Vermilion
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vermilion clear sky chart from 2005-11-06 to 2024-01-27.

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
35%
23616
9%
74600
6%
23563
38%
23563
10%
61048

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
12%
757
4%
2459
1%
757
17%
757
4%
2191
January11th to 20thNight
12%
760
3%
2470
1%
760
14%
760
3%
2261
January21st to endNight
17%
820
4%
2664
3%
820
20%
820
5%
2366
February1st to 10thNight
16%
720
4%
2340
1%
720
19%
720
6%
2013
February11th to 20thNight
17%
701
6%
2179
3%
700
21%
700
6%
1897
February21st to endNight
16%
592
8%
1776
1%
592
23%
592
7%
1519
March1st to 10thNight
26%
720
9%
2066
5%
720
30%
720
10%
1694
March11th to 20thNight
30%
720
12%
1980
6%
720
35%
720
12%
1614
March21st to endNight
30%
792
10%
2178
6%
792
33%
792
10%
1819
April1st to 10thNight
31%
707
9%
1967
4%
707
34%
707
12%
1591
April11th to 20thNight
33%
533
14%
1597
7%
533
39%
533
13%
1250
April21st to endNight
36%
540
11%
1620
4%
540
40%
540
12%
1288
May1st to 10thNight
39%
540
7%
1620
4%
540
41%
540
9%
1340
May11th to 20thNight
44%
531
13%
1592
10%
531
47%
531
13%
1246
May21st to endNight
58%
582
12%
1745
10%
582
60%
582
16%
1308
June1st to 10thNight
52%
455
10%
1535
9%
455
56%
455
14%
1133
June11th to 20thNight
55%
360
13%
1310
13%
360
60%
360
14%
957
June21st to endNight
56%
497
13%
1397
10%
497
59%
497
17%
1062
July1st to 10thNight
65%
525
11%
1400
10%
525
66%
525
19%
1056
July11th to 20thNight
63%
522
11%
1536
10%
522
64%
522
18%
1133
July21st to endNight
64%
591
12%
1672
10%
558
66%
558
17%
1241
August1st to 10thNight
65%
537
12%
1600
11%
534
66%
534
17%
1175
August11th to 20thNight
63%
534
15%
1598
11%
534
65%
534
17%
1171
August21st to endNight
60%
594
15%
1782
12%
594
62%
594
18%
1306
September1st to 10thNight
59%
702
13%
1930
9%
702
61%
702
16%
1485
September11th to 20thNight
60%
720
18%
1980
13%
720
63%
720
18%
1485
September21st to endNight
48%
720
10%
1980
8%
720
50%
720
13%
1592
October1st to 10thNight
46%
720
12%
2065
9%
720
48%
720
13%
1608
October11th to 20thNight
29%
720
9%
2160
5%
720
34%
720
10%
1762
October21st to endNight
24%
792
10%
2430
7%
792
28%
792
8%
2035
November1st to 10thNight
32%
740
11%
2406
11%
740
34%
740
12%
1861
November11th to 20thNight
20%
760
10%
2470
6%
760
26%
760
7%
2089
November21st to endNight
20%
760
7%
2596
5%
760
23%
760
6%
2250
December1st to 10thNight
15%
760
3%
2660
1%
760
17%
760
3%
2403
December11th to 20thNight
14%
760
5%
3267
2%
759
18%
759
4%
2725
December21st to endNight
15%
832
1%
4573
0%
817
17%
817
1%
4122

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
15%10%47%6%35%5%5%7%34%
75183
Night
17%11%47%6%35%45%6%32%
74836
TransparencyDay
32%38%9%12%7%1
74898
Night
34%39%8%11%7%1
74641
SeeingDay
18%12%26%26%15%4
14006
Night
21%10%25%27%14%2
23627

