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	12% 6% 2 6% 5% 4 5% 4 6% 9% 41%	100567
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 43%	98335
Transparency	Day	37% 8% 15% 21% 15% 4	100373
	Night	38% 7% 14% 20% 16% 4	98199
Seeing	Day	13% 3 17% 28% 28% 11%	15606
	Night	14% 5% 19% 30% 26% 7%	25891

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% 5% 2 4 3 3 4 3 5% 7% 50%	2836
	11th to 20th	Day	10% 6% 2 5% 4 4 5% 3 5% 7% 49%	2840
	21st to end	Day	13% 7% 2 7% 4 5% 4 3 5% 6% 44%	3124
February	1st to 10th	Day	15% 5% 2 7% 6% 4 3 3 6% 7% 41%	1710
	11th to 20th	Day	18% 6% 3 5% 4 3 3 3 4 5% 45%	1774
	21st to end	Day	14% 7% 2 6% 4 4 4 3 5% 7% 43%	1670
March	1st to 10th	Day	22% 11% 3 6% 3 3 3 3 4 6% 36%	3435
	11th to 20th	Day	9% 4 1 5% 3 3 4 4 6% 7% 54%	3480
	21st to end	Day	15% 6% 2 6% 4 4 4 3 4 5% 46%	3815
April	1st to 10th	Day	10% 4 2 5% 3 3 3 4 6% 7% 53%	2247
	11th to 20th	Day	9% 4 2 5% 4 3 3 4 6% 8% 51%	2254
	21st to end	Day	9% 4 1 4 4 3 4 4 5% 9% 54%	2280
May	1st to 10th	Day	6% 5% 2 7% 5% 6% 5% 5% 7% 10% 41%	3765
	11th to 20th	Day	16% 7% 3 8% 5% 5% 4 4 6% 8% 36%	4080
	21st to end	Day	6% 3 2 6% 5% 5% 6% 5% 8% 11% 44%	4476
June	1st to 10th	Day	10% 7% 3 7% 6% 5% 6% 5% 8% 9% 34%	2470
	11th to 20th	Day	8% 4 2 6% 4 4 5% 6% 9% 11% 40%	2470
	21st to end	Day	7% 5% 3 6% 6% 6% 7% 5% 9% 11% 35%	2470
July	1st to 10th	Day	10% 5% 2 7% 5% 5% 6% 5% 9% 14% 31%	4120
	11th to 20th	Day	8% 6% 3 8% 7% 6% 7% 6% 8% 12% 28%	4120
	21st to end	Day	8% 7% 3 8% 6% 6% 7% 6% 10% 13% 26%	4466
August	1st to 10th	Day	20% 12% 3 8% 5% 5% 5% 4 6% 10% 21%	4104
	11th to 20th	Day	7% 6% 2 7% 5% 6% 7% 6% 8% 12% 35%	3738
	21st to end	Day	7% 6% 2 7% 5% 4 5% 4 7% 10% 42%	4180
September	1st to 10th	Day	10% 6% 3 6% 5% 4 6% 5% 7% 9% 40%	2280
	11th to 20th	Day	16% 7% 2 7% 5% 4 5% 4 5% 8% 36%	2239
	21st to end	Day	17% 7% 3 7% 5% 5% 4 4 6% 6% 37%	2000
October	1st to 10th	Day	14% 6% 3 7% 4 4 4 3 5% 5% 44%	1900
	11th to 20th	Day	10% 4 2 5% 3 4 4 3 4 7% 55%	1900
	21st to end	Day	10% 5% 2 6% 3 3 3 3 4 6% 56%	2090
November	1st to 10th	Day	12% 6% 1 4 3 3 3 2 5% 6% 53%	1867
	11th to 20th	Day	13% 6% 2 6% 4 3 4 3 4 6% 50%	1900
	21st to end	Day	10% 6% 2 5% 4 5% 3 3 5% 8% 49%	1746
December	1st to 10th	Day	13% 9% 3 7% 4 4 4 4 5% 8% 39%	1520
	11th to 20th	Day	15% 5% 2 4 3 3 3 2 4 5% 54%	2077
