East-View Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the East-View Observatory clear sky chart from 2005-11-05 to 2018-10-08.

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
40%
17627
14%
50754
9%
17580
44%
17580
23%
34899

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
32%
975
12%
2716
6%
970
37%
970
19%
1969
January16th to endNight
26%
1040
12%
2853
5%
1040
32%
1040
17%
2194
February1st to 15thNight
33%
954
15%
2480
5%
950
40%
950
25%
1745
February16th to endNight
37%
796
15%
2162
7%
796
43%
796
22%
1530
March1st to 15thNight
36%
689
15%
2249
12%
689
40%
689
20%
1523
March16th to endNight
38%
624
17%
2233
15%
624
45%
624
19%
1468
April1st to 15thNight
36%
584
14%
1947
12%
584
42%
584
19%
1333
April16th to endNight
40%
579
15%
1783
12%
579
46%
579
21%
1218
May1st to 15thNight
39%
585
14%
1560
7%
585
43%
585
22%
1126
May16th to endNight
50%
611
11%
1626
5%
609
53%
609
27%
1119
June1st to 15thNight
50%
585
10%
1560
6%
585
52%
585
28%
1050
June16th to endNight
50%
585
11%
1368
7%
585
52%
585
31%
961
July1st to 15thNight
61%
555
14%
1394
8%
555
63%
555
41%
864
July16th to endNight
64%
612
15%
1545
8%
579
65%
579
41%
910
August1st to 15thNight
66%
575
22%
1627
17%
572
68%
572
39%
928
August16th to endNight
56%
621
20%
1955
19%
621
60%
621
32%
1139
September1st to 15thNight
61%
585
21%
1950
20%
585
67%
585
33%
1099
September16th to endNight
47%
666
14%
2128
12%
666
51%
666
27%
1332
October1st to 15thNight
42%
752
18%
2256
11%
752
48%
752
25%
1450
October16th to endNight
31%
768
13%
2383
8%
768
38%
768
18%
1708
November1st to 15thNight
31%
896
15%
2607
8%
896
38%
896
21%
1813
November16th to endNight
31%
975
15%
2730
8%
975
38%
975
18%
1986
December1st to 15thNight
23%
975
9%
2730
3%
975
28%
975
12%
2137
December16th to endNight
23%
1040
10%
2912
3%
1040
30%
1040
13%
2297

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
14%7%36%5%345%5%7%36%
52384
Night
14%8%36%5%3445%7%37%
50923
Cloud CoverDay
13%7%36%5%35%5%5%7%35%
52395
Night
13%8%36%5%3445%7%36%
50927
Cloud CoverDay
13%7%36%5%35%5%5%7%36%
52393
Night
13%8%36%5%3445%7%36%
50927
TransparencyDay
46%5%15%22%9%
52068
Night
46%5%14%22%9%
50757
SeeingDay
17%423%32%17%4
7626
Night
17%5%26%34%13%1
17628

