Durham
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Durham clear sky chart from 2005-11-06 to 2024-03-18.

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
42%
24773
22%
80294
13%
24674
52%
24674
24%
49573

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
24%
754
26%
3990
9%
737
41%
737
14%
2118
January11th to 20thNight
26%
757
28%
3952
10%
740
44%
740
14%
2171
January21st to endNight
24%
829
19%
4444
12%
814
45%
814
15%
2596
February1st to 10thNight
27%
760
21%
2470
12%
760
42%
760
24%
1512
February11th to 20thNight
16%
740
19%
2395
5%
739
33%
739
18%
1520
February21st to endNight
24%
628
27%
1739
10%
628
40%
628
26%
1116
March1st to 10thNight
30%
760
25%
2090
12%
760
43%
760
27%
1309
March11th to 20thNight
27%
752
21%
2068
9%
752
39%
752
23%
1375
March21st to endNight
26%
792
21%
2178
8%
792
36%
792
25%
1436
April1st to 10thNight
31%
720
24%
1868
9%
720
41%
720
29%
1185
April11th to 20thNight
34%
711
25%
1775
9%
711
42%
711
34%
1117
April21st to endNight
38%
720
23%
1800
8%
720
45%
720
31%
1175
May1st to 10thNight
38%
572
18%
1652
8%
572
45%
572
29%
1031
May11th to 20thNight
46%
531
16%
1593
11%
531
49%
531
24%
1064
May21st to endNight
62%
582
16%
1744
13%
582
63%
582
28%
1108
June1st to 10thNight
61%
540
15%
1620
14%
540
62%
540
28%
1046
June11th to 20thNight
58%
540
15%
1620
12%
540
61%
540
27%
1053
June21st to endNight
62%
540
16%
1620
12%
540
66%
540
28%
1049
July1st to 10thNight
68%
525
14%
1575
12%
525
69%
525
27%
1047
July11th to 20thNight
72%
522
13%
1566
12%
522
72%
522
27%
1021
July21st to endNight
67%
591
16%
1672
13%
558
69%
558
27%
1099
August1st to 10thNight
64%
537
13%
1600
11%
534
64%
534
24%
1116
August11th to 20thNight
63%
578
16%
1642
13%
578
64%
578
24%
1139
August21st to endNight
64%
792
17%
1980
11%
792
65%
792
29%
1374
September1st to 10thNight
64%
720
23%
1800
16%
720
66%
720
34%
1194
September11th to 20thNight
59%
720
24%
1918
19%
720
62%
720
31%
1260
September21st to endNight
46%
720
17%
2017
12%
720
51%
720
22%
1414
October1st to 10thNight
53%
720
23%
2160
20%
720
60%
720
30%
1343
October11th to 20thNight
46%
720
29%
2160
22%
720
58%
720
31%
1278
October21st to endNight
44%
792
31%
2376
19%
792
59%
792
33%
1363
November1st to 10thNight
44%
740
27%
2221
18%
740
55%
740
31%
1312
November11th to 20thNight
40%
760
28%
2294
16%
760
54%
760
29%
1363
November21st to endNight
40%
760
26%
2588
17%
760
54%
760
28%
1451
December1st to 10thNight
31%
760
21%
2660
11%
760
45%
760
18%
1693
December11th to 20thNight
34%
760
25%
3063
15%
758
48%
758
22%
1766
December21st to endNight
31%
828
17%
4384
12%
817
45%
817
14%
2359

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%5%25%5%35%5%5%8%44%
78648
Night
14%6%25%5%3445%7%45%
81124
TransparencyDay
38%7%12%21%18%4
78370
Night
38%6%11%20%20%5%
80921
SeeingDay
17%11%26%24%17%5%
14392
Night
16%10%25%31%16%2
24802

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
18%6%24323345%52%
2836
11th to 20thDay
14%6%345%23345%52%
