Palmetto State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Palmetto State Park clear sky chart from 2005-11-06 to 2025-12-18.

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% 4 4 4 4 6% 8% 44%	127136
	Night	14% 6% 2 5% 3 3 3 3 5% 7% 48%	124193
Transparency	Day	37% 5% 11% 21% 17% 9%	130891
	Night	35% 5% 11% 20% 17% 11%	128501
Seeing	Day	13% 6% 19% 27% 25% 10%	16233
	Night	15% 6% 24% 36% 17% 2	26172

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	20% 10% 3 6% 3 2 3 2 3 4 44%	4077
	11th to 20th	Day	17% 5% 2 5% 3 3 3 2 4 6% 52%	4080
	21st to end	Day	29% 8% 2 4 2 2 2 2 4 5% 38%	4741
February	1st to 10th	Day	21% 8% 2 5% 3 3 3 3 4 4 43%	2000
	11th to 20th	Day	21% 8% 3 6% 3 3 3 2 4 5% 41%	1949
	21st to end	Day	18% 8% 2 4 4 2 3 3 4 6% 44%	1669
March	1st to 10th	Day	13% 6% 3 7% 4 4 3 3 4 7% 47%	4936
	11th to 20th	Day	13% 6% 3 7% 4 4 3 2 3 5% 49%	4980
	21st to end	Day	18% 9% 3 6% 4 3 3 3 4 5% 43%	5462
April	1st to 10th	Day	14% 8% 2 6% 5% 4 4 4 5% 7% 42%	2200
	11th to 20th	Day	15% 7% 3 7% 5% 4 4 3 5% 5% 42%	2176
	21st to end	Day	14% 8% 2 6% 5% 4 4 4 5% 6% 43%	2490
May	1st to 10th	Day	19% 7% 3 7% 5% 5% 5% 4 6% 7% 33%	5862
	11th to 20th	Day	10% 6% 2 7% 5% 4 5% 4 6% 8% 45%	5862
	21st to end	Day	11% 6% 2 6% 5% 5% 6% 5% 7% 9% 39%	6434
June	1st to 10th	Day	5% 3 1 5% 5% 5% 6% 6% 8% 10% 46%	2600
	11th to 20th	Day	7% 3 1 6% 6% 5% 5% 5% 7% 10% 44%	2600
	21st to end	Day	6% 6% 2 7% 5% 6% 7% 6% 8% 11% 36%	2600
July	1st to 10th	Day	9% 7% 3 7% 6% 5% 6% 4 7% 9% 36%	5900
	11th to 20th	Day	7% 5% 2 6% 5% 5% 6% 6% 8% 13% 38%	5900
	21st to end	Day	8% 6% 2 6% 6% 5% 5% 5% 7% 11% 38%	6422
August	1st to 10th	Day	2 1 3 3 3 4 4 5% 10% 65%	4234
	11th to 20th	Day	3 2 1 4 3 4 5% 5% 8% 13% 51%	3918
	21st to end	Day	5% 4 2 5% 5% 6% 6% 5% 8% 11% 44%	4050
September	1st to 10th	Day	7% 6% 2 8% 6% 5% 5% 4 7% 7% 42%	2200
	11th to 20th	Day	9% 7% 2 7% 5% 5% 5% 4 6% 8% 42%	2200
	21st to end	Day	7% 4 2 5% 4 4 6% 4 7% 9% 48%	2200
October	1st to 10th	Day	6% 3 2 4 4 4 4 4 6% 8% 55%	2200
	11th to 20th	Day	11% 5% 2 4 3 4 4 3 4 7% 52%	2032
	21st to end	Day	10% 5% 2 5% 4 3 4 3 4 5% 56%	2200
November	1st to 10th	Day	12% 8% 2 5% 4 3 4 3 5% 7% 46%	2058
	11th to 20th	Day	11% 6% 2 6% 4 3 3 3 4 6% 52%	2042
	21st to end	Day	17% 8% 3 7% 3 4 3 3 4 6% 43%	1890
December	1st to 10th	Day	28% 9% 2 6% 5% 3 3 2 3 5% 35%	3030
	11th to 20th	Day	16% 8% 3 6% 4 4 4 3 4 5% 43%	3454
	21st to end	Day	14% 7% 2 5% 3 3 3 3 4 4 53%	4488
January	1st to 10th	Night	22% 8% 2 5% 3 2 2 2 3 5% 47%	5888
	11th to 20th	Night	13% 4 2 3 3 3 3 3 3 6% 58%	5900
	21st to end	Night	31% 6% 2 5% 3 3 2 2 3 6% 37%	6278
February	1st to 10th	Night	20% 7% 2 4 4 3 3 3 5% 5% 44%	2400
	11th to 20th	Night	21% 8% 2 4 3 2 2 2 4 6% 46%	2338
	21st to end	Night	22% 6% 3 4 4 3 3 3 5% 5% 43%	1960
