Houston
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Houston clear sky chart from 2005-11-05 to 2017-08-12.

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
55%
15255
23%
46519
18%
15209
59%
15209
31%
28025

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
37%
899
22%
2327
11%
895
43%
895
28%
1551
January16th to endNight
37%
960
24%
2496
11%
960
43%
960
29%
1651
February1st to 15thNight
37%
776
23%
2181
11%
771
44%
771
27%
1421
February16th to endNight
33%
516
25%
1778
13%
516
44%
516
23%
1090
March1st to 15thNight
37%
540
25%
1980
17%
540
48%
540
22%
1226
March16th to endNight
44%
576
22%
2112
18%
576
53%
576
27%
1191
April1st to 15thNight
41%
539
21%
1941
16%
539
50%
539
24%
1172
April16th to endNight
40%
540
22%
1800
18%
540
47%
540
24%
1128
May1st to 15thNight
44%
539
19%
1718
17%
539
50%
539
26%
1050
May16th to endNight
62%
562
23%
1685
25%
561
66%
561
34%
979
June1st to 15thNight
79%
540
20%
1620
22%
540
81%
540
47%
826
June16th to endNight
75%
540
16%
1620
20%
540
76%
540
33%
988
July1st to 15thNight
79%
510
18%
1530
22%
510
79%
510
37%
883
July16th to endNight
84%
564
19%
1594
23%
531
85%
531
36%
919
August1st to 15thNight
90%
527
26%
1578
30%
524
90%
524
54%
761
August16th to endNight
77%
525
15%
1770
17%
525
78%
525
28%
1091
September1st to 15thNight
71%
495
17%
1815
20%
495
72%
495
27%
1070
September16th to endNight
73%
492
27%
1815
31%
492
74%
492
29%
1020
October1st to 15thNight
75%
606
31%
1926
29%
606
76%
606
43%
1003
October16th to endNight
63%
704
35%
2112
26%
704
68%
704
43%
1123
November1st to 15thNight
61%
700
28%
2100
22%
700
63%
700
34%
1235
November16th to endNight
50%
745
32%
2185
21%
745
58%
745
35%
1277
December1st to 15thNight
40%
900
24%
2340
13%
900
45%
900
24%
1619
December16th to endNight
36%
960
19%
2496
9%
960
41%
960
24%
1751

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
12%6%36%6%35%5%6%7%36%
47439
Night
11%5%2442345%7%47%
46717
TransparencyDay
44%7%11%16%14%6%
47139
Night
34%6%13%20%16%8%
46522
SeeingDay
11%316%26%27%14%
5244
Night
13%420%32%25%3
15258

