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 2018-01-12.

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
47%
16595
20%
48532
13%
16556
55%
16556
24%
30846

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
30%
762
20%
2472
10%
761
42%
761
19%
1534
January16th to endNight
32%
768
23%
2496
14%
768
45%
768
23%
1527
February1st to 15thNight
32%
703
20%
2277
11%
701
45%
701
21%
1385
February16th to endNight
31%
631
26%
1828
12%
631
46%
631
25%
1138
March1st to 15thNight
41%
720
23%
1980
15%
720
49%
720
27%
1236
March16th to endNight
39%
768
21%
2112
12%
768
48%
768
26%
1326
April1st to 15thNight
45%
718
23%
1816
11%
718
52%
718
31%
1145
April16th to endNight
49%
720
22%
1800
10%
720
54%
720
32%
1140
May1st to 15thNight
52%
668
18%
1749
10%
668
55%
668
27%
1132
May16th to endNight
55%
561
17%
1683
10%
561
60%
561
24%
1029
June1st to 15thNight
57%
540
14%
1620
11%
540
59%
540
23%
1046
June16th to endNight
58%
540
12%
1620
9%
540
60%
540
23%
1055
July1st to 15thNight
70%
510
13%
1530
12%
510
71%
510
26%
974
July16th to endNight
62%
564
11%
1595
9%
531
67%
531
24%
1030
August1st to 15thNight
61%
581
13%
1651
9%
578
63%
578
22%
1141
August16th to endNight
61%
764
14%
1910
9%
764
62%
764
23%
1394
September1st to 15thNight
64%
720
19%
1800
15%
720
64%
720
26%
1275
September16th to endNight
47%
717
14%
1998
9%
717
53%
717
17%
1479
October1st to 15thNight
51%
720
24%
2160
23%
720
57%
720
25%
1375
October16th to endNight
54%
768
33%
2304
27%
768
64%
768
34%
1289
November1st to 15thNight
47%
760
27%
2281
19%
760
57%
760
30%
1343
November16th to endNight
43%
780
26%
2436
16%
780
56%
780
26%
1440
December1st to 15thNight
37%
780
20%
2710
12%
780
49%
780
18%
1683
December16th to endNight
33%
832
22%
2704
12%
832
46%
832
18%
1730

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
11%5%25%5%345%6%8%42%
48787
Night
11%5%2442445%8%44%
48730
TransparencyDay
36%7%15%20%15%3
48488
Night
37%7%13%20%16%5%
48533
SeeingDay
13%9%14%23%27%11%
6307
Night
12%17%15%25%23%6%
16602

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
15%43442434447%
1710
16th to endDay
15%5%26%325%335%44%
1728
February1st to 15thDay
15%5%25%5%23346%44%
1585
16th to endDay
14%41442435%6%48%
1643
March1st to 15thDay
11%5%2332345%7%50%
1980
16th to endDay
13%425%5%24447%43%
2111
April1st to 15thDay
10%41441345%7%52%
2131
16th to endDay
8%31343345%9%49%
2160
May1st to 15thDay
9%5%25%5%25%5%6%8%42%
2211
16th to endDay
7%325%5%35%5%6%9%42%
2431
June1st to 15thDay
9%425%5%35%6%7%10%37%
2340
16th to endDay
7%425%6%37%6%8%11%35%
2340
July1st to 15thDay
8%425%6%36%7%9%12%33%
2340
16th to endDay
6%5%35%6%37%8%8%13%32%
2465
August1st to 15thDay
11%5%26%6%45%7%7%12%30%
2286
16th to endDay
11%6%27%7%46%7%7%10%28%
2292
September1st to 15thDay
12%5%25%5%245%6%9%38%
2160
16th to endDay
18%7%26%6%35%45%6%30%
1957
October1st to 15thDay
15%5%25%433435%45%
1800
16th to endDay
10%414223236%60%
1920
November1st to 15thDay
12%414323246%53%
1907
16th to endDay
11%424323347%52%
1845
December1st to 15thDay
14%8%25%5%2445%6%40%
1573
16th to endDay
15%6%35%5%23346%43%
1872
January1st to 15thNight
11%6%25%425%45%6%44%
2472
16th to endNight
14%5%25%424445%45%
2496
February1st to 15thNight
16%5%24324436%47%
2268
16th to endNight
13%425%424447%46%
1828
March1st to 15thNight
10%42443445%6%48%
1980
16th to endNight
11%5%25%5%2345%7%47%
2112
April1st to 15thNight
9%5%2332446%7%48%
1816
16th to endNight
9%325%4245%5%6%51%
1800
May1st to 15thNight
9%5%245%3446%7%45%
1748
16th to endNight
10%4145%336%5%9%46%
1682
June1st to 15thNight
8%5%25%6%25%47%12%38%
1620
16th to endNight
8%5%24436%7%7%12%37%
1620
July1st to 15thNight
5%3246%5%6%6%7%11%39%
1620
16th to endNight
6%425%5%26%7%9%12%38%
1703
August1st to 15thNight
8%5%36%5%45%5%7%11%36%
1662
16th to endNight
9%5%25%6%46%7%7%11%33%
1910
September1st to 15thNight
11%414446%6%6%9%40%
1800
16th to endNight
16%7%35%5%35%5%5%7%33%
1998
October1st to 15thNight
13%5%25%424346%46%
2160
16th to endNight
9%423323345%56%
2304
November1st to 15thNight
10%423424346%54%
2281
16th to endNight
11%5%2431345%6%50%
2436
December1st to 15thNight
14%6%2442345%7%42%
2710
16th to endNight
15%5%35%424447%41%
2704

