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Blue Mountain Vista Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blue Mountain Vista Observatory clear sky chart from 2005-11-05 to 2017-02-18.

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
34%
14389
19%
44895
10%
14353
45%
14353
22%
28931

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
22%
720
18%
2506
8%
716
37%
716
16%
1637
January16th to endNight
21%
768
21%
2517
6%
768
40%
768
19%
1610
February1st to 15thNight
17%
704
17%
2287
5%
701
34%
701
16%
1497
February16th to endNight
18%
588
23%
1765
6%
588
37%
588
18%
1137
March1st to 15thNight
23%
660
20%
1898
9%
660
37%
660
20%
1268
March16th to endNight
23%
704
22%
1876
8%
704
35%
704
23%
1251
April1st to 15thNight
23%
658
17%
1646
5%
658
29%
658
21%
1151
April16th to endNight
30%
660
18%
1650
5%
660
36%
660
27%
1102
May1st to 15thNight
36%
437
19%
1427
11%
437
45%
437
21%
938
May16th to endNight
48%
343
16%
1369
15%
342
54%
342
19%
850
June1st to 15thNight
43%
330
16%
1320
14%
330
55%
330
19%
834
June16th to endNight
57%
330
15%
1320
19%
330
60%
330
25%
751
July1st to 15thNight
54%
310
14%
1240
18%
310
57%
310
21%
762
July16th to endNight
63%
386
14%
1341
15%
361
67%
361
27%
762
August1st to 15thNight
62%
502
19%
1482
14%
499
64%
499
32%
918
August16th to endNight
57%
700
17%
1750
10%
700
59%
700
32%
1164
September1st to 15thNight
49%
660
25%
1650
12%
660
55%
660
32%
1090
September16th to endNight
52%
657
24%
1788
18%
657
56%
657
31%
1148
October1st to 15thNight
44%
660
22%
1980
17%
660
53%
660
27%
1254
October16th to endNight
33%
704
22%
2135
12%
704
47%
704
25%
1312
November1st to 15thNight
34%
700
20%
2277
12%
700
47%
700
24%
1408
November16th to endNight
29%
720
19%
2463
10%
720
42%
720
18%
1572
December1st to 15thNight
24%
720
14%
2520
6%
720
34%
720
13%
1718
December16th to endNight
21%
768
17%
2688
5%
768
37%
768
15%
1797

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
16%6%25%5%345%5%7%37%
45271
Night
16%5%2442445%7%41%
45069
Cloud CoverDay
16%6%25%5%3445%7%37%
45281
Night
16%5%2442445%7%41%
45074
TransparencyDay
44%5%12%21%14%1
44963
Night
41%5%12%22%15%2
44895
SeeingDay
20%10%25%23%14%5%
4834
Night
20%11%27%28%11%1
14389

By Month

Percentage Cloud Cover NE (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
15%7%46%6%3445%6%34%
1432
16th to endDay
14%8%37%6%4445%6%34%
1707
February1st to 15thDay
15%7%37%7%3445%6%33%
1575
16th to endDay
15%8%38%434445%36%
1467
March1st to 15thDay
15%6%35%6%35%46%5%35%
1719
16th to endDay
18%7%35%5%24345%39%
1996
April1st to 15thDay
18%7%25%42445%5%38%
1972
16th to endDay
16%415%3345%47%43%
1980
May1st to 15thDay
20%5%25%5%35%5%5%5%34%
2202
16th to endDay
16%6%25%5%35%6%6%8%35%
2394
June1st to 15thDay
15%5%26%446%46%10%32%
2310
16th to endDay
12%425%6%45%6%6%9%36%
2310
July1st to 15thDay
11%6%26%7%36%6%6%9%33%
2310
16th to endDay
10%5%25%5%46%6%6%9%37%
2417
August1st to 15thDay
14%5%25%5%46%5%7%7%34%
2126
16th to endDay
15%5%244245%5%6%41%
2100
September1st to 15thDay
16%425%43446%6%43%
1980
16th to endDay
16%6%24423446%44%
1838
October1st to 15thDay
18%5%25%423447%41%
1650
16th to endDay
20%5%245%235%5%6%38%
1735
November1st to 15thDay
16%8%24413335%45%
1581
16th to endDay
20%5%3432446%6%41%
1494
December1st to 15thDay
19%6%36%435%45%7%34%
1440
16th to endDay
20%7%35%5%3446%7%31%
1536
January1st to 15thNight
16%7%345%3445%6%37%
2506
16th to endNight
14%8%245%2445%6%40%
2517
February1st to 15thNight
15%7%35%5%2445%7%37%
2285
16th to endNight
16%5%144245%5%6%42%
1765
March1st to 15thNight
16%7%2442445%6%40%
1886
16th to endNight
16%6%24424436%43%
1876
April1st to 15thNight
17%6%246%245%46%37%
1646
16th to endNight
17%42442445%5%46%
1650
May1st to 15thNight
19%6%24424446%40%
1427
16th to endNight
14%425%5%3445%7%40%
1367
June1st to 15thNight
19%5%13425%45%7%40%
1320
16th to endNight
11%424325%45%11%43%
1320
July1st to 15thNight
11%326%5%35%5%5%8%41%
1320
16th to endNight
8%3245%35%5%6%11%44%
1440
August1st to 15thNight
10%5%1443446%8%45%
1493
16th to endNight
13%41442446%7%45%
1750
September1st to 15thNight
15%424424346%48%
1650
16th to endNight
14%5%24424436%47%
1788
October1st to 15thNight
20%41342335%6%44%
1980
16th to endNight
18%413413447%45%
2135
November1st to 15thNight
13%6%25%423446%45%
2277
16th to endNight
18%5%25%424448%38%
2463
December1st to 15thNight
20%5%25%5%35%5%5%7%31%
2520
16th to endNight
18%8%345%2445%7%36%
2688

