Nelson
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Nelson clear sky chart from 2005-11-05 to

2017-09-12
.

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
36%
14928
8%
46769
7%
14897
38%
14897
14%
35526

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
18%
781
4%
2568
3%
778
19%
778
5%
2291
January16th to endNight
19%
768
3%
2688
3%
768
21%
768
5%
2365
February1st to 15thNight
26%
702
4%
2439
2%
698
29%
698
8%
2028
February16th to endNight
30%
632
7%
1903
7%
632
32%
632
11%
1550
March1st to 15thNight
26%
720
2%
2160
1%
720
27%
720
8%
1849
March16th to endNight
27%
768
5%
2022
2%
768
29%
768
11%
1701
April1st to 15thNight
37%
716
6%
1796
3%
716
39%
716
17%
1409
April16th to endNight
40%
534
9%
1614
7%
534
42%
534
17%
1178
May1st to 15thNight
52%
359
11%
1440
15%
359
55%
359
18%
918
May16th to endNight
45%
374
7%
1388
9%
374
46%
374
13%
1011
June1st to 15thNight
48%
360
3%
1260
1%
360
48%
360
16%
896
June16th to endNight
51%
360
6%
1260
1%
360
51%
360
21%
829
July1st to 15thNight
71%
340
8%
1233
6%
340
72%
340
36%
636
July16th to endNight
74%
376
17%
1416
25%
354
78%
354
42%
625
August1st to 15thNight
74%
360
21%
1432
28%
358
78%
358
39%
659
August16th to endNight
70%
622
26%
1768
22%
622
72%
622
48%
910
September1st to 15thNight
64%
706
21%
1768
12%
706
66%
706
45%
1042
September16th to endNight
58%
656
19%
1815
15%
656
60%
656
29%
1189
October1st to 15thNight
43%
660
12%
1947
11%
660
45%
660
20%
1374
October16th to endNight
33%
704
9%
2288
7%
704
38%
704
13%
1758
November1st to 15thNight
22%
700
5%
2314
4%
700
25%
700
7%
1956
November16th to endNight
21%
870
3%
2670
1%
870
23%
870
7%
2307
December1st to 15thNight
17%
900
3%
2700
2%
900
19%
900
6%
2401
December16th to endNight
13%
960
2%
2880
1%
960
14%
960
5%
2644

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
15%13%47%6%34446%28%
47919
Night
15%15%47%5%24446%28%
46929
Cloud CoverDay
15%13%5%7%6%34445%28%
47919
Night
15%15%5%7%5%2445%6%27%
46933
TransparencyDay
57%7%12%14%7%1
47584
Night
56%8%12%14%6%1
46769
SeeingDay
22%13%27%22%11%2
5811
Night
22%5%25%28%15%1
14934

