Starry Knight Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starry Knight Observatory clear sky chart from 2005-11-05 to 2017-09-23.

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
44%
15238
12%
46856
8%
15211
47%
15211
20%
32742

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
35%
895
9%
2685
7%
895
37%
895
14%
2078
January16th to endNight
42%
858
16%
2778
11%
858
49%
858
18%
1952
February1st to 15thNight
41%
699
12%
2405
11%
696
45%
696
15%
1710
February16th to endNight
45%
632
12%
2004
12%
632
48%
632
18%
1439
March1st to 15thNight
41%
720
12%
2103
8%
720
46%
720
19%
1523
March16th to endNight
36%
767
9%
2107
4%
767
39%
767
16%
1653
April1st to 15thNight
35%
605
9%
1685
4%
605
38%
605
16%
1263
April16th to endNight
41%
540
12%
1620
10%
540
43%
540
20%
1147
May1st to 15thNight
44%
431
11%
1391
9%
431
48%
431
22%
934
May16th to endNight
41%
374
5%
1309
2%
374
43%
374
16%
914
June1st to 15thNight
40%
360
0%
1260
0%
360
40%
360
14%
918
June16th to endNight
46%
360
0%
1260
0%
360
46%
360
18%
859
July1st to 15thNight
59%
340
0%
1190
0%
340
59%
340
24%
748
July16th to endNight
65%
376
7%
1239
6%
354
66%
354
28%
722
August1st to 15thNight
62%
410
8%
1482
10%
408
63%
408
24%
903
August16th to endNight
62%
573
18%
1719
15%
573
64%
573
37%
972
September1st to 15thNight
55%
633
16%
1794
12%
633
57%
633
33%
1109
September16th to endNight
54%
688
20%
1903
14%
688
60%
688
35%
1176
October1st to 15thNight
47%
660
15%
1947
9%
660
53%
660
22%
1340
October16th to endNight
46%
704
15%
2288
11%
704
52%
704
22%
1527
November1st to 15thNight
38%
853
17%
2428
11%
853
45%
853
22%
1694
November16th to endNight
37%
900
11%
2679
7%
900
41%
900
16%
1959
December1st to 15thNight
36%
900
10%
2700
7%
900
39%
900
14%
2099
December16th to endNight
40%
960
14%
2880
9%
960
44%
960
17%
2103

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%8%37%6%35%5%6%8%33%
48091
Night
8%9%47%6%35%5%6%8%33%
47005
TransparencyDay
46%8%15%20%7%
47742
Night
47%7%14%20%7%1
46858
SeeingDay
14%5%23%31%19%5%
6077
Night
13%425%37%17%2
15250

