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 2005-11-06 to 2024-01-12.

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%
24938
10%
74274
6%
24880
42%
24880
12%
59103

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
35%
950
8%
2648
5%
946
38%
946
10%
2190
January11th to 20thNight
25%
908
5%
2541
2%
908
28%
908
6%
2243
January21st to endNight
28%
990
7%
2691
3%
990
31%
990
10%
2283
February1st to 10thNight
30%
900
9%
2340
2%
900
34%
900
13%
1901
February11th to 20thNight
33%
878
13%
2273
5%
874
37%
874
15%
1814
February21st to endNight
34%
660
11%
1844
5%
660
38%
660
13%
1479
March1st to 10thNight
39%
681
9%
2122
7%
681
41%
681
12%
1692
March11th to 20thNight
37%
540
13%
1980
11%
540
42%
540
12%
1483
March21st to endNight
38%
594
11%
2102
10%
594
42%
594
9%
1677
April1st to 10thNight
33%
540
8%
1800
6%
540
38%
540
11%
1425
April11th to 20thNight
41%
533
11%
1775
11%
533
44%
533
11%
1403
April21st to endNight
40%
540
10%
1601
7%
540
45%
540
12%
1292
May1st to 10thNight
40%
540
10%
1440
5%
540
43%
540
13%
1166
May11th to 20thNight
48%
531
14%
1416
8%
531
51%
531
17%
1098
May21st to endNight
50%
584
8%
1552
4%
582
51%
582
14%
1257
June1st to 10thNight
51%
540
7%
1440
4%
540
52%
540
15%
1140
June11th to 20thNight
53%
540
10%
1354
6%
540
55%
540
19%
1042
June21st to endNight
52%
540
9%
1260
6%
540
52%
540
18%
992
July1st to 10thNight
69%
525
11%
1279
5%
525
70%
525
24%
948
July11th to 20thNight
60%
522
12%
1392
6%
522
62%
522
21%
1040
July21st to endNight
67%
591
12%
1487
6%
558
68%
558
21%
1084
August1st to 10thNight
64%
537
13%
1476
9%
534
66%
534
19%
1078
August11th to 20thNight
58%
534
16%
1600
14%
534
62%
534
19%
1143
August21st to endNight
57%
594
13%
1909
14%
594
59%
594
17%
1363
September1st to 10thNight
59%
540
14%
1800
15%
540
63%
540
18%
1265
September11th to 20thNight
59%
540
16%
1800
16%
540
62%
540
18%
1277
September21st to endNight
41%
654
10%
2044
5%
654
46%
654
15%
1533
October1st to 10thNight
42%
720
12%
2160
8%
720
45%
720
14%
1661
October11th to 20thNight
31%
720
10%
2160
3%
720
37%
720
10%
1766
October21st to endNight
31%
792
9%
2494
6%
792
35%
792
10%
1992
November1st to 10thNight
34%
844
10%
2510
6%
844
38%
844
11%
2030
November11th to 20thNight
27%
950
11%
2660
4%
950
33%
950
9%
2219
November21st to endNight
31%
950
10%
2660
5%
950
35%
950
12%
2138
December1st to 10thNight
26%
950
5%
2660
2%
950
29%
950
7%
2268
December11th to 20thNight
21%
948
7%
3194
1%
948
25%
948
6%
2669
December21st to endNight
19%
1038
3%
4810
1%
1026
23%
1026
4%
4052

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%8%46%6%35%5%5%7%37%
75105
Night
14%10%47%6%3445%7%37%
74609
TransparencyDay
32%36%10%15%6%1
74809
Night
33%36%9%15%6%1
74439
SeeingDay
16%6%24%33%17%4
14921
Night
18%6%27%34%14%1
24951

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 10thDay
8%12%7%9%7%45%5%5%5%32%
1517
11th to 20thDay
10%14%6%11%8%47%5%7%7%21%
1448
21st to endDay
