Norton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Norton clear sky chart from 2005-11-05 to 2017-12-02.

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%
16259
26%
47695
15%
16213
54%
16213
38%
26722

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
39%
900
26%
2506
12%
895
51%
895
39%
1408
January16th to endNight
37%
960
30%
2551
12%
960
48%
960
42%
1450
February1st to 15thNight
33%
760
20%
2172
8%
756
43%
756
30%
1364
February16th to endNight
37%
632
28%
1894
11%
632
50%
632
33%
1059
March1st to 15thNight
39%
666
25%
2106
14%
666
48%
666
34%
1161
March16th to endNight
33%
576
20%
2112
14%
576
45%
576
28%
1171
April1st to 15thNight
29%
539
20%
1805
12%
539
41%
539
27%
1055
April16th to endNight
34%
540
21%
1653
14%
540
45%
540
27%
1029
May1st to 15thNight
42%
540
19%
1620
14%
540
51%
540
33%
969
May16th to endNight
39%
562
18%
1685
10%
561
48%
561
30%
1026
June1st to 15thNight
44%
540
17%
1485
8%
540
49%
540
39%
876
June16th to endNight
56%
540
24%
1440
13%
540
61%
540
51%
777
July1st to 15thNight
62%
510
19%
1360
11%
510
66%
510
43%
788
July16th to endNight
69%
564
24%
1530
21%
531
71%
531
46%
830
August1st to 15thNight
67%
539
21%
1610
22%
536
70%
536
38%
924
August16th to endNight
64%
573
28%
1848
28%
573
71%
573
43%
933
September1st to 15thNight
56%
540
25%
1905
22%
540
66%
540
38%
971
September16th to endNight
53%
537
32%
1980
27%
537
65%
537
39%
946
October1st to 15thNight
44%
559
30%
1999
21%
559
54%
559
31%
1068
October16th to endNight
49%
887
33%
2423
16%
887
58%
887
48%
1246
November1st to 15thNight
50%
950
34%
2470
16%
950
59%
950
52%
1302
November16th to endNight
48%
975
34%
2535
17%
975
58%
975
48%
1392
December1st to 15thNight
39%
910
24%
2366
11%
910
48%
910
38%
1402
December16th to endNight
39%
960
27%
2640
13%
960
50%
960
35%
1575

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
8%42332345%7%53%
48758
Night
7%42332345%7%54%
47878
Cloud CoverDay
8%42432345%7%53%
48756
Night
7%42432345%7%54%
47878
TransparencyDay
30%413%28%18%3
48444
Night
28%414%26%20%5%
47695
SeeingDay
11%5%29%33%17%2
6153
Night
9%7%32%38%11%
16264

By Month

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
6%7%1442335%6%54%
1432
16th to endDay
5%6%24413245%59%
1671
February1st to 15thDay
7%6%36%6%2345%7%45%
1699
16th to endDay
5%6%25%32335%7%53%
1580
March1st to 15thDay
6%5%2432345%8%54%
1853
16th to endDay
13%6%33313447%47%
2112
April1st to 15thDay
12%5%2332435%7%49%
2141
16th to endDay
16%5%2442345%6%43%
2307
May1st to 15thDay
11%5%2442345%7%47%
2331
16th to endDay
12%5%1442445%8%47%
2430
June1st to 15thDay
8%31332345%9%55%
2472
16th to endDay
32231436%7%62%
2520
July1st to 15thDay
5%3133245%5%9%55%
2520
16th to endDay
5%31322447%10%54%
2532
August1st to 15thDay
9%414435%5%6%8%47%
2340
16th to endDay
6%423223347%58%
2351
September1st to 15thDay
10%5%13323345%54%
2055
16th to endDay
8%313323446%59%
1980
October1st to 15thDay
16%313213235%55%
1947
16th to endDay
8%412213335%63%
1800
November1st to 15thDay
6%314325%446%58%
1718
16th to endDay
7%413313346%59%
1755
December1st to 15thDay
8%6%35%432447%50%
1631
16th to endDay
8%7%36%423445%49%
1581
January1st to 15thNight
46%2342335%6%56%
2506
16th to endNight
5%5%24313445%58%
2551
February1st to 15thNight
8%5%36%42445%7%46%
2162
16th to endNight
5%5%24434446%54%
1894
March1st to 15thNight
7%6%2331445%6%52%
2106
16th to endNight
11%7%23423347%49%
2112
April1st to 15thNight
12%5%23325%5%5%7%46%
1805
16th to endNight
15%5%24423448%43%
1653
May1st to 15thNight
10%42443445%8%48%
1619
16th to endNight
12%424225%46%8%46%
1683
June1st to 15thNight
6%3244245%5%8%52%
1485
16th to endNight
321332346%10%57%
1440
July1st to 15thNight
5%224425%6%7%9%50%
1440
16th to endNight
5%13425%5%7%10%53%
1636
August1st to 15thNight
5%3145%345%7%9%49%
1620
16th to endNight
432242335%7%60%
1848
September1st to 15thNight
7%31232346%7%55%
1905
16th to endNight
7%413212446%61%
1980
October1st to 15thNight
12%413322335%56%
1999
16th to endNight
7%312212336%65%
2423
November1st to 15thNight
4212313448%63%
2470
16th to endNight
6%413212347%61%
2535
December1st to 15thNight
7%6%24423348%53%
2366
16th to endNight
8%6%25%413447%51%
2640

