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 2017-09-24.

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%
15205
9%
46707
5%
15175
39%
15175
16%
33890

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%
926
6%
2865
4%
925
29%
925
10%
2231
January16th to endNight
23%
919
12%
2847
6%
919
31%
919
12%
2114
February1st to 15thNight
32%
704
9%
2462
7%
699
37%
699
13%
1769
February16th to endNight
38%
632
10%
2037
8%
632
43%
632
16%
1472
March1st to 15thNight
31%
720
13%
2142
8%
720
37%
720
16%
1579
March16th to endNight
37%
768
12%
2052
7%
768
39%
768
17%
1536
April1st to 15thNight
39%
611
12%
1691
7%
611
42%
611
20%
1220
April16th to endNight
36%
486
9%
1566
8%
486
40%
486
15%
1139
May1st to 15thNight
46%
359
3%
1278
3%
359
46%
359
19%
817
May16th to endNight
40%
374
0%
1294
0%
374
40%
374
17%
895
June1st to 15thNight
44%
360
0%
1080
0%
360
44%
360
17%
794
June16th to endNight
50%
360
0%
1080
0%
360
50%
360
21%
750
July1st to 15thNight
55%
340
0%
1020
0%
340
55%
340
23%
688
July16th to endNight
55%
376
0%
1189
0%
354
55%
354
24%
745
August1st to 15thNight
61%
360
4%
1372
5%
358
63%
358
22%
846
August16th to endNight
47%
526
10%
1672
9%
526
51%
526
22%
1100
September1st to 15thNight
53%
645
13%
1758
9%
645
54%
645
30%
1132
September16th to endNight
40%
692
15%
1914
7%
692
45%
692
24%
1303
October1st to 15thNight
36%
660
12%
1999
8%
660
41%
660
17%
1427
October16th to endNight
29%
709
9%
2293
5%
709
35%
709
12%
1690
November1st to 15thNight
24%
875
13%
2558
7%
875
30%
875
14%
1915
November16th to endNight
21%
900
8%
2700
2%
900
26%
900
10%
2141
December1st to 15thNight
25%
911
7%
2766
4%
911
28%
911
9%
2255
December16th to endNight
29%
992
9%
3072
4%
992
34%
992
12%
2332

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
11%8%47%6%35%5%6%8%31%
48269
Night
8%9%48%7%46%5%6%7%30%
46843
TransparencyDay
49%10%17%16%4
47908
Night
50%8%16%17%5%
46709
SeeingDay
15%12%29%25%12%3
6752
Night
13%12%29%28%14%2
15211

