TBM Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the TBM Observatory clear sky chart from 2005-11-05 to 2018-01-12.

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
40%
15680
21%
48382
12%
15643
50%
15643
26%
30459

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
25%
763
21%
2628
9%
761
41%
761
20%
1611
January16th to endNight
24%
768
22%
2496
9%
768
41%
768
22%
1569
February1st to 15thNight
23%
703
19%
2272
7%
701
39%
701
22%
1419
February16th to endNight
20%
631
25%
1893
8%
631
41%
631
23%
1186
March1st to 15thNight
29%
720
21%
2055
10%
720
41%
720
27%
1306
March16th to endNight
28%
768
21%
2054
9%
768
38%
768
27%
1371
April1st to 15thNight
27%
718
20%
1796
5%
718
36%
718
31%
1178
April16th to endNight
41%
720
20%
1800
7%
720
46%
720
31%
1181
May1st to 15thNight
39%
560
17%
1640
10%
560
44%
560
24%
1117
May16th to endNight
57%
374
16%
1497
16%
374
62%
374
22%
912
June1st to 15thNight
56%
360
18%
1440
20%
360
63%
360
25%
843
June16th to endNight
60%
360
15%
1440
16%
360
64%
360
23%
843
July1st to 15thNight
60%
340
13%
1360
16%
340
61%
340
20%
861
July16th to endNight
71%
482
17%
1516
16%
452
74%
452
30%
887
August1st to 15thNight
67%
572
17%
1642
14%
569
67%
569
31%
1031
August16th to endNight
65%
764
18%
1910
10%
764
67%
764
34%
1268
September1st to 15thNight
61%
720
24%
1800
15%
720
64%
720
34%
1190
September16th to endNight
56%
717
24%
1950
19%
717
59%
717
30%
1276
October1st to 15thNight
47%
720
22%
2160
20%
720
54%
720
26%
1381
October16th to endNight
40%
768
29%
2304
19%
768
54%
768
32%
1348
November1st to 15thNight
39%
760
23%
2464
14%
760
51%
760
26%
1502
November16th to endNight
35%
780
23%
2623
13%
780
49%
780
22%
1599
December1st to 15thNight
28%
780
18%
2730
8%
780
42%
780
19%
1758
December16th to endNight
25%
832
22%
2912
9%
832
42%
832
20%
1822

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
13%5%2442445%8%44%
48951
Night
14%5%2442445%7%43%
48561
Cloud CoverDay
13%5%2442445%8%44%
48961
Night
14%5%2442445%7%43%
48566
TransparencyDay
37%6%12%24%16%2
48649
Night
39%5%11%23%17%3
48382
SeeingDay
16%6%24%24%18%8%
6091
Night
16%7%28%30%14%1
15684

By Month

Percentage Cloud Cover NE (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%5%2443345%7%42%
1553
16th to endDay
16%6%24424446%43%
1728
February1st to 15thDay
15%7%145%2445%7%42%
1589
16th to endDay
12%7%35%5%245%45%42%
1580
March1st to 15thDay
14%5%2432345%6%45%
1891
16th to endDay
16%5%25%434335%43%
2169
April1st to 15thDay
14%5%2432445%7%45%
2152
16th to endDay
15%5%23323347%46%
2160
May1st to 15thDay
15%5%243245%5%8%40%
2322
16th to endDay
13%423425%5%6%9%41%
2618
June1st to 15thDay
11%3234345%7%10%41%
2520
16th to endDay
9%3234245%7%10%46%
2520
July1st to 15thDay
8%424435%5%7%10%43%
2520
16th to endDay
5%314437%6%8%12%42%
2545
August1st to 15thDay
11%4244345%6%10%41%
2295
16th to endDay
9%415%5%345%6%10%44%
2292
September1st to 15thDay
12%32442445%7%47%
2160
16th to endDay
13%7%344245%46%41%
2007
October1st to 15thDay
17%5%24313347%45%
1800
16th to endDay
14%5%24313345%51%
1920
November1st to 15thDay
15%5%2432435%6%46%
1722
16th to endDay
14%5%243245%45%47%
1664
December1st to 15thDay
16%5%345%24447%43%
1560
16th to endDay
17%6%25%5%23346%40%
1664
January1st to 15thNight
15%6%3442435%7%42%
2628
16th to endNight
17%6%34424346%43%
2496
February1st to 15thNight
14%6%25%424446%42%
2270
16th to endNight
15%6%13423336%46%
1893
March1st to 15thNight
16%5%14314347%45%
2043
16th to endNight
16%6%35%423447%42%
2054
April1st to 15thNight
13%5%2442445%8%44%
1796
16th to endNight
17%41432445%6%46%
1800
May1st to 15thNight
16%6%24435%45%6%39%
1640
16th to endNight
12%6%25%435%5%5%8%41%
1495
June1st to 15thNight
11%434425%46%8%44%
1440
16th to endNight
8%425%5%45%6%7%9%41%
1440
July1st to 15thNight
7%436%5%47%6%6%9%37%
1440
16th to endNight
6%2145%37%6%6%12%42%
1620
August1st to 15thNight
7%5%245%35%5%6%9%43%
1653
16th to endNight
9%5%25%425%46%8%43%
1910
September1st to 15thNight
13%41442445%6%47%
1800
16th to endNight
13%5%15%5%3435%6%44%
1950
October1st to 15thNight
16%6%25%422446%44%
2160
16th to endNight
15%413422336%51%
2304
November1st to 15thNight
14%5%25%42335%448%
2464
16th to endNight
14%5%2443445%6%44%
2623
December1st to 15thNight
17%6%35%5%245%46%38%
2730
16th to endNight
16%5%25%42445%6%42%
2912

