Morrow Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Morrow Observatory clear sky chart from 2005-11-06 to 2024-01-27.

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
38%
24322
19%
74791
12%
24264
45%
24264
23%
49473

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
19%
950
14%
2648
4%
946
28%
946
15%
1953
January11th to 20thNight
15%
950
13%
2660
5%
950
22%
950
14%
2030
January21st to endNight
18%
927
14%
2721
5%
927
27%
927
15%
1995
February1st to 10thNight
17%
720
12%
2160
5%
720
24%
720
14%
1626
February11th to 20thNight
17%
703
16%
2099
6%
700
26%
700
16%
1477
February21st to endNight
15%
592
16%
1776
4%
592
25%
592
14%
1309
March1st to 10thNight
23%
720
19%
2160
10%
720
31%
720
20%
1450
March11th to 20thNight
23%
720
15%
2061
6%
720
31%
720
21%
1421
March21st to endNight
25%
698
15%
2084
7%
698
33%
698
16%
1503
April1st to 10thNight
31%
540
21%
1800
12%
540
44%
540
23%
1122
April11th to 20thNight
34%
533
21%
1775
14%
533
44%
533
24%
1117
April21st to endNight
30%
540
19%
1680
8%
540
41%
540
22%
1111
May1st to 10thNight
31%
540
15%
1620
7%
540
38%
540
21%
1120
May11th to 20thNight
41%
531
16%
1593
11%
531
46%
531
23%
1077
May21st to endNight
53%
582
18%
1724
12%
582
58%
582
28%
1114
June1st to 10thNight
58%
540
21%
1440
15%
540
62%
540
37%
884
June11th to 20thNight
61%
540
24%
1440
18%
540
65%
540
38%
871
June21st to endNight
63%
540
23%
1440
16%
540
68%
540
43%
837
July1st to 10thNight
65%
525
17%
1400
12%
525
69%
525
34%
893
July11th to 20thNight
70%
522
22%
1392
17%
522
71%
522
41%
824
July21st to endNight
67%
591
24%
1580
20%
558
70%
558
38%
931
August1st to 10thNight
69%
537
22%
1600
21%
534
70%
534
36%
935
August11th to 20thNight
70%
534
22%
1746
22%
534
74%
534
33%
1002
August21st to endNight
71%
594
26%
1980
27%
594
75%
594
41%
1017
September1st to 10thNight
63%
544
24%
1804
23%
544
68%
544
31%
1043
September11th to 20thNight
64%
720
31%
1980
24%
720
68%
720
41%
1144
September21st to endNight
53%
720
28%
1980
19%
720
59%
720
37%
1174
October1st to 10thNight
54%
720
30%
1980
22%
720
61%
720
41%
1125
October11th to 20thNight
37%
720
26%
2092
16%
720
49%
720
29%
1315
October21st to endNight
30%
792
22%
2574
14%
792
40%
792
22%
1659
November1st to 10thNight
38%
740
26%
2406
19%
740
49%
740
29%
1376
November11th to 20thNight
30%
760
25%
2470
14%
760
45%
760
23%
1522
November21st to endNight
30%
760
20%
2470
13%
760
39%
760
19%
1649
December1st to 10thNight
22%
760
15%
2470
8%
760
31%
760
16%
1715
December11th to 20thNight
25%
877
16%
3135
9%
876
32%
876
14%
2230
December21st to endNight
15%
1040
8%
4851
4%
1026
25%
1026
8%
3902

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%8%36%5%3445%7%39%
74975
Night
15%8%36%5%3445%7%40%
75085
TransparencyDay
44%5%11%23%15%2
74683
Night
44%5%11%22%15%3
74898
SeeingDay
18%13%27%23%14%5%
14381
Night
19%11%28%27%14%2
24330

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
17%13%48%433447%33%
1517
11th to 20thDay
