North Wind Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the North Wind Observatory clear sky chart from 2005-11-05 to 2017-03-22.

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
30%
15506
12%
45249
7%
15464
34%
15464
16%
33621

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
11%
900
4%
2506
2%
895
13%
895
5%
2250
January16th to endNight
14%
960
4%
2688
2%
960
16%
960
6%
2395
February1st to 15thNight
15%
758
6%
2257
2%
758
19%
758
7%
1905
February16th to endNight
19%
631
9%
1893
3%
631
24%
631
10%
1544
March1st to 15thNight
25%
720
14%
2148
8%
720
30%
720
16%
1581
March16th to endNight
31%
677
17%
1958
11%
677
38%
677
20%
1352
April1st to 15thNight
24%
494
14%
1647
8%
494
33%
494
17%
1158
April16th to endNight
31%
495
19%
1504
9%
495
40%
495
23%
1000
May1st to 15thNight
31%
495
14%
1485
6%
495
38%
495
20%
1034
May16th to endNight
38%
514
16%
1375
6%
513
46%
513
30%
883
June1st to 15thNight
41%
495
12%
1320
8%
495
45%
495
27%
872
June16th to endNight
50%
495
12%
1320
6%
495
54%
495
31%
850
July1st to 15thNight
61%
465
17%
1240
12%
465
63%
465
41%
731
July16th to endNight
56%
522
14%
1305
8%
489
60%
489
39%
802
August1st to 15thNight
60%
494
23%
1424
16%
491
66%
491
39%
809
August16th to endNight
57%
525
19%
1668
17%
525
61%
525
30%
1003
September1st to 15thNight
53%
544
22%
1699
19%
544
58%
544
33%
997
September16th to endNight
49%
657
19%
1815
13%
657
53%
657
30%
1150
October1st to 15thNight
37%
660
18%
1864
12%
660
42%
660
23%
1296
October16th to endNight
24%
704
10%
2288
6%
704
30%
704
13%
1723
November1st to 15thNight
24%
700
16%
2276
10%
700
32%
700
14%
1663
November16th to endNight
16%
741
6%
2361
3%
741
20%
741
8%
1988
December1st to 15thNight
10%
900
3%
2520
1%
900
12%
900
5%
2262
December16th to endNight
12%
960
5%
2688
2%
960
15%
960
6%
2373

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
16%10%5%7%6%34446%31%
45645
Night
15%11%5%8%6%34446%30%
45417
Cloud CoverDay
15%10%47%6%34446%31%
45654
Night
15%11%5%8%6%34446%30%
45422
TransparencyDay
53%5%11%19%9%
45331
Night
54%6%11%18%8%
45249
SeeingDay
20%12%31%21%10%4
5247
Night
21%11%29%27%9%1
15510

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
17%18%11%14%9%5%43239%
1432
16th to endDay
13%19%16%13%11%442228%
1536
February1st to 15thDay
12%15%9%13%14%45%32413%
1602
16th to endDay
13%16%9%13%11%4443315%
1580
March1st to 15thDay
14%11%6%9%7%2445%5%27%
1801
16th to endDay
14%10%46%6%24446%33%
2072
April1st to 15thDay
22%14%34423346%31%
1971
16th to endDay
18%10%36%423346%34%
2126
May1st to 15thDay
20%7%25%5%3335%7%34%
2136
16th to endDay
11%4244345%6%8%44%
2388
June1st to 15thDay
14%6%35%5%3445%7%38%
2310
16th to endDay
13%4245%345%6%8%42%
2310
July1st to 15thDay
10%4144245%6%7%47%
2310
16th to endDay
12%5%24425%5%6%8%43%
2459
August1st to 15thDay
9%415%6%35%5%7%8%42%
2197
16th to endDay
16%5%24324447%44%
2179
September1st to 15thDay
17%5%15%434447%42%
1920
16th to endDay
16%6%25%435%5%5%8%37%
1815
October1st to 15thDay
20%8%36%5%34236%34%
1763
16th to endDay
25%11%47%6%34337%22%
1584
November1st to 15thDay
17%13%5%5%5%2445%6%29%
1582
16th to endDay
21%22%6%9%5%2443415%
1596
December1st to 15thDay
19%19%11%15%8%2422211%
1440
16th to endDay
20%22%11%11%8%333337%
1536
January1st to 15thNight
19%17%9%14%10%4422213%
2506
16th to endNight
11%17%10%13%11%6%444311%
2688
February1st to 15thNight
11%15%7%12%11%5%6%33417%
2255
16th to endNight
15%15%7%11%8%445%5%5%17%
1893
March1st to 15thNight
15%10%5%8%6%34346%32%
2135
16th to endNight
12%8%46%5%34447%36%
1958
April1st to 15thNight
20%9%45%42345%6%32%
1647
16th to endNight
18%6%25%5%2335%5%41%
1504
May1st to 15thNight
16%425%7%45%5%6%7%32%
1485
16th to endNight
10%435%43445%9%44%
1373
June1st to 15thNight
14%5%2442446%8%41%
1320
16th to endNight
10%425%5%235%6%9%44%
1320
July1st to 15thNight
8%213225%45%8%52%
1320
16th to endNight
6%425%4245%5%8%50%
1401
August1st to 15thNight
6%42423446%8%53%
1433
16th to endNight
11%425%434446%49%
1668
September1st to 15thNight
14%413323346%51%
1699
16th to endNight
12%5%2442445%7%45%
1815
October1st to 15thNight
20%7%345%23346%37%
1864
16th to endNight
26%9%36%6%24446%27%
2288
November1st to 15thNight
15%13%46%4345%46%30%
2276
16th to endNight
20%20%5%8%5%345%4416%
2361
December1st to 15thNight
20%20%9%13%8%3343211%
2520
16th to endNight
18%20%8%13%7%2334411%
2688

