Morning Calm Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Morning Calm 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
43%
15800
21%
48415
13%
15764
52%
15764
27%
30299

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
31%
761
23%
2491
11%
761
47%
761
23%
1534
January16th to endNight
27%
768
23%
2496
11%
768
43%
768
24%
1557
February1st to 15thNight
29%
701
21%
2287
9%
701
45%
701
25%
1374
February16th to endNight
22%
631
25%
1921
9%
631
41%
631
25%
1179
March1st to 15thNight
30%
720
23%
1980
10%
720
42%
720
26%
1274
March16th to endNight
29%
768
20%
2112
10%
768
38%
768
26%
1401
April1st to 15thNight
32%
718
19%
1805
6%
718
40%
718
30%
1173
April16th to endNight
42%
720
21%
1800
10%
720
47%
720
32%
1196
May1st to 15thNight
42%
540
16%
1620
8%
540
47%
540
23%
1092
May16th to endNight
54%
431
17%
1554
15%
431
59%
431
25%
943
June1st to 15thNight
61%
360
19%
1440
21%
360
66%
360
26%
800
June16th to endNight
66%
360
18%
1440
20%
360
71%
360
26%
845
July1st to 15thNight
61%
413
12%
1433
13%
413
63%
413
22%
919
July16th to endNight
76%
564
16%
1595
13%
531
78%
531
37%
928
August1st to 15thNight
70%
539
18%
1609
14%
536
71%
536
29%
1047
August16th to endNight
62%
729
17%
1875
13%
729
63%
729
29%
1290
September1st to 15thNight
60%
720
24%
1800
16%
720
63%
720
34%
1197
September16th to endNight
53%
717
22%
2000
19%
717
56%
717
27%
1332
October1st to 15thNight
50%
720
22%
2160
21%
720
56%
720
27%
1377
October16th to endNight
42%
768
31%
2304
21%
768
56%
768
34%
1332
November1st to 15thNight
42%
760
26%
2344
16%
760
55%
760
30%
1412
November16th to endNight
36%
780
24%
2707
14%
780
51%
780
27%
1542
December1st to 15thNight
33%
780
19%
2730
10%
780
45%
780
20%
1731
December16th to endNight
33%
832
22%
2912
13%
832
47%
832
22%
1824

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
13%5%25%5%35%5%5%7%41%
48901
Night
13%5%2442445%7%45%
48604
Cloud CoverDay
13%5%245%345%5%7%42%
48911
Night
13%5%2442445%7%45%
48608
TransparencyDay
39%7%12%21%15%3
48608
Night
38%6%11%22%17%3
48415
SeeingDay
17%7%23%26%17%7%
5995
Night
16%7%27%31%15%1
15808

