Vulcan
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vulcan 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
41%
15230
14%
46790
9%
15204
46%
15204
22%
31300

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
32%
896
12%
2685
7%
895
36%
895
16%
1990
January16th to endNight
35%
822
17%
2742
12%
822
43%
822
20%
1831
February1st to 15thNight
42%
698
12%
2381
11%
697
46%
697
17%
1649
February16th to endNight
39%
632
12%
1989
10%
632
43%
632
17%
1458
March1st to 15thNight
31%
720
14%
2098
7%
720
39%
720
20%
1491
March16th to endNight
33%
768
11%
2112
3%
768
39%
768
17%
1586
April1st to 15thNight
33%
614
12%
1697
5%
614
36%
614
18%
1256
April16th to endNight
40%
540
14%
1620
11%
540
44%
540
20%
1138
May1st to 15thNight
45%
461
12%
1452
12%
461
48%
461
24%
937
May16th to endNight
43%
374
6%
1309
5%
374
45%
374
16%
925
June1st to 15thNight
44%
360
2%
1260
1%
360
44%
360
17%
864
June16th to endNight
53%
360
3%
1260
0%
360
53%
360
25%
751
July1st to 15thNight
61%
340
3%
1190
1%
340
61%
340
30%
667
July16th to endNight
63%
376
13%
1275
13%
354
69%
354
38%
638
August1st to 15thNight
65%
433
14%
1505
14%
431
69%
431
33%
826
August16th to endNight
61%
573
25%
1719
20%
573
64%
573
43%
916
September1st to 15thNight
57%
645
20%
1814
13%
645
59%
645
37%
1077
September16th to endNight
51%
664
21%
1837
13%
664
57%
664
37%
1089
October1st to 15thNight
42%
660
18%
1929
10%
660
49%
660
23%
1318
October16th to endNight
43%
704
21%
2288
13%
704
52%
704
27%
1413
November1st to 15thNight
31%
830
19%
2405
10%
830
41%
830
23%
1611
November16th to endNight
34%
900
14%
2643
8%
900
39%
900
23%
1790
December1st to 15thNight
38%
900
12%
2700
8%
900
41%
900
17%
1967
December16th to endNight
32%
960
14%
2880
7%
960
38%
960
17%
2112

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
9%8%36%5%35%5%6%8%37%
48013
Night
7%8%37%6%35%5%6%8%37%
46940
Cloud CoverDay
9%8%36%5%35%5%6%8%37%
48014
Night
7%8%37%5%35%5%6%8%37%
46943
TransparencyDay
42%8%15%22%9%1
47667
Night
42%7%15%21%10%1
46790
SeeingDay
13%7%25%29%17%4
6014
Night
12%6%30%33%15%2
15242

By Month

Percentage Cloud Cover NW (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
7%11%47%6%35%46%6%34%
1253
16th to endDay
5%9%39%7%47%6%6%9%31%
1491
February1st to 15thDay
8%10%48%6%47%6%5%6%31%
1480
16th to endDay
5%13%8%9%7%36%45%8%26%
1482
March1st to 15thDay
5%10%48%7%45%6%5%8%32%
1861
16th to endDay
9%12%5%8%5%45%5%5%8%28%
2111
April1st to 15thDay
11%11%5%7%6%35%6%47%29%
2249
16th to endDay
12%10%36%6%35%5%6%7%31%
2340
May1st to 15thDay
11%7%36%5%35%5%5%8%36%
2496
16th to endDay
20%7%26%5%35%5%5%8%27%
2802
June1st to 15thDay
15%7%46%5%345%7%7%31%
2700
16th to endDay
12%425%5%36%5%6%10%36%
2700
July1st to 15thDay
8%414435%5%7%9%46%
2700
16th to endDay
5%423425%46%8%53%
2805
August1st to 15thDay
8%4245%2446%11%45%
2445
16th to endDay
8%31342446%9%52%
2483
September1st to 15thDay
12%6%24313445%50%
2145
16th to endDay
10%42442345%7%49%
1828
October1st to 15thDay
13%8%36%6%35%45%7%34%
1699
16th to endDay
6%9%37%6%25%5%7%8%37%
1584
November1st to 15thDay
8%9%47%5%45%5%5%8%33%
1441
16th to endDay
5%11%5%8%5%2347%9%36%
1314
December1st to 15thDay
5%11%5%11%8%5%7%5%5%6%26%
1260
16th to endDay
49%410%7%5%7%6%6%9%27%
1344
January1st to 15thNight
5%10%6%8%7%46%6%6%9%27%
2685
16th to endNight
5%10%48%6%346%6%8%35%
2742
February1st to 15thNight
6%10%48%7%45%5%5%8%33%
2370
16th to endNight
5%10%6%9%9%36%5%5%6%29%
1989
March1st to 15thNight
49%49%7%35%6%8%8%31%
2098
16th to endNight
7%12%5%8%7%36%5%6%9%27%
2109
April1st to 15thNight
11%10%48%7%35%45%8%30%
1697
16th to endNight
11%9%46%5%445%5%8%33%
1620
May1st to 15thNight
10%8%45%435%35%7%41%
1451
16th to endNight
18%6%35%436%6%7%8%29%
1309
June1st to 15thNight
13%7%26%5%35%6%6%7%34%
1260
16th to endNight
9%425%5%345%8%9%40%
1260
July1st to 15thNight
5%425%5%235%7%8%49%
1260
16th to endNight
42143235%8%9%54%
1362
August1st to 15thNight
5%414435%5%5%9%48%
1513
16th to endNight
7%312323349%57%
1719
September1st to 15thNight
11%413323347%53%
1814
16th to endNight
9%424433448%50%
1837
October1st to 15thNight
12%8%26%6%245%6%6%37%
1929
16th to endNight
8%6%35%435%46%8%43%
2288
November1st to 15thNight
6%7%37%5%35%5%6%8%39%
2405
16th to endNight
7%10%46%5%345%6%9%36%
2643
December1st to 15thNight
5%10%49%7%5%6%5%6%8%30%
2700
16th to endNight
410%5%11%8%46%6%5%7%27%
2880

