Big Bend Community College
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Big Bend Community College clear sky chart from 2005-11-05 to 2017-10-31.

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%
14686
17%
47367
14%
14659
57%
14659
27%
29459

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
34%
717
8%
2506
6%
716
38%
716
12%
1939
January16th to endNight
39%
768
6%
2688
5%
768
42%
768
11%
2094
February1st to 15thNight
42%
698
9%
2339
6%
696
47%
696
17%
1653
February16th to endNight
45%
632
16%
1928
12%
632
52%
632
24%
1272
March1st to 15thNight
43%
720
14%
2160
10%
720
48%
720
22%
1464
March16th to endNight
41%
768
16%
2000
7%
768
45%
768
25%
1399
April1st to 15thNight
46%
719
16%
1799
7%
719
50%
719
28%
1242
April16th to endNight
53%
589
21%
1669
13%
589
59%
589
37%
1012
May1st to 15thNight
52%
359
26%
1439
27%
359
65%
359
34%
703
May16th to endNight
60%
374
16%
1496
23%
374
64%
374
26%
832
June1st to 15thNight
63%
360
13%
1440
14%
360
67%
360
31%
734
June16th to endNight
59%
360
15%
1440
17%
360
66%
360
37%
664
July1st to 15thNight
76%
340
19%
1360
26%
340
82%
340
57%
489
July16th to endNight
79%
376
29%
1416
41%
354
87%
354
63%
488
August1st to 15thNight
81%
360
33%
1432
40%
358
87%
358
61%
508
August16th to endNight
78%
714
35%
1860
24%
714
81%
714
66%
905
September1st to 15thNight
75%
720
34%
1800
18%
720
80%
720
69%
885
September16th to endNight
66%
716
32%
1942
24%
716
70%
716
49%
1035
October1st to 15thNight
56%
720
22%
2151
20%
720
62%
720
35%
1268
October16th to endNight
53%
768
20%
2451
18%
768
59%
768
26%
1542
November1st to 15thNight
46%
700
13%
2323
11%
700
51%
700
20%
1567
November16th to endNight
39%
720
10%
2520
7%
720
43%
720
14%
1844
December1st to 15thNight
42%
720
10%
2520
8%
720
45%
720
14%
1863
December16th to endNight
35%
768
9%
2688
6%
768
39%
768
11%
2057

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
7%6%35%5%2445%7%47%
48400
Night
8%7%36%5%3445%7%43%
47535
Cloud CoverDay
7%6%25%5%3445%7%47%
48400
Night
9%7%35%5%3445%7%43%
47539
TransparencyDay
36%412%23%17%5%
48071
Night
39%5%12%21%15%5%
47368
SeeingDay
9%6%20%25%24%14%
5564
Night
12%320%35%23%3
14697

By Month

Percentage Cloud Cover NW (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
16%17%6%9%7%35%345%19%
1432
16th to endDay
13%18%7%11%8%24435%20%
1536
February1st to 15thDay
13%12%5%8%6%35%5%5%6%28%
1525
16th to endDay
8%10%36%6%35%5%5%8%36%
1545
March1st to 15thDay
13%9%46%5%35%5%6%7%32%
1800
16th to endDay
8%7%47%7%37%6%7%8%32%
2221
April1st to 15thDay
7%5%36%6%36%5%7%8%38%
2149
16th to endDay
5%6%245%35%5%6%9%45%
2288
May1st to 15thDay
43234245%6%9%52%
2511
16th to endDay
6%426%6%45%5%7%8%41%
2615
June1st to 15thDay
7%325%325%5%6%7%48%
2520
16th to endDay
6%31441345%8%54%
2520
July1st to 15thDay
112212245%74%
2520
16th to endDay
11221233477%
2657
August1st to 15thDay
112111346%74%
2520
16th to endDay
2112212346%69%
2338
September1st to 15thDay
222212247%70%
2160
16th to endDay
441442445%7%56%
2017
October1st to 15thDay
8%4145%25%45%7%48%
1806
16th to endDay
12%5%25%6%345%5%7%40%
1770
November1st to 15thDay
13%6%37%8%45%45%6%33%
1534
16th to endDay
13%12%6%9%7%45%45%6%24%
1440
December1st to 15thDay
13%13%5%11%7%3445%5%23%
1440
16th to endDay
17%15%7%9%6%3435%5%21%
1536
January1st to 15thNight
17%12%49%6%3445%7%23%
2506
16th to endNight
12%12%8%11%7%35%446%23%
2688
February1st to 15thNight
11%12%47%6%35%5%5%7%31%
2327
16th to endNight
7%8%36%6%36%6%7%8%34%
1928
March1st to 15thNight
9%7%48%6%35%47%7%33%
2160
16th to endNight
7%7%45%6%36%6%6%10%33%
1996
April1st to 15thNight
8%6%48%6%3445%5%40%
1799
16th to endNight
5%5%35%425%5%6%9%46%
1669
May1st to 15thNight
6%32342345%7%55%
1439
16th to endNight
5%316%6%36%6%7%8%43%
1496
June1st to 15thNight
5%2235%35%5%5%7%53%
1440
16th to endNight
431332446%8%56%
1440
July1st to 15thNight
11112347%73%
1440
16th to endNight
121233478%
1512
August1st to 15thNight
112212237%75%
1440
16th to endNight
11121334472%
1860
September1st to 15thNight
112112345%73%
1800
16th to endNight
432341335%7%59%
1942
October1st to 15thNight
8%5%25%42445%6%49%
2151
16th to endNight
8%6%26%5%45%5%6%7%41%
2451
November1st to 15thNight
13%8%35%5%35%5%7%7%35%
2323
16th to endNight
13%11%47%6%45%45%6%30%
2520
December1st to 15thNight
13%11%6%8%5%25%5%5%7%27%
2520
16th to endNight
15%14%5%7%6%4445%7%23%
2688