By Month

Percentage Cloud Cover NE (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
9%12%7%9%5%35%45%6%30%
1552
16th to endDay
10%10%5%10%7%5%6%6%6%8%21%
1722
February1st to 15thDay
7%11%5%6%5%3445%6%36%
1710
16th to endDay
12%11%47%6%35%45%6%33%
1595
March1st to 15thDay
13%8%47%5%3445%5%37%
2043
16th to endDay
16%8%46%5%345%5%7%33%
2343
April1st to 15thDay
15%8%36%6%45%345%36%
2331
16th to endDay
20%7%35%5%34446%33%
2450
May1st to 15thDay
19%7%36%6%35%445%33%
2721
16th to endDay
16%5%345%345%5%8%37%
2841
June1st to 15thDay
14%5%25%5%346%48%39%
2730
16th to endDay
14%5%25%5%36%6%7%8%34%
2918
July1st to 15thDay
9%424425%5%5%8%47%
2815
16th to endDay
5%324435%46%8%49%
2879
August1st to 15thDay
9%426%5%35%5%47%44%
2574
16th to endDay
12%414413449%46%
2598
September1st to 15thDay
9%42443446%7%48%
2340
16th to endDay
17%6%25%43445%6%39%
2146
October1st to 15thDay
17%7%346%345%45%37%
1874
16th to endDay
21%9%26%5%33346%30%
1840
November1st to 15thDay
14%10%46%6%336%5%5%33%
1578
16th to endDay
16%11%47%6%45%6%5%6%24%
1560
December1st to 15thDay
15%13%5%9%7%45%5%47%20%
1560
16th to endDay
17%16%6%10%7%35%43420%
1664
January1st to 15thNight
11%9%6%6%6%345%5%8%31%
2716
16th to endNight
10%12%6%9%7%45%5%5%6%26%
2853
February1st to 15thNight
7%11%49%6%34345%38%
2480
16th to endNight
10%11%48%6%4436%6%34%
2162
March1st to 15thNight
12%10%46%5%35%435%38%
2237
16th to endNight
15%9%37%5%2434439%
2233
April1st to 15thNight
17%9%46%5%33346%34%
1947
16th to endNight
21%8%343335%5%7%33%
1783
May1st to 15thNight
18%7%36%5%3435%6%34%
1560
16th to endNight
14%4246%346%7%7%37%
1624
June1st to 15thNight
15%5%245%345%5%8%38%
1560
16th to endNight
15%7%24435%45%8%37%
1368
July1st to 15thNight
7%32432346%8%52%
1472
16th to endNight
7%3234245%7%9%49%
1641
August1st to 15thNight
9%413423347%53%
1636
16th to endNight
15%414312347%49%
1955
September1st to 15thNight
8%42442445%6%52%
1950
16th to endNight
15%6%2432445%8%42%
2128
October1st to 15thNight
16%6%2443345%6%42%
2256
16th to endNight
21%8%36%5%24436%33%
2383
November1st to 15thNight
16%9%36%434446%36%
2607
16th to endNight
15%9%36%5%345%47%32%
2730
December1st to 15thNight
15%13%6%9%6%345%47%23%
2730
16th to endNight
15%17%6%8%6%25%445%24%
2912

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
8%12%6%8%7%335%7%8%27%
1552
16th to endDay
10%10%5%11%8%47%6%7%8%20%
1722
February1st to 15thDay
8%11%47%5%25%46%7%35%
1710
16th to endDay
12%11%47%5%45%45%6%32%
1595
March1st to 15thDay
12%8%5%6%5%3445%5%37%
2054
16th to endDay
16%8%36%435%5%5%5%33%
2343
April1st to 15thDay
14%8%36%5%45%345%36%
2331
16th to endDay
19%7%45%5%3445%6%32%
2450
May1st to 15thDay
18%7%36%6%35%445%33%
2721
16th to endDay
16%5%25%5%35%5%47%36%
2841
June1st to 15thDay
14%5%25%5%35%5%6%8%37%
2730
16th to endDay
14%5%25%5%46%5%6%9%33%
2918
July1st to 15thDay
9%414435%5%6%8%46%
2815
16th to endDay
4424435%6%5%10%49%
2879
August1st to 15thDay
9%415%5%346%5%7%44%
2574
16th to endDay
12%4244235%5%8%46%
2598
September1st to 15thDay
8%424435%46%8%46%
2340
16th to endDay
16%5%25%6%34446%38%
2146
October1st to 15thDay
16%7%35%5%35%5%46%36%
1874
16th to endDay
20%9%36%5%3435%7%29%
1840
November1st to 15thDay
15%8%48%5%345%5%5%32%
1578
16th to endDay
15%10%47%6%46%5%6%6%23%
1560
December1st to 15thDay
14%13%6%9%6%46%6%5%6%19%
1560
16th to endDay
16%17%5%10%8%34445%17%
1664
January1st to 15thNight
11%10%5%6%6%35%5%6%10%27%
2716
16th to endNight
10%11%6%9%7%45%46%7%25%
2853
February1st to 15thNight
6%11%49%5%35%446%38%
2473
16th to endNight
10%10%38%6%3445%6%34%
2162
March1st to 15thNight
11%9%46%6%34446%37%
2249
16th to endNight
15%8%37%5%24445%38%
2233
April1st to 15thNight
16%10%36%6%24346%34%
1947
16th to endNight
21%8%344245%6%7%32%
1783
May1st to 15thNight
18%7%25%6%35%447%34%
1559
16th to endNight
13%6%245%35%6%7%6%37%
1624
June1st to 15thNight
14%6%245%345%6%8%38%
1560
16th to endNight
14%7%25%325%46%9%37%
1368
July1st to 15thNight
7%424335%36%8%52%
1472
16th to endNight
6%3144245%7%10%48%
1641
August1st to 15thNight
9%413323347%54%
1636
16th to endNight
14%5%14313347%50%
1955
September1st to 15thNight
8%41443435%7%52%
1950
16th to endNight
14%6%2443335%7%42%
2128
October1st to 15thNight
16%6%2442445%6%42%
2256
16th to endNight
20%8%35%6%34337%32%
2383
November1st to 15thNight
15%8%36%5%26%446%35%
2607
16th to endNight
15%9%36%6%35%5%5%7%31%
2730
December1st to 15thNight
14%13%6%8%7%35%6%6%7%20%
2730
16th to endNight
14%17%6%8%5%35%5%5%7%21%
2912

