South Bratt Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the South Bratt Observatory clear sky chart from 2005-11-05 to 2017-09-24.

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
58%
15228
23%
47079
19%
15185
63%
15185
31%
28109

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
41%
720
25%
2217
14%
716
52%
716
28%
1351
January16th to endNight
35%
768
26%
2304
14%
768
45%
768
27%
1461
February1st to 15thNight
41%
704
29%
2112
16%
701
52%
701
32%
1247
February16th to endNight
36%
631
24%
1893
12%
631
45%
631
26%
1211
March1st to 15thNight
42%
720
22%
2160
13%
720
50%
720
30%
1313
March16th to endNight
52%
669
27%
2028
20%
669
58%
669
34%
1160
April1st to 15thNight
53%
539
24%
1797
21%
539
59%
539
30%
1023
April16th to endNight
62%
540
28%
1800
27%
540
69%
540
41%
916
May1st to 15thNight
64%
539
21%
1745
20%
539
68%
539
35%
971
May16th to endNight
74%
561
22%
1682
22%
561
76%
561
36%
990
June1st to 15thNight
76%
540
14%
1620
14%
540
76%
540
33%
989
June16th to endNight
74%
540
16%
1620
16%
540
74%
540
28%
1029
July1st to 15thNight
83%
510
11%
1530
12%
510
83%
510
29%
979
July16th to endNight
81%
564
11%
1772
13%
531
81%
531
27%
1107
August1st to 15thNight
81%
539
9%
1788
10%
536
81%
536
27%
1131
August16th to endNight
70%
573
14%
1910
17%
573
70%
573
21%
1274
September1st to 15thNight
68%
606
18%
1866
19%
606
69%
606
28%
1180
September16th to endNight
67%
693
26%
1914
21%
693
69%
693
32%
1187
October1st to 15thNight
69%
660
33%
1815
26%
660
73%
660
45%
1001
October16th to endNight
61%
704
36%
2054
30%
704
67%
704
44%
1090
November1st to 15thNight
61%
700
31%
2276
30%
700
67%
700
37%
1214
November16th to endNight
53%
720
30%
2340
25%
720
62%
720
37%
1268
December1st to 15thNight
49%
720
25%
2340
22%
720
56%
720
29%
1383
December16th to endNight
38%
768
21%
2496
16%
768
46%
768
22%
1634

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
11%5%25%5%35%5%5%7%40%
47828
Night
9%42442445%8%47%
47291
TransparencyDay
40%7%11%16%16%7%
47542
Night
33%6%13%18%18%8%
47082
SeeingDay
12%312%20%27%23%
5171
Night
11%318%31%27%7%
15231

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
13%6%25%5%2435%7%43%
1719
16th to endDay
18%5%2343333446%
1920
February1st to 15thDay
12%42443445%7%47%
1750
16th to endDay
15%5%35%43335%5%43%
1580
March1st to 15thDay
14%5%245%2445%6%44%
1800
16th to endDay
12%5%24434446%46%
2202
April1st to 15thDay
12%5%25%434447%45%
2151
16th to endDay
8%4245%3445%8%48%
2160
May1st to 15thDay
10%5%245%36%46%8%42%
2205
16th to endDay
8%425%6%35%6%6%9%41%
2431
June1st to 15thDay
8%5%26%6%48%7%7%10%31%
2340
16th to endDay
7%427%7%5%8%7%7%11%31%
2340
July1st to 15thDay
9%5%38%7%5%7%9%8%8%24%
2337
16th to endDay
8%6%37%8%5%8%8%8%9%23%
2276
August1st to 15thDay
8%5%27%8%49%8%8%11%24%
2160
16th to endDay
11%8%37%7%46%6%7%7%28%
2292
September1st to 15thDay
10%7%37%7%46%5%5%8%32%
2082
16th to endDay
9%4247%45%5%5%6%44%
1905
October1st to 15thDay
8%31342445%7%53%
1815
16th to endDay
9%314425%335%56%
1813
November1st to 15thDay
10%313224346%56%
1582
16th to endDay
9%414335%445%53%
1620
December1st to 15thDay
12%6%345%24445%45%
1620
16th to endDay
21%8%35%433346%36%
1728
January1st to 15thNight
12%5%24424447%46%
2217
16th to endNight
17%6%25%323345%45%
2304
February1st to 15thNight
13%5%23323446%50%
2103
16th to endNight
14%6%35%324435%45%
1893
March1st to 15thNight
12%6%24425%45%7%45%
2160
16th to endNight
10%423323347%52%
2028
April1st to 15thNight
9%5%244245%5%7%49%
1797
16th to endNight
7%313323447%58%
1800
May1st to 15thNight
9%32342435%8%52%
1745
16th to endNight
6%324415%5%7%10%48%
1682
June1st to 15thNight
5%325%5%45%6%8%13%41%
1620
16th to endNight
7%4245%36%6%7%12%39%
1620
July1st to 15thNight
3324436%7%9%13%41%
1620
16th to endNight
32145%36%7%9%15%38%
1891
August1st to 15thNight
33146%46%6%9%14%38%
1800
16th to endNight
8%427%6%45%6%7%10%36%
1910
September1st to 15thNight
8%5%245%35%6%7%11%38%
1866
16th to endNight
9%4245%345%6%8%45%
1914
October1st to 15thNight
7%31332345%7%57%
1815
16th to endNight
9%412312345%61%
2054
November1st to 15thNight
8%32432345%5%56%
2276
16th to endNight
8%324413345%56%
2340
December1st to 15thNight
12%5%24433337%48%
2340
16th to endNight
17%7%36%423445%39%
2496

