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 2019-06-24.

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%
18646
33%
54077
28%
18605
75%
18605
47%
28219

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%
836
30%
2717
28%
836
68%
836
36%
1455
January16th to endNight
60%
896
33%
2691
27%
896
68%
896
36%
1525
February1st to 15thNight
61%
819
32%
2472
28%
819
68%
819
37%
1393
February16th to endNight
54%
736
27%
2207
29%
736
58%
736
29%
1356
March1st to 15thNight
57%
840
26%
2514
26%
840
62%
840
33%
1480
March16th to endNight
68%
896
27%
2391
24%
896
70%
896
41%
1392
April1st to 15thNight
60%
839
28%
2099
19%
839
63%
839
41%
1288
April16th to endNight
65%
832
30%
2080
18%
832
68%
832
49%
1184
May1st to 15thNight
66%
671
30%
1931
21%
671
68%
671
43%
1076
May16th to endNight
65%
657
27%
1973
20%
657
67%
657
42%
1079
June1st to 15thNight
83%
630
34%
1890
30%
630
84%
630
63%
846
June16th to endNight
91%
609
36%
1827
32%
609
91%
609
76%
721
July1st to 15thNight
92%
555
31%
1665
27%
555
92%
555
68%
698
July16th to endNight
90%
673
31%
1794
23%
636
90%
636
58%
864
August1st to 15thNight
93%
765
38%
1910
24%
761
94%
761
77%
880
August16th to endNight
93%
828
41%
2070
29%
828
93%
828
75%
977
September1st to 15thNight
91%
780
40%
2036
33%
780
91%
780
69%
967
September16th to endNight
86%
776
45%
2145
41%
776
89%
776
73%
924
October1st to 15thNight
75%
780
36%
2145
33%
780
77%
780
51%
1110
October16th to endNight
76%
832
38%
2483
37%
832
79%
832
52%
1199
November1st to 15thNight
73%
820
35%
2665
36%
820
79%
820
48%
1280
November16th to endNight
69%
840
33%
2730
35%
840
73%
840
41%
1397
December1st to 15thNight
62%
840
31%
2730
31%
840
67%
840
35%
1505
December16th to endNight
59%
896
31%
2912
28%
896
66%
896
34%
1623

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%312212346%65%
54737
Night
6%313313346%62%
54277
TransparencyDay
21%35%15%26%27%
54438
Night
23%35%14%23%29%
54078
SeeingDay
8%10%29%34%13%4
8291
Night
7%211%31%35%10%
18658