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
6%7%24423346%54%
1432
16th to endDay
5%5%24313345%58%
1671
February1st to 15thDay
6%7%36%6%245%5%7%45%
1699
16th to endDay
5%6%35%32335%8%52%
1580
March1st to 15thDay
6%5%2432336%7%54%
1853
16th to endDay
13%6%24323347%47%
2110
April1st to 15thDay
12%5%13424347%48%
2141
16th to endDay
17%5%2442445%5%43%
2307
May1st to 15thDay
11%5%2442345%7%47%
2331
16th to endDay
12%415%32445%8%47%
2430
June1st to 15thDay
7%31322345%8%55%
2472
16th to endDay
321232435%8%62%
2520
July1st to 15thDay
5%31332446%9%54%
2520
16th to endDay
5%3133245%6%10%54%
2532
August1st to 15thDay
8%4145%25%5%7%7%47%
2340
16th to endDay
6%414312347%58%
2351
September1st to 15thDay
10%5%23323346%54%
2055
16th to endDay
7%313423346%58%
1980
October1st to 15thDay
15%413213235%55%
1947
16th to endDay
8%412312335%62%
1800
November1st to 15thDay
5%314324446%57%
1718
16th to endDay
7%5%12323436%60%
1755
December1st to 15thDay
8%6%35%42335%6%50%
1631
16th to endDay
8%6%26%425%346%48%
1581
January1st to 15thNight
46%2442335%7%56%
2506
16th to endNight
5%5%24313445%57%
2551
February1st to 15thNight
8%5%46%435%447%46%
2162
16th to endNight
5%5%2443446%5%53%
1894
March1st to 15thNight
7%6%24324447%52%
2106
16th to endNight
11%6%34413347%49%
2112
April1st to 15thNight
11%5%2433445%7%46%
1805
16th to endNight
15%6%1342435%7%44%
1653
May1st to 15thNight
10%41442445%7%49%
1619
16th to endNight
12%41432446%8%46%
1683
June1st to 15thNight
6%3234245%6%9%51%
1485
16th to endNight
32133245%6%9%58%
1440
July1st to 15thNight
4223435%6%6%10%50%
1440
16th to endNight
42133345%7%10%53%
1636
August1st to 15thNight
5%2145%25%5%7%9%49%
1620
16th to endNight
341332335%7%60%
1848
September1st to 15thNight
7%31332345%7%55%
1905
16th to endNight
6%413213445%61%
1980
October1st to 15thNight
12%413323245%56%
1999
16th to endNight
7%32212336%65%
2423
November1st to 15thNight
4212313347%63%
2470
16th to endNight
6%314312346%61%
2535
December1st to 15thNight
6%6%2442335%7%53%
2366
16th to endNight
8%6%25%423347%51%
2640

