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 2024-10-20.

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%
23511
11%
96176
6%
23327
34%
23327
12%
68882

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
31%
814
7%
3428
February1st to 10thNight
19%
760
13%
2651
5%
760
31%
760
11%
1989
February11th to 20thNight
14%
742
10%
2241
2%
740
24%
740
11%
1735
February21st to endNight
23%
628
15%
1884
7%
628
33%
628
14%
1405
March1st to 10thNight
21%
757
12%
3723
6%
744
31%
744
8%
2698
March11th to 20thNight
21%
756
10%
3671
4%
740
30%
740
8%
2793
March21st to endNight
25%
836
12%
3458
5%
814
35%
814
12%
2459
April1st to 10thNight
22%
760
14%
1900
4%
760
27%
760
17%
1459
April11th to 20thNight
26%
676
15%
1800
5%
676
32%
676
20%
1320
April21st to endNight
22%
570
14%
1710
6%
570
30%
570
16%
1227
May1st to 10thNight
24%
506
15%
2676
9%
502
33%
502
10%
1755
May11th to 20thNight
30%
367
14%
2479
14%
364
42%
364
10%
1499
May21st to endNight
28%
406
8%
2728
8%
399
40%
399
10%
1628
June1st to 10thNight
35%
380
8%
1349
7%
380
41%
380
15%
945
June11th to 20thNight
42%
380
10%
1330
10%
380
46%
380
20%
875
June21st to endNight
38%
380
7%
1339
8%
380
41%
380
15%
967
July1st to 10thNight
44%
364
6%
2413
10%
360
48%
360
10%
1579
July11th to 20thNight
48%
363
7%
2377
14%
358
51%
358
10%
1543
July21st to endNight
51%
409
7%
2437
11%
383
54%
383
12%
1393
August1st to 10thNight
59%
373
12%
2351
15%
365
64%
365
11%
1560
August11th to 20thNight
45%
529
8%
2680
8%
524
48%
524
11%
1905
August21st to endNight
41%
747
13%
3223
9%
743
45%
743
14%
2300
September1st to 10thNight
42%
760
14%
1900
6%
760
45%
760
29%
1310
September11th to 20thNight
46%
760
15%
2052
9%
760
49%
760
27%
1384
September21st to endNight
38%
760
18%
2090
11%
760
44%
760
25%
1439
October1st to 10thNight
34%
760
20%
2114
12%
760
42%
760
22%
1484
October11th to 20thNight
30%
759
11%
2418
6%
759
37%
759
15%
1798
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
25%
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
17%
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
19%10%38%5%5%5%45%6%30%
101204
Night
19%12%48%5%4435%6%30%
97497
TransparencyDay
53%8%14%17%8%1
100962
Night
55%7%12%17%8%1
97360
SeeingDay
25%17%29%20%8%1
15059
Night
25%12%27%27%8%
23602

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%18%5%12%6%5%5%35%5%21%
2517
11th to 20thDay
11%15%6%18%7%5%5%23424%
2520
21st to endDay
11%13%5%11%5%5%5%45%6%30%
2772
February1st to 10thDay
11%16%7%12%7%6%5%34425%
1527
11th to 20thDay
14%16%6%12%6%5%5%35%5%24%
1825
21st to endDay
13%15%6%12%5%5%435%6%26%
1570
March1st to 10thDay
22%11%48%5%5%434429%
3116
11th to 20thDay
16%20%5%9%5%4434426%
3288
21st to endDay
15%14%38%5%45%34436%
4093
April1st to 10thDay
23%12%39%5%5%433429%
2280
11th to 20thDay
22%8%37%5%44345%35%
2328
21st to endDay
24%10%39%445%336%30%
2470
May1st to 10thDay
22%8%36%445%35%6%35%
4252
11th to 20thDay
17%7%38%5%5%5%46%9%32%
4398
21st to endDay
19%8%28%5%5%5%45%6%31%
4837
June1st to 10thDay
20%8%38%6%6%5%47%7%26%
2826
11th to 20thDay
19%8%36%445%5%6%7%34%
2850
21st to endDay
24%9%39%45%5%45%6%26%
2834
July1st to 10thDay
16%8%38%6%5%6%47%7%30%
4440
11th to 20thDay
18%7%37%5%5%6%5%8%8%28%
4440
