Mt. Norway Observatory
Clear Sky Chart
History

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

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
36%
22550
12%
74717
10%
22504
40%
22504
15%
54540

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
13%
759
7%
2646
3%
756
19%
756
6%
2223
January11th to 20thNight
17%
724
10%
2532
4%
724
25%
724
8%
2030
January21st to endNight
19%
792
13%
2650
6%
792
28%
792
10%
2069
February1st to 10thNight
19%
720
7%
2340
4%
720
23%
720
8%
1946
February11th to 20thNight
23%
700
8%
2274
3%
700
29%
700
9%
1827
February21st to endNight
20%
592
10%
1835
4%
592
28%
592
9%
1507
March1st to 10thNight
28%
720
9%
2098
6%
720
32%
720
11%
1719
March11th to 20thNight
25%
720
11%
1980
6%
720
29%
720
11%
1609
March21st to endNight
25%
792
5%
2116
3%
792
25%
792
8%
1862
April1st to 10thNight
27%
720
7%
1800
3%
720
28%
720
11%
1533
April11th to 20thNight
32%
711
10%
1779
5%
711
34%
711
14%
1431
April21st to endNight
34%
565
9%
1645
6%
565
36%
565
13%
1281
May1st to 10thNight
44%
374
13%
1454
14%
374
48%
374
15%
990
May11th to 20thNight
48%
354
11%
1416
15%
354
50%
354
13%
1014
May21st to endNight
43%
389
8%
1552
11%
388
46%
388
12%
1121
June1st to 10thNight
46%
360
7%
1440
10%
360
49%
360
15%
996
June11th to 20thNight
41%
360
7%
1440
11%
360
43%
360
14%
1013
June21st to endNight
62%
360
15%
1440
23%
360
66%
360
28%
774
July1st to 10thNight
74%
350
16%
1400
26%
350
76%
350
35%
677
July11th to 20thNight
76%
348
23%
1392
35%
348
80%
348
42%
606
July21st to endNight
84%
394
30%
1488
43%
372
88%
372
60%
530
August1st to 10thNight
76%
473
26%
1539
28%
471
78%
471
48%
714
August11th to 20thNight
80%
534
29%
1602
25%
534
81%
534
50%
777
August21st to endNight
69%
733
29%
1921
20%
733
71%
733
47%
1064
September1st to 10thNight
64%
720
27%
1800
16%
720
66%
720
48%
1033
September11th to 20thNight
56%
720
22%
1800
14%
720
58%
720
32%
1215
September21st to endNight
53%
720
20%
2054
16%
720
56%
720
28%
1340
October1st to 10thNight
48%
720
15%
2160
13%
720
52%
720
25%
1432
October11th to 20thNight
45%
720
17%
2160
17%
720
49%
720
20%
1528
October21st to endNight
31%
792
15%
2442
11%
792
38%
792
16%
1780
November1st to 10thNight
23%
740
11%
2485
9%
740
27%
740
9%
2023
November11th to 20thNight
18%
760
8%
2660
2%
760
25%
760
8%
2163
November21st to endNight
22%
760
8%
2660
4%
760
27%
760
11%
2038
December1st to 10thNight
21%
760
9%
2660
5%
760
26%
760
11%
2063
December11th to 20thNight
16%
760
8%
3212
4%
759
21%
759
5%
2605
December21st to endNight
14%
834
3%
4845
4%
817
18%
817
3%
4007

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
26%10%35%424345%33%
74730
Night
28%11%35%423335%33%
74980
TransparencyDay
55%6%10%16%10%3
74433
Night
55%6%10%16%10%3
74798
SeeingDay
30%11%23%23%10%2
13472
Night
34%7%17%24%16%2
22557