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
30%314%32%16%2
1433
16th to endDay
28%314%33%15%4
1671
February1st to 15thDay
37%5%17%25%10%3
1700
16th to endDay
30%317%24%19%4
1580
March1st to 15thDay
27%315%25%21%5%
1853
16th to endDay
37%5%13%25%15%2
2112
April1st to 15thDay
34%413%28%16%2
2141
16th to endDay
41%413%25%14%1
2307
May1st to 15thDay
35%5%12%28%16%1
2331
16th to endDay
34%5%18%25%12%3
2434
June1st to 15thDay
25%5%18%29%16%3
2472
16th to endDay
19%5%12%31%24%7%
2520
July1st to 15thDay
25%5%12%30%20%5%
2371
16th to endDay
22%5%16%32%21%2
2375
August1st to 15thDay
32%6%16%26%14%3
2326
16th to endDay
25%411%31%22%5%
2351
September1st to 15thDay
31%410%23%22%7%
2055
16th to endDay
25%311%30%25%2
1980
October1st to 15thDay
32%37%27%24%4
1947
16th to endDay
24%29%30%26%5%
1800
November1st to 15thDay
27%212%27%25%5%
1718
16th to endDay
25%211%29%25%5%
1755
December1st to 15thDay
34%317%30%13%1
1631
16th to endDay
36%314%26%16%1
1581
January1st to 15thNight
28%314%30%20%2
2506
16th to endNight
27%316%28%21%3
2551
February1st to 15thNight
37%5%15%26%12%3
2172
16th to endNight
29%413%26%19%6%
1894
March1st to 15thNight
31%311%24%21%7%
2106
16th to endNight
34%315%22%19%3
2112
April1st to 15thNight
35%5%12%24%20%2
1805
16th to endNight
39%414%23%16%1
1653
May1st to 15thNight
33%5%16%22%19%2
1620
16th to endNight
33%7%17%23%14%2
1685
June1st to 15thNight
28%6%19%27%13%3
1485
16th to endNight
21%415%27%24%6%
1440
July1st to 15thNight
25%6%15%27%18%6%
1360
16th to endNight
22%5%18%29%17%5%
1530
August1st to 15thNight
28%6%18%27%14%4
1610
16th to endNight
22%5%12%29%22%7%
1848
September1st to 15thNight
25%6%12%25%20%10%
1905
16th to endNight
23%49%28%28%5%
1980
October1st to 15thNight
31%38%23%25%7%
1999
16th to endNight
21%212%26%26%10%
2423
November1st to 15thNight
20%310%26%30%9%
2470
16th to endNight
23%211%28%25%7%
2535
December1st to 15thNight
31%316%31%15%2
2366
16th to endNight
32%316%24%19%2
2640

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
12%10%36%36%4
90
16th to endDay
17%6%47%17%8%2
96
February1st to 15thDay
12%6%42%35%21
90
16th to endDay
8%16%41%20%12%
81
March1st to 15thDay
5%11%46%27%7%1
90
16th to endDay
21%11%33%19%12%1
96
April1st to 15thDay
13%15%38%25%6%
260
16th to endDay
23%10%31%24%9%
417
May1st to 15thDay
13%9%29%29%16%1
468
16th to endDay
17%7%32%29%11%1
517
June1st to 15thDay
7%433%33%16%4
495
16th to endDay
4428%39%22%1
495
July1st to 15thDay
8%23%37%24%5%
475
16th to endDay
6%216%45%26%2
515
August1st to 15thDay
10%116%39%29%3
493
16th to endDay
6%223%43%19%3
391
September1st to 15thDay
5%228%39%20%4
210
16th to endDay
10%434%28%17%4
135
October1st to 15thDay
20%225%36%11%2
135
16th to endDay
10%9%27%31%15%5%
144
November1st to 15thDay
10%330%33%16%5%
135
16th to endDay
14%13%37%18%14%2
135
December1st to 15thDay
12%5%53%20%8%
94
16th to endDay
14%12%38%27%7%
96
January1st to 15thNight
8%10%37%35%8%
900
16th to endNight
8%9%40%35%6%
960
February1st to 15thNight
11%8%40%32%6%
764
16th to endNight
7%12%37%34%6%
632
March1st to 15thNight
11%10%35%34%6%
666
16th to endNight
14%11%36%29%7%
576
April1st to 15thNight
14%10%43%26%3
539
16th to endNight
17%13%30%29%8%
540
May1st to 15thNight
12%6%33%35%10%
540
16th to endNight
14%8%33%34%9%
563
June1st to 15thNight
7%6%37%36%10%
540
16th to endNight
4332%45%13%
540
July1st to 15thNight
424%51%17%
510
16th to endNight
4117%50%23%1
564
August1st to 15thNight
7%15%51%23%
539
16th to endNight
5%123%45%22%1
573
September1st to 15thNight
10%127%45%14%1
540
16th to endNight
10%6%27%37%18%
537
October1st to 15thNight
14%7%29%34%12%
559
16th to endNight
10%7%30%38%12%
887
November1st to 15thNight
6%8%29%44%10%
950
16th to endNight
9%6%33%38%11%
975
December1st to 15thNight
10%10%34%37%6%
910
16th to endNight
11%9%32%38%7%
960
Page generated at 2017-12-03 10:16:43. Version ac04

Copyright 2017 A. Danko


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