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 2018-03-11.

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%
13978
6%
49130
5%
13949
41%
13949
12%
37629

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
39%
866
8%
3418
6%
866
42%
866
12%
2514
January16th to endNight
38%
884
9%
3347
8%
884
40%
884
12%
2509
February1st to 15thNight
43%
808
9%
2815
8%
804
44%
804
15%
2021
February16th to endNight
30%
646
8%
2316
4%
646
34%
646
10%
1771
March1st to 15thNight
45%
614
15%
2317
14%
614
49%
614
18%
1532
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%
380
0%
1101
0%
380
48%
380
16%
855
May16th to endNight
53%
273
0%
961
0%
272
53%
272
15%
682
June1st to 15thNight
43%
180
0%
720
0%
180
43%
180
9%
570
June16th to endNight
51%
180
0%
720
0%
180
51%
180
6%
585
July1st to 15thNight
46%
173
0%
683
0%
173
46%
173
8%
555
July16th to endNight
36%
376
0%
998
0%
354
36%
354
9%
847
August1st to 15thNight
34%
385
0%
1173
0%
383
34%
383
8%
994
August16th to endNight
34%
573
1%
1528
1%
573
34%
573
8%
1318
September1st to 15thNight
30%
540
3%
1761
2%
540
31%
540
6%
1538
September16th to endNight
36%
549
5%
1962
5%
549
37%
549
8%
1591
October1st to 15thNight
42%
651
9%
2226
10%
651
42%
651
12%
1726
October16th to endNight
40%
816
8%
2655
6%
816
41%
816
13%
2059
November1st to 15thNight
40%
805
7%
2917
5%
805
43%
805
12%
2213
November16th to endNight
41%
825
10%
3221
8%
825
46%
825
13%
2301
December1st to 15thNight
36%
860
5%
3462
6%
860
37%
860
8%
2765
December16th to endNight
35%
928
5%
3744
4%
928
36%
928
8%
2930

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%
49580
Night
18%12%47%6%3445%6%25%
49232
TransparencyDay
57%12%15%10%3
49183
Night
56%10%14%11%5%1
49135
SeeingDay
19%6%19%27%21%5%
8938
Night
20%6%19%27%20%5%
13985

