Table Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Table Mountain clear sky chart from 2005-11-05 to

2017-09-12
.

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
41%
14486
15%
46795
11%
14460
47%
14460
22%
30255

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
33%
717
8%
2506
7%
716
36%
716
10%
1937
January16th to endNight
37%
768
10%
2688
9%
768
41%
768
13%
1983
February1st to 15thNight
32%
698
9%
2300
7%
697
36%
697
13%
1708
February16th to endNight
36%
632
13%
1963
11%
632
40%
632
15%
1410
March1st to 15thNight
31%
720
10%
2126
6%
720
37%
720
14%
1582
March16th to endNight
30%
768
12%
2022
5%
768
34%
768
17%
1485
April1st to 15thNight
35%
719
15%
1799
6%
719
38%
719
23%
1272
April16th to endNight
34%
578
17%
1658
8%
578
42%
578
26%
1073
May1st to 15thNight
42%
359
21%
1439
21%
359
53%
359
25%
767
May16th to endNight
47%
374
12%
1496
14%
374
54%
374
21%
881
June1st to 15thNight
41%
360
10%
1440
7%
360
49%
360
25%
780
June16th to endNight
38%
360
13%
1440
9%
360
49%
360
30%
713
July1st to 15thNight
61%
340
16%
1360
15%
340
73%
340
50%
518
July16th to endNight
57%
376
27%
1416
28%
354
77%
354
61%
486
August1st to 15thNight
70%
390
31%
1462
31%
388
80%
388
58%
553
August16th to endNight
60%
693
33%
1839
19%
693
67%
693
56%
926
September1st to 15thNight
64%
706
29%
1765
14%
706
68%
706
58%
911
September16th to endNight
55%
656
27%
1787
19%
656
61%
656
38%
1046
October1st to 15thNight
47%
660
19%
1980
16%
660
52%
660
29%
1215
October16th to endNight
40%
704
16%
2216
12%
704
47%
704
18%
1515
November1st to 15thNight
34%
700
12%
2365
8%
700
40%
700
14%
1686
November16th to endNight
33%
720
11%
2520
7%
720
40%
720
13%
1855
December1st to 15thNight
33%
720
11%
2520
8%
720
38%
720
12%
1879
December16th to endNight
23%
768
9%
2688
4%
768
29%
768
9%
2074

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
9%9%36%5%35%5%5%6%39%
47884
Night
10%9%36%5%345%5%7%38%
46963
Cloud CoverDay
8%9%36%6%35%45%6%39%
47884
Night
8%8%46%6%35%45%7%38%
46967
TransparencyDay
42%5%11%22%14%3
47555
Night
42%5%13%22%11%3
46796
SeeingDay
14%18%29%25%9%2
5432
Night
12%13%23%29%17%3
14497

By Month

Percentage Cloud Cover NW (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
14%15%5%9%6%5%6%6%46%19%
1432
16th to endDay
12%15%5%6%6%4445%7%26%
1536
February1st to 15thDay
14%15%5%7%8%36%5%5%6%21%
1561
16th to endDay
11%14%5%9%6%45%6%5%6%24%
1511
March1st to 15thDay
14%15%5%9%8%45%46%6%19%
1833
16th to endDay
10%14%6%9%7%46%5%7%6%20%
2201
April1st to 15thDay
10%14%5%8%7%37%6%5%7%23%
2149
16th to endDay
8%10%37%5%36%5%7%9%33%
2298
May1st to 15thDay
7%7%36%7%35%5%6%8%37%
2511
16th to endDay
11%7%37%6%36%6%6%8%31%
2615
June1st to 15thDay
8%5%25%5%36%5%7%8%40%
2520
16th to endDay
7%5%244245%6%8%48%
2520
July1st to 15thDay
2213324345%66%
2520
16th to endDay
4212213235%71%
2657
August1st to 15thDay
2212213446%67%
2487
16th to endDay
2314323446%62%
2363
September1st to 15thDay
3313323346%64%
2114
16th to endDay
9%4245%3445%6%48%
1841
October1st to 15thDay
12%7%25%5%35%5%5%7%38%
1650
16th to endDay
16%11%46%5%35%45%7%30%
1655
November1st to 15thDay
13%12%49%6%45%5%6%6%22%
1494
16th to endDay
13%17%5%8%6%36%5%47%21%
1440
December1st to 15thDay
11%15%6%9%7%46%45%425%
1440
16th to endDay
14%17%6%7%7%36%5%35%23%
1536
January1st to 15thNight
14%13%5%9%7%46%46%6%20%
2506
16th to endNight
13%12%47%6%47%5%5%6%26%
2688
February1st to 15thNight
13%14%5%7%7%3445%5%26%
2288
16th to endNight
9%12%47%7%46%6%6%7%28%
1963
March1st to 15thNight
13%13%48%7%35%5%5%7%25%
2126
16th to endNight
8%11%48%7%35%6%7%8%26%
2018
April1st to 15thNight
8%8%46%7%45%6%7%8%33%
1799
16th to endNight
8%7%45%435%46%9%39%
1658
May1st to 15thNight
5%6%445%3446%6%47%
1439
16th to endNight
7%5%37%6%36%6%7%7%38%
1496
June1st to 15thNight
7%5%145%446%5%8%48%
1440
16th to endNight
4425%43445%8%51%
1440
July1st to 15thNight
2112112336%71%
1440
16th to endNight
111111325%79%
1512
August1st to 15thNight
111212347%71%
1470
16th to endNight
3212313346%67%
1839
September1st to 15thNight
3212222246%68%
1765
16th to endNight
6%5%2343446%7%52%
1787
October1st to 15thNight
11%6%35%5%245%5%5%45%
1980
16th to endNight
14%8%26%6%35%6%6%7%32%
2216
November1st to 15thNight
17%10%26%6%45%5%6%6%28%
2365
16th to endNight
14%13%5%8%6%345%5%7%25%
2520
December1st to 15thNight
12%14%5%8%6%3445%7%25%
2520
16th to endNight
15%16%6%8%6%35%5%45%21%
2688

