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 2024-12-02.

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%	101292
	Night	14% 7% 2 6% 4 4 4 4 5% 7% 42%	98304
Transparency	Day	21% 47% 8% 13% 9% 2	104925
	Night	23% 47% 6% 13% 10% 2	102810
Seeing	Day	15% 5% 19% 31% 24% 7%	15336
	Night	16% 6% 23% 31% 20% 3	24868

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% 7% 3 5% 3 3 4 3 4 5% 49%	2586
	11th to 20th	Day	12% 7% 3 6% 5% 4 3 3 5% 5% 47%	2840
	21st to end	Day	12% 9% 3 7% 5% 4 4 4 5% 6% 39%	3124
February	1st to 10th	Day	12% 8% 2 7% 4 4 5% 5% 6% 8% 39%	1710
	11th to 20th	Day	20% 6% 2 4 3 4 3 4 5% 6% 44%	1826
	21st to end	Day	18% 8% 2 5% 4 4 3 4 6% 8% 39%	1570
March	1st to 10th	Day	21% 8% 3 6% 3 4 4 3 4 7% 37%	3268
	11th to 20th	Day	9% 5% 1 4 3 3 4 3 5% 7% 56%	3480
	21st to end	Day	17% 8% 3 5% 3 3 4 3 5% 6% 43%	3964
April	1st to 10th	Day	12% 6% 2 5% 4 4 3 3 5% 6% 50%	2280
	11th to 20th	Day	9% 5% 2 5% 5% 4 4 4 5% 6% 51%	2254
	21st to end	Day	12% 5% 2 5% 4 4 4 4 6% 7% 47%	2280
May	1st to 10th	Day	14% 7% 3 7% 4 4 5% 4 6% 9% 36%	3765
	11th to 20th	Day	18% 7% 2 6% 5% 4 5% 4 5% 8% 35%	4278
	21st to end	Day	9% 4 2 5% 3 4 4 4 7% 11% 49%	4823
June	1st to 10th	Day	9% 4 2 4 4 4 4 5% 8% 12% 44%	2660
	11th to 20th	Day	10% 5% 2 4 3 4 5% 4 7% 10% 46%	2660
	21st to end	Day	6% 5% 2 5% 4 4 4 5% 8% 10% 46%	2660
July	1st to 10th	Day	6% 4 1 5% 5% 4 6% 5% 8% 13% 44%	4440
	11th to 20th	Day	11% 7% 2 7% 5% 5% 4 4 6% 11% 38%	4313
	21st to end	Day	8% 6% 3 7% 6% 5% 6% 5% 7% 10% 36%	4466
August	1st to 10th	Day	14% 8% 3 7% 5% 5% 5% 4 7% 11% 31%	4050
	11th to 20th	Day	8% 6% 2 8% 5% 6% 6% 4 7% 9% 41%	3730
	21st to end	Day	7% 4 2 4 3 4 5% 4 7% 10% 49%	4180
September	1st to 10th	Day	14% 5% 2 5% 3 4 5% 4 6% 8% 44%	2280
	11th to 20th	Day	13% 6% 3 6% 4 3 5% 3 5% 7% 46%	2280
	21st to end	Day	18% 6% 3 8% 4 4 4 3 6% 6% 38%	2047
October	1st to 10th	Day	16% 5% 2 5% 5% 3 3 3 5% 5% 48%	1900
	11th to 20th	Day	13% 5% 3 4 4 3 3 2 3 6% 53%	1900
	21st to end	Day	12% 5% 2 6% 4 4 4 3 4 5% 50%	2090
November	1st to 10th	Day	13% 6% 2 5% 4 4 4 3 4 6% 49%	1825
	11th to 20th	Day	14% 7% 2 4 4 3 3 3 4 7% 48%	1800
	21st to end	Day	14% 4 2 4 3 4 4 3 4 6% 50%	1753
December	1st to 10th	Day	16% 8% 2 6% 4 4 4 4 5% 6% 43%	1528
	11th to 20th	Day	15% 7% 3 5% 3 2 3 2 4 4 50%	1910
	21st to end	Day	15% 7% 2 7% 4 3 3 3 5% 7% 44%	2772
January	1st to 10th	Night	13% 7% 3 5% 4 4 4 3 5% 7% 44%	4356
	11th to 20th	Night	15% 8% 3 7% 5% 4 4 2 5% 6% 43%	4120
	21st to end	Night	16% 9% 2 7% 5% 4 3 4 5% 5% 40%	4532
February	1st to 10th	Night	16% 8% 2 6% 4 4 4 3 5% 6% 43%	2470
	11th to 20th	Night	19% 8% 2 5% 5% 3 4 3 5% 6% 40%	2237
	21st to end	Night	17% 7% 2 6% 4 3 3 2 5% 6% 45%	1884
March	1st to 10th	Night	22% 8% 3 7% 5% 3 4 3 4 6% 34%	3583
