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 2017-03-21.

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
41%
15354
20%
45260
13%
15309
47%
15309
26%
29140

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
26%
899
18%
2506
8%
895
34%
895
22%
1706
January16th to endNight
23%
960
17%
2505
5%
960
30%
960
21%
1797
February1st to 15thNight
26%
851
12%
2260
3%
848
32%
848
19%
1663
February16th to endNight
27%
631
20%
1893
8%
631
37%
631
25%
1222
March1st to 15thNight
28%
657
17%
2097
9%
657
37%
657
20%
1421
March16th to endNight
31%
546
13%
1931
10%
546
38%
546
16%
1335
April1st to 15thNight
33%
494
21%
1647
14%
494
45%
494
25%
1011
April16th to endNight
38%
495
20%
1650
16%
495
46%
495
25%
1049
May1st to 15thNight
39%
494
19%
1476
13%
494
46%
494
23%
1005
May16th to endNight
50%
515
20%
1369
13%
513
55%
513
31%
904
June1st to 15thNight
60%
495
20%
1320
13%
495
63%
495
39%
793
June16th to endNight
58%
495
18%
1320
11%
495
61%
495
37%
818
July1st to 15thNight
67%
465
20%
1240
15%
465
68%
465
38%
757
July16th to endNight
74%
522
23%
1349
19%
489
76%
489
43%
766
August1st to 15thNight
76%
494
23%
1516
26%
491
77%
491
38%
843
August16th to endNight
70%
525
21%
1750
24%
525
73%
525
34%
980
September1st to 15thNight
64%
495
29%
1650
32%
495
68%
495
34%
920
September16th to endNight
61%
605
31%
1768
23%
605
67%
605
39%
990
October1st to 15thNight
50%
660
28%
1980
19%
660
58%
660
35%
1151
October16th to endNight
36%
704
24%
2137
15%
704
45%
704
29%
1290
November1st to 15thNight
38%
700
26%
2276
17%
700
50%
700
30%
1319
November16th to endNight
30%
792
21%
2412
12%
792
40%
792
26%
1525
December1st to 15thNight
25%
900
14%
2520
6%
900
32%
900
19%
1835
December16th to endNight
22%
960
13%
2688
4%
960
29%
960
15%
2040

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
13%6%35%5%3445%7%39%
45605
Night
13%6%35%424446%43%
45440
TransparencyDay
42%6%13%22%13%1
45288
Night
40%5%11%23%15%2
45262
SeeingDay
14%5%23%28%20%7%
5112
Night
16%7%28%31%14%1
15356

By Month

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
13%10%49%6%35%346%32%
1432
16th to endDay
13%12%5%6%6%33345%33%
1716
February1st to 15thDay
14%9%5%7%435%45%7%32%
1600
16th to endDay
11%9%47%7%3435%7%35%
1580
March1st to 15thDay
15%10%46%5%2435%6%34%
1872
16th to endDay
15%8%36%5%35%45%7%33%
2060
April1st to 15thDay
16%8%24424436%40%
1971
16th to endDay
18%6%25%5%345%5%6%36%
1980
May1st to 15thDay
21%6%35%5%345%5%7%31%
2140
16th to endDay
12%6%35%5%35%5%5%8%38%
2393
June1st to 15thDay
10%4245%35%6%7%9%40%
2310
16th to endDay
9%425%436%5%6%10%41%
2310
July1st to 15thDay
7%3245%35%5%7%10%43%
2310
16th to endDay
5%3135%346%7%9%47%
2411
August1st to 15thDay
8%416%6%345%6%9%43%
2103
16th to endDay
9%4244335%6%8%45%
2100
September1st to 15thDay
14%5%2333345%6%46%
1980
16th to endDay
9%42442445%8%48%
1849
October1st to 15thDay
15%5%14423346%49%
1650
16th to endDay
16%5%24323226%48%
1735
November1st to 15thDay
16%5%13423345%47%
1582
16th to endDay
15%9%45%422445%40%
1545
December1st to 15thDay
18%9%46%6%35%346%32%
1440
16th to endDay
18%10%5%6%5%2445%7%30%
1536
January1st to 15thNight
13%8%45%5%34445%40%
2506
16th to endNight
13%11%5%7%5%33445%36%
2505
February1st to 15thNight
13%9%6%7%43445%5%34%
2251
16th to endNight
15%7%35%433345%43%
1893
March1st to 15thNight
17%8%35%5%2435%438%
2097
16th to endNight
18%9%35%425%5%47%33%
1931
April1st to 15thNight
13%6%24434446%45%
1647
16th to endNight
17%6%24423446%42%
1650
May1st to 15thNight
17%5%35%5%3335%8%38%
1476
16th to endNight
11%425%43435%7%45%
1368
June1st to 15thNight
8%414315%5%5%8%50%
1320
16th to endNight
8%324435%46%10%46%
1320
July1st to 15thNight
7%4245%25%46%9%49%
1320
16th to endNight
4412425%46%9%53%
1449
August1st to 15thNight
5%3123345%6%10%52%
1526
16th to endNight
6%3244345%6%7%51%
1750
September1st to 15thNight
12%32331435%7%52%
1650
16th to endNight
8%32341435%7%55%
1768
October1st to 15thNight
11%414423446%52%
1980
16th to endNight
17%5%13323435%49%
2137
November1st to 15thNight
11%6%24422336%52%
2276
16th to endNight
15%7%34323346%44%
2412
December1st to 15thNight
20%9%36%424346%32%
2520
16th to endNight
20%11%46%6%24435%30%
2688

