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 2024-03-28.

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	13% 6% 2 5% 5% 3 5% 5% 6% 8% 43%	78840
	Night	14% 6% 2 5% 5% 3 4 5% 5% 8% 43%	81155
Transparency	Day	37% 8% 13% 23% 16% 3	78551
	Night	39% 7% 12% 23% 16% 3	80963
Seeing	Day	15% 6% 21% 29% 22% 6%	14425
	Night	17% 6% 23% 32% 19% 3	24098

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	15% 8% 3 6% 4 2 3 4 5% 5% 46%	2620
	11th to 20th	Day	12% 6% 3 5% 5% 2 4 4 6% 7% 46%	2840
	21st to end	Day	12% 11% 4 7% 6% 3 5% 4 5% 6% 39%	3124
February	1st to 10th	Day	13% 7% 2 6% 5% 3 5% 4 6% 8% 39%	1710
	11th to 20th	Day	20% 6% 3 5% 4 3 4 4 4 6% 42%	1840
	21st to end	Day	17% 8% 3 5% 4 3 4 4 5% 8% 39%	1570
March	1st to 10th	Day	15% 6% 2 4 3 2 4 3 5% 7% 50%	1985
	11th to 20th	Day	16% 6% 2 4 5% 3 3 4 4 7% 45%	2090
	21st to end	Day	15% 6% 2 5% 5% 3 5% 5% 5% 6% 42%	2336
April	1st to 10th	Day	13% 6% 2 4 4 3 3 4 5% 7% 51%	2160
	11th to 20th	Day	10% 5% 2 5% 5% 3 4 4 5% 8% 49%	2134
	21st to end	Day	13% 4 2 4 4 3 4 4 5% 7% 48%	2160
May	1st to 10th	Day	14% 5% 2 4 5% 3 4 6% 5% 8% 43%	2160
	11th to 20th	Day	15% 7% 2 5% 5% 3 5% 5% 5% 8% 40%	2360
	21st to end	Day	12% 6% 2 5% 5% 3 5% 5% 6% 9% 43%	2725
June	1st to 10th	Day	10% 4 2 4 5% 3 5% 6% 7% 12% 42%	2520
	11th to 20th	Day	10% 5% 2 5% 5% 3 5% 6% 6% 12% 41%	2520
	21st to end	Day	6% 4 3 5% 6% 3 6% 6% 8% 11% 42%	2520
July	1st to 10th	Day	8% 4 2 4 4 4 6% 7% 10% 11% 41%	2520
	11th to 20th	Day	8% 4 2 5% 6% 4 5% 6% 9% 13% 39%	2426
	21st to end	Day	6% 4 2 5% 6% 4 7% 8% 9% 12% 38%	2547
August	1st to 10th	Day	10% 4 2 6% 6% 4 6% 7% 8% 10% 37%	2284
	11th to 20th	Day	10% 5% 3 6% 6% 4 5% 6% 8% 10% 37%	2126
	21st to end	Day	12% 5% 2 5% 5% 3 5% 6% 7% 11% 39%	2376
September	1st to 10th	Day	13% 5% 3 5% 4 3 4 6% 5% 9% 43%	2160
	11th to 20th	Day	13% 6% 3 5% 6% 4 5% 5% 6% 7% 41%	2160
	21st to end	Day	20% 6% 3 5% 6% 3 5% 4 5% 7% 36%	1943
October	1st to 10th	Day	17% 5% 3 5% 3 3 4 4 5% 6% 46%	1800
	11th to 20th	Day	15% 5% 2 5% 4 3 4 4 4 5% 49%	1800
	21st to end	Day	13% 6% 2 5% 5% 3 4 4 4 6% 48%	1980
November	1st to 10th	Day	16% 6% 3 4 4 2 4 5% 4 6% 46%	1742
	11th to 20th	Day	15% 8% 3 4 3 2 4 4 4 7% 46%	1710
	21st to end	Day	14% 4 2 5% 4 3 4 4 5% 7% 47%	1690
December	1st to 10th	Day	16% 6% 3 7% 4 3 4 4 5% 7% 40%	1520
	11th to 20th	Day	15% 8% 3 4 4 2 4 4 4 6% 46%	1910
	21st to end	Day	16% 6% 2 4 4 3 4 4 4 8% 45%	2772
January	1st to 10th	Night	13% 8% 2 5% 4 3 4 5% 5% 8% 43%	4323
	11th to 20th	Night	16% 7% 2 6% 6% 3 4 4 5% 7% 41%	4120
	21st to end	Night	15% 7% 3 7% 6% 3 4 4 5% 6% 39%	4532
February	1st to 10th	Night	17% 7% 3 4 4 3 4 4 5% 6% 43%	2470
	11th to 20th	Night	20% 7% 3 5% 4 2 3 5% 5% 6% 40%	2223
	21st to end	Night	16% 7% 3 5% 5% 2 4 3 5% 7% 44%	1884
March	1st to 10th	Night	15% 5% 2 5% 4 3 4 4 4 6% 48%	2190
