Robert W. Woodruff Scout Reservation
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Robert W. Woodruff Scout Reservation clear sky chart from 2005-11-06 to 2025-10-19.

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	10% 8% 3 8% 5% 5% 5% 4 6% 8% 37%	126334
	Night	10% 8% 3 7% 5% 5% 5% 4 6% 7% 41%	123393
Transparency	Day	42% 8% 12% 19% 16% 4	130097
	Night	40% 7% 12% 19% 17% 5%	127686
Seeing	Day	17% 13% 23% 21% 17% 9%	16135
	Night	15% 11% 21% 28% 20% 4	26124

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	12% 10% 5% 7% 4 3 4 3 5% 5% 42%	4056
	11th to 20th	Day	9% 9% 7% 11% 3 3 3 3 3 4 46%	4060
	21st to end	Day	13% 14% 5% 8% 5% 3 3 3 4 5% 36%	4538
February	1st to 10th	Day	13% 11% 4 8% 5% 4 4 4 5% 5% 36%	2000
	11th to 20th	Day	16% 11% 4 9% 4 4 4 3 5% 6% 34%	1948
	21st to end	Day	17% 9% 3 8% 5% 5% 4 3 4 5% 38%	1650
March	1st to 10th	Day	15% 9% 4 8% 5% 5% 4 4 5% 6% 35%	4617
	11th to 20th	Day	9% 8% 2 6% 4 4 3 3 4 6% 50%	4980
	21st to end	Day	13% 9% 3 8% 4 4 3 3 4 5% 43%	5465
April	1st to 10th	Day	10% 7% 3 6% 5% 5% 5% 5% 6% 7% 41%	2261
	11th to 20th	Day	11% 8% 2 6% 5% 3 4 3 6% 6% 44%	2374
	21st to end	Day	10% 8% 2 7% 5% 5% 5% 4 6% 7% 42%	2590
May	1st to 10th	Day	13% 8% 3 8% 5% 5% 6% 5% 7% 8% 31%	5862
	11th to 20th	Day	13% 10% 4 10% 7% 6% 6% 5% 7% 7% 24%	5861
	21st to end	Day	10% 8% 3 8% 5% 6% 6% 5% 6% 8% 36%	6433
June	1st to 10th	Day	9% 6% 3 8% 6% 6% 7% 6% 8% 9% 32%	2600
	11th to 20th	Day	5% 6% 2 7% 6% 7% 7% 6% 9% 10% 36%	2600
	21st to end	Day	6% 6% 2 7% 6% 7% 7% 5% 9% 10% 35%	2600
July	1st to 10th	Day	5% 5% 2 8% 7% 6% 7% 6% 8% 11% 34%	5900
	11th to 20th	Day	7% 5% 2 8% 7% 8% 8% 7% 10% 11% 28%	5900
	21st to end	Day	8% 9% 4 11% 8% 8% 8% 6% 8% 9% 20%	6424
August	1st to 10th	Day	6% 5% 3 8% 6% 6% 7% 6% 9% 12% 33%	4234
	11th to 20th	Day	7% 5% 3 7% 5% 6% 5% 5% 8% 12% 37%	3991
	21st to end	Day	7% 5% 2 7% 6% 6% 5% 5% 5% 8% 43%	4312
September	1st to 10th	Day	9% 7% 3 8% 6% 6% 5% 5% 6% 8% 37%	2210
	11th to 20th	Day	13% 7% 2 6% 5% 6% 5% 5% 7% 9% 36%	2200
	21st to end	Day	12% 5% 2 7% 5% 5% 5% 4 6% 8% 40%	2200
October	1st to 10th	Day	9% 4 2 6% 5% 4 4 4 5% 6% 51%	2200
	11th to 20th	Day	10% 6% 2 4 3 3 4 3 5% 6% 54%	2049
	21st to end	Day	10% 7% 2 5% 3 3 4 3 4 5% 54%	2088
November	1st to 10th	Day	10% 5% 2 6% 3 4 4 3 5% 6% 54%	1762
	11th to 20th	Day	10% 7% 2 5% 4 3 4 4 5% 8% 48%	1800
	21st to end	Day	11% 9% 3 6% 4 3 4 3 5% 7% 44%	1800
December	1st to 10th	Day	14% 9% 2 6% 4 3 4 3 4 5% 45%	2930
	11th to 20th	Day	13% 11% 6% 9% 4 5% 5% 3 5% 5% 34%	3373
	21st to end	Day	11% 10% 5% 8% 4 4 4 3 6% 8% 36%	4466
January	1st to 10th	Night	11% 9% 3 11% 4 4 4 3 4 5% 41%	5889
	11th to 20th	Night	11% 10% 3 9% 5% 4 3 3 4 5% 42%	5900
	21st to end	Night	11% 13% 4 8% 4 4 4 3 4 5% 41%	6416
February	1st to 10th	Night	12% 11% 4 7% 5% 4 4 3 5% 6% 40%	2400
	11th to 20th	Night	17% 11% 4 9% 5% 4 4 3 4 4 36%	2338
