Casa Victoria Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Casa Victoria Observatory clear sky chart from 2005-11-05 to 2018-04-23.

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
58%
16592
31%
49547
21%
16549
68%
16549
46%
25450

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
58%
816
34%
2560
25%
814
70%
814
53%
1192
January16th to endNight
53%
832
36%
2704
25%
832
68%
832
50%
1253
February1st to 15thNight
51%
762
29%
2402
21%
760
61%
760
45%
1186
February16th to endNight
40%
684
36%
2050
18%
684
59%
684
47%
1030
March1st to 15thNight
49%
780
34%
2211
19%
780
61%
780
48%
1155
March16th to endNight
50%
777
36%
2233
19%
777
63%
777
50%
1105
April1st to 15thNight
39%
584
32%
1948
16%
584
60%
584
42%
934
April16th to endNight
41%
558
35%
1859
20%
558
64%
558
44%
879
May1st to 15thNight
47%
540
26%
1799
19%
539
61%
539
40%
899
May16th to endNight
56%
563
31%
1547
17%
561
69%
561
50%
797
June1st to 15thNight
62%
540
26%
1440
16%
540
69%
540
52%
759
June16th to endNight
71%
540
25%
1440
20%
540
74%
540
49%
769
July1st to 15thNight
76%
510
16%
1426
15%
510
77%
510
33%
881
July16th to endNight
78%
564
16%
1593
16%
531
79%
531
31%
964
August1st to 15thNight
78%
539
15%
1713
16%
536
79%
536
30%
1030
August16th to endNight
77%
573
22%
1910
25%
573
79%
573
32%
1105
September1st to 15thNight
72%
540
23%
1800
23%
540
76%
540
30%
1048
September16th to endNight
68%
560
35%
1931
31%
560
75%
560
43%
930
October1st to 15thNight
63%
720
34%
2160
23%
720
70%
720
50%
1071
October16th to endNight
64%
768
40%
2304
25%
768
75%
768
58%
1054
November1st to 15thNight
62%
852
38%
2372
23%
852
71%
852
63%
1096
November16th to endNight
62%
975
40%
2535
25%
975
69%
975
58%
1296
December1st to 15thNight
49%
975
31%
2698
17%
975
61%
975
48%
1413
December16th to endNight
46%
1040
32%
2912
18%
1040
57%
1040
45%
1604

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
221332445%8%61%
49963
Night
331332345%7%61%
49740
TransparencyDay
20%5%10%22%26%13%
49655
Night
21%5%10%22%26%13%
49549
SeeingDay
5%10%28%31%19%4
6256
Night
5%427%40%20%1
16596