March	1st to 10th	Night	17% 9% 2 5% 4 4 5% 3 4 5% 42%	4919
	11th to 20th	Night	17% 8% 2 5% 4 3 3 2 4 5% 47%	4980
	21st to end	Night	19% 10% 3 5% 3 3 3 2 4 5% 43%	5467
April	1st to 10th	Night	13% 7% 2 6% 4 4 4 3 6% 7% 45%	2200
	11th to 20th	Night	15% 8% 2 5% 4 3 3 3 5% 7% 44%	2173
	21st to end	Night	14% 8% 3 6% 5% 3 3 4 4 7% 43%	1901
May	1st to 10th	Night	25% 9% 3 7% 4 3 4 3 5% 6% 32%	4053
	11th to 20th	Night	10% 6% 2 6% 4 4 5% 4 6% 9% 46%	4053
	21st to end	Night	12% 8% 2 7% 4 5% 5% 5% 7% 11% 34%	4443
June	1st to 10th	Night	5% 4 1 4 4 4 4 3 6% 9% 57%	1800
	11th to 20th	Night	4 3 1 3 4 4 5% 3 7% 9% 57%	1800
	21st to end	Night	6% 6% 1 5% 4 5% 5% 5% 6% 8% 50%	1800
July	1st to 10th	Night	8% 6% 2 7% 5% 5% 4 4 7% 10% 42%	4078
	11th to 20th	Night	5% 4 2 5% 4 4 5% 4 7% 11% 48%	4077
	21st to end	Night	7% 6% 2 7% 4 4 4 4 7% 10% 44%	4449
August	1st to 10th	Night	1 1 2 2 2 2 3 4 8% 75%	2926
	11th to 20th	Night	2 2 1 3 3 3 5% 4 8% 11% 59%	3136
	21st to end	Night	5% 3 1 4 3 3 4 4 7% 12% 56%	3848
September	1st to 10th	Night	7% 5% 2 6% 4 4 4 4 5% 8% 50%	2200
	11th to 20th	Night	8% 5% 2 5% 4 5% 4 4 6% 8% 49%	2200
	21st to end	Night	7% 3 2 5% 4 5% 5% 4 6% 8% 53%	2200
October	1st to 10th	Night	4 3 1 3 4 3 3 3 5% 8% 63%	2200
	11th to 20th	Night	11% 4 2 4 3 3 3 3 4 6% 57%	2345
	21st to end	Night	11% 4 1 4 3 2 3 2 3 4 62%	2640
November	1st to 10th	Night	12% 6% 2 6% 3 3 3 2 4 5% 53%	2460
	11th to 20th	Night	11% 5% 2 5% 4 3 3 3 4 5% 55%	2573
	21st to end	Night	16% 6% 2 6% 4 3 4 2 4 6% 47%	2730
December	1st to 10th	Night	28% 10% 3 6% 4 3 3 2 3 4 34%	4380
	11th to 20th	Night	17% 9% 3 5% 4 3 3 2 3 5% 45%	4908
	21st to end	Night	16% 6% 2 4 2 2 3 2 3 4 56%	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	46% 3 4 18% 21% 9%	4078
	11th to 20th	Day	36% 2 5% 19% 21% 17%	4080
	21st to end	Day	49% 3 3 10% 23% 13%	4741
February	1st to 10th	Day	44% 4 6% 12% 20% 15%	2000
	11th to 20th	Day	46% 4 6% 17% 16% 11%	1959
	21st to end	Day	42% 5% 8% 16% 17% 13%	1669
March	1st to 10th	Day	38% 4 6% 20% 14% 18%	4936
	11th to 20th	Day	40% 4 4 9% 17% 26%	4980
	21st to end	Day	44% 4 7% 19% 18% 9%	5464
April	1st to 10th	Day	42% 5% 8% 16% 16% 12%	2200
	11th to 20th	Day	45% 4 7% 15% 18% 11%	2176
	21st to end	Day	42% 6% 6% 20% 17% 9%	2490
May	1st to 10th	Day	48% 7% 9% 20% 13% 4	5900
	11th to 20th	Day	36% 6% 11% 20% 20% 7%	5866
	21st to end	Day	37% 7% 12% 29% 13% 1	6447
June	1st to 10th	Day	28% 9% 14% 28% 19% 2	2600
	11th to 20th	Day	32% 7% 14% 24% 19% 4	2600
	21st to end	Day	38% 9% 16% 24% 12% 2	2600
July	1st to 10th	Day	43% 6% 21% 25% 4 1	5836
	11th to 20th	Day	36% 6% 22% 27% 9%	5831
	21st to end	Day	38% 7% 17% 25% 11% 2	6240
August	1st to 10th	Day	16% 6% 11% 45% 22% 1	4220
	11th to 20th	Day	23% 6% 28% 33% 8% 2	3956
	21st to end	Day	32% 9% 20% 23% 16% 1	4049
September	1st to 10th	Day	39% 7% 12% 19% 15% 7%	2200
