Norwich
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Norwich clear sky chart from 2005-11-05 to 2018-03-21.

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
29%
15616
13%
49231
8%
15585
34%
15585
15%
35770

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
13%
780
8%
2716
4%
776
18%
776
7%
2180
January16th to endNight
14%
832
9%
2798
4%
832
21%
832
8%
2226
February1st to 15thNight
11%
764
8%
2482
2%
761
17%
761
6%
2070
February16th to endNight
15%
683
12%
2062
5%
683
23%
683
10%
1620
March1st to 15thNight
17%
780
10%
2272
4%
780
23%
780
11%
1780
March16th to endNight
24%
792
17%
2097
8%
792
31%
792
16%
1558
April1st to 15thNight
20%
718
12%
1796
4%
718
25%
718
17%
1379
April16th to endNight
28%
720
17%
1800
6%
720
34%
720
24%
1267
May1st to 15thNight
32%
397
17%
1477
13%
397
40%
397
17%
984
May16th to endNight
41%
374
15%
1497
14%
374
50%
374
19%
942
June1st to 15thNight
40%
360
12%
1440
14%
360
48%
360
16%
929
June16th to endNight
50%
360
13%
1440
14%
360
58%
360
24%
844
July1st to 15thNight
55%
340
13%
1360
17%
340
57%
340
24%
799
July16th to endNight
57%
376
15%
1418
18%
354
61%
354
24%
825
August1st to 15thNight
53%
505
14%
1576
10%
503
56%
503
29%
968
August16th to endNight
57%
758
19%
1904
11%
758
58%
758
35%
1237
September1st to 15thNight
47%
720
17%
1800
9%
720
49%
720
30%
1223
September16th to endNight
49%
717
24%
1947
17%
717
54%
717
31%
1244
October1st to 15thNight
36%
720
17%
2160
13%
720
43%
720
20%
1506
October16th to endNight
24%
768
12%
2372
7%
768
31%
768
13%
1792
November1st to 15thNight
24%
760
15%
2472
9%
760
33%
760
15%
1759
November16th to endNight
22%
780
13%
2703
8%
780
29%
780
12%
1972
December1st to 15thNight
14%
780
6%
2730
4%
780
18%
780
7%
2194
December16th to endNight
12%
832
5%
2912
2%
832
16%
832
5%
2472

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%10%47%6%34446%28%
49627
Night
16%10%47%6%3445%6%30%
49400
Cloud CoverDay
17%10%47%6%35%446%28%
49636
Night
16%10%47%6%3445%6%30%
49406
TransparencyDay
56%410%18%9%
49314
Night
54%411%18%9%
49231
SeeingDay
25%13%26%20%10%4
6175
Night
23%15%26%24%9%1
15617

