Moran
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Moran clear sky chart from 2005-11-06 to 2024-01-12.

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
30%
24085
11%
74975
7%
24024
35%
24024
16%
55197

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 10thNight
14%
950
5%
2648
2%
946
18%
946
8%
2246
January11th to 20thNight
16%
910
5%
2547
2%
910
18%
910
8%
2177
January21st to endNight
17%
990
7%
2772
2%
990
22%
990
9%
2321
February1st to 10thNight
18%
804
10%
2424
4%
804
24%
804
11%
1892
February11th to 20thNight
21%
702
11%
2155
4%
699
29%
699
12%
1655
February21st to endNight
17%
592
11%
1776
3%
592
25%
592
12%
1384
March1st to 10thNight
26%
720
16%
2160
7%
720
34%
720
21%
1468
March11th to 20thNight
28%
720
17%
2016
8%
720
37%
720
20%
1429
March21st to endNight
32%
756
18%
2142
11%
756
39%
756
22%
1482
April1st to 10thNight
27%
540
10%
1800
6%
540
33%
540
16%
1296
April11th to 20thNight
33%
533
18%
1643
12%
533
40%
533
21%
1130
April21st to endNight
33%
540
16%
1620
8%
540
40%
540
20%
1114
May1st to 10thNight
37%
540
15%
1620
9%
540
42%
540
20%
1103
May11th to 20thNight
36%
531
15%
1498
10%
531
43%
531
22%
1054
May21st to endNight
45%
486
15%
1454
9%
484
51%
484
28%
929
June1st to 10thNight
43%
360
13%
1260
10%
360
49%
360
25%
763
June11th to 20thNight
47%
360
14%
1260
11%
360
51%
360
24%
775
June21st to endNight
47%
360
13%
1260
11%
360
51%
360
25%
772
July1st to 10thNight
55%
420
16%
1295
12%
420
59%
420
35%
737
July11th to 20thNight
53%
522
16%
1392
12%
522
56%
522
31%
889
July21st to endNight
56%
591
15%
1487
12%
558
58%
558
33%
941
August1st to 10thNight
57%
537
17%
1511
13%
534
60%
534
34%
912
August11th to 20thNight
61%
534
18%
1598
13%
534
66%
534
35%
925
August21st to endNight
51%
594
18%
1822
13%
594
55%
594
29%
1114
September1st to 10thNight
50%
560
17%
1820
14%
560
55%
560
27%
1118
September11th to 20thNight
44%
720
18%
1980
13%
720
48%
720
30%
1304
September21st to endNight
43%
720
16%
1980
12%
720
46%
720
23%
1380
October1st to 10thNight
35%
720
14%
2001
9%
720
41%
720
23%
1394
October11th to 20thNight
24%
720
10%
2253
4%
720
29%
720
13%
1699
October21st to endNight
22%
792
9%
2574
6%
792
27%
792
11%
2013
November1st to 10thNight
23%
740
13%
2406
8%
740
31%
740
13%
1740
November11th to 20thNight
17%
760
9%
2503
4%
760
23%
760
8%
1984
November21st to endNight
15%
821
5%
2721
3%
821
18%
821
7%
2254
December1st to 10thNight
14%
950
5%
2850
2%
950
17%
950
7%
2343
December11th to 20thNight
12%
950
4%
3508
1%
948
15%
948
5%
2831
December21st to endNight
11%
1040
3%
5219
1%
1026
15%
1026
3%
4629

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%10%47%6%35%5%5%7%33%
74543
Night
16%11%5%8%7%35%5%5%7%30%
75177
TransparencyDay
50%7%13%20%9%1
74247
Night
54%7%13%17%8%1
75007
SeeingDay
19%14%32%23%9%2
14433
Night
20%12%31%26%10%1
24091

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 10thDay
14%15%9%13%10%5%6%45%6%14%
1517
11th to 20thDay
15%18%6%14%9%46%5%45%14%
