Northern Skies Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Northern Skies Observatory clear sky chart from 2005-11-05 to 2018-01-12.

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
32%
15196
13%
48339
9%
15164
38%
15164
16%
34472

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
22%
765
10%
2662
6%
761
27%
761
10%
2031
January16th to endNight
20%
768
10%
2688
5%
768
28%
768
10%
2016
February1st to 15thNight
21%
704
9%
2270
4%
701
28%
701
9%
1796
February16th to endNight
24%
631
13%
1893
7%
631
34%
631
13%
1434
March1st to 15thNight
25%
720
14%
2160
9%
720
33%
720
14%
1619
March16th to endNight
27%
768
18%
2015
7%
768
35%
768
19%
1438
April1st to 15thNight
26%
718
16%
1796
5%
718
32%
718
18%
1342
April16th to endNight
29%
593
17%
1673
8%
593
36%
593
20%
1145
May1st to 15thNight
25%
487
16%
1567
9%
487
33%
487
17%
1074
May16th to endNight
39%
375
12%
1497
13%
374
46%
374
17%
971
June1st to 15thNight
34%
360
9%
1440
9%
360
41%
360
13%
1006
June16th to endNight
45%
360
9%
1440
10%
360
51%
360
19%
921
July1st to 15thNight
57%
340
11%
1360
20%
340
59%
340
22%
819
July16th to endNight
56%
376
12%
1418
15%
354
59%
354
21%
864
August1st to 15thNight
55%
434
15%
1505
15%
432
58%
432
25%
927
August16th to endNight
55%
720
20%
1866
12%
720
57%
720
35%
1175
September1st to 15thNight
48%
720
15%
1833
8%
720
51%
720
30%
1221
September16th to endNight
51%
717
24%
1980
18%
717
55%
717
34%
1214
October1st to 15thNight
39%
720
17%
2052
11%
720
45%
720
22%
1426
October16th to endNight
26%
768
12%
2494
8%
768
32%
768
14%
1817
November1st to 15thNight
31%
760
16%
2472
11%
760
38%
760
16%
1769
November16th to endNight
27%
780
15%
2616
12%
780
34%
780
14%
1894
December1st to 15thNight
18%
780
6%
2730
3%
780
22%
780
8%
2183
December16th to endNight
18%
832
9%
2912
4%
832
24%
832
6%
2370

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
17%10%47%6%35%45%6%28%
49005
Night
16%9%47%6%35%45%6%29%
48509
Cloud CoverDay
16%9%47%6%35%45%6%29%
49015
Night
15%9%47%6%35%45%6%30%
48514
TransparencyDay
54%410%19%9%1
48693
Night
53%411%20%9%
48339
SeeingDay
23%11%25%22%12%4
6056
Night
22%11%24%28%11%1
15196

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
15%10%5%12%8%46%6%6%6%17%
1520
16th to endDay
11%11%5%9%9%46%6%46%24%
1536
February1st to 15thDay
12%13%6%11%9%6%6%44419%
1589
16th to endDay
11%13%8%12%9%5%5%44420%
1580
March1st to 15thDay
15%13%7%8%6%35%43424%
1790
16th to endDay
16%10%5%9%7%23345%31%
2208
April1st to 15thDay
19%12%47%5%24345%30%
2152
16th to endDay
20%8%36%5%2445%5%32%
2286
May1st to 15thDay
22%9%47%6%33445%27%
2394
16th to endDay
20%8%35%435%5%5%6%30%
2618
June1st to 15thDay
26%8%36%6%2445%6%25%
2520
16th to endDay
20%8%36%6%45%447%28%
2520
July1st to 15thDay
15%7%36%6%45%45%7%31%
2520
16th to endDay
15%6%36%6%46%5%6%8%29%
2654
August1st to 15thDay
15%8%38%6%45%5%6%7%27%
2433
16th to endDay
13%6%25%5%45%46%9%36%
2333
September1st to 15thDay
17%7%36%434445%39%
2127
16th to endDay
13%6%35%42345%9%43%
1980
October1st to 15thDay
22%9%27%423346%32%
1907
16th to endDay
17%16%47%5%35%335%25%
1728
November1st to 15thDay
16%12%45%6%35%448%27%
1716
16th to endDay
16%11%5%9%7%34445%25%
1670
December1st to 15thDay
18%15%5%9%7%45%446%19%
1560
16th to endDay
19%15%7%11%8%3444415%
1664
January1st to 15thNight
12%10%6%10%8%46%7%6%7%18%
2662
16th to endNight
12%10%6%10%8%5%7%5%6%5%21%
2688
February1st to 15thNight
10%11%6%12%9%6%9%45%5%18%
2269
16th to endNight
11%11%7%10%8%35%45%5%25%
1893
March1st to 15thNight
15%10%48%7%35%6%4428%
2147
16th to endNight
15%9%37%5%35%446%33%
2015
April1st to 15thNight
18%10%47%6%43445%30%
1796
16th to endNight
20%7%245%3435%6%36%
1673
May1st to 15thNight
19%11%36%5%22447%33%
1567
16th to endNight
20%6%25%4235%6%8%32%
1495
June1st to 15thNight
25%5%35%6%35%45%6%28%
1440
16th to endNight
17%5%245%26%5%6%7%35%
1440
July1st to 15thNight
15%335%5%25%5%6%8%37%
1440
16th to endNight
12%5%34336%6%6%9%37%
1514
August1st to 15thNight
13%6%335%3446%8%39%
1515
16th to endNight
13%42442345%7%47%
1866
September1st to 15thNight
15%5%25%424347%43%
1833
16th to endNight
13%4233235%5%7%47%
1980
October1st to 15thNight
17%7%26%5%3445%6%34%
2052
16th to endNight
22%10%36%6%35%35%5%26%
2494
November1st to 15thNight
15%11%47%6%3445%6%28%
2472
16th to endNight
17%9%39%8%34345%27%
2616
December1st to 15thNight
19%13%6%9%8%46%5%4417%
2730
16th to endNight
17%15%6%10%8%46%45%6%14%
2912

