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 2017-03-24.

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
53%
14845
26%
45268
19%
14803
59%
14803
34%
26221

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
24%
2327
12%
895
50%
895
33%
1478
January16th to endNight
44%
849
28%
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
47%
632
32%
1087
March1st to 15thNight
37%
567
28%
2007
17%
567
50%
567
28%
1148
March16th to endNight
33%
555
22%
2035
15%
555
43%
555
26%
1154
April1st to 15thNight
31%
494
23%
1812
13%
494
46%
494
28%
1022
April16th to endNight
33%
495
22%
1631
16%
495
44%
495
24%
1036
May1st to 15thNight
32%
494
22%
1485
16%
494
41%
494
28%
930
May16th to endNight
48%
514
24%
1540
20%
513
57%
513
33%
918
June1st to 15thNight
67%
495
24%
1485
25%
495
72%
495
49%
748
June16th to endNight
66%
495
19%
1485
19%
495
70%
495
35%
876
July1st to 15thNight
74%
465
22%
1395
24%
465
78%
465
40%
784
July16th to endNight
80%
522
22%
1468
27%
489
82%
489
44%
794
August1st to 15thNight
89%
494
29%
1574
34%
491
90%
491
53%
741
August16th to endNight
79%
525
18%
1800
22%
525
80%
525
30%
1059
September1st to 15thNight
73%
495
20%
1815
24%
495
74%
495
28%
1062
September16th to endNight
71%
492
24%
1815
27%
492
72%
492
29%
1020
October1st to 15thNight
72%
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%
45651
Night
12%423323347%51%
45468
Cloud CoverDay
13%5%2442445%7%43%
45649
Night
13%423323347%51%
45468
TransparencyDay
38%5%10%18%17%9%
45349
Night
32%412%20%18%11%
45273
SeeingDay
12%417%30%27%7%
4573
Night
14%422%38%19%1
14852

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%24313345%45%
2033
April1st to 15thDay
16%434324445%44%
1806
16th to endDay
18%7%34423335%43%
1995
May1st to 15thDay
16%7%35%5%345%5%7%35%
2136
16th to endDay
16%7%26%5%345%5%7%35%
2222
June1st to 15thDay
6%425%5%36%7%7%10%42%
2145
16th to endDay
10%6%46%6%46%5%6%10%31%
2145
July1st to 15thDay
11%425%7%36%5%5%10%37%
2145
16th to endDay
9%3235%36%49%12%37%
2284
August1st to 15thDay
2213325%5%6%11%55%
2043
16th to endDay
7%426%7%45%6%7%10%35%
2048
September1st to 15thDay
9%6%37%6%36%6%7%7%34%
1815
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
17%5%22323336%48%
2035
April1st to 15thNight
14%4235%13347%49%
1812
16th to endNight
18%6%24324336%43%
1631
May1st to 15thNight
14%6%3432345%6%44%
1484
16th to endNight
12%4243233410%48%
1539
June1st to 15thNight
5%21222335%10%59%
1485
16th to endNight
7%3135%345%5%10%48%
1485
July1st to 15thNight
6%33332346%10%52%
1485
16th to endNight
6%2133136%6%10%53%
1576
August1st to 15thNight
111232346%9%63%
1584
16th to endNight
6%424435%5%6%11%45%
1800
September1st to 15thNight
8%425%425%45%10%46%
1815
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
19%6%24223335%45%
2031
April1st to 15thDay
16%425%32445%5%44%
1806
16th to endDay
18%6%45%423345%43%
1995
May1st to 15thDay
17%7%25%6%345%5%6%35%
2136
16th to endDay
17%5%36%5%35%45%7%35%
2222
June1st to 15thDay
7%425%437%6%6%9%42%
2145
16th to endDay
10%5%47%6%45%5%7%10%31%
2145
July1st to 15thDay
10%426%6%36%5%5%9%37%
2145
16th to endDay
9%3246%36%5%8%12%37%
2284
August1st to 15thDay
2212325%6%5%11%56%
2043
16th to endDay
8%427%7%36%6%6%11%35%
2048
September1st to 15thDay
9%6%46%6%46%6%6%8%34%
1815
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%23322436%47%
2035
April1st to 15thNight
15%324423346%49%
1812
16th to endNight
19%6%34324336%43%
1631
May1st to 15thNight
14%6%2342345%6%45%
1484
16th to endNight
12%414323349%48%
1539
June1st to 15thNight
421322335%10%59%
1485
16th to endNight
7%3134345%5%9%49%
1485
July1st to 15thNight
6%33332346%10%52%
1485
16th to endNight
6%3123145%5%10%53%
1576
August1st to 15thNight
111231346%9%63%
1584
16th to endNight
6%424445%5%6%11%45%
1800
September1st to 15thNight
8%5%25%42445%9%47%
1815
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
40%38%16%18%12%
2033
April1st to 15thDay
39%5%8%15%16%14%
1806
16th to endDay
43%37%18%15%11%
1995
May1st to 15thDay
46%5%10%15%16%5%
2136
16th to endDay
44%5%9%17%17%4
2226
June1st to 15thDay
32%8%13%22%18%5%
2145
16th to endDay
45%7%12%21%10%1
2145
July1st to 15thDay
40%6%14%21%14%2
2006
16th to endDay
32%10%18%29%8%
2129
August1st to 15thDay
20%6%17%37%15%1
2029
16th to endDay
40%8%18%21%9%1
2048
September1st to 15thDay
44%9%11%16%14%3
1815
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
36%411%15%20%12%
2035
April1st to 15thNight
34%410%16%17%16%
1812
16th to endNight
42%5%9%16%14%13%
1631
May1st to 15thNight
38%6%12%19%15%7%
1485
16th to endNight
32%7%14%26%15%4
1541
June1st to 15thNight
19%5%15%28%25%4
1485
16th to endNight
30%7%18%28%13%2
1485
July1st to 15thNight
25%8%20%31%12%1
1395
16th to endNight
21%8%28%31%8%1
1468
August1st to 15thNight
15%6%24%39%13%
1574
16th to endNight
30%9%23%25%8%1
1800
September1st to 15thNight
33%8%17%22%13%4
1815
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
18%9%24%41%6%
75
April1st to 15thDay
20%6%31%26%15%
45
16th to endDay
17%5%40%28%7%
225
May1st to 15thDay
18%8%34%31%7%
393
16th to endDay
21%323%32%17%
437
June1st to 15thDay
7%8%41%35%6%
420
16th to endDay
11%10%31%36%9%
420
July1st to 15thDay
7%210%34%38%7%
400
16th to endDay
6%16%24%47%14%
445
August1st to 15thDay
3226%46%20%
318
16th to endDay
10%18%34%32%12%
216
September1st to 15thDay
5%124%51%17%
90
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%37%33%4
555
April1st to 15thNight
15%5%42%31%3
494
16th to endNight
21%5%37%29%6%
495
May1st to 15thNight
16%5%41%33%3
495
16th to endNight
12%232%39%13%
515
June1st to 15thNight
419%53%20%1
495
16th to endNight
5%216%50%24%1
495
July1st to 15thNight
6%110%49%30%1
465
16th to endNight
6%446%39%2
522
August1st to 15thNight
1248%43%4
494
16th to endNight
7%342%41%4
525
September1st to 15thNight
10%1434%43%5%
495
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 2017-03-25 11:39:52. Version ac04

Copyright 2017 A. Danko


San Antonio Clear Sky Chart | Charts Home