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 2018-08-29.

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%
15922
15%
50618
9%
15890
40%
15890
19%
34672

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
16%
780
9%
2716
3%
776
24%
776
9%
2074
January16th to endNight
20%
832
12%
2744
6%
832
28%
832
11%
2105
February1st to 15thNight
15%
762
10%
2482
3%
761
23%
761
11%
1888
February16th to endNight
20%
683
14%
2165
5%
683
32%
683
15%
1541
March1st to 15thNight
22%
780
14%
2181
6%
780
29%
780
18%
1586
March16th to endNight
31%
832
22%
2268
9%
832
41%
832
26%
1510
April1st to 15thNight
26%
778
17%
1946
5%
778
33%
778
22%
1397
April16th to endNight
34%
659
19%
1815
7%
659
41%
659
26%
1194
May1st to 15thNight
41%
458
17%
1628
13%
458
49%
458
21%
1048
May16th to endNight
47%
406
17%
1625
16%
406
56%
406
25%
924
June1st to 15thNight
44%
390
14%
1560
14%
390
54%
390
21%
942
June16th to endNight
51%
390
12%
1560
16%
390
56%
390
22%
938
July1st to 15thNight
60%
370
18%
1480
24%
370
67%
370
33%
750
July16th to endNight
57%
440
16%
1576
18%
416
61%
416
29%
881
August1st to 15thNight
59%
575
16%
1715
13%
572
62%
572
32%
1040
August16th to endNight
58%
710
22%
1940
12%
710
62%
710
37%
1166
September1st to 15thNight
52%
720
19%
1800
9%
720
56%
720
33%
1179
September16th to endNight
54%
717
24%
1989
17%
717
58%
717
31%
1257
October1st to 15thNight
37%
720
16%
2160
12%
720
43%
720
22%
1486
October16th to endNight
22%
768
14%
2313
6%
768
32%
768
15%
1694
November1st to 15thNight
33%
760
17%
2583
14%
760
40%
760
19%
1723
November16th to endNight
22%
780
12%
2730
6%
780
29%
780
12%
1994
December1st to 15thNight
16%
780
7%
2730
3%
780
22%
780
10%
2096
December16th to endNight
13%
832
10%
2912
2%
832
22%
832
9%
2259

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%
51638
Night
15%8%36%5%3445%6%36%
50791
Cloud CoverDay
14%8%36%5%35%45%6%35%
51648
Night
15%8%36%5%3445%6%36%
50796
TransparencyDay
47%6%12%20%11%1
51329
Night
47%6%12%20%12%1
50618
SeeingDay
18%11%28%23%12%5%
6574
Night
19%10%30%26%11%1
15925

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%14%5%8%5%345%45%27%
1552
16th to endDay
11%14%6%10%9%45%5%45%22%
1830
February1st to 15thDay
12%13%5%11%9%35%45%5%23%
1710
16th to endDay
18%11%5%7%7%34335%27%
1594
March1st to 15thDay
15%11%47%7%34445%29%
2095
16th to endDay
15%9%245%35%335%40%
2307
April1st to 15thDay
21%9%37%5%34335%31%
2332
16th to endDay
18%6%35%5%33436%40%
2431
May1st to 15thDay
15%6%27%5%35%46%6%36%
2653
16th to endDay
12%5%35%5%35%5%47%41%
2842
June1st to 15thDay
17%6%25%6%35%46%8%33%
2730
16th to endDay
13%6%25%5%345%6%9%36%
2730
July1st to 15thDay
8%4245%35%5%6%8%45%
2730
16th to endDay
8%5%25%5%37%6%7%9%36%
2843
August1st to 15thDay
8%5%35%6%45%6%6%8%38%
2487
16th to endDay
11%5%2443446%9%41%
2546
September1st to 15thDay
14%5%245%35%45%6%43%
2160
16th to endDay
13%5%34424446%46%
1970
October1st to 15thDay
18%8%36%5%34446%33%
1800
16th to endDay
23%10%36%5%34445%27%
1910
November1st to 15thDay
15%8%45%6%35%346%35%
1602
16th to endDay
18%11%48%5%345%46%26%
1560
December1st to 15thDay
16%14%6%8%7%35%35%424%
1560
16th to endDay
19%12%5%9%7%34436%22%
1664
January1st to 15thNight
20%12%5%7%6%36%445%24%
2716
16th to endNight
14%13%5%8%6%35%445%26%
2744
February1st to 15thNight
12%15%5%7%7%35%5%46%26%
2480
16th to endNight
13%11%37%6%345%5%6%31%
2165
March1st to 15thNight
17%11%46%6%24445%33%
2169
16th to endNight
15%5%26%5%23445%44%
2268
April1st to 15thNight
19%7%35%4245%46%35%
1946
16th to endNight
17%5%145%235%5%6%43%
1815
May1st to 15thNight
14%426%5%35%5%6%7%37%
1628
16th to endNight
11%5%2442445%7%46%
1623
June1st to 15thNight
13%5%35%42446%8%40%
1560
16th to endNight
10%5%35%5%3446%8%42%
1560
July1st to 15thNight
5%314335%46%8%53%
1560
16th to endNight
7%5%245%3445%8%49%
1674
August1st to 15thNight
7%425%5%2446%9%46%
1726
16th to endNight
7%415%325%45%8%50%
1940
September1st to 15thNight
13%5%2432445%7%45%
1800
16th to endNight
13%5%24423436%49%
1989
October1st to 15thNight
18%6%35%5%2445%6%38%
2160
16th to endNight
20%8%38%5%3445%6%30%
2313
November1st to 15thNight
17%8%35%5%3436%6%36%
2583
16th to endNight
21%8%36%6%35%5%6%6%27%
2730
December1st to 15thNight
18%13%46%6%35%5%5%6%24%
2730
16th to endNight
19%13%5%7%6%35%45%6%21%
2912