9%10%7%12%9%5%6%7%6%8%22%
1664
February1st to 10thDay
7%12%5%8%7%35%6%6%7%33%
1620
11th to 20thDay
9%11%47%6%25%46%5%40%
1574
21st to endDay
10%11%48%7%35%45%6%37%
1410
March1st to 10thDay
13%9%47%5%45%6%6%7%35%
1852
11th to 20thDay
13%8%47%6%3345%7%40%
1980
21st to endDay
17%8%46%5%35%5%5%7%33%
2254
April1st to 10thDay
16%9%37%7%46%446%33%
2160
11th to 20thDay
19%8%46%5%45%5%5%7%32%
2134
21st to endDay
21%8%45%5%345%5%6%34%
2355
May1st to 10thDay
17%8%37%6%44446%37%
2520
11th to 20thDay
17%6%35%6%345%6%7%39%
2479
21st to endDay
16%6%35%5%35%5%5%8%38%
2725
June1st to 10thDay
11%5%25%5%45%6%5%9%43%
2520
11th to 20thDay
14%5%35%5%35%6%6%7%41%
2599
21st to endDay
14%5%245%37%6%8%10%37%
2700
July1st to 10thDay
8%3245%345%6%9%52%
2638
11th to 20thDay
8%5%25%6%36%5%6%9%46%
2520
21st to endDay
6%325%5%35%5%7%9%51%
2743
August1st to 10thDay
10%426%5%36%6%6%8%45%
2451
11th to 20thDay
12%5%25%5%35%5%5%7%46%
2301
21st to endDay
12%5%244245%5%8%49%
2446
September1st to 10thDay
11%5%344345%6%9%46%
2160
11th to 20thDay
14%5%26%5%345%5%6%45%
2160
21st to endDay
18%7%45%43445%6%40%
1893
October1st to 10thDay
20%6%36%5%345%5%6%37%
1800
11th to 20thDay
16%12%46%6%45%5%5%7%32%
1800
21st to endDay
19%11%37%6%4445%7%31%
1861
November1st to 10thDay
13%10%37%7%45%6%6%5%34%
1564
11th to 20thDay
15%14%7%9%8%45%5%5%5%25%
1520
21st to endDay
15%11%5%8%6%45%6%6%7%28%
1520
December1st to 10thDay
11%13%6%9%9%5%6%6%5%7%23%
1520
11th to 20thDay
14%15%7%9%7%5%7%7%5%5%21%
1914
21st to endDay
28%17%5%9%6%2342320%
2783
January1st to 10thNight
10%10%6%7%6%45%6%6%8%33%
2648
11th to 20thNight
11%12%7%11%9%45%5%5%6%26%
2541
21st to endNight
10%14%7%9%7%5%5%45%7%26%
2691
February1st to 10thNight
7%11%6%9%8%3445%6%36%
2340
11th to 20thNight
7%11%48%6%45%45%5%40%
2273
21st to endNight
13%12%5%7%5%3336%6%37%
1844
March1st to 10thNight
11%11%37%6%45%446%37%
2113
11th to 20thNight
14%8%5%7%434445%42%
1979
21st to endNight
17%10%47%6%2435%5%37%
2102
April1st to 10thNight
17%10%46%5%345%5%6%33%
1800
11th to 20thNight
19%10%36%5%44446%33%
1775
21st to endNight
22%10%35%5%335%5%6%33%
1601
May1st to 10thNight
16%9%47%6%3435%7%36%
1440
11th to 20thNight
17%6%246%3446%6%42%
1416
21st to endNight
17%5%25%6%445%7%8%36%
1551
June1st to 10thNight
13%5%26%6%45%5%6%9%38%
1440
11th to 20thNight
13%7%35%435%5%6%7%41%
1354
21st to endNight
13%7%25%6%35%5%6%8%41%
1260
July1st to 10thNight
6%3244245%6%9%54%
1317
11th to 20thNight
7%4244345%6%9%52%
1440
21st to endNight
7%323435%5%6%9%54%
1575
August1st to 10thNight
8%4245%3446%8%52%
1485
11th to 20thNight
13%5%25%5%23347%51%
1600
21st to endNight
15%6%15%42345%7%49%
1909
September1st to 10thNight
11%5%34425%5%47%51%
1800
11th to 20thNight
12%42432445%8%51%
1800
21st to endNight
18%6%25%42446%8%40%
2044
October1st to 10thNight
17%7%26%44445%6%40%
2160
11th to 20thNight
17%9%36%6%45%5%5%7%35%
2160
21st to endNight
21%9%37%6%345%47%31%
2494
November1st to 10thNight
14%9%47%5%35%5%5%7%35%