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
12%14%6%9%8%46%5%47%19%
1432
16th to endDay
11%15%5%7%6%45%5%5%6%27%
1536
February1st to 15thDay
11%18%5%8%8%36%5%5%6%21%
1561
16th to endDay
10%14%5%9%7%46%5%5%5%24%
1511
March1st to 15thDay
12%15%5%10%8%46%5%5%6%19%
1833
16th to endDay
9%15%6%9%8%46%5%7%6%20%
2201
April1st to 15thDay
9%15%49%7%47%5%5%7%23%
2149
16th to endDay
7%9%37%6%36%5%6%9%32%
2298
May1st to 15thDay
8%7%38%6%35%5%6%8%36%
2511
16th to endDay
11%8%47%7%46%6%7%6%30%
2615
June1st to 15thDay
8%6%35%6%35%5%6%8%39%
2520
16th to endDay
6%6%25%42445%9%47%
2520
July1st to 15thDay
221332435%5%66%
2520
16th to endDay
3212322325%70%
2657
August1st to 15thDay
2212213446%66%
2487
16th to endDay
1314423446%61%
2363
September1st to 15thDay
331331335%5%63%
2114
16th to endDay
8%5%245%25%45%6%48%
1841
October1st to 15thDay
11%8%26%5%45%6%6%6%37%
1650
16th to endDay
14%11%37%6%3446%6%29%
1655
November1st to 15thDay
10%13%5%10%8%45%5%5%7%22%
1494
16th to endDay
11%17%7%9%7%36%5%45%21%
1440
December1st to 15thDay
10%14%6%9%7%5%6%44425%
1440
16th to endDay
13%17%5%8%7%47%435%23%
1536
January1st to 15thNight
12%13%5%10%6%47%5%6%7%20%
2506
16th to endNight
11%11%47%8%37%5%5%7%25%
2688
February1st to 15thNight
12%13%6%8%7%35%45%5%26%
2288
16th to endNight
8%11%5%8%7%46%46%7%28%
1963
March1st to 15thNight
10%12%5%9%8%35%5%5%7%25%
2126
16th to endNight
8%9%5%9%8%47%5%7%8%26%
2022
April1st to 15thNight
8%8%47%7%46%5%7%8%33%
1799
16th to endNight
7%7%35%5%35%5%5%9%39%
1658
May1st to 15thNight
5%7%35%5%345%5%7%47%
1439
16th to endNight
7%6%36%7%36%5%6%9%36%
1496
June1st to 15thNight
7%5%236%345%5%7%48%
1440
16th to endNight
45%25%43445%8%52%
1440
July1st to 15thNight
222122336%71%
1440
16th to endNight
11111325%78%
1512
August1st to 15thNight
11121345%6%71%
1470
16th to endNight
3213214446%66%
1839
September1st to 15thNight
322212346%67%
1765
16th to endNight
6%42442446%7%52%
1787
October1st to 15thNight
10%7%36%5%24446%44%
1980
16th to endNight
12%8%27%6%35%6%6%6%32%
2216
November1st to 15thNight
13%9%48%6%36%45%7%28%
2365
16th to endNight
11%13%5%10%6%36%45%6%24%
2520
December1st to 15thNight
10%14%6%9%7%35%45%7%25%
2520
16th to endNight
14%15%6%9%7%46%445%21%
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
62%7%12%11%41
1432
16th to endDay
54%7%14%16%6%
1536
February1st to 15thDay
59%6%15%14%3
1561
16th to endDay
56%6%12%17%5%
1511
March1st to 15thDay
60%7%11%14%5%
1833
16th to endDay
58%7%14%15%4
2201
April1st to 15thDay
55%5%12%19%6%
2149
16th to endDay
44%7%15%24%7%1
2298
May1st to 15thDay
41%411%28%12%1
2511
16th to endDay
48%5%15%23%7%
2619
June1st to 15thDay
38%5%11%30%12%2
2520
16th to endDay
30%313%31%18%2
2520
July1st to 15thDay
19%37%25%30%13%
2371
16th to endDay
17%25%25%32%17%
2490
August1st to 15thDay
17%37%32%30%10%
2470
16th to endDay
21%37%32%28%6%
2363
September1st to 15thDay
21%28%26%31%8%
2114
16th to endDay
33%314%24%17%5%
1841
October1st to 15thDay
43%5%13%25%11%
1650
16th to endDay
50%412%21%9%
1655
November1st to 15thDay
57%6%12%16%41
1494
16th to endDay
61%5%11%16%4
1440
