San Bernardino County Museum
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the San Bernardino County Museum clear sky chart from 2005-11-05 to 2017-09-18.

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
78%
15991
34%
46762
31%
15950
80%
15950
52%
23109

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
68%
716
31%
2327
31%
716
73%
716
43%
1162
January16th to endNight
63%
768
33%
2316
27%
768
71%
768
39%
1275
February1st to 15thNight
70%
697
32%
2107
32%
697
74%
697
44%
1116
February16th to endNight
64%
632
28%
1895
31%
632
66%
632
33%
1129
March1st to 15thNight
69%
720
30%
2160
30%
720
74%
720
43%
1152
March16th to endNight
74%
768
30%
2029
26%
768
77%
768
49%
1113
April1st to 15thNight
67%
719
27%
1799
19%
719
69%
719
45%
1059
April16th to endNight
74%
720
32%
1800
21%
720
76%
720
54%
984
May1st to 15thNight
75%
572
32%
1652
23%
572
77%
572
54%
818
May16th to endNight
78%
561
31%
1685
26%
561
78%
561
51%
832
June1st to 15thNight
86%
540
32%
1620
30%
540
86%
540
62%
724
June16th to endNight
96%
417
41%
1497
45%
417
96%
417
80%
483
July1st to 15thNight
94%
409
35%
1429
36%
409
94%
409
69%
514
July16th to endNight
89%
612
33%
1637
27%
575
89%
575
63%
749
August1st to 15thNight
94%
717
38%
1790
25%
713
94%
713
79%
812
August16th to endNight
96%
764
45%
1910
30%
764
96%
764
80%
861
September1st to 15thNight
90%
720
39%
1860
32%
720
90%
720
69%
877
September16th to endNight
90%
667
46%
1847
44%
667
91%
667
75%
782
October1st to 15thNight
80%
660
38%
1815
36%
660
82%
660
57%
906
October16th to endNight
79%
704
39%
2136
39%
704
82%
704
55%
1003
November1st to 15thNight
81%
700
35%
2275
38%
700
84%
700
55%
1009
November16th to endNight
74%
720
37%
2340
40%
720
78%
720
47%
1132
December1st to 15thNight
67%
720
32%
2340
32%
720
72%
720
37%
1253
December16th to endNight
61%
768
33%
2496
30%
768
68%
768
37%
1364

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
5%212212336%68%
48010
Night
6%312212235%68%
46963
TransparencyDay
18%35%15%27%29%
47706
Night
19%35%15%26%28%
46768
SeeingDay
6%6%24%38%18%5%
5904
Night
6%17%32%38%12%
16005

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
8%212312346%62%
1611
16th to endDay
10%31321335%5%58%
1906
February1st to 15thDay
9%311322236%62%
1751
16th to endDay
14%5%13313246%51%
1579
March1st to 15thDay
6%3122135%5%7%60%
1800
16th to endDay
6%3222435%8%59%
2190
April1st to 15thDay
7%412324337%57%
2149
16th to endDay
6%312212135%69%
2160
May1st to 15thDay
4413312235%67%
2295
16th to endDay
4412212336%66%
2429
June1st to 15thDay
3311212236%71%
2340
16th to endDay
111287%
2454
July1st to 15thDay
1111112335%74%
2439
16th to endDay
212213346%70%
2416
August1st to 15thDay
111132482%
2160
16th to endDay
1111233480%
2292
September1st to 15thDay
211111235%78%
2100
16th to endDay
111122482%
1838
October1st to 15thDay
5%222222225%69%
1815
16th to endDay
5%3112223472%
1734
November1st to 15thDay
3212222335%70%
1584
16th to endDay
6%223212246%64%
1620
December1st to 15thDay
7%313213349%58%
1620
16th to endDay
13%312312346%57%
1728
January1st to 15thNight
8%313313235%63%
2327
16th to endNight
11%423222335%58%
2316
February1st to 15thNight
9%31331234462%
2101
16th to endNight
16%5%13123345%52%
1895
March1st to 15thNight
7%5%13323247%59%
2160
16th to endNight
7%412212347%62%
2029
April1st to 15thNight
9%5%13312335%59%
1799
16th to endNight
7%312212235%67%
1800
May1st to 15thNight
4313211126%68%
1652
16th to endNight
4312211236%68%
1684
June1st to 15thNight
22122225%75%
1620
16th to endNight
11389%
1497
July1st to 15thNight
11112135%79%
1515
16th to endNight
2112212345%73%
1749
August1st to 15thNight
1111222482%
1800
16th to endNight
1122385%
1910
September1st to 15thNight
12121212479%
1860
16th to endNight
1111111384%
1847
October1st to 15thNight
5%21231223472%
1815
16th to endNight
431221223372%
2136
November1st to 15thNight
3212212235%72%
2275
16th to endNight
6%312312345%63%
2340
December1st to 15thNight
10%313323347%57%
2340
16th to endNight
11%413213335%59%
2496

