Girdwood
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Girdwood clear sky chart from 2005-11-06 to 2024-01-15.

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
31%
21491
7%
74955
5%
21438
34%
21438
10%
59347

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 10thNight
40%
938
12%
3392
11%
936
42%
936
13%
2529
January11th to 20thNight
27%
857
9%
3028
6%
857
30%
857
8%
2449
January21st to endNight
27%
880
9%
3168
7%
880
29%
880
9%
2568
February1st to 10thNight
35%
800
12%
2700
7%
800
40%
800
14%
1997
February11th to 20thNight
21%
784
4%
2452
3%
780
22%
780
7%
2100
February21st to endNight
26%
564
16%
1978
9%
564
35%
564
14%
1402
March1st to 10thNight
35%
620
12%
2174
9%
620
40%
620
14%
1575
March11th to 20thNight
41%
620
13%
2114
11%
620
46%
620
17%
1482
March21st to endNight
36%
594
12%
1981
10%
594
40%
594
12%
1499
April1st to 10thNight
32%
540
6%
1770
5%
540
33%
540
11%
1394
April11th to 20thNight
46%
533
5%
1425
3%
533
47%
533
19%
1064
April21st to endNight
39%
540
1%
1414
1%
540
39%
540
15%
1109
May1st to 10thNight
36%
424
0%
1144
0%
424
36%
424
11%
967
May11th to 20thNight
45%
354
0%
1063
0%
354
45%
354
16%
798
May21st to endNight
40%
234
0%
969
0%
233
40%
233
10%
715
June1st to 10thNight
42%
180
0%
720
0%
180
42%
180
8%
563
June11th to 20thNight
43%
180
0%
720
0%
180
43%
180
10%
559
June21st to endNight
40%
180
0%
720
0%
180
40%
180
8%
577
July1st to 10thNight
45%
175
0%
700
0%
175
45%
175
8%
543
July11th to 20thNight
40%
263
0%
822
0%
263
40%
263
10%
670
July21st to endNight
39%
394
0%
1116
0%
372
38%
372
9%
935
August1st to 10thNight
27%
358
0%
1076
0%
356
27%
356
8%
910
August11th to 20thNight
23%
513
0%
1402
0%
513
23%
513
8%
1213
August21st to endNight
31%
594
3%
1584
1%
594
32%
594
11%
1310
September1st to 10thNight
20%
540
2%
1742
2%
540
20%
540
5%
1540
September11th to 20thNight
27%
540
6%
1808
7%
540
29%
540
7%
1539
September21st to endNight
32%
565
5%
2030
5%
565
34%
565
8%
1655
October1st to 10thNight
24%
652
6%
2182
6%
652
25%
652
8%
1820
October11th to 20thNight
27%
810
5%
2340
3%
810
28%
810
8%
2032
October21st to endNight
29%
891
9%
2797
5%
891
32%
891
10%
2300
November1st to 10thNight
30%
830
7%
2777
6%
830
31%
830
10%
2247
November11th to 20thNight
37%
850
13%
3007
10%
850
42%
850
12%
2244
November21st to endNight
31%
850
12%
3193
10%
850
35%
850
9%
2553
December1st to 10thNight
28%
879
8%
3291
7%
879
31%
879
6%
2760
December11th to 20thNight
28%
940
6%
4191
4%
939
31%
939
6%
3457
December21st to endNight
24%
1025
5%
5965
4%
1004
28%
1004
4%
4272

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
17%15%5%9%7%45%5%5%6%20%
74384
Night
14%16%5%9%7%45%5%5%6%23%
75421
TransparencyDay
66%7%11%10%41
74018
Night
65%5%8%11%8%3
75307
SeeingDay
24%14%22%24%12%3
16737
Night
23%13%22%24%15%3
21502

