Leach Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Leach 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
44%
15910
25%
46843
14%
15865
53%
15865
36%
26642

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
36%
900
27%
2327
12%
895
48%
895
39%
1364
January16th to endNight
36%
960
30%
2496
12%
960
47%
960
39%
1476
February1st to 15thNight
35%
804
19%
2214
8%
800
42%
800
27%
1454
February16th to endNight
32%
632
29%
1894
10%
632
47%
632
32%
1093
March1st to 15thNight
37%
621
25%
2061
15%
621
47%
621
32%
1131
March16th to endNight
29%
576
19%
2112
11%
576
40%
576
23%
1248
April1st to 15thNight
32%
539
19%
1875
13%
539
44%
539
28%
1057
April16th to endNight
32%
540
22%
1620
13%
540
46%
540
27%
1013
May1st to 15thNight
37%
540
18%
1620
13%
540
46%
540
28%
994
May16th to endNight
46%
561
16%
1685
11%
561
52%
561
33%
988
June1st to 15thNight
47%
540
18%
1620
9%
540
54%
540
40%
865
June16th to endNight
53%
540
24%
1542
12%
540
61%
540
52%
783
July1st to 15thNight
63%
510
18%
1502
13%
510
66%
510
44%
821
July16th to endNight
67%
564
23%
1594
19%
531
72%
531
42%
873
August1st to 15thNight
71%
539
21%
1610
22%
536
74%
536
39%
891
August16th to endNight
65%
573
27%
1790
28%
573
69%
573
40%
964
September1st to 15thNight
54%
540
23%
1953
21%
540
63%
540
33%
1031
September16th to endNight
55%
504
31%
1857
26%
504
65%
504
37%
915
October1st to 15thNight
43%
548
31%
1868
23%
548
53%
548
32%
1022
October16th to endNight
45%
744
31%
2152
16%
744
55%
744
46%
1127
November1st to 15thNight
47%
875
34%
2275
14%
875
59%
875
52%
1197
November16th to endNight
42%
900
30%
2340
13%
900
53%
900
44%
1329
December1st to 15thNight
37%
900
23%
2340
10%
900
47%
900
36%
1428
December16th to endNight
38%
960
28%
2496
14%
960
49%
960
34%
1578

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%42442345%7%52%
47943
Night
8%423323447%54%
47038
Cloud CoverDay
9%5%2442345%7%51%
47941
Night
8%42332335%7%54%
47038
TransparencyDay
31%5%13%27%18%3
47641
Night
29%5%13%26%20%5%
46843
SeeingDay
11%6%29%32%17%2
5902
Night
10%7%33%35%11%
15914

