Ursae Majoris Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ursae Majoris 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
39%
22386
10%
74283
10%
22345
41%
22345
14%
55983

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
20%
760
6%
2646
5%
756
23%
756
6%
2242
January11th to 20thNight
31%
744
9%
2604
8%
744
33%
744
10%
2049
January21st to endNight
31%
792
8%
2714
9%
792
33%
792
11%
2148
February1st to 10thNight
27%
720
7%
2340
5%
720
29%
720
8%
1941
February11th to 20thNight
30%
700
8%
2274
6%
700
33%
700
10%
1832
February21st to endNight
26%
592
9%
1856
6%
592
30%
592
9%
1513
March1st to 10thNight
31%
720
8%
2117
6%
720
34%
720
13%
1671
March11th to 20thNight
29%
720
11%
1980
8%
720
32%
720
12%
1593
March21st to endNight
26%
792
5%
2105
2%
792
27%
792
8%
1844
April1st to 10thNight
31%
720
5%
1800
2%
720
32%
720
10%
1531
April11th to 20thNight
35%
699
9%
1767
5%
699
37%
699
15%
1411
April21st to endNight
36%
504
6%
1584
6%
504
36%
504
10%
1283
May1st to 10thNight
42%
360
9%
1440
12%
360
44%
360
12%
1039
May11th to 20thNight
48%
354
9%
1416
13%
354
49%
354
12%
1027
May21st to endNight
42%
388
5%
1552
8%
388
44%
388
10%
1178
June1st to 10thNight
44%
360
4%
1440
6%
360
44%
360
12%
1049
June11th to 20thNight
41%
360
3%
1268
5%
360
41%
360
11%
983
June21st to endNight
58%
360
10%
1260
13%
360
60%
360
24%
778
July1st to 10thNight
66%
350
11%
1225
15%
350
67%
350
27%
722
July11th to 20thNight
70%
348
17%
1373
29%
348
71%
348
28%
734
July21st to endNight
77%
394
23%
1488
37%
372
79%
372
41%
658
August1st to 10thNight
74%
405
20%
1471
26%
403
75%
403
35%
740
August11th to 20thNight
77%
534
24%
1602
23%
534
77%
534
41%
872
August21st to endNight
65%
709
22%
1897
17%
709
65%
709
35%
1169
September1st to 10thNight
65%
720
20%
1800
13%
720
66%
720
38%
1136
September11th to 20thNight
56%
720
18%
1800
12%
720
57%
720
26%
1292
September21st to endNight
52%
720
17%
2052
15%
720
53%
720
24%
1414
October1st to 10thNight
46%
720
11%
2160
11%
720
48%
720
20%
1520
October11th to 20thNight
42%
720
13%
2160
13%
720
44%
720
16%
1613
October21st to endNight
36%
792
12%
2479
10%
792
39%
792
14%
1866
November1st to 10thNight
26%
740
6%
2531
7%
740
28%
740
9%
2050
November11th to 20thNight
26%
760
8%
2660
7%
760
29%
760
9%
2149
November21st to endNight
30%
760
6%
2660
5%
760
31%
760
9%
2119
December1st to 10thNight
29%
760
9%
2660
9%
760
31%
760
10%
2086
December11th to 20thNight
23%
759
4%
3259
3%
759
25%
759
6%
2677
December21st to endNight
19%
830
3%
4843
5%
817
20%
817
3%
4054

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
21%9%36%6%35%5%5%6%31%
75319
Night
23%8%36%6%35%45%6%31%
74497
TransparencyDay
54%9%13%15%7%1
75016
Night
55%9%12%15%7%1
74319
SeeingDay
25%11%21%25%15%3
13887
Night
28%9%17%26%18%2
22398

By Month

Percentage Cloud Cover NW (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
36%12%47%7%45%44316%
1519
11th to 20thDay
28%9%46%7%35%5%5%7%20%
1483
