This page made possible by the sponsorship of: Joseph Geiger.

Bolton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bolton clear sky chart from 2005-11-06 to 2024-01-16.

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
26%
22939
18%
74624
7%
22893
38%
22893
19%
48512

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 10thNight
15%
760
21%
2649
5%
757
34%
757
18%
1633
January11th to 20thNight
13%
741
16%
2591
3%
741
30%
741
12%
1744
January21st to endNight
16%
792
20%
2772
5%
792
35%
792
17%
1739
February1st to 10thNight
13%
720
16%
2283
4%
720
27%
720
16%
1549
February11th to 20thNight
12%
703
19%
2100
4%
700
30%
700
15%
1405
February21st to endNight
15%
592
25%
1776
7%
592
37%
592
16%
1186
March1st to 10thNight
17%
720
21%
2160
7%
720
35%
720
18%
1418
March11th to 20thNight
15%
720
17%
2075
5%
720
28%
720
16%
1441
March21st to endNight
19%
792
21%
2040
6%
792
31%
792
19%
1415
April1st to 10thNight
20%
720
19%
1800
4%
720
30%
720
19%
1271
April11th to 20thNight
22%
711
17%
1775
3%
711
30%
711
22%
1245
April21st to endNight
17%
540
19%
1620
6%
540
28%
540
17%
1097
May1st to 10thNight
20%
540
13%
1620
6%
540
27%
540
15%
1179
May11th to 20thNight
20%
488
16%
1550
7%
488
30%
488
16%
1041
May21st to endNight
31%
389
12%
1551
8%
388
40%
388
16%
1003
June1st to 10thNight
31%
360
14%
1440
9%
360
45%
360
17%
943
June11th to 20thNight
31%
360
12%
1440
12%
360
40%
360
16%
940
June21st to endNight
35%
360
12%
1440
10%
360
45%
360
22%
865
July1st to 10thNight
45%
350
13%
1400
13%
350
53%
350
21%
848
July11th to 20thNight
47%
348
12%
1392
12%
348
51%
348
20%
860
July21st to endNight
48%
394
18%
1486
17%
372
56%
372
23%
872
August1st to 10thNight
48%
471
17%
1535
12%
469
54%
469
26%
951
August11th to 20thNight
43%
573
16%
1637
9%
573
47%
573
24%
1090
August21st to endNight
48%
792
20%
1980
9%
792
52%
792
35%
1278
September1st to 10thNight
41%
720
19%
1800
8%
720
47%
720
32%
1188
September11th to 20thNight
44%
720
24%
1970
13%
720
52%
720
33%
1204
September21st to endNight
38%
720
24%
1980
14%
720
47%
720
28%
1287
October1st to 10thNight
32%
720
18%
1980
9%
720
40%
720
23%
1332
October11th to 20thNight
32%
720
21%
2203
9%
720
46%
720
25%
1382
October21st to endNight
22%
792
16%
2574
6%
792
34%
792
17%
1741
November1st to 10thNight
30%
740
22%
2407
11%
740
45%
740
23%
1495
November11th to 20thNight
22%
760
24%
2470
9%
760
40%
760
21%
1520
November21st to endNight
20%
760
22%
2470
7%
760
39%
760
19%
1534
December1st to 10thNight
17%
760
19%
2645
5%
760
32%
760
15%
1727
December11th to 20thNight
20%
760
17%
3198
5%
759
35%
759
14%
1965
December21st to endNight
14%
831
14%
4815
4%
817
34%
817
9%
3124

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%7%35%5%35%5%5%7%40%
74829
Night
17%7%35%5%3445%7%41%
74955
TransparencyDay
43%7%12%21%15%3
74534
Night
43%7%12%21%15%2
74784
SeeingDay
23%16%32%20%8%2
13903
Night
22%14%33%23%6%1
22944

