Port Dover
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Port Dover clear sky chart from 2005-11-05 to 2017-12-20.

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
33%
15302
14%
48114
9%
15265
39%
15265
17%
33429

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 15thNight
13%
716
9%
2410
5%
716
19%
716
7%
1907
January16th to endNight
14%
768
9%
2496
3%
768
22%
768
9%
1962
February1st to 15thNight
17%
702
7%
2287
2%
701
23%
701
10%
1812
February16th to endNight
24%
631
11%
1988
5%
631
32%
631
13%
1491
March1st to 15thNight
24%
720
14%
1983
7%
720
30%
720
14%
1516
March16th to endNight
29%
768
19%
2112
9%
768
38%
768
20%
1450
April1st to 15thNight
27%
718
15%
1844
6%
718
32%
718
20%
1347
April16th to endNight
36%
546
20%
1626
8%
546
45%
546
22%
1039
May1st to 15thNight
36%
540
16%
1620
8%
540
43%
540
20%
1088
May16th to endNight
44%
385
18%
1508
15%
385
55%
385
21%
863
June1st to 15thNight
42%
360
14%
1440
13%
360
51%
360
18%
869
June16th to endNight
47%
360
13%
1440
12%
360
56%
360
19%
864
July1st to 15thNight
62%
340
17%
1360
22%
340
66%
340
28%
699
July16th to endNight
54%
564
15%
1595
12%
531
63%
531
31%
932
August1st to 15thNight
62%
539
18%
1609
15%
536
65%
536
31%
960
August16th to endNight
62%
612
23%
1758
14%
612
67%
612
34%
1033
September1st to 15thNight
55%
720
23%
1846
13%
720
58%
720
32%
1182
September16th to endNight
56%
717
24%
1983
17%
717
61%
717
32%
1225
October1st to 15thNight
41%
720
18%
2160
17%
720
45%
720
23%
1414
October16th to endNight
25%
768
15%
2304
9%
768
33%
768
16%
1663
November1st to 15thNight
34%
760
18%
2530
15%
760
40%
760
19%
1688
November16th to endNight
19%
780
11%
2730
5%
780
27%
780
10%
1973
December1st to 15thNight
13%
780
6%
2730
3%
780
17%
780
7%
2174
December16th to endNight
12%
788
7%
2755
2%
788
18%
788
6%
2278

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%8%36%5%35%5%5%7%33%
48714
Night
15%8%36%5%3445%7%34%
48297
Cloud CoverDay
14%8%36%5%35%5%5%7%33%
48724
Night
15%8%36%5%3445%7%34%
48301
TransparencyDay
47%7%13%19%9%1
48415
Night
48%6%12%20%10%1
48114
SeeingDay
16%12%22%25%16%6%
5631
Night
17%20%22%24%12%1
15309

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 15thDay
18%12%5%10%5%45%447%19%
1526
16th to endDay
14%15%6%12%8%36%446%16%
1728
February1st to 15thDay
16%16%5%10%8%45%44418%
1575
16th to endDay
17%12%6%9%8%35%5%46%21%
1482
March1st to 15thDay
16%12%48%7%35%45%6%24%
1966
16th to endDay
16%10%47%6%3435%6%31%
2112
April1st to 15thDay
18%8%37%6%3445%5%30%
2107
16th to endDay
17%7%35%423347%39%
2340
May1st to 15thDay
15%5%36%6%35%35%7%37%
2331
16th to endDay
11%5%24435%5%5%8%43%
2605
June1st to 15thDay
12%5%25%5%345%6%8%40%
2520
16th to endDay
10%4145%35%5%7%10%41%
2520
July1st to 15thDay
8%424435%5%6%9%45%
2517
16th to endDay
9%425%5%36%6%7%10%39%
2465
August1st to 15thDay
7%3245%35%7%7%10%41%
2340
16th to endDay
11%4244345%6%8%45%
2430
September1st to 15thDay
13%5%245%335%5%8%41%
2112
16th to endDay
14%425%435%45%7%43%
1977
October1st to 15thDay
17%6%25%7%3445%8%33%
1800
16th to endDay
22%8%47%5%345%5%6%25%
1920
November1st to 15thDay
14%6%26%6%445%5%8%36%
1653
16th to endDay
20%11%36%5%345%5%7%24%
1560
December1st to 15thDay
18%15%6%8%6%345%47%19%
1560
16th to endDay
22%17%7%8%5%45%5%45%14%
1568
January1st to 15thNight
21%13%5%9%5%25%445%22%
2410
16th to endNight
14%15%7%8%6%35%5%5%6%21%
2496
February1st to 15thNight
15%14%6%9%6%35%5%45%22%
2285
16th to endNight
17%11%47%6%35%45%6%25%
1988
March1st to 15thNight
19%8%47%5%45%5%46%29%
1971
16th to endNight
15%8%46%424445%38%
2112
April1st to 15thNight
20%8%345%34446%34%
1844
16th to endNight
12%6%35%5%35%45%7%42%
1626
May1st to 15thNight
16%5%26%5%3446%8%36%
1620
16th to endNight
10%5%345%235%6%8%44%
1506
June1st to 15thNight
10%5%35%5%245%6%9%40%
1440
16th to endNight
9%5%25%5%36%5%5%9%41%
1440
July1st to 15thNight
5%31442445%8%53%
1440
16th to endNight
6%324435%5%6%8%49%
1703
August1st to 15thNight
6%2145%446%6%10%47%
1620
16th to endNight
9%314424448%51%
1758
September1st to 15thNight
12%5%25%323447%47%
1846
16th to endNight
12%315%41436%6%49%
1983
October1st to 15thNight
17%6%35%413446%41%
2160
16th to endNight
20%8%26%435%5%5%6%31%
2304
November1st to 15thNight
15%6%36%43446%7%36%
2530
16th to endNight
19%11%36%5%3445%7%27%
2730
December1st to 15thNight
22%15%5%6%5%34346%21%
2730
16th to endNight
21%14%7%9%5%35%45%5%17%
2755

