South Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the South Mountain clear sky chart from 2005-11-05 to 2018-11-30.

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
29%
16201
13%
51708
8%
16171
36%
16171
16%
37076

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
15%
780
6%
2716
2%
776
20%
776
7%
2204
January16th to endNight
20%
832
10%
2863
5%
832
26%
832
10%
2194
February1st to 15thNight
15%
762
10%
2482
4%
761
23%
761
9%
1966
February16th to endNight
19%
683
12%
2093
5%
683
29%
683
12%
1598
March1st to 15thNight
18%
780
13%
2288
6%
780
26%
780
13%
1756
March16th to endNight
31%
832
20%
2194
9%
832
39%
832
22%
1533
April1st to 15thNight
24%
778
16%
1946
6%
778
29%
778
19%
1454
April16th to endNight
28%
707
17%
1863
6%
707
35%
707
23%
1312
May1st to 15thNight
33%
390
17%
1560
16%
390
42%
390
17%
999
May16th to endNight
34%
407
14%
1625
10%
406
46%
406
19%
1004
June1st to 15thNight
36%
390
10%
1560
11%
390
43%
390
14%
1079
June16th to endNight
39%
390
9%
1560
13%
390
44%
390
19%
982
July1st to 15thNight
52%
370
15%
1480
22%
370
60%
370
28%
799
July16th to endNight
53%
408
14%
1546
17%
386
57%
386
25%
883
August1st to 15thNight
48%
464
14%
1605
12%
462
52%
462
21%
1037
August16th to endNight
50%
787
20%
2029
10%
787
55%
787
36%
1272
September1st to 15thNight
47%
780
18%
1950
9%
780
50%
780
31%
1330
September16th to endNight
47%
777
24%
2116
16%
777
52%
777
32%
1343
October1st to 15thNight
32%
780
17%
2340
11%
780
41%
780
20%
1634
October16th to endNight
23%
832
11%
2606
6%
832
31%
832
12%
1955
November1st to 15thNight
26%
820
16%
2706
11%
820
35%
820
15%
1921
November16th to endNight
20%
840
11%
2938
7%
840
27%
840
9%
2269
December1st to 15thNight
17%
780
7%
2730
3%
780
22%
780
8%
2191
December16th to endNight
14%
832
9%
2912
3%
832
20%
832
7%
2361

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
18%8%36%5%34446%32%
52606
Night
18%10%36%5%34446%32%
51877
Cloud CoverDay
18%9%36%5%34446%32%
52615
Night
18%10%36%5%34446%32%
51883
TransparencyDay
51%5%11%19%10%1
52293
Night
53%5%11%19%10%
51708
SeeingDay
24%12%29%20%9%3
6990
Night
24%11%28%25%9%
16203

By Month

Percentage Cloud Cover NE (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
22%15%5%9%6%4444319%
1552
16th to endDay
14%15%5%9%7%45%45%5%21%
1710
February1st to 15thDay
15%14%5%11%7%45%5%3421%
1710
16th to endDay
20%13%48%7%3434424%
1666
March1st to 15thDay
18%14%5%8%7%4433325%
1992
16th to endDay
17%9%35%423346%40%
2382
April1st to 15thDay
23%10%36%5%23335%31%
2332
16th to endDay
22%8%35%423435%35%
2380
May1st to 15thDay
19%7%35%5%2445%6%35%
2721
16th to endDay
18%6%25%5%245%5%7%36%
2842
June1st to 15thDay
23%6%25%5%2445%6%31%
2730
16th to endDay
18%6%25%6%3446%8%33%
2730
July1st to 15thDay
12%425%5%25%5%5%8%42%
2730
16th to endDay
12%5%25%5%36%5%7%8%36%
2878
August1st to 15thDay
12%6%36%7%45%5%5%7%34%
2596
16th to endDay
12%415%5%35%5%5%8%42%
2512
September1st to 15thDay
17%5%25%4245%6%6%41%
2340
16th to endDay
17%413423447%45%
2173
October1st to 15thDay
19%7%46%5%34446%32%
1950
16th to endDay
25%9%37%6%33445%25%
1969
November1st to 15thDay
17%8%45%6%45%45%6%31%
1810
16th to endDay
22%13%47%6%3344424%
1677
December1st to 15thDay
22%16%5%8%7%3343417%
1560
16th to endDay
25%15%5%7%6%2433421%
1664
January1st to 15thNight
19%15%6%10%7%35%34419%
2716
16th to endNight
14%16%5%9%6%34445%24%
2863
February1st to 15thNight
15%15%6%10%7%4444421%
2480
16th to endNight
17%13%49%6%2444427%
2093
March1st to 15thNight
21%14%5%7%5%2323428%
2275
16th to endNight
17%8%36%5%2334441%
2194
April1st to 15thNight
22%9%45%5%3324434%
1946
16th to endNight
21%6%25%42435%6%37%
1863
May1st to 15thNight
19%8%35%42445%6%36%
1560
16th to endNight
16%5%245%35%5%46%40%
1623
June1st to 15thNight
21%5%36%435%45%8%30%
1560
16th to endNight
17%6%245%2445%8%37%
1560
July1st to 15thNight
10%314425%46%9%47%
1560
16th to endNight
9%423435%5%6%9%43%
1642
August1st to 15thNight
11%7%25%6%345%5%9%38%
1615
16th to endNight
11%32432445%6%49%
2029
September1st to 15thNight
15%5%245%34447%43%
1950
16th to endNight
14%5%24422446%48%
2116
October1st to 15thNight
20%6%36%424447%35%
2340
16th to endNight
25%10%35%5%34446%26%
2606
November1st to 15thNight
22%9%35%5%23335%33%
2706
16th to endNight
23%11%48%6%34435%24%
2938
December1st to 15thNight
21%16%5%7%6%25%33420%
2730
16th to endNight
24%15%5%7%7%3433319%
2912

