Whitehorse
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Whitehorse clear sky chart from 2005-11-05 to 2018-03-21.

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%
14896
5%
49236
5%
14864
42%
14864
13%
37863

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%
908
4%
3375
4%
904
34%
904
8%
2790
January16th to endNight
30%
880
9%
3325
7%
880
34%
880
8%
2687
February1st to 15thNight
39%
808
8%
2796
6%
804
42%
804
12%
2124
February16th to endNight
39%
724
8%
2305
5%
724
40%
724
13%
1789
March1st to 15thNight
42%
785
12%
2363
11%
785
44%
785
16%
1759
March16th to endNight
47%
609
10%
2076
11%
609
48%
609
14%
1523
April1st to 15thNight
53%
539
7%
1664
6%
539
54%
539
21%
1148
April16th to endNight
54%
540
3%
1440
2%
540
55%
540
25%
1006
May1st to 15thNight
49%
362
0%
1113
0%
362
49%
362
23%
731
May16th to endNight
57%
341
0%
1019
0%
341
57%
341
26%
648
June1st to 15thNight
53%
180
0%
720
0%
180
53%
180
18%
468
June16th to endNight
54%
180
0%
720
0%
180
54%
180
14%
510
July1st to 15thNight
55%
170
0%
713
0%
170
55%
170
14%
480
July16th to endNight
49%
332
0%
1018
0%
310
48%
310
17%
714
August1st to 15thNight
52%
449
0%
1200
0%
447
52%
447
24%
829
August16th to endNight
40%
573
1%
1528
1%
573
40%
573
15%
1198
September1st to 15thNight
43%
540
7%
1772
5%
540
45%
540
16%
1286
September16th to endNight
37%
647
11%
1962
9%
647
39%
647
16%
1446
October1st to 15thNight
37%
720
8%
2220
7%
720
39%
720
13%
1723
October16th to endNight
38%
803
4%
2640
3%
803
40%
803
12%
2074
November1st to 15thNight
32%
805
2%
2903
2%
805
33%
805
6%
2458
November16th to endNight
33%
893
5%
3188
4%
893
35%
893
8%
2604
December1st to 15thNight
32%
1020
4%
3432
2%
1020
34%
1020
8%
2819
December16th to endNight
38%
1088
8%
3744
7%
1088
40%
1088
9%
3049

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
8%10%5%10%9%5%7%7%6%7%21%
49701
Night
5%10%5%10%9%5%8%7%7%8%21%
49339
TransparencyDay
59%6%16%13%3
49308
Night
59%7%15%14%3
49237
SeeingDay
17%10%24%26%15%3
8071
Night
12%6%25%32%20%3
14900

