Morrison Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Morrison Observatory clear sky chart from 2005-11-06 to 2024-03-06.

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
41%
24696
21%
80387
14%
24588
49%
24588
26%
50917

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
26%
943
15%
4243
8%
926
36%
926
14%
2914
January11th to 20thNight
24%
950
17%
4035
8%
930
32%
930
14%
2825
January21st to endNight
24%
1036
12%
4487
6%
1023
33%
1023
13%
3303
February1st to 10thNight
24%
950
15%
2470
5%
950
30%
950
21%
1783
February11th to 20thNight
25%
906
19%
2381
6%
902
33%
902
25%
1589
February21st to endNight
21%
628
21%
1884
6%
628
34%
628
23%
1217
March1st to 10thNight
26%
576
23%
2060
10%
576
41%
576
24%
1219
March11th to 20thNight
30%
540
19%
1980
12%
540
39%
540
17%
1302
March21st to endNight
22%
594
11%
2165
6%
594
29%
594
12%
1567
April1st to 10thNight
32%
540
22%
1800
13%
540
45%
540
26%
1079
April11th to 20thNight
34%
533
22%
1775
17%
533
46%
533
25%
1073
April21st to endNight
34%
540
19%
1800
13%
540
46%
540
23%
1145
May1st to 10thNight
41%
540
17%
1634
13%
540
48%
540
26%
1056
May11th to 20thNight
48%
531
19%
1514
17%
531
51%
531
27%
987
May21st to endNight
52%
584
20%
1552
13%
582
58%
582
30%
1014
June1st to 10thNight
69%
540
22%
1440
15%
540
71%
540
44%
829
June11th to 20thNight
62%
540
23%
1440
15%
540
66%
540
38%
877
June21st to endNight
68%
540
25%
1440
16%
540
72%
540
48%
797
July1st to 10thNight
69%
525
18%
1400
14%
525
70%
525
40%
832
July11th to 20thNight
75%
522
24%
1498
20%
522
77%
522
47%
804
July21st to endNight
69%
591
24%
1673
22%
558
73%
558
40%
917
August1st to 10thNight
74%
537
23%
1601
26%
534
76%
534
41%
873
August11th to 20thNight
73%
534
28%
1644
33%
534
75%
534
42%
885
August21st to endNight
75%
594
27%
1980
33%
594
76%
594
44%
991
September1st to 10thNight
67%
540
27%
1800
29%
540
71%
540
39%
945
September11th to 20thNight
65%
540
32%
1800
30%
540
71%
540
36%
990
September21st to endNight
59%
623
29%
2063
23%
623
65%
623
37%
1094
October1st to 10thNight
53%
720
27%
2160
19%
720
59%
720
40%
1181
October11th to 20thNight
38%
720
29%
2160
17%
720
48%
720
31%
1277
October21st to endNight
35%
792
24%
2376
13%
792
44%
792
26%
1476
November1st to 10thNight
43%
740
29%
2286
18%
740
55%
740
36%
1253
November11th to 20thNight
33%
817
26%
2527
14%
817
46%
817
30%
1488
November21st to endNight
32%
950
21%
2660
9%
950
42%
950
27%
1745
December1st to 10thNight
28%
950
19%
2660
7%
950
39%
950
25%
1765
December11th to 20thNight
31%
949
19%
3154
9%
948
38%
948
21%
2067
December21st to endNight
24%
1041
11%
4845
7%
1026
34%
1026
10%
3758

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%7%36%5%3445%7%42%
78636
Night
13%8%36%5%3445%6%44%
80930
TransparencyDay
42%5%12%25%15%2
78350
Night
42%411%24%16%3
80736
SeeingDay
15%8%25%28%18%5%
14668
Night
16%8%29%33%14%1
24717

