La Mesa Urban Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the La Mesa Urban Observatory clear sky chart from 2005-11-05 to 2017-09-23.

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
63%
15547
24%
46987
23%
15511
65%
15511
34%
27441

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
18%
2354
18%
716
65%
716
29%
1404
January16th to endNight
61%
768
24%
2496
26%
768
63%
768
26%
1552
February1st to 15thNight
57%
700
22%
2269
23%
700
60%
700
24%
1444
February16th to endNight
50%
632
20%
1895
20%
632
54%
632
23%
1279
March1st to 15thNight
56%
720
18%
2007
17%
720
58%
720
28%
1328
March16th to endNight
56%
768
19%
2085
16%
768
58%
768
29%
1377
April1st to 15thNight
52%
719
20%
1799
12%
719
53%
719
29%
1217
April16th to endNight
59%
720
22%
1800
11%
720
61%
720
38%
1126
May1st to 15thNight
62%
656
21%
1736
15%
656
63%
656
38%
1061
May16th to endNight
54%
420
20%
1543
18%
420
58%
420
27%
888
June1st to 15thNight
63%
360
21%
1440
24%
360
66%
360
30%
749
June16th to endNight
78%
360
31%
1440
40%
360
80%
360
51%
573
July1st to 15thNight
72%
417
23%
1437
26%
417
72%
417
48%
637
July16th to endNight
63%
564
25%
1593
23%
531
64%
531
41%
854
August1st to 15thNight
61%
583
22%
1656
17%
580
61%
580
39%
945
August16th to endNight
70%
764
29%
1910
19%
764
70%
764
54%
1061
September1st to 15thNight
79%
720
34%
1800
26%
720
79%
720
58%
952
September16th to endNight
77%
688
38%
1873
36%
688
78%
688
54%
963
October1st to 15thNight
75%
660
28%
1980
32%
660
76%
660
44%
1064
October16th to endNight
71%
704
31%
2112
35%
704
73%
704
39%
1168
November1st to 15thNight
68%
700
29%
2166
30%
700
70%
700
37%
1200
November16th to endNight
69%
720
26%
2388
28%
720
71%
720
34%
1317
December1st to 15thNight
58%
720
22%
2520
22%
720
62%
720
24%
1570
December16th to endNight
52%
768
20%
2688
20%
768
56%
768
21%
1712

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
7%5%2442445%9%49%
47912
Night
7%6%25%424447%48%
47178
TransparencyDay
30%47%19%23%14%
47603
Night
33%47%17%21%15%
46988
SeeingDay
9%8%22%35%20%4
6094
Night
10%48%27%35%12%
15557

