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 2024-11-04.

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	13% 6% 2 6% 4 4 4 4 6% 8% 41%	100981
	Night	14% 7% 2 6% 4 4 4 4 5% 7% 41%	97991
Transparency	Day	38% 7% 14% 23% 15% 3	104615
	Night	40% 6% 12% 23% 17% 3	102496
Seeing	Day	15% 6% 21% 29% 23% 7%	15309
	Night	16% 6% 23% 32% 19% 3	24835

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% 2 6% 4 3 3 3 5% 5% 46%	2620
	11th to 20th	Day	12% 6% 3 6% 4 4 4 3 6% 6% 46%	2840
	21st to end	Day	12% 11% 3 8% 5% 4 4 3 5% 6% 38%	3124
February	1st to 10th	Day	13% 8% 2 8% 4 5% 5% 3 7% 8% 39%	1710
	11th to 20th	Day	20% 6% 2 6% 3 4 4 3 4 6% 42%	1840
	21st to end	Day	17% 8% 2 6% 3 4 4 3 5% 8% 39%	1570
March	1st to 10th	Day	23% 9% 3 7% 4 3 3 3 4 6% 36%	3269
	11th to 20th	Day	10% 5% 1 4 3 3 3 3 5% 7% 55%	3480
	21st to end	Day	17% 8% 2 6% 3 3 4 3 4 6% 44%	3964
April	1st to 10th	Day	12% 6% 2 5% 3 4 3 3 5% 7% 50%	2280
	11th to 20th	Day	9% 6% 2 6% 4 3 4 3 5% 8% 49%	2254
	21st to end	Day	13% 5% 2 5% 4 4 4 3 6% 7% 48%	2280
May	1st to 10th	Day	14% 7% 3 7% 5% 5% 6% 5% 6% 10% 33%	3765
	11th to 20th	Day	18% 8% 3 8% 5% 5% 5% 4 6% 7% 32%	4210
	21st to end	Day	9% 6% 2 6% 4 4 5% 4 8% 10% 43%	4823
June	1st to 10th	Day	10% 5% 2 5% 5% 5% 5% 4 8% 11% 42%	2660
	11th to 20th	Day	10% 5% 2 5% 4 4 5% 4 6% 12% 42%	2660
	21st to end	Day	6% 5% 2 5% 5% 4 6% 5% 7% 11% 43%	2660
July	1st to 10th	Day	7% 4 2 5% 4 5% 6% 6% 10% 12% 39%	4440
	11th to 20th	Day	12% 6% 2 8% 6% 5% 5% 5% 8% 10% 34%	4262
	21st to end	Day	9% 6% 3 8% 6% 7% 6% 6% 8% 10% 32%	4466
August	1st to 10th	Day	15% 7% 3 9% 6% 6% 6% 5% 7% 10% 26%	4020
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 5% 7% 10% 39%	3730
	21st to end	Day	8% 5% 1 5% 4 4 5% 5% 7% 11% 45%	4180
September	1st to 10th	Day	13% 5% 2 6% 3 4 4 5% 6% 9% 43%	2280
	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 4 6% 45%	1772
	11th to 20th	Day	15% 8% 2 5% 3 3 4 3 4 7% 45%	1710
	21st to end	Day	14% 5% 2 6% 4 4 4 3 5% 7% 47%	1690
December	1st to 10th	Day	16% 6% 3 8% 4 3 4 3 6% 7% 40%	1520
	11th to 20th	Day	15% 8% 2 5% 4 3 3 3 4 6% 46%	1910
	21st to end	Day	16% 6% 2 5% 3 4 4 3 5% 8% 45%	2772
January	1st to 10th	Night	13% 8% 2 5% 4 4 4 4 6% 7% 43%	4323
	11th to 20th	Night	16% 8% 2 7% 5% 4 4 3 5% 6% 41%	4120
	21st to end	Night	15% 8% 3 8% 5% 4 4 3 5% 6% 39%	4532
February	1st to 10th	Night	17% 7% 2 5% 4 3 4 3 5% 6% 43%	2470
	11th to 20th	Night	20% 7% 3 6% 3 3 3 4 5% 6% 40%	2223
	21st to end	Night	16% 7% 3 6% 4 3 3 3 5% 6% 43%	1884
March	1st to 10th	Night	23% 9% 3 7% 4 4 3 3 4 6% 33%	3579
	11th to 20th	Night	14% 6% 2 5% 4 3 4 3 4 6% 49%	3480
