Burrell Memorial Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Burrell Memorial Observatory clear sky chart from 2005-11-06 to 2024-01-22.

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
33%
23462
14%
74699
10%
23411
38%
23411
17%
53891

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
11%
758
9%
2459
3%
757
18%
757
8%
2011
January11th to 20thNight
11%
760
5%
2470
3%
760
14%
760
6%
2108
January21st to endNight
15%
800
8%
2599
4%
800
21%
800
9%
2136
February1st to 10thNight
15%
720
7%
2340
3%
720
20%
720
8%
1910
February11th to 20thNight
17%
702
10%
2207
4%
700
23%
700
9%
1757
February21st to endNight
15%
592
11%
1776
2%
592
24%
592
11%
1404
March1st to 10thNight
22%
720
15%
2044
7%
720
29%
720
16%
1511
March11th to 20thNight
29%
720
17%
1980
10%
720
35%
720
20%
1417
March21st to endNight
30%
792
15%
2178
10%
792
34%
792
18%
1630
April1st to 10thNight
27%
720
12%
1958
5%
720
33%
720
19%
1436
April11th to 20thNight
29%
556
18%
1620
8%
556
37%
556
20%
1129
April21st to endNight
32%
540
18%
1620
7%
540
40%
540
23%
1102
May1st to 10thNight
36%
540
12%
1620
7%
540
39%
540
18%
1169
May11th to 20thNight
42%
531
16%
1592
11%
531
47%
531
22%
1080
May21st to endNight
56%
582
15%
1745
13%
582
59%
582
31%
1067
June1st to 10thNight
50%
360
16%
1440
17%
360
56%
360
22%
855
June11th to 20thNight
51%
360
17%
1417
17%
360
59%
360
23%
841
June21st to endNight
54%
401
20%
1301
18%
401
61%
401
29%
785
July1st to 10thNight
65%
525
15%
1468
15%
525
67%
525
35%
910
July11th to 20thNight
60%
522
18%
1566
16%
522
63%
522
33%
934
July21st to endNight
60%
591
18%
1672
15%
558
63%
558
30%
1057
August1st to 10thNight
64%
537
19%
1600
17%
534
66%
534
34%
947
August11th to 20thNight
61%
534
21%
1598
17%
534
63%
534
30%
989
August21st to endNight
59%
599
22%
1787
16%
599
63%
599
31%
1100
September1st to 10thNight
56%
720
20%
1912
13%
720
59%
720
31%
1250
September11th to 20thNight
60%
720
26%
1980
18%
720
64%
720
36%
1194
September21st to endNight
45%
720
21%
1980
15%
720
49%
720
26%
1321
October1st to 10thNight
47%
720
19%
2088
17%
720
50%
720
27%
1328
October11th to 20thNight
28%
720
15%
2160
10%
720
35%
720
18%
1522
October21st to endNight
22%
792
16%
2398
10%
792
30%
792
14%
1810
November1st to 10thNight
31%
740
17%
2406
14%
740
37%
740
20%
1618
November11th to 20thNight
20%
760
14%
2470
8%
760
29%
760
13%
1836
November21st to endNight
18%
760
10%
2656
7%
760
23%
760
10%
2061
December1st to 10thNight
14%
760
6%
2660
3%
760
18%
760
8%
2157
December11th to 20thNight
15%
759
7%
3261
2%
759
21%
759
7%
2529
December21st to endNight
13%
829
4%
4671
2%
817
18%
817
4%
3980

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
16%11%47%6%345%5%7%31%
74965
Night
17%12%47%6%3445%6%31%
74946
TransparencyDay
53%5%11%19%11%1
74686
Night
54%5%11%18%10%1
74745
SeeingDay
21%13%27%22%12%4
13780
Night
22%11%27%26%12%1
23475

