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 2026-09-14.

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% 10% 4 9% 5% 5% 5% 4 6% 7% 31%	150025
	Night	13% 10% 4 9% 5% 5% 5% 4 5% 7% 32%	141003
Transparency	Day	51% 5% 12% 20% 11% 1	153608
	Night	50% 5% 12% 20% 13% 1	145496
Seeing	Day	19% 12% 29% 23% 12% 5%	17323
	Night	19% 11% 29% 29% 11% 1	26290

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	14% 16% 7% 20% 7% 6% 5% 3 3 4 15%	4899
	11th to 20th	Day	9% 21% 9% 22% 9% 7% 4 3 4 4 8%	5246
	21st to end	Day	15% 15% 6% 17% 8% 7% 6% 3 4 5% 13%	5780
February	1st to 10th	Day	14% 18% 5% 13% 8% 6% 6% 4 4 5% 18%	1890
	11th to 20th	Day	13% 15% 6% 14% 9% 5% 5% 4 4 6% 20%	1843
	21st to end	Day	15% 15% 6% 12% 7% 6% 5% 4 4 5% 22%	1693
March	1st to 10th	Day	17% 12% 5% 12% 7% 4 4 3 4 5% 26%	4968
	11th to 20th	Day	11% 13% 5% 10% 5% 5% 5% 4 5% 8% 30%	5090
	21st to end	Day	17% 12% 5% 11% 6% 5% 4 3 4 5% 29%	5586
April	1st to 10th	Day	16% 14% 4 9% 5% 4 4 4 5% 7% 28%	2413
	11th to 20th	Day	17% 11% 3 9% 4 4 5% 3 5% 7% 32%	2650
	21st to end	Day	20% 10% 3 8% 4 4 4 3 4 6% 33%	2730
May	1st to 10th	Day	17% 10% 3 8% 4 4 4 4 5% 7% 33%	7642
	11th to 20th	Day	14% 10% 3 8% 4 4 4 4 7% 9% 33%	7781
	21st to end	Day	16% 7% 2 6% 4 4 4 3 5% 6% 42%	9060
June	1st to 10th	Day	13% 6% 3 7% 5% 5% 5% 4 6% 8% 39%	2940
	11th to 20th	Day	10% 6% 3 7% 5% 5% 6% 4 8% 9% 37%	3058
	21st to end	Day	11% 6% 2 6% 4 5% 5% 5% 7% 9% 40%	3150
July	1st to 10th	Day	10% 6% 2 7% 5% 5% 6% 5% 7% 9% 37%	8828
	11th to 20th	Day	6% 5% 2 6% 5% 5% 5% 5% 7% 10% 44%	7870
	21st to end	Day	7% 5% 3 7% 4 5% 6% 4 7% 8% 44%	8340
August	1st to 10th	Day	16% 7% 3 7% 4 5% 5% 4 5% 7% 37%	6014
	11th to 20th	Day	9% 6% 3 7% 5% 5% 6% 5% 7% 10% 36%	5951
	21st to end	Day	9% 7% 3 8% 5% 5% 6% 5% 7% 9% 36%	6458
September	1st to 10th	Day	11% 6% 2 7% 5% 5% 6% 5% 6% 8% 39%	2502
	11th to 20th	Day	10% 5% 2 6% 5% 4 6% 4 6% 7% 46%	2233
	21st to end	Day	15% 7% 3 8% 5% 5% 4 5% 6% 8% 35%	2200
October	1st to 10th	Day	15% 9% 4 6% 5% 5% 4 3 5% 7% 38%	2019
	11th to 20th	Day	18% 10% 3 7% 5% 5% 5% 4 6% 7% 30%	2000
	21st to end	Day	21% 12% 4 8% 6% 4 6% 5% 5% 7% 23%	2190
November	1st to 10th	Day	13% 11% 4 9% 6% 4 4 4 6% 8% 32%	1847
	11th to 20th	Day	14% 14% 4 9% 6% 5% 5% 4 7% 8% 24%	1680
	21st to end	Day	17% 17% 7% 10% 6% 5% 5% 4 6% 6% 18%	1680
December	1st to 10th	Day	17% 19% 7% 13% 7% 6% 6% 5% 5% 4 12%	2680
	11th to 20th	Day	20% 20% 6% 11% 4 5% 4 4 4 5% 18%	3066
	21st to end	Day	26% 19% 7% 14% 5% 4 4 3 4 4 10%	4048
January	1st to 10th	Night	14% 13% 7% 16% 8% 6% 5% 4 5% 6% 16%	7994
	11th to 20th	Night	9% 16% 8% 19% 9% 7% 6% 4 6% 5% 11%	7639
	21st to end	Night	13% 12% 7% 14% 8% 7% 5% 4 5% 6% 19%	8401
February	1st to 10th	Night	14% 15% 6% 11% 8% 6% 5% 3 5% 6% 21%	2730
	11th to 20th	Night	14% 13% 5% 11% 7% 5% 5% 4 6% 7% 24%	2663
