This page made possible by the sponsorship of: Stephen Craig.

Battersea Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Battersea Observatory clear sky chart from 2005-11-05 to 2017-10-16.

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
29%
14844
14%
47194
8%
14813
36%
14813
17%
33091

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
13%
720
8%
2506
3%
716
20%
716
6%
2000
January16th to endNight
18%
768
11%
2598
4%
768
27%
768
11%
1947
February1st to 15thNight
14%
704
9%
2287
3%
701
22%
701
10%
1774
February16th to endNight
18%
631
13%
1955
5%
631
28%
631
14%
1454
March1st to 15thNight
19%
720
14%
2073
6%
720
27%
720
16%
1514
March16th to endNight
29%
768
20%
2050
9%
768
36%
768
23%
1406
April1st to 15thNight
20%
718
16%
1796
4%
718
26%
718
21%
1299
April16th to endNight
28%
675
17%
1755
7%
675
34%
675
23%
1220
May1st to 15thNight
37%
362
17%
1442
15%
362
45%
362
18%
925
May16th to endNight
36%
374
15%
1497
12%
374
47%
374
20%
899
June1st to 15thNight
36%
360
11%
1440
10%
360
45%
360
17%
931
June16th to endNight
46%
360
10%
1440
12%
360
53%
360
20%
908
July1st to 15thNight
49%
340
16%
1360
21%
340
55%
340
27%
750
July16th to endNight
54%
376
16%
1418
16%
354
59%
354
28%
780
August1st to 15thNight
49%
490
14%
1561
10%
488
53%
488
26%
953
August16th to endNight
52%
705
22%
1851
11%
705
57%
705
38%
1108
September1st to 15thNight
49%
720
19%
1800
9%
720
52%
720
33%
1164
September16th to endNight
50%
717
24%
1965
17%
717
55%
717
33%
1231
October1st to 15thNight
32%
720
17%
2160
11%
720
40%
720
20%
1485
October16th to endNight
22%
708
9%
2183
3%
708
29%
708
11%
1690
November1st to 15thNight
28%
700
17%
2329
13%
700
36%
700
17%
1602
November16th to endNight
21%
720
12%
2520
7%
720
29%
720
9%
1904
December1st to 15thNight
14%
720
7%
2520
2%
720
20%
720
7%
1965
December16th to endNight
13%
768
8%
2688
3%
768
19%
768
7%
2182

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
17%8%36%5%34446%33%
48232
Night
17%9%36%5%34446%34%
47364
Cloud CoverDay
17%8%36%5%3445%6%33%
48242
Night
17%9%36%5%34446%33%
47369
TransparencyDay
50%6%11%20%10%1
47920
Night
50%5%11%20%10%1
47194
SeeingDay
21%12%29%20%10%4
5602
Night
22%12%29%23%10%1
14845

