Brentwood
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brentwood clear sky chart from 2005-11-06 to 2024-01-15.

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
64%
23624
30%
74799
25%
23578
71%
23578
44%
38311

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
55%
756
18%
2595
17%
756
59%
756
24%
1609
January11th to 20thNight
59%
738
22%
2397
19%
738
65%
738
28%
1463
January21st to endNight
59%
792
25%
2574
24%
792
63%
792
30%
1518
February1st to 10thNight
59%
720
27%
2340
25%
720
66%
720
30%
1358
February11th to 20thNight
56%
700
27%
2173
23%
700
65%
700
34%
1207
February21st to endNight
52%
592
28%
1776
23%
592
61%
592
36%
1005
March1st to 10thNight
50%
720
19%
2052
15%
720
57%
720
29%
1303
March11th to 20thNight
53%
720
26%
1980
21%
720
58%
720
32%
1234
March21st to endNight
49%
792
23%
2124
12%
792
58%
792
36%
1282
April1st to 10thNight
51%
720
26%
1800
12%
720
58%
720
38%
1112
April11th to 20thNight
46%
711
31%
1779
11%
711
56%
711
45%
1006
April21st to endNight
54%
720
30%
1800
11%
720
62%
720
58%
933
May1st to 10thNight
59%
676
31%
1756
15%
676
65%
676
57%
891
May11th to 20thNight
67%
426
36%
1488
29%
426
76%
426
58%
597
May21st to endNight
60%
388
32%
1552
25%
388
76%
388
56%
552
June1st to 10thNight
62%
360
30%
1440
27%
360
76%
360
50%
565
June11th to 20thNight
68%
360
38%
1440
36%
360
83%
360
70%
443
June21st to endNight
74%
360
39%
1440
41%
360
85%
360
73%
443
July1st to 10thNight
78%
350
39%
1400
41%
350
90%
350
86%
391
July11th to 20thNight
84%
440
39%
1484
37%
440
88%
440
82%
502
July21st to endNight
81%
591
41%
1674
29%
558
88%
558
80%
642
August1st to 10thNight
76%
537
40%
1602
28%
534
82%
534
76%
626
August11th to 20thNight
79%
665
42%
1733
23%
665
84%
665
87%
717
August21st to endNight
84%
792
44%
1980
27%
792
87%
792
88%
844
September1st to 10thNight
80%
720
46%
1800
28%
720
86%
720
86%
775
September11th to 20thNight
75%
720
46%
1800
30%
720
83%
720
77%
831
September21st to endNight
78%
720
44%
2029
38%
720
85%
720
75%
846
October1st to 10thNight
74%
720
35%
2160
32%
720
82%
720
62%
936
October11th to 20thNight
75%
720
39%
2160
39%
720
82%
720
58%
976
October21st to endNight
73%
792
40%
2376
39%
792
80%
792
57%
1091
November1st to 10thNight
71%
740
33%
2300
31%
740
78%
740
46%
1152
November11th to 20thNight
69%
760
28%
2470
28%
760
74%
760
39%
1293
November21st to endNight
67%
760
29%
2598
30%
760
72%
760
39%
1325
December1st to 10thNight
57%
760
22%
2660
20%
760
63%
760
29%
1531
December11th to 20thNight
53%
760
17%
3242
20%
759
58%
759
17%
2218
December21st to endNight
48%
826
13%
4825
18%
817
56%
817
13%
3094

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%313323346%66%
74732
Night
7%323323346%63%
75065
TransparencyDay
21%5%9%19%26%21%
74448
Night
22%5%9%19%23%20%
74870
SeeingDay
7%9%24%31%22%8%
14193
Night
7%5%19%37%27%5%
23643

