James C. Veen Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the James C. Veen Observatory clear sky chart from 2005-11-05 to 2018-02-14.

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
32%
16634
15%
48761
9%
16593
38%
16593
20%
34382

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
16%
975
7%
2716
3%
970
20%
970
9%
2241
January16th to endNight
16%
1040
7%
2912
2%
1040
20%
1040
10%
2413
February1st to 15thNight
15%
763
10%
2380
3%
763
22%
763
9%
1883
February16th to endNight
18%
631
12%
1893
5%
631
26%
631
12%
1454
March1st to 15thNight
26%
720
15%
2130
9%
720
31%
720
18%
1486
March16th to endNight
27%
735
19%
2079
10%
735
35%
735
22%
1430
April1st to 15thNight
24%
539
13%
1797
7%
539
32%
539
17%
1253
April16th to endNight
30%
540
21%
1636
9%
540
40%
540
24%
1051
May1st to 15thNight
30%
540
14%
1620
7%
540
37%
540
22%
1102
May16th to endNight
41%
561
15%
1565
9%
561
46%
561
28%
1036
June1st to 15thNight
46%
540
15%
1440
9%
540
50%
540
34%
904
June16th to endNight
48%
540
15%
1440
9%
540
53%
540
33%
912
July1st to 15thNight
58%
510
16%
1360
12%
510
61%
510
44%
773
July16th to endNight
58%
564
21%
1417
15%
531
61%
531
41%
837
August1st to 15thNight
60%
539
22%
1604
15%
536
65%
536
39%
897
August16th to endNight
59%
573
22%
1817
19%
573
64%
573
33%
1057
September1st to 15thNight
57%
615
26%
1875
21%
615
64%
615
36%
1061
September16th to endNight
54%
717
25%
1980
17%
717
59%
717
35%
1201
October1st to 15thNight
40%
720
21%
2019
16%
720
46%
720
28%
1309
October16th to endNight
25%
768
15%
2484
8%
768
34%
768
16%
1749
November1st to 15thNight
31%
760
18%
2471
15%
760
37%
760
19%
1669
November16th to endNight
22%
780
13%
2535
7%
780
30%
780
12%
1879
December1st to 15thNight
13%
924
5%
2679
2%
924
16%
924
7%
2278
December16th to endNight
11%
1040
6%
2912
0%
1040
17%
1040
7%
2507

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
14%9%47%6%3445%7%33%
49323
Night
15%9%47%5%34446%33%
48930
Cloud CoverDay
14%9%47%6%35%45%7%33%
49332
Night
14%9%47%5%34446%33%
48935
TransparencyDay
50%411%21%11%1
49010
Night
50%411%20%11%1
48761
SeeingDay
18%12%29%21%11%5%
6451
Night
19%11%29%27%11%1
16639

By Month

Percentage Cloud Cover NE (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
18%13%7%11%11%5%6%445%13%
1552
16th to endDay
13%20%11%11%10%4443412%
1664
February1st to 15thDay
13%15%8%12%11%4442417%
1780
16th to endDay
15%13%7%11%6%35%45%5%20%
1580
March1st to 15thDay
15%10%46%6%45%45%6%29%
1820
16th to endDay
16%10%47%5%23446%33%
2154
April1st to 15thDay
21%12%46%41435%5%31%
2151
16th to endDay
17%7%25%42445%6%38%
2323
May1st to 15thDay
20%7%35%5%3445%7%33%
2331
16th to endDay
11%6%26%5%25%5%47%40%
2548
June1st to 15thDay
11%6%245%35%5%5%7%41%
2520
16th to endDay
10%5%25%6%35%5%6%9%40%
2520
July1st to 15thDay
6%5%245%35%5%6%9%44%
2520
16th to endDay
8%424435%6%6%9%44%
2655
August1st to 15thDay
8%5%25%5%45%5%7%9%39%
2346
16th to endDay
11%425%5%25%5%7%8%40%
2383
September1st to 15thDay
11%5%25%6%2445%7%44%
2073
16th to endDay
11%435%5%3445%8%42%
1980
October1st to 15thDay
17%7%27%5%3333438%
1941
16th to endDay
23%8%37%6%45%345%26%
1737
November1st to 15thDay
16%10%45%424446%36%
1717
16th to endDay
18%16%48%5%33446%23%
1755
December1st to 15thDay
16%19%9%12%7%43235%14%
1609
16th to endDay
20%19%9%10%7%3435%312%
1664
January1st to 15thNight
20%14%7%10%8%3444419%
2716
16th to endNight
13%14%9%10%9%45%45%5%16%
2912
February1st to 15thNight
13%15%6%9%9%5%5%445%21%
2378
16th to endNight
14%12%5%9%7%35%5%46%24%
1893
March1st to 15thNight
15%10%36%5%24347%34%
2117
16th to endNight
15%8%36%5%3435%6%37%
2079
April1st to 15thNight
19%9%35%5%25%445%34%
1797
16th to endNight
17%6%35%32445%6%41%
1636
May1st to 15thNight
19%5%35%5%35%447%36%
1620
16th to endNight
11%6%26%6%3445%8%40%
1563
June1st to 15thNight
10%425%5%3436%8%45%
1440
16th to endNight
7%425%5%25%6%7%10%42%
1440
July1st to 15thNight
6%4235%2345%9%53%
1440
16th to endNight
6%226%41445%8%53%
1513
August1st to 15thNight
6%31342447%8%51%
1614
16th to endNight
10%42442335%7%50%
1817
September1st to 15thNight
11%313314347%53%
1875
16th to endNight
8%5%25%324437%49%
1980
October1st to 15thNight
18%7%24423346%42%
2019
16th to endNight
21%8%36%5%34346%32%
2484
November1st to 15thNight
15%10%36%43446%6%35%
2471
16th to endNight
18%14%47%5%3445%6%26%
2535
December1st to 15thNight
19%16%8%10%8%4443414%
2679
16th to endNight
21%16%8%10%7%3444413%
2912

