High Level Airport
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the High Level Airport clear sky chart from 2005-11-05 to 2017-10-06.

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
42%
15212
8%
46844
6%
15181
44%
15181
17%
33971

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
33%
930
4%
2877
2%
925
35%
925
9%
2369
January16th to endNight
35%
986
11%
3066
8%
986
39%
986
14%
2278
February1st to 15thNight
45%
703
11%
2473
11%
701
48%
701
18%
1692
February16th to endNight
38%
632
11%
2111
9%
632
43%
632
15%
1536
March1st to 15thNight
36%
720
14%
2160
10%
720
40%
720
19%
1541
March16th to endNight
45%
768
14%
2020
7%
768
48%
768
25%
1422
April1st to 15thNight
46%
629
11%
1709
8%
629
48%
629
23%
1208
April16th to endNight
41%
375
8%
1451
9%
375
44%
375
17%
951
May1st to 15thNight
49%
359
0%
1232
0%
359
49%
359
23%
769
May16th to endNight
53%
374
0%
1098
0%
374
53%
374
29%
691
June1st to 15thNight
53%
360
0%
900
0%
360
53%
360
25%
654
June16th to endNight
56%
360
0%
900
0%
360
56%
360
26%
638
July1st to 15thNight
57%
340
0%
935
0%
340
57%
340
25%
647
July16th to endNight
63%
376
0%
1062
0%
354
64%
354
28%
690
August1st to 15thNight
68%
360
0%
1301
0%
358
68%
358
25%
780
August16th to endNight
52%
436
9%
1582
10%
436
55%
436
20%
1032
September1st to 15thNight
55%
670
11%
1750
7%
670
57%
670
30%
1170
September16th to endNight
42%
716
12%
1962
7%
716
45%
716
21%
1431
October1st to 15thNight
43%
684
11%
2117
7%
684
47%
684
21%
1453
October16th to endNight
33%
720
8%
2347
5%
720
38%
720
14%
1769
November1st to 15thNight
33%
875
12%
2625
8%
875
37%
875
16%
1934
November16th to endNight
33%
917
7%
2842
5%
917
36%
917
13%
2192
December1st to 15thNight
27%
930
5%
3060
3%
930
28%
930
8%
2540
December16th to endNight
35%
992
8%
3264
5%
992
38%
992
10%
2584

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
10%8%47%6%35%5%6%8%31%
48418
Night
9%10%48%7%46%5%6%7%30%
46963
TransparencyDay
48%8%18%18%5%
48041
Night
50%8%16%18%5%
46845
SeeingDay
14%7%23%29%19%4
7233
Night
14%6%24%33%17%2
15216

