Eastlake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eastlake clear sky chart from 2005-11-06 to 2024-01-31.

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
33%
23359
12%
74938
9%
23310
37%
23310
15%
56044

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
9%
758
7%
2459
2%
757
14%
757
6%
2125
January11th to 20thNight
11%
760
4%
2470
2%
760
13%
760
5%
2142
January21st to endNight
13%
835
6%
2711
3%
835
17%
835
6%
2350
February1st to 10thNight
15%
720
5%
2340
2%
720
19%
720
7%
1973
February11th to 20thNight
17%
701
8%
2235
3%
700
22%
700
8%
1816
February21st to endNight
15%
592
10%
1776
2%
592
24%
592
10%
1415
March1st to 10thNight
23%
720
13%
2029
8%
720
29%
720
14%
1542
March11th to 20thNight
28%
720
17%
1980
9%
720
34%
720
19%
1446
March21st to endNight
30%
792
15%
2178
9%
792
34%
792
17%
1657
April1st to 10thNight
31%
720
11%
1936
5%
720
35%
720
19%
1436
April11th to 20thNight
33%
577
17%
1641
9%
577
39%
577
21%
1150
April21st to endNight
38%
540
16%
1620
9%
540
43%
540
22%
1115
May1st to 10thNight
40%
540
11%
1620
8%
540
41%
540
17%
1168
May11th to 20thNight
43%
531
15%
1592
12%
531
46%
531
21%
1100
May21st to endNight
60%
502
15%
1665
14%
502
63%
502
28%
1020
June1st to 10thNight
50%
360
15%
1440
17%
360
56%
360
20%
873
June11th to 20thNight
54%
360
17%
1440
20%
360
61%
360
22%
862
June21st to endNight
56%
360
18%
1286
19%
360
62%
360
25%
798
July1st to 10thNight
65%
474
15%
1465
17%
474
67%
474
33%
866
July11th to 20thNight
60%
522
17%
1566
16%
522
62%
522
32%
936
July21st to endNight
61%
591
16%
1672
15%
558
63%
558
29%
1059
August1st to 10thNight
65%
537
18%
1600
17%
534
65%
534
32%
964
August11th to 20thNight
63%
534
21%
1598
17%
534
65%
534
29%
1022
August21st to endNight
58%
614
20%
1802
15%
614
61%
614
30%
1126
September1st to 10thNight
56%
720
18%
1879
12%
720
59%
720
30%
1267
September11th to 20thNight
61%
720
24%
1980
19%
720
64%
720
32%
1239
September21st to endNight
47%
720
18%
1980
15%
720
50%
720
24%
1389
October1st to 10thNight
46%
720
17%
2106
16%
720
49%
720
23%
1429
October11th to 20thNight
28%
720
13%
2160
9%
720
35%
720
15%
1602
October21st to endNight
21%
792
12%
2381
8%
792
27%
792
11%
1879
November1st to 10thNight
30%
740
15%
2406
13%
740
35%
740
16%
1727
November11th to 20thNight
18%
760
11%
2527
8%
760
24%
760
10%
2012
November21st to endNight
16%
760
8%
2660
5%
760
21%
760
7%
2176
December1st to 10thNight
11%
760
3%
2660
2%
760
13%
760
4%
2341
December11th to 20thNight
11%
760
4%
3281
2%
759
15%
759
4%
2753
December21st to endNight
11%
827
3%
4797
2%
817
16%
817
2%
4269

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
16%11%47%6%3445%7%31%
74939
Night
17%13%5%8%6%3445%6%29%
75161
TransparencyDay
51%7%12%18%10%1
74660
Night
56%7%11%16%9%1
74959
SeeingDay
20%10%26%27%14%3
13671
Night
23%12%25%26%13%2
23374

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 10thDay
19%19%9%13%8%3433415%
1706
11th to 20thDay
18%20%10%14%8%35%33412%
