Varennes
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Varennes clear sky chart from 2005-11-06 to 2024-01-16.

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
31%
22534
8%
74751
5%
22496
35%
22496
9%
61094

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 10thNight
21%
760
5%
2649
4%
757
23%
757
4%
2337
January11th to 20thNight
20%
744
5%
2602
3%
744
22%
744
5%
2278
January21st to endNight
26%
792
7%
2772
5%
792
30%
792
7%
2283
February1st to 10thNight
18%
720
5%
2395
2%
720
22%
720
6%
2063
February11th to 20thNight
21%
702
7%
2172
2%
700
28%
700
7%
1834
February21st to endNight
26%
592
9%
1776
4%
592
32%
592
8%
1500
March1st to 10thNight
27%
720
9%
2160
6%
720
31%
720
8%
1817
March11th to 20thNight
26%
720
9%
2101
4%
720
31%
720
8%
1762
March21st to endNight
29%
792
14%
1980
6%
792
35%
792
14%
1627
April1st to 10thNight
26%
720
9%
1800
3%
720
29%
720
11%
1513
April11th to 20thNight
29%
711
11%
1775
3%
711
33%
711
14%
1445
April21st to endNight
27%
558
12%
1638
6%
558
32%
558
12%
1305
May1st to 10thNight
29%
424
10%
1504
7%
424
36%
424
10%
1182
May11th to 20thNight
33%
354
12%
1416
12%
354
39%
354
9%
1085
May21st to endNight
33%
389
10%
1551
8%
388
42%
388
10%
1175
June1st to 10thNight
35%
360
6%
1440
5%
360
41%
360
8%
1142
June11th to 20thNight
41%
360
8%
1440
9%
360
46%
360
9%
1100
June21st to endNight
41%
360
6%
1440
9%
360
45%
360
8%
1158
July1st to 10thNight
48%
350
7%
1400
10%
350
52%
350
11%
1058
July11th to 20thNight
54%
348
8%
1392
12%
348
56%
348
11%
1054
July21st to endNight
52%
394
8%
1486
9%
372
54%
372
10%
1128
August1st to 10thNight
56%
358
9%
1422
10%
356
58%
356
10%
1076
August11th to 20thNight
53%
518
13%
1582
8%
518
56%
518
17%
1178
August21st to endNight
51%
792
10%
1980
6%
792
52%
792
16%
1591
September1st to 10thNight
48%
720
8%
1800
3%
720
49%
720
16%
1443
September11th to 20thNight
49%
720
13%
1885
7%
720
52%
720
17%
1448
September21st to endNight
43%
720
12%
1980
9%
720
46%
720
14%
1580
October1st to 10thNight
38%
720
12%
2083
8%
720
43%
720
12%
1673
October11th to 20thNight
32%
720
9%
2214
7%
720
36%
720
9%
1834
October21st to endNight
25%
792
8%
2574
5%
792
30%
792
9%
2123
November1st to 10thNight
24%
740
9%
2407
6%
740
29%
740
9%
1953
November11th to 20thNight
25%
760
11%
2532
8%
760
30%
760
9%
2060
November21st to endNight
21%
760
7%
2660
5%
760
25%
760
6%
2263
December1st to 10thNight
18%
760
3%
2660
1%
760
21%
760
4%
2356
December11th to 20thNight
17%
760
8%
3241
3%
759
22%
759
5%
2679
December21st to endNight
15%
824
4%
4842
2%
817
19%
817
3%
3991

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%37%6%35%5%5%7%33%
74786
Night
19%10%47%6%3445%6%32%
75012
TransparencyDay
33%39%9%13%6%1
74491
Night
36%38%8%12%6%1
74841
SeeingDay
21%11%28%25%12%3
13470
Night
23%8%29%29%10%1
22547

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 10thDay
18%18%6%10%8%4443422%
1517
11th to 20thDay
20%13%5%9%6%44445%26%
1480
21st to endDay
