Burke Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Burke Observatory clear sky chart from 2005-11-05 to 2018-08-29.

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
45%
16869
18%
50644
14%
16826
51%
16826
22%
34348

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
26%
780
16%
2522
9%
776
35%
776
14%
1846
January16th to endNight
24%
832
18%
2704
9%
832
35%
832
15%
1933
February1st to 15thNight
25%
764
15%
2404
8%
761
33%
761
17%
1702
February16th to endNight
20%
683
16%
2049
8%
683
29%
683
14%
1533
March1st to 15thNight
29%
780
18%
2171
11%
780
34%
780
19%
1567
March16th to endNight
34%
832
14%
2288
9%
832
38%
832
20%
1664
April1st to 15thNight
37%
778
18%
2112
10%
778
43%
778
24%
1411
April16th to endNight
44%
585
19%
1741
11%
585
50%
585
24%
1173
May1st to 15thNight
47%
585
14%
1755
9%
585
51%
585
20%
1218
May16th to endNight
59%
609
13%
1828
10%
609
60%
609
22%
1270
June1st to 15thNight
67%
585
14%
1755
12%
585
68%
585
28%
1128
June16th to endNight
67%
585
16%
1755
14%
585
68%
585
26%
1138
July1st to 15thNight
63%
555
12%
1665
11%
555
63%
555
26%
1115
July16th to endNight
72%
612
13%
1739
11%
579
73%
579
27%
1131
August1st to 15thNight
69%
575
16%
1715
15%
572
70%
572
26%
1141
August16th to endNight
71%
652
19%
1918
18%
652
71%
652
29%
1237
September1st to 15thNight
59%
720
20%
1980
18%
720
59%
720
26%
1330
September16th to endNight
60%
717
25%
1980
22%
717
63%
717
32%
1248
October1st to 15thNight
56%
720
27%
2079
25%
720
60%
720
33%
1272
October16th to endNight
44%
768
27%
2304
23%
768
53%
768
27%
1452
November1st to 15thNight
53%
760
26%
2406
24%
760
59%
760
29%
1444
November16th to endNight
45%
780
26%
2535
21%
780
53%
780
26%
1558
December1st to 15thNight
32%
780
16%
2535
11%
780
39%
780
16%
1809
December16th to endNight
26%
832
16%
2704
10%
832
35%
832
13%
2028

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%7%36%5%35%5%5%7%34%
51608
Night
14%7%36%5%3445%7%38%
50841
TransparencyDay
47%7%10%18%12%2
51309
Night
45%6%11%19%14%2
50644
SeeingDay
21%9%18%22%18%10%
6721
Night
18%8%19%30%19%2
16871

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 15thDay
19%9%411%5%24345%29%
1746
16th to endDay
17%10%46%5%25%345%33%
1872
February1st to 15thDay
21%10%48%423345%30%
1786
16th to endDay
21%11%48%323346%29%
1710
March1st to 15thDay
18%10%35%423445%36%
2119
16th to endDay
19%10%35%5%3435%5%32%
2287
April1st to 15thDay
15%7%2442346%7%40%
2171
16th to endDay
17%7%25%5%35%446%38%
2500
May1st to 15thDay
17%6%36%5%46%5%5%7%31%
2526
16th to endDay
14%7%36%7%46%5%6%7%32%
2639
June1st to 15thDay
9%5%36%6%47%6%8%9%32%
2535
16th to endDay
8%6%27%7%46%6%8%9%33%
2535
July1st to 15thDay
12%6%37%6%46%6%7%8%30%
2535
16th to endDay
13%5%37%7%46%8%6%9%27%
2673
August1st to 15thDay
11%6%37%8%36%7%8%10%27%
2487
16th to endDay
11%5%26%5%37%6%7%9%34%
2565
September1st to 15thDay
12%5%26%5%35%6%49%35%
1980
16th to endDay
14%6%25%5%25%46%7%40%
1980
October1st to 15thDay
13%5%2433345%6%47%
1880
16th to endDay
18%7%24323335%46%
1920
November1st to 15thDay
14%6%245%2335%6%45%
1780
16th to endDay
13%8%35%42435%6%42%
1755
December1st to 15thDay
18%10%37%5%23345%33%
1755
16th to endDay
21%12%445%34347%28%
1872
January1st to 15thNight
17%10%5%9%6%24345%30%
2522
16th to endNight
18%10%47%5%24435%33%
2704
February1st to 15thNight
17%9%47%5%33346%33%
2395
16th to endNight
19%11%47%5%23336%29%
2049
March1st to 15thNight
17%11%37%423445%35%
2171
16th to endNight
16%8%36%5%3445%6%35%
2288
April1st to 15thNight
14%6%25%5%24447%41%
2112
16th to endNight
13%5%26%5%25%6%46%40%
1741
May1st to 15thNight
15%6%346%35%45%9%35%
1754
16th to endNight
9%6%46%6%35%6%7%10%34%
1826
June1st to 15thNight
9%415%435%6%7%12%40%
1755
16th to endNight
7%5%345%35%5%7%11%40%
1755
July1st to 15thNight
9%6%26%5%35%5%7%11%36%
1755
16th to endNight
8%425%6%36%6%8%11%36%
1847
August1st to 15thNight
9%5%25%5%345%7%11%38%
1726
16th to endNight
9%425%5%35%6%7%9%39%
1918
September1st to 15thNight
12%6%36%5%3445%7%40%
1980
16th to endNight
12%5%1442335%6%49%
1980
October1st to 15thNight
14%5%24313346%50%
2079
16th to endNight
14%7%24323346%46%
2304
November1st to 15thNight
15%6%24223335%49%
2406
16th to endNight
13%7%24324345%46%
2535
December1st to 15thNight
19%10%36%6%24346%32%
2535
16th to endNight
21%11%46%5%34435%28%
2704

