Diablo Valley College
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Diablo Valley College 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
65%
15205
25%
46543
22%
15169
69%
15169
36%
26088

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
61%
716
18%
2395
18%
716
65%
716
27%
1451
January16th to endNight
58%
768
24%
2496
25%
768
61%
768
27%
1540
February1st to 15thNight
55%
698
22%
2288
22%
698
61%
698
24%
1436
February16th to endNight
53%
632
22%
1900
18%
632
60%
632
28%
1210
March1st to 15thNight
52%
720
18%
2010
15%
720
55%
720
27%
1327
March16th to endNight
51%
768
21%
2088
15%
768
56%
768
30%
1352
April1st to 15thNight
49%
719
23%
1799
11%
719
54%
719
33%
1175
April16th to endNight
56%
720
25%
1800
12%
720
61%
720
44%
1051
May1st to 15thNight
70%
608
25%
1688
16%
608
73%
608
47%
893
May16th to endNight
64%
382
24%
1504
23%
382
71%
382
37%
710
June1st to 15thNight
67%
360
23%
1440
24%
360
75%
360
36%
672
June16th to endNight
80%
360
34%
1440
44%
360
85%
360
58%
522
July1st to 15thNight
87%
365
29%
1385
36%
365
89%
365
61%
514
July16th to endNight
83%
564
29%
1593
27%
531
84%
531
50%
753
August1st to 15thNight
79%
537
28%
1586
22%
534
80%
534
48%
782
August16th to endNight
84%
700
30%
1750
18%
700
84%
700
57%
943
September1st to 15thNight
84%
660
36%
1650
25%
660
85%
660
63%
844
September16th to endNight
80%
656
36%
1799
32%
656
84%
656
57%
898
October1st to 15thNight
71%
660
30%
1980
30%
660
77%
660
43%
1025
October16th to endNight
71%
704
31%
2112
32%
704
74%
704
41%
1153
November1st to 15thNight
68%
700
27%
2193
26%
700
73%
700
39%
1188
November16th to endNight
64%
720
24%
2439
26%
720
67%
720
32%
1371
December1st to 15thNight
55%
720
20%
2520
18%
720
60%
720
22%
1585
December16th to endNight
49%
768
20%
2688
18%
768
56%
768
22%
1693

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%313323346%60%
47433
Night
7%31332345%8%55%
46730
TransparencyDay
26%5%9%18%23%16%
47119
Night
28%6%10%18%20%15%
46544
SeeingDay
8%10%27%33%15%3
5848
Night
8%415%36%28%5%
15217

