Apsley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Apsley clear sky chart from 2005-11-05 to 2017-11-30.

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
29%
15014
14%
47816
8%
14983
36%
14983
17%
33518

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
14%
719
8%
2506
2%
716
20%
716
7%
2003
January16th to endNight
18%
768
12%
2547
6%
768
25%
768
11%
1958
February1st to 15thNight
15%
703
10%
2287
3%
701
23%
701
11%
1749
February16th to endNight
20%
631
14%
2009
5%
631
31%
631
14%
1469
March1st to 15thNight
18%
720
13%
2013
5%
720
25%
720
15%
1490
March16th to endNight
30%
768
20%
2094
10%
768
38%
768
23%
1409
April1st to 15thNight
24%
718
15%
1796
5%
718
30%
718
20%
1335
April16th to endNight
30%
603
19%
1683
8%
603
37%
603
24%
1144
May1st to 15thNight
35%
414
17%
1494
12%
414
44%
414
19%
957
May16th to endNight
39%
374
15%
1497
11%
374
51%
374
22%
882
June1st to 15thNight
38%
360
10%
1440
8%
360
49%
360
18%
892
June16th to endNight
45%
360
10%
1440
12%
360
50%
360
21%
881
July1st to 15thNight
51%
340
15%
1360
20%
340
57%
340
30%
712
July16th to endNight
51%
391
15%
1432
14%
368
58%
368
30%
781
August1st to 15thNight
58%
539
15%
1609
11%
536
62%
536
33%
974
August16th to endNight
53%
653
21%
1799
10%
653
59%
653
36%
1089
September1st to 15thNight
45%
720
18%
1800
8%
720
48%
720
31%
1186
September16th to endNight
48%
717
23%
1991
16%
717
53%
717
30%
1257
October1st to 15thNight
33%
720
16%
2160
11%
720
41%
720
19%
1515
October16th to endNight
19%
768
12%
2321
5%
768
28%
768
12%
1791
November1st to 15thNight
29%
760
16%
2602
14%
760
36%
760
17%
1778
November16th to endNight
19%
780
11%
2728
6%
780
26%
780
10%
2064
December1st to 15thNight
13%
720
6%
2520
2%
720
17%
720
7%
2019
December16th to endNight
12%
768
8%
2688
2%
768
18%
768
7%
2183

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
17%9%46%5%3445%6%31%
48599
Night
16%9%36%5%3445%6%33%
47988
Cloud CoverDay
17%9%36%5%3445%6%31%
48609
Night
16%9%46%5%3445%6%33%
47993
TransparencyDay
52%5%11%19%10%1
48289
Night
50%5%12%20%10%
47816
SeeingDay
22%12%30%20%9%4
5621
Night
21%11%30%23%10%1
15017

