Portes de l'enfer
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Portes de l'enfer clear sky chart from 2005-11-05 to 2017-09-17.

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
16%
14577
8%
46831
4%
14545
21%
14545
8%
37659

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
8%
722
8%
2518
2%
718
15%
718
4%
2123
January16th to endNight
12%
768
8%
2688
2%
768
21%
768
6%
2143
February1st to 15thNight
11%
704
8%
2387
2%
701
18%
701
7%
1900
February16th to endNight
10%
631
8%
1893
2%
631
17%
631
7%
1572
March1st to 15thNight
13%
720
10%
2160
5%
720
19%
720
9%
1706
March16th to endNight
17%
768
13%
2023
4%
768
23%
768
12%
1588
April1st to 15thNight
15%
709
10%
1787
2%
709
20%
709
11%
1456
April16th to endNight
18%
540
12%
1620
4%
540
25%
540
11%
1242
May1st to 15thNight
21%
435
10%
1515
7%
435
28%
435
10%
1138
May16th to endNight
20%
375
8%
1423
4%
374
29%
374
9%
1083
June1st to 15thNight
26%
360
5%
1260
2%
360
30%
360
10%
948
June16th to endNight
26%
360
5%
1260
3%
360
28%
360
11%
952
July1st to 15thNight
26%
340
5%
1273
4%
340
29%
340
11%
957
July16th to endNight
25%
376
6%
1418
8%
354
29%
354
10%
1047
August1st to 15thNight
32%
399
8%
1470
6%
397
36%
397
11%
1116
August16th to endNight
25%
628
9%
1774
4%
628
29%
628
16%
1339
September1st to 15thNight
24%
720
9%
1845
3%
720
27%
720
17%
1430
September16th to endNight
19%
665
13%
1836
5%
665
25%
665
15%
1380
October1st to 15thNight
13%
660
10%
1920
4%
660
19%
660
10%
1552
October16th to endNight
10%
704
5%
2288
3%
704
13%
704
4%
1997
November1st to 15thNight
11%
700
9%
2277
4%
700
17%
700
6%
1902
November16th to endNight
14%
743
6%
2616
5%
743
16%
743
5%
2228
December1st to 15thNight
8%
750
3%
2700
1%
750
11%
750
2%
2387
December16th to endNight
9%
800
6%
2880
3%
800
13%
800
3%
2473

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%14%6%9%7%35%445%20%
47945
Night
15%14%6%10%8%45%5%5%5%19%
46998
TransparencyDay
64%7%8%12%6%
47630
Night
63%7%9%12%5%
46831
SeeingDay
28%20%29%14%5%1
6127
Night
24%23%30%15%5%
14577

