Winchester
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Winchester clear sky chart from 2005-11-05 to 2018-08-29.

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
32%
15822
14%
50588
9%
15792
38%
15792
17%
35922

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
18%
780
7%
2716
3%
776
22%
776
8%
2191
January16th to endNight
22%
832
10%
2870
7%
832
28%
832
11%
2164
February1st to 15thNight
18%
762
10%
2482
5%
761
25%
761
10%
1943
February16th to endNight
24%
683
14%
2091
7%
683
33%
683
14%
1560
March1st to 15thNight
21%
780
13%
2291
7%
780
28%
780
15%
1746
March16th to endNight
34%
832
21%
2191
10%
832
41%
832
23%
1529
April1st to 15thNight
26%
778
16%
1946
6%
778
31%
778
21%
1454
April16th to endNight
31%
707
17%
1863
7%
707
37%
707
24%
1308
May1st to 15thNight
34%
390
18%
1560
16%
390
44%
390
17%
998
May16th to endNight
36%
407
13%
1625
11%
406
47%
406
20%
1008
June1st to 15thNight
39%
390
10%
1560
11%
390
46%
390
14%
1063
June16th to endNight
42%
390
10%
1560
14%
390
47%
390
20%
968
July1st to 15thNight
55%
370
16%
1480
23%
370
62%
370
29%
793
July16th to endNight
54%
408
14%
1546
19%
386
57%
386
25%
882
August1st to 15thNight
50%
457
14%
1598
13%
455
54%
455
23%
1010
August16th to endNight
54%
779
21%
2009
11%
779
57%
779
38%
1241
September1st to 15thNight
50%
720
16%
1800
8%
720
52%
720
30%
1230
September16th to endNight
51%
717
25%
1951
17%
717
55%
717
34%
1231
October1st to 15thNight
36%
720
18%
2160
13%
720
45%
720
23%
1470
October16th to endNight
25%
768
12%
2410
7%
768
34%
768
13%
1792
November1st to 15thNight
29%
760
16%
2507
12%
760
37%
760
17%
1755
November16th to endNight
22%
780
11%
2730
7%
780
29%
780
11%
2082
December1st to 15thNight
20%
780
7%
2730
4%
780
24%
780
9%
2165
December16th to endNight
15%
832
9%
2912
3%
832
22%
832
8%
2339

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
18%8%36%5%3445%6%32%
51673
Night
18%10%46%5%34446%32%
50757
Cloud CoverDay
18%8%36%5%34446%32%
51682
Night
18%10%46%5%34446%32%
50763
TransparencyDay
51%5%11%20%10%1
51360
Night
53%411%19%10%1
50588
SeeingDay
22%10%28%23%11%4
6672
Night
23%8%28%27%10%
15824

