Del Valle
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Del Valle clear sky chart from 2005-11-05 to 2018-02-22.

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
69%
16016
29%
48932
26%
15980
73%
15980
41%
26168

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
62%
776
19%
2604
19%
776
65%
776
27%
1568
January16th to endNight
58%
832
23%
2704
24%
832
61%
832
27%
1676
February1st to 15thNight
60%
759
27%
2469
27%
759
65%
759
28%
1480
February16th to endNight
57%
660
26%
1979
23%
660
63%
660
28%
1246
March1st to 15thNight
53%
720
19%
2025
18%
720
56%
720
28%
1327
March16th to endNight
52%
768
21%
2076
15%
768
57%
768
30%
1338
April1st to 15thNight
50%
719
22%
1799
12%
719
54%
719
32%
1178
April16th to endNight
59%
720
26%
1800
12%
720
63%
720
46%
1039
May1st to 15thNight
70%
635
30%
1715
19%
635
74%
635
58%
854
May16th to endNight
75%
374
29%
1496
29%
374
83%
374
45%
633
June1st to 15thNight
72%
360
29%
1440
31%
360
80%
360
48%
584
June16th to endNight
88%
360
39%
1440
49%
360
91%
360
72%
454
July1st to 15thNight
94%
357
36%
1377
44%
357
95%
357
77%
434
July16th to endNight
92%
564
38%
1593
35%
531
93%
531
74%
637
August1st to 15thNight
90%
572
39%
1645
30%
569
91%
569
71%
692
August16th to endNight
92%
764
44%
1910
29%
764
93%
764
81%
866
September1st to 15thNight
91%
720
42%
1800
31%
720
92%
720
77%
832
September16th to endNight
85%
716
45%
1953
40%
716
88%
716
68%
886
October1st to 15thNight
76%
720
31%
2160
32%
720
82%
720
51%
1047
October16th to endNight
77%
768
38%
2304
40%
768
81%
768
49%
1165
November1st to 15thNight
69%
760
27%
2391
27%
760
74%
760
40%
1280
November16th to endNight
66%
780
26%
2610
28%
780
69%
780
32%
1476
December1st to 15thNight
59%
780
23%
2730
22%
780
64%
780
26%
1633
December16th to endNight
50%
832
22%
2912
20%
832
56%
832
22%
1843

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
6%313313345%63%
49319
Night
7%313323346%59%
49118
TransparencyDay
24%37%18%25%20%
49004
Night
26%47%17%22%21%
48933
SeeingDay
9%11%25%33%16%3
6474
Night
8%5%10%32%33%10%
16027

