Tassi Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tassi Observatory clear sky chart from 2005-11-05 to 2017-09-24.

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%
16253
33%
47058
28%
16212
76%
16212
48%
24349

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
27%
716
68%
716
38%
1213
January16th to endNight
59%
768
33%
2307
27%
768
68%
768
35%
1322
February1st to 15thNight
61%
699
32%
2112
28%
699
69%
699
39%
1169
February16th to endNight
53%
632
27%
1895
29%
632
57%
632
29%
1167
March1st to 15thNight
60%
720
28%
2154
28%
720
66%
720
38%
1200
March16th to endNight
67%
768
28%
2049
25%
768
70%
768
42%
1185
April1st to 15thNight
59%
719
27%
1799
18%
719
62%
719
42%
1089
April16th to endNight
65%
720
31%
1800
19%
720
68%
720
51%
1013
May1st to 15thNight
66%
575
30%
1655
22%
575
69%
575
47%
889
May16th to endNight
68%
561
28%
1685
21%
561
70%
561
46%
879
June1st to 15thNight
82%
540
32%
1620
28%
540
83%
540
62%
737
June16th to endNight
92%
540
38%
1620
34%
540
92%
540
80%
622
July1st to 15thNight
91%
510
30%
1530
26%
510
91%
510
67%
647
July16th to endNight
89%
620
32%
1645
24%
583
89%
583
57%
798
August1st to 15thNight
93%
717
36%
1790
23%
713
93%
713
77%
829
August16th to endNight
93%
764
42%
1910
30%
764
93%
764
74%
907
September1st to 15thNight
90%
720
37%
1879
31%
720
91%
720
68%
900
September16th to endNight
85%
692
46%
1914
42%
692
88%
692
71%
838
October1st to 15thNight
74%
660
37%
1815
33%
660
77%
660
52%
933
October16th to endNight
75%
704
37%
2101
36%
704
78%
704
50%
1028
November1st to 15thNight
74%
700
33%
2275
35%
700
78%
700
49%
1082
November16th to endNight
69%
720
34%
2340
35%
720
73%
720
43%
1170
December1st to 15thNight
63%
720
30%
2340
30%
720
67%
720
35%
1298
December16th to endNight
55%
768
30%
2496
27%
768
63%
768
32%
1434

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%312212336%65%
47863
Night
6%312213336%63%
47258
TransparencyDay
20%35%14%26%28%
47564
Night
22%35%14%23%29%
47059
SeeingDay
8%10%31%34%11%3
5931
Night
7%211%30%35%11%
16265

