Brandon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brandon clear sky chart from 2005-11-06 to 2024-02-25.

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%
24610
19%
79886
16%
24506
63%
24506
27%
50520

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
43%
757
20%
4042
16%
737
54%
737
16%
2478
January11th to 20thNight
48%
757
18%
4073
19%
740
60%
740
15%
2747
January21st to endNight
36%
830
16%
4216
15%
814
47%
814
17%
2481
February1st to 10thNight
45%
760
24%
2280
16%
760
53%
760
31%
1402
February11th to 20thNight
48%
740
23%
2219
15%
740
57%
740
35%
1278
February21st to endNight
46%
611
26%
1771
17%
611
54%
611
35%
1041
March1st to 10thNight
47%
720
31%
1980
18%
720
58%
720
44%
1089
March11th to 20thNight
52%
720
28%
1980
17%
720
60%
720
38%
1152
March21st to endNight
52%
792
29%
2178
20%
792
60%
792
41%
1241
April1st to 10thNight
54%
720
23%
1980
17%
720
59%
720
41%
1114
April11th to 20thNight
48%
711
20%
1953
14%
711
54%
711
35%
1175
April21st to endNight
58%
720
30%
1825
19%
720
64%
720
45%
1060
May1st to 10thNight
74%
543
31%
1623
25%
543
78%
543
51%
815
May11th to 20thNight
66%
531
17%
1592
13%
531
70%
531
32%
993
May21st to endNight
74%
582
24%
1745
20%
582
75%
582
37%
1040
June1st to 10thNight
67%
540
13%
1620
12%
540
67%
540
23%
1127
June11th to 20thNight
77%
540
12%
1620
10%
540
77%
540
28%
1084
June21st to endNight
75%
540
9%
1620
8%
540
75%
540
22%
1158
July1st to 10thNight
74%
525
5%
1575
4%
525
74%
525
20%
1181
July11th to 20thNight
77%
522
4%
1566
4%
522
77%
522
18%
1206
July21st to endNight
73%
591
7%
1672
6%
558
74%
558
19%
1237
August1st to 10thNight
80%
537
5%
1600
5%
534
80%
534
23%
1144
August11th to 20thNight
76%
534
6%
1763
7%
534
76%
534
21%
1246
August21st to endNight
62%
785
8%
2171
8%
785
62%
785
16%
1675
September1st to 10thNight
66%
720
7%
1980
7%
720
67%
720
17%
1496
September11th to 20thNight
62%
720
8%
1980
9%
720
63%
720
18%
1481
September21st to endNight
60%
720
17%
1980
15%
720
62%
720
22%
1411
October1st to 10thNight
61%
720
21%
1980
18%
720
64%
720
28%
1312
October11th to 20thNight
64%
720
28%
2128
26%
720
69%
720
36%
1241
October21st to endNight
57%
792
26%
2376
23%
792
64%
792
34%
1395
November1st to 10thNight
56%
740
27%
2221
21%
740
64%
740
38%
1244
November11th to 20thNight
55%
760
29%
2280
23%
760
63%
760
32%
1381
November21st to endNight
50%
760
26%
2413
21%
760
58%
760
30%
1452
December1st to 10thNight
52%
760
27%
2470
22%
760
62%
760
32%
1423
December11th to 20thNight
49%
759
24%
2943
21%
758
55%
758
24%
1692
December21st to endNight
49%
831
15%
4471
22%
817
56%
817
16%
2828

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
8%5%36%7%46%6%7%9%39%
78855
Night
8%5%36%5%45%5%6%9%43%
80445
TransparencyDay
40%10%14%17%14%6%
78578
Night
36%9%16%19%15%5%
80241
SeeingDay
8%6%19%26%24%18%
14481
Night
9%420%34%25%8%
24633

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
11%6%37%5%35%5%6%8%40%
2836
11th to 20thDay
