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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 2005-11-05 to 2019-09-17.

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%
18690
18%
54778
11%
18645
45%
18645
26%
35843

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%
1050
13%
2926
6%
1045
36%
1045
21%
2061
January16th to endNight
24%
1120
15%
2947
5%
1120
31%
1120
20%
2155
February1st to 15thNight
23%
1028
14%
2678
4%
1026
30%
1026
20%
1952
February16th to endNight
27%
777
18%
2247
7%
777
36%
777
22%
1544
March1st to 15thNight
30%
731
20%
2411
11%
731
40%
731
24%
1520
March16th to endNight
28%
672
11%
2403
8%
672
35%
672
16%
1668
April1st to 15thNight
25%
629
17%
2097
11%
629
35%
629
20%
1396
April16th to endNight
36%
624
17%
2078
14%
624
46%
624
20%
1399
May1st to 15thNight
35%
630
17%
1751
9%
630
43%
630
25%
1215
May16th to endNight
46%
659
18%
1753
8%
657
53%
657
31%
1164
June1st to 15thNight
53%
630
17%
1680
9%
630
57%
630
35%
1047
June16th to endNight
53%
630
17%
1680
9%
630
57%
630
36%
1035
July1st to 15thNight
71%
600
21%
1600
13%
600
73%
600
47%
895
July16th to endNight
68%
660
23%
1709
17%
627
72%
627
44%
986
August1st to 15thNight
70%
620
23%
1852
23%
617
72%
617
40%
1027
August16th to endNight
62%
669
22%
2199
24%
669
66%
669
32%
1268
September1st to 15thNight
64%
630
28%
2100
29%
630
69%
630
35%
1147
September16th to endNight
57%
682
26%
2126
20%
682
65%
682
37%
1185
October1st to 15thNight
40%
780
23%
2340
15%
780
47%
780
27%
1464
October16th to endNight
35%
832
21%
2522
11%
832
44%
832
28%
1550
November1st to 15thNight
33%
820
24%
2666
15%
820
44%
820
25%
1626
November16th to endNight
27%
1047
17%
2937
7%
1047
37%
1047
25%
1952
December1st to 15thNight
23%
1050
13%
2940
4%
1050
31%
1050
17%
2184
December16th to endNight
23%
1120
13%
3136
4%
1120
30%
1120
15%
2403

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%37%
55916
Night
13%7%35%5%24446%42%
54950
Cloud CoverDay
14%7%36%5%3445%7%38%
55925
Night
13%7%35%424446%42%
54954
TransparencyDay
45%5%13%22%11%1
55606
Night
42%412%23%14%2
54779
SeeingDay
16%7%27%27%16%4
8755
Night
16%7%30%31%12%1
18692

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%6%45%447%29%
1672
16th to endDay
13%13%6%9%7%45%446%25%
1977
February1st to 15thDay
14%11%5%8%7%2445%6%30%
1845
16th to endDay
15%10%37%5%2445%7%32%
1797
March1st to 15thDay
15%9%37%5%34347%35%
2211
16th to endDay
18%9%47%5%3435%7%29%
2524
April1st to 15thDay
18%10%47%5%24445%31%
2511
16th to endDay
23%7%345%2345%5%33%
2487
May1st to 15thDay
19%8%46%5%35%5%5%6%30%
2858
16th to endDay
13%7%36%6%35%5%5%8%35%
3065
June1st to 15thDay
12%5%24435%5%5%8%42%
2940
16th to endDay
10%425%5%36%5%5%8%42%
2940
July1st to 15thDay
5%415%5%3448%9%46%
2940
16th to endDay
7%324436%6%7%9%44%
3061
August1st to 15thDay
7%425%5%35%6%6%8%44%
2681
16th to endDay
11%6%25%5%345%5%8%43%
2707
September1st to 15thDay
13%41442235%7%51%
2520
16th to endDay
10%425%5%3445%6%46%
2172
October1st to 15thDay
18%6%25%5%23335%42%
1950
16th to endDay
16%6%25%433345%43%
2053
November1st to 15thDay
13%8%36%5%3445%6%39%
1852
16th to endDay
18%8%25%423337%40%
1681
December1st to 15thDay
19%12%48%6%24346%27%
1680
16th to endDay
19%15%5%8%6%2344425%
1792
January1st to 15thNight
11%9%5%7%5%35%445%35%
2926
16th to endNight
12%10%6%7%6%34445%34%
2947
February1st to 15thNight
13%12%47%5%24445%34%
2675
16th to endNight
15%8%27%5%23435%39%
2247
March1st to 15thNight
15%8%25%424336%43%
2399
16th to endNight
16%8%46%6%345%46%32%
2403
April1st to 15thNight
17%9%36%423346%38%
2097
16th to endNight
18%8%25%5%24445%38%
2078
May1st to 15thNight
15%6%245%345%5%6%39%
1751
16th to endNight
10%5%25%5%345%6%8%41%
1752
June1st to 15thNight
9%5%145%2435%9%46%
1680
16th to endNight
7%425%4235%7%9%46%
1680
July1st to 15thNight
5%21332436%9%56%
1680
16th to endNight
5%214425%46%9%53%
1807
August1st to 15thNight
43145%2445%9%53%
1862
16th to endNight
9%424324447%51%
2199
September1st to 15thNight
10%413424346%55%
2100
16th to endNight
6%425%424347%54%
2126
October1st to 15thNight
16%6%23424345%47%
2340
16th to endNight
14%6%25%412345%47%
2522
November1st to 15thNight
13%6%34423345%47%
2666
16th to endNight
17%7%24424346%42%
2937
December1st to 15thNight
16%11%5%7%5%44445%31%
2940
16th to endNight
20%13%5%8%5%23445%27%
3136

