M&G Adler Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the M&G Adler 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
31%
14904
18%
46868
8%
14872
42%
14872
22%
30627

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
17%
720
19%
2506
6%
716
33%
716
17%
1607
January16th to endNight
15%
768
18%
2688
4%
768
33%
768
15%
1743
February1st to 15thNight
17%
704
16%
2195
4%
701
32%
701
18%
1482
February16th to endNight
20%
631
23%
1893
7%
631
40%
631
21%
1241
March1st to 15thNight
20%
720
17%
2145
7%
720
33%
720
19%
1475
March16th to endNight
24%
768
22%
2046
7%
768
36%
768
23%
1396
April1st to 15thNight
27%
718
18%
1796
5%
718
35%
718
24%
1270
April16th to endNight
31%
576
18%
1656
6%
576
39%
576
22%
1143
May1st to 15thNight
30%
540
15%
1620
7%
540
36%
540
20%
1129
May16th to endNight
33%
428
11%
1550
8%
427
40%
427
18%
1020
June1st to 15thNight
39%
360
12%
1440
13%
360
46%
360
15%
976
June16th to endNight
46%
360
11%
1440
12%
360
51%
360
21%
873
July1st to 15thNight
54%
340
12%
1360
18%
340
57%
340
23%
811
July16th to endNight
56%
376
15%
1418
17%
354
60%
354
21%
882
August1st to 15thNight
55%
518
16%
1589
13%
516
58%
516
28%
998
August16th to endNight
58%
700
21%
1846
12%
700
60%
700
32%
1187
September1st to 15thNight
49%
720
19%
1872
11%
720
53%
720
35%
1196
September16th to endNight
50%
685
26%
1891
18%
685
56%
685
35%
1164
October1st to 15thNight
35%
660
22%
1837
11%
660
45%
660
27%
1206
October16th to endNight
28%
704
16%
2288
7%
704
40%
704
21%
1469
November1st to 15thNight
31%
700
20%
2277
10%
700
43%
700
22%
1447
November16th to endNight
26%
720
19%
2340
8%
720
39%
720
19%
1500
December1st to 15thNight
19%
720
17%
2487
4%
720
35%
720
17%
1620
December16th to endNight
15%
768
18%
2688
3%
768
32%
768
15%
1792

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
17%6%2442445%7%39%
48018
Night
17%6%25%424446%40%
47038
Cloud CoverDay
17%6%2442445%7%40%
48028
Night
17%6%25%424446%40%
47043
TransparencyDay
42%6%11%22%14%2
47706
Night
43%5%11%21%14%2
46868
SeeingDay
20%9%29%26%11%2
5934
Night
20%10%32%27%9%1
14904

