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 2005-11-06 to 2024-01-13.

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 Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(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

By Month

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 Forecast	Data Points
Cloud Cover	Day	6% 4 2 5% 5% 3 5% 6% 7% 12% 44%	74719
	Night	6% 4 2 5% 5% 3 5% 6% 7% 11% 45%	75006
Transparency	Day	31% 9% 23% 23% 12% 2	74447
	Night	31% 8% 21% 24% 13% 2	74797
Seeing	Day	7% 2 5% 21% 36% 29%	14456
	Night	7% 2 7% 25% 38% 21%	24564

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
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	8% 3 2 5% 5% 3 5% 5% 8% 13% 43%	1706
	11th to 20th	Day	9% 5% 3 6% 6% 4 6% 6% 8% 8% 39%	1773
	21st to end	Day	9% 6% 3 5% 4 3 5% 6% 6% 10% 43%	1980
February	1st to 10th	Day	8% 5% 2 4 5% 4 5% 5% 6% 10% 46%	1800
	11th to 20th	Day	7% 3 2 3 4 1 4 4 6% 9% 57%	1748
	21st to end	Day	5% 2 1 4 3 2 3 4 5% 11% 60%	1542
March	1st to 10th	Day	4 3 1 3 4 2 4 4 6% 10% 60%	1980
	11th to 20th	Day	4 2 1 3 3 2 4 5% 7% 9% 58%	1980
	21st to end	Day	3 2 1 3 3 2 2 4 5% 10% 63%	2178
April	1st to 10th	Day	2 1 1 2 3 2 4 4 7% 12% 62%	1980
	11th to 20th	Day	3 3 1 4 4 2 5% 4 7% 9% 59%	1956
	21st to end	Day	5% 3 1 3 3 2 3 5% 6% 10% 61%	1998
May	1st to 10th	Day	2 1 1 2 2 1 2 4 5% 8% 71%	2270
	11th to 20th	Day	8% 4 2 4 5% 2 5% 6% 6% 10% 49%	2301
	21st to end	Day	8% 4 2 5% 5% 3 5% 5% 6% 10% 47%	2531
June	1st to 10th	Day	14% 6% 3 6% 5% 3 5% 6% 6% 12% 33%	2340
	11th to 20th	Day	7% 5% 3 5% 6% 4 6% 6% 8% 14% 36%	2340
	21st to end	Day	6% 4 2 5% 5% 3 5% 6% 8% 14% 40%	2340
July	1st to 10th	Day	5% 3 2 5% 5% 4 6% 8% 9% 15% 38%	2340
	11th to 20th	Day	2 3 3 5% 6% 4 7% 7% 9% 17% 37%	2340
	21st to end	Day	3 3 2 4 5% 4 7% 8% 11% 14% 40%	2458
August	1st to 10th	Day	2 3 1 4 5% 5% 7% 9% 10% 16% 36%	2148
	11th to 20th	Day	3 3 2 5% 6% 5% 8% 7% 9% 15% 37%	2085
	21st to end	Day	7% 4 3 7% 7% 5% 7% 7% 9% 13% 30%	2178
September	1st to 10th	Day	6% 5% 3 6% 6% 5% 7% 9% 10% 13% 30%	1980
	11th to 20th	Day	4 5% 2 7% 6% 5% 8% 8% 9% 14% 31%	1980
	21st to end	Day	9% 6% 3 6% 8% 5% 7% 9% 7% 13% 28%	1980
October	1st to 10th	Day	7% 6% 3 7% 6% 4 6% 8% 10% 13% 31%	1980
	11th to 20th	Day	9% 5% 3 6% 5% 4 7% 8% 8% 11% 34%	1920
	21st to end	Day	9% 6% 3 6% 6% 4 5% 6% 6% 10% 40%	1980
November	1st to 10th	Day	8% 4 3 5% 5% 3 5% 5% 8% 12% 42%	1857
