Roscommon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Roscommon 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
29%
16028
12%
47818
7%
15986
34%
15986
17%
34924

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
12%
900
6%
2506
2%
895
16%
895
7%
2170
January16th to endNight
14%
960
6%
2688
2%
960
18%
960
9%
2270
February1st to 15thNight
13%
713
7%
2267
3%
713
17%
713
7%
1856
February16th to endNight
19%
631
9%
1893
4%
631
24%
631
9%
1539
March1st to 15thNight
23%
720
14%
2112
7%
720
30%
720
17%
1516
March16th to endNight
27%
761
18%
2105
10%
761
34%
761
22%
1455
April1st to 15thNight
25%
539
14%
1773
8%
539
33%
539
16%
1257
April16th to endNight
30%
540
18%
1620
6%
540
40%
540
23%
1083
May1st to 15thNight
32%
540
13%
1620
7%
540
39%
540
21%
1121
May16th to endNight
40%
562
14%
1548
6%
561
48%
561
28%
1021
June1st to 15thNight
39%
375
14%
1275
10%
375
46%
375
24%
799
June16th to endNight
46%
385
13%
1285
10%
385
52%
385
26%
792
July1st to 15thNight
58%
510
15%
1360
10%
510
60%
510
40%
805
July16th to endNight
53%
564
15%
1417
10%
531
56%
531
36%
876
August1st to 15thNight
59%
539
18%
1596
14%
536
64%
536
35%
932
August16th to endNight
55%
573
20%
1758
15%
573
59%
573
31%
1056
September1st to 15thNight
52%
627
20%
1887
15%
627
56%
627
32%
1136
September16th to endNight
48%
717
20%
1980
14%
717
52%
717
30%
1282
October1st to 15thNight
34%
720
17%
2052
11%
720
41%
720
22%
1426
October16th to endNight
22%
768
11%
2472
7%
768
28%
768
13%
1861
November1st to 15thNight
25%
760
14%
2471
11%
760
32%
760
15%
1788
November16th to endNight
15%
780
8%
2626
3%
780
20%
780
8%
2114
December1st to 15thNight
11%
884
4%
2702
1%
884
15%
884
6%
2339
December16th to endNight
12%
960
5%
2805
1%
960
15%
960
6%
2430

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%10%47%6%3445%6%30%
48627
Night
14%10%47%6%3445%6%31%
47986
Cloud CoverDay
15%10%47%6%3445%6%30%
48636
Night
14%10%47%6%3445%6%31%
47991
TransparencyDay
52%6%12%18%9%
48313
Night
52%6%12%18%8%
47818
SeeingDay
19%13%31%21%10%4
6211
Night
19%12%32%25%9%1
16032

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
16%16%8%13%9%45%44313%
1432
16th to endDay
12%16%11%14%9%5%5%44311%
1536
February1st to 15thDay
12%15%8%12%12%4443316%
1595
16th to endDay
11%17%9%12%10%4344417%
1580
March1st to 15thDay
14%11%49%7%35%445%27%
1837
16th to endDay
15%12%5%8%5%3445%5%29%
2130
April1st to 15thDay
20%12%45%433345%31%
2174
16th to endDay
17%10%345%245%5%6%35%
2340
May1st to 15thDay
19%7%36%5%3446%6%33%
2331
16th to endDay
13%6%26%5%35%45%7%40%
2565
June1st to 15thDay
14%6%25%5%346%6%9%35%
2681
16th to endDay
13%436%5%35%5%6%8%36%
2670
July1st to 15thDay
10%5%245%45%5%6%9%40%
2520
16th to endDay
10%5%35%5%35%5%7%9%38%
2655
August1st to 15thDay
9%5%25%6%45%6%6%9%38%
2355
16th to endDay
15%6%25%5%3445%7%39%
2443
September1st to 15thDay
15%5%2443445%8%40%
2060
16th to endDay
14%5%245%35%5%6%8%38%
1980
October1st to 15thDay
22%9%36%5%24345%33%
1908
16th to endDay
23%14%38%7%3435%6%18%
1749
November1st to 15thDay
17%12%46%5%25%45%7%27%
1717
16th to endDay
19%19%7%9%6%24326%17%
1661
December1st to 15thDay
18%17%8%12%8%4434413%
1292
16th to endDay
21%19%10%12%7%2333311%
1416
January1st to 15thNight
18%14%7%12%9%5%443314%
2506
16th to endNight
12%15%7%13%8%46%45%6%15%
2688
February1st to 15thNight
12%14%8%11%10%45%5%4418%
2265
16th to endNight
14%15%5%12%8%35%5%3419%
1893
March1st to 15thNight
14%9%5%8%5%25%345%34%
2099
16th to endNight
14%10%45%42445%6%37%
2105
April1st to 15thNight
19%11%46%32445%6%31%
1773
16th to endNight
15%9%25%423446%40%
1620
May1st to 15thNight
13%6%25%6%45%5%5%7%35%
1620
16th to endNight
12%5%245%345%6%8%41%
1546
June1st to 15thNight
12%5%25%5%25%46%7%41%
1275
16th to endNight
8%5%25%5%35%46%9%43%
1285
July1st to 15thNight
6%41432446%8%51%
1440
16th to endNight
6%4244246%5%9%48%
1513
August1st to 15thNight
6%4244245%5%8%51%
1605
16th to endNight
10%5%2442345%7%49%
1758
September1st to 15thNight
13%425%323445%51%
1887
16th to endNight
12%6%245%2445%7%43%
1980
October1st to 15thNight
20%9%25%423346%37%
2052
16th to endNight
23%10%37%5%2345%6%26%
2472
November1st to 15thNight
14%12%37%6%35%5%48%29%
2471
16th to endNight
18%18%6%8%5%33445%19%
2626
December1st to 15thNight
18%15%7%10%7%45%44414%
2702
16th to endNight
20%17%9%11%6%35%34413%
2805

