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 2018-10-08.

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
42%
16590
14%
50950
10%
16564
47%
16564
22%
34007

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
34%
971
11%
2910
6%
970
38%
970
16%
2156
January16th to endNight
35%
890
18%
2970
13%
890
43%
890
20%
1967
February1st to 15thNight
42%
758
13%
2584
12%
757
46%
757
16%
1802
February16th to endNight
40%
684
13%
2153
11%
684
44%
684
17%
1560
March1st to 15thNight
34%
780
15%
2273
8%
780
41%
780
21%
1602
March16th to endNight
33%
832
11%
2288
3%
832
38%
832
17%
1718
April1st to 15thNight
33%
665
12%
1838
5%
665
37%
665
18%
1369
April16th to endNight
41%
579
14%
1737
11%
579
45%
579
21%
1202
May1st to 15thNight
46%
500
14%
1574
13%
500
50%
500
26%
1001
May16th to endNight
44%
406
6%
1421
5%
406
46%
406
17%
985
June1st to 15thNight
43%
390
3%
1365
1%
390
44%
390
18%
927
June16th to endNight
53%
390
3%
1365
0%
390
53%
390
25%
820
July1st to 15thNight
61%
370
4%
1295
2%
370
62%
370
31%
714
July16th to endNight
64%
408
13%
1390
13%
386
70%
386
39%
689
August1st to 15thNight
65%
460
15%
1604
15%
458
69%
458
33%
875
August16th to endNight
60%
621
25%
1863
20%
621
63%
621
42%
999
September1st to 15thNight
56%
699
19%
1965
13%
699
58%
699
35%
1189
September16th to endNight
49%
776
21%
2145
13%
776
55%
776
34%
1323
October1st to 15thNight
42%
752
18%
2195
10%
752
48%
752
23%
1494
October16th to endNight
42%
768
22%
2496
14%
768
52%
768
27%
1530
November1st to 15thNight
31%
901
19%
2611
9%
901
41%
901
23%
1769
November16th to endNight
33%
975
15%
2863
8%
975
39%
975
23%
1930
December1st to 15thNight
40%
975
13%
2925
9%
975
43%
975
19%
2083
December16th to endNight
32%
1040
14%
3120
8%
1040
38%
1040
16%
2303

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%
52214
Night
7%8%37%6%35%5%6%8%37%
51100
Cloud CoverDay
9%8%36%5%35%5%6%8%37%
52215
Night
7%8%37%5%35%5%6%8%37%
51103
TransparencyDay
42%8%15%22%9%1
51868
Night
42%7%14%21%11%1
50950
SeeingDay
14%7%25%29%18%5%
7387
Night
12%6%29%33%16%2
16602

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%10%48%7%35%46%7%33%
1358
16th to endDay
5%9%49%7%46%6%6%9%30%
1616
February1st to 15thDay
8%10%48%7%47%6%5%6%30%
1607
16th to endDay
413%7%9%8%36%45%8%27%
1604
March1st to 15thDay
6%10%48%7%46%6%5%8%31%
2016
16th to endDay
9%12%5%9%6%45%5%5%8%28%
2287
April1st to 15thDay
12%11%5%7%6%35%6%47%27%
2438
16th to endDay
12%9%37%6%35%5%6%7%32%
2498
May1st to 15thDay
11%7%35%5%35%5%5%8%37%
2704
16th to endDay
19%7%26%5%35%5%5%8%29%
3042
June1st to 15thDay
15%7%36%5%345%7%7%31%
2925
16th to endDay
12%5%25%5%36%5%6%9%37%
2925
July1st to 15thDay
7%414335%5%7%9%47%
2925
16th to endDay
4313425%46%8%54%
3042
August1st to 15thDay
7%4245%2447%10%46%
2599
16th to endDay
8%31342446%9%52%
2691
September1st to 15thDay
11%6%24413445%49%
2324
16th to endDay
11%5%2442345%7%46%
2145
October1st to 15thDay
14%9%36%6%3445%7%33%
1932
16th to endDay
6%8%36%6%25%5%7%9%37%
1728
November1st to 15thDay
8%10%5%8%5%45%5%6%7%32%
1564
16th to endDay
5%11%5%8%5%2347%9%37%
1423
December1st to 15thDay
5%11%5%10%8%5%7%5%5%6%28%
1365
16th to endDay
410%410%7%5%7%6%6%9%26%
1456
January1st to 15thNight
5%10%5%8%7%46%6%6%10%26%
2910
16th to endNight
5%10%48%6%346%6%9%35%
2970
February1st to 15thNight
6%10%48%7%5%5%5%5%8%32%
2573
16th to endNight
5%10%6%9%9%36%5%6%6%29%
2153
March1st to 15thNight
5%9%49%7%35%5%7%9%32%
2273
16th to endNight
8%12%5%8%7%36%5%5%9%27%
2285
April1st to 15thNight
11%10%5%8%7%35%45%8%29%
1838
16th to endNight
11%9%46%5%345%5%8%34%
1737
May1st to 15thNight
10%8%35%435%35%7%43%
1573
16th to endNight
17%5%35%435%6%7%7%31%
1421
June1st to 15thNight
13%7%26%5%35%5%6%7%35%
1365
16th to endNight
8%425%5%345%8%9%40%
1365
July1st to 15thNight
4415%5%235%7%8%49%
1365
16th to endNight
42143235%8%9%54%
1477
August1st to 15thNight
5%314435%5%5%9%49%
1612
16th to endNight
7%313323349%57%
1863
September1st to 15thNight
12%413423446%51%
1965
16th to endNight
10%6%25%433448%46%
2145
October1st to 15thNight
12%8%36%6%245%6%6%37%
2195
16th to endNight
8%6%35%425%46%8%43%
2496
November1st to 15thNight
6%8%38%5%345%5%8%38%
2611
16th to endNight
7%10%46%5%345%6%9%37%
2863
December1st to 15thNight
410%48%6%5%6%5%6%8%32%
2925
16th to endNight
5%10%5%11%8%45%6%5%7%26%
3120

