Burland Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Burland 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
42%
17200
27%
50611
13%
17154
56%
17154
38%
27030

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
28%
975
31%
2716
10%
970
49%
970
39%
1371
January16th to endNight
26%
848
35%
2720
13%
848
51%
848
38%
1299
February1st to 15thNight
21%
760
26%
2446
6%
757
43%
757
35%
1215
February16th to endNight
24%
684
34%
2050
7%
684
52%
684
38%
1040
March1st to 15thNight
31%
780
28%
2272
9%
780
47%
780
38%
1203
March16th to endNight
29%
747
27%
2203
10%
747
46%
747
34%
1220
April1st to 15thNight
29%
584
25%
1948
10%
584
49%
584
32%
1023
April16th to endNight
31%
579
21%
1929
11%
579
47%
579
26%
1105
May1st to 15thNight
42%
584
19%
1756
11%
584
52%
584
25%
1129
May16th to endNight
49%
611
17%
1626
10%
609
56%
609
35%
972
June1st to 15thNight
62%
585
26%
1560
17%
585
68%
585
54%
798
June16th to endNight
68%
585
25%
1560
19%
585
73%
585
53%
809
July1st to 15thNight
73%
555
19%
1480
17%
555
75%
555
38%
882
July16th to endNight
74%
612
18%
1602
17%
579
75%
579
34%
966
August1st to 15thNight
74%
575
18%
1772
17%
572
76%
572
34%
997
August16th to endNight
72%
615
24%
2050
25%
615
75%
615
34%
1145
September1st to 15thNight
67%
540
26%
1800
25%
540
72%
540
35%
979
September16th to endNight
60%
540
33%
1926
25%
540
73%
540
41%
925
October1st to 15thNight
44%
720
29%
2160
16%
720
55%
720
43%
1125
October16th to endNight
45%
781
35%
2317
17%
781
59%
781
44%
1188
November1st to 15thNight
39%
950
33%
2470
12%
950
52%
950
48%
1284
November16th to endNight
32%
975
35%
2606
10%
975
51%
975
48%
1320
December1st to 15thNight
27%
975
25%
2730
6%
975
43%
975
37%
1427
December16th to endNight
24%
1040
27%
2912
7%
1040
42%
1040
34%
1608

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
5%5%25%435%5%5%8%48%
51650
Night
342332345%7%59%
50788
TransparencyDay
32%6%12%22%19%5%
51330
Night
23%5%14%27%21%6%
50611
SeeingDay
11%15%33%25%11%2
7099
Night
6%11%34%30%14%2
17205

By Month

Percentage Cloud Cover SW (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
424324446%60%
1552
16th to endDay
435%323448%58%
1866
February1st to 15thDay
15%26%424448%55%
1744
16th to endDay
5%25%42335%7%58%
1710
March1st to 15thDay
25%25%424449%53%
2015
16th to endDay
310%3442446%9%47%
2372
April1st to 15thDay
47%24435%5%5%8%47%
2330
16th to endDay
9%12%345%3445%6%39%
2306
May1st to 15thDay
10%9%45%5%345%6%8%35%
2522
16th to endDay
9%6%25%5%46%5%7%8%37%
2840
June1st to 15thDay
6%423435%5%7%9%47%
2730
16th to endDay
4314436%6%7%9%48%
2730
July1st to 15thDay
7%425%6%47%6%8%9%36%
2730
16th to endDay
8%5%25%6%47%6%6%9%35%
2815
August1st to 15thDay
9%6%36%7%46%6%7%8%34%
2431
16th to endDay
7%5%25%6%46%6%6%7%41%
2449
September1st to 15thDay
8%425%43445%5%49%
2160
16th to endDay
5%424323446%57%
2030
October1st to 15thDay
6%414334445%58%
1800
16th to endDay
46%1431335%6%60%
1893
November1st to 15thDay
142431335%6%64%
1718
16th to endDay
324313347%64%
1683
December1st to 15thDay
5%26%421349%59%
1560
16th to endDay
1425%42336%9%56%
1664
January1st to 15thNight
31332335%7%65%
2716
16th to endNight
42431225%6%65%
2720
February1st to 15thNight
5%24213348%62%
2436
16th to endNight
5%1432336%7%62%
2050
March1st to 15thNight
142432346%8%58%
2272
16th to endNight
36%33323346%59%
2203
April1st to 15thNight
27%33313348%59%
1948
16th to endNight
8%10%34313336%52%
1929
May1st to 15thNight
9%7%243345%5%7%44%
1755
16th to endNight
5%3144245%5%7%53%
1625
June1st to 15thNight
32111345%9%65%
1560
16th to endNight
211221346%10%61%
1560
July1st to 15thNight
4324325%6%6%9%50%
1560
16th to endNight
3224445%7%8%10%45%
1702
August1st to 15thNight
3314435%5%7%7%52%
1781
16th to endNight
6%3134246%5%8%52%
2050
September1st to 15thNight
8%21442346%8%52%
1800
16th to endNight
441322335%5%63%
1926
October1st to 15thNight
5%212313345%65%
2160
16th to endNight
35%23222346%63%
2317
November1st to 15thNight
1312213248%67%
2470
16th to endNight
1413213348%65%
2606
December1st to 15thNight
13134133410%61%
2730
16th to endNight
1435%42345%8%56%
2912

