South Baymouth
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the South Baymouth clear sky chart from 2005-11-06 to 2024-10-25.

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
30%
24404
11%
95315
7%
24199
35%
24199
12%
68165

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
13%
945
3%
4697
2%
926
17%
926
3%
3983
January11th to 20thNight
15%
948
3%
4438
2%
930
19%
930
4%
3885
January21st to endNight
18%
925
4%
4675
3%
909
22%
909
5%
3887
February1st to 10thNight
16%
760
9%
2470
3%
760
23%
760
8%
1967
February11th to 20thNight
21%
741
10%
2403
3%
739
29%
739
11%
1820
February21st to endNight
18%
628
9%
1893
2%
628
26%
628
12%
1448
March1st to 10thNight
23%
758
21%
3560
7%
745
32%
745
13%
2148
March11th to 20thNight
25%
751
18%
3453
7%
740
34%
740
14%
2098
March21st to endNight
30%
832
11%
3758
7%
814
39%
814
14%
2431
April1st to 10thNight
25%
701
15%
1967
5%
701
33%
701
19%
1390
April11th to 20thNight
34%
563
20%
1687
10%
563
41%
563
23%
1110
April21st to endNight
32%
570
15%
1710
8%
570
37%
570
19%
1209
May1st to 10thNight
40%
566
17%
2783
10%
559
44%
559
15%
1698
May11th to 20thNight
42%
465
12%
2604
15%
458
49%
458
14%
1466
May21st to endNight
47%
405
12%
2562
16%
399
54%
399
14%
1445
June1st to 10thNight
40%
380
15%
1330
11%
380
49%
380
23%
820
June11th to 20thNight
53%
380
15%
1330
14%
380
59%
380
26%
782
June21st to endNight
51%
380
12%
1330
12%
380
55%
380
23%
848
July1st to 10thNight
59%
363
15%
2091
17%
360
66%
360
20%
1174
July11th to 20thNight
61%
415
15%
1888
18%
409
65%
409
23%
1099
July21st to endNight
54%
608
12%
2393
12%
569
57%
569
23%
1415
August1st to 10thNight
56%
556
17%
2551
13%
545
62%
545
21%
1510
August11th to 20thNight
59%
551
13%
2617
13%
543
64%
543
20%
1543
August21st to endNight
52%
611
15%
2815
11%
605
57%
605
21%
1573
September1st to 10thNight
48%
708
19%
1914
11%
708
52%
708
32%
1215
September11th to 20thNight
53%
760
20%
2090
13%
760
57%
760
34%
1301
September21st to endNight
43%
760
18%
2090
12%
760
47%
760
24%
1443
October1st to 10thNight
33%
760
17%
2223
11%
760
40%
760
20%
1562
October11th to 20thNight
25%
760
11%
2280
6%
760
31%
760
13%
1749
October21st to endNight
18%
812
10%
2571
5%
812
25%
812
10%
2041
November1st to 10thNight
25%
740
14%
2426
10%
740
33%
740
13%
1798
November11th to 20thNight
17%
760
7%
2660
5%
760
21%
760
7%
2154
November21st to endNight
12%
760
6%
2660
3%
760
16%
760
6%
2226
December1st to 10thNight
11%
793
4%
2693
1%
793
14%
793
4%
2347
December11th to 20thNight
9%
950
5%
3483
1%
948
13%
948
4%
2906
December21st to endNight
8%
1039
2%
5220
0%
1026
11%
1026
2%
4674

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%10%38%5%4445%7%35%
101437
Night
15%12%49%5%5%435%6%31%
97436
TransparencyDay
47%7%13%21%11%1
101189
Night
53%7%12%18%9%1
97304
SeeingDay
18%13%30%26%11%2
15307
Night
21%13%29%24%11%2
24528

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
19%19%11%13%5%43235%17%
2239
11th to 20thDay
