Norway House
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Norway House clear sky chart from 2005-11-06 to 2024-02-05.

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
31%
25053
8%
80530
5%
24971
35%
24971
14%
60488

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 10thNight
23%
939
5%
4722
4%
926
28%
926
6%
3787
January11th to 20thNight
26%
935
5%
4730
4%
929
30%
929
6%
3985
January21st to endNight
24%
1038
5%
5119
4%
1023
28%
1023
5%
4217
February1st to 10thNight
32%
923
10%
2583
4%
923
37%
923
17%
1956
February11th to 20thNight
35%
874
14%
2314
6%
874
40%
874
20%
1682
February21st to endNight
32%
722
15%
1906
5%
722
38%
722
19%
1432
March1st to 10thNight
37%
720
14%
2160
10%
720
41%
720
18%
1564
March11th to 20thNight
29%
544
15%
1984
8%
544
40%
544
16%
1342
March21st to endNight
39%
594
17%
2170
15%
594
48%
594
21%
1390
April1st to 10thNight
38%
540
19%
1687
15%
540
46%
540
24%
1109
April11th to 20thNight
39%
533
17%
1599
10%
533
45%
533
20%
1122
April21st to endNight
39%
540
16%
1620
7%
540
43%
540
30%
1011
May1st to 10thNight
31%
540
9%
1297
3%
540
34%
540
25%
944
May11th to 20thNight
37%
531
6%
1241
4%
531
39%
531
29%
870
May21st to endNight
32%
584
0%
1358
0%
582
33%
582
26%
1013
June1st to 10thNight
41%
540
0%
1260
0%
540
41%
540
28%
899
June11th to 20thNight
37%
463
0%
1183
0%
463
37%
463
24%
852
June21st to endNight
44%
360
0%
1080
0%
360
44%
360
26%
710
July1st to 10thNight
45%
466
0%
1166
0%
466
45%
466
32%
758
July11th to 20thNight
48%
522
0%
1218
0%
522
48%
522
32%
844
July21st to endNight
54%
591
2%
1302
2%
558
55%
558
32%
905
August1st to 10thNight
54%
537
10%
1305
5%
534
56%
534
37%
843
August11th to 20thNight
51%
534
10%
1535
5%
534
52%
534
28%
993
August21st to endNight
37%
594
11%
1782
6%
594
41%
594
23%
1206
September1st to 10thNight
40%
540
14%
1650
11%
540
47%
540
25%
1067
September11th to 20thNight
35%
540
11%
1980
9%
540
41%
540
17%
1353
September21st to endNight
36%
540
15%
1980
12%
540
44%
540
17%
1329
October1st to 10thNight
28%
669
14%
2109
9%
669
34%
669
15%
1553
October11th to 20thNight
26%
850
8%
2290
4%
850
29%
850
13%
1859
October21st to endNight
17%
990
7%
2632
2%
990
21%
990
9%
2243
November1st to 10thNight
18%
925
5%
2591
2%
925
21%
925
7%
2250
November11th to 20thNight
18%
950
5%
2802
3%
950
20%
950
6%
2423
November21st to endNight
17%
950
4%
2850
1%
950
19%
950
6%
2444
December1st to 10thNight
24%
950
4%
2850
1%
950
27%
950
8%
2427
December11th to 20thNight
22%
950
9%
3443
4%
949
27%
949
8%
2605
December21st to endNight
29%
1035
6%
5032
5%
1026
35%
1026
7%
3501

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
13%10%48%7%45%5%6%7%30%
77887
Night
11%11%5%10%8%5%6%6%6%6%26%
80955
TransparencyDay
51%8%14%19%7%
77589
Night
56%7%13%17%7%
80834
SeeingDay
16%12%33%26%10%2
15273
Night
17%9%31%30%12%1
25101

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 10thDay
8%13%7%16%11%7%6%9%8%410%
2219
11th to 20thDay
5%9%6%18%17%7%8%5%10%6%9%
2199