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
19%6%2442444440%
1611
16th to endDay
18%6%35%423235%44%
1728
February1st to 15thDay
18%7%46%42324442%
1687
16th to endDay
21%8%24423335%39%
1694
March1st to 15thDay
22%8%24424336%36%
1980
16th to endDay
16%6%35%5%2435%6%39%
2110
April1st to 15thDay
14%6%45%5%3445%7%38%
2004
16th to endDay
13%6%36%5%35%45%6%36%
2160
May1st to 15thDay
11%7%37%7%35%6%6%7%33%
2229
16th to endDay
8%6%36%9%37%6%8%9%30%
2430
June1st to 15thDay
5%426%7%5%7%7%8%9%34%
2340
16th to endDay
6%5%38%9%5%11%9%7%8%24%
2340
July1st to 15thDay
9%437%7%5%8%7%9%10%26%
2340
16th to endDay
6%438%9%5%8%8%8%11%25%
2466
August1st to 15thDay
32147%5%8%8%9%13%34%
2285
16th to endDay
6%5%27%8%5%7%8%8%8%29%
2075
September1st to 15thDay
9%5%26%8%47%7%7%8%29%
1815
16th to endDay
9%6%27%6%45%5%6%8%37%
1815
October1st to 15thDay
8%415%5%435%5%6%48%
1691
16th to endDay
9%414423445%55%
1760
November1st to 15thDay
10%6%36%6%35%35%8%42%
1758
16th to endDay
15%5%36%41433447%
1773
December1st to 15thDay
18%7%36%6%34446%34%
1620
16th to endDay
18%9%35%6%24446%35%
1728
January1st to 15thNight
19%6%24323345%43%
2327
16th to endNight
19%6%24423336%44%
2496
February1st to 15thNight
16%6%25%423336%45%
2174
16th to endNight
14%7%35%5%23335%45%
1778
March1st to 15thNight
19%7%2332235%6%41%
1980
16th to endNight
10%5%34424445%50%
2112
April1st to 15thNight
13%4344335%5%8%43%
1941
16th to endNight
15%5%245%24447%42%
1800
May1st to 15thNight
9%6%25%5%25%5%6%9%42%
1717
16th to endNight
5%423435%47%11%47%
1683
June1st to 15thNight
321332246%10%58%
1620
16th to endNight
4325%435%5%8%12%44%
1620
July1st to 15thNight
5%3235%25%36%11%50%
1620
16th to endNight
3213425%6%7%11%49%
1702
August1st to 15thNight
11222336%12%61%
1588
16th to endNight
3415%5%35%6%7%13%42%
1770
September1st to 15thNight
7%5%25%4335%7%10%45%
1815
16th to endNight
7%5%1443446%9%48%
1815
October1st to 15thNight
5%31332345%7%60%
1926
16th to endNight
8%41232323463%
2112
November1st to 15thNight
9%5%2442345%7%50%
2100
16th to endNight
13%5%13323345%54%
2185
December1st to 15thNight
16%7%36%5%24445%40%
2340
16th to endNight
17%8%35%5%34345%39%
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
46%45%13%19%9%
1612
16th to endDay
44%35%16%17%13%
1728
February1st to 15thDay
46%36%14%16%11%
1688
16th to endDay
47%46%13%17%9%
1694
March1st to 15thDay
49%5%7%11%18%6%
1980
16th to endDay
44%48%14%21%6%
2112
April1st to 15thDay
45%5%7%16%16%8%
2004
16th to endDay
46%5%8%16%14%7%
2160
May1st to 15thDay
48%7%10%13%13%7%
2229
16th to endDay
44%8%13%18%12%2
2434
June1st to 15thDay
40%9%15%17%14%1
2340
16th to endDay
49%12%14%16%6%
2340
July1st to 15thDay
45%11%19%18%5%
2201
16th to endDay
45%13%19%18%2
2311
August1st to 15thDay
36%11%19%25%6%
2271
16th to endDay
45%14%16%14%6%1
2075
September1st to 15thDay
45%12%16%14%7%3
1815
16th to endDay
42%7%11%15%16%5%
1815
October1st to 15thDay
34%6%9%18%15%15%
1691
16th to endDay
31%36%12%29%16%
1760
November1st to 15thDay
39%6%10%17%18%8%
1758
16th to endDay
40%4411%20%17%
1773
December1st to 15thDay
50%5%8%15%13%7%
1620
16th to endDay
49%5%7%15%15%6%
1728
January1st to 15thNight
42%36%14%20%12%
2327
16th to endNight
41%36%16%18%13%
2496
February1st to 15thNight
41%47%13%18%14%
2184
16th to endNight
42%36%15%19%12%
1778
March1st to 15thNight
42%48%16%18%9%
1980
16th to endNight
35%414%15%20%9%
2112
April1st to 15thNight
38%6%9%18%16%10%
1941
16th to endNight
41%5%11%17%14%9%
1800
May1st to 15thNight
35%8%13%19%13%9%
1718
16th to endNight
29%7%19%25%13%3
1685
June1st to 15thNight
20%6%21%28%22%1
1620
16th to endNight
30%10%22%26%10%
1620
July1st to 15thNight
29%7%27%29%6%
1530
16th to endNight
23%12%28%31%3
1594
August1st to 15thNight
14%6%30%38%9%
1578
16th to endNight
31%13%25%23%5%1
1770
September1st to 15thNight
32%10%22%21%10%2
1815
16th to endNight
30%9%13%21%18%6%
1815
October1st to 15thNight
22%7%10%25%19%14%
1926
16th to endNight
25%36%17%27%19%
2112
November1st to 15thNight
32%5%12%21%20%8%
2100
16th to endNight
32%48%15%22%17%
2185
December1st to 15thNight
45%5%8%18%14%7%
2340
16th to endNight
47%47%14%15%10%
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
27%424%36%6%
90
16th to endDay
17%9%40%25%7%
96
February1st to 15thDay
11%11%36%33%5%2
90
16th to endDay
14%11%44%23%6%
81
March1st to 15thDay
35%7%36%13%6%
90
16th to endDay
19%6%33%23%12%4
96
April1st to 15thDay
16%13%18%34%15%1
123
16th to endDay
21%5%27%24%19%1
270
May1st to 15thDay
13%8%32%28%15%1
366
16th to endDay
11%227%35%18%3
517
June1st to 15thDay
7%10%34%35%11%
495
16th to endDay
10%18%29%32%18%
495
July1st to 15thDay
7%18%26%35%21%
475
16th to endDay
5%1323%37%28%
515
August1st to 15thDay
4318%43%29%
470
16th to endDay
12%411%39%31%
243
September1st to 15thDay
7%1328%23%35%
90
16th to endDay
6%317%35%36%
90
October1st to 15thDay
211%38%40%7%
90
16th to endDay
17%318%22%29%8%
96
November1st to 15thDay
20%131%25%15%6%
90
16th to endDay
22%5%26%30%6%8%
90
December1st to 15thDay
20%5%23%34%10%6%
90
16th to endDay
27%13%32%20%6%
96
January1st to 15thNight
23%7%27%30%10%
900
16th to endNight
20%9%27%33%8%
960
February1st to 15thNight
19%8%28%34%8%
776
16th to endNight
19%7%35%30%6%
516
March1st to 15thNight
22%7%30%32%7%
540
16th to endNight
11%6%33%36%11%
576
April1st to 15thNight
14%5%33%36%9%
539
16th to endNight
18%6%30%32%12%
540
May1st to 15thNight
12%6%32%39%9%
540
16th to endNight
6%123%43%22%1
563
June1st to 15thNight
48%48%35%2
540
16th to endNight
5%16%35%45%5%
540
July1st to 15thNight
5%433%47%8%
510
16th to endNight
3227%55%10%
564
August1st to 15thNight
225%59%11%
527
16th to endNight
6%323%56%10%
525
September1st to 15thNight
9%16%20%52%10%
495
16th to endNight
10%7%26%47%7%
492
October1st to 15thNight
7%11%34%40%4
606
16th to endNight
10%318%33%30%3
704
November1st to 15thNight
12%318%37%25%2
700
16th to endNight
14%5%25%32%20%1
745
December1st to 15thNight
18%7%26%31%16%
900
16th to endNight
22%8%26%30%11%
960
Page generated at 2017-08-13 13:16:50. Version ac04

Copyright 2017 A. Danko


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