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 2024-01-27.

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	18% 10% 4 7% 6% 3 5% 5% 5% 7% 31%	74881
	Night	20% 12% 5% 8% 6% 3 4 4 4 5% 29%	75159
Transparency	Day	55% 4 11% 20% 9% 1	74586
	Night	59% 4 10% 18% 9% 1	74988
Seeing	Day	26% 15% 29% 20% 8% 2	13587
	Night	28% 13% 26% 24% 9% 1	22694

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	15% 20% 8% 10% 8% 4 7% 4 4 4 16%	1517
	11th to 20th	Day	17% 18% 6% 12% 8% 2 5% 4 4 4 20%	1520
	21st to end	Day	12% 14% 7% 12% 8% 5% 6% 5% 5% 5% 21%	1632
February	1st to 10th	Day	16% 14% 5% 12% 9% 5% 6% 4 5% 5% 19%	1575
	11th to 20th	Day	14% 16% 6% 11% 8% 4 5% 4 3 6% 23%	1708
	21st to end	Day	16% 16% 6% 11% 7% 4 4 4 4 5% 23%	1480
March	1st to 10th	Day	16% 16% 5% 9% 8% 3 5% 4 4 5% 26%	1797
	11th to 20th	Day	17% 13% 6% 9% 6% 3 4 4 3 5% 28%	1851
	21st to end	Day	20% 11% 5% 8% 6% 3 4 3 4 6% 31%	2376
April	1st to 10th	Day	21% 13% 4 7% 5% 3 3 4 5% 6% 29%	2160
	11th to 20th	Day	19% 8% 4 6% 6% 4 5% 4 3 6% 36%	2134
	21st to end	Day	25% 9% 4 6% 5% 3 4 4 4 6% 31%	2313
May	1st to 10th	Day	21% 8% 3 6% 5% 3 4 5% 5% 7% 32%	2421
	11th to 20th	Day	18% 6% 3 6% 5% 3 5% 4 5% 7% 38%	2478
	21st to end	Day	17% 6% 2 5% 6% 3 5% 6% 6% 8% 35%	2725
June	1st to 10th	Day	24% 7% 3 6% 6% 3 5% 5% 6% 8% 28%	2520
	11th to 20th	Day	16% 5% 2 6% 5% 3 5% 6% 6% 9% 37%	2520
	21st to end	Day	21% 7% 3 6% 6% 3 5% 5% 5% 8% 30%	2520
July	1st to 10th	Day	13% 6% 3 5% 5% 3 6% 5% 7% 8% 39%	2520
	11th to 20th	Day	13% 6% 3 5% 5% 4 6% 6% 6% 10% 36%	2520
	21st to end	Day	15% 5% 2 5% 5% 3 5% 6% 7% 9% 37%	2744
August	1st to 10th	Day	13% 6% 3 6% 6% 4 5% 6% 7% 8% 38%	2506
	11th to 20th	Day	13% 5% 2 6% 5% 4 4 6% 7% 10% 38%	2249
	21st to end	Day	13% 5% 2 6% 5% 3 5% 6% 7% 8% 40%	2376
September	1st to 10th	Day	16% 6% 2 4 5% 3 3 4 6% 8% 43%	2160
	11th to 20th	Day	17% 6% 2 4 4 2 4 4 3 6% 49%	2062
	21st to end	Day	16% 5% 3 5% 5% 3 5% 5% 6% 8% 39%	1980
October	1st to 10th	Day	24% 7% 3 7% 5% 3 5% 5% 5% 6% 30%	1899
	11th to 20th	Day	21% 9% 2 6% 6% 3 5% 6% 5% 6% 31%	1748
	21st to end	Day	27% 13% 4 7% 5% 3 4 4 4 4 25%	1782
November	1st to 10th	Day	20% 13% 3 7% 6% 3 4 4 4 6% 30%	1671
	11th to 20th	Day	19% 15% 5% 8% 6% 3 5% 4 4 5% 25%	1699
	21st to end	Day	20% 15% 6% 9% 7% 3 5% 6% 5% 4 21%	1520
December	1st to 10th	Day	22% 19% 6% 10% 8% 3 5% 2 4 4 16%	1520
	11th to 20th	Day	22% 15% 5% 8% 7% 3 5% 4 4 6% 22%	1906
	21st to end	Day	25% 15% 5% 11% 10% 3 4 5% 3 4 14%	2772
January	1st to 10th	Night	19% 19% 8% 11% 7% 4 5% 4 3 4 15%	2649
	11th to 20th	Night	18% 19% 6% 11% 7% 4 5% 5% 4 4 19%	2660
	21st to end	Night	14% 15% 7% 11% 9% 3 5% 5% 4 6% 22%	2868
February	1st to 10th	Night	17% 16% 7% 14% 8% 5% 4 3 4 4 18%	2381
	11th to 20th	Night	15% 14% 7% 12% 8% 4 6% 4 4 4 22%	2138
