Lorenz Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lorenz Observatory clear sky chart from 2005-11-05 to 2017-09-16.

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
33%
14759
15%
46863
9%
14727
40%
14727
19%
32182

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
14%
720
9%
2506
3%
716
22%
716
9%
1924
January16th to endNight
21%
768
12%
2533
6%
768
29%
768
11%
1931
February1st to 15thNight
15%
702
10%
2287
3%
701
23%
701
12%
1740
February16th to endNight
21%
631
14%
2000
5%
631
33%
631
15%
1431
March1st to 15thNight
22%
720
14%
2013
6%
720
30%
720
18%
1456
March16th to endNight
30%
768
21%
2094
8%
768
40%
768
26%
1404
April1st to 15thNight
27%
718
16%
1796
5%
718
34%
718
23%
1280
April16th to endNight
34%
617
19%
1697
7%
617
42%
617
27%
1113
May1st to 15thNight
41%
423
16%
1503
12%
423
48%
423
21%
977
May16th to endNight
46%
374
17%
1497
16%
374
56%
374
24%
861
June1st to 15thNight
45%
360
12%
1440
12%
360
55%
360
21%
883
June16th to endNight
51%
360
11%
1440
15%
360
57%
360
22%
873
July1st to 15thNight
57%
340
16%
1360
22%
340
64%
340
31%
706
July16th to endNight
60%
406
16%
1446
19%
382
64%
382
30%
801
August1st to 15thNight
61%
539
16%
1609
13%
536
64%
536
33%
965
August16th to endNight
58%
663
23%
1809
13%
663
63%
663
38%
1071
September1st to 15thNight
52%
720
19%
1800
9%
720
56%
720
33%
1179
September16th to endNight
52%
658
22%
1826
15%
658
56%
658
30%
1171
October1st to 15thNight
37%
660
17%
1980
13%
660
44%
660
22%
1364
October16th to endNight
21%
704
12%
2120
5%
704
30%
704
14%
1586
November1st to 15thNight
35%
700
18%
2379
15%
700
42%
700
19%
1574
November16th to endNight
22%
720
12%
2520
7%
720
30%
720
12%
1849
December1st to 15thNight
16%
720
7%
2520
3%
720
22%
720
10%
1935
December16th to endNight
13%
768
9%
2688
2%
768
21%
768
8%
2108

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
14%8%36%6%35%45%7%34%
47887
Night
15%8%36%5%3445%6%36%
47036
Cloud CoverDay
14%8%36%5%35%45%7%35%
47897
Night
15%8%36%5%3445%6%36%
47041
TransparencyDay
47%6%13%20%10%1
47578
Night
47%6%12%20%11%1
46863
SeeingDay
18%10%28%24%12%5%
5402
Night
19%10%30%26%12%1
14762

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%13%5%8%5%345%45%27%
1432
16th to endDay
11%14%6%9%9%45%5%45%23%
1689
February1st to 15thDay
11%13%5%11%9%35%45%5%22%
1575
16th to endDay
17%12%5%7%7%34335%27%
1473
March1st to 15thDay
16%10%38%7%3445%5%29%
1933
16th to endDay
15%9%245%34336%40%
2130
April1st to 15thDay
20%9%36%5%33346%33%
2152
16th to endDay
18%6%35%5%33436%39%
2274
May1st to 15thDay
16%6%27%5%35%46%6%35%
2448
16th to endDay
13%5%35%6%36%5%47%40%
2618
June1st to 15thDay
18%6%25%5%35%5%6%8%32%
2520
16th to endDay
13%6%25%5%35%5%6%9%36%
2520
July1st to 15thDay
9%4245%35%6%7%8%43%
2520
16th to endDay
8%5%25%6%37%6%7%9%36%
2622
August1st to 15thDay
8%425%6%45%6%6%7%39%
2340
16th to endDay
11%5%244345%6%9%41%
2381
September1st to 15thDay
14%5%245%35%45%6%43%
2160
16th to endDay
14%6%35%434436%44%
1807
October1st to 15thDay
17%8%25%5%35%5%46%33%
1650
16th to endDay
24%11%36%6%34435%26%
1751
November1st to 15thDay
14%8%45%6%35%35%6%35%
1476
16th to endDay
18%12%5%8%5%34436%26%
1440
December1st to 15thDay
17%14%6%7%7%35%35%5%23%
1440
16th to endDay
19%13%5%9%6%34446%21%
1536
January1st to 15thNight
20%12%5%7%6%35%445%24%
2506
16th to endNight
14%13%5%8%6%35%445%26%
2533
February1st to 15thNight
12%14%5%7%7%35%5%46%26%
2285
16th to endNight
13%11%37%6%3445%6%31%
2000
March1st to 15thNight
17%9%46%6%24445%33%
2001
16th to endNight
15%6%36%5%23345%43%
2094
April1st to 15thNight
18%7%35%4245%46%36%
1796
16th to endNight
16%5%145%235%5%6%43%
1697
May1st to 15thNight
15%5%26%5%35%5%6%7%37%
1503
16th to endNight
11%5%35%42445%7%46%
1495
June1st to 15thNight
14%5%35%5%2446%8%39%
1440
16th to endNight
11%425%5%3446%8%41%
1440
July1st to 15thNight
5%314335%46%9%52%
1440
16th to endNight
7%4235%3445%8%49%
1544
August1st to 15thNight
7%425%5%245%6%8%47%
1620
16th to endNight
7%415%325%45%8%52%
1809
September1st to 15thNight
13%5%2432445%7%45%
1800
16th to endNight
14%5%24323346%48%
1826
October1st to 15thNight
18%6%35%5%2435%6%37%
1980
16th to endNight
21%8%38%6%3445%6%28%
2120
November1st to 15thNight
16%7%35%5%3436%6%37%
2379
16th to endNight
22%8%36%5%35%46%6%27%
2520
December1st to 15thNight
19%13%46%6%345%5%6%24%
2520
16th to endNight
20%13%5%7%6%3445%6%20%
2688

