Torrance Barrens Dark-Sky Preserve
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Torrance Barrens Dark-Sky Preserve clear sky chart from 2005-11-05 to 2018-02-14.

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
30%
15320
13%
48492
8%
15286
36%
15286
16%
34883

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
13%
778
7%
2716
3%
776
18%
776
6%
2253
January16th to endNight
20%
832
11%
2708
5%
832
27%
832
9%
2146
February1st to 15thNight
16%
758
8%
2468
3%
757
22%
757
8%
1980
February16th to endNight
20%
631
12%
2034
5%
631
28%
631
12%
1526
March1st to 15thNight
20%
720
13%
1980
5%
720
27%
720
15%
1461
March16th to endNight
30%
768
20%
2112
11%
768
38%
768
23%
1422
April1st to 15thNight
24%
718
14%
1814
6%
718
28%
718
19%
1346
April16th to endNight
32%
545
19%
1625
9%
545
39%
545
21%
1107
May1st to 15thNight
40%
461
16%
1541
13%
461
47%
461
21%
994
May16th to endNight
42%
374
15%
1497
14%
374
51%
374
23%
838
June1st to 15thNight
40%
360
10%
1389
11%
360
45%
360
18%
863
June16th to endNight
47%
360
12%
1260
12%
360
53%
360
23%
781
July1st to 15thNight
59%
340
16%
1223
19%
340
63%
340
34%
650
July16th to endNight
51%
447
15%
1483
15%
419
54%
419
27%
872
August1st to 15thNight
59%
539
17%
1609
13%
536
62%
536
33%
956
August16th to endNight
55%
612
19%
1758
11%
612
59%
612
32%
1094
September1st to 15thNight
47%
720
16%
1806
8%
720
49%
720
31%
1203
September16th to endNight
50%
717
22%
2007
16%
717
54%
717
30%
1288
October1st to 15thNight
33%
720
16%
2160
10%
720
40%
720
19%
1511
October16th to endNight
19%
768
12%
2304
5%
768
26%
768
12%
1802
November1st to 15thNight
27%
760
15%
2626
12%
760
33%
760
15%
1862
November16th to endNight
19%
780
10%
2730
6%
780
24%
780
9%
2165
December1st to 15thNight
11%
780
5%
2730
2%
780
15%
780
6%
2310
December16th to endNight
11%
832
8%
2912
4%
832
17%
832
6%
2453

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
17%10%46%5%34446%31%
49564
Night
17%11%47%6%34446%30%
48662
Cloud CoverDay
18%10%46%5%34446%31%
49574
Night
17%11%47%6%34445%30%
48667
TransparencyDay
53%311%20%9%
49252
Night
55%311%19%9%
48492
SeeingDay
24%10%28%21%10%4
6089
Night
24%10%26%25%10%1
15325

By Month

Percentage Cloud Cover NE (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
21%16%5%10%6%35%335%18%
1529
16th to endDay
15%19%8%11%7%34335%17%
1866
February1st to 15thDay
14%16%8%13%7%45%33318%
1695
16th to endDay
16%16%7%11%7%2443421%
1435
March1st to 15thDay
15%12%46%7%44435%30%
1969
16th to endDay
13%9%46%6%24445%38%
2112
April1st to 15thDay
22%10%46%5%23335%32%
2140
16th to endDay
20%8%34324345%38%
2340
May1st to 15thDay
19%8%25%435%446%35%
2409
16th to endDay
14%7%245%2445%7%40%
2618
June1st to 15thDay
19%7%25%42446%8%34%
2568
16th to endDay
16%6%25%5%35%5%6%8%35%
2700
July1st to 15thDay
12%5%2442446%8%42%
2661
16th to endDay
12%5%35%5%35%5%6%9%38%
2580
August1st to 15thDay
13%6%25%5%3445%7%41%
2340
16th to endDay
13%5%25%5%35%5%6%8%38%
2432
September1st to 15thDay
18%5%25%6%3445%6%38%
2154
16th to endDay
18%5%25%5%2445%6%40%
1953
October1st to 15thDay
24%8%36%424446%31%
1800
16th to endDay
32%8%47%5%3344421%
1920
November1st to 15thDay
21%11%47%6%3445%7%23%
1559
16th to endDay
21%17%5%7%5%45%5%3418%
1560
December1st to 15thDay
19%22%8%10%5%3334414%
1560
16th to endDay
19%21%7%10%7%2434314%
1664
January1st to 15thNight
21%16%7%11%7%3434316%
2716
16th to endNight
16%15%6%10%9%44445%19%
2708
February1st to 15thNight
12%17%7%13%8%45%34419%
2466
16th to endNight
17%12%6%8%6%34346%25%
2034
March1st to 15thNight
17%11%46%6%35%435%31%
1968
16th to endNight
15%8%46%5%23445%40%
2112
April1st to 15thNight
23%9%46%42334433%
1814
16th to endNight
17%8%26%5%2445%6%36%
1625
May1st to 15thNight
19%7%25%42445%6%37%
1541
16th to endNight
12%5%234345%5%8%43%
1495
June1st to 15thNight
15%6%25%6%345%5%7%36%
1389
16th to endNight
12%6%35%435%5%5%8%40%
1260
July1st to 15thNight
7%4335%2345%8%51%
1296
16th to endNight
10%4245%35%46%8%44%
1585
August1st to 15thNight
8%425%5%25%45%8%46%
1620
16th to endNight
11%425%434445%48%
1758
September1st to 15thNight
14%5%25%42435%7%42%
1806
16th to endNight
14%5%245%33346%44%
2007
October1st to 15thNight
20%8%25%5%245%47%33%
2160
16th to endNight
28%9%37%5%3345%5%23%
2304
November1st to 15thNight
19%11%45%5%24347%29%
2626
16th to endNight
24%14%5%7%6%24446%18%
2730
December1st to 15thNight
19%23%8%10%6%2344412%
2730
16th to endNight
22%18%7%10%7%2433414%
2912

