Spruce Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Spruce Ridge Observatory clear sky chart from 2005-11-05 to 2017-10-31.

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
45%
15242
10%
47342
8%
15212
48%
15212
19%
33291

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
26%
838
4%
2626
3%
836
27%
836
7%
2236
January16th to endNight
31%
768
8%
2688
5%
768
36%
768
11%
2114
February1st to 15thNight
33%
702
6%
2439
4%
698
37%
698
11%
1911
February16th to endNight
43%
632
8%
1908
5%
632
46%
632
17%
1399
March1st to 15thNight
39%
720
7%
2154
3%
720
43%
720
16%
1616
March16th to endNight
41%
768
8%
2040
3%
768
44%
768
18%
1551
April1st to 15thNight
47%
680
8%
1760
4%
680
49%
680
23%
1273
April16th to endNight
45%
540
11%
1620
9%
540
47%
540
22%
1099
May1st to 15thNight
51%
401
12%
1482
14%
401
53%
401
23%
894
May16th to endNight
52%
374
8%
1328
10%
374
53%
374
17%
912
June1st to 15thNight
56%
360
3%
1260
1%
360
56%
360
21%
830
June16th to endNight
58%
360
6%
1260
1%
360
59%
360
26%
752
July1st to 15thNight
75%
340
9%
1190
6%
340
77%
340
45%
556
July16th to endNight
76%
376
17%
1394
25%
354
81%
354
46%
600
August1st to 15thNight
78%
380
22%
1452
29%
378
81%
378
44%
648
August16th to endNight
71%
591
28%
1737
25%
591
73%
591
51%
864
September1st to 15thNight
69%
720
21%
1836
13%
720
70%
720
48%
1040
September16th to endNight
64%
716
20%
1980
16%
716
66%
716
36%
1202
October1st to 15thNight
53%
720
14%
2112
11%
720
56%
720
27%
1391
October16th to endNight
49%
768
13%
2496
10%
768
54%
768
21%
1672
November1st to 15thNight
37%
728
9%
2303
6%
728
42%
728
15%
1708
November16th to endNight
29%
900
4%
2697
2%
900
31%
900
10%
2210
December1st to 15thNight
26%
900
4%
2700
2%
900
29%
900
8%
2327
December16th to endNight
26%
960
5%
2880
2%
960
29%
960
8%
2486

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%5%36%6%46%6%7%9%37%
48440
Night
37%36%6%35%5%7%9%41%
47500
Cloud CoverDay
5%6%37%6%46%6%7%8%36%
48441
Night
48%47%6%35%5%6%8%38%
47503
TransparencyDay
44%13%17%16%7%1
48101
Night
42%13%17%17%7%1
47342
SeeingDay
10%18%30%26%12%2
6057
Night
7%8%29%36%16%1
15249

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
27%411%9%5%8%7%8%10%24%
1322
16th to endDay
17%5%10%8%47%8%9%12%24%
1536
February1st to 15thDay
37%28%9%5%47%10%12%27%
1425
16th to endDay
16%49%8%46%8%11%11%27%
1565
March1st to 15thDay
16%47%8%5%8%8%9%10%29%
1806
16th to endDay
5%9%5%8%7%5%7%8%9%9%22%
2181
April1st to 15thDay
6%8%5%8%7%47%7%7%9%27%
2188
16th to endDay
6%8%47%7%45%6%7%8%32%
2340
May1st to 15thDay
7%7%25%6%46%6%6%8%39%
2469
16th to endDay
14%8%36%7%36%6%6%8%28%
2783
June1st to 15thDay
11%6%37%7%47%6%7%8%28%
2700
16th to endDay
7%415%7%47%7%8%8%36%
2700
July1st to 15thDay
4213436%47%8%53%
2700
16th to endDay
1112335%5%6%7%59%
2678
August1st to 15thDay
3134346%8%10%53%
2499
16th to endDay
41133245%7%8%57%
2465
September1st to 15thDay
5%3245%335%5%8%52%
2124
16th to endDay
7%335%35%6%7%9%47%
1980
October1st to 15thDay
6%435%6%45%5%7%9%40%
1847
16th to endDay
46%246%45%7%8%10%38%
1726
November1st to 15thDay
46%25%7%49%7%9%11%32%
1542
16th to endDay
19%6%8%7%45%6%7%10%33%
1260
December1st to 15thDay
39%6%11%8%6%7%7%8%8%21%
1260
16th to endDay
29%6%13%9%6%7%6%9%7%20%
1344
January1st to 15thNight
111%7%12%9%5%7%6%8%8%21%
2626
16th to endNight
111%6%9%7%5%6%6%7%10%28%
2688
February1st to 15thNight
211%48%8%35%6%7%11%30%
2428
16th to endNight
17%37%6%36%6%8%9%37%
1908
March1st to 15thNight
25%25%5%46%6%8%11%40%
2154
16th to endNight
5%7%36%5%26%6%8%10%37%
2037
April1st to 15thNight
5%5%24435%6%8%10%42%
1760
16th to endNight
46%35%6%35%5%6%8%44%
1620
May1st to 15thNight
3424436%5%7%8%48%
1481
16th to endNight
10%7%36%4445%6%7%39%
1328
June1st to 15thNight
7%325%5%45%5%5%11%44%
1260
16th to endNight
5%214445%6%8%8%48%
1260
July1st to 15thNight
111121445%7%67%
1260
16th to endNight
12223447%68%
1489
August1st to 15thNight
32321235%9%65%
1460
16th to endNight
1113213448%68%
1737
September1st to 15thNight
4314313346%64%
1836
16th to endNight
5%3144235%5%8%56%
1980
October1st to 15thNight
44145%25%6%7%8%48%
2112
16th to endNight
35%15%5%35%6%8%9%45%
2496
November1st to 15thNight
25%24445%6%9%11%41%
2303
16th to endNight
211%8%9%7%36%6%7%9%28%
2697
December1st to 15thNight
211%7%12%12%5%6%6%7%6%21%
2700
16th to endNight
112%7%13%9%5%7%6%6%6%22%
2880