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%10%5%7%7%36%45%9%32%
1358
16th to endDay
410%48%7%5%6%5%7%8%30%
1616
February1st to 15thDay
9%10%47%8%46%6%5%6%30%
1607
16th to endDay
412%7%9%8%45%45%8%27%
1604
March1st to 15thDay
6%10%48%7%46%5%5%9%31%
2016
16th to endDay
9%12%5%9%6%35%5%6%7%27%
2288
April1st to 15thDay
12%11%5%8%6%35%5%5%7%28%
2438
16th to endDay
12%9%47%6%35%5%6%7%32%
2498
May1st to 15thDay
11%7%35%5%35%5%5%8%37%
2704
16th to endDay
19%7%26%5%26%5%5%7%30%
3042
June1st to 15thDay
15%7%36%6%35%5%6%8%31%
2925
16th to endDay
11%5%25%5%35%5%6%9%37%
2925
July1st to 15thDay
7%413425%5%7%9%47%
2925
16th to endDay
43133245%5%9%54%
3042
August1st to 15thDay
7%315%4245%6%10%46%
2599
16th to endDay
8%41332346%10%52%
2691
September1st to 15thDay
11%7%2442335%5%49%
2324
16th to endDay
11%5%24423447%46%
2145
October1st to 15thDay
14%8%36%5%35%5%5%6%33%
1932
16th to endDay
6%8%46%6%35%5%7%8%37%
1728
November1st to 15thDay
8%10%48%6%36%5%6%8%32%
1564
16th to endDay
5%10%6%8%42446%9%37%
1423
December1st to 15thDay
5%10%5%10%8%5%7%6%5%6%28%
1365
16th to endDay
410%5%10%7%47%7%7%9%25%
1456
January1st to 15thNight
5%10%5%8%7%47%6%7%9%26%
2910
16th to endNight
410%38%6%35%6%6%9%34%
2970
February1st to 15thNight
6%10%48%7%45%5%5%7%32%
2573
16th to endNight
5%11%5%9%9%45%5%6%7%29%
2153
March1st to 15thNight
5%10%48%7%35%6%7%8%31%
2273
16th to endNight
8%12%5%8%7%35%6%6%8%27%
2288
April1st to 15thNight
11%10%5%9%6%45%45%8%29%
1838
16th to endNight
12%8%37%5%345%5%8%34%
1737
May1st to 15thNight
10%8%35%334447%42%
1573
16th to endNight
18%5%344348%5%9%31%
1421
June1st to 15thNight
13%7%26%5%45%6%6%6%34%
1365
16th to endNight
8%5%245%346%8%8%40%
1365
July1st to 15thNight
5%325%5%3346%9%49%
1365
16th to endNight
42233135%8%9%54%
1477
August1st to 15thNight
5%315%435%5%410%49%
1612
16th to endNight
7%313323349%57%
1863
September1st to 15thNight
12%413333445%51%
1965
16th to endNight
10%5%25%424448%47%
2145
October1st to 15thNight
12%8%36%5%245%6%6%37%
2195
16th to endNight
8%6%27%42446%9%42%
2496
November1st to 15thNight
6%8%47%6%35%5%5%7%38%
2611
16th to endNight
6%10%5%6%43446%8%37%
2863
December1st to 15thNight
5%9%49%6%5%6%6%5%8%31%
2925
16th to endNight
5%11%5%10%8%46%6%5%7%26%
3120

