Observatoires du Mont Notre Dame
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoires du Mont Notre Dame clear sky chart from 2005-11-05 to 2017-09-16.

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
23%
14590
8%
46787
5%
14558
28%
14558
11%
36723

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
11%
746
4%
2661
2%
742
14%
742
4%
2354
January16th to endNight
15%
768
8%
2688
4%
768
21%
768
6%
2266
February1st to 15thNight
17%
704
5%
2343
3%
701
21%
701
7%
1938
February16th to endNight
16%
631
5%
1952
2%
631
20%
631
7%
1634
March1st to 15thNight
22%
720
12%
2094
8%
720
27%
720
12%
1654
March16th to endNight
25%
768
15%
2112
7%
768
31%
768
15%
1603
April1st to 15thNight
21%
632
11%
1713
4%
632
26%
632
13%
1356
April16th to endNight
26%
540
15%
1620
9%
540
33%
540
17%
1159
May1st to 15thNight
27%
519
8%
1569
6%
519
30%
519
14%
1195
May16th to endNight
24%
375
9%
1310
5%
374
31%
374
11%
979
June1st to 15thNight
39%
360
5%
1260
4%
360
40%
360
15%
901
June16th to endNight
35%
360
5%
1260
3%
360
37%
360
14%
916
July1st to 15thNight
38%
340
6%
1190
6%
340
40%
340
16%
843
July16th to endNight
40%
376
7%
1344
7%
354
45%
354
14%
938
August1st to 15thNight
43%
473
7%
1544
7%
471
45%
471
18%
1082
August16th to endNight
39%
573
12%
1719
7%
573
42%
573
20%
1220
September1st to 15thNight
34%
665
11%
1853
5%
665
37%
665
22%
1287
September16th to endNight
30%
661
16%
1825
9%
661
36%
661
25%
1231
October1st to 15thNight
28%
660
15%
1928
8%
660
35%
660
16%
1390
October16th to endNight
21%
704
7%
2269
4%
704
25%
704
10%
1772
November1st to 15thNight
16%
715
12%
2370
6%
715
24%
715
9%
1868
November16th to endNight
17%
750
7%
2583
3%
750
21%
750
7%
2124
December1st to 15thNight
10%
750
2%
2700
1%
750
12%
750
2%
2444
December16th to endNight
12%
800
4%
2880
1%
800
15%
800
3%
2569

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
19%10%47%6%35%445%27%
48001
Night
18%11%48%7%45%445%24%
46944
TransparencyDay
59%6%11%15%6%
47676
Night
61%6%10%14%6%
46787
SeeingDay
25%17%27%19%8%1
6561
Night
23%17%27%21%8%1
14590

