Selkovitch's Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Selkovitch's Observatory clear sky chart from 2005-11-05 to 2017-10-31.

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
72%
16394
33%
47483
29%
16353
75%
16353
49%
24522

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
61%
716
29%
2327
26%
716
69%
716
39%
1212
January16th to endNight
58%
768
33%
2310
27%
768
67%
768
35%
1318
February1st to 15thNight
61%
698
32%
2112
29%
698
68%
698
39%
1165
February16th to endNight
53%
632
28%
1895
29%
632
57%
632
30%
1168
March1st to 15thNight
61%
720
29%
2153
29%
720
66%
720
39%
1190
March16th to endNight
66%
768
28%
2051
25%
768
69%
768
42%
1188
April1st to 15thNight
57%
719
27%
1799
17%
719
61%
719
41%
1093
April16th to endNight
63%
720
30%
1800
18%
720
67%
720
51%
1016
May1st to 15thNight
65%
572
31%
1652
21%
572
68%
572
46%
883
May16th to endNight
67%
561
28%
1685
21%
561
69%
561
46%
882
June1st to 15thNight
80%
540
32%
1620
28%
540
81%
540
62%
736
June16th to endNight
91%
540
38%
1620
34%
540
92%
540
80%
623
July1st to 15thNight
91%
510
30%
1530
26%
510
92%
510
68%
646
July16th to endNight
88%
617
32%
1642
24%
580
88%
580
57%
797
August1st to 15thNight
92%
717
36%
1790
23%
713
92%
713
76%
831
August16th to endNight
93%
764
43%
1910
31%
764
93%
764
75%
902
September1st to 15thNight
90%
720
38%
1881
32%
720
91%
720
69%
888
September16th to endNight
85%
716
47%
1980
42%
716
88%
716
72%
858
October1st to 15thNight
75%
720
36%
1980
33%
720
78%
720
53%
1012
October16th to endNight
75%
768
39%
2295
39%
768
78%
768
51%
1125
November1st to 15thNight
74%
700
33%
2275
35%
700
78%
700
49%
1080
November16th to endNight
68%
720
34%
2340
36%
720
72%
720
42%
1184
December1st to 15thNight
63%
720
31%
2340
30%
720
67%
720
35%
1297
December16th to endNight
55%
768
31%
2496
28%
768
63%
768
32%
1428

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%312212335%66%
48262
Night
6%412212335%64%
47683
TransparencyDay
20%35%14%26%29%
47962
Night
22%35%14%23%30%
47484
SeeingDay
8%10%31%34%11%3
6070
Night
8%212%30%34%11%
16407

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
9%5%13212335%59%
1611
16th to endDay
12%5%1232335%6%54%
1911
February1st to 15thDay
9%5%13314246%56%
1751
16th to endDay
14%8%14414446%45%
1579
March1st to 15thDay
8%5%12222448%57%
1806
16th to endDay
7%412324346%58%
2170
April1st to 15thDay
9%5%24323346%56%
2149
16th to endDay
7%312211247%66%
2160
May1st to 15thDay
5%412212235%66%
2298
16th to endDay
5%212211235%70%
2429
June1st to 15thDay
321221223475%
2340
16th to endDay
11111287%
2340
July1st to 15thDay
222212347%70%
2340
16th to endDay
221221446%6%65%
2413
August1st to 15thDay
1112223479%
2160
16th to endDay
111212335%76%
2292
September1st to 15thDay
11221223476%
2079
16th to endDay
21111222380%
1980
October1st to 15thDay
6%31221223468%
1980
16th to endDay
4412212225%70%
1922
November1st to 15thDay
5%313312235%66%
1584
16th to endDay
8%412213346%61%
1620
December1st to 15thDay
10%5%13422348%52%
1620
16th to endDay
14%6%13323335%52%
1728
January1st to 15thNight
7%413324345%58%
2327
16th to endNight
11%5%23323335%55%
2310
February1st to 15thNight
9%5%23223345%57%
2101
16th to endNight
13%8%2432344447%
1895
March1st to 15thNight
10%5%23313338%54%
2153
16th to endNight
7%5%2332345%8%53%
2051
April1st to 15thNight
9%7%33212437%54%
1799
16th to endNight
7%5%13223227%61%
1800
May1st to 15thNight
45%24313235%61%
1652
16th to endNight
46%33312336%62%
1684
June1st to 15thNight
142212235%72%
1620
16th to endNight
1111387%
1620
July1st to 15thNight
1111212235%75%
1620
16th to endNight
2112322336%70%
1754
August1st to 15thNight
1121246%78%
1800
16th to endNight
11111122481%
1910
September1st to 15thNight
11121223477%
1881
16th to endNight
1112112282%
1980
October1st to 15thNight
5%312213325%68%
1980
16th to endNight
5%313212235%67%
2295
November1st to 15thNight
5%41212323468%
2275
16th to endNight
7%5%13213345%62%
2340
December1st to 15thNight
10%414314346%53%
2340
16th to endNight
14%5%23222235%54%
2496

