Astro Acres
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Astro Acres clear sky chart from 2005-11-05 to 2017-09-10.

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
38%
15881
17%
46756
11%
15840
44%
15840
23%
31474

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
18%
900
13%
2506
5%
895
26%
895
15%
1880
January16th to endNight
21%
960
12%
2661
5%
960
27%
960
15%
2016
February1st to 15thNight
22%
746
12%
2157
4%
746
28%
746
17%
1548
February16th to endNight
24%
631
16%
1893
7%
631
33%
631
17%
1356
March1st to 15thNight
25%
720
12%
2160
8%
720
30%
720
16%
1582
March16th to endNight
27%
654
15%
2022
8%
654
36%
654
20%
1401
April1st to 15thNight
28%
539
16%
1797
9%
539
38%
539
21%
1181
April16th to endNight
33%
540
18%
1725
12%
540
42%
540
22%
1160
May1st to 15thNight
35%
540
14%
1620
8%
540
41%
540
21%
1147
May16th to endNight
53%
561
17%
1537
11%
561
58%
561
30%
1022
June1st to 15thNight
55%
540
18%
1440
11%
540
59%
540
37%
888
June16th to endNight
54%
540
18%
1440
11%
540
58%
540
32%
923
July1st to 15thNight
61%
510
17%
1360
13%
510
64%
510
39%
824
July16th to endNight
72%
564
23%
1417
17%
531
75%
531
44%
818
August1st to 15thNight
74%
539
21%
1612
20%
536
75%
536
39%
917
August16th to endNight
68%
573
21%
1910
21%
573
71%
573
32%
1094
September1st to 15thNight
63%
550
28%
1775
27%
550
68%
550
35%
992
September16th to endNight
62%
657
28%
1815
21%
657
65%
657
37%
1080
October1st to 15thNight
53%
660
28%
1862
21%
660
58%
660
35%
1111
October16th to endNight
30%
704
18%
2250
12%
704
39%
704
21%
1470
November1st to 15thNight
33%
700
23%
2276
17%
700
44%
700
26%
1376
November16th to endNight
29%
720
17%
2340
12%
720
36%
720
18%
1598
December1st to 15thNight
21%
873
11%
2493
5%
873
27%
873
15%
1900
December16th to endNight
17%
960
10%
2688
3%
960
24%
960
11%
2190

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
14%7%36%5%3445%7%37%
47880
Night
14%8%35%5%24446%39%
46924
Cloud CoverDay
14%8%36%5%3445%7%36%
47889
Night
14%8%36%5%2445%6%39%
46929
TransparencyDay
46%6%12%20%12%2
47566
Night
45%5%11%21%14%2
46756
SeeingDay
15%6%26%26%17%7%
5893
Night
18%8%28%29%13%1
15886