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
15%4245%245%5%7%42%
1687
16th to endDay
14%5%25%5%35%45%5%42%
1728
February1st to 15thDay
11%7%35%5%2445%5%42%
1575
16th to endDay
12%7%25%5%245%5%6%41%
1548
March1st to 15thDay
13%5%25%5%25%44446%
1969
16th to endDay
15%6%345%25%45%6%39%
2112
April1st to 15thDay
10%425%434446%47%
2143
16th to endDay
15%6%25%433345%44%
2169
May1st to 15thDay
17%5%24435%5%5%7%37%
2331
16th to endDay
13%5%25%435%6%5%8%38%
2560
June1st to 15thDay
10%414435%5%7%9%41%
2520
16th to endDay
8%325%5%46%6%7%9%41%
2520
July1st to 15thDay
10%5%25%5%46%6%7%10%35%
2437
16th to endDay
6%325%6%47%7%9%10%35%
2465
August1st to 15thDay
9%5%26%7%5%7%6%7%9%32%
2340
16th to endDay
11%425%5%45%7%6%9%36%
2315
September1st to 15thDay
11%5%245%2445%7%45%
2160
16th to endDay
16%6%25%4345%6%6%39%
1957
October1st to 15thDay
18%5%14423346%44%
1800
16th to endDay
13%414423345%51%
1920
November1st to 15thDay
12%5%14424346%49%
1842
16th to endDay
16%313424436%49%
1579
December1st to 15thDay
15%5%24423446%44%
1560
16th to endDay
17%6%25%434435%42%
1664
January1st to 15thNight
15%5%2332445%6%45%
2491
16th to endNight
14%7%34324445%45%
2496
February1st to 15thNight
13%6%2442345%6%46%
2285
16th to endNight
12%5%25%433447%45%
1921
March1st to 15thNight
15%415%324445%47%
1968
16th to endNight
15%5%25%42345%5%44%
2112
April1st to 15thNight
12%5%2442445%7%46%
1805
16th to endNight
14%425%32445%6%46%
1800
May1st to 15thNight
18%424334448%39%
1620
16th to endNight
13%5%143345%5%9%44%
1552
June1st to 15thNight
9%314425%46%10%47%
1440
16th to endNight
9%3146%35%5%6%9%44%
1440
July1st to 15thNight
9%5%25%5%35%5%6%9%40%
1519
16th to endNight
4312435%5%8%14%44%
1703
August1st to 15thNight
8%425%6%35%5%6%9%42%
1620
16th to endNight
10%5%26%5%35%6%5%9%38%
1875
September1st to 15thNight
12%42442346%6%46%
1800
16th to endNight
17%5%245%2435%6%42%
2000
October1st to 15thNight
18%414333447%43%
2160
16th to endNight
13%312323445%53%
2304
November1st to 15thNight
12%6%34323445%50%
2344
16th to endNight
15%423423445%50%
2707
December1st to 15thNight
14%6%35%5%3445%5%42%
2730
16th to endNight
15%5%25%42345%6%43%
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
15%5%25%4235%5%5%43%
1687
16th to endDay
15%6%2443445%5%42%
1728
February1st to 15thDay
12%8%35%5%2445%5%42%
1575
16th to endDay
12%7%25%5%345%5%6%41%
1548
March1st to 15thDay
14%5%25%43443445%
1980
16th to endDay
16%7%3442445%6%39%
2111
April1st to 15thDay
11%5%145%25%446%47%
2143
16th to endDay
16%6%25%424345%44%
2169
May1st to 15thDay
18%5%244345%5%6%37%
2331
16th to endDay
14%5%25%5%35%6%5%8%38%
2560
June1st to 15thDay
10%4145%35%6%6%9%42%
2520
16th to endDay
8%315%5%5%5%5%7%8%42%
2520
July1st to 15thDay
11%425%5%36%6%7%10%35%
2437
16th to endDay
7%315%6%47%6%8%10%37%
2465
August1st to 15thDay
9%5%26%7%5%6%6%7%9%33%
2340
16th to endDay
11%4245%45%7%6%9%37%
2315
September1st to 15thDay
11%5%145%25%45%8%45%
2160
16th to endDay
17%5%25%4245%5%6%39%
1957
October1st to 15thDay
18%424423446%45%
1800
16th to endDay
13%413423345%51%
1920
November1st to 15thDay
13%5%2342335%6%49%
1842
16th to endDay
16%413414445%49%
1579
December1st to 15thDay
16%5%24323447%44%
1560
16th to endDay
18%6%24433336%41%
1664
January1st to 15thNight
15%5%2432435%6%45%
2491
16th to endNight
15%7%34323346%45%
2496
February1st to 15thNight
14%6%24423446%46%
2278
16th to endNight
12%5%25%43345%6%45%
1921
March1st to 15thNight
15%42442435%6%47%
1980
16th to endNight
15%6%2442445%5%44%
2112
April1st to 15thNight
13%5%2441445%7%46%
1805
16th to endNight
14%425%32445%6%46%
1800
May1st to 15thNight
18%5%3442445%7%39%
1619
16th to endNight
13%5%1343445%9%43%
1552
June1st to 15thNight
9%314425%46%9%47%
1440
16th to endNight
9%3245%25%5%6%8%44%
1440
July1st to 15thNight
9%5%25%5%35%46%9%41%
1519
16th to endNight
5%413425%5%8%13%44%
1703
August1st to 15thNight
8%425%5%36%5%6%8%42%
1620
16th to endNight
11%5%25%5%35%5%6%9%38%
1875
September1st to 15thNight
13%5%2442436%6%46%
1800
16th to endNight
17%5%245%34446%42%
2000
October1st to 15thNight
18%414334437%43%
2160
16th to endNight
13%31231345%6%53%
2304
November1st to 15thNight