12%14%48%7%46%6%5%6%29%
1584
February1st to 10thDay
16%15%5%9%6%35%446%26%
1562
11th to 20thDay
14%12%5%10%7%35%5%6%5%28%
1674
21st to endDay
19%14%5%7%8%3445%5%28%
1480
March1st to 10thDay
16%11%49%8%46%45%5%30%
1797
11th to 20thDay
16%11%47%6%3445%6%32%
1856
21st to endDay
18%11%48%5%34445%35%
2376
April1st to 10thDay
22%10%38%5%35%435%31%
2160
11th to 20thDay
20%8%36%5%33446%38%
2134
21st to endDay
21%9%37%5%345%46%32%
2321
May1st to 10thDay
20%7%36%5%345%5%7%35%
2471
11th to 20thDay
17%6%36%5%35%5%5%7%38%
2478
21st to endDay
17%6%36%5%35%6%5%7%36%
2725
June1st to 10thDay
21%7%36%5%45%5%6%8%30%
2520
11th to 20thDay
15%6%36%5%345%6%8%39%
2520
21st to endDay
18%8%37%6%46%45%8%31%
2520
July1st to 10thDay
12%5%35%6%45%6%7%9%40%
2520
11th to 20thDay
12%5%25%6%46%6%8%10%37%
2520
21st to endDay
12%5%36%5%45%6%7%10%38%
2744
August1st to 10thDay
12%6%36%6%45%6%7%10%36%
2506
11th to 20thDay
9%5%36%5%36%6%6%10%41%
2297
21st to endDay
12%6%24445%5%7%8%43%
2376
September1st to 10thDay
12%426%6%35%6%6%8%42%
2160
11th to 20thDay
15%5%2432446%7%49%
2075
21st to endDay
16%5%25%5%35%5%5%7%41%
1980
October1st to 10thDay
19%6%36%7%4445%8%34%
1872
11th to 20thDay
17%9%37%7%5%6%6%6%7%27%
1746
21st to endDay
26%9%46%5%3435%5%30%
1782
November1st to 10thDay
17%10%46%5%35%5%6%7%33%
1671
11th to 20thDay
18%9%48%6%36%6%5%5%29%
1644
21st to endDay
21%11%38%6%26%5%46%26%
1520
December1st to 10thDay
25%13%5%10%6%34446%20%
1520
11th to 20thDay
22%13%5%8%42445%6%26%
1906
21st to endDay
27%15%5%8%6%3444420%
2772
January1st to 10thNight
18%17%6%10%7%445%45%21%
2649
11th to 20thNight
17%15%5%10%6%45%45%424%
2602
21st to endNight
13%12%6%8%8%45%5%46%29%
2772
February1st to 10thNight
15%14%6%12%8%45%45%5%22%
2395
11th to 20thNight
16%11%5%9%6%5%5%45%5%30%
2170
21st to endNight
17%13%49%6%35%445%31%
1776
March1st to 10thNight
18%12%5%8%6%35%35%5%30%
2150
11th to 20thNight
19%12%47%6%35%445%31%
2101
21st to endNight
17%11%47%5%3433438%
1980
April1st to 10thNight
24%9%47%5%34446%30%
1800
11th to 20thNight
23%7%45%5%34446%35%
1775
21st to endNight
22%10%36%5%3445%5%34%
1638
May1st to 10thNight
21%7%46%6%3445%6%35%
1504
11th to 20thNight
19%7%36%5%3446%7%36%
1415
21st to endNight
16%6%36%5%35%5%6%7%39%
1550
June1st to 10thNight
23%6%36%5%345%6%7%32%
1440
11th to 20thNight
16%6%36%5%25%48%7%38%
1440
21st to endNight
17%7%26%6%46%5%5%9%33%
1440
July1st to 10thNight
11%5%35%6%45%5%6%10%40%
1440
11th to 20thNight
11%6%25%5%45%6%7%10%39%
1440
21st to endNight
11%5%35%6%45%5%7%9%40%
1574
August1st to 10thNight
12%6%25%5%35%5%7%8%41%
1432
11th to 20thNight
13%5%36%5%45%5%6%8%42%
1582
21st to endNight
13%6%25%5%35%46%8%41%
1980
September1st to 10thNight
12%6%36%6%345%6%7%43%
1800
11th to 20thNight
16%6%3432335%7%48%
1885
21st to endNight
16%6%35%5%3345%7%43%
1980
October1st to 10thNight
18%7%36%5%3445%6%39%
2083
11th to 20thNight
21%8%46%5%34446%33%
2214
21st to endNight
24%8%47%6%44445%30%
2574
November1st to 10thNight
