Irondale
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Irondale clear sky chart from 2005-11-05 to 2017-03-25.

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
50%
14725
24%
45307
17%
14682
58%
14682
29%
27696

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
30%
720
24%
2327
11%
716
45%
716
24%
1451
January16th to endNight
28%
768
25%
2316
11%
768
42%
768
23%
1528
February1st to 15thNight
32%
704
25%
2112
10%
701
45%
701
27%
1308
February16th to endNight
28%
631
25%
1893
12%
631
40%
631
27%
1194
March1st to 15thNight
34%
720
21%
2151
12%
720
41%
720
27%
1356
March16th to endNight
39%
692
23%
1994
13%
692
47%
692
30%
1212
April1st to 15thNight
43%
494
25%
1647
19%
494
53%
494
30%
938
April16th to endNight
46%
495
25%
1650
19%
495
57%
495
32%
909
May1st to 15thNight
52%
495
23%
1504
16%
495
60%
495
30%
941
May16th to endNight
71%
513
23%
1538
19%
513
75%
513
35%
897
June1st to 15thNight
74%
495
17%
1485
15%
495
75%
495
33%
893
June16th to endNight
81%
495
20%
1485
18%
495
82%
495
38%
844
July1st to 15thNight
74%
465
14%
1395
12%
465
75%
465
27%
923
July16th to endNight
74%
522
15%
1494
15%
489
75%
489
28%
971
August1st to 15thNight
78%
494
19%
1638
22%
491
79%
491
31%
963
August16th to endNight
73%
525
18%
1750
22%
525
73%
525
24%
1151
September1st to 15thNight
65%
568
21%
1723
21%
568
66%
568
26%
1135
September16th to endNight
64%
657
27%
1815
21%
657
67%
657
34%
1113
October1st to 15thNight
59%
660
35%
1815
26%
660
66%
660
41%
1029
October16th to endNight
53%
704
33%
2123
28%
704
60%
704
37%
1197
November1st to 15thNight
52%
700
30%
2276
25%
700
62%
700
36%
1219
November16th to endNight
43%
720
27%
2340
19%
720
55%
720
29%
1369
December1st to 15thNight
38%
720
22%
2340
17%
720
47%
720
24%
1476
December16th to endNight
31%
768
20%
2496
15%
768
40%
768
19%
1679

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
12%5%25%5%35%5%5%7%40%
45639
Night
11%5%2442445%7%46%
45509
TransparencyDay
40%6%10%18%17%4
45343
Night
36%6%10%19%20%7%
45309
SeeingDay
14%5%18%23%22%14%
4477
Night
13%6%23%29%22%4
14727

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
20%7%2441433343%
1611
16th to endDay
18%6%24323435%45%
1905
February1st to 15thDay
16%9%34314336%41%
1750
16th to endDay
20%5%24424335%41%
1580
March1st to 15thDay
16%6%37%5%23346%40%
1807
16th to endDay
14%6%25%425%447%41%
2105
April1st to 15thDay
12%6%26%425%45%6%43%
1971
16th to endDay
10%425%435%45%7%46%
1980
May1st to 15thDay
11%5%245%35%5%6%7%42%
2117
16th to endDay
8%5%16%5%35%6%5%9%42%
2223
June1st to 15thDay
7%427%6%36%8%8%10%33%
2145
16th to endDay
4224436%6%7%12%44%
2145
July1st to 15thDay
9%436%6%5%8%8%7%12%26%
2145
16th to endDay
7%427%6%48%9%9%10%27%
2253
August1st to 15thDay
8%315%7%5%7%7%9%11%31%
1980
16th to endDay
10%6%37%8%47%7%7%8%27%
2100
September1st to 15thDay
12%6%26%6%36%5%6%7%35%
1895
16th to endDay
12%5%146%25%5%46%45%
1815
October1st to 15thDay
11%413423448%50%
1815
16th to endDay
11%424322225%58%
1747
November1st to 15thDay
13%6%13223235%54%
1582
16th to endDay
15%5%24323446%48%
1620
December1st to 15thDay
19%7%34423336%39%
1620
16th to endDay
23%9%35%42333435%
1728
January1st to 15thNight
15%6%2442435%445%
2327
16th to endNight
17%7%344335%45%40%
2316
February1st to 15thNight
16%5%25%323335%47%
2103
16th to endNight
16%5%24424345%46%
1893
March1st to 15thNight
15%6%23324347%43%
2151
16th to endNight
11%5%2442345%7%47%
1994
April1st to 15thNight
12%32342435%8%47%
1647
16th to endNight
9%42442345%6%52%
1650
May1st to 15thNight
9%45%5%35%5%6%8%44%
1503
16th to endNight
4314335%5%6%10%49%
1538
June1st to 15thNight
33145%46%7%8%11%43%
1485
16th to endNight
2123435%6%8%12%48%
1485
July1st to 15thNight
6%4346%47%7%8%10%36%
1485
16th to endNight
5%426%7%36%6%7%11%39%
1604
August1st to 15thNight
5%3145%35%6%9%11%44%
1650
16th to endNight
9%5%25%5%37%5%7%9%38%
1750
September1st to 15thNight
8%425%8%45%6%6%8%39%
1723
16th to endNight
8%425%5%2445%6%49%
1815
October1st to 15thNight
8%5%13322346%57%
1815
16th to endNight
11%42431333358%
2123
November1st to 15thNight
10%5%22313346%56%
2276
16th to endNight
11%6%2443433451%
2340
December1st to 15thNight
15%7%25%424346%43%
2340
16th to endNight
21%7%25%424446%36%
2496