11%15%7%20%12%6%5%35%412%
2530
21st to endDay
16%20%7%13%7%5%445%5%14%
2967
February1st to 10thDay
11%17%7%13%8%5%5%445%22%
1710
11th to 20thDay
12%14%5%12%5%5%445%6%27%
1663
21st to endDay
11%15%5%13%6%5%446%6%26%
1559
March1st to 10thDay
16%11%47%445%35%7%34%
3263
11th to 20thDay
10%13%5%10%6%6%5%45%7%30%
3480
21st to endDay
13%10%38%5%45%46%7%36%
3815
April1st to 10thDay
17%11%36%5%4436%7%32%
2229
11th to 20thDay
18%8%27%5%4445%7%38%
2442
21st to endDay
19%9%37%44335%7%37%
2470
May1st to 10thDay
15%6%27%5%4435%7%42%
4108
11th to 20thDay
13%7%38%44445%7%41%
4232
21st to endDay
14%6%27%5%4435%6%45%
4990
June1st to 10thDay
13%6%26%6%5%5%46%8%39%
2850
11th to 20thDay
10%6%35%5%45%5%6%9%42%
2850
21st to endDay
14%7%26%445%47%7%39%
2850
July1st to 10thDay
13%8%38%45%445%7%39%
4760
11th to 20thDay
8%5%25%44446%8%50%
4650
21st to endDay
9%5%25%44435%8%52%
4656
August1st to 10thDay
9%5%26%5%5%5%47%10%44%
4104
11th to 20thDay
13%5%26%44445%8%46%
4044
21st to endDay
9%5%26%445%46%8%46%
4532
September1st to 10thDay
11%6%27%5%4446%8%44%
2244
11th to 20thDay
12%425%435%36%8%49%
2090
21st to endDay
16%6%37%5%4446%8%39%
2090
October1st to 10thDay
16%8%36%5%4446%6%36%
1957
11th to 20thDay
23%11%38%6%44446%27%
1900
21st to endDay
24%12%38%7%5%4346%23%
1889
November1st to 10thDay
17%13%49%5%445%5%8%25%
1650
11th to 20thDay
17%16%5%11%5%5%5%36%6%20%
1520
21st to endDay
24%21%6%9%6%4445%5%13%
1520
December1st to 10thDay
15%24%7%12%6%5%5%345%14%
1482
11th to 20thDay
20%20%6%13%6%5%5%34416%
1671
21st to endDay
27%24%5%12%6%5%43438%
2431
January1st to 10thNight
16%20%10%14%6%44345%16%
4716
11th to 20thNight
12%16%7%21%8%5%5%45%414%
4440
21st to endNight
15%20%7%13%7%5%4345%18%
4692
February1st to 10thNight
11%18%6%13%7%6%445%422%
2470
11th to 20thNight
10%15%5%11%7%5%5%45%5%27%
2403
21st to endNight
14%17%49%6%45%46%6%25%
1893
March1st to 10thNight
13%8%37%5%5%435%6%42%
3577
11th to 20thNight
8%12%48%5%5%435%6%38%
3479
21st to endNight
11%9%5%9%5%5%5%35%7%36%
3817
April1st to 10thNight
20%9%27%44445%6%35%
1967
11th to 20thNight
19%8%36%34445%8%37%
1687
21st to endNight
18%10%48%5%5%435%6%34%
1710
May1st to 10thNight
15%6%39%6%5%445%5%39%
2833
11th to 20thNight
10%6%38%5%5%5%5%6%8%39%
2659
21st to endNight
13%7%37%44345%7%41%
2587
June1st to 10thNight
11%8%26%5%45%5%7%7%39%
1330
11th to 20thNight
10%6%25%447%47%8%44%
1330
21st to endNight
12%6%27%5%5%5%46%7%40%
1330
July1st to 10thNight
12%6%26%5%4445%8%45%
2210
11th to 20thNight
10%425%436%46%7%51%
2303
21st to endNight
8%5%37%44435%6%51%
2900
August1st to 10thNight
8%6%27%445%5%6%8%45%
2825
11th to 20thNight
11%5%26%345%37%8%45%
2785
21st to endNight
8%6%36%44435%7%50%
3124
September1st to 10thNight
12%5%26%34445%8%47%
1914
11th to 20thNight
10%5%25%45%436%7%50%
2090
21st to endNight
17%6%26%5%45%35%8%39%
2090
October1st to 10thNight
18%8%37%6%4445%6%36%
2223
11th to 20thNight
23%9%38%6%5%435%6%26%
2280
21st to endNight
25%12%48%6%4435%6%23%
2571
