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 2017-04-26.

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
48%
15155
29%
45588
20%
15110
58%
15110
38%
25073

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%
897
29%
2327
12%
895
48%
895
39%
1367
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%
528
26%
1689
17%
528
50%
528
34%
947
May1st to 15thNight
34%
495
24%
1485
14%
495
48%
495
30%
910
May16th to endNight
49%
515
25%
1540
21%
513
58%
513
38%
871
June1st to 15thNight
69%
495
26%
1485
26%
495
76%
495
53%
712
June16th to endNight
70%
495
24%
1485
26%
495
74%
495
45%
773
July1st to 15thNight
72%
465
26%
1395
28%
465
77%
465
47%
723
July16th to endNight
86%
522
29%
1468
35%
489
88%
489
54%
709
August1st to 15thNight
89%
494
39%
1475
46%
491
90%
491
62%
656
August16th to endNight
77%
525
28%
1723
32%
525
80%
525
41%
894
September1st to 15thNight
69%
495
24%
1815
29%
495
70%
495
33%
969
September16th to endNight
72%
492
33%
1815
34%
492
77%
492
41%
877
October1st to 15thNight
58%
575
35%
1895
27%
575
65%
575
43%
950
October16th to endNight
52%
704
37%
2112
22%
704
63%
704
47%
1062
November1st to 15thNight
51%
703
32%
2103
19%
703
61%
703
42%
1130
November16th to endNight
41%
900
32%
2340
16%
900
51%
900
38%
1382
December1st to 15thNight
36%
900
30%
2340
13%
900
46%
900
34%
1455
December16th to endNight
35%
960
27%
2496
12%
960
45%
960
34%
1570

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%
46064
Night
10%313313347%56%
45787
TransparencyDay
33%410%23%21%7%
45764
Night
28%39%22%23%10%
45592
SeeingDay
10%6%19%29%25%7%
4922
Night
12%6%28%34%16%1
15158

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%23312235%55%
1611
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%
2178
May1st to 15thDay
15%6%36%424346%40%
2136
16th to endDay
11%5%26%5%35%6%5%8%39%
2222
June1st to 15thDay
6%213435%45%8%53%
2145
16th to endDay
7%325%5%2445%8%51%
2145
July1st to 15thDay
6%3244245%6%9%47%
2145
16th to endDay
32145%36%6%7%10%48%
2284
August1st to 15thDay
3123225%6%9%61%
2145
16th to endDay
7%3145%35%7%8%10%42%
2124
September1st to 15thDay
12%32442445%7%48%
1815
16th to endDay
7%424422437%56%
1815
October1st to 15thDay
11%412323345%57%
1724
16th to endDay
10%31221222465%
1760
November1st to 15thDay
9%414313346%56%
1752
16th to endDay
14%42332223458%
1620
December1st to 15thDay
18%6%2332233449%
1620
16th to endDay
17%6%24312345%48%
1728
January1st to 15thNight
13%5%13312235%58%
2327
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%
1689
May1st to 15thNight
10%43442346%7%47%
1484
16th to endNight
7%42332446%9%51%
1539
June1st to 15thNight
321221335%9%64%
1485
16th to endNight
31134245%5%9%57%
1485
July1st to 15thNight
5%21332436%11%56%
1485
16th to endNight
211221346%12%60%
1576
August1st to 15thNight
112212349%71%
1485
16th to endNight
5%2143245%8%10%51%
1723
September1st to 15thNight
11%314323448%51%
1815
16th to endNight
7%313313448%58%
1815
October1st to 15thNight
9%313213336%61%
1895
16th to endNight
10%31211222467%
2112
November1st to 15thNight
8%42331223462%
2103
16th to endNight
12%423313345%56%
2340
December1st to 15thNight
14%5%23413336%51%
2340
16th to endNight
14%5%24322336%49%
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
33%27%20%28%8%
1612
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%24%5%
2178
May1st to 15thDay
44%49%17%16%7%
2136
16th to endDay
42%7%12%19%16%2
2226
June1st to 15thDay
26%7%13%29%19%3
2145
16th to endDay
30%412%27%20%3
2145
July1st to 15thDay
29%6%14%31%15%1
2006
16th to endDay
24%8%19%30%15%
2129
August1st to 15thDay
16%5%13%35%24%3
2131
16th to endDay
31%9%17%26%12%2
2124
September1st to 15thDay
33%5%13%23%16%7%
1815
16th to endDay
27%5%7%22%26%9%
1815
October1st to 15thDay
28%49%22%19%15%
1724
16th to endDay
23%26%20%30%16%
1760
November1st to 15thDay
29%49%25%22%8%
1752
16th to endDay
31%25%17%30%12%
1620
December1st to 15thDay
39%26%20%25%5%
1620
16th to endDay
39%27%22%21%7%
1728
January1st to 15thNight
31%17%17%29%12%
2327
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%10%
1689
May1st to 15thNight
35%6%11%20%17%8%
1485
16th to endNight
27%5%17%25%18%4
1541
June1st to 15thNight
17%413%34%23%6%
1485
16th to endNight
22%5%13%28%23%6%
1485
July1st to 15thNight
22%414%35%18%4
1395
16th to endNight
15%6%18%36%20%2
1468
August1st to 15thNight
12%412%32%31%6%
1475
16th to endNight
24%5%15%32%17%4
1723
September1st to 15thNight
31%412%21%19%9%
1815
16th to endNight
24%38%22%27%12%
1815
October1st to 15thNight
25%39%23%21%17%
1895
16th to endNight
23%2418%28%23%
2112
November1st to 15thNight
26%37%24%25%13%
2103
16th to endNight
30%36%13%31%14%
2340
December1st to 15thNight
35%38%19%23%9%
2340
16th to endNight
36%37%21%21%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%12%42%21%7%1
90
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%12%30%29%7%
321
May1st to 15thDay
16%13%35%25%7%1
393
16th to endDay
14%7%27%29%17%2
437
June1st to 15thDay
7%115%39%28%7%
420
16th to endDay
7%213%35%30%11%
420
July1st to 15thDay
6%212%38%34%5%
400
16th to endDay
3325%50%16%
445
August1st to 15thDay
2234%46%12%
418
16th to endDay
11%1432%37%11%
292
September1st to 15thDay
2221%44%30%
90
16th to endDay
6%220%47%23%
90
October1st to 15thDay
1121%38%31%6%
90
16th to endDay
15%413%42%21%2
96
November1st to 15thDay
21%5%26%30%13%3
90
16th to endDay
22%16%33%20%43
90
December1st to 15thDay
30%7%24%18%12%6%
90
16th to endDay
13%20%39%19%6%
96
January1st to 15thNight
16%10%31%33%8%
900
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%7%39%28%9%
528
May1st to 15thNight
10%6%43%30%7%1
495
16th to endNight
7%431%36%18%1
515
June1st to 15thNight
4219%47%25%2
495
16th to endNight
3215%45%28%4
495
July1st to 15thNight
414%44%32%3
465
16th to endNight
3444%41%4
522
August1st to 15thNight
2344%43%6%
494
16th to endNight
6%7%38%40%7%
525
September1st to 15thNight
12%19%36%35%4
495
16th to endNight
8%11%35%36%6%
492
October1st to 15thNight
11%125%33%24%4
575
16th to endNight
11%6%27%34%18%
704
November1st to 15thNight
10%5%29%35%17%1
703
16th to endNight
15%10%30%30%12%1
900
December1st to 15thNight
17%8%34%32%7%
900
16th to endNight
18%9%32%31%7%
960
Page generated at 2017-04-27 16:49:01. Version ac04

Copyright 2017 A. Danko


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