Calais
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Calais clear sky chart from 2005-11-05 to 2017-12-20.

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
24%
15253
16%
47999
6%
15215
35%
15215
17%
32729

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
18%
733
16%
2588
4%
729
33%
729
13%
1709
January16th to endNight
14%
768
17%
2616
2%
768
31%
768
14%
1765
February1st to 15thNight
17%
703
14%
2286
3%
701
30%
701
14%
1602
February16th to endNight
17%
631
15%
1944
2%
631
31%
631
13%
1369
March1st to 15thNight
17%
720
16%
2055
5%
720
29%
720
15%
1494
March16th to endNight
21%
768
18%
2112
6%
768
31%
768
19%
1472
April1st to 15thNight
17%
629
16%
1773
5%
629
26%
629
15%
1305
April16th to endNight
21%
540
16%
1620
6%
540
31%
540
18%
1117
May1st to 15thNight
23%
540
13%
1620
5%
540
32%
540
16%
1182
May16th to endNight
23%
507
11%
1468
4%
506
31%
506
16%
1078
June1st to 15thNight
28%
360
8%
1260
6%
360
33%
360
14%
917
June16th to endNight
33%
360
9%
1260
6%
360
39%
360
16%
887
July1st to 15thNight
36%
340
10%
1194
9%
340
42%
340
21%
768
July16th to endNight
37%
436
9%
1473
8%
409
42%
409
18%
1001
August1st to 15thNight
41%
539
12%
1608
8%
535
44%
535
23%
1087
August16th to endNight
41%
573
20%
1719
11%
573
46%
573
28%
1071
September1st to 15thNight
32%
654
17%
1890
9%
654
38%
654
27%
1217
September16th to endNight
38%
717
27%
1980
13%
717
50%
717
35%
1177
October1st to 15thNight
31%
720
21%
2115
9%
720
42%
720
25%
1364
October16th to endNight
21%
768
18%
2397
5%
768
34%
768
18%
1620
November1st to 15thNight
27%
773
18%
2527
8%
773
38%
773
18%
1683
November16th to endNight
24%
825
18%
2730
6%
825
39%
825
15%
1811
December1st to 15thNight
15%
825
15%
2813
3%
825
29%
825
12%
1973
December16th to endNight
12%
824
15%
2951
3%
824
28%
824
10%
2060

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%7%35%434446%35%
48848
Night
19%7%35%5%24446%35%
48167
TransparencyDay
49%411%22%12%1
48534
Night
49%311%22%11%1
47999
SeeingDay
24%14%29%21%7%1
7003
Night
24%13%31%22%7%
15254

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
16%9%35%5%25%446%35%
1349
16th to endDay
17%9%45%424447%35%
1607
February1st to 15thDay
15%10%37%5%45%35%6%31%
1575
16th to endDay
14%12%36%5%35%446%31%
1527
March1st to 15thDay
21%10%35%424445%32%
1894
16th to endDay
16%10%36%423436%36%
2112
April1st to 15thDay
21%10%36%5%23346%33%
2176
16th to endDay
24%7%25%42434436%
2340
May1st to 15thDay
25%8%36%434336%29%
2332
16th to endDay
25%7%35%433447%28%
2654
June1st to 15thDay
26%8%47%5%24345%27%
2700
16th to endDay
24%6%26%5%3445%7%28%
2700
July1st to 15thDay
16%5%245%35%45%8%36%
2694
16th to endDay
17%7%345%36%6%5%7%32%
2582
August1st to 15thDay
17%7%25%5%35%46%7%34%
2340
16th to endDay
13%4144346%6%8%42%
2483
September1st to 15thDay
15%5%14432336%48%
2067
16th to endDay
16%5%14222246%50%
1980
October1st to 15thDay
20%7%14423336%41%
1845
16th to endDay
22%7%25%5%24435%36%
1825
November1st to 15thDay
23%6%35%423345%37%
1659
16th to endDay
21%7%35%424345%36%
1560
December1st to 15thDay
25%9%34324345%31%
1475
16th to endDay
24%8%46%433445%30%
1372
January1st to 15thNight
17%8%35%5%34445%36%
2588
16th to endNight
14%9%46%6%25%5%6%7%32%
2616
February1st to 15thNight
14%10%35%5%36%5%5%7%31%
2285
16th to endNight
16%12%46%6%24445%32%
1944
March1st to 15thNight
20%10%35%5%34345%32%
2043
16th to endNight
18%8%45%434436%36%
2112
April1st to 15thNight
23%8%36%5%35%335%31%
1773
16th to endNight
24%8%14424346%34%
1620
May1st to 15thNight
23%7%35%5%345%5%5%29%
1620
16th to endNight
24%7%36%5%245%5%6%27%
1466
June1st to 15thNight
28%7%35%5%245%6%7%25%
1260
16th to endNight
21%7%26%6%26%45%7%29%
1260
July1st to 15thNight
15%7%345%35%6%6%9%32%
1264
16th to endNight
18%7%26%6%345%6%8%30%
1574
August1st to 15thNight
16%6%36%425%5%5%7%35%
1620
16th to endNight
14%5%245%3445%7%43%
1719
September1st to 15thNight
18%5%15%423346%43%
1890
16th to endNight
14%42321235%6%51%
1980
October1st to 15thNight
20%5%24423335%43%
2115
16th to endNight
23%6%35%423345%37%
2397
November1st to 15thNight
20%6%25%434446%37%
2527
16th to endNight
20%6%245%2335%6%37%
2730
December1st to 15thNight
25%8%3442434432%
2813
16th to endNight
23%9%35%434345%30%
2951

