TwinOaks Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the TwinOaks Observatory clear sky chart from 2005-11-05 to 2017-12-04.

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
47%
16091
23%
47841
15%
16053
55%
16053
28%
29816

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
31%
717
23%
2327
12%
716
46%
716
22%
1409
January16th to endNight
27%
768
25%
2496
12%
768
43%
768
24%
1503
February1st to 15thNight
27%
702
23%
2235
9%
701
44%
701
25%
1336
February16th to endNight
24%
631
27%
1863
10%
631
43%
631
27%
1139
March1st to 15thNight
31%
720
26%
1980
13%
720
43%
720
31%
1216
March16th to endNight
34%
768
21%
2112
10%
768
43%
768
26%
1377
April1st to 15thNight
37%
718
24%
1925
11%
718
47%
718
33%
1179
April16th to endNight
44%
638
25%
1718
13%
638
51%
638
33%
1055
May1st to 15thNight
47%
540
17%
1620
9%
540
54%
540
27%
1019
May16th to endNight
59%
561
18%
1683
15%
561
61%
561
28%
1078
June1st to 15thNight
62%
540
15%
1620
12%
540
64%
540
25%
1095
June16th to endNight
65%
540
15%
1620
12%
540
66%
540
26%
1061
July1st to 15thNight
65%
510
11%
1530
8%
510
66%
510
26%
1027
July16th to endNight
68%
564
14%
1595
11%
531
70%
531
26%
1067
August1st to 15thNight
67%
539
15%
1609
14%
536
67%
536
26%
1075
August16th to endNight
64%
666
18%
1812
13%
666
65%
666
27%
1259
September1st to 15thNight
66%
720
20%
1971
16%
720
68%
720
32%
1250
September16th to endNight
54%
717
20%
1980
16%
717
58%
717
25%
1363
October1st to 15thNight
52%
720
28%
2109
24%
720
59%
720
33%
1257
October16th to endNight
49%
768
35%
2304
24%
768
65%
768
37%
1270
November1st to 15thNight
50%
760
29%
2310
21%
760
61%
760
36%
1288
November16th to endNight
46%
780
29%
2535
21%
780
57%
780
29%
1435
December1st to 15thNight
40%
736
23%
2391
16%
736
50%
736
24%
1468
December16th to endNight
34%
768
24%
2496
17%
768
44%
768
22%
1590

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
13%42442445%7%43%
48650
Night
13%5%2442445%7%45%
48040
TransparencyDay
38%6%11%20%18%4
48351
Night
37%5%11%19%19%6%
47843
SeeingDay
15%6%21%24%21%10%
5914
Night
15%8%22%30%20%3
16098

By Month

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
17%7%24423245%43%
1611
16th to endDay
15%5%2432334449%
1728
February1st to 15thDay
15%5%13424446%46%
1624
16th to endDay
16%5%24322436%48%
1608
March1st to 15thDay
15%323223446%49%
1980
16th to endDay
17%5%243245%46%43%
2111
April1st to 15thDay
13%31332345%7%49%
2023
16th to endDay
13%424414446%47%
2252
May1st to 15thDay
12%415%426%5%6%7%41%
2331
16th to endDay
11%5%245%25%449%42%
2431
June1st to 15thDay
9%4245%36%5%6%10%39%
2340
16th to endDay
6%225%6%46%6%7%10%42%
2340
July1st to 15thDay
9%5%36%6%36%6%7%9%34%
2340
16th to endDay
7%425%6%48%6%7%11%33%
2465
August1st to 15thDay
13%5%25%6%45%7%7%10%30%
2340
16th to endDay
12%5%26%5%46%6%7%10%32%
2378
September1st to 15thDay
10%425%5%35%46%8%43%
1986
16th to endDay
17%6%244245%46%40%
1980
October1st to 15thDay
17%41331232454%
1851
16th to endDay
12%323312235%59%
1920
November1st to 15thDay
14%423312235%54%
1877
16th to endDay
14%413313445%51%
1755
December1st to 15thDay
17%6%2332335%6%44%
1651
16th to endDay
22%6%23423345%40%
1728
January1st to 15thNight
16%5%1442334448%
2327
16th to endNight
17%6%24323345%47%
2496
February1st to 15thNight
15%5%23424345%48%
2227
16th to endNight
13%42442345%5%48%
1863
March1st to 15thNight
14%423323446%49%
1980
16th to endNight
14%5%25%42335%7%44%
2112
April1st to 15thNight
12%423414347%50%
1925
16th to endNight
12%4245%24447%49%
1718
May1st to 15thNight
10%425%445%45%9%43%
1619
16th to endNight
10%415%5%35%5%5%10%42%
1682
June1st to 15thNight
10%5%25%5%37%6%7%9%35%
1620
16th to endNight
6%425%6%46%7%8%10%37%
1620
July1st to 15thNight
8%5%25%5%36%6%9%12%32%
1620
16th to endNight
7%425%5%37%7%8%11%35%
1703
August1st to 15thNight
11%6%15%5%35%6%8%12%33%
1620
16th to endNight
9%5%35%6%36%6%7%11%34%
1812
September1st to 15thNight
9%3246%345%6%10%43%
1971
16th to endNight
17%5%245%25%45%5%39%
1980
October1st to 15thNight
17%413312335%52%
2109
16th to endNight
11%413322335%58%
2304
November1st to 15thNight
13%313313236%56%
2310
16th to endNight
12%313423445%51%
2535
December1st to 15thNight
16%6%25%424345%46%
2391
16th to endNight
21%5%14423246%41%
2496