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 10thDay
19%7%36%6%345%5%7%35%
1566
11th to 20thDay
11%6%36%6%35%446%47%
1657
21st to endDay
13%7%36%6%35%5%6%6%41%
1782
February1st to 10thDay
13%5%35%5%3445%6%47%
1620
11th to 20thDay
11%5%25%424447%50%
1677
21st to endDay
12%5%144345%5%6%51%
1480
March1st to 10thDay
11%6%36%6%45%5%7%8%41%
1906
11th to 20thDay
12%5%35%5%35%5%6%8%43%
1980
21st to endDay
10%3245%345%5%7%50%
2232
April1st to 10thDay
11%5%2443445%7%50%
2160
11th to 20thDay
7%31342335%5%63%
2129
21st to endDay
4312223448%67%
2160
May1st to 10thDay
331332335%7%68%
2201
11th to 20thDay
3212313246%73%
2403
21st to endDay
2112222337%73%
2723
June1st to 10thDay
221322235%7%71%
2520
11th to 20thDay
1112235%85%
2520
21st to endDay
11111113386%
2520
July1st to 10thDay
11112489%
2520
11th to 20thDay
1111122388%
2423
21st to endDay
1112235%86%
2546
August1st to 10thDay
11121222386%
2328
11th to 20thDay
111113487%
2165
21st to endDay
1111112389%
2376
September1st to 10thDay
1121111289%
2160
11th to 20thDay
111122346%79%
2160
21st to endDay
21121223481%
1927
October1st to 10thDay
1112313335%76%
1800
11th to 20thDay
421221335%5%72%
1800
21st to endDay
5%213323346%68%
1980
November1st to 10thDay
6%414434448%58%
1779
11th to 20thDay
8%5%25%5%4445%7%51%
1710
21st to endDay
10%5%3442335%7%54%
1580
December1st to 10thDay
11%7%36%6%3345%7%45%
1520
11th to 20thDay
23%11%47%5%3445%430%
1928
21st to endDay
14%8%48%7%35%5%6%8%34%
2794
January1st to 10thNight
14%5%25%4345%6%8%43%
2595
11th to 20thNight
11%5%35%5%3446%7%48%
2397
21st to endNight
13%42443445%8%48%
2574
February1st to 10thNight
14%434334435%54%
2340
11th to 20thNight
9%32442445%8%53%
2171
21st to endNight
12%42332345%6%56%
1776
March1st to 10thNight
12%6%245%345%5%6%47%
2052
11th to 20thNight
12%5%2443445%8%50%
1980
21st to endNight
10%42331445%5%58%
2124
April1st to 10thNight
7%424435%45%8%55%
1800
11th to 20thNight
7%223324346%64%
1779
21st to endNight
421221335%8%70%
1800
May1st to 10thNight
3212323346%72%
1756
11th to 20thNight
2111112447%75%
1488
21st to endNight
211212237%78%
1552
June1st to 10thNight
3112322346%74%
1440
11th to 20thNight
1111212487%
1440
21st to endNight
1111223486%
1440
July1st to 10thNight
111112391%
1440
11th to 20thNight
1111112389%
1533
21st to endNight
1111212247%80%
1773
August1st to 10thNight
2111211225%82%
1611
11th to 20thNight
1111236%85%
1733
21st to endNight
111112489%
1980
September1st to 10thNight
111112488%
1800
11th to 20thNight
121211326%81%
1800
21st to endNight
111212235%83%
2029
October1st to 10thNight
3211212345%76%
2160
11th to 20thNight
3111223446%73%
2160
21st to endNight
4212222347%72%
2376
November1st to 10thNight
6%32322245%8%63%
2300
11th to 20thNight
7%32432345%8%57%
2470
21st to endNight
7%32342445%7%59%
2598
December1st to 10thNight
12%6%2442445%5%51%
2660
11th to 20thNight
19%7%36%5%3447%7%34%
3276
21st to endNight
15%6%27%6%45%5%5%6%37%
4862

