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 2005-11-05 to 2018-02-14.

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
38%
16683
18%
48833
11%
16638
46%
16638
26%
31782

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%
975
13%
2716
5%
970
36%
970
21%
1903
January16th to endNight
24%
1040
15%
2736
5%
1040
31%
1040
21%
1992
February1st to 15thNight
25%
948
15%
2470
4%
946
31%
946
21%
1771
February16th to endNight
28%
667
19%
1929
8%
667
38%
667
24%
1292
March1st to 15thNight
33%
627
19%
2067
11%
627
41%
627
24%
1291
March16th to endNight
27%
576
11%
2059
7%
576
35%
576
16%
1431
April1st to 15thNight
26%
539
17%
1797
12%
539
36%
539
21%
1174
April16th to endNight
36%
540
18%
1800
14%
540
46%
540
20%
1219
May1st to 15thNight
34%
540
17%
1500
8%
540
43%
540
26%
1027
May16th to endNight
45%
563
19%
1497
8%
561
52%
561
31%
997
June1st to 15thNight
53%
540
16%
1440
8%
540
56%
540
34%
906
June16th to endNight
53%
540
18%
1440
8%
540
57%
540
38%
876
July1st to 15thNight
69%
510
19%
1360
12%
510
71%
510
46%
770
July16th to endNight
70%
564
23%
1448
17%
531
73%
531
43%
842
August1st to 15thNight
70%
539
22%
1610
22%
536
72%
536
40%
891
August16th to endNight
65%
573
22%
1884
25%
573
68%
573
33%
1078
September1st to 15thNight
66%
540
28%
1800
28%
540
71%
540
38%
951
September16th to endNight
56%
627
27%
1952
20%
627
65%
627
37%
1092
October1st to 15thNight
43%
720
24%
2160
16%
720
49%
720
30%
1308
October16th to endNight
35%
768
21%
2328
12%
768
44%
768
27%
1438
November1st to 15thNight
34%
760
24%
2471
15%
760
45%
760
27%
1479
November16th to endNight
27%
972
18%
2727
7%
972
37%
972
25%
1795
December1st to 15thNight
22%
975
13%
2730
4%
975
31%
975
18%
2014
December16th to endNight
22%
1040
14%
2912
5%
1040
30%
1040
15%
2245

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%7%36%5%3445%7%38%
49248
Night
12%7%35%5%24446%42%
49005
Cloud CoverDay
14%7%35%5%3445%7%38%
49257
Night
13%7%35%424446%42%
49009
TransparencyDay
45%5%13%22%12%1
48938
Night
42%412%23%14%2
48834
SeeingDay
15%7%28%28%16%4
6473
Night
16%7%30%31%12%1
16685

By Month

Percentage Cloud Cover NE (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
11%10%6%8%7%45%45%7%29%
1552
16th to endDay
13%12%6%9%7%45%446%25%
1836
February1st to 15thDay
13%10%5%7%7%2445%6%31%
1694
16th to endDay
13%9%47%5%245%5%7%34%
1543
March1st to 15thDay
15%9%36%5%3435%7%35%
1894
16th to endDay
19%10%47%5%3435%7%30%
2164
April1st to 15thDay
17%9%47%5%23445%33%
2151
16th to endDay
24%7%345%2345%433%
2160
May1st to 15thDay
18%8%36%5%35%5%5%6%30%
2449
16th to endDay
14%6%36%5%35%5%5%7%35%
2617
June1st to 15thDay
13%5%24435%5%5%8%40%
2520
16th to endDay
10%4245%36%5%6%8%43%
2520
July1st to 15thDay
6%416%5%35%48%9%44%
2520
16th to endDay
8%324436%6%7%9%42%
2619
August1st to 15thDay
7%425%5%36%6%6%8%43%
2340
16th to endDay
11%6%1443445%8%44%
2318
September1st to 15thDay
12%31342335%6%52%
2160
16th to endDay
10%425%5%3446%6%46%
1994
October1st to 15thDay
17%6%25%5%13435%45%
1800
16th to endDay
17%6%25%434345%42%
1895
November1st to 15thDay
12%8%36%43445%6%41%
1717
16th to endDay
18%8%25%423337%41%
1561
December1st to 15thDay
19%13%37%6%24346%28%
1560
16th to endDay
18%16%5%7%6%2344425%
1664
January1st to 15thNight
11%8%5%7%6%35%45%5%36%
2716
16th to endNight
11%10%6%7%6%34345%34%
2736
February1st to 15thNight
12%12%46%5%24445%36%
2467
16th to endNight
13%7%27%5%23435%41%
1929
March1st to 15thNight
15%8%25%423346%43%
2055
16th to endNight
16%8%47%6%345%46%32%
2059
April1st to 15thNight
16%9%35%423346%40%
1797
16th to endNight
19%8%245%24445%37%
1800
May1st to 15thNight
16%6%245%345%5%6%40%
1500
16th to endNight
9%5%25%5%45%5%6%8%42%
1496
June1st to 15thNight
10%5%245%2435%9%45%
1440
16th to endNight
7%325%4235%7%9%47%
1440
July1st to 15thNight
5%21332446%9%55%
1440
16th to endNight
4214426%47%9%51%
1546
August1st to 15thNight
43145%2445%9%53%
1620
16th to endNight
9%42432345%7%51%
1884
September1st to 15thNight
9%413323346%57%
1800
16th to endNight
6%425%424347%53%
1952
October1st to 15thNight
14%5%23423345%49%
2160
16th to endNight
14%6%25%423346%46%
2328
November1st to 15thNight
12%6%24422345%48%
2471
16th to endNight
17%7%24424346%42%
2727
December1st to 15thNight
16%11%5%7%5%34345%32%
2730
16th to endNight
20%13%5%8%5%23445%27%
2912

