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 2017-09-20.

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
40%
15064
9%
46714
6%
15037
43%
15037
16%
34200

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
33%
926
7%
2865
5%
925
35%
925
11%
2279
January16th to endNight
31%
855
11%
2880
8%
855
36%
855
13%
2136
February1st to 15thNight
39%
697
8%
2464
8%
696
42%
696
13%
1817
February16th to endNight
48%
632
11%
2028
12%
632
50%
632
17%
1482
March1st to 15thNight
35%
720
12%
2160
8%
720
39%
720
16%
1625
March16th to endNight
43%
768
11%
2012
7%
767
45%
767
19%
1519
April1st to 15thNight
37%
680
10%
1760
5%
680
40%
680
18%
1360
April16th to endNight
40%
400
8%
1480
9%
400
44%
400
14%
1057
May1st to 15thNight
40%
359
4%
1362
2%
359
42%
359
18%
890
May16th to endNight
47%
374
0%
1184
0%
374
47%
374
20%
827
June1st to 15thNight
46%
360
0%
1080
0%
360
46%
360
18%
782
June16th to endNight
50%
360
0%
1080
0%
360
50%
360
22%
749
July1st to 15thNight
53%
340
0%
1020
0%
340
53%
340
25%
673
July16th to endNight
56%
376
0%
1128
0%
354
58%
354
22%
746
August1st to 15thNight
64%
360
5%
1432
6%
358
65%
358
24%
823
August16th to endNight
50%
472
13%
1618
13%
472
54%
472
22%
1052
September1st to 15thNight
54%
720
13%
1800
8%
720
55%
720
31%
1229
September16th to endNight
44%
675
15%
1839
8%
675
48%
675
24%
1282
October1st to 15thNight
40%
660
12%
2018
7%
660
45%
660
17%
1461
October16th to endNight
35%
704
10%
2296
4%
704
42%
704
14%
1705
November1st to 15thNight
30%
803
12%
2553
7%
803
35%
803
14%
1908
November16th to endNight
32%
901
8%
2703
4%
901
36%
901
11%
2130
December1st to 15thNight
33%
930
10%
2880
7%
930
36%
930
12%
2302
December16th to endNight
38%
992
11%
3072
6%
992
42%
992
13%
2366

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
12%9%46%6%35%5%6%7%32%
48180
Night
11%11%47%7%35%5%5%7%29%
46844
TransparencyDay
49%8%17%18%5%
47814
Night
52%8%15%17%5%
46715
SeeingDay
15%6%22%29%20%5%
6883
Night
15%5%24%34%17%2
15077

