Cape Charles
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cape Charles clear sky chart from 2005-11-06 to 2026-03-03.

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	12% 6% 2 6% 4 4 4 4 6% 8% 44%	130856
	Night	13% 6% 2 6% 4 4 4 4 5% 7% 43%	130331
Transparency	Day	24% 38% 9% 16% 11% 2	134445
	Night	26% 37% 7% 16% 12% 3	134812
Seeing	Day	15% 5% 20% 30% 23% 6%	16910
	Night	16% 7% 23% 31% 19% 3	26535

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	11% 5% 2 5% 3 3 4 3 4 5% 55%	4814
	11th to 20th	Day	13% 6% 2 5% 3 3 3 2 3 4 55%	5280
	21st to end	Day	11% 7% 3 7% 5% 5% 4 3 5% 5% 44%	5780
February	1st to 10th	Day	12% 8% 2 6% 4 4 5% 4 6% 7% 41%	1890
	11th to 20th	Day	21% 7% 2 4 3 3 3 3 5% 6% 43%	2024
	21st to end	Day	17% 7% 2 5% 4 4 4 4 6% 7% 40%	1730
March	1st to 10th	Day	17% 7% 3 7% 4 3 4 3 5% 7% 41%	4718
	11th to 20th	Day	9% 7% 2 5% 3 3 4 3 4 6% 52%	4980
	21st to end	Day	13% 7% 2 5% 4 3 4 3 5% 7% 47%	5684
April	1st to 10th	Day	12% 6% 2 5% 4 4 3 3 5% 7% 49%	2400
	11th to 20th	Day	9% 6% 2 5% 5% 4 4 3 5% 6% 51%	2374
	21st to end	Day	12% 5% 2 5% 4 4 4 4 6% 8% 47%	2400
May	1st to 10th	Day	12% 7% 3 7% 4 5% 5% 5% 6% 9% 36%	5405
	11th to 20th	Day	16% 8% 3 7% 5% 4 5% 4 6% 8% 34%	6142
	21st to end	Day	13% 5% 2 5% 3 4 4 3 6% 10% 44%	6934
June	1st to 10th	Day	9% 4 2 4 4 4 4 5% 8% 11% 45%	2800
	11th to 20th	Day	10% 5% 2 4 3 4 5% 4 7% 10% 46%	2800
	21st to end	Day	6% 5% 2 5% 4 4 4 5% 7% 10% 47%	2800
July	1st to 10th	Day	7% 4 1 5% 4 4 5% 5% 8% 13% 43%	6360
	11th to 20th	Day	10% 6% 2 8% 5% 5% 5% 5% 7% 12% 34%	6177
	21st to end	Day	6% 4 2 6% 5% 5% 5% 6% 8% 12% 41%	6424
August	1st to 10th	Day	14% 8% 3 7% 5% 5% 5% 4 7% 11% 31%	4178
	11th to 20th	Day	8% 6% 2 8% 6% 6% 6% 4 6% 9% 40%	3850
	21st to end	Day	7% 4 2 5% 4 4 5% 4 7% 10% 49%	4312
September	1st to 10th	Day	15% 5% 2 5% 3 4 5% 4 6% 8% 44%	2400
	11th to 20th	Day	14% 6% 3 6% 4 3 5% 3 4 7% 45%	2400
	21st to end	Day	19% 6% 3 8% 4 4 4 3 6% 7% 37%	2154
October	1st to 10th	Day	16% 5% 2 5% 5% 3 3 3 5% 5% 48%	2000
	11th to 20th	Day	14% 5% 3 4 4 3 3 2 3 6% 53%	2000
	21st to end	Day	12% 5% 2 5% 4 4 4 3 4 5% 51%	2200
November	1st to 10th	Day	13% 6% 2 5% 4 4 4 3 4 6% 49%	1918
	11th to 20th	Day	13% 7% 2 4 4 3 3 3 4 7% 49%	1890
	21st to end	Day	14% 4 2 4 4 4 4 3 4 6% 50%	1840
December	1st to 10th	Day	11% 6% 2 5% 4 3 4 3 4 5% 54%	2680
	11th to 20th	Day	15% 8% 3 7% 4 3 3 3 4 5% 45%	3070
	21st to end	Day	11% 6% 2 6% 4 3 4 3 5% 7% 49%	4048
January	1st to 10th	Night	11% 6% 3 4 4 4 4 3 5% 7% 48%	8076
	11th to 20th	Night	12% 6% 2 6% 4 3 3 2 4 5% 54%	7680
	21st to end	Night	15% 7% 2 7% 4 3 3 3 5% 5% 46%	8401
February	1st to 10th	Night	16% 8% 2 6% 4 4 4 3 5% 6% 43%	2730
	11th to 20th	Night	20% 8% 2 5% 4 3 4 3 5% 6% 40%	2479
	21st to end	Night	16% 7% 2 6% 4 3 3 2 5% 6% 45%	2076