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
49%7%13%18%11%2
1566
11th to 20thDay
38%7%11%17%20%7%
1657
21st to endDay
42%7%12%14%21%4
1782
February1st to 10thDay
39%5%9%21%19%7%
1620
11th to 20thDay
34%6%11%20%23%6%
1686
21st to endDay
34%5%10%23%21%6%
1480
March1st to 10thDay
42%8%10%20%17%3
1906
11th to 20thDay
39%8%10%21%16%6%
1980
21st to endDay
33%8%14%20%20%4
2232
April1st to 10thDay
33%8%12%21%20%6%
2160
11th to 20thDay
23%5%14%26%25%7%
2132
21st to endDay
17%5%13%29%31%6%
2160
May1st to 10thDay
16%5%9%26%33%10%
2201
11th to 20thDay
14%47%28%34%12%
2406
21st to endDay
13%5%13%33%27%9%
2724
June1st to 10thDay
13%6%10%25%31%15%
2520
11th to 20thDay
5%38%21%35%28%
2520
21st to endDay
7%1311%32%46%
2520
July1st to 10thDay
3148%24%60%
2451
11th to 20thDay
5%15%11%22%55%
2349
21st to endDay
315%6%27%57%
2405
August1st to 10thDay
6%2410%31%47%
2312
11th to 20thDay
41410%34%48%
2165
21st to endDay
31312%34%47%
2376
September1st to 10thDay
5%137%31%53%
2160
11th to 20thDay
8%36%20%39%23%
2160
21st to endDay
9%25%19%38%27%
1927
October1st to 10thDay
13%47%18%30%29%
1800
11th to 20thDay
15%410%21%25%26%
1800
21st to endDay
19%49%20%27%20%
1980
November1st to 10thDay
25%6%9%25%23%11%
1779
11th to 20thDay
32%6%12%24%21%5%
1710
21st to endDay
31%412%20%26%7%
1580
December1st to 10thDay
37%8%12%20%17%7%
1520
11th to 20thDay
57%5%10%13%13%2
1928
21st to endDay
45%10%15%17%11%2
2794
January1st to 10thNight
39%8%13%25%12%5%
2595
11th to 20thNight
36%8%11%19%16%11%
2397
21st to endNight
34%6%14%16%21%8%
2574
February1st to 10thNight
34%5%7%21%23%10%
2340
11th to 20thNight
28%7%11%21%24%9%
2173
21st to endNight
29%5%11%27%22%6%
1776
March1st to 10thNight
37%7%14%18%18%6%
2052
11th to 20thNight
34%7%8%23%20%8%
1980
21st to endNight
28%9%12%23%21%8%
2124
April1st to 10thNight
30%6%14%21%20%9%
1800
11th to 20thNight
23%5%12%28%20%12%
1779
21st to endNight
14%6%13%29%31%8%
1800
May1st to 10thNight
15%5%10%23%33%14%
1756
11th to 20thNight
10%6%9%26%34%15%
1488
21st to endNight
9%5%13%34%28%11%
1552
June1st to 10thNight
13%6%10%22%31%18%
1440
11th to 20thNight
5%38%17%32%35%
1440
21st to endNight
5%2312%30%48%
1440
July1st to 10thNight
3139%21%64%
1400
11th to 20thNight
4249%20%61%
1484
21st to endNight
6%146%22%60%
1674
August1st to 10thNight
8%1312%25%50%
1602
11th to 20thNight
415%9%29%53%
1733
21st to endNight
4148%33%50%
1980
September1st to 10thNight
3238%26%58%
1800
11th to 20thNight
7%37%19%35%30%
1800
21st to endNight
7%26%18%34%33%
2029
October1st to 10thNight
11%49%18%26%32%
2160
11th to 20thNight
13%5%9%19%24%30%
2160
21st to endNight
14%5%7%20%28%26%
2376
November1st to 10thNight
20%6%9%26%22%16%
2300
11th to 20thNight
24%7%11%25%25%7%
2470
21st to endNight
25%5%10%22%27%11%
2598
December1st to 10thNight
34%7%11%20%17%11%
2660
11th to 20thNight
49%6%11%14%16%3
3276
21st to endNight
44%10%13%18%12%3
4862