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 10thDay
14%8%37%5%34445%43%
1517
11th to 20thDay
17%8%345%45%5%5%6%38%
1480
21st to endDay
13%7%25%6%25%5%5%6%44%
1584
February1st to 10thDay
19%7%36%5%35%5%6%7%34%
1674
11th to 20thDay
13%8%36%5%36%6%5%7%39%
1748
21st to endDay
19%10%36%6%34436%37%
1480
March1st to 10thDay
17%7%35%5%345%6%7%39%
1797
11th to 20thDay
17%6%36%5%35%45%7%39%
1883
21st to endDay
18%9%35%5%34346%41%
2312
April1st to 10thDay
17%8%35%6%34446%39%
2160
11th to 20thDay
17%5%35%435%5%5%8%40%
2134
21st to endDay
20%7%35%5%45%5%46%35%
2340
May1st to 10thDay
24%8%35%435%45%7%32%
2340
11th to 20thDay
18%7%35%5%35%35%7%40%
2358
21st to endDay
14%5%35%5%35%46%7%44%
2725
June1st to 10thDay
18%6%346%45%5%7%8%35%
2520
11th to 20thDay
17%5%345%45%7%6%8%37%
2520
21st to endDay
17%6%35%6%45%6%6%9%34%
2520
July1st to 10thDay
13%5%36%5%45%5%5%8%41%
2520
11th to 20thDay
11%5%25%6%36%6%6%9%40%
2520
21st to endDay
11%5%25%5%45%6%7%9%40%
2744
August1st to 10thDay
9%6%27%6%46%5%7%9%39%
2374
11th to 20thDay
13%6%25%5%46%5%6%7%40%
2260
21st to endDay
12%425%5%346%6%8%45%
2376
September1st to 10thDay
14%6%244346%5%7%45%
2160
11th to 20thDay
15%6%24324446%50%
1989
21st to endDay
15%6%26%434346%46%
1980
October1st to 10thDay
23%6%244245%45%40%
1980
11th to 20thDay
13%6%3443446%7%46%
1753
21st to endDay
21%7%25%5%33445%40%
1782
November1st to 10thDay
15%6%35%5%3434449%
1671
11th to 20thDay
19%6%24324445%47%
1710
21st to endDay
18%6%35%5%3446%5%43%
1710
December1st to 10thDay
17%8%36%5%345%5%6%38%
1530
11th to 20thDay
22%7%2442335%5%45%
1906
21st to endDay
21%10%36%43345%6%34%
2772
January1st to 10thNight
16%8%34425%436%44%
2649
11th to 20thNight
18%8%37%5%3445%7%36%
2591
21st to endNight
12%8%46%6%345%5%7%41%
2772
February1st to 10thNight
17%9%36%5%3446%6%38%
2283
11th to 20thNight
14%8%36%5%35%46%7%39%
2098
21st to endNight
17%9%26%5%34447%39%
1776
March1st to 10thNight
15%8%36%425%5%46%42%
2150
11th to 20thNight
15%9%46%5%35%445%39%
2075
21st to endNight
15%9%46%5%24446%42%
2040
April1st to 10thNight
18%7%36%7%3446%7%38%
1800
11th to 20thNight
18%6%25%5%3446%6%40%
1775
21st to endNight
21%7%35%43335%6%39%
1620
May1st to 10thNight
24%8%36%5%345%5%5%32%
1620
11th to 20thNight
17%7%25%5%345%6%7%38%
1549
21st to endNight
15%7%26%5%35%35%7%39%
1550
June1st to 10thNight
18%8%35%5%3436%7%38%
1440
11th to 20thNight
20%6%35%5%35%5%47%38%
1440
21st to endNight
14%5%35%5%35%5%7%8%41%
1440
July1st to 10thNight
14%5%146%35%6%5%8%42%
1440
11th to 20thNight
12%6%35%6%35%6%6%9%39%
1440
21st to endNight
12%5%245%35%46%9%45%
1574
August1st to 10thNight
9%5%246%35%6%6%8%45%
1545
11th to 20thNight
12%425%6%46%7%7%10%37%
1637
21st to endNight
15%42442435%8%48%
1980
September1st to 10thNight
13%5%246%2345%7%48%
1800
11th to 20thNight
14%5%24323446%53%
1970
21st to endNight
16%6%25%42445%6%46%
1980
October1st to 10thNight
21%6%35%42335%5%43%
1980
11th to 20thNight
16%5%2443446%6%46%
2203
21st to endNight
23%8%25%434346%37%
2574
November1st to 10thNight
15%5%245%34445%49%
2407
11th to 20thNight
18%7%24324445%46%
2470
21st to endNight
16%7%2443445%7%45%
2470
December1st to 10thNight
18%8%35%5%34446%39%
2645
11th to 20thNight
19%6%25%42445%6%42%
3288
21st to endNight
20%9%46%5%3445%6%35%
4884

