This page made possible by the sponsorship of: Williamson County Astronomy Club.

Georgetown
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Georgetown 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
50%
16187
27%
49075
19%
16140
58%
16140
35%
27888

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
39%
974
28%
2522
12%
970
48%
970
35%
1551
January16th to endNight
34%
1001
30%
2665
12%
1001
46%
1001
34%
1640
February1st to 15thNight
33%
764
28%
2286
11%
758
46%
758
30%
1339
February16th to endNight
24%
684
27%
2050
8%
684
39%
684
27%
1225
March1st to 15thNight
33%
573
27%
2101
15%
573
48%
573
24%
1220
March16th to endNight
34%
576
24%
2112
16%
576
47%
576
27%
1176
April1st to 15thNight
31%
539
24%
1977
13%
539
48%
539
27%
1102
April16th to endNight
32%
540
25%
1758
15%
540
48%
540
29%
1045
May1st to 15thNight
37%
539
23%
1620
17%
539
46%
539
31%
974
May16th to endNight
50%
562
25%
1684
20%
561
60%
561
35%
975
June1st to 15thNight
70%
540
24%
1620
24%
540
75%
540
52%
790
June16th to endNight
70%
540
23%
1620
24%
540
74%
540
40%
893
July1st to 15thNight
78%
510
23%
1530
26%
510
81%
510
47%
795
July16th to endNight
82%
564
27%
1594
31%
531
85%
531
49%
806
August1st to 15thNight
88%
539
32%
1616
36%
536
89%
536
58%
748
August16th to endNight
77%
573
21%
1988
25%
573
78%
573
32%
1110
September1st to 15thNight
75%
540
20%
1980
25%
540
77%
540
33%
1090
September16th to endNight
71%
537
29%
1980
31%
537
73%
537
32%
1063
October1st to 15thNight
70%
571
34%
2011
33%
571
74%
571
40%
990
October16th to endNight
59%
768
37%
2304
25%
768
66%
768
49%
1135
November1st to 15thNight
51%
763
27%
2283
17%
763
57%
763
36%
1332
November16th to endNight
47%
975
33%
2535
17%
975
55%
975
40%
1492
December1st to 15thNight
41%
975
28%
2535
15%
975
48%
975
33%
1616
December16th to endNight
36%
1040
24%
2704
10%
1040
44%
1040
30%
1781

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
11%5%2442445%7%47%
49535
Night
10%423323347%53%
49277
TransparencyDay
36%49%20%19%9%
49235
Night
31%310%21%20%11%
49082
SeeingDay
12%317%29%27%8%
5947
Night
13%5%25%35%18%2
16190