21st to endDay
16%6%26%45%5%46%8%38%
4814
August1st to 10thDay
16%6%38%5%5%7%5%8%10%28%
4423
11th to 20thDay
21%7%37%5%5%5%5%7%8%27%
4054
21st to endDay
22%7%36%44436%6%35%
4290
September1st to 10thDay
19%7%36%34446%8%36%
2280
11th to 20thDay
19%5%2434435%7%44%
2128
21st to endDay
24%7%26%423447%36%
2090
October1st to 10thDay
23%8%36%45%5%45%6%31%
2064
11th to 20thDay
26%10%48%5%5%5%45%6%23%
1746
21st to endDay
29%10%39%5%44245%25%
1782
November1st to 10thDay
21%12%38%5%5%435%5%31%
1671
11th to 20thDay
22%14%410%6%4434425%
1691
21st to endDay
21%18%48%5%5%5%35%5%21%
1404
December1st to 10thDay
25%17%49%6%4333422%
1330
11th to 20thDay
22%13%5%11%5%4323427%
1668
21st to endDay
21%20%49%43434424%
2586
January1st to 10thNight
16%20%5%13%6%5%334421%
4429
11th to 20thNight
13%16%5%14%7%5%4345%24%
4440
21st to endNight
11%15%5%11%7%5%5%46%6%25%
4884
February1st to 10thNight
12%14%5%11%8%6%445%427%
2651
11th to 20thNight
14%15%6%12%5%5%445%426%
2239
21st to endNight
15%14%5%9%5%45%35%5%28%
1884
March1st to 10thNight
24%12%38%446%345%27%
3724
11th to 20thNight
18%18%410%5%5%4445%23%
3671
21st to endNight
17%14%48%444345%33%
3535
April1st to 10thNight
23%14%37%5%3335%6%28%
1900
11th to 20thNight
21%9%36%6%4445%6%33%
1800
21st to endNight
22%10%37%444347%34%
1710
May1st to 10thNight
24%7%37%445%446%33%
2718
11th to 20thNight
22%7%27%44435%7%36%
2495
21st to endNight
19%6%36%5%5%5%45%8%35%
2738
June1st to 10thNight
21%8%36%5%5%5%45%8%29%
1349
11th to 20thNight
20%6%25%5%4447%7%36%
1330
21st to endNight
24%8%37%6%4445%7%30%
1339
July1st to 10thNight
16%6%28%5%5%6%5%7%8%31%
2520
11th to 20thNight
20%8%36%44445%7%34%
2520
21st to endNight
14%5%25%44446%8%44%
2739
August1st to 10thNight
19%8%37%44436%8%34%
2506
11th to 20thNight
21%6%37%5%6%5%36%7%31%
2743
21st to endNight
19%8%39%5%5%4446%33%
3363
September1st to 10thNight
19%6%26%43435%6%41%
1900
11th to 20thNight
18%5%25%434345%45%
2052
21st to endNight
21%7%25%443246%40%
2090
October1st to 10thNight
21%8%35%44445%6%37%
2114
11th to 20thNight
26%9%36%45%4445%30%
2418
21st to endNight
28%11%36%34335%6%28%
2574
November1st to 10thNight
20%13%37%5%4435%7%30%
2407
11th to 20thNight
22%12%38%5%45%345%31%
2488
21st to endNight
24%15%48%5%44345%25%
2774
December1st to 10thNight
24%18%49%7%4434420%
2850
11th to 20thNight
22%16%411%5%43245%24%
3531
21st to endNight
23%21%5%8%43323324%
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
61%6%11%12%9%1
1834
21st to endDay
59%5%10%16%8%2
1570
March1st to 10thDay
57%8%10%15%8%2
3119
11th to 20thDay
58%9%10%15%7%1
3288
21st to endDay
51%5%8%18%13%5%
4093
April1st to 10thDay
59%6%10%12%9%4
2280
11th to 20thDay
49%6%11%21%10%3
2328
21st to endDay
56%5%10%15%12%2
2470
May1st to 10thDay
48%7%13%17%14%1
4266
11th to 20thDay
45%10%20%17%7%1
4402
21st to endDay
49%9%10%17%14%1
4837
June1st to 10thDay
53%9%12%18%7%2
2826
11th to 20thDay
46%8%16%17%11%1
2850
21st to endDay
58%7%12%15%9%
2834
July1st to 10thDay
50%8%15%20%7%
4370
11th to 20thDay
49%9%21%17%4
4365
21st to endDay
43%8%20%23%6%
4661
August1st to 10thDay
48%9%20%18%5%
4409
11th to 20thDay
51%10%19%16%4
4093
21st to endDay
47%8%15%16%14%
4290
September1st to 10thDay
44%8%16%22%10%
2280
11th to 20thDay
