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Robert Ferguson Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Robert Ferguson Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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
62%
23579
26%
74828
23%
23526
68%
23526
36%
41593

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
48%
758
17%
2557
16%
756
52%
756
21%
1679
January11th to 20thNight
52%
740
20%
2405
16%
740
58%
740
25%
1493
January21st to endNight
53%
792
24%
2574
22%
792
59%
792
27%
1566
February1st to 10thNight
54%
720
26%
2340
24%
720
61%
720
28%
1398
February11th to 20thNight
48%
701
23%
2227
18%
700
57%
700
28%
1327
February21st to endNight
49%
592
27%
1776
21%
592
58%
592
32%
1030
March1st to 10thNight
44%
720
16%
2000
11%
720
48%
720
23%
1408
March11th to 20thNight
49%
720
22%
1980
18%
720
54%
720
29%
1294
March21st to endNight
45%
792
20%
2160
11%
792
52%
792
32%
1363
April1st to 10thNight
47%
720
23%
1800
12%
720
52%
720
33%
1162
April11th to 20thNight
49%
711
28%
1779
13%
711
55%
711
39%
1062
April21st to endNight
56%
720
29%
1800
13%
720
63%
720
48%
1002
May1st to 10thNight
59%
591
28%
1671
16%
591
65%
591
43%
909
May11th to 20thNight
68%
470
26%
1533
22%
470
71%
470
43%
745
May21st to endNight
64%
388
25%
1552
23%
388
74%
388
36%
725
June1st to 10thNight
65%
360
24%
1440
24%
360
74%
360
37%
662
June11th to 20thNight
74%
360
34%
1440
38%
360
84%
360
55%
529
June21st to endNight
79%
360
32%
1440
41%
360
84%
360
54%
552
July1st to 10thNight
88%
350
33%
1400
43%
350
91%
350
60%
502
July11th to 20thNight
89%
486
32%
1530
32%
486
90%
486
62%
637
July21st to endNight
85%
591
32%
1674
30%
558
86%
558
50%
791
August1st to 10thNight
81%
537
30%
1602
26%
534
82%
534
48%
767
August11th to 20thNight
85%
606
34%
1674
24%
606
87%
606
60%
794
August21st to endNight
84%
792
34%
1980
23%
792
85%
792
60%
1016
September1st to 10thNight
86%
720
43%
1800
28%
720
89%
720
74%
838
September11th to 20thNight
77%
720
36%
1800
27%
720
79%
720
54%
982
September21st to endNight
78%
720
38%
2059
35%
720
83%
720
61%
953
October1st to 10thNight
71%
720
31%
2160
30%
720
78%
720
52%
1048
October11th to 20thNight
71%
720
34%
2160
34%
720
77%
720
46%
1100
October21st to endNight
68%
792
35%
2376
34%
792
74%
792
44%
1247
November1st to 10thNight
63%
740
30%
2255
26%
740
69%
740
39%
1233
November11th to 20thNight
62%
760
25%
2489
23%
760
68%
760
34%
1385
November21st to endNight
60%
760
27%
2660
28%
760
65%
760
34%
1398
December1st to 10thNight
52%
760
21%
2660
19%
760
58%
760
24%
1625
December11th to 20thNight
48%
760
17%
3250
18%
759
54%
759
15%
2284
December21st to endNight
44%
830
14%
4825
18%
817
52%
817
12%
3087

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%423323346%59%
74720
Night
11%424423447%56%
75087
TransparencyDay
27%5%9%19%24%16%
74439
Night
30%5%10%19%21%15%
74891
SeeingDay
10%9%23%31%20%6%
14212
Night
11%416%33%30%6%
23591

