Arrakis Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Arrakis Observatory clear sky chart from 2005-11-05 to 2017-09-10.

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
35%
16082
18%
46616
9%
16035
42%
16035
27%
30131

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
24%
900
15%
2564
5%
895
33%
895
21%
1780
January16th to endNight
20%
960
14%
2496
3%
960
28%
960
17%
1864
February1st to 15thNight
24%
879
11%
2288
3%
875
30%
875
20%
1670
February16th to endNight
25%
735
16%
1997
5%
735
33%
735
24%
1373
March1st to 15thNight
28%
566
17%
2006
9%
566
39%
566
21%
1301
March16th to endNight
29%
576
13%
2112
10%
576
36%
576
15%
1448
April1st to 15thNight
29%
539
17%
1818
11%
539
40%
539
22%
1159
April16th to endNight
29%
540
17%
1620
11%
540
39%
540
20%
1129
May1st to 15thNight
32%
540
15%
1613
8%
540
39%
540
27%
1022
May16th to endNight
39%
563
15%
1498
6%
561
44%
561
30%
988
June1st to 15thNight
47%
540
15%
1353
5%
540
50%
540
36%
865
June16th to endNight
54%
540
20%
1260
6%
540
58%
540
52%
736
July1st to 15thNight
63%
510
21%
1190
8%
510
66%
510
58%
666
July16th to endNight
64%
564
21%
1565
14%
531
66%
531
51%
787
August1st to 15thNight
65%
539
22%
1610
19%
536
69%
536
44%
865
August16th to endNight
57%
573
26%
1734
24%
573
65%
573
42%
946
September1st to 15thNight
54%
525
24%
1805
22%
525
65%
525
39%
937
September16th to endNight
42%
492
26%
1815
16%
492
59%
492
32%
953
October1st to 15thNight
33%
643
26%
1963
14%
643
43%
643
31%
1146
October16th to endNight
32%
723
19%
2131
9%
723
40%
723
27%
1359
November1st to 15thNight
31%
875
23%
2363
9%
875
42%
875
29%
1512
November16th to endNight
27%
900
18%
2520
8%
900
35%
900
25%
1695
December1st to 15thNight
21%
900
11%
2520
3%
900
28%
900
18%
1838
December16th to endNight
20%
960
14%
2775
4%
960
30%
960
16%
2092

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
13%7%35%5%3445%7%39%
48003
Night
11%7%36%5%24447%43%
46785
Cloud CoverDay
13%7%35%5%3445%7%39%
48014
Night
11%7%36%5%24446%43%
46789
Cloud CoverDay
12%7%35%5%3445%7%39%
48012
Night
11%7%36%5%24446%43%
46789
TransparencyDay
43%5%14%23%11%1
47691
Night
40%5%14%24%13%1
46616
SeeingDay
16%8%31%27%12%3
6083
Night
14%9%35%29%10%1
16083

