Del Valle
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Del Valle 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
66%
23954
28%
80692
26%
23865
71%
23865
36%
44384

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
55%
750
19%
4252
18%
736
59%
736
15%
2406
January11th to 20thNight
56%
751
15%
4091
20%
740
61%
740
14%
2795
January21st to endNight
53%
830
15%
4441
23%
814
59%
814
13%
3162
February1st to 10thNight
54%
760
26%
2470
24%
760
61%
760
28%
1474
February11th to 20thNight
54%
740
27%
2289
26%
740
60%
740
29%
1395
February21st to endNight
55%
628
25%
1884
22%
628
62%
628
31%
1132
March1st to 10thNight
47%
760
17%
2161
15%
760
51%
760
23%
1482
March11th to 20thNight
50%
760
24%
2090
21%
760
55%
760
29%
1350
March21st to endNight
50%
820
19%
2201
12%
820
55%
820
30%
1425
April1st to 10thNight
51%
720
23%
1800
13%
720
56%
720
34%
1162
April11th to 20thNight
51%
711
28%
1779
13%
711
57%
711
38%
1079
April21st to endNight
60%
720
29%
1800
13%
720
66%
720
50%
1005
May1st to 10thNight
62%
689
29%
1769
16%
689
67%
689
50%
968
May11th to 20thNight
73%
442
34%
1504
29%
442
78%
442
49%
680
May21st to endNight
72%
388
30%
1552
29%
388
80%
388
46%
644
June1st to 10thNight
69%
360
30%
1440
30%
360
78%
360
45%
604
June11th to 20thNight
78%
360
38%
1440
42%
360
86%
360
64%
482
June21st to endNight
83%
360
38%
1440
46%
360
88%
360
68%
470
July1st to 10thNight
89%
350
39%
1400
47%
350
93%
350
77%
427
July11th to 20thNight
94%
461
38%
1505
39%
461
95%
461
80%
533
July21st to endNight
90%
591
41%
1674
35%
558
91%
558
73%
671
August1st to 10thNight
87%
537
39%
1602
31%
534
89%
534
66%
678
August11th to 20thNight
89%
674
43%
1742
27%
674
91%
674
81%
758
August21st to endNight
91%
792
43%
1980
28%
792
92%
792
81%
896
September1st to 10thNight
90%
720
46%
1800
33%
720
91%
720
80%
809
September11th to 20thNight
83%
720
45%
1800
34%
720
87%
720
71%
871
September21st to endNight
82%
720
44%
2028
40%
720
87%
720
70%
881
October1st to 10thNight
78%
720
33%
2160
33%
720
84%
720
57%
996
October11th to 20thNight
77%
720
38%
2160
40%
720
82%
720
52%
1051
October21st to endNight
76%
792
39%
2376
40%
792
81%
792
53%
1141
November1st to 10thNight
69%
740
31%
2287
31%
740
73%
740
41%
1228
November11th to 20thNight
66%
760
29%
2470
27%
760
72%
760
36%
1347
November21st to endNight
64%
760
30%
2580
31%
760
69%
760
37%
1350
December1st to 10thNight
57%
760
24%
2660
23%
760
63%
760
28%
1548
December11th to 20thNight
51%
760
18%
3238
21%
759
56%
759
16%
2259
December21st to endNight
44%
828
13%
4827
18%
817
52%
817
11%
3225

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
7%423323346%62%
78921
Night
7%5%2442445%6%58%
81109
TransparencyDay
25%47%18%24%21%
78638
Night
28%6%8%17%21%21%
80913
SeeingDay
9%12%26%32%17%4
14496
Night
8%6%14%34%30%8%
23992

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
13%12%36%4335%5%6%40%
2644
