Cathead Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cathead Bay clear sky chart from 2005-11-05 to 2017-10-16.

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
34%
15967
10%
47233
8%
15924
37%
15924
15%
36372

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
11%
900
2%
2506
1%
895
12%
895
3%
2330
January16th to endNight
12%
960
3%
2688
2%
960
13%
960
4%
2476
February1st to 15thNight
16%
768
4%
2300
1%
767
19%
767
6%
2008
February16th to endNight
25%
631
8%
1893
4%
631
28%
631
9%
1585
March1st to 15thNight
34%
720
14%
2140
9%
720
37%
720
18%
1566
March16th to endNight
40%
720
17%
2064
12%
720
45%
720
22%
1452
April1st to 15thNight
34%
539
12%
1794
10%
539
39%
539
16%
1283
April16th to endNight
42%
540
18%
1620
12%
540
47%
540
22%
1119
May1st to 15thNight
46%
540
13%
1608
10%
540
50%
540
20%
1137
May16th to endNight
55%
562
16%
1498
12%
561
59%
561
32%
965
June1st to 15thNight
53%
414
12%
1314
9%
414
56%
414
24%
866
June16th to endNight
60%
420
13%
1320
10%
420
62%
420
27%
850
July1st to 15thNight
65%
510
14%
1360
10%
510
66%
510
36%
846
July16th to endNight
65%
564
16%
1417
12%
531
65%
531
36%
868
August1st to 15thNight
68%
539
18%
1542
15%
536
69%
536
37%
890
August16th to endNight
61%
573
15%
1787
14%
573
63%
573
28%
1102
September1st to 15thNight
54%
600
16%
1860
13%
600
57%
600
26%
1200
September16th to endNight
51%
717
17%
1980
14%
717
53%
717
26%
1354
October1st to 15thNight
36%
720
14%
2051
10%
720
41%
720
19%
1509
October16th to endNight
24%
708
8%
2300
5%
708
27%
708
8%
1905
November1st to 15thNight
27%
700
12%
2276
11%
700
31%
700
11%
1766
November16th to endNight
16%
762
5%
2434
4%
762
18%
762
5%
2156
December1st to 15thNight
7%
900
1%
2700
0%
900
7%
900
2%
2536
December16th to endNight
9%
960
2%
2781
1%
960
11%
960
3%
2603

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%47%5%34446%33%
48186
Night
17%12%5%9%6%34345%27%
47401
Cloud CoverDay
15%9%47%5%34446%33%
48195
Night
17%12%5%9%6%34335%27%
47406
TransparencyDay
51%6%12%19%9%
47872
Night
59%5%10%15%7%
47233
SeeingDay
17%420%31%20%5%
6133
Night
22%7%24%28%14%2
15970

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
17%19%12%17%11%332225%
1432
16th to endDay
14%16%12%18%12%443326%
1536
February1st to 15thDay
13%16%7%14%14%35%24411%
1561
16th to endDay
13%15%9%10%8%45%5%35%18%
1580
March1st to 15thDay
12%9%311%7%45%445%31%
1809
16th to endDay
15%6%47%5%35%447%34%
2170
April1st to 15thDay
19%10%35%42445%5%34%
2154
16th to endDay
16%9%35%5%24447%36%
2340
May1st to 15thDay
14%6%35%6%35%45%6%39%
2340
16th to endDay
11%5%2342445%8%45%
2617
June1st to 15thDay
13%5%2442446%9%41%
2643
16th to endDay
12%5%25%4245%5%8%42%
2634
July1st to 15thDay
9%3133145%6%8%51%
2520
16th to endDay
8%32332446%9%51%
2655
August1st to 15thDay
8%31443446%9%49%
2407
16th to endDay
15%5%2432335%7%46%
2414
September1st to 15thDay
14%6%1433345%7%43%
2088
16th to endDay
17%5%24325%448%40%
1980
October1st to 15thDay
22%10%36%5%23346%30%
1908
16th to endDay
28%15%47%5%3334415%
1593
November1st to 15thDay
19%17%5%7%433345%24%
1582
16th to endDay
23%24%8%11%6%1323311%
1523
December1st to 15thDay
21%21%14%19%7%221116%
1260
16th to endDay
22%24%10%13%7%232236%
1440
January1st to 15thNight
18%19%10%15%12%332238%
2506
16th to endNight
15%17%8%17%15%442228%
2688
February1st to 15thNight
12%17%8%14%13%4433314%
2298
16th to endNight
17%14%6%13%8%35%33418%
1893
March1st to 15thNight
14%9%49%6%3345%433%
2127
16th to endNight
14%8%5%7%5%3345%6%34%
2064
April1st to 15thNight
21%9%27%424445%32%
1794
16th to endNight
16%9%26%5%34345%38%
1620
May1st to 15thNight
15%6%35%5%46%46%7%33%
1608
16th to endNight
12%5%2442446%8%43%
1496
June1st to 15thNight
14%5%16%5%35%5%46%40%
1314
16th to endNight
11%5%245%25%45%9%42%
1320
July1st to 15thNight
9%414425%5%5%6%50%
1440
16th to endNight
8%42442345%7%52%
1513
August1st to 15thNight
7%32442347%8%50%
1551
16th to endNight
13%414444347%47%
1787
September1st to 15thNight
15%6%24333346%44%
1860
16th to endNight
17%6%25%424447%40%
1980
October1st to 15thNight
23%10%35%5%24336%32%
2051
16th to endNight
26%13%49%6%3434419%
2300
November1st to 15thNight
21%16%47%6%24345%25%
2276
16th to endNight
23%23%8%11%43333312%
2434
December1st to 15thNight
21%24%13%15%7%222116%
2700
16th to endNight
21%24%11%13%8%332127%
2781

