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 2017-04-28.

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%
15584
17%
45642
10%
15541
44%
15541
23%
30703

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
23%
900
13%
2506
5%
895
30%
895
18%
1849
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
40%
586
18%
1372
April1st to 15thNight
29%
539
15%
1797
10%
539
38%
539
19%
1229
April16th to endNight
35%
534
19%
1740
12%
534
45%
534
23%
1162
May1st to 15thNight
33%
495
15%
1413
9%
495
40%
495
20%
1019
May16th to endNight
48%
515
16%
1370
9%
513
53%
513
32%
888
June1st to 15thNight
50%
495
15%
1320
9%
495
53%
495
33%
844
June16th to endNight
51%
495
15%
1320
8%
495
55%
495
32%
866
July1st to 15thNight
64%
465
18%
1240
12%
465
66%
465
42%
743
July16th to endNight
68%
522
19%
1305
14%
489
71%
489
42%
769
August1st to 15thNight
76%
494
23%
1428
23%
491
77%
491
43%
784
August16th to endNight
66%
525
19%
1750
20%
525
69%
525
32%
990
September1st to 15thNight
60%
495
28%
1650
27%
495
67%
495
35%
894
September16th to endNight
55%
638
25%
1796
17%
638
60%
638
34%
1078
October1st to 15thNight
42%
660
24%
1937
17%
660
49%
660
30%
1205
October16th to endNight
31%
704
18%
2218
9%
704
41%
704
22%
1436
November1st to 15thNight
34%
700
23%
2276
16%
700
44%
700
26%
1390
November16th to endNight
26%
812
15%
2432
8%
812
34%
812
19%
1685
December1st to 15thNight
21%
900
12%
2520
4%
900
28%
900
16%
1914
December16th to endNight
19%
960
10%
2688
3%
960
25%
960
12%
2168

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%
46066
Night
14%8%35%424446%40%
45810
Cloud CoverDay
14%8%36%5%3445%7%36%
46074
Night
14%8%35%424446%39%
45815
TransparencyDay
46%6%13%21%10%1
45752
Night
44%5%12%22%13%1
45642
SeeingDay
17%7%26%26%16%6%
5360
Night
18%7%30%30%12%1
15587

