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 2005-11-06 to 2024-03-28.

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
48%
23895
22%
79985
17%
23791
56%
23791
26%
49156

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 10thNight
26%
751
22%
4014
10%
737
40%
737
13%
2422
January11th to 20thNight
28%
758
26%
3946
11%
740
41%
740
13%
2283
January21st to endNight
26%
832
19%
4132
13%
814
42%
814
14%
2685
February1st to 10thNight
32%
760
24%
2280
14%
760
42%
760
24%
1490
February11th to 20thNight
24%
743
20%
2218
9%
739
34%
739
22%
1496
February21st to endNight
22%
628
19%
1884
7%
628
32%
628
20%
1280
March1st to 10thNight
31%
760
23%
2280
13%
760
41%
760
26%
1456
March11th to 20thNight
31%
760
20%
2122
10%
760
39%
760
26%
1395
March21st to endNight
34%
820
22%
2255
11%
820
42%
820
27%
1481
April1st to 10thNight
40%
540
25%
1800
18%
540
51%
540
29%
1054
April11th to 20thNight
38%
533
27%
1775
17%
533
52%
533
30%
1021
April21st to endNight
51%
540
28%
1760
22%
540
59%
540
33%
990
May1st to 10thNight
54%
540
25%
1620
16%
540
62%
540
35%
957
May11th to 20thNight
58%
531
18%
1592
14%
531
62%
531
28%
1002
May21st to endNight
70%
582
22%
1744
19%
582
71%
582
32%
1054
June1st to 10thNight
69%
540
18%
1620
16%
540
69%
540
27%
1034
June11th to 20thNight
77%
540
17%
1620
13%
540
79%
540
39%
928
June21st to endNight
73%
540
18%
1620
15%
540
74%
540
34%
967
July1st to 10thNight
72%
525
14%
1575
13%
525
73%
525
28%
1019
July11th to 20thNight
77%
522
15%
1566
15%
522
78%
522
30%
998
July21st to endNight
72%
591
16%
1672
15%
558
74%
558
27%
1104
August1st to 10thNight
76%
537
17%
1719
19%
534
76%
534
32%
1023
August11th to 20thNight
69%
534
16%
1776
19%
534
69%
534
25%
1138
August21st to endNight
66%
594
20%
1980
23%
594
66%
594
24%
1289
September1st to 10thNight
73%
613
21%
1873
22%
613
73%
613
30%
1161
September11th to 20thNight
63%
720
23%
1980
19%
720
65%
720
31%
1274
September21st to endNight
65%
720
29%
1980
22%
720
70%
720
40%
1155
October1st to 10thNight
61%
720
32%
1980
25%
720
66%
720
42%
1123
October11th to 20thNight
51%
720
34%
1983
23%
720
61%
720
37%
1174
October21st to endNight
50%
792
29%
2474
26%
792
57%
792
31%
1446
November1st to 10thNight
55%
740
28%
2406
26%
740
62%
740
36%
1310
November11th to 20thNight
43%
760
30%
2470
22%
760
56%
760
33%
1357
November21st to endNight
41%
760
25%
2470
18%
760
52%
760
28%
1477
December1st to 10thNight
32%
760
23%
2470
14%
760
45%
760
20%
1633
December11th to 20thNight
35%
759
25%
2908
17%
758
44%
758
21%
1730
December21st to endNight
30%
830
14%
4421
13%
817
39%
817
12%
2750

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
13%6%35%5%35%5%6%8%41%
79227
Night
13%7%25%5%3445%7%45%
80774
TransparencyDay
41%7%11%19%18%4
78950
Night
38%6%11%19%20%6%
80570
SeeingDay
16%10%22%23%19%10%
13792
Night
15%8%22%30%21%4
23919

