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 2018-03-21.

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%
15248
16%
49257
11%
15222
47%
15222
21%
31996

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%
777
8%
2716
6%
776
34%
776
9%
2129
January16th to endNight
37%
832
10%
2912
9%
832
41%
832
12%
2162
February1st to 15thNight
31%
758
11%
2496
8%
757
37%
757
14%
1842
February16th to endNight
36%
684
14%
2125
11%
684
41%
684
15%
1524
March1st to 15thNight
33%
780
12%
2303
7%
780
39%
780
15%
1698
March16th to endNight
33%
792
13%
2088
6%
792
37%
792
18%
1518
April1st to 15thNight
36%
719
15%
1799
6%
719
39%
719
23%
1272
April16th to endNight
35%
578
17%
1658
8%
578
42%
578
26%
1073
May1st to 15thNight
44%
359
21%
1439
21%
359
55%
359
25%
767
May16th to endNight
48%
374
12%
1496
14%
374
55%
374
21%
881
June1st to 15thNight
42%
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
58%
376
27%
1416
28%
354
77%
354
61%
486
August1st to 15thNight
71%
390
31%
1462
31%
388
81%
388
58%
553
August16th to endNight
60%
693
33%
1839
19%
693
67%
693
56%
926
September1st to 15thNight
64%
720
29%
1800
14%
720
68%
720
58%
930
September16th to endNight
56%
716
27%
1950
19%
716
62%
716
38%
1148
October1st to 15thNight
48%
720
19%
2160
17%
720
54%
720
30%
1315
October16th to endNight
42%
768
18%
2418
15%
768
49%
768
19%
1633
November1st to 15thNight
34%
760
11%
2568
8%
760
39%
760
13%
1861
November16th to endNight
33%
780
11%
2730
7%
780
39%
780
12%
2027
December1st to 15thNight
38%
780
11%
2730
8%
780
42%
780
14%
1990
December16th to endNight
25%
832
10%
2912
5%
832
31%
832
9%
2250

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%
49612
Night
10%9%36%5%345%5%7%38%
49425
Cloud CoverDay
8%9%36%6%35%45%6%38%
49612
Night
8%9%47%6%35%45%7%38%
49429
TransparencyDay
42%5%11%22%13%3
49283
Night
43%5%13%22%11%2
49258
SeeingDay
15%18%29%25%9%2
5985
Night
12%13%23%29%17%3
15259

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%16%5%9%6%5%5%5%46%18%
1552
16th to endDay
13%15%5%6%6%4445%7%25%
1664
February1st to 15thDay
13%16%5%7%7%36%5%5%5%22%
1695
16th to endDay
11%14%5%9%7%45%6%5%5%23%
1635
March1st to 15thDay
14%15%5%9%7%45%45%6%21%
1986
16th to endDay
10%14%6%9%7%46%5%7%6%21%
2262
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%63%
2160
16th to endDay
9%5%25%5%3445%6%46%
2008
October1st to 15thDay
12%8%25%5%35%5%5%7%38%
1800
16th to endDay
15%10%37%42445%6%32%
1805
November1st to 15thDay
14%13%5%9%7%45%5%6%5%21%
1621
16th to endDay
14%17%5%9%6%36%5%46%20%
1560
December1st to 15thDay
11%14%5%9%7%46%45%5%26%
1560
16th to endDay
15%17%6%7%7%35%5%35%22%
1664
January1st to 15thNight
15%13%5%9%7%46%46%6%19%
2716
16th to endNight
14%12%47%6%47%5%5%6%25%
2912
February1st to 15thNight
14%14%47%7%3445%6%27%
2484
16th to endNight
9%13%47%7%45%5%6%7%28%
2125
March1st to 15thNight
13%13%47%7%35%5%5%7%26%
2303
16th to endNight
8%10%48%7%36%6%7%8%27%
2084
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
3212222346%68%
1800
16th to endNight
6%5%2343446%7%52%
1950
October1st to 15thNight
11%6%35%5%245%45%46%
2160
16th to endNight
14%8%26%6%35%5%6%7%34%
2418
November1st to 15thNight
17%11%37%5%45%5%6%6%26%
2568
16th to endNight
15%13%5%8%6%345%5%7%24%
2730
December1st to 15thNight
11%13%5%8%6%345%5%8%26%
2730
16th to endNight
15%16%6%8%6%35%5%45%22%
2912

