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Pembroke
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pembroke 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
31%
22539
13%
74809
9%
22497
37%
22497
15%
54260

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
16%
760
7%
2649
3%
757
21%
757
6%
2207
January11th to 20thNight
20%
741
8%
2591
4%
741
26%
741
8%
2070
January21st to endNight
26%
792
13%
2650
8%
792
33%
792
13%
1969
February1st to 10thNight
16%
720
8%
2340
3%
720
22%
720
9%
1873
February11th to 20thNight
20%
701
12%
2275
6%
700
29%
700
13%
1712
February21st to endNight
23%
592
14%
1834
7%
592
32%
592
13%
1377
March1st to 10thNight
23%
720
13%
2093
8%
720
29%
720
15%
1590
March11th to 20thNight
25%
720
15%
1980
8%
720
32%
720
18%
1435
March21st to endNight
30%
792
19%
2109
9%
792
37%
792
21%
1491
April1st to 10thNight
25%
720
14%
1800
5%
720
29%
720
18%
1369
April11th to 20thNight
28%
711
17%
1775
7%
711
33%
711
22%
1291
April21st to endNight
32%
572
16%
1652
9%
572
37%
572
18%
1212
May1st to 10thNight
36%
360
18%
1440
17%
360
44%
360
18%
922
May11th to 20thNight
35%
354
20%
1416
19%
354
49%
354
18%
893
May21st to endNight
40%
389
13%
1551
12%
388
51%
388
23%
912
June1st to 10thNight
39%
360
9%
1440
10%
360
46%
360
17%
943
June11th to 20thNight
44%
360
12%
1440
15%
360
52%
360
22%
870
June21st to endNight
44%
360
10%
1440
12%
360
50%
360
18%
934
July1st to 10thNight
49%
350
14%
1400
18%
350
56%
350
25%
801
July11th to 20thNight
53%
348
15%
1392
19%
348
59%
348
23%
829
July21st to endNight
54%
394
15%
1486
15%
372
59%
372
24%
865
August1st to 10thNight
55%
452
15%
1516
15%
450
57%
450
25%
939
August11th to 20thNight
60%
534
17%
1598
13%
534
64%
534
30%
996
August21st to endNight
50%
736
18%
1924
9%
736
54%
736
30%
1273
September1st to 10thNight
47%
720
17%
1800
8%
720
50%
720
32%
1211
September11th to 20thNight
50%
720
20%
1800
12%
720
53%
720
33%
1184
September21st to endNight
43%
720
18%
2063
14%
720
47%
720
25%
1391
October1st to 10thNight
36%
720
17%
2160
12%
720
43%
720
21%
1502
October11th to 20thNight
25%
720
11%
2160
7%
720
32%
720
15%
1628
October21st to endNight
25%
792
12%
2470
7%
792
33%
792
12%
1911
November1st to 10thNight
31%
740
14%
2483
11%
740
38%
740
16%
1772
November11th to 20thNight
21%
760
12%
2660
8%
760
28%
760
11%
2006
November21st to endNight
21%
760
8%
2660
4%
760
26%
760
8%
2135
December1st to 10thNight
17%
760
7%
2660
4%
760
21%
760
6%
2201
December11th to 20thNight
18%
759
9%
3255
5%
759
26%
759
8%
2528
December21st to endNight
16%
830
6%
4847
3%
817
22%
817
4%
4018

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
17%10%47%6%35%5%5%6%32%
74736
Night
18%11%48%6%3445%6%31%
75050
TransparencyDay
52%6%11%19%10%1
74441
Night
54%6%11%19%9%1
74879
SeeingDay
22%13%29%22%11%3
13263
Night
23%11%28%28%10%1
22548

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
16%16%7%11%9%4443421%
1517
11th to 20thDay
18%18%5%9%6%36%44422%
