Hanwell
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hanwell clear sky chart from 2005-11-05 to 2017-09-24.

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%
14831
14%
46846
6%
14793
33%
14793
16%
32880

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
15%
741
14%
2634
2%
737
29%
737
10%
1847
January16th to endNight
15%
768
15%
2616
3%
768
30%
768
13%
1799
February1st to 15thNight
17%
704
12%
2286
3%
701
28%
701
14%
1602
February16th to endNight
16%
631
12%
1970
2%
631
28%
631
11%
1476
March1st to 15thNight
17%
720
16%
2046
5%
720
28%
720
15%
1498
March16th to endNight
19%
768
17%
2112
5%
768
28%
768
18%
1520
April1st to 15thNight
17%
611
14%
1766
5%
611
25%
611
14%
1303
April16th to endNight
21%
540
16%
1620
6%
540
29%
540
17%
1134
May1st to 15thNight
23%
540
12%
1602
6%
540
29%
540
16%
1163
May16th to endNight
19%
501
10%
1436
3%
500
27%
500
14%
1098
June1st to 15thNight
25%
360
7%
1260
4%
360
29%
360
12%
932
June16th to endNight
33%
360
7%
1260
6%
360
36%
360
16%
878
July1st to 15thNight
37%
340
10%
1190
8%
340
45%
340
22%
780
July16th to endNight
36%
433
10%
1421
8%
407
40%
407
16%
988
August1st to 15thNight
40%
539
10%
1608
8%
535
42%
535
21%
1104
August16th to endNight
39%
573
19%
1719
9%
573
45%
573
28%
1068
September1st to 15thNight
31%
630
15%
1872
7%
630
38%
630
22%
1252
September16th to endNight
38%
693
25%
1913
14%
693
48%
693
33%
1154
October1st to 15thNight
30%
660
20%
1952
9%
660
40%
660
23%
1293
October16th to endNight
21%
704
15%
2192
4%
704
32%
704
14%
1565
November1st to 15thNight
23%
715
15%
2367
8%
715
33%
715
16%
1639
November16th to endNight
25%
750
15%
2520
6%
750
36%
750
13%
1778
December1st to 15thNight
14%
750
13%
2604
3%
750
26%
750
11%
1890
December16th to endNight
11%
800
12%
2880
3%
800
22%
800
8%
2119

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
21%8%35%5%24446%32%
48087
Night
20%8%35%5%2445%6%34%
47012
TransparencyDay
51%5%11%19%10%1
47771
Night
50%5%11%20%10%
46846
SeeingDay
27%14%29%19%7%1
6822
Night
25%14%31%22%6%
14831

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%10%47%434345%33%
1301
16th to endDay
15%11%47%5%34345%32%
1605
February1st to 15thDay
14%9%46%7%46%5%46%30%
1575
16th to endDay
16%12%5%7%7%25%445%27%
1501
March1st to 15thDay
21%13%36%43433431%
1903
16th to endDay
16%10%5%7%6%24436%32%
2112
April1st to 15thDay
23%11%36%333346%31%
2182
16th to endDay
26%7%24423345%34%
2340
May1st to 15thDay
26%7%45%5%24345%29%
2347
16th to endDay
27%7%35%5%3435%7%29%
2687
June1st to 15thDay
28%8%45%434345%26%
2700
16th to endDay
24%7%46%5%25%45%7%26%
2700
July1st to 15thDay
15%5%246%35%5%6%10%34%
2700
16th to endDay
17%7%35%5%35%7%7%7%29%
2632
August1st to 15thDay
19%6%26%5%35%5%46%33%
2340
16th to endDay
15%415%5%35%5%5%7%39%
2483
September1st to 15thDay
17%5%24435%345%42%
2087
16th to endDay
17%414323335%49%
1906
October1st to 15thDay
20%7%25%313445%40%
1678
16th to endDay
23%8%26%5%35%345%32%
1680
November1st to 15thDay
23%7%25%424347%34%
1491
16th to endDay
21%9%35%5%24446%32%
1440
December1st to 15thDay
26%9%24424345%30%
1353
16th to endDay
24%12%47%413345%26%
1344
January1st to 15thNight
16%9%46%6%3445%6%32%
2634
16th to endNight
14%9%47%5%245%5%7%31%
2616
February1st to 15thNight
14%11%36%5%35%5%47%31%
2285
16th to endNight
18%14%45%5%24445%29%
1970
March1st to 15thNight
20%9%36%4245%4433%
2034
16th to endNight
17%9%46%42345%5%35%
2112
April1st to 15thNight
24%9%25%5%34445%31%
1766
16th to endNight
26%8%24213345%36%
1620
May1st to 15thNight
24%7%25%5%2446%6%29%
1602
16th to endNight
23%8%37%6%34345%28%
1434
June1st to 15thNight
26%6%35%5%35%45%6%27%
1260
16th to endNight
21%6%24435%46%7%32%
1260
July1st to 15thNight
13%425%5%36%5%6%9%35%
1260
16th to endNight
18%6%25%5%35%46%8%31%
1520
August1st to 15thNight
17%6%25%5%3445%7%36%
1620
16th to endNight
13%425%43345%8%45%
1719
September1st to 15thNight
18%5%35%42335%6%40%
1872
16th to endNight
14%413323337%51%
1913
October1st to 15thNight
19%7%34323447%40%
1952
16th to endNight
24%8%25%423335%34%
2192
November1st to 15thNight
23%6%25%5%24345%36%
2367
16th to endNight
22%8%345%24446%34%
2520
December1st to 15thNight
25%8%35%42345%430%
2604
16th to endNight
25%11%45%423445%27%
2880