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
17%18%11%14%9%5%43239%
1432
16th to endDay
13%20%15%13%11%45%3228%
1536
February1st to 15thDay
12%15%9%13%14%45%32413%
1602
16th to endDay
12%15%10%13%10%4443415%
1580
March1st to 15thDay
14%11%6%9%7%25%45%5%27%
1811
16th to endDay
15%10%46%6%2445%6%32%
2071
April1st to 15thDay
22%14%34423346%30%
1971
16th to endDay
18%10%36%423346%34%
2126
May1st to 15thDay
20%7%25%5%3335%7%33%
2136
16th to endDay
11%5%244245%6%8%44%
2388
June1st to 15thDay
14%6%36%5%3445%7%38%
2310
16th to endDay
12%4245%335%6%8%42%
2310
July1st to 15thDay
9%4144235%6%8%47%
2310
16th to endDay
12%5%23425%5%6%8%43%
2459
August1st to 15thDay
9%425%6%35%5%7%8%41%
2197
16th to endDay
15%6%24324447%43%
2179
September1st to 15thDay
17%5%25%434447%41%
1920
16th to endDay
15%6%25%435%5%5%8%36%
1815
October1st to 15thDay
19%9%36%5%25%337%33%
1763
16th to endDay
25%10%47%5%33437%22%
1584
November1st to 15thDay
16%13%45%5%3445%7%29%
1582
16th to endDay
21%22%7%9%43343415%
1596
December1st to 15thDay
19%18%11%15%9%3422211%
1440
16th to endDay
20%22%11%12%8%333337%
1536
January1st to 15thNight
18%17%9%14%10%5%422213%
2506
16th to endNight
11%17%9%13%11%6%444411%
2688
February1st to 15thNight
11%15%8%12%11%5%6%33417%
2248
16th to endNight
15%14%7%10%8%445%5%5%17%
1893
March1st to 15thNight
15%10%48%6%34346%32%
2148
16th to endNight
13%8%46%5%34448%36%
1958
April1st to 15thNight
19%9%45%4235%5%6%32%
1647
16th to endNight
18%6%24423345%41%
1504
May1st to 15thNight
16%426%7%36%6%6%7%32%
1484
16th to endNight
9%435%42445%9%44%
1373
June1st to 15thNight
14%5%2442447%8%40%
1320
16th to endNight
10%425%5%2446%9%44%
1320
July1st to 15thNight
8%213225%5%6%8%52%
1320
16th to endNight
6%425%42445%8%50%
1401
August1st to 15thNight
5%42433446%8%53%
1433
16th to endNight
11%425%434446%49%
1668
September1st to 15thNight
14%41331345%6%51%
1699
16th to endNight
12%5%24425%45%7%45%
1815
October1st to 15thNight
20%7%35%5%23346%37%
1864
16th to endNight
25%9%36%6%24446%26%
2288
November1st to 15thNight
15%13%46%5%2445%6%30%
2276
16th to endNight
19%20%6%8%6%3444416%
2361
December1st to 15thNight
19%20%9%13%8%3333211%
2520
16th to endNight
18%21%8%13%7%2434411%
2688

