Foxtrotter Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Foxtrotter 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
58%
24368
21%
74478
17%
24314
63%
24314
29%
46449

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
41%
757
21%
2459
15%
757
51%
757
27%
1510
January11th to 20thNight
51%
735
28%
2386
23%
735
60%
735
33%
1335
January21st to endNight
34%
792
22%
2488
13%
792
46%
792
24%
1602
February1st to 10thNight
45%
720
23%
2160
16%
720
52%
720
30%
1344
February11th to 20thNight
42%
700
23%
2098
14%
699
51%
699
32%
1264
February21st to endNight
46%
592
26%
1736
16%
592
55%
592
30%
1091
March1st to 10thNight
49%
720
31%
1980
20%
720
58%
720
44%
1112
March11th to 20thNight
50%
720
25%
1980
17%
720
57%
720
35%
1198
March21st to endNight
52%
792
28%
2178
18%
792
60%
792
40%
1242
April1st to 10thNight
52%
720
24%
1980
16%
720
58%
720
37%
1192
April11th to 20thNight
50%
711
22%
1949
15%
711
55%
711
37%
1164
April21st to endNight
63%
666
31%
1746
20%
666
68%
666
46%
991
May1st to 10thNight
72%
540
29%
1620
22%
540
77%
540
46%
835
May11th to 20thNight
70%
531
20%
1592
15%
531
73%
531
36%
922
May21st to endNight
76%
582
24%
1744
20%
582
77%
582
36%
1022
June1st to 10thNight
68%
540
14%
1620
12%
540
69%
540
26%
1094
June11th to 20thNight
74%
540
12%
1620
10%
540
75%
540
26%
1083
June21st to endNight
75%
540
11%
1620
9%
540
75%
540
26%
1093
July1st to 10thNight
74%
525
8%
1575
7%
525
74%
525
21%
1132
July11th to 20thNight
78%
522
8%
1566
7%
522
78%
522
20%
1127
July21st to endNight
76%
591
10%
1672
11%
558
77%
558
26%
1134
August1st to 10thNight
75%
537
7%
1600
7%
534
76%
534
23%
1113
August11th to 20thNight
73%
534
7%
1700
8%
534
73%
534
22%
1192
August21st to endNight
62%
757
11%
2143
11%
757
62%
757
18%
1588
September1st to 10thNight
66%
720
11%
1980
10%
720
66%
720
20%
1432
September11th to 20thNight
61%
720
9%
1980
8%
720
61%
720
18%
1474
September21st to endNight
63%
720
20%
1980
19%
720
65%
720
27%
1329
October1st to 10thNight
60%
720
23%
1980
21%
720
62%
720
30%
1277
October11th to 20thNight
69%
720
32%
2145
32%
720
73%
720
42%
1161
October21st to endNight
62%
792
29%
2376
28%
792
68%
792
34%
1397
November1st to 10thNight
57%
740
27%
2221
23%
740
65%
740
37%
1270
November11th to 20thNight
54%
760
28%
2288
24%
760
61%
760
32%
1373
November21st to endNight
51%
760
25%
2470
21%
760
59%
760
30%
1461
December1st to 10thNight
53%
760
28%
2470
23%
760
62%
760
30%
1445
December11th to 20thNight
51%
760
24%
2935
19%
758
57%
758
24%
1744
December21st to endNight
49%
832
16%
4441
21%
817
56%
817
15%
2706

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
9%5%36%6%46%6%7%9%40%
74878
Night
9%5%35%5%35%5%6%9%45%
74885
TransparencyDay
39%9%14%18%14%6%
74601
Night
35%9%15%20%15%7%
74681
SeeingDay
10%5%17%24%24%20%
14272
Night
10%418%34%27%7%
24380

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
11%5%35%4445%6%7%46%
1706
11th to 20thDay
9%6%25%5%2445%8%51%
1647
21st to endDay
