Savannah
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Savannah clear sky chart from 2005-11-06 to 2026-08-30.

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	10% 5% 2 6% 5% 5% 5% 4 7% 9% 41%	143632
	Night	11% 6% 2 6% 4 4 5% 4 6% 8% 44%	138594
Transparency	Day	38% 5% 16% 20% 15% 6%	147304
	Night	38% 4 14% 19% 18% 7%	142994
Seeing	Day	13% 7% 24% 28% 19% 9%	17897
	Night	13% 6% 21% 32% 23% 5%	27921

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	9% 4 2 6% 4 4 4 3 5% 8% 52%	5258
	11th to 20th	Day	14% 5% 2 6% 4 4 3 3 5% 7% 47%	5280
	21st to end	Day	14% 6% 2 6% 4 4 4 4 6% 7% 44%	5780
February	1st to 10th	Day	13% 7% 2 6% 5% 4 4 4 5% 6% 43%	1976
	11th to 20th	Day	18% 5% 2 5% 3 3 3 3 5% 5% 47%	2048
	21st to end	Day	12% 8% 3 6% 4 3 3 3 4 6% 48%	1824
March	1st to 10th	Day	20% 8% 2 6% 3 3 4 3 5% 6% 39%	5045
	11th to 20th	Day	8% 4 2 4 3 4 4 3 6% 7% 57%	5090
	21st to end	Day	13% 6% 2 5% 4 4 4 3 4 5% 49%	5586
April	1st to 10th	Day	9% 5% 1 4 3 4 4 4 6% 9% 50%	2310
	11th to 20th	Day	11% 4 2 4 3 3 4 4 5% 6% 54%	2431
	21st to end	Day	5% 4 1 5% 5% 3 4 4 6% 8% 55%	2571
May	1st to 10th	Day	13% 6% 2 6% 3 5% 4 4 7% 10% 39%	7616
	11th to 20th	Day	13% 5% 2 5% 4 4 5% 4 6% 9% 43%	7626
	21st to end	Day	8% 4 2 7% 5% 6% 6% 5% 8% 10% 39%	8391
June	1st to 10th	Day	9% 6% 3 7% 6% 5% 7% 6% 9% 10% 34%	2730
	11th to 20th	Day	6% 5% 2 6% 6% 6% 7% 6% 8% 11% 38%	2730
	21st to end	Day	7% 5% 2 7% 5% 6% 7% 6% 9% 12% 33%	2730
July	1st to 10th	Day	7% 5% 2 8% 6% 8% 8% 7% 10% 13% 27%	7680
	11th to 20th	Day	4 4 2 7% 6% 7% 8% 7% 11% 15% 31%	7680
	21st to end	Day	3 3 2 6% 6% 6% 7% 6% 11% 16% 34%	8340
August	1st to 10th	Day	17% 8% 3 8% 5% 6% 7% 6% 9% 11% 22%	4364
	11th to 20th	Day	5% 5% 2 6% 5% 6% 6% 6% 9% 13% 37%	4278
	21st to end	Day	10% 7% 3 7% 6% 5% 5% 5% 8% 11% 32%	4295
September	1st to 10th	Day	11% 6% 3 8% 7% 6% 6% 5% 6% 9% 33%	2200
	11th to 20th	Day	14% 7% 3 7% 6% 6% 5% 5% 6% 9% 33%	2200
	21st to end	Day	13% 6% 3 6% 5% 5% 6% 4 6% 7% 39%	2200
October	1st to 10th	Day	12% 6% 2 6% 5% 4 4 4 5% 6% 46%	2108
	11th to 20th	Day	10% 4 1 3 3 2 3 3 4 6% 59%	2000
	21st to end	Day	10% 5% 2 5% 4 3 3 3 5% 6% 55%	2200
November	1st to 10th	Day	11% 5% 2 4 4 3 4 4 5% 6% 53%	2057
	11th to 20th	Day	11% 6% 2 5% 4 3 3 2 4 6% 53%	2070
	21st to end	Day	12% 6% 2 4 4 3 4 3 4 6% 51%	1890
December	1st to 10th	Day	8% 5% 2 6% 5% 4 4 3 4 6% 54%	3020
	11th to 20th	Day	13% 6% 2 5% 3 3 4 4 5% 6% 50%	3463
	21st to end	Day	17% 9% 3 7% 4 3 3 3 5% 6% 41%	4565
January	1st to 10th	Night	9% 5% 2 5% 4 4 4 3 5% 6% 52%	7635
	11th to 20th	Night	11% 6% 2 6% 3 4 4 4 5% 7% 47%	7680
	21st to end	Night	15% 8% 3 6% 4 4 4 3 4 6% 44%	8401
February	1st to 10th	Night	15% 6% 2 6% 5% 4 4 3 5% 6% 44%	2641
	11th to 20th	Night	15% 8% 2 6% 3 4 3 3 4 6% 46%	2458
	21st to end	Night	11% 6% 2 6% 5% 5% 5% 4 5% 7% 45%	1981
