Mt. Laurel Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mt. Laurel Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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
51%
15343
24%
47180
18%
15300
58%
15300
29%
28794

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
29%
720
24%
2327
11%
716
44%
716
24%
1426
January16th to endNight
27%
768
26%
2316
11%
768
41%
768
23%
1511
February1st to 15thNight
32%
704
25%
2112
10%
701
46%
701
27%
1301
February16th to endNight
29%
631
25%
1893
11%
631
41%
631
26%
1194
March1st to 15thNight
33%
720
21%
2148
12%
720
41%
720
26%
1350
March16th to endNight
39%
717
24%
2061
13%
717
47%
717
30%
1255
April1st to 15thNight
44%
539
24%
1797
18%
539
55%
539
30%
1027
April16th to endNight
49%
540
26%
1800
21%
540
59%
540
34%
983
May1st to 15thNight
53%
540
22%
1638
15%
540
61%
540
31%
1015
May16th to endNight
70%
561
24%
1682
19%
561
74%
561
35%
993
June1st to 15thNight
75%
540
15%
1620
14%
540
75%
540
31%
999
June16th to endNight
77%
540
19%
1620
18%
540
78%
540
35%
968
July1st to 15thNight
75%
510
13%
1530
13%
510
76%
510
29%
982
July16th to endNight
74%
564
16%
1623
16%
531
75%
531
29%
1037
August1st to 15thNight
76%
539
17%
1788
21%
536
76%
536
29%
1094
August16th to endNight
71%
573
19%
1910
24%
573
72%
573
24%
1265
September1st to 15thNight
66%
624
20%
1884
20%
624
67%
624
26%
1231
September16th to endNight
67%
717
29%
1980
24%
717
70%
717
37%
1183
October1st to 15thNight
58%
684
33%
1881
25%
684
64%
684
40%
1082
October16th to endNight
53%
704
34%
2118
29%
704
60%
704
37%
1198
November1st to 15thNight
52%
700
30%
2276
25%
700
62%
700
37%
1208
November16th to endNight
42%
720
27%
2340
19%
720
54%
720
30%
1349
December1st to 15thNight
38%
720
23%
2340
17%
720
46%
720
25%
1468
December16th to endNight
29%
768
20%
2496
14%
768
38%
768
19%
1675

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
12%5%25%5%35%5%5%7%41%
48004
Night
11%5%2442445%7%46%
47382
TransparencyDay
40%6%11%18%17%4
47708
Night
35%6%10%19%20%7%
47182
SeeingDay
14%5%18%23%24%14%
5256
Night
13%6%22%28%23%5%
15345

By Month

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
20%7%2432333443%
1611
16th to endDay
17%6%2442334446%
1905
February1st to 15thDay
16%7%35%424335%42%
1750
16th to endDay
19%6%245%24335%41%
1580
March1st to 15thDay
16%7%36%5%23345%41%
1810
16th to endDay
13%7%245%34446%42%
2171
April1st to 15thDay
13%425%435%35%6%44%
2151
16th to endDay
9%425%435%5%5%7%46%
2160
May1st to 15thDay
11%5%245%25%5%5%7%43%
2310
16th to endDay
8%5%25%5%45%5%6%9%41%
2431
June1st to 15thDay
8%5%26%6%5%7%8%7%9%33%
2340
16th to endDay
6%324446%7%7%10%42%
2340
July1st to 15thDay
9%436%6%5%8%8%8%10%28%
2340
16th to endDay
6%426%6%5%8%8%9%10%29%
2433
August1st to 15thDay
8%5%247%5%8%7%7%11%31%
2160
16th to endDay
11%6%37%7%47%7%6%9%27%
2292
September1st to 15thDay
12%6%25%7%445%6%7%36%
2064
16th to endDay
12%5%145%25%45%6%47%
1980
October1st to 15thDay
10%424414446%51%
1877
16th to endDay
11%42431223458%
1749
November1st to 15thDay
13%5%23312335%54%
1582
16th to endDay
15%5%25%323446%48%
1620
December1st to 15thDay
18%8%24434345%40%
1620
16th to endDay
22%9%36%42323436%
1728
January1st to 15thNight
16%6%24424445%45%
2327
16th to endNight
16%7%35%424445%41%
2316
February1st to 15thNight
15%6%24423346%46%
2103
16th to endNight
17%5%24424346%46%
1893
March1st to 15thNight
16%6%24324347%44%
2148
16th to endNight
11%425%32345%7%47%
2061
April1st to 15thNight
11%32443345%7%49%
1797
16th to endNight
9%41343335%6%54%
1800
May1st to 15thNight
9%3145%36%46%7%46%
1637
16th to endNight
5%3145%35%5%6%10%48%
1682
June1st to 15thNight
33135%37%7%8%12%41%
1620
16th to endNight
42236%26%5%8%12%45%
1620
July1st to 15thNight
6%425%5%37%6%8%10%40%
1620
16th to endNight
5%335%6%36%6%7%10%40%
1733
August1st to 15thNight
5%315%5%35%6%8%12%41%
1800
16th to endNight
8%5%15%5%36%6%7%10%38%
1910
September1st to 15thNight
9%435%5%445%6%9%41%
1884
16th to endNight
7%3245%2436%5%53%
1980
October1st to 15thNight
8%413413346%57%
1881
16th to endNight
10%5%2432232458%
2118
November1st to 15thNight
11%413312346%57%
2276
16th to endNight
11%5%25%424335%51%
2340
December1st to 15thNight
15%7%25%423346%43%
2340
16th to endNight
22%6%35%5%23345%37%
2496

