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 2017-09-16.

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%
12873
10%
46080
9%
12849
52%
12849
18%
30659

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
52%
776
12%
3223
10%
776
56%
776
19%
1966
January16th to endNight
53%
821
17%
3228
13%
821
57%
821
21%
1928
February1st to 15thNight
55%
731
19%
2690
17%
728
59%
728
27%
1490
February16th to endNight
41%
610
13%
2163
10%
610
45%
610
18%
1374
March1st to 15thNight
60%
570
20%
2205
21%
570
64%
570
25%
1235
March16th to endNight
67%
587
18%
2004
19%
587
69%
587
30%
1147
April1st to 15thNight
48%
539
6%
1604
5%
539
49%
539
21%
1106
April16th to endNight
62%
498
0%
1344
0%
498
62%
498
29%
884
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
36%
505
4%
1811
5%
505
36%
505
8%
1465
October1st to 15thNight
45%
595
9%
2050
9%
595
46%
595
15%
1490
October16th to endNight
54%
736
10%
2502
10%
736
54%
736
19%
1685
November1st to 15thNight
48%
730
9%
2753
9%
730
49%
730
16%
1863
November16th to endNight
50%
763
17%
3138
17%
763
53%
763
18%
1953
December1st to 15thNight
53%
780
14%
3240
16%
780
55%
780
17%
2081
December16th to endNight
46%
832
11%
3456
10%
832
48%
832
15%
2215

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%
48773
Night
47%38%7%46%7%7%9%32%
46170
TransparencyDay
53%8%18%13%5%1
48363
Night
45%8%17%16%9%2
46085
SeeingDay
17%7%17%23%23%11%
8719
Night
8%7%18%25%25%13%
12881

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
448%7%46%6%5%11%40%
716
16th to endDay
5%36%6%47%8%10%9%38%
994
February1st to 15thDay
4246%36%45%9%51%
1174
16th to endDay
4310%8%48%7%8%8%35%
1310
March1st to 15thDay
439%7%47%8%7%8%37%
1755
16th to endDay
327%8%6%7%6%7%9%39%
2214
April1st to 15thDay
15%5%13%9%47%6%7%9%29%
2340
16th to endDay
29%49%6%47%6%7%8%34%
2614
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%34446%22%
1837
October1st to 15thDay
413%46%6%35%6%6%12%29%
1580
16th to endDay
17%410%7%46%5%7%8%36%
1369
November1st to 15thDay
18%310%9%5%6%8%6%7%30%
1105
16th to endDay
1346%8%5%8%7%6%8%38%
822
December1st to 15thDay
25%5%7%6%6%7%5%7%10%34%
720
16th to endDay
3410%448%7%7%12%36%
768
January1st to 15thNight
15%38%7%47%7%7%9%37%
3223
16th to endNight
439%8%5%6%7%8%10%35%
3228
February1st to 15thNight
235%6%5%7%6%7%8%45%
2678
16th to endNight
1438%10%5%8%7%7%9%33%
2163
March1st to 15thNight
327%7%5%5%8%8%8%41%
2205
16th to endNight
216%8%448%7%11%43%
2004
April1st to 15thNight
5%6%11%8%37%6%8%10%30%
1604
16th to endNight
17%27%5%36%6%9%12%38%
1344
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
10%18%6%9%6%36%6%5%6%19%
1811
October1st to 15thNight
5%11%48%6%36%6%7%10%29%
2050
16th to endNight
29%49%7%35%6%7%9%34%
2502
November1st to 15thNight
17%49%9%5%6%7%6%10%31%
2753
16th to endNight
5%47%8%6%7%7%6%8%37%
3138
December1st to 15thNight
17%48%8%36%6%8%10%34%
3240
16th to endNight
5%410%7%47%8%9%10%31%
3456

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
38%7%17%16%12%6%
716
16th to endDay
38%7%14%24%12%2
994
February1st to 15thDay
30%416%23%18%6%
1174
16th to endDay
39%9%17%15%14%3
1310
March1st to 15thDay
36%413%19%18%7%
1755
16th to endDay
37%6%15%18%14%7%
2214
April1st to 15thDay
45%8%20%18%6%
2340
16th to endDay
46%5%18%18%8%1
2614
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%12%11%3
1837
October1st to 15thDay
48%9%24%10%43
1580
16th to endDay
44%10%21%17%41
1369
November1st to 15thDay
47%10%17%18%5%1
1105
16th to endDay
39%8%13%21%14%2
822
December1st to 15thDay
42%10%15%16%12%2
720
16th to endDay
38%8%24%19%6%2
768
January1st to 15thNight
39%8%17%18%9%6%
3223
16th to endNight
38%6%15%21%13%4
3228
February1st to 15thNight
32%6%14%22%19%5%
2690
16th to endNight
42%7%16%17%13%3
2163
March1st to 15thNight
34%5%12%19%18%8%
2205
16th to endNight
32%7%12%22%16%9%
2009
April1st to 15thNight
43%9%17%21%7%
1604
16th to endNight
37%7%20%23%10%
1344
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%6%12%8%5%
1811
October1st to 15thNight
51%9%18%12%44
2050
16th to endNight
45%7%21%16%7%
2502
November1st to 15thNight
48%7%15%21%5%1
2753
16th to endNight
42%7%13%19%14%2
3138
December1st to 15thNight
43%8%15%15%14%2
3240
16th to endNight
43%9%22%15%6%2
3456

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
320%10%30%26%10%
30
16th to endDay
11%22%31%26%7%
192
February1st to 15thDay
28%20%22%26%19%
208
16th to endDay
415%34%23%16%7%
211
March1st to 15thDay
29%21%31%24%10%
240
16th to endDay
1323%29%32%10%
433
April1st to 15thDay
39%24%26%27%8%
434
16th to endDay
5%6%20%30%29%7%
450
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
25%11%20%21%14%6%
297
October1st to 15thDay
14%12%17%24%21%9%
225
16th to endDay
7%5%13%32%20%20%
240
November1st to 15thDay
6%9%17%22%33%10%
214
16th to endDay
310%20%16%23%26%
30
December1st to 15thDay
36%20%33%36%
30
16th to endDay
321%15%15%31%12%
32
January1st to 15thNight
5%10%19%27%26%11%
780
16th to endNight
37%21%33%24%9%
821
February1st to 15thNight
18%21%27%26%13%
734
16th to endNight
415%27%25%20%6%
610
March1st to 15thNight
17%15%37%28%9%
570
16th to endNight
218%22%32%23%
588
April1st to 15thNight
27%20%25%27%17%
539
16th to endNight
46%15%22%33%17%
498
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
21%10%16%19%20%12%
505
October1st to 15thNight
12%9%19%19%23%14%
595
16th to endNight
6%6%15%26%27%17%
736
November1st to 15thNight
5%7%21%28%25%12%
730
16th to endNight
39%20%27%26%12%
763
December1st to 15thNight
5%6%19%25%27%15%
780
16th to endNight
39%22%29%22%12%
832
Page generated at 2017-09-17 08:05:40. Version ac04

Copyright 2017 A. Danko


Eielson Visitor Center Clear Sky Chart | Charts Home