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%
1552
16th to endDay
12%14%5%11%8%46%5%5%422%
1830
February1st to 15thDay
12%13%6%10%7%45%5%5%5%22%
1710
16th to endDay
18%12%47%7%34435%27%
1594
March1st to 15thDay
16%11%37%5%45%45%5%29%
2106
16th to endDay
15%9%25%434345%41%
2306
April1st to 15thDay
20%9%46%5%24345%31%
2332
16th to endDay
18%6%35%5%33435%40%
2431
May1st to 15thDay
14%6%36%5%25%5%5%6%36%
2653
16th to endDay
12%5%35%5%35%5%5%7%41%
2842
June1st to 15thDay
17%6%25%5%35%5%6%7%34%
2730
16th to endDay
13%5%24425%5%6%9%38%
2730
July1st to 15thDay
8%3245%35%5%6%7%47%
2730
16th to endDay
8%425%6%36%5%7%9%38%
2843
August1st to 15thDay
8%6%35%5%35%6%6%8%39%
2487
16th to endDay
11%4234345%6%9%43%
2546
September1st to 15thDay
14%4145%245%5%6%45%
2160
16th to endDay
13%425%42445%6%46%
1970
October1st to 15thDay
17%8%26%6%34446%34%
1800
16th to endDay
22%10%36%6%34445%28%
1910
November1st to 15thDay
14%7%46%6%34446%35%
1602
16th to endDay
18%11%37%6%34447%27%
1560
December1st to 15thDay
16%15%6%7%6%45%445%24%
1560
16th to endDay
20%12%48%6%45%446%23%
1664
January1st to 15thNight
20%13%47%6%35%445%25%
2716
16th to endNight
14%13%5%8%6%35%5%45%25%
2744
February1st to 15thNight
13%15%5%7%6%45%5%45%27%
2473
16th to endNight
14%10%46%6%445%5%5%31%
2165
March1st to 15thNight
18%10%46%5%34335%33%
2181
16th to endNight
15%5%36%5%24445%44%
2268
April1st to 15thNight
19%7%35%43445%5%36%
1946
16th to endNight
16%6%14425%45%5%43%
1815
May1st to 15thNight
14%5%246%35%5%5%7%38%
1628
16th to endNight
11%5%2441445%8%46%
1623
June1st to 15thNight
14%5%25%4245%6%8%40%
1560
16th to endNight
11%425%5%345%5%8%42%
1560
July1st to 15thNight
5%323435%46%8%54%
1560
16th to endNight
8%5%15%43445%8%48%
1674
August1st to 15thNight
8%5%25%43446%8%46%
1726
16th to endNight
7%5%2432445%8%50%
1940
September1st to 15thNight
14%41443446%7%46%
1800
16th to endNight
14%5%15%323346%49%
1989
October1st to 15thNight
18%5%35%5%34347%37%
2160
16th to endNight
20%8%37%5%3435%7%30%
2313
November1st to 15thNight
17%7%25%6%2445%7%36%
2583
16th to endNight
21%8%36%5%35%46%7%28%
2730
December1st to 15thNight
19%13%37%5%35%45%6%25%
2730
16th to endNight
20%13%5%7%6%345%46%21%
2912

