Eyeline Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eyeline Observatory clear sky chart from 2005-11-05 to 2018-01-12.

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
32%
15324
12%
48417
9%
15287
37%
15287
15%
35774

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
9%
762
6%
2638
3%
761
14%
761
4%
2277
January16th to endNight
11%
768
5%
2496
2%
768
15%
768
5%
2197
February1st to 15thNight
10%
704
5%
2287
2%
701
14%
701
5%
1952
February16th to endNight
19%
631
7%
2010
3%
631
24%
631
8%
1646
March1st to 15thNight
21%
720
11%
1980
5%
720
26%
720
13%
1578
March16th to endNight
32%
768
18%
2112
9%
768
38%
768
20%
1526
April1st to 15thNight
25%
718
13%
1805
5%
718
30%
718
19%
1375
April16th to endNight
41%
597
19%
1677
10%
597
47%
597
26%
1121
May1st to 15thNight
44%
480
15%
1560
13%
480
49%
480
21%
1063
May16th to endNight
47%
374
17%
1497
16%
374
57%
374
21%
891
June1st to 15thNight
49%
360
13%
1440
15%
360
57%
360
20%
910
June16th to endNight
51%
360
11%
1440
14%
360
57%
360
22%
864
July1st to 15thNight
57%
340
16%
1360
22%
340
62%
340
28%
722
July16th to endNight
60%
478
15%
1512
15%
448
62%
448
28%
904
August1st to 15thNight
62%
539
15%
1609
13%
536
64%
536
31%
987
August16th to endNight
62%
648
22%
1794
14%
648
66%
648
37%
1083
September1st to 15thNight
55%
720
19%
1800
11%
720
58%
720
32%
1208
September16th to endNight
55%
717
22%
2004
17%
717
57%
717
29%
1296
October1st to 15thNight
39%
720
15%
2160
14%
720
42%
720
19%
1527
October16th to endNight
23%
768
10%
2304
6%
768
28%
768
11%
1793
November1st to 15thNight
32%
760
16%
2560
14%
760
37%
760
16%
1804
November16th to endNight
20%
780
10%
2730
7%
780
25%
780
9%
2107
December1st to 15thNight
12%
780
3%
2730
2%
780
14%
780
4%
2350
December16th to endNight
9%
832
3%
2912
1%
832
12%
832
3%
2593

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%47%5%3445%7%32%
48923
Night
16%10%47%6%34446%29%
48596
Cloud CoverDay
16%9%37%6%3445%6%32%
48933
Night
16%10%47%6%34446%30%
48600
TransparencyDay
50%6%13%18%9%
48620
Night
54%6%11%16%9%
48417
SeeingDay
19%10%23%24%15%6%
5727
Night
22%11%26%26%12%1
15328

