Brighton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brighton 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
60%
15944
27%
46863
20%
15905
65%
15905
41%
25883

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
58%
897
30%
2506
22%
895
65%
895
47%
1338
January16th to endNight
53%
825
33%
2553
25%
825
62%
825
41%
1380
February1st to 15thNight
50%
698
24%
2241
17%
698
59%
698
36%
1246
February16th to endNight
47%
632
30%
1894
19%
632
59%
632
38%
1071
March1st to 15thNight
53%
720
28%
2128
16%
720
62%
720
42%
1162
March16th to endNight
51%
669
25%
2013
16%
669
60%
669
39%
1124
April1st to 15thNight
45%
539
22%
1798
16%
539
55%
539
33%
992
April16th to endNight
47%
540
21%
1800
18%
540
53%
540
28%
1075
May1st to 15thNight
53%
540
18%
1599
17%
540
56%
540
27%
1034
May16th to endNight
58%
562
18%
1498
13%
561
61%
561
37%
908
June1st to 15thNight
67%
540
20%
1440
16%
540
70%
540
45%
815
June16th to endNight
73%
540
26%
1440
20%
540
76%
540
54%
749
July1st to 15thNight
68%
510
16%
1360
15%
510
69%
510
35%
847
July16th to endNight
75%
564
26%
1422
23%
531
75%
531
42%
806
August1st to 15thNight
74%
539
19%
1674
20%
536
75%
536
37%
910
August16th to endNight
76%
573
28%
1910
31%
573
78%
573
41%
984
September1st to 15thNight
70%
540
27%
1800
28%
540
74%
540
38%
947
September16th to endNight
73%
498
34%
1799
36%
498
79%
498
47%
825
October1st to 15thNight
60%
638
28%
1958
20%
638
65%
638
41%
1051
October16th to endNight
65%
745
33%
2153
23%
745
70%
745
47%
1138
November1st to 15thNight
64%
875
32%
2275
19%
875
69%
875
52%
1226
November16th to endNight
62%
900
34%
2394
23%
900
68%
900
51%
1287
December1st to 15thNight
54%
900
25%
2520
16%
900
61%
900
44%
1404
December16th to endNight
52%
960
27%
2688
17%
960
60%
960
38%
1564

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
5%42342446%8%52%
47924
Night
5%5%2442345%7%55%
47036
Cloud CoverDay
6%42432445%8%53%
47922
Night
5%5%24323447%56%
47036
TransparencyDay
27%6%11%24%21%8%
47599
Night
27%5%12%25%21%7%
46863
SeeingDay
10%5%22%30%23%8%
5875
Night
7%223%47%17%1
15954

