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 2005-11-06 to 2024-01-16.

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
49%
23509
23%
74477
17%
23454
57%
23454
28%
45735

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 10thNight
26%
760
22%
2459
10%
757
41%
757
23%
1522
January11th to 20thNight
29%
744
23%
2345
11%
744
42%
744
19%
1569
January21st to endNight
27%
792
29%
2376
13%
792
42%
792
25%
1521
February1st to 10thNight
30%
720
24%
2160
12%
720
41%
720
24%
1400
February11th to 20thNight
26%
703
21%
2098
9%
699
37%
699
22%
1390
February21st to endNight
24%
592
21%
1776
9%
592
35%
592
22%
1193
March1st to 10thNight
34%
720
24%
2160
14%
720
42%
720
28%
1329
March11th to 20thNight
31%
720
19%
2053
8%
720
40%
720
25%
1352
March21st to endNight
34%
716
24%
2102
12%
716
44%
716
28%
1307
April1st to 10thNight
41%
540
25%
1800
19%
540
51%
540
28%
1061
April11th to 20thNight
42%
533
26%
1775
18%
533
54%
533
29%
1020
April21st to endNight
48%
540
27%
1800
21%
540
57%
540
32%
993
May1st to 10thNight
52%
540
25%
1649
18%
540
61%
540
36%
961
May11th to 20thNight
58%
531
20%
1592
15%
531
63%
531
30%
992
May21st to endNight
72%
582
23%
1744
19%
582
75%
582
34%
1042
June1st to 10thNight
68%
540
16%
1620
15%
540
69%
540
26%
1065
June11th to 20thNight
77%
540
18%
1620
15%
540
79%
540
41%
906
June21st to endNight
74%
540
18%
1620
16%
540
75%
540
32%
983
July1st to 10thNight
74%
525
13%
1575
13%
525
75%
525
26%
1048
July11th to 20thNight
77%
522
15%
1566
15%
522
78%
522
29%
1008
July21st to endNight
74%
591
16%
1713
16%
558
75%
558
29%
1096
August1st to 10thNight
80%
537
15%
1778
18%
534
80%
534
30%
1061
August11th to 20thNight
73%
534
15%
1776
18%
534
73%
534
25%
1151
August21st to endNight
68%
594
20%
1980
24%
594
68%
594
23%
1314
September1st to 10thNight
68%
574
22%
1834
22%
574
69%
574
28%
1151
September11th to 20thNight
65%
720
23%
1980
20%
720
66%
720
30%
1268
September21st to endNight
66%
720
30%
1980
23%
720
70%
720
39%
1171
October1st to 10thNight
60%
720
32%
1980
25%
720
66%
720
43%
1116
October11th to 20thNight
54%
720
35%
1980
24%
720
63%
720
38%
1165
October21st to endNight
50%
792
30%
2476
27%
792
56%
792
33%
1451
November1st to 10thNight
56%
740
28%
2406
25%
740
64%
740
36%
1285
November11th to 20thNight
45%
760
30%
2470
22%
760
57%
760
33%
1376
November21st to endNight
41%
760
25%
2470
18%
760
53%
760
28%
1469
December1st to 10thNight
33%
760
24%
2470
16%
760
44%
760
22%
1583
December11th to 20thNight
34%
759
24%
2902
15%
758
43%
758
21%
1745
December21st to endNight
30%
828
14%
4392
13%
817
39%
817
12%
2671

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%6%35%5%35%5%6%8%42%
74839
Night
12%6%25%5%345%5%7%46%
74969
TransparencyDay
39%7%11%19%18%5%
74565
Night
36%7%11%19%20%7%
74762
SeeingDay
15%10%22%24%20%9%
13458
Night
14%8%22%29%22%4
23520