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%11%6%8%6%46%447%29%
1672
16th to endDay
13%13%6%9%6%5%5%445%25%
1977
February1st to 15thDay
14%10%5%7%7%24446%30%
1845
16th to endDay
15%9%37%5%3445%8%32%
1797
March1st to 15thDay
16%9%37%5%3335%6%35%
2222
16th to endDay
18%9%37%5%35%35%6%30%
2522
April1st to 15thDay
19%10%46%5%3445%5%30%
2511
16th to endDay
23%7%24433446%34%
2487
May1st to 15thDay
20%7%36%5%35%45%6%30%
2858
16th to endDay
13%7%26%6%35%5%5%7%35%
3065
June1st to 15thDay
12%425%435%45%8%41%
2940
16th to endDay
11%4245%36%5%5%8%42%
2940
July1st to 15thDay
6%325%5%25%5%7%10%46%
2940
16th to endDay
8%314436%5%7%9%44%
3061
August1st to 15thDay
7%4245%35%6%6%8%44%
2681
16th to endDay
12%5%25%425%45%7%43%
2707
September1st to 15thDay
13%414332447%51%
2520
16th to endDay
10%425%5%3445%6%46%
2172
October1st to 15thDay
18%6%25%5%23335%43%
1950
16th to endDay
17%6%25%434346%43%
2053
November1st to 15thDay
12%9%36%5%3335%5%40%
1852
16th to endDay
18%8%35%413346%40%
1681
December1st to 15thDay
19%11%48%5%24436%27%
1680
16th to endDay
19%15%6%8%6%2433425%
1792
January1st to 15thNight
11%9%5%8%5%35%445%35%
2926
16th to endNight
12%10%6%8%6%44345%34%
2947
February1st to 15thNight
13%12%46%5%33445%35%
2668
16th to endNight
15%8%37%5%23435%39%
2247
March1st to 15thNight
15%7%25%423335%43%
2411
16th to endNight
16%8%37%6%345%46%32%
2403
April1st to 15thNight
17%9%36%423346%38%
2097
16th to endNight
19%8%3442345%438%
2078
May1st to 15thNight
16%5%344345%6%6%38%
1750
16th to endNight
10%425%5%35%46%8%42%
1752
June1st to 15thNight
10%42443445%10%46%
1680
16th to endNight
8%32442347%9%47%
1680
July1st to 15thNight
5%21332346%9%57%
1680
16th to endNight
5%214325%46%8%53%
1807
August1st to 15thNight
5%215%42445%9%53%
1862
16th to endNight
10%5%1432445%6%51%
2199
September1st to 15thNight
9%413324346%55%
2100
16th to endNight
6%425%424347%54%
2126
October1st to 15thNight
16%5%14423345%47%
2340
16th to endNight
15%6%24422345%47%
2522
November1st to 15thNight
13%7%25%423345%47%
2666
16th to endNight
16%8%245%24346%42%
2937
December1st to 15thNight
16%10%5%8%5%34345%31%
2940
16th to endNight
20%13%5%7%5%23345%27%
3136