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
39%45%15%23%11%
1720
16th to endDay
42%3315%24%10%
1920
February1st to 15thDay
36%48%16%22%11%
1752
16th to endDay
41%5%5%15%22%9%
1580
March1st to 15thDay
39%5%8%18%20%8%
1800
16th to endDay
38%49%18%19%8%
2203
April1st to 15thDay
38%47%17%21%9%
2151
16th to endDay
34%5%9%21%20%7%
2160
May1st to 15thDay
37%7%10%17%19%7%
2205
16th to endDay
37%8%12%21%16%3
2435
June1st to 15thDay
42%10%15%20%8%1
2340
16th to endDay
42%12%16%17%9%1
2340
July1st to 15thDay
51%13%17%11%4
2198
16th to endDay
51%11%17%15%3
2133
August1st to 15thDay
48%11%20%12%6%
2148
16th to endDay
50%10%16%11%8%2
2292
September1st to 15thDay
47%9%15%11%11%4
2082
16th to endDay
39%6%11%17%16%8%
1905
October1st to 15thDay
29%6%10%16%21%15%
1815
16th to endDay
29%4413%26%21%
1813
November1st to 15thDay
29%36%18%26%14%
1582
16th to endDay
31%47%15%22%17%
1620
December1st to 15thDay
40%5%7%19%20%7%
1620
16th to endDay
50%35%19%15%5%
1728
January1st to 15thNight
38%47%14%25%9%
2217
16th to endNight
42%26%13%23%10%
2304
February1st to 15thNight
34%35%19%22%14%
2112
16th to endNight
41%46%13%20%13%
1893
March1st to 15thNight
37%411%17%20%8%
2160
16th to endNight
32%39%21%22%10%
2028
April1st to 15thNight
33%5%11%15%22%11%
1797
16th to endNight
25%412%27%22%7%
1800
May1st to 15thNight
30%5%13%20%22%8%
1746
16th to endNight
28%8%17%24%17%4
1684
June1st to 15thNight
30%10%22%24%11%1
1620
16th to endNight
34%10%21%21%10%1
1620
July1st to 15thNight
28%16%31%17%6%
1530
16th to endNight
29%15%30%20%2
1772
August1st to 15thNight
29%16%31%17%5%
1788
16th to endNight
39%12%22%14%7%2
1910
September1st to 15thNight
35%9%18%18%11%6%
1866
16th to endNight
33%7%14%19%17%7%
1914
October1st to 15thNight
24%6%10%19%23%16%
1815
16th to endNight
25%36%14%27%22%
2054
November1st to 15thNight
28%45%18%27%15%
2276
16th to endNight
29%47%16%23%18%
2340
December1st to 15thNight
37%39%19%22%7%
2340
16th to endNight
45%47%20%15%6%
2496

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
15%13%27%21%15%6%
90
16th to endDay
19%17%32%18%10%1
96
February1st to 15thDay
7%17%31%22%21%
90
16th to endDay
12%13%33%27%13%
81
March1st to 15thDay
20%10%43%17%7%1
90
16th to endDay
15%421%31%23%4
271
April1st to 15thDay
19%6%22%26%22%2
270
16th to endDay
10%317%29%31%7%
270
May1st to 15thDay
10%416%23%30%14%
288
16th to endDay
9%19%26%22%29%
331
June1st to 15thDay
15%417%28%33%
315
16th to endDay
10%1313%27%43%
315
July1st to 15thDay
6%125%29%54%
305
16th to endDay
7%29%32%47%
326
August1st to 15thDay
8%128%32%46%
313
16th to endDay
12%39%34%38%
332
September1st to 15thDay
10%19%18%33%27%
315
16th to endDay
13%424%38%18%
287
October1st to 15thDay
5%13%33%31%14%
255
16th to endDay
10%312%33%24%14%
165
November1st to 15thDay
22%218%28%22%5%
90
16th to endDay
8%7%28%32%16%5%
90
December1st to 15thDay
17%10%27%33%6%4
90
16th to endDay
30%8%17%23%18%1
96
January1st to 15thNight
15%8%30%36%9%
720
16th to endNight
19%9%32%31%8%
768
February1st to 15thNight
16%6%32%33%11%
704
16th to endNight
16%7%34%34%7%
631
March1st to 15thNight
14%7%30%37%9%
720
16th to endNight
13%5%23%38%18%1
669
April1st to 15thNight
12%423%37%20%
539
16th to endNight
8%221%40%25%1
540
May1st to 15thNight
11%115%43%25%2
540
16th to endNight
6%7%32%45%6%
563
June1st to 15thNight
6%428%45%14%
540
16th to endNight
8%219%50%18%
540
July1st to 15thNight
4115%50%26%
510
16th to endNight
41115%52%25%
564
August1st to 15thNight
5%110%53%29%
539
16th to endNight
9%215%49%21%
573
September1st to 15thNight
11%15%18%45%17%
606
16th to endNight
12%16%28%43%8%
693
October1st to 15thNight
8%113%36%34%5%
660
16th to endNight
12%219%31%28%4
704
November1st to 15thNight
10%317%41%22%4
700
16th to endNight
10%426%38%18%1
720
December1st to 15thNight
13%6%25%35%16%1
720
16th to endNight
20%5%28%31%11%
768
Page generated at 2017-09-25 08:02:18. Version ac04

Copyright 2017 A. Danko


South Bratt Observatory Clear Sky Chart | Charts Home