Northdog Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Northdog Observatory clear sky chart from 2005-11-05 to 2017-09-18.

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
39%
15034
9%
46689
6%
15008
43%
15008
16%
34064

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
32%
925
8%
2865
5%
925
35%
925
11%
2256
January16th to endNight
31%
842
11%
2877
7%
842
36%
842
13%
2115
February1st to 15thNight
35%
697
8%
2464
7%
696
38%
696
12%
1825
February16th to endNight
48%
632
10%
2025
11%
632
50%
632
17%
1476
March1st to 15thNight
34%
720
12%
2160
8%
720
38%
720
16%
1605
March16th to endNight
42%
768
12%
2008
7%
767
44%
767
19%
1537
April1st to 15thNight
38%
689
9%
1769
4%
689
40%
689
17%
1370
April16th to endNight
38%
390
9%
1470
11%
390
42%
390
14%
1038
May1st to 15thNight
42%
359
4%
1374
2%
359
44%
359
17%
909
May16th to endNight
45%
374
0%
1173
0%
374
45%
374
20%
810
June1st to 15thNight
46%
360
0%
1080
0%
360
46%
360
19%
771
June16th to endNight
46%
360
0%
1080
0%
360
46%
360
22%
745
July1st to 15thNight
53%
340
0%
1020
0%
340
53%
340
24%
676
July16th to endNight
55%
376
0%
1132
0%
354
56%
354
23%
754
August1st to 15thNight
64%
360
5%
1432
7%
358
65%
358
23%
827
August16th to endNight
48%
476
12%
1622
12%
476
52%
476
20%
1056
September1st to 15thNight
54%
720
12%
1800
7%
720
55%
720
31%
1230
September16th to endNight
43%
667
15%
1812
8%
667
47%
667
24%
1242
October1st to 15thNight
38%
660
12%
2015
8%
660
44%
660
18%
1451
October16th to endNight
32%
704
10%
2304
5%
704
39%
704
14%
1704
November1st to 15thNight
31%
790
12%
2540
8%
790
37%
790
14%
1880
November16th to endNight
32%
903
9%
2715
5%
903
36%
903
12%
2134
December1st to 15thNight
31%
930
10%
2880
6%
930
34%
930
12%
2282
December16th to endNight
35%
992
11%
3072
6%
992
39%
992
13%
2371

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
11%9%47%6%35%5%6%7%32%
48153
Night
10%11%5%8%7%45%5%5%7%29%
46822
TransparencyDay
49%8%17%18%5%
47787
Night
52%7%15%18%6%
46693
SeeingDay
14%6%22%30%19%5%
6883
Night
15%6%25%33%17%2
15048

