The Lazy J
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Lazy J clear sky chart from 2005-11-06 to 2024-03-08.

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
52%
24202
33%
79705
20%
24097
66%
24097
41%
38191

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 10thNight
46%
755
36%
3997
20%
736
66%
736
28%
1692
January11th to 20thNight
42%
758
42%
3921
22%
740
60%
740
32%
1410
January21st to endNight
42%
828
23%
4277
20%
814
61%
814
25%
2045
February1st to 10thNight
43%
760
38%
2348
20%
760
64%
760
46%
1069
February11th to 20thNight
32%
743
34%
2218
14%
740
53%
740
42%
1066
February21st to endNight
27%
628
37%
1884
11%
628
54%
628
40%
875
March1st to 10thNight
36%
750
37%
2157
15%
750
56%
750
42%
1036
March11th to 20thNight
46%
720
34%
1980
16%
720
60%
720
44%
1016
March21st to endNight
36%
711
39%
2097
14%
711
59%
711
49%
946
April1st to 10thNight
29%
540
38%
1800
14%
540
58%
540
43%
777
April11th to 20thNight
35%
533
37%
1777
17%
533
62%
533
41%
772
April21st to endNight
34%
540
40%
1800
19%
540
64%
540
43%
785
May1st to 10thNight
40%
540
34%
1800
21%
540
62%
540
48%
782
May11th to 20thNight
54%
531
28%
1770
21%
531
67%
531
44%
824
May21st to endNight
50%
584
35%
1683
18%
582
69%
582
56%
785
June1st to 10thNight
62%
540
28%
1440
20%
540
68%
540
46%
783
June11th to 20thNight
66%
540
38%
1440
25%
540
75%
540
64%
683
June21st to endNight
65%
540
23%
1440
19%
540
68%
540
40%
847
July1st to 10thNight
74%
525
19%
1549
18%
525
75%
525
36%
906
July11th to 20thNight
83%
522
22%
1566
21%
522
83%
522
38%
880
July21st to endNight
79%
591
17%
1674
16%
558
78%
558
33%
992
August1st to 10thNight
80%
537
16%
1754
18%
534
80%
534
31%
1023
August11th to 20thNight
79%
534
24%
1778
26%
534
81%
534
35%
996
August21st to endNight
78%
594
23%
1980
25%
594
80%
594
34%
1106
September1st to 10thNight
77%
540
25%
1800
28%
540
79%
540
35%
990
September11th to 20thNight
73%
540
36%
1800
34%
540
79%
540
41%
917
September21st to endNight
73%
540
35%
1976
33%
540
80%
540
48%
848
October1st to 10thNight
64%
715
31%
2155
22%
715
70%
715
46%
1093
October11th to 20thNight
61%
720
40%
2160
21%
720
75%
720
57%
967
October21st to endNight
59%
792
41%
2376
23%
792
72%
792
54%
1061
November1st to 10thNight
59%
740
42%
2220
23%
740
73%
740
56%
975
November11th to 20thNight
55%
931
38%
2451
19%
931
66%
931
57%
1187
November21st to endNight
47%
950
37%
2470
19%
950
58%
950
45%
1317
December1st to 10thNight
45%
950
39%
2474
18%
950
59%
950
45%
1295
December11th to 20thNight
37%
948
33%
3124
14%
948
53%
948
36%
1573
December21st to endNight
40%
992
22%
4569
17%
979
55%
979
31%
1872

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
33244345%6%8%60%
78779
Night
231342446%8%62%
80823
TransparencyDay
23%5%9%18%27%18%
78505
Night
20%5%9%20%29%18%
80619
SeeingDay
7%17%26%27%19%4
13893
Night
5%13%25%34%21%3
24226

