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 2018-01-12.

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%
15279
14%
48199
8%
15241
38%
15241
18%
33621

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%
764
8%
2623
3%
761
20%
761
8%
2058
January16th to endNight
18%
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
34%
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
51%
360
14%
1290
16%
360
57%
360
27%
746
July1st to 15thNight
62%
340
17%
1289
21%
340
68%
340
34%
672
July16th to endNight
57%
496
16%
1528
13%
464
61%
464
31%
893
August1st to 15thNight
62%
539
16%
1609
11%
536
66%
536
36%
930
August16th to endNight
57%
615
23%
1761
13%
615
62%
615
35%
1050
September1st to 15thNight
52%
720
20%
1820
9%
720
57%
720
34%
1175
September16th to endNight
53%
717
22%
1998
16%
717
57%
717
32%
1249
October1st to 15thNight
36%
720
16%
2160
13%
720
42%
720
21%
1484
October16th to endNight
22%
768
12%
2304
6%
768
30%
768
14%
1713
November1st to 15thNight
30%
760
16%
2584
13%
760
37%
760
17%
1776
November16th to endNight
24%
780
10%
2730
6%
780
30%
780
11%
2046
December1st to 15thNight
14%
780
5%
2730
3%
780
17%
780
8%
2188
December16th to endNight
10%
832
6%
2912
1%
832
16%
832
6%
2401

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%
49130
Night
14%8%36%5%35%45%6%35%
48379
Cloud CoverDay
15%8%47%6%35%5%5%7%31%
49140
Night
14%8%36%5%35%45%6%34%
48383
TransparencyDay
50%8%13%18%9%
48828
Night
48%7%13%19%10%1
48199
SeeingDay
18%12%28%23%12%5%
5870
Night
19%10%31%25%10%1
15284

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%15%5%8%7%45%5%5%6%18%
1556
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%38%
2139
16th to endDay
13%6%36%6%3445%6%39%
1962
October1st to 15thDay
20%8%27%6%4335%5%32%
1800
16th to endDay
25%10%36%6%345%45%22%
1920
November1st to 15thDay
14%10%37%5%35%45%8%29%
1602
16th to endDay
17%13%6%9%6%345%6%7%20%
1560
December1st to 15thDay
16%15%7%11%8%44435%17%
1560
16th to endDay
20%14%7%7%7%35%5%6%7%15%
1664
January1st to 15thNight
19%12%5%8%6%35%45%5%21%
2623
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
11%3143345%6%6%49%
1820
16th to endNight
12%4145%2435%7%48%
1998
October1st to 15thNight
18%7%25%5%34446%38%
2160
16th to endNight
19%9%36%6%345%5%7%28%
2304
November1st to 15thNight
17%8%35%436%45%6%33%
2584
16th to endNight
19%9%47%6%35%5%6%7%25%
2730
December1st to 15thNight
19%13%5%8%6%35%5%5%7%20%
2730
16th to endNight
20%13%6%11%7%4445%5%16%
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
16%14%5%9%6%45%5%5%6%19%
1556
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%6%25%5%45%45%7%38%
2139
16th to endDay
14%6%36%6%34447%38%
1962
October1st to 15thDay
20%6%46%7%34445%32%
1800
16th to endDay
25%11%37%6%35%345%22%
1920
November1st to 15thDay
14%10%5%6%5%25%5%5%8%29%
1602
16th to endDay
17%12%7%7%7%35%5%5%6%20%
1560
December1st to 15thDay
16%14%8%12%9%25%5%35%17%
1560
16th to endDay
20%13%6%8%6%445%6%6%15%
1664
January1st to 15thNight
19%13%5%7%7%35%45%5%21%
2623
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
11%3233246%5%5%49%
1820
16th to endNight
11%5%2442346%7%48%
1998
October1st to 15thNight
18%7%25%434446%38%
2160
16th to endNight
19%8%36%5%45%5%6%6%27%
2304
November1st to 15thNight
17%7%36%5%35%447%34%
2584
16th to endNight
18%10%46%6%35%5%5%7%25%
2730
December1st to 15thNight
19%13%6%8%6%35%5%5%6%20%
2730
16th to endNight
20%13%6%9%7%45%45%5%16%
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
63%8%11%10%5%
1557
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
43%7%15%22%10%
2139
16th to endDay
42%8%11%27%9%
1962
October1st to 15thDay
52%7%10%19%9%1
1800
16th to endDay
61%8%13%11%4
1920
November1st to 15thDay
51%9%14%17%7%
1602
16th to endDay
60%8%14%11%4
1560
December1st to 15thDay
66%8%11%9%2
1560
16th to endDay
65%10%12%9%3
1664
January1st to 15thNight
62%7%11%11%6%
2623
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%15%
1820
16th to endNight
33%7%13%31%12%
1998
October1st to 15thNight
45%7%11%21%13%
2160
16th to endNight
53%8%15%15%7%
2304
November1st to 15thNight
48%7%14%18%10%1
2584
16th to endNight
56%8%16%14%4
2730
December1st to 15thNight
62%9%13%11%3
2730
16th to endNight
67%8%11%8%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
18%26%36%15%3
88
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
13%423%25%17%14%
315
16th to endDay
15%5%21%22%22%13%
314
October1st to 15thDay
20%9%29%22%12%5%
315
16th to endDay
28%18%27%19%5%
336
November1st to 15thDay
18%17%32%22%6%1
122
16th to endDay
21%21%42%12%3
90
December1st to 15thDay
15%26%37%15%4
90
16th to endDay
29%26%33%11%
96
January1st to 15thNight
26%18%34%14%4
765
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%
720
16th to endNight
15%420%31%22%5%
717
October1st to 15thNight
22%7%28%25%14%2
720
16th to endNight
24%12%34%22%5%
768
November1st to 15thNight
22%11%31%24%9%1
760
16th to endNight
24%15%30%22%6%
780
December1st to 15thNight
28%17%35%15%3
780
16th to endNight
28%14%38%16%2
832
Page generated at 2018-01-12 22:01:28. Version ac04

Copyright 2018 A. Danko


Bolton Clear Sky Chart |Charts Home