Firetail Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Firetail Observatory clear sky chart from 2005-11-06 to 2024-01-14.

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
46%
23721
25%
74315
17%
23662
55%
23662
31%
43570

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 10thNight
38%
947
29%
2458
13%
946
48%
946
35%
1518
January11th to 20thNight
35%
918
26%
2386
11%
918
44%
918
30%
1514
January21st to endNight
34%
855
30%
2439
12%
855
47%
855
28%
1513
February1st to 10thNight
29%
720
26%
2160
11%
720
42%
720
25%
1337
February11th to 20thNight
27%
704
22%
2098
10%
700
37%
700
26%
1302
February21st to endNight
19%
592
25%
1776
7%
592
35%
592
23%
1121
March1st to 10thNight
25%
570
24%
2010
10%
570
40%
570
22%
1237
March11th to 20thNight
28%
540
22%
1980
12%
540
40%
540
20%
1217
March21st to endNight
28%
594
24%
2178
13%
594
43%
594
24%
1253
April1st to 10thNight
26%
540
24%
1980
12%
540
42%
540
24%
1145
April11th to 20thNight
26%
533
21%
1949
13%
533
41%
533
22%
1182
April21st to endNight
28%
540
27%
1675
14%
540
46%
540
27%
1059
May1st to 10thNight
30%
540
23%
1620
15%
540
41%
540
28%
1034
May11th to 20thNight
38%
531
22%
1594
17%
531
47%
531
29%
985
May21st to endNight
41%
583
21%
1745
14%
582
54%
582
29%
1073
June1st to 10thNight
61%
540
23%
1620
22%
540
69%
540
44%
854
June11th to 20thNight
53%
540
23%
1620
19%
540
63%
540
45%
850
June21st to endNight
63%
540
22%
1620
22%
540
68%
540
37%
942
July1st to 10thNight
67%
525
16%
1575
17%
525
70%
525
34%
951
July11th to 20thNight
77%
522
26%
1566
27%
522
82%
522
48%
800
July21st to endNight
77%
591
23%
1673
25%
558
82%
558
50%
842
August1st to 10thNight
84%
537
27%
1625
29%
534
86%
534
60%
741
August11th to 20thNight
78%
534
24%
1778
28%
534
80%
534
37%
958
August21st to endNight
75%
594
19%
2072
22%
594
77%
594
34%
1118
September1st to 10thNight
71%
540
20%
1980
23%
540
73%
540
31%
1109
September11th to 20thNight
67%
540
21%
1980
24%
540
69%
540
27%
1171
September21st to endNight
66%
540
25%
1980
26%
540
69%
540
33%
1056
October1st to 10thNight
72%
540
33%
1980
35%
540
74%
540
39%
986
October11th to 20thNight
53%
630
31%
2070
23%
630
60%
630
33%
1180
October21st to endNight
51%
792
33%
2376
20%
792
59%
792
38%
1306
November1st to 10thNight
54%
740
28%
2220
20%
740
59%
740
33%
1339
November11th to 20thNight
48%
878
27%
2398
15%
878
55%
878
35%
1448
November21st to endNight
37%
950
27%
2470
12%
950
45%
950
30%
1605
December1st to 10thNight
41%
950
30%
2470
16%
950
48%
950
33%
1565
December11th to 20thNight
35%
950
25%
2887
13%
948
41%
948
23%
1886
December21st to endNight
37%
1041
17%
4307
12%
1026
44%
1026
22%
2373

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
13%6%35%5%3445%7%45%
74883
Night
14%5%2442345%7%50%
74896
TransparencyDay
39%39%21%18%9%
74608
Night
35%311%20%18%11%
74691
SeeingDay
15%7%22%30%21%5%
13669
Night
17%7%25%35%16%1
23729

