Brentwood
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brentwood clear sky chart from 2005-11-05 to 2019-07-16.

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
68%
17704
30%
54226
26%
17668
73%
17668
45%
27722

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
62%
836
19%
2818
20%
836
65%
836
27%
1710
January16th to endNight
61%
896
22%
2912
23%
896
64%
896
29%
1753
February1st to 15thNight
58%
816
26%
2669
25%
816
65%
816
29%
1589
February16th to endNight
55%
736
25%
2207
21%
736
62%
736
32%
1317
March1st to 15thNight
55%
840
21%
2366
17%
840
60%
840
29%
1511
March16th to endNight
55%
896
22%
2422
15%
896
61%
896
36%
1483
April1st to 15thNight
50%
839
25%
2099
11%
839
57%
839
36%
1329
April16th to endNight
59%
832
27%
2080
12%
832
64%
832
54%
1111
May1st to 15thNight
69%
721
33%
1981
20%
721
74%
721
63%
923
May16th to endNight
66%
438
29%
1752
27%
438
76%
438
51%
680
June1st to 15thNight
70%
420
32%
1680
32%
420
82%
420
55%
621
June16th to endNight
83%
420
37%
1680
44%
420
89%
420
74%
516
July1st to 15thNight
89%
403
39%
1603
47%
403
93%
403
82%
464
July16th to endNight
89%
615
37%
1746
32%
582
92%
582
79%
676
August1st to 15thNight
86%
604
41%
1749
30%
601
89%
601
83%
673
August16th to endNight
90%
828
44%
2070
28%
828
91%
828
89%
882
September1st to 15thNight
86%
780
45%
1950
30%
780
91%
780
83%
862
September16th to endNight
82%
776
44%
2116
38%
776
87%
776
76%
906
October1st to 15thNight
74%
780
35%
2340
33%
780
82%
780
57%
1063
October16th to endNight
78%
832
38%
2496
40%
832
83%
832
56%
1162
November1st to 15thNight
73%
820
32%
2589
32%
820
78%
820
46%
1293
November16th to endNight
66%
840
24%
2825
26%
840
70%
840
34%
1556
December1st to 15thNight
60%
840
22%
2940
22%
840
65%
840
27%
1732
December16th to endNight
52%
896
22%
3136
19%
896
59%
896
24%
1910

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
6%313212346%65%
55097
Night
7%212212346%63%
54411
TransparencyDay
21%48%19%25%19%
54781
Night
22%5%9%20%23%19%
54227
SeeingDay
7%8%22%30%22%8%
8311
Night
7%315%36%30%5%
17718

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
16%6%35%5%23446%39%
1777
16th to endDay
14%6%26%5%25%45%5%41%
2016
February1st to 15thDay
13%6%36%5%24346%44%
1856
16th to endDay
14%5%143245%5%7%44%
1839
March1st to 15thDay
11%5%36%435%46%9%39%
2252
16th to endDay
10%425%6%345%5%7%45%
2506
April1st to 15thDay
11%5%2442435%7%47%
2509
16th to endDay
4212213346%67%
2485
May1st to 15thDay
212212247%71%
2627
16th to endDay
3112323247%68%
3063
June1st to 15thDay
112112246%74%
2940
16th to endDay
11113385%
2940
July1st to 15thDay
112487%
2934
16th to endDay
112486%
2679
August1st to 15thDay
1111387%
2452
16th to endDay
112487%
2484
September1st to 15thDay
111122484%
2340
16th to endDay
111112235%78%
2171
October1st to 15thDay
3112213335%72%
1950
16th to endDay
5%22223346%66%
2080
November1st to 15thDay
7%31332435%7%55%
1930
16th to endDay
11%6%35%32335%7%47%
1795
December1st to 15thDay
13%8%35%5%23445%43%
1680
16th to endDay
14%6%35%42335%7%42%
1792
January1st to 15thNight
13%42432445%7%46%
2818
16th to endNight
13%424423447%47%
2912
February1st to 15thNight
13%324324446%48%
2657
16th to endNight
13%32332335%6%51%
2207
March1st to 15thNight
12%424434447%46%
2366
16th to endNight
11%42231345%6%54%
2422
April1st to 15thNight
8%32343445%8%50%
2099
16th to endNight
412213346%68%
2080
May1st to 15thNight
211112247%74%
1981
16th to endNight
211112337%72%
1752
June1st to 15thNight
111212236%76%
1680
16th to endNight
1112486%
1680
July1st to 15thNight
11389%
1683
16th to endNight
111126%82%
1854
August1st to 15thNight
11116%84%
1758
16th to endNight
1125%86%
2070
September1st to 15thNight
11225%85%
1950
16th to endNight
1111135%81%
2116
October1st to 15thNight
411212336%72%
2340
16th to endNight
32121235%6%69%
2496
November1st to 15thNight
6%312212349%62%
2589
16th to endNight
9%31332345%7%53%
2825
December1st to 15thNight
12%6%2432335%6%49%
2940
16th to endNight
16%5%14323446%46%
3136