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
5%5%2443325%7%54%
1611
16th to endDay
6%6%25%423346%52%
1728
February1st to 15thDay
7%8%36%5%245%46%46%
1657
16th to endDay
6%6%2442346%7%51%
1580
March1st to 15thDay
9%5%2432346%6%51%
1899
16th to endDay
15%7%34414345%45%
2112
April1st to 15thDay
12%5%2442345%5%48%
2069
16th to endDay
16%6%25%43345%6%41%
2340
May1st to 15thDay
11%42442445%6%48%
2331
16th to endDay
12%4233345%5%8%45%
2430
June1st to 15thDay
6%31342445%7%55%
2340
16th to endDay
421232446%9%59%
2402
July1st to 15thDay
6%2134246%5%11%49%
2354
16th to endDay
7%21242445%10%54%
2466
August1st to 15thDay
7%4144245%7%11%46%
2340
16th to endDay
7%31332445%7%55%
2410
September1st to 15thDay
11%5%24323345%52%
2007
16th to endDay
7%21342446%5%57%
1848
October1st to 15thDay
14%413212237%56%
1749
16th to endDay
9%42222323463%
1719
November1st to 15thDay
5%312314346%61%
1583
16th to endDay
8%5%2221223463%
1620
December1st to 15thDay
8%9%25%32345%6%48%
1620
16th to endDay
11%6%45%423447%45%
1728
January1st to 15thNight
6%5%25%422335%57%
2327
16th to endNight
6%424423336%58%
2496
February1st to 15thNight
7%6%46%435%446%46%
2204
16th to endNight
6%5%34414446%54%
1894
March1st to 15thNight
9%5%2341335%7%53%
2061
16th to endNight
15%7%24323336%48%
2112
April1st to 15thNight
11%5%2441345%7%49%
1875
16th to endNight
15%424324347%47%
1620
May1st to 15thNight
12%5%14425%45%6%47%
1619
16th to endNight
10%31332446%10%48%
1683
June1st to 15thNight
6%21231446%10%56%
1620
16th to endNight
32231445%12%59%
1542
July1st to 15thNight
5%2223245%7%10%52%
1592
16th to endNight
5%2133245%7%10%52%
1702
August1st to 15thNight
5%31442446%11%51%
1620
16th to endNight
6%323314447%57%
1790
September1st to 15thNight
9%31342335%7%56%
1953
16th to endNight
431332445%5%61%
1857
October1st to 15thNight
11%413313335%56%
1868
16th to endNight
9%312223345%63%
2152
November1st to 15thNight
6%312212246%66%
2275
16th to endNight
10%312213335%61%
2340
December1st to 15thNight
8%6%2442335%6%52%
2340
16th to endNight
10%7%34313347%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
5%6%24423348%54%
1611
16th to endDay
6%5%25%424446%52%
1728
February1st to 15thDay
7%7%35%5%245%46%46%
1657
16th to endDay
5%6%244235%5%6%51%
1580
March1st to 15thDay
9%5%2342345%6%51%
1899
16th to endDay
15%7%34414345%45%
2110
April1st to 15thDay
12%5%14423446%47%
2069
16th to endDay
16%6%35%43445%6%41%
2340
May1st to 15thDay
11%42442345%7%48%
2331
16th to endDay
11%4244245%5%8%45%
2430
June1st to 15thDay
6%31332445%7%55%
2340
16th to endDay
321332346%9%58%
2402
July1st to 15thDay
6%3134245%5%11%49%
2354
16th to endDay
6%2134245%5%10%54%
2466
August1st to 15thDay
7%4144245%7%10%46%
2340
16th to endDay
7%313424447%55%
2410
September1st to 15thDay
11%5%2431335%6%52%
2007
16th to endDay
6%31333445%6%57%
1848
October1st to 15thDay
14%412312236%56%
1749
16th to endDay
9%41222322463%
1719
November1st to 15thDay
5%312323346%61%
1583
16th to endDay
8%6%23112335%62%
1620
December1st to 15thDay
8%8%25%323446%47%
1620
16th to endDay
11%6%36%423447%45%
1728
January1st to 15thNight
5%5%26%422335%57%
2327
16th to endNight
6%425%423336%58%
2496
February1st to 15thNight
7%6%46%435%447%45%
2204
16th to endNight
6%5%34424446%54%
1894
March1st to 15thNight
9%5%14423347%53%
2061
16th to endNight
14%7%24323345%48%
2112
April1st to 15thNight
11%5%2342335%8%49%
1875
16th to endNight
14%5%24324346%47%
1620
May1st to 15thNight
12%5%344245%6%6%46%
1619
16th to endNight
10%31232446%10%48%
1683
June1st to 15thNight
6%21222445%11%55%
1620
16th to endNight
321232446%12%58%
1542
July1st to 15thNight
421242448%11%52%
1592
16th to endNight
43133345%7%11%52%
1702
August1st to 15thNight
5%22443347%10%51%
1620
16th to endNight
5%313324447%57%
1790
September1st to 15thNight
8%31342335%7%55%
1953
16th to endNight
431322445%5%60%
1857
October1st to 15thNight
11%42332333457%
1868
16th to endNight
9%312213335%63%
2152
November1st to 15thNight
6%33212246%66%
2275
16th to endNight
9%412212245%61%
2340
