Sullivan
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sullivan clear sky chart from 2005-11-05 to 2018-02-13.

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
37%
16492
22%
48797
13%
16445
46%
16445
27%
30444

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
19%
975
19%
2644
5%
970
31%
970
21%
1796
January16th to endNight
21%
1040
22%
2704
6%
1040
32%
1040
24%
1827
February1st to 15thNight
19%
916
15%
2421
4%
913
26%
913
20%
1721
February16th to endNight
18%
631
21%
1893
5%
631
31%
631
21%
1217
March1st to 15thNight
20%
616
18%
2056
8%
616
31%
616
18%
1370
March16th to endNight
22%
576
14%
2058
7%
576
31%
576
16%
1402
April1st to 15thNight
29%
539
22%
1797
11%
539
44%
539
26%
1048
April16th to endNight
30%
540
21%
1800
12%
540
43%
540
24%
1113
May1st to 15thNight
39%
540
17%
1682
12%
539
47%
539
25%
1072
May16th to endNight
47%
563
20%
1497
13%
561
53%
561
29%
993
June1st to 15thNight
58%
540
21%
1440
14%
540
63%
540
40%
849
June16th to endNight
62%
540
24%
1440
14%
540
68%
540
45%
817
July1st to 15thNight
66%
510
20%
1360
16%
510
68%
510
41%
807
July16th to endNight
72%
564
23%
1550
20%
531
77%
531
43%
857
August1st to 15thNight
74%
539
23%
1654
26%
536
75%
536
40%
894
August16th to endNight
72%
573
24%
1910
27%
573
75%
573
38%
1017
September1st to 15thNight
62%
540
27%
1800
28%
540
65%
540
31%
1030
September16th to endNight
59%
639
32%
1939
24%
639
66%
639
37%
1082
October1st to 15thNight
47%
720
29%
2160
21%
720
55%
720
37%
1222
October16th to endNight
33%
768
29%
2304
15%
768
46%
768
31%
1340
November1st to 15thNight
33%
760
28%
2443
15%
760
48%
760
29%
1395
November16th to endNight
27%
848
25%
2603
13%
848
40%
848
26%
1614
December1st to 15thNight
23%
975
18%
2730
6%
975
34%
975
23%
1852
December16th to endNight
17%
1040
18%
2912
5%
1040
29%
1040
18%
2109

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
12%6%25%43445%7%42%
49243
Night
12%6%24423346%46%
48984
TransparencyDay
40%5%11%24%15%2
48933
Night
38%411%24%17%2
48799
SeeingDay
14%8%25%26%18%5%
6314
Night
17%10%30%27%13%1
16492

By Month

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
12%8%48%423445%40%
1621
16th to endDay
10%9%35%5%2345%6%42%
1872
February1st to 15thDay
13%9%46%6%3445%5%35%
1704
16th to endDay
12%9%36%5%345%45%39%
1580
March1st to 15thDay
16%9%36%424435%38%
1914
16th to endDay
18%10%36%6%3445%431%
2163
April1st to 15thDay
14%5%24425%45%5%44%
2151
16th to endDay
20%6%25%5%3435%6%35%
2160
May1st to 15thDay
20%5%24434448%37%
2265
16th to endDay
12%5%36%5%35%5%5%6%39%
2617
June1st to 15thDay
9%425%5%35%6%5%9%44%
2520
16th to endDay
6%312435%5%7%12%46%
2520
July1st to 15thDay
9%424435%6%6%9%43%
2520
16th to endDay
5%425%5%35%6%7%9%44%
2508
August1st to 15thDay
8%425%5%35%6%6%9%41%
2295
16th to endDay
8%435%5%345%5%7%45%
2292
September1st to 15thDay
14%5%1442336%6%46%
2160
16th to endDay
9%425%434447%49%
2007
October1st to 15thDay
14%5%25%414236%49%
1800
16th to endDay
12%5%13423346%52%
1920
November1st to 15thDay
13%6%14324346%49%
1744
16th to endDay
15%8%24423345%45%
1686
December1st to 15thDay
15%10%35%5%2445%439%
1560
16th to endDay
14%12%46%424346%36%
1664
January1st to 15thNight
13%7%36%6%24335%41%
2644
16th to endNight
11%9%35%433446%42%
2704
February1st to 15thNight
14%10%46%424345%38%
2412
16th to endNight
13%8%37%5%23345%43%
1893
March1st to 15thNight
18%9%25%42433440%
2056
16th to endNight
20%7%35%5%25%45%6%33%
2058
April1st to 15thNight
12%5%25%423348%48%
1797
16th to endNight
17%5%2443245%6%43%
1800
May1st to 15thNight
17%5%23423337%44%
1682
16th to endNight
10%5%35%5%245%6%7%44%
1496
June1st to 15thNight
6%3245%2445%7%52%
1440
16th to endNight
5%31222447%10%53%
1440
July1st to 15thNight
8%31341445%10%51%
1440
16th to endNight
33144245%7%10%52%
1657
August1st to 15thNight
431333446%9%54%
1664
16th to endNight
4314425%35%8%54%
1910
September1st to 15thNight
13%42432345%5%51%
1800
16th to endNight
8%414423346%56%
1939
October1st to 15thNight
12%324322347%53%
2160
16th to endNight
15%5%13322335%53%
2304
November1st to 15thNight
12%6%23322346%52%
2443
16th to endNight
15%7%34423245%47%
2603
December1st to 15thNight
18%9%3442335%7%38%
2730
16th to endNight
17%12%45%5%3434434%
2912

