Boswell Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Boswell Observatory clear sky chart from 2005-11-06 to 2024-03-06.

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
39%
24818
22%
80339
13%
24723
49%
24723
29%
47796

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
29%
940
19%
4056
8%
926
41%
926
16%
2724
January11th to 20thNight
30%
947
23%
4003
9%
930
39%
930
19%
2400
January21st to endNight
28%
1030
15%
4471
8%
1023
38%
1023
17%
2889
February1st to 10thNight
25%
950
16%
2470
5%
950
32%
950
25%
1702
February11th to 20thNight
31%
853
19%
2328
7%
849
39%
849
28%
1484
February21st to endNight
28%
628
25%
1884
6%
628
43%
628
31%
1112
March1st to 10thNight
29%
621
25%
2105
11%
621
43%
621
27%
1200
March11th to 20thNight
30%
540
22%
1980
15%
540
41%
540
23%
1180
March21st to endNight
25%
594
15%
2178
8%
594
36%
594
17%
1447
April1st to 10thNight
27%
540
20%
1970
12%
540
41%
540
24%
1135
April11th to 20thNight
28%
533
24%
1627
12%
533
42%
533
27%
984
April21st to endNight
31%
540
21%
1620
15%
540
44%
540
26%
1027
May1st to 10thNight
34%
540
15%
1620
10%
540
43%
540
25%
1067
May11th to 20thNight
37%
531
18%
1594
11%
531
46%
531
28%
993
May21st to endNight
42%
583
13%
1746
7%
582
47%
582
27%
1111
June1st to 10thNight
60%
540
20%
1617
13%
540
63%
540
40%
879
June11th to 20thNight
53%
540
22%
1491
9%
540
59%
540
43%
832
June21st to endNight
55%
540
22%
1620
11%
540
60%
540
45%
841
July1st to 10thNight
67%
525
16%
1575
11%
525
68%
525
39%
891
July11th to 20thNight
70%
522
21%
1566
17%
522
74%
522
45%
842
July21st to endNight
73%
591
25%
1673
21%
558
79%
558
48%
853
August1st to 10thNight
69%
537
21%
1601
23%
534
71%
534
40%
888
August11th to 20thNight
66%
534
28%
1600
29%
534
73%
534
44%
853
August21st to endNight
61%
594
30%
1793
29%
594
67%
594
44%
947
September1st to 10thNight
57%
540
25%
1933
25%
540
65%
540
40%
955
September11th to 20thNight
54%
540
30%
1980
28%
540
64%
540
37%
995
September21st to endNight
49%
540
31%
1980
24%
540
62%
540
38%
971
October1st to 10thNight
42%
620
27%
2060
19%
620
50%
620
31%
1158
October11th to 20thNight
33%
720
27%
2160
12%
720
44%
720
36%
1193
October21st to endNight
36%
800
27%
2384
13%
800
46%
800
33%
1366
November1st to 10thNight
42%
925
31%
2405
12%
925
53%
925
44%
1335
November11th to 20thNight
34%
950
30%
2470
9%
950
48%
950
38%
1489
November21st to endNight
34%
950
25%
2574
11%
950
44%
950
36%
1522
December1st to 10thNight
30%
950
22%
2660
8%
950
41%
950
32%
1609
December11th to 20thNight
33%
949
26%
3084
10%
948
44%
948
27%
1765
December21st to endNight
27%
1041
16%
4461
8%
1026
41%
1026
15%
3157

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
10%7%36%5%3445%7%45%
78479
Night
10%7%35%43445%7%49%
81036
TransparencyDay
38%6%13%26%15%2
78202
Night
35%5%12%27%18%3
80833
SeeingDay
14%10%30%29%14%3
14748
Night
12%9%34%33%11%1
24852

