This page made possible by the sponsorship of: Delaware Valley Amateur Astronomers.

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 2019-09-17.

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%
17576
19%
54770
10%
17540
44%
17540
22%
35404

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
21%
840
19%
2926
8%
836
38%
836
16%
1894
January16th to endNight
20%
896
21%
2937
5%
896
39%
896
18%
1872
February1st to 15thNight
18%
824
18%
2677
6%
821
35%
821
16%
1765
February16th to endNight
17%
735
22%
2208
6%
735
37%
735
17%
1452
March1st to 15thNight
22%
840
21%
2416
8%
840
37%
840
20%
1608
March16th to endNight
23%
896
22%
2388
8%
896
35%
896
23%
1584
April1st to 15thNight
23%
838
17%
2096
5%
838
30%
838
22%
1454
April16th to endNight
29%
831
17%
2077
5%
831
35%
831
26%
1412
May1st to 15thNight
35%
557
17%
1817
10%
557
42%
557
19%
1243
May16th to endNight
43%
439
14%
1753
12%
438
50%
438
18%
1107
June1st to 15thNight
43%
420
17%
1680
15%
420
54%
420
20%
1046
June16th to endNight
50%
420
16%
1680
17%
420
56%
420
24%
966
July1st to 15thNight
55%
400
15%
1600
18%
400
58%
400
22%
953
July16th to endNight
60%
488
15%
1719
16%
463
64%
463
26%
1003
August1st to 15thNight
59%
630
17%
1860
12%
627
61%
627
28%
1198
August16th to endNight
57%
892
18%
2230
10%
892
59%
892
32%
1481
September1st to 15thNight
45%
840
22%
2100
11%
840
51%
840
29%
1426
September16th to endNight
52%
782
25%
2127
19%
782
57%
782
31%
1360
October1st to 15thNight
44%
780
20%
2340
16%
780
53%
780
26%
1511
October16th to endNight
34%
832
24%
2523
13%
832
47%
832
26%
1542
November1st to 15thNight
33%
820
20%
2667
11%
820
46%
820
23%
1676
November16th to endNight
29%
840
20%
2873
10%
840
42%
840
19%
1800
December1st to 15thNight
25%
840
15%
2940
7%
840
36%
840
14%
1993
December16th to endNight
21%
896
16%
3136
4%
896
37%
896
15%
2058

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%
55921
Night
16%6%2442445%7%41%
54944
Cloud CoverDay
16%6%25%5%3445%7%37%
55931
Night
16%6%2442445%7%41%
54949
TransparencyDay
44%5%11%21%13%1
55613
Night
42%5%12%22%15%2
54770
SeeingDay
21%13%26%21%12%4
8229
Night
20%11%27%27%11%1
17576

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
14%7%46%6%345%5%6%35%
1672
16th to endDay
14%8%37%6%4445%6%33%
1991
February1st to 15thDay
16%7%37%7%34446%33%
1845
16th to endDay
16%7%38%434445%35%
1837
March1st to 15thDay
15%7%36%7%345%5%5%35%
2190
16th to endDay
18%7%35%5%24345%38%
2540
April1st to 15thDay
18%7%25%5%3445%5%36%
2512
16th to endDay
17%5%25%4345%5%7%40%
2488
May1st to 15thDay
21%6%25%5%35%45%5%32%
2805
16th to endDay
18%5%25%5%345%6%8%34%
3066
June1st to 15thDay
15%5%26%446%46%9%33%
2940
16th to endDay
13%5%25%6%35%5%6%8%37%
2940
July1st to 15thDay
11%5%26%6%46%5%6%9%35%
2940
16th to endDay
11%5%25%5%46%5%6%9%37%
3050
August1st to 15thDay
14%5%26%6%45%5%7%7%33%
2658
16th to endDay
14%5%244345%6%7%40%
2676
September1st to 15thDay
18%425%5%3445%6%40%
2520
16th to endDay
16%6%24423446%43%
2184
October1st to 15thDay
20%5%24423447%39%
1950
16th to endDay
18%5%245%345%5%6%39%
2051
November1st to 15thDay
18%7%23413345%43%
1851
16th to endDay
19%5%2332436%6%42%
1743
December1st to 15thDay
18%7%36%434447%34%
1680
16th to endDay
19%7%35%5%345%6%7%31%
1792
January1st to 15thNight
16%7%245%3445%6%38%
2926
16th to endNight
14%8%2442435%6%41%
2937
February1st to 15thNight
16%7%25%5%2445%7%37%
2675
16th to endNight
17%6%245%2445%6%40%
2208
March1st to 15thNight
17%6%2442345%6%41%
2404
16th to endNight
16%6%25%423436%43%
2388
April1st to 15thNight
17%6%245%345%47%38%
2096
16th to endNight
17%5%2442445%5%43%
2077
May1st to 15thNight
21%6%24434446%37%
1817
16th to endNight
16%5%25%5%3445%8%37%
1751
June1st to 15thNight
18%5%13425%45%7%41%
1680
16th to endNight
11%424325%45%10%43%
1680
July1st to 15thNight
11%425%5%3445%9%43%
1680
16th to endNight
9%4245%35%5%6%10%43%
1818
August1st to 15thNight
11%5%2443446%8%42%
1871
16th to endNight
12%5%15%42446%7%44%
2230
September1st to 15thNight
17%5%24424346%44%
2100
16th to endNight
14%5%24424336%47%
2127
October1st to 15thNight
21%5%1342335%6%42%
2340
16th to endNight
18%413413446%46%
2523
November1st to 15thNight
15%6%25%423446%43%
2667
16th to endNight
17%5%25%42445%8%39%
2873
December1st to 15thNight
19%5%26%5%35%5%5%7%32%
2940
16th to endNight
18%7%3442445%7%37%
3136