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%5%11%15%8%
1553
16th to endDay
63%6%10%11%7%
1830
February1st to 15thDay
61%5%10%15%5%
1712
16th to endDay
58%5%11%14%9%1
1594
March1st to 15thDay
55%5%13%16%6%1
2106
16th to endDay
45%5%8%21%16%2
2307
April1st to 15thDay
54%39%18%12%1
2332
16th to endDay
45%39%21%17%2
2431
May1st to 15thDay
45%6%10%21%14%1
2653
16th to endDay
40%7%14%23%13%1
2846
June1st to 15thDay
45%6%14%20%11%
2730
16th to endDay
40%8%14%21%14%1
2730
July1st to 15thDay
31%8%12%30%15%1
2581
16th to endDay
39%9%15%24%9%
2678
August1st to 15thDay
39%9%17%20%11%1
2474
16th to endDay
35%6%15%30%11%1
2546
September1st to 15thDay
37%7%13%27%12%
2160
16th to endDay
37%6%13%30%11%
1970
October1st to 15thDay
50%5%12%21%9%1
1800
16th to endDay
57%5%14%15%6%
1910
November1st to 15thDay
48%6%15%18%10%1
1602
16th to endDay
56%6%14%13%8%
1560
December1st to 15thDay
61%6%14%13%4
1560
16th to endDay
62%7%10%13%5%
1664
January1st to 15thNight
60%5%11%13%7%1
2716
16th to endNight
59%7%9%15%8%
2744
February1st to 15thNight
58%6%12%15%6%
2482
16th to endNight
51%6%13%19%8%
2165
March1st to 15thNight
53%411%19%10%1
2181
16th to endNight
42%48%23%17%3
2268
April1st to 15thNight
47%5%10%18%16%1
1946
16th to endNight
39%7%11%18%21%2
1815
May1st to 15thNight
42%6%11%19%15%3
1628
16th to endNight
35%6%13%24%17%2
1625
June1st to 15thNight
40%6%12%22%16%1
1560
16th to endNight
39%7%12%21%16%2
1560
July1st to 15thNight
26%7%10%28%25%1
1480
16th to endNight
33%5%12%29%17%2
1576
August1st to 15thNight
33%7%17%27%12%
1715
16th to endNight
30%6%13%32%15%
1940
September1st to 15thNight
35%7%14%27%13%1
1800
16th to endNight
36%5%9%30%16%
1989
October1st to 15thNight
46%6%11%22%12%
2160
16th to endNight
53%6%14%17%8%
2313
November1st to 15thNight
45%6%14%18%12%1
2583
16th to endNight
54%7%14%16%6%
2730
December1st to 15thNight
58%8%14%13%4
2730
16th to endNight
61%7%11%11%6%
2912

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
21%26%33%13%41
90
16th to endDay
25%22%32%15%4
134
February1st to 15thDay
25%34%32%6%
135
16th to endDay
29%23%33%11%1
175
March1st to 15thDay
24%16%31%22%4
330
16th to endDay
22%11%36%19%8%1
352
April1st to 15thDay
26%16%30%16%8%2
330
16th to endDay
22%11%31%20%9%4
319
May1st to 15thDay
24%10%29%20%9%6%
348
16th to endDay
14%8%30%29%10%5%
395
June1st to 15thDay
20%6%33%25%12%2
375
16th to endDay
17%7%28%28%13%4
375
July1st to 15thDay
9%5%21%32%22%8%
365
16th to endDay
10%6%28%30%15%8%
390
August1st to 15thDay
11%322%33%18%10%
358
16th to endDay
13%421%28%20%11%
384
September1st to 15thDay
12%426%20%21%13%
315
16th to endDay
13%7%22%23%20%14%
314
October1st to 15thDay
18%9%28%23%12%6%
315
16th to endDay
25%18%27%21%6%
333
November1st to 15thDay
21%12%27%30%7%1
166
16th to endDay
25%17%32%17%6%
90
December1st to 15thDay
16%33%27%13%8%
90
16th to endDay
27%29%36%7%
96
January1st to 15thNight
26%18%31%16%6%
780
16th to endNight
22%13%34%24%5%
832
February1st to 15thNight
22%16%40%17%3
764
16th to endNight
20%15%37%21%4
683
March1st to 15thNight
22%14%34%24%3
780
16th to endNight
18%10%34%27%8%1
832
April1st to 15thNight
21%14%33%25%5%
778
16th to endNight
18%9%32%25%12%1
659
May1st to 15thNight
18%5%27%32%14%1
458
16th to endNight
11%231%37%16%
407
June1st to 15thNight
13%428%37%14%1
390
16th to endNight
11%324%41%17%
390
July1st to 15thNight
5%324%41%22%2
370
16th to endNight
7%223%40%23%1
440
August1st to 15thNight
9%218%39%26%3
575
16th to endNight
9%321%33%28%3
710
September1st to 15thNight
14%421%30%25%4
720
16th to endNight
14%5%18%28%25%7%
717
October1st to 15thNight
22%6%27%23%16%2
720
16th to endNight
25%12%32%23%6%
768
November1st to 15thNight
21%10%28%26%10%2
760
16th to endNight
25%15%30%20%8%
780
December1st to 15thNight
26%18%34%16%4
780
16th to endNight
27%14%36%18%3
832
Page generated at 2018-08-30 05:34:25. Version ac04

Copyright 2018 A. Danko


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