Ballard
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ballard clear sky chart from 2005-11-05 to 2017-09-22.

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
43%
15872
23%
47028
15%
15825
51%
15825
31%
28237

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
29%
900
23%
2327
8%
895
39%
895
32%
1453
January16th to endNight
29%
960
26%
2496
10%
960
39%
960
31%
1578
February1st to 15thNight
24%
880
18%
2288
5%
876
31%
876
24%
1561
February16th to endNight
26%
660
25%
1922
9%
660
37%
660
28%
1188
March1st to 15thNight
31%
540
22%
1980
13%
540
44%
540
23%
1191
March16th to endNight
27%
576
15%
2112
10%
576
36%
576
18%
1377
April1st to 15thNight
35%
539
22%
1836
15%
539
47%
539
27%
1063
April16th to endNight
35%
540
21%
1752
16%
540
47%
540
24%
1112
May1st to 15thNight
42%
539
19%
1620
15%
539
49%
539
27%
1054
May16th to endNight
46%
563
20%
1634
16%
561
52%
561
30%
1004
June1st to 15thNight
64%
540
21%
1440
14%
540
68%
540
43%
830
June16th to endNight
65%
540
25%
1440
16%
540
70%
540
49%
800
July1st to 15thNight
70%
510
18%
1522
16%
510
71%
510
39%
846
July16th to endNight
74%
564
25%
1594
26%
531
76%
531
46%
815
August1st to 15thNight
77%
539
26%
1610
31%
536
79%
536
44%
858
August16th to endNight
72%
573
27%
1842
31%
573
75%
573
41%
970
September1st to 15thNight
64%
540
27%
1821
29%
540
67%
540
33%
1016
September16th to endNight
62%
524
30%
1902
26%
524
69%
524
35%
984
October1st to 15thNight
49%
660
29%
1980
22%
660
53%
660
37%
1122
October16th to endNight
39%
704
29%
2112
15%
704
50%
704
36%
1188
November1st to 15thNight
40%
721
31%
2121
16%
721
53%
721
35%
1203
November16th to endNight
30%
900
24%
2517
10%
900
41%
900
30%
1542
December1st to 15thNight
29%
900
19%
2520
7%
900
38%
900
26%
1660
December16th to endNight
28%
960
21%
2640
9%
960
38%
960
23%
1822

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
13%6%25%42445%7%43%
47846
Night
11%5%24423346%49%
47223
TransparencyDay
39%413%25%14%2
47546
Night
35%311%27%18%3
47028
SeeingDay
13%5%22%30%21%6%
5897
Night
14%8%28%32%14%1
15873

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 15thDay
12%5%25%5%3344447%
1611
16th to endDay
14%8%35%413445%44%
1728
February1st to 15thDay
11%9%46%6%24346%39%
1575
16th to endDay
14%9%35%423346%41%
1562
March1st to 15thDay
15%8%47%43445%5%36%
1980
16th to endDay
23%9%35%424246%33%
2110
April1st to 15thDay
15%8%26%5%23335%42%
2111
16th to endDay
21%8%35%5%24346%33%
2205
May1st to 15thDay
19%7%245%34445%37%
2331
16th to endDay
15%5%35%6%24449%36%
2478
June1st to 15thDay
9%5%245%3445%9%44%
2520
16th to endDay
6%213425%5%5%10%51%
2520
July1st to 15thDay
8%425%4245%7%9%45%
2344
16th to endDay
6%3145%35%6%7%9%45%
2466
August1st to 15thDay
7%4145%35%5%5%10%45%
2340
16th to endDay
8%3144346%5%8%48%
2360
September1st to 15thDay
13%425%5%2335%6%47%
2136
16th to endDay
9%41343345%7%51%
1859
October1st to 15thDay
14%5%24322345%51%
1650
16th to endDay
12%6%14422235%52%
1760
November1st to 15thDay
12%6%2331335%6%52%
1737
16th to endDay
17%5%33212346%46%
1442
December1st to 15thDay
14%9%35%5%23446%40%
1440
16th to endDay
15%10%36%323346%39%
1581
January1st to 15thNight
12%5%24423335%50%
2327
16th to endNight
9%6%35%423446%48%
2496
February1st to 15thNight
11%9%46%5%24446%40%
2278
16th to endNight
11%7%26%423345%47%
1922
March1st to 15thNight
13%6%35%422445%45%
1980
16th to endNight
19%7%25%434445%38%
2112
April1st to 15thNight
12%6%2432335%6%48%
1836
16th to endNight
16%6%25%423345%43%
1752
May1st to 15thNight
14%6%35%424447%43%
1619
16th to endNight
14%414324348%46%
1632
June1st to 15thNight
5%2235%15%5%7%9%52%
1440
16th to endNight
321333435%9%58%
1440
July1st to 15thNight
7%31443446%9%51%
1612
16th to endNight
5%21332346%10%56%
1702
August1st to 15thNight
431242446%8%56%
1620
16th to endNight
5%31442446%6%57%
1842
September1st to 15thNight
10%323424447%51%
1821
16th to endNight
6%414433437%55%
1902
October1st to 15thNight
13%323323335%55%
1980
16th to endNight
10%424413235%57%
2112
November1st to 15thNight
10%423423335%56%
2121
16th to endNight
15%6%3431333451%
2517
December1st to 15thNight
17%7%35%313346%43%
2520
16th to endNight
16%9%45%42433441%
2640

