Firefly Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Firefly Observatory clear sky chart from 2005-11-06 to 2024-01-12.

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
44%
24037
18%
74425
12%
23982
51%
23982
21%
48557

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
24%
760
19%
2459
8%
757
37%
757
16%
1571
January11th to 20thNight
26%
728
19%
2365
9%
728
38%
728
17%
1546
January21st to endNight
24%
792
22%
2574
10%
792
40%
792
18%
1613
February1st to 10thNight
30%
720
20%
2264
10%
720
40%
720
21%
1442
February11th to 20thNight
20%
701
17%
2099
7%
700
30%
700
15%
1387
February21st to endNight
22%
592
21%
1776
9%
592
34%
592
16%
1228
March1st to 10thNight
28%
720
22%
2024
11%
720
37%
720
21%
1337
March11th to 20thNight
26%
720
15%
1980
7%
720
33%
720
20%
1367
March21st to endNight
29%
792
16%
2178
7%
792
36%
792
19%
1506
April1st to 10thNight
34%
720
20%
1980
10%
720
42%
720
25%
1240
April11th to 20thNight
36%
624
23%
1770
11%
624
46%
624
26%
1104
April21st to endNight
49%
540
24%
1620
15%
540
57%
540
26%
1019
May1st to 10thNight
45%
540
16%
1620
7%
540
51%
540
24%
1061
May11th to 20thNight
48%
531
12%
1593
8%
531
51%
531
19%
1112
May21st to endNight
62%
582
14%
1745
11%
582
63%
582
25%
1164
June1st to 10thNight
63%
540
12%
1620
9%
540
64%
540
23%
1104
June11th to 20thNight
64%
540
11%
1620
8%
540
68%
540
28%
1043
June21st to endNight
69%
540
15%
1620
12%
540
70%
540
28%
1059
July1st to 10thNight
68%
525
10%
1575
9%
525
69%
525
22%
1131
July11th to 20thNight
68%
522
10%
1566
9%
522
69%
522
21%
1128
July21st to endNight
70%
591
12%
1672
10%
558
71%
558
22%
1174
August1st to 10thNight
65%
537
10%
1600
9%
534
66%
534
20%
1149
August11th to 20thNight
61%
534
15%
1598
13%
534
63%
534
20%
1154
August21st to endNight
66%
643
14%
1939
13%
643
66%
643
20%
1358
September1st to 10thNight
61%
720
18%
1980
15%
720
62%
720
25%
1364
September11th to 20thNight
53%
720
17%
1980
15%
720
55%
720
22%
1407
September21st to endNight
55%
720
23%
1980
18%
720
58%
720
27%
1303
October1st to 10thNight
49%
720
22%
2013
18%
720
54%
720
28%
1299
October11th to 20thNight
45%
720
25%
2160
19%
720
54%
720
26%
1343
October21st to endNight
47%
792
30%
2376
22%
792
59%
792
31%
1376
November1st to 10thNight
49%
740
25%
2301
19%
740
58%
740
27%
1385
November11th to 20thNight
41%
760
26%
2470
19%
760
53%
760
27%
1434
November21st to endNight
40%
760
24%
2470
16%
760
51%
760
24%
1495
December1st to 10thNight
30%
760
18%
2470
10%
760
40%
760
16%
1671
December11th to 20thNight
33%
760
22%
2963
15%
759
45%
759
18%
1821
December21st to endNight
29%
831
13%
4405
11%
817
39%
817
10%
2662

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
11%7%36%6%46%6%6%8%37%
74891
Night
11%7%36%6%35%5%6%8%39%
74837
TransparencyDay
42%9%12%18%15%3
74614
Night
39%9%13%19%16%3
74633
SeeingDay
19%14%23%21%15%8%
13919
Night
17%12%21%28%19%3
24046

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
13%6%36%6%446%6%8%39%
1706
11th to 20thDay
13%8%36%6%36%5%5%7%39%
