Telegraph City
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Telegraph City clear sky chart from 2005-11-06 to 2024-03-28.

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
67%
23850
29%
80672
27%
23769
72%
23769
40%
42462

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
52%
748
17%
4359
17%
736
57%
736
15%
2505
January11th to 20thNight
60%
750
17%
4123
22%
740
65%
740
15%
2701
January21st to endNight
57%
828
15%
4431
25%
814
61%
814
15%
2950
February1st to 10thNight
58%
760
25%
2470
25%
760
63%
760
32%
1421
February11th to 20thNight
58%
740
29%
2236
28%
740
64%
740
36%
1278
February21st to endNight
57%
628
25%
1884
24%
628
61%
628
34%
1102
March1st to 10thNight
50%
760
18%
2237
16%
760
54%
760
26%
1473
March11th to 20thNight
55%
760
24%
2090
21%
760
59%
760
34%
1295
March21st to endNight
55%
820
20%
2155
14%
820
59%
820
36%
1343
April1st to 10thNight
55%
720
25%
1800
13%
720
61%
720
41%
1097
April11th to 20thNight
59%
711
29%
1779
14%
711
64%
711
47%
1024
April21st to endNight
66%
720
29%
1800
14%
720
70%
720
55%
970
May1st to 10thNight
65%
716
31%
1796
18%
716
68%
716
59%
924
May11th to 20thNight
69%
386
37%
1448
35%
386
76%
386
55%
565
May21st to endNight
70%
388
31%
1552
30%
388
79%
388
54%
584
June1st to 10thNight
67%
360
31%
1440
33%
360
76%
360
55%
540
June11th to 20thNight
78%
360
39%
1440
44%
360
87%
360
77%
431
June21st to endNight
78%
360
39%
1440
45%
360
87%
360
72%
451
July1st to 10thNight
87%
350
40%
1400
48%
350
92%
350
83%
396
July11th to 20thNight
84%
348
41%
1392
47%
348
88%
348
72%
436
July21st to endNight
84%
591
39%
1674
32%
558
87%
558
69%
703
August1st to 10thNight
81%
545
40%
1610
30%
542
85%
542
76%
638
August11th to 20thNight
80%
712
38%
1780
22%
712
83%
712
78%
811
August21st to endNight
85%
792
45%
1980
27%
792
88%
792
85%
860
September1st to 10thNight
88%
720
46%
1800
31%
720
90%
720
86%
782
September11th to 20thNight
80%
720
48%
1800
35%
720
85%
720
78%
822
September21st to endNight
81%
720
46%
1995
41%
720
86%
720
76%
841
October1st to 10thNight
77%
720
34%
2160
34%
720
83%
720
60%
964
October11th to 20thNight
77%
720
39%
2160
41%
720
82%
720
61%
960
October21st to endNight
78%
792
42%
2376
43%
792
83%
792
62%
1050
November1st to 10thNight
72%
740
32%
2367
33%
740
76%
740
46%
1158
November11th to 20thNight
70%
760
31%
2470
31%
760
75%
760
43%
1241
November21st to endNight
66%
760
30%
2527
30%
760
71%
760
39%
1305
December1st to 10thNight
63%
760
23%
2660
24%
760
67%
760
30%
1506
December11th to 20thNight
55%
760
19%
3216
23%
759
59%
759
18%
2170
December21st to endNight
51%
825
12%
4825
20%
817
58%
817
13%
3165

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
9%323323346%63%
78892
Night
11%423323346%60%
81136
TransparencyDay
24%48%19%23%22%
78608
Night
27%49%19%22%19%
80941
SeeingDay
9%6%20%35%24%7%
14372
Night
11%314%41%27%5%
23896