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 10thDay
5%16%6%9%7%5%5%45%10%29%
769
11th to 20thDay
13%18%5%9%8%45%46%5%21%
1036
21st to endDay
10%16%5%13%8%6%6%6%7%8%15%
1188
February1st to 10thDay
7%16%6%8%7%5%5%46%7%30%
1260
11th to 20thDay
11%22%6%14%9%46%5%45%14%
1399
21st to endDay
6%15%6%10%8%45%45%6%29%
1278
March1st to 10thDay
10%15%6%10%7%35%35%6%30%
1786
11th to 20thDay
413%5%10%9%6%7%7%6%7%26%
1842
21st to endDay
6%17%7%11%8%5%6%5%6%6%23%
2374
April1st to 10thDay
8%19%7%12%9%5%6%446%19%
2190
11th to 20thDay
7%15%5%10%8%36%6%7%7%27%
2481
21st to endDay
8%16%6%10%8%5%7%5%5%7%25%
2546
May1st to 10thDay
12%17%7%12%8%45%5%6%7%18%
2816
11th to 20thDay
12%15%5%8%6%45%5%5%6%29%
2833
21st to endDay
13%12%5%6%6%46%6%6%7%29%
3301
June1st to 10thDay
15%13%5%8%8%5%7%5%6%7%20%
3240
11th to 20thDay
14%13%6%9%7%46%7%7%6%20%
3240
21st to endDay
17%13%5%9%9%46%6%6%6%19%
3240
July1st to 10thDay
16%14%5%9%9%46%5%5%6%21%
3240
11th to 20thDay
22%11%5%9%7%46%6%6%7%18%
3110
21st to endDay
25%11%48%7%45%6%5%6%18%
3137
August1st to 10thDay
28%13%5%9%7%445%5%6%16%
2856
11th to 20thDay
32%11%49%7%45%45%5%14%
2498
21st to endDay
30%13%48%7%4445%6%15%
2772
September1st to 10thDay
34%15%5%9%6%4444412%
2214
11th to 20thDay
32%15%48%6%4444315%
2152
21st to endDay
27%17%5%7%6%44445%17%
1927
October1st to 10thDay
28%17%5%9%7%4444414%
1778
11th to 20thDay
20%17%5%11%9%45%5%5%5%16%
1620
21st to endDay
17%15%6%11%7%345%6%6%19%
1557
November1st to 10thDay
12%17%8%9%7%35%5%6%7%22%
1301
11th to 20thDay
10%15%49%6%5%5%6%7%10%22%
1169
21st to endDay
13%20%5%11%7%46%45%7%19%
986
December1st to 10thDay
19%16%7%10%7%26%5%5%8%14%
884
11th to 20thDay
8%23%7%8%9%5%5%6%7%8%14%
967
21st to endDay
7%15%7%10%8%46%5%7%6%26%
1397
January1st to 10thNight
5%15%5%10%8%5%5%5%7%7%28%
3392
11th to 20thNight
13%18%6%9%7%35%5%6%6%21%
3028
21st to endNight
11%18%7%10%9%5%6%6%6%7%17%
3168
February1st to 10thNight
7%15%6%9%7%45%5%5%6%30%
2700
11th to 20thNight
14%21%6%10%9%46%5%5%7%13%
2448
21st to endNight
8%15%6%8%7%45%6%6%7%29%
1978
March1st to 10thNight
8%16%6%8%7%45%5%5%6%31%
2174
11th to 20thNight
411%5%10%8%45%6%6%10%29%
2114
21st to endNight
6%17%7%8%7%46%5%5%5%30%
1981
April1st to 10thNight
7%20%6%10%8%45%5%6%5%23%
1770
11th to 20thNight
9%13%46%6%36%7%8%8%30%
1425
21st to endNight
7%14%7%9%7%46%6%6%7%28%
1414
May1st to 10thNight
10%14%5%9%9%5%9%6%6%7%21%
1144
11th to 20thNight
11%13%5%9%7%45%5%7%6%27%
1062
21st to endNight
12%10%5%8%7%47%7%6%9%25%
969
June1st to 10thNight
14%13%5%9%6%36%6%8%9%22%
720
11th to 20thNight
16%15%5%7%5%35%7%9%7%22%
720
21st to endNight
18%11%6%9%8%5%6%6%5%8%19%
720
July1st to 10thNight
19%9%38%7%5%5%7%6%7%24%
720
11th to 20thNight
25%8%37%7%45%6%7%7%22%
847
21st to endNight
25%11%47%6%47%45%7%21%
1182
August1st to 10thNight
26%11%48%6%345%47%21%
1082
11th to 20thNight
30%12%37%7%36%45%6%18%
1402
21st to endNight
27%11%48%6%44446%23%
1584
September1st to 10thNight
31%14%5%10%6%36%5%3414%
1742
11th to 20thNight
31%14%5%7%6%3445%417%
1808
21st to endNight
26%13%49%6%445%5%419%
2030
October1st to 10thNight
26%15%5%9%8%35%33420%
2182
11th to 20thNight
18%16%6%10%9%5%5%5%4419%
2340
21st to endNight
17%17%5%9%8%45%5%5%5%21%
2797
November1st to 10thNight
15%18%5%9%7%45%5%5%7%22%
2777
11th to 20thNight
10%14%47%6%36%7%8%10%26%
3007
21st to endNight
12%19%6%10%7%35%5%6%7%21%
3193
December1st to 10thNight
16%19%6%9%7%46%45%7%17%
3291
11th to 20thNight
8%20%9%12%8%5%6%5%7%6%15%
4240
21st to endNight
8%18%6%9%7%46%5%5%6%27%
6270

