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 2017-10-31.

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%
16224
12%
47345
7%
16182
35%
16182
17%
34976

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%
708
17%
2052
11%
708
37%
708
19%
1434
April1st to 15thNight
25%
539
14%
1797
8%
539
33%
539
17%
1266
April16th to endNight
29%
540
19%
1641
9%
540
39%
540
22%
1099
May1st to 15thNight
31%
540
13%
1620
6%
540
38%
540
20%
1126
May16th to endNight
36%
562
16%
1503
6%
561
45%
561
30%
976
June1st to 15thNight
42%
540
12%
1440
8%
540
46%
540
29%
936
June16th to endNight
49%
540
13%
1440
7%
540
53%
540
31%
930
July1st to 15thNight
62%
510
16%
1360
12%
510
64%
510
41%
798
July16th to endNight
56%
564
15%
1417
9%
531
60%
531
38%
877
August1st to 15thNight
61%
539
22%
1554
15%
536
66%
536
38%
894
August16th to endNight
57%
573
20%
1821
18%
573
61%
573
30%
1097
September1st to 15thNight
55%
594
22%
1854
19%
594
60%
594
34%
1069
September16th to endNight
50%
717
22%
1980
15%
717
54%
717
32%
1235
October1st to 15thNight
36%
720
17%
2034
12%
720
41%
720
23%
1414
October16th to endNight
24%
768
12%
2495
7%
768
31%
768
13%
1864
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
15%10%47%6%34446%32%
48415
Night
15%10%47%6%34446%31%
47513
Cloud CoverDay
15%10%47%6%34446%31%
48424
Night
15%11%5%8%6%34446%30%
47518
TransparencyDay
52%5%11%19%9%
48101
Night
54%6%11%18%9%
47345
SeeingDay
20%12%31%21%10%4
6195
Night
21%11%29%27%9%1
16228

