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 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
69%
15371
30%
46980
26%
15335
74%
15335
46%
23964

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
64%
716
20%
2414
20%
716
67%
716
30%
1406
January16th to endNight
63%
768
25%
2496
25%
768
66%
768
31%
1467
February1st to 15thNight
59%
696
24%
2281
23%
696
65%
696
28%
1372
February16th to endNight
58%
632
25%
1895
21%
632
65%
632
32%
1145
March1st to 15thNight
56%
720
20%
2028
17%
720
61%
720
31%
1271
March16th to endNight
55%
768
23%
2076
15%
768
61%
768
36%
1272
April1st to 15thNight
51%
719
25%
1799
12%
719
57%
719
37%
1131
April16th to endNight
57%
720
27%
1800
11%
720
63%
720
52%
982
May1st to 15thNight
68%
617
31%
1697
20%
617
73%
617
63%
792
May16th to endNight
69%
374
31%
1496
30%
374
78%
374
55%
548
June1st to 15thNight
70%
360
30%
1440
30%
360
80%
360
53%
544
June16th to endNight
83%
360
39%
1440
47%
360
89%
360
76%
439
July1st to 15thNight
91%
343
36%
1363
45%
343
94%
343
83%
391
July16th to endNight
89%
564
39%
1593
33%
531
92%
531
79%
619
August1st to 15thNight
86%
566
40%
1639
29%
563
88%
563
82%
635
August16th to endNight
89%
764
45%
1910
29%
764
90%
764
88%
818
September1st to 15thNight
87%
720
43%
1800
29%
720
91%
720
83%
797
September16th to endNight
82%
692
45%
1881
39%
692
87%
692
75%
815
October1st to 15thNight
75%
660
33%
1980
32%
660
82%
660
55%
918
October16th to endNight
76%
704
37%
2112
38%
704
81%
704
52%
1019
November1st to 15thNight
72%
700
30%
2211
30%
700
78%
700
45%
1113
November16th to endNight
67%
720
26%
2421
26%
720
71%
720
36%
1293
December1st to 15thNight
58%
720
21%
2520
19%
720
64%
720
25%
1527
December16th to endNight
52%
768
21%
2688
19%
768
59%
768
24%
1650

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%313212345%65%
47957
Night
7%212212346%64%
47165
TransparencyDay
21%49%19%25%20%
47641
Night
21%5%9%20%23%19%
46981
SeeingDay
7%9%23%31%21%7%
5990
Night
7%315%36%30%5%
15385