1453
21st to endDay
14%16%7%12%9%6%6%46%5%15%
1584
February1st to 10thDay
9%13%6%12%8%5%7%5%6%7%22%
1534
11th to 20thDay
14%11%6%10%9%46%5%5%7%22%
1690
21st to endDay
11%13%6%13%10%45%45%6%23%
1480
March1st to 10thDay
13%11%47%9%44446%34%
1798
11th to 20thDay
11%12%5%9%7%3445%5%35%
1944
21st to endDay
16%11%46%6%35%346%35%
2229
April1st to 10thDay
19%11%5%7%5%35%5%5%6%28%
2160
11th to 20thDay
19%10%47%43445%7%34%
2266
21st to endDay
16%10%38%6%345%5%6%33%
2340
May1st to 10thDay
17%8%36%5%3445%7%37%
2340
11th to 20thDay
16%9%35%5%3345%6%41%
2393
21st to endDay
12%6%26%435%5%6%9%43%
2819
June1st to 10thDay
14%5%25%435%5%6%9%42%
2700
11th to 20thDay
13%6%26%5%45%5%6%9%40%
2700
21st to endDay
15%7%35%43445%8%42%
2700
July1st to 10thDay
8%5%24435%5%6%9%49%
2622
11th to 20thDay
12%5%34435%5%5%8%46%
2520
21st to endDay
11%5%35%435%6%6%10%44%
2743
August1st to 10thDay
10%5%25%5%45%6%7%9%42%
2417
11th to 20thDay
11%5%245%25%5%7%7%47%
2303
21st to endDay
13%6%25%5%3445%9%44%
2531
September1st to 10thDay
17%6%244345%6%7%42%
2121
11th to 20thDay
14%6%25%6%35%5%6%8%40%
1980
21st to endDay
15%8%36%5%45%46%9%36%
1980
October1st to 10thDay
19%9%37%6%345%5%8%32%
1958
11th to 20thDay
23%13%47%7%45%6%5%7%20%
1706
21st to endDay
23%13%48%8%4445%6%20%
1782
November1st to 10thDay
20%11%48%7%35%5%7%7%24%
1672
11th to 20thDay
17%13%7%10%8%46%5%5%6%18%
1675
21st to endDay
20%19%6%10%8%5%6%45%5%13%
1454
December1st to 10thDay
14%18%7%12%9%45%5%45%16%
1330
11th to 20thDay
19%19%7%11%7%35%5%46%14%
1671
21st to endDay
23%20%8%14%8%3433411%
2431
January1st to 10thNight
15%16%7%12%8%46%5%46%16%
2648
11th to 20thNight
16%16%7%11%10%45%5%45%16%
2547
21st to endNight
15%15%6%11%11%46%5%5%6%16%
2772
February1st to 10thNight
9%15%6%9%10%5%7%5%5%6%23%
2424
11th to 20thNight
11%12%5%12%9%46%45%6%25%
2155
21st to endNight
13%14%6%12%8%45%6%46%24%
1776
March1st to 10thNight
11%10%47%6%45%5%5%6%39%
2149
11th to 20thNight
14%9%47%7%345%48%36%
2015
21st to endNight
15%9%46%6%35%446%38%
2142
April1st to 10thNight
19%10%5%6%6%45%5%6%7%28%
1800
11th to 20thNight
18%9%36%5%335%5%6%37%
1643
21st to endNight
17%8%45%7%34446%37%
1620
May1st to 10thNight
15%8%46%6%35%46%6%37%
1620
11th to 20thNight
15%8%36%7%35%5%5%7%35%
1498
21st to endNight
11%6%26%4345%6%8%43%
1453
June1st to 10thNight
12%436%5%35%5%6%9%41%
1260
11th to 20thNight
11%5%36%5%35%5%6%7%43%
1260
21st to endNight
14%7%36%42446%8%43%
1260
July1st to 10thNight
10%4244235%7%8%51%
1334
11th to 20thNight
9%426%5%35%46%8%46%
1440
21st to endNight
9%6%25%43445%8%49%
1575
August1st to 10thNight
7%5%344345%6%8%49%
1520
11th to 20thNight
9%4245%245%5%7%53%
1598
21st to endNight
11%6%3443446%7%48%
1822
September1st to 10thNight
12%6%25%5%35%45%7%46%
1820
11th to 20thNight
16%5%245%2445%8%45%
1980
21st to endNight
17%6%36%6%4446%6%38%
1980
October1st to 10thNight
17%8%35%5%3445%7%37%
2001
11th to 20thNight
23%10%47%6%345%5%7%27%
2253
21st to endNight
25%11%38%5%35%447%23%
2574
