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 2017-03-14.

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
46%
15159
23%
45128
14%
15121
54%
15121
27%
28159

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
32%
716
26%
1969
13%
716
44%
716
30%
1211
March16th to endNight
33%
704
19%
1936
9%
704
42%
704
26%
1272
April1st to 15thNight
35%
658
24%
1764
11%
658
45%
658
31%
1101
April16th to endNight
43%
585
25%
1575
13%
585
50%
585
33%
958
May1st to 15thNight
48%
495
18%
1485
9%
495
54%
495
26%
949
May16th to endNight
60%
513
18%
1539
14%
513
62%
513
29%
981
June1st to 15thNight
63%
495
16%
1485
13%
495
65%
495
25%
1000
June16th to endNight
67%
495
16%
1485
13%
495
68%
495
27%
958
July1st to 15thNight
65%
465
11%
1395
9%
465
66%
465
25%
940
July16th to endNight
68%
522
13%
1469
10%
489
70%
489
25%
989
August1st to 15thNight
70%
494
17%
1474
15%
491
70%
491
28%
954
August16th to endNight
63%
610
16%
1660
13%
610
64%
610
26%
1172
September1st to 15thNight
66%
660
21%
1807
17%
660
68%
660
31%
1155
September16th to endNight
51%
657
17%
1815
13%
657
55%
657
23%
1279
October1st to 15thNight
51%
660
30%
1933
25%
660
59%
660
33%
1146
October16th to endNight
49%
704
33%
2112
23%
704
64%
704
37%
1169
November1st to 15thNight
49%
700
30%
2128
22%
700
61%
700
37%
1169
November16th to endNight
44%
720
27%
2340
20%
720
55%
720
28%
1348
December1st to 15thNight
40%
720
24%
2340
17%
720
51%
720
24%
1431
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%
45579
Night
13%5%2442445%7%45%
45327
TransparencyDay
38%6%11%20%18%4
45280
Night
37%5%11%19%19%6%
45130
SeeingDay
16%6%21%24%21%10%
4884
Night
15%8%22%30%19%2
15166