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
23%6%17%29%18%4
1553
16th to endDay
24%412%32%19%6%
1866
February1st to 15thDay
27%319%30%15%3
1745
16th to endDay
26%310%28%25%5%
1710
March1st to 15thDay
27%412%28%21%5%
2015
16th to endDay
33%6%11%26%17%3
2372
April1st to 15thDay
34%6%12%24%15%6%
2330
16th to endDay
43%5%10%20%15%2
2306
May1st to 15thDay
44%8%12%19%13%1
2522
16th to endDay
42%8%12%18%12%5%
2844
June1st to 15thDay
30%9%12%16%19%11%
2730
16th to endDay
28%8%10%20%23%9%
2730
July1st to 15thDay
41%9%11%15%15%6%
2581
16th to endDay
42%10%14%19%9%3
2653
August1st to 15thDay
45%10%11%14%12%5%
2416
16th to endDay
39%7%11%19%17%3
2449
September1st to 15thDay
35%5%9%19%20%8%
2160
16th to endDay
27%48%24%28%5%
2030
October1st to 15thDay
28%5%9%22%26%7%
1800
16th to endDay
24%311%25%28%7%
1893
November1st to 15thDay
19%312%25%27%10%
1718
16th to endDay
19%49%28%28%8%
1683
December1st to 15thDay
23%416%30%19%4
1560
16th to endDay
24%6%16%26%20%5%
1664
January1st to 15thNight
17%5%16%32%23%4
2716
16th to endNight
20%312%29%25%7%
2720
February1st to 15thNight
21%5%15%36%16%4
2446
16th to endNight
20%49%32%25%7%
2050
March1st to 15thNight
22%411%28%27%4
2272
16th to endNight
27%412%30%21%3
2203
April1st to 15thNight
25%6%12%29%20%6%
1948
16th to endNight
33%5%13%26%16%3
1929
May1st to 15thNight
37%9%13%21%14%2
1756
16th to endNight
28%8%20%22%15%4
1626
June1st to 15thNight
15%7%18%25%18%15%
1560
16th to endNight
17%6%12%24%25%12%
1560
July1st to 15thNight
27%9%17%21%17%7%
1480
16th to endNight
26%12%21%24%11%3
1602
August1st to 15thNight
27%8%18%22%15%6%
1772
16th to endNight
27%8%16%25%17%4
2050
September1st to 15thNight
28%6%14%22%17%10%
1800
16th to endNight
21%5%11%29%27%4
1926
October1st to 15thNight
22%413%23%26%9%
2160
16th to endNight
21%410%25%31%6%
2317
November1st to 15thNight
17%312%25%27%12%
2470
16th to endNight
18%312%28%29%8%
2606
December1st to 15thNight
20%5%19%28%19%6%
2730
16th to endNight
25%5%18%25%20%4
2912

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
9%11%45%20%10%1
135
16th to endDay
414%45%29%6%
144
February1st to 15thDay
11%38%36%13%
135
16th to endDay
7%25%42%17%6%
120
March1st to 15thDay
16%25%35%20%3
200
16th to endDay
19%32%32%13%2
352
April1st to 15thDay
17%34%28%15%21
329
16th to endDay
24%28%28%14%3
318
May1st to 15thDay
14%16%35%24%7%1
471
16th to endDay
14%13%29%26%13%2
597
June1st to 15thDay
7%12%31%28%15%3
570
16th to endDay
48%37%29%16%4
570
July1st to 15thDay
9%422%33%22%7%
550
16th to endDay
10%423%30%23%7%
530
August1st to 15thDay
13%6%30%34%11%2
359
16th to endDay
11%8%34%32%11%1
385
September1st to 15thDay
10%14%35%27%10%1
315
16th to endDay
12%12%37%25%9%3
191
October1st to 15thDay
5%20%34%22%12%4
135
16th to endDay
9%16%38%26%7%2
144
November1st to 15thDay
6%14%37%24%14%2
135
16th to endDay
11%21%45%19%2
135
December1st to 15thDay
13%21%44%14%6%
135
16th to endDay
8%23%45%16%4
144
January1st to 15thNight
421%40%23%7%2
975
16th to endNight
5%16%45%23%7%
848
February1st to 15thNight
5%17%51%21%4
764
16th to endNight
319%45%26%4
684
March1st to 15thNight
316%43%25%8%1
780
16th to endNight
7%15%43%27%5%
747
April1st to 15thNight
8%16%42%26%5%
584
16th to endNight
12%16%34%26%8%
579
May1st to 15thNight
14%6%31%33%12%2
585
16th to endNight
6%7%28%37%16%2
611
June1st to 15thNight
5%327%45%16%3
585
16th to endNight
3122%44%25%2
585
July1st to 15thNight
6%19%39%39%3
555
16th to endNight
6%18%36%42%4
612
August1st to 15thNight
6%110%43%35%4
575
16th to endNight
7%111%40%33%5%
615
September1st to 15thNight
7%115%41%27%6%
540
16th to endNight
5%325%37%22%5%
540
October1st to 15thNight
6%8%36%29%13%4
720
16th to endNight
6%9%34%31%14%3
781
November1st to 15thNight
5%14%37%29%11%1
950
16th to endNight
416%44%26%8%
975
December1st to 15thNight
5%19%44%25%4
975
16th to endNight
6%17%45%23%6%
1040
Page generated at 2018-08-30 03:34:25. Version ac04

Copyright 2018 A. Danko


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