This page made possible by the sponsorship of: New Braunfels (TX) Astronomy Club.

Tye Preston Memorial Library
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tye Preston Memorial Library clear sky chart from 2005-11-05 to 2017-05-24.

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
49%
15059
26%
45867
18%
15014
57%
15014
33%
26876

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%
897
25%
2327
12%
895
48%
895
32%
1472
January16th to endNight
38%
876
30%
2412
14%
876
48%
876
31%
1484
February1st to 15thNight
35%
704
27%
2106
13%
698
47%
698
30%
1239
February16th to endNight
25%
632
28%
1894
9%
632
40%
632
29%
1117
March1st to 15thNight
32%
558
28%
1998
15%
558
48%
558
25%
1174
March16th to endNight
33%
576
22%
2112
15%
576
43%
576
24%
1226
April1st to 15thNight
29%
539
22%
1977
12%
539
44%
539
24%
1143
April16th to endNight
30%
540
24%
1773
13%
540
45%
540
25%
1115
May1st to 15thNight
35%
539
21%
1620
15%
539
44%
539
28%
1024
May16th to endNight
47%
541
24%
1621
19%
540
56%
540
32%
970
June1st to 15thNight
65%
495
24%
1485
24%
495
71%
495
47%
771
June16th to endNight
65%
495
19%
1485
19%
495
69%
495
35%
885
July1st to 15thNight
74%
465
21%
1395
22%
465
78%
465
41%
779
July16th to endNight
80%
522
22%
1468
26%
489
84%
489
43%
795
August1st to 15thNight
88%
494
29%
1538
34%
491
89%
491
52%
734
August16th to endNight
78%
525
19%
1808
23%
525
78%
525
31%
1027
September1st to 15thNight
73%
495
20%
1815
25%
495
74%
495
30%
1046
September16th to endNight
69%
492
24%
1815
27%
492
71%
492
28%
1038
October1st to 15thNight
68%
498
34%
1818
35%
498
72%
498
39%
910
October16th to endNight
60%
704
35%
2112
24%
704
67%
704
47%
1075
November1st to 15thNight
51%
712
28%
2112
18%
712
57%
712
34%
1245
November16th to endNight
47%
900
30%
2340
15%
900
54%
900
38%
1404
December1st to 15thNight
40%
900
28%
2340
15%
900
45%
900
30%
1540
December16th to endNight
38%
960
24%
2496
11%
960
44%
960
28%
1663

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%
46397
Night
13%423323347%51%
46069
Cloud CoverDay
13%5%2442445%7%44%
46395
Night
13%423323347%51%
46069
TransparencyDay
39%49%18%17%9%
46095
Night
33%411%20%18%11%
45874
SeeingDay
14%418%30%25%6%
4853
Night
15%5%23%34%18%1
15064