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
310%6%13%9%5%8%7%8%8%18%
1322
16th to endDay
110%5%9%9%6%9%8%7%9%21%
1536
February1st to 15thDay
48%49%9%37%7%8%10%26%
1425
16th to endDay
16%410%9%47%9%10%11%24%
1565
March1st to 15thDay
28%5%9%7%5%6%8%8%9%28%
1806
16th to endDay
5%10%5%8%8%5%7%7%7%10%22%
2182
April1st to 15thDay
6%10%48%7%47%6%7%8%28%
2188
16th to endDay
6%8%48%7%45%5%7%8%32%
2340
May1st to 15thDay
7%6%25%5%36%5%7%8%39%
2469
16th to endDay
13%8%27%6%46%6%7%7%29%
2783
June1st to 15thDay
11%7%37%6%5%7%6%7%7%30%
2700
16th to endDay
8%325%6%46%6%7%8%38%
2700
July1st to 15thDay
43134345%7%8%54%
2700
16th to endDay
11134235%6%8%60%
2678
August1st to 15thDay
2213335%5%7%10%53%
2499
16th to endDay
423425%5%6%9%57%
2465
September1st to 15thDay
4425%5%2346%7%52%
2124
16th to endDay
6%325%4336%7%10%46%
1980
October1st to 15thDay
6%5%26%7%46%6%6%9%38%
1847
16th to endDay
5%6%36%6%45%6%7%10%37%
1726
November1st to 15thDay
5%7%48%7%48%6%7%9%30%
1542
16th to endDay
210%6%9%9%46%7%8%8%28%
1260
December1st to 15thDay
411%7%13%9%5%8%6%5%8%18%
1260
16th to endDay
212%7%15%11%5%7%6%6%7%16%
1344
January1st to 15thNight
315%8%12%9%47%6%7%5%17%
2626
16th to endNight
213%8%11%7%5%7%7%5%7%23%
2688
February1st to 15thNight
313%5%9%8%5%7%5%7%8%26%
2428
16th to endNight
29%49%6%37%6%8%8%33%
1908
March1st to 15thNight
36%37%7%36%7%10%9%36%
2154
16th to endNight
5%7%37%5%45%6%7%10%36%
2040
April1st to 15thNight
6%6%345%25%6%6%11%41%
1760
16th to endNight
46%35%6%45%46%9%42%
1620
May1st to 15thNight
3425%5%35%47%7%48%
1481
16th to endNight
10%6%37%5%3445%6%39%
1328
June1st to 15thNight
7%325%5%45%5%7%9%43%
1260
16th to endNight
5%325%435%6%7%9%47%
1260
July1st to 15thNight
11123235%5%8%63%
1260
16th to endNight
11121345%8%68%
1489
August1st to 15thNight
321231226%8%64%
1460
16th to endNight
121221335%7%67%
1737
September1st to 15thNight
3413323336%64%
1836
16th to endNight
43134335%5%8%56%
1980
October1st to 15thNight
45%145%25%7%7%8%45%
2112
16th to endNight
45%25%5%35%6%7%9%41%
2496
November1st to 15thNight
47%36%5%36%7%6%11%37%
2303
16th to endNight
412%9%10%8%5%6%5%6%8%23%
2697
December1st to 15thNight
413%8%16%10%46%6%5%5%18%
2700
16th to endNight
215%9%14%10%5%6%5%5%6%17%
2880

