Dobie Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dobie Observatory clear sky chart from 2005-11-05 to 2017-09-23.

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
37%
15931
15%
46859
10%
15889
42%
15889
21%
32791

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
14%
900
10%
2506
3%
895
20%
895
12%
2007
January16th to endNight
20%
897
7%
2625
3%
897
24%
897
10%
2141
February1st to 15thNight
17%
701
9%
2223
3%
701
24%
701
11%
1723
February16th to endNight
23%
631
14%
1893
7%
631
31%
631
15%
1393
March1st to 15thNight
27%
720
14%
2101
9%
720
32%
720
17%
1519
March16th to endNight
30%
768
18%
2112
10%
768
38%
768
20%
1518
April1st to 15thNight
27%
551
13%
1803
8%
551
34%
551
18%
1249
April16th to endNight
35%
540
19%
1620
8%
540
44%
540
24%
1081
May1st to 15thNight
35%
540
14%
1620
8%
540
41%
540
21%
1146
May16th to endNight
49%
562
15%
1640
10%
561
54%
561
29%
1041
June1st to 15thNight
53%
540
15%
1440
11%
540
58%
540
34%
923
June16th to endNight
58%
540
16%
1440
12%
540
61%
540
35%
902
July1st to 15thNight
67%
510
17%
1360
14%
510
69%
510
39%
819
July16th to endNight
68%
564
20%
1470
16%
531
71%
531
39%
864
August1st to 15thNight
68%
539
21%
1609
17%
536
70%
536
35%
941
August16th to endNight
64%
573
21%
1782
18%
573
68%
573
33%
1045
September1st to 15thNight
60%
645
26%
1905
21%
645
63%
645
34%
1132
September16th to endNight
59%
689
24%
1903
18%
689
63%
689
33%
1195
October1st to 15thNight
46%
660
21%
1873
17%
660
52%
660
28%
1225
October16th to endNight
26%
704
16%
2233
9%
704
35%
704
17%
1561
November1st to 15thNight
35%
700
20%
2276
16%
700
41%
700
22%
1475
November16th to endNight
24%
720
14%
2340
10%
720
30%
720
14%
1727
December1st to 15thNight
19%
777
9%
2397
3%
777
24%
777
11%
1892
December16th to endNight
14%
960
8%
2688
1%
960
20%
960
8%
2272

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
14%8%46%6%35%45%7%32%
48046
Night
15%9%46%5%34446%34%
47033
Cloud CoverDay
13%8%47%6%35%5%5%7%32%
48055
Night
14%9%46%6%3445%6%34%
47038
TransparencyDay
49%6%11%19%11%1
47738
Night
48%5%11%20%11%1
46859
SeeingDay
16%7%26%24%16%8%
5927
Night
18%8%28%29%13%1
15935

By Month

Percentage Cloud Cover NE (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%16%8%9%8%5%4435%15%
1432
16th to endDay
14%18%10%11%10%3434414%
1597
February1st to 15thDay
14%13%7%11%10%36%435%19%
1636
16th to endDay
15%13%7%10%8%36%45%5%18%
1580
March1st to 15thDay
15%11%48%7%345%46%27%
1847
16th to endDay
17%10%47%6%24446%30%
2112
April1st to 15thDay
20%11%46%5%34436%30%
2154
16th to endDay
16%6%35%5%2445%6%37%
2340
May1st to 15thDay
18%8%36%6%35%447%31%
2331
16th to endDay
13%6%25%5%245%6%7%38%
2473
June1st to 15thDay
10%5%35%5%35%5%6%9%40%
2520
16th to endDay
10%425%6%46%7%7%9%35%
2520
July1st to 15thDay
7%5%15%5%35%5%6%8%45%
2520
16th to endDay
8%435%6%46%6%7%10%39%
2597
August1st to 15thDay
8%5%25%7%46%6%6%8%39%
2340
16th to endDay
12%425%5%35%5%6%8%39%
2417
September1st to 15thDay
12%5%246%345%5%8%41%
2043
16th to endDay
11%5%25%5%345%5%8%40%
1894
October1st to 15thDay
14%6%36%6%2445%6%38%
1757
16th to endDay
21%9%37%5%24446%30%
1636
November1st to 15thDay
14%9%37%5%24346%38%
1582
16th to endDay
18%13%6%8%6%34446%24%
1620
December1st to 15thDay
14%14%8%10%6%3445%421%
1562
16th to endDay
20%17%7%10%8%34335%14%
1536
January1st to 15thNight
20%14%5%9%7%34345%21%
2506
16th to endNight
12%12%8%11%10%5%5%446%16%
2625
February1st to 15thNight
15%14%6%9%6%4443425%
2221
16th to endNight
16%10%5%9%6%45%6%5%5%26%
1893
March1st to 15thNight
16%11%46%6%33346%33%
2088
16th to endNight
15%8%46%5%35%5%47%33%
2112
April1st to 15thNight
18%8%35%5%25%5%46%34%
1803
16th to endNight
16%7%345%3435%6%38%
1620
May1st to 15thNight
20%6%26%5%25%35%7%33%
1620
16th to endNight
12%6%245%2445%8%43%
1638
June1st to 15thNight
10%5%2443445%9%45%
1440
16th to endNight
8%5%23425%5%8%10%44%
1440
July1st to 15thNight
6%42442445%8%52%
1440
16th to endNight
5%314435%46%10%50%
1570
August1st to 15thNight
6%3146%35%5%5%8%48%
1620
16th to endNight
11%424424347%50%
1782
September1st to 15thNight
11%5%23423346%51%
1905
16th to endNight
12%425%32435%7%47%
1903
October1st to 15thNight
14%6%25%4245%46%42%
1873
16th to endNight
19%7%36%5%33446%34%
2233
November1st to 15thNight
14%9%35%43445%5%39%
2276
16th to endNight
19%12%5%6%5%24445%27%
2340
December1st to 15thNight
20%13%5%9%7%34445%21%
2397
16th to endNight
21%16%7%9%7%35%445%14%
2688