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
39%211%27%17%
1612
16th to endDay
41%314%25%13%1
1728
February1st to 15thDay
46%314%23%9%1
1576
16th to endDay
45%313%23%13%2
1562
March1st to 15thDay
48%311%22%12%2
1980
16th to endDay
53%313%18%9%1
2112
April1st to 15thDay
44%311%25%14%
2111
16th to endDay
52%311%20%12%
2205
May1st to 15thDay
49%5%10%22%11%
2331
16th to endDay
45%5%15%21%11%
2482
June1st to 15thDay
36%5%14%26%15%
2520
16th to endDay
26%5%16%32%15%2
2520
July1st to 15thDay
34%6%14%28%13%2
2205
16th to endDay
29%6%15%32%13%1
2311
August1st to 15thDay
33%6%16%26%17%1
2326
16th to endDay
31%6%12%25%17%5%
2360
September1st to 15thDay
36%49%24%18%5%
2136
16th to endDay
31%412%30%18%3
1859
October1st to 15thDay
36%210%23%20%5%
1650
16th to endDay
35%29%29%17%5%
1760
November1st to 15thDay
32%311%26%20%5%
1737
16th to endDay
39%310%26%20%
1442
December1st to 15thDay
44%412%26%11%
1440
16th to endDay
46%213%23%10%2
1581
January1st to 15thNight
36%313%27%18%1
2327
16th to endNight
37%312%28%16%2
2496
February1st to 15thNight
44%311%25%13%1
2288
16th to endNight
39%211%25%18%2
1922
March1st to 15thNight
41%39%24%16%4
1980
16th to endNight
48%311%22%12%1
2112
April1st to 15thNight
36%38%26%21%3
1836
16th to endNight
43%310%24%16%1
1752
May1st to 15thNight
41%5%13%22%16%1
1620
16th to endNight
36%5%16%27%11%1
1634
June1st to 15thNight
26%5%16%29%19%2
1440
16th to endNight
22%5%15%30%23%3
1440
July1st to 15thNight
28%5%12%33%17%3
1522
16th to endNight
22%415%32%21%2
1594
August1st to 15thNight
24%5%13%34%18%3
1610
16th to endNight
25%411%25%25%6%
1842
September1st to 15thNight
32%5%9%25%20%6%
1821
16th to endNight
29%310%30%22%3
1902
October1st to 15thNight
31%39%25%23%7%
1980
16th to endNight
31%38%30%21%5%
2112
November1st to 15thNight
30%310%24%23%7%
2121
16th to endNight
37%27%28%19%3
2517
December1st to 15thNight
43%313%26%13%
2520
16th to endNight
47%310%21%12%3
2640

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
24%13%34%21%6%
90
16th to endDay
19%15%34%21%7%1
96
February1st to 15thDay
7%22%34%30%5%
90
16th to endDay
17%19%41%13%6%1
81
March1st to 15thDay
23%15%43%15%2
90
16th to endDay
27%12%33%17%8%1
96
April1st to 15thDay
16%12%31%27%10%
230
16th to endDay
28%433%22%10%
315
May1st to 15thDay
19%8%30%27%10%2
468
16th to endDay
20%5%28%29%12%4
517
June1st to 15thDay
9%322%34%22%7%
495
16th to endDay
7%129%34%23%4
495
July1st to 15thDay
11%214%35%27%8%
475
16th to endDay
6%9%32%39%12%
515
August1st to 15thDay
7%17%38%35%9%
493
16th to endDay
7%212%32%34%11%
400
September1st to 15thDay
11%210%31%34%9%
291
16th to endDay
8%115%39%24%10%
108
October1st to 15thDay
12%328%34%11%10%
90
16th to endDay
12%5%32%35%11%3
96
November1st to 15thDay
11%6%22%26%21%12%
90
16th to endDay
31%20%22%18%7%
90
December1st to 15thDay
13%14%38%24%44
90
16th to endDay
25%12%37%22%2
96
January1st to 15thNight
15%13%38%24%6%1
900
16th to endNight
12%14%38%28%5%
960
February1st to 15thNight
16%14%39%25%3
880
16th to endNight
18%11%38%28%3
660
March1st to 15thNight
17%10%35%30%5%
540
16th to endNight
21%10%35%26%5%
576
April1st to 15thNight
15%10%34%31%7%
539
16th to endNight
19%5%33%31%9%
540
May1st to 15thNight
14%6%29%36%11%1
540
16th to endNight
16%327%33%17%1
563
June1st to 15thNight
5%220%45%24%1
540
16th to endNight
4123%48%20%1
540
July1st to 15thNight
9%12%44%28%4
510
16th to endNight
6%9%38%42%3
564
August1st to 15thNight
6%15%44%38%3
539
16th to endNight
5%112%38%36%4
573
September1st to 15thNight
11%114%39%28%4
540
16th to endNight
10%217%37%27%4
524
October1st to 15thNight
15%425%31%21%2
660
16th to endNight
12%9%35%29%12%
704
November1st to 15thNight
14%9%32%28%13%
721
16th to endNight
18%13%35%24%7%
900
December1st to 15thNight
21%11%34%28%5%
900
16th to endNight
21%11%32%30%3
960
Page generated at 2017-09-23 05:43:40. Version ac04

Copyright 2017 A. Danko


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