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
57%17%16%5%1
1322
16th to endDay
55%18%13%9%2
1536
February1st to 15thDay
52%17%16%9%4
1425
16th to endDay
51%18%19%8%2
1565
March1st to 15thDay
53%16%19%9%1
1806
16th to endDay
59%15%16%6%2
2182
April1st to 15thDay
53%13%18%10%3
2188
16th to endDay
49%13%17%15%2
2340
May1st to 15thDay
42%12%18%17%7%
2469
16th to endDay
54%12%17%12%3
2787
June1st to 15thDay
53%10%13%14%6%1
2700
16th to endDay
42%11%17%20%7%
2700
July1st to 15thDay
28%9%17%24%16%4
2541
16th to endDay
21%9%14%27%21%5%
2510
August1st to 15thDay
23%10%23%28%11%3
2482
16th to endDay
23%10%18%31%15%1
2465
September1st to 15thDay
31%8%16%28%14%1
2124
16th to endDay
33%12%21%23%8%
1980
October1st to 15thDay
42%14%17%19%4
1847
16th to endDay
42%15%23%15%3
1726
November1st to 15thDay
51%17%14%12%3
1542
16th to endDay
51%19%18%7%2
1260
December1st to 15thDay
62%14%12%8%1
1260
16th to endDay
65%11%11%8%2
1344
January1st to 15thNight
63%14%11%8%2
2626
16th to endNight
56%12%15%10%41
2688
February1st to 15thNight
53%16%16%9%4
2439
16th to endNight
45%14%21%14%3
1908
March1st to 15thNight
41%20%22%12%2
2154
16th to endNight
45%16%21%12%4
2040
April1st to 15thNight
37%17%23%15%6%
1760
16th to endNight
39%12%20%21%4
1620
May1st to 15thNight
34%11%18%23%12%
1482
16th to endNight
44%11%19%19%5%
1328
June1st to 15thNight
38%13%17%20%8%2
1260
16th to endNight
31%11%20%23%11%
1260
July1st to 15thNight
17%7%19%29%20%5%
1190
16th to endNight
14%8%15%31%23%6%
1394
August1st to 15thNight
17%7%19%36%15%3
1452
16th to endNight
15%7%15%35%22%3
1737
September1st to 15thNight
22%6%15%34%18%3
1836
16th to endNight
27%10%21%25%12%2
1980
October1st to 15thNight
33%14%21%22%7%
2112
16th to endNight
37%14%23%20%3
2496
November1st to 15thNight
40%21%18%14%4
2303
16th to endNight
58%14%15%8%2
2697
December1st to 15thNight
66%11%12%7%1
2700
16th to endNight
65%13%10%7%2
2880

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
10%316%40%21%8%
60
16th to endDay
9%434%28%15%7%
64
February1st to 15thDay
416%40%18%20%
65
16th to endDay
7%16%37%25%9%2
224
March1st to 15thDay
10%34%39%14%2
270
16th to endDay
11%29%37%19%2
288
April1st to 15thDay
15%30%28%18%41
269
16th to endDay
15%27%27%21%7%1
270
May1st to 15thDay
13%25%34%20%5%1
288
16th to endDay
18%10%22%27%18%2
498
June1st to 15thDay
14%16%26%27%13%2
495
16th to endDay
8%16%29%30%13%2
495
July1st to 15thDay
6%8%25%33%24%2
475
16th to endDay
417%41%23%11%1
347
August1st to 15thDay
39%30%36%16%2
315
16th to endDay
6%16%31%28%14%3
332
September1st to 15thDay
8%19%28%24%14%3
315
16th to endDay
7%22%26%26%15%1
315
October1st to 15thDay
15%17%29%29%8%
254
16th to endDay
12%13%35%26%9%2
144
November1st to 15thDay
10%18%34%32%4
90
16th to endDay
6%16%23%31%15%6%
60
December1st to 15thDay
8%13%23%26%20%8%
60
16th to endDay
7%429%37%18%1
64
January1st to 15thNight
8%15%32%31%10%1
841
16th to endNight
7%8%36%34%11%2
768
February1st to 15thNight
8%10%32%34%13%1
704
16th to endNight
7%7%31%37%13%2
632
March1st to 15thNight
5%10%39%32%11%
720
16th to endNight
9%10%35%34%10%
768
April1st to 15thNight
7%10%29%34%17%
680
16th to endNight
7%10%30%35%15%
540
May1st to 15thNight
7%7%29%34%19%1
402
16th to endNight
14%8%17%31%27%1
375
June1st to 15thNight
8%6%23%37%22%
360
16th to endNight
7%5%25%42%18%
360
July1st to 15thNight
2314%49%27%2
340
16th to endNight
1217%46%31%
376
August1st to 15thNight
4112%39%40%2
380
16th to endNight
2318%41%32%1
591
September1st to 15thNight
5%318%37%27%7%
720
16th to endNight
6%6%19%38%26%2
716
October1st to 15thNight
7%6%27%37%19%1
720
16th to endNight
8%8%27%40%13%1
768
November1st to 15thNight
8%11%36%36%6%
728
16th to endNight
8%16%32%29%11%1
900
December1st to 15thNight
8%9%34%34%11%1
900
16th to endNight
8%8%35%36%9%
960
Page generated at 2017-11-01 15:23:33. Version ac04

Copyright 2017 A. Danko


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