The Lair
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Lair 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
49%
15497
28%
46998
19%
15451
59%
15451
39%
25684

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%
898
29%
2327
11%
895
46%
895
37%
1402
January16th to endNight
33%
903
32%
2439
12%
903
47%
903
37%
1432
February1st to 15thNight
34%
704
29%
2106
12%
698
48%
698
34%
1170
February16th to endNight
23%
632
31%
1894
9%
632
41%
632
35%
1050
March1st to 15thNight
34%
569
28%
2009
15%
569
50%
569
28%
1124
March16th to endNight
31%
576
26%
2112
15%
576
47%
576
31%
1110
April1st to 15thNight
28%
539
25%
1977
11%
539
48%
539
30%
1070
April16th to endNight
30%
540
27%
1728
14%
540
49%
540
33%
981
May1st to 15thNight
32%
539
24%
1620
15%
539
47%
539
35%
933
May16th to endNight
44%
562
25%
1684
17%
561
57%
561
38%
945
June1st to 15thNight
66%
540
23%
1620
22%
540
73%
540
52%
784
June16th to endNight
69%
540
25%
1620
27%
540
73%
540
42%
875
July1st to 15thNight
80%
510
24%
1530
26%
510
83%
510
48%
791
July16th to endNight
84%
564
30%
1594
34%
531
88%
531
53%
781
August1st to 15thNight
88%
539
33%
1649
39%
536
89%
536
60%
741
August16th to endNight
76%
573
23%
1958
29%
573
77%
573
34%
1070
September1st to 15thNight
76%
540
21%
1980
26%
540
77%
540
33%
1059
September16th to endNight
72%
513
31%
1891
32%
513
77%
513
37%
971
October1st to 15thNight
69%
505
37%
1825
34%
505
76%
505
44%
852
October16th to endNight
54%
704
35%
2112
21%
704
63%
704
48%
1060
November1st to 15thNight
51%
747
31%
2147
18%
747
58%
747
44%
1167
November16th to endNight
46%
900
32%
2340
16%
900
55%
900
41%
1358
December1st to 15thNight
41%
900
29%
2340
15%
900
48%
900
37%
1426
December16th to endNight
38%
960
27%
2496
11%
960
47%
960
35%
1532

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
10%42442445%6%50%
47875
Night
8%313323347%56%
47200
Cloud CoverDay
10%42442445%6%50%
47873
Night
9%313323347%56%
47200
TransparencyDay
33%410%20%21%9%
47573
Night
27%411%22%21%12%
47005
SeeingDay
10%419%32%25%6%
5464
Night
10%6%29%36%16%1
15501

