Astor
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Astor 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
57%
15914
20%
46850
15%
15874
62%
15874
28%
29831

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
42%
719
20%
2327
14%
716
52%
716
24%
1444
January16th to endNight
41%
768
23%
2478
16%
768
52%
768
27%
1508
February1st to 15thNight
40%
701
23%
2107
14%
700
50%
700
31%
1274
February16th to endNight
40%
631
24%
1827
12%
631
52%
631
30%
1128
March1st to 15thNight
48%
720
29%
1980
17%
720
58%
720
40%
1129
March16th to endNight
50%
768
25%
2112
18%
768
56%
768
39%
1232
April1st to 15thNight
52%
718
23%
1976
15%
718
59%
718
40%
1148
April16th to endNight
56%
720
27%
1824
18%
720
61%
720
42%
1090
May1st to 15thNight
68%
566
25%
1646
17%
566
73%
566
42%
915
May16th to endNight
75%
561
22%
1682
18%
561
76%
561
33%
1038
June1st to 15thNight
66%
540
13%
1620
11%
540
66%
540
23%
1118
June16th to endNight
72%
540
7%
1620
6%
540
72%
540
21%
1171
July1st to 15thNight
70%
510
8%
1530
7%
510
70%
510
22%
1107
July16th to endNight
75%
564
9%
1595
9%
531
76%
531
22%
1143
August1st to 15thNight
77%
539
7%
1609
7%
536
77%
536
22%
1143
August16th to endNight
65%
720
10%
2004
10%
720
65%
720
21%
1453
September1st to 15thNight
66%
700
9%
1925
8%
700
66%
700
19%
1425
September16th to endNight
56%
657
11%
1815
11%
657
57%
657
16%
1397
October1st to 15thNight
64%
660
25%
1889
25%
660
66%
660
31%
1181
October16th to endNight
61%
704
27%
2112
26%
704
66%
704
32%
1266
November1st to 15thNight
56%
700
26%
2101
21%
700
63%
700
32%
1253
November16th to endNight
50%
720
27%
2235
19%
720
60%
720
31%
1328
December1st to 15thNight
48%
720
26%
2340
22%
720
56%
720
27%
1431
December16th to endNight
50%
768
23%
2496
20%
768
57%
768
27%
1509

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
9%5%27%7%46%6%6%8%35%
47761
Night
8%5%25%5%35%5%6%9%43%
47055
TransparencyDay
44%9%13%15%12%5%
47462
Night
35%9%15%19%13%6%
46858
SeeingDay
10%315%22%24%23%
5761
Night
10%319%31%27%7%
15921

By Month

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
12%7%25%5%3445%8%39%
1611
16th to endDay
11%425%435%5%47%45%
1745
February1st to 15thDay
12%5%35%6%25%445%45%
1750
16th to endDay
10%5%25%5%3445%7%44%
1643
March1st to 15thDay
8%425%4345%5%7%48%
1980
16th to endDay
9%5%145%45%5%5%5%46%
2111
April1st to 15thDay
6%325%7%45%5%5%8%43%
1972
16th to endDay
7%425%6%35%5%6%8%45%
2136
May1st to 15thDay
6%5%25%5%35%6%6%7%46%
2313
16th to endDay
7%426%6%47%6%7%9%34%
2431
June1st to 15thDay
9%6%37%9%6%8%7%7%8%25%
2340
16th to endDay
8%5%38%9%5%9%8%7%9%23%
2340
July1st to 15thDay
8%7%39%9%5%9%8%8%8%21%
2340
16th to endDay
7%7%49%10%6%9%8%7%8%20%
2465
August1st to 15thDay
6%6%410%10%5%7%8%8%10%19%
2340
16th to endDay
11%7%38%9%6%9%7%7%9%20%
2179
September1st to 15thDay
9%6%39%9%6%8%7%8%10%21%
1923
16th to endDay
13%9%39%9%6%7%6%6%7%20%
1815
October1st to 15thDay
10%6%27%8%27%5%5%8%35%
1740
16th to endDay
9%5%26%5%25%5%5%7%44%
1760
November1st to 15thDay
6%5%25%5%35%5%5%8%46%
1757
16th to endDay
10%5%25%6%445%47%43%
1722
December1st to 15thDay
11%6%26%6%35%46%8%38%
1620
16th to endDay
8%5%26%5%25%5%5%8%43%
1728
January1st to 15thNight
12%6%344345%5%9%42%
2327
16th to endNight
14%42442446%7%44%
2478
February1st to 15thNight
11%5%25%423345%50%
2103
16th to endNight
8%5%145%345%6%7%48%
1827
March1st to 15thNight
6%4143235%6%8%54%
1980
16th to endNight
7%324324346%57%
2112
April1st to 15thNight
6%42332346%8%53%
1976
16th to endNight
6%3145%2436%9%53%
1824
May1st to 15thNight
5%21332345%10%55%
1646
16th to endNight
6%3135%25%6%7%9%47%
1682
June1st to 15thNight
10%425%5%36%6%7%11%34%
1620
16th to endNight
6%435%7%48%8%8%11%30%
1620
July1st to 15thNight
5%6%36%6%47%6%8%10%34%
1620
16th to endNight
4426%7%37%7%8%11%32%
1703
August1st to 15thNight
4427%6%5%6%6%10%14%32%
1620
16th to endNight
9%6%36%5%35%6%8%11%33%
2004
September1st to 15thNight
9%436%7%36%6%8%12%30%
1925
16th to endNight
11%7%37%7%46%8%6%11%23%
1815
October1st to 15thNight
6%6%245%2446%9%45%
1889
16th to endNight
9%5%2442445%7%48%
2112
November1st to 15thNight
6%425%435%45%7%48%
2101
16th to endNight
7%425%5%35%46%8%46%
2235
December1st to 15thNight
10%436%434448%46%
2340
16th to endNight
8%6%25%5%25%5%5%8%45%
2496