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 15thDay
18%13%5%9%7%45%447%19%
1526
16th to endDay
14%14%6%12%8%46%446%16%
1728
February1st to 15thDay
16%15%6%10%7%46%44418%
1575
16th to endDay
17%11%5%9%7%3445%6%21%
1482
March1st to 15thDay
17%11%48%7%35%45%5%25%
1977
16th to endDay
16%9%46%6%34446%31%
2111
April1st to 15thDay
18%8%46%6%35%45%5%30%
2107
16th to endDay
17%7%26%423447%39%
2340
May1st to 15thDay
15%435%7%35%35%8%36%
2331
16th to endDay
10%5%24435%5%6%7%43%
2605
June1st to 15thDay
11%5%25%5%25%5%6%8%40%
2520
16th to endDay
10%424435%5%6%10%40%
2520
July1st to 15thDay
8%4244346%6%10%44%
2517
16th to endDay
8%5%246%36%6%8%10%38%
2465
August1st to 15thDay
7%4145%36%7%7%9%41%
2340
16th to endDay
10%5%2443446%8%44%
2430
September1st to 15thDay
12%5%34435%5%6%7%40%
2112
16th to endDay
13%425%5%345%5%7%42%
1977
October1st to 15thDay
17%6%36%6%3445%8%33%
1800
16th to endDay
22%9%46%5%25%5%5%7%25%
1920
November1st to 15thDay
14%6%26%7%345%48%36%
1653
16th to endDay
20%12%46%5%35%46%6%24%
1560
December1st to 15thDay
18%14%6%8%6%3445%7%19%
1560
16th to endDay
22%16%8%8%6%345%45%14%
1568
January1st to 15thNight
21%14%5%9%5%24445%21%
2410
16th to endNight
14%14%7%8%7%35%5%5%6%21%
2496
February1st to 15thNight
15%14%6%9%6%45%445%23%
2278
16th to endNight
17%11%48%6%35%45%7%25%
1988
March1st to 15thNight
19%8%47%6%45%446%28%
1983
16th to endNight
15%9%36%424445%38%
2112
April1st to 15thNight
20%7%35%5%34446%34%
1844
16th to endNight
11%6%35%5%35%45%7%42%
1626
May1st to 15thNight
16%5%26%6%25%5%6%7%35%
1619
16th to endNight
10%5%2442446%8%45%
1506
June1st to 15thNight
10%5%35%5%25%5%6%9%39%
1440
16th to endNight
8%6%25%5%35%5%6%8%42%
1440
July1st to 15thNight
5%31343445%8%53%
1440
16th to endNight
6%415%435%5%5%8%49%
1703
August1st to 15thNight
6%2145%346%7%9%47%
1620
16th to endNight
9%34424448%52%
1758
September1st to 15thNight
12%5%25%32335%7%47%
1846
16th to endNight
11%425%42345%6%49%
1983
October1st to 15thNight
17%6%3441435%7%41%
2160
16th to endNight
19%8%35%435%5%5%6%31%
2304
November1st to 15thNight
14%7%36%42446%7%37%
2530
16th to endNight
19%11%35%5%2445%6%28%
2730
December1st to 15thNight
22%15%6%7%5%33447%21%
2730
16th to endNight
21%14%7%8%6%3445%5%17%
2755