2510
11th to 20thNight
17%10%48%5%35%5%5%7%32%
2660
21st to endNight
13%10%47%5%346%5%7%36%
2660
December1st to 10thNight
11%13%7%10%7%45%5%5%7%26%
2660
11th to 20thNight
12%16%6%9%7%35%6%5%7%24%
3283
21st to endNight
29%18%46%42333423%
4884

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
36%40%8%13%3
1518
11th to 20thDay
40%42%9%7%2
1448
21st to endDay
39%38%7%10%5%
1664
February1st to 10thDay
32%36%10%13%8%1
1620
11th to 20thDay
30%37%11%15%6%1
1583
21st to endDay
32%36%11%12%7%1
1410
March1st to 10thDay
34%36%12%13%4
1854
11th to 20thDay
30%36%14%15%5%
1980
21st to endDay
35%37%10%14%4
2254
April1st to 10thDay
34%35%7%14%9%1
2160
11th to 20thDay
37%34%8%12%7%1
2134
21st to endDay
35%35%9%14%6%1
2355
May1st to 10thDay
34%36%8%14%7%1
2520
11th to 20thDay
28%37%10%17%6%2
2483
21st to endDay
29%37%9%15%9%
2725
June1st to 10thDay
27%37%11%17%8%
2520
11th to 20thDay
27%36%10%16%10%1
2599
21st to endDay
26%37%12%18%7%1
2700
July1st to 10thDay
19%38%9%21%12%1
2567
11th to 20thDay
21%38%10%19%10%1
2445
21st to endDay
21%38%12%19%9%1
2591
August1st to 10thDay
25%37%9%21%7%2
2436
11th to 20thDay
25%35%10%19%10%
2301
21st to endDay
22%36%9%22%11%1
2446
September1st to 10thDay
22%36%13%22%6%
2160
11th to 20thDay
27%35%13%20%4
2160
21st to endDay
29%36%10%20%4
1893
October1st to 10thDay
31%36%11%19%4
1800
11th to 20thDay
39%36%10%10%4
1800
21st to endDay
36%37%9%13%5%
1861
November1st to 10thDay
32%40%8%13%6%1
1564
11th to 20thDay
41%39%8%10%2
1520
21st to endDay
34%41%10%12%21
1520
December1st to 10thDay
38%40%11%9%1
1520
11th to 20thDay
46%33%8%10%31
1915
21st to endDay
58%24%5%8%4
2783
January1st to 10thNight
33%40%10%14%3
2648
11th to 20thNight
39%43%8%8%2
2541
21st to endNight
38%37%6%12%5%
2691
February1st to 10thNight
34%35%8%14%7%1
2340
11th to 20thNight
30%37%9%15%8%1
2274
21st to endNight
34%35%9%16%5%1
1844
March1st to 10thNight
33%37%11%13%6%1
2124
11th to 20thNight
29%36%10%17%7%
1980
21st to endNight
37%35%8%14%6%1
2102
April1st to 10thNight
34%36%5%12%11%1
1800
11th to 20thNight
35%35%7%14%9%
1775
21st to endNight
36%35%7%15%7%
1601
May1st to 10thNight
34%35%8%13%9%1
1440
11th to 20thNight
27%37%7%19%9%2
1417
21st to endNight
31%38%8%14%8%1
1552
June1st to 10thNight
30%37%10%17%6%1
1440
11th to 20thNight
24%37%9%17%11%2
1354
21st to endNight
27%37%10%16%10%
1260
July1st to 10thNight
18%38%10%19%14%1
1279
11th to 20thNight
20%38%8%19%12%2
1392
21st to endNight
19%38%13%19%9%2
1487
August1st to 10thNight
22%36%8%24%7%3
1476
11th to 20thNight
22%35%10%20%11%2
1600
21st to endNight
23%36%8%19%14%1
1909
September1st to 10thNight
21%36%9%24%9%
1800
11th to 20thNight
22%36%11%26%5%
1800
21st to endNight
26%37%11%20%6%
2044
October1st to 10thNight
29%36%9%20%5%1
2160
11th to 20thNight
36%36%9%14%4
2160
21st to endNight
33%37%9%15%5%
2494
November1st to 10thNight
31%40%9%14%5%1
2510
11th to 20thNight
35%39%8%12%6%
2660
21st to endNight
30%40%12%13%41
2660
December1st to 10thNight
