Hanwell
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hanwell clear sky chart from 2005-11-06 to 2024-01-27.

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
23%
23234
14%
75008
6%
23177
33%
23177
15%
52504

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
14%
850
11%
2838
2%
847
25%
847
9%
2075
January11th to 20thNight
16%
767
12%
2675
3%
767
27%
767
9%
1988
January21st to endNight
16%
820
17%
2758
4%
820
31%
820
14%
1844
February1st to 10thNight
16%
720
14%
2340
4%
720
29%
720
13%
1629
February11th to 20thNight
13%
703
12%
2276
1%
700
26%
700
10%
1662
February21st to endNight
18%
592
16%
1803
4%
592
33%
592
14%
1301
March1st to 10thNight
15%
720
18%
2079
5%
720
29%
720
15%
1521
March11th to 20thNight
19%
720
15%
1980
5%
720
27%
720
16%
1439
March21st to endNight
18%
792
17%
2178
5%
792
28%
792
17%
1584
April1st to 10thNight
15%
648
12%
1845
4%
648
23%
648
13%
1390
April11th to 20thNight
18%
534
18%
1598
6%
534
28%
534
16%
1109
April21st to endNight
20%
540
14%
1620
5%
540
27%
540
14%
1185
May1st to 10thNight
24%
540
14%
1620
6%
540
31%
540
16%
1162
May11th to 20thNight
16%
532
15%
1483
4%
532
28%
532
16%
1084
May21st to endNight
23%
494
12%
1462
5%
493
31%
493
17%
1059
June1st to 10thNight
24%
360
9%
1260
5%
360
32%
360
13%
915
June11th to 20thNight
32%
360
12%
1260
10%
360
39%
360
18%
850
June21st to endNight
32%
360
8%
1260
7%
360
36%
360
15%
886
July1st to 10thNight
32%
350
11%
1225
7%
350
41%
350
20%
805
July11th to 20thNight
41%
348
12%
1231
12%
348
47%
348
21%
802
July21st to endNight
35%
479
11%
1567
10%
453
40%
453
16%
1084
August1st to 10thNight
42%
538
10%
1600
8%
534
44%
534
24%
1056
August11th to 20thNight
38%
532
14%
1596
8%
532
43%
532
20%
1101
August21st to endNight
41%
594
19%
1782
10%
594
47%
594
28%
1102
September1st to 10thNight
31%
582
17%
1814
7%
582
41%
582
25%
1141
September11th to 20thNight
39%
720
20%
1980
11%
720
47%
720
28%
1263
September21st to endNight
32%
720
23%
1980
11%
720
43%
720
26%
1296
October1st to 10thNight
34%
720
20%
2114
11%
720
42%
720
25%
1370
October11th to 20thNight
28%
720
19%
2160
7%
720
40%
720
19%
1486
October21st to endNight
19%
792
14%
2505
4%
792
31%
792
13%
1811
November1st to 10thNight
23%
762
16%
2454
7%
762
33%
762
16%
1682
November11th to 20thNight
22%
850
18%
2660
7%
850
35%
850
15%
1832
November21st to endNight
20%
850
13%
2660
3%
850
30%
850
12%
1931
December1st to 10thNight
14%
850
14%
2698
3%
850
25%
850
11%
2012
December11th to 20thNight
14%
850
12%
3481
4%
849
25%
849
9%
2568
December21st to endNight
11%
925
9%
5166
2%
906
23%
906
5%
3479

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
20%8%36%5%35%45%6%34%
74754
Night
20%9%36%5%3445%6%34%
75294
TransparencyDay
50%6%12%20%11%1
74454
Night
50%6%12%20%10%1
75129
SeeingDay
27%17%30%18%6%1
15156
Night
26%15%31%22%6%
23244