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
21%13%47%6%25%435%25%
1432
16th to endDay
13%15%5%10%8%45%5%4422%
1623
February1st to 15thDay
15%13%5%12%7%36%5%4421%
1575
16th to endDay
18%13%6%7%7%26%43424%
1517
March1st to 15thDay
18%12%49%8%35%34425%
1873
16th to endDay
17%9%36%32344439%
2173
April1st to 15thDay
22%11%35%424335%33%
2152
16th to endDay
19%8%35%424336%37%
2215
May1st to 15thDay
19%8%36%4345%47%32%
2508
16th to endDay
15%5%35%5%3446%8%36%
2618
June1st to 15thDay
22%6%35%42445%8%32%
2520
16th to endDay
16%6%35%4345%6%7%35%
2520
July1st to 15thDay
12%425%435%6%7%9%39%
2520
16th to endDay
12%5%25%5%45%6%6%9%37%
2654
August1st to 15thDay
11%5%26%6%35%5%6%8%37%
2387
16th to endDay
12%5%24435%46%8%43%
2338
September1st to 15thDay
15%5%25%5%2445%7%43%
2160
16th to endDay
15%5%15%323346%47%
1994
October1st to 15thDay
21%7%25%5%23437%36%
1800
16th to endDay
26%9%46%5%34345%25%
1710
November1st to 15thDay
14%8%47%6%3445%7%34%
1527
16th to endDay
23%10%5%6%5%24445%26%
1440
December1st to 15thDay
22%15%5%7%5%345%45%20%
1440
16th to endDay
24%16%5%7%6%3333419%
1536
January1st to 15thNight
20%15%49%6%35%43420%
2506
16th to endNight
14%13%5%9%6%35%445%25%
2598
February1st to 15thNight
16%13%6%9%6%36%445%23%
2285
16th to endNight
17%10%47%7%45%435%28%
1955
March1st to 15thNight
19%11%46%6%2433431%
2061
16th to endNight
17%8%45%42333441%
2050
April1st to 15thNight
22%8%35%32434435%
1796
16th to endNight
18%6%245%3435%6%39%
1755
May1st to 15thNight
19%7%345%2445%6%37%
1442
16th to endNight
13%435%5%345%47%42%
1495
June1st to 15thNight
17%6%35%5%345%6%7%34%
1440
16th to endNight
14%5%245%345%6%8%38%
1440
July1st to 15thNight
9%325%5%25%5%48%47%
1440
16th to endNight
8%41343446%10%47%
1514
August1st to 15thNight
9%5%26%5%2446%9%43%
1571
16th to endNight
8%5%13423448%51%
1851
September1st to 15thNight
13%5%2442335%6%47%
1800
16th to endNight
15%42332345%8%47%
1965
October1st to 15thNight
20%6%25%42445%6%36%
2160
16th to endNight
24%10%37%6%3434426%
2183
November1st to 15thNight
18%8%35%5%245%46%34%
2329
16th to endNight
22%10%47%5%36%345%27%
2520
December1st to 15thNight
21%15%5%7%6%2434423%
2520
16th to endNight
24%14%5%8%6%44445%19%
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
23%12%5%7%6%35%335%24%
1432
16th to endDay
14%14%6%10%8%45%44421%
1623
February1st to 15thDay
15%14%5%11%8%45%445%19%
1575
16th to endDay
19%14%48%6%35%33424%
1517
March1st to 15thDay
19%11%5%9%7%45%33425%
1884
16th to endDay
17%9%35%42334439%
2172
April1st to 15thDay
22%10%35%324335%33%
2152
16th to endDay
18%8%26%334345%37%
2215
May1st to 15thDay
18%7%26%5%3445%7%32%
2508
16th to endDay
15%5%35%5%345%5%9%36%
2618
June1st to 15thDay
22%6%25%42435%8%33%
2520
16th to endDay
15%6%25%5%345%6%7%36%
2520
July1st to 15thDay
11%5%24435%5%6%9%41%
2520
16th to endDay
11%5%25%5%35%5%7%9%38%
2654
August1st to 15thDay
11%5%26%6%35%5%7%8%37%
2387
16th to endDay
11%5%244345%5%9%43%
2338
September1st to 15thDay
14%6%3442445%7%42%
2160
16th to endDay
15%5%2442235%6%46%
1994
October1st to 15thDay
21%6%25%42435%6%36%
1800
16th to endDay
27%8%37%5%34345%25%
1710
November1st to 15thDay
14%7%46%7%3445%7%33%
1527
16th to endDay
22%11%37%5%34446%26%
1440
December1st to 15thDay
22%15%5%8%6%3335%5%20%
1440
16th to endDay
25%15%5%8%5%3444418%
1536
January1st to 15thNight
20%15%5%9%6%34445%20%
2506
16th to endNight
14%15%5%8%6%35%35%5%25%
2598
February1st to 15thNight
16%13%6%9%6%46%45%423%
2278
16th to endNight
18%10%48%7%35%44428%
1955
March1st to 15thNight
20%11%46%5%2433431%
2073
16th to endNight
17%7%46%423335%41%
2050
April1st to 15thNight
23%7%44423445%35%
1796
16th to endNight
18%6%245%34346%39%
1755
May1st to 15thNight
19%7%2443345%6%36%
1442
16th to endNight
13%5%25%6%35%5%5%7%41%
1495
June1st to 15thNight
18%5%35%44446%8%34%
1440
16th to endNight
14%415%5%35%5%6%8%38%
1440
July1st to 15thNight
8%4245%35%5%6%7%47%
1440
16th to endNight
8%42433446%9%47%
1514
August1st to 15thNight
9%5%25%5%345%7%8%42%
1571
16th to endNight
9%42432445%7%51%
1851
September1st to 15thNight
13%5%2442335%7%47%
1800
16th to endNight
14%42432436%7%46%
1965
October1st to 15thNight
