Wilmington
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wilmington clear sky chart from 2005-11-05 to 2017-09-20.

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 TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(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

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
34%
15150
20%
46899
10%
15115
45%
15115
23%
29354

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 15thNight
22%
719
21%
2506
10%
716
38%
716
18%
1547
January16th to endNight
22%
768
23%
2505
7%
768
41%
768
21%
1544
February1st to 15thNight
19%
704
18%
2263
7%
701
34%
701
18%
1428
February16th to endNight
17%
631
26%
1893
8%
631
39%
631
22%
1168
March1st to 15thNight
23%
720
21%
2083
8%
720
37%
720
23%
1315
March16th to endNight
24%
768
22%
2037
8%
768
36%
768
24%
1352
April1st to 15thNight
23%
718
19%
1796
4%
718
31%
718
25%
1191
April16th to endNight
31%
720
19%
1800
5%
720
38%
720
25%
1203
May1st to 15thNight
27%
528
17%
1608
7%
528
35%
528
17%
1089
May16th to endNight
41%
374
16%
1497
12%
374
50%
374
16%
911
June1st to 15thNight
45%
360
17%
1440
16%
360
53%
360
20%
848
June16th to endNight
51%
360
17%
1440
16%
360
60%
360
23%
828
July1st to 15thNight
53%
340
12%
1360
13%
340
56%
340
17%
856
July16th to endNight
55%
429
15%
1467
14%
403
62%
403
26%
832
August1st to 15thNight
59%
578
18%
1648
12%
575
62%
575
29%
1030
August16th to endNight
59%
764
18%
1910
10%
764
60%
764
33%
1235
September1st to 15thNight
52%
720
25%
1800
14%
720
56%
720
34%
1165
September16th to endNight
50%
677
26%
1828
18%
677
57%
677
31%
1152
October1st to 15thNight
42%
660
22%
1980
17%
660
50%
660
26%
1228
October16th to endNight
35%
704
26%
2135
15%
704
51%
704
30%
1249
November1st to 15thNight
31%
700
23%
2277
13%
700
46%
700
24%
1377
November16th to endNight
28%
720
21%
2418
11%
720
42%
720
20%
1500
December1st to 15thNight
23%
720
17%
2520
7%
720
37%
720
16%
1616
December16th to endNight
20%
768
21%
2688
7%
768
38%
768
16%
1690

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 ForecastData
Points
Cloud CoverDay
14%5%24435%5%5%7%41%
47937
Night
15%5%2442445%7%43%
47074
Cloud CoverDay
14%5%2443445%7%41%
47946
Night
15%5%2442445%7%43%
47080
TransparencyDay
39%5%12%23%16%2
47630
Night
40%411%23%17%2
46899
SeeingDay
16%13%21%24%16%6%
5755
Night
15%19%24%27%11%1
15152

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
14%6%245%3445%6%41%
1432
16th to endDay
14%7%24325%446%43%
1716
February1st to 15thDay
15%6%344245%5%5%41%
1597
16th to endDay
13%7%35%5%3445%6%38%
1580
March1st to 15thDay
15%5%34444346%41%
1865
16th to endDay
18%5%24425%45%5%41%
2187
April1st to 15thDay
16%5%245%23447%43%
2152
16th to endDay
15%42442445%7%43%
2160
May1st to 15thDay
17%5%245%35%5%5%7%36%
2354
16th to endDay
15%5%245%25%5%6%8%39%
2618
June1st to 15thDay
12%5%35%426%5%7%9%37%
2520
16th to endDay
10%425%5%36%5%6%10%39%
2520
July1st to 15thDay
9%5%25%6%36%6%7%8%37%
2520
16th to endDay
6%425%6%47%6%8%10%36%
2600
August1st to 15thDay
11%425%6%35%5%6%9%38%
2286
16th to endDay
10%5%234346%8%9%41%
2292
September1st to 15thDay
13%5%245%2445%7%45%
2160
16th to endDay
14%6%25%4245%47%41%
1897
October1st to 15thDay
16%41442345%6%45%
1650
16th to endDay
17%413423446%46%
1735
November1st to 15thDay
15%6%24313345%47%
1581
16th to endDay
17%423324346%46%
1539
December1st to 15thDay
16%425%4245%5%7%41%
1440
16th to endDay
19%6%2432445%7%37%
1536
January1st to 15thNight
17%5%24424446%42%
2506
16th to endNight
17%5%24324346%43%
2505
February1st to 15thNight
14%7%35%433446%41%
2262
16th to endNight
16%5%2442335%5%45%
1893
March1st to 15thNight
17%423424446%45%
2070
16th to endNight
16%6%245%23335%44%
2037
April1st to 15thNight
16%6%24424446%43%
1796
16th to endNight
17%424324346%44%
1800
May1st to 15thNight
17%6%35%5%23447%37%
1608
16th to endNight
14%6%25%43435%9%39%
1495
June1st to 15thNight
14%6%2442435%9%42%
1440
16th to endNight
9%435%5%235%6%10%42%
1440
July1st to 15thNight
9%5%25%7%46%5%6%10%35%
1440
16th to endNight
7%4245%35%6%7%10%42%
1567
August1st to 15thNight
9%425%5%345%5%8%45%
1659
16th to endNight
11%41443445%7%46%
1910
September1st to 15thNight
13%5%2442345%7%47%
1800
16th to endNight
13%6%1442435%9%44%
1828
October1st to 15thNight
18%42442335%6%45%
1980
16th to endNight
16%415%213336%51%
2135
November1st to 15thNight
13%6%26%414245%48%
2277
16th to endNight
17%5%2442446%7%41%
2418
December1st to 15thNight
18%5%35%5%34446%38%
2520
16th to endNight
17%6%35%32445%7%39%
2688