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
23%15%5%8%6%3443419%
1552
16th to endDay
14%15%5%9%7%35%446%22%
1703
February1st to 15thDay
15%14%5%10%7%45%445%21%
1710
16th to endDay
19%14%48%6%3434424%
1667
March1st to 15thDay
19%13%5%9%7%35%43325%
1986
16th to endDay
17%9%35%424336%39%
2385
April1st to 15thDay
23%11%36%5%23345%30%
2332
16th to endDay
23%7%25%423345%35%
2384
May1st to 15thDay
19%7%35%5%2445%6%35%
2721
16th to endDay
17%6%35%5%25%45%7%36%
2842
June1st to 15thDay
23%5%25%5%35%45%6%31%
2730
16th to endDay
19%5%25%5%35%45%7%33%
2730
July1st to 15thDay
12%4245%345%5%8%42%
2730
16th to endDay
12%5%246%35%6%6%9%36%
2878
August1st to 15thDay
13%6%35%7%45%5%6%6%35%
2604
16th to endDay
12%4145%35%5%5%6%43%
2476
September1st to 15thDay
18%415%42445%6%41%
2160
16th to endDay
16%414323347%46%
2007
October1st to 15thDay
20%6%36%435%5%45%34%
1800
16th to endDay
25%10%36%7%2435%6%24%
1812
November1st to 15thDay
15%9%46%6%345%5%7%31%
1680
16th to endDay
22%12%48%6%23345%24%
1560
December1st to 15thDay
23%15%5%9%6%45%445%17%
1560
16th to endDay
25%16%47%43443421%
1664
January1st to 15thNight
19%15%6%10%6%3434419%
2716
16th to endNight
15%16%6%8%6%24345%25%
2870
February1st to 15thNight
15%14%6%11%7%35%45%421%
2480
16th to endNight
16%13%48%6%34345%28%
2091
March1st to 15thNight
21%13%5%8%5%3332429%
2278
16th to endNight
17%8%35%5%2433341%
2191
April1st to 15thNight
23%8%36%434335%33%
1946
16th to endNight
20%7%24423446%38%
1863
May1st to 15thNight
19%7%245%24346%36%
1560
16th to endNight
15%6%345%345%47%39%
1623
June1st to 15thNight
21%6%36%426%45%8%29%
1560
16th to endNight
17%5%25%42445%9%37%
1560
July1st to 15thNight
9%414325%5%5%10%46%
1560
16th to endNight
10%4145%346%6%8%44%
1642
August1st to 15thNight
11%7%26%5%345%5%9%38%
1608
16th to endNight
12%32342345%7%49%
2009
September1st to 15thNight
15%5%25%5%24445%43%
1800
16th to endNight
15%423423445%49%
1951
October1st to 15thNight
19%6%35%424446%37%
2160
16th to endNight
26%9%36%5%24446%26%
2410
November1st to 15thNight
22%9%35%5%33435%34%
2507
16th to endNight
21%11%5%8%5%24336%25%
2730
December1st to 15thNight
22%16%5%8%5%35%34420%
2730
16th to endNight
24%16%5%8%6%3433419%
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
23%15%5%9%6%3443418%
1552
16th to endDay
14%15%5%9%8%35%446%22%
1703
February1st to 15thDay
16%14%5%11%6%45%445%20%
1710
16th to endDay
20%14%5%9%6%3434424%
1667
March1st to 15thDay
19%14%5%9%7%3443325%
1996
16th to endDay
17%8%35%423446%39%
2384
April1st to 15thDay
23%11%46%5%23235%30%
2332
16th to endDay
23%8%26%423445%35%
2384
May1st to 15thDay
18%7%36%433446%35%
2721
16th to endDay
18%6%35%5%3445%8%36%
2842
June1st to 15thDay
23%6%25%5%345%5%6%31%
2730
16th to endDay
19%6%246%35%5%5%7%33%
2730
July1st to 15thDay
12%425%5%35%45%7%42%
2730
16th to endDay
12%5%25%5%36%6%6%9%35%
2878
August1st to 15thDay
12%6%26%7%45%6%6%7%33%
2604
16th to endDay
11%425%435%5%5%7%43%
2476
September1st to 15thDay
17%5%25%325%45%7%40%
2160
16th to endDay
16%41432335%7%46%
2007
October1st to 15thDay
20%7%36%5%3445%6%33%
1800
16th to endDay
26%9%47%6%34246%24%
1812
November1st to 15thDay
16%8%46%6%35%45%7%31%
1680
16th to endDay
23%12%48%6%33345%24%
1560
December1st to 15thDay
23%16%49%7%35%43417%
1560
16th to endDay
25%14%5%7%5%3443420%
1664
January1st to 15thNight
20%16%6%10%6%3434419%
2716
16th to endNight
15%16%6%8%6%34445%24%
2870
February1st to 15thNight
16%14%5%12%8%35%445%20%
2473
16th to endNight
17%13%5%9%6%24345%27%
2091
March1st to 15thNight
22%12%6%7%5%2323428%
2291
16th to endNight
18%8%35%5%2334340%
2191
April1st to 15thNight
23%8%36%5%24336%32%
1946
16th to endNight
21%7%25%5%23246%37%
1863
May1st to 15thNight
19%7%25%5%2435%7%36%
1560
16th to endNight
16%6%244345%47%39%
1623
June1st to 15thNight
21%6%36%5%35%45%8%28%
1560
16th to endNight
17%6%2443435%10%36%
1560
July1st to 15thNight
10%3233345%6%10%45%
1560
16th to endNight
9%5%24335%6%7%9%42%
1642
August1st to 15thNight
12%7%25%5%35%5%6%8%38%
1608
16th to endNight
11%424424447%48%
2009
September1st to 15thNight
16%5%25%5%24445%43%
1800
16th to endNight
15%42342335%5%48%
1951
October1st to 15thNight