December1st to 15thDay
60%5%12%15%5%
1440
16th to endDay
61%6%11%15%4
1536
January1st to 15thNight
60%7%12%13%5%
2506
16th to endNight
54%7%14%15%5%1
2688
February1st to 15thNight
55%6%15%16%4
2300
16th to endNight
51%6%14%19%6%
1963
March1st to 15thNight
54%6%13%18%6%
2126
16th to endNight
50%7%15%22%4
2022
April1st to 15thNight
44%7%14%24%9%
1799
16th to endNight
38%6%16%27%10%1
1658
May1st to 15thNight
34%311%34%13%2
1440
16th to endNight
39%5%17%28%8%
1496
June1st to 15thNight
32%6%15%29%13%2
1440
16th to endNight
29%314%33%16%3
1440
July1st to 15thNight
14%212%29%28%11%
1360
16th to endNight
9%28%27%31%19%
1416
August1st to 15thNight
12%29%32%29%12%
1462
16th to endNight
17%39%32%29%7%
1839
September1st to 15thNight
16%210%27%32%10%
1765
16th to endNight
28%5%12%29%15%8%
1787
October1st to 15thNight
38%312%29%14%1
1980
16th to endNight
46%7%11%24%10%
2216
November1st to 15thNight
51%7%14%18%6%1
2365
16th to endNight
56%5%11%19%7%
2520
December1st to 15thNight
56%7%13%18%4
2520
16th to endNight
61%6%13%11%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
16%321%21%31%5%
60
16th to endDay
32%6%18%23%12%6%
64
February1st to 15thDay
22%19%31%19%5%
221
16th to endDay
20%22%29%18%5%1
227
March1st to 15thDay
25%31%25%15%1
270
16th to endDay
22%33%27%11%4
288
April1st to 15thDay
21%25%27%15%7%2
269
16th to endDay
15%29%32%11%5%3
270
May1st to 15thDay
21%18%30%25%31
288
16th to endDay
16%14%25%27%13%2
330
June1st to 15thDay
14%18%33%23%8%1
315
16th to endDay
12%20%33%22%10%1
315
July1st to 15thDay
411%32%38%11%1
305
16th to endDay
312%36%32%12%1
327
August1st to 15thDay
5%10%29%35%13%4
315
16th to endDay
411%28%34%15%4
332
September1st to 15thDay
7%16%26%32%14%3
300
16th to endDay
10%17%32%30%9%
255
October1st to 15thDay
20%18%30%22%6%1
255
16th to endDay
22%15%20%31%7%1
167
November1st to 15thDay
10%25%30%32%1
75
16th to endDay
16%23%18%20%15%6%
60
December1st to 15thDay
18%20%33%25%3
60
16th to endDay
17%10%18%32%18%1
64
January1st to 15thNight
18%19%16%26%16%2
720
16th to endNight
17%13%19%28%16%3
768
February1st to 15thNight
18%13%21%27%16%2
704
16th to endNight
14%18%19%28%16%2
632
March1st to 15thNight
15%19%21%29%11%1
720
16th to endNight
12%20%26%26%12%1
768
April1st to 15thNight
11%17%27%25%15%2
719
16th to endNight
10%15%31%24%13%3
578
May1st to 15thNight
10%16%23%28%17%2
360
16th to endNight
11%7%25%34%17%4
375
June1st to 15thNight
9%8%33%32%14%1
360
16th to endNight
7%11%37%23%17%1
360
July1st to 15thNight
37%26%39%22%
340
16th to endNight
17%31%32%25%1
376
August1st to 15thNight
2320%37%30%5%
390
16th to endNight
47%23%30%27%7%
693
September1st to 15thNight
46%20%27%31%8%
706
16th to endNight
8%8%21%32%23%6%
656
October1st to 15thNight
12%11%22%27%22%4
660
16th to endNight
16%13%18%28%17%4
704
November1st to 15thNight
16%17%21%33%9%1
700
16th to endNight
16%18%21%23%16%4
720
December1st to 15thNight
16%14%24%29%13%1
720
16th to endNight
19%17%26%28%7%
768
Page generated at 2017-09-13 04:39:11. Version ac04

Copyright 2017 A. Danko


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