1710
21st to endDay
19%19%11%15%10%3344310%
1872
February1st to 10thDay
18%18%7%13%10%3434416%
1620
11th to 20thDay
15%15%8%14%10%44345%18%
1609
21st to endDay
19%13%5%11%7%25%5%46%21%
1480
March1st to 10thDay
18%14%6%8%6%245%5%7%26%
1930
11th to 20thDay
16%14%5%9%6%34345%30%
1980
21st to endDay
21%13%5%8%5%34445%28%
2178
April1st to 10thDay
17%11%5%7%5%3446%6%33%
2023
11th to 20thDay
19%11%35%5%35%5%5%6%34%
2284
21st to endDay
21%10%46%5%33446%35%
2340
May1st to 10thDay
17%10%37%7%35%45%6%34%
2340
11th to 20thDay
18%7%36%5%35%46%7%36%
2301
21st to endDay
11%5%25%7%36%5%6%9%40%
2607
June1st to 10thDay
15%6%25%5%26%6%7%8%39%
2520
11th to 20thDay
13%6%26%5%345%6%8%41%
2520
21st to endDay
13%5%245%45%5%6%10%42%
2659
July1st to 10thDay
10%425%5%35%5%6%10%46%
2432
11th to 20thDay
13%5%25%325%5%7%11%43%
2340
21st to endDay
11%5%245%345%7%10%43%
2547
August1st to 10thDay
9%5%25%5%35%5%7%10%44%
2327
11th to 20thDay
11%5%25%6%36%7%8%9%38%
2303
21st to endDay
13%5%25%435%5%6%10%41%
2534
September1st to 10thDay
16%5%35%4245%6%9%40%
2078
11th to 20thDay
12%6%25%435%5%6%9%43%
1980
21st to endDay
20%7%36%4345%5%8%37%
1980
October1st to 10thDay
18%5%36%6%345%5%8%38%
1854
11th to 20thDay
24%10%36%5%4345%7%30%
1800
21st to endDay
27%12%36%6%345%46%24%
1972
November1st to 10thDay
16%14%46%5%3445%6%33%
1672
11th to 20thDay
18%21%5%8%6%23435%25%
1649
21st to endDay
20%22%6%8%6%35%446%16%
1520
December1st to 10thDay
17%27%10%11%5%3433313%
1520
11th to 20thDay
18%21%10%14%5%24445%12%
1910
21st to endDay
24%23%9%11%7%343349%
2842
January1st to 10thNight
20%20%10%12%7%3333316%
2459
11th to 20thNight
19%21%10%13%8%3333315%
2470
21st to endNight
18%20%8%14%9%3333414%
2711
February1st to 10thNight
21%16%6%13%7%45%44418%
2340
11th to 20thNight
18%16%7%12%8%44345%19%
2233
21st to endNight
20%15%6%10%7%3445%323%
1776
March1st to 10thNight
16%14%5%8%6%35%445%29%
2029
11th to 20thNight
17%13%46%5%3435%6%33%
1980
21st to endNight
20%14%5%8%5%2345%5%30%
2178
April1st to 10thNight
18%13%5%6%5%2445%6%31%
1936
11th to 20thNight
17%9%37%5%35%46%7%34%
1641
21st to endNight
16%9%35%6%35%6%5%7%35%
1620
May1st to 10thNight
20%9%37%6%35%5%6%7%31%
1620
11th to 20thNight
15%8%47%6%3345%8%36%
1592
21st to endNight
11%5%245%345%7%10%43%
1664
June1st to 10thNight
10%7%36%6%35%5%6%6%42%
1440
11th to 20thNight
10%5%35%6%5%5%5%5%8%43%
1440
21st to endNight
10%5%25%6%46%5%6%10%41%
1286
July1st to 10thNight
10%5%25%4335%6%8%51%
1510
11th to 20thNight
8%5%26%4345%6%10%47%
1620
21st to endNight
10%5%25%446%47%9%43%
1771
August1st to 10thNight
8%5%35%5%35%5%6%8%48%
1611
11th to 20thNight
10%6%25%446%5%6%8%44%
1598
21st to endNight
12%5%25%435%5%6%9%45%
1802
September1st to 10thNight
13%6%345%35%5%5%8%43%
1879
11th to 20thNight
12%5%25%4345%6%7%48%
1980
21st to endNight
18%6%35%7%45%45%6%38%
1980
October1st to 10thNight
17%6%35%5%25%45%7%41%
2106
11th to 20thNight
22%9%37%6%3445%6%31%
2160
21st to endNight
30%10%47%5%33446%25%