19%7%35%434447%36%
2160
16th to endNight
25%10%36%5%34346%26%
2410
November1st to 15thNight
22%9%25%5%3434434%
2507
16th to endNight
22%12%48%5%34335%25%
2730
December1st to 15thNight
22%15%5%8%5%3444420%
2730
16th to endNight
24%15%5%7%6%3433419%
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
68%38%10%6%
1553
16th to endDay
62%5%12%13%6%
1703
February1st to 15thDay
64%49%18%2
1712
16th to endDay
62%310%13%8%
1667
March1st to 15thDay
64%311%12%7%
1996
16th to endDay
46%39%19%15%5%
2385
April1st to 15thDay
56%36%18%12%2
2332
16th to endDay
50%37%19%15%3
2384
May1st to 15thDay
48%48%22%14%1
2721
16th to endDay
45%6%12%21%12%1
2846
June1st to 15thDay
52%5%11%19%10%
2730
16th to endDay
47%5%12%21%11%1
2730
July1st to 15thDay
36%5%13%29%14%
2581
16th to endDay
42%6%15%24%10%
2711
August1st to 15thDay
46%7%16%21%8%
2590
16th to endDay
37%5%15%29%11%
2476
September1st to 15thDay
41%5%11%28%12%
2160
16th to endDay
37%411%34%10%
2007
October1st to 15thDay
50%5%11%22%9%
1800
16th to endDay
61%412%14%6%
1812
November1st to 15thDay
50%5%14%19%8%
1680
16th to endDay
60%412%15%6%
1560
December1st to 15thDay
69%5%10%11%2
1560
16th to endDay
67%5%10%11%5%
1664
January1st to 15thNight
68%410%11%4
2716
16th to endNight
61%310%16%6%
2870
February1st to 15thNight
64%410%16%4
2482
16th to endNight
58%39%17%10%
2091
March1st to 15thNight
60%39%18%7%
2291
16th to endNight
47%38%19%15%3
2191
April1st to 15thNight
53%37%19%14%
1946
16th to endNight
47%38%18%17%3
1863
May1st to 15thNight
47%47%20%16%3
1560
16th to endNight
43%5%13%20%14%2
1625
June1st to 15thNight
51%6%12%17%10%1
1560
16th to endNight
43%5%13%20%15%
1560
July1st to 15thNight
30%7%14%30%16%1
1480
16th to endNight
35%6%15%25%15%
1546
August1st to 15thNight
41%6%18%21%11%
1598
16th to endNight
33%416%32%13%
2009
September1st to 15thNight
42%5%11%27%12%
1800
16th to endNight
36%411%34%13%
1951
October1st to 15thNight
46%410%26%10%
2160
16th to endNight
58%413%18%5%
2410
November1st to 15thNight
52%413%17%10%1
2507
16th to endNight
61%411%16%4
2730
December1st to 15thNight
66%412%13%3
2730
16th to endNight
68%49%12%5%
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
27%14%24%23%10%
90
16th to endDay
31%13%33%17%4
105
February1st to 15thDay
30%16%40%12%
135
16th to endDay
33%10%33%18%3
248
March1st to 15thDay
27%9%36%18%7%
330
16th to endDay
21%11%32%22%8%3
352
April1st to 15thDay
29%14%28%18%6%1
330
16th to endDay
27%14%26%15%12%4
319
May1st to 15thDay
23%13%28%21%8%4
348
16th to endDay
20%12%35%16%13%1
395
June1st to 15thDay
26%7%26%28%8%2
375
16th to endDay
21%8%30%26%10%3
375
July1st to 15thDay
13%6%22%36%16%4
365
16th to endDay
14%6%24%32%17%4
390
August1st to 15thDay
16%425%31%17%5%
358
16th to endDay
12%422%30%17%11%
384
September1st to 15thDay
17%5%21%22%17%15%
315
16th to endDay
16%5%26%18%23%10%
314
October1st to 15thDay
22%9%27%22%13%4
315
16th to endDay
31%14%24%23%5%
309
November1st to 15thDay
19%15%28%22%12%1
244
16th to endDay
31%17%27%18%4
90
December1st to 15thDay
22%17%34%17%7%
90
16th to endDay
39%21%28%8%2
96
January1st to 15thNight
27%14%31%22%5%
780
16th to endNight
24%10%32%26%6%
832
February1st to 15thNight
21%12%37%23%4
764
16th to endNight
24%10%34%25%5%
683
March1st to 15thNight
28%11%32%23%4
780
16th to endNight
20%10%28%30%9%
832
April1st to 15thNight
27%10%29%27%5%
778
16th to endNight
25%10%28%24%9%
707
May1st to 15thNight
24%430%28%10%1
390
16th to endNight
17%435%28%12%
407
June1st to 15thNight
23%6%23%36%10%
390
16th to endNight
17%230%34%13%1
390
July1st to 15thNight
11%424%40%18%
370
16th to endNight
12%122%46%16%1
408
August1st to 15thNight
16%220%36%21%1
457
16th to endNight
13%222%36%22%2
779
September1st to 15thNight
19%420%34%19%2
720
16th to endNight
17%423%26%24%2
717
October1st to 15thNight
21%7%28%26%15%
720
16th to endNight
30%10%25%24%8%
768
November1st to 15thNight
27%8%27%24%10%
760
16th to endNight
27%15%26%20%9%
780
December1st to 15thNight
31%11%29%23%4
780
16th to endNight
32%10%31%20%31
832
Page generated at 2018-08-30 05:34:24. Version ac04

Copyright 2018 A. Danko


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