	11th to 20th	Night	17% 7% 2 5% 5% 3 5% 5% 5% 7% 40%	2090
	21st to end	Night	17% 7% 2 6% 5% 3 4 4 4 6% 42%	2174
April	1st to 10th	Night	14% 6% 2 6% 4 3 4 5% 5% 8% 43%	1800
	11th to 20th	Night	12% 6% 3 5% 4 2 3 5% 4 8% 49%	1775
	21st to end	Night	13% 6% 2 4 5% 3 4 4 5% 8% 46%	1800
May	1st to 10th	Night	14% 6% 2 6% 5% 4 5% 4 5% 10% 39%	1800
	11th to 20th	Night	14% 7% 3 4 4 3 5% 5% 7% 10% 39%	1543
	21st to end	Night	13% 7% 1 4 6% 3 4 5% 6% 9% 43%	1550
June	1st to 10th	Night	11% 6% 2 5% 5% 3 4 6% 6% 11% 41%	1440
	11th to 20th	Night	7% 4 4 6% 7% 4 5% 6% 7% 10% 40%	1440
	21st to end	Night	7% 5% 2 4 5% 4 5% 5% 7% 12% 42%	1440
July	1st to 10th	Night	6% 5% 3 6% 5% 3 5% 5% 7% 13% 42%	1440
	11th to 20th	Night	8% 4 2 4 6% 4 5% 7% 8% 11% 43%	1530
	21st to end	Night	8% 5% 2 6% 5% 4 7% 5% 9% 12% 36%	1771
August	1st to 10th	Night	8% 7% 3 6% 6% 4 5% 7% 7% 10% 38%	1634
	11th to 20th	Night	9% 7% 2 7% 6% 4 6% 5% 7% 9% 38%	1774
	21st to end	Night	12% 6% 3 6% 5% 3 5% 5% 6% 9% 38%	1980
September	1st to 10th	Night	12% 5% 3 5% 4 3 5% 5% 6% 8% 44%	1800
	11th to 20th	Night	12% 7% 3 6% 6% 3 4 4 5% 7% 43%	1800
	21st to end	Night	19% 6% 2 6% 5% 4 5% 4 4 7% 36%	2014
October	1st to 10th	Night	15% 4 3 4 4 2 4 5% 5% 5% 47%	2160
	11th to 20th	Night	15% 7% 2 4 4 3 3 4 5% 6% 48%	2160
	21st to end	Night	13% 5% 2 5% 5% 3 4 5% 5% 7% 48%	2376
November	1st to 10th	Night	17% 5% 2 4 5% 2 3 4 4 7% 45%	2335
	11th to 20th	Night	16% 6% 3 4 5% 2 4 4 4 7% 44%	2470
	21st to end	Night	13% 4 2 4 5% 3 4 4 5% 8% 48%	2488
December	1st to 10th	Night	15% 8% 3 6% 6% 3 5% 4 5% 6% 39%	2660
	11th to 20th	Night	18% 6% 2 4 4 3 4 4 5% 7% 44%	3285
	21st to end	Night	12% 6% 3 5% 5% 3 4 5% 5% 8% 45%	4884

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	38% 6% 7% 30% 16% 2	2621
	11th to 20th	Day	37% 6% 8% 21% 24% 4	2840
	21st to end	Day	45% 7% 11% 19% 16% 2	3124
February	1st to 10th	Day	42% 6% 13% 25% 13% 3	1710
	11th to 20th	Day	44% 5% 9% 19% 18% 5%	1849
	21st to end	Day	42% 6% 13% 19% 14% 6%	1570
March	1st to 10th	Day	35% 4 13% 24% 19% 4	1985
	11th to 20th	Day	39% 5% 11% 21% 18% 5%	2090
	21st to end	Day	41% 7% 12% 21% 17% 3	2336
April	1st to 10th	Day	34% 6% 13% 22% 20% 5%	2160
	11th to 20th	Day	32% 6% 12% 24% 20% 5%	2134
	21st to end	Day	35% 6% 14% 24% 18% 4	2160
May	1st to 10th	Day	37% 9% 15% 23% 14% 3	2160
	11th to 20th	Day	41% 8% 15% 24% 10% 2	2364
	21st to end	Day	36% 10% 17% 25% 12% 1	2725
June	1st to 10th	Day	32% 9% 18% 27% 13% 1	2520
	11th to 20th	Day	34% 10% 18% 24% 13% 2	2520
	21st to end	Day	33% 11% 16% 25% 13% 1	2520
July	1st to 10th	Day	30% 13% 19% 23% 12% 2	2450
	11th to 20th	Day	32% 12% 22% 24% 10% 1	2352
	21st to end	Day	32% 12% 19% 23% 12% 1	2405
August	1st to 10th	Day	35% 14% 19% 24% 7%	2271
	11th to 20th	Day	38% 12% 16% 24% 10% 1	2126
	21st to end	Day	36% 11% 17% 21% 12% 3	2376
