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 2017-09-19.

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%
14687
13%
46872
8%
14657
36%
14657
16%
33660

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%
720
6%
2506
2%
716
19%
716
7%
2047
January16th to endNight
21%
768
10%
2643
6%
768
27%
768
10%
2022
February1st to 15thNight
15%
702
9%
2287
4%
701
22%
701
9%
1809
February16th to endNight
19%
631
12%
1934
5%
631
29%
631
12%
1484
March1st to 15thNight
19%
720
14%
2112
7%
720
28%
720
15%
1584
March16th to endNight
30%
768
19%
2025
8%
768
38%
768
21%
1421
April1st to 15thNight
25%
718
16%
1796
6%
718
30%
718
20%
1335
April16th to endNight
27%
661
17%
1741
6%
661
34%
661
23%
1222
May1st to 15thNight
33%
360
16%
1440
14%
360
42%
360
16%
937
May16th to endNight
33%
375
13%
1497
10%
374
45%
374
18%
943
June1st to 15thNight
37%
360
10%
1440
10%
360
44%
360
14%
1000
June16th to endNight
40%
360
9%
1440
12%
360
45%
360
19%
909
July1st to 15thNight
50%
340
14%
1360
20%
340
57%
340
27%
750
July16th to endNight
55%
376
14%
1418
17%
354
59%
354
25%
810
August1st to 15thNight
48%
437
14%
1508
12%
435
52%
435
22%
963
August16th to endNight
50%
726
21%
1872
11%
726
55%
726
37%
1169
September1st to 15thNight
46%
720
17%
1800
8%
720
49%
720
30%
1232
September16th to endNight
48%
673
23%
1830
15%
673
52%
673
32%
1167
October1st to 15thNight
33%
660
18%
1980
12%
660
42%
660
19%
1386
October16th to endNight
23%
704
10%
2205
5%
704
30%
704
12%
1679
November1st to 15thNight
27%
700
17%
2310
12%
700
35%
700
16%
1631
November16th to endNight
20%
720
12%
2520
7%
720
27%
720
9%
1945
December1st to 15thNight
17%
720
7%
2520
3%
720
21%
720
7%
2020
December16th to endNight
14%
768
8%
2688
4%
768
20%
768
7%
2195

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%
47956
Night
18%10%46%5%34446%32%
47041
Cloud CoverDay
18%9%36%5%34446%32%
47965
Night
18%10%36%5%34446%32%
47047
TransparencyDay
52%5%11%19%9%1
47643
Night
53%5%11%19%9%1
46872
SeeingDay
23%12%29%20%10%3
5517
Night
24%11%28%25%9%
14689

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
23%15%5%9%6%4444318%
1432
16th to endDay
14%15%5%8%6%45%445%21%
1578
February1st to 15thDay
15%14%5%11%7%45%5%4421%
1575
16th to endDay
19%13%5%9%7%3434424%
1539
March1st to 15thDay
18%12%5%8%7%45%33327%
1838
16th to endDay
17%9%34424345%39%
2199
April1st to 15thDay
23%10%36%5%23335%32%
2152
16th to endDay
21%8%36%423436%36%
2227
May1st to 15thDay
19%8%35%5%2445%6%34%
2511
16th to endDay
18%6%25%5%245%5%7%36%
2618
June1st to 15thDay
23%6%35%5%2445%6%31%
2520
16th to endDay
18%6%35%6%35%46%8%32%
2520
July1st to 15thDay
13%435%5%25%5%5%8%39%
2520
16th to endDay
12%5%25%5%36%5%7%9%35%
2654
August1st to 15thDay
12%6%37%6%45%5%5%7%36%
2441
16th to endDay
12%415%5%35%5%5%8%42%
2318
September1st to 15thDay
18%5%2442345%6%41%
2160
16th to endDay
17%414423447%45%
1875
October1st to 15thDay
19%7%46%5%34446%33%
1650
16th to endDay
27%9%37%6%3343423%
1667
November1st to 15thDay
14%8%45%6%45%45%6%33%
1546
16th to endDay
22%13%48%6%2334425%
1440
December1st to 15thDay
23%16%5%8%7%335%3417%
1440
16th to endDay
25%16%5%7%6%2433420%
1536
January1st to 15thNight
19%16%6%10%7%35%34418%
2506
16th to endNight
14%16%5%9%6%34445%24%
2643
February1st to 15thNight
14%15%7%10%7%445%4421%
2285
16th to endNight
17%13%49%6%24445%27%
1934
March1st to 15thNight
21%12%5%7%5%2323430%
2099
16th to endNight
18%8%36%5%2334440%
2025
April1st to 15thNight
22%9%35%5%3323435%
1796
16th to endNight
19%6%25%42435%6%37%
1741
May1st to 15thNight
20%8%35%42445%5%35%
1440
16th to endNight
17%6%245%35%5%46%39%
1495
June1st to 15thNight
22%5%36%435%45%7%30%
1440
16th to endNight
17%6%245%2445%8%37%
1440
July1st to 15thNight
10%415%425%46%9%45%
1440
16th to endNight
9%423426%6%6%9%43%
1514
August1st to 15thNight
11%6%25%6%345%5%9%39%
1518
16th to endNight
11%32332445%6%50%
1872
September1st to 15thNight
15%5%245%34446%43%
1800
16th to endNight
15%424422446%48%
1830
October1st to 15thNight
20%6%35%424447%35%
1980
16th to endNight
27%11%35%434446%26%
2205
November1st to 15thNight
20%9%35%5%24435%34%
2310
16th to endNight
22%11%48%6%34435%25%
2520
December1st to 15thNight
23%15%5%7%6%25%33421%
2520
16th to endNight
25%16%5%7%6%3433319%
2688