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
23%15%5%10%7%3444319%
1552
16th to endDay
15%14%5%10%7%35%45%5%21%
1710
February1st to 15thDay
16%14%6%10%8%445%4421%
1710
16th to endDay
20%14%5%9%6%3433424%
1666
March1st to 15thDay
19%14%5%9%7%25%33325%
2002
16th to endDay
17%8%35%423335%40%
2381
April1st to 15thDay
23%11%36%5%33335%31%
2332
16th to endDay
22%8%35%422435%35%
2380
May1st to 15thDay
18%7%35%5%2445%6%35%
2721
16th to endDay
17%6%25%5%245%5%7%36%
2842
June1st to 15thDay
22%6%345%3445%7%31%
2730
16th to endDay
18%6%25%5%35%45%8%33%
2730
July1st to 15thDay
12%4245%25%5%6%8%41%
2730
16th to endDay
12%5%25%5%35%5%7%9%36%
2878
August1st to 15thDay
12%6%36%6%5%6%5%5%8%33%
2596
16th to endDay
11%4246%45%45%8%42%
2512
September1st to 15thDay
17%5%25%4245%5%7%40%
2340
16th to endDay
16%5%14423446%45%
2173
October1st to 15thDay
19%8%27%6%3345%6%32%
1950
16th to endDay
25%9%36%6%34336%25%
1969
November1st to 15thDay
17%7%36%6%345%5%7%30%
1810
16th to endDay
23%13%48%5%33445%23%
1677
December1st to 15thDay
22%17%5%8%7%3434417%
1560
16th to endDay
25%15%5%7%6%2433421%
1664
January1st to 15thNight
19%16%6%11%6%35%34418%
2716
16th to endNight
15%16%5%9%6%34445%23%
2863
February1st to 15thNight
16%14%6%11%8%4443421%
2473
16th to endNight
17%14%5%8%5%25%43427%
2093
March1st to 15thNight
22%13%5%8%433235%28%
2288
16th to endNight
18%8%36%5%2333440%
2194
April1st to 15thNight
23%9%36%5%23245%33%
1946
16th to endNight
21%6%26%423346%37%
1863
May1st to 15thNight
19%7%25%5%14446%37%
1560
16th to endNight
16%6%24436%45%6%40%
1623
June1st to 15thNight
20%6%35%5%35%5%48%29%
1560
16th to endNight
17%5%245%25%35%8%37%
1560
July1st to 15thNight
10%3143245%6%9%46%
1560
16th to endNight
10%423435%6%6%9%43%
1642
August1st to 15thNight
11%6%26%5%3446%9%37%
1615
16th to endNight
11%414424447%48%
2029
September1st to 15thNight
15%6%145%24445%43%
1950
16th to endNight
14%5%24423446%48%
2116
October1st to 15thNight
19%7%35%32445%6%35%
2340
16th to endNight
25%10%36%5%24446%26%
2606
November1st to 15thNight
22%9%25%5%34335%33%
2706
16th to endNight
23%11%48%5%34345%24%
2938
December1st to 15thNight
22%16%5%8%6%2444420%
2730
16th to endNight
24%16%5%8%6%3433419%
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
68%49%10%6%1
1553
16th to endDay
63%6%12%11%6%
1710
February1st to 15thDay
66%47%17%3
1712
16th to endDay
63%410%12%8%
1666
March1st to 15thDay
65%310%12%7%
2002
16th to endDay
47%49%18%16%5%
2382
April1st to 15thDay
56%37%17%12%2
2332
16th to endDay
50%48%17%15%3
2380
May1st to 15thDay
48%5%9%20%14%1
2721
16th to endDay
45%7%11%21%12%1
2846
June1st to 15thDay
51%5%10%20%10%
2730
16th to endDay
48%6%11%20%11%1
2730
July1st to 15thDay
36%7%12%29%13%
2581
16th to endDay
41%8%16%23%9%
2711
August1st to 15thDay
47%7%15%20%9%
2582
16th to endDay
38%6%15%28%11%
2512
September1st to 15thDay
41%7%11%26%13%
2340
16th to endDay
38%5%12%32%11%
2173
October1st to 15thDay
52%6%10%20%9%
1950
16th to endDay
60%5%12%14%6%
1969
November1st to 15thDay
52%5%13%18%8%
1810
16th to endDay
