Dundalk
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dundalk clear sky chart from 2005-11-05 to 2017-10-31.

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
24%
15106
11%
47147
6%
15068
30%
15068
14%
35163

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
6%
804
4%
2538
1%
802
9%
802
3%
2253
January16th to endNight
10%
768
5%
2496
2%
768
13%
768
5%
2169
February1st to 15thNight
10%
701
5%
2287
1%
701
15%
701
5%
1938
February16th to endNight
12%
631
8%
1997
1%
631
19%
631
7%
1602
March1st to 15thNight
14%
720
11%
1998
4%
720
20%
720
11%
1573
March16th to endNight
24%
768
19%
2112
8%
768
33%
768
19%
1501
April1st to 15thNight
19%
699
14%
1822
4%
699
26%
699
17%
1354
April16th to endNight
27%
540
17%
1620
8%
540
34%
540
19%
1115
May1st to 15thNight
37%
516
15%
1596
11%
516
42%
516
22%
1078
May16th to endNight
37%
374
16%
1497
11%
374
50%
374
23%
869
June1st to 15thNight
38%
360
11%
1374
9%
360
48%
360
19%
857
June16th to endNight
39%
360
14%
1260
12%
360
47%
360
26%
750
July1st to 15thNight
47%
340
17%
1207
19%
340
54%
340
33%
653
July16th to endNight
45%
516
14%
1547
11%
483
50%
483
27%
937
August1st to 15thNight
52%
539
15%
1609
11%
536
55%
536
30%
979
August16th to endNight
48%
595
20%
1741
12%
595
53%
595
30%
1073
September1st to 15thNight
43%
720
17%
1845
8%
720
47%
720
32%
1207
September16th to endNight
45%
717
20%
1981
13%
717
49%
717
28%
1303
October1st to 15thNight
27%
720
13%
2160
10%
720
32%
720
18%
1541
October16th to endNight
15%
768
9%
2312
4%
768
22%
768
9%
1855
November1st to 15thNight
23%
700
14%
2378
10%
700
29%
700
12%
1781
November16th to endNight
14%
720
8%
2520
5%
720
19%
720
8%
2057
December1st to 15thNight
5%
720
3%
2520
0%
720
9%
720
3%
2243
December16th to endNight
5%
810
3%
2730
0%
810
8%
810
3%
2475

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
15%11%48%6%35%45%6%27%
48581
Night
14%11%5%8%6%34446%29%
47320
Cloud CoverDay
15%11%5%7%6%35%45%6%27%
48591
Night
13%10%5%8%7%35%45%6%29%
47324
TransparencyDay
55%7%11%16%8%
48272
Night
54%7%11%16%9%1
47147
SeeingDay
19%17%30%20%9%3
5857
Night
18%19%31%20%8%1
15113

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
15%16%9%15%10%4442411%
1394
16th to endDay
10%17%9%14%11%46%45%410%
1728
February1st to 15thDay
12%15%10%15%11%6%6%33311%
1575
16th to endDay
14%16%7%11%9%47%34415%
1473
March1st to 15thDay
14%12%6%10%8%45%34423%
1951
16th to endDay
13%11%5%7%6%35%446%30%
2112
April1st to 15thDay
19%13%45%5%3435%5%27%
2137
16th to endDay
18%10%35%42335%5%36%
2340
May1st to 15thDay
18%8%36%5%3435%7%33%
2352
16th to endDay
14%7%35%5%3445%9%38%
2618
June1st to 15thDay
17%7%25%4345%5%8%35%
2581
16th to endDay
15%6%25%5%25%5%6%9%34%
2700
July1st to 15thDay
12%6%25%5%35%5%5%9%37%
2679
16th to endDay
11%6%36%6%35%5%6%10%32%
2512
August1st to 15thDay
12%5%27%7%45%5%5%8%34%
2340
16th to endDay
12%6%37%6%36%6%6%8%32%
2448
September1st to 15thDay
18%6%36%5%34446%35%
2112
16th to endDay
16%7%36%6%235%5%8%36%
1977
October1st to 15thDay
21%11%36%5%34445%30%
1800
16th to endDay
26%15%37%7%35%44417%
1908
November1st to 15thDay
15%16%46%6%35%35%5%26%
1479
16th to endDay
17%19%7%9%6%35%5%45%14%
1440
December1st to 15thDay
14%22%10%16%6%36%3339%
1440
16th to endDay
16%20%12%15%8%343238%
1485
January1st to 15thNight
18%15%8%13%9%44345%11%
2538
16th to endNight
11%13%8%15%11%6%6%5%45%11%
2496
February1st to 15thNight
12%14%7%12%10%5%6%5%5%5%14%
2285
16th to endNight
11%14%6%13%8%46%5%5%6%18%
1997
March1st to 15thNight
15%10%5%10%7%35%436%26%
1986
16th to endNight
11%9%47%6%34435%37%
2112
April1st to 15thNight
18%11%46%5%34446%32%
1822
16th to endNight
13%11%36%4345%45%37%
1620
May1st to 15thNight
14%8%26%5%245%6%7%36%
1596
16th to endNight
10%6%24425%5%48%44%
1495
June1st to 15thNight
12%5%35%5%35%447%40%
1374
16th to endNight
11%5%24425%45%9%45%
1260
July1st to 15thNight
7%5%14414448%52%
1278
16th to endNight
7%5%245%25%46%8%45%
1654
August1st to 15thNight
8%4145%25%46%10%46%
1620
16th to endNight
9%5%25%6%24446%48%
1741
September1st to 15thNight
13%5%15%42345%7%46%
1845
16th to endNight
13%6%245%33346%44%
1981
October1st to 15thNight
19%8%35%6%3435%7%33%
2160
16th to endNight
20%13%48%7%35%5%5%422%
2312
November1st to 15thNight
16%13%36%6%36%45%6%26%
2378
16th to endNight
18%15%7%8%6%3445%6%18%
2520
December1st to 15thNight
17%19%10%14%7%3433411%
2520
16th to endNight
18%18%11%15%8%344438%
2730

