Lake Runnemede Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Runnemede 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
28%
15430
15%
48890
8%
15398
37%
15398
16%
33773

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
20%
780
14%
2716
7%
776
30%
776
11%
1922
January16th to endNight
18%
832
12%
2912
4%
832
29%
832
11%
2035
February1st to 15thNight
14%
764
12%
2430
3%
761
26%
761
11%
1825
February16th to endNight
18%
659
15%
1976
5%
659
30%
659
12%
1435
March1st to 15thNight
17%
720
14%
2160
6%
720
27%
720
11%
1558
March16th to endNight
23%
768
20%
2012
6%
768
34%
768
17%
1400
April1st to 15thNight
20%
718
16%
1796
4%
718
27%
718
15%
1308
April16th to endNight
23%
609
17%
1689
4%
609
33%
609
17%
1176
May1st to 15thNight
20%
502
16%
1582
6%
502
31%
502
13%
1118
May16th to endNight
34%
375
11%
1497
10%
374
41%
374
13%
1022
June1st to 15thNight
29%
360
10%
1440
7%
360
39%
360
12%
1012
June16th to endNight
39%
360
10%
1440
10%
360
46%
360
15%
938
July1st to 15thNight
50%
340
12%
1360
17%
340
55%
340
21%
815
July16th to endNight
47%
376
15%
1418
16%
354
57%
354
23%
823
August1st to 15thNight
48%
443
15%
1514
11%
441
52%
441
21%
937
August16th to endNight
51%
747
19%
1893
10%
747
53%
747
32%
1221
September1st to 15thNight
45%
720
18%
1830
9%
720
49%
720
31%
1193
September16th to endNight
48%
717
26%
1980
17%
717
55%
717
33%
1176
October1st to 15thNight
36%
720
18%
2052
11%
720
44%
720
19%
1403
October16th to endNight
26%
768
13%
2481
6%
768
36%
768
15%
1773
November1st to 15thNight
29%
760
16%
2472
11%
760
37%
760
16%
1691
November16th to endNight
24%
780
17%
2598
8%
780
36%
780
14%
1795
December1st to 15thNight
17%
780
11%
2730
4%
780
25%
780
10%
2021
December16th to endNight
13%
832
12%
2912
4%
832
23%
832
8%
2176

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
16%7%36%5%35%5%5%7%34%
49372
Night
15%7%35%5%35%45%7%37%
49060
Cloud CoverDay
17%8%36%5%3445%6%34%
49382
Night
16%7%36%5%3445%6%36%
49065
TransparencyDay
49%6%12%18%11%1
49060
Night
48%6%12%20%11%1
48890
SeeingDay
21%21%25%19%10%3
6208
Night
18%24%23%23%8%
15430

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%8%46%7%46%5%7%8%27%
1552
16th to endDay
12%7%35%7%35%5%6%7%33%
1664
February1st to 15thDay
12%11%47%7%38%5%36%27%
1761
16th to endDay
12%11%5%8%6%345%46%31%
1644
March1st to 15thDay
16%10%48%5%25%6%5%6%28%
1790
16th to endDay
13%8%47%6%34435%37%
2208
April1st to 15thDay
17%8%36%434446%36%
2152
16th to endDay
17%7%25%5%345%36%37%
2270
May1st to 15thDay
23%8%36%6%24445%31%
2379
16th to endDay
18%6%35%5%45%448%35%
2618
June1st to 15thDay
23%7%25%6%24447%29%
2520
16th to endDay
17%5%37%6%35%6%6%7%31%
2520
July1st to 15thDay
13%5%36%6%46%5%5%8%33%
2520
16th to endDay
13%5%25%6%346%6%9%35%
2654
August1st to 15thDay
12%6%26%6%36%6%7%7%34%
2424
16th to endDay
11%425%5%3447%8%40%
2308
September1st to 15thDay
14%5%145%35%447%41%
2130
16th to endDay
12%5%23423446%51%
1980
October1st to 15thDay
19%7%35%5%23345%39%
1905
16th to endDay
18%8%36%4345%46%32%
1743
November1st to 15thDay
15%7%345%2446%7%37%
1716
16th to endDay
17%8%35%43445%5%37%
1690
December1st to 15thDay
17%10%47%6%35%446%28%
1560
16th to endDay
19%12%48%5%25%445%25%
1664
January1st to 15thNight
12%9%36%6%35%5%6%6%32%
2716
16th to endNight
12%7%37%5%45%6%6%7%33%
2912
February1st to 15thNight
10%10%48%7%46%6%6%7%27%
2429
16th to endNight
13%9%36%5%36%6%6%6%32%
1976
March1st to 15thNight
16%8%25%6%45%5%5%5%33%
2147
16th to endNight
13%7%35%5%35%446%40%
2012
April1st to 15thNight
16%6%25%5%35%5%5%7%36%
1796
16th to endNight
19%5%25%423446%40%
1689
May1st to 15thNight
19%7%25%5%25%346%35%
1582
16th to endNight
17%6%345%35%45%7%35%
1495
June1st to 15thNight
23%5%25%43435%7%34%
1440
16th to endNight
14%5%25%425%5%7%7%38%
1440
July1st to 15thNight
13%314435%46%6%44%
1440
16th to endNight
12%3225%35%46%9%43%
1514
August1st to 15thNight
10%5%145%345%48%45%
1524
16th to endNight
11%42342446%8%46%
1893
September1st to 15thNight
13%5%24324337%49%
1830
16th to endNight
12%5%14323347%52%
1980
October1st to 15thNight
17%5%25%434446%40%
2052
16th to endNight
19%6%25%5%3445%5%34%
2481
November1st to 15thNight
13%8%35%5%34447%37%
2472
16th to endNight
15%7%35%5%36%446%38%
2598
December1st to 15thNight
19%7%47%5%35%45%6%29%
2730
16th to endNight
17%10%47%6%34446%28%
2912