	21st to end	Night	14% 14% 4 12% 6% 5% 5% 4 5% 6% 23%	2110
March	1st to 10th	Night	12% 10% 4 9% 7% 5% 5% 4 6% 7% 33%	5092
	11th to 20th	Night	10% 8% 4 9% 5% 5% 5% 4 7% 8% 36%	5089
	21st to end	Night	18% 10% 4 8% 4 3 4 3 4 5% 37%	5588
April	1st to 10th	Night	18% 10% 3 8% 5% 4 5% 4 5% 7% 31%	2206
	11th to 20th	Night	17% 9% 3 7% 5% 5% 4 4 4 7% 35%	1935
	21st to end	Night	13% 10% 2 7% 5% 5% 5% 4 7% 8% 34%	1890
May	1st to 10th	Night	18% 8% 3 7% 5% 4 4 4 6% 7% 36%	5257
	11th to 20th	Night	13% 10% 4 8% 5% 5% 4 3 5% 7% 36%	5061
	21st to end	Night	18% 6% 2 5% 3 3 3 3 5% 6% 45%	5114
June	1st to 10th	Night	11% 5% 2 6% 4 4 4 4 6% 7% 46%	1680
	11th to 20th	Night	9% 6% 2 6% 4 4 5% 5% 7% 10% 43%	1554
	21st to end	Night	10% 5% 2 6% 4 5% 4 4 6% 8% 46%	1470
July	1st to 10th	Night	6% 6% 2 6% 5% 4 4 3 6% 10% 48%	4127
	11th to 20th	Night	7% 5% 2 6% 4 4 4 4 6% 9% 49%	5072
	21st to end	Night	7% 5% 2 6% 4 4 5% 4 5% 7% 50%	5737
August	1st to 10th	Night	13% 6% 2 6% 4 5% 4 4 6% 7% 42%	4135
	11th to 20th	Night	9% 6% 3 6% 4 4 5% 4 5% 9% 44%	4095
	21st to end	Night	9% 6% 2 7% 4 5% 4 4 6% 9% 44%	4621
September	1st to 10th	Night	9% 6% 2 7% 5% 4 4 3 5% 7% 47%	2115
	11th to 20th	Night	9% 5% 1 4 3 4 4 3 5% 7% 55%	2234
	21st to end	Night	16% 7% 3 7% 4 4 4 3 5% 6% 40%	2200
October	1st to 10th	Night	14% 8% 3 6% 4 3 4 3 5% 7% 44%	2380
	11th to 20th	Night	17% 9% 4 7% 5% 5% 4 4 5% 7% 35%	2400
	21st to end	Night	21% 9% 3 8% 5% 5% 4 4 6% 6% 30%	2647
November	1st to 10th	Night	14% 9% 3 7% 5% 4 4 4 6% 7% 37%	2669
	11th to 20th	Night	15% 12% 4 9% 5% 5% 4 4 7% 7% 27%	2940
	21st to end	Night	19% 14% 5% 9% 6% 5% 4 4 5% 7% 22%	2940
December	1st to 10th	Night	13% 16% 6% 13% 7% 8% 6% 5% 5% 5% 16%	4720
	11th to 20th	Night	13% 20% 6% 12% 5% 4 3 3 5% 6% 22%	5348
	21st to end	Night	22% 19% 6% 11% 6% 4 4 3 4 5% 16%	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	71% 5% 7% 10% 6%	4900
	11th to 20th	Day	80% 4 6% 6% 4	5280
	21st to end	Day	73% 4 8% 8% 6%	5780
February	1st to 10th	Day	67% 5% 9% 13% 5% 1	1890
	11th to 20th	Day	65% 5% 10% 14% 6%	1852
	21st to end	Day	65% 5% 11% 13% 6% 1	1693
March	1st to 10th	Day	60% 4 13% 17% 6% 1	4971
	11th to 20th	Day	52% 5% 16% 19% 7% 2	5090
	21st to end	Day	58% 4 10% 18% 10% 1	5586
April	1st to 10th	Day	56% 5% 10% 17% 11% 1	2413
	11th to 20th	Day	52% 5% 11% 20% 11% 1	2650
	21st to end	Day	53% 5% 9% 20% 11% 2	2730
May	1st to 10th	Day	51% 4 11% 19% 10% 4	7651
	11th to 20th	Day	47% 6% 12% 21% 12% 2	7785
	21st to end	Day	42% 5% 8% 22% 20% 3	9061
June	1st to 10th	Day	41% 7% 12% 24% 15% 2	2940
	11th to 20th	Day	42% 7% 12% 22% 15% 2	3058
	21st to end	Day	39% 7% 14% 24% 15%	3150
July	1st to 10th	Day	43% 4 12% 25% 14% 2	8755
	11th to 20th	Day	34% 4 12% 34% 16% 1	7797
	21st to end	Day	38% 4 12% 25% 21% 1	8156
August	1st to 10th	Day	47% 5% 13% 17% 15% 4	6001
	11th to 20th	Day	42% 5% 15% 31% 7%	5990
