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Anchorage
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Anchorage clear sky chart from 2005-11-05 to 2017-05-10.

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
40%
12870
6%
45729
5%
12841
41%
12841
11%
35061

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
40%
776
7%
3154
6%
776
42%
776
12%
2310
January16th to endNight
36%
803
8%
3090
6%
803
38%
803
11%
2348
February1st to 15thNight
42%
733
8%
2594
8%
729
43%
729
14%
1879
February16th to endNight
29%
587
8%
2140
4%
587
33%
587
10%
1636
March1st to 15thNight
45%
570
15%
2183
14%
570
50%
570
18%
1439
March16th to endNight
53%
587
13%
2005
15%
587
53%
587
18%
1385
April1st to 15thNight
43%
539
4%
1652
4%
539
43%
539
12%
1294
April16th to endNight
48%
540
1%
1428
1%
540
48%
540
19%
1074
May1st to 15thNight
48%
370
0%
1071
0%
370
48%
370
16%
832
May16th to endNight
55%
250
0%
879
0%
249
55%
249
15%
621
June1st to 15thNight
44%
165
0%
660
0%
165
44%
165
9%
518
June16th to endNight
50%
165
0%
660
0%
165
50%
165
6%
534
July1st to 15thNight
45%
158
0%
623
0%
158
45%
158
7%
514
July16th to endNight
36%
348
0%
919
0%
326
36%
326
10%
774
August1st to 15thNight
34%
353
0%
1075
0%
351
34%
351
8%
908
August16th to endNight
36%
525
2%
1400
1%
525
36%
525
9%
1193
September1st to 15thNight
32%
495
3%
1614
3%
495
32%
495
6%
1397
September16th to endNight
36%
500
5%
1798
5%
500
38%
500
8%
1446
October1st to 15thNight
42%
585
9%
2040
10%
585
43%
585
12%
1570
October16th to endNight
40%
736
7%
2433
6%
736
41%
736
12%
1889
November1st to 15thNight
38%
730
6%
2687
4%
730
40%
730
10%
2093
November16th to endNight
41%
750
9%
2973
7%
750
45%
750
13%
2131
December1st to 15thNight
38%
773
5%
3195
6%
773
39%
773
8%
2546
December16th to endNight
33%
832
4%
3456
3%
832
34%
832
7%
2730

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
18%10%47%6%35%5%5%6%27%
46312
Night
18%12%47%6%3445%6%25%
45831
TransparencyDay
56%12%15%10%3
45915
Night
56%10%14%11%5%
45734
SeeingDay
18%6%19%28%21%5%
7870
Night
20%6%19%27%21%5%
12877