	21st to end	Night	17% 15% 7% 10% 7% 3 4 4 3 4 26%	1776
March	1st to 10th	Night	18% 17% 7% 8% 8% 3 3 4 4 4 26%	2150
	11th to 20th	Night	20% 14% 5% 8% 6% 3 3 3 4 4 29%	2104
	21st to end	Night	21% 13% 4 7% 5% 3 4 3 4 4 33%	1980
April	1st to 10th	Night	22% 13% 5% 8% 5% 3 4 4 4 5% 27%	1800
	11th to 20th	Night	25% 10% 3 7% 7% 2 4 3 4 5% 31%	1775
	21st to end	Night	21% 13% 4 6% 5% 3 3 4 4 5% 31%	1645
May	1st to 10th	Night	24% 9% 3 7% 5% 3 4 4 4 7% 31%	1553
	11th to 20th	Night	19% 8% 3 6% 5% 3 4 4 4 6% 38%	1415
	21st to end	Night	17% 4 3 5% 5% 3 4 5% 6% 9% 38%	1550
June	1st to 10th	Night	25% 7% 2 6% 5% 3 4 5% 5% 8% 30%	1440
	11th to 20th	Night	17% 7% 3 6% 5% 3 4 5% 6% 9% 36%	1440
	21st to end	Night	19% 7% 3 7% 5% 3 5% 5% 6% 7% 34%	1440
July	1st to 10th	Night	13% 6% 2 6% 5% 4 4 5% 7% 8% 41%	1440
	11th to 20th	Night	11% 5% 2 5% 6% 4 6% 6% 6% 10% 40%	1440
	21st to end	Night	14% 6% 3 6% 5% 3 5% 6% 7% 8% 38%	1574
August	1st to 10th	Night	13% 4 2 6% 5% 3 4 5% 6% 10% 41%	1432
	11th to 20th	Night	14% 6% 3 6% 7% 3 5% 5% 5% 7% 40%	1629
	21st to end	Night	13% 6% 3 5% 5% 3 5% 4 6% 8% 41%	1980
September	1st to 10th	Night	15% 5% 3 5% 5% 4 4 5% 5% 7% 42%	1800
	11th to 20th	Night	16% 5% 3 4 4 3 3 4 5% 7% 47%	1898
	21st to end	Night	19% 6% 2 5% 4 3 4 5% 5% 6% 43%	1980
October	1st to 10th	Night	24% 7% 2 5% 6% 3 4 4 4 6% 33%	2059
	11th to 20th	Night	23% 9% 3 7% 6% 3 4 5% 5% 5% 30%	2211
	21st to end	Night	27% 11% 4 7% 6% 3 5% 4 4 4 25%	2574
November	1st to 10th	Night	21% 11% 4 7% 5% 3 4 4 4 5% 31%	2407
	11th to 20th	Night	20% 13% 5% 8% 6% 3 4 4 3 6% 28%	2479
	21st to end	Night	22% 17% 6% 9% 5% 3 4 4 4 5% 22%	2660
December	1st to 10th	Night	22% 22% 7% 11% 6% 3 5% 3 4 4 14%	2660
	11th to 20th	Night	24% 17% 6% 9% 6% 4 5% 4 3 4 19%	3288
	21st to end	Night	26% 16% 7% 11% 7% 3 4 3 3 3 17%	4884

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	73% 3 8% 13% 3	1518
	11th to 20th	Day	70% 3 9% 10% 7% 1	1520
	21st to end	Day	66% 4 11% 13% 6% 1	1632
February	1st to 10th	Day	69% 5% 6% 13% 5% 1	1575
	11th to 20th	Day	66% 3 9% 15% 6% 1	1717
	21st to end	Day	66% 3 8% 13% 8% 2	1480
March	1st to 10th	Day	64% 4 9% 15% 7% 2	1800
	11th to 20th	Day	61% 4 10% 13% 11% 1	1851
	21st to end	Day	58% 3 6% 19% 11% 3	2376
April	1st to 10th	Day	59% 4 6% 20% 9% 2	2160
	11th to 20th	Day	52% 3 8% 20% 16% 2	2134
	21st to end	Day	57% 3 9% 18% 10% 3	2313
May	1st to 10th	Day	52% 3 8% 21% 15% 1	2421
	11th to 20th	Day	47% 4 7% 23% 16% 2	2482
	21st to end	Day	48% 5% 13% 21% 12% 2	2725
June	1st to 10th	Day	54% 4 12% 20% 10% 1	2520
	11th to 20th	Day	46% 5% 10% 24% 13% 2	2520
	21st to end	Day	53% 4 11% 21% 9% 1	2520
July	1st to 10th	Day	42% 5% 13% 27% 13% 1	2450
	11th to 20th	Day	44% 5% 13% 30% 8%	2445
	21st to end	Day	45% 6% 14% 25% 9% 1	2591
August	1st to 10th	Day	44% 5% 17% 25% 8%	2492