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 10thDay
58%5%5%11%15%6%
769
11th to 20thDay
70%35%10%7%4
1036
21st to endDay
70%47%9%7%3
1188
February1st to 10thDay
57%5%8%14%10%6%
1260
11th to 20thDay
75%35%9%5%2
1406
21st to endDay
55%7%7%13%15%2
1278
March1st to 10thDay
58%5%7%13%11%7%
1786
11th to 20thDay
57%9%5%14%13%2
1842
21st to endDay
61%8%10%9%9%2
2374
April1st to 10thDay
69%7%8%10%5%1
2190
11th to 20thDay
57%8%12%15%8%
2481
21st to endDay
63%6%9%14%7%1
2546
May1st to 10thDay
69%7%10%10%4
2816
11th to 20thDay
58%5%12%19%5%
2836
21st to endDay
57%7%15%18%3
3302
June1st to 10thDay
65%7%15%11%1
3240
11th to 20thDay
64%9%13%13%2
3240
21st to endDay
66%8%18%7%
3240
July1st to 10thDay
65%9%17%9%
3151
11th to 20thDay
65%12%19%4
3012
21st to endDay
68%9%17%5%
2963
August1st to 10thDay
74%7%14%5%
2837
11th to 20thDay
75%7%10%7%1
2498
21st to endDay
71%7%12%7%2
2772
September1st to 10thDay
80%5%6%7%2
2214
11th to 20thDay
76%6%7%9%1
2152
21st to endDay
72%6%9%11%3
1927
October1st to 10thDay
77%5%7%8%2
1778
11th to 20thDay
76%49%7%4
1620
21st to endDay
69%5%6%8%9%2
1557
November1st to 10thDay
66%6%7%11%7%3
1301
11th to 20thDay
62%47%17%9%1
1169
21st to endDay
71%27%9%8%3
986
December1st to 10thDay
78%26%7%5%1
884
11th to 20thDay
71%8%5%10%5%1
970
21st to endDay
54%10%6%8%13%10%
1397
January1st to 10thNight
60%5%5%11%15%5%
3392
11th to 20thNight
71%35%8%7%6%
3028
21st to endNight
69%45%10%9%2
3168
February1st to 10thNight
58%5%7%12%13%6%
2700
11th to 20thNight
75%46%8%6%1
2452
21st to endNight
53%6%9%13%16%2
1978
March1st to 10thNight
58%47%11%12%8%
2174
11th to 20thNight
53%5%9%13%18%2
2116
21st to endNight
59%7%9%12%11%3
1981
April1st to 10thNight
64%5%10%14%6%1
1770
11th to 20thNight
53%7%14%17%9%
1425
21st to endNight
59%6%10%15%9%1
1414
May1st to 10thNight
67%8%11%12%3
1144
11th to 20thNight
57%5%15%17%6%
1063
21st to endNight
58%8%14%17%3
969
June1st to 10thNight
65%7%15%12%1
720
11th to 20thNight
60%10%18%11%2
720
21st to endNight
65%8%20%6%1
720
July1st to 10thNight
60%11%18%11%
700
11th to 20thNight
63%10%21%5%
822
21st to endNight
68%8%19%5%
1116
August1st to 10thNight
68%9%17%5%1
1076
11th to 20thNight
73%6%11%8%1
1402
21st to endNight
66%6%15%10%3
1584
September1st to 10thNight
78%5%8%7%1
1742
11th to 20thNight
74%5%9%9%3
1808
21st to endNight
69%5%11%12%3
2030
October1st to 10thNight
72%48%12%3
2182
11th to 20thNight
75%5%8%9%4
2340
21st to endNight
70%47%10%9%1
2797
November1st to 10thNight
68%48%10%7%3
2777
11th to 20thNight
59%6%7%17%11%1
3007
21st to endNight
68%46%10%9%3
3193
December1st to 10thNight
74%46%9%7%1
3291
11th to 20thNight
70%6%6%9%9%1
4236
21st to endNight
57%7%5%9%13%10%
6270

