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 2017-09-17.

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%
15924
27%
46871
13%
15878
55%
15878
38%
25154

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%
900
31%
2506
10%
895
48%
895
38%
1265
January16th to endNight
26%
783
34%
2511
12%
783
51%
783
37%
1209
February1st to 15thNight
22%
700
26%
2254
6%
697
44%
697
34%
1141
February16th to endNight
24%
632
34%
1894
7%
632
51%
632
38%
962
March1st to 15thNight
30%
720
27%
2097
8%
720
46%
720
36%
1131
March16th to endNight
28%
690
27%
2034
9%
690
46%
690
33%
1133
April1st to 15thNight
30%
539
25%
1798
10%
539
49%
539
32%
930
April16th to endNight
31%
540
22%
1800
11%
540
46%
540
26%
1036
May1st to 15thNight
41%
539
19%
1620
10%
539
51%
539
26%
1030
May16th to endNight
47%
563
17%
1498
9%
561
55%
561
34%
901
June1st to 15thNight
61%
540
24%
1440
15%
540
67%
540
52%
749
June16th to endNight
69%
540
27%
1440
20%
540
74%
540
53%
741
July1st to 15thNight
71%
510
17%
1360
15%
510
74%
510
35%
828
July16th to endNight
73%
564
18%
1469
17%
531
75%
531
35%
884
August1st to 15thNight
73%
539
16%
1662
16%
536
75%
536
33%
953
August16th to endNight
72%
573
24%
1910
26%
573
75%
573
34%
1069
September1st to 15thNight
67%
540
26%
1800
25%
540
72%
540
35%
979
September16th to endNight
62%
501
33%
1786
26%
501
74%
501
43%
839
October1st to 15thNight
43%
660
30%
1980
16%
660
54%
660
42%
1042
October16th to endNight
45%
716
33%
2124
16%
716
58%
716
43%
1097
November1st to 15thNight
39%
875
33%
2275
12%
875
53%
875
48%
1185
November16th to endNight
32%
900
35%
2405
11%
900
50%
900
48%
1218
December1st to 15thNight
26%
900
25%
2520
6%
900
43%
900
36%
1328
December16th to endNight
24%
960
26%
2688
7%
960
41%
960
34%
1504

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%6%25%435%45%8%48%
47915
Night
342332345%7%58%
47048
TransparencyDay
33%6%12%23%18%5%
47595
Night
23%5%14%27%21%6%
46871
SeeingDay
12%14%31%25%12%3
5834
Night
6%12%34%30%14%2
15929

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
5%34323446%60%
1432
16th to endDay
435%42335%7%58%
1722
February1st to 15thDay
16%26%424448%54%
1606
16th to endDay
6%25%42335%7%57%
1580
March1st to 15thDay
26%25%42445%9%52%
1860
16th to endDay
310%3442446%9%46%
2190
April1st to 15thDay
5%7%24425%5%5%8%47%
2150
16th to endDay
9%12%345%3445%6%39%
2160
May1st to 15thDay
11%9%35%5%2446%8%36%
2328
16th to endDay
9%6%35%6%46%6%6%8%36%
2616
June1st to 15thDay
6%413435%5%7%9%47%
2520
16th to endDay
4313436%6%7%9%48%
2520
July1st to 15thDay
8%5%25%6%47%6%8%9%35%
2520
16th to endDay
9%6%26%6%47%6%6%9%35%
2596
August1st to 15thDay
10%6%36%7%46%6%6%7%34%
2288
16th to endDay
8%5%25%6%46%6%6%7%41%
2292
September1st to 15thDay
8%425%43445%5%49%
2160
16th to endDay
4414323446%58%
1877
October1st to 15thDay
6%414334445%57%
1650
16th to endDay
5%6%1421335%6%60%
1735
November1st to 15thDay
142431335%6%63%
1583
16th to endDay
324313347%63%
1554
December1st to 15thDay
5%26%421349%58%
1440
16th to endDay
1425%5%2436%9%54%
1536
January1st to 15thNight
313323348%65%
2506
16th to endNight
425%31225%6%65%
2511
February1st to 15thNight
5%34223347%61%
2244
16th to endNight
5%1431336%7%61%
1894
March1st to 15thNight
15%2432346%8%57%
2097
16th to endNight
36%33323346%59%
2034
April1st to 15thNight
27%33313348%59%
1798
16th to endNight
8%10%34213336%52%
1800
May1st to 15thNight
9%7%243345%5%7%45%
1619
16th to endNight
5%3244245%6%7%52%
1497
June1st to 15thNight
42111245%9%65%
1440
16th to endNight
211222346%10%62%
1440
July1st to 15thNight
4324425%6%7%9%49%
1440
16th to endNight
4324445%7%8%10%45%
1569
August1st to 15thNight
43145%35%6%7%7%50%
1671
16th to endNight
6%3134246%5%8%52%
1910
September1st to 15thNight
8%21442346%8%52%
1800
16th to endNight
331222335%5%65%
1786
October1st to 15thNight
5%312323345%64%
1980
16th to endNight
35%13222346%62%
2124
November1st to 15thNight
1312213248%66%
2275
16th to endNight
1413213247%65%
2405
December1st to 15thNight
14134133410%60%
2520
16th to endNight
1435%5%2345%8%55%
2688