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
15%17%7%14%11%5%5%32411%
1394
16th to endDay
10%18%9%13%12%5%5%5%45%10%
1728
February1st to 15thDay
12%15%9%14%11%6%6%44310%
1575
16th to endDay
15%16%7%10%8%6%5%5%35%14%
1473
March1st to 15thDay
14%13%6%9%8%46%345%23%
1962
16th to endDay
13%11%47%6%35%445%30%
2111
April1st to 15thDay
18%12%5%6%5%25%446%27%
2137
16th to endDay
17%10%45%423346%36%
2340
May1st to 15thDay
17%9%46%5%3435%6%33%
2352
16th to endDay
14%7%35%5%3445%8%37%
2618
June1st to 15thDay
16%6%35%5%345%5%8%34%
2581
16th to endDay
15%6%25%6%25%5%7%9%34%
2700
July1st to 15thDay
11%6%26%6%36%5%5%9%37%
2679
16th to endDay
10%7%36%7%46%46%9%31%
2512
August1st to 15thDay
11%7%27%7%36%5%5%8%34%
2340
16th to endDay
11%7%37%6%46%6%6%8%31%
2448
September1st to 15thDay
17%8%35%5%34446%34%
2112
16th to endDay
16%7%35%5%2445%7%36%
1977
October1st to 15thDay
20%12%36%6%23445%29%
1800
16th to endDay
26%14%47%6%35%44417%
1908
November1st to 15thDay
14%15%6%7%6%3435%6%25%
1479
16th to endDay
16%19%6%10%7%35%5%5%5%13%
1440
December1st to 15thDay
15%20%11%14%8%434239%
1440
16th to endDay
16%21%11%14%9%343338%
1485
January1st to 15thNight
17%15%8%13%9%45%445%10%
2538
16th to endNight
11%12%8%15%11%6%6%5%5%5%11%
2496
February1st to 15thNight
11%13%7%12%10%5%6%5%6%5%14%
2278
16th to endNight
11%13%5%12%9%46%446%18%
1997
March1st to 15thNight
15%11%6%9%7%34446%25%
1998
16th to endNight
11%9%5%7%5%34445%37%
2112
April1st to 15thNight
17%10%46%5%34436%32%
1822
16th to endNight
12%11%35%6%24445%37%
1620
May1st to 15thNight
14%8%35%5%345%6%6%37%
1595
16th to endNight
10%6%245%245%5%7%45%
1495
June1st to 15thNight
12%7%36%335%5%5%7%40%
1374
16th to endNight
11%5%25%43445%9%44%
1260
July1st to 15thNight
7%5%244135%48%53%
1278
16th to endNight
7%415%5%35%47%7%45%
1654
August1st to 15thNight
7%3235%25%5%7%9%45%
1620
16th to endNight
7%5%35%5%24347%48%
1741
September1st to 15thNight
13%42442345%7%45%
1845
16th to endNight
13%6%25%5%33346%44%
1981
October1st to 15thNight
17%9%26%6%3335%8%33%
2160
16th to endNight
19%12%48%7%45%45%6%22%
2312
November1st to 15thNight
15%12%37%6%45%5%5%6%27%
2378
16th to endNight
17%15%6%9%7%25%45%6%18%
2520
December1st to 15thNight
17%18%9%14%7%35%34411%
2520
16th to endNight
17%17%10%16%8%343438%
2730

