Saint Peters Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Saint Peters Bay 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
24%
23670
9%
74408
5%
23608
29%
23608
12%
58377

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
9%
850
4%
2649
0%
847
12%
847
4%
2358
January11th to 20thNight
11%
829
4%
2601
1%
829
15%
829
5%
2280
January21st to endNight
16%
826
10%
2650
4%
826
23%
826
7%
2205
February1st to 10thNight
15%
720
7%
2340
2%
720
21%
720
8%
1871
February11th to 20thNight
12%
703
6%
2276
1%
700
17%
700
8%
1844
February21st to endNight
22%
592
13%
1862
4%
592
31%
592
12%
1388
March1st to 10thNight
20%
718
13%
2076
6%
718
27%
718
13%
1608
March11th to 20thNight
23%
720
12%
1980
5%
720
28%
720
13%
1539
March21st to endNight
23%
738
13%
2124
6%
738
30%
738
14%
1633
April1st to 10thNight
22%
540
10%
1800
6%
540
27%
540
11%
1380
April11th to 20thNight
27%
534
14%
1750
9%
534
33%
534
17%
1242
April21st to endNight
26%
540
13%
1620
7%
540
31%
540
16%
1205
May1st to 10thNight
31%
540
14%
1447
9%
540
35%
540
18%
1095
May11th to 20thNight
36%
532
14%
1417
6%
532
41%
532
23%
1014
May21st to endNight
31%
582
11%
1551
5%
582
35%
582
21%
1133
June1st to 10thNight
30%
540
6%
1440
4%
540
31%
540
17%
1122
June11th to 20thNight
41%
438
12%
1338
7%
438
44%
438
21%
914
June21st to endNight
35%
360
6%
1260
4%
360
36%
360
13%
932
July1st to 10thNight
44%
384
8%
1259
5%
384
46%
384
20%
858
July11th to 20thNight
46%
522
9%
1392
6%
522
48%
522
24%
1000
July21st to endNight
46%
590
11%
1486
9%
558
47%
558
21%
1107
August1st to 10thNight
53%
538
10%
1519
8%
534
54%
534
26%
1034
August11th to 20thNight
44%
532
11%
1596
7%
532
46%
532
19%
1158
August21st to endNight
50%
594
15%
1912
12%
594
54%
594
24%
1233
September1st to 10thNight
40%
540
13%
1800
11%
540
46%
540
22%
1177
September11th to 20thNight
39%
540
18%
1800
16%
540
44%
540
20%
1203
September21st to endNight
31%
698
15%
2070
9%
698
38%
698
21%
1442
October1st to 10thNight
33%
720
15%
2160
8%
720
38%
720
20%
1508
October11th to 20thNight
27%
720
12%
2160
7%
720
31%
720
14%
1629
October21st to endNight
17%
834
11%
2461
5%
834
22%
834
10%
2012
November1st to 10thNight
15%
830
8%
2525
3%
830
20%
830
9%
2042
November11th to 20thNight
15%
850
7%
2660
3%
850
20%
850
6%
2280
November21st to endNight
12%
850
2%
2660
1%
850
13%
850
4%
2370
December1st to 10thNight
9%
850
3%
2660
0%
850
12%
850
4%
2399
December11th to 20thNight
7%
850
3%
3259
0%
849
9%
849
2%
3007
December21st to endNight
7%
926
1%
4848
0%
907
9%
907
1%
4155

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
19%12%5%8%6%3445%6%27%
75153
Night
20%12%5%9%6%34446%25%
74646
TransparencyDay
58%7%12%16%7%1
74854
Night
62%6%11%15%6%1
74480
SeeingDay
25%13%28%24%9%1
16398
Night
27%13%28%24%8%1
23682

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
18%18%8%15%8%45%345%12%
1516
11th to 20thDay
20%16%7%14%10%6%444412%
1481
21st to endDay
