Slave Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Slave Lake clear sky chart from 2005-11-05 to 2019-07-16.

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
35%
17636
9%
53985
5%
17606
39%
17606
16%
39048

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
27%
1106
7%
3345
4%
1105
31%
1105
10%
2612
January16th to endNight
23%
1074
11%
3322
6%
1074
30%
1074
11%
2528
February1st to 15thNight
33%
824
11%
2882
9%
819
38%
819
14%
2055
February16th to endNight
37%
736
10%
2372
8%
736
42%
736
16%
1730
March1st to 15thNight
35%
840
15%
2500
10%
840
40%
840
18%
1789
March16th to endNight
39%
896
11%
2394
6%
896
41%
896
18%
1783
April1st to 15thNight
39%
713
13%
1973
8%
713
43%
713
21%
1410
April16th to endNight
37%
562
9%
1810
8%
562
40%
562
16%
1285
May1st to 15thNight
46%
419
5%
1492
4%
419
47%
419
21%
931
May16th to endNight
42%
438
0%
1516
0%
438
42%
438
19%
1008
June1st to 15thNight
42%
420
0%
1260
0%
420
42%
420
16%
938
June16th to endNight
51%
420
0%
1260
0%
420
51%
420
21%
874
July1st to 15thNight
56%
400
0%
1200
0%
400
56%
400
23%
806
July16th to endNight
56%
410
0%
1303
0%
388
56%
388
24%
815
August1st to 15thNight
61%
384
5%
1463
5%
382
63%
382
22%
902
August16th to endNight
47%
570
11%
1812
9%
570
51%
570
22%
1191
September1st to 15thNight
51%
699
13%
1905
9%
699
53%
699
28%
1256
September16th to endNight
40%
776
14%
2145
7%
776
45%
776
24%
1461
October1st to 15thNight
35%
780
12%
2364
7%
780
40%
780
17%
1704
October16th to endNight
30%
838
10%
2710
5%
838
37%
838
13%
1937
November1st to 15thNight
24%
1025
11%
2996
6%
1025
29%
1025
13%
2303
November16th to endNight
22%
1050
7%
3150
2%
1050
27%
1050
10%
2506
December1st to 15thNight
26%
1072
9%
3227
5%
1072
30%
1072
11%
2533
December16th to endNight
30%
1184
10%
3584
4%
1184
34%
1184
13%
2691

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%
55375
Night
8%9%48%7%46%5%6%7%31%
54121
TransparencyDay
49%10%17%17%5%
55014
Night
49%8%16%18%5%
53987
SeeingDay
14%12%30%26%12%3
9138
Night
13%12%29%28%14%2
17642