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%20%5%2
1358
16th to endDay
47%8%12%18%9%3
1616
February1st to 15thDay
51%8%13%16%7%1
1607
16th to endDay
54%6%14%18%6%
1604
March1st to 15thDay
49%8%17%16%7%
2016
16th to endDay
53%8%12%18%6%
2288
April1st to 15thDay
53%7%13%17%6%1
2438
16th to endDay
48%8%13%19%8%1
2498
May1st to 15thDay
42%7%13%23%11%
2704
16th to endDay
50%8%13%19%7%
3047
June1st to 15thDay
47%8%15%18%8%1
2925
16th to endDay
39%8%17%24%9%1
2925
July1st to 15thDay
29%9%17%30%11%1
2766
16th to endDay
24%8%18%28%16%3
2866
August1st to 15thDay
30%9%19%30%8%1
2582
16th to endDay
26%5%17%32%15%2
2691
September1st to 15thDay
34%5%12%24%16%5%
2324
16th to endDay
36%6%12%29%11%3
2145
October1st to 15thDay
48%7%13%21%8%1
1932
16th to endDay
40%8%16%24%9%1
1728
November1st to 15thDay
47%8%15%19%7%1
1564
16th to endDay
42%6%17%22%8%2
1423
December1st to 15thDay
55%7%12%18%6%1
1365
16th to endDay
50%10%12%17%7%1
1456
January1st to 15thNight
50%9%14%16%6%1
2910
16th to endNight
43%8%15%17%13%2
2970
February1st to 15thNight
49%6%12%19%10%1
2584
16th to endNight
52%7%12%18%9%
2153
March1st to 15thNight
45%9%16%20%6%
2273
16th to endNight
51%8%14%17%7%
2288
April1st to 15thNight
52%8%11%18%9%
1838
16th to endNight
45%8%12%22%9%1
1737
May1st to 15thNight
39%6%12%27%11%1
1574
16th to endNight
46%10%14%19%7%1
1421
June1st to 15thNight
46%8%14%19%10%1
1365
16th to endNight
35%8%19%23%11%
1365
July1st to 15thNight
29%7%16%29%14%1
1295
16th to endNight
21%8%19%27%18%3
1390
August1st to 15thNight
28%7%21%27%13%2
1604
16th to endNight
24%6%10%33%19%5%
1863
September1st to 15thNight
32%6%11%24%19%6%
1965
16th to endNight
34%5%14%25%14%4
2145
October1st to 15thNight
43%7%14%20%12%1
2195
16th to endNight
36%7%16%26%12%
2496
November1st to 15thNight
43%7%13%22%13%
2611
16th to endNight
41%8%20%16%10%2
2863
December1st to 15thNight
48%8%15%19%7%1
2925
16th to endNight
52%7%13%19%6%
3120

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
13%318%28%15%20%
90
16th to endDay
8%9%27%27%19%8%
96
February1st to 15thDay
14%8%21%37%14%4
112
16th to endDay
11%9%25%33%16%3
185
March1st to 15thDay
10%11%39%22%11%4
330
16th to endDay
13%13%33%25%11%2
352
April1st to 15thDay
18%12%27%25%13%1
329
16th to endDay
19%9%22%29%14%4
318
May1st to 15thDay
14%6%25%26%21%4
445
16th to endDay
20%418%28%22%4
597
June1st to 15thDay
15%7%26%30%18%1
570
16th to endDay
12%427%32%18%4
570
July1st to 15thDay
8%322%34%26%5%
550
16th to endDay
8%323%35%20%8%
551
August1st to 15thDay
10%217%32%26%10%
359
16th to endDay
10%7%20%30%21%11%
396
September1st to 15thDay
17%10%21%26%18%6%
375
16th to endDay
18%9%26%24%15%6%
375
October1st to 15thDay
24%9%18%26%16%4
219
16th to endDay
14%8%27%29%15%4
144
November1st to 15thDay
19%12%27%23%13%3
135
16th to endDay
410%38%30%7%7%
103
December1st to 15thDay
8%5%40%24%17%3
90
16th to endDay
16%231%30%15%4
96
January1st to 15thNight
11%10%32%30%13%1
975
16th to endNight
11%9%34%30%13%1
890
February1st to 15thNight
11%7%26%32%17%3
764
16th to endNight
10%427%36%17%3
684
March1st to 15thNight
9%6%37%30%13%2
780
16th to endNight
15%7%31%32%10%1
832
April1st to 15thNight
15%7%32%31%11%1
665
16th to endNight
18%5%25%33%16%1
579
May1st to 15thNight
13%426%32%21%1
501
16th to endNight
20%424%27%21%1
407
June1st to 15thNight
18%5%25%33%16%1
390
16th to endNight
12%324%35%22%1
390
July1st to 15thNight
7%221%44%23%1
370
16th to endNight
5%124%40%24%2
408
August1st to 15thNight
7%217%39%30%3
460
16th to endNight
8%322%40%23%1
621
September1st to 15thNight
14%222%34%22%3
699
16th to endNight
13%425%34%18%3
776
October1st to 15thNight
17%5%25%31%17%3
752
16th to endNight
11%6%32%33%13%1
768
November1st to 15thNight
11%9%40%25%10%2
901
16th to endNight
11%8%37%31%9%1
975
December1st to 15thNight
10%6%30%35%14%2
975
16th to endNight
11%6%33%33%11%3
1040
Page generated at 2018-10-09 08:39:12. Version ac04

Copyright 2018 A. Danko


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