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 2019-07-16.

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%
17215
15%
54086
6%
17177
33%
17177
16%
37850

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%
883
14%
3076
3%
879
28%
879
10%
2176
January16th to endNight
15%
896
14%
3052
3%
896
29%
896
12%
2117
February1st to 15thNight
16%
824
14%
2676
3%
821
30%
821
13%
1862
February16th to endNight
15%
735
13%
2295
3%
735
27%
735
11%
1691
March1st to 15thNight
16%
840
17%
2388
5%
840
28%
840
14%
1774
March16th to endNight
19%
896
16%
2464
5%
896
28%
896
19%
1756
April1st to 15thNight
16%
713
15%
2061
5%
713
25%
713
14%
1523
April16th to endNight
20%
623
14%
1869
5%
623
27%
623
15%
1349
May1st to 15thNight
22%
630
14%
1870
6%
630
31%
630
16%
1343
May16th to endNight
19%
587
10%
1682
4%
586
27%
586
14%
1278
June1st to 15thNight
26%
420
9%
1470
5%
420
32%
420
14%
1064
June16th to endNight
31%
420
8%
1470
6%
420
35%
420
16%
1013
July1st to 15thNight
38%
400
13%
1400
10%
400
48%
400
23%
889
July16th to endNight
36%
472
10%
1557
9%
446
41%
446
17%
1067
August1st to 15thNight
41%
574
9%
1713
8%
570
43%
570
21%
1179
August16th to endNight
39%
621
19%
1863
10%
621
46%
621
29%
1149
September1st to 15thNight
32%
682
17%
2028
9%
682
39%
682
23%
1334
September16th to endNight
37%
777
24%
2145
13%
777
47%
777
31%
1314
October1st to 15thNight
30%
780
19%
2307
9%
780
40%
780
23%
1527
October16th to endNight
20%
832
16%
2590
4%
832
32%
832
15%
1828
November1st to 15thNight
22%
850
16%
2772
7%
850
33%
850
15%
1930
November16th to endNight
23%
900
14%
2940
5%
900
35%
900
13%
2088
December1st to 15thNight
16%
900
15%
3038
4%
900
28%
900
12%
2181
December16th to endNight
12%
960
13%
3360
3%
960
24%
960
9%
2418

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%35%5%34446%33%
55233
Night
19%8%35%5%24446%34%
54252
TransparencyDay
50%5%11%19%10%1
54917
Night
50%5%11%20%10%1
54086
SeeingDay
28%15%29%18%6%1
9184
Night
25%14%31%21%6%
17215

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%10%48%5%34345%33%
1519
16th to endDay
16%10%46%5%34345%33%
1873
February1st to 15thDay
15%9%46%6%46%5%46%30%
1845
16th to endDay
15%13%47%6%25%445%29%
1748
March1st to 15thDay
21%15%36%43433429%
2221
16th to endDay
17%9%47%6%23436%33%
2464
April1st to 15thDay
22%10%36%433446%30%
2546
16th to endDay
27%8%25%423345%32%
2696
May1st to 15thDay
25%7%35%5%24345%31%
2739
16th to endDay
26%6%35%43435%6%29%
3147
June1st to 15thDay
26%8%45%434346%28%
3150
16th to endDay
25%6%35%5%25%45%7%28%
3150
July1st to 15thDay
15%4245%35%5%6%10%36%
3150
16th to endDay
17%7%35%5%35%7%7%7%29%
2859
August1st to 15thDay
19%6%26%5%45%5%46%32%
2488
16th to endDay
14%415%5%35%5%5%8%40%
2691
September1st to 15thDay
16%424434345%43%
2261
16th to endDay
17%414323345%49%
2145
October1st to 15thDay
20%7%25%313445%41%
1982
16th to endDay
23%7%25%5%35%345%33%
1986
November1st to 15thDay
24%6%25%424337%35%
1746
16th to endDay
21%9%35%5%24445%32%
1680
December1st to 15thDay
25%10%34424345%31%
1579
16th to endDay
23%11%46%5%13346%28%
1568
January1st to 15thNight
16%9%46%6%3445%5%32%
3076
16th to endNight
15%9%47%6%345%6%7%30%
3052
February1st to 15thNight
14%11%36%5%35%447%32%
2675
16th to endNight
18%13%35%5%245%45%30%
2295
March1st to 15thNight
20%12%36%42443432%
2376
16th to endNight
16%9%47%5%23445%36%
2464
April1st to 15thNight
23%9%25%6%35%335%31%
2061
16th to endNight
27%8%24323345%32%
1869
May1st to 15thNight
23%7%25%5%2346%6%31%
1870
16th to endNight
23%8%37%6%34345%29%
1680
June1st to 15thNight
24%6%35%5%35%45%6%29%
1470
16th to endNight
22%6%34325%45%7%33%
1470
July1st to 15thNight
12%425%436%5%6%9%38%
1470
16th to endNight
18%5%25%5%35%46%8%32%
1656
August1st to 15thNight
17%6%26%5%3445%7%37%
1725
16th to endNight
13%425%43345%7%46%
1863
September1st to 15thNight
17%5%35%42335%6%41%
2028
16th to endNight
14%413423337%50%
2145
October1st to 15thNight
19%6%24323447%40%
2307
16th to endNight
23%8%25%423345%35%
2590
November1st to 15thNight
23%6%25%5%24335%36%
2772
16th to endNight
22%8%3443445%6%33%
2940
December1st to 15thNight
23%8%35%5%2344432%
3038
16th to endNight
23%10%35%5%23445%30%
3360

