Cascade Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cascade Mountain Observatory clear sky chart from 2005-11-06 to 2024-01-31.

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
47%
24223
25%
74795
18%
24165
55%
24165
31%
44082

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
28%
949
26%
2458
9%
946
40%
946
30%
1581
January11th to 20thNight
25%
950
25%
2470
7%
950
37%
950
27%
1619
January21st to endNight
27%
1043
28%
2711
9%
1043
39%
1043
32%
1706
February1st to 10thNight
26%
900
20%
2340
7%
900
33%
900
25%
1585
February11th to 20thNight
24%
748
21%
2144
8%
745
33%
745
25%
1395
February21st to endNight
22%
587
25%
1771
9%
587
35%
587
23%
1143
March1st to 10thNight
31%
540
25%
1980
15%
540
44%
540
25%
1167
March11th to 20thNight
29%
540
20%
1980
13%
540
40%
540
20%
1257
March21st to endNight
31%
594
19%
2165
12%
594
42%
594
22%
1339
April1st to 10thNight
35%
540
27%
1800
17%
540
49%
540
30%
1005
April11th to 20thNight
37%
533
27%
1775
19%
533
51%
533
30%
1007
April21st to endNight
36%
540
24%
1800
16%
540
51%
540
29%
1041
May1st to 10thNight
49%
540
20%
1800
17%
540
58%
540
28%
1067
May11th to 20thNight
46%
531
23%
1629
20%
531
53%
531
31%
990
May21st to endNight
60%
584
21%
1692
17%
582
65%
582
32%
1045
June1st to 10thNight
71%
540
25%
1440
20%
540
75%
540
44%
825
June11th to 20thNight
80%
540
28%
1440
27%
540
82%
540
51%
776
June21st to endNight
78%
540
29%
1490
26%
540
80%
540
50%
802
July1st to 10thNight
77%
525
21%
1575
23%
525
78%
525
40%
872
July11th to 20thNight
81%
522
22%
1566
25%
522
83%
522
44%
831
July21st to endNight
78%
591
27%
1673
30%
558
79%
558
43%
896
August1st to 10thNight
78%
537
22%
1601
26%
534
78%
534
43%
879
August11th to 20thNight
75%
534
25%
1771
30%
534
77%
534
37%
959
August21st to endNight
75%
594
23%
1980
28%
594
76%
594
35%
1097
September1st to 10thNight
75%
540
28%
1800
32%
540
77%
540
37%
973
September11th to 20thNight
66%
540
32%
1800
32%
540
69%
540
34%
1002
September21st to endNight
69%
643
31%
2045
28%
643
73%
643
41%
1070
October1st to 10thNight
65%
720
31%
2160
26%
720
69%
720
44%
1146
October11th to 20thNight
49%
720
34%
2160
20%
720
60%
720
39%
1182
October21st to endNight
44%
792
30%
2376
20%
792
52%
792
31%
1431
November1st to 10thNight
50%
740
33%
2220
22%
740
60%
740
38%
1220
November11th to 20thNight
43%
760
31%
2391
19%
760
56%
760
37%
1277
November21st to endNight
38%
788
27%
2498
18%
788
48%
788
29%
1487
December1st to 10thNight
32%
950
23%
2660
10%
950
44%
950
28%
1709
December11th to 20thNight
34%
948
25%
3104
12%
948
43%
948
23%
1924
December21st to endNight
27%
1040
15%
4530
9%
1026
39%
1026
16%
2777

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
13%5%25%5%35%5%5%7%45%
74786
Night
13%5%2442445%7%50%
75338
TransparencyDay
38%5%11%23%19%4
74510
Night
34%410%24%22%6%
75135
SeeingDay
15%9%22%26%21%7%
14274
Night
15%8%25%32%18%2
24231