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
10%14%6%8%6%45%5%6%6%24%
1074
16th to endDay
10%13%5%8%6%46%45%6%26%
1355
February1st to 15thDay
9%10%411%8%45%6%6%7%26%
1400
16th to endDay
8%14%6%9%8%5%6%446%23%
1447
March1st to 15thDay
7%12%6%10%7%36%5%6%6%26%
1800
16th to endDay
8%14%5%9%6%45%6%6%8%24%
2211
April1st to 15thDay
7%9%5%8%7%36%6%5%7%31%
2179
16th to endDay
10%10%37%7%35%6%7%8%28%
2490
May1st to 15thDay
8%7%37%7%36%6%5%7%36%
2575
16th to endDay
15%7%36%6%46%5%6%7%29%
2936
June1st to 15thDay
13%7%47%6%46%6%5%8%29%
2880
16th to endDay
13%7%36%6%35%5%5%7%35%
2880
July1st to 15thDay
13%5%25%435%6%5%8%39%
2880
16th to endDay
8%435%5%35%5%7%8%41%
2955
August1st to 15thDay
9%425%5%35%5%7%9%40%
2520
16th to endDay
10%6%26%6%36%5%6%9%35%
2578
September1st to 15thDay
14%5%36%42445%6%42%
2160
16th to endDay
12%6%25%5%35%46%8%39%
1870
October1st to 15thDay
13%10%5%8%5%45%45%7%29%
1615
16th to endDay
14%11%47%6%35%5%6%6%29%
1565
November1st to 15thDay
13%13%6%8%6%35%36%5%26%
1306
16th to endDay
7%13%5%11%9%36%446%25%
1245
December1st to 15thDay
13%13%7%7%9%46%7%35%20%
1080
16th to endDay
8%15%5%9%8%46%5%7%6%22%
1152
January1st to 15thNight
8%13%7%10%9%5%6%446%23%
2865
16th to endNight
10%13%5%8%7%35%46%7%27%
2877
February1st to 15thNight
10%13%48%8%45%46%7%26%
2452
16th to endNight
5%12%5%9%8%46%5%6%8%27%
2025
March1st to 15thNight
9%12%6%9%9%35%45%6%28%
2160
16th to endNight
9%13%5%7%6%45%5%6%7%27%
2007
April1st to 15thNight
8%9%410%7%5%7%7%6%7%24%
1769
16th to endNight
11%10%5%7%7%35%45%7%31%
1470
May1st to 15thNight
10%8%46%6%45%6%48%33%
1374
16th to endNight
13%9%45%5%345%8%8%32%
1173
June1st to 15thNight
13%8%36%6%35%46%8%32%
1080
16th to endNight
15%6%26%5%25%5%6%8%34%
1080
July1st to 15thNight
10%425%5%35%6%6%8%40%
1080
16th to endNight
10%416%6%5%7%6%7%8%34%
1210
August1st to 15thNight
8%314436%5%7%8%44%
1440
16th to endNight
9%5%36%6%36%5%7%9%36%
1622
September1st to 15thNight
8%5%26%5%3446%8%41%
1800
16th to endNight
13%6%35%5%35%5%6%9%36%
1812
October1st to 15thNight
13%9%37%5%35%5%5%7%32%
2015
16th to endNight
12%12%48%7%35%5%5%6%28%
2304
November1st to 15thNight
12%13%6%7%6%35%5%5%6%27%
2540
16th to endNight
10%15%6%10%7%35%445%25%
2715
December1st to 15thNight
11%13%6%9%8%45%5%5%6%23%
2880
16th to endNight
7%14%6%9%8%46%6%6%6%23%
3072

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
57%6%16%14%31
1074
16th to endDay
56%7%11%17%6%1
1355
February1st to 15thDay
54%8%15%14%6%
1400
16th to endDay
61%6%14%12%5%
1447
March1st to 15thDay
55%7%14%16%5%
1800
16th to endDay
55%8%17%14%3
2211
April1st to 15thDay
50%9%16%17%6%
2179
16th to endDay
52%8%14%17%6%
2490
May1st to 15thDay
46%7%14%19%11%
2575
16th to endDay
50%8%14%18%8%
2941
June1st to 15thDay
51%9%15%19%5%
2880
16th to endDay
46%7%16%20%8%
2880
July1st to 15thDay
41%9%16%24%7%
2711
16th to endDay
37%10%24%21%6%
2770
August1st to 15thDay
38%11%22%23%4
2503
16th to endDay
43%9%22%20%4
2578
September1st to 15thDay
41%7%23%21%6%
2160
16th to endDay
41%9%17%23%7%
1870
October1st to 15thDay
53%6%17%19%2
1615
16th to endDay
52%7%16%19%3
1565
November1st to 15thDay
58%414%16%5%
1306
16th to endDay
59%6%13%14%41
1245
December1st to 15thDay
64%7%12%11%3
1080
16th to endDay
59%7%14%13%5%
1152
January1st to 15thNight
61%6%13%13%21
2865
16th to endNight
55%7%15%14%5%1
2877
February1st to 15thNight
56%7%15%14%5%
2464
16th to endNight
53%6%17%17%4
2025
March1st to 15thNight
56%5%13%18%6%
2160
16th to endNight
53%8%13%17%7%
2011
April1st to 15thNight
55%7%12%16%7%
1769
16th to endNight
51%8%14%17%7%
1470
May1st to 15thNight
47%6%11%20%12%1
1375
16th to endNight
46%7%16%18%10%
1173
June1st to 15thNight
49%7%16%20%6%
1080
16th to endNight
45%7%16%21%9%
1080
July1st to 15thNight
38%10%15%25%8%
1020
16th to endNight
41%9%23%19%5%
1132
August1st to 15thNight
32%11%21%27%7%
1432
16th to endNight
41%9%20%21%6%
1622
September1st to 15thNight
38%8%20%22%8%
1800
16th to endNight
42%7%17%22%9%
1812
October1st to 15thNight
49%8%16%20%4
2015
16th to endNight
55%7%15%18%3
2304
November1st to 15thNight
55%6%13%17%5%
2540
16th to endNight
59%8%10%15%41
2715
December1st to 15thNight
61%7%13%13%4
2880
16th to endNight
58%7%12%16%4
3072