1635
21st to endDay
10%8%36%5%3446%8%44%
1782
February1st to 10thDay
13%8%36%6%35%46%7%38%
1692
11th to 20thDay
14%10%5%7%5%445%47%36%
1748
21st to endDay
14%7%46%6%35%6%5%6%39%
1480
March1st to 10thDay
13%6%35%4345%6%8%44%
1934
11th to 20thDay
16%8%47%5%45%5%6%6%34%
1980
21st to endDay
14%8%47%6%35%5%5%7%35%
2178
April1st to 10thDay
10%6%25%5%46%5%6%9%43%
1980
11th to 20thDay
14%7%35%5%25%46%9%41%
2149
21st to endDay
11%6%26%5%35%5%6%6%44%
2340
May1st to 10thDay
9%6%48%6%46%5%6%8%39%
2340
11th to 20thDay
13%6%38%7%47%6%7%8%33%
2301
21st to endDay
9%6%37%7%46%6%7%10%34%
2531
June1st to 10thDay
10%6%26%8%48%6%8%9%32%
2340
11th to 20thDay
7%5%47%7%47%7%8%9%33%
2340
21st to endDay
8%6%36%7%5%8%8%8%9%34%
2340
July1st to 10thDay
8%7%48%9%5%8%8%8%10%26%
2340
11th to 20thDay
10%6%37%8%5%8%8%9%10%26%
2340
21st to endDay
8%5%37%8%6%8%8%8%10%28%
2547
August1st to 10thDay
11%7%37%8%5%7%8%9%10%24%
2327
11th to 20thDay
11%6%37%8%5%7%7%8%10%27%
2303
21st to endDay
10%7%36%7%5%7%9%7%9%31%
2394
September1st to 10thDay
10%6%37%7%47%7%6%8%35%
1980
11th to 20thDay
14%6%36%7%5%6%6%6%9%33%
1980
21st to endDay
11%7%36%6%46%6%6%7%38%
1980
October1st to 10thDay
10%7%35%5%345%46%48%
1945
11th to 20thDay
9%6%26%4345%46%52%
1800
21st to endDay
12%6%35%423446%52%
1980
November1st to 10thDay
8%7%24423336%56%
1772
11th to 20thDay
10%5%35%5%25%45%6%50%
1710
21st to endDay
12%7%35%42445%7%46%
1710
December1st to 10thDay
14%9%37%6%45%5%6%6%35%
1710
11th to 20thDay
12%7%45%5%346%6%8%41%
2153
21st to endDay
13%9%37%6%46%5%5%7%36%
3124
January1st to 10thNight
13%7%36%6%47%5%6%7%36%
2459
11th to 20thNight
13%7%47%7%35%46%8%35%
2365
21st to endNight
12%7%47%6%345%6%6%41%
2574
February1st to 10thNight
12%8%36%5%36%5%6%8%39%
2264
11th to 20thNight
16%8%36%5%45%5%5%6%37%
2098
21st to endNight
14%8%38%6%46%5%5%6%35%
1776
March1st to 10thNight
12%7%37%5%346%6%7%42%
2024
11th to 20thNight
13%7%37%6%45%5%5%8%35%
1980
21st to endNight
12%8%36%5%46%45%9%37%
2178
April1st to 10thNight
11%7%346%3446%8%45%
1980
11th to 20thNight
9%7%36%5%345%6%8%46%
1770
21st to endNight
10%6%45%5%3445%7%47%
1620
May1st to 10thNight
8%7%36%5%35%5%7%9%41%
1620
11th to 20thNight
10%6%38%6%46%6%7%8%37%
1592
21st to endNight
8%7%37%6%35%6%7%11%38%
1744
June1st to 10thNight
7%6%36%5%47%6%8%13%34%
1620
11th to 20thNight
6%6%35%5%346%9%12%41%
1620
21st to endNight
6%5%25%6%45%6%8%10%42%
1620
July1st to 10thNight
7%6%38%6%5%6%6%8%10%35%
1620
11th to 20thNight
8%5%36%6%47%7%10%11%33%
1620
21st to endNight
5%5%38%6%5%8%8%8%11%34%
1771
August1st to 10thNight
8%5%26%6%47%6%8%12%36%
1611
11th to 20thNight
9%6%37%8%45%7%7%10%34%
1598
21st to endNight
7%7%46%6%47%7%8%10%35%
1939
September1st to 10thNight
10%5%26%7%5%5%6%6%9%40%
1980
11th to 20thNight
12%7%38%7%35%5%5%7%37%
1980
21st to endNight
9%6%36%6%35%46%7%46%
1980
October1st to 10thNight
13%6%25%4435%46%47%
2013
11th to 20thNight
10%6%26%5%3447%6%46%
2160
21st to endNight
9%7%3442346%6%52%
2376
November1st to 10thNight
10%6%25%4345%6%6%49%
2301