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
311%6%13%14%9%12%5%7%6%10%
903
16th to endDay
210%7%12%11%7%8%10%8%8%11%
1251
February1st to 15thDay
110%6%12%7%5%9%8%8%9%21%
1398
16th to endDay
38%5%12%10%6%8%7%6%9%22%
1455
March1st to 15thDay
28%5%11%9%7%9%7%8%7%20%
1927
16th to endDay
29%6%10%9%48%8%7%6%25%
2274
April1st to 15thDay
212%5%10%9%5%8%7%6%8%23%
2283
16th to endDay
212%6%12%8%37%7%6%8%23%
2520
May1st to 15thDay
7%14%6%8%8%46%5%5%6%24%
2835
16th to endDay
6%8%48%7%46%7%6%8%29%
3093
June1st to 15thDay
13%10%48%7%46%6%5%7%25%
3240
16th to endDay
13%8%410%8%5%7%7%6%7%19%
3240
July1st to 15thDay
13%8%5%8%9%48%7%6%7%20%
3204
16th to endDay
15%9%5%8%7%47%6%6%7%22%
3079
August1st to 15thDay
11%7%37%7%5%6%6%6%9%28%
2754
16th to endDay
20%11%48%7%45%5%6%7%17%
2674
September1st to 15thDay
15%11%310%6%46%6%6%5%21%
2188
16th to endDay
11%12%49%8%5%6%7%5%7%21%
1998
October1st to 15thDay
10%12%49%9%46%5%6%7%24%
1740
16th to endDay
5%12%5%12%11%5%7%7%6%7%18%
1584
November1st to 15thDay
313%9%13%12%5%7%9%6%6%13%
1282
16th to endDay
312%8%15%10%5%9%8%9%8%10%
1089
December1st to 15thDay
312%6%13%13%8%8%7%8%8%8%
858
16th to endDay
211%7%9%13%6%9%8%8%9%12%
832
January1st to 15thNight
412%6%13%12%6%9%6%5%7%14%
3375
16th to endNight
311%6%10%11%6%9%9%8%8%13%
3325
February1st to 15thNight
28%5%10%11%6%8%8%8%8%19%
2784
16th to endNight
28%6%11%12%6%7%7%6%9%21%
2305
March1st to 15thNight
110%5%11%8%6%8%6%6%6%27%
2363
16th to endNight
110%7%11%9%5%6%7%6%7%26%
2071
April1st to 15thNight
28%5%9%8%46%6%7%8%31%
1664
16th to endNight
36%47%7%38%6%9%10%30%
1440
May1st to 15thNight
5%7%45%6%46%5%8%10%34%
1113
16th to endNight
46%36%6%47%6%8%7%38%
1019
June1st to 15thNight
9%8%37%7%5%445%9%33%
720
16th to endNight
8%7%47%7%48%8%9%9%23%
720
July1st to 15thNight
11%5%37%8%5%8%6%8%6%27%
756
16th to endNight
12%5%36%7%46%48%10%29%
1089
August1st to 15thNight
9%5%237%46%6%9%9%35%
1206
16th to endNight
17%10%48%6%45%5%6%7%22%
1528
September1st to 15thNight
10%7%36%7%6%7%5%6%8%29%
1772
16th to endNight
11%10%39%8%35%5%6%8%27%
1962
October1st to 15thNight
9%13%48%8%46%5%46%27%
2220
16th to endNight
6%15%5%11%8%46%6%5%7%20%
2640
November1st to 15thNight
311%8%14%12%6%7%7%7%6%11%
2903
16th to endNight
212%7%13%13%6%7%7%8%7%12%
3188
December1st to 15thNight
413%6%11%10%6%9%7%7%8%13%
3432
16th to endNight
211%6%12%10%6%9%8%7%8%14%
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
73%5%9%6%3
903
16th to endDay
65%8%13%9%2
1251
February1st to 15thDay
56%8%13%14%8%
1398
16th to endDay
56%8%17%12%5%
1455
March1st to 15thDay
58%6%12%16%41
1927
16th to endDay
55%7%14%14%7%
2274
April1st to 15thDay
57%6%19%12%4
2283
16th to endDay
57%5%16%16%3
2520
May1st to 15thDay
59%414%17%4
2835
16th to endDay
48%5%17%22%5%
3097
June1st to 15thDay
56%5%15%17%4
3240
16th to endDay
60%7%16%13%2
3240
July1st to 15thDay
57%6%19%13%2
3018
16th to endDay
58%7%19%13%
2887
August1st to 15thDay
51%7%22%15%2
2735
16th to endDay
65%7%17%9%
2674
September1st to 15thDay
61%8%16%13%
2188
16th to endDay
60%8%16%12%2
1998
October1st to 15thDay
59%7%15%13%3
1740
16th to endDay
63%8%19%8%
