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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 2017-03-26.

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%
15573
40%
45316
28%
15529
75%
15529
61%
19743

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%
748
37%
2024
22%
748
67%
748
58%
937
April1st to 15thNight
38%
659
41%
1649
13%
659
56%
659
53%
805
April16th to endNight
45%
660
42%
1650
13%
660
63%
660
65%
740
May1st to 15thNight
48%
508
44%
1498
21%
508
63%
508
68%
583
May16th to endNight
44%
514
40%
1541
17%
513
60%
513
66%
586
June1st to 15thNight
51%
495
40%
1485
23%
495
63%
495
78%
550
June16th to endNight
63%
495
37%
1485
25%
495
70%
495
82%
549
July1st to 15thNight
81%
465
32%
1395
26%
465
84%
465
66%
597
July16th to endNight
80%
547
35%
1490
25%
512
83%
512
65%
662
August1st to 15thNight
86%
657
40%
1640
24%
653
88%
653
77%
754
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%
45649
Night
111212335%75%
45521
TransparencyDay
12%3413%26%39%
45347
Night
10%3413%27%40%
45324
SeeingDay
316%30%32%14%3
5175
Night
19%21%32%26%8%
15582

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%6%70%
2083
April1st to 15thDay
112323346%70%
1969
16th to endDay
11145%80%
1980
May1st to 15thDay
1112135%80%
2122
16th to endDay
1122485%
2221
June1st to 15thDay
111112484%
2145
16th to endDay
1111287%
2145
July1st to 15thDay
2112212336%70%
2145
16th to endDay
121232345%7%65%
2258
August1st to 15thDay
1121334474%
1980
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
11111245%9%69%
2024
April1st to 15thNight
1221233475%
1649
16th to endNight
11113484%
1650
May1st to 15thNight
111326%82%
1498
16th to endNight
1112387%
1540
June1st to 15thNight
1111289%
1485
16th to endNight
1111289%
1485
July1st to 15thNight
121245%5%75%
1485
16th to endNight
1212212246%73%
1600
August1st to 15thNight
1112235%80%
1650
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
13%45%17%32%26%
2083
April1st to 15thDay
13%3413%40%24%
1969
16th to endDay
5%2316%35%36%
1980
May1st to 15thDay
7%2211%30%45%
2122
16th to endDay
42212%34%43%
2224
June1st to 15thDay
5%219%18%62%
2145
16th to endDay
6%11311%75%
2145
July1st to 15thDay
14%348%17%51%
2006
16th to endDay
15%46%18%25%28%
2105
August1st to 15thDay
13%339%24%46%
1966
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%46%16%31%29%
2024
April1st to 15thNight
11%26%16%36%25%
1649
16th to endNight
6%1313%35%40%
1650
May1st to 15thNight
5%2311%31%46%
1499
16th to endNight
5%119%38%43%
1541
June1st to 15thNight
49%21%62%
1485
16th to endNight
5%139%79%
1485
July1st to 15thNight
10%345%18%56%
1395
16th to endNight
13%27%15%27%34%
1490
August1st to 15thNight
7%2211%25%48%
1640
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
422%35%23%11%1
267
April1st to 15thDay
9%28%32%22%5%1
209
16th to endDay
429%33%24%6%1
210
May1st to 15thDay
224%39%24%6%2
228
16th to endDay
121%39%23%10%2
266
June1st to 15thDay
120%37%23%14%3
255
16th to endDay
25%40%30%16%4
255
July1st to 15thDay
1326%42%22%2
245
16th to endDay
3121%40%24%8%
271
August1st to 15thDay
1127%42%18%7%
255
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
115%27%26%21%6%
748
April1st to 15thNight
123%33%21%14%4
659
16th to endNight
121%31%22%17%6%
660
May1st to 15thNight
15%34%32%14%1
509
16th to endNight
118%35%28%13%2
515
June1st to 15thNight
8%39%35%15%1
495
16th to endNight
1232%42%18%2
495
July1st to 15thNight
1112%49%30%3
465
16th to endNight
210%49%33%3
547
August1st to 15thNight
18%42%38%8%
657
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 2017-03-27 08:15:13. Version ac04

Copyright 2017 A. Danko


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