11th to 20thNight
11%6%35%43445%7%47%
2470
21st to endNight
12%6%26%5%35%5%5%6%44%
2470
December1st to 10thNight
15%8%5%7%5%45%6%47%33%
2470
11th to 20thNight
13%10%38%5%3445%6%39%
3042
21st to endNight
13%10%37%6%46%6%7%8%30%
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
39%6%13%21%16%5%
1707
11th to 20thDay
42%5%12%18%17%5%
1635
21st to endDay
37%5%11%22%19%5%
1782
February1st to 10thDay
43%5%13%20%16%3
1692
11th to 20thDay
46%6%11%17%16%4
1758
21st to endDay
45%7%10%16%16%6%
1480
March1st to 10thDay
37%6%10%20%20%7%
1934
11th to 20thDay
47%7%12%16%14%4
1980
21st to endDay
46%8%13%18%13%2
2178
April1st to 10thDay
35%8%13%22%19%4
1980
11th to 20thDay
40%6%9%19%20%6%
2149
21st to endDay
39%7%13%24%15%2
2340
May1st to 10thDay
41%10%14%20%14%2
2340
11th to 20thDay
47%14%13%16%10%1
2305
21st to endDay
42%12%14%22%9%1
2531
June1st to 10thDay
45%13%17%17%7%1
2340
11th to 20thDay
41%13%17%16%11%2
2340
21st to endDay
42%13%14%18%11%2
2340
July1st to 10thDay
48%14%15%13%8%1
2275
11th to 20thDay
47%15%17%11%9%1
2271
21st to endDay
45%15%17%15%7%1
2405
August1st to 10thDay
49%17%14%16%4
2314
11th to 20thDay
48%15%15%15%6%1
2303
21st to endDay
46%14%14%16%7%3
2394
September1st to 10thDay
43%11%13%17%13%3
1980
11th to 20thDay
46%10%11%17%14%2
1980
21st to endDay
43%9%12%17%15%4
1980
October1st to 10thDay
35%8%11%17%23%5%
1945
11th to 20thDay
31%7%11%23%21%8%
1800
21st to endDay
33%5%8%22%23%9%
1980
November1st to 10thDay
30%410%20%27%8%
1772
11th to 20thDay
34%5%8%21%25%7%
1710
21st to endDay
36%6%8%23%22%5%
1710
December1st to 10thDay
48%7%8%18%15%5%
1710
11th to 20thDay
35%6%11%20%22%6%
2150
21st to endDay
41%7%10%24%17%2
3124
January1st to 10thNight
41%7%15%17%17%4
2459
11th to 20thNight
44%6%13%16%17%4
2365
21st to endNight
41%5%10%20%20%3
2574
February1st to 10thNight
40%6%13%20%17%3
2264
11th to 20thNight
44%5%12%19%15%5%
2099
21st to endNight
46%7%11%15%16%5%
1776
March1st to 10thNight
41%6%10%15%21%7%
2024
11th to 20thNight
43%8%14%18%13%3
1980
21st to endNight
44%8%12%22%13%2
2178
April1st to 10thNight
34%7%15%22%19%3
1980
11th to 20thNight
35%7%11%23%19%5%
1770
21st to endNight
35%8%13%25%16%2
1620
May1st to 10thNight
37%11%16%24%11%2
1620
11th to 20thNight
42%13%14%20%10%1
1593
21st to endNight
37%12%18%24%8%1
1745
June1st to 10thNight
38%15%20%20%7%1
1620
11th to 20thNight
32%14%24%21%9%1
1620
21st to endNight
33%14%19%20%12%2
1620
July1st to 10thNight
41%15%18%17%9%1
1575
11th to 20thNight
38%19%20%14%7%2
1566
21st to endNight
37%17%21%18%7%1
1672
August1st to 10thNight
37%20%20%17%7%
1600
11th to 20thNight
41%16%17%15%10%1
1598
21st to endNight
41%14%17%20%6%1
1939
September1st to 10thNight
40%12%14%20%12%3
1980
11th to 20thNight
45%10%13%16%16%1
1980
21st to endNight
37%10%11%22%18%3
1980
October1st to 10thNight
37%8%12%18%22%3
2013
11th to 20thNight
35%9%10%22%18%6%
2160
21st to endNight
31%6%8%22%26%7%
2376
November1st to 10thNight
34%8%9%20%22%8%
2301
11th to 20thNight
34%5%10%19%24%9%
2470
21st to endNight
