Spruce Knob
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Spruce Knob clear sky chart from 2005-11-05 to 2018-02-22.

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
33%
16040
16%
49005
9%
16003
40%
16003
18%
32776

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
14%
776
15%
2522
5%
776
25%
776
10%
1733
January16th to endNight
12%
832
14%
2704
4%
832
25%
832
11%
1853
February1st to 15thNight
12%
762
13%
2482
4%
761
24%
761
12%
1633
February16th to endNight
10%
659
15%
2004
3%
659
22%
659
10%
1429
March1st to 15thNight
18%
720
15%
1980
6%
720
26%
720
14%
1399
March16th to endNight
20%
768
13%
2112
6%
768
27%
768
15%
1527
April1st to 15thNight
22%
718
14%
1847
5%
718
28%
718
20%
1271
April16th to endNight
35%
646
17%
1726
7%
646
41%
646
23%
1180
May1st to 15thNight
35%
540
13%
1620
6%
540
41%
540
18%
1153
May16th to endNight
46%
525
12%
1648
9%
525
50%
525
23%
1088
June1st to 15thNight
53%
360
15%
1440
16%
360
59%
360
21%
882
June16th to endNight
49%
366
18%
1446
14%
366
59%
366
24%
850
July1st to 15thNight
53%
510
10%
1530
9%
510
54%
510
25%
1033
July16th to endNight
66%
564
15%
1595
11%
531
69%
531
33%
966
August1st to 15thNight
61%
539
17%
1609
13%
536
63%
536
27%
1058
August16th to endNight
63%
678
20%
1824
15%
678
64%
678
29%
1210
September1st to 15thNight
55%
720
22%
1839
13%
720
59%
720
30%
1204
September16th to endNight
49%
717
20%
1992
16%
717
53%
717
25%
1321
October1st to 15thNight
45%
720
21%
2160
17%
720
53%
720
24%
1390
October16th to endNight
30%
768
23%
2304
13%
768
44%
768
22%
1456
November1st to 15thNight
34%
760
22%
2330
15%
760
44%
760
22%
1484
November16th to endNight
25%
780
17%
2711
10%
780
35%
780
15%
1757
December1st to 15thNight
20%
780
11%
2730
6%
780
26%
780
10%
1917
December16th to endNight
15%
832
15%
2850
6%
832
28%
832
10%
1982

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
12%7%37%7%35%5%5%7%32%
49226
Night
9%6%36%6%35%6%6%8%37%
49198
Cloud CoverDay
12%7%37%6%45%5%6%7%34%
49236
Night
10%5%25%5%35%5%6%8%39%
49202
TransparencyDay
46%9%12%17%11%2
48937
Night
40%9%15%19%12%2
49005
SeeingDay
19%16%24%20%12%6%
6037
Night
18%17%25%24%12%1
16048

By Month

Percentage Cloud Cover NE (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%7%48%9%47%6%6%7%28%
1746
16th to endDay
9%7%5%10%6%45%5%5%7%33%
1872
February1st to 15thDay
10%9%48%7%35%6%6%7%31%
1710
16th to endDay
8%9%310%7%345%5%8%32%
1614
March1st to 15thDay
11%8%47%5%345%5%6%36%
1969
16th to endDay
13%9%48%6%45%5%5%6%31%
2112
April1st to 15thDay
11%6%5%7%6%2445%6%37%
2101
16th to endDay
15%6%36%6%3446%7%35%
2244
May1st to 15thDay
18%8%37%7%35%45%5%28%
2331
16th to endDay
14%6%47%7%46%5%5%7%29%
2464
June1st to 15thDay
12%6%36%6%46%6%6%7%34%
2520
16th to endDay
9%5%47%7%47%6%6%8%32%
2510
July1st to 15thDay
12%7%48%7%46%6%7%8%27%
2340
16th to endDay
10%6%47%8%47%7%7%8%27%
2465
August1st to 15thDay
11%6%39%8%5%6%7%6%9%25%
2340
16th to endDay
10%7%37%8%5%7%6%6%8%27%
2366
September1st to 15thDay
13%6%26%7%45%5%47%36%
2118
16th to endDay
15%8%37%6%35%446%34%
1968
October1st to 15thDay
16%7%25%5%34445%39%
1800
16th to endDay
13%8%35%5%2445%5%41%
1920
November1st to 15thDay
11%7%45%43445%7%42%
1857
16th to endDay
13%6%36%6%35%5%46%38%
1576
December1st to 15thDay
10%8%5%6%6%36%5%6%6%32%
1560
16th to endDay
10%8%38%7%46%7%5%7%29%
1723
January1st to 15thNight
8%6%48%9%46%5%8%9%28%
2522
16th to endNight
8%8%36%7%46%5%5%7%34%
2704
February1st to 15thNight
8%6%36%7%36%7%6%9%34%
2480
16th to endNight
6%8%37%9%5%6%8%6%8%29%
2004
March1st to 15thNight
11%6%26%6%45%7%6%7%34%
1968
16th to endNight
11%7%46%7%45%45%6%35%
2112
April1st to 15thNight
8%6%46%6%45%6%6%8%37%
1847
16th to endNight
10%6%35%5%45%45%8%39%
1726
May1st to 15thNight
14%8%36%6%35%6%6%7%33%
1620
16th to endNight
10%5%25%436%46%11%39%
1646
June1st to 15thNight
8%315%5%35%6%7%11%41%
1440
16th to endNight
6%3246%345%6%10%45%
1446
July1st to 15thNight
9%5%25%6%35%6%5%10%39%
1620
16th to endNight
5%224435%6%8%13%43%
1703
August1st to 15thNight
7%425%5%36%7%8%10%39%
1620
16th to endNight
7%425%5%25%6%6%9%43%
1824
September1st to 15thNight
10%425%445%45%7%45%
1839
16th to endNight
11%6%245%25%5%5%7%41%
1992
October1st to 15thNight
13%5%15%436%5%47%41%
2160
16th to endNight
11%5%346%345%6%6%42%
2304
November1st to 15thNight
9%9%36%435%5%5%5%41%
2330
16th to endNight
11%7%45%5%36%5%5%7%37%
2711
December1st to 15thNight
10%6%39%9%46%6%7%6%29%
2730
16th to endNight
9%7%37%8%46%6%7%9%29%
2850

