Jacksonville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Jacksonville clear sky chart from 2005-11-06 to 2026-04-17.

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	12% 6% 2 6% 5% 5% 5% 4 6% 8% 40%	130710
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 44%	131424
Transparency	Day	39% 8% 13% 19% 16% 5%	134309
	Night	37% 7% 13% 19% 18% 6%	135895
Seeing	Day	16% 13% 28% 25% 13% 5%	17393
	Night	15% 10% 27% 30% 15% 2	27588

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% 5% 2 5% 3 3 3 3 4 5% 56%	5258
	11th to 20th	Day	12% 5% 2 5% 3 3 3 3 4 5% 56%	5280
	21st to end	Day	16% 10% 4 7% 4 4 4 3 5% 5% 39%	5780
February	1st to 10th	Day	15% 7% 2 6% 4 5% 4 3 5% 6% 42%	1890
	11th to 20th	Day	19% 6% 3 6% 3 3 3 2 4 6% 44%	1988
	21st to end	Day	15% 6% 3 7% 4 3 5% 4 5% 7% 41%	1780
March	1st to 10th	Day	22% 8% 2 6% 4 3 4 4 5% 6% 37%	5045
	11th to 20th	Day	10% 4 2 4 4 4 4 4 5% 7% 54%	5090
	21st to end	Day	13% 5% 2 5% 3 4 3 3 5% 6% 51%	5586
April	1st to 10th	Day	11% 6% 2 4 4 3 3 3 5% 6% 53%	2520
	11th to 20th	Day	9% 4 2 5% 4 3 5% 4 6% 8% 52%	2446
	21st to end	Day	10% 4 1 6% 4 4 4 4 6% 7% 50%	2400
May	1st to 10th	Day	8% 6% 2 7% 5% 6% 6% 5% 7% 10% 38%	5405
	11th to 20th	Day	18% 8% 3 8% 5% 5% 5% 5% 7% 9% 29%	5813
	21st to end	Day	10% 6% 2 7% 4 5% 5% 4 7% 9% 39%	6433
June	1st to 10th	Day	12% 6% 3 8% 6% 5% 6% 5% 8% 9% 35%	2739
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 6% 9% 12% 38%	2800
	21st to end	Day	8% 5% 2 6% 6% 7% 7% 6% 9% 12% 33%	2610
July	1st to 10th	Day	8% 6% 3 8% 6% 6% 7% 6% 9% 13% 28%	5900
	11th to 20th	Day	7% 6% 3 9% 7% 8% 8% 8% 9% 13% 23%	5900
	21st to end	Day	8% 8% 3 9% 7% 7% 7% 6% 9% 11% 24%	6424
August	1st to 10th	Day	22% 12% 4 8% 5% 5% 5% 5% 7% 9% 19%	4212
	11th to 20th	Day	10% 6% 3 9% 5% 6% 6% 5% 7% 10% 33%	3850
	21st to end	Day	7% 6% 2 6% 5% 5% 6% 5% 7% 10% 40%	4312
September	1st to 10th	Day	10% 7% 2 7% 5% 4 5% 5% 8% 10% 36%	2400
	11th to 20th	Day	16% 8% 2 7% 5% 5% 5% 5% 6% 8% 34%	2400
	21st to end	Day	17% 8% 3 8% 4 4 4 4 6% 6% 36%	2092
October	1st to 10th	Day	15% 7% 3 6% 5% 3 4 4 4 7% 43%	2000
	11th to 20th	Day	12% 5% 3 5% 4 3 3 2 4 6% 55%	2000
	21st to end	Day	12% 5% 1 5% 3 3 4 3 5% 5% 55%	2200
November	1st to 10th	Day	13% 5% 2 4 3 3 4 3 5% 6% 53%	2057
	11th to 20th	Day	12% 6% 2 4 3 4 3 3 4 6% 52%	2030
	21st to end	Day	11% 5% 2 5% 5% 4 4 2 6% 7% 50%	1853
December	1st to 10th	Day	10% 5% 2 5% 3 4 4 4 5% 6% 52%	2680
	11th to 20th	Day	15% 7% 3 6% 4 4 3 3 4 6% 45%	3070
	21st to end	Day	13% 6% 2 6% 3 4 4 4 5% 7% 47%	4467
January	1st to 10th	Night	10% 6% 2 5% 4 3 3 3 4 6% 53%	7635
	11th to 20th	Night	11% 5% 2 5% 3 3 4 3 5% 6% 53%	7680
	21st to end	Night	16% 9% 2 7% 4 4 4 3 4 5% 42%	8401
February	1st to 10th	Night	19% 6% 2 4 3 4 4 3 4 6% 44%	2730
	11th to 20th	Night	19% 8% 3 6% 4 3 3 3 6% 6% 39%	2515
	21st to end	Night	16% 6% 2 6% 4 4 4 4 5% 6% 42%	2022
