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 2017-04-09.

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
39%
15715
14%
45261
9%
15668
44%
15668
22%
31267

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
31%
900
11%
2506
6%
895
35%
895
18%
1842
January16th to endNight
26%
960
12%
2634
5%
960
31%
960
16%
2028
February1st to 15thNight
33%
879
14%
2285
4%
875
39%
875
23%
1630
February16th to endNight
38%
735
15%
1997
7%
735
44%
735
23%
1411
March1st to 15thNight
36%
636
14%
2076
12%
636
40%
636
20%
1403
March16th to endNight
36%
576
16%
2061
14%
576
44%
576
19%
1366
April1st to 15thNight
37%
521
14%
1737
13%
521
42%
521
19%
1190
April16th to endNight
39%
495
15%
1528
12%
495
45%
495
21%
1047
May1st to 15thNight
35%
495
15%
1320
7%
495
40%
495
20%
971
May16th to endNight
49%
515
11%
1370
5%
513
52%
513
28%
935
June1st to 15thNight
48%
495
9%
1320
6%
495
50%
495
27%
899
June16th to endNight
49%
495
11%
1158
7%
495
50%
495
31%
812
July1st to 15thNight
58%
465
14%
1168
7%
465
61%
465
39%
735
July16th to endNight
62%
522
14%
1305
7%
489
63%
489
40%
775
August1st to 15thNight
64%
494
21%
1399
16%
491
67%
491
39%
802
August16th to endNight
56%
525
20%
1653
19%
525
60%
525
34%
943
September1st to 15thNight
61%
495
21%
1650
21%
495
67%
495
33%
934
September16th to endNight
49%
563
14%
1801
11%
563
53%
563
28%
1113
October1st to 15thNight
44%
660
20%
1980
12%
660
51%
660
27%
1246
October16th to endNight
32%
704
12%
2184
7%
704
38%
704
18%
1559
November1st to 15thNight
32%
825
16%
2401
9%
825
39%
825
22%
1655
November16th to endNight
32%
900
15%
2520
9%
900
38%
900
18%
1847
December1st to 15thNight
24%
900
9%
2520
4%
900
29%
900
12%
1967
December16th to endNight
23%
960
9%
2688
3%
960
29%
960
12%
2157

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%35%5%5%7%36%
46024
Night
14%9%36%5%3445%7%36%
45430
Cloud CoverDay
13%7%36%5%35%5%5%7%35%
46035
Night
13%9%36%5%3445%7%35%
45434
Cloud CoverDay
13%8%36%5%35%5%5%7%35%
46033
Night
13%9%36%5%3445%7%36%
45434
TransparencyDay
47%5%15%22%8%
45708
Night
47%5%14%22%9%
45264
SeeingDay
17%5%24%31%16%3
5429
Night
18%6%26%33%13%1
15716

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%8%9%5%35%46%6%28%
1432
16th to endDay
10%10%6%10%7%46%6%6%8%21%
1589
February1st to 15thDay
8%12%5%7%6%3445%7%35%
1575
16th to endDay
11%12%47%6%35%45%5%32%
1474
March1st to 15thDay
14%8%46%5%2445%5%36%
1885
16th to endDay
17%8%46%5%345%47%33%
2163
April1st to 15thDay
15%7%36%5%35%445%37%
2074
16th to endDay
21%7%45%5%25%446%31%
2100
May1st to 15thDay
20%8%37%6%35%445%31%
2301
16th to endDay
16%5%245%345%6%8%38%
2393
June1st to 15thDay
16%5%25%5%35%6%47%37%
2310
16th to endDay
15%5%245%26%6%6%8%36%
2469
July1st to 15thDay
8%424425%5%6%8%46%
2382
16th to endDay
6%325%5%35%5%7%9%46%
2459
August1st to 15thDay
8%426%5%35%5%47%43%
2219
16th to endDay
11%4144145%5%9%47%
2196
September1st to 15thDay
9%42443445%7%47%
1980
16th to endDay
16%6%25%42445%6%40%
1816
October1st to 15thDay
15%7%346%345%45%39%
1650
16th to endDay
21%9%26%6%44346%30%
1687
November1st to 15thDay
15%9%46%6%336%5%5%33%
1454
16th to endDay
17%11%47%6%35%6%5%7%23%
1440
December1st to 15thDay
15%13%5%8%7%46%5%47%21%
1440
16th to endDay
18%17%6%9%7%345%3418%
1536
January1st to 15thNight
11%10%6%7%6%345%5%8%29%
2506
16th to endNight
10%12%6%9%7%45%5%5%6%26%
2634
February1st to 15thNight
7%12%5%9%6%34346%36%
2285
16th to endNight
10%11%48%6%4436%6%34%
1997
March1st to 15thNight
12%9%46%5%35%436%37%
2064
16th to endNight
16%9%37%5%2435%438%
2061
April1st to 15thNight
17%9%46%43345%6%34%
1737
16th to endNight
22%9%2443345%7%31%
1528
May1st to 15thNight
20%8%35%6%3435%5%33%
1320
16th to endNight
14%4246%346%7%7%38%
1368
June1st to 15thNight
17%5%244346%5%7%37%
1320
16th to endNight
16%7%23335%45%8%38%
1158
July1st to 15thNight
7%42443446%7%51%
1246
16th to endNight
7%3234245%7%9%48%
1401
August1st to 15thNight
9%41342345%8%52%
1408
16th to endNight
13%413313448%49%
1653
September1st to 15thNight
8%42443445%6%52%
1650
16th to endNight
14%6%2432445%8%44%
1801
October1st to 15thNight
14%6%144345%5%6%43%
1980
16th to endNight
22%8%36%5%23436%33%
2184
November1st to 15thNight
15%9%36%435%446%36%
2401
16th to endNight
17%9%36%5%246%46%32%
2520
December1st to 15thNight
15%13%6%9%6%345%47%23%
2520
16th to endNight
15%17%6%8%6%25%435%22%
2688