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
16%16%7%13%9%4444413%
1432
16th to endDay
11%17%11%14%9%46%43411%
1536
February1st to 15thDay
12%16%8%12%12%45%44316%
1595
16th to endDay
11%16%9%11%9%5%444418%
1580
March1st to 15thDay
15%10%48%8%36%5%45%27%
1847
16th to endDay
15%11%5%8%6%3445%5%29%
2129
April1st to 15thDay
20%12%45%433336%31%
2174
16th to endDay
16%10%25%5%2445%7%34%
2340
May1st to 15thDay
18%8%35%5%3436%6%33%
2331
16th to endDay
13%6%26%5%25%45%7%40%
2565
June1st to 15thDay
14%6%25%5%35%6%6%9%35%
2681
16th to endDay
12%5%36%5%35%5%6%8%36%
2670
July1st to 15thDay
9%5%246%45%5%6%9%40%
2520
16th to endDay
10%5%35%5%35%5%7%9%38%
2655
August1st to 15thDay
8%5%25%6%35%5%6%10%38%
2355
16th to endDay
14%7%25%5%245%5%7%39%
2443
September1st to 15thDay
14%6%245%35%448%40%
2060
16th to endDay
13%6%25%5%35%5%5%8%37%
1980
October1st to 15thDay
20%9%36%5%24345%34%
1908
16th to endDay
23%13%38%7%3445%6%18%
1749
November1st to 15thDay
17%12%36%5%245%5%7%27%
1717
16th to endDay
19%20%6%8%7%34325%17%
1661
December1st to 15thDay
18%16%8%12%7%4444413%
1292
16th to endDay
21%19%10%12%7%2332410%
1416
January1st to 15thNight
19%14%7%12%8%5%5%44414%
2506
16th to endNight
12%15%8%12%8%46%45%7%15%
2688
February1st to 15thNight
12%14%8%10%9%45%5%4418%
2258
16th to endNight
14%15%5%12%8%45%44420%
1893
March1st to 15thNight
14%10%5%7%6%25%345%34%
2112
16th to endNight
14%9%45%42445%6%38%
2105
April1st to 15thNight
19%10%47%42445%6%30%
1773
16th to endNight
15%9%25%434446%40%
1620
May1st to 15thNight
13%6%26%6%445%5%7%34%
1619
16th to endNight
11%5%245%35%6%6%8%40%
1546
June1st to 15thNight
12%5%26%425%45%8%41%
1275
16th to endNight
8%6%24435%46%8%44%
1285
July1st to 15thNight
6%425%3245%6%9%50%
1440
16th to endNight
6%425%4245%6%8%48%
1513
August1st to 15thNight
7%3144245%48%51%
1605
16th to endNight
9%5%2443345%7%49%
1758
September1st to 15thNight
12%5%24323345%51%
1887
16th to endNight
12%6%25%5%3435%8%44%
1980
October1st to 15thNight
19%8%26%423246%38%
2052
16th to endNight
23%9%37%5%3345%7%26%
2472
November1st to 15thNight
14%12%37%5%35%45%8%29%
2471
16th to endNight
18%18%6%8%5%33445%20%
2626
December1st to 15thNight
18%15%8%10%8%35%45%5%14%
2702
16th to endNight
19%17%9%10%6%45%44413%
2805

