Clyde Sachtleben Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Clyde Sachtleben Observatory clear sky chart from 2005-11-05 to 2017-09-19.

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
42%
15973
23%
46688
13%
15927
51%
15927
34%
27276

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
34%
900
24%
2435
11%
895
45%
895
32%
1499
January16th to endNight
34%
960
28%
2496
12%
960
45%
960
35%
1521
February1st to 15thNight
30%
833
15%
2244
6%
829
37%
829
26%
1509
February16th to endNight
32%
632
25%
1894
8%
632
47%
632
32%
1104
March1st to 15thNight
33%
624
23%
2064
13%
624
44%
624
30%
1180
March16th to endNight
26%
576
18%
2112
10%
576
38%
576
23%
1269
April1st to 15thNight
30%
539
17%
1848
11%
539
41%
539
25%
1104
April16th to endNight
33%
540
20%
1620
15%
540
43%
540
25%
1038
May1st to 15thNight
37%
540
18%
1620
12%
540
46%
540
26%
1040
May16th to endNight
41%
562
15%
1685
7%
561
49%
561
28%
1064
June1st to 15thNight
46%
540
15%
1565
7%
540
50%
540
35%
918
June16th to endNight
58%
540
25%
1440
12%
540
62%
540
55%
750
July1st to 15thNight
65%
510
18%
1369
10%
510
68%
510
44%
789
July16th to endNight
72%
564
22%
1594
20%
531
75%
531
46%
827
August1st to 15thNight
71%
539
21%
1610
22%
536
74%
536
40%
895
August16th to endNight
64%
573
26%
1761
26%
573
70%
573
42%
928
September1st to 15thNight
55%
540
25%
1947
23%
540
64%
540
36%
1006
September16th to endNight
52%
504
31%
1857
25%
504
65%
504
38%
899
October1st to 15thNight
40%
560
28%
1880
20%
560
48%
560
30%
1058
October16th to endNight
47%
762
29%
2170
15%
762
55%
762
41%
1191
November1st to 15thNight
44%
875
33%
2275
13%
875
55%
875
48%
1235
November16th to endNight
41%
900
30%
2340
13%
900
51%
900
42%
1332
December1st to 15thNight
31%
900
22%
2340
8%
900
41%
900
32%
1501
December16th to endNight
35%
960
24%
2522
10%
960
46%
960
30%
1619

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
9%5%2442445%7%48%
48117
Night
8%5%2442345%7%52%
46873
Cloud CoverDay
9%5%2442445%7%48%
48115
Night
8%5%2442345%7%52%
46873
TransparencyDay
34%6%15%26%15%2
47806
Night
31%5%14%26%18%3
46688
SeeingDay
12%6%30%32%15%2
5965
Night
11%7%34%35%10%
15977

By Month

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%7%245%2345%7%49%
1495
16th to endDay
7%7%35%433346%50%
1728
February1st to 15thDay
9%8%47%6%24447%40%
1627
16th to endDay
7%6%35%423447%48%
1580
March1st to 15thDay
8%6%2342345%7%51%
1896
16th to endDay
13%9%35%32435%7%41%
2112
April1st to 15thDay
13%6%25%323446%45%
2096
16th to endDay
20%7%25%434346%37%
2340
May1st to 15thDay
12%5%35%425%45%8%42%
2331
16th to endDay
15%5%2443445%7%42%
2430
June1st to 15thDay
9%4134245%6%7%49%
2391
16th to endDay
42133245%7%8%55%
2520
July1st to 15thDay
6%313435%45%9%51%
2508
16th to endDay
6%2133245%6%8%55%
2466
August1st to 15thDay
7%325%5%245%7%9%45%
2340
16th to endDay
7%42332345%8%54%
2440
September1st to 15thDay
12%4245%33245%50%
2013
16th to endDay
7%31432345%7%57%
1848
October1st to 15thDay
14%6%23213335%52%
1738
16th to endDay
11%5%23313335%56%
1700
November1st to 15thDay
7%323323446%58%
1583
16th to endDay
8%7%25%224446%51%
1620
December1st to 15thDay
9%9%35%5%24445%44%
1620
16th to endDay
8%8%47%6%34346%42%
1695
January1st to 15thNight
5%8%25%43345%7%48%
2435
16th to endNight
7%6%24423436%53%
2496
February1st to 15thNight
9%8%46%424446%43%
2234
16th to endNight
6%5%245%345%6%6%49%
1894
March1st to 15thNight
9%6%34323346%52%
2064
16th to endNight
11%7%35%424347%44%
2112
April1st to 15thNight
11%6%3443445%7%45%
1848
16th to endNight
15%5%3442435%8%43%
1620
May1st to 15thNight
14%5%24425%5%5%6%43%
1619
16th to endNight
13%42342435%8%46%
1683
June1st to 15thNight
7%3234235%6%9%51%
1565
16th to endNight
3212313349%64%
1440
July1st to 15thNight
43143245%7%9%52%
1449
16th to endNight
32123145%6%11%55%
1702
August1st to 15thNight
42134346%6%9%52%
1620
16th to endNight
6%313313446%60%
1761
September1st to 15thNight
8%31432335%6%56%
1947
16th to endNight
6%21332335%7%59%
1857
October1st to 15thNight
14%41332323455%
1880
16th to endNight
10%312223246%59%
2170
November1st to 15thNight
5%312324345%64%
2275
16th to endNight
8%422313347%58%
2340
December1st to 15thNight
9%6%35%5%24347%47%
2340
16th to endNight
9%8%36%424347%46%
2522

