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 2025-04-11.

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	11% 6% 2 6% 5% 4 5% 4 6% 8% 42%	113956
	Night	11% 6% 2 6% 4 4 5% 4 6% 8% 45%	114346
Transparency	Day	38% 4 14% 20% 17% 7%	117672
	Night	37% 4 12% 19% 19% 8%	118769
Seeing	Day	13% 6% 24% 28% 20% 10%	15971
	Night	13% 6% 21% 32% 23% 5%	26128

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	10% 4 2 5% 3 3 4 3 5% 5% 56%	4056
	11th to 20th	Day	15% 6% 2 6% 4 3 3 3 5% 7% 47%	4060
	21st to end	Day	13% 7% 2 6% 4 3 3 3 5% 7% 46%	4466
February	1st to 10th	Day	14% 7% 2 6% 5% 4 4 4 5% 7% 42%	1882
	11th to 20th	Day	19% 5% 2 5% 3 3 3 3 5% 5% 47%	1948
	21st to end	Day	13% 7% 3 5% 4 3 3 3 4 7% 49%	1740
March	1st to 10th	Day	21% 8% 3 6% 3 3 4 3 5% 6% 39%	4935
	11th to 20th	Day	7% 4 2 4 3 3 4 3 6% 7% 57%	4980
	21st to end	Day	13% 6% 2 5% 4 4 4 3 4 5% 49%	5465
April	1st to 10th	Day	9% 5% 1 4 4 4 4 4 6% 9% 50%	2200
	11th to 20th	Day	12% 5% 2 5% 4 3 4 4 5% 6% 52%	2197
	21st to end	Day	5% 3 1 5% 5% 3 4 4 6% 8% 57%	2326
May	1st to 10th	Day	6% 4 2 5% 3 5% 5% 5% 8% 10% 48%	4082
	11th to 20th	Day	13% 6% 2 7% 4 4 5% 4 5% 8% 41%	4081
	21st to end	Day	6% 3 1 5% 4 4 5% 5% 7% 10% 49%	4476
June	1st to 10th	Day	9% 5% 3 7% 6% 6% 7% 6% 9% 10% 34%	2470
	11th to 20th	Day	6% 5% 2 6% 6% 6% 7% 6% 7% 11% 39%	2470
	21st to end	Day	7% 5% 2 7% 6% 6% 7% 6% 10% 11% 32%	2470
July	1st to 10th	Day	11% 6% 2 7% 6% 7% 7% 7% 9% 12% 25%	4120
	11th to 20th	Day	5% 4 2 7% 7% 8% 8% 8% 11% 15% 26%	4120
	21st to end	Day	5% 5% 2 9% 8% 8% 8% 7% 11% 14% 24%	4466
August	1st to 10th	Day	17% 8% 2 7% 5% 6% 7% 6% 8% 11% 23%	4104
	11th to 20th	Day	6% 5% 2 6% 5% 6% 6% 6% 9% 13% 37%	4020
	21st to end	Day	10% 8% 3 8% 5% 5% 5% 5% 8% 11% 32%	4061
September	1st to 10th	Day	11% 6% 3 8% 7% 7% 6% 5% 6% 9% 31%	2090
	11th to 20th	Day	15% 7% 3 7% 6% 6% 6% 4 6% 9% 32%	2090
	21st to end	Day	13% 6% 3 6% 5% 5% 6% 4 7% 7% 39%	2090
October	1st to 10th	Day	12% 6% 2 6% 5% 3 4 4 5% 5% 47%	2003
	11th to 20th	Day	10% 4 1 4 3 2 3 3 4 6% 59%	1900
	21st to end	Day	9% 5% 2 5% 4 3 3 3 5% 6% 55%	2090
November	1st to 10th	Day	12% 5% 2 4 4 3 4 4 5% 6% 52%	1957
	11th to 20th	Day	12% 6% 2 5% 4 4 4 2 4 6% 51%	1972
	21st to end	Day	13% 6% 2 5% 4 3 4 3 4 6% 51%	1800
December	1st to 10th	Day	7% 4 2 6% 5% 4 4 3 4 6% 55%	2930
	11th to 20th	Day	14% 6% 2 5% 3 3 4 4 5% 6% 49%	3373
	21st to end	Day	17% 10% 3 7% 4 3 3 3 5% 6% 40%	4466
January	1st to 10th	Night	10% 4 1 4 4 4 4 3 4 5% 56%	5889
	11th to 20th	Night	13% 7% 3 6% 4 4 4 4 6% 7% 43%	5900
	21st to end	Night	14% 7% 3 6% 4 4 4 3 4 7% 45%	6490
February	1st to 10th	Night	15% 6% 2 6% 5% 4 4 3 5% 6% 43%	2515
	11th to 20th	Night	16% 8% 3 5% 3 4 3 3 4 6% 46%	2338
	21st to end	Night	11% 5% 2 6% 5% 5% 5% 4 5% 7% 45%	1890
March	1st to 10th	Night	18% 9% 3 6% 3 3 3 2 4 5% 42%	4918
