Boston Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Boston Mountain clear sky chart from 2005-11-06 to 2024-01-31.

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%
24309
23%
75086
14%
24246
48%
24246
27%
45484

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
22%
949
25%
2458
6%
946
36%
946
25%
1581
January11th to 20thNight
21%
950
24%
2470
7%
950
33%
950
25%
1590
January21st to endNight
23%
1043
27%
2711
7%
1043
36%
1043
27%
1694
February1st to 10thNight
19%
900
19%
2340
5%
900
27%
900
21%
1614
February11th to 20thNight
14%
851
19%
2246
4%
847
24%
847
22%
1482
February21st to endNight
16%
489
24%
1673
7%
489
33%
489
17%
1047
March1st to 10thNight
26%
540
23%
1980
12%
540
38%
540
20%
1209
March11th to 20thNight
28%
540
18%
1980
14%
540
35%
540
17%
1276
March21st to endNight
20%
594
16%
2178
8%
594
32%
594
16%
1437
April1st to 10thNight
27%
540
23%
1854
12%
540
42%
540
21%
1094
April11th to 20thNight
29%
533
24%
1775
15%
533
44%
533
23%
1073
April21st to endNight
25%
540
20%
1800
8%
540
41%
540
21%
1152
May1st to 10thNight
33%
540
18%
1679
11%
540
43%
540
25%
1057
May11th to 20thNight
42%
531
20%
1594
17%
531
48%
531
30%
969
May21st to endNight
45%
584
16%
1746
11%
582
54%
582
26%
1138
June1st to 10thNight
66%
540
21%
1620
20%
540
69%
540
40%
897
June11th to 20thNight
63%
540
23%
1620
19%
540
68%
540
44%
854
June21st to endNight
68%
540
25%
1620
21%
540
72%
540
47%
835
July1st to 10thNight
71%
525
18%
1575
18%
525
73%
525
40%
885
July11th to 20thNight
73%
522
22%
1566
24%
522
75%
522
47%
803
July21st to endNight
75%
591
24%
1673
26%
558
77%
558
40%
929
August1st to 10thNight
74%
537
19%
1601
21%
534
76%
534
38%
906
August11th to 20thNight
71%
534
24%
1666
27%
534
74%
534
35%
965
August21st to endNight
72%
594
24%
1980
27%
594
74%
594
37%
1068
September1st to 10thNight
67%
540
27%
1800
28%
540
71%
540
38%
944
September11th to 20thNight
63%
540
27%
1894
26%
540
67%
540
30%
1070
September21st to endNight
59%
573
30%
2013
27%
573
66%
573
35%
1047
October1st to 10thNight
56%
720
28%
2160
19%
720
62%
720
41%
1163
October11th to 20thNight
35%
720
31%
2160
15%
720
49%
720
32%
1245
October21st to endNight
34%
792
27%
2376
16%
792
44%
792
27%
1447
November1st to 10thNight
35%
740
30%
2220
15%
740
50%
740
32%
1261
November11th to 20thNight
35%
760
30%
2280
15%
760
49%
760
32%
1297
November21st to endNight
30%
935
24%
2609
12%
935
41%
935
27%
1644
December1st to 10thNight
25%
950
23%
2660
7%
950
39%
950
25%
1695
December11th to 20thNight
26%
949
23%
3069
9%
948
35%
948
19%
2008
December21st to endNight
22%
1043
15%
4440
7%
1026
35%
1026
12%
3108

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
13%7%36%5%345%5%7%43%
74602
Night
11%7%35%43445%7%48%
75525
TransparencyDay
40%6%11%22%17%4
74325
Night
35%6%11%23%20%5%
75322
SeeingDay
18%13%27%25%15%3
14334
Night
18%13%26%28%14%2
24313

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
13%9%35%423436%47%
1707
