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 2005-11-05 to 2017-12-02.

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
48%
15968
26%
47917
18%
15923
56%
15923
33%
28227

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 15thNight
29%
899
28%
2327
10%
895
41%
895
31%
1474
January16th to endNight
28%
960
27%
2496
10%
960
39%
960
31%
1584
February1st to 15thNight
28%
853
21%
2262
7%
850
36%
850
29%
1456
February16th to endNight
26%
628
27%
1890
11%
628
39%
628
30%
1131
March1st to 15thNight
29%
540
22%
1980
14%
540
40%
540
23%
1216
March16th to endNight
37%
576
20%
2103
17%
576
46%
576
24%
1290
April1st to 15thNight
37%
539
26%
1797
16%
539
52%
539
31%
998
April16th to endNight
40%
540
25%
1800
19%
540
53%
540
31%
1016
May1st to 15thNight
48%
540
19%
1764
16%
540
56%
540
26%
1101
May16th to endNight
55%
563
22%
1648
19%
561
60%
561
32%
1015
June1st to 15thNight
78%
540
26%
1440
21%
540
81%
540
50%
784
June16th to endNight
77%
540
28%
1473
25%
540
79%
540
46%
828
July1st to 15thNight
75%
510
19%
1530
20%
510
77%
510
36%
876
July16th to endNight
83%
564
25%
1594
28%
531
84%
531
44%
846
August1st to 15thNight
78%
539
24%
1667
27%
536
79%
536
42%
891
August16th to endNight
76%
573
23%
1910
29%
573
77%
573
33%
1096
September1st to 15thNight
69%
540
26%
1800
28%
540
71%
540
33%
1030
September16th to endNight
68%
606
34%
1964
32%
606
71%
606
38%
1055
October1st to 15thNight
59%
720
31%
2160
25%
720
64%
720
39%
1202
October16th to endNight
51%
768
37%
2304
24%
768
62%
768
41%
1236
November1st to 15thNight
47%
760
31%
2290
21%
760
56%
760
35%
1290
November16th to endNight
41%
800
30%
2555
20%
800
52%
800
31%
1469
December1st to 15thNight
35%
910
21%
2547
10%
910
43%
910
28%
1646
December16th to endNight
31%
960
23%
2616
10%
960
41%
960
27%
1697

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%2443445%7%44%
48514
Night
12%424423446%50%
48114
TransparencyDay
38%5%10%23%18%4
48215
Night
33%410%24%21%5%
47918
SeeingDay
12%5%19%26%25%9%
5949
Night
14%6%25%31%19%2
15969

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 15thDay
20%42332233448%
1611
16th to endDay
15%5%34423235%47%
1728
February1st to 15thDay
17%6%24413325%47%
1599
16th to endDay
17%6%35%42335%6%40%
1594
March1st to 15thDay
20%6%24434345%41%
1980
16th to endDay
17%6%35%434345%41%
2119
April1st to 15thDay
14%6%24424346%46%
2151
16th to endDay
15%5%25%6%35%446%40%
2160
May1st to 15thDay
16%7%145%35%5%46%39%
2184
16th to endDay
9%5%36%6%45%6%6%9%35%
2463
June1st to 15thDay
5%425%5%36%6%7%9%43%
2520
16th to endDay
6%2245%35%6%7%10%45%
2481
July1st to 15thDay
6%5%37%6%46%7%6%10%35%
2340
16th to endDay
6%3245%46%6%6%8%44%
2466
August1st to 15thDay
7%425%5%35%6%7%9%41%
2283
16th to endDay
8%415%6%36%5%7%8%41%
2292
September1st to 15thDay
13%5%134345%5%7%43%
2160
16th to endDay
12%422334447%51%
1981
October1st to 15thDay
12%5%24422346%51%
1800
16th to endDay
14%213212245%58%
1920
November1st to 15thDay
12%5%24213235%55%
1895
16th to endDay
16%6%2431133449%
1732
December1st to 15thDay
18%6%2432335%445%
1450
16th to endDay
19%6%25%42333442%
1605
January1st to 15thNight
18%5%1331223451%
2327
16th to endNight
16%424323325%50%
2496
February1st to 15thNight
18%5%24312336%46%
2253
16th to endNight
14%5%23323235%52%
1890
March1st to 15thNight
17%6%2442434444%
1980
16th to endNight
15%5%245%23346%44%
2103
April1st to 15thNight
10%42432345%7%51%
1797
16th to endNight
10%5%1442445%7%49%
1800
May1st to 15thNight
14%5%243245%5%6%44%
1763
16th to endNight
8%425%435%45%9%46%
1647
June1st to 15thNight
221332446%10%57%
1440
16th to endNight
431433345%9%55%
1473
July1st to 15thNight
4315%5%35%6%7%11%45%
1620
16th to endNight
311332446%12%54%
1702
August1st to 15thNight
42144335%5%10%52%
1677
16th to endNight
6%2146%35%5%7%10%45%
1910
September1st to 15thNight
10%424424337%52%
1800
16th to endNight
7%414424346%56%
1964
October1st to 15thNight
9%314313335%57%
2160
16th to endNight
12%21232222462%
2304
November1st to 15thNight
11%423422346%54%
2290
16th to endNight
15%42431334452%
2555
December1st to 15thNight
20%5%24323345%45%
2547
16th to endNight
19%5%33323335%45%
2616