	21st to end	Night	16% 9% 3 8% 5% 4 4 4 5% 6% 36%	1980
March	1st to 10th	Night	15% 12% 3 8% 5% 5% 5% 3 5% 6% 33%	5235
	11th to 20th	Night	10% 7% 2 4 3 3 4 3 6% 8% 50%	4980
	21st to end	Night	11% 9% 3 8% 5% 5% 5% 3 5% 6% 42%	5467
April	1st to 10th	Night	10% 7% 2 5% 4 4 5% 4 6% 8% 45%	2154
	11th to 20th	Night	10% 7% 2 6% 4 4 4 3 4 7% 48%	1975
	21st to end	Night	10% 7% 2 5% 4 5% 4 3 5% 7% 48%	1810
May	1st to 10th	Night	10% 8% 3 8% 5% 6% 6% 5% 7% 10% 33%	4033
	11th to 20th	Night	13% 11% 3 9% 6% 6% 6% 5% 6% 8% 27%	4032
	21st to end	Night	10% 8% 3 7% 5% 5% 5% 5% 7% 10% 36%	4421
June	1st to 10th	Night	6% 6% 3 7% 6% 5% 7% 6% 8% 12% 36%	1800
	11th to 20th	Night	4 3 1 5% 4 6% 6% 5% 9% 12% 44%	1800
	21st to end	Night	4 4 2 6% 4 6% 6% 5% 8% 10% 45%	1800
July	1st to 10th	Night	7% 6% 3 8% 6% 5% 5% 5% 8% 11% 36%	4058
	11th to 20th	Night	6% 6% 3 7% 5% 6% 6% 5% 7% 11% 37%	4057
	21st to end	Night	9% 8% 3 9% 6% 6% 6% 5% 8% 11% 28%	4427
August	1st to 10th	Night	6% 5% 3 7% 6% 5% 5% 5% 8% 13% 39%	2915
	11th to 20th	Night	9% 7% 2 6% 4 5% 5% 4 6% 8% 44%	3040
	21st to end	Night	6% 5% 2 6% 4 4 5% 5% 6% 10% 48%	3586
September	1st to 10th	Night	8% 7% 2 7% 6% 6% 5% 5% 6% 8% 40%	2169
	11th to 20th	Night	9% 6% 3 7% 5% 4 5% 4 6% 8% 42%	2200
	21st to end	Night	9% 5% 2 7% 4 4 5% 4 6% 7% 47%	2200
October	1st to 10th	Night	10% 5% 2 5% 3 3 3 3 4 6% 56%	2200
	11th to 20th	Night	10% 5% 2 5% 4 3 3 3 4 5% 54%	2307
	21st to end	Night	10% 7% 2 5% 3 3 4 3 4 5% 55%	2508
November	1st to 10th	Night	10% 7% 2 5% 3 4 3 3 5% 6% 51%	2534
	11th to 20th	Night	12% 8% 2 5% 4 4 3 3 4 6% 49%	2600
	21st to end	Night	12% 9% 2 6% 5% 4 3 4 5% 6% 43%	2600
December	1st to 10th	Night	14% 9% 3 7% 4 4 4 3 4 6% 42%	4250
	11th to 20th	Night	16% 13% 5% 8% 3 4 4 3 5% 5% 34%	4822
	21st to end	Night	11% 11% 5% 10% 5% 4 4 3 5% 7% 35%	6490

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	43% 5% 5% 18% 27% 2	4057
	11th to 20th	Day	40% 5% 5% 14% 31% 6%	4060
	21st to end	Day	49% 3 6% 16% 19% 6%	4538
February	1st to 10th	Day	49% 4 7% 18% 18% 4	2000
	11th to 20th	Day	50% 6% 6% 15% 18% 5%	1958
	21st to end	Day	49% 4 7% 12% 21% 6%	1650
March	1st to 10th	Day	47% 5% 9% 12% 20% 8%	4617
	11th to 20th	Day	34% 4 7% 16% 22% 16%	4980
	21st to end	Day	43% 4 8% 25% 16% 3	5465
April	1st to 10th	Day	39% 7% 11% 21% 18% 4	2261
	11th to 20th	Day	39% 6% 8% 19% 23% 5%	2374
	21st to end	Day	39% 7% 12% 26% 14% 3	2590
May	1st to 10th	Day	47% 9% 14% 18% 10% 1	5897
	11th to 20th	Day	54% 10% 13% 17% 6%	5865
	21st to end	Day	43% 9% 12% 21% 14% 1	6447
June	1st to 10th	Day	43% 12% 17% 20% 7% 1	2600
	11th to 20th	Day	37% 12% 18% 20% 11% 1	2600
	21st to end	Day	39% 11% 17% 19% 11% 2	2600
July	1st to 10th	Day	38% 13% 19% 23% 7% 1	5835
	11th to 20th	Day	42% 14% 25% 15% 4 1	5831
	21st to end	Day	54% 12% 16% 13% 4	6240
August	1st to 10th	Day	38% 11% 17% 26% 7%	4221