1480
21st to endDay
13%16%6%10%8%45%445%25%
1701
February1st to 10thDay
12%15%7%12%8%45%45%5%21%
1620
11th to 20thDay
13%13%6%9%8%445%5%7%25%
1573
21st to endDay
18%14%5%8%6%45%5%46%24%
1422
March1st to 10thDay
16%12%5%9%7%45%45%5%29%
1859
11th to 20thDay
14%12%5%8%8%45%6%5%5%29%
1980
21st to endDay
18%9%47%434446%37%
2246
April1st to 10thDay
21%12%36%6%345%45%30%
2160
11th to 20thDay
22%9%26%5%33446%36%
2134
21st to endDay
22%8%47%5%3435%5%33%
2323
May1st to 10thDay
19%8%36%5%3445%6%35%
2519
11th to 20thDay
17%7%47%6%4445%5%37%
2478
21st to endDay
14%7%26%7%345%5%8%38%
2725
June1st to 10thDay
21%7%37%6%35%6%47%31%
2520
11th to 20thDay
15%5%35%5%45%6%6%8%40%
2520
21st to endDay
15%7%36%6%46%6%6%8%33%
2520
July1st to 10thDay
11%5%35%5%36%6%7%8%40%
2520
11th to 20thDay
11%5%35%6%47%7%7%9%37%
2520
21st to endDay
12%5%36%6%36%6%6%9%38%
2744
August1st to 10thDay
10%6%26%7%46%6%6%8%37%
2409
11th to 20thDay
13%6%26%446%5%6%8%39%
2303
21st to endDay
13%6%26%5%45%6%7%9%37%
2413
September1st to 10thDay
14%5%35%6%345%6%8%41%
2160
11th to 20thDay
13%6%35%6%3445%6%44%
2160
21st to endDay
18%7%26%5%45%6%5%7%35%
1895
October1st to 10thDay
19%9%36%6%35%5%5%6%34%
1800
11th to 20thDay
24%12%38%7%35%446%25%
1800
21st to endDay
27%9%48%6%35%45%7%22%
1886
November1st to 10thDay
16%10%47%6%45%5%5%7%33%
1591
11th to 20thDay
19%13%5%8%8%45%5%5%5%24%
1520
21st to endDay
24%16%6%9%7%345%5%416%
1520
December1st to 10thDay
23%17%6%9%7%46%5%5%416%
1520
11th to 20thDay
20%16%6%10%6%35%445%21%
1906
21st to endDay
27%19%6%14%42322418%
2772
January1st to 10thNight
17%18%7%11%8%46%44417%
2649
11th to 20thNight
18%16%5%11%7%45%44421%
2591
21st to endNight
12%14%6%9%8%45%5%45%28%
2650
February1st to 10thNight
14%14%7%12%8%45%45%5%21%
2340
11th to 20thNight
14%14%6%10%8%45%446%26%
2273
21st to endNight
15%13%6%9%8%4445%6%27%
1834
March1st to 10thNight
16%12%5%10%6%46%445%28%
2083
11th to 20thNight
15%13%48%6%345%5%6%32%
1979
21st to endNight
17%9%46%5%34346%39%
2109
April1st to 10thNight
20%11%48%6%35%446%30%
1800
11th to 20thNight
20%9%36%5%34445%36%
1775
21st to endNight
21%9%48%6%34446%31%
1652
May1st to 10thNight
19%8%46%5%3435%7%37%
1440
11th to 20thNight
19%7%15%5%35%447%39%
1415
21st to endNight
13%5%25%5%35%6%6%7%44%
1550
June1st to 10thNight
17%6%37%6%446%5%7%35%
1440
11th to 20thNight
15%5%25%435%6%6%7%42%
1440
21st to endNight
16%8%337%35%5%6%8%36%
1440
July1st to 10thNight
11%426%5%345%8%7%44%
1440
11th to 20thNight
12%6%34446%6%5%8%42%
1440
21st to endNight
9%5%25%5%45%6%6%9%43%
1574
August1st to 10thNight
11%336%7%35%5%6%8%43%
1526
11th to 20thNight
9%5%26%5%345%7%9%45%
1598
21st to endNight
11%6%25%5%45%5%5%9%42%
1924
September1st to 10thNight
12%5%37%6%345%5%7%45%
1800
11th to 20thNight
15%5%25%42445%7%46%
1800
21st to endNight
18%7%36%434447%41%
2063
October1st to 10thNight
21%7%35%5%3445%6%38%
2160
11th to 20thNight
22%10%37%7%44446%28%
2160
21st to endNight
24%12%47%5%45%446%26%
2470
November1st to 10thNight