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 15thDay
40%36%25%18%5%
1612
16th to endDay
39%28%25%19%3
1728
February1st to 15thDay
39%49%24%17%3
1601
16th to endDay
44%48%20%18%3
1594
March1st to 15thDay
45%310%17%16%6%
1980
16th to endDay
44%411%25%12%1
2121
April1st to 15thDay
38%49%23%19%4
2151
16th to endDay
43%49%21%17%3
2160
May1st to 15thDay
44%5%11%16%18%2
2184
16th to endDay
41%8%13%22%12%1
2467
June1st to 15thDay
32%7%13%27%17%
2520
16th to endDay
31%7%14%26%17%2
2481
July1st to 15thDay
38%8%14%23%12%2
2201
16th to endDay
32%7%14%27%15%2
2311
August1st to 15thDay
34%7%14%24%16%2
2269
16th to endDay
36%8%14%21%15%3
2292
September1st to 15thDay
38%7%10%19%17%7%
2160
16th to endDay
32%410%22%25%5%
1981
October1st to 15thDay
34%47%23%24%6%
1800
16th to endDay
28%25%25%27%10%
1920
November1st to 15thDay
32%28%25%22%8%
1895
16th to endDay
39%36%20%24%5%
1732
December1st to 15thDay
40%311%23%15%4
1450
16th to endDay
44%39%20%16%4
1605
January1st to 15thNight
38%26%22%26%4
2327
16th to endNight
37%36%24%21%5%
2496
February1st to 15thNight
39%38%24%18%5%
2262
16th to endNight
36%28%26%18%7%
1890
March1st to 15thNight
42%49%17%19%7%
1980
16th to endNight
41%410%23%17%2
2103
April1st to 15thNight
32%49%25%20%7%
1797
16th to endNight
33%410%24%23%4
1800
May1st to 15thNight
38%6%10%21%17%5%
1764
16th to endNight
35%6%16%23%16%1
1649
June1st to 15thNight
20%5%14%31%26%1
1440
16th to endNight
24%5%12%26%24%5%
1473
July1st to 15thNight
28%8%17%28%15%2
1530
16th to endNight
20%8%17%31%19%2
1594
August1st to 15thNight
25%5%17%31%18%2
1667
16th to endNight
31%6%15%24%17%3
1910
September1st to 15thNight
32%5%9%24%19%8%
1800
16th to endNight
28%48%23%25%8%
1964
October1st to 15thNight
29%38%22%23%11%
2160
16th to endNight
27%2420%33%11%
2304
November1st to 15thNight
31%36%25%23%10%
2290
16th to endNight
35%26%20%28%6%
2555
December1st to 15thNight
41%310%21%17%5%
2547
16th to endNight
41%38%22%19%4
2616

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 15thDay
25%15%37%14%5%1
90
16th to endDay
15%23%37%17%5%
96
February1st to 15thDay
10%23%47%13%41
90
16th to endDay
19%17%39%14%7%1
81
March1st to 15thDay
25%17%42%12%2
90
16th to endDay
15%23%21%33%5%
105
April1st to 15thDay
16%12%33%23%12%1
270
16th to endDay
20%8%31%21%15%2
270
May1st to 15thDay
19%7%26%26%15%3
321
16th to endDay
12%5%25%31%19%5%
517
June1st to 15thDay
6%216%28%31%14%
495
16th to endDay
6%214%33%32%11%
495
July1st to 15thDay
7%111%34%35%10%
475
16th to endDay
5%5%23%41%24%
515
August1st to 15thDay
9%6%29%36%16%
436
16th to endDay
13%5%24%37%17%
332
September1st to 15thDay
11%29%19%39%17%
315
16th to endDay
9%111%27%35%13%
217
October1st to 15thDay
11%5%28%25%23%5%
135
16th to endDay
15%6%29%31%13%3
144
November1st to 15thDay
16%8%26%27%20%
135
16th to endDay
22%14%30%17%13%2
135
December1st to 15thDay
17%17%27%23%9%5%
94
16th to endDay
21%19%39%15%3
96
January1st to 15thNight
22%11%33%25%6%
900
16th to endNight
18%10%39%28%3
960
February1st to 15thNight
19%13%33%28%3
853
16th to endNight
16%13%41%24%3
628
March1st to 15thNight
19%10%36%30%3
540
16th to endNight
17%7%33%31%9%
576
April1st to 15thNight
12%10%37%29%9%
539
16th to endNight
12%7%35%31%12%
540
May1st to 15thNight
16%5%25%37%13%1
540
16th to endNight
9%421%37%22%4
563
June1st to 15thNight
310%41%37%5%
540
16th to endNight
5%18%38%40%5%
540
July1st to 15thNight
48%35%42%7%
510
16th to endNight
4428%52%9%
564
August1st to 15thNight
48%31%42%12%
539
16th to endNight
7%6%32%46%6%
573
September1st to 15thNight
10%29%32%39%6%
540
16th to endNight
8%213%36%34%4
606
October1st to 15thNight
12%321%32%27%3
720
16th to endNight
13%5%26%34%18%1
768
November1st to 15thNight
14%6%27%34%15%1
760
16th to endNight
18%8%29%27%16%
800
December1st to 15thNight
23%7%30%30%7%
910
16th to endNight
23%9%31%29%6%
960
Page generated at 2017-12-03 10:16:40. Version ac04

Copyright 2017 A. Danko


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