Virginia Beach
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Virginia Beach clear sky chart from 2005-11-06 to 2025-09-04.

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 5% 4 6% 8% 42%	125670
	Night	13% 7% 2 6% 4 4 4 4 5% 8% 43%	123035
Transparency	Day	38% 6% 14% 23% 16% 3	129260
	Night	39% 6% 11% 23% 17% 4	127514
Seeing	Day	15% 6% 20% 29% 23% 7%	16387
	Night	17% 6% 23% 32% 19% 3	25899

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	13% 6% 2 5% 3 3 3 3 4 5% 54%	3756
	11th to 20th	Day	12% 6% 2 5% 4 3 3 3 5% 5% 52%	4060
	21st to end	Day	10% 10% 3 7% 5% 4 4 3 5% 5% 43%	4466
February	1st to 10th	Day	14% 8% 2 8% 4 4 5% 3 6% 8% 39%	1800
	11th to 20th	Day	20% 7% 2 6% 3 4 4 3 4 6% 41%	1940
	21st to end	Day	16% 8% 2 6% 3 4 4 3 5% 8% 41%	1650
March	1st to 10th	Day	18% 8% 2 7% 4 3 4 3 5% 6% 41%	4699
	11th to 20th	Day	10% 6% 2 7% 4 3 3 3 4 6% 52%	4980
	21st to end	Day	13% 7% 2 5% 3 3 4 3 5% 6% 47%	5684
April	1st to 10th	Day	12% 6% 2 5% 4 4 4 3 5% 7% 49%	2400
	11th to 20th	Day	10% 6% 2 6% 5% 3 4 3 5% 8% 49%	2374
	21st to end	Day	13% 5% 2 5% 4 4 4 3 6% 7% 47%	2400
May	1st to 10th	Day	13% 7% 3 7% 5% 5% 6% 5% 7% 10% 34%	5405
	11th to 20th	Day	16% 8% 3 7% 5% 5% 5% 4 6% 9% 31%	6032
	21st to end	Day	14% 6% 2 6% 4 4 4 4 7% 9% 40%	6934
June	1st to 10th	Day	10% 5% 2 5% 5% 4 5% 4 7% 11% 42%	2800
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 4 6% 12% 42%	2800
	21st to end	Day	6% 5% 2 5% 5% 4 6% 5% 7% 11% 44%	2800
July	1st to 10th	Day	7% 4 2 5% 4 5% 6% 6% 10% 13% 38%	6360
	11th to 20th	Day	10% 5% 3 8% 6% 6% 6% 6% 9% 12% 30%	6098
	21st to end	Day	7% 5% 2 6% 5% 6% 6% 6% 9% 12% 37%	6424
August	1st to 10th	Day	15% 7% 3 9% 6% 6% 6% 5% 7% 10% 26%	4147
	11th to 20th	Day	9% 5% 2 6% 6% 5% 5% 5% 7% 10% 39%	3850
	21st to end	Day	8% 5% 1 5% 4 4 5% 5% 7% 11% 45%	4312
September	1st to 10th	Day	13% 5% 2 6% 3 4 4 5% 6% 9% 43%	2316
	11th to 20th	Day	14% 6% 3 7% 5% 5% 4 4 5% 7% 40%	2280
	21st to end	Day	19% 7% 3 7% 5% 4 5% 4 5% 7% 36%	2050
October	1st to 10th	Day	17% 5% 2 5% 3 4 4 3 5% 6% 47%	1900
	11th to 20th	Day	14% 5% 2 6% 3 4 4 3 4 5% 50%	1900
	21st to end	Day	12% 6% 2 6% 4 4 4 3 5% 6% 49%	2090
November	1st to 10th	Day	16% 6% 3 5% 3 3 4 4 5% 6% 45%	1835
	11th to 20th	Day	15% 8% 2 5% 3 3 4 4 4 7% 44%	1800
	21st to end	Day	13% 4 2 6% 4 4 3 3 5% 7% 48%	1778
December	1st to 10th	Day	11% 5% 3 6% 3 3 4 3 5% 6% 51%	2600
	11th to 20th	Day	15% 7% 3 7% 5% 4 4 3 4 6% 41%	2990
	21st to end	Day	13% 5% 3 6% 3 4 3 3 5% 8% 47%	3960
January	1st to 10th	Night	12% 8% 3 4 3 3 4 3 5% 6% 50%	6187
	11th to 20th	Night	13% 6% 2 6% 4 3 3 3 4 6% 51%	5900
	21st to end	Night	13% 7% 2 7% 4 4 4 3 5% 7% 44%	6490
February	1st to 10th	Night	18% 7% 3 5% 4 3 4 3 5% 6% 42%	2600
	11th to 20th	Night	20% 7% 3 6% 3 3 3 4 5% 6% 40%	2343
	21st to end	Night	16% 7% 3 6% 4 3 3 3 5% 7% 45%	1980