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 10thDay
20%7%34424445%43%
1706
11th to 20thDay
20%9%35%423345%43%
1733
21st to endDay
17%7%25%423446%46%
1980
February1st to 10thDay
18%10%36%434345%39%
1800
11th to 20thDay
24%7%335%24345%40%
1748
21st to endDay
21%7%36%6%34445%37%
1480
March1st to 10thDay
14%7%26%5%33346%46%
1800
11th to 20thDay
17%8%45%5%35%5%5%6%37%
1905
21st to endDay
14%7%36%5%35%5%5%7%40%
2268
April1st to 10thDay
12%5%25%5%35%36%6%47%
2160
11th to 20thDay
13%6%26%435%5%47%46%
2134
21st to endDay
8%5%35%435%45%8%51%
2160
May1st to 10thDay
11%5%24425%5%5%8%48%
2308
11th to 20thDay
9%5%35%6%45%5%6%9%43%
2301
21st to endDay
9%5%36%6%46%5%6%9%43%
2531
June1st to 10thDay
10%7%36%7%5%6%8%8%9%33%
2340
11th to 20thDay
6%4245%47%7%9%11%42%
2340
21st to endDay
8%435%6%46%7%7%10%40%
2340
July1st to 10thDay
9%5%46%7%5%7%8%8%10%31%
2340
11th to 20thDay
7%5%26%7%6%8%9%9%11%30%
2340
21st to endDay
6%5%27%7%5%9%9%10%11%31%
2499
August1st to 10thDay
7%425%7%6%8%8%8%13%31%
2148
11th to 20thDay
11%6%37%7%5%7%7%7%10%31%
2125
21st to endDay
11%7%37%7%47%7%7%10%32%
2376
September1st to 10thDay
10%6%26%7%45%6%6%8%41%
2106
11th to 20thDay
13%7%246%35%5%5%7%43%
1980
21st to endDay
10%5%25%5%25%45%6%51%
1980
October1st to 10thDay
9%425%5%245%46%53%
1980
11th to 20thDay
10%5%25%42335%7%55%
1980
21st to endDay
12%5%25%434445%54%
1872
November1st to 10thDay
12%6%345%23335%54%
1672
11th to 20thDay
13%6%2442435%6%52%
1710
21st to endDay
14%6%35%4345%5%6%45%
1710
December1st to 10thDay
20%7%36%5%34346%39%
1710
11th to 20thDay
18%8%35%6%3443343%
2153
21st to endDay
19%9%47%5%3435%6%35%
3124
January1st to 10thNight
17%8%35%323445%45%
2459
11th to 20thNight
17%9%45%5%35%446%38%
2345
21st to endNight
16%7%45%5%25%44444%
2376
February1st to 10thNight
16%8%36%5%34346%42%
2160
11th to 20thNight
20%7%35%42434444%
2098
21st to endNight
20%5%35%5%35%45%7%38%
1776
March1st to 10thNight
15%7%25%42445%7%47%
2160
11th to 20thNight
15%6%35%4345%5%8%41%
2053
21st to endNight
13%5%25%4345%5%8%45%
2102
April1st to 10thNight
11%425%5%345%6%8%47%
1800
11th to 20thNight
14%6%2443335%7%50%
1775
21st to endNight
8%5%245%3445%7%53%
1800
May1st to 10thNight
8%42443446%8%52%
1649
11th to 20thNight
8%6%246%35%5%7%8%45%
1592
21st to endNight
7%324436%6%7%11%47%
1744
June1st to 10thNight
5%5%26%7%47%7%7%12%38%
1620
11th to 20thNight
42125%26%6%8%11%52%
1620
21st to endNight
5%3246%36%6%8%12%44%
1620
July1st to 10thNight
6%426%6%47%7%9%11%37%
1620
11th to 20thNight
5%435%6%47%7%8%11%41%
1620
21st to endNight
4435%7%46%7%9%10%41%
1814
August1st to 10thNight
4415%6%35%7%9%14%41%
1790
11th to 20thNight
7%5%25%5%46%7%8%11%40%
1776
21st to endNight
10%7%26%6%46%6%6%9%38%
1980
September1st to 10thNight
8%5%36%5%45%5%6%9%44%
1834
11th to 20thNight
11%5%25%5%4446%7%46%
1980
21st to endNight
6%425%5%2445%6%54%
1980
October1st to 10thNight
8%4145%23346%60%
1980
11th to 20thNight
11%5%24334347%55%
1980
21st to endNight
14%6%2442343454%
2476
November1st to 10thNight
11%5%2332335%5%58%
2406
11th to 20thNight
11%6%34423347%54%
2470
21st to endNight
13%6%25%435%5%5%6%47%
2470
December1st to 10thNight
18%6%36%5%35%446%41%
2470
11th to 20thNight
18%7%25%43344447%
3042
21st to endNight
18%8%36%5%345%6%8%34%
4532