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 10thDay
16%5%24333336%51%
1707
11th to 20thDay
20%7%24333335%48%
1647
21st to endDay
16%6%24323336%51%
1930
February1st to 10thDay
20%7%24423335%46%
1800
11th to 20thDay
21%7%24433436%43%
1749
21st to endDay
21%6%33313346%48%
1480
March1st to 10thDay
20%8%35%423345%41%
1948
11th to 20thDay
17%6%35%5%34446%45%
1980
21st to endDay
18%5%25%5%23346%46%
2178
April1st to 10thDay
14%7%37%435%446%43%
1980
11th to 20thDay
22%6%3442335%5%43%
1956
21st to endDay
15%6%35%5%34445%45%
2281
May1st to 10thDay
16%6%36%6%35%5%5%6%39%
2340
11th to 20thDay
14%7%37%5%46%46%6%37%
2302
21st to endDay
17%6%36%6%35%6%6%8%34%
2531
June1st to 10thDay
7%425%446%6%7%9%46%
2340
11th to 20thDay
8%5%36%5%36%5%6%9%44%
2340
21st to endDay
8%5%46%8%47%7%7%9%35%
2340
July1st to 10thDay
11%6%36%7%5%6%6%6%9%35%
2340
11th to 20thDay
5%3245%37%5%7%11%47%
2340
21st to endDay
6%325%446%6%7%11%47%
2546
August1st to 10thDay
2223435%5%5%10%60%
2299
11th to 20thDay
6%3245%35%5%7%10%49%
2123
21st to endDay
6%426%6%6%6%6%8%10%41%
2282
September1st to 10thDay
9%5%36%8%45%6%6%7%41%
1980
11th to 20thDay
11%6%35%6%45%6%7%8%38%
1980
21st to endDay
9%425%5%45%5%5%8%48%
1980
October1st to 10thDay
7%5%25%6%35%45%7%52%
1980
11th to 20thDay
13%6%2444445%6%49%
1872
21st to endDay
11%5%24423345%56%
1980
November1st to 10thDay
16%7%26%5%3435%6%44%
1858
11th to 20thDay
13%7%345%34446%48%
1778
21st to endDay
18%7%36%5%3334444%
1710
December1st to 10thDay
17%7%34433446%46%
1710
11th to 20thDay
18%7%35%434445%44%
2161
21st to endDay
18%6%23312335%53%
3135
January1st to 10thNight
18%413323446%52%
2458
11th to 20thNight
19%5%24323335%50%
2386
21st to endNight
18%6%23423435%49%
2439
February1st to 10thNight
20%7%24333345%47%
2160
11th to 20thNight
20%8%23332235%48%
2098
21st to endNight
22%6%24424345%44%
1776
March1st to 10thNight
19%7%35%5%24345%43%
2010
11th to 20thNight
18%8%35%423345%44%
1980
21st to endNight
17%7%33323446%47%
2178
April1st to 10thNight
15%6%25%42445%8%44%
1980
11th to 20thNight
20%7%34423346%45%
1949
21st to endNight
20%5%35%324345%46%
1675
May1st to 10thNight
16%6%35%5%235%5%6%45%
1620
11th to 20thNight
14%6%35%43346%8%44%
1593
21st to endNight
14%6%35%43436%10%41%
1745
June1st to 10thNight
7%32332435%9%59%
1620
11th to 20thNight
432443445%11%56%
1620
21st to endNight
8%5%25%4345%6%10%49%
1620
July1st to 10thNight
9%5%34435%5%7%11%45%
1620
11th to 20thNight
32224345%7%11%58%
1620
21st to endNight
5%31332446%12%56%
1772
August1st to 10thNight
21222335%10%69%
1635
11th to 20thNight
44244346%8%11%50%
1778
21st to endNight
7%414435%6%8%9%49%
2072
September1st to 10thNight
8%6%34435%46%8%49%
1980
11th to 20thNight
11%6%36%5%35%45%8%45%
1980
21st to endNight
9%5%2442445%9%51%
1980
October1st to 10thNight
7%42343345%7%58%
1980
11th to 20thNight
15%5%2432335%6%52%
2070
21st to endNight
15%5%2332322460%
2376
November1st to 10thNight
14%6%25%422335%53%
2220
11th to 20thNight
13%6%24424346%53%
2398
21st to endNight
20%6%2432345%5%46%
2470
December1st to 10thNight
17%7%24323445%49%
2470
11th to 20thNight
19%8%25%43233446%
3036
21st to endNight
20%6%23212335%52%
4532

