USNO Flagstaff Station
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the USNO Flagstaff Station 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
54%
23983
34%
74301
22%
23931
66%
23931
43%
36263

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
47%
760
35%
2457
22%
756
65%
756
39%
1205
January11th to 20thNight
45%
726
34%
2359
24%
726
60%
726
39%
1172
January21st to endNight
39%
792
34%
2574
20%
792
59%
792
31%
1374
February1st to 10thNight
45%
720
34%
2322
21%
720
66%
720
42%
1089
February11th to 20thNight
42%
700
33%
2099
21%
700
58%
700
39%
1092
February21st to endNight
39%
592
36%
1772
24%
592
55%
592
35%
941
March1st to 10thNight
36%
720
34%
1980
16%
720
55%
720
40%
1022
March11th to 20thNight
48%
720
34%
1980
20%
720
62%
720
41%
1062
March21st to endNight
39%
792
33%
2178
13%
792
57%
792
42%
1130
April1st to 10thNight
37%
720
31%
1980
11%
720
53%
720
42%
989
April11th to 20thNight
36%
579
37%
1812
15%
579
59%
579
40%
834
April21st to endNight
43%
540
44%
1620
19%
540
66%
540
49%
704
May1st to 10thNight
45%
540
37%
1620
20%
540
60%
540
50%
722
May11th to 20thNight
51%
531
39%
1594
24%
531
63%
531
51%
691
May21st to endNight
47%
582
34%
1746
18%
582
59%
582
51%
764
June1st to 10thNight
57%
540
35%
1620
25%
540
64%
540
60%
698
June11th to 20thNight
55%
540
36%
1620
26%
540
64%
540
64%
652
June21st to endNight
67%
540
33%
1620
26%
540
73%
540
62%
703
July1st to 10thNight
72%
525
25%
1575
20%
525
74%
525
45%
813
July11th to 20thNight
79%
522
22%
1566
18%
522
81%
522
43%
836
July21st to endNight
72%
591
19%
1674
17%
558
72%
558
32%
1012
August1st to 10thNight
79%
537
26%
1602
21%
534
80%
534
43%
827
August11th to 20thNight
79%
534
29%
1602
24%
534
81%
534
42%
847
August21st to endNight
80%
641
32%
1927
29%
641
81%
641
44%
1012
September1st to 10thNight
74%
720
30%
1980
24%
720
77%
720
46%
1071
September11th to 20thNight
76%
720
41%
1980
29%
720
83%
720
63%
932
September21st to endNight
68%
720
40%
1980
25%
720
78%
720
58%
933
October1st to 10thNight
57%
720
36%
2034
20%
720
70%
720
50%
999
October11th to 20thNight
62%
720
41%
2160
28%
720
74%
720
58%
946
October21st to endNight
55%
792
44%
2376
27%
792
71%
792
54%
1042
November1st to 10thNight
53%
740
41%
2229
25%
740
70%
740
51%
1020
November11th to 20thNight
56%
760
40%
2470
27%
760
73%
760
53%
1029
November21st to endNight
47%
760
37%
2470
26%
760
63%
760
41%
1188
December1st to 10thNight
49%
760
35%
2470
24%
760
64%
760
39%
1215
December11th to 20thNight
45%
758
32%
2922
23%
758
59%
758
27%
1599
December21st to endNight
41%
829
21%
4331
21%
817
56%
817
22%
2098

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
45%2443445%6%58%
74942
Night
35%2332345%6%64%
74816
TransparencyDay
24%5%6%18%28%19%
74669
Night
20%46%20%30%21%
74611
SeeingDay
12%18%27%26%13%4
13768
Night
7%12%22%31%23%5%
23998

