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 2024-03-06.

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	11% 5% 2 5% 5% 3 5% 5% 6% 8% 43%	78625
	Night	12% 6% 2 5% 5% 3 5% 5% 6% 8% 44%	80886
Transparency	Day	36% 8% 15% 21% 16% 4	78347
	Night	38% 7% 13% 20% 18% 5%	80683
Seeing	Day	13% 3 17% 28% 28% 11%	14642
	Night	14% 5% 20% 30% 26% 7%	25022

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% 4 2 4 3 2 4 4 5% 6% 50%	2836
	11th to 20th	Day	10% 5% 2 5% 4 3 6% 4 5% 7% 49%	2840
	21st to end	Day	13% 7% 3 6% 5% 3 5% 4 5% 6% 44%	3124
February	1st to 10th	Day	15% 5% 3 5% 7% 3 4 4 6% 7% 42%	1710
	11th to 20th	Day	18% 6% 3 5% 4 2 3 4 3 5% 46%	1774
	21st to end	Day	14% 7% 3 5% 5% 3 5% 4 5% 7% 43%	1670
March	1st to 10th	Day	12% 7% 2 4 4 2 4 4 4 6% 51%	2035
	11th to 20th	Day	14% 6% 2 5% 5% 3 5% 5% 6% 7% 43%	1980
	21st to end	Day	13% 6% 2 6% 5% 3 5% 5% 6% 7% 42%	2178
April	1st to 10th	Day	10% 4 2 4 4 3 4 4 6% 7% 53%	2128
	11th to 20th	Day	10% 4 2 5% 5% 3 3 5% 6% 8% 51%	2134
	21st to end	Day	9% 4 1 3 4 3 4 5% 5% 9% 53%	2160
May	1st to 10th	Day	7% 4 2 4 5% 3 5% 6% 6% 9% 50%	2160
	11th to 20th	Day	13% 5% 2 6% 5% 3 5% 5% 6% 8% 42%	2300
	21st to end	Day	8% 4 2 6% 7% 4 6% 6% 7% 10% 40%	2531
June	1st to 10th	Day	11% 6% 3 7% 6% 4 6% 6% 8% 9% 33%	2340
	11th to 20th	Day	9% 4 2 5% 5% 3 6% 7% 9% 11% 39%	2340
	21st to end	Day	8% 5% 3 5% 7% 4 7% 7% 8% 12% 35%	2340
July	1st to 10th	Day	10% 4 3 6% 5% 4 6% 6% 9% 13% 34%	2340
	11th to 20th	Day	8% 4 3 6% 6% 4 6% 8% 8% 13% 34%	2340
	21st to end	Day	6% 5% 3 6% 6% 3 7% 7% 9% 13% 34%	2547
August	1st to 10th	Day	11% 6% 2 7% 6% 4 6% 7% 7% 12% 31%	2327
	11th to 20th	Day	10% 6% 3 6% 6% 5% 6% 7% 9% 12% 31%	2134
	21st to end	Day	11% 6% 3 8% 7% 4 6% 7% 8% 11% 31%	2376
September	1st to 10th	Day	9% 5% 3 6% 6% 3 6% 6% 7% 10% 40%	2160
	11th to 20th	Day	15% 6% 3 6% 6% 3 5% 5% 5% 8% 37%	2122
	21st to end	Day	17% 7% 3 6% 6% 4 4 4 6% 6% 37%	1895
October	1st to 10th	Day	14% 5% 3 6% 6% 3 4 4 5% 5% 45%	1800
	11th to 20th	Day	11% 4 2 4 4 2 4 5% 4 7% 54%	1800
	21st to end	Day	10% 5% 2 5% 3 2 4 3 4 6% 56%	1980
November	1st to 10th	Day	12% 5% 2 4 3 3 3 3 5% 7% 53%	1857
	11th to 20th	Day	13% 5% 2 5% 5% 2 4 4 4 6% 51%	1900
	21st to end	Day	10% 5% 3 5% 4 3 4 4 5% 8% 50%	1746
December	1st to 10th	Day	14% 8% 3 6% 5% 3 4 5% 5% 8% 39%	1520
	11th to 20th	Day	15% 5% 2 4 3 2 3 3 4 5% 55%	2077
	21st to end	Day	14% 8% 3 5% 5% 2 4 4 5% 7% 41%	3124
January	1st to 10th	Night	13% 6% 2 6% 5% 3 4 4 5% 7% 46%	4109
	11th to 20th	Night	12% 6% 3 5% 5% 3 5% 5% 6% 8% 41%	4120
	21st to end	Night	12% 7% 3 6% 6% 3 4 4 4 6% 44%	4532
February	1st to 10th	Night	16% 5% 2 5% 5% 3 4 5% 4 6% 44%	2470
	11th to 20th	Night	17% 8% 3 5% 4 2 4 4 4 7% 42%	2292
	21st to end	Night	16% 6% 2 6% 5% 3 4 5% 5% 6% 43%	1781
March	1st to 10th	Night	13% 5% 2 5% 4 3 4 3 4 6% 50%	2042