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
7%11%5%7%6%36%45%8%33%
1253
16th to endDay
410%48%7%5%6%5%6%9%31%
1491
February1st to 15thDay
8%10%47%8%46%6%5%7%30%
1480
16th to endDay
5%13%8%10%8%35%45%8%26%
1482
March1st to 15thDay
5%10%48%7%46%5%5%9%32%
1861
16th to endDay
10%12%5%8%6%35%5%6%7%28%
2112
April1st to 15thDay
11%11%5%8%6%36%5%5%7%29%
2249
16th to endDay
12%10%47%6%35%5%6%7%31%
2340
May1st to 15thDay
11%7%35%5%35%5%5%8%36%
2496
16th to endDay
20%7%26%5%26%5%5%7%28%
2802
June1st to 15thDay
15%7%36%6%35%5%6%8%30%
2700
16th to endDay
11%5%25%5%35%5%6%9%37%
2700
July1st to 15thDay
7%413426%5%7%9%46%
2700
16th to endDay
5%3233245%6%9%53%
2805
August1st to 15thDay
8%41442447%10%46%
2445
16th to endDay
8%41342346%10%51%
2483
September1st to 15thDay
12%6%24323345%50%
2145
16th to endDay
10%4244235%48%49%
1828
October1st to 15thDay
14%8%37%6%36%5%5%6%34%
1699
16th to endDay
6%8%47%6%35%47%7%37%
1584
November1st to 15thDay
8%10%48%6%36%46%8%33%
1441
16th to endDay
5%11%6%8%4245%6%9%36%
1314
December1st to 15thDay
6%11%6%11%9%5%7%6%5%5%25%
1260
16th to endDay
49%410%7%5%7%7%7%9%27%
1344
January1st to 15thNight
5%11%5%8%7%47%6%7%8%27%
2685
16th to endNight
5%11%38%6%35%5%6%9%34%
2742
February1st to 15thNight
6%10%48%7%45%5%5%7%33%
2370
16th to endNight
5%11%5%9%9%45%5%5%7%28%
1989
March1st to 15thNight
5%10%5%9%7%35%6%8%8%31%
2098
16th to endNight
7%12%5%8%7%36%6%6%8%27%
2112
April1st to 15thNight
11%9%5%9%6%35%46%8%30%
1697
16th to endNight
12%8%47%5%345%5%9%33%
1620
May1st to 15thNight
10%9%35%3345%47%41%
1451
16th to endNight
18%5%345%348%5%9%29%
1309
June1st to 15thNight
13%8%26%5%45%6%6%6%33%
1260
16th to endNight
9%4245%345%9%8%41%
1260
July1st to 15thNight
5%325%5%335%6%9%48%
1260
16th to endNight
42233136%8%9%53%
1362
August1st to 15thNight
5%325%436%5%5%10%48%
1513
16th to endNight
7%313223348%58%
1719
September1st to 15thNight
11%413323446%53%
1814
16th to endNight
8%425%42445%8%50%
1837
October1st to 15thNight
12%7%36%5%25%5%6%6%37%
1929
16th to endNight
8%7%27%4245%6%8%42%
2288
November1st to 15thNight
6%8%37%5%35%5%5%8%39%
2405
16th to endNight
7%10%5%6%44446%9%36%
2643
December1st to 15thNight
5%10%410%6%5%6%6%6%8%29%
2700
16th to endNight
411%5%10%8%46%6%5%7%27%
2880

