Starlight Hills Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starlight Hills Observatory clear sky chart from 2005-11-05 to 2018-01-12.

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
54%
16427
28%
48367
18%
16385
64%
16385
43%
25994

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
50%
954
30%
2662
18%
951
61%
951
49%
1385
January16th to endNight
50%
800
35%
2528
22%
800
65%
800
46%
1243
February1st to 15thNight
40%
701
26%
2220
15%
699
53%
699
40%
1179
February16th to endNight
39%
632
36%
1894
15%
632
60%
632
46%
971
March1st to 15thNight
46%
720
28%
2127
16%
720
57%
720
45%
1121
March16th to endNight
45%
669
28%
2013
15%
669
59%
669
40%
1095
April1st to 15thNight
40%
539
25%
1798
14%
539
57%
539
38%
925
April16th to endNight
44%
540
23%
1800
18%
540
56%
540
32%
1021
May1st to 15thNight
49%
539
20%
1650
17%
539
55%
539
31%
992
May16th to endNight
51%
562
18%
1498
11%
561
58%
561
37%
901
June1st to 15thNight
62%
540
22%
1440
15%
540
66%
540
48%
761
June16th to endNight
69%
540
24%
1440
18%
540
72%
540
47%
783
July1st to 15thNight
70%
510
17%
1360
15%
510
71%
510
32%
872
July16th to endNight
76%
564
20%
1451
19%
531
76%
531
35%
895
August1st to 15thNight
72%
539
15%
1698
16%
536
73%
536
30%
1027
August16th to endNight
78%
573
24%
1910
26%
573
79%
573
37%
1022
September1st to 15thNight
70%
540
26%
1800
27%
540
74%
540
35%
992
September16th to endNight
69%
537
35%
1944
34%
537
76%
537
43%
921
October1st to 15thNight
55%
688
31%
2128
20%
688
64%
688
43%
1110
October16th to endNight
61%
800
38%
2336
22%
800
71%
800
52%
1156
November1st to 15thNight
57%
950
35%
2470
19%
950
64%
950
56%
1281
November16th to endNight
54%
975
39%
2558
21%
975
64%
975
57%
1295
December1st to 15thNight
44%
975
27%
2730
12%
975
56%
975
47%
1448
December16th to endNight
42%
1040
31%
2912
15%
1040
55%
1040
43%
1598

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
44234245%6%8%53%
48988
Night
341332345%7%58%
48543
Cloud CoverDay
44244245%6%8%52%
48986
Night
342342445%8%57%
48543
TransparencyDay
26%6%12%24%21%8%
48666
Night
23%6%12%26%22%8%
48367
SeeingDay
8%10%30%28%16%6%
6175
Night
5%429%38%18%3
16434

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
131321345%8%63%
1520
16th to endDay
1414323246%63%
1707
February1st to 15thDay
14345%13448%57%
1642
16th to endDay
15%25%42335%7%58%
1580
March1st to 15thDay
34245%1345%9%55%
1830
16th to endDay
47%2332436%9%52%
2210
April1st to 15thDay
45%243235%5%9%53%
2150
16th to endDay
8%7%24335%5%5%7%47%
2160
May1st to 15thDay
9%7%35%5%35%6%6%7%40%
2298
16th to endDay
7%5%23435%5%7%8%44%
2616
June1st to 15thDay
5%3134245%8%9%50%
2520
16th to endDay
32133246%8%9%53%
2520
July1st to 15thDay
6%4145%37%5%8%9%43%
2520
16th to endDay
5%3245%46%7%8%10%42%
2616
August1st to 15thDay
6%4245%36%7%8%10%41%
2253
16th to endDay
5%323435%6%7%8%49%
2292
September1st to 15thDay
6%3133346%7%8%51%
2160
16th to endDay
4313323446%62%
2016
October1st to 15thDay
5%313223346%63%
1830
16th to endDay
4313212335%69%
1875
November1st to 15thDay
121231336%8%64%
1718
16th to endDay
212313347%68%
1731
December1st to 15thDay
13235%24437%61%
1560
16th to endDay
25%33224438%58%
1664
January1st to 15thNight
1324323345%65%
2662
16th to endNight
132332343466%
2528
February1st to 15thNight
2425%42335%8%57%
2210
16th to endNight
15%1442335%463%
1894
March1st to 15thNight
141442446%7%60%
2127
16th to endNight
35%23324447%58%
2013
April1st to 15thNight
5%42322345%6%58%
1798
16th to endNight
8%7%23323347%52%
1800
May1st to 15thNight
8%6%2332446%8%48%
1649
16th to endNight
8%6%1242445%9%51%
1497
June1st to 15thNight
431222245%10%60%
1440
16th to endNight
22132245%7%9%58%
1440
July1st to 15thNight
5%3245%36%6%6%10%45%
1440
16th to endNight
5%4143346%8%10%47%
1550
August1st to 15thNight
6%315%5%26%5%7%8%46%
1707
16th to endNight
5%31343447%10%51%
1910
September1st to 15thNight
6%414335%46%9%50%
1800
16th to endNight
5%312313446%63%
1944
October1st to 15thNight
6%5%12313336%62%
2128
16th to endNight
3311322346%67%
2336
November1st to 15thNight
121232235%8%65%
2470
16th to endNight
1213212346%68%
2558
December1st to 15thNight
122442335%8%61%
2730
16th to endNight
242442435%8%58%
2912