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
14%5%23312245%53%
1611
16th to endDay
12%323323445%54%
1794
February1st to 15thDay
11%5%24212235%57%
1750
16th to endDay
13%5%13323345%54%
1580
March1st to 15thDay
15%6%14323445%48%
1950
16th to endDay
12%435%31244451%
2112
April1st to 15thDay
10%5%25%5%24346%49%
1971
16th to endDay
12%435%32444449%
2228
May1st to 15thDay
14%5%26%5%3445%7%41%
2331
16th to endDay
12%5%35%5%3447%7%38%
2430
June1st to 15thDay
5%312435%47%8%54%
2340
16th to endDay
8%3245%45%5%7%9%44%
2340
July1st to 15thDay
7%2245%35%6%7%9%46%
2340
16th to endDay
6%223435%5%7%10%49%
2466
August1st to 15thDay
221232436%8%61%
2298
16th to endDay
8%425%6%37%5%6%8%41%
2242
September1st to 15thDay
10%4245%35%45%7%46%
1980
16th to endDay
9%3145%2445%7%50%
1881
October1st to 15thDay
8%424323347%56%
1793
16th to endDay
8%2122233467%
1760
November1st to 15thDay
11%415%323345%52%
1710
16th to endDay
11%41332232459%
1620
December1st to 15thDay
14%6%24213335%50%
1620
16th to endDay
12%6%34423447%47%
1728
January1st to 15thNight
13%5%13322235%55%
2327
16th to endNight
13%324322236%55%
2439
February1st to 15thNight
10%424313325%58%
2102
16th to endNight
11%323313345%56%
1894
March1st to 15thNight
13%32342345%7%50%
2009
16th to endNight
9%323313446%56%
2112
April1st to 15thNight
7%32442445%6%53%
1977
16th to endNight
9%424324347%52%
1728
May1st to 15thNight
9%31342445%9%50%
1619
16th to endNight
7%3143235%6%9%50%
1683
June1st to 15thNight
111231345%8%64%
1620
16th to endNight
5%21222446%8%57%
1620
July1st to 15thNight
411331346%11%59%
1620
16th to endNight
311231436%12%60%
1702
August1st to 15thNight
2122123410%68%
1659
16th to endNight
7%3144245%5%10%50%
1958
September1st to 15thNight
8%312425%45%8%52%
1980
16th to endNight
8%41332345%7%54%
1891
October1st to 15thNight
7%312213346%64%
1825
16th to endNight
7%21321233465%
2112
November1st to 15thNight
8%322323236%61%
2147
16th to endNight
10%413312335%59%
2340
December1st to 15thNight
12%5%24313346%52%
2340
16th to endNight
12%5%24213345%52%
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
14%5%23313345%53%
1611
16th to endDay
12%323323445%55%
1794
February1st to 15thDay
11%5%24212335%57%
1750
16th to endDay
13%5%12313235%54%
1580
March1st to 15thDay
16%5%14313445%48%
1950
16th to endDay
13%425%22234451%
2110
April1st to 15thDay
11%4345%24346%49%
1971
16th to endDay
12%435%324445%49%
2228
May1st to 15thDay
14%5%25%5%3445%7%41%
2331
16th to endDay
13%5%345%345%6%7%39%
2430
June1st to 15thDay
5%212425%5%6%9%54%
2340
16th to endDay
9%3245%35%5%6%10%44%
2340
July1st to 15thDay
7%2245%35%5%7%9%46%
2340
16th to endDay
6%223425%5%7%10%48%
2466
August1st to 15thDay
211232345%9%61%
2298
16th to endDay
8%425%6%46%6%7%7%41%
2242
September1st to 15thDay
10%5%25%5%445%46%47%
1980
16th to endDay
8%3145%3445%7%50%
1881
October1st to 15thDay
8%424323346%56%
1793
16th to endDay
8%21221233468%
1760
November1st to 15thDay
11%415%323345%53%
1710
16th to endDay
12%31332222459%
1620
December1st to 15thDay
14%6%24312335%50%
1620
16th to endDay
12%6%25%423347%48%
1728
January1st to 15thNight
13%5%2332224455%
2327
16th to endNight
13%323313236%56%
2439
February1st to 15thNight
11%324312235%58%
2102
16th to endNight
12%313313345%56%
1894
March1st to 15thNight
13%42332345%7%50%
2009
16th to endNight
9%323323346%56%
2112
April1st to 15thNight
7%3245%2445%6%53%
1977
16th to endNight
9%43332335%7%52%
1728
May1st to 15thNight
10%31332445%8%51%
1619
16th to endNight
7%31441446%10%50%
1683
June1st to 15thNight
211232346%8%64%
1620
16th to endNight
6%21222445%9%57%
1620
July1st to 15thNight
411331345%10%60%
1620
16th to endNight
311221436%12%61%
1702
August1st to 15thNight
212212349%68%
1659
16th to endNight
7%313425%46%9%50%
1958
September1st to 15thNight
8%312425%36%8%52%
1980
16th to endNight
8%41332345%6%55%
1891
October1st to 15thNight
6%312213346%64%
1825
16th to endNight
7%21322224466%
2112
November1st to 15thNight
7%413313236%61%
2147
16th to endNight
10%423312335%59%
