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 2017-09-16.

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%
15965
28%
46858
19%
15924
66%
15924
42%
24985

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
46%
897
31%
2506
17%
895
59%
895
44%
1289
January16th to endNight
44%
825
34%
2553
19%
825
61%
825
41%
1284
February1st to 15thNight
40%
698
26%
2262
13%
697
57%
697
35%
1217
February16th to endNight
44%
632
32%
1894
18%
632
58%
632
39%
1010
March1st to 15thNight
51%
720
29%
2115
15%
720
63%
720
44%
1120
March16th to endNight
49%
679
27%
2023
17%
679
59%
679
39%
1102
April1st to 15thNight
49%
539
24%
1798
18%
539
60%
539
34%
957
April16th to endNight
45%
540
23%
1800
19%
540
55%
540
30%
1038
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
78%
495
37%
1778
38%
495
83%
495
52%
764
October1st to 15thNight
61%
656
29%
1976
22%
656
65%
656
42%
1058
October16th to endNight
62%
740
34%
2148
20%
740
69%
740
46%
1115
November1st to 15thNight
61%
875
32%
2275
19%
875
66%
875
51%
1220
November16th to endNight
54%
900
36%
2426
19%
900
65%
900
53%
1240
December1st to 15thNight
45%
900
25%
2520
10%
900
58%
900
40%
1389
December16th to endNight
49%
960
28%
2688
15%
960
59%
960
38%
1528

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%
47917
Night
5%413323347%58%
47031
TransparencyDay
27%5%12%26%20%7%
47593
Night
24%412%28%22%7%
46858
SeeingDay
11%6%25%32%18%6%
5889
Night
7%5%22%41%19%3
15974

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
15%24413348%59%
1432
16th to endDay
15%2441235%7%61%
1680
February1st to 15thDay
26%2432445%8%55%
1599
16th to endDay
16%2431336%7%58%
1580
March1st to 15thDay
3425%424448%55%
1842
16th to endDay
5%6%3442445%9%50%
2199
April1st to 15thDay
7%5%2332445%8%53%
2150
16th to endDay
13%6%2442445%8%42%
2160
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
4312312446%64%
1870
October1st to 15thDay
6%6%12313347%57%
1653
16th to endDay
5%41313347%64%
1711
November1st to 15thDay
35%12423348%60%
1583
16th to endDay
142321346%8%60%
1533
December1st to 15thDay
26%25%4235%5%8%54%
1440
16th to endDay
45%25%42245%7%55%
1536
January1st to 15thNight
131431345%7%62%
2506
16th to endNight
3424313346%62%
2553
February1st to 15thNight
27%26%323247%57%
2252
16th to endNight
28%35%422245%59%
1894
March1st to 15thNight
241332335%8%58%
2115
16th to endNight
6%5%23313447%56%
2023
April1st to 15thNight
6%5%2432445%6%54%
1798
16th to endNight
15%6%14313336%50%
1800
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
5%11213436%68%
1778
October1st to 15thNight
9%5%13212346%58%
1976
16th to endNight
6%5%12313335%63%
2148
November1st to 15thNight
2313322337%64%
2275
16th to endNight
15%1331235%6%64%
2426
December1st to 15thNight
35%25%423338%57%
2520
16th to endNight
36%3432345%7%55%
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
23%212%36%20%4
1433
16th to endDay
22%29%35%22%6%
1680
February1st to 15thDay
26%316%35%14%3
1600
16th to endDay
23%310%34%23%4
1580
March1st to 15thDay
27%311%30%23%5%
1842
16th to endDay
30%413%28%18%4
2199
April1st to 15thDay
28%413%27%19%7%
2150
16th to endDay
39%5%10%23%16%3
2160
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
20%37%25%35%6%
1870
October1st to 15thDay
26%5%11%22%26%7%
1653
16th to endDay
19%210%29%28%9%
1711
November1st to 15thDay
21%312%27%24%10%
1583
16th to endDay
20%210%28%29%8%
1533
December1st to 15thDay
26%413%35%17%2
1440
16th to endDay
27%416%26%20%5%
1536
January1st to 15thNight
20%312%33%25%4
2506
16th to endNight
22%310%29%26%7%
2553
February1st to 15thNight
28%311%33%17%4
2262
16th to endNight
28%18%29%24%7%
1894
March1st to 15thNight
24%39%29%26%6%
2115
16th to endNight
26%413%28%22%4
2023
April1st to 15thNight
28%411%28%18%7%
1798
16th to endNight
35%49%27%19%3
1800
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
17%37%31%32%9%
1778
October1st to 15thNight
25%413%18%28%8%
1976
16th to endNight
23%38%27%29%8%
2148
November1st to 15thNight
20%311%24%27%12%
2275
16th to endNight
19%29%29%29%9%
2426
December1st to 15thNight
26%314%32%19%4
2520
16th to endNight
28%414%29%20%2
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
8%11%15%41%12%11%
90
16th to endDay
5%8%33%31%19%2
96
February1st to 15thDay
418%34%37%4
90
16th to endDay
411%41%33%7%1
81
March1st to 15thDay
7%15%27%39%6%3
132
16th to endDay
12%14%42%23%41
288
April1st to 15thDay
13%17%39%20%7%1
269
16th to endDay
25%18%29%18%6%1
270
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
5%225%30%25%9%
139
October1st to 15thDay
11%220%41%15%10%
90
16th to endDay
10%6%25%34%16%7%
96
November1st to 15thDay
3422%30%22%17%
90
16th to endDay
15%10%27%41%5%
90
December1st to 15thDay
10%11%35%37%5%
90
16th to endDay
3131%54%9%1
96
January1st to 15thNight
312%32%35%12%3
900
16th to endNight
5%12%32%39%9%1
825
February1st to 15thNight
5%7%35%42%8%
704
16th to endNight
5%8%33%44%7%
632
March1st to 15thNight
46%31%44%10%1
720
16th to endNight
8%8%28%43%10%1
679
April1st to 15thNight
8%7%28%46%7%1
539
16th to endNight
19%425%34%13%1
540
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
5%111%42%30%7%
495
October1st to 15thNight
12%317%41%20%4
656
16th to endNight
10%318%45%17%3
740
November1st to 15thNight
5%6%22%47%15%3
875
16th to endNight
46%29%46%12%1
900
December1st to 15thNight
5%10%30%44%8%1
900
16th to endNight
7%7%28%45%9%1
960
Page generated at 2017-09-17 10:05:45. Version ac04

Copyright 2017 A. Danko


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