March	1st to 10th	Night	17% 7% 3 7% 4 4 3 3 4 6% 43%	5178
	11th to 20th	Night	12% 7% 2 6% 4 4 4 3 5% 6% 48%	4980
	21st to end	Night	14% 7% 3 6% 4 4 4 2 4 6% 45%	5247
April	1st to 10th	Night	13% 7% 2 7% 5% 3 4 4 6% 8% 40%	2000
	11th to 20th	Night	12% 5% 2 5% 4 4 3 3 6% 7% 49%	1975
	21st to end	Night	13% 6% 3 6% 4 4 4 3 6% 6% 45%	2000
May	1st to 10th	Night	13% 7% 3 8% 5% 5% 6% 5% 7% 9% 32%	4490
	11th to 20th	Night	18% 8% 3 8% 5% 5% 5% 4 6% 8% 31%	3778
	21st to end	Night	14% 8% 3 7% 5% 5% 5% 4 6% 8% 35%	3920
June	1st to 10th	Night	12% 5% 2 5% 5% 6% 5% 5% 6% 9% 40%	1600
	11th to 20th	Night	9% 4 3 6% 5% 6% 6% 5% 7% 9% 41%	1600
	21st to end	Night	6% 5% 2 6% 6% 5% 4 5% 7% 10% 44%	1600
July	1st to 10th	Night	7% 4 2 7% 5% 5% 6% 6% 9% 12% 36%	3598
	11th to 20th	Night	9% 7% 2 8% 5% 5% 6% 5% 8% 13% 32%	3775
	21st to end	Night	10% 6% 3 6% 6% 5% 6% 5% 7% 10% 35%	4427
August	1st to 10th	Night	15% 8% 4 7% 5% 5% 6% 4 7% 10% 29%	2938
	11th to 20th	Night	9% 6% 3 8% 5% 5% 5% 4 6% 8% 40%	3197
	21st to end	Night	8% 5% 2 6% 4 5% 4 4 6% 10% 46%	3586
September	1st to 10th	Night	12% 5% 2 5% 5% 4 4 4 6% 8% 46%	2000
	11th to 20th	Night	11% 6% 4 8% 4 4 4 4 5% 5% 45%	2000
	21st to end	Night	18% 7% 3 7% 5% 5% 4 4 4 6% 36%	2241
October	1st to 10th	Night	15% 5% 2 5% 4 4 4 3 5% 6% 48%	2400
	11th to 20th	Night	17% 5% 2 4 3 3 3 3 4 5% 50%	2400
	21st to end	Night	13% 5% 2 6% 4 4 3 3 3 6% 50%	2640
November	1st to 10th	Night	15% 7% 2 5% 4 4 3 3 5% 6% 47%	2597
	11th to 20th	Night	15% 6% 2 6% 4 3 3 3 5% 7% 45%	2730
	21st to end	Night	12% 5% 2 4 4 4 4 4 5% 7% 49%	2777
December	1st to 10th	Night	10% 5% 2 5% 4 4 4 3 4 6% 52%	4720
	11th to 20th	Night	17% 7% 3 7% 4 4 4 3 5% 6% 39%	5345
	21st to end	Night	10% 6% 2 6% 4 4 4 4 6% 6% 47%	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	26% 21% 9% 21% 16% 7%	4815
	11th to 20th	Day	26% 20% 3 16% 29% 6%	5280
	21st to end	Day	33% 23% 7% 24% 12% 1	5780
February	1st to 10th	Day	17% 59% 5% 12% 6% 1	1890
	11th to 20th	Day	21% 59% 4 7% 6% 3	2033
	21st to end	Day	19% 60% 4 9% 6% 2	1730
March	1st to 10th	Day	36% 29% 6% 11% 13% 5%	4718
	11th to 20th	Day	23% 29% 6% 15% 20% 7%	4980
	21st to end	Day	27% 29% 10% 13% 16% 5%	5684
April	1st to 10th	Day	15% 62% 4 9% 8% 1	2400
	11th to 20th	Day	13% 63% 5% 10% 8% 1	2374
	21st to end	Day	15% 62% 6% 10% 6% 2	2400
May	1st to 10th	Day	33% 32% 14% 14% 7% 1	5437
	11th to 20th	Day	36% 30% 11% 18% 5%	6146
	21st to end	Day	29% 29% 11% 20% 10% 2	6949
June	1st to 10th	Day	14% 63% 6% 10% 6% 1	2800
	11th to 20th	Day	11% 64% 7% 10% 7%	2800
	21st to end	Day	10% 62% 8% 12% 7%	2800
July	1st to 10th	Day	23% 30% 20% 16% 9% 1	6290
	11th to 20th	Day	35% 32% 20% 12% 2	6102
	21st to end	Day	26% 29% 12% 20% 13%	6240
August	1st to 10th	Day	34% 38% 12% 14% 2	4165
	11th to 20th	Day	24% 39% 10% 19% 6%	3886
	21st to end	Day	16% 37% 10% 22% 13% 1	4312
