Little Blair Valley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Little Blair Valley 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
64%
16030
40%
46591
28%
15986
75%
15986
62%
20246

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
65%
717
35%
2327
30%
716
75%
716
49%
1061
January16th to endNight
59%
768
40%
2328
29%
768
74%
768
48%
1111
February1st to 15thNight
62%
700
40%
2105
30%
697
77%
697
53%
954
February16th to endNight
49%
632
37%
1895
27%
632
66%
632
44%
918
March1st to 15thNight
53%
720
38%
2139
28%
720
70%
720
57%
929
March16th to endNight
53%
768
38%
2076
22%
768
68%
768
58%
957
April1st to 15thNight
41%
719
40%
1799
13%
719
58%
719
56%
866
April16th to endNight
46%
720
44%
1800
14%
720
64%
720
66%
805
May1st to 15thNight
50%
554
42%
1634
21%
554
64%
554
68%
636
May16th to endNight
46%
562
42%
1685
19%
561
62%
561
68%
634
June1st to 15thNight
52%
540
38%
1620
22%
540
64%
540
78%
598
June16th to endNight
64%
540
39%
1620
27%
540
71%
540
83%
597
July1st to 15thNight
82%
510
31%
1530
25%
510
85%
510
68%
646
July16th to endNight
81%
591
36%
1618
27%
556
83%
556
63%
728
August1st to 15thNight
87%
701
38%
1750
23%
697
88%
697
77%
799
August16th to endNight
88%
700
42%
1750
28%
700
90%
700
71%
840
September1st to 15thNight
84%
660
41%
1736
29%
660
89%
660
76%
773
September16th to endNight
78%
656
48%
1815
38%
656
87%
656
80%
727
October1st to 15thNight
63%
660
46%
1815
30%
660
79%
660
67%
789
October16th to endNight
74%
704
47%
2098
40%
704
85%
704
75%
818
November1st to 15thNight
74%
700
40%
2275
36%
700
84%
700
64%
888
November16th to endNight
70%
720
42%
2340
38%
720
81%
720
60%
947
December1st to 15thNight
65%
720
38%
2340
34%
720
74%
720
50%
1051
December16th to endNight
57%
768
37%
2496
30%
768
69%
768
45%
1174

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
111213346%73%
47371
Night
111212335%75%
46796
TransparencyDay
11%3413%26%40%
47069
Night
10%3413%27%40%
46599
SeeingDay
315%29%32%16%3
5721
Night
19%21%31%27%8%
16039

