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LÓr Na Cruinne Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the LÓr Na Cruinne Observatory clear sky chart from 2005-11-05 to 2019-09-17.

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
44%
17727
14%
54693
10%
17696
48%
17696
22%
36687

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
38%
1049
13%
3135
8%
1045
42%
1045
17%
2253
January16th to endNight
37%
950
19%
3190
12%
950
46%
950
20%
2103
February1st to 15thNight
42%
820
14%
2831
13%
817
47%
817
18%
1919
February16th to endNight
38%
736
13%
2299
11%
736
43%
736
18%
1637
March1st to 15thNight
40%
840
16%
2475
11%
840
46%
840
22%
1715
March16th to endNight
36%
896
11%
2433
4%
896
40%
896
20%
1773
April1st to 15thNight
33%
735
11%
1995
5%
735
37%
735
18%
1491
April16th to endNight
36%
624
12%
1872
8%
624
39%
624
19%
1324
May1st to 15thNight
42%
486
11%
1654
11%
486
47%
486
20%
1088
May16th to endNight
43%
438
6%
1533
4%
438
45%
438
16%
1085
June1st to 15thNight
44%
420
1%
1470
0%
420
45%
420
17%
1030
June16th to endNight
55%
420
1%
1470
0%
420
55%
420
25%
926
July1st to 15thNight
61%
400
3%
1400
0%
400
62%
400
27%
824
July16th to endNight
64%
440
11%
1516
12%
418
67%
418
32%
824
August1st to 15thNight
66%
456
13%
1690
18%
454
68%
454
26%
977
August16th to endNight
64%
669
20%
2007
17%
669
67%
669
39%
1102
September1st to 15thNight
55%
778
18%
2114
12%
778
57%
778
33%
1333
September16th to endNight
53%
780
20%
2157
14%
780
58%
780
33%
1359
October1st to 15thNight
44%
780
16%
2299
10%
780
49%
780
22%
1592
October16th to endNight
46%
832
20%
2704
14%
832
55%
832
27%
1682
November1st to 15thNight
37%
958
17%
2803
10%
958
45%
958
22%
1905
November16th to endNight
36%
1050
15%
3136
7%
1050
44%
1050
22%
2106
December1st to 15thNight
40%
1050
15%
3150
11%
1050
44%
1050
20%
2238
December16th to endNight
39%
1120
15%
3360
9%
1120
44%
1120
19%
2401

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
10%8%36%5%35%5%6%8%35%
56034
Night
8%8%47%6%35%5%6%8%37%
54844
Cloud CoverDay
10%8%36%6%35%5%6%8%34%
56035
Night
8%9%47%6%35%5%6%8%36%
54847
TransparencyDay
45%8%15%20%8%1
55689
Night
43%8%15%22%9%1
54693
SeeingDay
16%7%25%29%16%4
8609
Night
12%428%36%15%2
17734

By Month

Percentage Cloud Cover NW (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
6%9%5%7%5%25%46%8%37%
1463
16th to endDay
5%11%48%6%45%47%9%33%
1750
February1st to 15thDay
5%10%5%9%6%46%6%6%8%29%
1691
16th to endDay
310%6%9%8%5%6%5%6%7%29%
1746
March1st to 15thDay
410%48%8%45%6%6%7%33%
2145
16th to endDay
7%14%6%8%6%36%5%6%7%26%
2494
April1st to 15thDay
11%15%6%7%6%35%5%6%7%25%
2612
16th to endDay
13%11%37%6%345%5%7%30%
2693
May1st to 15thDay
12%9%36%6%36%5%5%7%32%
2954
16th to endDay
22%7%36%5%35%46%8%25%
3282
June1st to 15thDay
19%7%36%6%45%5%6%7%26%
3150
16th to endDay
14%5%35%6%35%5%6%9%33%
3150
July1st to 15thDay
11%4245%35%6%7%9%39%
3150
16th to endDay
7%3135%25%6%6%8%48%
3267
August1st to 15thDay
12%5%245%25%5%7%8%41%
2845
16th to endDay
9%3144245%6%9%48%
2899
September1st to 15thDay
14%6%24423335%47%
2504
16th to endDay
11%7%35%5%2445%7%42%
2157
October1st to 15thDay
14%10%37%5%3445%6%32%
1990
16th to endDay
7%8%35%5%346%6%8%40%
1872
November1st to 15thDay
7%11%47%7%345%7%7%33%
1701
16th to endDay
6%11%38%42346%7%39%
1481
December1st to 15thDay
38%411%7%5%7%6%6%7%31%
1470
16th to endDay
311%49%6%45%6%8%9%30%
1568
January1st to 15thNight
5%10%5%7%8%46%6%6%8%29%
3135
16th to endNight
49%5%7%5%35%5%7%8%36%
3190
February1st to 15thNight
5%9%5%9%6%46%45%8%34%
2820
16th to endNight
49%6%11%7%35%6%6%6%31%
2299
March1st to 15thNight
38%5%8%8%45%5%6%9%34%
2475
16th to endNight
6%13%6%8%5%35%5%6%8%29%
2430
April1st to 15thNight
12%13%49%5%35%45%7%29%
1995
16th to endNight
12%11%48%5%245%5%8%32%
1872
May1st to 15thNight
12%8%36%6%3446%7%36%
1653
16th to endNight
21%5%26%5%35%45%7%31%
1533
June1st to 15thNight
16%7%36%5%35%45%8%33%
1470
16th to endNight
12%425%435%6%7%9%38%
1470
July1st to 15thNight
8%324435%45%10%45%
1470
16th to endNight
6%4133245%6%8%52%
1604
August1st to 15thNight
11%3144235%7%9%45%
1698
16th to endNight
7%3133135%5%8%54%
2007
September1st to 15thNight
12%8%2332335%7%47%
2114
16th to endNight
12%5%2342445%8%46%
2157
October1st to 15thNight
12%9%36%5%345%5%7%35%
2299
16th to endNight
6%8%25%5%345%6%9%41%
2704
November1st to 15thNight
5%11%35%5%35%5%6%7%39%
2803
16th to endNight
5%10%47%5%45%45%7%37%
3136
December1st to 15thNight
410%5%9%7%46%6%6%7%32%
3150
16th to endNight
39%410%9%45%6%7%7%30%
3360

