ELAC-Stanleigh
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the ELAC-Stanleigh 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
30%
15661
13%
47736
7%
15618
36%
15618
18%
34043

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
17%
900
9%
2619
3%
895
22%
895
12%
2070
January16th to endNight
22%
944
11%
2672
5%
944
28%
944
12%
2120
February1st to 15thNight
19%
702
10%
2287
4%
701
26%
701
11%
1765
February16th to endNight
25%
631
12%
1947
6%
631
32%
631
14%
1468
March1st to 15thNight
25%
720
15%
2070
5%
720
34%
720
20%
1424
March16th to endNight
32%
768
18%
2112
10%
768
40%
768
25%
1417
April1st to 15thNight
27%
590
17%
1758
8%
590
35%
590
20%
1221
April16th to endNight
30%
540
17%
1620
8%
540
37%
540
22%
1099
May1st to 15thNight
38%
540
12%
1620
8%
540
43%
540
21%
1121
May16th to endNight
37%
377
14%
1379
10%
376
48%
376
20%
877
June1st to 15thNight
32%
360
10%
1260
7%
360
38%
360
20%
810
June16th to endNight
45%
360
9%
1260
7%
360
50%
360
24%
789
July1st to 15thNight
47%
340
14%
1190
12%
340
53%
340
29%
687
July16th to endNight
53%
535
14%
1394
10%
502
54%
502
32%
883
August1st to 15thNight
54%
539
16%
1609
11%
536
59%
536
32%
987
August16th to endNight
50%
573
18%
1719
11%
573
56%
573
30%
1065
September1st to 15thNight
46%
666
14%
1864
9%
666
49%
666
29%
1208
September16th to endNight
45%
717
19%
1980
14%
717
49%
717
29%
1288
October1st to 15thNight
33%
720
16%
2112
10%
720
41%
720
20%
1481
October16th to endNight
25%
768
12%
2428
8%
768
32%
768
13%
1819
November1st to 15thNight
24%
760
13%
2547
9%
760
31%
760
13%
1872
November16th to endNight
20%
780
11%
2730
6%
780
27%
780
10%
2122
December1st to 15thNight
16%
871
9%
2679
2%
871
22%
871
11%
2102
December16th to endNight
15%
960
8%
2880
2%
960
21%
960
9%
2348

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%9%36%5%3445%7%33%
48706
Night
16%10%46%5%34446%33%
47896
Cloud CoverDay
17%9%36%5%3445%7%33%
48716
Night
16%10%46%5%34446%33%
47900
TransparencyDay
50%6%12%19%10%1
48384
Night
51%5%12%19%9%
47736
SeeingDay
20%10%31%23%9%3
6188
Night
21%9%30%27%9%1
15663

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
17%16%7%9%5%445%5%6%19%
1319
16th to endDay
16%16%6%11%7%3443422%
1551
February1st to 15thDay
10%13%6%11%7%45%6%6%6%21%
1575
16th to endDay
13%13%6%8%7%45%435%25%
1524
March1st to 15thDay
15%11%37%5%23436%36%
1879
16th to endDay
13%8%35%5%24445%40%
2112
April1st to 15thDay
20%9%46%5%24446%31%
2199
16th to endDay
18%8%2442435%7%37%
2340
May1st to 15thDay
19%8%36%43445%6%33%
2331
16th to endDay
14%5%26%4335%5%8%38%
2735
June1st to 15thDay
16%6%26%5%35%45%8%35%
2700
16th to endDay
17%6%25%5%36%5%5%8%32%
2700
July1st to 15thDay
12%435%435%5%6%8%40%
2700
16th to endDay
12%425%5%35%5%5%9%40%
2679
August1st to 15thDay
13%5%26%5%45%45%8%37%
2340
16th to endDay
15%5%26%5%4445%8%36%
2483
September1st to 15thDay
14%6%36%5%34447%39%
2082
16th to endDay
19%5%35%434347%40%
1980
October1st to 15thDay
20%8%35%5%35%346%34%
1848
16th to endDay
25%12%46%5%24446%22%
1794
November1st to 15thDay
21%12%36%5%2445%7%26%
1639
16th to endDay
21%21%48%6%2433421%
1560
December1st to 15thDay
16%18%6%8%5%24445%24%
1292
16th to endDay
20%17%5%9%5%35%33419%
1344
January1st to 15thNight
17%16%5%7%6%33446%23%
2619
16th to endNight
15%14%7%9%8%45%34423%
2672
February1st to 15thNight
11%14%410%8%36%5%5%5%24%
2285
16th to endNight
13%14%6%8%5%35%446%27%
1947
March1st to 15thNight
14%8%46%5%34446%36%
2058
16th to endNight
12%8%35%434446%41%
2112
April1st to 15thNight
20%8%24424446%36%
1758
16th to endNight
17%6%26%5%34346%39%
1620
May1st to 15thNight
15%7%35%5%35%5%6%7%33%
1620
16th to endNight
14%6%25%4245%6%6%40%
1377
June1st to 15thNight
14%6%35%5%35%5%47%37%
1260
16th to endNight
12%6%25%5%25%5%5%8%41%
1260
July1st to 15thNight
10%425%5%24448%48%
1260
16th to endNight
10%3144246%49%47%
1489
August1st to 15thNight
11%42342345%6%49%
1620
16th to endNight
13%425%41345%6%47%
1719
September1st to 15thNight
14%4234335%48%44%
1864
16th to endNight
15%5%24324447%45%
1980
October1st to 15thNight
21%6%25%443435%37%
2112
16th to endNight
26%8%36%5%34446%28%
2428
November1st to 15thNight
18%11%47%5%34446%29%
2547
16th to endNight
22%15%46%424345%24%
2730
December1st to 15thNight
18%17%5%6%6%24445%24%
2679
16th to endNight
20%18%5%9%5%3333421%
2880