21st to endDay
32%11%47%6%35%45%6%17%
1638
February1st to 10thDay
32%11%46%6%3445%8%18%
1620
11th to 20thDay
33%11%47%7%34246%19%
1575
21st to endDay
27%12%5%7%7%46%445%20%
1399
March1st to 10thDay
25%12%48%8%46%5%5%6%19%
1840
11th to 20thDay
31%11%46%5%45%45%5%19%
1980
21st to endDay
26%12%48%6%47%6%6%6%14%
2250
April1st to 10thDay
26%11%47%7%46%5%5%6%18%
2160
11th to 20thDay
24%9%47%7%5%5%5%5%7%23%
2140
21st to endDay
20%9%5%8%8%5%5%5%6%6%23%
2375
May1st to 10thDay
18%9%26%6%45%6%5%7%32%
2520
11th to 20thDay
19%9%36%7%45%6%6%8%28%
2477
21st to endDay
24%9%48%6%35%5%5%6%25%
2723
June1st to 10thDay
22%8%37%6%36%45%8%28%
2520
11th to 20thDay
22%9%38%6%45%6%5%7%22%
2687
21st to endDay
12%7%36%6%45%46%8%40%
2700
July1st to 10thDay
11%5%35%5%25%445%51%
2700
11th to 20thDay
10%5%2442445%7%52%
2538
21st to endDay
8%423323346%63%
2741
August1st to 10thDay
9%5%24424447%55%
2457
11th to 20thDay
7%42442345%8%57%
2298
21st to endDay
11%6%36%5%345%47%47%
2458
September1st to 10thDay
10%5%25%5%33447%51%
2160
11th to 20thDay
14%6%46%6%4446%7%40%
2160
21st to endDay
18%7%26%5%345%5%7%40%
1904
October1st to 10thDay
20%9%37%5%345%5%6%31%
1800
11th to 20thDay
25%9%36%5%35%5%48%28%
1800
21st to endDay
29%9%37%6%34446%24%
1876
November1st to 10thDay
33%9%47%5%35%5%5%6%19%
1542
11th to 20thDay
30%12%36%5%35%446%21%
1520
21st to endDay
29%10%47%6%4435%6%21%
1520
December1st to 10thDay
29%7%47%445%45%5%25%
1520
11th to 20thDay
33%12%37%8%5%6%5%45%13%
1925
21st to endDay
27%13%49%9%45%446%15%
2794
January1st to 10thNight
38%10%46%5%34445%16%
2646
11th to 20thNight
33%10%36%5%34346%23%
2604
21st to endNight
30%9%38%6%34446%22%
2714
February1st to 10thNight
32%11%46%6%44446%20%
2340
11th to 20thNight
29%10%36%6%35%445%24%
2272
21st to endNight
27%11%36%6%345%5%5%23%
1856
March1st to 10thNight
26%11%46%435%5%5%7%25%
2117
11th to 20thNight
28%9%46%6%35%5%46%25%
1979
21st to endNight
27%13%47%6%46%5%6%5%18%
2105
April1st to 10thNight
23%10%38%6%36%7%5%7%22%
1800
11th to 20thNight
19%9%47%7%36%5%6%7%28%
1767
21st to endNight
20%8%37%6%45%5%5%8%27%
1584
May1st to 10thNight
17%8%47%7%35%46%6%34%
1440
11th to 20thNight
15%6%36%7%46%6%6%8%33%
1416
21st to endNight
16%7%47%6%45%6%5%7%33%
1552
June1st to 10thNight
16%6%46%7%37%5%47%35%
1440
11th to 20thNight
17%7%37%7%45%45%10%30%
1268
21st to endNight
10%5%45%335%45%7%48%
1260
July1st to 10thNight
8%5%2433435%7%56%
1260
11th to 20thNight
7%425%424435%61%
1419
21st to endNight
6%212223346%70%
1576
August1st to 10thNight
5%31442445%8%61%
1479
11th to 20thNight
7%213422336%66%
1602
21st to endNight
10%42442345%6%56%
1897
September1st to 10thNight
9%4244245%47%56%
1800
11th to 20thNight
15%6%35%5%35%346%46%
1800
21st to endNight
16%7%25%5%34346%43%
2052
October1st to 10thNight
19%6%27%6%3345%6%38%
2160
11th to 20thNight
24%7%37%5%34445%34%
2160
21st to endNight
27%7%25%5%3445%6%32%
2479
November1st to 10thNight
33%8%25%6%45%5%5%423%
2531
11th to 20thNight