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%36%
1672
16th to endDay
14%9%36%5%45%446%34%
1991
February1st to 15thDay
16%7%36%7%35%45%6%33%
1845
16th to endDay
16%8%27%5%34446%34%
1837
March1st to 15thDay
15%7%25%6%4445%6%35%
2201
16th to endDay
18%7%36%5%24445%38%
2539
April1st to 15thDay
18%7%35%5%3445%6%36%
2512
16th to endDay
17%5%244345%5%6%41%
2488
May1st to 15thDay
22%6%245%3445%5%33%
2805
16th to endDay
18%5%25%5%345%6%9%34%
3066
June1st to 15thDay
15%5%25%5%36%5%6%9%33%
2940
16th to endDay
13%5%25%5%35%5%5%9%37%
2940
July1st to 15thDay
10%5%25%6%46%5%6%9%36%
2940
16th to endDay
10%5%25%5%46%5%6%8%37%
3050
August1st to 15thDay
14%425%6%45%6%7%8%34%
2658
16th to endDay
14%5%244345%6%7%41%
2676
September1st to 15thDay
18%415%5%2445%5%40%
2520
16th to endDay
15%6%25%42435%6%43%
2184
October1st to 15thDay
19%5%25%42435%6%39%
1950
16th to endDay
18%5%245%235%5%6%40%
2051
November1st to 15thDay
18%8%23423246%42%
1851
16th to endDay
19%5%2432345%7%42%
1743
December1st to 15thDay
18%8%35%5%3435%6%34%
1680
16th to endDay
19%7%35%435%5%6%6%32%
1792
January1st to 15thNight
16%6%245%3445%7%38%
2926
16th to endNight
14%8%24424447%41%
2937
February1st to 15thNight
16%7%26%42445%7%37%
2668
16th to endNight
17%7%2443445%6%40%
2208
March1st to 15thNight
17%7%24324446%41%
2416
16th to endNight
16%7%25%424336%44%
2388
April1st to 15thNight
17%6%245%2445%6%38%
2096
16th to endNight
17%424434445%43%
2077
May1st to 15thNight
21%6%24434446%37%
1817
16th to endNight
16%5%25%5%35%447%38%
1751
June1st to 15thNight
17%6%23425%45%6%41%
1680
16th to endNight
11%424325%5%6%9%44%
1680
July1st to 15thNight
11%325%445%45%8%43%
1680
16th to endNight
10%3245%35%6%5%10%42%
1818
August1st to 15thNight
11%5%245%345%5%8%41%
1871
16th to endNight
12%5%25%42446%8%43%
2230
September1st to 15thNight
17%5%24424346%44%
2100
16th to endNight
15%5%15%424436%47%
2127
October1st to 15thNight
20%41332335%6%43%
2340
16th to endNight
18%413413445%47%
2523
November1st to 15thNight
15%6%25%42335%6%44%
2667
16th to endNight
17%5%25%43345%8%40%
2873
December1st to 15thNight
19%6%25%6%35%6%5%6%32%
2940
16th to endNight
18%7%35%42445%7%37%
3136

