ASTROTX Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the ASTROTX Observatory 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
49%
16082
29%
48344
20%
16037
58%
16037
38%
26575

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
37%
953
29%
2472
12%
951
47%
951
38%
1460
January16th to endNight
36%
960
33%
2496
13%
960
48%
960
39%
1462
February1st to 15thNight
33%
773
27%
2178
11%
768
44%
768
32%
1300
February16th to endNight
24%
607
30%
1869
11%
607
40%
607
33%
1043
March1st to 15thNight
33%
540
27%
1980
15%
540
48%
540
26%
1131
March16th to endNight
32%
576
24%
2112
14%
576
47%
576
28%
1160
April1st to 15thNight
31%
539
26%
1965
14%
539
50%
539
31%
1020
April16th to endNight
35%
540
26%
1725
17%
540
50%
540
34%
970
May1st to 15thNight
35%
540
23%
1620
14%
540
49%
540
32%
966
May16th to endNight
47%
563
25%
1684
20%
561
58%
561
38%
949
June1st to 15thNight
69%
540
25%
1620
24%
540
76%
540
53%
783
June16th to endNight
70%
540
26%
1620
27%
540
74%
540
46%
837
July1st to 15thNight
72%
510
25%
1530
27%
510
77%
510
47%
788
July16th to endNight
87%
564
31%
1594
37%
531
89%
531
56%
757
August1st to 15thNight
87%
539
37%
1610
43%
536
88%
536
60%
734
August16th to endNight
76%
573
28%
1881
32%
573
78%
573
39%
1005
September1st to 15thNight
71%
540
23%
1980
28%
540
72%
540
35%
1025
September16th to endNight
71%
537
34%
1980
35%
537
76%
537
40%
963
October1st to 15thNight
59%
627
33%
2067
26%
627
66%
627
43%
1029
October16th to endNight
52%
768
38%
2304
22%
768
63%
768
47%
1155
November1st to 15thNight
49%
763
30%
2283
18%
763
59%
763
40%
1251
November16th to endNight
41%
975
34%
2535
16%
975
52%
975
40%
1476
December1st to 15thNight
37%
975
30%
2535
13%
975
47%
975
35%
1575
December16th to endNight
34%
1040
27%
2704
12%
1040
43%
1040
32%
1736

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
11%424423447%50%
48985
Night
10%313313347%56%
48543
TransparencyDay
33%410%23%21%7%
48685
Night
28%310%23%23%10%
48348
SeeingDay
10%6%20%29%25%7%
5932
Night
12%6%27%34%16%1
16085

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
14%5%13312335%55%
1710
16th to endDay
16%413313236%53%
1728
February1st to 15thDay
16%6%25%21223452%
1691
16th to endDay
17%41331224453%
1604
March1st to 15thDay
19%5%23323335%45%
1980
16th to endDay
13%6%25%413336%47%
2110
April1st to 15thDay
12%424423447%48%
1982
16th to endDay
14%5%2333435%7%46%
2231
May1st to 15thDay
14%6%26%424346%43%
2331
16th to endDay
11%425%5%35%6%5%8%39%
2430
June1st to 15thDay
6%313435%45%8%52%
2340
16th to endDay
6%315%5%2445%8%50%
2340
July1st to 15thDay
6%3245%245%6%9%47%
2340
16th to endDay
32135%35%6%7%10%48%
2466
August1st to 15thDay
31123235%6%9%58%
2340
16th to endDay
7%4145%35%7%8%10%42%
2318
September1st to 15thDay
11%31432445%7%50%
1980
16th to endDay
7%424423436%55%
1980
October1st to 15thDay
10%312323345%57%
1881
16th to endDay
9%21221222466%
1920
November1st to 15thDay
9%414413346%54%
1901
16th to endDay
13%32332123459%
1755
December1st to 15thDay
17%6%1332233450%
1755
16th to endDay
18%7%24312345%46%
1872
January1st to 15thNight
12%5%13312235%57%
2472
16th to endNight
13%422212235%57%
2496
February1st to 15thNight
14%42331333454%
2171
16th to endNight
14%423222235%56%
1869
March1st to 15thNight
16%424313347%48%
1980
16th to endNight
11%414223436%54%
2112
April1st to 15thNight
9%32332345%7%54%
1965
16th to endNight
13%413223346%54%
1725
May1st to 15thNight
9%42442345%7%50%
1619
16th to endNight
7%42332446%10%50%
1683
June1st to 15thNight
321221335%9%64%
1620
16th to endNight
31134235%5%9%57%
1620
July1st to 15thNight
421332436%10%56%
1620
16th to endNight
21221346%12%61%
1702
August1st to 15thNight
122212248%69%
1620
16th to endNight
5%3143245%7%10%50%
1881
September1st to 15thNight
11%313323447%53%
1980
16th to endNight
7%313313447%58%
1980
October1st to 15thNight
9%313213346%61%
2067
16th to endNight
10%21221222468%
2304
November1st to 15thNight
7%424422235%60%
2283
16th to endNight
11%42331234458%
2535
December1st to 15thNight
14%5%24413336%51%
2535
16th to endNight
16%6%24322336%48%
2704

