Blue Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blue Mountain clear sky chart from 2005-11-06 to 2024-02-10.

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
41%
23981
11%
80829
8%
23924
45%
23924
18%
55261

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
32%
933
8%
4705
5%
926
38%
926
9%
3579
January11th to 20thNight
32%
939
11%
4656
6%
929
38%
929
9%
3490
January21st to endNight
26%
1031
7%
5172
5%
1023
31%
1023
8%
3550
February1st to 10thNight
35%
860
12%
2566
8%
860
41%
860
16%
1909
February11th to 20thNight
39%
703
13%
2272
12%
700
44%
700
17%
1637
February21st to endNight
53%
592
16%
1924
14%
592
57%
592
22%
1295
March1st to 10thNight
40%
720
13%
2161
10%
720
44%
720
18%
1589
March11th to 20thNight
38%
720
17%
1980
10%
720
44%
720
23%
1396
March21st to endNight
42%
720
12%
2106
9%
720
44%
720
20%
1527
April1st to 10thNight
45%
540
16%
1800
12%
540
50%
540
23%
1148
April11th to 20thNight
40%
533
15%
1619
10%
533
44%
533
22%
1095
April21st to endNight
38%
540
12%
1481
9%
540
41%
540
21%
1050
May1st to 10thNight
46%
540
13%
1440
7%
540
49%
540
32%
933
May11th to 20thNight
50%
461
9%
1346
7%
461
52%
461
31%
820
May21st to endNight
49%
388
2%
1322
2%
388
50%
388
20%
884
June1st to 10thNight
43%
360
0%
1080
0%
360
43%
360
21%
729
June11th to 20thNight
42%
360
0%
1080
0%
360
42%
360
18%
786
June21st to endNight
60%
360
0%
1080
0%
360
60%
360
29%
672
July1st to 10thNight
62%
350
0%
1133
0%
350
62%
350
31%
661
July11th to 20thNight
54%
348
1%
1218
1%
348
54%
348
25%
739
July21st to endNight
61%
394
8%
1302
9%
372
63%
372
35%
685
August1st to 10thNight
62%
503
11%
1391
7%
501
64%
501
35%
848
August11th to 20thNight
61%
534
13%
1497
10%
534
63%
534
34%
907
August21st to endNight
56%
594
19%
1785
14%
594
60%
594
34%
1067
September1st to 10thNight
51%
540
16%
1800
13%
540
54%
540
29%
1057
September11th to 20thNight
51%
540
18%
1800
17%
540
56%
540
26%
1090
September21st to endNight
49%
711
20%
2061
13%
711
56%
711
34%
1236
October1st to 10thNight
41%
720
18%
2160
11%
720
47%
720
23%
1458
October11th to 20thNight
44%
720
21%
2160
11%
720
51%
720
28%
1371
October21st to endNight
31%
972
15%
2680
7%
972
38%
972
20%
1930
November1st to 10thNight
30%
925
12%
2590
8%
925
33%
925
15%
2012
November11th to 20thNight
31%
950
10%
2660
6%
950
35%
950
14%
2113
November21st to endNight
26%
950
8%
2844
3%
950
32%
950
15%
2147
December1st to 10thNight
38%
950
9%
3040
5%
950
42%
950
15%
2262
December11th to 20thNight
27%
950
8%
3722
4%
949
33%
949
8%
2909
December21st to endNight
36%
1030
8%
5196
7%
1026
40%
1026
12%
2680

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
10%8%48%7%46%5%6%8%34%
77430
Night
8%9%49%8%46%6%6%8%33%
81464
TransparencyDay
47%9%16%21%7%1
77131
Night
47%8%15%21%8%1
81344
SeeingDay
13%8%26%31%17%5%
14609
Night
12%6%28%37%15%2
24040

