Sleaford Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sleaford Observatory clear sky chart from 2005-11-05 to 2018-02-22.

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
40%
16365
12%
48908
7%
16333
44%
16333
20%
34268

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
31%
970
8%
2942
5%
970
35%
970
14%
2219
January16th to endNight
24%
1040
13%
3019
6%
1040
31%
1040
13%
2330
February1st to 15thNight
38%
864
13%
2589
8%
864
43%
864
18%
1908
February16th to endNight
43%
660
13%
2110
9%
660
48%
660
19%
1511
March1st to 15thNight
38%
720
14%
2133
9%
720
42%
720
19%
1533
March16th to endNight
39%
679
13%
2023
11%
679
42%
679
18%
1463
April1st to 15thNight
42%
539
14%
1798
11%
539
47%
539
23%
1159
April16th to endNight
39%
540
13%
1511
9%
540
41%
540
20%
1074
May1st to 15thNight
42%
539
11%
1440
7%
539
45%
539
27%
981
May16th to endNight
44%
482
5%
1344
4%
480
46%
480
25%
916
June1st to 15thNight
46%
360
0%
1080
0%
360
46%
360
21%
743
June16th to endNight
52%
360
0%
1080
0%
360
52%
360
23%
727
July1st to 15thNight
61%
340
0%
1086
0%
340
61%
340
33%
623
July16th to endNight
64%
441
8%
1299
7%
414
66%
414
38%
711
August1st to 15thNight
68%
539
12%
1432
7%
536
71%
536
44%
812
August16th to endNight
58%
573
21%
1720
15%
573
63%
573
38%
966
September1st to 15thNight
55%
540
16%
1800
15%
540
59%
540
28%
1078
September16th to endNight
52%
592
24%
1957
20%
592
60%
592
34%
1079
October1st to 15thNight
42%
720
18%
2160
11%
720
48%
720
25%
1422
October16th to endNight
37%
927
17%
2478
8%
927
42%
927
22%
1746
November1st to 15thNight
30%
950
14%
2660
7%
950
35%
950
16%
2017
November16th to endNight
29%
975
10%
2857
4%
975
35%
975
14%
2179
December1st to 15thNight
30%
975
5%
3062
3%
975
34%
975
11%
2445
December16th to endNight
31%
1040
10%
3328
5%
1040
37%
1040
10%
2626

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
12%8%47%6%35%5%6%7%32%
49379
Night
9%9%47%6%35%5%5%7%33%
49057
Cloud CoverDay
12%8%37%6%35%5%6%7%32%
49380
Night
9%9%48%6%45%5%5%7%33%
49059
TransparencyDay
49%7%15%20%6%
49031
Night
48%6%14%21%7%
48910
SeeingDay
15%6%25%29%18%5%
6634
Night
13%5%27%34%16%2
16379

By Month

Percentage Cloud Cover NW (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
8%15%6%10%8%45%5%7%7%20%
1322
16th to endDay
7%11%5%10%9%5%7%5%6%7%23%
1556
February1st to 15thDay
7%11%5%10%10%48%8%7%6%20%
1613
16th to endDay
7%12%8%10%12%46%6%5%6%19%
1510
March1st to 15thDay
9%12%6%11%8%46%45%6%23%
1825
16th to endDay
11%11%5%9%6%3446%8%26%
2200
April1st to 15thDay
10%10%48%5%345%6%7%32%
2150
16th to endDay
16%10%47%6%34447%30%
2448
May1st to 15thDay
12%6%25%5%35%5%6%6%38%
2511
16th to endDay
17%6%26%6%35%45%8%32%
2766
June1st to 15thDay
18%8%36%6%35%5%6%7%26%
2880
16th to endDay
18%6%36%5%36%5%7%8%28%
2880
July1st to 15thDay
11%4145%35%5%5%9%42%
2807
16th to endDay
8%424435%5%7%8%45%
2780
August1st to 15thDay
11%5%25%5%2447%8%40%
2520
16th to endDay
12%4133235%6%8%48%
2482
September1st to 15thDay
10%5%245%3345%7%46%
2160
16th to endDay
12%42342446%7%46%
2001
October1st to 15thDay
15%11%36%423447%36%
1800
16th to endDay
14%11%46%6%3445%7%32%
1734
November1st to 15thDay
15%14%5%8%5%34446%27%
1528
16th to endDay
9%13%6%11%10%46%45%5%21%
1433
December1st to 15thDay
7%13%7%11%11%6%6%6%5%6%17%
1225
16th to endDay
7%12%9%12%9%5%7%5%7%7%16%
1248
January1st to 15thNight
8%12%5%9%7%5%6%6%7%8%22%
2942
16th to endNight
5%11%5%10%9%5%7%6%5%7%23%
3019
February1st to 15thNight
6%9%5%10%8%5%6%45%7%28%
2580
16th to endNight
5%9%6%10%7%46%5%5%8%28%
2110
March1st to 15thNight
9%10%5%7%7%45%5%6%7%31%
2133
16th to endNight
10%12%48%6%335%6%6%31%
2020
April1st to 15thNight
8%9%37%5%3446%7%39%
1798
16th to endNight
14%10%35%5%36%45%7%32%
1511
May1st to 15thNight
14%6%25%6%245%5%7%39%
1439
16th to endNight
15%5%25%5%26%5%47%38%
1344
June1st to 15thNight
15%6%36%6%35%5%6%8%33%
1080
16th to endNight
11%6%25%6%36%48%7%37%
1080
July1st to 15thNight
7%312335%5%7%9%48%
1151
16th to endNight
6%21333436%10%54%
1388
August1st to 15thNight
6%2133235%6%9%54%
1440
16th to endNight
9%31441336%7%54%
1720
September1st to 15thNight
12%5%144245%5%6%47%
1800
16th to endNight
9%41432435%8%52%
1957
October1st to 15thNight
13%9%35%42445%6%40%
2160
16th to endNight
11%9%36%6%445%5%7%35%
2478
November1st to 15thNight
12%14%6%8%5%35%436%29%
2660
16th to endNight
8%11%5%11%8%445%5%7%26%
2857
December1st to 15thNight
8%12%7%11%9%5%5%6%6%7%19%
3062
16th to endNight
5%11%5%11%11%5%8%6%6%7%18%
3328