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
45%36%14%25%5%
1612
16th to endDay
41%35%20%21%6%
1905
February1st to 15thDay
45%36%22%18%4
1752
16th to endDay
45%45%15%23%5%
1580
March1st to 15thDay
45%49%14%20%5%
1807
16th to endDay
41%411%20%18%3
2106
April1st to 15thDay
40%5%10%18%18%6%
1971
16th to endDay
35%6%8%22%23%3
1980
May1st to 15thDay
39%6%12%19%18%3
2117
16th to endDay
36%7%14%24%13%3
2227
June1st to 15thDay
40%10%16%20%11%1
2145
16th to endDay
29%9%17%23%15%4
2145
July1st to 15thDay
43%13%17%16%7%1
2006
16th to endDay
42%14%18%15%8%
2100
August1st to 15thDay
40%12%15%18%10%2
1968
16th to endDay
48%11%13%15%9%2
2100
September1st to 15thDay
44%9%13%16%10%5%
1895
16th to endDay
39%6%9%19%19%5%
1815
October1st to 15thDay
32%5%10%17%23%10%
1815
16th to endDay
31%3316%33%11%
1747
November1st to 15thDay
33%25%17%30%10%
1582
16th to endDay
36%46%16%25%9%
1620
December1st to 15thDay
46%47%19%15%6%
1620
16th to endDay
53%37%18%13%4
1728
January1st to 15thNight
41%46%17%25%5%
2327
16th to endNight
44%45%17%20%7%
2316
February1st to 15thNight
39%36%20%20%9%
2112
16th to endNight
40%35%18%23%6%
1893
March1st to 15thNight
39%49%19%19%7%
2151
16th to endNight
34%5%9%23%22%4
1994
April1st to 15thNight
34%311%22%18%8%
1647
16th to endNight
31%5%9%21%23%8%
1650
May1st to 15thNight
35%7%11%19%21%4
1504
16th to endNight
27%10%14%27%15%5%
1540
June1st to 15thNight
29%10%18%24%15%1
1485
16th to endNight
25%9%17%24%19%3
1485
July1st to 15thNight
36%12%19%19%9%3
1395
16th to endNight
34%12%21%20%10%
1494
August1st to 15thNight
28%11%19%22%13%3
1638
16th to endNight
38%11%15%18%12%3
1750
September1st to 15thNight
39%8%15%16%13%5%
1723
16th to endNight
33%6%9%20%22%7%
1815
October1st to 15thNight
27%48%20%24%14%
1815
16th to endNight
31%35%12%31%16%
2123
November1st to 15thNight
29%36%17%28%14%
2276
16th to endNight
35%46%16%25%12%
2340
December1st to 15thNight
42%48%17%21%5%
2340
16th to endNight
49%37%17%16%5%
2496

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
23%16%30%25%31
90
16th to endDay
22%25%40%8%21
96
February1st to 15thDay
23%22%35%17%1
90
16th to endDay
28%8%41%20%
81
March1st to 15thDay
27%17%37%11%6%
97
16th to endDay
20%5%32%23%16%1
264
April1st to 15thDay
20%8%36%20%14%
210
16th to endDay
13%7%22%30%20%6%
210
May1st to 15thDay
12%7%22%27%18%10%
228
16th to endDay
11%214%23%25%21%
267
June1st to 15thDay
12%18%24%27%25%
255
16th to endDay
416%21%33%32%
255
July1st to 15thDay
5%19%23%31%29%
245
16th to endDay
9%5%15%30%38%
270
August1st to 15thDay
13%422%29%28%
253
16th to endDay
13%5%25%33%22%
268
September1st to 15thDay
12%18%20%35%20%
255
16th to endDay
14%212%31%29%9%
254
October1st to 15thDay
13%5%19%29%27%5%
255
16th to endDay
16%221%31%24%4
168
November1st to 15thDay
17%15%27%26%11%1
90
16th to endDay
15%11%42%17%12%1
90
December1st to 15thDay
26%15%33%20%31
90
16th to endDay
33%10%36%13%6%
96
January1st to 15thNight
20%12%33%26%7%
720
16th to endNight
19%13%35%26%5%
768
February1st to 15thNight
19%10%34%30%4
704
16th to endNight
19%11%37%28%3
631
March1st to 15thNight
19%11%32%28%7%
720
16th to endNight
13%10%32%27%15%
692
April1st to 15thNight
13%9%31%30%14%1
494
16th to endNight
11%7%28%33%17%1
495
May1st to 15thNight
9%327%30%24%4
495
16th to endNight
6%14%32%39%6%
515
June1st to 15thNight
5%8%36%39%9%
495
16th to endNight
17%25%46%17%
495
July1st to 15thNight
7%7%25%45%13%
465
16th to endNight
6%6%22%43%20%
522
August1st to 15thNight
7%325%48%15%
494
16th to endNight
11%6%27%41%12%
525
September1st to 15thNight
10%210%23%43%10%
568
16th to endNight
9%13%35%36%4
657
October1st to 15thNight
11%321%31%27%4
660
16th to endNight
12%6%21%31%23%4
704
November1st to 15thNight
12%6%24%31%21%3
700
16th to endNight
14%9%29%32%13%1
720
December1st to 15thNight
20%9%26%32%10%1
720
16th to endNight
26%10%28%26%8%
768
Page generated at 2017-03-26 12:16:38. Version ac04

Copyright 2017 A. Danko


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