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%315%30%20%11%
60
16th to endDay
14%320%40%15%6%
64
February1st to 15thDay
6%15%20%33%16%8%
60
16th to endDay
14%6%18%30%26%3
197
March1st to 15thDay
15%6%29%32%13%1
270
16th to endDay
15%320%38%18%3
288
April1st to 15thDay
12%9%24%34%14%4
269
16th to endDay
18%8%24%29%16%2
270
May1st to 15thDay
11%10%24%31%20%1
352
16th to endDay
17%5%19%29%21%6%
652
June1st to 15thDay
15%6%24%27%21%4
675
16th to endDay
16%5%20%28%23%6%
675
July1st to 15thDay
14%423%31%20%5%
645
16th to endDay
9%6%24%32%22%4
623
August1st to 15thDay
11%422%24%26%10%
315
16th to endDay
12%10%27%36%11%1
332
September1st to 15thDay
18%7%25%24%17%6%
315
16th to endDay
14%10%27%26%15%4
264
October1st to 15thDay
23%11%21%25%14%4
220
16th to endDay
31%213%23%22%6%
93
November1st to 15thDay
15%6%30%36%11%
60
16th to endDay
18%8%13%33%11%15%
60
December1st to 15thDay
8%318%30%30%10%
60
16th to endDay
18%12%14%34%12%7%
64
January1st to 15thNight
14%7%24%33%15%3
930
16th to endNight
16%10%28%30%13%1
842
February1st to 15thNight
17%7%25%26%18%4
704
16th to endNight
11%318%36%25%3
632
March1st to 15thNight
13%7%30%33%13%1
720
16th to endNight
15%320%38%19%2
768
April1st to 15thNight
12%5%29%35%15%1
689
16th to endNight
16%7%25%27%21%1
390
May1st to 15thNight
14%6%27%35%14%1
360
16th to endNight
16%423%32%22%1
375
June1st to 15thNight
16%321%29%26%1
360
16th to endNight
17%322%32%21%2
360
July1st to 15thNight
13%223%38%19%2
340
16th to endNight
10%320%36%25%2
376
August1st to 15thNight
10%117%31%34%4
360
16th to endNight
12%225%37%19%1
476
September1st to 15thNight
12%321%36%23%2
720
16th to endNight
15%7%25%33%14%2
667
October1st to 15thNight
19%5%27%34%12%
660
16th to endNight
18%8%28%30%11%1
704
November1st to 15thNight
19%7%30%30%10%1
790
16th to endNight
17%8%25%33%12%3
903
December1st to 15thNight
17%7%24%32%15%2
930
16th to endNight
14%6%23%32%19%3
992
Page generated at 2017-09-19 05:32:26. Version ac04

Copyright 2017 A. Danko


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