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 10thDay
1329%6%3446%6%56%
2858
11th to 20thDay
1323322346%73%
2860
21st to endDay
410%45%5%345%6%7%48%
3146
February1st to 10thDay
15%2332345%7%66%
1828
11th to 20thDay
232332345%6%66%
1849
21st to endDay
1313214446%71%
1570
March1st to 10thDay
2323325%5%6%9%61%
1958
11th to 20thDay
25%25%42346%6%60%
1980
21st to endDay
231342346%8%65%
2258
April1st to 10thDay
221222445%7%71%
2160
11th to 20thDay
3313313436%69%
2131
21st to endDay
1212223346%73%
2160
May1st to 10thDay
111332345%6%71%
2160
11th to 20thDay
3313435%5%6%7%62%
2125
21st to endDay
211231345%7%71%
2583
June1st to 10thDay
22122246%8%10%62%
2520
11th to 20thDay
1212324447%70%
2520
21st to endDay
6%324435%5%7%10%51%
2520
July1st to 10thDay
5%425%6%48%9%8%11%38%
2358
11th to 20thDay
4326%6%47%8%10%12%39%
2340
21st to endDay
5%326%7%5%8%9%10%13%30%
2545
August1st to 10thDay
4326%8%5%8%9%9%12%35%
2172
11th to 20thDay
8%326%6%5%8%7%8%9%38%
2123
21st to endDay
6%325%6%47%7%8%11%42%
2376
September1st to 10thDay
6%425%6%46%5%7%8%47%
2160
11th to 20thDay
7%4145%35%5%47%54%
2160
21st to endDay
3312334447%67%
1982
October1st to 10thDay
5%32343335%6%63%
1800
11th to 20thDay
221232333475%
1800
21st to endDay
3112212235%76%
1980
November1st to 10thDay
1112222447%73%
1856
11th to 20thDay
111232335%6%71%
1710
21st to endDay
23245%2445%6%63%
1710
December1st to 10thDay
231332345%7%65%
1701
11th to 20thDay
15%35%425%5%5%8%57%
1926
21st to endDay
2324323337%69%
2894
January1st to 10thNight
1438%6%33445%60%
4097
11th to 20thNight
1313323435%71%
4110
21st to endNight
25%245%35%6%8%9%51%
4521
February1st to 10thNight
141332345%9%66%
2348
11th to 20thNight
232442335%7%66%
2218
21st to endNight
13133235%5%7%66%
1884
March1st to 10thNight
13223145%6%9%64%
2157
11th to 20thNight
3423423447%64%
1980
21st to endNight
231222335%7%70%
2097
April1st to 10thNight
221331445%7%69%
1800
11th to 20thNight
331322345%8%68%
1777
21st to endNight
3322323336%71%
1800
May1st to 10thNight
11123235%5%7%69%
1800
11th to 20thNight
2213324447%67%
1770
21st to endNight
211222345%8%70%
1683
June1st to 10thNight
3214345%5%9%10%55%
1440
11th to 20thNight
211221435%8%70%
1440
21st to endNight
4325%5%35%6%7%9%51%
1440
July1st to 10thNight
5%4245%36%5%8%11%48%
1594
11th to 20thNight
32245%46%7%7%13%47%
1620
21st to endNight
3215%447%8%9%14%41%
1773
August1st to 10thNight
3425%6%46%8%10%13%40%
1763
11th to 20thNight
4324435%7%9%12%48%
1778
21st to endNight
2215%6%36%7%7%12%47%
1980
September1st to 10thNight
5%2145%45%7%7%9%51%
1800
11th to 20thNight
5%41343446%8%59%
1800
21st to endNight
22133235%6%7%67%
1976
October1st to 10thNight
221432445%8%63%
2155
11th to 20thNight
111212244476%
2160
21st to endNight
3212212346%74%
2376
November1st to 10thNight
211122345%7%71%
2220
11th to 20thNight
1213223447%72%
2451
21st to endNight
341342335%8%64%
2470
December1st to 10thNight
331442345%8%64%
2474
11th to 20thNight
23245%3445%8%61%
3271
21st to endNight
25%24423345%65%
4800

