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 2026-09-29.

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% 6% 2 6% 4 4 5% 4 6% 9% 41%	147792
	Night	11% 6% 2 6% 4 4 4 4 6% 8% 44%	143603
Transparency	Day	37% 8% 16% 20% 15% 4	151392
	Night	37% 7% 14% 20% 17% 5%	148075
Seeing	Day	13% 3 17% 28% 28% 11%	18193
	Night	13% 5% 19% 30% 26% 7%	28490

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	11% 5% 2 4 3 3 3 3 5% 6% 55%	5258
	11th to 20th	Day	12% 5% 2 5% 3 3 4 2 4 6% 54%	5280
	21st to end	Day	15% 9% 3 7% 4 4 4 3 5% 6% 40%	5780
February	1st to 10th	Day	15% 6% 3 6% 6% 4 3 3 5% 7% 42%	1890
	11th to 20th	Day	19% 6% 3 5% 4 3 3 4 4 5% 44%	1966
	21st to end	Day	14% 7% 2 6% 4 4 4 3 5% 7% 43%	1840
March	1st to 10th	Day	20% 9% 3 6% 3 3 4 3 4 6% 38%	5045
	11th to 20th	Day	8% 4 1 5% 3 4 4 4 5% 7% 54%	5090
	21st to end	Day	12% 6% 2 5% 4 4 4 3 5% 6% 51%	5586
April	1st to 10th	Day	9% 5% 2 5% 3 3 3 5% 6% 7% 52%	2483
	11th to 20th	Day	9% 4 2 5% 4 3 4 4 6% 8% 53%	2494
	21st to end	Day	8% 4 1 4 4 4 4 4 5% 9% 53%	2520
May	1st to 10th	Day	10% 6% 3 7% 5% 5% 5% 5% 7% 9% 38%	7021
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 6% 9% 40%	7625
	21st to end	Day	9% 5% 2 7% 5% 6% 6% 5% 8% 10% 36%	8391
June	1st to 10th	Day	10% 7% 3 7% 5% 5% 6% 5% 8% 9% 35%	2730
	11th to 20th	Day	8% 4 2 6% 4 4 5% 6% 9% 12% 39%	2730
	21st to end	Day	7% 5% 3 5% 6% 6% 7% 5% 9% 12% 36%	2730
July	1st to 10th	Day	7% 4 2 7% 5% 5% 6% 5% 9% 14% 36%	7680
	11th to 20th	Day	6% 5% 3 8% 6% 6% 7% 6% 9% 13% 31%	7680
	21st to end	Day	9% 7% 3 8% 6% 6% 7% 6% 9% 12% 27%	8340
August	1st to 10th	Day	16% 10% 4 9% 6% 5% 6% 5% 7% 12% 20%	6014
	11th to 20th	Day	6% 5% 2 6% 4 5% 6% 6% 9% 13% 38%	5496
	21st to end	Day	8% 8% 3 8% 6% 5% 5% 4 7% 10% 35%	6080
September	1st to 10th	Day	9% 6% 3 6% 5% 4 6% 5% 7% 9% 42%	2520
	11th to 20th	Day	15% 7% 2 7% 5% 4 5% 4 6% 8% 37%	2475
	21st to end	Day	17% 8% 3 7% 5% 5% 4 4 5% 6% 37%	2190
October	1st to 10th	Day	14% 6% 3 7% 4 5% 4 3 5% 6% 44%	2000
	11th to 20th	Day	11% 4 2 5% 3 4 4 3 4 7% 55%	2000
	21st to end	Day	11% 5% 2 5% 3 3 3 3 4 6% 56%	2200
November	1st to 10th	Day	11% 5% 1 4 3 4 3 3 5% 7% 53%	2057
	11th to 20th	Day	12% 5% 2 6% 4 3 4 3 4 6% 52%	2100
	21st to end	Day	9% 5% 2 5% 4 5% 3 3 5% 8% 50%	1929
December	1st to 10th	Day	10% 6% 2 5% 4 4 4 4 5% 6% 52%	2680
	11th to 20th	Day	15% 7% 3 6% 3 3 4 3 5% 6% 45%	3327
	21st to end	Day	13% 7% 2 5% 4 3 4 3 5% 7% 46%	4565
January	1st to 10th	Night	10% 5% 2 6% 4 3 3 3 5% 6% 53%	7635
	11th to 20th	Night	11% 5% 2 5% 3 3 4 3 5% 7% 51%	7680
	21st to end	Night	14% 8% 3 7% 5% 4 4 3 4 5% 44%	8401
February	1st to 10th	Night	17% 6% 2 6% 4 3 4 4 4 6% 44%	2730
	11th to 20th	Night	17% 9% 3 6% 4 3 4 3 5% 7% 41%	2539
	21st to end	Night	16% 6% 2 7% 4 4 4 3 5% 6% 43%	1962
March	1st to 10th	Night	17% 10% 3 7% 5% 4 4 2 4 5% 40%	5028
