VERITAS
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the VERITAS clear sky chart from 2005-11-06 to 2024-01-12.

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
71%
23986
34%
74290
30%
23940
77%
23940
50%
36101

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 10thNight
69%
759
33%
2457
31%
756
76%
756
46%
1202
January11th to 20thNight
67%
724
36%
2353
32%
724
77%
724
51%
1089
January21st to endNight
59%
792
36%
2574
32%
792
70%
792
41%
1316
February1st to 10thNight
67%
720
37%
2277
35%
720
76%
720
51%
1078
February11th to 20thNight
56%
700
33%
2099
25%
700
67%
700
44%
1088
February21st to endNight
57%
592
39%
1678
30%
592
68%
592
49%
867
March1st to 10thNight
56%
720
37%
1980
26%
720
68%
720
50%
1018
March11th to 20thNight
67%
720
37%
1980
27%
720
75%
720
55%
994
March21st to endNight
66%
792
37%
2178
26%
792
75%
792
55%
1092
April1st to 10thNight
67%
720
38%
1980
26%
720
76%
720
63%
919
April11th to 20thNight
60%
582
41%
1826
30%
582
72%
582
59%
782
April21st to endNight
69%
540
45%
1800
40%
540
79%
540
68%
674
May1st to 10thNight
68%
540
43%
1620
31%
540
79%
540
67%
670
May11th to 20thNight
76%
531
43%
1594
36%
531
82%
531
70%
650
May21st to endNight
74%
582
44%
1746
34%
582
83%
582
79%
669
June1st to 10thNight
82%
540
37%
1620
32%
540
83%
540
66%
690
June11th to 20thNight
82%
540
38%
1620
31%
540
85%
540
73%
644
June21st to endNight
82%
540
28%
1620
24%
540
83%
540
56%
760
July1st to 10thNight
80%
525
22%
1575
18%
525
80%
525
42%
852
July11th to 20thNight
77%
522
14%
1566
12%
522
77%
522
26%
1018
July21st to endNight
77%
591
12%
1674
10%
558
76%
558
23%
1149
August1st to 10thNight
83%
537
19%
1602
18%
534
83%
534
37%
910
August11th to 20thNight
81%
534
24%
1611
22%
534
81%
534
35%
932
August21st to endNight
82%
648
25%
2034
26%
648
82%
648
33%
1206
September1st to 10thNight
77%
720
26%
1980
24%
720
78%
720
38%
1193
September11th to 20thNight
85%
720
40%
1980
34%
720
86%
720
59%
983
September21st to endNight
80%
720
37%
1980
28%
720
84%
720
60%
972
October1st to 10thNight
78%
720
39%
2051
31%
720
84%
720
65%
939
October11th to 20thNight
81%
720
42%
2160
35%
720
86%
720
67%
926
October21st to endNight
80%
792
45%
2376
38%
792
86%
792
71%
975
November1st to 10thNight
77%
740
44%
2220
37%
740
83%
740
66%
941
November11th to 20thNight
75%
760
42%
2280
35%
760
81%
760
60%
1022
November21st to endNight
60%
760
37%
2465
32%
760
68%
760
44%
1213
December1st to 10thNight
67%
760
37%
2470
36%
760
72%
760
47%
1182
December11th to 20thNight
62%
759
31%
2943
32%
759
69%
759
32%
1597
December21st to endNight
58%
824
23%
4321
32%
817
67%
817
30%
1889

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
432343445%6%62%
74950
Night
431332345%6%65%
74794
TransparencyDay
22%46%11%25%31%
74677
Night
20%47%13%27%31%
74589
SeeingDay
7%8%20%31%24%9%
13794
Night
5%315%39%32%6%
24006

