All-Star Telescope Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the All-Star Telescope Observing Site 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
42%
15139
13%
46716
8%
15109
46%
15109
22%
31732

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
33%
897
11%
2685
7%
895
37%
895
16%
1990
January16th to endNight
35%
834
18%
2754
11%
834
44%
834
20%
1850
February1st to 15thNight
40%
699
12%
2424
11%
696
45%
696
18%
1630
February16th to endNight
40%
632
13%
1983
12%
632
44%
632
19%
1405
March1st to 15thNight
39%
720
13%
2121
8%
720
45%
720
21%
1488
March16th to endNight
36%
768
12%
2080
5%
767
40%
767
19%
1549
April1st to 15thNight
33%
624
12%
1704
5%
624
38%
624
19%
1267
April16th to endNight
37%
540
11%
1620
8%
540
40%
540
20%
1144
May1st to 15thNight
43%
404
10%
1389
9%
404
47%
404
21%
882
May16th to endNight
47%
374
4%
1309
2%
374
49%
374
18%
890
June1st to 15thNight
43%
360
0%
1260
0%
360
43%
360
15%
909
June16th to endNight
50%
360
0%
1260
0%
360
50%
360
20%
829
July1st to 15thNight
61%
340
0%
1190
0%
340
61%
340
21%
761
July16th to endNight
63%
376
7%
1265
6%
354
65%
354
31%
704
August1st to 15thNight
61%
387
8%
1459
11%
385
62%
385
24%
866
August16th to endNight
64%
573
17%
1719
15%
573
66%
573
36%
1002
September1st to 15thNight
57%
640
17%
1749
12%
640
59%
640
35%
1068
September16th to endNight
50%
656
19%
1815
12%
656
56%
656
37%
1092
October1st to 15thNight
42%
660
16%
1953
9%
660
49%
660
23%
1327
October16th to endNight
42%
704
17%
2288
12%
704
50%
704
23%
1483
November1st to 15thNight
35%
831
18%
2409
10%
831
43%
831
24%
1617
November16th to endNight
33%
900
13%
2700
8%
900
39%
900
19%
1931
December1st to 15thNight
35%
900
12%
2700
8%
900
38%
900
16%
2003
December16th to endNight
35%
960
16%
2880
9%
960
41%
960
20%
2045

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%9%47%6%35%5%6%8%32%
47949
Night
8%9%47%6%35%5%6%8%33%
46870
TransparencyDay
47%6%17%20%7%1
47602
Night
46%5%16%21%8%1
46721
SeeingDay
15%6%25%32%16%4
6007
Night
12%428%35%16%2
15149

By Month

Percentage Cloud Cover NW (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
7%12%6%8%7%25%35%7%33%
1253
16th to endDay
6%12%5%9%6%345%6%7%30%
1480
February1st to 15thDay
8%11%48%7%36%45%9%29%
1436
16th to endDay
5%10%7%9%7%47%6%6%7%26%
1491
March1st to 15thDay
411%6%9%8%45%6%5%7%29%
1839
16th to endDay
8%15%6%9%7%36%5%6%7%23%
2138
April1st to 15thDay
10%15%6%8%7%35%5%6%7%23%
2243
16th to endDay
14%12%47%5%35%5%5%8%28%
2340
May1st to 15thDay
11%9%36%6%45%6%6%8%33%
2561
16th to endDay
20%7%36%6%36%45%8%25%
2802
June1st to 15thDay
17%8%37%6%45%5%6%7%24%
2700
16th to endDay
14%6%36%6%46%6%6%8%29%
2700
July1st to 15thDay
12%5%25%5%35%6%7%9%35%
2700
16th to endDay
9%4245%35%6%6%9%42%
2816
August1st to 15thDay
14%5%14435%5%6%8%40%
2492
16th to endDay
10%3145%25%5%6%8%46%
2483
September1st to 15thDay
14%6%24423446%46%
2097
16th to endDay
9%6%15%4345%6%8%43%
1815
October1st to 15thDay
13%9%37%436%5%6%7%32%
1677
16th to endDay
7%9%38%6%35%46%8%35%
1584
November1st to 15thDay
8%12%5%7%6%35%46%7%31%
1438
16th to endDay
6%12%6%7%6%3445%8%34%
1260
December1st to 15thDay
5%13%5%11%8%46%6%5%6%26%
1260
16th to endDay
410%410%7%46%6%6%9%28%
1344
January1st to 15thNight
5%12%6%10%8%36%6%6%7%25%
2685
16th to endNight
5%12%47%7%36%5%7%8%31%
2754
February1st to 15thNight
7%9%5%10%7%45%46%6%32%
2415
16th to endNight
413%6%8%7%46%5%5%7%30%
1983
March1st to 15thNight
5%10%47%7%46%6%6%9%29%
2121
16th to endNight
6%12%5%10%7%45%6%6%8%26%
2080
April1st to 15thNight
10%13%5%5%7%46%47%7%27%
1704
16th to endNight
12%11%38%7%45%47%6%29%
1620
May1st to 15thNight
13%8%25%5%345%7%8%34%
1388
16th to endNight
20%5%24445%46%8%31%
1309
June1st to 15thNight
18%7%35%7%37%5%6%7%27%
1260
16th to endNight
12%7%36%6%36%47%7%34%
1260
July1st to 15thNight
7%436%5%36%8%6%10%37%
1260
16th to endNight
7%4234245%7%10%47%
1351
August1st to 15thNight
10%6%246%3447%9%40%
1467
16th to endNight
7%4145%245%5%8%49%
1719
September1st to 15thNight
12%5%23423448%48%
1749
16th to endNight
10%4134245%6%8%47%
1815
October1st to 15thNight
11%9%36%6%35%45%7%37%
1953
16th to endNight
8%8%46%5%35%6%6%8%36%
2288
November1st to 15thNight
6%10%47%5%26%5%6%8%36%
2409
16th to endNight
412%5%8%7%45%5%5%7%31%
2700
December1st to 15thNight
5%12%6%10%7%5%6%5%5%6%28%
2700
16th to endNight
312%5%9%9%36%5%5%9%29%
2880

