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San Antonio
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the San Antonio clear sky chart from 2005-11-05 to 2017-09-10.

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
54%
15349
26%
46887
19%
15307
60%
15307
34%
27052

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
44%
895
25%
2327
12%
895
50%
895
33%
1478
January16th to endNight
44%
849
29%
2385
16%
849
52%
849
33%
1457
February1st to 15thNight
42%
704
28%
2108
17%
699
51%
699
32%
1234
February16th to endNight
33%
632
28%
1894
11%
632
46%
632
32%
1087
March1st to 15thNight
37%
567
28%
2007
17%
567
50%
567
28%
1148
March16th to endNight
34%
576
23%
2112
16%
576
45%
576
27%
1190
April1st to 15thNight
31%
539
23%
1977
12%
539
46%
539
29%
1113
April16th to endNight
32%
540
24%
1779
16%
540
45%
540
25%
1109
May1st to 15thNight
34%
539
22%
1620
16%
539
42%
539
29%
999
May16th to endNight
46%
562
24%
1684
19%
561
56%
561
32%
1011
June1st to 15thNight
69%
540
23%
1620
24%
540
74%
540
50%
806
June16th to endNight
65%
540
21%
1620
21%
540
70%
540
36%
946
July1st to 15thNight
76%
510
21%
1530
23%
510
79%
510
41%
849
July16th to endNight
81%
564
23%
1594
27%
531
84%
531
44%
859
August1st to 15thNight
88%
539
27%
1718
32%
536
89%
536
51%
823
August16th to endNight
78%
573
20%
1965
23%
573
79%
573
31%
1147
September1st to 15thNight
74%
525
19%
1925
23%
525
75%
525
29%
1103
September16th to endNight
71%
492
24%
1815
27%
492
72%
492
29%
1020
October1st to 15thNight
73%
495
36%
1815
36%
495
76%
495
42%
876
October16th to endNight
65%
690
35%
2098
27%
690
68%
690
48%
1060
November1st to 15thNight
56%
718
28%
2118
19%
718
60%
718
35%
1237
November16th to endNight
53%
900
29%
2340
16%
900
59%
900
41%
1365
December1st to 15thNight
48%
900
28%
2340
17%
900
51%
900
32%
1513
December16th to endNight
43%
960
24%
2496
13%
960
48%
960
31%
1622

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%5%2442445%7%43%
47726
Night
12%423323347%51%
47087
Cloud CoverDay
13%5%2442445%7%44%
47724
Night
12%413323347%51%
47087
TransparencyDay
38%5%10%19%17%9%
47424
Night
32%5%12%20%18%11%
46892
SeeingDay
12%317%30%27%8%
5304
Night
14%422%38%19%1
15356

By Month

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
18%6%24423326%46%
1611
16th to endDay
17%423312345%49%
1848
February1st to 15thDay
16%5%24213235%50%
1750
16th to endDay
17%6%13313346%47%
1580
March1st to 15thDay
21%6%14223335%45%
1950
16th to endDay
19%6%24213335%46%
2112
April1st to 15thDay
16%424424445%44%
1971
16th to endDay
17%6%34423335%43%
2177
May1st to 15thDay
15%7%35%5%2445%6%38%
2331
16th to endDay
16%7%36%5%345%5%7%34%
2430
June1st to 15thDay
5%425%5%36%6%6%10%42%
2340
16th to endDay
9%5%46%6%46%5%7%10%33%
2340
July1st to 15thDay
10%425%7%36%5%5%10%38%
2340
16th to endDay
8%3235%46%5%9%12%37%
2466
August1st to 15thDay
2213325%6%6%11%54%
2228
16th to endDay
8%426%6%45%6%7%10%36%
2235
September1st to 15thDay
8%6%36%6%36%6%7%8%36%
1922
16th to endDay
10%6%35%5%3445%7%43%
1815
October1st to 15thDay
10%41342435%6%50%
1815
16th to endDay
8%313213336%61%
1760
November1st to 15thDay
14%6%35%424446%42%
1737
16th to endDay
16%5%1332223453%
1620
December1st to 15thDay
22%6%3424335%42%
1620
16th to endDay
16%6%25%424345%43%
1728
January1st to 15thNight
18%423413336%49%
2327
16th to endNight
18%413312345%50%
2385
February1st to 15thNight
16%5%12322235%53%
2102
16th to endNight
17%413412235%53%
1894
March1st to 15thNight
19%5%23312135%51%
2007
16th to endNight
16%5%22323336%48%
2112
April1st to 15thNight
14%4235%23347%49%
1977
16th to endNight
17%6%23324336%44%
1779
May1st to 15thNight
13%5%2442445%6%46%
1619
16th to endNight
11%42441335%10%47%
1683
June1st to 15thNight
421222335%10%60%
1620
16th to endNight
7%31443445%9%50%
1620
July1st to 15thNight
5%33331346%10%53%
1620
16th to endNight
6%2133146%6%10%53%
1702
August1st to 15thNight
111222346%9%62%
1728
16th to endNight
7%424435%5%6%11%46%
1965
September1st to 15thNight
8%424425%45%10%47%
1925
16th to endNight
9%5%25%4335%5%7%47%
1815
October1st to 15thNight
8%213213447%59%
1815
16th to endNight
8%313212135%65%
2098
November1st to 15thNight
9%425%324346%53%
2118
16th to endNight
14%5%23212225%58%
2340
December1st to 15thNight
18%5%14322336%47%
2340
16th to endNight
18%5%25%322245%47%
2496