11th to 20thDay
13%9%38%8%45%45%7%35%
2860
21st to endDay
18%8%38%6%45%5%6%6%31%
3146
February1st to 10thDay
13%9%24425%45%7%45%
1710
11th to 20thDay
10%7%35%6%25%46%7%45%
1780
21st to endDay
13%7%25%5%2445%6%47%
1570
March1st to 10thDay
12%9%37%6%445%7%8%35%
2015
11th to 20thDay
11%8%26%6%36%5%6%7%40%
2090
21st to endDay
12%6%36%435%5%5%7%46%
2309
April1st to 10thDay
12%6%35%5%35%45%8%44%
2160
11th to 20thDay
9%423323447%58%
2129
21st to endDay
5%31332445%9%62%
2160
May1st to 10thDay
5%41332345%7%64%
2186
11th to 20thDay
4313312346%70%
2387
21st to endDay
421331335%7%67%
2723
June1st to 10thDay
3313323347%68%
2520
11th to 20thDay
111111224483%
2520
21st to endDay
21121123385%
2520
July1st to 10thDay
11112390%
2520
11th to 20thDay
11111222486%
2400
21st to endDay
11111123486%
2546
August1st to 10thDay
111211222385%
2328
11th to 20thDay
111113488%
2157
21st to endDay
1111112389%
2376
September1st to 10thDay
11111112289%
2160
11th to 20thDay
111212345%78%
2160
21st to endDay
311121223480%
1927
October1st to 10thDay
2223323236%73%
1800
11th to 20thDay
3212313346%71%
1800
21st to endDay
5%41232245%6%66%
1980
November1st to 10thDay
7%424435%46%7%54%
1790
11th to 20thDay
7%4245%2445%8%54%
1710
21st to endDay
10%5%2442336%7%55%
1596
December1st to 10thDay
10%6%35%5%345%5%6%48%
1520
11th to 20thDay
17%11%37%5%35%5%6%6%32%
1928
21st to endDay
12%10%47%6%35%6%6%7%36%
2794
January1st to 10thNight
12%10%35%4345%5%6%43%
4301
11th to 20thNight
13%9%49%7%5%6%5%5%5%33%
4110
21st to endNight
15%12%46%7%45%5%5%6%32%
4521
February1st to 10thNight
12%7%2443445%6%49%
2470
11th to 20thNight
8%7%35%5%345%6%8%47%
2287
21st to endNight
9%7%2442447%6%50%
1884
March1st to 10thNight
13%9%36%5%35%45%6%42%
2161
11th to 20thNight
10%8%25%5%245%48%46%
2090
21st to endNight
9%7%35%43445%7%49%
2201
April1st to 10thNight
8%5%35%5%35%5%6%7%48%
1800
11th to 20thNight
7%4335%3445%6%57%
1779
21st to endNight
432222445%10%63%
1800
May1st to 10thNight
431332335%7%66%
1769
11th to 20thNight
241222235%8%68%
1504
21st to endNight
311122346%8%70%
1552
June1st to 10thNight
221332335%6%70%
1440
11th to 20thNight
111112335%81%
1440
21st to endNight
11111112387%
1440
July1st to 10thNight
11111112389%
1440
11th to 20thNight
111111135%86%
1555
21st to endNight
11121135%6%79%
1773
August1st to 10thNight
111121124381%
1611
11th to 20thNight
1111114486%
1742
21st to endNight
1111113487%
1980
September1st to 10thNight
1111123388%
1800
11th to 20thNight
211111345%79%
1800
21st to endNight
211111235%81%
2028
October1st to 10thNight
4212223345%73%
2160
11th to 20thNight
331232335%6%70%
2160
21st to endNight
431222335%5%69%
2376
November1st to 10thNight
6%5%133245%5%8%58%
2287
11th to 20thNight
7%5%344245%5%7%54%
2470
21st to endNight
9%42442445%8%55%
2580
December1st to 10thNight
11%6%25%434347%50%
2660
11th to 20thNight
16%10%36%6%35%5%6%8%32%
3276
21st to endNight
12%8%37%7%5%6%6%6%6%35%