	21st to end	Day	14% 9% 3 6% 4 3 4 3 5% 7% 41%	3124
January	1st to 10th	Night	13% 7% 2 6% 4 3 4 3 5% 7% 46%	4109
	11th to 20th	Night	12% 7% 3 6% 5% 4 5% 4 6% 8% 41%	4120
	21st to end	Night	12% 8% 3 7% 5% 4 5% 3 5% 5% 44%	4532
February	1st to 10th	Night	16% 6% 2 6% 4 4 4 4 4 6% 44%	2470
	11th to 20th	Night	17% 9% 3 5% 3 3 4 3 5% 7% 41%	2292
	21st to end	Night	16% 6% 2 7% 4 3 5% 4 5% 6% 43%	1781
March	1st to 10th	Night	22% 12% 3 7% 4 4 3 2 4 5% 32%	3418
	11th to 20th	Night	11% 6% 2 6% 4 4 4 4 6% 7% 47%	3480
	21st to end	Night	15% 4 2 5% 3 4 3 3 5% 6% 50%	3817
April	1st to 10th	Night	10% 6% 2 5% 3 3 4 4 6% 7% 50%	1932
	11th to 20th	Night	10% 5% 2 6% 4 4 5% 4 6% 6% 49%	1875
	21st to end	Night	7% 4 2 5% 3 3 4 4 5% 7% 56%	1900
May	1st to 10th	Night	6% 5% 3 7% 5% 5% 5% 5% 6% 9% 44%	3130
	11th to 20th	Night	12% 7% 2 8% 6% 4 5% 4 5% 7% 40%	2827
	21st to end	Night	8% 4 2 6% 4 4 4 6% 6% 10% 46%	3079
June	1st to 10th	Night	9% 7% 2 8% 5% 6% 5% 4 8% 11% 35%	1710
	11th to 20th	Night	9% 5% 1 6% 4 4 5% 5% 9% 12% 41%	1710
	21st to end	Night	8% 6% 1 7% 5% 6% 6% 6% 9% 11% 34%	1710
July	1st to 10th	Night	7% 5% 3 7% 6% 7% 6% 6% 8% 12% 34%	2840
	11th to 20th	Night	7% 6% 3 8% 7% 6% 6% 5% 10% 12% 31%	2840
	21st to end	Night	8% 5% 2 7% 6% 6% 7% 6% 9% 13% 30%	3087
August	1st to 10th	Night	19% 10% 3 8% 4 4 4 4 7% 11% 26%	2825
	11th to 20th	Night	7% 6% 2 7% 4 5% 6% 5% 8% 11% 39%	3058
	21st to end	Night	6% 4 2 7% 5% 5% 5% 5% 7% 11% 44%	3476
September	1st to 10th	Night	11% 5% 2 6% 4 5% 5% 5% 6% 10% 41%	1900
	11th to 20th	Night	13% 7% 3 7% 5% 5% 5% 5% 7% 9% 36%	1935
	21st to end	Night	17% 7% 3 6% 4 5% 5% 3 5% 6% 39%	2178
October	1st to 10th	Night	13% 7% 2 6% 4 4 4 3 4 6% 46%	2280
	11th to 20th	Night	9% 4 2 5% 4 3 4 3 5% 6% 55%	2280
	21st to end	Night	9% 4 2 4 3 4 4 3 5% 7% 55%	2508
November	1st to 10th	Night	11% 6% 2 4 4 4 4 3 5% 5% 53%	2234
	11th to 20th	Night	13% 7% 2 6% 4 4 3 3 5% 7% 46%	2280
	21st to end	Night	10% 7% 2 5% 3 3 4 4 6% 7% 50%	2421
December	1st to 10th	Night	15% 7% 2 6% 4 4 4 4 7% 7% 40%	2660
	11th to 20th	Night	15% 7% 2 5% 4 2 3 3 4 6% 49%	3109
	21st to end	Night	15% 6% 2 6% 4 3 4 3 4 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	49% 6% 9% 15% 14% 7%	3435
	11th to 20th	Day	27% 6% 11% 18% 25% 13%	3480
	21st to end	Day	39% 6% 8% 23% 17% 6%	3815
April	1st to 10th	Day	29% 5% 15% 23% 23% 6%	2247