20%12%5%8%6%2334431%
1520
21st to endDay
14%15%47%5%35%45%5%33%
1776
February1st to 10thDay
18%12%6%7%5%3435%6%31%
1800
11th to 20thDay
16%10%5%7%6%3445%6%33%
1748
21st to endDay
17%14%5%8%5%3435%6%31%
1480
March1st to 10thDay
18%9%35%5%245%45%39%
1800
11th to 20thDay
20%10%47%5%2435%6%35%
1898
21st to endDay
19%11%47%7%3445%6%31%
2286
April1st to 10thDay
14%8%35%5%3446%8%39%
2160
11th to 20thDay
17%9%35%5%3445%6%38%
2134
21st to endDay
21%7%35%435%447%37%
2278
May1st to 10thDay
19%8%26%6%3445%7%35%
2340
11th to 20thDay
20%7%36%435%35%7%36%
2301
21st to endDay
10%5%46%7%46%6%7%9%35%
2548
June1st to 10thDay
12%5%26%5%35%5%5%8%44%
2520
11th to 20thDay
8%5%25%6%35%5%7%9%46%
2520
21st to endDay
10%5%246%36%6%7%9%42%
2520
July1st to 10thDay
11%5%26%6%45%5%7%11%38%
2520
11th to 20thDay
8%4246%35%6%8%11%43%
2520
21st to endDay
9%425%6%46%6%7%10%42%
2642
August1st to 10thDay
9%5%245%45%6%7%11%43%
2327
11th to 20thDay
10%5%35%5%5%5%5%7%9%42%
2151
21st to endDay
6%5%245%35%46%10%49%
2376
September1st to 10thDay
13%5%26%5%35%447%46%
2138
11th to 20thDay
11%5%25%4345%6%8%48%
1980
21st to endDay
12%435%42345%7%52%
1980
October1st to 10thDay
11%425%5%33447%51%
1980
11th to 20thDay
13%7%345%335%5%8%45%
1863
21st to endDay
20%8%345%35%445%38%
1782
November1st to 10thDay
10%434424447%54%
1672
11th to 20thDay
16%8%46%424447%40%
1710
21st to endDay
21%8%36%423435%41%
1710
December1st to 10thDay
21%13%5%6%43443434%
1710
11th to 20thDay
17%14%6%7%5%34346%31%
1985
21st to endDay
24%18%6%6%5%34445%20%
2783
January1st to 10thNight
17%11%49%7%35%6%45%31%
2648
11th to 20thNight
19%14%6%8%6%44345%28%
2660
21st to endNight
17%13%5%8%5%45%445%30%
2721
February1st to 10thNight
22%11%5%8%6%3445%5%27%
2160
11th to 20thNight
17%10%49%7%3435%7%32%
2098
21st to endNight
21%10%5%8%5%35%45%431%
1776
March1st to 10thNight
18%9%36%5%2445%6%39%
2160
11th to 20thNight
19%8%46%5%245%5%7%37%
2061
21st to endNight
20%8%47%5%35%45%7%32%
2084
April1st to 10thNight
13%7%36%5%345%6%6%42%
1800
11th to 20thNight
16%7%25%5%2445%7%42%
1775
21st to endNight
18%7%35%5%25%45%7%38%
1680
May1st to 10thNight
17%9%36%5%3445%7%35%
1620
11th to 20thNight
15%7%36%6%4445%7%40%
1592
21st to endNight
7%5%26%6%47%6%6%12%38%
1723
June1st to 10thNight
11%424425%46%10%48%
1440
11th to 20thNight
7%5%25%5%3446%9%50%
1440
21st to endNight
6%3134345%8%11%52%
1440
July1st to 10thNight
10%4245%35%5%6%9%46%
1440
11th to 20thNight
5%425%435%6%6%9%51%
1440
21st to endNight
8%425%5%35%5%49%51%
1673
August1st to 10thNight
7%4246%345%6%9%49%
1611
11th to 20thNight
6%3245%45%6%7%10%47%
1746
21st to endNight
6%32443446%9%55%
1980
September1st to 10thNight
12%5%25%4245%5%7%50%
1804
11th to 20thNight
7%5%244345%5%9%54%
1980
21st to endNight
12%5%2432445%7%53%
1980
October1st to 10thNight
9%42442335%7%58%
1980
11th to 20thNight
15%7%344245%46%46%
2092
21st to endNight
18%8%35%434346%42%
2574
November1st to 10thNight
13%6%2442435%6%50%
2406
11th to 20thNight
16%8%35%434347%43%
