University of Georgia Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the University of Georgia Observatory clear sky chart from 2005-11-06 to 2024-04-10.

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	14% 5% 2 5% 5% 3 5% 5% 6% 7% 42%	83487
	Night	14% 5% 2 5% 5% 3 4 5% 5% 7% 44%	85305
Transparency	Day	40% 5% 10% 20% 19% 6%	83210
	Night	39% 5% 10% 19% 21% 7%	85101
Seeing	Day	18% 8% 22% 23% 19% 9%	14177
	Night	17% 8% 21% 30% 21% 4	24336

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	17% 8% 2 5% 5% 3 4 4 5% 7% 40%	2836
	11th to 20th	Day	13% 5% 2 4 3 2 3 4 5% 6% 53%	2840
	21st to end	Day	27% 6% 2 5% 4 2 3 2 3 4 43%	3131
February	1st to 10th	Day	16% 7% 3 6% 5% 3 4 4 4 6% 41%	1900
	11th to 20th	Day	22% 6% 2 4 3 2 4 4 3 5% 44%	1848
	21st to end	Day	20% 7% 3 5% 5% 3 4 4 4 6% 41%	1570
March	1st to 10th	Day	24% 9% 3 6% 5% 2 3 3 3 5% 37%	3306
	11th to 20th	Day	12% 4 2 5% 4 3 4 4 5% 6% 50%	3480
	21st to end	Day	19% 5% 2 6% 5% 3 3 4 5% 6% 41%	3815
April	1st to 10th	Day	12% 4 2 4 6% 3 5% 4 6% 6% 48%	2080
	11th to 20th	Day	12% 5% 2 6% 5% 3 4 4 4 7% 47%	2116
	21st to end	Day	9% 4 2 4 4 3 4 4 5% 8% 52%	2340
May	1st to 10th	Day	10% 4 2 5% 4 3 5% 4 6% 8% 49%	2340
	11th to 20th	Day	11% 6% 3 6% 5% 4 6% 4 6% 7% 42%	2301
	21st to end	Day	11% 5% 2 6% 6% 4 5% 5% 7% 9% 40%	2531
June	1st to 10th	Day	10% 5% 2 6% 6% 4 7% 8% 7% 10% 34%	2340
	11th to 20th	Day	5% 4 2 3 5% 5% 7% 7% 8% 11% 42%	2340
	21st to end	Day	5% 4 2 7% 7% 5% 6% 8% 8% 10% 39%	2340
July	1st to 10th	Day	8% 5% 3 7% 7% 5% 8% 8% 8% 10% 31%	2340
	11th to 20th	Day	8% 6% 2 6% 7% 5% 8% 8% 9% 12% 29%	2340
	21st to end	Day	6% 5% 2 7% 6% 6% 8% 8% 10% 11% 32%	2547
August	1st to 10th	Day	9% 6% 3 7% 8% 5% 7% 7% 8% 11% 29%	2327
	11th to 20th	Day	12% 5% 2 7% 7% 4 7% 7% 8% 9% 31%	2250
	21st to end	Day	14% 7% 4 6% 8% 5% 6% 7% 7% 8% 30%	2332
September	1st to 10th	Day	11% 6% 2 5% 7% 4 6% 6% 6% 9% 39%	1980
	11th to 20th	Day	16% 5% 3 5% 5% 3 5% 6% 6% 7% 41%	1980
	21st to end	Day	15% 6% 2 4 4 3 4 4 4 5% 48%	1980
October	1st to 10th	Day	13% 5% 2 4 3 2 3 4 5% 6% 54%	1980
	11th to 20th	Day	12% 4 2 3 4 2 3 3 4 6% 55%	1830
	21st to end	Day	12% 4 2 4 4 3 2 3 4 5% 56%	1980
November	1st to 10th	Day	12% 4 2 4 4 3 3 3 4 4 56%	1760
	11th to 20th	Day	14% 4 2 3 3 2 4 4 5% 7% 53%	1710
	21st to end	Day	14% 5% 2 4 4 2 5% 4 5% 6% 49%	1710
December	1st to 10th	Day	19% 8% 3 4 4 4 5% 4 5% 5% 38%	1710
	11th to 20th	Day	18% 5% 2 5% 4 3 4 3 4 5% 48%	2153
	21st to end	Day	22% 7% 2 4 4 3 3 4 5% 7% 39%	3124
January	1st to 10th	Night	18% 6% 2 4 5% 3 4 4 4 6% 44%	4109
	11th to 20th	Night	13% 6% 2 4 5% 3 5% 4 5% 6% 47%	4120
	21st to end	Night	24% 8% 2 5% 4 2 3 3 3 4 42%	4523
February	1st to 10th	Night	15% 5% 2 4 5% 3 5% 4 4 6% 46%	2280
	11th to 20th	Night	21% 6% 3 6% 4 2 4 4 4 4 44%	2218
	21st to end	Night	19% 6% 2 5% 5% 3 4 3 4 6% 43%	1884