12%11%9%17%11%5%5%5%5%5%17%
1701
February1st to 10thDay
18%13%6%11%8%5%6%445%20%
1620
11th to 20thDay
18%14%5%10%7%6%5%5%45%22%
1573
21st to endDay
10%13%6%10%8%45%5%5%6%28%
1394
March1st to 10thDay
14%15%6%9%7%35%5%5%5%26%
1876
11th to 20thDay
13%13%6%11%8%45%45%6%26%
1980
21st to endDay
18%15%7%10%6%23335%29%
2232
April1st to 10thDay
19%13%5%8%6%34346%29%
2160
11th to 20thDay
21%12%45%5%33347%34%
2156
21st to endDay
21%13%5%6%434446%31%
2340
May1st to 10thDay
26%12%36%5%34345%29%
2511
11th to 20thDay
20%9%46%5%3445%6%34%
2478
21st to endDay
20%9%35%5%2445%8%33%
2724
June1st to 10thDay
25%11%46%6%35%5%5%6%24%
2520
11th to 20thDay
21%8%36%5%45%45%7%35%
2633
21st to endDay
23%10%46%5%3336%7%29%
2700
July1st to 10thDay
15%7%35%5%35%5%5%9%38%
2642
11th to 20thDay
15%7%36%5%25%5%6%8%37%
2520
21st to endDay
17%11%47%6%35%46%8%30%
2745
August1st to 10thDay
16%6%26%5%45%5%6%9%35%
2406
11th to 20thDay
20%7%35%5%35%6%7%8%31%
2304
21st to endDay
16%6%26%5%35%5%6%8%37%
2444
September1st to 10thDay
18%5%35%43446%8%39%
2160
11th to 20thDay
21%10%35%5%2445%6%35%
2160
21st to endDay
20%8%35%5%34447%37%
1886
October1st to 10thDay
20%9%47%5%3445%7%32%
1800
11th to 20thDay
20%14%48%7%446%6%6%22%
1800
21st to endDay
23%18%5%7%6%44447%20%
1893
November1st to 10thDay
21%19%5%8%7%34435%21%
1549
11th to 20thDay
20%23%8%8%5%34445%15%
1520
21st to endDay
18%20%9%12%7%45%447%11%
1520
December1st to 10thDay
23%20%10%15%6%333349%
1520
11th to 20thDay
25%19%11%15%6%343346%
1906
21st to endDay
20%19%11%14%7%3342414%
2783
January1st to 10thNight
19%16%8%15%8%44445%14%
2649
11th to 20thNight
18%14%6%14%9%445%45%15%
2601
21st to endNight
15%12%8%12%8%45%5%5%5%20%
2650
February1st to 10thNight
18%13%410%8%44445%24%
2340
11th to 20thNight
18%15%5%10%8%5%4445%21%
2273
21st to endNight
12%14%7%9%6%45%5%5%5%28%
1862
March1st to 10thNight
15%15%6%10%6%3445%5%27%
2067
11th to 20thNight
18%11%6%9%8%34445%27%
1979
21st to endNight
20%14%5%8%6%33345%29%
2124
April1st to 10thNight
22%11%5%9%6%45%45%5%25%
1800
11th to 20thNight
22%12%45%43435%5%33%
1750
21st to endNight
23%14%46%433445%30%
1620
May1st to 10thNight
26%9%47%43445%6%28%
1447
11th to 20thNight
21%9%346%445%5%5%35%
1416
21st to endNight
18%10%36%5%35%5%5%9%31%
1550
June1st to 10thNight
28%7%5%6%7%345%5%6%26%
1440
11th to 20thNight
19%8%35%43445%6%39%
1338
21st to endNight
23%9%47%6%345%5%7%28%
1260
July1st to 10thNight
15%9%36%5%35%6%6%7%35%
1296
11th to 20thNight
14%7%36%7%35%6%6%8%34%
1440
21st to endNight
17%8%36%6%35%5%6%8%30%
1573
August1st to 10thNight
15%5%25%5%35%5%7%9%37%
1530
11th to 20thNight
17%8%46%6%36%5%5%6%34%
1596
21st to endNight
13%6%26%5%35%5%7%8%40%
1912
September1st to 10thNight
16%7%27%6%345%46%40%
1800
11th to 20thNight
21%7%25%5%235%45%41%
1800
21st to endNight
20%7%26%5%3435%7%38%
2070
October1st to 10thNight
21%8%36%43445%7%36%
2160
11th to 20thNight
22%11%46%5%34447%29%
2160
21st to endNight