19%10%46%6%35%5%46%32%
2483
11th to 20thNight
18%11%48%8%45%5%5%6%26%
2660
21st to endNight
23%15%5%10%7%345%5%5%19%
2660
December1st to 10thNight
22%17%6%10%7%44445%17%
2660
11th to 20thNight
20%18%6%8%6%34445%22%
3288
21st to endNight
28%19%5%11%5%3333416%
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
68%6%8%13%5%
1518
11th to 20thDay
66%6%8%11%10%1
1480
21st to endDay
63%49%14%9%1
1701
February1st to 10thDay
65%5%8%16%5%1
1620
11th to 20thDay
58%6%13%13%9%1
1582
21st to endDay
61%5%9%15%9%1
1422
March1st to 10thDay
59%39%18%10%1
1862
11th to 20thDay
57%5%10%15%11%2
1980
21st to endDay
50%39%20%13%5%
2246
April1st to 10thDay
55%48%19%11%3
2160
11th to 20thDay
51%47%22%14%2
2134
21st to endDay
53%5%7%15%16%3
2323
May1st to 10thDay
49%6%8%19%13%5%
2519
11th to 20thDay
49%5%7%20%17%2
2482
21st to endDay
44%7%12%21%13%4
2725
June1st to 10thDay
51%7%10%19%12%1
2520
11th to 20thDay
42%7%11%23%14%3
2520
21st to endDay
47%9%11%20%12%1
2520
July1st to 10thDay
37%8%12%27%14%1
2450
11th to 20thDay
39%9%13%25%13%1
2445
21st to endDay
40%9%15%27%9%
2591
August1st to 10thDay
43%9%15%22%12%
2395
11th to 20thDay
41%9%18%24%8%1
2303
21st to endDay
41%9%16%23%10%1
2413
September1st to 10thDay
39%7%15%27%12%
2160
11th to 20thDay
39%7%12%31%10%1
2160
21st to endDay
47%8%13%24%8%
1895
October1st to 10thDay
51%8%10%20%11%1
1800
11th to 20thDay
61%6%14%15%41
1800
21st to endDay
61%6%12%15%5%1
1886
November1st to 10thDay
49%7%14%22%6%
1591
11th to 20thDay
60%7%13%13%6%1
1520
21st to endDay
70%7%10%8%5%
1520
December1st to 10thDay
71%6%10%9%4
1520
11th to 20thDay
65%8%7%13%7%
1906
21st to endDay
74%37%13%3
2772
January1st to 10thNight
71%6%9%10%4
2649
11th to 20thNight
67%5%10%11%6%1
2591
21st to endNight
58%5%9%17%10%
2650
February1st to 10thNight
65%6%9%13%6%1
2340
11th to 20thNight
60%411%18%7%1
2275
21st to endNight
57%6%9%19%8%1
1834
March1st to 10thNight
59%410%17%9%1
2093
11th to 20thNight
52%5%12%17%13%1
1980
21st to endNight
48%5%8%20%15%4
2109
April1st to 10thNight
56%5%8%18%12%2
1800
11th to 20thNight
50%5%8%21%14%2
1775
21st to endNight
54%6%7%15%16%2
1652
May1st to 10thNight
47%5%8%20%16%4
1440
11th to 20thNight
45%6%7%22%17%3
1416
21st to endNight
37%7%15%20%17%3
1551
June1st to 10thNight
46%8%12%23%10%1
1440
11th to 20thNight
37%9%11%24%16%2
1440
21st to endNight
44%8%14%21%13%1
1440
July1st to 10thNight
34%9%13%24%18%2
1400
11th to 20thNight
38%8%13%27%13%1
1392
21st to endNight
35%9%16%28%11%
1486
August1st to 10thNight
38%8%16%24%13%
1516
11th to 20thNight
33%10%18%27%11%1
1598
21st to endNight
37%8%16%27%11%1
1924
September1st to 10thNight
38%7%13%28%14%1
1800
11th to 20thNight
37%7%16%31%9%
1800
21st to endNight
42%8%14%28%8%
2063
October1st to 10thNight
47%6%11%23%13%
2160
11th to 20thNight
57%6%12%18%7%
2160
21st to endNight
60%7%11%15%7%
2470
November1st to 10thNight
52%7%14%19%8%
2483
11th to 20thNight
58%7%12%14%7%1
2660
21st to endNight
65%7%11%13%3
2660