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
23%35%13%26%26%
1612
16th to endDay
27%36%13%21%26%
1906
February1st to 15thDay
24%35%13%26%26%
1751
16th to endDay
35%4414%26%14%
1579
March1st to 15thDay
21%47%19%23%22%
1800
16th to endDay
22%6%9%23%23%15%
2190
April1st to 15thDay
26%5%7%22%25%13%
2149
16th to endDay
18%38%20%29%18%
2160
May1st to 15thDay
20%46%20%27%21%
2295
16th to endDay
19%37%25%30%13%
2432
June1st to 15thDay
16%2317%33%25%
2340
16th to endDay
6%236%26%55%
2454
July1st to 15thDay
12%3411%24%44%
2296
16th to endDay
14%47%20%26%26%
2265
August1st to 15thDay
6%3311%32%43%
2146
16th to endDay
9%339%35%38%
2292
September1st to 15thDay
10%2410%32%40%
2100
16th to endDay
8%2211%32%42%
1838
October1st to 15thDay
19%3414%29%28%
1815
16th to endDay
16%3410%22%41%
1734
November1st to 15thDay
16%37%12%26%32%
1584
16th to endDay
22%5%411%23%33%
1620
December1st to 15thDay
24%5%8%17%19%25%
1620
16th to endDay
29%5%7%16%23%18%
1728
January1st to 15thNight
25%25%13%24%28%
2327
16th to endNight
28%47%12%19%28%
2316
February1st to 15thNight
25%36%14%22%27%
2112
16th to endNight
34%4416%23%15%
1895
March1st to 15thNight
25%46%18%24%21%
2160
16th to endNight
22%410%22%24%15%
2029
April1st to 15thNight
27%48%24%20%14%
1799
16th to endNight
20%46%23%26%18%
1800
May1st to 15thNight
18%38%22%26%20%
1653
16th to endNight
19%49%26%26%13%
1685
June1st to 15thNight
13%36%17%31%28%
1620
16th to endNight
4137%25%56%
1497
July1st to 15thNight
8%2410%28%45%
1429
16th to endNight
13%38%21%29%24%
1637
August1st to 15thNight
6%3214%36%37%
1790
16th to endNight
6%2212%35%40%
1910
September1st to 15thNight
11%3410%33%37%
1860
16th to endNight
8%1113%32%41%
1847
October1st to 15thNight
18%2415%34%23%
1815
16th to endNight
18%2310%22%42%
2136
November1st to 15thNight
16%35%14%26%34%
2275
16th to endNight
22%2414%20%35%
2340
December1st to 15thNight
27%5%5%15%20%25%
2340
16th to endNight
29%48%12%25%19%
2496

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
30%310%44%10%2
90
16th to endDay
14%6%25%34%16%2
274
February1st to 15thDay
9%6%30%30%18%4
266
16th to endDay
18%12%24%30%12%
238
March1st to 15thDay
11%9%25%32%16%4
270
16th to endDay
8%10%33%31%13%2
288
April1st to 15thDay
10%16%30%28%10%3
269
16th to endDay
418%40%27%6%2
270
May1st to 15thDay
10%10%31%31%11%4
288
16th to endDay
10%6%31%33%14%3
330
June1st to 15thDay
5%329%36%20%5%
315
16th to endDay
20%40%23%13%
315
July1st to 15thDay
111%49%26%10%
305
16th to endDay
118%47%27%12%
327
August1st to 15thDay
115%53%17%10%
315
16th to endDay
29%53%21%12%
332
September1st to 15thDay
3123%50%16%5%
315
16th to endDay
1228%44%18%4
264
October1st to 15thDay
5%7%30%39%16%1
255
16th to endDay
8%5%21%34%26%3
212
November1st to 15thDay
3214%32%32%15%
90
16th to endDay
47%26%34%26%
90
December1st to 15thDay
45%17%43%24%4
90
16th to endDay
15%7%16%36%21%2
96
January1st to 15thNight
10%112%41%24%10%
720
16th to endNight
12%213%35%27%8%
768
February1st to 15thNight
9%211%40%27%9%
704
16th to endNight
17%49%39%23%7%
632
March1st to 15thNight
8%211%41%27%7%
720
16th to endNight
6%39%39%31%8%
768
April1st to 15thNight
10%411%41%26%6%
719
16th to endNight
7%311%39%30%8%
720
May1st to 15thNight
5%110%34%38%8%
573
16th to endNight
5%19%36%38%8%
563
June1st to 15thNight
26%36%48%5%
540
16th to endNight
129%59%8%
417
July1st to 15thNight
214%65%16%
409
16th to endNight
2111%66%15%
612
August1st to 15thNight
117%59%20%
717
16th to endNight
110%59%28%
764
September1st to 15thNight
2120%51%22%
720
16th to endNight
1326%49%18%
667
October1st to 15thNight
5%16%36%38%11%
660
16th to endNight
6%26%29%36%17%
704
November1st to 15thNight
418%37%34%14%
700
16th to endNight
7%19%34%33%13%
720
December1st to 15thNight
11%210%36%29%9%
720
16th to endNight
14%215%37%22%7%
768
Page generated at 2017-09-19 04:32:21. Version ac04

Copyright 2017 A. Danko


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