Juneau
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Juneau clear sky chart from 2005-11-05 to 2018-10-08.

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
21%
15554
5%
50636
3%
15522
23%
15522
7%
42892

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
13%
825
7%
3105
5%
821
18%
821
5%
2642
January16th to endNight
13%
880
7%
3263
4%
880
17%
880
5%
2829
February1st to 15thNight
16%
809
8%
2725
4%
805
19%
805
8%
2229
February16th to endNight
23%
721
14%
2269
6%
721
30%
721
11%
1764
March1st to 15thNight
14%
780
10%
2340
4%
780
20%
780
8%
1932
March16th to endNight
27%
648
6%
2176
5%
648
29%
648
7%
1831
April1st to 15thNight
27%
584
4%
1862
4%
584
28%
584
8%
1577
April16th to endNight
27%
579
2%
1544
1%
579
28%
579
10%
1311
May1st to 15thNight
26%
440
0%
1343
0%
440
26%
440
8%
1116
May16th to endNight
47%
406
0%
1218
0%
406
47%
406
16%
913
June1st to 15thNight
32%
390
0%
1102
0%
390
32%
390
10%
928
June16th to endNight
25%
255
0%
901
0%
255
25%
255
4%
807
July1st to 15thNight
35%
370
0%
1110
0%
370
35%
370
6%
969
July16th to endNight
28%
408
0%
1158
0%
386
30%
386
8%
975
August1st to 15thNight
35%
537
0%
1410
0%
535
36%
535
10%
1204
August16th to endNight
19%
621
1%
1680
1%
621
19%
621
4%
1557
September1st to 15thNight
25%
585
5%
1950
4%
585
26%
585
6%
1682
September16th to endNight
16%
716
5%
2120
4%
716
17%
716
5%
1887
October1st to 15thNight
20%
752
6%
2307
4%
752
22%
752
6%
1993
October16th to endNight
14%
790
5%
2583
3%
790
16%
790
6%
2283
November1st to 15thNight
15%
805
4%
2818
3%
805
18%
805
6%
2447
November16th to endNight
15%
825
7%
3081
3%
825
20%
825
6%
2587
December1st to 15thNight
14%
880
8%
3175
3%
880
20%
880
7%
2614
December16th to endNight
18%
948
8%
3396
6%
948
21%
948
7%
2815

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
37%14%46%42333315%
52535
Night
36%16%46%42222317%
50756
TransparencyDay
75%38%9%3
52160
Night
74%36%9%4
50636
SeeingDay
51%5%9%16%13%3
8744
Night
51%6%13%14%10%2
15556

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
44%18%3421121316%
1164
16th to endDay
36%19%45%42332413%
1310
February1st to 15thDay
29%22%37%32222321%
1469
16th to endDay
20%21%35%423225%29%
1487
March1st to 15thDay
20%24%6%6%5%2333322%
1950
16th to endDay
20%21%5%7%7%34445%15%
2398
April1st to 15thDay
29%20%48%5%2323315%
2413
16th to endDay
29%16%46%5%34335%16%
2690
May1st to 15thDay
38%12%36%5%2433315%
2935
16th to endDay
25%8%37%6%34445%24%
3247
June1st to 15thDay
37%10%38%5%34335%14%
3185
16th to endDay
41%11%47%6%3433310%
3373
July1st to 15thDay
44%12%36%5%2332311%
3120
16th to endDay
46%11%46%42222311%
3291
August1st to 15thDay
42%9%26%42224417%
2794
16th to endDay
56%12%35%4221226%
2873
September1st to 15thDay
47%8%35%42332313%
2340
16th to endDay
51%9%36%42232212%
2169
October1st to 15thDay
44%11%37%43311214%
1822
16th to endDay
50%13%45%32211312%
1639
November1st to 15thDay
36%20%45%32122317%
1370
16th to endDay
30%22%46%42212416%
1209
December1st to 15thDay
36%19%45%211215%19%
1098
16th to endDay
32%18%45%42333318%
1189
January1st to 15thNight
41%19%3331212316%
3105
16th to endNight
38%17%5%6%42222313%
3263
February1st to 15thNight
32%18%36%42223319%
2713
16th to endNight
21%23%45%42322227%
2269
March1st to 15thNight
22%26%5%6%41322421%
2340
16th to endNight
18%21%5%9%5%35%45%416%
2171
April1st to 15thNight
27%21%46%5%2322318%
1862
16th to endNight
29%15%5%8%5%2333219%
1544
May1st to 15thNight
40%10%35%42332418%
1342
16th to endNight
24%8%26%5%245%6%6%27%
1218
June1st to 15thNight
37%11%47%412325%19%
1102
16th to endNight
42%8%48%5%443339%
901
July1st to 15thNight
42%10%45%42334414%
1170
16th to endNight
47%7%35%41223417%
1230
August1st to 15thNight
39%9%35%5%22235%21%
1416
16th to endNight
54%10%35%4222238%
1680
September1st to 15thNight
46%7%35%5%2333315%
1950
16th to endNight
54%10%35%31211213%
2120
October1st to 15thNight
46%10%36%41222315%
2307
16th to endNight
49%13%35%31222213%
2583
November1st to 15thNight
38%18%45%41322214%
2818
16th to endNight
30%20%46%42233416%
3081
December1st to 15thNight
38%17%35%31221319%
3175
16th to endNight
31%19%45%41222320%
3396