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
10%414313245%59%
1611
16th to endDay
13%413213346%54%
1915
February1st to 15thDay
9%413323345%57%
1751
16th to endDay
15%6%33423348%44%
1579
March1st to 15thDay
8%313223449%56%
1806
16th to endDay
7%213324346%58%
2172
April1st to 15thDay
9%424223346%56%
2149
16th to endDay
7%312111237%66%
2160
May1st to 15thDay
6%412213236%65%
2295
16th to endDay
5%32212246%68%
2429
June1st to 15thDay
3311212135%72%
2340
16th to endDay
1112386%
2340
July1st to 15thDay
212212348%69%
2340
16th to endDay
21221346%8%65%
2408
August1st to 15thDay
11111235%79%
2160
16th to endDay
111212235%76%
2292
September1st to 15thDay
11221223476%
2079
16th to endDay
11121122379%
1904
October1st to 15thDay
6%412213335%65%
1815
16th to endDay
6%31321222470%
1766
November1st to 15thDay
6%322312335%65%
1584
16th to endDay
7%422213346%61%
1620
December1st to 15thDay
10%413323348%52%
1620
16th to endDay
14%5%13422345%52%
1728
January1st to 15thNight
7%313323346%59%
2327
16th to endNight
11%413323245%55%
2307
February1st to 15thNight
9%423313345%57%
2101
16th to endNight
14%7%24414435%47%
1895
March1st to 15thNight
10%5%13323347%54%
2154
16th to endNight
7%42331445%8%53%
2049
April1st to 15thNight
9%7%23312346%54%
1799
16th to endNight
8%422312337%61%
1800
May1st to 15thNight
46%23313246%60%
1655
16th to endNight
5%6%23323246%59%
1684
June1st to 15thNight
242313238%68%
1620
16th to endNight
1112485%
1620
July1st to 15thNight
1211325%8%71%
1620
16th to endNight
21222335%7%68%
1757
August1st to 15thNight
111111237%77%
1800
16th to endNight
1111123479%
1910
September1st to 15thNight
1221223477%
1879
16th to endNight
21111111381%
1914
October1st to 15thNight
5%312213235%67%
1815
16th to endNight
5%312213336%65%
2101
November1st to 15thNight
5%31221323467%
2275
16th to endNight
6%412322336%62%
2340
December1st to 15thNight
10%41332345%5%54%
2340
16th to endNight
13%424322235%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%3412%26%25%
1612
16th to endDay
31%45%12%18%27%
1915
February1st to 15thDay
28%3413%22%26%
1751
16th to endDay
39%46%13%23%13%
1579
March1st to 15thDay
25%46%16%24%23%
1806
16th to endDay
26%47%21%24%15%
2172
April1st to 15thDay
29%36%21%27%11%
2149
16th to endDay
18%37%22%27%20%
2160
May1st to 15thDay
21%26%18%28%22%
2295
16th to endDay
17%27%21%35%15%
2432
June1st to 15thDay
15%1317%27%33%
2340
16th to endDay
6%126%20%62%
2340
July1st to 15thDay
13%46%11%24%39%
2201
16th to endDay
15%7%10%20%27%18%
2258
August1st to 15thDay
9%3413%32%36%
2146
16th to endDay
12%3411%34%34%
2292
September1st to 15thDay
12%35%10%31%36%
2079
16th to endDay
11%138%34%40%
1904
October1st to 15thDay
22%35%14%26%28%
1815
16th to endDay
19%2310%20%42%
1766
November1st to 15thDay
21%25%12%21%34%
1584
16th to endDay
23%3411%23%32%
1620
December1st to 15thDay
30%48%13%17%25%
1620
16th to endDay
34%46%14%22%17%
1728
January1st to 15thNight
26%45%12%20%29%
2327
16th to endNight
31%46%10%16%30%
2307
February1st to 15thNight
28%45%12%22%27%
2112
16th to endNight
38%3412%21%18%
1895
March1st to 15thNight
29%36%16%19%24%
2154
16th to endNight
26%6%8%16%23%18%
2049
April1st to 15thNight
30%38%19%24%13%
1799
16th to endNight
23%28%20%20%23%
1800
May1st to 15thNight
24%38%17%22%23%
1656
16th to endNight
24%29%18%25%18%
1685
June1st to 15thNight
15%26%16%26%32%
1620
16th to endNight
5%128%19%62%
1620
July1st to 15thNight
10%25%11%25%42%
1530
16th to endNight
15%5%7%24%26%20%
1645
August1st to 15thNight
7%3319%32%33%
1790
16th to endNight
9%2314%30%38%
1910
September1st to 15thNight
12%3413%29%37%
1879
16th to endNight
11%128%34%41%
1914
October1st to 15thNight
20%35%15%27%27%
1815
16th to endNight
21%25%10%18%41%
2101
November1st to 15thNight
20%3412%22%35%
2275
16th to endNight
24%35%13%20%33%
2340
December1st to 15thNight
30%5%7%13%19%24%
2340
16th to endNight
33%47%12%19%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
37%6%12%37%5%
90
16th to endDay
17%16%34%25%41
283
February1st to 15thDay
9%15%37%27%9%
266
16th to endDay
18%19%33%20%7%
238
March1st to 15thDay
11%18%33%23%10%2
270
16th to endDay
6%20%36%25%8%2
288
April1st to 15thDay
11%20%39%17%8%1
269
16th to endDay
7%22%41%19%6%2
270
May1st to 15thDay
14%13%34%27%5%3
288
16th to endDay
10%11%38%28%8%2
330
June1st to 15thDay
28%37%33%13%3
315
16th to endDay
1328%40%18%7%
315
July1st to 15thDay
3120%51%16%6%
305
16th to endDay
5%12%55%15%10%
327
August1st to 15thDay
1126%46%13%9%
315
16th to endDay
118%55%15%8%
332
September1st to 15thDay
3234%46%8%4
315
16th to endDay
49%35%37%10%2
288
October1st to 15thDay
5%16%41%29%7%
255
16th to endDay
11%8%30%31%16%1
206
November1st to 15thDay
8%8%20%31%25%5%
90
16th to endDay
17%8%27%31%14%
90
December1st to 15thDay
310%22%38%24%1
90
16th to endDay
19%10%31%27%11%
96
January1st to 15thNight
7%6%19%33%24%10%
720
16th to endNight
14%415%33%25%6%
768
February1st to 15thNight
12%316%32%27%7%
704
16th to endNight
16%6%15%35%20%5%
632
March1st to 15thNight
11%417%35%25%5%
720
16th to endNight
8%5%14%34%29%8%
768
April1st to 15thNight
12%5%16%35%23%6%
719
16th to endNight
9%317%33%27%9%
720
May1st to 15thNight
6%217%35%29%7%
576
16th to endNight
7%315%33%33%6%
563
June1st to 15thNight
310%44%35%6%
540
16th to endNight
2433%52%7%
540
July1st to 15thNight
1220%65%10%
510
16th to endNight
2215%61%17%
620
August1st to 15thNight
221%54%20%
717
16th to endNight
2110%56%29%
764
September1st to 15thNight
321%56%17%
720
16th to endNight
27%31%41%15%
692
October1st to 15thNight
7%212%34%33%10%
660
16th to endNight
8%110%31%31%17%
704
November1st to 15thNight
7%112%35%31%11%
700
16th to endNight
9%313%31%27%14%
720
December1st to 15thNight
12%414%33%25%9%
720
16th to endNight
16%5%17%29%23%7%
768
Page generated at 2017-09-25 06:02:21. Version ac04

Copyright 2017 A. Danko


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