13%6%24323345%50%
2344
16th to endNight
15%413423436%50%
2707
December1st to 15thNight
15%7%244345%4442%
2730
16th to endNight
15%5%35%42345%6%42%
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
40%5%13%19%16%4
1688
16th to endDay
42%410%23%15%4
1728
February1st to 15thDay
41%411%23%15%3
1577
16th to endDay
40%6%13%20%17%1
1548
March1st to 15thDay
41%49%22%16%5%
1980
16th to endDay
44%6%11%17%16%4
2112
April1st to 15thDay
36%5%12%22%17%5%
2143
16th to endDay
41%5%10%18%17%6%
2169
May1st to 15thDay
44%8%13%17%14%1
2331
16th to endDay
40%8%15%22%11%1
2564
June1st to 15thDay
36%9%16%23%13%1
2520
16th to endDay
35%10%15%21%15%1
2520
July1st to 15thDay
40%10%14%18%12%3
2294
16th to endDay
36%11%14%22%13%2
2310
August1st to 15thDay
42%10%14%19%12%
2327
16th to endDay
39%9%14%23%11%1
2315
September1st to 15thDay
37%7%12%18%19%4
2160
16th to endDay
42%6%9%21%18%
1957
October1st to 15thDay
40%5%8%26%15%3
1800
16th to endDay
34%37%27%22%3
1920
November1st to 15thDay
36%5%10%21%20%6%
1842
16th to endDay
35%312%24%21%3
1579
December1st to 15thDay
39%412%23%13%4
1560
16th to endDay
44%410%23%14%1
1664
January1st to 15thNight
39%5%11%19%17%7%
2491
16th to endNight
40%411%23%17%2
2496
February1st to 15thNight
37%410%24%17%4
2287
16th to endNight
38%410%24%19%3
1921
March1st to 15thNight
38%6%11%26%14%3
1980
16th to endNight
40%6%11%21%17%2
2112
April1st to 15thNight
37%5%11%21%20%4
1805
16th to endNight
37%6%11%21%16%7%
1800
May1st to 15thNight
43%7%11%20%13%2
1620
16th to endNight
37%7%15%23%13%2
1554
June1st to 15thNight
31%9%15%27%14%2
1440
16th to endNight
33%9%16%19%18%2
1440
July1st to 15thNight
39%10%16%16%13%3
1433
16th to endNight
26%9%21%25%15%1
1595
August1st to 15thNight
37%9%13%23%15%1
1609
16th to endNight
40%8%13%24%11%1
1875
September1st to 15thNight
36%7%12%21%18%4
1800
16th to endNight
42%6%9%20%18%2
2000
October1st to 15thNight
40%5%10%21%17%4
2160
16th to endNight
31%5%9%27%22%4
2304
November1st to 15thNight
37%38%21%21%8%
2344
16th to endNight
35%39%23%22%4
2707
December1st to 15thNight
43%5%11%20%15%3
2730
16th to endNight
41%6%12%22%14%3
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
22%22%35%15%4
118
16th to endDay
28%23%35%10%2
96
February1st to 15thDay
26%25%37%10%
90
16th to endDay
18%18%32%28%2
183
March1st to 15thDay
20%14%28%29%6%
270
16th to endDay
19%13%35%21%7%2
288
April1st to 15thDay
14%15%24%27%14%2
270
16th to endDay
26%425%21%17%4
270
May1st to 15thDay
25%12%26%18%12%5%
288
16th to endDay
21%422%25%18%8%
331
June1st to 15thDay
12%427%22%22%10%
315
16th to endDay
11%325%33%19%6%
315
July1st to 15thDay
16%118%32%22%7%
305
16th to endDay
7%19%34%30%15%
326
August1st to 15thDay
13%216%27%27%13%
313
16th to endDay
11%111%31%24%19%
332
September1st to 15thDay
14%318%23%20%18%
315
16th to endDay
26%214%22%19%14%
314
October1st to 15thDay
23%316%28%19%8%
315
16th to endDay
12%9%28%27%16%4
336
November1st to 15thDay
18%7%24%27%17%4
310
16th to endDay
16%13%30%30%8%
109
December1st to 15thDay
17%14%35%20%11%1
90
16th to endDay
27%16%39%14%2
96
January1st to 15thNight
19%12%32%30%5%
765
16th to endNight
19%10%39%28%2
768
February1st to 15thNight
18%10%38%30%1
704
16th to endNight
16%14%41%25%2
631
March1st to 15thNight
18%13%33%28%5%
720
16th to endNight
17%9%38%25%7%1
768
April1st to 15thNight
16%12%36%27%7%
718
16th to endNight
17%7%28%33%12%1
720
May1st to 15thNight
21%5%26%27%17%1
540
16th to endNight
15%220%36%22%2
432
June1st to 15thNight
10%18%43%25%1
360
16th to endNight
9%215%47%24%1
360
July1st to 15thNight
9%214%37%34%1
413
16th to endNight
6%9%36%39%6%
564
August1st to 15thNight
10%9%45%29%4
539
16th to endNight
13%111%35%33%4
729
September1st to 15thNight
13%216%31%32%3
720
16th to endNight
19%115%31%28%3
717
October1st to 15thNight
19%5%17%31%22%3
720
16th to endNight
15%7%32%28%14%1
768
November1st to 15thNight
16%7%27%32%13%2
760
16th to endNight
17%7%33%26%13%
780
December1st to 15thNight
18%8%34%28%9%
780
16th to endNight
18%8%34%35%3
832
Page generated at 2018-01-12 22:01:36. Version ac04

Copyright 2018 A. Danko


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