Clearview Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Clearview Observatory clear sky chart from 2005-11-05 to 2019-06-02.

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
42%
16710
10%
53622
10%
16681
43%
16681
15%
40021

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
33%
875
9%
3049
11%
871
33%
871
9%
2456
January16th to endNight
34%
896
9%
3110
9%
896
35%
896
10%
2459
February1st to 15thNight
32%
820
8%
2678
7%
819
34%
819
10%
2159
February16th to endNight
34%
736
10%
2343
10%
736
36%
736
12%
1848
March1st to 15thNight
32%
840
8%
2423
8%
840
33%
840
12%
1949
March16th to endNight
33%
896
6%
2402
4%
896
33%
896
11%
1979
April1st to 15thNight
33%
839
6%
2099
4%
839
33%
839
12%
1778
April16th to endNight
38%
633
7%
1881
6%
633
39%
633
14%
1483
May1st to 15thNight
53%
419
12%
1679
18%
419
54%
419
19%
1050
May16th to endNight
48%
438
5%
1752
9%
438
49%
438
12%
1267
June1st to 15thNight
43%
392
4%
1467
5%
392
43%
392
13%
1080
June16th to endNight
46%
390
7%
1365
7%
390
47%
390
16%
970
July1st to 15thNight
65%
370
13%
1308
17%
370
66%
370
31%
713
July16th to endNight
73%
408
17%
1544
29%
386
74%
386
35%
754
August1st to 15thNight
77%
461
20%
1606
25%
459
78%
459
38%
813
August16th to endNight
68%
699
21%
1941
17%
699
68%
699
38%
1142
September1st to 15thNight
67%
780
20%
1950
12%
780
68%
780
40%
1207
September16th to endNight
53%
776
17%
2131
14%
776
53%
776
24%
1496
October1st to 15thNight
48%
780
11%
2340
12%
780
49%
780
21%
1654
October16th to endNight
40%
832
10%
2582
10%
832
41%
832
14%
1969
November1st to 15thNight
29%
820
6%
2837
7%
820
30%
820
8%
2339
November16th to endNight
30%
840
6%
2940
6%
840
31%
840
9%
2380
December1st to 15thNight
37%
840
10%
2940
11%
840
38%
840
11%
2290
December16th to endNight
22%
930
5%
3255
5%
930
23%
930
6%
2786

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
25%8%35%424445%30%
54721
Night
26%8%35%5%24345%30%
53781
Cloud CoverDay
26%8%36%5%24345%29%
54721
Night
28%8%35%424345%29%
53784
TransparencyDay
57%413%16%6%
54383
Night
58%412%16%6%1
53623
SeeingDay
27%5%17%25%17%6%
8003
Night
32%411%25%21%4
16716

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 15thDay
39%8%35%5%2333419%
1547
16th to endDay
34%10%36%5%34435%17%
1817
February1st to 15thDay
32%11%46%6%3444417%
1846
16th to endDay
28%13%45%5%2433422%
1703
March1st to 15thDay
35%11%36%5%2434419%
2194
16th to endDay
31%11%47%6%3444416%
2525
April1st to 15thDay
31%11%46%5%4445%6%15%
2509
16th to endDay
25%9%46%6%45%5%5%5%21%
2680
May1st to 15thDay
19%8%26%5%3445%6%33%
2931
16th to endDay
25%9%36%435%5%5%7%24%
3063
June1st to 15thDay
27%7%25%5%35%445%27%
2843
16th to endDay
20%7%37%6%35%5%5%6%30%
2925
July1st to 15thDay
11%5%24223345%53%
2909
16th to endDay
12%413313245%57%
2881
August1st to 15thDay
11%413323346%54%
2595
16th to endDay
12%5%24423447%48%
2612
September1st to 15thDay
11%6%25%413236%51%
2340
16th to endDay
21%6%26%5%2445%6%35%
2156
October1st to 15thDay
23%9%26%5%2345%6%29%
1950
16th to endDay
32%9%36%43335%6%20%
1992
November1st to 15thDay
42%9%3442443317%
1677
16th to endDay
39%10%35%325%33418%
1680
December1st to 15thDay
30%11%47%423335%21%
1680
16th to endDay
37%12%47%43433316%
1666
January1st to 15thNight
39%8%25%42343421%
3049
16th to endNight
34%9%35%424445%19%
3110
February1st to 15thNight
33%10%45%5%34345%20%
2666
16th to endNight
28%12%45%42434424%
2343
March1st to 15thNight
31%8%35%434445%22%
2423
16th to endNight
28%10%46%6%345%45%20%
2398
April1st to 15thNight
28%9%27%6%26%5%5%6%18%
2099
16th to endNight
25%8%27%435%5%46%25%
1881
May1st to 15thNight
18%7%25%42445%6%39%
1679
16th to endNight
21%7%35%6%36%45%7%28%
1752
June1st to 15thNight
24%8%46%5%24345%29%
1467
16th to endNight
19%6%27%6%3345%6%33%
1365
July1st to 15thNight
9%42441234457%
1379
16th to endNight
8%314213345%59%
1640
August1st to 15thNight
8%312312147%61%
1614
16th to endNight
10%423422245%56%
1941
September1st to 15thNight
8%5%24413335%55%
1950
16th to endNight
19%6%25%5%34345%39%
2131
October1st to 15thNight
21%8%35%5%23345%36%
2340
16th to endNight
30%9%24423346%27%
2582
November1st to 15thNight
38%9%35%43344419%
2837
16th to endNight
37%9%36%5%2433421%
2940
December1st to 15thNight
30%9%36%5%2334424%
2940
16th to endNight
38%13%36%5%2333315%
3255

