Lee DaSilva Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lee DaSilva Observatory clear sky chart from 2005-11-05 to 2017-09-16.

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
69%
15418
31%
46868
27%
15382
74%
15382
50%
23085

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
65%
717
20%
2467
23%
716
68%
716
31%
1406
January16th to endNight
66%
768
24%
2496
27%
768
67%
768
31%
1470
February1st to 15thNight
67%
698
26%
2192
28%
698
69%
698
36%
1236
February16th to endNight
63%
632
25%
1895
26%
632
67%
632
35%
1101
March1st to 15thNight
63%
720
21%
2106
20%
720
67%
720
39%
1196
March16th to endNight
60%
768
26%
2024
19%
768
65%
768
46%
1137
April1st to 15thNight
51%
719
28%
1799
13%
719
58%
719
44%
1047
April16th to endNight
56%
720
30%
1800
11%
720
63%
720
55%
943
May1st to 15thNight
59%
644
31%
1724
15%
644
67%
644
64%
813
May16th to endNight
52%
404
34%
1527
23%
404
68%
404
53%
588
June1st to 15thNight
50%
360
34%
1440
25%
360
69%
360
57%
510
June16th to endNight
70%
360
40%
1440
39%
360
84%
360
81%
415
July1st to 15thNight
77%
340
36%
1360
39%
340
85%
340
76%
410
July16th to endNight
83%
497
41%
1527
35%
465
87%
465
69%
596
August1st to 15thNight
80%
655
39%
1729
21%
652
85%
652
82%
733
August16th to endNight
87%
764
46%
1910
28%
764
89%
764
86%
839
September1st to 15thNight
87%
720
44%
1800
30%
720
90%
720
83%
797
September16th to endNight
79%
660
46%
1788
37%
660
86%
660
80%
742
October1st to 15thNight
75%
660
34%
1952
32%
660
82%
660
58%
899
October16th to endNight
79%
704
40%
2112
42%
704
83%
704
60%
956
November1st to 15thNight
79%
700
33%
2265
37%
700
81%
700
50%
1062
November16th to endNight
72%
720
29%
2340
30%
720
75%
720
42%
1197
December1st to 15thNight
66%
720
24%
2487
25%
720
69%
720
31%
1418
December16th to endNight
60%
768
23%
2688
24%
768
64%
768
29%
1574

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
6%212212235%68%
47894
Night
7%212212235%67%
47051
TransparencyDay
19%38%19%25%23%
47576
Night
20%39%21%25%20%
46869
SeeingDay
7%415%30%28%13%
5884
Night
7%215%38%29%5%
15429