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 15thDay
14%6%243235%47%43%
1663
16th to endDay
14%6%26%5%3435%5%43%
1872
February1st to 15thDay
12%7%245%24346%44%
1725
16th to endDay
15%6%35%5%2445%7%40%
1641
March1st to 15thDay
11%6%26%6%345%7%8%36%
1932
16th to endDay
12%6%36%435%5%46%41%
2148
April1st to 15thDay
13%6%3443435%8%42%
2149
16th to endDay
6%313323338%60%
2160
May1st to 15thDay
432212346%68%
2229
16th to endDay
4213313347%63%
2615
June1st to 15thDay
3212312345%69%
2520
16th to endDay
11113384%
2520
July1st to 15thDay
112388%
2500
16th to endDay
1112386%
2468
August1st to 15thDay
11112386%
2304
16th to endDay
11112387%
2292
September1st to 15thDay
111113385%
2160
16th to endDay
211212245%75%
2004
October1st to 15thDay
3213212236%69%
1800
16th to endDay
5%32312446%64%
1920
November1st to 15thDay
9%32432446%7%51%
1796
16th to endDay
10%5%2342335%7%49%
1677
December1st to 15thDay
13%7%35%423446%43%
1560
16th to endDay
15%8%35%5%1445%6%40%
1664
January1st to 15thNight
12%424335%5%6%8%42%
2604
16th to endNight
13%6%24423446%45%
2704
February1st to 15thNight
11%5%244245%5%7%46%
2457
16th to endNight
11%6%2442447%7%45%
1979
March1st to 15thNight
13%6%345%24347%44%
2025
16th to endNight
10%6%25%4235%5%7%45%
2076
April1st to 15thNight
8%425%5%35%5%6%7%45%
1799
16th to endNight
6%22222435%8%60%
1800
May1st to 15thNight
321221225%8%67%
1715
16th to endNight
22121346%8%67%
1496
June1st to 15thNight
211231235%6%69%
1440
16th to endNight
111112385%
1440
July1st to 15thNight
1112485%
1458
16th to endNight
1111245%80%
1701
August1st to 15thNight
111114382%
1654
16th to endNight
1114385%
1910
September1st to 15thNight
11123384%
1800
16th to endNight
211111245%78%
1953
October1st to 15thNight
4112222346%67%
2160
16th to endNight
4212323346%65%
2304
November1st to 15thNight
7%3222145%5%9%55%
2391
16th to endNight
9%424424447%50%
2610
December1st to 15thNight
11%6%2442435%7%45%
2730
16th to endNight
16%6%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%410%20%16%8%
1663
16th to endDay
43%5%7%13%19%10%
1872
February1st to 15thDay
40%47%19%22%6%
1725
16th to endDay
45%47%24%16%3
1641
March1st to 15thDay
43%5%10%18%15%6%
1932
16th to endDay
42%6%11%18%16%4
2148
April1st to 15thDay
41%412%20%18%3
2149
16th to endDay
24%412%24%25%7%
2160
May1st to 15thDay
18%36%27%34%9%
2229
16th to endDay
22%410%26%27%8%
2619
June1st to 15thDay
18%48%22%25%21%
2520
16th to endDay
7%1315%30%41%
2520
July1st to 15thDay
5%226%24%59%
2352
16th to endDay
6%138%25%55%
2313
August1st to 15thDay
6%2111%29%48%
2288
16th to endDay
5%2210%39%40%
2292
September1st to 15thDay
6%2213%32%41%
2160
16th to endDay
11%4323%34%22%
2004
October1st to 15thDay
18%26%21%25%24%
1800
16th to endDay
21%48%21%25%18%
1920
November1st to 15thDay
32%410%23%21%7%
1796
16th to endDay
35%48%20%26%4
1677
December1st to 15thDay
41%48%16%19%9%
1560
16th to endDay
44%5%10%15%19%4
1664
January1st to 15thNight
37%5%11%20%17%8%
2604
16th to endNight
40%410%12%17%15%
2704
February1st to 15thNight
37%46%19%22%9%
2469
16th to endNight
38%6%9%24%16%5%
1979
March1st to 15thNight
41%410%19%15%8%
2025
16th to endNight
37%6%11%18%17%8%
2076
April1st to 15thNight
37%5%13%21%18%4
1799
16th to endNight
23%5%11%25%22%11%
1800
May1st to 15thNight
15%47%21%34%16%
1716
16th to endNight
16%6%10%23%31%12%
1496
June1st to 15thNight
16%48%18%23%28%
1440
16th to endNight
7%1311%26%50%
1440
July1st to 15thNight
5%116%16%68%
1377
16th to endNight
7%348%18%58%
1593
August1st to 15thNight
7%419%25%51%
1645
16th to endNight
4328%33%46%
1910
September1st to 15thNight
6%3210%26%49%
1800
16th to endNight
10%3220%32%29%
1953
October1st to 15thNight
19%37%19%23%27%
2160
16th to endNight
20%5%5%19%28%21%
2304
November1st to 15thNight
26%5%11%24%23%9%
2391
16th to endNight
33%47%21%24%9%
2610
December1st to 15thNight
38%48%15%20%12%
2730
16th to endNight
43%5%9%15%19%7%
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
22%13%22%28%9%1
201
16th to endDay
16%11%25%28%17%1
304
February1st to 15thDay
16%14%22%30%15%1
285
16th to endDay
21%17%26%23%10%
264
March1st to 15thDay
16%20%25%21%12%2
270
16th to endDay
18%19%30%24%6%1
288
April1st to 15thDay
18%27%27%16%8%
269
16th to endDay
12%27%29%21%7%1
270
May1st to 15thDay
10%16%36%27%8%1
288
16th to endDay
6%13%29%32%13%4
330
June1st to 15thDay
7%15%32%32%9%2
315
16th to endDay
3427%39%19%5%
315
July1st to 15thDay
23%49%20%4
305
16th to endDay
121%48%19%7%
327
August1st to 15thDay
2220%44%21%7%
315
16th to endDay
219%43%23%10%
332
September1st to 15thDay
221%46%24%5%
315
16th to endDay
47%22%40%20%3
315
October1st to 15thDay
5%13%29%32%18%2
315
16th to endDay
8%9%25%30%22%3
336
November1st to 15thDay
12%5%22%27%27%5%
212
16th to endDay
9%10%23%31%23%
117
December1st to 15thDay
14%12%24%24%18%5%
90
16th to endDay
15%11%13%32%22%4
96
January1st to 15thNight
14%5%10%30%28%11%
780
16th to endNight
16%6%10%30%26%10%
832
February1st to 15thNight
14%6%10%31%28%9%
764
16th to endNight
13%11%11%35%21%6%
660
March1st to 15thNight
14%10%13%27%28%6%
720
16th to endNight
11%9%17%32%24%4
768
April1st to 15thNight
9%11%18%34%20%5%
719
16th to endNight
7%7%21%29%25%8%
720
May1st to 15thNight
3218%38%28%8%
636
16th to endNight
2314%37%34%6%
375
June1st to 15thNight
2317%37%33%5%
360
16th to endNight
17%47%38%5%
360
July1st to 15thNight
332%52%11%
357
16th to endNight
1225%55%15%
564
August1st to 15thNight
1430%51%11%
572
16th to endNight
430%52%12%
764
September1st to 15thNight
1428%50%14%
720
16th to endNight
217%31%41%15%
716
October1st to 15thNight
6%39%35%30%13%
720
16th to endNight
5%28%30%33%18%
768
November1st to 15thNight
8%412%30%32%11%
760
16th to endNight
11%49%33%31%9%
780
December1st to 15thNight
13%7%9%33%25%9%
780
16th to endNight
16%10%13%30%22%6%
832
Page generated at 2018-02-23 08:21:41. Version ac04

Copyright 2018 A. Danko


Del Valle Clear Sky Chart |Charts Home