20%6%25%5%2435%6%36%
2160
16th to endNight
24%9%37%5%34445%25%
2183
November1st to 15thNight
17%8%35%434446%34%
2329
16th to endNight
22%10%46%5%35%436%27%
2520
December1st to 15thNight
22%14%49%6%33345%23%
2520
16th to endNight
24%14%48%6%35%445%18%
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
62%410%15%6%
1433
16th to endDay
63%6%9%11%8%
1623
February1st to 15thDay
65%49%14%4
1577
16th to endDay
62%5%9%12%9%1
1517
March1st to 15thDay
63%310%15%6%1
1884
16th to endDay
47%48%19%15%4
2173
April1st to 15thDay
53%47%18%12%2
2152
16th to endDay
48%48%20%14%3
2215
May1st to 15thDay
49%6%9%19%13%2
2508
16th to endDay
43%6%14%21%11%1
2622
June1st to 15thDay
49%6%11%20%10%
2520
16th to endDay
45%6%13%21%11%
2520
July1st to 15thDay
36%8%13%27%12%
2371
16th to endDay
41%8%16%23%9%
2487
August1st to 15thDay
40%8%16%22%10%
2373
16th to endDay
36%6%15%29%11%
2338
September1st to 15thDay
39%6%14%26%12%
2160
16th to endDay
37%6%11%31%12%
1994
October1st to 15thDay
48%5%12%22%10%
1800
16th to endDay
60%6%11%16%5%
1710
November1st to 15thDay
48%7%14%19%9%
1527
16th to endDay
57%7%12%15%6%
1440
December1st to 15thDay
65%6%12%12%3
1440
16th to endDay
69%5%8%12%3
1536
January1st to 15thNight
65%6%8%13%5%
2506
16th to endNight
59%5%10%16%7%
2598
February1st to 15thNight
62%5%12%15%4
2287
16th to endNight
57%411%17%8%
1955
March1st to 15thNight
56%311%21%7%
2073
16th to endNight
46%39%20%17%2
2050
April1st to 15thNight
50%38%19%15%1
1796
16th to endNight
45%5%9%18%17%3
1755
May1st to 15thNight
46%410%18%14%4
1442
16th to endNight
40%6%13%21%14%2
1497
June1st to 15thNight
47%5%13%21%11%
1440
16th to endNight
41%7%13%20%14%1
1440
July1st to 15thNight
33%6%11%29%18%1
1360
16th to endNight
31%7%15%29%14%1
1418
August1st to 15thNight
36%7%16%25%12%
1561
16th to endNight
30%5%15%33%14%
1851
September1st to 15thNight
36%5%13%31%11%1
1800
16th to endNight
35%5%11%32%14%
1965
October1st to 15thNight
47%5%11%22%12%
2160
16th to endNight
59%6%12%13%6%
2183
November1st to 15thNight
47%7%14%18%10%1
2329
16th to endNight
59%6%10%17%6%
2520
December1st to 15thNight
63%6%13%14%3
2520
16th to endNight
67%6%10%10%4
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
21%28%28%11%8%1
60
16th to endDay
34%13%29%17%5%
79
February1st to 15thDay
27%35%33%3
90
16th to endDay
30%20%30%14%3
176
March1st to 15thDay
25%18%27%21%6%
270
16th to endDay
25%16%32%15%7%1
288
April1st to 15thDay
28%19%29%12%9%
270
16th to endDay
20%22%26%17%8%5%
270
May1st to 15thDay
29%9%28%19%9%3
288
16th to endDay
19%13%33%19%9%4
331
June1st to 15thDay
26%8%34%20%8%2
315
16th to endDay
20%9%29%25%12%2
315
July1st to 15thDay
13%9%26%29%15%5%
305
16th to endDay
14%5%30%30%13%5%
326
August1st to 15thDay
13%5%27%30%16%7%
313
16th to endDay
14%6%25%24%18%10%
332
September1st to 15thDay
14%7%27%21%16%12%
315
16th to endDay
16%8%24%22%19%8%
314
October1st to 15thDay
26%12%26%18%11%4
315
16th to endDay
31%16%29%17%3
265
November1st to 15thDay
19%12%34%23%7%2
181
16th to endDay
28%8%33%20%10%
60
December1st to 15thDay
23%23%31%16%5%
60
16th to endDay
37%31%26%4
64
January1st to 15thNight
31%18%28%16%4
720
16th to endNight
23%15%34%21%4
768
February1st to 15thNight
23%18%35%19%2
704
16th to endNight
24%13%36%19%4
631
March1st to 15thNight
27%14%34%20%2
720
16th to endNight
21%14%30%23%9%
768
April1st to 15thNight
25%15%33%21%4
718
16th to endNight
21%13%31%20%11%
675
May1st to 15thNight
22%7%28%31%9%
362
16th to endNight
12%8%36%29%12%1
375
June1st to 15thNight
20%8%29%29%11%1
360
16th to endNight
16%327%38%13%
360
July1st to 15thNight
8%329%39%18%1
340
16th to endNight
10%227%41%17%1
376
August1st to 15thNight
12%326%31%23%2
490
16th to endNight
10%427%34%20%2
705
September1st to 15thNight
16%5%24%29%20%3
720
16th to endNight
15%8%22%25%23%4
717
October1st to 15thNight
24%11%26%20%15%2
720
16th to endNight
30%13%27%23%5%
708
November1st to 15thNight
23%13%30%21%10%
700
16th to endNight
29%18%25%16%9%
720
December1st to 15thNight
30%20%29%15%4
720
16th to endNight
32%16%31%16%11
768
Page generated at 2017-10-17 16:35:18. Version ac04

Copyright 2017 A. Danko


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