	11th to 20th	Day	39% 8% 12% 20% 18% 5%	2200
	21st to end	Day	30% 6% 12% 22% 16% 14%	2200
October	1st to 10th	Day	17% 4 7% 14% 22% 36%	3590
	11th to 20th	Day	23% 4 8% 19% 28% 19%	3285
	21st to end	Day	28% 4 6% 19% 26% 16%	3538
November	1st to 10th	Day	36% 6% 8% 18% 20% 12%	2058
	11th to 20th	Day	33% 4 10% 17% 20% 16%	2042
	21st to end	Day	43% 4 8% 15% 19% 12%	1890
December	1st to 10th	Day	55% 2 5% 15% 16% 8%	3030
	11th to 20th	Day	42% 5% 9% 12% 20% 12%	3452
	21st to end	Day	35% 3 4 20% 23% 15%	4488
January	1st to 10th	Night	42% 3 6% 17% 20% 13%	5888
	11th to 20th	Night	30% 2 5% 19% 28% 16%	5900
	21st to end	Night	51% 2 3 11% 20% 13%	6278
February	1st to 10th	Night	42% 4 7% 12% 19% 16%	2400
	11th to 20th	Night	42% 3 7% 17% 18% 13%	2338
	21st to end	Night	44% 5% 6% 15% 16% 14%	1960
March	1st to 10th	Night	44% 4 7% 16% 15% 14%	4919
	11th to 20th	Night	40% 5% 7% 11% 14% 23%	4980
	21st to end	Night	44% 4 8% 17% 17% 10%	5467
April	1st to 10th	Night	38% 5% 10% 19% 16% 12%	2200
	11th to 20th	Night	40% 4 10% 15% 15% 15%	2173
	21st to end	Night	41% 5% 9% 20% 16% 9%	1901
May	1st to 10th	Night	52% 6% 8% 19% 12% 4	4080
	11th to 20th	Night	34% 6% 12% 22% 18% 8%	4054
	21st to end	Night	42% 7% 16% 27% 8%	4452
June	1st to 10th	Night	23% 7% 17% 30% 21% 2	1800
	11th to 20th	Night	23% 5% 15% 32% 21% 4	1800
	21st to end	Night	30% 8% 20% 28% 13% 2	1800
July	1st to 10th	Night	38% 7% 25% 26% 3	4035
	11th to 20th	Night	29% 6% 26% 30% 9%	4026
	21st to end	Night	34% 7% 21% 25% 11% 2	4320
August	1st to 10th	Night	10% 4 17% 48% 19%	2916
	11th to 20th	Night	18% 7% 35% 33% 6% 1	3164
	21st to end	Night	21% 11% 26% 27% 13% 2	3848
September	1st to 10th	Night	31% 7% 19% 22% 14% 7%	2200
	11th to 20th	Night	31% 8% 16% 24% 16% 5%	2200
	21st to end	Night	28% 5% 17% 22% 16% 12%	2200
October	1st to 10th	Night	14% 4 7% 17% 21% 37%	3590
	11th to 20th	Night	19% 3 9% 19% 28% 22%	3818
	21st to end	Night	21% 3 5% 25% 28% 17%	4252
November	1st to 10th	Night	33% 5% 9% 18% 22% 14%	2460
	11th to 20th	Night	31% 4 10% 18% 20% 16%	2573
	21st to end	Night	39% 4 9% 17% 18% 13%	2730
December	1st to 10th	Night	55% 3 5% 15% 13% 10%	4380
	11th to 20th	Night	43% 3 8% 10% 21% 15%	4909
	21st to end	Night	34% 3 5% 15% 30% 14%	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	23% 10% 35% 22% 9% 1	300
	11th to 20th	Day	24% 12% 25% 28% 9% 2	300
	21st to end	Day	24% 10% 33% 23% 10%	330
February	1st to 10th	Day	27% 13% 22% 26% 11% 1	300
	11th to 20th	Day	27% 14% 31% 19% 8% 1	300
	21st to end	Day	27% 10% 37% 21% 4	249
March	1st to 10th	Day	21% 11% 37% 23% 7% 1	300
	11th to 20th	Day	15% 11% 45% 22% 6% 1	300
	21st to end	Day	20% 10% 35% 27% 7% 1	330
April	1st to 10th	Day	17% 13% 37% 23% 10%	300
	11th to 20th	Day	17% 14% 30% 28% 10% 2	294
	21st to end	Day	19% 11% 33% 26% 10% 1	590
