Boulder (UT)
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Boulder (UT) clear sky chart from 2005-11-06 to 2024-03-08.

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
63%
24041
33%
79610
26%
23956
72%
23956
48%
37148

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
60%
749
37%
3997
26%
736
71%
736
34%
1702
January11th to 20thNight
61%
755
34%
3977
27%
740
73%
740
38%
1507
January21st to endNight
60%
827
24%
4266
31%
814
70%
814
29%
2016
February1st to 10thNight
54%
760
30%
2470
23%
760
67%
760
49%
1160
February11th to 20thNight
55%
740
32%
2296
25%
740
67%
740
47%
1143
February21st to endNight
50%
628
32%
1884
24%
628
61%
628
45%
976
March1st to 10thNight
54%
750
33%
2072
22%
750
66%
750
48%
1093
March11th to 20thNight
57%
720
34%
1980
23%
720
67%
720
51%
1023
March21st to endNight
51%
792
35%
2178
16%
792
67%
792
51%
1110
April1st to 10thNight
45%
716
29%
1976
14%
716
58%
716
52%
986
April11th to 20thNight
46%
533
36%
1725
20%
533
63%
533
47%
786
April21st to endNight
47%
540
39%
1620
20%
540
64%
540
53%
732
May1st to 10thNight
53%
540
32%
1620
21%
540
62%
540
46%
809
May11th to 20thNight
62%
531
34%
1595
24%
531
69%
531
54%
728
May21st to endNight
57%
582
30%
1746
20%
582
67%
582
53%
795
June1st to 10thNight
64%
540
33%
1620
26%
540
70%
540
59%
713
June11th to 20thNight
65%
540
32%
1620
27%
540
72%
540
62%
703
June21st to endNight
70%
540
31%
1620
28%
540
75%
540
62%
705
July1st to 10thNight
73%
525
23%
1575
21%
525
75%
525
46%
800
July11th to 20thNight
77%
522
25%
1566
22%
522
78%
522
47%
782
July21st to endNight
79%
591
24%
1674
22%
558
79%
558
40%
906
August1st to 10thNight
76%
537
29%
1602
24%
534
76%
534
46%
811
August11th to 20thNight
77%
534
34%
1602
29%
534
78%
534
49%
780
August21st to endNight
79%
594
37%
1856
34%
594
81%
594
51%
880
September1st to 10thNight
77%
680
34%
1940
29%
680
81%
680
53%
985
September11th to 20thNight
74%
720
40%
1980
30%
720
80%
720
61%
959
September21st to endNight
74%
720
42%
1980
29%
720
81%
720
67%
909
October1st to 10thNight
65%
720
33%
2068
22%
720
74%
720
52%
1061
October11th to 20thNight
69%
720
42%
2160
31%
720
79%
720
66%
920
October21st to endNight
68%
792
43%
2376
32%
792
79%
792
62%
1055
November1st to 10thNight
69%
740
39%
2300
31%
740
78%
740
60%
1001
November11th to 20thNight
70%
760
41%
2470
35%
760
80%
760
63%
998
November21st to endNight
63%
760
38%
2470
30%
760
74%
760
53%
1105
December1st to 10thNight
65%
760
33%
2470
29%
760
73%
760
51%
1133
December11th to 20thNight
61%
759
32%
2911
27%
758
70%
758
38%
1444
December21st to endNight
52%
824
18%
4348
21%
817
62%
817
27%
1932

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
44244345%5%7%58%
79030
Night
342342445%7%63%
80606
TransparencyDay
24%27%22%26%18%
78757
Night
21%28%24%28%17%
80401
SeeingDay
7%11%28%31%17%6%
13834
Night
5%322%38%25%6%
24085

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
