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Austin
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Austin clear sky chart from 2005-11-05 to 2020-10-22.

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
52%
19445
26%
59255
19%
19400
59%
19400
33%
34560

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
41%
1122
27%
2912
13%
1120
49%
1120
35%
1819
January16th to endNight
39%
1140
30%
3060
14%
1140
49%
1140
33%
1916
February1st to 15thNight
32%
884
25%
2646
11%
878
43%
878
27%
1636
February16th to endNight
25%
792
26%
2374
8%
792
39%
792
26%
1470
March1st to 15thNight
32%
675
25%
2475
14%
675
45%
675
23%
1498
March16th to endNight
35%
720
22%
2640
16%
720
45%
720
24%
1547
April1st to 15thNight
32%
674
23%
2472
14%
674
46%
674
25%
1443
April16th to endNight
32%
669
26%
2191
15%
669
48%
669
29%
1293
May1st to 15thNight
40%
674
23%
2024
17%
674
48%
674
28%
1273
May16th to endNight
52%
706
26%
2116
20%
705
62%
705
37%
1199
June1st to 15thNight
72%
675
25%
2025
25%
675
77%
675
52%
995
June16th to endNight
68%
675
22%
2025
23%
675
72%
675
38%
1163
July1st to 15thNight
76%
645
20%
1935
21%
645
79%
645
44%
1038
July16th to endNight
82%
708
26%
2026
29%
675
84%
675
46%
1048
August1st to 15thNight
88%
665
29%
2012
32%
662
89%
662
56%
944
August16th to endNight
79%
717
22%
2487
26%
717
80%
717
35%
1350
September1st to 15thNight
73%
675
19%
2475
23%
675
74%
675
30%
1413
September16th to endNight
70%
672
24%
2475
27%
672
71%
672
28%
1422
October1st to 15thNight
72%
707
33%
2507
32%
707
75%
707
38%
1276
October16th to endNight
58%
924
35%
2772
23%
924
65%
924
42%
1487
November1st to 15thNight
53%
880
27%
2640
19%
880
57%
880
33%
1595
November16th to endNight
47%
1121
30%
2921
15%
1121
55%
1121
38%
1774
December1st to 15thNight
43%
1125
29%
2925
15%
1125
49%
1125
32%
1882
December16th to endNight
38%
1200
24%
3120
12%
1200
45%
1200
29%
2079

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%45%
60251
Night
12%413323347%51%
59458
TransparencyDay
37%5%9%20%18%8%
59951
Night
33%411%21%18%10%
59263
SeeingDay
13%317%27%27%9%
9476
Night
15%423%36%19%1
19450

By Month

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%5%24313336%48%
2016
16th to endDay
16%5%23323235%51%
2232
February1st to 15thDay
19%6%24312335%46%
2200
16th to endDay
21%6%23323335%44%
1980
March1st to 15thDay
21%6%25%313345%40%
2472
16th to endDay
17%5%24324346%44%
2638
April1st to 15thDay
15%6%35%424446%43%
2466
16th to endDay
15%5%35%423345%45%
2699
May1st to 15thDay
17%6%36%5%35%446%38%
2916
16th to endDay
14%5%25%5%36%5%5%8%37%
3054
June1st to 15thDay
6%3145%25%5%6%9%48%
2925
16th to endDay
9%5%25%7%47%6%8%9%34%
2925
July1st to 15thDay
7%3245%46%5%7%10%42%
2925
16th to endDay
6%3235%345%6%10%47%
3090
August1st to 15thDay
221232446%10%60%
2846
16th to endDay
6%315%5%35%6%6%10%45%
2770
September1st to 15thDay
11%436%6%245%5%7%40%
2475
16th to endDay
10%5%25%435%5%6%6%42%
2475
October1st to 15thDay
10%5%13424447%52%
2426
16th to endDay
12%31222224461%
2303
November1st to 15thDay
14%5%25%5%24346%44%
2208
16th to endDay
15%5%2331333452%
2025
December1st to 15thDay
17%7%24323236%46%
2025
16th to endDay
18%7%34324345%43%
2160
January1st to 15thNight
17%6%13212336%50%
2912
16th to endNight
17%5%13313345%49%
3060
February1st to 15thNight
19%6%24312235%49%
2642
16th to endNight
17%6%23323346%45%
2374
March1st to 15thNight
18%6%13324446%43%
2475
16th to endNight
15%6%24324446%46%
2640
April1st to 15thNight
14%5%24324446%47%
2472
16th to endNight
16%5%23323346%47%
2191
May1st to 15thNight
13%5%24424448%44%
2024
16th to endNight
10%3133245%6%11%48%
2115
June1st to 15thNight
321221435%8%63%
2025
16th to endNight
6%32442446%9%52%
2025
July1st to 15thNight
5%31331347%11%53%
2025
16th to endNight
431322335%11%57%
2134
August1st to 15thNight
211221335%9%66%
2022
16th to endNight
5%2144245%6%11%50%
2487
September1st to 15thNight
10%325%42445%8%48%
2475
16th to endNight
9%5%2442446%6%48%
2475
October1st to 15thNight
8%313413346%59%
2507
16th to endNight
13%312212225%61%
2772
November1st to 15thNight
12%414423446%50%
2640
16th to endNight
15%413322335%54%
2921
December1st to 15thNight
15%6%2432333449%
2925
16th to endNight
19%7%1432333445%
3120

