This page made possible by the sponsorship of: Thomas Walker.

TOMS Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the TOMS Observatory clear sky chart from 2005-11-05 to 2019-05-11.

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
46%
17736
24%
53554
17%
17692
54%
17692
29%
32656

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
23%
1050
23%
2896
9%
1045
35%
1045
23%
1929
January16th to endNight
23%
1016
25%
2808
8%
1016
36%
1016
25%
1849
February1st to 15thNight
23%
824
19%
2472
8%
821
33%
821
21%
1657
February16th to endNight
21%
735
21%
2205
9%
735
31%
735
20%
1476
March1st to 15thNight
27%
840
19%
2520
10%
840
35%
840
23%
1633
March16th to endNight
36%
714
21%
2338
13%
714
45%
714
26%
1428
April1st to 15thNight
37%
629
25%
2097
16%
629
50%
629
27%
1233
April16th to endNight
43%
624
23%
2078
16%
624
55%
624
31%
1179
May1st to 15thNight
51%
617
23%
1931
18%
617
57%
617
30%
1165
May16th to endNight
63%
609
20%
1826
17%
609
66%
609
32%
1114
June1st to 15thNight
73%
585
24%
1609
20%
585
76%
585
41%
937
June16th to endNight
80%
585
25%
1560
20%
585
82%
585
46%
877
July1st to 15thNight
72%
555
17%
1480
15%
555
74%
555
37%
919
July16th to endNight
81%
612
21%
1725
22%
579
83%
579
42%
949
August1st to 15thNight
81%
575
21%
1906
25%
572
81%
572
35%
1049
August16th to endNight
76%
621
21%
2070
26%
621
77%
621
31%
1223
September1st to 15thNight
66%
606
22%
1971
22%
606
68%
606
30%
1158
September16th to endNight
64%
777
31%
2145
26%
777
67%
777
40%
1263
October1st to 15thNight
60%
780
34%
2181
27%
780
64%
780
41%
1245
October16th to endNight
50%
832
32%
2544
24%
832
60%
832
34%
1438
November1st to 15thNight
46%
820
29%
2666
24%
820
56%
820
31%
1529
November16th to endNight
37%
840
27%
2730
18%
840
49%
840
29%
1595
December1st to 15thNight
32%
840
24%
2730
14%
840
46%
840
23%
1723
December16th to endNight
26%
1050
19%
3066
9%
1050
36%
1050
21%
2088

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
12%6%25%5%3445%7%41%
54285
Night
12%5%2442445%7%46%
53747
TransparencyDay
40%5%10%22%17%3
53980
Night
36%410%22%19%5%
53556
SeeingDay
15%7%19%24%22%10%
7690
Night
15%8%23%27%19%4
17738

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 15thDay
19%9%34423335%39%
1700
16th to endDay
16%7%34313335%46%
2117
February1st to 15thDay
19%9%35%423235%39%
2050
16th to endDay
21%7%345%23445%36%
1840
March1st to 15thDay
17%8%36%6%3434437%
2100
16th to endDay
14%6%35%5%2445%7%39%
2599
April1st to 15thDay
14%6%24433446%44%
2511
16th to endDay
12%6%15%5%3445%7%43%
2487
May1st to 15thDay
13%5%25%5%35%45%6%41%
2575
16th to endDay
9%6%26%7%45%5%5%7%39%
2639
June1st to 15thDay
7%425%5%45%6%6%9%42%
2677
16th to endDay
43145%46%6%8%11%44%
2730
July1st to 15thDay
7%5%25%6%47%7%7%10%33%
2730
16th to endDay
6%425%6%5%6%7%7%11%36%
2678
August1st to 15thDay
5%325%6%47%7%7%11%38%
2295
16th to endDay
9%425%6%46%6%6%9%36%
2484
September1st to 15thDay
11%5%25%6%35%46%8%39%
2304
16th to endDay
11%414424446%50%
2145
October1st to 15thDay
11%425%423446%50%
2106
16th to endDay
13%31332233457%
2031
November1st to 15thDay
15%434313435%51%
1852
16th to endDay
15%7%2432344448%
1890
December1st to 15thDay
21%7%35%42344438%
1890
16th to endDay
20%10%26%323336%37%
1855
January1st to 15thNight
18%9%34423345%42%
2896
16th to endNight
17%7%34324335%43%
2808
February1st to 15thNight
20%8%35%423235%40%
2463
16th to endNight
18%7%35%424435%38%
2205
March1st to 15thNight
17%7%24424346%42%
2520
16th to endNight
13%6%35%424446%44%
2338
April1st to 15thNight
13%5%144245%5%7%46%
2097
16th to endNight
11%424324447%50%
2078
May1st to 15thNight
11%5%3443345%8%46%
1930
16th to endNight
6%425%5%35%5%7%9%44%
1826
June1st to 15thNight
4224425%6%6%11%50%
1609
16th to endNight
3213325%6%6%10%55%
1560
July1st to 15thNight
5%424435%6%7%11%43%
1560
16th to endNight
33134245%9%13%48%
1836
August1st to 15thNight
4213435%6%7%11%48%
1918
16th to endNight
5%3145%35%6%8%11%43%
2070
September1st to 15thNight
10%4244345%6%7%46%
1971
16th to endNight
9%314423445%54%
2145
October1st to 15thNight
9%423322336%58%
2181
16th to endNight
16%6%12212235%55%
2544
November1st to 15thNight
13%413323346%51%
2666
16th to endNight
14%6%14323335%51%
2730
December1st to 15thNight
17%8%25%423336%42%
2730
16th to endNight
19%9%25%42335%5%37%
3066