2425%5%345%6%8%56%
2858
11th to 20thDay
25%23334447%63%
2860
21st to endDay
5%8%24433346%59%
3146
February1st to 10thDay
25%134235%5%9%60%
1710
11th to 20thDay
35%23425%5%5%7%60%
1770
21st to endDay
35%3443445%7%57%
1570
March1st to 10thDay
35%244245%6%8%57%
2048
11th to 20thDay
36%144345%6%8%55%
1980
21st to endDay
36%2443447%9%55%
2178
April1st to 10thDay
35%244235%6%8%59%
1984
11th to 20thDay
2415%4246%5%7%59%
2180
21st to endDay
431442445%7%61%
2340
May1st to 10thDay
44245%45%5%6%7%54%
2340
11th to 20thDay
5%4245%35%5%6%9%52%
2301
21st to endDay
5%415%435%5%5%8%54%
2530
June1st to 10thDay
222342445%7%64%
2340
11th to 20thDay
3213323446%68%
2340
21st to endDay
12134245%5%6%66%
2340
July1st to 10thDay
44246%45%6%7%7%51%
2340
11th to 20thDay
5%325%6%5%7%8%8%9%41%
2340
21st to endDay
6%436%8%5%7%8%9%10%35%
2545
August1st to 10thDay
5%425%7%46%7%7%7%47%
2328
11th to 20thDay
4326%7%46%6%7%9%47%
2299
21st to endDay
5%3246%35%6%7%8%51%
2498
September1st to 10thDay
5%3145%35%5%5%6%57%
2016
11th to 20thDay
43144345%5%5%63%
1980
21st to endDay
421232345%6%68%
1980
October1st to 10thDay
8%31332346%8%60%
1890
11th to 20thDay
4212223345%72%
1800
21st to endDay
3213323346%72%
1980
November1st to 10thDay
3312222345%72%
1774
11th to 20thDay
1212213346%75%
1710
21st to endDay
341332335%6%67%
1710
December1st to 10thDay
242433446%8%61%
1710
11th to 20thDay
46%24435%5%5%10%53%
2169
21st to endDay
5%6%35%435%5%5%7%54%
3146
January1st to 10thNight
25%24434446%62%
4097
11th to 20thNight
232342435%7%64%
4110
21st to endNight
48%2442345%6%56%
4521
February1st to 10thNight
34244235%47%63%
2470
11th to 20thNight
342432345%7%62%
2295
21st to endNight
27%2442346%7%58%
1884
March1st to 10thNight
3424425%5%7%8%57%
2072
11th to 20thNight
36%2432346%9%59%
1980
21st to endNight
3312425%5%6%9%60%
2178
April1st to 10thNight
242332345%7%64%
1976
11th to 20thNight
33133245%5%7%64%
1725
21st to endNight
2213424348%67%
1620
May1st to 10thNight
4224335%5%6%7%60%
1620
11th to 20thNight
22134245%5%8%65%
1594
21st to endNight
231332345%6%68%
1746
June1st to 10thNight
3112324348%70%
1620
11th to 20thNight
221222345%7%71%
1620
21st to endNight
2212323348%71%
1620
July1st to 10thNight
3224435%6%6%9%56%
1620
11th to 20thNight
33245%25%6%9%11%51%
1620
21st to endNight
3315%5%47%8%9%12%42%
1773
August1st to 10thNight
32145%35%5%7%7%58%
1611
11th to 20thNight
23145%345%5%9%58%
1602
21st to endNight
32133345%6%8%60%
1856
September1st to 10thNight
33144345%5%6%63%
1940
11th to 20thNight
3213323336%72%
1980
21st to endNight
321221223477%
1980
October1st to 10thNight
6%313423445%65%
2068
11th to 20thNight
4112212235%78%
2160
21st to endNight
2312222345%73%
2376
November1st to 10thNight
2312323346%72%
2300
11th to 20thNight
1212213346%74%
2470
21st to endNight
3413323346%69%
2470
December1st to 10thNight
342332235%7%66%
2470
11th to 20thNight
45%245%345%6%9%55%
3041