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
38%35%19%20%12%
2017
16th to endDay
36%25%15%25%13%
2232
February1st to 15thDay
41%36%15%19%13%
2201
16th to endDay
44%35%16%18%12%
1980
March1st to 15thDay
46%38%11%19%10%
2472
16th to endDay
40%48%17%21%8%
2640
April1st to 15thDay
42%37%17%17%11%
2466
16th to endDay
40%45%19%19%9%
2699
May1st to 15thDay
46%47%16%17%6%
2916
16th to endDay
43%6%9%19%17%3
3058
June1st to 15thDay
29%6%12%24%21%5%
2925
16th to endDay
42%9%9%22%14%2
2925
July1st to 15thDay
33%7%16%26%13%1
2786
16th to endDay
28%6%19%31%13%
2935
August1st to 15thDay
18%5%16%39%18%2
2832
16th to endDay
31%8%15%27%14%2
2770
September1st to 15thDay
41%7%11%20%14%5%
2475
16th to endDay
39%6%8%19%16%9%
2475
October1st to 15thDay
31%49%20%20%13%
2426
16th to endDay
27%25%16%28%20%
2303
November1st to 15thDay
41%48%20%17%8%
2208
16th to endDay
35%25%16%23%16%
2025
December1st to 15thDay
42%27%17%21%8%
2025
16th to endDay
43%38%15%19%10%
2160
January1st to 15thNight
36%25%17%20%17%
2912
16th to endNight
37%2415%22%16%
3060
February1st to 15thNight
40%25%14%20%17%
2652
16th to endNight
40%36%16%17%15%
2374
March1st to 15thNight
41%310%13%18%12%
2475
16th to endNight
38%410%16%20%9%
2640
April1st to 15thNight
38%39%17%17%13%
2472
16th to endNight
37%310%19%17%11%
2191
May1st to 15thNight
39%410%21%17%7%
2025
16th to endNight
29%5%15%31%15%3
2117
June1st to 15thNight
17%5%16%28%26%5%
2025
16th to endNight
27%8%16%30%14%2
2025
July1st to 15thNight
22%7%24%30%14%1
1935
16th to endNight
21%6%24%36%10%
2026
August1st to 15thNight
14%5%22%38%17%1
2012
16th to endNight
26%8%20%29%11%2
2487
September1st to 15thNight
33%5%18%24%13%4
2475
16th to endNight
33%7%13%20%15%9%
2475
October1st to 15thNight
26%49%24%20%14%
2507
16th to endNight
27%25%16%25%22%
2772
November1st to 15thNight
35%5%10%19%19%11%
2640
16th to endNight
33%36%17%21%17%
2921
December1st to 15thNight
39%26%20%20%10%
2925
16th to endNight
42%35%13%21%13%
3120

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%30%27%13%1
225
16th to endDay
20%9%34%26%8%1
240
February1st to 15thDay
26%8%33%23%7%
225
16th to endDay
30%10%35%19%4
201
March1st to 15thDay
27%12%35%19%41
225
16th to endDay
17%5%35%30%8%2
240
April1st to 15thDay
18%10%35%25%9%1
225
16th to endDay
16%8%35%25%12%1
471
May1st to 15thDay
17%5%30%31%13%1
693
16th to endDay
14%323%34%20%3
757
June1st to 15thDay
7%8%40%34%8%
720
16th to endDay
9%210%34%32%10%
720
July1st to 15thDay
6%6%30%43%12%
700
16th to endDay
5%221%50%18%
755
August1st to 15thDay
4320%54%17%
669
16th to endDay
7%323%35%29%
426
September1st to 15thDay
10%217%38%30%
270
16th to endDay
14%8%17%35%24%
270
October1st to 15thDay
5%9%27%39%18%
270
16th to endDay
23%418%22%22%8%
259
November1st to 15thDay
26%419%26%19%4
225
16th to endDay
16%6%31%26%15%4
225
December1st to 15thDay
20%333%21%15%5%
225
16th to endDay
25%12%25%24%10%2
240
January1st to 15thNight
21%7%25%33%12%
1125
16th to endNight
20%6%29%35%8%
1140
February1st to 15thNight
23%10%30%29%6%
884
16th to endNight
24%8%40%24%2
792
March1st to 15thNight
21%7%34%31%5%
675
16th to endNight
15%8%36%33%4
720
April1st to 15thNight
16%7%39%32%2
674
16th to endNight
16%6%40%27%7%
669
May1st to 15thNight
15%7%32%35%8%
675
16th to endNight
11%229%38%18%
707
June1st to 15thNight
4117%49%25%1
675
16th to endNight
6%15%48%25%3
675
July1st to 15thNight
6%18%44%35%3
645
16th to endNight
5%445%39%3
708
August1st to 15thNight
2349%38%5%
665
16th to endNight
6%5%40%43%4
717
September1st to 15thNight
11%432%45%5%
675
16th to endNight
10%17%33%41%5%
672
October1st to 15thNight
9%19%40%34%4
707
16th to endNight
14%320%32%26%2
924
November1st to 15thNight
14%322%36%21%1
880
16th to endNight
17%425%33%17%1
1121
December1st to 15thNight
20%6%26%35%10%
1125
16th to endNight
23%5%26%33%9%
1200
Page generated at 2020-10-23 14:21:09. Version ac04

Copyright 2020 A. Danko


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