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Palisades-Dows Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Palisades-Dows 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
37%
24656
18%
74704
11%
24600
44%
24600
24%
49112

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%
950
14%
2648
5%
946
34%
946
21%
1840
January11th to 20thNight
24%
926
12%
2546
4%
926
30%
926
16%
1937
January21st to endNight
22%
990
14%
2574
4%
990
29%
990
18%
1932
February1st to 10thNight
22%
900
13%
2340
3%
900
28%
900
19%
1720
February11th to 20thNight
26%
842
18%
2239
7%
840
32%
840
23%
1543
February21st to endNight
21%
592
19%
1776
6%
592
34%
592
19%
1234
March1st to 10thNight
25%
669
17%
2109
8%
669
34%
669
23%
1376
March11th to 20thNight
32%
540
19%
1980
14%
540
41%
540
20%
1245
March21st to endNight
24%
594
10%
2100
5%
594
32%
594
13%
1529
April1st to 10thNight
23%
540
17%
1800
10%
540
35%
540
21%
1171
April11th to 20thNight
29%
533
20%
1775
14%
533
41%
533
20%
1164
April21st to endNight
33%
540
17%
1800
11%
540
44%
540
22%
1177
May1st to 10thNight
30%
540
17%
1531
9%
540
38%
540
26%
1034
May11th to 20thNight
38%
531
17%
1417
10%
531
45%
531
27%
976
May21st to endNight
46%
584
17%
1551
8%
582
51%
582
30%
1040
June1st to 10thNight
55%
540
18%
1440
9%
540
59%
540
37%
879
June11th to 20thNight
52%
540
19%
1440
10%
540
55%
540
37%
876
June21st to endNight
53%
540
19%
1440
10%
540
57%
540
37%
884
July1st to 10thNight
70%
525
19%
1400
12%
525
72%
525
44%
809
July11th to 20thNight
67%
522
24%
1392
15%
522
70%
522
49%
768
July21st to endNight
65%
591
23%
1534
17%
558
68%
558
41%
901
August1st to 10thNight
68%
537
21%
1601
20%
534
71%
534
39%
893
August11th to 20thNight
67%
534
25%
1648
27%
534
71%
534
37%
944
August21st to endNight
66%
594
25%
1980
28%
594
70%
594
37%
1063
September1st to 10thNight
61%
540
24%
1800
23%
540
67%
540
34%
992
September11th to 20thNight
60%
540
32%
1800
30%
540
67%
540
36%
994
September21st to endNight
51%
674
25%
2026
16%
674
60%
674
36%
1145
October1st to 10thNight
46%
720
23%
2160
15%
720
51%
720
33%
1260
October11th to 20thNight
35%
720
22%
2160
11%
720
44%
720
27%
1336
October21st to endNight
30%
792
19%
2412
11%
792
39%
792
23%
1570
November1st to 10thNight
34%
740
25%
2406
15%
740
47%
740
30%
1379
November11th to 20thNight
25%
850
20%
2560
8%
850
36%
850
22%
1677
November21st to endNight
28%
950
18%
2660
8%
950
37%
950
23%
1793
December1st to 10thNight
24%
950
13%
2660
5%
950
32%
950
20%
1900
December11th to 20thNight
25%
948
15%
3164
5%
948
32%
948
16%
2207
December21st to endNight
19%
1038
9%
4835
4%
1026
29%
1026
8%
3924

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
14%8%36%5%35%5%5%7%38%
74764
Night
13%8%36%5%3445%6%41%
75054
TransparencyDay
45%6%13%22%13%2
74467
Night
43%5%12%23%14%2
74871
SeeingDay
16%10%29%27%14%4
14678
Night
16%9%31%31%12%1
24667

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
11%11%6%10%9%6%6%45%7%26%
1517
