Sea Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sea Ranch clear sky chart from 2005-11-05 to 2017-09-18.

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
50%
15320
26%
46939
19%
15282
59%
15282
31%
26337

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
46%
717
18%
2350
14%
716
52%
716
21%
1455
January16th to endNight
45%
768
26%
2496
21%
768
54%
768
22%
1546
February1st to 15thNight
40%
700
22%
2288
19%
700
46%
700
19%
1462
February16th to endNight
37%
632
21%
1935
12%
632
49%
632
21%
1236
March1st to 15thNight
39%
720
14%
1980
10%
720
43%
720
19%
1401
March16th to endNight
34%
768
20%
2112
10%
768
43%
768
24%
1375
April1st to 15thNight
33%
719
22%
1814
8%
719
40%
719
24%
1209
April16th to endNight
38%
699
27%
1779
9%
699
47%
699
34%
1027
May1st to 15thNight
44%
539
29%
1619
13%
539
56%
539
38%
794
May16th to endNight
45%
437
26%
1559
16%
436
59%
436
33%
725
June1st to 15thNight
45%
360
24%
1440
17%
360
60%
360
29%
690
June16th to endNight
56%
360
34%
1440
31%
360
74%
360
47%
520
July1st to 15thNight
72%
423
30%
1443
29%
423
79%
423
57%
549
July16th to endNight
69%
564
35%
1593
27%
531
81%
531
50%
726
August1st to 15thNight
75%
538
37%
1611
27%
535
80%
535
57%
685
August16th to endNight
72%
717
40%
1863
22%
717
79%
717
53%
938
September1st to 15thNight
72%
720
40%
1800
24%
720
77%
720
59%
892
September16th to endNight
68%
667
39%
1858
28%
667
78%
667
54%
884
October1st to 15thNight
59%
660
30%
1980
27%
660
67%
660
40%
1033
October16th to endNight
58%
704
33%
2112
26%
704
70%
704
34%
1157
November1st to 15thNight
52%
700
24%
2139
20%
700
58%
700
30%
1237
November16th to endNight
45%
720
20%
2520
18%
720
52%
720
22%
1474
December1st to 15thNight
41%
720
20%
2520
18%
720
48%
720
18%
1590
December16th to endNight
37%
768
20%
2688
17%
768
44%
768
18%
1732

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
10%413313347%55%
47849
Night
12%413323347%53%
47130
TransparencyDay
28%38%21%23%13%
47540
Night
31%38%19%22%14%
46940
SeeingDay
11%17%22%25%18%5%
6071
Night
12%19%12%23%24%8%
15328

