Pont Rouge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pont Rouge Observatory clear sky chart from 2005-11-06 to 2024-02-20.

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%
22829
12%
80773
6%
22737
34%
22737
13%
58807

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
12%
757
8%
4390
2%
737
20%
737
4%
3353
January11th to 20thNight
15%
759
9%
4394
3%
740
24%
740
5%
3227
January21st to endNight
21%
825
8%
4845
6%
814
32%
814
7%
3428
February1st to 10thNight
19%
760
13%
2651
5%
760
31%
760
11%
1989
February11th to 20thNight
14%
741
10%
2236
2%
739
24%
739
11%
1740
February21st to endNight
23%
592
15%
1776
7%
592
34%
592
14%
1328
March1st to 10thNight
21%
720
14%
2160
6%
720
31%
720
14%
1604
March11th to 20thNight
21%
720
14%
2088
4%
720
30%
720
13%
1583
March21st to endNight
27%
792
18%
2021
5%
792
36%
792
20%
1476
April1st to 10thNight
22%
720
12%
1800
4%
720
26%
720
16%
1400
April11th to 20thNight
28%
641
16%
1705
5%
641
34%
641
20%
1236
April21st to endNight
23%
540
15%
1620
7%
540
31%
540
16%
1173
May1st to 10thNight
25%
480
14%
1560
9%
480
33%
480
15%
1103
May11th to 20thNight
30%
354
17%
1416
14%
354
42%
354
15%
940
May21st to endNight
29%
389
11%
1551
8%
388
41%
388
16%
1026
June1st to 10thNight
35%
360
7%
1278
7%
360
41%
360
15%
902
June11th to 20thNight
42%
360
11%
1260
10%
360
46%
360
19%
835
June21st to endNight
39%
360
8%
1268
8%
360
42%
360
15%
908
July1st to 10thNight
44%
350
7%
1400
10%
350
48%
350
18%
899
July11th to 20thNight
48%
348
10%
1392
14%
348
51%
348
18%
890
July21st to endNight
51%
394
9%
1486
11%
372
53%
372
16%
984
August1st to 10thNight
60%
358
13%
1422
15%
356
65%
356
20%
900
August11th to 20thNight
46%
506
11%
1570
8%
506
48%
506
19%
1100
August21st to endNight
42%
721
17%
1909
9%
721
45%
721
24%
1311
September1st to 10thNight
41%
720
12%
1800
5%
720
44%
720
28%
1247
September11th to 20thNight
44%
720
15%
1944
9%
720
48%
720
26%
1329
September21st to endNight
38%
720
18%
1980
10%
720
44%
720
25%
1358
October1st to 10thNight
34%
720
20%
2002
12%
720
43%
720
22%
1395
October11th to 20thNight
30%
720
11%
2296
6%
720
36%
720
14%
1718
October21st to endNight
22%
792
9%
2574
5%
792
29%
792
13%
1927
November1st to 10thNight
26%
740
13%
2407
7%
740
34%
740
14%
1744
November11th to 20thNight
26%
760
15%
2488
9%
760
34%
760
14%
1832
November21st to endNight
20%
814
10%
2774
4%
814
27%
814
9%
2152
December1st to 10thNight
18%
850
8%
2850
4%
850
22%
850
8%
2308
December11th to 20thNight
18%
850
10%
3458
5%
848
24%
848
7%
2667
December21st to endNight
12%
876
7%
5002
2%
863
20%
863
4%
3795

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
20%10%47%6%35%5%5%6%29%
77970
Night
19%11%47%6%3445%6%30%
81211
TransparencyDay
54%7%13%17%8%1
77675
Night
55%6%12%17%8%1
81041
SeeingDay
25%17%29%20%8%1
14066
Night
25%12%28%27%8%
22857

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
16%17%6%11%7%35%5%45%21%
2517
11th to 20thDay
11%14%7%16%9%45%43424%