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 10thDay
14%12%49%4345%5%7%33%
2655
11th to 20thDay
12%11%49%6%48%33436%
2850
21st to endDay
17%16%6%8%5%2344430%
3135
February1st to 10thDay
17%8%5%7%6%44446%34%
1710
11th to 20thDay
14%9%46%5%35%345%42%
1685
21st to endDay
14%12%46%5%34446%40%
1570
March1st to 10thDay
14%9%5%6%5%33447%40%
2030
11th to 20thDay
20%9%46%5%3435%6%34%
1980
21st to endDay
22%12%47%6%33346%29%
2190
April1st to 10thDay
15%7%36%5%34347%43%
2160
11th to 20thDay
18%8%36%42435%6%40%
2134
21st to endDay
22%6%36%5%35%5%5%6%35%
2160
May1st to 10thDay
17%8%36%6%35%5%5%7%35%
2323
11th to 20thDay
18%6%36%5%3445%7%39%
2380
21st to endDay
14%7%37%7%35%6%6%8%36%
2725
June1st to 10thDay
7%425%5%35%6%6%10%47%
2520
11th to 20thDay
9%5%35%5%35%5%6%8%48%
2520
21st to endDay
7%425%5%45%5%7%9%48%
2520
July1st to 10thDay
8%4245%35%5%7%11%44%
2520
11th to 20thDay
5%3245%35%5%7%9%51%
2408
21st to endDay
8%5%35%5%35%6%6%9%45%
2546
August1st to 10thDay
8%5%35%5%36%6%8%10%43%
2328
11th to 20thDay
8%435%5%345%7%9%45%
2255
21st to endDay
8%5%233345%6%9%52%
2376
September1st to 10thDay
11%5%33425%447%51%
2160
11th to 20thDay
10%424424349%53%
2156
21st to endDay
7%415%6%345%5%6%54%
1878
October1st to 10thDay
12%5%26%42335%5%53%
1800
11th to 20thDay
15%7%24323345%52%
1800
21st to endDay
18%7%35%323345%46%
1980
November1st to 10thDay
11%7%2433335%7%52%
1792
11th to 20thDay
15%6%25%413338%49%
1649
21st to endDay
18%9%35%423346%43%
1520
December1st to 10thDay
10%11%47%433446%43%
1520
11th to 20thDay
13%10%5%6%424436%42%
1918
21st to endDay
20%15%7%8%5%35%445%24%
2783
January1st to 10thNight
10%11%7%11%7%3444435%
4296
11th to 20thNight
13%10%5%9%5%47%6%5%5%31%
4120
21st to endNight
19%15%6%7%5%33435%30%
4532
February1st to 10thNight
15%10%5%7%6%35%445%36%
2470
11th to 20thNight
15%8%46%42445%6%42%
2380
21st to endNight
15%9%46%423445%44%
1884
March1st to 10thNight
14%8%36%424345%48%
2060
11th to 20thNight
19%6%46%5%345%5%6%37%
1980
21st to endNight
22%10%47%6%45%45%7%27%
2165
April1st to 10thNight
12%7%35%43445%5%48%
1800
11th to 20thNight
16%5%35%5%2345%6%46%
1775
21st to endNight
18%6%36%43445%6%41%
1800
May1st to 10thNight
15%5%35%5%445%6%8%41%
1634
11th to 20thNight
16%5%25%6%25%5%47%44%
1513
21st to endNight
13%5%245%35%5%6%9%42%
1551
June1st to 10thNight
6%323345%46%8%55%
1440
11th to 20thNight
5%4345%45%5%7%9%50%
1440
21st to endNight
42135%345%5%10%58%
1440
July1st to 10thNight
9%5%144235%6%10%51%
1440
11th to 20thNight
4214435%45%8%58%
1548
21st to endNight
7%3245%25%5%6%9%52%
1772
August1st to 10thNight
6%324425%5%7%10%52%
1611
11th to 20thNight
7%32343445%8%56%
1644
21st to endNight
6%32332446%8%59%
1980
September1st to 10thNight
11%323424445%58%
1800
11th to 20thNight
9%4144345%6%7%52%
1800
21st to endNight
8%414433446%58%
2063
October1st to 10thNight
10%4243245%5%7%56%
2160
11th to 20thNight
15%6%25%423345%52%
2160
21st to endNight
18%7%24323445%48%
2376
November1st to 10thNight
10%424423446%57%
2286
11th to 20thNight
12%6%26%423346%50%
2527
21st to endNight
18%7%35%42433446%
2660
December1st to 10thNight
14%9%36%5%34347%41%
2660
11th to 20thNight
15%9%36%5%34446%42%
3279
21st to endNight
21%18%6%8%5%3433426%
4884

