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Williams Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Williams Lake clear sky chart from 2005-11-05 to 2017-09-10.

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
41%
14711
8%
46658
6%
14683
43%
14683
15%
34937

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
25%
750
5%
2686
3%
746
27%
746
6%
2254
January16th to endNight
31%
791
7%
2831
6%
791
33%
791
9%
2241
February1st to 15thNight
36%
696
6%
2357
5%
696
38%
696
11%
1845
February16th to endNight
47%
632
11%
2047
10%
632
50%
632
19%
1420
March1st to 15thNight
33%
720
9%
2100
6%
720
36%
720
14%
1592
March16th to endNight
43%
768
11%
2049
6%
768
44%
768
17%
1553
April1st to 15thNight
44%
703
9%
1783
5%
703
46%
703
19%
1348
April16th to endNight
39%
438
10%
1518
10%
438
41%
438
13%
1162
May1st to 15thNight
42%
359
8%
1440
10%
359
45%
359
13%
1020
May16th to endNight
44%
374
3%
1355
1%
374
45%
374
11%
1022
June1st to 15thNight
43%
360
0%
1080
0%
360
43%
360
16%
822
June16th to endNight
47%
360
0%
1080
0%
360
47%
360
14%
825
July1st to 15thNight
54%
340
0%
1142
0%
340
54%
340
20%
768
July16th to endNight
59%
376
6%
1264
5%
354
61%
354
23%
772
August1st to 15thNight
70%
360
11%
1432
16%
358
73%
358
25%
810
August16th to endNight
58%
584
15%
1730
13%
584
59%
584
23%
1175
September1st to 15thNight
60%
700
18%
1750
11%
700
61%
700
34%
1144
September16th to endNight
48%
656
17%
1805
10%
656
52%
656
24%
1256
October1st to 15thNight
45%
660
11%
1980
9%
660
49%
660
21%
1373
October16th to endNight
34%
704
9%
2277
6%
704
38%
704
13%
1745
November1st to 15thNight
31%
700
9%
2450
7%
700
35%
700
12%
1856
November16th to endNight
32%
771
8%
2571
6%
771
36%
771
10%
2062
December1st to 15thNight
34%
929
7%
2871
6%
929
36%
929
10%
2332
December16th to endNight
27%
980
6%
3060
3%
980
30%
980
9%
2540

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%9%47%7%46%5%6%7%30%
48002
Night
9%11%5%8%7%46%5%6%7%27%
46805
TransparencyDay
50%9%16%17%6%
47653
Night
53%9%14%15%5%
46658
SeeingDay
13%10%24%28%17%4
6550
Night
14%7%23%32%18%2
14721