2520
21st to endDay
11%13%6%10%6%35%5%5%6%31%
2772
February1st to 10thDay
12%15%7%11%8%5%6%335%25%
1527
11th to 20thDay
14%15%7%11%7%36%445%24%
1815
21st to endDay
13%14%7%11%6%4435%6%26%
1480
March1st to 10thDay
16%12%5%8%7%45%45%5%30%
1797
11th to 20thDay
17%13%5%7%6%345%45%30%
1872
21st to endDay
15%11%47%7%46%5%5%432%
2331
April1st to 10thDay
24%10%48%6%4443428%
2160
11th to 20thDay
22%7%35%6%34445%36%
2204
21st to endDay
24%10%37%6%35%436%30%
2340
May1st to 10thDay
22%8%46%5%25%45%5%33%
2416
11th to 20thDay
20%7%36%6%45%5%5%6%33%
2478
21st to endDay
22%8%26%6%35%5%5%6%32%
2725
June1st to 10thDay
21%7%37%7%46%5%6%8%26%
2677
11th to 20thDay
20%7%36%5%35%6%5%7%34%
2700
21st to endDay
24%8%48%5%36%45%7%26%
2685
July1st to 10thDay
17%6%36%6%36%6%7%8%31%
2520
11th to 20thDay
16%7%36%5%46%6%8%10%29%
2520
21st to endDay
17%6%27%6%47%5%7%8%30%
2744
August1st to 10thDay
19%6%37%6%36%7%6%9%27%
2506
11th to 20thDay
18%7%36%5%35%5%6%8%33%
2313
21st to endDay
18%7%25%5%35%5%6%8%35%
2444
September1st to 10thDay
20%6%35%4345%6%8%35%
2160
11th to 20thDay
20%5%2443345%7%43%
2016
21st to endDay
25%7%35%5%23447%37%
1980
October1st to 10thDay
23%8%35%5%36%45%6%32%
1956
11th to 20thDay
27%9%46%6%35%5%5%6%23%
1663
21st to endDay
30%9%38%6%34345%25%
1782
November1st to 10thDay
22%10%47%6%4445%5%31%
1671
11th to 20thDay
23%13%5%9%7%34445%25%
1691
21st to endDay
21%17%47%6%45%45%5%21%
1404
December1st to 10thDay
26%16%47%8%33435%22%
1330
11th to 20thDay
22%12%5%10%7%3333427%
1668
21st to endDay
22%19%48%5%2344424%
2586
January1st to 10thNight
17%19%6%11%7%4434422%
4429
11th to 20thNight
13%16%6%12%8%44445%24%
4440
21st to endNight
11%14%6%10%8%45%5%6%6%25%
4884
February1st to 10thNight
12%14%6%9%9%45%5%45%27%
2651
11th to 20thNight
14%14%6%11%7%45%5%45%25%
2234
21st to endNight
16%13%6%9%5%45%45%5%28%
1776
March1st to 10thNight
15%11%5%9%7%45%45%5%30%
2150
11th to 20thNight
18%12%48%6%45%5%5%6%28%
2087
21st to endNight
17%10%47%5%2445%6%35%
2021
April1st to 10thNight
24%13%46%6%3345%6%27%
1800
11th to 20thNight
20%8%35%6%35%5%5%6%34%
1705
21st to endNight
22%10%46%5%24447%33%
1620
May1st to 10thNight
25%7%36%5%35%5%45%33%
1560
11th to 20thNight
22%7%36%5%26%346%36%
1415
21st to endNight
23%6%35%5%34447%37%
1550
June1st to 10thNight
22%7%36%6%45%6%5%8%29%
1278
11th to 20thNight
21%6%35%5%35%46%7%36%
1260
21st to endNight
23%7%36%6%345%6%7%31%
1268
July1st to 10thNight
18%5%27%5%35%6%6%9%35%
1440
11th to 20thNight
17%6%45%5%35%6%7%8%36%
1440
21st to endNight
16%7%35%5%36%5%6%8%36%
1574
August1st to 10thNight
17%425%5%35%5%7%10%38%
1432
11th to 20thNight
16%7%36%6%46%45%8%35%
1570
21st to endNight
18%6%35%6%345%47%40%
1909
September1st to 10thNight
19%6%25%5%2445%7%41%
1800
11th to 20thNight
19%5%35%424445%44%
1944
21st to endNight
22%6%24433347%41%
1980
October1st to 10thNight
20%7%345%3445%7%38%
2002
11th to 20thNight
26%9%36%5%35%5%45%30%
2296
21st to endNight
28%10%35%44345%6%28%
2574