November1st to 10thNight
19%14%37%45%445%7%28%
2426
11th to 20thNight
17%18%5%10%7%6%5%346%19%
2660
21st to endNight
21%19%6%9%6%5%435%5%16%
2660
December1st to 10thNight
19%23%7%11%6%4334414%
2693
11th to 20thNight
18%21%5%11%6%5%435%5%17%
3526
21st to endNight
24%21%6%13%5%5%424412%
5236

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
72%9%11%7%1
2240
11th to 20thDay
78%8%7%5%2
2530
21st to endDay
72%10%10%7%2
2967
February1st to 10thDay
65%7%12%13%3
1710
11th to 20thDay
57%8%14%14%6%1
1672
21st to endDay
56%8%14%18%5%
1559
March1st to 10thDay
48%8%16%15%11%1
3266
11th to 20thDay
51%9%13%20%6%1
3480
21st to endDay
44%9%16%15%13%3
3815
April1st to 10thDay
49%7%13%19%11%1
2229
11th to 20thDay
45%5%10%25%14%2
2442
21st to endDay
46%5%13%20%14%3
2470
May1st to 10thDay
39%7%12%23%17%2
4120
11th to 20thDay
38%8%14%25%14%1
4236
21st to endDay
39%7%13%17%22%3
4990
June1st to 10thDay
40%7%13%25%13%2
2850
11th to 20thDay
36%7%13%26%17%2
2850
21st to endDay
41%7%12%24%13%2
2850
July1st to 10thDay
43%6%14%23%13%1
4686
11th to 20thDay
29%8%16%34%13%1
4569
21st to endDay
29%7%12%29%23%1
4509
August1st to 10thDay
33%8%17%29%13%1
4091
11th to 20thDay
35%7%18%29%11%
4083
21st to endDay
33%9%15%33%10%1
4531
September1st to 10thDay
37%8%16%28%10%1
2244
11th to 20thDay
33%7%17%31%11%1
2090
21st to endDay
43%9%15%23%9%
2090
October1st to 10thDay
47%8%12%20%13%
1957
11th to 20thDay
57%7%14%16%6%
1900
21st to endDay
62%7%12%13%5%
1889
November1st to 10thDay
56%8%14%17%5%
1650
11th to 20thDay
64%8%14%10%5%
1520
21st to endDay
72%6%12%8%2
1520
December1st to 10thDay
74%8%10%6%2
1482
11th to 20thDay
74%6%9%10%1
1671
21st to endDay
80%9%6%5%
2431
January1st to 10thNight
70%10%10%8%2
4716
11th to 20thNight
74%9%9%6%2
4440
21st to endNight
71%7%11%9%2
4692
February1st to 10thNight
65%5%10%14%4
2470
11th to 20thNight
58%8%13%15%5%1
2405
21st to endNight
57%8%13%14%7%
1893
March1st to 10thNight
43%7%16%22%11%1
3587
11th to 20thNight
44%6%14%23%10%2
3480
21st to endNight
45%8%13%20%11%2
3817
April1st to 10thNight
49%6%10%20%13%2
1967
11th to 20thNight
43%6%9%23%17%2
1687
21st to endNight
50%6%9%17%15%3
1710
May1st to 10thNight
44%6%12%21%15%2
2840
11th to 20thNight
39%7%12%22%17%2
2660
21st to endNight
40%8%12%19%16%5%
2588
June1st to 10thNight
39%8%10%23%18%2
1330
11th to 20thNight
34%8%13%23%20%2
1330
21st to endNight
41%7%14%22%13%2
1330
July1st to 10thNight
37%5%13%24%16%4
2175
11th to 20thNight
30%7%11%38%13%1
2261
21st to endNight
33%6%12%23%26%1
2808
August1st to 10thNight
34%8%14%30%13%1
2814
11th to 20thNight
35%8%18%25%13%
2812
21st to endNight
33%7%14%32%13%1
3124
September1st to 10thNight
35%7%14%28%14%2
1914
11th to 20thNight
33%7%16%33%11%1
2090
21st to endNight
43%8%15%23%10%
2090
October1st to 10thNight
49%6%11%22%12%
2223
11th to 20thNight
58%7%12%17%5%
2280
21st to endNight
62%7%12%13%5%
2571
November1st to 10thNight
55%7%12%19%6%
2426
11th to 20thNight
67%7%12%10%4
2660
21st to endNight
