Trubble Terrestrial Telescope
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Trubble Terrestrial Telescope clear sky chart from 2005-11-05 to 2018-04-23.

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
58%
16876
28%
49541
19%
16835
66%
16835
42%
26395

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
47%
972
31%
2716
17%
970
59%
970
45%
1396
January16th to endNight
46%
894
34%
2766
20%
894
62%
894
42%
1383
February1st to 15thNight
40%
758
26%
2454
12%
757
57%
757
36%
1316
February16th to endNight
45%
684
32%
2050
18%
684
58%
684
39%
1099
March1st to 15thNight
51%
780
30%
2291
15%
780
64%
780
46%
1189
March16th to endNight
50%
736
27%
2192
17%
736
60%
736
39%
1201
April1st to 15thNight
48%
584
24%
1948
18%
584
60%
584
33%
1050
April16th to endNight
45%
558
24%
1859
20%
558
56%
558
30%
1073
May1st to 15thNight
51%
540
19%
1570
15%
540
56%
540
30%
975
May16th to endNight
63%
563
18%
1498
14%
561
66%
561
40%
892
June1st to 15thNight
71%
540
20%
1440
16%
540
72%
540
47%
801
June16th to endNight
80%
540
29%
1440
23%
540
81%
540
58%
719
July1st to 15thNight
76%
510
20%
1360
17%
510
77%
510
43%
770
July16th to endNight
82%
564
27%
1425
24%
531
82%
531
48%
779
August1st to 15thNight
78%
539
22%
1653
24%
536
79%
536
44%
838
August16th to endNight
80%
573
31%
1910
36%
573
81%
573
42%
968
September1st to 15thNight
73%
540
28%
1800
30%
540
78%
540
42%
912
September16th to endNight
76%
537
36%
1929
37%
537
81%
537
49%
863
October1st to 15thNight
61%
716
28%
2156
21%
716
66%
716
42%
1145
October16th to endNight
61%
808
36%
2344
21%
808
69%
808
46%
1218
November1st to 15thNight
60%
950
31%
2470
19%
950
65%
950
51%
1324
November16th to endNight
55%
975
36%
2628
20%
975
66%
975
53%
1335
December1st to 15thNight
45%
975
26%
2730
11%
975
58%
975
42%
1488
December16th to endNight
49%
1040
29%
2912
16%
1040
59%
1040
38%
1661

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
5%4134245%6%8%52%
49993
Night
5%413323347%58%
49714
TransparencyDay
27%5%12%26%21%7%
49669
Night
24%411%28%23%7%
49541
SeeingDay
10%6%26%33%16%5%
6579
Night
7%5%22%42%18%3
16885

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
16%24313348%58%
1552
16th to endDay
142442235%8%60%
1820
February1st to 15thDay
26%24323448%56%
1737
16th to endDay
16%25%41335%7%58%
1710
March1st to 15thDay
3424424448%56%
1996
16th to endDay
5%6%3442445%8%49%
2382
April1st to 15thDay
7%6%2331345%8%53%
2330
16th to endDay
13%6%2442445%8%42%
2215
May1st to 15thDay
13%6%144345%5%8%40%
2379
16th to endDay
11%5%24446%6%6%8%40%
2616
June1st to 15thDay
6%312435%6%7%10%48%
2520
16th to endDay
312335%6%6%8%57%
2520
July1st to 15thDay
7%314436%6%7%8%46%
2520
16th to endDay
5%2135%36%7%7%9%47%
2644
August1st to 15thDay
5%3245%36%8%9%9%41%
2298
16th to endDay
4313436%6%6%8%52%
2292
September1st to 15thDay
8%3132235%6%6%55%
2160
16th to endDay
6%322322445%62%
2030
October1st to 15thDay
7%6%12313347%58%
1803
16th to endDay
5%41312347%65%
1866
November1st to 15thDay
35%13423348%60%
1718
16th to endDay
142321346%8%60%
1661
December1st to 15thDay
25%243235%5%8%55%
1560
16th to endDay
35%25%42335%7%55%
1664
January1st to 15thNight
141431345%7%62%
2716
16th to endNight
3424313346%62%
2766
February1st to 15thNight
27%26%323347%57%
2444
16th to endNight
28%35%423235%58%
2050
March1st to 15thNight
241332335%8%59%
2291
16th to endNight
6%5%23323447%56%
2192
April1st to 15thNight
6%6%2432335%6%54%
1948
16th to endNight
15%5%13313336%50%
1859
May1st to 15thNight
15%5%23314447%46%
1569
16th to endNight
11%3123235%5%8%52%
1497
June1st to 15thNight
6%21232445%8%58%
1440
16th to endNight
211222335%8%66%
1440
July1st to 15thNight
7%21232447%9%53%
1440
16th to endNight
32134345%7%8%56%
1521
August1st to 15thNight
42133245%7%9%54%
1662
16th to endNight
431332435%6%60%
1910
September1st to 15thNight
8%312324346%60%
1800
16th to endNight
6%22213335%66%
1929
October1st to 15thNight
9%5%13212346%59%
2156
16th to endNight
6%5%12313335%63%
2344
November1st to 15thNight
2313322347%63%
2470
16th to endNight
141231235%7%64%
2628
December1st to 15thNight
35%25%423338%58%
2730
16th to endNight
36%3432345%7%54%
2912