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%19%12%16%12%332325%
1432
16th to endDay
14%16%12%17%13%442227%
1536
February1st to 15thDay
14%15%8%14%13%4443412%
1561
16th to endDay
13%15%7%10%8%45%43420%
1580
March1st to 15thDay
12%9%410%7%35%445%31%
1819
16th to endDay
15%7%46%5%34447%35%
2169
April1st to 15thDay
19%11%25%434445%34%
2154
16th to endDay
16%9%35%5%24447%36%
2340
May1st to 15thDay
15%6%25%5%3446%5%39%
2340
16th to endDay
11%5%1442445%8%45%
2617
June1st to 15thDay
13%5%244245%6%8%41%
2643
16th to endDay
13%425%43445%9%41%
2634
July1st to 15thDay
9%4233245%5%8%51%
2520
16th to endDay
8%41332446%8%51%
2655
August1st to 15thDay
8%31443446%9%49%
2407
16th to endDay
15%5%25%32335%6%46%
2414
September1st to 15thDay
15%5%2433445%7%44%
2088
16th to endDay
17%6%2433345%8%40%
1980
October1st to 15thDay
23%9%36%5%34346%30%
1908
16th to endDay
31%14%46%5%35%345%15%
1593
November1st to 15thDay
19%18%47%42335%5%24%
1582
16th to endDay
23%24%9%11%5%1233311%
1523
December1st to 15thDay
21%22%15%18%6%221116%
1260
16th to endDay
23%25%11%13%7%232227%
1440
January1st to 15thNight
19%20%10%15%12%332228%
2506
16th to endNight
16%17%9%16%13%442228%
2688
February1st to 15thNight
12%17%8%15%12%4433314%
2291
16th to endNight
17%14%6%14%8%35%33418%
1893
March1st to 15thNight
14%10%5%9%6%23445%33%
2140
16th to endNight
14%9%47%6%2445%6%35%
2064
April1st to 15thNight
21%10%36%5%24445%32%
1794
16th to endNight
16%9%35%6%2434439%
1620
May1st to 15thNight
15%7%26%5%45%6%5%7%33%
1607
16th to endNight
12%5%25%43445%8%44%
1496
June1st to 15thNight
15%5%16%445%5%36%41%
1314
16th to endNight
11%5%24435%45%9%41%
1320
July1st to 15thNight
10%424425%446%50%
1440
16th to endNight
7%325%42345%7%51%
1513
August1st to 15thNight
7%4144235%6%8%50%
1551
16th to endNight
13%42443435%6%47%
1787
September1st to 15thNight
17%6%24423346%44%
1860
16th to endNight
18%5%25%424447%40%
1980
October1st to 15thNight
24%9%35%433346%31%
2051
16th to endNight
28%14%48%6%3423418%
2300
November1st to 15thNight
21%17%46%5%23345%24%
2276
16th to endNight
24%24%9%10%42322312%
2434
December1st to 15thNight
21%26%14%14%6%121116%
2700
16th to endNight
21%24%12%13%7%232227%
2781

