Bradley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bradley clear sky chart from 2005-11-05 to 2017-09-18.

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
38%
15932
18%
46847
11%
15890
45%
15890
24%
31381

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%
900
14%
2506
4%
895
27%
895
17%
1844
January16th to endNight
22%
960
13%
2649
5%
960
27%
960
16%
2000
February1st to 15thNight
22%
770
13%
2181
4%
770
29%
770
18%
1581
February16th to endNight
24%
631
17%
1893
7%
631
34%
631
18%
1358
March1st to 15thNight
26%
720
13%
2160
8%
720
31%
720
17%
1539
March16th to endNight
30%
635
15%
2016
9%
635
37%
635
20%
1387
April1st to 15thNight
28%
539
16%
1797
10%
539
39%
539
21%
1187
April16th to endNight
33%
540
18%
1737
11%
540
43%
540
22%
1166
May1st to 15thNight
38%
540
16%
1620
9%
540
45%
540
23%
1121
May16th to endNight
51%
562
18%
1508
10%
561
56%
561
31%
989
June1st to 15thNight
51%
540
18%
1440
11%
540
57%
540
36%
895
June16th to endNight
52%
540
17%
1440
10%
540
58%
540
34%
923
July1st to 15thNight
62%
510
17%
1360
13%
510
65%
510
37%
840
July16th to endNight
72%
564
23%
1417
18%
531
75%
531
42%
842
August1st to 15thNight
77%
539
22%
1604
21%
536
78%
536
42%
891
August16th to endNight
68%
573
22%
1910
22%
573
72%
573
33%
1080
September1st to 15thNight
66%
553
28%
1813
29%
553
70%
553
35%
1001
September16th to endNight
61%
669
28%
1848
21%
669
65%
669
36%
1111
October1st to 15thNight
51%
660
27%
1882
21%
660
58%
660
34%
1128
October16th to endNight
28%
704
19%
2239
11%
704
38%
704
21%
1454
November1st to 15thNight
33%
700
25%
2276
16%
700
44%
700
25%
1364
November16th to endNight
28%
723
17%
2343
11%
723
36%
723
19%
1580
December1st to 15thNight
21%
900
12%
2520
5%
900
27%
900
16%
1906
December16th to endNight
17%
960
11%
2688
3%
960
24%
960
11%
2194

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
14%7%36%5%35%45%7%36%
47954
Night
14%7%36%424446%39%
47016
Cloud CoverDay
14%8%36%5%35%45%7%36%
47963
Night
14%7%36%5%24446%39%
47021
TransparencyDay
46%6%11%21%12%1
47640
Night
44%5%11%21%14%2
46848
SeeingDay
15%6%26%25%18%7%
5943
Night
18%8%28%30%13%1
15936

