Fort Pickens
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fort Pickens clear sky chart from 2005-11-06 to 2025-07-21.

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 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	10% 5% 2 6% 4 4 5% 4 7% 9% 44%	119962
	Night	10% 6% 2 5% 4 4 4 4 6% 9% 46%	119155
Transparency	Day	33% 8% 16% 20% 16% 7%	123894
	Night	33% 7% 15% 19% 18% 8%	123352
Seeing	Day	11% 3 13% 26% 31% 17%	15449
	Night	11% 4 16% 27% 29% 12%	25367

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	13% 4 2 4 4 4 4 3 5% 6% 52%	4286
	11th to 20th	Day	13% 6% 2 6% 4 4 3 3 5% 7% 47%	4520
	21st to end	Day	21% 7% 2 5% 4 4 4 4 5% 7% 36%	4972
February	1st to 10th	Day	14% 10% 3 6% 5% 4 3 3 4 6% 42%	2000
	11th to 20th	Day	15% 6% 2 6% 4 3 5% 3 5% 8% 43%	1948
	21st to end	Day	14% 7% 3 7% 3 4 4 4 5% 8% 42%	1650
March	1st to 10th	Day	16% 9% 3 6% 4 3 3 3 4 6% 41%	4480
	11th to 20th	Day	9% 5% 2 5% 4 4 4 3 5% 7% 51%	4720
	21st to end	Day	16% 6% 2 7% 4 4 4 4 5% 5% 43%	5829
April	1st to 10th	Day	12% 7% 2 5% 4 4 4 4 5% 7% 47%	2400
	11th to 20th	Day	9% 5% 2 6% 4 4 4 3 6% 8% 48%	2374
	21st to end	Day	6% 4 1 5% 3 4 5% 3 6% 8% 56%	2400
May	1st to 10th	Day	10% 6% 3 6% 4 4 5% 4 7% 10% 40%	5405
	11th to 20th	Day	10% 4 2 6% 4 4 4 4 6% 10% 46%	5805
	21st to end	Day	5% 3 2 5% 4 4 5% 4 7% 12% 51%	6433
June	1st to 10th	Day	7% 5% 2 6% 5% 5% 5% 5% 10% 11% 38%	2600
	11th to 20th	Day	5% 4 2 5% 6% 5% 6% 6% 10% 14% 39%	2600
	21st to end	Day	6% 5% 2 6% 5% 6% 6% 5% 10% 14% 35%	2600
July	1st to 10th	Day	6% 6% 2 7% 5% 6% 6% 6% 9% 15% 32%	4250
	11th to 20th	Day	4 4 2 6% 6% 6% 8% 7% 10% 12% 36%	4025
	21st to end	Day	3 4 2 7% 6% 6% 8% 7% 10% 16% 30%	4118
August	1st to 10th	Day	4 3 1 4 4 4 5% 5% 8% 14% 48%	3785
	11th to 20th	Day	5% 3 2 5% 4 4 5% 5% 9% 12% 46%	3729
	21st to end	Day	6% 4 2 7% 5% 6% 7% 6% 9% 12% 37%	4180
September	1st to 10th	Day	10% 5% 2 5% 4 6% 6% 5% 8% 10% 38%	2237
	11th to 20th	Day	10% 7% 3 6% 4 5% 5% 4 7% 10% 40%	2090
	21st to end	Day	7% 4 2 5% 4 4 5% 4 6% 7% 52%	2090
October	1st to 10th	Day	8% 4 2 4 3 2 4 4 6% 9% 55%	2090
	11th to 20th	Day	7% 4 1 4 3 3 4 2 5% 8% 60%	2090
	21st to end	Day	9% 4 2 6% 4 3 3 3 5% 6% 55%	2125
November	1st to 10th	Day	8% 5% 1 5% 3 3 4 3 5% 6% 56%	1762
	11th to 20th	Day	9% 5% 2 5% 4 4 4 3 4 7% 54%	1800
	21st to end	Day	9% 4 2 6% 4 4 5% 4 6% 7% 48%	1800
December	1st to 10th	Day	12% 6% 3 6% 4 4 3 3 5% 7% 48%	2930
	11th to 20th	Day	12% 7% 3 7% 4 4 3 3 4 5% 48%	3373
	21st to end	Day	16% 8% 3 6% 3 4 3 2 4 6% 45%	4466
January	1st to 10th	Night	12% 6% 2 6% 4 4 4 3 5% 6% 48%	5641
	11th to 20th	Night	17% 8% 3 6% 4 3 3 2 4 6% 43%	5440
	21st to end	Night	16% 8% 2 6% 4 4 4 3 5% 8% 40%	5984
February	1st to 10th	Night	14% 8% 2 5% 4 4 4 3 5% 6% 46%	2400
	11th to 20th	Night	16% 7% 2 5% 4 3 4 4 4 7% 44%	2338
	21st to end	Night	14% 8% 3 6% 4 4 4 4 5% 6% 43%	1980