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%49%19%12%
1433
16th to endDay
52%413%20%7%
1716
February1st to 15thDay
51%5%14%20%7%
1602
16th to endDay
48%5%13%22%9%
1580
March1st to 15thDay
50%5%13%21%7%1
1872
16th to endDay
49%6%15%18%8%
2062
April1st to 15thDay
45%49%24%15%1
1971
16th to endDay
46%6%12%21%12%1
1980
May1st to 15thDay
50%6%12%21%7%
2140
16th to endDay
43%7%13%17%14%2
2397
June1st to 15thDay
36%8%16%22%14%1
2310
16th to endDay
35%9%14%21%15%3
2310
July1st to 15thDay
35%7%14%26%12%3
2161
16th to endDay
31%7%17%28%13%
2248
August1st to 15thDay
36%7%13%26%15%1
2089
16th to endDay
33%9%12%22%17%5%
2100
September1st to 15thDay
36%6%9%23%19%5%
1980
16th to endDay
32%6%10%29%19%2
1849
October1st to 15thDay
36%410%25%20%3
1650
16th to endDay
37%411%26%17%3
1735
November1st to 15thDay
37%411%20%20%4
1582
16th to endDay
45%413%24%11%
1545
December1st to 15thDay
52%5%14%18%8%
1440
16th to endDay
53%5%12%18%8%1
1536
January1st to 15thNight
45%5%11%23%13%
2506
16th to endNight
49%413%21%10%
2505
February1st to 15thNight
50%6%11%19%10%1
2260
16th to endNight
42%314%25%11%1
1893
March1st to 15thNight
47%5%10%22%11%2
2097
16th to endNight
50%6%12%19%9%
1931
April1st to 15thNight
38%5%9%26%16%3
1647
16th to endNight
41%5%10%24%15%3
1650
May1st to 15thNight
44%7%11%21%14%
1477
16th to endNight
36%8%13%19%17%4
1370
June1st to 15thNight
29%6%15%29%16%2
1320
16th to endNight
30%8%15%22%19%4
1320
July1st to 15thNight
31%6%12%29%17%3
1240
16th to endNight
25%6%16%32%16%2
1349
August1st to 15thNight
26%7%14%27%20%3
1516
16th to endNight
29%6%12%22%22%6%
1750
September1st to 15thNight
31%410%22%23%7%
1650
16th to endNight
28%49%26%26%3
1768
October1st to 15thNight
32%49%24%22%5%
1980
16th to endNight
36%48%26%20%3
2137
November1st to 15thNight
34%410%23%19%7%
2276
16th to endNight
40%410%27%15%
2412
December1st to 15thNight
53%412%19%9%
2520
16th to endNight
57%5%10%16%9%1
2688

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%11%37%20%22
90
16th to endDay
13%16%43%22%3
96
February1st to 15thDay
22%11%40%20%6%
90
16th to endDay
13%14%34%29%7%
81
March1st to 15thDay
28%10%40%16%4
90
16th to endDay
17%13%33%23%8%2
134
April1st to 15thDay
20%11%28%25%12%1
210
16th to endDay
16%8%27%29%15%2
210
May1st to 15thDay
20%8%32%25%9%4
291
16th to endDay
17%5%29%26%15%6%
437
June1st to 15thDay
11%225%31%22%7%
420
16th to endDay
11%221%35%20%7%
420
July1st to 15thDay
9%218%34%25%10%
400
16th to endDay
8%112%32%35%10%
445
August1st to 15thDay
9%10%33%32%12%
376
16th to endDay
9%12%23%38%16%
268
September1st to 15thDay
16%29%30%32%9%
255
16th to endDay
9%6%16%30%25%11%
247
October1st to 15thDay
10%8%21%28%23%7%
90
16th to endDay
22%430%32%9%1
96
November1st to 15thDay
46%26%26%24%11%
90
16th to endDay
32%14%31%15%5%1
90
December1st to 15thDay
18%11%38%21%6%3
90
16th to endDay
27%14%42%11%4
96
January1st to 15thNight
17%12%39%24%5%
900
16th to endNight
18%13%38%25%4
960
February1st to 15thNight
19%12%35%27%4
851
16th to endNight
20%11%37%27%3
631
March1st to 15thNight
22%11%34%26%5%
657
16th to endNight
22%10%30%26%9%
546
April1st to 15thNight
16%11%36%27%7%
494
16th to endNight
18%6%32%32%9%
495
May1st to 15thNight
18%329%37%9%1
495
16th to endNight
11%327%36%18%2
515
June1st to 15thNight
8%320%47%18%1
495
16th to endNight
10%122%41%23%2
495
July1st to 15thNight
8%112%46%28%3
465
16th to endNight
5%11%37%39%4
522
August1st to 15thNight
8%7%41%38%3
494
16th to endNight
7%12%36%37%4
525
September1st to 15thNight
13%213%33%31%5%
495
16th to endNight
10%417%33%28%5%
605
October1st to 15thNight
13%426%31%20%3
660
16th to endNight
20%8%32%29%9%
704
November1st to 15thNight
15%9%34%28%12%1
700
16th to endNight
18%11%36%26%6%
792
December1st to 15thNight
25%10%33%24%5%
900
16th to endNight
26%10%34%24%3
960
Page generated at 2017-03-22 01:42:22. Version ac04

Copyright 2017 A. Danko


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