Bolton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bolton clear sky chart from 2005-11-05 to 2017-10-06.

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
26%
14968
18%
47029
7%
14936
38%
14936
20%
30778

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%
720
19%
2506
6%
716
32%
716
16%
1606
January16th to endNight
14%
768
19%
2688
4%
768
34%
768
15%
1708
February1st to 15thNight
14%
704
16%
2193
4%
701
29%
701
16%
1485
February16th to endNight
16%
631
23%
1893
6%
631
36%
631
18%
1250
March1st to 15thNight
17%
720
16%
2160
5%
720
30%
720
16%
1499
March16th to endNight
20%
768
22%
2022
7%
768
32%
768
21%
1376
April1st to 15thNight
20%
718
17%
1796
3%
718
29%
718
21%
1284
April16th to endNight
21%
599
18%
1679
4%
599
31%
599
19%
1151
May1st to 15thNight
23%
540
15%
1620
7%
540
31%
540
17%
1138
May16th to endNight
26%
402
11%
1524
7%
401
34%
401
14%
1027
June1st to 15thNight
30%
360
12%
1440
8%
360
42%
360
15%
969
June16th to endNight
33%
360
11%
1440
10%
360
42%
360
20%
886
July1st to 15thNight
43%
340
11%
1360
13%
340
49%
340
22%
828
July16th to endNight
47%
376
15%
1418
13%
354
53%
354
22%
854
August1st to 15thNight
44%
495
16%
1566
11%
493
49%
493
26%
977
August16th to endNight
51%
734
20%
1880
10%
734
54%
734
35%
1208
September1st to 15thNight
38%
720
19%
1854
9%
720
44%
720
31%
1205
September16th to endNight
45%
717
25%
1980
17%
717
52%
717
34%
1212
October1st to 15thNight
33%
684
22%
1908
11%
684
44%
684
26%
1227
October16th to endNight
23%
704
16%
2286
5%
704
38%
704
19%
1500
November1st to 15thNight
28%
700
21%
2277
10%
700
43%
700
22%
1457
November16th to endNight
24%
720
20%
2340
8%
720
38%
720
18%
1508
December1st to 15thNight
20%
720
17%
2511
5%
720
34%
720
16%
1626
December16th to endNight
14%
768
18%
2688
4%
768
31%
768
15%
1797

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
16%6%25%43445%6%39%
48169
Night
16%6%25%424446%41%
47199
Cloud CoverDay
16%6%25%43445%6%39%
48179
Night
16%6%25%424446%41%
47204
TransparencyDay
43%6%12%20%14%2
47857
Night
43%5%12%21%14%2
47029
SeeingDay
21%14%32%20%8%2
5950
Night
21%13%34%23%7%
14968

