Georgia Shore Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Georgia Shore Observatory clear sky chart from 2005-11-06 to 2026-05-17.

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	17% 11% 4 9% 5% 5% 5% 4 5% 7% 29%	131865
	Night	17% 14% 5% 10% 6% 5% 4 3 4 5% 26%	130964
Transparency	Day	56% 4 11% 20% 8% 1	135334
	Night	61% 3 10% 17% 8% 1	135582
Seeing	Day	27% 15% 29% 20% 8% 2	16539
	Night	28% 13% 26% 24% 9% 1	25589

By Month

Percentage Cloud Cover NE (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% 20% 8% 17% 7% 5% 4 3 4 4 15%	4661
	11th to 20th	Day	10% 17% 8% 19% 8% 5% 5% 3 4 4 17%	4650
	21st to end	Day	11% 15% 6% 12% 10% 8% 6% 4 5% 5% 19%	5124
February	1st to 10th	Day	14% 15% 5% 12% 10% 7% 5% 3 5% 5% 20%	1838
	11th to 20th	Day	13% 17% 6% 13% 7% 5% 4 4 4 6% 22%	2001
	21st to end	Day	15% 16% 6% 11% 7% 5% 4 3 4 5% 23%	1730
March	1st to 10th	Day	20% 14% 5% 12% 6% 4 4 3 4 5% 24%	4576
	11th to 20th	Day	13% 16% 4 10% 5% 4 5% 4 5% 5% 28%	4772
	21st to end	Day	19% 13% 4 9% 4 4 4 3 4 5% 30%	6102
April	1st to 10th	Day	21% 14% 3 8% 5% 4 3 3 5% 6% 29%	2520
	11th to 20th	Day	19% 10% 4 7% 6% 5% 5% 3 3 5% 34%	2494
	21st to end	Day	23% 10% 3 7% 4 4 4 3 4 6% 33%	2700
May	1st to 10th	Day	28% 11% 3 9% 5% 4 4 3 5% 5% 22%	6242
	11th to 20th	Day	19% 8% 3 8% 5% 5% 5% 4 5% 7% 30%	6402
	21st to end	Day	19% 9% 3 6% 5% 4 5% 4 6% 7% 31%	6949
June	1st to 10th	Day	23% 7% 2 7% 5% 5% 5% 4 6% 8% 29%	2800
	11th to 20th	Day	15% 5% 2 7% 4 4 5% 5% 7% 8% 36%	2800
	21st to end	Day	21% 8% 3 7% 5% 5% 5% 4 6% 8% 30%	2800
July	1st to 10th	Day	11% 6% 2 7% 6% 6% 6% 5% 8% 9% 32%	6360
	11th to 20th	Day	11% 6% 2 6% 4 5% 6% 5% 7% 10% 37%	6360
	21st to end	Day	13% 6% 2 5% 4 4 5% 4 6% 9% 41%	6926
August	1st to 10th	Day	15% 8% 3 7% 5% 5% 5% 4 7% 8% 33%	4563
	11th to 20th	Day	14% 7% 3 8% 5% 5% 5% 4 6% 8% 36%	4060
	21st to end	Day	14% 5% 2 7% 4 4 4 4 6% 9% 41%	4312
September	1st to 10th	Day	15% 6% 2 5% 4 3 3 4 5% 8% 45%	2400
	11th to 20th	Day	15% 6% 1 5% 3 3 4 3 4 6% 50%	2290
	21st to end	Day	16% 5% 2 6% 4 4 5% 3 6% 8% 39%	2200
October	1st to 10th	Day	22% 7% 3 8% 4 4 4 3 5% 6% 33%	2109
	11th to 20th	Day	20% 9% 2 6% 5% 4 5% 5% 5% 6% 32%	1942
	21st to end	Day	25% 14% 3 8% 4 5% 4 3 4 4 26%	1980
November	1st to 10th	Day	20% 15% 3 8% 5% 4 4 3 5% 6% 29%	1851
	11th to 20th	Day	17% 17% 4 9% 5% 4 5% 4 4 5% 25%	1877