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%9%46%7%35%6%7%7%27%
1552
16th to endDay
12%8%36%7%4446%7%33%
1664
February1st to 15thDay
13%12%48%7%36%5%45%28%
1761
16th to endDay
13%11%6%7%6%4335%5%30%
1644
March1st to 15thDay
18%10%47%5%35%5%5%5%28%
1800
16th to endDay
15%9%46%5%34436%36%
2208
April1st to 15thDay
19%7%37%434345%36%
2152
16th to endDay
18%7%26%5%235%45%37%
2270
May1st to 15thDay
24%8%35%6%33445%30%
2379
16th to endDay
19%6%25%5%35%347%36%
2618
June1st to 15thDay
24%7%35%5%34437%29%
2520
16th to endDay
18%6%26%6%35%5%5%6%31%
2520
July1st to 15thDay
13%6%36%6%45%5%6%9%33%
2520
16th to endDay
13%5%25%6%35%6%6%8%35%
2654
August1st to 15thDay
13%6%26%6%35%6%6%7%33%
2424
16th to endDay
12%425%435%47%8%41%
2308
September1st to 15thDay
15%5%25%5%35%446%41%
2130
16th to endDay
12%5%24323445%50%
1980
October1st to 15thDay
20%8%25%424245%39%
1905
16th to endDay
19%8%35%6%24446%32%
1743
November1st to 15thDay
16%8%25%4245%5%7%37%
1716
16th to endDay
18%8%344245%45%37%
1690
December1st to 15thDay
19%10%47%6%43446%28%
1560
16th to endDay
21%13%47%5%25%44425%
1664
January1st to 15thNight
13%9%37%6%35%6%5%6%31%
2716
16th to endNight
12%9%47%6%345%6%7%32%
2912
February1st to 15thNight
12%9%48%7%36%6%6%7%26%
2422
16th to endNight
14%9%37%6%36%5%6%6%31%
1976
March1st to 15thNight
18%8%36%6%35%35%5%32%
2160
16th to endNight
14%8%36%425%445%39%
2011
April1st to 15thNight
17%7%36%5%35%5%5%5%35%
1796
16th to endNight
19%6%35%42325%5%40%
1689
May1st to 15thNight
20%7%36%5%44345%34%
1582
16th to endNight
18%5%25%7%3445%7%34%
1495
June1st to 15thNight
24%5%25%5%24448%32%
1440
16th to endNight
15%425%5%245%7%7%38%
1440
July1st to 15thNight
14%4244345%6%8%43%
1440
16th to endNight
12%413425%46%9%43%
1514
August1st to 15thNight
11%5%15%5%3445%8%44%
1524
16th to endNight
12%4243245%5%9%45%
1893
September1st to 15thNight
14%6%23323446%48%
1830
16th to endNight
12%5%2331335%6%52%
1980
October1st to 15thNight
18%6%26%434345%40%
2052
16th to endNight
20%8%25%6%34445%34%
2481
November1st to 15thNight
15%8%26%6%34446%37%
2472
16th to endNight
16%8%36%434446%37%
2598
December1st to 15thNight
20%9%46%5%35%445%29%
2730
16th to endNight
19%12%47%6%34445%27%
2912

