Astro Hut
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Astro Hut 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
32%
15941
13%
46743
9%
15899
36%
15899
17%
34275

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
11%
900
5%
2506
1%
895
14%
895
6%
2194
January16th to endNight
12%
960
4%
2688
1%
960
14%
960
5%
2403
February1st to 15thNight
14%
730
6%
2194
1%
730
19%
730
7%
1851
February16th to endNight
19%
631
11%
1893
5%
631
24%
631
10%
1521
March1st to 15thNight
27%
720
13%
2151
9%
720
32%
720
16%
1577
March16th to endNight
28%
705
17%
2049
10%
705
35%
705
19%
1443
April1st to 15thNight
26%
539
13%
1797
9%
539
33%
539
17%
1247
April16th to endNight
33%
540
20%
1664
11%
540
41%
540
22%
1096
May1st to 15thNight
32%
540
15%
1620
9%
540
38%
540
20%
1126
May16th to endNight
43%
562
15%
1543
9%
561
48%
561
28%
1016
June1st to 15thNight
51%
540
16%
1440
10%
540
55%
540
33%
916
June16th to endNight
51%
540
14%
1440
10%
540
54%
540
30%
935
July1st to 15thNight
61%
510
16%
1360
11%
510
63%
510
40%
806
July16th to endNight
62%
564
20%
1417
15%
531
65%
531
37%
858
August1st to 15thNight
66%
539
21%
1584
17%
536
69%
536
35%
921
August16th to endNight
62%
573
20%
1858
18%
573
65%
573
30%
1088
September1st to 15thNight
56%
574
25%
1799
21%
574
62%
574
32%
1051
September16th to endNight
51%
657
22%
1815
15%
657
55%
657
30%
1156
October1st to 15thNight
43%
660
22%
1840
16%
660
49%
660
26%
1232
October16th to endNight
21%
704
12%
2288
7%
704
29%
704
13%
1696
November1st to 15thNight
27%
700
17%
2276
13%
700
35%
700
17%
1609
November16th to endNight
18%
720
10%
2340
7%
720
22%
720
9%
1884
December1st to 15thNight
10%
873
3%
2493
1%
873
12%
873
5%
2223
December16th to endNight
9%
960
5%
2688
1%
960
12%
960
5%
2426

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%9%46%5%34447%34%
47893
Night
16%11%5%7%5%23345%31%
46911
Cloud CoverDay
14%9%46%5%3445%7%34%
47902
Night
16%11%5%7%5%33345%31%
46916
TransparencyDay
49%5%11%20%11%1
47579
Night
54%410%18%10%1
46743
SeeingDay
17%12%29%22%12%4
5944
Night
22%11%26%26%11%1
15945

