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 2018-10-27.

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%
17423
18%
51226
11%
17381
45%
17381
24%
34207

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%
975
14%
2716
5%
970
29%
970
18%
1982
January16th to endNight
21%
1040
13%
2870
5%
1040
28%
1040
17%
2160
February1st to 15thNight
22%
836
14%
2367
5%
836
29%
836
18%
1721
February16th to endNight
24%
683
17%
2049
7%
683
33%
683
17%
1481
March1st to 15thNight
27%
780
15%
2340
9%
780
32%
780
19%
1632
March16th to endNight
30%
688
16%
2184
10%
688
37%
688
20%
1500
April1st to 15thNight
27%
584
16%
1947
10%
584
38%
584
21%
1300
April16th to endNight
35%
579
18%
1860
11%
579
44%
579
22%
1244
May1st to 15thNight
39%
585
16%
1755
9%
585
46%
585
24%
1200
May16th to endNight
52%
610
17%
1637
10%
609
57%
609
31%
1076
June1st to 15thNight
51%
585
18%
1560
11%
585
57%
585
36%
974
June16th to endNight
52%
585
17%
1560
10%
585
57%
585
33%
1005
July1st to 15thNight
65%
555
19%
1480
14%
555
67%
555
38%
899
July16th to endNight
72%
612
23%
1545
18%
579
75%
579
42%
913
August1st to 15thNight
77%
575
22%
1708
22%
572
78%
572
42%
948
August16th to endNight
66%
621
21%
2070
21%
621
70%
621
33%
1167
September1st to 15thNight
66%
599
29%
1964
30%
599
70%
599
35%
1084
September16th to endNight
61%
777
28%
2145
23%
777
64%
777
37%
1292
October1st to 15thNight
49%
780
25%
2224
18%
780
55%
780
30%
1390
October16th to endNight
29%
816
20%
2594
13%
816
38%
816
23%
1653
November1st to 15thNight
32%
760
23%
2471
16%
760
42%
760
24%
1508
November16th to endNight
27%
783
19%
2538
11%
783
38%
783
20%
1680
December1st to 15thNight
21%
975
12%
2730
4%
975
28%
975
17%
2034
December16th to endNight
18%
1040
11%
2912
3%
1040
24%
1040
11%
2364

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%3445%7%37%
52334
Night
14%7%35%424446%40%
51395
Cloud CoverDay
14%7%36%5%3445%7%36%
52343
Night
14%7%35%424446%40%
51400
TransparencyDay
45%6%11%21%12%2
52020
Night
44%5%11%21%14%2
51227
SeeingDay
15%6%26%25%17%7%
7438
Night
18%7%28%30%13%1
17427

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%7%6%43435%26%
1552
16th to endDay
14%16%7%7%6%24346%26%
1704
February1st to 15thDay
17%11%47%6%25%447%27%
1822
16th to endDay
17%11%5%7%6%3424432%
1710
March1st to 15thDay
17%12%38%5%25%347%29%
1940
16th to endDay
18%9%46%5%35%46%7%29%
2403
April1st to 15thDay
19%9%36%5%33346%33%
2331
16th to endDay
19%7%25%5%245%46%35%
2375
May1st to 15thDay
19%8%45%5%35%45%7%31%
2526
16th to endDay
13%5%25%5%35%45%8%38%
2828
June1st to 15thDay
11%5%15%425%46%8%43%
2730
16th to endDay
9%425%5%36%6%7%9%38%
2730
July1st to 15thDay
7%425%6%35%5%6%8%44%
2730
16th to endDay
6%3245%46%6%7%9%42%
2879
August1st to 15thDay
6%4245%35%6%6%8%45%
2494
16th to endDay
9%426%4345%6%7%43%
2484
September1st to 15thDay
12%5%145%3445%6%45%
2312
16th to endDay
8%42443445%9%46%
2145
October1st to 15thDay
15%7%25%5%235%5%6%40%
2064
16th to endDay
18%8%25%434446%37%
1886
November1st to 15thDay
16%6%25%32345%6%43%
1717
16th to endDay
17%8%47%423336%38%
1748
December1st to 15thDay
18%12%49%435%34427%
1560
16th to endDay
21%14%5%7%6%33345%23%
1664
January1st to 15thNight
17%11%47%5%2334433%
2716
16th to endNight
14%12%6%8%6%24346%29%
2870
February1st to 15thNight
17%11%5%6%5%23336%32%
2365
16th to endNight
17%10%47%5%3435%5%32%
2049
March1st to 15thNight
17%10%36%5%24445%35%
2327
16th to endNight
16%8%37%4335%5%7%35%
2184
April1st to 15thNight
16%7%36%5%24346%37%
1947
16th to endNight
18%6%25%5%3345%5%39%
1860
May1st to 15thNight
18%5%24435%45%8%37%
1755
16th to endNight
9%5%244345%6%9%44%
1636
June1st to 15thNight
9%4245%23348%49%
1560
16th to endNight
8%5%35%5%345%5%9%44%
1560
July1st to 15thNight
6%4134245%5%9%51%
1560
16th to endNight
422443446%8%53%
1641
August1st to 15thNight
342443446%10%52%
1717
16th to endNight
8%3244245%5%7%51%
2070
September1st to 15thNight
11%314323347%54%
1964
16th to endNight
7%4244245%6%8%50%
2145
October1st to 15thNight
12%5%2433335%6%47%
2224
16th to endNight
17%7%35%423235%43%
2594
November1st to 15thNight
13%6%444235%45%45%
2471
16th to endNight
17%7%26%5%34246%38%
2538
December1st to 15thNight
19%11%47%43434432%
2730
16th to endNight
22%13%6%7%6%35%33422%
2912