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%7%12%16%8%1
1553
16th to endDay
48%7%15%18%8%
1664
February1st to 15thDay
56%6%11%16%7%
1764
16th to endDay
55%410%15%12%1
1644
March1st to 15thDay
56%5%12%13%9%1
1800
16th to endDay
49%5%10%15%14%3
2208
April1st to 15thDay
50%49%19%12%2
2152
16th to endDay
49%6%8%19%13%2
2270
May1st to 15thDay
56%47%18%11%2
2379
16th to endDay
48%7%11%19%10%1
2622
June1st to 15thDay
56%6%11%16%9%
2520
16th to endDay
52%7%11%16%10%1
2520
July1st to 15thDay
45%9%12%20%11%
2371
16th to endDay
43%8%16%21%9%
2487
August1st to 15thDay
45%9%15%19%8%
2410
16th to endDay
38%7%15%24%12%
2308
September1st to 15thDay
41%7%11%23%14%1
2130
16th to endDay
35%410%27%18%1
1980
October1st to 15thDay
49%49%22%11%1
1905
16th to endDay
53%6%12%19%7%1
1743
November1st to 15thDay
45%7%15%19%11%1
1716
16th to endDay
49%5%14%17%12%1
1690
December1st to 15thDay
57%5%15%14%7%
1560
16th to endDay
61%5%9%13%9%
1664
January1st to 15thNight
51%6%12%16%10%1
2716
16th to endNight
50%6%13%16%11%1
2912
February1st to 15thNight
54%7%11%15%9%
2430
16th to endNight
52%6%11%18%8%2
1976
March1st to 15thNight
53%412%18%9%1
2160
16th to endNight
45%5%11%16%16%4
2012
April1st to 15thNight
49%5%10%19%14%1
1796
16th to endNight
46%5%9%19%15%2
1689
May1st to 15thNight
52%47%17%16%1
1582
16th to endNight
49%7%12%19%9%1
1497
June1st to 15thNight
52%7%14%17%8%
1440
16th to endNight
42%10%13%20%11%
1440
July1st to 15thNight
36%8%17%25%11%
1360
16th to endNight
36%6%17%26%11%1
1418
August1st to 15thNight
38%8%14%25%12%
1514
16th to endNight
35%6%15%28%13%
1893
September1st to 15thNight
37%414%27%14%
1830
16th to endNight
31%5%12%30%19%1
1980
October1st to 15thNight
46%5%11%21%11%2
2052
16th to endNight
52%6%12%20%7%
2481
November1st to 15thNight
48%5%12%19%11%1
2472
16th to endNight
48%6%13%20%9%1
2598
December1st to 15thNight
56%6%13%16%6%
2730
16th to endNight
58%5%11%14%8%
2912

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
24%22%28%15%8%
90
16th to endDay
22%21%36%15%3
96
February1st to 15thDay
25%28%28%13%2
212
16th to endDay
20%30%25%19%3
265
March1st to 15thDay
27%25%25%16%4
270
16th to endDay
23%30%22%14%6%3
288
April1st to 15thDay
25%27%22%17%5%2
270
16th to endDay
22%28%22%14%10%2
270
May1st to 15thDay
31%24%19%13%7%3
288
16th to endDay
20%21%31%19%5%1
331
June1st to 15thDay
27%21%26%16%7%
315
16th to endDay
18%21%27%17%12%1
315
July1st to 15thDay
13%16%32%21%10%4
305
16th to endDay
12%15%31%24%12%3
326
August1st to 15thDay
13%15%28%20%16%5%
313
16th to endDay
14%12%18%25%18%10%
332
September1st to 15thDay
17%13%21%20%19%6%
315
16th to endDay
13%13%22%19%14%15%
314
October1st to 15thDay
21%13%21%25%13%5%
315
16th to endDay
24%21%19%25%9%
292
November1st to 15thDay
23%20%21%22%11%1
280
16th to endDay
25%26%21%15%10%
220
December1st to 15thDay
23%28%24%12%11%
90
16th to endDay
38%21%30%8%1
96
January1st to 15thNight
16%31%26%22%2
780
16th to endNight
17%28%30%20%2
832
February1st to 15thNight
20%28%31%18%2
764
16th to endNight
20%31%26%19%2
659
March1st to 15thNight
24%30%22%20%2
720
16th to endNight
18%31%22%19%7%
768
April1st to 15thNight
18%33%22%20%4
718
16th to endNight
20%30%23%18%7%
609
May1st to 15thNight
20%26%26%19%6%
502
16th to endNight
16%21%22%28%9%
375
June1st to 15thNight
21%22%23%24%8%
360
16th to endNight
12%21%21%35%8%
360
July1st to 15thNight
12%15%17%38%15%1
340
16th to endNight
11%18%18%34%16%1
376
August1st to 15thNight
12%12%20%35%16%1
443
16th to endNight
13%11%17%30%23%3
747
September1st to 15thNight
16%14%20%28%20%1
720
16th to endNight
13%14%18%28%20%5%
717
October1st to 15thNight
22%18%17%26%14%1
720
16th to endNight
23%19%24%24%7%
768
November1st to 15thNight
18%23%23%25%8%
760
16th to endNight
18%28%24%18%8%
780
December1st to 15thNight
24%27%25%17%3
780
16th to endNight
25%29%25%16%2
832
Page generated at 2018-02-23 11:21:27. Version ac04

Copyright 2018 A. Danko


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