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
57%48%15%11%2
1747
16th to endDay
53%48%22%11%1
1872
February1st to 15thDay
57%47%17%12%
1788
16th to endDay
56%49%16%11%1
1710
March1st to 15thDay
49%48%19%14%3
2119
16th to endDay
53%5%10%19%9%1
2288
April1st to 15thDay
42%410%23%14%3
2171
16th to endDay
47%5%8%19%14%4
2500
May1st to 15thDay
50%7%11%19%8%1
2526
16th to endDay
48%8%13%19%6%2
2643
June1st to 15thDay
43%12%15%18%9%
2535
16th to endDay
44%9%13%16%14%1
2535
July1st to 15thDay
47%10%14%13%11%1
2396
16th to endDay
49%11%13%15%9%1
2518
August1st to 15thDay
48%12%14%16%8%
2474
16th to endDay
43%9%15%17%12%1
2565
September1st to 15thDay
45%8%11%18%12%3
1980
16th to endDay
42%7%10%18%19%1
1980
October1st to 15thDay
37%49%22%20%5%
1880
16th to endDay
42%46%23%17%4
1920
November1st to 15thDay
40%46%17%25%5%
1780
16th to endDay
43%47%20%21%3
1755
December1st to 15thDay
52%5%8%20%11%2
1755
16th to endDay
56%410%16%9%1
1872
January1st to 15thNight
56%48%13%12%4
2522
16th to endNight
53%47%18%13%1
2704
February1st to 15thNight
52%39%21%10%1
2404
16th to endNight
57%48%19%8%2
2049
March1st to 15thNight
52%48%18%14%2
2171
16th to endNight
48%7%11%19%11%
2288
April1st to 15thNight
42%5%10%22%15%3
2112
16th to endNight
44%6%10%18%14%4
1741
May1st to 15thNight
46%8%13%21%9%1
1755
16th to endNight
42%11%15%19%8%2
1828
June1st to 15thNight
34%11%20%19%12%1
1755
16th to endNight
36%10%15%20%13%2
1755
July1st to 15thNight
40%9%16%18%12%2
1665
16th to endNight
35%11%19%19%10%2
1739
August1st to 15thNight
38%9%18%18%12%1
1715
16th to endNight
36%9%16%25%11%
1918
September1st to 15thNight
41%7%13%19%14%3
1980
16th to endNight
35%6%11%22%22%1
1980
October1st to 15thNight
35%49%24%21%4
2079
16th to endNight
39%46%23%21%5%
2304
November1st to 15thNight
38%37%19%24%6%
2406
16th to endNight
40%47%22%22%3
2535
December1st to 15thNight
54%49%17%10%3
2535
16th to endNight
58%5%9%13%12%1
2704

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
28%28%26%9%5%1
135
16th to endDay
32%24%23%16%2
144
February1st to 15thDay
42%19%28%8%
135
16th to endDay
36%19%33%8%2
120
March1st to 15thDay
28%17%23%23%6%
304
16th to endDay
27%12%28%20%8%1
352
April1st to 15thDay
25%15%20%24%11%3
330
16th to endDay
22%11%20%22%17%5%
319
May1st to 15thDay
24%12%18%22%12%8%
348
16th to endDay
21%417%19%20%16%
395
June1st to 15thDay
10%5%14%25%30%12%
375
16th to endDay
14%7%20%20%22%14%
375
July1st to 15thDay
20%113%22%24%16%
365
16th to endDay
16%211%26%25%17%
390
August1st to 15thDay
17%212%24%24%19%
358
16th to endDay
14%19%26%23%25%
384
September1st to 15thDay
15%7%10%15%33%17%
315
16th to endDay
16%5%13%25%25%14%
314
October1st to 15thDay
18%5%14%29%25%6%
315
16th to endDay
22%10%20%22%19%5%
336
November1st to 15thDay
20%8%20%29%17%4
198
16th to endDay
16%19%26%22%13%1
135
December1st to 15thDay
31%18%30%17%2
135
16th to endDay
35%20%30%11%2
144
January1st to 15thNight
24%16%26%26%6%
780
16th to endNight
24%15%30%26%2
832
February1st to 15thNight
25%15%29%27%2
764
16th to endNight
27%18%28%22%2
683
March1st to 15thNight
23%14%27%28%6%
780
16th to endNight
20%12%27%29%9%
832
April1st to 15thNight
20%13%24%30%10%
778
16th to endNight
17%7%23%35%14%1
585
May1st to 15thNight
16%7%19%34%19%2
585
16th to endNight
11%213%31%33%7%
611
June1st to 15thNight
9%111%34%35%7%
585
16th to endNight
9%10%32%40%5%
585
July1st to 15thNight
16%18%30%38%4
555
16th to endNight
9%17%29%41%11%
612
August1st to 15thNight
12%5%32%42%6%
575
16th to endNight
11%5%30%42%8%
652
September1st to 15thNight
15%211%28%35%5%
720
16th to endNight
15%213%29%34%4
717
October1st to 15thNight
16%5%16%29%26%4
720
16th to endNight
19%10%21%28%18%1
768
November1st to 15thNight
18%6%17%35%19%2
760
16th to endNight
18%11%21%34%12%
780
December1st to 15thNight
25%12%24%28%8%
780
16th to endNight
29%11%24%28%5%
832
Page generated at 2018-08-30 05:34:19. Version ac04

Copyright 2018 A. Danko


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