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
1213213446%68%
1719
16th to endDay
331323245%68%
1872
February1st to 15thDay
231332325%6%64%
1790
16th to endDay
242331235%9%61%
1710
March1st to 15thDay
332221345%8%61%
2077
16th to endDay
2222223447%64%
2343
April1st to 15thDay
221332345%7%62%
2330
16th to endDay
3312323346%65%
2215
May1st to 15thDay
12133235%6%8%61%
2151
16th to endDay
2212223447%67%
2560
June1st to 15thDay
11221446%7%66%
2520
16th to endDay
11131445%7%68%
2520
July1st to 15thDay
24145%36%8%7%11%43%
2445
16th to endDay
33245%37%8%9%12%40%
2467
August1st to 15thDay
22135%35%7%8%12%47%
2236
16th to endDay
3313435%6%8%11%46%
2292
September1st to 15thDay
6%3134345%7%10%48%
2160
16th to endDay
3112323346%66%
2026
October1st to 15thDay
5%11231233468%
1800
16th to endDay
22222223474%
1920
November1st to 15thDay
1111112447%70%
1802
16th to endDay
3311213235%70%
1755
December1st to 15thDay
2412322346%65%
1589
16th to endDay
35%1442335%8%57%
1664
January1st to 15thNight
2312212236%69%
2560
16th to endNight
4312212336%68%
2704
February1st to 15thNight
35%23213346%63%
2392
16th to endNight
25%23222346%62%
2050
March1st to 15thNight
35%13323346%62%
2211
16th to endNight
3312312336%67%
2233
April1st to 15thNight
331232435%8%60%
1948
16th to endNight
33431343466%
1859
May1st to 15thNight
331332445%7%60%
1799
16th to endNight
221221345%8%64%
1547
June1st to 15thNight
1134245%6%8%61%
1440
16th to endNight
133245%7%8%61%
1440
July1st to 15thNight
33145%45%7%10%12%42%
1512
16th to endNight
32145%46%6%10%13%41%
1701
August1st to 15thNight
3323436%8%10%11%41%
1722
16th to endNight
32146%45%7%9%11%44%
1910
September1st to 15thNight
43235%36%7%8%11%43%
1800
16th to endNight
4213313346%64%
1931
October1st to 15thNight
4212214335%67%
2160
16th to endNight
3112212245%71%
2304
November1st to 15thNight
121212336%74%
2372
16th to endNight
3212213235%71%
2535
December1st to 15thNight
441231235%6%64%
2698
16th to endNight
45%14323347%60%
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
16%411%30%32%4
1720
16th to endDay
19%39%25%33%8%
1872
February1st to 15thDay
21%411%29%23%10%
1791
16th to endDay
20%37%24%31%12%
1710
March1st to 15thDay
20%38%22%31%13%
2077
16th to endDay
19%39%22%33%12%
2343
April1st to 15thDay
20%48%20%31%13%
2330
16th to endDay
20%38%18%32%16%
2215
May1st to 15thDay
20%6%10%17%30%15%
2151
16th to endDay
18%48%19%26%22%
2563
June1st to 15thDay
15%5%10%16%21%30%
2520
16th to endDay
14%5%9%18%23%29%
2520
July1st to 15thDay
31%10%15%14%14%12%
2302
16th to endDay
29%12%19%27%10%1
2312
August1st to 15thDay
26%11%18%21%15%6%
2221
16th to endDay
27%10%14%23%17%5%
2292
September1st to 15thDay
29%8%15%22%16%8%
2160
16th to endDay
18%47%21%30%17%
2026
October1st to 15thDay
18%46%18%31%19%
1800
16th to endDay
14%37%20%36%17%
1920
November1st to 15thDay
13%37%24%37%13%
1802
16th to endDay
17%26%23%36%12%
1755
December1st to 15thDay
19%413%32%24%5%
1589
16th to endDay
25%414%26%25%3
1664
January1st to 15thNight
17%49%32%30%6%
2560
16th to endNight
18%39%24%36%7%
2704
February1st to 15thNight
21%411%28%23%10%
2402
16th to endNight
22%26%21%32%13%
2050
March1st to 15thNight
22%36%24%30%12%
2211
16th to endNight
19%36%21%35%14%
2233
April1st to 15thNight
21%48%21%28%15%
1948
16th to endNight
20%37%18%31%17%
1859
May1st to 15thNight
22%5%9%17%28%16%
1800
16th to endNight
18%6%12%19%20%23%
1548
June1st to 15thNight
18%6%13%15%17%28%
1440
16th to endNight
18%7%11%15%17%28%
1440
July1st to 15thNight
29%11%18%16%12%12%
1426
16th to endNight
28%12%24%22%10%1
1593
August1st to 15thNight
28%13%21%18%12%6%
1713
16th to endNight
28%10%17%24%12%6%
1910
September1st to 15thNight
28%11%19%18%14%8%
1800
16th to endNight
21%5%9%16%26%19%
1931
October1st to 15thNight
19%47%17%29%21%
2160
16th to endNight
14%37%17%36%19%
2304
November1st to 15thNight
13%27%24%38%13%
2372
16th to endNight
18%25%22%34%16%
2535
December1st to 15thNight
20%410%31%26%6%
2698
16th to endNight
24%5%11%30%24%3
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
7%8%39%31%12%
135
16th to endDay
5%11%33%29%19%
144
February1st to 15thDay
212%36%37%11%
135
16th to endDay
10%17%40%24%7%
120
March1st to 15thDay
5%19%33%30%9%
262
16th to endDay
6%25%38%21%6%
352
April1st to 15thDay
6%28%35%19%7%
329
16th to endDay
9%26%42%15%6%
288
May1st to 15thDay
419%45%21%7%
288
16th to endDay
5%9%32%37%13%1
483
June1st to 15thDay
27%24%36%25%3
495
16th to endDay
2218%34%36%5%
495
July1st to 15thDay
4114%35%35%7%
406
16th to endDay
5%7%32%36%17%
327
August1st to 15thDay
3113%38%33%8%
315
16th to endDay
6%16%38%30%7%
332
September1st to 15thDay
6%122%43%19%6%
315
16th to endDay
6%5%29%42%14%1
207
October1st to 15thDay
39%35%30%17%3
135
16th to endDay
6%6%27%31%20%7%
144
November1st to 15thDay
5%11%34%31%15%2
135
16th to endDay
8%8%43%26%12%
135
December1st to 15thDay
5%14%35%29%14%
135
16th to endDay
8%9%41%35%4
144
January1st to 15thNight
5%329%43%16%1
818
16th to endNight
6%433%39%14%1
832
February1st to 15thNight
7%433%43%10%
764
16th to endNight
6%8%43%36%4
684
March1st to 15thNight
6%6%34%42%10%
780
16th to endNight
49%33%42%9%
777
April1st to 15thNight
413%39%35%7%
584
16th to endNight
6%8%40%36%8%
558
May1st to 15thNight
5%7%35%38%13%
540
16th to endNight
4432%40%17%
563
June1st to 15thNight
2327%45%20%
540
16th to endNight
1220%45%29%1
540
July1st to 15thNight
410%40%41%3
510
16th to endNight
46%28%54%6%
564
August1st to 15thNight
47%29%50%7%
539
16th to endNight
39%38%41%6%
573
September1st to 15thNight
5%112%42%35%2
540
16th to endNight
7%218%43%24%3
560
October1st to 15thNight
5%225%44%19%2
720
16th to endNight
4224%39%24%4
768
November1st to 15thNight
3327%43%20%1
852
16th to endNight
5%5%24%43%18%3
975
December1st to 15thNight
7%6%32%40%11%
975
16th to endNight
8%436%39%10%
1040
Page generated at 2018-04-24 08:03:06. Version ac04

Copyright 2018 A. Danko


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