Embro Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Embro Observatory clear sky chart from 2005-11-05 to 2017-09-22.

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
35%
14936
15%
46642
10%
14898
41%
14898
20%
32164

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
15%
717
11%
2392
5%
716
22%
716
9%
1885
January16th to endNight
16%
768
11%
2496
4%
768
24%
768
9%
1998
February1st to 15thNight
17%
702
8%
2287
2%
701
23%
701
9%
1795
February16th to endNight
24%
631
12%
1967
5%
631
32%
631
13%
1464
March1st to 15thNight
25%
720
15%
2005
8%
720
31%
720
16%
1492
March16th to endNight
32%
768
20%
2112
11%
768
39%
768
24%
1447
April1st to 15thNight
28%
691
16%
1835
8%
691
34%
691
22%
1319
April16th to endNight
39%
540
22%
1620
10%
540
48%
540
26%
1024
May1st to 15thNight
41%
540
17%
1620
11%
540
47%
540
26%
1051
May16th to endNight
46%
406
17%
1529
15%
406
56%
406
27%
855
June1st to 15thNight
50%
360
14%
1410
15%
360
57%
360
26%
779
June16th to endNight
53%
360
17%
1260
17%
360
61%
360
30%
713
July1st to 15thNight
63%
362
20%
1256
24%
362
67%
362
39%
645
July16th to endNight
63%
564
16%
1595
14%
531
66%
531
37%
921
August1st to 15thNight
67%
539
19%
1609
15%
536
70%
536
36%
930
August16th to endNight
62%
591
25%
1737
17%
591
67%
591
39%
991
September1st to 15thNight
54%
720
23%
1875
14%
720
58%
720
34%
1179
September16th to endNight
57%
685
23%
1892
17%
685
60%
685
34%
1163
October1st to 15thNight
43%
660
19%
1966
16%
660
48%
660
25%
1295
October16th to endNight
24%
704
14%
2121
9%
704
33%
704
16%
1565
November1st to 15thNight
36%
700
19%
2330
18%
700
41%
700
21%
1529
November16th to endNight
23%
720
11%
2520
7%
720
30%
720
12%
1873
December1st to 15thNight
13%
720
6%
2520
2%
720
18%
720
7%
2036
December16th to endNight
12%
768
7%
2688
3%
768
18%
768
7%
2215

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%9%47%6%35%45%7%30%
48226
Night
14%8%47%6%3445%7%33%
46820
Cloud CoverDay
15%9%47%6%35%5%5%7%30%
48236
Night
14%9%47%6%3445%7%33%
46824
TransparencyDay
52%311%20%10%1
47923
Night
51%311%21%11%1
46642
SeeingDay
18%6%25%25%15%7%
5644
Night
19%8%27%29%12%1
14942