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
17%6%35%32345%5%42%
1432
16th to endDay
16%5%25%5%2335%5%44%
1536
February1st to 15thDay
18%6%35%5%245%5%6%35%
1663
16th to endDay
14%9%35%425%45%5%40%
1580
March1st to 15thDay
21%6%35%424446%35%
1805
16th to endDay
18%7%245%23346%40%
2175
April1st to 15thDay
18%6%25%5%33446%38%
2152
16th to endDay
18%5%14424447%40%
2303
May1st to 15thDay
23%7%25%43345%6%32%
2332
16th to endDay
17%5%245%24448%40%
2573
June1st to 15thDay
24%5%24435%45%6%33%
2520
16th to endDay
15%5%15%6%35%46%9%35%
2520
July1st to 15thDay
12%4245%35%5%6%9%38%
2520
16th to endDay
11%5%25%5%36%5%7%9%39%
2654
August1st to 15thDay
11%425%5%26%6%6%10%38%
2348
16th to endDay
11%4134246%5%8%45%
2354
September1st to 15thDay
13%5%2432335%7%47%
2088
16th to endDay
14%5%24313345%50%
1881
October1st to 15thDay
20%5%25%423345%42%
1789
16th to endDay
17%415%5%24446%42%
1584
November1st to 15thDay
21%7%24323345%42%
1581
16th to endDay
18%6%24423246%43%
1620
December1st to 15thDay
18%7%345%43335%40%
1472
16th to endDay
23%8%35%434335%35%
1536
January1st to 15thNight
16%7%35%424346%40%
2506
16th to endNight
16%8%35%5%24435%39%
2688
February1st to 15thNight
15%8%36%4345%46%37%
2194
16th to endNight
17%8%24423336%42%
1893
March1st to 15thNight
19%7%25%5%34345%38%
2132
16th to endNight
16%7%35%424425%43%
2046
April1st to 15thNight
17%9%34434447%37%
1796
16th to endNight
21%5%25%424345%39%
1656
May1st to 15thNight
21%7%35%5%34346%35%
1620
16th to endNight
21%5%36%41346%8%34%
1548
June1st to 15thNight
24%7%24423347%34%
1440
16th to endNight
16%5%25%42445%9%40%
1440
July1st to 15thNight
12%7%245%3445%8%40%
1440
16th to endNight
12%5%25%5%36%5%5%8%38%
1514
August1st to 15thNight
10%4245%46%5%6%8%41%
1599
16th to endNight
11%5%15%425%448%44%
1846
September1st to 15thNight
14%424423446%47%
1872
16th to endNight
14%5%24223336%50%
1891
October1st to 15thNight
19%5%25%413346%43%
1837
16th to endNight
19%6%1442345%6%40%
2288
November1st to 15thNight
16%5%16%333445%44%
2277
16th to endNight
17%6%35%424346%41%
2340
December1st to 15thNight
19%7%24424446%38%
2487
16th to endNight
19%8%25%5%2345%5%37%
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
17%6%3442445%5%42%
1432
16th to endDay
16%5%25%432345%44%
1536
February1st to 15thDay
18%6%25%5%245%5%6%36%
1663
16th to endDay
14%8%25%4245%5%6%39%
1580
March1st to 15thDay
21%7%25%4235%47%34%
1815
16th to endDay
17%7%24423445%41%
2175
April1st to 15thDay
18%6%25%5%24446%38%
2152
16th to endDay
18%4235%24447%41%
2303
May1st to 15thDay
23%7%35%5%23346%33%
2332
16th to endDay
17%5%245%24348%40%
2573
June1st to 15thDay
24%5%23435%45%7%33%
2520
16th to endDay
15%5%15%5%35%5%7%9%36%
2520
July1st to 15thDay
12%5%24435%6%5%9%40%
2520
16th to endDay
11%5%15%435%5%7%9%39%
2654
August1st to 15thDay
11%424435%6%7%10%38%
2348
16th to endDay
11%423425%6%5%8%46%
2354
September1st to 15thDay
13%5%24423447%47%
2088
16th to endDay
14%5%14423346%50%
1881
October1st to 15thDay
20%5%24423445%42%
1789
16th to endDay
16%5%25%434446%42%
1584
November1st to 15thDay
21%7%2422333442%
1581
16th to endDay
17%6%24424346%43%
1620
December1st to 15thDay
18%7%245%34326%40%
1472
16th to endDay
23%8%34325%335%35%
1536
January1st to 15thNight
17%8%35%424436%41%
2506
16th to endNight
17%8%35%423445%39%
2688
February1st to 15thNight
15%9%35%4345%46%37%
2187
16th to endNight
17%8%34423435%43%
1893
March1st to 15thNight
19%7%25%423446%37%
2145
16th to endNight
16%7%35%425%33443%
2045
April1st to 15thNight
17%8%35%42445%6%37%
1796
16th to endNight
20%5%25%5%34345%39%
1656
May1st to 15thNight
21%6%25%5%34446%34%
1620
16th to endNight
20%6%25%41345%8%35%
1548
June1st to 15thNight
24%7%25%424347%34%
1440
16th to endNight
16%5%25%425%35%8%41%
1440
July1st to 15thNight
11%7%25%5%3445%8%41%
1440
16th to endNight
12%5%35%5%36%5%6%8%37%
1514
August1st to 15thNight
9%4246%35%6%6%8%42%
1599
16th to endNight
12%42443445%8%44%
1846
September1st to 15thNight
13%425%41345%6%47%
1872
16th to endNight
14%5%23323336%50%
1891
October1st to 15thNight
19%5%25%423336%43%
1837
16th to endNight
19%5%2432445%6%41%
2288