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
13%15%6%9%8%46%5%47%19%
1552
16th to endDay
11%15%5%7%6%45%5%5%6%26%
1664
February1st to 15thDay
11%17%5%8%9%36%45%6%21%
1695
16th to endDay
9%14%5%10%8%46%5%5%424%
1635
March1st to 15thDay
12%14%5%10%8%45%5%5%6%20%
1986
16th to endDay
9%15%6%9%8%46%5%7%6%21%
2262
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%
2160
16th to endDay
8%5%25%5%35%45%6%46%
2008
October1st to 15thDay
11%8%25%5%45%6%6%6%38%
1800
16th to endDay
13%11%37%5%4446%6%32%
1805
November1st to 15thDay
11%14%5%10%8%45%45%7%21%
1621
16th to endDay
11%17%7%9%7%45%5%45%20%
1560
December1st to 15thDay
10%13%6%9%7%46%445%27%
1560
16th to endDay
13%17%5%8%7%46%435%22%
1664
January1st to 15thNight
13%12%5%10%6%47%5%6%6%19%
2716
16th to endNight
12%12%47%8%37%5%5%7%24%
2912
February1st to 15thNight
11%13%6%8%7%35%45%5%26%
2484
16th to endNight
8%11%5%8%8%46%46%7%28%
2125
March1st to 15thNight
10%12%5%9%8%35%5%5%7%25%
2303
16th to endNight
7%9%48%8%47%6%7%8%27%
2088
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%
1800
16th to endNight
6%5%2442446%7%52%
1950
October1st to 15thNight
9%7%26%424446%45%
2160
16th to endNight
12%8%27%6%35%6%5%6%34%
2418
November1st to 15thNight
13%11%5%8%6%36%5%5%7%26%
2568
16th to endNight
11%12%6%10%7%46%5%5%6%23%
2730
December1st to 15thNight
9%13%5%9%7%35%5%5%7%26%
2730
16th to endNight
14%15%6%9%7%46%445%21%
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
63%7%12%11%31
1552
16th to endDay
55%7%14%16%6%
1664
February1st to 15thDay
58%7%15%14%3
1695
16th to endDay
57%7%12%16%5%
1635
March1st to 15thDay
59%7%11%15%5%
1986
16th to endDay
58%7%14%15%4
2262
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%
2160
16th to endDay
35%414%23%16%5%
2008
October1st to 15thDay
42%5%12%26%11%
1800
16th to endDay
49%412%22%10%
1805
November1st to 15thDay
59%6%12%15%41
1621
16th to endDay
62%5%11%15%4
1560
December1st to 15thDay
59%5%12%17%5%
1560
16th to endDay
62%6%11%14%4
1664
January1st to 15thNight
61%7%12%12%4
2716
16th to endNight
55%7%14%15%5%1
2912
February1st to 15thNight
54%6%15%16%5%
2496
16th to endNight
51%6%14%20%6%
2125
March1st to 15thNight
54%6%12%20%5%
2303
16th to endNight
49%7%15%23%5%
2088
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%
1800
16th to endNight
29%5%13%29%15%7%
1950
October1st to 15thNight
37%311%29%15%1
2160
16th to endNight
45%6%10%24%12%
2418
November1st to 15thNight
53%7%14%17%6%1
2568
16th to endNight
57%5%11%18%6%
2730
December1st to 15thNight
54%7%13%19%4
2730
16th to endNight
62%6%12%12%6%
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
24%320%16%30%5%
90
16th to endDay
29%13%23%19%9%4
96
February1st to 15thDay
21%20%32%18%5%
265
16th to endDay
20%23%29%19%5%1
273
March1st to 15thDay
24%27%24%18%4
330
16th to endDay
21%31%26%13%7%
311
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
6%15%28%31%14%3
315
16th to endDay
10%17%30%29%10%1
315
October1st to 15thDay
20%17%28%25%6%
315
16th to endDay
21%16%18%30%9%2
221
November1st to 15thDay
19%22%30%26%
112
16th to endDay
17%24%22%20%11%4
90
December1st to 15thDay
14%13%27%20%13%11%
90
16th to endDay
21%11%19%32%13%1
96
January1st to 15thNight
18%18%16%26%17%2
780
16th to endNight
18%14%18%29%15%3
832
February1st to 15thNight
17%13%23%27%15%2
764
16th to endNight
14%18%21%28%15%2
684
March1st to 15thNight
16%18%20%29%13%1
780
16th to endNight
11%20%25%26%13%2
792
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%28%31%8%
720
16th to endNight
8%8%20%31%24%6%
716
October1st to 15thNight
11%11%21%28%22%4
720
16th to endNight
16%13%17%28%18%4
768
November1st to 15thNight
17%17%20%33%10%1
760
16th to endNight
16%18%21%23%15%4
780
December1st to 15thNight
15%13%22%30%15%3
780
16th to endNight
20%16%25%29%6%
832
Page generated at 2018-03-22 08:34:21. Version ac04

Copyright 2018 A. Danko


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