	11th to 20th	Night	12% 6% 3 6% 6% 3 6% 5% 6% 7% 39%	1980
	21st to end	Night	12% 6% 3 5% 4 3 4 5% 5% 7% 47%	2178
April	1st to 10th	Night	10% 6% 2 5% 3 3 4 5% 6% 7% 50%	1831
	11th to 20th	Night	11% 5% 2 5% 5% 3 5% 5% 6% 6% 48%	1775
	21st to end	Night	7% 3 2 4 4 3 4 5% 5% 7% 56%	1800
May	1st to 10th	Night	8% 4 2 5% 5% 4 4 5% 6% 9% 48%	1800
	11th to 20th	Night	13% 6% 1 4 6% 3 4 4 5% 9% 43%	1607
	21st to end	Night	10% 5% 2 5% 5% 3 3 6% 6% 9% 45%	1744
June	1st to 10th	Night	9% 7% 3 7% 6% 4 6% 5% 7% 11% 35%	1620
	11th to 20th	Night	10% 4 2 4 5% 3 5% 6% 8% 13% 40%	1620
	21st to end	Night	8% 5% 2 6% 6% 4 6% 8% 9% 12% 34%	1620
July	1st to 10th	Night	6% 5% 3 5% 8% 5% 6% 7% 8% 12% 35%	1620
	11th to 20th	Night	6% 3 2 5% 7% 4 5% 6% 9% 13% 39%	1620
	21st to end	Night	6% 4 2 6% 5% 3 6% 7% 9% 12% 39%	1771
August	1st to 10th	Night	8% 5% 3 6% 5% 4 5% 6% 8% 12% 38%	1611
	11th to 20th	Night	8% 6% 3 6% 6% 4 6% 6% 8% 11% 36%	1748
	21st to end	Night	10% 6% 3 6% 6% 4 5% 7% 8% 12% 34%	1980
September	1st to 10th	Night	11% 4 2 5% 5% 4 6% 7% 6% 10% 41%	1800
	11th to 20th	Night	11% 6% 3 6% 6% 3 5% 6% 7% 10% 38%	1833
	21st to end	Night	17% 7% 3 5% 5% 4 5% 5% 4 7% 38%	2063
October	1st to 10th	Night	13% 7% 3 6% 4 3 5% 4 4 6% 45%	2160
	11th to 20th	Night	10% 4 3 5% 5% 3 4 4 5% 6% 53%	2160
	21st to end	Night	9% 4 2 3 4 3 5% 4 5% 7% 54%	2376
November	1st to 10th	Night	11% 5% 3 4 4 3 4 4 4 5% 54%	2221
	11th to 20th	Night	13% 6% 2 6% 5% 3 4 4 5% 8% 46%	2280
	21st to end	Night	11% 6% 2 4 4 2 4 5% 6% 7% 50%	2421
December	1st to 10th	Night	15% 7% 3 6% 5% 3 4 5% 6% 7% 40%	2660
	11th to 20th	Night	15% 6% 2 4 4 2 3 4 4 6% 49%	3109
	21st to end	Night	15% 6% 3 5% 4 3 3 4 5% 6% 46%	4532

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% 5% 9% 21% 25% 6%	2837
	11th to 20th	Day	35% 5% 6% 21% 23% 9%	2840
	21st to end	Day	43% 5% 7% 19% 18% 7%	3124
February	1st to 10th	Day	42% 5% 9% 21% 18% 5%	1710
	11th to 20th	Day	43% 4 8% 16% 22% 8%	1783
	21st to end	Day	40% 6% 12% 17% 16% 9%	1670
March	1st to 10th	Day	35% 5% 11% 19% 22% 8%	2035
	11th to 20th	Day	38% 7% 13% 20% 16% 5%	1980
	21st to end	Day	39% 8% 11% 20% 17% 4	2178
April	1st to 10th	Day	28% 5% 15% 23% 23% 6%	2128
	11th to 20th	Day	30% 5% 14% 24% 18% 9%	2134
	21st to end	Day	26% 7% 14% 26% 24% 3	2160
May	1st to 10th	Day	28% 8% 19% 26% 16% 3	2160
	11th to 20th	Day	36% 7% 19% 25% 12% 1	2304
	21st to end	Day	33% 12% 20% 23% 12% 1	2531
June	1st to 10th	Day	40% 10% 17% 22% 11%	2340
	11th to 20th	Day	32% 13% 21% 23% 10% 1	2340
	21st to end	Day	36% 13% 21% 21% 8% 1	2340
July	1st to 10th	Day	37% 12% 23% 20% 7% 1	2275
	11th to 20th	Day	34% 13% 26% 20% 7%	2271
	21st to end	Day	33% 13% 26% 24% 4	2405
August	1st to 10th	Day	39% 12% 26% 20% 3	2314
	11th to 20th	Day	39% 13% 22% 19% 7%	2134
	21st to end	Day	41% 12% 23% 18% 5% 1	2376