21%8%36%5%34448%35%
2840
21st to endDay
10%6%35%5%345%6%8%45%
3358
February1st to 10thDay
12%5%25%5%245%6%9%46%
1900
11th to 20thDay
7%325%5%3445%7%55%
1848
21st to endDay
7%6%345%35%45%8%51%
1578
March1st to 10thDay
43144245%6%9%58%
1980
11th to 20thDay
7%3245%35%5%6%7%54%
1980
21st to endDay
7%325%4245%6%7%54%
2178
April1st to 10thDay
7%3245%45%6%6%10%50%
1980
11th to 20thDay
7%5%26%6%35%6%6%9%44%
1956
21st to endDay
43245%35%6%5%9%53%
2140
May1st to 10thDay
42234245%6%9%58%
2340
11th to 20thDay
8%5%26%6%37%7%6%9%40%
2301
21st to endDay
6%5%35%8%5%8%8%8%9%37%
2531
June1st to 10thDay
12%7%38%7%47%8%9%10%24%
2340
11th to 20thDay
6%5%37%8%5%7%9%10%12%27%
2340
21st to endDay
7%6%37%8%5%8%8%10%11%27%
2340
July1st to 10thDay
9%5%37%10%6%9%9%9%11%22%
2340
11th to 20thDay
7%6%49%10%6%9%9%8%11%22%
2340
21st to endDay
6%6%49%10%6%9%8%8%12%23%
2547
August1st to 10thDay
7%5%38%10%7%10%8%9%11%23%
2327
11th to 20thDay
6%7%39%10%7%10%8%9%10%22%
2120
21st to endDay
11%6%49%9%48%7%7%11%24%
2178
September1st to 10thDay
7%6%38%9%6%8%9%10%12%23%
1980
11th to 20thDay
9%7%38%8%6%8%8%8%10%24%
1980
21st to endDay
7%7%27%8%47%7%9%10%31%
1980
October1st to 10thDay
7%7%37%7%5%7%6%7%9%36%
1980
11th to 20thDay
6%425%6%46%6%5%8%47%
1830
21st to endDay
7%425%5%345%6%9%49%
1980
November1st to 10thDay
7%425%5%35%5%5%8%51%
1857
11th to 20thDay
8%5%36%6%35%5%5%8%46%
1900
21st to endDay
9%5%25%6%446%7%8%45%
1763
December1st to 10thDay
8%425%5%35%5%6%10%47%
1710
11th to 20thDay
11%5%36%5%3445%9%45%
2153
21st to endDay
13%7%48%7%46%5%5%7%35%
3124
January1st to 10thNight
11%7%47%6%45%46%8%37%
4109
11th to 20thNight
19%11%46%5%3445%7%32%
4120
21st to endNight
11%6%36%6%45%5%6%8%39%
4294
February1st to 10thNight
11%7%25%5%345%5%8%47%
2280
11th to 20thNight
9%5%2443445%7%52%
2218
21st to endNight
7%5%26%5%3445%7%51%
1771
March1st to 10thNight
5%3145%2445%7%59%
1980
11th to 20thNight
6%324435%5%5%9%53%
1980
21st to endNight
6%324425%45%7%56%
2178
April1st to 10thNight
6%42343446%11%54%
1980
11th to 20thNight
7%425%5%25%5%6%9%49%
1953
21st to endNight
6%424434448%58%
1825
May1st to 10thNight
3213323449%65%
1623
11th to 20thNight
6%6%25%5%36%6%7%8%47%
1592
21st to endNight
6%3245%45%5%6%8%52%
1744
June1st to 10thNight
11%6%35%6%5%5%6%7%10%35%
1620
11th to 20thNight
5%6%36%436%8%7%13%38%
1620
21st to endNight
7%436%7%47%7%9%13%33%
1620
July1st to 10thNight
6%5%26%6%5%7%7%9%14%31%
1620
11th to 20thNight
5%5%36%7%49%10%11%12%28%
1620
21st to endNight
45%47%7%5%7%8%10%14%30%
1771
August1st to 10thNight
4425%6%5%7%9%11%13%33%
1611
11th to 20thNight
45%37%7%5%7%8%8%15%32%
1763
21st to endNight
9%7%38%8%5%6%7%8%11%29%
2171
September1st to 10thNight
6%5%27%8%5%7%9%10%13%28%
1980
11th to 20thNight
9%6%38%7%5%7%7%8%12%29%
1980
21st to endNight
8%7%38%6%46%6%7%9%35%
1980
October1st to 10thNight
7%5%36%6%36%6%7%9%42%
1980
11th to 20thNight
6%5%26%5%35%5%5%7%51%
2128
21st to endNight
7%6%26%5%3445%8%51%
2376
November1st to 10thNight
7%424435%45%7%54%