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 10thDay
5%42443345%5%61%
1708
11th to 20thDay
5%32343444462%
1629
21st to endDay
5%5%1432335%5%64%
1782
February1st to 10thDay
6%413314335%67%
1678
11th to 20thDay
7%5%245%24345%59%
1750
21st to endDay
6%5%13322335%66%
1577
March1st to 10thDay
443342435%7%60%
1980
11th to 20thDay
5%424323346%66%
1980
21st to endDay
2313323336%70%
2178
April1st to 10thDay
2212223447%70%
1980
11th to 20thDay
321211223479%
2081
21st to endDay
111221223481%
2160
May1st to 10thDay
1213212245%77%
2335
11th to 20thDay
1112223345%78%
2301
21st to endDay
11211222385%
2530
June1st to 10thDay
221231225%7%74%
2340
11th to 20thDay
111122223481%
2340
21st to endDay
3313434446%64%
2340
July1st to 10thDay
4425%7%47%7%7%8%45%
2340
11th to 20thDay
7%5%37%8%6%9%8%9%11%29%
2340
21st to endDay
8%6%47%8%5%9%8%9%10%26%
2545
August1st to 10thDay
6%436%6%5%7%8%8%9%38%
2328
11th to 20thDay
5%426%7%47%7%9%9%39%
2287
21st to endDay
5%325%7%5%7%7%7%9%43%
2317
September1st to 10thDay
8%5%25%6%45%5%5%8%45%
1980
11th to 20thDay
42134245%6%7%62%
1980
21st to endDay
331233445%6%67%
1980
October1st to 10thDay
22123235%5%6%72%
1908
11th to 20thDay
2212312335%78%
1800
21st to endDay
2112223346%76%
1980
November1st to 10thDay
1212223346%72%
1859
11th to 20thDay
3312313445%71%
1900
21st to endDay
5%424423436%63%
1712
December1st to 10thDay
6%31432445%6%61%
1710
11th to 20thDay
7%6%35%5%35%36%7%51%
2169
21st to endDay
6%42443335%5%60%
3146
January1st to 10thNight
5%41442445%6%61%
2457
11th to 20thNight
6%313323446%66%
2353
21st to endNight
7%423433445%60%
2574
February1st to 10thNight
4412323346%67%
2277
11th to 20thNight
5%5%2442444462%
2098
21st to endNight
36%24323446%64%
1678
March1st to 10thNight
342332435%8%62%
1980
11th to 20thNight
4413323335%69%
1980
21st to endNight
3323323446%66%
2178
April1st to 10thNight
1213313336%73%
1980
11th to 20thNight
231232312378%
1826
21st to endNight
221111123481%
1800
May1st to 10thNight
111112244479%
1620
11th to 20thNight
1112212336%78%
1594
21st to endNight
11111112387%
1746
June1st to 10thNight
3112212346%75%
1620
11th to 20thNight
1112112245%80%
1620
21st to endNight
22134335%5%6%67%
1620
July1st to 10thNight
32245%45%47%10%54%
1620
11th to 20thNight
3435%7%5%8%8%11%15%34%
1620
21st to endNight
4435%6%5%8%9%11%16%28%
1773
August1st to 10thNight
3325%436%6%7%11%51%
1611
11th to 20thNight
4415%5%45%6%8%13%46%
1611
21st to endNight
5%3245%47%6%7%10%47%
2034
September1st to 10thNight
6%5%245%35%5%6%8%50%
1980
11th to 20thNight
3213333345%71%
1980
21st to endNight
3213323346%69%
1980
October1st to 10thNight
211221335%6%73%
2051
11th to 20thNight
2211212235%79%
2160
21st to endNight
1112212235%80%
2376
November1st to 10thNight
2112213346%74%
2220
11th to 20thNight
3213323346%71%
2280
21st to endNight
6%414423346%63%
2465
December1st to 10thNight
6%413323447%63%
2470
11th to 20thNight
6%6%36%5%34445%56%
3041
21st to endNight
7%5%144245%45%59%
4521

