Tom's Yard
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tom's Yard clear sky chart from 2005-11-06 to 2024-01-11.

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
34%
23239
17%
74771
10%
23188
42%
23188
18%
50803

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
15%
757
15%
2621
6%
757
27%
757
11%
1872
January11th to 20thNight
19%
724
12%
2352
4%
724
28%
724
11%
1767
January21st to endNight
17%
792
15%
2574
5%
792
28%
792
12%
1868
February1st to 10thNight
19%
720
14%
2340
7%
720
28%
720
12%
1695
February11th to 20thNight
14%
703
14%
2275
3%
700
27%
700
11%
1635
February21st to endNight
18%
592
17%
1794
6%
592
31%
592
12%
1307
March1st to 10thNight
22%
720
20%
1980
8%
720
34%
720
19%
1323
March11th to 20thNight
22%
720
18%
1980
8%
720
32%
720
16%
1397
March21st to endNight
22%
792
18%
2173
7%
792
32%
792
19%
1529
April1st to 10thNight
20%
720
14%
1800
4%
720
26%
720
17%
1341
April11th to 20thNight
31%
711
17%
1775
7%
711
36%
711
25%
1232
April21st to endNight
31%
666
18%
1746
6%
666
38%
666
22%
1213
May1st to 10thNight
37%
540
15%
1620
8%
540
42%
540
18%
1145
May11th to 20thNight
37%
413
16%
1475
11%
413
44%
413
18%
972
May21st to endNight
50%
388
17%
1551
16%
388
56%
388
20%
931
June1st to 10thNight
48%
360
18%
1440
18%
360
58%
360
22%
850
June11th to 20thNight
46%
360
15%
1440
16%
360
52%
360
19%
896
June21st to endNight
53%
360
18%
1440
17%
360
61%
360
25%
816
July1st to 10thNight
61%
350
15%
1400
18%
350
65%
350
22%
843
July11th to 20thNight
64%
396
18%
1440
20%
396
67%
396
30%
818
July21st to endNight
59%
591
16%
1672
12%
558
62%
558
29%
1047
August1st to 10thNight
63%
537
17%
1600
12%
534
66%
534
30%
1004
August11th to 20thNight
58%
535
19%
1599
14%
535
61%
535
28%
1035
August21st to endNight
56%
792
20%
1980
11%
792
58%
792
32%
1312
September1st to 10thNight
52%
720
20%
1800
11%
720
55%
720
30%
1210
September11th to 20thNight
55%
720
29%
1818
19%
720
59%
720
36%
1129
September21st to endNight
45%
720
21%
2070
15%
720
51%
720
25%
1366
October1st to 10thNight
46%
720
17%
2160
15%
720
51%
720
25%
1407
October11th to 20thNight
35%
720
19%
2160
14%
720
45%
720
24%
1398
October21st to endNight
31%
792
21%
2376
13%
792
43%
792
21%
1613
November1st to 10thNight
41%
740
24%
2311
17%
740
53%
740
29%
1384
November11th to 20thNight
29%
760
18%
2601
12%
760
40%
760
15%
1734
November21st to endNight
27%
760
17%
2660
10%
760
38%
760
15%
1798
December1st to 10thNight
21%
760
11%
2660
5%
760
29%
760
11%
1958
December11th to 20thNight
25%
760
12%
3234
5%
759
34%
759
9%
2289
December21st to endNight
23%
828
8%
4854
7%
817
32%
817
7%
3669

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
16%8%37%6%35%5%5%7%34%
74647
Night
15%8%36%5%35%5%5%7%37%
75046
TransparencyDay
48%7%12%19%12%2
74357
Night
46%7%12%21%12%2
74855
SeeingDay
24%16%25%20%11%4
13648
Night
21%13%25%28%12%1
23251

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
13%12%6%11%6%45%446%30%
1540
11th to 20thDay
16%13%7%9%8%45%5%5%5%25%
1620
21st to endDay