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 10thDay
16%13%5%9%6%3435%5%29%
1327
11th to 20thDay
20%14%5%9%6%3433429%
1502
21st to endDay
13%9%47%5%45%45%6%38%
1739
February1st to 10thDay
17%10%46%7%36%5%5%6%31%
1620
11th to 20thDay
17%12%48%6%36%5%46%28%
1573
21st to endDay
11%12%47%7%36%5%5%6%35%
1451
March1st to 10thDay
18%15%38%5%35%445%30%
1876
11th to 20thDay
17%10%47%6%5%4446%34%
1980
21st to endDay
19%11%47%6%34435%32%
2178
April1st to 10thDay
23%14%47%433446%27%
2114
11th to 20thDay
21%9%35%5%2345%7%35%
2312
21st to endDay
28%9%35%5%33446%30%
2340
May1st to 10thDay
25%9%45%6%3445%5%30%
2340
11th to 20thDay
26%6%35%43345%5%35%
2410
21st to endDay
20%7%35%5%35%45%8%33%
2827
June1st to 10thDay
26%8%47%5%35%45%6%28%
2700
11th to 20thDay
22%7%35%5%33447%36%
2700
21st to endDay
26%7%46%6%35%45%6%28%
2700
July1st to 10thDay
17%6%246%35%5%6%9%35%
2700
11th to 20thDay
16%6%25%435%7%7%10%34%
2683
21st to endDay
17%7%35%6%46%6%7%8%31%
2639
August1st to 10thDay
18%6%36%6%45%5%5%7%35%
2327
11th to 20thDay
17%6%36%7%45%6%6%7%34%
2304
21st to endDay
16%5%25%435%45%7%43%
2574
September1st to 10thDay
13%4245%45%46%7%45%
2142
11th to 20thDay
19%6%24434445%46%
1980
21st to endDay
20%5%25%5%23346%45%
1980
October1st to 10thDay
18%7%36%4245%5%6%40%
1845
11th to 20thDay
20%8%26%5%35%45%7%37%
1800
21st to endDay
23%9%37%6%35%445%31%
1850
November1st to 10thDay
22%8%36%5%25%347%36%
1624
11th to 20thDay
21%7%35%5%3446%8%35%
1520
21st to endDay
21%11%47%5%34436%31%
1520
December1st to 10thDay
25%11%35%5%34446%30%
1478
11th to 20thDay
23%11%38%8%3444427%
1668
21st to endDay
22%11%46%5%23335%34%
2431
January1st to 10thNight
16%12%5%8%8%4445%6%29%
2838
11th to 20thNight
18%12%5%7%7%45%45%5%28%
2675
21st to endNight
13%9%47%6%345%6%7%35%
2758
February1st to 10thNight
16%12%36%6%35%5%5%8%32%
2340
11th to 20thNight
18%12%47%6%35%5%5%7%28%
2273
21st to endNight
15%13%35%7%45%5%5%5%33%
1803
March1st to 10thNight
17%14%47%5%3444433%
2070
11th to 20thNight
18%10%46%6%346%5%6%33%
1979
21st to endNight
17%11%47%5%44445%35%
2178
April1st to 10thNight
26%11%35%6%35%345%30%
1845
11th to 20thNight
23%7%35%435%35%6%36%
1598
21st to endNight
26%11%35%42445%6%31%
1620
May1st to 10thNight
23%8%36%5%345%6%7%32%
1620
11th to 20thNight
26%9%35%5%34346%33%
1482
21st to endNight
18%7%38%6%35%45%6%34%
1461
June1st to 10thNight
25%7%36%5%45%5%5%7%28%
1260
11th to 20thNight
20%6%36%5%3446%7%36%
1260
21st to endNight
27%6%35%435%45%6%33%
1260
July1st to 10thNight
16%6%35%5%36%5%6%8%37%
1260
11th to 20thNight
16%7%245%45%5%6%9%36%
1273
21st to endNight
19%6%36%6%36%5%7%7%32%
1659
August1st to 10thNight
16%6%25%446%5%5%8%40%
1612
11th to 20thNight
16%7%36%5%35%5%6%8%36%
1596
21st to endNight
14%5%25%5%43448%47%
1782
September1st to 10thNight
15%5%25%5%3346%7%45%
1814
11th to 20thNight
18%6%24423346%47%
1980
21st to endNight
19%5%245%34337%46%
1980
October1st to 10thNight
19%7%2442345%7%42%
2114
11th to 20thNight
19%7%35%5%44447%38%
2160
21st to endNight
23%9%37%5%34446%33%
2505
November1st to 10thNight
22%7%26%5%25%346%37%
2454
11th to 20thNight
21%7%35%6%345%5%6%36%
2660
21st to endNight
22%9%35%5%445%6%7%31%
2660
December1st to 10thNight
26%10%47%5%335%45%29%
2698
11th to 20thNight
25%10%46%6%35%5%5%5%28%
3531
21st to endNight
22%12%36%5%3444433%
5236