By Month

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 10thDay
9%11%5%10%10%45%446%30%
2847
11th to 20thDay
8%12%49%5%26%5%46%38%
2850
21st to endDay
7%11%6%13%6%34446%36%
3135
February1st to 10thDay
9%11%47%8%3445%8%37%
1710
11th to 20thDay
9%8%47%5%25%45%7%44%
1758
21st to endDay
8%8%45%5%35%45%7%47%
1570
March1st to 10thDay
8%7%46%5%34447%49%
1969
11th to 20thDay
16%9%36%5%3345%6%41%
1980
21st to endDay
16%12%47%6%4445%6%33%
2178
April1st to 10thDay
15%5%35%43345%6%46%
1989
11th to 20thDay
14%7%35%5%4345%7%42%
2280
21st to endDay
20%6%36%5%3445%6%39%
2340
May1st to 10thDay
15%8%36%6%35%5%5%7%39%
2340
11th to 20thDay
15%6%35%5%3445%7%43%
2302
21st to endDay
14%6%36%6%35%6%6%8%36%
2531
June1st to 10thDay
6%4245%3447%9%52%
2340
11th to 20thDay
9%435%425%5%6%9%48%
2414
21st to endDay
6%425%5%36%5%6%8%49%
2340
July1st to 10thDay
8%5%136%245%6%10%50%
2340
11th to 20thDay
5%42443445%8%57%
2340
21st to endDay
6%4245%35%5%7%11%47%
2546
August1st to 10thDay
8%5%246%35%6%7%11%43%
2328
11th to 20thDay
7%4245%245%6%9%52%
2301
21st to endDay
8%5%3432345%7%56%
2561
September1st to 10thDay
14%42332345%6%54%
2025
11th to 20thDay
9%43442335%8%55%
1980
21st to endDay
10%42432345%6%58%
1980
October1st to 10thDay
14%6%24424436%52%
1882
11th to 20thDay
11%5%24423345%58%
1800
21st to endDay
13%7%35%423345%52%
1968
November1st to 10thDay
9%414423447%57%
1673
11th to 20thDay
8%6%35%5%34447%52%
1710
21st to endDay
12%8%345%235%48%46%
1600
December1st to 10thDay
8%7%25%5%345%6%7%47%
1520
11th to 20thDay
8%9%46%6%3445%8%43%
1918
21st to endDay
14%11%5%13%7%45%446%28%
3134
January1st to 10thNight
7%11%412%7%35%5%5%6%35%
4108
11th to 20thNight
8%9%35%5%38%6%5%5%43%
4120
21st to endNight
11%12%5%10%423346%39%
4532
February1st to 10thNight
11%10%46%5%35%5%6%6%39%
2470
11th to 20thNight
8%7%36%6%35%46%8%43%
2327
21st to endNight
9%8%25%5%2345%6%51%
1884
March1st to 10thNight
9%7%45%5%245%4453%
2105
11th to 20thNight
16%8%35%42335%5%46%
1980
21st to endNight
16%9%36%6%3446%7%36%
2178
April1st to 10thNight
12%6%35%42445%6%49%
1970
11th to 20thNight
11%8%35%5%24448%47%
1627
21st to endNight
16%6%25%42445%6%45%
1620
May1st to 10thNight
14%6%35%5%35%5%6%7%41%
1620
11th to 20thNight
11%7%35%43445%7%47%
1593
21st to endNight
13%6%345%25%46%9%43%
1745
June1st to 10thNight
5%3235%345%6%8%56%
1617
11th to 20thNight
7%3233245%6%10%54%
1491
21st to endNight
431332445%9%60%
1620
July1st to 10thNight
6%5%25%43345%11%53%
1620
11th to 20thNight
32133345%7%8%61%
1620
21st to endNight
3114335%6%7%10%56%
1772
August1st to 10thNight
42245%345%7%11%53%
1611
11th to 20thNight
6%22443447%7%57%
1600
21st to endNight
6%424423447%61%
1793
September1st to 10thNight
9%323333347%60%
1933
11th to 20thNight
8%42342445%7%58%
1980
21st to endNight
8%5%2342334462%
1980
October1st to 10thNight
14%4234235%6%7%51%
2060
11th to 20thNight
12%5%24422235%59%
2160
21st to endNight
14%5%24423346%54%
2384
November1st to 10thNight
6%42432335%7%61%
2405
11th to 20thNight
9%5%25%434446%55%
2470
21st to endNight
11%6%24423247%54%
2574
December1st to 10thNight
8%7%35%5%3435%7%51%
2660
11th to 20thNight
9%7%36%32335%6%53%
3275
21st to endNight
17%12%49%5%33335%35%
4532