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
19%5%25%423447%40%
1586
16th to endDay
20%5%25%32435%6%41%
1728
February1st to 15thDay
23%5%2442335%6%38%
1576
16th to endDay
21%6%2442345%7%36%
1535
March1st to 15thDay
22%6%45%424447%33%
1980
16th to endDay
19%6%2432345%7%39%
2112
April1st to 15thDay
16%6%245%2445%8%39%
2134
16th to endDay
9%32332435%9%52%
2178
May1st to 15thDay
6%3221336%9%61%
2331
16th to endDay
7%41331325%9%58%
2550
June1st to 15thDay
6%413223347%60%
2520
16th to endDay
311111235%76%
2520
July1st to 15thDay
11112236%78%
2427
16th to endDay
1112121410%71%
2468
August1st to 15thDay
121111248%72%
2340
16th to endDay
2221225%9%69%
2339
September1st to 15thDay
11121122310%71%
2160
16th to endDay
422112237%70%
1823
October1st to 15thDay
10%213212245%62%
1650
16th to endDay
12%41431335%8%50%
1760
November1st to 15thDay
10%423325%45%8%48%
1716
16th to endDay
17%5%24424246%46%
1440
December1st to 15thDay
23%7%24423336%37%
1440
16th to endDay
26%6%3332345%6%34%
1536
January1st to 15thNight
18%5%2432445%7%40%
2350
16th to endNight
21%5%23313347%43%
2496
February1st to 15thNight
22%5%2342345%5%40%
2276
16th to endNight
20%6%1322446%8%39%
1935
March1st to 15thNight
21%6%25%425%5%46%35%
1980
16th to endNight
20%415%313346%44%
2112
April1st to 15thNight
13%7%25%42435%7%42%
1814
16th to endNight
8%323323236%59%
1779
May1st to 15thNight
4313222339%63%
1619
16th to endNight
432321225%8%60%
1558
June1st to 15thNight
5%6%13223348%58%
1440
16th to endNight
31111122478%
1440
July1st to 15thNight
111112235%78%
1530
16th to endNight
2311112338%70%
1701
August1st to 15thNight
21112247%74%
1620
16th to endNight
1312212236%71%
1863
September1st to 15thNight
211212236%74%
1800
16th to endNight
421111236%72%
1858
October1st to 15thNight
7%323312235%62%
1980
16th to endNight
12%413222248%55%
2112
November1st to 15thNight
14%3133235%5%9%48%
2139
16th to endNight
17%42432345%7%45%
2520
December1st to 15thNight
25%5%1332335%7%38%
2520
16th to endNight
24%5%24313336%39%
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
43%311%19%12%8%
1586
16th to endDay
42%47%16%17%11%
1728
February1st to 15thDay
44%39%17%20%3
1576
16th to endDay
45%411%24%11%3
1535
March1st to 15thDay
50%411%15%14%4
1980
16th to endDay
43%412%20%14%3
2112
April1st to 15thDay
41%215%25%12%1
2134
16th to endDay
28%415%24%21%5%
2178
May1st to 15thDay
19%211%32%25%7%
2331
16th to endDay
24%314%31%21%5%
2554
June1st to 15thDay
24%311%24%25%10%
2520
16th to endDay
12%2417%40%22%
2520
July1st to 15thDay
8%3314%35%33%
2285
16th to endDay
13%2312%30%37%
2313
August1st to 15thDay
13%2321%29%28%
2324
16th to endDay
14%3318%35%23%
2339
September1st to 15thDay
11%3321%32%27%
2160
16th to endDay
16%2327%29%20%
1823
October1st to 15thDay
24%26%24%27%13%
1650
16th to endDay
30%38%25%23%9%
1760
November1st to 15thDay
32%5%12%30%11%7%
1716
16th to endDay
40%312%19%18%6%
1440
December1st to 15thDay
47%48%18%17%3
1440
16th to endDay
49%39%17%15%5%
1536
January1st to 15thNight
41%313%19%13%8%
2350
16th to endNight
41%27%18%17%12%
2496
February1st to 15thNight
45%39%19%17%6%
2288
16th to endNight
42%312%22%15%3
1935
March1st to 15thNight
48%411%14%16%4
1980
16th to endNight
41%312%22%15%3
2112
April1st to 15thNight
40%413%23%15%2
1814
16th to endNight
27%39%30%22%6%
1779
May1st to 15thNight
21%38%26%30%10%
1620
16th to endNight
22%313%33%19%8%
1559
June1st to 15thNight
26%410%22%24%12%
1440
16th to endNight
13%15%14%37%27%
1440
July1st to 15thNight
10%2110%33%41%
1443
16th to endNight
15%337%26%43%
1593
August1st to 15thNight
11%3217%29%35%
1611
16th to endNight
17%2213%30%32%
1863
September1st to 15thNight
13%3112%34%34%
1800
16th to endNight
15%2320%31%25%
1858
October1st to 15thNight
25%25%21%28%15%
1980
16th to endNight
29%26%22%27%11%
2112
November1st to 15thNight
33%415%23%14%8%
2139
16th to endNight
37%410%22%19%6%
2520
December1st to 15thNight
45%28%20%17%4
2520
16th to endNight
46%39%17%18%5%
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
25%21%14%17%16%3
215
16th to endDay
23%19%14%21%17%3
256
February1st to 15thDay
24%19%20%19%14%1
236
16th to endDay
18%25%23%18%11%2
227
March1st to 15thDay
24%20%25%17%9%3
270
16th to endDay
18%25%31%18%42
288
April1st to 15thDay
17%27%21%21%10%1
269
16th to endDay
12%31%28%18%6%3
270
May1st to 15thDay
8%22%35%17%14%1
288
16th to endDay
7%22%20%23%18%6%
330
June1st to 15thDay
6%21%28%30%10%3
315
16th to endDay
313%32%28%19%3
315
July1st to 15thDay
11%16%34%27%9%
305
16th to endDay
11%17%34%27%9%
327
August1st to 15thDay
39%18%35%27%5%
315
16th to endDay
7%18%34%30%9%
332
September1st to 15thDay
28%19%32%25%11%
315
16th to endDay
5%13%17%29%23%11%
264
October1st to 15thDay
10%14%19%23%20%11%
255
16th to endDay
15%11%25%25%18%3
272
November1st to 15thDay
10%18%15%25%23%6%
223
16th to endDay
11%13%38%16%15%5%
60
December1st to 15thDay
43%11%18%21%13
60
16th to endDay
18%15%14%20%20%10%
64
January1st to 15thNight
18%19%7%21%24%8%
720
16th to endNight
21%20%6%19%24%8%
768
February1st to 15thNight
20%21%10%19%19%7%
704
16th to endNight
19%21%15%23%14%4
632
March1st to 15thNight
19%23%11%21%19%5%
720
16th to endNight
18%22%20%22%13%3
768
April1st to 15thNight
11%26%19%20%15%5%
719
16th to endNight
9%27%20%22%14%5%
699
May1st to 15thNight
423%22%26%16%5%
540
16th to endNight
425%17%25%20%6%
437
June1st to 15thNight
5%23%19%26%23%1
360
16th to endNight
419%17%38%16%2
360
July1st to 15thNight
212%9%26%32%15%
423
16th to endNight
418%423%35%13%
564
August1st to 15thNight
210%7%29%36%13%
538
16th to endNight
310%7%24%43%11%
717
September1st to 15thNight
210%9%22%38%15%
720
16th to endNight
6%12%7%26%32%13%
667
October1st to 15thNight
7%14%11%23%30%12%
660
16th to endNight
13%13%7%24%29%11%
704
November1st to 15thNight
13%17%11%20%30%8%
700
16th to endNight
15%21%10%22%23%6%
720
December1st to 15thNight
23%20%10%23%17%5%
720
16th to endNight
19%23%13%21%18%4
768
Page generated at 2017-09-19 04:32:31. Version ac04

Copyright 2017 A. Danko


Sea Ranch Clear Sky Chart | Charts Home