Vista
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vista clear sky chart from 2005-11-05 to 2018-02-14.

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%
16868
29%
48828
27%
16824
75%
16824
41%
27555

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
74%
777
29%
2506
31%
776
76%
776
40%
1315
January16th to endNight
68%
832
33%
2496
33%
832
71%
832
40%
1381
February1st to 15thNight
74%
754
33%
2274
35%
754
77%
754
43%
1219
February16th to endNight
62%
632
26%
1895
29%
632
63%
632
29%
1196
March1st to 15thNight
72%
720
27%
2160
31%
720
73%
720
39%
1197
March16th to endNight
72%
768
23%
2029
21%
768
73%
768
39%
1234
April1st to 15thNight
65%
719
24%
1799
17%
719
66%
719
38%
1124
April16th to endNight
72%
720
27%
1800
18%
720
73%
720
43%
1088
May1st to 15thNight
67%
593
23%
1674
17%
593
67%
593
33%
1077
May16th to endNight
64%
561
20%
1685
17%
561
64%
561
30%
1095
June1st to 15thNight
63%
540
16%
1620
14%
540
63%
540
27%
1098
June16th to endNight
80%
540
24%
1620
21%
540
80%
540
43%
906
July1st to 15thNight
77%
510
20%
1530
17%
510
77%
510
39%
895
July16th to endNight
78%
645
22%
1668
17%
606
77%
606
38%
1021
August1st to 15thNight
75%
717
25%
1790
15%
713
75%
713
43%
1100
August16th to endNight
83%
764
33%
1910
24%
764
83%
764
55%
1049
September1st to 15thNight
83%
720
32%
1863
27%
720
83%
720
51%
1028
September16th to endNight
85%
716
40%
1980
39%
716
85%
716
56%
975
October1st to 15thNight
79%
720
33%
1980
33%
720
80%
720
50%
1051
October16th to endNight
75%
768
36%
2305
39%
768
75%
768
45%
1196
November1st to 15thNight
81%
760
31%
2470
36%
760
81%
760
46%
1213
November16th to endNight
78%
780
34%
2535
38%
780
79%
780
42%
1304
December1st to 15thNight
70%
780
31%
2535
34%
780
72%
780
38%
1346
December16th to endNight
67%
832
33%
2704
33%
832
72%
832
38%
1447

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
4413313347%62%
49230
Night
6%6%24323347%54%
49035
TransparencyDay
22%37%17%24%23%
48933
Night
29%37%15%21%22%
48834
SeeingDay
7%320%40%22%6%
6459
Night
8%16%30%40%12%
16880

