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 2024-11-05.

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	13% 6% 2 6% 4 4 5% 4 6% 8% 42%	101011
	Night	14% 6% 2 6% 4 4 4 4 6% 7% 44%	97986
Transparency	Day	39% 5% 11% 20% 19% 6%	104805
	Night	38% 5% 10% 19% 20% 7%	102331
Seeing	Day	18% 8% 22% 23% 20% 9%	15012
	Night	17% 8% 21% 30% 21% 4	25033

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 6% 4 3 5% 3 5% 7% 40%	2836
	11th to 20th	Day	13% 5% 2 5% 3 3 3 3 5% 6% 52%	2840
	21st to end	Day	27% 6% 2 5% 3 2 3 2 3 4 43%	3131
February	1st to 10th	Day	16% 7% 3 7% 5% 4 4 3 5% 5% 41%	1900
	11th to 20th	Day	22% 6% 2 4 3 3 4 3 3 5% 44%	1848
	21st to end	Day	20% 7% 3 6% 4 4 4 3 4 5% 41%	1570
March	1st to 10th	Day	24% 9% 3 7% 4 3 3 2 4 5% 37%	3306
	11th to 20th	Day	12% 5% 2 6% 3 4 4 3 5% 6% 50%	3480
	21st to end	Day	19% 5% 2 7% 5% 4 3 4 5% 6% 41%	3815
April	1st to 10th	Day	12% 5% 2 5% 5% 4 4 3 6% 5% 48%	2090
	11th to 20th	Day	11% 6% 2 6% 4 4 4 3 4 7% 48%	2235
	21st to end	Day	10% 4 2 5% 3 4 4 3 6% 8% 52%	2470
May	1st to 10th	Day	11% 7% 3 7% 4 4 4 4 7% 9% 41%	4082
	11th to 20th	Day	16% 8% 3 7% 4 4 4 3 5% 7% 38%	4081
	21st to end	Day	8% 4 2 6% 4 4 5% 4 7% 10% 45%	4476
June	1st to 10th	Day	9% 5% 3 7% 6% 6% 8% 6% 7% 10% 33%	2470
	11th to 20th	Day	5% 5% 1 4 5% 7% 6% 6% 8% 10% 43%	2470
	21st to end	Day	5% 4 2 8% 6% 6% 6% 6% 8% 10% 39%	2470
July	1st to 10th	Day	9% 6% 3 8% 6% 8% 7% 6% 8% 10% 29%	4120
	11th to 20th	Day	7% 6% 2 7% 6% 6% 7% 6% 8% 11% 34%	4120
	21st to end	Day	10% 8% 3 9% 7% 9% 8% 6% 9% 11% 21%	4466
August	1st to 10th	Day	11% 6% 2 7% 5% 5% 6% 5% 8% 11% 33%	4104
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 5% 8% 10% 42%	3949
	21st to end	Day	8% 5% 2 5% 4 5% 4 4 6% 8% 49%	4094
September	1st to 10th	Day	10% 6% 2 6% 6% 5% 5% 5% 7% 9% 39%	2090
	11th to 20th	Day	16% 5% 3 6% 5% 4 4 4 6% 6% 39%	2090
	21st to end	Day	15% 6% 2 5% 4 4 4 4 4 6% 47%	2090
October	1st to 10th	Day	13% 5% 2 5% 3 2 3 3 5% 6% 54%	2090
	11th to 20th	Day	12% 5% 2 4 3 3 3 2 4 6% 57%	1931
	21st to end	Day	11% 4 1 5% 3 3 2 3 4 5% 57%	2090
November	1st to 10th	Day	11% 4 2 5% 4 3 3 3 4 4 55%	1800
	11th to 20th	Day	14% 4 1 3 3 3 3 3 5% 7% 52%	1710
	21st to end	Day	14% 6% 2 5% 3 4 4 3 5% 7% 48%	1710
December	1st to 10th	Day	19% 8% 3 5% 4 4 4 3 5% 5% 38%	1710
	11th to 20th	Day	18% 6% 2 5% 3 4 4 3 4 5% 48%	2153
	21st to end	Day	22% 7% 2 5% 3 3 3 3 5% 8% 39%	3124
January	1st to 10th	Night	18% 6% 2 5% 4 4 4 3 4 6% 44%	4109
	11th to 20th	Night	12% 6% 2 5% 4 4 4 3 5% 6% 47%	4120
	21st to end	Night	23% 8% 2 6% 3 3 3 2 3 4 42%	4523
February	1st to 10th	Night	15% 6% 2 5% 4 4 4 3 4 6% 46%	2280
	11th to 20th	Night	20% 6% 2 6% 4 3 4 3 4 4 44%	2218
	21st to end	Night	18% 7% 1 6% 4 4 4 2 4 6% 43%	1884
March	1st to 10th	Night	23% 8% 2 5% 4 3 4 3 4 6% 37%	3546
	11th to 20th	Night	11% 5% 1 4 3 3 3 4 7% 8% 51%	3480
	21st to end	Night	19% 6% 2 5% 3 4 3 4 4 6% 42%	3817