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 10thDay
24%8%36%5%23445%36%
1604
11th to 20thDay
16%6%35%5%23346%47%
1666
21st to endDay
14%7%35%5%35%5%47%41%
1782
February1st to 10thDay
18%5%26%5%2434447%
1620
11th to 20thDay
14%7%25%424447%45%
1620
21st to endDay
17%6%25%5%32336%49%
1480
March1st to 10thDay
18%8%47%5%3445%7%36%
1957
11th to 20thDay
19%6%35%5%345%7%6%38%
1980
21st to endDay
16%5%35%435%5%5%6%44%
2196
April1st to 10thDay
16%7%35%5%3445%7%41%
2160
11th to 20thDay
10%424424447%53%
2129
21st to endDay
7%42342435%9%58%
2160
May1st to 10thDay
6%423323447%62%
2286
11th to 20thDay
6%323223448%62%
2360
21st to endDay
5%42442345%7%60%
2723
June1st to 10thDay
6%5%2322345%9%60%
2520
11th to 20thDay
1112322346%75%
2520
21st to endDay
2112213335%78%
2520
July1st to 10thDay
1212212235%79%
2520
11th to 20thDay
1111212346%78%
2374
21st to endDay
1112212236%79%
2546
August1st to 10thDay
1212323336%74%
2328
11th to 20thDay
112222236%79%
2224
21st to endDay
1213212236%77%
2376
September1st to 10thDay
112211236%81%
2160
11th to 20thDay
4213223347%69%
2160
21st to endDay
3312212345%75%
1896
October1st to 10thDay
6%213223335%70%
1800
11th to 20thDay
7%313323336%67%
1800
21st to endDay
10%323322336%63%
1980
November1st to 10thDay
12%313423447%56%
1821
11th to 20thDay
12%436%5%3345%6%50%
1690
21st to endDay
12%41443445%5%54%
1520
December1st to 10thDay
17%8%25%424446%45%
1520
11th to 20thDay
34%8%34323345%31%
1928
21st to endDay
24%8%25%424447%35%
2794
January1st to 10thNight
18%8%35%4345%49%37%
2557
11th to 20thNight
17%6%3443445%6%44%
2405
21st to endNight
16%5%24433447%47%
2574
February1st to 10thNight
17%5%24333446%50%
2340
11th to 20thNight
12%6%25%5%24448%47%
2225
21st to endNight
14%5%13424346%53%
1776
March1st to 10thNight
18%8%35%6%35%445%39%
2000
11th to 20thNight
16%7%35%43445%6%43%
1980
21st to endNight
16%7%24423445%50%
2160
April1st to 10thNight
12%6%36%43335%6%50%
1800
11th to 20thNight
10%424323347%57%
1779
21st to endNight
6%31332345%8%62%
1800
May1st to 10thNight
6%313424347%62%
1671
11th to 20thNight
431333446%8%62%
1532
21st to endNight
5%2133345%47%63%
1552
June1st to 10thNight
5%324223348%63%
1440
11th to 20thNight
211222225%6%76%
1440
21st to endNight
3213212246%75%
1440
July1st to 10thNight
1212112235%82%
1440
11th to 20thNight
1111212337%77%
1581
21st to endNight
211232345%8%68%
1773
August1st to 10thNight
2113324447%68%
1611
11th to 20thNight
113332447%73%
1674
21st to endNight
1212423347%73%
1980
September1st to 10thNight
12213245%80%
1800
11th to 20thNight
4313423347%66%
1800
21st to endNight
3212312345%75%
2059
October1st to 10thNight
4413313345%70%
2160
11th to 20thNight
5%31332435%6%64%
2160
21st to endNight
9%312423346%62%
2376
November1st to 10thNight
10%5%24322448%56%
2255
11th to 20thNight
11%6%2442445%8%51%
2489
21st to endNight
10%5%24424336%58%
2660
December1st to 10thNight
20%5%2442335%7%45%
2660
11th to 20thNight
32%7%2432345%6%31%
3276
21st to endNight
23%7%25%5%34446%36%
4862