March	1st to 10th	Night	19% 10% 3 6% 4 3 3 3 5% 6% 38%	5373
	11th to 20th	Night	9% 5% 2 5% 4 4 4 4 6% 8% 50%	5238
	21st to end	Night	13% 5% 2 6% 4 4 4 3 5% 7% 48%	5114
April	1st to 10th	Night	12% 7% 2 5% 4 4 4 4 5% 8% 46%	2000
	11th to 20th	Night	11% 5% 2 5% 4 4 4 3 5% 7% 50%	1975
	21st to end	Night	5% 4 2 3 4 3 4 4 5% 6% 60%	2000
May	1st to 10th	Night	10% 6% 3 6% 5% 5% 5% 4 7% 10% 40%	4490
	11th to 20th	Night	8% 5% 2 6% 3 4 4 4 6% 9% 49%	4083
	21st to end	Night	4 3 2 5% 4 4 5% 4 7% 13% 49%	4421
June	1st to 10th	Night	7% 5% 2 6% 5% 5% 4 4 8% 12% 42%	1800
	11th to 20th	Night	3 3 2 4 5% 5% 6% 5% 9% 11% 49%	1800
	21st to end	Night	5% 5% 2 5% 4 5% 5% 6% 9% 14% 40%	1800
July	1st to 10th	Night	3 3 2 5% 5% 5% 7% 7% 11% 16% 36%	2930
	11th to 20th	Night	2 2 1 4 4 4 5% 5% 9% 15% 49%	3149
	21st to end	Night	2 3 1 5% 6% 5% 8% 7% 13% 17% 34%	3435
August	1st to 10th	Night	3 2 1 4 5% 4 5% 5% 8% 14% 49%	3144
	11th to 20th	Night	4 3 1 4 4 4 4 4 8% 12% 52%	3100
	21st to end	Night	4 5% 2 6% 5% 6% 6% 6% 8% 13% 39%	3476
September	1st to 10th	Night	9% 5% 2 7% 5% 5% 5% 5% 7% 14% 36%	1921
	11th to 20th	Night	10% 6% 2 8% 5% 5% 5% 4 6% 8% 41%	2090
	21st to end	Night	8% 4 2 5% 3 4 5% 3 6% 8% 51%	2090
October	1st to 10th	Night	7% 5% 2 5% 3 4 3 4 6% 9% 52%	2090
	11th to 20th	Night	5% 4 1 3 3 3 4 3 4 7% 62%	2090
	21st to end	Night	9% 5% 2 5% 4 4 4 3 5% 6% 54%	2465
November	1st to 10th	Night	8% 6% 2 4 3 3 3 3 5% 7% 55%	2536
	11th to 20th	Night	11% 6% 2 5% 4 3 4 3 4 6% 53%	2600
	21st to end	Night	10% 5% 2 5% 4 4 3 4 5% 7% 50%	2600
December	1st to 10th	Night	11% 5% 2 6% 3 4 4 4 6% 7% 48%	4250
	11th to 20th	Night	12% 5% 2 5% 3 3 4 3 5% 7% 50%	4822
	21st to end	Night	16% 8% 3 6% 4 4 4 2 4 5% 44%	6490

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	31% 5% 8% 20% 27% 8%	4287
	11th to 20th	Day	37% 5% 7% 17% 26% 8%	4520
	21st to end	Day	47% 4 8% 16% 16% 9%	4972
February	1st to 10th	Day	42% 5% 8% 16% 19% 10%	2000
	11th to 20th	Day	37% 7% 11% 17% 19% 9%	1958
	21st to end	Day	37% 9% 12% 18% 16% 9%	1650
March	1st to 10th	Day	43% 6% 8% 20% 15% 8%	4480
	11th to 20th	Day	29% 7% 11% 15% 24% 13%	4720
	21st to end	Day	40% 6% 12% 20% 15% 7%	5831
April	1st to 10th	Day	35% 7% 13% 18% 19% 8%	2400
	11th to 20th	Day	33% 6% 11% 22% 20% 8%	2374
	21st to end	Day	24% 7% 14% 26% 21% 8%	2400
May	1st to 10th	Day	35% 10% 18% 23% 12% 3	5440
	11th to 20th	Day	31% 6% 20% 29% 13% 1	5809
	21st to end	Day	24% 8% 21% 32% 14% 2	6447
June	1st to 10th	Day	33% 10% 21% 27% 9% 1	2600
	11th to 20th	Day	29% 11% 24% 25% 10% 1	2600
	21st to end	Day	34% 13% 24% 19% 9% 1	2600
July	1st to 10th	Day	37% 12% 38% 11% 2	4185
	11th to 20th	Day	34% 14% 41% 8% 2	3958
	21st to end	Day	34% 18% 32% 13% 2	3987
August	1st to 10th	Day	24% 10% 22% 30% 12% 2	3773
	11th to 20th	Day	26% 10% 24% 27% 12%	3765