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
15%8%25%435%445%40%
1432
16th to endDay
14%5%245%24445%44%
1536
February1st to 15thDay
16%6%36%435%6%5%7%33%
1665
16th to endDay
14%8%36%5%24425%40%
1580
March1st to 15thDay
21%7%3442445%6%36%
1790
16th to endDay
17%7%35%423346%41%
2198
April1st to 15thDay
17%7%35%6%24446%38%
2152
16th to endDay
17%424424447%41%
2280
May1st to 15thDay
24%8%35%434446%31%
2332
16th to endDay
16%5%35%425%36%7%38%
2599
June1st to 15thDay
24%5%2343346%7%33%
2520
16th to endDay
15%4246%45%6%6%8%34%
2520
July1st to 15thDay
11%5%26%5%35%6%5%8%37%
2520
16th to endDay
12%5%25%5%36%6%6%8%39%
2654
August1st to 15thDay
11%5%26%5%36%5%6%8%38%
2370
16th to endDay
10%425%5%35%5%5%7%44%
2321
September1st to 15thDay
13%6%234245%46%45%
2105
16th to endDay
13%5%25%324245%50%
1980
October1st to 15thDay
19%424424446%42%
1848
16th to endDay
16%6%245%335%46%43%
1584
November1st to 15thDay
20%6%2332334344%
1581
16th to endDay
16%5%2442445%444%
1620
December1st to 15thDay
17%6%25%5%2335%5%40%
1446
16th to endDay
21%9%2442445%5%36%
1536
January1st to 15thNight
16%7%35%424436%41%
2506
16th to endNight
15%9%35%423346%40%
2688
February1st to 15thNight
14%8%36%5%3436%6%38%
2192
16th to endNight
15%8%25%423346%40%
1893
March1st to 15thNight
18%7%35%325%446%37%
2147
16th to endNight
13%8%45%42433445%
2022
April1st to 15thNight
16%6%26%5%3445%6%38%
1796
16th to endNight
20%5%25%5%23345%40%
1679
May1st to 15thNight
21%7%25%5%2345%5%36%
1620
16th to endNight
18%7%25%43445%8%35%
1522
June1st to 15thNight
22%6%3442435%8%35%
1440
16th to endNight
15%424425%5%5%7%40%
1440
July1st to 15thNight
12%5%146%25%5%5%8%41%
1440
16th to endNight
11%5%246%35%5%5%8%42%
1514
August1st to 15thNight
10%3236%35%6%5%8%44%
1576
16th to endNight
12%3143245%5%9%46%
1880
September1st to 15thNight
13%4145%2345%6%47%
1854
16th to endNight
13%5%13313337%51%
1980
October1st to 15thNight
19%42432235%5%47%
1908
16th to endNight
19%7%24324346%40%
2286
November1st to 15thNight
17%6%24423345%45%
2277
16th to endNight
18%6%24324445%41%
2340
December1st to 15thNight
18%7%24424346%40%
2511
16th to endNight
17%8%36%32345%5%38%
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
15%7%35%5%25%346%40%
1432
16th to endDay
15%5%244245%46%43%
1536
February1st to 15thDay
16%6%35%435%46%7%33%
1665
16th to endDay
14%8%26%6%34425%40%
1580
March1st to 15thDay
21%7%3442445%6%35%
1800
16th to endDay
18%7%25%424347%41%
2198
April1st to 15thDay
17%7%35%433445%38%
2152
16th to endDay
18%4245%3445%6%40%
2280
May1st to 15thDay
24%8%25%424346%31%
2332
16th to endDay
17%425%5%3435%7%39%
2599
June1st to 15thDay
25%5%2443445%7%33%
2520
16th to endDay
15%425%6%36%6%7%8%34%
2520
July1st to 15thDay
12%5%25%5%35%5%6%8%37%
2520
16th to endDay
11%5%25%5%46%5%5%8%38%
2654
August1st to 15thDay
11%5%25%6%46%45%9%38%
2370
16th to endDay
10%424435%5%5%7%44%
2321
September1st to 15thDay
14%5%24424446%46%
2105
16th to endDay
14%5%24323345%50%
1980
October1st to 15thDay
19%5%15%423346%43%
1848
16th to endDay
16%5%245%23445%43%
1584
November1st to 15thDay
21%6%2332334444%
1581
16th to endDay
16%5%25%42435%5%43%
1620
December1st to 15thDay
16%7%35%5%14346%40%
1446
16th to endDay
23%7%244245%45%36%
1536
January1st to 15thNight
16%8%34424335%40%
2506
16th to endNight
15%9%35%42335%5%41%
2688
February1st to 15thNight
14%9%26%5%2445%5%38%
2185
16th to endNight
16%9%34423345%41%
1893
March1st to 15thNight
18%8%35%435%446%36%
2160
16th to endNight
14%8%45%42433444%
2021
April1st to 15thNight
16%7%36%5%33445%37%
1796
16th to endNight
20%6%245%2434440%
1679
May1st to 15thNight
21%6%15%42435%5%36%
1620
16th to endNight
17%7%246%3345%8%35%
1522
June1st to 15thNight
22%5%345%24447%34%
1440
16th to endNight
14%5%24435%5%6%8%39%
1440
July1st to 15thNight
12%5%25%5%35%45%9%40%
1440
16th to endNight
11%435%5%3445%9%41%
1514
August1st to 15thNight
10%3245%35%5%6%7%44%
1576
16th to endNight
12%3144235%6%8%46%
1880
September1st to 15thNight
13%4245%2345%6%47%
1854
16th to endNight
14%5%23223436%51%
1980
October1st to 15thNight
19%5%23322346%46%
1908
16th to endNight
20%6%24323346%40%
2286