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
14%10%5%12%8%45%7%6%6%18%
1520
16th to endDay
11%11%49%9%5%5%6%5%6%25%
1536
February1st to 15thDay
12%13%7%10%9%47%445%20%
1589
16th to endDay
11%12%8%12%8%46%445%21%
1580
March1st to 15thDay
14%13%7%9%6%35%5%4425%
1800
16th to endDay
15%10%5%9%7%33245%32%
2208
April1st to 15thDay
18%12%46%5%34435%31%
2152
16th to endDay
19%9%35%5%3445%5%33%
2286
May1st to 15thDay
21%9%46%5%34445%28%
2394
16th to endDay
19%8%35%5%35%5%46%31%
2618
June1st to 15thDay
25%7%36%5%35%35%7%25%
2520
16th to endDay
19%7%46%6%35%5%47%29%
2520
July1st to 15thDay
14%7%46%6%35%5%6%8%31%
2520
16th to endDay
15%6%36%6%46%5%7%8%30%
2654
August1st to 15thDay
14%7%38%7%46%5%6%7%29%
2433
16th to endDay
13%5%25%445%5%6%9%36%
2333
September1st to 15thDay
15%7%26%432446%40%
2127
16th to endDay
13%6%25%42335%7%44%
1980
October1st to 15thDay
21%9%46%5%23346%33%
1907
16th to endDay
17%14%47%5%35%445%27%
1728
November1st to 15thDay
16%11%46%5%2445%7%29%
1716
16th to endDay
16%12%49%6%35%45%6%26%
1670
December1st to 15thDay
17%14%5%8%7%45%446%20%
1560
16th to endDay
20%15%7%9%8%3434416%
1664
January1st to 15thNight
12%10%5%9%10%46%5%6%8%18%
2662
16th to endNight
12%10%6%9%8%47%5%6%6%22%
2688
February1st to 15thNight
10%11%6%11%9%5%8%5%5%6%19%
2262
16th to endNight
11%10%7%9%6%5%5%45%5%25%
1893
March1st to 15thNight
15%10%47%6%45%5%5%428%
2160
16th to endNight
13%8%47%5%45%45%5%34%
2014
April1st to 15thNight
17%10%5%6%5%34446%30%
1796
16th to endNight
20%6%34434447%37%
1673
May1st to 15thNight
18%11%45%423446%33%
1567
16th to endNight
18%6%25%5%2447%8%33%
1495
June1st to 15thNight
25%5%26%6%34445%29%
1440
16th to endNight
16%435%5%246%6%8%34%
1440
July1st to 15thNight
14%5%25%5%35%46%9%38%
1440
16th to endNight
12%4345%36%6%6%9%37%
1514
August1st to 15thNight
13%6%245%35%46%8%39%
1515
16th to endNight
13%42442345%8%46%
1866
September1st to 15thNight
15%5%35%423446%44%
1833
16th to endNight
12%32343445%7%47%
1980
October1st to 15thNight
17%7%35%6%3445%6%35%
2052
16th to endNight
21%10%27%5%3446%6%26%
2494
November1st to 15thNight
15%10%48%6%3445%7%29%
2472
16th to endNight
16%8%48%7%35%45%5%29%
2616
December1st to 15thNight
19%13%6%7%8%46%45%6%17%
2730
16th to endNight
17%15%6%9%8%45%5%46%15%
2912