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
44%14%35%5%3334412%
1519
11th to 20thDay
42%10%235%2333423%
1440
21st to endDay
33%15%36%434345%22%
1703
February1st to 10thDay
39%13%36%5%24435%17%
1620
11th to 20thDay
35%17%37%5%3332320%
1575
21st to endDay
35%18%45%412335%19%
1419
March1st to 10thDay
35%13%47%5%34345%16%
1858
11th to 20thDay
37%13%37%5%3343419%
1980
21st to endDay
37%16%5%7%6%3433412%
2240
April1st to 10thDay
35%16%37%6%3433416%
2160
11th to 20thDay
32%14%46%5%3333422%
2129
21st to endDay
29%12%46%5%35%5%45%23%
2312
May1st to 10thDay
23%11%46%5%35%445%32%
2506
11th to 20thDay
26%9%46%6%335%5%7%27%
2477
21st to endDay
34%9%35%434446%24%
2723
June1st to 10thDay
28%10%35%5%34447%27%
2520
11th to 20thDay
27%11%37%5%345%6%6%23%
2520
21st to endDay
13%7%35%43435%7%47%
2520
July1st to 10thDay
11%5%24323446%54%
2520
11th to 20thDay
10%423324346%59%
2520
21st to endDay
8%312313335%68%
2741
August1st to 10thDay
9%5%23223436%60%
2388
11th to 20thDay
7%413323346%65%
2298
21st to endDay
11%5%2343445%7%52%
2434
September1st to 10thDay
13%313313346%60%
2160
11th to 20thDay
17%8%35%434446%43%
2160
21st to endDay
20%7%25%5%24346%41%
1904
October1st to 10thDay
25%8%35%32444438%
1800
11th to 20thDay
28%7%35%5%33447%33%
1800
21st to endDay
36%8%25%32333431%
1913
November1st to 10thDay
39%11%47%5%24345%16%
1589
11th to 20thDay
41%10%35%43334420%
1520
21st to endDay
35%12%46%42343323%
1520
December1st to 10thDay
33%13%36%5%2333426%
1520
11th to 20thDay
39%13%36%423345%19%
1928
21st to endDay
35%16%48%5%2433416%
2794
January1st to 10thNight
42%14%35%42333416%
2646
11th to 20thNight
41%12%35%412346%20%
2532
21st to endNight
35%12%35%5%2334424%
2650
February1st to 10thNight
36%15%36%42434419%
2340
11th to 20thNight
35%15%35%42333324%
2272
21st to endNight
34%18%35%423335%20%
1835
March1st to 10thNight
34%13%35%43343423%
2098
11th to 20thNight
34%12%35%5%23446%22%
1980
21st to endNight
35%18%45%5%24435%15%
2116
April1st to 10thNight
32%16%47%5%3433320%
1800
11th to 20thNight
27%14%35%6%23345%27%
1779
21st to endNight
30%13%45%324436%25%
1645
May1st to 10thNight
23%11%35%424445%37%
1454
11th to 20thNight
24%8%35%5%36%5%5%6%30%
1416
21st to endNight
24%8%36%6%345%47%30%
1552
June1st to 10thNight
24%7%35%5%24346%35%
1440
11th to 20thNight
23%11%46%434345%33%
1440
21st to endNight
12%6%24324335%55%
1440
July1st to 10thNight
8%423323245%64%
1440
11th to 20thNight
8%312323335%68%
1440
21st to endNight
5%112112245%78%
1576
August1st to 10thNight
5%413322236%68%
1547
11th to 20thNight
6%312323335%70%
1602
21st to endNight
9%413322246%64%
1921
September1st to 10thNight
10%313322345%65%
1800
11th to 20thNight
17%6%25%5%24335%48%
1800
21st to endNight
18%7%25%4235%45%46%
2054
October1st to 10thNight
24%7%25%323235%44%
2160
11th to 20thNight
26%8%25%324436%36%
2160
21st to endNight
33%8%2442333434%
2442
November1st to 10thNight
39%12%35%5%2343420%
2485
11th to 20thNight