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
56%5%14%15%9%1
1328
11th to 20thDay
60%5%9%17%8%1
1502
21st to endDay
46%6%12%21%14%2
1739
February1st to 10thDay
54%6%12%18%9%2
1620
11th to 20thDay
56%5%10%17%10%1
1581
21st to endDay
49%6%11%22%10%3
1451
March1st to 10thDay
57%410%17%10%2
1880
11th to 20thDay
52%5%11%17%13%2
1980
21st to endDay
54%5%8%18%10%4
2178
April1st to 10thDay
59%49%13%12%2
2114
11th to 20thDay
50%5%10%21%12%1
2312
21st to endDay
55%6%9%15%12%5%
2340
May1st to 10thDay
55%5%8%19%11%2
2340
11th to 20thDay
51%5%10%20%12%2
2414
21st to endDay
48%8%12%22%9%1
2827
June1st to 10thDay
57%7%10%16%10%1
2700
11th to 20thDay
48%5%12%19%13%1
2700
21st to endDay
56%8%10%15%9%1
2700
July1st to 10thDay
44%9%16%20%10%1
2625
11th to 20thDay
43%9%16%21%10%1
2602
21st to endDay
48%8%14%21%9%
2491
August1st to 10thDay
47%8%16%23%6%
2314
11th to 20thDay
48%8%14%23%8%
2304
21st to endDay
40%7%15%25%13%
2574
September1st to 10thDay
37%8%14%27%14%1
2142
11th to 20thDay
40%6%9%27%16%2
1980
21st to endDay
41%5%10%26%17%1
1980
October1st to 10thDay
44%6%12%26%12%
1845
11th to 20thDay
46%5%16%24%8%
1800
21st to endDay
55%6%10%18%11%
1850
November1st to 10thDay
49%5%12%21%12%1
1624
11th to 20thDay
46%6%15%18%13%1
1520
21st to endDay
54%6%14%19%6%
1520
December1st to 10thDay
56%6%12%18%7%1
1478
11th to 20thDay
60%410%16%9%1
1668
21st to endDay
54%5%13%16%10%3
2431
January1st to 10thNight
55%6%11%17%9%1
2838
11th to 20thNight
56%7%10%17%8%1
2675
21st to endNight
48%6%11%23%11%2
2758
February1st to 10thNight
51%5%13%18%12%1
2340
11th to 20thNight
55%6%11%17%10%2
2276
21st to endNight
53%5%10%18%12%2
1803
March1st to 10thNight
53%5%7%20%12%2
2079
11th to 20thNight
51%6%11%16%13%2
1980
21st to endNight
53%49%19%12%2
2178
April1st to 10thNight
57%5%9%14%11%4
1845
11th to 20thNight
49%5%10%19%16%1
1598
21st to endNight
55%5%9%16%12%3
1620
May1st to 10thNight
51%6%10%19%12%2
1620
11th to 20thNight
54%5%10%19%11%2
1483
21st to endNight
50%8%12%18%11%1
1462
June1st to 10thNight
55%7%10%19%8%1
1260
11th to 20thNight
48%7%12%22%11%1
1260
21st to endNight
52%7%11%20%8%2
1260
July1st to 10thNight
42%9%18%21%10%
1225
11th to 20thNight
42%8%17%22%10%
1231
21st to endNight
48%9%13%20%10%1
1567
August1st to 10thNight
41%9%17%25%8%
1600
11th to 20thNight
45%10%16%24%6%
1596
21st to endNight
36%7%16%27%13%1
1782
September1st to 10thNight
39%7%14%28%12%1
1814
11th to 20thNight
39%5%12%27%16%1
1980
21st to endNight
40%6%10%28%15%2
1980
October1st to 10thNight
41%6%11%25%15%1
2114
11th to 20thNight
46%7%12%25%10%1
2160
21st to endNight
54%5%10%19%11%
2505
November1st to 10thNight
49%5%13%22%10%1
2454
11th to 20thNight
48%6%13%20%11%1
2660
21st to endNight
52%8%14%16%10%
2660
December1st to 10thNight
58%5%11%19%7%
2698
11th to 20thNight
58%5%10%19%8%
3532
21st to endNight
55%5%12%18%6%4
5236