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
6%12%8%16%12%5%6%45%5%21%
2219
11th to 20thDay
5%7%410%11%8%12%7%8%12%16%
2199
21st to endDay
6%12%7%15%9%45%5%6%8%25%
2442
February1st to 10thDay
8%12%6%12%9%5%7%7%6%7%21%
1613
11th to 20thDay
7%12%5%10%10%5%7%6%6%8%23%
1575
21st to endDay
5%9%6%12%11%5%9%5%6%8%24%
1332
March1st to 10thDay
7%12%6%11%9%5%7%7%6%8%21%
1798
11th to 20thDay
8%11%6%9%7%45%5%6%7%32%
1979
21st to endDay
8%11%5%11%8%46%5%5%7%30%
2250
April1st to 10thDay
6%10%38%8%5%5%5%6%7%36%
2160
11th to 20thDay
11%9%48%7%46%6%6%9%30%
2292
21st to endDay
13%9%47%5%45%5%6%9%34%
2479
May1st to 10thDay
11%8%37%7%46%5%6%7%35%
2520
11th to 20thDay
9%6%36%6%46%5%6%8%40%
2546
21st to endDay
15%6%37%6%45%6%7%8%33%
2953
June1st to 10thDay
14%7%37%7%46%6%6%8%33%
2880
11th to 20thDay
21%10%47%6%345%5%8%26%
2880
21st to endDay
12%6%37%6%36%6%7%9%36%
2880
July1st to 10thDay
9%5%25%5%36%5%7%10%43%
2790
11th to 20thDay
10%5%25%5%35%6%7%10%40%
2700
21st to endDay
9%4245%45%6%7%9%46%
2938
August1st to 10thDay
9%6%26%6%35%6%6%10%41%
2540
11th to 20thDay
10%5%245%35%5%6%10%44%
2401
21st to endDay
11%5%35%4345%5%10%44%
2571
September1st to 10thDay
11%5%25%5%35%5%5%9%44%
2160
11th to 20thDay
15%6%36%5%3446%7%40%
2160
21st to endDay
9%7%34435%5%5%8%47%
1895
October1st to 10thDay
13%10%47%5%35%5%5%7%37%
1800
11th to 20thDay
9%9%46%6%445%5%8%41%
1800
21st to endDay
9%11%6%11%7%45%6%5%6%30%
1656
November1st to 10thDay
13%13%6%10%8%5%46%46%25%
1488
11th to 20thDay
10%14%6%12%9%5%45%6%7%22%
1520
21st to endDay
7%10%6%13%10%5%6%7%5%8%23%
1331
December1st to 10thDay
6%12%6%13%10%46%5%6%5%26%
1140
11th to 20thDay
6%11%8%14%10%5%6%5%5%6%25%
1439
21st to endDay
37%5%9%7%35%5%6%8%41%
2104
January1st to 10thNight
6%12%6%14%11%6%6%6%7%7%18%
4726
11th to 20thNight
37%412%11%8%12%9%8%8%18%
4699
21st to endNight
7%12%5%12%10%45%5%7%8%26%
5214
February1st to 10thNight
7%11%5%12%10%47%7%7%8%23%
2566
11th to 20thNight
6%10%49%9%5%7%7%8%7%28%
2272
21st to endNight
28%5%10%9%47%6%8%10%30%
1924
March1st to 10thNight
6%10%5%10%8%5%7%6%7%8%28%
2161
11th to 20thNight
7%11%5%8%6%46%5%6%9%34%
1980
21st to endNight
8%9%49%9%46%7%7%8%29%
2106
April1st to 10thNight
5%10%37%7%47%5%6%8%40%
1800
11th to 20thNight
9%9%37%8%46%5%7%9%33%
1619
21st to endNight
14%8%37%8%445%5%7%35%
1481
May1st to 10thNight
11%6%35%5%346%7%10%40%
1440
11th to 20thNight
9%5%35%425%5%7%9%45%
1346
21st to endNight
13%7%25%7%46%6%6%8%35%
1322
June1st to 10thNight
13%7%27%7%45%5%6%8%35%
1080
11th to 20thNight
17%9%36%6%45%6%6%8%30%
1080
21st to endNight
9%325%5%47%46%10%44%
1080
July1st to 10thNight
8%326%5%25%5%6%11%47%
1167
11th to 20thNight
8%5%25%6%36%46%10%44%
1260
21st to endNight
5%3244335%7%9%55%
1379
August1st to 10thNight
6%325%5%35%5%6%9%51%
1398
11th to 20thNight
8%315%6%25%5%8%11%47%
1497
21st to endNight
8%5%245%445%7%8%49%
1785
September1st to 10thNight
10%6%25%5%245%7%8%46%
1800
11th to 20thNight
11%6%25%435%46%8%46%
1800
21st to endNight
7%6%25%4346%6%8%49%
2061
October1st to 10thNight
12%11%36%6%34447%40%
2160
11th to 20thNight
8%9%36%5%3445%7%44%
2160
21st to endNight
9%11%5%10%6%45%45%6%35%
2680
November1st to 10thNight
15%13%6%8%7%45%5%6%6%24%
2590
11th to 20thNight
9%11%414%9%5%7%5%6%6%24%
2660
21st to endNight
7%11%6%12%10%36%46%9%27%
2844
December1st to 10thNight
7%10%5%10%10%6%8%7%7%7%24%
3040
11th to 20thNight
8%13%7%13%9%5%6%6%6%8%18%
3753
21st to endNight
36%38%8%46%5%5%6%47%
5534