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%13%5%6%6%36%46%11%18%
851
16th to endDay
13%15%5%9%5%36%5%6%7%21%
1228
February1st to 15thDay
13%13%5%7%6%36%445%29%
1378
16th to endDay
13%16%47%7%35%45%6%26%
1444
March1st to 15thDay
8%13%36%5%2346%441%
1879
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%
2850
16th to endDay
15%6%35%5%3445%8%37%
3150
June1st to 15thDay
17%8%47%6%345%6%7%26%
3240
16th to endDay
16%6%37%6%45%6%6%8%27%
3240
July1st to 15thDay
18%8%47%6%46%5%5%7%25%
3237
16th to endDay
25%7%36%5%3445%6%26%
3101
August1st to 15thDay
29%9%36%5%34445%22%
2779
16th to endDay
29%8%26%5%3445%5%21%
2674
September1st to 15thDay
32%9%37%6%33445%18%
2198
16th to endDay
31%9%36%5%3343424%
1995
October1st to 15thDay
26%9%45%5%33445%26%
1734
16th to endDay
17%10%37%5%246%7%7%27%
1566
November1st to 15thDay
13%13%49%7%35%5%46%27%
1269
16th to endDay
14%13%36%6%25%6%6%7%27%
1069
December1st to 15thDay
19%15%6%8%5%2445%7%21%
825
16th to endDay
9%15%7%10%6%6%6%5%6%7%17%
832
January1st to 15thNight
14%13%5%7%5%3446%8%24%
3418
16th to endNight
14%14%5%7%6%345%7%9%21%
3347
February1st to 15thNight
12%13%5%7%6%345%5%6%29%
2803
16th to endNight
13%16%5%8%6%34446%25%
2316
March1st to 15thNight
9%11%47%6%34345%38%
2317
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%9%46%5%35%5%6%5%30%
1100
16th to endNight
15%7%247%35%6%5%8%33%
960
June1st to 15thNight
19%9%6%8%6%35%6%5%6%23%
720
16th to endNight
20%6%39%5%5%5%6%7%9%20%
720
July1st to 15thNight
24%8%26%7%47%35%5%22%
723
16th to endNight
32%8%47%5%245%45%20%
1068
August1st to 15thNight
31%9%45%6%345%45%19%
1179
16th to endNight
34%8%46%5%35%345%19%
1528
September1st to 15thNight
36%9%36%5%34445%17%
1761
16th to endNight
32%8%36%5%4443422%
1962
October1st to 15thNight
30%10%25%42344329%
2226
16th to endNight
20%12%48%5%24446%25%
2655
November1st to 15thNight
15%12%48%5%35%45%7%26%
2917
16th to endNight
14%13%5%6%5%245%48%29%
3221
December1st to 15thNight
20%14%5%7%7%35%5%46%19%
3462
16th to endNight
12%14%6%9%7%36%5%6%7%20%
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
55%11%14%8%7%3
851
16th to endDay
57%10%16%8%5%1
1228
February1st to 15thDay
53%7%12%14%8%3
1378
16th to endDay
56%9%12%14%6%
1444
March1st to 15thDay
44%9%12%12%14%5%
1879
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%16%13%5%
2850
16th to endDay
46%9%18%21%4
3154
June1st to 15thDay
55%16%16%10%1
3240
16th to endDay
55%16%19%6%1
3240
July1st to 15thDay
58%17%19%4
3048
16th to endDay
59%16%18%5%
2908
August1st to 15thDay
65%13%15%5%
2760
16th to endDay
65%14%12%5%2
2674
September1st to 15thDay
68%12%11%6%1
2198
16th to endDay
66%8%12%10%2
1995
October1st to 15thDay
59%11%13%12%2
1734
16th to endDay
52%14%17%10%5%
1566
November1st to 15thDay
56%11%13%11%6%
1269
16th to endDay
53%10%16%11%6%1
1069
December1st to 15thDay
61%11%13%7%4
825
16th to endDay
62%10%16%7%2
832
January1st to 15thNight
53%10%14%10%7%3
3418
16th to endNight
54%10%14%11%6%1
3347
February1st to 15thNight
51%8%12%14%7%5%
2815
16th to endNight
57%10%11%13%6%
2316
March1st to 15thNight
46%6%10%14%15%6%
2317
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
1101
16th to endNight
46%13%15%19%4
961
June1st to 15thNight
58%13%17%9%1
720
16th to endNight
59%16%15%6%1
720
July1st to 15thNight
59%14%18%7%
683
16th to endNight
65%11%17%5%
998
August1st to 15thNight
65%12%15%6%
1173
16th to endNight
67%10%11%7%2
1528
September1st to 15thNight
69%12%9%7%1
1761
16th to endNight
64%9%12%10%2
1962
October1st to 15thNight
59%8%12%14%4
2226
16th to endNight
57%9%15%10%6%
2655
November1st to 15thNight
55%10%14%13%6%
2917
16th to endNight
51%9%17%11%7%1
3221
December1st to 15thNight
61%11%13%8%5%
3462
16th to endNight
58%12%15%10%2
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
20%6%22%20%20%9%
120
16th to endDay
12%8%21%32%14%9%
256
February1st to 15thDay
13%7%19%27%16%15%
251
16th to endDay
16%9%30%27%14%3
250
March1st to 15thDay
12%6%22%30%20%6%
271
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
14%8%22%27%22%4
468
16th to endDay
16%6%21%33%18%3
575
June1st to 15thDay
14%8%22%31%19%3
675
16th to endDay
15%416%30%26%6%
675
July1st to 15thDay
17%316%30%27%5%
645
16th to endDay
24%318%26%21%5%
580
August1st to 15thDay
27%5%16%23%20%6%
494
16th to endDay
29%415%29%17%3
523
September1st to 15thDay
35%6%17%19%18%2
454
16th to endDay
33%5%15%16%21%7%
336
October1st to 15thDay
26%418%25%18%6%
270
16th to endDay
19%8%17%25%20%8%
288
November1st to 15thDay
18%429%20%18%8%
264
16th to endDay
12%6%22%33%17%7%
139
December1st to 15thDay
15%413%24%31%11%
45
16th to endDay
12%433%25%16%8%
48
January1st to 15thNight
15%7%24%29%19%3
870
16th to endNight
16%6%23%30%17%5%
884
February1st to 15thNight
15%7%21%32%18%4
809
16th to endNight
17%7%27%29%14%2
646
March1st to 15thNight
12%5%24%34%19%3
614
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
16%417%29%27%4
381
16th to endNight
17%215%30%31%2
273
June1st to 15thNight
22%5%15%32%22%2
180
16th to endNight
21%211%28%33%1
180
July1st to 15thNight
27%211%20%34%4
173
16th to endNight
31%212%21%22%8%
376
August1st to 15thNight
35%416%21%17%4
385
16th to endNight
36%313%21%18%6%
573
September1st to 15thNight
37%6%16%18%16%5%
540
16th to endNight
32%6%13%21%18%8%
549
October1st to 15thNight
28%5%14%25%20%5%
651
16th to endNight
21%5%17%27%21%5%
816
November1st to 15thNight
18%5%24%30%17%3
805
16th to endNight
17%7%21%28%21%4
825
December1st to 15thNight
21%7%19%26%16%7%
860
16th to endNight
14%8%26%25%20%4
928
Page generated at 2018-03-12 09:28:10. Version ac04

Copyright 2018 A. Danko


Anchorage Clear Sky Chart |Charts Home