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 10thDay
17%13%35%43445%5%36%
2836
11th to 20thDay
14%7%35%433435%48%
2840
21st to endDay
23%10%35%423236%40%
3453
February1st to 10thDay
19%9%45%5%34445%39%
1900
11th to 20thDay
22%8%36%423345%39%
1848
21st to endDay
20%8%36%5%33446%37%
1570
March1st to 10thDay
17%7%26%5%3435%6%43%
1900
11th to 20thDay
17%8%35%6%445%5%6%37%
2057
21st to endDay
16%6%36%5%346%5%7%38%
2270
April1st to 10thDay
13%6%25%5%3445%7%46%
2160
11th to 20thDay
14%6%35%5%3445%6%46%
2134
21st to endDay
10%425%5%345%5%8%49%
2198
May1st to 10thDay
11%5%245%35%5%6%7%48%
2340
11th to 20thDay
9%5%35%6%35%6%6%8%44%
2301
21st to endDay
8%5%25%5%36%6%7%9%43%
2531
June1st to 10thDay
11%6%26%7%5%7%7%8%10%32%
2340
11th to 20thDay
6%325%5%46%5%8%11%44%
2340
21st to endDay
8%425%5%5%7%8%9%10%37%
2340
July1st to 10thDay
11%6%36%6%5%8%7%9%10%30%
2340
11th to 20thDay
6%426%6%6%8%8%9%13%32%
2340
21st to endDay
7%5%35%7%5%8%8%8%14%31%
2547
August1st to 10thDay
7%425%7%5%8%7%9%13%34%
2203
11th to 20thDay
10%5%36%6%5%7%6%8%11%33%
2125
21st to endDay
11%6%36%7%5%6%7%7%9%33%
2376
September1st to 10thDay
9%5%36%7%46%6%6%8%40%
2066
11th to 20thDay
12%6%26%5%45%5%6%6%42%
1980
21st to endDay
11%425%5%4445%6%50%
1980
October1st to 10thDay
11%42443445%5%53%
1980
11th to 20thDay
11%5%2342245%6%56%
1976
21st to endDay
14%5%25%424345%53%
1877
November1st to 10thDay
14%5%2442332456%
1672
11th to 20thDay
13%6%24424446%52%
1710
21st to endDay
14%6%25%5%235%5%7%45%
1710
December1st to 10thDay
21%6%36%42445%6%39%
1710
11th to 20thDay
18%6%35%6%34445%42%
2153
21st to endDay
20%8%5%6%5%34346%35%
3124
January1st to 10thNight
18%12%34434446%39%
4109
11th to 20thNight
16%9%35%424445%44%
4120
21st to endNight
21%14%3442333439%
4198
February1st to 10thNight
17%7%35%5%3445%6%42%
2280
11th to 20thNight
22%7%35%42334443%
2218
21st to endNight
19%8%25%435%45%7%38%
1884
March1st to 10thNight
17%8%24424446%45%
2280
11th to 20thNight
15%7%36%4245%6%8%41%
2122
21st to endNight
15%7%345%35%448%44%
2255
April1st to 10thNight
12%4145%445%7%8%48%
1800
11th to 20thNight
14%5%2433435%7%50%
1775
21st to endNight
9%5%35%43445%6%53%
1760
May1st to 10thNight
9%4345%345%5%8%52%
1620
11th to 20thNight
9%5%26%6%36%5%6%9%43%
1592
21st to endNight
8%5%245%35%5%7%9%48%
1744
June1st to 10thNight
5%436%6%46%7%9%12%38%
1620
11th to 20thNight
3323435%7%7%11%52%
1620
21st to endNight
5%5%25%425%6%6%13%46%
1620
July1st to 10thNight
7%425%6%35%7%9%13%38%
1620
11th to 20thNight
5%326%6%45%7%9%12%42%
1620
21st to endNight
45%36%6%5%7%7%7%13%38%
1771
August1st to 10thNight
6%325%5%36%5%9%13%43%
1730
11th to 20thNight
9%5%25%6%36%7%6%10%40%
1776
21st to endNight
13%6%35%5%345%6%9%41%
1980
September1st to 10thNight
7%4345%37%6%7%9%44%
1873
11th to 20thNight
10%5%36%4245%5%8%47%
1980
21st to endNight
8%42443346%8%53%
1980
October1st to 10thNight
9%414423346%60%
1980
11th to 20thNight
12%42443335%6%53%
1983
21st to endNight
14%5%15%5%2333454%
2474
November1st to 10thNight
11%423423346%57%
2406
11th to 20thNight
13%6%24313346%55%
2470
21st to endNight
14%7%25%424446%48%
2470
December1st to 10thNight
18%7%35%5%3445%6%40%
2470
11th to 20thNight
17%9%24424335%48%
3042
21st to endNight
17%9%46%5%345%6%8%33%
4532

