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

2017-09-12
.

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
32%
14793
14%
46622
8%
14755
38%
14755
18%
32543

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%
719
8%
2467
3%
716
20%
716
7%
1958
January16th to endNight
17%
768
10%
2496
4%
768
25%
768
10%
1947
February1st to 15thNight
14%
701
10%
2287
2%
701
23%
701
10%
1765
February16th to endNight
19%
631
11%
2015
4%
631
29%
631
12%
1486
March1st to 15thNight
20%
720
13%
1980
5%
720
26%
720
15%
1480
March16th to endNight
27%
768
20%
2112
9%
768
36%
768
23%
1439
April1st to 15thNight
23%
718
14%
1826
4%
718
28%
718
21%
1333
April16th to endNight
35%
550
19%
1630
8%
550
43%
550
25%
1072
May1st to 15thNight
41%
498
16%
1578
11%
498
48%
498
24%
1036
May16th to endNight
44%
374
17%
1497
13%
374
55%
374
26%
831
June1st to 15thNight
40%
360
13%
1440
10%
360
50%
360
20%
851
June16th to endNight
49%
360
14%
1290
16%
360
55%
360
27%
746
July1st to 15thNight
61%
340
17%
1289
21%
340
67%
340
34%
672
July16th to endNight
57%
496
16%
1528
13%
464
61%
464
31%
893
August1st to 15thNight
61%
539
17%
1609
11%
536
65%
536
36%
930
August16th to endNight
58%
615
23%
1761
13%
615
62%
615
35%
1050
September1st to 15thNight
50%
707
20%
1786
9%
707
55%
707
34%
1156
September16th to endNight
52%
657
20%
1831
13%
657
55%
657
32%
1152
October1st to 15thNight
37%
660
17%
1980
13%
660
43%
660
21%
1360
October16th to endNight
22%
704
10%
2112
5%
704
29%
704
13%
1590
November1st to 15thNight
31%
700
17%
2380
14%
700
37%
700
18%
1613
November16th to endNight
24%
720
9%
2520
6%
720
30%
720
11%
1903
December1st to 15thNight
15%
720
6%
2520
3%
720
18%
720
8%
2027
December16th to endNight
11%
768
5%
2688
1%
768
16%
768
6%
2253

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
14%8%37%6%35%5%5%7%31%
48029
Night
14%8%36%5%35%45%6%35%
46802
Cloud CoverDay
15%8%47%6%35%5%5%7%31%
48039
Night
14%8%36%5%35%45%6%34%
46806
TransparencyDay
50%8%13%17%9%
47727
Night
48%7%13%19%10%1
46622
SeeingDay
17%11%28%23%12%5%
5520
Night
19%10%31%26%10%1
14798

