Sunset Bay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sunset Bay clear sky chart from 2005-11-05 to 2017-03-14.

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%
14139
12%
45215
7%
14109
31%
14109
16%
32122

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%
720
6%
2506
2%
716
18%
716
6%
2031
January16th to endNight
19%
768
11%
2613
5%
768
26%
768
11%
1965
February1st to 15thNight
14%
702
9%
2287
3%
701
22%
701
10%
1746
February16th to endNight
16%
631
13%
1970
5%
631
27%
631
12%
1431
March1st to 15thNight
14%
716
10%
2059
5%
716
20%
716
14%
1537
March16th to endNight
21%
704
12%
1883
5%
704
28%
704
21%
1287
April1st to 15thNight
19%
658
15%
1646
5%
658
26%
658
18%
1209
April16th to endNight
28%
592
17%
1582
7%
592
36%
592
23%
1097
May1st to 15thNight
27%
330
16%
1320
14%
330
39%
330
18%
842
May16th to endNight
31%
343
13%
1369
9%
342
42%
342
20%
838
June1st to 15thNight
31%
330
10%
1320
8%
330
42%
330
14%
886
June16th to endNight
43%
330
8%
1320
11%
330
48%
330
19%
824
July1st to 15thNight
50%
310
16%
1240
23%
310
56%
310
28%
671
July16th to endNight
52%
348
13%
1306
12%
326
58%
326
28%
722
August1st to 15thNight
35%
436
12%
1417
9%
434
40%
434
27%
864
August16th to endNight
35%
632
14%
1682
6%
632
40%
632
37%
1041
September1st to 15thNight
40%
660
15%
1650
6%
660
43%
660
28%
1143
September16th to endNight
43%
657
20%
1804
13%
657
48%
657
31%
1155
October1st to 15thNight
29%
660
17%
1980
10%
660
38%
660
19%
1378
October16th to endNight
20%
704
11%
2178
4%
704
28%
704
12%
1661
November1st to 15thNight
22%
700
15%
2355
12%
700
30%
700
16%
1650
November16th to endNight
17%
720
9%
2520
6%
720
22%
720
9%
1938
December1st to 15thNight
13%
720
7%
2520
2%
720
19%
720
7%
2036
December16th to endNight
10%
768
8%
2688
4%
768
17%
768
7%
2170

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%9%36%6%34446%31%
45503
Night
16%10%47%5%34445%32%
45385
Cloud CoverDay
28%7%35%423335%31%
45513
Night
26%8%35%42333434%
45390
TransparencyDay
52%5%11%19%10%1
45191
Night
52%5%11%19%9%
45215
SeeingDay
22%13%29%20%9%3
4701
Night
23%13%30%23%8%
14141

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%13%6%10%6%43445%21%
1432
16th to endDay
13%15%5%10%8%46%345%22%
1611
February1st to 15thDay
11%14%6%12%8%45%43423%
1575
16th to endDay
17%13%5%7%6%45%44326%
1503
March1st to 15thDay
16%12%48%9%35%44426%
1859
16th to endDay
13%10%45%6%2434440%
1988
April1st to 15thDay
21%12%45%423335%33%
1972
16th to endDay
20%7%35%424435%37%
2057
May1st to 15thDay
17%7%47%5%33446%35%
2301
16th to endDay
15%6%35%5%345%5%7%36%
2394
June1st to 15thDay
21%8%35%5%25%5%5%6%29%
2310
16th to endDay
16%6%26%5%45%5%5%7%34%
2310
July1st to 15thDay
12%425%5%46%5%7%9%37%
2310
16th to endDay
11%426%6%36%6%7%9%34%
2458
August1st to 15thDay
13%6%26%6%345%5%8%36%
2200
16th to endDay
13%425%6%45%5%5%9%37%
2157
September1st to 15thDay
18%5%245%3345%8%38%
1980
16th to endDay
15%5%24434447%43%
1825
October1st to 15thDay
21%9%35%5%34346%31%
1650
16th to endDay
26%10%47%5%35%43424%
1694
November1st to 15thDay
15%10%36%5%345%46%34%
1501
16th to endDay
20%12%6%7%6%35%345%23%
1440
December1st to 15thDay
20%15%7%10%7%35%35%416%
1440
16th to endDay
21%17%6%8%5%345%3420%
1536
January1st to 15thNight
15%13%6%12%8%46%5%4418%
2506
16th to endNight
13%14%5%9%7%345%45%25%
2613
February1st to 15thNight
12%15%6%10%7%35%5%45%23%
2285
16th to endNight
15%10%48%7%34446%29%
1970
March1st to 15thNight
16%12%49%7%33335%29%
2047
16th to endNight
14%7%45%5%33346%40%
1883
April1st to 15thNight
20%9%35%434345%34%
1646
16th to endNight
18%8%25%5%23346%38%
1582
May1st to 15thNight
17%8%35%42343440%
1320
16th to endNight
14%6%25%4245%6%8%40%
1367
June1st to 15thNight
18%6%37%5%345%46%34%
1320
16th to endNight
15%5%25%325%5%5%8%39%
1320
July1st to 15thNight
8%425%4245%48%48%
1320
16th to endNight
8%3245%25%47%8%46%
1402
August1st to 15thNight
8%5%25%5%35%5%6%8%43%
1427
16th to endNight
9%425%42435%6%50%
1682
September1st to 15thNight
16%5%25%42445%5%42%
1650
16th to endNight
15%5%245%23236%48%
1804
October1st to 15thNight
20%8%26%5%24446%35%
1980
16th to endNight
23%10%37%5%25%45%5%25%
2178
November1st to 15thNight
17%10%35%5%34345%32%
2355
16th to endNight
21%12%5%9%6%33445%24%
2520
December1st to 15thNight
20%16%5%9%6%3443420%
2520
16th to endNight
22%15%6%10%5%3343420%
2688