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
27%3432335%7%61%
1708
11th to 20thDay
27%24322347%63%
1629
21st to endDay
5%8%3442445%7%55%
1782
February1st to 10thDay
28%33313347%62%
1634
11th to 20thDay
39%35%31446%6%56%
1750
21st to endDay
28%46%5%24345%57%
1484
March1st to 10thDay
37%343245%5%8%56%
1980
11th to 20thDay
38%24434446%57%
1980
21st to endDay
45%23424447%60%
2178
April1st to 10thDay
242434445%7%61%
1980
11th to 20thDay
2424323346%68%
2093
21st to endDay
4424423336%66%
2340
May1st to 10thDay
432442335%6%63%
2340
11th to 20thDay
33243345%5%6%63%
2301
21st to endDay
4313323345%68%
2530
June1st to 10thDay
3113323446%71%
2340
11th to 20thDay
211121223480%
2340
21st to endDay
3223434446%65%
2340
July1st to 10thDay
5%325%6%47%6%6%7%49%
2340
11th to 20thDay
7%426%8%6%8%7%9%9%33%
2340
21st to endDay
9%6%48%9%48%8%8%9%27%
2545
August1st to 10thDay
8%427%6%5%6%6%6%7%44%
2328
11th to 20thDay
6%5%36%7%6%7%7%7%9%38%
2299
21st to endDay
7%426%6%5%6%7%6%7%44%
2424
September1st to 10thDay
6%6%15%6%36%7%6%7%46%
1980
11th to 20thDay
4324324445%64%
1980
21st to endDay
4213424446%66%
1980
October1st to 10thDay
6%323423445%64%
1926
11th to 20thDay
421431222476%
1800
21st to endDay
2212213346%73%
1980
November1st to 10thDay
3322223346%71%
1846
11th to 20thDay
2312223446%71%
1710
21st to endDay
46%24312235%67%
1710
December1st to 10thDay
47%2343335%7%59%
1710
11th to 20thDay
38%47%5%345%6%8%48%
2169
21st to endDay
5%9%46%5%3445%6%50%
3146
January1st to 10thNight
27%3333345%7%61%
2457
11th to 20thNight
28%35%32335%6%61%
2359
21st to endNight
5%8%35%423445%58%
2574
February1st to 10thNight
17%3332235%7%66%
2322
11th to 20thNight
28%34325%35%5%60%
2098
21st to endNight
29%45%21335%6%59%
1772
March1st to 10thNight
35%2341436%7%63%
1980
11th to 20thNight
37%24323447%60%
1980
21st to endNight
342342445%6%64%
2178
April1st to 10thNight
1423323446%68%
1980
11th to 20thNight
2424224445%69%
1812
21st to endNight
1112323246%75%
1620
May1st to 10thNight
1212323446%71%
1620
11th to 20thNight
2212223336%74%
1594
21st to endNight
2312223345%75%
1746
June1st to 10thNight
222221245%475%
1620
11th to 20thNight
121221122383%
1620
21st to endNight
2311323345%74%
1620
July1st to 10thNight
2324435%5%7%9%57%
1620
11th to 20thNight
3214437%7%7%10%53%
1620
21st to endNight
5%5%35%6%36%7%10%10%40%
1773
August1st to 10thNight
3213435%5%6%9%58%
1611
11th to 20thNight
3314435%6%8%11%51%
1602
21st to endNight
3214435%5%6%9%57%
1927
September1st to 10thNight
4415%5%25%5%6%9%56%
1980
11th to 20thNight
3112222336%74%
1980
21st to endNight
2212322335%75%
1980
October1st to 10thNight
3313323446%68%
2034
11th to 20thNight
231231222478%
2160
21st to endNight
2212212345%75%
2376
November1st to 10thNight
3322223345%72%
2229
11th to 20thNight
221222335%5%73%
2470
21st to endNight
36%2432334466%
2470
December1st to 10thNight
47%23323448%60%
2470
11th to 20thNight
39%36%42445%7%52%
3041
21st to endNight
49%35%434445%55%
4521