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 10thDay
20%8%35%5%3445%7%36%
2539
11th to 20thDay
20%8%48%7%44445%32%
2805
21st to endDay
21%8%36%6%345%5%8%29%
3146
February1st to 10thDay
18%6%24423446%47%
1710
11th to 20thDay
15%5%25%42445%8%47%
1831
21st to endDay
17%5%25%434446%47%
1570
March1st to 10thDay
15%7%38%435%5%6%7%38%
1938
11th to 20thDay
17%5%234245%5%9%44%
2090
21st to endDay
13%5%2442445%8%49%
2356
April1st to 10thDay
12%5%2342445%7%51%
2160
11th to 20thDay
10%42332345%6%60%
2129
21st to endDay
8%312213436%66%
2160
May1st to 10thDay
5%413323346%68%
2163
11th to 20thDay
4313312346%70%
2441
21st to endDay
5%212313447%68%
2723
June1st to 10thDay
4212322336%72%
2520
11th to 20thDay
111112235%84%
2520
21st to endDay
21111112385%
2520
July1st to 10thDay
1111122389%
2520
11th to 20thDay
111111222484%
2516
21st to endDay
111221223384%
2546
August1st to 10thDay
211121221285%
2318
11th to 20thDay
1111122486%
2122
21st to endDay
11111111389%
2376
September1st to 10thDay
21111111389%
2160
11th to 20thDay
211211223480%
2160
21st to endDay
311211222481%
1959
October1st to 10thDay
4212223236%75%
1800
11th to 20thDay
423313345%73%
1800
21st to endDay
6%213312445%69%
1980
November1st to 10thDay
7%3245%2436%7%56%
1710
11th to 20thDay
9%42442345%6%57%
1710
21st to endDay
12%32443445%8%53%
1652
December1st to 10thDay
13%6%25%5%34348%48%
1520
11th to 20thDay
26%8%45%5%23346%32%
1928
21st to endDay
14%7%36%6%45%6%7%9%32%
2794
January1st to 10thNight
16%7%35%42345%7%44%
4406
11th to 20thNight
21%8%25%5%3445%7%35%
4158
21st to endNight
23%8%25%5%24447%35%
4521
February1st to 10thNight
17%5%24423336%52%
2470
11th to 20thNight
15%42332435%8%51%
2235
21st to endNight
18%5%23323345%53%
1884
March1st to 10thNight
18%7%26%43445%5%42%
2237
11th to 20thNight
16%5%24423347%48%
2090
21st to endNight
16%5%2433345%6%51%
2155
April1st to 10thNight
12%4233235%5%7%53%
1800
11th to 20thNight
9%323223447%60%
1779
21st to endNight
6%322323447%66%
1800
May1st to 10thNight
5%322312346%70%
1796
11th to 20thNight
5%212212248%71%
1448
21st to endNight
3212322346%72%
1552
June1st to 10thNight
4212212335%76%
1440
11th to 20thNight
111223486%
1440
21st to endNight
11121122386%
1440
July1st to 10thNight
111112290%
1440
11th to 20thNight
21111222385%
1440
21st to endNight
211222233479%
1773
August1st to 10thNight
21221122384%
1619
11th to 20thNight
11121223482%
1780
21st to endNight
11111112289%
1980
September1st to 10thNight
11111111390%
1800
11th to 20thNight
221111122484%
1800
21st to endNight
211121112384%
1995
October1st to 10thNight
5%21222334474%
2160
11th to 20thNight
4212322235%75%
2160
21st to endNight
5%112212235%75%
2376
November1st to 10thNight
10%314312337%62%
2367
11th to 20thNight
9%42331346%7%59%
2470
21st to endNight
11%323324346%59%
2527
December1st to 10thNight
15%42443335%6%51%
2660
11th to 20thNight
25%7%35%42345%6%36%
3276
21st to endNight
17%6%37%6%45%5%6%7%34%
4862