By Month

Percentage Cloud Cover SE (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
20%6%35%42334446%
1707
11th to 20thDay
17%7%46%5%33346%43%
1710
21st to endDay
17%7%33423336%50%
1872
February1st to 10thDay
22%8%26%423325%43%
1620
11th to 20thDay
18%6%46%5%24445%41%
1702
21st to endDay
24%7%36%423345%37%
1501
March1st to 10thDay
19%6%25%5%34445%44%
1980
11th to 20thDay
20%6%37%5%3444441%
1980
21st to endDay
18%7%35%5%45%445%40%
2191
April1st to 10thDay
14%6%245%35%35%8%44%
2160
11th to 20thDay
16%5%246%34446%44%
2134
21st to endDay
16%6%37%5%35%45%6%41%
2160
May1st to 10thDay
16%7%25%6%35%5%46%41%
2160
11th to 20thDay
13%6%25%435%6%7%9%41%
2262
21st to endDay
8%5%36%7%5%6%6%7%10%37%
2575
June1st to 10thDay
8%5%25%6%36%6%7%9%42%
2520
11th to 20thDay
5%3245%46%5%7%11%48%
2520
21st to endDay
5%324436%5%7%9%52%
2463
July1st to 10thDay
5%437%6%47%7%7%10%38%
2340
11th to 20thDay
6%426%5%36%7%7%11%44%
2340
21st to endDay
7%4345%46%5%7%9%45%
2546
August1st to 10thDay
7%426%6%46%6%7%10%42%
2328
11th to 20thDay
10%5%25%436%5%6%9%44%
2130
21st to endDay
8%5%26%5%36%5%6%9%46%
2376
September1st to 10thDay
12%5%245%35%6%5%8%46%
2160
11th to 20thDay
13%4244445%6%8%46%
2160
21st to endDay
10%5%2343445%6%54%
1893
October1st to 10thDay
8%4245%23446%58%
1800
11th to 20thDay
14%5%23323346%55%
1800
21st to endDay
19%424323345%50%
1980
November1st to 10thDay
12%5%24323337%58%
1858
11th to 20thDay
11%5%35%323445%54%
1786
21st to endDay
20%7%25%422345%45%
1677
December1st to 10thDay
19%6%35%42334448%
1520
11th to 20thDay
15%8%36%6%34435%44%
1918
21st to endDay
16%7%37%6%3445%6%38%
2957
January1st to 10thNight
19%6%23323245%49%
2458
11th to 20thNight
17%6%26%42335%448%
2470
21st to endNight
18%424323435%51%
2711
February1st to 10thNight
20%7%35%5%23346%42%
2340
11th to 20thNight
18%7%36%423335%45%
2143
21st to endNight
19%6%24424335%46%
1771
March1st to 10thNight
18%6%2432445%5%47%
1980
11th to 20thNight
17%7%35%6%3435%5%43%
1980
21st to endNight
16%6%35%6%34446%43%
2165
April1st to 10thNight
11%5%25%4235%5%7%51%
1800
11th to 20thNight
12%5%2443446%7%50%
1775
21st to endNight
14%5%25%5%2445%7%48%
1800
May1st to 10thNight
15%5%244245%5%6%48%
1800
11th to 20thNight
14%6%25%42345%8%47%
1629
21st to endNight
8%425%5%47%5%7%10%44%
1691
June1st to 10thNight
6%4133345%7%11%52%
1440
11th to 20thNight
322443445%9%61%
1440
21st to endNight
43133245%6%9%60%
1490
July1st to 10thNight
43245%35%6%7%11%51%
1620
11th to 20thNight
4214435%6%7%11%54%
1620
21st to endNight
4315%425%46%12%54%
1772
August1st to 10thNight
3225%6%446%7%10%51%
1611
11th to 20thNight
7%325%5%345%7%9%51%
1771
21st to endNight
5%325%7%35%5%5%10%50%
1980
September1st to 10thNight
7%425%424448%56%
1800
11th to 20thNight
10%425%5%24447%54%
1800
21st to endNight
8%5%13423347%60%
2045
October1st to 10thNight
8%324423346%61%
2160
11th to 20thNight
12%314323435%60%
2160
21st to endNight
17%5%2443322454%
2376
November1st to 10thNight
10%5%24423345%58%
2220
11th to 20thNight
13%323423346%57%
2391
21st to endNight
15%5%25%43435%5%49%
2498
December1st to 10thNight
20%5%245%24445%46%
2660
11th to 20thNight
17%5%345%3343449%
3279
21st to endNight
17%7%35%5%34446%42%
4692