	21st to end	Night	19% 9% 2 5% 3 3 3 2 3 4 46%	3667
April	1st to 10th	Night	13% 6% 2 7% 4 4 4 4 6% 8% 42%	1900
	11th to 20th	Night	11% 6% 3 6% 3 3 3 4 4 8% 48%	1875
	21st to end	Night	13% 6% 2 5% 4 4 4 3 6% 8% 46%	1900
May	1st to 10th	Night	14% 7% 3 9% 5% 5% 5% 4 5% 9% 33%	3130
	11th to 20th	Night	20% 8% 2 6% 4 4 5% 4 5% 7% 34%	2707
	21st to end	Night	10% 7% 3 8% 5% 4 5% 4 6% 10% 40%	2732
June	1st to 10th	Night	11% 6% 1 6% 5% 4 4 5% 7% 11% 39%	1520
	11th to 20th	Night	6% 5% 3 7% 6% 5% 5% 5% 7% 10% 41%	1520
	21st to end	Night	7% 6% 2 5% 4 5% 4 5% 7% 12% 44%	1520
July	1st to 10th	Night	7% 4 2 7% 5% 5% 6% 5% 8% 13% 38%	2520
	11th to 20th	Night	8% 5% 3 8% 6% 5% 5% 5% 8% 10% 37%	2694
	21st to end	Night	14% 7% 2 9% 6% 6% 7% 4 7% 8% 30%	3087
August	1st to 10th	Night	15% 8% 3 8% 5% 5% 6% 5% 6% 9% 31%	2876
	11th to 20th	Night	9% 7% 2 8% 5% 5% 5% 4 6% 9% 39%	3097
	21st to end	Night	11% 5% 2 5% 4 4 5% 4 7% 10% 44%	3476
September	1st to 10th	Night	12% 5% 2 6% 4 4 5% 4 6% 8% 44%	1900
	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 4 3 5% 7% 45%	2378
	11th to 20th	Night	16% 7% 3 5% 4 2 4 3 5% 7% 44%	2470
	21st to end	Night	13% 4 2 4 4 4 4 3 5% 7% 48%	2488
December	1st to 10th	Night	15% 9% 3 7% 5% 4 4 4 5% 6% 38%	2660
	11th to 20th	Night	17% 6% 2 5% 4 4 3 4 5% 7% 44%	3285
	21st to end	Night	12% 7% 2 6% 4 4 4 3 6% 7% 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	48% 6% 11% 18% 13% 5%	3269
	11th to 20th	Day	28% 5% 10% 23% 25% 9%	3480
	21st to end	Day	42% 6% 13% 18% 18% 3	3964
April	1st to 10th	Day	34% 6% 13% 22% 21% 5%	2280
	11th to 20th	Day	33% 5% 12% 24% 20% 5%	2254
	21st to end	Day	35% 6% 13% 25% 17% 4	2280
May	1st to 10th	Day	44% 12% 15% 20% 9% 1	3800
	11th to 20th	Day	47% 11% 14% 20% 7% 1	4214
	21st to end	Day	31% 14% 16% 24% 13% 2	4837
June	1st to 10th	Day	32% 9% 18% 27% 13% 2	2660
	11th to 20th	Day	33% 9% 17% 26% 14% 2	2660
	21st to end	Day	33% 10% 16% 27% 13% 1	2660
July	1st to 10th	Day	32% 12% 24% 21% 10% 2	4370
	11th to 20th	Day	42% 9% 25% 18% 5%	4188
	21st to end	Day	43% 10% 15% 19% 12% 1	4324
August	1st to 10th	Day	50% 8% 19% 19% 4	4007
	11th to 20th	Day	37% 7% 17% 26% 12% 1	3766
	21st to end	Day	32% 7% 14% 30% 16% 2	4180
September	1st to 10th	Day	36% 11% 15% 18% 17% 3	2280
	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% 10% 24% 18% 3	1772
	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	51% 7% 9% 18% 13% 2	3579
	11th to 20th	Night	35% 6% 9% 19% 24% 8%	3480
	21st to end	Night	43% 5% 7% 26% 15% 5%	3667
April	1st to 10th	Night	39% 7% 12% 17% 21% 4	1900
	11th to 20th	Night	34% 6% 12% 22% 20% 6%	1875