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
18%18%9%12%7%45%44416%
1706
11th to 20thDay
20%20%9%12%8%4433412%
1710
21st to endDay
18%20%9%14%10%3334412%
1791
February1st to 10thDay
18%18%7%10%9%3343420%
1620
11th to 20thDay
15%15%8%13%10%45%445%18%
1639
21st to endDay
19%14%5%12%6%35%45%5%22%
1480
March1st to 10thDay
20%14%7%8%5%33447%27%
1916
11th to 20thDay
17%14%6%9%5%34346%29%
1980
21st to endDay
23%12%5%7%6%35%446%26%
2178
April1st to 10thDay
17%11%5%6%6%345%5%7%31%
2002
11th to 20thDay
19%11%45%5%35%446%34%
2304
21st to endDay
23%10%36%434446%33%
2340
May1st to 10thDay
18%9%36%6%46%5%5%6%32%
2340
11th to 20thDay
19%9%26%5%345%6%7%34%
2301
21st to endDay
10%6%35%6%45%6%7%9%39%
2531
June1st to 10thDay
15%6%35%5%36%5%6%9%37%
2512
11th to 20thDay
13%6%35%6%35%6%5%8%40%
2532
21st to endDay
11%5%35%5%35%6%7%10%40%
2653
July1st to 10thDay
11%5%27%5%3447%9%44%
2440
11th to 20thDay
12%5%25%5%35%5%7%10%41%
2340
21st to endDay
11%5%25%5%35%6%7%10%40%
2547
August1st to 10thDay
9%5%36%6%45%6%7%9%40%
2327
11th to 20thDay
11%6%27%6%45%6%7%10%36%
2303
21st to endDay
12%5%26%5%35%6%7%10%39%
2549
September1st to 10thDay
14%5%25%5%35%6%6%7%40%
2044
11th to 20thDay
12%6%35%6%245%6%8%42%
1980
21st to endDay
19%7%35%5%3345%8%39%
1980
October1st to 10thDay
15%7%36%5%35%46%7%38%
1872
11th to 20thDay
21%8%37%5%345%5%6%34%
1800
21st to endDay
25%11%36%6%3445%5%26%
1954
November1st to 10thDay
15%11%47%5%3445%6%36%
1672
11th to 20thDay
19%18%38%5%3345%6%28%
1710
21st to endDay
19%17%8%8%6%45%446%19%
1520
December1st to 10thDay
18%22%9%10%7%34345%16%
1520
11th to 20thDay
19%18%7%15%6%34446%15%
1910
21st to endDay
23%24%8%10%6%344449%
2962
January1st to 10thNight
20%18%8%11%6%3434419%
2459
11th to 20thNight
20%19%8%12%8%3434415%
2470
21st to endNight
18%18%7%12%7%4433418%
2599
February1st to 10thNight
21%15%7%11%8%3344420%
2340
11th to 20thNight
18%15%7%11%6%45%445%22%
2205
21st to endNight
21%13%6%11%7%3434423%
1776
March1st to 10thNight
18%12%6%7%6%34345%30%
2044
11th to 20thNight
17%11%46%435%6%5%6%34%
1980
21st to endNight
21%12%5%7%5%33446%31%
2178
April1st to 10thNight
17%12%46%7%245%5%7%31%
1958
11th to 20thNight
16%10%46%6%345%6%7%33%
1620
21st to endNight
16%9%35%5%35%46%7%36%
1620
May1st to 10thNight
19%10%47%5%346%6%6%30%
1620
11th to 20thNight
16%9%35%6%26%5%6%8%35%
1592
21st to endNight
10%5%235%45%7%6%10%42%
1744
June1st to 10thNight
10%5%36%5%37%5%5%6%44%
1440
11th to 20thNight
10%5%37%6%446%7%9%40%
1417
21st to endNight
11%425%6%35%6%7%10%43%
1301
July1st to 10thNight
9%5%245%35%5%5%8%49%
1512
11th to 20thNight
8%425%6%35%5%7%10%46%
1620
21st to endNight
9%5%35%6%46%5%6%8%44%
1771
August1st to 10thNight
7%426%445%5%6%9%48%
1611
11th to 20thNight
10%6%26%6%345%6%8%44%
1598
21st to endNight
10%6%36%5%35%5%5%8%45%
1787
September1st to 10thNight
12%6%35%6%445%6%8%43%
1912
11th to 20thNight
11%424435%45%8%50%
1980
21st to endNight
16%6%26%6%35%5%46%41%
1980
October1st to 10thNight
15%6%25%5%3445%7%43%
2088
11th to 20thNight
21%9%36%5%3445%6%34%
2160
21st to endNight
28%9%37%6%34446%27%
2398
November1st to 10thNight
17%10%36%5%3445%6%36%
2406
11th to 20thNight
19%16%48%6%34445%27%
2470
21st to endNight
23%17%47%5%3445%5%23%
2656
December1st to 10thNight
21%19%8%9%5%34345%18%
2660
11th to 20thNight
18%20%7%10%5%33445%21%
3285
21st to endNight
25%21%7%9%7%34445%11%
4689