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
48%414%20%9%1
1350
16th to endDay
49%211%24%11%1
1607
February1st to 15thDay
53%311%19%10%1
1578
16th to endDay
52%311%20%9%2
1527
March1st to 15thDay
53%39%18%12%2
1905
16th to endDay
49%38%20%15%3
2112
April1st to 15thDay
51%37%19%15%2
2176
16th to endDay
50%49%17%13%4
2340
May1st to 15thDay
55%47%18%10%2
2332
16th to endDay
53%5%10%21%7%1
2658
June1st to 15thDay
58%410%16%9%1
2700
16th to endDay
53%5%11%17%11%
2700
July1st to 15thDay
43%5%13%23%12%1
2535
16th to endDay
47%5%14%22%9%
2421
August1st to 15thDay
47%5%13%23%10%
2327
16th to endDay
37%5%13%30%13%
2483
September1st to 15thDay
37%310%28%17%1
2067
16th to endDay
36%28%31%19%1
1980
October1st to 15thDay
44%310%27%13%
1845
16th to endDay
48%49%24%11%
1825
November1st to 15thDay
48%413%19%14%
1659
16th to endDay
50%414%19%10%1
1560
December1st to 15thDay
54%411%20%8%
1475
16th to endDay
55%49%19%10%
1372
January1st to 15thNight
48%312%22%10%1
2588
16th to endNight
50%310%24%10%
2616
February1st to 15thNight
51%413%20%9%1
2286
16th to endNight
54%210%18%12%1
1944
March1st to 15thNight
54%39%18%13%1
2055
16th to endNight
49%28%22%14%2
2112
April1st to 15thNight
55%36%16%14%3
1773
16th to endNight
50%39%18%15%2
1620
May1st to 15thNight
55%49%17%12%1
1620
16th to endNight
54%5%12%18%7%
1468
June1st to 15thNight
56%5%10%20%5%1
1260
16th to endNight
53%410%20%9%
1260
July1st to 15thNight
44%6%17%20%11%
1194
16th to endNight
50%414%20%8%1
1473
August1st to 15thNight
45%5%15%21%11%
1608
16th to endNight
38%5%14%29%12%
1719
September1st to 15thNight
42%310%27%15%
1890
16th to endNight
33%310%32%19%1
1980
October1st to 15thNight
43%39%27%14%1
2115
16th to endNight
48%310%25%11%
2397
November1st to 15thNight
48%313%21%12%1
2527
16th to endNight
46%5%12%22%12%
2730
December1st to 15thNight
53%310%23%8%
2813
16th to endNight
54%410%20%10%
2951

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
25%21%35%15%3
60
16th to endDay
20%20%34%19%4
135
February1st to 15thDay
19%23%34%19%2
236
16th to endDay
23%21%31%18%5%
230
March1st to 15thDay
25%25%30%13%4
270
16th to endDay
23%22%30%12%7%3
288
April1st to 15thDay
29%21%30%12%32
270
16th to endDay
27%18%31%16%42
270
May1st to 15thDay
32%15%30%14%41
288
16th to endDay
29%14%28%19%7%
491
June1st to 15thDay
28%12%30%21%5%1
495
16th to endDay
30%7%30%22%7%1
495
July1st to 15thDay
24%5%28%26%13%1
469
16th to endDay
20%7%28%32%9%
326
August1st to 15thDay
20%6%30%30%9%1
313
16th to endDay
15%8%28%27%15%3
332
September1st to 15thDay
18%11%28%30%8%2
315
16th to endDay
17%10%30%23%13%4
314
October1st to 15thDay
20%13%29%19%12%4
281
16th to endDay
25%18%30%18%6%
288
November1st to 15thDay
24%18%25%22%7%2
280
16th to endDay
25%18%27%20%6%1
285
December1st to 15thDay
36%18%27%14%5%
200
16th to endDay
31%30%25%9%2
72
January1st to 15thNight
22%20%32%21%3
733
16th to endNight
21%22%35%17%3
768
February1st to 15thNight
21%18%36%19%3
704
16th to endNight
24%21%30%18%3
631
March1st to 15thNight
26%17%32%19%3
720
16th to endNight
23%17%32%19%6%
768
April1st to 15thNight
29%15%34%17%4
629
16th to endNight
29%12%33%18%5%
540
May1st to 15thNight
26%10%34%23%5%
540
16th to endNight
25%11%32%24%6%
507
June1st to 15thNight
31%5%28%27%6%
360
16th to endNight
24%331%31%8%
360
July1st to 15thNight
17%336%31%11%
340
16th to endNight
21%329%34%11%
436
August1st to 15thNight
19%425%36%13%
539
16th to endNight
16%330%35%13%
573
September1st to 15thNight
21%5%33%26%12%
654
16th to endNight
16%8%31%28%13%1
717
October1st to 15thNight
22%7%32%24%11%
720
16th to endNight
24%15%33%18%7%
768
November1st to 15thNight
24%13%28%23%8%1
773
16th to endNight
24%19%28%20%6%
825
December1st to 15thNight
31%16%30%17%3
825
16th to endNight
30%21%29%15%2
824
Page generated at 2017-12-21 07:04:52. Version ac04

Copyright 2017 A. Danko


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