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
49%5%13%24%5%2
1253
16th to endDay
49%6%14%16%9%3
1480
February1st to 15thDay
51%5%15%17%7%1
1436
16th to endDay
53%6%15%17%6%
1491
March1st to 15thDay
51%5%17%16%7%
1839
16th to endDay
57%6%14%17%4
2139
April1st to 15thDay
56%6%14%15%6%
2243
16th to endDay
52%5%15%18%6%1
2340
May1st to 15thDay
45%5%17%20%10%
2561
16th to endDay
54%6%16%16%5%
2807
June1st to 15thDay
54%7%15%17%41
2700
16th to endDay
48%7%18%21%3
2700
July1st to 15thDay
40%8%22%22%4
2541
16th to endDay
33%8%23%25%7%
2639
August1st to 15thDay
39%8%24%22%5%
2475
16th to endDay
32%6%22%27%8%1
2483
September1st to 15thDay
38%417%22%13%3
2097
16th to endDay
36%6%14%28%11%2
1815
October1st to 15thDay
47%7%15%21%7%
1677
16th to endDay
44%5%15%25%8%
1584
November1st to 15thDay
50%5%15%19%7%1
1438
16th to endDay
47%5%18%18%8%2
1260
December1st to 15thDay
57%414%16%6%
1260
16th to endDay
50%416%17%9%1
1344
January1st to 15thNight
55%5%14%16%6%2
2685
16th to endNight
47%5%13%20%9%3
2754
February1st to 15thNight
50%414%21%8%1
2426
16th to endNight
51%5%11%18%11%1
1983
March1st to 15thNight
47%6%19%19%6%
2121
16th to endNight
53%5%14%19%5%
2083
April1st to 15thNight
53%6%13%17%8%
1704
16th to endNight
52%315%20%6%1
1620
May1st to 15thNight
43%5%16%22%10%
1389
16th to endNight
48%6%19%18%5%1
1309
June1st to 15thNight
53%7%16%16%5%
1260
16th to endNight
45%6%20%20%5%
1260
July1st to 15thNight
38%11%20%23%6%
1190
16th to endNight
29%8%23%28%9%
1265
August1st to 15thNight
37%6%24%23%6%
1459
16th to endNight
30%6%21%28%11%2
1719
September1st to 15thNight
34%416%24%14%4
1749
16th to endNight
32%5%19%26%12%4
1815
October1st to 15thNight
45%5%14%23%8%1
1953
16th to endNight
42%6%17%24%8%
2288
November1st to 15thNight
43%6%14%23%11%1
2409
16th to endNight
50%6%15%16%7%3
2700
December1st to 15thNight
55%5%13%19%4
2700
16th to endNight
51%413%22%7%
2880

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%123%30%18%11%
60
16th to endDay
14%26%25%23%10%
64
February1st to 15thDay
11%7%23%34%17%4
67
16th to endDay
14%5%23%40%14%1
150
March1st to 15thDay
8%7%42%34%6%1
270
16th to endDay
14%342%28%8%2
288
April1st to 15thDay
18%10%29%29%11%
269
16th to endDay
23%9%25%27%11%1
270
May1st to 15thDay
13%8%25%29%18%4
384
16th to endDay
21%5%17%31%20%4
517
June1st to 15thDay
19%8%24%29%14%3
495
16th to endDay
14%5%26%31%15%6%
495
July1st to 15thDay
15%318%33%23%5%
475
16th to endDay
9%322%37%19%6%
485
August1st to 15thDay
13%322%32%20%8%
315
16th to endDay
10%5%25%35%17%5%
332
September1st to 15thDay
22%424%27%15%6%
294
16th to endDay
12%10%27%33%11%4
255
October1st to 15thDay
19%8%27%30%11%2
153
16th to endDay
14%120%42%17%3
96
November1st to 15thDay
16%5%25%38%10%3
89
16th to endDay
10%10%25%23%18%13%
60
December1st to 15thDay
10%331%30%20%5%
60
16th to endDay
7%6%20%31%29%4
64
January1st to 15thNight
12%7%34%33%11%1
900
16th to endNight
11%6%34%33%11%1
834
February1st to 15thNight
10%7%26%34%18%2
704
16th to endNight
8%5%30%33%18%3
632
March1st to 15thNight
9%5%33%36%13%1
720
16th to endNight
13%428%38%12%2
768
April1st to 15thNight
16%7%28%31%14%1
624
16th to endNight
18%6%24%37%12%
540
May1st to 15thNight
15%329%33%17%
405
16th to endNight
21%219%38%16%
375
June1st to 15thNight
19%5%23%33%16%1
360
16th to endNight
13%420%38%21%1
360
July1st to 15thNight
10%216%41%28%1
340
16th to endNight
9%219%44%23%1
376
August1st to 15thNight
11%310%37%33%3
387
16th to endNight
9%217%43%26%1
573
September1st to 15thNight
15%218%35%23%4
640
16th to endNight
12%327%37%16%3
656
October1st to 15thNight
16%326%34%15%3
660
16th to endNight
12%230%40%11%1
704
November1st to 15thNight
11%7%35%32%10%2
831
16th to endNight
8%6%38%33%10%2
900
December1st to 15thNight
11%6%31%33%14%2
900
16th to endNight
9%434%35%13%3
960
Page generated at 2017-09-11 17:35:19. Version ac04

Copyright 2017 A. Danko


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