ROC St-Romain
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the ROC St-Romain clear sky chart from 2005-11-05 to 2017-09-23.

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%
14702
10%
46961
6%
14670
28%
14670
12%
36195

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
9%
720
6%
2506
2%
716
14%
716
5%
2141
January16th to endNight
12%
768
6%
2688
2%
768
17%
768
6%
2247
February1st to 15thNight
11%
704
7%
2322
2%
701
17%
701
7%
1949
February16th to endNight
12%
631
9%
1893
3%
631
21%
631
9%
1550
March1st to 15thNight
15%
720
12%
2154
6%
720
22%
720
11%
1681
March16th to endNight
23%
768
15%
2031
6%
768
31%
768
16%
1543
April1st to 15thNight
20%
718
14%
1796
4%
718
26%
718
16%
1416
April16th to endNight
22%
546
15%
1626
6%
546
30%
546
17%
1153
May1st to 15thNight
21%
489
13%
1569
8%
489
30%
489
15%
1134
May16th to endNight
27%
375
10%
1497
10%
374
35%
374
12%
1076
June1st to 15thNight
28%
360
7%
1311
5%
360
34%
360
11%
986
June16th to endNight
37%
360
8%
1311
9%
360
41%
360
17%
910
July1st to 15thNight
37%
340
9%
1360
12%
340
42%
340
16%
903
July16th to endNight
43%
376
10%
1418
13%
354
45%
354
16%
949
August1st to 15thNight
44%
440
10%
1511
8%
438
47%
438
16%
1059
August16th to endNight
41%
651
16%
1797
8%
651
45%
651
27%
1204
September1st to 15thNight
37%
720
10%
1854
5%
720
39%
720
23%
1332
September16th to endNight
40%
689
20%
1902
13%
689
45%
689
28%
1244
October1st to 15thNight
27%
660
15%
1892
8%
660
34%
660
18%
1398
October16th to endNight
17%
704
8%
2288
4%
704
23%
704
9%
1825
November1st to 15thNight
20%
700
13%
2277
9%
700
27%
700
10%
1765
November16th to endNight
20%
729
12%
2472
9%
729
26%
729
9%
1953
December1st to 15thNight
10%
750
4%
2700
0%
750
13%
750
4%
2321
December16th to endNight
9%
784
5%
2786
2%
784
13%
784
3%
2456

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
21%12%47%5%34445%25%
47940
Night
19%12%5%8%6%34445%26%
47131
TransparencyDay
60%5%9%15%6%
47628
Night
60%5%9%15%7%
46961
SeeingDay
29%15%27%17%7%1
5990
Night
26%15%29%20%7%
14702

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
17%17%8%12%10%25%5%3312%
1432
16th to endDay
11%15%8%13%9%5%6%44416%
1536
February1st to 15thDay
12%19%8%12%10%5%6%23315%
1536
16th to endDay
13%19%7%11%8%5%6%43416%
1580
March1st to 15thDay
16%16%6%10%6%2434423%
1795
16th to endDay
18%13%5%8%6%4333328%
2191
April1st to 15thDay
22%14%46%5%2423427%
2152
16th to endDay
23%12%35%324236%32%
2334
May1st to 15thDay
25%8%36%5%34345%27%
2391
16th to endDay
23%10%36%6%3445%7%23%
2618
June1st to 15thDay
31%7%25%5%2445%6%23%
2646
16th to endDay
23%7%46%6%245%5%7%25%
2644
July1st to 15thDay
19%7%36%5%36%5%6%8%28%
2520
16th to endDay
22%7%27%5%45%5%6%8%24%
2654
August1st to 15thDay
22%7%26%6%35%5%6%8%23%
2427
16th to endDay
19%5%245%345%46%36%
2402
September1st to 15thDay
24%7%24423346%36%
2106
16th to endDay
20%6%25%32345%8%39%
1895
October1st to 15thDay
23%12%26%5%23445%28%
1736
16th to endDay
26%20%35%43443419%
1584
November1st to 15thDay
22%18%5%442433425%
1581
16th to endDay
19%16%6%9%5%2424423%
1486
December1st to 15thDay
23%20%6%10%6%3433313%
1260
16th to endDay
21%20%10%11%6%35%21213%
1434
January1st to 15thNight
15%16%8%14%7%45%43315%
2506
16th to endNight
11%16%8%11%9%5%7%5%3316%
2688
February1st to 15thNight
11%15%7%13%11%5%6%42318%
2321
16th to endNight
15%18%7%10%6%25%43322%
1893
March1st to 15thNight
19%13%6%7%6%3433327%
2141
16th to endNight
15%13%5%7%6%24335%31%
2031
April1st to 15thNight
22%13%46%5%34345%27%
1796
16th to endNight
22%9%25%43335%6%34%
1626
May1st to 15thNight
24%8%36%423446%30%
1569
16th to endNight
22%8%36%5%3445%6%29%
1495
June1st to 15thNight
29%8%35%43445%5%26%
1311
16th to endNight
20%5%25%426%45%8%33%
1311
July1st to 15thNight
17%6%35%6%3447%8%32%
1440
16th to endNight
15%6%35%5%35%5%5%7%35%
1514
August1st to 15thNight
17%7%35%5%26%5%5%8%33%
1521
16th to endNight
16%5%15%5%3445%7%41%
1797
September1st to 15thNight
22%5%25%42345%6%36%
1854
16th to endNight
19%413423346%45%
1902
October1st to 15thNight
21%10%25%434446%31%
1892
16th to endNight
28%15%36%5%2333422%
2288
November1st to 15thNight
20%14%5%6%6%34345%25%
2277
16th to endNight
20%16%7%8%5%2332425%
2472
December1st to 15thNight
21%18%9%11%7%3432314%
2700
16th to endNight
22%20%7%10%8%4423312%
2786

