Bellvale Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bellvale Observatory clear sky chart from 2005-11-05 to 2017-09-21.

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
30%
14999
19%
46892
9%
14968
42%
14968
22%
29907

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
19%
720
20%
2506
6%
716
37%
716
17%
1574
January16th to endNight
16%
768
20%
2598
5%
768
35%
768
17%
1633
February1st to 15thNight
13%
704
17%
2240
3%
701
30%
701
16%
1459
February16th to endNight
17%
631
25%
1893
8%
631
39%
631
18%
1215
March1st to 15thNight
18%
720
18%
2145
7%
720
32%
720
18%
1402
March16th to endNight
21%
768
23%
1998
7%
768
33%
768
22%
1331
April1st to 15thNight
21%
718
17%
1796
4%
718
28%
718
21%
1271
April16th to endNight
26%
705
18%
1785
4%
705
35%
705
25%
1212
May1st to 15thNight
27%
480
19%
1560
9%
480
38%
480
18%
1015
May16th to endNight
40%
374
15%
1497
13%
374
49%
374
19%
907
June1st to 15thNight
40%
360
14%
1440
11%
360
51%
360
18%
904
June16th to endNight
47%
360
15%
1440
14%
360
58%
360
27%
796
July1st to 15thNight
52%
340
14%
1360
18%
340
55%
340
22%
800
July16th to endNight
53%
376
15%
1418
16%
354
60%
354
23%
816
August1st to 15thNight
50%
538
18%
1609
12%
536
55%
536
31%
978
August16th to endNight
55%
764
20%
1910
10%
764
58%
764
34%
1251
September1st to 15thNight
45%
720
23%
1800
11%
720
50%
720
33%
1169
September16th to endNight
50%
681
26%
1865
18%
681
56%
681
35%
1139
October1st to 15thNight
36%
660
21%
1941
14%
660
45%
660
25%
1250
October16th to endNight
25%
704
20%
2197
8%
704
41%
704
24%
1377
November1st to 15thNight
29%
700
21%
2277
8%
700
46%
700
23%
1425
November16th to endNight
26%
720
20%
2409
11%
720
39%
720
19%
1534
December1st to 15thNight
22%
720
16%
2520
6%
720
35%
720
15%
1653
December16th to endNight
15%
768
17%
2688
3%
768
31%
768
14%
1796

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%38%
47974
Night
16%6%2442445%7%41%
47062
Cloud CoverDay
16%6%25%5%3445%7%38%
47983
Night
16%6%2442445%7%41%
47068
TransparencyDay
44%5%11%22%14%1
47662
Night
42%412%23%15%1
46892
SeeingDay
20%13%28%22%11%4
5764
Night
19%13%30%25%9%
15000