March	1st to 10th	Night	19% 9% 3 6% 4 4 3 3 4 5% 39%	5028
	11th to 20th	Night	14% 5% 2 5% 3 3 4 3 6% 6% 48%	5090
	21st to end	Night	13% 5% 2 5% 3 3 3 3 5% 6% 51%	5588
April	1st to 10th	Night	11% 6% 2 5% 4 4 4 3 6% 5% 49%	2100
	11th to 20th	Night	10% 5% 2 5% 3 4 4 4 5% 7% 51%	2036
	21st to end	Night	8% 4 1 4 4 5% 4 4 6% 8% 53%	2000
May	1st to 10th	Night	8% 6% 3 7% 6% 5% 6% 5% 7% 10% 39%	4490
	11th to 20th	Night	16% 7% 3 8% 5% 4 5% 4 6% 8% 35%	4108
	21st to end	Night	13% 6% 2 7% 5% 5% 4 4 5% 9% 39%	4421
June	1st to 10th	Night	9% 7% 2 8% 5% 5% 5% 4 7% 9% 38%	1650
	11th to 20th	Night	8% 5% 2 6% 4 5% 4 5% 7% 11% 43%	1600
	21st to end	Night	9% 7% 2 6% 5% 4 5% 4 7% 12% 39%	1775
July	1st to 10th	Night	7% 5% 2 8% 6% 6% 6% 6% 8% 13% 33%	4058
	11th to 20th	Night	7% 6% 3 9% 7% 6% 7% 6% 11% 15% 25%	4057
	21st to end	Night	9% 7% 3 9% 6% 6% 7% 7% 9% 12% 27%	4427
August	1st to 10th	Night	17% 11% 4 9% 5% 5% 6% 4 7% 10% 23%	2915
	11th to 20th	Night	8% 6% 3 8% 6% 6% 6% 6% 8% 10% 35%	3188
	21st to end	Night	7% 5% 2 6% 5% 5% 6% 5% 8% 9% 42%	3586
September	1st to 10th	Night	11% 5% 1 6% 4 4 5% 4 7% 9% 44%	2000
	11th to 20th	Night	14% 6% 3 7% 5% 5% 5% 4 6% 7% 39%	2000
	21st to end	Night	17% 8% 3 8% 4 4 4 3 5% 7% 37%	2301
October	1st to 10th	Night	14% 6% 2 5% 4 4 3 3 4 6% 48%	2400
	11th to 20th	Night	11% 5% 2 5% 3 3 3 3 4 5% 55%	2400
	21st to end	Night	12% 5% 2 5% 3 4 3 3 4 6% 55%	2640
November	1st to 10th	Night	12% 6% 2 4 3 3 4 3 5% 6% 52%	2461
	11th to 20th	Night	13% 7% 3 5% 4 3 3 2 4 6% 49%	2586
	21st to end	Night	11% 6% 2 5% 4 4 3 4 4 8% 51%	2762
December	1st to 10th	Night	11% 6% 2 5% 3 3 2 3 4 6% 54%	4720
	11th to 20th	Night	15% 6% 3 6% 5% 3 4 4 5% 7% 43%	5345
	21st to end	Night	13% 5% 2 6% 3 4 3 3 5% 7% 49%	6709

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% 4 11% 21% 26% 7%	5259
	11th to 20th	Day	32% 3 5% 16% 32% 12%	5280
	21st to end	Day	48% 4 6% 15% 17% 10%	5780
February	1st to 10th	Day	42% 4 10% 20% 18% 6%	1890
	11th to 20th	Day	44% 4 7% 16% 22% 7%	1997
	21st to end	Day	41% 6% 9% 19% 17% 8%	1780
March	1st to 10th	Day	47% 5% 9% 13% 18% 8%	5045
	11th to 20th	Day	30% 5% 9% 16% 25% 15%	5090
	21st to end	Day	35% 4 10% 22% 20% 8%	5586
April	1st to 10th	Day	31% 6% 10% 23% 23% 7%	2520
	11th to 20th	Day	30% 6% 12% 26% 18% 8%	2446
	21st to end	Day	31% 7% 15% 23% 21% 4	2400
May	1st to 10th	Day	37% 11% 20% 23% 8% 1	5437
	11th to 20th	Day	49% 9% 14% 18% 10%	5817
	21st to end	Day	37% 10% 14% 24% 14% 2	6447
June	1st to 10th	Day	42% 10% 15% 20% 11% 1	2739
	11th to 20th	Day	35% 13% 20% 21% 10% 1	2800
	21st to end	Day	39% 13% 19% 22% 8% 1	2610
July	1st to 10th	Day	41% 14% 27% 15% 4	5835
	11th to 20th	Day	45% 17% 26% 9% 3	5831
	21st to end	Day	46% 13% 18% 17% 5%	6240
August	1st to 10th	Day	60% 11% 18% 9% 3	4199
	11th to 20th	Day	43% 12% 15% 21% 10%	3886
	21st to end	Day	36% 10% 18% 28% 8% 1	4312