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%414313335%57%
1881
16th to endDay
11%313314346%55%
2235
February1st to 15thDay
10%413313345%57%
2051
16th to endDay
15%5%33324337%45%
1839
March1st to 15thDay
9%3233235%48%52%
2106
16th to endDay
7%313324347%57%
2534
April1st to 15thDay
8%424324346%55%
2509
16th to endDay
7%212212247%65%
2485
May1st to 15thDay
7%413212236%62%
2679
16th to endDay
6%412212247%65%
2845
June1st to 15thDay
2211212235%74%
2730
16th to endDay
111112385%
2641
July1st to 15thDay
212212348%68%
2535
16th to endDay
21121346%8%66%
2611
August1st to 15thDay
11111225%80%
2293
16th to endDay
111212235%76%
2484
September1st to 15thDay
11121223477%
2252
16th to endDay
11121122381%
2145
October1st to 15thDay
6%41322223465%
2145
16th to endDay
5%31321222471%
2087
November1st to 15thDay
5%412312335%64%
1854
16th to endDay
7%422213347%59%
1890
December1st to 15thDay
9%413324348%54%
1890
16th to endDay
13%5%12423345%53%
2016
January1st to 15thNight
8%423324346%56%
2717
16th to endNight
10%423323235%56%
2691
February1st to 15thNight
9%5%23323345%56%
2461
16th to endNight
14%6%23424435%48%
2207
March1st to 15thNight
11%5%14423347%50%
2514
16th to endNight
7%42332346%9%52%
2391
April1st to 15thNight
8%7%24423447%52%
2099
16th to endNight
7%423323337%59%
2080
May1st to 15thNight
5%7%24313346%57%
1931
16th to endNight
6%7%24323246%56%
1972
June1st to 15thNight
132312238%69%
1890
16th to endNight
1111122482%
1827
July1st to 15thNight
12113249%72%
1755
16th to endNight
21222335%7%69%
1906
August1st to 15thNight
111111237%78%
1920
16th to endNight
1111123480%
2070
September1st to 15thNight
1221223477%
2036
16th to endNight
11111112382%
2145
October1st to 15thNight
5%313212335%66%
2145
16th to endNight
5%32222235%67%
2483
November1st to 15thNight
4312213235%66%
2665
16th to endNight
6%423323347%59%
2730
December1st to 15thNight
10%41332345%6%54%
2730
16th to endNight
11%423322335%56%
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
29%3412%24%24%
1882
16th to endDay
30%46%12%19%26%
2235
February1st to 15thDay
29%3413%22%26%
2051
16th to endDay
39%45%13%23%13%
1839
March1st to 15thDay
29%46%16%22%21%
2106
16th to endDay
27%47%20%24%15%
2534
April1st to 15thDay
29%37%21%25%12%
2509
16th to endDay
19%37%22%29%18%
2485
May1st to 15thDay
24%27%18%26%20%
2679
16th to endDay
20%27%22%33%13%
2848
June1st to 15thDay
13%1318%29%32%
2730
16th to endDay
6%127%21%59%
2641
July1st to 15thDay
13%46%12%23%38%
2396
16th to endDay
14%7%12%20%27%17%
2461
August1st to 15thDay
8%35%13%32%36%
2279
16th to endDay
11%3413%34%31%
2484
September1st to 15thDay
11%3410%31%38%
2252
16th to endDay
9%138%35%41%
2145
October1st to 15thDay
22%2414%26%29%
2145
16th to endDay
18%2310%21%43%
2087
November1st to 15thDay
22%25%12%21%34%
1854
16th to endDay
24%3411%24%30%
1890
December1st to 15thDay
29%47%14%17%26%
1890
16th to endDay
33%45%14%22%18%
2016
January1st to 15thNight
28%45%14%19%27%
2717
16th to endNight
30%45%11%17%30%
2691
February1st to 15thNight
30%4411%22%26%
2472
16th to endNight
38%3412%22%17%
2207
March1st to 15thNight
33%46%15%19%21%
2514
16th to endNight
27%5%8%15%24%18%
2391
April1st to 15thNight
31%38%19%22%14%
2099
16th to endNight
25%27%19%22%22%
2080
May1st to 15thNight
27%38%17%21%21%
1932
16th to endNight
28%28%19%24%16%
1973
June1st to 15thNight
14%16%17%26%32%
1890
16th to endNight
7%1210%19%58%
1827
July1st to 15thNight
10%25%13%24%42%
1665
16th to endNight
14%5%9%24%26%18%
1794
August1st to 15thNight
6%3419%31%34%
1910
16th to endNight
9%2316%31%36%
2070
September1st to 15thNight
11%2313%28%40%
2036
16th to endNight
9%139%33%42%
2145
October1st to 15thNight
21%35%15%26%27%
2145
16th to endNight
20%2410%18%43%
2483
November1st to 15thNight
21%3413%23%34%
2665
16th to endNight
26%35%13%20%31%
2730
December1st to 15thNight
30%5%6%12%19%25%
2730
16th to endNight
31%47%13%20%22%
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
29%6%13%33%15%1
180
16th to endDay
13%16%31%28%8%2
411
February1st to 15thDay
13%14%30%27%10%3
386
16th to endDay
19%19%29%22%9%
342
March1st to 15thDay
13%18%35%22%7%2
390
16th to endDay
7%17%36%27%8%1
416
April1st to 15thDay
10%19%34%23%9%2
389
16th to endDay
8%19%40%20%7%3
378
May1st to 15thDay
14%12%33%25%9%3
408
16th to endDay
11%16%35%27%8%1
458
June1st to 15thDay
26%33%34%17%5%
435
16th to endDay
1226%38%21%8%
408
July1st to 15thDay
3118%49%18%9%
365
16th to endDay
410%53%18%11%
391
August1st to 15thDay
1123%45%15%11%
359
16th to endDay
117%52%17%9%
396
September1st to 15thDay
2133%47%9%5%
375
16th to endDay
37%32%39%13%3
375
October1st to 15thDay
5%14%38%30%9%
375
16th to endDay
8%7%28%32%18%4
322
November1st to 15thDay
8%8%22%37%18%4
180
16th to endDay
13%11%20%32%18%3
180
December1st to 15thDay
311%25%36%22%
180
16th to endDay
13%10%21%29%21%4
192
January1st to 15thNight
8%5%17%33%25%9%
840
16th to endNight
13%415%34%26%5%
896
February1st to 15thNight
12%415%32%26%8%
824
16th to endNight
16%6%14%34%22%4
736
March1st to 15thNight
12%5%18%35%23%4
840
16th to endNight
8%413%37%28%7%
896
April1st to 15thNight
11%5%16%35%24%6%
839
16th to endNight
9%417%33%27%8%
832
May1st to 15thNight
7%317%34%31%6%
672
16th to endNight
8%416%34%30%5%
659
June1st to 15thNight
39%42%37%6%
630
16th to endNight
15%33%51%7%
609
July1st to 15thNight
1119%65%12%
555
16th to endNight
2214%62%17%
673
August1st to 15thNight
220%54%22%
765
16th to endNight
1110%56%29%
828
September1st to 15thNight
322%55%17%
780
16th to endNight
26%31%43%15%
776
October1st to 15thNight
7%211%36%33%8%
780
16th to endNight
7%19%31%31%17%
832
November1st to 15thNight
6%113%37%31%9%
820
16th to endNight
9%211%32%29%14%
840
December1st to 15thNight
12%415%34%25%8%
840
16th to endNight
14%415%31%24%8%
896
Page generated at 2019-06-24 17:41:29. Version ac04

Copyright 2019 A. Danko


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