TBM Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the TBM Observatory clear sky chart from 2005-11-06 to 2024-03-01.

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
38%
23590
21%
80200
12%
23495
49%
23495
23%
49822

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 10thNight
21%
752
24%
4343
8%
737
41%
737
12%
2473
January11th to 20thNight
26%
759
25%
4040
10%
740
41%
740
13%
2319
January21st to endNight
22%
831
16%
4446
10%
814
41%
814
13%
2720
February1st to 10thNight
26%
760
19%
2470
10%
760
39%
760
21%
1580
February11th to 20thNight
15%
742
20%
2286
5%
740
33%
740
20%
1469
February21st to endNight
20%
628
24%
1884
8%
628
39%
628
21%
1213
March1st to 10thNight
24%
723
23%
2100
9%
723
40%
723
27%
1287
March11th to 20thNight
24%
720
21%
1980
9%
720
37%
720
24%
1303
March21st to endNight
26%
792
21%
2091
8%
792
37%
792
25%
1417
April1st to 10thNight
22%
720
20%
1800
4%
720
32%
720
26%
1223
April11th to 20thNight
34%
711
21%
1775
7%
711
41%
711
31%
1164
April21st to endNight
34%
720
20%
1800
7%
720
41%
720
29%
1194
May1st to 10thNight
36%
661
17%
1741
8%
661
41%
661
26%
1191
May11th to 20thNight
39%
354
18%
1416
12%
354
49%
354
18%
907
May21st to endNight
55%
388
15%
1551
16%
388
59%
388
21%
955
June1st to 10thNight
50%
360
19%
1440
19%
360
58%
360
24%
840
June11th to 20thNight
53%
360
16%
1440
17%
360
58%
360
22%
859
June21st to endNight
58%
360
16%
1440
17%
360
64%
360
24%
839
July1st to 10thNight
60%
350
15%
1400
19%
350
63%
350
20%
868
July11th to 20thNight
67%
348
18%
1392
21%
348
69%
348
26%
779
July21st to endNight
67%
554
19%
1638
16%
524
71%
524
29%
1008
August1st to 10thNight
66%
537
16%
1600
13%
534
67%
534
28%
1025
August11th to 20thNight
60%
671
16%
1735
10%
671
62%
671
29%
1172
August21st to endNight
62%
792
18%
1980
10%
792
63%
792
32%
1329
September1st to 10thNight
60%
720
22%
1800
13%
720
63%
720
32%
1209
September11th to 20thNight
62%
720
29%
1800
20%
720
66%
720
39%
1134
September21st to endNight
47%
720
22%
2023
16%
720
53%
720
25%
1359
October1st to 10thNight
47%
720
19%
2160
16%
720
53%
720
25%
1401
October11th to 20thNight
44%
720
25%
2160
19%
720
54%
720
30%
1286
October21st to endNight
37%
792
27%
2376
17%
792
50%
792
28%
1453
November1st to 10thNight
40%
740
26%
2394
15%
740
54%
740
31%
1369
November11th to 20thNight
33%
760
25%
2470
14%
760
47%
760
23%
1506
November21st to endNight
35%
760
24%
2598
13%
760
51%
760
25%
1504
December1st to 10thNight
25%
760
20%
2660
7%
760
40%
760
19%
1689
December11th to 20thNight
26%
760
21%
3178
8%
759
43%
759
17%
1892
December21st to endNight
29%
825
15%
4793
12%
817
43%
817
12%
2886

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
14%6%25%5%345%5%8%44%
78488
Night
15%6%25%5%3445%7%43%
80907
TransparencyDay
38%6%12%25%16%3
78196
Night
40%6%11%23%17%3
80719
SeeingDay
17%10%27%24%15%6%
14063
Night
17%9%29%30%13%1
23617