Percentage Cloud Cover SW (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
9%14%5%11%8%45%47%7%20%
1322
16th to endDay
7%11%5%11%8%5%7%5%6%7%22%
1556
February1st to 15thDay
8%10%5%10%9%5%8%9%7%5%20%
1613
16th to endDay
7%12%6%11%11%46%6%5%7%18%
1510
March1st to 15thDay
9%13%6%11%8%46%5%47%23%
1825
16th to endDay
12%11%49%6%3446%7%27%
2201
April1st to 15thDay
10%9%5%7%6%345%6%6%33%
2150
16th to endDay
16%9%47%5%34447%30%
2448
May1st to 15thDay
13%6%25%5%35%5%6%6%38%
2511
16th to endDay
17%6%36%5%36%45%8%32%
2766
June1st to 15thDay
19%8%36%6%35%5%6%7%27%
2880
16th to endDay
18%6%26%5%45%5%7%8%29%
2880
July1st to 15thDay
11%413445%46%8%42%
2807
16th to endDay
9%324435%5%6%8%45%
2780
August1st to 15thDay
11%5%25%4345%6%8%40%
2520
16th to endDay
12%42332346%8%48%
2482
September1st to 15thDay
11%5%245%3345%7%46%
2160
16th to endDay
12%4234345%5%7%46%
2001
October1st to 15thDay
15%11%35%5%2345%7%36%
1800
16th to endDay
14%11%46%6%245%5%7%31%
1734
November1st to 15thDay
16%14%47%6%24446%26%
1528
16th to endDay
9%13%6%10%10%46%5%5%5%21%
1433
December1st to 15thDay
7%13%8%12%10%5%6%7%5%5%17%
1225
16th to endDay
7%11%8%13%9%5%7%6%7%6%16%
1248
January1st to 15thNight
7%12%5%9%7%5%7%6%7%8%22%
2942
16th to endNight
6%11%6%11%9%5%6%5%6%6%23%
3019
February1st to 15thNight
6%9%5%10%8%47%45%7%29%
2580
16th to endNight
5%10%6%10%6%46%5%6%9%28%
2110
March1st to 15thNight
9%10%48%5%45%6%6%6%31%
2133
16th to endNight
11%11%48%6%345%5%6%31%
2023
April1st to 15thNight
8%9%47%5%2446%6%39%
1798
16th to endNight
15%10%36%5%35%45%7%32%
1511
May1st to 15thNight
14%6%25%5%245%48%38%
1439
16th to endNight
15%5%35%6%25%45%7%38%
1343
June1st to 15thNight
16%6%36%5%245%6%8%33%
1080
16th to endNight
12%5%345%36%5%8%7%37%
1080
July1st to 15thNight
8%323325%5%7%9%49%
1151
16th to endNight
6%21333435%10%54%
1388
August1st to 15thNight
6%2133235%6%10%54%
1440
16th to endNight
9%31442435%7%54%
1720
September1st to 15thNight
12%5%243245%5%6%47%
1800
16th to endNight
9%41332335%8%52%
1957
October1st to 15thNight
14%9%36%433447%40%
2160
16th to endNight
11%9%36%6%345%5%7%35%
2478
November1st to 15thNight
12%14%5%8%5%34446%29%
2660
16th to endNight
8%11%5%11%8%45%5%5%7%26%
2857
December1st to 15thNight
9%12%6%11%9%5%6%6%5%7%19%
3062
16th to endNight
6%11%5%12%10%6%8%6%6%7%18%
3328

