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St. James Plantation
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the St. James Plantation clear sky chart from 2005-11-05 to 2019-07-11.

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
53%
18591
20%
54122
14%
18552
58%
18552
27%
34721

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
35%
837
20%
2717
11%
836
47%
836
21%
1711
January16th to endNight
37%
896
23%
2912
15%
896
49%
896
25%
1787
February1st to 15thNight
37%
822
20%
2671
13%
820
49%
820
25%
1627
February16th to endNight
37%
735
24%
2111
14%
735
49%
735
26%
1370
March1st to 15thNight
43%
840
23%
2310
15%
840
52%
840
32%
1472
March16th to endNight
46%
896
22%
2464
14%
896
53%
896
31%
1560
April1st to 15thNight
50%
838
22%
2131
12%
838
55%
838
34%
1367
April16th to endNight
56%
831
23%
2077
13%
831
60%
831
39%
1296
May1st to 15thNight
61%
773
19%
2034
12%
773
63%
773
33%
1311
May16th to endNight
65%
657
17%
1971
14%
657
66%
657
30%
1233
June1st to 15thNight
66%
630
13%
1890
11%
630
66%
630
26%
1234
June16th to endNight
68%
630
13%
1890
11%
630
69%
630
26%
1218
July1st to 15thNight
73%
588
14%
1764
12%
588
74%
588
25%
1159
July16th to endNight
67%
612
10%
1739
9%
579
68%
579
24%
1161
August1st to 15thNight
66%
613
12%
1753
10%
610
66%
610
23%
1212
August16th to endNight
68%
828
13%
2070
9%
828
68%
828
26%
1516
September1st to 15thNight
65%
780
17%
1950
14%
780
65%
780
27%
1396
September16th to endNight
55%
777
13%
2174
14%
777
56%
777
21%
1584
October1st to 15thNight
58%
780
24%
2340
24%
780
64%
780
29%
1466
October16th to endNight
56%
832
31%
2496
26%
832
65%
832
35%
1408
November1st to 15thNight
52%
820
26%
2461
20%
820
62%
820
31%
1488
November16th to endNight
48%
840
26%
2555
18%
840
58%
840
31%
1508
December1st to 15thNight
39%
840
21%
2730
14%
840
49%
840
22%
1778
December16th to endNight
39%
896
21%
2912
16%
896
47%
896
22%
1859

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
11%5%2443446%8%43%
55017
Night
11%5%25%42445%8%44%
54320
TransparencyDay
36%8%15%20%15%3
54718
Night
37%8%13%19%15%4
54123
SeeingDay
13%317%27%27%10%
8376
Night
13%5%20%29%25%6%
18599