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
11%15%8%8%6%35%46%7%23%
1074
16th to endDay
11%14%5%8%6%36%5%5%5%26%
1354
February1st to 15thDay
10%11%5%8%9%5%6%5%5%7%25%
1400
16th to endDay
9%12%6%9%9%5%6%5%5%6%23%
1445
March1st to 15thDay
9%11%6%8%6%45%5%6%6%27%
1800
16th to endDay
9%13%6%9%7%35%6%6%7%25%
2208
April1st to 15thDay
8%10%47%6%46%6%6%6%31%
2188
16th to endDay
11%10%36%6%46%5%6%7%30%
2478
May1st to 15thDay
10%6%35%6%46%5%6%7%36%
2589
16th to endDay
15%7%36%6%35%5%5%8%30%
2924
June1st to 15thDay
15%6%36%7%35%6%6%7%30%
2880
16th to endDay
14%6%26%6%35%5%6%8%35%
2880
July1st to 15thDay
14%5%25%435%6%5%7%40%
2880
16th to endDay
10%5%245%35%5%7%8%41%
2962
August1st to 15thDay
10%5%245%35%5%7%8%41%
2520
16th to endDay
11%5%27%6%45%6%6%8%35%
2582
September1st to 15thDay
15%5%25%5%2445%5%42%
2160
16th to endDay
13%6%26%5%3445%7%39%
1890
October1st to 15thDay
14%10%5%7%5%25%45%6%31%
1609
16th to endDay
13%12%47%6%245%5%7%30%
1576
November1st to 15thDay
11%14%5%9%7%34346%27%
1292
16th to endDay
8%13%5%10%9%35%5%5%7%26%
1257
December1st to 15thDay
15%14%5%8%10%36%45%5%20%
1080
16th to endDay
9%15%5%9%7%36%6%6%7%22%
1152
January1st to 15thNight
9%13%6%11%8%46%446%23%
2865
16th to endNight
10%14%6%7%6%3445%7%27%
2880
February1st to 15thNight
11%13%47%8%45%45%7%26%
2452
16th to endNight
6%11%5%9%8%46%5%6%7%28%
2028
March1st to 15thNight
10%12%6%8%7%45%45%6%28%
2160
16th to endNight
10%13%5%7%6%36%47%7%28%
2009
April1st to 15thNight
8%10%49%8%5%6%6%6%6%26%
1760
16th to endNight
13%10%47%6%36%5%5%6%30%
1480
May1st to 15thNight
11%9%36%6%35%5%5%7%35%
1361
16th to endNight
14%7%35%7%45%5%6%7%32%
1184
June1st to 15thNight
14%7%37%7%35%5%5%7%31%
1080
16th to endNight
15%6%26%6%25%5%6%10%32%
1080
July1st to 15thNight
11%425%5%36%5%6%8%39%
1080
16th to endNight
11%425%6%37%6%7%9%35%
1206
August1st to 15thNight
8%325%4346%6%8%46%
1440
16th to endNight
11%425%6%45%6%7%8%37%
1618
September1st to 15thNight
10%7%25%6%3345%7%43%
1800
16th to endNight
14%5%25%5%25%6%6%9%36%
1839
October1st to 15thNight
13%8%47%5%346%6%7%32%
2018
16th to endNight
12%11%5%6%6%35%6%6%7%27%
2296
November1st to 15thNight
12%14%5%9%6%25%45%6%27%
2553
16th to endNight
10%15%6%10%8%3445%6%24%
2703
December1st to 15thNight
10%15%5%8%8%5%5%5%46%22%
2880
16th to endNight
7%15%5%9%7%46%6%5%7%22%
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
59%7%14%13%3
1074
16th to endDay
57%7%12%15%6%1
1354
February1st to 15thDay
55%8%15%13%7%
1400
16th to endDay
60%6%15%11%5%
1445
March1st to 15thDay
54%8%15%16%5%
1800
16th to endDay
54%10%17%14%3
2208
April1st to 15thDay
50%10%14%17%6%
2188
16th to endDay
51%9%13%17%6%
2478
May1st to 15thDay
45%7%16%18%11%
2589
16th to endDay
50%8%12%18%8%
2929
June1st to 15thDay
51%8%16%19%4
2880
16th to endDay
46%8%16%20%7%
2880
July1st to 15thDay
42%9%16%23%6%
2711
16th to endDay
38%10%24%20%5%
2777
August1st to 15thDay
37%11%23%22%4
2503
16th to endDay
43%10%21%20%4
2582
September1st to 15thDay
42%6%22%21%5%
2160
16th to endDay
43%8%17%23%7%
1890
October1st to 15thDay
52%8%16%20%2
1609
16th to endDay
52%7%16%19%3
1576
