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 2018-08-29.

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%
17224
27%
50601
20%
17185
66%
17185
41%
27917

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%
972
29%
2716
21%
970
65%
970
46%
1463
January16th to endNight
55%
894
33%
2766
27%
894
63%
894
42%
1472
February1st to 15thNight
50%
758
24%
2431
18%
758
59%
758
36%
1348
February16th to endNight
48%
684
30%
2050
18%
684
59%
684
38%
1161
March1st to 15thNight
54%
780
29%
2305
17%
780
63%
780
44%
1237
March16th to endNight
52%
725
26%
2181
16%
725
61%
725
39%
1218
April1st to 15thNight
44%
584
22%
1948
16%
584
54%
584
32%
1095
April16th to endNight
47%
579
20%
1929
18%
579
54%
579
29%
1146
May1st to 15thNight
53%
585
18%
1732
17%
585
55%
585
27%
1129
May16th to endNight
59%
610
18%
1626
13%
609
62%
609
37%
985
June1st to 15thNight
68%
585
22%
1560
17%
585
71%
585
47%
871
June16th to endNight
72%
585
24%
1560
20%
585
74%
585
53%
821
July1st to 15thNight
70%
555
19%
1480
17%
555
71%
555
37%
906
July16th to endNight
75%
612
26%
1551
23%
579
75%
579
42%
883
August1st to 15thNight
74%
575
19%
1784
20%
572
75%
572
37%
969
August16th to endNight
77%
615
27%
2050
30%
615
79%
615
41%
1053
September1st to 15thNight
71%
540
27%
1800
29%
540
75%
540
38%
947
September16th to endNight
71%
537
34%
1941
34%
537
78%
537
45%
909
October1st to 15thNight
59%
696
28%
2136
20%
696
65%
696
41%
1146
October16th to endNight
64%
813
36%
2349
24%
813
70%
813
47%
1237
November1st to 15thNight
64%
950
32%
2470
19%
950
69%
950
52%
1332
November16th to endNight
61%
975
35%
2594
23%
975
67%
975
51%
1385
December1st to 15thNight
54%
975
25%
2730
16%
975
61%
975
44%
1513
December16th to endNight
52%
1040
28%
2912
18%
1040
60%
1040
38%
1691

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%
51661
Night
5%5%2442345%7%55%
50774
Cloud CoverDay
6%42432446%8%53%
51659
Night
5%5%2432345%7%56%
50774
TransparencyDay
27%6%11%24%21%8%
51336
Night
26%5%12%25%22%8%
50601
SeeingDay
9%5%22%31%22%7%
7143
Night
7%223%48%17%1
17234

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%34313247%59%
1552
16th to endDay
25%34423348%58%
1820
February1st to 15thDay
26%45%41446%8%52%
1760
16th to endDay
25%25%423446%57%
1710
March1st to 15thDay
35%2443345%9%53%
1982
16th to endDay
6%6%2432446%8%50%
2393
April1st to 15thDay
8%6%24324348%51%
2330
16th to endDay
11%8%2442445%7%44%
2306
May1st to 15thDay
11%6%24435%5%6%8%41%
2545
16th to endDay
9%423435%5%7%8%44%
2840
June1st to 15thDay
5%313435%5%6%9%50%
2730
16th to endDay
3123246%8%10%53%
2730
July1st to 15thDay
6%314425%5%7%11%48%
2730
16th to endDay
4314435%6%7%10%48%
2870
August1st to 15thDay
42245%37%7%7%10%44%
2417
16th to endDay
4213435%6%6%8%52%
2449
September1st to 15thDay
6%31233345%7%57%
2160
16th to endDay
5%412322435%63%
2019
October1st to 15thDay
7%313324347%59%
1821
16th to endDay
6%413212235%66%
1862
November1st to 15thDay
25%23314447%58%
1718
16th to endDay
243331235%8%61%
1693
December1st to 15thDay
35%25%42335%8%56%
1560
16th to endDay
47%2443235%7%53%
1664
January1st to 15thNight
15%34423346%60%
2716
16th to endNight
36%34313335%59%
2766
February1st to 15thNight
27%45%423447%52%
2421
16th to endNight
39%35%424345%54%
2050
March1st to 15thNight
35%24423347%57%
2305
16th to endNight
7%6%2432335%7%54%
2181
April1st to 15thNight
8%7%33423446%51%
1948
16th to endNight
14%6%23424346%47%
1929
May1st to 15thNight
15%5%2342445%7%42%
1731
16th to endNight
7%42442435%8%51%
1625
June1st to 15thNight
5%2123145%5%9%59%
1560
16th to endNight
321232347%8%59%
1560
July1st to 15thNight
5%3145%35%5%5%9%50%
1560
16th to endNight
33243245%6%10%52%
1647
August1st to 15thNight
4313425%5%7%9%52%
1793
16th to endNight
43143245%6%8%53%
2050
September1st to 15thNight
7%2135%2346%7%55%
1800
16th to endNight
5%313213446%63%
1941
October1st to 15thNight
8%423323345%58%
2136
16th to endNight
6%413312345%61%
2349
November1st to 15thNight
3314322446%62%
2470
16th to endNight
35%14313347%61%
2594
December1st to 15thNight
45%34323347%56%
2730
16th to endNight
38%3342445%7%52%
2912