14%15%6%10%8%46%445%25%
1782
February1st to 10thDay
17%15%5%8%8%35%45%5%24%
1620
11th to 20thDay
15%10%5%11%7%4436%5%28%
1573
21st to endDay
19%9%411%5%35%45%430%
1461
March1st to 10thDay
15%10%5%6%6%445%46%37%
1975
11th to 20thDay
18%11%47%6%3445%6%31%
1980
21st to endDay
20%10%46%6%2445%6%33%
2182
April1st to 10thDay
16%10%46%7%35%446%34%
2160
11th to 20thDay
16%10%35%6%345%5%6%37%
2134
21st to endDay
22%8%36%5%35%45%5%35%
2227
May1st to 10thDay
19%7%37%6%36%5%5%8%31%
2340
11th to 20thDay
22%6%35%5%35%45%7%33%
2418
21st to endDay
15%7%35%5%35%5%5%9%39%
2725
June1st to 10thDay
14%6%35%6%46%6%6%8%36%
2520
11th to 20thDay
14%6%26%6%46%6%7%9%35%
2520
21st to endDay
12%425%6%46%6%7%10%39%
2520
July1st to 10thDay
10%5%26%6%46%6%7%8%38%
2520
11th to 20thDay
7%5%36%6%5%6%6%7%9%40%
2467
21st to endDay
10%6%37%7%47%6%7%9%35%
2547
August1st to 10thDay
10%5%26%7%5%7%7%8%10%33%
2327
11th to 20thDay
12%6%26%6%46%6%6%9%36%
2282
21st to endDay
13%5%26%6%35%6%6%10%38%
2376
September1st to 10thDay
18%5%25%5%3445%6%43%
2160
11th to 20thDay
14%5%2442445%7%47%
2138
21st to endDay
17%7%25%5%35%5%6%6%38%
1890
October1st to 10thDay
18%6%26%6%34446%40%
1800
11th to 20thDay
18%6%36%6%35%5%5%7%37%
1800
21st to endDay
19%8%36%5%3445%6%37%
1980
November1st to 10thDay
12%7%35%44446%7%44%
1764
11th to 20thDay
17%9%46%6%35%6%5%7%34%
1577
21st to endDay
18%10%47%6%3446%6%32%
1520
December1st to 10thDay
19%12%5%9%6%45%5%5%6%25%
1520
11th to 20thDay
18%14%5%6%5%3445%6%29%
1910
21st to endDay
21%16%5%9%9%445%5%418%
2772
January1st to 10thNight
15%12%5%9%7%4445%7%29%
2621
11th to 20thNight
18%11%5%9%6%45%5%5%6%26%
2352
21st to endNight
13%12%5%10%7%45%5%5%6%29%
2574
February1st to 10thNight
17%10%5%7%6%35%5%5%6%29%
2340
11th to 20thNight
16%9%49%7%45%5%5%7%30%
2273
21st to endNight
16%11%5%8%6%445%5%5%31%
1794
March1st to 10thNight
14%7%36%5%35%46%7%40%
1980
11th to 20thNight
18%10%36%5%3445%5%38%
1980
21st to endNight
18%7%37%6%45%345%38%
2173
April1st to 10thNight
18%10%47%6%345%5%6%32%
1800
11th to 20thNight
15%7%26%6%335%5%8%39%
1775
21st to endNight
18%6%26%5%35%5%5%7%39%
1746
May1st to 10thNight
18%9%35%5%35%6%5%7%34%
1620
11th to 20thNight
18%7%35%6%25%5%5%8%37%
1474
21st to endNight
11%7%25%4445%6%10%41%
1550
June1st to 10thNight
12%6%35%5%345%6%7%46%
1440
11th to 20thNight
12%5%27%5%36%5%7%9%38%
1440
21st to endNight
10%4245%45%5%5%12%44%
1440
July1st to 10thNight
10%5%25%5%345%6%9%44%
1440
11th to 20thNight
6%4345%35%5%6%10%48%
1488
21st to endNight
10%435%5%45%5%7%10%42%
1771
August1st to 10thNight
7%5%25%7%35%47%11%43%
1611
11th to 20thNight
11%7%36%5%345%6%7%45%
1599
21st to endNight
12%6%25%4445%6%9%44%
1980
September1st to 10thNight
15%5%26%5%3435%6%45%
1800
11th to 20thNight
12%5%244345%47%51%
1818
21st to endNight
15%6%36%5%335%5%7%42%
2070
October1st to 10thNight
17%6%244335%5%6%44%
2160
11th to 20thNight
18%5%3443445%7%42%
2160
21st to endNight
21%8%35%4245%46%38%
2376
November1st to 10thNight
11%7%25%43445%6%50%
2311
11th to 20thNight