	11th to 20th	Night	15% 6% 1 5% 3 3 4 3 5% 6% 49%	3480
	21st to end	Night	17% 9% 3 6% 3 3 3 2 3 5% 46%	3667
April	1st to 10th	Night	13% 7% 2 7% 5% 3 5% 4 6% 8% 40%	1900
	11th to 20th	Night	12% 5% 2 5% 4 4 3 3 6% 7% 50%	1875
	21st to end	Night	13% 6% 3 6% 4 4 4 3 6% 6% 45%	1900
May	1st to 10th	Night	16% 7% 3 8% 5% 5% 5% 4 7% 8% 33%	3130
	11th to 20th	Night	20% 7% 3 7% 5% 5% 5% 4 6% 7% 32%	2642
	21st to end	Night	10% 6% 3 6% 4 5% 5% 4 7% 9% 40%	2732
June	1st to 10th	Night	12% 5% 2 5% 5% 6% 5% 5% 6% 10% 39%	1520
	11th to 20th	Night	8% 4 3 6% 5% 6% 6% 5% 7% 10% 41%	1520
	21st to end	Night	6% 6% 2 6% 6% 5% 4 5% 8% 10% 43%	1520
July	1st to 10th	Night	8% 4 2 7% 5% 5% 6% 6% 8% 12% 38%	2520
	11th to 20th	Night	9% 7% 2 7% 5% 4 6% 5% 8% 11% 38%	2642
	21st to end	Night	13% 8% 3 7% 6% 6% 6% 6% 7% 8% 31%	3087
August	1st to 10th	Night	15% 8% 4 7% 5% 5% 6% 4 7% 10% 29%	2847
	11th to 20th	Night	9% 6% 3 8% 5% 5% 5% 4 6% 8% 41%	3097
	21st to end	Night	9% 5% 2 5% 3 5% 4 4 6% 11% 46%	3476
September	1st to 10th	Night	12% 5% 2 5% 5% 5% 4 4 6% 8% 45%	1900
	11th to 20th	Night	10% 6% 4 8% 4 4 4 4 5% 5% 46%	1900
	21st to end	Night	18% 7% 3 7% 5% 4 4 4 4 6% 37%	2129
October	1st to 10th	Night	15% 5% 2 6% 4 4 4 4 5% 6% 47%	2280
	11th to 20th	Night	16% 5% 2 4 3 3 3 3 5% 5% 50%	2280
	21st to end	Night	13% 5% 2 6% 4 4 3 3 3 6% 51%	2508
November	1st to 10th	Night	15% 7% 2 5% 4 4 3 3 5% 6% 46%	2470
	11th to 20th	Night	15% 6% 2 6% 4 3 3 3 5% 7% 45%	2600
	21st to end	Night	12% 5% 2 4 4 4 3 4 5% 7% 49%	2645
December	1st to 10th	Night	17% 7% 3 7% 4 5% 4 4 5% 6% 39%	2686
	11th to 20th	Night	18% 6% 2 5% 3 3 3 3 4 6% 45%	3285
	21st to end	Night	12% 7% 2 6% 4 4 4 4 6% 6% 44%	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	25% 37% 2 22% 13% 1	2587
	11th to 20th	Day	24% 37% 5% 13% 19% 3	2840
	21st to end	Day	30% 41% 6% 13% 9% 1	3124
February	1st to 10th	Day	15% 65% 4 11% 4 1	1710
	11th to 20th	Day	17% 65% 3 7% 5% 3	1835
	21st to end	Day	17% 65% 4 6% 5% 2	1570
March	1st to 10th	Day	37% 41% 6% 7% 7% 2	3268
	11th to 20th	Day	15% 40% 5% 17% 18% 5%	3480
	21st to end	Day	27% 40% 8% 10% 13% 3	3964
April	1st to 10th	Day	13% 65% 4 9% 8% 1	2280
	11th to 20th	Day	12% 66% 5% 9% 7% 1	2254
	21st to end	Day	14% 65% 5% 10% 4 2	2280
May	1st to 10th	Day	30% 43% 11% 12% 3 1	3800
	11th to 20th	Day	32% 40% 8% 16% 3	4282
	21st to end	Day	18% 40% 10% 19% 10% 3	4837
June	1st to 10th	Day	12% 67% 6% 10% 5% 1	2660
	11th to 20th	Day	9% 67% 7% 10% 7%	2660
	21st to end	Day	10% 65% 7% 11% 7%	2660
July	1st to 10th	Day	19% 41% 21% 11% 6% 1	4370
	11th to 20th	Day	30% 39% 17% 12% 2	4238
	21st to end	Day	30% 40% 9% 12% 9% 1	4324
August	1st to 10th	Day	34% 39% 12% 13% 2	4037
	11th to 20th	Day	23% 40% 10% 20% 6%	3766
	21st to end	Day	15% 38% 11% 22% 13% 1	4180
September	1st to 10th	Day	15% 62% 8% 9% 5% 2	2280