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
44%5%10%28%9%3
2644
11th to 20thDay
50%5%10%16%11%7%
2860
21st to endDay
51%9%7%15%14%4
3146
February1st to 10thDay
39%5%6%20%19%10%
1710
11th to 20thDay
38%6%8%18%23%7%
1789
21st to endDay
39%6%7%24%19%6%
1570
March1st to 10thDay
46%6%9%18%16%4
2015
11th to 20thDay
43%6%8%20%17%6%
2090
21st to endDay
39%8%13%19%17%4
2309
April1st to 10thDay
39%5%12%20%19%5%
2160
11th to 20thDay
28%5%13%23%24%7%
2132
21st to endDay
21%412%29%28%5%
2160
May1st to 10thDay
20%5%9%26%33%8%
2186
11th to 20thDay
18%37%27%33%11%
2390
21st to endDay
19%5%12%31%27%6%
2724
June1st to 10thDay
19%49%24%30%15%
2520
11th to 20thDay
7%37%20%36%27%
2520
21st to endDay
8%2311%28%48%
2520
July1st to 10thDay
4227%22%63%
2451
11th to 20thDay
6%2410%22%55%
2327
21st to endDay
5%227%28%57%
2405
August1st to 10thDay
8%3210%27%49%
2312
11th to 20thDay
42210%34%49%
2157
21st to endDay
4229%35%47%
2376
September1st to 10thDay
6%218%28%54%
2160
11th to 20thDay
9%5%420%36%26%
2160
21st to endDay
11%3320%38%27%
1927
October1st to 10thDay
16%36%17%30%28%
1800
11th to 20thDay
16%47%21%24%28%
1800
21st to endDay
20%47%20%27%23%
1980
November1st to 10thDay
29%5%8%20%24%14%
1790
11th to 20thDay
30%5%10%22%25%8%
1710
21st to endDay
29%5%8%18%29%10%
1596
December1st to 10thDay
36%5%11%19%19%11%
1520
11th to 20thDay
54%6%7%14%13%6%
1928
21st to endDay
47%7%11%20%13%3
2794
January1st to 10thNight
39%7%15%22%13%3
4301
11th to 20thNight
51%7%12%13%10%8%
4110
21st to endNight
51%10%8%13%12%7%
4521
February1st to 10thNight
36%5%6%19%20%13%
2470
11th to 20thNight
35%7%7%18%23%9%
2289
21st to endNight
32%7%9%27%19%6%
1884
March1st to 10thNight
43%8%10%17%15%6%
2161
11th to 20thNight
38%6%7%21%19%8%
2090
21st to endNight
36%9%11%19%18%7%
2201
April1st to 10thNight
34%7%14%19%19%7%
1800
11th to 20thNight
29%6%10%25%20%11%
1779
21st to endNight
19%7%9%29%27%8%
1800
May1st to 10thNight
18%8%7%21%31%15%
1769
11th to 20thNight
16%6%7%21%36%14%
1504
21st to endNight
14%8%12%26%31%9%
1552
June1st to 10thNight
18%5%9%19%28%22%
1440
11th to 20thNight
8%46%14%30%38%
1440
21st to endNight
7%3310%25%52%
1440
July1st to 10thNight
4325%17%69%
1400
11th to 20thNight
5%248%17%63%
1505
21st to endNight
6%436%19%62%
1674
August1st to 10thNight
9%5%39%19%55%
1602
11th to 20thNight
4428%28%54%
1742
21st to endNight
4437%31%51%
1980
September1st to 10thNight
5%326%21%63%
1800
11th to 20thNight
9%5%418%30%34%
1800
21st to endNight
9%3217%36%32%
2028
October1st to 10thNight
15%47%17%24%33%
2160
11th to 20thNight
17%5%5%17%23%32%
2160
21st to endNight
17%45%17%30%26%
2376
November1st to 10thNight
25%6%8%21%21%19%
2287
11th to 20thNight
29%6%8%21%27%10%
2470
21st to endNight
28%48%20%25%15%
2580
December1st to 10thNight
36%49%18%19%14%
2660
11th to 20thNight
51%6%8%13%17%5%
3276
21st to endNight
49%9%10%15%12%5%
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