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%6%25%5%25%5%5%6%40%
1432
16th to endDay
13%7%25%43445%6%38%
1623
February1st to 15thDay
15%8%36%5%35%348%35%
1619
16th to endDay
14%7%35%435%436%40%
1580
March1st to 15thDay
18%6%3443436%7%35%
1802
16th to endDay
17%7%25%424445%40%
2226
April1st to 15thDay
19%8%34323446%40%
2152
16th to endDay
16%425%6%34336%42%
2175
May1st to 15thDay
20%7%245%3436%7%33%
2401
16th to endDay
15%6%35%5%345%5%7%35%
2618
June1st to 15thDay
20%5%245%35%5%6%8%33%
2520
16th to endDay
12%5%26%5%35%6%5%8%36%
2520
July1st to 15thDay
11%5%36%6%45%5%7%9%34%
2520
16th to endDay
11%427%6%45%6%6%8%36%
2654
August1st to 15thDay
12%6%25%6%345%6%7%37%
2325
16th to endDay
13%5%25%425%5%6%7%41%
2292
September1st to 15thDay
14%4245%35%45%6%41%
2160
16th to endDay
14%425%434446%45%
1888
October1st to 15thDay
18%6%24424347%40%
1688
16th to endDay
18%6%245%335%47%39%
1674
November1st to 15thDay
17%6%23423346%45%
1581
16th to endDay
17%6%23333447%41%
1548
December1st to 15thDay
17%7%35%5%24346%39%
1440
16th to endDay
19%8%25%3345%5%7%33%
1536
January1st to 15thNight
16%6%25%4245%5%7%40%
2506
16th to endNight
14%8%345%24447%39%
2598
February1st to 15thNight
14%7%35%43445%6%39%
2239
16th to endNight
15%6%25%424446%42%
1893
March1st to 15thNight
19%6%2342345%6%40%
2132
16th to endNight
17%7%24423347%42%
1998
April1st to 15thNight
17%7%345%25%447%36%
1796
16th to endNight
17%5%3442435%6%42%
1785
May1st to 15thNight
18%5%35%5%2345%6%38%
1560
16th to endNight
15%6%26%42437%8%39%
1495
June1st to 15thNight
20%4245%145%5%7%38%
1440
16th to endNight
9%415%4245%5%9%46%
1440
July1st to 15thNight
12%425%435%45%8%43%
1440
16th to endNight
11%3145%36%6%6%9%42%
1514
August1st to 15thNight
11%4245%245%5%9%45%
1619
16th to endNight
14%415%434447%45%
1910
September1st to 15thNight
15%5%2432335%6%48%
1800
16th to endNight
11%424423336%51%
1865
October1st to 15thNight
16%6%35%423345%44%
1941
16th to endNight
18%6%24423446%43%
2197
November1st to 15thNight
15%7%24423346%44%
2277
16th to endNight
17%6%24425%35%7%39%
2409
December1st to 15thNight
20%7%25%43445%6%36%
2520
16th to endNight
18%7%345%3445%7%35%
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
14%6%25%435%5%5%6%39%
1432
16th to endDay
13%7%36%425%5%5%6%39%
1623
February1st to 15thDay
15%7%36%6%34447%35%
1619
16th to endDay
14%6%36%435%346%40%
1580
March1st to 15thDay
18%7%25%43446%7%35%
1812
16th to endDay
18%7%25%424445%40%
2225
April1st to 15thDay
18%9%24313446%40%
2152
16th to endDay
16%5%246%34336%42%
2175
May1st to 15thDay
20%7%345%3445%7%33%
2401
16th to endDay
15%7%35%5%345%5%7%35%
2618
June1st to 15thDay
20%5%25%435%5%6%8%33%
2520
16th to endDay
12%5%26%5%45%6%6%8%35%
2520
July1st to 15thDay
11%6%25%6%36%5%7%9%34%
2520
16th to endDay
11%5%36%6%35%6%6%8%36%
2654
August1st to 15thDay
13%6%26%6%35%46%7%36%
2325
16th to endDay
13%4244345%6%7%40%
2292
September1st to 15thDay
14%5%25%5%36%45%6%42%
2160
16th to endDay
14%425%43445%5%44%
1888
October1st to 15thDay
18%6%24434347%40%
1688
16th to endDay
18%7%235%34447%39%
1674
November1st to 15thDay
17%6%2332225%6%45%
1581
16th to endDay
18%6%23324447%41%
1548
December1st to 15thDay
16%7%45%5%24446%39%
1440
16th to endDay
19%8%25%425%45%7%34%
1536
January1st to 15thNight
16%5%25%4345%5%6%40%
2506
16th to endNight
14%8%345%24447%39%
2598
February1st to 15thNight
13%7%35%435%45%6%39%
2232
16th to endNight
14%7%25%423346%42%
1893
March1st to 15thNight
19%6%2342345%6%40%
2145
16th to endNight
16%7%24423347%42%
1998
April1st to 15thNight
16%8%245%35%5%47%36%
1796
16th to endNight
17%6%25%5%2335%6%42%
1785
May1st to 15thNight
18%6%25%42345%7%38%
1560
16th to endNight
15%5%35%42446%8%39%
1495
June1st to 15thNight
20%4245%236%5%7%38%
1440
16th to endNight
9%4244245%5%9%46%
1440
July1st to 15thNight
12%325%5%3445%8%43%
1440
16th to endNight
11%3145%26%6%6%10%41%
1514
August1st to 15thNight
11%415%43445%9%45%
1619
16th to endNight
13%424424447%45%
1910
September1st to 15thNight
15%5%2432345%5%48%
1800
16th to endNight
12%425%423336%51%
1865
October1st to 15thNight
17%6%25%423345%44%
1941
16th to endNight
18%5%23423446%43%
