Astro-Physics
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Astro-Physics clear sky chart from 2005-11-05 to 2018-01-12.

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
37%
16519
17%
48358
10%
16476
44%
16476
24%
32393

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
24%
956
13%
2662
5%
951
31%
951
19%
1950
January16th to endNight
23%
960
11%
2634
4%
960
29%
960
16%
1996
February1st to 15thNight
23%
839
14%
2250
4%
839
31%
839
21%
1618
February16th to endNight
26%
631
18%
1893
8%
631
35%
631
18%
1323
March1st to 15thNight
31%
720
14%
2160
7%
720
36%
720
20%
1481
March16th to endNight
32%
586
15%
1999
11%
586
39%
586
18%
1372
April1st to 15thNight
29%
539
15%
1797
10%
539
38%
539
19%
1229
April16th to endNight
34%
540
18%
1758
12%
540
44%
540
22%
1180
May1st to 15thNight
34%
540
15%
1541
8%
540
40%
540
21%
1100
May16th to endNight
46%
563
17%
1498
9%
561
51%
561
31%
980
June1st to 15thNight
53%
540
15%
1440
9%
540
56%
540
36%
897
June16th to endNight
50%
540
16%
1440
8%
540
54%
540
32%
940
July1st to 15thNight
65%
510
17%
1360
11%
510
67%
510
42%
809
July16th to endNight
68%
564
21%
1417
15%
531
71%
531
42%
829
August1st to 15thNight
77%
539
22%
1559
22%
536
77%
536
42%
859
August16th to endNight
66%
573
20%
1910
21%
573
69%
573
33%
1079
September1st to 15thNight
61%
540
28%
1800
27%
540
67%
540
37%
960
September16th to endNight
56%
696
27%
1959
19%
696
62%
696
35%
1162
October1st to 15thNight
40%
720
22%
2113
15%
720
47%
720
29%
1334
October16th to endNight
31%
768
19%
2420
11%
768
41%
768
22%
1571
November1st to 15thNight
33%
760
22%
2471
16%
760
43%
760
25%
1533
November16th to endNight
26%
880
17%
2635
8%
880
36%
880
20%
1791
December1st to 15thNight
21%
975
12%
2730
4%
975
29%
975
16%
2063
December16th to endNight
18%
1040
10%
2912
3%
1040
25%
1040
12%
2337

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%8%36%5%3445%7%36%
48992
Night
14%7%35%424446%40%
48526
Cloud CoverDay
14%8%36%5%3445%7%36%
49000
Night
14%8%35%424446%40%
48531
TransparencyDay
46%6%13%21%11%1
48678
Night
44%5%12%22%13%1
48358
SeeingDay
16%7%26%26%16%5%
6381
Night
18%7%30%30%12%1
16522