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
14%13%6%13%7%45%5%5%320%
1552
16th to endDay
11%13%8%12%10%45%35%5%19%
1778
February1st to 15thDay
16%15%7%13%11%445%3314%
1710
16th to endDay
18%12%5%11%11%34435%20%
1696
March1st to 15thDay
17%16%7%8%6%25%345%23%
2005
16th to endDay
17%12%5%7%424345%32%
2255
April1st to 15thDay
20%13%46%42423432%
2152
16th to endDay
17%10%35%5%33436%36%
2160
May1st to 15thDay
19%9%36%5%3345%6%31%
2481
16th to endDay
16%7%36%6%345%5%7%32%
2618
June1st to 15thDay
23%6%25%6%34448%29%
2520
16th to endDay
18%6%36%5%45%5%5%8%30%
2520
July1st to 15thDay
14%6%25%7%36%6%6%8%31%
2520
16th to endDay
14%5%36%5%36%5%7%9%32%
2654
August1st to 15thDay
15%6%27%7%45%6%6%8%28%
2367
16th to endDay
15%6%26%5%45%45%9%32%
2292
September1st to 15thDay
19%7%25%5%2445%7%36%
2160
16th to endDay
16%5%245%34446%42%
2010
October1st to 15thDay
21%7%37%6%23346%33%
1800
16th to endDay
22%13%46%5%3445%5%24%
1851
November1st to 15thDay
16%13%37%5%3445%6%31%
1716
16th to endDay
19%13%47%6%35%446%24%
1586
December1st to 15thDay
18%17%7%11%7%2434417%
1560
16th to endDay
17%18%11%10%6%35%34413%
1664
January1st to 15thNight
15%13%6%11%8%46%5%6%5%16%
2716
16th to endNight
12%13%6%11%9%45%446%19%
2798
February1st to 15thNight
12%13%9%14%9%46%445%16%
2480
16th to endNight
14%12%5%11%8%36%445%21%
2062
March1st to 15thNight
17%11%5%10%7%33445%25%
2259
16th to endNight
15%11%6%7%5%24445%32%
2097
April1st to 15thNight
20%12%45%5%34336%30%
1796
16th to endNight
18%8%25%424345%40%
1800
May1st to 15thNight
20%8%25%42435%6%35%
1477
16th to endNight
12%6%35%446%47%8%37%
1495
June1st to 15thNight
21%6%2442445%6%36%
1440
16th to endNight
12%4134345%7%9%42%
1440
July1st to 15thNight
7%5%345%25%6%6%10%41%
1440
16th to endNight
12%3244345%6%6%46%
1514
August1st to 15thNight
11%4245%25%46%8%43%
1586
16th to endNight
13%42442445%7%46%
1904
September1st to 15thNight
17%5%24334348%42%
1800
16th to endNight
14%5%23324447%45%
1947
October1st to 15thNight
21%7%26%5%2334438%
2160
16th to endNight
24%9%36%5%34446%26%
2372
November1st to 15thNight
14%13%47%5%24446%30%
2472
16th to endNight
16%12%46%6%3435%6%28%
2703
December1st to 15thNight
19%14%7%10%7%34435%19%
2730
16th to endNight
19%15%8%12%7%4444414%
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%11%7%13%7%36%5%4419%
1552
16th to endDay
11%13%7%12%10%35%445%19%
1778
February1st to 15thDay
16%16%6%14%10%35%42415%
1710
16th to endDay
18%12%5%11%9%4433421%
1696
March1st to 15thDay
17%16%6%8%6%2444422%
2015
16th to endDay
17%13%5%7%433345%32%
2254
April1st to 15thDay
20%12%46%42423432%
2152
16th to endDay
17%11%25%5%24345%36%
2160
May1st to 15thDay
19%9%36%5%24446%31%
2481
16th to endDay
16%7%36%6%35%45%7%32%
2618
June1st to 15thDay
23%6%35%5%35%447%29%
2520
16th to endDay
18%7%36%5%35%5%5%8%30%
2520
July1st to 15thDay
14%6%35%6%46%6%6%8%31%
2520
16th to endDay
13%5%36%6%36%5%6%9%32%
2654
August1st to 15thDay
15%6%27%7%45%6%5%9%28%
2367
16th to endDay
15%6%36%5%35%5%6%8%32%
2292
September1st to 15thDay
18%7%35%5%245%5%6%35%
2160
16th to endDay
16%5%25%5%34445%42%
2010
October1st to 15thDay
21%8%36%5%33346%33%
1800
16th to endDay
22%14%36%6%2445%5%24%
1851
November1st to 15thDay
17%13%35%6%2445%6%31%
1716
16th to endDay
18%13%47%6%35%435%25%
1586
December1st to 15thDay
19%16%8%11%7%3333417%
1560
16th to endDay
18%17%11%11%6%35%34413%
1664
January1st to 15thNight
16%12%6%11%8%46%46%5%17%
2716
16th to endNight
12%14%7%11%9%46%445%20%
2798
February1st to 15thNight
12%13%8%15%8%46%5%4416%
2473
16th to endNight
15%12%5%11%8%35%45%5%21%
2062
March1st to 15thNight
18%12%6%10%7%33345%24%
2272
16th to endNight
15%12%6%7%424445%33%
2097
April1st to 15thNight
20%12%45%433345%30%
1796
16th to endNight
19%8%24424345%40%
1800
May1st to 15thNight
19%8%35%42335%6%36%
1477
16th to endNight
12%6%26%5%36%46%8%36%
1495
June1st to 15thNight
20%6%343245%5%7%36%
1440
16th to endNight
12%4234345%6%9%42%
1440
July1st to 15thNight
7%4345%346%7%9%42%
1440
16th to endNight
12%424435%5%5%6%45%
1514
August1st to 15thNight
11%5%25%5%245%6%8%43%
1586
16th to endNight
12%5%2442345%7%45%
1904
September1st to 15thNight
17%5%25%334447%43%
1800
16th to endNight