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
11%10%6%7%6%46%35%7%29%
1552
16th to endDay
13%13%6%8%6%45%345%26%
1836
February1st to 15thDay
13%10%6%7%7%24446%31%
1694
16th to endDay
13%9%37%5%345%5%8%33%
1543
March1st to 15thDay
16%9%36%5%3345%6%35%
1905
16th to endDay
19%9%37%5%2435%6%30%
2162
April1st to 15thDay
18%9%46%5%34445%32%
2151
16th to endDay
24%8%24433445%32%
2160
May1st to 15thDay
19%7%36%5%35%5%5%6%30%
2449
16th to endDay
14%6%26%6%35%5%5%7%35%
2617
June1st to 15thDay
14%425%436%45%8%40%
2520
16th to endDay
10%4245%36%5%5%7%43%
2520
July1st to 15thDay
7%425%5%25%47%10%44%
2520
16th to endDay
8%423436%6%7%10%43%
2619
August1st to 15thDay
7%4245%35%6%6%7%44%
2340
16th to endDay
12%5%25%425%45%8%45%
2318
September1st to 15thDay
13%314332446%52%
2160
16th to endDay
10%425%6%3445%7%46%
1994
October1st to 15thDay
17%5%25%5%22345%45%
1800
16th to endDay
17%6%25%434346%41%
1895
November1st to 15thDay
12%9%35%5%3345%5%41%
1717
16th to endDay
18%7%35%413246%42%
1561
December1st to 15thDay
19%11%47%5%24446%28%
1560
16th to endDay
19%15%6%8%6%2433425%
1664
January1st to 15thNight
11%8%5%8%5%35%45%5%36%
2716
16th to endNight
11%10%6%8%5%44345%34%
2736
February1st to 15thNight
12%12%46%5%23345%37%
2460
16th to endNight
13%8%37%5%23435%41%
1929
March1st to 15thNight
15%7%35%423335%43%
2067
16th to endNight
16%8%47%6%345%45%32%
2059
April1st to 15thNight
16%9%36%423346%40%
1797
16th to endNight
20%8%24424445%37%
1800
May1st to 15thNight
17%6%2443446%6%39%
1499
16th to endNight
10%5%25%6%35%5%6%7%42%
1496
June1st to 15thNight
10%5%244333410%45%
1440
16th to endNight
7%32442347%9%47%
1440
July1st to 15thNight
6%21332445%9%56%
1440
16th to endNight
4224436%47%8%52%
1546
August1st to 15thNight
5%215%42445%10%53%
1620
16th to endNight
10%41431435%7%52%
1884
September1st to 15thNight
9%313314346%57%
1800
16th to endNight
6%425%324347%54%
1952
October1st to 15thNight
14%5%14423345%50%
2160
16th to endNight
15%7%25%422346%46%
2328
November1st to 15thNight
12%6%25%422345%48%
2471
16th to endNight
16%7%23424346%42%
2727
December1st to 15thNight
16%10%5%7%5%34345%32%
2730
16th to endNight
20%13%5%7%5%24345%27%
2912