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
17%5%24324335%47%
1611
16th to endDay
15%5%23123335%52%
1821
February1st to 15thDay
15%5%23323345%50%
1750
16th to endDay
19%6%13222335%48%
1580
March1st to 15thDay
22%6%14313235%45%
1962
16th to endDay
18%5%24313335%47%
2112
April1st to 15thDay
15%5%24434445%44%
1971
16th to endDay
16%6%25%433346%42%
2184
May1st to 15thDay
17%7%36%5%245%46%36%
2331
16th to endDay
18%6%36%5%3446%7%34%
2336
June1st to 15thDay
6%435%436%5%6%8%42%
2145
16th to endDay
13%5%36%6%47%5%6%9%30%
2145
July1st to 15thDay
10%435%6%46%5%7%8%37%
2145
16th to endDay
9%325%5%45%6%7%11%38%
2284
August1st to 15thDay
22123345%5%11%57%
2079
16th to endDay
8%5%25%8%46%5%6%10%35%
2040
September1st to 15thDay
10%6%37%7%46%5%7%7%34%
1815
16th to endDay
11%5%25%6%245%5%7%43%
1815
October1st to 15thDay
11%41442445%6%50%
1800
16th to endDay
7%412223335%62%
1760
November1st to 15thDay
14%6%25%5%24346%43%
1743
16th to endDay
15%5%1441323453%
1620
December1st to 15thDay
20%6%23323335%43%
1620
16th to endDay
16%7%24424436%42%
1728
January1st to 15thNight
17%413323435%48%
2327
16th to endNight
18%413313345%50%
2412
February1st to 15thNight
17%5%2331223453%
2102
16th to endNight
17%5%12313336%50%
1894
March1st to 15thNight
17%7%23223325%49%
1998
16th to endNight
18%5%23312445%47%
2112
April1st to 15thNight
16%5%23423337%47%
1977
16th to endNight
19%5%23323345%45%
1773
May1st to 15thNight
15%5%2432445%7%44%
1619
16th to endNight
13%43342335%9%45%
1620
June1st to 15thNight
431332335%9%59%
1485
16th to endNight
6%324425%5%49%50%
1485
July1st to 15thNight
7%32332445%10%53%
1485
16th to endNight
6%22241446%11%53%
1576
August1st to 15thNight
11212346%11%62%
1548
16th to endNight
7%214435%5%6%12%45%
1808
September1st to 15thNight
8%426%4245%5%9%46%
1815
16th to endNight
9%5%1443345%7%48%
1815
October1st to 15thNight
11%313323347%57%
1818
16th to endNight
9%312212135%65%
2112
November1st to 15thNight
12%423423345%52%
2112
16th to endNight
16%42221224456%
2340
December1st to 15thNight
18%5%2432333448%
2340
16th to endNight
18%7%2441333446%
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
17%5%24323335%47%
1611
16th to endDay
15%5%22113335%52%
1821
February1st to 15thDay
15%6%13423345%50%
1750
16th to endDay
19%5%13232335%48%
1580
March1st to 15thDay
21%6%24313335%45%
1962
16th to endDay
18%5%2431334447%
2110
April1st to 15thDay
15%6%2443445%5%44%
1971
16th to endDay
16%6%25%434346%42%
2184
May1st to 15thDay
16%7%36%5%2445%6%36%
2331
16th to endDay
18%6%25%43446%7%34%
2336
June1st to 15thDay
6%435%5%36%6%6%9%42%
2145
16th to endDay
13%6%36%6%46%7%5%10%30%
2145
July1st to 15thDay
10%5%25%6%46%5%6%9%37%
2145
16th to endDay
8%4245%46%5%6%11%38%
2284
August1st to 15thDay
22123345%5%11%57%
2079
16th to endDay
8%6%248%46%5%6%10%35%
2040
September1st to 15thDay
10%5%36%7%46%5%7%7%34%
1815
16th to endDay
10%5%25%6%35%45%7%43%
1815
October1st to 15thDay
10%5%24424346%50%
1800
16th to endDay
8%312312335%62%
1760
November1st to 15thDay
13%6%25%5%2435%6%43%
1743
16th to endDay
15%6%2331323353%
1620
December1st to 15thDay
21%6%23323336%43%
1620
16th to endDay
16%7%24423446%43%
1728
January1st to 15thNight
17%5%13313435%48%
2327
16th to endNight
18%413323345%50%
2412
February1st to 15thNight
17%5%2321223453%
2102
16th to endNight
16%5%13313345%51%
1894
March1st to 15thNight
17%6%23223325%49%
1998
16th to endNight
17%5%2331245%5%47%
2112
April1st to 15thNight
16%5%23423347%47%
1977
16th to endNight
19%5%24423345%45%
1773
May1st to 15thNight
15%5%2431445%7%44%
1619
16th to endNight
13%42442335%9%45%
1620
June1st to 15thNight
5%31222335%9%59%
1485
16th to endNight
7%2344345%410%50%
1485
July1st to 15thNight
6%32322445%10%53%
1485
16th to endNight
6%21241446%11%53%
1576
August1st to 15thNight
12222346%11%62%
1548
16th to endNight
7%314435%5%6%11%45%
1808
September1st to 15thNight
8%5%25%4245%5%9%47%
1815
16th to endNight
9%5%145%2435%8%48%
1815
October1st to 15thNight
11%312323346%57%
1818
16th to endNight
9%312221235%65%
2112
November1st to 15thNight