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%15%7%9%8%46%346%15%
1432
16th to endDay
13%18%10%11%10%4433415%
1597
February1st to 15thDay
13%14%7%11%9%37%436%18%
1636
16th to endDay
15%12%6%11%7%46%45%5%18%
1580
March1st to 15thDay
16%10%48%7%345%5%6%27%
1857
16th to endDay
17%10%47%6%2445%6%29%
2111
April1st to 15thDay
19%11%46%434346%30%
2154
16th to endDay
16%6%35%5%25%447%37%
2340
May1st to 15thDay
18%7%36%6%35%447%31%
2331
16th to endDay
13%6%35%5%3446%7%38%
2473
June1st to 15thDay
9%5%35%5%35%5%5%9%39%
2520
16th to endDay
9%425%6%36%7%7%10%34%
2520
July1st to 15thDay
7%425%5%35%6%6%8%45%
2520
16th to endDay
7%4346%46%6%6%10%39%
2597
August1st to 15thDay
8%5%25%6%46%6%5%8%38%
2340
16th to endDay
11%5%25%5%35%5%5%8%39%
2417
September1st to 15thDay
11%5%25%5%35%5%5%8%40%
2043
16th to endDay
11%5%25%5%35%5%6%8%40%
1894
October1st to 15thDay
14%6%37%6%34446%38%
1757
16th to endDay
20%9%37%5%34446%31%
1636
November1st to 15thDay
13%8%37%6%24436%38%
1582
16th to endDay
18%12%5%7%6%25%436%25%
1620
December1st to 15thDay
15%14%8%10%6%35%45%421%
1562
16th to endDay
20%17%8%9%8%34335%14%
1536
January1st to 15thNight
20%14%6%8%7%24345%21%
2506
16th to endNight
13%12%8%11%10%5%5%45%6%16%
2625
February1st to 15thNight
14%14%6%9%7%3443426%
2214
16th to endNight
15%10%5%9%6%35%5%46%26%
1893
March1st to 15thNight
17%11%36%6%33346%33%
2101
16th to endNight
15%8%36%5%35%5%47%33%
2112
April1st to 15thNight
18%8%35%5%35%5%5%6%33%
1803
16th to endNight
16%7%25%5%35%35%7%37%
1620
May1st to 15thNight
20%7%25%6%3445%7%33%
1619
16th to endNight
13%5%25%425%36%8%43%
1638
June1st to 15thNight
9%5%245%2446%8%45%
1440
16th to endNight
7%434425%5%7%11%43%
1440
July1st to 15thNight
5%3245%2445%8%52%
1440
16th to endNight
5%3144245%7%10%50%
1570
August1st to 15thNight
5%315%5%35%46%9%48%
1620
16th to endNight
10%5%24423447%50%
1782
September1st to 15thNight
11%5%23423346%51%
1905
16th to endNight
11%5%2442445%7%47%
1903
October1st to 15thNight
14%6%25%5%245%5%6%42%
1873
16th to endNight
19%8%37%5%34445%34%
2233
November1st to 15thNight
13%9%35%43445%5%39%
2276
16th to endNight
18%12%5%7%6%24445%27%
2340
December1st to 15thNight
20%12%5%9%7%24345%21%
2397
16th to endNight
21%16%6%9%6%345%45%14%
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
70%411%10%3
1433
16th to endDay
73%39%9%3
1597
February1st to 15thDay
66%5%7%14%5%
1638
16th to endDay
64%6%9%13%4
1580
March1st to 15thDay
56%6%12%16%6%1
1857
16th to endDay
53%6%10%20%8%1
2112
April1st to 15thDay
55%39%19%11%
2154
16th to endDay
46%5%12%17%14%3
2340
May1st to 15thDay
52%6%10%19%10%1
2331
16th to endDay
43%6%12%24%11%1
2477
June1st to 15thDay
39%7%12%23%15%1
2520
16th to endDay
41%9%12%19%16%1
2520
July1st to 15thDay
33%8%11%23%20%2
2371
16th to endDay
37%8%14%21%16%1
2434
August1st to 15thDay
39%8%12%24%13%1
2327
16th to endDay
40%7%10%23%16%2
2417
September1st to 15thDay
38%7%11%25%14%1
2043
16th to endDay
39%6%10%28%14%
1894
October1st to 15thDay
45%5%10%24%12%1
1757
16th to endDay
54%413%19%6%
1636
November1st to 15thDay
46%5%9%22%13%1
1582