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
55%413%16%9%
1673
16th to endDay
60%413%14%7%
1977
February1st to 15thDay
54%415%19%6%
1846
16th to endDay
49%6%14%20%7%1
1797
March1st to 15thDay
48%314%22%9%
2222
16th to endDay
53%5%13%20%6%
2524
April1st to 15thDay
54%411%21%7%
2511
16th to endDay
51%5%10%20%11%2
2487
May1st to 15thDay
53%6%12%20%7%
2858
16th to endDay
46%7%12%19%11%1
3069
June1st to 15thDay
39%6%14%22%16%1
2940
16th to endDay
38%7%13%23%15%1
2940
July1st to 15thDay
31%9%14%27%13%3
2791
16th to endDay
31%8%17%24%15%2
2897
August1st to 15thDay
34%7%14%27%14%1
2667
16th to endDay
38%6%12%25%15%2
2707
September1st to 15thDay
32%5%10%27%20%3
2520
16th to endDay
36%412%29%15%1
2172
October1st to 15thDay
44%39%23%17%1
1950
16th to endDay
42%313%25%14%1
2053
November1st to 15thDay
45%311%25%13%1
1852
16th to endDay
45%418%23%7%
1681
December1st to 15thDay
58%313%17%6%
1680
16th to endDay
62%312%13%6%
1792
January1st to 15thNight
49%415%17%13%
2926
16th to endNight
52%415%17%9%
2947
February1st to 15thNight
51%410%22%9%
2678
16th to endNight
47%412%23%11%1
2247
March1st to 15thNight
42%313%26%12%1
2411
16th to endNight
53%414%17%9%
2403
April1st to 15thNight
47%49%24%12%2
2097
16th to endNight
47%5%9%20%13%3
2078
May1st to 15thNight
44%6%13%23%12%
1751
16th to endNight
38%6%13%23%15%2
1754
June1st to 15thNight
34%5%14%25%16%3
1680
16th to endNight
31%7%15%25%16%3
1680
July1st to 15thNight
23%5%16%32%16%5%
1600
16th to endNight
24%6%15%32%17%1
1709
August1st to 15thNight
26%6%14%32%16%3
1852
16th to endNight
32%6%10%27%19%4
2199
September1st to 15thNight
30%49%27%25%3
2100
16th to endNight
29%410%32%20%2
2126
October1st to 15thNight
39%49%22%21%3
2340
16th to endNight
39%313%23%16%2
2522
November1st to 15thNight
39%411%24%16%3
2666
16th to endNight
43%314%27%10%
2937
December1st to 15thNight
55%412%19%8%
2940
16th to endNight
59%311%16%7%
3136

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
25%12%30%22%7%1
180
16th to endDay
21%12%36%19%8%1
192
February1st to 15thDay
22%16%37%18%4
180
16th to endDay
27%11%39%13%8%
159
March1st to 15thDay
24%20%37%13%3
180
16th to endDay
27%9%29%23%7%1
252
April1st to 15thDay
25%9%36%20%8%
390
16th to endDay
26%10%26%21%13%1
379
May1st to 15thDay
21%11%30%23%10%1
612
16th to endDay
15%10%27%27%15%5%
677
June1st to 15thDay
10%428%31%21%3
645
16th to endDay
11%6%25%34%17%4
645
July1st to 15thDay
6%221%32%25%11%
625
16th to endDay
8%121%36%25%6%
675
August1st to 15thDay
8%123%34%25%6%
624
16th to endDay
13%319%33%21%8%
491
September1st to 15thDay
11%416%32%22%10%
435
16th to endDay
11%5%26%26%25%3
310
October1st to 15thDay
27%9%28%24%6%3
180
16th to endDay
21%7%40%21%8%
192
November1st to 15thDay
18%12%29%22%12%5%
180
16th to endDay
31%9%31%21%5%
180
December1st to 15thDay
20%16%32%21%7%2
180
16th to endDay
28%13%39%16%2
192
January1st to 15thNight
15%12%35%27%8%
1050
16th to endNight
17%9%37%28%6%
1120
February1st to 15thNight
20%11%35%26%5%
1030
16th to endNight
21%9%36%26%5%
777
March1st to 15thNight
19%9%35%25%9%
731
16th to endNight
19%9%35%27%7%
672
April1st to 15thNight
22%12%33%25%4
629
16th to endNight
23%8%27%30%9%
624
May1st to 15thNight
17%8%32%30%9%1
630
16th to endNight
13%430%33%17%
659
June1st to 15thNight
12%325%42%15%
630
16th to endNight
10%227%41%17%1
630
July1st to 15thNight
6%114%42%31%2
600
16th to endNight
5%117%44%29%2
660
August1st to 15thNight
5%13%46%30%2
620
16th to endNight
12%114%40%25%4
669
September1st to 15thNight
11%314%39%24%6%
630
16th to endNight
8%424%36%23%2
682
October1st to 15thNight
19%6%28%27%15%1
780
16th to endNight
19%9%30%30%9%
832
November1st to 15thNight
16%10%33%28%10%
820
16th to endNight
21%10%37%23%6%
1047
December1st to 15thNight
20%12%36%23%6%
1050
16th to endNight
26%9%31%26%5%
1120
Page generated at 2019-09-17 20:12:19. Version ac04

Copyright 2019 A. Danko


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