17%9%36%5%35%5%5%6%36%
2601
21st to endNight
16%9%36%6%35%46%6%35%
2660
December1st to 10thNight
19%11%5%7%5%45%6%5%6%27%
2660
11th to 20thNight
18%11%47%6%45%5%5%6%30%
3285
21st to endNight
19%13%5%9%7%45%5%5%6%22%
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
55%5%13%18%7%1
1541
11th to 20thDay
61%5%13%14%6%1
1620
21st to endDay
63%5%10%15%7%1
1782
February1st to 10thDay
61%5%13%14%7%1
1620
11th to 20thDay
56%6%10%20%7%1
1582
21st to endDay
56%5%11%17%8%3
1461
March1st to 10thDay
49%6%13%22%10%1
1975
11th to 20thDay
54%5%11%17%9%3
1980
21st to endDay
52%5%10%19%12%2
2182
April1st to 10thDay
50%5%11%18%13%2
2160
11th to 20thDay
47%7%9%18%17%2
2134
21st to endDay
50%6%8%20%13%3
2227
May1st to 10thDay
51%7%10%18%13%2
2340
11th to 20thDay
50%7%11%16%13%3
2422
21st to endDay
43%8%16%21%11%2
2725
June1st to 10thDay
44%8%12%21%14%1
2520
11th to 20thDay
42%11%13%19%13%2
2520
21st to endDay
39%8%14%26%13%1
2520
July1st to 10thDay
41%10%12%20%14%3
2450
11th to 20thDay
36%9%14%23%17%1
2392
21st to endDay
42%9%12%20%16%2
2405
August1st to 10thDay
41%11%15%21%11%
2314
11th to 20thDay
42%10%13%22%12%1
2282
21st to endDay
40%8%13%22%15%3
2376
September1st to 10thDay
41%7%10%21%16%3
2160
11th to 20thDay
35%6%11%27%18%3
2138
21st to endDay
44%7%11%18%18%2
1890
October1st to 10thDay
45%6%12%20%15%2
1800
11th to 20thDay
46%7%13%23%11%
1800
21st to endDay
48%6%12%21%13%1
1980
November1st to 10thDay
38%6%15%21%16%4
1764
11th to 20thDay
49%6%11%20%11%2
1577
21st to endDay
52%6%11%23%8%
1520
December1st to 10thDay
59%8%13%14%6%
1520
11th to 20thDay
56%5%12%21%5%
1906
21st to endDay
67%6%12%11%4
2772
January1st to 10thNight
55%5%11%19%9%1
2621
11th to 20thNight
58%6%13%16%6%1
2352
21st to endNight
54%6%12%18%9%1
2574
February1st to 10thNight
54%6%11%20%8%1
2340
11th to 20thNight
53%6%11%18%12%1
2275
21st to endNight
54%6%9%18%11%2
1794
March1st to 10thNight
42%6%12%25%14%1
1980
11th to 20thNight
47%7%11%19%14%2
1980
21st to endNight
49%5%10%20%14%3
2173
April1st to 10thNight
52%6%10%17%13%2
1800
11th to 20thNight
42%7%11%21%16%3
1775
21st to endNight
43%8%10%21%14%3
1746
May1st to 10thNight
48%8%9%19%12%4
1620
11th to 20thNight
45%7%12%18%15%2
1475
21st to endNight
37%9%15%24%12%3
1551
June1st to 10thNight
38%7%12%26%15%2
1440
11th to 20thNight
39%11%13%22%14%2
1440
21st to endNight
33%9%15%27%16%1
1440
July1st to 10thNight
36%10%12%23%14%4
1400
11th to 20thNight
30%9%15%25%19%2
1440
21st to endNight
33%11%17%21%16%3
1672
August1st to 10thNight
33%10%16%25%15%1
1600
11th to 20thNight
37%8%14%23%16%1
1599
21st to endNight
36%8%13%24%15%3
1980
September1st to 10thNight
40%6%11%22%17%4
1800
11th to 20thNight
32%6%10%29%21%2
1818
21st to endNight
41%7%11%22%18%2
2070
October1st to 10thNight
39%8%13%24%14%1
2160
11th to 20thNight
40%6%12%26%14%1
2160
21st to endNight
47%5%9%24%14%1
2376
November1st to 10thNight
35%5%14%25%17%3
2311
11th to 20thNight
48%5%10%21%14%3
2601
21st to endNight
48%6%13%21%10%1
2660
December1st to 10thNight
