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 2017-04-25.

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
44%
14718
10%
45665
7%
14688
47%
14688
19%
32426

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
7%
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%
525
11%
1575
9%
525
47%
525
23%
1060
May1st to 15thNight
51%
368
12%
1359
15%
368
53%
368
23%
829
May16th to endNight
50%
342
7%
1214
9%
342
51%
342
17%
842
June1st to 15thNight
56%
330
4%
1155
1%
330
56%
330
21%
769
June16th to endNight
57%
330
5%
1155
1%
330
58%
330
26%
694
July1st to 15thNight
73%
310
10%
1085
6%
310
75%
310
44%
515
July16th to endNight
75%
348
15%
1284
21%
326
79%
326
43%
570
August1st to 15thNight
77%
348
23%
1330
31%
346
81%
346
43%
594
August16th to endNight
69%
541
25%
1591
22%
541
71%
541
49%
808
September1st to 15thNight
67%
660
22%
1683
13%
660
69%
660
46%
967
September16th to endNight
64%
656
20%
1815
15%
656
67%
656
36%
1098
October1st to 15thNight
52%
660
15%
1936
11%
660
56%
660
26%
1283
October16th to endNight
48%
704
12%
2288
10%
704
53%
704
20%
1566
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%6%36%6%46%6%7%9%36%
46003
Night
37%37%6%35%5%7%9%40%
45823
Cloud CoverDay
5%6%37%6%46%6%7%8%35%
46004
Night
48%47%6%35%5%6%8%37%
45826
TransparencyDay
45%13%17%16%6%
45664
Night
43%13%17%17%6%
45665
SeeingDay
10%18%31%25%11%1
5269
Night
7%8%29%36%16%1
14725