12%5%23413345%52%
2112
16th to endNight
15%422212235%56%
2340
December1st to 15thNight
19%5%1432334447%
2340
16th to endNight
18%7%2432333446%
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%2317%20%13%
1612
16th to endDay
36%35%14%24%14%
1821
February1st to 15thDay
38%26%14%21%16%
1751
16th to endDay
39%25%17%20%13%
1580
March1st to 15thDay
43%37%12%19%13%
1962
16th to endDay
40%27%17%20%11%
2112
April1st to 15thDay
41%38%15%18%12%
1971
16th to endDay
44%35%19%15%10%
2184
May1st to 15thDay
48%48%14%17%6%
2331
16th to endDay
48%5%8%16%16%4
2340
June1st to 15thDay
35%6%11%21%19%4
2145
16th to endDay
47%7%10%19%11%2
2145
July1st to 15thDay
40%7%13%24%12%2
2006
16th to endDay
35%7%19%27%9%
2129
August1st to 15thDay
21%5%16%36%17%1
2065
16th to endDay
42%7%16%22%9%1
2040
September1st to 15thDay
45%6%11%18%13%4
1815
16th to endDay
37%5%10%18%17%9%
1815
October1st to 15thDay
33%410%18%19%13%
1800
16th to endDay
25%35%17%27%20%
1760
November1st to 15thDay
41%37%20%16%10%
1743
16th to endDay
36%25%12%21%20%
1620
December1st to 15thDay
43%37%17%18%9%
1620
16th to endDay
43%37%14%19%10%
1728
January1st to 15thNight
37%26%16%19%17%
2327
16th to endNight
37%25%15%21%17%
2412
February1st to 15thNight
36%26%13%21%20%
2112
16th to endNight
36%25%17%21%15%
1894
March1st to 15thNight
40%27%15%19%15%
1998
16th to endNight
38%49%15%20%11%
2112
April1st to 15thNight
38%38%16%17%15%
1977
16th to endNight
41%48%17%14%12%
1773
May1st to 15thNight
38%5%11%17%16%9%
1620
16th to endNight
35%414%26%15%3
1622
June1st to 15thNight
22%413%28%26%3
1485
16th to endNight
30%7%18%27%13%2
1485
July1st to 15thNight
24%7%21%31%12%1
1395
16th to endNight
22%7%28%31%8%
1468
August1st to 15thNight
14%8%23%37%15%
1538
16th to endNight
29%9%23%27%8%1
1808
September1st to 15thNight
33%6%19%21%14%4
1815
16th to endNight
33%6%13%19%16%9%
1815
October1st to 15thNight
27%311%26%19%13%
1818
16th to endNight
24%16%17%27%21%
2112
November1st to 15thNight
34%39%20%18%13%
2112
16th to endNight
32%27%13%20%22%
2340
December1st to 15thNight
41%35%18%20%10%
2340
16th to endNight
42%3413%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
16%7%35%32%7%
90
16th to endDay
19%10%35%19%12%2
96
February1st to 15thDay
14%15%35%26%6%1
90
16th to endDay
22%16%37%22%11
81
March1st to 15thDay
27%12%38%13%7%
90
16th to endDay
14%7%33%34%9%1
96
April1st to 15thDay
14%13%33%34%4
90
16th to endDay
19%8%39%24%8%
294
May1st to 15thDay
17%9%36%29%6%
468
16th to endDay
25%6%19%31%15%1
481
June1st to 15thDay
9%12%42%31%3
420
16th to endDay
13%111%33%30%10%
420
July1st to 15thDay
9%211%38%34%5%
400
16th to endDay
7%426%49%10%
445
August1st to 15thDay
31226%51%14%
352
16th to endDay
12%2238%28%14%
208
September1st to 15thDay
8%5%14%50%21%
90
16th to endDay
8%114%52%23%
90
October1st to 15thDay
4240%44%8%
90
16th to endDay
16%214%35%26%5%
96
November1st to 15thDay
26%5%26%25%10%5%
90
16th to endDay
23%14%25%21%12%3
90
December1st to 15thDay
27%222%26%8%12%
90
16th to endDay
26%10%34%22%5%1
96
January1st to 15thNight
20%8%25%35%9%
900
16th to endNight
20%9%28%32%9%
876
February1st to 15thNight
21%10%29%29%8%
704
16th to endNight
22%10%40%23%3
632
March1st to 15thNight
21%7%33%31%5%
558
16th to endNight
19%8%35%30%5%
576
April1st to 15thNight
17%10%37%29%4
539
16th to endNight
20%7%38%24%7%
540
May1st to 15thNight
16%6%37%32%6%
540
16th to endNight
15%427%35%16%
542
June1st to 15thNight
5%122%47%23%1
495
16th to endNight
6%114%49%24%2
495
July1st to 15thNight
6%11%47%32%2
465
16th to endNight
6%446%35%4
522
August1st to 15thNight
11444%44%5%
494
16th to endNight
8%340%42%4
525
September1st to 15thNight
9%436%41%6%
495
16th to endNight
11%18%29%44%5%
492
October1st to 15thNight
12%112%39%28%4
498
16th to endNight
11%320%34%26%2
704
November1st to 15thNight
13%5%23%33%23%1
712
16th to endNight
17%8%22%34%16%1
900
December1st to 15thNight
22%7%26%29%12%1
900
16th to endNight
23%7%25%32%9%
960
Page generated at 2017-05-25 12:27:32. Version ac04

Copyright 2017 A. Danko


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