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
43%36%23%19%6%
1708
11th to 20thDay
44%48%23%19%2
1710
21st to endDay
39%37%25%21%5%
1872
February1st to 10thDay
45%410%21%16%3
1620
11th to 20thDay
46%47%20%18%4
1712
21st to endDay
50%47%15%16%8%
1501
March1st to 10thDay
44%39%17%19%9%
1980
11th to 20thDay
47%48%20%17%4
1980
21st to endDay
46%411%24%13%2
2191
April1st to 10thDay
39%5%9%23%21%3
2160
11th to 20thDay
41%5%8%23%17%6%
2134
21st to endDay
43%5%9%23%18%2
2160
May1st to 10thDay
44%6%12%18%18%2
2160
11th to 20thDay
38%7%15%24%14%1
2266
21st to endDay
40%8%14%25%12%1
2575
June1st to 10thDay
36%7%12%27%17%2
2520
11th to 20thDay
28%7%16%29%18%2
2520
21st to endDay
27%7%13%27%21%4
2463
July1st to 10thDay
35%10%17%23%14%1
2276
11th to 20thDay
31%9%14%26%17%4
2271
21st to endDay
32%7%17%30%12%1
2405
August1st to 10thDay
34%8%17%28%12%1
2314
11th to 20thDay
36%8%13%25%17%2
2130
21st to endDay
33%8%14%26%15%4
2376
September1st to 10thDay
36%7%10%22%18%7%
2160
11th to 20thDay
35%6%11%18%25%5%
2160
21st to endDay
31%5%9%21%28%7%
1893
October1st to 10thDay
28%5%9%24%28%7%
1800
11th to 20thDay
32%36%21%29%9%
1800
21st to endDay
37%37%23%21%9%
1980
November1st to 10thDay
30%39%26%25%8%
1858
11th to 20thDay
31%38%22%27%9%
1786
21st to endDay
43%36%19%23%6%
1677
December1st to 10thDay
42%39%25%17%5%
1520
11th to 20thDay
44%46%20%21%5%
1915
21st to endDay
44%6%9%19%17%5%
2957
January1st to 10thNight
39%37%20%26%4
2458
11th to 20thNight
41%49%22%20%4
2470
21st to endNight
37%36%25%24%5%
2711
February1st to 10thNight
45%38%20%18%5%
2340
11th to 20thNight
44%36%23%19%6%
2144
21st to endNight
43%36%18%20%9%
1771
March1st to 10thNight
40%38%16%21%11%
1980
11th to 20thNight
45%5%8%20%17%6%
1980
21st to endNight
43%49%22%19%3
2165
April1st to 10thNight
33%411%25%20%7%
1800
11th to 20thNight
33%5%8%24%21%9%
1775
21st to endNight
35%411%24%23%2
1800
May1st to 10thNight
36%5%11%24%19%5%
1800
11th to 20thNight
36%6%13%25%18%2
1630
21st to endNight
35%6%16%26%15%2
1692
June1st to 10thNight
26%6%14%30%22%2
1440
11th to 20thNight
21%5%13%32%26%3
1440
21st to endNight
21%5%14%28%25%7%
1490
July1st to 10thNight
25%8%19%29%17%2
1575
11th to 20thNight
22%8%19%29%16%6%
1566
21st to endNight
23%7%16%35%19%1
1673
August1st to 10thNight
25%6%20%36%13%1
1601
11th to 20thNight
27%7%15%29%20%2
1771
21st to endNight
29%6%15%26%19%4
1980
September1st to 10thNight
28%6%11%25%22%8%
1800
11th to 20thNight
32%5%9%22%26%7%
1800
21st to endNight
25%5%9%22%29%9%
2045
October1st to 10thNight
25%410%24%25%11%
2160
11th to 20thNight
29%35%20%32%10%
2160
21st to endNight
37%36%19%26%9%
2376
November1st to 10thNight
29%47%24%26%10%
2220
11th to 20thNight
29%36%26%27%10%
2391
21st to endNight
38%37%21%27%5%
2498
December1st to 10thNight
42%38%20%21%6%
2660
11th to 20thNight
40%46%21%25%5%
3281
21st to endNight
43%49%22%19%3
4692

