13% 1	4138
November	1st to 10th	Night	43% 6% 14% 23% 13% 1	2539
	11th to 20th	Night	52% 7% 13% 18% 9% 1	2800
	21st to end	Night	60% 6% 16% 13% 5% 1	2800
December	1st to 10th	Night	67% 5% 14% 11% 3	4580
	11th to 20th	Night	64% 4 10% 12% 9% 1	5208
	21st to end	Night	71% 4 9% 10% 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	21% 20% 35% 19% 5% 1	240
	11th to 20th	Day	22% 21% 40% 13% 4 1	300
	21st to end	Day	28% 17% 33% 20% 2 1	330
February	1st to 10th	Day	24% 20% 38% 15% 3 1	300
	11th to 20th	Day	26% 21% 38% 12% 3	300
	21st to end	Day	28% 26% 32% 14% 1	249
March	1st to 10th	Day	25% 14% 37% 19% 5%	465
	11th to 20th	Day	24% 16% 36% 19% 5% 1	500
	21st to end	Day	28% 15% 28% 22% 6% 1	550
April	1st to 10th	Day	22% 18% 31% 22% 5% 2	500
	11th to 20th	Day	28% 15% 25% 17% 11% 4	492
	21st to end	Day	24% 13% 32% 22% 7% 3	500
May	1st to 10th	Day	25% 10% 27% 22% 12% 4	503
	11th to 20th	Day	17% 9% 29% 21% 19% 5%	487
	21st to end	Day	14% 7% 24% 30% 18% 7%	529
June	1st to 10th	Day	14% 9% 30% 30% 13% 4	490
	11th to 20th	Day	11% 9% 29% 32% 14% 4	596
	21st to end	Day	14% 9% 30% 31% 13% 4	680
July	1st to 10th	Day	9% 6% 24% 28% 25% 8%	661
	11th to 20th	Day	13% 4 25% 27% 21% 11%	484
	21st to end	Day	8% 4 23% 34% 23% 8%	532
August	1st to 10th	Day	9% 6% 20% 29% 21% 14%	486
	11th to 20th	Day	12% 5% 19% 27% 21% 15%	479
	21st to end	Day	11% 7% 20% 29% 22% 12%	539
September	1st to 10th	Day	13% 8% 22% 26% 21% 11%	490
	11th to 20th	Day	9% 4 18% 26% 29% 14%	490
	21st to end	Day	17% 10% 24% 27% 13% 8%	490
October	1st to 10th	Day	19% 9% 26% 23% 18% 6%	490
	11th to 20th	Day	19% 18% 30% 22% 8% 2	490
	21st to end	Day	27% 14% 31% 21% 6% 1	530
November	1st to 10th	Day	20% 23% 32% 16% 7% 2	297
	11th to 20th	Day	26% 18% 34% 14% 6% 3	200
	21st to end	Day	25% 17% 40% 15% 3	200
December	1st to 10th	Day	30% 19% 32% 14% 6% 1	200
	11th to 20th	Day	29% 23% 31% 15% 3	200
	21st to end	Day	31% 18% 35% 11% 4	220
January	1st to 10th	Night	21% 18% 37% 16% 6% 1	800
	11th to 20th	Night	28% 16% 33% 21% 3	800
	21st to end	Night	19% 13% 36% 26% 6%	880
February	1st to 10th	Night	23% 17% 36% 23% 2	800
	11th to 20th	Night	22% 15% 34% 24% 5%	783
	21st to end	Night	22% 17% 35% 22% 3	660
March	1st to 10th	Night	18% 16% 35% 25% 6%	800
	11th to 20th	Night	18% 15% 38% 21% 7% 1	800
	21st to end	Night	21% 13% 32% 25% 10%	880
April	1st to 10th	Night	23% 14% 31% 28% 4	800
	11th to 20th	Night	21% 13% 31% 26% 9% 1	658
	21st to end	Night	18% 11% 32% 32% 8% 1	600
May	1st to 10th	Night	20% 6% 28% 31% 14% 1	600
	11th to 20th	Night	17% 4 26% 37% 14% 1	513
	21st to end	Night	10% 5% 27% 39% 18% 1	411
June	1st to 10th	Night	14% 4 27% 42% 11% 1	380
	11th to 20th	Night	9% 5% 30% 43% 12%	380
	21st to end	Night	13% 4 24% 44% 15%	380
July	1st to 10th	Night	5% 3 23% 45% 21% 2	370
	11th to 20th	Night	9% 3 20% 41% 25% 2	485
	21st to end	Night	10% 3 15% 47% 23% 2	624
August	1st to 10th	Night	9% 2 15% 43% 28% 2	567
	11th to 20th	Night	9% 3 13% 39% 30% 5%	564
	21st to end	Night	9% 3 21% 37% 27% 3	660
September	1st to 10th	Night	13% 5% 23% 31% 23% 5%	760
	11th to 20th	Night	12% 4 15% 38% 27% 5%	760
	21st to end	Night	19% 6% 19% 32% 19% 5%	760
October	1st to 10th	Night	18% 6% 25% 30% 18% 2	760
	11th to 20th	Night	21% 12% 29% 26% 11% 1	760
	21st to end	Night	26% 11% 31% 26% 5%	836
November	1st to 10th	Night	20% 12% 27% 29% 10% 2	780
	11th to 20th	Night	20% 16% 34% 21% 7% 1	800
	21st to end	Night	25% 13% 33% 23% 6%	800
December	1st to 10th	Night	26% 17% 33% 19% 5%	800
	11th to 20th	Night	24% 19% 36% 17% 5%	800
	21st to end	Night	30% 14% 34% 19% 3	880

Page generated at 2025-05-08 09:33:54. Version ac07

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