27%15%47%6%43345%22%
2461
November1st to 10thNight
20%15%49%7%35%445%24%
2525
11th to 20thNight
21%19%6%9%6%45%446%17%
2660
21st to endNight
25%18%7%9%6%34445%14%
2660
December1st to 10thNight
24%19%9%12%6%34445%11%
2660
11th to 20thNight
27%18%9%14%7%3332311%
3293
21st to endNight
27%16%8%15%6%2323415%
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
81%5%6%6%3
1517
11th to 20thDay
78%8%8%5%1
1481
21st to endDay
73%7%8%8%4
1701
February1st to 10thDay
70%5%9%11%4
1620
11th to 20thDay
65%7%11%13%4
1581
21st to endDay
56%6%13%13%10%2
1394
March1st to 10thDay
58%5%10%19%8%
1880
11th to 20thDay
58%6%12%18%6%1
1980
21st to endDay
60%5%10%15%8%2
2232
April1st to 10thDay
57%5%10%16%10%2
2160
11th to 20thDay
51%5%10%20%13%1
2156
21st to endDay
53%6%13%16%10%1
2340
May1st to 10thDay
58%410%15%11%1
2511
11th to 20thDay
49%7%10%23%11%
2482
21st to endDay
49%7%13%20%9%
2724
June1st to 10thDay
58%8%12%17%5%
2520
11th to 20thDay
49%7%12%24%8%1
2633
21st to endDay
55%8%11%15%9%1
2700
July1st to 10thDay
42%9%18%25%6%
2570
11th to 20thDay
42%9%17%22%9%
2444
21st to endDay
52%8%16%17%7%
2592
August1st to 10thDay
44%9%17%24%6%
2392
11th to 20thDay
46%10%15%23%5%
2304
21st to endDay
44%8%16%25%7%
2444
September1st to 10thDay
41%8%18%25%9%
2160
11th to 20thDay
51%5%12%22%10%
2160
21st to endDay
47%7%13%22%11%
1886
October1st to 10thDay
52%6%13%21%8%
1800
11th to 20thDay
61%7%14%14%41
1800
21st to endDay
66%6%11%12%4
1893
November1st to 10thDay
68%5%11%13%3
1549
11th to 20thDay
76%5%9%8%2
1520
21st to endDay
76%6%12%41
1520
December1st to 10thDay
82%7%7%42
1520
11th to 20thDay
87%5%332
1905
21st to endDay
77%6%9%43
2783
January1st to 10thNight
78%6%7%6%2
2649
11th to 20thNight
74%8%9%7%2
2601
21st to endNight
69%6%9%10%5%
2650
February1st to 10thNight
66%5%11%11%6%1
2340
11th to 20thNight
66%7%10%12%41
2276
21st to endNight
57%6%11%16%9%1
1862
March1st to 10thNight
59%7%9%16%8%1
2076
11th to 20thNight
59%6%9%16%7%2
1980
21st to endNight
59%5%9%16%10%2
2124
April1st to 10thNight
61%5%10%13%10%1
1800
11th to 20thNight
52%5%10%19%11%2
1750
21st to endNight
56%5%9%17%11%1
1620
May1st to 10thNight
56%5%10%18%10%1
1447
11th to 20thNight
49%5%12%21%12%1
1417
21st to endNight
50%6%13%21%9%1
1551
June1st to 10thNight
58%6%12%18%5%
1440
11th to 20thNight
47%6%11%22%14%
1338
21st to endNight
56%8%14%13%8%
1260
July1st to 10thNight
45%9%18%22%6%
1259
11th to 20thNight
44%10%16%21%8%1
1392
21st to endNight
50%9%16%19%6%
1486
August1st to 10thNight
41%10%18%25%6%
1519
11th to 20thNight
49%9%16%20%6%
1596
21st to endNight
40%9%18%26%7%
1912
September1st to 10thNight
44%7%13%27%9%
1800
11th to 20thNight
47%6%12%25%11%
1800
21st to endNight
48%7%12%25%9%
2070
October1st to 10thNight
49%6%13%23%9%
2160
11th to 20thNight
58%6%13%20%3
2160
21st to endNight
67%5%8%14%6%
2461
November1st to 10thNight
64%7%12%12%5%
2525
11th to 20thNight
72%7%9%9%3
2660
21st to endNight
76%8%10%5%1
2660