2221
11th to 20thNight
8%5%26%5%35%46%7%50%
2280
21st to endNight
7%5%36%6%45%5%6%8%46%
2413
December1st to 10thNight
8%425%6%345%6%7%49%
2470
11th to 20thNight
12%6%35%5%3445%7%48%
3042
21st to endNight
13%8%37%6%45%5%6%8%35%
4532

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
41%6%9%19%18%8%
2837
11th to 20thDay
49%47%16%17%8%
2840
21st to endDay
36%6%8%19%23%7%
3358
February1st to 10thDay
35%7%9%19%19%11%
1900
11th to 20thDay
28%5%9%19%26%12%
1858
21st to endDay
32%5%12%15%25%11%
1578
March1st to 10thDay
23%6%12%24%24%11%
1980
11th to 20thDay
28%6%12%25%20%10%
1980
21st to endDay
28%5%11%25%22%9%
2178
April1st to 10thDay
30%8%15%22%18%8%
1980
11th to 20thDay
34%10%12%16%21%7%
1956
21st to endDay
27%6%11%23%25%8%
2140
May1st to 10thDay
22%8%12%24%24%10%
2340
11th to 20thDay
39%9%14%19%16%3
2305
21st to endDay
40%11%12%19%16%3
2531
June1st to 10thDay
52%12%17%14%5%
2340
11th to 20thDay
45%15%19%18%3
2340
21st to endDay
47%15%22%14%21
2340
July1st to 10thDay
51%17%23%7%1
2275
11th to 20thDay
52%17%22%9%
2271
21st to endDay
50%16%22%11%1
2405
August1st to 10thDay
48%17%26%8%
2314
11th to 20thDay
52%17%21%9%1
2120
21st to endDay
52%16%20%11%2
2178
September1st to 10thDay
48%18%20%12%2
1980
11th to 20thDay
50%15%19%11%5%
1980
21st to endDay
45%13%14%15%10%3
1980
October1st to 10thDay
43%11%12%16%11%8%
1980
11th to 20thDay
34%7%11%21%22%5%
1830
21st to endDay
31%7%12%18%21%12%
1980
November1st to 10thDay
30%7%11%21%19%12%
1857
11th to 20thDay
36%7%9%20%20%9%
1900
21st to endDay
36%6%10%20%20%8%
1763
December1st to 10thDay
33%7%12%26%16%6%
1710
11th to 20thDay
37%5%11%18%18%12%
2150
21st to endDay
46%6%11%16%15%5%
3124
January1st to 10thNight
44%6%10%17%18%6%
4109
11th to 20thNight
52%48%19%13%5%
4120
21st to endNight
40%7%12%15%19%7%
4294
February1st to 10thNight
36%6%11%18%20%10%
2280
11th to 20thNight
31%6%12%18%23%10%
2219
21st to endNight
32%5%15%18%22%8%
1771
March1st to 10thNight
23%6%11%27%24%8%
1980
11th to 20thNight
28%7%13%28%17%8%
1980
21st to endNight
27%5%11%27%22%7%
2178
April1st to 10thNight
26%6%20%25%17%7%
1980
11th to 20thNight
30%8%14%22%20%5%
1953
21st to endNight
26%5%12%27%23%7%
1825
May1st to 10thNight
18%6%13%29%24%9%
1623
11th to 20thNight
32%10%20%20%16%2
1593
21st to endNight
29%9%19%23%19%2
1745
June1st to 10thNight
41%12%21%20%6%
1620
11th to 20thNight
36%12%28%21%4
1620
21st to endNight
38%18%25%14%5%
1620
July1st to 10thNight
40%20%30%8%2
1575
11th to 20thNight
42%21%28%9%1
1566
21st to endNight
39%21%29%11%
1672
August1st to 10thNight
34%20%35%10%1
1600
11th to 20thNight
38%17%32%12%
1763
21st to endNight
46%19%20%13%2
2171
September1st to 10thNight
41%21%23%13%2
1980
11th to 20thNight
46%15%22%15%2
1980
21st to endNight
43%12%17%16%9%3
1980
October1st to 10thNight
35%12%14%19%13%7%
1980
11th to 20thNight
30%7%12%24%22%5%
2128
21st to endNight
32%6%13%18%22%10%
2376
November1st to 10thNight
28%6%14%20%21%11%
2221
11th to 20thNight
34%7%10%20%20%9%
2280