March	1st to 10th	Night	18% 7% 2 6% 4 4 4 3 4 6% 42%	5149
	11th to 20th	Night	12% 6% 3 6% 4 4 4 4 5% 6% 47%	4980
	21st to end	Night	16% 8% 2 5% 4 3 4 3 4 5% 47%	5247
April	1st to 10th	Night	13% 6% 2 7% 4 4 4 4 6% 8% 42%	2000
	11th to 20th	Night	11% 7% 3 6% 3 3 3 4 4 8% 48%	1975
	21st to end	Night	13% 6% 2 5% 4 4 4 4 6% 8% 46%	2000
May	1st to 10th	Night	12% 7% 3 9% 6% 5% 6% 4 6% 10% 33%	4490
	11th to 20th	Night	18% 9% 3 7% 5% 5% 5% 4 5% 7% 32%	3871
	21st to end	Night	14% 8% 3 8% 5% 4 4 3 6% 8% 35%	3920
June	1st to 10th	Night	11% 6% 2 6% 5% 4 4 5% 7% 11% 39%	1600
	11th to 20th	Night	7% 5% 3 7% 6% 5% 5% 5% 7% 10% 41%	1600
	21st to end	Night	7% 6% 2 5% 4 5% 4 5% 7% 12% 45%	1600
July	1st to 10th	Night	7% 4 2 6% 5% 5% 5% 5% 10% 15% 36%	3598
	11th to 20th	Night	8% 5% 3 8% 6% 6% 6% 5% 8% 13% 33%	3841
	21st to end	Night	11% 6% 2 8% 5% 6% 6% 4 7% 10% 35%	4427
August	1st to 10th	Night	15% 8% 3 8% 5% 5% 6% 5% 6% 9% 30%	2968
	11th to 20th	Night	10% 7% 2 8% 5% 5% 5% 4 6% 9% 38%	3197
	21st to end	Night	10% 5% 2 5% 4 4 5% 4 7% 10% 44%	3586
September	1st to 10th	Night	12% 5% 2 6% 4 4 5% 4 6% 8% 45%	1931
	11th to 20th	Night	12% 8% 2 8% 5% 4 4 3 5% 7% 42%	1900
	21st to end	Night	19% 7% 2 7% 4 5% 5% 3 5% 7% 35%	2126
October	1st to 10th	Night	15% 5% 2 5% 4 3 4 4 5% 5% 47%	2280
	11th to 20th	Night	15% 7% 2 4 3 4 3 3 5% 6% 49%	2280
	21st to end	Night	12% 4 2 6% 3 3 4 4 5% 7% 50%	2508
November	1st to 10th	Night	16% 6% 2 6% 4 3 3 3 5% 7% 45%	2461
	11th to 20th	Night	16% 7% 3 5% 4 2 5% 3 5% 7% 43%	2600
	21st to end	Night	13% 4 2 4 5% 4 4 4 5% 7% 49%	2619
December	1st to 10th	Night	9% 6% 2 6% 4 3 4 3 5% 5% 52%	4580
	11th to 20th	Night	16% 7% 3 8% 5% 5% 4 4 5% 6% 37%	5205
	21st to end	Night	10% 6% 2 6% 4 4 4 3 6% 7% 47%	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	33% 4 5% 26% 20% 10%	3757
	11th to 20th	Day	35% 4 6% 20% 31% 5%	4060
	21st to end	Day	43% 5% 9% 25% 16% 2	4466
February	1st to 10th	Day	42% 5% 13% 25% 13% 3	1800
	11th to 20th	Day	45% 5% 9% 19% 18% 5%	1949
	21st to end	Day	41% 6% 12% 20% 16% 5%	1650
March	1st to 10th	Day	44% 4 8% 19% 18% 7%	4699
	11th to 20th	Day	34% 4 9% 19% 25% 9%	4980
	21st to end	Day	38% 4 14% 20% 19% 5%	5684
April	1st to 10th	Day	35% 6% 13% 22% 20% 5%	2400
	11th to 20th	Day	33% 5% 12% 25% 20% 5%	2374
	21st to end	Day	36% 6% 13% 24% 18% 4	2400
May	1st to 10th	Day	45% 9% 17% 19% 10% 1	5437
	11th to 20th	Day	47% 8% 16% 20% 8% 1	6036
	21st to end	Day	38% 10% 15% 24% 12% 2	6949
June	1st to 10th	Day	32% 9% 17% 27% 13% 2	2800
	11th to 20th	Day	34% 9% 17% 25% 13% 2	2800
	21st to end	Day	32% 10% 16% 28% 14% 1	2800
July	1st to 10th	Day	34% 8% 22% 24% 10% 2	6290
	11th to 20th	Day	43% 10% 26% 17% 4	6024
	21st to end	Day	37% 8% 16% 26% 13%	6240
August	1st to 10th	Day	50% 8% 18% 19% 4	4134
	11th to 20th	Day	38% 7% 17% 25% 12% 1	3886