September	1st to 10th	Day	36% 11% 16% 19% 15% 3	2160
	11th to 20th	Day	39% 8% 11% 21% 19% 2	2160
	21st to end	Day	47% 7% 9% 21% 15% 2	1943
October	1st to 10th	Day	38% 6% 11% 23% 19% 2	1800
	11th to 20th	Day	37% 6% 8% 26% 19% 3	1800
	21st to end	Day	37% 5% 8% 24% 21% 5%	1980
November	1st to 10th	Day	38% 6% 11% 24% 18% 3	1742
	11th to 20th	Day	39% 6% 12% 19% 20% 4	1710
	21st to end	Day	37% 4 9% 28% 19% 2	1690
December	1st to 10th	Day	44% 5% 13% 22% 13% 2	1520
	11th to 20th	Day	38% 6% 9% 25% 16% 5%	1906
	21st to end	Day	39% 4 10% 30% 16% 1	2772
January	1st to 10th	Night	38% 5% 9% 26% 18% 4	4323
	11th to 20th	Night	43% 5% 8% 22% 20% 2	4120
	21st to end	Night	44% 7% 9% 20% 17% 3	4532
February	1st to 10th	Night	42% 5% 10% 24% 16% 2	2470
	11th to 20th	Night	45% 5% 8% 21% 17% 4	2225
	21st to end	Night	42% 5% 9% 21% 17% 6%	1884
March	1st to 10th	Night	38% 6% 10% 24% 19% 3	2190
	11th to 20th	Night	42% 7% 11% 19% 17% 4	2090
	21st to end	Night	43% 7% 9% 22% 15% 4	2174
April	1st to 10th	Night	39% 7% 12% 18% 21% 4	1800
	11th to 20th	Night	34% 6% 11% 22% 20% 6%	1775
	21st to end	Night	37% 6% 11% 24% 18% 3	1800
May	1st to 10th	Night	40% 8% 13% 23% 13% 3	1800
	11th to 20th	Night	39% 8% 17% 21% 12% 2	1544
	21st to end	Night	37% 9% 17% 22% 13% 1	1551
June	1st to 10th	Night	36% 8% 17% 25% 13% 1	1440
	11th to 20th	Night	36% 11% 19% 20% 13% 1	1440
	21st to end	Night	34% 10% 17% 24% 14% 1	1440
July	1st to 10th	Night	34% 11% 17% 24% 11% 3	1400
	11th to 20th	Night	30% 12% 20% 26% 11% 1	1481
	21st to end	Night	35% 12% 17% 25% 10% 1	1672
August	1st to 10th	Night	38% 11% 22% 21% 8%	1623
	11th to 20th	Night	39% 11% 18% 21% 11%	1774
	21st to end	Night	40% 10% 17% 21% 11% 2	1980
September	1st to 10th	Night	37% 9% 16% 21% 14% 3	1800
	11th to 20th	Night	40% 6% 11% 22% 18% 2	1800
	21st to end	Night	47% 7% 11% 19% 15% 1	2014
October	1st to 10th	Night	37% 6% 10% 24% 20% 3	2160
	11th to 20th	Night	37% 5% 9% 24% 22% 3	2160
	21st to end	Night	35% 6% 9% 25% 20% 6%	2376
November	1st to 10th	Night	39% 5% 10% 24% 19% 3	2335
	11th to 20th	Night	40% 5% 10% 21% 17% 6%	2470
	21st to end	Night	35% 5% 10% 27% 20% 3	2488
December	1st to 10th	Night	46% 6% 11% 21% 13% 2	2660
	11th to 20th	Night	40% 5% 10% 23% 18% 4	3288
	21st to end	Night	37% 6% 15% 26% 15% 2	4884

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	16% 13% 32% 31% 8%	211
	11th to 20th	Day	14% 16% 36% 30% 4	270
	21st to end	Day	18% 10% 33% 31% 6% 1	297
February	1st to 10th	Day	16% 13% 27% 35% 8%	270
	11th to 20th	Day	25% 11% 39% 21% 4	448
	21st to end	Day	19% 10% 37% 29% 4 1	382
March	1st to 10th	Day	18% 12% 34% 28% 8%	460
	11th to 20th	Day	18% 10% 34% 29% 7% 2	460
	21st to end	Day	15% 8% 34% 33% 10%	490
April	1st to 10th	Day	15% 11% 32% 31% 10% 1	420
	11th to 20th	Day	12% 4 30% 35% 15% 4	412