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
13%15%7%13%11%7%6%5%5%5%8%
1275
16th to endDay
10%13%6%11%9%5%11%9%4413%
1536
February1st to 15thDay
8%12%6%9%12%9%12%5%3415%
1518
16th to endDay
15%15%7%11%6%5%6%44418%
1521
March1st to 15thDay
17%11%5%8%5%5%7%5%45%21%
1856
16th to endDay
14%15%6%8%5%34335%27%
2112
April1st to 15thDay
21%14%46%6%23345%26%
2236
16th to endDay
22%10%35%424345%33%
2340
May1st to 15thDay
22%9%25%5%33345%33%
2391
16th to endDay
24%9%35%42445%6%28%
2805
June1st to 15thDay
22%7%35%5%35%45%7%29%
2700
16th to endDay
24%6%37%5%345%6%6%26%
2700
July1st to 15thDay
18%6%35%5%35%5%6%7%31%
2700
16th to endDay
17%5%36%6%35%5%6%6%34%
2731
August1st to 15thDay
17%6%25%5%35%6%7%8%32%
2394
16th to endDay
17%5%25%5%345%5%8%35%
2483
September1st to 15thDay
22%6%24323346%39%
2106
16th to endDay
19%6%25%423335%43%
1825
October1st to 15thDay
20%9%37%5%2435%5%31%
1702
16th to endDay
28%15%25%5%2433424%
1601
November1st to 15thDay
21%14%6%6%6%435%4421%
1488
16th to endDay
22%16%6%11%6%2333417%
1377
December1st to 15thDay
18%15%6%15%10%6%6%32410%
1260
16th to endDay
19%14%7%13%10%6%8%4339%
1344
January1st to 15thNight
15%15%8%11%12%7%7%43310%
2661
16th to endNight
10%14%7%10%10%8%11%6%3214%
2688
February1st to 15thNight
8%11%7%11%11%8%8%5%4417%
2342
16th to endNight
14%18%6%10%8%45%43418%
1952
March1st to 15thNight
16%14%5%7%7%47%43423%
2081
16th to endNight
15%14%6%7%5%44235%31%
2112
April1st to 15thNight
23%14%37%5%3434424%
1713
16th to endNight
26%8%35%322345%33%
1620
May1st to 15thNight
25%8%46%5%25%445%27%
1569
16th to endNight
24%9%36%5%36%44427%
1308
June1st to 15thNight
21%8%26%435%45%5%30%
1260
16th to endNight
23%6%35%6%35%45%7%28%
1260
July1st to 15thNight
19%7%35%5%36%5%5%8%29%
1260
16th to endNight
15%6%25%6%36%6%7%8%31%
1437
August1st to 15thNight
16%6%15%5%36%6%6%6%34%
1554
16th to endNight
17%6%25%436%6%6%7%33%
1719
September1st to 15thNight
19%6%26%423345%39%
1853
16th to endNight
23%423413346%43%
1825
October1st to 15thNight
20%8%246%24445%35%
1928
16th to endNight
27%13%26%5%24345%24%
2269
November1st to 15thNight
23%13%5%7%5%3323425%
2370
16th to endNight
19%16%7%11%6%3433320%
2583
December1st to 15thNight
19%16%7%13%11%5%5%4329%
2700
16th to endNight
19%15%7%14%10%5%6%43310%
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
77%5%9%5%1
1276
16th to endDay
71%8%8%9%2
1536
February1st to 15thDay
71%5%11%8%2
1521
16th to endDay
70%5%8%10%4
1521
March1st to 15thDay
65%49%13%6%
1866
16th to endDay
59%5%8%16%9%1
2112
April1st to 15thDay
63%38%14%8%1
2236
16th to endDay
54%49%17%12%1
2340
May1st to 15thDay
56%49%19%10%1
2391
16th to endDay
58%6%9%17%7%
2809
June1st to 15thDay
54%7%11%14%11%1
2700
16th to endDay
58%8%10%14%7%
2700
July1st to 15thDay
51%8%14%18%6%
2541
16th to endDay
51%9%12%18%8%
2561
August1st to 15thDay
49%11%16%18%3
2380
16th to endDay
47%9%17%20%5%
2483
September1st to 15thDay
46%6%15%22%7%
2106
16th to endDay
45%6%15%23%9%
1825
October1st to 15thDay
56%6%13%15%7%1
1702
16th to endDay
67%5%9%12%4
1601
November1st to 15thDay
66%7%8%12%4
1488
16th to endDay
72%410%9%2
1377
December1st to 15thDay
80%48%5%
1260
16th to endDay
80%5%5%6%1
1344
January1st to 15thNight
77%6%7%6%1
2661
16th to endNight
71%6%7%12%2
2688
February1st to 15thNight
68%6%11%10%3
2343
16th to endNight
70%5%8%11%4
1952
March1st to 15thNight
63%48%15%7%
2094
16th to endNight
58%38%18%9%1
2112
April1st to 15thNight
63%38%10%12%1
1713
16th to endNight
52%48%17%15%1
1620
May1st to 15thNight
59%48%15%9%1
1569
16th to endNight
57%6%8%16%8%1
1310
June1st to 15thNight
53%6%11%17%9%1
1260
16th to endNight
54%7%12%15%9%
1260
July1st to 15thNight
50%8%16%19%5%
1190
16th to endNight
48%10%15%18%8%
1344
August1st to 15thNight
45%11%18%20%4
1544
16th to endNight
45%10%18%19%5%
1719
September1st to 15thNight
46%5%14%23%8%
1853
16th to endNight
42%6%16%23%10%1
1825
October1st to 15thNight
50%7%12%21%7%
1928
16th to endNight
61%6%13%14%4
2269
November1st to 15thNight
63%5%11%13%5%
2370
16th to endNight
69%5%11%9%3
2583
December1st to 15thNight
81%5%7%5%
2700
16th to endNight
79%5%7%6%1
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
11%40%36%10%1
60
16th to endDay
18%15%42%18%4
64
February1st to 15thDay
16%16%34%24%7%
179
16th to endDay
24%19%29%16%6%2
229
March1st to 15thDay
24%24%27%15%6%2
270
16th to endDay
20%21%27%19%9%2
288
April1st to 15thDay
27%20%31%13%5%2
270
16th to endDay
27%18%30%12%8%2
270
May1st to 15thDay
30%15%27%17%8%
318
16th to endDay
30%18%25%18%6%1
519
June1st to 15thDay
27%14%22%24%8%1
495
16th to endDay
28%12%26%20%8%2
495
July1st to 15thDay
22%12%27%23%11%2
475
16th to endDay
20%11%29%27%9%
402
August1st to 15thDay
17%13%28%26%11%1
313
16th to endDay
22%13%28%20%12%2
332
September1st to 15thDay
26%12%27%20%9%2
315
16th to endDay
22%17%31%15%10%3
257
October1st to 15thDay
23%20%23%17%10%3
234
16th to endDay
37%20%18%12%7%1
240
November1st to 15thDay
34%21%21%12%8%
235
16th to endDay
27%23%22%18%5%2
177
December1st to 15thDay
28%13%41%8%6%1
60
16th to endDay
29%39%21%9%
64
January1st to 15thNight
23%25%32%14%4
746
16th to endNight
16%26%32%17%7%
768
February1st to 15thNight
13%22%33%20%8%
704
16th to endNight
22%21%29%16%8%1
631
March1st to 15thNight
22%21%25%21%7%
720
16th to endNight
21%19%25%24%7%1
768
April1st to 15thNight
29%18%24%18%7%
632
16th to endNight
28%14%26%19%9%
540
May1st to 15thNight
28%10%26%25%8%1
519
16th to endNight
26%12%28%22%8%1
375
June1st to 15thNight
23%8%22%35%9%1
360
16th to endNight
21%9%24%31%11%
360
July1st to 15thNight
18%8%29%29%12%2
340
16th to endNight
16%7%26%33%14%1
376
August1st to 15thNight
18%6%25%28%19%1
473
16th to endNight
19%7%27%30%13%1
573
September1st to 15thNight
23%9%26%26%12%1
665
16th to endNight
22%11%31%25%7%1
661
October1st to 15thNight
23%18%25%22%8%1
660
16th to endNight
32%20%18%20%7%
704
November1st to 15thNight
29%20%26%16%6%
715
16th to endNight
25%21%28%16%7%
750
December1st to 15thNight
26%26%29%14%3
750
16th to endNight
25%22%26%18%5%2
800
Page generated at 2017-09-17 12:05:42. Version ac04

Copyright 2017 A. Danko


Observatoires du Mont Notre Dame Clear Sky Chart | Charts Home