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
18%15%5%7%8%44345%23%
1432
16th to endDay
14%15%8%8%6%24436%26%
1562
February1st to 15thDay
15%12%5%8%5%36%445%28%
1705
16th to endDay
15%12%5%8%5%34445%31%
1580
March1st to 15thDay
18%13%47%5%24446%28%
1790
16th to endDay
17%9%47%5%345%5%7%29%
2211
April1st to 15thDay
18%9%35%434446%36%
2151
16th to endDay
19%6%25%6%34437%34%
2235
May1st to 15thDay
21%7%26%6%3445%5%32%
2331
16th to endDay
12%5%35%5%35%45%8%38%
2575
June1st to 15thDay
10%425%435%5%5%8%43%
2520
16th to endDay
9%425%6%35%5%7%11%38%
2520
July1st to 15thDay
9%425%5%35%6%5%9%41%
2520
16th to endDay
6%325%5%35%6%7%11%41%
2655
August1st to 15thDay
8%3236%35%5%5%8%46%
2336
16th to endDay
8%5%245%35%5%5%7%44%
2292
September1st to 15thDay
12%5%2443446%6%46%
2061
16th to endDay
10%5%25%5%24348%47%
1815
October1st to 15thDay
15%6%243345%5%6%43%
1766
16th to endDay
18%7%35%6%3445%7%33%
1621
November1st to 15thDay
16%7%23422345%46%
1582
16th to endDay
18%9%45%424336%36%
1620
December1st to 15thDay
18%12%49%6%34345%26%
1464
16th to endDay
21%16%6%7%5%14436%23%
1536
January1st to 15thNight
19%13%38%5%23345%30%
2506
16th to endNight
15%12%7%8%6%34435%28%
2661
February1st to 15thNight
16%11%5%7%5%33346%33%
2155
16th to endNight
16%11%46%5%24436%32%
1893
March1st to 15thNight
17%12%46%5%3344432%
2147
16th to endNight
15%7%36%5%35%45%7%35%
2022
April1st to 15thNight
16%6%45%5%34447%37%
1797
16th to endNight
18%6%25%43435%6%38%
1725
May1st to 15thNight
20%5%26%5%2436%7%34%
1620
16th to endNight
10%326%5%3445%8%44%
1535
June1st to 15thNight
11%42342335%9%50%
1440
16th to endNight
8%5%25%5%35%5%5%9%43%
1440
July1st to 15thNight
7%3145%2445%9%51%
1440
16th to endNight
42144345%6%8%54%
1513
August1st to 15thNight
43144345%6%9%51%
1621
16th to endNight
8%315%415%45%7%50%
1910
September1st to 15thNight
12%414313247%54%
1775
16th to endNight
7%5%2432445%8%50%
1815
October1st to 15thNight
13%414323246%52%
1862
16th to endNight
18%7%26%42234441%
2250
November1st to 15thNight
13%6%3442335%6%45%
2276
16th to endNight
19%9%34434445%35%
2340
December1st to 15thNight
20%12%5%8%5%23335%29%
2493
16th to endNight
22%15%5%8%6%3434422%
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
17%15%5%7%7%4435%5%23%
1432
16th to endDay
14%15%7%8%6%24436%25%
1562
February1st to 15thDay
14%12%5%7%6%36%445%27%
1705
16th to endDay
15%12%5%8%5%34445%30%
1580
March1st to 15thDay
19%12%5%6%5%33446%28%
1800
16th to endDay
16%10%47%5%35%447%29%
2210
April1st to 15thDay
18%9%34433446%36%
2151
16th to endDay
19%6%25%6%34347%34%
2235
May1st to 15thDay
20%8%36%5%3445%5%32%
2331
16th to endDay
12%5%36%6%35%45%8%38%
2575
June1st to 15thDay
10%425%436%5%5%8%43%
2520
16th to endDay
9%425%6%35%5%7%10%37%
2520
July1st to 15thDay
9%5%25%5%25%6%5%8%41%
2520
16th to endDay
6%315%5%36%6%7%10%41%
2655
August1st to 15thDay
7%4245%46%5%5%9%45%
2336
16th to endDay
8%4246%35%6%6%7%43%
2292
September1st to 15thDay
12%424425%46%6%46%
2061
16th to endDay
9%6%25%5%25%348%47%
1815
October1st to 15thDay
14%6%15%3245%5%6%43%
1766
16th to endDay
18%7%45%6%2445%6%33%
1621
November1st to 15thDay
15%7%24422346%46%
1582
16th to endDay
18%9%45%5%23336%35%
1620
December1st to 15thDay
18%13%49%6%33345%26%
1464
16th to endDay
21%15%6%7%5%23336%22%
1536
January1st to 15thNight
18%13%38%5%2334429%
2506
16th to endNight
14%12%7%8%6%35%445%28%
2661
February1st to 15thNight
16%11%5%7%5%24346%33%
2148
16th to endNight
16%11%5%6%5%24446%32%
1893
March1st to 15thNight
17%12%45%5%3444432%
2160
16th to endNight
15%7%46%5%35%45%7%35%
2022
April1st to 15thNight
15%7%35%5%3445%7%36%
1797
16th to endNight
18%6%35%5%2435%6%38%
1725
May1st to 15thNight
19%6%35%5%3446%7%34%
1619
16th to endNight
10%426%5%3346%7%45%
1535
June1st to 15thNight
10%42342425%8%50%
1440
16th to endNight
7%5%245%35%5%6%9%43%
1440
July1st to 15thNight
7%2245%2445%9%51%
1440
16th to endNight
42145%2446%8%54%
1513
August1st to 15thNight
43144346%7%9%50%
1621
16th to endNight
8%3245%245%6%7%49%
1910
September1st to 15thNight
12%414313247%54%
1775
16th to endNight
7%5%25%42445%7%50%
1815
October1st to 15thNight
12%424323336%52%
1862
