Key West
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Key West clear sky chart from 2005-11-05 to 2017-09-16.

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
70%
16130
18%
47006
17%
16091
71%
16091
30%
29903

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
63%
717
17%
2327
20%
716
64%
716
26%
1490
January16th to endNight
64%
768
25%
2340
23%
768
68%
768
32%
1391
February1st to 15thNight
61%
701
25%
2107
21%
699
65%
699
34%
1257
February16th to endNight
72%
631
29%
1785
25%
631
75%
631
45%
985
March1st to 15thNight
70%
720
25%
1980
20%
720
74%
720
43%
1143
March16th to endNight
72%
768
26%
2112
22%
768
75%
768
42%
1210
April1st to 15thNight
81%
718
22%
1976
19%
718
82%
718
45%
1108
April16th to endNight
75%
720
25%
1901
19%
720
77%
720
43%
1120
May1st to 15thNight
84%
701
24%
1781
18%
701
84%
701
52%
996
May16th to endNight
70%
561
16%
1683
15%
561
70%
561
29%
1067
June1st to 15thNight
62%
540
10%
1620
9%
540
62%
540
16%
1196
June16th to endNight
75%
540
6%
1620
6%
540
75%
540
21%
1112
July1st to 15thNight
78%
510
7%
1530
7%
510
78%
510
25%
1011
July16th to endNight
83%
564
13%
1595
13%
531
84%
531
32%
963
August1st to 15thNight
80%
557
8%
1750
8%
554
79%
554
26%
1123
August16th to endNight
72%
764
6%
2101
6%
764
72%
764
22%
1538
September1st to 15thNight
71%
720
4%
1980
3%
720
71%
720
17%
1519
September16th to endNight
64%
658
5%
1818
5%
658
64%
658
17%
1391
October1st to 15thNight
66%
660
14%
1848
15%
660
66%
660
21%
1346
October16th to endNight
59%
704
16%
2112
17%
704
60%
704
22%
1474
November1st to 15thNight
66%
700
23%
2101
23%
700
69%
700
32%
1284
November16th to endNight
65%
720
24%
2160
25%
720
68%
720
32%
1315
December1st to 15thNight
66%
720
20%
2283
23%
720
67%
720
27%
1437
December16th to endNight
71%
768
23%
2496
26%
768
73%
768
33%
1427

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
6%425%5%36%6%8%12%38%
47717
Night
6%425%5%35%6%7%10%41%
47210
TransparencyDay
34%11%19%21%10%1
47418
Night
35%8%19%22%11%2
47013
SeeingDay
9%8%20%32%27%
5957
Night
8%8%25%35%20%
16139

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
7%425%6%46%6%7%13%35%
1611
16th to endDay
7%325%5%46%6%6%9%42%
1881
February1st to 15thDay
8%42342445%10%49%
1750
16th to endDay
421232346%11%56%
1686
March1st to 15thDay
32145%246%7%11%50%
1980
16th to endDay
43133145%6%10%54%
2111
April1st to 15thDay
32232447%12%55%
1972
16th to endDay
422232446%10%55%
2058
May1st to 15thDay
321221345%10%60%
2176
16th to endDay
6%4345%25%6%8%12%40%
2431
June1st to 15thDay
11%7%37%6%46%7%6%11%26%
2340
16th to endDay
6%326%6%47%9%9%14%28%
2340
July1st to 15thDay
4425%7%48%8%10%16%26%
2340
16th to endDay
32135%37%9%13%18%30%
2465
August1st to 15thDay
4326%6%47%8%11%16%26%
2181
16th to endDay
5%426%9%5%8%9%9%13%25%
2101
September1st to 15thDay
6%5%36%8%5%9%10%11%14%19%
1980
16th to endDay
9%7%35%7%5%8%7%10%12%22%
1815
October1st to 15thDay
6%5%36%8%48%8%9%12%26%
1780
16th to endDay
11%7%35%6%46%6%6%10%32%
1760
November1st to 15thDay
7%426%435%47%9%45%
1757
16th to endDay
8%4245%25%5%6%8%46%
1800
December1st to 15thDay
7%5%26%6%35%5%6%10%41%
1674
16th to endDay
5%3145%35%5%8%13%43%
1728
January1st to 15thNight
9%5%26%5%35%5%8%11%36%
2327
16th to endNight
5%4245%35%6%6%10%46%
2340
February1st to 15thNight
8%4244245%5%7%49%
2103
16th to endNight
4315%423449%56%
1785
March1st to 15thNight
43244245%5%9%54%
1980
16th to endNight
43135%236%6%9%53%
2112
April1st to 15thNight
3212335%5%7%10%54%
1976
16th to endNight
5%3134345%6%8%52%
1901
May1st to 15thNight
121332346%9%59%
1781
16th to endNight
8%4346%346%7%11%39%
1682
June1st to 15thNight
11%7%36%6%46%7%8%11%25%
1620
16th to endNight
5%425%7%5%8%7%8%12%33%
1620
July1st to 15thNight
4315%5%46%7%10%14%35%
1620
16th to endNight
2223435%8%8%15%41%
1703
August1st to 15thNight
2325%5%5%7%8%10%13%34%
1761
16th to endNight
45%36%7%5%6%9%8%12%30%
2101
September1st to 15thNight
5%5%26%7%6%7%9%11%12%23%
1980
16th to endNight
8%8%38%6%47%7%8%13%23%
1818
October1st to 15thNight
7%6%38%7%36%7%8%10%29%
1848
16th to endNight
12%8%35%6%46%6%7%8%30%
2112
November1st to 15thNight
9%425%5%345%6%10%44%
2101
16th to endNight
8%325%5%246%6%9%44%
2160
December1st to 15thNight
7%425%6%35%6%5%9%42%
2283
16th to endNight
7%4244345%7%9%47%
2496