November1st to 15thNight
17%6%25%322445%44%
2277
16th to endNight
19%6%24424446%41%
2340
December1st to 15thNight
18%7%25%424346%39%
2511
16th to endNight
17%9%36%32445%5%37%
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
44%5%11%24%11%3
1433
16th to endDay
39%6%12%25%13%1
1536
February1st to 15thDay
46%7%14%18%12%
1668
16th to endDay
46%49%22%13%3
1580
March1st to 15thDay
49%411%19%11%3
1800
16th to endDay
44%410%20%14%5%
2198
April1st to 15thDay
46%5%11%18%15%2
2152
16th to endDay
42%5%10%19%18%3
2280
May1st to 15thDay
54%5%8%17%12%2
2332
16th to endDay
44%7%12%20%12%2
2603
June1st to 15thDay
49%6%13%19%9%
2520
16th to endDay
43%9%12%18%13%
2520
July1st to 15thDay
42%8%11%20%14%1
2371
16th to endDay
40%9%14%19%12%3
2487
August1st to 15thDay
42%8%14%22%12%1
2356
16th to endDay
37%7%12%24%16%1
2321
September1st to 15thDay
37%6%12%21%19%2
2105
16th to endDay
36%38%23%24%2
1980
October1st to 15thDay
42%410%24%14%3
1848
16th to endDay
40%6%13%22%14%1
1584
November1st to 15thDay
44%413%22%14%1
1581
16th to endDay
41%5%13%21%16%1
1620
December1st to 15thDay
44%417%16%16%
1446
16th to endDay
49%6%13%17%11%
1536
January1st to 15thNight
46%412%21%13%2
2506
16th to endNight
44%412%20%15%2
2688
February1st to 15thNight
46%5%13%20%11%2
2193
16th to endNight
45%39%22%15%2
1893
March1st to 15thNight
47%5%10%19%12%3
2160
16th to endNight
43%49%17%19%5%
2022
April1st to 15thNight
47%5%10%18%16%2
1796
16th to endNight
45%5%8%18%16%4
1679
May1st to 15thNight
49%5%9%17%14%2
1620
16th to endNight
47%8%14%17%10%1
1524
June1st to 15thNight
48%7%12%20%9%1
1440
16th to endNight
39%8%13%22%14%1
1440
July1st to 15thNight
38%8%13%24%13%
1360
16th to endNight
38%8%15%24%10%2
1418
August1st to 15thNight
36%9%14%22%15%1
1566
16th to endNight
33%7%13%27%17%
1880
September1st to 15thNight
37%6%13%23%18%
1854
16th to endNight
34%48%23%27%1
1980
October1st to 15thNight
39%5%12%23%16%3
1908
16th to endNight
45%413%22%13%
2286
November1st to 15thNight
41%5%11%20%17%3
2277
16th to endNight
43%5%12%21%14%2
2340
December1st to 15thNight
45%5%14%22%12%
2511
16th to endNight
47%5%12%22%11%
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
23%30%25%20%1
60
16th to endDay
26%18%43%10%
64
February1st to 15thDay
25%19%37%14%3
212
16th to endDay
21%23%30%18%4
239
March1st to 15thDay
30%20%31%14%2
270
16th to endDay
22%24%31%13%6%1
288
April1st to 15thDay
25%18%33%13%8%
270
16th to endDay
21%14%36%18%5%2
270
May1st to 15thDay
36%14%25%15%7%1
288
16th to endDay
20%12%36%22%7%
331
June1st to 15thDay
24%12%32%20%9%
315
16th to endDay
18%11%38%24%5%2
315
July1st to 15thDay
16%9%35%26%11%1
305
16th to endDay
12%9%30%31%11%3
326
August1st to 15thDay
12%9%32%28%14%2
313
16th to endDay
10%7%33%25%16%6%
332
September1st to 15thDay
19%7%32%22%13%5%
315
16th to endDay
20%6%25%21%13%13%
314
October1st to 15thDay
20%10%25%22%15%5%
278
16th to endDay
20%17%32%23%6%
240
November1st to 15thDay
27%12%28%19%8%2
235
16th to endDay
23%16%30%18%10%1
240
December1st to 15thDay
24%30%28%13%3
66
16th to endDay
34%25%28%10%1
64
January1st to 15thNight
23%18%38%17%2
720
16th to endNight
22%20%36%17%2
768
February1st to 15thNight
19%19%41%17%1
704
16th to endNight
23%19%35%17%2
631
March1st to 15thNight
23%20%36%16%3
720
16th to endNight
20%19%36%19%4
768
April1st to 15thNight
21%18%36%19%3
718
16th to endNight
21%17%34%18%6%
599
May1st to 15thNight
26%13%33%20%5%
540
16th to endNight
20%10%38%26%4
402
June1st to 15thNight
23%435%29%6%
360
16th to endNight
16%341%33%5%
360
July1st to 15thNight
12%334%37%10%
340
16th to endNight
12%231%40%12%
376
August1st to 15thNight
11%332%41%10%
495
16th to endNight
13%324%39%16%1
734
September1st to 15thNight
16%5%34%30%12%
720
16th to endNight
18%5%26%25%20%3
717
October1st to 15thNight
22%10%28%25%10%2
684
16th to endNight
26%13%33%20%5%
704
November1st to 15thNight
21%12%33%22%9%1
700
16th to endNight
23%17%30%19%7%1
720
December1st to 15thNight
24%17%34%18%4
720
16th to endNight
25%17%38%15%2
768
Page generated at 2017-10-07 14:07:47. Version ac04

Copyright 2017 A. Danko


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