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
73%410%10%3
1707
11th to 20thDay
77%39%8%2
1710
21st to endDay
77%47%9%3
1791
February1st to 10thDay
70%211%12%5%
1620
11th to 20thDay
69%5%8%12%5%1
1648
21st to endDay
64%412%13%6%1
1480
March1st to 10thDay
59%412%20%6%
1916
11th to 20thDay
59%310%17%10%1
1980
21st to endDay
60%48%19%8%1
2178
April1st to 10thDay
53%5%11%18%13%1
2002
11th to 20thDay
52%5%11%18%13%2
2304
21st to endDay
53%410%21%10%2
2340
May1st to 10thDay
53%6%9%20%10%2
2340
11th to 20thDay
48%7%10%18%14%3
2305
21st to endDay
40%6%15%24%13%2
2531
June1st to 10thDay
44%6%11%24%14%1
2512
11th to 20thDay
42%6%14%22%13%2
2532
21st to endDay
38%7%12%24%16%3
2653
July1st to 10thDay
39%6%10%25%18%2
2375
11th to 20thDay
38%5%13%27%16%2
2271
21st to endDay
37%7%13%25%15%2
2405
August1st to 10thDay
39%7%13%28%13%1
2314
11th to 20thDay
42%6%14%24%12%2
2303
21st to endDay
40%6%13%23%15%3
2549
September1st to 10thDay
40%7%14%21%15%3
2044
11th to 20thDay
39%6%14%24%15%2
1980
21st to endDay
45%410%23%17%1
1980
October1st to 10thDay
44%6%10%23%14%1
1872
11th to 20thDay
51%5%12%21%10%1
1800
21st to endDay
59%5%12%13%9%1
1954
November1st to 10thDay
49%5%11%21%13%1
1672
11th to 20thDay
59%310%17%8%2
1710
21st to endDay
68%49%13%6%
1520
December1st to 10thDay
73%311%10%3
1520
11th to 20thDay
72%310%12%3
1906
21st to endDay
80%39%6%1
2962
January1st to 10thNight
70%49%13%5%
2459
11th to 20thNight
75%49%10%2
2470
21st to endNight
71%310%12%41
2599
February1st to 10thNight
69%410%13%4
2340
11th to 20thNight
66%5%8%15%6%
2207
21st to endNight
65%39%14%7%1
1776
March1st to 10thNight
57%310%21%9%1
2044
11th to 20thNight
51%5%11%19%12%2
1980
21st to endNight
56%48%20%10%2
2178
April1st to 10thNight
53%5%11%17%13%1
1958
11th to 20thNight
50%5%11%17%15%3
1620
21st to endNight
46%5%11%20%14%3
1620
May1st to 10thNight
52%6%11%17%12%3
1620
11th to 20thNight
46%6%11%18%16%3
1593
21st to endNight
35%7%15%27%14%2
1745
June1st to 10thNight
40%6%10%27%14%3
1440
11th to 20thNight
39%6%15%20%18%2
1417
21st to endNight
35%7%13%27%16%2
1301
July1st to 10thNight
34%6%12%24%20%4
1468
11th to 20thNight
32%7%12%26%20%2
1566
21st to endNight
37%7%13%22%18%3
1672
August1st to 10thNight
32%6%15%29%18%1
1600
11th to 20thNight
37%6%15%27%13%2
1598
21st to endNight
36%6%12%25%18%4
1787
September1st to 10thNight
38%6%12%26%14%4
1912
11th to 20thNight
33%5%13%27%21%2
1980
21st to endNight
44%411%22%18%1
1980
October1st to 10thNight
40%5%13%22%19%1
2088
11th to 20thNight
51%411%21%12%1
2160
21st to endNight
59%49%18%9%1
2398
November1st to 10thNight
48%5%12%20%13%2
2406
11th to 20thNight
59%311%17%8%2
2470
21st to endNight
64%411%15%5%
2656
December1st to 10thNight
69%411%11%4
2660
11th to 20thNight
67%414%14%2
3288
21st to endNight
77%411%7%1
4689