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
75%47%8%3
1433
16th to endDay
70%46%13%5%
1536
February1st to 15thDay
76%449%4
1539
16th to endDay
72%35%10%5%1
1580
March1st to 15thDay
64%5%8%12%7%1
1805
16th to endDay
61%46%14%10%1
2191
April1st to 15thDay
61%37%15%9%2
2152
16th to endDay
55%48%17%11%2
2334
May1st to 15thDay
58%48%17%8%1
2391
16th to endDay
60%7%10%13%7%
2622
June1st to 15thDay
60%6%9%16%5%
2646
16th to endDay
58%6%10%18%5%
2644
July1st to 15thDay
51%7%15%19%5%
2371
16th to endDay
57%9%11%16%4
2487
August1st to 15thDay
57%7%16%16%2
2413
16th to endDay
47%5%15%21%9%
2402
September1st to 15thDay
50%6%12%19%10%
2106
16th to endDay
44%5%11%26%10%
1895
October1st to 15thDay
57%5%10%18%6%
1736
16th to endDay
69%5%8%12%4
1584
November1st to 15thDay
63%5%9%14%6%1
1581
16th to endDay
65%310%14%5%
1486
December1st to 15thDay
76%5%6%9%1
1260
16th to endDay
80%345%5%
1434
January1st to 15thNight
73%5%7%8%3
2506
16th to endNight
72%47%10%3
2688
February1st to 15thNight
71%46%11%4
2322
16th to endNight
68%36%11%8%
1893
March1st to 15thNight
62%5%6%16%8%1
2154
16th to endNight
55%5%9%15%11%2
2031
April1st to 15thNight
60%36%16%11%1
1796
16th to endNight
50%410%19%11%3
1626
May1st to 15thNight
55%49%17%11%
1569
16th to endNight
55%6%11%17%8%
1497
June1st to 15thNight
60%5%10%17%5%
1311
16th to endNight
48%7%12%21%8%
1311
July1st to 15thNight
45%10%16%18%9%
1360
16th to endNight
46%8%16%19%8%
1418
August1st to 15thNight
48%9%16%21%3
1511
16th to endNight
41%6%17%25%8%
1797
September1st to 15thNight
48%5%14%24%6%
1854
16th to endNight
40%5%12%28%11%
1902
October1st to 15thNight
54%411%20%9%
1892
16th to endNight
65%49%14%5%
2288
November1st to 15thNight
62%5%10%13%6%1
2277
16th to endNight
65%48%14%6%
2472
December1st to 15thNight
76%47%9%2
2700
16th to endNight
79%45%6%3
2786

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
23%21%45%10%
60
16th to endDay
21%26%39%7%31
64
February1st to 15thDay
27%27%27%12%5%
150
16th to endDay
27%23%28%17%3
239
March1st to 15thDay
26%24%32%12%3
270
16th to endDay
24%20%26%16%9%2
288
April1st to 15thDay
35%15%31%10%41
270
16th to endDay
34%17%26%11%7%2
270
May1st to 15thDay
37%13%28%12%6%1
288
16th to endDay
26%18%30%18%4
331
June1st to 15thDay
36%12%23%18%8%
441
16th to endDay
24%12%31%21%8%
439
July1st to 15thDay
21%11%36%20%8%1
305
16th to endDay
26%9%26%30%7%
326
August1st to 15thDay
27%9%26%24%11%
313
16th to endDay
26%10%22%21%13%5%
332
September1st to 15thDay
25%9%29%18%10%6%
315
16th to endDay
21%11%24%21%14%7%
283
October1st to 15thDay
29%15%22%16%11%3
248
16th to endDay
42%14%23%14%4
240
November1st to 15thDay
33%16%25%17%5%1
235
16th to endDay
33%18%18%17%9%1
159
December1st to 15thDay
50%21%18%6%3
60
16th to endDay
46%29%18%31
64
January1st to 15thNight
24%26%33%13%2
720
16th to endNight
22%23%35%15%3
768
February1st to 15thNight
19%24%37%16%2
704
16th to endNight
26%19%35%15%3
631
March1st to 15thNight
29%17%33%16%2
720
16th to endNight
23%18%27%22%5%1
768
April1st to 15thNight
30%15%30%19%4
718
16th to endNight
28%16%29%19%5%
546
May1st to 15thNight
30%12%32%17%6%1
489
16th to endNight
25%11%30%25%6%
375
June1st to 15thNight
32%6%24%27%8%
360
16th to endNight
21%7%28%31%11%
360
July1st to 15thNight
19%431%29%13%1
340
16th to endNight
19%425%37%13%
376
August1st to 15thNight
19%325%32%18%
440
16th to endNight
18%6%26%29%15%2
651
September1st to 15thNight
24%7%25%29%11%1
720
16th to endNight
22%6%27%27%14%1
689
October1st to 15thNight
27%11%29%20%9%1
660
16th to endNight
38%15%24%16%3
704
November1st to 15thNight
28%17%28%18%6%
700
16th to endNight
31%18%24%16%8%1
729
December1st to 15thNight
33%22%28%12%2
750
16th to endNight
34%23%24%13%3
784
Page generated at 2017-09-24 09:15:45. Version ac04

Copyright 2017 A. Danko


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