Dry Tortugas National Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dry Tortugas National Park clear sky chart from 2005-11-05 to 2017-09-21.

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%
15982
19%
47086
18%
15943
72%
15943
31%
29073

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
62%
718
17%
2294
18%
716
63%
716
25%
1444
January16th to endNight
63%
768
25%
2304
22%
768
66%
768
33%
1372
February1st to 15thNight
58%
700
23%
2105
20%
699
61%
699
33%
1266
February16th to endNight
72%
631
30%
1850
25%
631
75%
631
43%
1001
March1st to 15thNight
73%
720
26%
1980
21%
720
75%
720
46%
1094
March16th to endNight
74%
768
28%
2112
24%
768
76%
768
46%
1169
April1st to 15thNight
83%
718
24%
1976
21%
718
84%
718
50%
1053
April16th to endNight
77%
720
25%
1965
19%
720
79%
720
44%
1104
May1st to 15thNight
85%
593
28%
1673
25%
593
85%
593
52%
840
May16th to endNight
72%
561
20%
1683
18%
561
72%
561
32%
1012
June1st to 15thNight
64%
540
10%
1620
8%
540
64%
540
20%
1130
June16th to endNight
76%
540
9%
1620
9%
540
76%
540
27%
1036
July1st to 15thNight
80%
510
7%
1530
7%
510
80%
510
29%
963
July16th to endNight
82%
564
11%
1644
11%
531
83%
531
32%
984
August1st to 15thNight
81%
539
6%
1788
6%
536
81%
536
26%
1137
August16th to endNight
72%
719
6%
2056
6%
719
72%
719
23%
1451
September1st to 15thNight
69%
720
4%
1980
4%
720
69%
720
19%
1476
September16th to endNight
64%
681
7%
1881
7%
681
64%
681
19%
1410
October1st to 15thNight
68%
660
17%
1815
18%
660
69%
660
23%
1282
October16th to endNight
54%
704
16%
2093
18%
704
54%
704
20%
1498
November1st to 15thNight
69%
700
25%
2101
27%
700
70%
700
32%
1270
November16th to endNight
66%
720
25%
2180
26%
720
68%
720
33%
1297
December1st to 15thNight
65%
720
21%
2340
24%
720
67%
720
29%
1405
December16th to endNight
71%
768
25%
2496
28%
768
73%
768
36%
1379

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%4245%35%6%7%11%41%
47751
Night
6%4245%35%5%7%10%42%
47297
TransparencyDay
33%9%22%22%10%1
47457
Night
34%8%20%23%12%2
47095
SeeingDay
9%15%20%32%30%
5837
Night
8%17%25%36%20%
15991

