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 2019-06-24.

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%
17859
24%
54056
23%
17823
65%
17823
34%
31558

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%
836
19%
2748
19%
836
63%
836
27%
1688
January16th to endNight
61%
896
22%
2912
24%
896
63%
896
25%
1834
February1st to 15thNight
57%
820
23%
2655
25%
820
60%
820
24%
1677
February16th to endNight
50%
736
20%
2207
19%
736
53%
736
23%
1482
March1st to 15thNight
52%
840
18%
2342
16%
840
55%
840
25%
1588
March16th to endNight
57%
896
19%
2433
17%
896
59%
896
29%
1595
April1st to 15thNight
52%
839
20%
2099
12%
839
54%
839
28%
1430
April16th to endNight
59%
832
22%
2080
11%
832
61%
832
39%
1290
May1st to 15thNight
60%
766
21%
2026
15%
766
61%
766
37%
1257
May16th to endNight
51%
492
17%
1807
16%
492
55%
492
23%
1108
June1st to 15thNight
65%
420
24%
1680
28%
420
68%
420
33%
838
June16th to endNight
76%
406
29%
1624
37%
406
78%
406
49%
663
July1st to 15thNight
72%
454
24%
1564
27%
454
72%
454
49%
691
July16th to endNight
64%
612
25%
1737
22%
579
65%
579
43%
916
August1st to 15thNight
61%
622
24%
1767
18%
619
62%
619
40%
995
August16th to endNight
70%
828
28%
2070
18%
828
70%
828
54%
1142
September1st to 15thNight
78%
780
35%
1950
27%
780
78%
780
60%
1024
September16th to endNight
79%
776
38%
2120
36%
776
80%
776
56%
1061
October1st to 15thNight
76%
780
29%
2340
33%
780
77%
780
46%
1231
October16th to endNight
73%
832
32%
2496
36%
832
74%
832
43%
1338
November1st to 15thNight
70%
820
31%
2537
33%
820
72%
820
40%
1371
November16th to endNight
67%
840
25%
2786
27%
840
69%
840
31%
1599
December1st to 15thNight
61%
840
24%
2940
25%
840
64%
840
26%
1767
December16th to endNight
53%
896
21%
3136
21%
896
57%
896
22%
1973

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%48%
54755
Night
8%6%25%42445%8%47%
54247
TransparencyDay
30%47%20%23%14%
54446
Night
33%47%17%21%15%
54057
SeeingDay
9%8%20%33%21%5%
8355
Night
10%48%27%36%12%
17869

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%5%245%34446%43%
1846
16th to endDay
11%6%246%2345%6%44%
2016
February1st to 15thDay
13%6%24425%5%5%6%44%
1868
16th to endDay
13%7%25%6%2435%7%39%
1839
March1st to 15thDay
11%7%25%5%246%6%10%37%
2275
16th to endDay
10%6%36%5%45%5%5%8%40%
2495
April1st to 15thDay
10%7%36%43446%7%41%
2509
16th to endDay
6%6%35%42335%7%51%
2485
May1st to 15thDay
46%2442445%10%49%
2581
16th to endDay
10%10%25%42445%8%40%
3006
June1st to 15thDay
45%25%5%2445%9%49%
2940
16th to endDay
242331335%10%58%
2844
July1st to 15thDay
25%234235%6%13%50%
2636
16th to endDay
142433446%13%51%
2676
August1st to 15thDay
26%35%5%2347%13%44%
2437
16th to endDay
425%42447%12%49%
2484
September1st to 15thDay
231232335%10%59%
2340
16th to endDay
3213313447%62%
2167
October1st to 15thDay
431332335%7%60%
1950
16th to endDay
5%5%23323447%56%
2080
November1st to 15thDay
7%314434447%53%
1978
16th to endDay
10%6%2432345%8%48%
1831
December1st to 15thDay
11%5%35%5%24347%43%
1680
16th to endDay
12%5%35%5%2335%6%46%
1792
January1st to 15thNight
11%6%25%5%2445%8%42%
2748
16th to endNight
12%6%245%34447%45%
2912
February1st to 15thNight
12%6%25%5%2445%7%42%
2644
16th to endNight
14%7%35%42345%7%41%
2207
March1st to 15thNight
11%8%35%5%345%5%7%39%
2342
16th to endNight
10%6%35%4245%49%43%
2433
April1st to 15thNight
11%6%26%4245%5%8%42%
2099
16th to endNight
7%42432335%9%52%
2080
May1st to 15thNight
5%8%35%5%23448%48%
2026
16th to endNight
11%10%35%424348%40%
1806
June1st to 15thNight
46%345%3445%8%48%
1680
16th to endNight
26%15%423337%58%
1624
July1st to 15thNight
17%25%6%4436%8%48%
1650
16th to endNight
211%47%6%45%45%10%36%
1845
August1st to 15thNight
211%5%9%5%34446%39%
1776
16th to endNight
17%39%6%3435%10%45%
2070
September1st to 15thNight
3415%435%35%7%55%
1950
16th to endNight
3422213348%62%
2120
October1st to 15thNight
5%313423446%59%
2340
16th to endNight
45%24433347%54%
2496
November1st to 15thNight
6%5%24323448%53%
2537
16th to endNight
8%5%2431445%7%51%
2786
December1st to 15thNight
10%7%25%42445%7%46%
2940
16th to endNight
15%5%25%424346%44%
3136