	11th to 20th	Day	36% 10% 22% 19% 13% 1	4030
	21st to end	Day	37% 8% 11% 28% 15% 1	4311
September	1st to 10th	Day	43% 9% 12% 16% 16% 4	2210
	11th to 20th	Day	43% 8% 12% 19% 16% 1	2200
	21st to end	Day	40% 6% 14% 16% 19% 5%	2200
October	1st to 10th	Day	27% 5% 8% 15% 34% 11%	3590
	11th to 20th	Day	22% 3 6% 19% 27% 22%	3328
	21st to end	Day	27% 4 6% 25% 25% 13%	3414
November	1st to 10th	Day	31% 5% 9% 15% 31% 9%	1762
	11th to 20th	Day	34% 5% 8% 19% 25% 9%	1800
	21st to end	Day	40% 5% 7% 17% 25% 5%	1800
December	1st to 10th	Day	42% 3 6% 17% 26% 6%	2930
	11th to 20th	Day	50% 6% 7% 16% 17% 4	3370
	21st to end	Day	43% 6% 10% 25% 13% 2	4466
January	1st to 10th	Night	45% 4 7% 17% 25% 3	5889
	11th to 20th	Night	42% 6% 6% 15% 22% 9%	5900
	21st to end	Night	46% 3 6% 16% 23% 6%	6416
February	1st to 10th	Night	45% 5% 8% 19% 20% 4	2400
	11th to 20th	Night	52% 5% 6% 15% 17% 5%	2339
	21st to end	Night	48% 6% 7% 16% 18% 5%	1980
March	1st to 10th	Night	51% 5% 8% 13% 20% 4	5235
	11th to 20th	Night	32% 5% 8% 19% 23% 14%	4980
	21st to end	Night	43% 5% 9% 24% 15% 4	5467
April	1st to 10th	Night	36% 7% 12% 20% 21% 4	2154
	11th to 20th	Night	35% 5% 9% 22% 22% 6%	1975
	21st to end	Night	36% 6% 13% 28% 16% 2	1810
May	1st to 10th	Night	43% 11% 17% 20% 8% 1	4060
	11th to 20th	Night	53% 9% 16% 15% 6%	4033
	21st to end	Night	39% 11% 15% 23% 11% 1	4429
June	1st to 10th	Night	37% 14% 18% 22% 9% 1	1800
	11th to 20th	Night	28% 13% 24% 24% 10% 1	1800
	21st to end	Night	31% 12% 20% 21% 14% 3	1800
July	1st to 10th	Night	39% 11% 21% 24% 6%	4015
	11th to 20th	Night	37% 14% 28% 16% 3 1	4006
	21st to end	Night	48% 12% 19% 16% 4	4297
August	1st to 10th	Night	34% 11% 23% 27% 5%	2904
	11th to 20th	Night	35% 10% 22% 20% 12%	3067
	21st to end	Night	31% 9% 17% 27% 15% 1	3586
September	1st to 10th	Night	38% 11% 16% 17% 14% 4	2169
	11th to 20th	Night	39% 11% 13% 20% 17%	2200
	21st to end	Night	34% 9% 13% 21% 18% 5%	2200
October	1st to 10th	Night	26% 5% 10% 18% 33% 9%	3590
	11th to 20th	Night	22% 3 7% 19% 32% 18%	3767
	21st to end	Night	24% 4 5% 27% 27% 13%	4120
November	1st to 10th	Night	33% 6% 8% 21% 24% 9%	2534
	11th to 20th	Night	37% 4 7% 18% 24% 9%	2600
	21st to end	Night	41% 5% 7% 21% 21% 5%	2600
December	1st to 10th	Night	43% 5% 7% 16% 25% 4	4250
	11th to 20th	Night	51% 6% 7% 14% 19% 4	4824
	21st to end	Night	48% 5% 10% 22% 15% 1	6490

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	29% 27% 33% 9% 2	300
	11th to 20th	Day	29% 28% 26% 12% 5%	300
	21st to end	Day	23% 35% 26% 13% 3	330
February	1st to 10th	Day	25% 24% 37% 12% 2	300
	11th to 20th	Day	36% 33% 23% 8% 1	300
	21st to end	Day	35% 26% 28% 8% 3	249
March	1st to 10th	Day	29% 19% 32% 14% 7%	359
	11th to 20th	Day	25% 22% 26% 20% 7% 1	500
	21st to end	Day	24% 24% 27% 18% 6% 1	550
April	1st to 10th	Day	23% 19% 26% 21% 10% 2	500
	11th to 20th	Day	17% 20% 29% 20% 13% 1	492