September	1st to 10th	Day	16% 59% 8% 11% 5% 1	2400
	11th to 20th	Day	18% 57% 6% 10% 7% 2	2400
	21st to end	Day	25% 57% 5% 10% 3 1	2154
October	1st to 10th	Day	17% 38% 7% 19% 17% 2	3260
	11th to 20th	Day	13% 36% 4 12% 29% 6%	3240
	21st to end	Day	10% 35% 7% 21% 18% 9%	3538
November	1st to 10th	Day	18% 53% 5% 15% 8% 2	1918
	11th to 20th	Day	18% 54% 5% 10% 10% 3	1890
	21st to end	Day	17% 54% 5% 13% 10% 1	1840
December	1st to 10th	Day	22% 36% 5% 21% 14% 2	2680
	11th to 20th	Day	31% 31% 11% 12% 12% 4	3066
	21st to end	Day	26% 27% 12% 23% 11%	4048
January	1st to 10th	Night	30% 21% 8% 19% 18% 5%	8077
	11th to 20th	Night	27% 20% 3 19% 24% 7%	7680
	21st to end	Night	32% 23% 6% 22% 14% 3	8401
February	1st to 10th	Night	17% 59% 6% 10% 7% 1	2730
	11th to 20th	Night	21% 58% 3 9% 7% 2	2481
	21st to end	Night	17% 59% 3 11% 7% 4	2076
March	1st to 10th	Night	34% 30% 4 13% 12% 7%	5178
	11th to 20th	Night	26% 29% 5% 14% 18% 7%	4980
	21st to end	Night	29% 29% 5% 18% 12% 5%	5247
April	1st to 10th	Night	17% 62% 5% 6% 9% 1	2000
	11th to 20th	Night	15% 63% 4 10% 7% 1	1975
	21st to end	Night	16% 62% 5% 8% 6% 1	2000
May	1st to 10th	Night	36% 31% 14% 13% 6%	4520
	11th to 20th	Night	39% 30% 9% 17% 4	3779
	21st to end	Night	36% 30% 8% 18% 8%	3927
June	1st to 10th	Night	18% 63% 5% 6% 7% 1	1600
	11th to 20th	Night	14% 63% 6% 9% 7%	1600
	21st to end	Night	11% 62% 5% 13% 7% 1	1600
July	1st to 10th	Night	30% 31% 14% 16% 8% 1	3560
	11th to 20th	Night	35% 32% 18% 13% 1	3730
	21st to end	Night	32% 29% 9% 18% 11%	4297
August	1st to 10th	Night	37% 37% 11% 13% 2	2927
	11th to 20th	Night	25% 38% 10% 19% 7%	3227
	21st to end	Night	19% 37% 6% 20% 18% 1	3586
September	1st to 10th	Night	16% 59% 8% 11% 4 2	2000
	11th to 20th	Night	19% 57% 5% 10% 8% 1	2000
	21st to end	Night	26% 58% 5% 8% 3	2241
October	1st to 10th	Night	23% 37% 7% 16% 16% 1	3920
	11th to 20th	Night	15% 36% 4 14% 25% 8%	3899
	21st to end	Night	10% 35% 4 22% 20% 8%	4252
November	1st to 10th	Night	20% 53% 5% 11% 9% 2	2597
	11th to 20th	Night	18% 54% 4 9% 9% 5%	2730
	21st to end	Night	15% 55% 5% 13% 11% 1	2777
December	1st to 10th	Night	21% 35% 5% 19% 17% 2	4720
	11th to 20th	Night	34% 32% 8% 13% 9% 4	5348
	21st to end	Night	28% 27% 11% 23% 10% 1	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	17% 14% 30% 32% 7%	247
	11th to 20th	Day	18% 11% 39% 28% 4	330
	21st to end	Day	17% 6% 36% 33% 7%	363
February	1st to 10th	Day	16% 11% 26% 38% 8% 1	330
	11th to 20th	Day	27% 9% 37% 23% 4	512
	21st to end	Day	20% 9% 31% 32% 7%	446
March	1st to 10th	Day	15% 8% 34% 34% 8% 1	508
	11th to 20th	Day	17% 9% 29% 33% 10% 1	500
	21st to end	Day	16% 7% 29% 38% 9% 1	550
April	1st to 10th	Day	12% 8% 36% 30% 13% 1	500
	11th to 20th	Day	10% 5% 28% 37% 17% 3	492
	21st to end	Day	14% 4 23% 35% 22% 2	500
May	1st to 10th	Day	17% 4 23% 36% 17% 3	503