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
63%8%10%13%6%
2219
11th to 20thDay
58%8%11%17%6%1
2220
21st to endDay
56%7%14%17%6%
2442
February1st to 10thDay
58%7%13%15%8%
1613
11th to 20thDay
55%7%15%15%8%1
1584
21st to endDay
55%8%11%18%8%1
1332
March1st to 10thDay
59%8%14%14%4
1798
11th to 20thDay
50%8%15%20%7%
1980
21st to endDay
54%9%15%17%5%
2250
April1st to 10thDay
45%8%15%20%11%
2160
11th to 20thDay
49%8%14%20%9%1
2292
21st to endDay
46%8%15%22%8%1
2479
May1st to 10thDay
45%7%13%23%10%1
2520
11th to 20thDay
40%8%13%26%12%1
2550
21st to endDay
47%9%13%20%10%1
2954
June1st to 10thDay
46%10%16%18%8%1
2880
11th to 20thDay
56%8%13%15%7%
2880
21st to endDay
43%10%19%22%6%
2880
July1st to 10thDay
34%11%22%25%8%
2716
11th to 20thDay
37%11%24%24%4
2619
21st to endDay
32%11%24%27%5%
2775
August1st to 10thDay
37%11%23%24%4
2522
11th to 20thDay
34%11%25%25%5%
2401
21st to endDay
35%8%22%30%5%1
2571
September1st to 10thDay
37%8%19%24%10%2
2160
11th to 20thDay
43%7%17%26%6%
2160
21st to endDay
34%8%19%27%10%1
1895
October1st to 10thDay
45%8%16%23%7%
1800
11th to 20thDay
42%7%16%28%8%
1800
21st to endDay
52%9%14%19%5%
1656
November1st to 10thDay
59%8%13%14%6%
1488
11th to 20thDay
60%10%13%13%4
1520
21st to endDay
59%9%15%15%3
1331
December1st to 10thDay
56%9%12%16%6%1
1140
11th to 20thDay
59%7%15%13%6%
1440
21st to endDay
39%7%14%19%19%2
2104
January1st to 10thNight
60%8%13%13%5%
4726
11th to 20thNight
59%7%13%14%6%1
4740
21st to endNight
54%8%15%18%5%
5214
February1st to 10thNight
54%7%13%18%8%
2566
11th to 20thNight
51%8%15%17%8%
2273
21st to endNight
45%7%16%22%10%
1924
March1st to 10thNight
50%10%15%18%7%
2161
11th to 20thNight
46%8%14%22%10%
1980
21st to endNight
49%8%16%18%9%
2106
April1st to 10thNight
41%7%14%22%15%1
1800
11th to 20thNight
46%6%13%22%12%1
1619
21st to endNight
48%6%12%21%11%2
1481
May1st to 10thNight
38%6%13%25%18%1
1440
11th to 20thNight
34%7%12%28%16%3
1346
21st to endNight
44%9%14%21%11%1
1322
June1st to 10thNight
46%7%16%22%9%2
1080
11th to 20thNight
49%10%15%18%8%1
1080
21st to endNight
35%9%24%23%9%1
1080
July1st to 10thNight
30%10%22%31%6%1
1133
11th to 20thNight
35%10%23%27%6%
1218
21st to endNight
24%9%29%31%6%1
1302
August1st to 10thNight
28%11%23%31%7%
1391
11th to 20thNight
30%9%24%28%7%1
1497
21st to endNight
31%8%17%35%10%
1785
September1st to 10thNight
33%8%17%28%10%4
1800
11th to 20thNight
35%9%15%30%10%1
1800
21st to endNight
31%7%17%30%13%2
2061
October1st to 10thNight
45%6%15%25%8%
2160
11th to 20thNight
38%6%15%28%12%1
2160
21st to endNight
49%7%13%22%8%
2680
November1st to 10thNight
58%7%13%16%6%1
2590
11th to 20thNight
59%8%14%14%4
2660
21st to endNight
54%9%17%15%4
2844
December1st to 10thNight
55%7%15%16%5%1
3040
11th to 20thNight
61%9%13%12%4
3751
21st to endNight
36%7%13%26%17%2
5534