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
19%18%5%8%5%3433423%
1432
16th to endDay
13%16%7%12%7%3434422%
1675
February1st to 15thDay
13%15%7%13%8%35%44420%
1575
16th to endDay
16%16%5%8%6%3433426%
1464
March1st to 15thDay
16%12%5%7%7%34446%27%
1933
16th to endDay
15%10%46%423445%38%
2130
April1st to 15thDay
23%11%45%43334431%
2152
16th to endDay
21%8%35%423336%37%
2289
May1st to 15thDay
19%8%36%5%3435%6%32%
2457
16th to endDay
16%5%25%5%35%45%6%38%
2618
June1st to 15thDay
22%6%35%6%4445%7%29%
2520
16th to endDay
16%6%25%5%36%5%5%8%32%
2520
July1st to 15thDay
13%425%5%45%5%6%9%37%
2520
16th to endDay
11%5%26%6%36%6%6%9%33%
2636
August1st to 15thDay
12%6%35%6%36%7%5%8%33%
2340
16th to endDay
13%6%246%345%6%7%38%
2390
September1st to 15thDay
16%6%25%5%2445%7%39%
2160
16th to endDay
15%5%25%43345%6%42%
1967
October1st to 15thDay
24%6%35%5%34446%29%
1800
16th to endDay
29%10%36%43435%5%22%
1902
November1st to 15thDay
19%8%36%5%34446%32%
1585
16th to endDay
22%15%5%7%43445%422%
1558
December1st to 15thDay
19%21%7%9%6%2243416%
1440
16th to endDay
21%20%7%8%5%3333319%
1536
January1st to 15thNight
20%17%7%8%6%3443419%
2506
16th to endNight
14%15%6%9%7%43445%23%
2547
February1st to 15thNight
13%14%6%10%7%35%45%5%23%
2285
16th to endNight
15%13%37%5%3446%6%27%
2009
March1st to 15thNight
18%10%47%5%3435%431%
2001
16th to endNight
14%7%35%5%34445%41%
2094
April1st to 15thNight
20%8%46%5%24345%32%
1796
16th to endNight
17%7%25%5%235%5%6%39%
1683
May1st to 15thNight
19%5%25%6%24446%38%
1494
16th to endNight
12%5%24445%5%5%6%43%
1495
June1st to 15thNight
16%6%25%336%45%9%37%
1440
16th to endNight
12%5%25%5%36%45%7%40%
1440
July1st to 15thNight
8%32443445%7%50%
1440
16th to endNight
9%414326%5%6%9%46%
1529
August1st to 15thNight
9%5%45%345%5%9%47%
1620
16th to endNight
8%325%435%5%5%8%49%
1799
September1st to 15thNight
14%425%42346%7%44%
1800
16th to endNight
16%5%13424345%47%
1991
October1st to 15thNight
20%6%26%5%35%446%34%
2160
16th to endNight
23%10%46%5%3445%5%25%
2321
November1st to 15thNight
18%8%25%5%34446%34%
2602
16th to endNight
22%11%46%7%35%447%24%
2728
December1st to 15thNight
21%17%6%8%5%33346%18%
2520
16th to endNight
22%15%7%10%5%3434418%
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
19%17%5%8%6%3343423%
1432
16th to endDay
14%15%7%11%7%35%345%21%
1675
February1st to 15thDay
13%15%7%13%7%345%4419%
1575
16th to endDay
16%16%5%9%5%35%33426%
1464
March1st to 15thDay
16%11%5%8%7%44446%27%
1944
16th to endDay
14%10%46%433445%38%
2129
April1st to 15thDay
22%10%45%43334431%
2152
16th to endDay
20%8%25%433346%37%
2289
May1st to 15thDay
19%8%36%5%3435%6%33%
2457
16th to endDay
15%5%25%5%35%46%6%38%
2618
June1st to 15thDay
21%6%36%5%35%45%7%29%
2520
16th to endDay
16%6%35%5%46%5%5%9%32%
2520
July1st to 15thDay
12%5%25%6%35%5%6%8%37%
2520
16th to endDay
10%6%26%7%36%6%7%8%33%
2636
August1st to 15thDay
11%6%26%6%36%6%6%8%33%
2340
16th to endDay
13%6%25%5%445%6%7%37%
2390
September1st to 15thDay
16%6%25%5%3445%7%40%
2160
16th to endDay
14%6%25%5%34346%42%
1967
October1st to 15thDay
23%7%35%6%34446%30%
1800
16th to endDay
28%11%37%5%24346%23%
1902
November1st to 15thDay
18%8%36%5%445%45%32%
1585
16th to endDay
22%15%5%7%5%34445%21%
1558
December1st to 15thDay
20%19%6%10%6%2333417%
1440
16th to endDay
21%19%7%9%6%2333319%
1536
January1st to 15thNight
20%16%7%8%7%3443419%
2506
16th to endNight
14%15%6%10%7%345%45%23%
2547
February1st to 15thNight
12%14%6%10%6%36%5%45%23%
2278
16th to endNight
15%13%37%6%35%45%6%28%
2009
March1st to 15thNight
18%10%47%5%3444430%
2013
16th to endNight
14%7%35%434435%41%
2094
April1st to 15thNight
20%7%47%5%34446%32%
1796
16th to endNight
16%7%25%5%3445%6%38%
1683
May1st to 15thNight
17%6%25%5%245%46%38%
1494
16th to endNight
12%4245%35%5%5%6%43%
1495
June1st to 15thNight
16%6%34435%5%5%7%37%
1440
16th to endNight
11%5%25%6%45%45%8%39%
1440
July1st to 15thNight
9%32443445%7%50%
1440
16th to endNight
9%323335%5%7%8%46%
1529
August1st to 15thNight
9%4145%345%5%9%46%
1620
16th to endNight
7%4245%245%5%8%48%
1799
September1st to 15thNight
13%5%25%5%2435%8%44%
1800
16th to endNight
16%5%1442345%5%47%
1991
October1st to 15thNight