	11th to 20th	Day	16% 60% 6% 10% 6% 2	2280
	21st to end	Day	23% 60% 4 9% 3 1	2047
October	1st to 10th	Day	16% 39% 7% 18% 16% 2	3160
	11th to 20th	Day	11% 37% 4 12% 30% 6%	3140
	21st to end	Day	9% 36% 7% 21% 17% 9%	3428
November	1st to 10th	Day	18% 55% 5% 13% 8% 2	1825
	11th to 20th	Day	18% 56% 4 8% 10% 3	1800
	21st to end	Day	16% 57% 4 13% 10% 1	1753
December	1st to 10th	Day	21% 60% 4 8% 5% 1	1528
	11th to 20th	Day	18% 48% 4 14% 11% 5%	1906
	21st to end	Day	26% 37% 8% 19% 10%	2772
January	1st to 10th	Night	26% 37% 3 17% 13% 3	4356
	11th to 20th	Night	28% 37% 4 15% 15% 2	4120
	21st to end	Night	30% 41% 4 11% 11% 2	4532
February	1st to 10th	Night	14% 65% 6% 9% 5% 1	2470
	11th to 20th	Night	18% 64% 3 7% 6% 2	2239
	21st to end	Night	15% 64% 3 10% 6% 2	1884
March	1st to 10th	Night	39% 41% 4 10% 6% 1	3583
	11th to 20th	Night	20% 40% 4 14% 18% 5%	3480
	21st to end	Night	27% 39% 3 17% 11% 3	3667
April	1st to 10th	Night	16% 65% 4 5% 9% 1	1900
	11th to 20th	Night	13% 66% 4 9% 7% 1	1875
	21st to end	Night	15% 65% 5% 8% 5% 1	1900
May	1st to 10th	Night	33% 41% 10% 12% 4	3160
	11th to 20th	Night	32% 41% 8% 17% 2	2643
	21st to end	Night	25% 41% 9% 15% 9%	2739
June	1st to 10th	Night	17% 66% 5% 6% 6% 1	1520
	11th to 20th	Night	11% 67% 6% 9% 7%	1520
	21st to end	Night	11% 65% 5% 11% 6% 1	1520
July	1st to 10th	Night	27% 42% 12% 13% 6% 1	2480
	11th to 20th	Night	28% 39% 17% 14% 2	2594
	21st to end	Night	35% 39% 7% 11% 8%	2988
August	1st to 10th	Night	36% 38% 11% 13% 2	2836
	11th to 20th	Night	24% 39% 10% 20% 7%	3127
	21st to end	Night	18% 38% 6% 20% 18%	3476
September	1st to 10th	Night	15% 62% 8% 9% 4 2	1900
	11th to 20th	Night	17% 60% 4 9% 8% 2	1900
	21st to end	Night	24% 60% 4 8% 3	2129
October	1st to 10th	Night	22% 38% 7% 16% 15% 1	3800
	11th to 20th	Night	13% 37% 3 13% 25% 8%	3779
	21st to end	Night	9% 36% 4 23% 20% 8%	4120
November	1st to 10th	Night	20% 56% 5% 11% 7% 1	2470
	11th to 20th	Night	17% 57% 4 9% 9% 5%	2600
	21st to end	Night	14% 57% 4 13% 10% 1	2645
December	1st to 10th	Night	23% 60% 3 8% 4 1	2686
	11th to 20th	Night	20% 49% 4 13% 11% 3	3288
	21st to end	Night	26% 37% 9% 18% 9% 1	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	18% 11% 25% 35% 9%	201
	11th to 20th	Day	18% 11% 34% 31% 5%	270
	21st to end	Day	19% 6% 32% 35% 8%	297
February	1st to 10th	Day	14% 10% 23% 41% 10% 1	270
	11th to 20th	Day	26% 9% 37% 24% 5%	434
	21st to end	Day	21% 9% 31% 31% 7% 1	382
March	1st to 10th	Day	16% 8% 32% 34% 9% 1	460
	11th to 20th	Day	18% 8% 29% 33% 10% 1	460
	21st to end	Day	17% 7% 26% 39% 10% 1	506
April	1st to 10th	Day	13% 8% 35% 30% 13% 1	460
	11th to 20th	Day	10% 4 26% 38% 18% 4	452
	21st to end	Day	15% 4 23% 35% 21% 2	460
May	1st to 10th	Day	16% 5% 21% 37% 18% 3	463
	11th to 20th	Day	19% 2 15% 35% 24% 5%	487