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
5%11%49%9%5%8%8%6%8%22%
1254
16th to endDay
6%12%5%9%8%47%5%5%7%26%
1617
February1st to 15thDay
49%5%9%7%47%7%7%9%27%
1640
16th to endDay
313%6%12%8%5%7%5%6%6%24%
1670
March1st to 15thDay
6%9%5%7%7%46%6%7%9%29%
2119
16th to endDay
7%10%6%11%7%35%6%6%7%25%
2533
April1st to 15thDay
9%11%48%7%36%5%5%8%28%
2635
16th to endDay
12%12%37%6%35%5%6%6%30%
2754
May1st to 15thDay
10%6%35%6%35%6%7%8%37%
3119
16th to endDay
14%6%35%5%35%5%6%7%36%
3298
June1st to 15thDay
16%7%36%7%46%5%7%9%26%
3360
16th to endDay
14%6%36%6%35%5%6%8%33%
3360
July1st to 15thDay
14%5%25%5%35%5%6%8%37%
3360
16th to endDay
12%4245%35%5%7%9%38%
3147
August1st to 15thDay
10%6%25%6%36%5%7%9%36%
2741
16th to endDay
12%5%26%5%45%6%7%9%34%
2742
September1st to 15thDay
14%7%36%5%3445%8%36%
2382
16th to endDay
12%8%26%6%345%6%7%36%
2145
October1st to 15thDay
13%10%48%6%35%45%6%30%
1924
16th to endDay
10%12%48%5%445%6%8%28%
1853
November1st to 15thDay
9%11%5%9%9%445%47%26%
1519
16th to endDay
5%12%5%11%9%36%45%9%26%
1470
December1st to 15thDay
6%10%7%9%9%5%8%6%6%7%21%
1389
16th to endDay
29%5%12%10%47%8%6%8%24%
1344
January1st to 15thNight
6%12%5%9%9%5%7%6%7%8%22%
3345
16th to endNight
6%10%5%10%9%47%6%5%7%27%
3322
February1st to 15thNight
5%10%49%9%46%5%5%7%29%
2872
16th to endNight
5%9%6%9%6%5%6%7%5%8%29%
2372
March1st to 15thNight
6%10%49%6%45%5%6%8%31%
2500
16th to endNight
7%11%5%8%7%46%5%6%9%27%
2391
April1st to 15thNight
8%9%46%6%36%6%7%7%33%
1973
16th to endNight
12%11%46%5%36%45%6%32%
1810
May1st to 15thNight
9%6%37%6%35%5%7%7%38%
1491
16th to endNight
16%6%36%5%2445%8%35%
1516
June1st to 15thNight
12%7%27%7%5%7%6%6%8%27%
1260
16th to endNight
14%5%16%5%37%5%7%8%33%
1260
July1st to 15thNight
10%325%6%36%6%6%10%37%
1260
16th to endNight
12%425%3246%6%9%43%
1386
August1st to 15thNight
9%425%5%35%5%6%7%44%
1470
16th to endNight
13%6%345%345%6%8%39%
1812
September1st to 15thNight
11%6%25%43446%7%44%
1905
16th to endNight
10%7%25%5%25%46%8%40%
2145
October1st to 15thNight
13%10%46%5%25%5%5%7%33%
2364
16th to endNight
9%10%47%5%35%6%6%7%31%
2710
November1st to 15thNight
9%12%5%10%8%45%445%26%
2996
16th to endNight
6%11%5%11%10%46%5%6%8%23%
3150
December1st to 15thNight
6%11%5%10%10%6%7%5%6%6%24%
3227
16th to endNight
311%5%10%9%5%7%6%7%9%24%
3584

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
58%8%17%11%4
1254
16th to endDay
54%9%13%15%5%1
1617
February1st to 15thDay
48%10%19%15%5%
1640
16th to endDay
56%9%16%12%5%
1670
March1st to 15thDay
49%9%18%17%4
2119
16th to endDay
54%10%14%15%4
2534
April1st to 15thDay
52%9%13%17%6%
2635
16th to endDay
52%8%13%16%8%
2754
May1st to 15thDay
42%9%16%22%8%
3119
16th to endDay
44%9%13%21%10%
3303
June1st to 15thDay
52%11%15%17%3
3360
16th to endDay
46%10%16%19%5%
3360
July1st to 15thDay
42%11%20%20%4
3191
16th to endDay
39%13%25%18%3
2967
August1st to 15thDay
41%14%26%15%1
2723
16th to endDay
42%12%24%17%3
2742
September1st to 15thDay
45%9%22%17%4
2382
16th to endDay
44%9%19%19%6%
2145
October1st to 15thDay
53%10%16%17%2
1924
16th to endDay
52%9%16%17%3
1853
November1st to 15thDay
57%7%17%14%3
1519
16th to endDay
57%8%17%13%21
1470
December1st to 15thDay
60%8%13%12%3
1389
16th to endDay
54%9%14%14%6%
1344
January1st to 15thNight
56%10%16%11%4
3345
16th to endNight
55%9%15%12%5%1
3322
February1st to 15thNight
50%9%16%17%6%
2884
16th to endNight
50%9%17%16%5%
2372
March1st to 15thNight
48%8%15%19%7%
2500
16th to endNight
50%8%13%19%6%
2394
April1st to 15thNight
46%8%13%19%10%1
1973
16th to endNight
51%6%9%19%10%1
1810
May1st to 15thNight
41%6%14%23%13%
1492
16th to endNight
46%6%11%23%11%
1516
June1st to 15thNight
50%10%16%16%5%
1260
16th to endNight
44%10%17%22%5%
1260
July1st to 15thNight
38%12%22%20%6%
1200
16th to endNight
36%10%25%24%2
1303
August1st to 15thNight
36%11%24%24%2
1463
16th to endNight
41%8%22%21%5%
1812
September1st to 15thNight
37%9%22%24%6%1
1905
16th to endNight
39%9%19%23%6%
2145
October1st to 15thNight
48%9%15%21%3
2364
16th to endNight
49%9%17%19%3
2710
November1st to 15thNight
59%5%13%17%3
2996
16th to endNight
60%8%15%11%2
3150
December1st to 15thNight
59%8%14%14%3
3227
16th to endNight
53%9%16%14%6%
3584