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%411%21%10%2
1673
16th to endDay
49%413%20%11%1
1991
February1st to 15thDay
49%5%13%19%10%1
1847
16th to endDay
48%411%24%9%1
1837
March1st to 15thDay
48%5%13%20%11%1
2201
16th to endDay
47%48%19%16%2
2540
April1st to 15thDay
47%49%20%13%3
2512
16th to endDay
41%5%9%20%18%4
2488
May1st to 15thDay
50%5%9%18%13%1
2805
16th to endDay
45%7%12%20%12%1
3070
June1st to 15thDay
44%7%13%21%11%1
2940
16th to endDay
41%7%12%23%12%1
2940
July1st to 15thDay
42%6%12%20%15%1
2791
16th to endDay
40%7%12%23%13%2
2886
August1st to 15thDay
42%8%13%20%14%
2645
16th to endDay
39%5%10%23%18%2
2676
September1st to 15thDay
42%5%11%19%18%1
2520
16th to endDay
41%47%21%21%2
2184
October1st to 15thDay
43%413%21%14%1
1950
16th to endDay
41%5%11%25%14%1
2051
November1st to 15thDay
43%313%21%14%3
1851
16th to endDay
41%411%28%13%1
1743
December1st to 15thDay
48%5%15%20%8%
1680
16th to endDay
49%5%15%18%9%
1792
January1st to 15thNight
45%5%11%21%13%2
2926
16th to endNight
42%412%25%12%2
2937
February1st to 15thNight
46%413%23%11%1
2677
16th to endNight
44%49%23%16%2
2208
March1st to 15thNight
43%5%11%23%15%1
2416
16th to endNight
42%49%23%17%2
2388
April1st to 15thNight
43%5%11%22%15%2
2096
16th to endNight
41%5%8%20%19%3
2077
May1st to 15thNight
47%6%10%18%15%2
1817
16th to endNight
43%6%14%17%14%2
1753
June1st to 15thNight
42%6%10%23%15%
1680
16th to endNight
36%7%13%27%14%1
1680
July1st to 15thNight
39%6%13%21%17%2
1600
16th to endNight
34%8%16%23%13%2
1719
August1st to 15thNight
38%7%14%20%17%1
1860
16th to endNight
37%6%12%20%20%2
2230
September1st to 15thNight
40%6%9%22%18%1
2100
16th to endNight
39%37%23%23%2
2127
October1st to 15thNight
41%5%11%24%14%2
2340
16th to endNight
37%5%11%29%15%1
2523
November1st to 15thNight
41%412%22%13%4
2667
16th to endNight
42%411%25%13%1
2873
December1st to 15thNight
49%5%13%19%10%
2940
16th to endNight
46%414%22%9%
3136

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
26%27%29%12%4
120
16th to endDay
28%21%32%15%1
185
February1st to 15thDay
25%32%31%8%2
180
16th to endDay
25%20%34%18%1
340
March1st to 15thDay
20%25%28%20%4
390
16th to endDay
23%23%30%15%6%1
416
April1st to 15thDay
25%20%27%17%7%1
390
16th to endDay
23%15%31%16%8%4
379
May1st to 15thDay
32%12%27%15%8%3
408
16th to endDay
24%9%25%22%14%3
459
June1st to 15thDay
19%14%28%21%13%2
435
16th to endDay
19%9%32%24%12%2
435
July1st to 15thDay
14%422%29%23%6%
425
16th to endDay
14%423%30%20%6%
454
August1st to 15thDay
16%423%27%17%10%
418
16th to endDay
15%221%30%16%12%
460
September1st to 15thDay
20%8%20%21%20%8%
435
16th to endDay
20%5%20%21%19%12%
378
October1st to 15thDay
25%5%18%26%16%6%
375
16th to endDay
16%19%29%20%12%
391
November1st to 15thDay
25%12%23%25%12%1
325
16th to endDay
22%21%31%17%6%
183
December1st to 15thDay
21%26%30%12%8%
120
16th to endDay
29%26%34%8%
128
January1st to 15thNight
20%17%35%21%4
840
16th to endNight
20%18%35%23%2
896
February1st to 15thNight
22%17%35%22%1
824
16th to endNight
23%20%34%19%2
735
March1st to 15thNight
22%18%32%21%4
840
16th to endNight
21%15%34%22%5%
896
April1st to 15thNight
20%15%36%22%5%
838
16th to endNight
21%11%32%24%9%
831
May1st to 15thNight
24%8%27%29%10%
557
16th to endNight
19%6%21%37%14%1
439
June1st to 15thNight
20%5%25%32%16%
420
16th to endNight
13%226%43%13%
420
July1st to 15thNight
14%219%38%23%1
400
16th to endNight
11%215%39%27%2
488
August1st to 15thNight
16%114%39%26%2
630
16th to endNight
15%214%35%28%2
892
September1st to 15thNight
19%420%32%20%2
840
16th to endNight
17%318%29%25%5%
782
October1st to 15thNight
24%6%19%29%16%3
780
16th to endNight
22%12%27%28%9%
832
November1st to 15thNight
18%12%29%26%11%1
820
16th to endNight
20%17%26%27%6%
840
December1st to 15thNight
24%14%28%24%6%
840
16th to endNight
25%14%32%24%2
896
Page generated at 2019-09-17 21:12:15. Version ac04

Copyright 2019 A. Danko


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