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%12%6%6%5%35%45%7%27%
1520
16th to endDay
15%13%7%11%5%235%45%25%
1588
February1st to 15thDay
13%14%6%7%6%35%345%29%
1611
16th to endDay
14%12%38%6%24345%33%
1580
March1st to 15thDay
15%9%47%5%23347%34%
1790
16th to endDay
19%9%47%5%3435%6%31%
2235
April1st to 15thDay
19%10%5%6%5%3445%5%30%
2151
16th to endDay
21%9%25%5%2345%6%33%
2202
May1st to 15thDay
21%8%36%5%36%446%28%
2409
16th to endDay
13%6%25%5%35%5%6%7%37%
2617
June1st to 15thDay
13%5%25%5%345%6%7%40%
2520
16th to endDay
10%5%245%35%5%7%10%38%
2520
July1st to 15thDay
7%415%5%35%5%6%10%42%
2520
16th to endDay
7%5%26%5%35%5%7%8%41%
2655
August1st to 15thDay
7%425%5%35%5%6%10%43%
2390
16th to endDay
12%5%25%43445%7%44%
2292
September1st to 15thDay
13%314334338%50%
2160
16th to endDay
10%416%5%2345%8%45%
1989
October1st to 15thDay
18%7%25%423346%43%
1845
16th to endDay
19%8%25%6%3244438%
1803
November1st to 15thDay
14%8%35%4345%46%38%
1717
16th to endDay
16%11%45%5%23236%39%
1654
December1st to 15thDay
18%11%48%5%34446%28%
1560
16th to endDay
20%14%6%7%6%3444423%
1664
January1st to 15thNight
15%11%5%7%5%34345%34%
2662
16th to endNight
13%10%6%9%7%35%446%28%
2634
February1st to 15thNight
13%13%5%6%434335%36%
2248
16th to endNight
15%11%46%5%23346%35%
1893
March1st to 15thNight
16%9%35%5%24446%38%
2147
16th to endNight
18%8%345%3445%6%34%
1999
April1st to 15thNight
20%7%34424445%36%
1797
16th to endNight
20%6%25%323445%40%
1758
May1st to 15thNight
18%5%246%35%5%6%7%34%
1541
16th to endNight
10%425%425%46%10%42%
1496
June1st to 15thNight
11%3144245%5%8%48%
1440
16th to endNight
9%425%435%6%6%9%42%
1440
July1st to 15thNight
7%31431346%9%53%
1440
16th to endNight
6%322325%46%10%50%
1513
August1st to 15thNight
5%21343445%9%55%
1568
16th to endNight
8%41442445%7%50%
1910
September1st to 15thNight
8%424312345%58%
1800
16th to endNight
9%414424446%51%
1959
October1st to 15thNight
13%6%25%433336%47%
2113
16th to endNight
19%6%24323346%41%
2420
November1st to 15thNight
13%7%24424345%46%
2471
16th to endNight
18%8%35%423436%38%
2635
December1st to 15thNight
18%11%38%5%34445%30%
2730
16th to endNight
21%13%5%8%6%25%34423%
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
13%13%5%6%5%36%46%6%27%
1520
16th to endDay
14%13%7%11%6%2444425%
1588
February1st to 15thDay
13%13%5%8%5%45%445%28%
1611
16th to endDay
14%12%38%6%34346%33%
1580
March1st to 15thDay
16%9%46%5%24447%33%
1800
16th to endDay
19%8%37%6%34346%30%
2233
April1st to 15thDay
19%9%5%7%5%335%45%30%
2151
16th to endDay
21%8%36%42345%6%33%
2202
May1st to 15thDay
20%9%36%6%35%5%46%28%
2409
16th to endDay
13%6%25%6%35%6%5%7%37%
2617
June1st to 15thDay
13%425%5%35%5%6%7%40%
2520
16th to endDay
10%435%6%35%5%7%10%37%
2520
July1st to 15thDay
7%415%5%26%6%7%10%42%
2520
16th to endDay
7%5%25%5%35%6%6%9%41%
2655
August1st to 15thDay
7%425%5%35%5%7%10%42%
2390
16th to endDay
11%5%25%5%35%45%7%43%
2292
September1st to 15thDay
12%314423347%50%
2160
16th to endDay
10%425%5%2345%8%45%
1989
October1st to 15thDay
17%7%25%323446%43%
1845
16th to endDay
18%8%25%6%23445%37%
1803
November1st to 15thDay
14%8%35%5%2445%5%38%
1717
16th to endDay
17%10%36%5%23236%38%
1654
December1st to 15thDay
17%12%47%5%34446%28%
1560
16th to endDay
19%14%7%7%6%3434423%
1664
January1st to 15thNight
16%11%47%5%34345%34%
2662
16th to endNight
13%11%5%9%6%35%446%28%
2634
February1st to 15thNight
13%13%5%6%434335%36%
2241
16th to endNight
15%11%46%5%23446%35%
1893
March1st to 15thNight
16%9%35%423447%37%
2160
16th to endNight
17%9%35%5%34447%33%
1999
April1st to 15thNight
20%8%35%424445%36%
1797
16th to endNight
19%8%24423445%40%
1758
May1st to 15thNight
17%6%246%36%5%5%7%34%
1540
16th to endNight
10%5%244345%6%9%42%
1496
June1st to 15thNight
10%414425%5%5%8%47%
1440
16th to endNight
8%5%245%35%5%6%8%42%
1440
July1st to 15thNight
6%3243135%6%9%53%
1440
16th to endNight
6%4223345%7%9%50%
1513
August1st to 15thNight
5%21443435%9%55%
1568
16th to endNight
8%32443345%8%50%
1910
September1st to 15thNight
8%425%323245%58%
1800
16th to endNight
9%4145%34446%51%
1959
October1st to 15thNight
14%5%25%433336%47%
2113
16th to endNight
