Eyeline Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eyeline Observatory clear sky chart from 2005-11-06 to 2024-01-27.

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
30%
22936
12%
75041
8%
22888
35%
22888
14%
55530

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
10%
757
7%
2649
2%
757
15%
757
4%
2251
January11th to 20thNight
10%
760
3%
2527
2%
760
12%
760
4%
2245
January21st to endNight
13%
820
6%
2664
3%
820
16%
820
5%
2315
February1st to 10thNight
8%
720
6%
2340
1%
720
13%
720
5%
1986
February11th to 20thNight
13%
703
7%
2275
2%
700
21%
700
8%
1863
February21st to endNight
16%
592
7%
1862
2%
592
22%
592
8%
1495
March1st to 10thNight
21%
720
12%
1980
6%
720
26%
720
14%
1532
March11th to 20thNight
23%
720
15%
1980
7%
720
30%
720
15%
1497
March21st to endNight
29%
792
17%
2178
8%
792
36%
792
19%
1596
April1st to 10thNight
23%
720
13%
1814
4%
720
29%
720
18%
1382
April11th to 20thNight
31%
707
16%
1771
6%
707
35%
707
22%
1280
April21st to endNight
34%
540
17%
1620
9%
540
40%
540
20%
1147
May1st to 10thNight
40%
540
14%
1620
10%
540
44%
540
22%
1121
May11th to 20thNight
42%
354
20%
1416
18%
354
52%
354
21%
863
May21st to endNight
52%
388
16%
1551
18%
388
59%
388
23%
896
June1st to 10thNight
46%
360
15%
1440
15%
360
56%
360
20%
909
June11th to 20thNight
48%
360
15%
1440
18%
360
56%
360
23%
840
June21st to endNight
50%
360
14%
1440
15%
360
57%
360
21%
845
July1st to 10thNight
58%
350
17%
1400
22%
350
64%
350
30%
734
July11th to 20thNight
53%
348
17%
1392
22%
348
57%
348
26%
783
July21st to endNight
59%
548
16%
1632
13%
518
62%
518
30%
997
August1st to 10thNight
63%
537
18%
1600
16%
534
64%
534
32%
964
August11th to 20thNight
60%
534
19%
1598
14%
534
63%
534
31%
989
August21st to endNight
56%
706
20%
1894
11%
706
59%
706
34%
1201
September1st to 10thNight
53%
720
16%
1800
9%
720
56%
720
31%
1212
September11th to 20thNight
56%
720
25%
1867
16%
720
59%
720
35%
1183
September21st to endNight
46%
720
19%
2038
14%
720
49%
720
23%
1387
October1st to 10thNight
40%
720
15%
2160
14%
720
44%
720
20%
1506
October11th to 20thNight
27%
720
11%
2160
8%
720
33%
720
14%
1611
October21st to endNight
22%
792
12%
2376
8%
792
28%
792
11%
1864
November1st to 10thNight
30%
740
17%
2437
13%
740
38%
740
17%
1679
November11th to 20thNight
21%
760
13%
2660
8%
760
28%
760
12%
1948
November21st to endNight
17%
760
8%
2660
5%
760
22%
760
8%
2086
December1st to 10thNight
12%
760
4%
2660
3%
760
14%
760
4%
2292
December11th to 20thNight
11%
760
4%
3260
2%
759
15%
759
4%
2747
December21st to endNight
9%
828
2%
4880
1%
817
13%
817
2%
4284

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
15%10%47%6%35%5%5%7%32%
74791
Night
17%11%48%7%45%5%5%6%29%
75253
TransparencyDay
50%7%13%18%9%1
74505
Night
54%8%11%17%9%1
75073
SeeingDay
20%13%26%23%12%4
13414
Night
22%13%27%26%11%1
22948

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
16%15%8%11%11%46%5%6%414%
1517
11th to 20thDay
18%19%7%14%8%5%5%45%5%11%