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
77%6%6%6%2
1395
16th to endDay
74%7%8%5%3
1728
February1st to 15thDay
77%5%5%9%1
1577
16th to endDay
70%7%7%8%5%
1473
March1st to 15thDay
63%5%10%13%7%
1962
16th to endDay
53%6%10%15%12%1
2112
April1st to 15thDay
57%5%8%18%9%
2137
16th to endDay
47%5%11%19%14%1
2340
May1st to 15thDay
50%5%10%21%12%
2352
16th to endDay
43%7%13%20%13%1
2622
June1st to 15thDay
46%7%12%21%12%
2581
16th to endDay
44%8%14%21%10%
2700
July1st to 15thDay
41%8%13%22%14%1
2521
16th to endDay
47%7%13%20%8%1
2356
August1st to 15thDay
46%8%15%16%12%1
2327
16th to endDay
47%9%14%19%8%1
2448
September1st to 15thDay
49%6%11%21%9%1
2112
16th to endDay
46%6%13%23%8%
1977
October1st to 15thDay
55%6%9%16%10%
1800
16th to endDay
68%7%10%9%4
1908
November1st to 15thDay
59%6%12%13%7%
1479
16th to endDay
70%7%10%8%2
1440
December1st to 15thDay
79%7%6%5%
1440
16th to endDay
80%6%46%1
1485
January1st to 15thNight
75%8%7%5%2
2538
16th to endNight
72%8%9%6%1
2496
February1st to 15thNight
68%9%9%9%2
2287
16th to endNight
63%8%11%10%6%
1997
March1st to 15thNight
59%7%9%16%6%
1998
16th to endNight
48%6%8%19%15%2
2112
April1st to 15thNight
53%48%18%13%
1822
16th to endNight
47%6%9%15%18%2
1620
May1st to 15thNight
44%7%11%20%14%1
1596
16th to endNight
36%6%14%26%13%2
1497
June1st to 15thNight
41%7%12%22%15%1
1374
16th to endNight
35%7%15%26%14%
1260
July1st to 15thNight
27%7%12%28%21%2
1207
16th to endNight
35%7%13%25%16%1
1547
August1st to 15thNight
31%10%17%24%14%
1609
16th to endNight
35%7%13%28%14%1
1741
September1st to 15thNight
36%6%15%26%13%
1845
16th to endNight
40%5%13%27%12%
1981
October1st to 15thNight
48%8%12%17%12%1
2160
16th to endNight
61%8%12%12%4
2312
November1st to 15thNight
55%8%12%14%7%1
2378
16th to endNight
65%8%11%10%21
2520
December1st to 15thNight
76%8%7%5%1
2520
16th to endNight
79%6%6%5%
2730

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%42%30%10%
69
16th to endDay
28%26%37%7%1
96
February1st to 15thDay
26%37%34%1
90
16th to endDay
23%39%32%4
81
March1st to 15thDay
21%26%33%12%5%
252
16th to endDay
23%16%32%18%7%1
288
April1st to 15thDay
22%21%34%14%7%
270
16th to endDay
21%22%27%14%8%4
270
May1st to 15thDay
23%12%33%20%6%3
288
16th to endDay
16%17%32%21%8%3
331
June1st to 15thDay
20%14%28%27%8%
376
16th to endDay
14%14%36%23%8%2
495
July1st to 15thDay
15%11%29%27%10%5%
455
16th to endDay
10%10%33%26%13%6%
326
August1st to 15thDay
12%7%28%26%16%8%
313
16th to endDay
15%6%26%28%16%6%
332
September1st to 15thDay
14%10%22%25%17%9%
315
16th to endDay
16%8%25%22%19%7%
314
October1st to 15thDay
22%16%30%18%9%3
315
16th to endDay
29%27%25%16%2
324
November1st to 15thDay
17%19%35%19%6%1
73
16th to endDay
25%30%33%5%6%
60
December1st to 15thDay
26%41%23%8%
60
16th to endDay
26%53%18%1
64
January1st to 15thNight
24%31%30%10%2
807
16th to endNight
16%22%41%16%3
768
February1st to 15thNight
19%29%34%14%1
704
16th to endNight
18%25%35%16%3
631
March1st to 15thNight
19%28%33%15%2
720
16th to endNight
18%19%34%20%7%
768
April1st to 15thNight
22%21%34%18%3
699
16th to endNight
20%16%32%21%7%1
540
May1st to 15thNight
17%12%29%29%10%1
516
16th to endNight
13%12%33%28%12%
375
June1st to 15thNight
14%8%33%33%9%
360
16th to endNight
11%9%35%31%12%
360
July1st to 15thNight
7%5%34%34%17%
340
16th to endNight
9%6%32%33%16%1
516
August1st to 15thNight
9%426%36%20%1
539
16th to endNight
11%7%27%30%20%2
595
September1st to 15thNight
15%10%28%23%15%6%
720
16th to endNight
15%9%24%29%16%4
717
October1st to 15thNight
22%15%31%17%11%1
720
16th to endNight
25%25%30%15%3
768
November1st to 15thNight
19%24%28%20%6%
700
16th to endNight
23%25%31%14%4
720
December1st to 15thNight
25%30%32%9%1
720
16th to endNight
26%29%30%11%2
810
Page generated at 2017-11-01 17:23:34. Version ac04

Copyright 2017 A. Danko


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