11th to 20thDay
13%13%6%11%7%5%5%36%6%26%
1521
21st to endDay
14%13%7%9%7%5%6%446%25%
1782
February1st to 10thDay
14%11%6%8%7%45%5%5%6%29%
1620
11th to 20thDay
15%10%46%6%37%45%8%32%
1608
21st to endDay
14%10%5%11%6%345%5%7%32%
1480
March1st to 10thDay
16%10%48%5%34446%36%
1867
11th to 20thDay
14%8%5%7%8%35%46%7%34%
1980
21st to endDay
22%11%48%5%35%45%6%27%
2254
April1st to 10thDay
17%11%47%6%34446%32%
2160
11th to 20thDay
18%10%36%5%445%6%6%34%
2134
21st to endDay
22%7%35%5%3445%6%35%
2160
May1st to 10thDay
18%7%36%6%46%6%6%7%31%
2426
11th to 20thDay
19%8%36%5%46%45%7%35%
2479
21st to endDay
15%7%37%6%35%6%6%8%34%
2725
June1st to 10thDay
11%424446%5%7%9%44%
2520
11th to 20thDay
11%425%5%35%5%5%7%47%
2520
21st to endDay
12%6%26%6%36%6%6%8%40%
2520
July1st to 10thDay
8%425%5%25%5%7%10%47%
2520
11th to 20thDay
9%4245%36%5%6%9%47%
2520
21st to endDay
7%4245%36%6%7%10%46%
2690
August1st to 10thDay
8%5%25%6%45%7%7%8%43%
2328
11th to 20thDay
10%6%25%5%25%5%6%7%47%
2252
21st to endDay
10%425%5%35%45%8%51%
2376
September1st to 10thDay
14%5%25%43345%7%49%
2160
11th to 20thDay
11%3245%35%45%7%52%
2160
21st to endDay
11%5%25%5%35%5%6%8%46%
1913
October1st to 10thDay
15%6%25%6%23346%46%
1800
11th to 20thDay
19%6%35%5%3436%6%41%
1800
21st to endDay
18%8%35%5%34446%41%
1943
November1st to 10thDay
10%8%35%5%3445%6%45%
1672
11th to 20thDay
14%10%38%5%3445%7%35%
1616
21st to endDay
17%8%37%5%24446%40%
1520
December1st to 10thDay
14%12%49%6%24447%33%
1520
11th to 20thDay
15%9%48%6%45%5%5%7%33%
1918
21st to endDay
23%18%9%10%6%2343417%
2783
January1st to 10thNight
11%8%6%9%6%35%5%5%5%37%
2648
11th to 20thNight
12%12%8%10%8%45%45%5%28%
2546
21st to endNight
13%11%6%10%6%4445%6%31%
2574
February1st to 10thNight
13%13%5%7%7%4445%5%33%
2340
11th to 20thNight
13%9%47%5%445%5%6%39%
2238
21st to endNight
15%10%48%6%34435%38%
1776
March1st to 10thNight
17%9%35%5%34446%41%
2109
11th to 20thNight
13%8%47%6%44446%40%
1980
21st to endNight
19%11%49%6%45%5%5%6%28%
2100
April1st to 10thNight
16%9%46%43435%6%41%
1800
11th to 20thNight
18%9%35%5%3345%5%40%
1775
21st to endNight
19%8%35%5%245%6%6%39%
1800
May1st to 10thNight
17%5%35%5%35%5%6%7%40%
1531
11th to 20thNight
16%7%35%5%445%6%6%39%
1416
21st to endNight
11%5%27%6%45%46%7%43%
1551
June1st to 10thNight
9%4345%3445%10%49%
1440
11th to 20thNight
9%426%4345%7%11%46%
1440
21st to endNight
10%4344245%6%8%49%
1440
July1st to 10thNight
7%3145%25%5%7%9%54%
1440
11th to 20thNight
5%32332446%9%59%
1440
21st to endNight
6%325%435%5%6%8%51%
1624
August1st to 10thNight
5%325%5%345%6%10%53%
1611
11th to 20thNight
7%425%4245%5%8%53%
1648
21st to endNight
9%5%1442445%7%57%
1980
September1st to 10thNight
10%424435%35%6%55%
1800
11th to 20thNight
10%5%2432435%6%55%
1800
21st to endNight
7%425%5%35%447%54%
2026
October1st to 10thNight
13%5%245%24346%53%
2160
11th to 20thNight
16%7%25%4335%46%46%
2160
21st to endNight
18%7%36%5%33346%42%
2412
November1st to 10thNight
10%6%24433346%53%