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 10thDay
16%5%24423346%49%
2517
11th to 20thDay
16%9%37%5%34445%40%
2758
21st to endDay
19%7%36%5%345%45%39%
3124
February1st to 10thDay
15%7%25%5%35%5%5%7%41%
1710
11th to 20thDay
18%6%245%3445%6%44%
1781
21st to endDay
18%7%35%6%3435%7%39%
1570
March1st to 10thDay
12%5%25%425%45%7%50%
1862
11th to 20thDay
17%7%245%35%447%43%
1980
21st to endDay
18%6%37%5%34446%41%
2263
April1st to 10thDay
13%6%25%5%35%447%46%
2160
11th to 20thDay
13%424433449%48%
2134
21st to endDay
17%5%3442445%9%43%
2160
May1st to 10thDay
15%6%344345%6%8%42%
2234
11th to 20thDay
16%6%25%5%345%6%9%40%
2478
21st to endDay
13%5%25%5%35%5%6%10%42%
2725
June1st to 10thDay
10%425%5%25%6%7%11%43%
2520
11th to 20thDay
11%425%5%35%6%7%10%43%
2520
21st to endDay
10%323425%5%7%11%48%
2520
July1st to 10thDay
8%5%35%6%35%5%6%9%45%
2520
11th to 20thDay
5%3235%25%6%8%12%49%
2520
21st to endDay
8%4246%47%6%8%11%40%
2580
August1st to 10thDay
9%5%25%5%35%5%8%11%42%
2327
11th to 20thDay
10%425%6%45%6%6%9%43%
2148
21st to endDay
10%5%25%5%45%5%6%9%44%
2376
September1st to 10thDay
13%5%245%35%5%5%7%46%
2160
11th to 20thDay
11%5%2443445%7%51%
2160
21st to endDay
18%8%345%245%47%40%
1931
October1st to 10thDay
16%6%25%434446%46%
1800
11th to 20thDay
16%5%24323347%50%
1800
21st to endDay
15%6%35%433345%49%
1980
November1st to 10thDay
13%5%14324447%53%
1681
11th to 20thDay
13%6%24335%5%5%6%49%
1710
21st to endDay
15%5%24435%446%48%
1577
December1st to 10thDay
16%6%345%3445%7%43%
1520
11th to 20thDay
17%8%345%2335%5%45%
1910
21st to endDay
14%8%26%5%345%5%6%41%
2772
January1st to 10thNight
16%8%35%435%446%43%
4429
11th to 20thNight
18%7%35%433445%44%
4186
21st to endNight
20%8%35%423345%42%
4532
February1st to 10thNight
16%6%35%5%35%5%46%42%
2470
11th to 20thNight
19%7%25%433346%42%
2284
21st to endNight
18%7%245%34346%44%
1884
March1st to 10thNight
15%425%43445%6%49%
2100
11th to 20thNight
16%6%25%5%35%5%5%7%43%
1980
21st to endNight
16%7%36%5%3445%6%41%
2091
April1st to 10thNight
15%7%35%434447%43%
1800
11th to 20thNight
13%5%35%5%345%5%6%47%
1775
21st to endNight
19%42443345%8%44%
1800
May1st to 10thNight
15%6%26%5%35%6%6%7%39%
1741
11th to 20thNight
16%7%35%6%35%6%6%7%38%
1415
21st to endNight
12%6%36%435%5%5%9%41%
1550
June1st to 10thNight
11%5%35%445%5%6%9%44%
1440
11th to 20thNight
9%5%36%6%36%5%7%9%41%
1440
21st to endNight
10%4245%37%6%8%10%40%
1440
July1st to 10thNight
9%5%25%6%46%6%7%10%40%
1440
11th to 20thNight
6%426%5%45%7%6%11%43%
1440
21st to endNight
8%5%25%5%46%6%7%11%41%
1734
August1st to 10thNight
8%5%26%6%46%6%8%10%40%
1611
11th to 20thNight
9%6%26%6%36%6%7%9%40%
1735
21st to endNight
10%5%27%5%35%5%7%8%43%
1980
September1st to 10thNight
15%5%25%5%335%5%7%45%
1800
11th to 20thNight
9%5%35%43345%7%53%
1800
21st to endNight
17%6%35%5%3445%7%41%
2023
October1st to 10thNight
17%7%35%433445%44%
2160
11th to 20thNight
15%5%25%413346%51%
2160
21st to endNight
17%5%24424446%48%
2376
November1st to 10thNight
12%425%42445%5%53%
2394
11th to 20thNight
15%6%35%5%24345%48%
2470
21st to endNight
13%5%245%345%6%7%48%
2598
December1st to 10thNight
18%7%35%4345%5%7%40%
2660
11th to 20thNight
17%5%25%5%3445%7%43%
3285
21st to endNight
15%6%36%5%35%5%6%7%38%
4884