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
15%5%2321333452%
1746
16th to endDay
14%424323336%51%
1921
February1st to 15thDay
15%5%24323235%51%
1900
16th to endDay
18%7%24213335%48%
1710
March1st to 15thDay
19%5%25%323335%44%
2092
16th to endDay
14%6%23423236%48%
2110
April1st to 15thDay
12%7%345%3335%6%44%
1971
16th to endDay
14%6%35%5%24346%44%
2195
May1st to 15thDay
14%6%35%5%35%45%6%38%
2331
16th to endDay
14%6%25%5%46%6%6%8%34%
2430
June1st to 15thDay
4324436%6%7%8%48%
2340
16th to endDay
9%5%26%5%35%5%6%9%39%
2340
July1st to 15thDay
6%325%6%46%5%6%9%43%
2340
16th to endDay
7%3235%35%6%6%9%46%
2466
August1st to 15thDay
111232445%10%61%
2331
16th to endDay
6%4246%46%5%6%11%41%
2214
September1st to 15thDay
8%4246%36%45%7%43%
1980
16th to endDay
8%4235%445%5%8%46%
1980
October1st to 15thDay
9%414423335%56%
1935
16th to endDay
7%312312236%66%
1920
November1st to 15thDay
11%6%35%423445%48%
1901
16th to endDay
13%31321334457%
1755
December1st to 15thDay
16%7%24323435%46%
1755
16th to endDay
16%7%25%413445%43%
1872
January1st to 15thNight
15%5%14212336%52%
2522
16th to endNight
15%423423336%51%
2665
February1st to 15thNight
16%6%1321222454%
2282
16th to endNight
14%5%23424335%49%
2050
March1st to 15thNight
15%5%24322445%47%
2101
16th to endNight
12%424323446%50%
2112
April1st to 15thNight
11%424333346%50%
1977
16th to endNight
13%5%25%324447%47%
1758
May1st to 15thNight
10%5%2432436%8%47%
1619
16th to endNight
7%5%134345%7%9%47%
1683
June1st to 15thNight
321222346%10%61%
1620
16th to endNight
5%312425%46%9%53%
1620
July1st to 15thNight
421332446%10%57%
1620
16th to endNight
321232345%12%57%
1702
August1st to 15thNight
21221325%10%67%
1626
16th to endNight
6%325%4245%6%10%47%
1988
September1st to 15thNight
7%32342446%9%49%
1980
16th to endNight
7%4245%2345%7%51%
1980
October1st to 15thNight
9%23213336%62%
2011
16th to endNight
7%312212245%66%
2304
November1st to 15thNight
10%425%323247%53%
2283
16th to endNight
12%42332222459%
2535
December1st to 15thNight
14%7%24323336%48%
2535
16th to endNight
17%7%24323335%47%
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
36%36%19%22%12%
1747
16th to endDay
36%3413%27%14%
1921
February1st to 15thDay
38%26%15%22%15%
1901
16th to endDay
41%25%18%19%12%
1710
March1st to 15thDay
43%26%13%22%11%
2092
16th to endDay
38%28%18%23%9%
2112
April1st to 15thDay
40%37%18%16%12%
1971
16th to endDay
42%35%18%18%10%
2195
May1st to 15thDay
46%48%14%17%8%
2331
16th to endDay
45%5%11%18%16%3
2434
June1st to 15thDay
32%5%10%23%22%5%
2340
16th to endDay
40%5%12%22%16%3
2340
July1st to 15thDay
34%7%15%26%14%1
2201
16th to endDay
31%6%17%29%14%1
2311
August1st to 15thDay
18%5%16%38%19%2
2317
16th to endDay
34%8%16%25%11%3
2214
September1st to 15thDay
37%5%10%23%15%6%
1980
16th to endDay
34%411%21%19%8%
1980
October1st to 15thDay
30%310%22%18%14%
1935
16th to endDay
21%25%17%32%20%
1920
November1st to 15thDay
38%39%20%18%10%
1901
16th to endDay
31%26%16%23%19%
1755
December1st to 15thDay
41%18%17%21%9%
1755
16th to endDay
43%39%15%19%9%
1872
January1st to 15thNight
35%25%18%21%17%
2522
16th to endNight
36%2413%25%18%
2665
February1st to 15thNight
35%25%15%21%19%
2292
16th to endNight
37%36%17%20%15%
2050
March1st to 15thNight
39%37%13%22%13%
2101
16th to endNight
35%310%16%22%11%
2112
April1st to 15thNight
35%38%18%18%15%
1977
16th to endNight
37%310%18%17%11%
1758
May1st to 15thNight
35%5%10%21%18%8%
1620
16th to endNight
30%5%14%27%16%3
1685
June1st to 15thNight
17%5%15%28%27%5%
1620
16th to endNight
26%5%16%29%17%3
1620
July1st to 15thNight
20%7%22%33%14%1
1530
16th to endNight
20%5%24%36%13%
1594
August1st to 15thNight
13%5%20%37%19%2
1616
16th to endNight
30%6%20%26%11%3
1988
September1st to 15thNight
30%6%17%25%13%7%
1980
16th to endNight
30%5%12%23%17%9%
1980
October1st to 15thNight
24%410%26%19%14%
2011
16th to endNight
21%25%17%27%25%
2304
November1st to 15thNight
33%210%21%19%12%
2283
16th to endNight
31%25%16%23%20%
2535
December1st to 15thNight
39%28%18%20%11%
2535
16th to endNight
41%26%15%22%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
17%6%34%29%10%2
135
16th to endDay
16%10%33%27%10%1
144
February1st to 15thDay
16%6%39%31%5%
135
16th to endDay
25%11%38%21%3
120
March1st to 15thDay
23%8%35%20%10%1
121
16th to endDay
16%7%34%26%14%1
96
April1st to 15thDay
11%13%41%24%10%
90
16th to endDay
18%7%34%25%11%1
305
May1st to 15thDay
16%7%39%24%11%1
468
16th to endDay
21%423%30%17%2
517
June1st to 15thDay
5%11%45%29%7%
495
16th to endDay
6%39%38%30%10%
495
July1st to 15thDay
417%39%39%8%
475
16th to endDay
41230%48%13%
515
August1st to 15thDay
2225%52%16%
484
16th to endDay
12%226%38%18%
254
September1st to 15thDay
11217%51%25%
135
16th to endDay
8%20%42%27%
135
October1st to 15thDay
25%22%46%21%
135
16th to endDay
15%6%15%22%31%8%
144
November1st to 15thDay
25%116%36%17%3
135
16th to endDay
18%5%30%23%17%4
135
December1st to 15thDay
20%428%22%16%7%
135
16th to endDay
28%13%27%22%6%1
144
January1st to 15thNight
19%9%28%32%10%
975
16th to endNight
18%7%33%32%7%
1001
February1st to 15thNight
20%10%32%30%6%
764
16th to endNight
19%11%42%23%3
684
March1st to 15thNight
16%9%35%32%5%
573
16th to endNight
12%10%38%31%5%
576
April1st to 15thNight
12%8%44%30%3
539
16th to endNight
15%6%42%26%10%
540
May1st to 15thNight
11%6%40%32%8%
540
16th to endNight
9%329%38%17%1
563
June1st to 15thNight
420%48%24%2
540
16th to endNight
5%115%46%27%2
540
July1st to 15thNight
49%47%32%4
510
16th to endNight
4445%40%4
564
August1st to 15thNight
3345%39%7%
539
16th to endNight
8%338%44%4
573
September1st to 15thNight
7%1436%45%5%
540
16th to endNight
9%7%34%42%5%
537
October1st to 15thNight
8%112%41%28%7%
571
16th to endNight
9%423%34%26%2
768
November1st to 15thNight
11%327%33%21%1
763
16th to endNight
15%5%26%34%17%1
975
December1st to 15thNight
19%5%27%35%11%
975
16th to endNight
22%7%28%32%8%
1040
Page generated at 2018-03-12 12:28:12. Version ac04

Copyright 2018 A. Danko


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