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%9%7%3444319%
1432
16th to endDay
15%14%5%9%7%35%45%5%22%
1578
February1st to 15thDay
15%14%6%10%8%4444421%
1575
16th to endDay
19%14%5%9%6%3433425%
1539
March1st to 15thDay
19%12%5%9%8%25%33326%
1848
16th to endDay
18%9%34423335%39%
2198
April1st to 15thDay
23%10%36%423335%32%
2152
16th to endDay
20%8%35%5%22446%36%
2227
May1st to 15thDay
19%8%35%5%2445%6%34%
2511
16th to endDay
17%6%25%5%245%5%7%35%
2618
June1st to 15thDay
22%6%345%3445%7%31%
2520
16th to endDay
18%6%35%5%35%5%5%8%32%
2520
July1st to 15thDay
13%5%25%5%25%6%6%8%39%
2520
16th to endDay
12%5%25%5%36%6%7%9%35%
2654
August1st to 15thDay
12%6%36%5%46%5%5%8%35%
2441
16th to endDay
11%4245%45%45%8%42%
2318
September1st to 15thDay
18%5%25%4245%5%7%40%
2160
16th to endDay
17%5%14423446%44%
1875
October1st to 15thDay
18%8%26%5%335%5%6%33%
1650
16th to endDay
27%10%37%6%34335%23%
1667
November1st to 15thDay
15%7%36%6%45%5%47%31%
1546
16th to endDay
22%13%5%8%5%33345%25%
1440
December1st to 15thDay
23%16%5%8%7%3344417%
1440
16th to endDay
25%15%5%7%6%2433420%
1536
January1st to 15thNight
19%16%6%11%6%35%43418%
2506
16th to endNight
14%16%5%9%6%34445%24%
2643
February1st to 15thNight
16%14%6%11%8%34435%21%
2278
16th to endNight
17%14%5%8%6%25%435%26%
1934
March1st to 15thNight
21%12%47%433235%30%
2112
16th to endNight
18%8%35%5%2333440%
2025
April1st to 15thNight
23%9%35%5%3324434%
1796
16th to endNight
20%6%36%424346%37%
1741
May1st to 15thNight
20%8%25%5%14446%35%
1440
16th to endNight
17%6%245%36%446%39%
1495
June1st to 15thNight
21%6%35%5%35%5%48%29%
1440
16th to endNight
18%5%24425%35%9%36%
1440
July1st to 15thNight
11%3243245%6%9%44%
1440
16th to endNight
9%4235%35%6%7%9%43%
1514
August1st to 15thNight
11%6%25%5%3446%9%38%
1518
16th to endNight
11%414424447%49%
1872
September1st to 15thNight
16%6%145%34445%43%
1800
16th to endNight
15%5%24423446%48%
1830
October1st to 15thNight
20%8%45%33445%6%35%
1980
16th to endNight
26%10%36%5%24446%25%
2205
November1st to 15thNight
20%10%25%5%34335%34%
2310
16th to endNight
23%11%48%5%3433425%
2520
December1st to 15thNight
23%16%5%7%6%2444420%
2520
16th to endNight
25%16%5%8%6%3433419%
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
69%49%10%5%1
1433
16th to endDay
63%6%11%11%7%
1578
February1st to 15thDay
66%48%17%2
1577
16th to endDay
62%410%12%9%
1539
March1st to 15thDay
62%311%13%7%
1848
16th to endDay
47%49%17%15%5%
2199
April1st to 15thDay
55%37%18%12%2
2152
16th to endDay
48%48%19%15%3
2227
May1st to 15thDay
49%5%9%20%13%1
2511
16th to endDay
46%7%12%20%12%1
2622
June1st to 15thDay
52%5%10%20%9%
2520
16th to endDay
48%7%11%20%10%
2520
July1st to 15thDay
39%7%12%28%12%
2371
16th to endDay
42%8%16%23%9%
2487
August1st to 15thDay
45%7%15%21%9%
2427
16th to endDay
37%6%15%28%11%
2318
September1st to 15thDay
41%7%10%27%12%
2160
16th to endDay
40%5%10%33%10%
1875
October1st to 15thDay
51%6%10%21%9%
1650
16th to endDay
63%5%11%13%6%
1667
November1st to 15thDay
51%5%14%19%8%
1546
16th to endDay
61%411%14%6%