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 10thDay
36%5%8%32%15%3
2518
11th to 20thDay
47%410%21%14%4
2758
21st to endDay
46%5%11%24%11%2
3124
February1st to 10thDay
41%6%13%25%14%2
1710
11th to 20thDay
41%39%27%17%2
1790
21st to endDay
46%412%20%15%4
1570
March1st to 10thDay
34%5%12%27%19%3
1862
11th to 20thDay
42%410%19%19%5%
1980
21st to endDay
45%5%8%21%18%3
2263
April1st to 10thDay
38%6%12%21%18%6%
2160
11th to 20thDay
33%7%11%24%19%6%
2134
21st to endDay
38%5%12%21%19%4
2160
May1st to 10thDay
38%8%13%21%17%3
2234
11th to 20thDay
39%8%15%22%14%2
2482
21st to endDay
37%8%14%27%12%1
2725
June1st to 10thDay
34%9%15%25%15%2
2520
11th to 20thDay
34%9%14%24%16%2
2520
21st to endDay
29%9%15%25%20%1
2520
July1st to 10thDay
36%8%13%24%16%3
2450
11th to 20thDay
26%10%17%30%14%4
2445
21st to endDay
34%10%14%23%17%1
2436
August1st to 10thDay
33%9%17%27%13%1
2314
11th to 20thDay
36%9%16%23%15%2
2148
21st to endDay
35%8%14%24%16%4
2376
September1st to 10thDay
37%6%13%22%17%4
2160
11th to 20thDay
33%5%11%25%23%3
2160
21st to endDay
45%5%8%20%19%3
1931
October1st to 10thDay
39%6%10%25%18%3
1800
11th to 20thDay
35%49%27%22%3
1800
21st to endDay
37%48%28%19%3
1980
November1st to 10thDay
32%5%12%29%20%3
1681
11th to 20thDay
35%5%11%23%22%3
1710
21st to endDay
38%49%29%17%3
1577
December1st to 10thDay
41%6%14%25%12%2
1520
11th to 20thDay
42%49%31%11%3
1906
21st to endDay
42%5%16%23%13%
2772
January1st to 10thNight
42%49%26%15%3
4429
11th to 20thNight
43%410%25%16%2
4186
21st to endNight
46%47%27%15%1
4532
February1st to 10thNight
42%5%13%23%15%2
2470
11th to 20thNight
44%38%22%19%4
2286
21st to endNight
43%410%21%17%4
1884
March1st to 10thNight
37%411%26%20%3
2100
11th to 20thNight
41%6%11%21%18%4
1980
21st to endNight
44%410%19%18%6%
2091
April1st to 10thNight
42%5%10%19%20%5%
1800
11th to 20thNight
38%5%10%21%20%6%
1775
21st to endNight
39%6%10%23%17%5%
1800
May1st to 10thNight
43%5%11%22%15%3
1741
11th to 20thNight
43%8%13%16%17%2
1416
21st to endNight
39%9%16%21%12%3
1551
June1st to 10thNight
37%7%13%23%18%1
1440
11th to 20thNight
37%9%14%23%14%2
1440
21st to endNight
35%9%14%22%17%3
1440
July1st to 10thNight
37%12%16%19%13%3
1400
11th to 20thNight
32%9%16%26%15%2
1392
21st to endNight
34%9%13%28%15%1
1638
August1st to 10thNight
37%9%17%22%15%
1600
11th to 20thNight
38%10%15%22%14%1
1735
21st to endNight
36%9%14%21%16%3
1980
September1st to 10thNight
38%7%12%21%17%5%
1800
11th to 20thNight
31%7%9%26%23%4
1800
21st to endNight
43%6%8%20%18%4
2023
October1st to 10thNight
42%5%9%22%19%3
2160
11th to 20thNight
36%410%27%19%3
2160
21st to endNight
38%49%26%20%3
2376
November1st to 10thNight
33%5%10%27%19%6%
2394
11th to 20thNight
40%49%21%21%6%
2470
21st to endNight
35%5%12%26%19%3
2598
December1st to 10thNight
43%5%12%24%13%2
2660
11th to 20thNight
41%411%22%18%4
3288
21st to endNight
43%7%14%24%11%1
4884