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
9%12%5%12%11%5%7%5%6%5%18%
1060
16th to endDay
7%11%7%8%7%46%6%7%6%26%
1167
February1st to 15thDay
7%10%48%9%46%5%6%6%29%
1391
16th to endDay
6%13%5%8%9%446%7%7%24%
1363
March1st to 15thDay
6%13%7%10%7%346%6%7%26%
1800
16th to endDay
7%12%5%8%6%345%6%7%33%
2202
April1st to 15thDay
6%8%38%7%46%6%7%8%33%
2239
16th to endDay
10%9%37%7%35%5%5%7%34%
2508
May1st to 15thDay
9%6%36%5%35%5%6%9%39%
2717
16th to endDay
12%6%35%5%25%46%7%39%
3015
June1st to 15thDay
13%7%47%6%45%5%5%8%29%
3060
16th to endDay
13%6%35%5%36%6%7%10%30%
3060
July1st to 15thDay
13%6%46%6%46%6%7%8%29%
2967
16th to endDay
9%5%35%6%46%6%7%10%32%
3035
August1st to 15thDay
9%6%35%5%46%6%7%7%37%
2652
16th to endDay
12%5%26%7%46%6%6%8%33%
2620
September1st to 15thDay
12%6%35%5%25%45%7%42%
2208
16th to endDay
14%7%37%5%335%5%8%34%
1998
October1st to 15thDay
13%10%36%6%35%45%6%34%
1638
16th to endDay
13%14%5%9%7%445%47%23%
1513
November1st to 15thDay
12%12%6%8%6%34446%30%
1232
16th to endDay
7%14%6%10%10%26%6%6%7%21%
1113
December1st to 15thDay
10%18%7%11%8%46%437%17%
900
16th to endDay
7%13%7%13%10%6%7%5%5%6%17%
960
January1st to 15thNight
9%11%6%11%10%6%7%6%6%6%16%
2877
16th to endNight
7%12%5%8%8%5%6%6%6%6%27%
3066
February1st to 15thNight
5%10%49%7%45%5%6%6%33%
2461
16th to endNight
7%11%5%9%9%47%5%46%29%
2111
March1st to 15thNight
7%10%6%10%6%345%6%6%31%
2160
16th to endNight
6%10%5%6%6%35%6%7%6%35%
2016
April1st to 15thNight
6%7%36%7%5%7%6%6%9%31%
1709
16th to endNight
9%9%46%6%37%45%7%34%
1451
May1st to 15thNight
10%6%26%6%45%6%5%7%38%
1232
16th to endNight
9%5%446%245%5%8%43%
1098
June1st to 15thNight
9%6%28%6%45%6%49%35%
900
16th to endNight
10%6%37%5%36%6%7%9%35%
900
July1st to 15thNight
11%6%25%6%26%5%6%11%34%
992
16th to endNight
10%424435%7%8%11%36%
1134
August1st to 15thNight
5%415%5%36%6%6%12%41%
1307
16th to endNight
8%6%25%5%35%5%7%9%38%
1582
September1st to 15thNight
10%5%245%35%5%5%8%43%
1750
16th to endNight
12%6%26%7%45%7%6%8%31%
1962
October1st to 15thNight
11%8%36%7%45%5%5%7%35%
2117
16th to endNight
10%15%48%6%35%5%6%6%27%
2347
November1st to 15thNight
13%13%47%6%3345%6%30%
2625
16th to endNight
9%12%5%10%9%45%5%6%7%24%
2842
December1st to 15thNight
12%14%6%9%9%46%6%5%7%17%
3060
16th to endNight
7%12%6%13%9%47%6%5%7%19%
3264

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
64%8%11%10%4
1060
16th to endDay
55%8%14%14%6%
1167
February1st to 15thDay
52%6%14%20%6%
1391
16th to endDay
55%8%17%14%3
1363
March1st to 15thDay
55%7%14%17%3
1800
16th to endDay
48%7%15%22%5%
2202
April1st to 15thDay
44%9%15%20%9%
2239
16th to endDay
47%6%14%20%10%
2508
May1st to 15thDay
40%6%15%24%12%
2717
16th to endDay
42%6%12%22%14%
3020
June1st to 15thDay
50%7%15%19%6%
3060
16th to endDay
44%10%19%20%5%
3060
July1st to 15thDay
47%10%22%15%3
2795
16th to endDay
42%13%25%18%
2844
August1st to 15thDay
40%12%24%20%2
2633
16th to endDay
45%10%22%19%1
2620
September1st to 15thDay
39%9%28%19%3
2208
16th to endDay
47%8%22%18%2
1998
October1st to 15thDay
49%6%18%21%4
1638
16th to endDay
59%8%16%13%1
1513
November1st to 15thDay
54%6%17%17%4
1232
16th to endDay
60%8%15%12%2
1113
December1st to 15thDay
68%7%11%11%
900
16th to endDay
65%7%9%14%2
960
January1st to 15thNight
64%9%13%10%2
2877
16th to endNight
54%8%16%13%5%1
3066
February1st to 15thNight
49%6%17%20%6%
2473
16th to endNight
54%6%13%21%4
2111
March1st to 15thNight
51%5%14%20%7%
2160
16th to endNight
45%6%15%24%8%
2020
April1st to 15thNight
46%7%14%19%10%2
1709
16th to endNight
47%5%12%20%12%1
1451
May1st to 15thNight
41%5%11%24%15%1
1233
16th to endNight
37%6%11%22%19%2
1098
June1st to 15thNight
44%9%15%20%9%
900
16th to endNight
43%8%16%21%9%
900
July1st to 15thNight
41%9%23%21%4
935
16th to endNight
36%9%26%25%1
1062
August1st to 15thNight
32%12%27%23%4
1301
16th to endNight
39%12%19%23%4
1582
September1st to 15thNight
36%9%22%24%6%
1750
16th to endNight
46%9%18%18%5%
1962
October1st to 15thNight
45%7%18%22%5%
2117
16th to endNight
55%8%19%14%2
2347
November1st to 15thNight
53%7%16%19%2
2625
16th to endNight
58%8%15%15%2
2842
December1st to 15thNight
64%10%13%10%
3060
16th to endNight
62%7%12%15%2
3264

