New London
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the New London clear sky chart from 2005-11-05 to 2019-07-16.

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
37%
17927
15%
54235
10%
17887
42%
17887
19%
38363

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
15%
838
10%
2717
4%
836
22%
836
9%
2166
January16th to endNight
16%
896
10%
2912
4%
896
24%
896
10%
2300
February1st to 15thNight
16%
823
9%
2664
4%
821
21%
821
9%
2113
February16th to endNight
20%
735
9%
2205
3%
735
26%
735
11%
1742
March1st to 15thNight
26%
840
14%
2377
8%
840
31%
840
16%
1777
March16th to endNight
32%
896
16%
2464
11%
896
36%
896
21%
1778
April1st to 15thNight
28%
762
12%
2164
6%
762
33%
762
19%
1583
April16th to endNight
35%
624
18%
1870
8%
624
43%
624
24%
1265
May1st to 15thNight
38%
630
12%
1890
7%
630
43%
630
17%
1368
May16th to endNight
51%
657
14%
1972
11%
657
54%
657
27%
1278
June1st to 15thNight
54%
630
14%
1890
11%
630
58%
630
28%
1196
June16th to endNight
57%
630
16%
1680
12%
630
60%
630
32%
1089
July1st to 15thNight
64%
600
16%
1671
15%
600
65%
600
34%
1022
July16th to endNight
67%
615
17%
1748
15%
582
70%
582
34%
1040
August1st to 15thNight
68%
575
21%
1715
19%
572
69%
572
33%
1049
August16th to endNight
66%
621
21%
1863
19%
621
69%
621
34%
1116
September1st to 15thNight
61%
770
24%
2119
17%
770
64%
770
34%
1298
September16th to endNight
56%
777
25%
2145
20%
777
60%
777
32%
1347
October1st to 15thNight
45%
780
19%
2268
16%
780
49%
780
26%
1488
October16th to endNight
27%
832
18%
2532
12%
832
35%
832
19%
1774
November1st to 15thNight
35%
820
19%
2666
14%
820
43%
820
21%
1762
November16th to endNight
23%
840
14%
2792
9%
840
29%
840
13%
2072
December1st to 15thNight
17%
840
9%
2940
5%
840
23%
840
10%
2321
December16th to endNight
16%
896
7%
2971
3%
896
21%
896
9%
2419

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
15%9%47%6%3445%7%30%
55057
Night
15%9%46%5%3445%6%33%
54423
Cloud CoverDay
15%9%47%6%3445%7%31%
55067
Night
15%9%46%5%3445%6%33%
54427
TransparencyDay
52%6%11%17%10%1
54763
Night
49%6%11%19%11%1
54235
SeeingDay
19%9%26%22%15%7%
7975
Night
19%9%27%28%13%1
17932

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
18%15%7%10%9%4434417%
1881
16th to endDay
14%18%8%12%9%4443414%
2016
February1st to 15thDay
17%15%7%9%8%3444418%
1855
16th to endDay
16%13%5%12%7%34446%21%
1840
March1st to 15thDay
18%14%7%9%6%3343422%
2232
16th to endDay
19%11%6%9%5%24435%27%
2464
April1st to 15thDay
17%11%47%5%35%446%28%
2457
16th to endDay
19%8%36%424336%36%
2695
May1st to 15thDay
17%8%47%6%35%5%46%29%
2721
16th to endDay
10%5%26%6%35%6%6%9%36%
2847
June1st to 15thDay
15%6%25%6%245%5%8%36%
2730
16th to endDay
11%5%25%5%46%6%6%9%36%
2932
July1st to 15thDay
10%5%26%6%345%6%8%40%
2860
16th to endDay
9%425%6%46%5%6%10%37%
2676
August1st to 15thDay
8%5%16%6%37%6%7%9%37%
2487
16th to endDay
11%5%25%6%35%5%6%10%38%
2688
September1st to 15thDay
15%5%35%5%245%5%8%38%
2158
16th to endDay
15%6%35%5%33346%41%
2145
October1st to 15thDay
15%8%35%435%6%5%6%35%
2022
16th to endDay
21%9%26%5%3345%5%32%
2043
November1st to 15thDay
14%11%46%5%34447%32%
1852
16th to endDay
18%15%48%6%34446%23%
1823
December1st to 15thDay
18%17%6%10%7%34335%18%
1680
16th to endDay
19%17%7%11%7%34345%15%
1953
January1st to 15thNight
19%16%5%9%6%4444421%
2717
16th to endNight
15%15%6%10%7%36%345%21%
2912
February1st to 15thNight
18%13%6%9%6%3444422%
2662
16th to endNight
17%13%6%9%7%35%45%5%21%
2205
March1st to 15thNight
16%11%5%7%6%34445%29%
2365
16th to endNight
15%9%5%7%5%34447%33%
2464
April1st to 15thNight
16%10%36%5%45%5%5%6%30%
2164
16th to endNight
14%8%25%5%3445%6%38%
1870
May1st to 15thNight
16%8%26%6%35%5%6%7%30%
1890
16th to endNight
11%5%25%435%46%9%40%
1970
June1st to 15thNight
9%435%5%35%5%5%7%43%
1890
16th to endNight
9%326%435%5%6%10%41%
1680
July1st to 15thNight
7%4244345%7%9%46%
1756
16th to endNight
6%314435%5%6%9%47%
1856
August1st to 15thNight
6%425%435%6%6%9%45%
1726
16th to endNight
8%425%42445%6%50%
1863
September1st to 15thNight
12%5%24423337%50%
2119
16th to endNight
11%5%245%23447%47%
2145
October1st to 15thNight
15%7%25%42445%6%41%
2268
16th to endNight
20%6%35%5%3345%5%35%
2532
November1st to 15thNight
16%8%35%42446%7%36%
2666
16th to endNight
20%11%46%7%3445%6%26%
2792
December1st to 15thNight
19%15%6%8%6%24446%21%
2940
16th to endNight
19%15%7%8%6%3345%6%17%
2971