By Month

Percentage Cloud Cover SE (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
18%15%8%10%8%5%445%5%18%
1706
11th to 20thDay
18%19%9%12%8%46%33415%
1710
21st to endDay
16%19%8%13%9%34446%14%
1836
February1st to 10thDay
18%16%6%10%8%35%45%5%21%
1620
11th to 20thDay
16%13%7%12%8%5%445%5%21%
1666
21st to endDay
18%13%5%11%7%35%45%6%24%
1480
March1st to 10thDay
20%11%6%8%6%34446%28%
1892
11th to 20thDay
15%11%6%7%6%44446%32%
1980
21st to endDay
20%11%5%8%6%34446%28%
2178
April1st to 10thDay
13%12%48%5%35%46%6%33%
2007
11th to 20thDay
17%10%36%6%35%45%6%35%
2312
21st to endDay
19%10%46%424447%35%
2340
May1st to 10thDay
17%8%47%6%45%5%46%35%
2340
11th to 20thDay
16%8%36%5%35%6%6%7%35%
2301
21st to endDay
10%5%35%5%46%5%6%9%42%
2531
June1st to 10thDay
13%6%26%5%35%6%5%9%41%
2416
11th to 20thDay
11%5%35%5%35%5%6%8%43%
2643
21st to endDay
10%5%245%35%5%7%9%44%
2551
July1st to 10thDay
10%425%5%35%5%6%9%46%
2520
11th to 20thDay
9%5%245%35%5%6%10%46%
2367
21st to endDay
9%5%25%5%35%6%7%9%44%
2547
August1st to 10thDay
8%5%25%5%45%5%7%8%46%
2327
11th to 20thDay
9%6%246%46%6%6%9%40%
2303
21st to endDay
11%5%26%425%5%6%10%43%
2573
September1st to 10thDay
15%5%25%5%35%46%8%43%
2008
11th to 20thDay
13%5%26%5%345%6%8%44%
1980
21st to endDay
17%6%25%5%35%5%6%6%40%
1980
October1st to 10thDay
14%7%37%5%3446%7%39%
1895
11th to 20thDay
20%7%36%44445%7%35%
1800
21st to endDay
22%11%37%5%35%5%5%7%27%
1922
November1st to 10thDay
13%11%46%5%3445%7%38%
1672
11th to 20thDay
17%16%47%5%44446%31%
1710
21st to endDay
17%18%6%8%7%3445%6%22%
1580
December1st to 10thDay
17%19%7%11%7%45%435%18%
1520
11th to 20thDay
17%16%6%13%7%35%45%6%18%
1910
21st to endDay
24%22%8%10%6%3344411%
3060
January1st to 10thNight
20%16%6%10%7%4444421%
2459
11th to 20thNight
19%18%7%12%8%4434416%
2470
21st to endNight
18%16%7%11%8%3444421%
2664
February1st to 10thNight
20%13%7%11%6%4445%5%22%
2340
11th to 20thNight
17%14%6%10%7%5%5%445%23%
2177
21st to endNight
22%11%5%10%7%3435%5%25%
1776
March1st to 10thNight
17%11%6%6%7%445%46%31%
2066
11th to 20thNight
15%10%46%6%35%5%6%5%35%
1980
21st to endNight
20%11%47%5%33446%32%
2178
April1st to 10thNight
14%12%46%6%35%45%7%34%
1967
11th to 20thNight
16%10%36%5%35%5%5%8%34%
1597
21st to endNight
17%8%36%5%35%45%8%35%
1620
May1st to 10thNight
18%8%47%6%36%5%5%7%29%
1620
11th to 20thNight
18%7%35%5%345%5%9%36%
1592
21st to endNight
9%436%5%35%6%6%10%44%
1744
June1st to 10thNight
11%5%345%35%5%6%7%44%
1535
11th to 20thNight
10%5%35%6%35%7%6%10%41%
1310
21st to endNight
10%5%35%445%6%6%9%44%
1397
July1st to 10thNight
9%425%5%36%46%8%49%
1440
11th to 20thNight
8%4145%45%6%7%9%47%
1588
21st to endNight
8%5%245%35%6%7%10%46%
1771
August1st to 10thNight
7%425%5%35%46%10%49%
1611
11th to 20thNight
10%5%25%5%25%7%7%7%46%
1598
21st to endNight
9%436%5%35%6%5%8%45%
1782
September1st to 10thNight
11%6%25%5%35%5%6%8%44%
1930
11th to 20thNight
11%5%25%5%35%45%7%49%
1980
21st to endNight
14%5%27%6%3446%6%41%
1980
October1st to 10thNight
16%5%25%6%3445%7%43%
2065
11th to 20thNight
21%7%27%5%44446%35%
2160
21st to endNight
26%10%36%6%3445%6%29%
2430
November1st to 10thNight
16%10%45%5%3445%7%36%
2406
11th to 20thNight
17%14%5%8%6%3445%6%29%
2470
21st to endNight
22%16%5%7%6%3445%5%23%
2596
December1st to 10thNight
19%17%8%9%6%35%445%19%
2660
11th to 20thNight
18%17%6%9%6%25%45%5%22%
3285
21st to endNight
26%19%7%8%7%34445%12%
4592

