AST@RHO
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the AST@RHO 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
56%
15772
21%
46871
16%
15733
62%
15733
30%
28920

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
41%
717
20%
2327
13%
716
49%
716
23%
1434
January16th to endNight
38%
768
24%
2424
15%
768
49%
768
25%
1506
February1st to 15thNight
42%
701
26%
2107
16%
699
51%
699
32%
1260
February16th to endNight
37%
631
24%
1881
13%
631
48%
631
29%
1155
March1st to 15thNight
45%
720
28%
1980
15%
720
56%
720
37%
1154
March16th to endNight
48%
768
26%
2112
17%
768
56%
768
39%
1211
April1st to 15thNight
48%
718
23%
1976
13%
718
55%
718
38%
1164
April16th to endNight
55%
658
29%
1808
18%
658
63%
658
44%
996
May1st to 15thNight
66%
539
27%
1619
20%
539
72%
539
43%
855
May16th to endNight
74%
561
24%
1682
19%
561
76%
561
39%
950
June1st to 15thNight
67%
540
14%
1620
11%
540
69%
540
26%
1081
June16th to endNight
77%
540
10%
1620
9%
540
77%
540
27%
1069
July1st to 15thNight
78%
510
9%
1530
8%
510
78%
510
23%
1065
July16th to endNight
78%
564
7%
1595
7%
531
79%
531
23%
1104
August1st to 15thNight
75%
539
7%
1642
7%
536
75%
536
23%
1144
August16th to endNight
66%
669
11%
2006
12%
669
66%
669
21%
1391
September1st to 15thNight
65%
700
9%
1925
9%
700
65%
700
21%
1393
September16th to endNight
57%
657
16%
1815
14%
657
59%
657
21%
1303
October1st to 15thNight
65%
660
27%
1849
25%
660
69%
660
36%
1111
October16th to endNight
60%
704
30%
2112
27%
704
66%
704
35%
1226
November1st to 15thNight
56%
700
30%
2101
24%
700
65%
700
40%
1150
November16th to endNight
47%
720
28%
2304
20%
720
59%
720
33%
1304
December1st to 15thNight
46%
720
27%
2340
23%
720
54%
720
29%
1387
December16th to endNight
50%
768
24%
2496
21%
768
57%
768
27%
1507

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%25%6%46%6%6%8%38%
47743
Night
8%5%245%35%5%6%9%45%
47076
TransparencyDay
39%8%13%16%13%6%
47444
Night
34%7%15%19%15%7%
46879
SeeingDay
9%314%22%26%23%
5641
Night
10%419%32%25%6%
15781

