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

2017-09-12
.

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%
13972
5%
46446
4%
13940
41%
13940
12%
35846

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%
827
3%
3115
3%
823
34%
823
7%
2587
January16th to endNight
27%
800
8%
3069
6%
800
32%
800
8%
2490
February1st to 15thNight
37%
733
6%
2577
4%
729
40%
729
11%
1990
February16th to endNight
39%
659
8%
2130
6%
659
40%
659
13%
1652
March1st to 15thNight
42%
723
12%
2181
11%
723
43%
723
16%
1625
March16th to endNight
47%
590
9%
2009
10%
590
47%
590
14%
1477
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
42%
529
6%
1736
5%
529
44%
529
15%
1273
September16th to endNight
35%
593
10%
1799
8%
593
37%
593
15%
1339
October1st to 15thNight
38%
660
9%
2035
7%
660
40%
660
14%
1577
October16th to endNight
38%
727
4%
2419
2%
727
40%
727
11%
1893
November1st to 15thNight
31%
730
2%
2674
2%
730
32%
730
6%
2272
November16th to endNight
31%
813
5%
2943
4%
813
33%
813
8%
2403
December1st to 15thNight
32%
930
4%
3168
2%
930
34%
930
8%
2631
December16th to endNight
34%
992
5%
3456
4%
992
36%
992
7%
2905

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
9%10%5%9%9%5%7%7%6%7%21%
48301
Night
5%10%5%10%9%5%8%7%7%8%20%
46549
TransparencyDay
59%6%16%13%3
47908
Night
59%7%15%14%3
46447
SeeingDay
18%11%24%26%15%3
7617
Night
12%6%26%31%19%3
13976

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
312%6%13%14%9%12%5%7%6%8%
832
16th to endDay
210%8%11%11%7%8%9%8%8%12%
1155
February1st to 15thDay
110%5%12%8%5%10%9%8%9%18%
1287
16th to endDay
38%5%11%10%6%8%7%6%9%22%
1344
March1st to 15thDay
29%6%11%9%7%9%7%8%7%20%
1779
16th to endDay
29%6%10%9%5%8%8%7%6%25%
2214
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
16%11%310%6%46%6%7%5%20%
2143
16th to endDay
12%13%49%8%5%6%7%47%21%
1831
October1st to 15thDay
10%11%49%9%45%5%6%7%24%
1595
16th to endDay
6%12%5%11%11%5%7%7%6%7%18%
1453
November1st to 15thDay
312%9%12%12%5%7%9%6%6%13%
1181
16th to endDay
312%8%14%9%5%9%8%10%8%10%
1005
December1st to 15thDay
313%7%14%13%8%9%7%7%8%7%
792
16th to endDay
212%7%10%14%7%9%9%9%9%9%
768
January1st to 15thNight
412%6%13%12%6%9%6%5%7%13%
3115
16th to endNight
312%6%10%11%6%9%8%8%9%13%
3069
February1st to 15thNight
28%5%11%11%7%9%9%8%8%17%
2565
16th to endNight
28%6%11%12%6%7%7%6%9%21%
2130
March1st to 15thNight
110%6%11%8%6%8%6%6%6%27%
2181
16th to endNight
19%7%12%9%5%6%7%6%7%26%
2004
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%8%37%7%6%7%5%6%8%28%
1736
16th to endNight
11%11%39%8%35%5%6%8%26%
1799
October1st to 15thNight
9%12%48%8%5%6%6%46%27%
2035
16th to endNight
6%14%5%11%8%5%6%6%5%7%20%
2419
November1st to 15thNight
311%8%14%12%7%8%7%8%6%11%
2674
16th to endNight
212%7%13%13%6%7%7%8%7%12%
2943
December1st to 15thNight
5%13%7%11%11%6%9%7%7%8%11%
3168
16th to endNight
312%7%12%10%7%10%8%8%8%10%
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
76%6%8%6%2
832
16th to endDay
65%8%14%9%2
1155
February1st to 15thDay
57%8%14%14%5%
1287
16th to endDay
55%8%17%11%6%
1344
March1st to 15thDay
59%6%11%17%41
1779
16th to endDay
55%7%14%14%7%
2214
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%15%13%
2143
16th to endDay
61%7%16%12%1
1831
October1st to 15thDay
59%7%15%13%3
1595
16th to endDay
63%7%20%7%
1453
November1st to 15thDay
70%8%12%8%
1181
16th to endDay
68%7%13%7%2
1005
December1st to 15thDay
74%6%11%7%
792
16th to endDay
70%8%9%10%1
768
January1st to 15thNight
69%6%12%8%3
3115
16th to endNight
65%8%10%12%2
3069
February1st to 15thNight
60%6%12%16%2
2577
16th to endNight
58%9%13%12%6%
2130
March1st to 15thNight
55%5%11%18%7%1
2181
16th to endNight
56%5%13%14%9%
2009
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
53%8%19%17%1
1736
16th to endNight
54%7%17%18%1
1799
October1st to 15thNight
56%9%16%14%2
2035
16th to endNight
61%6%19%10%
2419
November1st to 15thNight
70%8%13%6%
2674
16th to endNight
67%6%12%11%1
2943
December1st to 15thNight
68%7%14%8%1
3168
16th to endNight
70%7%11%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
12%322%29%29%3
31
16th to endDay
10%7%32%29%17%1
67
February1st to 15thDay
6%10%31%36%11%4
236
16th to endDay
8%8%32%27%18%4
211
March1st to 15thDay
7%13%30%30%12%4
240
16th to endDay
10%9%26%28%22%2
276
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
29%13%25%17%11%1
316
16th to endDay
24%15%26%16%13%2
246
October1st to 15thDay
19%16%25%23%11%3
225
16th to endDay
18%10%25%28%11%4
235
November1st to 15thDay
5%10%31%40%10%3
60
16th to endDay
6%133%26%16%15%
60
December1st to 15thDay
2219%26%38%11%
42
16th to endDay
328%37%28%3
32
January1st to 15thNight
10%5%32%35%14%2
828
16th to endNight
10%8%40%28%12%
800
February1st to 15thNight
6%7%33%38%12%1
734
16th to endNight
6%5%30%35%17%3
659
March1st to 15thNight
7%9%26%37%18%1
723
16th to endNight
5%5%19%28%34%6%
590
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%22%30%17%3
529
16th to endNight
21%8%24%25%18%2
593
October1st to 15thNight
21%9%21%29%16%2
660
16th to endNight
18%5%24%31%17%3
727
November1st to 15thNight
11%6%26%34%17%2
730
16th to endNight
10%5%29%30%20%1
813
December1st to 15thNight
12%7%30%31%15%3
930
16th to endNight
10%5%31%32%17%2
992
Page generated at 2017-09-13 04:39:16. Version ac04

Copyright 2017 A. Danko


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