South Fork Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the South Fork Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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
73%
15568
30%
47068
27%
15536
76%
15536
46%
24242

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
66%
716
23%
2503
25%
716
69%
716
36%
1315
January16th to endNight
57%
768
27%
2496
25%
768
63%
768
32%
1431
February1st to 15thNight
60%
700
24%
2118
23%
700
64%
700
31%
1290
February16th to endNight
58%
632
22%
1895
23%
632
60%
632
29%
1190
March1st to 15thNight
66%
720
20%
2160
22%
720
67%
720
34%
1278
March16th to endNight
64%
768
22%
1991
17%
768
67%
768
39%
1197
April1st to 15thNight
61%
719
23%
1799
15%
719
63%
719
39%
1111
April16th to endNight
67%
720
26%
1800
14%
720
70%
720
51%
996
May1st to 15thNight
71%
602
30%
1682
21%
602
73%
602
53%
844
May16th to endNight
65%
492
28%
1616
25%
492
70%
492
44%
782
June1st to 15thNight
80%
360
32%
1440
37%
360
84%
360
52%
555
June16th to endNight
93%
360
40%
1440
50%
360
94%
360
77%
431
July1st to 15thNight
93%
340
35%
1360
44%
340
93%
340
64%
474
July16th to endNight
91%
458
39%
1492
39%
430
92%
430
62%
592
August1st to 15thNight
91%
717
38%
1790
25%
713
91%
713
81%
800
August16th to endNight
94%
764
45%
1910
29%
764
94%
764
80%
857
September1st to 15thNight
92%
720
41%
1800
31%
720
93%
720
75%
846
September16th to endNight
89%
716
45%
1977
41%
716
91%
716
73%
861
October1st to 15thNight
79%
684
32%
1958
32%
684
81%
684
54%
960
October16th to endNight
79%
704
36%
2138
39%
704
82%
704
50%
1056
November1st to 15thNight
75%
700
30%
2275
33%
700
78%
700
44%
1143
November16th to endNight
72%
720
27%
2340
30%
720
74%
720
39%
1228
December1st to 15thNight
64%
720
24%
2400
23%
720
68%
720
31%
1392
December16th to endNight
58%
768
23%
2688
23%
768
63%
768
26%
1613

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
6%412212335%65%
48133
Night
7%312212235%66%
47248
TransparencyDay
23%5%7%20%27%14%
47813
Night
23%49%22%27%13%
47069
SeeingDay
11%12%31%32%8%3
5919
Night
9%111%32%34%10%
15579