By Month

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
2213413347%65%
1611
16th to endDay
321332345%8%61%
1893
February1st to 15thDay
2212213448%66%
1751
16th to endDay
1135%2446%9%59%
1579
March1st to 15thDay
2112113347%70%
1821
16th to endDay
1222445%5%70%
2145
April1st to 15thDay
112323346%71%
2149
16th to endDay
11145%81%
2160
May1st to 15thDay
11112135%80%
2316
16th to endDay
1122485%
2429
June1st to 15thDay
111112484%
2340
16th to endDay
1111288%
2340
July1st to 15thDay
2112212436%69%
2340
16th to endDay
121232346%8%64%
2437
August1st to 15thDay
1221334474%
2114
16th to endDay
21221335%6%69%
2100
September1st to 15thDay
111213335%74%
1892
16th to endDay
1121112283%
1815
October1st to 15thDay
11212345%77%
1815
16th to endDay
1111232480%
1772
November1st to 15thDay
111112345%75%
1584
16th to endDay
112223446%71%
1620
December1st to 15thDay
332325%45%7%61%
1620
16th to endDay
22232435%8%63%
1728
January1st to 15thNight
1212323347%65%
2327
16th to endNight
3212214346%66%
2328
February1st to 15thNight
22224338%68%
2101
16th to endNight
134345%5%7%62%
1895
March1st to 15thNight
1111213348%70%
2139
16th to endNight
11111235%8%70%
2076
April1st to 15thNight
1221233476%
1799
16th to endNight
11113484%
1800
May1st to 15thNight
111325%82%
1634
16th to endNight
1112388%
1684
June1st to 15thNight
1111289%
1620
16th to endNight
11290%
1620
July1st to 15thNight
1212445%76%
1620
16th to endNight
1211212236%72%
1728
August1st to 15thNight
112235%81%
1760
16th to endNight
21111123479%
1750
September1st to 15thNight
111223481%
1736
16th to endNight
111290%
1815
October1st to 15thNight
111123480%
1815
16th to endNight
112235%80%
2098
November1st to 15thNight
111333478%
2275
16th to endNight
1112112245%75%
2340
December1st to 15thNight
223313447%66%
2340
16th to endNight
32232335%7%64%
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
17%45%15%28%27%
1612
16th to endDay
19%36%17%27%24%
1893
February1st to 15thDay
15%45%15%30%29%
1751
16th to endDay
17%6%7%20%27%20%
1579
March1st to 15thDay
12%3316%32%31%
1821
16th to endDay
12%45%17%32%27%
2145
April1st to 15thDay
12%3412%41%25%
2149
16th to endDay
5%2316%34%37%
2160
May1st to 15thDay
7%2311%31%44%
2316
16th to endDay
41312%32%44%
2432
June1st to 15thDay
5%218%20%61%
2340
16th to endDay
5%11310%77%
2340
July1st to 15thDay
15%348%18%49%
2201
16th to endDay
16%5%7%17%25%27%
2284
August1st to 15thDay
13%339%23%46%
2100
16th to endDay
15%348%24%42%
2100
September1st to 15thDay
12%348%21%49%
1892
16th to endDay
7%125%23%58%
1815
October1st to 15thDay
10%2211%30%42%
1815
16th to endDay
8%249%23%51%
1772
November1st to 15thDay
9%3414%30%37%
1584
16th to endDay
11%45%15%26%37%
1620
December1st to 15thDay
18%5%5%20%22%27%
1620
16th to endDay
17%5%7%22%27%18%
1728
January1st to 15thNight
16%46%16%27%29%
2327
16th to endNight
17%45%18%22%30%
2328
February1st to 15thNight
13%45%16%28%32%
2112
16th to endNight
16%5%7%17%27%24%
1895
March1st to 15thNight
12%26%16%31%30%
2139
16th to endNight
10%36%17%32%29%
2076
April1st to 15thNight
10%25%15%38%26%
1799
16th to endNight
5%1313%35%40%
1800
May1st to 15thNight
5%1311%30%46%
1635
16th to endNight
5%119%36%45%
1685
June1st to 15thNight
49%22%61%
1620
16th to endNight
5%138%81%
1620
July1st to 15thNight
10%346%19%57%
1530
16th to endNight
13%27%15%28%33%
1618
August1st to 15thNight
7%2311%25%49%
1750
16th to endNight
10%228%25%50%
1750
September1st to 15thNight
7%237%23%55%
1736
16th to endNight
5%1327%60%
1815
October1st to 15thNight
7%3213%29%43%
1815
16th to endNight
6%1410%24%51%
2098
November1st to 15thNight
8%3310%34%39%
2275
16th to endNight
12%2314%31%35%
2340
December1st to 15thNight
15%47%19%27%26%
2340
16th to endNight
17%5%8%22%24%21%
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
8%25%18%36%10%
90
16th to endDay
5%24%29%29%10%1
261
February1st to 15thDay
418%31%36%8%
266
16th to endDay
5%32%28%24%8%
238
March1st to 15thDay
422%33%24%12%1
270
16th to endDay
423%35%23%11%1
288
April1st to 15thDay
7%25%33%21%10%1
269
16th to endDay
327%34%24%8%2
270
May1st to 15thDay
223%36%26%7%2
288
16th to endDay
119%38%26%11%2
330
June1st to 15thDay
117%34%25%18%3
315
16th to endDay
1436%31%21%4
315
July1st to 15thDay
1224%42%24%4
305
16th to endDay
318%36%29%11%
327
August1st to 15thDay
1123%41%25%7%
300
16th to endDay
221%41%23%10%
268
September1st to 15thDay
2432%43%12%4
255
16th to endDay
310%25%42%15%2
255
October1st to 15thDay
119%32%34%11%
255
16th to endDay
211%26%33%24%1
190
November1st to 15thDay
117%17%26%30%6%
90
16th to endDay
124%24%31%17%1
90
December1st to 15thDay
111%14%45%26%1
90
16th to endDay
425%25%31%14%
96
January1st to 15thNight
29%17%33%26%11%
720
16th to endNight
5%9%20%31%26%6%
768
February1st to 15thNight
111%19%31%26%9%
704
16th to endNight
217%27%27%18%6%
632
March1st to 15thNight
214%26%28%22%4
720
16th to endNight
116%27%26%21%6%
768
April1st to 15thNight
121%32%22%15%4
719
16th to endNight
120%31%23%17%6%
720
May1st to 15thNight
14%33%32%16%2
555
16th to endNight
117%33%28%15%2
563
June1st to 15thNight
8%37%34%17%1
540
16th to endNight
1231%42%20%2
540
July1st to 15thNight
1111%47%33%4
510
16th to endNight
210%47%35%4
591
August1st to 15thNight
8%40%40%8%
701
16th to endNight
35%32%47%11%
700
September1st to 15thNight
110%32%43%10%
660
16th to endNight
1413%32%36%11%
656
October1st to 15thNight
111%22%30%26%8%
660
16th to endNight
417%30%28%17%
704
November1st to 15thNight
6%16%33%31%12%
700
16th to endNight
28%16%26%30%16%
720
December1st to 15thNight
28%17%32%27%10%
720
16th to endNight
412%21%29%24%7%
768
Page generated at 2017-08-13 11:16:34. Version ac04

Copyright 2017 A. Danko


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