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 2017-08-12.

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%
15237
29%
46537
26%
15201
72%
15201
41%
24969

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%
716
19%
2403
19%
716
66%
716
28%
1427
January16th to endNight
58%
768
24%
2496
26%
768
61%
768
27%
1534
February1st to 15thNight
57%
699
24%
2275
25%
699
62%
699
26%
1410
February16th to endNight
56%
632
24%
1895
22%
632
61%
632
27%
1210
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%
557
39%
1606
30%
554
91%
554
71%
674
August16th to endNight
92%
700
41%
1750
27%
700
93%
700
79%
800
September1st to 15thNight
92%
660
44%
1650
33%
660
92%
660
79%
756
September16th to endNight
85%
656
43%
1790
38%
656
88%
656
67%
824
October1st to 15thNight
75%
660
31%
1980
32%
660
81%
660
48%
985
October16th to endNight
76%
704
35%
2112
37%
704
80%
704
47%
1091
November1st to 15thNight
70%
700
28%
2202
28%
700
74%
700
40%
1174
November16th to endNight
67%
720
26%
2409
27%
720
70%
720
33%
1344
December1st to 15thNight
57%
720
21%
2520
21%
720
62%
720
24%
1559
December16th to endNight
50%
768
21%
2688
20%
768
56%
768
22%
1703

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%
47435
Night
7%313323346%59%
46723
TransparencyDay
24%37%18%25%20%
47120
Night
26%47%17%22%20%
46538
SeeingDay
9%11%26%33%15%3
5840
Night
8%5%11%31%32%10%
15248

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
13%6%243235%47%45%
1534
16th to endDay
15%6%26%434345%44%
1728
February1st to 15thDay
13%8%245%24346%43%
1589
16th to endDay
16%6%35%5%2445%7%38%
1579
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%
2258
16th to endDay
11112486%
2100
September1st to 15thDay
11112287%
1980
16th to endDay
31121234475%
1837
October1st to 15thDay
3213312237%67%
1650
16th to endDay
6%32312446%63%
1760
November1st to 15thDay
8%32332446%7%51%
1655
16th to endDay
10%5%2442335%7%50%
1548
December1st to 15thDay
14%7%46%5%23446%41%
1440
16th to endDay
15%8%25%5%14346%40%
1536
January1st to 15thNight
11%424335%46%8%44%
2403
16th to endNight
13%5%24423446%47%
2496
February1st to 15thNight
12%5%244245%5%7%43%
2263
16th to endNight
12%6%2442447%7%43%
1895
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%
1615
16th to endNight
11114384%
1750
September1st to 15thNight
123385%
1650
16th to endNight
211111245%77%
1790
October1st to 15thNight
421222345%7%64%
1980
16th to endNight
4212323346%64%
2112
November1st to 15thNight
7%3222145%5%9%56%
2202
16th to endNight
8%424424448%51%
2409
December1st to 15thNight
12%7%25%5%2435%7%43%
2520
16th to endNight
16%6%2442445%6%42%
2688

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
38%410%20%16%8%
1534
16th to endDay
43%5%6%13%19%11%
1728
February1st to 15thDay
42%47%18%21%5%
1589
16th to endDay
45%47%24%14%2
1579
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
7%2110%28%49%
2242
16th to endDay
5%229%40%39%
2100
September1st to 15thDay
6%2212%33%43%
1980
16th to endDay
11%3322%34%24%
1837
October1st to 15thDay
20%27%22%25%20%
1650
16th to endDay
22%47%22%25%15%
1760
November1st to 15thDay
31%410%23%21%8%
1655
16th to endDay
35%48%20%27%4
1548
December1st to 15thDay
44%49%16%20%4
1440
16th to endDay
44%410%16%17%5%
1536
January1st to 15thNight
36%5%10%20%17%9%
2403
16th to endNight
39%49%12%17%16%
2496
February1st to 15thNight
39%5%7%20%19%7%
2275
16th to endNight
39%6%9%24%15%4
1895
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%418%25%51%
1606
16th to endNight
5%319%34%45%
1750
September1st to 15thNight
6%328%27%52%
1650
16th to endNight
11%3218%32%30%
1790
October1st to 15thNight
21%38%20%24%21%
1980
16th to endNight
21%5%421%28%18%
2112
November1st to 15thNight
25%5%10%23%23%10%
2202
16th to endNight
32%47%21%24%9%
2409
December1st to 15thNight
41%48%16%20%8%
2520
16th to endNight
43%49%15%18%7%
2688

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
19%17%23%30%7%1
162
16th to endDay
17%11%26%27%15%1
256
February1st to 15thDay
19%15%22%30%12%
239
16th to endDay
22%15%26%23%10%
238
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
3321%45%21%6%
300
16th to endDay
222%48%18%6%
268
September1st to 15thDay
321%45%23%6%
255
16th to endDay
5%7%20%41%20%4
255
October1st to 15thDay
6%11%29%33%16%2
255
16th to endDay
9%10%28%32%18%
272
November1st to 15thDay
11%6%20%25%29%6%
161
16th to endDay
8%14%28%26%20%1
78
December1st to 15thDay
21%15%33%23%6%
60
16th to endDay
20%10%15%34%15%3
64
January1st to 15thNight
13%5%10%30%27%12%
720
16th to endNight
16%6%10%29%25%11%
768
February1st to 15thNight
15%6%10%30%26%9%
704
16th to endNight
14%11%12%34%20%6%
632
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%
557
16th to endNight
5%30%52%10%
700
September1st to 15thNight
1426%51%14%
660
16th to endNight
27%30%42%16%
656
October1st to 15thNight
6%49%33%31%14%
660
16th to endNight
6%28%32%32%17%
704
November1st to 15thNight
8%412%29%32%12%
700
16th to endNight
10%49%33%31%10%
720
December1st to 15thNight
14%8%10%33%25%8%
720
16th to endNight
16%10%14%31%22%5%
768
Page generated at 2017-08-13 11:16:59. Version ac04

Copyright 2017 A. Danko


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