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%8%25%423447%49%
1495
16th to endDay
8%7%35%433346%49%
1728
February1st to 15thDay
9%8%46%6%34447%40%
1627
16th to endDay
7%6%35%43345%7%48%
1580
March1st to 15thDay
8%5%2442336%7%51%
1896
16th to endDay
13%9%35%42345%6%41%
2110
April1st to 15thDay
13%6%35%42435%6%45%
2096
16th to endDay
20%7%25%423447%36%
2340
May1st to 15thDay
13%435%43446%7%42%
2331
16th to endDay
15%5%2433445%7%42%
2430
June1st to 15thDay
9%42343346%7%49%
2391
16th to endDay
431242447%9%55%
2520
July1st to 15thDay
7%3234445%5%8%51%
2508
16th to endDay
5%213325%46%8%55%
2466
August1st to 15thDay
7%326%5%245%6%10%45%
2340
16th to endDay
7%42442345%7%54%
2440
September1st to 15thDay
12%415%5%33345%50%
2013
16th to endDay
7%31432335%7%57%
1848
October1st to 15thDay
14%5%23323435%52%
1738
16th to endDay
11%5%23212335%57%
1700
November1st to 15thDay
7%423323347%57%
1583
16th to endDay
8%6%25%314346%51%
1620
December1st to 15thDay
9%8%36%5%34436%44%
1620
16th to endDay
8%8%47%6%33446%42%
1695
January1st to 15thNight
5%8%25%433447%49%
2435
16th to endNight
7%6%245%22447%53%
2496
February1st to 15thNight
9%8%46%42445%6%42%
2234
16th to endNight
6%5%244345%5%7%49%
1894
March1st to 15thNight
8%6%34423346%52%
2064
16th to endNight
11%7%35%423446%45%
2112
April1st to 15thNight
11%5%35%434447%45%
1848
16th to endNight
14%6%3442335%7%43%
1620
May1st to 15thNight
14%5%244245%5%6%43%
1619
16th to endNight
13%414424449%46%
1683
June1st to 15thNight
7%3243235%6%9%51%
1565
16th to endNight
321221245%9%64%
1440
July1st to 15thNight
42144245%7%8%53%
1449
16th to endNight
321331447%10%55%
1702
August1st to 15thNight
42133445%6%9%52%
1620
16th to endNight
6%313323346%60%
1761
September1st to 15thNight
8%31332335%6%56%
1947
16th to endNight
6%21333335%7%59%
1857
October1st to 15thNight
14%413323235%55%
1880
16th to endNight
10%312213336%60%
2170
November1st to 15thNight
5%312324346%64%
2275
16th to endNight
8%412313347%58%
2340
December1st to 15thNight
9%6%25%6%2345%7%47%
2340
16th to endNight
9%8%36%423347%46%
2522