	11th to 20th	Day	29% 5% 14% 24% 19% 9%	2254
	21st to end	Day	25% 7% 15% 26% 23% 3	2280
May	1st to 10th	Day	32% 11% 23% 22% 10% 2	3800
	11th to 20th	Day	41% 7% 15% 24% 13%	4084
	21st to end	Day	27% 11% 20% 28% 13% 1	4489
June	1st to 10th	Day	39% 10% 17% 22% 11%	2470
	11th to 20th	Day	31% 12% 20% 25% 11% 1	2470
	21st to end	Day	36% 13% 21% 23% 8% 1	2470
July	1st to 10th	Day	37% 12% 26% 21% 4 1	4055
	11th to 20th	Day	42% 14% 28% 12% 4	4051
	21st to end	Day	40% 14% 24% 15% 7%	4324
August	1st to 10th	Day	55% 10% 21% 12% 2	4091
	11th to 20th	Day	35% 12% 21% 23% 9%	3774
	21st to end	Day	34% 8% 21% 32% 5% 1	4180
September	1st to 10th	Day	37% 11% 19% 17% 13% 3	2280
	11th to 20th	Day	44% 8% 14% 17% 14% 3	2239
	21st to end	Day	44% 8% 12% 18% 15% 3	2000
October	1st to 10th	Day	42% 4 9% 21% 20% 3	1900
	11th to 20th	Day	29% 6% 10% 23% 24% 9%	1900
	21st to end	Day	31% 4 8% 21% 28% 8%	2090
November	1st to 10th	Day	32% 4 9% 20% 26% 9%	1867
	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	54% 6% 9% 14% 12% 5%	3418
	11th to 20th	Night	35% 6% 10% 13% 21% 14%	3480
	21st to end	Night	35% 5% 11% 26% 17% 5%	3817
April	1st to 10th	Night	33% 6% 14% 17% 22% 8%	1932
	11th to 20th	Night	35% 5% 12% 21% 18% 9%	1875
	21st to end	Night	27% 7% 14% 28% 20% 4	1900
May	1st to 10th	Night	34% 9% 20% 23% 12% 2	3160
	11th to 20th	Night	42% 8% 13% 23% 14%	2828
	21st to end	Night	30% 10% 19% 26% 15%	3087
June	1st to 10th	Night	41% 9% 19% 21% 10%	1710
	11th to 20th	Night	32% 12% 20% 26% 9% 1	1710
	21st to end	Night	38% 13% 19% 22% 7%	1710
July	1st to 10th	Night	39% 11% 23% 22% 5% 1	2795
	11th to 20th	Night	39% 16% 30% 11% 3	2786
	21st to end	Night	41% 16% 20% 18% 6%	2988
August	1st to 10th	Night	51% 10% 24% 13% 2	2814
	11th to 20th	Night	35% 12% 22% 23% 6%	3088
	21st to end	Night	34% 9% 18% 33% 6% 1	3476
September	1st to 10th	Night	38% 12% 20% 16% 11% 3	1900
	11th to 20th	Night	45% 8% 14% 18% 13% 2	1935
	21st to end	Night	46% 7% 12% 20% 13% 2	2178
October	1st to 10th	Night	40% 6% 9% 20% 19% 6%	2280
	11th to 20th	Night	30% 6% 9% 22% 24% 9%	2280
	21st to end	Night	30% 5% 9% 21% 26% 10%	2508
November	1st to 10th	Night	34% 5% 9% 18% 24% 10%	2234
	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% 29% 32% 18% 2	460
	11th to 20th	Day	15% 8% 28% 36% 12% 2	460