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%24313337%59%
1552
16th to endDay
26%24413437%58%
1820
February1st to 15thDay
36%45%42445%7%52%
1760
16th to endDay
26%25%424346%58%
1710
March1st to 15thDay
35%15%42345%8%54%
1982
16th to endDay
6%6%2432446%8%50%
2391
April1st to 15thDay
9%6%2432435%8%50%
2330
16th to endDay
12%6%25%33445%7%44%
2306
May1st to 15thDay
13%5%24425%5%7%7%40%
2545
16th to endDay
10%4234345%6%9%45%
2840
June1st to 15thDay
6%313435%5%6%8%51%
2730
16th to endDay
31133246%8%9%54%
2730
July1st to 15thDay
7%213335%5%6%10%49%
2730
16th to endDay
5%323425%5%8%10%49%
2870
August1st to 15thDay
4214436%7%8%10%45%
2417
16th to endDay
5%213425%5%7%8%53%
2449
September1st to 15thDay
6%31332445%7%57%
2160
16th to endDay
5%313323345%64%
2019
October1st to 15thDay
7%313413346%59%
1821
16th to endDay
6%412212335%66%
1862
November1st to 15thDay
25%1341435%7%58%
1718
16th to endDay
232331235%8%61%
1693
December1st to 15thDay
35%25%423348%55%
1560
16th to endDay
46%25%42345%7%52%
1664
January1st to 15thNight
25%34423346%60%
2716
16th to endNight
36%34312335%59%
2766
February1st to 15thNight
38%45%423446%52%
2421
16th to endNight
38%35%323345%55%
2050
March1st to 15thNight
35%24433346%57%
2305
16th to endNight
7%6%24323346%54%
2181
April1st to 15thNight
9%6%24423446%51%
1948
16th to endNight
15%6%24323346%47%
1929
May1st to 15thNight
15%4244245%48%43%
1731
16th to endNight
8%5%2441435%8%51%
1625
June1st to 15thNight
5%3231435%8%60%
1560
16th to endNight
41123136%6%7%60%
1560
July1st to 15thNight
6%3235%345%6%8%51%
1560
16th to endNight
43233245%6%9%53%
1647
August1st to 15thNight
5%213425%5%6%10%53%
1793
16th to endNight
5%3234145%6%8%53%
2050
September1st to 15thNight
7%2135%2446%7%55%
1800
16th to endNight
6%21231235%6%62%
1941
October1st to 15thNight
8%413323345%58%
2136
16th to endNight
6%413323245%62%
2349
November1st to 15thNight
3413323446%61%
2470
16th to endNight
35%24313347%61%
2594
December1st to 15thNight
46%24323347%56%
2730
16th to endNight
48%2442345%7%52%
2912

