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 2017-08-12.

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%
15517
11%
46356
7%
15485
44%
15485
20%
32637

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%
895
7%
2715
4%
895
34%
895
13%
2068
January16th to endNight
22%
960
12%
2787
5%
960
29%
960
13%
2163
February1st to 15thNight
38%
796
12%
2386
8%
796
42%
796
17%
1783
February16th to endNight
42%
632
12%
2019
9%
632
47%
632
18%
1461
March1st to 15thNight
38%
720
14%
2133
9%
720
42%
720
19%
1533
March16th to endNight
39%
679
13%
2023
11%
679
43%
679
18%
1463
April1st to 15thNight
43%
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
43%
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
53%
360
0%
1080
0%
360
53%
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%
527
12%
1400
7%
524
71%
524
44%
796
August16th to endNight
57%
525
18%
1575
13%
525
61%
525
36%
905
September1st to 15thNight
56%
495
16%
1650
16%
495
59%
495
27%
1011
September16th to endNight
51%
542
22%
1793
18%
542
59%
542
34%
982
October1st to 15thNight
41%
660
19%
1980
11%
660
48%
660
25%
1301
October16th to endNight
37%
850
16%
2272
8%
850
42%
850
22%
1597
November1st to 15thNight
31%
875
15%
2450
7%
875
36%
875
17%
1833
November16th to endNight
30%
900
10%
2637
5%
900
36%
900
14%
2022
December1st to 15thNight
31%
900
5%
2826
4%
900
34%
900
10%
2292
December16th to endNight
30%
960
8%
3072
4%
960
35%
960
9%
2493

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%
47652
Night
9%9%47%6%35%5%5%7%33%
46505
Cloud CoverDay
12%8%37%6%35%5%6%7%32%
47653
Night
9%9%48%6%45%5%5%7%33%
46507
TransparencyDay
49%7%15%20%6%
47304
Night
48%6%15%21%7%
46358
SeeingDay
16%6%24%29%18%5%
6053
Night
13%5%27%34%16%2
15531

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%14%7%10%8%5%5%5%6%7%19%
1220
16th to endDay
7%11%410%8%5%6%5%6%8%24%
1436
February1st to 15thDay
8%11%5%10%10%48%8%7%5%19%
1485
16th to endDay
7%12%7%11%12%46%6%5%7%18%
1455
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%245%7%9%39%
2466
16th to endDay
13%41342346%8%46%
2275
September1st to 15thDay
11%5%245%3445%8%44%
1980
16th to endDay
12%4135%2446%7%47%
1835
October1st to 15thDay
16%11%36%433447%35%
1650
16th to endDay
14%11%46%6%345%5%7%31%
1589
November1st to 15thDay
16%14%46%5%34446%27%
1408
16th to endDay
9%13%6%11%11%45%45%5%21%
1323
December1st to 15thDay
7%14%8%11%11%6%6%6%5%6%16%
1131
16th to endDay
7%13%9%13%10%47%5%6%6%15%
1152
January1st to 15thNight
8%13%5%9%7%5%6%6%6%8%21%
2715
16th to endNight
5%12%5%10%9%5%7%6%5%7%23%
2787
February1st to 15thNight
6%10%5%11%8%5%7%45%7%27%
2377
16th to endNight
6%10%6%10%7%45%5%5%9%27%
2019
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%10%54%
1408
16th to endNight
9%31441436%7%52%
1575
September1st to 15thNight
13%5%244245%5%6%45%
1650
16th to endNight
10%41322336%8%52%
1793
October1st to 15thNight
13%8%35%42445%7%40%
1980
16th to endNight
11%9%36%6%3445%7%35%
2272
November1st to 15thNight
13%13%5%7%5%34436%31%
2450
16th to endNight
9%11%5%11%8%445%5%7%26%
2637
December1st to 15thNight
9%13%7%11%9%5%5%6%6%6%17%
2826
16th to endNight
6%12%6%12%11%5%8%6%6%6%17%
3072

