Irondale
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Irondale clear sky chart from 2005-11-06 to 2024-02-10.

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
49%
23584
23%
79396
17%
23477
56%
23477
26%
48504

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
26%
754
21%
4018
10%
737
41%
737
14%
2465
January11th to 20thNight
29%
758
27%
3831
12%
740
41%
740
14%
2210
January21st to endNight
26%
834
19%
4112
12%
814
42%
814
14%
2686
February1st to 10thNight
31%
759
24%
2275
12%
759
42%
759
24%
1483
February11th to 20thNight
25%
703
21%
2098
9%
699
36%
699
23%
1385
February21st to endNight
24%
592
21%
1776
8%
592
35%
592
22%
1200
March1st to 10thNight
34%
720
24%
2160
14%
720
43%
720
28%
1333
March11th to 20thNight
31%
720
19%
2058
9%
720
39%
720
25%
1357
March21st to endNight
34%
707
24%
2093
12%
707
44%
707
27%
1313
April1st to 10thNight
41%
540
25%
1800
19%
540
50%
540
29%
1043
April11th to 20thNight
40%
533
26%
1775
18%
533
53%
533
30%
1020
April21st to endNight
46%
540
27%
1800
20%
540
57%
540
31%
993
May1st to 10thNight
52%
540
25%
1652
18%
540
61%
540
36%
950
May11th to 20thNight
55%
531
20%
1592
14%
531
60%
531
30%
993
May21st to endNight
71%
582
23%
1744
19%
582
74%
582
34%
1039
June1st to 10thNight
67%
540
17%
1620
16%
540
68%
540
28%
1050
June11th to 20thNight
78%
540
19%
1620
15%
540
81%
540
42%
879
June21st to endNight
72%
540
19%
1620
16%
540
74%
540
32%
981
July1st to 10thNight
75%
525
13%
1575
12%
525
76%
525
27%
1047
July11th to 20thNight
77%
522
15%
1566
15%
522
78%
522
29%
1004
July21st to endNight
73%
591
16%
1714
16%
558
75%
558
28%
1101
August1st to 10thNight
80%
537
15%
1778
18%
534
81%
534
31%
1042
August11th to 20thNight
72%
534
15%
1776
18%
534
73%
534
25%
1147
August21st to endNight
70%
594
20%
1980
24%
594
70%
594
23%
1295
September1st to 10thNight
67%
569
22%
1829
23%
569
68%
569
28%
1145
September11th to 20thNight
64%
720
23%
1980
20%
720
66%
720
30%
1279
September21st to endNight
65%
720
30%
1980
22%
720
70%
720
40%
1167
October1st to 10thNight
61%
720
33%
1980
25%
720
67%
720
44%
1102
October11th to 20thNight
52%
720
34%
1980
23%
720
62%
720
39%
1163
October21st to endNight
49%
792
30%
2483
26%
792
57%
792
32%
1452
November1st to 10thNight
55%
740
28%
2406
25%
740
63%
740
36%
1301
November11th to 20thNight
45%
760
30%
2470
21%
760
58%
760
34%
1367
November21st to endNight
41%
760
25%
2470
18%
760
53%
760
28%
1481
December1st to 10thNight
34%
760
23%
2470
15%
760
45%
760
21%
1603
December11th to 20thNight
34%
759
24%
2907
15%
758
43%
758
21%
1741
December21st to endNight
29%
828
14%
4408
14%
817
39%
817
12%
2687

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%35%5%35%5%6%8%41%
78789
Night
12%6%35%5%345%5%7%45%
80187
TransparencyDay
40%7%11%19%18%5%
78515
Night
37%7%10%19%20%6%
79980
SeeingDay
16%9%23%24%19%9%
13520
Night
14%7%23%29%21%4
23605

