Grande-Vallee
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grande-Vallee clear sky chart from 2005-11-05 to 2017-12-01.

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
27%
14937
9%
47714
5%
14902
31%
14902
11%
37047

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
12%
750
4%
2685
2%
746
16%
746
3%
2348
January16th to endNight
14%
785
6%
2762
3%
785
19%
785
5%
2258
February1st to 15thNight
20%
704
5%
2285
2%
701
24%
701
8%
1835
February16th to endNight
21%
631
6%
2051
3%
631
26%
631
8%
1665
March1st to 15thNight
21%
720
14%
2029
5%
720
29%
720
12%
1590
March16th to endNight
25%
768
14%
2112
5%
768
32%
768
15%
1608
April1st to 15thNight
26%
552
11%
1729
7%
552
31%
552
12%
1321
April16th to endNight
31%
540
15%
1620
9%
540
38%
540
18%
1151
May1st to 15thNight
40%
540
10%
1467
7%
540
42%
540
20%
1071
May16th to endNight
33%
439
9%
1374
4%
438
38%
438
14%
1024
June1st to 15thNight
41%
360
4%
1260
3%
360
43%
360
14%
901
June16th to endNight
42%
360
4%
1260
4%
360
43%
360
16%
901
July1st to 15thNight
49%
340
5%
1190
5%
340
50%
340
22%
766
July16th to endNight
52%
391
10%
1255
10%
368
55%
368
20%
825
August1st to 15thNight
53%
539
9%
1573
9%
535
54%
535
24%
1068
August16th to endNight
48%
573
15%
1719
10%
573
52%
573
21%
1192
September1st to 15thNight
40%
549
13%
1806
9%
549
45%
549
19%
1222
September16th to endNight
34%
717
17%
1999
11%
717
40%
717
24%
1351
October1st to 15thNight
31%
720
15%
2160
6%
720
40%
720
18%
1512
October16th to endNight
22%
775
8%
2415
4%
775
26%
775
10%
1914
November1st to 15thNight
20%
805
9%
2663
4%
805
26%
805
9%
2088
November16th to endNight
17%
825
5%
2730
2%
825
21%
825
5%
2323
December1st to 15thNight
11%
754
3%
2690
0%
754
13%
754
3%
2456
December16th to endNight
9%
800
3%
2880
1%
800
12%
800
2%
2657

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
17%9%36%6%35%45%6%29%
48738
Night
17%11%5%9%7%45%445%24%
47866
TransparencyDay
55%8%12%15%7%
48407
Night
60%6%11%14%6%
47715
SeeingDay
24%11%26%24%11%2
7211
Night
24%14%25%23%10%1
14937

By Month

Percentage Cloud Cover NE (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
12%17%7%12%15%6%5%5%447%
1253
16th to endDay
11%14%6%8%11%6%8%6%5%5%13%
1461
February1st to 15thDay
8%11%48%9%9%9%6%6%6%19%
1575
16th to endDay
14%12%49%8%5%7%45%6%22%
1422
March1st to 15thDay
15%11%46%5%36%445%29%
1920
16th to endDay
14%13%36%7%25%45%5%30%
2112
April1st to 15thDay
15%12%47%7%35%5%5%5%28%
2217
16th to endDay
20%7%46%32445%6%34%
2340
May1st to 15thDay
19%8%35%5%35%6%46%31%
2485
16th to endDay
24%7%35%5%2445%6%31%
2749
June1st to 15thDay
20%7%35%435%45%8%33%
2700
16th to endDay
19%6%25%5%35%5%6%7%33%
2700
July1st to 15thDay
14%5%245%345%6%9%38%
2700
16th to endDay
14%6%25%5%35%5%5%7%37%
2816
August1st to 15thDay
12%5%25%5%35%5%6%8%37%
2374
16th to endDay
16%5%24445%46%8%37%
2483
September1st to 15thDay
20%6%24434346%39%
2152
16th to endDay
18%5%25%425%45%5%41%
1960
October1st to 15thDay
17%8%26%5%3435%7%35%
1800
16th to endDay
26%12%36%433335%27%
1806
November1st to 15thDay
22%13%47%6%34446%21%
1525
16th to endDay
19%14%8%13%6%2443417%
1560
December1st to 15thDay
18%15%7%17%11%45%2438%
1284
16th to endDay
16%18%10%16%11%5%42237%
1344
January1st to 15thNight
15%15%6%13%13%5%6%4439%
2685
16th to endNight
9%13%6%13%13%6%10%5%4412%
2762
February1st to 15thNight
9%12%5%10%10%7%10%45%5%17%
2285
16th to endNight
13%17%5%9%8%46%445%20%
2051
March1st to 15thNight
15%13%5%7%8%4444426%
2017
16th to endNight
14%14%5%6%7%34336%29%
2112
April1st to 15thNight
19%11%47%7%4435%5%26%
1729
16th to endNight
20%8%37%423426%35%
1620
May1st to 15thNight
23%7%345%23337%34%
1467
16th to endNight
25%7%26%5%2445%6%29%
1372
June1st to 15thNight
21%7%36%6%35%446%29%
1260
16th to endNight
20%5%25%6%45%47%6%30%
1260
July1st to 15thNight
15%6%45%325%46%8%37%
1260
16th to endNight
12%6%26%6%35%5%5%7%37%
1340
August1st to 15thNight
13%6%25%6%245%5%8%39%
1584
16th to endNight
15%425%6%35%5%6%8%36%
1719
September1st to 15thNight
19%5%25%5%33445%40%
1806
16th to endNight
20%6%24422347%39%
1999
October1st to 15thNight
19%8%35%434346%36%
2160
16th to endNight
26%11%36%5%25%445%23%
2415
November1st to 15thNight
22%13%47%5%3445%6%22%
2663
16th to endNight
18%15%8%14%6%3433415%
2730
December1st to 15thNight
17%14%10%19%11%45%3337%
2690
16th to endNight
20%17%10%15%12%5%32227%
2880

