Eielson Visitor Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eielson Visitor Center clear sky chart from 2005-11-05 to 2018-04-23.

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
50%
13903
11%
49183
10%
13879
52%
13879
18%
32657

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
53%
866
14%
3493
12%
866
58%
866
21%
2081
January16th to endNight
54%
911
17%
3496
14%
911
58%
911
22%
2099
February1st to 15thNight
55%
806
20%
2919
17%
803
59%
803
28%
1614
February16th to endNight
40%
671
13%
2341
9%
671
45%
671
17%
1520
March1st to 15thNight
58%
630
20%
2389
20%
630
63%
630
24%
1354
March16th to endNight
66%
641
18%
2171
19%
641
68%
641
29%
1255
April1st to 15thNight
49%
584
7%
1738
6%
584
50%
584
22%
1177
April16th to endNight
62%
516
0%
1392
0%
516
62%
516
29%
907
May1st to 15thNight
58%
357
0%
1077
0%
357
58%
357
19%
767
May16th to endNight
61%
188
0%
767
0%
187
61%
187
17%
503
June1st to 15thNight
47%
180
0%
639
0%
180
47%
180
11%
493
June16th to endNight
52%
180
0%
419
0%
180
52%
180
13%
364
July1st to 15thNight
45%
170
0%
638
0%
170
45%
170
8%
502
July16th to endNight
39%
277
0%
812
0%
259
40%
259
8%
683
August1st to 15thNight
41%
358
0%
1096
0%
356
41%
356
10%
902
August16th to endNight
37%
550
0%
1505
0%
550
37%
550
11%
1249
September1st to 15thNight
43%
540
3%
1716
2%
540
44%
540
13%
1314
September16th to endNight
37%
552
4%
1965
5%
552
37%
552
8%
1586
October1st to 15thNight
43%
662
9%
2237
9%
662
45%
662
14%
1634
October16th to endNight
54%
816
11%
2730
11%
816
54%
816
20%
1842
November1st to 15thNight
48%
805
9%
2989
9%
805
49%
805
16%
2044
November16th to endNight
51%
845
17%
3400
18%
845
53%
845
18%
2131
December1st to 15thNight
50%
870
14%
3510
15%
870
53%
870
17%
2240
December16th to endNight
46%
928
12%
3744
10%
928
50%
928
16%
2396

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
12%9%47%6%46%6%7%8%26%
50428
Night
47%38%7%46%6%7%9%32%
49273
TransparencyDay
52%8%17%13%5%1
50018
Night
45%7%16%16%9%3
49188
SeeingDay
16%7%17%23%23%11%
9254
Night
8%7%18%26%25%13%
13911

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
437%7%36%6%6%10%41%
776
16th to endDay
5%36%6%47%7%10%8%38%
1078
February1st to 15thDay
5%246%35%45%9%51%
1275
16th to endDay
5%311%8%48%7%8%8%33%
1418
March1st to 15thDay
439%6%47%8%7%8%37%
1901
16th to endDay
338%8%5%6%6%7%9%40%
2399
April1st to 15thDay
16%5%12%8%36%6%7%9%31%
2536
16th to endDay
29%48%6%47%6%7%8%34%
2679
May1st to 15thDay
416%5%7%5%26%5%7%9%29%
2874
16th to endDay
9%10%35%5%26%7%8%8%30%
3346
June1st to 15thDay
18%10%47%6%47%5%8%8%17%
3318
16th to endDay
24%9%37%5%35%6%6%8%18%
3538
July1st to 15thDay
27%8%37%5%35%5%6%7%18%
3282
16th to endDay
30%11%37%5%36%5%6%6%12%
3300
August1st to 15thDay
24%11%36%7%47%6%6%6%16%
2856
16th to endDay
27%15%47%6%35%5%5%5%12%
2697
September1st to 15thDay
16%11%37%7%46%6%7%8%20%
2244
16th to endDay
13%19%5%8%6%345%5%6%21%
1994
October1st to 15thDay
415%46%6%35%5%6%11%28%
1723
16th to endDay
16%410%7%46%5%7%9%35%
1493
November1st to 15thDay
19%411%9%5%6%8%6%7%30%
1199
16th to endDay
1347%8%5%7%6%6%8%38%
890
December1st to 15thDay
15%5%7%6%5%8%5%7%10%34%
780
16th to endDay
3410%5%49%7%6%12%36%
832
January1st to 15thNight
15%37%7%46%7%7%8%40%
3493
16th to endNight
439%8%5%6%7%7%10%36%
3496
February1st to 15thNight
335%6%46%6%7%8%47%
2907
16th to endNight
15%38%11%6%8%7%7%9%31%
2341
March1st to 15thNight
338%7%5%5%8%7%8%40%
2389
16th to endNight
217%8%447%7%11%43%
2171
April1st to 15thNight
6%6%11%7%36%6%7%9%32%
1738
16th to endNight
17%27%436%5%9%11%39%
1392
May1st to 15thNight
5%10%45%6%36%7%8%10%30%
1076
16th to endNight
8%8%25%316%8%10%10%32%
767
June1st to 15thNight
19%10%35%346%6%7%9%22%
639
16th to endNight
20%6%26%9%45%7%9%10%16%
419
July1st to 15thNight
24%8%45%5%36%5%8%8%19%
678
16th to endNight
28%8%38%6%5%7%5%45%16%
869
August1st to 15thNight
18%9%37%8%5%7%6%7%7%17%
1102
16th to endNight
22%12%37%6%36%5%5%6%20%
1505
September1st to 15thNight
12%9%25%7%5%8%7%9%8%23%
1716
16th to endNight
11%18%5%9%6%36%6%5%6%18%
1965
October1st to 15thNight
6%12%48%6%36%5%7%9%28%
2237
16th to endNight
29%49%7%45%6%7%9%32%
2730
November1st to 15thNight
18%410%9%5%5%6%6%9%30%
2989
16th to endNight
15%48%9%6%7%6%6%8%36%
3400
December1st to 15thNight
17%48%7%36%6%8%10%34%
3510
16th to endNight
4410%7%47%8%9%10%31%
3744