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
44%6%12%14%17%2
1777
16th to endDay
44%6%9%15%17%6%
2016
February1st to 15thDay
41%5%10%19%18%4
1856
16th to endDay
38%7%11%23%16%3
1839
March1st to 15thDay
40%9%10%20%14%4
2252
16th to endDay
38%7%13%19%18%3
2506
April1st to 15thDay
35%7%12%21%19%3
2509
16th to endDay
18%413%28%28%7%
2485
May1st to 15thDay
12%48%28%35%10%
2627
16th to endDay
16%5%12%31%23%9%
3067
June1st to 15thDay
12%5%9%23%29%20%
2940
16th to endDay
6%1314%34%39%
2940
July1st to 15thDay
3148%25%56%
2785
16th to endDay
4149%26%52%
2524
August1st to 15thDay
5%1210%31%48%
2436
16th to endDay
3313%38%40%
2484
September1st to 15thDay
5%1412%34%40%
2340
16th to endDay
8%27%20%36%24%
2171
October1st to 15thDay
14%48%20%26%24%
1950
16th to endDay
19%410%24%26%15%
2080
November1st to 15thDay
27%6%11%27%20%6%
1930
16th to endDay
36%6%12%21%20%3
1795
December1st to 15thDay
42%5%10%18%18%4
1680
16th to endDay
40%7%13%18%16%3
1792
January1st to 15thNight
36%7%11%23%15%6%
2818
16th to endNight
36%6%11%17%16%11%
2912
February1st to 15thNight
35%5%9%21%20%7%
2669
16th to endNight
31%7%11%24%20%3
2207
March1st to 15thNight
36%7%12%20%16%7%
2366
16th to endNight
30%7%11%22%21%6%
2422
April1st to 15thNight
32%6%13%23%18%5%
2099
16th to endNight
16%6%13%27%27%9%
2080
May1st to 15thNight
11%48%25%33%15%
1982
16th to endNight
12%5%13%31%24%12%
1752
June1st to 15thNight
11%49%21%28%24%
1680
16th to endNight
5%2314%28%46%
1680
July1st to 15thNight
427%23%61%
1603
16th to endNight
5%25%8%20%57%
1746
August1st to 15thNight
5%311%26%52%
1749
16th to endNight
349%36%45%
2070
September1st to 15thNight
42411%29%47%
1950
16th to endNight
7%26%19%32%32%
2116
October1st to 15thNight
13%49%20%25%25%
2340
16th to endNight
14%5%7%22%26%23%
2496
November1st to 15thNight
20%6%11%28%20%12%
2589
16th to endNight
29%6%10%22%24%6%
2825
December1st to 15thNight
36%5%10%18%19%9%
2940
16th to endNight
38%6%11%19%17%5%
3136

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%6%20%24%16%4
225
16th to endDay
16%5%22%24%21%9%
352
February1st to 15thDay
16%12%20%20%19%10%
329
16th to endDay
16%15%23%23%16%4
342
March1st to 15thDay
16%13%26%20%15%7%
390
16th to endDay
13%14%26%26%13%4
416
April1st to 15thDay
15%20%26%19%14%4
389
16th to endDay
5%18%25%26%16%8%
378
May1st to 15thDay
5%11%32%31%15%4
408
16th to endDay
410%29%29%21%4
458
June1st to 15thDay
211%27%32%18%6%
435
16th to endDay
1425%38%25%4
435
July1st to 15thDay
20%42%29%6%
425
16th to endDay
115%42%26%13%
392
August1st to 15thDay
1319%39%26%9%
359
16th to endDay
116%36%30%14%
396
September1st to 15thDay
417%41%25%10%
375
16th to endDay
15%20%31%25%15%
375
October1st to 15thDay
48%25%27%24%9%
375
16th to endDay
7%414%27%28%18%
400
November1st to 15thDay
8%415%25%35%12%
256
16th to endDay
13%6%15%28%32%3
153
December1st to 15thDay
18%10%17%23%18%11%
120
16th to endDay
13%14%17%21%25%8%
128
January1st to 15thNight
15%312%33%28%7%
840
16th to endNight
14%315%33%26%7%
896
February1st to 15thNight
14%5%14%32%27%5%
824
16th to endNight
13%7%18%33%22%4
736
March1st to 15thNight
14%6%17%31%25%4
840
16th to endNight
11%5%22%35%21%2
896
April1st to 15thNight
9%7%25%35%19%2
839
16th to endNight
5%6%25%31%25%4
832
May1st to 15thNight
2322%41%25%4
722
16th to endNight
3324%43%24%
439
June1st to 15thNight
2321%51%20%1
420
16th to endNight
13%53%29%1
420
July1st to 15thNight
8%51%37%1
403
16th to endNight
6%38%50%4
615
August1st to 15thNight
19%39%43%5%
604
16th to endNight
7%40%45%6%
828
September1st to 15thNight
18%38%43%6%
780
16th to endNight
1110%36%39%9%
776
October1st to 15thNight
3413%38%31%7%
780
16th to endNight
3212%31%37%12%
832
November1st to 15thNight
6%113%35%34%7%
820
16th to endNight
10%313%33%31%8%
840
December1st to 15thNight
13%414%35%24%7%
840
16th to endNight
16%6%17%33%23%2
896
Page generated at 2019-07-17 05:53:08. Version ac04

Copyright 2019 A. Danko


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