Larry's Backyard Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Larry's Backyard Observing Site clear sky chart from 2005-11-05 to 2017-09-22.

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
44%
15933
25%
46976
14%
15888
53%
15888
35%
26834

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
38%
900
25%
2327
11%
895
48%
895
36%
1418
January16th to endNight
36%
960
29%
2496
12%
960
47%
960
39%
1474
February1st to 15thNight
34%
838
18%
2247
7%
834
41%
834
26%
1510
February16th to endNight
32%
632
28%
1894
9%
632
47%
632
31%
1089
March1st to 15thNight
35%
601
24%
2041
15%
601
46%
601
32%
1102
March16th to endNight
29%
576
19%
2112
12%
576
40%
576
22%
1279
April1st to 15thNight
32%
539
19%
1879
13%
539
43%
539
28%
1069
April16th to endNight
32%
540
22%
1620
14%
540
45%
540
27%
1011
May1st to 15thNight
35%
540
18%
1620
14%
540
42%
540
26%
1036
May16th to endNight
48%
561
16%
1684
11%
561
54%
561
32%
1007
June1st to 15thNight
48%
540
18%
1620
10%
540
54%
540
41%
881
June16th to endNight
55%
540
23%
1620
12%
540
61%
540
50%
803
July1st to 15thNight
63%
510
18%
1530
13%
510
66%
510
44%
814
July16th to endNight
70%
564
23%
1594
22%
531
72%
531
41%
860
August1st to 15thNight
71%
539
23%
1610
23%
536
75%
536
41%
875
August16th to endNight
64%
573
28%
1749
26%
573
70%
573
41%
918
September1st to 15thNight
54%
540
24%
1971
22%
540
63%
540
35%
1010
September16th to endNight
55%
513
31%
1891
26%
513
66%
513
38%
927
October1st to 15thNight
45%
569
31%
1889
23%
569
53%
569
31%
1047
October16th to endNight
46%
723
31%
2131
16%
723
56%
723
44%
1107
November1st to 15thNight
48%
875
33%
2275
15%
875
59%
875
49%
1213
November16th to endNight
41%
900
29%
2340
13%
900
51%
900
42%
1348
December1st to 15thNight
36%
900
23%
2340
10%
900
45%
900
34%
1466
December16th to endNight
37%
960
28%
2496
12%
960
48%
960
33%
1570

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
9%5%24424447%50%
47904
Night
8%42432345%7%53%
47172
Cloud CoverDay
9%5%2442445%7%49%
47902
Night
8%42432345%7%53%
47172
TransparencyDay
33%5%13%27%17%3
47602
Night
29%5%13%27%19%4
46977
SeeingDay
11%7%28%32%17%2
5930
Night
11%7%32%36%11%
15936

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
6%6%24324448%52%
1611
16th to endDay
8%5%25%43435%7%48%
1728
February1st to 15thDay
8%9%35%5%24448%43%
1624
16th to endDay
6%6%25%5%34346%51%
1580
March1st to 15thDay
9%6%243245%5%7%49%
1917
16th to endDay
16%8%34413346%43%
2112
April1st to 15thDay
13%7%24424346%45%
2066
16th to endDay
17%7%25%434446%39%
2340
May1st to 15thDay
12%5%24424447%45%
2331
16th to endDay
13%5%25%5%2445%7%43%
2430
June1st to 15thDay
7%32442445%8%53%
2340
16th to endDay
421333446%8%57%
2340
July1st to 15thDay
7%214436%6%6%10%48%
2340
16th to endDay
7%21443345%9%53%
2466
August1st to 15thDay
6%315%5%345%6%8%48%
2340
16th to endDay
6%41432435%6%56%
2450
September1st to 15thDay
12%5%23423447%49%
1989
16th to endDay
8%213424347%56%
1881
October1st to 15thDay
14%41332334454%
1730
16th to endDay
8%42232333461%
1738
November1st to 15thDay
6%313322346%61%
1583
16th to endDay
10%5%22312246%57%
1620
December1st to 15thDay
9%7%25%5%24447%45%
1620
16th to endDay
11%7%46%434447%43%
1728
January1st to 15thNight
6%5%25%423445%53%
2327
16th to endNight
7%325%31335%6%56%
2496
February1st to 15thNight
9%6%36%5%35%5%45%44%
2237
16th to endNight
7%42442345%7%52%
1894
March1st to 15thNight
9%6%14313338%53%
2041
16th to endNight
15%7%24323346%45%
2112
April1st to 15thNight
10%5%24423447%49%
1879
16th to endNight
15%5%2432235%6%45%
1620
May1st to 15thNight
13%6%245%23447%44%
1619
16th to endNight
10%32432346%11%46%
1683
June1st to 15thNight
6%21332345%10%56%
1620
16th to endNight
221222346%10%59%
1620
July1st to 15thNight
41133245%7%11%53%
1620
16th to endNight
42234245%7%10%52%
1702
August1st to 15thNight
42134345%6%10%52%
1620
16th to endNight
5%32342345%6%58%
1749
September1st to 15thNight
8%32342335%6%55%
1971
16th to endNight
5%21232445%6%60%
1891
October1st to 15thNight
12%423323335%55%
1889
16th to endNight
9%41221233463%
2131
November1st to 15thNight
6%312223346%64%
2275
16th to endNight
10%422222346%59%
2340
December1st to 15thNight
9%6%2431345%7%49%
2340
16th to endNight
11%8%24312347%48%
2496