2406
11th to 20thNight
14%8%37%5%2445%6%41%
2560
21st to endNight
16%8%35%5%3435%5%41%
2660
December1st to 10thNight
13%10%48%6%35%45%6%35%
2660
11th to 20thNight
14%10%5%8%6%44446%34%
3279
21st to endNight
22%15%7%10%7%35%445%19%
4884

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
59%5%11%15%10%1
1518
11th to 20thDay
60%313%17%6%
1521
21st to endDay
60%5%13%13%8%1
1782
February1st to 10thDay
55%415%19%6%1
1620
11th to 20thDay
50%6%13%20%9%2
1617
21st to endDay
52%5%13%19%8%2
1480
March1st to 10thDay
49%315%22%9%1
1867
11th to 20thDay
49%5%12%22%11%1
1980
21st to endDay
57%5%11%19%6%1
2254
April1st to 10thDay
53%411%22%9%
2160
11th to 20thDay
50%6%10%23%11%1
2134
21st to endDay
49%5%10%21%12%2
2160
May1st to 10thDay
52%6%12%21%8%1
2426
11th to 20thDay
50%5%12%21%11%1
2483
21st to endDay
47%8%11%18%13%2
2725
June1st to 10thDay
35%8%16%24%16%1
2520
11th to 20thDay
36%7%11%21%22%3
2520
21st to endDay
41%7%13%23%15%1
2520
July1st to 10thDay
32%8%14%29%15%3
2451
11th to 20thDay
32%9%14%26%15%3
2445
21st to endDay
30%8%19%26%16%2
2540
August1st to 10thDay
35%9%15%28%12%1
2314
11th to 20thDay
35%7%15%25%17%1
2252
21st to endDay
32%5%11%28%20%3
2376
September1st to 10thDay
35%5%10%25%21%3
2160
11th to 20thDay
31%5%12%31%18%3
2160
21st to endDay
36%5%11%30%17%1
1913
October1st to 10thDay
42%310%26%19%1
1800
11th to 20thDay
44%411%25%15%2
1800
21st to endDay
46%313%23%14%2
1943
November1st to 10thDay
40%413%26%14%3
1672
11th to 20thDay
49%313%22%12%1
1616
21st to endDay
47%416%24%9%1
1520
December1st to 10thDay
53%414%20%8%1
1520
11th to 20thDay
52%415%18%9%2
1915
21st to endDay
72%49%10%4
2783
January1st to 10thNight
49%413%19%14%1
2648
11th to 20thNight
58%415%14%8%
2546
21st to endNight
55%5%13%17%9%1
2574
February1st to 10thNight
53%5%11%20%11%1
2340
11th to 20thNight
45%5%12%23%13%2
2239
21st to endNight
50%410%20%14%2
1776
March1st to 10thNight
45%413%26%11%1
2109
11th to 20thNight
45%413%22%14%2
1980
21st to endNight
57%5%12%16%9%1
2100
April1st to 10thNight
45%410%25%15%2
1800
11th to 20thNight
47%48%22%16%3
1775
21st to endNight
45%6%12%22%14%3
1800
May1st to 10thNight
43%6%13%23%14%1
1531
11th to 20thNight
44%6%14%22%12%2
1417
21st to endNight
40%7%12%22%16%3
1552
June1st to 10thNight
32%6%15%26%18%3
1440
11th to 20thNight
32%6%14%24%20%5%
1440
21st to endNight
32%6%17%25%16%4
1440
July1st to 10thNight
25%7%16%32%15%5%
1400
11th to 20thNight
22%6%16%35%19%3
1392
21st to endNight
27%7%15%30%18%3
1534
August1st to 10thNight
26%7%17%34%12%3
1601
11th to 20thNight
29%7%12%30%21%2
1648
21st to endNight
28%5%10%28%23%6%
1980
September1st to 10thNight
31%5%10%26%25%3
1800
11th to 20thNight
30%5%10%34%18%4
1800
21st to endNight
31%49%30%23%2
2026
October1st to 10thNight
34%410%25%24%3
2160
11th to 20thNight
39%5%12%23%19%3
2160
21st to endNight
45%411%22%16%2
2412
November1st to 10thNight
33%5%13%26%18%4
2406
11th to 20thNight
44%413%24%13%2
2560
21st to endNight
46%312%26%11%1
