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 2017-10-06.

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
30%
15143
11%
46920
8%
15105
34%
15105
15%
35283

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
8%
867
4%
2583
1%
865
11%
865
5%
2294
January16th to endNight
14%
768
4%
2496
2%
768
16%
768
5%
2202
February1st to 15thNight
15%
701
5%
2287
1%
701
19%
701
6%
1979
February16th to endNight
17%
631
9%
1982
3%
631
24%
631
9%
1611
March1st to 15thNight
19%
720
12%
2010
5%
720
24%
720
13%
1581
March16th to endNight
33%
768
18%
2112
10%
768
39%
768
21%
1511
April1st to 15thNight
26%
682
14%
1817
6%
682
31%
682
19%
1357
April16th to endNight
36%
540
17%
1620
11%
540
40%
540
20%
1122
May1st to 15thNight
40%
534
15%
1614
11%
534
45%
534
22%
1100
May16th to endNight
44%
374
16%
1497
14%
374
55%
374
23%
907
June1st to 15thNight
41%
360
12%
1341
11%
360
49%
360
21%
842
June16th to endNight
50%
360
15%
1260
17%
360
56%
360
26%
760
July1st to 15thNight
62%
340
18%
1190
22%
340
66%
340
34%
648
July16th to endNight
56%
538
14%
1558
13%
505
58%
505
28%
966
August1st to 15thNight
60%
539
16%
1609
11%
536
62%
536
30%
994
August16th to endNight
56%
583
21%
1729
15%
583
59%
583
30%
1080
September1st to 15thNight
49%
720
17%
1863
10%
720
52%
720
30%
1243
September16th to endNight
51%
717
20%
1980
14%
717
54%
717
28%
1299
October1st to 15thNight
36%
684
14%
2042
11%
684
40%
684
19%
1455
October16th to endNight
20%
704
8%
2135
4%
704
25%
704
10%
1719
November1st to 15thNight
26%
700
14%
2362
12%
700
31%
700
13%
1787
November16th to endNight
19%
720
8%
2520
7%
720
23%
720
9%
2046
December1st to 15thNight
10%
720
3%
2520
1%
720
12%
720
4%
2246
December16th to endNight
7%
873
3%
2793
0%
873
10%
873
4%
2534

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%11%47%6%34446%28%
48269
Night
16%11%5%8%6%34445%28%
47091
Cloud CoverDay
17%11%47%6%3445%6%28%
48279
Night
16%12%5%8%6%34445%28%
47095
TransparencyDay
55%6%10%17%9%
47958
Night
57%5%10%16%8%1
46920
SeeingDay
21%8%26%24%13%5%
5801
Night
22%9%29%26%10%1
15150

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
17%16%10%15%10%35%32310%
1351
16th to endDay
11%21%8%15%10%444449%
1728
February1st to 15thDay
13%19%8%17%10%5%433310%
1575
16th to endDay
16%19%8%11%8%45%44412%
1488
March1st to 15thDay
15%12%5%11%9%3433424%
1939
16th to endDay
15%10%5%7%6%35%5%45%29%
2112
April1st to 15thDay
20%12%5%5%32445%5%28%
2142
16th to endDay
19%10%34323347%37%
2340
May1st to 15thDay
19%8%25%4235%5%6%36%
2334
16th to endDay
14%7%245%2445%7%40%
2618
June1st to 15thDay
16%7%3442446%8%36%
2616
16th to endDay
17%5%245%245%6%8%36%
2700
July1st to 15thDay
12%5%25%5%35%5%5%8%38%
2700
16th to endDay
11%5%35%5%36%5%6%10%35%
2501
August1st to 15thDay
12%6%27%6%445%6%9%34%
2340
16th to endDay
13%5%26%6%45%6%6%8%34%
2460
September1st to 15thDay
18%7%27%5%2335%6%36%
2094
16th to endDay
18%5%25%423447%39%
1980
October1st to 15thDay
24%9%45%5%33345%31%
1716
16th to endDay
33%14%37%44433416%
1735
November1st to 15thDay
19%15%47%6%34435%25%
1495
16th to endDay
22%20%7%7%6%3444414%
1440
December1st to 15thDay
18%22%11%12%7%35%3236%
1440
16th to endDay
19%24%12%12%7%332337%
1425
January1st to 15thNight
19%18%7%14%9%45%24310%
2583
16th to endNight
14%17%9%13%12%5%5%4339%
2496
February1st to 15thNight
13%17%10%14%10%45%33313%
2285
16th to endNight
15%13%9%12%8%35%436%18%
1982
March1st to 15thNight
16%13%6%10%8%3444425%
1998
16th to endNight
15%9%5%7%5%34335%36%
2112
April1st to 15thNight
20%11%46%423346%31%
1817
16th to endNight
15%10%25%435%445%37%
1620
May1st to 15thNight
16%7%35%5%3445%6%37%
1614
16th to endNight
11%5%25%435%46%7%43%
1495
June1st to 15thNight
16%5%35%5%2445%8%38%
1341
16th to endNight
13%415%42446%7%44%
1260
July1st to 15thNight
8%5%1442346%8%50%
1260
16th to endNight
9%425%43447%9%43%
1664
August1st to 15thNight
10%424435%45%8%45%
1620
16th to endNight
11%425%433446%48%
1729
September1st to 15thNight
15%42443435%7%44%
1863
16th to endNight
14%5%25%444346%43%
1980
October1st to 15thNight
21%8%36%43335%7%33%
2042
16th to endNight
28%11%36%6%34445%20%
2135
November1st to 15thNight
18%13%37%5%345%5%5%27%
2362
16th to endNight
23%16%6%8%5%34445%17%
2520
December1st to 15thNight
20%23%8%11%7%2432310%
2520
16th to endNight
20%19%13%12%7%343328%
2793