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
16%13%46%5%3444437%
2836
11th to 20thDay
14%7%36%43333449%
2965
21st to endDay
24%8%34323336%41%
3476
February1st to 10thDay
18%10%45%424446%38%
1890
11th to 20thDay
24%7%34424445%39%
1748
21st to endDay
20%8%36%6%34445%37%
1480
March1st to 10thDay
15%7%26%5%33446%45%
1800
11th to 20thDay
17%8%37%435%45%6%36%
1900
21st to endDay
14%7%35%5%36%5%5%7%40%
2276
April1st to 10thDay
11%6%35%43445%7%47%
2160
11th to 20thDay
13%5%26%5%26%45%7%45%
2134
21st to endDay
9%4245%445%5%8%49%
2160
May1st to 10thDay
11%4245%35%5%6%8%48%
2308
11th to 20thDay
9%6%26%5%35%5%6%9%44%
2301
21st to endDay
8%5%26%5%36%6%5%10%42%
2531
June1st to 10thDay
10%6%28%6%46%7%9%11%32%
2340
11th to 20thDay
6%325%5%46%7%8%11%43%
2340
21st to endDay
8%426%6%46%6%7%11%40%
2340
July1st to 10thDay
8%5%37%7%5%7%9%8%11%30%
2340
11th to 20thDay
7%5%36%7%6%9%8%9%11%30%
2340
21st to endDay
7%5%26%7%48%9%10%12%30%
2497
August1st to 10thDay
7%425%8%6%8%7%10%13%30%
2148
11th to 20thDay
10%6%37%7%5%6%7%8%10%31%
2125
21st to endDay
10%7%37%7%46%6%8%9%32%
2376
September1st to 10thDay
10%5%26%6%46%5%6%8%41%
2111
11th to 20thDay
13%7%245%35%5%6%7%43%
1980
21st to endDay
10%5%246%3445%6%51%
1980
October1st to 10thDay
10%4245%34447%53%
1980
11th to 20thDay
10%5%34423448%54%
1980
21st to endDay
13%4245%23345%54%
1868
November1st to 10thDay
12%6%24423345%54%
1672
11th to 20thDay
13%6%24324446%52%
1710
21st to endDay
15%6%25%5%3445%7%45%
1710
December1st to 10thDay
21%7%345%34446%38%
1710
11th to 20thDay
18%8%36%6%3333443%
2153
21st to endDay
19%10%46%5%3346%6%34%
3124
January1st to 10thNight
17%13%35%43435%5%40%
4109
11th to 20thNight
16%9%45%423435%44%
3992
21st to endNight
21%13%35%43333339%
4180
February1st to 10thNight
17%7%37%5%34346%42%
2275
11th to 20thNight
20%7%35%42434444%
2098
21st to endNight
19%7%35%5%35%5%5%6%38%
1776
March1st to 10thNight
15%7%24424447%46%
2160
11th to 20thNight
14%7%35%5%35%5%5%8%40%
2058
21st to endNight
13%5%35%5%35%45%7%45%
2093
April1st to 10thNight
11%425%5%35%5%5%9%46%
1800
11th to 20thNight
13%6%3442345%7%50%
1775
21st to endNight
10%5%245%3445%7%53%
1800
May1st to 10thNight
9%5%14425%45%9%52%
1652
11th to 20thNight
8%5%26%6%35%5%7%10%45%
1592
21st to endNight
6%424446%7%7%11%46%
1744
June1st to 10thNight
5%5%26%6%46%7%8%11%39%
1620
11th to 20thNight
4213335%6%8%11%53%
1620
21st to endNight
5%435%6%35%6%7%12%45%
1620
July1st to 10thNight
5%5%35%5%5%7%8%8%10%37%
1620
11th to 20thNight
5%425%6%46%7%8%11%42%
1620
21st to endNight
5%426%6%47%8%8%11%40%
1815
August1st to 10thNight
5%325%446%7%10%14%42%
1790
11th to 20thNight
7%5%26%6%36%6%8%10%41%
1776
21st to endNight
10%6%35%5%46%6%6%8%40%
1980
September1st to 10thNight
8%436%7%35%5%5%9%44%
1829
11th to 20thNight
10%5%35%6%346%5%8%46%
1980
21st to endNight
6%5%25%6%2436%7%54%
1980
October1st to 10thNight
8%5%23433346%60%
1980
11th to 20thNight
11%424423446%55%
1980
21st to endNight
13%6%345%2333355%
2483
November1st to 10thNight
11%5%23423445%58%
2406
11th to 20thNight
11%6%34333346%54%
2470
21st to endNight
13%6%245%345%5%6%47%
2470
December1st to 10thNight
18%8%35%5%35%446%40%
2470
11th to 20thNight
16%8%25%423345%47%
3042
21st to endNight
18%8%37%5%345%5%8%33%
4532