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
18%15%6%11%10%46%46%413%
1541
16th to endDay
14%16%7%15%10%6%5%4449%
1728
February1st to 15thDay
17%16%9%12%7%45%44413%
1575
16th to endDay
17%13%6%11%9%46%45%5%16%
1461
March1st to 15thDay
17%11%5%10%8%35%445%23%
1969
16th to endDay
16%7%46%5%3445%6%34%
2112
April1st to 15thDay
20%8%35%434346%33%
2143
16th to endDay
17%7%35%5%33346%40%
2294
May1st to 15thDay
14%6%25%5%25%5%6%7%37%
2391
16th to endDay
10%5%25%5%25%5%6%8%41%
2618
June1st to 15thDay
13%7%35%334448%40%
2520
16th to endDay
12%3244346%6%10%41%
2520
July1st to 15thDay
7%424335%46%9%47%
2520
16th to endDay
10%325%5%35%6%8%10%38%
2550
August1st to 15thDay
8%425%5%345%7%10%43%
2340
16th to endDay
10%42442446%9%45%
2396
September1st to 15thDay
15%5%34425%45%8%39%
2160
16th to endDay
12%6%35%42446%7%40%
1953
October1st to 15thDay
20%7%36%5%34446%32%
1800
16th to endDay
23%11%37%6%33445%25%
1920
November1st to 15thDay
12%11%49%5%445%47%29%
1628
16th to endDay
19%14%5%8%6%2445%6%22%
1560
December1st to 15thDay
18%18%7%10%8%33445%14%
1560
16th to endDay
21%18%7%12%7%4434410%
1664
January1st to 15thNight
19%17%7%11%8%4434413%
2638
16th to endNight
15%15%8%14%10%6%444410%
2496
February1st to 15thNight
16%16%7%13%8%35%43415%
2285
16th to endNight
16%13%6%11%9%3445%5%17%
2010
March1st to 15thNight
20%11%410%8%34435%24%
1968
16th to endNight
16%9%5%7%5%2434436%
2112
April1st to 15thNight
21%10%36%5%2443432%
1805
16th to endNight
15%425%5%345%46%41%
1677
May1st to 15thNight
17%6%25%5%345%5%9%34%
1560
16th to endNight
11%5%25%4345%5%7%42%
1495
June1st to 15thNight
13%425%6%45%6%5%7%37%
1440
16th to endNight
10%5%25%435%5%6%8%41%
1440
July1st to 15thNight
5%415%42445%7%52%
1440
16th to endNight
8%425%435%6%6%8%45%
1616
August1st to 15thNight
8%5%25%5%25%5%7%9%43%
1620
16th to endNight
9%324335%36%6%50%
1794
September1st to 15thNight
15%5%25%32445%7%44%
1800
16th to endNight
14%5%25%32445%6%44%
2004
October1st to 15thNight
20%7%36%5%2435%5%35%
2160
16th to endNight
25%10%36%5%345%45%24%
2304
November1st to 15thNight
17%9%46%5%34447%32%
2560
16th to endNight
20%13%47%6%345%45%22%
2730
December1st to 15thNight
21%18%7%10%7%24445%12%
2730
16th to endNight
21%18%7%11%8%45%43410%
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
18%15%7%10%9%35%45%414%
1541
16th to endDay
14%16%8%12%10%6%5%44410%
1728
February1st to 15thDay
17%18%7%12%7%46%43414%
1575
16th to endDay
18%14%6%10%10%45%44416%
1461
March1st to 15thDay
18%12%5%10%7%445%3422%
1980
16th to endDay
17%9%45%5%34447%33%
2111
April1st to 15thDay
21%9%35%5%34346%32%
2143
16th to endDay
18%7%25%423345%40%
2294
May1st to 15thDay
15%6%25%5%35%45%7%36%
2391
16th to endDay
12%6%35%42447%7%41%
2618
June1st to 15thDay
15%6%3442445%7%39%
2520
16th to endDay
14%414425%5%7%10%39%
2520
July1st to 15thDay
8%425%425%5%6%8%46%
2520
16th to endDay
11%415%5%35%6%8%10%37%
2550
August1st to 15thDay
9%5%25%5%345%6%9%41%
2340
16th to endDay
12%4245%35%5%5%8%43%
2396
September1st to 15thDay
16%5%25%43446%7%39%
2160
16th to endDay
13%6%25%5%2446%8%39%
1953
October1st to 15thDay
21%7%36%6%3435%5%32%
1800
16th to endDay
24%12%37%6%34435%24%
1920
November1st to 15thDay
13%12%48%6%35%447%29%
1628
16th to endDay
20%14%49%5%24345%24%
1560
December1st to 15thDay
19%19%7%9%8%3433417%
1560
16th to endDay
21%19%7%11%7%3434412%
1664
January1st to 15thNight
20%17%6%11%7%45%33415%
2638
16th to endNight
16%16%7%11%9%5%45%4412%
2496
February1st to 15thNight
16%16%7%13%8%35%33318%
2278
16th to endNight
15%14%7%12%8%34445%18%
2010
March1st to 15thNight
21%10%49%7%3443424%
1980
16th to endNight
16%9%5%7%5%2433436%
2112
April1st to 15thNight
22%10%35%5%3344332%
1805
16th to endNight
15%425%5%3435%7%41%
1677
May1st to 15thNight
17%5%26%5%35%36%8%34%
1559
16th to endNight
12%5%26%425%5%5%7%42%
1495
June1st to 15thNight
13%5%25%5%45%5%5%8%36%
1440
16th to endNight
10%5%25%5%35%5%5%8%41%
1440
July1st to 15thNight
6%4245%34447%51%
1440
16th to endNight
8%325%4345%7%8%45%
1616
August1st to 15thNight
8%425%5%245%7%7%45%
1620
16th to endNight
9%3244245%5%7%50%
1794
September1st to 15thNight
15%5%24414447%44%
1800
16th to endNight
14%6%14424446%45%
2004