	11th to 20th	Day	8% 4 2 5% 5% 4 6% 6% 7% 9% 43%	1900
	21st to end	Day	7% 4 2 4 5% 3 5% 6% 8% 11% 45%	1863
December	1st to 10th	Day	9% 4 2 4 4 3 4 6% 7% 10% 47%	1710
	11th to 20th	Day	8% 4 2 4 4 3 4 6% 8% 13% 44%	2153
	21st to end	Day	9% 6% 3 6% 6% 4 5% 6% 7% 12% 37%	3124
January	1st to 10th	Night	9% 4 3 4 5% 4 4 6% 7% 11% 43%	2459
	11th to 20th	Night	8% 6% 3 5% 6% 3 6% 6% 7% 8% 41%	2227
	21st to end	Night	8% 6% 2 5% 5% 4 5% 7% 7% 10% 41%	2376
February	1st to 10th	Night	10% 4 3 5% 5% 3 5% 5% 7% 8% 45%	2160
	11th to 20th	Night	7% 4 2 4 5% 2 4 4 5% 8% 56%	2098
	21st to end	Night	5% 3 2 3 4 2 4 5% 5% 8% 60%	1711
March	1st to 10th	Night	3 3 1 4 4 2 4 5% 5% 8% 61%	1980
	11th to 20th	Night	4 2 1 3 3 3 4 4 6% 8% 60%	1980
	21st to end	Night	4 3 1 4 4 3 4 4 6% 8% 60%	2178
April	1st to 10th	Night	3 2 1 3 3 2 4 5% 6% 11% 61%	1980
	11th to 20th	Night	3 2 1 4 4 4 5% 5% 6% 9% 57%	1953
	21st to end	Night	4 3 1 3 3 3 3 5% 6% 10% 58%	1960
May	1st to 10th	Night	3 1 1 2 3 2 4 5% 5% 9% 66%	1702
	11th to 20th	Night	7% 4 2 5% 5% 3 5% 5% 6% 10% 48%	1592
	21st to end	Night	7% 4 3 4 5% 2 5% 6% 6% 10% 47%	1744
June	1st to 10th	Night	13% 7% 3 7% 6% 4 6% 7% 6% 9% 31%	1620
	11th to 20th	Night	5% 5% 3 5% 4 4 6% 7% 7% 12% 44%	1620
	21st to end	Night	5% 4 1 5% 5% 3 6% 7% 8% 15% 41%	1620
July	1st to 10th	Night	4 3 2 4 4 4 6% 5% 9% 15% 45%	1620
	11th to 20th	Night	2 2 1 4 5% 3 6% 7% 8% 17% 45%	1620
	21st to end	Night	2 3 2 4 4 4 6% 6% 9% 16% 46%	1852
August	1st to 10th	Night	2 3 2 4 5% 4 7% 8% 10% 15% 40%	1790
	11th to 20th	Night	2 2 2 5% 6% 3 7% 7% 9% 15% 42%	1795
	21st to end	Night	6% 5% 3 6% 6% 5% 7% 7% 10% 14% 30%	2178
September	1st to 10th	Night	4 4 2 4 6% 4 7% 8% 10% 14% 36%	1980
	11th to 20th	Night	5% 6% 3 6% 8% 5% 6% 8% 9% 13% 30%	1980
	21st to end	Night	8% 6% 3 6% 8% 4 7% 6% 7% 14% 30%	1980
October	1st to 10th	Night	7% 6% 3 7% 7% 5% 7% 6% 9% 11% 30%	1980
	11th to 20th	Night	8% 5% 2 6% 6% 4 5% 8% 8% 10% 37%	2038
	21st to end	Night	11% 7% 3 6% 7% 3 5% 7% 7% 10% 35%	2376
November	1st to 10th	Night	9% 4 2 4 5% 3 5% 6% 7% 11% 44%	2221
	11th to 20th	Night	9% 5% 2 6% 5% 3 5% 5% 7% 10% 44%	2280
	21st to end	Night	6% 5% 2 5% 4 4 5% 6% 6% 10% 47%	2312
December	1st to 10th	Night	8% 5% 2 5% 5% 3 4 6% 6% 8% 47%	2470
	11th to 20th	Night	8% 4 2 4 4 3 5% 7% 8% 12% 43%	3042
	21st to end	Night	9% 5% 3 6% 6% 4 6% 6% 7% 11% 36%	4532