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
48%5%6%14%23%5%
2837
11th to 20thDay
38%5%7%25%22%4
2965
21st to endDay
46%37%17%20%7%
3476
February1st to 10thDay
49%37%19%18%4
1890
11th to 20thDay
48%5%418%19%6%
1758
21st to endDay
50%5%6%11%21%7%
1480
March1st to 10thDay
40%5%8%15%21%10%
1800
11th to 20thDay
47%6%11%14%17%5%
1900
21st to endDay
42%7%9%20%19%3
2276
April1st to 10thDay
37%6%11%20%19%8%
2160
11th to 20thDay
39%5%7%19%23%7%
2134
21st to endDay
31%7%9%26%24%3
2160
May1st to 10thDay
33%8%11%22%22%4
2308
11th to 20thDay
36%8%15%23%15%3
2305
21st to endDay
37%7%12%24%17%3
2531
June1st to 10thDay
42%10%15%18%14%1
2340
11th to 20thDay
31%10%18%25%14%2
2340
21st to endDay
35%11%18%22%10%4
2340
July1st to 10thDay
40%14%19%17%9%1
2275
11th to 20thDay
40%15%19%16%8%2
2271
21st to endDay
39%16%18%19%8%1
2357
August1st to 10thDay
38%14%19%22%6%
2136
11th to 20thDay
44%12%16%16%10%3
2125
21st to endDay
44%11%15%17%9%3
2376
September1st to 10thDay
39%9%14%16%17%5%
2111
11th to 20thDay
39%8%11%18%19%4
1980
21st to endDay
34%6%9%21%22%7%
1980
October1st to 10thDay
32%6%10%18%25%9%
1980
11th to 20thDay
29%5%8%22%28%8%
1980
21st to endDay
33%45%17%31%10%
1868
November1st to 10thDay
34%37%16%29%11%
1672
11th to 20thDay
34%47%18%26%11%
1710
21st to endDay
38%6%7%17%24%8%
1710
December1st to 10thDay
47%5%7%16%18%6%
1710
11th to 20thDay
47%45%17%22%6%
2150
21st to endDay
47%6%8%18%18%2
3124
January1st to 10thNight
46%5%6%15%25%4
4109
11th to 20thNight
42%46%22%19%8%
3992
21st to endNight
50%4415%23%5%
4180
February1st to 10thNight
44%46%18%21%8%
2275
11th to 20thNight
45%45%18%19%9%
2099
21st to endNight
45%6%8%14%18%9%
1776
March1st to 10thNight
38%47%17%22%12%
2160
11th to 20thNight
41%6%11%16%19%6%
2058
21st to endNight
38%6%8%23%19%5%
2093
April1st to 10thNight
35%5%13%21%19%8%
1800
11th to 20thNight
34%5%7%20%22%11%
1775
21st to endNight
31%6%10%24%23%6%
1800
May1st to 10thNight
29%7%11%23%25%5%
1652
11th to 20thNight
34%9%17%20%17%3
1593
21st to endNight
28%11%13%27%17%5%
1745
June1st to 10thNight
35%12%14%21%17%1
1620
11th to 20thNight
22%9%23%28%15%3
1620
21st to endNight
30%10%17%22%17%4
1620
July1st to 10thNight
35%13%20%19%10%2
1575
11th to 20thNight
30%15%23%22%9%2
1566
21st to endNight
32%14%23%21%10%1
1714
August1st to 10thNight
28%13%23%29%8%1
1778
11th to 20thNight
34%14%20%16%12%4
1776
21st to endNight
39%11%15%19%12%4
1980
September1st to 10thNight
36%9%16%17%17%5%
1829
11th to 20thNight
35%9%11%19%21%5%
1980
21st to endNight
29%6%10%23%24%8%
1980
October1st to 10thNight
26%5%9%23%25%13%
1980
11th to 20thNight
31%48%20%25%12%
1980
21st to endNight
34%5%5%14%29%12%
2483
November1st to 10thNight
29%48%18%26%14%
2406
11th to 20thNight
32%37%18%27%13%
2470
21st to endNight
37%5%7%18%24%9%
2470
December1st to 10thNight
43%6%8%17%21%5%
2470
11th to 20thNight
41%47%14%29%5%
3044
21st to endNight
46%5%9%19%18%3
4532