November1st to 10thNight
17%10%47%7%345%6%7%30%
2406
11th to 20thNight
18%13%5%9%8%46%5%6%6%22%
2503
21st to endNight
19%17%6%9%6%45%5%5%7%18%
2721
December1st to 10thNight
13%18%7%11%9%35%5%5%6%18%
2850
11th to 20thNight
18%16%6%11%7%34446%19%
3526
21st to endNight
26%21%8%10%7%3443410%
5232

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 10thDay
70%9%10%8%2
1518
11th to 20thDay
72%7%9%9%21
1453
21st to endDay
69%7%11%9%31
1584
February1st to 10thDay
61%6%15%14%4
1534
11th to 20thDay
60%7%14%12%8%1
1699
21st to endDay
61%6%11%16%6%
1480
March1st to 10thDay
52%6%13%16%11%2
1800
11th to 20thDay
51%5%13%22%7%2
1944
21st to endDay
51%6%10%21%10%2
2229
April1st to 10thDay
56%5%11%19%9%1
2160
11th to 20thDay
51%5%10%21%12%2
2266
21st to endDay
49%6%11%17%14%3
2340
May1st to 10thDay
46%7%10%21%13%4
2340
11th to 20thDay
44%6%10%24%15%1
2397
21st to endDay
37%9%15%25%12%2
2819
June1st to 10thDay
38%8%13%25%14%2
2700
11th to 20thDay
40%7%12%25%14%1
2700
21st to endDay
41%7%14%24%12%2
2700
July1st to 10thDay
30%8%16%27%18%1
2552
11th to 20thDay
34%7%13%30%14%2
2445
21st to endDay
36%7%17%25%14%1
2591
August1st to 10thDay
37%8%16%28%10%1
2402
11th to 20thDay
35%8%16%28%12%1
2303
21st to endDay
38%7%18%24%12%1
2531
September1st to 10thDay
40%7%14%26%12%1
2121
11th to 20thDay
40%8%18%28%6%
1980
21st to endDay
45%8%19%21%6%
1980
October1st to 10thDay
50%8%13%22%7%1
1958
11th to 20thDay
63%7%13%13%3
1706
21st to endDay
65%7%13%12%4
1782
November1st to 10thDay
57%8%14%16%4
1672
11th to 20thDay
65%9%14%8%4
1675
21st to endDay
73%9%10%7%1
1454
December1st to 10thDay
70%8%10%9%3
1330
11th to 20thDay
70%10%11%8%1
1671
21st to endDay
77%7%6%6%4
2431
January1st to 10thNight
69%7%12%8%3
2648
11th to 20thNight
70%8%10%9%3
2547
21st to endNight
67%7%10%11%4
2772
February1st to 10thNight
62%6%11%15%6%1
2424
11th to 20thNight
60%6%13%17%5%
2156
21st to endNight
61%6%12%14%7%
1776
March1st to 10thNight
46%6%15%22%11%1
2160
11th to 20thNight
48%6%11%23%10%2
2016
21st to endNight
47%5%12%21%12%2
2142
April1st to 10thNight
55%5%11%18%11%1
1800
11th to 20thNight
49%5%9%23%12%2
1643
21st to endNight
49%5%10%20%14%3
1620
May1st to 10thNight
47%6%10%20%13%4
1620
11th to 20thNight
47%7%8%22%13%2
1499
21st to endNight
37%9%12%25%14%4
1454
June1st to 10thNight
38%7%14%23%17%2
1260
11th to 20thNight
38%8%13%24%14%3
1260
21st to endNight
39%6%14%26%12%3
1260
July1st to 10thNight
29%7%15%28%18%2
1295
11th to 20thNight
35%8%11%28%17%2
1392
21st to endNight
34%8%16%24%17%1
1487
August1st to 10thNight
31%8%18%29%12%2
1511
11th to 20thNight
30%7%18%31%13%1
1598
21st to endNight
36%7%16%26%14%1
1822
September1st to 10thNight
37%7%12%28%14%1
1820
11th to 20thNight
38%8%19%28%8%1
1980
21st to endNight
45%8%16%24%6%
1980
October1st to 10thNight
46%7%15%22%9%1
2001
11th to 20thNight
57%8%16%16%4
2253
21st to endNight
61%7%14%13%4
2574
November1st to 10thNight
53%7%15%18%7%
2406
11th to 20thNight
61%10%15%10%5%
2503
21st to endNight
66%9%15%8%2