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
21%20%7%11%6%3333413%
1381
16th to endDay
15%22%8%9%6%23435%18%
1536
February1st to 15thDay
16%23%7%8%5%23335%19%
1424
16th to endDay
12%23%7%7%5%25%45%420%
1571
March1st to 15thDay
22%23%5%8%6%33335%13%
1800
16th to endDay
20%26%6%9%5%2334412%
2201
April1st to 15thDay
17%18%6%10%6%45%44417%
2152
16th to endDay
15%16%5%9%8%45%346%19%
2343
May1st to 15thDay
14%13%47%6%35%347%30%
2511
16th to endDay
20%11%5%8%7%4445%5%20%
2723
June1st to 15thDay
24%9%48%7%45%44421%
2700
16th to endDay
17%8%48%7%35%446%27%
2700
July1st to 15thDay
8%4245%25%5%7%7%46%
2652
16th to endDay
6%3145%35%45%7%52%
2657
August1st to 15thDay
5%415%5%35%46%8%48%
2520
16th to endDay
7%425%42445%8%50%
2431
September1st to 15thDay
8%5%25%423447%50%
2111
16th to endDay
17%6%25%5%2435%6%38%
1815
October1st to 15thDay
19%9%38%5%24336%31%
1683
16th to endDay
24%15%36%5%2344425%
1584
November1st to 15thDay
26%19%47%42445%5%15%
1542
16th to endDay
20%20%7%6%5%2335%5%19%
1278
December1st to 15thDay
16%20%9%8%5%2335%6%17%
1260
16th to endDay
12%29%8%10%5%2432415%
1344
January1st to 15thNight
21%24%7%11%5%3323412%
2568
16th to endNight
15%18%8%13%8%35%337%10%
2688
February1st to 15thNight
18%23%6%6%5%24436%18%
2427
16th to endNight
13%22%5%8%424446%22%
1903
March1st to 15thNight
21%21%6%7%5%33445%16%
2160
16th to endNight
19%19%47%6%34445%19%
2018
April1st to 15thNight
14%16%45%5%3445%6%28%
1796
16th to endNight
12%12%5%7%435%46%7%31%
1614
May1st to 15thNight
8%7%35%5%36%5%6%6%40%
1439
16th to endNight
16%9%38%6%36%5%6%6%27%
1388
June1st to 15thNight
17%6%35%435%5%6%8%32%
1260
16th to endNight
10%6%25%7%35%6%6%7%37%
1260
July1st to 15thNight
42135%25%45%8%55%
1306
16th to endNight
22232335%9%62%
1512
August1st to 15thNight
5%2231445%8%60%
1440
16th to endNight
32123235%5%9%60%
1768
September1st to 15thNight
6%21332345%6%58%
1768
16th to endNight
12%5%25%4235%6%8%43%
1815
October1st to 15thNight
17%8%25%5%345%5%7%35%
1947
16th to endNight
22%13%36%5%34447%25%
2288
November1st to 15thNight
27%19%45%424446%15%
2314
16th to endNight
19%22%6%9%5%24435%14%
2670
December1st to 15thNight
18%21%9%11%6%2345%5%12%
2700
16th to endNight
16%26%8%12%5%23445%9%
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
21%18%8%12%6%3334313%
1381
16th to endDay
14%22%7%10%6%24435%18%
1536
February1st to 15thDay
16%24%7%8%5%3334419%
1424
16th to endDay
12%23%6%9%5%3445%420%
1571
March1st to 15thDay
22%23%7%8%5%3333413%
1800
16th to endDay
19%27%7%8%6%3324411%
2201
April1st to 15thDay
16%20%7%10%7%35%43417%
2152
16th to endDay
14%17%6%10%7%35%345%19%
2343
May1st to 15thDay
14%13%47%6%34447%29%
2511
16th to endDay
20%12%5%8%7%445%5%5%19%
2723
June1st to 15thDay
25%9%49%7%45%335%21%
2700
16th to endDay
18%8%48%7%445%45%27%
2700
July1st to 15thDay
8%425%435%5%7%7%45%
2652
16th to endDay
6%315%6%3345%7%51%
2657
August1st to 15thDay
6%325%5%345%6%7%47%
2520
16th to endDay
7%425%434448%50%
2431
September1st to 15thDay
9%5%25%5%23446%50%
2111
16th to endDay
17%8%35%434346%37%
1815
October1st to 15thDay
20%10%47%5%33336%31%
1683
16th to endDay
23%14%46%6%24345%25%
1584
November1st to 15thDay
26%20%46%6%3435%415%
1542
16th to endDay
18%19%8%7%6%24245%19%
1278
December1st to 15thDay
15%21%8%8%6%2345%7%16%
1260
16th to endDay
12%27%8%10%6%3433414%
1344
January1st to 15thNight
22%23%8%11%6%2333411%
2568
16th to endNight
14%19%9%13%8%35%436%10%
2688
February1st to 15thNight
18%22%6%8%5%34346%17%
2427
16th to endNight
13%22%6%7%6%2345%5%20%
1903
March1st to 15thNight
19%21%7%7%6%3435%416%
2160
16th to endNight
18%21%47%7%25%345%19%
2022
April1st to 15thNight
13%17%5%5%6%245%5%6%27%
1796
16th to endNight
11%12%6%7%5%245%5%7%31%
1614
May1st to 15thNight
8%8%26%5%35%5%5%6%40%
1439
16th to endNight
16%9%47%6%35%6%6%6%27%
1388
June1st to 15thNight
17%6%46%5%236%5%7%33%
1260
16th to endNight
10%7%26%5%46%5%6%6%38%
1260
July1st to 15thNight
33134245%6%7%56%
1306
16th to endNight
221242435%7%63%
1512
August1st to 15thNight
5%31332336%9%59%
1440
16th to endNight
311332446%9%60%
1768
September1st to 15thNight
6%31342345%6%58%
1768
16th to endNight
12%5%25%4245%6%8%43%