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%5%34435%26%
1552
16th to endDay
14%16%7%7%6%24336%25%
1704
February1st to 15thDay
17%12%47%6%25%446%27%
1822
16th to endDay
16%11%47%6%34245%32%
1710
March1st to 15thDay
17%12%37%5%24447%28%
1950
16th to endDay
18%9%46%5%3445%7%28%
2402
April1st to 15thDay
19%9%36%5%34347%33%
2331
16th to endDay
18%8%25%5%24446%35%
2375
May1st to 15thDay
19%8%35%5%26%45%7%31%
2526
16th to endDay
13%5%25%5%35%46%8%38%
2828
June1st to 15thDay
10%425%5%3446%8%43%
2730
16th to endDay
9%425%5%36%5%7%9%38%
2730
July1st to 15thDay
7%425%6%345%6%9%43%
2730
16th to endDay
6%3245%46%6%8%9%42%
2879
August1st to 15thDay
6%4245%45%6%6%9%45%
2494
16th to endDay
9%436%435%5%6%7%43%
2484
September1st to 15thDay
12%5%245%3445%6%45%
2312
16th to endDay
8%424435%45%8%46%
2145
October1st to 15thDay
15%7%25%5%235%5%6%40%
2064
16th to endDay
17%8%25%434446%37%
1886
November1st to 15thDay
15%7%25%32345%6%43%
1717
16th to endDay
17%8%47%423336%37%
1748
December1st to 15thDay
18%12%48%5%35%445%27%
1560
16th to endDay
21%14%6%6%6%33335%23%
1664
January1st to 15thNight
17%11%47%5%2334433%
2716
16th to endNight
14%12%6%8%6%34346%29%
2870
February1st to 15thNight
17%11%46%5%24336%32%
2358
16th to endNight
18%10%47%6%24445%32%
2049
March1st to 15thNight
17%10%36%5%24345%35%
2340
16th to endNight
16%9%36%4235%5%7%35%
2184
April1st to 15thNight
16%7%36%5%24346%37%
1947
16th to endNight
18%5%345%33445%38%
1860
May1st to 15thNight
17%5%3443445%8%37%
1754
16th to endNight
8%5%25%4345%5%9%44%
1636
June1st to 15thNight
9%5%245%2335%7%49%
1560
16th to endNight
8%5%35%5%2446%9%44%
1560
July1st to 15thNight
6%4144245%5%9%51%
1560
16th to endNight
422443446%9%53%
1641
August1st to 15thNight
332433437%10%52%
1717
16th to endNight
8%3244245%5%7%51%
2070
September1st to 15thNight
11%313323338%54%
1964
16th to endNight
7%4244245%6%7%50%
2145
October1st to 15thNight
12%5%2433335%6%48%
2224
16th to endNight
17%7%35%423245%43%
2594
November1st to 15thNight
13%6%35%4235%46%44%
2471
16th to endNight
17%7%25%5%34346%38%
2538
December1st to 15thNight
19%12%47%42433432%
2730
16th to endNight
22%14%6%7%6%35%34422%
2912