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
8%9%6%9%7%446%6%7%28%
1367
16th to endDay
8%12%5%10%9%46%5%46%25%
1728
February1st to 15thDay
11%10%5%10%8%445%6%6%27%
1575
16th to endDay
10%10%47%7%36%5%5%6%30%
1488
March1st to 15thDay
16%9%5%8%5%24446%31%
1942
16th to endDay
15%12%5%6%6%34446%30%
2112
April1st to 15thDay
16%8%35%5%2445%7%37%
2127
16th to endDay
24%10%25%433345%32%
2340
May1st to 15thDay
21%6%25%5%34446%33%
2337
16th to endDay
16%6%25%4345%5%7%37%
2617
June1st to 15thDay
16%6%25%425%5%5%7%38%
2604
16th to endDay
8%4134345%6%9%48%
2700
July1st to 15thDay
6%2134245%5%9%53%
2700
16th to endDay
5%3133345%6%9%53%
2493
August1st to 15thDay
10%425%6%45%6%6%8%41%
2340
16th to endDay
9%42433345%8%50%
2468
September1st to 15thDay
11%5%23433347%49%
2039
16th to endDay
10%5%2432335%6%50%
1815
October1st to 15thDay
15%6%23414436%46%
1656
16th to endDay
15%8%35%423345%43%
1739
November1st to 15thDay
10%7%35%423446%46%
1493
16th to endDay
12%11%37%42446%7%34%
1440
December1st to 15thDay
13%11%49%8%35%446%27%
1440
16th to endDay
15%11%6%7%7%45%437%24%
1443
January1st to 15thNight
7%7%5%8%6%37%5%5%8%33%
2564
16th to endNight
9%11%410%7%46%5%6%7%26%
2496
February1st to 15thNight
9%11%5%9%6%35%5%35%33%
2285
16th to endNight
7%7%48%8%35%5%48%36%
1997
March1st to 15thNight
11%9%37%434346%40%
1994
16th to endNight
16%10%46%5%24436%34%
2112
April1st to 15thNight
15%8%245%24436%41%
1818
16th to endNight
20%7%25%425%346%36%
1620
May1st to 15thNight
16%6%24423245%46%
1613
16th to endNight
12%415%5%35%46%9%41%
1496
June1st to 15thNight
10%5%23325%35%8%48%
1353
16th to endNight
5%21232345%8%60%
1260
July1st to 15thNight
311331345%7%65%
1260
16th to endNight
321231336%9%61%
1671
August1st to 15thNight
5%3333346%8%57%
1620
16th to endNight
8%413313346%59%
1734
September1st to 15thNight
9%313323336%58%
1805
16th to endNight
9%413323446%56%
1815
October1st to 15thNight
14%6%23312235%52%
1963
16th to endNight
16%7%24413346%44%
2131
November1st to 15thNight
10%7%26%424445%48%
2363
16th to endNight
11%9%36%5%3445%6%40%
2520
December1st to 15thNight
11%11%38%8%35%437%31%
2520
16th to endNight
16%9%5%8%6%445%46%26%
2775

Percentage Cloud Cover SW (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
7%10%5%9%8%446%6%7%28%
1367
16th to endDay
8%12%5%10%9%47%5%46%25%
1728
February1st to 15thDay
11%11%49%8%35%5%5%7%26%
1575
16th to endDay
10%10%5%8%7%36%5%5%6%30%
1488
March1st to 15thDay
16%9%5%8%5%24346%31%
1953
16th to endDay
16%11%5%6%6%34446%30%
2112
April1st to 15thDay
16%7%35%5%24447%36%
2127
16th to endDay
24%10%35%423345%32%
2340
May1st to 15thDay
21%6%246%34346%33%
2337
16th to endDay
16%6%25%425%5%5%7%36%
2617
June1st to 15thDay
16%5%345%25%5%5%7%38%
2604
16th to endDay
8%413425%5%5%9%49%
2700
July1st to 15thDay
6%2134235%6%9%53%
2700
16th to endDay
5%213325%5%6%8%53%
2493
August1st to 15thDay
10%5%25%5%35%5%6%8%40%
2340
16th to endDay
10%41442345%7%50%
2468
September1st to 15thDay
11%5%23424346%50%
2039
16th to endDay
10%6%2342335%6%50%
1815
October1st to 15thDay
15%6%23324446%46%
1656
16th to endDay
15%9%34423346%43%
1739
November1st to 15thDay
10%7%36%41345%6%46%
1493
16th to endDay
12%11%37%5%2437%7%34%
1440
December1st to 15thDay
13%11%5%9%7%44446%27%
1440
16th to endDay
16%11%6%7%8%35%446%25%
1443
January1st to 15thNight
7%7%5%8%6%46%6%5%7%33%
2564
16th to endNight
8%11%410%6%46%6%6%7%26%
2496
February1st to 15thNight
9%11%49%7%445%46%33%
2278
16th to endNight
7%6%48%8%35%5%48%36%
1997
March1st to 15thNight
11%10%37%424346%39%
2006
16th to endNight
16%9%5%6%5%24437%33%
2112
April1st to 15thNight
16%8%24424346%41%
1818
16th to endNight
20%7%35%424346%36%
1620
May1st to 15thNight
16%6%24413246%46%
1612
16th to endNight
12%4145%345%6%8%41%
1496
June1st to 15thNight
10%5%2432435%8%48%
1353
16th to endNight
5%312323348%61%
1260
July1st to 15thNight
311231435%7%65%
1260
16th to endNight
321232336%9%61%
1671
August1st to 15thNight
5%31233346%8%56%
1620
16th to endNight
9%314322336%59%
1734
September1st to 15thNight
9%313223346%58%
1805
16th to endNight
9%413323347%55%
1815
October1st to 15thNight
15%5%24213235%53%
1963
16th to endNight
17%7%24413345%44%
2131
November1st to 15thNight
10%7%26%424435%47%
2363
16th to endNight
11%8%36%5%345%46%40%
2520
December1st to 15thNight
12%10%48%8%35%5%37%31%
2520
16th to endNight
17%10%5%9%6%3445%6%27%
2775

