Lavell Sky observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lavell Sky observatory clear sky chart from 2005-11-05 to 2017-09-24.

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
38%
16229
14%
46724
8%
16182
43%
16182
22%
32316

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
31%
900
11%
2625
8%
895
35%
895
16%
1949
January16th to endNight
27%
960
13%
2622
5%
960
33%
960
16%
2026
February1st to 15thNight
33%
879
14%
2285
5%
875
38%
875
21%
1666
February16th to endNight
37%
759
15%
2021
6%
759
42%
759
21%
1470
March1st to 15thNight
33%
613
14%
2053
10%
613
39%
613
19%
1401
March16th to endNight
35%
576
16%
2078
12%
576
43%
576
19%
1362
April1st to 15thNight
34%
539
14%
1797
12%
539
41%
539
19%
1241
April16th to endNight
34%
540
16%
1646
9%
540
40%
540
18%
1171
May1st to 15thNight
33%
540
14%
1440
6%
540
37%
540
23%
1017
May16th to endNight
42%
563
11%
1498
4%
561
46%
561
29%
1011
June1st to 15thNight
46%
540
10%
1341
5%
540
48%
540
32%
906
June16th to endNight
51%
540
11%
1260
7%
540
52%
540
36%
842
July1st to 15thNight
58%
510
14%
1193
7%
510
60%
510
47%
721
July16th to endNight
59%
564
16%
1417
8%
531
60%
531
44%
818
August1st to 15thNight
63%
539
19%
1544
15%
536
66%
536
42%
871
August16th to endNight
53%
573
21%
1779
19%
573
60%
573
36%
990
September1st to 15thNight
60%
540
18%
1800
16%
540
66%
540
35%
993
September16th to endNight
44%
574
15%
1903
14%
574
49%
574
26%
1175
October1st to 15thNight
39%
660
19%
1980
13%
660
44%
660
26%
1275
October16th to endNight
30%
704
12%
2171
7%
704
35%
704
17%
1575
November1st to 15thNight
31%
856
15%
2432
8%
856
37%
856
21%
1706
November16th to endNight
31%
900
14%
2520
9%
900
36%
900
17%
1876
December1st to 15thNight
26%
900
9%
2520
5%
900
31%
900
14%
1995
December16th to endNight
22%
960
10%
2799
3%
960
28%
960
11%
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%47%6%3445%7%32%
48211
Night
13%8%46%5%35%45%7%35%
46885
Cloud CoverDay
15%8%47%6%35%45%7%32%
48222
Night
13%8%46%5%35%45%7%35%
46889
Cloud CoverDay
14%8%47%6%35%45%7%32%
48220
Night
12%8%46%5%35%45%7%35%
46889
TransparencyDay
50%413%22%8%
47887
Night
48%413%23%9%
46727
SeeingDay
19%6%27%27%14%4
6227
Night
17%5%29%33%12%1
16230