2840
21st to endDay
18%10%35%433445%41%
3124
February1st to 10thDay
14%6%25%5%3446%7%44%
1710
11th to 20thDay
22%6%2342344446%
1669
21st to endDay
18%7%36%5%2345%7%40%
1712
March1st to 10thDay
15%423334446%50%
2090
11th to 20thDay
14%6%25%435%45%9%42%
2058
21st to endDay
16%8%36%5%345%5%6%40%
2178
April1st to 10thDay
11%41243445%7%54%
2091
11th to 20thDay
11%4345%3445%9%48%
2134
21st to endDay
14%5%25%5%3445%9%45%
2160
May1st to 10thDay
11%5%25%5%36%6%6%9%42%
2323
11th to 20thDay
14%6%25%6%36%5%6%8%38%
2301
21st to endDay
12%5%26%6%46%5%6%8%40%
2531
June1st to 10thDay
9%5%26%5%46%6%8%9%40%
2340
11th to 20thDay
9%5%35%5%35%6%6%11%43%
2340
21st to endDay
7%5%26%5%46%7%8%12%38%
2340
July1st to 10thDay
8%5%26%7%47%7%7%11%36%
2340
11th to 20thDay
7%6%25%6%47%8%9%13%33%
2340
21st to endDay
6%436%7%47%7%8%12%35%
2547
August1st to 10thDay
10%6%36%6%5%7%7%7%10%32%
2327
11th to 20thDay
10%6%36%7%48%6%8%9%31%
2239
21st to endDay
10%6%36%6%37%6%7%11%36%
2376
September1st to 10thDay
10%425%6%35%5%7%8%46%
2160
11th to 20thDay
14%5%36%5%345%5%8%43%
2037
21st to endDay
21%6%35%43346%6%40%
1941
October1st to 10thDay
14%6%36%423446%50%
1800
11th to 20thDay
14%423323446%56%
1800
21st to endDay
12%4245%24335%56%
1980
November1st to 10thDay
12%424423336%55%
1857
11th to 20thDay
15%424423346%53%
1884
21st to endDay
14%5%2342345%7%50%
1585
December1st to 10thDay
18%7%35%434447%42%
1520
11th to 20thDay
15%324322345%56%
2014
21st to endDay
17%6%25%43445%8%42%
3124
January1st to 10thNight
15%6%25%5%3345%6%47%
4109
11th to 20thNight
14%7%35%424446%47%
4120
21st to endNight
19%7%24424345%44%
4532
February1st to 10thNight
17%5%245%2446%6%45%
2470
11th to 20thNight
20%6%35%423445%44%
2395
21st to endNight
16%6%15%435%45%6%45%
1739
March1st to 10thNight
14%5%34424445%50%
2090
11th to 20thNight
16%5%25%5%35%45%7%43%
2068
21st to endNight
16%6%35%4245%5%7%43%
2178
April1st to 10thNight
14%5%2343435%8%48%
1868
11th to 20thNight
12%5%25%5%2335%7%50%
1775
21st to endNight
12%4245%35%5%5%6%48%
1800
May1st to 10thNight
11%5%25%5%346%6%8%45%
1652
11th to 20thNight
15%6%26%435%45%9%40%
1592
21st to endNight
11%6%25%5%35%5%6%10%42%
1744
June1st to 10thNight
10%4345%46%6%7%11%41%
1620
11th to 20thNight
10%5%36%5%25%6%7%10%40%
1620
21st to endNight
8%5%26%5%445%9%11%40%
1620
July1st to 10thNight
7%6%35%6%45%7%9%11%38%
1620
11th to 20thNight
7%5%25%5%46%7%8%13%39%
1620
21st to endNight
6%426%7%47%7%7%13%37%
1771
August1st to 10thNight
10%6%36%6%46%5%9%11%33%
1611
11th to 20thNight
10%6%27%6%37%6%9%8%35%
1642
21st to endNight
10%5%26%6%47%6%8%10%38%
1980
September1st to 10thNight
12%6%25%32446%8%46%
1800
11th to 20thNight
13%6%35%425%46%7%44%
1918
21st to endNight
20%7%27%5%345%5%6%37%
2017
October1st to 10thNight
15%6%35%433445%48%
2160
11th to 20thNight
15%5%25%423336%52%
2160
21st to endNight
13%5%24433345%54%
2376
November1st to 10thNight
13%6%24424335%54%
2221
11th to 20thNight
13%5%25%42445%5%51%
2294
21st to endNight
14%42442445%7%51%
