Distant Thunder Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Distant Thunder 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
51%
15116
23%
47196
17%
15072
59%
15072
26%
28319

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%
882
25%
2309
10%
877
45%
877
27%
1466
January16th to endNight
36%
787
26%
2323
13%
787
45%
787
24%
1475
February1st to 15thNight
35%
704
26%
2112
12%
701
47%
701
25%
1291
February16th to endNight
31%
631
22%
1893
9%
631
42%
631
24%
1197
March1st to 15thNight
33%
621
23%
2061
13%
621
44%
621
19%
1290
March16th to endNight
44%
576
25%
2037
18%
576
56%
576
26%
1115
April1st to 15thNight
44%
539
25%
1797
19%
539
53%
539
24%
1056
April16th to endNight
47%
540
27%
1800
20%
540
59%
540
28%
977
May1st to 15thNight
54%
539
21%
1799
19%
539
62%
539
28%
1011
May16th to endNight
60%
561
21%
1870
17%
561
68%
561
27%
1057
June1st to 15thNight
65%
540
14%
1783
15%
540
67%
540
25%
1052
June16th to endNight
65%
540
14%
1620
13%
540
68%
540
26%
1032
July1st to 15thNight
75%
510
14%
1530
15%
510
75%
510
30%
955
July16th to endNight
67%
564
11%
1751
14%
531
71%
531
24%
1133
August1st to 15thNight
76%
539
12%
1788
15%
536
77%
536
27%
1089
August16th to endNight
68%
573
14%
1910
15%
573
69%
573
22%
1246
September1st to 15thNight
69%
540
21%
1800
22%
540
72%
540
26%
1115
September16th to endNight
66%
658
28%
1872
21%
658
70%
658
32%
1122
October1st to 15thNight
69%
660
33%
1906
27%
660
73%
660
43%
1006
October16th to endNight
58%
704
35%
2112
26%
704
66%
704
39%
1119
November1st to 15thNight
52%
700
33%
2100
25%
700
60%
700
32%
1187
November16th to endNight
45%
720
31%
2337
19%
720
60%
720
28%
1275
December1st to 15thNight
41%
720
24%
2340
17%
720
49%
720
22%
1443
December16th to endNight
32%
768
19%
2346
10%
768
41%
768
17%
1610

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
10%5%25%5%35%5%6%8%39%
47664
Night
10%42442445%8%47%
47407
TransparencyDay
39%9%11%17%16%6%
47378
Night
33%7%13%19%17%8%
47198
SeeingDay
11%8%10%21%28%18%
5283
Night
10%17%14%25%24%7%
15119

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
13%7%24444446%43%
1620
16th to endDay
19%5%24423345%45%
1894
February1st to 15thDay
13%5%24424347%46%
1750
16th to endDay
16%6%36%5%23446%41%
1580
March1st to 15thDay
16%6%25%423346%42%
1908
16th to endDay
9%6%35%5%2445%7%45%
2185
April1st to 15thDay
11%5%25%5%25%5%6%8%40%
2151
16th to endDay
10%5%25%5%3446%8%43%
2160
May1st to 15thDay
11%424426%5%6%9%41%
2151
16th to endDay
8%4245%36%6%9%9%40%
2244
June1st to 15thDay
6%426%7%5%8%7%8%10%30%
2171
16th to endDay
6%5%36%7%5%8%9%9%11%27%
2340
July1st to 15thDay
7%5%36%7%5%8%8%9%10%27%
2340
16th to endDay
8%5%37%8%5%8%9%9%11%22%
2294
August1st to 15thDay
7%326%7%5%9%8%9%11%27%
2160
16th to endDay
9%5%37%7%5%7%7%8%9%27%
2292
September1st to 15thDay
10%5%246%36%6%7%10%34%
2160
16th to endDay
7%5%25%6%47%5%8%7%40%
1912
October1st to 15thDay
6%32432445%8%55%
1722
16th to endDay
7%313423346%58%
1760
November1st to 15thDay
8%415%32345%7%53%
1758
16th to endDay
9%32332345%5%56%
1620
December1st to 15thDay
14%6%35%424346%42%
1620
16th to endDay
20%7%35%434446%34%
1872
January1st to 15thNight
15%5%23313347%47%
2309
16th to endNight
18%5%24413435%45%
2323
February1st to 15thNight
14%5%24323447%47%
2103
16th to endNight
18%6%2431335%6%44%
1893
March1st to 15thNight
14%5%245%34446%43%
2061
16th to endNight
11%423323347%52%
2037
April1st to 15thNight
11%424433446%49%
1797
16th to endNight
7%5%133245%5%7%52%
1800
May1st to 15thNight
7%424435%46%9%48%
1799
16th to endNight
6%41432446%8%52%
1869
June1st to 15thNight
5%4235%35%6%8%12%42%
1783
16th to endNight
44346%37%6%7%9%41%
1620
July1st to 15thNight
3325%435%7%8%13%43%
1620
16th to endNight
6%315%6%5%5%6%8%14%35%
1870
August1st to 15thNight
3214436%7%11%12%42%
1800
16th to endNight
7%4245%36%6%8%11%37%
1910
September1st to 15thNight
7%424445%6%6%12%41%
1800
16th to endNight
6%415%5%25%5%5%9%48%
1872
October1st to 15thNight
4313223337%63%
1906
16th to endNight
9%313323345%59%
2112
November1st to 15thNight
8%414424336%55%
2100
16th to endNight
9%424423335%56%
2337
December1st to 15thNight
12%5%25%5%24446%45%
2340
16th to endNight
19%9%24424346%37%
2346