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%16%5%8%6%44445%25%
1432
16th to endDay
13%16%8%7%6%24346%25%
1573
February1st to 15thDay
16%11%5%7%6%25%446%27%
1678
16th to endDay
15%10%5%7%6%44345%32%
1580
March1st to 15thDay
17%13%38%5%24347%27%
1790
16th to endDay
17%9%46%5%35%46%7%29%
2218
April1st to 15thDay
19%8%36%5%33346%34%
2151
16th to endDay
19%7%25%5%245%46%34%
2223
May1st to 15thDay
20%8%45%435%45%6%31%
2331
16th to endDay
13%5%25%5%35%45%8%38%
2605
June1st to 15thDay
11%5%15%425%46%8%43%
2520
16th to endDay
9%426%5%36%6%7%9%37%
2520
July1st to 15thDay
8%425%6%35%5%6%9%42%
2520
16th to endDay
6%3245%36%6%7%10%42%
2655
August1st to 15thDay
6%4245%35%6%6%8%45%
2345
16th to endDay
9%426%4345%6%7%43%
2292
September1st to 15thDay
12%5%14435%45%6%46%
2134
16th to endDay
9%5%25%435%45%8%45%
1837
October1st to 15thDay
14%6%244235%5%6%43%
1746
16th to endDay
18%7%26%4345%47%34%
1632
November1st to 15thDay
14%6%25%323446%45%
1582
16th to endDay
18%8%47%424336%35%
1614
December1st to 15thDay
19%13%49%435%34426%
1440
16th to endDay
23%14%5%7%6%33345%22%
1536
January1st to 15thNight
17%11%48%5%2334432%
2506
16th to endNight
15%12%6%8%6%24346%28%
2649
February1st to 15thNight
16%11%46%5%23336%33%
2179
16th to endNight
16%9%47%5%3445%5%33%
1893
March1st to 15thNight
17%10%47%5%24445%33%
2147
16th to endNight
16%8%36%4345%5%7%35%
2016
April1st to 15thNight
15%7%36%5%24346%39%
1797
16th to endNight
19%5%25%5%3335%5%38%
1737
May1st to 15thNight
19%5%24435%45%7%36%
1620
16th to endNight
9%5%3443446%9%43%
1507
June1st to 15thNight
10%5%24423448%50%
1440
16th to endNight
7%5%35%5%345%5%9%44%
1440
July1st to 15thNight
7%4135%245%5%9%50%
1440
16th to endNight
42244345%5%8%53%
1513
August1st to 15thNight
342343447%11%52%
1613
16th to endNight
9%3244235%5%7%51%
1910
September1st to 15thNight
11%314323347%54%
1813
16th to endNight
7%424425%5%6%7%49%
1848
October1st to 15thNight
11%423323346%51%
1882
16th to endNight
18%7%36%423245%41%
2239
November1st to 15thNight
12%6%35%413445%46%
2276
16th to endNight
18%8%36%5%34346%36%
2343
December1st to 15thNight
20%12%48%43334430%
2520
16th to endNight
23%13%6%7%6%35%33421%
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
15%16%5%8%6%44435%25%
1432
16th to endDay
13%16%8%7%6%24336%25%
1573
February1st to 15thDay
16%12%47%6%25%446%27%
1678
16th to endDay
15%11%5%7%6%35%345%32%
1580
March1st to 15thDay
18%13%37%5%24347%27%
1800
16th to endDay
17%9%46%5%345%5%7%29%
2217
April1st to 15thDay
19%8%36%5%34347%34%
2151
16th to endDay
19%8%25%5%2445%6%34%
2223
May1st to 15thDay
20%8%45%5%25%45%6%31%
2331
16th to endDay
13%5%25%6%36%45%8%37%
2605
June1st to 15thDay
10%5%25%435%46%8%43%
2520
16th to endDay
9%436%5%36%5%7%9%38%
2520
July1st to 15thDay
8%425%6%345%6%9%42%
2520
16th to endDay
6%3245%46%6%8%9%42%
2655
August1st to 15thDay
6%4245%35%6%6%9%45%
2345
16th to endDay
9%426%435%5%6%7%43%
2292
September1st to 15thDay
12%5%245%3445%6%45%
2134
16th to endDay
9%5%25%435%45%8%45%
1837
October1st to 15thDay
14%6%245%235%5%6%43%
1746
16th to endDay
18%8%25%4345%5%6%34%
1632
November1st to 15thDay
14%7%25%313446%45%
1582
16th to endDay
18%8%47%424337%35%
1614
December1st to 15thDay
19%13%48%5%35%445%25%
1440
16th to endDay
22%14%6%6%6%33345%22%
1536
January1st to 15thNight
17%11%48%5%2334432%
2506
16th to endNight
15%12%6%8%5%34346%28%
2649
February1st to 15thNight
16%11%47%5%24436%33%
2172
16th to endNight
16%9%47%6%24445%32%
1893
March1st to 15thNight
18%10%47%5%24445%33%
2160
16th to endNight
16%8%36%4245%5%7%35%
2016
April1st to 15thNight
15%7%36%5%24346%38%
1797
16th to endNight
19%5%35%5%3345%5%38%
1737
May1st to 15thNight
19%5%3443445%7%35%
1619
16th to endNight
9%5%25%4345%6%9%43%
1507
June1st to 15thNight
9%5%2442335%7%50%
1440
16th to endNight
7%5%35%5%25%5%5%9%44%
1440
July1st to 15thNight
7%3144245%5%9%50%
1440
16th to endNight
422443445%9%53%
1513
August1st to 15thNight
332433447%11%51%
1613
16th to endNight
9%3244235%5%7%51%
1910
September1st to 15thNight
11%313423338%54%
1813
16th to endNight
7%4244245%6%7%50%
1848
October1st to 15thNight
11%5%24323346%51%
1882
16th to endNight