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
27%4311%27%25%
1612
16th to endDay
31%35%12%18%27%
1911
February1st to 15thDay
29%3413%22%26%
1751
16th to endDay
39%45%14%23%13%
1579
March1st to 15thDay
25%45%17%23%23%
1806
16th to endDay
27%47%21%24%15%
2170
April1st to 15thDay
29%35%22%28%10%
2149
16th to endDay
18%37%22%27%20%
2160
May1st to 15thDay
21%26%18%27%22%
2298
16th to endDay
17%27%21%35%15%
2432
June1st to 15thDay
15%1317%27%33%
2340
16th to endDay
6%125%20%63%
2340
July1st to 15thDay
12%45%11%25%40%
2201
16th to endDay
16%7%8%20%25%20%
2262
August1st to 15thDay
9%3313%32%37%
2146
16th to endDay
11%4311%33%35%
2292
September1st to 15thDay
12%3410%30%37%
2079
16th to endDay
10%228%34%41%
1980
October1st to 15thDay
20%2413%26%31%
1980
16th to endDay
18%2310%20%43%
1922
November1st to 15thDay
21%25%12%22%34%
1584
16th to endDay
24%3311%24%32%
1620
December1st to 15thDay
30%47%14%16%25%
1620
16th to endDay
34%45%13%23%17%
1728
January1st to 15thNight
26%35%12%22%29%
2327
16th to endNight
32%36%10%17%30%
2310
February1st to 15thNight
28%35%12%22%27%
2112
16th to endNight
38%3412%22%18%
1895
March1st to 15thNight
29%36%16%20%23%
2153
16th to endNight
27%5%8%16%23%18%
2051
April1st to 15thNight
30%37%19%24%13%
1799
16th to endNight
24%28%19%21%23%
1800
May1st to 15thNight
25%27%17%23%23%
1653
16th to endNight
24%39%18%26%18%
1685
June1st to 15thNight
15%17%16%26%33%
1620
16th to endNight
6%118%18%63%
1620
July1st to 15thNight
10%25%11%26%43%
1530
16th to endNight
15%5%7%23%26%21%
1642
August1st to 15thNight
7%3318%32%34%
1790
16th to endNight
9%2313%31%39%
1910
September1st to 15thNight
11%2413%29%38%
1881
16th to endNight
10%128%33%43%
1980
October1st to 15thNight
19%3415%28%29%
1980
16th to endNight
20%2410%18%43%
2295
November1st to 15thNight
21%2412%23%35%
2275
16th to endNight
25%3413%20%33%
2340
December1st to 15thNight
30%5%6%13%19%24%
2340
16th to endNight
33%47%12%20%21%
2496

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
34%5%16%36%6%
90
16th to endDay
17%17%33%25%5%1
279
February1st to 15thDay
11%13%38%26%9%
266
16th to endDay
19%19%31%20%7%
238
March1st to 15thDay
12%17%33%22%10%2
270
16th to endDay
6%20%36%24%9%2
288
April1st to 15thDay
13%19%37%18%8%2
269
16th to endDay
7%22%41%20%5%2
270
May1st to 15thDay
14%12%36%26%5%3
288
16th to endDay
10%12%39%27%8%2
330
June1st to 15thDay
49%36%33%13%3
315
16th to endDay
1229%40%17%7%
315
July1st to 15thDay
321%52%15%6%
305
16th to endDay
5%14%51%18%10%
327
August1st to 15thDay
1126%45%14%9%
315
16th to endDay
1118%54%15%8%
332
September1st to 15thDay
3232%47%9%4
315
16th to endDay
49%34%37%11%2
315
October1st to 15thDay
413%40%31%10%
315
16th to endDay
9%8%29%30%18%3
262
November1st to 15thDay
10%6%21%31%25%5%
90
16th to endDay
16%10%28%31%13%
90
December1st to 15thDay
5%8%17%43%23%1
90
16th to endDay
21%10%29%30%8%
96
January1st to 15thNight
8%5%18%34%23%10%
720
16th to endNight
14%416%33%24%6%
768
February1st to 15thNight
12%315%33%26%7%
704
16th to endNight
17%5%15%34%21%5%
632
March1st to 15thNight
12%5%16%36%24%5%
720
16th to endNight
8%415%34%28%7%
768
April1st to 15thNight
11%5%18%34%23%5%
719
16th to endNight
8%420%30%27%8%
720
May1st to 15thNight
7%218%35%29%6%
573
16th to endNight
8%415%32%32%6%
563
June1st to 15thNight
312%43%33%5%
540
16th to endNight
2437%48%6%
540
July1st to 15thNight
1222%62%10%
510
16th to endNight
2315%60%17%
617
August1st to 15thNight
1221%53%21%
717
16th to endNight
2111%55%29%
764
September1st to 15thNight
1321%55%17%
720
16th to endNight
37%30%43%14%
716
October1st to 15thNight
6%310%35%35%9%
720
16th to endNight
8%110%31%32%16%
768
November1st to 15thNight
7%112%35%33%10%
700
16th to endNight
9%213%31%27%15%
720
December1st to 15thNight
12%413%34%25%9%
720
16th to endNight
16%5%16%31%22%7%
768
Page generated at 2017-11-01 14:23:29. Version ac04

Copyright 2017 A. Danko


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