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 2024-11-08.

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% 4 5% 5% 5% 8% 12% 44%	100666
	Night	6% 4 2 5% 4 4 5% 5% 8% 11% 44%	98391
Transparency	Day	30% 9% 25% 25% 10% 1	104525
	Night	32% 8% 23% 24% 12% 2	102672
Seeing	Day	7% 2 6% 21% 36% 29%	15612
	Night	7% 2 7% 26% 38% 21%	25660

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	11% 6% 3 6% 5% 5% 6% 4 8% 11% 36%	2836
	11th to 20th	Day	16% 8% 3 9% 6% 6% 7% 5% 7% 7% 27%	3073
	21st to end	Day	8% 7% 3 7% 5% 6% 7% 5% 7% 9% 36%	3476
February	1st to 10th	Day	8% 6% 2 5% 4 5% 4 4 6% 10% 46%	1900
	11th to 20th	Day	7% 3 2 4 3 3 4 3 6% 9% 56%	1848
	21st to end	Day	5% 2 1 4 3 3 3 3 6% 10% 61%	1636
March	1st to 10th	Day	5% 3 1 4 4 4 6% 4 8% 11% 48%	3435
	11th to 20th	Day	3 2 1 3 3 3 4 4 7% 11% 60%	3480
	21st to end	Day	7% 4 1 4 2 3 3 3 5% 8% 59%	3815
April	1st to 10th	Day	2 2 1 2 3 3 3 4 7% 11% 62%	2090
	11th to 20th	Day	3 3 1 5% 3 3 4 3 6% 9% 59%	2066
	21st to end	Day	5% 3 1 3 2 3 4 4 7% 9% 60%	2109
May	1st to 10th	Day	2 1 1 2 2 2 2 2 4 9% 74%	3972
	11th to 20th	Day	6% 3 1 3 3 3 4 4 6% 10% 58%	4081
	21st to end	Day	5% 3 1 4 3 3 3 3 4 8% 63%	4476
June	1st to 10th	Day	13% 6% 2 7% 4 5% 5% 5% 7% 12% 33%	2470
	11th to 20th	Day	7% 5% 3 6% 6% 6% 6% 5% 8% 13% 34%	2470
	21st to end	Day	6% 5% 2 6% 5% 4 5% 5% 9% 14% 39%	2470
July	1st to 10th	Day	3 4 1 6% 4 5% 6% 6% 10% 17% 36%	4120
	11th to 20th	Day	1 2 1 4 5% 5% 6% 6% 10% 17% 43%	4120
	21st to end	Day	2 2 1 4 4 5% 6% 6% 11% 16% 43%	4310
August	1st to 10th	Day	2 2 1 5% 5% 8% 8% 8% 12% 17% 32%	3785
	11th to 20th	Day	2 2 2 6% 5% 8% 9% 7% 11% 16% 33%	3647
	21st to end	Day	4 3 1 5% 6% 6% 9% 7% 12% 18% 28%	3828
September	1st to 10th	Day	5% 5% 2 7% 5% 7% 7% 7% 10% 14% 30%	2090
	11th to 20th	Day	4 5% 2 8% 5% 7% 7% 7% 10% 14% 31%	2090
	21st to end	Day	9% 7% 3 7% 7% 6% 8% 6% 7% 12% 29%	2090
October	1st to 10th	Day	7% 6% 3 7% 6% 5% 7% 6% 11% 13% 31%	2090
	11th to 20th	Day	9% 6% 3 7% 5% 5% 7% 5% 8% 11% 33%	2026
	21st to end	Day	9% 6% 3 6% 5% 5% 6% 4 7% 11% 39%	2090
November	1st to 10th	Day	8% 5% 2 6% 4 4 5% 4 8% 11% 42%	1927
	11th to 20th	Day	8% 5% 2 5% 5% 5% 6% 5% 8% 9% 42%	1900
	21st to end	Day	7% 5% 2 5% 4 4 5% 5% 9% 11% 44%	1863
December	1st to 10th	Day	8% 5% 2 5% 4 4 4 5% 8% 9% 47%	1710
	11th to 20th	Day	8% 5% 1 5% 3 4 5% 5% 8% 12% 44%	2153
	21st to end	Day	9% 6% 2 7% 5% 5% 6% 5% 7% 12% 36%	3124
January	1st to 10th	Night	9% 6% 2 7% 6% 5% 5% 4 7% 9% 40%	4109
	11th to 20th	Night	17% 9% 4 9% 6% 5% 6% 5% 7% 7% 26%	3882