19%6%25%323446%41%
2420
November1st to 15thNight
13%7%35%424345%46%
2471
16th to endNight
18%8%35%5%23345%38%
2635
December1st to 15thNight
18%11%37%6%34445%29%
2730
16th to endNight
21%13%5%8%6%2443423%
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
54%6%13%16%8%
1521
16th to endDay
60%6%11%14%6%
1588
February1st to 15thDay
56%5%11%17%7%
1613
16th to endDay
52%5%10%22%7%
1580
March1st to 15thDay
49%5%14%20%8%
1800
16th to endDay
54%5%13%18%6%
2235
April1st to 15thDay
55%410%20%8%
2151
16th to endDay
51%5%11%18%10%2
2202
May1st to 15thDay
55%6%11%19%5%
2409
16th to endDay
44%7%13%20%13%1
2621
June1st to 15thDay
40%7%13%23%14%
2520
16th to endDay
38%7%15%22%14%1
2520
July1st to 15thDay
34%7%15%25%14%1
2371
16th to endDay
35%8%17%21%13%2
2488
August1st to 15thDay
34%7%14%29%12%1
2375
16th to endDay
37%6%12%25%15%1
2292
September1st to 15thDay
33%5%8%29%20%1
2160
16th to endDay
35%5%12%29%15%1
1989
October1st to 15thDay
42%411%26%14%
1845
16th to endDay
48%5%12%22%10%1
1803
November1st to 15thDay
45%5%12%22%12%1
1717
16th to endDay
48%315%25%5%
1654
December1st to 15thDay
56%5%14%16%6%
1560
16th to endDay
63%5%11%11%7%
1664
January1st to 15thNight
52%5%10%19%11%
2662
16th to endNight
56%5%13%14%8%
2634
February1st to 15thNight
51%312%20%10%1
2250
16th to endNight
49%5%12%21%8%2
1893
March1st to 15thNight
47%5%14%18%12%1
2160
16th to endNight
50%5%13%21%8%1
1999
April1st to 15thNight
48%5%9%21%14%1
1797
16th to endNight
46%5%10%22%12%3
1758
May1st to 15thNight
47%8%12%20%11%
1541
16th to endNight
36%8%14%21%16%2
1498
June1st to 15thNight
33%6%14%24%20%1
1440
16th to endNight
35%7%13%20%20%2
1440
July1st to 15thNight
26%7%14%29%19%2
1360
16th to endNight
26%7%16%28%17%3
1417
August1st to 15thNight
25%6%14%31%19%2
1559
16th to endNight
31%6%13%26%18%3
1910
September1st to 15thNight
28%49%26%27%2
1800
16th to endNight
32%5%10%32%17%1
1959
October1st to 15thNight
39%410%24%19%1
2113
16th to endNight
43%412%24%12%1
2420
November1st to 15thNight
40%410%23%17%2
2471
16th to endNight
47%414%22%10%
2635
December1st to 15thNight
56%5%10%19%7%
2730
16th to endNight
64%410%13%5%
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
21%8%33%30%5%
123
16th to endDay
22%6%31%29%8%2
96
February1st to 15thDay
18%17%41%16%5%
90
16th to endDay
25%17%24%23%8%
81
March1st to 15thDay
30%13%36%17%2
90
16th to endDay
32%6%26%20%12%1
219
April1st to 15thDay
25%8%32%22%10%1
270
16th to endDay
23%9%25%24%10%5%
270
May1st to 15thDay
24%11%27%24%8%3
366
16th to endDay
16%9%31%23%14%4
517
June1st to 15thDay
13%5%29%29%17%4
495
16th to endDay
12%6%30%29%14%5%
495
July1st to 15thDay
9%324%30%22%9%
475
16th to endDay
9%220%32%22%11%
515
August1st to 15thDay
8%318%30%26%12%
445
16th to endDay
14%314%27%26%12%
332
September1st to 15thDay
10%217%29%29%9%
315
16th to endDay
9%5%22%28%27%7%
314
October1st to 15thDay
17%8%27%23%18%2
180
16th to endDay
23%13%25%30%6%
144
November1st to 15thDay
17%8%31%20%16%5%
135
16th to endDay
32%8%36%14%8%
135
December1st to 15thDay
17%14%40%21%41
135
16th to endDay
23%16%47%11%1
144
January1st to 15thNight
21%11%36%24%5%
956
16th to endNight
17%10%37%29%5%
960
February1st to 15thNight
20%9%38%25%5%
842
16th to endNight
21%11%33%26%7%
631
March1st to 15thNight
21%8%33%29%7%
720
16th to endNight
20%9%30%27%10%
586
April1st to 15thNight
24%11%31%27%5%
539
16th to endNight
23%5%32%28%8%
540
May1st to 15thNight
20%6%32%29%10%
540
16th to endNight
12%431%36%15%
563
June1st to 15thNight
12%326%43%14%
540
16th to endNight
10%429%39%16%
540
July1st to 15thNight
8%19%43%26%2
510
16th to endNight
6%116%47%26%1
564
August1st to 15thNight
5%10%48%30%3
539
16th to endNight
10%213%38%29%4
573
September1st to 15thNight
8%320%34%28%5%
540
16th to endNight
12%421%32%26%3
696
October1st to 15thNight
15%6%30%30%15%1
720
16th to endNight
23%9%32%25%8%
768
November1st to 15thNight
18%7%36%25%10%
760
16th to endNight
21%11%33%25%6%
880
December1st to 15thNight
24%10%37%22%5%
975
16th to endNight
28%8%34%25%3
1040
Page generated at 2018-01-12 21:01:27. Version ac04

Copyright 2018 A. Danko


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