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
82%45%6%1
1433
16th to endDay
84%45%41
1536
February1st to 15thDay
75%5%6%11%1
1604
16th to endDay
73%5%7%10%2
1580
March1st to 15thDay
57%5%13%16%6%
1811
16th to endDay
51%5%13%21%6%1
2072
April1st to 15thDay
55%39%20%11%
1971
16th to endDay
50%411%15%15%2
2126
May1st to 15thDay
49%5%10%23%9%
2136
16th to endDay
36%7%13%26%14%1
2392
June1st to 15thDay
45%5%11%22%14%
2310
16th to endDay
38%6%15%22%14%
2310
July1st to 15thDay
34%6%11%27%18%1
2161
16th to endDay
36%8%12%24%14%2
2292
August1st to 15thDay
36%7%14%28%11%1
2182
16th to endDay
39%5%12%24%15%1
2179
September1st to 15thDay
42%5%12%27%11%1
1920
16th to endDay
43%6%14%23%11%
1815
October1st to 15thDay
52%410%23%8%
1763
16th to endDay
63%5%14%12%3
1584
November1st to 15thDay
53%6%11%19%7%
1582
16th to endDay
73%411%8%2
1596
December1st to 15thDay
81%45%6%1
1440
16th to endDay
81%48%31
1536
January1st to 15thNight
79%45%7%2
2506
16th to endNight
75%7%9%6%1
2688
February1st to 15thNight
70%6%7%12%2
2257
16th to endNight
66%5%11%11%4
1893
March1st to 15thNight
53%5%11%17%10%
2148
16th to endNight
46%5%13%23%9%1
1958
April1st to 15thNight
51%5%9%19%14%
1647
16th to endNight
44%5%10%20%15%3
1504
May1st to 15thNight
47%6%12%21%10%
1485
16th to endNight
36%5%11%26%15%3
1375
June1st to 15thNight
39%6%15%22%14%
1320
16th to endNight
34%8%15%23%16%1
1320
July1st to 15thNight
26%7%12%30%19%3
1240
16th to endNight
29%7%17%28%15%2
1305
August1st to 15thNight
27%7%15%34%14%
1424
16th to endNight
35%6%12%26%17%1
1668
September1st to 15thNight
32%5%13%31%15%1
1699
16th to endNight
36%6%15%29%11%
1815
October1st to 15thNight
47%5%9%25%11%
1864
16th to endNight
57%6%14%16%5%
2288
November1st to 15thNight
54%6%11%18%8%1
2276
16th to endNight
69%6%12%8%1
2361
December1st to 15thNight
78%5%7%6%1
2520
16th to endNight
76%5%10%6%1
2688

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
18%20%48%11%1
90
16th to endDay
29%11%40%15%21
96
February1st to 15thDay
27%31%27%13%
90
16th to endDay
28%24%34%9%2
81
March1st to 15thDay
29%21%34%7%5%
101
16th to endDay
25%10%29%22%10%2
250
April1st to 15thDay
30%13%23%23%6%2
210
16th to endDay
23%10%30%19%12%4
210
May1st to 15thDay
28%14%30%17%5%3
228
16th to endDay
15%15%33%23%8%3
432
June1st to 15thDay
19%14%35%19%8%2
420
16th to endDay
15%10%35%26%8%4
420
July1st to 15thDay
12%9%32%27%13%5%
400
16th to endDay
11%9%34%25%11%6%
445
August1st to 15thDay
9%6%26%25%20%11%
305
16th to endDay
23%322%23%18%8%
268
September1st to 15thDay
16%225%28%16%9%
255
16th to endDay
19%10%22%24%18%5%
254
October1st to 15thDay
21%9%29%26%10%2
230
16th to endDay
26%19%45%7%1
96
November1st to 15thDay
22%16%38%15%5%1
90
16th to endDay
34%22%28%11%3
90
December1st to 15thDay
35%32%22%7%2
90
16th to endDay
38%33%25%3
96
January1st to 15thNight
27%18%29%19%5%
900
16th to endNight
21%14%36%23%4
960
February1st to 15thNight
20%16%34%23%3
761
16th to endNight
25%16%30%23%3
631
March1st to 15thNight
20%15%33%21%7%
720
16th to endNight
17%13%32%27%7%1
677
April1st to 15thNight
23%14%33%22%4
494
16th to endNight
23%10%31%25%7%1
495
May1st to 15thNight
18%11%36%27%6%
495
16th to endNight
12%9%34%31%11%1
515
June1st to 15thNight
16%9%26%33%12%1
495
16th to endNight
11%6%26%40%13%1
495
July1st to 15thNight
9%322%43%18%2
465
16th to endNight
9%223%41%21%
522
August1st to 15thNight
9%222%42%21%2
494
16th to endNight
13%319%40%21%1
525
September1st to 15thNight
16%5%21%34%18%4
544
16th to endNight
14%9%22%31%19%3
657
October1st to 15thNight
23%5%26%32%10%1
660
16th to endNight
31%12%26%22%6%
704
November1st to 15thNight
24%12%31%22%7%1
700
16th to endNight
30%14%29%20%4
741
December1st to 15thNight
31%18%31%15%2
900
16th to endNight
27%16%33%19%3
960
Page generated at 2017-03-23 07:36:17. Version ac04

Copyright 2017 A. Danko


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