23%18%26%24%9%1
246
11th to 20thDay
15%14%28%29%12%2
370
21st to endDay
16%13%27%26%16%2
407
February1st to 10thDay
19%17%25%24%13%2
370
11th to 20thDay
21%17%25%29%6%1
421
21st to endDay
17%17%32%24%9%1
382
March1st to 10thDay
20%19%29%25%6%1
460
11th to 20thDay
19%20%23%24%12%2
460
21st to endDay
19%19%31%23%8%1
491
April1st to 10thDay
19%19%28%21%11%1
420
11th to 20thDay
14%22%31%22%9%2
412
21st to endDay
8%21%26%27%13%5%
420
May1st to 10thDay
11%15%34%28%10%2
423
11th to 20thDay
6%16%35%26%14%3
448
21st to endDay
6%13%29%31%17%4
485
June1st to 10thDay
8%12%28%31%17%4
450
11th to 20thDay
410%31%36%15%4
450
21st to endDay
37%27%37%21%6%
450
July1st to 10thDay
423%46%22%4
446
11th to 20thDay
122%47%23%7%
444
21st to endDay
220%44%25%9%
487
August1st to 10thDay
2426%41%20%7%
447
11th to 20thDay
325%39%22%11%
437
21st to endDay
1218%44%25%10%
495
September1st to 10thDay
15%20%41%26%7%
450
11th to 20thDay
28%26%40%20%4
450
21st to endDay
48%22%40%23%4
450
October1st to 10thDay
311%26%34%22%4
450
11th to 20thDay
412%20%33%28%4
450
21st to endDay
8%8%25%33%22%4
495
November1st to 10thDay
9%10%22%30%27%2
386
11th to 20thDay
6%11%21%32%24%6%
270
21st to endDay
11%9%29%32%18%2
216
December1st to 10thDay
14%12%23%28%18%4
180
11th to 20thDay
17%11%23%29%18%2
180
21st to endDay
17%18%28%21%15%2
198
January1st to 10thNight
16%7%14%33%21%9%
760
11th to 20thNight
13%8%14%35%23%8%
760
21st to endNight
17%7%13%31%25%6%
836
February1st to 10thNight
16%7%14%32%24%6%
760
11th to 20thNight
12%9%15%35%21%7%
744
21st to endNight
13%11%16%39%18%3
628
March1st to 10thNight
16%12%16%31%21%4
760
11th to 20thNight
14%10%18%31%23%5%
760
21st to endNight
11%12%20%33%21%3
820
April1st to 10thNight
11%8%20%35%21%4
720
11th to 20thNight
8%12%21%33%20%6%
711
21st to endNight
6%7%24%31%26%7%
720
May1st to 10thNight
6%5%21%36%24%8%
689
11th to 20thNight
4314%39%34%5%
442
21st to endNight
3418%35%34%5%
389
June1st to 10thNight
3419%38%30%5%
360
11th to 20thNight
2315%44%34%3
360
21st to endNight
114%43%38%5%
360
July1st to 10thNight
9%39%45%7%
350
11th to 20thNight
11234%51%12%
461
21st to endNight
15%32%49%13%
591
August1st to 10thNight
26%35%47%10%
537
11th to 20thNight
118%38%44%9%
674
21st to endNight
115%32%50%11%
792
September1st to 10thNight
17%34%47%11%
720
11th to 20thNight
2210%36%40%9%
720
21st to endNight
3210%33%39%14%
720
October1st to 10thNight
4410%38%32%11%
720
11th to 20thNight
6%49%36%35%11%
720
21st to endNight
5%312%34%29%16%
792
November1st to 10thNight
8%6%12%32%32%11%
740
11th to 20thNight
9%5%13%35%30%8%
760
21st to endNight
11%414%36%28%7%
760
December1st to 10thNight
13%8%12%36%24%7%
760
11th to 20thNight
18%8%13%34%21%6%
760
21st to endNight
16%11%19%31%18%4
836
Page generated at 2024-03-24 20:36:58. Version ac07

Copyright © 2024 Attilla Danko.


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