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
60%311%13%9%1
1553
16th to endDay
60%312%16%6%
1704
February1st to 15thDay
57%5%11%16%7%1
1824
16th to endDay
55%411%21%5%1
1710
March1st to 15thDay
55%412%19%6%
1950
16th to endDay
53%6%11%20%5%1
2403
April1st to 15thDay
52%411%19%12%
2331
16th to endDay
48%5%11%16%12%4
2375
May1st to 15thDay
51%6%11%21%8%
2526
16th to endDay
42%5%11%20%16%2
2832
June1st to 15thDay
37%7%10%24%18%1
2730
16th to endDay
38%8%12%22%15%1
2730
July1st to 15thDay
35%8%11%23%16%4
2581
16th to endDay
34%9%16%24%14%2
2712
August1st to 15thDay
33%7%13%25%17%1
2479
16th to endDay
36%7%11%22%17%3
2484
September1st to 15thDay
38%5%9%22%17%6%
2312
16th to endDay
34%6%10%25%21%2
2145
October1st to 15thDay
43%5%10%24%13%2
2064
16th to endDay
47%411%21%13%1
1886
November1st to 15thDay
41%413%22%16%2
1717
16th to endDay
48%312%24%10%
1748
December1st to 15thDay
60%49%18%7%
1560
16th to endDay
63%411%12%6%
1664
January1st to 15thNight
53%410%17%12%1
2716
16th to endNight
56%413%16%8%
2870
February1st to 15thNight
53%410%20%9%1
2367
16th to endNight
53%411%19%10%1
2049
March1st to 15thNight
51%311%21%10%1
2340
16th to endNight
48%5%13%20%10%1
2184
April1st to 15thNight
46%410%21%14%2
1947
16th to endNight
46%5%9%19%14%5%
1860
May1st to 15thNight
44%6%12%22%13%
1755
16th to endNight
36%8%13%19%18%3
1638
June1st to 15thNight
33%6%10%26%20%3
1560
16th to endNight
36%6%13%24%16%2
1560
July1st to 15thNight
30%6%12%26%18%4
1480
16th to endNight
26%6%14%28%18%4
1545
August1st to 15thNight
25%6%16%28%19%3
1708
16th to endNight
30%6%11%25%20%4
2070
September1st to 15thNight
29%5%9%25%23%6%
1964
16th to endNight
30%6%8%26%23%3
2145
October1st to 15thNight
37%5%9%24%21%2
2224
16th to endNight
44%39%24%16%1
2594
November1st to 15thNight
40%39%24%17%4
2471
16th to endNight
47%312%24%11%
2538
December1st to 15thNight
56%310%18%10%
2730
16th to endNight
66%38%13%6%
2912

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%22%6%
135
16th to endDay
18%13%40%20%5%
144
February1st to 15thDay
28%17%38%15%
135
16th to endDay
27%13%30%20%7%
120
March1st to 15thDay
25%12%32%24%4
135
16th to endDay
27%9%30%22%8%2
311
April1st to 15thDay
24%13%29%20%9%1
330
16th to endDay
21%8%30%20%13%5%
319
May1st to 15thDay
20%8%29%21%15%4
348
16th to endDay
17%5%28%23%16%8%
584
June1st to 15thDay
11%327%30%20%6%
570
16th to endDay
12%8%29%28%15%6%
570
July1st to 15thDay
9%322%24%23%16%
550
16th to endDay
7%119%35%24%11%
595
August1st to 15thDay
6%115%32%26%17%
426
16th to endDay
11%218%29%25%13%
396
September1st to 15thDay
13%215%25%30%13%
375
16th to endDay
7%420%25%31%10%
374
October1st to 15thDay
19%6%24%28%17%4
294
16th to endDay
23%11%31%26%6%
178
November1st to 15thDay
14%8%29%23%15%8%
135
16th to endDay
29%8%37%15%8%
135
December1st to 15thDay
17%22%34%17%8%
135
16th to endDay
24%22%44%6%2
144
January1st to 15thNight
23%13%36%20%5%
975
16th to endNight
20%12%36%27%3
1040
February1st to 15thNight
24%11%34%24%4
839
16th to endNight
23%12%34%24%5%
683
March1st to 15thNight
22%11%35%24%5%
780
16th to endNight
20%7%36%26%7%1
688
April1st to 15thNight
19%11%35%26%5%
584
16th to endNight
21%8%30%28%10%
579
May1st to 15thNight
20%432%30%11%
585
16th to endNight
11%225%38%20%
611
June1st to 15thNight
12%224%43%15%
585
16th to endNight
10%226%41%17%1
585
July1st to 15thNight
9%117%41%27%2
555
16th to endNight
5%16%41%32%3
612
August1st to 15thNight
47%53%29%4
575
16th to endNight
9%14%35%35%4
621
September1st to 15thNight
12%311%36%28%6%
599
16th to endNight
9%318%34%30%3
777
October1st to 15thNight
14%7%24%34%17%1
780
16th to endNight
21%11%33%23%9%
816
November1st to 15thNight
16%10%36%24%10%1
760
16th to endNight
22%12%32%24%8%
783
December1st to 15thNight
25%11%32%24%5%
975
16th to endNight
29%10%34%22%3
1040
Page generated at 2018-10-28 07:41:02. Version ac04

Copyright 2018 A. Danko


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