37%6%8%23%21%6%
2470
December1st to 10thNight
46%7%13%16%14%4
2470
11th to 20thNight
38%8%10%17%22%4
3044
21st to endNight
44%7%12%19%16%2
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
31%29%31%7%2
270
11th to 20thDay
32%25%25%16%2
245
21st to endDay
27%33%29%8%3
264
February1st to 10thDay
32%26%29%11%2
240
11th to 20thDay
44%30%19%6%
240
21st to endDay
40%30%21%8%1
198
March1st to 10thDay
25%22%31%17%5%
374
11th to 20thDay
29%25%25%17%5%1
420
21st to endDay
27%23%25%18%6%
462
April1st to 10thDay
24%20%25%21%9%1
420
11th to 20thDay
22%20%24%20%11%3
412
21st to endDay
20%17%27%20%12%5%
420
May1st to 10thDay
17%21%26%20%11%5%
423
11th to 20thDay
17%11%24%25%15%8%
447
21st to endDay
14%7%24%23%19%13%
485
June1st to 10thDay
14%6%23%27%20%11%
450
11th to 20thDay
9%6%24%22%25%14%
450
21st to endDay
11%8%26%26%17%12%
450
July1st to 10thDay
9%416%25%29%17%
445
11th to 20thDay
8%415%26%25%22%
444
21st to endDay
8%312%27%30%19%
488
August1st to 10thDay
18%5%19%21%18%19%
446
11th to 20thDay
10%320%25%24%18%
439
21st to endDay
11%317%25%28%15%
495
September1st to 10thDay
10%415%29%27%15%
450
11th to 20thDay
15%6%16%23%29%11%
450
21st to endDay
13%9%21%28%24%5%
450
October1st to 10thDay
17%10%20%26%19%7%
450
11th to 20thDay
15%17%24%25%16%4
450
21st to endDay
20%14%24%27%12%2
495
November1st to 10thDay
19%14%26%28%10%3
370
11th to 20thDay
24%20%31%19%5%1
270
21st to endDay
20%20%34%18%7%1
270
December1st to 10thDay
29%26%30%13%2
270
11th to 20thDay
24%21%31%17%6%1
270
21st to endDay
27%23%31%14%41
297
January1st to 10thNight
26%20%25%23%6%
760
11th to 20thNight
22%20%27%26%5%
728
21st to endNight
21%21%30%26%3
792
February1st to 10thNight
21%19%27%28%5%
720
11th to 20thNight
27%25%25%22%1
703
21st to endNight
24%24%28%22%3
592
March1st to 10thNight
19%21%28%29%3
720
11th to 20thNight
23%16%30%23%8%1
720
21st to endNight
20%18%29%25%8%
792
April1st to 10thNight
19%20%24%29%8%1
720
11th to 20thNight
18%17%24%27%12%1
624
21st to endNight
15%13%20%35%17%1
540
May1st to 10thNight
16%10%23%31%18%1
540
11th to 20thNight
15%7%21%31%24%2
531
21st to endNight
11%316%27%35%8%
584
June1st to 10thNight
10%314%34%33%6%
540
11th to 20thNight
8%315%30%34%11%
540
21st to endNight
6%312%34%39%7%
540
July1st to 10thNight
9%210%26%46%7%
525
11th to 20thNight
8%29%23%45%13%
522
21st to endNight
7%17%25%47%13%
591
August1st to 10thNight
10%113%23%43%11%
537
11th to 20thNight
11%312%25%40%10%
534
21st to endNight
10%19%28%42%10%
643
September1st to 10thNight
9%314%28%39%7%
720
11th to 20thNight
15%416%25%34%7%
720
21st to endNight
14%6%17%32%28%4
720
October1st to 10thNight
16%10%19%23%25%7%
720
11th to 20thNight
15%12%22%30%18%2
720
21st to endNight
16%14%19%34%15%2
792
November1st to 10thNight
16%9%22%33%17%3
740
11th to 20thNight
19%13%22%34%12%1
760
21st to endNight
19%16%21%31%13%1
760
December1st to 10thNight
25%18%21%29%7%
760
11th to 20thNight
19%16%25%31%8%1
760
21st to endNight
25%16%23%29%5%
836
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