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
24%312%30%23%4
1553
16th to endDay
23%311%32%21%7%
1820
February1st to 15thDay
28%5%15%32%13%3
1761
16th to endDay
25%39%29%26%5%
1710
March1st to 15thDay
26%411%25%23%9%
1982
16th to endDay
29%5%14%24%20%5%
2393
April1st to 15thDay
30%411%24%20%8%
2330
16th to endDay
36%6%12%20%19%4
2306
May1st to 15thDay
38%8%11%24%13%3
2545
16th to endDay
33%8%14%22%15%5%
2844
June1st to 15thDay
27%8%12%19%19%12%
2730
16th to endDay
20%6%12%20%27%12%
2730
July1st to 15thDay
28%8%11%19%19%13%
2581
16th to endDay
27%8%13%23%18%8%
2703
August1st to 15thDay
30%9%13%19%15%10%
2402
16th to endDay
26%7%10%21%24%9%
2449
September1st to 15thDay
24%5%9%21%21%16%
2160
16th to endDay
21%47%20%35%10%
2019
October1st to 15thDay
24%5%10%19%27%11%
1821
16th to endDay
21%27%26%28%12%
1862
November1st to 15thDay
22%410%25%26%11%
1718
16th to endDay
19%39%25%32%10%
1693
December1st to 15thDay
26%412%31%19%4
1560
16th to endDay
29%414%26%19%5%
1664
January1st to 15thNight
23%411%30%24%5%
2716
16th to endNight
26%38%28%25%7%
2766
February1st to 15thNight
30%413%30%17%3
2431
16th to endNight
30%37%25%23%9%
2050
March1st to 15thNight
25%48%25%27%8%
2305
16th to endNight
30%313%24%23%5%
2181
April1st to 15thNight
31%5%12%24%17%7%
1948
16th to endNight
37%411%24%17%5%
1929
May1st to 15thNight
38%9%14%20%13%3
1732
16th to endNight
30%7%20%22%12%6%
1626
June1st to 15thNight
20%8%16%26%16%11%
1560
16th to endNight
19%5%13%24%27%9%
1560
July1st to 15thNight
29%8%12%21%18%9%
1480
16th to endNight
24%8%15%26%17%7%
1551
August1st to 15thNight
25%8%17%24%16%8%
1784
16th to endNight
24%5%13%24%23%8%
2050
September1st to 15thNight
26%5%13%21%19%14%
1800
16th to endNight
21%410%23%31%9%
1941
October1st to 15thNight
26%413%19%25%11%
2136
16th to endNight
23%38%25%26%12%
2349
November1st to 15thNight
21%39%25%26%13%
2470
16th to endNight
22%38%26%28%10%
2594
December1st to 15thNight
26%413%28%19%6%
2730
16th to endNight
30%414%28%19%3
2912

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
8%419%44%17%5%
135
16th to endDay
5%120%47%20%4
144
February1st to 15thDay
5%9%33%45%6%
135
16th to endDay
1135%49%7%4
120
March1st to 15thDay
5%10%26%42%14%1
167
16th to endDay
12%16%32%29%7%1
352
April1st to 15thDay
11%15%33%28%8%3
329
16th to endDay
24%13%30%18%10%3
318
May1st to 15thDay
17%5%22%31%19%3
510
16th to endDay
14%7%20%28%21%7%
597
June1st to 15thDay
7%222%31%26%9%
570
16th to endDay
6%223%30%28%7%
570
July1st to 15thDay
10%114%25%37%10%
550
16th to endDay
6%115%23%40%12%
585
August1st to 15thDay
7%425%30%21%11%
359
16th to endDay
6%321%29%28%11%
385
September1st to 15thDay
7%420%32%23%11%
315
16th to endDay
10%215%37%20%13%
174
October1st to 15thDay
12%214%31%25%12%
135
16th to endDay
7%420%34%23%10%
144
November1st to 15thDay
2119%42%21%13%
135
16th to endDay
8%425%45%14%
135
December1st to 15thDay
5%5%36%39%11%2
135
16th to endDay
6%25%52%13%
144
January1st to 15thNight
4126%52%12%2
975
16th to endNight
5%228%50%11%1
894
February1st to 15thNight
6%130%52%8%
764
16th to endNight
5%433%50%5%
684
March1st to 15thNight
5%233%47%10%
780
16th to endNight
9%429%46%9%
725
April1st to 15thNight
11%6%33%42%5%
584
16th to endNight
17%426%38%12%
579
May1st to 15thNight
16%319%43%15%1
585
16th to endNight
10%219%44%21%
611
June1st to 15thNight
6%218%49%21%2
585
16th to endNight
4115%52%25%
585
July1st to 15thNight
7%113%40%35%2
555
16th to endNight
49%42%40%2
612
August1st to 15thNight
5%19%44%36%1
575
16th to endNight
5%9%49%32%2
615
September1st to 15thNight
7%11%47%27%5%
540
16th to endNight
5%16%44%28%2
537
October1st to 15thNight
10%321%42%19%2
696
16th to endNight
8%117%50%18%2
813
November1st to 15thNight
5%222%52%15%1
950
16th to endNight
6%125%53%12%1
975
December1st to 15thNight
7%229%50%9%
975
16th to endNight
6%228%50%10%1
1040
Page generated at 2018-08-30 03:34:22. Version ac04

Copyright 2018 A. Danko


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