21st to endNight
46%24425%46%7%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
26%214%34%21%3
2859
11th to 20thDay
23%212%37%22%6%
2860
21st to endDay
28%211%33%22%4
3146
February1st to 10thDay
22%215%30%24%7%
1710
11th to 20thDay
23%19%29%29%9%
1780
21st to endDay
27%36%24%29%10%
1570
March1st to 10thDay
24%26%29%34%6%
2048
11th to 20thDay
25%27%33%26%8%
1980
21st to endDay
24%28%29%30%7%
2178
April1st to 10thDay
23%26%25%29%16%
1984
11th to 20thDay
23%25%24%30%15%
2183
21st to endDay
23%15%20%38%13%
2340
May1st to 10thDay
27%25%19%31%15%
2340
11th to 20thDay
28%26%19%31%15%
2304
21st to endDay
25%25%19%31%18%
2530
June1st to 10thDay
19%2213%34%31%
2340
11th to 20thDay
17%228%25%45%
2340
21st to endDay
17%219%23%48%
2340
July1st to 10thDay
29%3410%16%37%
2276
11th to 20thDay
34%48%16%18%21%
2271
21st to endDay
38%413%18%14%13%
2404
August1st to 10thDay
32%39%15%15%26%
2313
11th to 20thDay
30%36%13%20%28%
2299
21st to endDay
27%47%16%25%23%
2498
September1st to 10thDay
25%25%14%20%35%
2016
11th to 20thDay
22%25%17%24%30%
1980
21st to endDay
16%2314%35%30%
1980
October1st to 10thDay
23%25%21%28%22%
1890
11th to 20thDay
16%2318%35%27%
1800
21st to endDay
16%1429%34%16%
1980
November1st to 10thDay
15%16%28%35%15%
1774
11th to 20thDay
12%17%32%38%9%
1710
21st to endDay
18%17%30%34%10%
1710
December1st to 10thDay
23%213%32%21%9%
1710
11th to 20thDay
29%312%34%19%3
2168
21st to endDay
32%210%22%22%12%
3146
January1st to 10thNight
26%19%36%23%5%
4097
11th to 20thNight
21%117%35%23%3
4110
21st to endNight
30%111%30%22%5%
4521
February1st to 10thNight
22%112%30%24%10%
2470
11th to 20thNight
24%27%26%32%11%
2296
21st to endNight
26%27%23%31%10%
1884
March1st to 10thNight
24%26%29%32%7%
2072
11th to 20thNight
23%16%29%32%9%
1980
21st to endNight
20%28%32%30%8%
2178
April1st to 10thNight
20%26%26%30%16%
1976
11th to 20thNight
19%25%26%30%18%
1725
21st to endNight
16%25%27%38%11%
1620
May1st to 10thNight
23%27%18%34%15%
1620
11th to 20thNight
18%27%22%35%17%
1595
21st to endNight
18%16%21%37%17%
1746
June1st to 10thNight
16%1214%34%33%
1620
11th to 20thNight
14%1312%22%48%
1620
21st to endNight
15%119%24%50%
1620
July1st to 10thNight
25%26%13%16%39%
1575
11th to 20thNight
23%310%18%20%26%
1566
21st to endNight
29%316%24%15%13%
1674
August1st to 10thNight
24%38%20%18%27%
1602
11th to 20thNight
22%28%15%19%33%
1602
21st to endNight
21%27%17%25%28%
1856
September1st to 10thNight
21%25%14%22%36%
1940
11th to 20thNight
17%16%16%25%34%
1980
21st to endNight
14%1216%35%32%
1980
October1st to 10thNight
22%25%19%29%23%
2068
11th to 20thNight
12%1417%36%28%
2160
21st to endNight
15%15%22%39%17%
2376
November1st to 10thNight
16%16%25%36%16%
2300
11th to 20thNight
12%27%27%42%10%
2470
21st to endNight
19%16%22%37%15%
2470
December1st to 10thNight
20%213%34%22%10%
2470
11th to 20thNight
27%212%32%23%4
3041
21st to endNight
29%213%19%24%13%