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 10thDay
50%47%14%21%4
2837
11th to 20thDay
40%47%23%23%3
2840
21st to endDay
49%27%17%19%5%
3453
February1st to 10thDay
48%38%18%19%3
1900
11th to 20thDay
49%35%18%19%6%
1858
21st to endDay
49%5%6%12%21%7%
1570
March1st to 10thDay
44%48%15%20%9%
1900
11th to 20thDay
47%5%11%14%18%5%
2057
21st to endDay
44%6%10%19%18%3
2270
April1st to 10thDay
37%6%11%21%18%7%
2160
11th to 20thDay
39%5%7%18%24%7%
2134
21st to endDay
33%6%9%25%24%3
2198
May1st to 10thDay
34%6%12%23%20%4
2340
11th to 20thDay
38%7%15%23%15%1
2305
21st to endDay
35%9%13%24%17%2
2531
June1st to 10thDay
44%11%14%17%13%1
2340
11th to 20thDay
32%9%21%22%16%1
2340
21st to endDay
37%11%16%22%11%2
2340
July1st to 10thDay
43%12%17%17%9%1
2275
11th to 20thDay
38%15%21%17%8%1
2271
21st to endDay
40%14%19%19%8%
2405
August1st to 10thDay
38%13%20%23%6%1
2190
11th to 20thDay
43%12%16%17%9%2
2125
21st to endDay
45%11%15%15%12%3
2376
September1st to 10thDay
39%10%14%17%14%6%
2066
11th to 20thDay
40%9%11%18%19%3
1980
21st to endDay
36%5%12%19%22%7%
1980
October1st to 10thDay
32%6%10%16%27%8%
1980
11th to 20thDay
30%5%7%23%27%8%
1976
21st to endDay
34%45%17%31%9%
1877
November1st to 10thDay
34%37%16%30%10%
1672
11th to 20thDay
34%47%18%26%10%
1710
21st to endDay
38%5%7%19%25%6%
1710
December1st to 10thDay
46%6%8%16%19%5%
1710
11th to 20thDay
46%36%17%21%6%
2150
21st to endDay
51%48%17%17%2
3124
January1st to 10thNight
46%36%17%24%3
4109
11th to 20thNight
43%46%22%19%6%
4120
21st to endNight
51%35%14%23%5%
4198
February1st to 10thNight
44%47%18%20%7%
2280
11th to 20thNight
47%45%16%20%8%
2219
21st to endNight
46%6%7%13%19%9%
1884
March1st to 10thNight
41%47%17%21%10%
2280
11th to 20thNight
40%6%11%17%19%6%
2122
21st to endNight
41%5%8%23%19%4
2255
April1st to 10thNight
34%6%11%21%20%7%
1800
11th to 20thNight
35%47%20%22%12%
1775
21st to endNight
32%5%10%26%22%5%
1760
May1st to 10thNight
31%7%11%21%26%4
1620
11th to 20thNight
36%8%16%21%16%2
1593
21st to endNight
31%10%12%27%18%3
1745
June1st to 10thNight
34%12%15%22%15%2
1620
11th to 20thNight
22%12%24%24%16%2
1620
21st to endNight
29%10%19%22%16%4
1620
July1st to 10thNight
33%13%21%19%11%2
1575
11th to 20thNight
30%14%24%20%9%3
1566
21st to endNight
36%13%20%20%10%1
1672
August1st to 10thNight
29%11%23%27%9%1
1719
11th to 20thNight
37%11%20%16%13%3
1776
21st to endNight
40%9%16%19%12%4
1980
September1st to 10thNight
33%10%18%18%16%5%
1873
11th to 20thNight
35%10%11%20%21%3
1980
21st to endNight
29%6%12%21%24%8%
1980
October1st to 10thNight
27%5%8%25%25%10%
1980
11th to 20thNight
32%47%20%26%10%
1983
21st to endNight
35%35%15%30%11%
2474
November1st to 10thNight
29%49%19%25%13%
2406
11th to 20thNight
32%47%19%27%12%
2470
21st to endNight
38%47%20%24%7%
2470
December1st to 10thNight
45%6%7%18%19%4
2470
11th to 20thNight
41%37%15%29%5%
3044
21st to endNight
48%410%19%17%2
4532