	11th to 20th	Night	8% 4 2 5% 3 3 4 4 6% 9% 52%	4980
	21st to end	Night	12% 5% 2 5% 4 3 4 3 5% 7% 50%	5467
April	1st to 10th	Night	10% 4 2 4 4 4 5% 4 5% 8% 49%	2200
	11th to 20th	Night	12% 4 2 6% 3 3 3 4 4 7% 52%	1938
	21st to end	Night	7% 4 1 5% 3 3 4 3 6% 8% 56%	1869
May	1st to 10th	Night	6% 3 1 4 4 4 5% 4 6% 11% 51%	2813
	11th to 20th	Night	11% 5% 2 6% 4 4 5% 4 7% 9% 45%	2812
	21st to end	Night	8% 4 2 4 3 4 4 4 6% 9% 53%	3079
June	1st to 10th	Night	9% 5% 2 6% 5% 5% 6% 5% 9% 13% 35%	1710
	11th to 20th	Night	6% 6% 2 6% 5% 5% 6% 5% 9% 12% 38%	1710
	21st to end	Night	7% 5% 2 6% 5% 6% 7% 8% 9% 13% 32%	1710
July	1st to 10th	Night	9% 6% 3 8% 6% 6% 6% 5% 9% 11% 30%	2840
	11th to 20th	Night	5% 5% 2 7% 6% 7% 8% 7% 10% 15% 29%	2840
	21st to end	Night	6% 6% 3 8% 7% 7% 8% 7% 10% 13% 25%	3087
August	1st to 10th	Night	16% 6% 2 7% 5% 5% 6% 6% 9% 12% 26%	2825
	11th to 20th	Night	6% 4 2 6% 5% 5% 7% 6% 9% 12% 38%	2785
	21st to end	Night	9% 6% 2 7% 5% 5% 5% 4 6% 9% 41%	3580
September	1st to 10th	Night	12% 7% 3 6% 5% 5% 6% 5% 8% 10% 33%	2090
	11th to 20th	Night	10% 7% 3 7% 6% 5% 6% 4 7% 8% 36%	2090
	21st to end	Night	12% 6% 3 8% 5% 4 5% 4 7% 7% 38%	2090
October	1st to 10th	Night	12% 6% 2 6% 3 4 4 3 5% 7% 47%	2175
	11th to 20th	Night	9% 4 1 4 3 3 4 3 4 6% 59%	2280
	21st to end	Night	9% 4 2 6% 3 4 4 3 5% 5% 56%	2508
November	1st to 10th	Night	11% 4 2 6% 3 3 4 3 4 5% 54%	2341
	11th to 20th	Night	13% 6% 2 5% 4 3 4 3 4 7% 49%	2425
	21st to end	Night	11% 6% 2 6% 4 5% 4 3 5% 6% 48%	2600
December	1st to 10th	Night	10% 4 2 4 3 3 3 3 4 6% 57%	4250
	11th to 20th	Night	13% 9% 3 8% 5% 4 3 3 4 5% 44%	4822
	21st to end	Night	17% 7% 2 6% 4 4 4 3 4 5% 43%	6490

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	31% 2 5% 17% 33% 11%	4057
	11th to 20th	Day	39% 1 5% 18% 25% 11%	4060
	21st to end	Day	39% 2 8% 19% 20% 11%	4466
February	1st to 10th	Day	42% 3 9% 20% 20% 7%	1882
	11th to 20th	Day	40% 3 7% 18% 24% 8%	1958
	21st to end	Day	38% 2 8% 19% 20% 12%	1740
March	1st to 10th	Day	48% 2 7% 16% 19% 8%	4935
	11th to 20th	Day	28% 3 12% 17% 19% 22%	4980
	21st to end	Day	39% 2 9% 20% 19% 11%	5465
April	1st to 10th	Day	31% 4 13% 24% 19% 10%	2200
	11th to 20th	Day	34% 3 11% 22% 20% 10%	2197
	21st to end	Day	25% 4 13% 29% 23% 6%	2326
May	1st to 10th	Day	30% 3 18% 31% 14% 3	4120
	11th to 20th	Day	42% 3 13% 25% 15% 1	4085
	21st to end	Day	29% 4 19% 25% 21% 1	4489
June	1st to 10th	Day	41% 8% 20% 19% 11%	2470
	11th to 20th	Day	37% 6% 20% 27% 11%	2470
	21st to end	Day	40% 9% 24% 18% 7% 1	2470
July	1st to 10th	Day	48% 8% 23% 18% 3 1	4055
	11th to 20th	Day	40% 11% 37% 11% 2	4051
	21st to end	Day	44% 12% 28% 13% 2	4324
August	1st to 10th	Day	52% 7% 27% 12% 3	4091
	11th to 20th	Day	35% 8% 23% 25% 9%	4059
	21st to end	Day	44% 7% 18% 28% 4	4061
September	1st to 10th	Day	49% 7% 18% 14% 11% 2	2090