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
36%7%17%18%12%7%
776
16th to endDay
38%6%13%23%13%4
1078
February1st to 15thDay
30%415%22%17%9%
1275
16th to endDay
40%9%16%16%14%3
1418
March1st to 15thDay
37%413%19%18%6%
1901
16th to endDay
38%6%14%18%14%8%
2399
April1st to 15thDay
44%8%19%18%8%1
2536
16th to endDay
46%5%18%19%8%1
2679
May1st to 15thDay
51%8%18%16%4
2874
16th to endDay
46%9%19%19%5%
3350
June1st to 15thDay
60%8%18%9%2
3318
16th to endDay
60%10%18%9%1
3538
July1st to 15thDay
59%8%23%8%
3093
16th to endDay
70%8%16%4
3094
August1st to 15thDay
64%10%18%5%
2837
16th to endDay
71%8%12%5%1
2697
September1st to 15thDay
60%10%17%9%2
2244
16th to endDay
64%7%13%11%3
1994
October1st to 15thDay
50%8%22%10%42
1723
16th to endDay
43%9%22%18%5%1
1493
November1st to 15thDay
48%10%15%18%5%1
1199
16th to endDay
39%7%13%21%14%3
890
December1st to 15thDay
41%10%15%18%12%2
780
16th to endDay
38%8%23%19%7%3
832
January1st to 15thNight
37%7%16%20%10%7%
3493
16th to endNight
38%6%14%20%14%5%
3496
February1st to 15thNight
31%5%13%20%18%9%
2919
16th to endNight
44%7%15%16%13%2
2341
March1st to 15thNight
35%5%11%19%18%8%
2389
16th to endNight
33%6%12%22%16%9%
2176
April1st to 15thNight
42%8%15%21%9%1
1738
16th to endNight
37%7%19%23%10%1
1392
May1st to 15thNight
48%8%16%20%5%
1077
16th to endNight
41%11%19%22%4
767
June1st to 15thNight
58%10%17%12%
639
16th to endNight
62%12%14%8%1
419
July1st to 15thNight
60%11%23%4
638
16th to endNight
69%6%19%3
812
August1st to 15thNight
63%10%19%5%
1096
16th to endNight
65%7%19%5%2
1505
September1st to 15thNight
55%9%21%10%2
1716
16th to endNight
67%5%12%8%5%
1965
October1st to 15thNight
52%8%18%12%33
2237
16th to endNight
45%7%21%17%7%
2730
November1st to 15thNight
49%6%15%20%6%1
2989
16th to endNight
43%7%13%18%14%3
3400
December1st to 15thNight
43%8%15%16%14%2
3510
16th to endNight
43%9%21%15%7%3
3744

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
217%13%28%28%8%
45
16th to endDay
10%20%32%26%9%
222
February1st to 15thDay
37%20%22%28%17%
239
16th to endDay
314%34%24%15%7%
250
March1st to 15thDay
29%20%35%23%8%
285
16th to endDay
1421%28%32%11%
496
April1st to 15thDay
39%22%27%27%9%
501
16th to endDay
5%6%19%31%29%7%
474
May1st to 15thDay
13%5%21%22%21%14%
468
16th to endDay
13%6%17%24%28%8%
686
June1st to 15thDay
21%5%13%21%26%12%
705
16th to endDay
21%38%16%25%24%
793
July1st to 15thDay
26%49%16%24%17%
645
16th to endDay
34%411%22%19%7%
679
August1st to 15thDay
26%420%24%15%7%
494
16th to endDay
34%7%18%18%15%4
523
September1st to 15thDay
23%11%21%21%16%5%
460
16th to endDay
26%9%18%23%15%6%
345
October1st to 15thDay
17%11%18%24%19%8%
270
16th to endDay
7%6%13%32%20%20%
288
November1st to 15thDay
6%10%17%24%32%8%
248
16th to endDay
46%22%24%24%17%
45
December1st to 15thDay
28%17%20%26%24%
45
16th to endDay
220%14%22%29%10%
48
January1st to 15thNight
410%18%27%27%10%
870
16th to endNight
37%19%34%25%10%
911
February1st to 15thNight
28%21%28%25%13%
809
16th to endNight
5%15%26%27%19%5%
671
March1st to 15thNight
17%15%38%28%8%
630
16th to endNight
317%23%32%23%
642
April1st to 15thNight
27%19%26%27%16%
584
16th to endNight
45%15%22%34%17%
516
May1st to 15thNight
8%316%20%30%18%
357
16th to endNight
11%5%11%21%36%12%
188
June1st to 15thNight
27%29%21%27%11%
180
16th to endNight
23%45%17%27%20%
180
July1st to 15thNight
28%28%15%27%17%
170
16th to endNight
28%5%7%19%25%13%
277
August1st to 15thNight
24%215%27%22%8%
358
16th to endNight
29%5%14%18%23%10%
550
September1st to 15thNight
17%6%20%21%19%14%
540
16th to endNight
22%9%15%19%21%11%
552
October1st to 15thNight
14%9%19%19%22%14%
662
16th to endNight
6%5%15%26%27%18%
816
November1st to 15thNight
5%7%21%30%24%11%
805
16th to endNight
39%20%28%25%11%
845
December1st to 15thNight
5%8%20%24%26%14%
870
16th to endNight
28%23%30%23%11%
928
Page generated at 2018-04-24 06:02:58. Version ac04

Copyright 2018 A. Danko


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