21st to endDay
8%18%7%15%9%46%8%8%6%11%
2542
February1st to 10thDay
7%10%5%8%8%6%10%9%9%7%20%
1472
11th to 20thDay
6%10%410%9%5%7%8%8%8%25%
1534
21st to endDay
410%5%9%10%6%9%7%8%8%24%
1365
March1st to 10thDay
8%13%5%9%9%6%6%6%5%6%27%
1800
11th to 20thDay
10%10%5%8%7%45%47%7%33%
1973
21st to endDay
8%9%37%7%35%5%7%7%37%
2183
April1st to 10thDay
8%10%5%8%6%345%5%7%40%
2272
11th to 20thDay
11%8%48%7%36%446%38%
2312
21st to endDay
8%7%47%7%45%6%5%7%41%
2340
May1st to 10thDay
15%7%47%6%45%5%5%7%34%
2659
11th to 20thDay
13%6%25%5%35%5%6%7%44%
2655
21st to endDay
17%8%35%435%46%7%37%
2918
June1st to 10thDay
15%7%36%6%46%5%6%8%34%
2700
11th to 20thDay
18%7%46%5%45%6%5%8%34%
2772
21st to endDay
14%8%26%5%35%5%6%8%38%
2880
July1st to 10thDay
12%5%25%5%35%5%6%9%42%
2754
11th to 20thDay
14%5%245%35%6%6%9%40%
2700
21st to endDay
16%5%35%5%45%5%6%9%39%
2939
August1st to 10thDay
12%5%25%5%35%6%6%8%43%
2625
11th to 20thDay
14%4246%35%6%6%7%42%
2366
21st to endDay
21%6%35%5%345%6%7%34%
2574
September1st to 10thDay
16%7%26%6%45%5%6%8%35%
2307
11th to 20thDay
20%10%36%5%3446%5%34%
1980
21st to endDay
14%10%36%6%35%5%47%36%
1980
October1st to 10thDay
20%17%47%5%3346%6%25%
1832
11th to 20thDay
20%20%6%8%6%34445%18%
1668
21st to endDay
23%22%7%9%7%3433415%
1724
November1st to 10thDay
14%17%8%15%12%45%44412%
1487
11th to 20thDay
13%17%6%12%12%7%6%44415%
1375
21st to endDay
10%17%7%14%10%8%7%5%45%13%
1330
December1st to 10thDay
6%14%6%14%14%6%7%7%5%5%15%
1330
11th to 20thDay
9%13%8%14%12%5%8%6%7%7%13%
1679
21st to endDay
6%11%410%12%6%6%6%6%6%25%
2442
January1st to 10thNight
6%12%7%13%12%7%8%10%7%5%12%
4737
11th to 20thNight
49%6%21%16%6%9%7%8%5%9%
4709
21st to endNight
10%18%8%15%7%48%6%5%5%12%
5122
February1st to 10thNight
6%10%5%8%8%6%11%9%9%8%20%
2583
11th to 20thNight
6%10%5%8%9%5%8%8%9%7%26%
2313
21st to endNight
5%10%6%10%12%6%6%5%6%5%30%
1906
March1st to 10thNight
8%11%6%9%9%46%45%6%31%
2160
11th to 20thNight
11%10%49%8%45%5%46%34%
1984
21st to endNight
9%9%36%6%46%6%5%7%38%
2170
April1st to 10thNight
9%11%47%7%3445%6%41%
1687
11th to 20thNight
11%9%5%8%7%45%5%46%35%
1599
21st to endNight
6%7%36%6%36%6%6%9%42%
1620
May1st to 10thNight
18%9%36%4245%6%7%36%
1297
11th to 20thNight
14%8%26%6%435%6%6%41%
1241
21st to endNight
16%6%47%6%35%45%5%38%
1358
June1st to 10thNight
14%7%35%6%45%35%7%39%
1260
11th to 20thNight
15%6%37%6%46%6%5%7%36%
1183
21st to endNight
13%8%37%5%345%6%9%38%
1080
July1st to 10thNight
11%425%7%345%5%8%46%
1201
11th to 20thNight
12%6%34446%5%6%8%42%
1260
21st to endNight
10%4346%36%5%7%10%41%
1379
August1st to 10thNight
11%4244345%6%9%48%
1312
11th to 20thNight
13%435%5%345%6%10%43%
1535
21st to endNight
18%6%35%5%245%5%8%40%
1782
September1st to 10thNight
14%7%35%434447%44%
1650
11th to 20thNight
18%10%27%5%3445%7%35%
1980
21st to endNight
15%8%37%6%45%5%47%37%
1980
October1st to 10thNight
18%13%37%6%35%5%5%6%30%
2109
11th to 20thNight
20%17%5%8%43445%6%23%
2290
21st to endNight
23%20%6%10%6%34345%18%