19%9%36%6%4445%6%33%
2407
11th to 20thNight
19%10%37%6%35%45%6%32%
2532
21st to endNight
23%12%47%6%34446%27%
2660
December1st to 10thNight
22%14%7%10%6%35%445%21%
2660
11th to 20thNight
23%15%48%5%34435%26%
3288
21st to endNight
27%15%6%9%5%2334422%
4884

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 10thDay
42%41%7%8%2
1518
11th to 20thDay
40%41%6%8%5%
1480
21st to endDay
36%39%8%10%6%
1584
February1st to 10thDay
40%36%7%12%41
1562
11th to 20thDay
39%40%8%8%41
1683
21st to endDay
40%37%7%11%5%
1480
March1st to 10thDay
39%38%7%11%5%1
1800
11th to 20thDay
35%39%10%12%4
1856
21st to endDay
33%38%8%12%8%1
2376
April1st to 10thDay
38%37%6%13%6%1
2160
11th to 20thDay
31%37%7%15%10%1
2134
21st to endDay
35%38%6%12%7%3
2321
May1st to 10thDay
31%37%7%13%11%2
2471
11th to 20thDay
30%38%8%13%8%3
2482
21st to endDay
29%39%8%12%11%2
2725
June1st to 10thDay
35%39%8%11%6%1
2520
11th to 20thDay
27%39%8%17%8%2
2520
21st to endDay
36%40%9%11%4
2520
July1st to 10thDay
26%41%9%17%6%
2450
11th to 20thDay
28%40%11%15%6%
2445
21st to endDay
26%42%12%14%6%
2591
August1st to 10thDay
30%39%11%16%5%
2492
11th to 20thDay
24%39%14%17%7%
2297
21st to endDay
25%39%12%15%9%
2376
September1st to 10thDay
26%38%11%17%7%
2160
11th to 20thDay
25%38%9%19%10%
2075
21st to endDay
29%39%10%15%6%
1980
October1st to 10thDay
33%39%10%13%6%
1872
11th to 20thDay
36%40%9%11%4
1746
21st to endDay
36%38%9%11%6%1
1782
November1st to 10thDay
27%44%9%14%6%1
1671
11th to 20thDay
35%43%8%8%7%
1644
21st to endDay
35%43%9%10%2
1520
December1st to 10thDay
43%41%7%7%3
1520
11th to 20thDay
42%34%7%13%3
1906
21st to endDay
53%29%9%6%3
2772
January1st to 10thNight
42%41%6%8%2
2649
11th to 20thNight
41%42%6%8%3
2602
21st to endNight
37%39%7%10%7%1
2772
February1st to 10thNight
43%37%6%8%5%1
2395
11th to 20thNight
39%38%8%10%4
2172
21st to endNight
39%38%7%10%6%1
1776
March1st to 10thNight
39%37%7%12%41
2160
11th to 20thNight
38%37%8%11%5%
2102
21st to endNight
33%36%6%13%9%2
1980
April1st to 10thNight
36%37%6%12%7%1
1800
11th to 20thNight
32%36%7%14%10%1
1775
21st to endNight
33%36%6%14%8%3
1638
May1st to 10thNight
34%36%5%11%9%5%
1504
11th to 20thNight
31%38%7%11%10%4
1416
21st to endNight
30%38%6%13%12%2
1551
June1st to 10thNight
34%38%7%14%6%1
1440
11th to 20thNight
29%40%8%14%8%2
1440
21st to endNight
33%40%8%11%8%
1440
July1st to 10thNight
26%41%9%17%7%
1400
11th to 20thNight
26%41%10%15%9%
1392
21st to endNight
27%41%11%15%6%
1486
August1st to 10thNight
28%39%10%15%8%
1422
11th to 20thNight
23%38%12%18%9%
1582
21st to endNight
27%40%10%15%8%1
1980
September1st to 10thNight
28%39%8%16%9%
1800
11th to 20thNight
26%37%9%19%9%
1885
21st to endNight
28%40%7%15%9%
1980
October1st to 10thNight
31%39%7%15%8%
2083
11th to 20thNight
36%38%8%13%4
2214
21st to endNight
36%39%8%11%6%1
2574
November1st to 10thNight
31%42%8%14%5%
2407
11th to 20thNight
32%41%10%10%6%1
2532
21st to endNight
38%41%7%11%3
2660
December1st to 10thNight