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%6%11%8%5%6%46%7%19%
1220
16th to endDay
7%11%411%8%47%5%6%8%23%
1436
February1st to 15thDay
8%11%5%10%9%5%7%8%7%5%19%
1485
16th to endDay
7%12%6%11%11%47%6%5%7%18%
1455
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%
2466
16th to endDay
13%42332446%8%46%
2275
September1st to 15thDay
11%5%245%3445%7%44%
1980
16th to endDay
12%42343445%7%46%
1835
October1st to 15thDay
16%11%35%5%2345%6%35%
1650
16th to endDay
14%11%46%7%245%47%31%
1589
November1st to 15thDay
17%14%46%6%24447%27%
1408
16th to endDay
9%13%6%11%10%46%5%45%22%
1323
December1st to 15thDay
7%13%8%12%10%5%6%7%5%5%16%
1131
16th to endDay
8%12%9%14%9%5%6%6%6%5%15%
1152
January1st to 15thNight
8%13%5%10%7%5%7%6%6%8%22%
2715
16th to endNight
6%11%6%11%9%5%6%5%6%6%23%
2787
February1st to 15thNight
6%10%5%11%9%47%45%6%28%
2377
16th to endNight
5%10%6%11%6%45%5%6%9%27%
2019
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%3133235%6%10%53%
1408
16th to endNight
9%31442436%7%52%
1575
September1st to 15thNight
13%5%244345%5%6%45%
1650
16th to endNight
10%41331345%8%52%
1793
October1st to 15thNight
14%8%36%424447%40%
1980
16th to endNight
11%9%36%6%345%5%7%35%
2272
November1st to 15thNight
13%14%47%5%34446%31%
2450
16th to endNight
9%11%6%10%7%45%5%5%7%26%
2637
December1st to 15thNight
9%12%7%12%9%5%6%6%5%6%18%
2826
16th to endNight
6%11%6%12%10%6%8%6%6%6%17%
3072

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
61%6%11%15%4
1220
16th to endDay
56%6%14%15%6%
1436
February1st to 15thDay
61%7%14%12%3
1485
16th to endDay
63%5%11%13%6%
1455
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%22%5%
2450
16th to endDay
34%7%20%30%7%
2275
September1st to 15thDay
37%6%18%25%11%
1980
16th to endDay
35%6%18%28%10%1
1835
October1st to 15thDay
48%6%15%23%5%
1650
16th to endDay
51%6%17%20%3
1589
November1st to 15thDay
57%5%15%14%6%
1408
16th to endDay
64%5%14%13%2
1323
December1st to 15thDay
67%7%12%9%1
1131
16th to endDay
66%7%13%11%2
1152
January1st to 15thNight
57%7%16%15%3
2715
16th to endNight
58%6%11%15%6%
2787
February1st to 15thNight
54%6%12%19%6%
2388
16th to endNight
52%6%14%18%8%
2019
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%29%31%8%
1400
16th to endNight
29%6%15%35%12%
1575
September1st to 15thNight
37%6%14%26%12%2
1650
16th to endNight
29%5%14%33%15%1
1793
October1st to 15thNight
43%5%15%27%8%
1980
16th to endNight
47%6%16%23%5%
2272
November1st to 15thNight
54%5%12%18%6%
2450
16th to endNight
56%8%16%15%3
2637
December1st to 15thNight
65%6%13%11%1
2826
16th to endNight
65%7%10%12%4
3072

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
10%6%18%33%26%5%
60
16th to endDay
16%6%31%32%10%2
79
February1st to 15thDay
16%433%33%12%
90
16th to endDay
19%324%41%8%1
81
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%28%25%11%
474
16th to endDay
12%423%31%21%5%
317
September1st to 15thDay
18%5%26%30%17%2
255
16th to endDay
16%7%22%33%16%4
162
October1st to 15thDay
28%5%25%24%10%5%
90
16th to endDay
22%437%15%18%1
96
November1st to 15thDay
25%332%27%6%4
90
16th to endDay
26%421%22%16%8%
90
December1st to 15thDay
8%20%42%18%10%
69
16th to endDay
17%129%35%10%4
64
January1st to 15thNight
14%6%33%29%14%1
900
16th to endNight
11%7%41%29%9%1
960
February1st to 15thNight
11%5%26%35%17%2
804
16th to endNight
8%425%33%22%5%
632
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
527
16th to endNight
11%322%37%22%2
525
September1st to 15thNight
15%219%36%23%2
495
16th to endNight
12%427%37%15%1
542
October1st to 15thNight
18%326%32%15%2
660
16th to endNight
17%5%28%35%11%1
850
November1st to 15thNight
19%6%30%29%11%1
875
16th to endNight
14%8%31%33%10%1
900
December1st to 15thNight
14%5%27%34%15%3
900
16th to endNight
10%6%28%33%17%4
960
Page generated at 2017-08-13 12:16:39. Version ac04

Copyright 2017 A. Danko


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