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
48%8%14%21%5%1
1253
16th to endDay
46%9%13%17%8%3
1491
February1st to 15thDay
50%8%14%17%6%1
1480
16th to endDay
54%6%14%17%6%
1482
March1st to 15thDay
48%8%17%17%7%
1861
16th to endDay
52%9%13%18%6%
2112
April1st to 15thDay
52%7%13%18%7%1
2249
16th to endDay
48%9%13%18%8%1
2340
May1st to 15thDay
43%8%13%22%11%
2496
16th to endDay
52%8%13%18%6%
2807
June1st to 15thDay
48%8%15%17%7%1
2700
16th to endDay
39%8%17%24%9%1
2700
July1st to 15thDay
29%10%18%30%9%1
2541
16th to endDay
25%8%18%28%16%3
2629
August1st to 15thDay
30%9%20%29%8%1
2428
16th to endDay
26%6%17%32%15%2
2483
September1st to 15thDay
34%5%12%25%16%5%
2145
16th to endDay
32%6%12%31%12%4
1828
October1st to 15thDay
47%7%13%20%8%1
1699
16th to endDay
41%8%16%23%8%1
1584
November1st to 15thDay
46%8%15%20%7%1
1441
16th to endDay
42%7%17%21%8%1
1314
December1st to 15thDay
57%7%12%16%5%
1260
16th to endDay
48%10%13%18%7%1
1344
January1st to 15thNight
50%9%14%17%6%1
2685
16th to endNight
44%8%15%18%11%2
2742
February1st to 15thNight
49%7%12%19%9%1
2381
16th to endNight
53%6%12%18%8%
1989
March1st to 15thNight
46%9%16%20%6%
2098
16th to endNight
51%9%14%17%7%
2112
April1st to 15thNight
51%8%11%18%9%
1697
16th to endNight
46%8%13%22%7%1
1620
May1st to 15thNight
41%6%12%26%11%1
1452
16th to endNight
48%10%14%18%6%1
1309
June1st to 15thNight
46%9%15%18%9%1
1260
16th to endNight
35%8%20%23%11%
1260
July1st to 15thNight
30%7%17%28%14%1
1190
16th to endNight
22%8%19%28%17%3
1275
August1st to 15thNight
29%7%21%26%12%2
1505
16th to endNight
23%6%10%34%20%4
1719
September1st to 15thNight
31%5%11%24%20%6%
1814
16th to endNight
31%5%16%26%15%4
1837
October1st to 15thNight
43%8%14%19%12%1
1929
16th to endNight
36%7%17%26%11%
2288
November1st to 15thNight
42%7%13%21%13%
2405
16th to endNight
42%8%20%15%10%2
2643
December1st to 15thNight
50%8%16%17%6%
2700
16th to endNight
51%8%13%19%5%
2880

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
16%123%21%15%21%
60
16th to endDay
10%6%23%28%18%12%
64
February1st to 15thDay
12%10%24%33%16%4
75
16th to endDay
14%8%28%34%13%
141
March1st to 15thDay
8%13%44%23%8%1
270
16th to endDay
12%15%35%25%9%1
288
April1st to 15thDay
15%14%28%25%14%
269
16th to endDay
20%9%24%31%12%1
270
May1st to 15thDay
15%7%25%26%20%4
378
16th to endDay
21%5%19%27%20%4
517
June1st to 15thDay
15%7%25%29%19%2
495
16th to endDay
11%427%33%18%3
495
July1st to 15thDay
7%222%34%26%5%
475
16th to endDay
9%425%37%17%5%
474
August1st to 15thDay
10%218%33%25%8%
315
16th to endDay
10%7%21%29%19%10%
332
September1st to 15thDay
17%10%21%25%19%6%
315
16th to endDay
11%13%28%26%15%4
260
October1st to 15thDay
19%12%19%31%13%2
142
16th to endDay
15%5%20%32%18%7%
96
November1st to 15thDay
18%18%26%24%8%2
90
16th to endDay
45%30%39%8%11%
69
December1st to 15thDay
11%6%43%21%15%1
60
16th to endDay
15%129%25%21%6%
64
January1st to 15thNight
11%11%33%29%13%1
900
16th to endNight
11%9%33%30%13%1
822
February1st to 15thNight
11%7%26%31%18%3
704
16th to endNight
10%427%35%17%3
632
March1st to 15thNight
9%7%39%30%11%1
720
16th to endNight
15%7%31%33%10%1
768
April1st to 15thNight
14%7%33%30%11%2
614
16th to endNight
18%5%26%33%14%1
540
May1st to 15thNight
14%5%26%31%20%1
462
16th to endNight
22%424%26%21%1
375
June1st to 15thNight
18%5%24%33%17%1
360
16th to endNight
11%424%37%20%1
360
July1st to 15thNight
7%220%43%23%
340
16th to endNight
5%125%43%21%2
376
August1st to 15thNight
7%217%39%29%3
433
16th to endNight
8%322%39%23%1
573
September1st to 15thNight
13%222%33%24%3
645
16th to endNight
10%426%36%18%3
664
October1st to 15thNight
17%5%26%32%15%3
660
16th to endNight
11%5%32%33%14%1
704
November1st to 15thNight
10%9%42%26%8%1
830
16th to endNight
11%7%37%31%10%1
900
December1st to 15thNight
10%6%31%35%13%2
900
16th to endNight
10%6%34%32%12%3
960
Page generated at 2017-09-18 06:38:19. Version ac04

Copyright 2017 A. Danko


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