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 2017-12-01.

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%
16192
20%
47795
13%
16147
48%
16147
27%
30588

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
30%
576
13%
2034
9%
576
37%
576
16%
1413
April1st to 15thNight
33%
539
20%
1797
14%
539
44%
539
25%
1114
April16th to endNight
38%
540
20%
1800
17%
540
46%
540
25%
1144
May1st to 15thNight
41%
539
18%
1610
12%
539
48%
539
24%
1076
May16th to endNight
50%
563
21%
1497
13%
561
55%
561
32%
979
June1st to 15thNight
61%
540
19%
1440
13%
540
64%
540
41%
848
June16th to endNight
57%
540
20%
1440
12%
540
61%
540
38%
880
July1st to 15thNight
67%
510
19%
1360
15%
510
68%
510
39%
822
July16th to endNight
75%
564
24%
1466
21%
531
77%
531
43%
826
August1st to 15thNight
76%
539
22%
1655
25%
536
77%
536
39%
917
August16th to endNight
71%
573
23%
1910
27%
573
74%
573
35%
1052
September1st to 15thNight
65%
540
28%
1800
30%
540
68%
540
35%
990
September16th to endNight
62%
660
33%
1929
25%
660
68%
660
39%
1073
October1st to 15thNight
49%
720
27%
2160
18%
720
56%
720
34%
1277
October16th to endNight
36%
768
26%
2331
17%
768
46%
768
29%
1398
November1st to 15thNight
37%
760
25%
2471
16%
760
49%
760
28%
1461
November16th to endNight
31%
858
23%
2613
13%
858
42%
858
27%
1629
December1st to 15thNight
26%
905
14%
2533
6%
905
33%
905
19%
1840
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%40%
48637
Night
13%6%34424446%44%
47975
TransparencyDay
41%6%12%22%13%2
48320
Night
40%5%11%23%16%2
47797
SeeingDay
14%5%24%28%20%7%
6150
Night
16%7%28%31%14%1
16194