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%17%8%11%9%5%6%5%5%5%14%
1253
16th to endDay
9%13%6%12%7%46%5%6%7%19%
1392
February1st to 15thDay
11%14%6%10%9%345%46%22%
1505
16th to endDay
411%6%9%8%5%5%6%6%8%28%
1427
March1st to 15thDay
7%13%6%9%7%46%5%7%8%24%
1860
16th to endDay
5%9%5%9%8%48%7%6%9%25%
2175
April1st to 15thDay
7%11%6%10%7%47%6%6%7%23%
2164
16th to endDay
9%11%6%9%8%5%7%6%7%6%21%
2442
May1st to 15thDay
11%9%48%7%46%5%5%7%29%
2511
16th to endDay
13%9%48%7%46%6%6%7%24%
2752
June1st to 15thDay
13%8%37%7%46%6%6%8%27%
2880
16th to endDay
10%8%47%7%48%6%6%8%27%
2880
July1st to 15thDay
9%5%245%36%6%6%7%41%
2745
16th to endDay
7%3245%35%6%7%7%46%
2819
August1st to 15thDay
5%4245%35%6%6%9%46%
2520
16th to endDay
9%5%25%6%35%5%7%8%38%
2471
September1st to 15thDay
9%5%245%2445%7%47%
2097
16th to endDay
13%7%25%6%35%45%8%36%
1824
October1st to 15thDay
11%8%36%6%35%46%8%35%
1650
16th to endDay
14%13%46%5%46%47%6%25%
1593
November1st to 15thDay
12%12%48%6%36%6%6%8%23%
1408
16th to endDay
9%14%7%11%11%45%46%7%17%
1375
December1st to 15thDay
10%11%7%10%9%46%7%6%6%18%
1086
16th to endDay
7%16%6%8%7%5%7%6%6%8%19%
1173
January1st to 15thNight
10%15%7%13%9%5%6%5%5%6%15%
2686
16th to endNight
10%13%6%10%8%46%5%6%8%18%
2831
February1st to 15thNight
12%15%5%9%6%5%5%5%46%22%
2345
16th to endNight
6%11%48%6%35%5%5%6%34%
2047
March1st to 15thNight
7%11%5%9%8%47%6%6%6%26%
2100
16th to endNight
411%38%8%48%6%7%8%27%
2045
April1st to 15thNight
5%10%5%8%7%47%6%7%8%27%
1783
16th to endNight
8%10%5%9%8%6%6%6%6%7%23%
1518
May1st to 15thNight
11%10%47%7%36%5%5%6%29%
1439
16th to endNight
12%9%37%6%47%6%7%8%23%
1355
June1st to 15thNight
16%8%36%7%45%7%6%7%26%
1080
16th to endNight
10%8%48%8%5%6%6%6%8%26%
1080
July1st to 15thNight
8%5%26%5%36%6%7%8%38%
1212
16th to endNight
8%325%6%35%5%6%9%41%
1350
August1st to 15thNight
43245%35%6%6%8%46%
1440
16th to endNight
9%5%36%7%36%5%7%8%36%
1730
September1st to 15thNight
7%6%25%6%2446%6%47%
1750
16th to endNight
14%6%25%6%34448%38%
1805
October1st to 15thNight
10%9%36%6%3445%7%38%
1980
16th to endNight
13%12%47%7%35%6%5%7%25%
2277
November1st to 15thNight
11%12%48%6%46%5%6%6%26%
2450
16th to endNight
10%13%7%9%8%45%6%6%7%19%
2571
December1st to 15thNight
11%13%6%9%9%45%6%5%6%20%
2871
16th to endNight
8%15%7%10%9%47%6%5%6%18%
3060

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
68%10%13%5%1
1253
16th to endDay
60%9%16%9%3
1392
February1st to 15thDay
60%9%13%11%4
1505
16th to endDay
51%8%17%16%6%
1427
March1st to 15thDay
56%8%15%13%5%
1860
16th to endDay
53%9%19%13%4
2175
April1st to 15thDay
57%9%13%13%5%
2164
16th to endDay
58%10%11%13%5%
2442
May1st to 15thDay
51%7%14%16%9%
2511
16th to endDay
55%10%14%16%3
2756
June1st to 15thDay
52%9%15%14%6%1
2880
16th to endDay
51%10%15%16%5%
2880
July1st to 15thDay
38%10%15%21%12%1
2586
16th to endDay
31%9%19%28%9%
2642
August1st to 15thDay
31%9%21%27%8%
2503
16th to endDay
39%9%21%21%7%
2471
September1st to 15thDay
34%8%19%25%10%1
2097
16th to endDay
46%8%17%18%7%1
1824
October1st to 15thDay
46%8%20%19%3
1650
16th to endDay
55%10%18%13%2
1593
November1st to 15thDay
55%10%13%13%5%
1408
16th to endDay
64%10%9%12%2
1375
December1st to 15thDay
62%11%14%9%1
1086
16th to endDay
60%9%15%11%3
1173
January1st to 15thNight
68%9%12%8%2
2686
16th to endNight
60%11%14%10%3
2831
February1st to 15thNight
61%7%14%12%4
2357
16th to endNight
48%6%20%16%7%
2047
March1st to 15thNight
54%8%14%16%5%
2100
16th to endNight
51%10%17%16%4
2049
April1st to 15thNight
51%8%13%18%7%
1783
16th to endNight
55%10%13%14%5%
1518
May1st to 15thNight
54%6%11%16%10%
1440
16th to endNight
54%11%16%12%3
1355
June1st to 15thNight
53%9%14%15%6%
1080
16th to endNight
52%11%14%14%5%1
1080
July1st to 15thNight
43%10%14%16%13%1
1142
16th to endNight
36%9%18%27%7%
1264
August1st to 15thNight
31%10%20%26%11%
1432
16th to endNight
42%9%18%21%7%1
1730
September1st to 15thNight
36%6%13%30%11%2
1750
16th to endNight
44%6%14%22%10%1
1805
October1st to 15thNight
45%8%19%20%6%
1980
16th to endNight
56%9%15%17%1
2277
November1st to 15thNight
56%9%14%13%5%
2450
16th to endNight
61%9%11%13%3
2571
December1st to 15thNight
62%9%14%11%2
2871
16th to endNight
63%11%12%9%2
3060