2588
December1st to 10thNight
17%6%36%5%34436%42%
2660
11th to 20thNight
17%6%25%424445%49%
3162
21st to endNight
17%6%34433447%46%
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
37%35%27%22%6%
2837
11th to 20thDay
36%36%18%31%5%
2840
21st to endDay
46%5%6%17%20%6%
3124
February1st to 10thDay
40%412%20%20%5%
1710
11th to 20thDay
42%46%18%22%7%
1678
21st to endDay
45%5%10%16%19%6%
1712
March1st to 10thDay
35%5%9%23%22%7%
2090
11th to 20thDay
40%5%10%20%17%8%
2058
21st to endDay
44%6%9%20%17%4
2178
April1st to 10thDay
28%5%11%24%23%9%
2091
11th to 20thDay
34%5%12%22%20%8%
2134
21st to endDay
37%5%12%22%19%4
2160
May1st to 10thDay
37%8%16%20%16%3
2323
11th to 20thDay
42%9%13%22%12%2
2305
21st to endDay
41%8%15%23%13%1
2531
June1st to 10thDay
37%10%15%23%14%1
2340
11th to 20thDay
34%9%17%22%15%2
2340
21st to endDay
35%11%17%21%14%2
2340
July1st to 10thDay
39%12%16%18%13%3
2275
11th to 20thDay
37%12%22%19%9%2
2271
21st to endDay
37%12%21%22%8%
2405
August1st to 10thDay
44%10%17%20%8%1
2314
11th to 20thDay
44%12%15%19%8%1
2239
21st to endDay
40%10%17%20%10%3
2376
September1st to 10thDay
34%9%15%19%17%5%
2160
11th to 20thDay
38%8%12%17%21%4
2037
21st to endDay
45%6%9%20%17%4
1941
October1st to 10thDay
37%5%10%23%23%4
1800
11th to 20thDay
31%5%8%28%21%8%
1800
21st to endDay
32%47%23%25%9%
1980
November1st to 10thDay
33%47%22%27%8%
1857
11th to 20thDay
33%38%22%26%7%
1884
21st to endDay
34%49%22%25%6%
1585
December1st to 10thDay
43%411%21%17%4
1520
11th to 20thDay
32%38%26%23%9%
2011
21st to endDay
39%5%11%23%19%2
3124
January1st to 10thNight
37%47%21%25%5%
4109
11th to 20thNight
39%47%18%26%6%
4120
21st to endNight
43%45%19%22%7%
4532
February1st to 10thNight
39%410%21%21%5%
2470
11th to 20thNight
44%48%15%21%8%
2397
21st to endNight
38%5%9%19%20%8%
1739
March1st to 10thNight
36%5%9%20%22%8%
2090
11th to 20thNight
41%6%8%19%18%7%
2068
21st to endNight
40%7%9%21%18%5%
2178
April1st to 10thNight
36%5%10%17%25%7%
1868
11th to 20thNight
34%5%10%23%21%8%
1775
21st to endNight
36%7%10%24%18%5%
1800
May1st to 10thNight
34%8%15%22%17%4
1652
11th to 20thNight
41%9%12%21%16%1
1593
21st to endNight
37%9%16%24%13%1
1745
June1st to 10thNight
36%10%16%22%15%1
1620
11th to 20thNight
37%10%17%19%15%3
1620
21st to endNight
35%12%17%20%13%3
1620
July1st to 10thNight
36%13%16%21%13%3
1575
11th to 20thNight
32%15%21%21%9%2
1566
21st to endNight
35%12%20%21%11%
1672
August1st to 10thNight
41%12%18%19%9%1
1600
11th to 20thNight
40%12%19%18%9%2
1642
21st to endNight
38%11%17%22%10%2
1980
September1st to 10thNight
35%9%14%21%16%6%
1800
11th to 20thNight
37%8%11%19%21%3
1918
21st to endNight
46%8%11%16%15%4
2017
October1st to 10thNight
38%5%9%22%23%4
2160
11th to 20thNight
35%48%23%23%8%
2160
21st to endNight
32%47%21%26%10%
2376
November1st to 10thNight
35%48%18%26%8%
2221
11th to 20thNight
35%49%16%24%12%
2294
21st to endNight
33%48%22%26%7%
2588
December1st to 10thNight
45%5%8%19%19%4
2660
11th to 20thNight