1584
November1st to 15thDay
70%8%12%8%
1282
16th to endDay
69%6%13%7%2
1089
December1st to 15thDay
71%6%12%7%1
858
16th to endDay
66%7%9%11%3
832
January1st to 15thNight
68%6%12%8%3
3375
16th to endNight
65%8%10%12%3
3325
February1st to 15thNight
59%6%12%16%41
2796
16th to endNight
58%8%13%12%6%
2305
March1st to 15thNight
55%5%11%18%7%
2363
16th to endNight
56%5%13%15%9%
2076
April1st to 15thNight
47%6%22%19%4
1664
16th to endNight
44%7%20%24%3
1440
May1st to 15thNight
43%5%19%25%5%
1114
16th to endNight
40%5%21%23%8%
1019
June1st to 15thNight
48%419%23%4
720
16th to endNight
51%9%18%18%2
720
July1st to 15thNight
51%5%20%19%2
713
16th to endNight
49%8%22%18%1
1018
August1st to 15thNight
41%9%25%18%4
1200
16th to endNight
58%7%22%10%1
1528
September1st to 15thNight
52%7%19%18%1
1772
16th to endNight
53%7%17%18%2
1962
October1st to 15thNight
57%9%16%14%3
2220
16th to endNight
62%6%18%10%1
2640
November1st to 15thNight
69%8%13%6%
2903
16th to endNight
67%6%12%11%1
3188
December1st to 15thNight
66%7%14%9%1
3432
16th to endNight
66%6%10%10%4
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
12%221%40%21%2
47
16th to endDay
8%6%24%29%25%7%
99
February1st to 15thDay
6%8%29%35%15%4
281
16th to endDay
7%9%34%29%16%3
250
March1st to 15thDay
7%13%31%30%12%3
285
16th to endDay
10%8%26%28%22%2
293
April1st to 15thDay
12%12%32%22%17%2
341
16th to endDay
17%17%27%27%8%1
450
May1st to 15thDay
22%16%25%25%8%1
468
16th to endDay
14%12%25%26%16%4
587
June1st to 15thDay
21%7%25%26%17%1
675
16th to endDay
17%7%18%30%21%5%
675
July1st to 15thDay
18%6%17%29%21%4
612
16th to endDay
21%11%19%27%16%4
515
August1st to 15thDay
17%10%21%27%18%4
494
16th to endDay
29%12%27%19%9%1
523
September1st to 15thDay
28%13%25%17%12%2
331
16th to endDay
21%14%27%18%15%3
302
October1st to 15thDay
19%16%27%22%10%2
270
16th to endDay
18%10%23%30%12%3
282
November1st to 15thDay
6%11%28%37%13%2
90
16th to endDay
5%128%30%21%13%
90
December1st to 15thDay
19%23%28%25%11%
63
16th to endDay
420%35%27%12%
48
January1st to 15thNight
11%431%36%14%2
909
16th to endNight
9%7%36%29%15%1
880
February1st to 15thNight
7%7%30%39%13%1
809
16th to endNight
6%6%30%36%16%3
724
March1st to 15thNight
6%9%26%37%18%1
785
16th to endNight
5%6%18%28%34%6%
609
April1st to 15thNight
6%5%19%34%29%5%
539
16th to endNight
8%6%20%30%30%4
540
May1st to 15thNight
12%8%21%29%23%4
363
16th to endNight
8%7%16%30%33%3
342
June1st to 15thNight
15%218%33%26%3
180
16th to endNight
11%316%35%29%3
180
July1st to 15thNight
15%14%28%35%5%
170
16th to endNight
20%417%27%25%4
332
August1st to 15thNight
15%420%26%25%8%
449
16th to endNight
26%419%26%19%4
573
September1st to 15thNight
17%8%21%30%18%4
540
16th to endNight
20%8%23%25%19%2
647
October1st to 15thNight
20%9%22%29%16%2
720
16th to endNight
18%5%23%32%16%2
803
November1st to 15thNight
10%7%25%35%17%2
805
16th to endNight
9%5%28%33%21%2
893
December1st to 15thNight
11%8%30%31%14%2
1020
16th to endNight
9%5%29%32%20%3
1088
Page generated at 2018-03-22 08:34:26. Version ac04

Copyright 2018 A. Danko


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