April	1st to 10th	Night	11% 4 2 5% 4 4 4 4 7% 6% 49%	2090
	11th to 20th	Night	12% 5% 2 5% 3 3 3 4 6% 8% 49%	1906
	21st to end	Night	9% 4 2 5% 3 4 4 3 6% 7% 52%	1710
May	1st to 10th	Night	9% 7% 2 7% 4 5% 5% 5% 7% 9% 42%	2813
	11th to 20th	Night	15% 7% 1 6% 5% 5% 4 3 6% 6% 42%	2812
	21st to end	Night	7% 4 1 4 4 4 4 4 8% 11% 48%	3079
June	1st to 10th	Night	7% 5% 3 8% 5% 6% 5% 5% 8% 12% 37%	1710
	11th to 20th	Night	5% 5% 1 6% 5% 5% 6% 6% 8% 12% 43%	1710
	21st to end	Night	7% 4 1 6% 5% 6% 6% 5% 8% 10% 40%	1710
July	1st to 10th	Night	12% 6% 3 8% 6% 5% 6% 4 8% 10% 32%	2840
	11th to 20th	Night	6% 5% 3 8% 7% 6% 6% 6% 10% 13% 31%	2840
	21st to end	Night	12% 8% 3 9% 6% 6% 7% 6% 9% 11% 23%	3087
August	1st to 10th	Night	10% 6% 2 7% 5% 5% 6% 5% 9% 14% 30%	2825
	11th to 20th	Night	10% 5% 2 6% 5% 6% 5% 5% 7% 10% 40%	2875
	21st to end	Night	8% 5% 2 5% 5% 5% 5% 4 6% 8% 47%	3528
September	1st to 10th	Night	9% 6% 2 7% 4 5% 4 4 7% 10% 41%	2090
	11th to 20th	Night	14% 7% 2 4 5% 4 5% 4 6% 7% 41%	2090
	21st to end	Night	13% 5% 2 5% 4 4 4 4 5% 7% 47%	2090
October	1st to 10th	Night	12% 5% 2 5% 3 4 3 4 4 6% 53%	2090
	11th to 20th	Night	12% 5% 1 4 4 3 3 3 4 4 57%	2247
	21st to end	Night	11% 4 2 3 3 3 4 3 4 5% 59%	2508
November	1st to 10th	Night	13% 6% 2 4 3 3 2 3 4 6% 55%	2375
	11th to 20th	Night	15% 5% 2 4 3 3 3 3 4 6% 53%	2470
	21st to end	Night	16% 5% 2 4 4 4 3 3 5% 6% 48%	2470
December	1st to 10th	Night	17% 6% 2 6% 4 4 4 3 5% 5% 43%	2470
	11th to 20th	Night	17% 6% 1 5% 3 3 3 2 4 5% 51%	3042
	21st to end	Night	19% 7% 3 7% 5% 4 4 4 6% 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%	2090
	11th to 20th	Day	36% 4 8% 19% 23% 10%	2235
	21st to end	Day	31% 4 9% 28% 24% 4	2470
May	1st to 10th	Day	39% 5% 13% 23% 18% 3	4120
	11th to 20th	Day	45% 4 12% 24% 14% 1	4085
	21st to end	Day	33% 7% 14% 23% 21% 2	4489
June	1st to 10th	Day	42% 8% 17% 21% 10% 2	2470
	11th to 20th	Day	31% 8% 19% 26% 15% 1	2470
	21st to end	Day	36% 8% 18% 21% 13% 4	2470
July	1st to 10th	Day	45% 10% 19% 20% 5% 1	4055
	11th to 20th	Day	40% 11% 23% 20% 4 2	4051
	21st to end	Day	53% 12% 15% 14% 5%	4324
August	1st to 10th	Day	41% 8% 16% 29% 6%	4091
	11th to 20th	Day	34% 7% 18% 24% 14% 2	3988
	21st to end	Day	33% 6% 15% 24% 19% 4	4094
September	1st to 10th	Day	40% 7% 13% 18% 18% 4	2090
	11th to 20th	Day	43% 6% 9% 19% 22% 2	2090
	21st to end	Day	38% 3 10% 22% 20% 7%	2090
October	1st to 10th	Day	27% 2 7% 15% 37% 12%	3480
	11th to 20th	Day	21% 2 4 16% 29% 29%	3184
	21st to end	Day	25% 3 4 22% 32% 14%	3428
November	1st to 10th	Day	33% 3 8% 15% 29% 12%	1800
	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	34% 4 10% 20% 23% 9%	2090
	11th to 20th	Night	33% 4 7% 22% 24% 11%	1906
	21st to end	Night	31% 4 10% 26% 23% 6%	1710
May	1st to 10th	Night	36% 7% 15% 22% 17% 3	2840
	11th to 20th	Night	42% 5% 13% 23% 16% 1	2813
	21st to end	Night	27% 7% 15% 28% 20% 3	3087
June	1st to 10th	Night	37% 7% 20% 21% 13% 2	1710