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
8%12%7%8%7%345%7%7%26%
1552
16th to endDay
10%10%5%12%8%47%6%7%7%20%
1722
February1st to 15thDay
8%11%47%5%25%5%5%6%36%
1710
16th to endDay
12%11%47%5%35%447%32%
1595
March1st to 15thDay
12%8%5%6%5%2445%5%37%
2054
16th to endDay
16%8%36%5%35%45%5%34%
2341
April1st to 15thDay
14%9%36%6%44445%36%
2331
16th to endDay
19%7%35%5%3445%6%32%
2450
May1st to 15thDay
19%6%27%6%44445%33%
2721
16th to endDay
16%5%26%5%345%5%7%36%
2841
June1st to 15thDay
14%5%25%5%35%5%6%7%38%
2730
16th to endDay
14%6%25%5%45%6%6%9%34%
2918
July1st to 15thDay
9%4244345%6%8%46%
2815
16th to endDay
5%3144345%6%9%49%
2879
August1st to 15thDay
9%415%5%346%5%8%44%
2574
16th to endDay
12%42442346%8%46%
2598
September1st to 15thDay
8%5%244345%6%8%46%
2340
16th to endDay
17%5%25%5%44446%38%
2146
October1st to 15thDay
16%7%35%5%345%46%36%
1874
16th to endDay
20%10%36%5%34447%30%
1840
November1st to 15thDay
15%9%47%5%3445%5%33%
1578
16th to endDay
16%10%48%7%45%6%5%7%24%
1560
December1st to 15thDay
14%13%6%9%6%46%6%6%5%19%
1560
16th to endDay
16%18%6%10%7%345%5%5%16%
1664
January1st to 15thNight
11%10%5%6%7%35%6%7%9%26%
2716
16th to endNight
10%12%6%9%7%36%5%6%6%25%
2853
February1st to 15thNight
6%11%48%5%34446%38%
2473
16th to endNight
11%10%47%6%3435%6%34%
2162
March1st to 15thNight
12%9%46%5%35%5%45%37%
2249
16th to endNight
15%9%36%5%24445%38%
2233
April1st to 15thNight
17%9%36%5%34445%34%
1947
16th to endNight
21%8%344245%5%7%32%
1783
May1st to 15thNight
19%7%25%6%35%45%7%34%
1559
16th to endNight
13%5%15%5%345%7%6%37%
1624
June1st to 15thNight
14%6%245%3446%8%38%
1560
16th to endNight
15%7%24425%47%8%37%
1368
July1st to 15thNight
7%423335%36%8%52%
1472
16th to endNight
6%32342447%10%49%
1641
August1st to 15thNight
9%413323347%54%
1636
16th to endNight
14%5%14223247%50%
1955
September1st to 15thNight
8%41442445%7%52%
1950
16th to endNight
14%5%2442345%8%42%
2128
October1st to 15thNight
16%6%2443445%6%42%
2256
16th to endNight
21%8%35%6%34436%32%
2383
November1st to 15thNight
15%9%35%5%25%446%36%
2607
16th to endNight
15%9%36%5%35%5%5%7%31%
2730
December1st to 15thNight
15%13%5%8%7%35%6%5%7%20%
2730
16th to endNight
14%16%6%8%6%25%5%5%6%20%
2912