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
27%19%29%19%5%1
270
11th to 20thDay
25%21%40%12%11
270
21st to endDay
21%21%38%17%3
294
February1st to 10thDay
26%20%33%15%41
240
11th to 20thDay
25%29%32%12%2
240
21st to endDay
36%19%32%11%3
198
March1st to 10thDay
25%19%35%17%4
240
11th to 20thDay
30%25%27%18%1
240
21st to endDay
25%22%36%13%4
277
April1st to 10thDay
19%16%33%23%8%1
420
11th to 20thDay
22%13%33%21%9%1
412
21st to endDay
19%15%32%22%10%2
420
May1st to 10thDay
19%12%29%28%11%1
423
11th to 20thDay
16%6%25%28%19%5%
585
21st to endDay
9%5%24%35%22%6%
679
June1st to 10thDay
10%417%28%29%11%
630
11th to 20thDay
5%216%38%31%9%
630
21st to endDay
6%317%35%28%12%
630
July1st to 10thDay
6%210%30%38%15%
621
11th to 20thDay
6%210%30%35%17%
618
21st to endDay
6%110%29%37%16%
684
August1st to 10thDay
7%29%35%36%11%
626
11th to 20thDay
15%37%29%34%12%
444
21st to endDay
11%16%23%39%20%
495
September1st to 10thDay
10%210%24%38%16%
450
11th to 20thDay
10%213%23%40%12%
450
21st to endDay
12%5%14%35%25%9%
304
October1st to 10thDay
9%430%30%22%5%
270
11th to 20thDay
13%15%34%23%14%2
270
21st to endDay
27%12%31%20%9%1
297
November1st to 10thDay
15%13%31%24%16%1
270
11th to 20thDay
11%16%37%27%8%1
270
21st to endDay
27%16%26%20%10%1
270
December1st to 10thDay
22%20%29%20%7%2
270
11th to 20thDay
25%18%32%17%9%
270
21st to endDay
24%20%36%17%21
297
January1st to 10thNight
23%10%35%26%5%
950
11th to 20thNight
22%13%36%26%31
950
21st to endNight
20%12%38%27%3
1043
February1st to 10thNight
24%13%33%26%4
900
11th to 20thNight
21%15%37%25%2
748
21st to endNight
24%15%38%20%3
587
March1st to 10thNight
20%10%35%31%4
540
11th to 20thNight
19%13%35%27%41
540
21st to endNight
17%12%35%27%8%
594
April1st to 10thNight
14%12%37%29%8%
540
11th to 20thNight
15%10%35%28%11%1
533
21st to endNight
16%8%36%29%11%
540
May1st to 10thNight
16%6%24%42%12%
540
11th to 20thNight
14%6%29%30%18%3
531
21st to endNight
8%419%40%24%6%
584
June1st to 10thNight
6%313%35%38%5%
540
11th to 20thNight
318%49%36%4
540
21st to endNight
5%111%39%38%7%
540
July1st to 10thNight
417%35%43%10%
525
11th to 20thNight
427%31%47%9%
522
21st to endNight
5%18%36%44%7%
591
August1st to 10thNight
316%41%41%9%
537
11th to 20thNight
8%18%38%38%7%
534
21st to endNight
6%19%32%45%7%
594
September1st to 10thNight
9%26%39%39%6%
540
11th to 20thNight
8%212%35%38%4
540
21st to endNight
9%414%36%35%4
643
October1st to 10thNight
10%218%34%31%4
720
11th to 20thNight
14%5%28%35%17%1
720
21st to endNight
19%8%27%31%14%1
792
November1st to 10thNight
14%6%26%37%15%1
740
11th to 20thNight
14%8%31%35%12%
760
21st to endNight
18%9%31%28%13%
788
December1st to 10thNight
22%9%33%30%7%
950
11th to 20thNight
23%10%28%33%6%
950
21st to endNight
22%13%32%27%5%
1045
Page generated at 2024-01-28 04:26:32. Version ac07

Copyright 2024 Attilla Danko


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