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%16%10%16%10%4333311%
1351
16th to endDay
11%20%8%16%11%35%44410%
1728
February1st to 15thDay
13%19%9%17%10%4433210%
1575
16th to endDay
15%19%7%11%9%45%44412%
1488
March1st to 15thDay
16%12%6%11%8%4434424%
1950
16th to endDay
15%10%48%7%25%5%4430%
2111
April1st to 15thDay
21%12%5%6%433445%28%
2142
16th to endDay
19%11%34333347%36%
2340
May1st to 15thDay
19%8%26%42345%7%35%
2334
16th to endDay
14%7%345%3445%6%40%
2618
June1st to 15thDay
17%7%2443446%8%35%
2616
16th to endDay
17%5%25%5%25%5%5%8%36%
2700
July1st to 15thDay
13%5%25%5%246%6%8%37%
2700
16th to endDay
11%6%35%5%36%5%7%10%34%
2501
August1st to 15thDay
13%6%26%6%345%6%8%34%
2340
16th to endDay
13%6%26%6%46%5%5%8%33%
2460
September1st to 15thDay
19%7%36%5%2345%7%35%
2094
16th to endDay
17%6%35%424447%39%
1980
October1st to 15thDay
24%9%45%423346%30%
1716
16th to endDay
33%14%26%6%35%435%15%
1735
November1st to 15thDay
18%18%46%5%25%446%24%
1495
16th to endDay
20%21%7%7%6%34445%13%
1440
December1st to 15thDay
18%21%12%13%6%25%3446%
1440
16th to endDay
19%23%12%13%7%232337%
1425
January1st to 15thNight
20%17%8%14%10%443349%
2583
16th to endNight
13%17%9%14%12%5%6%4339%
2496
February1st to 15thNight
12%17%10%13%10%45%33313%
2278
16th to endNight
14%13%8%12%8%35%346%17%
1982
March1st to 15thNight
16%13%6%9%8%34435%24%
2010
16th to endNight
14%10%47%6%23435%36%
2112
April1st to 15thNight
20%12%45%414445%31%
1817
16th to endNight
15%11%34435%445%36%
1620
May1st to 15thNight
16%8%35%5%2445%6%36%
1613
16th to endNight
12%5%25%425%45%8%42%
1495
June1st to 15thNight
16%5%35%5%2445%7%38%
1341
16th to endNight
13%5%2432446%8%43%
1260
July1st to 15thNight
9%5%243145%5%7%51%
1260
16th to endNight
10%4245%3447%8%44%
1664
August1st to 15thNight
10%4145%35%5%49%45%
1620
16th to endNight
12%5%15%5%34346%47%
1729
September1st to 15thNight
14%5%245%34347%44%
1863
16th to endNight
14%6%25%5%34346%43%
1980
October1st to 15thNight
21%8%25%5%3345%6%33%
2042
16th to endNight
27%12%37%6%34345%20%
2135
November1st to 15thNight
17%13%37%5%35%44427%
2362
16th to endNight
22%17%5%9%6%24345%18%
2520
December1st to 15thNight
20%23%8%12%6%2432310%
2520
16th to endNight
20%20%13%13%7%332338%
2793