	21st to end	Day	43% 5% 14% 29% 9% 1	6458
September	1st to 10th	Day	41% 7% 14% 25% 13% 1	2502
	11th to 20th	Day	35% 6% 14% 30% 16%	2233
	21st to end	Day	45% 7% 13% 24% 10% 1	2200
October	1st to 10th	Day	41% 4 12% 24% 18% 1	3279
	11th to 20th	Day	40% 4 13% 22% 20%	3240
	21st to end	Day	51% 4 15% 22% 8%	3516
November	1st to 10th	Day	50% 6% 12% 23% 8% 2	1847
	11th to 20th	Day	55% 6% 15% 15% 9% 1	1680
	21st to end	Day	65% 5% 14% 12% 4	1680
December	1st to 10th	Day	72% 5% 12% 8% 3	2680
	11th to 20th	Day	69% 4 10% 9% 8%	3066
	21st to end	Day	77% 5% 7% 7% 4	4048
January	1st to 10th	Night	66% 5% 10% 14% 5%	7994
	11th to 20th	Night	71% 5% 7% 9% 7%	7680
	21st to end	Night	65% 4 7% 13% 10%	8401
February	1st to 10th	Night	63% 5% 10% 15% 5% 1	2730
	11th to 20th	Night	59% 5% 12% 16% 7%	2665
	21st to end	Night	61% 5% 11% 16% 7%	2110
March	1st to 10th	Night	50% 5% 14% 19% 11% 2	5102
	11th to 20th	Night	43% 5% 18% 22% 11% 1	5090
	21st to end	Night	49% 4 10% 19% 16% 2	5588
April	1st to 10th	Night	53% 5% 10% 18% 14% 1	2206
	11th to 20th	Night	49% 4 9% 19% 16% 2	1935
	21st to end	Night	46% 5% 11% 21% 14% 3	1890
May	1st to 10th	Night	49% 4 11% 15% 16% 6%	5264
	11th to 20th	Night	48% 6% 11% 22% 11% 2	5062
	21st to end	Night	40% 4 10% 25% 19% 2	5115
June	1st to 10th	Night	36% 6% 11% 26% 18% 3	1680
	11th to 20th	Night	35% 7% 13% 25% 17% 2	1554
	21st to end	Night	36% 6% 14% 23% 20% 1	1470
July	1st to 10th	Night	33% 3 16% 27% 18% 3	4092
	11th to 20th	Night	33% 3 10% 29% 22% 3	5022
	21st to end	Night	34% 4 12% 23% 25% 3	5606
August	1st to 10th	Night	42% 4 12% 22% 16% 5%	4124
	11th to 20th	Night	37% 4 17% 29% 11% 1	4122
	21st to end	Night	37% 3 14% 30% 14% 1	4621
September	1st to 10th	Night	38% 6% 11% 27% 16% 2	2115
	11th to 20th	Night	28% 6% 13% 33% 19% 1	2234
	21st to end	Night	44% 6% 11% 25% 13% 1	2200
October	1st to 10th	Night	32% 4 7% 30% 25% 1	3887
	11th to 20th	Night	42% 4 14% 23% 17%	3899
	21st to end	Night	42% 4 13% 26% 14% 1	4271
November	1st to 10th	Night	43% 6% 14% 23% 13% 1	2669
	11th to 20th	Night	52% 7% 13% 18% 9% 1	2940
	21st to end	Night	61% 6% 15% 13% 5% 1	2940
December	1st to 10th	Night	66% 5% 14% 11% 4	4720
	11th to 20th	Night	63% 4 10% 12% 10% 1	5348
	21st to end	Night	71% 4 9% 10% 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	22% 20% 36% 17% 4 1	264
	11th to 20th	Day	23% 22% 39% 12% 4 1	330
	21st to end	Day	27% 18% 32% 20% 2 1	363
February	1st to 10th	Day	23% 21% 36% 17% 3 1	330
	11th to 20th	Day	25% 21% 38% 13% 3	330
	21st to end	Day	26% 27% 34% 13% 1	273
March	1st to 10th	Day	25% 14% 36% 19% 5%	503
	11th to 20th	Day	26% 17% 34% 18% 5% 1	540
	21st to end	Day	28% 15% 29% 21% 6% 1	594
April	1st to 10th	Day	24% 19% 31% 21% 5% 2	540
	11th to 20th	Day	28% 15% 26% 17% 11% 4	532
	21st to end	Day	23% 13% 34% 22% 6% 2	540
