Firefly Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Firefly Observatory clear sky chart from 2005-11-05 to 2018-10-27.

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
47%
17093
19%
51312
13%
17053
53%
17053
22%
33593

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
29%
779
19%
2522
10%
776
41%
776
17%
1587
January16th to endNight
27%
832
21%
2704
11%
832
40%
832
18%
1714
February1st to 15thNight
29%
762
20%
2367
10%
761
40%
761
20%
1488
February16th to endNight
24%
683
21%
2049
9%
683
35%
683
18%
1344
March1st to 15thNight
29%
780
20%
2177
11%
780
37%
780
21%
1447
March16th to endNight
31%
832
15%
2288
8%
832
37%
832
19%
1596
April1st to 15thNight
37%
778
19%
2135
10%
778
44%
778
27%
1334
April16th to endNight
48%
579
21%
1735
13%
579
54%
579
25%
1120
May1st to 15thNight
49%
585
15%
1755
8%
585
54%
585
23%
1174
May16th to endNight
60%
609
13%
1828
10%
609
61%
609
22%
1246
June1st to 15thNight
67%
585
12%
1755
9%
585
69%
585
24%
1168
June16th to endNight
73%
585
14%
1755
12%
585
74%
585
30%
1116
July1st to 15thNight
72%
555
10%
1665
9%
555
72%
555
22%
1192
July16th to endNight
72%
612
11%
1739
9%
579
73%
579
23%
1206
August1st to 15thNight
67%
575
13%
1715
12%
572
68%
572
22%
1204
August16th to endNight
68%
657
15%
1977
15%
657
69%
657
21%
1388
September1st to 15thNight
59%
780
16%
2145
14%
780
60%
780
21%
1527
September16th to endNight
57%
777
20%
2145
18%
777
59%
777
25%
1451
October1st to 15thNight
52%
780
25%
2234
21%
780
58%
780
27%
1432
October16th to endNight
49%
816
30%
2447
22%
816
60%
816
31%
1430
November1st to 15thNight
51%
760
26%
2401
21%
760
60%
760
28%
1412
November16th to endNight
44%
780
26%
2535
19%
780
55%
780
25%
1507
December1st to 15thNight
36%
780
20%
2535
13%
780
45%
780
19%
1629
December16th to endNight
32%
832
19%
2704
12%
832
41%
832
15%
1881

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%6%36%6%35%5%6%7%36%
52234
Night
10%6%25%5%35%5%6%8%40%
51509
TransparencyDay
43%9%12%17%13%3
51935
Night
39%9%13%19%15%3
51312
SeeingDay
17%10%19%21%18%12%
6955
Night
15%11%18%28%21%4
17098

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 15thDay
11%6%36%5%35%6%5%7%38%
1746
16th to endDay
11%7%25%42445%7%43%
1872
February1st to 15thDay
13%7%35%5%3445%7%39%
1822
16th to endDay
11%5%46%5%345%5%7%39%
1710
March1st to 15thDay
15%6%35%43445%6%40%
2112
16th to endDay
14%7%46%5%35%5%5%7%34%
2287
April1st to 15thDay
11%6%24425%5%5%9%42%
2152
16th to endDay
13%6%36%5%24446%41%
2500
May1st to 15thDay
11%5%48%5%36%46%7%36%
2526
16th to endDay
11%5%37%7%46%6%6%9%32%
2639
June1st to 15thDay
9%5%36%7%48%7%7%9%29%
2535
16th to endDay
7%435%7%47%7%8%10%33%
2535
July1st to 15thDay
10%7%37%8%48%6%8%9%25%
2535
16th to endDay
9%5%36%7%5%8%8%8%10%27%
2673
August1st to 15thDay
11%7%36%7%5%6%7%8%9%25%
2487
16th to endDay
10%6%36%7%5%7%8%7%8%27%
2560
September1st to 15thDay
12%6%37%9%46%6%6%8%28%
2145
16th to endDay
13%6%25%5%46%6%5%8%33%
2145
October1st to 15thDay
11%6%25%423446%49%
2054
16th to endDay
11%5%2432233454%
2034
November1st to 15thDay
7%6%25%424346%51%
1783
16th to endDay
13%6%35%414346%48%
1755
December1st to 15thDay
11%7%36%6%45%5%5%5%38%
1755
16th to endDay
14%9%46%5%35%447%35%
1872
January1st to 15thNight
11%5%25%6%46%45%7%39%
2522
16th to endNight
13%6%35%5%35%46%6%39%
2704
February1st to 15thNight
12%8%35%336%45%7%40%
2358
16th to endNight
11%6%36%6%46%45%6%38%
2049
March1st to 15thNight
12%6%36%5%345%5%6%40%
2177
16th to endNight
12%7%26%5%46%5%5%8%36%
2288
April1st to 15thNight
10%6%2443446%7%45%
2135
16th to endNight
10%5%35%434347%45%
1735
May1st to 15thNight
9%6%26%5%3447%8%39%
1754
16th to endNight
7%6%26%5%35%6%7%10%38%
1826
June1st to 15thNight
5%5%25%436%6%8%14%36%
1755
16th to endNight
6%4145%346%8%10%43%
1755
July1st to 15thNight
6%426%5%48%7%8%9%35%
1755
16th to endNight
5%426%5%46%7%8%11%36%
1847
August1st to 15thNight
7%426%6%35%6%7%11%36%
1726
16th to endNight
7%5%35%6%46%7%7%10%35%
1977
September1st to 15thNight
9%5%26%7%45%6%6%9%35%
2145
16th to endNight
11%6%26%5%2345%6%44%
2145
October1st to 15thNight
10%5%244335%5%7%47%
2234
16th to endNight
9%5%2442445%453%
2447
November1st to 15thNight
9%5%2442445%6%49%
2401
16th to endNight
11%5%24335%446%47%
2535
December1st to 15thNight
13%6%36%435%6%47%37%
2535
16th to endNight
15%8%36%6%445%6%7%31%
2704