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%13%7%8%7%335%7%7%26%
1432
16th to endDay
10%10%5%11%7%47%5%7%8%20%
1589
February1st to 15thDay
8%11%48%5%25%45%7%34%
1575
16th to endDay
11%11%5%7%5%45%45%6%32%
1474
March1st to 15thDay
13%9%5%6%5%345%5%5%36%
1896
16th to endDay
17%8%36%435%5%5%5%33%
2163
April1st to 15thDay
14%8%36%5%35%445%37%
2074
16th to endDay
20%8%35%5%3445%6%30%
2100
May1st to 15thDay
20%7%37%7%35%445%30%
2301
16th to endDay
15%5%345%345%5%8%37%
2393
June1st to 15thDay
16%5%25%5%35%5%6%8%35%
2310
16th to endDay
14%6%245%36%5%6%8%35%
2469
July1st to 15thDay
8%424435%5%6%9%45%
2382
16th to endDay
5%3145%35%6%5%10%47%
2459
August1st to 15thDay
7%5%16%6%35%6%5%7%44%
2219
16th to endDay
11%4144235%5%9%46%
2196
September1st to 15thDay
8%425%43446%8%46%
1980
16th to endDay
15%5%25%6%34446%40%
1816
October1st to 15thDay
14%7%35%5%345%46%38%
1650
16th to endDay
20%9%36%5%34447%29%
1687
November1st to 15thDay
15%9%47%5%345%5%5%32%
1454
16th to endDay
16%11%47%6%46%5%6%6%23%
1440
December1st to 15thDay
14%12%6%9%6%46%6%6%6%19%
1440
16th to endDay
17%18%6%9%7%3444417%
1536
January1st to 15thNight
11%10%5%6%7%35%5%6%9%26%
2506
16th to endNight
10%11%6%10%7%45%46%7%25%
2634
February1st to 15thNight
7%11%5%9%5%35%446%36%
2278
16th to endNight
10%11%38%6%3445%6%35%
1997
March1st to 15thNight
11%9%46%6%34446%37%
2076
16th to endNight
15%8%37%5%24445%38%
2061
April1st to 15thNight
16%10%36%5%25%45%6%34%
1737
16th to endNight
22%8%334245%6%7%31%
1528
May1st to 15thNight
20%8%25%6%35%447%32%
1319
16th to endNight
14%6%145%35%6%7%6%38%
1368
June1st to 15thNight
16%5%245%345%7%8%36%
1320
16th to endNight
15%8%24225%46%8%38%
1158
July1st to 15thNight
7%424335%46%7%50%
1246
16th to endNight
7%3134245%7%10%48%
1401
August1st to 15thNight
8%413333347%54%
1408
16th to endNight
13%414313348%50%
1653
September1st to 15thNight
7%4145%3335%7%52%
1650
16th to endNight
13%6%2443335%7%44%
1801
October1st to 15thNight
13%5%24425%45%6%43%
1980
16th to endNight
21%8%35%5%34336%33%
2184
November1st to 15thNight
15%8%36%5%26%447%36%
2401
16th to endNight
16%9%36%6%35%5%5%6%31%
2520
December1st to 15thNight
14%13%6%8%7%35%6%6%7%21%
2520
16th to endNight
15%17%6%9%5%35%5%46%20%
2688