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
15%6%245%2435%6%43%
1553
16th to endDay
16%5%24424445%44%
1728
February1st to 15thDay
15%7%145%2345%6%43%
1589
16th to endDay
13%6%35%5%2445%6%42%
1580
March1st to 15thDay
14%5%24425%446%45%
1902
16th to endDay
16%6%25%5%24335%43%
2168
April1st to 15thDay
14%5%14434447%46%
2152
16th to endDay
15%5%34323247%46%
2160
May1st to 15thDay
15%5%2442446%8%41%
2322
16th to endDay
13%4244345%6%9%41%
2618
June1st to 15thDay
11%324425%5%6%11%42%
2520
16th to endDay
9%3234245%7%10%47%
2520
July1st to 15thDay
8%4245%25%5%7%9%43%
2520
16th to endDay
5%3145%36%5%8%12%42%
2545
August1st to 15thDay
10%5%244345%7%10%42%
2295
16th to endDay
9%4145%345%6%9%44%
2292
September1st to 15thDay
12%4235%2445%7%47%
2160
16th to endDay
14%7%25%4345%46%41%
2007
October1st to 15thDay
17%5%14323446%45%
1800
16th to endDay
14%414313345%51%
1920
November1st to 15thDay
16%414324346%46%
1722
16th to endDay
14%5%23424445%47%
1664
December1st to 15thDay
16%5%335%2445%6%43%
1560
16th to endDay
17%7%25%5%23346%41%
1664
January1st to 15thNight
15%5%34324447%42%
2628
16th to endNight
17%6%3342435%5%44%
2496
February1st to 15thNight
14%6%35%424346%43%
2263
16th to endNight
15%6%14424336%46%
1893
March1st to 15thNight
16%5%24324447%45%
2055
16th to endNight
16%6%25%5%24347%42%
2054
April1st to 15thNight
13%5%24324448%44%
1796
16th to endNight
17%42332345%7%45%
1800
May1st to 15thNight
15%7%25%5%3445%6%39%
1640
16th to endNight
11%6%34435%5%49%41%
1495
June1st to 15thNight
10%425%435%46%8%44%
1440
16th to endNight
8%425%5%35%5%7%9%40%
1440
July1st to 15thNight
7%5%26%6%46%6%6%9%37%
1440
16th to endNight
6%3145%46%6%6%12%41%
1620
August1st to 15thNight
7%426%5%35%5%6%9%43%
1653
16th to endNight
9%5%25%4245%7%8%43%
1910
September1st to 15thNight
12%5%2443345%6%47%
1800
16th to endNight
14%5%245%3345%7%43%
1950
October1st to 15thNight
16%6%25%423345%45%
2160
16th to endNight
15%413413336%51%
2304
November1st to 15thNight
14%425%423345%48%
2464
16th to endNight
14%5%2442445%6%44%
2623
December1st to 15thNight
16%6%35%4345%5%7%38%
2730
16th to endNight
16%5%2442445%6%42%
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
40%5%14%22%13%4
1554
16th to endDay
41%410%25%14%3
1728
February1st to 15thDay
40%412%25%14%2
1591
16th to endDay
41%311%26%14%1
1580
March1st to 15thDay
38%5%12%25%15%2
1902
16th to endDay
43%49%21%18%2
2169
April1st to 15thDay
37%5%10%24%17%4
2152
16th to endDay
37%411%18%22%6%
2160
May1st to 15thDay
38%8%13%21%16%2
2322
16th to endDay
36%8%14%26%12%1
2622
June1st to 15thDay
34%8%14%27%13%1
2520
16th to endDay
30%9%15%23%19%1
2520
July1st to 15thDay
35%8%13%24%14%3
2371
16th to endDay
29%10%16%25%15%1
2387
August1st to 15thDay
35%7%14%24%15%1
2282
16th to endDay
33%7%14%22%17%4
2292
September1st to 15thDay
36%413%23%19%2
2160
16th to endDay
43%5%8%19%21%1
2007
October1st to 15thDay
39%5%9%26%16%2
1800
16th to endDay
35%38%29%20%2
1920
November1st to 15thDay
37%5%12%23%17%3
1722
16th to endDay
37%5%9%27%17%3
1664
December1st to 15thDay