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 10thDay
38%2418%22%15%
1708
11th to 20thDay
41%2415%20%17%
1647
21st to endDay
38%35%14%25%15%
1930
February1st to 10thDay
44%35%13%21%15%
1800
11th to 20thDay
44%26%18%18%12%
1759
21st to endDay
41%27%16%18%16%
1480
March1st to 10thDay
47%38%14%18%10%
1948
11th to 20thDay
43%27%13%19%15%
1980
21st to endDay
41%37%18%19%12%
2178
April1st to 10thDay
45%27%18%17%11%
1980
11th to 20thDay
45%36%17%18%12%
1956
21st to endDay
42%35%21%19%10%
2281
May1st to 10thDay
47%37%17%18%7%
2340
11th to 20thDay
47%38%20%18%4
2306
21st to endDay
48%412%21%15%1
2531
June1st to 10thDay
32%5%13%28%19%3
2340
11th to 20thDay
36%411%26%18%4
2340
21st to endDay
44%5%11%24%13%3
2340
July1st to 10thDay
44%5%13%25%10%2
2276
11th to 20thDay
30%5%19%27%17%2
2271
21st to endDay
27%5%20%34%13%1
2405
August1st to 10thDay
22%416%39%18%1
2285
11th to 20thDay
30%5%17%31%12%4
2123
21st to endDay
36%6%17%26%13%3
2282
September1st to 10thDay
42%5%10%20%16%8%
1980
11th to 20thDay
41%7%11%19%17%5%
1980
21st to endDay
34%410%22%18%11%
1980
October1st to 10thDay
31%410%22%24%10%
1980
11th to 20thDay
37%37%17%19%16%
1872
21st to endDay
32%2417%25%20%
1980
November1st to 10thDay
42%27%20%18%11%
1858
11th to 20thDay
38%38%18%20%13%
1778
21st to endDay
45%35%15%19%13%
1710
December1st to 10thDay
41%28%20%20%9%
1710
11th to 20thDay
45%26%11%21%15%
2159
21st to endDay
37%2415%27%14%
3135
January1st to 10thNight
35%26%16%23%18%
2458
11th to 20thNight
39%25%17%20%16%
2386
21st to endNight
40%2415%20%19%
2439
February1st to 10thNight
41%36%13%20%17%
2160
11th to 20thNight
41%25%16%19%15%
2098
21st to endNight
43%25%16%17%16%
1776
March1st to 10thNight
44%39%16%18%11%
2010
11th to 20thNight
44%48%12%17%16%
1980
21st to endNight
39%310%16%18%14%
2178
April1st to 10thNight
39%49%20%16%13%
1980
11th to 20thNight
43%38%14%17%15%
1949
21st to endNight
42%38%20%17%11%
1675
May1st to 10thNight
42%410%18%17%10%
1620
11th to 20thNight
39%410%26%16%5%
1594
21st to endNight
38%416%26%14%1
1746
June1st to 10thNight
25%416%30%23%3
1620
11th to 20thNight
24%416%32%19%5%
1620
21st to endNight
31%5%19%27%14%3
1620
July1st to 10thNight
32%8%21%29%10%1
1575
11th to 20thNight
20%6%23%33%17%1
1566
21st to endNight
20%5%30%35%9%1
1673
August1st to 10thNight
14%424%40%17%1
1625
11th to 20thNight
27%7%23%30%11%2
1778
21st to endNight
29%7%23%28%11%3
2072
September1st to 10thNight
34%5%17%22%16%7%
1980
11th to 20thNight
38%5%15%23%14%5%
1980
21st to endNight
30%5%15%21%18%11%
1980
October1st to 10thNight
27%311%26%21%12%
1980
11th to 20thNight
35%38%18%19%17%
2070
21st to endNight
31%15%17%23%22%
2376
November1st to 10thNight
36%37%19%21%13%
2220
11th to 20thNight
33%49%19%20%15%
2398
21st to endNight
41%27%16%19%14%
2470
December1st to 10thNight
38%27%21%20%12%
2470
11th to 20thNight
44%2412%20%19%
3037
21st to endNight
37%2414%29%13%
4532