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
8%6%49%8%5%6%6%5%8%30%
1746
16th to endDay
9%7%49%6%35%45%7%36%
1872
February1st to 15thDay
9%9%37%6%45%5%5%8%33%
1710
16th to endDay
8%9%39%6%3446%7%35%
1614
March1st to 15thDay
12%7%38%5%35%36%6%37%
1980
16th to endDay
13%9%37%6%445%5%5%33%
2111
April1st to 15thDay
10%6%47%6%3445%7%39%
2101
16th to endDay
16%5%35%5%345%5%7%36%
2244
May1st to 15thDay
19%7%37%6%35%5%46%29%
2331
16th to endDay
14%7%38%6%46%5%5%7%30%
2464
June1st to 15thDay
12%5%25%6%45%6%7%7%35%
2520
16th to endDay
10%5%37%6%46%6%6%8%34%
2510
July1st to 15thDay
12%7%38%6%45%6%7%9%27%
2340
16th to endDay
9%6%37%6%47%6%8%9%28%
2465
August1st to 15thDay
11%7%38%7%46%6%8%9%25%
2340
16th to endDay
12%5%37%7%5%7%6%7%8%28%
2366
September1st to 15thDay
14%5%25%6%46%45%6%38%
2118
16th to endDay
16%7%37%6%25%447%34%
1968
October1st to 15thDay
17%6%25%5%34445%39%
1800
16th to endDay
13%8%35%5%2335%6%44%
1920
November1st to 15thDay
10%7%35%42445%7%44%
1857
16th to endDay
13%6%36%5%35%35%6%40%
1576
December1st to 15thDay
11%7%46%6%25%5%6%7%34%
1560
16th to endDay
11%7%38%6%46%5%5%7%31%
1723
January1st to 15thNight
8%6%37%8%46%5%6%9%32%
2522
16th to endNight
9%7%36%5%46%5%6%6%38%
2704
February1st to 15thNight
8%6%26%6%45%6%6%9%36%
2473
16th to endNight
6%7%37%8%46%6%7%8%31%
2004
March1st to 15thNight
11%6%25%6%35%5%8%6%37%
1980
16th to endNight
12%8%36%5%45%46%7%37%
2112
April1st to 15thNight
9%5%46%5%45%45%9%38%
1847
16th to endNight
12%5%3443445%9%41%
1726
May1st to 15thNight
14%6%35%5%25%6%5%7%35%
1619
16th to endNight
11%425%425%46%10%41%
1646
June1st to 15thNight
9%2135%35%7%6%11%42%
1440
16th to endNight
6%3245%445%6%10%45%
1446
July1st to 15thNight
9%415%5%35%5%6%9%41%
1620
16th to endNight
5%2245%25%6%8%12%45%
1703
August1st to 15thNight
8%425%5%45%6%7%10%40%
1620
16th to endNight
8%425%5%35%6%5%9%44%
1824
September1st to 15thNight
10%425%5%245%6%7%45%
1839
16th to endNight
13%5%25%435%5%5%7%41%
1992
October1st to 15thNight
15%324425%6%5%6%42%
2160
16th to endNight
11%425%5%345%6%6%44%
2304
November1st to 15thNight
9%8%36%4245%5%5%44%
2330
16th to endNight
11%6%35%5%36%5%5%6%39%
2711
December1st to 15thNight
10%6%28%8%46%5%6%7%31%
2730
16th to endNight
10%6%36%7%46%5%7%9%32%
2850