	21st to end	Day	19% 14% 25% 25% 13% 4	500
May	1st to 10th	Day	16% 19% 29% 20% 11% 5%	503
	11th to 20th	Day	14% 12% 27% 24% 14% 9%	527
	21st to end	Day	12% 8% 24% 25% 19% 12%	573
June	1st to 10th	Day	10% 6% 22% 28% 21% 12%	530
	11th to 20th	Day	7% 4 19% 26% 25% 19%	530
	21st to end	Day	8% 4 23% 24% 23% 18%	530
July	1st to 10th	Day	9% 4 11% 25% 28% 23%	525
	11th to 20th	Day	8% 3 10% 25% 29% 26%	524
	21st to end	Day	9% 3 10% 25% 28% 25%	576
August	1st to 10th	Day	13% 4 16% 23% 22% 21%	526
	11th to 20th	Day	11% 4 15% 21% 29% 21%	519
	21st to end	Day	13% 3 12% 19% 30% 23%	583
September	1st to 10th	Day	8% 3 14% 26% 32% 15%	530
	11th to 20th	Day	14% 6% 15% 20% 32% 14%	530
	21st to end	Day	13% 7% 17% 25% 28% 9%	530
October	1st to 10th	Day	12% 6% 21% 29% 24% 8%	530
	11th to 20th	Day	14% 12% 25% 25% 19% 5%	522
	21st to end	Day	15% 13% 24% 26% 19% 4	537
November	1st to 10th	Day	16% 14% 34% 23% 10% 3	300
	11th to 20th	Day	22% 16% 36% 19% 6% 1	300
	21st to end	Day	17% 20% 37% 18% 8% 1	300
December	1st to 10th	Day	29% 26% 24% 17% 3 1	300
	11th to 20th	Day	25% 18% 33% 17% 6% 1	300
	21st to end	Day	24% 25% 28% 15% 7% 1	330
January	1st to 10th	Night	25% 20% 30% 20% 6%	800
	11th to 20th	Night	24% 20% 28% 22% 6%	800
	21st to end	Night	19% 21% 33% 25% 2	880
February	1st to 10th	Night	21% 16% 28% 30% 5%	800
	11th to 20th	Night	27% 21% 29% 21% 2	783
	21st to end	Night	25% 22% 31% 20% 3	660
March	1st to 10th	Night	20% 19% 32% 24% 4	800
	11th to 20th	Night	19% 19% 29% 25% 7% 1	800
	21st to end	Night	19% 16% 30% 28% 8%	880
April	1st to 10th	Night	17% 17% 27% 29% 9% 1	754
	11th to 20th	Night	14% 14% 26% 32% 12% 1	593
	21st to end	Night	13% 8% 27% 35% 17% 1	600
May	1st to 10th	Night	11% 10% 25% 35% 18% 2	600
	11th to 20th	Night	13% 8% 20% 32% 22% 5%	591
	21st to end	Night	8% 5% 15% 34% 32% 7%	650
June	1st to 10th	Night	7% 3 15% 36% 35% 5%	600
	11th to 20th	Night	4 3 11% 32% 37% 13%	600
	21st to end	Night	5% 2 9% 32% 44% 9%	600
July	1st to 10th	Night	9% 2 5% 24% 50% 8%	585
	11th to 20th	Night	8% 2 8% 19% 47% 16%	582
	21st to end	Night	7% 2 7% 23% 48% 13%	657
August	1st to 10th	Night	9% 2 7% 26% 42% 14%	597
	11th to 20th	Night	9% 2 7% 29% 42% 10%	594
	21st to end	Night	12% 2 8% 26% 43% 10%	660
September	1st to 10th	Night	10% 2 12% 29% 38% 9%	769
	11th to 20th	Night	13% 4 12% 29% 38% 4	800
	21st to end	Night	12% 5% 14% 35% 32% 4	800
October	1st to 10th	Night	11% 6% 20% 31% 26% 6%	800
	11th to 20th	Night	13% 8% 21% 35% 21% 2	793
	21st to end	Night	14% 11% 20% 36% 17% 2	836
November	1st to 10th	Night	14% 9% 22% 33% 19% 3	780
	11th to 20th	Night	17% 14% 23% 31% 13% 2	800
	21st to end	Night	18% 17% 23% 29% 12% 1	800
December	1st to 10th	Night	23% 16% 26% 27% 7% 1	800
	11th to 20th	Night	22% 14% 26% 29% 8% 1	800
	21st to end	Night	24% 17% 25% 27% 7%	880

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