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
16%9%36%6%35%45%7%31%
2188
April1st to 15thDay
16%8%25%434346%39%
2151
16th to endDay
19%6%26%5%345%5%6%35%
2160
May1st to 15thDay
20%6%35%5%245%5%7%33%
2336
16th to endDay
12%6%35%5%35%5%5%8%38%
2617
June1st to 15thDay
9%4245%35%6%7%9%43%
2520
16th to endDay
9%425%5%36%5%6%10%41%
2520
July1st to 15thDay
7%3245%35%5%7%10%43%
2520
16th to endDay
5%3135%346%7%9%48%
2602
August1st to 15thDay
8%415%6%346%6%8%43%
2294
16th to endDay
9%4244336%6%8%45%
2292
September1st to 15thDay
13%42333345%6%48%
2160
16th to endDay
8%4245%2445%8%48%
2017
October1st to 15thDay
16%6%24423346%46%
1800
16th to endDay
16%6%24323336%48%
1892
November1st to 15thDay
16%5%1442345%5%46%
1717
16th to endDay
15%8%45%422345%42%
1674
December1st to 15thDay
18%9%46%6%35%346%32%
1441
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%4245%47%32%
2034
April1st to 15thNight
13%7%24434447%43%
1797
16th to endNight
17%6%3432345%7%41%
1800
May1st to 15thNight
17%5%25%5%23348%40%
1610
16th to endNight
10%425%43436%7%45%
1496
June1st to 15thNight
7%4143145%5%8%52%
1440
16th to endNight
8%323435%46%10%47%
1440
July1st to 15thNight
7%4245%2446%9%49%
1440
16th to endNight
4312425%46%9%54%
1566
August1st to 15thNight
6%31233446%10%53%
1665
16th to endNight
6%32443446%7%52%
1910
September1st to 15thNight
11%32331335%6%53%
1800
16th to endNight
7%32341435%7%55%
1929
October1st to 15thNight
13%414423446%51%
2160
16th to endNight
16%5%13423435%50%
2331
November1st to 15thNight
12%6%24422336%50%
2471
16th to endNight
14%6%24323446%45%
2613
December1st to 15thNight
20%9%36%424346%33%
2533
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
51%6%15%17%8%
2190
April1st to 15thDay
46%49%23%14%1
2151
16th to endDay
47%6%12%20%12%1
2160
May1st to 15thDay
48%6%12%23%8%
2336
16th to endDay
42%8%13%18%15%2
2621
June1st to 15thDay
34%7%15%22%17%2
2520
16th to endDay
35%9%14%22%16%3
2520
July1st to 15thDay
34%7%13%27%13%4
2371
16th to endDay
30%7%17%28%15%
2439
August1st to 15thDay
35%7%13%26%15%1
2280
16th to endDay
32%9%13%22%17%4
2292
September1st to 15thDay
34%6%9%24%20%5%
2160
16th to endDay
31%6%10%29%19%1
2017
October1st to 15thDay
39%410%23%18%3
1800
16th to endDay
37%410%26%18%2
1892
November1st to 15thDay
38%411%21%19%3
1717
16th to endDay
44%312%26%12%
1674
December1st to 15thDay
52%5%14%18%8%
1441
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%7%12%19%9%
2034
April1st to 15thNight
39%5%10%25%16%3
1797
16th to endNight
42%5%10%23%15%3
1800
May1st to 15thNight
43%6%11%22%15%
1611
16th to endNight
35%8%13%19%17%4
1498
June1st to 15thNight
27%6%14%28%20%2
1440
16th to endNight
29%7%14%22%19%5%
1440
July1st to 15thNight
30%5%11%30%16%4
1360
16th to endNight
24%6%15%31%18%2
1466
August1st to 15thNight
26%7%14%28%20%3
1655
16th to endNight
28%6%12%23%22%6%
1910
September1st to 15thNight
30%410%22%24%7%
1800
16th to endNight
27%49%27%26%3
1929
October1st to 15thNight
33%49%24%21%5%
2160
16th to endNight
36%48%26%20%3
2331
November1st to 15thNight
36%410%23%18%6%
2471
16th to endNight
39%410%28%16%
2613
December1st to 15thNight
53%412%19%9%
2533
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
22%13%32%21%7%1
174
April1st to 15thDay
20%10%30%25%11%1
270
16th to endDay
18%8%28%28%13%2
270
May1st to 15thDay
20%8%31%24%11%3
357
16th to endDay
16%5%32%26%13%5%
517
June1st to 15thDay
9%224%30%24%8%
495
16th to endDay
10%426%34%18%6%
495
July1st to 15thDay
9%117%36%24%10%
475
16th to endDay
8%112%31%34%10%
515
August1st to 15thDay
9%11%34%32%12%
447
16th to endDay
9%13%24%38%13%
332
September1st to 15thDay
13%310%28%30%13%
315
16th to endDay
9%415%30%29%10%
306
October1st to 15thDay
19%10%17%31%16%5%
135
16th to endDay
20%8%30%27%10%2
144
November1st to 15thDay
8%5%35%24%18%8%
135
16th to endDay
25%12%33%20%8%
135
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%9%31%26%9%
576
April1st to 15thNight
16%11%36%27%7%
539
16th to endNight
19%6%32%32%9%
540
May1st to 15thNight
18%328%37%10%1
540
16th to endNight
11%328%37%17%2
563
June1st to 15thNight
7%320%47%19%1
540
16th to endNight
9%124%40%21%2
540
July1st to 15thNight
9%112%46%28%2
510
16th to endNight
5%11%39%38%4
564
August1st to 15thNight
8%7%41%38%3
539
16th to endNight
7%12%36%38%4
573
September1st to 15thNight
13%113%33%31%5%
540
16th to endNight
9%417%34%28%5%
660
October1st to 15thNight
14%426%31%20%2
720
16th to endNight
19%8%32%28%9%
768
November1st to 15thNight
16%9%34%27%11%1
760
16th to endNight
17%10%37%27%6%
858
December1st to 15thNight
24%10%33%24%6%
905
16th to endNight
26%10%34%24%3
960
Page generated at 2017-12-02 08:14:17. Version ac04

Copyright 2017 A. Danko


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