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	30% 7% 20% 24% 15% 3	1707
	11th to 20th	Day	39% 6% 15% 23% 14% 3	1773
	21st to end	Day	35% 6% 14% 24% 18% 3	1980
February	1st to 10th	Day	32% 5% 15% 29% 17% 2	1800
	11th to 20th	Day	23% 5% 14% 27% 23% 7%	1758
	21st to end	Day	19% 6% 12% 31% 26% 5%	1542
March	1st to 10th	Day	20% 5% 13% 37% 22% 3	1980
	11th to 20th	Day	21% 6% 16% 36% 17% 4	1980
	21st to end	Day	17% 4 17% 35% 24% 3	2178
April	1st to 10th	Day	16% 5% 21% 43% 12% 3	1980
	11th to 20th	Day	19% 6% 23% 32% 17% 2	1956
	21st to end	Day	18% 6% 17% 39% 19% 2	1998
May	1st to 10th	Day	13% 4 20% 35% 24% 4	2270
	11th to 20th	Day	30% 7% 24% 27% 11% 1	2305
	21st to end	Day	32% 7% 16% 29% 15%	2531
June	1st to 10th	Day	42% 9% 25% 20% 3	2340
	11th to 20th	Day	36% 14% 34% 15% 1	2340
	21st to end	Day	33% 12% 39% 14% 1	2340
July	1st to 10th	Day	32% 15% 42% 10%	2275
	11th to 20th	Day	29% 15% 40% 15% 1	2271
	21st to end	Day	27% 15% 39% 18%	2320
August	1st to 10th	Day	28% 18% 36% 17% 1	2136
	11th to 20th	Day	32% 14% 40% 14%	2085
	21st to end	Day	40% 16% 34% 10%	2178
September	1st to 10th	Day	38% 15% 35% 12% 1	1980
	11th to 20th	Day	38% 15% 31% 13% 3	1980
	21st to end	Day	43% 14% 24% 15% 4 1	1980
October	1st to 10th	Day	38% 13% 22% 17% 8% 2	1980
	11th to 20th	Day	39% 10% 19% 19% 11% 2	1920
	21st to end	Day	38% 7% 15% 22% 15% 3	1980
November	1st to 10th	Day	33% 8% 11% 27% 18% 3	1857
	11th to 20th	Day	35% 6% 15% 24% 17% 3	1900
	21st to end	Day	30% 7% 17% 22% 22% 2	1863
December	1st to 10th	Day	30% 6% 13% 33% 17% 1	1710
	11th to 20th	Day	28% 7% 13% 27% 22% 2	2150
	21st to end	Day	39% 7% 18% 20% 15% 1	3124
January	1st to 10th	Night	33% 6% 16% 28% 13% 3	2459
	11th to 20th	Night	38% 6% 16% 22% 15% 3	2227
	21st to end	Night	35% 6% 14% 23% 18% 3	2376
February	1st to 10th	Night	35% 6% 14% 26% 17% 2	2160
	11th to 20th	Night	26% 5% 11% 25% 25% 8%	2099
	21st to end	Night	21% 5% 10% 28% 29% 7%	1711
March	1st to 10th	Night	21% 5% 12% 34% 23% 4	1980
	11th to 20th	Night	22% 5% 17% 33% 21% 3	1980
	21st to end	Night	21% 5% 13% 31% 24% 5%	2178
April	1st to 10th	Night	18% 6% 19% 41% 14% 2	1980
	11th to 20th	Night	23% 5% 19% 32% 17% 3	1953
	21st to end	Night	22% 6% 14% 34% 20% 4	1960
May	1st to 10th	Night	16% 5% 17% 35% 24% 3	1702
	11th to 20th	Night	31% 6% 21% 27% 13% 1	1593
	21st to end	Night	31% 8% 16% 29% 15% 1	1745
June	1st to 10th	Night	47% 8% 21% 20% 3	1620
	11th to 20th	Night	33% 12% 37% 17% 2	1620
	21st to end	Night	29% 13% 38% 18% 2	1620
July	1st to 10th	Night	26% 13% 44% 17%	1575
	11th to 20th	Night	23% 11% 44% 21% 1	1566
	21st to end	Night	23% 14% 41% 22% 1	1749
August	1st to 10th	Night	27% 13% 41% 18% 1	1778
	11th to 20th	Night	28% 14% 43% 15% 1	1795
	21st to end	Night	40% 13% 35% 12%	2178
September	1st to 10th	Night	33% 17% 35% 14% 1	1980
	11th to 20th	Night	41% 12% 30% 13% 3	1980
	21st to end	Night	43% 12% 25% 17% 3	1980
October	1st to 10th	Night	43% 11% 20% 17% 8% 2	1980
	11th to 20th	Night	39% 8% 18% 23% 10% 2	2038
	21st to end	Night	42% 6% 12% 23% 14% 4	2376
November	1st to 10th	Night	31% 7% 14% 25% 18% 4	2221
	11th to 20th	Night	34% 7% 14% 25% 18% 3	2280
	21st to end	Night	31% 6% 13% 26% 22% 2	2312
December	1st to 10th	Night	31% 7% 15% 31% 15% 1	2470
	11th to 20th	Night	30% 7% 12% 29% 20% 2	3044
	21st to end	Night	39% 7% 19% 19% 15% 1	4532

