Wilmington
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wilmington clear sky chart from 2005-11-06 to 2024-11-02.

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	15% 6% 2 6% 4 4 5% 4 6% 7% 41%	101286
	Night	16% 7% 2 6% 4 4 4 3 5% 7% 42%	97691
Transparency	Day	23% 49% 7% 13% 8% 1	101044
	Night	23% 49% 6% 13% 8% 2	97552
Seeing	Day	17% 9% 26% 26% 16% 6%	15004
	Night	18% 7% 30% 32% 12% 1	24301

By Month

Percentage Cloud Cover NE (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% 6% 2 5% 4 5% 3 3 5% 5% 47%	2517
	11th to 20th	Day	14% 9% 3 7% 5% 5% 5% 3 5% 5% 38%	2648
	21st to end	Day	21% 8% 2 6% 4 4 5% 3 4 5% 37%	3124
February	1st to 10th	Day	15% 8% 2 6% 4 5% 5% 4 6% 7% 39%	1710
	11th to 20th	Day	16% 7% 2 6% 4 3 5% 4 5% 6% 41%	1795
	21st to end	Day	18% 10% 3 6% 4 4 3 2 5% 6% 38%	1570
March	1st to 10th	Day	25% 6% 2 4 3 4 4 3 4 6% 39%	3166
	11th to 20th	Day	10% 4 2 5% 4 5% 5% 4 6% 7% 48%	3480
	21st to end	Day	22% 7% 1 5% 3 3 3 3 4 5% 44%	4024
April	1st to 10th	Day	15% 6% 2 6% 5% 4 4 4 5% 7% 42%	2280
	11th to 20th	Day	14% 7% 1 5% 4 4 4 3 6% 7% 44%	2254
	21st to end	Day	17% 5% 2 6% 4 4 4 4 6% 7% 40%	2280
May	1st to 10th	Day	29% 8% 3 5% 4 4 4 3 5% 7% 29%	4022
	11th to 20th	Day	24% 8% 3 7% 5% 5% 4 4 5% 7% 28%	4398
	21st to end	Day	12% 5% 2 5% 4 4 4 4 5% 9% 45%	4837
June	1st to 10th	Day	11% 6% 2 6% 4 5% 5% 5% 7% 9% 40%	2660
	11th to 20th	Day	12% 6% 2 6% 5% 4 5% 5% 8% 9% 39%	2660
	21st to end	Day	10% 5% 2 6% 4 4 5% 5% 7% 10% 42%	2660
July	1st to 10th	Day	7% 5% 2 6% 5% 6% 7% 5% 8% 11% 39%	4440
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 5% 8% 11% 39%	4440
	21st to end	Day	10% 7% 3 8% 6% 6% 6% 5% 8% 9% 32%	4665
August	1st to 10th	Day	17% 6% 3 6% 5% 4 6% 4 7% 8% 33%	4104
	11th to 20th	Day	12% 5% 2 5% 4 4 5% 4 7% 10% 41%	3741
	21st to end	Day	10% 5% 2 5% 4 4 5% 4 6% 8% 47%	4180
September	1st to 10th	Day	14% 6% 2 5% 4 4 4 4 6% 6% 44%	2280
	11th to 20th	Day	12% 5% 1 5% 3 4 4 3 5% 8% 50%	2262
	21st to end	Day	19% 8% 3 7% 4 4 4 3 6% 5% 38%	2071
October	1st to 10th	Day	16% 6% 2 5% 5% 4 4 3 5% 6% 44%	1900
	11th to 20th	Day	16% 4 2 4 4 3 4 3 5% 7% 49%	1900
	21st to end	Day	17% 6% 2 5% 4 4 3 3 4 5% 47%	2048
November	1st to 10th	Day	13% 6% 2 5% 3 2 3 3 4 6% 53%	1680
	11th to 20th	Day	16% 5% 1 5% 3 3 4 3 6% 6% 48%	1710
	21st to end	Day	15% 5% 2 5% 4 3 4 3 5% 6% 48%	1582
December	1st to 10th	Day	18% 6% 2 5% 4 4 3 3 5% 8% 40%	1520
	11th to 20th	Day	19% 6% 2 4 4 4 4 3 5% 6% 43%	1906
	21st to end	Day	16% 6% 2 7% 4 5% 5% 5% 6% 7% 37%	2772
January	1st to 10th	Night	17% 7% 2 5% 4 3 4 3 4 6% 45%	4429
	11th to 20th	Night	19% 8% 3 5% 3 3 3 3 4 5% 44%	4308
	21st to end	Night	23% 8% 2 6% 4 4 3 3 4 5% 38%	4532
February	1st to 10th	Night	16% 9% 3 6% 4 4 4 3 5% 6% 41%	2470
	11th to 20th	Night	19% 7% 3 5% 4 4 3 3 4 6% 42%	2270