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%16%5%8%7%45%5%5%6%19%
1468
16th to endDay
11%16%8%10%10%46%446%15%
1728
February1st to 15thDay
13%14%7%11%8%35%5%5%5%17%
1575
16th to endDay
17%12%49%5%345%46%24%
1457
March1st to 15thDay
14%10%5%8%8%4445%5%28%
1969
16th to endDay
14%10%47%6%35%445%34%
2112
April1st to 15thDay
19%10%46%6%24446%30%
2122
16th to endDay
18%7%36%424345%39%
2340
May1st to 15thDay
17%6%26%6%35%45%6%35%
2373
16th to endDay
11%5%16%5%35%5%5%7%40%
2618
June1st to 15thDay
15%6%25%4245%6%8%36%
2520
16th to endDay
12%4245%45%5%6%10%36%
2665
July1st to 15thDay
9%426%6%36%6%6%9%39%
2587
16th to endDay
11%5%36%5%46%7%7%8%34%
2533
August1st to 15thDay
8%5%26%7%46%6%6%8%37%
2340
16th to endDay
11%5%25%6%36%6%6%8%36%
2428
September1st to 15thDay
14%6%25%6%35%5%5%7%37%
2093
16th to endDay
14%7%36%6%3445%7%37%
1799
October1st to 15thDay
19%8%37%6%4335%5%32%
1650
16th to endDay
26%11%36%6%445%45%21%
1760
November1st to 15thDay
13%10%38%5%35%5%5%8%30%
1476
16th to endDay
17%13%6%9%6%345%5%7%19%
1440
December1st to 15thDay
17%15%7%11%8%445%35%16%
1440
16th to endDay
20%14%7%7%7%35%5%6%6%14%
1536
January1st to 15thNight
20%12%5%8%7%45%45%5%20%
2467
16th to endNight
12%12%7%9%7%46%45%7%21%
2496
February1st to 15thNight
14%11%5%7%8%35%5%5%6%25%
2285
16th to endNight
11%12%49%7%4445%6%27%
2015
March1st to 15thNight
17%8%46%7%35%345%31%
1968
16th to endNight
13%8%36%5%34335%42%
2112
April1st to 15thNight
18%8%35%5%3445%6%35%
1826
16th to endNight
11%8%35%5%24446%42%
1630
May1st to 15thNight
15%425%5%25%5%5%8%39%
1578
16th to endNight
11%42442335%7%50%
1495
June1st to 15thNight
11%4245%35%5%5%8%41%
1440
16th to endNight
9%415%425%5%5%8%46%
1290
July1st to 15thNight
5%2235%33447%57%
1368
16th to endNight
7%314435%5%5%8%49%
1634
August1st to 15thNight
6%32443446%8%51%
1620
16th to endNight
8%424424446%52%
1761
September1st to 15thNight
12%3143345%6%6%49%
1786
16th to endNight
12%415%42436%7%47%
1831
October1st to 15thNight
17%7%25%43445%6%38%
1980
16th to endNight
20%9%36%6%345%5%6%26%
2112
November1st to 15thNight
16%7%35%436%5%5%6%34%
2380
16th to endNight
19%9%47%6%35%5%6%7%24%
2520
December1st to 15thNight
20%13%5%8%6%25%5%5%7%20%
2520
16th to endNight
20%13%7%11%7%45%45%5%14%
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
16%14%5%9%6%45%5%5%5%19%
1468
16th to endDay
12%16%7%11%9%46%5%46%15%
1728
February1st to 15thDay
14%15%6%10%8%47%45%5%18%
1575
16th to endDay
17%12%5%8%6%35%5%5%5%24%
1457
March1st to 15thDay
15%10%49%7%45%445%28%
1980
16th to endDay
14%9%46%6%34435%34%
2111
April1st to 15thDay
19%10%37%5%2445%7%29%
2122
16th to endDay
19%6%35%42345%5%38%
2340
May1st to 15thDay
16%7%36%5%35%447%35%
2373
16th to endDay
11%5%26%6%35%46%7%40%
2618
June1st to 15thDay
15%6%245%345%5%9%36%
2520
16th to endDay
13%415%6%35%6%6%10%36%
2665
July1st to 15thDay
8%426%6%36%5%6%9%40%
2587
16th to endDay
10%5%36%6%46%6%7%9%33%
2533
August1st to 15thDay
8%5%27%5%46%7%6%9%37%
2340
16th to endDay
11%5%26%5%46%5%7%8%36%
2428
September1st to 15thDay
14%7%25%5%45%45%7%37%
2093
16th to endDay
15%6%36%6%34448%36%
1799
October1st to 15thDay
20%7%36%7%34445%32%
1650
16th to endDay
26%12%37%6%35%345%21%
1760
November1st to 15thDay
14%9%5%6%5%26%5%5%8%30%
1476
16th to endDay
17%12%7%8%6%35%5%5%6%19%
1440
December1st to 15thDay
17%13%8%12%9%35%5%35%15%
1440
16th to endDay
20%14%7%8%6%45%5%6%6%15%
1536
January1st to 15thNight
20%14%5%7%7%35%45%5%20%
2467
16th to endNight
12%14%6%9%7%46%5%5%5%22%
2496
February1st to 15thNight
13%12%5%8%7%45%5%46%25%
2278
16th to endNight
12%12%49%6%36%45%6%26%
2015
March1st to 15thNight
17%9%47%6%44435%31%
1980
16th to endNight
14%8%36%5%2433442%
2112
April1st to 15thNight
18%8%35%5%3445%6%35%
1826
16th to endNight
12%8%35%42345%6%42%
1630
May1st to 15thNight
14%5%25%5%245%5%7%40%
1577
16th to endNight
11%425%32435%7%49%
1495
June1st to 15thNight
11%5%25%5%35%5%5%8%40%
1440
16th to endNight
9%425%5%245%5%9%45%
1290
July1st to 15thNight
5%413425%45%6%56%
1368
16th to endNight
7%314436%5%6%8%48%
1634
August1st to 15thNight
6%3145%2436%8%51%
1620
16th to endNight
8%413434447%52%
1761
September1st to 15thNight
12%3233246%5%5%48%
1786
16th to endNight
12%5%2442346%7%47%