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
36%34213347%60%
1432
16th to endDay
25%34423347%59%
1680
February1st to 15thDay
26%45%41446%7%52%
1621
16th to endDay
25%25%42345%6%57%
1580
March1st to 15thDay
25%2443345%9%52%
1830
16th to endDay
6%6%2432446%8%50%
2209
April1st to 15thDay
8%6%24324348%51%
2150
16th to endDay
11%8%2442445%7%43%
2160
May1st to 15thDay
11%6%24435%5%6%8%42%
2349
16th to endDay
9%423425%5%7%8%44%
2616
June1st to 15thDay
5%3135%35%5%6%9%50%
2520
16th to endDay
2124246%8%10%55%
2520
July1st to 15thDay
6%314425%5%7%11%47%
2520
16th to endDay
4313435%6%7%10%49%
2647
August1st to 15thDay
4224437%7%7%11%44%
2274
16th to endDay
4213435%6%6%9%52%
2292
September1st to 15thDay
6%31233345%7%57%
2160
16th to endDay
4312412435%65%
1866
October1st to 15thDay
6%313424347%58%
1669
16th to endDay
6%413212235%66%
1707
November1st to 15thDay
25%233145%47%59%
1583
16th to endDay
243331235%7%60%
1563
December1st to 15thDay
35%25%423348%54%
1440
16th to endDay
47%2443336%8%51%
1536
January1st to 15thNight
1434423346%61%
2506
16th to endNight
36%34413345%58%
2553
February1st to 15thNight
37%45%423446%52%
2231
16th to endNight
39%34424345%55%
1894
March1st to 15thNight
35%245%23347%56%
2128
16th to endNight
7%6%2432335%7%54%
2013
April1st to 15thNight
7%6%33423446%52%
1798
16th to endNight
15%7%24424346%46%
1800
May1st to 15thNight
13%5%2442446%7%43%
1598
16th to endNight
8%41442425%8%51%
1497
June1st to 15thNight
5%2123145%5%9%57%
1440
16th to endNight
221232347%8%60%
1440
July1st to 15thNight
5%4245%35%5%5%9%48%
1440
16th to endNight
32243245%6%10%52%
1518
August1st to 15thNight
4313425%5%7%9%52%
1683
16th to endNight
5%3133245%6%8%53%
1910
September1st to 15thNight
7%2135%2346%7%55%
1800
16th to endNight
4214213446%64%
1799
October1st to 15thNight
7%423323345%58%
1958
16th to endNight
6%423312345%61%
2153
November1st to 15thNight
3314322446%62%
2275
16th to endNight
35%14313347%61%
2394
December1st to 15thNight
45%3432345%8%55%
2520
16th to endNight
38%2342445%7%52%
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
27%24213237%60%
1432
16th to endDay
26%24413337%59%
1680
February1st to 15thDay
36%4442345%7%52%
1621
16th to endDay
26%15%423446%58%
1580
March1st to 15thDay
35%15%4235%5%9%53%
1830
16th to endDay
6%5%2432446%8%50%
2207
April1st to 15thDay
9%6%2432435%8%51%
2150
16th to endDay
12%6%24335%45%7%43%
2160
May1st to 15thDay
13%5%24425%5%7%7%41%
2349
16th to endDay
11%4234345%6%9%45%
2616
June1st to 15thDay
6%313435%5%6%8%50%
2520
16th to endDay
31123246%8%9%56%
2520
July1st to 15thDay
7%214335%5%7%10%48%
2520
16th to endDay
5%223425%5%7%9%50%
2647
August1st to 15thDay
5%214436%7%7%10%45%
2274
16th to endDay
5%1134345%7%8%53%
2292
September1st to 15thDay
6%31332445%7%57%
2160
16th to endDay
433322345%65%
1866
October1st to 15thDay
7%313423346%58%
1669
16th to endDay
6%412212335%65%
1707
November1st to 15thDay
25%13315%35%7%58%
1583
16th to endDay
242331235%8%61%
1563
December1st to 15thDay
35%25%423348%54%
1440
16th to endDay
47%25%42345%7%51%
1536
January1st to 15thNight
25%34413346%61%
2506
16th to endNight
37%35%322335%58%
2553
February1st to 15thNight
38%45%423446%53%
2231
16th to endNight
39%35%323345%55%
1894
March1st to 15thNight
35%24433346%56%
2128
16th to endNight
7%6%24323346%54%
2013
April1st to 15thNight
8%6%24423346%52%
1798
16th to endNight
15%6%24323346%46%
1800
May1st to 15thNight
14%424424448%44%
1598
16th to endNight
8%42442335%8%51%
1497
June1st to 15thNight
6%3231435%9%58%
1440
16th to endNight
31123136%6%7%61%
1440
July1st to 15thNight
6%3235%345%6%8%49%
1440
16th to endNight
43233245%6%9%53%
1518
August1st to 15thNight
5%2134245%7%10%52%
1683
16th to endNight
5%2234145%6%8%54%
1910
September1st to 15thNight
7%2135%2446%7%55%
1800
16th to endNight
5%21331245%6%64%
1799
October1st to 15thNight
8%413323336%58%
1958
16th to endNight
6%413323245%61%
2153
November1st to 15thNight
3413323446%62%
2275
16th to endNight
35%24313346%61%
2394
December1st to 15thNight
