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 2017-12-02.

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
51%
15561
24%
47888
18%
15518
58%
15518
29%
29163

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%
711
24%
2055
13%
711
47%
711
29%
1256
April1st to 15thNight
44%
539
24%
1797
18%
539
54%
539
31%
1015
April16th to endNight
47%
540
27%
1800
20%
540
58%
540
33%
982
May1st to 15thNight
52%
540
22%
1641
15%
540
60%
540
31%
1016
May16th to endNight
70%
561
24%
1682
19%
561
74%
561
35%
991
June1st to 15thNight
73%
540
16%
1620
14%
540
74%
540
33%
980
June16th to endNight
77%
540
20%
1620
18%
540
79%
540
36%
948
July1st to 15thNight
75%
510
13%
1530
12%
510
76%
510
29%
983
July16th to endNight
74%
564
16%
1623
17%
531
75%
531
29%
1040
August1st to 15thNight
78%
539
17%
1788
21%
536
78%
536
30%
1072
August16th to endNight
73%
573
19%
1910
24%
573
73%
573
24%
1248
September1st to 15thNight
64%
620
20%
1880
20%
620
65%
620
26%
1230
September16th to endNight
67%
717
29%
1980
24%
717
69%
717
37%
1182
October1st to 15thNight
59%
720
33%
1980
25%
720
66%
720
41%
1125
October16th to endNight
52%
768
35%
2316
29%
768
61%
768
38%
1300
November1st to 15thNight
53%
760
29%
2471
24%
760
63%
760
36%
1339
November16th to endNight
45%
780
29%
2535
20%
780
57%
780
31%
1449
December1st to 15thNight
39%
728
22%
2365
16%
728
47%
728
24%
1491
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%
48550
Night
11%5%2442445%7%46%
48090
TransparencyDay
40%7%10%18%17%4
48254
Night
35%6%10%19%20%7%
47890
SeeingDay
14%5%18%23%23%13%
5433
Night
13%6%22%29%23%5%
15563