	21st to end	Night	8% 7% 3 8% 6% 5% 5% 5% 7% 8% 37%	4180
February	1st to 10th	Night	9% 5% 2 5% 4 5% 4 4 7% 8% 46%	2280
	11th to 20th	Night	8% 4 1 4 4 4 3 4 5% 7% 55%	2218
	21st to end	Night	4 3 1 3 3 3 4 4 5% 8% 61%	1815
March	1st to 10th	Night	5% 5% 2 7% 4 6% 5% 5% 7% 9% 44%	3418
	11th to 20th	Night	4 3 1 4 3 3 4 3 6% 10% 59%	3480
	21st to end	Night	7% 3 1 4 3 3 4 4 6% 9% 56%	3817
April	1st to 10th	Night	3 2 1 3 2 3 4 4 6% 10% 61%	2090
	11th to 20th	Night	3 3 1 4 4 5% 4 3 6% 9% 57%	2063
	21st to end	Night	4 3 1 3 3 3 3 4 6% 10% 58%	2068
May	1st to 10th	Night	2 1 1 2 2 2 2 3 4 8% 74%	2948
	11th to 20th	Night	5% 3 1 5% 4 4 4 4 5% 9% 54%	2812
	21st to end	Night	4 4 1 4 3 3 4 3 5% 8% 61%	3079
June	1st to 10th	Night	12% 8% 3 7% 5% 5% 5% 6% 7% 9% 33%	1710
	11th to 20th	Night	6% 6% 2 6% 4 5% 6% 5% 7% 12% 42%	1710
	21st to end	Night	5% 4 1 5% 5% 4 6% 6% 9% 14% 41%	1710
July	1st to 10th	Night	3 3 1 3 4 4 6% 6% 11% 19% 41%	2840
	11th to 20th	Night	1 2 1 4 4 4 5% 5% 8% 16% 51%	2840
	21st to end	Night	1 2 1 3 3 4 6% 4 10% 20% 46%	3235
August	1st to 10th	Night	2 2 1 4 4 5% 8% 7% 11% 17% 37%	3144
	11th to 20th	Night	1 1 1 4 4 5% 7% 6% 12% 20% 38%	3147
	21st to end	Night	4 3 2 4 4 5% 7% 7% 12% 18% 35%	3828
September	1st to 10th	Night	4 4 2 5% 5% 6% 7% 7% 11% 14% 36%	2090
	11th to 20th	Night	5% 6% 2 8% 7% 7% 6% 6% 9% 13% 31%	2090
	21st to end	Night	8% 6% 3 8% 7% 7% 6% 4 7% 14% 30%	2090
October	1st to 10th	Night	7% 6% 3 8% 6% 7% 7% 6% 9% 11% 30%	2090
	11th to 20th	Night	9% 6% 2 7% 5% 5% 6% 6% 9% 10% 35%	2152
	21st to end	Night	10% 7% 2 7% 5% 5% 5% 5% 8% 10% 34%	2508
November	1st to 10th	Night	8% 4 2 5% 4 4 5% 5% 8% 10% 45%	2312
	11th to 20th	Night	8% 6% 2 6% 5% 3 5% 4 7% 10% 43%	2280
	21st to end	Night	6% 6% 2 5% 4 5% 5% 4 7% 9% 47%	2312
December	1st to 10th	Night	8% 5% 1 5% 4 5% 4 5% 7% 8% 47%	2470
	11th to 20th	Night	8% 5% 2 5% 3 4 5% 6% 8% 12% 43%	3042
	21st to end	Night	8% 6% 3 8% 5% 5% 5% 5% 8% 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	38% 8% 19% 24% 10% 2	2837
	11th to 20th	Day	51% 7% 15% 16% 8% 2	3073
	21st to end	Day	41% 7% 11% 23% 14% 3	3476
February	1st to 10th	Day	31% 5% 14% 29% 17% 3	1900
	11th to 20th	Day	24% 5% 14% 27% 23% 8%	1858
	21st to end	Day	19% 5% 12% 31% 28% 6%	1636
March	1st to 10th	Day	25% 7% 22% 30% 14% 2	3435
	11th to 20th	Day	16% 6% 27% 38% 11% 2	3480
	21st to end	Day	23% 5% 11% 35% 21% 6%	3815
April	1st to 10th	Day	16% 5% 20% 43% 13% 3	2090
	11th to 20th	Day	19% 6% 23% 32% 18% 2	2066
	21st to end	Day	18% 7% 17% 39% 19% 2	2109
May	1st to 10th	Day	9% 4 14% 49% 21% 2	4008