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
41%47%14%21%10%
1621
16th to endDay
42%35%16%21%9%
1894
February1st to 15thDay
37%47%17%21%10%
1752
16th to endDay
43%47%15%20%8%
1580
March1st to 15thDay
42%5%7%19%17%6%
1908
16th to endDay
37%6%10%17%21%6%
2187
April1st to 15thDay
38%7%8%17%18%7%
2151
16th to endDay
36%8%9%22%18%4
2160
May1st to 15thDay
37%8%10%21%14%7%
2151
16th to endDay
34%12%12%22%16%1
2248
June1st to 15thDay
41%14%11%19%11%
2171
16th to endDay
43%13%15%18%8%
2340
July1st to 15thDay
43%14%18%17%5%1
2201
16th to endDay
48%14%17%16%3
2150
August1st to 15thDay
43%15%18%14%6%
2148
16th to endDay
47%14%15%13%6%2
2292
September1st to 15thDay
39%12%15%16%10%4
2160
16th to endDay
37%9%11%16%17%6%
1912
October1st to 15thDay
25%8%7%18%23%16%
1722
16th to endDay
27%45%14%29%18%
1760
November1st to 15thDay
29%6%7%17%30%9%
1758
16th to endDay
29%47%17%25%16%
1620
December1st to 15thDay
42%5%8%19%17%6%
1620
16th to endDay
50%5%6%16%16%4
1872
January1st to 15thNight
37%38%16%22%11%
2309
16th to endNight
42%36%15%22%10%
2323
February1st to 15thNight
37%37%18%20%12%
2112
16th to endNight
40%47%15%19%11%
1893
March1st to 15thNight
40%6%8%16%21%7%
2061
16th to endNight
32%411%20%23%7%
2037
April1st to 15thNight
35%5%10%21%17%10%
1797
16th to endNight
29%5%12%23%20%8%
1800
May1st to 15thNight
30%6%12%24%18%6%
1800
16th to endNight
28%8%15%27%17%2
1871
June1st to 15thNight
30%10%20%27%11%
1783
16th to endNight
34%10%22%21%10%
1620
July1st to 15thNight
27%15%29%22%5%
1530
16th to endNight
34%13%28%20%3
1751
August1st to 15thNight
25%17%30%19%6%
1788
16th to endNight
35%14%24%14%7%3
1910
September1st to 15thNight
33%10%19%17%12%6%
1800
16th to endNight
31%7%15%19%17%7%
1872
October1st to 15thNight
22%5%10%20%23%17%
1906
16th to endNight
26%26%14%26%21%
2112
November1st to 15thNight
31%37%17%28%11%
2100
16th to endNight
30%45%17%22%19%
2337
December1st to 15thNight
39%5%9%21%18%6%
2340
16th to endNight
48%48%16%15%6%
2346

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
24%432%26%11%1
90
16th to endDay
18%10%39%27%4
96
February1st to 15thDay
14%10%28%36%8%1
90
16th to endDay
12%440%30%11%
81
March1st to 15thDay
27%5%27%37%1
90
16th to endDay
16%12%16%29%23%
171
April1st to 15thDay
15%14%21%28%17%1
270
16th to endDay
12%14%13%32%23%3
270
May1st to 15thDay
13%13%12%31%25%4
288
16th to endDay
12%11%9%25%25%14%
331
June1st to 15thDay
11%9%415%37%20%
326
16th to endDay
6%12%5%15%34%24%
495
July1st to 15thDay
6%8%211%35%36%
475
16th to endDay
7%9%37%33%38%
343
August1st to 15thDay
9%5%37%35%38%
313
16th to endDay
10%6%5%10%33%33%
332
September1st to 15thDay
11%45%18%33%26%
315
16th to endDay
8%5%419%43%19%
283
October1st to 15thDay
6%48%30%39%11%
162
16th to endDay
14%29%30%36%7%
96
November1st to 15thDay
20%414%36%18%5%
90
16th to endDay
5%5%32%37%15%3
90
December1st to 15thDay
25%323%33%12%2
90
16th to endDay
33%5%22%28%10%
96
January1st to 15thNight
15%23%23%30%6%1
882
16th to endNight
14%22%23%30%8%
787
February1st to 15thNight
14%21%25%28%9%
704
16th to endNight
17%20%25%29%6%
631
March1st to 15thNight
15%22%23%27%10%
621
16th to endNight
12%21%17%29%17%1
576
April1st to 15thNight
11%21%18%31%16%
539
16th to endNight
10%19%18%32%17%1
540
May1st to 15thNight
7%18%14%38%19%1
540
16th to endNight
6%17%8%28%31%6%
563
June1st to 15thNight
6%17%220%43%9%
540
16th to endNight
417%214%41%19%
540
July1st to 15thNight
311%18%47%27%
510
16th to endNight
6%16%18%39%28%
564
August1st to 15thNight
39%19%43%31%
539
16th to endNight
8%8%311%40%27%
573
September1st to 15thNight
8%10%415%40%21%
540
16th to endNight
10%8%323%43%9%
658
October1st to 15thNight
5%10%10%35%33%5%
660
16th to endNight
10%11%15%28%29%4
704
November1st to 15thNight
10%16%15%32%21%3
700
16th to endNight
11%20%18%30%19%
720
December1st to 15thNight
12%21%19%27%17%1
720
16th to endNight
20%21%19%29%8%
768
Page generated at 2017-09-24 08:15:46. Version ac04

Copyright 2017 A. Danko


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