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%
1963
16th to endDay
18%5%244245%46%42%
1935
April1st to 15thDay
13%3233235%5%7%48%
1854
16th to endDay
12%334414446%48%
2064
May1st to 15thDay
12%415%5%26%5%6%8%40%
2136
16th to endDay
11%5%246%25%448%42%
2223
June1st to 15thDay
9%4245%35%6%6%10%40%
2145
16th to endDay
5%2246%46%6%7%10%43%
2145
July1st to 15thDay
9%6%36%6%35%5%7%9%34%
2145
16th to endDay
8%325%6%48%7%8%12%32%
2283
August1st to 15thDay
12%5%146%46%7%7%10%32%
2145
16th to endDay
12%5%26%6%46%6%7%10%32%
2179
September1st to 15thDay
9%425%5%35%46%9%42%
1821
16th to endDay
18%7%25%424446%38%
1815
October1st to 15thDay
17%41331232454%
1697
16th to endDay
12%323312235%59%
1760
November1st to 15thDay
14%422312236%56%
1730
16th to endDay
16%413313445%50%
1620
December1st to 15thDay
16%6%2332335%6%43%
1620
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%48%
1969
16th to endNight
15%6%25%42435%7%43%
1936
April1st to 15thNight
13%423414347%48%
1764
16th to endNight
11%424414437%51%
1575
May1st to 15thNight
10%5%25%445%449%42%
1484
16th to endNight
10%415%5%35%5%5%10%42%
1538
June1st to 15thNight
10%4245%37%6%7%10%35%
1485
16th to endNight
5%425%5%46%7%8%11%38%
1485
July1st to 15thNight
8%5%26%5%37%6%8%11%33%
1485
16th to endNight
7%425%5%37%7%8%11%33%
1577
August1st to 15thNight
10%5%14435%6%8%13%35%
1485
16th to endNight
9%5%35%6%36%6%6%10%34%
1660
September1st to 15thNight
9%3246%345%6%10%42%
1807
16th to endNight
19%6%245%25%45%6%37%
1815
October1st to 15thNight
17%413312335%52%
1933
16th to endNight
11%413322335%57%
2112
November1st to 15thNight
12%313313236%57%
2128
16th to endNight
13%423423445%50%
2340
December1st to 15thNight
16%6%25%42434447%
2340
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%5%
1963
16th to endDay
41%5%10%19%18%3
1936
April1st to 15thDay
33%410%23%22%5%
1854
16th to endDay
35%5%9%17%22%8%
2064
May1st to 15thDay
39%7%15%21%14%1
2136
16th to endDay
38%6%13%24%14%2
2227
June1st to 15thDay
37%8%15%26%11%
2145
16th to endDay
33%9%17%22%15%2
2145
July1st to 15thDay
42%10%16%18%9%2
2006
16th to endDay
38%11%18%20%9%1
2128
August1st to 15thDay
42%9%16%18%11%1
2132
16th to endDay
44%8%16%18%10%1
2179
September1st to 15thDay
36%7%14%20%16%4
1821
16th to endDay
46%6%7%17%16%5%
1815
October1st to 15thDay
34%39%20%26%5%
1697
16th to endDay
29%26%21%29%9%
1760
November1st to 15thDay
30%27%18%30%9%
1730
16th to endDay
35%47%20%24%7%
1620
December1st to 15thDay
41%39%21%19%5%
1620
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%7%
1969
16th to endNight
41%410%18%19%4
1936
April1st to 15thNight
35%38%22%22%6%
1764
16th to endNight
34%48%21%21%9%
1575
May1st to 15thNight
38%7%15%19%16%2
1485
16th to endNight
36%8%13%26%13%1
1540
June1st to 15thNight
40%9%16%22%9%1
1485
16th to endNight
34%11%15%22%11%3
1485
July1st to 15thNight
38%11%18%18%9%3
1395
16th to endNight
37%12%19%18%9%2
1469
August1st to 15thNight
35%10%20%20%11%1
1474
16th to endNight
42%9%17%18%10%
1660
September1st to 15thNight
35%8%16%19%14%5%
1807
16th to endNight
46%7%10%13%16%4
1815
October1st to 15thNight
34%49%20%25%6%
1933
16th to endNight
30%26%20%26%12%
2112
November1st to 15thNight
30%27%16%29%13%
2128
16th to endNight
35%36%19%26%8%
2340
December1st to 15thNight
40%39%19%20%7%
2340
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%11%35%26%8%
264
16th to endDay
22%11%30%25%9%1
224
April1st to 15thDay
18%12%31%25%10%2
210
16th to endDay
16%425%23%22%6%
210
May1st to 15thDay
13%5%31%23%17%9%
228
16th to endDay
13%215%20%29%18%
267
June1st to 15thDay
13%114%25%28%16%
255
16th to endDay
6%16%24%34%17%
255
July1st to 15thDay
9%212%31%26%18%
245
16th to endDay
8%27%23%36%21%
270
August1st to 15thDay
17%17%24%27%21%
253
16th to endDay
14%8%26%27%22%
268
September1st to 15thDay
12%27%23%35%18%
255
16th to endDay
26%315%22%21%9%
254
October1st to 15thDay
20%5%22%25%18%7%
255
16th to endDay
11%6%19%29%25%6%
272
November1st to 15thDay
20%6%21%27%17%7%
238
16th to endDay
11%13%22%33%18%1
90
December1st to 15thDay
22%12%41%15%8%
90
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%34%28%7%
716
16th to endNight
18%11%30%29%9%
704
April1st to 15thNight
17%12%30%28%10%
658
16th to endNight
13%9%27%29%18%
585
May1st to 15thNight
11%7%26%35%18%
495
16th to endNight
12%214%35%32%2
515
June1st to 15thNight
11%114%38%27%7%
495
16th to endNight
7%111%32%36%10%
495
July1st to 15thNight
10%10%36%35%6%
465
16th to endNight
8%18%29%42%9%
522
August1st to 15thNight
11%16%29%42%7%
494
16th to endNight
10%19%28%42%7%
610
September1st to 15thNight
10%28%30%41%6%
660
16th to endNight
21%314%28%27%3
657
October1st to 15thNight
19%419%27%24%4
660
16th to endNight
13%8%22%29%21%3
704
November1st to 15thNight
13%6%25%33%17%3
700
16th to endNight
14%12%24%31%16%1
720
December1st to 15thNight
18%10%22%34%11%1
720
16th to endNight
24%11%23%32%9%
768
Page generated at 2017-03-15 11:32:39. Version ac04

Copyright 2017 A. Danko


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