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
86%5%34
1433
16th to endDay
84%45%4
1536
February1st to 15thDay
76%5%8%7%1
1563
16th to endDay
67%7%9%10%4
1580
March1st to 15thDay
54%6%13%17%6%1
1819
16th to endDay
48%7%13%22%6%1
2170
April1st to 15thDay
49%5%11%21%10%
2154
16th to endDay
47%6%11%16%15%2
2340
May1st to 15thDay
44%6%11%23%11%3
2340
16th to endDay
35%7%14%25%15%1
2621
June1st to 15thDay
38%7%14%25%13%
2643
16th to endDay
38%7%17%23%12%
2634
July1st to 15thDay
28%8%14%31%16%1
2371
16th to endDay
30%7%16%27%17%
2488
August1st to 15thDay
30%6%18%31%11%
2392
16th to endDay
37%6%15%26%12%1
2414
September1st to 15thDay
39%7%14%26%10%
2088
16th to endDay
41%6%16%25%9%
1980
October1st to 15thDay
55%6%9%20%7%
1908
16th to endDay
71%6%12%7%2
1593
November1st to 15thDay
61%5%11%14%6%
1582
16th to endDay
79%5%8%41
1523
December1st to 15thDay
89%234
1260
16th to endDay
86%35%31
1440
January1st to 15thNight
84%45%4
2506
16th to endNight
83%35%5%
2688
February1st to 15thNight
76%47%8%2
2300
16th to endNight
70%5%10%9%3
1893
March1st to 15thNight
53%5%11%20%8%
2140
16th to endNight
49%5%12%20%11%1
2064
April1st to 15thNight
53%5%8%19%11%1
1794
16th to endNight
47%5%9%18%15%2
1620
May1st to 15thNight
48%7%10%19%10%3
1608
16th to endNight
36%6%13%27%13%2
1498
June1st to 15thNight
42%6%11%23%14%1
1314
16th to endNight
38%8%13%24%13%1
1320
July1st to 15thNight
32%7%12%28%17%2
1360
16th to endNight
31%6%15%26%17%1
1417
August1st to 15thNight
29%6%19%30%12%
1542
16th to endNight
36%7%16%22%14%1
1787
September1st to 15thNight
40%6%13%23%14%
1860
16th to endNight
43%7%14%25%9%
1980
October1st to 15thNight
54%410%21%9%
2051
16th to endNight
69%6%9%11%3
2300
November1st to 15thNight
61%6%10%14%6%
2276
16th to endNight
78%5%8%5%1
2434
December1st to 15thNight
87%343
2700
16th to endNight
85%45%31
2781

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
21%14%28%28%6%
90
16th to endDay
33%7%22%26%10%
96
February1st to 15thDay
18%14%37%22%6%
90
16th to endDay
17%9%40%24%7%
81
March1st to 15thDay
15%10%28%27%16%1
109
16th to endDay
23%324%33%13%2
288
April1st to 15thDay
26%424%28%14%2
270
16th to endDay
23%324%28%14%4
270
May1st to 15thDay
15%327%32%16%4
297
16th to endDay
15%122%35%20%4
517
June1st to 15thDay
16%220%34%22%4
495
16th to endDay
15%116%37%22%5%
495
July1st to 15thDay
11%116%35%26%7%
475
16th to endDay
9%117%36%29%6%
515
August1st to 15thDay
10%10%35%33%8%
380
16th to endDay
18%214%31%24%8%
332
September1st to 15thDay
16%213%26%27%14%
315
16th to endDay
15%5%15%28%28%6%
314
October1st to 15thDay
27%325%25%14%3
294
16th to endDay
32%5%31%27%4
99
November1st to 15thDay
12%11%28%33%13%1
90
16th to endDay
30%18%22%18%9%
81
December1st to 15thDay
41%16%23%13%13
60
16th to endDay
36%25%37%1
80
January1st to 15thNight
27%12%30%22%5%
900
16th to endNight
23%11%33%24%5%
960
February1st to 15thNight
21%11%33%26%6%
770
16th to endNight
22%10%26%31%8%
631
March1st to 15thNight
19%7%30%30%11%1
720
16th to endNight
16%427%33%15%2
720
April1st to 15thNight
23%5%27%30%10%1
539
16th to endNight
20%424%34%14%1
540
May1st to 15thNight
16%224%37%18%
540
16th to endNight
14%220%36%23%2
563
June1st to 15thNight
16%119%37%21%2
414
16th to endNight
11%215%37%30%2
420
July1st to 15thNight
11%112%39%29%5%
510
16th to endNight
9%115%36%32%4
564
August1st to 15thNight
9%113%38%33%3
539
16th to endNight
15%212%35%30%3
573
September1st to 15thNight
20%215%30%23%7%
600
16th to endNight
20%317%29%22%6%
717
October1st to 15thNight
28%5%22%27%14%1
720
16th to endNight
34%10%23%23%7%1
708
November1st to 15thNight
32%8%25%24%9%
700
16th to endNight
35%14%24%19%5%
762
December1st to 15thNight
32%18%30%15%3
900
16th to endNight
31%11%32%19%31
960
Page generated at 2017-10-17 16:35:24. Version ac04

Copyright 2017 A. Danko


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