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
24%37%23%31%12%
1709
11th to 20thDay
22%36%25%31%13%
1629
21st to endDay
28%46%20%30%12%
1782
February1st to 10thDay
24%37%20%26%21%
1634
11th to 20thDay
26%45%22%24%19%
1760
21st to endDay
29%5%5%18%26%18%
1484
March1st to 10thDay
24%5%5%21%31%14%
1980
11th to 20thDay
25%5%5%21%32%12%
1980
21st to endDay
22%5%6%25%31%11%
2178
April1st to 10thDay
22%5%422%34%14%
1980
11th to 20thDay
18%3419%35%21%
2096
21st to endDay
21%4318%40%14%
2340
May1st to 10thDay
21%4418%37%16%
2340
11th to 20thDay
20%5%5%20%35%16%
2304
21st to endDay
18%3317%37%21%
2530
June1st to 10thDay
14%4213%33%33%
2340
11th to 20thDay
9%318%30%50%
2340
21st to endDay
18%4211%30%35%
2340
July1st to 10thDay
28%8%7%14%17%25%
2276
11th to 20thDay
39%9%15%16%13%8%
2271
21st to endDay
45%10%17%14%10%3
2404
August1st to 10thDay
35%7%11%14%17%16%
2313
11th to 20thDay
37%7%9%18%16%12%
2299
21st to endDay
34%8%9%18%24%8%
2424
September1st to 10thDay
32%7%9%14%18%20%
1980
11th to 20thDay
20%5%5%16%32%22%
1980
21st to endDay
19%4317%33%24%
1980
October1st to 10thDay
22%4420%24%26%
1926
11th to 20thDay
15%2312%34%34%
1800
21st to endDay
13%35%18%41%21%
1980
November1st to 10thDay
15%3427%33%18%
1846
11th to 20thDay
14%45%19%36%22%
1710
21st to endDay
22%2418%35%19%
1710
December1st to 10thDay
25%37%24%24%17%
1710
11th to 20thDay
34%38%21%22%12%
2168
21st to endDay
34%4420%25%12%
3146
January1st to 10thNight
22%45%25%33%11%
2457
11th to 20thNight
25%3324%30%15%
2359
21st to endNight
29%4416%33%13%
2574
February1st to 10thNight
20%37%21%28%22%
2322
11th to 20thNight
24%45%21%26%20%
2099
21st to endNight
25%5%417%30%19%
1772
March1st to 10thNight
20%45%22%35%14%
1980
11th to 20thNight
23%4424%32%13%
1980
21st to endNight
19%5%8%25%30%13%
2178
April1st to 10thNight
18%35%23%35%15%
1980
11th to 20thNight
17%3218%36%23%
1812
21st to endNight
12%3423%39%19%
1620
May1st to 10thNight
13%36%23%35%19%
1620
11th to 20thNight
12%3423%37%19%
1595
21st to endNight
13%3417%38%25%
1746
June1st to 10thNight
11%3212%34%37%
1620
11th to 20thNight
9%29%30%50%
1620
21st to endNight
13%239%27%45%
1620
July1st to 10thNight
22%7%10%13%19%30%
1575
11th to 20thNight
24%7%18%24%17%11%
1566
21st to endNight
33%8%21%20%12%5%
1674
August1st to 10thNight
23%6%15%18%20%19%
1602
11th to 20thNight
25%5%17%20%20%14%
1602
21st to endNight
22%7%10%25%26%11%
1927
September1st to 10thNight
24%5%10%18%24%19%
1980
11th to 20thNight
13%35%20%31%27%
1980
21st to endNight
13%3415%36%28%
1980
October1st to 10thNight
18%46%22%23%28%
2034
11th to 20thNight
13%2313%36%33%
2160
21st to endNight
12%3418%39%24%
2376
November1st to 10thNight
16%3324%35%19%
2229
11th to 20thNight
13%36%18%37%24%
2470
21st to endNight
22%3418%30%23%
2470
December1st to 10thNight
22%5%7%22%24%20%
2470
11th to 20thNight
31%46%19%25%15%
3041
21st to endNight
31%4420%22%20%
4521

