Durham
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Durham clear sky chart from 2005-11-05 to 2017-09-17.

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
28%
14971
19%
46832
8%
14939
40%
14939
21%
30206

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
17%
720
21%
2506
7%
716
35%
716
17%
1566
January16th to endNight
18%
768
21%
2664
6%
768
38%
768
16%
1658
February1st to 15thNight
15%
704
18%
2180
4%
701
31%
701
16%
1443
February16th to endNight
15%
631
25%
1893
7%
631
38%
631
19%
1231
March1st to 15thNight
19%
720
17%
2160
6%
720
33%
720
18%
1433
March16th to endNight
20%
768
24%
2007
7%
768
34%
768
23%
1322
April1st to 15thNight
19%
718
16%
1796
4%
718
26%
718
21%
1271
April16th to endNight
23%
647
17%
1727
4%
647
32%
647
22%
1178
May1st to 15thNight
25%
540
17%
1620
7%
540
33%
540
18%
1122
May16th to endNight
30%
384
12%
1506
9%
383
38%
383
18%
941
June1st to 15thNight
31%
360
13%
1440
10%
360
44%
360
17%
942
June16th to endNight
44%
360
14%
1440
13%
360
53%
360
26%
827
July1st to 15thNight
41%
340
11%
1360
13%
340
45%
340
21%
840
July16th to endNight
50%
376
15%
1418
15%
354
57%
354
23%
851
August1st to 15thNight
43%
514
17%
1585
10%
512
48%
512
29%
959
August16th to endNight
51%
764
19%
1910
10%
764
54%
764
33%
1262
September1st to 15thNight
40%
720
21%
1829
10%
720
45%
720
32%
1180
September16th to endNight
46%
665
25%
1836
18%
665
51%
665
31%
1155
October1st to 15thNight
34%
660
23%
1877
12%
660
46%
660
26%
1220
October16th to endNight
25%
704
18%
2247
6%
704
39%
704
22%
1439
November1st to 15thNight
28%
700
21%
2277
9%
700
44%
700
22%
1425
November16th to endNight
24%
720
21%
2346
10%
720
38%
720
19%
1503
December1st to 15thNight
22%
720
16%
2520
6%
720
35%
720
16%
1649
December16th to endNight
16%
768
19%
2688
4%
768
34%
768
15%
1789

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
17%6%2442445%7%40%
47947
Night
17%6%24424446%41%
47002
Cloud CoverDay
17%5%2442445%7%40%
47957
Night
17%6%24424446%41%
47007
TransparencyDay
43%411%22%15%2
47635
Night
43%411%22%15%2
46832
SeeingDay
21%14%30%21%9%2
5850
Night
21%14%31%24%7%
14971