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
18%15%6%10%9%4434417%
1881
16th to endDay
14%18%8%12%9%3444414%
2016
February1st to 15thDay
17%15%8%10%8%34435%19%
1855
16th to endDay
17%12%6%10%7%43445%22%
1840
March1st to 15thDay
19%14%7%8%7%3343422%
2243
16th to endDay
19%11%5%9%424346%27%
2463
April1st to 15thDay
17%11%46%5%35%45%6%27%
2457
16th to endDay
19%8%36%424346%36%
2695
May1st to 15thDay
17%8%47%6%45%45%6%29%
2721
16th to endDay
11%5%25%6%35%5%7%8%37%
2847
June1st to 15thDay
14%6%26%6%245%5%8%36%
2730
16th to endDay
12%5%25%6%36%5%6%9%36%
2932
July1st to 15thDay
10%5%25%7%345%5%8%40%
2860
16th to endDay
10%5%25%5%47%5%6%9%37%
2676
August1st to 15thDay
9%5%15%6%36%6%7%8%37%
2487
16th to endDay
10%5%26%5%35%46%10%38%
2688
September1st to 15thDay
15%5%35%5%245%5%7%38%
2158
16th to endDay
16%5%25%434346%41%
2145
October1st to 15thDay
15%8%26%5%346%5%6%35%
2022
16th to endDay
21%8%36%5%3345%5%33%
2043
November1st to 15thDay
14%11%46%5%3435%6%33%
1852
16th to endDay
18%15%47%6%34446%23%
1823
December1st to 15thDay
18%17%6%11%7%24445%18%
1680
16th to endDay
20%17%7%10%7%34345%14%
1953
January1st to 15thNight
19%15%5%10%6%4434421%
2717
16th to endNight
15%14%6%10%7%35%445%21%
2912
February1st to 15thNight
19%13%6%10%6%35%345%22%
2655
16th to endNight
17%13%6%9%7%34446%21%
2205
March1st to 15thNight
16%11%5%7%6%34445%29%
2377
16th to endNight
15%9%5%6%5%3435%6%33%
2464
April1st to 15thNight
16%10%46%5%35%5%5%6%30%
2164
16th to endNight
14%8%35%6%2445%7%37%
1870
May1st to 15thNight
16%8%36%6%445%6%7%30%
1889
16th to endNight
11%6%245%345%6%9%40%
1970
June1st to 15thNight
9%5%35%5%35%6%5%7%43%
1890
16th to endNight
9%3245%35%5%7%10%42%
1680
July1st to 15thNight
7%4244345%7%10%45%
1756
16th to endNight
6%325%3346%6%9%48%
1856
August1st to 15thNight
6%415%435%6%7%9%45%
1726
16th to endNight
8%4145%2445%7%50%
1863
September1st to 15thNight
12%5%24424347%50%
2119
16th to endNight
12%4245%24447%47%
2145
October1st to 15thNight
15%6%25%43445%6%41%
2268
16th to endNight
20%7%345%2445%5%35%
2532
November1st to 15thNight
16%9%35%42446%7%36%
2666
16th to endNight
20%11%37%6%3435%6%26%
2792
December1st to 15thNight
19%15%6%8%5%24445%22%
2940
16th to endNight
19%15%6%9%6%34446%18%
2971

