Salisbury
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Salisbury clear sky chart from 2005-11-05 to 2017-09-21.

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
39%
15295
20%
46919
12%
15260
49%
15260
25%
29718

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
27%
718
22%
2472
10%
716
43%
716
20%
1532
January16th to endNight
23%
768
22%
2496
8%
768
40%
768
21%
1569
February1st to 15thNight
22%
701
20%
2245
9%
701
38%
701
22%
1402
February16th to endNight
21%
631
26%
1893
8%
631
43%
631
24%
1180
March1st to 15thNight
24%
720
20%
2073
8%
720
38%
720
24%
1330
March16th to endNight
27%
768
21%
2041
10%
768
36%
768
25%
1377
April1st to 15thNight
26%
718
18%
1796
5%
718
35%
718
29%
1204
April16th to endNight
37%
720
18%
1800
7%
720
40%
720
30%
1211
May1st to 15thNight
35%
598
16%
1678
8%
598
41%
598
25%
1147
May16th to endNight
52%
374
16%
1497
15%
374
57%
374
21%
911
June1st to 15thNight
55%
360
16%
1440
16%
360
60%
360
23%
853
June16th to endNight
56%
360
13%
1440
13%
360
60%
360
21%
867
July1st to 15thNight
62%
340
13%
1360
15%
340
63%
340
20%
848
July16th to endNight
64%
480
15%
1514
13%
450
67%
450
28%
909
August1st to 15thNight
66%
602
16%
1672
11%
599
67%
599
30%
1076
August16th to endNight
64%
764
18%
1910
11%
764
65%
764
34%
1249
September1st to 15thNight
59%
720
24%
1800
16%
720
62%
720
35%
1173
September16th to endNight
55%
681
21%
1836
17%
681
58%
681
28%
1218
October1st to 15thNight
49%
660
24%
1980
21%
660
55%
660
27%
1255
October16th to endNight
40%
704
27%
2112
18%
704
54%
704
29%
1282
November1st to 15thNight
39%
700
22%
2277
14%
700
51%
700
26%
1390
November16th to endNight
35%
720
22%
2379
14%
720
47%
720
23%
1460
December1st to 15thNight
26%
720
19%
2520
10%
720
39%
720
18%
1609
December16th to endNight
24%
768
22%
2688
10%
768
41%
768
20%
1666

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%5%2442445%7%43%
47936
Night
14%6%2442445%7%43%
47099
Cloud CoverDay
13%5%2442445%7%43%
47946
Night
14%5%2442445%7%43%
47104
TransparencyDay
38%6%12%22%16%2
47635
Night
39%6%11%22%16%3
46919
SeeingDay
17%9%26%24%16%6%
5828
Night
16%9%28%30%13%1
15301

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
13%7%25%5%24446%43%
1465
16th to endDay
16%5%25%5%24346%42%
1728
February1st to 15thDay
14%7%25%5%2445%5%42%
1615
16th to endDay
14%7%35%324446%42%
1580
March1st to 15thDay
15%6%14414446%46%
1873
16th to endDay
17%6%2442434444%
2181
April1st to 15thDay
13%414433447%49%
2152
16th to endDay
14%6%24324346%47%
2160
May1st to 15thDay
14%6%2432445%8%42%
2282
16th to endDay
12%4234235%5%9%44%
2618
June1st to 15thDay
12%3244245%6%10%41%
2520
16th to endDay
8%4244345%7%11%43%
2520
July1st to 15thDay
9%3245%35%47%9%42%
2520
16th to endDay
6%325%6%37%7%8%11%37%
2547
August1st to 15thDay
9%6%26%5%36%6%6%10%37%
2265
16th to endDay
9%5%25%6%45%5%5%8%41%
2292
September1st to 15thDay
12%5%25%5%2445%6%44%
2160
16th to endDay
17%6%36%5%3445%5%37%
1913
October1st to 15thDay
16%6%15%5%24446%42%
1650
16th to endDay
13%5%14323335%50%
1760
November1st to 15thDay
16%423414447%45%
1581
16th to endDay
14%4145%33347%47%
1578
December1st to 15thDay
13%6%25%5%2445%7%42%
1440
16th to endDay
19%6%25%423346%40%
1536
January1st to 15thNight
15%6%24424446%43%
2472
16th to endNight
16%7%24324345%43%
2496
February1st to 15thNight
15%7%25%423346%44%
2244
16th to endNight
14%6%24423345%47%
1893
March1st to 15thNight
16%6%2442345%6%43%
2061
16th to endNight
17%7%44423336%42%
2041
April1st to 15thNight
12%6%24425%446%44%
1796
16th to endNight
16%5%24423446%44%
1800
May1st to 15thNight
14%7%35%4235%7%9%37%
1678
16th to endNight
11%5%25%426%5%5%7%42%
1495
June1st to 15thNight
11%425%425%5%5%10%43%
1440
16th to endNight
7%435%6%45%6%7%9%38%
1440
July1st to 15thNight
9%5%16%5%26%7%6%9%39%
1440
16th to endNight
5%4345%37%5%7%10%40%
1618
August1st to 15thNight
7%436%5%346%6%9%42%
1683
16th to endNight
8%425%5%25%5%6%9%43%
1910
September1st to 15thNight
12%5%25%42336%7%45%
1800
16th to endNight
16%5%244235%5%8%41%
1836
October1st to 15thNight
16%425%324446%44%
1980
16th to endNight
15%5%23323346%48%
2112
November1st to 15thNight
15%6%24423245%48%
2277
16th to endNight
14%6%2442335%6%45%
2379
December1st to 15thNight
16%6%35%5%2445%6%40%
2520
16th to endNight
17%6%25%323346%43%
2688