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
16%7%244245%5%441%
1432
16th to endDay
15%7%3442345%6%41%
1560
February1st to 15thDay
16%6%25%5%35%45%6%37%
1678
16th to endDay
17%7%25%5%34446%38%
1580
March1st to 15thDay
19%7%245%24437%37%
1790
16th to endDay
18%6%35%433335%41%
2214
April1st to 15thDay
21%6%24413346%40%
2152
16th to endDay
19%323424346%44%
2232
May1st to 15thDay
24%6%25%423347%35%
2332
16th to endDay
18%5%2442445%8%39%
2618
June1st to 15thDay
23%5%24424447%33%
2520
16th to endDay
13%6%25%5%35%46%10%37%
2520
July1st to 15thDay
13%5%25%5%35%5%6%8%38%
2520
16th to endDay
13%5%25%5%25%6%7%8%37%
2654
August1st to 15thDay
13%5%246%35%5%6%8%38%
2349
16th to endDay
11%6%25%5%3445%7%43%
2292
September1st to 15thDay
14%5%14434445%46%
2130
16th to endDay
16%423434446%47%
1830
October1st to 15thDay
19%6%24414435%42%
1752
16th to endDay
16%5%335%24446%42%
1624
November1st to 15thDay
18%7%24424325%44%
1581
16th to endDay
17%5%24424337%43%
1611
December1st to 15thDay
18%6%25%5%24346%40%
1440
16th to endDay
21%9%24424345%37%
1536
January1st to 15thNight
18%7%24423346%42%
2506
16th to endNight
17%8%35%323346%42%
2664
February1st to 15thNight
15%9%35%5%33346%39%
2179
16th to endNight
18%6%24434445%41%
1893
March1st to 15thNight
20%6%24423446%39%
2147
16th to endNight
17%6%35%323345%44%
2007
April1st to 15thNight
18%6%45%424345%38%
1796
16th to endNight
20%6%35%5%22346%40%
1727
May1st to 15thNight
21%6%344345%47%35%
1620
16th to endNight
19%6%344145%48%37%
1504
June1st to 15thNight
21%5%25%434336%37%
1440
16th to endNight
12%5%2442435%8%45%
1440
July1st to 15thNight
13%5%24435%5%7%8%37%
1440
16th to endNight
11%5%25%5%35%5%7%9%36%
1514
August1st to 15thNight
10%425%435%6%7%8%42%
1595
16th to endNight
12%414436%447%45%
1910
September1st to 15thNight
14%5%23434445%46%
1829
16th to endNight
14%5%2442443449%
1836
October1st to 15thNight
17%6%25%424445%44%
1877
16th to endNight
19%6%24423446%40%
2247
November1st to 15thNight
18%5%24423335%45%
2277
16th to endNight
20%5%25%324346%40%
2346
December1st to 15thNight
20%7%24434345%38%
2520
16th to endNight
21%7%2432445%5%36%
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
17%6%2342445%5%42%
1432
16th to endDay
16%7%34423347%41%
1560
February1st to 15thDay
16%6%25%6%35%446%38%
1678
16th to endDay
17%5%35%5%35%35%6%38%
1580
March1st to 15thDay
20%6%345%24347%37%
1800
16th to endDay
18%6%25%423335%42%
2214
April1st to 15thDay
21%6%23423346%40%
2152
16th to endDay
19%413423446%44%
2232
May1st to 15thDay
24%6%2442335%6%35%
2332
16th to endDay
18%5%24424447%40%
2618
June1st to 15thDay
24%5%25%42445%7%33%
2520
16th to endDay
13%5%25%4345%5%9%39%
2520
July1st to 15thDay
14%5%24435%5%6%9%38%
2520
16th to endDay
13%425%425%5%6%9%38%
2654
August1st to 15thDay
14%415%5%346%7%8%39%
2349
16th to endDay
12%5%16%43446%7%43%
2292
September1st to 15thDay
14%42442445%6%45%
2130
16th to endDay
16%413424346%47%
1830
October1st to 15thDay
18%6%245%23345%42%
1752
16th to endDay
16%5%24434447%42%
1624
November1st to 15thDay
19%6%2332433444%
1581
16th to endDay
17%5%14424346%44%
1611
December1st to 15thDay
19%5%16%424346%40%
1440
16th to endDay
22%9%25%42225%6%36%
1536
January1st to 15thNight
19%6%24323346%42%
2506
16th to endNight
17%9%24313335%43%
2664
February1st to 15thNight
14%8%445%34345%40%
2172
16th to endNight
18%6%2442435%5%42%
1893
March1st to 15thNight
20%6%24424346%39%
2160
16th to endNight
17%6%24324335%45%
2006
April1st to 15thNight
19%6%35%5%24446%38%
1796
16th to endNight
21%5%35%43234440%
1727
May1st to 15thNight
21%7%24425%45%6%35%
1620
16th to endNight
20%6%2442446%8%36%
1504
June1st to 15thNight
21%6%34424436%37%
1440
16th to endNight
14%41442345%8%45%
1440
July1st to 15thNight
14%5%245%25%5%7%8%37%
1440
16th to endNight
12%5%35%5%36%5%7%10%36%
1514
August1st to 15thNight
10%4244346%7%8%41%
1595
16th to endNight
12%5%246%34448%44%
1910
September1st to 15thNight
15%5%23424446%45%
1829
16th to endNight
15%5%25%32433449%
1836
October1st to 15thNight
17%7%14423445%44%
1877
16th to endNight
18%6%24435%446%41%
2247
November1st to 15thNight