55%8%14%17%7%
2660
11th to 20thNight
55%6%12%20%8%
3288
21st to endNight
61%7%13%15%3
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
37%23%27%10%31
191
11th to 20thDay
37%23%30%8%1
240
21st to endDay
32%32%27%5%31
264
February1st to 10thDay
37%29%23%9%2
240
11th to 20thDay
41%29%27%3
240
21st to endDay
38%22%25%14%1
327
March1st to 10thDay
35%19%24%18%4
420
11th to 20thDay
34%21%25%13%42
420
21st to endDay
31%23%25%14%5%2
462
April1st to 10thDay
33%21%24%16%5%2
420
11th to 20thDay
26%19%24%18%9%5%
412
21st to endDay
32%20%26%14%6%2
420
May1st to 10thDay
30%19%25%14%7%4
423
11th to 20thDay
26%19%25%18%10%2
447
21st to endDay
19%15%25%19%15%7%
485
June1st to 10thDay
18%16%27%22%13%3
450
11th to 20thDay
21%14%24%25%14%3
450
21st to endDay
13%13%33%26%12%3
450
July1st to 10thDay
15%8%25%25%19%9%
445
11th to 20thDay
9%6%29%29%20%7%
444
21st to endDay
14%8%29%27%18%5%
488
August1st to 10thDay
13%6%26%27%20%9%
446
11th to 20thDay
14%7%25%26%18%10%
439
21st to endDay
15%8%26%24%17%11%
495
September1st to 10thDay
21%8%19%24%20%8%
450
11th to 20thDay
15%7%20%28%20%9%
450
21st to endDay
25%14%24%18%14%5%
450
October1st to 10thDay
24%9%20%26%17%4
450
11th to 20thDay
24%17%25%24%10%2
450
21st to endDay
26%18%28%20%8%1
495
November1st to 10thDay
22%15%25%22%14%1
410
11th to 20thDay
31%19%24%17%7%1
237
21st to endDay
29%24%29%14%31
180
December1st to 10thDay
34%25%26%7%6%2
180
11th to 20thDay
35%19%28%14%3
180
21st to endDay
32%23%24%16%5%
198
January1st to 10thNight
26%22%30%18%3
760
11th to 20thNight
28%18%29%22%3
724
21st to endNight
24%21%29%23%2
792
February1st to 10thNight
29%16%28%24%3
720
11th to 20thNight
29%23%30%17%1
703
21st to endNight
31%17%30%20%2
592
March1st to 10thNight
25%19%30%22%4
720
11th to 20thNight
28%18%27%21%6%
720
21st to endNight
23%18%32%21%6%1
792
April1st to 10thNight
27%18%30%20%5%
720
11th to 20thNight
21%15%28%27%8%1
711
21st to endNight
23%13%25%31%7%
666
May1st to 10thNight
22%10%22%31%13%1
540
11th to 20thNight
20%8%29%35%8%
413
21st to endNight
13%8%21%36%19%2
389
June1st to 10thNight
14%6%24%38%18%
360
11th to 20thNight
14%6%24%37%18%1
360
21st to endNight
10%328%44%14%
360
July1st to 10thNight
11%417%43%23%3
350
11th to 20thNight
7%417%41%29%2
396
21st to endNight
10%319%43%24%2
591
August1st to 10thNight
9%214%41%32%2
537
11th to 20thNight
13%416%35%28%4
535
21st to endNight
15%318%33%28%3
792
September1st to 10thNight
17%417%33%26%3
720
11th to 20thNight
14%6%19%27%30%4
720
21st to endNight
18%9%22%27%21%3
720
October1st to 10thNight
19%7%23%27%21%3
720
11th to 20thNight
21%13%26%28%11%1
720
21st to endNight
26%12%26%28%7%1
792
November1st to 10thNight
16%11%28%34%11%1
740
11th to 20thNight
26%18%22%25%8%1
760
21st to endNight
25%16%27%25%6%1
760
December1st to 10thNight
29%17%28%20%7%
760
11th to 20thNight
28%16%26%27%4
760
21st to endNight
25%18%28%28%2
836
Page generated at 2024-01-08 11:14:19. Version ac07

Copyright 2024 Attilla Danko


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