	11th to 20th	Night	12% 5% 2 5% 3 3 3 4 6% 7% 49%	5090
	21st to end	Night	12% 5% 2 5% 3 3 3 3 4 6% 53%	5588
April	1st to 10th	Night	10% 6% 2 6% 3 3 4 4 6% 7% 49%	2135
	11th to 20th	Night	9% 5% 2 5% 3 4 5% 4 6% 6% 51%	2075
	21st to end	Night	7% 4 2 5% 3 4 4 4 5% 7% 55%	2100
May	1st to 10th	Night	10% 6% 3 8% 4 5% 5% 4 6% 10% 39%	5833
	11th to 20th	Night	11% 6% 2 6% 5% 4 4 4 5% 8% 44%	5276
	21st to end	Night	12% 6% 2 7% 5% 5% 5% 6% 7% 10% 35%	5761
June	1st to 10th	Night	9% 7% 2 8% 5% 5% 5% 4 8% 10% 36%	1890
	11th to 20th	Night	9% 5% 1 6% 4 4 5% 5% 9% 12% 40%	1890
	21st to end	Night	8% 6% 1 7% 5% 5% 6% 6% 9% 11% 37%	1890
July	1st to 10th	Night	5% 4 3 6% 5% 6% 6% 5% 8% 13% 39%	5278
	11th to 20th	Night	7% 5% 2 7% 6% 6% 6% 5% 9% 14% 32%	5277
	21st to end	Night	8% 6% 2 8% 6% 6% 7% 5% 9% 13% 29%	5736
August	1st to 10th	Night	14% 8% 3 9% 5% 4 5% 4 8% 12% 27%	4135
	11th to 20th	Night	6% 5% 2 6% 4 5% 6% 5% 8% 15% 40%	4489
	21st to end	Night	6% 5% 3 8% 6% 5% 6% 5% 7% 10% 39%	5045
September	1st to 10th	Night	11% 4 2 6% 4 5% 5% 5% 6% 10% 43%	2100
	11th to 20th	Night	12% 7% 3 6% 5% 5% 5% 5% 7% 9% 37%	2139
	21st to end	Night	17% 7% 3 6% 4 5% 5% 3 5% 6% 39%	2385
October	1st to 10th	Night	13% 7% 2 6% 4 5% 5% 3 5% 7% 45%	2400
	11th to 20th	Night	10% 4 2 5% 3 3 4 3 5% 6% 55%	2400
	21st to end	Night	10% 4 2 4 3 4 4 3 5% 7% 55%	2640
November	1st to 10th	Night	11% 6% 2 4 4 4 4 3 5% 5% 53%	2461
	11th to 20th	Night	12% 7% 2 6% 4 4 3 3 5% 7% 48%	2520
	21st to end	Night	10% 6% 2 5% 3 3 4 4 6% 7% 50%	2678
December	1st to 10th	Night	11% 5% 2 5% 3 4 3 3 5% 6% 52%	4720
	11th to 20th	Night	13% 8% 2 7% 5% 3 4 4 5% 6% 44%	5064
	21st to end	Night	13% 5% 3 6% 4 3 4 3 5% 7% 47%	6633

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	30% 4 13% 21% 27% 5%	5259
	11th to 20th	Day	33% 3 4 18% 30% 11%	5280
	21st to end	Day	47% 4 6% 19% 16% 8%	5780
February	1st to 10th	Day	42% 5% 9% 22% 17% 5%	1890
	11th to 20th	Day	43% 4 8% 16% 22% 7%	1975
	21st to end	Day	40% 6% 11% 17% 18% 8%	1840
March	1st to 10th	Day	47% 5% 9% 14% 19% 7%	5045
	11th to 20th	Day	27% 5% 10% 17% 25% 16%	5090
	21st to end	Day	34% 5% 11% 23% 19% 8%	5586
April	1st to 10th	Day	29% 5% 14% 24% 22% 6%	2483
	11th to 20th	Day	27% 5% 13% 27% 19% 8%	2494
	21st to end	Day	26% 7% 16% 26% 23% 3	2520
May	1st to 10th	Day	38% 9% 21% 23% 8% 2	7053
	11th to 20th	Day	37% 6% 18% 25% 14% 1	7629
	21st to end	Day	37% 10% 18% 21% 12% 1	8405
June	1st to 10th	Day	38% 9% 17% 23% 12%	2730
	11th to 20th	Day	30% 12% 22% 24% 10% 1	2730
	21st to end	Day	33% 12% 22% 25% 8% 1	2730
July	1st to 10th	Day	33% 11% 30% 20% 5%	7615
	11th to 20th	Day	37% 13% 32% 14% 3	7611
	21st to end	Day	41% 11% 23% 17% 7% 1	8156
August	1st to 10th	Day	53% 12% 23% 11% 1	6001
	11th to 20th	Day	30% 11% 26% 26% 6%	5532
	21st to end	Day	40% 9% 20% 26% 5%	6080
September	1st to 10th	Day	35% 11% 18% 19% 14% 3	2520