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
9%435%6%3447%12%38%
1641
16th to endDay
9%5%24435%6%6%8%43%
1920
February1st to 15thDay
10%5%2443445%10%45%
1750
16th to endDay
5%21331345%11%55%
1622
March1st to 15thDay
32133245%7%11%54%
1980
16th to endDay
32133235%6%11%57%
2111
April1st to 15thDay
3212325%45%11%58%
1972
16th to endDay
32133235%7%11%55%
1992
May1st to 15thDay
211231345%8%65%
2285
16th to endDay
7%3245%35%5%5%9%47%
2431
June1st to 15thDay
13%6%25%5%36%6%6%12%29%
2340
16th to endDay
7%425%6%36%6%8%13%34%
2340
July1st to 15thDay
5%425%6%46%7%9%15%32%
2340
16th to endDay
22246%48%8%11%16%30%
2407
August1st to 15thDay
33246%47%8%10%15%33%
2160
16th to endDay
6%426%7%5%7%7%9%12%29%
2133
September1st to 15thDay
7%6%37%6%5%7%8%10%13%22%
1980
16th to endDay
9%6%36%6%48%9%8%13%22%
1872
October1st to 15thDay
6%6%37%6%46%8%10%12%27%
1815
16th to endDay
13%7%36%5%346%6%9%32%
1778
November1st to 15thDay
7%426%435%5%7%10%42%
1757
16th to endDay
8%423425%5%7%9%45%
1777
December1st to 15thDay
10%5%244245%6%10%42%
1620
16th to endDay
6%4244245%7%12%43%
1728
January1st to 15thNight
11%5%346%35%6%7%10%35%
2294
16th to endNight
7%5%24435%5%6%9%44%
2304
February1st to 15thNight
10%42442446%7%46%
2103
16th to endNight
5%3234245%5%7%56%
1850
March1st to 15thNight
4333245%5%8%56%
1980
16th to endNight
431332346%8%55%
2112
April1st to 15thNight
2213335%45%9%59%
1976
16th to endNight
43134335%7%11%52%
1965
May1st to 15thNight
211232445%9%61%
1673
16th to endNight
7%434425%5%6%10%44%
1682
June1st to 15thNight
11%7%36%5%35%6%6%10%31%
1620
16th to endNight
5%415%5%37%6%8%13%38%
1620
July1st to 15thNight
3315%5%36%6%9%15%38%
1620
16th to endNight
2324435%7%9%14%41%
1756
August1st to 15thNight
33246%47%8%9%15%34%
1800
16th to endNight
5%5%36%6%47%6%9%12%31%
2056
September1st to 15thNight
5%6%35%8%5%7%8%10%12%25%
1980
16th to endNight
7%7%47%9%46%6%7%12%25%
1881
October1st to 15thNight
6%6%37%7%47%7%9%10%29%
1815
16th to endNight
15%8%26%6%45%6%5%8%29%
2093
November1st to 15thNight
9%4244345%6%9%43%
2101
16th to endNight
8%5%245%35%5%6%9%44%
2180
December1st to 15thNight
9%5%25%5%25%5%6%8%43%
2340
16th to endNight
7%42333446%11%46%
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
37%5%19%22%11%2
1642
16th to endDay
35%5%15%24%16%2
1920
February1st to 15thDay
35%311%26%16%5%
1752
16th to endDay
22%6%16%31%17%6%
1622
March1st to 15thDay
22%5%16%35%17%2
1980
16th to endDay
20%5%18%32%19%3
2112
April1st to 15thDay
20%420%36%15%2
1972
16th to endDay
20%6%19%33%18%1
1992
May1st to 15thDay
17%5%21%33%17%4
2285
16th to endDay
31%7%17%31%11%
2435
June1st to 15thDay
44%11%25%17%1
2340
16th to endDay
38%12%34%13%1
2340
July1st to 15thDay
37%15%37%9%
2201
16th to endDay
31%17%34%15%
2256
August1st to 15thDay
32%17%34%15%
2148
16th to endDay
40%15%32%11%
2133
September1st to 15thDay
45%14%30%8%1
1980
16th to endDay
44%15%22%14%2
1872
October1st to 15thDay
42%12%17%17%7%1
1815
16th to endDay
46%6%13%18%11%3
1778
November1st to 15thDay
34%6%10%26%19%2
1757
16th to endDay
32%6%13%19%22%5%
1777
December1st to 15thDay
33%6%15%24%17%
1620
16th to endDay
31%6%14%32%15%
1728
January1st to 15thNight
40%6%16%25%9%2
2294
16th to endNight
34%5%15%24%17%2
2304
February1st to 15thNight
34%5%11%23%18%5%
2112
16th to endNight
25%413%30%19%7%
1850
March1st to 15thNight
24%415%31%21%3
1980
16th to endNight
24%416%29%18%5%
2112
April1st to 15thNight
20%5%18%34%17%2
1976
16th to endNight
25%5%14%30%20%2
1965
May1st to 15thNight
18%5%19%33%20%2
1674
16th to endNight
33%6%17%28%12%
1684
June1st to 15thNight
45%9%24%17%2
1620
16th to endNight
33%13%35%16%1
1620
July1st to 15thNight
30%13%41%14%
1530
16th to endNight
26%13%38%20%
1644
August1st to 15thNight
31%15%36%16%
1788
16th to endNight
40%13%32%13%
2056
September1st to 15thNight
44%15%29%8%1
1980
16th to endNight
48%11%23%13%2
1881
October1st to 15thNight
43%10%17%18%7%2
1815
16th to endNight
51%5%10%18%10%3
2093
November1st to 15thNight
34%6%11%23%21%3
2101
16th to endNight
33%5%13%22%20%4
2180
December1st to 15thNight
35%7%15%25%15%1
2340
16th to endNight
30%5%14%31%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
20%214%37%24%1
90
16th to endDay
17%10%14%31%22%3
96
February1st to 15thDay
7%315%42%25%5%
90
16th to endDay
7%311%52%24%
123
March1st to 15thDay
5%9%51%30%2
270
16th to endDay
6%114%40%31%5%
288
April1st to 15thDay
416%45%36%4
270
16th to endDay
4337%49%5%
270
May1st to 15thDay
4324%52%14%
288
16th to endDay
41213%46%31%
331
June1st to 15thDay
20%1312%27%33%
315
16th to endDay
8%1418%66%
315
July1st to 15thDay
211223%68%
305
16th to endDay
8%223%63%
326
August1st to 15thDay
6%2130%58%
313
16th to endDay
10%11327%56%
332
September1st to 15thDay
13%145%18%57%
315
16th to endDay
17%1421%55%
275
October1st to 15thDay
9%1417%42%25%
255
16th to endDay
19%110%26%32%8%
272
November1st to 15thDay
10%17%25%44%11%
265
16th to endDay
11%113%33%36%4
247
December1st to 15thDay
25%17%20%38%6%
90
16th to endDay
5%8%25%54%7%
96
January1st to 15thNight
13%211%31%38%3
720
16th to endNight
9%315%38%29%2
768
February1st to 15thNight
10%219%34%30%1
704
16th to endNight
6%211%38%38%2
631
March1st to 15thNight
6%113%42%33%3
720
16th to endNight
6%111%39%35%6%
768
April1st to 15thNight
316%43%40%5%
718
16th to endNight
6%6%39%41%4
720
May1st to 15thNight
2333%47%12%
594
16th to endNight
9%1422%48%14%
563
June1st to 15thNight
15%2212%38%29%
540
16th to endNight
8%5%32%52%
540
July1st to 15thNight
41333%57%
510
16th to endNight
41126%65%
564
August1st to 15thNight
31235%56%
539
16th to endNight
8%26%30%51%
719
September1st to 15thNight
9%26%30%50%
720
16th to endNight
12%126%33%44%
681
October1st to 15thNight
11%215%44%25%
660
16th to endNight
20%17%22%31%15%
704
November1st to 15thNight
11%18%28%40%10%
700
16th to endNight
9%210%33%37%6%
720
December1st to 15thNight
10%29%33%40%3
720
16th to endNight
8%210%32%37%8%
768
Page generated at 2017-09-22 07:35:38. Version ac04

Copyright 2017 A. Danko


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