16th to endDay
60%412%17%5%
1620
December1st to 15thDay
63%6%10%14%3
1562
16th to endDay
72%411%7%3
1536
January1st to 15thNight
63%410%14%5%
2506
16th to endNight
66%5%13%10%3
2625
February1st to 15thNight
60%6%10%15%5%1
2223
16th to endNight
56%412%18%6%1
1893
March1st to 15thNight
52%5%11%18%9%1
2101
16th to endNight
49%6%10%21%10%1
2112
April1st to 15thNight
49%5%10%18%14%
1803
16th to endNight
46%312%18%16%3
1620
May1st to 15thNight
50%5%9%21%11%2
1620
16th to endNight
38%6%13%23%15%3
1640
June1st to 15thNight
35%6%11%29%16%1
1440
16th to endNight
32%8%16%24%18%
1440
July1st to 15thNight
29%6%11%29%20%2
1360
16th to endNight
27%8%14%25%22%2
1470
August1st to 15thNight
30%6%12%30%16%2
1609
16th to endNight
34%410%26%19%3
1782
September1st to 15thNight
33%5%8%29%21%2
1905
16th to endNight
35%5%11%29%17%
1903
October1st to 15thNight
40%6%10%22%18%1
1873
16th to endNight
50%5%11%23%8%
2233
November1st to 15thNight
45%412%22%14%2
2276
16th to endNight
57%411%18%6%
2340
December1st to 15thNight
63%411%13%5%
2397
16th to endNight
70%5%9%10%4
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
23%12%42%17%4
90
16th to endDay
29%9%42%14%4
96
February1st to 15thDay
22%15%46%15%
90
16th to endDay
19%14%38%22%4
81
March1st to 15thDay
28%11%32%20%6%
147
16th to endDay
23%7%32%24%9%2
288
April1st to 15thDay
24%9%30%25%8%1
270
16th to endDay
20%8%30%24%10%7%
270
May1st to 15thDay
23%6%29%20%13%5%
288
16th to endDay
16%10%24%24%16%8%
373
June1st to 15thDay
10%6%29%31%16%5%
495
16th to endDay
12%7%30%26%17%5%
495
July1st to 15thDay
8%425%27%23%11%
475
16th to endDay
10%321%28%23%13%
457
August1st to 15thDay
9%18%25%23%21%
313
16th to endDay
15%218%21%25%16%
332
September1st to 15thDay
11%319%20%28%17%
315
16th to endDay
16%413%22%29%13%
283
October1st to 15thDay
16%423%32%16%6%
255
16th to endDay
24%13%25%27%8%
148
November1st to 15thDay
415%27%34%14%3
90
16th to endDay
23%14%42%12%7%
90
December1st to 15thDay
25%23%34%12%4
90
16th to endDay
26%27%40%6%
96
January1st to 15thNight
26%13%37%17%4
900
16th to endNight
17%12%36%27%6%
897
February1st to 15thNight
22%13%36%23%3
704
16th to endNight
21%10%36%26%4
631
March1st to 15thNight
22%11%31%26%7%
720
16th to endNight
19%9%35%24%10%
768
April1st to 15thNight
21%10%34%26%6%
551
16th to endNight
20%6%34%27%10%1
540
May1st to 15thNight
23%5%28%31%8%1
540
16th to endNight
14%326%35%17%1
563
June1st to 15thNight
12%223%45%15%
540
16th to endNight
8%223%42%20%2
540
July1st to 15thNight
7%215%44%26%3
510
16th to endNight
6%215%44%28%2
564
August1st to 15thNight
8%14%45%25%5%
539
16th to endNight
13%112%34%32%5%
573
September1st to 15thNight
13%316%34%26%5%
645
16th to endNight
15%415%30%28%6%
689
October1st to 15thNight
16%5%25%31%18%2
660
16th to endNight
23%12%32%22%8%
704
November1st to 15thNight
19%8%30%28%12%
700
16th to endNight
25%13%31%22%7%
720
December1st to 15thNight
24%11%37%21%4
777
16th to endNight
30%10%36%18%3
960
Page generated at 2017-09-24 09:15:47. Version ac04

Copyright 2017 A. Danko


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