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
50%5%11%19%9%5%
1604
11th to 20thDay
40%5%10%15%17%12%
1666
21st to endDay
42%5%10%15%20%8%
1782
February1st to 10thDay
42%47%19%20%9%
1620
11th to 20thDay
39%6%8%20%20%7%
1629
21st to endDay
39%49%25%16%8%
1480
March1st to 10thDay
47%5%12%16%16%3
1957
11th to 20thDay
44%6%9%22%14%5%
1980
21st to endDay
38%8%13%20%18%4
2196
April1st to 10thDay
41%7%12%19%17%4
2160
11th to 20thDay
31%6%14%22%21%6%
2132
21st to endDay
24%6%14%29%23%4
2160
May1st to 10thDay
24%410%27%28%7%
2286
11th to 20thDay
22%5%10%33%22%8%
2363
21st to endDay
23%7%17%28%20%5%
2724
June1st to 10thDay
24%5%11%28%25%7%
2520
11th to 20thDay
12%411%21%35%17%
2520
21st to endDay
12%36%16%35%28%
2520
July1st to 10thDay
12%4413%26%42%
2451
11th to 20thDay
10%5%7%13%28%37%
2303
21st to endDay
10%35%10%27%45%
2405
August1st to 10thDay
15%46%16%31%28%
2312
11th to 20thDay
11%35%12%37%31%
2224
21st to endDay
13%36%14%34%30%
2376
September1st to 10thDay
9%35%11%30%42%
2160
11th to 20thDay
17%5%8%24%34%13%
2160
21st to endDay
13%36%21%32%25%
1896
October1st to 10thDay
18%46%15%32%25%
1800
11th to 20thDay
21%5%8%19%25%23%
1800
21st to endDay
25%48%20%26%17%
1980
November1st to 10thDay
28%5%9%27%19%12%
1821
11th to 20thDay
36%5%12%22%18%8%
1690
21st to endDay
32%5%12%18%20%13%
1520
December1st to 10thDay
41%6%8%18%19%9%
1520
11th to 20thDay
57%47%12%16%5%
1928
21st to endDay
48%6%14%19%9%4
2794
January1st to 10thNight
45%6%12%20%11%6%
2557
11th to 20thNight
40%6%11%16%14%13%
2405
21st to endNight
38%5%12%12%22%10%
2574
February1st to 10thNight
37%5%8%19%20%12%
2340
11th to 20thNight
37%411%19%20%9%
2227
21st to endNight
33%411%25%21%6%
1776
March1st to 10thNight
47%6%11%14%17%4
2000
11th to 20thNight
41%49%21%18%6%
1980
21st to endNight
36%5%12%22%18%6%
2160
April1st to 10thNight
36%6%14%19%21%5%
1800
11th to 20thNight
28%5%12%26%18%11%
1779
21st to endNight
21%5%13%30%25%6%
1800
May1st to 10thNight
24%6%8%22%31%11%
1671
11th to 20thNight
21%6%13%25%26%9%
1533
21st to endNight
21%7%15%28%22%6%
1552
June1st to 10thNight
21%7%12%22%30%9%
1440
11th to 20thNight
11%410%23%33%19%
1440
21st to endNight
15%38%14%32%29%
1440
July1st to 10thNight
10%45%13%27%41%
1400
11th to 20thNight
11%49%14%22%39%
1530
21st to endNight
16%7%8%10%18%40%
1674
August1st to 10thNight
19%5%8%16%24%28%
1602
11th to 20thNight
14%49%12%26%35%
1674
21st to endNight
15%5%8%15%25%32%
1980
September1st to 10thNight
9%27%11%29%41%
1800
11th to 20thNight
21%37%19%33%16%
1800
21st to endNight
15%36%21%26%30%
2059
October1st to 10thNight
19%48%17%27%25%
2160
11th to 20thNight
21%5%9%19%22%24%
2160
21st to endNight
24%5%8%19%24%21%
2376
November1st to 10thNight
28%5%11%26%17%13%
2255
11th to 20thNight
31%5%12%24%18%9%
2489
21st to endNight
30%49%21%23%14%
2660
December1st to 10thNight
40%5%9%17%18%11%
2660
11th to 20thNight
54%5%10%12%15%4
3276
21st to endNight
48%7%12%17%12%4
4862