30%9%46%7%34445%23%
2660
21st to endNight
29%10%46%6%35%5%5%5%23%
2660
December1st to 10thNight
28%10%37%7%34445%25%
2660
11th to 20thNight
29%12%48%7%5%6%44416%
3280
21st to endNight
29%11%5%9%8%5%5%44415%
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
73%7%5%10%41
1519
11th to 20thDay
61%10%12%8%6%2
1483
21st to endDay
63%8%11%12%5%1
1638
February1st to 10thDay
67%9%11%8%41
1620
11th to 20thDay
67%9%9%10%5%1
1584
21st to endDay
68%8%11%9%5%
1399
March1st to 10thDay
65%9%11%12%2
1840
11th to 20thDay
68%8%8%12%21
1980
21st to endDay
72%10%10%8%
2250
April1st to 10thDay
67%11%14%8%1
2160
11th to 20thDay
63%8%11%12%5%1
2140
21st to endDay
64%10%12%10%41
2375
May1st to 10thDay
53%11%17%14%5%
2520
11th to 20thDay
55%12%17%13%4
2480
21st to endDay
61%11%14%12%1
2724
June1st to 10thDay
59%10%17%10%4
2520
11th to 20thDay
64%10%14%10%2
2687
21st to endDay
44%10%19%18%8%2
2700
July1st to 10thDay
36%10%15%23%13%2
2626
11th to 20thDay
33%7%14%28%16%1
2462
21st to endDay
23%7%13%36%18%4
2589
August1st to 10thDay
32%8%16%28%14%2
2440
11th to 20thDay
27%8%18%29%15%3
2298
21st to endDay
38%8%14%29%9%1
2458
September1st to 10thDay
33%8%16%25%13%5%
2160
11th to 20thDay
43%11%12%17%14%2
2160
21st to endDay
45%9%16%16%11%2
1904
October1st to 10thDay
51%9%13%19%7%1
1800
11th to 20thDay
53%9%16%15%5%1
1800
21st to endDay
61%7%11%12%9%
1876
November1st to 10thDay
67%9%10%11%3
1542
11th to 20thDay
66%10%8%8%7%2
1520
21st to endDay
64%9%8%10%9%1
1520
December1st to 10thDay
61%8%10%11%8%1
1520
11th to 20thDay
67%10%12%9%21
1928
21st to endDay
67%11%11%8%3
2794
January1st to 10thNight
70%8%9%7%42
2646
11th to 20thNight
63%7%11%11%6%2
2604
21st to endNight
62%8%10%10%7%2
2714
February1st to 10thNight
68%7%11%9%5%1
2340
11th to 20thNight
63%9%10%10%7%1
2274
21st to endNight
63%10%11%11%5%
1856
March1st to 10thNight
59%9%13%15%4
2117
11th to 20thNight
63%7%10%15%41
1980
21st to endNight
67%13%11%9%1
2105
April1st to 10thNight
63%12%13%9%2
1800
11th to 20thNight
57%10%13%13%6%1
1767
21st to endNight
61%11%12%11%41
1584
May1st to 10thNight
52%11%15%14%8%1
1440
11th to 20thNight
51%12%17%13%6%1
1416
21st to endNight
55%13%15%15%2
1552
June1st to 10thNight
54%10%17%14%5%
1440
11th to 20thNight
56%12%19%11%2
1268
21st to endNight
38%9%22%20%9%2
1260
July1st to 10thNight
32%10%15%24%14%4
1225
11th to 20thNight
31%7%12%31%18%2
1373
21st to endNight
18%8%12%36%21%5%
1488
August1st to 10thNight
26%6%15%31%19%3
1471
11th to 20thNight
23%9%18%31%16%4
1602
21st to endNight
33%7%16%30%13%1
1897
September1st to 10thNight
29%9%16%26%15%5%
1800
11th to 20thNight
43%10%10%19%14%5%
1800
21st to endNight
42%10%13%20%13%3
2052
October1st to 10thNight
47%8%14%22%8%1
2160
11th to 20thNight
54%8%11%18%8%1
2160
21st to endNight
55%9%11%15%10%
2479
November1st to 10thNight
63%10%12%10%4
2531
11th to 20thNight
64%8%10%9%6%2
2660
21st to endNight
63%9%9%10%8%1
2660
December1st to 10thNight
63%7%10%11%7%1
2660
11th to 20thNight