	21st to end	Day	16% 5% 26% 35% 16% 2	420
May	1st to 10th	Day	16% 6% 29% 30% 15% 3	423
	11th to 20th	Day	17% 5% 17% 34% 23% 4	447
	21st to end	Day	18% 3 11% 32% 27% 9%	485
June	1st to 10th	Day	12% 3 10% 34% 33% 8%	450
	11th to 20th	Day	12% 2 15% 30% 28% 11%	450
	21st to end	Day	8% 2 10% 35% 36% 8%	450
July	1st to 10th	Day	10% 2 5% 26% 44% 13%	445
	11th to 20th	Day	7% 2 5% 20% 47% 18%	444
	21st to end	Day	8% 1 7% 31% 40% 13%	488
August	1st to 10th	Day	11% 2 8% 32% 35% 12%	446
	11th to 20th	Day	10% 2 6% 23% 42% 16%	439
	21st to end	Day	13% 1 8% 24% 39% 16%	495
September	1st to 10th	Day	15% 2 10% 26% 30% 16%	450
	11th to 20th	Day	14% 4 12% 25% 34% 11%	450
	21st to end	Day	20% 6% 16% 24% 29% 4	450
October	1st to 10th	Day	20% 3 15% 26% 29% 8%	450
	11th to 20th	Day	14% 6% 19% 31% 25% 3	450
	21st to end	Day	16% 7% 24% 29% 19% 5%	495
November	1st to 10th	Day	20% 8% 22% 31% 14% 6%	400
	11th to 20th	Day	17% 11% 31% 25% 12% 3	370
	21st to end	Day	16% 11% 25% 28% 17% 3	350
December	1st to 10th	Day	23% 9% 36% 21% 9% 2	180
	11th to 20th	Day	17% 8% 39% 23% 11% 2	180
	21st to end	Day	20% 10% 28% 28% 15%	198
January	1st to 10th	Night	18% 15% 34% 26% 7%	760
	11th to 20th	Night	20% 14% 31% 28% 7%	760
	21st to end	Night	19% 12% 38% 27% 4	836
February	1st to 10th	Night	21% 8% 36% 30% 5%	760
	11th to 20th	Night	24% 11% 39% 23% 3	743
	21st to end	Night	20% 10% 32% 31% 6%	628
March	1st to 10th	Night	18% 8% 34% 30% 9%	760
	11th to 20th	Night	19% 8% 35% 28% 8% 1	760
	21st to end	Night	20% 7% 31% 34% 8%	821
April	1st to 10th	Night	16% 7% 35% 32% 9% 1	720
	11th to 20th	Night	14% 6% 28% 36% 14% 1	711
	21st to end	Night	16% 5% 23% 42% 13% 1	720
May	1st to 10th	Night	15% 6% 26% 38% 14% 1	720
	11th to 20th	Night	16% 4 18% 41% 20% 2	482
	21st to end	Night	17% 2 9% 36% 29% 7%	389
June	1st to 10th	Night	12% 2 10% 41% 28% 7%	360
	11th to 20th	Night	8% 2 8% 45% 33% 5%	360
	21st to end	Night	8% 2 9% 42% 35% 4	360
July	1st to 10th	Night	9% 1 6% 35% 42% 6%	350
	11th to 20th	Night	8% 1 4 26% 52% 8%	437
	21st to end	Night	10% 2 9% 35% 38% 7%	591
August	1st to 10th	Night	9% 3 6% 36% 39% 7%	560
	11th to 20th	Night	12% 2 7% 32% 38% 9%	710
	21st to end	Night	15% 1 8% 27% 40% 10%	792
September	1st to 10th	Night	14% 2 10% 29% 34% 12%	720
	11th to 20th	Night	15% 2 10% 30% 36% 7%	720
	21st to end	Night	22% 4 13% 30% 28% 3	720
October	1st to 10th	Night	17% 3 16% 29% 28% 7%	720
	11th to 20th	Night	19% 6% 21% 31% 20% 2	720
	21st to end	Night	16% 8% 23% 28% 20% 4	792
November	1st to 10th	Night	19% 6% 22% 29% 19% 4	740
	11th to 20th	Night	18% 10% 26% 30% 14% 1	760
	21st to end	Night	14% 10% 26% 33% 15% 1	760
December	1st to 10th	Night	21% 9% 31% 28% 10% 1	760
	11th to 20th	Night	19% 7% 35% 30% 9%	760
	21st to end	Night	17% 9% 32% 32% 10%	836

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