September	1st to 10th	Day	36% 12% 20% 17% 13% 2	2160
	11th to 20th	Day	43% 8% 14% 17% 15% 4	2122
	21st to end	Day	44% 8% 11% 19% 15% 3	1895
October	1st to 10th	Day	41% 4 9% 21% 20% 3	1800
	11th to 20th	Day	30% 6% 11% 23% 23% 7%	1800
	21st to end	Day	31% 4 8% 21% 28% 8%	1980
November	1st to 10th	Day	32% 4 9% 20% 26% 9%	1857
	11th to 20th	Day	36% 4 8% 20% 24% 8%	1900
	21st to end	Day	33% 6% 9% 23% 22% 6%	1746
December	1st to 10th	Day	43% 7% 12% 18% 13% 6%	1520
	11th to 20th	Day	34% 5% 6% 22% 24% 9%	2074
	21st to end	Day	40% 7% 11% 21% 19% 3	3124
January	1st to 10th	Night	38% 5% 8% 21% 22% 6%	4109
	11th to 20th	Night	40% 6% 8% 18% 24% 5%	4120
	21st to end	Night	41% 5% 7% 15% 26% 6%	4532
February	1st to 10th	Night	42% 5% 9% 18% 20% 6%	2470
	11th to 20th	Night	44% 5% 8% 15% 20% 8%	2294
	21st to end	Night	42% 5% 11% 17% 16% 9%	1781
March	1st to 10th	Night	37% 5% 9% 21% 20% 8%	2042
	11th to 20th	Night	43% 7% 13% 15% 16% 5%	1980
	21st to end	Night	37% 6% 14% 22% 16% 5%	2178
April	1st to 10th	Night	33% 6% 14% 17% 23% 7%	1831
	11th to 20th	Night	36% 6% 12% 21% 17% 8%	1775
	21st to end	Night	27% 6% 14% 29% 20% 4	1800
May	1st to 10th	Night	33% 6% 16% 23% 19% 3	1800
	11th to 20th	Night	38% 7% 16% 24% 14% 1	1608
	21st to end	Night	34% 10% 18% 26% 11% 1	1745
June	1st to 10th	Night	41% 9% 19% 21% 9%	1620
	11th to 20th	Night	33% 12% 21% 24% 9% 1	1620
	21st to end	Night	38% 14% 19% 22% 7%	1620
July	1st to 10th	Night	38% 13% 21% 19% 9% 1	1575
	11th to 20th	Night	33% 13% 28% 20% 6%	1566
	21st to end	Night	34% 12% 23% 25% 5%	1672
August	1st to 10th	Night	37% 12% 27% 20% 4	1600
	11th to 20th	Night	39% 14% 21% 20% 5%	1748
	21st to end	Night	43% 12% 20% 19% 5% 1	1980
September	1st to 10th	Night	37% 12% 20% 17% 12% 2	1800
	11th to 20th	Night	44% 8% 15% 18% 13% 2	1833
	21st to end	Night	47% 7% 11% 19% 14% 2	2063
October	1st to 10th	Night	41% 6% 9% 20% 19% 5%	2160
	11th to 20th	Night	32% 6% 9% 23% 24% 6%	2160
	21st to end	Night	30% 5% 9% 21% 26% 10%	2376
November	1st to 10th	Night	34% 5% 9% 18% 24% 10%	2221
	11th to 20th	Night	39% 5% 9% 15% 23% 9%	2280
	21st to end	Night	34% 5% 10% 22% 23% 6%	2421
December	1st to 10th	Night	42% 7% 12% 16% 17% 5%	2660
	11th to 20th	Night	38% 5% 7% 19% 25% 6%	3111
	21st to end	Night	40% 5% 9% 21% 22% 3	4532

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% 6% 36% 31% 11%	270
	11th to 20th	Day	11% 5% 29% 39% 16% 1	270
	21st to end	Day	17% 6% 32% 34% 10% 1	297
February	1st to 10th	Day	16% 6% 26% 40% 12%	270
	11th to 20th	Day	24% 5% 30% 30% 11% 1	382
	21st to end	Day	16% 7% 29% 36% 10% 2	382
March	1st to 10th	Day	13% 5% 28% 33% 19% 2	440
	11th to 20th	Day	16% 9% 28% 34% 12% 2	420
	21st to end	Day	13% 5% 28% 35% 16% 3	462
April	1st to 10th	Day	12% 6% 26% 32% 20% 3	420
	11th to 20th	Day	10% 4 24% 31% 24% 8%	412
	21st to end	Day	10% 3 19% 35% 25% 9%	420
