Lazy J Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lazy J Observatory clear sky chart from 2005-11-05 to 2017-09-19.

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
41%
15864
27%
46897
13%
15819
55%
15819
36%
25234

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
33%
876
29%
2482
12%
871
50%
871
41%
1222
January16th to endNight
29%
768
33%
2496
14%
768
52%
768
39%
1163
February1st to 15thNight
23%
701
25%
2226
9%
699
41%
699
32%
1164
February16th to endNight
21%
632
36%
1894
8%
632
49%
632
39%
945
March1st to 15thNight
32%
720
26%
2094
10%
720
46%
720
35%
1117
March16th to endNight
31%
690
30%
2034
11%
690
49%
690
38%
1059
April1st to 15thNight
27%
539
24%
1798
9%
539
45%
539
32%
889
April16th to endNight
31%
540
24%
1800
12%
540
49%
540
26%
992
May1st to 15thNight
34%
539
20%
1698
10%
539
47%
539
26%
1019
May16th to endNight
40%
563
19%
1498
8%
561
51%
561
32%
894
June1st to 15thNight
51%
540
23%
1440
14%
540
59%
540
41%
785
June16th to endNight
60%
540
22%
1440
15%
540
66%
540
41%
824
July1st to 15thNight
64%
510
15%
1360
12%
510
66%
510
26%
928
July16th to endNight
74%
564
14%
1512
15%
531
74%
531
25%
1017
August1st to 15thNight
69%
539
13%
1692
14%
536
70%
536
25%
1067
August16th to endNight
69%
573
19%
1910
20%
573
71%
573
28%
1151
September1st to 15thNight
65%
540
22%
1800
20%
540
71%
540
32%
1027
September16th to endNight
59%
504
34%
1805
25%
504
72%
504
41%
840
October1st to 15thNight
50%
654
31%
1974
17%
654
61%
654
43%
1022
October16th to endNight
48%
704
36%
2112
16%
704
63%
704
45%
1038
November1st to 15thNight
43%
868
34%
2268
15%
868
55%
868
49%
1148
November16th to endNight
37%
900
38%
2356
13%
900
53%
900
50%
1190
December1st to 15thNight
25%
900
27%
2520
6%
900
42%
900
39%
1295
December16th to endNight
25%
960
28%
2688
8%
960
43%
960
35%
1438

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
35%2442446%8%51%
47921
Night
231332445%8%58%
47078
Cloud CoverDay
35%244245%6%8%51%
47919
Night
231332445%7%59%
47078
TransparencyDay
28%7%13%23%20%6%
47605
Night
22%7%14%26%22%6%
46897
SeeingDay
10%18%31%24%12%3
5761
Night
5%14%33%28%15%2
15868

