Begich Boggs Visitor Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Begich Boggs Visitor Center clear sky chart from 2005-11-05 to 2017-09-18.

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
28%
13164
6%
46481
5%
13131
31%
13131
9%
37352

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
27%
773
9%
3117
8%
769
30%
769
9%
2417
January16th to endNight
23%
800
11%
3072
8%
800
27%
800
9%
2466
February1st to 15thNight
29%
734
7%
2573
5%
730
31%
730
9%
2083
February16th to endNight
23%
599
9%
2152
5%
599
28%
599
9%
1672
March1st to 15thNight
36%
570
12%
2163
10%
570
41%
570
14%
1522
March16th to endNight
35%
583
9%
2007
10%
583
36%
583
10%
1582
April1st to 15thNight
33%
539
5%
1664
4%
539
33%
539
11%
1349
April16th to endNight
37%
540
1%
1419
1%
540
38%
540
15%
1129
May1st to 15thNight
39%
411
0%
1132
0%
411
39%
411
14%
913
May16th to endNight
51%
270
0%
1009
0%
269
52%
269
15%
709
June1st to 15thNight
38%
180
0%
720
0%
180
38%
180
7%
600
June16th to endNight
41%
180
0%
720
0%
180
41%
180
8%
585
July1st to 15thNight
44%
172
0%
682
0%
172
44%
172
9%
539
July16th to endNight
33%
376
0%
1045
0%
354
32%
354
9%
871
August1st to 15thNight
25%
412
0%
1192
0%
410
25%
410
6%
1052
August16th to endNight
25%
573
1%
1531
1%
573
25%
573
8%
1334
September1st to 15thNight
20%
540
2%
1764
2%
540
20%
540
4%
1596
September16th to endNight
28%
505
6%
1821
6%
505
30%
505
8%
1486
October1st to 15thNight
25%
596
8%
2051
7%
596
28%
596
9%
1686
October16th to endNight
27%
736
7%
2420
5%
736
28%
736
8%
2024
November1st to 15thNight
18%
730
7%
2657
3%
730
23%
730
7%
2159
November16th to endNight
28%
750
12%
2976
8%
750
35%
750
11%
2208
December1st to 15thNight
23%
763
7%
3138
6%
763
26%
763
7%
2545
December16th to endNight
24%
832
6%
3456
5%
832
26%
832
6%
2825

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
24%16%5%8%6%34445%17%
48387
Night
19%19%5%9%6%34445%17%
46584
TransparencyDay
69%5%10%9%3
47991
Night
68%48%11%6%1
46486
SeeingDay
39%9%14%19%14%3
8433
Night
36%9%15%18%16%3
13166