2470
21st to endNight
20%10%36%434346%37%
2470
December1st to 10thNight
18%11%5%7%5%3445%6%32%
2470
11th to 20thNight
19%12%48%5%3345%6%32%
3207
21st to endNight
23%18%5%8%7%3444420%
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
53%49%20%13%1
1518
11th to 20thDay
58%410%19%9%1
1520
21st to endDay
53%5%11%25%6%1
1776
February1st to 10thDay
56%39%22%10%2
1800
11th to 20thDay
52%410%22%11%2
1758
21st to endDay
55%49%19%10%3
1480
March1st to 10thDay
47%5%7%24%15%2
1800
11th to 20thDay
52%49%21%12%2
1898
21st to endDay
55%5%9%22%8%1
2286
April1st to 10thDay
44%5%12%23%16%1
2160
11th to 20thDay
46%410%23%14%3
2134
21st to endDay
48%49%23%13%3
2278
May1st to 10thDay
49%6%13%22%10%1
2340
11th to 20thDay
48%6%11%18%16%1
2305
21st to endDay
43%8%15%18%14%2
2548
June1st to 10thDay
38%6%10%26%17%3
2520
11th to 20thDay
33%7%14%24%19%3
2520
21st to endDay
37%6%15%22%16%4
2520
July1st to 10thDay
40%8%14%20%15%3
2451
11th to 20thDay
32%8%15%25%18%3
2445
21st to endDay
36%8%15%23%17%2
2495
August1st to 10thDay
33%9%14%27%16%2
2314
11th to 20thDay
37%7%12%26%16%1
2151
21st to endDay
30%6%14%26%18%6%
2376
September1st to 10thDay
39%5%11%24%17%5%
2138
11th to 20thDay
33%5%11%27%19%4
1980
21st to endDay
32%5%8%26%25%3
1980
October1st to 10thDay
33%5%8%26%25%2
1980
11th to 20thDay
38%5%8%25%22%3
1863
21st to endDay
48%48%23%16%2
1782
November1st to 10thDay
32%410%29%20%5%
1672
11th to 20thDay
45%49%22%17%3
1710
21st to endDay
47%39%23%16%1
1710
December1st to 10thDay
55%410%20%11%1
1710
11th to 20thDay
55%47%22%11%1
1982
21st to endDay
66%49%13%7%1
2783
January1st to 10thNight
54%5%9%20%11%1
2648
11th to 20thNight
61%311%18%8%
2660
21st to endNight
56%410%19%9%1
2721
February1st to 10thNight
60%312%19%5%1
2160
11th to 20thNight
53%310%20%12%1
2099
21st to endNight
56%410%17%10%2
1776
March1st to 10thNight
47%47%23%17%2
2160
11th to 20thNight
48%413%21%13%2
2061
21st to endNight
53%5%11%22%7%2
2084
April1st to 10thNight
41%411%26%14%3
1800
11th to 20thNight
42%5%10%18%20%5%
1775
21st to endNight
45%5%9%23%14%3
1680
May1st to 10thNight
47%6%11%23%10%2
1620
11th to 20thNight
44%7%12%20%16%1
1593
21st to endNight
37%9%15%20%14%5%
1724
June1st to 10thNight
32%6%10%26%21%4
1440
11th to 20thNight
31%6%12%24%21%6%
1440
21st to endNight
25%8%17%24%20%7%
1440
July1st to 10thNight
34%9%14%23%18%4
1400
11th to 20thNight
28%7%16%27%17%5%
1392
21st to endNight
30%6%13%30%18%3
1580
August1st to 10thNight
30%7%16%26%18%3
1600
11th to 20thNight
29%9%15%27%18%2
1746
21st to endNight
24%6%14%29%21%6%
1980
September1st to 10thNight
33%6%8%28%18%7%
1804
11th to 20thNight
28%6%9%26%26%5%
1980
21st to endNight
32%5%9%24%25%5%
1980
October1st to 10thNight
28%410%26%27%5%
1980
11th to 20thNight
39%47%25%21%4
2092
21st to endNight
45%37%22%18%4
2574
November1st to 10thNight
36%39%25%22%4
2406
11th to 20thNight
43%29%22%20%4
2470
21st to endNight
49%310%22%15%1
2470
December1st to 10thNight
53%411%20%11%1
2470
11th to 20thNight