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 10thDay
43%410%27%13%3
1518
11th to 20thDay
46%8%12%20%12%3
1480
21st to endDay
38%6%14%23%15%3
1584
February1st to 10thDay
48%6%14%18%12%3
1674
11th to 20thDay
44%7%11%20%15%3
1757
21st to endDay
50%5%8%20%14%3
1480
March1st to 10thDay
44%6%12%20%13%5%
1800
11th to 20thDay
44%6%12%20%15%4
1883
21st to endDay
47%5%8%18%17%6%
2312
April1st to 10thDay
46%6%10%19%16%4
2160
11th to 20thDay
41%7%12%20%18%3
2134
21st to endDay
48%7%9%16%16%4
2340
May1st to 10thDay
52%6%9%19%12%2
2340
11th to 20thDay
44%7%10%19%18%3
2362
21st to endDay
39%8%13%24%13%2
2725
June1st to 10thDay
45%9%14%22%10%1
2520
11th to 20thDay
43%9%12%18%15%2
2520
21st to endDay
45%9%13%21%12%1
2520
July1st to 10thDay
41%8%12%22%15%2
2450
11th to 20thDay
39%9%15%24%12%1
2445
21st to endDay
38%9%14%22%14%3
2591
August1st to 10thDay
39%10%15%23%12%1
2360
11th to 20thDay
41%8%14%23%12%1
2260
21st to endDay
35%8%13%24%18%2
2376
September1st to 10thDay
37%7%13%23%18%2
2160
11th to 20thDay
35%5%10%24%23%3
1989
21st to endDay
39%5%10%21%22%2
1980
October1st to 10thDay
46%6%9%21%14%4
1980
11th to 20thDay
37%6%12%28%16%2
1753
21st to endDay
45%7%13%19%14%3
1782
November1st to 10thDay
40%412%25%17%2
1671
11th to 20thDay
39%5%11%23%20%2
1710
21st to endDay
41%6%14%24%12%2
1710
December1st to 10thDay
46%6%15%16%17%1
1530
11th to 20thDay
42%5%14%18%17%4
1906
21st to endDay
50%8%12%19%11%1
2772
January1st to 10thNight
42%412%22%16%3
2649
11th to 20thNight
48%7%14%20%9%2
2591
21st to endNight
43%5%12%19%19%3
2772
February1st to 10thNight
47%5%14%19%12%2
2283
11th to 20thNight
46%5%10%21%15%3
2100
21st to endNight
45%5%8%24%15%4
1776
March1st to 10thNight
44%5%10%23%14%4
2160
11th to 20thNight
46%7%11%16%17%4
2076
21st to endNight
46%5%8%17%19%5%
2040
April1st to 10thNight
46%6%11%19%16%3
1800
11th to 20thNight
44%6%10%20%18%2
1775
21st to endNight
46%7%10%19%14%5%
1620
May1st to 10thNight
52%6%10%17%12%3
1620
11th to 20thNight
44%9%12%18%15%3
1550
21st to endNight
45%8%14%19%13%1
1551
June1st to 10thNight
46%8%12%22%11%1
1440
11th to 20thNight
46%8%12%20%13%1
1440
21st to endNight
35%11%16%23%14%1
1440
July1st to 10thNight
39%8%14%22%16%1
1400
11th to 20thNight
40%10%17%23%9%1
1392
21st to endNight
35%9%16%26%12%2
1486
August1st to 10thNight
34%11%14%24%15%2
1535
11th to 20thNight
38%12%18%21%12%
1637
21st to endNight
34%7%13%26%19%1
1980
September1st to 10thNight
38%6%14%23%18%1
1800
11th to 20thNight
32%6%11%22%26%2
1970
21st to endNight
38%7%9%24%20%3
1980
October1st to 10thNight
43%6%13%22%12%4
1980
11th to 20thNight
37%8%14%26%14%1
2203
21st to endNight
48%5%12%20%14%1
2574
November1st to 10thNight
38%7%10%22%19%4
2407
11th to 20thNight
40%412%22%19%3
2470
21st to endNight
40%5%14%26%13%2
2470
December1st to 10thNight
46%5%13%22%13%1
2645
11th to 20thNight
42%7%15%19%16%2
3288
21st to endNight
48%8%10%24%10%1
4884

