Old Broadwell Mill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Old Broadwell Mill Observatory clear sky chart from 2005-11-05 to

2017-09-12
.

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
50%
15321
23%
46903
17%
15278
57%
15278
29%
28870

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
28%
720
23%
2327
11%
716
44%
716
22%
1478
January16th to endNight
27%
768
24%
2367
12%
768
41%
768
22%
1557
February1st to 15thNight
31%
704
24%
2112
11%
701
44%
701
26%
1329
February16th to endNight
27%
631
24%
1893
10%
631
38%
631
24%
1221
March1st to 15thNight
31%
720
21%
2121
11%
720
40%
720
25%
1371
March16th to endNight
39%
766
22%
2110
13%
766
46%
766
30%
1333
April1st to 15thNight
42%
539
25%
1797
18%
539
53%
539
31%
1020
April16th to endNight
48%
540
27%
1773
20%
540
58%
540
33%
994
May1st to 15thNight
55%
540
22%
1620
15%
540
62%
540
30%
999
May16th to endNight
68%
561
23%
1682
18%
561
71%
561
33%
1011
June1st to 15thNight
75%
540
17%
1620
14%
540
75%
540
33%
991
June16th to endNight
77%
540
18%
1620
16%
540
79%
540
36%
948
July1st to 15thNight
76%
510
15%
1530
14%
510
76%
510
32%
938
July16th to endNight
73%
564
16%
1595
15%
531
75%
531
28%
1045
August1st to 15thNight
76%
539
20%
1750
22%
536
76%
536
31%
1038
August16th to endNight
67%
573
20%
1910
23%
573
68%
573
23%
1259
September1st to 15thNight
67%
637
20%
1874
20%
637
68%
637
28%
1213
September16th to endNight
63%
657
25%
1815
19%
657
66%
657
34%
1110
October1st to 15thNight
55%
660
34%
1815
25%
660
62%
660
39%
1057
October16th to endNight
50%
704
32%
2120
27%
704
59%
704
35%
1201
November1st to 15thNight
51%
700
30%
2276
26%
700
60%
700
36%
1211
November16th to endNight
41%
720
26%
2340
19%
720
53%
720
29%
1356
December1st to 15thNight
37%
720
23%
2340
16%
720
47%
720
23%
1488
December16th to endNight
32%
768
19%
2496
14%
768
40%
768
19%
1702

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
12%5%25%5%35%5%5%7%40%
47750
Night
11%5%2442445%7%46%
47102
TransparencyDay
41%7%11%18%17%4
47451
Night
36%6%10%20%20%6%
46905
SeeingDay
15%6%17%23%22%14%
5222
Night
14%7%21%29%22%4
15323

By Month

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
18%7%25%33435%5%42%
1611
16th to endDay
16%6%34424335%44%
1854
February1st to 15thDay
16%8%35%323335%42%
1750
16th to endDay
19%6%35%423346%40%
1580
March1st to 15thDay
16%8%35%42335%6%39%
1839
16th to endDay
15%6%245%235%46%42%
2122
April1st to 15thDay
13%6%25%5%23446%44%
2151
16th to endDay
10%415%5%245%5%6%46%
2186
May1st to 15thDay
11%425%5%35%5%5%7%43%
2331
16th to endDay
8%5%25%6%35%6%6%8%41%
2431
June1st to 15thDay
9%426%6%47%6%8%10%34%
2340
16th to endDay
6%324436%6%8%11%42%
2340
July1st to 15thDay
9%5%35%6%5%8%6%8%10%30%
2340
16th to endDay
7%425%7%5%8%7%8%12%30%
2465
August1st to 15thDay
7%3246%5%8%7%9%11%33%
2196
16th to endDay
11%5%26%7%5%7%7%7%9%28%
2292
September1st to 15thDay
11%5%26%7%36%6%6%7%36%
1993
16th to endDay
13%5%25%4345%6%5%43%
1815
October1st to 15thDay
12%31442335%5%51%
1815
16th to endDay
13%42431232457%
1749
November1st to 15thDay
14%5%24313325%54%
1582
16th to endDay
14%5%2431345%6%48%
1620
December1st to 15thDay
19%5%35%424445%40%
1620
16th to endDay
23%8%445%34335%34%
1728
January1st to 15thNight
16%6%24334445%43%
2327
16th to endNight
18%8%33424445%40%
2367
February1st to 15thNight
16%6%14423345%45%
2103
16th to endNight
16%6%25%424335%45%
1893
March1st to 15thNight
15%6%25%41445%7%43%
2121
16th to endNight
12%6%24324348%47%
2110
April1st to 15thNight
12%31332335%7%50%
1797
16th to endNight
9%42442435%6%53%
1773
May1st to 15thNight
9%325%5%35%447%46%
1619
16th to endNight
5%424435%5%6%8%48%
1682
June1st to 15thNight
4324436%7%8%11%43%
1620
16th to endNight
32144246%6%13%48%
1620
July1st to 15thNight
5%215%5%35%6%8%11%42%
1620
16th to endNight
4425%6%46%7%7%12%38%
1703
August1st to 15thNight
5%315%5%25%5%7%12%44%
1761
16th to endNight
11%5%25%5%25%6%6%10%38%
1910
September1st to 15thNight
7%425%5%26%5%6%9%42%
1874
16th to endNight
9%425%43445%6%50%
1815
October1st to 15thNight
10%314323346%56%
1815
16th to endNight
11%42441233357%
2120
November1st to 15thNight
11%412313336%57%
2276
16th to endNight
12%5%24413335%52%
2340
December1st to 15thNight
16%7%34423345%44%
2340
16th to endNight
20%8%25%5%24435%37%
2496

