Dorcas Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dorcas Bay clear sky chart from 2005-11-05 to 2017-09-19.

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%
15247
11%
46781
8%
15207
37%
15207
15%
34906

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
8%
898
2%
2616
1%
895
9%
895
3%
2399
January16th to endNight
17%
852
6%
2580
3%
852
19%
852
5%
2269
February1st to 15thNight
16%
701
6%
2287
2%
701
19%
701
7%
1913
February16th to endNight
24%
631
10%
1967
4%
631
29%
631
10%
1570
March1st to 15thNight
26%
720
13%
2036
7%
720
31%
720
17%
1506
March16th to endNight
39%
768
19%
2112
11%
768
45%
768
24%
1439
April1st to 15thNight
33%
641
17%
1789
8%
641
39%
641
23%
1235
April16th to endNight
42%
540
19%
1620
11%
540
47%
540
24%
1083
May1st to 15thNight
50%
537
14%
1617
13%
537
52%
537
22%
1094
May16th to endNight
53%
375
15%
1476
17%
374
58%
374
24%
836
June1st to 15thNight
52%
360
14%
1260
14%
360
57%
360
24%
760
June16th to endNight
61%
360
13%
1260
14%
360
65%
360
28%
748
July1st to 15thNight
65%
340
17%
1190
19%
340
68%
340
36%
623
July16th to endNight
62%
534
16%
1470
15%
501
62%
501
33%
872
August1st to 15thNight
62%
539
18%
1609
15%
536
66%
536
34%
940
August16th to endNight
59%
573
20%
1719
13%
573
63%
573
33%
1020
September1st to 15thNight
54%
702
16%
1869
10%
702
57%
702
30%
1228
September16th to endNight
51%
673
19%
1858
13%
673
54%
673
28%
1218
October1st to 15thNight
36%
660
13%
1955
11%
660
40%
660
17%
1440
October16th to endNight
23%
704
9%
2175
5%
704
29%
704
10%
1762
November1st to 15thNight
25%
700
13%
2357
12%
700
29%
700
11%
1817
November16th to endNight
18%
720
5%
2520
5%
720
19%
720
5%
2151
December1st to 15thNight
9%
759
2%
2559
1%
759
11%
759
3%
2336
December16th to endNight
8%
960
3%
2880
1%
960
10%
960
3%
2647

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
15%9%46%5%3445%6%34%
48031
Night
17%12%5%8%6%34445%27%
46948
Cloud CoverDay
15%9%46%5%34446%34%
48041
Night
17%12%5%8%6%34445%28%
46952
TransparencyDay
50%312%21%10%
47716
Night
59%310%17%8%
46781
SeeingDay
19%422%30%17%5%
5851
Night
24%8%22%26%14%3
15252

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
20%20%8%13%7%45%4328%
1319
16th to endDay
16%20%8%11%9%5%5%5%439%
1643
February1st to 15thDay
12%16%9%12%10%36%335%15%
1575
16th to endDay
14%16%7%8%7%45%445%21%
1503
March1st to 15thDay
13%9%47%5%35%5%5%6%33%
1912
16th to endDay
13%8%37%5%35%45%6%38%
2112
April1st to 15thDay
20%8%25%5%23445%35%
2167
16th to endDay
17%7%3432335%7%41%
2340
May1st to 15thDay
18%7%2443345%6%39%
2334
16th to endDay
12%5%14324447%48%
2636
June1st to 15thDay
12%6%25%435%5%6%8%40%
2700
16th to endDay
11%5%35%5%35%5%6%9%40%
2700
July1st to 15thDay
7%42443446%8%50%
2700
16th to endDay
9%31442446%10%48%
2592
August1st to 15thDay
11%42342345%8%49%
2340
16th to endDay
11%6%25%5%2345%8%44%
2483
September1st to 15thDay
14%5%25%42335%7%44%
2076
16th to endDay
17%5%2442445%8%39%
1848
October1st to 15thDay
22%9%36%5%34336%31%
1674
16th to endDay
28%12%48%7%34335%18%
1694
November1st to 15thDay
20%13%48%6%35%446%21%
1501
16th to endDay
24%19%5%10%7%35%33412%
1440
December1st to 15thDay
20%23%8%13%9%423327%
1398
16th to endDay
20%24%10%13%8%333335%
1344
January1st to 15thNight
20%20%9%13%11%433227%
2616
16th to endNight
15%17%9%14%10%45%33311%
2580
February1st to 15thNight
13%18%7%14%8%4444414%
2285
16th to endNight
14%15%7%10%7%35%45%5%20%
1967
March1st to 15thNight
16%11%5%6%6%34445%31%
2024
16th to endNight
14%7%37%6%34446%39%
2112
April1st to 15thNight
22%9%35%32435%6%36%
1789
16th to endNight
19%7%25%5%3445%6%37%
1620
May1st to 15thNight
17%7%45%5%35%5%5%5%35%
1617
16th to endNight
11%6%345%3445%8%43%
1474
June1st to 15thNight
12%6%35%5%3446%8%39%
1260
16th to endNight
9%5%15%5%45%6%5%8%42%
1260
July1st to 15thNight
7%4245%2435%8%51%
1260
16th to endNight
8%4135%2446%8%49%
1572
August1st to 15thNight
8%5%2443445%8%48%
1620
16th to endNight
9%5%15%5%2445%7%46%
1719
September1st to 15thNight
15%415%4345%6%5%42%
1869
16th to endNight
17%6%245%2335%7%41%
1858
October1st to 15thNight
22%9%36%6%34345%29%
1955
16th to endNight
28%12%47%5%34446%18%
2175
November1st to 15thNight
20%14%5%8%6%34445%22%
2357
16th to endNight
25%18%5%9%6%2443413%
2520
December1st to 15thNight
24%22%8%13%8%342237%
2559
16th to endNight
24%22%9%12%6%243237%
2880

