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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 2018-02-22.

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%
15680
19%
48917
10%
15644
45%
15644
22%
31431

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%
780
18%
2716
8%
776
37%
776
16%
1758
January16th to endNight
20%
832
21%
2727
6%
832
39%
832
19%
1745
February1st to 15thNight
17%
764
17%
2482
4%
761
33%
761
16%
1642
February16th to endNight
18%
659
24%
1979
7%
659
39%
659
19%
1274
March1st to 15thNight
22%
720
20%
2070
8%
720
36%
720
20%
1375
March16th to endNight
23%
768
22%
2046
8%
768
35%
768
23%
1363
April1st to 15thNight
24%
718
16%
1796
5%
718
30%
718
23%
1238
April16th to endNight
30%
720
18%
1800
5%
720
37%
720
27%
1206
May1st to 15thNight
35%
477
18%
1557
10%
477
44%
477
20%
1037
May16th to endNight
44%
375
16%
1497
14%
374
51%
374
18%
940
June1st to 15thNight
45%
360
16%
1440
14%
360
55%
360
20%
895
June16th to endNight
52%
360
15%
1440
18%
360
57%
360
24%
825
July1st to 15thNight
52%
340
13%
1360
17%
340
55%
340
21%
836
July16th to endNight
61%
418
15%
1457
15%
393
65%
393
27%
837
August1st to 15thNight
61%
548
18%
1618
13%
545
63%
545
30%
1014
August16th to endNight
58%
764
19%
1910
11%
764
59%
764
33%
1256
September1st to 15thNight
47%
720
24%
1800
11%
720
53%
720
32%
1187
September16th to endNight
53%
717
26%
1951
19%
717
58%
717
33%
1231
October1st to 15thNight
44%
720
21%
2160
17%
720
53%
720
26%
1372
October16th to endNight
34%
768
24%
2329
14%
768
48%
768
26%
1413
November1st to 15thNight
34%
760
20%
2472
11%
760
46%
760
24%
1535
November16th to endNight
29%
780
21%
2668
11%
780
43%
780
19%
1667
December1st to 15thNight
24%
780
14%
2730
5%
780
34%
780
13%
1864
December16th to endNight
21%
832
17%
2912
4%
832
37%
832
15%
1921

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%3445%7%37%
49335
Night
16%5%2442445%7%41%
49091
Cloud CoverDay
16%6%25%5%3445%7%37%
49345
Night
15%5%2442445%7%41%
49096
TransparencyDay
44%5%11%21%14%1
49027
Night
41%5%12%23%15%2
48917
SeeingDay
20%12%26%22%13%4
6136
Night
20%11%27%27%11%1
15680

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%5%36%
1552
16th to endDay
14%8%37%6%4445%6%34%
1849
February1st to 15thDay
16%7%37%7%34446%33%
1710
16th to endDay
15%7%38%434445%36%
1641
March1st to 15thDay
15%6%36%6%345%5%5%35%
1876
16th to endDay
19%7%35%424345%39%
2178
April1st to 15thDay
18%7%25%42445%5%39%
2152
16th to endDay
16%5%25%3345%5%7%41%
2160
May1st to 15thDay
21%5%25%5%35%5%5%5%33%
2403
16th to endDay
17%5%25%5%35%6%6%7%34%
2618
June1st to 15thDay
14%5%26%446%46%10%33%
2520
16th to endDay
13%425%6%45%5%6%9%36%
2520
July1st to 15thDay
11%6%26%6%36%6%7%8%33%
2520
16th to endDay
10%5%26%5%46%6%6%9%36%
2609
August1st to 15thDay
14%5%25%5%46%5%7%7%34%
2319
16th to endDay
14%5%244245%6%7%41%
2292
September1st to 15thDay
16%425%5%3445%6%42%
2160
16th to endDay
15%6%24423446%45%
2005
October1st to 15thDay
19%5%25%423447%40%
1800
16th to endDay
19%5%244335%5%6%39%
1893
November1st to 15thDay
17%8%24413345%44%
1716
16th to endDay
19%5%2332345%6%43%
1618
December1st to 15thDay
18%6%36%43445%7%34%
1560
16th to endDay
19%7%36%5%345%6%7%31%
1664
January1st to 15thNight
16%6%245%3445%6%38%
2716
16th to endNight
14%8%35%42435%6%41%
2727
February1st to 15thNight
15%8%36%5%2445%7%36%
2480
16th to endNight
16%5%1442445%6%41%
1979
March1st to 15thNight
17%6%2442345%6%41%
2058
16th to endNight
16%6%24424436%43%
2046
April1st to 15thNight
16%5%246%345%5%7%38%
1796
16th to endNight
17%5%2432445%5%45%
1800
May1st to 15thNight
19%6%24434446%39%
1557
16th to endNight
15%5%25%5%3445%7%39%
1495
June1st to 15thNight
18%5%13425%45%7%41%
1440
16th to endNight
12%424325%45%10%43%
1440
July1st to 15thNight
11%426%5%35%5%5%9%40%
1440
16th to endNight
8%4245%35%5%6%10%44%
1556
August1st to 15thNight
11%5%1443446%8%44%
1629
16th to endNight
13%41442446%6%46%
1910
September1st to 15thNight
15%424424346%47%
1800
16th to endNight
13%5%24424337%48%
1951
October1st to 15thNight
20%41332335%6%44%
2160
16th to endNight
18%413413446%46%
2329
November1st to 15thNight
14%6%25%42345%6%44%
2472
16th to endNight
17%5%24424448%39%
2668
December1st to 15thNight
19%5%26%5%35%5%5%7%31%
2730
16th to endNight
17%8%345%2445%7%37%
2912

