ME Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the ME Observatory clear sky chart from 2005-11-05 to 2018-02-13.

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
50%
16108
23%
48773
16%
16067
58%
16067
29%
29972

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
28%
779
24%
2522
10%
776
44%
776
23%
1543
January16th to endNight
28%
832
26%
2659
13%
832
44%
832
24%
1649
February1st to 15thNight
32%
752
25%
2256
11%
750
47%
750
27%
1400
February16th to endNight
26%
631
25%
1893
9%
631
40%
631
26%
1170
March1st to 15thNight
34%
720
24%
2056
12%
720
43%
720
29%
1283
March16th to endNight
41%
768
22%
2112
13%
768
48%
768
31%
1307
April1st to 15thNight
46%
650
25%
1908
17%
650
55%
650
35%
1101
April16th to endNight
51%
540
25%
1695
17%
540
60%
540
34%
978
May1st to 15thNight
51%
540
20%
1620
12%
540
58%
540
29%
1005
May16th to endNight
65%
561
21%
1682
15%
561
69%
561
32%
1032
June1st to 15thNight
73%
540
17%
1620
16%
540
74%
540
30%
1020
June16th to endNight
77%
540
16%
1620
14%
540
78%
540
33%
973
July1st to 15thNight
73%
510
12%
1530
12%
510
73%
510
29%
988
July16th to endNight
76%
564
16%
1595
14%
531
77%
531
28%
1024
August1st to 15thNight
72%
539
18%
1627
19%
536
72%
536
27%
1064
August16th to endNight
66%
573
18%
1910
20%
573
67%
573
21%
1278
September1st to 15thNight
67%
712
20%
1972
18%
712
68%
712
28%
1327
September16th to endNight
65%
717
25%
1980
20%
717
68%
717
31%
1262
October1st to 15thNight
59%
720
31%
1994
25%
720
65%
720
36%
1184
October16th to endNight
54%
768
35%
2304
27%
768
66%
768
39%
1266
November1st to 15thNight
53%
760
30%
2444
26%
760
63%
760
36%
1325
November16th to endNight
44%
780
28%
2535
20%
780
57%
780
32%
1422
December1st to 15thNight
38%
780
24%
2535
15%
780
49%
780
26%
1553
December16th to endNight
31%
832
21%
2704
14%
832
42%
832
20%
1818

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
12%5%244345%5%8%42%
49255
Night
12%42442445%7%46%
48973
TransparencyDay
37%7%12%20%17%4
48956
Night
35%6%11%20%20%6%
48776
SeeingDay
14%5%16%22%23%15%
5884
Night
14%6%22%29%23%4
16112

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
15%5%35%424445%44%
1746
16th to endDay
17%6%24322446%45%
1914
February1st to 15thDay
16%5%243245%46%42%
1870
16th to endDay
18%5%24414446%43%
1580
March1st to 15thDay
15%5%25%42345%8%43%
1902
16th to endDay
16%4143245%5%8%43%
2111
April1st to 15thDay
11%5%35%5%2345%7%46%
2049
16th to endDay
11%4224245%5%8%49%
2264
May1st to 15thDay
10%5%34424449%46%
2331
16th to endDay
9%324435%5%7%9%43%
2431
June1st to 15thDay
8%425%5%35%6%8%12%37%
2340
16th to endDay
42145%36%5%7%12%45%
2340
July1st to 15thDay
9%435%5%47%7%8%11%31%
2340
16th to endDay
7%336%6%48%8%8%10%32%
2465
August1st to 15thDay
8%5%26%5%47%7%8%11%32%
2318
16th to endDay
13%6%36%6%46%6%6%9%29%
2286
September1st to 15thDay
11%6%25%5%35%6%6%8%37%
1980
16th to endDay
14%5%15%43345%7%45%
1980
October1st to 15thDay
12%5%22323345%54%
1965
16th to endDay
11%314313335%59%
1920
November1st to 15thDay
12%42331335%6%53%
1741
16th to endDay
14%423233345%50%
1755
December1st to 15thDay
18%6%34423445%42%
1755
16th to endDay
23%7%35%423345%35%
1872
January1st to 15thNight
16%6%24423346%45%
2522
16th to endNight
16%6%24423435%45%
2659
February1st to 15thNight
16%424413346%47%
2248
16th to endNight
16%5%25%32335%5%46%
1893
March1st to 15thNight
13%5%24424346%48%
2056
16th to endNight
12%5%23324446%49%
2112
April1st to 15thNight
11%41232445%8%50%
1908
16th to endNight
9%423424447%51%
1695
May1st to 15thNight
9%425%5%345%5%7%46%
1619
16th to endNight
7%424435%5%6%8%47%
1682
June1st to 15thNight
6%424436%7%6%11%41%
1620
16th to endNight
42135%36%6%8%12%43%
1620
July1st to 15thNight
6%3246%46%6%8%13%35%
1620
16th to endNight
4325%5%48%7%8%13%35%
1703
August1st to 15thNight
6%5%15%6%45%6%9%11%37%
1638
16th to endNight
11%5%26%5%27%5%7%9%35%
1910
September1st to 15thNight
8%425%5%46%5%7%8%41%
1972
16th to endNight
12%5%144345%47%46%
1980
October1st to 15thNight
11%41331345%7%53%
1994
16th to endNight
9%32431233460%
2304
November1st to 15thNight
11%313213346%57%
2444
16th to endNight
13%413323345%52%
2535
December1st to 15thNight
15%5%24424346%45%
2535
16th to endNight
20%7%25%423447%36%
2704