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
33%28%20%27%7%
1711
16th to endDay
33%25%20%28%9%
1728
February1st to 15thDay
37%25%21%24%8%
1692
16th to endDay
35%27%20%21%12%
1604
March1st to 15thDay
41%36%18%21%8%
1980
16th to endDay
39%310%18%21%6%
2112
April1st to 15thDay
35%49%22%16%10%
1982
16th to endDay
37%49%18%23%6%
2231
May1st to 15thDay
42%48%17%19%7%
2331
16th to endDay
40%6%13%19%17%2
2434
June1st to 15thDay
28%7%13%29%19%3
2340
16th to endDay
30%412%27%20%3
2340
July1st to 15thDay
29%6%14%32%14%1
2201
16th to endDay
24%8%19%30%15%
2311
August1st to 15thDay
19%6%14%34%22%2
2326
16th to endDay
33%9%17%25%12%2
2318
September1st to 15thDay
32%412%25%18%6%
1980
16th to endDay
28%5%8%23%25%8%
1980
October1st to 15thDay
28%411%22%18%15%
1881
16th to endDay
23%26%18%30%18%
1920
November1st to 15thDay
31%49%24%22%8%
1901
16th to endDay
30%25%19%30%11%
1755
December1st to 15thDay
38%37%19%25%6%
1755
16th to endDay
41%26%22%19%6%
1872
January1st to 15thNight
31%27%19%28%11%
2472
16th to endNight
30%26%18%28%13%
2496
February1st to 15thNight
34%36%17%24%14%
2181
16th to endNight
32%28%20%22%13%
1869
March1st to 15thNight
36%48%17%21%11%
1980
16th to endNight
33%411%19%25%5%
2112
April1st to 15thNight
28%5%10%23%18%14%
1965
16th to endNight
31%49%21%23%9%
1725
May1st to 15thNight
33%6%11%19%20%8%
1620
16th to endNight
27%5%18%24%19%3
1685
June1st to 15thNight
17%5%13%35%22%5%
1620
16th to endNight
22%5%13%29%24%5%
1620
July1st to 15thNight
21%5%14%37%17%3
1530
16th to endNight
14%6%19%37%20%2
1594
August1st to 15thNight
13%413%32%29%5%
1610
16th to endNight
26%5%15%31%17%4
1881
September1st to 15thNight
29%411%22%21%10%
1980
16th to endNight
25%39%23%26%11%
1980
October1st to 15thNight
24%310%24%20%17%
2067
16th to endNight
22%2417%29%23%
2304
November1st to 15thNight
27%37%24%24%12%
2283
16th to endNight
29%25%15%32%13%
2535
December1st to 15thNight
35%38%18%22%10%
2535
16th to endNight
38%37%20%20%9%
2704

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%9%43%21%8%
123
16th to endDay
13%9%47%18%9%1
96
February1st to 15thDay
13%18%42%21%4
90
16th to endDay
16%24%38%17%3
81
March1st to 15thDay
26%18%30%18%41
90
16th to endDay
10%16%37%22%11%1
96
April1st to 15thDay
9%19%32%25%11%
101
16th to endDay
18%14%29%28%7%
341
May1st to 15thDay
14%13%35%26%8%1
468
16th to endDay
14%7%31%28%16%2
517
June1st to 15thDay
6%215%40%26%8%
495
16th to endDay
7%212%36%30%10%
495
July1st to 15thDay
5%112%35%36%7%
475
16th to endDay
2326%50%15%
515
August1st to 15thDay
4334%44%12%
493
16th to endDay
12%17%30%35%12%
358
September1st to 15thDay
2225%45%23%
135
16th to endDay
7%327%45%15%
135
October1st to 15thDay
122%31%33%9%
135
16th to endDay
11%7%18%38%20%4
144
November1st to 15thDay
18%332%26%13%5%
135
16th to endDay
16%14%30%25%9%2
135
December1st to 15thDay
23%8%29%22%11%4
135
16th to endDay
25%15%35%20%4
144
January1st to 15thNight
15%10%30%33%8%
956
16th to endNight
14%11%35%32%6%
960
February1st to 15thNight
18%11%34%30%5%
773
16th to endNight
16%13%43%23%3
607
March1st to 15thNight
18%10%34%30%5%
540
16th to endNight
12%11%42%27%6%
576
April1st to 15thNight
9%12%44%27%5%
539
16th to endNight
14%8%39%28%8%
540
May1st to 15thNight
10%6%42%31%7%1
540
16th to endNight
8%432%35%17%1
563
June1st to 15thNight
4119%46%25%2
540
16th to endNight
3215%46%27%3
540
July1st to 15thNight
414%43%32%3
510
16th to endNight
3444%41%5%
564
August1st to 15thNight
2344%42%6%
539
16th to endNight
7%7%37%40%6%
573
September1st to 15thNight
11%19%37%35%4
540
16th to endNight
8%12%37%35%5%
537
October1st to 15thNight
11%124%33%25%4
627
16th to endNight
11%6%28%34%18%
768
November1st to 15thNight
10%5%30%34%17%1
763
16th to endNight
14%10%31%30%12%1
975
December1st to 15thNight
17%8%33%32%7%
975
16th to endNight
20%9%31%31%6%
1040
Page generated at 2018-01-12 21:01:31. Version ac04

Copyright 2018 A. Danko


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