La Mesa
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the La Mesa clear sky chart from 2005-11-05 to 2018-01-12.

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
74%
16729
30%
48414
28%
16685
75%
16685
43%
26705

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
72%
761
28%
2455
29%
760
74%
760
39%
1303
January16th to endNight
68%
768
34%
2304
33%
768
72%
768
40%
1283
February1st to 15thNight
72%
698
32%
2108
33%
698
75%
698
42%
1132
February16th to endNight
63%
632
27%
1895
31%
632
64%
632
31%
1174
March1st to 15thNight
70%
720
28%
2160
32%
720
72%
720
40%
1195
March16th to endNight
70%
768
25%
2035
24%
768
71%
768
40%
1225
April1st to 15thNight
66%
719
25%
1799
19%
719
67%
719
41%
1116
April16th to endNight
69%
720
27%
1800
19%
720
70%
720
44%
1089
May1st to 15thNight
68%
590
25%
1670
18%
590
68%
590
36%
1031
May16th to endNight
64%
561
22%
1685
17%
561
65%
561
33%
1051
June1st to 15thNight
67%
540
20%
1620
17%
540
67%
540
35%
1014
June16th to endNight
82%
540
30%
1620
27%
540
82%
540
54%
802
July1st to 15thNight
81%
510
22%
1530
19%
510
81%
510
45%
831
July16th to endNight
79%
645
27%
1668
20%
606
78%
606
43%
959
August1st to 15thNight
79%
717
29%
1790
19%
713
79%
713
53%
985
August16th to endNight
84%
764
36%
1910
25%
764
84%
764
57%
1029
September1st to 15thNight
83%
720
32%
1872
28%
720
83%
720
53%
1018
September16th to endNight
84%
716
42%
1980
41%
716
85%
716
62%
932
October1st to 15thNight
79%
720
33%
1980
32%
720
80%
720
49%
1044
October16th to endNight
76%
768
37%
2289
39%
768
77%
768
46%
1176
November1st to 15thNight
79%
760
31%
2470
37%
760
80%
760
46%
1201
November16th to endNight
78%
780
35%
2535
40%
780
79%
780
44%
1266
December1st to 15thNight
69%
780
31%
2535
33%
780
71%
780
36%
1370
December16th to endNight
68%
832
33%
2704
34%
832
71%
832
37%
1479

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%413323346%61%
48907
Night
6%6%24323447%55%
48620
TransparencyDay
23%26%17%25%23%
48610
Night
28%26%16%22%23%
48419
SeeingDay
8%5%24%39%17%4
6327
Night
8%25%31%39%12%
16741

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%324423346%57%
1725
16th to endDay
10%424312346%54%
1920
February1st to 15thDay
7%314413447%56%
1751
16th to endDay
10%5%35%4345%47%45%
1579
March1st to 15thDay
6%42332435%9%55%
1800
16th to endDay
5%324334348%56%
2183
April1st to 15thDay
6%5%2333345%6%53%
2149
16th to endDay
5%412212247%65%
2160
May1st to 15thDay
6%423422446%59%
2277
16th to endDay
45%23322337%61%
2429
June1st to 15thDay
5%6%13313436%60%
2340
16th to endDay
1313213345%71%
2340
July1st to 15thDay
25%1332345%7%59%
2340
16th to endDay
231231446%8%59%
2383
August1st to 15thDay
1312212345%70%
2160
16th to endDay
121221245%7%68%
2292
September1st to 15thDay
1212323345%68%
2086
16th to endDay
221221223474%
1980
October1st to 15thDay
3423324346%62%
1980
16th to endDay
5%412211235%67%
1932
November1st to 15thDay
5%313424446%60%
1719
16th to endDay
5%413313346%61%
1755
December1st to 15thDay
6%413333448%55%
1755
16th to endDay
10%413314337%54%
1872
January1st to 15thNight
7%423323446%56%
2455
16th to endNight
10%414313346%56%
2304
February1st to 15thNight
7%315%32335%5%57%
2101
16th to endNight
11%7%35%423445%46%
1895
March1st to 15thNight
7%5%24323348%52%
2160
16th to endNight
6%7%3332446%8%49%
2035
April1st to 15thNight
9%7%24413348%51%
1799
16th to endNight
7%7%34313346%55%
1800
May1st to 15thNight
6%11%35%334349%44%
1670
16th to endNight
8%11%36%323437%43%
1684
June1st to 15thNight
5%11%45%5%2446%7%41%
1620
16th to endNight
15%2442345%7%58%
1620
July1st to 15thNight
29%2442446%8%49%
1620
16th to endNight
35%245%3446%8%49%
1782
August1st to 15thNight
26%15%4244410%54%
1800
16th to endNight
15%13312447%63%
1910
September1st to 15thNight
2413423446%62%
1872
16th to endNight
342222237%67%
1980
October1st to 15thNight
3413423347%60%
1980
16th to endNight
6%5%13323336%60%
2289
November1st to 15thNight
4423313436%62%
2470
16th to endNight
4313433347%58%
2535
December1st to 15thNight
8%424423447%54%
2535
16th to endNight
11%324313345%55%
2704