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%5%13313346%58%
1760
16th to endDay
8%413323246%57%
2080
February1st to 15thDay
7%213323345%60%
1883
16th to endDay
11%5%24424347%49%
1579
March1st to 15thDay
4323323349%58%
1800
16th to endDay
5%32332245%9%57%
2190
April1st to 15thDay
6%314424348%56%
2149
16th to endDay
4312312346%65%
2160
May1st to 15thDay
5%5%23314337%58%
2274
16th to endDay
46%22212247%61%
2429
June1st to 15thDay
5%8%23212336%59%
2340
16th to endDay
1412213235%71%
2340
July1st to 15thDay
25%1331345%7%60%
2340
16th to endDay
231322435%8%61%
2382
August1st to 15thDay
2412212335%71%
2160
16th to endDay
1212213338%69%
2292
September1st to 15thDay
2212212337%69%
2097
16th to endDay
1212212236%72%
1980
October1st to 15thDay
3314313346%63%
1980
16th to endDay
5%312212235%68%
1914
November1st to 15thDay
431232345%7%62%
1719
16th to endDay
5%31231235%7%62%
1755
December1st to 15thDay
6%213323449%57%
1755
16th to endDay
10%313323346%56%
1872
January1st to 15thNight
6%414323347%57%
2506
16th to endNight
9%424313245%57%
2496
February1st to 15thNight
7%324313445%59%
2269
16th to endNight
12%6%346%23435%46%
1895
March1st to 15thNight
7%6%23324348%54%
2160
16th to endNight
6%6%234235%48%51%
2029
April1st to 15thNight
9%8%34313347%50%
1799
16th to endNight
6%7%23313337%56%
1800
May1st to 15thNight
9%10%3432345%9%43%
1673
16th to endNight
8%12%36%423347%44%
1684
June1st to 15thNight
7%13%47%5%23348%38%
1620
16th to endNight
28%3431436%10%50%
1620
July1st to 15thNight
410%244235%5%10%45%
1620
16th to endNight
47%24335%5%6%10%45%
1782
August1st to 15thNight
210%235%245%410%49%
1800
16th to endNight
26%13213349%60%
1910
September1st to 15thNight
26%13324347%60%
1863
16th to endNight
2411213346%67%
1980
October1st to 15thNight
2323324347%61%
1980
16th to endNight
7%5%13312236%61%
2305
November1st to 15thNight
3323324336%63%
2470
16th to endNight
4423424447%57%
2535
December1st to 15thNight
7%42442335%6%55%
2535
16th to endNight
11%413323346%57%
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
27%27%15%22%24%
1761
16th to endDay
28%37%16%15%28%
2080
February1st to 15thDay
24%47%14%22%26%
1883
16th to endDay
34%48%17%25%10%
1579
March1st to 15thDay
23%39%21%20%21%
1800
16th to endDay
24%5%11%24%20%13%
2190
April1st to 15thDay
26%48%26%22%10%
2149
16th to endDay
19%411%22%24%17%
2160
May1st to 15thDay
26%38%20%23%16%
2274
16th to endDay
23%39%26%28%9%
2432
June1st to 15thDay
27%3416%30%16%
2340
16th to endDay
17%248%24%43%
2340
July1st to 15thDay
22%36%12%24%30%
2201
16th to endDay
20%5%10%22%26%14%
2234
August1st to 15thDay
16%2415%32%29%
2146
16th to endDay
14%35%13%33%28%
2292
September1st to 15thDay
16%35%11%33%29%
2097
16th to endDay
15%2310%35%31%
1980
October1st to 15thDay
21%35%18%24%26%
1980
16th to endDay
19%25%12%20%38%
1914
November1st to 15thDay
21%39%17%17%30%
1719
16th to endDay
21%47%14%19%32%
1755
December1st to 15thDay
25%310%15%17%27%
1755
16th to endDay
29%38%16%22%19%
1872
January1st to 15thNight
27%37%13%20%27%
2506
16th to endNight
29%37%13%15%31%
2496
February1st to 15thNight
26%36%15%21%25%
2280
16th to endNight
40%35%13%22%14%
1895
March1st to 15thNight
29%47%19%18%20%
2160
16th to endNight
30%6%11%17%19%14%
2029
April1st to 15thNight
34%38%22%19%11%
1799
16th to endNight
28%5%9%19%19%17%
1800
May1st to 15thNight
37%5%9%15%16%15%
1674
16th to endNight
40%48%19%16%10%
1685
June1st to 15thNight
44%47%10%21%11%
1620
16th to endNight
26%46%8%24%29%
1620
July1st to 15thNight
32%27%12%20%23%
1530
16th to endNight
31%5%10%19%22%9%
1668
August1st to 15thNight
29%5%5%17%26%15%
1790
16th to endNight
21%26%12%31%24%
1910
September1st to 15thNight
24%25%11%29%26%
1863
16th to endNight
18%2413%32%28%
1980
October1st to 15thNight
23%36%18%25%22%
1980
16th to endNight
25%2411%19%35%
2305
November1st to 15thNight
23%37%17%16%32%
2470
16th to endNight
26%37%14%16%31%
2535
December1st to 15thNight
29%38%14%17%26%
2535
16th to endNight
29%39%13%22%21%
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
23%39%34%26%3
149
16th to endDay
11%326%35%16%6%
352
February1st to 15thDay
7%5%23%35%19%8%
320
16th to endDay
11%8%34%33%11%1
238
March1st to 15thDay
6%6%29%34%17%5%
270
16th to endDay
6%6%29%40%11%5%
288
April1st to 15thDay
9%6%36%30%13%4
269
16th to endDay
39%36%35%10%5%
270
May1st to 15thDay
10%5%27%42%11%2
288
16th to endDay
10%426%39%16%2
330
June1st to 15thDay
8%23%41%22%3
315
16th to endDay
211%46%30%7%
315
July1st to 15thDay
5%7%45%31%8%
305
16th to endDay
6%242%38%10%
327
August1st to 15thDay
5%8%48%30%6%
315
16th to endDay
5%6%43%36%7%
332
September1st to 15thDay
415%53%22%3
315
16th to endDay
4119%46%20%6%
315
October1st to 15thDay
5%426%39%20%4
315
16th to endDay
7%119%37%21%11%
282
November1st to 15thDay
5%211%33%33%13%
135
16th to endDay
5%5%14%33%28%13%
135
December1st to 15thDay
2116%36%31%11%
135
16th to endDay
11%213%29%32%10%
144
January1st to 15thNight
8%17%40%31%10%
780
16th to endNight
12%18%36%33%8%
832
February1st to 15thNight
8%16%35%35%11%
760
16th to endNight
14%38%40%27%6%
632
March1st to 15thNight
10%18%40%32%7%
720
16th to endNight
9%25%37%36%8%
768
April1st to 15thNight
11%410%36%31%5%
719
16th to endNight
8%28%37%33%9%
720
May1st to 15thNight
11%38%32%35%8%
594
16th to endNight
11%311%29%38%5%
563
June1st to 15thNight
12%26%33%38%5%
540
16th to endNight
41225%57%7%
540
July1st to 15thNight
8%215%55%17%
510
16th to endNight
7%129%53%25%
645
August1st to 15thNight
7%2212%54%20%
717
16th to endNight
5%19%52%30%
764
September1st to 15thNight
6%214%57%18%
720
16th to endNight
41226%49%15%
716
October1st to 15thNight
5%5%35%44%9%
720
16th to endNight
10%1427%38%17%
768
November1st to 15thNight
41436%39%13%
760
16th to endNight
6%15%31%37%17%
780
December1st to 15thNight
9%18%37%33%8%
780
16th to endNight
13%210%35%28%9%
832
Page generated at 2018-02-15 07:58:45. Version ac04

Copyright 2018 A. Danko


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