	11th to 20th	Day	18% 2 15% 35% 24% 5%	527
	21st to end	Day	17% 2 13% 33% 28% 8%	573
June	1st to 10th	Day	12% 2 10% 34% 34% 9%	530
	11th to 20th	Day	11% 2 9% 35% 34% 10%	530
	21st to end	Day	9% 2 9% 32% 37% 10%	530
July	1st to 10th	Day	10% 1 3 26% 45% 14%	525
	11th to 20th	Day	9% 2 4 22% 47% 16%	524
	21st to end	Day	9% 2 5% 29% 42% 14%	576
August	1st to 10th	Day	13% 1 9% 30% 36% 10%	526
	11th to 20th	Day	13% 2 9% 23% 41% 13%	519
	21st to end	Day	11% 1 9% 27% 35% 18%	583
September	1st to 10th	Day	16% 3 9% 26% 32% 14%	530
	11th to 20th	Day	15% 3 10% 26% 32% 13%	530
	21st to end	Day	24% 4 13% 29% 24% 5%	530
October	1st to 10th	Day	17% 5% 13% 27% 28% 11%	530
	11th to 20th	Day	17% 8% 21% 28% 22% 5%	530
	21st to end	Day	16% 7% 25% 29% 19% 6%	583
November	1st to 10th	Day	16% 7% 23% 32% 16% 6%	461
	11th to 20th	Day	16% 10% 29% 32% 11% 2	430
	21st to end	Day	13% 12% 29% 26% 17% 2	380
December	1st to 10th	Day	25% 4 32% 29% 9% 1	220
	11th to 20th	Day	19% 9% 32% 28% 11%	220
	21st to end	Day	16% 9% 31% 29% 14% 1	242
January	1st to 10th	Night	15% 17% 34% 27% 7%	840
	11th to 20th	Night	18% 13% 33% 28% 7%	840
	21st to end	Night	21% 11% 35% 30% 4	924
February	1st to 10th	Night	20% 7% 35% 32% 5%	840
	11th to 20th	Night	24% 11% 39% 23% 4	823
	21st to end	Night	18% 12% 32% 32% 5% 1	692
March	1st to 10th	Night	16% 9% 35% 31% 9%	809
	11th to 20th	Night	20% 8% 33% 30% 9% 2	800
	21st to end	Night	19% 7% 31% 34% 8%	880
April	1st to 10th	Night	17% 7% 36% 31% 9% 1	800
	11th to 20th	Night	14% 6% 27% 38% 15% 1	791
	21st to end	Night	16% 4 24% 40% 15% 1	800
May	1st to 10th	Night	17% 5% 24% 39% 14% 2	800
	11th to 20th	Night	16% 4 18% 40% 19% 2	493
	21st to end	Night	16% 3 9% 35% 30% 6%	433
June	1st to 10th	Night	14% 1 11% 36% 32% 6%	400
	11th to 20th	Night	11% 2 9% 40% 32% 6%	400
	21st to end	Night	8% 1 9% 39% 39% 5%	400
July	1st to 10th	Night	8% 1 6% 38% 40% 7%	390
	11th to 20th	Night	9% 1 5% 25% 50% 10%	462
	21st to end	Night	11% 2 8% 33% 40% 6%	657
August	1st to 10th	Night	12% 1 7% 38% 35% 8%	607
	11th to 20th	Night	13% 2 8% 32% 37% 9%	790
	21st to end	Night	11% 2 8% 28% 41% 11%	880
September	1st to 10th	Night	13% 2 11% 30% 34% 11%	800
	11th to 20th	Night	15% 3 10% 29% 35% 9%	800
	21st to end	Night	22% 4 13% 30% 28% 3	800
October	1st to 10th	Night	17% 4 16% 28% 27% 8%	800
	11th to 20th	Night	18% 8% 22% 28% 21% 2	800
	21st to end	Night	17% 8% 24% 28% 20% 4	880
November	1st to 10th	Night	18% 8% 22% 29% 18% 5%	820
	11th to 20th	Night	17% 10% 27% 31% 13% 2	840
	21st to end	Night	13% 12% 27% 30% 16% 2	840
December	1st to 10th	Night	21% 10% 31% 26% 10% 1	840
	11th to 20th	Night	20% 8% 34% 27% 10%	840
	21st to end	Night	17% 10% 31% 31% 11% 1	924

Page generated at 2026-02-28 01:40:18. Version ac07

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