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
19%19%8%14%7%45%4228%
1319
16th to endDay
16%20%8%11%9%46%43310%
1643
February1st to 15thDay
12%18%9%12%9%45%33415%
1575
16th to endDay
14%16%7%8%8%36%335%21%
1503
March1st to 15thDay
14%9%46%7%35%5%45%32%
1923
16th to endDay
13%8%46%5%25%45%5%37%
2111
April1st to 15thDay
20%9%35%424345%35%
2167
16th to endDay
18%7%34323447%41%
2340
May1st to 15thDay
18%6%2432445%6%39%
2334
16th to endDay
12%42342346%7%47%
2636
June1st to 15thDay
12%5%35%4345%5%8%40%
2700
16th to endDay
11%5%25%435%5%6%8%40%
2700
July1st to 15thDay
8%42433446%7%50%
2700
16th to endDay
9%41342446%9%48%
2592
August1st to 15thDay
11%41442335%7%49%
2340
16th to endDay
12%6%2442445%8%43%
2483
September1st to 15thDay
14%5%25%42435%7%43%
2076
16th to endDay
17%6%2442345%8%39%
1848
October1st to 15thDay
22%8%36%5%25%436%30%
1674
16th to endDay
30%12%47%7%33435%18%
1694
November1st to 15thDay
20%13%38%5%36%445%22%
1501
16th to endDay
24%19%6%8%7%4443412%
1440
December1st to 15thDay
20%24%7%11%9%443346%
1398
16th to endDay
20%24%9%13%8%323336%
1344
January1st to 15thNight
20%19%8%14%10%344327%
2616
16th to endNight
15%17%9%12%9%46%33412%
2580
February1st to 15thNight
13%18%8%14%8%3434415%
2278
16th to endNight
14%15%6%9%7%45%5%45%21%
1967
March1st to 15thNight
16%11%47%7%34345%31%
2036
16th to endNight
14%7%37%6%24445%38%
2112
April1st to 15thNight
22%9%3432335%5%36%
1789
16th to endNight
19%7%25%5%2445%6%37%
1620
May1st to 15thNight
17%7%45%5%345%5%6%35%
1616
16th to endNight
10%6%345%34449%42%
1474
June1st to 15thNight
12%7%25%5%25%5%5%7%40%
1260
16th to endNight
9%4246%35%6%5%8%42%
1260
July1st to 15thNight
7%315%42445%8%51%
1260
16th to endNight
8%4144245%5%8%49%
1572
August1st to 15thNight
8%5%2443445%7%49%
1620
16th to endNight
10%425%5%2445%7%47%
1719
September1st to 15thNight
15%4245%25%45%6%43%
1869
16th to endNight
17%6%24424347%41%
1858
October1st to 15thNight
22%8%36%6%34346%29%
1955
16th to endNight
28%11%47%6%34345%20%
2175
November1st to 15thNight
20%14%5%8%6%34445%22%
2357
16th to endNight
25%18%5%8%6%35%43414%
2520
December1st to 15thNight
24%21%8%12%7%343238%
2559
16th to endNight
24%22%8%12%6%342237%
2880