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
42%5%10%15%17%8%
1612
16th to endDay
38%5%8%16%20%10%
1745
February1st to 15thDay
41%46%12%19%14%
1752
16th to endDay
39%410%15%19%11%
1643
March1st to 15thDay
34%5%10%22%18%9%
1980
16th to endDay
37%6%12%17%17%8%
2112
April1st to 15thDay
35%8%10%17%21%7%
1972
16th to endDay
34%6%11%21%17%8%
2136
May1st to 15thDay
34%6%12%20%17%8%
2313
16th to endDay
39%10%15%18%13%3
2435
June1st to 15thDay
51%11%14%17%4
2340
16th to endDay
53%13%18%11%2
2340
July1st to 15thDay
54%13%18%11%1
2201
16th to endDay
54%13%18%11%1
2310
August1st to 15thDay
51%16%22%8%1
2327
16th to endDay
55%14%17%11%1
2179
September1st to 15thDay
53%15%17%10%3
1923
16th to endDay
58%12%12%9%42
1815
October1st to 15thDay
44%7%9%13%14%10%
1740
16th to endDay
38%6%7%13%22%11%
1760
November1st to 15thDay
34%6%10%18%19%9%
1757
16th to endDay
40%5%8%16%19%10%
1722
December1st to 15thDay
43%6%11%17%16%5%
1620
16th to endDay
37%7%13%20%13%8%
1728
January1st to 15thNight
38%6%10%19%15%8%
2327
16th to endNight
37%5%10%16%21%8%
2478
February1st to 15thNight
34%5%9%15%18%15%
2112
16th to endNight
34%7%13%16%19%9%
1827
March1st to 15thNight
26%6%13%27%19%7%
1980
16th to endNight
28%5%11%23%19%10%
2112
April1st to 15thNight
26%7%13%23%19%9%
1976
16th to endNight
27%6%12%26%19%7%
1824
May1st to 15thNight
24%7%17%24%18%7%
1647
16th to endNight
29%11%16%24%16%2
1684
June1st to 15thNight
39%12%19%22%4
1620
16th to endNight
41%14%22%15%5%
1620
July1st to 15thNight
42%14%26%14%2
1530
16th to endNight
39%16%26%15%2
1595
August1st to 15thNight
36%18%31%12%
1609
16th to endNight
41%15%24%17%1
2004
September1st to 15thNight
42%17%20%13%5%
1925
16th to endNight
49%14%15%13%41
1815
October1st to 15thNight
32%9%12%19%17%8%
1889
16th to endNight
33%6%10%15%23%11%
2112
November1st to 15thNight
33%6%11%19%20%8%
2101
16th to endNight
32%7%11%18%17%12%
2235
December1st to 15thNight
37%5%11%24%13%6%
2340
16th to endNight
36%6%14%21%13%8%
2496

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
17%14%32%21%10%4
90
16th to endDay
21%11%33%21%8%3
96
February1st to 15thDay
8%20%35%15%17%2
90
16th to endDay
9%14%37%26%11%1
144
March1st to 15thDay
8%10%30%30%16%3
270
16th to endDay
11%7%24%26%25%4
288
April1st to 15thDay
8%7%26%26%23%7%
270
16th to endDay
7%419%27%22%18%
270
May1st to 15thDay
7%5%15%26%27%17%
288
16th to endDay
8%28%23%30%27%
331
June1st to 15thDay
14%19%19%24%30%
315
16th to endDay
10%5%13%26%43%
315
July1st to 15thDay
6%112%24%53%
305
16th to endDay
11%15%12%26%42%
326
August1st to 15thDay
9%5%16%27%40%
313
16th to endDay
12%15%11%24%45%
332
September1st to 15thDay
13%15%14%30%34%
294
16th to endDay
15%318%29%33%
254
October1st to 15thDay
13%116%27%30%10%
255
16th to endDay
8%422%31%26%8%
272
November1st to 15thDay
6%221%29%32%7%
265
16th to endDay
13%129%29%19%6%
192
December1st to 15thDay
13%7%36%34%6%1
90
16th to endDay
8%5%17%46%17%4
96
January1st to 15thNight
12%8%30%31%15%1
720
16th to endNight
15%9%30%33%11%
768
February1st to 15thNight
12%6%35%32%10%1
704
16th to endNight
11%8%34%37%7%
631
March1st to 15thNight
8%8%31%38%12%
720
16th to endNight
8%6%30%36%16%1
768
April1st to 15thNight
9%429%37%17%
718
16th to endNight
9%326%40%20%
720
May1st to 15thNight
7%117%44%27%1
567
16th to endNight
8%8%34%40%6%
563
June1st to 15thNight
12%7%29%39%10%
540
16th to endNight
7%422%44%20%
540
July1st to 15thNight
9%315%43%27%
510
16th to endNight
5%320%49%21%
564
August1st to 15thNight
6%317%51%21%
539
16th to endNight
12%6%18%39%22%
720
September1st to 15thNight
12%5%22%40%18%
700
16th to endNight
16%7%24%39%12%
657
October1st to 15thNight
10%210%35%35%5%
660
16th to endNight
11%314%36%29%4
704
November1st to 15thNight
9%222%38%24%2
700
16th to endNight
10%329%36%18%2
720
December1st to 15thNight
12%426%33%21%1
720
16th to endNight
10%6%24%36%20%
768
Page generated at 2017-09-11 19:35:30. Version ac04

Copyright 2017 A. Danko


Astor Clear Sky Chart | Charts Home