March	1st to 10th	Night	23% 7% 3 5% 5% 2 3 4 4 6% 37%	3546
	11th to 20th	Night	11% 4 2 3 4 2 4 5% 6% 8% 51%	3480
	21st to end	Night	19% 6% 2 4 4 3 4 4 5% 6% 43%	3817
April	1st to 10th	Night	11% 4 1 4 4 2 5% 4 6% 7% 50%	2090
	11th to 20th	Night	13% 5% 2 4 4 2 3 4 5% 8% 51%	1806
	21st to end	Night	9% 4 2 4 4 3 4 4 6% 7% 53%	1620
May	1st to 10th	Night	9% 5% 1 4 5% 3 5% 4 7% 8% 50%	1620
	11th to 20th	Night	10% 5% 2 6% 6% 4 6% 5% 7% 7% 42%	1592
	21st to end	Night	10% 5% 2 5% 5% 3 5% 5% 7% 10% 43%	1744
June	1st to 10th	Night	7% 4 3 6% 6% 4 6% 6% 8% 13% 37%	1620
	11th to 20th	Night	5% 4 2 5% 5% 3 6% 7% 8% 11% 44%	1620
	21st to end	Night	7% 4 2 5% 6% 4 6% 7% 8% 11% 40%	1620
July	1st to 10th	Night	9% 5% 3 7% 6% 3 6% 6% 9% 12% 33%	1620
	11th to 20th	Night	6% 4 3 6% 8% 4 6% 7% 9% 13% 34%	1620
	21st to end	Night	5% 5% 2 6% 6% 4 8% 8% 10% 13% 34%	1771
August	1st to 10th	Night	8% 5% 2 7% 7% 4 6% 7% 8% 14% 32%	1611
	11th to 20th	Night	12% 5% 2 5% 6% 4 6% 6% 7% 11% 34%	1646
	21st to end	Night	13% 7% 3 6% 7% 4 6% 7% 7% 8% 33%	2004
September	1st to 10th	Night	9% 5% 2 6% 5% 4 5% 5% 7% 11% 42%	1980
	11th to 20th	Night	13% 7% 2 4 5% 3 5% 5% 6% 7% 43%	1980
	21st to end	Night	12% 5% 2 4 4 3 5% 5% 5% 7% 48%	1980
October	1st to 10th	Night	12% 5% 2 4 4 3 4 5% 4 6% 53%	1980
	11th to 20th	Night	12% 4 2 4 5% 3 4 4 4 4 55%	2128
	21st to end	Night	12% 4 2 3 3 3 3 4 4 5% 58%	2376
November	1st to 10th	Night	13% 5% 2 3 3 2 3 3 4 6% 57%	2316
	11th to 20th	Night	15% 4 2 3 4 2 3 3 4 6% 53%	2470
	21st to end	Night	16% 4 2 3 4 3 4 4 5% 6% 48%	2470
December	1st to 10th	Night	17% 6% 3 5% 5% 3 4 4 5% 5% 43%	2470
	11th to 20th	Night	17% 6% 1 4 4 2 3 3 4 5% 51%	3042
	21st to end	Night	19% 7% 3 6% 6% 3 4 4 5% 6% 36%	4532

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	44% 4 6% 18% 20% 8%	2837
	11th to 20th	Day	33% 3 6% 24% 25% 9%	2840
	21st to end	Day	47% 2 3 17% 22% 9%	3131
February	1st to 10th	Day	46% 3 7% 19% 20% 6%	1900
	11th to 20th	Day	44% 3 5% 19% 22% 7%	1858
	21st to end	Day	45% 3 7% 16% 19% 9%	1570
March	1st to 10th	Day	52% 3 8% 14% 14% 10%	3306
	11th to 20th	Day	35% 4 7% 17% 26% 11%	3480
	21st to end	Day	45% 3 6% 21% 20% 4	3815
April	1st to 10th	Day	37% 4 9% 21% 23% 7%	2080
	11th to 20th	Day	37% 4 7% 20% 23% 9%	2116
	21st to end	Day	31% 4 9% 28% 24% 4	2340
May	1st to 10th	Day	33% 4 12% 24% 23% 4	2340
	11th to 20th	Day	41% 4 16% 22% 15% 2	2305
	21st to end	Day	39% 6% 11% 25% 17% 2	2531
June	1st to 10th	Day	42% 8% 17% 21% 10% 2	2340
	11th to 20th	Day	33% 8% 20% 26% 13% 1	2340
	21st to end	Day	36% 8% 18% 22% 12% 4	2340
July	1st to 10th	Day	43% 9% 18% 19% 8% 3	2275
	11th to 20th	Day	43% 10% 21% 17% 7% 3	2271
	21st to end	Day	40% 9% 20% 22% 9% 1	2405
August	1st to 10th	Day	45% 10% 17% 22% 6%	2314
	11th to 20th	Day	44% 8% 18% 17% 10% 2	2250
	21st to end	Day	50% 7% 14% 17% 10% 2	2332