43%11%335%2333421%
2660
21st to endNight
34%12%34433335%26%
2660
December1st to 10thNight
35%11%35%423345%25%
2660
11th to 20thNight
37%14%36%433346%18%
3276
21st to endNight
35%17%47%6%3333316%
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
78%45%7%5%1
1519
11th to 20thDay
68%310%7%8%5%
1440
21st to endDay
67%47%12%10%1
1703
February1st to 10thDay
71%5%9%8%6%
1620
11th to 20thDay
73%46%11%42
1584
21st to endDay
71%5%8%7%7%2
1419
March1st to 10thDay
70%6%8%10%5%1
1858
11th to 20thDay
71%47%12%5%1
1980
21st to endDay
78%6%8%8%1
2240
April1st to 10thDay
73%5%10%9%3
2160
11th to 20thDay
68%5%8%10%7%2
2132
21st to endDay
65%7%9%11%7%2
2312
May1st to 10thDay
55%6%14%17%8%
2506
11th to 20thDay
56%8%12%17%5%1
2480
21st to endDay
62%8%13%15%3
2724
June1st to 10thDay
57%9%13%15%5%
2520
11th to 20thDay
61%8%15%11%4
2520
21st to endDay
38%8%15%26%9%5%
2520
July1st to 10thDay
32%7%13%24%18%5%
2451
11th to 20thDay
27%6%10%25%26%5%
2445
21st to endDay
19%49%29%33%6%
2589
August1st to 10thDay
27%6%13%30%18%6%
2371
11th to 20thDay
22%6%13%32%18%9%
2298
21st to endDay
32%7%10%27%19%4
2434
September1st to 10thDay
27%5%11%24%19%13%
2160
11th to 20thDay
43%6%11%16%14%10%
2160
21st to endDay
44%6%11%17%15%7%
1904
October1st to 10thDay
51%5%7%18%15%4
1800
11th to 20thDay
52%6%10%15%14%3
1800
21st to endDay
59%5%7%13%15%1
1913
November1st to 10thDay
71%5%7%11%41
1589
11th to 20thDay
68%6%9%9%6%2
1520
21st to endDay
67%46%8%13%2
1520
December1st to 10thDay
66%5%7%11%10%2
1520
11th to 20thDay
69%413%10%4
1928
21st to endDay
74%5%9%9%3
2794
January1st to 10thNight
74%37%8%5%2
2646
11th to 20thNight
68%47%10%7%3
2532
21st to endNight
64%47%12%10%2
2650
February1st to 10thNight
70%6%8%9%6%1
2340
11th to 20thNight
66%6%9%10%6%2
2274
21st to endNight
69%49%9%7%1
1835
March1st to 10thNight
67%5%9%14%5%1
2098
11th to 20thNight
64%6%9%13%6%1
1980
21st to endNight
73%7%9%9%2
2116
April1st to 10thNight
69%6%10%11%5%
1800
11th to 20thNight
60%8%10%12%7%3
1779
21st to endNight
61%6%12%12%5%3
1645
May1st to 10thNight
50%8%12%20%9%1
1454
11th to 20thNight
51%11%14%16%5%4
1416
21st to endNight
52%10%15%18%5%
1552
June1st to 10thNight
51%7%14%21%6%
1440
11th to 20thNight
53%7%18%18%4
1440
21st to endNight
32%6%17%30%9%5%
1440
July1st to 10thNight
25%6%13%28%21%6%
1400
11th to 20thNight
20%413%27%29%6%
1392
21st to endNight
10%410%35%32%9%
1488
August1st to 10thNight
19%5%15%37%19%6%
1539
11th to 20thNight
18%5%15%34%17%10%
1602
21st to endNight
22%6%13%33%18%7%
1921
September1st to 10thNight
23%6%12%28%19%11%
1800
11th to 20thNight
39%6%11%20%11%12%
1800
21st to endNight
39%7%12%17%15%9%
2054
October1st to 10thNight
44%5%8%20%18%5%
2160
11th to 20thNight
50%6%8%14%18%4
2160
21st to endNight
55%5%7%13%16%4
2442
November1st to 10thNight
68%5%6%13%7%1
2485
11th to 20thNight
69%5%7%9%8%2
2660
21st to endNight
62%46%11%14%3
2660
December1st to 10thNight
63%5%10%10%11%1
2660
11th to 20thNight
69%5%9%10%7%