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
20%16%6%10%6%24335%18%
1529
16th to endDay
15%19%8%10%7%33345%17%
1866
February1st to 15thDay
14%17%7%13%7%5%433318%
1695
16th to endDay
17%17%6%10%6%4433321%
1435
March1st to 15thDay
16%12%47%6%44436%29%
1980
16th to endDay
13%8%5%5%6%34445%37%
2111
April1st to 15thDay
23%10%35%5%33335%32%
2140
16th to endDay
20%9%24324335%38%
2340
May1st to 15thDay
20%7%245%35%446%34%
2409
16th to endDay
14%7%2443445%7%40%
2618
June1st to 15thDay
19%7%25%42445%8%34%
2568
16th to endDay
16%6%25%5%35%5%6%8%34%
2700
July1st to 15thDay
12%5%244245%5%8%42%
2661
16th to endDay
12%5%25%5%345%6%8%38%
2580
August1st to 15thDay
13%6%26%43445%8%40%
2340
16th to endDay
13%5%25%5%45%45%7%38%
2432
September1st to 15thDay
18%5%35%6%25%445%38%
2154
16th to endDay
17%6%25%434446%39%
1953
October1st to 15thDay
25%8%25%5%34345%31%
1800
16th to endDay
32%8%47%6%3444421%
1920
November1st to 15thDay
22%11%47%6%34446%24%
1559
16th to endDay
22%16%5%7%6%35%445%17%
1560
December1st to 15thDay
20%22%7%11%5%3434313%
1560
16th to endDay
19%20%8%9%6%2343415%
1664
January1st to 15thNight
20%16%8%11%6%3433316%
2716
16th to endNight
16%15%6%10%8%44445%19%
2708
February1st to 15thNight
12%16%7%13%8%45%34419%
2459
16th to endNight
17%12%6%9%6%34445%24%
2034
March1st to 15thNight
17%12%5%7%6%3433431%
1980
16th to endNight
15%8%45%5%23345%40%
2112
April1st to 15thNight
23%9%46%5%2333433%
1814
16th to endNight
17%8%27%5%24446%36%
1625
May1st to 15thNight
18%7%2443435%7%37%
1541
16th to endNight
13%6%134345%6%9%42%
1495
June1st to 15thNight
15%7%25%4445%5%8%36%
1389
16th to endNight
12%6%35%5%25%5%48%39%
1260
July1st to 15thNight
8%435%42335%7%51%
1296
16th to endNight
11%5%235%336%5%7%44%
1585
August1st to 15thNight
9%5%15%5%2446%7%46%
1620
16th to endNight
11%5%245%34347%47%
1758
September1st to 15thNight
14%6%25%4235%48%42%
1806
16th to endNight
14%5%245%43346%45%
2007
October1st to 15thNight
20%7%26%434446%34%
2160
16th to endNight
28%10%47%5%2334424%
2304
November1st to 15thNight
20%12%35%5%34345%30%
2626
16th to endNight
24%14%5%7%6%24446%18%
2730
December1st to 15thNight
20%23%7%9%6%2334412%
2730
16th to endNight
22%18%8%9%7%3333414%
2912