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
84%45%5%
1320
16th to endDay
80%45%7%3
1643
February1st to 15thDay
72%39%12%2
1577
16th to endDay
66%29%14%6%
1503
March1st to 15thDay
52%313%20%10%
1923
16th to endDay
46%312%21%13%2
2112
April1st to 15thDay
50%38%24%12%1
2167
16th to endDay
42%312%24%14%2
2340
May1st to 15thDay
44%38%24%15%2
2334
16th to endDay
35%315%27%16%1
2640
June1st to 15thDay
40%412%29%13%
2700
16th to endDay
39%6%13%27%12%
2700
July1st to 15thDay
30%315%31%16%1
2541
16th to endDay
31%5%16%30%15%
2431
August1st to 15thDay
32%418%30%13%
2327
16th to endDay
38%416%28%11%
2483
September1st to 15thDay
40%414%30%9%
2076
16th to endDay
43%316%27%8%
1848
October1st to 15thDay
55%39%20%10%
1674
16th to endDay
69%211%12%4
1694
November1st to 15thDay
63%410%14%6%
1501
16th to endDay
78%28%7%2
1440
December1st to 15thDay
86%25%41
1398
16th to endDay
85%36%4
1344
January1st to 15thNight
84%25%5%1
2616
16th to endNight
79%35%8%2
2580
February1st to 15thNight
73%38%11%2
2287
16th to endNight
66%38%13%6%
1967
March1st to 15thNight
56%211%19%8%
2036
16th to endNight
46%39%20%16%2
2112
April1st to 15thNight
49%38%25%12%1
1789
16th to endNight
46%27%20%19%2
1620
May1st to 15thNight
48%37%22%14%2
1617
16th to endNight
39%312%25%16%2
1476
June1st to 15thNight
41%310%25%17%1
1260
16th to endNight
37%414%26%15%
1260
July1st to 15thNight
29%314%29%20%2
1190
16th to endNight
33%5%15%26%18%
1470
August1st to 15thNight
33%416%28%14%1
1609
16th to endNight
34%416%29%12%1
1719
September1st to 15thNight
40%5%13%27%11%1
1869
16th to endNight
43%313%29%9%
1858
October1st to 15thNight
57%29%19%10%
1955
16th to endNight
68%39%13%4
2175
November1st to 15thNight
64%310%16%4
2357
16th to endNight
76%310%7%1
2520
December1st to 15thNight
85%16%41
2559
16th to endNight
85%25%5%1
2880

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
28%12%35%19%4
71
16th to endDay
39%127%17%13%1
96
February1st to 15thDay
28%13%36%17%3
90
16th to endDay
27%11%28%28%4
81
March1st to 15thDay
22%9%30%30%6%
213
16th to endDay
21%426%31%10%4
288
April1st to 15thDay
27%425%28%11%2
270
16th to endDay
22%5%28%23%13%5%
270
May1st to 15thDay
22%421%31%15%4
288
16th to endDay
14%424%30%19%6%
349
June1st to 15thDay
16%221%34%19%4
495
16th to endDay
14%219%37%20%5%
495
July1st to 15thDay
9%217%41%22%6%
475
16th to endDay
10%20%35%25%6%
422
August1st to 15thDay
13%114%31%31%7%
313
16th to endDay
16%313%31%26%8%
332
September1st to 15thDay
15%19%26%24%13%
315
16th to endDay
20%218%29%20%9%
266
October1st to 15thDay
27%421%28%13%3
255
16th to endDay
31%10%27%20%8%
206
November1st to 15thDay
9%11%33%38%5%1
77
16th to endDay
30%11%36%18%3
60
December1st to 15thDay
33%13%36%11%5%
60
16th to endDay
35%25%35%3
64
January1st to 15thNight
30%18%26%19%5%
900
16th to endNight
24%11%29%24%8%1
852
February1st to 15thNight
22%14%32%22%7%
704
16th to endNight
23%9%28%29%9%
631
March1st to 15thNight
21%11%30%26%8%1
720
16th to endNight
17%6%26%31%15%2
768
April1st to 15thNight
26%5%27%30%8%1
641
16th to endNight
23%5%21%29%17%2
540
May1st to 15thNight
19%315%36%21%3
537
16th to endNight
13%318%34%26%4
375
June1st to 15thNight
16%316%36%23%3
360
16th to endNight
11%114%40%26%4
360
July1st to 15thNight
7%215%40%28%5%
340
16th to endNight
9%214%36%31%4
534
August1st to 15thNight
11%213%33%30%7%
539
16th to endNight
13%115%29%31%7%
573
September1st to 15thNight
17%415%28%21%12%
702
16th to endNight
20%416%26%23%8%
673
October1st to 15thNight
28%5%19%26%16%3
660
16th to endNight
37%8%21%23%6%1
704
November1st to 15thNight
30%11%24%20%10%2
700
16th to endNight
38%13%21%18%7%
720
December1st to 15thNight
37%15%28%13%4
759
16th to endNight
36%15%27%15%4
960
Page generated at 2017-09-20 04:49:52. Version ac04

Copyright 2017 A. Danko


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