2381
November1st to 10thNight
18%13%36%5%2345%6%33%
2406
11th to 20thNight
19%21%5%9%5%33345%22%
2527
21st to endNight
22%21%6%7%6%34345%19%
2660
December1st to 10thNight
23%25%9%8%5%2333414%
2660
11th to 20thNight
18%24%8%10%7%3434416%
3285
21st to endNight
23%24%7%10%7%3444410%
4810

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
75%6%8%8%3
1707
11th to 20thDay
77%6%9%5%2
1710
21st to endDay
78%5%7%7%3
1872
February1st to 10thDay
72%5%9%10%3
1620
11th to 20thDay
69%5%9%11%5%1
1618
21st to endDay
62%8%13%11%6%2
1480
March1st to 10thDay
57%5%15%17%6%
1930
11th to 20thDay
56%7%10%16%9%2
1980
21st to endDay
58%5%9%18%8%1
2178
April1st to 10thDay
50%6%13%17%13%1
2023
11th to 20thDay
49%7%13%16%13%2
2284
21st to endDay
50%7%12%19%9%3
2340
May1st to 10thDay
50%8%10%20%10%2
2340
11th to 20thDay
46%8%11%18%13%3
2305
21st to endDay
39%9%15%23%14%1
2607
June1st to 10thDay
40%9%12%24%14%1
2520
11th to 20thDay
38%10%16%21%13%2
2520
21st to endDay
36%9%12%26%16%2
2659
July1st to 10thDay
33%8%14%25%18%2
2367
11th to 20thDay
34%7%16%26%16%1
2271
21st to endDay
32%10%16%24%16%2
2405
August1st to 10thDay
32%10%16%28%13%
2314
11th to 20thDay
36%11%18%23%11%2
2303
21st to endDay
36%9%16%22%16%2
2534
September1st to 10thDay
40%7%16%20%14%2
2078
11th to 20thDay
36%8%16%24%15%1
1980
21st to endDay
45%8%11%22%14%1
1980
October1st to 10thDay
44%9%13%20%13%1
1854
11th to 20thDay
52%7%13%18%8%1
1800
21st to endDay
61%8%12%12%7%1
1972
November1st to 10thDay
52%7%11%18%11%1
1672
11th to 20thDay
64%410%13%7%2
1649
21st to endDay
70%6%9%10%4
1520
December1st to 10thDay
76%5%9%8%2
1520
11th to 20thDay
75%6%9%9%2
1906
21st to endDay
81%6%7%5%1
2842
January1st to 10thNight
75%5%7%9%3
2459
11th to 20thNight
76%5%9%8%2
2470
21st to endNight
76%5%8%8%3
2711
February1st to 10thNight
71%7%9%10%3
2340
11th to 20thNight
68%5%9%13%5%
2235
21st to endNight
64%6%9%13%7%1
1776
March1st to 10thNight
57%6%11%18%8%
2029
11th to 20thNight
52%6%11%18%11%2
1980
21st to endNight
57%5%7%18%11%2
2178
April1st to 10thNight
53%6%11%16%12%2
1936
11th to 20thNight
48%6%12%19%13%3
1641
21st to endNight
45%7%13%18%13%3
1620
May1st to 10thNight
52%7%10%16%11%3
1620
11th to 20thNight
46%8%10%17%15%5%
1593
21st to endNight
34%10%16%25%14%2
1665
June1st to 10thNight
40%8%10%24%15%3
1440
11th to 20thNight
38%8%12%21%18%3
1440
21st to endNight
36%11%12%24%16%1
1286
July1st to 10thNight
32%7%12%24%20%5%
1465
11th to 20thNight
33%7%14%25%19%3
1566
21st to endNight
35%9%14%22%17%3
1672
August1st to 10thNight
31%9%15%28%15%1
1600
11th to 20thNight
36%9%14%27%12%2
1598
21st to endNight
35%8%13%25%17%3
1802
September1st to 10thNight
38%9%13%24%13%3
1879
11th to 20thNight
35%7%14%24%19%1
1980
21st to endNight
46%7%11%19%16%1
1980
October1st to 10thNight
42%9%13%18%18%1
2106
11th to 20thNight
53%8%11%18%10%
2160
21st to endNight
61%7%10%13%7%1
2381
November1st to 10thNight
53%6%10%17%11%2
2406
11th to 20thNight
66%5%9%12%6%2
2527
21st to endNight