	21st to end	Night	18% 7% 2 5% 4 4 3 4 6% 6% 41%	1884
March	1st to 10th	Night	22% 8% 2 5% 4 4 4 3 4 6% 39%	3671
	11th to 20th	Night	11% 6% 2 5% 4 4 4 3 5% 5% 51%	3479
	21st to end	Night	17% 9% 2 6% 4 3 3 3 4 4 46%	3608
April	1st to 10th	Night	17% 7% 3 6% 4 3 4 3 4 7% 42%	1900
	11th to 20th	Night	15% 6% 2 6% 4 4 4 3 5% 7% 44%	1875
	21st to end	Night	19% 5% 2 5% 4 4 4 3 5% 7% 43%	1900
May	1st to 10th	Night	23% 9% 3 8% 5% 4 4 4 5% 8% 30%	2947
	11th to 20th	Night	24% 9% 3 7% 5% 4 4 4 5% 7% 28%	2495
	21st to end	Night	14% 6% 2 5% 4 3 4 4 6% 9% 43%	2738
June	1st to 10th	Night	15% 6% 2 5% 4 4 3 3 6% 8% 44%	1520
	11th to 20th	Night	10% 6% 3 7% 6% 5% 4 4 6% 10% 39%	1520
	21st to end	Night	10% 5% 2 5% 5% 4 4 5% 7% 11% 42%	1520
July	1st to 10th	Night	7% 6% 2 8% 5% 6% 6% 4 7% 10% 38%	2520
	11th to 20th	Night	11% 5% 2 6% 6% 5% 5% 5% 8% 11% 36%	2520
	21st to end	Night	14% 8% 3 7% 5% 5% 4 5% 7% 8% 36%	2885
August	1st to 10th	Night	20% 5% 2 8% 4 4 5% 4 5% 9% 34%	2825
	11th to 20th	Night	13% 6% 2 6% 5% 4 4 3 6% 7% 43%	3054
	21st to end	Night	11% 5% 1 5% 4 4 5% 3 5% 7% 50%	3476
September	1st to 10th	Night	14% 7% 2 6% 4 4 4 3 4 7% 46%	1900
	11th to 20th	Night	13% 6% 2 4 3 2 3 2 5% 7% 53%	1917
	21st to end	Night	20% 7% 2 6% 3 4 4 3 5% 8% 38%	2104
October	1st to 10th	Night	20% 6% 3 6% 4 3 4 3 4 5% 43%	2280
	11th to 20th	Night	16% 4 2 5% 3 3 3 2 5% 6% 51%	2280
	21st to end	Night	16% 5% 1 6% 2 3 3 3 4 6% 50%	2548
November	1st to 10th	Night	11% 5% 2 5% 4 3 3 3 5% 5% 52%	2421
	11th to 20th	Night	17% 7% 2 5% 3 3 3 3 4 5% 48%	2470
	21st to end	Night	13% 5% 2 4 4 4 5% 4 6% 7% 46%	2593
December	1st to 10th	Night	19% 7% 2 6% 4 4 4 3 5% 6% 40%	2660
	11th to 20th	Night	18% 5% 2 6% 4 4 4 3 6% 6% 43%	3288
	21st to end	Night	17% 7% 3 6% 4 4 4 4 6% 7% 38%	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	24% 37% 8% 18% 10% 4	2518
	11th to 20th	Day	32% 37% 4 15% 8% 3	2648
	21st to end	Day	32% 39% 11% 12% 5% 1	3124
February	1st to 10th	Day	17% 66% 6% 7% 4 1	1710
	11th to 20th	Day	16% 64% 3 9% 7% 2	1804
	21st to end	Day	18% 65% 4 8% 4 2	1570
March	1st to 10th	Day	33% 40% 3 16% 5% 2	3169
	11th to 20th	Day	18% 40% 5% 22% 13% 2	3480
	21st to end	Day	27% 39% 6% 11% 14% 3	4024
April	1st to 10th	Day	17% 65% 4 7% 5% 1	2280
	11th to 20th	Day	14% 66% 5% 9% 5% 1	2254
	21st to end	Day	16% 66% 4 7% 7% 1	2280
May	1st to 10th	Day	38% 39% 7% 11% 4 1	4034
	11th to 20th	Day	37% 41% 9% 11% 2	4402
	21st to end	Day	20% 41% 9% 18% 12% 1	4837
June	1st to 10th	Day	15% 66% 3 10% 6% 1	2660
	11th to 20th	Day	14% 66% 3 10% 7% 1	2660
	21st to end	Day	12% 64% 5% 10% 8% 1	2660
July	1st to 10th	Day	22% 44% 13% 11% 8% 2	4370
	11th to 20th	Day	26% 39% 12% 15% 7% 1	4365
	21st to end	Day	31% 39% 7% 13% 10% 1	4516
August	1st to 10th	Day	31% 40% 9% 15% 4	4091
	11th to 20th	Day	21% 40% 9% 22% 7%	3777