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%6%46%45%6%26%
1432
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%
2167
May1st to 15thDay
22%8%36%5%36%446%26%
2207
16th to endDay
13%6%25%6%35%5%6%7%38%
2393
June1st to 15thDay
14%5%25%5%346%6%7%38%
2310
16th to endDay
11%5%245%35%5%7%10%38%
2310
July1st to 15thDay
8%415%5%35%5%6%10%42%
2310
16th to endDay
8%5%26%5%36%5%7%9%40%
2459
August1st to 15thDay
7%425%5%35%5%6%10%43%
2191
16th to endDay
12%5%2443445%7%44%
2100
September1st to 15thDay
14%314334338%48%
1980
16th to endDay
11%5%16%5%2345%8%42%
1823
October1st to 15thDay
16%7%25%422346%45%
1691
16th to endDay
19%8%25%6%3244437%
1653
November1st to 15thDay
13%8%35%4245%46%39%
1582
16th to endDay
17%11%45%5%23236%36%
1527
December1st to 15thDay
19%12%48%5%34436%27%
1440
16th to endDay
21%14%6%7%6%2444423%
1536
January1st to 15thNight
16%11%5%7%5%34445%33%
2506
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
19%6%25%323445%40%
1740
May1st to 15thNight
18%5%25%6%35%5%6%7%33%
1413
16th to endNight
11%424425%46%10%42%
1368
June1st to 15thNight
12%415%4245%5%8%45%
1320
16th to endNight
9%425%435%6%5%9%42%
1320
July1st to 15thNight
7%31431346%9%53%
1320
16th to endNight
6%422325%5%6%10%49%
1401
August1st to 15thNight
5%21333445%8%56%
1437
16th to endNight
9%42442345%7%50%
1750
September1st to 15thNight
9%424412345%57%
1650
16th to endNight
9%5%14434446%50%
1796
October1st to 15thNight
12%6%25%433346%48%
1937
16th to endNight
19%6%24323345%42%
2218
November1st to 15thNight
12%7%24424346%48%
2276
16th to endNight
19%8%35%5%24435%36%
2432
December1st to 15thNight
19%11%38%5%34445%29%
2520
16th to endNight
23%13%5%8%6%2434422%
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
13%13%5%6%5%36%46%6%26%
1432
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
20%8%36%42345%6%34%
2167
May1st to 15thDay
21%9%46%6%36%5%46%26%
2207
16th to endDay
12%5%25%6%35%6%5%7%38%
2393
June1st to 15thDay
14%5%35%5%35%5%6%7%37%
2310
16th to endDay
10%4345%35%5%7%10%38%
2310
July1st to 15thDay
7%415%5%26%6%7%9%42%
2310
16th to endDay
7%5%36%5%35%6%6%9%40%
2459
August1st to 15thDay
7%425%5%35%5%7%10%43%
2191
16th to endDay
11%5%25%5%3445%7%44%
2100
September1st to 15thDay
13%414423347%49%
1980
16th to endDay
11%5%26%5%3345%8%43%
1823
October1st to 15thDay
16%7%25%322446%45%
1691
16th to endDay
19%8%25%6%23445%36%
1653
November1st to 15thDay
13%8%36%5%245%5%5%39%
1582
16th to endDay
18%11%36%5%23236%36%
1527
December1st to 15thDay
18%13%47%5%34436%27%
1440
16th to endDay
20%14%7%8%6%3434422%
1536
January1st to 15thNight
16%11%5%7%5%34445%33%
2506
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
18%8%24423445%40%
1740
May1st to 15thNight
17%6%246%36%5%5%7%33%
1412
16th to endNight
11%5%244345%6%9%43%
1368
June1st to 15thNight
11%415%5%25%5%5%8%44%
1320
16th to endNight
8%5%245%35%5%6%8%42%
1320
July1st to 15thNight
6%32431446%9%52%
1320
16th to endNight
6%4223345%7%9%50%
1401
August1st to 15thNight
5%21333435%8%56%
1437
16th to endNight
9%42443345%8%50%
1750
September1st to 15thNight
9%425%322245%57%
1650
16th to endNight
9%4145%24446%50%
1796
October1st to 15thNight
12%5%25%433346%48%
1937
16th to endNight
19%6%25%323446%41%
2218
November1st to 15thNight
13%6%35%424245%47%
2276
16th to endNight
18%8%35%5%23345%36%
2432
December1st to 15thNight
19%12%37%6%34445%29%
2520
16th to endNight
23%13%5%8%6%2443422%
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
55%6%13%16%7%
1433
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
50%5%11%18%11%2
2167
May1st to 15thDay
57%6%12%19%5%
2207
16th to endDay
43%7%13%21%13%1
2397
June1st to 15thDay
43%8%13%22%12%
2310
16th to endDay
37%8%14%22%14%1
2310
July1st to 15thDay
35%6%15%25%15%1
2161
16th to endDay
36%8%17%21%12%2
2292
August1st to 15thDay
34%7%14%29%12%1
2176
16th to endDay
37%6%12%25%15%2
2100
September1st to 15thDay
34%6%8%29%18%1
1980
16th to endDay
38%5%11%28%14%
1823
October1st to 15thDay
41%411%27%14%
1691
16th to endDay
49%5%12%21%9%1
1653
November1st to 15thDay
44%412%23%12%1
1582
16th to endDay
51%315%23%5%
1527
December1st to 15thDay
58%414%15%5%
1440
16th to endDay
64%5%11%10%7%
1536
January1st to 15thNight
53%5%10%19%10%
2506
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
45%5%10%22%12%3
1740
May1st to 15thNight
47%8%12%19%11%
1413
16th to endNight
36%7%13%21%17%2
1370
June1st to 15thNight
35%6%14%24%17%
1320
16th to endNight
36%7%13%19%20%2
1320
July1st to 15thNight
27%6%13%29%19%2
1240
16th to endNight
26%7%17%29%16%2
1305
August1st to 15thNight
25%6%15%31%20%2
1428
16th to endNight
31%6%12%26%18%3
1750
September1st to 15thNight
30%49%27%26%1
1650
16th to endNight
33%5%10%32%17%1
1796
October1st to 15thNight
37%410%25%20%1
1937
16th to endNight
43%412%24%12%1
2218
November1st to 15thNight
38%410%23%18%3
2276
16th to endNight
49%414%20%10%
2432
December1st to 15thNight
57%5%10%18%7%
2520
16th to endNight
65%410%13%5%
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%8%32%28%4
90
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
21%10%26%24%11%5%
259
May1st to 15thDay
26%11%28%22%7%3
299
16th to endDay
15%8%30%25%15%4
437
June1st to 15thDay
15%6%30%27%15%4
420
16th to endDay
12%6%27%30%16%6%
420
July1st to 15thDay
10%423%30%22%10%
400
16th to endDay
10%321%31%22%10%
445
August1st to 15thDay
8%317%31%26%12%
374
16th to endDay
15%311%27%29%11%
268
September1st to 15thDay
12%316%32%25%10%
255
16th to endDay
11%5%21%27%25%7%
254
October1st to 15thDay
12%8%26%25%22%3
131
16th to endDay
22%12%26%34%4
96
November1st to 15thDay
8%8%31%23%20%7%
90
16th to endDay
42%6%33%8%8%
90
December1st to 15thDay
22%10%38%23%32
90
16th to endDay
29%14%48%6%1
96
January1st to 15thNight
21%12%36%23%5%
900
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%29%8%
534
May1st to 15thNight
20%6%33%28%10%
495
16th to endNight
13%329%36%16%
515
June1st to 15thNight
13%327%40%14%
495
16th to endNight
10%427%39%17%1
495
July1st to 15thNight
8%18%43%25%2
465
16th to endNight
7%116%47%25%1
522
August1st to 15thNight
6%11%49%28%3
494
16th to endNight
10%213%38%29%4
525
September1st to 15thNight
9%320%34%27%5%
495
16th to endNight
13%421%32%25%2
638
October1st to 15thNight
14%6%30%30%16%1
660
16th to endNight
23%8%32%25%8%
704
November1st to 15thNight
17%7%36%26%11%
700
16th to endNight
22%11%32%26%6%
812
December1st to 15thNight
25%9%36%22%5%
900
16th to endNight
29%9%32%25%3
960
Page generated at 2017-04-29 08:45:00. Version ac04

Copyright 2017 A. Danko


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