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
16%11%46%6%24446%32%
2182
April1st to 15thDay
21%14%34423346%31%
2151
16th to endDay
18%10%36%423346%34%
2319
May1st to 15thDay
20%6%26%5%3335%7%35%
2331
16th to endDay
12%5%244345%6%8%43%
2612
June1st to 15thDay
14%6%35%5%3445%7%39%
2520
16th to endDay
13%425%5%345%6%8%41%
2520
July1st to 15thDay
10%4144245%6%8%47%
2520
16th to endDay
11%5%234245%6%8%44%
2655
August1st to 15thDay
9%415%6%35%5%7%8%42%
2397
16th to endDay
16%5%24324447%43%
2378
September1st to 15thDay
16%5%14434346%43%
2094
16th to endDay
14%5%25%435%5%5%8%38%
1980
October1st to 15thDay
20%8%36%5%34336%34%
1923
16th to endDay
25%11%47%6%24337%23%
1728
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
14%8%45%5%34447%35%
2052
April1st to 15thNight
20%9%46%423447%32%
1797
16th to endNight
19%6%25%5%23345%40%
1641
May1st to 15thNight
16%425%6%46%5%6%6%33%
1620
16th to endNight
11%435%42445%9%43%
1501
June1st to 15thNight
13%5%2442446%8%42%
1440
16th to endNight
11%425%5%235%6%9%43%
1440
July1st to 15thNight
8%213325%5%5%8%53%
1440
16th to endNight
6%425%4245%5%8%50%
1513
August1st to 15thNight
6%31433446%8%52%
1563
16th to endNight
12%425%434446%49%
1821
September1st to 15thNight
13%413323346%52%
1854
16th to endNight
11%5%2442445%7%46%
1980
October1st to 15thNight
21%7%345%23346%38%
2034
16th to endNight
25%8%36%6%23446%27%
2495
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
16%10%47%6%24446%31%
2181
April1st to 15thDay
21%14%34423346%30%
2151
16th to endDay
18%10%36%423346%34%
2319
May1st to 15thDay
19%7%26%5%3435%7%35%
2331
16th to endDay
11%5%24435%5%6%8%42%
2612
June1st to 15thDay
13%6%35%5%3445%7%39%
2520
16th to endDay
13%425%5%345%6%8%41%
2520
July1st to 15thDay
9%4244235%6%8%47%
2520
16th to endDay
11%5%234245%6%8%44%
2655
August1st to 15thDay
9%425%6%35%5%7%8%42%
2397
16th to endDay
15%5%2432445%7%43%
2378
September1st to 15thDay
16%5%24434446%43%
2094
16th to endDay
14%6%25%435%5%5%8%38%
1980
October1st to 15thDay
20%9%36%5%24336%34%
1923
16th to endDay
25%11%47%5%33436%23%
1728
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
14%8%46%5%34447%35%
2052
April1st to 15thNight
20%9%45%423447%32%
1797
16th to endNight
19%6%25%5%23345%40%
1641
May1st to 15thNight
16%426%7%45%6%6%7%33%
1619
16th to endNight
10%5%35%42445%9%43%
1501
June1st to 15thNight
13%5%2441447%8%42%
1440
16th to endNight
11%425%5%245%6%9%43%
1440
July1st to 15thNight
8%2133245%5%8%53%
1440
16th to endNight
6%425%425%45%8%50%
1513
August1st to 15thNight
6%42433445%8%52%
1563
16th to endNight
11%424424446%48%
1821
September1st to 15thNight
13%413313446%52%
1854
16th to endNight
11%5%24425%45%7%46%
1980
October1st to 15thNight
21%7%345%23336%38%
2034
16th to endNight
25%9%36%6%23346%27%
2495
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
52%5%12%21%6%1
2182
April1st to 15thDay
55%39%19%11%
2151
16th to endDay
50%411%16%14%2
2319
May1st to 15thDay
48%5%10%23%10%2
2331
16th to endDay
38%6%14%25%13%1
2616
June1st to 15thDay
43%5%11%23%14%
2520
16th to endDay
39%6%15%22%14%
2520
July1st to 15thDay
33%6%11%28%18%1
2371
16th to endDay
36%7%12%25%16%2
2488
August1st to 15thDay
36%7%14%29%10%1
2382
16th to endDay
40%5%12%24%15%1
2378
September1st to 15thDay
41%5%12%27%12%1
2094
16th to endDay
41%6%14%25%11%
1980
October1st to 15thDay
52%410%23%9%
1923
16th to endDay
63%5%13%13%3
1728
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
48%5%12%23%8%1
2052
April1st to 15thNight
51%5%10%18%13%
1797
16th to endNight
45%5%10%20%14%3
1641
May1st to 15thNight
47%6%12%20%11%1
1620
16th to endNight
37%5%11%26%14%3
1503
June1st to 15thNight
37%6%15%23%15%
1440
16th to endNight
35%8%14%24%15%1
1440
July1st to 15thNight
26%7%13%30%20%2
1360
16th to endNight
30%6%16%27%16%2
1417
August1st to 15thNight
28%6%15%33%14%
1554
16th to endNight
35%6%12%26%17%1
1821
September1st to 15thNight
31%5%12%31%16%1
1854
16th to endNight
35%6%15%29%12%
1980
October1st to 15thNight
47%5%9%25%12%
2034
16th to endNight
57%6%14%17%5%
2495
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
29%10%26%21%9%2
288
April1st to 15thDay
31%14%27%19%5%1
270
16th to endDay
26%12%32%15%9%3
270
May1st to 15thDay
26%16%29%17%6%3
288
16th to endDay
17%15%34%21%7%2
512
June1st to 15thDay
18%13%37%20%8%2
495
16th to endDay
15%13%35%24%7%3
495
July1st to 15thDay
12%9%32%26%13%5%
475
16th to endDay
11%9%34%26%11%7%
515
August1st to 15thDay
10%5%26%26%20%10%
370
16th to endDay
23%322%25%16%8%
332
September1st to 15thDay
14%324%27%18%11%
315
16th to endDay
16%10%22%26%18%5%
314
October1st to 15thDay
22%10%30%25%9%2
288
16th to endDay
32%14%44%6%1
144
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
19%13%31%27%7%1
708
April1st to 15thNight
24%14%32%22%4
539
16th to endNight
23%10%33%23%7%1
540
May1st to 15thNight
18%10%35%28%6%
540
16th to endNight
13%9%34%29%10%1
563
June1st to 15thNight
15%8%27%34%12%1
540
16th to endNight
12%6%26%40%13%1
540
July1st to 15thNight
8%321%44%19%2
510
16th to endNight
9%224%40%21%1
564
August1st to 15thNight
10%221%43%21%2
539
16th to endNight
13%319%39%22%1
573
September1st to 15thNight
15%5%20%34%19%5%
594
16th to endNight
12%9%23%31%20%3
717
October1st to 15thNight
24%6%26%31%10%1
720
16th to endNight
31%12%26%22%6%
768
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 2017-11-01 17:23:31. Version ac04

Copyright 2017 A. Danko


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