By Month

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
31442335%7%63%
1465
16th to endDay
423213336%66%
1728
February1st to 15thDay
436%31235%8%58%
1633
16th to endDay
424423447%59%
1580
March1st to 15thDay
15%36%43346%9%52%
1863
16th to endDay
26%2443445%7%52%
2190
April1st to 15thDay
27%3433435%8%52%
2150
16th to endDay
5%9%46%43446%6%44%
2160
May1st to 15thDay
8%8%35%5%345%6%7%40%
2249
16th to endDay
5%5%24435%5%6%9%47%
2616
June1st to 15thDay
33233346%7%10%50%
2520
16th to endDay
2213326%6%9%7%53%
2520
July1st to 15thDay
6%5%25%5%37%7%8%9%37%
2520
16th to endDay
6%5%26%6%48%7%9%11%31%
2549
August1st to 15thDay
7%6%35%6%46%6%7%8%36%
2256
16th to endDay
7%5%15%5%35%5%7%8%44%
2292
September1st to 15thDay
6%425%425%6%7%9%44%
2160
16th to endDay
331331345%465%
1899
October1st to 15thDay
5%323333435%60%
1655
16th to endDay
3413212235%68%
1755
November1st to 15thDay
32431225%7%66%
1583
16th to endDay
121221335%6%68%
1602
December1st to 15thDay
32431326%7%62%
1440
16th to endDay
1425%42236%9%56%
1536
January1st to 15thNight
21332335%7%67%
2482
16th to endNight
312312347%67%
2496
February1st to 15thNight
1426%423336%61%
2216
16th to endNight
31431345%7%64%
1894
March1st to 15thNight
142322345%7%60%
2094
16th to endNight
241332335%7%62%
2034
April1st to 15thNight
142331445%7%61%
1798
16th to endNight
47%245%23448%52%
1800
May1st to 15thNight
6%7%25%425%45%7%47%
1697
16th to endNight
6%424315%45%8%52%
1497
June1st to 15thNight
22143235%5%8%60%
1440
16th to endNight
1213325%6%7%9%55%
1440
July1st to 15thNight
6%415%5%37%8%6%9%38%
1440
16th to endNight
45%245%37%7%9%11%37%
1616
August1st to 15thNight
4315%5%46%6%7%10%41%
1701
16th to endNight
5%424426%6%7%10%45%
1910
September1st to 15thNight
7%4234345%6%10%47%
1800
16th to endNight
321222335%6%65%
1805
October1st to 15thNight
321221335%6%65%
1974
16th to endNight
2313212445%67%
2112
November1st to 15thNight
2221345%7%68%
2268
16th to endNight
1312212236%70%
2356
December1st to 15thNight
31332335%8%64%
2520
16th to endNight
132442335%7%61%
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
314423346%63%
1465
16th to endDay
423313336%66%
1728
February1st to 15thDay
1436%31235%8%58%
1633
16th to endDay
424423448%59%
1580
March1st to 15thDay
15%26%43346%9%52%
1863
16th to endDay
26%2443445%7%52%
2188
April1st to 15thDay
26%25%424448%52%
2150
16th to endDay
5%9%36%43446%7%44%
2160
May1st to 15thDay
8%8%35%5%35%5%5%8%40%
2249
16th to endDay
5%5%24425%5%6%9%47%
2616
June1st to 15thDay
43233346%7%10%51%
2520
16th to endDay
2213326%6%8%8%53%
2520
July1st to 15thDay
7%5%25%5%46%7%8%9%37%
2520
16th to endDay
6%5%35%6%48%7%10%10%31%
2549
August1st to 15thDay
8%6%35%6%46%6%7%8%36%
2256
16th to endDay
7%426%5%35%5%7%8%43%
2292
September1st to 15thDay
5%5%24435%6%7%9%44%
2160
16th to endDay
331431335%465%
1899
October1st to 15thDay
5%323323436%59%
1655
16th to endDay
3413212236%68%
1755
November1st to 15thDay
32331325%7%66%
1583
16th to endDay
1212313346%68%
1602
December1st to 15thDay
31431326%8%62%
1440
16th to endDay
1425%32246%9%56%
1536
January1st to 15thNight
21332325%6%67%
2482
16th to endNight
322312347%68%
2496
February1st to 15thNight
1426%423336%61%
2216
16th to endNight
31431345%7%64%
1894
March1st to 15thNight
15%2321345%8%60%
2094
16th to endNight
241332335%7%63%
2034
April1st to 15thNight
142332345%7%61%
1798
16th to endNight
47%25%42345%7%52%
1800
May1st to 15thNight
6%7%345%25%45%7%48%
1697
16th to endNight
6%3243245%5%8%53%
1497
June1st to 15thNight
221431445%8%61%
1440
16th to endNight
2213325%6%6%9%55%
1440
July1st to 15thNight
6%415%5%37%8%7%9%38%
1440
16th to endNight
45%245%47%7%8%11%37%
1616
August1st to 15thNight
3415%5%46%6%7%10%42%
1701
16th to endNight
5%324435%7%7%9%45%
1910
September1st to 15thNight
7%4234345%6%10%48%
1800
16th to endNight
3213223446%65%
1805
October1st to 15thNight
321221335%6%65%
1974
16th to endNight
2313212446%67%
2112
November1st to 15thNight
21221345%7%69%
2268
16th to endNight
1322213236%69%
2356
December1st to 15thNight