11th to 20thDay
13%7%36%5%335%35%46%
1710
21st to endDay
15%8%35%423445%47%
1872
February1st to 10thDay
16%11%45%5%3334442%
1620
11th to 20thDay
15%9%47%5%3345%6%40%
1601
21st to endDay
19%11%46%423345%38%
1596
March1st to 10thDay
15%8%36%4245%46%43%
1980
11th to 20thDay
20%9%36%43434440%
1980
21st to endDay
18%10%47%5%34445%36%
2178
April1st to 10thDay
13%9%35%6%345%5%6%42%
2105
11th to 20thDay
18%8%35%6%35%446%38%
2134
21st to endDay
20%9%47%5%33445%37%
2160
May1st to 10thDay
18%9%36%5%35%346%38%
2276
11th to 20thDay
14%6%36%6%45%5%6%7%37%
2302
21st to endDay
11%7%47%8%5%6%5%6%8%34%
2531
June1st to 10thDay
9%7%26%7%45%5%6%8%42%
2340
11th to 20thDay
8%5%26%7%46%7%6%9%41%
2340
21st to endDay
6%4245%36%5%6%10%49%
2340
July1st to 10thDay
10%5%26%7%5%7%6%7%11%35%
2340
11th to 20thDay
5%425%6%46%7%7%9%45%
2340
21st to endDay
7%425%6%47%7%8%11%39%
2546
August1st to 10thDay
7%426%7%46%7%7%11%38%
2328
11th to 20thDay
13%6%245%35%5%7%8%42%
2234
21st to endDay
7%426%6%45%6%5%8%46%
2376
September1st to 10thDay
12%5%25%43445%6%49%
2160
11th to 20thDay
11%5%25%5%45%5%6%9%44%
2062
21st to endDay
8%425%6%246%6%5%53%
1927
October1st to 10thDay
9%6%25%4245%46%54%
1800
11th to 20thDay
13%6%25%323345%54%
1800
21st to endDay
19%8%2342332449%
1980
November1st to 10thDay
11%7%34323236%56%
1858
11th to 20thDay
10%8%35%433346%52%
1900
21st to endDay
16%9%35%423346%45%
1560
December1st to 10thDay
14%8%25%43445%5%46%
1520
11th to 20thDay
13%9%47%5%34345%43%
1964
21st to endDay
15%13%8%7%43445%5%33%
3135
January1st to 10thNight
13%6%46%5%2445%5%47%
2458
11th to 20thNight
12%7%46%5%24346%47%
2470
21st to endNight
14%7%34433445%50%
2711
February1st to 10thNight
15%9%47%5%33445%40%
2340
11th to 20thNight
14%9%46%423446%44%
2245
21st to endNight
15%10%46%5%23445%43%
1673
March1st to 10thNight
14%8%46%5%34446%43%
1980
11th to 20thNight
17%9%35%5%35%45%5%39%
1980
21st to endNight
17%9%36%6%34446%39%
2178
April1st to 10thNight
12%8%3443445%6%47%
1854
11th to 20thNight
13%8%35%42435%7%46%
1775
21st to endNight
17%6%26%5%3446%6%42%
1800
May1st to 10thNight
14%7%35%42445%7%45%
1679
11th to 20thNight
15%6%2442446%7%46%
1593
21st to endNight
10%7%35%5%36%5%7%10%40%
1745
June1st to 10thNight
6%4144335%6%11%54%
1620
11th to 20thNight
431342447%11%56%
1620
21st to endNight
5%31332446%9%60%
1620
July1st to 10thNight
5%315%4347%8%9%51%
1620
11th to 20thNight
332432448%10%57%
1620
21st to endNight
5%414445%6%7%9%52%
1772
August1st to 10thNight
4324445%6%7%11%50%
1611
11th to 20thNight
6%424435%5%6%10%49%
1666
21st to endNight
44244345%6%10%54%
1980
September1st to 10thNight
8%42433345%8%57%
1800
11th to 20thNight
9%5%25%4345%5%7%50%
1894
21st to endNight
8%5%2343445%6%57%
2013
October1st to 10thNight
6%3233345%5%8%58%
2160
11th to 20thNight
12%6%2432333457%
2160
21st to endNight
17%6%2432333451%
2376
November1st to 10thNight
12%5%24323435%58%
2220
11th to 20thNight
11%7%2442345%5%54%
2280
21st to endNight