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
11%11%7%10%8%445%6%8%21%
1310
16th to endDay
11%13%5%11%8%5%7%5%5%8%16%
1602
February1st to 15thDay
8%11%6%9%8%3445%7%31%
1575
16th to endDay
11%11%5%9%7%446%5%7%26%
1451
March1st to 15thDay
12%9%5%8%6%3445%6%32%
1906
16th to endDay
17%10%47%5%33445%32%
2145
April1st to 15thDay
14%9%47%6%35%445%34%
2151
16th to endDay
22%9%35%5%2435%6%29%
2313
May1st to 15thDay
21%8%46%6%25%34431%
2511
16th to endDay
17%6%25%5%3445%8%33%
2617
June1st to 15thDay
17%6%35%5%35%45%8%34%
2616
16th to endDay
15%6%27%6%35%5%5%8%32%
2700
July1st to 15thDay
11%325%5%345%6%8%43%
2694
16th to endDay
8%425%5%35%5%6%9%42%
2655
August1st to 15thDay
8%6%26%6%345%6%7%41%
2406
16th to endDay
13%425%43446%8%43%
2422
September1st to 15thDay
10%5%26%5%344410%42%
2160
16th to endDay
18%7%35%333446%39%
1901
October1st to 15thDay
16%8%36%5%245%5%6%35%
1650
16th to endDay
22%12%46%5%2345%6%27%
1700
November1st to 15thDay
15%10%5%7%435%45%5%30%
1424
16th to endDay
16%12%6%8%7%46%45%5%21%
1440
December1st to 15thDay
14%11%6%10%10%45%5%7%6%17%
1440
16th to endDay
16%18%9%11%6%45%435%13%
1422
January1st to 15thNight
10%10%5%8%7%35%6%6%8%25%
2625
16th to endNight
11%12%6%10%6%35%5%5%7%24%
2622
February1st to 15thNight
8%10%47%6%46%5%47%33%
2285
16th to endNight
8%11%5%7%6%46%6%5%8%29%
2021
March1st to 15thNight
12%8%5%7%6%345%46%34%
2041
16th to endNight
15%9%46%4245%46%35%
2078
April1st to 15thNight
16%8%47%5%35%34435%
1797
16th to endNight
19%9%46%5%3445%6%29%
1646
May1st to 15thNight
20%7%35%424447%34%
1440
16th to endNight
15%5%15%5%345%5%7%40%
1496
June1st to 15thNight
14%425%43445%6%43%
1341
16th to endNight
10%4244245%7%9%43%
1260
July1st to 15thNight
7%3133235%410%54%
1263
16th to endNight
7%31332446%10%52%
1513
August1st to 15thNight
8%314323347%56%
1553
16th to endNight
11%423313348%53%
1779
September1st to 15thNight
8%42342445%7%51%
1800
16th to endNight
13%6%35%424447%43%
1903
October1st to 15thNight
14%7%25%424446%42%
1980
16th to endNight
19%9%37%6%34446%30%
2171
November1st to 15thNight
13%10%47%5%35%347%34%
2432
16th to endNight
15%10%5%8%5%35%5%5%7%28%
2520
December1st to 15thNight
12%12%6%10%7%36%5%5%7%20%
2520
16th to endNight
14%15%8%11%7%35%347%17%
2799

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
11%11%7%10%8%346%6%8%21%
1310
16th to endDay
11%13%5%11%8%47%5%5%8%16%
1602
February1st to 15thDay
8%11%6%9%8%25%45%7%31%
1575
16th to endDay
11%11%5%9%7%5%45%5%7%26%
1451
March1st to 15thDay
12%9%6%8%6%3445%6%32%
1917
16th to endDay
17%10%47%6%24445%32%
2145
April1st to 15thDay
14%9%37%5%35%446%34%
2151
16th to endDay
22%9%36%425%35%5%29%
2313
May1st to 15thDay
21%9%36%6%35%34431%
2511
16th to endDay
17%6%25%5%35%46%7%33%
2617
June1st to 15thDay
18%5%35%6%35%46%8%33%
2616
16th to endDay
16%6%36%6%35%45%8%32%
2700
July1st to 15thDay
11%4245%245%6%8%44%
2694
16th to endDay
8%426%5%35%5%6%9%42%
2655
August1st to 15thDay
9%5%26%5%345%5%8%41%
2406
16th to endDay
13%4244345%5%8%43%
2422
September1st to 15thDay
10%5%25%5%34349%43%
2160
16th to endDay
18%6%35%424446%40%
1901
October1st to 15thDay
16%8%36%4345%5%6%35%
1650
16th to endDay
22%12%36%5%2345%5%27%
1700
November1st to 15thDay
15%11%6%6%435%45%5%30%
1424
16th to endDay
16%13%5%10%6%45%5%45%21%
1440
December1st to 15thDay
15%12%5%10%9%5%5%5%6%5%17%
1440
16th to endDay
16%19%8%11%7%45%34412%
1422
January1st to 15thNight
11%10%5%9%7%46%5%5%7%25%
2625
16th to endNight
11%12%6%10%6%45%45%7%24%
2622
February1st to 15thNight
8%11%47%7%47%5%46%33%
2278
16th to endNight
8%11%5%7%6%46%5%5%8%29%
2021
March1st to 15thNight
12%8%5%6%6%35%446%35%
2053
16th to endNight
15%9%46%5%245%46%36%
2078
April1st to 15thNight
16%9%46%6%4444435%
1797
16th to endNight
20%8%46%6%2445%5%30%
1646
May1st to 15thNight
20%7%35%5%2345%6%35%
1439
16th to endNight
15%5%25%435%5%5%7%40%
1496
June1st to 15thNight
14%425%42445%6%42%
1341
16th to endNight
11%424425%48%9%43%
1260
July1st to 15thNight
7%3332445%9%55%
1263
16th to endNight
7%31341446%9%53%
1513
August1st to 15thNight
8%313413446%56%
1553
16th to endNight
12%323322348%53%
1779
September1st to 15thNight
9%41342345%8%51%
1800
16th to endNight
13%5%36%42345%6%44%
1903
October1st to 15thNight
14%7%35%5%23446%42%
1980
16th to endNight
19%9%36%6%345%45%30%
2171
November1st to 15thNight
13%10%46%5%25%447%34%
2432
16th to endNight
15%10%48%6%36%5%46%28%
2520
December1st to 15thNight
13%13%6%9%7%46%5%5%7%20%
2520
16th to endNight
14%15%9%11%7%35%447%17%
2799