2632
November1st to 10thNight
15%17%9%14%10%45%44415%
2591
11th to 20thNight
14%15%8%12%13%6%5%44415%
2802
21st to endNight
8%19%8%14%12%5%5%5%45%14%
2850
December1st to 10thNight
8%15%9%13%11%6%8%7%5%6%13%
2850
11th to 20thNight
8%13%6%10%9%6%7%8%5%7%20%
3518
21st to endNight
8%12%6%12%9%5%5%5%6%6%25%
5225

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 10thDay
69%7%10%12%2
2219
11th to 20thDay
70%6%9%12%3
2220
21st to endDay
67%9%12%8%4
2542
February1st to 10thDay
54%9%14%16%6%1
1472
11th to 20thDay
52%7%12%21%8%
1543
21st to endDay
54%7%11%19%8%
1365
March1st to 10thDay
57%7%12%15%9%
1800
11th to 20thDay
49%6%14%22%7%1
1975
21st to endDay
43%8%14%25%8%2
2183
April1st to 10thDay
43%8%12%23%14%1
2272
11th to 20thDay
47%6%8%21%17%
2312
21st to endDay
40%8%12%25%13%2
2340
May1st to 10thDay
48%8%12%23%9%
2659
11th to 20thDay
36%7%14%24%16%3
2659
21st to endDay
45%7%10%25%12%1
2918
June1st to 10thDay
44%10%14%21%10%
2700
11th to 20thDay
47%7%14%21%10%
2772
21st to endDay
42%10%16%23%9%
2880
July1st to 10thDay
35%10%18%26%11%1
2680
11th to 20thDay
37%9%19%26%8%
2619
21st to endDay
41%9%20%26%4
2776
August1st to 10thDay
35%12%22%26%6%
2608
11th to 20thDay
39%10%24%23%4
2366
21st to endDay
47%10%21%18%4
2574
September1st to 10thDay
45%9%19%20%5%1
2307
11th to 20thDay
50%8%18%20%3
1980
21st to endDay
47%7%19%22%5%
1980
October1st to 10thDay
59%7%14%15%4
1832
11th to 20thDay
68%7%12%11%2
1668
21st to endDay
73%6%9%10%2
1724
November1st to 10thDay
75%8%9%7%1
1487
11th to 20thDay
72%6%13%8%1
1375
21st to endDay
73%7%10%8%1
1330
December1st to 10thDay
66%9%11%10%4
1330
11th to 20thDay
65%9%11%12%3
1680
21st to endDay
54%9%10%21%6%1
2442
January1st to 10thNight
64%10%13%10%2
4737
11th to 20thNight
71%7%9%10%3
4750
21st to endNight
70%8%10%9%4
5122
February1st to 10thNight
54%8%14%18%6%
2583
11th to 20thNight
51%6%12%23%9%
2314
21st to endNight
56%410%21%8%
1906
March1st to 10thNight
53%5%12%20%9%
2160
11th to 20thNight
49%6%13%21%10%2
1984
21st to endNight
43%7%14%24%10%2
2170
April1st to 10thNight
44%5%9%23%17%2
1687
11th to 20thNight
49%6%6%20%17%2
1599
21st to endNight
37%6%12%28%15%2
1620
May1st to 10thNight
46%8%10%22%13%1
1297
11th to 20thNight
41%7%12%22%16%3
1241
21st to endNight
49%6%8%19%17%1
1358
June1st to 10thNight
42%8%13%22%14%1
1260
11th to 20thNight
44%9%12%21%13%1
1183
21st to endNight
41%8%18%25%8%
1080
July1st to 10thNight
35%7%15%28%14%
1166
11th to 20thNight
36%10%16%26%11%1
1218
21st to endNight
37%10%21%26%6%
1302
August1st to 10thNight
30%9%20%32%9%
1305
11th to 20thNight
37%9%22%27%6%
1535
21st to endNight
43%8%21%22%6%
1782
September1st to 10thNight
38%9%20%24%8%1
1650
11th to 20thNight
49%8%16%25%3
1980
21st to endNight
47%8%16%22%7%
1980
October1st to 10thNight
54%7%13%20%5%
2109
11th to 20thNight
62%8%14%14%2
2290
21st to endNight
69%8%10%11%2
2632
November1st to 10thNight
72%8%10%6%4
2591
11th to 20thNight
73%7%9%9%2
2802
21st to endNight
72%7%11%9%1
2850
December1st to 10thNight