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
14%5%34423445%46%
1881
16th to endDay
14%5%35%423445%46%
2016
February1st to 15thDay
16%5%2443345%6%42%
1849
16th to endDay
13%6%25%424345%46%
1930
March1st to 15thDay
12%5%24424346%49%
2310
16th to endDay
12%325%5%35%45%6%43%
2463
April1st to 15thDay
10%41432445%7%50%
2476
16th to endDay
7%32332445%7%54%
2488
May1st to 15thDay
8%4245%345%5%7%48%
2587
16th to endDay
9%5%144245%6%9%45%
2847
June1st to 15thDay
9%425%5%35%5%7%11%39%
2730
16th to endDay
6%4245%36%6%8%12%38%
2730
July1st to 15thDay
7%425%6%26%7%8%12%36%
2668
16th to endDay
8%5%35%5%46%6%7%12%34%
2673
August1st to 15thDay
11%5%246%45%7%7%13%31%
2436
16th to endDay
9%5%37%6%45%6%8%11%32%
2484
September1st to 15thDay
12%5%24435%46%8%40%
2340
16th to endDay
15%7%27%6%35%45%6%33%
2113
October1st to 15thDay
12%4245%24446%47%
1950
16th to endDay
9%423323335%59%
2080
November1st to 15thDay
11%5%24423346%51%
2057
16th to endDay
10%324423346%54%
2061
December1st to 15thDay
16%6%35%335%5%46%38%
1832
16th to endDay
16%6%25%42335%6%44%
2016
January1st to 15thNight
11%7%25%42445%5%45%
2717
16th to endNight
13%424434446%46%
2912
February1st to 15thNight
16%5%14324446%46%
2662
16th to endNight
13%5%26%42345%5%43%
2111
March1st to 15thNight
11%42442445%7%46%
2310
16th to endNight
11%425%42435%6%48%
2464
April1st to 15thNight
9%5%244245%6%7%47%
2131
16th to endNight
7%32442445%7%52%
2077
May1st to 15thNight
8%4245%35%5%5%9%46%
2033
16th to endNight
10%5%3342445%10%45%
1970
June1st to 15thNight
9%5%25%5%35%5%7%11%38%
1890
16th to endNight
7%4246%246%8%14%38%
1890
July1st to 15thNight
6%425%5%46%8%7%12%36%
1854
16th to endNight
8%5%35%6%25%7%8%10%35%
1847
August1st to 15thNight
8%5%35%7%45%6%8%10%34%
1764
16th to endNight
9%5%25%6%35%7%9%10%34%
2070
September1st to 15thNight
10%5%25%5%35%5%7%9%39%
1950
16th to endNight
16%6%25%6%25%46%8%34%
2174
October1st to 15thNight
11%5%24424447%47%
2340
16th to endNight
9%424323346%56%
2496
November1st to 15thNight
10%414423446%52%
2461
16th to endNight
10%5%2442335%7%50%
2555
December1st to 15thNight
15%6%25%5%23447%41%
2730
16th to endNight
15%6%25%42445%7%41%
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
39%6%10%15%20%7%
1882
16th to endDay
40%5%6%18%23%6%
2016
February1st to 15thDay
41%5%9%20%18%4
1851
16th to endDay
39%5%9%21%18%6%
1930
March1st to 15thDay
35%5%12%20%20%7%
2310
16th to endDay
37%7%12%20%17%4
2464
April1st to 15thDay
32%5%14%24%18%4
2476
16th to endDay
26%7%14%21%22%6%
2488
May1st to 15thDay
32%7%15%25%16%2
2587
16th to endDay
32%9%20%23%12%
2851
June1st to 15thDay
35%11%20%21%10%
2730
16th to endDay
32%13%23%22%7%
2730
July1st to 15thDay
35%13%22%21%6%1
2529
16th to endDay
37%12%23%20%4
2518
August1st to 15thDay
39%12%22%20%5%
2423
16th to endDay
40%13%23%17%4
2484
September1st to 15thDay
38%12%17%16%11%3
2340
16th to endDay
47%9%11%15%13%2
2113
October1st to 15thDay
37%6%11%21%19%3
1950
16th to endDay
28%5%9%22%26%8%
2080
November1st to 15thDay
35%5%8%18%23%8%
2057
16th to endDay
31%6%9%19%24%8%
2061
December1st to 15thDay
44%8%10%16%14%5%
1832
16th to endDay
41%5%12%18%16%5%
2016
January1st to 15thNight
39%6%11%15%19%6%
2717
16th to endNight
38%5%7%18%22%7%
2912
February1st to 15thNight
39%410%18%20%7%
2671
16th to endNight
40%5%9%18%17%6%
2111
March1st to 15thNight
35%6%11%20%19%6%
2310
16th to endNight
36%6%12%22%17%4
2464
April1st to 15thNight
34%6%13%21%18%5%
2131
16th to endNight
30%6%14%24%16%7%
2077
May1st to 15thNight
34%8%15%22%18%1
2034
16th to endNight
33%10%16%27%11%
1972
June1st to 15thNight
37%10%22%21%7%
1890
16th to endNight
33%14%21%24%6%
1890
July1st to 15thNight
34%13%21%21%7%
1764
16th to endNight
37%12%22%20%5%
1739
August1st to 15thNight
39%12%21%19%6%
1753
16th to endNight
38%15%19%20%5%
2070
September1st to 15thNight
39%12%18%15%11%2
1950
16th to endNight
47%9%12%16%11%1
2174
October1st to 15thNight
37%6%12%20%17%5%
2340
16th to endNight
30%49%19%25%9%
2496
November1st to 15thNight
34%6%8%17%23%10%
2461
16th to endNight
34%411%18%22%8%
2555
December1st to 15thNight
42%6%11%17%16%5%
2730
16th to endNight
41%6%10%19%15%6%
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
17%8%35%26%10%
180
16th to endDay
14%5%31%40%6%1
192
February1st to 15thDay
18%6%30%34%9%
184
16th to endDay
15%6%35%29%11%
343
March1st to 15thDay
12%6%34%33%12%1
390
16th to endDay
14%5%32%31%12%3
416
April1st to 15thDay
13%8%25%25%20%6%
390
16th to endDay
8%318%35%25%7%
379
May1st to 15thDay
6%219%35%27%8%
408
16th to endDay
12%39%21%34%18%
459
June1st to 15thDay
13%8%26%33%17%
435
16th to endDay
8%6%25%40%18%
435
July1st to 15thDay
8%1420%47%17%
406
16th to endDay
11%15%21%48%12%
390
August1st to 15thDay
15%5%25%34%18%
358
16th to endDay
11%25%19%37%24%
396
September1st to 15thDay
16%7%22%32%19%
375
16th to endDay
21%110%22%32%12%
374
October1st to 15thDay
16%414%23%27%13%
375
16th to endDay
9%421%31%25%8%
400
November1st to 15thDay
13%5%25%27%23%5%
385
16th to endDay
12%425%32%21%3
351
December1st to 15thDay
29%426%19%17%1
163
16th to endDay
27%6%23%31%10%
192
January1st to 15thNight
13%12%31%28%13%
840
16th to endNight
15%8%32%34%7%
896
February1st to 15thNight
19%8%29%34%8%
824
16th to endNight
15%8%32%31%12%
735
March1st to 15thNight
12%6%32%34%12%1
840
16th to endNight
13%5%28%32%17%2
896
April1st to 15thNight
12%426%28%22%4
838
16th to endNight
9%5%23%33%25%3
831
May1st to 15thNight
9%417%34%28%5%
774
16th to endNight
13%110%22%36%15%
659
June1st to 15thNight
11%19%30%35%12%
630
16th to endNight
8%7%29%39%13%
630
July1st to 15thNight
7%5%25%50%10%
588
16th to endNight
9%15%26%47%10%
612
August1st to 15thNight
12%5%22%47%11%
613
16th to endNight
11%5%21%42%17%
828
September1st to 15thNight
14%7%23%39%14%
780
16th to endNight
19%211%24%31%10%
777
October1st to 15thNight
14%316%28%28%8%
780
16th to endNight
11%6%20%28%24%8%
832
November1st to 15thNight
12%6%23%30%22%4
820
16th to endNight
13%8%25%29%21%2
840
December1st to 15thNight
19%7%26%28%15%1
840
16th to endNight
18%7%27%33%12%
896
Page generated at 2019-07-12 07:32:32. Version ac04

Copyright 2019 A. Danko


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