21st to endNight
35%7%10%23%19%7%
2413
December1st to 10thNight
32%7%14%27%16%5%
2470
11th to 20thNight
36%6%10%19%17%13%
3044
21st to endNight
45%8%13%16%15%4
4532

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
9%15%41%25%9%1
270
11th to 20thDay
10%13%33%31%10%2
270
21st to endDay
15%15%46%17%6%
297
February1st to 10thDay
12%12%33%28%14%1
270
11th to 20thDay
9%10%37%28%11%4
270
21st to endDay
6%13%31%30%18%1
268
March1st to 10thDay
310%38%35%12%1
420
11th to 20thDay
9%9%28%31%21%2
420
21st to endDay
5%9%28%34%21%3
462
April1st to 10thDay
7%10%31%30%19%3
420
11th to 20thDay
8%10%27%32%19%4
412
21st to endDay
6%6%24%30%26%7%
420
May1st to 10thDay
5%417%34%29%10%
423
11th to 20thDay
8%316%28%30%14%
447
21st to endDay
8%28%21%33%27%
485
June1st to 10thDay
15%310%19%28%26%
450
11th to 20thDay
6%38%22%30%31%
450
21st to endDay
42413%31%46%
450
July1st to 10thDay
7%1311%24%54%
445
11th to 20thDay
41315%31%46%
444
21st to endDay
7%2319%27%41%
488
August1st to 10thDay
7%1411%31%46%
446
11th to 20thDay
8%16%12%25%48%
439
21st to endDay
9%27%18%30%35%
495
September1st to 10thDay
9%18%14%29%40%
450
11th to 20thDay
9%26%24%31%27%
450
21st to endDay
7%26%24%34%26%
450
October1st to 10thDay
7%418%36%27%8%
450
11th to 20thDay
6%318%32%33%8%
450
21st to endDay
6%418%40%28%4
495
November1st to 10thDay
10%5%23%33%25%5%
455
11th to 20thDay
11%7%24%35%19%4
460
21st to endDay
8%7%33%32%17%3
323
December1st to 10thDay
6%11%35%27%16%6%
270
11th to 20thDay
10%11%33%30%13%2
270
21st to endDay
8%11%31%34%15%2
297
January1st to 10thNight
11%10%29%37%13%
760
11th to 20thNight
12%8%27%40%12%1
760
21st to endNight
14%9%35%33%9%
836
February1st to 10thNight
16%5%31%34%14%
760
11th to 20thNight
11%7%29%39%12%1
743
21st to endNight
9%6%31%44%10%
611
March1st to 10thNight
6%6%37%43%9%1
720
11th to 20thNight
8%5%31%41%15%1
720
21st to endNight
6%5%31%42%16%
792
April1st to 10thNight
7%5%28%43%16%
720
11th to 20thNight
7%5%32%40%15%1
711
21st to endNight
7%425%45%18%
720
May1st to 10thNight
5%117%47%28%3
543
11th to 20thNight
7%216%42%29%3
531
21st to endNight
5%211%38%39%6%
584
June1st to 10thNight
10%39%27%42%9%
540
11th to 20thNight
6%15%20%45%24%
540
21st to endNight
5%1418%42%29%
540
July1st to 10thNight
8%1211%46%33%
525
11th to 20thNight
7%310%44%36%
522
21st to endNight
5%1412%46%34%
591
August1st to 10thNight
4210%50%33%
537
11th to 20thNight
5%139%42%39%
534
21st to endNight
11%18%21%36%23%
785
September1st to 10thNight
8%19%22%42%18%
720
11th to 20thNight
10%29%26%37%15%
720
21st to endNight
11%211%30%35%11%
720
October1st to 10thNight
9%219%41%25%4
720
11th to 20thNight
6%317%39%31%3
720
21st to endNight
10%320%41%24%2
792
November1st to 10thNight
9%327%37%21%3
740
11th to 20thNight
10%423%41%20%2
760
21st to endNight
9%5%29%43%14%1
760
December1st to 10thNight
8%427%39%22%1
760
11th to 20thNight
11%6%25%38%19%1
760
21st to endNight
10%7%28%39%16%1
836
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