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
40%6%14%17%15%5%
1747
16th to endDay
37%412%22%17%5%
1872
February1st to 15thDay
41%5%12%19%18%2
1824
16th to endDay
41%6%13%19%15%3
1710
March1st to 15thDay
43%410%18%17%5%
2112
16th to endDay
46%7%13%17%12%2
2288
April1st to 15thDay
37%7%12%22%16%3
2152
16th to endDay
43%6%9%19%16%5%
2500
May1st to 15thDay
44%10%12%19%11%1
2526
16th to endDay
46%11%12%17%9%1
2643
June1st to 15thDay
46%13%18%15%5%
2535
16th to endDay
41%12%14%16%12%1
2535
July1st to 15thDay
50%12%14%13%7%
2396
16th to endDay
46%13%18%14%6%1
2518
August1st to 15thDay
49%15%13%14%5%1
2474
16th to endDay
48%14%14%14%6%1
2560
September1st to 15thDay
50%10%12%14%9%3
2145
16th to endDay
47%10%11%14%15%1
2145
October1st to 15thDay
35%7%11%18%21%5%
2054
16th to endDay
33%48%22%23%9%
2034
November1st to 15thDay
33%410%17%26%8%
1783
16th to endDay
37%47%20%23%6%
1755
December1st to 15thDay
43%6%10%18%16%4
1755
16th to endDay
47%5%10%17%14%3
1872
January1st to 15thNight
39%6%14%16%18%4
2522
16th to endNight
42%5%11%18%18%4
2704
February1st to 15thNight
40%5%13%20%16%3
2367
16th to endNight
42%6%13%20%15%2
2049
March1st to 15thNight
41%6%12%17%17%5%
2177
16th to endNight
44%8%13%20%11%1
2288
April1st to 15thNight
34%6%14%23%17%2
2135
16th to endNight
38%7%12%19%18%4
1735
May1st to 15thNight
40%10%14%21%11%1
1755
16th to endNight
38%13%17%21%7%1
1828
June1st to 15thNight
35%14%22%20%5%
1755
16th to endNight
31%12%21%20%12%1
1755
July1st to 15thNight
39%15%16%17%8%1
1665
16th to endNight
35%17%21%16%7%1
1739
August1st to 15thNight
38%16%18%14%11%
1715
16th to endNight
41%13%16%21%6%1
1977
September1st to 15thNight
44%11%13%17%10%2
2145
16th to endNight
41%8%11%18%19%1
2145
October1st to 15thNight
35%8%11%20%19%3
2234
16th to endNight
31%5%7%21%26%7%
2447
November1st to 15thNight
33%6%7%19%23%8%
2401
16th to endNight
34%6%8%20%22%7%
2535
December1st to 15thNight
41%6%14%16%15%4
2535
16th to endNight
48%7%10%16%14%2
2704

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
26%25%31%11%3
135
16th to endDay
27%29%25%12%5%
144
February1st to 15thDay
25%35%28%9%
135
16th to endDay
32%33%23%9%
120
March1st to 15thDay
26%21%24%19%7%
297
16th to endDay
21%20%27%20%8%1
352
April1st to 15thDay
20%16%22%24%12%3
330
16th to endDay
19%11%23%21%16%7%
319
May1st to 15thDay
13%15%20%22%17%9%
348
16th to endDay
19%5%21%19%17%17%
395
June1st to 15thDay
12%217%22%25%18%
375
16th to endDay
9%5%20%20%23%20%
375
July1st to 15thDay
11%115%19%27%24%
365
16th to endDay
8%19%26%27%25%
390
August1st to 15thDay
19%116%20%16%24%
358
16th to endDay
11%12%19%29%26%
396
September1st to 15thDay
14%410%23%28%19%
375
16th to endDay
14%317%26%26%11%
374
October1st to 15thDay
17%9%17%23%22%9%
375
16th to endDay
18%12%18%29%16%5%
382
November1st to 15thDay
21%8%22%29%13%3
201
16th to endDay
19%14%30%20%12%2
135
December1st to 15thDay
25%20%33%14%4
135
16th to endDay
33%16%34%13%1
144
January1st to 15thNight
22%19%23%27%7%
780
16th to endNight
21%19%28%27%3
832
February1st to 15thNight
21%20%25%28%3
764
16th to endNight
19%25%28%24%2
683
March1st to 15thNight
19%19%27%29%4
780
16th to endNight
18%17%28%25%9%
832
April1st to 15thNight
17%18%23%28%10%1
778
16th to endNight
16%11%18%32%18%1
579
May1st to 15thNight
15%7%20%31%22%2
585
16th to endNight
11%216%27%34%7%
611
June1st to 15thNight
8%113%30%36%10%
585
16th to endNight
6%28%28%43%11%
585
July1st to 15thNight
7%18%24%48%9%
555
16th to endNight
7%16%20%48%15%
612
August1st to 15thNight
10%10%22%43%11%
575
16th to endNight
9%16%24%45%11%
657
September1st to 15thNight
11%213%23%40%8%
780
16th to endNight
16%313%29%31%5%
777
October1st to 15thNight
15%9%17%25%24%7%
780
16th to endNight
13%12%20%31%18%2
816
November1st to 15thNight
14%8%20%33%19%3
760
16th to endNight
19%14%18%32%14%1
780
December1st to 15thNight
21%14%21%32%9%1
780
16th to endNight
24%14%22%31%6%
832
Page generated at 2018-10-28 08:41:00. Version ac04

Copyright 2018 A. Danko


Firefly Observatory Clear Sky Chart |Charts Home