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
23%312%35%20%4
1553
16th to endDay
22%39%35%22%6%
1820
February1st to 15thDay
26%316%34%15%3
1738
16th to endDay
23%39%33%24%4
1710
March1st to 15thDay
25%310%29%24%6%
1996
16th to endDay
31%413%28%17%4
2382
April1st to 15thDay
27%413%27%18%7%
2330
16th to endDay
39%5%10%23%16%3
2215
May1st to 15thDay
40%6%11%23%15%2
2379
16th to endDay
38%7%16%21%12%4
2620
June1st to 15thDay
27%8%15%21%18%8%
2520
16th to endDay
20%6%10%23%26%11%
2520
July1st to 15thDay
32%7%11%19%16%12%
2371
16th to endDay
28%8%11%25%17%8%
2478
August1st to 15thDay
30%8%14%18%16%11%
2283
16th to endDay
25%6%11%25%22%8%
2292
September1st to 15thDay
26%5%8%23%23%13%
2160
16th to endDay
22%37%25%34%6%
2030
October1st to 15thDay
25%5%11%22%27%7%
1803
16th to endDay
19%210%28%28%10%
1866
November1st to 15thDay
21%212%27%25%10%
1718
16th to endDay
19%310%27%30%7%
1661
December1st to 15thDay
25%412%35%18%3
1560
16th to endDay
26%415%27%20%4
1664
January1st to 15thNight
20%312%33%24%4
2716
16th to endNight
21%310%30%26%7%
2766
February1st to 15thNight
28%412%33%17%4
2454
16th to endNight
28%18%28%25%7%
2050
March1st to 15thNight
23%39%28%29%6%
2291
16th to endNight
26%413%28%22%4
2192
April1st to 15thNight
29%411%29%18%6%
1948
16th to endNight
35%49%27%19%3
1859
May1st to 15thNight
37%5%15%22%16%3
1570
16th to endNight
28%6%20%26%12%5%
1498
June1st to 15thNight
23%5%18%26%14%11%
1440
16th to endNight
15%5%9%26%28%15%
1440
July1st to 15thNight
24%7%13%25%18%10%
1360
16th to endNight
23%5%12%29%18%10%
1425
August1st to 15thNight
22%5%17%24%19%10%
1653
16th to endNight
23%5%8%27%25%10%
1910
September1st to 15thNight
25%411%24%18%16%
1800
16th to endNight
19%37%30%30%9%
1929
October1st to 15thNight
25%412%20%27%9%
2156
16th to endNight
23%37%26%28%10%
2344
November1st to 15thNight
20%410%26%26%11%
2470
16th to endNight
18%39%29%29%9%
2628
December1st to 15thNight
25%313%31%20%6%
2730
16th to endNight
28%413%29%20%2
2912

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%8%17%49%9%7%
135
16th to endDay
47%33%35%16%2
144
February1st to 15thDay
5%17%34%38%3
135
16th to endDay
38%49%33%5%
120
March1st to 15thDay
7%14%29%38%7%2
181
16th to endDay
14%14%41%23%5%1
352
April1st to 15thDay
12%19%38%22%5%1
329
16th to endDay
25%17%29%18%7%1
288
May1st to 15thDay
19%7%24%31%11%4
435
16th to endDay
18%5%22%27%19%6%
517
June1st to 15thDay
8%221%33%26%7%
495
16th to endDay
3125%34%25%8%
495
July1st to 15thDay
11%216%32%24%13%
475
16th to endDay
6%114%32%33%11%
503
August1st to 15thDay
9%326%39%16%4
315
16th to endDay
7%320%41%20%6%
332
September1st to 15thDay
10%229%36%14%6%
315
16th to endDay
10%327%29%22%7%
185
October1st to 15thDay
11%324%39%11%8%
135
16th to endDay
7%7%31%33%13%6%
144
November1st to 15thDay
47%23%34%17%11%
135
16th to endDay
10%9%28%47%3
135
December1st to 15thDay
6%11%34%39%6%
135
16th to endDay
2429%55%8%
144
January1st to 15thNight
311%31%37%11%3
975
16th to endNight
5%11%30%40%9%1
894
February1st to 15thNight
6%6%36%42%7%
764
16th to endNight
5%8%32%46%7%
684
March1st to 15thNight
45%31%45%10%1
780
16th to endNight
8%7%28%44%9%
736
April1st to 15thNight
9%8%27%46%6%1
584
16th to endNight
19%426%34%13%1
558
May1st to 15thNight
19%419%36%16%3
540
16th to endNight
12%116%38%26%4
563
June1st to 15thNight
7%114%50%23%2
540
16th to endNight
3110%48%33%3
540
July1st to 15thNight
8%17%32%42%7%
510
16th to endNight
5%5%30%51%6%
564
August1st to 15thNight
6%15%37%44%5%
539
16th to endNight
5%5%36%43%7%
573
September1st to 15thNight
10%19%38%30%9%
540
16th to endNight
7%112%43%28%7%
537
October1st to 15thNight
12%317%43%18%4
716
16th to endNight
10%319%45%17%3
808
November1st to 15thNight
5%6%22%48%14%2
950
16th to endNight
46%28%47%11%1
975
December1st to 15thNight
5%10%30%44%8%1
975
16th to endNight
7%7%28%45%8%1
1040
Page generated at 2018-04-24 08:03:02. Version ac04

Copyright 2018 A. Danko


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