VERITAS
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the VERITAS clear sky chart from 2005-11-05 to 2017-09-17.

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%
15594
35%
46906
31%
15555
79%
15555
52%
22709

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%
719
33%
2327
34%
716
79%
716
51%
1076
January16th to endNight
65%
768
34%
2496
32%
768
73%
768
39%
1301
February1st to 15thNight
70%
698
37%
2186
35%
698
79%
698
53%
1012
February16th to endNight
64%
632
39%
1829
35%
632
71%
632
47%
948
March1st to 15thNight
66%
720
40%
1980
31%
720
74%
720
58%
968
March16th to endNight
71%
768
38%
2112
28%
768
79%
768
59%
1024
April1st to 15thNight
67%
691
35%
1950
25%
691
75%
691
55%
946
April16th to endNight
69%
540
44%
1800
38%
540
80%
540
68%
675
May1st to 15thNight
71%
539
41%
1619
31%
539
80%
539
71%
649
May16th to endNight
75%
561
43%
1684
33%
561
83%
561
74%
664
June1st to 15thNight
83%
540
35%
1620
30%
540
84%
540
69%
672
June16th to endNight
86%
540
30%
1620
26%
540
86%
540
60%
735
July1st to 15thNight
81%
510
18%
1530
16%
510
81%
510
38%
872
July16th to endNight
79%
564
14%
1593
11%
531
79%
531
25%
1046
August1st to 15thNight
85%
539
23%
1611
21%
536
85%
536
38%
905
August16th to endNight
83%
609
28%
1893
27%
609
83%
609
36%
1078
September1st to 15thNight
78%
720
27%
1980
23%
720
79%
720
39%
1175
September16th to endNight
85%
664
42%
1837
34%
664
88%
664
66%
855
October1st to 15thNight
77%
660
40%
1914
31%
660
84%
660
64%
866
October16th to endNight
84%
704
43%
2112
38%
704
87%
704
68%
900
November1st to 15thNight
78%
700
42%
2100
36%
700
84%
700
68%
885
November16th to endNight
68%
720
38%
2277
36%
720
73%
720
50%
1081
December1st to 15thNight
70%
720
37%
2340
38%
720
74%
720
48%
1094
December16th to endNight
64%
768
34%
2496
34%
768
69%
768
42%
1282

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
4313323446%62%
47861
Night
3212323346%66%
47106
TransparencyDay
23%36%10%26%29%
47556
Night
19%36%13%27%29%
46912
SeeingDay
8%8%21%31%22%8%
5426
Night
5%212%35%36%8%
15604

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
4313333345%62%
1611
16th to endDay
6%414323345%60%
1728
February1st to 15thDay
6%312212235%67%
1670
16th to endDay
6%413313345%61%
1644
March1st to 15thDay
3222213346%65%
1980
16th to endDay
2212213335%71%
2112
April1st to 15thDay
2212122346%69%
1997
16th to endDay
1211112381%
2160
May1st to 15thDay
112112245%77%
2328
16th to endDay
1111222382%
2429
June1st to 15thDay
211112135%78%
2340
16th to endDay
2212323345%69%
2340
July1st to 15thDay
5%426%8%47%7%7%9%35%
2340
16th to endDay
9%6%37%8%5%8%8%8%9%23%
2467
August1st to 15thDay
7%426%7%48%7%8%7%34%
2340
16th to endDay
5%325%6%45%6%7%8%42%
2302
September1st to 15thDay
7%5%25%6%45%45%8%43%
1980
16th to endDay
4212323445%64%
1828
October1st to 15thDay
212213335%73%
1716
16th to endDay
12212236%75%
1760
November1st to 15thDay
121212335%75%
1759
16th to endDay
3213312335%69%
1682
December1st to 15thDay
6%313213346%61%
1620
16th to endDay
6%41321435%7%59%
1728
January1st to 15thNight
4213313345%66%
2327
16th to endNight
7%323334445%57%
2496
February1st to 15thNight
3311213346%67%
2179
16th to endNight
3413323345%62%
1829
March1st to 15thNight
3312222246%68%
1980
16th to endNight
2211313335%71%
2112
April1st to 15thNight
2212323225%70%
1950
16th to endNight
21111112382%
1800
May1st to 15thNight
1111345%78%
1619
16th to endNight
111122384%
1684
June1st to 15thNight
2111223479%
1620
16th to endNight
1112222445%70%
1620
July1st to 15thNight
3214445%5%8%12%46%
1620
16th to endNight
34245%47%8%11%16%30%
1701
August1st to 15thNight
2213436%6%7%10%51%
1620
16th to endNight
4314435%6%6%11%48%
1893
September1st to 15thNight
5%41443445%7%53%
1980
16th to endNight
211212245%73%
1837
October1st to 15thNight
11121233476%
1914
16th to endNight
111122225%78%
2112
November1st to 15thNight
112212235%75%
2100
16th to endNight
4313312225%67%
2277
December1st to 15thNight
6%313212346%65%
2340
16th to endNight
7%314313345%60%
2496