43%41%7%7%2
2660
11th to 20thNight
43%34%7%14%3
3288
21st to endNight
52%26%8%11%2
4884

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 10thDay
28%13%29%18%12%
180
11th to 20thDay
26%14%34%19%6%1
170
21st to endDay
19%11%35%23%11%1
176
February1st to 10thDay
32%18%34%15%1
214
11th to 20thDay
24%13%34%25%41
342
21st to endDay
29%12%31%24%5%
346
March1st to 10thDay
23%11%30%26%10%
420
11th to 20thDay
22%13%34%22%7%1
420
21st to endDay
28%9%31%22%9%2
462
April1st to 10thDay
29%14%27%20%9%1
420
11th to 20thDay
27%17%23%20%9%3
412
21st to endDay
28%12%30%19%10%1
420
May1st to 10thDay
23%9%35%20%10%2
423
11th to 20thDay
18%11%29%26%13%4
447
21st to endDay
19%12%32%25%10%2
485
June1st to 10thDay
23%11%26%28%10%2
450
11th to 20thDay
16%11%25%31%15%2
450
21st to endDay
22%10%23%27%15%3
450
July1st to 10thDay
13%7%22%31%20%5%
445
11th to 20thDay
14%6%26%34%16%5%
444
21st to endDay
15%7%24%33%17%4
488
August1st to 10thDay
14%5%24%30%21%6%
446
11th to 20thDay
11%5%21%32%21%10%
439
21st to endDay
15%8%23%25%18%11%
495
September1st to 10thDay
12%8%27%29%16%7%
450
11th to 20thDay
16%8%21%28%16%11%
450
21st to endDay
18%8%27%23%17%7%
450
October1st to 10thDay
22%13%24%23%14%4
450
11th to 20thDay
23%12%28%23%12%2
423
21st to endDay
31%11%27%23%8%1
396
November1st to 10thDay
25%13%31%21%10%
365
11th to 20thDay
25%15%30%20%8%2
304
21st to endDay
31%12%31%17%9%1
180
December1st to 10thDay
30%11%23%22%12%3
180
11th to 20thDay
24%22%33%16%41
180
21st to endDay
34%17%26%18%41
198
January1st to 10thNight
28%10%30%27%5%
760
11th to 20thNight
25%10%33%24%6%
744
21st to endNight
20%9%33%31%7%1
792
February1st to 10thNight
23%9%36%27%5%1
720
11th to 20thNight
20%11%37%26%5%1
703
21st to endNight
22%10%32%31%5%
592
March1st to 10thNight
26%8%31%30%6%
720
11th to 20thNight
26%9%31%26%7%
720
21st to endNight
23%8%30%30%8%
792
April1st to 10thNight
28%11%26%28%7%
720
11th to 20thNight
25%12%29%27%6%1
711
21st to endNight
28%10%30%25%7%1
558
May1st to 10thNight
25%7%32%27%8%1
424
11th to 20thNight
23%9%29%31%8%1
354
21st to endNight
18%8%35%30%9%
389
June1st to 10thNight
23%5%28%34%9%1
360
11th to 20thNight
19%429%35%13%
360
21st to endNight
17%6%28%34%15%1
360
July1st to 10thNight
12%5%29%38%16%1
350
11th to 20thNight
11%224%46%15%1
348
21st to endNight
13%422%45%16%1
394
August1st to 10thNight
13%5%17%43%20%2
358
11th to 20thNight
13%320%39%23%2
518
21st to endNight
16%421%36%20%2
792
September1st to 10thNight
15%5%23%41%15%1
720
11th to 20thNight
18%5%22%34%20%2
720
21st to endNight
18%7%26%31%15%3
720
October1st to 10thNight
21%7%27%31%12%1
720
11th to 20thNight
26%8%27%29%9%1
720
21st to endNight
28%9%31%25%7%
792
November1st to 10thNight
24%11%31%25%8%
740
11th to 20thNight
25%11%32%22%9%1
760
21st to endNight
30%11%30%22%8%
760
December1st to 10thNight
29%11%29%24%7%
760
11th to 20thNight
28%12%31%22%6%1
760
21st to endNight
32%11%30%21%6%
836
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