	21st to end	Day	17% 39% 8% 21% 15% 1	4180
September	1st to 10th	Day	15% 61% 6% 9% 8% 1	2280
	11th to 20th	Day	15% 61% 3 11% 8% 3	2262
	21st to end	Day	23% 60% 3 9% 6%	2071
October	1st to 10th	Day	16% 60% 5% 9% 9% 1	1900
	11th to 20th	Day	12% 60% 5% 9% 13% 2	1900
	21st to end	Day	13% 58% 4 13% 9% 1	2048
November	1st to 10th	Day	16% 59% 6% 10% 6% 3	1680
	11th to 20th	Day	13% 60% 3 9% 13% 1	1710
	21st to end	Day	14% 59% 5% 15% 5% 2	1582
December	1st to 10th	Day	21% 59% 6% 7% 6% 1	1520
	11th to 20th	Day	22% 48% 4 17% 6% 3	1906
	21st to end	Day	30% 37% 10% 14% 8%	2772
January	1st to 10th	Night	28% 36% 6% 18% 9% 3	4429
	11th to 20th	Night	29% 36% 5% 17% 10% 2	4308
	21st to end	Night	35% 39% 4 16% 5% 1	4532
February	1st to 10th	Night	15% 65% 6% 9% 3 1	2470
	11th to 20th	Night	17% 63% 2 7% 9% 2	2272
	21st to end	Night	15% 65% 5% 7% 5% 3	1884
March	1st to 10th	Night	34% 41% 5% 14% 5% 1	3681
	11th to 20th	Night	17% 40% 8% 21% 11% 2	3480
	21st to end	Night	27% 40% 4 10% 16% 3	3608
April	1st to 10th	Night	16% 65% 2 8% 7% 1	1900
	11th to 20th	Night	14% 66% 5% 8% 6% 1	1875
	21st to end	Night	15% 65% 4 6% 8% 1	1900
May	1st to 10th	Night	36% 40% 7% 13% 4 1	2954
	11th to 20th	Night	38% 40% 10% 9% 3	2496
	21st to end	Night	22% 41% 11% 14% 10% 3	2739
June	1st to 10th	Night	15% 65% 2 9% 9%	1520
	11th to 20th	Night	14% 66% 4 11% 6%	1520
	21st to end	Night	12% 64% 5% 10% 6% 2	1520
July	1st to 10th	Night	25% 40% 15% 11% 8% 2	2480
	11th to 20th	Night	27% 39% 13% 16% 6%	2472
	21st to end	Night	31% 39% 8% 12% 10%	2793
August	1st to 10th	Night	34% 41% 12% 9% 4	2814
	11th to 20th	Night	24% 38% 8% 21% 9%	3084
	21st to end	Night	18% 38% 6% 23% 14% 1	3476
September	1st to 10th	Night	15% 60% 6% 9% 8% 1	1900
	11th to 20th	Night	14% 60% 4 10% 10% 2	1917
	21st to end	Night	21% 60% 3 8% 6%	2104
October	1st to 10th	Night	18% 60% 6% 7% 7% 2	2280
	11th to 20th	Night	12% 59% 4 13% 10% 2	2280
	21st to end	Night	14% 59% 4 13% 9% 2	2548
November	1st to 10th	Night	15% 59% 6% 11% 5% 3	2421
	11th to 20th	Night	15% 59% 3 9% 12% 3	2470
	21st to end	Night	13% 60% 5% 14% 7% 1	2593
December	1st to 10th	Night	21% 59% 6% 9% 5%	2660
	11th to 20th	Night	21% 49% 6% 9% 11% 4	3288
	21st to end	Night	30% 39% 9% 15% 7% 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% 19% 33% 22% 7% 1	180
	11th to 20th	Day	19% 31% 30% 17% 3	216
	21st to end	Day	21% 15% 36% 21% 6% 2	297
February	1st to 10th	Day	22% 19% 34% 19% 7%	270
	11th to 20th	Day	22% 18% 40% 18% 2	403
	21st to end	Day	21% 18% 35% 21% 5% 1	382
March	1st to 10th	Day	17% 19% 34% 22% 7% 1	460
	11th to 20th	Day	19% 18% 32% 23% 6% 2	460
	21st to end	Day	23% 13% 32% 24% 7% 1	506
April	1st to 10th	Day	20% 16% 35% 20% 8% 1	460
	11th to 20th	Day	16% 14% 31% 24% 11% 3	452
	21st to end	Day	21% 14% 28% 27% 9% 1	460
