Starry Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starry Hill Observatory clear sky chart from 2005-11-05 to 2017-09-23.

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
43%
14575
10%
46610
10%
14547
44%
14547
14%
35197

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
32%
720
9%
2506
10%
716
34%
716
9%
2030
January16th to endNight
38%
768
11%
2637
12%
768
38%
768
12%
2049
February1st to 15thNight
35%
700
6%
2288
6%
700
36%
700
9%
1885
February16th to endNight
34%
632
9%
2008
9%
632
36%
632
10%
1623
March1st to 15thNight
26%
720
5%
2064
4%
720
27%
720
9%
1746
March16th to endNight
25%
768
4%
2067
2%
768
25%
768
7%
1817
April1st to 15thNight
31%
719
6%
1799
3%
719
32%
719
10%
1556
April16th to endNight
39%
582
7%
1662
6%
582
39%
582
13%
1331
May1st to 15thNight
46%
359
10%
1439
15%
359
47%
359
13%
1025
May16th to endNight
45%
374
6%
1496
9%
374
46%
374
10%
1147
June1st to 15thNight
46%
360
4%
1407
6%
360
46%
360
11%
1063
June16th to endNight
48%
360
8%
1260
11%
360
49%
360
16%
898
July1st to 15thNight
72%
340
13%
1251
19%
340
73%
340
33%
662
July16th to endNight
74%
376
20%
1416
33%
354
76%
354
36%
678
August1st to 15thNight
77%
466
19%
1540
23%
464
77%
464
38%
806
August16th to endNight
72%
651
22%
1797
18%
651
73%
651
40%
1045
September1st to 15thNight
73%
720
22%
1800
15%
720
73%
720
44%
1077
September16th to endNight
55%
688
19%
1887
16%
688
56%
688
26%
1286
October1st to 15thNight
47%
660
12%
1980
13%
660
49%
660
19%
1439
October16th to endNight
41%
704
9%
2167
9%
704
42%
704
14%
1652
November1st to 15thNight
30%
700
6%
2411
6%
700
31%
700
8%
2030
November16th to endNight
31%
720
6%
2520
6%
720
32%
720
9%
2056
December1st to 15thNight
37%
720
7%
2520
7%
720
38%
720
10%
2004
December16th to endNight
25%
768
6%
2688
5%
768
26%
768
6%
2292

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
21%10%47%5%34445%28%
48319
Night
20%10%36%5%34445%30%
46773
Cloud CoverDay
22%11%36%5%24445%28%
48319
Night
22%10%36%5%24445%29%
46777
TransparencyDay
58%6%10%14%7%1
47985
Night
57%6%11%15%7%1
46611
SeeingDay
28%10%21%25%11%2
5892
Night
28%7%12%25%21%3
14581

By Month

Percentage Cloud Cover NW (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
30%11%48%6%3433320%
1432
16th to endDay
27%10%45%6%2435%425%
1587
February1st to 15thDay
22%15%5%8%6%35%446%16%
1576
16th to endDay
27%17%47%6%3443318%
1466
March1st to 15thDay
25%17%5%9%8%45%43312%
1893
16th to endDay
27%17%7%10%7%35%4339%
2157
April1st to 15thDay
27%14%5%7%7%345%5%5%12%
2149
16th to endDay
24%14%48%7%35%435%18%
2298
May1st to 15thDay
23%10%35%5%3445%5%27%
2511
16th to endDay
26%9%5%8%6%35%45%5%18%
2615
June1st to 15thDay
28%9%37%6%3445%5%20%
2550
16th to endDay
21%9%47%5%4445%5%26%
2700
July1st to 15thDay
11%5%24423435%51%
2631
16th to endDay
12%32432335%8%50%
2657
August1st to 15thDay
9%5%24423448%51%
2411
16th to endDay
11%415%42445%7%47%
2405
September1st to 15thDay
10%5%24423347%52%
2160
16th to endDay
19%8%26%434336%35%
1906
October1st to 15thDay
21%9%47%5%24347%29%
1650
16th to endDay
28%9%37%5%33446%23%
1705
November1st to 15thDay
29%11%5%7%6%45%5%5%413%
1444
16th to endDay
26%13%5%9%5%3434418%
1440
December1st to 15thDay
19%13%5%8%7%36%43421%
1440
16th to endDay
27%17%46%6%3443417%
1536
January1st to 15thNight
29%11%46%5%34335%20%
2506
16th to endNight
26%11%35%5%23446%23%
2637
February1st to 15thNight
23%11%48%8%34446%19%
2276
16th to endNight
23%13%37%6%36%44422%
2008
March1st to 15thNight
23%13%5%7%7%36%445%17%
2064
16th to endNight
25%15%49%7%35%45%413%
2063
April1st to 15thNight
20%14%5%8%8%45%445%19%
1799
16th to endNight
21%11%37%6%35%45%7%23%
1662
May1st to 15thNight
18%8%36%5%3446%5%32%
1439
16th to endNight
20%8%45%6%45%5%6%5%26%
1496
June1st to 15thNight
20%7%46%7%4445%7%27%
1407
16th to endNight
15%10%26%6%24348%35%
1260
July1st to 15thNight
6%323423346%59%
1326
16th to endNight
5%313323245%63%
1512
August1st to 15thNight
6%313223336%63%
1548
16th to endNight
6%414313346%59%
1797
September1st to 15thNight
7%413323335%60%
1800
16th to endNight
17%5%16%3245%46%41%
1887
October1st to 15thNight
19%7%35%6%24345%35%
1980
16th to endNight
22%8%47%5%35%45%7%25%
2167
November1st to 15thNight
32%9%36%6%3444418%
2411
16th to endNight
24%13%46%6%35%445%20%
2520
December1st to 15thNight
21%11%47%6%35%445%24%
2520
16th to endNight
28%14%48%5%3433318%
2688