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
45%310%22%15%1
1622
16th to endDay
40%313%28%11%1
1872
February1st to 15thDay
50%410%22%10%1
1706
16th to endDay
45%410%24%12%2
1580
March1st to 15thDay
48%49%21%13%3
1914
16th to endDay
54%5%12%17%8%
2165
April1st to 15thDay
40%411%23%18%2
2151
16th to endDay
49%410%21%12%1
2160
May1st to 15thDay
45%6%11%22%12%
2265
16th to endDay
43%6%13%19%14%2
2621
June1st to 15thDay
35%7%12%25%16%1
2520
16th to endDay
28%6%17%26%17%3
2520
July1st to 15thDay
35%7%13%26%13%3
2371
16th to endDay
32%7%15%28%14%1
2352
August1st to 15thDay
36%7%13%23%17%1
2281
16th to endDay
36%6%13%21%17%4
2292
September1st to 15thDay
37%49%24%20%3
2160
16th to endDay
34%47%30%19%2
2007
October1st to 15thDay
37%38%25%19%5%
1800
16th to endDay
32%49%28%20%4
1920
November1st to 15thDay
36%310%23%20%6%
1744
16th to endDay
41%29%28%17%1
1686
December1st to 15thDay
47%411%23%12%
1560
16th to endDay
49%313%20%11%1
1664
January1st to 15thNight
45%410%22%15%1
2644
16th to endNight
43%412%23%15%
2704
February1st to 15thNight
48%410%22%12%1
2421
16th to endNight
43%312%23%15%1
1893
March1st to 15thNight
49%39%21%15%2
2056
16th to endNight
50%5%11%22%9%
2058
April1st to 15thNight
36%311%26%17%3
1797
16th to endNight
41%49%28%14%2
1800
May1st to 15thNight
41%5%13%22%16%1
1683
16th to endNight
38%8%14%20%14%3
1498
June1st to 15thNight
29%5%14%30%18%2
1440
16th to endNight
24%6%15%27%21%4
1440
July1st to 15thNight
30%414%30%16%4
1360
16th to endNight
25%6%16%30%19%1
1550
August1st to 15thNight
25%6%14%29%20%2
1654
16th to endNight
26%5%14%24%23%5%
1910
September1st to 15thNight
34%48%24%22%5%
1800
16th to endNight
29%49%26%26%3
1939
October1st to 15thNight
31%310%25%23%6%
2160
16th to endNight
35%27%28%21%5%
2304
November1st to 15thNight
34%310%24%19%7%
2443
16th to endNight
40%28%27%19%1
2603
December1st to 15thNight
46%312%21%14%1
2730
16th to endNight
53%39%19%11%2
2912

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%16%39%14%2
135
16th to endDay
9%30%40%16%2
144
February1st to 15thDay
19%23%41%12%2
126
16th to endDay
18%23%37%18%11
81
March1st to 15thDay
33%20%33%10%21
90
16th to endDay
25%20%34%17%2
149
April1st to 15thDay
19%12%37%20%9%
270
16th to endDay
24%10%32%19%10%2
270
May1st to 15thDay
20%14%29%20%11%2
354
16th to endDay
17%7%34%25%10%4
517
June1st to 15thDay
10%5%24%31%22%6%
495
16th to endDay
8%5%30%33%17%4
495
July1st to 15thDay
14%215%35%25%5%
475
16th to endDay
6%211%33%33%11%
515
August1st to 15thDay
13%112%30%32%9%
448
16th to endDay
9%16%30%33%9%
332
September1st to 15thDay
13%413%26%30%12%
315
16th to endDay
9%5%17%28%26%13%
275
October1st to 15thDay
16%11%24%36%10%
135
16th to endDay
13%13%33%31%7%
144
November1st to 15thDay
16%6%34%24%14%4
135
16th to endDay
25%17%30%19%8%
135
December1st to 15thDay
13%26%34%17%34
135
16th to endDay
20%20%49%9%1
144
January1st to 15thNight
21%20%35%18%4
975
16th to endNight
19%18%37%21%2
1040
February1st to 15thNight
21%19%36%20%1
916
16th to endNight
19%18%40%19%1
631
March1st to 15thNight
25%15%36%19%2
616
16th to endNight
22%12%38%20%5%
576
April1st to 15thNight
15%14%37%26%5%
539
16th to endNight
20%9%36%24%8%
540
May1st to 15thNight
19%5%28%32%11%
540
16th to endNight
14%328%34%17%1
563
June1st to 15thNight
10%220%39%24%1
540
16th to endNight
7%124%41%22%2
540
July1st to 15thNight
12%12%41%29%3
510
16th to endNight
4112%41%35%5%
564
August1st to 15thNight
7%12%36%39%3
539
16th to endNight
6%13%39%33%6%
573
September1st to 15thNight
16%213%29%31%6%
540
16th to endNight
11%5%17%30%29%6%
639
October1st to 15thNight
14%5%28%29%18%3
720
16th to endNight
19%12%32%25%9%
768
November1st to 15thNight
16%11%34%25%10%
760
16th to endNight
21%14%35%22%6%
848
December1st to 15thNight
24%14%35%20%5%
975
16th to endNight
25%13%40%18%1
1040
Page generated at 2018-02-13 19:45:59. Version ac04

Copyright 2018 A. Danko


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