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
27%10%23%22%16%3
227
11th to 20thDay
16%7%24%25%21%7%
353
21st to endDay
15%7%21%25%22%10%
374
February1st to 10thDay
15%12%19%21%23%10%
340
11th to 20thDay
13%16%25%22%18%7%
381
21st to endDay
12%16%23%27%20%3
346
March1st to 10thDay
15%14%28%27%14%3
420
11th to 20thDay
16%12%27%21%16%7%
420
21st to endDay
13%16%31%24%15%2
462
April1st to 10thDay
13%18%28%21%15%5%
420
11th to 20thDay
8%17%31%25%13%5%
412
21st to endDay
318%28%29%15%7%
420
May1st to 10thDay
5%12%34%29%14%5%
423
11th to 20thDay
5%11%35%27%17%4
448
21st to endDay
312%27%32%22%6%
485
June1st to 10thDay
312%27%34%18%6%
450
11th to 20thDay
11%28%39%19%3
450
21st to endDay
1427%38%26%4
450
July1st to 10thDay
225%43%25%4
446
11th to 20thDay
116%45%32%7%
444
21st to endDay
120%44%25%10%
487
August1st to 10thDay
1421%44%23%7%
447
11th to 20thDay
224%38%24%12%
437
21st to endDay
1117%40%32%9%
495
September1st to 10thDay
417%41%28%10%
450
11th to 20thDay
28%22%37%22%9%
450
21st to endDay
26%20%35%27%11%
450
October1st to 10thDay
27%25%24%30%12%
450
11th to 20thDay
5%6%16%27%31%15%
450
21st to endDay
7%7%17%28%27%15%
495
November1st to 10thDay
7%7%22%21%31%13%
375
11th to 20thDay
7%7%14%29%31%13%
270
21st to endDay
9%7%18%31%30%5%
208
December1st to 10thDay
18%9%19%23%19%11%
180
11th to 20thDay
17%12%17%22%22%11%
180
21st to endDay
19%11%23%23%20%5%
198
January1st to 10thNight
16%417%34%22%7%
760
11th to 20thNight
13%5%16%35%26%5%
738
21st to endNight
15%418%33%26%5%
792
February1st to 10thNight
14%7%14%36%25%5%
720
11th to 20thNight
10%9%19%33%25%5%
704
21st to endNight
12%9%22%35%19%3
592
March1st to 10thNight
15%7%22%31%22%3
720
11th to 20thNight
13%9%22%32%22%3
720
21st to endNight
10%7%29%34%18%1
792
April1st to 10thNight
10%7%26%36%19%2
720
11th to 20thNight
7%11%32%29%18%4
711
21st to endNight
47%32%32%22%3
720
May1st to 10thNight
37%29%38%20%4
676
11th to 20thNight
3423%44%25%2
426
21st to endNight
36%30%41%20%1
389
June1st to 10thNight
2428%47%18%1
360
11th to 20thNight
15%24%50%19%1
360
21st to endNight
1220%50%26%1
360
July1st to 10thNight
119%50%29%1
350
11th to 20thNight
13%49%35%3
440
21st to endNight
1115%40%41%3
591
August1st to 10thNight
2119%39%34%5%
537
11th to 20thNight
118%42%35%4
665
21st to endNight
1111%44%37%5%
792
September1st to 10thNight
1216%39%37%6%
720
11th to 20thNight
2218%42%31%5%
720
21st to endNight
2315%37%36%8%
720
October1st to 10thNight
3416%38%32%7%
720
11th to 20thNight
3415%36%36%6%
720
21st to endNight
5%315%33%32%12%
792
November1st to 10thNight
6%414%35%33%9%
740
11th to 20thNight
7%214%40%31%6%
760
21st to endNight
8%415%36%31%6%
760
December1st to 10thNight
13%5%16%37%24%6%
760
11th to 20thNight
19%5%15%35%23%4
760
21st to endNight
16%8%20%34%20%1
836
Page generated at 2024-01-12 04:31:53. Version ac07

Copyright 2024 Attilla Danko


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