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 10thDay
24%35%13%29%26%
1709
11th to 20thDay
24%36%10%28%29%
1629
21st to endDay
23%2316%29%28%
1782
February1st to 10thDay
22%2411%24%38%
1678
11th to 20thDay
28%2413%24%29%
1760
21st to endDay
22%248%27%37%
1577
March1st to 10thDay
24%338%31%31%
1980
11th to 20thDay
21%348%29%36%
1980
21st to endDay
17%2310%38%30%
2178
April1st to 10thDay
15%238%36%36%
1980
11th to 20thDay
13%126%29%50%
2084
21st to endDay
10%137%31%47%
2160
May1st to 10thDay
13%127%23%53%
2335
11th to 20thDay
11%249%26%49%
2304
21st to endDay
8%12427%58%
2530
June1st to 10thDay
12%246%27%49%
2340
11th to 20thDay
9%125%21%63%
2340
21st to endDay
21%5%6%8%21%40%
2340
July1st to 10thDay
33%8%11%13%17%18%
2276
11th to 20thDay
42%13%19%16%6%3
2271
21st to endDay
47%15%18%12%7%1
2404
August1st to 10thDay
38%11%14%13%17%7%
2313
11th to 20thDay
36%11%14%17%14%8%
2287
21st to endDay
34%11%13%18%15%10%
2317
September1st to 10thDay
36%6%11%15%16%16%
1980
11th to 20thDay
21%48%12%27%27%
1980
21st to endDay
19%48%13%32%25%
1980
October1st to 10thDay
14%48%13%29%32%
1908
11th to 20thDay
11%248%33%41%
1800
21st to endDay
13%1411%28%44%
1980
November1st to 10thDay
13%2412%35%34%
1859
11th to 20thDay
17%2411%31%36%
1900
21st to endDay
24%35%12%24%32%
1712
December1st to 10thDay
24%35%16%26%27%
1710
11th to 20thDay
32%35%13%27%20%
2168
21st to endDay
24%36%11%38%19%
3146
January1st to 10thNight
24%25%14%31%24%
2457
11th to 20thNight
20%25%14%29%30%
2353
21st to endNight
27%3413%29%24%
2574
February1st to 10thNight
20%3412%22%39%
2277
11th to 20thNight
26%25%14%25%29%
2099
21st to endNight
23%2410%27%35%
1678
March1st to 10thNight
22%1412%29%31%
1980
11th to 20thNight
19%3411%26%38%
1980
21st to endNight
19%25%12%35%27%
2178
April1st to 10thNight
15%1311%35%35%
1980
11th to 20thNight
15%127%28%46%
1826
21st to endNight
10%139%32%45%
1800
May1st to 10thNight
11%138%27%49%
1620
11th to 20thNight
10%249%27%49%
1595
21st to endNight
6%116%32%54%
1746
June1st to 10thNight
12%236%26%52%
1620
11th to 20thNight
8%24421%62%
1620
21st to endNight
16%47%9%19%44%
1620
July1st to 10thNight
24%7%15%15%16%22%
1575
11th to 20thNight
32%15%20%20%9%3
1566
21st to endNight
36%16%24%15%6%2
1674
August1st to 10thNight
24%11%17%20%17%10%
1602
11th to 20thNight
26%11%19%19%17%8%
1611
21st to endNight
30%10%14%18%18%10%
2034
September1st to 10thNight
30%7%12%19%18%14%
1980
11th to 20thNight
17%36%15%31%27%
1980
21st to endNight
16%47%15%33%26%
1980
October1st to 10thNight
12%48%16%27%34%
2051
11th to 20thNight
11%3412%28%42%
2160
21st to endNight
10%1412%30%43%
2376
November1st to 10thNight
12%2414%35%34%
2220
11th to 20thNight
16%2414%31%34%
2280
21st to endNight
24%2411%28%29%
2465
December1st to 10thNight
23%26%16%28%26%
2470
11th to 20thNight
31%45%12%27%21%
3041
21st to endNight
25%46%12%31%22%
4521