	21st to end	Day	20% 17% 6% 10% 6% 4 5% 5% 4 4 20%	1680
December	1st to 10th	Day	17% 19% 8% 15% 8% 6% 5% 3 4 4 11%	2680
	11th to 20th	Day	18% 14% 5% 11% 5% 5% 4 3 5% 5% 23%	3066
	21st to end	Day	20% 15% 5% 12% 8% 4 5% 5% 5% 5% 16%	4048
January	1st to 10th	Night	14% 24% 10% 16% 6% 4 3 2 3 3 16%	8234
	11th to 20th	Night	12% 21% 9% 19% 8% 5% 4 3 4 3 12%	8235
	21st to end	Night	12% 16% 5% 14% 11% 7% 6% 4 4 4 17%	9057
February	1st to 10th	Night	15% 17% 6% 15% 8% 6% 4 3 4 4 19%	2778
	11th to 20th	Night	14% 16% 6% 14% 7% 6% 5% 4 4 4 21%	2505
	21st to end	Night	16% 17% 6% 11% 6% 4 4 2 4 4 26%	2076
March	1st to 10th	Night	20% 17% 5% 10% 6% 4 3 3 3 4 24%	5484
	11th to 20th	Night	16% 16% 4 9% 5% 4 4 3 5% 6% 28%	5403
	21st to end	Night	18% 18% 5% 11% 5% 4 4 3 3 3 27%	5072
April	1st to 10th	Night	22% 13% 4 8% 4 3 4 4 4 5% 27%	2100
	11th to 20th	Night	25% 12% 3 8% 6% 4 3 2 4 4 29%	2075
	21st to end	Night	20% 13% 4 7% 4 3 3 3 4 5% 34%	1918
May	1st to 10th	Night	27% 13% 4 8% 5% 4 4 3 4 6% 21%	3961
	11th to 20th	Night	20% 11% 4 9% 4 4 4 3 5% 6% 30%	3623
	21st to end	Night	19% 9% 3 9% 5% 5% 4 3 6% 7% 30%	3926
June	1st to 10th	Night	25% 8% 2 7% 4 4 4 4 5% 7% 30%	1600
	11th to 20th	Night	16% 7% 2 7% 5% 4 4 4 6% 9% 36%	1600
	21st to end	Night	19% 8% 2 7% 4 4 5% 4 5% 7% 33%	1600
July	1st to 10th	Night	12% 6% 3 7% 5% 6% 5% 5% 7% 10% 34%	3600
	11th to 20th	Night	14% 6% 3 7% 5% 5% 5% 4 5% 7% 39%	3600
	21st to end	Night	11% 7% 2 8% 5% 4 5% 4 6% 7% 39%	3926
August	1st to 10th	Night	18% 8% 3 8% 5% 4 4 3 5% 7% 36%	2586
	11th to 20th	Night	13% 8% 3 9% 6% 5% 5% 4 4 6% 36%	2937
	21st to end	Night	15% 6% 2 5% 3 4 5% 4 5% 8% 42%	3586
September	1st to 10th	Night	14% 5% 3 5% 4 4 3 4 5% 7% 43%	2000
	11th to 20th	Night	14% 5% 2 5% 3 4 3 3 5% 6% 48%	2110
	21st to end	Night	19% 6% 2 5% 3 4 4 4 5% 5% 42%	2200
October	1st to 10th	Night	23% 8% 2 6% 5% 4 4 3 5% 6% 35%	2289
	11th to 20th	Night	22% 10% 3 8% 4 4 4 4 5% 5% 32%	2457
	21st to end	Night	26% 11% 3 8% 5% 4 5% 3 4 4 26%	2860
November	1st to 10th	Night	22% 12% 4 8% 4 4 4 3 4 5% 30%	2667
	11th to 20th	Night	19% 15% 4 9% 5% 4 4 3 3 6% 28%	2741
	21st to end	Night	21% 18% 6% 10% 4 4 4 3 4 5% 21%	2940
December	1st to 10th	Night	18% 28% 8% 13% 6% 4 3 2 3 3 11%	4720
	11th to 20th	Night	23% 19% 5% 11% 5% 5% 3 2 3 3 19%	5348
	21st to end	Night	21% 17% 7% 12% 6% 5% 5% 4 4 6% 15%	7150

