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 2024-01-12.

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% 3 5% 5% 3 5% 5% 6% 7% 43%	74844
	Night	13% 6% 2 5% 4 3 4 4 5% 7% 46%	74864
Transparency	Day	40% 7% 11% 21% 18% 4	74561
	Night	38% 6% 10% 22% 19% 5%	74668
Seeing	Day	15% 6% 19% 25% 22% 12%	14073
	Night	16% 6% 21% 32% 21% 3	23927

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	18% 10% 2 6% 4 3 4 3 4 5% 42%	1517
	11th to 20th	Day	21% 9% 3 6% 5% 2 4 4 4 5% 37%	1560
	21st to end	Day	16% 7% 3 4 4 3 3 3 4 5% 47%	1899
February	1st to 10th	Day	20% 10% 4 6% 4 2 3 3 4 6% 39%	1800
	11th to 20th	Day	21% 9% 4 5% 4 3 4 4 4 5% 37%	1748
	21st to end	Day	23% 7% 3 6% 4 3 4 4 4 6% 36%	1480
March	1st to 10th	Day	16% 9% 3 6% 5% 3 5% 4 4 5% 41%	1800
	11th to 20th	Day	18% 8% 4 7% 5% 4 5% 4 6% 5% 36%	1866
	21st to end	Day	17% 7% 3 6% 6% 3 6% 4 6% 7% 37%	2376
April	1st to 10th	Day	14% 6% 2 4 4 3 5% 4 5% 6% 46%	2160
	11th to 20th	Day	15% 7% 3 5% 4 3 3 4 3 6% 46%	2134
	21st to end	Day	13% 5% 2 5% 5% 3 5% 4 6% 8% 44%	2160
May	1st to 10th	Day	16% 5% 3 5% 4 3 5% 5% 5% 7% 43%	2246
	11th to 20th	Day	11% 7% 2 6% 5% 3 4 6% 6% 8% 41%	2301
	21st to end	Day	9% 5% 3 6% 6% 4 6% 6% 7% 10% 38%	2531
June	1st to 10th	Day	9% 6% 3 6% 5% 4 4 5% 7% 10% 41%	2462
	11th to 20th	Day	5% 3 2 5% 5% 3 5% 6% 7% 10% 49%	2520
	21st to end	Day	5% 3 2 5% 4 4 6% 7% 7% 11% 46%	2520
July	1st to 10th	Day	8% 6% 3 6% 6% 5% 7% 8% 8% 10% 33%	2520
	11th to 20th	Day	9% 5% 3 5% 5% 4 6% 7% 8% 11% 38%	2520
	21st to end	Day	7% 4 2 6% 6% 4 6% 7% 8% 10% 40%	2494
August	1st to 10th	Day	4 4 2 6% 7% 5% 7% 7% 8% 12% 39%	2148
	11th to 20th	Day	10% 4 2 6% 6% 4 5% 6% 7% 11% 39%	2125
	21st to end	Day	10% 5% 3 7% 5% 4 6% 5% 6% 8% 41%	2376
September	1st to 10th	Day	10% 4 2 5% 6% 3 5% 6% 6% 8% 44%	2160
	11th to 20th	Day	12% 6% 2 5% 5% 3 5% 5% 6% 7% 44%	2022
	21st to end	Day	10% 4 2 4 4 3 5% 4 4 8% 52%	1980
October	1st to 10th	Day	11% 4 2 4 4 2 4 4 4 6% 56%	1980
	11th to 20th	Day	10% 5% 2 4 3 2 3 4 4 6% 55%	1836
	21st to end	Day	16% 6% 2 4 3 3 3 4 4 5% 50%	1905
November	1st to 10th	Day	13% 5% 1 4 3 1 3 4 4 6% 57%	1672
	11th to 20th	Day	15% 6% 3 4 3 2 3 4 4 6% 51%	1710
	21st to end	Day	17% 8% 2 4 4 2 3 4 5% 6% 44%	1710