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
53%5%12%19%8%
1553
16th to endDay
59%6%14%15%4
1722
February1st to 15thDay
46%418%20%9%1
1711
16th to endDay
52%414%21%6%
1595
March1st to 15thDay
48%5%17%20%8%
2054
16th to endDay
49%5%16%20%6%
2343
April1st to 15thDay
50%311%18%13%1
2331
16th to endDay
52%313%19%9%1
2450
May1st to 15thDay
52%413%21%7%
2721
16th to endDay
44%5%15%22%11%1
2845
June1st to 15thDay
42%5%18%24%9%
2730
16th to endDay
43%6%16%22%9%
2918
July1st to 15thDay
33%5%14%27%17%2
2664
16th to endDay
31%5%18%28%13%1
2712
August1st to 15thDay
37%5%15%28%10%1
2559
16th to endDay
34%5%18%27%12%
2598
September1st to 15thDay
34%5%19%32%8%
2340
16th to endDay
45%5%16%26%5%
2146
October1st to 15thDay
48%5%14%22%8%
1874
16th to endDay
54%415%18%7%
1840
November1st to 15thDay
52%5%13%19%8%
1578
16th to endDay
58%6%11%15%6%
1560
December1st to 15thDay
63%7%12%13%2
1560
16th to endDay
68%48%11%5%
1664
January1st to 15thNight
49%7%14%20%6%
2716
16th to endNight
57%5%13%17%5%
2853
February1st to 15thNight
48%314%22%10%
2483
16th to endNight
49%412%23%9%
2162
March1st to 15thNight
47%5%14%20%11%
2249
16th to endNight
48%313%22%10%1
2233
April1st to 15thNight
50%310%18%15%1
1947
16th to endNight
49%311%22%12%
1783
May1st to 15thNight
50%5%11%22%8%
1560
16th to endNight
43%6%12%24%12%1
1626
June1st to 15thNight
41%5%14%26%10%1
1560
16th to endNight
42%5%14%24%11%1
1368
July1st to 15thNight
29%6%14%28%17%2
1394
16th to endNight
27%7%18%28%14%3
1545
August1st to 15thNight
30%316%33%12%3
1627
16th to endNight
35%313%29%15%2
1955
September1st to 15thNight
31%5%14%36%10%
1950
16th to endNight
38%6%18%28%7%
2128
October1st to 15thNight
41%5%14%27%10%
2256
16th to endNight
53%412%20%8%
2383
November1st to 15thNight
49%414%22%8%
2607
16th to endNight
50%6%16%18%6%1
2730
December1st to 15thNight
59%6%12%17%2
2730
16th to endNight
62%5%13%12%6%
2912

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
20%5%21%30%21%
135
16th to endDay
18%231%37%9%2
144
February1st to 15thDay
10%5%40%34%8%
135
16th to endDay
26%134%30%7%
120
March1st to 15thDay
11%6%29%34%14%3
135
16th to endDay
21%6%24%30%11%6%
199
April1st to 15thDay
17%7%23%34%13%2
330
16th to endDay
24%6%24%27%13%3
441
May1st to 15thDay
22%5%30%28%9%3
543
16th to endDay
20%420%29%18%5%
597
June1st to 15thDay
15%425%34%16%2
570
16th to endDay
15%425%32%18%4
570
July1st to 15thDay
14%222%28%23%7%
550
16th to endDay
8%320%36%21%9%
595
August1st to 15thDay
13%217%32%29%4
549
16th to endDay
17%314%31%25%7%
510
September1st to 15thDay
9%117%40%26%5%
375
16th to endDay
22%6%25%30%13%1
278
October1st to 15thDay
22%325%29%14%4
157
16th to endDay
25%431%26%12%
144
November1st to 15thDay
15%8%32%35%7%
135
16th to endDay
25%9%21%31%11%
135
December1st to 15thDay
21%5%31%34%6%
135
16th to endDay
24%9%30%31%4
144
January1st to 15thNight
15%7%32%32%10%1
975
16th to endNight
16%5%37%32%6%
1040
February1st to 15thNight
13%5%33%37%9%1
955
16th to endNight
16%431%34%12%
796
March1st to 15thNight
18%5%29%35%10%1
689
16th to endNight
18%6%25%33%12%3
624
April1st to 15thNight
21%426%35%10%1
584
16th to endNight
26%321%33%11%1
579
May1st to 15thNight
20%5%27%34%9%2
585
16th to endNight
15%418%39%20%1
611
June1st to 15thNight
16%320%42%15%1
585
16th to endNight
18%417%40%17%1
585
July1st to 15thNight
9%220%38%26%2
555
16th to endNight
8%118%40%27%3
612
August1st to 15thNight
10%212%42%27%3
575
16th to endNight
16%417%34%24%2
621
September1st to 15thNight
9%318%38%25%4
585
16th to endNight
17%424%33%18%1
666
October1st to 15thNight
21%5%25%34%12%
752
16th to endNight
24%8%29%27%9%
768
November1st to 15thNight
19%8%31%29%10%
896
16th to endNight
19%10%31%29%8%
975
December1st to 15thNight
20%10%30%29%7%
975
16th to endNight
23%7%30%27%9%2
1040
Page generated at 2018-10-09 09:39:09. Version ac04

Copyright 2018 A. Danko


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