2721
December1st to 10thNight
66%8%15%10%1
2850
11th to 20thNight
65%10%14%9%2
3525
21st to endNight
77%8%8%6%2
5232

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 10thDay
23%16%34%21%41
270
11th to 20thDay
23%14%41%17%41
245
21st to endDay
26%12%33%23%5%
264
February1st to 10thDay
16%27%40%13%31
240
11th to 20thDay
18%29%35%14%41
240
21st to endDay
22%30%36%11%1
198
March1st to 10thDay
19%20%40%17%5%
240
11th to 20thDay
18%16%39%17%8%1
384
21st to endDay
27%16%26%21%8%1
462
April1st to 10thDay
25%14%36%18%5%1
420
11th to 20thDay
26%21%25%18%8%2
412
21st to endDay
21%17%34%19%8%2
420
May1st to 10thDay
26%14%30%18%9%2
423
11th to 20thDay
19%13%37%21%7%3
539
21st to endDay
14%12%33%28%10%3
679
June1st to 10thDay
15%12%36%27%8%2
630
11th to 20thDay
16%11%37%26%8%2
630
21st to endDay
19%8%33%30%9%1
630
July1st to 10thDay
8%6%38%32%13%3
621
11th to 20thDay
12%9%30%32%11%5%
618
21st to endDay
12%6%32%32%13%5%
684
August1st to 10thDay
13%6%27%35%14%5%
536
11th to 20thDay
12%7%23%32%19%8%
439
21st to endDay
16%10%26%28%16%3
495
September1st to 10thDay
20%9%26%23%16%6%
450
11th to 20thDay
14%9%29%31%13%4
450
21st to endDay
18%11%28%29%11%3
450
October1st to 10thDay
22%15%31%19%12%2
450
11th to 20thDay
28%18%33%17%41
356
21st to endDay
31%16%36%13%41
297
November1st to 10thDay
22%23%31%19%5%
270
11th to 20thDay
21%26%35%12%5%
253
21st to endDay
22%26%38%12%2
180
December1st to 10thDay
23%19%33%18%6%1
180
11th to 20thDay
28%25%33%8%6%1
180
21st to endDay
32%26%28%10%32
198
January1st to 10thNight
22%19%33%22%4
950
11th to 20thNight
23%15%34%21%6%
910
21st to endNight
21%13%35%24%6%1
990
February1st to 10thNight
18%17%36%25%4
804
11th to 20thNight
19%17%32%24%8%
703
21st to endNight
18%17%36%23%5%
592
March1st to 10thNight
17%11%38%25%9%
720
11th to 20thNight
18%14%34%25%7%1
720
21st to endNight
18%12%31%30%8%
756
April1st to 10thNight
22%11%32%28%5%1
540
11th to 20thNight
25%9%29%26%11%1
533
21st to endNight
20%10%31%29%9%1
540
May1st to 10thNight
17%9%31%31%12%
540
11th to 20thNight
18%6%33%30%13%1
531
21st to endNight
13%6%30%34%17%
486
June1st to 10thNight
13%7%30%39%11%
360
11th to 20thNight
13%6%29%33%18%1
360
21st to endNight
14%8%23%39%15%1
360
July1st to 10thNight
12%423%43%17%2
420
11th to 20thNight
12%425%31%25%4
522
21st to endNight
12%421%40%21%2
591
August1st to 10thNight
9%424%40%22%1
537
11th to 20thNight
10%420%33%29%4
534
21st to endNight
12%7%23%40%17%1
594
September1st to 10thNight
17%324%31%21%4
560
11th to 20thNight
17%8%27%28%18%3
720
21st to endNight
19%9%24%28%17%3
720
October1st to 10thNight
20%11%28%27%13%1
720
11th to 20thNight
25%15%30%23%7%
720
21st to endNight
29%14%29%23%4
792
November1st to 10thNight
23%16%33%21%6%1
740
11th to 20thNight
23%19%33%19%5%
760
21st to endNight
27%20%33%17%3
821
December1st to 10thNight
23%19%35%17%5%
950
11th to 20thNight
27%18%35%15%41
950
21st to endNight
32%14%33%18%4
1045
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