Norris Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Norris Lake clear sky chart from 2005-11-05 to 2017-10-06.

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
47%
15547
20%
47143
15%
15506
53%
15506
26%
30250

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
25%
720
17%
2327
10%
716
35%
716
18%
1581
January16th to endNight
23%
768
18%
2496
10%
768
34%
768
17%
1709
February1st to 15thNight
23%
702
18%
2126
7%
701
34%
701
20%
1455
February16th to endNight
22%
631
20%
1893
10%
631
31%
631
18%
1319
March1st to 15thNight
32%
720
19%
2067
12%
720
38%
720
21%
1403
March16th to endNight
36%
768
17%
2112
10%
768
40%
768
24%
1446
April1st to 15thNight
43%
623
23%
1881
14%
623
53%
623
31%
1122
April16th to endNight
46%
540
22%
1665
15%
540
54%
540
27%
1047
May1st to 15thNight
47%
540
18%
1620
11%
540
53%
540
26%
1055
May16th to endNight
59%
561
16%
1683
11%
561
62%
561
27%
1073
June1st to 15thNight
68%
540
15%
1620
12%
540
71%
540
30%
1012
June16th to endNight
74%
540
18%
1620
17%
540
75%
540
32%
977
July1st to 15thNight
67%
510
11%
1530
10%
510
67%
510
27%
997
July16th to endNight
73%
564
17%
1595
15%
531
77%
531
32%
956
August1st to 15thNight
75%
539
19%
1609
18%
536
76%
536
30%
991
August16th to endNight
72%
573
18%
1872
19%
573
73%
573
27%
1158
September1st to 15thNight
64%
695
20%
1955
17%
695
66%
695
30%
1271
September16th to endNight
60%
717
27%
1980
21%
717
63%
717
33%
1218
October1st to 15thNight
57%
684
32%
1911
28%
684
62%
684
38%
1112
October16th to endNight
46%
704
30%
2129
23%
704
55%
704
33%
1258
November1st to 15thNight
50%
700
29%
2276
25%
700
59%
700
32%
1280
November16th to endNight
42%
720
24%
2340
19%
720
50%
720
25%
1472
December1st to 15thNight
35%
720
18%
2340
15%
720
41%
720
18%
1598
December16th to endNight
29%
768
19%
2496
12%
768
40%
768
16%
1740

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%6%35%5%35%5%5%7%38%
48053
Night
11%5%25%5%3445%7%42%
47341
TransparencyDay
42%7%11%19%14%3
47754
Night
40%6%11%21%16%3
47144
SeeingDay
14%7%19%23%22%13%
5419
Night
14%8%22%29%20%3
15551

By Month

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
16%9%49%6%3445%6%30%
1611
16th to endDay
14%9%45%434346%39%
1728
February1st to 15thDay
15%9%47%6%35%335%34%
1735
16th to endDay
14%8%47%435%45%7%35%
1580
March1st to 15thDay
16%9%37%5%2445%5%36%
1893
16th to endDay
14%7%46%5%25%45%6%35%
2111
April1st to 15thDay
11%6%3433446%6%44%
2076
16th to endDay
13%6%25%5%2445%7%40%
2295
May1st to 15thDay
13%6%35%6%35%5%5%8%36%
2331
16th to endDay
9%5%26%5%46%5%6%8%38%
2431
June1st to 15thDay
7%426%6%5%7%6%8%8%37%
2340
16th to endDay
6%425%6%36%8%7%10%38%
2340
July1st to 15thDay
10%5%36%6%5%7%6%7%9%30%
2340
16th to endDay
9%436%7%47%8%7%10%31%
2465
August1st to 15thDay
7%5%25%5%47%8%8%11%32%
2340
16th to endDay
10%5%25%5%46%5%7%9%36%
2327
September1st to 15thDay
13%6%26%5%25%5%5%8%37%
1992
16th to endDay
13%5%15%42445%7%46%
1980
October1st to 15thDay
11%424323336%55%
1847
16th to endDay
15%5%15%313345%50%
1741
November1st to 15thDay
11%424423337%52%
1582
16th to endDay
14%5%33424345%47%
1620
December1st to 15thDay
14%9%36%5%345%46%35%
1620
16th to endDay
17%9%36%5%35%5%46%32%
1728
January1st to 15thNight
14%8%36%6%34445%36%
2327
16th to endNight
15%7%5%6%6%345%4436%
2496
February1st to 15thNight
14%7%46%5%3445%6%35%
2117
16th to endNight
16%6%36%6%35%5%5%6%35%
1893
March1st to 15thNight
14%7%36%6%3345%6%38%
2067
16th to endNight
13%6%35%435%5%5%6%40%
2112
April1st to 15thNight
11%42432446%7%47%
1881
16th to endNight
10%5%3443445%7%44%
1665
May1st to 15thNight
9%5%36%5%345%6%9%40%
1619
16th to endNight
7%426%5%35%6%6%11%41%
1682
June1st to 15thNight
5%4245%26%7%8%11%42%
1620
16th to endNight
4424437%5%6%11%46%
1620
July1st to 15thNight
9%4245%37%5%7%9%40%
1620
16th to endNight
5%225%6%35%6%7%12%41%
1703
August1st to 15thNight
6%3135%35%6%8%11%44%
1620
16th to endNight
7%4145%36%5%7%10%41%
1872
September1st to 15thNight
10%5%15%435%5%5%8%44%
1955
16th to endNight
9%335%5%23346%51%
1980
October1st to 15thNight
11%413412237%56%
1911
16th to endNight
12%5%24313335%52%
2129
November1st to 15thNight
11%423324335%53%
2276
16th to endNight
14%5%35%424445%45%
2340
December1st to 15thNight
15%7%36%6%35%45%5%36%
2340
16th to endNight
19%8%27%5%34345%34%
2496

