Galveston Island State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Galveston Island State Park clear sky chart from 2005-11-05 to 2017-09-18.

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
60%
15320
22%
46912
19%
15278
63%
15278
30%
28702

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
42%
897
20%
2327
10%
895
47%
895
26%
1613
January16th to endNight
42%
960
22%
2496
10%
960
48%
960
28%
1679
February1st to 15thNight
45%
788
23%
2196
13%
784
50%
784
28%
1436
February16th to endNight
43%
488
23%
1750
16%
488
50%
488
24%
1070
March1st to 15thNight
42%
540
23%
1980
18%
540
50%
540
21%
1229
March16th to endNight
60%
576
22%
2112
21%
576
64%
576
29%
1164
April1st to 15thNight
53%
539
21%
1929
20%
539
59%
539
26%
1129
April16th to endNight
54%
540
20%
1800
20%
540
59%
540
26%
1104
May1st to 15thNight
61%
539
19%
1767
20%
539
65%
539
29%
1037
May16th to endNight
72%
561
25%
1684
28%
561
73%
561
37%
959
June1st to 15thNight
82%
540
18%
1620
22%
540
82%
540
42%
876
June16th to endNight
74%
540
15%
1620
18%
540
74%
540
30%
1014
July1st to 15thNight
77%
510
16%
1530
21%
510
77%
510
32%
924
July16th to endNight
79%
564
17%
1594
20%
531
80%
531
32%
970
August1st to 15thNight
86%
539
24%
1643
28%
536
86%
536
44%
865
August16th to endNight
74%
573
15%
1910
17%
573
74%
573
25%
1189
September1st to 15thNight
71%
540
14%
1977
17%
540
71%
540
24%
1220
September16th to endNight
69%
501
25%
1848
30%
501
69%
501
24%
1131
October1st to 15thNight
77%
619
31%
1939
29%
619
78%
619
42%
1026
October16th to endNight
68%
704
33%
2112
27%
704
72%
704
44%
1123
November1st to 15thNight
64%
700
26%
2100
21%
700
66%
700
33%
1266
November16th to endNight
59%
720
32%
2160
23%
720
66%
720
36%
1250
December1st to 15thNight
48%
882
24%
2322
15%
882
51%
882
25%
1627
December16th to endNight
40%
960
18%
2496
10%
960
43%
960
21%
1801

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%244345%6%9%42%
47875
Night
11%5%2442445%8%46%
47108
TransparencyDay
37%8%15%19%13%5%
47575
Night
35%6%14%20%15%7%
46913
SeeingDay
11%19%21%36%20%
5335
Night
12%315%27%30%10%
15326