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 10thDay
44%47%17%24%5%
1707
11th to 20thDay
45%46%19%21%5%
1733
21st to endDay
40%46%20%24%6%
1980
February1st to 10thDay
49%37%19%18%4
1800
11th to 20thDay
48%35%18%19%6%
1758
21st to endDay
50%46%11%21%8%
1480
March1st to 10thDay
40%49%16%21%10%
1800
11th to 20thDay
47%6%11%14%17%5%
1905
21st to endDay
42%6%9%19%20%3
2268
April1st to 10thDay
37%5%11%20%19%8%
2160
11th to 20thDay
38%5%8%19%24%7%
2134
21st to endDay
31%6%10%25%26%3
2160
May1st to 10thDay
33%8%11%22%23%4
2308
11th to 20thDay
36%8%15%22%16%3
2305
21st to endDay
37%7%12%23%18%3
2531
June1st to 10thDay
42%10%14%18%14%1
2340
11th to 20thDay
31%11%18%24%14%2
2340
21st to endDay
35%10%18%23%10%4
2340
July1st to 10thDay
39%14%20%16%8%1
2275
11th to 20thDay
40%15%20%15%8%1
2271
21st to endDay
39%14%20%19%8%
2359
August1st to 10thDay
37%14%20%23%6%
2136
11th to 20thDay
44%11%17%16%9%3
2125
21st to endDay
43%11%16%17%9%3
2376
September1st to 10thDay
40%9%15%15%16%5%
2106
11th to 20thDay
40%9%10%18%19%4
1980
21st to endDay
33%7%10%20%22%8%
1980
October1st to 10thDay
32%6%9%19%24%10%
1980
11th to 20thDay
30%38%23%27%8%
1980
21st to endDay
33%45%17%30%10%
1872
November1st to 10thDay
34%46%17%28%11%
1672
11th to 20thDay
34%36%19%26%11%
1710
21st to endDay
39%48%17%24%8%
1710
December1st to 10thDay
46%6%7%16%18%6%
1710
11th to 20thDay
47%36%17%22%6%
2150
21st to endDay
47%5%8%19%19%2
3124
January1st to 10thNight
41%47%19%24%5%
2459
11th to 20thNight
47%46%18%20%5%
2345
21st to endNight
43%35%19%24%7%
2376
February1st to 10thNight
44%47%18%20%7%
2160
11th to 20thNight
45%4418%19%10%
2099
21st to endNight
44%6%8%14%18%9%
1776
March1st to 10thNight
38%47%17%22%12%
2160
11th to 20thNight
41%6%10%16%19%6%
2053
21st to endNight
37%6%9%24%20%5%
2102
April1st to 10thNight
35%6%11%21%20%8%
1800
11th to 20thNight
34%5%7%19%23%11%
1775
21st to endNight
31%6%10%25%23%6%
1800
May1st to 10thNight
29%7%10%23%24%6%
1649
11th to 20thNight
34%9%17%20%17%3
1593
21st to endNight
29%10%13%27%17%5%
1745
June1st to 10thNight
36%13%14%19%17%1
1620
11th to 20thNight
23%10%22%27%15%3
1620
21st to endNight
30%11%17%21%17%4
1620
July1st to 10thNight
35%14%19%20%10%3
1575
11th to 20thNight
32%13%23%20%10%2
1566
21st to endNight
31%14%23%21%10%1
1713
August1st to 10thNight
28%13%22%28%8%1
1778
11th to 20thNight
34%14%21%16%11%4
1776
21st to endNight
39%12%14%19%12%4
1980
September1st to 10thNight
35%10%15%18%17%5%
1834
11th to 20thNight
35%9%11%20%20%5%
1980
21st to endNight
29%6%11%22%23%8%
1980
October1st to 10thNight
26%5%9%22%25%13%
1980
11th to 20thNight
31%5%7%21%25%12%
1980
21st to endNight
34%46%14%29%13%
2476
November1st to 10thNight
28%48%18%27%14%
2406
11th to 20thNight
33%36%18%26%14%
2470
21st to endNight
37%5%7%18%24%9%
2470
December1st to 10thNight
43%5%8%18%20%5%
2470
11th to 20thNight
41%47%14%29%5%
3044
21st to endNight
46%5%8%20%18%3
4532

