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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 2018-03-11.

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%
16102
26%
49096
19%
16060
59%
16060
34%
28444

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%
970
26%
2522
13%
970
51%
970
34%
1592
January16th to endNight
45%
920
28%
2584
16%
920
52%
920
33%
1584
February1st to 15thNight
41%
764
27%
2288
16%
759
49%
759
31%
1365
February16th to endNight
31%
684
26%
2050
11%
684
44%
684
29%
1222
March1st to 15thNight
36%
602
27%
2130
16%
602
49%
602
28%
1233
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%
540
20%
1980
24%
540
75%
540
30%
1118
September16th to endNight
69%
537
24%
1980
27%
537
70%
537
28%
1126
October1st to 15thNight
73%
540
33%
1980
34%
540
77%
540
41%
962
October16th to endNight
65%
753
37%
2289
28%
753
69%
753
49%
1139
November1st to 15thNight
56%
780
26%
2300
17%
780
60%
780
34%
1358
November16th to endNight
55%
975
31%
2535
17%
975
61%
975
43%
1457
December1st to 15thNight
48%
975
27%
2535
17%
975
51%
975
32%
1641
December16th to endNight
41%
1040
23%
2704
12%
1040
46%
1040
29%
1795

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%
49518
Night
12%423323347%51%
49296
Cloud CoverDay
13%5%2442445%7%43%
49516
Night
13%413323347%51%
49296
TransparencyDay
38%5%10%18%17%9%
49216
Night
32%5%12%20%17%11%
49101
SeeingDay
13%417%30%26%7%
5849
Night
14%422%38%19%1
16109

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%24323325%46%
1746
16th to endDay
17%5%23312345%48%
2002
February1st to 15thDay
18%6%34213235%48%
1900
16th to endDay
19%7%13413346%44%
1710
March1st to 15thDay
21%7%14323325%44%
2063
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%37%
1980
16th to endDay
11%6%35%6%3445%7%42%
1980
October1st to 15thDay
10%41342445%6%51%
1980
16th to endDay
8%313213346%62%
1920
November1st to 15thDay
15%7%35%434446%40%
1885
16th to endDay
15%5%1332223454%
1755
December1st to 15thDay
22%6%34314435%41%
1755
16th to endDay
18%7%25%324345%41%
1872
January1st to 15thNight
17%423413335%50%
2522
16th to endNight
18%413312345%49%
2584
February1st to 15thNight
17%5%1232224451%
2282
16th to endNight
19%413422235%50%
2050
March1st to 15thNight
18%5%23312235%50%
2130
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
7%424425%45%10%49%
1980
16th to endNight
10%5%25%4335%5%8%46%
1980
October1st to 15thNight
7%31331445%7%58%
1980
16th to endNight
7%31321223466%
2289
November1st to 15thNight
10%5%25%424346%51%
2300
16th to endNight
13%413212225%59%
2535
December1st to 15thNight
19%5%14322336%47%
2535
16th to endNight
19%5%25%322235%45%
2704

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%
1746
16th to endDay
17%5%2331234449%
2002
February1st to 15thDay
18%6%24313225%48%
1900
16th to endDay
19%6%24313345%45%
1710
March1st to 15thDay
21%7%14323335%44%
2063
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%36%6%35%6%6%8%38%
1980
16th to endDay
11%5%345%4345%7%42%
1980
October1st to 15thDay
10%3135%2445%6%51%
1980
16th to endDay
8%313213335%62%
1920
November1st to 15thDay
15%7%35%433446%40%
1885
16th to endDay
15%5%1331232454%
1755
December1st to 15thDay
22%6%33313345%41%
1755
16th to endDay
18%6%25%424346%41%
1872
January1st to 15thNight
18%423412336%49%
2522
16th to endNight
18%413312345%49%
2584
February1st to 15thNight
18%413223245%51%
2282
16th to endNight
19%413312245%50%
2050
March1st to 15thNight
19%423413335%50%
2130
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
7%41442445%9%49%
1980
16th to endNight
10%5%15%4245%6%7%46%
1980
October1st to 15thNight
8%212314448%58%
1980
16th to endNight
7%312212235%66%
2289
November1st to 15thNight
10%5%25%323436%52%
2300
16th to endNight
13%422212225%60%
2535
December1st to 15thNight
20%5%23323336%48%
2535
16th to endNight
19%5%25%322335%45%
2704

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%13%
1747
16th to endDay
38%37%13%22%14%
2002
February1st to 15thDay
40%25%15%18%16%
1901
16th to endDay
40%46%15%20%12%
1710
March1st to 15thDay
43%37%14%16%14%
2063
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
41%8%11%17%16%4
1980
16th to endDay
40%6%10%18%15%9%
1980
October1st to 15thDay
33%5%11%18%20%11%
1980
16th to endDay
23%37%15%27%22%
1920
November1st to 15thDay
43%49%16%15%10%
1885
16th to endDay
34%27%14%21%19%
1755
December1st to 15thDay
45%37%15%17%9%
1755
16th to endDay
44%37%16%17%9%
1872
January1st to 15thNight
37%26%16%19%17%
2522
16th to endNight
37%26%15%21%16%
2584
February1st to 15thNight
36%36%14%18%19%
2292
16th to endNight
36%36%18%20%15%
2050
March1st to 15thNight
36%310%15%17%15%
2130
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
30%8%16%23%15%5%
1980
16th to endNight
34%6%15%21%14%8%
1980
October1st to 15thNight
23%412%28%17%12%
1980
16th to endNight
22%26%17%27%23%
2289
November1st to 15thNight
33%411%19%17%12%
2300
16th to endNight
28%29%15%22%21%
2535
December1st to 15thNight
39%37%17%19%11%
2535
16th to endNight
42%36%14%21%12%
2704

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
21%5%32%28%9%1
135
16th to endDay
18%10%31%24%13%1
144
February1st to 15thDay
25%12%23%20%15%1
135
16th to endDay
30%11%34%19%4
120
March1st to 15thDay
25%12%29%24%7%
121
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
3229%50%14%
135
16th to endDay
12%223%42%19%
135
October1st to 15thDay
25%33%42%14%
135
16th to endDay
14%315%30%29%6%
144
November1st to 15thDay
23%10%17%26%18%2
135
16th to endDay
19%6%27%25%14%6%
135
December1st to 15thDay
27%7%18%28%11%6%
135
16th to endDay
32%6%29%23%6%1
144
January1st to 15thNight
21%6%24%35%12%
975
16th to endNight
20%425%38%10%
920
February1st to 15thNight
21%7%27%35%8%
764
16th to endNight
23%8%33%30%3
684
March1st to 15thNight
20%5%33%34%5%
602
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%1437%42%4
540
16th to endNight
10%8%36%39%3
537
October1st to 15thNight
7%111%41%34%3
540
16th to endNight
8%319%40%25%3
753
November1st to 15thNight
12%321%37%23%1
780
16th to endNight
15%421%35%21%1
975
December1st to 15thNight
21%5%19%36%16%
975
16th to endNight
22%6%23%34%12%
1040
Page generated at 2018-03-12 12:28:05. Version ac04

Copyright 2018 A. Danko


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