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%245%24347%37%
1611
16th to endDay
19%6%34422336%43%
1728
February1st to 15thDay
17%7%3442343443%
1675
16th to endDay
20%9%35%32324441%
1724
March1st to 15thDay
20%6%35%413446%40%
1980
16th to endDay
12%5%35%413446%47%
2110
April1st to 15thDay
12%6%345%1445%8%42%
2016
16th to endDay
12%5%35%43435%6%44%
2160
May1st to 15thDay
9%6%25%435%5%6%10%40%
2181
16th to endDay
7%413435%5%8%11%41%
2430
June1st to 15thDay
4323435%6%8%12%44%
2340
16th to endDay
8%3145%46%7%9%14%35%
2340
July1st to 15thDay
9%324425%6%8%14%36%
2340
16th to endDay
5%425%5%46%6%8%13%35%
2466
August1st to 15thDay
32133347%9%14%45%
2304
16th to endDay
11%425%5%45%6%8%11%34%
2292
September1st to 15thDay
10%3246%45%6%7%11%37%
1980
16th to endDay
12%6%25%6%35%5%5%6%40%
1837
October1st to 15thDay
7%31342436%7%53%
1680
16th to endDay
10%21332335%5%57%
1760
November1st to 15thDay
10%425%42446%7%47%
1758
16th to endDay
14%5%23423336%50%
1800
December1st to 15thDay
18%5%244335%5%7%39%
1635
16th to endDay
18%8%36%5%34347%34%
1728
January1st to 15thNight
18%7%35%423345%41%
2327
16th to endNight
18%6%34423345%43%
2496
February1st to 15thNight
17%6%25%323336%44%
2186
16th to endNight
15%6%34433336%45%
1750
March1st to 15thNight
17%7%24423445%42%
1980
16th to endNight
9%5%14325%45%6%51%
2112
April1st to 15thNight
10%5%345%235%5%8%45%
1929
16th to endNight
11%5%35%425%448%44%
1800
May1st to 15thNight
7%5%244345%8%8%44%
1766
16th to endNight
6%32333446%12%47%
1683
June1st to 15thNight
33143235%6%12%52%
1620
16th to endNight
6%4245%45%6%7%13%38%
1620
July1st to 15thNight
5%325%435%6%7%14%40%
1620
16th to endNight
3225%5%36%5%7%13%43%
1702
August1st to 15thNight
221342346%14%55%
1653
16th to endNight
8%4144245%7%12%40%
1910
September1st to 15thNight
8%435%5%35%5%6%9%41%
1977
16th to endNight
11%5%245%245%5%9%43%
1848
October1st to 15thNight
7%223323348%58%
1939
16th to endNight
9%312312345%60%
2112
November1st to 15thNight
9%4245%3445%6%49%
2100
16th to endNight
12%423422336%54%
2160
December1st to 15thNight
18%6%25%433447%39%
2322
16th to endNight
19%8%36%424346%36%
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
45%5%7%16%16%7%
1612
16th to endDay
43%36%18%16%11%
1728
February1st to 15thDay
45%37%18%15%10%
1676
16th to endDay
46%39%16%17%6%
1724
March1st to 15thDay
45%6%10%15%16%5%
1980
16th to endDay
36%6%14%15%21%5%
2112
April1st to 15thDay
38%7%13%17%15%7%
2016
16th to endDay
39%6%14%20%14%5%
2160
May1st to 15thDay
36%9%15%18%12%6%
2181
16th to endDay
31%10%18%25%12%2
2434
June1st to 15thDay
28%11%19%26%14%1
2340
16th to endDay
34%14%21%22%6%
2340
July1st to 15thDay
32%12%26%23%5%
2201
16th to endDay
35%13%27%20%2
2311
August1st to 15thDay
24%13%28%29%4
2290
16th to endDay
40%14%20%17%5%1
2292
September1st to 15thDay
37%15%17%18%8%2
1980
16th to endDay
41%9%10%18%15%3
1837
October1st to 15thDay
27%7%10%24%18%11%
1680
16th to endDay
28%37%20%26%13%
1760
November1st to 15thDay
34%7%13%20%17%7%
1758
16th to endDay
36%48%16%21%13%
1800
December1st to 15thDay
44%6%13%16%13%6%
1635
16th to endDay
50%5%9%14%14%5%
1728
January1st to 15thNight
46%46%12%20%9%
2327
16th to endNight
43%37%15%17%12%
2496
February1st to 15thNight
41%49%12%19%12%
2196
16th to endNight
41%48%15%20%9%
1750
March1st to 15thNight
42%5%10%17%15%8%
1980
16th to endNight
32%5%14%17%20%9%
2112
April1st to 15thNight
36%6%11%20%16%9%
1929
16th to endNight
37%6%14%18%14%8%
1800
May1st to 15thNight
31%9%16%21%12%9%
1767
16th to endNight
28%7%17%28%15%2
1685
June1st to 15thNight
23%7%20%27%20%
1620
16th to endNight
34%9%23%24%8%
1620
July1st to 15thNight
31%9%28%25%5%
1530
16th to endNight
28%12%27%28%2
1594
August1st to 15thNight
19%10%26%37%6%
1643
16th to endNight
33%12%25%21%5%
1910
September1st to 15thNight
36%10%20%19%10%2
1977
16th to endNight
37%8%12%20%17%4
1848
October1st to 15thNight
24%5%10%26%19%12%
1939
16th to endNight
26%28%19%27%15%
2112
November1st to 15thNight
33%6%13%23%15%7%
2100
16th to endNight
31%49%17%23%13%
2160
December1st to 15thNight
45%6%10%18%13%6%
2322
16th to endNight
50%5%7%15%11%9%
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
24%222%35%15%
90
16th to endDay
13%9%18%43%14%
96
February1st to 15thDay
15%30%32%18%3
90
16th to endDay
17%124%46%9%
81
March1st to 15thDay
22%333%30%11%
90
16th to endDay
17%221%32%21%4
96
April1st to 15thDay
13%222%31%29%
135
16th to endDay
18%217%36%22%2
270
May1st to 15thDay
12%119%38%25%2
318
16th to endDay
9%11%36%37%4
517
June1st to 15thDay
8%219%54%14%
495
16th to endDay
9%413%43%27%
495
July1st to 15thDay
5%310%48%30%
475
16th to endDay
6%27%45%37%
515
August1st to 15thDay
415%44%44%
457
16th to endDay
15%39%31%38%
332
September1st to 15thDay
9%28%41%37%
135
16th to endDay
7%8%36%47%
96
October1st to 15thDay
3421%50%21%
90
16th to endDay
12%13%27%37%9%
96
November1st to 15thDay
14%218%31%25%7%
90
16th to endDay
14%322%35%17%6%
90
December1st to 15thDay
33%27%32%18%5%
90
16th to endDay
26%331%20%18%
96
January1st to 15thNight
22%424%30%17%1
900
16th to endNight
19%6%26%32%15%
960
February1st to 15thNight
19%423%35%15%
788
16th to endNight
17%5%27%36%13%
488
March1st to 15thNight
20%425%32%16%
540
16th to endNight
11%319%38%24%3
576
April1st to 15thNight
11%5%21%39%21%
539
16th to endNight
13%321%37%23%1
540
May1st to 15thNight
9%220%45%20%1
540
16th to endNight
7%110%38%37%5%
563
June1st to 15thNight
4323%58%10%
540
16th to endNight
6%214%52%22%
540
July1st to 15thNight
6%18%47%35%
510
16th to endNight
335%48%39%
564
August1st to 15thNight
2448%42%
539
16th to endNight
10%129%43%33%
573
September1st to 15thNight
8%5%12%45%27%
540
16th to endNight
12%6%14%46%19%
501
October1st to 15thNight
6%17%24%47%13%
619
16th to endNight
8%313%29%34%10%
704
November1st to 15thNight
11%212%32%34%7%
700
16th to endNight
12%319%36%25%2
720
December1st to 15thNight
19%6%15%34%20%2
882
16th to endNight
22%6%22%29%16%1
960
Page generated at 2017-09-19 06:32:30. Version ac04

Copyright 2017 A. Danko


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