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
14%21%31%23%10%1
270
11th to 20thDay
13%21%30%25%7%4
243
21st to endDay
13%22%28%24%11%1
264
February1st to 10thDay
16%20%28%24%11%2
254
11th to 20thDay
19%27%28%21%4
415
21st to endDay
25%28%29%14%3
346
March1st to 10thDay
23%28%28%16%4
420
11th to 20thDay
18%23%28%20%9%2
420
21st to endDay
19%30%33%13%41
462
April1st to 10thDay
14%28%33%15%8%2
420
11th to 20thDay
19%31%29%15%5%2
412
21st to endDay
18%30%27%15%9%1
420
May1st to 10thDay
13%25%37%18%5%2
423
11th to 20thDay
8%25%32%21%10%4
448
21st to endDay
14%21%34%20%9%2
485
June1st to 10thDay
5%18%36%28%11%3
450
11th to 20thDay
6%19%36%24%11%4
450
21st to endDay
412%35%36%12%2
450
July1st to 10thDay
5%7%30%33%19%6%
446
11th to 20thDay
6%5%16%39%23%11%
444
21st to endDay
11%48%35%29%12%
487
August1st to 10thDay
6%5%19%39%22%9%
447
11th to 20thDay
7%319%39%23%8%
437
21st to endDay
6%5%18%34%25%11%
495
September1st to 10thDay
9%7%22%32%22%8%
450
11th to 20thDay
6%10%32%28%18%5%
450
21st to endDay
10%12%25%31%16%6%
450
October1st to 10thDay
10%21%24%25%16%4
396
11th to 20thDay
8%17%22%28%19%6%
270
21st to endDay
9%21%26%25%15%3
297
November1st to 10thDay
13%17%25%28%14%3
270
11th to 20thDay
8%17%26%27%19%4
270
21st to endDay
15%19%26%22%13%4
270
December1st to 10thDay
13%17%32%23%13%2
270
11th to 20thDay
9%19%30%28%12%2
270
21st to endDay
22%16%30%24%6%1
297
January1st to 10thNight
9%14%25%29%16%6%
760
11th to 20thNight
11%10%28%29%16%6%
726
21st to endNight
13%15%26%29%13%3
792
February1st to 10thNight
7%16%27%31%15%4
720
11th to 20thNight
10%18%28%29%13%3
704
21st to endNight
11%21%27%28%11%2
592
March1st to 10thNight
10%22%27%28%11%2
720
11th to 20thNight
10%15%22%30%18%4
720
21st to endNight
8%18%31%28%14%1
792
April1st to 10thNight
6%22%30%29%12%2
720
11th to 20thNight
10%19%31%29%10%1
579
21st to endNight
6%21%28%25%16%3
540
May1st to 10thNight
5%16%32%34%12%1
540
11th to 20thNight
417%24%32%20%4
531
21st to endNight
5%15%29%31%18%2
584
June1st to 10thNight
210%28%41%18%1
540
11th to 20thNight
310%29%37%18%2
540
21st to endNight
2422%40%30%2
540
July1st to 10thNight
4213%38%39%5%
525
11th to 20thNight
317%37%44%8%
522
21st to endNight
7%3327%50%10%
591
August1st to 10thNight
417%30%47%11%
537
11th to 20thNight
316%33%47%9%
534
21st to endNight
325%29%48%13%
641
September1st to 10thNight
5%47%28%45%11%
720
11th to 20thNight
4314%36%37%6%
720
21st to endNight
5%9%14%30%34%9%
720
October1st to 10thNight
7%10%22%35%23%3
720
11th to 20thNight
5%9%21%37%22%6%
720
21st to endNight
5%13%22%29%22%9%
792
November1st to 10thNight
6%12%24%32%22%4
740
11th to 20thNight
413%23%34%20%6%
760
21st to endNight
11%13%24%30%18%5%
760
December1st to 10thNight
10%14%23%29%21%3
760
11th to 20thNight
13%11%25%31%18%2
760
21st to endNight
12%13%28%32%12%3
836
Page generated at 2024-01-09 05:14:41. Version ac07

Copyright 2024 Attilla Danko


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