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
51%6%14%17%7%1
1302
16th to endDay
52%5%9%20%11%
1605
February1st to 15thDay
53%6%12%18%7%1
1578
16th to endDay
57%5%9%17%7%1
1501
March1st to 15thDay
57%39%16%10%1
1914
16th to endDay
52%49%18%11%2
2112
April1st to 15thDay
54%38%16%13%2
2182
16th to endDay
51%49%17%13%3
2340
May1st to 15thDay
56%48%18%9%2
2347
16th to endDay
54%6%12%19%6%
2691
June1st to 15thDay
60%5%10%14%8%
2700
16th to endDay
55%7%11%15%8%
2700
July1st to 15thDay
42%9%15%18%12%
2541
16th to endDay
49%7%16%18%6%
2469
August1st to 15thDay
50%7%13%22%6%
2327
16th to endDay
42%7%15%24%10%
2483
September1st to 15thDay
42%6%11%26%12%
2087
16th to endDay
37%49%29%18%1
1906
October1st to 15thDay
44%414%24%11%
1678
16th to endDay
54%412%20%8%
1680
November1st to 15thDay
50%6%13%15%13%
1491
16th to endDay
52%6%13%17%9%
1440
December1st to 15thDay
55%5%12%19%5%
1353
16th to endDay
59%49%16%8%
1344
January1st to 15thNight
50%7%11%19%9%
2634
16th to endNight
50%411%21%10%
2616
February1st to 15thNight
50%5%14%19%9%
2286
16th to endNight
56%6%9%15%10%2
1970
March1st to 15thNight
52%5%8%19%11%2
2046
16th to endNight
51%49%20%12%1
2112
April1st to 15thNight
55%49%15%12%3
1766
16th to endNight
50%48%17%14%2
1620
May1st to 15thNight
53%5%11%18%9%1
1602
16th to endNight
57%6%11%15%8%
1436
June1st to 15thNight
56%6%11%17%5%1
1260
16th to endNight
50%7%13%19%9%
1260
July1st to 15thNight
41%9%17%23%8%
1190
16th to endNight
48%8%14%19%8%
1421
August1st to 15thNight
46%7%15%22%7%
1608
16th to endNight
36%6%16%29%9%
1719
September1st to 15thNight
43%6%11%25%12%1
1872
16th to endNight
33%413%31%16%
1913
October1st to 15thNight
43%5%11%25%13%
1952
16th to endNight
52%49%22%9%
2192
November1st to 15thNight
49%5%14%19%9%1
2367
16th to endNight
51%6%13%19%9%
2520
December1st to 15thNight
56%5%10%21%5%
2604
16th to endNight
57%5%11%17%7%
2880

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
26%20%36%15%1
60
16th to endDay
23%18%36%16%5%
133
February1st to 15thDay
20%16%36%22%4
236
16th to endDay
23%20%27%22%4
226
March1st to 15thDay
31%19%30%12%4
270
16th to endDay
26%18%29%15%6%3
288
April1st to 15thDay
35%20%25%14%31
270
16th to endDay
31%16%30%13%5%2
270
May1st to 15thDay
36%17%26%13%41
303
16th to endDay
31%15%29%15%6%
519
June1st to 15thDay
35%13%25%19%5%
495
16th to endDay
28%10%32%19%8%1
495
July1st to 15thDay
22%9%30%22%12%2
475
16th to endDay
21%6%34%26%9%1
373
August1st to 15thDay
23%7%31%23%12%2
313
16th to endDay
18%11%25%26%13%4
332
September1st to 15thDay
19%11%32%25%7%2
315
16th to endDay
19%11%29%20%12%6%
287
October1st to 15thDay
27%14%22%18%11%5%
230
16th to endDay
30%20%28%12%7%
240
November1st to 15thDay
28%14%28%19%8%1
235
16th to endDay
29%20%24%20%5%
240
December1st to 15thDay
36%16%24%18%3
153
16th to endDay
45%18%26%9%
64
January1st to 15thNight
25%17%33%19%3
741
16th to endNight
22%20%34%19%3
768
February1st to 15thNight
20%18%35%20%4
704
16th to endNight
28%18%31%17%3
631
March1st to 15thNight
25%18%34%20%1
720
16th to endNight
24%15%34%19%5%
768
April1st to 15thNight
30%17%31%16%4
611
16th to endNight
29%14%32%18%5%
540
May1st to 15thNight
28%13%31%22%4
540
16th to endNight
26%12%36%19%4
501
June1st to 15thNight
28%9%31%24%6%
360
16th to endNight
24%7%31%29%6%
360
July1st to 15thNight
15%437%32%10%
340
16th to endNight
21%5%31%32%9%
433
August1st to 15thNight
21%425%35%12%
539
16th to endNight
16%7%31%31%13%
573
September1st to 15thNight
22%10%31%26%9%
630
16th to endNight
17%10%30%29%11%1
693
October1st to 15thNight
22%11%30%25%8%
660
16th to endNight
28%16%29%19%5%
704
November1st to 15thNight
25%14%30%20%7%
715
16th to endNight
25%18%26%21%7%
750
December1st to 15thNight
32%17%29%17%3
750
16th to endNight
35%18%28%14%2
800
Page generated at 2017-09-25 10:02:18. Version ac04

Copyright 2017 A. Danko


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