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 10thDay
23%5%8%17%35%11%
2859
11th to 20thDay
15%28%26%40%10%
2860
21st to endDay
34%46%17%28%10%
3146
February1st to 10thDay
19%37%20%29%23%
1828
11th to 20thDay
19%36%19%30%22%
1859
21st to endDay
16%35%13%34%30%
1570
March1st to 10thDay
20%47%16%32%22%
1958
11th to 20thDay
25%35%14%30%24%
1980
21st to endDay
17%36%18%37%19%
2258
April1st to 10thDay
14%3416%37%25%
2160
11th to 20thDay
18%3414%30%30%
2134
21st to endDay
14%26%19%37%23%
2160
May1st to 10thDay
15%3414%33%30%
2160
11th to 20thDay
23%6%8%15%27%21%
2128
21st to endDay
14%47%18%28%30%
2583
June1st to 10thDay
16%6%11%21%24%22%
2520
11th to 20thDay
15%45%13%24%39%
2520
21st to endDay
29%7%10%16%21%17%
2520
July1st to 10thDay
36%11%14%15%14%11%
2294
11th to 20thDay
32%11%17%21%13%5%
2271
21st to endDay
38%13%23%19%7%1
2404
August1st to 10thDay
40%8%17%24%8%3
2157
11th to 20thDay
40%9%15%19%13%5%
2123
21st to endDay
35%9%15%22%16%3
2376
September1st to 10thDay
36%6%11%18%21%9%
2160
11th to 20thDay
31%5%8%18%26%12%
2160
21st to endDay
19%47%23%32%15%
1982
October1st to 10thDay
24%410%17%25%19%
1800
11th to 20thDay
16%3314%31%33%
1800
21st to endDay
14%2422%39%19%
1980
November1st to 10thDay
13%26%20%38%21%
1856
11th to 20thDay
15%37%23%32%21%
1710
21st to endDay
22%46%19%31%19%
1710
December1st to 10thDay
18%45%27%31%14%
1701
11th to 20thDay
26%310%16%31%14%
1924
21st to endDay
17%27%18%32%23%
2894
January1st to 10thNight
23%46%17%35%14%
4097
11th to 20thNight
17%46%23%40%11%
4110
21st to endNight
25%7%10%20%29%10%
4521
February1st to 10thNight
16%47%21%30%22%
2348
11th to 20thNight
18%45%21%30%22%
2218
21st to endNight
16%45%15%32%28%
1884
March1st to 10thNight
16%5%7%19%31%22%
2157
11th to 20thNight
20%37%17%35%17%
1980
21st to endNight
14%39%19%36%20%
2097
April1st to 10thNight
15%45%17%36%24%
1800
11th to 20thNight
15%46%15%30%29%
1777
21st to endNight
16%35%18%37%21%
1800
May1st to 10thNight
15%4413%36%29%
1800
11th to 20thNight
18%5%10%19%26%22%
1771
21st to endNight
13%47%17%26%32%
1684
June1st to 10thNight
21%7%11%18%21%22%
1440
11th to 20thNight
12%45%20%19%41%
1440
21st to endNight
29%6%12%16%17%20%
1440
July1st to 10thNight
28%9%17%20%19%7%
1549
11th to 20thNight
24%11%17%29%14%5%
1566
21st to endNight
27%12%27%23%10%1
1674
August1st to 10thNight
30%10%22%26%9%3
1754
11th to 20thNight
27%9%19%26%14%4
1778
21st to endNight
27%9%16%27%18%2
1980
September1st to 10thNight
29%6%14%20%21%11%
1800
11th to 20thNight
24%5%11%21%25%13%
1800
21st to endNight
17%49%23%32%14%
1976
October1st to 10thNight
20%6%10%21%25%18%
2155
11th to 20thNight
14%35%13%32%33%
2160
21st to endNight
15%26%18%37%22%
2376
November1st to 10thNight
13%35%20%36%23%
2220
11th to 20thNight
13%4421%35%22%
2451
21st to endNight
21%36%18%33%19%
2470
December1st to 10thNight
19%48%24%30%15%
2474
11th to 20thNight
23%310%20%29%16%
3272
21st to endNight
21%36%18%33%19%
4800