54%48%20%12%1
3209
21st to endNight
68%48%12%7%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
28%21%30%17%31
270
11th to 20thDay
33%25%30%10%2
270
21st to endDay
26%28%33%10%2
282
February1st to 10thDay
30%29%30%8%3
240
11th to 20thDay
29%28%32%11%
240
21st to endDay
30%22%38%10%1
198
March1st to 10thDay
25%28%33%11%2
240
11th to 20thDay
29%21%32%13%41
338
21st to endDay
31%20%29%14%6%
462
April1st to 10thDay
20%20%31%21%6%1
420
11th to 20thDay
22%23%24%21%8%2
412
21st to endDay
25%19%33%14%7%1
420
May1st to 10thDay
24%16%32%19%7%2
423
11th to 20thDay
23%12%29%22%9%4
447
21st to endDay
13%7%29%25%17%9%
502
June1st to 10thDay
13%7%26%29%20%5%
630
11th to 20thDay
11%7%27%33%18%5%
630
21st to endDay
11%8%30%27%17%7%
630
July1st to 10thDay
12%421%24%24%15%
621
11th to 20thDay
8%5%23%32%22%10%
618
21st to endDay
9%421%34%23%8%
583
August1st to 10thDay
10%418%30%26%12%
446
11th to 20thDay
15%420%30%24%6%
439
21st to endDay
9%416%32%27%12%
495
September1st to 10thDay
12%419%30%28%8%
450
11th to 20thDay
10%317%30%28%11%
450
21st to endDay
14%7%23%26%23%7%
450
October1st to 10thDay
10%8%28%31%16%5%
450
11th to 20thDay
18%15%37%22%8%2
381
21st to endDay
31%14%36%18%1
297
November1st to 10thDay
13%19%33%24%8%3
270
11th to 20thDay
24%19%31%19%6%1
270
21st to endDay
29%12%34%21%5%
270
December1st to 10thDay
23%28%27%16%5%1
270
11th to 20thDay
28%18%36%13%41
270
21st to endDay
33%23%30%11%3
297
January1st to 10thNight
23%20%33%21%4
950
11th to 20thNight
27%20%34%17%2
950
21st to endNight
23%19%35%20%2
927
February1st to 10thNight
28%15%36%19%1
720
11th to 20thNight
25%19%35%19%1
703
21st to endNight
29%16%37%17%1
592
March1st to 10thNight
23%18%34%23%3
720
11th to 20thNight
25%14%34%20%7%
720
21st to endNight
25%13%33%24%5%
698
April1st to 10thNight
16%15%34%28%7%1
540
11th to 20thNight
21%12%29%26%11%
533
21st to endNight
23%9%34%27%6%1
540
May1st to 10thNight
21%8%34%26%10%1
540
11th to 20thNight
17%7%27%30%16%3
531
21st to endNight
10%325%33%24%5%
584
June1st to 10thNight
12%421%39%22%2
540
11th to 20thNight
9%321%43%22%1
540
21st to endNight
7%222%40%26%2
540
July1st to 10thNight
13%212%33%30%11%
525
11th to 20thNight
6%315%35%36%5%
522
21st to endNight
9%314%36%33%5%
591
August1st to 10thNight
9%113%36%36%5%
537
11th to 20thNight
6%213%39%36%4
534
21st to endNight
6%114%35%38%6%
594
September1st to 10thNight
13%413%32%35%4
544
11th to 20thNight
8%317%32%35%5%
720
21st to endNight
14%5%23%29%25%3
720
October1st to 10thNight
10%6%24%32%23%5%
720
11th to 20thNight
17%12%29%27%14%1
720
21st to endNight
22%13%32%23%9%
792
November1st to 10thNight
17%9%32%28%13%1
740
11th to 20thNight
21%15%30%26%8%1
760
21st to endNight
25%14%27%26%7%
760
December1st to 10thNight
25%15%33%22%5%
760
11th to 20thNight
28%12%31%24%5%1
878
21st to endNight
32%16%32%17%3
1045
Page generated at 2024-01-24 09:37:32. Version ac07

Copyright 2024 Attilla Danko


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