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
11%11%7%10%8%445%6%8%21%
1310
16th to endDay
11%12%6%11%8%47%5%5%8%16%
1602
February1st to 15thDay
8%11%6%9%7%3445%7%31%
1575
16th to endDay
11%11%5%9%7%446%5%7%25%
1451
March1st to 15thDay
12%9%5%8%6%3445%6%32%
1917
16th to endDay
17%10%46%6%33446%32%
2143
April1st to 15thDay
14%9%47%6%35%45%5%34%
2151
16th to endDay
22%9%35%5%2435%6%29%
2313
May1st to 15thDay
21%8%46%6%25%34431%
2511
16th to endDay
17%6%25%5%345%5%8%33%
2617
June1st to 15thDay
17%6%35%5%35%45%8%33%
2616
16th to endDay
15%6%36%6%35%5%5%8%32%
2700
July1st to 15thDay
11%425%43446%8%43%
2694
16th to endDay
8%425%5%36%5%6%9%42%
2655
August1st to 15thDay
8%6%26%6%345%5%8%41%
2406
16th to endDay
13%42443446%8%43%
2422
September1st to 15thDay
10%5%26%5%35%45%9%42%
2160
16th to endDay
18%7%35%333446%39%
1901
October1st to 15thDay
16%8%36%5%25%5%5%6%35%
1650
16th to endDay
22%12%46%5%2345%5%27%
1700
November1st to 15thDay
15%10%5%7%435%445%30%
1424
16th to endDay
16%12%6%9%7%46%45%5%21%
1440
December1st to 15thDay
14%11%6%10%10%5%5%5%6%6%17%
1440
16th to endDay
16%18%9%11%7%45%345%12%
1422
January1st to 15thNight
10%10%5%8%7%45%6%6%8%25%
2625
16th to endNight
11%12%6%10%6%35%5%5%7%24%
2622
February1st to 15thNight
8%10%47%6%46%6%47%32%
2278
16th to endNight
8%12%5%7%6%36%6%5%8%29%
2021
March1st to 15thNight
12%8%5%7%6%445%46%35%
2053
16th to endNight
15%9%36%4245%46%35%
2078
April1st to 15thNight
16%9%47%5%35%34435%
1797
16th to endNight
19%9%46%5%34446%29%
1646
May1st to 15thNight
20%7%35%42445%6%34%
1439
16th to endNight
15%5%15%4345%5%7%40%
1496
June1st to 15thNight
14%435%42445%6%43%
1341
16th to endNight
10%5%243245%7%9%43%
1260
July1st to 15thNight
7%3133235%410%54%
1263
16th to endNight
7%32332446%10%52%
1513
August1st to 15thNight
7%314323347%56%
1553
16th to endNight
11%413313348%52%
1779
September1st to 15thNight
8%42342445%7%51%
1800
16th to endNight
13%6%35%424447%43%
1903
October1st to 15thNight
14%7%25%424446%42%
1980
16th to endNight
19%9%27%6%345%46%30%
2171
November1st to 15thNight
13%10%47%5%35%347%34%
2432
16th to endNight
15%10%5%8%5%36%5%5%7%28%
2520
December1st to 15thNight
13%12%6%10%7%37%5%5%7%20%
2520
16th to endNight
14%15%8%11%7%35%347%17%
2799