Percentage Cloud Cover SE (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
7%10%6%9%8%5%36%5%7%28%
1367
16th to endDay
8%12%5%10%8%5%6%6%5%6%24%
1728
February1st to 15thDay
10%11%5%9%8%45%5%5%7%26%
1575
16th to endDay
10%10%48%7%36%6%5%5%30%
1488
March1st to 15thDay
15%10%5%8%5%34446%31%
1953
16th to endDay
15%11%5%6%6%34446%30%
2110
April1st to 15thDay
16%7%35%434347%36%
2127
16th to endDay
23%10%35%433345%32%
2340
May1st to 15thDay
21%7%246%35%346%33%
2337
16th to endDay
15%6%35%435%5%5%7%36%
2617
June1st to 15thDay
16%5%25%5%25%45%8%38%
2604
16th to endDay
8%4143345%5%9%48%
2700
July1st to 15thDay
5%2134245%6%9%53%
2700
16th to endDay
4313325%5%6%8%53%
2493
August1st to 15thDay
9%5%25%5%35%5%6%9%39%
2340
16th to endDay
10%42442345%8%50%
2468
September1st to 15thDay
11%5%2342435%6%50%
2039
16th to endDay
10%5%2443245%7%50%
1815
October1st to 15thDay
14%6%34423436%46%
1656
16th to endDay
16%7%35%323336%42%
1739
November1st to 15thDay
9%8%36%423446%46%
1493
16th to endDay
11%11%46%5%2446%7%34%
1440
December1st to 15thDay
13%11%410%7%45%446%27%
1440
16th to endDay
16%10%7%7%8%35%446%25%
1443
January1st to 15thNight
7%7%5%8%7%47%6%5%7%33%
2564
16th to endNight
9%12%410%7%45%6%6%7%26%
2496
February1st to 15thNight
9%11%49%7%35%5%36%33%
2278
16th to endNight
7%6%48%8%46%447%35%
1997
March1st to 15thNight
11%10%46%5%24346%39%
2006
16th to endNight
15%9%5%7%5%24446%33%
2112
April1st to 15thNight
15%8%24425%346%41%
1818
16th to endNight
20%8%35%5%24345%36%
1620
May1st to 15thNight
16%7%24423245%46%
1612
16th to endNight
12%425%5%445%6%8%41%
1496
June1st to 15thNight
10%5%2442435%8%48%
1353
16th to endNight
5%31132335%8%60%
1260
July1st to 15thNight
32321435%6%64%
1260
16th to endNight
321222346%8%61%
1671
August1st to 15thNight
431332346%8%56%
1620
16th to endNight
8%313313345%59%
1734
September1st to 15thNight
9%313313446%58%
1805
16th to endNight
8%5%1332335%7%55%
1815
October1st to 15thNight
14%5%34312235%52%
1963
16th to endNight
17%8%24413346%44%
2131
November1st to 15thNight
9%7%26%424435%47%
2363
16th to endNight
10%8%37%5%3445%6%40%
2520
December1st to 15thNight
12%10%48%7%35%446%30%
2520
16th to endNight
16%11%49%6%35%5%45%27%
2775