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
51%410%24%9%1
2656
11th to 20thDay
55%212%21%10%
2850
21st to endDay
58%410%16%11%2
3135
February1st to 10thDay
52%312%21%12%1
1710
11th to 20thDay
46%412%20%16%3
1694
21st to endDay
48%29%23%15%3
1570
March1st to 10thDay
46%311%26%13%2
2030
11th to 20thDay
51%410%22%11%2
1980
21st to endDay
58%412%18%8%1
2190
April1st to 10thDay
43%311%27%15%1
2160
11th to 20thDay
46%311%25%13%2
2134
21st to endDay
50%411%22%12%1
2160
May1st to 10thDay
48%6%13%21%11%1
2323
11th to 20thDay
45%5%12%25%12%1
2384
21st to endDay
45%7%13%21%12%2
2725
June1st to 10thDay
31%7%15%31%15%1
2520
11th to 20thDay
33%6%13%28%17%3
2520
21st to endDay
31%6%16%28%15%4
2520
July1st to 10thDay
33%7%15%27%15%3
2451
11th to 20thDay
29%6%17%28%18%3
2335
21st to endDay
34%6%12%33%14%1
2405
August1st to 10thDay
34%6%19%26%13%1
2314
11th to 20thDay
33%6%13%32%16%1
2255
21st to endDay
28%6%15%26%20%6%
2376
September1st to 10thDay
33%5%11%26%19%6%
2160
11th to 20thDay
30%410%28%24%5%
2156
21st to endDay
30%5%10%28%23%4
1878
October1st to 10thDay
34%310%26%23%3
1800
11th to 20thDay
37%38%27%21%4
1800
21st to endDay
42%310%24%18%4
1980
November1st to 10thDay
33%313%24%21%5%
1792
11th to 20thDay
37%210%27%21%3
1649
21st to endDay
45%38%28%15%1
1520
December1st to 10thDay
43%412%28%12%1
1520
11th to 20thDay
45%314%27%9%2
1915
21st to endDay
63%410%15%8%1
2783
January1st to 10thNight
53%310%23%10%1
4296
11th to 20thNight
55%312%19%10%1
4120
21st to endNight
58%410%19%8%1
4532
February1st to 10thNight
51%411%20%11%3
2470
11th to 20thNight
43%411%22%17%2
2381
21st to endNight
44%310%22%17%4
1884
March1st to 10thNight
40%310%26%17%3
2060
11th to 20thNight
49%49%21%14%3
1980
21st to endNight
58%411%18%8%1
2165
April1st to 10thNight
38%5%10%26%18%3
1800
11th to 20thNight
41%39%28%15%5%
1775
21st to endNight
44%410%23%18%2
1800
May1st to 10thNight
41%6%14%22%15%2
1634
11th to 20thNight
41%5%12%23%17%1
1514
21st to endNight
39%6%14%24%15%3
1552
June1st to 10thNight
26%5%16%32%17%3
1440
11th to 20thNight
30%7%11%27%21%5%
1440
21st to endNight
24%416%31%20%5%
1440
July1st to 10thNight
30%5%14%30%17%4
1400
11th to 20thNight
24%5%14%33%23%2
1498
21st to endNight
27%6%14%35%17%2
1673
August1st to 10thNight
27%5%17%33%16%2
1601
11th to 20thNight
27%413%34%21%2
1644
21st to endNight
23%5%13%28%24%7%
1980
September1st to 10thNight
28%412%25%25%6%
1800
11th to 20thNight
29%6%10%26%23%6%
1800
21st to endNight
29%48%30%26%4
2063
October1st to 10thNight
28%410%26%26%6%
2160
11th to 20thNight
36%36%28%20%6%
2160
21st to endNight
40%39%22%22%3
2376
November1st to 10thNight
30%312%27%21%6%
2286
11th to 20thNight
36%38%27%22%4
2527
21st to endNight
44%39%25%17%2
2660
December1st to 10thNight
45%313%26%13%1
2660
11th to 20thNight
44%410%27%13%1
3281
21st to endNight
65%38%15%8%1
4884