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 10thDay
27%25%28%15%5%
180
11th to 20thDay
32%24%32%9%4
170
21st to endDay
24%26%35%11%4
176
February1st to 10thDay
34%22%29%13%2
325
11th to 20thDay
28%28%32%11%2
416
21st to endDay
32%20%33%12%4
346
March1st to 10thDay
29%21%34%13%2
420
11th to 20thDay
27%26%29%14%31
420
21st to endDay
31%18%33%12%5%2
462
April1st to 10thDay
32%22%28%12%6%1
420
11th to 20thDay
29%21%32%11%7%
412
21st to endDay
29%20%33%14%32
420
May1st to 10thDay
32%20%29%13%41
423
11th to 20thDay
23%14%41%16%41
447
21st to endDay
19%14%34%23%9%2
485
June1st to 10thDay
17%13%38%20%10%2
450
11th to 20thDay
19%12%39%22%6%2
450
21st to endDay
19%11%36%22%9%3
450
July1st to 10thDay
17%10%29%27%15%2
445
11th to 20thDay
14%7%31%32%13%3
444
21st to endDay
13%8%35%33%10%2
488
August1st to 10thDay
9%10%31%33%14%2
446
11th to 20thDay
17%7%30%30%13%3
439
21st to endDay
13%9%32%28%14%5%
495
September1st to 10thDay
19%9%28%24%15%6%
450
11th to 20thDay
21%8%30%22%11%8%
450
21st to endDay
19%12%30%25%9%5%
450
October1st to 10thDay
28%12%25%21%10%4
450
11th to 20thDay
18%17%31%23%10%2
405
21st to endDay
30%12%30%20%7%1
396
November1st to 10thDay
21%16%32%20%9%2
365
11th to 20thDay
30%21%25%19%41
370
21st to endDay
28%19%31%17%6%
370
December1st to 10thDay
19%30%29%17%4
190
11th to 20thDay
31%27%32%7%3
180
21st to endDay
27%22%32%14%41
198
January1st to 10thNight
22%19%40%17%2
760
11th to 20thNight
27%19%36%16%2
741
21st to endNight
20%20%38%19%3
792
February1st to 10thNight
25%17%40%16%2
720
11th to 20thNight
22%21%40%16%1
703
21st to endNight
26%21%34%17%2
592
March1st to 10thNight
24%19%37%18%3
720
11th to 20thNight
22%21%38%17%3
720
21st to endNight
23%20%34%19%4
792
April1st to 10thNight
24%22%30%20%3
720
11th to 20thNight
23%19%33%19%6%
711
21st to endNight
23%20%35%19%2
540
May1st to 10thNight
30%15%30%21%3
540
11th to 20thNight
21%18%36%19%5%
488
21st to endNight
19%9%36%30%6%
389
June1st to 10thNight
21%5%37%29%8%
360
11th to 20thNight
22%8%34%31%5%1
360
21st to endNight
15%438%36%7%
360
July1st to 10thNight
15%5%29%39%11%1
350
11th to 20thNight
14%428%42%12%
348
21st to endNight
13%430%43%9%
394
August1st to 10thNight
11%431%41%12%1
471
11th to 20thNight
13%5%29%38%14%1
573
21st to endNight
15%5%25%39%15%2
792
September1st to 10thNight
16%6%31%33%13%1
720
11th to 20thNight
17%8%26%29%18%2
720
21st to endNight
20%8%29%28%13%2
720
October1st to 10thNight
26%10%28%24%10%2
720
11th to 20thNight
20%12%32%24%11%1
720
21st to endNight
28%14%32%19%6%
792
November1st to 10thNight
20%13%32%26%8%1
740
11th to 20thNight
24%18%33%18%7%1
760
21st to endNight
23%19%33%19%5%1
760
December1st to 10thNight
26%19%34%17%4
760
11th to 20thNight
25%18%34%21%3
760
21st to endNight
27%17%37%17%3
836
Page generated at 2024-01-13 01:38:15. Version ac07

Copyright 2024 Attilla Danko


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