69%5%9%12%4
2660
December1st to 10thNight
77%7%7%7%3
2660
11th to 20thNight
72%7%11%8%2
3288
21st to endNight
78%8%8%5%1
4810

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
26%21%34%14%5%
270
11th to 20thDay
28%22%35%11%4
270
21st to endDay
28%19%35%16%2
294
February1st to 10thDay
29%19%35%17%
240
11th to 20thDay
29%18%37%16%1
240
21st to endDay
24%23%40%13%1
198
March1st to 10thDay
24%17%32%21%5%1
370
11th to 20thDay
22%15%35%23%41
420
21st to endDay
31%10%32%23%5%
462
April1st to 10thDay
20%12%34%25%7%1
420
11th to 20thDay
24%11%31%22%11%2
412
21st to endDay
25%10%30%26%7%1
420
May1st to 10thDay
25%6%31%28%7%2
423
11th to 20thDay
18%5%31%29%16%2
447
21st to endDay
13%321%33%24%5%
485
June1st to 10thDay
15%423%41%14%3
450
11th to 20thDay
16%6%20%36%21%2
450
21st to endDay
12%5%24%36%20%2
589
July1st to 10thDay
11%217%35%27%8%
491
11th to 20thDay
15%316%36%25%6%
444
21st to endDay
10%319%38%25%5%
488
August1st to 10thDay
9%318%35%25%9%
446
11th to 20thDay
13%415%36%26%7%
439
21st to endDay
13%319%34%24%8%
495
September1st to 10thDay
16%6%16%31%24%7%
450
11th to 20thDay
12%416%31%27%11%
450
21st to endDay
19%10%20%28%16%7%
450
October1st to 10thDay
15%10%24%26%21%5%
450
11th to 20thDay
26%11%29%25%7%1
450
21st to endDay
34%13%26%19%6%
487
November1st to 10thDay
19%19%26%24%10%2
270
11th to 20thDay
32%19%25%17%6%1
241
21st to endDay
32%21%29%17%1
180
December1st to 10thDay
25%24%29%18%21
180
11th to 20thDay
23%29%30%16%2
180
21st to endDay
30%21%32%15%1
220
January1st to 10thNight
29%22%32%13%4
760
11th to 20thNight
31%18%32%18%3
760
21st to endNight
25%17%34%19%4
835
February1st to 10thNight
31%16%31%19%3
720
11th to 20thNight
27%17%31%22%3
703
21st to endNight
26%16%36%20%1
592
March1st to 10thNight
21%14%34%26%4
720
11th to 20thNight
24%13%32%23%7%1
720
21st to endNight
25%10%28%26%9%1
792
April1st to 10thNight
22%12%28%31%8%
720
11th to 20thNight
21%9%33%25%11%2
577
21st to endNight
19%6%29%35%9%1
540
May1st to 10thNight
23%5%22%34%14%1
540
11th to 20thNight
17%6%23%33%18%2
531
21st to endNight
12%318%38%26%4
504
June1st to 10thNight
12%127%38%20%2
360
11th to 20thNight
13%320%37%26%1
360
21st to endNight
10%422%39%23%1
360
July1st to 10thNight
9%313%34%34%7%
474
11th to 20thNight
11%418%32%29%6%
522
21st to endNight
10%5%16%36%30%3
591
August1st to 10thNight
9%313%39%30%6%
537
11th to 20thNight
10%411%38%31%6%
534
21st to endNight
12%5%17%30%30%6%
614
September1st to 10thNight
16%416%31%26%7%
720
11th to 20thNight
13%5%14%32%30%7%
720
21st to endNight
18%8%21%27%20%6%
720
October1st to 10thNight
19%9%22%27%19%3
720
11th to 20thNight
26%13%26%25%9%1
720
21st to endNight
36%14%25%21%4
792
November1st to 10thNight
26%14%26%24%9%1
740
11th to 20thNight
33%16%28%16%5%1
760
21st to endNight
34%19%27%16%5%
760
December1st to 10thNight
35%20%28%13%5%
760
11th to 20thNight
29%23%32%14%3
760
21st to endNight
33%20%28%17%2
836
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