38%48%21%22%8%
3164
21st to endNight
39%47%24%23%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
26%23%35%13%3
270
11th to 20thDay
27%24%33%12%3
270
21st to endDay
20%23%44%11%2
297
February1st to 10thDay
21%20%40%16%4
270
11th to 20thDay
38%21%32%8%2
276
21st to endDay
25%20%34%18%3
382
March1st to 10thDay
24%18%33%18%7%
460
11th to 20thDay
21%21%40%12%5%1
449
21st to endDay
22%18%37%18%5%
462
April1st to 10thDay
21%17%35%19%8%1
420
11th to 20thDay
14%20%31%22%10%4
412
21st to endDay
20%11%30%25%12%1
420
May1st to 10thDay
17%18%30%24%9%3
423
11th to 20thDay
16%9%23%29%19%4
447
21st to endDay
18%6%19%28%22%7%
485
June1st to 10thDay
11%6%25%30%22%6%
450
11th to 20thDay
8%7%23%28%26%8%
450
21st to endDay
11%322%34%24%6%
450
July1st to 10thDay
10%112%31%36%9%
445
11th to 20thDay
7%212%30%36%12%
444
21st to endDay
7%215%37%28%10%
488
August1st to 10thDay
13%318%29%25%11%
446
11th to 20thDay
11%413%29%29%14%
439
21st to endDay
12%313%29%28%16%
495
September1st to 10thDay
12%318%24%26%17%
450
11th to 20thDay
14%413%32%25%12%
450
21st to endDay
25%6%24%23%18%4
450
October1st to 10thDay
16%8%23%23%22%8%
450
11th to 20thDay
15%9%26%27%19%5%
450
21st to endDay
15%12%26%30%15%3
495
November1st to 10thDay
17%11%29%26%14%3
455
11th to 20thDay
18%15%28%25%12%1
444
21st to endDay
15%18%30%21%13%2
210
December1st to 10thDay
22%20%39%11%7%1
180
11th to 20thDay
19%17%32%23%8%
211
21st to endDay
24%17%31%16%10%1
297
January1st to 10thNight
20%20%31%25%4
760
11th to 20thNight
19%18%32%25%6%
760
21st to endNight
19%16%37%25%3
836
February1st to 10thNight
19%15%35%27%3
760
11th to 20thNight
24%20%36%19%1
743
21st to endNight
19%16%38%24%4
628
March1st to 10thNight
16%17%33%28%6%
760
11th to 20thNight
20%16%34%21%8%
752
21st to endNight
19%13%39%25%5%
792
April1st to 10thNight
18%17%32%26%7%
720
11th to 20thNight
15%14%34%25%11%
711
21st to endNight
15%9%32%35%8%
720
May1st to 10thNight
14%11%33%33%9%
572
11th to 20thNight
17%6%24%34%18%1
531
21st to endNight
13%315%41%27%1
584
June1st to 10thNight
12%219%43%23%2
540
11th to 20thNight
11%219%38%26%4
540
21st to endNight
8%316%42%28%3
540
July1st to 10thNight
8%113%36%38%4
525
11th to 20thNight
7%29%41%37%4
522
21st to endNight
6%114%39%35%5%
591
August1st to 10thNight
12%210%37%35%4
537
11th to 20thNight
13%210%36%33%6%
578
21st to endNight
11%212%31%37%6%
792
September1st to 10thNight
14%310%34%33%6%
720
11th to 20thNight
15%315%32%31%4
720
21st to endNight
23%5%17%33%20%2
720
October1st to 10thNight
17%5%18%31%24%6%
720
11th to 20thNight
17%9%24%28%21%2
720
21st to endNight
15%10%26%29%18%2
792
November1st to 10thNight
16%8%27%32%14%2
740
11th to 20thNight
15%12%28%33%11%
760
21st to endNight
15%13%27%30%14%1
760
December1st to 10thNight
21%13%29%29%7%
760
11th to 20thNight
18%11%32%32%7%
760
21st to endNight
21%15%26%30%7%
836
Page generated at 2024-03-15 14:01:39. Version ac07

Copyright © 2024 Attilla Danko.


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