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
60%5%12%15%5%
1322
16th to endDay
57%6%13%14%6%
1556
February1st to 15thDay
60%8%15%13%3
1613
16th to endDay
63%5%11%13%6%
1510
March1st to 15thDay
61%5%13%14%4
1825
16th to endDay
55%7%12%18%5%
2201
April1st to 15thDay
48%7%15%19%8%
2150
16th to endDay
54%6%13%18%7%
2448
May1st to 15thDay
42%5%14%26%9%1
2511
16th to endDay
49%6%13%18%11%
2770
June1st to 15thDay
53%6%13%19%7%
2880
16th to endDay
49%9%16%19%4
2880
July1st to 15thDay
36%8%19%29%5%
2644
16th to endDay
35%9%21%27%5%
2606
August1st to 15thDay
39%9%22%23%5%
2504
16th to endDay
32%7%19%32%7%
2482
September1st to 15thDay
36%6%18%25%11%1
2160
16th to endDay
35%6%18%27%10%1
2001
October1st to 15thDay
47%6%16%24%5%
1800
16th to endDay
50%6%18%20%3
1734
November1st to 15thDay
58%6%15%14%5%
1528
16th to endDay
63%6%14%12%2
1433
December1st to 15thDay
66%7%13%10%2
1225
16th to endDay
63%6%12%11%4
1248
January1st to 15thNight
56%7%15%16%4
2942
16th to endNight
58%6%11%15%7%
3019
February1st to 15thNight
53%6%12%21%5%
2591
16th to endNight
51%6%14%19%7%
2110
March1st to 15thNight
49%7%16%19%6%
2133
16th to endNight
52%6%14%18%7%
2023
April1st to 15thNight
43%5%15%21%11%1
1798
16th to endNight
50%5%12%17%11%2
1511
May1st to 15thNight
43%5%11%25%12%1
1440
16th to endNight
44%5%14%17%15%1
1344
June1st to 15thNight
45%7%12%23%10%
1080
16th to endNight
41%9%19%21%7%
1080
July1st to 15thNight
28%9%19%34%7%
1086
16th to endNight
26%6%25%32%8%
1299
August1st to 15thNight
24%6%28%31%8%
1432
16th to endNight
28%6%14%37%12%
1720
September1st to 15thNight
35%6%14%26%13%3
1800
16th to endNight
29%5%14%33%15%1
1957
October1st to 15thNight
43%5%15%27%7%
2160
16th to endNight
47%6%16%23%5%
2478
November1st to 15thNight
56%5%12%17%6%
2660
16th to endNight
56%8%16%15%3
2857
December1st to 15thNight
63%6%14%12%2
3062
16th to endNight
62%7%9%12%7%
3328

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
11%6%24%27%25%4
90
16th to endDay
16%7%29%31%13%1
119
February1st to 15thDay
13%340%31%11%
135
16th to endDay
16%325%39%16%1
100
March1st to 15thDay
20%342%20%12%1
115
16th to endDay
21%8%27%29%12%1
288
April1st to 15thDay
12%11%32%27%13%3
269
16th to endDay
21%6%23%28%17%2
399
May1st to 15thDay
14%8%24%33%16%2
468
16th to endDay
16%8%20%28%17%9%
517
June1st to 15thDay
17%8%27%27%14%4
495
16th to endDay
21%6%23%25%19%4
495
July1st to 15thDay
14%220%29%26%7%
475
16th to endDay
7%6%25%30%21%8%
515
August1st to 15thDay
11%418%27%25%12%
493
16th to endDay
10%423%34%21%5%
385
September1st to 15thDay
17%8%25%31%15%2
315
16th to endDay
15%6%20%33%20%4
213
October1st to 15thDay
24%5%26%21%15%5%
135
16th to endDay
21%6%38%18%13%
144
November1st to 15thDay
20%229%34%9%3
135
16th to endDay
22%8%25%23%14%5%
135
December1st to 15thDay
9%26%38%16%7%
103
16th to endDay
12%131%36%12%6%
96
January1st to 15thNight
13%6%33%30%13%2
975
16th to endNight
11%7%40%29%9%1
1040
February1st to 15thNight
11%5%28%35%17%2
872
16th to endNight
8%424%34%23%5%
660
March1st to 15thNight
12%6%30%36%11%2
720
16th to endNight
16%7%26%33%14%2
679
April1st to 15thNight
10%6%30%38%12%1
539
16th to endNight
21%5%24%32%15%1
540
May1st to 15thNight
15%7%25%34%16%1
540
16th to endNight
16%7%25%31%15%3
482
June1st to 15thNight
16%5%23%33%19%1
360
16th to endNight
15%5%20%37%18%3
360
July1st to 15thNight
9%220%38%27%2
340
16th to endNight
7%320%41%24%2
441
August1st to 15thNight
8%116%36%33%4
539
16th to endNight
10%322%38%22%2
573
September1st to 15thNight
15%220%36%22%2
540
16th to endNight
11%426%39%15%1
592
October1st to 15thNight
19%326%32%15%2
720
16th to endNight
17%6%28%36%10%1
927
November1st to 15thNight
19%6%30%29%11%1
950
16th to endNight
13%9%32%33%9%1
975
December1st to 15thNight
13%5%29%33%14%2
975
16th to endNight
9%5%29%33%17%4
1040
Page generated at 2018-02-23 10:21:35. Version ac04

Copyright 2018 A. Danko


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