By Month

Percentage Cloud Cover SW (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%41322336%8%51%
1432
16th to endDay
13%8%24323335%46%
1728
February1st to 15thDay
14%9%22213248%47%
1744
16th to endDay
18%8%34323346%40%
1579
March1st to 15thDay
10%9%3332345%7%47%
1800
16th to endDay
12%7%24413336%49%
2230
April1st to 15thDay
13%7%2433224450%
2149
16th to endDay
9%5%23313247%56%
2160
May1st to 15thDay
5%312212136%67%
2265
16th to endDay
5%312213346%62%
2495
June1st to 15thDay
222213335%72%
2520
16th to endDay
11112187%
2520
July1st to 15thDay
11111222479%
2520
16th to endDay
111121223479%
2569
August1st to 15thDay
11121287%
2160
16th to endDay
11122384%
2292
September1st to 15thDay
11111122383%
2160
16th to endDay
1111122383%
1983
October1st to 15thDay
4312113435%68%
1797
16th to endDay
5%313213336%65%
1733
November1st to 15thDay
6%423213346%60%
1584
16th to endDay
8%412223348%58%
1620
December1st to 15thDay
11%7%13323347%51%
1557
16th to endDay
15%8%22322339%45%
1536
January1st to 15thNight
12%312212347%57%
2503
16th to endNight
13%413313348%52%
2496
February1st to 15thNight
12%6%23324347%49%
2107
16th to endNight
17%6%23212346%48%
1895
March1st to 15thNight
9%5%2332335%7%53%
2160
16th to endNight
10%412323347%56%
1991
April1st to 15thNight
11%411312446%57%
1799
16th to endNight
6%311212336%66%
1800
May1st to 15thNight
5%12212237%71%
1682
16th to endNight
6%212212225%70%
1615
June1st to 15thNight
3112211125%76%
1440
16th to endNight
111289%
1440
July1st to 15thNight
111122382%
1440
16th to endNight
11121222381%
1594
August1st to 15thNight
111111288%
1800
16th to endNight
1121387%
1910
September1st to 15thNight
1111212384%
1800
16th to endNight
111112384%
1977
October1st to 15thNight
4111322335%71%
1958
16th to endNight
4212212235%70%
2138
November1st to 15thNight
7%323212346%64%
2275
16th to endNight
6%413323337%58%
2340
December1st to 15thNight
11%413414346%54%
2400
16th to endNight
15%5%24324337%48%
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
31%7%10%22%21%6%
1432
16th to endDay
41%49%16%17%9%
1728
February1st to 15thDay
37%410%23%17%5%
1744
16th to endDay
47%48%24%14%
1579
March1st to 15thDay
37%7%11%22%16%4
1800
16th to endDay
38%7%15%22%15%1
2230
April1st to 15thDay
37%6%10%26%15%2
2149
16th to endDay
29%7%11%29%20%1
2160
May1st to 15thDay
21%5%9%31%30%2
2265
16th to endDay
23%7%8%35%22%2
2498
June1st to 15thDay
17%49%21%33%13%
2520
16th to endDay
7%2211%46%29%
2520
July1st to 15thDay
11%4310%28%42%
2371
16th to endDay
12%4412%32%33%
2409
August1st to 15thDay
8%3111%38%37%
2146
16th to endDay
7%3114%43%29%
2292
September1st to 15thDay
9%3315%39%28%
2160
16th to endDay
8%4225%41%17%
1983
October1st to 15thDay
20%5%423%31%14%
1797
16th to endDay
23%4422%27%16%
1733
November1st to 15thDay
27%49%22%27%8%
1584
16th to endDay
27%5%11%19%27%9%
1620
December1st to 15thDay
33%8%10%20%22%5%
1557
16th to endDay
40%5%14%19%15%5%
1536
January1st to 15thNight
28%5%11%26%23%5%
2503
16th to endNight
32%5%10%19%21%10%
2496
February1st to 15thNight
37%48%24%19%5%
2118
16th to endNight
38%6%12%22%18%1
1895
March1st to 15thNight
31%6%13%22%20%4
2160
16th to endNight
29%6%17%28%15%2
1991
April1st to 15thNight
31%6%13%30%14%4
1799
16th to endNight
21%5%16%34%21%1
1800
May1st to 15thNight
17%49%33%31%2
1683
16th to endNight
20%5%8%31%30%2
1616
June1st to 15thNight
14%310%24%31%15%
1440
16th to endNight
5%1312%47%29%
1440
July1st to 15thNight
9%3313%29%41%
1360
16th to endNight
12%2413%28%38%
1492
August1st to 15thNight
6%1215%35%38%
1790
16th to endNight
6%2114%49%26%
1910
September1st to 15thNight
8%3314%35%34%
1800
16th to endNight
8%2326%39%19%
1977
October1st to 15thNight
17%45%25%31%15%
1958
16th to endNight
19%5%6%23%31%15%
2138
November1st to 15thNight
24%310%24%25%11%
2275
16th to endNight
27%411%20%26%9%
2340
December1st to 15thNight
34%5%10%22%21%5%
2400
16th to endNight
39%412%19%17%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
50%5%23%11%6%3
60
16th to endDay
21%5%30%25%13%3
256
February1st to 15thDay
23%7%30%21%13%4
265
16th to endDay
28%10%31%23%5%
238
March1st to 15thDay
17%14%33%20%12%2
270
16th to endDay
19%20%31%20%5%1
288
April1st to 15thDay
24%22%27%19%41
269
16th to endDay
12%29%33%20%21
270
May1st to 15thDay
14%19%32%23%6%2
288
16th to endDay
13%20%28%28%6%2
330
June1st to 15thDay
417%35%33%6%3
315
16th to endDay
10%33%37%10%6%
315
July1st to 15thDay
3333%46%8%5%
305
16th to endDay
3223%54%8%7%
327
August1st to 15thDay
28%38%38%6%6%
315
16th to endDay
134%47%8%7%
332
September1st to 15thDay
35%36%42%7%3
315
16th to endDay
411%35%37%9%1
315
October1st to 15thDay
5%17%38%31%6%
278
16th to endDay
12%11%27%34%13%
245
November1st to 15thDay
8%10%7%33%32%7%
90
16th to endDay
14%12%28%30%13%1
90
December1st to 15thDay
18%7%30%30%12%
79
16th to endDay
26%131%18%20%1
64
January1st to 15thNight
14%13%35%22%12%
720
16th to endNight
16%217%32%22%8%
768
February1st to 15thNight
15%115%35%22%8%
704
16th to endNight
21%212%34%22%5%
632
March1st to 15thNight
11%413%38%24%8%
720
16th to endNight
14%215%35%27%5%
768
April1st to 15thNight
15%315%36%23%5%
719
16th to endNight
8%416%33%29%7%
720
May1st to 15thNight
6%216%35%33%4
603
16th to endNight
10%417%31%31%5%
494
June1st to 15thNight
6%17%36%40%7%
360
16th to endNight
438%48%7%
360
July1st to 15thNight
1215%68%12%
340
16th to endNight
1315%63%16%
458
August1st to 15thNight
1425%56%11%
717
16th to endNight
218%59%18%
764
September1st to 15thNight
1224%53%16%
720
16th to endNight
16%32%42%16%
716
October1st to 15thNight
5%11%35%35%11%
684
16th to endNight
5%9%32%34%16%
704
November1st to 15thNight
10%18%34%31%14%
700
16th to endNight
10%12%35%30%11%
720
December1st to 15thNight
14%212%37%25%8%
720
16th to endNight
16%316%36%19%5%
768
Page generated at 2017-10-07 11:07:45. Version ac04

Copyright 2017 A. Danko


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