	21st to end	Day	32% 7% 14% 30% 16% 2	4312
September	1st to 10th	Day	37% 11% 16% 18% 16% 3	2316
	11th to 20th	Day	41% 7% 11% 21% 18% 2	2280
	21st to end	Day	47% 6% 10% 20% 15% 2	2050
October	1st to 10th	Day	31% 4 9% 29% 24% 3	3160
	11th to 20th	Day	27% 3 7% 20% 34% 8%	3140
	21st to end	Day	25% 3 10% 28% 25% 9%	3428
November	1st to 10th	Day	38% 6% 11% 25% 18% 3	1835
	11th to 20th	Day	40% 5% 12% 19% 19% 4	1800
	21st to end	Day	37% 4 9% 28% 19% 2	1778
December	1st to 10th	Day	36% 4 9% 29% 20% 2	2600
	11th to 20th	Day	44% 5% 13% 19% 15% 4	2986
	21st to end	Day	38% 3 13% 31% 15% 1	3960
January	1st to 10th	Night	35% 3 6% 22% 25% 8%	6187
	11th to 20th	Night	36% 3 5% 22% 28% 4	5900
	21st to end	Night	39% 5% 8% 27% 18% 3	6490
February	1st to 10th	Night	43% 5% 10% 23% 16% 2	2600
	11th to 20th	Night	46% 5% 8% 21% 17% 4	2345
	21st to end	Night	40% 5% 8% 21% 18% 7%	1980
March	1st to 10th	Night	43% 5% 8% 18% 17% 7%	5149
	11th to 20th	Night	37% 4 9% 16% 23% 9%	4980
	21st to end	Night	41% 4 9% 25% 15% 6%	5247
April	1st to 10th	Night	39% 7% 12% 17% 21% 4	2000
	11th to 20th	Night	34% 6% 12% 23% 20% 6%	1975
	21st to end	Night	37% 7% 11% 24% 18% 3	2000
May	1st to 10th	Night	45% 8% 18% 19% 9% 1	4520
	11th to 20th	Night	50% 6% 13% 21% 8% 1	3872
	21st to end	Night	45% 8% 13% 22% 11% 1	3927
June	1st to 10th	Night	37% 8% 16% 24% 14% 1	1600
	11th to 20th	Night	37% 10% 18% 21% 13% 1	1600
	21st to end	Night	32% 9% 16% 26% 14% 2	1600
July	1st to 10th	Night	37% 8% 21% 23% 10% 1	3560
	11th to 20th	Night	41% 11% 24% 19% 4	3795
	21st to end	Night	43% 8% 13% 23% 13%	4297
August	1st to 10th	Night	50% 7% 20% 19% 5%	2957
	11th to 20th	Night	42% 6% 15% 25% 12%	3227
	21st to end	Night	35% 6% 11% 27% 20% 1	3586
September	1st to 10th	Night	37% 8% 16% 21% 15% 3	1931
	11th to 20th	Night	41% 6% 12% 21% 18% 2	1900
	21st to end	Night	47% 7% 10% 19% 15% 1	2126
October	1st to 10th	Night	38% 4 8% 25% 24% 2	3800
	11th to 20th	Night	29% 3 6% 20% 33% 9%	3779
	21st to end	Night	22% 3 7% 32% 28% 9%	4120
November	1st to 10th	Night	39% 5% 9% 25% 19% 3	2461
	11th to 20th	Night	41% 5% 10% 21% 17% 7%	2600
	21st to end	Night	35% 4 10% 28% 20% 3	2619
December	1st to 10th	Night	34% 3 7% 27% 25% 3	4580
	11th to 20th	Night	48% 4 11% 17% 14% 5%	5208
	21st to end	Night	36% 4 16% 29% 14% 1	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	15% 14% 35% 29% 7%	235
	11th to 20th	Day	14% 15% 36% 31% 4	300
	21st to end	Day	17% 10% 34% 33% 6% 1	330
February	1st to 10th	Day	17% 11% 29% 35% 8%	300
	11th to 20th	Day	26% 11% 39% 21% 4	488
	21st to end	Day	17% 10% 36% 30% 6% 1	414
March	1st to 10th	Day	17% 11% 34% 29% 8%	500
	11th to 20th	Day	18% 10% 34% 29% 8% 2	500
	21st to end	Day	14% 7% 35% 35% 9%	550
April	1st to 10th	Day	14% 10% 32% 33% 9% 1	500
	11th to 20th	Day	12% 5% 29% 36% 15% 3	492
	21st to end	Day	15% 5% 25% 32% 19% 3	500