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
63%5%9%14%6%
1521
16th to endDay
58%312%17%7%
1536
February1st to 15thDay
65%48%16%5%
1592
16th to endDay
66%37%10%10%1
1580
March1st to 15thDay
62%310%14%7%1
1800
16th to endDay
55%38%17%13%2
2208
April1st to 15thDay
56%28%18%12%2
2152
16th to endDay
51%39%20%11%2
2286
May1st to 15thDay
57%36%19%11%1
2394
16th to endDay
52%5%10%19%10%1
2622
June1st to 15thDay
58%410%19%6%
2520
16th to endDay
53%410%20%9%
2520
July1st to 15thDay
47%5%13%23%10%
2371
16th to endDay
49%6%13%22%8%
2487
August1st to 15thDay
51%415%19%7%
2419
16th to endDay
42%414%25%12%
2333
September1st to 15thDay
44%39%28%12%
2127
16th to endDay
38%313%27%15%1
1980
October1st to 15thDay
53%210%21%10%
1907
16th to endDay
59%312%17%6%
1728
November1st to 15thDay
53%5%12%17%9%1
1716
16th to endDay
58%412%14%8%1
1670
December1st to 15thDay
64%311%14%4
1560
16th to endDay
71%46%9%8%
1664
January1st to 15thNight
60%5%11%14%6%
2662
16th to endNight
59%5%9%17%7%
2688
February1st to 15thNight
65%48%14%7%
2270
16th to endNight
59%49%16%9%1
1893
March1st to 15thNight
57%38%20%7%1
2160
16th to endNight
50%39%17%15%2
2015
April1st to 15thNight
54%36%20%13%
1796
16th to endNight
46%49%22%14%2
1673
May1st to 15thNight
50%47%18%16%2
1567
16th to endNight
46%6%13%23%8%1
1497
June1st to 15thNight
55%5%11%19%7%
1440
16th to endNight
44%6%13%24%9%
1440
July1st to 15thNight
40%6%17%25%10%
1360
16th to endNight
40%7%15%24%11%
1418
August1st to 15thNight
40%5%17%26%9%
1505
16th to endNight
35%5%15%31%12%
1866
September1st to 15thNight
40%413%30%10%
1833
16th to endNight
34%5%12%32%14%1
1980
October1st to 15thNight
48%313%22%11%
2052
16th to endNight
56%411%19%7%
2494
November1st to 15thNight
54%411%19%8%1
2472
16th to endNight
56%311%19%7%1
2616
December1st to 15thNight
67%410%13%3
2730
16th to endNight
69%48%10%6%
2912

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
15%24%29%17%12%1
82
16th to endDay
23%25%25%18%6%1
64
February1st to 15thDay
28%15%30%18%6%
150
16th to endDay
21%17%29%24%6%1
239
March1st to 15thDay
31%12%22%26%6%
270
16th to endDay
24%17%27%16%11%4
288
April1st to 15thDay
30%13%24%23%6%1
270
16th to endDay
28%15%26%12%12%4
270
May1st to 15thDay
33%11%25%17%6%4
288
16th to endDay
25%13%28%21%9%1
331
June1st to 15thDay
30%11%28%17%10%2
315
16th to endDay
22%9%30%23%11%1
315
July1st to 15thDay
18%6%30%27%13%4
305
16th to endDay
17%7%29%26%14%4
326
August1st to 15thDay
18%7%25%23%20%5%
313
16th to endDay
18%8%17%24%21%9%
332
September1st to 15thDay
17%7%20%22%21%10%
315
16th to endDay
14%8%20%22%18%15%
314
October1st to 15thDay
21%10%22%23%16%6%
315
16th to endDay
29%11%24%24%10%
288
November1st to 15thDay
24%11%23%27%12%1
280
16th to endDay
26%16%22%20%14%1
200
December1st to 15thDay
20%18%31%21%6%2
90
16th to endDay
41%13%28%14%2
96
January1st to 15thNight
19%15%30%29%5%
765
16th to endNight
20%18%27%28%4
768
February1st to 15thNight
17%17%32%27%5%
704
16th to endNight
21%13%31%26%7%
631
March1st to 15thNight
26%15%25%28%3
720
16th to endNight
23%15%25%24%9%
768
April1st to 15thNight
25%16%24%27%6%
718
16th to endNight
24%16%26%23%8%
593
May1st to 15thNight
25%9%31%24%8%
487
16th to endNight
21%8%24%33%11%
375
June1st to 15thNight
28%6%20%32%10%
360
16th to endNight
19%423%38%13%
360
July1st to 15thNight
15%116%44%18%2
340
16th to endNight
14%317%41%21%1
376
August1st to 15thNight
16%215%36%28%
434
16th to endNight
16%416%33%25%3
720
September1st to 15thNight
18%6%18%36%18%2
720
16th to endNight
15%7%21%27%24%4
717
October1st to 15thNight
21%9%21%27%17%1
720
16th to endNight
29%11%25%23%9%
768
November1st to 15thNight
22%12%23%29%10%1
760
16th to endNight
22%13%26%24%11%1
780
December1st to 15thNight
27%14%27%24%4
780
16th to endNight
29%15%24%26%3
832
Page generated at 2018-01-12 22:01:34. Version ac04

Copyright 2018 A. Danko


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