69%9%12%8%3
2850
11th to 20thNight
59%8%14%14%5%
3516
21st to endNight
55%6%10%17%11%1
5225

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 10thDay
13%9%40%30%8%
270
11th to 20thDay
10%10%42%28%10%1
270
21st to endDay
20%11%32%29%9%
297
February1st to 10thDay
10%9%40%30%9%3
252
11th to 20thDay
11%11%41%24%13%
240
21st to endDay
7%13%42%21%14%4
198
March1st to 10thDay
10%13%33%23%18%3
240
11th to 20thDay
8%17%43%22%8%3
240
21st to endDay
12%14%34%28%8%3
269
April1st to 10thDay
12%8%42%27%10%2
532
11th to 20thDay
16%12%30%29%11%2
590
21st to endDay
10%14%36%30%9%1
600
May1st to 10thDay
17%12%36%26%8%
603
11th to 20thDay
13%16%34%25%9%2
625
21st to endDay
19%13%33%26%8%1
679
June1st to 10thDay
18%14%31%23%11%2
630
11th to 20thDay
20%13%32%24%8%3
630
21st to endDay
17%9%29%33%9%3
630
July1st to 10thDay
13%10%34%30%10%4
621
11th to 20thDay
15%9%29%29%13%5%
618
21st to endDay
16%9%28%28%15%5%
684
August1st to 10thDay
14%10%30%29%13%3
626
11th to 20thDay
14%9%31%26%15%5%
615
21st to endDay
22%10%27%26%13%2
693
September1st to 10thDay
20%14%34%24%8%1
597
11th to 20thDay
26%15%29%22%7%1
270
21st to endDay
19%14%36%23%7%
270
October1st to 10thDay
26%14%36%15%6%3
270
11th to 20thDay
27%16%36%14%6%1
270
21st to endDay
33%11%22%25%8%1
297
November1st to 10thDay
17%15%34%26%7%1
270
11th to 20thDay
17%14%43%19%6%1
270
21st to endDay
23%17%35%21%4
270
December1st to 10thDay
11%9%39%26%13%1
270
11th to 20thDay
14%14%39%24%8%1
270
21st to endDay
9%7%34%35%13%1
297
January1st to 10thNight
14%9%35%31%9%1
950
11th to 20thNight
12%9%35%32%10%1
950
21st to endNight
19%8%34%28%10%
1045
February1st to 10thNight
10%7%37%33%11%1
923
11th to 20thNight
12%8%31%32%15%4
879
21st to endNight
8%7%37%32%15%1
722
March1st to 10thNight
12%7%29%35%15%2
720
11th to 20thNight
15%12%35%26%11%1
544
21st to endNight
15%8%32%27%15%3
594
April1st to 10thNight
13%8%33%31%13%2
540
11th to 20thNight
15%7%29%35%12%2
533
21st to endNight
9%7%39%32%12%1
540
May1st to 10thNight
20%7%35%28%9%1
540
11th to 20thNight
18%12%29%31%10%1
531
21st to endNight
19%9%34%29%9%
584
June1st to 10thNight
18%7%29%31%14%1
540
11th to 20thNight
18%7%30%30%13%2
463
21st to endNight
14%6%28%36%15%1
360
July1st to 10thNight
12%6%30%35%16%
466
11th to 20thNight
16%6%25%32%19%3
522
21st to endNight
11%6%21%36%21%4
591
August1st to 10thNight
12%5%24%38%20%1
537
11th to 20thNight
14%6%23%35%21%1
534
21st to endNight
20%7%29%31%13%
594
September1st to 10thNight
18%9%29%31%13%1
540
11th to 20thNight
25%8%26%32%7%1
540
21st to endNight
19%7%33%31%10%
540
October1st to 10thNight
25%8%32%27%7%1
669
11th to 20thNight
31%10%25%24%9%1
850
21st to endNight
32%11%28%23%6%1
990
November1st to 10thNight
21%15%31%25%7%1
925
11th to 20thNight
22%10%33%25%9%1
950
21st to endNight
17%14%36%26%6%1
950
December1st to 10thNight
14%9%35%30%10%2
950
11th to 20thNight
17%10%35%27%10%2
950
21st to endNight
15%7%31%32%13%2
1045
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