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 10thDay
24%15%35%20%5%
270
11th to 20thDay
29%13%27%23%7%2
249
21st to endDay
18%16%40%20%6%
264
February1st to 10thDay
34%12%30%18%6%
240
11th to 20thDay
31%17%31%18%31
240
21st to endDay
29%21%35%14%1
198
March1st to 10thDay
27%15%40%15%2
240
11th to 20thDay
20%17%43%15%5%
240
21st to endDay
23%14%39%19%5%
264
April1st to 10thDay
22%15%43%18%3
240
11th to 20thDay
24%16%34%22%4
234
21st to endDay
20%13%37%22%7%
541
May1st to 10thDay
18%11%37%27%6%
603
11th to 20thDay
17%9%29%34%9%2
625
21st to endDay
18%5%24%37%14%1
679
June1st to 10thDay
9%217%41%27%4
630
11th to 20thDay
8%217%47%23%2
630
21st to endDay
8%215%39%29%8%
630
July1st to 10thDay
9%310%35%34%9%
621
11th to 20thDay
417%35%46%8%
618
21st to endDay
416%36%43%9%
684
August1st to 10thDay
416%35%43%12%
597
11th to 20thDay
6%1339%41%10%
437
21st to endDay
5%15%28%41%19%
401
September1st to 10thDay
12%9%25%41%13%
270
11th to 20thDay
7%7%29%44%13%
270
21st to endDay
11%19%28%36%14%
270
October1st to 10thDay
7%315%39%30%7%
270
11th to 20thDay
12%7%20%40%17%4
270
21st to endDay
21%13%25%26%13%3
297
November1st to 10thDay
20%6%30%28%13%4
270
11th to 20thDay
22%11%27%29%9%2
270
21st to endDay
27%16%31%16%8%1
270
December1st to 10thDay
19%9%33%28%7%3
270
11th to 20thDay
23%16%29%26%6%
270
21st to endDay
24%9%41%20%6%1
297
January1st to 10thNight
21%9%29%33%8%1
950
11th to 20thNight
23%10%28%30%8%
918
21st to endNight
23%10%29%31%7%
855
February1st to 10thNight
26%11%29%26%7%
720
11th to 20thNight
27%13%31%25%4
704
21st to endNight
27%14%38%20%2
592
March1st to 10thNight
22%14%34%27%3
570
11th to 20thNight
23%10%34%28%5%
540
21st to endNight
21%11%38%27%31
594
April1st to 10thNight
18%11%40%26%4
540
11th to 20thNight
22%11%38%26%3
533
21st to endNight
21%9%38%24%7%1
540
May1st to 10thNight
18%9%41%27%5%
540
11th to 20thNight
17%5%34%34%9%
531
21st to endNight
16%7%29%36%12%
584
June1st to 10thNight
7%225%43%22%1
540
11th to 20thNight
5%232%46%15%
540
21st to endNight
8%217%43%26%3
540
July1st to 10thNight
8%215%44%29%3
525
11th to 20thNight
3112%51%30%2
522
21st to endNight
6%19%48%32%3
591
August1st to 10thNight
210%51%33%4
537
11th to 20thNight
5%19%50%31%4
534
21st to endNight
8%17%40%40%5%
594
September1st to 10thNight
9%18%39%38%5%
540
11th to 20thNight
12%18%39%37%3
540
21st to endNight
11%212%34%37%4
540
October1st to 10thNight
9%113%44%29%4
540
11th to 20thNight
15%321%38%20%3
630
21st to endNight
17%7%21%32%19%3
792
November1st to 10thNight
15%6%19%38%20%1
740
11th to 20thNight
16%7%25%36%15%1
878
21st to endNight
22%10%26%29%12%1
950
December1st to 10thNight
21%7%28%31%12%1
950
11th to 20thNight
26%9%24%32%8%
950
21st to endNight
22%8%28%33%8%
1045
Page generated at 2024-01-11 03:22:40. Version ac07

Copyright 2024 Attilla Danko


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