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
77%1312%41
1164
16th to endDay
76%3311%5%
1310
February1st to 15thDay
71%249%10%2
1469
16th to endDay
61%29%13%11%2
1487
March1st to 15thDay
69%35%10%8%3
1950
16th to endDay
73%36%9%7%
2398
April1st to 15thDay
75%37%10%3
2413
16th to endDay
72%411%9%2
2690
May1st to 15thDay
73%45%12%4
2935
16th to endDay
60%5%14%15%3
3251
June1st to 15thDay
74%410%8%1
3185
16th to endDay
79%410%5%
3373
July1st to 15thDay
79%410%4
2951
16th to endDay
78%411%6%
3100
August1st to 15thDay
72%411%10%1
2775
16th to endDay
87%27%2
2873
September1st to 15thDay
77%46%9%1
2340
16th to endDay
80%347%3
2169
October1st to 15thDay
79%25%6%5%
1822
16th to endDay
82%16%6%3
1639
November1st to 15thDay
76%25%11%3
1370
16th to endDay
75%35%9%4
1209
December1st to 15thDay
71%17%13%5%
1098
16th to endDay
74%247%6%4
1189
January1st to 15thNight
77%2410%5%1
3105
16th to endNight
78%249%4
3263
February1st to 15thNight
71%239%9%2
2725
16th to endNight
65%27%13%9%2
2269
March1st to 15thNight
70%229%11%2
2340
16th to endNight
72%5%7%8%5%
2176
April1st to 15thNight
73%46%11%3
1862
16th to endNight
71%411%9%2
1544
May1st to 15thNight
71%47%10%5%
1343
16th to endNight
55%6%16%19%2
1218
June1st to 15thNight
70%5%12%8%2
1102
16th to endNight
79%5%9%4
901
July1st to 15thNight
73%8%10%6%
1110
16th to endNight
72%317%5%
1158
August1st to 15thNight
69%7%13%8%
1410
16th to endNight
84%37%4
1680
September1st to 15thNight
74%5%8%9%2
1950
16th to endNight
81%246%3
2120
October1st to 15thNight
76%36%8%4
2307
16th to endNight
80%25%7%3
2583
November1st to 15thNight
78%25%9%3
2818
16th to endNight
74%35%10%5%
3081
December1st to 15thNight
72%27%10%6%
3175
16th to endNight
72%348%8%2
3396

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
46%416%18%11%2
90
16th to endDay
51%8%10%17%11%
158
February1st to 15thDay
50%9%18%14%6%
281
16th to endDay
36%10%23%21%7%1
250
March1st to 15thDay
38%13%22%20%4
285
16th to endDay
40%7%12%22%14%2
336
April1st to 15thDay
46%6%11%18%13%4
360
16th to endDay
46%7%11%16%15%3
511
May1st to 15thDay
51%5%9%18%11%4
543
16th to endDay
34%310%24%24%3
598
June1st to 15thDay
52%35%15%20%2
635
16th to endDay
47%47%17%18%5%
700
July1st to 15thDay
57%4412%16%3
550
16th to endDay
61%3411%13%5%
595
August1st to 15thDay
53%4413%18%6%
550
16th to endDay
68%4412%8%1
584
September1st to 15thDay
50%5%12%19%11%
375
16th to endDay
60%49%14%9%1
364
October1st to 15thDay
52%7%15%14%8%1
292
16th to endDay
63%5%11%13%5%
288
November1st to 15thDay
58%8%17%13%1
123
16th to endDay
58%6%8%18%6%
90
December1st to 15thDay
54%6%14%12%10%2
90
16th to endDay
48%6%10%18%14%1
96
January1st to 15thNight
56%10%16%13%3
825
16th to endNight
53%10%17%12%6%
880
February1st to 15thNight
49%9%20%15%5%
809
16th to endNight
39%11%19%21%7%
721
March1st to 15thNight
41%12%24%15%5%
780
16th to endNight
38%417%21%15%3
648
April1st to 15thNight
47%411%15%16%4
584
16th to endNight
44%5%12%18%16%3
579
May1st to 15thNight
47%6%9%14%17%4
441
16th to endNight
30%5%5%21%30%7%
407
June1st to 15thNight
46%5%212%26%5%
390
16th to endNight
48%9%5%10%20%5%
255
July1st to 15thNight
51%2115%21%7%
370
16th to endNight
56%2113%18%7%
408
August1st to 15thNight
47%4311%22%9%
537
16th to endNight
64%4313%11%2
621
September1st to 15thNight
54%47%12%16%3
585
16th to endNight
66%47%8%11%2
716
October1st to 15thNight
58%5%8%15%10%2
752
16th to endNight
65%411%11%6%
790
November1st to 15thNight
59%6%14%15%4
805
16th to endNight
51%8%19%14%4
825
December1st to 15thNight
52%7%20%14%3
880
16th to endNight
49%7%20%15%6%
948
Page generated at 2018-10-09 06:39:16. Version ac04

Copyright 2018 A. Danko


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