	21st to end	Night	37% 7% 11% 24% 18% 3	1900
May	1st to 10th	Night	46% 10% 15% 19% 9% 2	3160
	11th to 20th	Night	47% 8% 14% 23% 7% 1	2708
	21st to end	Night	37% 11% 16% 22% 13% 1	2739
June	1st to 10th	Night	36% 9% 16% 24% 13% 1	1520
	11th to 20th	Night	35% 11% 18% 21% 13% 1	1520
	21st to end	Night	33% 10% 17% 25% 14% 2	1520
July	1st to 10th	Night	38% 11% 19% 21% 10% 2	2480
	11th to 20th	Night	39% 9% 24% 21% 6% 1	2645
	21st to end	Night	49% 10% 12% 17% 11%	2988
August	1st to 10th	Night	49% 7% 20% 19% 5%	2865
	11th to 20th	Night	41% 6% 16% 25% 12%	3127
	21st to end	Night	35% 6% 11% 26% 21% 1	3476
September	1st to 10th	Night	37% 8% 16% 21% 15% 3	1900
	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% 24% 19% 3	2378
	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% 35% 33% 9%	506
April	1st to 10th	Day	14% 11% 33% 31% 9% 1	460
	11th to 20th	Day	11% 5% 30% 35% 15% 4	452
	21st to end	Day	16% 5% 27% 33% 17% 2	460
May	1st to 10th	Day	16% 6% 27% 32% 16% 3	463
	11th to 20th	Day	17% 5% 18% 34% 22% 3	487
	21st to end	Day	17% 3 11% 34% 26% 9%	529
June	1st to 10th	Day	11% 3 10% 35% 32% 8%	490
	11th to 20th	Day	12% 2 14% 30% 32% 11%	490
	21st to end	Day	9% 1 9% 34% 37% 10%	490
July	1st to 10th	Day	9% 2 5% 25% 44% 16%	485
	11th to 20th	Day	8% 2 5% 20% 48% 18%	484
	21st to end	Day	9% 1 6% 32% 39% 13%	532
August	1st to 10th	Day	13% 2 8% 31% 35% 12%	486
	11th to 20th	Day	10% 2 5% 25% 42% 15%	479
	21st to end	Day	12% 1 8% 23% 41% 16%	539
September	1st to 10th	Day	15% 2 10% 27% 29% 16%	490
	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% 32% 14% 6%	412
	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%	836
April	1st to 10th	Night	16% 8% 36% 32% 8% 1	760
	11th to 20th	Night	14% 7% 28% 36% 14% 1	751
	21st to end	Night	16% 5% 23% 43% 12% 1	760
May	1st to 10th	Night	15% 6% 25% 39% 14% 1	760
	11th to 20th	Night	16% 4 19% 41% 19% 2	508
	21st to end	Night	16% 2 9% 37% 29% 7%	411
June	1st to 10th	Night	12% 3 10% 41% 28% 6%	380
	11th to 20th	Night	8% 2 8% 44% 34% 5%	380
	21st to end	Night	8% 2 8% 41% 36% 4	380
July	1st to 10th	Night	8% 1 6% 34% 43% 7%	370
	11th to 20th	Night	9% 1 4 25% 53% 8%	463
	21st to end	Night	10% 2 8% 34% 38% 7%	624
August	1st to 10th	Night	9% 3 7% 37% 38% 7%	592
	11th to 20th	Night	12% 2 7% 33% 38% 8%	750
	21st to end	Night	14% 1 7% 27% 41% 10%	836
September	1st to 10th	Night	14% 1 11% 29% 34% 11%	760
	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	18% 6% 22% 29% 20% 4	755
	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

Page generated at 2024-11-01 22:47:39. Version ac07

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