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
79%45%7%1
1352
16th to endDay
76%46%7%3
1728
February1st to 15thDay
80%349%1
1577
16th to endDay
74%46%9%5%
1488
March1st to 15thDay
64%410%12%7%
1950
16th to endDay
54%6%9%15%12%1
2112
April1st to 15thDay
57%5%7%19%10%
2142
16th to endDay
48%410%20%14%1
2340
May1st to 15thDay
47%6%9%22%13%
2334
16th to endDay
43%5%13%20%14%1
2622
June1st to 15thDay
45%6%11%23%13%
2616
16th to endDay
44%7%13%23%11%
2700
July1st to 15thDay
40%7%11%22%15%1
2541
16th to endDay
43%8%13%22%11%1
2344
August1st to 15thDay
44%8%13%18%12%1
2327
16th to endDay
45%8%13%20%9%1
2460
September1st to 15thDay
46%7%11%22%10%1
2094
16th to endDay
44%5%11%27%9%
1980
October1st to 15thDay
55%49%17%12%
1716
16th to endDay
71%5%9%9%3
1735
November1st to 15thDay
60%6%11%13%7%
1495
16th to endDay
72%49%9%2
1440
December1st to 15thDay
82%5%6%4
1440
16th to endDay
82%35%6%1
1425
January1st to 15thNight
79%47%6%2
2583
16th to endNight
78%5%8%5%2
2496
February1st to 15thNight
75%5%7%10%1
2287
16th to endNight
67%5%8%11%6%
1982
March1st to 15thNight
61%5%8%16%6%
2010
16th to endNight
50%48%18%15%2
2112
April1st to 15thNight
55%47%18%12%
1817
16th to endNight
48%5%8%16%17%2
1620
May1st to 15thNight
47%5%8%23%13%2
1614
16th to endNight
38%7%11%27%12%2
1497
June1st to 15thNight
42%5%12%24%14%1
1341
16th to endNight
37%7%12%27%15%1
1260
July1st to 15thNight
28%6%12%28%22%1
1190
16th to endNight
37%6%13%23%16%1
1558
August1st to 15thNight
34%8%16%25%13%1
1609
16th to endNight
37%6%11%29%14%1
1729
September1st to 15thNight
39%6%11%28%12%1
1863
16th to endNight
40%5%13%27%12%
1980
October1st to 15thNight
50%6%10%19%12%
2042
16th to endNight
65%5%11%12%4
2135
November1st to 15thNight
58%6%11%16%6%1
2362
16th to endNight
68%411%11%2
2520
December1st to 15thNight
79%5%8%5%1
2520
16th to endNight
81%46%6%
2793

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
16%27%43%11%1
72
16th to endDay
30%10%36%20%2
96
February1st to 15thDay
30%23%36%10%
90
16th to endDay
27%24%35%9%2
81
March1st to 15thDay
24%15%34%18%6%1
240
16th to endDay
24%7%32%21%10%2
288
April1st to 15thDay
24%12%31%20%10%1
270
16th to endDay
27%11%22%21%10%6%
270
May1st to 15thDay
25%7%26%23%12%4
288
16th to endDay
19%8%28%22%16%4
331
June1st to 15thDay
20%9%22%29%15%2
411
16th to endDay
16%6%32%29%12%2
495
July1st to 15thDay
15%6%25%28%17%6%
475
16th to endDay
12%422%33%17%9%
336
August1st to 15thDay
16%419%26%20%14%
313
16th to endDay
18%318%23%22%13%
332
September1st to 15thDay
17%418%26%19%14%
315
16th to endDay
17%5%19%25%22%10%
314
October1st to 15thDay
21%7%26%28%12%4
278
16th to endDay
42%10%24%19%4
247
November1st to 15thDay
21%12%33%21%9%2
75
16th to endDay
35%15%31%13%31
60
December1st to 15thDay
36%28%20%13%1
60
16th to endDay
35%20%43%
64
January1st to 15thNight
27%17%34%15%4
870
16th to endNight
21%11%35%25%5%
768
February1st to 15thNight
21%14%38%21%3
704
16th to endNight
22%12%33%26%4
631
March1st to 15thNight
21%15%36%20%5%
720
16th to endNight
21%10%30%26%10%1
768
April1st to 15thNight
27%10%30%24%7%
682
16th to endNight
22%10%27%27%9%2
540
May1st to 15thNight
22%5%25%32%13%1
534
16th to endNight
14%332%33%15%
375
June1st to 15thNight
16%5%28%37%11%
360
16th to endNight
16%326%39%13%
360
July1st to 15thNight
10%21%50%16%
340
16th to endNight
13%220%42%20%1
538
August1st to 15thNight
12%215%39%28%1
539
16th to endNight
15%119%30%29%2
583
September1st to 15thNight
18%323%29%18%7%
720
16th to endNight
18%319%32%19%4
717
October1st to 15thNight
24%7%25%26%13%2
684
16th to endNight
34%9%29%21%3
704
November1st to 15thNight
25%10%31%21%9%1
700
16th to endNight
31%14%28%20%5%
720
December1st to 15thNight
31%17%31%16%3
720
16th to endNight
29%15%36%15%2
873
Page generated at 2017-10-07 14:07:45. Version ac04

Copyright 2017 A. Danko


Durham Clear Sky Chart | Charts Home