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	75% 4 10% 10% 1	4662
	11th to 20th	Day	74% 3 8% 10% 5% 1	4680
	21st to end	Day	69% 4 9% 11% 7%	5124
February	1st to 10th	Day	68% 5% 6% 15% 6% 1	1838
	11th to 20th	Day	66% 3 9% 15% 6% 1	2010
	21st to end	Day	65% 3 8% 14% 7% 2	1730
March	1st to 10th	Day	65% 3 8% 14% 6% 3	4579
	11th to 20th	Day	58% 4 13% 15% 9% 1	4772
	21st to end	Day	59% 4 5% 15% 15% 1	6102
April	1st to 10th	Day	60% 3 6% 20% 9% 2	2520
	11th to 20th	Day	55% 3 7% 19% 15% 1	2494
	21st to end	Day	55% 3 9% 19% 11% 3	2700
May	1st to 10th	Day	65% 4 8% 16% 7% 1	6253
	11th to 20th	Day	54% 5% 14% 18% 8% 1	6406
	21st to end	Day	52% 4 12% 23% 9% 1	6949
June	1st to 10th	Day	54% 4 11% 20% 11% 1	2800
	11th to 20th	Day	45% 5% 11% 24% 13% 2	2800
	21st to end	Day	52% 4 11% 22% 9% 1	2800
July	1st to 10th	Day	47% 4 15% 24% 9%	6290
	11th to 20th	Day	41% 5% 13% 31% 10%	6285
	21st to end	Day	40% 5% 12% 35% 8%	6728
August	1st to 10th	Day	49% 4 16% 23% 8%	4549
	11th to 20th	Day	47% 4 17% 25% 7%	4100
	21st to end	Day	41% 4 18% 22% 15%	4312
September	1st to 10th	Day	39% 5% 11% 32% 12% 1	2400
	11th to 20th	Day	38% 3 10% 34% 15% 1	2290
	21st to end	Day	43% 4 15% 26% 11% 1	2200
October	1st to 10th	Day	46% 3 12% 30% 9%	3434
	11th to 20th	Day	50% 3 15% 24% 8%	3145
	21st to end	Day	52% 3 14% 24% 6% 1	3180
November	1st to 10th	Day	57% 4 12% 19% 7% 1	1851
	11th to 20th	Day	63% 4 10% 14% 8% 1	1877
	21st to end	Day	69% 4 12% 11% 4	1680
December	1st to 10th	Day	79% 2 8% 9% 2	2680
	11th to 20th	Day	65% 3 9% 18% 5%	3066
	21st to end	Day	69% 4 8% 12% 7%	4048
January	1st to 10th	Night	76% 2 10% 9% 3	8234
	11th to 20th	Night	76% 4 7% 9% 4	8280
	21st to end	Night	71% 3 7% 10% 8%	9057
February	1st to 10th	Night	70% 3 7% 13% 6% 1	2778
	11th to 20th	Night	67% 4 8% 15% 6%	2507
	21st to end	Night	63% 3 8% 15% 10% 1	2076
March	1st to 10th	Night	64% 3 8% 13% 11% 1	5494
	11th to 20th	Night	59% 4 12% 15% 8% 1	5404
	21st to end	Night	63% 4 4 17% 11% 1	5072
April	1st to 10th	Night	59% 3 8% 17% 11% 2	2100
	11th to 20th	Night	60% 2 7% 17% 12% 1	2075
	21st to end	Night	54% 3 8% 17% 15% 3	1918
May	1st to 10th	Night	65% 3 9% 15% 7% 2	3967
	11th to 20th	Night	56% 3 10% 20% 9% 1	3624
	21st to end	Night	54% 3 10% 20% 12% 1	3927
June	1st to 10th	Night	54% 4 9% 21% 10% 1	1600
	11th to 20th	Night	46% 4 12% 22% 13% 2	1600
	21st to end	Night	50% 5% 12% 21% 11% 1	1600
July	1st to 10th	Night	47% 3 17% 23% 9%	3560
	11th to 20th	Night	43% 4 13% 28% 11%	3552
	21st to end	Night	44% 4 13% 26% 12%	3809
August	1st to 10th	Night	49% 4 14% 25% 8%	2576
	11th to 20th	Night	50% 4 16% 21% 9% 1	2963
	21st to end	Night	42% 3 15% 25% 14% 1	3586
September	1st to 10th	Night	40% 5% 13% 30% 12% 1	2000
	11th to 20th	Night	37% 3 14% 33% 12% 1	2110
	21st to end	Night	43% 5% 11% 26% 14% 1	2200
October	1st to 10th	Night	53% 3 10% 25% 9%	3744
	11th to 20th	Night	52% 2 10% 24% 11%	3993
	21st to end	Night	53% 3 13% 21% 10%	4610
November	1st to 10th	Night	58% 3 11% 19% 8% 1	2667
	11th to 20th	Night	60% 4 9% 16% 9% 1	2741
	21st to end	Night	67% 4 11% 14% 4	2940
December	1st to 10th	Night	80% 2 8% 8% 2	4720
	11th to 20th	Night	72% 3 7% 12% 7%	5348
	21st to end	Night	70% 3 8% 12% 6%	7150