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
32%17%35%14%2
180
11th to 20thDay
34%22%32%8%31
180
21st to endDay
25%19%35%17%3
295
February1st to 10thDay
30%18%34%16%3
340
11th to 20thDay
29%24%29%13%41
336
21st to endDay
25%25%28%20%2
334
March1st to 10thDay
32%21%33%12%2
420
11th to 20thDay
28%21%32%13%5%1
420
21st to endDay
31%21%27%13%5%1
462
April1st to 10thDay
40%23%21%12%21
420
11th to 20thDay
33%21%28%13%41
412
21st to endDay
35%18%30%12%5%1
420
May1st to 10thDay
35%19%28%13%4
423
11th to 20thDay
31%19%27%15%5%2
556
21st to endDay
27%17%35%15%6%
680
June1st to 10thDay
33%17%28%16%5%
630
11th to 20thDay
27%15%28%21%8%
630
21st to endDay
28%11%31%22%7%1
630
July1st to 10thDay
23%12%36%20%9%1
620
11th to 20thDay
21%8%34%24%11%2
601
21st to endDay
16%8%40%27%7%1
488
August1st to 10thDay
18%10%36%24%9%2
446
11th to 20thDay
18%12%30%27%11%2
439
21st to endDay
22%12%26%27%10%3
495
September1st to 10thDay
12%14%36%27%9%3
450
11th to 20thDay
24%13%28%22%9%4
450
21st to endDay
22%18%30%16%9%5%
450
October1st to 10thDay
23%16%25%21%11%3
382
11th to 20thDay
24%19%27%18%9%3
360
21st to endDay
30%20%29%15%5%
396
November1st to 10thDay
30%15%29%19%6%1
365
11th to 20thDay
33%19%26%14%7%
370
21st to endDay
32%22%28%16%21
370
December1st to 10thDay
34%16%31%15%4
328
11th to 20thDay
39%24%24%11%1
180
21st to endDay
32%26%28%12%21
198
January1st to 10thNight
27%19%30%21%2
850
11th to 20thNight
30%17%30%19%4
767
21st to endNight
20%22%34%20%3
820
February1st to 10thNight
24%23%31%19%3
720
11th to 20thNight
28%22%32%15%3
703
21st to endNight
24%19%32%21%3
592
March1st to 10thNight
25%19%36%18%2
720
11th to 20thNight
23%18%35%19%5%
720
21st to endNight
25%16%34%20%5%
792
April1st to 10thNight
34%17%31%15%3
648
11th to 20thNight
29%19%31%16%5%
534
21st to endNight
31%16%30%18%5%
540
May1st to 10thNight
27%14%32%24%3
540
11th to 20thNight
31%14%33%17%4
532
21st to endNight
21%16%37%23%4
494
June1st to 10thNight
28%10%33%24%5%
360
11th to 20thNight
22%11%31%29%7%1
360
21st to endNight
31%6%28%31%4
360
July1st to 10thNight
18%6%39%29%8%
350
11th to 20thNight
20%5%29%35%11%
348
21st to endNight
20%6%32%34%8%
479
August1st to 10thNight
18%5%30%37%10%
538
11th to 20thNight
20%7%28%34%11%
532
21st to endNight
16%9%29%33%13%1
594
September1st to 10thNight
18%9%37%25%10%1
582
11th to 20thNight
21%9%25%31%11%1
720
21st to endNight
22%13%29%26%9%
720
October1st to 10thNight
22%10%29%27%10%1
720
11th to 20thNight
21%14%31%24%9%1
720
21st to endNight
29%17%30%19%5%
792
November1st to 10thNight
28%15%28%22%6%1
762
11th to 20thNight
29%17%27%20%7%1
850
21st to endNight
27%20%29%20%4
850
December1st to 10thNight
34%15%30%17%4
850
11th to 20thNight
31%21%28%17%3
850
21st to endNight
31%21%28%17%3
935
Page generated at 2024-01-24 10:37:27. Version ac07

Copyright 2024 Attilla Danko


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