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
54%412%16%10%
1553
16th to endDay
59%413%14%7%
1836
February1st to 15thDay
52%415%20%6%
1695
16th to endDay
47%6%15%20%8%1
1543
March1st to 15thDay
48%415%21%8%
1905
16th to endDay
53%414%20%5%
2164
April1st to 15thDay
52%410%23%8%
2151
16th to endDay
52%5%10%19%10%1
2160
May1st to 15thDay
53%5%12%20%8%
2449
16th to endDay
46%7%12%19%12%1
2621
June1st to 15thDay
40%5%14%23%14%
2520
16th to endDay
37%7%11%23%17%1
2520
July1st to 15thDay
34%8%13%27%13%2
2371
16th to endDay
32%8%17%22%15%2
2455
August1st to 15thDay
34%8%14%26%15%1
2326
16th to endDay
37%5%12%26%15%2
2318
September1st to 15thDay
31%5%10%29%21%2
2160
16th to endDay
36%413%29%15%1
1994
October1st to 15thDay
42%39%24%18%1
1800
16th to endDay
43%313%24%13%1
1895
November1st to 15thDay
43%311%26%13%1
1717
16th to endDay
44%318%23%8%
1561
December1st to 15thDay
57%313%17%6%
1560
16th to endDay
62%312%13%6%
1664
January1st to 15thNight
48%414%17%14%
2716
16th to endNight
51%416%17%9%
2736
February1st to 15thNight
49%411%23%10%
2470
16th to endNight
44%413%24%11%1
1929
March1st to 15thNight
42%314%25%12%1
2067
16th to endNight
52%415%17%9%
2059
April1st to 15thNight
45%310%24%13%2
1797
16th to endNight
48%5%9%20%13%3
1800
May1st to 15thNight
43%5%13%23%12%
1500
16th to endNight
39%6%12%21%17%2
1498
June1st to 15thNight
35%414%26%15%3
1440
16th to endNight
30%7%14%24%18%4
1440
July1st to 15thNight
25%5%16%31%16%4
1360
16th to endNight
25%7%15%32%17%1
1448
August1st to 15thNight
26%6%14%31%17%3
1610
16th to endNight
31%6%10%27%19%4
1884
September1st to 15thNight
27%49%29%26%2
1800
16th to endNight
29%411%32%19%2
1952
October1st to 15thNight
37%49%23%22%3
2160
16th to endNight
39%314%24%15%2
2328
November1st to 15thNight
37%411%25%17%3
2471
16th to endNight
43%313%27%10%
2727
December1st to 15thNight
54%312%19%8%
2730
16th to endNight
60%311%15%7%
2912

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
23%9%35%24%5%1
135
16th to endDay
18%10%38%20%10%2
144
February1st to 15thDay
16%16%40%20%5%
130
16th to endDay
19%8%40%16%14%
81
March1st to 15thDay
27%16%38%12%4
90
16th to endDay
34%10%27%18%8%1
148
April1st to 15thDay
20%8%36%23%10%
270
16th to endDay
28%8%28%21%11%1
270
May1st to 15thDay
19%12%31%24%9%1
463
16th to endDay
14%10%28%29%12%4
517
June1st to 15thDay
12%428%30%20%3
495
16th to endDay
9%7%29%32%16%4
495
July1st to 15thDay
7%225%34%19%10%
475
16th to endDay
9%119%36%26%6%
515
August1st to 15thDay
8%122%34%25%6%
493
16th to endDay
11%216%34%25%9%
358
September1st to 15thDay
10%415%33%25%9%
315
16th to endDay
10%327%28%25%3
251
October1st to 15thDay
23%8%28%27%8%4
135
16th to endDay
19%9%43%18%10%
144
November1st to 15thDay
14%11%30%23%14%5%
135
16th to endDay
34%11%32%15%5%
135
December1st to 15thDay
20%17%34%20%6%
135
16th to endDay
28%14%42%13%
144
January1st to 15thNight
14%12%36%27%7%
975
16th to endNight
17%10%37%28%6%
1040
February1st to 15thNight
19%10%36%27%6%
950
16th to endNight
18%9%38%26%5%
667
March1st to 15thNight
19%9%33%26%10%
627
16th to endNight
18%10%35%27%6%
576
April1st to 15thNight
20%11%34%27%5%
539
16th to endNight
24%7%26%30%8%
540
May1st to 15thNight
18%8%34%28%8%1
540
16th to endNight
12%431%34%16%
563
June1st to 15thNight
13%324%42%15%
540
16th to endNight
9%228%41%16%1
540
July1st to 15thNight
7%116%41%30%2
510
16th to endNight
4115%45%30%2
564
August1st to 15thNight
5%13%46%30%3
539
16th to endNight
11%113%42%26%4
573
September1st to 15thNight
11%314%39%25%5%
540
16th to endNight
8%325%36%23%2
627
October1st to 15thNight
17%5%28%29%16%1
720
16th to endNight
19%9%30%31%9%
768
November1st to 15thNight
16%9%33%29%10%
760
16th to endNight
20%10%37%23%7%
972
December1st to 15thNight
21%13%36%23%5%
975
16th to endNight
27%9%31%27%4
1040
Page generated at 2018-02-15 09:58:52. Version ac04

Copyright 2018 A. Danko


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