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
9%15%8%13%10%5%6%5%6%6%12%
1417
16th to endDay
5%11%9%14%10%47%7%8%7%13%
1536
February1st to 15thDay
5%11%7%14%10%6%10%7%6%5%13%
1472
16th to endDay
5%16%10%13%10%5%8%5%6%414%
1580
March1st to 15thDay
10%14%6%12%9%45%5%5%421%
1790
16th to endDay
10%17%7%8%8%36%44425%
2200
April1st to 15thDay
17%19%7%8%6%3443320%
2161
16th to endDay
16%16%6%7%5%2334428%
2340
May1st to 15thDay
20%15%5%6%5%24345%26%
2448
16th to endDay
24%13%46%6%2435%422%
2690
June1st to 15thDay
25%12%37%5%3445%6%22%
2700
16th to endDay
27%9%5%8%6%35%445%19%
2700
July1st to 15thDay
27%8%47%6%35%5%5%6%18%
2607
16th to endDay
26%10%48%5%45%445%20%
2654
August1st to 15thDay
27%11%48%6%45%5%5%5%15%
2466
16th to endDay
23%11%47%6%35%5%47%19%
2426
September1st to 15thDay
25%11%35%423345%29%
2115
16th to endDay
21%15%25%3245%46%27%
1830
October1st to 15thDay
22%22%5%7%5%13225%20%
1705
16th to endDay
19%28%9%7%5%2322315%
1584
November1st to 15thDay
16%20%10%12%7%3332316%
1581
16th to endDay
15%20%9%12%9%3333315%
1339
December1st to 15thDay
12%21%10%11%11%35%34311%
1260
16th to endDay
12%18%11%13%9%36%33314%
1344
January1st to 15thNight
9%13%9%15%11%5%8%6%6%48%
2518
16th to endNight
5%11%7%14%10%6%9%8%9%6%10%
2688
February1st to 15thNight
410%6%12%11%6%11%9%6%5%13%
2386
16th to endNight
7%16%9%14%10%28%5%4315%
1893
March1st to 15thNight
11%13%7%11%8%37%6%6%5%17%
2147
16th to endNight
8%14%6%11%9%45%44425%
2023
April1st to 15thNight
17%17%8%9%7%2433322%
1787
16th to endNight
16%13%5%8%6%35%33428%
1620
May1st to 15thNight
20%12%5%7%6%3344426%
1515
16th to endNight
23%12%5%6%5%34435%24%
1421
June1st to 15thNight
23%11%45%6%34446%25%
1260
16th to endNight
17%9%48%7%35%5%46%26%
1260
July1st to 15thNight
22%8%46%6%336%5%8%24%
1350
16th to endNight
21%8%36%6%35%5%6%6%27%
1514
August1st to 15thNight
19%10%46%6%2446%7%26%
1480
16th to endNight
18%10%36%5%345%6%8%27%
1774
September1st to 15thNight
22%11%36%433345%30%
1845
16th to endNight
23%15%2441333431%
1836
October1st to 15thNight
18%20%47%5%25%435%22%
1920
16th to endNight
21%26%9%8%5%2332213%
2288
November1st to 15thNight
15%19%11%13%6%2433415%
2277
16th to endNight
13%17%8%15%11%5%433313%
2616
December1st to 15thNight
12%18%10%15%11%5%5%4438%
2700
16th to endNight
11%16%8%14%10%5%7%5%6%38%
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
65%7%7%11%7%
1418
16th to endDay
61%7%7%12%8%1
1536
February1st to 15thDay
66%6%8%8%8%1
1475
16th to endDay
68%6%5%10%7%1
1580
March1st to 15thDay
62%6%7%10%11%2
1800
16th to endDay
59%5%8%13%11%2
2200
April1st to 15thDay
65%5%7%10%7%2
2161
16th to endDay
58%5%8%12%12%1
2340
May1st to 15thDay
59%5%10%14%9%1
2448
16th to endDay
63%7%7%15%5%
2694
June1st to 15thDay
62%6%10%14%5%
2700
16th to endDay
65%8%10%10%6%
2700
July1st to 15thDay
63%8%12%12%3
2455
16th to endDay
66%7%9%12%4
2487
August1st to 15thDay
69%9%10%8%2
2452
16th to endDay
61%9%14%12%2
2426
September1st to 15thDay
56%6%13%16%7%
2115
16th to endDay
55%8%10%18%6%
1830
October1st to 15thDay
67%5%7%13%6%
1705
16th to endDay
74%46%10%2
1584
November1st to 15thDay
71%7%5%11%3
1581
16th to endDay
72%5%6%11%3
1339
December1st to 15thDay
74%6%5%9%3
1260
16th to endDay
70%6%5%7%8%1
1344
January1st to 15thNight
70%7%5%9%5%1
2518
16th to endNight
62%9%7%12%7%
2688
February1st to 15thNight
60%10%8%11%7%1
2387
16th to endNight
68%6%6%9%8%1
1893
March1st to 15thNight
61%7%8%12%7%2
2160
16th to endNight
58%7%9%14%8%2
2023
April1st to 15thNight
64%5%6%12%8%1
1787
16th to endNight
57%7%7%14%10%1
1620
May1st to 15thNight
58%7%10%13%9%
1515
16th to endNight
60%6%10%14%5%
1423
June1st to 15thNight
59%6%11%16%4
1260
16th to endNight
56%8%11%15%6%
1260
July1st to 15thNight
54%11%14%15%4
1273
16th to endNight
54%11%11%17%4
1418
August1st to 15thNight
53%12%14%15%2
1470
16th to endNight
50%12%16%17%3
1774
September1st to 15thNight
54%8%11%19%6%
1845
16th to endNight
55%6%11%21%4
1836
October1st to 15thNight
63%6%9%13%6%
1920
16th to endNight
76%5%5%8%4
2288
November1st to 15thNight
70%6%8%9%4
2277
16th to endNight
73%6%7%8%4
2616
December1st to 15thNight
77%6%5%7%2
2700
16th to endNight
73%7%6%6%41
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
15%40%36%8%
60
16th to endDay
10%23%43%14%6%1
64
February1st to 15thDay
19%22%35%14%5%1
107
16th to endDay
20%28%32%13%31
239
March1st to 15thDay
23%26%33%11%4
270
16th to endDay
21%22%28%16%10%1
288
April1st to 15thDay
30%23%32%8%41
270
16th to endDay
26%27%30%8%5%2
270
May1st to 15thDay
31%17%28%12%9%
288
16th to endDay
29%23%26%15%31
403
June1st to 15thDay
35%14%23%19%5%1
495
16th to endDay
27%17%29%18%6%
495
July1st to 15thDay
27%13%35%16%6%
389
16th to endDay
26%14%34%19%4
326
August1st to 15thDay
28%11%30%18%8%3
313
16th to endDay
27%18%26%14%9%3
332
September1st to 15thDay
29%15%28%16%6%2
315
16th to endDay
24%22%28%12%8%2
259
October1st to 15thDay
30%26%23%13%42
246
16th to endDay
32%26%28%8%2
240
November1st to 15thDay
29%29%24%11%3
235
16th to endDay
38%18%26%12%32
99
December1st to 15thDay
33%21%38%33
60
16th to endDay
39%26%29%31
64
January1st to 15thNight
21%29%33%12%2
722
16th to endNight
16%27%34%15%31
768
February1st to 15thNight
12%30%38%14%3
704
16th to endNight
19%26%39%10%4
631
March1st to 15thNight
22%27%33%12%3
720
16th to endNight
19%25%33%15%5%1
768
April1st to 15thNight
27%24%29%13%4
709
16th to endNight
25%22%30%15%5%
540
May1st to 15thNight
26%16%29%19%7%
435
16th to endNight
27%19%27%21%4
375
June1st to 15thNight
26%15%25%25%7%
360
16th to endNight
18%16%32%23%7%
360
July1st to 15thNight
23%16%30%20%7%1
340
16th to endNight
20%11%36%22%9%
376
August1st to 15thNight
22%8%29%26%12%
399
16th to endNight
20%16%32%17%10%1
628
September1st to 15thNight
27%15%27%20%6%1
720
16th to endNight
28%19%29%14%6%1
665
October1st to 15thNight
27%23%31%12%41
660
16th to endNight
36%25%21%10%4
704
November1st to 15thNight
30%26%28%9%41
700
16th to endNight
26%28%26%11%5%1
743
December1st to 15thNight
26%32%26%12%2
750
16th to endNight
28%26%28%12%3
800
Page generated at 2017-09-18 08:38:26. Version ac04

Copyright 2017 A. Danko


Portes de l'enfer Clear Sky Chart | Charts Home