This page made possible by the sponsorship of: Jim Gerlach.

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 2020-04-13.

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
52%
19667
20%
57286
14%
19628
58%
19628
27%
36829

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%
897
20%
2912
10%
896
47%
896
21%
1838
January16th to endNight
37%
960
24%
3120
15%
960
50%
960
25%
1918
February1st to 15thNight
36%
882
20%
2866
12%
880
48%
880
25%
1756
February16th to endNight
36%
791
24%
2272
14%
791
48%
791
25%
1491
March1st to 15thNight
42%
900
22%
2475
14%
900
51%
900
31%
1595
March16th to endNight
45%
960
21%
2640
13%
960
52%
960
30%
1693
April1st to 15thNight
49%
890
22%
2263
11%
890
54%
890
35%
1437
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
74%
600
13%
1800
12%
600
74%
600
25%
1189
July16th to endNight
68%
660
10%
1883
9%
627
69%
627
24%
1259
August1st to 15thNight
67%
661
12%
1891
9%
658
67%
658
23%
1303
August16th to endNight
68%
892
12%
2230
9%
892
68%
892
25%
1633
September1st to 15thNight
65%
840
17%
2100
13%
840
65%
840
27%
1497
September16th to endNight
58%
837
15%
2341
15%
837
59%
837
23%
1653
October1st to 15thNight
59%
840
24%
2520
23%
840
64%
840
29%
1586
October16th to endNight
55%
896
30%
2688
25%
896
64%
896
33%
1548
November1st to 15thNight
51%
880
26%
2641
19%
880
61%
880
30%
1611
November16th to endNight
48%
900
27%
2737
19%
900
58%
900
31%
1617
December1st to 15thNight
38%
900
21%
2925
13%
900
48%
900
22%
1905
December16th to endNight
39%
960
22%
3120
16%
960
47%
960
22%
2008

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%
57951
Night
11%5%25%42445%8%44%
57484
TransparencyDay
36%8%15%20%15%3
57652
Night
37%8%13%19%15%4
57287
SeeingDay
13%318%27%26%10%
9404
Night
13%5%20%29%25%6%
19675

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%45%
2016
16th to endDay
14%6%25%433445%45%
2160
February1st to 15thDay
16%5%2443345%6%42%
1984
16th to endDay
14%6%25%424345%45%
2077
March1st to 15thDay
12%5%24423346%49%
2475
16th to endDay
13%3245%35%46%7%42%
2639
April1st to 15thDay
10%41432445%7%51%
2629
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%36%7%8%12%36%
2730
16th to endDay
7%425%5%46%6%7%12%35%
2881
August1st to 15thDay
11%5%25%6%45%7%8%13%31%
2627
16th to endDay
9%5%36%6%45%6%8%11%33%
2676
September1st to 15thDay
13%5%24435%46%8%40%
2520
16th to endDay
14%7%26%5%35%45%6%37%
2276
October1st to 15thDay
12%425%5%34446%47%
2100
16th to endDay
9%423423345%57%
2240
November1st to 15thDay
11%5%24423346%51%
2207
16th to endDay
10%324424346%53%
2209
December1st to 15thDay
16%5%35%335%5%46%39%
1963
16th to endDay
16%6%25%42335%6%43%
2160
January1st to 15thNight
11%7%25%5%2445%5%45%
2912
16th to endNight
13%42443445%6%46%
3120
February1st to 15thNight
15%6%1442335%6%45%
2857
16th to endNight
15%5%26%42345%5%42%
2272
March1st to 15thNight
11%5%25%425%45%7%45%
2475
16th to endNight
11%425%42445%7%46%
2640
April1st to 15thNight
9%5%244245%6%7%48%
2263
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
5%425%5%46%8%7%12%36%
1890
16th to endNight
7%5%35%6%25%7%9%10%35%
1991
August1st to 15thNight
7%5%35%7%45%6%8%10%34%
1902
16th to endNight
9%5%25%6%35%6%9%11%34%
2230
September1st to 15thNight
11%5%25%6%35%5%6%9%39%
2100
16th to endNight
15%6%25%5%2446%8%37%
2341
October1st to 15thNight
11%5%24434447%47%
2520
16th to endNight
9%424423346%54%
2688
November1st to 15thNight
10%5%25%423436%52%
2641
16th to endNight
11%5%2442335%7%50%
2737
December1st to 15thNight
15%6%245%24447%41%
2925
16th to endNight
15%6%25%42445%6%40%
3120