37%40%10%10%2
2660
11th to 20thNight
42%34%9%12%3
3281
21st to endNight
54%25%8%11%2
4884

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
14%429%32%20%1
270
11th to 20thDay
19%5%23%37%16%
243
21st to endDay
12%5%24%42%13%4
264
February1st to 10thDay
13%8%35%37%7%1
240
11th to 20thDay
13%8%42%24%11%2
240
21st to endDay
16%11%29%40%5%
198
March1st to 10thDay
15%5%28%37%14%1
240
11th to 20thDay
14%5%25%43%10%4
240
21st to endDay
22%9%24%29%13%4
340
April1st to 10thDay
20%10%25%34%10%1
420
11th to 20thDay
24%6%19%34%15%2
412
21st to endDay
23%7%24%29%14%3
588
May1st to 10thDay
19%7%29%32%10%3
603
11th to 20thDay
19%7%24%30%16%4
625
21st to endDay
18%6%21%33%20%3
679
June1st to 10thDay
10%6%25%36%19%4
630
11th to 20thDay
15%6%25%37%16%2
630
21st to endDay
14%5%22%32%21%5%
630
July1st to 10thDay
10%219%37%25%7%
621
11th to 20thDay
11%424%32%21%8%
618
21st to endDay
7%318%42%22%7%
684
August1st to 10thDay
12%217%35%27%5%
626
11th to 20thDay
14%5%15%32%29%6%
615
21st to endDay
17%5%17%29%25%7%
565
September1st to 10thDay
12%420%37%23%3
450
11th to 20thDay
16%423%30%22%5%
450
21st to endDay
22%9%25%24%16%4
316
October1st to 10thDay
21%6%23%31%14%4
270
11th to 20thDay
18%9%33%27%10%2
270
21st to endDay
24%9%36%24%6%
297
November1st to 10thDay
18%10%30%30%10%1
270
11th to 20thDay
19%10%34%28%9%1
270
21st to endDay
19%11%27%34%8%1
270
December1st to 10thDay
16%7%34%29%12%1
270
11th to 20thDay
20%13%31%27%8%1
270
21st to endDay
27%8%28%30%6%1
297
January1st to 10thNight
14%7%32%35%11%1
950
11th to 20thNight
17%6%34%32%10%1
908
21st to endNight
18%6%32%34%10%1
990
February1st to 10thNight
12%6%35%37%8%1
900
11th to 20thNight
13%5%37%33%11%1
879
21st to endNight
17%6%31%35%10%
660
March1st to 10thNight
16%6%27%39%11%1
684
11th to 20thNight
19%431%35%10%1
540
21st to endNight
21%5%24%31%16%3
594
April1st to 10thNight
22%5%30%33%9%1
540
11th to 20thNight
24%6%21%37%11%1
533
21st to endNight
26%5%19%34%12%3
540
May1st to 10thNight
18%6%28%35%13%2
540
11th to 20thNight
20%421%36%18%2
531
21st to endNight
18%5%16%37%22%2
584
June1st to 10thNight
16%419%40%20%1
540
11th to 20thNight
16%417%46%16%1
540
21st to endNight
16%417%39%22%3
540
July1st to 10thNight
9%114%39%33%3
525
11th to 20thNight
10%222%37%27%3
522
21st to endNight
8%216%42%28%3
591
August1st to 10thNight
10%215%42%28%2
537
11th to 20thNight
14%315%34%30%4
534
21st to endNight
17%5%15%35%25%4
594
September1st to 10thNight
12%419%38%25%3
540
11th to 20thNight
15%418%37%24%2
540
21st to endNight
21%5%26%29%17%2
654
October1st to 10thNight
20%6%24%33%15%1
720
11th to 20thNight
21%9%32%28%9%1
720
21st to endNight
25%8%28%29%9%
792
November1st to 10thNight
19%9%30%32%10%
844
11th to 20thNight
20%12%31%26%11%1
950
21st to endNight
19%9%35%30%7%
950
December1st to 10thNight
18%11%32%32%7%
950
11th to 20thNight
21%9%34%26%9%1
950
21st to endNight
28%7%32%25%7%1
1045
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