	11th to 20th	Day	49% 6% 13% 18% 11% 2	2090
	21st to end	Day	42% 4 15% 20% 15% 3	2090
October	1st to 10th	Day	44% 3 7% 13% 22% 11%	3328
	11th to 20th	Day	16% 3 5% 15% 31% 30%	3140
	21st to end	Day	23% 3 6% 23% 35% 10%	3428
November	1st to 10th	Day	33% 3 10% 19% 23% 12%	1957
	11th to 20th	Day	36% 2 8% 20% 24% 10%	1972
	21st to end	Day	36% 3 8% 24% 20% 9%	1800
December	1st to 10th	Day	32% 2 10% 18% 25% 12%	2930
	11th to 20th	Day	36% 3 8% 26% 22% 5%	3370
	21st to end	Day	46% 2 6% 20% 22% 3	4466
January	1st to 10th	Night	32% 2 5% 13% 37% 11%	5889
	11th to 20th	Night	41% 2 5% 18% 26% 9%	5900
	21st to end	Night	42% 2 7% 15% 24% 11%	6490
February	1st to 10th	Night	43% 2 7% 19% 21% 8%	2515
	11th to 20th	Night	42% 2 8% 16% 20% 12%	2339
	21st to end	Night	40% 3 8% 20% 15% 13%	1890
March	1st to 10th	Night	46% 2 8% 15% 17% 12%	4918
	11th to 20th	Night	31% 3 9% 15% 22% 20%	4980
	21st to end	Night	35% 2 10% 18% 22% 12%	5467
April	1st to 10th	Night	34% 4 12% 21% 19% 10%	2200
	11th to 20th	Night	33% 3 8% 24% 20% 11%	1938
	21st to end	Night	26% 3 14% 26% 24% 6%	1869
May	1st to 10th	Night	29% 4 18% 32% 14% 4	2840
	11th to 20th	Night	37% 5% 16% 25% 15% 2	2813
	21st to end	Night	29% 4 16% 30% 19% 2	3087
June	1st to 10th	Night	39% 6% 22% 22% 10%	1710
	11th to 20th	Night	34% 9% 23% 26% 7%	1710
	21st to end	Night	37% 10% 28% 19% 6% 1	1710
July	1st to 10th	Night	44% 8% 24% 21% 2 1	2795
	11th to 20th	Night	40% 12% 35% 10% 2	2786
	21st to end	Night	45% 14% 26% 13% 2	2988
August	1st to 10th	Night	48% 10% 27% 13% 2	2814
	11th to 20th	Night	32% 9% 27% 24% 7%	2812
	21st to end	Night	39% 7% 21% 31% 3	3580
September	1st to 10th	Night	43% 8% 21% 15% 11% 2	2090
	11th to 20th	Night	45% 7% 18% 17% 11% 2	2090
	21st to end	Night	44% 5% 13% 19% 16% 2	2090
October	1st to 10th	Night	39% 4 9% 16% 22% 10%	3630
	11th to 20th	Night	17% 2 4 15% 31% 31%	3779
	21st to end	Night	23% 3 5% 18% 34% 15%	4120
November	1st to 10th	Night	35% 2 9% 18% 24% 12%	2341
	11th to 20th	Night	38% 2 7% 19% 24% 11%	2425
	21st to end	Night	37% 2 9% 20% 22% 10%	2600
December	1st to 10th	Night	31% 2 10% 18% 27% 12%	4250
	11th to 20th	Night	45% 2 10% 16% 20% 7%	4824
	21st to end	Night	45% 2 7% 21% 22% 3	6490

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% 16% 46% 20% 4	300
	11th to 20th	Day	12% 14% 40% 24% 8% 2	300
	21st to end	Day	22% 20% 39% 15% 4	330
February	1st to 10th	Day	16% 14% 42% 22% 6%	300
	11th to 20th	Day	26% 11% 41% 19% 2	300
	21st to end	Day	14% 15% 42% 24% 6% 1	339
March	1st to 10th	Day	18% 13% 33% 24% 10% 1	500
	11th to 20th	Day	15% 10% 39% 24% 10% 2	500
	21st to end	Day	15% 12% 40% 24% 9% 1	550
April	1st to 10th	Day	14% 12% 37% 24% 11% 2	500
	11th to 20th	Day	12% 11% 34% 25% 12% 7%	452
	21st to end	Day	6% 8% 29% 31% 18% 7%	460
May	1st to 10th	Day	5% 10% 33% 28% 15% 9%	463