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
20%13%6%9%5%34345%24%
1432
16th to endDay
15%14%5%9%8%45%33424%
1611
February1st to 15thDay
19%13%410%8%3433325%
1575
16th to endDay
23%12%46%6%35%33326%
1503
March1st to 15thDay
40%6%245%3322226%
1870
16th to endDay
42%5%2321222232%
1987
April1st to 15thDay
33%8%2431322434%
1972
16th to endDay
31%5%2431332436%
2057
May1st to 15thDay
40%42431223330%
2301
16th to endDay
38%32332223434%
2394
June1st to 15thDay
35%5%24423335%28%
2310
16th to endDay
32%32343444432%
2310
July1st to 15thDay
13%4245%35%47%9%39%
2310
16th to endDay
12%325%6%36%5%7%8%37%
2458
August1st to 15thDay
41%41442333426%
2200
16th to endDay
41%33323335%29%
2157
September1st to 15thDay
21%424433347%39%
1980
16th to endDay
20%424424336%43%
1825
October1st to 15thDay
25%7%26%43444433%
1650
16th to endDay
28%9%36%5%2443327%
1694
November1st to 15thDay
25%7%2332324438%
1501
16th to endDay
27%8%5%5%43423430%
1440
December1st to 15thDay
24%15%5%8%6%33335%20%
1440
16th to endDay
24%16%5%6%42444422%
1536
January1st to 15thNight
19%11%5%9%8%345%4323%
2506
16th to endNight
17%13%48%6%2444428%
2613
February1st to 15thNight
21%13%5%8%5%2334426%
2278
16th to endNight
23%9%37%6%2334429%
1970
March1st to 15thNight
42%6%25%32213327%
2059
16th to endNight
41%42331221333%
1883
April1st to 15thNight
28%7%3432223438%
1646
16th to endNight
24%6%24322335%41%
1582
May1st to 15thNight
34%5%1421222339%
1320
16th to endNight
31%31331232440%
1367
June1st to 15thNight
24%5%35%42344438%
1320
16th to endNight
21%424424445%41%
1320
July1st to 15thNight
8%4244345%5%8%48%
1320
16th to endNight
9%3144345%7%8%48%
1402
August1st to 15thNight
35%31332324435%
1427
16th to endNight
37%2331222439%
1682
September1st to 15thNight
20%5%135%23345%44%
1650
16th to endNight
19%5%1441222449%
1804
October1st to 15thNight
24%7%25%423335%36%
1980
16th to endNight
26%9%36%5%23335%29%
2178
November1st to 15thNight
32%7%2431222334%
2355
16th to endNight
35%8%36%41232328%
2520
December1st to 15thNight
27%13%36%5%2334325%
2520
16th to endNight
30%13%47%5%2333223%
2688