May	1st to 10th	Day	16% 6% 26% 33% 17% 3	503
	11th to 20th	Day	17% 4 17% 36% 22% 3	527
	21st to end	Day	18% 3 13% 33% 25% 8%	573
June	1st to 10th	Day	11% 3 10% 35% 32% 8%	530
	11th to 20th	Day	12% 2 13% 29% 33% 11%	530
	21st to end	Day	8% 1 8% 32% 38% 12%	530
July	1st to 10th	Day	10% 2 4 24% 44% 16%	525
	11th to 20th	Day	9% 2 4 18% 48% 19%	524
	21st to end	Day	9% 1 6% 30% 39% 16%	576
August	1st to 10th	Day	16% 2 8% 30% 34% 11%	526
	11th to 20th	Day	9% 2 5% 24% 43% 17%	519
	21st to end	Day	12% 1 8% 25% 39% 14%	583
September	1st to 10th	Day	15% 2 10% 27% 30% 16%	502
	11th to 20th	Day	16% 3 13% 24% 33% 11%	490
	21st to end	Day	21% 5% 16% 26% 28% 4	490
October	1st to 10th	Day	19% 2 15% 26% 29% 9%	490
	11th to 20th	Day	13% 6% 20% 31% 26% 4	490
	21st to end	Day	14% 7% 23% 28% 21% 7%	539
November	1st to 10th	Day	19% 7% 21% 31% 15% 6%	433
	11th to 20th	Day	18% 11% 30% 27% 12% 3	400
	21st to end	Day	15% 10% 26% 29% 17% 3	378
December	1st to 10th	Day	21% 10% 36% 24% 9% 2	200
	11th to 20th	Day	18% 8% 38% 23% 12% 2	200
	21st to end	Day	18% 9% 28% 30% 15%	220
January	1st to 10th	Night	18% 16% 35% 25% 7%	800
	11th to 20th	Night	19% 14% 32% 28% 7%	800
	21st to end	Night	19% 11% 39% 28% 4	880
February	1st to 10th	Night	22% 7% 35% 31% 5%	800
	11th to 20th	Night	25% 11% 39% 23% 3	783
	21st to end	Night	20% 10% 32% 32% 6%	660
March	1st to 10th	Night	18% 7% 35% 30% 9%	800
	11th to 20th	Night	19% 8% 34% 29% 9% 1	800
	21st to end	Night	19% 7% 31% 35% 8%	880
April	1st to 10th	Night	17% 7% 36% 32% 8% 1	800
	11th to 20th	Night	14% 7% 28% 37% 14% 1	791
	21st to end	Night	16% 5% 22% 43% 13% 1	800
May	1st to 10th	Night	15% 6% 25% 39% 13% 2	800
	11th to 20th	Night	17% 3 19% 41% 18% 2	534
	21st to end	Night	17% 2 10% 37% 28% 7%	433
June	1st to 10th	Night	13% 3 10% 42% 28% 6%	400
	11th to 20th	Night	9% 2 8% 43% 34% 5%	400
	21st to end	Night	8% 2 8% 40% 38% 5%	400
July	1st to 10th	Night	8% 1 6% 33% 45% 7%	390
	11th to 20th	Night	9% 1 4 24% 53% 9%	488
	21st to end	Night	10% 2 8% 33% 38% 9%	657
August	1st to 10th	Night	11% 2 7% 36% 38% 7%	624
	11th to 20th	Night	13% 2 6% 31% 39% 9%	790
	21st to end	Night	14% 1 7% 28% 41% 10%	880
September	1st to 10th	Night	14% 1 11% 29% 34% 11%	773
	11th to 20th	Night	16% 2 10% 30% 35% 7%	760
	21st to end	Night	22% 4 13% 30% 28% 3	760
October	1st to 10th	Night	17% 3 16% 29% 28% 7%	760
	11th to 20th	Night	18% 6% 22% 31% 20% 2	760
	21st to end	Night	15% 8% 22% 29% 21% 4	836
November	1st to 10th	Night	19% 6% 21% 30% 20% 4	780
	11th to 20th	Night	19% 9% 27% 31% 13% 1	800
	21st to end	Night	14% 10% 26% 33% 15% 1	800
December	1st to 10th	Night	20% 9% 33% 28% 10% 1	800
	11th to 20th	Night	20% 7% 34% 31% 9%	800
	21st to end	Night	16% 9% 31% 33% 10%	880

Page generated at 2025-09-01 01:51:08. Version ac07

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