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
27%22%33%11%6%1
270
11th to 20thDay
31%24%32%10%31
270
21st to endDay
28%25%31%14%2
267
February1st to 10thDay
33%20%35%11%
240
11th to 20thDay
30%26%32%12%
240
21st to endDay
30%30%31%9%1
198
March1st to 10thDay
28%19%30%17%5%1
356
11th to 20thDay
26%16%33%18%5%1
420
21st to endDay
34%15%26%18%6%
462
April1st to 10thDay
23%18%32%19%6%1
420
11th to 20thDay
27%17%23%20%9%4
412
21st to endDay
29%14%31%17%6%2
420
May1st to 10thDay
25%15%26%24%6%4
423
11th to 20thDay
22%12%29%23%11%4
447
21st to endDay
14%8%26%29%17%6%
485
June1st to 10thDay
15%7%30%32%12%3
450
11th to 20thDay
18%8%23%32%16%4
462
21st to endDay
14%7%32%30%14%3
630
July1st to 10thDay
12%423%29%23%10%
545
11th to 20thDay
16%421%31%21%7%
444
21st to endDay
11%6%26%30%21%6%
488
August1st to 10thDay
11%5%20%30%24%10%
446
11th to 20thDay
15%5%22%29%21%9%
439
21st to endDay
12%6%22%28%23%9%
495
September1st to 10thDay
16%5%23%26%20%10%
450
11th to 20thDay
14%419%26%25%12%
450
21st to endDay
20%12%25%21%13%8%
450
October1st to 10thDay
14%9%26%25%19%6%
450
11th to 20thDay
22%16%33%20%8%1
450
21st to endDay
32%18%28%17%5%
469
November1st to 10thDay
20%23%30%16%10%1
270
11th to 20thDay
31%21%31%11%5%1
270
21st to endDay
29%21%34%16%1
180
December1st to 10thDay
23%27%30%13%5%2
180
11th to 20thDay
23%29%34%12%2
180
21st to endDay
29%23%33%14%1
252
January1st to 10thNight
30%21%31%14%4
760
11th to 20thNight
33%18%30%15%4
760
21st to endNight
27%17%32%21%3
800
February1st to 10thNight
31%16%30%21%2
720
11th to 20thNight
27%16%33%20%4
703
21st to endNight
28%17%34%18%2
592
March1st to 10thNight
23%15%34%22%6%
720
11th to 20thNight
23%14%31%24%8%1
720
21st to endNight
26%11%26%27%9%1
792
April1st to 10thNight
21%16%30%28%5%1
720
11th to 20thNight
21%12%33%23%10%1
556
21st to endNight
19%10%34%28%8%1
540
May1st to 10thNight
22%9%26%33%9%1
540
11th to 20thNight
20%6%24%35%12%2
531
21st to endNight
13%322%37%23%3
584
June1st to 10thNight
10%427%41%17%1
360
11th to 20thNight
12%424%41%18%1
360
21st to endNight
9%426%39%22%
401
July1st to 10thNight
11%114%39%31%3
525
11th to 20thNight
11%220%36%26%4
522
21st to endNight
11%416%40%28%2
591
August1st to 10thNight
10%213%43%27%4
537
11th to 20thNight
12%412%39%29%4
534
21st to endNight
12%318%32%30%5%
599
September1st to 10thNight
15%6%15%34%25%5%
720
11th to 20thNight
13%417%31%29%5%
720
21st to endNight
18%7%24%28%18%5%
720
October1st to 10thNight
18%8%22%29%20%3
720
11th to 20thNight
25%14%28%23%8%1
720
21st to endNight
34%13%27%22%5%
792
November1st to 10thNight
23%14%29%24%10%1
740
11th to 20thNight
30%16%30%17%6%1
760
21st to endNight
33%16%29%17%5%
760
December1st to 10thNight
32%16%32%15%5%
760
11th to 20thNight
29%19%31%18%3
760
21st to endNight
30%16%33%18%2
836
Page generated at 2024-01-19 09:28:34. Version ac07

Copyright 2024 Attilla Danko


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