	21st to end	Day	36% 12% 26% 16% 9% 2	4179
September	1st to 10th	Day	36% 12% 22% 17% 10% 3	2237
	11th to 20th	Day	37% 11% 16% 17% 14% 5%	2090
	21st to end	Day	28% 9% 13% 21% 21% 7%	2090
October	1st to 10th	Day	30% 5% 8% 14% 17% 26%	3480
	11th to 20th	Day	15% 3 6% 23% 22% 30%	3458
	21st to end	Day	21% 3 6% 14% 38% 17%	3476
November	1st to 10th	Day	28% 4 11% 21% 23% 12%	1762
	11th to 20th	Day	30% 5% 9% 18% 26% 12%	1800
	21st to end	Day	32% 7% 11% 21% 19% 10%	1800
December	1st to 10th	Day	35% 5% 13% 18% 23% 6%	2930
	11th to 20th	Day	40% 4 7% 21% 21% 9%	3370
	21st to end	Day	41% 5% 8% 15% 28% 3	4466
January	1st to 10th	Night	37% 5% 6% 15% 27% 10%	5641
	11th to 20th	Night	43% 5% 6% 14% 28% 5%	5440
	21st to end	Night	44% 4 9% 18% 17% 8%	5984
February	1st to 10th	Night	38% 6% 7% 16% 22% 10%	2400
	11th to 20th	Night	40% 5% 10% 14% 19% 12%	2339
	21st to end	Night	39% 7% 10% 17% 14% 11%	1980
March	1st to 10th	Night	45% 6% 8% 16% 17% 7%	5373
	11th to 20th	Night	29% 7% 12% 16% 20% 16%	5238
	21st to end	Night	35% 5% 12% 21% 16% 11%	5114
April	1st to 10th	Night	35% 7% 14% 15% 19% 11%	2000
	11th to 20th	Night	33% 5% 10% 21% 22% 9%	1975
	21st to end	Night	22% 6% 11% 28% 24% 7%	2000
May	1st to 10th	Night	35% 9% 21% 19% 12% 3	4520
	11th to 20th	Night	30% 7% 19% 29% 14% 1	4084
	21st to end	Night	24% 7% 19% 35% 13% 1	4429
June	1st to 10th	Night	32% 9% 24% 24% 9% 1	1800
	11th to 20th	Night	25% 12% 25% 25% 12% 1	1800
	21st to end	Night	28% 15% 28% 19% 9% 1	1800
July	1st to 10th	Night	32% 13% 39% 13% 3	2885
	11th to 20th	Night	22% 14% 52% 10% 2	3093
	21st to end	Night	29% 22% 33% 14% 2	3325
August	1st to 10th	Night	23% 10% 27% 26% 13% 1	3132
	11th to 20th	Night	24% 9% 27% 33% 7%	3130
	21st to end	Night	34% 12% 24% 18% 9% 2	3476
September	1st to 10th	Night	36% 12% 24% 15% 11% 3	1921
	11th to 20th	Night	40% 9% 16% 16% 14% 5%	2090
	21st to end	Night	28% 8% 15% 23% 19% 7%	2090
October	1st to 10th	Night	35% 6% 7% 13% 17% 22%	3480
	11th to 20th	Night	15% 3 5% 21% 28% 28%	3461
	21st to end	Night	21% 4 5% 12% 44% 15%	4052
November	1st to 10th	Night	29% 4 10% 19% 25% 13%	2536
	11th to 20th	Night	34% 4 6% 19% 26% 11%	2600
	21st to end	Night	33% 6% 11% 19% 21% 12%	2600
December	1st to 10th	Night	35% 4 11% 19% 22% 9%	4250
	11th to 20th	Night	35% 4 8% 23% 20% 10%	4824
	21st to end	Night	42% 5% 6% 18% 26% 4	6490

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	14% 8% 29% 32% 16% 1	300
	11th to 20th	Day	9% 7% 26% 40% 16% 2	300
	21st to end	Day	24% 7% 29% 31% 8% 1	330
February	1st to 10th	Day	17% 8% 23% 33% 17% 2	300
	11th to 20th	Day	18% 5% 26% 39% 11%	300
	21st to end	Day	10% 7% 26% 45% 11% 1	249
March	1st to 10th	Day	12% 7% 30% 36% 15%	300
	11th to 20th	Day	14% 4 25% 36% 20% 1	383
	21st to end	Day	14% 6% 22% 37% 19% 1	550
April	1st to 10th	Day	14% 7% 21% 37% 18% 2	500