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
17%16%6%9%5%25%5%46%19%
1319
16th to endDay
15%16%6%10%6%4433422%
1551
February1st to 15thDay
10%13%6%9%8%45%6%6%6%21%
1575
16th to endDay
13%14%6%8%7%4444426%
1524
March1st to 15thDay
15%10%37%5%24445%36%
1890
16th to endDay
13%8%35%434445%40%
2111
April1st to 15thDay
20%9%45%5%34446%31%
2199
16th to endDay
19%8%34324447%37%
2340
May1st to 15thDay
19%7%36%5%2445%6%34%
2331
16th to endDay
15%5%26%5%235%5%8%39%
2735
June1st to 15thDay
17%6%36%5%3445%8%34%
2700
16th to endDay
17%7%25%6%35%5%6%8%32%
2700
July1st to 15thDay
12%5%25%435%5%6%8%40%
2700
16th to endDay
13%415%5%35%46%9%39%
2679
August1st to 15thDay
13%5%26%6%35%447%37%
2340
16th to endDay
15%5%36%6%35%45%8%35%
2483
September1st to 15thDay
15%6%25%5%3345%7%39%
2082
16th to endDay
18%6%35%433246%40%
1980
October1st to 15thDay
20%8%35%5%34346%34%
1848
16th to endDay
27%10%46%6%24445%23%
1794
November1st to 15thDay
22%13%46%42445%7%26%
1639
16th to endDay
21%19%5%7%6%33335%21%
1560
December1st to 15thDay
16%18%6%7%5%34435%24%
1292
16th to endDay
20%18%6%8%5%35%34419%
1344
January1st to 15thNight
17%16%5%8%6%33347%22%
2619
16th to endNight
15%15%6%8%8%45%345%22%
2672
February1st to 15thNight
12%13%5%9%8%46%5%5%5%24%
2278
16th to endNight
12%13%6%8%6%35%45%6%27%
1947
March1st to 15thNight
15%8%36%5%44446%36%
2070
16th to endNight
12%7%45%5%34437%41%
2112
April1st to 15thNight
20%8%345%24446%35%
1758
16th to endNight
17%8%25%5%34245%38%
1620
May1st to 15thNight
15%7%36%6%35%5%6%6%34%
1619
16th to endNight
13%6%25%426%5%5%7%40%
1377
June1st to 15thNight
13%7%26%5%35%5%5%7%37%
1260
16th to endNight
11%6%245%245%5%8%41%
1260
July1st to 15thNight
11%3145%3335%8%48%
1260
16th to endNight
10%413435%5%5%7%48%
1489
August1st to 15thNight
10%5%2333345%7%49%
1620
16th to endNight
13%5%15%41345%6%47%
1719
September1st to 15thNight
13%5%2433445%8%44%
1864
16th to endNight
15%6%24424346%45%
1980
October1st to 15thNight
21%6%345%24345%37%
2112
16th to endNight
26%8%45%434345%28%
2428
November1st to 15thNight
19%11%36%6%34445%29%
2547
16th to endNight
22%14%46%5%3334425%
2730
December1st to 15thNight
17%18%5%7%6%24445%24%
2679
16th to endNight
21%18%6%8%5%2443420%
2880