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
44%36%14%25%5%
1612
16th to endDay
41%35%19%22%7%
1905
February1st to 15thDay
45%26%23%18%4
1752
16th to endDay
44%36%15%23%6%
1580
March1st to 15thDay
45%39%15%20%5%
1810
16th to endDay
41%5%11%20%18%3
2172
April1st to 15thDay
39%410%19%18%7%
2151
16th to endDay
35%6%10%20%24%3
2160
May1st to 15thDay
39%6%11%17%20%4
2310
16th to endDay
38%7%13%23%14%3
2435
June1st to 15thDay
41%11%15%18%12%1
2340
16th to endDay
32%9%16%22%14%3
2340
July1st to 15thDay
41%14%18%16%7%1
2201
16th to endDay
42%12%18%16%9%
2280
August1st to 15thDay
41%12%15%17%9%2
2148
16th to endDay
47%10%14%15%9%1
2292
September1st to 15thDay
45%8%12%16%12%4
2064
16th to endDay
37%6%10%20%18%5%
1980
October1st to 15thDay
32%5%9%19%23%10%
1877
16th to endDay
30%2417%33%11%
1749
November1st to 15thDay
33%25%18%29%10%
1582
16th to endDay
36%37%17%25%9%
1620
December1st to 15thDay
45%48%19%15%6%
1620
16th to endDay
52%37%18%13%4
1728
January1st to 15thNight
39%47%17%25%5%
2327
16th to endNight
44%35%17%20%8%
2316
February1st to 15thNight
39%36%21%20%9%
2112
16th to endNight
40%35%18%23%7%
1893
March1st to 15thNight
39%48%19%19%7%
2148
16th to endNight
34%5%9%23%22%4
2061
April1st to 15thNight
33%410%21%20%9%
1797
16th to endNight
29%5%10%23%22%7%
1800
May1st to 15thNight
34%7%10%18%23%5%
1638
16th to endNight
28%9%14%26%15%5%
1684
June1st to 15thNight
30%11%17%22%16%1
1620
16th to endNight
28%10%17%22%17%3
1620
July1st to 15thNight
33%11%20%21%9%3
1530
16th to endNight
33%11%21%20%12%
1623
August1st to 15thNight
30%12%17%22%12%3
1788
16th to endNight
38%11%15%18%12%2
1910
September1st to 15thNight
38%9%13%18%14%5%
1884
16th to endNight
30%6%10%22%21%7%
1980
October1st to 15thNight
28%5%8%20%23%13%
1881
16th to endNight
30%3411%31%16%
2118
November1st to 15thNight
28%37%17%28%15%
2276
16th to endNight
35%36%17%25%12%
2340
December1st to 15thNight
41%48%18%21%5%
2340
16th to endNight
48%37%17%16%6%
2496

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
22%18%33%17%6%1
90
16th to endDay
19%25%44%6%31
96
February1st to 15thDay
21%26%32%18%1
90
16th to endDay
28%12%39%19%
81
March1st to 15thDay
27%18%36%13%6%
100
16th to endDay
19%6%32%24%15%1
288
April1st to 15thDay
17%10%28%24%18%1
270
16th to endDay
11%7%26%29%19%5%
270
May1st to 15thDay
14%6%23%26%18%10%
288
16th to endDay
12%6%16%26%20%17%
331
June1st to 15thDay
11%19%24%30%22%
315
16th to endDay
9%18%21%31%27%
315
July1st to 15thDay
5%7%22%35%28%
305
16th to endDay
8%5%15%34%35%
326
August1st to 15thDay
11%6%23%33%23%
313
16th to endDay
13%6%25%34%19%
332
September1st to 15thDay
13%39%22%31%19%
315
16th to endDay
12%19%31%32%12%
314
October1st to 15thDay
13%422%28%26%4
278
16th to endDay
19%219%30%23%5%
173
November1st to 15thDay
17%14%26%31%8%1
90
16th to endDay
13%12%41%20%12%1
90
December1st to 15thDay
24%18%33%15%7%
90
16th to endDay
30%13%33%17%5%
96
January1st to 15thNight
20%13%33%24%7%
720
16th to endNight
19%14%35%26%5%
768
February1st to 15thNight
19%11%33%30%4
704
16th to endNight
18%12%37%27%3
631
March1st to 15thNight
20%10%33%29%6%
720
16th to endNight
13%10%31%27%14%
717
April1st to 15thNight
12%8%32%29%15%1
539
16th to endNight
11%5%28%34%18%1
540
May1st to 15thNight
10%327%29%25%4
540
16th to endNight
7%12%35%37%5%
563
June1st to 15thNight
5%8%35%40%9%
540
16th to endNight
46%25%46%16%
540
July1st to 15thNight
6%5%24%46%16%
510
16th to endNight
6%5%23%45%19%
564
August1st to 15thNight
6%425%47%15%
539
16th to endNight
11%427%42%13%
573
September1st to 15thNight
11%29%24%40%11%
624
16th to endNight
9%111%33%39%4
717
October1st to 15thNight
11%321%31%27%4
684
16th to endNight
13%6%21%29%25%3
704
November1st to 15thNight
12%6%24%30%23%3
700
16th to endNight
12%11%28%31%13%1
720
December1st to 15thNight
19%10%27%30%11%1
720
16th to endNight
25%11%29%25%8%
768
Page generated at 2017-10-07 13:07:46. Version ac04

Copyright 2017 A. Danko


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