1650
21st to endDay
15%17%7%15%11%7%6%44410%
1836
February1st to 10thDay
20%15%7%13%8%5%5%445%14%
1620
11th to 20thDay
13%16%9%14%10%5%5%5%45%15%
1573
21st to endDay
20%14%411%10%46%45%418%
1389
March1st to 10thDay
16%10%6%11%9%46%5%45%24%
1977
11th to 20thDay
14%13%48%6%4445%5%32%
1980
21st to endDay
19%9%48%6%4445%6%32%
2178
April1st to 10thDay
17%10%5%8%5%44446%33%
2146
11th to 20thDay
18%9%36%5%345%5%7%37%
2154
21st to endDay
19%9%46%5%4445%6%35%
2340
May1st to 10thDay
14%9%36%5%35%5%6%8%35%
2340
11th to 20thDay
15%7%25%5%35%5%6%7%40%
2478
21st to endDay
10%426%5%25%6%6%8%45%
2725
June1st to 10thDay
14%6%35%435%5%5%9%41%
2520
11th to 20thDay
11%5%35%445%5%6%11%41%
2520
21st to endDay
12%5%344346%6%9%44%
2520
July1st to 10thDay
7%424435%5%7%9%51%
2520
11th to 20thDay
10%6%35%5%45%5%7%11%40%
2520
21st to endDay
10%425%6%37%6%8%10%39%
2586
August1st to 10thDay
9%4345%345%7%10%45%
2327
11th to 20thDay
9%5%35%6%36%6%8%9%41%
2303
21st to endDay
10%5%25%43447%10%45%
2444
September1st to 10thDay
14%6%35%5%25%5%5%9%42%
2160
11th to 20thDay
11%5%25%5%35%46%8%45%
2089
21st to endDay
13%7%36%5%45%6%6%9%36%
1922
October1st to 10thDay
19%8%37%5%35%447%34%
1800
11th to 20thDay
21%12%38%6%3445%8%27%
1800
21st to endDay
25%14%48%6%34445%23%
1980
November1st to 10thDay
13%12%49%6%45%5%5%8%30%
1639
11th to 20thDay
15%13%5%9%5%35%5%6%6%27%
1520
21st to endDay
21%16%5%9%6%3445%6%20%
1520
December1st to 10thDay
19%20%8%10%8%4445%5%13%
1520
11th to 20thDay
21%17%7%12%8%44445%13%
1906
21st to endDay
28%20%7%11%6%3333311%
2772
January1st to 10thNight
18%18%7%11%9%5%5%445%15%
2649
11th to 20thNight
19%19%8%13%10%4443411%
2527
21st to endNight
15%15%7%14%11%6%5%5%5%5%12%
2664
February1st to 10thNight
17%17%6%13%9%35%45%5%15%
2340
11th to 20thNight
16%14%6%12%10%5%5%5%45%18%
2273
21st to endNight
18%14%6%12%8%3445%5%19%
1862
March1st to 10thNight
15%11%411%9%45%446%26%
1970
11th to 20thNight
18%12%48%7%3445%5%29%
1979
21st to endNight
17%10%5%9%5%34445%34%
2178
April1st to 10thNight
19%11%47%6%3445%433%
1814
11th to 20thNight
18%8%36%6%45%5%45%37%
1771
21st to endNight
19%7%46%5%35%6%5%7%33%
1620
May1st to 10thNight
17%8%35%6%35%5%5%8%35%
1620
11th to 20thNight
14%6%35%5%446%5%8%40%
1415
21st to endNight
11%5%25%5%35%5%6%7%45%
1550
June1st to 10thNight
13%435%7%5%6%6%7%8%36%
1440
11th to 20thNight
9%6%36%5%36%6%5%8%43%
1440
21st to endNight
12%6%25%5%45%5%6%9%42%
1440
July1st to 10thNight
7%325%435%46%7%54%
1440
11th to 20thNight
10%5%25%5%35%6%5%9%45%
1440
21st to endNight
10%425%5%346%7%9%46%
1728
August1st to 10thNight
8%6%25%5%346%7%9%45%
1611
11th to 20thNight
9%5%35%445%6%7%8%44%
1598
21st to endNight
10%435%435%47%8%46%
1894
September1st to 10thNight
13%6%36%5%25%5%6%8%43%
1800
11th to 20thNight
13%5%25%3345%5%6%49%
1867
21st to endNight
17%6%36%5%35%5%6%7%38%
2038
October1st to 10thNight
17%7%37%5%345%6%6%36%
2160
11th to 20thNight
23%9%47%6%3445%6%28%
2160
21st to endNight
27%11%36%7%445%5%5%24%
