Skyline Rd
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Skyline Rd 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
48%
14660
16%
46927
13%
14635
53%
14635
24%
29876

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
30%
716
7%
2506
4%
716
33%
716
8%
1996
January16th to endNight
41%
768
9%
2636
8%
768
44%
768
13%
1981
February1st to 15thNight
43%
696
9%
2288
7%
696
46%
696
15%
1685
February16th to endNight
38%
632
13%
1966
11%
632
43%
632
18%
1346
March1st to 15thNight
38%
720
9%
2091
6%
720
42%
720
17%
1526
March16th to endNight
36%
768
11%
2046
5%
768
40%
768
19%
1489
April1st to 15thNight
39%
719
12%
1799
5%
719
42%
719
23%
1278
April16th to endNight
44%
636
15%
1716
8%
636
49%
636
28%
1121
May1st to 15thNight
50%
359
20%
1439
20%
359
59%
359
29%
733
May16th to endNight
58%
375
11%
1496
13%
374
63%
374
25%
826
June1st to 15thNight
49%
360
12%
1440
14%
360
57%
360
24%
804
June16th to endNight
53%
360
18%
1440
23%
360
62%
360
35%
678
July1st to 15thNight
73%
340
20%
1360
26%
340
83%
340
60%
481
July16th to endNight
71%
376
31%
1416
37%
354
84%
354
66%
472
August1st to 15thNight
79%
462
32%
1536
29%
460
86%
460
62%
610
August16th to endNight
72%
693
37%
1839
23%
693
76%
693
66%
858
September1st to 15thNight
75%
720
34%
1800
19%
720
78%
720
71%
849
September16th to endNight
63%
688
30%
1875
23%
688
67%
688
43%
1053
October1st to 15thNight
54%
660
19%
1980
16%
660
60%
660
31%
1211
October16th to endNight
50%
704
16%
2177
15%
704
55%
704
23%
1445
November1st to 15thNight
43%
700
11%
2353
10%
700
46%
700
15%
1713
November16th to endNight
40%
720
9%
2520
6%
720
45%
720
14%
1799
December1st to 15thNight
38%
720
9%
2520
8%
720
41%
720
13%
1898
December16th to endNight
30%
768
9%
2688
6%
768
36%
768
11%
2024

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
5%6%36%6%35%5%6%7%43%
48004
Night
5%6%36%5%35%5%6%8%42%
47095
Cloud CoverDay
5%5%35%5%35%5%5%7%45%
48004
Night
6%6%36%5%35%5%6%7%44%
47099
TransparencyDay
36%9%14%21%14%4
47675
Night
36%9%16%21%11%4
46928
SeeingDay
10%18%30%25%12%2
5582
Night
9%9%24%34%19%2
14673