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%13%7%8%7%345%7%7%25%
1432
16th to endDay
10%10%5%11%8%37%6%7%8%20%
1589
February1st to 15thDay
8%12%48%5%25%5%5%6%35%
1575
16th to endDay
11%11%5%6%5%36%447%32%
1474
March1st to 15thDay
13%9%5%6%5%2445%5%36%
1896
16th to endDay
17%9%36%435%45%5%34%
2161
April1st to 15thDay
14%8%36%6%34445%37%
2074
16th to endDay
21%8%35%5%35%46%6%30%
2100
May1st to 15thDay
21%7%37%6%45%44431%
2301
16th to endDay
16%5%25%4345%5%8%37%
2393
June1st to 15thDay
16%5%245%35%5%6%7%36%
2310
16th to endDay
14%6%25%5%35%6%6%9%36%
2469
July1st to 15thDay
8%424445%6%6%9%45%
2382
16th to endDay
5%3245%35%5%6%9%47%
2459
August1st to 15thDay
8%5%25%5%35%6%5%8%44%
2219
16th to endDay
11%42442346%8%47%
2196
September1st to 15thDay
8%5%25%42446%8%46%
1980
16th to endDay
16%5%25%5%44446%40%
1816
October1st to 15thDay
14%7%35%5%345%46%38%
1650
16th to endDay
20%10%36%5%34447%29%
1687
November1st to 15thDay
15%8%47%5%3445%5%33%
1454
16th to endDay
17%11%48%6%45%6%5%7%23%
1440
December1st to 15thDay
14%13%5%9%6%46%6%6%5%19%
1440
16th to endDay
17%18%6%9%7%345%5%416%
1536
January1st to 15thNight
11%11%5%6%7%35%6%7%8%25%
2506
16th to endNight
10%12%6%9%7%36%46%6%25%
2634
February1st to 15thNight
7%11%5%9%5%34446%37%
2278
16th to endNight
10%11%47%6%4446%6%35%
1997
March1st to 15thNight
12%9%46%5%35%445%37%
2076
16th to endNight
15%9%36%5%24445%38%
2061
April1st to 15thNight
16%9%36%5%2445%5%34%
1737
16th to endNight
22%8%3442446%7%31%
1528
May1st to 15thNight
21%7%25%6%35%446%33%
1319
16th to endNight
14%6%15%5%35%6%7%6%38%
1368
June1st to 15thNight
16%6%245%3446%8%36%
1320
16th to endNight
15%8%23325%47%8%37%
1158
July1st to 15thNight
7%423335%46%7%50%
1246
16th to endNight
6%3235%245%7%10%48%
1401
August1st to 15thNight
8%413323347%54%
1408
16th to endNight
13%414213347%51%
1653
September1st to 15thNight
7%41443435%7%52%
1650
16th to endNight
14%5%2432335%8%44%
1801
October1st to 15thNight
14%5%25%43445%6%43%
1980
16th to endNight
21%7%35%5%34436%33%
2184
November1st to 15thNight
15%9%35%5%25%446%37%
2401
16th to endNight
16%9%36%5%35%5%5%7%31%
2520
December1st to 15thNight
15%13%5%8%7%35%6%5%7%21%
2520
16th to endNight
15%17%7%8%5%25%5%45%20%
2688