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
12%9%23%35%16%5%
180
11th to 20thDay
13%228%29%22%5%
180
21st to endDay
12%9%25%31%19%5%
198
February1st to 10thDay
12%7%33%33%13%1
267
11th to 20thDay
10%5%31%35%17%3
240
21st to endDay
5%5%24%38%22%6%
198
March1st to 10thDay
9%7%28%37%16%3
266
11th to 20thDay
11%7%35%28%13%6%
420
21st to endDay
12%7%30%33%15%3
462
April1st to 10thDay
9%10%33%32%11%5%
420
11th to 20thDay
13%10%31%31%11%4
412
21st to endDay
16%10%31%28%12%3
559
May1st to 10thDay
13%9%26%30%17%5%
603
11th to 20thDay
9%9%23%32%20%6%
625
21st to endDay
14%7%24%28%19%9%
679
June1st to 10thDay
14%8%27%35%13%3
630
11th to 20thDay
23%10%24%23%16%4
630
21st to endDay
13%7%21%30%21%8%
630
July1st to 10thDay
12%5%21%36%21%6%
621
11th to 20thDay
11%7%23%32%21%6%
618
21st to endDay
8%423%32%25%7%
684
August1st to 10thDay
12%5%21%30%23%9%
626
11th to 20thDay
10%8%20%34%24%4
539
21st to endDay
15%5%25%29%22%5%
495
September1st to 10thDay
15%8%31%28%14%4
450
11th to 20thDay
20%7%27%31%13%2
450
21st to endDay
15%11%23%31%18%3
360
October1st to 10thDay
15%427%36%11%6%
270
11th to 20thDay
13%9%29%35%11%3
270
21st to endDay
14%9%34%29%11%3
297
November1st to 10thDay
19%7%29%30%13%2
270
11th to 20thDay
15%10%34%31%8%1
270
21st to endDay
6%13%31%37%12%3
232
December1st to 10thDay
8%7%22%36%21%7%
180
11th to 20thDay
8%9%34%37%11%1
180
21st to endDay
8%5%26%33%19%9%
198
January1st to 10thNight
11%7%31%34%15%1
950
11th to 20thNight
9%6%32%39%11%1
950
21st to endNight
14%8%33%34%10%1
1045
February1st to 10thNight
11%6%27%37%17%2
860
11th to 20thNight
10%5%29%37%15%3
704
21st to endNight
5%322%39%27%4
592
March1st to 10thNight
10%5%30%39%14%2
720
11th to 20thNight
9%7%34%35%13%1
720
21st to endNight
12%7%27%37%15%3
720
April1st to 10thNight
9%7%29%37%15%3
540
11th to 20thNight
13%8%32%30%15%2
533
21st to endNight
16%7%28%36%12%1
540
May1st to 10thNight
13%6%27%36%15%2
540
11th to 20thNight
11%6%27%35%19%3
461
21st to endNight
17%7%20%34%20%2
389
June1st to 10thNight
16%428%33%16%3
360
11th to 20thNight
21%423%30%18%3
360
21st to endNight
9%422%41%23%2
360
July1st to 10thNight
9%419%46%21%2
350
11th to 20thNight
11%5%22%43%18%1
348
21st to endNight
7%423%42%22%3
394
August1st to 10thNight
8%420%36%29%3
503
11th to 20thNight
8%419%39%27%3
534
21st to endNight
9%325%40%22%2
594
September1st to 10thNight
13%228%38%17%2
540
11th to 20thNight
13%425%41%16%1
540
21st to endNight
11%6%30%39%13%1
711
October1st to 10thNight
18%7%27%35%13%1
720
11th to 20thNight
13%5%27%39%14%3
720
21st to endNight
16%9%33%33%9%1
972
November1st to 10thNight
21%6%28%33%10%1
925
11th to 20thNight
13%6%33%34%12%2
950
21st to endNight
10%8%36%36%9%1
950
December1st to 10thNight
10%6%29%37%15%3
950
11th to 20thNight
12%8%29%38%11%1
950
21st to endNight
9%427%39%19%2
1045
Page generated at 2024-02-07 05:11:54. Version ac07

Copyright 2024 Attilla Danko


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