18%7%35%423245%41%
2239
November1st to 15thNight
12%6%35%413446%46%
2276
16th to endNight
18%7%36%5%34346%36%
2343
December1st to 15thNight
20%12%47%42434430%
2520
16th to endNight
23%14%6%7%6%35%33421%
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
61%311%12%9%
1433
16th to endDay
61%411%16%6%
1573
February1st to 15thDay
57%5%11%16%7%1
1680
16th to endDay
54%412%22%5%1
1580
March1st to 15thDay
56%412%18%6%
1800
16th to endDay
53%6%12%20%6%1
2218
April1st to 15thDay
50%410%20%13%
2151
16th to endDay
49%6%12%17%10%4
2223
May1st to 15thDay
52%6%11%21%7%
2331
16th to endDay
43%6%11%19%16%2
2609
June1st to 15thDay
37%7%10%23%19%1
2520
16th to endDay
39%8%12%21%16%1
2520
July1st to 15thDay
37%8%12%22%16%3
2371
16th to endDay
33%8%17%24%13%2
2488
August1st to 15thDay
33%7%13%25%18%1
2330
16th to endDay
36%8%11%22%17%3
2292
September1st to 15thDay
37%6%9%23%18%4
2134
16th to endDay
36%5%9%26%20%1
1837
October1st to 15thDay
40%5%10%26%15%2
1746
16th to endDay
48%412%22%10%1
1632
November1st to 15thDay
39%312%23%17%3
1582
16th to endDay
50%313%22%9%
1614
December1st to 15thDay
61%49%17%6%
1440
16th to endDay
64%410%12%6%
1536
January1st to 15thNight
54%411%17%11%
2506
16th to endNight
57%414%16%8%
2649
February1st to 15thNight
53%411%20%9%1
2181
16th to endNight
52%411%20%10%
1893
March1st to 15thNight
53%312%19%9%1
2160
16th to endNight
47%6%14%20%9%1
2016
April1st to 15thNight
45%410%21%15%2
1797
16th to endNight
46%5%9%19%13%4
1737
May1st to 15thNight
46%6%12%21%13%
1620
16th to endNight
35%8%13%19%18%3
1509
June1st to 15thNight
33%5%10%26%20%3
1440
16th to endNight
35%6%13%23%17%3
1440
July1st to 15thNight
31%6%12%26%18%3
1360
16th to endNight
27%6%14%28%18%4
1417
August1st to 15thNight
24%7%16%28%19%3
1604
16th to endNight
31%6%11%25%20%5%
1910
September1st to 15thNight
29%5%9%26%23%5%
1813
16th to endNight
31%6%8%27%23%3
1848
October1st to 15thNight
33%49%25%24%1
1882
16th to endNight
45%310%24%14%1
2239
November1st to 15thNight
39%39%25%18%4
2276
16th to endNight
49%312%22%11%
2343
December1st to 15thNight
58%310%17%9%
2520
16th to endNight
67%38%13%6%
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
28%11%31%20%7%1
90
16th to endDay
18%13%36%23%6%1
96
February1st to 15thDay
25%20%41%12%1
90
16th to endDay
20%11%29%25%11%1
81
March1st to 15thDay
33%16%26%18%4
90
16th to endDay
26%11%30%22%7%2
250
April1st to 15thDay
22%12%29%22%10%2
270
16th to endDay
22%8%31%20%12%4
270
May1st to 15thDay
23%7%29%21%13%4
288
16th to endDay
16%6%30%23%17%5%
505
June1st to 15thDay
11%328%30%20%5%
495
16th to endDay
11%8%31%27%15%5%
495
July1st to 15thDay
10%325%26%21%12%
475
16th to endDay
6%119%33%25%12%
515
August1st to 15thDay
6%215%31%25%18%
376
16th to endDay
9%119%27%26%14%
332
September1st to 15thDay
12%215%25%32%11%
315
16th to endDay
9%417%25%33%9%
262
October1st to 15thDay
13%5%23%29%21%6%
186
16th to endDay
22%9%33%30%4
96
November1st to 15thDay
7%8%25%28%20%8%
90
16th to endDay
38%7%32%12%7%1
90
December1st to 15thDay
21%18%33%17%7%1
90
16th to endDay
29%21%42%33
96
January1st to 15thNight
23%14%37%20%5%
900
16th to endNight
20%12%35%27%3
960
February1st to 15thNight
23%11%34%25%4
773
16th to endNight
22%11%35%24%5%
631
March1st to 15thNight
23%11%34%24%5%
720
16th to endNight
20%7%35%26%7%1
635
April1st to 15thNight
17%11%36%27%6%
539
16th to endNight
21%8%31%27%10%
540
May1st to 15thNight
21%431%30%11%
540
16th to endNight
11%326%38%19%
563
June1st to 15thNight
13%324%43%15%
540
16th to endNight
9%227%40%18%1
540
July1st to 15thNight
9%118%42%25%1
510
16th to endNight
6%16%40%33%3
564
August1st to 15thNight
47%52%29%5%
539
16th to endNight
10%13%35%36%4
573
September1st to 15thNight
12%311%37%28%5%
553
16th to endNight
10%317%35%30%3
669
October1st to 15thNight
13%6%23%34%19%1
660
16th to endNight
22%11%33%22%9%
704
November1st to 15thNight
15%11%35%25%11%1
700
16th to endNight
23%12%30%24%8%
723
December1st to 15thNight
27%11%31%23%5%
900
16th to endNight
30%10%33%22%3
960
Page generated at 2017-09-19 06:32:32. Version ac04

Copyright 2017 A. Danko


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