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
29%25%15%21%25%
1726
16th to endDay
30%36%15%14%29%
1920
February1st to 15thDay
27%26%14%22%26%
1751
16th to endDay
37%46%15%23%12%
1579
March1st to 15thDay
25%37%20%21%21%
1800
16th to endDay
27%37%25%20%14%
2183
April1st to 15thDay
29%37%23%26%9%
2149
16th to endDay
19%28%25%23%19%
2160
May1st to 15thDay
25%36%22%25%16%
2277
16th to endDay
23%27%23%32%9%
2432
June1st to 15thDay
25%25%17%28%19%
2340
16th to endDay
13%138%29%43%
2340
July1st to 15thDay
21%2414%27%28%
2201
16th to endDay
20%311%24%28%11%
2235
August1st to 15thDay
16%1418%34%24%
2146
16th to endDay
14%3417%34%27%
2292
September1st to 15thDay
16%2313%35%28%
2086
16th to endDay
13%2312%36%31%
1980
October1st to 15thDay
23%2416%26%26%
1980
16th to endDay
20%2313%22%37%
1932
November1st to 15thDay
24%26%16%16%32%
1719
16th to endDay
23%3415%19%33%
1755
December1st to 15thDay
27%38%14%17%27%
1755
16th to endDay
30%47%15%21%20%
1872
January1st to 15thNight
28%36%14%20%27%
2455
16th to endNight
30%27%12%14%31%
2304
February1st to 15thNight
27%27%14%19%27%
2112
16th to endNight
39%25%14%21%16%
1895
March1st to 15thNight
29%37%19%17%22%
2160
16th to endNight
31%49%20%21%13%
2035
April1st to 15thNight
33%27%24%21%10%
1799
16th to endNight
30%27%20%20%18%
1800
May1st to 15thNight
35%37%20%16%16%
1671
16th to endNight
38%38%21%16%11%
1685
June1st to 15thNight
38%18%16%21%13%
1620
16th to endNight
21%1212%27%35%
1620
July1st to 15thNight
27%2413%26%24%
1530
16th to endNight
29%39%23%25%8%
1668
August1st to 15thNight
23%1422%30%16%
1790
16th to endNight
20%2414%32%26%
1910
September1st to 15thNight
22%3313%30%27%
1872
16th to endNight
15%1212%37%30%
1980
October1st to 15thNight
23%25%19%23%24%
1980
16th to endNight
24%2212%20%36%
2289
November1st to 15thNight
23%26%17%15%33%
2470
16th to endNight
25%25%16%18%31%
2535
December1st to 15thNight
30%37%14%17%26%
2535
16th to endNight
30%38%14%19%23%
2704

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%220%30%18%2
138
16th to endDay
13%8%33%33%10%1
288
February1st to 15thDay
8%7%31%33%14%3
266
16th to endDay
10%14%37%26%9%1
238
March1st to 15thDay
8%9%32%33%12%4
270
16th to endDay
6%12%33%35%10%3
288
April1st to 15thDay
10%13%39%23%9%3
269
16th to endDay
5%12%41%29%6%4
270
May1st to 15thDay
13%9%32%31%10%2
288
16th to endDay
13%7%30%35%12%1
330
June1st to 15thDay
7%228%43%14%3
315
16th to endDay
2114%51%23%6%
315
July1st to 15thDay
7%19%49%26%6%
305
16th to endDay
7%451%25%9%
327
August1st to 15thDay
412%54%22%6%
315
16th to endDay
5%9%50%26%7%
332
September1st to 15thDay
4121%53%14%4
315
16th to endDay
4423%48%12%6%
315
October1st to 15thDay
45%37%35%13%3
315
16th to endDay
11%124%32%21%7%
279
November1st to 15thDay
8%315%34%30%6%
135
16th to endDay
11%6%16%27%27%10%
135
December1st to 15thDay
5%314%41%28%5%
135
16th to endDay
13%414%32%27%8%
144
January1st to 15thNight
9%27%39%28%12%
764
16th to endNight
13%28%35%31%9%
768
February1st to 15thNight
7%37%36%34%10%
704
16th to endNight
13%38%42%25%5%
632
March1st to 15thNight
9%5%6%41%30%7%
720
16th to endNight
9%36%36%36%7%
768
April1st to 15thNight
11%38%40%30%5%
719
16th to endNight
10%47%38%29%9%
720
May1st to 15thNight
10%27%36%35%7%
591
16th to endNight
14%28%32%36%6%
563
June1st to 15thNight
10%7%37%37%5%
540
16th to endNight
2230%55%8%
540
July1st to 15thNight
5%118%60%13%
510
16th to endNight
5%112%56%22%
645
August1st to 15thNight
5%15%55%21%
717
16th to endNight
49%54%31%
764
September1st to 15thNight
5%18%55%19%
720
16th to endNight
5%227%48%16%
716
October1st to 15thNight
7%1335%41%9%
720
16th to endNight
10%1329%36%19%
768
November1st to 15thNight
6%1336%36%14%
760
16th to endNight
6%1433%37%17%
780
December1st to 15thNight
10%36%37%30%11%
780
16th to endNight
13%27%34%30%11%
832
Page generated at 2018-01-12 19:01:29. Version ac04

Copyright 2018 A. Danko


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