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%8%35%45%5%15%
1544
16th to endDay
13%18%8%13%9%46%44413%
1728
February1st to 15thDay
15%16%8%11%8%45%445%15%
1575
16th to endDay
15%15%6%8%7%46%45%6%19%
1504
March1st to 15thDay
16%13%5%10%7%34446%23%
1942
16th to endDay
15%10%6%7%6%3446%5%29%
2112
April1st to 15thDay
19%10%46%5%35%45%6%28%
2123
16th to endDay
18%9%36%423346%37%
2340
May1st to 15thDay
18%7%36%5%3445%7%34%
2331
16th to endDay
13%5%25%5%25%5%5%8%38%
2584
June1st to 15thDay
13%5%25%435%5%6%9%37%
2545
16th to endDay
12%425%5%35%6%6%10%36%
2700
July1st to 15thDay
9%5%245%36%6%6%9%39%
2623
16th to endDay
9%5%26%6%46%5%7%9%36%
2465
August1st to 15thDay
8%5%26%7%46%6%7%8%35%
2340
16th to endDay
12%5%25%6%35%5%6%8%37%
2453
September1st to 15thDay
14%5%36%5%345%6%8%35%
2082
16th to endDay
16%5%26%425%46%7%39%
1881
October1st to 15thDay
20%7%37%6%2435%6%33%
1664
16th to endDay
24%11%37%6%3435%5%21%
1749
November1st to 15thDay
14%9%47%6%4445%8%32%
1525
16th to endDay
19%14%5%9%7%245%48%18%
1440
December1st to 15thDay
17%17%9%10%7%35%34415%
1440
16th to endDay
20%17%8%12%7%345%45%9%
1536
January1st to 15thNight
21%12%6%9%8%35%445%18%
2392
16th to endNight
13%14%9%11%8%45%445%17%
2496
February1st to 15thNight
14%14%7%10%7%46%436%19%
2285
16th to endNight
15%10%5%9%7%45%45%6%24%
1967
March1st to 15thNight
17%9%38%7%4445%7%28%
1993
16th to endNight
14%8%47%5%24345%38%
2112
April1st to 15thNight
20%8%46%424347%32%
1835
16th to endNight
11%7%36%5%3446%7%39%
1620
May1st to 15thNight
15%6%36%5%2446%8%36%
1620
16th to endNight
10%5%244245%5%7%47%
1527
June1st to 15thNight
10%4245%25%48%8%42%
1410
16th to endNight
9%424435%5%6%8%45%
1260
July1st to 15thNight
5%32442336%8%55%
1331
16th to endNight
7%414426%46%9%47%
1703
August1st to 15thNight
5%415%425%5%7%8%48%
1620
16th to endNight
8%415%42435%7%52%
1737
September1st to 15thNight
12%425%42345%6%47%
1875
16th to endNight
12%5%245%2345%8%45%
1892
October1st to 15thNight
17%6%35%5%3345%7%39%
1966
16th to endNight
22%8%36%5%35%35%6%28%
2121
November1st to 15thNight
14%8%26%5%35%45%8%34%
2330
16th to endNight
20%11%5%7%6%3445%7%22%
2520
December1st to 15thNight
18%16%7%10%6%35%445%16%
2520
16th to endNight
20%15%8%11%7%35%336%13%
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
18%14%7%10%7%4445%5%15%
1544
16th to endDay
13%18%7%14%8%45%44413%
1728
February1st to 15thDay
15%16%7%11%8%36%5%45%15%
1575
16th to endDay
16%14%6%8%7%36%446%19%
1504
March1st to 15thDay
16%13%410%6%3445%6%23%
1953
16th to endDay
15%10%6%7%6%3445%5%29%
2111
April1st to 15thDay
19%10%46%5%35%447%27%
2123
16th to endDay
18%9%35%423446%37%
2340
May1st to 15thDay
17%7%36%5%245%5%6%34%
2331
16th to endDay
13%5%35%5%35%5%49%38%
2584
June1st to 15thDay
13%5%25%4345%6%8%37%
2545
16th to endDay
12%425%5%35%6%7%10%36%
2700
July1st to 15thDay
9%425%5%37%5%6%9%40%
2623
16th to endDay
9%5%26%6%46%5%7%8%36%
2465
August1st to 15thDay
8%5%26%7%46%6%6%9%36%
2340
16th to endDay
12%5%25%5%35%5%6%8%38%
2453
September1st to 15thDay
13%6%27%6%25%5%6%8%35%
2082
16th to endDay
15%5%25%5%2346%7%38%
1881
October1st to 15thDay
19%7%37%6%35%346%33%
1664
16th to endDay
25%10%46%7%3446%5%21%
1749
November1st to 15thDay
13%9%37%7%2445%8%32%
1525
16th to endDay
19%14%5%9%6%3445%7%18%
1440
December1st to 15thDay
16%17%9%10%6%45%44415%
1440
16th to endDay
20%18%8%12%7%35%5%449%
1536
January1st to 15thNight
21%12%6%8%7%3445%5%18%
2392
16th to endNight
13%13%9%11%8%45%5%45%17%
2496
February1st to 15thNight
14%14%6%10%8%45%446%19%
2278
16th to endNight
15%11%410%7%445%5%6%24%
1967
March1st to 15thNight
17%9%38%6%44446%28%
2005
16th to endNight
15%8%47%5%23445%38%
2112
April1st to 15thNight
19%8%36%5%33347%33%
1835
16th to endNight
12%7%25%5%2446%8%39%
1620
May1st to 15thNight
15%6%35%5%2347%7%36%
1619
16th to endNight
10%5%244246%5%7%47%
1527
June1st to 15thNight
9%425%5%25%47%8%42%
1410
16th to endNight
9%4244345%6%8%45%
1260
July1st to 15thNight
422442335%9%55%
1331
16th to endNight
7%3245%25%46%9%47%
1703
August1st to 15thNight
5%3245%345%6%9%48%
1620
16th to endNight
8%42442435%6%52%
1737
September1st to 15thNight
11%5%25%42435%7%47%
1875
16th to endNight