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
26%24%30%17%3
270
11th to 20thDay
27%21%29%16%7%
270
21st to endDay
24%26%35%12%31
297
February1st to 10thDay
28%21%34%14%2
267
11th to 20thDay
39%17%29%14%
240
21st to endDay
30%19%41%9%1
198
March1st to 10thDay
25%20%33%17%4
240
11th to 20thDay
24%17%35%16%8%1
340
21st to endDay
22%18%31%20%9%
462
April1st to 10thDay
19%13%32%24%11%1
420
11th to 20thDay
18%14%30%23%13%1
412
21st to endDay
12%12%31%30%12%3
420
May1st to 10thDay
12%11%26%31%16%5%
423
11th to 20thDay
9%5%26%29%21%9%
447
21st to endDay
12%419%29%20%16%
485
June1st to 10thDay
12%416%29%25%13%
450
11th to 20thDay
7%412%28%27%22%
450
21st to endDay
11%411%26%31%18%
450
July1st to 10thDay
6%28%26%32%25%
445
11th to 20thDay
8%29%19%33%30%
444
21st to endDay
7%110%21%34%27%
488
August1st to 10thDay
10%210%23%34%23%
446
11th to 20thDay
10%26%27%37%18%
439
21st to endDay
16%39%23%31%18%
495
September1st to 10thDay
10%210%31%33%14%
450
11th to 20thDay
13%314%29%32%10%
450
21st to endDay
12%316%30%30%8%
450
October1st to 10thDay
11%6%25%30%22%7%
450
11th to 20thDay
13%6%27%33%20%1
450
21st to endDay
19%12%26%29%14%2
325
November1st to 10thDay
17%10%35%24%10%3
270
11th to 20thDay
17%15%41%20%7%
270
21st to endDay
13%19%37%21%9%1
270
December1st to 10thDay
30%16%29%23%3
270
11th to 20thDay
26%14%37%15%6%1
270
21st to endDay
29%16%34%16%5%
297
January1st to 10thNight
22%14%34%25%4
760
11th to 20thNight
22%18%28%25%7%
760
21st to endNight
19%14%36%26%4
836
February1st to 10thNight
22%11%33%30%4
759
11th to 20thNight
24%13%34%26%3
703
21st to endNight
23%13%37%25%2
592
March1st to 10thNight
19%12%32%31%6%
720
11th to 20thNight
18%11%36%24%10%1
720
21st to endNight
17%13%33%27%10%
707
April1st to 10thNight
13%11%32%30%13%1
540
11th to 20thNight
16%9%30%30%14%2
533
21st to endNight
12%9%26%32%19%2
540
May1st to 10thNight
10%6%26%32%22%3
540
11th to 20thNight
9%224%33%27%5%
531
21st to endNight
8%213%33%39%6%
584
June1st to 10thNight
8%211%39%34%6%
540
11th to 20thNight
4110%29%42%14%
540
21st to endNight
5%111%28%43%12%
540
July1st to 10thNight
6%7%28%45%14%
525
11th to 20thNight
6%15%22%44%21%
522
21st to endNight
6%18%25%45%15%
591
August1st to 10thNight
5%1426%48%16%
537
11th to 20thNight
9%17%28%46%10%
534
21st to endNight
13%17%28%39%12%
594
September1st to 10thNight
9%210%28%41%9%
569
11th to 20thNight
11%312%28%40%6%
720
21st to endNight
8%115%33%39%3
720
October1st to 10thNight
10%421%32%27%6%
720
11th to 20thNight
12%6%25%34%20%3
720
21st to endNight
16%8%21%34%19%2
792
November1st to 10thNight
13%7%20%37%20%3
740
11th to 20thNight
14%9%30%34%13%1
760
21st to endNight
17%8%29%33%12%1
760
December1st to 10thNight
22%11%28%30%9%1
760
11th to 20thNight
24%9%30%29%8%
760
21st to endNight
25%12%29%27%7%
836
Page generated at 2024-02-07 05:11:57. Version ac07

Copyright 2024 Attilla Danko


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