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
34%5%18%26%14%
1496
16th to endDay
34%419%23%14%2
1728
February1st to 15thDay
42%6%16%22%9%2
1628
16th to endDay
34%5%17%25%13%2
1580
March1st to 15thDay
31%6%15%25%17%3
1896
16th to endDay
43%5%15%23%10%2
2112
April1st to 15thDay
38%5%14%27%12%1
2096
16th to endDay
47%6%11%21%11%
2340
May1st to 15thDay
40%5%14%24%14%1
2331
16th to endDay
39%8%17%21%10%1
2434
June1st to 15thDay
31%7%17%27%13%2
2391
16th to endDay
23%6%15%31%18%4
2520
July1st to 15thDay
29%6%13%28%17%4
2360
16th to endDay
23%7%17%30%20%1
2311
August1st to 15thDay
31%9%18%25%13%1
2326
16th to endDay
27%7%14%27%19%3
2440
September1st to 15thDay
35%5%11%22%19%5%
2013
16th to endDay
25%5%13%32%22%1
1848
October1st to 15thDay
34%49%26%22%2
1738
16th to endDay
30%312%29%20%3
1700
November1st to 15thDay
27%411%27%25%3
1583
16th to endDay
32%5%14%26%18%3
1620
December1st to 15thDay
41%5%16%25%10%1
1620
16th to endDay
42%416%22%12%
1695
January1st to 15thNight
34%5%13%27%17%1
2435
16th to endNight
31%5%15%29%16%2
2496
February1st to 15thNight
41%6%14%24%10%2
2244
16th to endNight
32%415%25%16%5%
1894
March1st to 15thNight
33%411%24%20%5%
2064
16th to endNight
39%5%15%23%12%2
2112
April1st to 15thNight
37%5%13%24%17%1
1848
16th to endNight
39%6%14%22%15%1
1620
May1st to 15thNight
39%6%12%23%16%1
1620
16th to endNight
35%8%18%22%12%2
1685
June1st to 15thNight
27%9%18%27%14%2
1565
16th to endNight
18%415%34%22%4
1440
July1st to 15thNight
24%7%15%27%19%5%
1369
16th to endNight
20%7%17%31%19%3
1594
August1st to 15thNight
24%8%19%28%15%3
1610
16th to endNight
23%6%13%26%22%6%
1761
September1st to 15thNight
27%411%26%20%9%
1947
16th to endNight
24%410%29%27%3
1857
October1st to 15thNight
33%49%22%24%5%
1880
16th to endNight
26%411%29%24%4
2170
November1st to 15thNight
21%410%27%29%6%
2275
16th to endNight
26%413%29%22%5%
2340
December1st to 15thNight
36%415%29%12%
2340
16th to endNight
37%5%16%22%15%2
2522

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
20%12%37%28%1
90
16th to endDay
16%6%42%26%7%1
96
February1st to 15thDay
7%11%48%25%6%
90
16th to endDay
6%19%40%18%13%1
81
March1st to 15thDay
13%8%51%22%31
90
16th to endDay
26%437%21%10%
96
April1st to 15thDay
13%16%38%26%4
215
16th to endDay
26%11%35%17%8%1
450
May1st to 15thDay
10%10%35%28%13%1
468
16th to endDay
20%7%32%25%12%1
517
June1st to 15thDay
9%7%30%30%18%3
495
16th to endDay
6%333%37%16%2
495
July1st to 15thDay
9%221%38%24%4
475
16th to endDay
5%115%50%24%3
515
August1st to 15thDay
9%119%41%25%2
493
16th to endDay
8%123%39%22%3
480
September1st to 15thDay
12%330%34%14%4
168
16th to endDay
10%430%29%21%5%
99
October1st to 15thDay
16%6%24%35%11%5%
90
16th to endDay
9%6%40%30%11%2
96
November1st to 15thDay
8%6%23%37%17%5%
90
16th to endDay
31%11%32%20%5%
90
December1st to 15thDay
14%13%48%15%6%1
90
16th to endDay
18%12%48%17%2
96
January1st to 15thNight
10%11%38%32%6%
900
16th to endNight
10%10%39%31%7%
960
February1st to 15thNight
13%8%41%30%5%
836
16th to endNight
9%10%43%29%6%
632
March1st to 15thNight
11%10%40%31%41
624
16th to endNight
14%11%44%22%6%
576
April1st to 15thNight
14%10%40%31%2
539
16th to endNight
18%10%34%28%7%
540
May1st to 15thNight
17%5%35%32%9%
540
16th to endNight
15%7%32%33%10%
563
June1st to 15thNight
9%435%37%11%
540
16th to endNight
3332%46%13%
540
July1st to 15thNight
5%122%45%24%
510
16th to endNight
3114%54%24%
564
August1st to 15thNight
5%117%53%20%2
539
16th to endNight
8%121%42%24%1
573
September1st to 15thNight
11%227%38%19%1
540
16th to endNight
7%433%35%18%1
504
October1st to 15thNight
17%8%31%28%13%
560
16th to endNight
11%9%28%39%11%
762
November1st to 15thNight
7%9%35%37%9%
875
16th to endNight
11%9%35%31%10%
900
December1st to 15thNight
13%10%40%30%5%
900
16th to endNight
13%10%35%33%7%
960
Page generated at 2017-09-20 03:49:45. Version ac04

Copyright 2017 A. Danko


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