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%13%25%17%11%3
265
11th to 20thDay
22%11%23%26%15%3
356
21st to endDay
16%10%24%29%16%4
374
February1st to 10thDay
21%9%21%25%19%4
340
11th to 20thDay
20%17%25%22%14%1
355
21st to endDay
18%15%25%27%14%1
346
March1st to 10thDay
24%17%28%20%10%2
420
11th to 20thDay
23%13%28%20%12%4
420
21st to endDay
17%18%30%25%10%1
462
April1st to 10thDay
18%15%29%24%11%3
420
11th to 20thDay
15%17%29%23%12%4
412
21st to endDay
7%17%29%28%13%7%
420
May1st to 10thDay
10%15%30%27%14%4
423
11th to 20thDay
9%14%30%26%16%5%
448
21st to endDay
7%11%26%32%18%6%
485
June1st to 10thDay
8%11%25%33%16%7%
450
11th to 20thDay
410%28%39%15%3
450
21st to endDay
1426%36%27%6%
450
July1st to 10thDay
2420%46%23%5%
446
11th to 20thDay
1115%40%32%11%
444
21st to endDay
1112%47%30%9%
487
August1st to 10thDay
1418%41%28%9%
447
11th to 20thDay
2321%38%27%10%
437
21st to endDay
2218%39%31%8%
495
September1st to 10thDay
1417%39%30%10%
450
11th to 20thDay
6%423%36%23%9%
450
21st to endDay
47%23%34%25%8%
450
October1st to 10thDay
6%8%25%27%24%10%
450
11th to 20thDay
7%10%18%28%26%11%
450
21st to endDay
12%8%19%30%24%6%
495
November1st to 10thDay
14%7%18%24%31%7%
417
11th to 20thDay
9%8%17%26%29%11%
260
21st to endDay
13%6%23%29%23%6%
180
December1st to 10thDay
19%13%19%23%18%8%
180
11th to 20thDay
24%14%21%18%18%6%
180
21st to endDay
22%12%24%23%17%3
198
January1st to 10thNight
21%6%16%31%22%5%
760
11th to 20thNight
20%416%36%19%5%
740
21st to endNight
18%418%32%24%4
792
February1st to 10thNight
18%5%15%36%22%3
720
11th to 20thNight
14%7%21%33%21%4
704
21st to endNight
18%8%19%33%19%2
592
March1st to 10thNight
20%7%22%28%20%3
720
11th to 20thNight
19%5%17%31%24%3
720
21st to endNight
18%6%24%33%17%2
792
April1st to 10thNight
14%6%24%35%18%3
720
11th to 20thNight
11%10%23%30%22%4
711
21st to endNight
7%8%24%32%24%5%
720
May1st to 10thNight
6%7%22%33%27%5%
591
11th to 20thNight
5%219%33%36%5%
470
21st to endNight
5%6%20%33%32%4
389
June1st to 10thNight
6%418%36%34%2
360
11th to 20thNight
2415%45%32%2
360
21st to endNight
3113%41%39%3
360
July1st to 10thNight
117%36%50%4
350
11th to 20thNight
115%30%52%12%
486
21st to endNight
25%33%52%8%
591
August1st to 10thNight
219%30%49%9%
537
11th to 20thNight
118%34%45%10%
606
21st to endNight
116%34%48%9%
792
September1st to 10thNight
118%35%47%8%
720
11th to 20thNight
5%210%35%40%8%
720
21st to endNight
3312%35%36%10%
720
October1st to 10thNight
5%415%33%34%9%
720
11th to 20thNight
7%412%33%36%7%
720
21st to endNight
10%312%30%33%11%
792
November1st to 10thNight
10%5%15%30%32%8%
740
11th to 20thNight
12%315%34%30%6%
760
21st to endNight
12%5%15%36%26%6%
760
December1st to 10thNight
20%7%14%33%21%6%
760
11th to 20thNight
25%6%15%30%21%3
760
21st to endNight
22%6%20%33%17%2
836
Page generated at 2024-01-12 22:38:13. Version ac07

Copyright 2024 Attilla Danko


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