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
7%11%6%9%9%47%7%6%8%20%
1432
16th to endDay
8%11%5%8%7%46%6%8%9%22%
1587
February1st to 15thDay
8%10%5%8%7%47%7%8%9%21%
1576
16th to endDay
6%9%37%7%5%7%7%6%9%28%
1507
March1st to 15thDay
7%10%5%8%9%5%8%7%8%8%21%
1867
16th to endDay
6%10%5%9%9%6%8%7%6%7%21%
2178
April1st to 15thDay
8%7%49%9%46%5%6%8%28%
2149
16th to endDay
5%6%36%6%46%6%6%10%36%
2244
May1st to 15thDay
45%36%6%46%5%5%7%44%
2511
16th to endDay
7%5%36%6%35%5%6%7%41%
2615
June1st to 15thDay
6%426%5%35%5%6%7%45%
2520
16th to endDay
431442445%7%54%
2520
July1st to 15thDay
112222346%71%
2520
16th to endDay
211121222377%
2657
August1st to 15thDay
111212445%73%
2415
16th to endDay
12332334470%
2361
September1st to 15thDay
211312336%72%
2160
16th to endDay
4326%5%35%45%7%50%
1919
October1st to 15thDay
8%6%37%6%345%6%7%40%
1650
16th to endDay
8%7%36%7%35%47%7%37%
1694
November1st to 15thDay
6%10%48%8%5%7%6%8%8%25%
1506
16th to endDay
7%10%6%7%7%48%7%8%8%23%
1440
December1st to 15thDay
8%13%6%10%8%36%5%5%6%25%
1440
16th to endDay
8%11%5%11%6%36%7%7%8%21%
1536
January1st to 15thNight
6%10%6%10%8%48%6%7%7%22%
2506
16th to endNight
7%7%49%8%48%7%8%9%25%
2636
February1st to 15thNight
8%9%37%7%47%6%6%9%29%
2276
16th to endNight
7%7%36%6%45%5%6%9%36%
1966
March1st to 15thNight
7%8%47%8%35%7%8%9%28%
2091
16th to endNight
5%5%48%7%46%7%7%10%29%
2042
April1st to 15thNight
7%6%46%6%36%7%8%9%33%
1799
16th to endNight
5%5%25%5%36%6%6%10%41%
1716
May1st to 15thNight
44145%35%5%6%8%50%
1439
16th to endNight
3424436%6%8%10%44%
1496
June1st to 15thNight
7%226%435%6%5%7%48%
1440
16th to endNight
3223424447%60%
1440
July1st to 15thNight
111112445%75%
1440
16th to endNight
11112225%80%
1512
August1st to 15thNight
12222235%76%
1544
16th to endNight
112212335%75%
1839
September1st to 15thNight
111112235%78%
1800
16th to endNight
322442445%9%56%
1875
October1st to 15thNight
7%436%5%33446%49%
1980
16th to endNight
7%5%26%6%35%6%6%8%38%
2177
November1st to 15thNight
7%7%47%7%47%7%7%7%29%
2353
16th to endNight
5%8%47%6%47%7%6%9%30%
2520
December1st to 15thNight
7%12%47%6%46%6%7%6%28%
2520
16th to endNight
8%11%5%9%6%46%6%7%8%25%
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
9%12%5%10%8%5%8%6%5%8%20%
1432
16th to endDay
9%11%5%9%8%46%6%6%8%23%
1587
February1st to 15thDay
9%10%47%7%47%7%8%9%23%
1576
16th to endDay
7%7%36%7%47%6%7%8%30%
1507
March1st to 15thDay
7%9%48%9%5%7%7%7%9%23%
1867
16th to endDay
7%9%49%9%5%9%7%6%8%23%
2178
April1st to 15thDay
7%6%48%8%5%6%5%6%9%30%
2149
16th to endDay
5%6%26%5%46%6%6%10%40%
2244
May1st to 15thDay
4426%5%35%5%6%7%47%
2511
16th to endDay
8%436%5%36%5%6%7%43%
2615
June1st to 15thDay
6%325%5%35%46%8%47%
2520
16th to endDay
42144245%48%57%
2520
July1st to 15thDay
112212346%73%
2520
16th to endDay
21111123378%
2657
August1st to 15thDay
111122346%74%
2415
16th to endDay
113222345%71%
2361
September1st to 15thDay
212212245%74%
2160
16th to endDay
44145%35%45%7%52%
1919
October1st to 15thDay
9%5%37%6%345%6%6%42%
1650
16th to endDay
9%7%25%6%45%5%6%7%38%
1694
November1st to 15thDay
7%8%47%8%47%6%8%9%27%
1506
16th to endDay
7%10%6%7%6%5%6%7%8%9%23%
1440
December1st to 15thDay
9%13%6%9%7%36%6%46%26%
1440
16th to endDay
9%11%6%9%6%45%8%6%8%23%
1536
January1st to 15thNight
8%12%5%10%8%46%5%6%8%22%
2506
16th to endNight
8%8%5%9%7%47%7%6%8%25%
2636
February1st to 15thNight
8%8%47%6%46%6%6%9%30%
2276
16th to endNight
7%6%46%6%36%5%6%9%38%
1966
March1st to 15thNight
7%8%46%8%46%6%7%9%30%
2091
16th to endNight
5%6%37%8%36%6%8%9%33%
2046
April1st to 15thNight
7%6%36%6%36%5%7%10%35%
1799
16th to endNight
5%5%15%435%5%7%10%45%
1716
May1st to 15thNight
43145%245%6%6%53%
1439
16th to endNight
3424437%5%8%11%45%
1496
June1st to 15thNight
6%5%245%25%5%5%7%49%
1440
16th to endNight
3313314445%63%
1440
July1st to 15thNight
1111225%5%76%
1440
16th to endNight
1111122481%
1512
August1st to 15thNight
1121224477%
1544
16th to endNight
112212225%77%
1839
September1st to 15thNight
11111134478%
1800
16th to endNight
32145%2345%8%58%
1875
October1st to 15thNight
7%426%5%24446%50%
1980
16th to endNight
7%5%25%6%46%6%6%9%40%
2177