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
44%47%16%22%4
1612
16th to endDay
43%35%21%19%6%
1854
February1st to 15thDay
45%37%22%18%3
1752
16th to endDay
45%36%16%22%5%
1580
March1st to 15thDay
46%39%15%19%5%
1839
16th to endDay
41%6%11%19%17%2
2123
April1st to 15thDay
40%5%9%19%18%7%
2151
16th to endDay
36%5%10%20%23%3
2186
May1st to 15thDay
40%5%11%20%18%3
2331
16th to endDay
37%8%14%23%13%2
2435
June1st to 15thDay
41%10%16%19%11%
2340
16th to endDay
32%9%16%23%16%2
2340
July1st to 15thDay
42%10%17%17%9%1
2201
16th to endDay
41%13%17%18%8%
2310
August1st to 15thDay
40%12%16%19%9%2
2183
16th to endDay
48%11%12%15%10%1
2292
September1st to 15thDay
43%9%13%16%11%4
1993
16th to endDay
40%6%10%18%19%4
1815
October1st to 15thDay
34%5%8%16%25%9%
1815
16th to endDay
31%3416%32%10%
1749
November1st to 15thDay
34%25%17%30%9%
1582
16th to endDay
36%46%17%27%7%
1620
December1st to 15thDay
44%5%8%19%16%5%
1620
16th to endDay
54%38%16%13%4
1728
January1st to 15thNight
41%5%7%17%23%4
2327
16th to endNight
45%35%18%19%7%
2367
February1st to 15thNight
40%37%20%19%8%
2112
16th to endNight
42%35%18%24%5%
1893
March1st to 15thNight
41%49%19%18%6%
2121
16th to endNight
36%5%9%23%20%3
2110
April1st to 15thNight
32%410%22%20%9%
1797
16th to endNight
31%49%23%22%7%
1773
May1st to 15thNight
35%7%11%18%24%2
1620
16th to endNight
30%9%12%28%14%4
1684
June1st to 15thNight
30%10%18%25%13%1
1620
16th to endNight
25%11%19%20%19%3
1620
July1st to 15thNight
30%11%22%22%10%3
1530
16th to endNight
35%11%19%20%12%
1595
August1st to 15thNight
30%10%20%22%13%2
1750
16th to endNight
39%10%15%18%13%2
1910
September1st to 15thNight
35%10%15%18%15%4
1874
16th to endNight
34%5%10%21%21%6%
1815
October1st to 15thNight
29%47%22%24%11%
1815
16th to endNight
32%3413%33%14%
2120
November1st to 15thNight
29%36%18%28%13%
2276
16th to endNight
35%47%17%25%10%
2340
December1st to 15thNight
42%48%18%20%5%
2340
16th to endNight
49%47%17%16%4
2496

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%17%36%15%5%1
90
16th to endDay
20%23%46%332
96
February1st to 15thDay
17%31%37%11%2
90
16th to endDay
28%13%41%14%1
81
March1st to 15thDay
23%20%32%17%41
129
16th to endDay
19%7%33%22%15%
288
April1st to 15thDay
18%13%27%20%19%1
270
16th to endDay
14%7%23%32%18%4
270
May1st to 15thDay
15%6%24%24%15%13%
288
16th to endDay
12%6%14%29%21%16%
331
June1st to 15thDay
13%6%23%27%26%
315
16th to endDay
10%12%19%27%29%
315
July1st to 15thDay
9%15%25%27%31%
305
16th to endDay
9%320%32%33%
326
August1st to 15thDay
10%9%20%35%23%
313
16th to endDay
15%16%25%31%19%
332
September1st to 15thDay
11%29%21%34%20%
299
16th to endDay
14%314%32%25%8%
254
October1st to 15thDay
14%318%31%23%7%
255
16th to endDay
15%5%18%28%27%4
209
November1st to 15thDay
24%14%21%24%12%3
90
16th to endDay
15%15%32%23%12%1
90
December1st to 15thDay
26%16%30%20%42
90
16th to endDay
30%14%31%19%31
96
January1st to 15thNight
21%14%32%24%6%
720
16th to endNight
22%14%33%26%3
768
February1st to 15thNight
19%12%32%30%5%
704
16th to endNight
20%15%33%26%3
631
March1st to 15thNight
20%12%32%27%6%
720
16th to endNight
17%11%28%28%14%
766
April1st to 15thNight
15%8%31%27%15%1
539
16th to endNight
10%5%29%36%16%
540
May1st to 15thNight
11%325%32%23%4
540
16th to endNight
8%113%36%35%4
563
June1st to 15thNight
5%9%32%41%10%
540
16th to endNight
47%27%45%14%
540
July1st to 15thNight
6%5%24%49%12%
510
16th to endNight
6%7%23%46%15%
564
August1st to 15thNight
7%426%47%12%
539
16th to endNight
14%16%24%42%11%
573
September1st to 15thNight
10%19%27%40%10%
637
16th to endNight
11%115%35%33%2
657
October1st to 15thNight
12%324%30%25%4
660
16th to endNight
13%7%22%30%22%3
704
November1st to 15thNight
13%7%23%32%21%2
700
16th to endNight
17%11%25%31%13%
720
December1st to 15thNight
21%10%27%31%9%1
720
16th to endNight
26%11%27%26%8%
768
Page generated at 2017-09-13 06:39:09. Version ac04

Copyright 2017 A. Danko


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