2340
December1st to 15thNight
12%425%213347%53%
2340
16th to endNight
13%5%24213345%52%
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
34%25%18%25%13%
1612
16th to endDay
31%36%15%26%16%
1794
February1st to 15thDay
31%26%16%23%19%
1751
16th to endDay
33%2419%24%15%
1580
March1st to 15thDay
38%48%13%22%13%
1950
16th to endDay
35%49%17%22%10%
2112
April1st to 15thDay
36%39%18%17%15%
1971
16th to endDay
36%46%18%21%11%
2228
May1st to 15thDay
41%5%10%15%17%9%
2331
16th to endDay
41%7%10%19%17%3
2434
June1st to 15thDay
25%5%13%25%24%5%
2340
16th to endDay
34%6%14%21%19%4
2340
July1st to 15thDay
31%7%16%27%15%2
2201
16th to endDay
26%7%18%30%16%1
2311
August1st to 15thDay
19%5%16%35%21%2
2284
16th to endDay
37%7%15%24%12%2
2242
September1st to 15thDay
36%411%22%19%5%
1980
16th to endDay
32%5%9%20%21%9%
1881
October1st to 15thDay
29%310%21%19%15%
1793
16th to endDay
21%3318%32%20%
1760
November1st to 15thDay
33%38%21%21%11%
1710
16th to endDay
31%35%14%23%23%
1620
December1st to 15thDay
37%48%18%22%10%
1620
16th to endDay
37%38%16%23%10%
1728
January1st to 15thNight
32%25%18%22%18%
2327
16th to endNight
32%2415%25%19%
2439
February1st to 15thNight
30%36%13%23%22%
2112
16th to endNight
30%27%17%22%19%
1894
March1st to 15thNight
34%39%13%23%14%
2009
16th to endNight
29%5%11%19%24%10%
2112
April1st to 15thNight
30%5%8%18%19%16%
1977
16th to endNight
31%411%18%21%12%
1728
May1st to 15thNight
29%6%13%21%19%9%
1620
16th to endNight
28%5%16%27%17%3
1685
June1st to 15thNight
16%6%15%29%26%6%
1620
16th to endNight
23%7%14%29%20%4
1620
July1st to 15thNight
19%7%20%34%17%1
1530
16th to endNight
15%6%22%36%16%2
1594
August1st to 15thNight
12%418%38%22%3
1649
16th to endNight
28%6%19%27%12%4
1958
September1st to 15thNight
28%6%15%23%19%6%
1980
16th to endNight
28%312%25%19%10%
1891
October1st to 15thNight
21%412%25%19%16%
1825
16th to endNight
22%25%17%26%24%
2112
November1st to 15thNight
25%38%23%24%14%
2147
16th to endNight
28%37%15%22%23%
2340
December1st to 15thNight
33%310%17%22%13%
2340
16th to endNight
34%37%15%24%14%
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%33%33%41
90
16th to endDay
11%17%41%20%7%1
96
February1st to 15thDay
415%36%37%5%
90
16th to endDay
14%9%48%23%3
81
March1st to 15thDay
26%12%32%21%7%
90
16th to endDay
5%6%48%27%12%
96
April1st to 15thDay
16%12%41%24%5%
90
16th to endDay
12%14%42%20%8%
338
May1st to 15thDay
16%10%37%27%7%
468
16th to endDay
17%5%28%33%13%2
517
June1st to 15thDay
5%116%46%24%5%
495
16th to endDay
9%210%39%30%8%
495
July1st to 15thDay
5%18%41%36%8%
475
16th to endDay
4432%43%13%
515
August1st to 15thDay
2334%47%11%
451
16th to endDay
12%6%31%32%15%
282
September1st to 15thDay
5%219%50%22%
135
16th to endDay
5%25%48%19%
108
October1st to 15thDay
217%34%46%7%
90
16th to endDay
20%29%33%32%2
96
November1st to 15thDay
28%326%22%13%5%
90
16th to endDay
23%13%28%21%11%2
90
December1st to 15thDay
20%6%24%24%18%5%
90
16th to endDay
14%16%38%22%6%1
96
January1st to 15thNight
16%9%34%31%9%
900
16th to endNight
14%8%39%29%7%
903
February1st to 15thNight
13%12%36%31%5%
704
16th to endNight
14%11%48%22%2
632
March1st to 15thNight
14%10%37%33%3
569
16th to endNight
9%11%45%28%5%
576
April1st to 15thNight
9%10%48%29%2
539
16th to endNight
9%8%47%25%7%
540
May1st to 15thNight
11%7%45%30%5%
540
16th to endNight
7%339%34%15%
563
June1st to 15thNight
126%50%19%1
540
16th to endNight
4217%50%21%3
540
July1st to 15thNight
47%54%29%2
510
16th to endNight
35%50%35%4
564
August1st to 15thNight
2345%42%6%
539
16th to endNight
8%1441%38%5%
573
September1st to 15thNight
8%16%41%37%4
540
16th to endNight
9%7%41%37%3
513
October1st to 15thNight
7%118%44%24%3
505
16th to endNight
8%5%28%35%20%1
704
November1st to 15thNight
10%331%38%14%2
747
16th to endNight
12%8%30%34%12%1
900
December1st to 15thNight
15%7%31%34%10%
900
16th to endNight
16%9%31%33%7%
960
Page generated at 2017-09-23 05:43:40. Version ac04

Copyright 2017 A. Danko


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