Percentage Cloud Cover SE (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
15%6%47%6%345%46%35%
1432
16th to endDay
13%8%46%5%44447%34%
1707
February1st to 15thDay
15%7%46%7%3445%6%33%
1575
16th to endDay
15%8%27%5%35%345%35%
1467
March1st to 15thDay
15%7%25%6%3445%6%35%
1730
16th to endDay
18%7%36%424445%39%
1995
April1st to 15thDay
18%6%35%43445%6%38%
1972
16th to endDay
15%4244245%5%6%43%
1980
May1st to 15thDay
20%5%246%35%46%5%34%
2202
16th to endDay
15%5%25%5%345%6%8%35%
2394
June1st to 15thDay
15%5%25%5%36%5%6%9%33%
2310
16th to endDay
12%5%25%5%36%5%6%9%36%
2310
July1st to 15thDay
10%6%25%6%46%5%6%9%34%
2310
16th to endDay
9%5%25%5%46%5%7%8%38%
2417
August1st to 15thDay
14%4245%45%6%7%7%35%
2126
16th to endDay
15%5%244345%5%7%42%
2100
September1st to 15thDay
16%4145%2445%6%43%
1980
16th to endDay
15%6%25%424346%44%
1838
October1st to 15thDay
17%5%25%42345%7%41%
1650
16th to endDay
19%5%25%5%235%5%6%39%
1735
November1st to 15thDay
16%8%23423236%44%
1581
16th to endDay
20%5%24313447%41%
1494
December1st to 15thDay
18%7%35%43446%6%34%
1440
16th to endDay
20%7%35%425%5%6%6%31%
1536
January1st to 15thNight
16%6%345%3445%7%37%
2506
16th to endNight
14%8%3443445%7%40%
2517
February1st to 15thNight
14%7%36%5%2445%7%38%
2278
16th to endNight
16%5%2443445%6%42%
1765
March1st to 15thNight
16%7%3432445%6%41%
1898
16th to endNight
16%6%25%424336%43%
1876
April1st to 15thNight
16%6%25%6%2445%6%38%
1646
16th to endNight
17%4134345%45%45%
1650
May1st to 15thNight
19%5%23434445%40%
1427
16th to endNight
14%5%26%5%25%447%41%
1367
June1st to 15thNight
18%6%23425%35%7%41%
1320
16th to endNight
11%423325%5%6%9%44%
1320
July1st to 15thNight
11%325%445%46%8%41%
1320
16th to endNight
8%3235%25%6%5%11%44%
1440
August1st to 15thNight
10%5%244235%5%9%44%
1493
16th to endNight
13%5%2442446%7%43%
1750
September1st to 15thNight
15%424424346%48%
1650
16th to endNight
15%5%15%424436%47%
1788
October1st to 15thNight
19%41332335%6%45%
1980
16th to endNight
18%413323446%46%
2135
November1st to 15thNight
13%7%25%42335%6%45%
2277
16th to endNight
18%5%25%434448%38%
2463
December1st to 15thNight
20%5%25%6%35%5%6%6%32%
2520
16th to endNight
18%7%35%42445%7%35%
2688