2197
November1st to 15thNight
15%6%245%23346%44%
2277
16th to endNight
17%6%24425%35%6%39%
2409
December1st to 15thNight
19%7%25%43445%7%36%
2520
16th to endNight
18%7%25%5%3435%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
42%5%14%22%12%3
1433
16th to endDay
44%412%24%12%2
1623
February1st to 15thDay
47%5%10%22%12%2
1622
16th to endDay
44%410%24%14%1
1580
March1st to 15thDay
46%314%21%10%1
1812
16th to endDay
45%49%21%17%2
2226
April1st to 15thDay
44%49%22%14%4
2152
16th to endDay
43%47%21%19%3
2175
May1st to 15thDay
48%5%8%20%14%2
2401
16th to endDay
46%5%14%19%13%1
2622
June1st to 15thDay
47%6%12%21%11%
2520
16th to endDay
43%7%11%24%13%
2520
July1st to 15thDay
43%7%10%20%16%1
2371
16th to endDay
41%6%12%23%13%2
2487
August1st to 15thDay
43%5%13%20%15%
2311
16th to endDay
39%5%9%27%16%1
2292
September1st to 15thDay
41%5%9%22%19%1
2160
16th to endDay
40%39%22%22%2
1888
October1st to 15thDay
44%5%10%22%16%2
1688
16th to endDay
43%412%23%14%1
1674
November1st to 15thDay
41%313%21%17%3
1581
16th to endDay
41%311%26%14%1
1548
December1st to 15thDay
46%416%20%11%1
1440
16th to endDay
47%6%14%20%10%
1536
January1st to 15thNight
42%413%23%12%2
2506
16th to endNight
43%311%25%14%1
2598
February1st to 15thNight
45%413%21%12%2
2240
16th to endNight
41%47%26%17%2
1893
March1st to 15thNight
44%314%22%12%3
2145
16th to endNight
42%310%22%17%3
1998
April1st to 15thNight
47%49%22%15%2
1796
16th to endNight
42%48%21%20%2
1785
May1st to 15thNight
44%5%10%20%16%1
1560
16th to endNight
41%5%17%19%13%2
1497
June1st to 15thNight
43%6%13%22%13%
1440
16th to endNight
33%6%16%28%14%
1440
July1st to 15thNight
38%6%13%24%14%2
1360
16th to endNight
35%8%16%23%14%2
1418
August1st to 15thNight
35%5%14%26%15%1
1609
16th to endNight
38%412%23%20%1
1910
September1st to 15thNight
37%411%26%19%
1800
16th to endNight
35%39%24%27%1
1865
October1st to 15thNight
41%411%22%17%1
1941
16th to endNight
40%314%25%15%
2197
November1st to 15thNight
41%411%20%18%3
2277
16th to endNight
44%312%25%12%2
2409
December1st to 15thNight
47%414%21%12%
2520
16th to endNight
48%5%12%21%11%
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
23%30%25%20%1
60
16th to endDay
22%22%37%12%3
79
February1st to 15thDay
23%36%26%11%1
135
16th to endDay
17%24%36%17%3
239
March1st to 15thDay
24%23%27%18%5%
270
16th to endDay
23%19%34%13%5%3
288
April1st to 15thDay
24%16%35%12%9%
270
16th to endDay
22%14%31%15%11%3
270
May1st to 15thDay
34%14%23%14%10%2
288
16th to endDay
19%10%29%24%14%1
331
June1st to 15thDay
20%12%28%23%11%2
315
16th to endDay
16%11%30%27%10%3
315
July1st to 15thDay
15%7%30%29%14%3
305
16th to endDay
12%5%24%33%21%3
326
August1st to 15thDay
16%5%22%31%13%9%
313
16th to endDay
13%421%28%21%10%
332
September1st to 15thDay
14%12%24%23%13%10%
315
16th to endDay
18%325%21%14%16%
275
October1st to 15thDay
22%7%23%25%16%5%
255
16th to endDay
17%17%33%19%10%
256
November1st to 15thDay
23%13%25%25%8%2
235
16th to endDay
22%23%28%17%42
168
December1st to 15thDay
25%28%26%11%6%1
60
16th to endDay
28%28%34%7%1
64
January1st to 15thNight
20%19%36%19%4
720
16th to endNight
21%19%36%20%2
768
February1st to 15thNight
19%19%40%19%
704
16th to endNight
21%23%34%17%3
631
March1st to 15thNight
25%20%31%18%3
720
16th to endNight
22%20%30%19%6%
768
April1st to 15thNight
21%20%33%21%3
718
16th to endNight
20%16%33%21%7%
705
May1st to 15thNight
22%15%30%25%6%
480
16th to endNight
18%8%26%34%10%1
375
June1st to 15thNight
20%7%25%34%11%
360
16th to endNight
11%331%42%10%
360
July1st to 15thNight
14%322%42%16%
340
16th to endNight
10%224%40%19%1
376
August1st to 15thNight
14%125%39%17%1
538
16th to endNight
15%216%37%25%2
764
September1st to 15thNight
16%5%24%35%15%1
720
16th to endNight
14%422%29%23%3
681
October1st to 15thNight
20%10%26%27%14%
660
16th to endNight
21%15%34%22%6%
704
November1st to 15thNight
20%14%30%23%10%1
700
16th to endNight
21%17%29%22%9%
720
December1st to 15thNight
25%16%32%19%6%
720
16th to endNight
25%19%35%17%2
768
Page generated at 2017-09-22 07:35:33. Version ac04

Copyright 2017 A. Danko


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