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
31%11%37%5%3433420%
1432
16th to endDay
28%11%36%5%2344425%
1587
February1st to 15thDay
25%14%5%8%5%35%436%16%
1576
16th to endDay
28%17%47%5%3333319%
1466
March1st to 15thDay
27%17%5%9%6%4443312%
1893
16th to endDay
28%19%6%9%6%344439%
2157
April1st to 15thDay
26%16%47%6%35%45%5%13%
2149
16th to endDay
25%15%5%7%6%34445%18%
2298
May1st to 15thDay
23%10%46%5%24445%27%
2511
16th to endDay
27%10%47%6%35%5%5%6%18%
2615
June1st to 15thDay
29%9%5%6%5%35%345%20%
2550
16th to endDay
22%10%46%6%345%5%5%25%
2700
July1st to 15thDay
11%6%14423436%51%
2631
16th to endDay
12%5%2331335%8%50%
2657
August1st to 15thDay
9%6%2332335%8%51%
2411
16th to endDay
10%6%25%5%24347%48%
2405
September1st to 15thDay
10%5%23313447%52%
2160
16th to endDay
21%6%35%434345%36%
1906
October1st to 15thDay
21%10%37%5%24346%29%
1650
16th to endDay
30%9%37%5%23435%23%
1705
November1st to 15thDay
31%11%5%7%5%35%5%6%413%
1444
16th to endDay
27%14%5%8%5%2443418%
1440
December1st to 15thDay
21%13%49%5%35%435%21%
1440
16th to endDay
29%17%5%5%6%2434317%
1536
January1st to 15thNight
31%11%45%5%24445%21%
2506
16th to endNight
28%11%35%424346%23%
2637
February1st to 15thNight
25%12%47%6%35%5%36%18%
2276
16th to endNight
24%14%36%6%3443422%
2008
March1st to 15thNight
25%14%46%7%36%44417%
2064
16th to endNight
27%16%5%8%6%34445%12%
2067
April1st to 15thNight
21%16%5%7%6%36%5%46%18%
1799
16th to endNight
22%12%47%5%2445%6%23%
1662
May1st to 15thNight
19%8%36%5%3445%6%31%
1439
16th to endNight
23%8%36%5%35%46%6%25%
1496
June1st to 15thNight
20%10%6%6%43445%7%25%
1407
16th to endNight
17%9%26%6%2445%6%33%
1260
July1st to 15thNight
6%32431335%6%57%
1326
16th to endNight
5%42331225%6%60%
1512
August1st to 15thNight
7%413312226%62%
1548
16th to endNight
8%324312445%58%
1797
September1st to 15thNight
9%5%13322245%60%
1800
16th to endNight
17%6%25%42445%7%39%
1887
October1st to 15thNight
20%8%35%5%34345%35%
1980
16th to endNight
24%8%26%5%25%35%7%26%
2167
November1st to 15thNight
34%9%45%5%34445%18%
2411
16th to endNight
26%13%46%6%345%35%19%
2520
December1st to 15thNight
22%12%47%6%35%445%23%
2520
16th to endNight
29%15%47%6%3334417%
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
69%46%9%7%1
1432
16th to endDay
62%49%10%9%3
1587
February1st to 15thDay
69%7%7%9%4
1576
16th to endDay
70%6%7%11%4
1466
March1st to 15thDay
78%46%8%2
1893
16th to endDay
80%6%6%5%
2157
April1st to 15thDay
73%5%11%8%1
2149
16th to endDay
69%6%11%9%2
2298
May1st to 15thDay
58%6%13%15%5%
2511
16th to endDay
66%8%12%11%1
2619
June1st to 15thDay
66%6%13%9%4
2550
16th to endDay
58%7%13%14%5%
2700
July1st to 15thDay
36%6%11%26%17%2
2477
16th to endDay
31%7%12%27%17%3
2490
August1st to 15thDay
32%7%14%27%13%3
2394
16th to endDay
37%414%28%11%2
2405
September1st to 15thDay
32%6%13%23%19%5%
2160
16th to endDay
50%5%14%15%10%3
1906
October1st to 15thDay
56%5%11%16%7%1
1650
16th to endDay
64%5%9%13%7%
1705
November1st to 15thDay
72%7%8%7%21
1444
16th to endDay
70%5%5%8%8%1
1440
December1st to 15thDay
