Wilton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wilton clear sky chart from 2005-11-05 to 2017-09-17.

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
71%
15278
29%
46891
27%
15242
74%
15242
45%
24172

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
62%
716
18%
2452
19%
716
64%
716
30%
1427
January16th to endNight
63%
768
25%
2496
26%
768
67%
768
29%
1500
February1st to 15thNight
60%
696
24%
2270
25%
696
64%
696
28%
1356
February16th to endNight
59%
632
26%
1895
25%
632
64%
632
32%
1155
March1st to 15thNight
57%
720
18%
2052
18%
720
59%
720
31%
1309
March16th to endNight
59%
768
22%
2061
17%
768
63%
768
35%
1274
April1st to 15thNight
57%
719
24%
1799
13%
719
62%
719
37%
1136
April16th to endNight
65%
720
26%
1800
12%
720
69%
720
51%
1000
May1st to 15thNight
73%
589
30%
1669
22%
589
77%
589
60%
788
May16th to endNight
75%
374
29%
1496
33%
374
79%
374
53%
569
June1st to 15thNight
76%
360
28%
1440
32%
360
83%
360
54%
537
June16th to endNight
88%
360
37%
1440
49%
360
90%
360
71%
453
July1st to 15thNight
94%
340
36%
1360
47%
340
96%
340
78%
402
July16th to endNight
91%
520
39%
1549
37%
487
92%
487
72%
602
August1st to 15thNight
89%
576
39%
1649
30%
573
89%
573
75%
675
August16th to endNight
89%
764
44%
1910
28%
764
90%
764
83%
844
September1st to 15thNight
90%
720
42%
1800
30%
720
92%
720
81%
812
September16th to endNight
85%
664
44%
1802
39%
664
88%
664
73%
793
October1st to 15thNight
76%
660
32%
1980
32%
660
81%
660
54%
945
October16th to endNight
76%
704
35%
2112
37%
704
80%
704
51%
1038
November1st to 15thNight
73%
700
30%
2239
31%
700
76%
700
45%
1119
November16th to endNight
66%
720
26%
2412
27%
720
70%
720
37%
1279
December1st to 15thNight
59%
720
21%
2520
20%
720
64%
720
26%
1518
December16th to endNight
52%
768
22%
2688
20%
768
57%
768
24%
1641

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
8%312212335%63%
47886
Night
9%312212335%62%
47076
TransparencyDay
23%38%20%24%19%
47569
Night
24%39%20%24%18%
46892
SeeingDay
8%314%26%30%16%
5897
Night
10%211%37%34%5%
15292