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
14%6%35%5%15%346%43%
1465
16th to endDay
17%5%25%5%24345%42%
1728
February1st to 15thDay
15%6%345%3345%6%42%
1615
16th to endDay
14%7%3432346%5%42%
1580
March1st to 15thDay
15%6%24413446%46%
1884
16th to endDay
17%6%24424435%43%
2180
April1st to 15thDay
13%413433447%49%
2152
16th to endDay
15%5%24423346%46%
2160
May1st to 15thDay
14%6%2432446%8%42%
2282
16th to endDay
13%4233235%5%9%45%
2618
June1st to 15thDay
13%3235%25%46%10%42%
2520
16th to endDay
8%424435%5%7%10%43%
2520
July1st to 15thDay
9%415%5%35%46%10%43%
2520
16th to endDay
6%3146%36%7%9%10%38%
2547
August1st to 15thDay
9%6%26%5%36%6%6%10%37%
2265
16th to endDay
9%5%25%6%45%5%6%8%40%
2292
September1st to 15thDay
12%5%245%33447%44%
2160
16th to endDay
18%6%36%5%3345%5%37%
1913
October1st to 15thDay
16%5%25%5%24446%43%
1650
16th to endDay
14%5%24423345%50%
1760
November1st to 15thDay
17%42342435%6%46%
1581
16th to endDay
14%4145%33347%47%
1578
December1st to 15thDay
13%6%25%42445%7%42%
1440
16th to endDay
19%5%245%33436%40%
1536
January1st to 15thNight
15%5%25%434447%42%
2472
16th to endNight
16%7%34424345%43%
2496
February1st to 15thNight
15%7%2441335%6%44%
2237
16th to endNight
14%7%24324346%46%
1893
March1st to 15thNight
16%6%2442335%6%43%
2073
16th to endNight
17%7%35%413336%42%
2041
April1st to 15thNight
13%5%345%145%46%44%
1796
16th to endNight
17%5%23424447%44%
1800
May1st to 15thNight
15%6%35%3235%6%9%37%
1678
16th to endNight
11%434426%5%5%8%43%
1495
June1st to 15thNight
10%4244245%5%10%43%
1440
16th to endNight
7%425%7%46%6%6%10%38%
1440
July1st to 15thNight
9%5%26%426%6%6%10%39%
1440
16th to endNight
5%425%6%36%7%7%10%40%
1618
August1st to 15thNight
7%5%35%5%35%6%6%8%42%
1683
16th to endNight
8%4245%3446%9%44%
1910
September1st to 15thNight
12%6%2442346%7%46%
1800
16th to endNight
15%6%244245%5%6%42%
1836
October1st to 15thNight
16%5%24324446%44%
1980
16th to endNight
16%5%23223436%49%
2112
November1st to 15thNight
16%5%25%323245%48%
2277
16th to endNight
15%5%335%23447%45%
2379
December1st to 15thNight
16%7%35%42445%5%40%
2520
16th to endNight
18%6%25%323336%43%
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
42%412%20%14%4
1466
16th to endDay
43%410%23%16%2
1728
February1st to 15thDay
42%5%10%23%15%2
1618
16th to endDay
40%6%11%24%15%2
1580
March1st to 15thDay
38%5%13%22%16%2
1884
16th to endDay
43%48%22%17%3
2181
April1st to 15thDay
34%6%10%26%17%4
2152
16th to endDay
37%5%10%19%20%6%
2160
May1st to 15thDay
38%7%15%21%15%1
2282
16th to endDay
34%8%15%25%13%2
2622
June1st to 15thDay
35%8%15%25%13%1
2520
16th to endDay
33%8%17%21%17%2
2520
July1st to 15thDay
35%8%15%24%13%2
2371
16th to endDay
32%11%17%22%14%2
2389
August1st to 15thDay
39%7%14%22%15%1
2252
16th to endDay
39%8%13%19%15%3
2292
September1st to 15thDay
37%7%13%20%17%3
2160
16th to endDay
47%5%8%16%19%1
1913
October1st to 15thDay
42%5%9%24%14%3
1650
16th to endDay
36%47%27%20%3
1760
November1st to 15thDay
37%5%11%23%18%3
1581
16th to endDay
37%410%26%16%3
1578
December1st to 15thDay