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
51%5%14%22%7%1
2539
11th to 20thDay
54%8%9%14%11%5%
2805
21st to endDay
53%7%12%17%10%2
3146
February1st to 10thDay
39%6%11%23%15%6%
1710
11th to 20thDay
35%5%11%22%21%6%
1841
21st to endDay
37%5%11%24%20%4
1570
March1st to 10thDay
42%6%11%22%16%3
1938
11th to 20thDay
35%6%11%25%18%4
2090
21st to endDay
34%5%16%24%17%4
2356
April1st to 10thDay
31%6%12%25%17%9%
2160
11th to 20thDay
25%412%27%23%8%
2132
21st to endDay
20%311%29%30%7%
2160
May1st to 10thDay
17%310%26%32%11%
2163
11th to 20thDay
16%37%27%33%14%
2444
21st to endDay
16%413%29%28%10%
2724
June1st to 10thDay
15%39%24%31%18%
2520
11th to 20thDay
6%16%20%33%33%
2520
21st to endDay
8%129%32%47%
2520
July1st to 10thDay
4127%22%64%
2451
11th to 20thDay
7%238%22%57%
2441
21st to endDay
8%126%24%58%
2405
August1st to 10thDay
9%137%25%54%
2302
11th to 20thDay
5%129%29%54%
2122
21st to endDay
5%128%33%51%
2376
September1st to 10thDay
5%127%26%59%
2160
11th to 20thDay
10%2418%39%27%
2160
21st to endDay
9%1417%38%31%
1959
October1st to 10thDay
14%26%19%28%31%
1800
11th to 20thDay
15%37%22%27%27%
1800
21st to endDay
18%47%22%28%22%
1980
November1st to 10thDay
27%39%26%24%11%
1710
11th to 20thDay
28%5%12%26%24%4
1710
21st to endDay
30%5%11%24%23%7%
1652
December1st to 10thDay
38%6%12%20%17%7%
1520
11th to 20thDay
55%5%10%15%11%3
1928
21st to endDay
47%10%19%14%8%2
2794
January1st to 10thNight
40%8%17%24%9%2
4406
11th to 20thNight
49%6%13%16%9%7%
4158
21st to endNight
49%5%12%18%12%4
4521
February1st to 10thNight
35%310%24%19%8%
2470
11th to 20thNight
31%5%10%24%24%7%
2236
21st to endNight
34%410%28%19%5%
1884
March1st to 10thNight
42%6%11%18%18%6%
2237
11th to 20thNight
36%49%23%20%8%
2090
21st to endNight
33%6%13%24%16%7%
2155
April1st to 10thNight
29%6%14%23%20%7%
1800
11th to 20thNight
25%413%26%21%11%
1779
21st to endNight
19%5%13%28%29%7%
1800
May1st to 10thNight
16%310%25%33%13%
1796
11th to 20thNight
14%39%31%30%14%
1448
21st to endNight
13%413%34%27%10%
1552
June1st to 10thNight
13%311%23%33%16%
1440
11th to 20thNight
5%27%19%35%33%
1440
21st to endNight
7%1213%30%47%
1440
July1st to 10thNight
4128%20%65%
1400
11th to 20thNight
7%237%22%60%
1392
21st to endNight
11%235%22%57%
1674
August1st to 10thNight
9%1211%26%52%
1610
11th to 20thNight
7%239%26%53%
1780
21st to endNight
5%128%30%54%
1980
September1st to 10thNight
5%136%27%58%
1800
11th to 20thNight
9%1319%39%29%
1800
21st to endNight
8%1416%38%33%
1995
October1st to 10thNight
15%36%18%26%32%
2160
11th to 20thNight
14%27%18%27%31%
2160
21st to endNight
13%36%20%32%26%
2376
November1st to 10thNight
23%39%24%24%17%
2367
11th to 20thNight
24%410%25%27%9%
2470
21st to endNight
27%49%23%29%8%
2527
December1st to 10thNight
34%5%10%22%19%10%
2660
11th to 20thNight
48%6%10%18%14%4
3276
21st to endNight
48%9%15%18%8%4
4862