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 10thDay
21%20%36%17%6%1
180
11th to 20thDay
29%21%31%15%5%
249
21st to endDay
24%16%42%13%41
297
February1st to 10thDay
24%20%34%14%7%
270
11th to 20thDay
26%19%40%12%2
389
21st to endDay
28%17%33%18%4
382
March1st to 10thDay
20%21%33%22%4
420
11th to 20thDay
22%19%32%20%5%2
420
21st to endDay
21%18%32%21%7%1
462
April1st to 10thDay
22%15%35%20%6%2
420
11th to 20thDay
17%14%31%21%13%3
412
21st to endDay
23%13%31%23%9%1
420
May1st to 10thDay
21%15%31%21%8%4
423
11th to 20thDay
16%10%33%26%12%3
447
21st to endDay
18%5%20%28%20%10%
485
June1st to 10thDay
12%426%28%20%9%
450
11th to 20thDay
15%6%21%29%20%9%
450
21st to endDay
11%324%33%22%8%
450
July1st to 10thDay
9%316%33%25%14%
445
11th to 20thDay
4115%32%33%15%
444
21st to endDay
9%219%30%31%9%
488
August1st to 10thDay
11%215%31%28%13%
446
11th to 20thDay
11%216%29%29%12%
439
21st to endDay
8%417%31%22%16%
495
September1st to 10thDay
15%419%24%21%17%
450
11th to 20thDay
12%422%28%22%13%
450
21st to endDay
23%8%24%26%13%6%
450
October1st to 10thDay
20%7%22%26%17%9%
450
11th to 20thDay
16%12%26%24%18%4
450
21st to endDay
18%11%34%23%12%3
495
November1st to 10thDay
17%10%30%25%15%4
370
11th to 20thDay
16%18%30%24%12%1
370
21st to endDay
20%14%30%24%10%2
237
December1st to 10thDay
18%20%38%16%7%2
180
11th to 20thDay
24%24%29%16%7%
180
21st to endDay
25%15%28%22%9%1
198
January1st to 10thNight
21%17%38%22%3
760
11th to 20thNight
21%13%34%27%4
760
21st to endNight
18%16%40%24%2
836
February1st to 10thNight
20%12%37%28%3
760
11th to 20thNight
24%19%39%18%1
743
21st to endNight
23%16%36%22%4
628
March1st to 10thNight
17%15%41%23%4
723
11th to 20thNight
20%14%37%22%6%1
720
21st to endNight
19%11%39%26%5%
792
April1st to 10thNight
20%15%38%20%6%
720
11th to 20thNight
15%11%35%31%8%
711
21st to endNight
21%9%33%29%8%
720
May1st to 10thNight
18%9%31%31%11%
661
11th to 20thNight
16%6%32%35%11%1
354
21st to endNight
13%322%41%20%1
389
June1st to 10thNight
14%325%39%18%1
360
11th to 20thNight
10%323%44%19%1
360
21st to endNight
10%221%48%19%1
360
July1st to 10thNight
11%116%41%29%2
350
11th to 20thNight
7%114%43%32%2
348
21st to endNight
7%113%46%29%3
554
August1st to 10thNight
9%114%44%31%2
537
11th to 20thNight
11%315%36%31%3
671
21st to endNight
10%315%35%32%5%
792
September1st to 10thNight
16%114%37%26%4
720
11th to 20thNight
11%217%35%30%4
720
21st to endNight
19%421%34%20%2
720
October1st to 10thNight
21%6%18%32%19%4
720
11th to 20thNight
17%7%26%35%15%1
720
21st to endNight
19%8%32%28%12%1
792
November1st to 10thNight
15%6%32%31%14%2
740
11th to 20thNight
17%13%31%30%8%1
760
21st to endNight
15%15%32%29%9%1
760
December1st to 10thNight
22%14%34%20%9%1
760
11th to 20thNight
19%12%37%25%7%
760
21st to endNight
19%12%35%31%4
836
Page generated at 2024-02-27 06:30:13. Version ac07

Copyright © 2024 Attilla Danko.


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