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
11%7%25%413347%46%
1468
16th to endDay
15%7%34424437%41%
1728
February1st to 15thDay
14%5%23313447%48%
1670
16th to endDay
16%5%23324345%48%
1579
March1st to 15thDay
10%31432446%8%50%
1853
16th to endDay
10%31331445%6%53%
2199
April1st to 15thDay
11%413213345%58%
2149
16th to endDay
6%212213336%66%
2160
May1st to 15thDay
213111235%75%
2226
16th to endDay
311212236%73%
2583
June1st to 15thDay
21111222478%
2520
16th to endDay
1112289%
2520
July1st to 15thDay
111111486%
2520
16th to endDay
1111212382%
2534
August1st to 15thDay
1111388%
2220
16th to endDay
111111386%
2292
September1st to 15thDay
1111286%
2160
16th to endDay
1111122482%
1860
October1st to 15thDay
3211212345%72%
1675
16th to endDay
4212212345%70%
1760
November1st to 15thDay
7%313323325%61%
1592
16th to endDay
11%422223346%55%
1620
December1st to 15thDay
13%6%345%24347%44%
1470
16th to endDay
15%7%34424346%44%
1536
January1st to 15thNight
12%6%23322337%51%
2467
16th to endNight
16%423223447%48%
2496
February1st to 15thNight
11%41321335%8%53%
2181
16th to endNight
16%322223346%52%
1895
March1st to 15thNight
10%324423336%55%
2106
16th to endNight
9%312223448%58%
2024
April1st to 15thNight
8%313313347%58%
1799
16th to endNight
5%111212235%71%
1800
May1st to 15thNight
212212235%75%
1724
16th to endNight
42111223475%
1526
June1st to 15thNight
2111222479%
1440
16th to endNight
11290%
1440
July1st to 15thNight
11112385%
1440
16th to endNight
21112213380%
1633
August1st to 15thNight
1111288%
1738
16th to endNight
111388%
1910
September1st to 15thNight
1211287%
1800
16th to endNight
111112385%
1788
October1st to 15thNight
421212346%69%
1952
16th to endNight
412212235%73%
2112
November1st to 15thNight
6%312212235%68%
2265
16th to endNight
8%323213346%60%
2340
December1st to 15thNight
12%424323345%52%
2487
16th to endNight
17%423313236%50%
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
38%5%15%20%16%3
1468
16th to endDay
43%6%10%18%15%5%
1728
February1st to 15thDay
36%6%13%24%16%2
1670
16th to endDay
37%5%11%28%15%1
1579
March1st to 15thDay
30%5%16%24%17%4
1853
16th to endDay
29%415%27%19%3
2199
April1st to 15thDay
29%310%28%20%7%
2149
16th to endDay
19%312%26%27%10%
2160
May1st to 15thDay
13%37%23%37%15%
2226
16th to endDay
13%35%29%33%13%
2587
June1st to 15thDay
11%37%17%31%29%
2520
16th to endDay
4119%30%51%
2520
July1st to 15thDay
5%116%20%63%
2371
16th to endDay
9%228%19%57%
2377
August1st to 15thDay
5%118%27%55%
2204
16th to endDay
6%17%34%48%
2292
September1st to 15thDay
6%1310%31%45%
2160
16th to endDay
7%1319%39%28%
1860
October1st to 15thDay
14%27%25%29%21%
1675
16th to endDay
17%27%26%29%17%
1760
November1st to 15thDay
26%313%27%25%3
1592
16th to endDay
30%5%11%26%23%2
1620
December1st to 15thDay
41%5%10%21%19%2
1470
16th to endDay
41%5%14%23%13%1
1536
January1st to 15thNight
34%412%24%19%4
2467
16th to endNight
35%412%18%17%10%
2496
February1st to 15thNight
30%5%12%27%18%5%
2192
16th to endNight
33%312%30%17%2
1895
March1st to 15thNight
29%415%21%22%6%
2106
16th to endNight
24%414%28%20%6%
2024
April1st to 15thNight
26%412%31%19%7%
1799
16th to endNight
16%411%26%31%8%
1800
May1st to 15thNight
12%37%23%37%16%
1725
16th to endNight
13%38%27%33%14%
1527
June1st to 15thNight
11%27%22%29%27%
1440
16th to endNight
3119%25%57%
1440
July1st to 15thNight
6%2421%64%
1360
16th to endNight
10%117%20%57%
1527
August1st to 15thNight
6%17%26%56%
1729
16th to endNight
4117%31%53%
1910
September1st to 15thNight
5%1210%29%49%
1800
16th to endNight
6%1315%41%32%
1788
October1st to 15thNight
15%38%22%28%22%
1952
16th to endNight
14%25%23%33%19%
2112
November1st to 15thNight
20%210%28%30%7%
2265
16th to endNight
24%410%27%25%6%
2340
December1st to 15thNight
33%5%12%23%18%6%
2487
16th to endNight
36%414%23%16%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
28%18%25%13%14%
96
16th to endDay
19%310%25%23%18%
256
February1st to 15thDay
18%411%24%19%21%
253
16th to endDay
16%7%18%25%21%11%
238
March1st to 15thDay
12%5%21%22%24%14%
270
16th to endDay
14%9%20%26%19%9%
288
April1st to 15thDay
16%10%26%21%16%7%
269
16th to endDay
10%11%26%28%16%7%
270
May1st to 15thDay
5%7%21%34%21%9%
288
16th to endDay
39%21%25%31%8%
330
June1st to 15thDay
2424%34%24%9%
315
16th to endDay
111%34%35%15%
315
July1st to 15thDay
8%31%35%23%
305
16th to endDay
15%31%39%20%
327
August1st to 15thDay
48%44%28%12%
315
16th to endDay
17%30%40%19%
332
September1st to 15thDay
18%42%35%11%
315
16th to endDay
3417%29%29%15%
258
October1st to 15thDay
3320%32%30%9%
255
16th to endDay
7%414%31%29%13%
272
November1st to 15thDay
8%1411%36%38%
98
16th to endDay
5%6%16%31%34%5%
90
December1st to 15thDay
13%13%38%33%
65
16th to endDay
20%12%21%35%9%
64
January1st to 15thNight
14%18%33%30%11%
720
16th to endNight
17%18%31%31%8%
768
February1st to 15thNight
12%39%35%30%8%
704
16th to endNight
16%310%36%25%6%
632
March1st to 15thNight
10%315%36%29%6%
720
16th to endNight
9%421%35%26%1
768
April1st to 15thNight
8%7%27%33%20%2
719
16th to endNight
5%7%26%33%23%3
720
May1st to 15thNight
2431%42%17%2
645
16th to endNight
46%34%39%15%
405
June1st to 15thNight
36%38%42%8%
360
16th to endNight
1126%56%13%
360
July1st to 15thNight
118%57%22%
340
16th to endNight
19%48%37%3
497
August1st to 15thNight
115%48%30%3
655
16th to endNight
9%43%42%3
764
September1st to 15thNight
9%40%43%5%
720
16th to endNight
1115%35%37%8%
660
October1st to 15thNight
5%213%34%35%9%
660
16th to endNight
5%28%33%36%13%
704
November1st to 15thNight
7%26%36%37%10%
700
16th to endNight
7%27%39%31%10%
720
December1st to 15thNight
15%17%40%27%7%
720
16th to endNight
18%210%40%23%4
768
Page generated at 2017-09-17 09:05:45. Version ac04

Copyright 2017 A. Danko


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