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%14%28%28%12%4
120
16th to endDay
10%21%30%25%9%2
128
February1st to 15thDay
9%20%32%23%14%
120
16th to endDay
415%41%27%46%
197
March1st to 15thDay
10%21%32%25%8%1
390
16th to endDay
14%15%32%24%11%1
416
April1st to 15thDay
16%18%35%21%6%1
389
16th to endDay
20%19%33%19%6%
378
May1st to 15thDay
12%14%29%25%14%3
596
16th to endDay
15%9%26%29%14%4
693
June1st to 15thDay
18%12%28%25%12%2
855
16th to endDay
15%7%23%27%20%5%
855
July1st to 15thDay
13%6%27%35%14%3
825
16th to endDay
12%8%27%26%17%8%
652
August1st to 15thDay
12%6%28%25%19%8%
424
16th to endDay
11%15%39%26%7%
396
September1st to 15thDay
20%14%30%23%8%2
375
16th to endDay
18%13%33%21%11%1
375
October1st to 15thDay
22%14%29%19%12%1
251
16th to endDay
20%16%25%26%9%2
192
November1st to 15thDay
16%15%36%20%8%2
143
16th to endDay
11%13%40%22%8%4
120
December1st to 15thDay
13%18%32%20%10%4
120
16th to endDay
5%14%31%30%12%5%
128
January1st to 15thNight
11%17%32%27%9%1
1110
16th to endNight
13%18%34%25%6%1
1074
February1st to 15thNight
12%13%28%28%15%1
824
16th to endNight
7%7%35%32%15%2
736
March1st to 15thNight
10%13%32%29%12%2
840
16th to endNight
12%10%28%31%14%2
896
April1st to 15thNight
12%10%28%32%13%2
713
16th to endNight
18%10%27%28%13%2
562
May1st to 15thNight
11%6%26%32%20%1
420
16th to endNight
16%7%25%29%18%2
439
June1st to 15thNight
14%7%26%27%21%3
420
16th to endNight
14%5%20%27%27%4
420
July1st to 15thNight
11%421%38%22%
400
16th to endNight
13%5%21%28%24%7%
410
August1st to 15thNight
10%116%32%30%8%
384
16th to endNight
15%7%23%32%19%1
570
September1st to 15thNight
11%7%23%30%23%3
699
16th to endNight
12%14%26%29%15%1
776
October1st to 15thNight
18%10%27%28%12%1
780
16th to endNight
15%16%28%28%9%
838
November1st to 15thNight
18%13%35%22%9%1
1025
16th to endNight
13%17%34%24%8%1
1050
December1st to 15thNight
13%16%32%26%8%2
1072
16th to endNight
8%16%30%28%13%3
1184
Page generated at 2019-07-17 06:53:06. Version ac04

Copyright 2019 A. Danko


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