November1st to 10thNight
20%12%46%6%3445%7%30%
2407
11th to 20thNight
22%11%37%5%35%446%31%
2488
21st to endNight
24%14%47%6%34345%25%
2774
December1st to 10thNight
24%17%5%8%8%35%44420%
2850
11th to 20thNight
22%15%5%9%6%33345%24%
3531
21st to endNight
24%20%5%7%5%2333424%
5072

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
63%8%11%13%5%
2518
11th to 20thDay
62%7%10%15%5%1
2520
21st to endDay
51%8%11%21%8%1
2772
February1st to 10thDay
61%6%10%13%8%2
1527
11th to 20thDay
62%6%11%11%9%1
1824
21st to endDay
59%5%9%16%9%2
1480
March1st to 10thDay
55%6%10%16%12%2
1800
11th to 20thDay
54%8%10%16%12%1
1872
21st to endDay
53%7%10%17%11%3
2331
April1st to 10thDay
60%6%11%11%9%4
2160
11th to 20thDay
49%6%11%21%11%3
2204
21st to endDay
57%5%10%15%12%2
2340
May1st to 10thDay
51%6%10%17%14%3
2416
11th to 20thDay
49%7%12%18%12%1
2482
21st to endDay
52%8%10%17%12%1
2725
June1st to 10thDay
54%9%11%17%7%2
2677
11th to 20thDay
47%8%15%18%11%1
2700
21st to endDay
58%7%12%15%8%
2685
July1st to 10thDay
46%10%17%20%6%
2450
11th to 20thDay
46%10%18%19%6%
2445
21st to endDay
49%11%18%17%6%
2591
August1st to 10thDay
50%10%21%16%3
2492
11th to 20thDay
45%10%18%20%6%
2313
21st to endDay
45%9%16%22%9%
2444
September1st to 10thDay
45%8%16%21%10%
2160
11th to 20thDay
41%6%17%26%10%
2016
21st to endDay
47%6%15%23%8%
1980
October1st to 10thDay
51%7%13%21%8%
1956
11th to 20thDay
60%8%15%14%2
1663
21st to endDay
62%6%11%15%5%1
1782
November1st to 10thDay
55%7%13%18%7%
1671
11th to 20thDay
63%5%10%16%6%
1691
21st to endDay
65%6%13%12%41
1404
December1st to 10thDay
66%5%10%14%5%
1330
11th to 20thDay
61%5%9%17%7%
1668
21st to endDay
63%6%11%12%7%1
2586
January1st to 10thNight
65%6%11%12%5%
4429
11th to 20thNight
61%6%12%16%41
4440
21st to endNight
57%7%12%15%8%1
4884
February1st to 10thNight
59%6%8%18%9%1
2651
11th to 20thNight
60%7%10%14%9%1
2236
21st to endNight
57%5%8%16%12%2
1776
March1st to 10thNight
56%6%9%16%11%2
2160
11th to 20thNight
56%7%9%13%12%2
2088
21st to endNight
50%5%10%19%12%4
2021
April1st to 10thNight
57%6%10%14%11%2
1800
11th to 20thNight
49%7%8%22%12%2
1705
21st to endNight
52%7%9%17%14%2
1620
May1st to 10thNight
52%6%11%16%13%3
1560
11th to 20thNight
48%7%11%17%15%2
1416
21st to endNight
47%7%10%20%14%2
1551
June1st to 10thNight
51%8%13%18%9%1
1278
11th to 20thNight
46%7%13%20%12%3
1260
21st to endNight
53%7%13%16%10%
1268
July1st to 10thNight
42%10%21%19%8%
1400
11th to 20thNight
44%8%18%22%7%1
1392
21st to endNight
45%10%18%20%8%
1486
August1st to 10thNight
41%9%19%26%5%
1422
11th to 20thNight
47%9%20%18%6%1
1570
21st to endNight
43%7%15%27%8%
1909
September1st to 10thNight
42%7%15%23%11%1
1800
11th to 20thNight
42%8%17%25%8%1
1944
21st to endNight
45%5%13%25%12%
1980
October1st to 10thNight
47%6%11%25%11%
2002
11th to 20thNight
55%8%13%18%5%
2296
21st to endNight
57%6%13%17%7%
2574
November1st to 10thNight
54%7%14%19%7%1
2407
11th to 20thNight
55%6%13%16%9%
2488
21st to endNight
63%5%11%15%6%