Percentage Cloud Cover SW (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
6%10%5%7%5%25%5%6%8%35%
1463
16th to endDay
5%11%48%7%35%5%7%9%32%
1750
February1st to 15thDay
6%9%5%9%8%5%7%46%7%29%
1691
16th to endDay
410%7%9%7%46%6%6%7%29%
1746
March1st to 15thDay
410%5%9%7%46%6%5%8%32%
2145
16th to endDay
8%14%6%8%7%35%5%6%7%26%
2495
April1st to 15thDay
11%15%6%8%6%25%5%6%7%23%
2612
16th to endDay
14%11%36%6%35%5%6%7%30%
2693
May1st to 15thDay
11%9%36%7%35%5%6%7%32%
2954
16th to endDay
21%7%25%6%345%6%7%26%
3282
June1st to 15thDay
19%7%36%6%36%5%6%8%26%
3150
16th to endDay
13%5%25%5%35%6%7%8%34%
3150
July1st to 15thDay
10%415%5%35%6%7%8%40%
3150
16th to endDay
6%314425%6%7%9%48%
3267
August1st to 15thDay
12%6%24425%5%6%8%41%
2845
16th to endDay
9%4145%235%7%7%49%
2899
September1st to 15thDay
14%7%24423336%47%
2504
16th to endDay
11%8%35%5%23448%41%
2157
October1st to 15thDay
14%11%47%5%3445%7%31%
1990
16th to endDay
6%9%36%5%25%6%6%8%39%
1872
November1st to 15thDay
7%12%5%8%6%345%6%7%32%
1701
16th to endDay
6%11%47%5%3346%7%38%
1481
December1st to 15thDay
49%5%10%7%47%5%6%7%31%
1470
16th to endDay
311%49%7%35%6%7%9%29%
1568
January1st to 15thNight
5%9%5%9%8%45%6%6%8%28%
3135
16th to endNight
410%47%5%45%5%7%9%34%
3190
February1st to 15thNight
5%9%5%9%7%45%5%6%7%33%
2820
16th to endNight
49%6%10%7%5%5%6%5%7%30%
2299
March1st to 15thNight
39%5%8%7%45%6%7%9%33%
2475
16th to endNight
7%13%6%8%6%346%6%8%29%
2433
April1st to 15thNight
12%12%48%6%35%447%28%
1995
16th to endNight
12%11%5%6%5%3445%8%32%
1872
May1st to 15thNight
11%9%36%6%3445%8%36%
1653
16th to endNight
19%6%25%5%36%35%8%31%
1533
June1st to 15thNight
16%8%27%435%46%8%32%
1470
16th to endNight
11%425%5%45%5%6%9%38%
1470
July1st to 15thNight
7%425%5%445%6%8%45%
1470
16th to endNight
6%42332446%8%53%
1604
August1st to 15thNight
10%4144345%6%10%44%
1698
16th to endNight
7%4133235%5%8%54%
2007
September1st to 15thNight
13%7%1332345%7%47%
2114
16th to endNight
12%5%15%32445%8%46%
2157
October1st to 15thNight
11%10%36%5%3446%7%35%
2299
16th to endNight
6%8%35%5%246%6%9%40%
2704
November1st to 15thNight
6%11%36%5%346%5%7%38%
2803
16th to endNight
5%10%47%6%45%5%5%8%36%
3136
December1st to 15thNight
410%5%9%8%5%5%5%6%8%32%
3150
16th to endNight
39%410%9%46%6%6%7%29%
3360