20%6%36%5%3435%6%34%
2160
16th to endNight
22%10%36%5%3445%6%25%
2321
November1st to 15thNight
18%8%35%5%2445%6%34%
2602
16th to endNight
21%11%46%6%3445%6%24%
2728
December1st to 15thNight
21%17%6%8%5%33346%18%
2520
16th to endNight
22%15%6%11%6%3433418%
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
63%410%13%6%
1433
16th to endDay
66%39%10%8%1
1675
February1st to 15thDay
67%5%9%13%4
1577
16th to endDay
62%38%13%11%
1464
March1st to 15thDay
57%414%15%5%1
1944
16th to endDay
47%47%20%15%3
2130
April1st to 15thDay
55%48%18%11%2
2152
16th to endDay
48%38%22%14%2
2289
May1st to 15thDay
51%48%19%14%1
2457
16th to endDay
44%6%12%21%13%1
2622
June1st to 15thDay
52%5%11%20%9%
2520
16th to endDay
48%6%12%21%11%1
2520
July1st to 15thDay
39%6%13%26%12%
2371
16th to endDay
45%6%14%23%8%
2470
August1st to 15thDay
45%8%14%19%11%
2327
16th to endDay
42%6%12%27%10%1
2390
September1st to 15thDay
43%5%12%25%12%
2160
16th to endDay
41%5%11%29%10%
1967
October1st to 15thDay
54%410%18%9%
1800
16th to endDay
62%412%14%5%
1902
November1st to 15thDay
52%5%13%17%9%1
1585
16th to endDay
62%6%12%12%5%1
1558
December1st to 15thDay
70%5%11%9%3
1440
16th to endDay
70%47%12%5%
1536
January1st to 15thNight
68%49%11%5%
2506
16th to endNight
61%5%7%15%8%
2547
February1st to 15thNight
61%411%15%6%
2287
16th to endNight
55%411%19%8%
2009
March1st to 15thNight
55%411%18%8%
2013
16th to endNight
44%49%22%16%2
2094
April1st to 15thNight
51%5%7%19%13%1
1796
16th to endNight
43%5%10%20%17%2
1683
May1st to 15thNight
44%5%10%19%15%3
1494
16th to endNight
38%6%12%24%15%2
1497
June1st to 15thNight
43%5%13%21%14%
1440
16th to endNight
41%5%15%22%13%
1440
July1st to 15thNight
29%6%11%32%19%
1360
16th to endNight
31%6%17%30%13%
1432
August1st to 15thNight
32%7%19%26%13%
1609
16th to endNight
31%6%15%31%13%1
1799
September1st to 15thNight
38%5%16%26%12%1
1800
16th to endNight
38%312%33%11%
1991
October1st to 15thNight
49%5%10%21%12%
2160
16th to endNight
58%6%11%16%6%
2321
November1st to 15thNight
49%5%14%20%9%
2602
16th to endNight
58%6%13%15%5%
2728
December1st to 15thNight
65%6%12%11%3
2520
16th to endNight
69%49%10%6%
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
26%23%30%13%6%
60
16th to endDay
39%13%32%12%2
87
February1st to 15thDay
32%25%37%4
90
16th to endDay
34%17%34%11%2
123
March1st to 15thDay
26%12%35%19%5%
270
16th to endDay
25%14%34%15%8%2
288
April1st to 15thDay
26%19%27%17%7%1
270
16th to endDay
26%15%28%17%9%2
270
May1st to 15thDay
31%10%27%15%7%7%
288
16th to endDay
18%13%38%18%8%3
331
June1st to 15thDay
25%9%33%22%8%1
315
16th to endDay
19%9%33%24%11%2
315
July1st to 15thDay
15%6%30%28%12%7%
305
16th to endDay
12%10%32%25%13%5%
326
August1st to 15thDay
11%429%30%14%9%
313
16th to endDay
17%6%24%25%14%11%
332
September1st to 15thDay
15%7%26%20%17%11%
315
16th to endDay
16%10%20%25%16%11%
314
October1st to 15thDay
24%10%29%19%11%4
315
16th to endDay
32%17%24%19%5%
331
November1st to 15thDay
25%13%32%18%8%2
149
16th to endDay
31%17%38%10%2
90
December1st to 15thDay
36%18%26%15%3
60
16th to endDay
39%29%26%4
64
January1st to 15thNight
30%18%30%15%4
720
16th to endNight
21%15%33%22%5%
768
February1st to 15thNight
22%18%37%18%2
704
16th to endNight
22%18%33%19%5%
631
March1st to 15thNight
25%18%33%19%2
720
16th to endNight
20%12%31%23%10%1
768
April1st to 15thNight
24%14%32%22%5%
718
16th to endNight
20%12%33%22%10%1
603
May1st to 15thNight
21%6%31%24%14%1
414
16th to endNight
14%6%34%33%9%
375
June1st to 15thNight
18%8%30%30%11%
360
16th to endNight
12%5%30%40%11%
360
July1st to 15thNight
7%430%39%17%1
340
16th to endNight
9%230%37%18%1
391
August1st to 15thNight
12%319%37%24%3
539
16th to endNight
9%327%29%26%2
653
September1st to 15thNight
15%5%27%28%19%3
720
16th to endNight
18%7%20%26%22%4
717
October1st to 15thNight
23%10%27%22%13%2
720
16th to endNight
30%13%30%18%6%
768
November1st to 15thNight
23%11%29%23%9%1
760
16th to endNight
29%14%30%19%5%
780
December1st to 15thNight
30%19%31%15%3
720
16th to endNight
31%14%34%15%3
768
Page generated at 2017-12-01 12:13:45. Version ac04

Copyright 2017 A. Danko


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