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
15%5%345%1445%6%42%
1540
16th to endDay
14%6%25%5%34345%44%
1728
February1st to 15thDay
14%7%25%5%24446%41%
1576
16th to endDay
15%6%35%6%2445%6%39%
1573
March1st to 15thDay
12%6%36%5%25%46%8%38%
1948
16th to endDay
10%5%25%6%35%45%8%41%
2136
April1st to 15thDay
12%6%25%42445%7%43%
2149
16th to endDay
5%414213347%60%
2160
May1st to 15thDay
231122235%8%67%
2260
16th to endDay
421331235%7%63%
2607
June1st to 15thDay
321221346%7%64%
2520
16th to endDay
11111246%78%
2520
July1st to 15thDay
111245%79%
2490
16th to endDay
1112235%78%
2468
August1st to 15thDay
11212336%76%
2277
16th to endDay
1113245%78%
2100
September1st to 15thDay
111212326%77%
1980
16th to endDay
2111212345%73%
1829
October1st to 15thDay
4212314436%65%
1650
16th to endDay
6%413322346%60%
1760
November1st to 15thDay
7%42333446%7%52%
1666
16th to endDay
10%7%26%32345%5%47%
1520
December1st to 15thDay
14%10%36%41444442%
1440
16th to endDay
17%7%24424447%40%
1536
January1st to 15thNight
12%5%2432445%8%45%
2395
16th to endNight
13%5%24324446%47%
2496
February1st to 15thNight
12%6%25%5%34445%44%
2276
16th to endNight
13%4244245%5%8%44%
1900
March1st to 15thNight
12%6%35%423448%43%
2010
16th to endNight
10%5%34434446%48%
2088
April1st to 15thNight
8%5%1442446%8%48%
1799
16th to endNight
5%21331435%7%61%
1800
May1st to 15thNight
22321335%9%64%
1688
16th to endNight
21223346%9%61%
1504
June1st to 15thNight
21122226%5%10%62%
1440
16th to endNight
1112346%76%
1440
July1st to 15thNight
111225%10%72%
1467
16th to endNight
1215%5%8%12%59%
1701
August1st to 15thNight
1112235%9%14%56%
1595
16th to endNight
221448%11%62%
1750
September1st to 15thNight
11121245%9%68%
1650
16th to endNight
11222235%8%69%
1799
October1st to 15thNight
421331345%7%62%
1980
16th to endNight
5%21342446%7%57%
2112
November1st to 15thNight
6%323314349%55%
2193
16th to endNight
7%5%33433446%53%
2439
December1st to 15thNight
13%7%25%424447%43%
2520
16th to endNight
16%5%25%324446%43%
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
41%5%14%15%17%5%
1540
16th to endDay
43%5%8%12%19%9%
1728
February1st to 15thDay
43%5%8%19%20%3
1576
16th to endDay
44%6%9%23%12%3
1573
March1st to 15thDay
42%5%12%19%14%5%
1948
16th to endDay
41%6%13%17%17%3
2136
April1st to 15thDay
40%414%18%18%2
2149
16th to endDay
24%6%12%26%23%7%
2160
May1st to 15thDay
17%6%7%28%30%9%
2260
16th to endDay
22%8%11%27%23%7%
2611
June1st to 15thDay
20%7%10%21%23%16%
2520
16th to endDay
9%5%416%33%29%
2520
July1st to 15thDay
9%5%6%8%24%46%
2343
16th to endDay
9%45%8%24%46%
2313
August1st to 15thDay
12%46%11%28%36%
2261
16th to endDay
10%5%413%38%28%
2100
September1st to 15thDay
11%46%11%33%32%
1980
16th to endDay
15%4423%31%20%
1829
October1st to 15thDay
21%47%21%27%17%
1650
16th to endDay
25%49%23%24%12%
1760
November1st to 15thDay
31%5%12%27%15%7%
1666
16th to endDay
38%5%8%19%22%5%
1520
December1st to 15thDay
44%5%9%19%18%3
1440
16th to endDay
44%5%11%18%16%4
1536
January1st to 15thNight
37%6%11%19%16%8%
2395
16th to endNight
39%49%14%17%14%
2496
February1st to 15thNight
40%5%9%19%17%7%
2288
16th to endNight
38%6%12%24%15%2
1900
March1st to 15thNight
41%5%12%19%15%5%
2010
16th to endNight
37%6%11%19%18%5%
2088
April1st to 15thNight
34%7%14%19%18%4
1799
16th to endNight
24%6%12%25%22%9%
1800
May1st to 15thNight
19%8%10%21%28%12%
1689
16th to endNight
20%8%15%25%21%8%
1504
June1st to 15thNight
20%8%11%19%22%16%
1440
16th to endNight
10%46%15%32%30%
1440
July1st to 15thNight
10%410%7%20%47%
1385
16th to endNight
16%6%12%11%15%36%
1593
August1st to 15thNight
17%7%12%10%22%29%
1586
16th to endNight
14%8%10%10%26%29%
1750
September1st to 15thNight
13%5%10%8%26%36%
1650
16th to endNight
15%5%5%21%28%23%
1799
October1st to 15thNight
22%5%7%22%23%18%
1980
16th to endNight
25%5%8%20%23%15%
2112
November1st to 15thNight
27%5%13%28%16%8%
2193
16th to endNight
32%5%8%21%24%8%
2439
December1st to 15thNight
41%6%9%17%18%7%
2520
16th to endNight
42%5%11%15%18%6%
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
22%10%24%24%14%2
168
16th to endDay
16%10%21%28%17%3
256
February1st to 15thDay
21%9%23%25%19%2
236
16th to endDay
19%13%23%26%14%2
237
March1st to 15thDay
18%17%25%19%15%4
270
16th to endDay
13%20%31%22%10%1
288
April1st to 15thDay
17%21%28%21%8%1
269
16th to endDay
11%24%27%24%8%2
270
May1st to 15thDay
6%15%38%31%7%
288
16th to endDay
6%13%29%36%13%1
330
June1st to 15thDay
5%14%38%31%6%2
315
16th to endDay
1432%42%17%1
315
July1st to 15thDay
129%50%18%
305
16th to endDay
127%48%16%5%
327
August1st to 15thDay
2328%45%17%3
300
16th to endDay
130%48%15%2
268
September1st to 15thDay
2317%50%18%7%
255
16th to endDay
38%24%33%21%8%
255
October1st to 15thDay
6%9%27%33%16%6%
255
16th to endDay
13%8%27%26%21%2
272
November1st to 15thDay
7%8%20%20%34%7%
172
16th to endDay
6%16%28%30%17%
73
December1st to 15thDay
18%23%28%20%10%
60
16th to endDay
14%15%20%25%21%3
64
January1st to 15thNight
15%311%34%27%7%
720
16th to endNight
16%413%31%25%7%
768
February1st to 15thNight
14%6%14%33%25%5%
704
16th to endNight
14%7%19%29%23%5%
632
March1st to 15thNight
16%7%16%28%27%4
720
16th to endNight
12%7%21%35%19%2
768
April1st to 15thNight
9%10%24%33%18%2
719
16th to endNight
6%9%24%33%22%4
720
May1st to 15thNight
3318%45%25%2
609
16th to endNight
4325%40%24%2
383
June1st to 15thNight
2323%50%18%1
360
16th to endNight
16%52%29%1
360
July1st to 15thNight
110%46%39%1
365
16th to endNight
119%40%40%6%
564
August1st to 15thNight
2114%37%39%4
537
16th to endNight
11%46%34%5%
700
September1st to 15thNight
19%37%41%7%
660
16th to endNight
1111%36%38%9%
656
October1st to 15thNight
5%5%13%35%32%7%
660
16th to endNight
6%314%30%32%12%
704
November1st to 15thNight
7%216%31%33%8%
700
16th to endNight
9%6%13%31%29%8%
720
December1st to 15thNight
16%7%13%34%21%6%
720
16th to endNight
18%7%17%32%22%1
768
Page generated at 2017-08-13 11:16:13. Version ac04

Copyright 2017 A. Danko


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