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 2017-03-22.

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%
15436
24%
45037
13%
15390
51%
15390
34%
26328

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
44%
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
46%
632
32%
1104
March1st to 15thNight
33%
624
23%
2064
13%
624
44%
624
30%
1180
March16th to endNight
26%
549
19%
2013
10%
549
39%
549
24%
1180
April1st to 15thNight
29%
494
19%
1694
12%
494
41%
494
26%
1007
April16th to endNight
34%
495
19%
1485
14%
495
44%
495
26%
939
May1st to 15thNight
36%
495
19%
1485
12%
495
45%
495
26%
962
May16th to endNight
42%
514
14%
1541
7%
513
50%
513
28%
973
June1st to 15thNight
44%
495
16%
1435
8%
495
48%
495
34%
856
June16th to endNight
60%
495
24%
1320
12%
495
64%
495
55%
684
July1st to 15thNight
64%
465
19%
1248
11%
465
67%
465
42%
728
July16th to endNight
73%
522
21%
1468
19%
489
75%
489
47%
751
August1st to 15thNight
71%
494
22%
1475
23%
491
74%
491
39%
824
August16th to endNight
64%
525
24%
1613
24%
525
69%
525
41%
865
September1st to 15thNight
53%
495
26%
1785
23%
495
64%
495
35%
936
September16th to endNight
51%
492
31%
1815
25%
492
63%
492
39%
874
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
52%
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%
45838
Night
8%5%2442345%7%52%
45222
Cloud CoverDay
9%5%2442445%7%48%
45836
Night
8%5%24423447%52%
45222
TransparencyDay
34%6%15%25%15%2
45527
Night
31%5%14%26%18%3
45037
SeeingDay
12%6%30%32%15%2
5147
Night
11%8%34%35%10%
15440

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
11%8%35%32435%7%43%
2007
April1st to 15thDay
13%6%25%323446%46%
1920
16th to endDay
20%6%25%434346%37%
2145
May1st to 15thDay
13%5%35%435%45%8%40%
2136
16th to endDay
15%5%2443446%7%42%
2222
June1st to 15thDay
9%5%134345%6%8%48%
2192
16th to endDay
42133245%7%8%55%
2310
July1st to 15thDay
7%313435%45%9%50%
2299
16th to endDay
6%2133246%6%8%54%
2284
August1st to 15thDay
7%426%5%245%7%9%45%
2145
16th to endDay
7%42432345%8%52%
2236
September1st to 15thDay
13%5%145%33345%48%
1845
16th to endDay
6%31432345%7%57%
1815
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%324447%46%
2013
April1st to 15thNight
11%5%3442445%6%46%
1694
16th to endNight
14%5%3442435%8%44%
1485
May1st to 15thNight
15%6%24425%5%5%6%42%
1484
16th to endNight
13%42442435%9%46%
1539
June1st to 15thNight
8%3244235%6%8%49%
1435
16th to endNight
3112213349%65%
1320
July1st to 15thNight
43144245%7%9%51%
1328
16th to endNight
32133235%6%11%56%
1576
August1st to 15thNight
42134346%6%9%52%
1485
16th to endNight
6%424313446%59%
1613
September1st to 15thNight
9%314323346%55%
1785
16th to endNight
6%21332335%6%60%
1815
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
11%8%35%42345%7%42%
2005
April1st to 15thDay
13%6%35%32335%6%46%
1920
16th to endDay
20%7%26%423447%36%
2145
May1st to 15thDay
14%435%43446%7%40%
2136
16th to endDay
15%5%2443445%7%42%
2222
June1st to 15thDay
10%42443346%8%48%
2192
16th to endDay
32134245%7%9%55%
2310
July1st to 15thDay
7%3234445%5%9%49%
2299
16th to endDay
5%213325%46%8%54%
2284
August1st to 15thDay
7%326%4245%6%10%45%
2145
16th to endDay
7%42442345%8%52%
2236
September1st to 15thDay
13%5%15%6%33345%48%
1845
16th to endDay
7%31422335%7%58%
1815
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%6%35%323446%47%
2013
April1st to 15thNight
12%5%34433447%46%
1694
16th to endNight
13%5%3442345%7%44%
1485
May1st to 15thNight
14%6%244245%5%6%42%
1484
16th to endNight
12%414425%349%46%
1539
June1st to 15thNight
7%3243235%6%9%49%
1435
16th to endNight
311221245%9%65%
1320
July1st to 15thNight
42144245%8%8%52%
1328
16th to endNight
321331447%10%56%
1576
August1st to 15thNight
42134445%6%9%52%
1485
16th to endNight
6%413323346%59%
1613
September1st to 15thNight
9%414323346%55%
1785
16th to endNight
6%21233335%7%60%
1815
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
41%5%16%23%11%2
2007
April1st to 15thDay
38%5%14%27%12%1
1920
16th to endDay
47%6%11%22%11%
2145
May1st to 15thDay
41%5%14%24%12%1
2136
16th to endDay
39%8%18%21%10%1
2226
June1st to 15thDay
33%7%18%25%12%2
2192
16th to endDay
22%7%15%30%18%4
2310
July1st to 15thDay
30%6%13%27%16%4
2151
16th to endDay
23%7%16%30%19%1
2129
August1st to 15thDay
32%8%17%24%14%1
2131
16th to endDay
28%7%14%27%18%4
2236
September1st to 15thDay
37%5%11%20%19%6%
1845
16th to endDay
24%5%13%32%22%1
1815
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
37%5%15%24%13%3
2013
April1st to 15thNight
37%5%13%23%18%1
1694
16th to endNight
38%6%15%22%16%
1485
May1st to 15thNight
40%6%12%23%14%1
1485
16th to endNight
35%8%19%21%12%2
1541
June1st to 15thNight
29%8%18%25%14%2
1435
16th to endNight
17%415%33%22%5%
1320
July1st to 15thNight
25%7%15%27%18%5%
1248
16th to endNight
19%7%17%32%19%3
1468
August1st to 15thNight
25%8%18%27%16%3
1475
16th to endNight
25%6%13%26%21%7%
1613
September1st to 15thNight
28%411%24%20%10%
1785
16th to endNight
24%410%29%27%3
1815
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
8%5%49%23%11%
67
April1st to 15thDay
13%17%37%27%3
159
16th to endDay
24%11%36%17%8%1
375
May1st to 15thDay
11%11%36%28%9%1
393
16th to endDay
19%8%31%25%13%1
437
June1st to 15thDay
11%7%31%31%15%1
420
16th to endDay
4331%38%19%2
420
July1st to 15thDay
10%222%38%22%3
400
16th to endDay
5%116%50%22%2
445
August1st to 15thDay
9%118%41%26%2
418
16th to endDay
9%123%38%23%2
404
September1st to 15thDay
15%332%35%10%3
120
16th to endDay
10%428%30%21%5%
90
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
13%12%45%22%6%
549
April1st to 15thNight
15%11%40%30%2
494
16th to endNight
17%11%34%29%7%
495
May1st to 15thNight
17%6%35%32%7%
495
16th to endNight
14%7%31%33%11%
515
June1st to 15thNight
10%5%35%37%10%
495
16th to endNight
3230%47%15%
495
July1st to 15thNight
5%123%46%23%
465
16th to endNight
3114%56%23%
522
August1st to 15thNight
5%117%53%20%2
494
16th to endNight
8%120%44%23%1
525
September1st to 15thNight
12%227%38%18%1
495
16th to endNight
7%433%34%18%1
492
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 2017-03-23 06:36:17. Version ac04

Copyright 2017 A. Danko


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