December1st to 10thNight
70%6%9%11%4
2660
11th to 20thNight
64%6%10%14%7%
3288
21st to endNight
74%47%11%4
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
25%13%34%22%6%1
180
11th to 20thDay
31%14%33%18%42
170
21st to endDay
26%14%32%18%9%1
228
February1st to 10thDay
28%21%35%14%31
240
11th to 20thDay
25%22%39%13%
240
21st to endDay
31%17%33%18%2
288
March1st to 10thDay
23%16%35%21%4
420
11th to 20thDay
24%16%31%22%5%1
420
21st to endDay
29%16%27%20%6%1
462
April1st to 10thDay
28%16%31%14%10%1
420
11th to 20thDay
32%14%21%18%11%4
412
21st to endDay
29%14%31%16%7%3
420
May1st to 10thDay
26%13%25%25%8%3
423
11th to 20thDay
19%16%29%21%11%3
447
21st to endDay
18%11%35%21%12%3
485
June1st to 10thDay
24%9%32%23%11%1
450
11th to 20thDay
17%12%28%25%13%6%
450
21st to endDay
18%10%30%23%16%3
450
July1st to 10thDay
10%7%25%38%16%4
445
11th to 20thDay
12%8%30%29%18%4
444
21st to endDay
13%8%29%30%17%4
488
August1st to 10thDay
13%7%26%29%18%7%
446
11th to 20thDay
15%323%29%21%9%
439
21st to endDay
14%9%28%24%16%8%
495
September1st to 10thDay
13%8%28%24%18%8%
450
11th to 20thDay
15%9%23%24%19%10%
450
21st to endDay
16%12%28%22%16%6%
450
October1st to 10thDay
26%13%22%20%15%4
450
11th to 20thDay
29%18%28%17%7%1
450
21st to endDay
32%14%25%21%6%1
448
November1st to 10thDay
24%16%31%21%8%1
285
11th to 20thDay
23%21%37%11%7%1
180
21st to endDay
33%22%30%10%33
180
December1st to 10thDay
28%12%38%16%6%1
180
11th to 20thDay
27%19%34%14%32
180
21st to endDay
28%22%27%19%32
198
January1st to 10thNight
26%14%31%24%4
760
11th to 20thNight
28%12%27%24%7%
741
21st to endNight
20%11%31%29%9%1
792
February1st to 10thNight
21%14%36%23%5%1
720
11th to 20thNight
21%12%36%24%5%
703
21st to endNight
23%15%30%27%6%
592
March1st to 10thNight
23%13%33%26%4
720
11th to 20thNight
24%15%30%24%7%1
720
21st to endNight
21%11%31%27%9%
792
April1st to 10thNight
26%13%29%26%6%
720
11th to 20thNight
26%12%30%24%9%
711
21st to endNight
26%10%26%28%10%1
572
May1st to 10thNight
23%5%28%32%11%1
360
11th to 20thNight
21%9%28%33%8%1
354
21st to endNight
15%6%33%33%12%1
389
June1st to 10thNight
19%5%29%40%7%1
360
11th to 20thNight
15%8%27%35%15%1
360
21st to endNight
19%7%25%34%14%1
360
July1st to 10thNight
10%5%26%42%15%1
350
11th to 20thNight
14%323%41%18%1
348
21st to endNight
10%425%44%17%1
394
August1st to 10thNight
11%320%38%26%1
452
11th to 20thNight
11%316%40%27%3
534
21st to endNight
13%7%23%36%19%2
736
September1st to 10thNight
14%5%27%31%21%2
720
11th to 20thNight
18%6%20%30%21%4
720
21st to endNight
21%8%21%27%20%2
720
October1st to 10thNight
25%7%27%26%14%2
720
11th to 20thNight
28%10%30%21%9%1
720
21st to endNight
30%12%25%27%6%1
792
November1st to 10thNight
24%14%25%28%8%1
740
11th to 20thNight
23%17%31%19%9%1
760
21st to endNight
32%15%23%24%6%
760
December1st to 10thNight
30%15%29%19%6%
760
11th to 20thNight
28%14%30%23%5%1
760
21st to endNight
34%13%26%22%4
836
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