December	1st to 10th	Day	23% 8% 3 6% 4 3 5% 4 4 5% 36%	1710
	11th to 20th	Day	16% 8% 3 6% 6% 3 3 4 4 6% 43%	2113
	21st to end	Day	15% 12% 4 6% 6% 3 4 4 5% 6% 35%	2783
January	1st to 10th	Night	19% 9% 3 5% 3 2 4 4 3 5% 43%	2648
	11th to 20th	Night	19% 10% 4 7% 6% 2 4 4 4 5% 35%	2424
	21st to end	Night	17% 7% 3 5% 4 2 3 3 4 5% 46%	2453
February	1st to 10th	Night	21% 9% 3 5% 5% 3 4 4 4 4 38%	2160
	11th to 20th	Night	20% 10% 4 6% 5% 2 4 3 3 5% 39%	2098
	21st to end	Night	23% 7% 3 6% 5% 3 4 4 4 5% 37%	1776
March	1st to 10th	Night	16% 7% 2 4 5% 2 4 4 4 6% 45%	2160
	11th to 20th	Night	18% 8% 4 5% 5% 3 4 4 4 7% 39%	2108
	21st to end	Night	14% 8% 3 5% 5% 3 5% 5% 5% 7% 41%	1980
April	1st to 10th	Night	13% 5% 2 5% 5% 2 4 5% 5% 7% 47%	1800
	11th to 20th	Night	15% 5% 2 3 3 2 4 3 5% 7% 50%	1775
	21st to end	Night	12% 5% 3 5% 4 2 5% 4 5% 8% 46%	1800
May	1st to 10th	Night	13% 5% 2 5% 4 2 5% 4 5% 7% 48%	1710
	11th to 20th	Night	9% 6% 4 5% 5% 2 4 5% 6% 9% 44%	1592
	21st to end	Night	6% 4 2 5% 4 4 5% 5% 7% 12% 46%	1744
June	1st to 10th	Night	8% 5% 2 5% 5% 3 5% 4 7% 11% 44%	1493
	11th to 20th	Night	3 3 1 4 4 3 4 5% 7% 11% 56%	1440
	21st to end	Night	3 3 2 4 4 2 5% 4 6% 10% 56%	1440
July	1st to 10th	Night	6% 5% 2 5% 5% 4 5% 6% 8% 12% 41%	1440
	11th to 20th	Night	7% 3 2 5% 3 4 5% 5% 7% 10% 48%	1440
	21st to end	Night	4 3 1 4 5% 3 5% 6% 8% 12% 48%	1818
August	1st to 10th	Night	4 2 2 4 4 4 6% 7% 8% 12% 47%	1790
	11th to 20th	Night	6% 3 1 4 5% 3 6% 7% 7% 11% 45%	1776
	21st to end	Night	8% 5% 2 4 5% 3 4 6% 8% 10% 46%	1980
September	1st to 10th	Night	8% 4 2 4 3 3 3 6% 7% 9% 50%	1800
	11th to 20th	Night	9% 4 2 5% 5% 3 4 6% 6% 8% 49%	1918
	21st to end	Night	8% 4 2 3 3 3 4 4 5% 6% 59%	1980
October	1st to 10th	Night	9% 3 1 3 3 2 3 4 4 6% 62%	1980
	11th to 20th	Night	13% 5% 2 4 4 2 3 4 4 6% 52%	2119
	21st to end	Night	16% 7% 2 4 3 2 3 4 3 5% 50%	2448
November	1st to 10th	Night	11% 4 2 4 4 2 3 3 4 7% 55%	2406
	11th to 20th	Night	12% 5% 2 4 4 2 4 4 6% 8% 51%	2470
	21st to end	Night	17% 5% 2 3 4 3 4 4 4 6% 48%	2470
December	1st to 10th	Night	19% 9% 3 6% 5% 3 4 3 4 6% 39%	2470
	11th to 20th	Night	17% 8% 2 4 4 2 3 3 4 6% 48%	3074
	21st to end	Night	17% 10% 3 6% 6% 4 5% 5% 5% 6% 33%	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	47% 3 8% 20% 18% 4	1518
