Emerald Lane Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Emerald Lane Observatory clear sky chart from 2005-11-05 to 2017-09-18.

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
48%
15229
24%
46754
17%
15186
56%
15186
29%
28235

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
24%
720
24%
2327
10%
716
40%
716
21%
1476
January16th to endNight
26%
768
25%
2331
11%
768
39%
768
21%
1541
February1st to 15thNight
26%
704
22%
2112
9%
701
38%
701
25%
1350
February16th to endNight
25%
631
24%
1893
9%
631
36%
631
22%
1242
March1st to 15thNight
29%
720
19%
2160
10%
720
37%
720
22%
1397
March16th to endNight
37%
693
23%
2039
14%
693
45%
693
30%
1244
April1st to 15thNight
37%
539
25%
1797
16%
539
51%
539
30%
1016
April16th to endNight
45%
540
27%
1800
19%
540
57%
540
33%
971
May1st to 15thNight
49%
540
21%
1632
12%
540
58%
540
30%
995
May16th to endNight
65%
561
22%
1682
17%
561
68%
561
36%
968
June1st to 15thNight
69%
540
20%
1620
16%
540
72%
540
36%
944
June16th to endNight
75%
540
22%
1494
18%
540
77%
540
43%
863
July1st to 15thNight
73%
510
16%
1429
14%
510
75%
510
34%
888
July16th to endNight
76%
564
19%
1606
18%
531
77%
531
36%
939
August1st to 15thNight
80%
539
20%
1788
23%
536
82%
536
35%
1001
August16th to endNight
71%
573
21%
1910
25%
573
72%
573
27%
1164
September1st to 15thNight
65%
606
20%
1866
19%
606
67%
606
32%
1106
September16th to endNight
62%
669
28%
1848
22%
669
65%
669
35%
1115
October1st to 15thNight
56%
660
35%
1815
27%
660
61%
660
39%
1050
October16th to endNight
51%
704
34%
2153
28%
704
59%
704
36%
1208
November1st to 15thNight
48%
700
29%
2276
25%
700
58%
700
34%
1249
November16th to endNight
37%
720
27%
2340
18%
720
51%
720
27%
1372
December1st to 15thNight
34%
720
23%
2340
14%
720
45%
720
23%
1459
December16th to endNight
28%
768
20%
2496
13%
768
37%
768
19%
1677

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
11%5%25%5%35%5%5%7%40%
48021
Night
11%5%2442445%7%46%
46951
TransparencyDay
40%411%21%17%4
47720
Night
36%411%21%19%5%
46756
SeeingDay
13%6%17%24%22%14%
5347
Night
14%8%22%28%22%4
15231

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 15thDay
18%8%36%423435%40%
1611
16th to endDay
17%6%34423345%44%
1890
February1st to 15thDay
14%10%46%5%23335%40%
1750
16th to endDay
15%7%36%5%23436%40%
1580
March1st to 15thDay
14%9%36%5%25%436%37%
1800
16th to endDay
13%6%25%5%25%5%5%7%38%
2192
April1st to 15thDay
12%5%25%423447%45%
2151
16th to endDay
10%5%25%5%35%45%8%43%
2160
May1st to 15thDay
12%5%25%5%25%45%7%41%
2319
16th to endDay
9%5%25%5%35%5%6%8%40%
2431
June1st to 15thDay
6%425%6%5%6%7%6%9%38%
2340
16th to endDay
5%3246%37%6%7%10%42%
2457
July1st to 15thDay
9%5%35%6%5%7%7%7%10%30%
2439
16th to endDay
5%425%6%5%8%8%8%12%32%
2450
August1st to 15thDay
5%325%6%5%7%7%9%10%35%
2160
16th to endDay
10%5%25%8%5%7%7%7%8%31%
2292
September1st to 15thDay
11%5%25%6%35%5%6%9%37%
2081
16th to endDay
12%324424446%47%
1837
October1st to 15thDay
9%315%5%345%45%51%
1815
16th to endDay
12%314422325%56%
1716
November1st to 15thDay
11%5%13423335%55%
1582
16th to endDay
13%6%14324445%48%
1620
December1st to 15thDay
17%7%36%4245%45%37%
1620
16th to endDay
19%9%45%423246%35%
1728
January1st to 15thNight
15%7%25%43443444%
2327
16th to endNight
16%8%36%423335%41%
2331
February1st to 15thNight
16%7%25%423345%43%
2103
16th to endNight
15%6%26%5%24335%42%
1893
March1st to 15thNight
15%6%25%434447%39%
2160
16th to endNight
11%6%2442345%7%46%
2039
April1st to 15thNight
12%42342436%8%48%
1797
16th to endNight
10%5%1341435%7%52%
1800
May1st to 15thNight
9%4245%35%45%7%46%
1631
16th to endNight
43245%35%5%6%9%48%
1682
June1st to 15thNight
4325%5%25%5%7%11%46%
1620
16th to endNight
32235%35%6%8%11%49%
1494
July1st to 15thNight
6%425%436%7%7%9%41%
1515
16th to endNight
4225%5%46%5%7%14%41%
1715
August1st to 15thNight
42145%35%7%8%11%45%
1800
16th to endNight
7%4245%48%5%7%10%40%
1910
September1st to 15thNight
8%425%5%3446%8%46%
1866
16th to endNight
8%5%2443435%7%49%
1848
October1st to 15thNight
10%413423346%55%
1815
16th to endNight
13%5%1331223457%
2153
November1st to 15thNight
11%423314335%55%
2276
16th to endNight
14%6%2432334450%
2340
December1st to 15thNight
16%7%2442335%7%41%
2340
16th to endNight
18%8%35%5%34345%37%
2496