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%46%5%34446%36%
1552
16th to endDay
14%8%46%5%45%447%34%
1849
February1st to 15thDay
16%7%46%7%3445%6%33%
1710
16th to endDay
15%8%27%5%34446%36%
1641
March1st to 15thDay
16%7%25%6%3445%6%35%
1887
16th to endDay
19%6%36%423345%39%
2177
April1st to 15thDay
18%6%35%43445%5%39%
2152
16th to endDay
16%5%244345%5%6%42%
2160
May1st to 15thDay
21%5%246%35%46%5%33%
2403
16th to endDay
17%5%25%5%345%6%8%34%
2618
June1st to 15thDay
14%5%25%5%36%5%6%9%34%
2520
16th to endDay
13%5%25%5%36%6%6%9%36%
2520
July1st to 15thDay
11%5%25%7%46%5%6%9%34%
2520
16th to endDay
9%5%25%6%46%5%7%8%37%
2609
August1st to 15thDay
14%425%6%45%6%7%7%34%
2319
16th to endDay
14%4244345%5%7%41%
2292
September1st to 15thDay
16%415%5%2445%5%43%
2160
16th to endDay
14%5%2442435%6%45%
2005
October1st to 15thDay
18%5%25%42445%6%41%
1800
16th to endDay
18%5%244235%5%6%40%
1893
November1st to 15thDay
17%8%23423246%43%
1716
16th to endDay
19%5%2431345%7%43%
1618
December1st to 15thDay
18%8%35%43446%6%35%
1560
16th to endDay
19%7%35%435%5%6%6%32%
1664
January1st to 15thNight
16%6%346%3445%7%38%
2716
16th to endNight
14%8%35%434446%41%
2727
February1st to 15thNight
15%7%36%5%2445%7%37%
2473
16th to endNight
16%5%2443445%6%42%
1979
March1st to 15thNight
17%7%24324346%42%
2070
16th to endNight
17%6%25%424336%43%
2046
April1st to 15thNight
16%5%25%6%2446%6%39%
1796
16th to endNight
17%4244345%45%45%
1800
May1st to 15thNight
19%6%24434445%39%
1557
16th to endNight
15%5%25%5%35%447%40%
1495
June1st to 15thNight
17%6%23425%347%42%
1440
16th to endNight
11%424325%5%6%9%44%
1440
July1st to 15thNight
12%325%5%45%46%8%40%
1440
16th to endNight
9%3235%35%6%5%11%44%
1556
August1st to 15thNight
11%5%244245%5%9%44%
1629
16th to endNight
12%5%2442445%7%45%
1910
September1st to 15thNight
15%424424346%47%
1800
16th to endNight
13%415%424436%48%
1951
October1st to 15thNight
19%41332335%6%45%
2160
16th to endNight
18%413323445%47%
2329
November1st to 15thNight
14%6%25%42335%6%44%
2472
16th to endNight
17%5%25%434448%40%
2668
December1st to 15thNight
19%6%25%6%35%6%6%6%31%
2730
16th to endNight
17%7%35%42445%7%36%
2912