3276
21st to endNight
74%5%10%8%3
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
54%13%19%10%4
180
11th to 20thDay
53%10%21%11%5%
160
21st to endDay
48%9%19%17%6%
295
February1st to 10thDay
50%11%19%17%3
340
11th to 20thDay
49%14%19%14%41
335
21st to endDay
48%13%23%14%3
320
March1st to 10thDay
46%12%23%13%5%
420
11th to 20thDay
38%16%24%15%6%1
420
21st to endDay
45%16%16%17%5%1
462
April1st to 10thDay
45%13%21%13%6%2
420
11th to 20thDay
39%19%20%14%6%3
412
21st to endDay
33%16%25%18%7%1
420
May1st to 10thDay
24%18%26%21%8%3
423
11th to 20thDay
36%13%20%21%7%3
448
21st to endDay
32%10%21%22%10%4
485
June1st to 10thDay
29%10%20%24%13%4
450
11th to 20thDay
27%14%29%20%9%2
450
21st to endDay
11%8%32%29%16%3
450
July1st to 10thDay
15%6%25%37%13%3
446
11th to 20thDay
9%8%27%35%17%5%
444
21st to endDay
7%423%42%19%5%
487
August1st to 10thDay
10%5%21%38%19%7%
447
11th to 20thDay
6%424%39%21%6%
437
21st to endDay
11%10%27%34%14%4
495
September1st to 10thDay
14%431%32%15%3
450
11th to 20thDay
20%7%24%28%18%2
450
21st to endDay
22%11%26%29%10%2
450
October1st to 10thDay
27%9%25%27%11%2
450
11th to 20thDay
31%10%21%25%10%3
450
21st to endDay
39%13%21%17%7%3
428
November1st to 10thDay
44%17%17%16%5%1
230
11th to 20thDay
46%14%20%14%6%1
180
21st to endDay
45%12%23%18%2
180
December1st to 10thDay
44%16%19%15%7%
180
11th to 20thDay
59%12%18%9%2
180
21st to endDay
54%10%21%12%5%
198
January1st to 10thNight
50%12%21%13%31
760
11th to 20thNight
48%8%20%17%5%
724
21st to endNight
43%8%23%18%7%1
792
February1st to 10thNight
45%8%22%19%6%1
720
11th to 20thNight
46%8%18%21%7%
704
21st to endNight
48%9%17%19%6%
592
March1st to 10thNight
41%10%16%23%10%1
720
11th to 20thNight
40%10%20%22%9%
720
21st to endNight
47%7%14%22%9%2
792
April1st to 10thNight
42%8%14%23%11%1
720
11th to 20thNight
34%9%18%22%14%3
711
21st to endNight
36%8%15%26%14%1
565
May1st to 10thNight
25%7%17%27%21%2
374
11th to 20thNight
25%6%13%27%26%4
354
21st to endNight
25%5%16%25%25%3
389
June1st to 10thNight
28%5%14%28%23%2
360
11th to 20thNight
26%7%18%27%20%1
360
21st to endNight
12%6%16%33%32%1
360
July1st to 10thNight
10%38%34%43%2
350
11th to 20thNight
8%210%43%34%3
348
21st to endNight
338%39%42%5%
394
August1st to 10thNight
8%18%29%48%6%
473
11th to 20thNight
7%17%31%44%10%
534
21st to endNight
10%412%39%30%4
733
September1st to 10thNight
12%316%34%30%4
720
11th to 20thNight
18%313%30%30%5%
720
21st to endNight
21%416%33%24%3
720
October1st to 10thNight
26%416%30%20%4
720
11th to 20thNight
31%6%13%31%17%3
720
21st to endNight
38%7%20%24%10%2
792
November1st to 10thNight
45%7%19%21%8%
740
11th to 20thNight
49%9%21%16%4
760
21st to endNight
41%9%24%22%4
760
December1st to 10thNight
42%10%24%17%6%1
760
11th to 20thNight
51%9%19%18%3
760
21st to endNight
53%12%17%15%3
836
Page generated at 2024-01-08 08:14:18. Version ac07

Copyright 2024 Attilla Danko


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