1831
October1st to 15thNight
18%7%25%434446%38%
1980
16th to endNight
20%8%46%5%4446%6%26%
2112
November1st to 15thNight
16%7%36%5%35%447%35%
2380
16th to endNight
19%10%46%6%35%5%5%7%24%
2520
December1st to 15thNight
19%13%6%7%6%35%5%5%6%20%
2520
16th to endNight
20%13%6%10%8%45%45%5%14%
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
64%8%11%10%5%
1469
16th to endDay
67%8%11%8%4
1728
February1st to 15thDay
65%9%9%12%2
1577
16th to endDay
59%8%11%13%7%1
1457
March1st to 15thDay
57%6%12%15%7%
1980
16th to endDay
50%6%10%17%13%1
2112
April1st to 15thDay
53%5%11%18%10%
2122
16th to endDay
46%5%11%20%14%1
2340
May1st to 15thDay
47%7%10%20%13%
2373
16th to endDay
40%8%14%20%13%1
2622
June1st to 15thDay
42%7%13%23%12%
2520
16th to endDay
40%9%16%21%12%
2665
July1st to 15thDay
37%9%13%22%15%1
2437
16th to endDay
43%9%15%19%10%1
2376
August1st to 15thDay
40%10%16%18%13%1
2327
16th to endDay
40%8%15%24%9%1
2428
September1st to 15thDay
44%7%15%22%9%
2093
16th to endDay
44%8%12%26%8%
1799
October1st to 15thDay
52%7%10%19%9%1
1650
16th to endDay
63%8%13%11%3
1760
November1st to 15thDay
49%9%14%17%8%
1476
16th to endDay
61%9%14%10%4
1440
December1st to 15thDay
68%9%11%9%1
1440
16th to endDay
66%10%12%8%2
1536
January1st to 15thNight
63%7%11%10%5%
2467
16th to endNight
60%7%14%12%4
2496
February1st to 15thNight
57%9%10%16%5%
2287
16th to endNight
55%6%14%15%7%
2015
March1st to 15thNight
54%6%13%18%6%
1980
16th to endNight
45%410%21%16%2
2112
April1st to 15thNight
49%6%11%18%14%
1826
16th to endNight
41%6%11%20%17%3
1630
May1st to 15thNight
41%7%11%21%15%2
1578
16th to endNight
34%5%15%26%14%3
1497
June1st to 15thNight
38%8%12%23%16%1
1440
16th to endNight
34%7%14%26%17%
1290
July1st to 15thNight
25%8%11%27%23%2
1289
16th to endNight
32%7%14%25%16%3
1528
August1st to 15thNight
29%7%20%28%13%1
1609
16th to endNight
31%6%11%31%16%1
1761
September1st to 15thNight
33%8%14%27%14%1
1786
16th to endNight
34%7%13%31%12%
1831
October1st to 15thNight
45%7%11%21%12%
1980
16th to endNight
54%8%15%14%6%
2112
November1st to 15thNight
47%7%14%19%10%1
2380
16th to endNight
57%8%15%13%3
2520
December1st to 15thNight
62%9%13%11%2
2520
16th to endNight
68%8%11%8%2
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
19%27%34%13%4
66
16th to endDay
34%25%26%13%1
96
February1st to 15thDay
21%34%35%8%
90
16th to endDay
25%25%34%14%1
84
March1st to 15thDay
22%16%34%19%6%
270
16th to endDay
22%14%33%18%8%2
288
April1st to 15thDay
22%18%31%18%7%1
270
16th to endDay
21%16%30%16%11%4
270
May1st to 15thDay
22%10%25%22%12%7%
288
16th to endDay
16%9%31%24%14%3
331
June1st to 15thDay
18%12%24%30%12%1
315
16th to endDay
14%9%32%30%10%3
460
July1st to 15thDay
10%7%26%35%14%6%
371
16th to endDay
9%5%28%32%15%9%
326
August1st to 15thDay
9%326%26%21%12%
313
16th to endDay
13%5%21%24%21%13%
332
September1st to 15thDay
14%5%25%26%16%13%
299
16th to endDay
17%422%25%17%11%
254
October1st to 15thDay
18%8%30%23%13%4
255
16th to endDay
30%17%27%19%4
272
November1st to 15thDay
10%17%36%24%9%2
86
16th to endDay
25%20%35%16%3
60
December1st to 15thDay
18%26%36%13%5%
60
16th to endDay
31%28%34%6%
64
January1st to 15thNight
27%19%34%13%3
720
16th to endNight
19%11%38%23%5%
768
February1st to 15thNight
19%19%39%18%3
704
16th to endNight
19%16%37%22%4
631
March1st to 15thNight
23%17%34%21%3
720
16th to endNight
19%12%37%20%9%
768
April1st to 15thNight
22%12%37%22%4
718
16th to endNight
16%10%32%29%8%1
550
May1st to 15thNight
17%6%27%32%13%2
498
16th to endNight
12%5%31%33%15%
375
June1st to 15thNight
13%7%31%33%12%
360
16th to endNight
11%328%39%15%
360
July1st to 15thNight
7%224%45%20%1
340
16th to endNight
9%226%40%19%2
496
August1st to 15thNight
8%19%44%24%2
539
16th to endNight
11%222%32%27%3
615
September1st to 15thNight
15%425%28%21%5%
707
16th to endNight
16%421%32%21%3
657
October1st to 15thNight
21%7%28%25%14%2
660
16th to endNight
25%12%35%21%5%
704
November1st to 15thNight
20%11%32%24%9%1
700
16th to endNight
24%15%29%23%6%
720
December1st to 15thNight
29%16%35%15%3
720
16th to endNight
28%13%38%17%2
768
Page generated at 2017-09-13 07:39:17. Version ac04

Copyright 2017 A. Danko


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