12%6%36%5%35%45%7%44%
1865
February1st to 10thDay
15%5%26%5%4445%7%42%
1800
11th to 20thDay
11%425%434438%54%
1748
21st to endDay
11%6%36%5%35%5%5%5%47%
1520
March1st to 10thDay
8%41442346%10%55%
1980
11th to 20thDay
9%5%2443446%8%52%
1980
21st to endDay
8%5%36%435%45%6%51%
2178
April1st to 10thDay
8%4235%45%5%6%9%51%
1980
11th to 20thDay
9%5%36%6%35%6%5%7%44%
1958
21st to endDay
5%213436%5%7%9%54%
2227
May1st to 10thDay
5%32343446%10%56%
2340
11th to 20thDay
8%436%5%46%6%7%10%41%
2301
21st to endDay
7%5%36%7%47%6%7%8%41%
2531
June1st to 10thDay
11%6%37%8%5%8%8%7%10%28%
2340
11th to 20thDay
6%437%9%5%8%9%9%11%29%
2340
21st to endDay
8%6%37%8%5%8%8%8%11%27%
2340
July1st to 10thDay
10%6%37%7%5%8%10%9%11%24%
2340
11th to 20thDay
7%6%49%9%6%9%8%8%10%24%
2340
21st to endDay
7%6%38%9%5%8%8%9%11%25%
2547
August1st to 10thDay
9%438%8%5%8%8%10%12%25%
2327
11th to 20thDay
9%7%37%9%6%9%9%10%11%19%
2195
21st to endDay
11%7%48%9%47%8%8%11%23%
2192
September1st to 10thDay
9%6%38%8%5%8%10%10%10%22%
1980
11th to 20thDay
10%6%38%9%5%8%8%8%10%26%
1980
21st to endDay
10%6%38%7%47%6%6%9%34%
1980
October1st to 10thDay
10%5%37%7%46%7%6%8%38%
1980
11th to 20thDay
7%325%5%345%5%7%54%
1814
21st to endDay
7%425%6%35%5%6%8%49%
1980
November1st to 10thDay
8%5%25%5%345%5%8%51%
1857
11th to 20thDay
9%6%45%6%35%5%5%7%46%
1888
21st to endDay
11%6%245%345%5%8%47%
1710
December1st to 10thDay
9%5%25%445%5%6%8%48%
1710
11th to 20thDay
12%6%25%435%5%5%8%43%
2153
21st to endDay
15%8%36%6%34436%43%
3124
January1st to 10thNight
11%5%36%5%35%5%5%7%45%
2459
11th to 20thNight
9%5%245%25%46%9%49%
2386
21st to endNight
16%7%35%5%3445%7%42%
2488
February1st to 10thNight
13%6%36%43445%7%46%
2160
11th to 20thNight
10%7%35%42445%7%49%
2098
21st to endNight
10%6%26%5%445%47%46%
1736
March1st to 10thNight
7%424423447%58%
1980
11th to 20thNight
10%5%245%345%6%9%48%
1980
21st to endNight
7%425%43446%7%55%
2178
April1st to 10thNight
8%5%245%3445%8%52%
1980
11th to 20thNight
8%435%5%3446%9%50%
1949
21st to endNight
7%3244245%5%10%56%
1746
May1st to 10thNight
421342446%8%61%
1620
11th to 20thNight
5%4245%35%7%6%10%50%
1592
21st to endNight
5%3245%46%6%6%9%51%
1744
June1st to 10thNight
10%6%35%6%36%6%7%11%36%
1620
11th to 20thNight
5%5%25%7%46%7%10%14%35%
1620
21st to endNight
7%5%25%5%36%7%9%13%37%
1620
July1st to 10thNight
6%5%36%6%46%7%10%14%32%
1620
11th to 20thNight
36%36%6%6%7%9%9%14%31%
1620
21st to endNight
3437%7%46%7%10%12%36%
1771
August1st to 10thNight
6%5%26%7%5%6%7%9%12%36%
1611
11th to 20thNight
6%5%37%7%47%8%9%14%32%
1700
21st to endNight
11%7%47%7%47%7%7%10%31%
2143
September1st to 10thNight
7%7%36%7%5%6%8%8%12%31%
1980
11th to 20thNight
11%7%37%8%5%6%7%7%10%29%
1980
21st to endNight
9%6%36%6%46%6%7%9%39%
1980
October1st to 10thNight
9%6%25%6%35%5%6%8%46%
1980
11th to 20thNight
5%42443446%8%56%
2145
21st to endNight
8%5%25%5%245%5%7%51%
2376
November1st to 10thNight
9%425%42445%8%54%
2221
11th to 20thNight