22231335%8%64%
2520
16th to endNight
132432335%8%61%
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
20%417%32%19%4
1466
16th to endDay
18%416%31%21%7%
1728
February1st to 15thDay
24%5%15%30%18%5%
1634
16th to endDay
22%413%27%25%5%
1580
March1st to 15thDay
26%413%23%25%6%
1863
16th to endDay
28%7%10%28%21%3
2190
April1st to 15thDay
29%5%13%25%18%6%
2150
16th to endDay
37%6%11%22%17%5%
2160
May1st to 15thDay
40%8%13%17%17%3
2249
16th to endDay
31%9%13%19%18%8%
2620
June1st to 15thDay
25%8%15%17%20%13%
2520
16th to endDay
21%8%12%19%25%12%
2520
July1st to 15thDay
37%9%16%16%13%6%
2371
16th to endDay
37%13%19%20%7%1
2391
August1st to 15thDay
40%11%15%13%12%5%
2241
16th to endDay
34%9%14%21%16%3
2292
September1st to 15thDay
31%9%14%20%16%6%
2160
16th to endDay
20%5%10%23%32%7%
1899
October1st to 15thDay
25%5%8%21%31%6%
1655
16th to endDay
19%38%26%34%6%
1755
November1st to 15thDay
17%413%22%31%10%
1583
16th to endDay
16%48%29%30%9%
1602
December1st to 15thDay
20%5%20%29%19%3
1440
16th to endDay
22%7%19%28%16%5%
1536
January1st to 15thNight
16%5%18%30%25%4
2482
16th to endNight
16%6%13%32%24%6%
2496
February1st to 15thNight
25%5%15%32%18%3
2226
16th to endNight
19%411%30%27%6%
1894
March1st to 15thNight
21%6%14%27%25%4
2094
16th to endNight
20%6%12%29%27%3
2034
April1st to 15thNight
21%5%16%28%21%6%
1798
16th to endNight
29%6%13%26%19%4
1800
May1st to 15thNight
34%6%13%22%17%4
1698
16th to endNight
28%7%17%21%15%8%
1498
June1st to 15thNight
19%8%14%20%19%17%
1440
16th to endNight
21%9%12%19%21%14%
1440
July1st to 15thNight
38%11%14%16%11%7%
1360
16th to endNight
34%15%20%20%8%1
1512
August1st to 15thNight
31%15%18%17%11%5%
1692
16th to endNight
30%13%18%20%13%4
1910
September1st to 15thNight
29%9%18%23%13%6%
1800
16th to endNight
18%6%11%26%30%6%
1805
October1st to 15thNight
19%7%12%21%30%8%
1974
16th to endNight
18%5%8%26%33%8%
2112
November1st to 15thNight
14%5%13%26%27%12%
2268
16th to endNight
16%38%30%31%9%
2356
December1st to 15thNight
18%6%19%30%20%4
2520
16th to endNight
21%6%20%27%20%4
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
13%18%33%21%13%
90
16th to endDay
327%36%26%7%
96
February1st to 15thDay
10%31%37%18%2
90
16th to endDay
11%27%32%22%6%1
81
March1st to 15thDay
9%30%39%16%3
153
16th to endDay
15%37%34%9%2
288
April1st to 15thDay
16%37%30%11%21
269
16th to endDay
20%40%29%8%2
270
May1st to 15thDay
14%22%36%17%6%2
370
16th to endDay
10%19%32%23%12%2
517
June1st to 15thDay
5%17%28%26%16%4
495
16th to endDay
49%32%26%21%5%
495
July1st to 15thDay
10%227%32%18%7%
475
16th to endDay
6%220%40%24%6%
408
August1st to 15thDay
13%429%35%13%3
315
16th to endDay
12%5%28%36%14%2
332
September1st to 15thDay
9%13%37%23%12%3
315
16th to endDay
410%39%27%15%2
150
October1st to 15thDay
415%23%34%15%6%
90
16th to endDay
10%19%27%27%11%4
96
November1st to 15thDay
217%21%31%23%4
90
16th to endDay
6%40%30%18%4
90
December1st to 15thDay
10%33%44%11%1
90
16th to endDay
5%36%37%18%2
96
January1st to 15thNight
322%37%24%9%2
876
16th to endNight
419%43%24%7%1
768
February1st to 15thNight
317%50%23%4
704
16th to endNight
420%51%19%4
632
March1st to 15thNight
5%21%38%25%9%
720
16th to endNight
7%17%41%27%5%
690
April1st to 15thNight
8%20%41%24%5%
539
16th to endNight
12%18%32%27%8%
540
May1st to 15thNight
10%11%37%30%9%1
540
16th to endNight
8%14%30%28%15%1
563
June1st to 15thNight
410%27%38%17%2
540
16th to endNight
16%25%37%26%2
540
July1st to 15thNight
8%113%35%34%5%
510
16th to endNight
7%1433%42%9%
564
August1st to 15thNight
429%36%40%5%
539
16th to endNight
7%211%34%38%5%
573
September1st to 15thNight
7%415%38%27%6%
540
16th to endNight
47%23%34%22%6%
504
October1st to 15thNight
5%9%30%33%15%4
654
16th to endNight
411%33%30%17%3
704
November1st to 15thNight
416%32%31%13%2
868
16th to endNight
5%16%39%27%10%1
900
December1st to 15thNight
421%47%19%6%
900
16th to endNight
6%21%42%21%6%
960
Page generated at 2017-09-20 02:49:56. Version ac04

Copyright 2017 A. Danko


Lazy J Observatory Clear Sky Chart | Charts Home