	11th to 20th	Day	21% 7% 20% 44% 8%	4085
	21st to end	Day	20% 6% 13% 48% 13%	4489
June	1st to 10th	Day	41% 9% 26% 21% 3	2470
	11th to 20th	Day	37% 14% 33% 15% 1	2470
	21st to end	Day	33% 12% 40% 13% 1	2470
July	1st to 10th	Day	31% 12% 43% 13%	4055
	11th to 20th	Day	25% 11% 52% 11%	4051
	21st to end	Day	25% 12% 47% 16%	4172
August	1st to 10th	Day	33% 14% 37% 15% 1	3773
	11th to 20th	Day	34% 11% 43% 12%	3683
	21st to end	Day	36% 17% 40% 7%	3828
September	1st to 10th	Day	36% 15% 37% 12%	2090
	11th to 20th	Day	38% 14% 32% 13% 3	2090
	21st to end	Day	42% 13% 24% 16% 5% 1	2090
October	1st to 10th	Day	40% 12% 25% 16% 7% 1	3480
	11th to 20th	Day	47% 10% 20% 15% 7% 1	3344
	21st to end	Day	36% 5% 14% 32% 11% 2	3428
November	1st to 10th	Day	33% 8% 11% 27% 18% 3	1927
	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	38% 6% 15% 27% 13% 2	4109
	11th to 20th	Night	53% 7% 15% 14% 9% 2	3882
	21st to end	Night	42% 6% 11% 21% 19% 2	4180
February	1st to 10th	Night	34% 6% 14% 26% 17% 3	2280
	11th to 20th	Night	26% 6% 11% 24% 25% 8%	2219
	21st to end	Night	20% 5% 10% 28% 29% 8%	1815
March	1st to 10th	Night	33% 7% 15% 28% 15% 2	3418
	11th to 20th	Night	20% 5% 24% 34% 16% 1	3480
	21st to end	Night	23% 6% 11% 30% 22% 7%	3817
April	1st to 10th	Night	17% 6% 18% 41% 15% 3	2090
	11th to 20th	Night	22% 5% 19% 33% 17% 3	2063
	21st to end	Night	21% 6% 14% 34% 22% 4	2068
May	1st to 10th	Night	10% 4 11% 50% 23% 2	2978
	11th to 20th	Night	25% 7% 18% 41% 9% 1	2813
	21st to end	Night	20% 6% 12% 42% 19% 1	3087
June	1st to 10th	Night	45% 8% 21% 23% 4	1710
	11th to 20th	Night	35% 12% 36% 16% 2	1710
	21st to end	Night	29% 13% 39% 17% 2	1710
July	1st to 10th	Night	26% 12% 41% 20%	2795
	11th to 20th	Night	20% 9% 53% 18%	2786
	21st to end	Night	20% 11% 50% 19%	3132
August	1st to 10th	Night	29% 13% 39% 18% 1	3132
	11th to 20th	Night	26% 11% 48% 14%	3177
	21st to end	Night	31% 12% 48% 9%	3828
September	1st to 10th	Night	32% 17% 36% 13% 1	2090
	11th to 20th	Night	40% 12% 31% 13% 3	2090
	21st to end	Night	42% 11% 25% 18% 3	2090
October	1st to 10th	Night	41% 10% 28% 15% 5% 1	3480
	11th to 20th	Night	48% 10% 18% 15% 7% 1	3573
	21st to end	Night	43% 5% 13% 27% 11% 2	4120
November	1st to 10th	Night	31% 7% 14% 25% 19% 4	2312
	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% 37% 34% 3	270
	11th to 20th	Day	12% 5% 17% 35% 27% 4	270
	21st to end	Day	13% 5% 19% 39% 23% 1	297
February	1st to 10th	Day	7% 3 14% 39% 34% 3	270
	11th to 20th	Day	6% 1 10% 34% 40% 9%	270
	21st to end	Day	4 2 12% 32% 41% 8%	291
March	1st to 10th	Day	6% 2 13% 43% 32% 4	460