March	1st to 10th	Night	18% 9% 3 6% 3 3 3 2 4 5% 42%	5028
	11th to 20th	Night	8% 4 2 5% 3 3 4 4 6% 9% 52%	5090
	21st to end	Night	12% 5% 2 5% 4 3 4 3 5% 7% 51%	5588
April	1st to 10th	Night	10% 4 2 4 4 5% 5% 4 5% 8% 48%	2310
	11th to 20th	Night	11% 4 2 5% 3 3 3 3 4 7% 55%	2137
	21st to end	Night	7% 4 2 5% 3 3 4 3 7% 8% 54%	2065
May	1st to 10th	Night	10% 6% 2 7% 5% 5% 5% 3 5% 9% 42%	5237
	11th to 20th	Night	13% 5% 2 5% 4 4 4 4 8% 10% 43%	5234
	21st to end	Night	9% 5% 2 6% 5% 5% 6% 5% 8% 9% 38%	5761
June	1st to 10th	Night	10% 5% 2 6% 5% 5% 6% 5% 8% 12% 35%	1890
	11th to 20th	Night	6% 6% 2 6% 5% 5% 6% 5% 9% 13% 36%	1890
	21st to end	Night	6% 5% 2 6% 4 6% 7% 8% 9% 13% 34%	1890
July	1st to 10th	Night	6% 5% 3 7% 6% 6% 7% 6% 9% 13% 31%	5278
	11th to 20th	Night	4 5% 2 8% 6% 6% 7% 6% 9% 13% 34%	5277
	21st to end	Night	5% 4 3 7% 6% 6% 7% 7% 10% 14% 33%	5736
August	1st to 10th	Night	16% 7% 2 7% 5% 5% 6% 6% 9% 12% 25%	3005
	11th to 20th	Night	5% 4 2 6% 5% 5% 6% 6% 9% 13% 38%	2965
	21st to end	Night	9% 6% 2 7% 5% 5% 5% 4 6% 9% 40%	3785
September	1st to 10th	Night	12% 6% 3 6% 4 5% 6% 5% 8% 10% 34%	2200
	11th to 20th	Night	10% 7% 3 7% 6% 5% 6% 4 6% 9% 37%	2200
	21st to end	Night	13% 6% 3 8% 5% 4 5% 4 7% 7% 38%	2200
October	1st to 10th	Night	13% 7% 2 6% 3 4 4 3 5% 7% 46%	2290
	11th to 20th	Night	9% 4 1 4 3 3 4 3 4 6% 59%	2400
	21st to end	Night	10% 4 2 5% 3 4 4 3 5% 5% 56%	2640
November	1st to 10th	Night	11% 4 2 5% 4 3 4 3 4 5% 55%	2461
	11th to 20th	Night	12% 6% 2 5% 4 3 4 3 4 7% 51%	2546
	21st to end	Night	11% 6% 2 6% 4 5% 4 3 5% 6% 48%	2730
December	1st to 10th	Night	11% 5% 2 5% 3 3 3 3 4 6% 56%	4380
	11th to 20th	Night	13% 9% 3 8% 4 4 3 3 4 5% 44%	4952
	21st to end	Night	17% 7% 2 6% 4 4 4 3 4 5% 43%	6633

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	33% 2 9% 22% 26% 9%	5259
	11th to 20th	Day	39% 1 4 18% 25% 13%	5280
	21st to end	Day	40% 2 9% 20% 17% 11%	5780
February	1st to 10th	Day	41% 3 8% 20% 20% 8%	1976
	11th to 20th	Day	40% 3 8% 19% 23% 8%	2058
	21st to end	Day	39% 2 8% 19% 19% 12%	1824
March	1st to 10th	Day	48% 2 7% 17% 19% 8%	5045
	11th to 20th	Day	28% 2 12% 17% 19% 21%	5090
	21st to end	Day	39% 2 10% 21% 18% 11%	5586
April	1st to 10th	Day	31% 4 13% 24% 18% 9%	2310
	11th to 20th	Day	32% 3 10% 24% 21% 10%	2431
	21st to end	Day	26% 4 13% 29% 23% 5%	2571
May	1st to 10th	Day	41% 4 17% 23% 13% 2	7651
	11th to 20th	Day	38% 3 17% 27% 13% 2	7630
	21st to end	Day	38% 6% 20% 18% 16% 1	8405
June	1st to 10th	Day	42% 7% 20% 18% 12% 1	2730
	11th to 20th	Day	38% 6% 21% 25% 10%	2730
	21st to end	Day	38% 9% 25% 19% 7% 1	2730
July	1st to 10th	Day	44% 8% 29% 16% 2	7615
	11th to 20th	Day	37% 10% 38% 13% 2	7611
	21st to end	Day	33% 9% 32% 21% 4	8156
August	1st to 10th	Day	53% 7% 27% 11% 2	4351
	11th to 20th	Day	35% 8% 24% 25% 8%	4317
	21st to end	Day	44% 7% 18% 27% 3	4295