41%6%13%24%11%2
1560
16th to endDay
44%412%24%13%
1664
January1st to 15thNight
41%411%22%16%4
2628
16th to endNight
41%410%26%15%1
2496
February1st to 15thNight
41%411%24%16%2
2272
16th to endNight
39%39%24%19%2
1893
March1st to 15thNight
39%411%25%15%2
2055
16th to endNight
42%411%20%17%3
2054
April1st to 15thNight
38%411%21%20%4
1796
16th to endNight
37%6%9%20%19%6%
1800
May1st to 15thNight
43%6%10%21%15%2
1640
16th to endNight
38%8%16%19%14%2
1497
June1st to 15thNight
37%6%13%24%17%
1440
16th to endNight
35%8%13%22%17%2
1440
July1st to 15thNight
40%9%14%18%13%3
1360
16th to endNight
32%8%16%27%14%1
1516
August1st to 15thNight
35%7%15%22%18%1
1642
16th to endNight
35%7%12%21%19%2
1910
September1st to 15thNight
36%7%10%23%18%4
1800
16th to endNight
39%6%8%21%21%4
1950
October1st to 15thNight
41%49%23%17%3
2160
16th to endNight
34%39%29%20%3
2304
November1st to 15thNight
38%49%23%17%6%
2464
16th to endNight
39%5%10%22%19%3
2623
December1st to 15thNight
44%5%11%23%12%2
2730
16th to endNight
42%412%23%13%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
16%20%36%16%9%1
87
16th to endDay
27%16%40%10%5%
96
February1st to 15thDay
26%15%41%11%4
105
16th to endDay
16%15%39%25%1
239
March1st to 15thDay
19%12%31%28%8%
270
16th to endDay
17%12%37%20%8%3
288
April1st to 15thDay
19%8%30%26%12%2
270
16th to endDay
20%5%25%24%19%5%
270
May1st to 15thDay
25%12%27%17%10%5%
288
16th to endDay
19%221%22%21%12%
331
June1st to 15thDay
14%222%23%22%13%
315
16th to endDay
11%221%33%22%8%
315
July1st to 15thDay
10%116%34%25%12%
305
16th to endDay
6%18%29%38%15%
326
August1st to 15thDay
13%114%24%31%14%
313
16th to endDay
6%10%31%31%19%
332
September1st to 15thDay
12%321%21%22%19%
315
16th to endDay
22%314%28%15%15%
314
October1st to 15thDay
22%219%24%20%11%
315
16th to endDay
15%7%30%24%19%2
336
November1st to 15thDay
19%8%23%28%17%2
281
16th to endDay
17%12%35%19%11%3
194
December1st to 15thDay
21%20%26%16%12%3
90
16th to endDay
33%13%33%15%4
96
January1st to 15thNight
19%14%34%26%5%
765
16th to endNight
19%12%39%25%2
768
February1st to 15thNight
18%12%39%26%1
704
16th to endNight
18%17%37%23%2
631
March1st to 15thNight
19%12%35%27%5%
720
16th to endNight
18%8%38%26%7%1
768
April1st to 15thNight
16%10%41%25%5%
718
16th to endNight
19%6%29%31%12%
720
May1st to 15thNight
18%7%29%30%13%
560
16th to endNight
12%420%41%21%1
375
June1st to 15thNight
12%121%41%22%
360
16th to endNight
7%219%49%20%1
360
July1st to 15thNight
11%17%40%29%
340
16th to endNight
6%110%43%34%4
482
August1st to 15thNight
10%12%42%32%2
572
16th to endNight
11%112%34%35%4
764
September1st to 15thNight
14%15%36%29%3
720
16th to endNight
16%116%32%28%4
717
October1st to 15thNight
20%6%18%33%18%3
720
16th to endNight
17%8%30%27%14%
768
November1st to 15thNight
17%6%30%28%14%1
760
16th to endNight
15%14%30%28%9%1
780
December1st to 15thNight
20%11%33%22%10%1
780
16th to endNight
20%11%37%26%3
832
Page generated at 2018-01-12 22:01:24. Version ac04

Copyright 2018 A. Danko


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