2376
November1st to 10thNight
17%9%46%6%34447%35%
2437
11th to 20thNight
17%12%48%6%5%5%5%5%6%27%
2660
21st to endNight
20%15%5%9%7%45%6%5%5%20%
2660
December1st to 10thNight
21%19%7%12%7%35%5%45%12%
2660
11th to 20thNight
17%20%7%11%8%35%445%16%
3288
21st to endNight
30%17%6%9%7%45%45%49%
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
70%9%8%10%2
1518
11th to 20thDay
74%8%9%7%1
1650
21st to endDay
77%7%9%5%2
1836
February1st to 10thDay
73%7%10%9%1
1620
11th to 20thDay
72%6%8%10%3
1582
21st to endDay
68%6%11%10%5%
1389
March1st to 10thDay
61%6%14%14%5%1
1980
11th to 20thDay
53%7%12%16%10%1
1980
21st to endDay
53%6%10%20%10%2
2178
April1st to 10thDay
53%5%13%19%10%1
2146
11th to 20thDay
47%6%11%20%14%2
2154
21st to endDay
50%413%18%12%2
2340
May1st to 10thDay
46%6%11%22%12%2
2340
11th to 20thDay
43%8%12%23%12%2
2482
21st to endDay
36%8%17%24%14%2
2725
June1st to 10thDay
40%7%14%22%15%2
2520
11th to 20thDay
37%7%15%25%14%1
2520
21st to endDay
35%8%16%24%16%1
2520
July1st to 10thDay
28%9%14%26%19%3
2450
11th to 20thDay
36%8%18%27%11%1
2445
21st to endDay
37%10%18%20%13%1
2441
August1st to 10thDay
32%8%19%27%12%1
2314
11th to 20thDay
37%9%18%25%11%1
2303
21st to endDay
36%6%16%28%12%1
2444
September1st to 10thDay
39%7%16%26%11%1
2160
11th to 20thDay
36%7%15%26%15%1
2089
21st to endDay
44%7%17%22%9%1
1922
October1st to 10thDay
49%7%13%18%12%1
1800
11th to 20thDay
55%8%15%16%6%1
1800
21st to endDay
64%6%12%13%5%1
1980
November1st to 10thDay
52%9%13%17%9%1
1639
11th to 20thDay
54%9%17%13%7%1
1520
21st to endDay
64%8%14%11%3
1520
December1st to 10thDay
73%8%11%7%1
1520
11th to 20thDay
70%11%10%7%2
1906
21st to endDay
78%6%9%6%1
2772
January1st to 10thNight
70%9%8%9%3
2649
11th to 20thNight
77%7%9%6%1
2527
21st to endNight
72%8%8%8%3
2664
February1st to 10thNight
69%9%9%10%3
2340
11th to 20thNight
67%7%11%11%4
2275
21st to endNight
65%6%11%12%6%
1862
March1st to 10thNight
57%7%12%17%6%1
1980
11th to 20thNight
55%6%10%18%10%1
1980
21st to endNight
53%5%7%20%13%2
2178
April1st to 10thNight
54%6%9%20%10%1
1814
11th to 20thNight
48%6%9%20%14%2
1771
21st to endNight
49%7%10%19%14%2
1620
May1st to 10thNight
46%6%10%20%15%2
1620
11th to 20thNight
41%7%11%24%14%3
1416
21st to endNight
36%8%13%23%17%3
1551
June1st to 10thNight
43%7%11%20%18%1
1440
11th to 20thNight
37%7%13%22%19%3
1440
21st to endNight
38%7%15%20%18%1
1440
July1st to 10thNight
30%7%12%27%22%3
1400
11th to 20thNight
34%8%14%27%16%2
1392
21st to endNight
34%8%15%23%17%3
1632
August1st to 10thNight
32%8%18%28%14%1
1600
11th to 20thNight
34%8%16%29%13%
1598
21st to endNight
34%8%14%29%14%2
1894
September1st to 10thNight
38%8%16%24%14%2
1800
11th to 20thNight
34%7%12%29%17%1
1867
21st to endNight
43%8%12%23%13%1
2038
October1st to 10thNight
46%8%11%20%14%1
2160
11th to 20thNight
54%7%13%18%7%1
2160
21st to endNight
61%7%11%13%8%1
2376
November1st to 10thNight
48%8%11%21%11%2
2437
11th to 20thNight
55%8%13%16%8%
2660
21st to endNight