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
1313224448%62%
1520
16th to endDay
141442325%7%62%
1707
February1st to 15thDay
1425%5%2445%7%56%
1642
16th to endDay
5%244235%5%6%58%
1580
March1st to 15thDay
35%15%42446%8%54%
1830
16th to endDay
46%2432445%9%50%
2208
April1st to 15thDay
45%25%4245%6%9%50%
2150
16th to endDay
8%6%25%425%5%5%8%44%
2160
May1st to 15thDay
8%7%36%5%36%5%7%7%37%
2298
16th to endDay
7%415%437%5%7%8%43%
2616
June1st to 15thDay
4314435%5%7%9%50%
2520
16th to endDay
3213435%6%8%9%52%
2520
July1st to 15thDay
6%424446%6%8%9%42%
2520
16th to endDay
5%3246%46%7%8%10%40%
2616
August1st to 15thDay
6%325%5%47%7%7%10%39%
2253
16th to endDay
5%323325%6%7%9%48%
2292
September1st to 15thDay
6%3133345%6%8%51%
2160
16th to endDay
4314323446%61%
2016
October1st to 15thDay
5%313323346%62%
1830
16th to endDay
4313212335%67%
1875
November1st to 15thDay
131241336%9%62%
1718
16th to endDay
213313347%67%
1731
December1st to 15thDay
13245%2445%6%60%
1560
16th to endDay
243433345%8%56%
1664
January1st to 15thNight
324323346%65%
2662
16th to endNight
1313324336%65%
2528
February1st to 15thNight
15%25%42346%8%55%
2210
16th to endNight
1424424345%62%
1894
March1st to 15thNight
13135%335%6%7%58%
2127
16th to endNight
3423424348%57%
2013
April1st to 15thNight
442342345%7%57%
1798
16th to endNight
8%8%2432335%8%50%
1800
May1st to 15thNight
8%6%23425%5%6%8%45%
1649
16th to endNight
6%5%2432445%9%49%
1497
June1st to 15thNight
331322335%10%60%
1440
16th to endNight
23122245%8%10%57%
1440
July1st to 15thNight
5%325%6%36%7%6%9%44%
1440
16th to endNight
5%424435%6%8%10%45%
1550
August1st to 15thNight
5%4245%45%6%7%9%44%
1707
16th to endNight
43134345%7%10%50%
1910
September1st to 15thNight
6%3135%35%5%6%9%48%
1800
16th to endNight
4312323446%62%
1944
October1st to 15thNight
5%6%1321235%6%60%
2128
16th to endNight
3312313346%66%
2336
November1st to 15thNight
122341335%7%64%
2470
16th to endNight
121331335%6%67%
2558
December1st to 15thNight
132442335%8%60%
2730
16th to endNight
142443435%7%58%
2912