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
11%6%36%5%34448%42%
1611
16th to endDay
12%5%2442435%8%45%
1799
February1st to 15thDay
15%5%34424345%47%
1750
16th to endDay
10%6%244245%5%5%48%
1592
March1st to 15thDay
9%423324447%52%
1980
16th to endDay
7%4245%23448%50%
2111
April1st to 15thDay
6%4145%25%6%6%8%48%
1972
16th to endDay
6%324435%46%8%50%
2158
May1st to 15thDay
5%3145%25%46%9%50%
2331
16th to endDay
6%325%5%47%6%7%9%41%
2431
June1st to 15thDay
9%436%7%47%7%8%10%27%
2340
16th to endDay
8%5%26%6%5%9%8%9%10%26%
2340
July1st to 15thDay
7%5%27%8%5%10%8%10%11%21%
2340
16th to endDay
6%6%38%10%6%9%8%9%10%19%
2465
August1st to 15thDay
9%6%36%9%6%9%9%10%10%17%
2304
16th to endDay
11%6%38%8%5%8%9%8%9%20%
2184
September1st to 15thDay
11%7%28%8%5%8%8%9%7%23%
1923
16th to endDay
12%8%37%7%5%6%7%7%7%26%
1815
October1st to 15thDay
8%5%37%7%35%447%41%
1779
16th to endDay
8%425%4345%46%50%
1760
November1st to 15thDay
6%415%32345%7%53%
1757
16th to endDay
9%5%25%435%35%6%49%
1653
December1st to 15thDay
10%7%25%435%35%6%45%
1620
16th to endDay
9%5%245%35%6%6%8%42%
1728
January1st to 15thNight
11%7%25%4345%5%8%41%
2327
16th to endNight
15%5%2442446%7%43%
2424
February1st to 15thNight
10%6%24424335%51%
2103
16th to endNight
10%6%2442445%6%48%
1881
March1st to 15thNight
6%4245%2445%7%52%
1980
16th to endNight
8%423424347%55%
2112
April1st to 15thNight
7%423324448%53%
1976
16th to endNight
5%21443235%8%57%
1808
May1st to 15thNight
5%21331345%8%59%
1619
16th to endNight
43143245%49%54%
1682
June1st to 15thNight
9%435%5%25%6%7%11%37%
1620
16th to endNight
5%3236%35%5%10%14%37%
1620
July1st to 15thNight
44146%5%9%8%9%13%33%
1620
16th to endNight
2425%6%48%8%9%12%32%
1703
August1st to 15thNight
5%415%6%37%8%9%13%32%
1653
16th to endNight
6%7%26%6%36%6%6%10%35%
2006
September1st to 15thNight
8%6%36%7%46%8%7%11%29%
1925
16th to endNight
11%8%36%7%346%7%10%30%
1815
October1st to 15thNight
6%4244345%5%8%49%
1849
16th to endNight
7%424423447%52%
2112
November1st to 15thNight
6%32342345%7%55%
2101
16th to endNight
7%4145%25%45%6%50%
2304
December1st to 15thNight
11%6%25%32435%8%46%
2340
16th to endNight
9%6%25%4345%5%7%44%
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
40%5%7%18%17%9%
1612
16th to endDay
36%5%8%18%21%10%
1799
February1st to 15thDay
39%46%14%20%16%
1752
16th to endDay
35%5%11%12%22%11%
1592
March1st to 15thDay
30%410%22%22%10%
1980
16th to endDay
32%5%10%22%18%10%
2112
April1st to 15thDay
30%6%11%19%22%9%
1972
16th to endDay
28%6%11%22%20%10%
2158
May1st to 15thDay
29%5%13%22%20%8%
2331
16th to endDay
34%9%14%21%15%4
2435
June1st to 15thDay
44%12%16%19%6%
2340
16th to endDay
46%13%19%15%4
2340
July1st to 15thDay
48%14%24%10%1
2201
16th to endDay
51%13%21%10%2
2310
August1st to 15thDay
51%16%22%8%1
2291
16th to endDay
51%14%20%12%1
2184
September1st to 15thDay
51%13%19%9%5%
1923
16th to endDay
51%10%11%14%8%3
1815
October1st to 15thDay
40%6%8%15%16%11%
1779
16th to endDay
33%5%8%14%23%15%
1760
November1st to 15thDay
29%410%22%20%12%
1757
16th to endDay
34%49%18%20%13%
1653
December1st to 15thDay
38%410%21%17%6%
1620
16th to endDay
35%6%13%22%13%9%
1728
January1st to 15thNight
40%5%10%18%17%8%
2327
16th to endNight
39%48%13%23%9%
2424
February1st to 15thNight
35%37%16%21%15%
2112
16th to endNight
36%5%9%15%22%10%
1881
March1st to 15thNight
29%5%11%22%20%9%
1980
16th to endNight
28%412%23%19%10%
2112
April1st to 15thNight
29%6%12%19%24%7%
1976
16th to endNight
25%412%28%19%8%
1808
May1st to 15thNight
22%6%14%27%20%8%
1620
16th to endNight
25%7%17%26%19%2
1684
June1st to 15thNight
38%11%21%23%5%
1620
16th to endNight
33%13%26%20%5%
1620
July1st to 15thNight
37%15%30%14%2
1530
16th to endNight
34%18%31%11%3
1595
August1st to 15thNight
36%17%31%13%1
1642
16th to endNight
41%12%25%16%3
2006
September1st to 15thNight
42%14%24%12%4
1925
16th to endNight
45%10%14%18%8%2
1815
October1st to 15thNight
30%7%12%18%19%10%
1849
16th to endNight
31%5%8%16%24%13%
2112
November1st to 15thNight
27%410%23%23%11%
2101
16th to endNight
31%5%9%19%18%15%
2304
December1st to 15thNight
36%49%27%14%7%
2340
16th to endNight
37%411%22%14%9%
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
15%8%38%20%11%5%
90
16th to endDay
16%15%37%19%9%1
96
February1st to 15thDay
10%21%25%23%17%2
90
16th to endDay
9%11%35%31%11%
93
March1st to 15thDay
12%9%28%30%16%1
270
16th to endDay
11%6%25%28%26%2
288
April1st to 15thDay
10%7%24%28%24%4
270
16th to endDay
5%319%30%30%10%
270
May1st to 15thDay
6%318%27%25%18%
288
16th to endDay
6%16%24%30%29%
331
June1st to 15thDay
13%15%17%28%33%
315
16th to endDay
8%212%32%43%
315
July1st to 15thDay
6%18%26%56%
305
16th to endDay
7%39%25%52%
326
August1st to 15thDay
13%413%20%47%
313
16th to endDay
9%1311%28%44%
332
September1st to 15thDay
19%315%31%29%
294
16th to endDay
14%6%17%40%21%
254
October1st to 15thDay
10%211%34%28%10%
255
16th to endDay
5%420%35%27%5%
272
November1st to 15thDay
5%420%35%27%6%
265
16th to endDay
8%427%32%22%3
123
December1st to 15thDay
5%7%47%24%13%1
90
16th to endDay
5%8%23%41%17%3
96
January1st to 15thNight
15%9%27%33%12%1
720
16th to endNight
17%9%29%32%10%
768
February1st to 15thNight
14%7%32%33%11%
704
16th to endNight
12%10%33%36%6%
631
March1st to 15thNight
8%9%31%37%11%
720
16th to endNight
10%7%29%35%17%
768
April1st to 15thNight
10%5%31%37%14%
718
16th to endNight
8%326%40%18%1
658
May1st to 15thNight
7%220%43%23%2
540
16th to endNight
6%19%39%34%7%
563
June1st to 15thNight
12%27%27%37%12%
540
16th to endNight
7%221%43%24%
540
July1st to 15thNight
5%314%45%31%
510
16th to endNight
4214%55%23%
564
August1st to 15thNight
6%211%53%24%
539
16th to endNight
11%15%19%41%20%
669
September1st to 15thNight
12%6%25%38%16%
700
16th to endNight
15%18%35%35%5%
657
October1st to 15thNight
10%13%40%31%3
660
16th to endNight
9%418%39%27%1
704
November1st to 15thNight
9%424%39%21%1
700
16th to endNight
9%6%30%36%16%1
720
December1st to 15thNight
13%6%27%36%15%
720
16th to endNight
12%8%22%37%17%1
768
Page generated at 2017-09-11 19:35:20. Version ac04

Copyright 2017 A. Danko


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