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
73%5%9%9%2
1433
16th to endDay
76%5%7%7%2
1536
February1st to 15thDay
72%6%8%10%3
1597
16th to endDay
69%49%12%3
1580
March1st to 15thDay
56%6%12%16%6%
1847
16th to endDay
55%5%11%18%7%1
2130
April1st to 15thDay
54%410%19%10%
2174
16th to endDay
48%5%13%14%14%2
2340
May1st to 15thDay
50%6%10%20%9%2
2331
16th to endDay
42%6%12%23%12%1
2569
June1st to 15thDay
43%7%12%23%11%
2681
16th to endDay
42%8%15%20%11%
2670
July1st to 15thDay
38%7%12%24%15%1
2371
16th to endDay
39%7%14%21%14%1
2488
August1st to 15thDay
38%9%15%24%11%
2340
16th to endDay
42%6%14%21%12%1
2443
September1st to 15thDay
41%7%12%24%12%1
2060
16th to endDay
41%8%16%24%9%
1980
October1st to 15thDay
53%5%10%21%8%
1908
16th to endDay
65%6%13%10%3
1749
November1st to 15thDay
54%7%13%17%6%
1717
16th to endDay
69%6%10%9%3
1661
December1st to 15thDay
74%5%10%7%1
1292
16th to endDay
78%5%8%6%1
1416
January1st to 15thNight
72%6%7%9%4
2506
16th to endNight
67%8%12%8%2
2688
February1st to 15thNight
66%7%9%13%3
2267
16th to endNight
65%6%10%11%4
1893
March1st to 15thNight
51%5%12%18%10%
2112
16th to endNight
45%5%12%23%10%1
2105
April1st to 15thNight
53%49%19%11%
1773
16th to endNight
44%5%11%20%15%2
1620
May1st to 15thNight
46%6%11%21%10%3
1620
16th to endNight
39%7%14%23%13%2
1548
June1st to 15thNight
39%6%12%23%17%
1275
16th to endNight
36%8%13%25%15%
1285
July1st to 15thNight
26%8%14%28%20%1
1360
16th to endNight
31%7%16%28%14%1
1417
August1st to 15thNight
29%7%18%28%15%
1596
16th to endNight
33%7%15%27%15%1
1758
September1st to 15thNight
33%6%12%30%15%1
1887
16th to endNight
38%6%16%29%9%
1980
October1st to 15thNight
48%410%24%11%1
2052
16th to endNight
56%7%14%16%5%
2472
November1st to 15thNight
53%6%14%16%8%
2471
16th to endNight
65%6%13%10%2
2626
December1st to 15thNight
70%9%9%8%2
2702
16th to endNight
74%5%10%7%2
2805

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
22%17%52%5%2
90
16th to endDay
35%12%37%11%3
96
February1st to 15thDay
23%30%38%6%1
90
16th to endDay
24%23%40%7%3
81
March1st to 15thDay
28%18%35%13%4
137
16th to endDay
26%12%28%21%9%2
288
April1st to 15thDay
25%17%28%19%8%
270
16th to endDay
22%15%32%16%8%4
270
May1st to 15thDay
23%17%29%15%9%3
288
16th to endDay
18%15%32%22%8%3
465
June1st to 15thDay
17%15%30%25%8%2
495
16th to endDay
13%13%37%22%8%3
495
July1st to 15thDay
10%11%32%27%14%4
475
16th to endDay
10%8%33%27%12%6%
515
August1st to 15thDay
10%326%30%16%12%
328
16th to endDay
21%5%24%20%20%7%
332
September1st to 15thDay
14%6%21%25%19%12%
315
16th to endDay
14%8%22%27%18%7%
314
October1st to 15thDay
25%11%30%22%9%1
315
16th to endDay
27%24%33%9%4
165
November1st to 15thDay
24%16%35%17%5%1
135
16th to endDay
25%25%36%9%2
113
December1st to 15thDay
26%31%30%6%31
63
16th to endDay
35%38%23%2
76
January1st to 15thNight
24%18%34%18%3
900
16th to endNight
19%14%39%20%5%
960
February1st to 15thNight
21%19%36%18%3
716
16th to endNight
24%17%30%23%3
631
March1st to 15thNight
19%17%34%21%6%
720
16th to endNight
18%13%35%24%6%1
761
April1st to 15thNight
21%15%33%23%5%
539
16th to endNight
18%12%35%25%7%1
540
May1st to 15thNight
16%10%36%28%7%
540
16th to endNight
15%8%30%31%13%
563
June1st to 15thNight
15%6%34%31%10%
375
16th to endNight
9%433%37%13%1
385
July1st to 15thNight
9%323%42%20%1
510
16th to endNight
8%428%36%21%1
564
August1st to 15thNight
9%122%40%23%2
539
16th to endNight
12%422%36%22%1
573
September1st to 15thNight
14%5%23%29%21%5%
627
16th to endNight
14%7%24%30%17%4
717
October1st to 15thNight
24%7%28%27%11%
720
16th to endNight
29%13%29%22%5%
768
November1st to 15thNight
22%14%32%21%8%
760
16th to endNight
26%17%35%17%3
780
December1st to 15thNight
26%17%36%16%2
884
16th to endNight
26%17%36%15%3
960
Page generated at 2017-12-03 11:16:38. Version ac04

Copyright 2017 A. Danko


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