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
14%5%245%35%346%42%
1432
16th to endDay
14%6%34325%446%43%
1716
February1st to 15thDay
15%7%24425%46%5%41%
1597
16th to endDay
13%7%45%5%25%5%5%6%39%
1580
March1st to 15thDay
15%5%24444446%41%
1875
16th to endDay
18%5%1442445%5%41%
2186
April1st to 15thDay
16%4245%24447%43%
2152
16th to endDay
15%3344245%5%7%44%
2160
May1st to 15thDay
17%425%435%45%7%37%
2354
16th to endDay
15%4245%345%6%8%39%
2618
June1st to 15thDay
12%5%34436%5%7%8%38%
2520
16th to endDay
11%424435%6%5%10%40%
2520
July1st to 15thDay
9%5%25%6%45%6%7%8%39%
2520
16th to endDay
6%4246%47%6%7%11%38%
2600
August1st to 15thDay
11%425%6%35%5%6%8%40%
2286
16th to endDay
10%424435%5%7%8%43%
2292
September1st to 15thDay
13%42442445%7%46%
2160
16th to endDay
15%5%25%5%3445%6%42%
1897
October1st to 15thDay
16%5%1342345%6%46%
1650
16th to endDay
17%413323445%46%
1735
November1st to 15thDay
15%6%15%323345%47%
1581
16th to endDay
17%423423346%46%
1539
December1st to 15thDay
17%4244245%5%6%41%
1440
16th to endDay
19%5%3441445%7%38%
1536
January1st to 15thNight
17%5%24424446%42%
2506
16th to endNight
17%6%24324446%44%
2505
February1st to 15thNight
14%7%44424446%41%
2255
16th to endNight
16%5%2442345%6%46%
1893
March1st to 15thNight
17%5%23324446%45%
2083
16th to endNight
16%6%25%434335%44%
2037
April1st to 15thNight
16%5%24324446%44%
1796
16th to endNight
17%42342345%6%44%
1800
May1st to 15thNight
17%6%26%433447%38%
1608
16th to endNight
15%6%25%43345%8%40%
1495
June1st to 15thNight
14%5%245%23449%42%
1440
16th to endNight
8%5%35%42446%10%42%
1440
July1st to 15thNight
10%435%6%47%5%6%8%37%
1440
16th to endNight
7%4245%25%5%8%9%43%
1567
August1st to 15thNight
9%4236%345%5%8%45%
1659
16th to endNight
11%5%145%3445%7%46%
1910
September1st to 15thNight
13%42442335%6%48%
1800
16th to endNight
14%5%24423448%45%
1828
October1st to 15thNight
18%42433325%6%45%
1980
16th to endNight
16%423313336%51%
2135
November1st to 15thNight
13%6%26%414235%48%
2277
16th to endNight
17%5%24425%46%7%40%
2418
December1st to 15thNight
18%5%35%5%24445%39%
2520
16th to endNight
17%5%244245%5%7%39%
2688