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
38%7%18%21%11%2
1612
16th to endDay
35%7%14%23%16%3
1881
February1st to 15thDay
30%5%12%28%18%5%
1752
16th to endDay
20%5%16%33%17%6%
1686
March1st to 15thDay
27%6%16%28%19%1
1980
16th to endDay
23%7%17%29%19%3
2112
April1st to 15thDay
21%7%18%33%16%1
1972
16th to endDay
22%6%17%31%19%2
2058
May1st to 15thDay
20%7%18%32%15%4
2176
16th to endDay
34%11%19%27%8%
2435
June1st to 15thDay
49%13%20%14%1
2340
16th to endDay
41%17%31%9%
2340
July1st to 15thDay
39%19%31%9%
2201
16th to endDay
31%19%34%14%
2310
August1st to 15thDay
37%17%27%16%
2168
16th to endDay
41%18%27%12%
2101
September1st to 15thDay
46%20%23%8%1
1980
16th to endDay
46%16%23%11%
1815
October1st to 15thDay
46%13%15%16%5%2
1780
16th to endDay
45%8%12%18%12%3
1760
November1st to 15thDay
34%6%10%23%22%2
1757
16th to endDay
34%7%11%18%21%6%
1800
December1st to 15thDay
37%8%14%20%17%1
1674
16th to endDay
31%8%12%27%17%1
1728
January1st to 15thNight
40%7%16%25%8%2
2327
16th to endNight
33%6%14%24%17%3
2340
February1st to 15thNight
32%5%10%27%16%6%
2112
16th to endNight
25%415%26%20%7%
1785
March1st to 15thNight
27%415%28%21%2
1980
16th to endNight
26%5%15%27%18%5%
2112
April1st to 15thNight
24%6%18%30%17%2
1976
16th to endNight
28%5%13%31%18%2
1901
May1st to 15thNight
20%6%17%33%18%4
1782
16th to endNight
37%6%18%25%11%
1684
June1st to 15thNight
50%10%20%14%3
1620
16th to endNight
41%12%33%11%1
1620
July1st to 15thNight
34%14%36%14%
1530
16th to endNight
28%12%35%21%1
1595
August1st to 15thNight
34%12%30%20%1
1750
16th to endNight
41%14%29%13%
2101
September1st to 15thNight
44%18%26%8%1
1980
16th to endNight
49%13%23%12%1
1818
October1st to 15thNight
46%10%15%18%7%1
1848
16th to endNight
47%7%12%18%11%3
2112
November1st to 15thNight
35%6%13%22%20%2
2101
16th to endNight
34%6%15%18%21%4
2160
December1st to 15thNight
39%6%15%22%15%1
2283
16th to endNight
32%5%13%29%17%1
2496

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%416%36%24%1
90
16th to endDay
12%10%20%37%15%3
96
February1st to 15thDay
4323%40%24%4
90
16th to endDay
8%14%41%34%1
187
March1st to 15thDay
7%14%43%31%2
270
16th to endDay
6%115%40%29%6%
288
April1st to 15thDay
210%42%39%3
270
16th to endDay
6%10%38%39%4
270
May1st to 15thDay
4430%48%11%
288
16th to endDay
7%5%12%46%27%
331
June1st to 15thDay
18%17%12%28%32%
315
16th to endDay
6%27%25%57%
315
July1st to 15thDay
34330%58%
305
16th to endDay
8%1327%57%
326
August1st to 15thDay
7%1133%54%
313
16th to endDay
7%15%7%26%52%
332
September1st to 15thDay
9%27%19%61%
315
16th to endDay
16%4421%52%
254
October1st to 15thDay
7%6%16%45%23%
255
16th to endDay
16%113%27%29%11%
272
November1st to 15thDay
10%12%21%42%13%
265
16th to endDay
12%120%31%30%4
270
December1st to 15thDay
18%113%27%32%6%
144
16th to endDay
6%111%27%45%8%
96
January1st to 15thNight
12%112%32%36%3
720
16th to endNight
7%217%38%29%3
768
February1st to 15thNight
10%119%35%30%2
704
16th to endNight
4212%41%35%3
631
March1st to 15thNight
6%115%40%33%3
720
16th to endNight
4114%38%37%4
768
April1st to 15thNight
47%41%42%3
718
16th to endNight
7%8%42%37%4
720
May1st to 15thNight
36%31%49%9%
702
16th to endNight
10%5%23%42%16%
563
June1st to 15thNight
15%5%13%34%30%
540
16th to endNight
6%15%37%47%
540
July1st to 15thNight
5%1435%52%
510
16th to endNight
31429%60%
564
August1st to 15thNight
415%38%50%
557
16th to endNight
8%27%30%51%
764
September1st to 15thNight
8%37%29%51%
720
16th to endNight
12%45%26%50%
658
October1st to 15thNight
10%6%17%42%22%
660
16th to endNight
18%11%20%33%16%
704
November1st to 15thNight
9%12%30%35%10%
700
16th to endNight
10%11%33%36%6%
720
December1st to 15thNight
10%110%35%36%4
720
16th to endNight
9%10%30%40%7%
768
Page generated at 2017-09-16 17:07:00. Version ac04

Copyright 2017 A. Danko


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