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
47%5%11%22%10%3
1553
16th to endDay
49%413%20%11%1
1849
February1st to 15thDay
49%5%12%20%11%1
1712
16th to endDay
48%411%25%9%1
1641
March1st to 15thDay
48%5%13%20%10%1
1887
16th to endDay
47%49%20%16%1
2178
April1st to 15thDay
45%49%23%13%4
2152
16th to endDay
41%5%9%20%19%4
2160
May1st to 15thDay
49%5%8%19%14%1
2403
16th to endDay
46%7%12%19%13%1
2622
June1st to 15thDay
44%8%13%21%10%1
2520
16th to endDay
41%8%13%24%10%1
2520
July1st to 15thDay
44%6%12%20%14%1
2371
16th to endDay
40%7%12%23%13%2
2445
August1st to 15thDay
42%8%13%19%15%
2306
16th to endDay
39%5%9%24%19%2
2292
September1st to 15thDay
40%5%11%19%21%1
2160
16th to endDay
39%47%22%23%2
2005
October1st to 15thDay
42%413%21%15%1
1800
16th to endDay
41%5%11%24%14%1
1893
November1st to 15thDay
43%313%21%14%3
1716
16th to endDay
40%311%29%14%1
1618
December1st to 15thDay
48%5%16%19%9%1
1560
16th to endDay
50%5%15%17%10%
1664
January1st to 15thNight
45%5%12%20%13%2
2716
16th to endNight
43%411%26%12%1
2727
February1st to 15thNight
46%413%22%11%1
2482
16th to endNight
41%410%24%16%2
1979
March1st to 15thNight
42%5%11%24%14%1
2070
16th to endNight
42%410%23%16%2
2046
April1st to 15thNight
43%5%10%21%16%2
1796
16th to endNight
39%6%9%20%20%3
1800
May1st to 15thNight
45%6%10%19%16%2
1557
16th to endNight
43%6%13%17%15%3
1497
June1st to 15thNight
41%7%11%24%15%
1440
16th to endNight
35%7%13%29%13%
1440
July1st to 15thNight
41%6%13%21%14%2
1360
16th to endNight
33%8%17%23%14%2
1457
August1st to 15thNight
36%7%14%22%18%1
1618
16th to endNight
36%6%12%20%20%2
1910
September1st to 15thNight
37%5%9%23%21%2
1800
16th to endNight
37%37%22%25%2
1951
October1st to 15thNight
39%5%10%26%15%2
2160
16th to endNight
36%5%11%29%15%1
2329
November1st to 15thNight
40%413%22%14%5%
2472
16th to endNight
42%411%25%14%2
2668
December1st to 15thNight
49%6%13%18%10%
2730
16th to endNight
47%414%22%10%
2912

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
30%25%28%11%4
90
16th to endDay
25%19%36%16%1
139
February1st to 15thDay
27%35%29%7%
135
16th to endDay
21%18%35%21%2
262
March1st to 15thDay
21%21%26%25%4
270
16th to endDay
22%23%28%16%7%2
288
April1st to 15thDay
25%13%29%20%9%2
270
16th to endDay
21%11%31%18%10%5%
270
May1st to 15thDay
34%13%24%14%9%4
288
16th to endDay
23%8%24%22%16%3
331
June1st to 15thDay
19%11%28%21%15%3
315
16th to endDay
19%7%33%22%13%2
315
July1st to 15thDay
16%426%27%21%2
305
16th to endDay
12%325%29%21%7%
326
August1st to 15thDay
16%423%25%18%11%
313
16th to endDay
15%218%31%17%15%
332
September1st to 15thDay
14%10%21%21%22%9%
315
16th to endDay
17%5%19%21%21%14%
314
October1st to 15thDay
23%419%28%16%8%
315
16th to endDay
18%16%27%22%14%
329
November1st to 15thDay
23%11%23%26%13%1
280
16th to endDay
20%20%33%18%7%
148
December1st to 15thDay
21%27%28%12%8%1
90
16th to endDay
30%26%35%7%1
96
January1st to 15thNight
20%17%35%22%4
780
16th to endNight
20%18%35%24%1
832
February1st to 15thNight
21%18%36%21%1
764
16th to endNight
22%20%35%19%3
659
March1st to 15thNight
23%18%31%22%4
720
16th to endNight
21%15%34%21%5%1
768
April1st to 15thNight
20%15%36%22%4
718
16th to endNight
20%11%31%25%10%
720
May1st to 15thNight
22%8%28%29%10%1
477
16th to endNight
18%5%21%37%15%1
375
June1st to 15thNight
20%5%23%32%17%
360
16th to endNight
13%225%43%14%1
360
July1st to 15thNight
14%220%38%23%
340
16th to endNight
10%316%39%26%3
418
August1st to 15thNight
15%113%41%25%2
548
16th to endNight
15%214%35%29%2
764
September1st to 15thNight
17%5%21%32%21%1
720
16th to endNight
16%318%28%26%5%
717
October1st to 15thNight
23%6%20%29%16%3
720
16th to endNight
21%12%27%28%9%
768
November1st to 15thNight
18%11%29%27%12%1
760
16th to endNight
20%17%27%27%7%
780
December1st to 15thNight
24%15%28%23%6%
780
16th to endNight
25%14%33%24%2
832
Page generated at 2018-02-23 11:21:30. Version ac04

Copyright 2018 A. Danko


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