November1st to 15thNight
7%7%38%7%47%7%7%8%30%
2353
16th to endNight
7%8%47%6%46%7%7%7%32%
2520
December1st to 15thNight
8%11%5%8%6%36%6%6%6%29%
2520
16th to endNight
8%11%6%8%7%36%6%6%8%25%
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
60%12%13%9%3
1432
16th to endDay
55%11%17%10%4
1587
February1st to 15thDay
52%15%19%10%1
1576
16th to endDay
47%14%18%13%5%
1507
March1st to 15thDay
54%11%14%13%5%
1867
16th to endDay
55%13%15%13%2
2178
April1st to 15thDay
48%9%18%17%5%
2149
16th to endDay
38%11%21%17%9%1
2244
May1st to 15thDay
33%8%14%27%15%
2511
16th to endDay
38%8%18%26%8%
2619
June1st to 15thDay
34%7%15%27%11%2
2520
16th to endDay
25%6%16%31%15%4
2520
July1st to 15thDay
12%410%26%32%14%
2371
16th to endDay
12%35%21%34%22%
2490
August1st to 15thDay
11%310%28%33%12%
2398
16th to endDay
14%310%32%30%7%
2361
September1st to 15thDay
12%310%30%31%11%
2160
16th to endDay
30%6%15%25%16%5%
1919
October1st to 15thDay
39%8%14%20%15%1
1650
16th to endDay
41%11%17%20%9%
1694
November1st to 15thDay
50%14%15%15%4
1506
16th to endDay
51%15%16%12%3
1440
December1st to 15thDay
57%10%12%14%5%
1440
16th to endDay
54%14%16%11%3
1536
January1st to 15thNight
59%12%14%10%3
2506
16th to endNight
51%12%16%13%4
2636
February1st to 15thNight
47%13%20%16%1
2288
16th to endNight
41%11%19%20%5%
1966
March1st to 15thNight
46%11%17%17%5%1
2091
16th to endNight
43%12%21%18%4
2046
April1st to 15thNight
40%11%19%21%7%
1799
16th to endNight
33%11%21%23%9%1
1716
May1st to 15thNight
27%6%17%32%13%2
1440
16th to endNight
31%9%25%25%7%1
1496
June1st to 15thNight
33%8%15%28%12%2
1440
16th to endNight
23%5%12%36%16%5%
1440
July1st to 15thNight
10%313%23%30%18%
1360
16th to endNight
8%28%18%32%29%
1416
August1st to 15thNight
10%39%27%33%15%
1536
16th to endNight
11%310%29%34%10%
1839
September1st to 15thNight
9%310%31%29%15%
1800
16th to endNight
23%7%12%29%19%7%
1875
October1st to 15thNight
33%7%13%25%17%2
1980
16th to endNight
38%11%16%18%14%
2177
November1st to 15thNight
47%13%15%19%4
2353
16th to endNight
46%12%17%18%4
2520
December1st to 15thNight
51%13%15%15%3
2520
16th to endNight
52%13%17%12%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
20%326%23%21%5%
60
16th to endDay
21%12%26%25%12%1
115
February1st to 15thDay
17%18%30%25%7%
236
16th to endDay
15%25%31%19%7%
226
March1st to 15thDay
17%26%37%14%4
270
16th to endDay
21%28%30%13%4
288
April1st to 15thDay
14%26%28%18%10%1
269
16th to endDay
16%27%30%14%7%3
270
May1st to 15thDay
13%25%27%23%10%
288
16th to endDay
10%17%27%26%14%3
330
June1st to 15thDay
6%24%32%21%12%3
315
16th to endDay
8%18%33%26%10%2
315
July1st to 15thDay
311%33%31%19%1
305
16th to endDay
111%36%29%15%4
327
August1st to 15thDay
19%31%31%16%9%
315
16th to endDay
311%22%33%22%6%
332
September1st to 15thDay
5%13%24%29%22%4
315
16th to endDay
7%13%33%32%13%
284
October1st to 15thDay
12%20%26%27%12%
255
16th to endDay
19%11%33%21%11%1
206
November1st to 15thDay
11%14%28%36%7%1
77
16th to endDay
16%16%25%28%11%1
60
December1st to 15thDay
21%20%40%18%
60
16th to endDay
9%15%23%37%14%
64
January1st to 15thNight
14%13%24%29%16%1
720
16th to endNight
12%9%21%32%20%2
768
February1st to 15thNight
12%12%22%32%19%1
704
16th to endNight
12%13%27%29%15%
632
March1st to 15thNight
11%12%29%30%15%
720
16th to endNight
9%16%29%29%14%1
768
April1st to 15thNight
10%13%29%26%16%1
719
16th to endNight
8%10%32%27%18%3
636
May1st to 15thNight
5%9%30%32%19%2
360
16th to endNight
5%6%23%42%19%2
375
June1st to 15thNight
7%7%29%40%14%1
360
16th to endNight
5%6%30%41%15%1
360
July1st to 15thNight
1120%51%22%1
340
16th to endNight
123%52%18%2
376
August1st to 15thNight
1114%46%30%6%
462
16th to endNight
2319%37%30%7%
693
September1st to 15thNight
1316%35%33%8%
720
16th to endNight
45%20%35%29%4
688
October1st to 15thNight
10%324%35%21%4
660
16th to endNight
11%7%23%32%21%3
704
November1st to 15thNight
10%13%23%37%13%1
700
16th to endNight
12%13%22%30%18%2
720
December1st to 15thNight
15%9%26%32%15%1
720
16th to endNight
14%14%29%28%13%
768
Page generated at 2017-09-24 06:15:51. Version ac04

Copyright 2017 A. Danko


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