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
6%11%410%9%5%8%8%5%7%21%
1074
16th to endDay
6%11%5%9%8%46%5%5%8%28%
1386
February1st to 15thDay
5%10%49%7%47%7%7%8%28%
1400
16th to endDay
413%6%12%8%46%5%6%6%24%
1435
March1st to 15thDay
7%10%5%6%7%5%6%6%7%9%26%
1817
16th to endDay
8%10%6%11%8%35%6%6%7%23%
2171
April1st to 15thDay
9%11%5%8%7%36%5%5%9%28%
2257
16th to endDay
14%12%37%6%45%5%5%6%27%
2393
May1st to 15thDay
11%5%35%6%35%6%7%8%35%
2673
16th to endDay
16%7%35%6%35%5%6%7%32%
2816
June1st to 15thDay
17%7%36%7%36%5%6%9%26%
2880
16th to endDay
15%5%36%5%35%5%6%8%33%
2880
July1st to 15thDay
14%5%25%435%5%6%9%37%
2880
16th to endDay
13%4245%35%5%7%9%37%
2897
August1st to 15thDay
10%6%25%6%36%5%7%9%35%
2580
16th to endDay
12%5%25%5%45%6%7%9%34%
2530
September1st to 15thDay
13%7%36%5%3445%8%38%
2199
16th to endDay
13%7%245%35%5%6%7%37%
1904
October1st to 15thDay
13%10%48%6%35%45%6%32%
1629
16th to endDay
10%13%5%9%5%445%6%8%27%
1568
November1st to 15thDay
10%9%5%8%8%445%5%7%29%
1297
16th to endDay
5%12%6%11%9%25%46%8%27%
1260
December1st to 15thDay
6%10%8%10%9%5%8%6%6%6%18%
1191
16th to endDay
210%5%12%10%47%8%6%8%23%
1152
January1st to 15thNight
6%12%5%9%9%5%7%6%7%8%22%
2865
16th to endNight
5%10%5%10%7%47%6%5%7%29%
2847
February1st to 15thNight
6%10%5%9%9%46%5%5%7%29%
2452
16th to endNight
5%9%6%10%6%46%7%6%8%29%
2037
March1st to 15thNight
7%10%410%7%46%5%7%7%29%
2142
16th to endNight
7%11%5%8%7%46%5%7%9%26%
2049
April1st to 15thNight
8%10%47%6%36%6%7%7%32%
1691
16th to endNight
13%12%46%5%36%45%6%30%
1566
May1st to 15thNight
10%6%37%6%35%46%7%37%
1277
16th to endNight
18%6%36%6%345%47%32%
1294
June1st to 15thNight
12%7%27%6%37%6%7%9%28%
1080
16th to endNight
15%5%16%5%27%5%7%8%34%
1080
July1st to 15thNight
10%315%6%37%6%6%10%38%
1080
16th to endNight
12%4243246%6%9%41%
1272
August1st to 15thNight
10%425%5%35%5%6%7%43%
1379
16th to endNight
12%5%346%345%7%8%39%
1672
September1st to 15thNight
10%5%25%33346%8%46%
1758
16th to endNight
10%7%25%5%25%46%8%41%
1914
October1st to 15thNight
13%9%47%5%25%5%5%7%34%
1999
16th to endNight
9%11%5%8%6%36%6%6%7%29%
2293
November1st to 15thNight
9%12%5%10%8%45%45%5%29%
2558
16th to endNight
6%11%6%12%10%46%5%6%7%23%
2700
December1st to 15thNight
7%12%5%11%11%6%7%5%5%6%20%
2766
16th to endNight
312%6%10%8%5%7%6%6%9%24%
3072

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
59%7%17%10%3
1074
16th to endDay
52%9%14%15%6%1
1386
February1st to 15thDay
50%10%19%13%5%
1400
16th to endDay
56%8%17%12%5%
1435
March1st to 15thDay
52%9%17%16%4
1817
16th to endDay
55%10%13%15%3
2172
April1st to 15thDay
53%8%14%17%6%
2257
16th to endDay
55%9%12%13%7%
2393
May1st to 15thDay
44%9%15%20%8%
2673
16th to endDay
48%9%13%18%9%
2821
June1st to 15thDay
52%11%15%17%3
2880
16th to endDay
46%11%17%19%5%
2880
July1st to 15thDay
41%11%19%21%4
2711
16th to endDay
40%13%24%17%3
2717
August1st to 15thDay
42%13%26%15%1
2562
16th to endDay
42%12%24%17%2
2530
September1st to 15thDay
43%9%23%18%4
2199
16th to endDay
43%9%19%20%6%
1904
October1st to 15thDay
52%9%17%18%2
1629
16th to endDay
54%9%17%16%2
1568
November1st to 15thDay
54%7%17%16%4
1297
16th to endDay
56%8%17%13%21
1260
December1st to 15thDay
64%8%13%11%2
1191
16th to endDay
55%11%15%15%3
1152
January1st to 15thNight
56%10%17%12%2
2865
16th to endNight
53%8%16%13%6%1
2847
February1st to 15thNight
51%8%17%14%6%
2464
16th to endNight
50%8%18%16%5%
2037
March1st to 15thNight
51%8%14%19%6%
2142
16th to endNight
51%8%13%18%6%
2052
April1st to 15thNight
47%8%13%19%8%1
1691
16th to endNight
53%7%10%18%9%1
1566
May1st to 15thNight
43%6%14%20%14%
1278
16th to endNight
50%6%11%21%9%
1294
June1st to 15thNight
49%10%17%17%4
1080
16th to endNight
45%8%18%21%6%
1080
July1st to 15thNight
38%12%21%20%6%
1020
16th to endNight
36%10%25%24%2
1189
August1st to 15thNight
36%11%24%24%2
1372
16th to endNight
41%9%23%21%5%
1672
September1st to 15thNight
34%9%23%25%6%1
1758
16th to endNight
40%9%19%23%7%
1914
October1st to 15thNight
48%8%16%21%4
1999
16th to endNight
51%10%17%17%2
2293
November1st to 15thNight
56%5%14%19%4
2558
16th to endNight
59%9%15%11%3
2700
December1st to 15thNight
63%8%13%11%2
2766
16th to endNight
54%9%17%14%4
3072