May	1st to 10th	Day	16% 10% 36% 28% 9% 1	703
	11th to 20th	Day	14% 7% 26% 34% 17% 2	725
	21st to end	Day	12% 5% 25% 34% 21% 3	789
June	1st to 10th	Day	6% 2 12% 39% 33% 9%	730
	11th to 20th	Day	7% 2 11% 40% 33% 7%	730
	21st to end	Day	6% 3 8% 31% 35% 16%	730
July	1st to 10th	Day	8% 3 7% 27% 40% 17%	721
	11th to 20th	Day	6% 1 4 23% 49% 17%	718
	21st to end	Day	5% 2 5% 26% 45% 19%	794
August	1st to 10th	Day	2 2 2 21% 47% 25%	726
	11th to 20th	Day	4 1 3 25% 41% 26%	565
	21st to end	Day	6% 2 4 18% 32% 38%	425
September	1st to 10th	Day	7% 2 5% 20% 39% 27%	330
	11th to 20th	Day	5% 2 2 21% 40% 30%	330
	21st to end	Day	8% 1 4 25% 38% 24%	330
October	1st to 10th	Day	6% 1 8% 26% 39% 19%	330
	11th to 20th	Day	9% 3 15% 30% 30% 13%	330
	21st to end	Day	14% 9% 23% 22% 25% 7%	363
November	1st to 10th	Day	17% 5% 18% 32% 19% 8%	330
	11th to 20th	Day	16% 5% 20% 34% 21% 5%	330
	21st to end	Day	22% 11% 30% 21% 12% 4	330
December	1st to 10th	Day	26% 7% 23% 28% 11% 5%	330
	11th to 20th	Day	21% 11% 23% 29% 14% 2	321
	21st to end	Day	22% 8% 31% 24% 13% 2	330
January	1st to 10th	Night	22% 8% 29% 32% 9%	1000
	11th to 20th	Night	21% 10% 28% 33% 8%	1000
	21st to end	Night	25% 7% 27% 34% 6%	1005
February	1st to 10th	Night	26% 10% 29% 31% 5%	800
	11th to 20th	Night	25% 11% 32% 29% 4	784
	21st to end	Night	27% 12% 35% 23% 3	640
March	1st to 10th	Night	22% 12% 33% 30% 3	600
	11th to 20th	Night	21% 9% 37% 29% 5%	600
	21st to end	Night	18% 9% 38% 29% 4	660
April	1st to 10th	Night	17% 9% 44% 28% 3	600
	11th to 20th	Night	18% 9% 37% 31% 5%	593
	21st to end	Night	18% 8% 42% 25% 8%	600
May	1st to 10th	Night	17% 9% 42% 28% 5%	600
	11th to 20th	Night	13% 6% 34% 37% 10% 1	591
	21st to end	Night	11% 3 34% 37% 14%	650
June	1st to 10th	Night	6% 3 18% 52% 22% 1	600
	11th to 20th	Night	5% 2 25% 50% 17% 1	600
	21st to end	Night	6% 3 12% 44% 31% 5%	600
July	1st to 10th	Night	7% 3 8% 45% 32% 5%	585
	11th to 20th	Night	4 1 9% 48% 35% 4	582
	21st to end	Night	5% 8% 45% 37% 5%	657
August	1st to 10th	Night	2 1 6% 50% 38% 4	597
	11th to 20th	Night	4 1 5% 48% 38% 4	594
	21st to end	Night	7% 1 4 35% 46% 7%	660
September	1st to 10th	Night	9% 1 6% 36% 44% 5%	600
	11th to 20th	Night	10% 2 4 37% 44% 4	600
	21st to end	Night	9% 1 11% 36% 40% 4	600
October	1st to 10th	Night	5% 1 9% 46% 35% 4	600
	11th to 20th	Night	11% 3 19% 42% 23% 1	745
	21st to end	Night	12% 7% 25% 34% 20% 2	880
November	1st to 10th	Night	14% 5% 19% 41% 20% 1	820
	11th to 20th	Night	14% 4 26% 39% 16% 2	893
	21st to end	Night	19% 8% 27% 32% 14% 1	1050
December	1st to 10th	Night	22% 7% 23% 36% 11% 1	1050
	11th to 20th	Night	25% 9% 25% 32% 9%	1036
	21st to end	Night	20% 7% 26% 37% 9% 1	1100

Page generated at 2025-12-15 00:13:52. Version ac07

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