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
55%5%12%18%9%1
2848
11th to 20thDay
47%5%16%20%11%1
2850
21st to endDay
50%6%11%20%13%
3135
February1st to 10thDay
45%5%16%22%9%2
1710
11th to 20thDay
40%5%13%24%15%3
1767
21st to endDay
37%6%12%25%17%3
1570
March1st to 10thDay
36%5%12%28%16%3
1969
11th to 20thDay
44%6%9%24%16%2
1980
21st to endDay
52%6%14%19%9%1
2178
April1st to 10thDay
39%6%12%25%16%2
1989
11th to 20thDay
42%5%13%24%13%2
2280
21st to endDay
45%5%11%26%13%1
2340
May1st to 10thDay
45%7%12%22%13%1
2340
11th to 20thDay
39%7%15%26%12%
2306
21st to endDay
45%7%16%20%10%2
2531
June1st to 10thDay
28%8%16%34%13%2
2340
11th to 20thDay
31%7%13%28%18%2
2414
21st to endDay
30%8%14%29%13%5%
2340
July1st to 10thDay
29%8%14%30%17%2
2276
11th to 20thDay
25%7%13%30%21%5%
2271
21st to endDay
29%8%15%33%15%1
2405
August1st to 10thDay
32%10%20%26%10%2
2314
11th to 20thDay
27%7%16%29%20%1
2301
21st to endDay
28%5%11%27%22%6%
2561
September1st to 10thDay
31%5%11%29%18%6%
2025
11th to 20thDay
29%5%12%29%23%2
1980
21st to endDay
28%310%33%25%1
1980
October1st to 10thDay
36%5%10%24%24%1
1882
11th to 20thDay
31%47%28%24%7%
1800
21st to endDay
36%313%23%21%5%
1968
November1st to 10thDay
28%414%27%22%3
1673
11th to 20thDay
33%5%11%28%21%2
1710
21st to endDay
38%411%29%17%2
1600
December1st to 10thDay
35%5%14%30%14%2
1520
11th to 20thDay
41%5%14%30%10%
1915
21st to endDay
57%5%9%18%9%1
3134
January1st to 10thNight
49%5%12%21%13%1
4108
11th to 20thNight
41%5%13%26%14%
4120
21st to endNight
47%413%19%15%1
4532
February1st to 10thNight
44%6%13%20%14%3
2470
11th to 20thNight
38%6%14%24%16%3
2328
21st to endNight
35%411%23%21%7%
1884
March1st to 10thNight
34%5%10%29%18%3
2105
11th to 20thNight
40%49%25%18%3
1980
21st to endNight
47%6%14%21%10%2
2178
April1st to 10thNight
36%5%10%27%19%3
1970
11th to 20thNight
36%6%11%28%17%2
1627
21st to endNight
39%6%11%26%18%1
1620
May1st to 10thNight
41%7%14%23%13%2
1620
11th to 20thNight
37%6%13%28%15%1
1594
21st to endNight
37%9%18%21%14%1
1746
June1st to 10thNight
25%7%16%33%18%2
1617
11th to 20thNight
24%7%15%30%19%5%
1491
21st to endNight
21%7%13%33%22%3
1620
July1st to 10thNight
27%8%13%29%18%5%
1575
11th to 20thNight
21%9%13%28%23%6%
1566
21st to endNight
18%8%17%36%19%1
1673
August1st to 10thNight
24%8%19%30%16%2
1601
11th to 20thNight
24%5%14%35%19%3
1600
21st to endNight
24%5%12%28%22%9%
1793
September1st to 10thNight
25%5%12%28%22%9%
1933
11th to 20thNight
26%5%10%31%23%4
1980
21st to endNight
26%47%30%30%3
1980
October1st to 10thNight
32%6%10%25%24%3
2060
11th to 20thNight
31%37%26%26%7%
2160
21st to endNight
32%411%25%24%4
2384
November1st to 10thNight
24%413%28%26%6%
2405
11th to 20thNight
31%410%29%22%3
2470
21st to endNight
32%311%28%22%3
2574
December1st to 10thNight
34%5%13%32%16%2
2660
11th to 20thNight
33%411%37%14%1
3277
21st to endNight
52%5%9%24%8%1
4532