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
18%6%14423335%46%
1611
16th to endDay
16%42431234450%
1848
February1st to 15thDay
16%6%24313235%51%
1750
16th to endDay
17%5%23313345%48%
1580
March1st to 15thDay
21%7%14322235%45%
1950
16th to endDay
18%6%24223335%46%
2110
April1st to 15thDay
16%425%42345%5%44%
1971
16th to endDay
17%6%35%423345%43%
2177
May1st to 15thDay
16%6%25%5%2445%6%38%
2331
16th to endDay
17%5%36%5%3445%8%34%
2430
June1st to 15thDay
6%324437%6%6%9%43%
2340
16th to endDay
10%5%46%6%45%5%7%10%32%
2340
July1st to 15thDay
9%425%6%36%5%5%10%38%
2340
16th to endDay
9%3246%36%5%9%11%38%
2466
August1st to 15thDay
2212325%6%6%11%54%
2228
16th to endDay
8%426%6%35%6%6%11%37%
2235
September1st to 15thDay
8%6%46%6%35%6%6%8%36%
1922
16th to endDay
11%5%345%3345%7%44%
1815
October1st to 15thDay
11%31342445%6%51%
1815
16th to endDay
9%312213335%61%
1760
November1st to 15thDay
14%7%35%433447%42%
1737
16th to endDay
16%5%1431232353%
1620
December1st to 15thDay
22%6%33313345%42%
1620
16th to endDay
16%6%25%424346%43%
1728
January1st to 15thNight
18%423412336%49%
2327
16th to endNight
18%413312345%50%
2385
February1st to 15thNight
16%5%13223245%53%
2102
16th to endNight
17%413312235%52%
1894
March1st to 15thNight
19%42241223452%
2007
16th to endNight
17%5%23323436%47%
2112
April1st to 15thNight
15%324423347%49%
1977
16th to endNight
18%5%24323336%44%
1779
May1st to 15thNight
13%5%2342345%6%47%
1619
16th to endNight
12%42432335%9%47%
1683
June1st to 15thNight
421322335%10%60%
1620
16th to endNight
7%3135%345%5%9%50%
1620
July1st to 15thNight
5%32332346%11%53%
1620
16th to endNight
6%2123145%6%10%53%
1702
August1st to 15thNight
11123235%5%9%62%
1728
16th to endNight
7%3144445%6%10%46%
1965
September1st to 15thNight
8%41442445%9%48%
1925
16th to endNight
9%5%25%42446%7%47%
1815
October1st to 15thNight
8%212313447%59%
1815
16th to endNight
8%312212235%65%
2098
November1st to 15thNight
9%425%323436%53%
2118
16th to endNight
14%5%22212225%58%
2340
December1st to 15thNight
19%5%23323335%48%
2340
16th to endNight
18%5%25%322335%47%
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
40%35%16%20%14%
1612
16th to endDay
37%37%14%22%15%
1848
February1st to 15thDay
38%25%15%19%17%
1751
16th to endDay
37%36%16%22%13%
1580
March1st to 15thDay
43%27%14%17%14%
1950
16th to endDay
39%38%17%18%12%
2112
April1st to 15thDay
40%5%7%15%17%13%
1971
16th to endDay
42%37%19%15%11%
2177
May1st to 15thDay
44%5%10%15%17%6%
2331
16th to endDay
44%6%10%17%17%3
2434
June1st to 15thDay
32%8%13%22%18%5%
2340
16th to endDay
43%7%12%21%12%1
2340
July1st to 15thDay
38%6%15%22%13%2
2201
16th to endDay
32%10%19%29%8%
2311
August1st to 15thDay
21%7%18%36%14%1
2214
16th to endDay
39%8%17%22%9%1
2235
September1st to 15thDay
42%9%11%17%15%3
1922
16th to endDay
38%6%10%18%16%10%
1815
October1st to 15thDay
34%49%17%21%12%
1815
16th to endDay
24%37%17%27%20%
1760
November1st to 15thDay
41%48%17%16%11%
1737
16th to endDay
36%27%11%20%21%
1620
December1st to 15thDay