62%5%11%13%6%
1677
December1st to 15thDay
69%6%9%10%2
1560
16th to endDay
68%5%9%10%6%
1664
January1st to 15thNight
69%410%10%4
2716
16th to endNight
63%410%15%6%
2863
February1st to 15thNight
65%49%15%4
2482
16th to endNight
60%48%16%9%
2093
March1st to 15thNight
60%49%17%7%
2288
16th to endNight
48%38%19%16%3
2194
April1st to 15thNight
54%37%19%14%
1946
16th to endNight
47%49%18%17%3
1863
May1st to 15thNight
46%5%8%19%15%3
1560
16th to endNight
43%5%14%20%14%2
1625
June1st to 15thNight
51%7%11%17%11%1
1560
16th to endNight
44%5%13%19%15%
1560
July1st to 15thNight
30%6%14%29%16%1
1480
16th to endNight
35%7%15%25%16%
1546
August1st to 15thNight
41%8%17%20%11%
1605
16th to endNight
33%5%15%30%14%
2029
September1st to 15thNight
41%5%11%28%12%
1950
16th to endNight
37%411%33%12%
2116
October1st to 15thNight
48%5%10%23%10%
2340
16th to endNight
57%5%14%16%5%
2606
November1st to 15thNight
53%412%16%10%1
2706
16th to endNight
62%5%10%16%4
2938
December1st to 15thNight
66%5%11%13%3
2730
16th to endNight
69%49%11%5%
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
28%21%24%16%8%
90
16th to endDay
32%15%34%12%4
107
February1st to 15thDay
30%27%33%8%
135
16th to endDay
34%16%30%15%2
247
March1st to 15thDay
31%14%31%16%6%
330
16th to endDay
25%15%28%19%8%3
352
April1st to 15thDay
32%16%27%15%6%1
330
16th to endDay
29%15%26%15%8%3
319
May1st to 15thDay
26%15%29%16%8%2
348
16th to endDay
21%17%30%18%9%1
395
June1st to 15thDay
27%9%32%21%7%1
375
16th to endDay
21%12%32%21%9%1
375
July1st to 15thDay
15%6%29%32%13%3
365
16th to endDay
14%8%29%30%13%3
390
August1st to 15thDay
18%5%28%31%12%3
358
16th to endDay
12%6%29%26%15%9%
396
September1st to 15thDay
18%5%25%22%14%13%
375
16th to endDay
16%11%27%18%16%9%
374
October1st to 15thDay
25%12%29%17%10%3
375
16th to endDay
34%15%25%19%4
365
November1st to 15thDay
27%15%27%18%9%1
284
16th to endDay
36%17%27%15%1
119
December1st to 15thDay
30%20%33%8%7%
90
16th to endDay
41%25%26%6%1
96
January1st to 15thNight
30%15%31%18%4
780
16th to endNight
25%14%31%23%5%
832
February1st to 15thNight
24%17%34%20%3
764
16th to endNight
26%12%35%21%4
683
March1st to 15thNight
29%13%32%19%3
780
16th to endNight
21%13%26%28%9%
832
April1st to 15thNight
28%12%28%25%4
778
16th to endNight
25%13%28%23%8%
707
May1st to 15thNight
23%7%29%28%9%1
390
16th to endNight
17%7%36%26%11%
407
June1st to 15thNight
21%9%24%35%8%
390
16th to endNight
18%6%27%32%13%1
390
July1st to 15thNight
10%5%26%40%17%
370
16th to endNight
11%324%43%15%1
408
August1st to 15thNight
16%5%20%36%19%1
464
16th to endNight
13%424%35%20%1
787
September1st to 15thNight
17%6%24%30%18%2
780
16th to endNight
17%7%24%25%22%2
777
October1st to 15thNight
24%10%28%22%13%
780
16th to endNight
32%13%24%22%6%
832
November1st to 15thNight
29%13%25%21%9%
820
16th to endNight
32%14%24%19%8%
840
December1st to 15thNight
30%17%28%18%3
780
16th to endNight
32%14%30%19%21
832
Page generated at 2018-12-01 11:35:36. Version ac04

Copyright 2018 A. Danko


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