	11th to 20th	Day	43% 8% 14% 18% 14% 3	2475
	21st to end	Day	45% 7% 12% 18% 15% 2	2190
October	1st to 10th	Day	40% 4 7% 22% 22% 4	3260
	11th to 20th	Day	21% 4 6% 17% 28% 24%	3240
	21st to end	Day	29% 4 6% 26% 26% 9%	3538
November	1st to 10th	Day	32% 4 10% 20% 25% 9%	2057
	11th to 20th	Day	35% 4 8% 20% 24% 8%	2100
	21st to end	Day	32% 6% 10% 22% 23% 6%	1929
December	1st to 10th	Day	33% 5% 8% 17% 25% 11%	2680
	11th to 20th	Day	41% 5% 10% 19% 20% 6%	3324
	21st to end	Day	36% 6% 14% 26% 17% 2	4565
January	1st to 10th	Night	33% 4 9% 22% 28% 5%	7636
	11th to 20th	Night	34% 4 6% 16% 31% 9%	7680
	21st to end	Night	43% 3 6% 16% 25% 8%	8401
February	1st to 10th	Night	42% 4 8% 19% 20% 6%	2730
	11th to 20th	Night	44% 5% 8% 15% 20% 7%	2541
	21st to end	Night	42% 4 10% 16% 17% 9%	1962
March	1st to 10th	Night	47% 5% 7% 15% 20% 5%	5028
	11th to 20th	Night	33% 5% 9% 13% 23% 16%	5090
	21st to end	Night	34% 4 12% 24% 20% 7%	5588
April	1st to 10th	Night	33% 5% 13% 19% 21% 7%	2135
	11th to 20th	Night	33% 5% 12% 24% 18% 8%	2075
	21st to end	Night	28% 6% 14% 28% 20% 3	2100
May	1st to 10th	Night	39% 8% 20% 23% 9% 1	5863
	11th to 20th	Night	38% 7% 16% 24% 13% 2	5277
	21st to end	Night	40% 11% 18% 18% 12%	5771
June	1st to 10th	Night	41% 9% 18% 21% 10% 1	1890
	11th to 20th	Night	33% 12% 21% 25% 8%	1890
	21st to end	Night	36% 13% 21% 24% 6%	1890
July	1st to 10th	Night	34% 11% 29% 19% 6%	5235
	11th to 20th	Night	37% 14% 33% 14% 3	5226
	21st to end	Night	41% 13% 21% 18% 6% 1	5606
August	1st to 10th	Night	48% 12% 26% 12% 2	4124
	11th to 20th	Night	31% 12% 25% 27% 5%	4519
	21st to end	Night	39% 10% 18% 27% 5% 1	5045
September	1st to 10th	Night	36% 11% 19% 19% 12% 2	2100
	11th to 20th	Night	45% 8% 15% 19% 12% 2	2139
	21st to end	Night	47% 7% 12% 20% 13% 2	2385
October	1st to 10th	Night	40% 6% 9% 18% 23% 6%	3920
	11th to 20th	Night	21% 4 6% 16% 22% 31%	3899
	21st to end	Night	25% 4 7% 26% 28% 11%	4252
November	1st to 10th	Night	34% 5% 9% 19% 24% 9%	2461
	11th to 20th	Night	37% 5% 9% 16% 25% 9%	2520
	21st to end	Night	33% 5% 10% 23% 23% 6%	2678
December	1st to 10th	Night	34% 4 8% 15% 28% 11%	4720
	11th to 20th	Night	41% 5% 12% 18% 18% 6%	5066
	21st to end	Night	37% 5% 12% 25% 18% 3	6633

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	14% 6% 35% 33% 11%	330
	11th to 20th	Day	11% 6% 31% 38% 14% 1	330
	21st to end	Day	17% 6% 33% 34% 9% 1	363
February	1st to 10th	Day	16% 7% 24% 41% 12%	330
	11th to 20th	Day	24% 6% 29% 30% 10% 1	454
	21st to end	Day	16% 7% 28% 37% 10% 2	446
March	1st to 10th	Day	13% 6% 29% 31% 19% 2	540
	11th to 20th	Day	14% 8% 27% 37% 13% 1	540
	21st to end	Day	12% 5% 28% 36% 16% 3	594
April	1st to 10th	Day	12% 6% 24% 34% 19% 5%	540
	11th to 20th	Day	9% 4 23% 31% 27% 7%	532
	21st to end	Day	10% 3 16% 34% 28% 9%	540
May	1st to 10th	Day	7% 3 20% 41% 21% 9%	543