By Month

Percentage Cloud Cover SW (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
17%5%25%323447%42%
1483
16th to endDay
18%6%245%24336%41%
1728
February1st to 15thDay
18%5%35%424246%42%
1593
16th to endDay
17%5%3442335%7%42%
1579
March1st to 15thDay
16%5%245%145%5%7%39%
1905
16th to endDay
14%5%244345%5%6%43%
2163
April1st to 15thDay
13%6%2432345%7%45%
2149
16th to endDay
8%312212336%62%
2160
May1st to 15thDay
3212212235%71%
2277
16th to endDay
5%213212346%64%
2615
June1st to 15thDay
3211213335%70%
2520
16th to endDay
111122383%
2520
July1st to 15thDay
1112486%
2520
16th to endDay
11112384%
2510
August1st to 15thDay
1111111385%
2301
16th to endDay
111112484%
2292
September1st to 15thDay
111112483%
2160
16th to endDay
321111123477%
1860
October1st to 15thDay
41222225%6%69%
1650
16th to endDay
8%413322235%62%
1760
November1st to 15thDay
9%31232345%7%54%
1620
16th to endDay
12%7%25%423446%47%
1545
December1st to 15thDay
17%6%5%7%423236%39%
1440
16th to endDay
20%6%24414348%39%
1536
January1st to 15thNight
14%5%23313347%49%
2452
16th to endNight
16%314324346%47%
2496
February1st to 15thNight
17%41432335%6%46%
2259
16th to endNight
17%424323346%49%
1895
March1st to 15thNight
16%5%24423346%46%
2052
16th to endNight
14%413223447%50%
2061
April1st to 15thNight
11%42442435%6%51%
1799
16th to endNight
7%212212345%64%
1800
May1st to 15thNight
421212336%71%
1669
16th to endNight
421112246%71%
1496
June1st to 15thNight
31221123475%
1440
16th to endNight
111111385%
1440
July1st to 15thNight
1111288%
1440
16th to endNight
1111112383%
1656
August1st to 15thNight
1111112383%
1658
16th to endNight
11112484%
1910
September1st to 15thNight
111112385%
1800
16th to endNight
11121122480%
1802
October1st to 15thNight
5%21212346%68%
1980
16th to endNight
4213212346%66%
2112
November1st to 15thNight
9%31221235%8%59%
2239
16th to endNight
11%314322345%57%
2412
December1st to 15thNight
18%5%13323435%47%
2520
16th to endNight
21%423322345%45%
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
41%5%14%16%19%2
1483
16th to endDay
45%48%17%17%7%
1728
February1st to 15thDay
44%49%23%13%4
1593
16th to endDay
41%5%12%25%12%3
1579
March1st to 15thDay
40%5%13%20%14%4
1905
16th to endDay
39%6%15%18%16%3
2163
April1st to 15thDay
38%5%10%24%16%5%
2149
16th to endDay
23%412%25%26%7%
2160
May1st to 15thDay
16%28%28%33%10%
2277
16th to endDay
20%312%28%25%9%
2619
June1st to 15thDay
17%310%23%25%19%
2520
16th to endDay
7%1414%37%34%
2520
July1st to 15thDay
5%29%26%54%
2371
16th to endDay
6%1310%24%53%
2354
August1st to 15thDay
7%1211%30%45%
2285
16th to endDay
6%1213%36%39%
2292
September1st to 15thDay
6%1414%35%38%
2160
16th to endDay
12%25%21%34%23%
1860
October1st to 15thDay
15%49%23%28%18%
1650
16th to endDay
25%29%22%27%11%
1760
November1st to 15thDay
28%314%29%19%4
1620
16th to endDay
37%5%11%23%17%4
1545
December1st to 15thDay
47%410%19%14%3
1440
16th to endDay
45%6%12%17%14%4
1536
January1st to 15thNight
35%413%21%17%6%
2452
16th to endNight
37%410%17%16%12%
2496
February1st to 15thNight
37%410%23%18%6%
2270
16th to endNight
36%411%25%19%3
1895
March1st to 15thNight
39%312%19%17%7%
2052
16th to endNight
33%5%11%21%20%7%
2061
April1st to 15thNight
33%412%23%18%6%
1799
16th to endNight
21%5%14%22%27%9%
1800
May1st to 15thNight
14%49%25%31%15%
1670
16th to endNight
15%214%33%22%11%
1496
June1st to 15thNight
14%211%25%26%19%
1440
16th to endNight
7%1313%34%38%
1440
July1st to 15thNight
5%28%27%54%
1360
16th to endNight
9%129%24%53%
1549
August1st to 15thNight
8%1114%26%47%
1649
16th to endNight
6%1211%34%43%
1910
September1st to 15thNight
5%2412%35%39%
1800
16th to endNight
9%15%21%35%26%
1802
October1st to 15thNight
17%38%22%26%20%
1980
16th to endNight
19%38%23%26%18%
2112
November1st to 15thNight
23%312%27%23%8%
2239
16th to endNight
29%38%25%25%7%
2412
December1st to 15thNight
38%5%11%19%18%6%
2520
16th to endNight
41%411%18%17%7%
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
24%9%12%27%15%10%
111
16th to endDay
21%316%21%19%19%
256
February1st to 15thDay
19%414%18%27%15%
239
16th to endDay
18%9%17%19%20%13%
238
March1st to 15thDay
18%8%18%18%21%14%
270
16th to endDay
18%6%17%22%23%10%
288
April1st to 15thDay
17%8%20%24%17%11%
269
16th to endDay
9%8%19%28%21%12%
270
May1st to 15thDay
4421%31%25%12%
288
16th to endDay
5%318%23%30%18%
330
June1st to 15thDay
5%420%32%27%9%
315
16th to endDay
210%28%40%17%
315
July1st to 15thDay
6%29%45%16%
305
16th to endDay
9%31%39%18%
327
August1st to 15thDay
212%35%35%12%
315
16th to endDay
8%29%39%21%
332
September1st to 15thDay
9%31%40%18%
315
16th to endDay
3211%25%29%26%
260
October1st to 15thDay
6%316%27%27%20%
255
16th to endDay
12%411%21%30%19%
272
November1st to 15thDay
10%17%19%35%25%
126
16th to endDay
14%39%37%29%5%
77
December1st to 15thDay
30%5%10%35%20%
60
16th to endDay
14%118%21%32%10%
64
January1st to 15thNight
16%210%35%28%7%
720
16th to endNight
18%37%35%27%7%
768
February1st to 15thNight
17%410%34%27%4
704
16th to endNight
18%313%38%22%4
632
March1st to 15thNight
17%212%34%28%3
720
16th to endNight
15%414%37%25%2
768
April1st to 15thNight
11%420%36%25%2
719
16th to endNight
7%220%36%29%4
720
May1st to 15thNight
417%41%31%4
590
16th to endNight
5%112%37%39%2
375
June1st to 15thNight
4113%44%35%1
360
16th to endNight
16%49%40%1
360
July1st to 15thNight
244%51%
340
16th to endNight
1334%54%5%
520
August1st to 15thNight
2439%51%3
576
16th to endNight
16%39%47%4
764
September1st to 15thNight
15%36%50%5%
720
16th to endNight
19%36%41%9%
664
October1st to 15thNight
6%29%39%35%7%
660
16th to endNight
6%210%32%38%10%
704
November1st to 15thNight
9%110%39%33%6%
700
16th to endNight
11%112%38%29%6%
720
December1st to 15thNight
20%210%37%22%6%
720
16th to endNight
23%313%32%24%2
768
Page generated at 2017-09-18 05:38:29. Version ac04

Copyright 2017 A. Danko


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