	21st to end	Day	16% 1 11% 33% 30% 9%	529
June	1st to 10th	Day	12% 2 10% 33% 34% 9%	490
	11th to 20th	Day	10% 1 9% 34% 34% 11%	490
	21st to end	Day	10% 2 10% 33% 37% 9%	490
July	1st to 10th	Day	10% 1 3 25% 46% 15%	485
	11th to 20th	Day	9% 1 4 22% 47% 16%	484
	21st to end	Day	9% 2 5% 29% 42% 12%	532
August	1st to 10th	Day	12% 1 8% 30% 38% 11%	486
	11th to 20th	Day	12% 1 9% 23% 41% 13%	479
	21st to end	Day	11% 1 8% 25% 36% 19%	539
September	1st to 10th	Day	15% 3 8% 25% 33% 15%	490
	11th to 20th	Day	14% 3 10% 26% 33% 13%	490
	21st to end	Day	23% 4 14% 29% 25% 5%	490
October	1st to 10th	Day	17% 5% 13% 27% 28% 10%	490
	11th to 20th	Day	16% 8% 19% 29% 23% 5%	490
	21st to end	Day	15% 6% 23% 30% 20% 6%	539
November	1st to 10th	Day	16% 7% 22% 32% 17% 6%	428
	11th to 20th	Day	17% 10% 29% 31% 12% 2	400
	21st to end	Day	14% 13% 27% 25% 18% 3	353
December	1st to 10th	Day	25% 2 32% 29% 10% 1	182
	11th to 20th	Day	19% 8% 32% 27% 14% 1	180
	21st to end	Day	19% 9% 27% 28% 16% 1	198
January	1st to 10th	Night	16% 15% 34% 28% 7%	760
	11th to 20th	Night	19% 11% 32% 29% 8%	760
	21st to end	Night	21% 10% 35% 30% 4	836
February	1st to 10th	Night	20% 7% 35% 32% 6% 1	760
	11th to 20th	Night	23% 11% 39% 23% 4	743
	21st to end	Night	19% 11% 32% 32% 5% 1	628
March	1st to 10th	Night	17% 8% 34% 32% 9%	760
	11th to 20th	Night	20% 7% 33% 29% 9% 2	760
	21st to end	Night	19% 7% 30% 34% 8%	836
April	1st to 10th	Night	17% 7% 36% 31% 9% 1	760
	11th to 20th	Night	13% 6% 26% 38% 16% 1	751
	21st to end	Night	16% 4 24% 40% 14% 1	760
May	1st to 10th	Night	17% 5% 24% 39% 14% 2	760
	11th to 20th	Night	16% 4 18% 39% 20% 3	469
	21st to end	Night	16% 2 8% 35% 32% 7%	411
June	1st to 10th	Night	14% 1 11% 35% 33% 6%	380
	11th to 20th	Night	10% 2 9% 41% 32% 6%	380
	21st to end	Night	8% 1 9% 41% 37% 5%	380
July	1st to 10th	Night	8% 1 5% 38% 41% 7%	370
	11th to 20th	Night	9% 1 5% 24% 52% 9%	438
	21st to end	Night	11% 2 8% 34% 39% 5%	624
August	1st to 10th	Night	11% 1 6% 38% 35% 8%	576
	11th to 20th	Night	13% 1 8% 32% 37% 9%	750
	21st to end	Night	11% 2 7% 28% 42% 11%	836
September	1st to 10th	Night	13% 2 10% 29% 34% 11%	760
	11th to 20th	Night	14% 3 10% 29% 35% 9%	760
	21st to end	Night	22% 4 13% 29% 28% 3	760
October	1st to 10th	Night	17% 4 16% 28% 28% 7%	760
	11th to 20th	Night	17% 7% 23% 29% 22% 3	760
	21st to end	Night	17% 7% 23% 28% 21% 4	836
November	1st to 10th	Night	19% 7% 21% 29% 19% 5%	780
	11th to 20th	Night	17% 9% 27% 31% 13% 2	800
	21st to end	Night	14% 12% 26% 30% 16% 2	800
December	1st to 10th	Night	21% 10% 31% 26% 11% 1	768
	11th to 20th	Night	20% 8% 34% 27% 11%	760
	21st to end	Night	18% 9% 30% 31% 11% 1	836

Page generated at 2024-11-29 10:43:08. Version ac07

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