	11th to 20th	Day	13% 3 14% 27% 31% 11%	567
	21st to end	Day	12% 2 9% 26% 33% 18%	617
June	1st to 10th	Day	12% 1 9% 28% 36% 13%	570
	11th to 20th	Day	10% 1 9% 23% 38% 20%	570
	21st to end	Day	7% 1 8% 21% 46% 17%	570
July	1st to 10th	Day	9% 1 4 15% 45% 25%	565
	11th to 20th	Day	9% 1 3 14% 48% 25%	564
	21st to end	Day	8% 1 6% 20% 45% 19%	620
August	1st to 10th	Day	18% 2 6% 16% 36% 22%	566
	11th to 20th	Day	9% 1 6% 17% 38% 29%	559
	21st to end	Day	12% 2 7% 17% 40% 22%	627
September	1st to 10th	Day	10% 1 8% 21% 37% 24%	570
	11th to 20th	Day	21% 1 9% 21% 37% 11%	570
	21st to end	Day	20% 2 8% 25% 31% 14%	562
October	1st to 10th	Day	16% 4 14% 23% 31% 12%	530
	11th to 20th	Day	12% 18% 30% 31% 9%	530
	21st to end	Day	10% 5% 18% 32% 28% 7%	583
November	1st to 10th	Day	14% 6% 16% 31% 25% 8%	535
	11th to 20th	Day	15% 6% 24% 36% 18% 2	540
	21st to end	Day	11% 6% 28% 32% 20% 4	427
December	1st to 10th	Day	20% 3 25% 34% 17%	220
	11th to 20th	Day	16% 5% 25% 33% 18% 3	286
	21st to end	Day	16% 7% 25% 32% 15% 4	363
January	1st to 10th	Night	13% 12% 35% 30% 10%	840
	11th to 20th	Night	14% 9% 29% 36% 11% 1	840
	21st to end	Night	15% 9% 34% 35% 6%	924
February	1st to 10th	Night	21% 6% 29% 35% 10%	840
	11th to 20th	Night	20% 9% 32% 33% 6%	823
	21st to end	Night	19% 7% 29% 34% 10% 1	692
March	1st to 10th	Night	14% 6% 30% 34% 15% 1	840
	11th to 20th	Night	14% 7% 26% 37% 14% 2	840
	21st to end	Night	14% 5% 29% 34% 17% 2	924
April	1st to 10th	Night	12% 6% 27% 33% 19% 3	840
	11th to 20th	Night	12% 4 21% 33% 25% 5%	831
	21st to end	Night	7% 4 20% 38% 27% 5%	840
May	1st to 10th	Night	8% 5% 19% 39% 24% 5%	840
	11th to 20th	Night	14% 2 17% 33% 26% 7%	638
	21st to end	Night	11% 1 9% 25% 36% 17%	683
June	1st to 10th	Night	11% 1 10% 32% 36% 9%	630
	11th to 20th	Night	11% 2 7% 26% 42% 13%	630
	21st to end	Night	7% 3 7% 25% 45% 12%	630
July	1st to 10th	Night	7% 1 6% 20% 51% 15%	615
	11th to 20th	Night	7% 1 5% 18% 52% 17%	612
	21st to end	Night	6% 1 7% 24% 47% 14%	690
August	1st to 10th	Night	13% 2 5% 22% 42% 16%	627
	11th to 20th	Night	11% 1 6% 18% 45% 19%	800
	21st to end	Night	12% 2 7% 21% 41% 17%	924
September	1st to 10th	Night	11% 2 7% 22% 44% 14%	840
	11th to 20th	Night	16% 1 8% 26% 39% 10%	840
	21st to end	Night	20% 3 11% 25% 31% 10%	833
October	1st to 10th	Night	17% 3 12% 27% 32% 9%	800
	11th to 20th	Night	13% 2 22% 32% 25% 6%	800
	21st to end	Night	12% 5% 18% 30% 27% 8%	880
November	1st to 10th	Night	13% 4 22% 33% 24% 4	820
	11th to 20th	Night	15% 7% 27% 29% 19% 3	840
	21st to end	Night	11% 8% 26% 32% 19% 3	840
December	1st to 10th	Night	19% 9% 25% 33% 12% 2	840
	11th to 20th	Night	15% 8% 27% 32% 16% 2	840
	21st to end	Night	16% 7% 27% 35% 15% 1	924

Page generated at 2026-09-26 04:18:44. Version ac07

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