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 15thDay
65%6%12%12%3
1527
16th to endDay
68%5%12%10%2
1728
February1st to 15thDay
68%5%10%11%3
1577
16th to endDay
62%6%12%13%4
1482
March1st to 15thDay
59%7%12%16%4
1977
16th to endDay
52%6%9%21%8%1
2112
April1st to 15thDay
53%6%11%18%10%
2107
16th to endDay
44%5%10%20%15%2
2340
May1st to 15thDay
45%8%11%21%12%
2331
16th to endDay
37%8%14%24%13%1
2609
June1st to 15thDay
40%8%13%23%12%1
2520
16th to endDay
35%10%16%22%14%
2520
July1st to 15thDay
32%8%13%25%18%1
2368
16th to endDay
36%11%16%22%12%1
2310
August1st to 15thDay
33%12%15%24%12%1
2327
16th to endDay
34%10%14%26%12%2
2430
September1st to 15thDay
40%8%13%25%11%
2112
16th to endDay
40%7%13%25%11%
1977
October1st to 15thDay
48%8%12%18%11%1
1800
16th to endDay
56%7%15%14%4
1920
November1st to 15thDay
45%7%17%19%8%1
1653
16th to endDay
58%6%15%14%4
1560
December1st to 15thDay
64%6%16%10%1
1560
16th to endDay
72%6%11%9%
1568
January1st to 15thNight
65%5%10%11%6%
2410
16th to endNight
63%6%12%13%4
2496
February1st to 15thNight
63%6%12%12%5%
2287
16th to endNight
57%5%13%17%5%
1988
March1st to 15thNight
56%6%10%19%6%
1983
16th to endNight
46%411%21%13%2
2112
April1st to 15thNight
50%5%9%20%13%
1844
16th to endNight
40%410%21%18%4
1626
May1st to 15thNight
44%5%12%24%10%2
1620
16th to endNight
36%6%12%24%16%3
1508
June1st to 15thNight
39%7%11%26%13%2
1440
16th to endNight
38%7%12%22%17%1
1440
July1st to 15thNight
28%6%11%26%23%3
1360
16th to endNight
31%6%16%25%17%3
1595
August1st to 15thNight
29%9%15%30%13%1
1609
16th to endNight
30%6%13%31%15%2
1758
September1st to 15thNight
36%5%13%27%15%2
1846
16th to endNight
34%5%11%30%16%1
1983
October1st to 15thNight
42%5%12%22%15%1
2160
16th to endNight
51%7%14%19%7%
2304
November1st to 15thNight
44%7%13%20%11%1
2530
16th to endNight
55%5%17%16%4
2730
December1st to 15thNight
64%6%14%10%3
2730
16th to endNight
68%7%11%9%2
2755

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 15thDay
23%22%38%6%7%1
76
16th to endDay
27%13%44%12%2
96
February1st to 15thDay
17%13%52%16%
90
16th to endDay
17%18%33%29%1
81
March1st to 15thDay
20%18%25%27%7%
267
16th to endDay
21%17%26%25%7%1
288
April1st to 15thDay
20%18%27%22%9%1
270
16th to endDay
16%15%23%25%11%7%
270
May1st to 15thDay
19%14%21%25%14%5%
288
16th to endDay
12%12%21%32%16%4
331
June1st to 15thDay
11%11%22%36%16%2
315
16th to endDay
12%11%20%32%17%5%
315
July1st to 15thDay
9%9%16%25%29%9%
305
16th to endDay
9%9%17%30%23%9%
326
August1st to 15thDay
8%6%13%30%28%12%
313
16th to endDay
12%6%12%24%28%15%
332
September1st to 15thDay
9%6%16%23%29%15%
315
16th to endDay
15%7%14%18%23%19%
314
October1st to 15thDay
20%9%22%22%16%8%
315
16th to endDay
23%13%30%23%8%
336
November1st to 15thDay
16%11%28%25%14%2
136
16th to endDay
27%15%30%17%8%
90
December1st to 15thDay
21%27%27%16%6%
90
16th to endDay
31%30%29%8%
72
January1st to 15thNight
23%27%27%15%4
720
16th to endNight
17%28%30%19%3
768
February1st to 15thNight
21%25%27%21%3
704
16th to endNight
19%21%27%25%5%
631
March1st to 15thNight
21%21%25%22%8%
720
16th to endNight
19%19%26%25%8%
768
April1st to 15thNight
20%22%24%25%6%
718
16th to endNight
13%20%23%30%10%1
546
May1st to 15thNight
15%18%21%27%15%1
540
16th to endNight
12%18%18%28%19%2
386
June1st to 15thNight
13%18%18%31%16%
360
16th to endNight
11%16%16%35%18%
360
July1st to 15thNight
5%12%16%36%26%3
340
16th to endNight
7%16%14%35%21%4
564
August1st to 15thNight
7%10%11%37%28%4
539
16th to endNight
10%9%12%31%31%5%
612
September1st to 15thNight
11%12%15%27%27%6%
720
16th to endNight
11%11%13%24%28%9%
717
October1st to 15thNight
21%12%19%24%18%3
720
16th to endNight
23%18%28%23%6%
768
November1st to 15thNight
17%19%24%24%11%1
760
16th to endNight
23%27%26%15%5%1
780
December1st to 15thNight
29%26%26%13%4
780
16th to endNight
25%28%28%14%3
788
Page generated at 2017-12-21 07:04:55. Version ac04

Copyright 2017 A. Danko


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