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
49%8%11%15%10%2
1747
16th to endDay
45%8%14%16%11%2
1872
February1st to 15thDay
48%8%13%17%10%1
1712
16th to endDay
47%8%14%18%10%1
1614
March1st to 15thDay
45%7%12%19%11%2
1980
16th to endDay
50%7%10%17%11%1
2112
April1st to 15thDay
43%6%12%19%14%2
2101
16th to endDay
45%8%10%17%14%3
2244
May1st to 15thDay
53%8%11%16%8%1
2331
16th to endDay
49%11%12%17%7%1
2468
June1st to 15thDay
43%11%13%20%10%
2520
16th to endDay
45%11%13%16%10%1
2510
July1st to 15thDay
50%11%10%15%10%1
2201
16th to endDay
46%12%11%17%11%1
2310
August1st to 15thDay
50%10%14%15%8%
2327
16th to endDay
49%10%12%18%8%
2366
September1st to 15thDay
45%8%10%16%17%2
2118
16th to endDay
49%5%8%19%15%1
1968
October1st to 15thDay
44%6%11%19%13%4
1800
16th to endDay
40%5%11%24%15%2
1920
November1st to 15thDay
38%7%12%18%17%6%
1857
16th to endDay
42%5%14%17%17%1
1576
December1st to 15thDay
45%11%11%16%11%2
1560
16th to endDay
49%9%12%16%9%1
1723
January1st to 15thNight
45%9%16%13%11%3
2522
16th to endNight
44%9%17%15%10%1
2704
February1st to 15thNight
41%9%19%18%9%1
2482
16th to endNight
46%11%14%17%8%1
2004
March1st to 15thNight
43%11%14%21%8%2
1980
16th to endNight
44%11%13%17%11%1
2112
April1st to 15thNight
40%8%15%20%12%2
1847
16th to endNight
39%9%14%17%15%3
1726
May1st to 15thNight
45%11%14%18%9%1
1620
16th to endNight
37%11%19%21%7%1
1648
June1st to 15thNight
32%14%16%25%10%
1440
16th to endNight
32%11%16%26%12%1
1446
July1st to 15thNight
38%12%17%17%12%2
1530
16th to endNight
27%12%20%24%14%1
1595
August1st to 15thNight
35%11%17%21%13%
1609
16th to endNight
35%10%12%28%10%1
1824
September1st to 15thNight
35%8%14%19%20%1
1839
16th to endNight
40%7%11%22%16%
1992
October1st to 15thNight
40%6%12%23%14%2
2160
16th to endNight
35%9%13%22%16%1
2304
November1st to 15thNight
39%6%12%16%17%7%
2330
16th to endNight
42%7%13%16%17%2
2711
December1st to 15thNight
47%10%15%13%10%2
2730
16th to endNight
46%10%16%16%8%1
2850

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
24%31%27%9%5%
135
16th to endDay
34%34%22%8%
144
February1st to 15thDay
38%40%20%1
135
16th to endDay
28%29%28%13%
151
March1st to 15thDay
24%24%29%15%5%
270
16th to endDay
20%27%26%16%7%1
288
April1st to 15thDay
16%27%28%20%6%1
270
16th to endDay
20%17%28%14%14%4
270
May1st to 15thDay
28%19%19%18%8%5%
288
16th to endDay
20%11%20%22%15%9%
331
June1st to 15thDay
13%15%21%22%20%6%
315
16th to endDay
11%15%32%22%9%7%
315
July1st to 15thDay
14%8%36%24%9%6%
305
16th to endDay
10%322%30%19%13%
326
August1st to 15thDay
12%5%24%25%18%13%
313
16th to endDay
10%320%27%21%16%
332
September1st to 15thDay
15%9%20%22%20%12%
315
16th to endDay
22%6%16%23%19%10%
314
October1st to 15thDay
16%9%20%27%20%5%
315
16th to endDay
19%20%27%18%12%1
336
November1st to 15thDay
17%16%26%25%13%1
275
16th to endDay
24%23%29%14%7%
94
December1st to 15thDay
28%30%21%14%32
90
16th to endDay
33%32%21%10%1
110
January1st to 15thNight
26%30%25%14%2
780
16th to endNight
24%29%30%14%
832
February1st to 15thNight
24%29%31%13%
764
16th to endNight
24%33%30%11%
659
March1st to 15thNight
23%25%30%17%2
720
16th to endNight
22%22%30%17%5%1
768
April1st to 15thNight
16%27%30%20%4
718
16th to endNight
19%13%27%27%11%
646
May1st to 15thNight
18%12%26%27%13%1
540
16th to endNight
14%6%26%29%18%3
527
June1st to 15thNight
8%5%26%33%23%1
360
16th to endNight
6%430%44%14%
366
July1st to 15thNight
12%222%40%20%1
510
16th to endNight
7%315%36%31%6%
564
August1st to 15thNight
8%119%40%27%2
539
16th to endNight
9%216%38%30%3
678
September1st to 15thNight
13%5%19%30%27%3
720
16th to endNight
17%6%19%26%26%3
717
October1st to 15thNight
19%12%17%27%20%2
720
16th to endNight
20%19%26%22%10%1
768
November1st to 15thNight
19%15%27%24%11%1
760
16th to endNight
23%21%25%20%7%1
780
December1st to 15thNight
21%28%25%19%4
780
16th to endNight
21%25%32%18%1
832
Page generated at 2018-02-23 11:21:36. Version ac04

Copyright 2018 A. Danko


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