	11th to 20th	Day	9% 6% 23% 34% 23% 4	492
	21st to end	Day	7% 3 15% 35% 36% 5%	500
May	1st to 10th	Day	8% 4 11% 38% 33% 6%	503
	11th to 20th	Day	6% 1 9% 33% 40% 11%	527
	21st to end	Day	6% 1 5% 26% 44% 18%	573
June	1st to 10th	Day	9% 2 5% 19% 46% 19%	530
	11th to 20th	Day	7% 1 6% 17% 42% 27%	530
	21st to end	Day	8% 1 3 16% 37% 34%	530
July	1st to 10th	Day	7% 3 3 9% 35% 44%	525
	11th to 20th	Day	5% 1 3 7% 32% 51%	524
	21st to end	Day	5% 1 3 10% 38% 43%	532
August	1st to 10th	Day	7% 1 2 8% 32% 50%	486
	11th to 20th	Day	8% 1 3 8% 33% 47%	479
	21st to end	Day	9% 2 4 14% 38% 34%	539
September	1st to 10th	Day	12% 1 5% 13% 32% 37%	490
	11th to 20th	Day	14% 3 4 16% 43% 20%	490
	21st to end	Day	9% 5% 22% 45% 18%	490
October	1st to 10th	Day	9% 1 11% 32% 39% 7%	490
	11th to 20th	Day	6% 2 11% 31% 35% 14%	490
	21st to end	Day	12% 5% 13% 27% 34% 9%	387
November	1st to 10th	Day	13% 1 10% 30% 41% 5%	300
	11th to 20th	Day	13% 4 18% 33% 28% 5%	300
	21st to end	Day	10% 2 20% 35% 27% 5%	300
December	1st to 10th	Day	16% 4 25% 31% 23% 2	300
	11th to 20th	Day	18% 7% 22% 35% 17% 1	300
	21st to end	Day	21% 5% 18% 36% 18% 2	330
January	1st to 10th	Night	16% 10% 31% 29% 12% 2	800
	11th to 20th	Night	14% 10% 26% 32% 16% 2	800
	21st to end	Night	18% 9% 31% 33% 9%	880
February	1st to 10th	Night	16% 8% 26% 34% 15% 1	800
	11th to 20th	Night	18% 9% 28% 29% 16% 1	783
	21st to end	Night	16% 5% 29% 35% 14%	660
March	1st to 10th	Night	15% 5% 26% 37% 16% 1	800
	11th to 20th	Night	11% 5% 26% 33% 21% 4	800
	21st to end	Night	12% 5% 20% 36% 26% 2	734
April	1st to 10th	Night	13% 6% 20% 37% 22% 2	600
	11th to 20th	Night	12% 4 21% 33% 27% 3	593
	21st to end	Night	5% 3 16% 34% 35% 8%	600
May	1st to 10th	Night	9% 2 13% 34% 35% 7%	600
	11th to 20th	Night	6% 2 10% 32% 38% 12%	591
	21st to end	Night	6% 1 7% 22% 48% 17%	650
June	1st to 10th	Night	9% 1 4 20% 49% 17%	600
	11th to 20th	Night	4 1 3 17% 49% 26%	600
	21st to end	Night	8% 3 13% 47% 29%	600
July	1st to 10th	Night	5% 1 3 10% 43% 39%	585
	11th to 20th	Night	2 1 2 6% 37% 51%	582
	21st to end	Night	3 1 2 7% 44% 43%	624
August	1st to 10th	Night	4 1 8% 38% 48%	567
	11th to 20th	Night	7% 1 3 7% 41% 41%	564
	21st to end	Night	9% 1 6% 12% 42% 30%	627
September	1st to 10th	Night	10% 2 4 14% 40% 30%	591
	11th to 20th	Night	12% 3 7% 20% 43% 16%	760
	21st to end	Night	9% 1 8% 22% 45% 15%	760
October	1st to 10th	Night	10% 1 12% 33% 37% 7%	760
	11th to 20th	Night	8% 3 13% 31% 34% 12%	760
	21st to end	Night	10% 4 17% 31% 33% 4	836
November	1st to 10th	Night	11% 4 18% 35% 26% 6%	780
	11th to 20th	Night	13% 7% 20% 34% 23% 3	800
	21st to end	Night	12% 4 27% 33% 21% 4	800
December	1st to 10th	Night	14% 7% 24% 30% 20% 5%	800
	11th to 20th	Night	17% 7% 25% 30% 20% 2	800
	21st to end	Night	20% 8% 23% 31% 16% 1	880

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