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%5%18%30%18%4
1433
16th to endDay
24%412%32%18%6%
1722
February1st to 15thDay
28%317%30%16%3
1607
16th to endDay
26%310%30%22%5%
1580
March1st to 15thDay
29%413%28%20%4
1860
16th to endDay
34%6%11%26%17%4
2190
April1st to 15thDay
35%6%12%23%15%6%
2150
16th to endDay
44%6%10%21%14%2
2160
May1st to 15thDay
45%8%11%19%13%1
2328
16th to endDay
43%9%12%19%11%4
2620
June1st to 15thDay
30%9%13%17%18%10%
2520
16th to endDay
27%8%10%20%23%9%
2520
July1st to 15thDay
42%9%11%15%13%6%
2371
16th to endDay
43%10%14%19%9%3
2434
August1st to 15thDay
46%9%11%13%12%5%
2273
16th to endDay
39%7%11%20%17%4
2292
September1st to 15thDay
35%5%9%19%20%8%
2160
16th to endDay
25%5%8%25%29%5%
1877
October1st to 15thDay
29%5%9%23%26%6%
1650
16th to endDay
24%311%24%28%6%
1735
November1st to 15thDay
20%413%25%25%10%
1583
16th to endDay
20%39%29%28%8%
1554
December1st to 15thDay
25%417%30%18%3
1440
16th to endDay
25%6%17%25%18%5%
1536
January1st to 15thNight
17%5%17%32%23%4
2506
16th to endNight
20%312%30%24%8%
2511
February1st to 15thNight
23%413%36%17%4
2254
16th to endNight
20%410%34%23%7%
1894
March1st to 15thNight
23%412%28%25%4
2097
16th to endNight
27%412%30%20%4
2034
April1st to 15thNight
24%5%12%30%19%6%
1798
16th to endNight
34%5%14%26%16%3
1800
May1st to 15thNight
36%9%14%21%15%2
1620
16th to endNight
28%8%21%22%13%5%
1498
June1st to 15thNight
16%7%19%25%17%13%
1440
16th to endNight
16%7%12%25%25%12%
1440
July1st to 15thNight
29%9%17%20%15%7%
1360
16th to endNight
26%12%20%24%12%3
1469
August1st to 15thNight
29%8%18%21%16%5%
1662
16th to endNight
28%8%15%24%18%4
1910
September1st to 15thNight
28%6%14%22%17%10%
1800
16th to endNight
20%5%12%30%27%4
1786
October1st to 15thNight
22%5%14%23%26%8%
1980
16th to endNight
22%410%25%31%5%
2124
November1st to 15thNight
17%313%26%25%12%
2275
16th to endNight
18%212%27%29%8%
2405
December1st to 15thNight
20%5%20%29%18%5%
2520
16th to endNight
26%5%18%25%19%4
2688

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
14%11%36%20%15%2
90
16th to endDay
5%10%46%29%8%
96
February1st to 15thDay
12%35%38%13%
90
16th to endDay
8%22%40%18%9%
81
March1st to 15thDay
16%24%36%19%2
150
16th to endDay
20%35%29%12%2
288
April1st to 15thDay
19%30%28%17%21
269
16th to endDay
26%29%28%12%2
270
May1st to 15thDay
15%16%34%24%6%1
402
16th to endDay
15%14%29%26%13%1
517
June1st to 15thDay
8%11%31%29%16%3
495
16th to endDay
47%36%28%18%4
495
July1st to 15thDay
9%5%22%34%20%8%
475
16th to endDay
10%423%29%23%8%
455
August1st to 15thDay
14%7%27%35%12%2
315
16th to endDay
12%8%32%33%12%1
332
September1st to 15thDay
10%14%35%27%10%1
315
16th to endDay
7%10%38%26%12%4
147
October1st to 15thDay
414%34%26%15%4
90
16th to endDay
11%16%32%29%7%3
96
November1st to 15thDay
6%12%30%26%20%4
90
16th to endDay
11%23%43%18%3
90
December1st to 15thDay
15%24%45%11%3
90
16th to endDay
5%20%50%16%6%1
96
January1st to 15thNight
5%22%38%22%8%2
900
16th to endNight
5%17%45%22%7%1
783
February1st to 15thNight
5%17%50%21%4
704
16th to endNight
320%45%26%4
632
March1st to 15thNight
416%43%25%8%1
720
16th to endNight
7%15%43%26%6%
690
April1st to 15thNight
8%16%41%27%5%
539
16th to endNight
12%17%34%26%7%
540
May1st to 15thNight
13%7%32%32%11%2
540
16th to endNight
6%8%29%36%16%2
563
June1st to 15thNight
5%327%45%15%3
540
16th to endNight
2221%44%26%2
540
July1st to 15thNight
6%110%40%37%3
510
16th to endNight
6%19%35%42%4
564
August1st to 15thNight
6%110%43%34%4
539
16th to endNight
8%110%39%34%5%
573
September1st to 15thNight
7%115%41%27%6%
540
16th to endNight
4324%37%23%5%
501
October1st to 15thNight
6%9%37%28%14%4
660
16th to endNight
6%10%33%30%15%3
716
November1st to 15thNight
5%14%37%28%12%1
875
16th to endNight
416%45%25%8%
900
December1st to 15thNight
5%20%44%24%4
900
16th to endNight
6%17%46%23%6%1
960
Page generated at 2017-09-18 06:38:25. Version ac04

Copyright 2017 A. Danko


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