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
70%49%10%5%
1882
16th to endDay
72%6%10%8%2
2016
February1st to 15thDay
67%6%9%11%4
1857
16th to endDay
63%6%11%12%5%
1840
March1st to 15thDay
64%5%9%13%5%
2243
16th to endDay
58%5%9%18%7%
2464
April1st to 15thDay
55%6%12%15%9%
2457
16th to endDay
50%411%17%13%3
2695
May1st to 15thDay
54%7%11%17%7%1
2721
16th to endDay
41%8%14%21%11%1
2851
June1st to 15thDay
44%6%11%23%12%
2730
16th to endDay
42%8%13%19%13%1
2932
July1st to 15thDay
41%7%11%20%17%3
2716
16th to endDay
39%8%14%22%12%1
2521
August1st to 15thDay
40%9%13%23%11%
2474
16th to endDay
39%8%13%21%13%3
2688
September1st to 15thDay
43%6%13%20%13%2
2158
16th to endDay
43%5%10%20%18%1
2145
October1st to 15thDay
45%8%11%19%14%
2022
16th to endDay
53%5%12%18%9%
2043
November1st to 15thDay
51%5%9%20%10%2
1852
16th to endDay
61%7%10%14%6%
1823
December1st to 15thDay
69%6%8%12%4
1680
16th to endDay
71%6%9%9%2
1953
January1st to 15thNight
66%49%13%6%
2717
16th to endNight
64%411%13%5%
2912
February1st to 15thNight
64%5%9%13%5%
2664
16th to endNight
62%6%9%15%5%
2205
March1st to 15thNight
55%5%10%18%8%1
2377
16th to endNight
50%5%10%21%9%1
2464
April1st to 15thNight
52%6%12%14%12%1
2164
16th to endNight
45%5%11%18%15%3
1870
May1st to 15thNight
50%8%11%16%10%1
1890
16th to endNight
38%8%13%22%14%2
1972
June1st to 15thNight
37%7%12%24%16%1
1890
16th to endNight
35%8%15%24%12%3
1680
July1st to 15thNight
32%7%15%21%19%4
1671
16th to endNight
30%8%15%25%15%4
1748
August1st to 15thNight
32%8%12%26%18%1
1715
16th to endNight
32%6%13%24%19%3
1863
September1st to 15thNight
34%5%13%24%18%3
2119
16th to endNight
36%5%10%23%21%1
2145
October1st to 15thNight
41%6%12%20%17%1
2268
16th to endNight
49%5%11%22%9%1
2532
November1st to 15thNight
45%5%13%19%12%3
2666
16th to endNight
57%5%11%17%7%
2792
December1st to 15thNight
64%5%9%14%5%
2940
16th to endNight
66%6%12%12%2
2971

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%18%39%7%8%1
180
16th to endDay
25%23%38%9%2
192
February1st to 15thDay
34%17%36%12%
180
16th to endDay
28%20%32%17%
159
March1st to 15thDay
25%15%34%18%4
323
16th to endDay
27%10%33%19%7%1
416
April1st to 15thDay
27%14%30%17%8%1
390
16th to endDay
25%10%29%16%12%5%
379
May1st to 15thDay
23%6%34%20%10%4
408
16th to endDay
15%6%28%25%16%6%
459
June1st to 15thDay
16%5%24%30%19%3
435
16th to endDay
14%7%26%30%16%4
637
July1st to 15thDay
12%221%26%21%15%
550
16th to endDay
11%218%25%27%13%
391
August1st to 15thDay
13%212%29%27%14%
358
16th to endDay
12%314%25%26%17%
396
September1st to 15thDay
17%214%21%25%18%
375
16th to endDay
18%6%16%18%22%17%
374
October1st to 15thDay
14%8%24%26%18%6%
375
16th to endDay
21%16%33%21%5%1
363
November1st to 15thDay
25%14%26%16%15%2
180
16th to endDay
25%14%40%17%2
161
December1st to 15thDay
20%15%40%13%8%2
120
16th to endDay
25%24%32%14%2
174
January1st to 15thNight
28%16%34%17%4
840
16th to endNight
23%15%37%19%3
896
February1st to 15thNight
26%16%33%20%2
824
16th to endNight
24%12%36%22%3
735
March1st to 15thNight
23%13%30%25%6%
840
16th to endNight
18%9%33%26%10%1
896
April1st to 15thNight
22%11%33%25%5%
762
16th to endNight
19%7%33%28%9%1
624
May1st to 15thNight
18%7%27%32%11%1
630
16th to endNight
14%324%33%20%3
659
June1st to 15thNight
10%322%44%16%
630
16th to endNight
12%120%42%21%
630
July1st to 15thNight
10%115%39%29%3
600
16th to endNight
8%14%41%30%3
615
August1st to 15thNight
8%112%42%29%4
575
16th to endNight
10%14%34%33%5%
621
September1st to 15thNight
14%314%31%29%6%
770
16th to endNight
14%417%29%27%6%
777
October1st to 15thNight
19%424%31%17%2
780
16th to endNight
23%12%32%23%7%
832
November1st to 15thNight
20%10%30%26%11%1
820
16th to endNight
26%15%30%19%7%
840
December1st to 15thNight
28%13%32%20%4
840
16th to endNight
27%14%34%19%3
896
Page generated at 2019-07-17 08:53:07. Version ac04

Copyright 2019 A. Danko


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