	11th to 20th	Day	42% 5% 17% 26% 11%	2249
	21st to end	Day	41% 5% 13% 26% 14%	2376
September	1st to 10th	Day	40% 5% 12% 29% 13% 1	2160
	11th to 20th	Day	39% 4 9% 33% 14% 1	2062
	21st to end	Day	44% 4 16% 26% 9% 1	1980
October	1st to 10th	Day	56% 4 10% 21% 10%	1899
	11th to 20th	Day	54% 5% 15% 18% 7% 1	1748
	21st to end	Day	65% 3 9% 16% 6% 1	1782
November	1st to 10th	Day	56% 4 13% 19% 7% 1	1671
	11th to 20th	Day	63% 4 10% 13% 8% 1	1699
	21st to end	Day	67% 4 13% 12% 4	1520
December	1st to 10th	Day	74% 3 10% 10% 3	1520
	11th to 20th	Day	67% 3 10% 14% 5%	1906
	21st to end	Day	74% 4 10% 9% 3	2772
January	1st to 10th	Night	76% 3 7% 10% 3	2649
	11th to 20th	Night	70% 4 10% 11% 5%	2660
	21st to end	Night	66% 4 8% 13% 8% 1	2868
February	1st to 10th	Night	72% 3 7% 11% 6% 1	2381
	11th to 20th	Night	67% 4 8% 14% 7%	2140
	21st to end	Night	64% 3 8% 15% 10% 1	1776
March	1st to 10th	Night	63% 4 8% 16% 8% 1	2160
	11th to 20th	Night	61% 3 7% 17% 10% 2	2105
	21st to end	Night	56% 3 6% 19% 13% 3	1980
April	1st to 10th	Night	60% 3 8% 17% 11% 2	1800
	11th to 20th	Night	58% 2 7% 18% 13% 1	1775
	21st to end	Night	56% 3 8% 16% 14% 3	1645
May	1st to 10th	Night	55% 3 5% 18% 16% 4	1553
	11th to 20th	Night	49% 4 7% 20% 18% 2	1416
	21st to end	Night	45% 5% 12% 21% 14% 2	1551
June	1st to 10th	Night	54% 4 10% 22% 9% 1	1440
	11th to 20th	Night	46% 5% 12% 23% 13% 3	1440
	21st to end	Night	50% 6% 13% 21% 11%	1440
July	1st to 10th	Night	41% 5% 15% 24% 15% 1	1400
	11th to 20th	Night	39% 5% 14% 30% 11%	1392
	21st to end	Night	43% 6% 15% 25% 11% 1	1486
August	1st to 10th	Night	39% 5% 18% 28% 10%	1422
	11th to 20th	Night	44% 4 15% 24% 13% 1	1629
	21st to end	Night	42% 4 14% 27% 13%	1980
September	1st to 10th	Night	41% 5% 13% 29% 11% 1	1800
	11th to 20th	Night	38% 3 14% 33% 11% 1	1898
	21st to end	Night	42% 5% 12% 27% 13% 1	1980
October	1st to 10th	Night	52% 3 12% 23% 11% 1	2059
	11th to 20th	Night	57% 4 11% 21% 7%	2211
	21st to end	Night	62% 4 11% 14% 9% 1	2574
November	1st to 10th	Night	57% 3 11% 19% 9% 1	2407
	11th to 20th	Night	59% 4 10% 17% 8% 2	2479
	21st to end	Night	66% 4 12% 15% 4	2660
December	1st to 10th	Night	76% 3 7% 11% 2	2660
	11th to 20th	Night	72% 4 8% 11% 5%	3288
	21st to end	Night	74% 2 9% 12% 2	4884

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	34% 16% 26% 17% 6% 1	180
	11th to 20th	Day	36% 20% 29% 12% 3 1	180
	21st to end	Day	27% 20% 32% 17% 5%	188
February	1st to 10th	Day	34% 29% 28% 8% 2	220
	11th to 20th	Day	28% 27% 31% 11% 3	376
	21st to end	Day	29% 23% 30% 15% 3	346
March	1st to 10th	Day	34% 15% 30% 18% 3	420
	11th to 20th	Day	28% 23% 28% 15% 5% 1	420
	21st to end	Day	34% 19% 23% 17% 6% 1	462
April	1st to 10th	Day	33% 19% 25% 19% 4 1	420
	11th to 20th	Day	30% 20% 25% 15% 8% 3	412
	21st to end	Day	33% 16% 30% 14% 5% 2	420