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%9%19%15%8%
1846
16th to endDay
41%6%7%13%20%11%
2016
February1st to 15thDay
40%47%17%21%7%
1868
16th to endDay
44%6%8%21%13%4
1839
March1st to 15thDay
42%7%10%18%14%5%
2275
16th to endDay
42%6%13%18%16%2
2495
April1st to 15thDay
42%6%10%23%14%2
2509
16th to endDay
32%411%27%19%5%
2485
May1st to 15thDay
29%39%28%22%5%
2581
16th to endDay
40%310%22%17%4
3010
June1st to 15thDay
26%48%22%24%12%
2940
16th to endDay
15%1321%32%25%
2844
July1st to 15thDay
17%1210%30%37%
2494
16th to endDay
14%1416%33%29%
2521
August1st to 15thDay
20%1113%33%29%
2421
16th to endDay
15%1220%36%23%
2484
September1st to 15thDay
14%1318%31%30%
2340
16th to endDay
18%2422%31%19%
2167
October1st to 15thDay
22%48%21%24%19%
1950
16th to endDay
24%47%23%21%18%
2080
November1st to 15thDay
30%5%8%21%24%8%
1978
16th to endDay
34%5%11%17%25%6%
1831
December1st to 15thDay
41%5%7%17%16%11%
1680
16th to endDay
40%5%11%18%16%7%
1792
January1st to 15thNight
39%411%17%18%8%
2748
16th to endNight
40%5%8%13%15%15%
2912
February1st to 15thNight
41%5%7%16%19%10%
2655
16th to endNight
44%6%8%22%13%4
2207
March1st to 15thNight
43%5%11%16%15%6%
2342
16th to endNight
38%6%11%19%17%5%
2433
April1st to 15thNight
40%6%11%23%14%3
2099
16th to endNight
30%6%10%25%20%6%
2080
May1st to 15thNight
34%47%21%23%9%
2027
16th to endNight
42%48%19%19%5%
1807
June1st to 15thNight
28%47%21%20%17%
1680
16th to endNight
19%1413%28%33%
1624
July1st to 15thNight
20%117%30%37%
1564
16th to endNight
27%2313%26%27%
1737
August1st to 15thNight
31%1111%23%29%
1767
16th to endNight
23%1115%28%30%
2070
September1st to 15thNight
19%1212%30%33%
1950
16th to endNight
19%2319%32%22%
2120
October1st to 15thNight
24%37%20%22%21%
2340
16th to endNight
26%35%22%23%18%
2496
November1st to 15thNight
27%410%21%24%11%
2537
16th to endNight
32%6%9%20%22%9%
2786
December1st to 15thNight
37%6%8%15%18%13%
2940
16th to endNight
41%5%10%17%16%8%
3136

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
25%12%18%20%21%2
295
16th to endDay
16%11%21%28%19%4
352
February1st to 15thDay
16%14%23%22%16%6%
333
16th to endDay
18%16%27%25%11%1
342
March1st to 15thDay
17%14%27%24%12%2
390
16th to endDay
13%14%31%27%10%1
416
April1st to 15thDay
16%17%27%26%10%1
389
16th to endDay
8%16%27%27%15%4
378
May1st to 15thDay
8%10%28%34%15%3
408
16th to endDay
15%12%25%29%13%3
458
June1st to 15thDay
6%5%23%37%21%5%
435
16th to endDay
118%44%28%5%
408
July1st to 15thDay
310%48%29%7%
365
16th to endDay
110%45%32%10%
391
August1st to 15thDay
3113%48%26%7%
359
16th to endDay
111%49%30%7%
396
September1st to 15thDay
2217%43%28%5%
375
16th to endDay
45%15%35%30%8%
375
October1st to 15thDay
5%6%22%37%24%4
375
16th to endDay
6%321%28%31%9%
400
November1st to 15thDay
6%5%15%28%32%10%
304
16th to endDay
11%12%15%29%23%7%
163
December1st to 15thDay
17%8%19%22%23%9%
120
16th to endDay
10%14%9%28%26%10%
128
January1st to 15thNight
14%5%9%31%28%9%
840
16th to endNight
16%5%9%27%32%9%
896
February1st to 15thNight
14%7%11%28%29%8%
824
16th to endNight
17%9%13%26%27%5%
736
March1st to 15thNight
15%8%12%28%27%7%
840
16th to endNight
13%7%13%30%30%5%
896
April1st to 15thNight
14%10%13%28%27%5%
839
16th to endNight
10%6%14%26%30%11%
832
May1st to 15thNight
8%310%32%33%11%
767
16th to endNight
15%310%25%32%11%
493
June1st to 15thNight
6%29%32%39%9%
420
16th to endNight
2429%47%14%
406
July1st to 15thNight
2120%52%22%
454
16th to endNight
219%50%26%
612
August1st to 15thNight
5%125%49%17%
622
16th to endNight
2223%53%17%
828
September1st to 15thNight
4122%50%20%
780
16th to endNight
5%1324%43%21%
776
October1st to 15thNight
7%2431%37%15%
780
16th to endNight
6%35%25%35%23%
832
November1st to 15thNight
8%37%29%37%13%
820
16th to endNight
10%48%30%33%12%
840
December1st to 15thNight
14%48%32%29%10%
840
16th to endNight
18%8%10%30%25%5%
896
Page generated at 2019-06-24 17:41:28. Version ac04

Copyright 2019 A. Danko


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