	11th to 20th	Day	11% 3 20% 36% 19% 12%	487
	21st to end	Day	11% 2 17% 28% 28% 15%	529
June	1st to 10th	Day	11% 1 15% 31% 26% 16%	490
	11th to 20th	Day	10% 2 16% 29% 19% 23%	490
	21st to end	Day	7% 2 11% 32% 28% 19%	490
July	1st to 10th	Day	7% 2 4 28% 35% 25%	485
	11th to 20th	Day	7% 1 3 27% 37% 25%	484
	21st to end	Day	6% 2 5% 35% 36% 16%	532
August	1st to 10th	Day	13% 1 6% 27% 36% 17%	486
	11th to 20th	Day	8% 2 4 27% 37% 23%	479
	21st to end	Day	16% 3 6% 24% 33% 19%	539
September	1st to 10th	Day	14% 2 9% 26% 33% 15%	490
	11th to 20th	Day	19% 2 11% 31% 27% 11%	490
	21st to end	Day	14% 3 11% 30% 29% 13%	490
October	1st to 10th	Day	16% 3 24% 31% 17% 9%	490
	11th to 20th	Day	10% 7% 26% 29% 21% 7%	490
	21st to end	Day	11% 5% 25% 35% 19% 5%	539
November	1st to 10th	Day	17% 5% 25% 31% 18% 4	495
	11th to 20th	Day	18% 6% 36% 28% 11% 1	472
	21st to end	Day	16% 8% 34% 30% 10% 2	300
December	1st to 10th	Day	15% 11% 41% 22% 10% 2	300
	11th to 20th	Day	18% 11% 35% 27% 9% 1	300
	21st to end	Day	25% 8% 32% 26% 8% 1	330
January	1st to 10th	Night	14% 12% 39% 27% 8%	800
	11th to 20th	Night	15% 10% 30% 33% 11% 1	800
	21st to end	Night	19% 10% 37% 30% 5%	880
February	1st to 10th	Night	19% 7% 34% 30% 9%	800
	11th to 20th	Night	21% 11% 30% 32% 6%	783
	21st to end	Night	15% 9% 35% 35% 7%	660
March	1st to 10th	Night	13% 9% 33% 35% 11%	800
	11th to 20th	Night	14% 9% 31% 35% 12% 1	800
	21st to end	Night	12% 9% 32% 34% 13% 1	880
April	1st to 10th	Night	13% 8% 32% 33% 13% 1	800
	11th to 20th	Night	14% 7% 29% 30% 19% 1	754
	21st to end	Night	9% 5% 25% 40% 20% 2	729
May	1st to 10th	Night	8% 3 21% 39% 25% 4	570
	11th to 20th	Night	9% 2 18% 39% 26% 7%	561
	21st to end	Night	12% 2 7% 34% 34% 11%	617
June	1st to 10th	Night	12% 1 8% 39% 33% 7%	570
	11th to 20th	Night	8% 2 7% 32% 33% 18%	570
	21st to end	Night	7% 2 9% 34% 36% 12%	570
July	1st to 10th	Night	9% 2 5% 25% 45% 14%	555
	11th to 20th	Night	9% 1 2 23% 50% 15%	552
	21st to end	Night	6% 2 3 34% 47% 8%	624
August	1st to 10th	Night	11% 1 4 26% 44% 14%	567
	11th to 20th	Night	8% 1 3 24% 48% 15%	564
	21st to end	Night	16% 3 5% 23% 38% 14%	826
September	1st to 10th	Night	14% 3 6% 24% 44% 9%	760
	11th to 20th	Night	12% 3 9% 30% 39% 6%	760
	21st to end	Night	17% 2 9% 29% 36% 8%	760
October	1st to 10th	Night	15% 2 18% 32% 27% 6%	760
	11th to 20th	Night	11% 5% 18% 34% 27% 6%	760
	21st to end	Night	11% 4 20% 37% 25% 3	836
November	1st to 10th	Night	13% 6% 21% 36% 22% 2	780
	11th to 20th	Night	17% 7% 25% 33% 16% 2	800
	21st to end	Night	14% 7% 29% 32% 17% 1	800
December	1st to 10th	Night	16% 7% 29% 32% 14% 1	800
	11th to 20th	Night	18% 8% 26% 32% 14% 2	800
	21st to end	Night	21% 7% 30% 30% 12%	880

Page generated at 2025-04-08 09:17:24. Version ac07

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