September	1st to 10th	Day	40% 7% 13% 18% 18% 4	1980
	11th to 20th	Day	42% 6% 9% 19% 23% 2	1980
	21st to end	Day	38% 4 8% 23% 20% 7%	1980
October	1st to 10th	Day	32% 4 10% 21% 28% 7%	1980
	11th to 20th	Day	32% 3 7% 24% 26% 8%	1830
	21st to end	Day	31% 3 5% 18% 31% 11%	1980
November	1st to 10th	Day	32% 3 8% 15% 30% 12%	1760
	11th to 20th	Day	32% 3 7% 21% 27% 10%	1710
	21st to end	Day	36% 4 7% 21% 25% 7%	1710
December	1st to 10th	Day	47% 4 6% 19% 16% 7%	1710
	11th to 20th	Day	41% 3 6% 17% 24% 10%	2150
	21st to end	Day	44% 4 7% 21% 22% 3	3124
January	1st to 10th	Night	41% 4 5% 16% 25% 8%	4109
	11th to 20th	Night	38% 4 5% 22% 23% 9%	4120
	21st to end	Night	47% 2 4 13% 26% 7%	4523
February	1st to 10th	Night	40% 3 8% 19% 21% 9%	2280
	11th to 20th	Night	45% 3 4 18% 21% 9%	2219
	21st to end	Night	45% 3 6% 16% 20% 10%	1884
March	1st to 10th	Night	48% 3 9% 15% 16% 8%	3546
	11th to 20th	Night	31% 4 9% 15% 28% 13%	3480
	21st to end	Night	43% 3 7% 19% 19% 10%	3817
April	1st to 10th	Night	33% 4 10% 20% 23% 9%	2090
	11th to 20th	Night	32% 3 7% 23% 24% 11%	1806
	21st to end	Night	30% 4 10% 26% 24% 6%	1620
May	1st to 10th	Night	31% 5% 14% 23% 23% 5%	1620
	11th to 20th	Night	39% 7% 15% 20% 17% 2	1593
	21st to end	Night	36% 7% 12% 26% 16% 3	1745
June	1st to 10th	Night	37% 7% 20% 22% 13% 2	1620
	11th to 20th	Night	31% 7% 20% 28% 12% 2	1620
	21st to end	Night	35% 8% 20% 20% 12% 3	1620
July	1st to 10th	Night	41% 9% 22% 18% 9% 2	1575
	11th to 20th	Night	37% 11% 24% 17% 8% 2	1566
	21st to end	Night	34% 12% 24% 21% 7% 1	1672
August	1st to 10th	Night	40% 10% 20% 23% 6%	1600
	11th to 20th	Night	41% 9% 17% 18% 13% 1	1646
	21st to end	Night	46% 9% 16% 17% 10% 2	2004
September	1st to 10th	Night	36% 6% 17% 18% 18% 4	1980
	11th to 20th	Night	39% 7% 12% 19% 20% 4	1980
	21st to end	Night	36% 5% 12% 19% 21% 7%	1980
October	1st to 10th	Night	34% 3 10% 19% 27% 7%	1980
	11th to 20th	Night	33% 4 7% 22% 25% 10%	2128
	21st to end	Night	29% 3 5% 19% 30% 14%	2376
November	1st to 10th	Night	31% 3 7% 19% 27% 14%	2316
	11th to 20th	Night	33% 3 6% 18% 26% 14%	2470
	21st to end	Night	38% 2 6% 20% 26% 8%	2470
December	1st to 10th	Night	43% 4 7% 21% 19% 6%	2470
	11th to 20th	Night	37% 2 7% 18% 28% 8%	3044
	21st to end	Night	48% 4 6% 21% 18% 3	4532

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	26% 19% 39% 13% 3	270
	11th to 20th	Day	30% 15% 31% 18% 5%	270
	21st to end	Day	30% 16% 39% 12% 3	297
February	1st to 10th	Day	26% 15% 37% 18% 4	270
	11th to 20th	Day	38% 17% 32% 11% 1	270
	21st to end	Day	34% 20% 35% 10% 2	225
March	1st to 10th	Day	25% 13% 30% 21% 10% 1	378
	11th to 20th	Day	24% 15% 34% 18% 7% 1	460
	21st to end	Day	22% 15% 32% 23% 8%	506
April	1st to 10th	Day	22% 12% 31% 22% 12% 1	457
	11th to 20th	Day	15% 16% 29% 22% 16% 3	412
	21st to end	Day	18% 9% 27% 24% 18% 4	420