9%6%35%43435%8%49%
2288
21st to endNight
10%6%25%5%345%6%7%47%
2470
December1st to 10thNight
10%5%25%5%3446%8%48%
2470
11th to 20thNight
12%8%35%324347%48%
3042
21st to endNight
15%7%36%5%35%45%7%39%
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
36%6%10%18%18%12%
1707
11th to 20thDay
34%48%21%23%10%
1647
21st to endDay
39%48%18%21%10%
1865
February1st to 10thDay
41%6%9%14%19%12%
1800
11th to 20thDay
31%5%9%18%25%12%
1758
21st to endDay
37%6%9%16%22%10%
1520
March1st to 10thDay
25%5%11%24%25%10%
1980
11th to 20thDay
31%5%14%23%16%11%
1980
21st to endDay
32%5%11%23%19%9%
2178
April1st to 10thDay
30%6%13%20%20%10%
1980
11th to 20thDay
38%7%9%19%21%6%
1958
21st to endDay
25%7%11%25%23%9%
2227
May1st to 10thDay
25%6%11%24%24%9%
2340
11th to 20thDay
35%7%17%22%14%4
2305
21st to endDay
37%8%13%21%18%3
2531
June1st to 10thDay
47%11%17%18%6%1
2340
11th to 20thDay
43%14%20%19%3
2340
21st to endDay
46%13%22%14%5%
2340
July1st to 10thDay
48%16%22%13%1
2275
11th to 20thDay
49%15%23%11%1
2271
21st to endDay
46%15%25%13%2
2405
August1st to 10thDay
45%16%25%12%2
2314
11th to 20thDay
52%16%22%9%1
2195
21st to endDay
50%15%18%15%2
2192
September1st to 10thDay
49%17%18%10%5%
1980
11th to 20thDay
49%12%20%13%6%1
1980
21st to endDay
44%10%13%18%12%4
1980
October1st to 10thDay
42%9%9%15%14%11%
1980
11th to 20thDay
29%6%8%22%26%8%
1814
21st to endDay
31%7%9%16%24%13%
1980
November1st to 10thDay
32%6%10%22%18%13%
1857
11th to 20thDay
37%5%9%18%21%10%
1888
21st to endDay
36%5%9%20%24%6%
1710
December1st to 10thDay
34%6%13%25%17%6%
1710
11th to 20thDay
38%7%8%19%17%11%
2150
21st to endDay
43%5%7%20%18%7%
3124
January1st to 10thNight
38%6%10%17%19%11%
2459
11th to 20thNight
32%49%21%24%9%
2386
21st to endNight
43%5%9%14%20%10%
2488
February1st to 10thNight
37%6%9%16%19%13%
2160
11th to 20thNight
34%6%8%19%20%13%
2099
21st to endNight
37%7%10%18%19%10%
1736
March1st to 10thNight
26%412%23%23%11%
1980
11th to 20thNight
32%6%15%22%14%10%
1980
21st to endNight
27%5%11%28%19%10%
2178
April1st to 10thNight
30%7%15%20%19%9%
1980
11th to 20thNight
31%6%10%26%20%7%
1949
21st to endNight
25%5%14%29%19%8%
1746
May1st to 10thNight
21%7%13%27%24%8%
1620
11th to 20thNight
28%8%19%27%15%3
1593
21st to endNight
28%9%16%23%22%2
1745
June1st to 10thNight
40%10%23%22%6%
1620
11th to 20thNight
35%14%26%22%3
1620
21st to endNight
35%15%26%18%5%1
1620
July1st to 10thNight
39%17%29%13%2
1575
11th to 20thNight
38%19%28%12%2
1566
21st to endNight
33%17%31%16%3
1672
August1st to 10thNight
35%18%32%13%2
1600
11th to 20thNight
36%18%30%14%1
1700
21st to endNight
45%15%20%17%3
2143
September1st to 10thNight
41%17%24%13%5%
1980
11th to 20thNight
46%14%19%15%5%1
1980
21st to endNight
40%9%18%17%13%3
1980
October1st to 10thNight
36%9%14%19%13%10%
1980
11th to 20thNight
25%6%11%25%27%7%
2145
21st to endNight
31%7%9%17%24%12%
2376
November1st to 10thNight
28%7%11%22%19%13%
2221
11th to 20thNight
34%5%9%20%20%12%
2288
21st to endNight