	11th to 20th	Day	7% 1 9% 40% 39% 5%	460
	21st to end	Day	6% 2 8% 38% 40% 6%	506
April	1st to 10th	Day	3 1 7% 41% 44% 4	460
	11th to 20th	Day	3 2 8% 43% 40% 4	452
	21st to end	Day	4 2 4 34% 51% 5%	460
May	1st to 10th	Day	2 2 27% 56% 13%	463
	11th to 20th	Day	9% 1 3 24% 47% 15%	487
	21st to end	Day	8% 2 1 14% 52% 24%	529
June	1st to 10th	Day	14% 2 3 11% 39% 30%	490
	11th to 20th	Day	10% 2 3 8% 31% 46%	490
	21st to end	Day	4 2 4 21% 69%	490
July	1st to 10th	Day	4 1 2 23% 69%	485
	11th to 20th	Day	2 1 2 21% 72%	484
	21st to end	Day	5% 1 2 26% 66%	532
August	1st to 10th	Day	5% 1 1 1 29% 64%	486
	11th to 20th	Day	4 1 1 3 24% 67%	479
	21st to end	Day	7% 2 1 6% 30% 54%	539
September	1st to 10th	Day	6% 2 1 3 28% 60%	490
	11th to 20th	Day	7% 1 1 6% 23% 62%	490
	21st to end	Day	11% 2 1 8% 29% 49%	490
October	1st to 10th	Day	8% 3 3 13% 47% 25%	490
	11th to 20th	Day	10% 2 5% 18% 44% 20%	490
	21st to end	Day	9% 2 8% 24% 41% 16%	539
November	1st to 10th	Day	7% 3 8% 27% 44% 11%	483
	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% 2 11% 34% 37% 5%	760
	11th to 20th	Night	10% 3 14% 39% 30% 3	760
	21st to end	Night	10% 3 17% 43% 26% 1	836
February	1st to 10th	Night	10% 3 17% 37% 32% 1	760
	11th to 20th	Night	7% 3 14% 36% 36% 4	743
	21st to end	Night	6% 2 9% 33% 46% 4	628
March	1st to 10th	Night	4 3 14% 42% 35% 3	760
	11th to 20th	Night	6% 1 9% 43% 36% 5%	760
	21st to end	Night	5% 1 10% 41% 38% 4	836
April	1st to 10th	Night	3 1 6% 44% 42% 4	760
	11th to 20th	Night	3 1 8% 46% 36% 5%	751
	21st to end	Night	5% 1 5% 41% 44% 4	760
May	1st to 10th	Night	4 1 1 35% 48% 11%	656
	11th to 20th	Night	8% 2 3 30% 47% 9%	561
	21st to end	Night	7% 2 3 19% 54% 14%	617
June	1st to 10th	Night	15% 3 2 16% 42% 22%	570
	11th to 20th	Night	7% 2 1 9% 41% 40%	570
	21st to end	Night	6% 1 1 4 32% 57%	570
July	1st to 10th	Night	4 1 3 34% 57%	555
	11th to 20th	Night	2 1 2 28% 66%	552
	21st to end	Night	3 1 3 30% 63%	624
August	1st to 10th	Night	4 1 1 4 36% 56%	567
	11th to 20th	Night	2 1 4 31% 62%	585
	21st to end	Night	8% 2 2 8% 31% 50%	836
September	1st to 10th	Night	5% 1 1 5% 33% 56%	760
	11th to 20th	Night	8% 2 1 6% 31% 53%	760
	21st to end	Night	10% 2 3 9% 35% 40%	760
October	1st to 10th	Night	10% 2 2 17% 44% 24%	760
	11th to 20th	Night	11% 3 3 18% 42% 24%	760
	21st to end	Night	13% 3 7% 25% 38% 13%	836
November	1st to 10th	Night	9% 2 9% 29% 42% 9%	771
	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 2024-11-05 08:15:47. Version ac07

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