Mount Diablo
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mount Diablo clear sky chart from 2005-11-05 to 2018-03-11.

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%
16054
29%
49128
26%
16017
72%
16017
44%
25205

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
60%
777
19%
2602
18%
776
64%
776
29%
1527
January16th to endNight
60%
832
24%
2704
24%
832
63%
832
30%
1589
February1st to 15thNight
57%
757
26%
2481
25%
757
64%
757
30%
1447
February16th to endNight
55%
684
27%
2051
22%
684
63%
684
33%
1199
March1st to 15thNight
54%
764
20%
2140
17%
764
57%
764
30%
1352
March16th to endNight
50%
768
22%
2082
15%
768
57%
768
34%
1274
April1st to 15thNight
50%
719
24%
1799
12%
719
55%
719
36%
1126
April16th to endNight
57%
720
27%
1800
12%
720
62%
720
50%
974
May1st to 15thNight
69%
617
30%
1697
19%
617
73%
617
62%
789
May16th to endNight
70%
375
30%
1497
29%
375
78%
375
55%
559
June1st to 15thNight
69%
360
28%
1440
28%
360
79%
360
51%
560
June16th to endNight
83%
360
38%
1440
47%
360
88%
360
71%
455
July1st to 15thNight
91%
358
35%
1378
42%
358
94%
358
79%
422
July16th to endNight
87%
564
39%
1593
34%
531
89%
531
74%
633
August1st to 15thNight
84%
559
39%
1632
29%
556
86%
556
74%
658
August16th to endNight
89%
764
44%
1910
29%
764
90%
764
83%
843
September1st to 15thNight
86%
720
42%
1800
29%
720
88%
720
79%
816
September16th to endNight
82%
716
45%
1958
39%
716
86%
716
71%
868
October1st to 15thNight
73%
720
32%
2160
32%
720
80%
720
56%
992
October16th to endNight
75%
768
38%
2304
40%
768
79%
768
53%
1112
November1st to 15thNight
70%
760
28%
2387
28%
760
75%
760
43%
1228
November16th to endNight
64%
780
26%
2631
27%
780
68%
780
34%
1435
December1st to 15thNight
58%
780
22%
2730
21%
780
63%
780
28%
1587
December16th to endNight
50%
832
22%
2912
20%
832
57%
832
24%
1760

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%
49500
Night
7%31332345%7%57%
49314
TransparencyDay
23%28%20%25%19%
49185
Night
24%29%20%23%18%
49129
SeeingDay
8%11%26%31%17%4
6539
Night
8%412%37%30%7%
16066