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
32%9%18%23%13%5%
180
11th to 20thDay
18%6%20%28%20%8%
341
21st to endDay
19%418%29%23%8%
407
February1st to 10thDay
21%8%16%25%21%9%
370
11th to 20thDay
17%8%27%25%17%6%
446
21st to endDay
16%7%23%34%18%3
382
March1st to 10thDay
19%8%23%33%13%3
460
11th to 20thDay
21%8%22%26%17%6%
460
21st to endDay
17%9%24%30%18%2
491
April1st to 10thDay
15%9%31%24%15%5%
420
11th to 20thDay
12%11%31%27%14%5%
412
21st to endDay
7%10%27%30%19%8%
420
May1st to 10thDay
6%13%26%34%17%5%
423
11th to 20thDay
6%9%28%31%21%3
448
21st to endDay
6%8%22%35%25%5%
485
June1st to 10thDay
48%23%36%23%5%
450
11th to 20thDay
17%29%40%21%2
450
21st to endDay
2222%42%27%5%
450
July1st to 10thDay
117%47%31%4
446
11th to 20thDay
1112%44%37%5%
444
21st to endDay
1110%46%35%7%
487
August1st to 10thDay
3215%46%28%6%
447
11th to 20thDay
2118%44%27%8%
437
21st to endDay
1117%44%32%5%
495
September1st to 10thDay
2213%49%27%8%
450
11th to 20thDay
3224%38%26%7%
450
21st to endDay
4415%40%30%7%
450
October1st to 10thDay
38%20%32%28%10%
450
11th to 20thDay
5%5%17%27%32%13%
450
21st to endDay
7%417%32%28%11%
495
November1st to 10thDay
8%5%13%29%31%14%
306
11th to 20thDay
7%6%13%37%26%11%
270
21st to endDay
10%217%32%33%7%
242
December1st to 10thDay
17%318%32%21%9%
180
11th to 20thDay
16%7%19%28%22%8%
180
21st to endDay
19%8%22%28%17%6%
198
January1st to 10thNight
21%5%14%30%24%7%
760
11th to 20thNight
16%311%38%24%9%
760
21st to endNight
20%49%33%27%6%
836
February1st to 10thNight
18%314%36%24%5%
760
11th to 20thNight
17%5%15%33%24%6%
744
21st to endNight
20%414%43%16%4
628
March1st to 10thNight
21%416%35%20%3
760
11th to 20thNight
18%415%34%23%6%
760
21st to endNight
18%418%39%20%2
820
April1st to 10thNight
14%322%36%23%3
720
11th to 20thNight
9%5%21%40%20%5%
711
21st to endNight
7%319%44%23%5%
720
May1st to 10thNight
6%322%43%22%4
716
11th to 20thNight
5%320%45%25%2
386
21st to endNight
4221%46%26%1
389
June1st to 10thNight
4223%43%25%2
360
11th to 20thNight
219%52%26%2
360
21st to endNight
2216%49%29%2
360
July1st to 10thNight
10%58%31%1
350
11th to 20thNight
2111%59%27%1
348
21st to endNight
1110%44%38%5%
591
August1st to 10thNight
311%46%36%3
545
11th to 20thNight
115%48%31%4
712
21st to endNight
210%49%35%3
792
September1st to 10thNight
118%49%35%5%
720
11th to 20thNight
3213%44%33%6%
720
21st to endNight
3112%38%38%9%
720
October1st to 10thNight
6%211%42%32%7%
720
11th to 20thNight
5%311%38%35%8%
720
21st to endNight
5%211%38%30%13%
792
November1st to 10thNight
11%19%38%29%10%
740
11th to 20thNight
11%311%41%29%7%
760
21st to endNight
13%212%38%29%6%
760
December1st to 10thNight
17%311%40%22%7%
760
11th to 20thNight
23%212%36%23%4
760
21st to endNight
21%414%36%20%4
836
Page generated at 2024-03-24 20:36:58. Version ac07

Copyright © 2024 Attilla Danko.


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