2660
December1st to 10thNight
51%413%22%9%1
2660
11th to 20thNight
51%413%24%7%1
3281
21st to endNight
68%5%8%13%5%
4884

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
22%10%34%24%8%2
270
11th to 20thDay
22%15%38%18%5%1
255
21st to endDay
21%12%39%20%7%1
264
February1st to 10thDay
22%15%41%19%3
240
11th to 20thDay
22%18%35%20%5%1
240
21st to endDay
23%15%45%13%4
198
March1st to 10thDay
19%21%40%14%6%
240
11th to 20thDay
23%17%30%22%7%2
240
21st to endDay
32%15%30%16%6%1
340
April1st to 10thDay
22%14%40%17%6%
420
11th to 20thDay
23%16%30%21%10%
412
21st to endDay
24%14%32%19%10%1
420
May1st to 10thDay
19%11%37%24%7%2
595
11th to 20thDay
21%13%26%25%13%2
625
21st to endDay
15%10%27%28%15%5%
679
June1st to 10thDay
8%427%33%23%5%
630
11th to 20thDay
11%6%28%35%18%2
630
21st to endDay
11%9%29%33%14%4
630
July1st to 10thDay
8%319%33%24%14%
621
11th to 20thDay
9%423%35%23%6%
618
21st to endDay
7%223%38%24%5%
684
August1st to 10thDay
7%323%36%24%8%
626
11th to 20thDay
11%319%33%24%8%
566
21st to endDay
9%419%36%24%8%
495
September1st to 10thDay
15%8%17%31%21%7%
450
11th to 20thDay
9%5%20%38%21%8%
450
21st to endDay
14%9%29%21%23%3
356
October1st to 10thDay
21%7%27%30%11%4
270
11th to 20thDay
21%22%34%14%9%
270
21st to endDay
27%12%34%19%7%2
297
November1st to 10thDay
14%13%38%23%10%2
270
11th to 20thDay
20%18%32%20%9%2
270
21st to endDay
26%11%37%20%6%
270
December1st to 10thDay
13%15%41%21%7%3
270
11th to 20thDay
16%14%37%24%9%1
270
21st to endDay
27%17%38%15%2
297
January1st to 10thNight
15%13%38%27%7%1
950
11th to 20thNight
19%13%33%28%7%
926
21st to endNight
19%11%37%27%6%
990
February1st to 10thNight
21%12%38%24%5%
900
11th to 20thNight
18%12%37%27%6%
844
21st to endNight
21%13%39%22%41
592
March1st to 10thNight
20%13%38%22%7%1
669
11th to 20thNight
18%10%32%31%9%1
540
21st to endNight
22%12%36%25%5%1
594
April1st to 10thNight
19%14%40%24%3
540
11th to 20thNight
23%14%28%28%7%
533
21st to endNight
22%8%32%28%9%1
540
May1st to 10thNight
18%8%39%27%7%1
540
11th to 20thNight
18%9%30%32%11%
531
21st to endNight
14%430%33%18%1
584
June1st to 10thNight
9%426%43%16%2
540
11th to 20thNight
10%329%44%14%
540
21st to endNight
11%427%42%15%1
540
July1st to 10thNight
8%113%43%32%4
525
11th to 20thNight
6%221%43%26%3
522
21st to endNight
6%318%45%27%1
591
August1st to 10thNight
5%215%47%28%3
537
11th to 20thNight
7%315%41%29%5%
534
21st to endNight
11%214%45%26%3
594
September1st to 10thNight
12%417%40%22%4
540
11th to 20thNight
11%321%36%24%4
540
21st to endNight
10%7%28%35%19%1
674
October1st to 10thNight
16%6%28%31%18%2
720
11th to 20thNight
19%11%32%30%9%
720
21st to endNight
22%12%32%27%8%
792
November1st to 10thNight
13%10%37%29%10%1
740
11th to 20thNight
19%14%39%22%7%
850
21st to endNight
21%11%36%26%6%1
950
December1st to 10thNight
17%13%37%26%6%1
950
11th to 20thNight
22%9%35%28%6%
950
21st to endNight
26%13%33%24%4
1045
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