Blue Mountain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blue Mountain clear sky chart from 2005-11-05 to 2017-12-02.

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%
15813
11%
47720
7%
15786
44%
15786
19%
33922

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
31%
895
8%
2685
5%
895
34%
895
14%
2045
January16th to endNight
29%
960
12%
2880
7%
960
35%
960
15%
2170
February1st to 15thNight
39%
764
10%
2347
7%
761
43%
761
16%
1745
February16th to endNight
45%
632
13%
2052
11%
632
49%
632
18%
1491
March1st to 15thNight
37%
720
13%
2100
9%
720
42%
720
17%
1561
March16th to endNight
37%
720
12%
2064
8%
720
40%
720
17%
1571
April1st to 15thNight
41%
539
14%
1751
11%
539
46%
539
21%
1155
April16th to endNight
39%
540
13%
1527
9%
540
43%
540
22%
1063
May1st to 15thNight
46%
539
10%
1440
6%
539
48%
539
29%
957
May16th to endNight
49%
385
3%
1296
3%
385
50%
385
21%
863
June1st to 15thNight
43%
360
0%
1080
0%
360
43%
360
18%
774
June16th to endNight
53%
360
0%
1080
0%
360
53%
360
22%
747
July1st to 15thNight
60%
340
0%
1128
0%
340
60%
340
28%
674
July16th to endNight
59%
376
5%
1239
6%
354
59%
354
29%
714
August1st to 15thNight
66%
517
10%
1411
7%
515
68%
515
34%
876
August16th to endNight
58%
573
17%
1713
13%
573
62%
573
35%
1006
September1st to 15thNight
54%
540
15%
1800
13%
540
57%
540
30%
1057
September16th to endNight
52%
650
20%
1974
15%
650
59%
650
34%
1160
October1st to 15thNight
41%
720
16%
2160
10%
720
47%
720
22%
1488
October16th to endNight
36%
888
16%
2507
9%
888
42%
888
21%
1761
November1st to 15thNight
33%
950
12%
2660
8%
950
36%
950
16%
2041
November16th to endNight
30%
975
8%
2855
4%
975
35%
975
14%
2215
December1st to 15thNight
34%
910
5%
2911
3%
910
36%
910
10%
2370
December16th to endNight
32%
960
10%
3060
6%
960
37%
960
11%
2418

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%8%47%6%35%5%5%8%32%
48760
Night
9%9%48%7%35%5%6%7%32%
47872
TransparencyDay
49%8%17%18%5%
48410
Night
48%7%15%20%6%
47727
SeeingDay
15%6%25%29%17%5%
6413
Night
13%5%26%35%16%2
15825

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
9%13%6%11%9%46%36%6%21%
1253
16th to endDay
7%10%6%12%8%45%5%6%8%24%
1344
February1st to 15thDay
8%12%5%9%10%6%8%7%5%6%20%
1519
16th to endDay
7%12%7%11%10%38%45%6%21%
1422
March1st to 15thDay
8%12%6%10%8%36%6%5%7%23%
1860
16th to endDay
9%11%6%11%7%36%5%5%7%26%
2159
April1st to 15thDay
10%10%5%7%7%35%5%5%8%30%
2197
16th to endDay
15%9%46%436%45%7%31%
2433
May1st to 15thDay
10%7%35%6%45%5%7%7%36%
2511
16th to endDay
15%5%37%6%35%5%6%7%31%
2815
June1st to 15thDay
16%8%47%7%45%5%5%7%28%
2880
16th to endDay
18%7%37%6%35%46%8%28%
2880
July1st to 15thDay
10%5%25%425%5%6%9%41%
2760
16th to endDay
9%4245%35%6%6%10%42%
2846
August1st to 15thDay
11%6%25%5%35%5%5%9%38%
2541
16th to endDay
9%5%244245%6%10%44%
2488
September1st to 15thDay
13%425%424348%45%
2160
16th to endDay
11%5%2443446%8%44%
1983
October1st to 15thDay
14%10%38%434447%34%
1800
16th to endDay
10%10%47%5%45%5%47%33%
1704
November1st to 15thDay
13%12%6%8%6%345%47%28%
1528
16th to endDay
9%11%5%12%10%5%5%5%6%6%20%
1430
December1st to 15thDay
9%12%8%12%10%5%5%5%6%5%17%
1086
16th to endDay
413%7%14%10%48%6%5%7%16%
1161
January1st to 15thNight
7%12%7%11%8%46%5%6%8%21%
2685
16th to endNight
7%10%5%10%8%46%5%6%7%26%
2880
February1st to 15thNight
6%10%5%11%8%46%7%7%7%25%
2343
16th to endNight
5%11%5%10%8%46%5%7%8%26%
2052
March1st to 15thNight
8%10%5%9%7%46%5%6%8%28%
2100
16th to endNight
10%11%5%8%8%36%6%6%7%26%
2061
April1st to 15thNight
7%9%36%6%35%5%6%8%36%
1751
16th to endNight
13%10%36%6%3445%6%35%
1527
May1st to 15thNight
11%6%35%5%345%6%8%39%
1439
16th to endNight
14%6%25%6%25%5%5%6%38%
1296
June1st to 15thNight
13%10%37%5%35%5%5%7%30%
1080
16th to endNight
13%5%25%5%46%46%9%36%
1080
July1st to 15thNight
6%425%425%47%11%44%
1197
16th to endNight
7%315%43446%8%49%
1323
August1st to 15thNight
7%2135%25%47%10%48%
1418
16th to endNight
6%3245%3446%8%49%
1713
September1st to 15thNight
11%6%2342435%7%47%
1800
16th to endNight
8%4143245%5%8%50%
1974
October1st to 15thNight
12%11%35%5%34446%37%
2160
16th to endNight
10%10%47%5%3435%6%36%
2507
November1st to 15thNight
13%12%5%9%7%45%446%27%
2660
16th to endNight
7%12%5%11%9%46%45%8%24%
2855
December1st to 15thNight
11%12%6%10%9%5%7%6%5%8%16%
2911
16th to endNight
5%12%6%13%12%5%6%6%6%7%18%
3060