14%5%24324447%45%
1947
October1st to 15thNight
21%7%36%5%33335%38%
2160
16th to endNight
24%10%36%5%34447%26%
2372
November1st to 15thNight
15%14%36%42445%6%31%
2472
16th to endNight
16%12%46%6%3435%6%28%
2703
December1st to 15thNight
19%14%6%10%7%35%435%18%
2730
16th to endNight
19%14%9%12%7%3444414%
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
66%39%11%7%1
1553
16th to endDay
66%5%11%10%5%
1778
February1st to 15thDay
74%45%10%4
1712
16th to endDay
67%48%13%7%
1696
March1st to 15thDay
64%5%10%12%6%
2015
16th to endDay
54%38%16%14%1
2255
April1st to 15thDay
57%28%20%8%2
2152
16th to endDay
50%37%20%15%1
2160
May1st to 15thDay
53%49%21%10%1
2481
16th to endDay
49%7%12%20%10%
2622
June1st to 15thDay
54%5%11%19%9%
2520
16th to endDay
52%5%13%19%9%
2520
July1st to 15thDay
49%6%11%22%10%
2371
16th to endDay
47%6%15%21%9%
2487
August1st to 15thDay
51%6%13%19%9%
2353
16th to endDay
47%5%11%24%10%
2292
September1st to 15thDay
48%5%10%22%12%
2160
16th to endDay
43%410%23%16%1
2010
October1st to 15thDay
52%49%21%11%1
1800
16th to endDay
61%411%16%6%
1851
November1st to 15thDay
54%413%17%9%1
1716
16th to endDay
61%312%14%7%
1586
December1st to 15thDay
71%310%10%3
1560
16th to endDay
75%48%8%2
1664
January1st to 15thNight
67%5%9%10%6%
2716
16th to endNight
66%49%13%5%
2798
February1st to 15thNight
70%5%8%11%4
2482
16th to endNight
63%410%13%7%
2062
March1st to 15thNight
63%311%14%6%
2272
16th to endNight
54%49%18%11%1
2097
April1st to 15thNight
56%410%16%11%1
1796
16th to endNight
46%49%21%16%2
1800
May1st to 15thNight
49%5%11%18%13%1
1477
16th to endNight
44%5%14%22%11%1
1497
June1st to 15thNight
47%5%12%24%9%
1440
16th to endNight
37%6%16%26%12%
1440
July1st to 15thNight
35%8%13%26%13%1
1360
16th to endNight
38%5%15%25%13%1
1418
August1st to 15thNight
37%6%19%26%10%1
1576
16th to endNight
36%5%14%29%14%
1904
September1st to 15thNight
41%5%13%24%13%1
1800
16th to endNight
38%410%27%17%1
1947
October1st to 15thNight
50%49%20%14%1
2160
16th to endNight
59%412%16%7%
2372
November1st to 15thNight
53%410%17%10%2
2472
16th to endNight
57%413%17%7%
2703
December1st to 15thNight
68%312%11%3
2730
16th to endNight
73%5%8%9%2
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%28%22%14%41
90
16th to endDay
28%27%34%8%1
122
February1st to 15thDay
36%30%28%4
135
16th to endDay
34%21%27%13%3
277
March1st to 15thDay
33%16%28%17%4
330
16th to endDay
27%20%26%15%6%2
311
April1st to 15thDay
32%16%27%13%8%1
270
16th to endDay
24%12%27%19%8%7%
270
May1st to 15thDay
31%12%22%16%10%6%
288
16th to endDay
17%9%35%24%9%3
331
June1st to 15thDay
26%11%24%22%11%2
315
16th to endDay
22%8%34%22%9%3
315
July1st to 15thDay
19%5%26%27%14%5%
305
16th to endDay
17%426%32%15%3
326
August1st to 15thDay
15%9%24%24%16%8%
313
16th to endDay
17%5%18%27%16%13%
332
September1st to 15thDay
20%7%19%23%19%10%
315
16th to endDay
15%7%22%20%18%14%
314
October1st to 15thDay
23%7%24%21%17%6%
315
16th to endDay
33%15%25%17%6%
319
November1st to 15thDay
28%13%23%23%9%1
280
16th to endDay
31%26%23%13%5%
116
December1st to 15thDay
27%22%27%16%41
90
16th to endDay
40%26%31%2
96
January1st to 15thNight
26%24%31%15%2
780
16th to endNight
24%22%31%18%2
832
February1st to 15thNight
23%25%32%16%1
764
16th to endNight
26%20%30%18%3
683
March1st to 15thNight
29%20%27%19%2
780
16th to endNight
25%22%23%20%6%
792
April1st to 15thNight
28%17%29%21%3
718
16th to endNight
25%14%27%21%10%
720
May1st to 15thNight
27%7%25%28%9%
397
16th to endNight
14%6%30%37%10%1
375
June1st to 15thNight
23%7%21%33%12%
360
16th to endNight
12%426%41%15%
360
July1st to 15thNight
9%125%40%22%
340
16th to endNight
13%119%46%16%2
376
August1st to 15thNight
14%221%36%21%2
505
16th to endNight
16%316%34%26%3
758
September1st to 15thNight
19%5%21%33%18%2
720
16th to endNight
16%7%22%24%24%5%
717
October1st to 15thNight
25%10%21%24%15%1
720
16th to endNight
30%13%26%24%4
768
November1st to 15thNight
22%15%30%21%7%1
760
16th to endNight
25%20%26%18%7%
780
December1st to 15thNight
30%22%26%17%3
780
16th to endNight
30%23%29%14%2
832
Page generated at 2018-03-22 11:34:28. Version ac04

Copyright 2018 A. Danko


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