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%18%8%12%9%45%34312%
1432
16th to endDay
14%21%11%14%10%443239%
1536
February1st to 15thDay
13%15%9%15%11%5%332315%
1666
16th to endDay
15%14%6%13%7%34435%19%
1580
March1st to 15thDay
14%11%5%8%6%35%448%26%
1799
16th to endDay
16%9%46%5%34346%35%
2184
April1st to 15thDay
20%11%34434346%32%
2151
16th to endDay
16%7%25%425%45%6%39%
2295
May1st to 15thDay
18%5%35%6%2446%7%35%
2331
16th to endDay
9%425%5%35%5%5%8%44%
2570
June1st to 15thDay
10%5%2443445%8%45%
2520
16th to endDay
8%5%245%2446%9%45%
2520
July1st to 15thDay
6%3134345%5%10%50%
2520
16th to endDay
7%413435%46%9%49%
2655
August1st to 15thDay
8%4145%245%6%10%46%
2367
16th to endDay
11%425%32445%7%47%
2342
September1st to 15thDay
12%5%245%2445%7%44%
2036
16th to endDay
11%436%43445%9%40%
1815
October1st to 15thDay
18%7%25%5%34435%39%
1788
16th to endDay
27%9%346%345%45%25%
1584
November1st to 15thDay
15%14%35%4245%35%34%
1582
16th to endDay
22%20%6%8%5%24335%17%
1620
December1st to 15thDay
18%26%12%11%5%2221212%
1464
16th to endDay
22%22%9%10%5%2323410%
1536
January1st to 15thNight
21%17%9%12%9%3332313%
2506
16th to endNight
15%17%12%14%10%3333311%
2688
February1st to 15thNight
13%18%8%14%9%3333318%
2192
16th to endNight
17%13%7%11%7%4334422%
1893
March1st to 15thNight
17%11%38%5%23345%33%
2138
16th to endNight
16%8%45%5%25%446%35%
2049
April1st to 15thNight
19%9%36%43445%7%32%
1797
16th to endNight
17%6%25%424447%40%
1664
May1st to 15thNight
17%6%36%5%3445%6%35%
1620
16th to endNight
12%6%26%42445%8%41%
1541
June1st to 15thNight
10%5%145%3345%7%46%
1440
16th to endNight
7%5%25%5%35%5%6%9%42%
1440
July1st to 15thNight
6%2245%35%46%7%52%
1440
16th to endNight
8%2143245%6%10%50%
1513
August1st to 15thNight
5%3245%345%6%7%51%
1593
16th to endNight
10%425%42345%6%50%
1858
September1st to 15thNight
13%313424446%51%
1799
16th to endNight
11%5%26%5%2345%6%46%
1815
October1st to 15thNight
20%5%24423345%42%
1840
16th to endNight
27%9%46%423235%30%
2288
November1st to 15thNight
19%11%46%423436%34%
2276
16th to endNight
21%19%7%8%42323420%
2340
December1st to 15thNight
23%25%10%9%5%1322411%
2493
16th to endNight
24%23%9%11%42333310%
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
18%18%8%12%9%4443312%
1432
16th to endDay
14%21%11%14%10%443239%
1536
February1st to 15thDay
13%15%9%15%12%5%332315%
1666
16th to endDay
15%13%7%12%8%35%435%19%
1580
March1st to 15thDay
14%11%5%8%6%45%45%7%26%
1809
16th to endDay
16%9%46%5%34446%34%
2183
April1st to 15thDay
20%11%35%424346%32%
2151
16th to endDay
17%7%24425%5%46%39%
2295
May1st to 15thDay
17%6%26%5%2446%7%35%
2331
16th to endDay
9%5%15%5%35%5%5%8%43%
2570
June1st to 15thDay
10%4245%3445%8%45%
2520
16th to endDay
8%5%25%5%3446%8%45%
2520
July1st to 15thDay
6%31342446%10%50%
2520
16th to endDay
7%313435%46%9%49%
2655
August1st to 15thDay
8%41443446%10%46%
2367
16th to endDay
11%5%25%32345%8%47%
2342
September1st to 15thDay
12%5%245%2445%7%44%
2036
16th to endDay
11%5%36%42445%9%41%
1815
October1st to 15thDay
18%8%35%5%34435%39%
1788
16th to endDay
27%8%346%345%5%5%25%
1584
November1st to 15thDay
15%13%35%5%25%435%34%
1582
16th to endDay
22%20%7%8%5%24335%17%
1620
December1st to 15thDay
18%26%12%11%5%3322212%
1464
16th to endDay
22%22%10%10%5%2324410%
1536
January1st to 15thNight
21%17%9%12%9%2433313%
2506
16th to endNight
15%18%12%14%10%3333311%
2688
February1st to 15thNight
14%17%8%14%9%3333318%
2185
16th to endNight
17%13%7%11%7%4334422%
1893
March1st to 15thNight
17%11%47%5%24245%33%
2151
16th to endNight
16%8%45%5%34446%35%
2049
April1st to 15thNight
19%9%36%4245%5%7%32%
1797
16th to endNight
17%7%25%424447%40%
1664
May1st to 15thNight
17%6%37%5%24447%35%
1619
16th to endNight
12%5%26%5%2445%8%42%
1541
June1st to 15thNight
10%5%236%2446%7%46%
1440
16th to endNight
8%5%25%435%6%6%9%43%
1440
July1st to 15thNight
6%2245%3446%8%51%
1440
16th to endNight
7%2143245%6%10%50%
1513
August1st to 15thNight
5%324435%46%7%51%
1593
16th to endNight
10%425%42435%6%50%
1858
September1st to 15thNight
13%313423446%51%
1799
16th to endNight
11%5%26%5%33446%46%
1815