36%5%10%20%21%8%
2470
December1st to 10thNight
34%6%12%27%15%6%
2470
11th to 20thNight
38%5%9%17%21%10%
3044
21st to endNight
44%6%11%19%16%5%
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
11%7%44%26%8%3
270
11th to 20thDay
8%12%33%28%15%4
249
21st to endDay
14%16%42%22%6%
264
February1st to 10thDay
13%11%34%24%16%3
240
11th to 20thDay
12%10%27%36%10%5%
240
21st to endDay
8%8%29%30%21%3
238
March1st to 10thDay
8%9%30%34%18%1
420
11th to 20thDay
11%7%28%30%20%3
420
21st to endDay
9%8%27%31%21%4
462
April1st to 10thDay
12%9%24%28%26%2
420
11th to 20thDay
10%11%24%29%22%5%
412
21st to endDay
6%419%33%25%13%
420
May1st to 10thDay
4419%30%26%16%
423
11th to 20thDay
10%210%26%30%22%
447
21st to endDay
9%38%18%32%30%
485
June1st to 10thDay
14%27%20%29%27%
450
11th to 20thDay
8%38%17%30%34%
450
21st to endDay
42417%28%44%
450
July1st to 10thDay
8%3410%25%50%
445
11th to 20thDay
6%15%8%27%54%
444
21st to endDay
8%25%13%28%45%
488
August1st to 10thDay
11%1313%25%46%
446
11th to 20thDay
10%25%8%25%50%
439
21st to endDay
11%15%17%28%38%
495
September1st to 10thDay
11%25%15%29%38%
450
11th to 20thDay
10%38%21%33%25%
450
21st to endDay
8%36%21%36%26%
450
October1st to 10thDay
13%318%34%21%10%
450
11th to 20thDay
6%314%31%34%11%
450
21st to endDay
7%418%38%28%6%
495
November1st to 10thDay
11%422%33%25%6%
455
11th to 20thDay
13%7%24%32%20%4
448
21st to endDay
9%7%28%38%15%2
270
December1st to 10thDay
7%8%34%28%17%6%
270
11th to 20thDay
16%9%29%29%15%1
270
21st to endDay
12%7%26%34%16%4
297
January1st to 10thNight
13%7%33%34%12%1
760
11th to 20thNight
10%8%24%43%15%1
735
21st to endNight
18%9%31%35%7%
792
February1st to 10thNight
15%6%29%38%11%1
720
11th to 20thNight
13%6%31%38%11%1
703
21st to endNight
11%7%30%44%7%
592
March1st to 10thNight
8%7%32%41%12%1
720
11th to 20thNight
10%7%28%39%14%1
720
21st to endNight
8%6%29%41%15%
792
April1st to 10thNight
9%6%28%40%17%
720
11th to 20thNight
9%429%39%17%1
711
21st to endNight
8%322%45%21%1
666
May1st to 10thNight
5%216%48%25%3
540
11th to 20thNight
6%213%41%33%5%
531
21st to endNight
7%27%36%42%8%
584
June1st to 10thNight
13%16%32%39%9%
540
11th to 20thNight
6%35%22%43%21%
540
21st to endNight
8%25%17%44%24%
540
July1st to 10thNight
7%2313%44%30%
525
11th to 20thNight
4211%50%33%
522
21st to endNight
5%1312%56%23%
591
August1st to 10thNight
6%1312%52%25%
537
11th to 20thNight
7%2210%50%29%
534
21st to endNight
13%25%18%43%18%
757
September1st to 10thNight
9%26%23%42%18%
720
11th to 20thNight
13%37%29%39%10%
720
21st to endNight
11%37%30%41%8%
720
October1st to 10thNight
11%216%38%30%3
720
11th to 20thNight
7%214%40%35%2
720
21st to endNight
10%415%42%28%2
792
November1st to 10thNight
10%424%36%25%2
740
11th to 20thNight
11%5%22%41%19%1
760
21st to endNight
13%5%24%40%17%1
760
December1st to 10thNight
11%5%23%38%22%1
760
11th to 20thNight
12%6%25%40%17%1
760
21st to endNight
15%6%23%39%17%1
836
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