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
41%410%16%23%3
1747
16th to endDay
39%37%20%20%8%
1914
February1st to 15thDay
41%48%19%21%3
1872
16th to endDay
42%46%20%19%6%
1580
March1st to 15thDay
39%411%19%19%4
1902
16th to endDay
38%6%12%21%16%3
2112
April1st to 15thDay
37%5%9%22%20%5%
2049
16th to endDay
31%6%11%24%22%4
2264
May1st to 15thDay
35%7%14%21%19%3
2331
16th to endDay
34%8%15%25%14%1
2435
June1st to 15thDay
35%9%21%24%7%1
2340
16th to endDay
28%8%18%26%15%2
2340
July1st to 15thDay
39%12%20%19%6%1
2201
16th to endDay
39%13%18%18%8%1
2310
August1st to 15thDay
41%12%16%19%8%1
2305
16th to endDay
47%11%14%14%10%
2286
September1st to 15thDay
40%9%14%17%15%2
1980
16th to endDay
37%5%12%19%20%3
1980
October1st to 15thDay
31%410%18%26%7%
1965
16th to endDay
28%35%18%31%11%
1920
November1st to 15thDay
30%48%16%30%9%
1741
16th to endDay
34%45%17%28%8%
1755
December1st to 15thDay
43%47%20%15%7%
1755
16th to endDay
51%47%17%13%5%
1872
January1st to 15thNight
40%37%18%24%5%
2522
16th to endNight
41%35%18%23%8%
2659
February1st to 15thNight
39%36%19%21%9%
2257
16th to endNight
38%36%19%24%6%
1893
March1st to 15thNight
37%49%18%20%8%
2056
16th to endNight
34%5%10%22%21%5%
2112
April1st to 15thNight
31%410%23%22%8%
1908
16th to endNight
32%5%10%22%21%8%
1695
May1st to 15thNight
36%6%13%20%20%2
1620
16th to endNight
32%8%13%26%15%3
1684
June1st to 15thNight
33%10%18%26%9%1
1620
16th to endNight
28%10%19%22%15%2
1620
July1st to 15thNight
33%11%23%22%6%2
1530
16th to endNight
32%13%22%19%10%2
1595
August1st to 15thNight
35%11%16%24%10%1
1627
16th to endNight
41%10%17%17%12%
1910
September1st to 15thNight
37%11%14%18%15%4
1972
16th to endNight
35%7%12%19%17%5%
1980
October1st to 15thNight
31%6%10%18%26%7%
1994
16th to endNight
28%3416%32%14%
2304
November1st to 15thNight
29%35%18%29%12%
2444
16th to endNight
32%37%17%26%11%
2535
December1st to 15thNight
39%49%20%18%7%
2535
16th to endNight
47%48%16%17%5%
2704

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%16%30%28%5%1
135
16th to endDay
15%25%35%14%7%1
144
February1st to 15thDay
19%18%35%23%3
126
16th to endDay
20%14%40%19%3
81
March1st to 15thDay
17%13%27%30%9%1
192
16th to endDay
18%7%25%30%16%1
288
April1st to 15thDay
13%14%27%19%21%4
270
16th to endDay
14%322%27%26%4
270
May1st to 15thDay
13%6%23%22%20%13%
288
16th to endDay
12%213%24%25%21%
331
June1st to 15thDay
10%18%19%26%33%
315
16th to endDay
7%16%26%27%30%
315
July1st to 15thDay
9%5%18%30%35%
305
16th to endDay
8%415%34%36%
326
August1st to 15thDay
15%7%20%29%27%
313
16th to endDay
15%8%19%31%25%
332
September1st to 15thDay
13%211%19%31%21%
315
16th to endDay
17%18%23%36%12%
314
October1st to 15thDay
14%318%29%23%10%
315
16th to endDay
12%6%16%25%30%7%
336
November1st to 15thDay
23%8%20%22%22%4
159
16th to endDay
10%8%28%28%20%5%
135
December1st to 15thDay
28%8%29%24%9%
135
16th to endDay
31%16%25%19%5%
144
January1st to 15thNight
21%13%31%25%7%
780
16th to endNight
20%13%33%26%6%
832
February1st to 15thNight
19%12%31%31%5%
753
16th to endNight
17%14%38%26%3
631
March1st to 15thNight
16%10%34%31%6%
720
16th to endNight
14%9%28%30%15%
768
April1st to 15thNight
14%8%28%30%16%1
650
16th to endNight
10%5%25%34%21%2
540
May1st to 15thNight
10%425%32%23%3
540
16th to endNight
9%15%31%35%6%
563
June1st to 15thNight
8%10%31%37%11%
540
16th to endNight
5%8%31%42%12%
540
July1st to 15thNight
7%6%23%47%14%
510
16th to endNight
5%7%21%52%13%
564
August1st to 15thNight
8%5%27%46%11%
539
16th to endNight
13%15%24%45%9%
573
September1st to 15thNight
10%17%25%43%10%
712
16th to endNight
14%110%33%35%3
717
October1st to 15thNight
13%318%31%26%5%
720
16th to endNight
10%5%24%30%24%4
768
November1st to 15thNight
14%5%22%30%25%1
760
16th to endNight
15%8%28%28%17%1
780
December1st to 15thNight
16%8%31%30%12%1
780
16th to endNight
23%10%29%29%7%
832
Page generated at 2018-02-13 20:46:00. Version ac04

Copyright 2018 A. Danko


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