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
13%120%35%21%8%
60
16th to endDay
14%12%23%21%20%7%
64
February1st to 15thDay
15%8%29%32%12%1
165
16th to endDay
9%15%25%25%19%4
213
March1st to 15thDay
15%25%29%21%6%1
270
16th to endDay
10%22%34%25%42
288
April1st to 15thDay
15%18%23%26%11%4
269
16th to endDay
16%20%27%24%8%2
270
May1st to 15thDay
18%11%25%23%14%5%
288
16th to endDay
16%8%23%26%18%6%
468
June1st to 15thDay
15%10%24%29%17%2
675
16th to endDay
13%8%21%29%22%4
675
July1st to 15thDay
10%426%36%18%4
520
16th to endDay
6%6%23%32%26%3
488
August1st to 15thDay
6%316%33%27%12%
315
16th to endDay
9%7%24%32%20%4
332
September1st to 15thDay
14%7%22%24%23%7%
294
16th to endDay
18%9%23%28%13%5%
255
October1st to 15thDay
14%16%23%23%18%3
255
16th to endDay
21%8%23%28%13%5%
142
November1st to 15thDay
20%20%26%23%8%1
60
16th to endDay
26%8%8%25%16%15%
60
December1st to 15thDay
11%6%18%26%21%15%
60
16th to endDay
18%315%35%20%6%
64
January1st to 15thNight
18%11%24%29%14%1
750
16th to endNight
17%8%28%28%14%1
791
February1st to 15thNight
19%6%24%33%13%2
704
16th to endNight
12%6%20%39%19%2
632
March1st to 15thNight
14%11%32%29%9%2
720
16th to endNight
9%10%26%32%19%1
768
April1st to 15thNight
11%7%25%32%20%3
703
16th to endNight
14%7%28%34%13%2
438
May1st to 15thNight
13%6%26%35%16%1
360
16th to endNight
16%422%28%24%3
375
June1st to 15thNight
17%5%23%32%20%1
360
16th to endNight
13%421%36%22%2
360
July1st to 15thNight
8%222%37%27%1
340
16th to endNight
9%319%36%28%3
376
August1st to 15thNight
6%112%35%36%7%
360
16th to endNight
13%213%34%32%2
584
September1st to 15thNight
11%413%34%31%5%
700
16th to endNight
17%6%20%29%21%3
656
October1st to 15thNight
15%7%23%31%20%1
660
16th to endNight
19%9%25%28%14%2
704
November1st to 15thNight
19%12%28%28%10%1
700
16th to endNight
18%10%24%32%11%2
771
December1st to 15thNight
15%10%22%33%16%2
929
16th to endNight
15%9%29%32%11%1
980
Page generated at 2017-09-11 16:35:21. Version ac04

Copyright 2017 A. Danko


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