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
54%5%8%16%13%1
1612
16th to endDay
45%5%10%24%13%1
1728
February1st to 15thDay
53%5%7%19%12%2
1737
16th to endDay
47%5%12%19%12%2
1580
March1st to 15thDay
49%48%19%14%3
1893
16th to endDay
49%6%10%20%11%1
2112
April1st to 15thDay
38%6%12%22%18%3
2076
16th to endDay
41%6%10%21%15%4
2295
May1st to 15thDay
44%7%12%21%11%2
2331
16th to endDay
41%8%15%20%10%3
2435
June1st to 15thDay
39%10%15%20%12%1
2340
16th to endDay
35%12%14%19%14%4
2340
July1st to 15thDay
45%9%16%14%11%2
2201
16th to endDay
41%12%14%18%11%2
2310
August1st to 15thDay
40%12%17%16%11%1
2327
16th to endDay
40%10%14%18%14%1
2327
September1st to 15thDay
43%9%10%17%13%5%
1992
16th to endDay
36%6%11%19%20%4
1980
October1st to 15thDay
31%39%23%24%7%
1847
16th to endDay
36%37%23%23%4
1741
November1st to 15thDay
34%36%22%27%5%
1582
16th to endDay
39%38%23%22%2
1620
December1st to 15thDay
48%6%9%20%12%2
1620
16th to endDay
52%5%11%17%12%1
1728
January1st to 15thNight
48%410%17%14%3
2327
16th to endNight
49%5%8%20%14%2
2496
February1st to 15thNight
48%49%21%13%2
2126
16th to endNight
49%5%10%20%12%2
1893
March1st to 15thNight
46%5%10%18%15%4
2067
16th to endNight
43%7%11%24%12%1
2112
April1st to 15thNight
34%5%11%24%19%4
1881
16th to endNight
37%7%10%22%17%4
1665
May1st to 15thNight
39%7%14%24%12%1
1620
16th to endNight
36%9%17%22%11%2
1684
June1st to 15thNight
31%11%19%21%14%1
1620
16th to endNight
30%10%16%24%15%3
1620
July1st to 15thNight
38%9%19%16%13%2
1530
16th to endNight
30%10%20%22%13%2
1595
August1st to 15thNight
31%11%18%20%16%1
1609
16th to endNight
36%8%17%23%13%1
1872
September1st to 15thNight
36%8%15%18%16%4
1955
16th to endNight
35%410%19%26%3
1980
October1st to 15thNight
30%49%22%25%7%
1911
16th to endNight
34%45%21%26%7%
2129
November1st to 15thNight
33%26%20%27%9%
2276
16th to endNight
41%5%5%23%21%3
2340
December1st to 15thNight
48%5%9%18%13%3
2340
16th to endNight
52%49%17%15%1
2496

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
31%21%24%18%22
90
16th to endDay
21%23%42%9%2
96
February1st to 15thDay
26%26%34%11%1
90
16th to endDay
30%17%29%17%4
81
March1st to 15thDay
18%20%28%25%41
183
16th to endDay
17%11%31%24%14%1
288
April1st to 15thDay
14%12%21%29%18%2
270
16th to endDay
17%7%22%27%21%4
270
May1st to 15thDay
14%9%31%18%15%9%
288
16th to endDay
15%415%29%16%17%
331
June1st to 15thDay
9%111%22%32%22%
315
16th to endDay
5%219%24%27%20%
315
July1st to 15thDay
14%214%23%26%17%
305
16th to endDay
9%9%19%33%27%
326
August1st to 15thDay
10%19%23%30%24%
313
16th to endDay
12%16%26%29%22%
332
September1st to 15thDay
13%411%19%27%23%
315
16th to endDay
14%213%25%27%17%
314
October1st to 15thDay
13%318%25%28%10%
278
16th to endDay
16%8%20%25%24%3
253
November1st to 15thDay
15%12%23%23%18%6%
90
16th to endDay
16%8%31%27%14%1
90
December1st to 15thDay
21%14%38%18%5%1
90
16th to endDay
25%19%37%12%5%
96
January1st to 15thNight
20%17%33%22%5%
720
16th to endNight
19%15%35%28%1
768
February1st to 15thNight
20%13%38%25%2
704
16th to endNight
19%16%37%22%2
631
March1st to 15thNight
19%13%29%33%4
720
16th to endNight
15%10%31%30%10%1
768
April1st to 15thNight
14%9%30%33%11%
623
16th to endNight
14%6%27%36%14%
540
May1st to 15thNight
12%427%33%20%2
540
16th to endNight
9%116%32%31%9%
563
June1st to 15thNight
6%12%35%36%7%
540
16th to endNight
5%10%34%40%8%
540
July1st to 15thNight
11%18%30%40%6%
510
16th to endNight
49%23%45%15%
564
August1st to 15thNight
8%5%30%46%8%
539
16th to endNight
10%16%28%45%7%
573
September1st to 15thNight
11%210%27%41%6%
695
16th to endNight
10%216%29%35%5%
717
October1st to 15thNight
14%6%17%27%26%7%
684
16th to endNight
16%5%25%29%20%1
704
November1st to 15thNight
14%9%22%30%19%3
700
16th to endNight
15%13%24%33%12%
720
December1st to 15thNight
18%12%27%31%9%
720
16th to endNight
23%12%28%29%6%
768
Page generated at 2017-10-07 14:07:45. Version ac04

Copyright 2017 A. Danko


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