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 15thDay
41%8%26%42233420%
1547
16th to endDay
37%9%35%424445%18%
1817
February1st to 15thDay
34%10%36%6%3344417%
1846
16th to endDay
30%14%45%43333422%
1703
March1st to 15thDay
36%13%35%5%2333417%
2194
16th to endDay
33%10%47%6%3443416%
2525
April1st to 15thDay
33%11%47%6%35%445%13%
2509
16th to endDay
27%9%47%6%345%5%5%19%
2680
May1st to 15thDay
20%8%35%5%35%446%31%
2931
16th to endDay
27%8%36%6%34447%23%
3063
June1st to 15thDay
27%8%36%5%35%445%25%
2843
16th to endDay
21%7%37%6%245%46%28%
2925
July1st to 15thDay
11%5%24324335%52%
2909
16th to endDay
12%413323245%56%
2881
August1st to 15thDay
11%423322446%53%
2595
16th to endDay
13%42442345%7%47%
2612
September1st to 15thDay
11%6%25%423335%50%
2340
16th to endDay
21%6%35%424446%35%
2156
October1st to 15thDay
23%8%25%43346%6%29%
1950
16th to endDay
35%8%36%434346%20%
1992
November1st to 15thDay
44%8%25%42333416%
1677
16th to endDay
39%10%36%42323418%
1680
December1st to 15thDay
32%10%47%5%2343422%
1680
16th to endDay
40%12%46%42322316%
1666
January1st to 15thNight
40%7%35%42234421%
3048
16th to endNight
36%9%24434346%20%
3110
February1st to 15thNight
33%11%45%424335%20%
2666
16th to endNight
31%12%35%42333424%
2343
March1st to 15thNight
33%9%35%434445%21%
2423
16th to endNight
30%10%47%5%2445%419%
2402
April1st to 15thNight
29%10%46%6%45%45%5%17%
2099
16th to endNight
26%9%35%5%45%5%46%24%
1881
May1st to 15thNight
20%5%35%42436%5%39%
1679
16th to endNight
22%6%37%5%445%5%7%27%
1752
June1st to 15thNight
26%7%45%6%35%345%28%
1467
16th to endNight
20%6%37%6%35%445%32%
1365
July1st to 15thNight
9%42441434456%
1379
16th to endNight
9%314322245%58%
1640
August1st to 15thNight
8%313213237%61%
1614
16th to endNight
11%414323346%55%
1941
September1st to 15thNight
9%5%25%31333455%
1950
16th to endNight
20%6%25%5%23336%39%
2131
October1st to 15thNight
22%7%35%5%24435%36%
2340
16th to endNight
33%7%24433346%25%
2582
November1st to 15thNight
40%8%36%42434417%
2837
16th to endNight
39%8%25%5%2432420%
2940
December1st to 15thNight
32%8%35%5%2434424%
2940
16th to endNight
41%12%46%5%1333315%
3255