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
42%7%15%25%6%2
1463
16th to endDay
46%7%14%18%10%3
1750
February1st to 15thDay
49%8%14%18%7%1
1691
16th to endDay
50%10%11%17%9%
1746
March1st to 15thDay
46%9%17%18%6%1
2145
16th to endDay
54%8%14%15%6%
2495
April1st to 15thDay
56%7%13%14%6%
2612
16th to endDay
51%8%12%18%7%
2693
May1st to 15thDay
47%9%14%19%8%
2954
16th to endDay
54%8%13%16%5%
3287
June1st to 15thDay
53%9%14%15%6%1
3150
16th to endDay
44%8%17%21%6%1
3150
July1st to 15thDay
38%11%18%22%7%1
2991
16th to endDay
30%10%17%27%12%1
3092
August1st to 15thDay
37%9%21%23%6%
2828
16th to endDay
30%9%18%30%10%1
2899
September1st to 15thDay
38%5%15%22%14%2
2504
16th to endDay
40%7%13%26%10%2
2157
October1st to 15thDay
50%7%13%19%8%
1990
16th to endDay
39%7%15%25%10%
1872
November1st to 15thDay
48%9%13%20%7%1
1701
16th to endDay
41%7%17%22%8%2
1481
December1st to 15thDay
48%8%13%17%9%1
1470
16th to endDay
46%8%14%18%9%1
1568
January1st to 15thNight
48%8%14%18%7%2
3135
16th to endNight
41%9%13%20%11%3
3190
February1st to 15thNight
46%7%12%21%10%1
2831
16th to endNight
49%7%11%19%11%
2299
March1st to 15thNight
42%10%16%23%6%
2475
16th to endNight
50%7%14%17%9%1
2433
April1st to 15thNight
54%6%12%17%9%
1995
16th to endNight
48%7%12%21%7%1
1872
May1st to 15thNight
44%7%13%24%9%
1654
16th to endNight
50%8%14%19%5%1
1533
June1st to 15thNight
48%8%14%18%8%
1470
16th to endNight
38%8%20%23%8%
1470
July1st to 15thNight
33%9%20%26%9%
1400
16th to endNight
27%8%16%31%13%1
1516
August1st to 15thNight
32%10%19%29%8%
1690
16th to endNight
25%7%19%30%13%2
2007
September1st to 15thNight
34%6%16%23%15%3
2114
16th to endNight
34%7%16%25%12%4
2157
October1st to 15thNight
45%7%13%21%9%1
2299
16th to endNight
36%8%17%25%11%
2704
November1st to 15thNight
42%9%14%21%12%
2803
16th to endNight
43%7%17%19%9%2
3136
December1st to 15thNight
48%7%13%20%7%1
3150
16th to endNight
48%8%12%20%8%
3360

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
11%5%12%34%23%13%
120
16th to endDay
9%321%42%17%5%
128
February1st to 15thDay
12%8%19%39%13%7%
136
16th to endDay
8%5%27%37%19%2
249
March1st to 15thDay
9%10%36%26%12%4
390
16th to endDay
15%16%30%22%10%5%
416
April1st to 15thDay
23%11%33%22%7%1
389
16th to endDay
22%13%25%25%9%3
378
May1st to 15thDay
17%7%29%24%18%3
499
16th to endDay
24%419%24%21%4
677
June1st to 15thDay
21%8%24%27%14%3
645
16th to endDay
16%427%28%18%4
645
July1st to 15thDay
14%422%30%23%4
625
16th to endDay
9%427%31%20%6%
616
August1st to 15thDay
17%221%31%21%5%
419
16th to endDay
11%5%25%33%18%7%
460
September1st to 15thDay
21%5%27%27%13%4
435
16th to endDay
21%10%21%31%11%3
380
October1st to 15thDay
26%7%18%32%11%3
259
16th to endDay
12%8%23%29%19%6%
192
November1st to 15thDay
19%426%37%7%4
180
16th to endDay
9%5%26%29%18%10%
123
December1st to 15thDay
5%326%37%19%8%
120
16th to endDay
10%425%33%17%7%
128
January1st to 15thNight
10%8%31%37%10%1
1050
16th to endNight
9%8%32%36%10%1
950
February1st to 15thNight
8%7%28%35%15%4
824
16th to endNight
8%232%33%19%2
736
March1st to 15thNight
7%435%35%13%3
840
16th to endNight
13%5%31%35%12%2
896
April1st to 15thNight
17%5%30%31%13%
735
16th to endNight
19%429%30%15%
624
May1st to 15thNight
15%5%28%33%16%
487
16th to endNight
23%221%31%20%
439
June1st to 15thNight
20%224%33%17%1
420
16th to endNight
14%319%37%24%
420
July1st to 15thNight
11%118%41%24%2
400
16th to endNight
9%117%43%23%2
440
August1st to 15thNight
12%113%36%32%4
456
16th to endNight
8%319%42%25%
669
September1st to 15thNight
18%218%33%23%3
778
16th to endNight
16%321%35%18%4
780
October1st to 15thNight
18%324%32%17%3
780
16th to endNight
12%428%38%14%2
832
November1st to 15thNight
12%7%34%35%8%1
958
16th to endNight
10%6%37%34%9%1
1050
December1st to 15thNight
8%6%31%36%14%2
1050
16th to endNight
7%5%31%40%12%2
1120
Page generated at 2019-09-17 19:12:18. Version ac04

Copyright 2019 A. Danko


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