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 15thDay
17%13%8%10%10%5%7%43413%
1552
16th to endDay
13%19%10%12%10%4443412%
1664
February1st to 15thDay
13%14%8%12%11%45%42417%
1780
16th to endDay
15%13%7%11%7%36%45%5%20%
1580
March1st to 15thDay
15%10%47%6%35%5%5%6%29%
1830
16th to endDay
16%10%47%5%24445%33%
2153
April1st to 15thDay
20%12%46%5%1335%5%31%
2151
16th to endDay
17%7%26%42445%7%38%
2323
May1st to 15thDay
19%7%25%5%3445%7%33%
2331
16th to endDay
11%6%36%5%35%5%5%7%40%
2548
June1st to 15thDay
10%6%35%5%35%5%5%8%40%
2520
16th to endDay
10%435%6%35%5%6%9%39%
2520
July1st to 15thDay
6%5%245%36%5%6%9%44%
2520
16th to endDay
8%425%435%5%6%9%44%
2655
August1st to 15thDay
8%5%25%5%46%5%7%9%39%
2346
16th to endDay
11%5%25%435%5%6%8%40%
2383
September1st to 15thDay
10%5%345%345%5%7%43%
2073
16th to endDay
11%425%5%3445%8%42%
1980
October1st to 15thDay
17%7%36%6%33445%38%
1941
16th to endDay
22%8%47%6%35%346%26%
1737
November1st to 15thDay
16%11%45%423346%36%
1717
16th to endDay
18%16%48%5%34436%23%
1755
December1st to 15thDay
15%19%9%13%8%34235%14%
1609
16th to endDay
19%19%9%10%8%3434312%
1664
January1st to 15thNight
19%14%6%10%8%3443418%
2716
16th to endNight
12%14%9%11%8%5%5%45%6%16%
2912
February1st to 15thNight
13%15%7%9%9%45%335%21%
2371
16th to endNight
14%12%6%8%8%445%46%24%
1893
March1st to 15thNight
16%10%36%5%24347%34%
2130
16th to endNight
15%7%36%5%34446%37%
2079
April1st to 15thNight
19%9%35%5%25%445%34%
1797
16th to endNight
17%7%24323446%41%
1636
May1st to 15thNight
18%5%35%435%446%36%
1619
16th to endNight
11%6%35%6%25%36%8%40%
1563
June1st to 15thNight
10%4245%3445%7%46%
1440
16th to endNight
7%425%435%7%6%11%42%
1440
July1st to 15thNight
6%3235%2345%8%54%
1440
16th to endNight
6%315%4135%6%9%52%
1513
August1st to 15thNight
6%41342447%8%51%
1614
16th to endNight
10%43432345%6%50%
1817
September1st to 15thNight
11%31431445%7%52%
1875
16th to endNight
8%5%35%334438%49%
1980
October1st to 15thNight
17%6%24423337%42%
2019
16th to endNight
21%8%36%5%34346%32%
2484
November1st to 15thNight
15%9%36%5%3445%6%35%
2471
16th to endNight
18%13%5%6%6%3445%6%26%
2535
December1st to 15thNight
19%15%8%11%7%35%33414%
2679
16th to endNight
20%16%8%10%7%45%34413%
2912