November1st to 15thDay
59%5%14%15%5%
1292
16th to endDay
58%7%14%13%41
1257
December1st to 15thDay
65%5%14%11%2
1080
16th to endDay
57%9%15%12%5%
1152
January1st to 15thNight
61%7%13%12%21
2865
16th to endNight
55%7%14%14%5%1
2880
February1st to 15thNight
56%6%14%15%5%
2464
16th to endNight
53%7%16%17%3
2028
March1st to 15thNight
56%6%13%17%6%
2160
16th to endNight
52%7%14%17%7%
2013
April1st to 15thNight
54%7%12%15%8%
1760
16th to endNight
52%7%14%17%6%
1480
May1st to 15thNight
47%5%10%22%12%1
1362
16th to endNight
48%6%13%19%11%
1184
June1st to 15thNight
51%7%13%20%5%
1080
16th to endNight
45%8%16%21%8%
1080
July1st to 15thNight
39%9%17%24%8%
1020
16th to endNight
39%10%25%18%5%
1128
August1st to 15thNight
32%10%22%27%7%
1432
16th to endNight
41%9%21%21%7%
1618
September1st to 15thNight
39%7%19%24%8%
1800
16th to endNight
41%10%16%21%9%
1839
October1st to 15thNight
49%9%15%20%4
2018
16th to endNight
53%9%16%17%3
2296
November1st to 15thNight
56%7%13%17%5%
2553
16th to endNight
60%8%12%13%31
2703
December1st to 15thNight
61%8%11%14%3
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
23%5%8%30%20%13%
60
16th to endDay
17%117%37%18%7%
64
February1st to 15thDay
16%5%20%33%16%8%
60
16th to endDay
13%320%34%23%3
187
March1st to 15thDay
15%5%30%31%14%1
270
16th to endDay
17%419%37%15%3
288
April1st to 15thDay
15%7%23%37%12%3
269
16th to endDay
17%9%24%29%17%2
270
May1st to 15thDay
12%8%26%30%19%2
366
16th to endDay
18%5%18%30%22%5%
640
June1st to 15thDay
14%8%23%26%23%3
675
16th to endDay
15%5%19%27%23%7%
675
July1st to 15thDay
14%423%30%22%5%
645
16th to endDay
12%420%34%23%5%
630
August1st to 15thDay
12%320%24%27%12%
315
16th to endDay
12%10%28%32%14%
332
September1st to 15thDay
19%8%21%24%19%6%
315
16th to endDay
16%9%29%22%16%5%
272
October1st to 15thDay
24%9%24%24%13%4
211
16th to endDay
28%113%32%18%5%
95
November1st to 15thDay
15%6%28%41%6%1
60
16th to endDay
15%6%20%31%15%11%
60
December1st to 15thDay
38%16%26%28%16%
60
16th to endDay
14%12%10%32%14%15%
64
January1st to 15thNight
15%7%22%35%15%3
930
16th to endNight
16%10%28%31%12%1
855
February1st to 15thNight
17%5%23%28%20%3
704
16th to endNight
10%319%37%25%2
632
March1st to 15thNight
14%6%30%32%14%1
720
16th to endNight
15%222%38%18%1
768
April1st to 15thNight
12%5%29%34%17%1
680
16th to endNight
17%6%22%33%19%1
400
May1st to 15thNight
13%8%24%37%13%2
360
16th to endNight
14%421%38%19%1
375
June1st to 15thNight
18%320%34%22%1
360
16th to endNight
16%121%33%23%2
360
July1st to 15thNight
13%222%38%21%2
340
16th to endNight
12%221%36%24%2
376
August1st to 15thNight
11%16%34%32%4
360
16th to endNight
13%225%38%19%1
472
September1st to 15thNight
13%221%35%24%2
720
16th to endNight
17%5%25%35%14%1
675
October1st to 15thNight
19%5%27%32%14%
660
16th to endNight
19%7%27%32%11%1
704
November1st to 15thNight
18%6%32%29%11%1
803
16th to endNight
15%7%25%34%13%2
901
December1st to 15thNight
17%7%23%32%15%2
930
16th to endNight
14%5%21%34%19%3
992
Page generated at 2017-09-21 05:18:17. Version ac04

Copyright 2017 A. Danko


Northdog Observatory Clear Sky Chart | Charts Home