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
15%6%35%5%23446%44%
1522
16th to endDay
15%6%26%435%34443%
1728
February1st to 15thDay
14%6%35%5%33345%43%
1584
16th to endDay
15%5%2432445%8%43%
1579
March1st to 15thDay
10%5%35%43446%10%40%
1930
16th to endDay
9%325%6%345%5%7%45%
2148
April1st to 15thDay
11%42442436%7%47%
2149
16th to endDay
5%212213346%66%
2160
May1st to 15thDay
212212246%72%
2251
16th to endDay
3112213237%70%
2615
June1st to 15thDay
2212212246%72%
2520
16th to endDay
1113385%
2520
July1st to 15thDay
112487%
2514
16th to endDay
112386%
2468
August1st to 15thDay
1111387%
2310
16th to endDay
112486%
2292
September1st to 15thDay
111122484%
2160
16th to endDay
21112235%77%
1934
October1st to 15thDay
3212213336%71%
1650
16th to endDay
6%22323345%65%
1760
November1st to 15thDay
7%41332445%7%54%
1648
16th to endDay
10%6%35%42335%7%48%
1539
December1st to 15thDay
14%7%35%6%23445%42%
1440
16th to endDay
16%6%35%32335%7%42%
1536
January1st to 15thNight
12%42432345%7%49%
2414
16th to endNight
13%423323447%49%
2496
February1st to 15thNight
13%434324446%47%
2269
16th to endNight
13%42332345%7%49%
1895
March1st to 15thNight
12%423424347%48%
2028
16th to endNight
10%42231445%6%54%
2076
April1st to 15thNight
9%323425%45%7%51%
1799
16th to endNight
5%212213346%67%
1800
May1st to 15thNight
211112236%75%
1697
16th to endNight
21112237%75%
1496
June1st to 15thNight
211212236%76%
1440
16th to endNight
1112486%
1440
July1st to 15thNight
11389%
1443
16th to endNight
111126%82%
1701
August1st to 15thNight
1111116%83%
1648
16th to endNight
1125%86%
1910
September1st to 15thNight
11225%85%
1800
16th to endNight
11111125%81%
1881
October1st to 15thNight
411212447%69%
1980
16th to endNight
32221335%6%67%
2112
November1st to 15thNight
6%312212349%62%
2211
16th to endNight
8%31332345%6%56%
2421
December1st to 15thNight
13%6%2432435%6%47%
2520
16th to endNight
17%5%24323446%46%
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
40%6%13%16%19%3
1522
16th to endDay
43%6%9%14%18%7%
1728
February1st to 15thDay
42%5%10%20%17%3
1584
16th to endDay
39%7%11%25%13%3
1579
March1st to 15thDay
38%9%11%20%15%4
1930
16th to endDay
37%8%14%18%18%3
2148
April1st to 15thDay
35%7%12%21%19%3
2149
16th to endDay
19%414%26%27%7%
2160
May1st to 15thDay
12%47%27%36%11%
2251
16th to endDay
15%411%30%26%11%
2619
June1st to 15thDay
14%5%9%23%25%21%
2520
16th to endDay
5%1314%33%40%
2520
July1st to 15thDay
3148%23%58%
2365
16th to endDay
4148%25%55%
2313
August1st to 15thDay
5%1211%30%47%
2294
16th to endDay
31312%38%41%
2292
September1st to 15thDay
5%1413%35%40%
2160
16th to endDay
9%27%21%36%22%
1934
October1st to 15thDay
15%49%22%27%20%
1650
16th to endDay
21%49%24%25%13%
1760
November1st to 15thDay
28%7%12%28%18%5%
1648
16th to endDay
35%6%12%20%21%3
1539
December1st to 15thDay
44%5%10%19%17%3
1440
16th to endDay
41%6%14%17%15%3
1536
January1st to 15thNight
33%6%11%23%17%7%
2414
16th to endNight
34%5%11%17%17%13%
2496
February1st to 15thNight
35%6%10%22%18%6%
2281
16th to endNight
32%8%12%25%18%3
1895
March1st to 15thNight
35%6%12%21%16%7%
2028
16th to endNight
29%8%12%22%19%7%
2076
April1st to 15thNight
31%5%14%24%17%6%
1799
16th to endNight
17%6%14%23%26%10%
1800
May1st to 15thNight
11%5%8%23%34%17%
1698
16th to endNight
11%412%31%27%13%
1496
June1st to 15thNight
11%5%9%21%26%25%
1440
16th to endNight
42313%28%47%
1440
July1st to 15thNight
327%21%64%
1363
16th to endNight
5%248%20%58%
1593
August1st to 15thNight
5%311%27%50%
1639
16th to endNight
439%36%45%
1910
September1st to 15thNight
42411%29%47%
1800
16th to endNight
8%26%20%34%28%
1881
October1st to 15thNight
14%5%10%22%26%21%
1980
16th to endNight
16%6%7%24%26%19%
2112
November1st to 15thNight
20%6%12%30%20%9%
2211
16th to endNight
27%5%9%23%25%7%
2421
December1st to 15thNight
38%6%10%18%20%6%
2520
16th to endNight
38%6%11%17%18%6%
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
24%6%22%25%16%6%
150
16th to endDay
18%5%21%22%19%12%
256
February1st to 15thDay
17%10%20%20%21%9%
237
16th to endDay
17%12%22%23%18%6%
238
March1st to 15thDay
14%12%26%19%18%8%
270
16th to endDay
11%17%29%24%13%3
288
April1st to 15thDay
15%20%29%17%12%5%
269
16th to endDay
6%22%27%27%11%4
270
May1st to 15thDay
5%12%35%28%14%3
288
16th to endDay
311%27%30%22%5%
330
June1st to 15thDay
314%32%33%12%3
315
16th to endDay
424%39%26%4
315
July1st to 15thDay
21%44%27%4
305
16th to endDay
117%45%24%9%
327
August1st to 15thDay
1420%41%24%6%
315
16th to endDay
118%36%30%12%
332
September1st to 15thDay
216%43%26%10%
315
16th to endDay
27%22%31%21%14%
288
October1st to 15thDay
5%9%20%28%23%12%
255
16th to endDay
11%5%16%32%22%11%
272
November1st to 15thDay
8%6%14%19%35%15%
154
16th to endDay
7%10%19%36%25%
77
December1st to 15thDay
23%15%23%25%13%
60
16th to endDay
14%15%15%21%25%7%
64
January1st to 15thNight
13%312%33%29%8%
720
16th to endNight
14%314%32%26%8%
768
February1st to 15thNight
13%5%13%33%27%5%
704
16th to endNight
13%6%16%34%22%5%
632
March1st to 15thNight
14%5%18%30%26%4
720
16th to endNight
10%6%24%34%21%2
768
April1st to 15thNight
8%7%25%35%20%2
719
16th to endNight
6%7%26%31%24%4
720
May1st to 15thNight
2223%42%24%4
618
16th to endNight
3222%42%27%1
375
June1st to 15thNight
1321%52%19%
360
16th to endNight
13%52%31%1
360
July1st to 15thNight
6%51%40%1
343
16th to endNight
6%38%50%4
564
August1st to 15thNight
19%39%43%5%
566
16th to endNight
7%40%45%6%
764
September1st to 15thNight
18%38%44%7%
720
16th to endNight
2110%35%39%10%
692
October1st to 15thNight
4313%37%33%8%
660
16th to endNight
4212%33%34%12%
704
November1st to 15thNight
6%114%34%34%8%
700
16th to endNight
8%314%34%31%8%
720
December1st to 15thNight
14%5%14%35%22%7%
720
16th to endNight
17%6%18%34%22%2
768
Page generated at 2017-09-25 06:02:18. Version ac04

Copyright 2017 A. Danko


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