18%5%34423345%45%
2277
16th to endNight
20%5%24324436%41%
2346
December1st to 15thNight
21%6%24433346%38%
2520
16th to endNight
21%6%24424446%36%
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
42%413%22%12%3
1433
16th to endDay
42%311%25%14%2
1560
February1st to 15thDay
46%412%21%14%1
1681
16th to endDay
44%49%25%13%2
1580
March1st to 15thDay
47%313%23%9%2
1800
16th to endDay
45%39%19%17%3
2214
April1st to 15thDay
45%39%21%16%3
2152
16th to endDay
40%49%23%18%3
2232
May1st to 15thDay
49%49%21%14%2
2332
16th to endDay
42%6%15%20%13%2
2622
June1st to 15thDay
49%5%12%21%10%1
2520
16th to endDay
40%7%13%24%13%
2520
July1st to 15thDay
43%5%10%22%16%1
2371
16th to endDay
38%6%15%22%13%2
2487
August1st to 15thDay
40%6%14%22%15%
2335
16th to endDay
38%410%26%18%1
2292
September1st to 15thDay
37%6%12%21%20%2
2130
16th to endDay
37%46%23%25%2
1830
October1st to 15thDay
43%310%23%16%2
1752
16th to endDay
41%410%25%15%2
1624
November1st to 15thDay
43%312%19%17%2
1581
16th to endDay
41%311%26%14%2
1611
December1st to 15thDay
45%316%19%14%1
1440
16th to endDay
49%414%19%11%
1536
January1st to 15thNight
43%312%24%13%2
2506
16th to endNight
43%310%23%16%2
2664
February1st to 15thNight
45%412%22%12%2
2180
16th to endNight
43%39%24%16%2
1893
March1st to 15thNight
45%313%20%13%3
2160
16th to endNight
41%38%23%18%4
2007
April1st to 15thNight
47%410%20%15%2
1796
16th to endNight
46%38%21%16%4
1727
May1st to 15thNight
48%5%10%18%14%2
1620
16th to endNight
44%5%19%17%11%1
1506
June1st to 15thNight
48%5%12%18%13%1
1440
16th to endNight
36%5%15%27%15%
1440
July1st to 15thNight
41%6%13%22%14%1
1360
16th to endNight
40%5%16%23%11%2
1418
August1st to 15thNight
36%5%15%24%15%2
1585
16th to endNight
39%411%27%16%
1910
September1st to 15thNight
38%310%26%18%1
1829
16th to endNight
39%36%23%25%2
1836
October1st to 15thNight
42%49%23%17%3
1877
16th to endNight
44%213%23%14%
2247
November1st to 15thNight
41%311%20%19%3
2277
16th to endNight
45%310%25%12%2
2346
December1st to 15thNight
47%414%20%13%
2520
16th to endNight
48%412%20%13%1
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
21%28%33%16%
60
16th to endDay
29%25%33%11%
68
February1st to 15thDay
23%23%36%14%1
194
16th to endDay
18%25%35%15%3
239
March1st to 15thDay
27%21%30%17%2
270
16th to endDay
22%23%34%13%41
288
April1st to 15thDay
28%17%32%14%7%
270
16th to endDay
22%15%32%18%7%2
270
May1st to 15thDay
34%17%25%13%7%2
288
16th to endDay
22%13%30%22%10%
331
June1st to 15thDay
25%13%26%21%11%1
315
16th to endDay
17%13%31%26%9%1
315
July1st to 15thDay
20%5%32%28%11%1
305
16th to endDay
13%6%32%29%13%3
326
August1st to 15thDay
13%7%26%33%13%5%
313
16th to endDay
12%432%26%15%8%
332
September1st to 15thDay
16%11%28%21%15%6%
315
16th to endDay
18%6%30%17%17%10%
259
October1st to 15thDay
23%9%23%27%11%5%
255
16th to endDay
17%20%31%21%8%
247
November1st to 15thDay
23%14%28%22%10%2
235
16th to endDay
19%19%29%20%9%
231
December1st to 15thDay
18%31%33%10%6%
60
16th to endDay
37%23%25%12%1
64
January1st to 15thNight
24%21%34%16%3
720
16th to endNight
23%21%32%19%2
768
February1st to 15thNight
19%20%38%19%1
704
16th to endNight
22%21%35%18%2
631
March1st to 15thNight
26%19%32%18%3
720
16th to endNight
19%21%35%20%3
768
April1st to 15thNight
22%18%36%19%2
718
16th to endNight
23%15%33%21%5%
647
May1st to 15thNight
22%16%32%22%5%
540
16th to endNight
20%8%32%30%8%
384
June1st to 15thNight
24%7%28%31%7%
360
16th to endNight
15%5%30%38%9%
360
July1st to 15thNight
15%232%32%15%
340
16th to endNight
12%423%41%15%1
376
August1st to 15thNight
13%331%37%13%
514
16th to endNight
14%421%39%18%2
764
September1st to 15thNight
17%6%30%30%14%1
720
16th to endNight
18%5%23%27%22%2
665
October1st to 15thNight
20%10%29%26%11%1
660
16th to endNight
24%12%34%21%6%
704
November1st to 15thNight
22%14%30%21%10%1
700
16th to endNight
23%16%30%21%7%
720
December1st to 15thNight
26%15%30%20%5%
720
16th to endNight
26%18%35%17%2
768
Page generated at 2017-09-18 08:38:26. Version ac04

Copyright 2017 A. Danko


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