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
8%5%34%33%16%4
270
11th to 20thDay
11%5%26%38%16%5%
270
21st to endDay
5%7%20%40%23%5%
297
February1st to 10thDay
8%10%30%31%14%8%
270
11th to 20thDay
10%9%38%30%13%1
376
21st to endDay
8%19%33%30%9%2
382
March1st to 10thDay
10%17%33%27%12%1
449
11th to 20thDay
12%11%29%34%11%3
420
21st to endDay
11%24%37%20%6%2
462
April1st to 10thDay
10%20%35%22%10%4
420
11th to 20thDay
13%24%33%20%7%2
412
21st to endDay
8%22%30%27%11%3
420
May1st to 10thDay
10%17%36%26%8%3
423
11th to 20thDay
9%15%31%25%13%6%
448
21st to endDay
10%15%30%26%13%6%
485
June1st to 10thDay
411%31%32%16%6%
450
11th to 20thDay
7%13%32%30%13%6%
450
21st to endDay
38%34%33%18%4
450
July1st to 10thDay
5%5%22%37%24%7%
446
11th to 20thDay
4417%34%27%13%
444
21st to endDay
5%311%37%30%14%
487
August1st to 10thDay
6%5%19%36%24%9%
447
11th to 20thDay
6%421%34%23%12%
437
21st to endDay
6%320%37%23%11%
495
September1st to 10thDay
6%6%24%31%22%12%
450
11th to 20thDay
5%9%30%31%17%8%
450
21st to endDay
7%9%24%34%18%9%
450
October1st to 10thDay
10%10%29%25%17%9%
360
11th to 20thDay
7%10%23%30%23%8%
270
21st to endDay
5%9%30%30%23%3
297
November1st to 10thDay
9%10%23%28%25%6%
270
11th to 20thDay
36%25%38%20%8%
270
21st to endDay
5%6%30%27%25%7%
270
December1st to 10thDay
5%6%26%38%19%6%
270
11th to 20thDay
37%31%31%24%4
270
21st to endDay
13%7%31%34%12%3
297
January1st to 10thNight
6%227%33%23%8%
760
11th to 20thNight
7%324%37%23%6%
760
21st to endNight
7%323%39%21%7%
836
February1st to 10thNight
5%232%36%20%5%
760
11th to 20thNight
6%230%40%18%4
744
21st to endNight
6%433%40%13%3
628
March1st to 10thNight
7%6%29%39%17%3
750
11th to 20thNight
6%426%36%24%4
720
21st to endNight
5%7%32%38%15%4
792
April1st to 10thNight
6%6%37%33%15%3
716
11th to 20thNight
5%8%35%36%13%2
533
21st to endNight
39%36%32%15%4
540
May1st to 10thNight
6%5%29%40%17%2
540
11th to 20thNight
36%23%39%23%6%
531
21st to endNight
48%25%36%22%4
584
June1st to 10thNight
4422%43%23%4
540
11th to 20thNight
25%23%46%21%3
540
21st to endNight
3119%43%30%4
540
July1st to 10thNight
6%19%37%38%9%
525
11th to 20thNight
5%26%36%41%10%
522
21st to endNight
32328%53%10%
591
August1st to 10thNight
416%38%45%6%
537
11th to 20thNight
427%40%39%8%
534
21st to endNight
419%39%37%11%
594
September1st to 10thNight
419%36%38%11%
680
11th to 20thNight
4115%39%29%11%
720
21st to endNight
4216%33%33%12%
720
October1st to 10thNight
8%220%39%24%7%
720
11th to 20thNight
5%321%38%24%9%
720
21st to endNight
3322%36%25%11%
792
November1st to 10thNight
4221%41%24%8%
740
11th to 20thNight
3220%43%25%7%
760
21st to endNight
5%423%35%26%8%
760
December1st to 10thNight
6%221%43%22%6%
760
11th to 20thNight
7%223%40%24%4
760
21st to endNight
8%427%40%19%3
836
Page generated at 2024-03-05 05:24:01. Version ac07

Copyright © 2024 Attilla Danko.


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