October1st to 15thNight
20%5%24423345%42%
1840
16th to endNight
26%10%46%423235%30%
2288
November1st to 15thNight
19%11%45%423435%34%
2276
16th to endNight
21%19%6%9%5%2324420%
2340
December1st to 15thNight
23%25%10%9%5%2222411%
2493
16th to endNight
24%23%9%10%5%2333310%
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
77%5%8%7%1
1433
16th to endDay
82%36%5%2
1536
February1st to 15thDay
76%45%10%2
1668
16th to endDay
67%6%10%12%4
1580
March1st to 15thDay
57%413%15%7%
1809
16th to endDay
50%5%12%25%6%1
2184
April1st to 15thDay
53%48%20%13%
2151
16th to endDay
44%5%12%19%13%3
2295
May1st to 15thDay
46%6%12%23%9%1
2331
16th to endDay
38%6%12%27%13%1
2574
June1st to 15thDay
36%6%10%27%18%
2520
16th to endDay
34%7%15%23%17%1
2520
July1st to 15thDay
30%5%13%26%20%3
2371
16th to endDay
30%7%12%27%18%2
2488
August1st to 15thDay
32%7%11%31%14%2
2352
16th to endDay
35%5%14%24%16%2
2342
September1st to 15thDay
38%5%11%24%16%3
2036
16th to endDay
39%5%11%28%14%
1815
October1st to 15thDay
48%38%24%13%
1788
16th to endDay
58%5%14%15%5%
1584
November1st to 15thDay
52%5%10%20%10%1
1582
16th to endDay
70%47%13%2
1620
December1st to 15thDay
80%348%2
1464
16th to endDay
77%49%6%1
1536
January1st to 15thNight
77%37%8%3
2506
16th to endNight
79%48%5%1
2688
February1st to 15thNight
72%37%10%4
2194
16th to endNight
66%38%15%4
1893
March1st to 15thNight
54%5%11%17%9%1
2151
16th to endNight
50%411%23%7%1
2049
April1st to 15thNight
50%5%9%18%15%
1797
16th to endNight
44%410%19%15%4
1664
May1st to 15thNight
49%410%22%10%2
1620
16th to endNight
39%6%12%22%15%2
1543
June1st to 15thNight
36%5%10%27%18%1
1440
16th to endNight
36%7%15%22%16%1
1440
July1st to 15thNight
29%5%13%26%20%3
1360
16th to endNight
28%8%12%25%20%3
1417
August1st to 15thNight
30%6%13%27%20%2
1584
16th to endNight
34%5%10%26%19%3
1858
September1st to 15thNight
33%410%27%19%3
1799
16th to endNight
38%5%10%27%17%1
1815
October1st to 15thNight
44%48%25%16%
1840
16th to endNight
58%312%17%7%
2288
November1st to 15thNight
53%49%19%11%1
2276
16th to endNight
68%310%14%2
2340
December1st to 15thNight
79%36%7%2
2493
16th to endNight
80%47%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
21%26%36%13%2
90
16th to endDay
32%14%39%9%4
96
February1st to 15thDay
25%41%25%5%2
90
16th to endDay
20%25%30%17%4
81
March1st to 15thDay
29%26%27%13%4
99
16th to endDay
28%14%27%19%7%2
288
April1st to 15thDay
28%14%32%17%7%
270
16th to endDay
23%15%30%15%11%3
270
May1st to 15thDay
22%16%30%18%7%4
288
16th to endDay
11%14%36%22%9%4
470
June1st to 15thDay
12%7%40%25%10%3
495
16th to endDay
12%12%35%22%13%3
495
July1st to 15thDay
7%8%33%30%13%7%
475
16th to endDay
7%431%33%15%8%
515
August1st to 15thDay
10%222%25%27%11%
340
16th to endDay
19%318%29%18%10%
332
September1st to 15thDay
14%422%28%20%8%
294
16th to endDay
13%8%20%24%25%8%
254
October1st to 15thDay
20%12%20%29%15%2
240
16th to endDay
29%22%35%12%
96
November1st to 15thDay
15%17%27%25%11%2
90
16th to endDay
36%26%26%5%4
90
December1st to 15thDay
35%33%18%8%3
90
16th to endDay
32%39%23%31
96
January1st to 15thNight
31%19%29%16%3
900
16th to endNight
24%17%32%22%2
960
February1st to 15thNight
24%19%31%19%5%
733
16th to endNight
24%19%28%22%4
631
March1st to 15thNight
24%17%25%24%7%
720
16th to endNight
19%12%33%25%7%1
705
April1st to 15thNight
23%13%30%25%5%1
539
16th to endNight
21%10%31%27%8%1
540
May1st to 15thNight
22%7%30%28%9%1
540
16th to endNight
14%6%28%34%14%
563
June1st to 15thNight
12%425%39%17%
540
16th to endNight
9%5%27%35%20%1
540
July1st to 15thNight
9%120%40%24%3
510
16th to endNight
8%218%37%28%3
564
August1st to 15thNight
6%115%44%26%5%
539
16th to endNight
12%216%33%29%5%
573
September1st to 15thNight
14%5%18%33%23%4
574
16th to endNight
15%7%19%28%22%6%
657
October1st to 15thNight
23%6%21%30%16%1
660
16th to endNight
34%14%26%17%6%
704
November1st to 15thNight
25%12%28%21%10%
700
16th to endNight
35%17%24%18%4
720
December1st to 15thNight
36%17%28%14%2
873
16th to endNight
36%18%28%13%2
960
Page generated at 2017-09-11 19:35:27. Version ac04

Copyright 2017 A. Danko


Astro Hut Clear Sky Chart | Charts Home