May	1st to 10th	Day	14% 11% 32% 22% 13% 7%	423
	11th to 20th	Day	15% 4 21% 29% 21% 10%	447
	21st to end	Day	15% 5% 14% 27% 26% 13%	485
June	1st to 10th	Day	13% 3 13% 29% 28% 14%	450
	11th to 20th	Day	8% 3 16% 28% 24% 21%	450
	21st to end	Day	8% 3 17% 30% 26% 16%	450
July	1st to 10th	Day	11% 2 7% 22% 30% 28%	445
	11th to 20th	Day	12% 2 5% 22% 35% 25%	444
	21st to end	Day	7% 2 7% 25% 38% 23%	488
August	1st to 10th	Day	15% 2 11% 23% 26% 22%	446
	11th to 20th	Day	14% 2 6% 21% 36% 20%	439
	21st to end	Day	17% 2 6% 23% 31% 21%	495
September	1st to 10th	Day	12% 2 9% 28% 34% 15%	450
	11th to 20th	Day	20% 2 10% 23% 31% 14%	450
	21st to end	Day	18% 3 15% 26% 29% 10%	450
October	1st to 10th	Day	18% 4 20% 30% 19% 10%	450
	11th to 20th	Day	14% 7% 26% 24% 23% 6%	450
	21st to end	Day	17% 7% 24% 27% 20% 4	495
November	1st to 10th	Day	20% 5% 27% 28% 16% 3	358
	11th to 20th	Day	20% 11% 38% 24% 6% 1	270
	21st to end	Day	13% 14% 33% 27% 10% 2	270
December	1st to 10th	Day	30% 12% 32% 22% 3	270
	11th to 20th	Day	27% 10% 37% 17% 7% 1	270
	21st to end	Day	34% 14% 27% 16% 5% 2	297
January	1st to 10th	Night	25% 15% 28% 24% 6% 1	760
	11th to 20th	Night	23% 14% 31% 24% 8%	760
	21st to end	Night	22% 16% 33% 25% 3	836
February	1st to 10th	Night	20% 12% 32% 32% 5%	760
	11th to 20th	Night	24% 15% 33% 23% 4	743
	21st to end	Night	22% 13% 35% 26% 3	628
March	1st to 10th	Night	19% 13% 29% 33% 5%	760
	11th to 20th	Night	18% 11% 33% 27% 10% 1	760
	21st to end	Night	18% 12% 30% 30% 9%	836
April	1st to 10th	Night	16% 14% 32% 26% 13%	760
	11th to 20th	Night	15% 10% 27% 31% 16% 1	583
	21st to end	Night	11% 7% 25% 35% 21% 1	540
May	1st to 10th	Night	11% 8% 25% 34% 21% 1	540
	11th to 20th	Night	13% 5% 19% 34% 24% 5%	531
	21st to end	Night	14% 1 12% 34% 34% 5%	584
June	1st to 10th	Night	11% 1 14% 36% 32% 6%	540
	11th to 20th	Night	6% 2 11% 32% 36% 12%	540
	21st to end	Night	8% 1 10% 37% 34% 9%	540
July	1st to 10th	Night	13% 2 4 26% 42% 13%	525
	11th to 20th	Night	7% 1 4 26% 49% 13%	522
	21st to end	Night	7% 1 5% 31% 46% 9%	591
August	1st to 10th	Night	11% 4 28% 45% 11%	537
	11th to 20th	Night	14% 2 4 27% 42% 11%	534
	21st to end	Night	17% 1 6% 26% 40% 10%	618
September	1st to 10th	Night	11% 1 8% 27% 42% 11%	720
	11th to 20th	Night	19% 1 10% 27% 39% 5%	720
	21st to end	Night	16% 2 13% 32% 34% 4	720
October	1st to 10th	Night	15% 3 18% 32% 26% 6%	720
	11th to 20th	Night	15% 5% 23% 34% 21% 3	720
	21st to end	Night	14% 7% 21% 34% 21% 3	792
November	1st to 10th	Night	16% 6% 22% 33% 21% 2	740
	11th to 20th	Night	18% 10% 25% 33% 13% 1	760
	21st to end	Night	18% 10% 25% 31% 14% 2	760
December	1st to 10th	Night	21% 11% 24% 34% 9% 1	760
	11th to 20th	Night	21% 11% 27% 30% 10% 1	760
	21st to end	Night	28% 10% 27% 29% 7%	836

Page generated at 2024-04-07 09:28:10. Version ac07

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