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
64%5%9%12%6%1
1433
16th to endDay
65%38%12%8%
1611
February1st to 15thDay
64%410%15%4
1577
16th to endDay
61%49%12%10%1
1503
March1st to 15thDay
61%310%16%7%
1870
16th to endDay
46%39%20%15%5%
1988
April1st to 15thDay
54%36%18%13%3
1972
16th to endDay
48%47%18%17%3
2057
May1st to 15thDay
49%49%18%16%2
2301
16th to endDay
46%6%10%21%13%2
2398
June1st to 15thDay
53%6%10%18%10%
2310
16th to endDay
47%6%11%21%12%1
2310
July1st to 15thDay
38%6%13%29%11%
2161
16th to endDay
43%8%14%23%9%
2291
August1st to 15thDay
45%6%14%22%10%
2186
16th to endDay
41%7%15%24%9%
2157
September1st to 15thDay
42%5%14%26%10%
1980
16th to endDay
40%5%12%30%10%
1825
October1st to 15thDay
53%5%10%20%9%
1650
16th to endDay
63%5%10%15%4
1694
November1st to 15thDay
50%5%14%19%9%
1501
16th to endDay
63%5%10%12%6%1
1440
December1st to 15thDay
69%5%10%11%2
1440
16th to endDay
66%5%11%10%5%
1536
January1st to 15thNight
67%7%8%11%4
2506
16th to endNight
60%5%9%16%8%
2613
February1st to 15thNight
61%411%16%5%
2287
16th to endNight
55%5%10%19%10%
1970
March1st to 15thNight
57%311%19%7%
2059
16th to endNight
45%411%20%15%2
1883
April1st to 15thNight
52%47%19%14%1
1646
16th to endNight
47%36%21%17%3
1582
May1st to 15thNight
46%47%21%16%4
1320
16th to endNight
41%6%12%20%15%2
1369
June1st to 15thNight
49%6%11%20%10%1
1320
16th to endNight
42%7%13%21%15%
1320
July1st to 15thNight
31%6%13%32%15%1
1240
16th to endNight
32%6%18%26%14%
1306
August1st to 15thNight
36%7%18%24%12%1
1417
16th to endNight
32%416%32%12%
1682
September1st to 15thNight
42%7%11%28%10%
1650
16th to endNight
39%312%34%8%
1804
October1st to 15thNight
49%5%10%21%12%
1980
16th to endNight
59%5%12%16%6%
2178
November1st to 15thNight
52%5%13%17%11%
2355
16th to endNight
62%5%10%16%4
2520
December1st to 15thNight
66%6%10%13%3
2520
16th to endNight
68%49%11%6%
2688

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
30%26%20%20%3
60
16th to endDay
36%16%31%11%3
77
February1st to 15thDay
31%25%36%42
90
16th to endDay
32%20%30%12%3
162
March1st to 15thDay
26%17%32%18%4
264
16th to endDay
24%20%24%17%9%2
224
April1st to 15thDay
27%24%24%15%7%1
210
16th to endDay
23%17%24%15%13%4
210
May1st to 15thDay
23%12%29%19%9%5%
228
16th to endDay
20%13%34%20%7%2
267
June1st to 15thDay
29%12%22%22%11%1
255
16th to endDay
14%10%31%27%14%1
255
July1st to 15thDay
14%5%31%30%13%5%
245
16th to endDay
12%7%34%28%12%4
270
August1st to 15thDay
15%5%26%34%9%8%
253
16th to endDay
14%5%28%27%15%8%
268
September1st to 15thDay
18%5%27%20%15%11%
255
16th to endDay
18%7%32%19%14%7%
254
October1st to 15thDay
26%14%24%23%7%3
255
16th to endDay
33%16%30%13%5%
260
November1st to 15thDay
23%11%32%21%8%2
155
16th to endDay
36%11%35%10%5%1
60
December1st to 15thDay
20%25%40%10%5%
60
16th to endDay
39%26%31%3
64
January1st to 15thNight
25%19%34%15%4
720
16th to endNight
22%14%35%21%4
768
February1st to 15thNight
21%18%37%18%3
704
16th to endNight
22%19%35%17%4
631
March1st to 15thNight
27%17%31%20%2
716
16th to endNight
19%18%27%23%9%1
704
April1st to 15thNight
26%17%30%20%4
658
16th to endNight
22%16%27%23%7%
592
May1st to 15thNight
21%10%29%27%9%1
330
16th to endNight
16%6%35%27%12%
343
June1st to 15thNight
20%11%30%29%8%
330
16th to endNight
20%6%24%35%11%
330
July1st to 15thNight
7%5%30%40%15%1
310
16th to endNight
8%329%41%15%1
348
August1st to 15thNight
12%426%38%17%1
436
16th to endNight
10%5%29%35%17%1
632
September1st to 15thNight
21%5%26%26%17%1
660
16th to endNight
19%7%25%26%19%2
657
October1st to 15thNight
26%10%26%24%10%1
660
16th to endNight
30%14%27%20%7%
704
November1st to 15thNight
24%12%32%20%9%
700
16th to endNight
31%18%25%17%6%
720
December1st to 15thNight
29%18%32%16%2
720
16th to endNight
35%13%31%16%2
768
Page generated at 2017-03-15 11:32:35. Version ac04

Copyright 2017 A. Danko


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