16%8%24424345%48%
2609
December1st to 10thNight
13%9%25%434435%47%
2660
11th to 20thNight
13%10%46%5%3444444%
3211
21st to endNight
15%12%7%8%5%3433435%
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
40%38%23%20%5%
1708
11th to 20thDay
41%49%23%20%2
1710
21st to endDay
39%38%27%18%4
1872
February1st to 10thDay
47%410%21%15%4
1620
11th to 20thDay
45%5%9%20%17%4
1610
21st to endDay
49%47%16%16%8%
1596
March1st to 10thDay
42%5%8%17%18%9%
1980
11th to 20thDay
48%49%20%14%5%
1980
21st to endDay
51%5%9%19%13%2
2178
April1st to 10thDay
42%6%10%21%19%2
2105
11th to 20thDay
46%5%10%19%16%4
2134
21st to endDay
49%5%8%21%14%2
2160
May1st to 10thDay
48%6%10%19%15%1
2276
11th to 20thDay
44%9%12%21%12%1
2306
21st to endDay
47%10%12%19%12%1
2531
June1st to 10thDay
38%9%14%26%12%1
2340
11th to 20thDay
36%9%15%25%14%2
2340
21st to endDay
29%8%15%27%17%4
2340
July1st to 10thDay
38%11%17%21%12%1
2276
11th to 20thDay
30%9%16%27%16%2
2271
21st to endDay
34%12%16%28%10%1
2405
August1st to 10thDay
36%11%18%24%11%1
2314
11th to 20thDay
37%9%12%25%15%1
2234
21st to endDay
34%8%15%23%15%5%
2376
September1st to 10thDay
34%6%12%24%17%7%
2160
11th to 20thDay
34%7%12%21%22%4
2062
21st to endDay
30%7%9%22%27%5%
1927
October1st to 10thDay
32%5%11%21%23%8%
1800
11th to 20thDay
34%36%24%24%9%
1800
21st to endDay
40%5%7%22%19%7%
1980
November1st to 10thDay
32%49%25%21%9%
1858
11th to 20thDay
34%48%22%23%9%
1900
21st to endDay
42%39%18%23%6%
1560
December1st to 10thDay
39%5%9%23%19%5%
1520
11th to 20thDay
44%46%16%26%3
1961
21st to endDay
49%7%9%16%14%4
3135
January1st to 10thNight
37%5%9%21%23%5%
2458
11th to 20thNight
39%311%23%21%3
2470
21st to endNight
36%49%24%22%6%
2711
February1st to 10thNight
45%49%21%16%4
2340
11th to 20thNight
41%49%24%17%5%
2246
21st to endNight
43%48%19%17%9%
1673
March1st to 10thNight
42%49%16%20%9%
1980
11th to 20thNight
45%6%10%18%16%5%
1980
21st to endNight
47%5%8%23%14%3
2178
April1st to 10thNight
37%5%10%23%20%5%
1854
11th to 20thNight
38%5%8%24%19%6%
1775
21st to endNight
42%7%10%24%17%2
1800
May1st to 10thNight
39%6%14%20%18%3
1679
11th to 20thNight
35%7%17%24%15%2
1594
21st to endNight
38%9%17%22%13%
1746
June1st to 10thNight
24%8%16%32%17%2
1620
11th to 20thNight
20%9%16%35%19%2
1620
21st to endNight
21%6%18%26%24%5%
1620
July1st to 10thNight
24%9%22%26%18%1
1575
11th to 20thNight
20%7%17%31%23%2
1566
21st to endNight
25%8%18%34%14%1
1673
August1st to 10thNight
25%10%20%33%12%
1601
11th to 20thNight
28%9%16%24%20%2
1666
21st to endNight
26%7%16%27%19%4
1980
September1st to 10thNight
26%6%12%30%18%8%
1800
11th to 20thNight
31%8%12%20%23%6%
1894
21st to endNight
27%6%9%23%29%6%
2013
October1st to 10thNight
24%6%15%23%23%10%
2160
11th to 20thNight
32%47%19%29%9%
2160
21st to endNight
37%47%21%22%9%
2376
November1st to 10thNight
31%48%23%24%9%
2220
11th to 20thNight
30%5%9%23%25%8%
2280
21st to endNight
39%38%20%24%6%
2609
December1st to 10thNight
39%410%20%21%6%
2660