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
24%25%12%27%28%
1612
16th to endDay
25%2416%26%25%
1728
February1st to 15thDay
20%1312%28%33%
1670
16th to endDay
25%1313%28%26%
1644
March1st to 15thDay
20%137%33%33%
1980
16th to endDay
16%139%36%32%
2112
April1st to 15thDay
15%127%39%33%
1997
16th to endDay
11%27%27%50%
2160
May1st to 15thDay
12%128%26%49%
2328
16th to endDay
9%125%30%50%
2432
June1st to 15thDay
10%125%24%55%
2340
16th to endDay
18%246%21%46%
2340
July1st to 15thDay
39%9%14%12%13%10%
2201
16th to endDay
51%12%18%12%5%
2312
August1st to 15thDay
43%9%11%13%16%5%
2325
16th to endDay
36%9%12%16%14%10%
2302
September1st to 15thDay
38%5%10%14%18%12%
1980
16th to endDay
22%36%10%32%24%
1828
October1st to 15thDay
15%26%10%31%33%
1716
16th to endDay
12%1310%30%40%
1760
November1st to 15thDay
12%1311%35%35%
1759
16th to endDay
20%410%28%35%
1682
December1st to 15thDay
24%1416%30%22%
1620
16th to endDay
24%18%15%31%17%
1728
January1st to 15thNight
20%25%12%30%29%
2327
16th to endNight
28%3415%28%20%
2496
February1st to 15thNight
18%25%14%25%33%
2190
16th to endNight
23%2313%32%24%
1829
March1st to 15thNight
18%311%29%36%
1980
16th to endNight
16%1411%33%31%
2112
April1st to 15thNight
19%1210%36%29%
1950
16th to endNight
9%128%29%48%
1800
May1st to 15thNight
9%138%30%46%
1620
16th to endNight
8%126%32%48%
1685
June1st to 15thNight
10%12423%57%
1620
16th to endNight
15%25%6%22%47%
1620
July1st to 15thNight
25%10%19%17%15%12%
1530
16th to endNight
33%14%25%18%5%1
1593
August1st to 15thNight
24%10%16%20%19%7%
1611
16th to endNight
27%8%16%18%19%10%
1893
September1st to 15thNight
30%5%11%20%20%11%
1980
16th to endNight
13%25%15%36%26%
1837
October1st to 15thNight
12%25%15%29%33%
1914
16th to endNight
11%1412%27%42%
2112
November1st to 15thNight
11%1416%32%33%
2100
16th to endNight
21%1310%27%35%
2277
December1st to 15thNight
21%1415%32%23%
2340
16th to endNight
27%27%16%28%19%
2496

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
18%6%16%33%24%
90
16th to endDay
10%6%17%34%22%8%
96
February1st to 15thDay
8%9%22%32%23%2
185
16th to endDay
11%20%30%24%10%2
238
March1st to 15thDay
9%18%25%27%12%7%
270
16th to endDay
5%19%29%26%13%4
288
April1st to 15thDay
5%15%36%23%13%5%
269
16th to endDay
5%20%35%24%9%4
270
May1st to 15thDay
417%35%24%13%5%
288
16th to endDay
29%35%36%12%3
330
June1st to 15thDay
46%31%37%15%4
315
16th to endDay
5%16%43%25%8%
315
July1st to 15thDay
8%18%38%34%8%
305
16th to endDay
18%1428%29%17%
327
August1st to 15thDay
9%7%27%36%18%
315
16th to endDay
7%5%30%37%18%
332
September1st to 15thDay
15%11%35%27%8%
315
16th to endDay
9%415%35%25%9%
260
October1st to 15thDay
5%7%23%33%18%11%
156
16th to endDay
4111%29%39%14%
96
November1st to 15thDay
211%18%32%28%6%
90
16th to endDay
7%8%25%28%26%2
90
December1st to 15thDay
10%315%27%35%7%
90
16th to endDay
20%7%20%30%18%2
96
January1st to 15thNight
6%213%41%30%5%
720
16th to endNight
10%215%40%26%5%
768
February1st to 15thNight
5%316%40%28%5%
704
16th to endNight
6%6%19%46%19%2
632
March1st to 15thNight
5%5%19%39%26%4
720
16th to endNight
3316%40%30%5%
768
April1st to 15thNight
4418%47%23%1
691
16th to endNight
2422%42%24%3
540
May1st to 15thNight
1321%38%30%3
540
16th to endNight
1217%41%34%2
563
June1st to 15thNight
219%45%36%3
540
16th to endNight
2433%52%5%
540
July1st to 15thNight
5%221%58%10%
510
16th to endNight
5%214%58%18%
564
August1st to 15thNight
3213%58%21%
539
16th to endNight
7%114%55%20%
609
September1st to 15thNight
6%422%49%16%
720
16th to endNight
46%31%45%11%
664
October1st to 15thNight
2113%36%35%9%
660
16th to endNight
28%34%41%11%
704
November1st to 15thNight
2114%37%37%7%
700
16th to endNight
6%215%36%30%8%
720
December1st to 15thNight
8%412%39%28%7%
720
16th to endNight
10%315%39%24%6%
768
Page generated at 2017-09-18 05:38:27. Version ac04

Copyright 2017 A. Danko


VERITAS Clear Sky Chart | Charts Home