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 10thDay
22%25%37%13%3
270
11th to 20thDay
26%22%31%16%4
270
21st to endDay
24%27%35%11%31
297
February1st to 10thDay
25%21%36%14%4
270
11th to 20thDay
35%21%29%12%3
270
21st to endDay
28%26%35%10%
225
March1st to 10thDay
26%21%33%15%31
270
11th to 20thDay
22%18%33%18%7%1
427
21st to endDay
22%16%33%21%7%
490
April1st to 10thDay
20%14%31%20%12%2
420
11th to 20thDay
18%14%29%26%13%1
412
21st to endDay
15%11%30%28%14%2
420
May1st to 10thDay
15%10%28%24%18%6%
423
11th to 20thDay
11%5%21%32%21%11%
447
21st to endDay
10%5%17%30%22%16%
485
June1st to 10thDay
13%413%32%24%14%
450
11th to 20thDay
7%315%23%27%24%
450
21st to endDay
11%414%24%27%20%
450
July1st to 10thDay
10%27%26%28%27%
445
11th to 20thDay
6%17%23%32%31%
444
21st to endDay
7%29%22%34%26%
488
August1st to 10thDay
9%210%20%34%25%
446
11th to 20thDay
8%48%26%34%20%
439
21st to endDay
16%39%21%33%18%
495
September1st to 10thDay
8%39%29%37%15%
450
11th to 20thDay
13%412%25%32%14%
450
21st to endDay
12%317%27%32%10%
450
October1st to 10thDay
11%422%31%21%11%
450
11th to 20thDay
12%8%23%30%22%4
450
21st to endDay
17%11%21%31%18%2
392
November1st to 10thDay
20%9%25%31%11%4
270
11th to 20thDay
15%15%37%26%7%
270
21st to endDay
14%18%35%23%9%1
270
December1st to 10thDay
28%19%30%19%41
270
11th to 20thDay
23%17%33%19%7%1
270
21st to endDay
27%18%33%18%4
297
January1st to 10thNight
22%16%31%26%5%
760
11th to 20thNight
22%16%30%24%7%
760
21st to endNight
23%15%33%26%3
836
February1st to 10thNight
21%12%30%32%5%
760
11th to 20thNight
25%16%32%24%3
743
21st to endNight
23%17%34%24%2
628
March1st to 10thNight
21%13%31%30%5%
760
11th to 20thNight
19%12%35%25%9%1
760
21st to endNight
20%13%30%28%10%
820
April1st to 10thNight
14%9%33%29%13%1
540
11th to 20thNight
17%10%31%28%14%1
533
21st to endNight
12%6%25%40%16%1
540
May1st to 10thNight
10%5%27%32%23%3
540
11th to 20thNight
10%319%34%28%5%
531
21st to endNight
9%211%36%36%6%
584
June1st to 10thNight
6%212%37%38%5%
540
11th to 20thNight
3111%30%40%16%
540
21st to endNight
7%19%29%43%10%
540
July1st to 10thNight
8%26%23%45%16%
525
11th to 20thNight
5%5%23%51%16%
522
21st to endNight
6%17%26%46%14%
591
August1st to 10thNight
7%26%27%44%15%
537
11th to 20thNight
10%27%27%45%10%
534
21st to endNight
15%18%25%40%11%
594
September1st to 10thNight
8%27%28%43%11%
613
11th to 20thNight
13%312%28%39%5%
720
21st to endNight
9%215%34%37%3
720
October1st to 10thNight
10%421%34%25%6%
720
11th to 20thNight
13%7%25%33%21%2
720
21st to endNight
16%8%20%35%18%2
792
November1st to 10thNight
13%7%19%37%22%2
740
11th to 20thNight
16%9%28%33%12%1
760
21st to endNight
17%11%25%35%11%1
760
December1st to 10thNight
22%13%28%28%8%1
760
11th to 20thNight
25%9%28%29%9%1
760
21st to endNight
25%13%27%28%7%
836
Page generated at 2024-03-24 22:37:03. Version ac07

Copyright © 2024 Attilla Danko.


Old Broadwell Mill Observatory Clear Sky Chart |Charts Home