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
8%12%5%7%7%45%5%6%6%28%
1253
16th to endDay
8%12%5%9%6%36%46%8%28%
1456
February1st to 15thDay
8%13%5%9%6%45%46%7%27%
1458
16th to endDay
6%14%7%9%8%45%5%6%8%23%
1467
March1st to 15thDay
8%10%5%11%10%46%5%6%6%25%
1857
16th to endDay
10%14%6%10%6%35%5%5%7%23%
2114
April1st to 15thDay
13%13%46%5%35%6%6%7%27%
2263
16th to endDay
15%10%46%7%35%45%7%30%
2340
May1st to 15thDay
11%7%35%5%36%5%6%8%35%
2559
16th to endDay
20%5%36%5%35%5%6%8%28%
2802
June1st to 15thDay
16%6%37%5%35%6%6%8%28%
2700
16th to endDay
12%5%35%7%46%6%7%8%33%
2700
July1st to 15thDay
9%5%25%5%35%5%7%9%40%
2700
16th to endDay
7%314425%5%7%9%46%
2844
August1st to 15thDay
11%5%2443446%9%42%
2469
16th to endDay
9%313436%5%6%8%47%
2483
September1st to 15thDay
14%6%25%423347%44%
2162
16th to endDay
10%6%2442436%9%44%
1893
October1st to 15thDay
13%8%37%6%3445%7%34%
1683
16th to endDay
7%9%36%5%36%6%47%37%
1584
November1st to 15thDay
9%13%6%9%6%245%48%28%
1419
16th to endDay
8%11%5%11%7%345%5%6%30%
1281
December1st to 15thDay
8%15%6%11%8%6%6%5%45%23%
1260
16th to endDay
411%6%11%8%48%6%6%7%24%
1344
January1st to 15thNight
7%12%6%10%9%46%5%6%7%21%
2685
16th to endNight
5%13%5%7%6%35%6%6%7%31%
2778
February1st to 15thNight
6%10%6%11%7%35%5%5%7%29%
2394
16th to endNight
6%12%5%10%7%45%5%7%9%27%
2004
March1st to 15thNight
6%10%5%9%8%45%5%7%9%27%
2103
16th to endNight
9%13%7%9%7%46%6%6%7%22%
2106
April1st to 15thNight
12%10%47%7%46%5%5%7%27%
1685
16th to endNight
12%10%36%6%345%5%7%32%
1620
May1st to 15thNight
11%8%26%6%345%6%8%35%
1390
16th to endNight
18%7%25%5%345%5%7%32%
1309
June1st to 15thNight
15%7%46%7%35%5%8%7%28%
1260
16th to endNight
12%6%36%8%45%5%6%9%33%
1260
July1st to 15thNight
7%425%7%37%6%7%10%38%
1260
16th to endNight
5%325%4345%7%9%47%
1323
August1st to 15thNight
8%5%25%5%2447%10%42%
1490
16th to endNight
7%42432436%10%50%
1719
September1st to 15thNight
12%6%23323446%49%
1794
16th to endNight
10%5%2442446%9%47%
1903
October1st to 15thNight
11%10%26%5%45%6%5%7%35%
1947
16th to endNight
8%8%37%5%35%5%6%9%36%
2288
November1st to 15thNight
7%9%5%6%6%35%5%6%7%35%
2428
16th to endNight
7%11%5%10%7%45%5%5%7%29%
2679
December1st to 15thNight
6%13%7%12%8%5%5%45%7%25%
2700
16th to endNight
5%10%6%10%7%5%6%5%5%7%28%
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
52%7%14%18%5%
1253
16th to endDay
51%6%14%15%9%2
1456
February1st to 15thDay
54%5%15%16%7%1
1458
16th to endDay
58%7%12%15%5%
1467
March1st to 15thDay
54%9%14%14%5%
1857
16th to endDay
58%7%12%16%4
2115
April1st to 15thDay
53%7%15%15%6%
2263
16th to endDay
52%7%12%17%7%1
2340
May1st to 15thDay
43%8%14%21%11%
2559
16th to endDay
51%8%14%19%5%
2807
June1st to 15thDay
51%9%14%18%5%
2700
16th to endDay
44%9%17%24%4
2700
July1st to 15thDay
37%10%20%25%5%
2541
16th to endDay
31%10%21%26%8%
2665
August1st to 15thDay
36%10%22%23%6%
2452
16th to endDay
30%8%21%28%9%1
2483
September1st to 15thDay
38%6%14%24%12%3
2162
16th to endDay
35%7%14%28%9%3
1893
October1st to 15thDay
46%7%15%22%7%
1683
16th to endDay
44%9%13%23%9%
1584
November1st to 15thDay
52%6%14%18%6%1
1419
16th to endDay
52%7%13%17%7%1
1281
December1st to 15thDay
63%6%12%13%4
1260
16th to endDay
54%8%14%15%6%
1344
January1st to 15thNight
57%8%12%14%42
2685
16th to endNight
49%7%13%18%8%2
2778
February1st to 15thNight
52%7%12%19%8%
2405
16th to endNight
51%7%13%16%10%
2004
March1st to 15thNight
50%7%17%18%5%
2103
16th to endNight
57%7%13%15%41
2109
April1st to 15thNight
54%7%14%14%8%
1685
16th to endNight
49%6%12%23%6%2
1620
May1st to 15thNight
44%7%12%22%12%1
1391
16th to endNight
50%7%13%19%7%1
1309
June1st to 15thNight
51%10%11%19%6%
1260
16th to endNight
46%9%15%22%6%
1260
July1st to 15thNight
36%10%22%22%6%
1190
16th to endNight
30%11%20%27%9%
1239
August1st to 15thNight
35%10%22%24%6%
1482
16th to endNight
27%7%19%31%11%2
1719
September1st to 15thNight
34%6%15%24%14%5%
1794
16th to endNight
33%5%15%26%14%3
1903
October1st to 15thNight
45%6%15%21%8%1
1947
16th to endNight
42%8%17%24%6%
2288
November1st to 15thNight
45%8%13%22%9%1
2428
16th to endNight
52%7%14%15%7%2
2679
December1st to 15thNight
58%8%12%17%3
2700
16th to endNight
52%6%13%19%6%
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
13%113%33%21%16%
60
16th to endDay
7%128%25%25%12%
64
February1st to 15thDay
21%221%32%18%4
71
16th to endDay
19%120%38%18%1
126
March1st to 15thDay
10%434%37%10%2
270
16th to endDay
12%5%34%30%14%2
288
April1st to 15thDay
21%9%23%32%10%2
269
16th to endDay
24%6%25%25%14%4
270
May1st to 15thDay
12%9%23%28%20%5%
408
16th to endDay
21%419%28%21%5%
517
June1st to 15thDay
16%7%24%30%16%3
495
16th to endDay
12%5%24%31%18%6%
495
July1st to 15thDay
12%118%34%24%8%
475
16th to endDay
9%322%32%25%6%
513
August1st to 15thDay
12%316%31%24%10%
315
16th to endDay
9%6%22%31%22%7%
332
September1st to 15thDay
20%6%21%28%15%6%
315
16th to endDay
11%9%26%28%18%5%
284
October1st to 15thDay
20%7%18%34%14%4
137
16th to endDay
15%316%37%21%5%
96
November1st to 15thDay
22%422%41%7%2
90
16th to endDay
9%6%28%15%28%11%
63
December1st to 15thDay
11%38%28%18%3
60
16th to endDay
9%131%23%25%9%
64
January1st to 15thNight
14%5%26%35%14%2
900
16th to endNight
12%426%39%13%3
858
February1st to 15thNight
11%6%24%34%19%3
704
16th to endNight
10%224%38%21%3
632
March1st to 15thNight
10%329%38%16%2
720
16th to endNight
14%427%37%14%1
768
April1st to 15thNight
16%8%26%31%14%2
605
16th to endNight
18%5%25%36%12%1
540
May1st to 15thNight
14%426%37%15%1
431
16th to endNight
21%425%25%21%1
375
June1st to 15thNight
21%424%32%15%2
360
16th to endNight
14%423%34%21%1
360
July1st to 15thNight
9%118%40%29%1
340
16th to endNight
6%122%42%24%2
376
August1st to 15thNight
12%14%38%30%3
410
16th to endNight
9%219%40%27%
573
September1st to 15thNight
18%217%37%21%2
633
16th to endNight
11%325%38%18%2
688
October1st to 15thNight
16%223%37%16%2
660
16th to endNight
12%424%43%14%1
704
November1st to 15thNight
12%5%33%35%10%2
853
16th to endNight
12%431%35%14%1
900
December1st to 15thNight
13%5%28%33%16%2
900
16th to endNight
10%327%38%15%4
960
Page generated at 2017-09-24 07:15:48. Version ac04

Copyright 2017 A. Danko


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