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
48%5%12%22%9%2
1433
16th to endDay
48%413%20%11%1
1707
February1st to 15thDay
49%5%12%20%11%1
1577
16th to endDay
48%411%24%9%1
1467
March1st to 15thDay
47%5%14%21%9%1
1730
16th to endDay
47%49%20%16%1
1996
April1st to 15thDay
45%49%22%13%4
1972
16th to endDay
39%5%8%20%20%5%
1980
May1st to 15thDay
48%6%8%20%14%2
2202
16th to endDay
44%7%12%19%14%1
2398
June1st to 15thDay
45%8%14%21%9%
2310
16th to endDay
41%8%14%23%10%1
2310
July1st to 15thDay
44%6%12%21%13%1
2161
16th to endDay
39%8%12%23%14%1
2253
August1st to 15thDay
41%8%13%19%16%
2113
16th to endDay
39%5%8%24%19%2
2100
September1st to 15thDay
39%5%11%19%21%1
1980
16th to endDay
40%47%21%22%2
1838
October1st to 15thDay
40%414%23%14%1
1650
16th to endDay
43%5%11%24%13%1
1735
November1st to 15thDay
42%313%21%16%3
1581
16th to endDay
42%411%27%13%1
1494
December1st to 15thDay
48%6%16%19%8%1
1440
16th to endDay
50%5%14%18%10%
1536
January1st to 15thNight
46%412%20%12%2
2506
16th to endNight
42%5%12%25%12%1
2517
February1st to 15thNight
45%413%22%12%1
2287
16th to endNight
41%410%24%17%1
1765
March1st to 15thNight
43%5%12%24%12%
1898
16th to endNight
42%410%23%16%2
1876
April1st to 15thNight
44%5%10%19%16%2
1646
16th to endNight
39%6%8%20%22%3
1650
May1st to 15thNight
44%6%11%20%16%2
1427
16th to endNight
42%7%13%17%16%3
1369
June1st to 15thNight
42%7%11%23%14%
1320
16th to endNight
34%7%13%30%13%
1320
July1st to 15thNight
42%5%12%22%14%2
1240
16th to endNight
32%8%18%23%14%2
1341
August1st to 15thNight
35%6%14%22%19%1
1482
16th to endNight
38%6%12%19%20%3
1750
September1st to 15thNight
37%6%9%23%22%1
1650
16th to endNight
39%37%22%24%3
1788
October1st to 15thNight
39%5%10%26%15%2
1980
16th to endNight
37%5%12%27%15%1
2135
November1st to 15thNight
40%412%22%15%5%
2277
16th to endNight
44%411%24%13%2
2463
December1st to 15thNight
49%6%14%18%10%
2520
16th to endNight
47%5%14%22%9%
2688

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
36%18%31%10%3
60
16th to endDay
24%20%34%18%2
93
February1st to 15thDay
23%37%28%10%
90
16th to endDay
20%20%34%21%2
192
March1st to 15thDay
19%16%26%31%5%
210
16th to endDay
18%24%25%19%9%2
224
April1st to 15thDay
26%12%27%20%10%2
210
16th to endDay
18%11%29%20%12%7%
210
May1st to 15thDay
33%9%25%14%11%5%
228
16th to endDay
19%8%25%23%18%4
267
June1st to 15thDay
21%9%28%21%14%3
255
16th to endDay
18%433%23%16%3
255
July1st to 15thDay
16%324%25%25%3
245
16th to endDay
11%325%30%21%6%
270
August1st to 15thDay
16%321%26%21%10%
253
16th to endDay
16%116%28%17%19%
268
September1st to 15thDay
14%8%19%22%23%10%
255
16th to endDay
22%222%20%18%14%
254
October1st to 15thDay
21%418%30%15%7%
255
16th to endDay
19%15%28%23%12%
267
November1st to 15thDay
22%11%22%25%15%2
235
16th to endDay
23%14%34%20%7%
114
December1st to 15thDay
20%33%23%10%11%1
60
16th to endDay
37%21%32%6%1
64
January1st to 15thNight
20%17%34%23%4
720
16th to endNight
20%18%34%25%1
768
February1st to 15thNight
21%18%36%22%1
704
16th to endNight
22%20%34%19%2
588
March1st to 15thNight
23%16%32%23%5%
660
16th to endNight
21%16%34%20%5%1
704
April1st to 15thNight
20%15%36%22%4
658
16th to endNight
20%11%31%24%10%
660
May1st to 15thNight
21%7%29%29%10%1
437
16th to endNight
17%6%20%39%15%1
343
June1st to 15thNight
21%6%24%30%16%
330
16th to endNight
12%123%46%15%1
330
July1st to 15thNight
13%220%37%24%
310
16th to endNight
9%217%40%26%3
386
August1st to 15thNight
14%112%44%24%1
502
16th to endNight
16%313%34%29%3
700
September1st to 15thNight
16%5%20%33%22%1
660
16th to endNight
17%319%29%25%4
657
October1st to 15thNight
23%7%20%29%16%2
660
16th to endNight
21%13%27%28%8%
704
November1st to 15thNight
18%11%29%27%12%1
700
16th to endNight
20%17%25%27%7%
720
December1st to 15thNight
24%15%28%24%6%
720
16th to endNight
25%14%32%24%2
768
Page generated at 2017-02-18 16:04:31. Version ac04

Copyright 2017 A. Danko


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