40%6%13%23%13%3
1440
16th to endDay
44%412%24%12%1
1536
January1st to 15thNight
41%5%11%21%17%3
2472
16th to endNight
42%49%26%14%2
2496
February1st to 15thNight
40%49%26%16%2
2245
16th to endNight
39%49%24%20%2
1893
March1st to 15thNight
40%411%26%14%2
2073
16th to endNight
43%49%20%18%3
2041
April1st to 15thNight
38%5%11%20%19%4
1796
16th to endNight
39%6%10%18%19%5%
1800
May1st to 15thNight
40%9%13%20%14%1
1678
16th to endNight
37%9%16%21%13%1
1497
June1st to 15thNight
36%9%14%23%15%1
1440
16th to endNight
38%8%15%18%17%1
1440
July1st to 15thNight
38%10%15%20%12%2
1360
16th to endNight
33%9%17%24%13%1
1514
August1st to 15thNight
35%9%17%20%17%
1672
16th to endNight
35%7%15%20%18%2
1910
September1st to 15thNight
35%5%13%24%16%3
1800
16th to endNight
39%6%10%19%19%3
1836
October1st to 15thNight
39%5%10%25%16%3
1980
16th to endNight
36%49%25%21%3
2112
November1st to 15thNight
39%39%22%18%6%
2277
16th to endNight
39%5%9%23%17%4
2379
December1st to 15thNight
43%5%11%22%13%2
2520
16th to endNight
42%312%22%14%3
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
15%26%43%10%4
65
16th to endDay
27%21%37%11%2
96
February1st to 15thDay
26%21%33%16%1
131
16th to endDay
19%20%38%18%3
239
March1st to 15thDay
21%13%29%27%7%
270
16th to endDay
19%12%38%19%6%3
288
April1st to 15thDay
18%13%31%24%11%1
270
16th to endDay
19%7%33%24%11%4
270
May1st to 15thDay
28%13%29%14%10%2
288
16th to endDay
18%5%23%27%18%6%
331
June1st to 15thDay
17%7%22%27%19%6%
315
16th to endDay
10%7%27%33%15%5%
315
July1st to 15thDay
14%121%32%21%8%
305
16th to endDay
5%215%34%28%13%
326
August1st to 15thDay
12%215%31%24%13%
313
16th to endDay
7%214%28%32%14%
332
September1st to 15thDay
13%5%24%20%20%16%
315
16th to endDay
27%316%24%14%14%
275
October1st to 15thDay
21%225%24%18%7%
255
16th to endDay
11%13%30%22%18%2
272
November1st to 15thDay
20%11%26%21%17%3
235
16th to endDay
18%16%24%22%13%4
198
December1st to 15thDay
20%23%28%13%15%
60
16th to endDay
35%15%34%9%4
64
January1st to 15thNight
18%16%33%26%5%
720
16th to endNight
20%14%37%25%1
768
February1st to 15thNight
17%16%37%26%1
704
16th to endNight
17%20%38%20%3
631
March1st to 15thNight
20%16%34%22%5%
720
16th to endNight
21%10%35%24%6%1
768
April1st to 15thNight
16%12%41%24%4
718
16th to endNight
19%7%32%31%8%
720
May1st to 15thNight
17%8%35%29%8%1
598
16th to endNight
13%324%41%16%1
375
June1st to 15thNight
9%125%45%17%
360
16th to endNight
7%123%45%21%
360
July1st to 15thNight
10%116%45%25%
340
16th to endNight
5%213%42%32%3
480
August1st to 15thNight
10%12%44%29%2
602
16th to endNight
11%112%40%29%4
764
September1st to 15thNight
16%115%35%27%3
720
16th to endNight
18%416%34%21%4
681
October1st to 15thNight
18%5%19%34%18%3
660
16th to endNight
19%12%25%26%14%1
704
November1st to 15thNight
18%8%28%27%13%2
700
16th to endNight
17%12%28%28%11%1
720
December1st to 15thNight
20%13%33%21%10%1
720
16th to endNight
20%15%36%23%4
768
Page generated at 2017-09-22 07:35:35. Version ac04

Copyright 2017 A. Danko


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