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	33% 16% 30% 16% 5%	220
	11th to 20th	Day	34% 23% 30% 10% 2 1	220
	21st to end	Day	29% 20% 30% 16% 5%	242
February	1st to 10th	Day	32% 24% 31% 11% 3	303
	11th to 20th	Day	27% 27% 32% 11% 2	489
	21st to end	Day	29% 23% 33% 13% 2	446
March	1st to 10th	Day	34% 16% 30% 16% 3	540
	11th to 20th	Day	32% 22% 28% 14% 4 1	540
	21st to end	Day	35% 21% 24% 14% 5% 1	594
April	1st to 10th	Day	35% 20% 24% 17% 3 1	540
	11th to 20th	Day	34% 18% 26% 14% 6% 2	532
	21st to end	Day	33% 17% 30% 14% 5% 2	540
May	1st to 10th	Day	34% 16% 26% 16% 5% 2	543
	11th to 20th	Day	26% 12% 30% 22% 9% 1	551
	21st to end	Day	22% 14% 32% 24% 7% 1	573
June	1st to 10th	Day	28% 11% 33% 21% 6% 1	530
	11th to 20th	Day	21% 14% 33% 21% 9% 2	530
	21st to end	Day	26% 10% 33% 21% 8% 2	530
July	1st to 10th	Day	17% 6% 33% 32% 10% 2	525
	11th to 20th	Day	17% 7% 36% 26% 12% 2	524
	21st to end	Day	20% 6% 33% 30% 9% 2	576
August	1st to 10th	Day	15% 7% 29% 32% 15% 2	526
	11th to 20th	Day	18% 5% 27% 30% 16% 4	519
	21st to end	Day	17% 9% 31% 24% 13% 6%	583
September	1st to 10th	Day	18% 11% 29% 24% 11% 7%	530
	11th to 20th	Day	17% 9% 22% 24% 21% 7%	530
	21st to end	Day	17% 11% 29% 23% 14% 6%	530
October	1st to 10th	Day	25% 13% 26% 18% 15% 3	530
	11th to 20th	Day	31% 17% 25% 18% 9% 1	497
	21st to end	Day	37% 14% 26% 18% 6%	462
November	1st to 10th	Day	38% 16% 27% 13% 6%	425
	11th to 20th	Day	32% 21% 24% 15% 7% 1	417
	21st to end	Day	38% 23% 24% 12% 3	220
December	1st to 10th	Day	29% 22% 29% 16% 4	220
	11th to 20th	Day	31% 23% 36% 8% 2	220
	21st to end	Day	31% 24% 24% 17% 3 1	242
January	1st to 10th	Night	32% 17% 30% 18% 4	840
	11th to 20th	Night	32% 20% 25% 18% 5%	840
	21st to end	Night	25% 16% 30% 24% 5% 1	924
February	1st to 10th	Night	25% 16% 31% 23% 4	840
	11th to 20th	Night	26% 17% 33% 21% 3	823
	21st to end	Night	26% 16% 30% 23% 5%	692
March	1st to 10th	Night	30% 15% 29% 22% 3	840
	11th to 20th	Night	33% 18% 23% 20% 5%	840
	21st to end	Night	31% 16% 24% 22% 7% 1	924
April	1st to 10th	Night	32% 13% 28% 22% 5%	840
	11th to 20th	Night	34% 15% 23% 21% 7% 1	831
	21st to end	Night	31% 13% 29% 20% 7%	658
May	1st to 10th	Night	30% 10% 27% 25% 7% 1	551
	11th to 20th	Night	25% 8% 30% 27% 8% 1	406
	21st to end	Night	21% 8% 30% 31% 9% 1	433
June	1st to 10th	Night	29% 7% 26% 29% 10% 1	400
	11th to 20th	Night	22% 6% 30% 31% 12% 1	400
	21st to end	Night	23% 5% 27% 34% 11% 1	400
July	1st to 10th	Night	17% 6% 28% 35% 14% 1	390
	11th to 20th	Night	12% 3 25% 43% 15% 2	388
	21st to end	Night	18% 4 20% 45% 13%	438
August	1st to 10th	Night	17% 2 19% 43% 18% 1	398
	11th to 20th	Night	17% 3 20% 37% 21% 2	629
	21st to end	Night	18% 5% 23% 33% 19% 2	880
September	1st to 10th	Night	19% 6% 25% 32% 16% 2	800
	11th to 20th	Night	19% 6% 20% 29% 23% 3	800
	21st to end	Night	24% 8% 25% 23% 18% 2	800
October	1st to 10th	Night	27% 9% 26% 24% 13% 1	800
	11th to 20th	Night	29% 11% 26% 25% 8% 1	800
	21st to end	Night	33% 14% 27% 22% 5%	880
November	1st to 10th	Night	33% 15% 29% 18% 5% 1	820
	11th to 20th	Night	32% 16% 25% 18% 8% 1	840
	21st to end	Night	35% 18% 25% 16% 5% 1	840
December	1st to 10th	Night	36% 19% 25% 16% 4	840
	11th to 20th	Night	32% 18% 27% 17% 5% 1	840
	21st to end	Night	37% 18% 22% 19% 3	924

Page generated at 2026-05-14 01:58:54. Version ac07

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