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
64%6%11%12%4
1320
16th to endDay
65%46%13%8%1
1551
February1st to 15thDay
58%7%14%12%6%
1577
16th to endDay
60%5%7%15%10%
1524
March1st to 15thDay
49%5%11%17%14%1
1890
16th to endDay
44%5%10%23%10%4
2112
April1st to 15thDay
53%410%19%11%1
2199
16th to endDay
45%5%10%21%13%3
2340
May1st to 15thDay
49%410%17%14%3
2331
16th to endDay
42%6%14%21%14%
2739
June1st to 15thDay
46%6%11%21%13%
2700
16th to endDay
48%7%11%21%10%1
2700
July1st to 15thDay
38%6%13%26%13%
2541
16th to endDay
40%7%13%25%12%
2511
August1st to 15thDay
44%6%16%20%10%
2327
16th to endDay
44%7%14%24%7%
2483
September1st to 15thDay
43%6%16%23%8%1
2082
16th to endDay
45%416%25%8%
1980
October1st to 15thDay
50%5%11%22%9%
1848
16th to endDay
62%7%11%11%6%1
1794
November1st to 15thDay
57%7%12%16%7%
1639
16th to endDay
66%5%10%11%5%
1560
December1st to 15thDay
62%6%10%15%5%
1292
16th to endDay
67%410%12%3
1344
January1st to 15thNight
61%6%12%14%5%
2619
16th to endNight
63%48%15%7%
2672
February1st to 15thNight
60%7%11%14%5%
2287
16th to endNight
57%6%11%15%8%
1947
March1st to 15thNight
48%413%21%11%1
2070
16th to endNight
43%5%12%18%15%3
2112
April1st to 15thNight
48%5%7%23%13%1
1758
16th to endNight
47%49%20%15%2
1620
May1st to 15thNight
47%5%10%19%13%2
1620
16th to endNight
41%8%9%25%13%1
1379
June1st to 15thNight
44%5%13%21%13%1
1260
16th to endNight
39%7%17%22%12%1
1260
July1st to 15thNight
33%6%12%30%15%
1190
16th to endNight
35%7%15%26%15%
1394
August1st to 15thNight
33%7%19%27%10%1
1609
16th to endNight
36%6%16%28%11%
1719
September1st to 15thNight
37%7%18%24%10%1
1864
16th to endNight
39%6%15%30%8%
1980
October1st to 15thNight
49%5%11%24%9%
2112
16th to endNight
57%5%13%16%6%
2428
November1st to 15thNight
56%5%13%16%8%
2547
16th to endNight
62%6%11%13%6%
2730
December1st to 15thNight
62%5%12%14%4
2679
16th to endNight
67%410%11%5%
2880

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
25%12%38%18%41
71
16th to endDay
25%6%27%26%12%3
96
February1st to 15thDay
30%16%38%14%
90
16th to endDay
29%18%39%12%
81
March1st to 15thDay
23%17%32%21%41
180
16th to endDay
23%9%35%19%9%2
288
April1st to 15thDay
24%9%27%25%11%1
270
16th to endDay
24%11%30%19%9%4
270
May1st to 15thDay
22%11%28%21%11%5%
288
16th to endDay
19%11%34%22%9%2
450
June1st to 15thDay
19%14%36%20%6%2
495
16th to endDay
20%11%32%24%8%2
495
July1st to 15thDay
13%8%37%29%7%3
475
16th to endDay
14%7%33%27%11%5%
509
August1st to 15thDay
16%323%30%16%10%
313
16th to endDay
22%420%28%15%8%
332
September1st to 15thDay
18%6%24%24%18%8%
315
16th to endDay
19%9%25%29%11%5%
314
October1st to 15thDay
23%10%32%22%10%1
315
16th to endDay
26%16%33%18%4
210
November1st to 15thDay
29%19%26%20%4
117
16th to endDay
25%20%40%12%2
90
December1st to 15thDay
23%20%35%16%31
60
16th to endDay
35%25%37%1
64
January1st to 15thNight
26%10%34%22%6%
900
16th to endNight
23%10%29%27%9%
944
February1st to 15thNight
17%11%40%24%5%
704
16th to endNight
18%11%33%28%7%
631
March1st to 15thNight
19%13%34%27%5%
720
16th to endNight
17%9%34%27%9%1
768
April1st to 15thNight
23%9%33%26%6%
590
16th to endNight
21%8%34%25%8%1
540
May1st to 15thNight
17%7%27%34%11%1
540
16th to endNight
17%8%32%32%9%
377
June1st to 15thNight
13%5%40%30%8%
360
16th to endNight
13%5%27%41%12%
360
July1st to 15thNight
11%5%29%40%12%
340
16th to endNight
13%225%39%17%1
535
August1st to 15thNight
14%125%35%22%1
539
16th to endNight
17%221%36%20%1
573
September1st to 15thNight
17%328%25%20%4
666
16th to endNight
17%5%27%29%16%3
717
October1st to 15thNight
25%7%30%25%10%1
720
16th to endNight
29%11%27%23%5%
768
November1st to 15thNight
23%13%31%22%8%
760
16th to endNight
31%13%26%22%5%
780
December1st to 15thNight
28%13%34%18%5%
871
16th to endNight
31%12%30%19%5%
960
Page generated at 2017-12-02 09:14:27. Version ac04

Copyright 2017 A. Danko


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