1440
December1st to 15thDay
70%7%10%10%1
1440
16th to endDay
69%5%9%9%5%
1536
January1st to 15thNight
69%410%10%4
2506
16th to endNight
62%410%15%6%
2643
February1st to 15thNight
65%5%9%15%4
2287
16th to endNight
61%48%16%9%
1934
March1st to 15thNight
57%49%19%8%
2112
16th to endNight
48%39%19%15%4
2025
April1st to 15thNight
53%37%20%14%
1796
16th to endNight
46%49%18%17%3
1741
May1st to 15thNight
48%5%8%18%14%4
1440
16th to endNight
45%5%13%20%13%2
1497
June1st to 15thNight
51%7%12%17%10%1
1440
16th to endNight
44%5%14%19%14%
1440
July1st to 15thNight
32%6%15%30%14%
1360
16th to endNight
34%7%16%25%15%
1418
August1st to 15thNight
40%8%17%20%12%
1508
16th to endNight
32%5%15%30%14%
1872
September1st to 15thNight
41%5%10%29%11%
1800
16th to endNight
37%411%33%12%
1830
October1st to 15thNight
49%5%10%23%11%
1980
16th to endNight
59%5%13%16%5%
2205
November1st to 15thNight
52%5%13%16%10%1
2310
16th to endNight
62%5%10%16%4
2520
December1st to 15thNight
66%5%11%13%2
2520
16th to endNight
70%49%11%3
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
28%25%21%16%8%
60
16th to endDay
33%12%33%12%7%
71
February1st to 15thDay
30%28%31%10%
90
16th to endDay
33%14%29%18%3
198
March1st to 15thDay
27%15%30%19%7%
270
16th to endDay
25%16%26%19%8%3
288
April1st to 15thDay
31%17%29%14%7%1
270
16th to endDay
25%17%27%17%8%3
270
May1st to 15thDay
29%13%26%18%9%2
288
16th to endDay
21%17%31%17%10%1
331
June1st to 15thDay
26%10%33%19%8%1
315
16th to endDay
21%11%33%21%10%1
315
July1st to 15thDay
16%6%31%27%13%4
305
16th to endDay
14%8%29%30%14%3
326
August1st to 15thDay
17%5%28%31%12%4
313
16th to endDay
12%6%28%26%15%10%
332
September1st to 15thDay
19%5%24%23%13%13%
315
16th to endDay
17%9%29%17%14%11%
266
October1st to 15thDay
22%14%25%20%14%3
255
16th to endDay
38%10%23%20%5%
255
November1st to 15thDay
18%16%32%19%11%2
200
16th to endDay
36%11%26%23%1
60
December1st to 15thDay
26%20%40%6%6%
60
16th to endDay
48%18%25%6%1
64
January1st to 15thNight
30%14%31%18%4
720
16th to endNight
25%13%30%23%6%
768
February1st to 15thNight
23%17%34%21%3
704
16th to endNight
26%12%34%21%4
631
March1st to 15thNight
29%13%32%20%3
720
16th to endNight
22%14%26%26%9%
768
April1st to 15thNight
28%12%28%25%4
718
16th to endNight
23%14%29%22%8%
661
May1st to 15thNight
24%7%28%28%8%1
360
16th to endNight
19%6%36%25%12%
375
June1st to 15thNight
21%8%24%35%8%
360
16th to endNight
19%5%28%32%12%1
360
July1st to 15thNight
11%5%26%40%15%
340
16th to endNight
10%324%44%14%1
376
August1st to 15thNight
16%5%20%37%19%1
437
16th to endNight
13%424%35%19%1
726
September1st to 15thNight
18%6%24%30%18%1
720
16th to endNight
17%7%24%26%22%1
673
October1st to 15thNight
24%10%26%24%13%
660
16th to endNight
33%13%23%22%7%
704
November1st to 15thNight
27%12%26%21%10%
700
16th to endNight
30%15%24%18%9%
720
December1st to 15thNight
31%17%28%18%4
720
16th to endNight
33%14%29%18%21
768
Page generated at 2017-09-20 04:49:49. Version ac04

Copyright 2017 A. Danko


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