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%13%5%7%5%35%446%26%
1432
16th to endDay
12%13%5%11%8%46%5%5%423%
1689
February1st to 15thDay
11%13%6%11%7%45%5%6%5%22%
1575
16th to endDay
17%12%5%7%7%34435%27%
1473
March1st to 15thDay
17%9%37%6%46%45%6%29%
1944
16th to endDay
15%8%25%434345%41%
2129
April1st to 15thDay
20%8%45%5%24346%33%
2152
16th to endDay
17%6%35%5%34446%39%
2274
May1st to 15thDay
15%6%36%5%35%5%5%6%36%
2448
16th to endDay
12%5%35%5%35%5%5%7%40%
2618
June1st to 15thDay
18%6%25%5%35%5%5%8%34%
2520
16th to endDay
13%5%25%425%5%6%9%38%
2520
July1st to 15thDay
9%3245%35%5%7%8%45%
2520
16th to endDay
8%425%6%37%5%7%9%37%
2622
August1st to 15thDay
8%5%25%5%35%6%6%8%40%
2340
16th to endDay
11%4234345%6%9%43%
2381
September1st to 15thDay
14%4145%245%5%6%45%
2160
16th to endDay
14%435%424446%44%
1807
October1st to 15thDay
17%8%26%6%34446%34%
1650
16th to endDay
23%11%36%6%3434427%
1751
November1st to 15thDay
13%7%46%6%34446%36%
1476
16th to endDay
18%12%47%6%25%446%26%
1440
December1st to 15thDay
16%15%6%7%6%35%445%23%
1440
16th to endDay
20%13%5%8%6%45%446%21%
1536
January1st to 15thNight
20%13%47%6%35%345%24%
2506
16th to endNight
14%13%5%8%7%35%5%45%26%
2533
February1st to 15thNight
13%15%5%7%6%45%5%35%27%
2278
16th to endNight
14%11%46%6%445%5%5%31%
2000
March1st to 15thNight
18%9%46%5%34345%33%
2013
16th to endNight
15%6%36%5%2334443%
2094
April1st to 15thNight
19%7%35%43345%5%37%
1796
16th to endNight
15%6%2442446%5%44%
1697
May1st to 15thNight
15%6%246%25%5%5%8%37%
1503
16th to endNight
11%5%25%41445%7%46%
1495
June1st to 15thNight
15%5%25%4245%6%8%39%
1440
16th to endNight
11%425%5%345%5%8%41%
1440
July1st to 15thNight
5%323435%46%8%52%
1440
16th to endNight
7%41443445%9%49%
1544
August1st to 15thNight
8%5%1443446%8%47%
1620
16th to endNight
7%42432445%8%52%
1809
September1st to 15thNight
14%41443446%7%46%
1800
16th to endNight
14%5%25%323346%48%
1826
October1st to 15thNight
19%6%35%5%3435%6%37%
1980
16th to endNight
21%8%47%5%3435%6%28%
2120
November1st to 15thNight
16%6%25%6%25%45%7%37%
2379
16th to endNight
22%8%36%5%35%45%7%27%
2520
December1st to 15thNight
20%12%36%5%35%45%5%25%
2520
16th to endNight
20%13%5%7%6%345%46%20%
2688