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
52%6%14%16%10%
1368
16th to endDay
58%415%17%4
1728
February1st to 15thDay
54%5%15%18%5%
1576
16th to endDay
51%8%12%16%9%1
1488
March1st to 15thDay
53%413%20%6%
1953
16th to endDay
54%6%14%20%4
2112
April1st to 15thDay
46%5%14%24%8%1
2127
16th to endDay
54%412%19%8%
2340
May1st to 15thDay
50%6%11%22%8%
2337
16th to endDay
45%7%13%22%10%
2621
June1st to 15thDay
44%6%15%23%9%
2604
16th to endDay
31%7%16%29%13%2
2700
July1st to 15thDay
25%7%17%32%14%3
2541
16th to endDay
25%6%16%29%19%2
2337
August1st to 15thDay
38%7%15%24%11%2
2326
16th to endDay
31%6%14%31%13%3
2468
September1st to 15thDay
34%5%13%27%18%
2039
16th to endDay
33%414%30%16%
1815
October1st to 15thDay
38%5%13%23%16%1
1656
16th to endDay
43%314%24%12%
1739
November1st to 15thDay
37%5%13%23%18%1
1493
16th to endDay
46%5%17%18%9%1
1440
December1st to 15thDay
57%5%11%15%8%1
1440
16th to endDay
59%413%14%6%1
1443
January1st to 15thNight
47%5%13%22%11%
2564
16th to endNight
52%5%15%18%7%
2496
February1st to 15thNight
50%5%13%20%9%
2288
16th to endNight
44%5%13%20%13%2
1997
March1st to 15thNight
45%413%25%9%1
2006
16th to endNight
51%5%14%21%6%
2112
April1st to 15thNight
43%411%26%13%
1818
16th to endNight
48%5%10%21%10%2
1620
May1st to 15thNight
40%414%24%14%2
1613
16th to endNight
37%7%16%22%14%1
1498
June1st to 15thNight
33%6%17%27%13%1
1353
16th to endNight
21%5%15%30%22%3
1260
July1st to 15thNight
17%5%17%36%18%4
1190
16th to endNight
18%5%18%32%19%4
1565
August1st to 15thNight
23%6%16%32%18%2
1610
16th to endNight
26%414%31%18%4
1734
September1st to 15thNight
27%413%31%21%2
1805
16th to endNight
28%5%11%35%17%1
1815
October1st to 15thNight
34%311%27%20%3
1963
16th to endNight
41%315%24%14%
2131
November1st to 15thNight
38%412%23%19%2
2363
16th to endNight
43%417%21%12%1
2520
December1st to 15thNight
52%5%15%17%8%
2520
16th to endNight
56%5%12%17%7%
2775

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%10%42%24%6%1
90
16th to endDay
20%11%35%27%41
96
February1st to 15thDay
17%18%43%18%1
90
16th to endDay
23%14%32%20%7%1
81
March1st to 15thDay
26%16%31%23%2
90
16th to endDay
28%7%31%23%8%1
96
April1st to 15thDay
19%11%41%17%7%2
246
16th to endDay
30%13%27%19%7%2
450
May1st to 15thDay
23%10%32%25%7%1
468
16th to endDay
22%7%33%22%11%1
517
June1st to 15thDay
16%7%33%24%13%3
495
16th to endDay
8%6%40%28%14%2
495
July1st to 15thDay
6%5%29%36%17%5%
475
16th to endDay
6%328%37%19%4
515
August1st to 15thDay
9%423%33%24%4
493
16th to endDay
13%326%31%18%6%
508
September1st to 15thDay
14%326%37%13%4
236
16th to endDay
16%8%28%27%8%8%
90
October1st to 15thDay
11%12%38%24%8%4
90
16th to endDay
16%9%40%20%10%2
96
November1st to 15thDay
5%8%38%36%7%2
90
16th to endDay
32%12%31%22%2
90
December1st to 15thDay
25%17%35%13%6%1
90
16th to endDay
26%26%32%12%3
96
January1st to 15thNight
11%15%41%24%5%1
900
16th to endNight
15%13%42%25%3
960
February1st to 15thNight
15%13%38%24%7%
880
16th to endNight
11%12%42%22%8%2
735
March1st to 15thNight
15%11%38%27%6%
566
16th to endNight
20%10%33%26%8%
576
April1st to 15thNight
20%10%35%25%7%
539
16th to endNight
25%9%32%20%9%1
540
May1st to 15thNight
18%9%36%24%9%
540
16th to endNight
16%5%32%33%11%
563
June1st to 15thNight
14%5%29%36%14%
540
16th to endNight
6%233%44%12%
540
July1st to 15thNight
5%225%44%20%1
510
16th to endNight
4125%47%19%1
564
August1st to 15thNight
6%22%46%22%1
539
16th to endNight
10%125%38%21%3
573
September1st to 15thNight
10%228%37%17%3
525
16th to endNight
10%7%36%28%14%2
492
October1st to 15thNight
17%11%35%26%9%
643
16th to endNight
21%9%32%28%8%
723
November1st to 15thNight
15%11%37%27%8%
875
16th to endNight
15%14%39%23%6%
900
December1st to 15thNight
18%12%40%25%3
900
16th to endNight
22%11%37%22%5%
960
Page generated at 2017-09-11 18:35:19. Version ac04

Copyright 2017 A. Danko


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