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
16%6%25%425%45%6%40%
1663
16th to endDay
14%7%26%5%345%45%41%
1872
February1st to 15thDay
14%7%34434446%43%
1711
16th to endDay
14%6%35%5%2445%8%40%
1709
March1st to 15thDay
13%6%35%6%35%47%8%36%
2053
16th to endDay
11%6%25%5%35%5%5%7%41%
2142
April1st to 15thDay
13%5%25%42445%7%43%
2149
16th to endDay
6%312223437%61%
2160
May1st to 15thDay
32221235%7%67%
2250
16th to endDay
4213323347%62%
2613
June1st to 15thDay
3212313347%65%
2520
16th to endDay
111235%80%
2520
July1st to 15thDay
111225%82%
2498
16th to endDay
112135%81%
2468
August1st to 15thDay
1111235%80%
2319
16th to endDay
11235%82%
2292
September1st to 15thDay
11111225%80%
2160
16th to endDay
212113236%73%
1998
October1st to 15thDay
3212322336%69%
1800
16th to endDay
6%313323345%63%
1920
November1st to 15thDay
8%4243245%5%8%50%
1802
16th to endDay
11%6%45%323346%47%
1657
December1st to 15thDay
14%8%35%323436%43%
1560
16th to endDay
17%7%35%42335%7%39%
1664
January1st to 15thNight
13%5%2423446%8%42%
2602
16th to endNight
14%42442345%6%46%
2704
February1st to 15thNight
12%5%2442445%5%47%
2469
16th to endNight
13%424324447%47%
2051
March1st to 15thNight
13%6%25%42445%8%42%
2140
16th to endNight
11%5%345%2435%6%48%
2082
April1st to 15thNight
8%4345%3446%6%48%
1799
16th to endNight
6%21332335%6%61%
1800
May1st to 15thNight
221222246%9%64%
1697
16th to endNight
2111225%46%10%61%
1497
June1st to 15thNight
2112223448%65%
1440
16th to endNight
1111326%78%
1440
July1st to 15thNight
112236%79%
1459
16th to endNight
111224410%68%
1701
August1st to 15thNight
11125%5%11%66%
1641
16th to endNight
111235%9%73%
1910
September1st to 15thNight
111113437%74%
1800
16th to endNight
11213338%72%
1958
October1st to 15thNight
4112313346%66%
2160
16th to endNight
5%3222336%6%62%
2304
November1st to 15thNight
7%41332445%8%55%
2387
16th to endNight
10%424324347%51%
2631
December1st to 15thNight
13%6%25%433447%45%
2730
16th to endNight
16%6%2432435%6%43%
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
41%412%17%18%4
1663
16th to endDay
43%48%15%19%8%
1872
February1st to 15thDay
40%39%20%21%4
1711
16th to endDay
40%310%24%16%3
1709
March1st to 15thDay
42%411%21%15%5%
2053
16th to endDay
38%5%14%19%17%3
2142
April1st to 15thDay
38%312%21%19%3
2149
16th to endDay
22%213%27%26%8%
2160
May1st to 15thDay
15%28%28%35%10%
2250
16th to endDay
18%212%31%25%9%
2617
June1st to 15thDay
17%310%23%25%20%
2520
16th to endDay
6%1316%34%37%
2520
July1st to 15thDay
5%129%24%56%
2350
16th to endDay
6%138%26%53%
2313
August1st to 15thDay
7%112%31%45%
2303
16th to endDay
5%114%39%38%
2292
September1st to 15thDay
7%1214%35%37%
2160
16th to endDay
12%1424%35%21%
1998
October1st to 15thDay
17%28%21%26%24%
1800
16th to endDay
21%110%24%26%15%
1920
November1st to 15thDay
30%411%30%16%6%
1802
16th to endDay
37%210%22%22%3
1657
December1st to 15thDay
41%39%19%19%6%
1560
16th to endDay
43%212%19%17%4
1664
January1st to 15thNight
36%313%22%16%7%
2602
16th to endNight
36%312%16%17%13%
2704
February1st to 15thNight
36%29%21%20%9%
2481
16th to endNight
33%312%27%18%3
2051
March1st to 15thNight
38%412%22%15%6%
2140
16th to endNight
34%313%21%18%7%
2082
April1st to 15thNight
32%414%23%18%5%
1799
16th to endNight
20%313%26%25%10%
1800
May1st to 15thNight
14%210%25%32%15%
1698
16th to endNight
13%214%31%27%10%
1497
June1st to 15thNight
14%39%23%25%23%
1440
16th to endNight
7%1214%30%43%
1440
July1st to 15thNight
5%18%23%60%
1378
16th to endNight
8%129%24%52%
1593
August1st to 15thNight
8%114%29%45%
1632
16th to endNight
6%110%38%42%
1910
September1st to 15thNight
7%1313%31%43%
1800
16th to endNight
10%1422%33%27%
1958
October1st to 15thNight
16%28%21%24%26%
2160
16th to endNight
20%17%24%26%20%
2304
November1st to 15thNight
24%312%31%19%8%
2387
16th to endNight
32%28%23%24%7%
2631
December1st to 15thNight
37%310%17%20%10%
2730
16th to endNight
40%311%18%18%6%
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
24%9%21%23%17%2
201
16th to endDay
15%11%18%27%22%4
304
February1st to 15thDay
18%11%20%23%22%3
281
16th to endDay
17%18%25%21%14%3
290
March1st to 15thDay
19%16%24%20%15%3
312
16th to endDay
14%21%30%22%8%2
288
April1st to 15thDay
17%23%27%17%10%2
269
16th to endDay
9%29%25%23%10%1
270
May1st to 15thDay
6%17%40%23%11%1
288
16th to endDay
6%13%32%30%14%2
330
June1st to 15thDay
5%16%38%28%7%2
315
16th to endDay
26%28%40%20%1
315
July1st to 15thDay
225%50%17%3
305
16th to endDay
226%48%14%7%
327
August1st to 15thDay
1427%44%18%3
315
16th to endDay
1223%43%21%8%
332
September1st to 15thDay
1323%42%21%7%
315
16th to endDay
27%26%32%22%9%
315
October1st to 15thDay
412%27%30%18%6%
315
16th to endDay
9%7%22%24%25%8%
336
November1st to 15thDay
11%9%16%25%28%7%
218
16th to endDay
9%11%21%35%21%
112
December1st to 15thDay
16%17%13%22%22%7%
90
16th to endDay
12%15%19%21%21%8%
96
January1st to 15thNight
15%38%31%30%8%
780
16th to endNight
15%49%33%27%8%
832
February1st to 15thNight
14%6%10%34%27%7%
764
16th to endNight
13%8%13%34%23%5%
684
March1st to 15thNight
15%8%12%31%26%4
764
16th to endNight
12%8%19%35%20%3
768
April1st to 15thNight
9%11%19%34%21%3
719
16th to endNight
7%8%21%34%23%5%
720
May1st to 15thNight
3318%44%25%5%
618
16th to endNight
3319%44%27%1
376
June1st to 15thNight
2319%52%20%1
360
16th to endNight
12%53%30%1
360
July1st to 15thNight
15%50%39%3
358
16th to endNight
16%39%46%6%
564
August1st to 15thNight
28%41%40%6%
559
16th to endNight
6%40%43%8%
764
September1st to 15thNight
118%36%42%9%
720
16th to endNight
129%36%38%11%
716
October1st to 15thNight
4410%40%30%9%
720
16th to endNight
5%29%32%35%13%
768
November1st to 15thNight
7%210%36%31%11%
760
16th to endNight
10%410%34%30%9%
780
December1st to 15thNight
15%5%9%36%25%8%
780
16th to endNight
18%7%13%32%24%3
832
Page generated at 2018-03-12 10:28:15. Version ac04

Copyright 2018 A. Danko


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