	11th to 20th	Night	31% 6% 20% 28% 13% 2	1710
	21st to end	Night	35% 8% 20% 20% 13% 4	1710
July	1st to 10th	Night	46% 10% 21% 17% 5% 1	2795
	11th to 20th	Night	39% 13% 23% 19% 5% 1	2786
	21st to end	Night	52% 13% 18% 13% 4 1	2988
August	1st to 10th	Night	41% 9% 21% 24% 5%	2814
	11th to 20th	Night	38% 8% 20% 20% 13% 1	2902
	21st to end	Night	34% 7% 13% 23% 21% 2	3528
September	1st to 10th	Night	37% 6% 17% 18% 17% 4	2090
	11th to 20th	Night	40% 7% 12% 19% 19% 4	2090
	21st to end	Night	36% 5% 12% 18% 21% 7%	2090
October	1st to 10th	Night	29% 3 8% 15% 36% 9%	3480
	11th to 20th	Night	19% 2 4 17% 28% 30%	3733
	21st to end	Night	23% 3 4 21% 31% 19%	4120
November	1st to 10th	Night	32% 3 7% 19% 26% 13%	2375
	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% 11% 32% 21% 12% 1	460
	11th to 20th	Day	15% 15% 31% 22% 14% 3	452
	21st to end	Day	18% 8% 27% 25% 18% 4	460
May	1st to 10th	Day	14% 11% 31% 22% 14% 7%	463
	11th to 20th	Day	16% 4 22% 28% 21% 9%	487
	21st to end	Day	14% 5% 16% 29% 25% 12%	529
June	1st to 10th	Day	13% 3 15% 29% 27% 12%	490
	11th to 20th	Day	8% 3 16% 29% 24% 20%	490
	21st to end	Day	8% 3 16% 30% 27% 16%	490
July	1st to 10th	Day	11% 2 7% 22% 30% 29%	485
	11th to 20th	Day	11% 2 5% 21% 35% 26%	484
	21st to end	Day	8% 2 7% 25% 37% 22%	532
August	1st to 10th	Day	15% 2 13% 23% 26% 22%	486
	11th to 20th	Day	13% 2 8% 22% 35% 19%	479
	21st to end	Day	15% 2 6% 24% 31% 22%	539
September	1st to 10th	Day	12% 2 10% 29% 32% 14%	490
	11th to 20th	Day	23% 2 10% 23% 30% 13%	490
	21st to end	Day	18% 4 17% 24% 28% 9%	490
October	1st to 10th	Day	17% 3 20% 31% 20% 9%	490
	11th to 20th	Day	13% 7% 27% 25% 22% 6%	490
	21st to end	Day	16% 7% 24% 28% 22% 3	539
November	1st to 10th	Day	20% 5% 27% 29% 16% 3	374
	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% 31% 26% 13%	760
	11th to 20th	Night	16% 10% 28% 31% 15% 1	615
	21st to end	Night	12% 6% 25% 35% 20% 1	570
May	1st to 10th	Night	12% 8% 25% 34% 21% 1	570
	11th to 20th	Night	14% 4 19% 33% 24% 5%	561
	21st to end	Night	13% 1 13% 35% 33% 5%	617
June	1st to 10th	Night	12% 1 14% 36% 32% 6%	570
	11th to 20th	Night	6% 2 12% 32% 36% 11%	570
	21st to end	Night	8% 1 10% 37% 34% 9%	570
July	1st to 10th	Night	13% 2 5% 26% 42% 13%	555
	11th to 20th	Night	7% 1 4 26% 48% 13%	552
	21st to end	Night	8% 1 6% 32% 45% 9%	624
August	1st to 10th	Night	11% 1 5% 28% 44% 11%	567
	11th to 20th	Night	14% 2 5% 27% 41% 10%	564
	21st to end	Night	16% 1 6% 27% 40% 10%	653
September	1st to 10th	Night	11% 1 9% 27% 41% 10%	760
	11th to 20th	Night	19% 1 10% 27% 38% 5%	760
	21st to end	Night	16% 2 14% 32% 33% 3	760
October	1st to 10th	Night	14% 3 18% 34% 26% 6%	760
	11th to 20th	Night	14% 5% 22% 35% 21% 3	760
	21st to end	Night	14% 7% 20% 35% 22% 2	836
November	1st to 10th	Night	16% 6% 22% 33% 20% 2	760
	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

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