December1st to 15thNight
8%6%2442335%7%52%
2340
16th to endNight
10%7%35%323346%49%
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
29%315%33%15%2
1612
16th to endDay
31%5%16%27%15%3
1728
February1st to 15thDay
37%7%18%21%9%3
1658
16th to endDay
29%6%15%26%17%5%
1580
March1st to 15thDay
31%5%11%27%19%4
1899
16th to endDay
42%5%11%23%13%2
2112
April1st to 15thDay
36%5%13%26%15%3
2069
16th to endDay
42%5%11%24%14%1
2340
May1st to 15thDay
35%7%13%25%17%1
2331
16th to endDay
36%7%14%27%11%2
2434
June1st to 15thDay
27%7%15%28%16%4
2340
16th to endDay
21%6%13%30%22%6%
2402
July1st to 15thDay
28%7%13%26%20%4
2215
16th to endDay
24%6%14%28%22%3
2311
August1st to 15thDay
30%7%17%26%14%3
2326
16th to endDay
27%5%12%27%20%5%
2410
September1st to 15thDay
33%5%11%22%20%7%
2007
16th to endDay
25%6%11%30%21%4
1848
October1st to 15thDay
31%39%26%24%4
1749
16th to endDay
25%29%30%25%6%
1719
November1st to 15thDay
22%411%26%29%5%
1583
16th to endDay
25%310%31%23%4
1620
December1st to 15thDay
36%5%16%24%15%
1620
16th to endDay
39%415%25%14%1
1728
January1st to 15thNight
30%314%28%21%2
2327
16th to endNight
28%5%12%28%20%4
2496
February1st to 15thNight
38%7%12%24%12%4
2214
16th to endNight
31%411%26%18%7%
1894
March1st to 15thNight
30%411%24%21%7%
2061
16th to endNight
38%413%23%15%4
2112
April1st to 15thNight
32%5%15%23%20%2
1875
16th to endNight
36%6%13%23%18%2
1620
May1st to 15thNight
36%6%14%20%18%3
1620
16th to endNight
30%7%22%24%12%2
1685
June1st to 15thNight
22%8%17%28%17%4
1620
16th to endNight
18%5%15%29%26%4
1542
July1st to 15thNight
23%6%15%26%22%4
1502
16th to endNight
24%7%15%29%18%4
1594
August1st to 15thNight
25%7%17%28%14%5%
1610
16th to endNight
25%6%11%27%22%7%
1790
September1st to 15thNight
27%6%12%25%17%9%
1953
16th to endNight
23%6%10%23%30%5%
1857
October1st to 15thNight
30%5%8%23%24%7%
1868
16th to endNight
23%39%27%28%6%
2152
November1st to 15thNight
19%29%25%31%9%
2275
16th to endNight
26%310%28%24%6%
2340
December1st to 15thNight
32%415%28%17%1
2340
16th to endNight
36%314%24%18%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
11%11%40%26%11%
90
16th to endDay
14%9%42%25%8%
96
February1st to 15thDay
17%6%43%26%41
90
16th to endDay
117%50%16%13%1
81
March1st to 15thDay
13%12%47%22%22
90
16th to endDay
17%10%43%23%4
96
April1st to 15thDay
13%13%38%27%5%1
188
16th to endDay
22%14%36%20%6%1
450
May1st to 15thDay
12%10%33%30%12%1
468
16th to endDay
17%9%32%24%13%1
517
June1st to 15thDay
5%6%32%33%18%3
495
16th to endDay
4431%37%20%1
495
July1st to 15thDay
7%122%42%21%4
475
16th to endDay
8%13%42%31%3
515
August1st to 15thDay
8%113%41%30%3
493
16th to endDay
8%225%37%22%3
450
September1st to 15thDay
7%329%38%17%3
162
16th to endDay
12%5%19%33%24%6%
99
October1st to 15thDay
8%7%26%34%16%5%
90
16th to endDay
9%238%29%16%4
96
November1st to 15thDay
8%10%25%34%16%4
90
16th to endDay
24%7%44%17%41
90
December1st to 15thDay
13%14%46%18%42
90
16th to endDay
25%13%36%21%3
96
January1st to 15thNight
8%10%38%36%6%
900
16th to endNight
9%9%39%34%6%
960
February1st to 15thNight
11%8%37%37%4
806
16th to endNight
9%12%41%29%6%
632
March1st to 15thNight
11%12%36%30%8%
621
16th to endNight
19%11%38%23%6%
576
April1st to 15thNight
14%11%41%28%5%
539
16th to endNight
16%11%36%28%7%
540
May1st to 15thNight
12%8%36%32%8%1
540
16th to endNight
12%7%31%35%10%2
563
June1st to 15thNight
7%337%35%14%
540
16th to endNight
3336%41%14%
540
July1st to 15thNight
5%224%47%19%
510
16th to endNight
6%120%47%23%1
564
August1st to 15thNight
6%13%56%22%
539
16th to endNight
7%119%45%24%1
573
September1st to 15thNight
8%330%36%18%2
540
16th to endNight
6%429%40%17%
504
October1st to 15thNight
13%9%29%31%15%
548
16th to endNight
11%6%34%32%13%
744
November1st to 15thNight
8%9%33%36%12%
875
16th to endNight
12%9%33%31%11%1
900
December1st to 15thNight
12%9%36%34%5%
900
16th to endNight
13%8%33%35%8%
960
Page generated at 2017-09-20 03:49:54. Version ac04

Copyright 2017 A. Danko


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