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%17%7%8%6%35%445%19%
1432
16th to endDay
15%18%6%11%7%34345%19%
1536
February1st to 15thDay
14%12%47%7%45%446%27%
1525
16th to endDay
8%11%37%5%35%5%5%7%36%
1545
March1st to 15thDay
13%9%46%5%35%45%8%32%
1800
16th to endDay
9%8%36%7%36%6%7%7%32%
2221
April1st to 15thDay
8%5%26%6%46%46%8%39%
2149
16th to endDay
5%6%246%345%6%9%45%
2288
May1st to 15thDay
441442446%8%52%
2511
16th to endDay
7%5%25%6%35%5%6%8%42%
2615
June1st to 15thDay
8%3244245%6%8%48%
2520
16th to endDay
6%32442345%8%54%
2520
July1st to 15thDay
11121333474%
2520
16th to endDay
112112325%77%
2657
August1st to 15thDay
112212336%74%
2520
16th to endDay
2212312346%69%
2338
September1st to 15thDay
223312336%70%
2160
16th to endDay
5%3145%235%5%7%56%
2017
October1st to 15thDay
8%4245%35%5%5%6%48%
1806
16th to endDay
12%7%25%5%3345%7%41%
1770
November1st to 15thDay
14%6%38%7%45%45%6%32%
1534
16th to endDay
12%14%5%11%7%45%445%24%
1440
December1st to 15thDay
13%13%5%10%6%45%5%45%23%
1440
16th to endDay
18%16%6%9%7%34345%20%
1536
January1st to 15thNight
18%12%5%8%6%3445%7%23%
2506
16th to endNight
13%12%8%10%7%35%447%22%
2688
February1st to 15thNight
12%12%36%6%25%5%5%7%32%
2327
16th to endNight
8%8%36%5%35%6%7%7%35%
1928
March1st to 15thNight
11%8%37%7%345%7%7%34%
2160
16th to endNight
8%7%36%6%46%5%6%10%33%
2000
April1st to 15thNight
8%7%47%7%4445%5%40%
1799
16th to endNight
5%6%25%5%345%6%8%46%
1669
May1st to 15thNight
7%413325%347%56%
1439
16th to endNight
6%325%6%46%6%6%9%43%
1496
June1st to 15thNight
6%214435%46%5%53%
1440
16th to endNight
43223245%5%7%57%
1440
July1st to 15thNight
112112347%73%
1440
16th to endNight
1111234478%
1512
August1st to 15thNight
11222336%76%
1440
16th to endNight
21121235%472%
1860
September1st to 15thNight
1112212346%73%
1800
16th to endNight
341342245%7%59%
1942
October1st to 15thNight
8%5%145%3445%7%49%
2151
16th to endNight
9%6%26%5%445%6%7%40%
2451
November1st to 15thNight
13%7%36%435%5%6%6%36%
2323
16th to endNight
14%11%47%7%345%5%6%29%
2520
December1st to 15thNight
14%10%6%8%6%35%45%7%26%
2520
16th to endNight
17%13%6%7%6%34447%23%
2688