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
42%314%21%13%4
1433
16th to endDay
41%312%24%14%3
1716
February1st to 15thDay
42%411%26%12%2
1600
16th to endDay
43%311%27%12%2
1580
March1st to 15thDay
41%312%25%14%2
1875
16th to endDay
43%410%21%18%3
2187
April1st to 15thDay
40%311%23%15%4
2152
16th to endDay
38%49%18%22%5%
2160
May1st to 15thDay
44%5%12%20%15%2
2354
16th to endDay
39%6%15%23%13%2
2622
June1st to 15thDay
39%6%13%26%12%1
2520
16th to endDay
35%7%14%23%17%1
2520
July1st to 15thDay
37%7%13%23%15%3
2371
16th to endDay
34%8%14%26%15%2
2437
August1st to 15thDay
38%6%13%22%17%1
2273
16th to endDay
35%6%12%23%18%4
2292
September1st to 15thDay
35%5%12%21%21%3
2160
16th to endDay
40%47%20%24%2
1897
October1st to 15thDay
38%311%26%18%2
1650
16th to endDay
38%29%27%19%1
1735
November1st to 15thDay
38%312%22%19%3
1581
16th to endDay
39%310%29%15%2
1539
December1st to 15thDay
40%5%16%24%11%1
1440
16th to endDay
44%415%22%12%1
1536
January1st to 15thNight
42%312%21%16%3
2506
16th to endNight
42%211%26%15%1
2505
February1st to 15thNight
43%311%25%14%2
2263
16th to endNight
39%210%24%19%3
1893
March1st to 15thNight
39%313%24%16%2
2083
16th to endNight
42%410%21%18%3
2037
April1st to 15thNight
39%411%21%18%4
1796
16th to endNight
39%5%9%19%20%5%
1800
May1st to 15thNight
46%5%9%17%17%2
1608
16th to endNight
41%6%15%17%16%2
1497
June1st to 15thNight
38%6%13%23%17%
1440
16th to endNight
35%6%13%26%16%2
1440
July1st to 15thNight
42%8%14%18%13%2
1360
16th to endNight
32%7%18%24%14%1
1467
August1st to 15thNight
35%6%13%23%18%1
1648
16th to endNight
36%5%12%22%20%2
1910
September1st to 15thNight
35%5%10%22%22%3
1800
16th to endNight
37%37%23%25%3
1828
October1st to 15thNight
39%412%23%18%2
1980
16th to endNight
35%29%29%20%2
2135
November1st to 15thNight
39%39%22%17%7%
2277
16th to endNight
41%410%24%16%2
2418
December1st to 15thNight
46%312%22%13%1
2520
16th to endNight
43%413%24%12%2
2688

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
16%26%38%13%31
60
16th to endDay
24%13%34%25%2
94
February1st to 15thDay
18%24%35%20%1
114
16th to endDay
15%21%38%20%4
239
March1st to 15thDay
16%24%27%23%7%
270
16th to endDay
20%19%29%20%7%2
288
April1st to 15thDay
20%17%29%21%8%2
270
16th to endDay
18%18%19%24%15%3
270
May1st to 15thDay
29%21%20%16%10%2
288
16th to endDay
19%12%13%25%23%5%
331
June1st to 15thDay
14%14%20%24%17%8%
315
16th to endDay
11%12%21%32%16%5%
315
July1st to 15thDay
14%7%15%29%25%8%
305
16th to endDay
6%11%9%31%29%11%
326
August1st to 15thDay
13%6%13%27%25%12%
313
16th to endDay
9%5%11%28%27%17%
332
September1st to 15thDay
13%8%20%23%21%13%
315
16th to endDay
20%7%13%26%16%15%
270
October1st to 15thDay
21%9%15%24%20%8%
255
16th to endDay
14%11%28%26%16%1
267
November1st to 15thDay
17%13%25%23%17%1
235
16th to endDay
15%19%31%19%12%1
159
December1st to 15thDay
20%16%28%18%15%1
60
16th to endDay
39%6%31%18%4
64
January1st to 15thNight
15%25%31%22%4
720
16th to endNight
17%24%33%23%1
768
February1st to 15thNight
16%25%33%22%1
704
16th to endNight
16%26%36%18%2
631
March1st to 15thNight
19%25%29%20%5%
720
16th to endNight
16%22%33%19%7%
768
April1st to 15thNight
16%24%31%22%4
718
16th to endNight
15%21%26%27%9%
720
May1st to 15thNight
18%21%28%25%7%
528
16th to endNight
15%19%16%33%14%1
375
June1st to 15thNight
14%17%17%34%15%
360
16th to endNight
7%16%16%41%17%
360
July1st to 15thNight
11%12%13%40%21%
340
16th to endNight
6%17%10%37%23%3
429
August1st to 15thNight
12%10%8%42%24%2
578
16th to endNight
13%9%10%34%29%3
764
September1st to 15thNight
12%10%16%35%23%2
720
16th to endNight
16%10%14%28%25%4
677
October1st to 15thNight
19%12%19%29%17%1
660
16th to endNight
16%14%30%27%10%
704
November1st to 15thNight
15%19%28%24%11%1
700
16th to endNight
16%22%28%23%8%
720
December1st to 15thNight
20%23%26%19%8%1
720
16th to endNight
18%26%31%22%1
768
Page generated at 2017-09-21 07:18:15. Version ac04

Copyright 2017 A. Danko


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