September	1st to 10th	Day	48% 6% 17% 14% 12% 2	2200
	11th to 20th	Day	48% 6% 13% 20% 11% 2	2200
	21st to end	Day	43% 4 16% 20% 15% 3	2200
October	1st to 10th	Day	45% 3 7% 14% 21% 11%	3433
	11th to 20th	Day	17% 3 5% 15% 31% 29%	3240
	21st to end	Day	24% 3 6% 22% 35% 11%	3538
November	1st to 10th	Day	32% 3 10% 18% 24% 13%	2057
	11th to 20th	Day	34% 2 8% 20% 26% 11%	2070
	21st to end	Day	36% 3 9% 24% 21% 9%	1890
December	1st to 10th	Day	33% 3 10% 18% 25% 12%	3020
	11th to 20th	Day	36% 3 8% 26% 22% 6%	3460
	21st to end	Day	46% 2 6% 21% 22% 3	4565
January	1st to 10th	Night	34% 2 8% 16% 31% 9%	7636
	11th to 20th	Night	37% 2 5% 16% 28% 12%	7680
	21st to end	Night	44% 2 8% 15% 21% 10%	8401
February	1st to 10th	Night	42% 2 7% 19% 22% 9%	2641
	11th to 20th	Night	42% 2 9% 17% 19% 12%	2459
	21st to end	Night	41% 3 8% 19% 15% 13%	1981
March	1st to 10th	Night	45% 2 8% 16% 17% 12%	5028
	11th to 20th	Night	30% 3 9% 16% 22% 19%	5090
	21st to end	Night	35% 2 11% 19% 22% 12%	5588
April	1st to 10th	Night	34% 4 13% 21% 18% 10%	2310
	11th to 20th	Night	31% 3 8% 25% 22% 11%	2137
	21st to end	Night	27% 3 14% 26% 22% 6%	2065
May	1st to 10th	Night	40% 4 18% 24% 12% 2	5264
	11th to 20th	Night	37% 4 20% 25% 12% 2	5235
	21st to end	Night	41% 7% 16% 23% 12% 1	5771
June	1st to 10th	Night	40% 6% 22% 21% 10% 1	1890
	11th to 20th	Night	37% 9% 23% 25% 7%	1890
	21st to end	Night	36% 11% 28% 19% 6% 1	1890
July	1st to 10th	Night	41% 9% 30% 19% 1	5235
	11th to 20th	Night	39% 11% 36% 12% 2	5226
	21st to end	Night	37% 10% 29% 19% 4	5606
August	1st to 10th	Night	49% 10% 27% 12% 2	2994
	11th to 20th	Night	32% 9% 28% 24% 7%	2992
	21st to end	Night	40% 7% 20% 30% 3	3785
September	1st to 10th	Night	43% 8% 20% 16% 12% 2	2200
	11th to 20th	Night	44% 7% 18% 19% 11% 1	2200
	21st to end	Night	44% 5% 14% 19% 16% 2	2200
October	1st to 10th	Night	40% 4 10% 16% 21% 9%	3745
	11th to 20th	Night	18% 2 4 15% 32% 30%	3899
	21st to end	Night	24% 3 5% 18% 34% 15%	4252
November	1st to 10th	Night	34% 2 9% 18% 24% 13%	2461
	11th to 20th	Night	36% 2 7% 20% 24% 11%	2546
	21st to end	Night	37% 2 9% 19% 22% 10%	2730
December	1st to 10th	Night	32% 2 10% 18% 27% 12%	4380
	11th to 20th	Night	44% 2 10% 16% 20% 8%	4954
	21st to end	Night	44% 2 7% 21% 22% 3	6633

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	14% 15% 47% 20% 4	330
	11th to 20th	Day	13% 13% 42% 23% 7% 2	330
	21st to end	Day	23% 19% 40% 15% 3	363
February	1st to 10th	Day	16% 16% 41% 21% 5%	330
	11th to 20th	Day	26% 14% 40% 18% 2	330
	21st to end	Day	16% 16% 40% 22% 5% 1	367
March	1st to 10th	Day	18% 12% 32% 25% 11% 2	540
	11th to 20th	Day	16% 10% 39% 23% 9% 2	540
	21st to end	Day	15% 11% 40% 24% 10% 1	594
April	1st to 10th	Day	15% 11% 37% 23% 11% 2	540
	11th to 20th	Day	11% 10% 35% 26% 12% 6%	532
	21st to end	Day	7% 7% 30% 31% 18% 7%	540