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
11%15%23%26%16%6%
60
16th to endDay
321%29%29%12%3
64
February1st to 15thDay
15%16%36%23%8%
60
16th to endDay
5%15%43%27%44
118
March1st to 15thDay
13%23%34%21%6%
270
16th to endDay
18%16%35%20%8%1
288
April1st to 15thDay
17%21%34%20%5%
269
16th to endDay
21%17%35%17%7%
270
May1st to 15thDay
14%14%26%25%15%4
450
16th to endDay
16%10%23%29%14%4
531
June1st to 15thDay
18%11%27%25%14%2
675
16th to endDay
15%7%24%28%18%4
675
July1st to 15thDay
11%6%28%34%14%3
645
16th to endDay
13%9%29%25%16%5%
565
August1st to 15thDay
12%7%27%25%18%8%
375
16th to endDay
10%16%42%23%7%
332
September1st to 15thDay
16%15%31%24%8%3
315
16th to endDay
19%15%33%21%8%1
288
October1st to 15thDay
25%17%24%19%13%
151
16th to endDay
19%9%22%33%11%3
96
November1st to 15thDay
16%18%36%25%2
71
16th to endDay
11%16%36%13%13%8%
60
December1st to 15thDay
10%11%33%30%10%5%
60
16th to endDay
6%15%31%23%14%9%
64
January1st to 15thNight
12%16%32%27%8%2
930
16th to endNight
13%18%34%25%7%1
919
February1st to 15thNight
13%13%29%27%14%1
704
16th to endNight
7%7%34%33%15%1
632
March1st to 15thNight
11%14%32%28%10%2
720
16th to endNight
12%11%29%30%14%1
768
April1st to 15thNight
13%11%27%32%13%1
611
16th to endNight
18%10%26%29%12%2
486
May1st to 15thNight
12%7%25%33%19%1
360
16th to endNight
17%7%24%29%17%3
375
June1st to 15thNight
13%7%25%26%23%3
360
16th to endNight
15%5%20%29%25%3
360
July1st to 15thNight
11%422%37%23%
340
16th to endNight
14%5%22%28%24%5%
376
August1st to 15thNight
10%115%33%29%8%
360
16th to endNight
14%7%23%32%20%1
526
September1st to 15thNight
10%7%22%32%22%3
645
16th to endNight
13%14%26%29%14%1
692
October1st to 15thNight
17%10%28%28%13%1
660
16th to endNight
16%16%28%28%9%
709
November1st to 15thNight
17%14%36%22%8%1
875
16th to endNight
12%18%34%24%8%2
900
December1st to 15thNight
15%16%31%26%7%2
911
16th to endNight
8%16%30%27%13%3
992
Page generated at 2017-09-25 07:02:26. Version ac04

Copyright 2017 A. Danko


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