November1st to 15thNight
17%6%24423345%44%
2277
16th to endNight
17%6%34423446%41%
2340
December1st to 15thNight
20%6%34423445%39%
2487
16th to endNight
19%8%25%5%2345%6%37%
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
42%5%11%25%11%3
1433
16th to endDay
41%412%26%13%1
1536
February1st to 15thDay
47%5%13%20%12%
1666
16th to endDay
43%5%11%22%13%2
1580
March1st to 15thDay
48%5%12%19%11%2
1815
16th to endDay
43%49%21%15%5%
2175
April1st to 15thDay
46%49%19%15%3
2152
16th to endDay
41%6%8%22%17%3
2303
May1st to 15thDay
51%5%7%17%14%2
2332
16th to endDay
42%6%14%21%13%1
2577
June1st to 15thDay
49%7%11%20%10%1
2520
16th to endDay
41%8%12%20%15%
2520
July1st to 15thDay
38%8%11%23%15%1
2371
16th to endDay
38%7%15%22%12%3
2487
August1st to 15thDay
38%9%13%24%12%1
2334
16th to endDay
32%8%11%27%18%1
2354
September1st to 15thDay
35%5%12%22%22%1
2088
16th to endDay
36%39%24%23%2
1881
October1st to 15thDay
43%5%9%23%15%3
1789
16th to endDay
41%6%10%25%14%1
1584
November1st to 15thDay
45%312%23%14%1
1581
16th to endDay
43%411%23%15%1
1620
December1st to 15thDay
47%315%16%16%
1472
16th to endDay
52%5%12%19%10%
1536
January1st to 15thNight
45%313%22%12%1
2506
16th to endNight
46%410%20%15%2
2688
February1st to 15thNight
46%5%13%20%11%2
2195
16th to endNight
43%311%23%14%2
1893
March1st to 15thNight
47%410%19%13%3
2145
16th to endNight
44%48%18%19%5%
2046
April1st to 15thNight
46%49%19%17%2
1796
16th to endNight
48%48%19%16%3
1656
May1st to 15thNight
50%410%16%14%3
1620
16th to endNight
46%6%15%18%10%1
1550
June1st to 15thNight
50%6%10%20%10%
1440
16th to endNight
40%6%12%22%15%1
1440
July1st to 15thNight
39%6%13%25%14%
1360
16th to endNight
40%7%14%25%9%2
1418
August1st to 15thNight
36%8%14%23%15%2
1589
16th to endNight
36%6%11%26%19%
1846
September1st to 15thNight
35%5%12%25%19%1
1872
16th to endNight
35%46%25%26%1
1891
October1st to 15thNight
42%411%22%15%3
1837
16th to endNight
43%5%13%23%14%
2288
November1st to 15thNight
42%5%12%21%15%2
2277
16th to endNight
44%313%21%14%2
2340
December1st to 15thNight
45%5%14%21%12%
2487
16th to endNight
47%5%12%21%12%
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
16%26%25%28%3
60
16th to endDay
26%18%37%17%
64
February1st to 15thDay
26%16%36%18%2
232
16th to endDay
15%17%37%23%4
239
March1st to 15thDay
22%18%35%19%2
270
16th to endDay
22%17%35%15%7%1
288
April1st to 15thDay
23%13%32%21%8%
270
16th to endDay
22%10%34%23%5%2
270
May1st to 15thDay
32%8%28%19%10%1
288
16th to endDay
22%330%33%9%
331
June1st to 15thDay
25%433%24%11%
315
16th to endDay
16%436%31%8%2
315
July1st to 15thDay
17%223%37%16%2
305
16th to endDay
14%222%38%20%1
326
August1st to 15thDay
13%423%36%19%3
313
16th to endDay
13%319%36%19%7%
332
September1st to 15thDay
17%5%24%30%16%4
315
16th to endDay
20%424%22%14%14%
278
October1st to 15thDay
24%7%23%23%16%5%
252
16th to endDay
20%13%30%27%8%
240
November1st to 15thDay
26%7%29%23%10%2
235
16th to endDay
22%13%34%17%10%1
240
December1st to 15thDay
20%21%34%17%5%
92
16th to endDay
26%20%39%14%
64
January1st to 15thNight
20%16%39%19%3
720
16th to endNight
22%18%37%18%3
768
February1st to 15thNight
19%16%41%20%1
704
16th to endNight
21%16%36%19%4
631
March1st to 15thNight
22%14%38%20%3
720
16th to endNight
21%12%36%21%7%
768
April1st to 15thNight
19%11%36%25%5%
718
16th to endNight
21%9%32%27%7%
576
May1st to 15thNight
24%433%28%6%1
540
16th to endNight
24%332%29%9%
428
June1st to 15thNight
24%5%23%32%11%1
360
16th to endNight
17%224%43%11%
360
July1st to 15thNight
10%222%49%13%2
340
16th to endNight
13%119%43%21%
376
August1st to 15thNight
11%122%46%18%
518
16th to endNight
15%216%40%22%2
700
September1st to 15thNight
15%225%36%17%2
720
16th to endNight
17%422%28%23%4
685
October1st to 15thNight
21%7%28%27%12%2
660
16th to endNight
22%10%34%24%8%
704
November1st to 15thNight
18%11%32%25%10%1
700
16th to endNight
20%15%31%21%9%
720
December1st to 15thNight
23%13%38%19%4
720
16th to endNight
24%17%38%17%2
768
Page generated at 2017-09-23 06:43:41. Version ac04

Copyright 2017 A. Danko


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