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%
2273
May1st to 15thDay
7%7%25%6%46%6%6%8%39%
2262
16th to endDay
14%8%36%7%36%7%6%7%27%
2545
June1st to 15thDay
11%6%37%7%47%6%6%8%28%
2475
16th to endDay
8%425%7%48%7%7%8%34%
2475
July1st to 15thDay
4213436%5%6%8%52%
2475
16th to endDay
1112435%6%6%7%57%
2480
August1st to 15thDay
31134346%8%9%52%
2291
16th to endDay
4213425%5%7%8%55%
2259
September1st to 15thDay
5%3246%345%5%8%50%
1947
16th to endDay
7%3135%35%6%7%9%47%
1815
October1st to 15thDay
6%435%6%45%5%7%10%40%
1693
16th to endDay
45%246%46%7%8%10%37%
1584
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
47%35%5%35%5%6%8%44%
1575
May1st to 15thNight
45%25%436%5%6%8%48%
1358
16th to endNight
10%8%46%44345%7%38%
1214
June1st to 15thNight
7%325%5%45%5%5%11%43%
1155
16th to endNight
5%214445%6%8%8%47%
1155
July1st to 15thNight
111221445%7%66%
1155
16th to endNight
1222345%8%66%
1379
August1st to 15thNight
32321225%9%64%
1338
16th to endNight
121321345%8%65%
1591
September1st to 15thNight
4314313346%62%
1683
16th to endNight
5%233235%5%9%57%
1815
October1st to 15thNight
44145%25%6%7%8%47%
1936
16th to endNight
35%15%5%35%6%8%9%43%
2288
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%6%45%5%7%8%33%
2273
May1st to 15thDay
7%7%25%5%36%6%7%8%39%
2262
16th to endDay
13%8%37%6%46%6%7%7%28%
2545
June1st to 15thDay
11%7%37%6%5%7%6%7%7%29%
2475
16th to endDay
9%426%7%46%6%7%7%36%
2475
July1st to 15thDay
4313435%5%7%8%53%
2475
16th to endDay
11134246%6%8%58%
2480
August1st to 15thDay
2213335%5%7%9%53%
2291
16th to endDay
423435%5%6%9%55%
2259
September1st to 15thDay
5%425%5%3446%7%50%
1947
16th to endDay
7%325%4346%7%10%45%
1815
October1st to 15thDay
6%5%26%7%46%6%6%9%37%
1693
16th to endDay
5%6%36%6%46%7%7%10%36%
1584
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%43%
1575
May1st to 15thNight
45%25%5%35%46%7%48%
1358
16th to endNight
11%7%47%5%35%45%6%39%
1214
June1st to 15thNight
7%326%5%45%5%7%9%42%
1155
16th to endNight
5%325%5%35%6%7%9%47%
1155
July1st to 15thNight
11123245%5%9%62%
1155
16th to endNight
11131346%8%66%
1379
August1st to 15thNight
321231226%8%64%
1338
16th to endNight
121231345%7%65%
1591
September1st to 15thNight
3423323346%62%
1683
16th to endNight
5%3124335%5%8%57%
1815
October1st to 15thNight
5%415%5%25%7%6%9%44%
1936
16th to endNight
45%26%5%35%7%8%9%39%
2288
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%16%2
2273
May1st to 15thDay
42%12%17%18%8%
2262
16th to endDay
55%11%16%11%4
2549
June1st to 15thDay
54%9%13%14%6%1
2475
16th to endDay
45%11%16%19%7%
2475
July1st to 15thDay
29%9%17%24%15%3
2316
16th to endDay
23%10%15%28%18%3
2312
August1st to 15thDay
24%10%23%27%11%3
2274
16th to endDay
25%10%18%30%13%1
2259
September1st to 15thDay
33%8%16%28%12%1
1947
16th to endDay
34%12%21%22%9%
1815
October1st to 15thDay
43%14%17%19%4
1693
16th to endDay
43%15%22%15%2
1584
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
38%12%21%22%4
1575
May1st to 15thNight
34%11%18%23%11%
1359
16th to endNight
46%10%19%18%5%
1214
June1st to 15thNight
38%13%18%18%8%2
1155
16th to endNight
31%11%21%24%10%
1155
July1st to 15thNight
18%7%20%30%18%4
1085
16th to endNight
15%8%16%33%20%5%
1284
August1st to 15thNight
17%7%19%35%16%3
1330
16th to endNight
17%7%16%35%21%2
1591
September1st to 15thNight
23%6%16%34%16%2
1683
16th to endNight
26%10%21%25%13%2
1815
October1st to 15thNight
34%14%21%22%7%
1936
16th to endNight
39%15%21%20%3
2288
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%28%26%22%7%1
250
May1st to 15thDay
14%26%34%17%5%1
228
16th to endDay
18%10%24%26%16%2
420
June1st to 15thDay
13%15%28%26%12%2
420
16th to endDay
9%14%30%29%13%2
420
July1st to 15thDay
6%9%25%32%23%2
400
16th to endDay
418%41%24%10%1
289
August1st to 15thDay
310%34%33%14%2
255
16th to endDay
7%19%33%24%13%1
268
September1st to 15thDay
9%21%29%23%13%3
255
16th to endDay
7%24%25%27%13%
255
October1st to 15thDay
16%18%29%27%8%
199
16th to endDay
13%10%36%26%11%2
96
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
8%10%30%35%15%
525
May1st to 15thNight
7%7%29%33%19%1
369
16th to endNight
15%7%19%31%25%
343
June1st to 15thNight
9%6%23%37%22%
330
16th to endNight
7%5%25%41%19%
330
July1st to 15thNight
2315%49%27%1
310
16th to endNight
1218%47%30%
348
August1st to 15thNight
4112%39%39%2
348
16th to endNight
3319%42%30%1
541
September1st to 15thNight
5%319%36%27%7%
660
16th to endNight
6%6%19%39%25%2
656
October1st to 15thNight
8%6%28%37%18%
660
16th to endNight
9%8%27%39%14%1
704
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 2017-04-26 15:21:39. Version ac04

Copyright 2017 A. Danko


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