45%37%16%17%9%
1620
16th to endDay
42%37%16%18%10%
1728
January1st to 15thNight
37%36%15%18%17%
2327
16th to endNight
37%26%15%21%16%
2385
February1st to 15thNight
34%36%14%19%21%
2112
16th to endNight
34%35%18%21%16%
1894
March1st to 15thNight
36%39%15%18%16%
2007
16th to endNight
35%411%15%19%13%
2112
April1st to 15thNight
34%410%16%16%16%
1977
16th to endNight
40%5%9%17%14%12%
1779
May1st to 15thNight
36%6%11%19%16%9%
1620
16th to endNight
32%7%14%25%15%4
1685
June1st to 15thNight
19%5%16%28%26%3
1620
16th to endNight
30%6%17%28%14%2
1620
July1st to 15thNight
24%8%21%32%12%1
1530
16th to endNight
21%9%28%31%9%
1594
August1st to 15thNight
16%6%24%38%12%
1718
16th to endNight
30%9%22%26%8%2
1965
September1st to 15thNight
31%8%17%23%14%4
1925
16th to endNight
33%6%14%21%15%9%
1815
October1st to 15thNight
23%411%29%18%13%
1815
16th to endNight
23%26%17%28%21%
2098
November1st to 15thNight
32%410%19%19%13%
2118
16th to endNight
30%210%13%20%22%
2340
December1st to 15thNight
39%38%17%19%11%
2340
16th to endNight
39%37%14%22%13%
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
17%5%33%34%7%1
90
16th to endDay
15%15%29%21%15%2
96
February1st to 15thDay
16%14%27%20%20%1
90
16th to endDay
16%12%38%28%4
81
March1st to 15thDay
24%13%28%23%10%
90
16th to endDay
14%7%31%39%7%
96
April1st to 15thDay
18%6%32%31%11%
90
16th to endDay
14%6%40%29%8%
287
May1st to 15thDay
16%8%35%32%7%
468
16th to endDay
21%423%33%15%
517
June1st to 15thDay
6%8%43%35%6%
495
16th to endDay
10%9%32%36%10%
495
July1st to 15thDay
7%18%31%41%10%
475
16th to endDay
6%16%23%47%15%
515
August1st to 15thDay
3226%45%20%
383
16th to endDay
12%19%30%29%17%
275
September1st to 15thDay
4126%52%15%
119
16th to endDay
5%116%47%28%
90
October1st to 15thDay
27%36%44%8%
90
16th to endDay
15%213%31%31%6%
96
November1st to 15thDay
18%11%23%27%15%3
90
16th to endDay
23%5%33%23%8%5%
90
December1st to 15thDay
26%6%20%26%12%7%
90
16th to endDay
23%9%33%26%6%1
96
January1st to 15thNight
21%6%23%36%11%
900
16th to endNight
20%5%26%38%10%
849
February1st to 15thNight
19%7%27%35%9%
704
16th to endNight
21%8%34%31%4
632
March1st to 15thNight
20%432%35%6%
567
16th to endNight
16%7%36%34%4
576
April1st to 15thNight
15%6%42%31%4
539
16th to endNight
20%5%38%28%6%
540
May1st to 15thNight
15%5%41%33%4
540
16th to endNight
12%234%38%12%
563
June1st to 15thNight
419%53%20%1
540
16th to endNight
5%116%50%24%2
540
July1st to 15thNight
6%110%49%30%1
510
16th to endNight
5%447%38%3
564
August1st to 15thNight
1247%43%4
539
16th to endNight
8%442%39%5%
573
September1st to 15thNight
9%1436%43%4
525
16th to endNight
9%7%35%42%4
492
October1st to 15thNight
8%112%42%33%2
495
16th to endNight
9%318%40%25%3
690
November1st to 15thNight
11%322%36%23%2
718
16th to endNight
16%421%34%21%1
900
December1st to 15thNight
21%5%20%36%15%
900
16th to endNight
21%6%23%35%13%
960
Page generated at 2017-09-11 18:35:18. Version ac04

Copyright 2017 A. Danko


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