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
6%5%2433445%7%52%
1611
16th to endDay
8%6%26%43345%7%48%
1728
February1st to 15thDay
8%8%35%5%24448%43%
1624
16th to endDay
5%6%25%5%34346%50%
1580
March1st to 15thDay
8%6%243245%5%6%49%
1917
16th to endDay
16%8%24422346%43%
2110
April1st to 15thDay
13%7%24424346%46%
2066
16th to endDay
17%7%345%34445%39%
2340
May1st to 15thDay
12%5%34434448%44%
2331
16th to endDay
12%5%25%5%3445%7%42%
2430
June1st to 15thDay
6%32433446%7%53%
2340
16th to endDay
43134245%6%8%57%
2340
July1st to 15thDay
7%314435%5%6%10%48%
2340
16th to endDay
6%31342446%9%53%
2466
August1st to 15thDay
6%315%5%346%6%8%48%
2340
16th to endDay
7%42332335%7%55%
2450
September1st to 15thDay
12%6%1442335%6%49%
1989
16th to endDay
8%21332335%7%55%
1881
October1st to 15thDay
14%414323245%53%
1730
16th to endDay
8%5%2231334460%
1738
November1st to 15thDay
6%313322346%61%
1583
16th to endDay
9%6%23313245%57%
1620
December1st to 15thDay
9%7%25%5%25%347%45%
1620
16th to endDay
10%7%46%434347%42%
1728
January1st to 15thNight
6%5%25%423345%53%
2327
16th to endNight
7%424323346%57%
2496
February1st to 15thNight
9%6%36%435%5%5%5%43%
2237
16th to endNight
7%5%245%235%5%7%52%
1894
March1st to 15thNight
9%6%24413339%52%
2041
16th to endNight
15%6%34423346%45%
2112
April1st to 15thNight
10%5%25%32445%7%49%
1879
16th to endNight
15%6%2442235%7%45%
1620
May1st to 15thNight
13%6%345%24446%44%
1619
16th to endNight
10%31432346%10%46%
1683
June1st to 15thNight
6%21331436%9%55%
1620
16th to endNight
221231447%10%59%
1620
July1st to 15thNight
42134245%7%10%54%
1620
16th to endNight
4114425%5%7%10%52%
1702
August1st to 15thNight
42134345%6%11%52%
1620
16th to endNight
5%32432335%6%58%
1749
September1st to 15thNight
8%42432345%6%56%
1971
16th to endNight
5%21332445%5%60%
1891
October1st to 15thNight
12%413323335%55%
1889
16th to endNight
9%412122235%63%
2131
November1st to 15thNight
5%312213346%64%
2275
16th to endNight
10%413222346%58%
2340
December1st to 15thNight
9%6%2432345%7%49%
2340
16th to endNight
11%8%24312447%48%
2496