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 10thDay
13%8%21%33%23%2
270
11th to 20thDay
10%7%19%39%21%4
243
21st to endDay
5%9%26%34%22%4
264
February1st to 10thDay
8%9%20%36%22%5%
298
11th to 20thDay
13%18%30%27%10%
415
21st to endDay
13%19%35%25%8%1
346
March1st to 10thDay
10%19%29%31%9%3
420
11th to 20thDay
9%15%25%28%16%6%
420
21st to endDay
7%21%30%29%11%2
462
April1st to 10thDay
313%34%29%16%5%
420
11th to 20thDay
5%16%35%26%13%5%
412
21st to endDay
415%32%26%15%7%
420
May1st to 10thDay
414%31%25%18%7%
423
11th to 20thDay
38%30%36%19%4
448
21st to endDay
39%33%33%16%6%
485
June1st to 10thDay
46%23%41%20%6%
450
11th to 20thDay
2424%38%24%7%
450
21st to endDay
4116%40%30%9%
450
July1st to 10thDay
5%18%35%37%14%
446
11th to 20thDay
9%15%27%37%20%
444
21st to endDay
12%1422%39%22%
487
August1st to 10thDay
8%1423%40%24%
447
11th to 20thDay
6%17%24%38%23%
437
21st to endDay
6%422%41%26%
495
September1st to 10thDay
10%210%33%32%12%
450
11th to 20thDay
7%11%35%34%13%
450
21st to endDay
6%418%32%28%13%
450
October1st to 10thDay
36%19%34%26%12%
378
11th to 20thDay
3415%33%34%12%
270
21st to endDay
3316%35%30%13%
297
November1st to 10thDay
5%7%19%40%24%6%
270
11th to 20thDay
3416%39%33%5%
270
21st to endDay
8%10%23%38%17%4
270
December1st to 10thDay
11%6%20%34%26%3
270
11th to 20thDay
11%5%24%39%19%2
270
21st to endDay
14%10%21%34%17%4
297
January1st to 10thNight
8%216%44%26%4
760
11th to 20thNight
7%318%43%25%4
724
21st to endNight
11%321%42%21%3
792
February1st to 10thNight
6%319%43%24%5%
720
11th to 20thNight
8%6%24%42%17%3
704
21st to endNight
7%6%26%44%15%2
592
March1st to 10thNight
6%7%26%42%17%2
720
11th to 20thNight
6%320%39%27%5%
720
21st to endNight
45%19%46%23%3
792
April1st to 10thNight
3322%48%23%2
720
11th to 20thNight
45%27%42%19%1
582
21st to endNight
3422%47%22%2
540
May1st to 10thNight
2423%43%25%2
540
11th to 20thNight
1218%47%29%3
531
21st to endNight
1320%47%28%1
584
June1st to 10thNight
419%49%34%3
540
11th to 20thNight
1112%48%36%1
540
21st to endNight
316%38%45%6%
540
July1st to 10thNight
41429%56%7%
525
11th to 20thNight
5%1318%62%11%
522
21st to endNight
5%1219%56%16%
591
August1st to 10thNight
4316%58%18%
537
11th to 20thNight
5%1418%59%13%
534
21st to endNight
6%317%57%17%
648
September1st to 10thNight
6%16%25%48%13%
720
11th to 20thNight
41335%48%9%
720
21st to endNight
4110%37%39%8%
720
October1st to 10thNight
2213%40%36%6%
720
11th to 20thNight
3211%43%34%7%
720
21st to endNight
2212%39%35%9%
792
November1st to 10thNight
4214%42%32%6%
740
11th to 20thNight
3214%42%34%5%
760
21st to endNight
8%421%41%22%5%
760
December1st to 10thNight
9%216%44%23%6%
760
11th to 20thNight
9%6%17%46%20%3
760
21st to endNight
9%6%19%39%22%5%
836
Page generated at 2024-01-08 20:31:24. Version ac07

Copyright 2024 Attilla Danko


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