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 2017-04-28.

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
59%
15524
27%
45639
20%
15485
65%
15485
41%
25200

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
51%
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
61%
669
39%
1124
April1st to 15thNight
45%
539
22%
1798
16%
539
56%
539
33%
992
April16th to endNight
47%
534
21%
1780
19%
534
54%
534
29%
1057
May1st to 15thNight
53%
495
19%
1466
17%
495
56%
495
26%
955
May16th to endNight
58%
514
17%
1370
12%
513
62%
513
38%
822
June1st to 15thNight
67%
495
22%
1320
17%
495
69%
495
43%
759
June16th to endNight
74%
495
24%
1320
19%
495
77%
495
55%
680
July1st to 15thNight
68%
465
17%
1240
15%
465
69%
465
35%
776
July16th to endNight
75%
522
26%
1309
24%
489
76%
489
44%
733
August1st to 15thNight
73%
494
20%
1534
21%
491
74%
491
37%
830
August16th to endNight
77%
525
26%
1750
29%
525
79%
525
40%
913
September1st to 15thNight
69%
495
29%
1650
30%
495
73%
495
37%
885
September16th to endNight
74%
492
35%
1779
36%
492
80%
492
47%
807
October1st to 15thNight
59%
638
28%
1958
20%
638
65%
638
41%
1051
October16th to endNight
65%
745
34%
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
67%
900
51%
1287
December1st to 15thNight
53%
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%
46069
Night
5%5%2442345%7%55%
45812
Cloud CoverDay
6%42432445%8%53%
46067
Night
5%5%24323447%56%
45812
TransparencyDay
27%5%11%24%21%8%
45744
Night
27%5%12%25%21%8%
45639
SeeingDay
10%5%22%31%22%6%
5228
Night
7%223%48%17%1
15534

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%44%
2127
May1st to 15thDay
12%6%24335%46%8%41%
2152
16th to endDay
8%423425%5%7%8%45%
2392
June1st to 15thDay
6%3135%35%5%6%9%48%
2310
16th to endDay
2123246%9%10%54%
2310
July1st to 15thDay
7%314425%5%7%10%47%
2310
16th to endDay
43134346%7%10%50%
2452
August1st to 15thDay
4224437%7%7%11%44%
2085
16th to endDay
5%213435%6%6%9%52%
2100
September1st to 15thDay
7%3133335%5%6%56%
1980
16th to endDay
4312412435%65%
1851
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
14%6%23424246%47%
1780
May1st to 15thNight
14%5%2342446%7%43%
1465
16th to endNight
7%41442425%9%52%
1369
June1st to 15thNight
6%2133145%5%9%56%
1320
16th to endNight
12123235%7%8%60%
1320
July1st to 15thNight
5%4245%35%5%5%9%48%
1320
16th to endNight
32243345%6%11%52%
1405
August1st to 15thNight
44134245%7%9%52%
1543
16th to endNight
5%3143246%6%8%53%
1750
September1st to 15thNight
7%2135%2346%7%53%
1650
16th to endNight
4213213446%64%
1779
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%44%
2127
May1st to 15thDay
14%5%2442446%7%41%
2152
16th to endDay
10%42343446%9%46%
2392
June1st to 15thDay
7%3135%35%5%6%8%49%
2310
16th to endDay
21133246%8%9%56%
2310
July1st to 15thDay
8%214335%46%10%49%
2310
16th to endDay
5%213425%5%8%9%51%
2452
August1st to 15thDay
4224436%7%7%10%45%
2085
16th to endDay
6%213335%5%7%8%53%
2100
September1st to 15thDay
7%31332445%7%56%
1980
16th to endDay
433322345%66%
1851
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%23323346%47%
1780
May1st to 15thNight
15%424424447%44%
1465
16th to endNight
7%42442436%8%52%
1369
June1st to 15thNight
6%31232435%9%57%
1320
16th to endNight
21123136%7%7%62%
1320
July1st to 15thNight
7%3235%345%6%8%49%
1320
16th to endNight
42134245%6%10%53%
1405
August1st to 15thNight
5%2134245%6%9%53%
1543
16th to endNight
6%32342446%8%53%
1750
September1st to 15thNight
8%2235%2446%7%53%
1650
16th to endNight
5%21331245%6%64%
1779
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%21%18%4
2127
May1st to 15thDay
38%8%12%24%13%3
2152
16th to endDay
34%7%14%22%14%6%
2396
June1st to 15thDay
29%9%13%18%19%10%
2310
16th to endDay
19%7%12%19%28%12%
2310
July1st to 15thDay
30%8%11%20%16%13%
2161
16th to endDay
26%8%13%23%18%9%
2285
August1st to 15thDay
30%8%14%18%15%11%
2070
16th to endDay
25%8%10%22%24%9%
2100
September1st to 15thDay
25%5%9%21%21%16%
1980
16th to endDay
19%47%21%36%10%
1851
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%412%23%16%5%
1780
May1st to 15thNight
37%9%14%19%13%4
1466
16th to endNight
29%7%21%21%11%7%
1370
June1st to 15thNight
23%9%18%26%14%9%
1320
16th to endNight
17%5%14%24%28%10%
1320
July1st to 15thNight
31%8%13%21%14%9%
1240
16th to endNight
23%7%14%28%17%7%
1309
August1st to 15thNight
26%7%16%23%17%9%
1534
16th to endNight
25%5%13%24%22%9%
1750
September1st to 15thNight
28%5%13%19%18%15%
1650
16th to endNight
19%49%23%33%8%
1779
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
23%15%32%19%7%1
259
May1st to 15thDay
18%7%21%32%18%1
365
16th to endDay
15%8%19%29%21%6%
437
June1st to 15thDay
9%223%29%27%7%
420
16th to endDay
4322%29%32%8%
420
July1st to 15thDay
12%116%27%35%7%
400
16th to endDay
6%216%23%42%9%
437
August1st to 15thDay
7%426%27%19%13%
255
16th to endDay
6%322%31%25%10%
268
September1st to 15thDay
8%423%35%23%4
255
16th to endDay
4212%39%22%18%
126
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
17%326%40%11%
534
May1st to 15thNight
16%420%44%14%1
495
16th to endNight
9%221%43%21%1
515
June1st to 15thNight
8%218%51%18%1
495
16th to endNight
2115%52%27%
495
July1st to 15thNight
7%113%41%34%2
465
16th to endNight
49%42%42%1
522
August1st to 15thNight
6%110%43%37%2
494
16th to endNight
5%19%49%32%2
525
September1st to 15thNight
8%112%49%25%3
495
16th to endNight
415%45%31%3
492
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 2017-04-29 07:44:59. Version ac04

Copyright 2017 A. Danko


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