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%10%41
1254
16th to endDay
65%6%14%9%3
1461
February1st to 15thDay
61%7%15%11%3
1578
16th to endDay
61%9%10%13%4
1422
March1st to 15thDay
58%5%9%15%9%
1931
16th to endDay
56%7%9%15%9%1
2112
April1st to 15thDay
58%6%8%14%10%1
2217
16th to endDay
51%7%10%15%13%1
2340
May1st to 15thDay
53%7%9%16%10%1
2485
16th to endDay
55%8%10%15%9%1
2753
June1st to 15thDay
50%9%11%17%10%
2700
16th to endDay
50%13%10%16%8%
2700
July1st to 15thDay
42%12%16%20%8%
2541
16th to endDay
46%11%12%20%9%
2639
August1st to 15thDay
44%12%17%20%4
2360
16th to endDay
44%12%18%19%4
2483
September1st to 15thDay
47%8%16%21%7%
2152
16th to endDay
45%8%13%24%7%
1960
October1st to 15thDay
49%8%14%18%7%1
1800
16th to endDay
62%6%10%13%5%1
1806
November1st to 15thDay
65%8%11%9%4
1525
16th to endDay
71%5%11%7%3
1560
December1st to 15thDay
80%8%7%3
1284
16th to endDay
83%36%41
1344
January1st to 15thNight
75%6%9%6%1
2685
16th to endNight
69%5%13%8%3
2762
February1st to 15thNight
64%6%12%11%3
2286
16th to endNight
66%6%7%13%6%
2051
March1st to 15thNight
61%5%7%17%9%
2029
16th to endNight
57%49%16%9%1
2112
April1st to 15thNight
60%5%8%14%9%
1729
16th to endNight
51%48%17%15%1
1620
May1st to 15thNight
51%6%9%22%10%
1467
16th to endNight
55%7%9%17%9%
1374
June1st to 15thNight
55%5%10%16%11%
1260
16th to endNight
50%8%13%18%8%
1260
July1st to 15thNight
42%7%16%27%5%
1190
16th to endNight
44%7%16%20%10%
1255
August1st to 15thNight
41%9%18%24%5%
1573
16th to endNight
43%10%15%23%7%
1719
September1st to 15thNight
46%7%12%24%9%
1806
16th to endNight
43%6%14%25%8%
1999
October1st to 15thNight
48%5%13%21%9%1
2160
16th to endNight
62%7%11%14%4
2415
November1st to 15thNight
62%6%12%12%5%
2663
16th to endNight
73%5%11%6%2
2730
December1st to 15thNight
81%6%6%4
2690
16th to endNight
83%5%5%41
2880

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
18%23%41%15%1
60
16th to endDay
21%14%37%20%6%
94
February1st to 15thDay
14%13%37%22%10%1
236
16th to endDay
23%17%25%21%10%2
212
March1st to 15thDay
25%19%30%14%7%1
270
16th to endDay
18%18%30%19%8%4
288
April1st to 15thDay
25%15%32%15%7%2
270
16th to endDay
26%15%26%21%7%2
270
May1st to 15thDay
27%10%24%20%12%5%
441
16th to endDay
32%9%25%22%9%1
519
June1st to 15thDay
29%7%21%26%13%2
495
16th to endDay
23%6%23%30%12%3
495
July1st to 15thDay
18%428%30%15%1
475
16th to endDay
18%5%19%36%17%2
514
August1st to 15thDay
14%326%33%19%2
347
16th to endDay
21%225%30%15%4
332
September1st to 15thDay
28%6%26%24%10%2
315
16th to endDay
21%13%32%23%8%1
309
October1st to 15thDay
24%17%25%20%10%1
270
16th to endDay
36%17%21%13%10%
288
November1st to 15thDay
29%17%24%19%7%1
280
16th to endDay
29%16%28%18%6%
285
December1st to 15thDay
21%19%26%26%4
82
16th to endDay
15%34%31%18%
64
January1st to 15thNight
23%23%30%17%4
750
16th to endNight
18%23%28%22%6%
785
February1st to 15thNight
14%17%33%25%8%
704
16th to endNight
24%16%27%18%11%2
631
March1st to 15thNight
20%18%30%19%10%
720
16th to endNight
22%16%27%22%8%1
768
April1st to 15thNight
26%14%25%19%11%1
552
16th to endNight
25%11%27%23%10%2
540
May1st to 15thNight
27%5%20%25%17%3
540
16th to endNight
28%7%23%28%10%1
439
June1st to 15thNight
25%5%16%33%17%
360
16th to endNight
26%418%30%18%1
360
July1st to 15thNight
18%222%34%19%2
340
16th to endNight
17%317%35%24%1
391
August1st to 15thNight
15%319%33%24%2
539
16th to endNight
17%421%34%19%2
573
September1st to 15thNight
22%7%23%31%13%
549
16th to endNight
24%8%27%28%9%
717
October1st to 15thNight
27%13%23%23%10%1
720
16th to endNight
35%13%24%17%9%
775
November1st to 15thNight
29%16%29%18%5%1
805
16th to endNight
27%19%26%18%7%
825
December1st to 15thNight
23%24%30%16%3
754
16th to endNight
29%21%25%16%5%2
800
Page generated at 2017-12-02 09:14:17. Version ac04

Copyright 2017 A. Danko


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