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
58%6%11%16%7%
1433
16th to endDay
62%6%10%11%7%
1689
February1st to 15thDay
61%6%11%15%4
1577
16th to endDay
58%5%10%14%10%1
1473
March1st to 15thDay
54%5%14%17%6%1
1944
16th to endDay
45%5%8%21%16%2
2130
April1st to 15thDay
52%310%19%12%1
2152
16th to endDay
45%39%22%16%2
2274
May1st to 15thDay
46%6%10%20%13%1
2448
16th to endDay
41%7%14%21%13%1
2622
June1st to 15thDay
46%6%14%21%10%
2520
16th to endDay
40%8%14%21%13%
2520
July1st to 15thDay
32%8%13%29%14%
2371
16th to endDay
39%9%15%25%9%
2457
August1st to 15thDay
38%9%17%21%12%1
2327
16th to endDay
35%7%15%29%11%1
2381
September1st to 15thDay
37%7%13%27%12%
2160
16th to endDay
40%6%12%29%10%
1807
October1st to 15thDay
49%5%12%21%9%1
1650
16th to endDay
58%414%15%6%
1751
November1st to 15thDay
47%6%16%18%10%1
1476
16th to endDay
57%6%13%12%8%
1440
December1st to 15thDay
62%6%15%13%3
1440
16th to endDay
63%7%10%13%4
1536
January1st to 15thNight
61%5%11%13%6%
2506
16th to endNight
58%6%9%15%8%
2533
February1st to 15thNight
58%6%12%15%5%
2287
16th to endNight
52%6%13%19%8%
2000
March1st to 15thNight
52%412%19%9%
2013
16th to endNight
43%48%22%17%2
2094
April1st to 15thNight
47%5%10%18%16%1
1796
16th to endNight
38%7%11%19%20%2
1697
May1st to 15thNight
43%6%11%19%14%3
1503
16th to endNight
36%6%13%23%16%2
1497
June1st to 15thNight
41%6%13%22%15%1
1440
16th to endNight
39%7%13%21%15%1
1440
July1st to 15thNight
27%7%11%28%24%
1360
16th to endNight
32%5%12%29%16%2
1446
August1st to 15thNight
31%7%17%28%13%1
1609
16th to endNight
28%6%13%33%15%1
1809
September1st to 15thNight
35%7%14%27%13%1
1800
16th to endNight
38%5%9%31%14%
1826
October1st to 15thNight
46%5%12%22%11%
1980
16th to endNight
55%6%13%15%8%
2120
November1st to 15thNight
44%7%14%19%12%1
2379
16th to endNight
54%7%14%15%6%
2520
December1st to 15thNight
58%8%15%13%3
2520
16th to endNight
62%7%12%11%5%
2688

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
18%30%31%13%5%1
60
16th to endDay
26%16%33%17%4
89
February1st to 15thDay
21%31%40%6%1
90
16th to endDay
28%19%34%15%2
132
March1st to 15thDay
22%16%32%22%5%
270
16th to endDay
23%9%36%20%7%2
288
April1st to 15thDay
22%14%33%18%8%2
270
16th to endDay
22%11%31%21%8%4
270
May1st to 15thDay
26%9%26%20%10%7%
288
16th to endDay
14%10%30%27%10%6%
331
June1st to 15thDay
21%6%30%25%13%2
315
16th to endDay
17%7%26%28%14%5%
315
July1st to 15thDay
11%5%20%33%21%7%
305
16th to endDay
9%429%30%16%8%
326
August1st to 15thDay
9%220%34%20%11%
313
16th to endDay
12%420%28%20%12%
332
September1st to 15thDay
12%426%20%21%13%
315
16th to endDay
15%6%24%26%16%10%
254
October1st to 15thDay
16%9%29%26%13%5%
255
16th to endDay
27%14%29%22%5%
270
November1st to 15thDay
17%8%30%33%9%1
130
16th to endDay
26%13%25%26%8%
60
December1st to 15thDay
15%35%26%13%10%
60
16th to endDay
31%32%29%6%
64
January1st to 15thNight
26%18%31%16%6%
720
16th to endNight
22%12%34%25%5%
768
February1st to 15thNight
21%16%39%17%3
704
16th to endNight
21%14%36%22%5%
631
March1st to 15thNight
22%14%34%24%3
720
16th to endNight
18%10%33%26%9%1
768
April1st to 15thNight
21%12%34%25%6%
718
16th to endNight
17%10%33%25%12%
617
May1st to 15thNight
19%5%26%32%14%1
423
16th to endNight
11%231%36%17%
375
June1st to 15thNight
14%329%36%15%1
360
16th to endNight
11%323%42%17%
360
July1st to 15thNight
6%325%40%21%2
340
16th to endNight
6%323%41%23%1
406
August1st to 15thNight
10%117%40%26%3
539
16th to endNight
8%323%33%28%3
663
September1st to 15thNight
14%421%30%25%4
720
16th to endNight
15%5%18%29%24%4
658
October1st to 15thNight
22%6%27%24%16%1
660
16th to endNight
26%11%32%23%6%
704
November1st to 15thNight
20%10%29%27%10%2
700
16th to endNight
25%15%29%21%8%
720
December1st to 15thNight
28%17%34%16%4
720
16th to endNight
27%13%35%18%3
768
Page generated at 2017-09-16 17:07:02. Version ac04

Copyright 2017 A. Danko


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