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
12%4235%2445%7%47%
1581
16th to endDay
12%7%245%23346%45%
1728
February1st to 15thDay
13%6%34425%5%5%6%43%
1594
16th to endDay
14%8%25%6%2435%7%38%
1579
March1st to 15thDay
10%6%25%4246%6%11%38%
1950
16th to endDay
10%6%36%5%45%5%6%7%39%
2139
April1st to 15thDay
9%7%36%42446%7%42%
2149
16th to endDay
6%6%3442345%7%52%
2160
May1st to 15thDay
46%2432445%10%50%
2211
16th to endDay
9%8%2442445%9%43%
2567
June1st to 15thDay
5%5%35%5%3445%9%47%
2520
16th to endDay
232331335%10%59%
2520
July1st to 15thDay
25%234236%6%12%50%
2433
16th to endDay
142433446%12%51%
2468
August1st to 15thDay
26%35%5%2347%13%44%
2295
16th to endDay
425%42446%12%51%
2292
September1st to 15thDay
241232435%10%59%
2160
16th to endDay
4313213447%62%
1921
October1st to 15thDay
431332336%8%57%
1650
16th to endDay
5%5%2332445%7%55%
1760
November1st to 15thDay
8%424433447%52%
1690
16th to endDay
9%6%24323448%49%
1569
December1st to 15thDay
12%6%36%6%25%347%41%
1440
16th to endDay
14%5%35%5%23346%45%
1536
January1st to 15thNight
10%6%25%424448%46%
2354
16th to endNight
12%6%245%24446%47%
2496
February1st to 15thNight
12%6%35%42445%7%42%
2258
16th to endNight
14%7%35%42346%7%40%
1895
March1st to 15thNight
10%7%35%43445%8%42%
2007
16th to endNight
9%7%35%4245%49%42%
2085
April1st to 15thNight
11%6%25%4245%5%7%43%
1799
16th to endNight
7%424323349%54%
1800
May1st to 15thNight
47%34423448%51%
1736
16th to endNight
8%8%35%424348%44%
1542
June1st to 15thNight
5%7%345%34448%47%
1440
16th to endNight
15%15%323337%62%
1440
July1st to 15thNight
18%25%6%4436%8%48%
1523
16th to endNight
212%46%6%3445%10%37%
1701
August1st to 15thNight
311%5%9%5%44446%39%
1665
16th to endNight
16%39%6%333410%46%
1910
September1st to 15thNight
3414435%35%7%56%
1800
16th to endNight
35%22213348%61%
1873
October1st to 15thNight
6%31342345%7%56%
1980
16th to endNight
5%5%245%34447%54%
2112
November1st to 15thNight
7%5%24323448%52%
2166
16th to endNight
7%5%2331445%7%54%
2388
December1st to 15thNight
11%7%25%42445%7%44%
2520
16th to endNight
16%5%25%424346%44%
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
37%5%9%21%16%9%
1581
16th to endDay
41%5%7%12%21%12%
1728
February1st to 15thDay
40%47%18%21%6%
1594
16th to endDay
46%5%8%22%12%4
1579
March1st to 15thDay
40%8%11%18%14%6%
1950
16th to endDay
42%6%14%18%15%2
2139
April1st to 15thDay
42%6%10%23%14%2
2149
16th to endDay
33%412%24%18%6%
2160
May1st to 15thDay
29%38%28%23%6%
2211
16th to endDay
36%310%24%19%5%
2571
June1st to 15thDay
29%48%21%22%13%
2520
16th to endDay
16%1420%31%26%
2520
July1st to 15thDay
17%1210%29%38%
2291
16th to endDay
15%1315%32%31%
2313
August1st to 15thDay
21%1114%33%27%
2279
16th to endDay
15%1219%35%25%
2292
September1st to 15thDay
15%1317%32%30%
2160
16th to endDay
20%3423%29%18%
1921
October1st to 15thDay
24%49%22%24%15%
1650
16th to endDay
26%48%24%20%16%
1760
November1st to 15thDay
31%5%8%21%25%6%
1690
16th to endDay
33%5%10%17%26%7%
1569
December1st to 15thDay
44%5%7%16%18%7%
1440
16th to endDay
42%5%12%16%16%6%
1536
January1st to 15thNight
37%411%17%19%9%
2354
16th to endNight
40%5%8%12%16%17%
2496
February1st to 15thNight
41%5%7%17%18%8%
2269
16th to endNight
44%6%8%22%12%4
1895
March1st to 15thNight
41%5%11%17%16%7%
2007
16th to endNight
39%6%12%17%17%6%
2085
April1st to 15thNight
40%5%11%23%14%3
1799
16th to endNight
30%6%11%23%19%7%
1800
May1st to 15thNight
32%47%20%24%9%
1737
16th to endNight
37%49%20%22%6%
1543
June1st to 15thNight
31%48%19%17%19%
1440
16th to endNight
17%1413%28%34%
1440
July1st to 15thNight
21%116%28%40%
1437
16th to endNight
29%2310%24%29%
1593
August1st to 15thNight
33%1111%23%28%
1656
16th to endNight
24%115%27%30%
1910
September1st to 15thNight
19%1211%29%34%
1800
16th to endNight
20%2221%32%20%
1873
October1st to 15thNight
26%37%22%22%17%
1980
16th to endNight
28%45%23%22%15%
2112
November1st to 15thNight
29%49%22%25%9%
2166
16th to endNight
30%5%9%20%23%10%
2388
December1st to 15thNight
40%6%9%14%20%9%
2520
16th to endNight
42%6%10%17%14%8%
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
21%14%20%20%20%2
210
16th to endDay
17%11%24%25%17%3
256
February1st to 15thDay
15%12%25%25%16%4
239
16th to endDay
18%13%29%28%9%1
238
March1st to 15thDay
13%15%30%24%14%2
270
16th to endDay
12%15%35%27%8%1
288
April1st to 15thDay
16%17%30%26%7%
269
16th to endDay
8%20%32%27%10%1
270
May1st to 15thDay
9%13%30%32%11%3
288
16th to endDay
13%11%23%31%15%4
330
June1st to 15thDay
7%7%29%38%13%2
315
16th to endDay
220%45%26%4
315
July1st to 15thDay
412%49%26%6%
305
16th to endDay
112%47%29%9%
327
August1st to 15thDay
3114%51%23%5%
315
16th to endDay
111%51%28%6%
332
September1st to 15thDay
3314%45%28%5%
315
16th to endDay
5%7%15%34%29%7%
284
October1st to 15thDay
6%7%23%37%21%3
255
16th to endDay
9%427%30%25%2
272
November1st to 15thDay
10%6%16%27%29%10%
196
16th to endDay
7%14%17%34%22%3
81
December1st to 15thDay
21%10%25%23%18%1
60
16th to endDay
14%12%7%29%28%7%
64
January1st to 15thNight
13%5%9%31%29%10%
720
16th to endNight
16%5%9%27%30%10%
768
February1st to 15thNight
13%6%11%29%29%8%
704
16th to endNight
17%8%14%27%27%5%
632
March1st to 15thNight
14%8%12%27%29%8%
720
16th to endNight
11%8%14%27%31%5%
768
April1st to 15thNight
13%11%14%28%26%6%
719
16th to endNight
10%6%15%25%30%10%
720
May1st to 15thNight
7%311%33%33%10%
657
16th to endNight
13%310%25%33%12%
421
June1st to 15thNight
7%310%34%36%7%
360
16th to endNight
2428%49%14%
360
July1st to 15thNight
2122%51%22%
417
16th to endNight
320%48%27%
564
August1st to 15thNight
6%225%49%16%
583
16th to endNight
2223%53%17%
764
September1st to 15thNight
5%120%51%21%
720
16th to endNight
6%2423%42%21%
688
October1st to 15thNight
8%2428%36%18%
660
16th to endNight
7%36%26%34%21%
704
November1st to 15thNight
10%38%27%36%14%
700
16th to endNight
9%49%29%34%12%
720
December1st to 15thNight
15%49%32%28%9%
720
16th to endNight
19%8%11%31%23%5%
768
Page generated at 2017-09-24 06:15:58. Version ac04

Copyright 2017 A. Danko


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