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
17%5%11%32%25%6%
1521
16th to endDay
20%48%31%25%9%
1707
February1st to 15thDay
25%5%13%32%17%5%
1643
16th to endDay
24%48%28%26%8%
1580
March1st to 15thDay
25%412%24%24%8%
1830
16th to endDay
27%7%11%24%22%5%
2210
April1st to 15thDay
26%6%13%25%19%7%
2150
16th to endDay
36%5%13%22%16%5%
2160
May1st to 15thDay
40%7%11%21%16%2
2298
16th to endDay
32%9%16%21%13%6%
2620
June1st to 15thDay
26%7%15%19%19%11%
2520
16th to endDay
21%7%11%20%25%12%
2520
July1st to 15thDay
33%7%13%20%15%9%
2371
16th to endDay
31%10%17%22%14%3
2452
August1st to 15thDay
34%10%14%19%12%8%
2238
16th to endDay
27%7%13%23%22%5%
2292
September1st to 15thDay
25%7%12%23%19%10%
2160
16th to endDay
21%5%8%23%31%9%
2016
October1st to 15thDay
21%5%11%22%29%9%
1830
16th to endDay
18%39%26%29%13%
1875
November1st to 15thDay
17%49%26%27%13%
1718
16th to endDay
15%37%27%33%12%
1731
December1st to 15thDay
22%6%11%30%23%6%
1560
16th to endDay
24%6%12%27%21%6%
1664
January1st to 15thNight
20%410%31%26%6%
2662
16th to endNight
20%5%9%28%26%10%
2528
February1st to 15thNight
25%6%12%32%19%4
2220
16th to endNight
21%47%31%25%9%
1894
March1st to 15thNight
21%5%10%27%28%6%
2127
16th to endNight
23%7%12%23%27%5%
2013
April1st to 15thNight
23%6%14%25%21%8%
1798
16th to endNight
31%5%13%26%16%5%
1800
May1st to 15thNight
33%7%15%22%16%4
1650
16th to endNight
28%8%18%23%13%7%
1498
June1st to 15thNight
20%6%19%24%14%14%
1440
16th to endNight
20%8%14%22%21%14%
1440
July1st to 15thNight
33%9%15%21%12%7%
1360
16th to endNight
28%11%18%25%13%2
1451
August1st to 15thNight
32%9%17%21%11%7%
1698
16th to endNight
25%7%16%28%16%4
1910
September1st to 15thNight
28%6%13%24%17%9%
1800
16th to endNight
20%6%9%26%29%7%
1944
October1st to 15thNight
23%5%10%21%28%10%
2128
16th to endNight
18%38%27%29%12%
2336
November1st to 15thNight
17%410%25%27%14%
2470
16th to endNight
16%39%28%31%11%
2558
December1st to 15thNight
20%5%14%29%21%7%
2730
16th to endNight
23%5%14%26%24%5%
2912

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%7%26%38%13%3
123
16th to endDay
8%5%29%38%18%
96
February1st to 15thDay
8%8%50%26%5%
90
16th to endDay
116%46%25%7%2
81
March1st to 15thDay
216%45%26%8%
120
16th to endDay
10%26%43%13%31
288
April1st to 15thDay
10%20%43%18%42
269
16th to endDay
19%26%33%17%21
270
May1st to 15thDay
12%14%31%29%8%3
420
16th to endDay
13%12%26%27%16%4
517
June1st to 15thDay
6%10%26%30%20%6%
495
16th to endDay
46%25%29%25%8%
495
July1st to 15thDay
9%220%27%29%10%
475
16th to endDay
7%214%30%30%14%
475
August1st to 15thDay
12%423%35%17%7%
315
16th to endDay
7%324%42%13%8%
332
September1st to 15thDay
7%440%24%15%8%
315
16th to endDay
12%9%29%21%16%9%
171
October1st to 15thDay
7%10%25%31%17%7%
135
16th to endDay
49%32%27%19%6%
144
November1st to 15thDay
28%34%28%17%7%
135
16th to endDay
6%9%42%30%9%
135
December1st to 15thDay
5%12%45%25%9%1
135
16th to endDay
47%41%33%12%
144
January1st to 15thNight
25%36%36%13%5%
956
16th to endNight
35%37%39%12%2
800
February1st to 15thNight
3447%36%7%
704
16th to endNight
27%45%35%7%
632
March1st to 15thNight
35%41%35%13%2
720
16th to endNight
5%8%37%38%9%
669
April1st to 15thNight
8%11%37%33%8%
539
16th to endNight
13%9%29%36%9%1
540
May1st to 15thNight
12%7%26%37%15%
540
16th to endNight
9%429%37%17%2
563
June1st to 15thNight
4324%43%20%2
540
16th to endNight
3217%47%26%2
540
July1st to 15thNight
7%110%39%37%4
510
16th to endNight
6%6%35%44%6%
564
August1st to 15thNight
7%18%37%39%5%
539
16th to endNight
6%7%40%38%6%
573
September1st to 15thNight
7%112%40%29%7%
540
16th to endNight
7%216%41%25%6%
537
October1st to 15thNight
10%327%36%16%5%
688
16th to endNight
4425%35%24%5%
800
November1st to 15thNight
2332%41%15%4
950
16th to endNight
25%33%41%13%3
975
December1st to 15thNight
26%41%37%9%1
975
16th to endNight
36%41%35%10%2
1040
Page generated at 2018-01-12 20:01:25. Version ac04

Copyright 2018 A. Danko


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