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
62%5%11%14%5%
1253
16th to endDay
57%6%14%14%6%
1344
February1st to 15thDay
59%8%15%11%4
1519
16th to endDay
61%6%11%13%6%
1422
March1st to 15thDay
59%7%16%13%3
1860
16th to endDay
57%8%14%16%3
2160
April1st to 15thDay
51%8%14%16%8%1
2197
16th to endDay
51%7%14%19%6%
2433
May1st to 15thDay
43%7%13%24%9%1
2511
16th to endDay
50%8%13%17%10%
2820
June1st to 15thDay
53%9%14%16%6%
2880
16th to endDay
53%8%16%16%4
2880
July1st to 15thDay
37%9%22%23%6%
2601
16th to endDay
36%10%26%23%2
2667
August1st to 15thDay
41%10%25%19%3
2523
16th to endDay
33%8%25%27%4
2488
September1st to 15thDay
38%7%19%24%9%1
2160
16th to endDay
36%7%21%26%7%
1983
October1st to 15thDay
49%7%14%23%3
1800
16th to endDay
49%8%18%20%3
1704
November1st to 15thDay
55%7%15%14%6%
1528
16th to endDay
61%10%13%12%1
1430
December1st to 15thDay
64%7%11%13%2
1086
16th to endDay
63%9%12%10%3
1161
January1st to 15thNight
57%7%16%15%4
2685
16th to endNight
54%8%13%15%7%
2880
February1st to 15thNight
53%7%15%18%4
2354
16th to endNight
52%6%14%18%7%
2052
March1st to 15thNight
51%9%15%18%5%
2100
16th to endNight
55%7%13%17%6%
2064
April1st to 15thNight
44%6%15%20%12%
1751
16th to endNight
48%5%11%20%12%1
1527
May1st to 15thNight
40%5%12%25%14%1
1440
16th to endNight
44%7%14%19%12%2
1296
June1st to 15thNight
51%6%15%21%5%
1080
16th to endNight
43%9%20%18%7%
1080
July1st to 15thNight
31%10%23%27%5%
1128
16th to endNight
31%8%28%26%3
1239
August1st to 15thNight
28%12%25%28%4
1411
16th to endNight
30%7%19%33%8%
1713
September1st to 15thNight
34%6%16%28%10%3
1800
16th to endNight
30%7%17%32%10%1
1974
October1st to 15thNight
46%6%15%23%8%
2160
16th to endNight
46%7%16%22%5%
2507
November1st to 15thNight
56%6%13%17%5%1
2660
16th to endNight
56%9%17%12%3
2855
December1st to 15thNight
63%9%12%12%1
2911
16th to endNight
61%7%12%13%4
3060

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%125%26%23%8%
60
16th to endDay
18%418%29%20%7%
64
February1st to 15thDay
20%328%27%18%1
90
16th to endDay
16%230%28%17%4
81
March1st to 15thDay
15%6%42%23%8%2
168
16th to endDay
14%9%35%29%9%1
288
April1st to 15thDay
15%11%35%25%8%2
269
16th to endDay
22%8%23%28%13%3
363
May1st to 15thDay
13%8%23%33%17%3
468
16th to endDay
14%7%24%26%18%9%
517
June1st to 15thDay
16%6%30%26%15%4
495
16th to endDay
17%8%22%26%19%5%
495
July1st to 15thDay
14%220%34%22%5%
475
16th to endDay
10%5%22%32%22%6%
515
August1st to 15thDay
16%317%27%23%11%
493
16th to endDay
10%5%28%32%20%3
340
September1st to 15thDay
17%7%25%31%14%3
315
16th to endDay
17%5%19%34%18%3
255
October1st to 15thDay
21%7%24%28%12%5%
135
16th to endDay
22%10%29%28%7%2
144
November1st to 15thDay
16%237%30%11%1
135
16th to endDay
9%16%22%31%14%4
122
December1st to 15thDay
9%120%37%20%9%
62
16th to endDay
4134%39%10%9%
64
January1st to 15thNight
12%5%29%35%14%1
900
16th to endNight
12%7%35%35%7%1
960
February1st to 15thNight
10%425%38%18%2
769
16th to endNight
10%324%35%22%4
632
March1st to 15thNight
11%6%31%35%13%2
720
16th to endNight
14%5%29%33%14%2
720
April1st to 15thNight
12%7%29%34%13%2
539
16th to endNight
18%5%26%31%15%1
540
May1st to 15thNight
14%6%26%34%15%2
540
16th to endNight
17%6%20%35%17%3
386
June1st to 15thNight
18%324%31%19%2
360
16th to endNight
13%421%35%22%1
360
July1st to 15thNight
9%417%43%24%
340
16th to endNight
8%322%42%20%2
376
August1st to 15thNight
8%215%34%35%4
517
16th to endNight
8%322%41%22%2
573
September1st to 15thNight
14%222%38%20%2
540
16th to endNight
10%327%37%18%1
650
October1st to 15thNight
19%425%35%13%1
720
16th to endNight
17%6%28%35%10%1
888
November1st to 15thNight
18%5%28%32%12%2
950
16th to endNight
11%7%33%35%10%1
975
December1st to 15thNight
15%5%24%36%14%3
910
16th to endNight
10%326%36%19%3
960
Page generated at 2017-12-03 10:16:35. Version ac04

Copyright 2017 A. Danko


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