2774
December1st to 10thNight
68%5%11%12%4
2850
11th to 20thNight
63%5%8%16%7%
3532
21st to endNight
65%5%8%15%6%1
5072

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%20%31%18%3
180
11th to 20thDay
27%21%31%18%3
180
21st to endDay
17%22%40%14%7%1
198
February1st to 10thDay
26%27%34%12%21
184
11th to 20thDay
22%24%35%15%3
429
21st to endDay
24%26%30%17%3
346
March1st to 10thDay
26%21%30%17%5%
420
11th to 20thDay
28%23%26%16%6%1
420
21st to endDay
23%22%28%17%9%1
462
April1st to 10thDay
30%18%30%17%5%
420
11th to 20thDay
29%18%26%19%5%2
412
21st to endDay
31%19%30%13%5%1
420
May1st to 10thDay
29%19%32%15%5%
423
11th to 20thDay
22%17%32%21%7%1
447
21st to endDay
24%21%31%18%6%
485
June1st to 10thDay
24%14%34%21%7%
607
11th to 20thDay
22%13%29%24%11%1
630
21st to endDay
26%11%28%23%11%1
615
July1st to 10thDay
20%11%33%23%11%2
445
11th to 20thDay
19%11%33%26%9%2
444
21st to endDay
19%13%30%27%10%2
488
August1st to 10thDay
20%10%28%29%11%2
446
11th to 20thDay
22%9%24%29%15%3
439
21st to endDay
24%14%24%17%15%6%
495
September1st to 10thDay
22%12%28%22%13%2
450
11th to 20thDay
21%13%26%23%13%5%
450
21st to endDay
24%16%23%20%13%4
450
October1st to 10thDay
25%16%27%20%11%1
450
11th to 20thDay
31%15%26%18%8%1
381
21st to endDay
35%16%27%17%5%
396
November1st to 10thDay
33%16%23%22%6%1
365
11th to 20thDay
28%20%26%17%9%1
351
21st to endDay
32%23%27%16%21
180
December1st to 10thDay
33%14%29%16%7%1
180
11th to 20thDay
29%22%28%16%32
180
21st to endDay
32%20%31%11%41
198
January1st to 10thNight
27%14%33%22%4
760
11th to 20thNight
26%18%29%22%6%
760
21st to endNight
15%13%35%30%6%
836
February1st to 10thNight
19%14%35%26%5%
760
11th to 20thNight
22%17%37%19%5%
742
21st to endNight
23%16%31%25%5%
592
March1st to 10thNight
21%13%37%23%5%
720
11th to 20thNight
25%15%33%20%6%1
720
21st to endNight
23%16%28%25%7%1
792
April1st to 10thNight
30%14%27%23%5%
720
11th to 20thNight
26%12%29%27%5%
641
21st to endNight
28%16%29%20%6%
540
May1st to 10thNight
27%13%31%24%6%
480
11th to 20thNight
25%9%31%28%7%1
354
21st to endNight
27%7%31%26%9%
389
June1st to 10thNight
25%8%25%37%6%
360
11th to 20thNight
23%5%25%34%13%
360
21st to endNight
25%422%37%11%
360
July1st to 10thNight
19%426%40%11%1
350
11th to 20thNight
20%419%41%15%1
348
21st to endNight
18%6%19%41%16%
394
August1st to 10thNight
20%213%43%22%
358
11th to 20thNight
17%5%23%37%18%
506
21st to endNight
20%8%23%32%16%1
721
September1st to 10thNight
22%427%31%15%1
720
11th to 20thNight
22%7%22%31%17%2
720
21st to endNight
24%8%24%28%15%1
720
October1st to 10thNight
23%11%26%30%10%
720
11th to 20thNight
29%11%24%25%10%
720
21st to endNight
34%11%28%23%4
792
November1st to 10thNight
29%12%26%25%7%1
740
11th to 20thNight
27%15%26%22%8%1
760
21st to endNight
31%16%25%21%6%1
814
December1st to 10thNight
33%12%25%23%7%
850
11th to 20thNight
27%20%25%22%6%1
850
21st to endNight
34%15%28%19%31
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