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
45%41%7%6%1
1707
11th to 20thDay
47%41%6%5%1
1710
21st to endDay
51%37%5%5%2
1836
February1st to 10thDay
42%38%9%7%4
1620
11th to 20thDay
43%38%7%7%41
1675
21st to endDay
41%38%10%8%4
1480
March1st to 10thDay
36%38%9%14%3
1892
11th to 20thDay
35%38%8%10%7%1
1980
21st to endDay
39%38%6%14%31
2178
April1st to 10thDay
29%38%9%13%10%1
2007
11th to 20thDay
34%36%9%11%9%1
2312
21st to endDay
32%38%9%14%7%1
2340
May1st to 10thDay
32%38%8%13%8%1
2340
11th to 20thDay
29%39%8%11%11%2
2305
21st to endDay
24%40%10%16%9%1
2531
June1st to 10thDay
25%39%8%17%9%1
2416
11th to 20thDay
22%39%12%15%10%2
2643
21st to endDay
24%39%9%14%10%3
2551
July1st to 10thDay
21%39%9%16%14%1
2451
11th to 20thDay
21%40%11%17%11%1
2296
21st to endDay
22%40%11%15%11%1
2405
August1st to 10thDay
23%39%11%18%9%
2314
11th to 20thDay
23%38%12%16%8%2
2303
21st to endDay
22%39%10%14%13%3
2573
September1st to 10thDay
26%39%10%12%11%2
2008
11th to 20thDay
24%38%11%15%11%
1980
21st to endDay
31%39%9%11%11%
1980
October1st to 10thDay
29%38%7%17%9%
1895
11th to 20thDay
36%38%9%12%5%1
1800
21st to endDay
36%39%9%10%6%1
1922
November1st to 10thDay
24%43%8%15%10%
1672
11th to 20thDay
35%40%7%11%7%
1710
21st to endDay
36%43%7%10%4
1580
December1st to 10thDay
44%41%7%6%2
1520
11th to 20thDay
46%37%6%9%2
1906
21st to endDay
63%28%6%31
3060
January1st to 10thNight
44%40%6%7%2
2459
11th to 20thNight
47%41%6%6%1
2470
21st to endNight
45%38%7%7%1
2664
February1st to 10thNight
41%38%8%9%3
2340
11th to 20thNight
42%38%7%8%4
2179
21st to endNight
41%37%7%9%41
1776
March1st to 10thNight
35%37%9%13%6%
2066
11th to 20thNight
33%38%7%12%9%1
1980
21st to endNight
36%38%5%15%5%1
2178
April1st to 10thNight
32%38%7%10%11%2
1967
11th to 20thNight
29%38%9%12%11%2
1597
21st to endNight
31%38%8%12%10%2
1620
May1st to 10thNight
36%38%8%10%6%2
1620
11th to 20thNight
29%39%7%10%13%3
1593
21st to endNight
22%40%9%18%9%2
1745
June1st to 10thNight
24%39%9%15%10%3
1535
11th to 20thNight
20%42%11%14%11%2
1310
21st to endNight
23%40%9%16%12%1
1397
July1st to 10thNight
22%39%7%16%14%2
1400
11th to 20thNight
20%40%10%17%12%1
1536
21st to endNight
19%42%12%13%12%2
1672
August1st to 10thNight
21%39%11%17%10%1
1600
11th to 20thNight
21%39%10%17%10%2
1598
21st to endNight
21%39%9%15%13%3
1782
September1st to 10thNight
25%38%7%15%11%3
1930
11th to 20thNight
22%39%9%16%13%1
1980
21st to endNight
30%39%8%12%11%1
1980
October1st to 10thNight
27%39%7%14%12%1
2065
11th to 20thNight
34%38%8%11%8%
2160
21st to endNight
37%39%5%12%5%1
2430
November1st to 10thNight
25%42%8%14%10%1
2406
11th to 20thNight
36%42%7%10%5%1
2470
21st to endNight
39%42%6%10%3
2596
December1st to 10thNight
45%42%5%6%2
2660
11th to 20thNight
43%36%10%10%2
3288
21st to endNight
59%29%7%41
4592