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
70%38%11%6%
1547
16th to endDay
68%310%11%41
1817
February1st to 15thDay
70%410%8%41
1846
16th to endDay
67%38%13%6%
1703
March1st to 15thDay
71%310%11%3
2194
16th to endDay
72%410%10%1
2525
April1st to 15thDay
73%412%8%
2509
16th to endDay
66%411%12%4
2680
May1st to 15thDay
53%417%18%6%
2931
16th to endDay
61%5%18%12%2
3067
June1st to 15thDay
61%416%11%4
2843
16th to endDay
55%5%16%17%4
2925
July1st to 15thDay
36%413%28%15%1
2751
16th to endDay
31%313%32%17%2
2714
August1st to 15thDay
32%418%29%12%1
2578
16th to endDay
37%415%30%9%2
2612
September1st to 15thDay
36%314%25%17%2
2340
16th to endDay
49%5%17%17%8%1
2156
October1st to 15thDay
54%5%13%18%7%
1950
16th to endDay
65%410%13%6%
1992
November1st to 15thDay
73%48%9%21
1677
16th to endDay
70%37%10%6%
1680
December1st to 15thDay
66%46%13%7%
1680
16th to endDay
75%36%9%3
1666
January1st to 15thNight
67%48%12%5%
3049
16th to endNight
66%310%11%5%1
3110
February1st to 15thNight
67%410%11%5%1
2678
16th to endNight
64%410%15%5%
2343
March1st to 15thNight
65%411%15%3
2423
16th to endNight
66%6%12%12%1
2402
April1st to 15thNight
68%5%12%12%2
2099
16th to endNight
62%5%13%13%4
1881
May1st to 15thNight
46%320%20%8%
1680
16th to endNight
56%7%19%13%2
1752
June1st to 15thNight
59%415%15%4
1467
16th to endNight
53%5%16%19%31
1365
July1st to 15thNight
33%313%31%14%3
1308
16th to endNight
27%312%32%20%3
1544
August1st to 15thNight
25%5%16%33%15%3
1606
16th to endNight
31%417%33%9%2
1941
September1st to 15thNight
33%314%26%17%4
1950
16th to endNight
47%413%22%9%2
2131
October1st to 15thNight
51%414%21%7%
2340
16th to endNight
61%313%15%6%
2582
November1st to 15thNight
70%410%10%22
2837
16th to endNight
69%39%9%7%
2940
December1st to 15thNight
64%411%11%7%
2940
16th to endNight
76%37%7%4
3255

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
30%36%16%22%20%
120
16th to endDay
48%8%9%13%13%7%
153
February1st to 15thDay
47%5%16%18%9%2
326
16th to endDay
40%8%21%18%8%1
303
March1st to 15thDay
40%8%21%17%10%1
390
16th to endDay
39%9%20%15%12%2
416
April1st to 15thDay
40%9%22%16%8%2
389
16th to endDay
31%10%23%20%9%4
378
May1st to 15thDay
24%6%19%28%16%4
408
16th to endDay
28%411%24%22%8%
458
June1st to 15thDay
24%6%21%24%18%3
477
16th to endDay
19%5%21%33%16%3
570
July1st to 15thDay
10%319%36%26%3
535
16th to endDay
10%113%37%26%9%
391
August1st to 15thDay
11%112%33%26%15%
359
16th to endDay
11%314%36%24%9%
396
September1st to 15thDay
17%318%31%20%8%
375
16th to endDay
21%6%17%29%18%6%
375
October1st to 15thDay
30%6%18%23%15%5%
375
16th to endDay
37%410%18%18%9%
312
November1st to 15thDay
55%9%13%10%7%3
129
16th to endDay
44%5%12%15%8%14%
120
December1st to 15thDay
35%5%11%11%20%15%
120
16th to endDay
48%8%9%18%10%4
128
January1st to 15thNight
44%5%8%16%20%4
875
16th to endNight
41%5%10%21%17%3
896
February1st to 15thNight
40%410%25%14%3
824
16th to endNight
37%412%27%15%2
736
March1st to 15thNight
39%6%14%21%15%2
840
16th to endNight
37%6%13%27%13%1
896
April1st to 15thNight
35%6%13%25%17%1
839
16th to endNight
29%414%29%17%3
633
May1st to 15thNight
21%411%30%27%4
420
16th to endNight
24%29%28%27%6%
439
June1st to 15thNight
29%211%30%22%3
392
16th to endNight
22%413%33%21%5%
390
July1st to 15thNight
12%211%31%37%5%
370
16th to endNight
10%27%32%41%6%
408
August1st to 15thNight
10%223%46%15%
461
16th to endNight
12%28%27%37%11%
699
September1st to 15thNight
11%36%25%39%12%
780
16th to endNight
24%38%25%29%7%
776
October1st to 15thNight
26%310%30%25%4
780
16th to endNight
37%310%21%19%7%
832
November1st to 15thNight
43%5%13%24%11%1
820
16th to endNight
43%412%19%14%5%
840
December1st to 15thNight
38%5%8%23%19%4
840
16th to endNight
48%413%20%10%1
930
Page generated at 2019-06-02 16:43:07. Version ac04

Copyright 2019 A. Danko


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