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
16%13%5%6%6%36%46%11%19%
785
16th to endDay
14%16%5%9%5%35%5%6%8%19%
1133
February1st to 15thDay
12%13%5%7%7%46%5%45%27%
1269
16th to endDay
13%16%47%7%35%45%6%26%
1334
March1st to 15thDay
8%12%36%4235%6%5%42%
1777
16th to endDay
8%13%46%6%345%48%34%
2214
April1st to 15thDay
10%13%5%8%7%35%5%5%6%28%
2295
16th to endDay
9%9%38%6%36%7%6%7%30%
2532
May1st to 15thDay
14%11%47%6%35%446%30%
2760
16th to endDay
14%6%345%3445%8%39%
2880
June1st to 15thDay
17%8%47%6%345%6%7%27%
2970
16th to endDay
16%6%37%6%45%6%6%8%28%
2970
July1st to 15thDay
18%8%48%6%46%5%6%7%23%
2967
16th to endDay
25%7%36%5%3445%6%26%
2872
August1st to 15thDay
30%9%36%5%34445%23%
2547
16th to endDay
29%8%26%5%3445%6%22%
2450
September1st to 15thDay
33%9%36%5%33445%19%
2016
16th to endDay
30%9%36%5%3333426%
1829
October1st to 15thDay
27%8%45%5%33445%27%
1590
16th to endDay
16%11%37%5%246%7%7%26%
1436
November1st to 15thDay
13%14%5%9%7%35%5%5%6%23%
1169
16th to endDay
15%13%36%6%26%6%5%7%26%
987
December1st to 15thDay
17%15%6%9%5%3445%7%21%
762
16th to endDay
9%15%7%10%7%6%6%5%6%7%17%
768
January1st to 15thNight
15%12%5%7%5%35%47%8%24%
3154
16th to endNight
15%14%5%7%6%345%7%9%20%
3090
February1st to 15thNight
12%13%5%7%6%345%5%6%28%
2582
16th to endNight
13%16%5%8%6%3445%6%25%
2140
March1st to 15thNight
9%11%5%7%5%34345%39%
2183
16th to endNight
8%14%47%424347%38%
2005
April1st to 15thNight
11%17%5%8%7%45%44426%
1652
16th to endNight
10%11%5%6%7%47%5%5%6%29%
1428
May1st to 15thNight
16%10%46%5%35%5%6%5%30%
1070
16th to endNight
14%6%247%35%7%5%8%32%
878
June1st to 15thNight
19%9%5%8%6%346%46%24%
660
16th to endNight
19%6%39%5%5%5%5%7%9%21%
660
July1st to 15thNight
25%9%36%7%48%35%5%20%
663
16th to endNight
32%7%36%5%235%45%20%
989
August1st to 15thNight
31%9%46%6%34445%19%
1081
16th to endNight
32%7%46%5%45%345%20%
1400
September1st to 15thNight
36%9%35%434445%18%
1614
16th to endNight
30%8%36%5%4443423%
1798
October1st to 15thNight
29%10%25%42333330%
2040
16th to endNight
20%12%48%5%245%46%25%
2433
November1st to 15thNight
16%13%48%6%45%45%6%23%
2687
16th to endNight
14%13%5%6%4245%48%28%
2973
December1st to 15thNight
20%13%5%7%7%35%5%46%20%
3195
16th to endNight
12%14%6%9%7%36%5%6%7%19%
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
54%11%14%8%7%3
785
16th to endDay
59%10%16%7%5%
1133
February1st to 15thDay
54%8%13%15%7%1
1269
16th to endDay
56%9%12%13%6%
1334
March1st to 15thDay
43%9%12%13%14%6%
1777
16th to endDay
49%11%14%14%9%
2214
April1st to 15thDay
57%10%14%12%4
2295
16th to endDay
51%10%16%17%3
2532
May1st to 15thDay
56%8%15%13%4
2760
16th to endDay
44%10%19%21%3
2884
June1st to 15thDay
55%15%16%10%1
2970
16th to endDay
54%16%19%6%1
2970
July1st to 15thDay
59%17%18%4
2778
16th to endDay
59%15%19%5%
2679
August1st to 15thDay
65%13%14%5%
2528
16th to endDay
64%14%12%6%2
2450
September1st to 15thDay
68%12%11%6%1
2016
16th to endDay
65%8%12%10%2
1829
October1st to 15thDay
59%11%13%12%2
1590
16th to endDay
52%15%16%9%5%
1436
November1st to 15thDay
58%12%13%9%5%
1169
16th to endDay
55%10%15%12%5%1
987
December1st to 15thDay
61%12%14%6%4
762
16th to endDay
63%10%16%7%1
768
January1st to 15thNight
52%11%15%10%7%3
3154
16th to endNight
55%10%14%11%6%
3090
February1st to 15thNight
52%8%13%15%7%2
2594
16th to endNight
57%10%11%12%6%1
2140
March1st to 15thNight
46%6%10%14%15%6%
2183
16th to endNight
46%9%13%17%11%1
2010
April1st to 15thNight
59%8%13%14%3
1652
16th to endNight
50%10%18%15%5%
1428
May1st to 15thNight
55%9%14%16%4
1071
16th to endNight
45%14%16%19%4
879
June1st to 15thNight
57%13%17%10%1
660
16th to endNight
57%17%16%6%2
660
July1st to 15thNight
61%14%17%6%
623
16th to endNight
64%10%17%6%
919
August1st to 15thNight
65%11%15%7%
1075
16th to endNight
65%11%12%8%2
1400
September1st to 15thNight
67%12%10%8%1
1614
16th to endNight
63%9%12%11%2
1798
October1st to 15thNight
59%7%13%14%5%
2040
16th to endNight
58%9%15%10%6%
2433
November1st to 15thNight
58%10%14%12%4
2687
16th to endNight
51%10%18%12%6%1
2973
December1st to 15thNight
60%12%13%7%5%
3195
16th to endNight
59%13%14%9%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
21%324%19%21%11%
99
16th to endDay
13%9%22%32%13%7%
224
February1st to 15thDay
11%7%22%27%16%14%
216
16th to endDay
14%10%32%24%14%3
211
March1st to 15thDay
10%7%22%31%20%6%
240
16th to endDay
13%316%27%29%9%
430
April1st to 15thDay
12%7%19%29%22%6%
431
16th to endDay
10%8%20%31%24%4
450
May1st to 15thDay
15%9%22%29%20%3
440
16th to endDay
12%6%21%35%20%3
490
June1st to 15thDay
13%9%23%31%19%2
585
16th to endDay
12%417%30%27%6%
585
July1st to 15thDay
16%316%30%26%5%
555
16th to endDay
23%419%27%20%4
505
August1st to 15thDay
26%5%17%23%20%5%
419
16th to endDay
27%5%14%30%18%3
443
September1st to 15thDay
35%7%17%18%18%2
393
16th to endDay
31%5%15%16%22%9%
286
October1st to 15thDay
26%416%24%20%6%
225
16th to endDay
18%8%18%25%20%8%
240
November1st to 15thDay
20%427%20%18%8%
224
16th to endDay
15%6%23%29%17%7%
117
December1st to 15thDay
36%26%46%16%
30
16th to endDay
15%334%25%12%9%
32
January1st to 15thNight
15%6%24%30%19%3
780
16th to endNight
17%6%23%30%15%5%
803
February1st to 15thNight
14%7%22%32%17%4
734
16th to endNight
17%8%28%27%15%2
587
March1st to 15thNight
11%5%25%34%18%3
570
16th to endNight
12%415%27%28%11%
588
April1st to 15thNight
16%8%14%26%27%6%
539
16th to endNight
11%6%18%29%29%5%
540
May1st to 15thNight
15%5%17%30%26%4
371
16th to endNight
15%214%32%32%2
250
June1st to 15thNight
21%6%13%33%23%1
165
16th to endNight
20%212%29%32%1
165
July1st to 15thNight
27%111%18%35%4
158
16th to endNight
31%213%22%22%7%
348
August1st to 15thNight
35%416%21%16%4
353
16th to endNight
34%313%22%19%6%
525
September1st to 15thNight
36%5%16%18%17%5%
495
16th to endNight
32%6%13%20%19%8%
500
October1st to 15thNight
27%6%14%26%20%5%
585
16th to endNight
21%5%18%27%21%5%
736
November1st to 15thNight
20%6%23%29%17%3
730
16th to endNight
17%8%21%26%22%4
750
December1st to 15thNight
20%7%18%27%18%8%
773
16th to endNight
14%9%26%24%20%4
832
Page generated at 2017-05-11 01:20:01. Version ac04

Copyright 2017 A. Danko


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