September	1st to 10th	Day	40% 13% 16% 15% 13% 4	2400
	11th to 20th	Day	46% 9% 11% 17% 14% 3	2400
	21st to end	Day	46% 7% 12% 17% 14% 3	2092
October	1st to 10th	Day	38% 5% 8% 20% 23% 5%	3260
	11th to 20th	Day	23% 3 6% 19% 24% 26%	3240
	21st to end	Day	27% 5% 7% 23% 29% 10%	3538
November	1st to 10th	Day	32% 6% 9% 19% 27% 8%	2057
	11th to 20th	Day	35% 4 8% 19% 25% 9%	2030
	21st to end	Day	35% 5% 8% 22% 24% 7%	1853
December	1st to 10th	Day	33% 5% 8% 18% 25% 11%	2680
	11th to 20th	Day	40% 5% 10% 18% 20% 7%	3066
	21st to end	Day	36% 5% 13% 25% 18% 2	4467
January	1st to 10th	Night	32% 3 11% 21% 27% 6%	7636
	11th to 20th	Night	32% 4 7% 15% 32% 10%	7680
	21st to end	Night	44% 4 6% 16% 20% 9%	8401
February	1st to 10th	Night	41% 4 10% 17% 21% 6%	2730
	11th to 20th	Night	45% 4 9% 16% 19% 6%	2517
	21st to end	Night	42% 5% 10% 15% 19% 8%	2022
March	1st to 10th	Night	47% 5% 7% 14% 20% 6%	5028
	11th to 20th	Night	35% 6% 9% 12% 23% 16%	5090
	21st to end	Night	35% 4 12% 24% 20% 5%	5588
April	1st to 10th	Night	35% 5% 13% 18% 22% 7%	2100
	11th to 20th	Night	32% 6% 13% 24% 18% 7%	2036
	21st to end	Night	28% 8% 14% 28% 18% 4	2000
May	1st to 10th	Night	37% 10% 21% 22% 8% 1	4520
	11th to 20th	Night	46% 8% 16% 21% 10%	4109
	21st to end	Night	39% 9% 17% 21% 13% 1	4429
June	1st to 10th	Night	41% 8% 17% 24% 10% 1	1650
	11th to 20th	Night	34% 10% 20% 27% 9% 1	1600
	21st to end	Night	37% 10% 20% 25% 8% 1	1775
July	1st to 10th	Night	39% 13% 28% 17% 3	4015
	11th to 20th	Night	43% 15% 30% 10% 3	4006
	21st to end	Night	43% 16% 17% 18% 5%	4297
August	1st to 10th	Night	54% 12% 20% 12% 2	2904
	11th to 20th	Night	39% 14% 19% 20% 8%	3218
	21st to end	Night	33% 11% 17% 31% 8% 1	3586
September	1st to 10th	Night	36% 11% 19% 18% 13% 3	2000
	11th to 20th	Night	43% 9% 12% 19% 14% 3	2000
	21st to end	Night	46% 8% 13% 18% 14% 2	2301
October	1st to 10th	Night	41% 6% 7% 18% 23% 4	3920
	11th to 20th	Night	21% 3 6% 17% 21% 32%	3899
	21st to end	Night	25% 4 8% 25% 29% 10%	4252
November	1st to 10th	Night	33% 6% 9% 18% 26% 8%	2461
	11th to 20th	Night	37% 4 8% 16% 26% 8%	2586
	21st to end	Night	33% 5% 8% 23% 24% 7%	2762
December	1st to 10th	Night	32% 4 8% 13% 31% 12%	4720
	11th to 20th	Night	41% 5% 14% 15% 18% 7%	5348
	21st to end	Night	35% 5% 12% 25% 20% 3	6709

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	21% 28% 37% 11% 3	330
	11th to 20th	Day	19% 27% 39% 12% 2	330
	21st to end	Day	23% 28% 34% 13% 2	363
February	1st to 10th	Day	25% 20% 40% 13% 3	330
	11th to 20th	Day	31% 25% 29% 13% 2	476
	21st to end	Day	23% 24% 33% 15% 4	446
March	1st to 10th	Day	21% 19% 35% 18% 6%	540
	11th to 20th	Day	22% 24% 35% 13% 5% 1	540
	21st to end	Day	19% 20% 40% 13% 7% 1	594
April	1st to 10th	Day	21% 21% 32% 17% 8% 1	540
	11th to 20th	Day	14% 18% 34% 21% 8% 4	516
	21st to end	Day	13% 14% 33% 26% 12% 3	500