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%
2017
16th to endDay
40%5%6%18%22%6%
2160
February1st to 15thDay
40%5%9%20%18%4
1986
16th to endDay
40%5%9%19%17%8%
2077
March1st to 15thDay
35%5%12%19%20%7%
2475
16th to endDay
38%7%12%20%16%4
2640
April1st to 15thDay
31%5%14%25%18%4
2629
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
2591
16th to endDay
36%13%22%21%5%
2726
August1st to 15thDay
39%12%22%19%4
2614
16th to endDay
40%13%24%16%41
2676
September1st to 15thDay
38%12%17%16%12%3
2520
16th to endDay
44%9%13%15%14%1
2276
October1st to 15thDay
37%6%11%22%19%3
2100
16th to endDay
29%5%9%21%26%8%
2240
November1st to 15thDay
35%5%8%18%23%8%
2207
16th to endDay
32%6%9%20%23%7%
2209
December1st to 15thDay
44%8%10%17%14%5%
1963
16th to endDay
41%5%12%18%15%6%
2160
January1st to 15thNight
40%6%11%15%19%7%
2912
16th to endNight
38%5%7%18%23%6%
3120
February1st to 15thNight
39%49%17%20%7%
2866
16th to endNight
42%5%9%17%17%8%
2272
March1st to 15thNight
36%7%11%19%18%6%
2475
16th to endNight
37%6%13%21%16%4
2640
April1st to 15thNight
33%6%13%21%18%5%
2263
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%14%21%21%7%
1800
16th to endNight
37%13%22%21%5%
1883
August1st to 15thNight
39%13%22%19%5%
1891
16th to endNight
38%15%20%19%4
2230
September1st to 15thNight
39%11%18%15%11%2
2100
16th to endNight
44%9%13%18%12%1
2341
October1st to 15thNight
37%7%11%21%16%5%
2520
16th to endNight
31%5%9%18%24%9%
2688
November1st to 15thNight
35%6%8%17%23%9%
2641
16th to endNight
34%411%18%22%8%
2737
December1st to 15thNight
42%6%11%16%16%5%
2925
16th to endNight
41%6%10%18%14%6%
3120

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
16%8%34%31%9%
225
16th to endDay
14%6%33%39%5%1
240
February1st to 15thDay
18%7%32%31%9%
229
16th to endDay
18%7%33%28%10%1
399
March1st to 15thDay
13%6%34%31%13%1
450
16th to endDay
15%5%31%31%12%2
480
April1st to 15thDay
13%8%27%26%18%6%
442
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%46%18%
425
16th to endDay
10%5%22%48%13%
454
August1st to 15thDay
15%5%26%34%17%
418
16th to endDay
10%2419%38%23%
460
September1st to 15thDay
17%7%22%34%18%
435
16th to endDay
18%110%23%33%13%
434
October1st to 15thDay
15%314%25%27%12%
435
16th to endDay
9%321%33%23%7%
464
November1st to 15thDay
14%424%28%22%4
445
16th to endDay
12%425%33%20%3
409
December1st to 15thDay
25%6%30%22%14%1
204
16th to endDay
24%6%25%29%12%2
240
January1st to 15thNight
13%12%31%29%12%
900
16th to endNight
15%8%33%34%6%
960
February1st to 15thNight
19%8%30%33%7%
884
16th to endNight
18%7%31%31%11%
791
March1st to 15thNight
12%6%33%34%12%1
900
16th to endNight
13%5%29%32%17%2
960
April1st to 15thNight
12%5%27%28%22%3
890
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%
600
16th to endNight
9%15%25%46%11%
660
August1st to 15thNight
12%5%22%47%11%
661
16th to endNight
11%5%21%43%17%
892
September1st to 15thNight
14%6%23%40%14%
840
16th to endNight
18%210%25%33%10%
837
October1st to 15thNight
14%216%29%28%8%
840
16th to endNight
11%6%20%28%24%7%
896
November1st to 15thNight
12%6%23%31%20%4
880
16th to endNight
13%7%25%29%21%2
900
December1st to 15thNight
19%7%27%28%14%1
900
16th to endNight
18%6%27%33%12%
960
Page generated at 2020-04-14 17:18:43. Version ac04

Copyright 2020 A. Danko


St. James Plantation Clear Sky Chart |Charts Home