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
59%49%18%7%
1311
16th to endDay
65%310%15%5%
1602
February1st to 15thDay
53%314%17%10%
1576
16th to endDay
57%412%18%6%
1451
March1st to 15thDay
51%315%19%8%
1917
16th to endDay
54%413%21%41
2145
April1st to 15thDay
50%311%18%13%1
2151
16th to endDay
54%310%19%10%1
2313
May1st to 15thDay
56%310%21%6%1
2511
16th to endDay
48%5%12%21%11%
2621
June1st to 15thDay
47%315%26%6%
2616
16th to endDay
49%414%22%9%
2700
July1st to 15thDay
35%413%30%15%
2535
16th to endDay
38%5%16%27%11%1
2488
August1st to 15thDay
40%414%29%9%2
2391
16th to endDay
38%417%26%12%
2422
September1st to 15thDay
39%316%31%8%
2160
16th to endDay
45%416%27%5%
1901
October1st to 15thDay
49%315%22%8%
1650
16th to endDay
57%413%17%6%
1700
November1st to 15thDay
54%412%18%8%
1424
16th to endDay
64%310%13%6%
1440
December1st to 15thDay
65%411%14%3
1440
16th to endDay
75%25%11%3
1422
January1st to 15thNight
56%410%21%6%
2625
16th to endNight
59%410%17%7%
2622
February1st to 15thNight
51%411%20%11%
2288
16th to endNight
51%411%22%9%
2021
March1st to 15thNight
50%414%18%11%
2053
16th to endNight
48%415%21%9%1
2078
April1st to 15thNight
51%38%21%12%1
1797
16th to endNight
54%28%22%10%
1646
May1st to 15thNight
49%313%23%9%
1440
16th to endNight
42%412%26%12%1
1498
June1st to 15thNight
41%314%28%10%1
1341
16th to endNight
35%5%18%26%10%1
1260
July1st to 15thNight
26%417%34%15%2
1193
16th to endNight
26%419%31%15%2
1417
August1st to 15thNight
28%418%32%13%3
1544
16th to endNight
31%318%28%16%1
1779
September1st to 15thNight
30%418%35%10%
1800
16th to endNight
40%418%29%7%
1903
October1st to 15thNight
43%215%29%8%
1980
16th to endNight
55%314%19%6%
2171
November1st to 15thNight
50%314%22%8%
2432
16th to endNight
56%414%16%6%
2520
December1st to 15thNight
63%312%17%3
2520
16th to endNight
68%211%12%5%
2799

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%7%31%24%16%1
90
16th to endDay
21%426%33%11%3
96
February1st to 15thDay
17%12%41%23%5%
90
16th to endDay
30%233%23%7%2
81
March1st to 15thDay
17%5%32%34%6%3
90
16th to endDay
24%8%29%22%13%2
129
April1st to 15thDay
17%7%32%26%13%1
270
16th to endDay
29%6%26%27%7%1
417
May1st to 15thDay
26%9%30%22%7%3
468
16th to endDay
23%5%29%23%12%5%
517
June1st to 15thDay
19%8%30%25%11%5%
495
16th to endDay
17%9%29%24%13%5%
495
July1st to 15thDay
14%6%22%28%19%9%
475
16th to endDay
10%7%25%28%20%7%
515
August1st to 15thDay
11%419%32%24%6%
493
16th to endDay
17%422%28%21%5%
462
September1st to 15thDay
9%423%35%23%3
315
16th to endDay
25%5%32%20%11%4
177
October1st to 15thDay
7%8%38%22%15%6%
90
16th to endDay
31%7%23%28%7%2
96
November1st to 15thDay
18%237%32%7%1
90
16th to endDay
42%7%16%21%12%
90
December1st to 15thDay
17%337%32%6%2
90
16th to endDay
29%6%28%27%5%4
96
January1st to 15thNight
17%7%30%31%12%1
900
16th to endNight
18%6%35%31%7%
960
February1st to 15thNight
14%6%31%33%12%1
880
16th to endNight
14%8%30%32%11%2
759
March1st to 15thNight
15%6%32%32%11%
613
16th to endNight
19%6%28%29%12%2
576
April1st to 15thNight
22%5%30%32%8%
539
16th to endNight
25%5%27%30%9%
540
May1st to 15thNight
23%6%32%29%7%1
540
16th to endNight
17%430%33%12%1
563
June1st to 15thNight
16%5%24%41%10%
540
16th to endNight
14%224%41%15%
540
July1st to 15thNight
11%224%38%22%
510
16th to endNight
8%124%43%20%1
564
August1st to 15thNight
10%118%42%24%3
539
16th to endNight
13%322%39%18%2
573
September1st to 15thNight
10%223%40%19%3
540
16th to endNight
16%5%28%32%15%1
574
October1st to 15thNight
20%7%27%31%12%
660
16th to endNight
25%7%29%28%9%
704
November1st to 15thNight
17%7%33%31%8%1
856
16th to endNight
21%8%29%28%10%
900
December1st to 15thNight
19%6%33%28%10%
900
16th to endNight
22%7%30%28%9%1
960
Page generated at 2017-09-25 08:02:20. Version ac04

Copyright 2017 A. Danko


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