May	1st to 10th	Day	24% 11% 28% 22% 11% 3	543
	11th to 20th	Day	17% 11% 30% 21% 17% 5%	567
	21st to end	Day	15% 8% 27% 27% 17% 6%	617
June	1st to 10th	Day	14% 9% 31% 29% 13% 4	570
	11th to 20th	Day	12% 11% 31% 30% 13% 4	688
	21st to end	Day	13% 8% 31% 32% 12% 3	780
July	1st to 10th	Day	10% 6% 25% 29% 23% 8%	759
	11th to 20th	Day	12% 4 27% 27% 21% 10%	564
	21st to end	Day	8% 5% 23% 34% 23% 8%	620
August	1st to 10th	Day	10% 5% 21% 30% 20% 14%	566
	11th to 20th	Day	11% 6% 21% 29% 20% 14%	559
	21st to end	Day	12% 7% 21% 29% 22% 10%	627
September	1st to 10th	Day	12% 7% 23% 25% 21% 11%	570
	11th to 20th	Day	9% 4 17% 26% 30% 14%	542
	21st to end	Day	18% 10% 22% 27% 14% 8%	530
October	1st to 10th	Day	18% 9% 25% 23% 19% 6%	530
	11th to 20th	Day	19% 17% 32% 22% 8% 2	530
	21st to end	Day	26% 16% 31% 21% 6% 1	573
November	1st to 10th	Day	21% 22% 32% 15% 7% 2	327
	11th to 20th	Day	25% 19% 32% 15% 6% 3	220
	21st to end	Day	26% 19% 38% 15% 3	220
December	1st to 10th	Day	29% 19% 32% 15% 5%	220
	11th to 20th	Day	29% 25% 30% 15% 2	220
	21st to end	Day	32% 19% 34% 11% 4	242
January	1st to 10th	Night	21% 19% 37% 17% 5% 1	840
	11th to 20th	Night	27% 18% 32% 20% 3	840
	21st to end	Night	19% 14% 36% 26% 5%	924
February	1st to 10th	Night	22% 17% 35% 24% 2	840
	11th to 20th	Night	22% 15% 34% 24% 4	823
	21st to end	Night	22% 18% 35% 23% 3	692
March	1st to 10th	Night	19% 16% 35% 25% 5%	840
	11th to 20th	Night	20% 15% 38% 21% 6% 1	840
	21st to end	Night	21% 13% 32% 24% 9%	924
April	1st to 10th	Night	23% 14% 31% 27% 4	840
	11th to 20th	Night	21% 13% 30% 26% 9% 1	691
	21st to end	Night	18% 11% 31% 33% 7%	630
May	1st to 10th	Night	20% 6% 29% 30% 14% 1	630
	11th to 20th	Night	17% 5% 27% 36% 13% 1	565
	21st to end	Night	12% 6% 28% 38% 16% 1	455
June	1st to 10th	Night	14% 4 28% 42% 11% 1	420
	11th to 20th	Night	10% 6% 30% 43% 11%	420
	21st to end	Night	13% 4 25% 43% 15%	420
July	1st to 10th	Night	5% 2 23% 46% 21% 2	410
	11th to 20th	Night	9% 3 22% 41% 24% 2	538
	21st to end	Night	10% 3 16% 47% 22% 2	690
August	1st to 10th	Night	9% 2 14% 44% 29% 2	627
	11th to 20th	Night	9% 3 14% 40% 29% 4	624
	21st to end	Night	9% 3 21% 38% 26% 3	730
September	1st to 10th	Night	12% 6% 23% 32% 24% 4	840
	11th to 20th	Night	12% 3 15% 38% 28% 4	813
	21st to end	Night	19% 6% 19% 32% 19% 5%	800
October	1st to 10th	Night	17% 6% 24% 31% 19% 2	800
	11th to 20th	Night	21% 12% 30% 26% 10% 1	800
	21st to end	Night	25% 11% 31% 27% 5%	880
November	1st to 10th	Night	19% 13% 27% 29% 10% 1	820
	11th to 20th	Night	20% 16% 34% 22% 7% 1	840
	21st to end	Night	26% 13% 33% 22% 6%	840
December	1st to 10th	Night	26% 17% 33% 19% 5%	840
	11th to 20th	Night	23% 19% 36% 17% 4	840
	21st to end	Night	30% 15% 33% 19% 3	924

Page generated at 2026-09-11 04:11:56. Version ac07

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