70%7%12%9%2
2660
December1st to 10thNight
75%7%9%8%1
2693
11th to 20thNight
70%7%11%9%3
3525
21st to endNight
77%9%8%5%1
5236

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%21%32%16%4
189
11th to 20thDay
21%17%37%20%5%
270
21st to endDay
28%13%32%19%8%
297
February1st to 10thDay
22%25%34%13%5%
270
11th to 20thDay
19%23%38%17%2
270
21st to endDay
25%28%37%8%1
225
March1st to 10thDay
21%18%36%19%41
351
11th to 20thDay
19%15%37%23%5%1
460
21st to endDay
21%17%32%23%5%1
506
April1st to 10thDay
23%15%32%23%7%1
460
11th to 20thDay
27%17%27%17%9%3
452
21st to endDay
26%13%34%18%8%1
460
May1st to 10thDay
20%9%37%24%8%2
463
11th to 20thDay
17%10%29%30%13%2
487
21st to endDay
13%8%33%29%15%3
617
June1st to 10thDay
14%9%32%31%13%1
680
11th to 20thDay
12%8%31%34%13%1
680
21st to endDay
17%8%30%31%11%2
680
July1st to 10thDay
9%428%39%17%2
671
11th to 20thDay
10%6%28%38%14%4
668
21st to endDay
11%330%36%16%4
644
August1st to 10thDay
12%6%25%33%20%5%
486
11th to 20thDay
12%5%21%35%20%8%
479
21st to endDay
13%8%28%29%18%4
539
September1st to 10thDay
13%10%28%26%18%5%
490
11th to 20thDay
13%7%23%31%19%7%
490
21st to endDay
19%11%24%26%17%4
490
October1st to 10thDay
19%19%24%24%12%2
490
11th to 20thDay
24%19%34%17%6%1
490
21st to endDay
28%23%32%14%31
376
November1st to 10thDay
28%18%34%15%5%
259
11th to 20thDay
26%22%34%14%3
180
21st to endDay
33%23%31%11%2
180
December1st to 10thDay
27%24%29%15%5%
180
11th to 20thDay
32%23%35%9%2
180
21st to endDay
31%28%33%5%31
198
January1st to 10thNight
23%22%30%20%4
950
11th to 20thNight
25%19%31%20%5%1
950
21st to endNight
22%12%35%22%8%1
931
February1st to 10thNight
19%21%35%20%4
760
11th to 20thNight
18%17%34%24%6%
743
21st to endNight
21%17%37%20%4
628
March1st to 10thNight
17%17%37%22%6%1
760
11th to 20thNight
17%15%36%23%8%1
760
21st to endNight
19%12%32%29%8%1
836
April1st to 10thNight
25%11%33%25%5%1
701
11th to 20thNight
23%11%30%23%11%2
563
21st to endNight
22%11%28%25%13%1
570
May1st to 10thNight
15%6%28%34%14%3
570
11th to 20thNight
16%7%26%33%16%1
473
21st to endNight
14%5%26%34%19%2
411
June1st to 10thNight
15%431%34%13%2
380
11th to 20thNight
11%8%22%38%20%2
380
21st to endNight
14%321%37%22%2
380
July1st to 10thNight
10%320%42%23%1
370
11th to 20thNight
8%320%39%25%4
422
21st to endNight
9%423%34%27%4
624
August1st to 10thNight
10%421%37%24%4
567
11th to 20thNight
11%417%31%32%5%
564
21st to endNight
12%422%32%23%6%
627
September1st to 10thNight
14%6%26%27%20%7%
708
11th to 20thNight
12%6%24%30%18%10%
760
21st to endNight
18%9%24%26%19%4
760
October1st to 10thNight
21%12%26%26%13%2
760
11th to 20thNight
28%15%28%19%10%
760
21st to endNight
29%17%29%20%41
812
November1st to 10thNight
26%15%30%21%7%1
740
11th to 20thNight
26%23%28%17%6%
760
21st to endNight
32%18%29%16%5%
760
December1st to 10thNight
31%22%29%12%5%
793
11th to 20thNight
28%22%32%12%41
950
21st to endNight
34%17%30%14%4
1045
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