May	1st to 10th	Day	8% 10% 33% 27% 13% 8%	543
	11th to 20th	Day	12% 3 23% 35% 17% 10%	567
	21st to end	Day	10% 3 20% 28% 25% 13%	617
June	1st to 10th	Day	12% 3 16% 31% 24% 14%	570
	11th to 20th	Day	10% 3 17% 31% 19% 21%	570
	21st to end	Day	6% 2 12% 34% 29% 18%	570
July	1st to 10th	Day	6% 3 5% 29% 34% 22%	565
	11th to 20th	Day	6% 1 3 30% 36% 24%	564
	21st to end	Day	5% 2 7% 35% 34% 16%	620
August	1st to 10th	Day	14% 1 7% 27% 34% 17%	566
	11th to 20th	Day	7% 2 4 28% 37% 22%	559
	21st to end	Day	16% 3 7% 24% 32% 17%	619
September	1st to 10th	Day	14% 2 11% 27% 32% 14%	530
	11th to 20th	Day	17% 2 13% 31% 27% 10%	530
	21st to end	Day	15% 3 12% 31% 27% 12%	530
October	1st to 10th	Day	17% 3 25% 30% 16% 8%	530
	11th to 20th	Day	11% 7% 25% 30% 21% 7%	530
	21st to end	Day	11% 6% 27% 33% 18% 5%	583
November	1st to 10th	Day	17% 5% 26% 31% 17% 4	535
	11th to 20th	Day	17% 6% 38% 27% 11% 1	510
	21st to end	Day	15% 9% 37% 28% 9% 2	330
December	1st to 10th	Day	18% 12% 41% 20% 9% 2	330
	11th to 20th	Day	18% 12% 33% 26% 9% 1	330
	21st to end	Day	23% 8% 32% 28% 8% 1	363
January	1st to 10th	Night	14% 12% 38% 28% 8%	840
	11th to 20th	Night	14% 11% 31% 32% 11% 1	840
	21st to end	Night	19% 10% 37% 29% 4	924
February	1st to 10th	Night	19% 8% 34% 30% 9%	840
	11th to 20th	Night	20% 12% 31% 32% 5%	823
	21st to end	Night	15% 10% 35% 33% 6%	692
March	1st to 10th	Night	13% 8% 32% 35% 11%	840
	11th to 20th	Night	13% 9% 31% 35% 11% 1	840
	21st to end	Night	12% 9% 32% 34% 13% 1	924
April	1st to 10th	Night	13% 8% 32% 33% 13% 1	840
	11th to 20th	Night	13% 8% 30% 30% 18% 2	831
	21st to end	Night	9% 5% 25% 40% 20% 2	805
May	1st to 10th	Night	10% 3 22% 38% 23% 3	630
	11th to 20th	Night	10% 2 19% 38% 24% 6%	621
	21st to end	Night	12% 3 9% 34% 32% 11%	683
June	1st to 10th	Night	13% 2 9% 38% 32% 6%	630
	11th to 20th	Night	9% 2 7% 34% 31% 16%	630
	21st to end	Night	7% 2 9% 35% 37% 11%	630
July	1st to 10th	Night	8% 2 5% 29% 43% 13%	615
	11th to 20th	Night	9% 1 2 25% 49% 15%	612
	21st to end	Night	6% 2 3 35% 47% 8%	690
August	1st to 10th	Night	12% 1 5% 27% 42% 13%	627
	11th to 20th	Night	7% 1 3 25% 48% 15%	624
	21st to end	Night	17% 4 6% 25% 36% 13%	906
September	1st to 10th	Night	13% 3 7% 24% 43% 9%	800
	11th to 20th	Night	12% 3 10% 31% 39% 6%	800
	21st to end	Night	17% 2 9% 30% 35% 8%	800
October	1st to 10th	Night	16% 3 18% 32% 26% 6%	800
	11th to 20th	Night	11% 5% 17% 33% 28% 5%	800
	21st to end	Night	12% 4 21% 36% 25% 3	880
November	1st to 10th	Night	13% 6% 22% 36% 21% 2	820
	11th to 20th	Night	17% 7% 26% 34% 15% 2	840
	21st to end	Night	13% 7% 30% 32% 16% 1	840
December	1st to 10th	Night	18% 7% 29% 31% 13% 1	840
	11th to 20th	Night	18% 9% 26% 32% 14% 2	840
	21st to end	Night	20% 8% 30% 30% 12%	924

Page generated at 2026-08-27 04:07:16. Version ac07

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