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
47%37%17%20%4
1612
16th to endDay
43%27%22%20%4
1890
February1st to 15thDay
47%27%21%17%3
1752
16th to endDay
46%28%19%18%4
1580
March1st to 15thDay
47%5%8%17%16%5%
1800
16th to endDay
43%414%21%14%1
2193
April1st to 15thDay
38%210%23%17%6%
2151
16th to endDay
37%48%25%20%3
2160
May1st to 15thDay
41%410%22%16%4
2319
16th to endDay
38%5%13%26%13%1
2435
June1st to 15thDay
38%7%14%23%15%1
2340
16th to endDay
33%7%13%23%18%4
2457
July1st to 15thDay
41%8%16%20%9%3
2296
16th to endDay
38%7%20%23%8%
2296
August1st to 15thDay
37%7%17%21%13%2
2148
16th to endDay
46%6%13%22%9%1
2292
September1st to 15thDay
42%5%15%18%13%4
2081
16th to endDay
36%49%23%20%5%
1837
October1st to 15thDay
34%46%20%26%7%
1815
16th to endDay
32%2420%31%9%
1716
November1st to 15thDay
33%2420%29%9%
1582
16th to endDay
37%35%21%25%6%
1620
December1st to 15thDay
49%26%20%15%5%
1620
16th to endDay
51%29%19%13%3
1728
January1st to 15thNight
44%37%19%21%4
2327
16th to endNight
46%25%19%19%5%
2331
February1st to 15thNight
42%28%21%19%5%
2112
16th to endNight
44%35%21%20%4
1893
March1st to 15thNight
43%39%19%16%7%
2160
16th to endNight
36%311%27%18%2
2039
April1st to 15thNight
33%410%25%18%7%
1797
16th to endNight
30%39%27%23%5%
1800
May1st to 15thNight
35%6%12%20%22%3
1632
16th to endNight
30%5%17%26%14%4
1684
June1st to 15thNight
30%6%16%25%18%2
1620
16th to endNight
25%6%17%25%21%3
1494
July1st to 15thNight
32%7%21%23%10%4
1429
16th to endNight
30%6%22%25%14%
1606
August1st to 15thNight
27%8%19%25%16%3
1788
16th to endNight
36%8%17%22%12%3
1910
September1st to 15thNight
33%6%20%18%16%4
1866
16th to endNight
33%49%20%23%8%
1848
October1st to 15thNight
30%36%23%24%11%
1815
16th to endNight
32%2317%31%13%
2153
November1st to 15thNight
31%35%20%25%14%
2276
16th to endNight
37%25%19%26%8%
2340
December1st to 15thNight
42%29%20%19%5%
2340
16th to endNight
48%48%18%16%3
2496

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
20%22%35%12%7%2
90
16th to endDay
23%22%39%9%4
96
February1st to 15thDay
18%31%35%12%2
90
16th to endDay
22%17%39%20%
81
March1st to 15thDay
21%26%36%11%31
90
16th to endDay
18%10%33%22%12%1
285
April1st to 15thDay
15%13%28%28%11%2
270
16th to endDay
14%9%23%31%16%4
270
May1st to 15thDay
15%8%23%27%14%10%
288
16th to endDay
15%418%23%22%15%
331
June1st to 15thDay
8%19%23%29%26%
315
16th to endDay
6%112%28%27%23%
432
July1st to 15thDay
9%19%30%28%21%
400
16th to endDay
7%318%28%41%
326
August1st to 15thDay
7%7%23%34%25%
313
16th to endDay
15%16%22%33%20%
332
September1st to 15thDay
11%37%23%30%23%
315
16th to endDay
17%18%27%33%9%
262
October1st to 15thDay
12%320%31%25%6%
255
16th to endDay
18%5%17%35%17%6%
140
November1st to 15thDay
20%11%22%31%15%
90
16th to endDay
13%22%32%20%10%2
90
December1st to 15thDay
23%17%34%17%5%1
90
16th to endDay
21%19%41%10%5%1
96
January1st to 15thNight
19%19%33%20%6%
720
16th to endNight
19%16%34%26%3
768
February1st to 15thNight
21%13%35%25%4
704
16th to endNight
20%15%34%25%3
631
March1st to 15thNight
20%15%31%26%6%
720
16th to endNight
14%13%30%24%15%
693
April1st to 15thNight
14%10%33%26%13%1
539
16th to endNight
12%7%30%31%17%1
540
May1st to 15thNight
11%426%29%23%4
540
16th to endNight
5%215%37%32%5%
563
June1st to 15thNight
5%112%33%38%9%
540
16th to endNight
48%28%47%8%
540
July1st to 15thNight
7%16%31%41%10%
510
16th to endNight
5%16%24%42%19%
564
August1st to 15thNight
5%326%53%11%
539
16th to endNight
9%15%28%43%10%
573
September1st to 15thNight
10%112%26%39%10%
606
16th to endNight
10%213%32%36%3
669
October1st to 15thNight
12%5%20%29%26%6%
660
16th to endNight
16%6%20%29%24%2
704
November1st to 15thNight
14%7%24%29%20%3
700
16th to endNight
17%11%28%28%12%1
720
December1st to 15thNight
21%12%26%29%8%
720
16th to endNight
23%14%29%25%6%
768
Page generated at 2017-09-19 06:32:26. Version ac04

Copyright 2017 A. Danko


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