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
17%18%6%10%5%2345%5%18%
821
16th to endDay
15%21%7%11%6%36%5%5%6%9%
1152
February1st to 15thDay
11%22%8%11%6%35%45%5%13%
1288
16th to endDay
9%20%410%7%45%5%6%7%17%
1320
March1st to 15thDay
6%15%5%9%7%445%5%5%28%
1797
16th to endDay
9%24%7%10%6%24446%20%
2210
April1st to 15thDay
14%21%6%9%6%34345%18%
2281
16th to endDay
11%20%6%9%6%35%45%6%21%
2541
May1st to 15thDay
17%22%5%8%5%3334421%
2817
16th to endDay
20%10%35%5%3445%6%31%
3101
June1st to 15thDay
30%12%5%7%6%2433417%
3240
16th to endDay
29%11%46%5%4445%6%17%
3240
July1st to 15thDay
24%14%5%7%7%345%45%16%
3237
16th to endDay
36%13%45%42333418%
3053
August1st to 15thDay
41%16%35%42333311%
2759
16th to endDay
43%11%26%5%2433411%
2671
September1st to 15thDay
46%14%37%5%222239%
2196
16th to endDay
39%11%46%5%2332415%
1862
October1st to 15thDay
32%18%5%7%6%2322315%
1579
16th to endDay
23%19%6%12%6%3433312%
1452
November1st to 15thDay
16%20%6%11%7%346%5%5%10%
1201
16th to endDay
15%19%7%9%6%15%6%6%7%13%
982
December1st to 15thDay
20%18%7%10%7%35%7%25%9%
819
16th to endDay
12%25%7%11%9%245%6%5%9%
768
January1st to 15thNight
14%20%6%12%5%3445%5%18%
3117
16th to endNight
14%23%7%10%5%345%6%5%12%
3072
February1st to 15thNight
11%21%6%12%7%35%5%6%414%
2561
16th to endNight
9%20%6%11%7%36%447%18%
2152
March1st to 15thNight
8%17%5%8%7%46%5%5%428%
2163
16th to endNight
8%22%8%10%5%34436%21%
2007
April1st to 15thNight
13%23%5%9%7%2433420%
1664
16th to endNight
10%21%7%7%5%34446%24%
1419
May1st to 15thNight
16%19%49%42345%5%25%
1131
16th to endNight
19%9%47%413447%31%
1008
June1st to 15thNight
30%11%46%425%5%5%5%19%
720
16th to endNight
27%12%26%5%4445%7%20%
720
July1st to 15thNight
24%11%46%44436%5%24%
722
16th to endNight
35%11%35%5%23235%21%
1116
August1st to 15thNight
39%14%37%41322316%
1198
16th to endNight
38%13%47%42223318%
1531
September1st to 15thNight
43%14%5%6%43431210%
1764
16th to endNight
39%10%26%43222319%
1821
October1st to 15thNight
31%18%36%5%2212419%
2051
16th to endNight
22%21%6%8%6%3433314%
2420
November1st to 15thNight
18%21%5%11%7%35%5%4413%
2657
16th to endNight
14%18%6%9%6%346%5%7%16%
2976
December1st to 15thNight
19%22%7%9%7%345%4412%
3138
16th to endNight
13%22%7%11%8%35%5%46%10%
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
66%16%11%9%4
821
16th to endDay
71%46%10%5%2
1152
February1st to 15thDay
70%4312%6%2
1288
16th to endDay
63%6%7%11%10%1
1320
March1st to 15thDay
54%5%7%11%14%7%
1797
16th to endDay
65%5%8%10%7%1
2210
April1st to 15thDay
68%5%10%11%4
2281
16th to endDay
64%6%11%14%3
2541
May1st to 15thDay
67%5%9%12%5%
2817
16th to endDay
53%8%15%18%4
3105
June1st to 15thDay
71%6%11%9%
3240
16th to endDay
67%9%14%6%1
3240
July1st to 15thDay
68%10%15%4
3048
16th to endDay
72%6%15%5%
2861
August1st to 15thDay
78%5%12%4
2740
16th to endDay
77%5%9%5%2
2671
September1st to 15thDay
82%46%5%1
2196
16th to endDay
71%5%9%9%3
1862
October1st to 15thDay
75%46%10%3
1579
16th to endDay
75%46%6%5%1
1452
November1st to 15thDay
70%47%11%4
1201
16th to endDay
64%18%16%7%2
982
December1st to 15thDay
72%48%6%7%1
819
16th to endDay
73%37%9%5%
768
January1st to 15thNight
66%3410%9%5%
3117
16th to endNight
69%25%12%6%2
3072
February1st to 15thNight
69%45%10%8%2
2573
16th to endNight
63%5%7%11%9%1
2152
March1st to 15thNight
55%46%10%15%7%
2163
16th to endNight
66%36%12%9%1
2012
April1st to 15thNight
68%38%14%5%
1664
16th to endNight
62%5%12%15%4
1419
May1st to 15thNight
62%6%11%14%5%
1132
16th to endNight
52%6%15%19%5%
1009
June1st to 15thNight
67%10%11%9%1
720
16th to endNight
66%8%15%8%1
720
July1st to 15thNight
62%9%20%7%
682
16th to endNight
69%5%19%4
1045
August1st to 15thNight
76%5%10%6%
1192
16th to endNight
73%5%10%7%3
1531
September1st to 15thNight
81%5%6%5%1
1764
16th to endNight
69%5%10%10%4
1821
October1st to 15thNight
71%27%13%4
2051
16th to endNight
73%27%8%5%1
2420
November1st to 15thNight
70%38%12%4
2657
16th to endNight
61%38%15%9%1
2976
December1st to 15thNight
71%37%8%7%1
3138
16th to endNight
72%37%10%5%1
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
37%7%15%21%15%4
99
16th to endDay
37%14%18%19%8%1
224
February1st to 15thDay
29%12%21%17%11%7%
221
16th to endDay
32%10%25%18%9%4
211
March1st to 15thDay
17%14%26%23%16%2
240
16th to endDay
26%11%16%20%18%6%
411
April1st to 15thDay
29%17%16%19%15%2
433
16th to endDay
32%11%14%20%18%3
450
May1st to 15thDay
36%12%11%20%16%2
468
16th to endDay
28%7%18%28%14%2
524
June1st to 15thDay
38%7%11%24%14%2
675
16th to endDay
38%6%11%20%18%3
675
July1st to 15thDay
39%5%10%23%17%4
645
16th to endDay
45%10%11%15%14%2
532
August1st to 15thDay
54%6%9%14%10%3
494
16th to endDay
53%6%16%14%8%
523
September1st to 15thDay
55%9%13%10%9%1
459
16th to endDay
48%7%11%15%13%2
280
October1st to 15thDay
43%8%15%12%17%3
225
16th to endDay
43%7%14%19%11%3
240
November1st to 15thDay
36%13%20%18%9%2
230
16th to endDay
32%8%22%23%12%1
112
December1st to 15thDay
13%323%26%23%10%
30
16th to endDay
53%318%15%9%
32
January1st to 15thNight
31%12%19%20%13%2
773
16th to endNight
35%11%19%19%11%2
800
February1st to 15thNight
32%12%16%22%14%2
734
16th to endNight
29%13%22%23%10%1
599
March1st to 15thNight
21%9%22%26%15%3
570
16th to endNight
29%10%13%18%21%6%
584
April1st to 15thNight
34%9%13%16%22%3
539
16th to endNight
29%11%14%16%24%4
540
May1st to 15thNight
31%12%10%16%23%5%
412
16th to endNight
28%4422%34%5%
270
June1st to 15thNight
35%10%8%16%26%3
180
16th to endNight
36%6%8%13%30%4
180
July1st to 15thNight
34%48%17%29%5%
172
16th to endNight
45%6%7%12%21%5%
376
August1st to 15thNight
53%5%7%13%16%2
412
16th to endNight
50%6%10%15%12%4
573
September1st to 15thNight
58%5%10%10%14%2
540
16th to endNight
48%5%10%14%17%3
505
October1st to 15thNight
48%412%16%16%1
596
16th to endNight
43%6%13%17%16%3
736
November1st to 15thNight
38%10%21%18%10%1
730
16th to endNight
28%8%23%23%12%3
750
December1st to 15thNight
33%9%20%20%10%5%
763
16th to endNight
33%13%17%23%10%2
832
Page generated at 2017-09-19 03:32:29. Version ac04

Copyright 2017 A. Danko


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