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%
2177
April1st to 15thDay
12%6%25%425%45%7%43%
2151
16th to endDay
10%425%5%35%45%7%45%
2160
May1st to 15thDay
11%5%245%245%5%6%44%
2310
16th to endDay
8%5%16%5%35%6%5%9%41%
2431
June1st to 15thDay
7%427%6%36%8%8%10%33%
2340
16th to endDay
6%3245%36%6%7%12%42%
2340
July1st to 15thDay
8%436%6%5%8%8%7%12%27%
2340
16th to endDay
7%426%7%48%9%10%10%28%
2432
August1st to 15thDay
8%425%7%5%7%7%9%11%30%
2160
16th to endDay
10%7%37%7%47%7%7%9%27%
2292
September1st to 15thDay
12%6%26%6%35%5%6%7%37%
2067
16th to endDay
11%5%146%245%5%6%47%
1980
October1st to 15thDay
11%424423448%50%
1980
16th to endDay
10%424322235%58%
1905
November1st to 15thDay
12%6%23323335%53%
1717
16th to endDay
14%5%24323445%49%
1755
December1st to 15thDay
19%7%34423336%39%
1632
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
12%5%2443345%7%47%
2055
April1st to 15thNight
11%32442445%8%48%
1797
16th to endNight
9%32442345%6%53%
1800
May1st to 15thNight
9%415%5%25%5%5%8%46%
1640
16th to endNight
4314435%5%6%11%48%
1682
June1st to 15thNight
43145%36%7%7%12%43%
1620
16th to endNight
3224435%6%8%11%46%
1620
July1st to 15thNight
5%4345%46%7%7%10%40%
1620
16th to endNight
5%426%6%36%6%7%10%40%
1733
August1st to 15thNight
5%3145%36%6%8%11%42%
1800
16th to endNight
8%5%25%5%37%5%7%9%39%
1910
September1st to 15thNight
9%425%7%45%6%5%8%40%
1880
16th to endNight
7%425%5%2435%6%52%
1980
October1st to 15thNight
8%413322346%57%
1980
16th to endNight
11%42431322359%
2316
November1st to 15thNight
10%412313346%55%
2471
16th to endNight
10%6%23434435%52%
2535
December1st to 15thNight
15%7%25%424346%42%
2365
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%5%11%20%18%2
2178
April1st to 15thDay
39%410%18%19%7%
2151
16th to endDay
36%7%8%21%23%3
2160
May1st to 15thDay
38%6%11%18%20%4
2310
16th to endDay
37%7%13%24%13%3
2435
June1st to 15thDay
40%10%16%19%12%1
2340
16th to endDay
32%9%16%22%14%3
2340
July1st to 15thDay
41%13%17%17%7%1
2201
16th to endDay
41%13%17%16%8%
2279
August1st to 15thDay
41%12%15%17%9%2
2148
16th to endDay
48%11%13%15%9%1
2292
September1st to 15thDay
43%8%12%17%12%4
2067
16th to endDay
37%6%10%20%19%5%
1980
October1st to 15thDay
32%5%10%19%22%9%
1980
16th to endDay
30%3416%34%11%
1905
November1st to 15thDay
34%36%16%29%9%
1717
16th to endDay
35%46%16%26%9%
1755
December1st to 15thDay
46%5%7%19%15%6%
1632
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
35%5%9%23%22%4
2055
April1st to 15thNight
33%411%22%19%9%
1797
16th to endNight
30%5%10%22%23%7%
1800
May1st to 15thNight
35%7%10%18%23%4
1641
16th to endNight
28%9%14%27%14%5%
1684
June1st to 15thNight
29%10%18%24%16%1
1620
16th to endNight
28%8%17%23%18%3
1620
July1st to 15thNight
33%11%20%20%9%3
1530
16th to endNight
33%11%21%21%12%
1623
August1st to 15thNight
30%11%18%23%12%3
1788
16th to endNight
38%11%15%19%12%3
1910
September1st to 15thNight
39%8%15%17%14%5%
1880
16th to endNight
31%6%10%22%22%7%
1980
October1st to 15thNight
28%48%22%23%12%
1980
16th to endNight
30%35%12%32%16%
2316
November1st to 15thNight
29%38%17%27%13%
2471
16th to endNight
33%46%16%25%12%
2535
December1st to 15thNight
41%49%17%21%5%
2365
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
19%7%32%22%16%1
288
April1st to 15thDay
18%8%30%24%17%
270
16th to endDay
10%8%25%28%20%5%
270
May1st to 15thDay
13%8%21%28%17%10%
288
16th to endDay
12%418%24%22%17%
331
June1st to 15thDay
12%110%22%28%24%
315
16th to endDay
9%18%22%29%27%
315
July1st to 15thDay
5%7%23%31%30%
305
16th to endDay
9%6%15%30%36%
326
August1st to 15thDay
14%5%24%30%24%
313
16th to endDay
15%6%24%33%21%
332
September1st to 15thDay
14%29%21%31%19%
315
16th to endDay
11%111%31%32%11%
314
October1st to 15thDay
13%421%27%27%4
315
16th to endDay
14%7%21%30%22%3
222
November1st to 15thDay
17%11%31%31%8%
135
16th to endDay
11%11%37%22%14%1
135
December1st to 15thDay
25%14%31%23%31
94
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
14%10%31%27%15%
711
April1st to 15thNight
12%9%30%30%15%1
539
16th to endNight
11%6%27%32%19%2
540
May1st to 15thNight
9%426%31%24%4
540
16th to endNight
7%14%33%37%5%
563
June1st to 15thNight
6%8%34%40%9%
540
16th to endNight
37%25%44%17%
540
July1st to 15thNight
7%6%25%45%15%
510
16th to endNight
6%6%22%43%20%
564
August1st to 15thNight
7%325%48%14%
539
16th to endNight
11%6%28%41%11%
573
September1st to 15thNight
11%211%23%41%10%
620
16th to endNight
9%12%33%38%5%
717
October1st to 15thNight
11%321%30%28%4
720
16th to endNight
12%6%22%30%23%3
768
November1st to 15thNight
12%5%24%33%20%3
760
16th to endNight
13%9%28%32%14%1
780
December1st to 15thNight
20%9%26%32%10%1
728
16th to endNight
26%10%28%26%8%
768
Page generated at 2017-12-03 10:16:40. Version ac04

Copyright 2017 A. Danko


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