16th to endNight
17%7%26%423345%41%
2250
November1st to 15thNight
13%6%3442435%7%44%
2276
16th to endNight
19%9%34434446%35%
2340
December1st to 15thNight
20%12%5%8%5%33335%28%
2493
16th to endNight
22%15%5%7%6%3434422%
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
62%5%10%12%8%
1433
16th to endDay
60%313%15%6%
1562
February1st to 15thDay
58%412%15%7%1
1707
16th to endDay
54%5%12%20%5%
1580
March1st to 15thDay
57%413%17%6%
1800
16th to endDay
53%6%12%20%5%1
2211
April1st to 15thDay
48%5%10%20%13%
2151
16th to endDay
49%5%11%18%10%4
2235
May1st to 15thDay
52%6%11%20%8%
2331
16th to endDay
42%8%12%18%15%2
2579
June1st to 15thDay
36%8%11%23%18%2
2520
16th to endDay
39%8%13%19%16%2
2520
July1st to 15thDay
40%6%11%20%17%3
2371
16th to endDay
34%8%17%23%13%2
2488
August1st to 15thDay
33%8%14%24%17%1
2321
16th to endDay
35%8%13%22%15%4
2292
September1st to 15thDay
36%6%10%22%17%5%
2061
16th to endDay
35%6%9%25%21%2
1815
October1st to 15thDay
39%5%11%24%16%2
1766
16th to endDay
48%413%20%11%1
1621
November1st to 15thDay
39%312%23%17%3
1582
16th to endDay
50%412%22%9%
1620
December1st to 15thDay
61%410%17%6%
1464
16th to endDay
64%5%12%11%5%
1536
January1st to 15thNight
56%310%17%10%
2506
16th to endNight
58%414%15%7%
2661
February1st to 15thNight
53%413%18%8%1
2157
16th to endNight
53%412%19%9%
1893
March1st to 15thNight
53%5%10%17%10%1
2160
16th to endNight
47%6%14%20%9%1
2022
April1st to 15thNight
45%5%11%21%14%1
1797
16th to endNight
46%5%9%19%13%5%
1725
May1st to 15thNight
48%7%12%20%11%
1620
16th to endNight
37%8%12%18%18%3
1537
June1st to 15thNight
32%6%12%25%21%2
1440
16th to endNight
35%7%13%22%16%3
1440
July1st to 15thNight
30%6%15%24%19%3
1360
16th to endNight
24%7%15%29%18%3
1417
August1st to 15thNight
25%8%16%26%20%2
1612
16th to endNight
30%8%10%24%20%5%
1910
September1st to 15thNight
30%410%26%20%7%
1775
16th to endNight
31%5%8%26%24%3
1815
October1st to 15thNight
33%49%26%24%1
1862
16th to endNight
45%410%24%13%1
2250
November1st to 15thNight
38%410%23%18%4
2276
16th to endNight
50%412%22%10%
2340
December1st to 15thNight
59%410%16%9%
2493
16th to endNight
66%47%14%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
25%12%37%17%6%
90
16th to endDay
22%12%36%25%3
96
February1st to 15thDay
20%17%43%15%3
90
16th to endDay
20%12%38%18%8%1
81
March1st to 15thDay
35%13%31%18%1
90
16th to endDay
29%8%28%23%9%
264
April1st to 15thDay
23%11%29%21%11%2
270
16th to endDay
22%9%29%22%10%5%
270
May1st to 15thDay
22%10%27%22%11%4
288
16th to endDay
15%7%33%25%14%5%
475
June1st to 15thDay
11%426%32%18%6%
495
16th to endDay
12%6%30%30%15%4
495
July1st to 15thDay
11%326%26%17%14%
475
16th to endDay
6%119%32%26%13%
515
August1st to 15thDay
9%112%28%27%21%
351
16th to endDay
9%217%26%28%16%
332
September1st to 15thDay
13%414%26%33%8%
294
16th to endDay
10%6%14%28%31%9%
254
October1st to 15thDay
15%6%20%27%24%6%
206
16th to endDay
26%6%39%23%4
96
November1st to 15thDay
11%7%24%27%21%7%
90
16th to endDay
31%15%34%13%5%
90
December1st to 15thDay
18%17%37%18%6%
90
16th to endDay
22%22%42%8%3
96
January1st to 15thNight
25%15%35%18%4
900
16th to endNight
19%15%34%27%3
960
February1st to 15thNight
21%13%35%25%4
749
16th to endNight
21%11%35%25%5%
631
March1st to 15thNight
22%11%34%24%6%
720
16th to endNight
18%8%40%24%8%
654
April1st to 15thNight
18%11%37%24%7%
539
16th to endNight
21%7%33%26%10%
540
May1st to 15thNight
21%432%31%8%
540
16th to endNight
10%425%40%18%
563
June1st to 15thNight
12%223%45%15%
540
16th to endNight
10%224%43%19%
540
July1st to 15thNight
9%20%39%27%2
510
16th to endNight
5%14%42%33%4
564
August1st to 15thNight
412%46%30%4
539
16th to endNight
8%112%35%37%5%
573
September1st to 15thNight
14%313%38%26%3
550
16th to endNight
9%417%32%32%3
657
October1st to 15thNight
15%5%21%34%20%1
660
16th to endNight
21%13%31%24%8%
704
November1st to 15thNight
16%10%35%25%10%2
700
16th to endNight
22%13%30%24%8%
720
December1st to 15thNight
27%10%32%23%5%
873
16th to endNight
30%12%30%22%3
960
Page generated at 2017-09-11 18:35:29. Version ac04

Copyright 2017 A. Danko


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