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 10thDay
20%14%16%22%23%5%
100
11th to 20thDay
22%12%30%21%13%3
269
21st to endDay
22%16%27%19%11%5%
286
February1st to 10thDay
15%13%25%25%15%7%
272
11th to 20thDay
27%13%26%23%8%2
335
21st to endDay
20%18%28%21%6%7%
280
March1st to 10thDay
19%10%33%20%14%4
340
11th to 20thDay
13%17%25%25%15%4
382
21st to endDay
15%18%28%23%13%3
572
April1st to 10thDay
16%23%28%24%9%1
534
11th to 20thDay
14%16%19%32%15%4
590
21st to endDay
19%15%23%29%12%4
600
May1st to 10thDay
25%17%26%21%9%1
603
11th to 20thDay
20%12%27%26%14%2
625
21st to endDay
22%10%30%26%11%1
716
June1st to 10thDay
19%12%19%29%18%3
810
11th to 20thDay
17%10%20%36%16%2
810
21st to endDay
20%13%19%30%15%3
810
July1st to 10thDay
21%14%20%30%14%2
796
11th to 20thDay
27%11%20%29%12%2
754
21st to endDay
29%11%18%26%15%1
684
August1st to 10thDay
31%14%21%23%9%2
626
11th to 20thDay
36%16%20%18%8%2
615
21st to endDay
36%11%20%22%10%1
693
September1st to 10thDay
39%17%17%17%8%2
563
11th to 20thDay
40%14%17%16%11%2
532
21st to endDay
36%17%17%18%10%3
360
October1st to 10thDay
39%16%19%15%9%2
360
11th to 20thDay
28%13%24%21%10%4
360
21st to endDay
30%13%22%19%13%4
396
November1st to 10thDay
22%13%23%20%16%5%
365
11th to 20thDay
18%13%25%24%13%6%
294
21st to endDay
23%13%19%29%12%5%
126
December1st to 10thDay
22%16%19%21%18%4
90
11th to 20thDay
23%17%27%26%6%2
90
21st to endDay
22%17%31%15%10%4
99
January1st to 10thNight
15%17%20%26%17%4
940
11th to 20thNight
23%15%25%22%11%4
857
21st to endNight
22%14%26%21%14%3
880
February1st to 10thNight
14%12%26%30%13%4
800
11th to 20thNight
27%15%29%20%8%1
784
21st to endNight
17%15%32%21%12%4
564
March1st to 10thNight
18%10%27%28%15%2
620
11th to 20thNight
12%12%25%33%15%4
620
21st to endNight
16%12%26%24%17%6%
594
April1st to 10thNight
19%15%21%26%16%3
540
11th to 20thNight
15%10%19%29%24%3
533
21st to endNight
14%15%21%29%18%3
540
May1st to 10thNight
17%14%24%24%19%2
424
11th to 20thNight
19%9%15%31%24%3
354
21st to endNight
18%8%21%26%22%4
234
June1st to 10thNight
18%13%14%30%21%4
180
11th to 20thNight
22%11%11%31%24%2
180
21st to endNight
23%9%13%33%17%4
180
July1st to 10thNight
21%7%16%27%26%3
175
11th to 20thNight
28%8%15%27%21%2
263
21st to endNight
30%7%16%27%17%3
394
August1st to 10thNight
34%12%19%20%12%3
358
11th to 20thNight
37%11%22%18%12%1
513
21st to endNight
33%9%16%27%13%2
594
September1st to 10thNight
37%14%21%16%11%1
540
11th to 20thNight
38%12%14%19%15%1
540
21st to endNight
33%11%15%21%16%3
565
October1st to 10thNight
34%13%19%19%12%1
652
11th to 20thNight
28%13%20%23%13%3
810
21st to endNight
27%11%22%23%14%3
891
November1st to 10thNight
23%13%24%24%14%2
830
11th to 20thNight
18%12%24%28%16%3
850
21st to endNight
24%13%21%24%13%5%
850
December1st to 10thNight
27%13%22%20%13%5%
879
11th to 20thNight
20%13%26%26%13%3
940
21st to endNight
24%19%22%19%12%4
1034
Page generated at 2024-01-12 12:17:45. Version ac07

Copyright 2024 Attilla Danko


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