May	1st to 10th	Day	32% 15% 28% 16% 6% 2	423
	11th to 20th	Day	24% 13% 32% 21% 9% 1	447
	21st to end	Day	20% 14% 33% 24% 8% 1	485
June	1st to 10th	Day	28% 12% 32% 20% 7% 1	450
	11th to 20th	Day	22% 13% 31% 23% 9% 2	450
	21st to end	Day	26% 10% 32% 22% 8% 2	450
July	1st to 10th	Day	18% 5% 30% 33% 11% 2	445
	11th to 20th	Day	17% 7% 36% 24% 13% 3	444
	21st to end	Day	20% 5% 32% 32% 10% 2	488
August	1st to 10th	Day	15% 7% 31% 29% 15% 2	446
	11th to 20th	Day	17% 5% 26% 31% 16% 4	439
	21st to end	Day	17% 9% 31% 24% 13% 6%	495
September	1st to 10th	Day	19% 10% 30% 23% 11% 8%	450
	11th to 20th	Day	19% 10% 23% 22% 20% 6%	450
	21st to end	Day	16% 12% 30% 22% 14% 6%	450
October	1st to 10th	Day	27% 14% 24% 16% 16% 3	450
	11th to 20th	Day	31% 17% 24% 17% 9% 1	423
	21st to end	Day	37% 13% 27% 18% 5%	396
November	1st to 10th	Day	35% 15% 28% 15% 7% 1	365
	11th to 20th	Day	32% 22% 26% 13% 7% 1	359
	21st to end	Day	36% 21% 26% 14% 3	180
December	1st to 10th	Day	31% 21% 27% 17% 4 1	180
	11th to 20th	Day	31% 23% 35% 9% 3	180
	21st to end	Day	32% 25% 22% 16% 4 1	198
January	1st to 10th	Night	32% 17% 28% 18% 4	760
	11th to 20th	Night	31% 20% 25% 19% 6%	760
	21st to end	Night	25% 16% 29% 24% 5% 1	820
February	1st to 10th	Night	27% 17% 30% 22% 3	720
	11th to 20th	Night	25% 18% 32% 21% 3	703
	21st to end	Night	26% 17% 29% 22% 6%	592
March	1st to 10th	Night	30% 14% 29% 24% 3 1	720
	11th to 20th	Night	33% 17% 23% 21% 6%	720
	21st to end	Night	30% 15% 24% 23% 8% 1	792
April	1st to 10th	Night	31% 13% 28% 23% 6%	720
	11th to 20th	Night	32% 15% 23% 22% 8% 1	711
	21st to end	Night	32% 12% 29% 20% 7% 1	565
May	1st to 10th	Night	30% 10% 26% 25% 8% 1	473
	11th to 20th	Night	25% 7% 29% 29% 8% 2	354
	21st to end	Night	21% 7% 30% 32% 9% 1	389
June	1st to 10th	Night	28% 7% 25% 29% 10% 1	360
	11th to 20th	Night	21% 4 29% 31% 13% 1	360
	21st to end	Night	22% 5% 27% 34% 12% 1	360
July	1st to 10th	Night	17% 5% 29% 35% 14% 1	350
	11th to 20th	Night	10% 2 24% 45% 16% 2	348
	21st to end	Night	18% 4 19% 45% 14%	394
August	1st to 10th	Night	16% 2 18% 44% 19% 1	358
	11th to 20th	Night	17% 3 19% 38% 21% 2	565
	21st to end	Night	18% 4 22% 33% 20% 2	792
September	1st to 10th	Night	19% 7% 23% 32% 17% 2	720
	11th to 20th	Night	20% 6% 22% 28% 21% 3	720
	21st to end	Night	24% 9% 25% 22% 17% 3	720
October	1st to 10th	Night	27% 10% 26% 23% 13% 1	720
	11th to 20th	Night	29% 12% 25% 24% 9% 1	720
	21st to end	Night	33% 14% 26% 22% 5%	792
November	1st to 10th	Night	31% 14% 30% 19% 5% 1	740
	11th to 20th	Night	32% 17% 24% 18% 8% 1	760
	21st to end	Night	35% 18% 24% 17% 6% 1	760
December	1st to 10th	Night	37% 18% 25% 16% 4	760
	11th to 20th	Night	32% 18% 27% 18% 5% 1	760
	21st to end	Night	37% 18% 23% 19% 3	836

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