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
39%5%12%14%20%7%
1711
16th to endDay
42%45%18%23%5%
1728
February1st to 15thDay
41%46%21%20%5%
1587
16th to endDay
36%411%21%19%6%
1643
March1st to 15thDay
33%5%13%21%19%6%
1980
16th to endDay
38%6%11%21%17%4
2112
April1st to 15thDay
29%414%25%20%4
2131
16th to endDay
28%7%14%20%21%6%
2160
May1st to 15thDay
33%7%18%24%13%1
2211
16th to endDay
31%9%21%24%12%
2435
June1st to 15thDay
33%10%20%23%11%
2340
16th to endDay
35%12%21%21%8%
2340
July1st to 15thDay
34%11%24%20%7%1
2201
16th to endDay
33%12%24%22%6%
2310
August1st to 15thDay
39%11%21%21%5%
2273
16th to endDay
42%12%20%18%4
2292
September1st to 15thDay
38%9%17%17%13%3
2160
16th to endDay
49%8%11%14%13%2
1957
October1st to 15thDay
41%410%19%21%3
1800
16th to endDay
28%38%23%28%8%
1920
November1st to 15thDay
33%39%20%24%8%
1907
16th to endDay
32%410%20%24%8%
1845
December1st to 15thDay
43%6%11%18%14%5%
1573
16th to endDay
41%413%18%15%5%
1872
January1st to 15thNight
39%5%11%15%20%6%
2472
16th to endNight
39%48%19%20%7%
2496
February1st to 15thNight
39%38%17%22%8%
2277
16th to endNight
37%410%20%19%7%
1828
March1st to 15thNight
35%5%11%22%18%6%
1980
16th to endNight
37%413%22%17%4
2112
April1st to 15thNight
32%6%12%20%21%5%
1816
16th to endNight
31%6%15%23%16%6%
1800
May1st to 15thNight
36%6%15%22%17%1
1749
16th to endNight
32%9%17%28%11%
1684
June1st to 15thNight
37%9%20%21%9%
1620
16th to endNight
35%12%20%22%8%
1620
July1st to 15thNight
33%11%22%22%8%
1530
16th to endNight
34%12%23%22%6%
1595
August1st to 15thNight
40%11%20%19%7%
1651
16th to endNight
43%11%18%21%41
1910
September1st to 15thNight
40%10%16%17%12%2
1800
16th to endNight
51%8%11%15%12%1
1998
October1st to 15thNight
40%5%8%20%19%5%
2160
16th to endNight
30%38%19%26%10%
2304
November1st to 15thNight
33%48%18%23%10%
2281
16th to endNight
34%5%10%18%22%9%
2436
December1st to 15thNight
40%6%12%17%17%5%
2710
16th to endNight
42%5%11%18%15%6%
2704

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
18%5%32%22%19%
123
16th to endDay
15%334%37%8%1
96
February1st to 15thDay
17%9%32%28%10%
101
16th to endDay
11%15%32%29%10%
239
March1st to 15thDay
11%14%25%28%18%1
270
16th to endDay
13%14%22%30%15%2
288
April1st to 15thDay
11%16%22%19%20%10%
270
16th to endDay
10%12%14%23%32%6%
270
May1st to 15thDay
10%12%12%38%23%3
288
16th to endDay
10%11%9%16%29%22%
331
June1st to 15thDay
10%9%6%20%29%23%
315
16th to endDay
7%10%7%21%35%17%
315
July1st to 15thDay
8%6%216%48%17%
305
16th to endDay
7%10%313%47%18%
326
August1st to 15thDay
16%5%6%17%30%23%
313
16th to endDay
11%6%315%37%25%
332
September1st to 15thDay
15%6%8%20%33%15%
315
16th to endDay
25%410%18%27%12%
314
October1st to 15thDay
20%6%14%20%28%9%
315
16th to endDay
8%7%17%28%28%9%
336
November1st to 15thDay
16%11%15%27%22%6%
325
16th to endDay
11%13%19%27%23%3
283
December1st to 15thDay
27%224%22%21%1
93
16th to endDay
26%225%29%14%1
144
January1st to 15thNight
11%26%25%24%11%1
765
16th to endNight
11%22%28%31%6%
768
February1st to 15thNight
16%22%23%31%6%
704
16th to endNight
13%20%28%27%9%
631
March1st to 15thNight
10%20%22%31%13%1
720
16th to endNight
13%19%20%27%16%2
768
April1st to 15thNight
10%20%20%24%20%4
718
16th to endNight
10%18%15%25%25%4
720
May1st to 15thNight
9%18%12%33%23%3
669
16th to endNight
10%18%8%18%28%15%
563
June1st to 15thNight
8%17%5%23%32%12%
540
16th to endNight
8%17%6%21%35%10%
540
July1st to 15thNight
6%11%420%44%12%
510
16th to endNight
7%17%419%43%8%
564
August1st to 15thNight
13%9%320%38%13%
581
16th to endNight
11%9%5%18%37%18%
764
September1st to 15thNight
11%8%6%21%40%11%
720
16th to endNight
22%9%10%20%26%10%
717
October1st to 15thNight
17%9%12%24%28%7%
720
16th to endNight
10%12%16%27%23%8%
768
November1st to 15thNight
12%16%18%29%19%4
760
16th to endNight
11%21%18%25%19%3
780
December1st to 15thNight
16%21%19%24%15%2
780
16th to endNight
15%20%22%28%11%
832
Page generated at 2018-01-12 22:01:26. Version ac04

Copyright 2018 A. Danko


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