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
10%118%40%28%1
60
16th to endDay
17%6%28%35%12%
64
February1st to 15thDay
23%6%18%26%16%8%
60
16th to endDay
11%6%36%33%12%
116
March1st to 15thDay
12%16%26%25%14%4
270
16th to endDay
15%13%31%28%9%1
288
April1st to 15thDay
8%14%30%33%11%
269
16th to endDay
14%15%28%25%15%
273
May1st to 15thDay
13%10%23%26%20%5%
494
16th to endDay
13%6%19%30%23%5%
705
June1st to 15thDay
14%6%22%33%18%3
675
16th to endDay
14%318%30%24%7%
675
July1st to 15thDay
14%422%28%24%5%
645
16th to endDay
12%418%30%25%9%
703
August1st to 15thDay
11%316%28%29%10%
446
16th to endDay
17%8%33%31%8%
332
September1st to 15thDay
19%7%27%24%15%5%
315
16th to endDay
14%10%30%26%16%2
315
October1st to 15thDay
16%8%33%26%12%2
196
16th to endDay
34%9%21%20%11%3
88
November1st to 15thDay
11%5%45%21%15%1
60
16th to endDay
15%6%23%35%18%1
60
December1st to 15thDay
36%5%13%31%11%1
60
16th to endDay
6%325%32%28%4
64
January1st to 15thNight
14%6%25%36%15%2
930
16th to endNight
14%9%27%36%10%1
986
February1st to 15thNight
11%6%24%36%17%3
705
16th to endNight
12%5%28%36%14%2
632
March1st to 15thNight
12%9%30%30%14%3
720
16th to endNight
10%7%24%37%17%2
768
April1st to 15thNight
10%6%30%34%15%1
629
16th to endNight
11%10%27%32%15%2
375
May1st to 15thNight
11%7%23%31%23%3
360
16th to endNight
11%420%36%25%1
375
June1st to 15thNight
14%318%35%25%3
360
16th to endNight
12%217%34%27%5%
360
July1st to 15thNight
15%217%35%28%1
340
16th to endNight
11%215%29%34%6%
376
August1st to 15thNight
8%313%33%32%9%
360
16th to endNight
14%221%31%27%2
436
September1st to 15thNight
13%320%35%22%4
670
16th to endNight
16%7%24%30%18%2
716
October1st to 15thNight
16%7%24%32%17%1
684
16th to endNight
19%7%28%30%12%1
720
November1st to 15thNight
19%7%29%28%13%1
875
16th to endNight
17%6%26%32%13%3
917
December1st to 15thNight
20%8%26%30%12%1
930
16th to endNight
12%7%21%37%17%3
992
Page generated at 2017-10-07 12:07:50. Version ac04

Copyright 2017 A. Danko


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