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
67%6%11%9%3
1432
16th to endDay
68%5%15%8%2
1536
February1st to 15thDay
55%8%16%14%4
1525
16th to endDay
45%6%17%23%6%
1545
March1st to 15thDay
49%5%15%21%7%
1800
16th to endDay
46%6%16%21%7%
2221
April1st to 15thDay
41%5%16%23%12%1
2149
16th to endDay
33%416%28%14%2
2288
May1st to 15thDay
26%310%32%23%3
2511
16th to endDay
36%5%14%26%14%1
2619
June1st to 15thDay
32%410%27%19%5%
2520
16th to endDay
27%38%29%22%7%
2520
July1st to 15thDay
13%25%25%35%19%
2371
16th to endDay
12%25%17%36%24%
2490
August1st to 15thDay
12%26%26%33%17%
2503
16th to endDay
15%37%28%32%12%
2338
September1st to 15thDay
15%28%26%34%12%
2160
16th to endDay
26%416%26%20%5%
2017
October1st to 15thDay
33%416%29%14%
1806
16th to endDay
42%6%16%24%10%
1770
November1st to 15thDay
51%8%14%17%6%1
1534
16th to endDay
60%6%13%13%6%
1440
December1st to 15thDay
61%5%14%12%5%
1440
16th to endDay
67%412%11%3
1536
January1st to 15thNight
60%7%14%12%3
2506
16th to endNight
61%7%16%11%2
2688
February1st to 15thNight
49%8%19%15%7%
2339
16th to endNight
43%6%18%23%7%
1928
March1st to 15thNight
46%5%13%25%8%
2160
16th to endNight
45%6%13%26%8%
2000
April1st to 15thNight
43%5%11%24%13%1
1799
16th to endNight
32%5%11%29%18%2
1669
May1st to 15thNight
28%36%28%27%6%
1440
16th to endNight
35%5%11%29%15%3
1496
June1st to 15thNight
29%48%27%24%4
1440
16th to endNight
24%39%26%27%8%
1440
July1st to 15thNight
12%25%20%33%26%
1360
16th to endNight
9%3415%33%33%
1416
August1st to 15thNight
11%25%17%41%22%
1432
16th to endNight
13%25%24%34%19%
1860
September1st to 15thNight
11%27%24%34%19%
1800
16th to endNight
22%311%29%22%9%
1942
October1st to 15thNight
33%410%27%23%1
2151
16th to endNight
40%6%13%26%12%1
2451
November1st to 15thNight
45%7%17%18%8%2
2323
16th to endNight
54%7%14%16%6%
2520
December1st to 15thNight
55%7%16%16%3
2520
16th to endNight
60%6%14%12%5%
2688

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
28%6%10%20%26%8%
60
16th to endDay
35%7%10%17%15%12%
64
February1st to 15thDay
19%8%25%20%21%5%
185
16th to endDay
15%8%25%28%14%6%
233
March1st to 15thDay
20%11%32%22%9%2
270
16th to endDay
17%13%30%23%12%2
288
April1st to 15thDay
7%12%28%24%16%9%
269
16th to endDay
8%10%28%26%14%12%
270
May1st to 15thDay
9%10%22%23%26%7%
288
16th to endDay
6%414%23%31%19%
330
June1st to 15thDay
6%420%29%23%15%
315
16th to endDay
5%420%25%26%18%
315
July1st to 15thDay
111%32%30%22%
305
16th to endDay
3213%24%35%20%
327
August1st to 15thDay
2110%21%32%30%
315
16th to endDay
2312%21%34%25%
332
September1st to 15thDay
5%314%26%28%21%
315
16th to endDay
6%318%25%31%15%
315
October1st to 15thDay
10%5%26%25%21%10%
315
16th to endDay
19%316%29%21%10%
188
November1st to 15thDay
9%12%19%38%17%2
81
16th to endDay
21%6%15%30%13%13%
60
December1st to 15thDay
13%8%28%30%20%
60
16th to endDay
18%23%31%23%3
64
January1st to 15thNight
22%5%21%31%16%2
720
16th to endNight
16%315%36%23%2
768
February1st to 15thNight
18%320%33%19%3
704
16th to endNight
12%5%27%32%19%2
632
March1st to 15thNight
13%6%25%37%15%2
720
16th to endNight
12%5%30%34%15%1
768
April1st to 15thNight
10%5%25%34%21%2
719
16th to endNight
7%328%35%20%5%
589
May1st to 15thNight
8%5%28%28%25%3
360
16th to endNight
6%318%34%32%4
375
June1st to 15thNight
6%219%45%24%2
360
16th to endNight
6%223%40%22%3
360
July1st to 15thNight
2216%36%38%2
340
16th to endNight
1115%38%38%4
376
August1st to 15thNight
211%29%46%8%
360
16th to endNight
213%32%41%9%
714
September1st to 15thNight
2215%34%34%10%
720
16th to endNight
7%117%32%34%6%
716
October1st to 15thNight
11%221%36%25%3
720
16th to endNight
13%319%35%24%4
768
November1st to 15thNight
17%422%42%12%1
700
16th to endNight
19%5%19%30%21%3
720
December1st to 15thNight
19%5%15%42%15%1
720
16th to endNight
23%5%18%39%12%
768
Page generated at 2017-11-01 14:23:37. Version ac04

Copyright 2017 A. Danko


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