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%37%17%22%5%
1612
16th to endDay
37%36%21%22%8%
1728
February1st to 15thDay
38%39%20%23%4
1626
16th to endDay
37%47%25%20%5%
1608
March1st to 15thDay
35%48%21%23%6%
1980
16th to endDay
40%5%11%20%18%3
2112
April1st to 15thDay
32%311%24%22%5%
2023
16th to endDay
36%5%10%18%21%7%
2252
May1st to 15thDay
38%7%14%20%16%2
2331
16th to endDay
38%6%14%24%14%1
2435
June1st to 15thDay
38%8%14%26%11%
2340
16th to endDay
34%9%17%21%15%2
2340
July1st to 15thDay
41%10%17%18%9%2
2201
16th to endDay
38%11%17%20%10%1
2310
August1st to 15thDay
45%9%15%17%10%1
2327
16th to endDay
44%8%16%18%10%1
2378
September1st to 15thDay
36%7%13%21%17%3
1986
16th to endDay
43%6%8%19%17%5%
1980
October1st to 15thDay
35%38%21%25%5%
1851
16th to endDay
29%26%21%30%9%
1920
November1st to 15thDay
32%28%19%28%8%
1877
16th to endDay
33%48%20%24%8%
1755
December1st to 15thDay
41%39%22%19%4
1651
16th to endDay
46%39%17%17%6%
1728
January1st to 15thNight
39%39%16%24%7%
2327
16th to endNight
39%26%19%23%7%
2496
February1st to 15thNight
38%27%21%23%6%
2236
16th to endNight
37%39%21%23%5%
1863
March1st to 15thNight
35%410%20%21%8%
1980
16th to endNight
40%410%19%19%5%
2112
April1st to 15thNight
34%38%22%24%6%
1925
16th to endNight
34%49%21%20%8%
1718
May1st to 15thNight
37%7%15%20%16%3
1620
16th to endNight
36%8%12%26%14%1
1684
June1st to 15thNight
40%9%16%21%10%1
1620
16th to endNight
36%11%15%21%11%3
1620
July1st to 15thNight
38%11%20%18%8%3
1530
16th to endNight
37%12%19%19%9%2
1595
August1st to 15thNight
38%10%19%19%10%1
1609
16th to endNight
40%9%18%20%9%
1812
September1st to 15thNight
34%8%16%19%16%5%
1971
16th to endNight
44%6%11%15%18%4
1980
October1st to 15thNight
34%49%20%24%6%
2109
16th to endNight
29%26%20%26%13%
2304
November1st to 15thNight
31%27%18%27%12%
2310
16th to endNight
33%36%19%27%9%
2535
December1st to 15thNight
40%38%20%19%7%
2391
16th to endNight
44%29%17%18%6%
2496

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
30%12%34%17%5%
90
16th to endDay
18%25%41%11%3
96
February1st to 15thDay
20%22%51%5%1
90
16th to endDay
14%15%46%17%5%
109
March1st to 15thDay
16%13%35%26%8%
270
16th to endDay
20%13%28%25%10%1
288
April1st to 15thDay
17%11%27%25%14%2
270
16th to endDay
20%325%25%19%5%
270
May1st to 15thDay
13%9%31%21%16%7%
288
16th to endDay
13%316%22%27%15%
331
June1st to 15thDay
13%213%25%28%15%
315
16th to endDay
9%18%26%29%15%
315
July1st to 15thDay
8%111%29%30%17%
305
16th to endDay
8%18%25%36%18%
326
August1st to 15thDay
18%19%24%26%19%
313
16th to endDay
13%19%27%26%21%
332
September1st to 15thDay
13%213%23%30%15%
315
16th to endDay
21%414%25%25%9%
314
October1st to 15thDay
19%419%26%21%7%
315
16th to endDay
11%7%20%28%24%7%
336
November1st to 15thDay
20%6%22%27%17%5%
295
16th to endDay
8%13%23%30%20%3
135
December1st to 15thDay
21%11%40%18%10%
100
16th to endDay
31%14%33%11%9%
96
January1st to 15thNight
19%17%25%30%7%
720
16th to endNight
20%14%34%27%2
768
February1st to 15thNight
19%12%36%27%2
704
16th to endNight
16%17%38%24%3
631
March1st to 15thNight
17%11%35%28%7%
720
16th to endNight
17%11%30%29%10%
768
April1st to 15thNight
16%13%29%27%12%
718
16th to endNight
14%8%26%30%18%1
638
May1st to 15thNight
11%7%27%35%17%
540
16th to endNight
12%315%35%31%2
563
June1st to 15thNight
11%113%37%28%7%
540
16th to endNight
8%112%32%35%9%
540
July1st to 15thNight
10%19%34%37%6%
510
16th to endNight
8%18%29%43%9%
564
August1st to 15thNight
12%16%29%42%7%
539
16th to endNight
10%19%29%41%7%
666
September1st to 15thNight
10%29%31%39%6%
720
16th to endNight
19%314%27%30%4
717
October1st to 15thNight
19%418%26%26%4
720
16th to endNight
13%8%23%29%21%4
768
November1st to 15thNight
14%6%24%33%18%3
760
16th to endNight
13%11%23%32%17%1
780
December1st to 15thNight
19%10%22%34%11%1
736
16th to endNight
24%11%23%32%9%
768
Page generated at 2017-12-05 10:19:02. Version ac04

Copyright 2017 A. Danko


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