12%4145%2445%8%45%
1892
October1st to 15thNight
17%6%34433447%39%
1966
16th to endNight
23%7%36%5%3445%7%28%
2121
November1st to 15thNight
13%8%26%5%35%5%6%8%34%
2330
16th to endNight
20%12%5%7%6%2445%7%23%
2520
December1st to 15thNight
18%16%6%10%6%35%445%17%
2520
16th to endNight
19%15%7%12%7%35%446%13%
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
71%29%11%4
1545
16th to endDay
75%27%9%4
1728
February1st to 15thDay
71%18%13%4
1577
16th to endDay
65%211%13%5%
1504
March1st to 15thDay
62%310%16%6%
1953
16th to endDay
55%310%18%11%1
2112
April1st to 15thDay
56%310%19%9%
2123
16th to endDay
48%210%21%14%2
2340
May1st to 15thDay
48%211%24%11%
2331
16th to endDay
44%312%24%13%1
2588
June1st to 15thDay
42%314%25%12%1
2545
16th to endDay
41%5%13%24%14%
2700
July1st to 15thDay
38%49%28%17%2
2470
16th to endDay
42%5%13%23%13%2
2310
August1st to 15thDay
43%414%22%12%1
2327
16th to endDay
42%411%25%13%1
2453
September1st to 15thDay
44%312%25%12%
2082
16th to endDay
43%312%29%10%
1881
October1st to 15thDay
52%211%18%14%1
1664
16th to endDay
63%312%14%5%
1749
November1st to 15thDay
51%411%21%10%1
1525
16th to endDay
65%311%15%4
1440
December1st to 15thDay
71%312%9%2
1440
16th to endDay
78%36%9%2
1536
January1st to 15thNight
67%29%12%7%
2392
16th to endNight
68%28%15%4
2496
February1st to 15thNight
66%39%15%5%
2287
16th to endNight
60%212%17%7%
1967
March1st to 15thNight
57%210%21%6%
2005
16th to endNight
48%29%23%12%2
2112
April1st to 15thNight
52%28%22%13%1
1835
16th to endNight
42%29%22%19%3
1620
May1st to 15thNight
44%211%25%13%2
1620
16th to endNight
36%314%27%14%3
1529
June1st to 15thNight
37%214%27%15%2
1410
16th to endNight
34%415%24%19%1
1260
July1st to 15thNight
26%49%32%23%3
1256
16th to endNight
32%316%26%18%3
1595
August1st to 15thNight
31%415%32%13%1
1609
16th to endNight
31%312%33%17%2
1737
September1st to 15thNight
37%311%30%15%2
1875
16th to endNight
36%312%32%14%
1892
October1st to 15thNight
44%310%23%16%1
1966
16th to endNight
56%312%19%8%
2121
November1st to 15thNight
46%412%22%12%1
2330
16th to endNight
61%213%15%5%
2520
December1st to 15thNight
69%311%11%3
2520
16th to endNight
72%210%11%2
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
18%17%43%15%31
79
16th to endDay
39%10%32%16%1
96
February1st to 15thDay
23%14%51%11%
90
16th to endDay
24%14%50%8%1
81
March1st to 15thDay
25%10%32%23%7%
243
16th to endDay
26%6%32%21%10%2
288
April1st to 15thDay
24%13%26%22%10%2
270
16th to endDay
21%9%28%24%10%6%
270
May1st to 15thDay
20%7%27%23%14%5%
288
16th to endDay
15%6%29%28%13%7%
331
June1st to 15thDay
16%422%34%17%4
340
16th to endDay
12%6%31%30%14%4
495
July1st to 15thDay
12%422%31%20%9%
428
16th to endDay
10%218%30%26%11%
326
August1st to 15thDay
9%16%29%24%18%
313
16th to endDay
14%5%14%21%24%20%
332
September1st to 15thDay
13%314%24%29%14%
315
16th to endDay
19%315%23%22%16%
278
October1st to 15thDay
19%7%20%26%21%4
255
16th to endDay
29%8%32%22%6%1
261
November1st to 15thDay
16%16%29%22%9%6%
81
16th to endDay
28%11%41%10%8%
60
December1st to 15thDay
35%21%23%15%5%
60
16th to endDay
32%18%42%6%
64
January1st to 15thNight
28%14%33%17%41
720
16th to endNight
22%11%34%25%5%
768
February1st to 15thNight
21%15%34%23%4
704
16th to endNight
23%10%31%27%5%
631
March1st to 15thNight
23%12%33%23%7%
720
16th to endNight
19%8%32%26%11%1
768
April1st to 15thNight
24%10%29%28%6%
691
16th to endNight
16%8%29%34%10%1
540
May1st to 15thNight
17%5%25%34%15%1
540
16th to endNight
13%329%36%16%1
407
June1st to 15thNight
12%226%41%16%
360
16th to endNight
12%123%47%14%
360
July1st to 15thNight
5%20%49%20%2
362
16th to endNight
9%116%45%23%3
564
August1st to 15thNight
8%112%43%30%3
539
16th to endNight
9%117%38%27%6%
591
September1st to 15thNight
14%319%32%23%6%
720
16th to endNight
15%216%32%26%6%
685
October1st to 15thNight
20%6%22%30%18%2
660
16th to endNight
28%9%30%25%6%
704
November1st to 15thNight
19%9%29%29%11%1
700
16th to endNight
28%11%28%22%9%
720
December1st to 15thNight
29%13%33%18%4
720
16th to endNight
26%15%34%18%4
768
Page generated at 2017-09-23 06:43:44. Version ac04

Copyright 2017 A. Danko


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