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 10thDay
27%24%30%14%4
270
11th to 20thDay
26%20%29%18%6%
255
21st to endDay
23%26%36%11%41
264
February1st to 10thDay
30%20%34%14%3
240
11th to 20thDay
38%19%29%13%1
240
21st to endDay
27%21%43%8%1
198
March1st to 10thDay
26%20%34%15%5%
240
11th to 20thDay
23%19%32%17%8%1
345
21st to endDay
23%17%30%21%9%
462
April1st to 10thDay
19%15%30%23%11%1
420
11th to 20thDay
18%14%31%22%13%2
412
21st to endDay
13%12%30%31%11%3
420
May1st to 10thDay
12%11%25%31%17%5%
423
11th to 20thDay
9%5%27%28%20%11%
447
21st to endDay
11%6%16%30%20%17%
485
June1st to 10thDay
11%5%16%31%24%13%
450
11th to 20thDay
8%311%28%28%21%
450
21st to endDay
9%413%24%34%18%
450
July1st to 10thDay
8%19%24%34%24%
445
11th to 20thDay
6%29%19%34%30%
444
21st to endDay
5%210%21%35%26%
488
August1st to 10thDay
8%28%23%34%24%
446
11th to 20thDay
8%27%28%38%17%
439
21st to endDay
14%39%23%31%19%
495
September1st to 10thDay
9%49%32%32%15%
450
11th to 20thDay
12%413%28%32%11%
450
21st to endDay
12%317%28%33%7%
450
October1st to 10thDay
13%5%23%30%22%7%
450
11th to 20thDay
12%7%26%31%22%1
450
21st to endDay
19%11%24%30%14%2
333
November1st to 10thDay
16%11%29%30%9%5%
270
11th to 20thDay
17%16%37%23%8%
270
21st to endDay
14%21%32%22%10%1
270
December1st to 10thDay
29%17%29%20%6%
270
11th to 20thDay
25%18%36%13%6%1
270
21st to endDay
30%15%31%19%5%
297
January1st to 10thNight
22%15%34%25%5%
760
11th to 20thNight
22%17%28%26%7%
744
21st to endNight
18%15%36%26%4
792
February1st to 10thNight
21%12%33%29%4
720
11th to 20thNight
25%14%31%26%4
703
21st to endNight
21%14%38%25%2
592
March1st to 10thNight
19%13%31%33%5%
720
11th to 20thNight
18%12%36%24%10%1
720
21st to endNight
17%13%32%27%11%
716
April1st to 10thNight
13%10%33%29%14%1
540
11th to 20thNight
15%10%29%30%15%1
533
21st to endNight
11%7%28%34%18%2
540
May1st to 10thNight
10%5%28%31%23%3
540
11th to 20thNight
9%321%34%27%5%
531
21st to endNight
8%110%34%39%6%
584
June1st to 10thNight
7%210%39%35%7%
540
11th to 20thNight
419%29%43%14%
540
21st to endNight
5%18%28%46%12%
540
July1st to 10thNight
6%16%25%47%15%
525
11th to 20thNight
7%1321%47%21%
522
21st to endNight
5%16%26%46%16%
591
August1st to 10thNight
45%24%49%18%
537
11th to 20thNight
9%16%29%45%9%
534
21st to endNight
12%36%25%41%13%
594
September1st to 10thNight
9%29%26%44%10%
574
11th to 20thNight
12%411%29%38%6%
720
21st to endNight
9%214%32%40%3
720
October1st to 10thNight
10%421%32%28%5%
720
11th to 20thNight
12%7%23%33%23%2
720
21st to endNight
16%8%21%32%21%2
792
November1st to 10thNight
12%7%21%35%21%3
740
11th to 20thNight
13%10%29%33%14%1
760
21st to endNight
15%10%29%32%12%1
760
December1st to 10thNight
20%12%29%29%9%1
760
11th to 20thNight
24%10%29%28%9%
760
21st to endNight
25%13%28%28%7%
836
Page generated at 2024-01-13 08:37:54. Version ac07

Copyright 2024 Attilla Danko


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