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 10thDay
9%29%32%26%4
270
11th to 20thDay
11%27%27%25%8%2
270
21st to endDay
7%28%32%21%12%1
297
February1st to 10thDay
8%33%26%24%8%1
270
11th to 20thDay
12%29%37%17%5%
270
21st to endDay
20%37%24%15%4
225
March1st to 10thDay
13%30%34%17%5%1
349
11th to 20thDay
15%25%33%19%8%1
420
21st to endDay
14%37%31%13%4
462
April1st to 10thDay
8%34%35%15%6%1
420
11th to 20thDay
13%33%35%15%3
412
21st to endDay
9%31%38%17%4
420
May1st to 10thDay
428%45%19%31
423
11th to 20thDay
6%20%34%28%10%2
448
21st to endDay
319%38%27%11%1
617
June1st to 10thDay
37%26%36%25%3
630
11th to 20thDay
37%25%39%23%3
630
21st to endDay
5%5%19%33%30%7%
630
July1st to 10thDay
2211%42%35%8%
464
11th to 20thDay
47%31%43%14%
444
21st to endDay
217%29%43%18%
487
August1st to 10thDay
418%31%45%12%
447
11th to 20thDay
5%310%38%33%9%
437
21st to endDay
5%211%35%36%11%
495
September1st to 10thDay
6%315%36%32%8%
450
11th to 20thDay
6%222%40%23%7%
450
21st to endDay
27%26%36%22%6%
272
October1st to 10thDay
6%11%27%31%21%5%
270
11th to 20thDay
6%14%29%29%19%3
270
21st to endDay
10%16%28%25%15%6%
297
November1st to 10thDay
7%25%30%22%13%3
270
11th to 20thDay
416%27%30%18%4
270
21st to endDay
8%30%31%20%10%1
270
December1st to 10thDay
8%26%29%26%11%
270
11th to 20thDay
7%27%34%25%7%
270
21st to endDay
15%29%29%20%7%
297
January1st to 10thNight
415%29%36%13%3
760
11th to 20thNight
5%20%30%30%13%2
760
21st to endNight
6%16%32%31%13%1
836
February1st to 10thNight
6%18%30%34%11%2
760
11th to 20thNight
7%20%39%27%7%1
744
21st to endNight
7%26%37%25%4
628
March1st to 10thNight
6%25%30%29%9%1
750
11th to 20thNight
6%18%28%33%15%
720
21st to endNight
7%19%37%29%8%
711
April1st to 10thNight
420%44%26%6%
540
11th to 20thNight
6%24%33%29%8%1
533
21st to endNight
5%21%38%29%7%
540
May1st to 10thNight
116%39%37%6%
540
11th to 20thNight
311%28%40%17%1
531
21st to endNight
29%35%41%13%
584
June1st to 10thNight
26%25%47%19%1
540
11th to 20thNight
2424%51%17%1
540
21st to endNight
5%416%40%32%3
540
July1st to 10thNight
5%29%39%40%5%
525
11th to 20thNight
25%31%53%8%
522
21st to endNight
317%26%52%11%
591
August1st to 10thNight
315%24%57%9%
537
11th to 20thNight
427%31%48%9%
534
21st to endNight
318%29%51%9%
594
September1st to 10thNight
5%27%37%43%5%
540
11th to 20thNight
6%213%40%37%2
540
21st to endNight
25%16%43%31%4
540
October1st to 10thNight
37%20%42%26%3
715
11th to 20thNight
37%27%41%20%2
720
21st to endNight
5%13%21%32%24%6%
792
November1st to 10thNight
313%23%35%23%4
740
11th to 20thNight
214%26%37%19%2
931
21st to endNight
6%17%27%29%19%3
950
December1st to 10thNight
7%18%26%33%15%2
950
11th to 20thNight
5%20%33%31%9%1
950
21st to endNight
10%16%30%33%9%1
998
Page generated at 2024-03-05 05:24:03. Version ac07

Copyright © 2024 Attilla Danko.


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