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
53%6%14%16%8%1
1520
16th to endDay
51%5%9%20%12%
1873
February1st to 15thDay
54%5%12%17%8%1
1848
16th to endDay
55%5%10%18%8%1
1748
March1st to 15thDay
59%310%15%9%1
2232
16th to endDay
51%49%18%12%2
2464
April1st to 15thDay
55%49%16%12%2
2546
16th to endDay
53%49%16%12%3
2696
May1st to 15thDay
54%48%19%10%2
2739
16th to endDay
53%6%11%20%7%
3151
June1st to 15thDay
57%5%10%15%10%
3150
16th to endDay
54%6%11%16%9%
3150
July1st to 15thDay
40%9%15%21%12%
2991
16th to endDay
49%7%15%19%7%
2696
August1st to 15thDay
50%7%14%21%5%
2475
16th to endDay
40%7%15%25%11%
2691
September1st to 15thDay
40%6%11%25%14%1
2261
16th to endDay
37%410%28%17%1
2145
October1st to 15thDay
44%413%25%10%
1982
16th to endDay
52%412%20%9%
1986
November1st to 15thDay
50%5%12%16%13%
1746
16th to endDay
53%5%14%17%8%
1680
December1st to 15thDay
54%5%12%20%7%
1579
16th to endDay
57%49%17%10%1
1568
January1st to 15thNight
51%7%11%18%10%
3076
16th to endNight
51%5%11%21%9%
3052
February1st to 15thNight
50%5%13%19%10%
2676
16th to endNight
55%5%9%16%11%2
2295
March1st to 15thNight
54%5%8%19%10%1
2388
16th to endNight
50%49%18%15%1
2464
April1st to 15thNight
55%39%14%13%3
2061
16th to endNight
53%5%8%16%13%2
1869
May1st to 15thNight
51%5%10%20%9%1
1870
16th to endNight
57%5%10%15%9%
1682
June1st to 15thNight
54%6%10%18%8%1
1470
16th to endNight
49%7%13%19%9%
1470
July1st to 15thNight
38%9%17%23%10%
1400
16th to endNight
47%8%14%19%9%
1557
August1st to 15thNight
46%7%16%22%7%
1713
16th to endNight
35%7%16%29%11%
1863
September1st to 15thNight
42%6%11%25%13%1
2028
16th to endNight
34%413%30%16%1
2145
October1st to 15thNight
43%5%11%26%12%
2307
16th to endNight
51%49%22%11%
2590
November1st to 15thNight
50%5%13%19%10%1
2772
16th to endNight
50%7%13%18%9%
2940
December1st to 15thNight
55%5%10%21%7%
3038
16th to endNight
55%5%11%17%9%
3360

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
30%24%31%11%1
120
16th to endDay
29%20%33%13%3
209
February1st to 15thDay
26%17%34%17%3
326
16th to endDay
24%25%28%17%3
317
March1st to 15thDay
34%17%31%12%4
390
16th to endDay
25%19%31%14%5%2
416
April1st to 15thDay
36%23%24%11%3
390
16th to endDay
36%17%27%12%41
379
May1st to 15thDay
34%20%26%13%31
425
16th to endDay
32%16%29%15%6%
679
June1st to 15thDay
33%14%26%19%5%
645
16th to endDay
28%11%34%18%6%
645
July1st to 15thDay
19%9%34%22%11%1
625
16th to endDay
20%6%33%27%10%2
443
August1st to 15thDay
22%7%32%23%11%2
358
16th to endDay
17%11%25%28%12%4
396
September1st to 15thDay
17%10%32%25%9%4
375
16th to endDay
21%12%29%20%10%4
374
October1st to 15thDay
27%14%25%18%9%4
324
16th to endDay
31%20%29%12%6%
336
November1st to 15thDay
33%15%24%16%7%1
325
16th to endDay
30%20%26%17%4
330
December1st to 15thDay
33%15%26%20%4
229
16th to endDay
34%28%24%12%
128
January1st to 15thNight
26%18%32%19%3
883
16th to endNight
23%21%33%18%3
896
February1st to 15thNight
22%20%33%19%3
824
16th to endNight
27%20%30%17%3
735
March1st to 15thNight
26%17%34%19%2
840
16th to endNight
23%15%35%19%6%
896
April1st to 15thNight
30%17%31%16%4
713
16th to endNight
31%14%29%17%5%
623
May1st to 15thNight
28%13%31%22%4
630
16th to endNight
28%13%33%20%4
587
June1st to 15thNight
26%9%32%26%5%
420
16th to endNight
27%7%31%27%5%
420
July1st to 15thNight
14%5%37%33%9%
400
16th to endNight
20%5%31%31%10%
472
August1st to 15thNight
21%425%36%12%
574
16th to endNight
15%7%31%32%12%
621
September1st to 15thNight
21%9%31%25%10%
682
16th to endNight
18%10%29%29%10%1
777
October1st to 15thNight
22%11%32%24%8%
780
16th to endNight
27%16%31%18%5%
832
November1st to 15thNight
28%15%28%19%7%1
850
16th to endNight
27%17%26%20%7%
900
December1st to 15thNight
31%16%30%18%4
900
16th to endNight
33%19%28%16%2
960
Page generated at 2019-07-17 09:53:07. Version ac04

Copyright 2019 A. Danko


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