May	1st to 10th	Day	12% 19% 34% 21% 10% 3	503
	11th to 20th	Day	18% 11% 30% 28% 11% 3	527
	21st to end	Day	16% 8% 23% 29% 17% 7%	573
June	1st to 10th	Day	11% 7% 30% 33% 16% 4	530
	11th to 20th	Day	12% 4 22% 35% 18% 9%	530
	21st to end	Day	9% 4 23% 37% 20% 8%	530
July	1st to 10th	Day	11% 2 15% 38% 25% 8%	525
	11th to 20th	Day	9% 3 15% 35% 28% 10%	524
	21st to end	Day	9% 3 19% 38% 22% 8%	576
August	1st to 10th	Day	17% 5% 19% 29% 20% 9%	526
	11th to 20th	Day	13% 4 17% 28% 25% 13%	519
	21st to end	Day	11% 4 17% 31% 23% 13%	583
September	1st to 10th	Day	13% 4 21% 32% 19% 12%	530
	11th to 20th	Day	21% 7% 21% 28% 16% 8%	530
	21st to end	Day	21% 6% 23% 27% 16% 7%	530
October	1st to 10th	Day	17% 7% 26% 27% 17% 7%	530
	11th to 20th	Day	13% 11% 28% 30% 14% 5%	530
	21st to end	Day	14% 12% 28% 26% 16% 4	583
November	1st to 10th	Day	18% 10% 32% 27% 11% 2	535
	11th to 20th	Day	15% 20% 33% 23% 9% 1	502
	21st to end	Day	13% 18% 31% 21% 15% 2	393
December	1st to 10th	Day	19% 22% 36% 17% 5%	220
	11th to 20th	Day	21% 19% 35% 16% 9%	220
	21st to end	Day	19% 20% 36% 16% 7% 1	339
January	1st to 10th	Night	18% 20% 33% 23% 6%	840
	11th to 20th	Night	17% 17% 29% 30% 7%	840
	21st to end	Night	19% 17% 35% 25% 3	924
February	1st to 10th	Night	23% 14% 35% 24% 4	840
	11th to 20th	Night	24% 19% 35% 20% 2	823
	21st to end	Night	20% 18% 32% 24% 5%	692
March	1st to 10th	Night	17% 17% 36% 25% 5%	840
	11th to 20th	Night	19% 15% 37% 23% 6%	840
	21st to end	Night	17% 15% 37% 24% 7%	924
April	1st to 10th	Night	15% 17% 35% 26% 7%	840
	11th to 20th	Night	13% 13% 35% 28% 11% 1	816
	21st to end	Night	10% 10% 38% 33% 9% 1	800
May	1st to 10th	Night	11% 12% 36% 32% 9% 1	800
	11th to 20th	Night	17% 8% 26% 36% 12%	628
	21st to end	Night	11% 4 17% 35% 28% 4	650
June	1st to 10th	Night	11% 3 22% 43% 18% 3	450
	11th to 20th	Night	10% 3 19% 41% 24% 4	400
	21st to end	Night	12% 3 15% 41% 25% 3	575
July	1st to 10th	Night	8% 2 13% 41% 32% 5%	585
	11th to 20th	Night	7% 2 10% 36% 36% 8%	582
	21st to end	Night	8% 2 13% 40% 32% 4	657
August	1st to 10th	Night	12% 3 14% 32% 33% 6%	597
	11th to 20th	Night	10% 2 13% 39% 29% 7%	781
	21st to end	Night	13% 2 14% 32% 31% 8%	880
September	1st to 10th	Night	14% 3 15% 32% 30% 7%	800
	11th to 20th	Night	17% 2 18% 36% 22% 5%	800
	21st to end	Night	21% 4 19% 29% 23% 4	800
October	1st to 10th	Night	17% 6% 21% 30% 21% 5%	800
	11th to 20th	Night	14% 7% 28% 31% 18% 2	800
	21st to end	Night	14% 8% 25% 31% 19% 3	880
November	1st to 10th	Night	14% 9% 29% 33% 14% 2	820
	11th to 20th	Night	18% 13% 31% 26% 11% 2	840
	21st to end	Night	14% 13% 30% 29% 13% 1	840
December	1st to 10th	Night	21% 14% 28% 29% 7% 1	840
	11th to 20th	Night	18% 13% 29% 30% 10% 1	840
	21st to end	Night	18% 14% 30% 30% 7% 1	924

Page generated at 2026-04-14 02:44:27. Version ac07

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