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
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	8% 3 14% 38% 34% 3	270
	11th to 20th	Day	11% 4 16% 36% 29% 4	246
	21st to end	Day	14% 6% 17% 39% 23% 2	264
February	1st to 10th	Day	7% 3 12% 38% 36% 4	240
	11th to 20th	Day	5% 1 7% 33% 44% 10%	240
	21st to end	Day	5% 3 11% 31% 42% 9%	260
March	1st to 10th	Day	6% 2 15% 43% 31% 4	420
	11th to 20th	Day	7% 1 9% 39% 40% 5%	420
	21st to end	Day	5% 2 8% 38% 41% 6%	462
April	1st to 10th	Day	3 1 6% 40% 45% 4	420
	11th to 20th	Day	3 2 8% 42% 40% 5%	412
	21st to end	Day	5% 1 4 34% 52% 5%	420
May	1st to 10th	Day	2 2 27% 55% 13%	423
	11th to 20th	Day	10% 1 3 21% 47% 17%	447
	21st to end	Day	8% 2 1 14% 50% 24%	485
June	1st to 10th	Day	16% 2 3 12% 37% 31%	450
	11th to 20th	Day	8% 2 2 6% 32% 50%	450
	21st to end	Day	5% 2 4 20% 70%	450
July	1st to 10th	Day	4 1 2 20% 72%	445
	11th to 20th	Day	2 2 2 22% 71%	444
	21st to end	Day	6% 1 2 25% 66%	488
August	1st to 10th	Day	4 1 1 1 27% 66%	446
	11th to 20th	Day	4 1 1 4 26% 66%	439
	21st to end	Day	7% 2 1 6% 29% 55%	495
September	1st to 10th	Day	6% 2 1 3 28% 60%	450
	11th to 20th	Day	6% 1 1 7% 22% 62%	450
	21st to end	Day	11% 2 1 7% 29% 50%	450
October	1st to 10th	Day	8% 2 4 14% 48% 24%	450
	11th to 20th	Day	9% 1 5% 18% 46% 21%	450
	21st to end	Day	9% 2 7% 22% 42% 18%	495
November	1st to 10th	Day	7% 3 8% 26% 44% 12%	455
	11th to 20th	Day	10% 2 9% 33% 39% 7%	460
	21st to end	Day	7% 2 9% 32% 41% 9%	423
December	1st to 10th	Day	10% 2 12% 23% 46% 8%	270
	11th to 20th	Day	8% 1 11% 29% 43% 7%	270
	21st to end	Day	7% 2 14% 32% 37% 7%	297
January	1st to 10th	Night	10% 3 11% 34% 37% 5%	760
	11th to 20th	Night	10% 3 14% 40% 30% 3	729
	21st to end	Night	10% 4 16% 43% 26% 2	792
February	1st to 10th	Night	10% 3 17% 36% 32% 2	720
	11th to 20th	Night	7% 2 14% 36% 37% 4	703
	21st to end	Night	6% 2 8% 33% 47% 4	592
March	1st to 10th	Night	4 2 14% 41% 35% 3	720
	11th to 20th	Night	6% 1 10% 42% 36% 5%	720
	21st to end	Night	5% 1 9% 41% 39% 5%	792
April	1st to 10th	Night	3 1 6% 43% 43% 4	720
	11th to 20th	Night	3 1 8% 45% 37% 5%	711
	21st to end	Night	5% 1 5% 39% 44% 5%	720
May	1st to 10th	Night	4 1 1 35% 48% 11%	622
	11th to 20th	Night	9% 2 3 29% 47% 10%	531
	21st to end	Night	8% 2 3 20% 53% 15%	584
June	1st to 10th	Night	16% 3 2 15% 41% 23%	540
	11th to 20th	Night	6% 2 1 7% 43% 42%	540
	21st to end	Night	6% 1 1 4 31% 57%	540
July	1st to 10th	Night	5% 1 3 32% 59%	525
	11th to 20th	Night	2 2 29% 66%	522
	21st to end	Night	3 1 3 29% 64%	591
August	1st to 10th	Night	4 1 4 35% 56%	537
	11th to 20th	Night	3 1 4 32% 60%	553
	21st to end	Night	8% 2 2 8% 31% 50%	792
September	1st to 10th	Night	5% 1 1 5% 32% 56%	720
	11th to 20th	Night	9% 2 1 6% 31% 53%	720
	21st to end	Night	11% 2 3 8% 35% 41%	720
October	1st to 10th	Night	10% 2 2 18% 45% 24%	720
	11th to 20th	Night	10% 3 2 18% 43% 25%	720
	21st to end	Night	13% 3 7% 24% 39% 14%	792
November	1st to 10th	Night	9% 2 10% 29% 42% 9%	740
	11th to 20th	Night	11% 2 8% 29% 41% 9%	760
	21st to end	Night	8% 2 9% 35% 41% 5%	760
December	1st to 10th	Night	10% 2 9% 32% 41% 6%	760
	11th to 20th	Night	9% 2 10% 31% 41% 6%	760
	21st to end	Night	8% 3 13% 32% 36% 8%	836

Page generated at 2024-01-10 01:25:06. Version ac07

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