1815
October1st to 15thNight
16%9%25%4345%5%6%35%
1947
16th to endNight
22%12%36%6%24446%25%
2288
November1st to 15thNight
25%20%46%434345%15%
2314
16th to endNight
20%22%6%9%6%34445%13%
2670
December1st to 15thNight
17%20%8%12%7%3335%5%11%
2700
16th to endNight
15%25%9%13%6%334438%
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
75%7%8%5%2
1381
16th to endDay
68%8%10%8%21
1536
February1st to 15thDay
69%7%10%7%3
1424
16th to endDay
65%8%13%9%2
1571
March1st to 15thDay
77%6%10%4
1800
16th to endDay
77%6%9%5%
2201
April1st to 15thDay
71%6%12%7%2
2152
16th to endDay
68%6%12%10%1
2343
May1st to 15thDay
54%6%14%17%6%
2511
16th to endDay
65%8%12%11%2
2727
June1st to 15thDay
66%7%8%10%6%1
2700
16th to endDay
58%6%10%16%7%
2700
July1st to 15thDay
36%7%13%21%16%4
2497
16th to endDay
31%6%13%23%21%4
2490
August1st to 15thDay
32%8%14%26%14%3
2503
16th to endDay
31%7%14%28%16%1
2431
September1st to 15thDay
35%6%12%25%17%2
2111
16th to endDay
48%7%13%19%9%1
1815
October1st to 15thDay
54%8%13%18%4
1683
16th to endDay
61%8%14%12%2
1584
November1st to 15thDay
71%10%8%6%2
1542
16th to endDay
68%8%12%7%3
1278
December1st to 15thDay
68%9%12%6%2
1260
16th to endDay
74%8%10%42
1344
January1st to 15thNight
76%8%7%42
2568
16th to endNight
73%9%8%421
2688
February1st to 15thNight
67%8%12%6%3
2439
16th to endNight
61%10%13%9%3
1903
March1st to 15thNight
68%9%13%6%
2160
16th to endNight
66%7%12%9%3
2022
April1st to 15thNight
55%8%19%11%4
1796
16th to endNight
51%8%18%17%4
1614
May1st to 15thNight
42%8%16%20%11%
1440
16th to endNight
54%8%15%17%3
1388
June1st to 15thNight
49%9%13%17%7%1
1260
16th to endNight
43%8%16%19%11%
1260
July1st to 15thNight
25%7%17%23%19%6%
1233
16th to endNight
19%6%13%29%26%5%
1416
August1st to 15thNight
21%6%15%34%17%4
1432
16th to endNight
18%7%17%33%19%3
1768
September1st to 15thNight
24%7%14%29%21%3
1768
16th to endNight
37%9%15%23%11%2
1815
October1st to 15thNight
48%6%18%20%6%
1947
16th to endNight
58%7%14%17%2
2288
November1st to 15thNight
69%8%10%6%4
2314
16th to endNight
72%7%10%7%2
2670
December1st to 15thNight
74%8%7%7%1
2700
16th to endNight
78%8%6%5%1
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
20%26%31%18%3
60
16th to endDay
32%9%28%18%7%3
64
February1st to 15thDay
26%15%29%13%14%1
84
16th to endDay
23%15%30%21%7%
237
March1st to 15thDay
41%21%25%9%1
270
16th to endDay
35%19%27%14%3
288
April1st to 15thDay
27%19%27%18%5%1
269
16th to endDay
28%17%29%17%5%2
270
May1st to 15thDay
22%17%32%20%5%
288
16th to endDay
27%12%17%21%15%4
438
June1st to 15thDay
24%12%21%25%14%2
495
16th to endDay
18%10%26%25%16%2
495
July1st to 15thDay
10%7%26%31%21%3
431
16th to endDay
10%12%38%25%9%2
327
August1st to 15thDay
8%9%30%31%15%4
315
16th to endDay
8%13%30%28%13%4
332
September1st to 15thDay
17%13%29%20%16%3
300
16th to endDay
20%14%26%25%10%1
255
October1st to 15thDay
29%16%30%16%7%
230
16th to endDay
43%7%23%13%8%3
96
November1st to 15thDay
38%7%20%26%7%
83
16th to endDay
31%8%23%20%5%11%
60
December1st to 15thDay
30%15%15%28%8%3
60
16th to endDay
21%6%32%31%6%1
64
January1st to 15thNight
33%8%27%23%6%1
783
16th to endNight
22%7%34%25%9%
768
February1st to 15thNight
31%5%25%25%10%
704
16th to endNight
23%5%30%26%11%1
632
March1st to 15thNight
30%8%24%24%11%
720
16th to endNight
28%7%27%26%9%1
768
April1st to 15thNight
23%5%24%29%16%
716
16th to endNight
19%6%25%31%16%
534
May1st to 15thNight
13%5%23%34%23%
360
16th to endNight
19%5%20%28%25%1
375
June1st to 15thNight
18%5%20%29%24%1
360
16th to endNight
12%424%37%19%1
360
July1st to 15thNight
4217%36%38%1
340
16th to endNight
3116%42%34%1
376
August1st to 15thNight
8%10%35%41%4
360
16th to endNight
6%216%36%35%3
622
September1st to 15thNight
8%120%32%31%5%
706
16th to endNight
14%319%37%23%1
656
October1st to 15thNight
21%425%32%15%
660
16th to endNight
29%6%22%29%8%2
704
November1st to 15thNight
36%9%26%22%5%
700
16th to endNight
32%7%28%19%10%1
870
December1st to 15thNight
26%5%35%23%8%
900
16th to endNight
28%7%38%20%4
960
Page generated at 2017-09-13 04:39:23. Version ac04

Copyright 2017 A. Danko


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