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
74%5%9%8%2
1553
16th to endDay
76%48%8%3
1664
February1st to 15thDay
71%37%13%3
1782
16th to endDay
65%410%13%5%
1580
March1st to 15thDay
54%5%13%18%7%
1830
16th to endDay
51%412%23%6%1
2154
April1st to 15thDay
54%38%20%11%
2151
16th to endDay
46%413%18%14%3
2323
May1st to 15thDay
49%411%22%9%1
2331
16th to endDay
41%5%12%27%12%
2552
June1st to 15thDay
40%412%25%15%
2520
16th to endDay
39%6%12%21%18%1
2520
July1st to 15thDay
33%5%11%27%18%2
2371
16th to endDay
33%6%12%26%17%2
2488
August1st to 15thDay
38%5%11%29%12%2
2332
16th to endDay
37%5%12%26%14%2
2383
September1st to 15thDay
38%5%9%28%15%1
2073
16th to endDay
38%312%27%16%
1980
October1st to 15thDay
49%39%22%12%1
1941
16th to endDay
59%314%15%5%
1737
November1st to 15thDay
48%411%23%10%1
1717
16th to endDay
61%314%15%4
1755
December1st to 15thDay
73%310%10%2
1609
16th to endDay
75%49%8%2
1664
January1st to 15thNight
69%310%11%4
2716
16th to endNight
67%5%13%9%3
2912
February1st to 15thNight
65%48%16%5%
2380
16th to endNight
60%411%15%6%
1893
March1st to 15thNight
50%412%21%9%1
2130
16th to endNight
47%412%24%10%2
2079
April1st to 15thNight
51%49%18%15%1
1797
16th to endNight
43%312%21%15%4
1636
May1st to 15thNight
48%313%20%11%2
1620
16th to endNight
42%412%22%15%2
1565
June1st to 15thNight
36%412%28%16%1
1440
16th to endNight
33%7%16%24%17%
1440
July1st to 15thNight
27%414%29%21%3
1360
16th to endNight
28%5%14%27%20%3
1417
August1st to 15thNight
28%5%13%32%17%2
1604
16th to endNight
33%49%28%19%3
1817
September1st to 15thNight
30%5%11%31%18%1
1875
16th to endNight
34%312%31%16%1
1980
October1st to 15thNight
42%310%26%16%1
2019
16th to endNight
53%313%21%7%
2484
November1st to 15thNight
48%411%21%12%1
2471
16th to endNight
57%5%13%19%4
2535
December1st to 15thNight
72%48%8%5%
2679
16th to endNight
73%49%9%2
2912

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
17%20%41%17%2
135
16th to endDay
25%18%39%15%
144
February1st to 15thDay
27%33%32%6%
130
16th to endDay
20%20%34%19%3
81
March1st to 15thDay
32%20%27%11%6%
120
16th to endDay
28%9%29%22%6%3
288
April1st to 15thDay
28%14%30%20%5%2
270
16th to endDay
21%16%32%15%9%5%
270
May1st to 15thDay
25%18%24%20%5%5%
288
16th to endDay
15%14%29%24%10%5%
448
June1st to 15thDay
13%10%37%25%9%3
495
16th to endDay
12%13%38%19%11%4
495
July1st to 15thDay
10%7%29%28%16%8%
475
16th to endDay
9%6%29%29%15%8%
515
August1st to 15thDay
10%5%21%24%22%15%
319
16th to endDay
16%5%20%25%19%12%
332
September1st to 15thDay
13%320%28%23%10%
315
16th to endDay
14%7%18%24%24%11%
314
October1st to 15thDay
23%9%25%25%13%3
315
16th to endDay
27%13%41%13%3
153
November1st to 15thDay
23%13%37%17%6%
135
16th to endDay
27%26%29%12%3
135
December1st to 15thDay
29%32%24%8%4
135
16th to endDay
27%38%27%41
144
January1st to 15thNight
26%19%29%17%6%
975
16th to endNight
19%15%33%27%3
1040
February1st to 15thNight
21%18%34%21%3
766
16th to endNight
19%17%33%24%4
631
March1st to 15thNight
20%16%29%24%7%
720
16th to endNight
18%13%34%24%7%1
735
April1st to 15thNight
23%12%34%23%5%
539
16th to endNight
22%11%34%24%6%1
540
May1st to 15thNight
19%8%34%27%8%
540
16th to endNight
14%6%30%32%16%1
563
June1st to 15thNight
11%6%30%34%16%
540
16th to endNight
9%430%37%16%1
540
July1st to 15thNight
8%124%41%20%2
510
16th to endNight
6%125%35%27%2
564
August1st to 15thNight
8%120%40%25%3
539
16th to endNight
12%218%35%26%4
573
September1st to 15thNight
12%420%34%22%6%
615
16th to endNight
11%7%20%32%24%3
717
October1st to 15thNight
20%6%26%29%14%
720
16th to endNight
25%15%29%21%7%
768
November1st to 15thNight
21%12%30%24%10%
760
16th to endNight
25%16%29%22%5%
780
December1st to 15thNight
27%16%32%20%3
924
16th to endNight
27%15%34%18%2
1040
Page generated at 2018-02-15 10:58:44. Version ac04

Copyright 2018 A. Danko


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