46%24323347%55%
2520
16th to endNight
48%2442345%6%52%
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
23%312%31%23%4
1433
16th to endDay
23%210%33%21%7%
1680
February1st to 15thDay
29%5%14%33%13%3
1622
16th to endDay
25%39%30%25%4
1580
March1st to 15thDay
27%411%25%22%8%
1830
16th to endDay
29%5%14%23%20%6%
2209
April1st to 15thDay
30%412%23%20%7%
2150
16th to endDay
36%6%12%20%18%4
2160
May1st to 15thDay
37%8%12%24%14%3
2349
16th to endDay
34%7%14%22%14%5%
2620
June1st to 15thDay
27%8%13%19%20%10%
2520
16th to endDay
19%6%12%20%28%12%
2520
July1st to 15thDay
29%8%11%20%17%12%
2371
16th to endDay
26%8%13%23%19%8%
2480
August1st to 15thDay
31%8%13%19%15%10%
2259
16th to endDay
25%7%10%21%25%9%
2292
September1st to 15thDay
24%5%9%21%21%16%
2160
16th to endDay
19%47%21%36%10%
1866
October1st to 15thDay
25%5%10%20%27%11%
1669
16th to endDay
21%27%27%29%11%
1707
November1st to 15thDay
22%311%25%25%12%
1583
16th to endDay
20%38%25%31%10%
1563
December1st to 15thDay
27%412%32%19%3
1440
16th to endDay
30%414%25%18%5%
1536
January1st to 15thNight
23%412%30%24%5%
2506
16th to endNight
28%38%28%23%8%
2553
February1st to 15thNight
31%413%30%17%3
2241
16th to endNight
30%37%26%23%8%
1894
March1st to 15thNight
26%49%25%26%7%
2128
16th to endNight
30%313%23%24%5%
2013
April1st to 15thNight
30%5%13%24%18%8%
1798
16th to endNight
37%411%23%16%5%
1800
May1st to 15thNight
37%9%14%20%14%4
1599
16th to endNight
30%7%20%22%12%6%
1498
June1st to 15thNight
21%8%17%27%14%10%
1440
16th to endNight
17%5%13%24%28%9%
1440
July1st to 15thNight
31%8%13%20%16%9%
1360
16th to endNight
24%7%14%27%17%7%
1422
August1st to 15thNight
25%8%17%23%16%8%
1674
16th to endNight
24%5%12%24%24%8%
1910
September1st to 15thNight
26%5%13%21%19%14%
1800
16th to endNight
19%49%23%33%8%
1799
October1st to 15thNight
26%413%18%25%10%
1958
16th to endNight
24%38%26%26%11%
2153
November1st to 15thNight
21%39%24%26%14%
2275
16th to endNight
22%38%26%29%10%
2394
December1st to 15thNight
26%414%30%19%4
2520
16th to endNight
30%5%14%28%18%3
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
10%5%18%37%18%8%
90
16th to endDay
7%117%45%22%5%
96
February1st to 15thDay
5%7%26%53%6%
90
16th to endDay
2234%43%11%6%
81
March1st to 15thDay
5%12%22%43%14%1
120
16th to endDay
12%17%33%27%7%1
288
April1st to 15thDay
12%14%32%27%10%4
269
16th to endDay
24%14%31%19%7%1
270
May1st to 15thDay
17%6%22%31%19%2
438
16th to endDay
15%8%19%29%19%7%
517
June1st to 15thDay
7%223%30%27%9%
495
16th to endDay
4323%29%30%8%
495
July1st to 15thDay
11%114%26%35%10%
475
16th to endDay
6%114%22%42%12%
506
August1st to 15thDay
8%425%28%20%12%
315
16th to endDay
5%319%30%29%11%
332
September1st to 15thDay
7%420%32%23%11%
315
16th to endDay
5%214%38%21%17%
131
October1st to 15thDay
8%211%31%30%16%
90
16th to endDay
8%113%37%27%12%
96
November1st to 15thDay
2114%35%26%20%
90
16th to endDay
10%5%25%43%14%1
90
December1st to 15thDay
6%340%38%10%1
90
16th to endDay
6%123%55%12%1
96
January1st to 15thNight
3127%51%13%2
900
16th to endNight
5%229%49%11%1
825
February1st to 15thNight
7%130%52%8%
704
16th to endNight
6%433%49%6%
632
March1st to 15thNight
5%133%46%11%
720
16th to endNight
9%430%46%9%
669
April1st to 15thNight
10%6%33%43%6%
539
16th to endNight
18%426%39%11%
540
May1st to 15thNight
15%319%45%14%1
540
16th to endNight
10%220%43%21%1
563
June1st to 15thNight
7%218%49%20%1
540
16th to endNight
3115%52%27%
540
July1st to 15thNight
7%112%39%36%2
510
16th to endNight
49%41%42%1
564
August1st to 15thNight
5%110%44%36%2
539
16th to endNight
5%19%49%32%2
573
September1st to 15thNight
7%11%47%27%5%
540
16th to endNight
415%45%31%3
498
October1st to 15thNight
9%322%41%20%2
638
16th to endNight
8%117%51%18%2
745
November1st to 15thNight
5%222%51%16%1
875
16th to endNight
6%224%53%13%1
900
December1st to 15thNight
7%230%50%9%
900
16th to endNight
6%228%49%10%1
960
Page generated at 2017-09-18 06:38:23. Version ac04

Copyright 2017 A. Danko


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