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
17%14%38%23%6%2
270
11th to 20thDay
20%16%35%20%9%1
270
21st to endDay
14%11%45%22%6%
297
February1st to 10thDay
14%23%39%20%4
270
11th to 20thDay
14%13%42%23%7%1
270
21st to endDay
12%19%48%17%4
225
March1st to 10thDay
16%15%44%18%6%1
255
11th to 20thDay
30%10%33%19%7%1
240
21st to endDay
29%20%35%11%4
264
April1st to 10thDay
19%19%41%18%2
249
11th to 20thDay
19%16%37%21%7%1
558
21st to endDay
22%16%31%20%9%2
600
May1st to 10thDay
18%11%37%25%8%1
603
11th to 20thDay
18%10%32%26%12%2
625
21st to endDay
18%7%30%30%11%3
679
June1st to 10thDay
5%6%22%38%22%7%
630
11th to 20thDay
8%5%32%33%18%4
630
21st to endDay
7%6%33%36%15%2
630
July1st to 10thDay
9%319%35%28%7%
621
11th to 20thDay
5%420%41%22%7%
618
21st to endDay
8%117%40%31%3
684
August1st to 10thDay
8%416%42%24%6%
626
11th to 20thDay
8%5%19%42%23%4
615
21st to endDay
10%420%34%26%6%
680
September1st to 10thDay
16%424%34%17%4
315
11th to 20thDay
8%5%27%37%17%7%
270
21st to endDay
13%10%32%30%13%3
270
October1st to 10thDay
23%7%24%28%12%5%
270
11th to 20thDay
10%17%43%20%8%2
270
21st to endDay
17%19%35%18%9%2
297
November1st to 10thDay
17%14%35%24%7%2
270
11th to 20thDay
13%14%44%20%8%
270
21st to endDay
23%13%31%24%7%1
270
December1st to 10thDay
10%12%43%26%8%1
270
11th to 20thDay
18%11%37%27%7%
270
21st to endDay
19%18%41%21%1
297
January1st to 10thNight
13%12%37%32%6%1
950
11th to 20thNight
13%13%38%29%7%
950
21st to endNight
13%10%40%30%7%
1045
February1st to 10thNight
15%10%43%27%4
950
11th to 20thNight
12%12%41%32%4
853
21st to endNight
14%13%42%26%5%
628
March1st to 10thNight
12%15%41%25%6%1
621
11th to 20thNight
19%13%35%27%6%
540
21st to endNight
21%11%39%24%5%
594
April1st to 10thNight
14%14%42%26%4
540
11th to 20thNight
16%14%38%28%4
533
21st to endNight
18%10%36%27%8%1
540
May1st to 10thNight
17%10%36%29%9%
540
11th to 20thNight
15%9%34%31%10%1
531
21st to endNight
14%8%31%32%14%1
584
June1st to 10thNight
7%424%46%18%1
540
11th to 20thNight
7%5%30%44%14%
540
21st to endNight
46%32%45%13%
540
July1st to 10thNight
8%216%44%29%1
525
11th to 20thNight
4121%48%25%1
522
21st to endNight
3116%54%26%1
591
August1st to 10thNight
4217%53%22%1
537
11th to 20thNight
6%220%48%22%1
534
21st to endNight
8%222%40%25%2
594
September1st to 10thNight
11%227%40%19%1
540
11th to 20thNight
9%230%39%18%1
540
21st to endNight
9%6%33%36%14%1
540
October1st to 10thNight
16%7%32%32%12%2
620
11th to 20thNight
14%11%38%29%8%
720
21st to endNight
17%12%32%30%9%1
800
November1st to 10thNight
8%10%36%36%9%
925
11th to 20thNight
11%12%41%29%7%
950
21st to endNight
14%11%39%28%8%1
950
December1st to 10thNight
12%11%41%29%6%
950
11th to 20thNight
15%11%35%32%7%
950
21st to endNight
20%11%36%28%5%
1045
Page generated at 2024-03-03 05:28:58. Version ac07

Copyright © 2024 Attilla Danko.


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