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
27%20%32%14%6%1
270
11th to 20thDay
27%20%39%10%5%
270
21st to endDay
24%25%30%16%31
282
February1st to 10thDay
25%23%36%15%
240
11th to 20thDay
29%21%35%13%2
240
21st to endDay
22%30%37%10%1
198
March1st to 10thDay
21%20%32%21%5%
332
11th to 20thDay
20%19%32%22%6%1
420
21st to endDay
27%16%30%22%41
462
April1st to 10thDay
17%15%33%25%9%1
420
11th to 20thDay
20%17%29%21%8%4
412
21st to endDay
24%15%29%24%7%2
420
May1st to 10thDay
23%11%28%25%11%2
423
11th to 20thDay
18%6%30%28%14%4
447
21st to endDay
12%5%24%29%23%6%
485
June1st to 10thDay
14%324%39%16%3
450
11th to 20thDay
11%6%24%34%21%3
573
21st to endDay
10%7%23%35%22%3
630
July1st to 10thDay
8%318%33%26%11%
621
11th to 20thDay
10%5%17%34%25%10%
469
21st to endDay
9%322%33%26%7%
488
August1st to 10thDay
10%317%30%30%10%
446
11th to 20thDay
11%5%16%32%28%8%
439
21st to endDay
11%418%31%27%8%
495
September1st to 10thDay
18%316%27%25%11%
450
11th to 20thDay
12%415%29%29%11%
450
21st to endDay
19%10%21%27%17%7%
450
October1st to 10thDay
17%6%22%27%21%7%
450
11th to 20thDay
21%15%30%25%7%2
450
21st to endDay
29%19%27%20%5%
437
November1st to 10thDay
15%21%28%22%11%2
270
11th to 20thDay
27%21%30%15%6%1
270
21st to endDay
31%21%34%13%1
208
December1st to 10thDay
23%26%31%15%41
180
11th to 20thDay
24%26%34%16%
180
21st to endDay
27%20%35%16%3
279
January1st to 10thNight
28%17%33%18%5%
760
11th to 20thNight
31%15%31%18%4
760
21st to endNight
25%14%33%23%5%
820
February1st to 10thNight
28%13%33%23%4
720
11th to 20thNight
24%16%34%22%4
703
21st to endNight
27%15%35%20%3
592
March1st to 10thNight
22%13%32%26%7%
720
11th to 20thNight
20%13%32%26%8%2
720
21st to endNight
23%10%29%27%10%1
792
April1st to 10thNight
20%13%31%30%6%
707
11th to 20thNight
20%9%32%26%11%2
533
21st to endNight
19%7%30%32%10%1
540
May1st to 10thNight
21%8%22%33%14%1
540
11th to 20thNight
21%5%23%31%18%2
531
21st to endNight
11%318%34%28%5%
584
June1st to 10thNight
13%422%40%21%1
455
11th to 20thNight
11%222%41%23%1
360
21st to endNight
11%421%37%25%2
497
July1st to 10thNight
9%312%38%32%5%
525
11th to 20thNight
11%318%33%29%6%
522
21st to endNight
9%315%40%30%3
591
August1st to 10thNight
11%312%39%29%7%
537
11th to 20thNight
12%312%37%29%6%
534
21st to endNight
11%5%15%33%30%6%
594
September1st to 10thNight
13%7%13%34%27%6%
702
11th to 20thNight
13%413%33%30%6%
720
21st to endNight
17%8%18%29%24%4
720
October1st to 10thNight
19%8%21%27%22%4
720
11th to 20thNight
26%12%28%23%10%1
720
21st to endNight
32%14%25%22%6%
792
November1st to 10thNight
23%15%25%24%11%1
740
11th to 20thNight
29%14%31%18%6%2
760
21st to endNight
32%16%28%18%6%
760
December1st to 10thNight
29%19%28%19%5%
760
11th to 20thNight
27%17%34%17%41
760
21st to endNight
33%14%30%20%3
836
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