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
47%27%20%19%3
1701
16th to endDay
41%28%23%21%2
2117
February1st to 15thDay
49%26%21%16%3
2052
16th to endDay
49%28%19%16%3
1840
March1st to 15thDay
50%47%16%14%7%
2100
16th to endDay
43%5%12%22%15%
2600
April1st to 15thDay
39%410%22%18%4
2511
16th to endDay
39%49%23%20%3
2487
May1st to 15thDay
41%5%10%23%15%3
2575
16th to endDay
42%6%14%22%10%2
2643
June1st to 15thDay
36%6%12%24%18%2
2677
16th to endDay
30%8%13%24%18%3
2730
July1st to 15thDay
40%8%19%18%9%3
2581
16th to endDay
37%7%16%25%11%
2526
August1st to 15thDay
34%9%17%21%14%2
2283
16th to endDay
41%7%12%24%10%2
2484
September1st to 15thDay
40%7%11%22%12%4
2304
16th to endDay
33%6%10%22%22%5%
2145
October1st to 15thDay
34%48%22%23%6%
2106
16th to endDay
31%35%21%31%8%
2031
November1st to 15thDay
36%36%17%27%7%
1852
16th to endDay
39%27%20%25%4
1890
December1st to 15thDay
50%36%20%14%4
1890
16th to endDay
50%210%19%14%2
1855
January1st to 15thNight
45%27%22%19%3
2896
16th to endNight
43%37%21%19%4
2808
February1st to 15thNight
47%38%20%16%3
2472
16th to endNight
46%37%20%18%3
2205
March1st to 15thNight
43%39%19%16%7%
2520
16th to endNight
39%411%23%19%1
2338
April1st to 15thNight
36%410%24%18%5%
2097
16th to endNight
33%311%23%21%5%
2078
May1st to 15thNight
35%5%11%24%19%3
1931
16th to endNight
33%7%15%24%15%3
1828
June1st to 15thNight
26%7%16%26%19%3
1609
16th to endNight
24%5%14%30%21%3
1560
July1st to 15thNight
28%10%21%24%11%4
1480
16th to endNight
24%6%22%30%13%1
1725
August1st to 15thNight
26%8%19%26%17%2
1906
16th to endNight
31%8%17%25%12%4
2070
September1st to 15thNight
33%6%15%21%17%5%
1971
16th to endNight
29%5%9%23%24%7%
2145
October1st to 15thNight
28%48%24%24%10%
2181
16th to endNight
33%2416%32%10%
2544
November1st to 15thNight
34%36%21%23%10%
2666
16th to endNight
36%36%20%26%7%
2730
December1st to 15thNight
43%38%22%17%4
2730
16th to endNight
48%29%19%15%3
3066

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
30%18%30%16%21
180
16th to endDay
19%25%36%12%4
192
February1st to 15thDay
32%20%29%10%6%1
180
16th to endDay
35%15%32%12%5%
159
March1st to 15thDay
24%21%39%12%2
180
16th to endDay
18%13%34%23%9%
359
April1st to 15thDay
20%13%28%23%11%2
390
16th to endDay
16%10%23%29%17%2
379
May1st to 15thDay
17%6%23%28%14%9%
388
16th to endDay
16%317%26%23%13%
395
June1st to 15thDay
10%114%27%25%21%
517
16th to endDay
4215%32%30%12%
570
July1st to 15thDay
9%112%27%32%16%
550
16th to endDay
7%19%22%33%24%
488
August1st to 15thDay
9%5%27%35%21%
358
16th to endDay
13%15%28%36%14%
396
September1st to 15thDay
14%25%22%35%18%
375
16th to endDay
13%19%25%34%15%
374
October1st to 15thDay
13%121%27%26%9%
336
16th to endDay
16%8%26%29%16%3
192
November1st to 15thDay
25%10%21%30%11%1
180
16th to endDay
17%12%31%24%10%4
180
December1st to 15thDay
26%14%37%13%7%
180
16th to endDay
26%15%39%14%4
192
January1st to 15thNight
23%17%31%21%4
1050
16th to endNight
20%14%39%22%3
1016
February1st to 15thNight
22%15%34%22%4
824
16th to endNight
22%16%36%22%2
735
March1st to 15thNight
21%15%32%27%3
840
16th to endNight
17%8%32%27%12%
714
April1st to 15thNight
13%11%33%26%12%
629
16th to endNight
14%6%30%31%15%1
624
May1st to 15thNight
14%424%34%18%3
617
16th to endNight
9%214%36%27%8%
611
June1st to 15thNight
5%110%39%33%10%
585
16th to endNight
38%34%43%9%
585
July1st to 15thNight
7%9%25%40%16%
555
16th to endNight
5%15%29%39%19%
612
August1st to 15thNight
5%15%27%46%14%
575
16th to endNight
7%5%32%43%9%
621
September1st to 15thNight
12%112%25%38%9%
606
16th to endNight
11%312%31%34%5%
777
October1st to 15thNight
12%119%30%29%5%
780
16th to endNight
19%7%20%28%22%1
832
November1st to 15thNight
15%8%25%31%17%1
820
16th to endNight
19%10%29%24%15%1
840
December1st to 15thNight
22%13%29%25%9%
840
16th to endNight
26%12%31%25%4
1050
Page generated at 2019-05-11 23:31:05. Version ac04

Copyright 2019 A. Danko


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