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
21%14%34%26%6%
270
11th to 20thDay
32%13%37%15%2
270
21st to endDay
19%11%45%20%5%
297
February1st to 10thDay
23%14%42%17%4
270
11th to 20thDay
21%19%36%18%6%
270
21st to endDay
23%17%40%14%4
225
March1st to 10thDay
18%16%44%20%2
255
11th to 20thDay
30%9%32%24%5%
240
21st to endDay
37%16%28%15%4
276
April1st to 10thDay
21%12%33%25%7%1
420
11th to 20thDay
22%12%31%25%9%2
412
21st to endDay
24%10%30%27%9%1
420
May1st to 10thDay
19%8%32%29%10%1
586
11th to 20thDay
20%8%25%29%13%4
625
21st to endDay
16%5%28%25%20%7%
679
June1st to 10thDay
7%316%35%28%10%
630
11th to 20thDay
10%222%34%24%7%
630
21st to endDay
7%5%25%37%20%5%
630
July1st to 10thDay
9%212%27%35%15%
621
11th to 20thDay
7%117%35%30%10%
618
21st to endDay
8%214%35%33%8%
684
August1st to 10thDay
7%214%38%32%8%
626
11th to 20thDay
9%213%37%31%9%
569
21st to endDay
10%211%31%35%12%
495
September1st to 10thDay
11%214%33%28%11%
450
11th to 20thDay
8%214%36%29%11%
446
21st to endDay
7%6%25%29%27%7%
270
October1st to 10thDay
17%7%28%24%17%6%
270
11th to 20thDay
14%17%36%24%8%1
270
21st to endDay
28%14%31%21%6%
297
November1st to 10thDay
16%9%36%23%11%4
270
11th to 20thDay
17%15%30%27%9%2
270
21st to endDay
27%10%30%27%7%
270
December1st to 10thDay
13%16%36%25%8%3
270
11th to 20thDay
20%14%35%24%41
270
21st to endDay
25%20%36%19%1
297
January1st to 10thNight
16%14%37%26%7%
950
11th to 20thNight
18%15%37%24%5%1
950
21st to endNight
18%12%38%28%4
1045
February1st to 10thNight
20%12%38%27%4
950
11th to 20thNight
20%13%36%27%4
906
21st to endNight
21%13%40%21%4
628
March1st to 10thNight
18%13%39%26%5%
576
11th to 20thNight
23%10%31%29%6%1
540
21st to endNight
27%11%33%24%5%
594
April1st to 10thNight
16%10%39%30%6%
540
11th to 20thNight
18%11%31%31%9%
533
21st to endNight
19%6%36%33%6%
540
May1st to 10thNight
15%6%29%38%10%
540
11th to 20thNight
18%423%38%16%1
531
21st to endNight
14%5%23%34%23%2
584
June1st to 10thNight
8%313%46%27%3
540
11th to 20thNight
6%321%42%26%2
540
21st to endNight
4220%53%20%1
540
July1st to 10thNight
11%28%37%37%5%
525
11th to 20thNight
6%111%43%36%2
522
21st to endNight
8%212%44%33%2
591
August1st to 10thNight
7%110%47%32%3
537
11th to 20thNight
7%110%44%35%3
534
21st to endNight
6%110%39%40%4
594
September1st to 10thNight
13%113%40%29%4
540
11th to 20thNight
11%214%41%27%5%
540
21st to endNight
8%5%22%37%23%4
623
October1st to 10thNight
12%327%33%22%3
720
11th to 20thNight
18%9%32%32%9%
720
21st to endNight
22%10%29%29%9%1
792
November1st to 10thNight
13%8%32%36%12%
740
11th to 20thNight
15%10%38%29%8%
817
21st to endNight
21%10%33%29%7%
950
December1st to 10thNight
19%11%37%27%6%1
950
11th to 20thNight
22%9%32%32%6%
950
21st to endNight
24%13%33%27%3
1045
Page generated at 2024-03-03 05:28:55. Version ac07

Copyright © 2024 Attilla Danko.


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