December1st to 10thNight
79%7%7%5%2
2660
11th to 20thNight
84%45%5%1
3295
21st to endNight
78%5%9%7%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
26%23%35%14%3
370
11th to 20thDay
27%22%28%19%4
356
21st to endDay
18%22%39%18%2
374
February1st to 10thDay
27%24%34%13%2
340
11th to 20thDay
22%27%31%15%41
336
21st to endDay
17%20%33%24%6%1
280
March1st to 10thDay
22%15%36%22%41
376
11th to 20thDay
21%19%33%23%5%1
420
21st to endDay
27%18%29%18%6%1
462
April1st to 10thDay
27%19%36%13%5%
420
11th to 20thDay
25%18%32%18%6%1
412
21st to endDay
24%13%30%25%8%1
420
May1st to 10thDay
32%10%27%20%8%3
594
11th to 20thDay
23%8%29%28%11%2
624
21st to endDay
24%11%30%26%9%1
680
June1st to 10thDay
32%7%27%23%11%1
630
11th to 20thDay
21%7%25%36%10%1
630
21st to endDay
26%7%23%30%12%2
630
July1st to 10thDay
19%6%26%36%11%2
620
11th to 20thDay
17%5%27%32%17%2
618
21st to endDay
22%5%22%33%16%1
685
August1st to 10thDay
16%223%38%18%2
525
11th to 20thDay
20%5%24%31%16%4
439
21st to endDay
20%7%21%32%16%3
495
September1st to 10thDay
17%5%32%34%9%3
450
11th to 20thDay
27%10%26%25%10%1
450
21st to endDay
25%9%30%23%12%2
394
October1st to 10thDay
24%12%24%25%13%2
360
11th to 20thDay
26%12%29%21%10%2
360
21st to endDay
32%17%29%15%6%1
396
November1st to 10thDay
32%19%27%17%41
365
11th to 20thDay
38%15%28%14%41
370
21st to endDay
34%21%28%16%1
370
December1st to 10thDay
35%18%28%16%3
370
11th to 20thDay
34%24%30%11%1
370
21st to endDay
26%29%29%14%2
407
January1st to 10thNight
28%22%31%16%4
850
11th to 20thNight
27%19%33%17%4
829
21st to endNight
23%23%29%20%5%
826
February1st to 10thNight
27%18%31%21%4
720
11th to 20thNight
25%19%36%16%31
703
21st to endNight
19%17%32%24%8%
592
March1st to 10thNight
24%13%36%23%3
720
11th to 20thNight
23%14%30%23%9%
720
21st to endNight
27%14%27%23%9%1
738
April1st to 10thNight
26%14%28%25%6%
540
11th to 20thNight
26%9%31%23%9%1
534
21st to endNight
29%9%30%21%10%1
540
May1st to 10thNight
31%8%23%24%11%3
540
11th to 20thNight
25%5%23%31%14%2
532
21st to endNight
23%7%33%28%9%
583
June1st to 10thNight
31%6%26%27%9%1
540
11th to 20thNight
22%7%24%37%10%1
438
21st to endNight
27%423%35%9%1
360
July1st to 10thNight
20%424%36%15%1
384
11th to 20thNight
16%423%41%14%1
522
21st to endNight
22%418%44%12%1
590
August1st to 10thNight
16%420%42%16%1
538
11th to 20thNight
21%419%37%17%2
532
21st to endNight
16%5%22%35%22%1
594
September1st to 10thNight
20%6%28%32%13%1
540
11th to 20thNight
26%7%23%31%13%1
540
21st to endNight
26%8%30%27%8%2
698
October1st to 10thNight
28%8%27%26%12%
720
11th to 20thNight
29%11%26%23%10%1
720
21st to endNight
37%15%25%19%3
834
November1st to 10thNight
33%17%28%16%5%1
830
11th to 20thNight
32%19%29%15%41
850
21st to endNight
36%19%26%15%3
850
December1st to 10thNight
35%19%28%13%4
850
11th to 20thNight
32%24%29%13%2
850
21st to endNight
35%19%27%14%31
935
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