	21st to end	Day	14% 5% 28% 36% 14% 3	506
April	1st to 10th	Day	12% 6% 26% 34% 19% 3	460
	11th to 20th	Day	10% 4 24% 31% 25% 7%	452
	21st to end	Day	10% 3 18% 35% 25% 9%	460
May	1st to 10th	Day	5% 3 20% 40% 21% 10%	463
	11th to 20th	Day	13% 3 14% 26% 33% 10%	487
	21st to end	Day	11% 2 7% 26% 34% 20%	529
June	1st to 10th	Day	13% 1 8% 29% 36% 13%	490
	11th to 20th	Day	10% 1 10% 22% 34% 22%	490
	21st to end	Day	8% 1 9% 22% 44% 16%	490
July	1st to 10th	Day	10% 1 5% 14% 46% 24%	485
	11th to 20th	Day	10% 1 4 15% 48% 23%	484
	21st to end	Day	8% 1 6% 19% 48% 19%	532
August	1st to 10th	Day	17% 2 7% 17% 35% 22%	486
	11th to 20th	Day	9% 2 6% 18% 38% 27%	479
	21st to end	Day	11% 2 7% 15% 41% 24%	539
September	1st to 10th	Day	11% 1 8% 19% 37% 23%	490
	11th to 20th	Day	22% 1 9% 21% 37% 11%	490
	21st to end	Day	20% 2 9% 25% 30% 14%	490
October	1st to 10th	Day	17% 3 13% 23% 30% 13%	490
	11th to 20th	Day	11% 17% 31% 31% 9%	490
	21st to end	Day	9% 5% 17% 32% 29% 9%	539
November	1st to 10th	Day	16% 6% 15% 31% 24% 8%	459
	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	15% 6% 30% 35% 13% 1	760
	11th to 20th	Night	15% 6% 26% 36% 14% 2	760
	21st to end	Night	14% 5% 29% 34% 17% 2	836
April	1st to 10th	Night	13% 5% 28% 34% 18% 2	760
	11th to 20th	Night	13% 4 21% 33% 23% 5%	751
	21st to end	Night	7% 4 22% 37% 26% 4	760
May	1st to 10th	Night	7% 5% 19% 39% 25% 5%	760
	11th to 20th	Night	15% 3 18% 33% 26% 6%	576
	21st to end	Night	11% 1 7% 25% 37% 19%	617
June	1st to 10th	Night	11% 1 10% 32% 36% 10%	570
	11th to 20th	Night	11% 2 7% 25% 41% 14%	570
	21st to end	Night	8% 4 7% 26% 44% 11%	570
July	1st to 10th	Night	8% 1 5% 20% 50% 15%	555
	11th to 20th	Night	7% 1 5% 19% 53% 15%	552
	21st to end	Night	6% 1 6% 25% 49% 13%	624
August	1st to 10th	Night	13% 2 5% 23% 42% 17%	567
	11th to 20th	Night	11% 1 6% 20% 45% 17%	723
	21st to end	Night	12% 1 7% 19% 43% 18%	836
September	1st to 10th	Night	12% 2 6% 22% 44% 14%	760
	11th to 20th	Night	17% 1 8% 26% 38% 10%	760
	21st to end	Night	20% 2 11% 24% 32% 10%	760
October	1st to 10th	Night	17% 3 12% 26% 32% 10%	760
	11th to 20th	Night	12% 2 22% 32% 25% 7%	760
	21st to end	Night	11% 5% 18% 29% 28% 8%	836
November	1st to 10th	Night	13% 4 22% 33% 23% 4	745
	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

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