40%6%17%27%10%
2128
21st to endDay
48%6%15%23%8%
2090
October1st to 10thDay
51%7%13%21%7%
2064
11th to 20thDay
59%8%16%15%2
1746
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%6%9%14%9%1
2241
21st to endNight
57%5%8%16%12%2
1884
March1st to 10thNight
59%6%12%14%7%2
3734
11th to 20thNight
61%7%10%13%7%1
3672
21st to endNight
54%6%8%20%10%3
3535
April1st to 10thNight
56%5%10%14%12%2
1900
11th to 20thNight
50%7%8%22%12%2
1800
21st to endNight
51%7%9%17%14%2
1710
May1st to 10thNight
50%7%12%20%10%1
2724
11th to 20thNight
45%9%16%18%12%1
2496
21st to endNight
45%8%12%18%16%1
2739
June1st to 10thNight
51%8%13%19%9%1
1349
11th to 20thNight
45%7%14%19%12%3
1330
21st to endNight
54%7%12%16%10%
1339
July1st to 10thNight
48%9%19%19%6%
2480
11th to 20thNight
48%7%20%20%4
2472
21st to endNight
38%8%23%23%8%
2651
August1st to 10thNight
48%7%16%22%6%
2496
11th to 20thNight
51%10%19%16%5%
2770
21st to endNight
51%6%12%20%10%
3363
September1st to 10thNight
42%7%15%24%11%1
1900
11th to 20thNight
40%8%17%27%8%
2052
21st to endNight
45%5%13%25%11%
2090
October1st to 10thNight
47%6%11%25%11%
2114
11th to 20thNight
55%8%14%19%5%
2418
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%25%35%15%3
433
21st to endDay
24%27%29%17%3
382
March1st to 10thDay
27%20%30%18%5%
460
11th to 20thDay
27%23%28%16%6%1
460
21st to endDay
25%23%27%16%8%1
506
April1st to 10thDay
30%18%29%17%5%
460
11th to 20thDay
29%18%27%19%5%2
452
21st to endDay
31%20%30%12%5%1
460
May1st to 10thDay
29%19%32%15%5%
463
11th to 20thDay
22%16%32%22%7%1
487
21st to endDay
24%22%31%18%6%
529
June1st to 10thDay
23%14%34%22%8%
656
11th to 20thDay
21%13%30%24%11%1
680
21st to endDay
27%12%28%22%10%1
664
July1st to 10thDay
20%12%33%23%10%1
485
11th to 20thDay
20%12%33%25%9%1
484
21st to endDay
19%13%30%27%11%2
532
August1st to 10thDay
20%11%28%28%11%2
486
11th to 20thDay
23%9%23%29%14%3
479
21st to endDay
24%14%25%18%14%5%
539
September1st to 10thDay
22%12%28%22%13%2
490
11th to 20thDay
20%12%24%25%15%5%
490
21st to endDay
24%15%23%21%13%4
490
October1st to 10thDay
25%17%26%20%11%1
490
11th to 20thDay
31%16%26%18%8%1
410
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%
743
21st to endNight
23%16%31%25%4
628
March1st to 10thNight
22%14%36%23%5%
760
11th to 20thNight
25%16%32%21%6%1
760
21st to endNight
23%16%30%24%7%1
836
April1st to 10thNight
30%14%27%24%5%
760
11th to 20thNight
27%13%29%26%5%
676
21st to endNight
28%17%29%20%6%
570
May1st to 10thNight
27%13%32%23%6%
506
11th to 20thNight
25%8%30%29%7%1
374
21st to endNight
27%7%31%27%8%
411
June1st to 10thNight
25%7%26%36%6%
380
11th to 20thNight
23%5%25%34%13%
380
21st to endNight
26%422%37%11%
380
July1st to 10thNight
18%5%25%40%11%1
370
11th to 20thNight
21%418%41%15%1
368
21st to endNight
18%6%19%42%17%
416
August1st to 10thNight
19%214%44%21%
378
11th to 20thNight
18%5%22%37%18%
535
21st to endNight
20%7%23%32%17%1
762
September1st to 10thNight
22%426%32%15%1
760
11th to 20thNight
21%7%21%32%19%2
760
21st to endNight
24%8%24%29%15%1
760
October1st to 10thNight
24%11%25%30%10%1
760
11th to 20thNight
30%11%24%25%10%
759
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
888
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