May	1st to 10th	Day	6% 4 21% 42% 21% 8%	423
	11th to 20th	Day	13% 3 14% 25% 34% 11%	447
	21st to end	Day	12% 2 8% 23% 34% 21%	485
June	1st to 10th	Day	13% 1 8% 30% 34% 14%	450
	11th to 20th	Day	11% 1 10% 22% 32% 24%	450
	21st to end	Day	8% 1 9% 24% 43% 16%	450
July	1st to 10th	Day	10% 1 5% 15% 46% 23%	445
	11th to 20th	Day	10% 1 4 15% 48% 23%	444
	21st to end	Day	8% 1 5% 19% 48% 19%	488
August	1st to 10th	Day	15% 1 7% 17% 36% 23%	446
	11th to 20th	Day	10% 1 5% 16% 39% 29%	439
	21st to end	Day	10% 2 7% 15% 41% 24%	495
September	1st to 10th	Day	9% 1 7% 19% 39% 25%	450
	11th to 20th	Day	20% 9% 21% 38% 12%	450
	21st to end	Day	20% 2 9% 24% 31% 15%	450
October	1st to 10th	Day	17% 3 14% 23% 30% 13%	450
	11th to 20th	Day	11% 16% 30% 32% 10%	450
	21st to end	Day	9% 5% 19% 33% 27% 7%	495
November	1st to 10th	Day	16% 6% 15% 31% 24% 8%	455
	11th to 20th	Day	16% 5% 24% 35% 18% 2	460
	21st to end	Day	12% 6% 26% 33% 20% 4	364
December	1st to 10th	Day	19% 2 24% 34% 19% 1	180
	11th to 20th	Day	18% 5% 26% 31% 17% 4	234
	21st to end	Day	19% 7% 24% 31% 14% 5%	297
January	1st to 10th	Night	14% 12% 33% 31% 10% 1	760
	11th to 20th	Night	14% 8% 28% 37% 12% 1	760
	21st to end	Night	15% 9% 35% 35% 6%	836
February	1st to 10th	Night	20% 5% 29% 36% 10%	760
	11th to 20th	Night	20% 9% 32% 33% 6%	743
	21st to end	Night	19% 6% 29% 33% 11% 1	628
March	1st to 10th	Night	14% 6% 31% 34% 14% 1	743
	11th to 20th	Night	15% 6% 26% 36% 14% 3	720
	21st to end	Night	15% 5% 28% 34% 18% 2	792
April	1st to 10th	Night	13% 5% 28% 33% 19% 2	720
	11th to 20th	Night	14% 4 22% 32% 23% 5%	711
	21st to end	Night	7% 4 22% 38% 25% 4	720
May	1st to 10th	Night	8% 6% 19% 38% 25% 4	720
	11th to 20th	Night	15% 2 17% 32% 27% 6%	546
	21st to end	Night	11% 1 7% 24% 37% 19%	584
June	1st to 10th	Night	11% 1 10% 33% 35% 10%	540
	11th to 20th	Night	12% 1 7% 24% 40% 15%	540
	21st to end	Night	8% 3 7% 26% 45% 11%	540
July	1st to 10th	Night	8% 1 6% 21% 51% 14%	525
	11th to 20th	Night	7% 1 5% 19% 52% 15%	522
	21st to end	Night	6% 1 7% 25% 48% 13%	591
August	1st to 10th	Night	11% 1 5% 23% 42% 17%	537
	11th to 20th	Night	12% 1 6% 19% 45% 18%	684
	21st to end	Night	12% 1 7% 19% 43% 18%	792
September	1st to 10th	Night	11% 1 6% 22% 45% 15%	720
	11th to 20th	Night	16% 1 8% 27% 39% 11%	720
	21st to end	Night	21% 2 12% 23% 32% 10%	720
October	1st to 10th	Night	17% 3 12% 26% 32% 10%	720
	11th to 20th	Night	13% 2 20% 32% 26% 7%	720
	21st to end	Night	11% 6% 19% 30% 27% 7%	792
November	1st to 10th	Night	13% 4 22% 33% 23% 4	740
	11th to 20th	Night	16% 7% 26% 29% 19% 3	760
	21st to end	Night	12% 9% 25% 31% 20% 4	760
December	1st to 10th	Night	18% 9% 24% 33% 14% 2	760
	11th to 20th	Night	15% 8% 28% 31% 16% 2	760
	21st to end	Night	17% 7% 27% 33% 15% 1	836

Page generated at 2024-03-03 06:28:55. Version ac07

Copyright © 2024 Attilla Danko.