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
69%310%10%5%
1530
16th to endDay
70%36%9%8%1
1866
February1st to 15thDay
71%28%13%3
1697
16th to endDay
68%26%14%7%
1435
March1st to 15thDay
57%313%18%6%
1980
16th to endDay
48%29%19%16%2
2112
April1st to 15thDay
55%28%20%11%
2140
16th to endDay
48%28%23%14%1
2340
May1st to 15thDay
50%29%23%13%1
2409
16th to endDay
42%412%24%13%1
2622
June1st to 15thDay
47%312%25%10%
2568
16th to endDay
45%416%21%11%
2700
July1st to 15thDay
37%415%28%14%
2505
16th to endDay
42%5%11%28%10%
2419
August1st to 15thDay
42%317%23%12%
2327
16th to endDay
43%413%28%8%1
2432
September1st to 15thDay
47%313%25%9%
2154
16th to endDay
44%411%30%8%
1953
October1st to 15thDay
54%310%20%10%
1800
16th to endDay
66%311%12%5%
1920
November1st to 15thDay
61%313%14%6%
1559
16th to endDay
69%310%12%31
1560
December1st to 15thDay
74%29%9%3
1560
16th to endDay
73%37%10%4
1664
January1st to 15thNight
73%38%8%5%
2716
16th to endNight
67%37%12%8%
2708
February1st to 15thNight
69%29%13%4
2468
16th to endNight
61%211%17%7%
2034
March1st to 15thNight
56%212%19%8%
1980
16th to endNight
46%29%22%16%2
2112
April1st to 15thNight
55%27%20%12%1
1814
16th to endNight
48%37%19%18%2
1625
May1st to 15thNight
47%210%20%16%2
1541
16th to endNight
37%415%25%16%1
1497
June1st to 15thNight
45%412%23%14%
1389
16th to endNight
42%314%24%14%
1260
July1st to 15thNight
31%313%29%21%1
1223
16th to endNight
38%412%29%14%
1483
August1st to 15thNight
34%317%28%14%
1609
16th to endNight
37%414%29%13%
1758
September1st to 15thNight
40%416%24%12%1
1806
16th to endNight
41%212%32%10%
2007
October1st to 15thNight
51%410%22%10%
2160
16th to endNight
62%310%15%6%
2304
November1st to 15thNight
55%312%19%7%1
2626
16th to endNight
66%410%14%3
2730
December1st to 15thNight
75%210%8%2
2730
16th to endNight
75%26%9%5%
2912

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
23%17%40%15%3
90
16th to endDay
41%11%31%10%4
143
February1st to 15thDay
34%20%35%9%
130
16th to endDay
39%15%31%13%
82
March1st to 15thDay
25%15%32%21%4
270
16th to endDay
23%11%30%20%11%1
288
April1st to 15thDay
28%12%30%18%8%1
270
16th to endDay
25%13%27%17%11%4
270
May1st to 15thDay
31%8%22%22%8%6%
288
16th to endDay
19%12%31%22%10%3
331
June1st to 15thDay
24%11%25%26%9%1
363
16th to endDay
20%8%36%22%9%1
495
July1st to 15thDay
16%7%29%28%14%5%
439
16th to endDay
15%7%26%29%12%7%
326
August1st to 15thDay
17%420%30%13%13%
313
16th to endDay
18%6%18%25%20%10%
332
September1st to 15thDay
15%6%25%24%17%11%
315
16th to endDay
18%6%22%22%21%8%
314
October1st to 15thDay
27%9%27%21%9%5%
315
16th to endDay
35%16%25%16%5%
336
November1st to 15thDay
28%15%27%18%10%
103
16th to endDay
35%21%32%8%2
90
December1st to 15thDay
36%10%32%15%5%
90
16th to endDay
38%20%30%8%2
96
January1st to 15thNight
31%16%28%18%4
780
16th to endNight
25%12%31%22%7%
832
February1st to 15thNight
22%16%32%22%4
760
16th to endNight
25%15%29%20%6%
631
March1st to 15thNight
25%16%31%21%4
720
16th to endNight
21%11%29%25%10%
768
April1st to 15thNight
30%13%27%22%5%
718
16th to endNight
23%10%28%25%10%
545
May1st to 15thNight
22%7%21%31%14%1
461
16th to endNight
15%5%29%33%15%
375
June1st to 15thNight
19%7%25%34%12%
360
16th to endNight
15%6%24%38%14%
360
July1st to 15thNight
10%221%45%19%1
340
16th to endNight
13%325%35%21%
447
August1st to 15thNight
12%315%39%25%3
539
16th to endNight
12%320%32%28%2
612
September1st to 15thNight
18%5%22%28%20%4
720
16th to endNight
18%5%19%32%20%4
717
October1st to 15thNight
25%8%25%26%11%1
720
16th to endNight
33%14%26%18%6%
768
November1st to 15thNight
27%13%25%23%9%1
760
16th to endNight
35%13%25%19%5%
780
December1st to 15thNight
38%15%27%14%3
780
16th to endNight
34%13%31%17%3
832
Page generated at 2018-02-15 10:58:43. Version ac04

Copyright 2018 A. Danko


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