61%9%14%13%3
2660
December1st to 10thNight
71%10%10%6%2
2660
11th to 20thNight
69%10%10%9%2
3288
21st to endNight
76%9%10%41
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
25%26%28%16%5%1
180
11th to 20thDay
26%29%29%12%22
242
21st to endDay
24%24%29%18%41
282
February1st to 10thDay
35%24%32%10%
240
11th to 20thDay
25%26%37%11%1
240
21st to endDay
35%19%34%10%2
247
March1st to 10thDay
23%20%34%17%5%
420
11th to 20thDay
25%15%33%22%41
420
21st to endDay
29%16%28%18%6%2
462
April1st to 10thDay
22%18%32%22%6%1
420
11th to 20thDay
27%16%23%20%9%4
412
21st to endDay
25%9%35%21%8%2
420
May1st to 10thDay
24%10%29%21%12%4
423
11th to 20thDay
17%9%25%27%17%4
447
21st to endDay
13%8%25%32%16%7%
485
June1st to 10thDay
16%10%26%34%12%2
450
11th to 20thDay
15%9%22%33%18%3
450
21st to endDay
17%6%27%33%14%3
450
July1st to 10thDay
9%419%34%25%9%
445
11th to 20thDay
14%7%20%31%20%8%
444
21st to endDay
11%6%27%32%18%6%
488
August1st to 10thDay
10%422%31%21%11%
446
11th to 20thDay
11%5%20%32%23%9%
439
21st to endDay
12%7%21%30%20%9%
495
September1st to 10thDay
14%8%22%28%19%9%
450
11th to 20thDay
12%6%20%25%24%13%
450
21st to endDay
16%11%28%22%16%8%
450
October1st to 10thDay
23%15%21%18%16%7%
450
11th to 20thDay
24%22%28%18%7%2
450
21st to endDay
37%14%24%18%7%
495
November1st to 10thDay
23%18%28%20%8%2
304
11th to 20thDay
28%24%25%18%32
180
21st to endDay
29%24%30%12%4
180
December1st to 10thDay
29%21%33%11%6%1
180
11th to 20thDay
31%27%28%12%2
180
21st to endDay
29%29%30%9%3
198
January1st to 10thNight
28%24%29%13%5%
760
11th to 20thNight
31%22%28%16%3
760
21st to endNight
24%18%33%20%4
820
February1st to 10thNight
27%23%31%16%2
720
11th to 20thNight
23%21%34%17%4
703
21st to endNight
28%19%31%21%2
592
March1st to 10thNight
23%16%34%22%6%
720
11th to 20thNight
24%18%28%23%6%1
720
21st to endNight
22%10%32%26%10%1
792
April1st to 10thNight
25%16%30%25%4
720
11th to 20thNight
21%13%30%25%9%1
707
21st to endNight
22%8%28%32%10%
540
May1st to 10thNight
20%6%25%31%15%2
540
11th to 20thNight
18%429%40%10%1
354
21st to endNight
13%7%23%37%18%2
389
June1st to 10thNight
16%328%37%15%1
360
11th to 20thNight
12%5%28%37%17%1
360
21st to endNight
13%5%26%43%13%1
360
July1st to 10thNight
11%420%42%22%1
350
11th to 20thNight
10%424%39%20%2
348
21st to endNight
11%420%43%22%1
548
August1st to 10thNight
11%5%14%39%28%4
537
11th to 20thNight
11%418%35%29%4
534
21st to endNight
13%421%35%24%4
706
September1st to 10thNight
15%6%18%35%23%4
720
11th to 20thNight
16%419%28%26%6%
720
21st to endNight
19%7%22%29%18%5%
720
October1st to 10thNight
20%10%23%28%16%3
720
11th to 20thNight
28%14%26%24%8%1
720
21st to endNight
34%14%23%24%5%1
792
November1st to 10thNight
24%13%28%24%10%1
740
11th to 20thNight
25%19%29%17%8%1
760
21st to endNight
28%18%30%17%6%
760
December1st to 10thNight
34%21%24%16%4
760
11th to 20thNight
25%23%32%16%4
760
21st to endNight
33%18%32%15%2
836
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