67%6%9%12%4
1440
16th to endDay
72%5%7%8%5%
1536
January1st to 15thNight
68%47%10%7%1
2506
16th to endNight
62%6%7%10%9%3
2637
February1st to 15thNight
68%6%9%8%5%1
2288
16th to endNight
65%5%9%12%5%
2008
March1st to 15thNight
70%411%10%2
2064
16th to endNight
73%7%9%7%1
2067
April1st to 15thNight
68%8%9%10%1
1799
16th to endNight
62%6%15%11%3
1662
May1st to 15thNight
53%8%12%17%7%1
1440
16th to endNight
58%10%15%12%2
1496
June1st to 15thNight
57%8%15%14%4
1407
16th to endNight
51%7%16%17%5%1
1260
July1st to 15thNight
28%6%14%29%16%4
1251
16th to endNight
24%5%13%31%18%5%
1416
August1st to 15thNight
25%6%15%30%16%4
1540
16th to endNight
28%6%18%31%12%2
1797
September1st to 15thNight
27%6%13%26%20%5%
1800
16th to endNight
44%6%15%17%12%4
1887
October1st to 15thNight
52%6%10%19%9%2
1980
16th to endNight
57%7%12%14%8%
2167
November1st to 15thNight
68%8%9%8%21
2411
16th to endNight
66%7%7%8%9%1
2520
December1st to 15thNight
65%6%10%12%5%
2520
16th to endNight
71%7%7%8%3
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
18%10%13%26%21%10%
60
16th to endDay
39%16%13%18%10%1
115
February1st to 15thDay
42%11%18%16%8%1
236
16th to endDay
41%15%21%15%5%1
219
March1st to 15thDay
48%21%19%8%2
270
16th to endDay
45%14%21%12%5%
288
April1st to 15thDay
33%18%23%15%7%2
269
16th to endDay
36%13%26%16%42
270
May1st to 15thDay
32%14%23%21%6%1
288
16th to endDay
33%8%20%24%10%3
330
June1st to 15thDay
29%11%22%23%9%3
345
16th to endDay
21%8%28%29%10%1
495
July1st to 15thDay
15%320%39%17%2
411
16th to endDay
13%421%38%18%3
327
August1st to 15thDay
14%316%41%16%7%
315
16th to endDay
10%7%20%37%15%8%
332
September1st to 15thDay
18%5%21%34%16%4
315
16th to endDay
22%11%23%27%14%
284
October1st to 15thDay
32%12%16%24%11%2
255
16th to endDay
37%8%19%20%10%3
217
November1st to 15thDay
38%22%11%23%2
67
16th to endDay
28%18%16%11%11%13%
60
December1st to 15thDay
48%21%20%8%1
60
16th to endDay
43%6%17%15%15%1
64
January1st to 15thNight
40%9%10%18%17%2
720
16th to endNight
33%8%11%25%15%4
768
February1st to 15thNight
33%9%11%30%13%1
704
16th to endNight
34%10%14%24%15%1
632
March1st to 15thNight
36%14%15%19%11%1
720
16th to endNight
38%11%16%22%9%1
768
April1st to 15thNight
32%10%15%22%16%2
719
16th to endNight
27%9%14%29%17%2
582
May1st to 15thNight
23%7%13%27%25%2
360
16th to endNight
26%6%11%24%28%2
375
June1st to 15thNight
21%9%14%24%28%2
360
16th to endNight
21%415%28%26%2
360
July1st to 15thNight
9%18%31%43%5%
340
16th to endNight
7%29%27%47%5%
376
August1st to 15thNight
9%2423%45%14%
466
16th to endNight
11%36%27%43%7%
651
September1st to 15thNight
11%27%26%41%10%
720
16th to endNight
21%410%28%29%4
688
October1st to 15thNight
25%6%11%28%23%4
660
16th to endNight
29%8%14%26%17%3
704
November1st to 15thNight
37%10%15%27%8%1
700
16th to endNight
36%9%15%18%15%5%
720
December1st to 15thNight
32%7%15%28%14%1
720
16th to endNight
43%9%15%20%10%
768
Page generated at 2017-09-24 06:15:53. Version ac04

Copyright 2017 A. Danko


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