October1st to 15thNight
19%8%35%5%24345%36%
2160
16th to endNight
26%9%36%5%3445%5%25%
2304
November1st to 15thNight
17%10%45%5%34447%33%
2560
16th to endNight
20%13%46%5%3445%6%23%
2730
December1st to 15thNight
22%18%7%9%6%33435%16%
2730
16th to endNight
20%18%8%10%7%35%44411%
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
71%7%7%9%2
1542
16th to endDay
76%7%8%5%1
1728
February1st to 15thDay
74%7%7%8%
1577
16th to endDay
70%5%10%9%3
1461
March1st to 15thDay
63%6%12%12%4
1980
16th to endDay
49%6%12%21%9%1
2112
April1st to 15thDay
52%412%18%10%
2143
16th to endDay
45%410%20%15%2
2294
May1st to 15thDay
44%7%11%23%12%
2391
16th to endDay
38%7%15%23%13%1
2622
June1st to 15thDay
41%6%15%22%11%1
2520
16th to endDay
36%7%17%23%13%
2520
July1st to 15thDay
31%8%14%24%19%1
2371
16th to endDay
38%9%17%21%11%1
2391
August1st to 15thDay
35%8%19%21%13%1
2327
16th to endDay
36%5%15%28%12%1
2396
September1st to 15thDay
41%6%15%22%12%1
2160
16th to endDay
40%7%14%23%13%
1953
October1st to 15thDay
52%5%11%18%11%
1800
16th to endDay
60%6%15%12%3
1920
November1st to 15thDay
53%8%14%15%7%1
1628
16th to endDay
62%6%13%11%5%
1560
December1st to 15thDay
71%8%10%8%1
1560
16th to endDay
75%7%9%6%
1664
January1st to 15thNight
73%6%8%8%3
2638
16th to endNight
74%8%8%6%2
2496
February1st to 15thNight
70%8%8%10%2
2287
16th to endNight
66%6%11%10%4
2010
March1st to 15thNight
62%5%11%15%5%
1980
16th to endNight
51%5%7%21%13%1
2112
April1st to 15thNight
55%5%8%18%11%
1805
16th to endNight
41%6%10%22%15%3
1677
May1st to 15thNight
46%6%10%21%13%1
1560
16th to endNight
38%7%12%24%15%2
1497
June1st to 15thNight
43%6%11%21%15%1
1440
16th to endNight
39%7%15%20%16%1
1440
July1st to 15thNight
31%5%11%26%22%2
1360
16th to endNight
33%8%14%22%16%3
1512
August1st to 15thNight
34%7%19%24%14%
1609
16th to endNight
31%6%12%32%15%1
1794
September1st to 15thNight
38%6%13%24%15%1
1800
16th to endNight
38%6%11%26%16%
2004
October1st to 15thNight
49%6%9%19%14%
2160
16th to endNight
58%7%13%13%5%
2304
November1st to 15thNight
51%6%12%18%10%
2560
16th to endNight
61%7%13%14%4
2730
December1st to 15thNight
72%8%10%6%2
2730
16th to endNight
76%7%8%6%1
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
17%32%22%20%7%
85
16th to endDay
32%18%30%16%2
96
February1st to 15thDay
21%33%33%12%
90
16th to endDay
24%14%38%15%6%
114
March1st to 15thDay
26%16%27%21%6%
270
16th to endDay
24%11%28%25%6%3
288
April1st to 15thDay
24%14%30%22%7%1
270
16th to endDay
21%7%27%25%12%5%
270
May1st to 15thDay
21%6%24%22%18%5%
288
16th to endDay
12%10%29%26%15%5%
331
June1st to 15thDay
19%8%17%39%13%1
315
16th to endDay
18%6%24%31%17%2
315
July1st to 15thDay
12%417%32%21%10%
305
16th to endDay
12%323%27%22%9%
326
August1st to 15thDay
10%219%29%23%14%
313
16th to endDay
13%5%14%25%25%14%
332
September1st to 15thDay
13%318%25%23%14%
315
16th to endDay
15%5%18%21%22%17%
314
October1st to 15thDay
21%11%21%20%18%7%
315
16th to endDay
32%16%22%19%7%
336
November1st to 15thDay
17%14%30%26%7%3
163
16th to endDay
27%24%22%17%7%
90
December1st to 15thDay
21%27%27%16%6%
90
16th to endDay
25%34%32%8%
96
January1st to 15thNight
29%24%28%13%3
765
16th to endNight
26%16%33%19%4
768
February1st to 15thNight
23%21%33%16%4
704
16th to endNight
23%17%29%26%3
631
March1st to 15thNight
28%13%30%21%6%
720
16th to endNight
19%9%30%27%10%1
768
April1st to 15thNight
26%13%28%26%5%
718
16th to endNight
16%7%30%31%13%1
597
May1st to 15thNight
20%323%33%16%2
480
16th to endNight
14%426%36%16%1
375
June1st to 15thNight
16%125%38%16%1
360
16th to endNight
11%227%43%13%
360
July1st to 15thNight
9%420%42%22%1
340
16th to endNight
9%220%43%22%1
478
August1st to 15thNight
10%214%38%28%4
539
16th to endNight
10%218%34%29%4
648
September1st to 15thNight
16%417%31%25%4
720
16th to endNight
17%5%17%27%24%8%
717
October1st to 15thNight
24%7%21%27%16%2
720
16th to endNight
32%13%24%23%5%
768
November1st to 15thNight
22%10%28%23%12%1
760
16th to endNight
27%18%26%17%8%
780
December1st to 15thNight
33%20%26%16%3
780
16th to endNight
28%20%32%15%2
832
Page generated at 2018-01-12 22:01:32. Version ac04

Copyright 2018 A. Danko


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