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
30%416%31%14%2
1612
16th to endDay
34%5%17%25%14%2
1728
February1st to 15thDay
38%7%18%22%9%3
1625
16th to endDay
33%413%27%17%3
1580
March1st to 15thDay
32%6%12%27%17%3
1917
16th to endDay
42%5%12%24%12%2
2112
April1st to 15thDay
39%412%25%15%2
2066
16th to endDay
46%5%11%23%12%
2340
May1st to 15thDay
38%6%12%25%15%1
2331
16th to endDay
40%5%14%26%11%1
2434
June1st to 15thDay
28%7%15%28%15%4
2340
16th to endDay
23%6%13%29%22%3
2340
July1st to 15thDay
29%7%12%27%19%3
2201
16th to endDay
25%6%13%31%20%3
2311
August1st to 15thDay
30%8%15%27%15%2
2326
16th to endDay
28%412%29%19%5%
2450
September1st to 15thDay
34%5%10%23%19%6%
1989
16th to endDay
28%411%30%21%3
1881
October1st to 15thDay
33%38%24%24%4
1730
16th to endDay
26%48%28%25%5%
1738
November1st to 15thDay
23%411%27%28%4
1583
16th to endDay
29%410%31%21%2
1620
December1st to 15thDay
38%416%25%13%
1620
16th to endDay
41%413%25%13%1
1728
January1st to 15thNight
31%5%15%27%18%2
2327
16th to endNight
28%5%14%29%19%3
2496
February1st to 15thNight
40%6%12%24%11%3
2247
16th to endNight
31%5%12%27%18%5%
1894
March1st to 15thNight
30%412%25%19%6%
2041
16th to endNight
40%412%24%12%3
2112
April1st to 15thNight
33%5%13%25%20%1
1879
16th to endNight
38%5%12%24%16%1
1620
May1st to 15thNight
39%6%12%22%16%2
1620
16th to endNight
31%8%20%23%13%2
1685
June1st to 15thNight
23%7%17%30%15%5%
1620
16th to endNight
18%6%14%33%22%5%
1620
July1st to 15thNight
22%7%15%30%19%4
1530
16th to endNight
23%7%15%30%17%5%
1594
August1st to 15thNight
24%7%17%30%15%5%
1610
16th to endNight
26%411%29%20%8%
1749
September1st to 15thNight
28%412%27%18%9%
1971
16th to endNight
24%5%11%25%28%4
1891
October1st to 15thNight
32%47%24%24%6%
1889
16th to endNight
24%38%31%26%6%
2131
November1st to 15thNight
20%38%28%29%8%
2275
16th to endNight
27%410%29%23%5%
2340
December1st to 15thNight
32%6%14%29%15%
2340
16th to endNight
35%414%25%17%2
2496

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
17%10%37%27%6%
90
16th to endDay
17%8%38%29%5%1
96
February1st to 15thDay
14%14%37%25%7%
90
16th to endDay
217%46%22%8%2
81
March1st to 15thDay
14%15%45%18%41
90
16th to endDay
17%12%46%16%6%
96
April1st to 15thDay
15%12%40%21%9%
185
16th to endDay
20%16%36%18%6%1
450
May1st to 15thDay
13%12%30%27%13%1
468
16th to endDay
16%9%33%27%11%2
517
June1st to 15thDay
7%430%36%17%3
495
16th to endDay
45%30%38%18%1
495
July1st to 15thDay
10%217%41%24%4
475
16th to endDay
8%113%41%30%4
515
August1st to 15thDay
7%114%43%28%4
493
16th to endDay
10%122%36%26%3
490
September1st to 15thDay
9%231%38%13%3
144
16th to endDay
12%5%21%37%18%4
108
October1st to 15thDay
14%6%27%34%14%2
90
16th to endDay
3245%35%11%2
96
November1st to 15thDay
8%7%32%25%21%4
90
16th to endDay
27%10%38%17%5%
90
December1st to 15thDay
13%16%44%20%23
90
16th to endDay
17%18%37%23%2
96
January1st to 15thNight
10%11%34%37%6%
900
16th to endNight
9%10%38%33%7%
960
February1st to 15thNight
11%9%37%35%5%
839
16th to endNight
10%13%39%29%5%
632
March1st to 15thNight
11%10%36%33%6%
601
16th to endNight
19%9%38%25%6%
576
April1st to 15thNight
12%10%41%29%5%
539
16th to endNight
19%9%35%27%7%
540
May1st to 15thNight
16%7%33%30%9%1
540
16th to endNight
12%6%29%37%11%2
563
June1st to 15thNight
7%436%37%13%
540
16th to endNight
2235%45%14%
540
July1st to 15thNight
5%23%45%23%1
510
16th to endNight
415%52%26%
564
August1st to 15thNight
6%16%52%24%
539
16th to endNight
7%119%44%24%3
573
September1st to 15thNight
11%325%38%17%2
540
16th to endNight
6%330%39%18%
513
October1st to 15thNight
15%7%27%33%15%
569
16th to endNight
12%5%33%35%11%
723
November1st to 15thNight
7%8%32%38%12%
875
16th to endNight
13%9%34%32%9%
900
December1st to 15thNight
14%9%36%34%5%
900
16th to endNight
15%8%32%34%8%
960
Page generated at 2017-09-23 05:43:43. Version ac04

Copyright 2017 A. Danko


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