11th to 20thNight
43%47%19%20%6%
3213
21st to endNight
52%5%9%17%15%3
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
29%22%33%14%2
270
11th to 20thDay
29%28%33%9%1
270
21st to endDay
29%25%33%12%2
294
February1st to 10thDay
35%26%28%8%2
240
11th to 20thDay
35%29%28%7%1
240
21st to endDay
45%24%24%5%2
198
March1st to 10thDay
33%23%30%13%2
240
11th to 20thDay
39%18%33%10%1
240
21st to endDay
34%31%26%6%3
264
April1st to 10thDay
25%24%32%13%6%1
365
11th to 20thDay
30%19%32%14%5%
412
21st to endDay
28%21%31%13%6%
420
May1st to 10thDay
23%18%37%17%4
539
11th to 20thDay
18%14%33%24%8%2
625
21st to endDay
14%12%35%25%11%4
679
June1st to 10thDay
11%6%23%34%23%3
630
11th to 20thDay
8%5%28%37%20%2
630
21st to endDay
5%6%31%34%20%3
630
July1st to 10thDay
9%416%36%28%7%
621
11th to 20thDay
6%321%35%29%7%
618
21st to endDay
7%212%37%32%10%
684
August1st to 10thDay
10%317%41%25%5%
626
11th to 20thDay
15%114%37%26%6%
548
21st to endDay
8%215%32%34%9%
495
September1st to 10thDay
11%415%32%31%7%
450
11th to 20thDay
8%321%37%25%7%
352
21st to endDay
10%8%26%33%21%3
270
October1st to 10thDay
11%11%35%26%14%2
270
11th to 20thDay
18%17%42%18%41
270
21st to endDay
35%13%31%17%31
297
November1st to 10thDay
17%17%39%21%6%1
270
11th to 20thDay
22%22%34%17%5%1
270
21st to endDay
34%16%27%18%42
270
December1st to 10thDay
21%28%30%17%41
270
11th to 20thDay
25%24%34%13%4
270
21st to endDay
30%24%33%12%1
297
January1st to 10thNight
22%21%32%20%4
950
11th to 20thNight
24%22%31%19%3
950
21st to endNight
22%21%31%23%3
1043
February1st to 10thNight
28%18%32%20%3
900
11th to 20thNight
24%24%35%15%1
851
21st to endNight
28%24%30%17%1
489
March1st to 10thNight
23%18%30%25%4
540
11th to 20thNight
25%17%27%26%4
540
21st to endNight
23%21%33%18%41
594
April1st to 10thNight
20%22%29%25%4
540
11th to 20thNight
20%19%29%26%6%1
533
21st to endNight
20%18%36%18%7%1
540
May1st to 10thNight
18%11%33%29%9%
540
11th to 20thNight
17%11%27%29%15%1
531
21st to endNight
13%8%30%29%18%3
584
June1st to 10thNight
9%5%16%39%30%2
540
11th to 20thNight
6%224%42%24%2
540
21st to endNight
5%220%39%29%4
540
July1st to 10thNight
7%113%33%39%6%
525
11th to 20thNight
4215%35%38%7%
522
21st to endNight
6%19%35%41%8%
591
August1st to 10thNight
5%110%44%33%5%
537
11th to 20thNight
7%114%40%33%4
534
21st to endNight
7%212%37%38%5%
594
September1st to 10thNight
9%315%35%36%2
540
11th to 20thNight
11%316%39%26%5%
540
21st to endNight
10%6%20%34%26%3
573
October1st to 10thNight
9%6%25%35%22%3
720
11th to 20thNight
17%14%32%29%9%
720
21st to endNight
22%16%25%26%9%1
792
November1st to 10thNight
15%14%32%27%11%1
740
11th to 20thNight
20%13%29%30%7%
760
21st to endNight
25%16%27%25%8%
935
December1st to 10thNight
22%18%32%23%4
950
11th to 20thNight
24%17%29%27%3
950
21st to endNight
24%22%28%23%3
1045
Page generated at 2024-01-28 04:26:36. Version ac07

Copyright 2024 Attilla Danko


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