May	1st to 10th	Day	29% 12% 24% 20% 12% 2	463
	11th to 20th	Day	22% 8% 25% 29% 14% 2	487
	21st to end	Day	16% 5% 20% 26% 23% 9%	529
June	1st to 10th	Day	12% 6% 22% 32% 21% 7%	490
	11th to 20th	Day	14% 4 26% 30% 20% 6%	490
	21st to end	Day	11% 6% 23% 34% 19% 9%	490
July	1st to 10th	Day	12% 3 15% 28% 28% 13%	485
	11th to 20th	Day	7% 1 11% 36% 31% 14%	484
	21st to end	Day	10% 4 17% 33% 28% 9%	532
August	1st to 10th	Day	10% 5% 16% 31% 26% 12%	486
	11th to 20th	Day	12% 3 14% 31% 29% 12%	479
	21st to end	Day	11% 2 19% 29% 24% 15%	539
September	1st to 10th	Day	16% 4 21% 23% 23% 12%	490
	11th to 20th	Day	14% 2 20% 28% 22% 14%	490
	21st to end	Day	26% 5% 21% 27% 15% 6%	490
October	1st to 10th	Day	23% 5% 19% 28% 16% 10%	490
	11th to 20th	Day	13% 11% 27% 25% 20% 4	490
	21st to end	Day	19% 6% 32% 27% 13% 4	516
November	1st to 10th	Day	16% 8% 30% 26% 17% 3	368
	11th to 20th	Day	16% 13% 33% 26% 12%	370
	21st to end	Day	14% 10% 36% 29% 10% 1	242
December	1st to 10th	Day	22% 15% 33% 21% 8% 1	180
	11th to 20th	Day	25% 17% 35% 16% 8%	180
	21st to end	Day	24% 15% 28% 21% 11% 2	198
January	1st to 10th	Night	20% 10% 42% 24% 4	760
	11th to 20th	Night	22% 11% 36% 26% 5%	760
	21st to end	Night	19% 11% 42% 27% 2	836
February	1st to 10th	Night	20% 10% 40% 28% 2	760
	11th to 20th	Night	23% 13% 43% 20% 1	743
	21st to end	Night	21% 13% 42% 21% 3	628
March	1st to 10th	Night	18% 13% 38% 26% 5%	760
	11th to 20th	Night	18% 12% 41% 23% 6% 1	760
	21st to end	Night	19% 8% 40% 27% 6%	836
April	1st to 10th	Night	20% 13% 39% 22% 6%	760
	11th to 20th	Night	16% 10% 34% 34% 6%	751
	21st to end	Night	20% 8% 32% 33% 7%	760
May	1st to 10th	Night	20% 7% 33% 32% 8%	645
	11th to 20th	Night	17% 5% 33% 37% 8%	374
	21st to end	Night	17% 2 18% 40% 21% 2	411
June	1st to 10th	Night	16% 3 22% 41% 18%	380
	11th to 20th	Night	11% 3 23% 46% 17% 1	380
	21st to end	Night	9% 1 20% 51% 18%	380
July	1st to 10th	Night	12% 2 18% 41% 26% 2	370
	11th to 20th	Night	6% 4 12% 48% 29% 2	368
	21st to end	Night	9% 2 15% 45% 26% 2	500
August	1st to 10th	Night	12% 2 11% 46% 27% 3	567
	11th to 20th	Night	14% 3 12% 39% 29% 3	719
	21st to end	Night	14% 3 14% 38% 29% 3	836
September	1st to 10th	Night	15% 3 19% 37% 24% 3	760
	11th to 20th	Night	14% 3 12% 39% 28% 4	760
	21st to end	Night	23% 3 20% 32% 21% 1	760
October	1st to 10th	Night	22% 5% 23% 29% 18% 4	760
	11th to 20th	Night	17% 5% 26% 37% 13% 1	760
	21st to end	Night	19% 6% 31% 31% 12% 1	836
November	1st to 10th	Night	14% 6% 33% 34% 13% 1	745
	11th to 20th	Night	20% 8% 31% 31% 8% 1	760
	21st to end	Night	14% 9% 38% 29% 9%	760
December	1st to 10th	Night	23% 11% 33% 25% 7% 1	760
	11th to 20th	Night	18% 8% 38% 30% 6%	760
	21st to end	Night	20% 9% 37% 32% 2	836

Page generated at 2024-10-30 01:22:56. Version ac07

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