66%10%13%8%3
3276
21st to endNight
67%13%10%7%2
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
37%17%15%15%14%3
180
11th to 20thDay
30%15%20%21%10%4
171
21st to endDay
42%10%17%17%12%3
230
February1st to 10thDay
44%9%19%16%11%1
340
11th to 20thDay
43%13%20%14%8%1
335
21st to endDay
36%15%22%19%7%
310
March1st to 10thDay
31%17%25%19%7%1
420
11th to 20thDay
33%16%20%20%9%2
420
21st to endDay
35%15%25%17%8%
462
April1st to 10thDay
36%15%20%18%10%1
420
11th to 20thDay
28%18%26%16%7%5%
412
21st to endDay
25%16%27%23%8%1
420
May1st to 10thDay
22%12%24%29%11%2
423
11th to 20thDay
27%8%22%26%13%4
448
21st to endDay
28%7%24%26%12%3
485
June1st to 10thDay
26%9%23%22%15%4
450
11th to 20thDay
23%12%28%24%11%2
617
21st to endDay
14%8%21%32%22%3
630
July1st to 10thDay
13%5%17%37%25%3
621
11th to 20thDay
11%5%21%39%20%3
461
21st to endDay
8%415%40%28%5%
487
August1st to 10thDay
13%5%13%36%26%8%
447
11th to 20thDay
6%6%11%39%29%9%
437
21st to endDay
13%8%23%33%16%6%
495
September1st to 10thDay
15%6%26%36%15%4
450
11th to 20thDay
19%7%20%29%21%4
450
21st to endDay
19%11%22%26%19%2
450
October1st to 10thDay
26%10%20%21%19%4
450
11th to 20thDay
30%11%14%23%15%5%
450
21st to endDay
32%15%20%18%10%4
391
November1st to 10thDay
38%14%16%18%12%
207
11th to 20thDay
41%12%16%11%14%6%
180
21st to endDay
33%14%18%16%11%8%
180
December1st to 10thDay
46%9%14%12%12%7%
180
11th to 20thDay
41%12%18%19%9%1
180
21st to endDay
39%13%15%21%11%2
198
January1st to 10thNight
41%16%16%17%9%1
760
11th to 20thNight
38%10%16%24%12%1
744
21st to endNight
34%9%16%29%12%1
792
February1st to 10thNight
39%10%17%25%8%1
720
11th to 20thNight
36%12%15%25%11%1
704
21st to endNight
35%12%21%21%9%1
592
March1st to 10thNight
30%13%20%23%13%1
720
11th to 20thNight
32%13%18%26%11%1
720
21st to endNight
33%15%18%23%10%1
792
April1st to 10thNight
31%10%19%25%13%2
720
11th to 20thNight
27%12%20%26%14%2
699
21st to endNight
26%11%19%29%14%1
504
May1st to 10thNight
20%12%18%31%19%1
360
11th to 20thNight
22%5%16%30%26%1
354
21st to endNight
22%8%16%27%24%3
389
June1st to 10thNight
21%8%19%26%23%2
360
11th to 20thNight
24%8%20%29%18%1
360
21st to endNight
15%417%35%28%2
360
July1st to 10thNight
11%215%32%35%4
350
11th to 20thNight
11%211%41%32%3
348
21st to endNight
6%311%31%45%4
394
August1st to 10thNight
11%29%30%39%9%
405
11th to 20thNight
9%27%29%43%10%
534
21st to endNight
12%413%30%36%5%
709
September1st to 10thNight
13%412%36%32%3
720
11th to 20thNight
19%5%12%23%35%6%
720
21st to endNight
20%5%15%30%27%2
720
October1st to 10thNight
24%5%15%28%27%2
720
11th to 20thNight
28%8%15%27%19%4
720
21st to endNight
32%8%17%26%14%3
792
November1st to 10thNight
36%10%21%24%7%
740
11th to 20thNight
36%11%19%23%10%1
760
21st to endNight
34%12%18%23%13%1
760
December1st to 10thNight
31%10%22%25%12%1
760
11th to 20thNight
39%10%19%23%8%1
760
21st to endNight
46%11%17%18%7%
836
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