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
54%5%12%19%7%
1433
16th to endDay
58%6%14%15%4
1589
February1st to 15thDay
48%418%18%9%1
1576
16th to endDay
52%415%21%5%
1474
March1st to 15thDay
48%5%18%19%7%
1896
16th to endDay
50%5%17%20%5%1
2163
April1st to 15thDay
49%312%19%14%1
2074
16th to endDay
53%314%18%8%1
2100
May1st to 15thDay
55%412%19%6%1
2301
16th to endDay
43%5%15%23%11%1
2397
June1st to 15thDay
44%5%18%23%7%
2310
16th to endDay
42%6%17%22%10%
2469
July1st to 15thDay
33%5%15%27%17%2
2231
16th to endDay
33%6%19%28%11%1
2292
August1st to 15thDay
38%5%15%27%11%1
2204
16th to endDay
33%5%18%27%13%
2196
September1st to 15thDay
34%5%18%33%7%
1980
16th to endDay
44%5%16%28%5%
1816
October1st to 15thDay
45%5%16%23%8%
1650
16th to endDay
55%415%17%7%
1687
November1st to 15thDay
51%5%13%19%9%
1454
16th to endDay
59%7%11%15%5%
1440
December1st to 15thDay
62%7%12%14%2
1440
16th to endDay
70%49%11%3
1536
January1st to 15thNight
51%7%14%21%4
2506
16th to endNight
57%5%12%17%5%
2634
February1st to 15thNight
49%314%21%10%
2288
16th to endNight
49%413%23%8%
1997
March1st to 15thNight
47%5%15%20%10%
2076
16th to endNight
48%414%22%8%1
2061
April1st to 15thNight
50%310%19%14%1
1737
16th to endNight
50%212%22%11%
1528
May1st to 15thNight
52%5%11%20%8%
1320
16th to endNight
42%6%11%24%13%1
1370
June1st to 15thNight
43%5%15%25%8%1
1320
16th to endNight
42%413%23%13%1
1158
July1st to 15thNight
31%6%13%27%17%2
1168
16th to endNight
27%7%18%29%14%2
1305
August1st to 15thNight
30%317%31%12%3
1399
16th to endNight
33%413%29%16%2
1653
September1st to 15thNight
31%5%14%37%10%
1650
16th to endNight
38%5%18%29%7%
1801
October1st to 15thNight
39%5%15%29%9%
1980
16th to endNight
53%413%20%7%
2184
November1st to 15thNight
48%314%23%9%
2401
16th to endNight
52%6%15%18%6%1
2520
December1st to 15thNight
59%6%13%17%2
2520
16th to endNight
64%5%13%11%4
2688

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
23%5%24%27%18%
90
16th to endDay
20%329%35%10%1
96
February1st to 15thDay
14%8%40%28%7%
90
16th to endDay
28%227%32%9%
81
March1st to 15thDay
15%6%24%38%13%1
90
16th to endDay
23%7%23%29%11%3
147
April1st to 15thDay
15%8%26%33%13%2
245
16th to endDay
26%7%23%30%10%2
313
May1st to 15thDay
26%7%31%22%8%3
393
16th to endDay
19%5%22%27%17%6%
437
June1st to 15thDay
18%5%25%31%15%2
420
16th to endDay
15%5%28%28%17%4
420
July1st to 15thDay
14%225%28%21%8%
400
16th to endDay
8%423%37%19%6%
445
August1st to 15thDay
11%220%34%26%3
418
16th to endDay
15%318%30%25%6%
364
September1st to 15thDay
9%217%40%25%5%
255
16th to endDay
22%6%23%28%16%2
173
October1st to 15thDay
10%423%35%20%6%
90
16th to endDay
28%428%26%12%1
96
November1st to 15thDay
12%5%35%40%6%
90
16th to endDay
34%8%13%28%13%1
90
December1st to 15thDay
22%6%30%32%8%
90
16th to endDay
33%9%32%20%4
96
January1st to 15thNight
15%7%32%31%10%1
900
16th to endNight
16%6%37%32%6%
960
February1st to 15thNight
14%6%31%36%9%1
880
16th to endNight
15%430%35%13%
735
March1st to 15thNight
17%5%29%35%10%1
636
16th to endNight
18%6%27%32%12%3
576
April1st to 15thNight
22%426%35%10%
521
16th to endNight
28%421%34%10%1
495
May1st to 15thNight
22%6%29%30%9%2
495
16th to endNight
15%5%19%38%20%1
515
June1st to 15thNight
18%320%41%14%1
495
16th to endNight
19%5%18%37%17%1
495
July1st to 15thNight
10%222%38%24%2
465
16th to endNight
8%119%42%26%1
522
August1st to 15thNight
10%214%43%25%3
494
16th to endNight
15%319%35%23%2
525
September1st to 15thNight
9%318%39%24%4
495
16th to endNight
17%422%32%19%1
563
October1st to 15thNight
19%5%25%35%12%
660
16th to endNight
25%8%28%28%9%
704
November1st to 15thNight
18%8%31%30%9%
825
16th to endNight
20%11%29%29%9%
900
December1st to 15thNight
20%11%30%29%7%
900
16th to endNight
24%7%29%26%8%2
960
Page generated at 2017-04-10 08:00:35. Version ac04

Copyright 2017 A. Danko


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