	11th to 20th	Day	50% 5% 8% 19% 16% 2	1560
	21st to end	Day	40% 4 8% 23% 23% 2	1899
February	1st to 10th	Day	48% 3 8% 20% 18% 3	1800
	11th to 20th	Day	50% 5% 5% 20% 16% 4	1758
	21st to end	Day	50% 4 8% 15% 16% 7%	1480
March	1st to 10th	Day	47% 5% 7% 16% 19% 8%	1800
	11th to 20th	Day	50% 5% 9% 17% 16% 3	1866
	21st to end	Day	46% 7% 10% 21% 15% 1	2376
April	1st to 10th	Day	38% 6% 9% 22% 20% 4	2160
	11th to 20th	Day	40% 5% 7% 20% 21% 6%	2134
	21st to end	Day	38% 7% 10% 26% 18% 2	2160
May	1st to 10th	Day	41% 7% 10% 24% 16% 3	2246
	11th to 20th	Day	40% 9% 13% 21% 16% 1	2305
	21st to end	Day	40% 9% 14% 24% 12% 2	2531
June	1st to 10th	Day	37% 8% 13% 22% 18% 2	2462
	11th to 20th	Day	29% 8% 16% 27% 18% 2	2520
	21st to end	Day	31% 10% 15% 23% 18% 3	2520
July	1st to 10th	Day	41% 11% 16% 18% 11% 3	2451
	11th to 20th	Day	36% 11% 19% 20% 11% 3	2445
	21st to end	Day	36% 11% 16% 26% 10% 1	2355
August	1st to 10th	Day	34% 11% 19% 25% 10% 1	2136
	11th to 20th	Day	37% 10% 14% 20% 16% 2	2125
	21st to end	Day	38% 9% 13% 24% 12% 4	2376
September	1st to 10th	Day	36% 9% 11% 24% 16% 4	2160
	11th to 20th	Day	38% 8% 9% 19% 21% 4	2022
	21st to end	Day	31% 6% 10% 23% 23% 7%	1980
October	1st to 10th	Day	30% 5% 11% 23% 25% 6%	1980
	11th to 20th	Day	30% 4 9% 22% 28% 8%	1836
	21st to end	Day	38% 3 6% 20% 26% 7%	1905
November	1st to 10th	Day	31% 3 8% 21% 30% 7%	1672
	11th to 20th	Day	35% 4 9% 18% 27% 8%	1710
	21st to end	Day	41% 4 8% 20% 23% 4	1710
December	1st to 10th	Day	51% 4 6% 19% 16% 4	1710
	11th to 20th	Day	45% 4 8% 20% 20% 3	2110
	21st to end	Day	48% 6% 11% 21% 13% 2	2783
January	1st to 10th	Night	46% 4 7% 21% 19% 4	2648
	11th to 20th	Night	53% 4 7% 19% 15% 3	2424
	21st to end	Night	42% 3 8% 23% 21% 3	2453
February	1st to 10th	Night	50% 4 9% 16% 17% 3	2160
	11th to 20th	Night	50% 3 6% 18% 17% 5%	2099
	21st to end	Night	52% 4 6% 16% 16% 6%	1776
March	1st to 10th	Night	40% 5% 9% 16% 20% 10%	2160
	11th to 20th	Night	47% 6% 8% 20% 16% 3	2108
	21st to end	Night	43% 5% 11% 21% 18% 2	1980
April	1st to 10th	Night	37% 5% 12% 22% 20% 4	1800
	11th to 20th	Night	35% 4 8% 21% 24% 8%	1775
	21st to end	Night	36% 6% 11% 26% 19% 3	1800
May	1st to 10th	Night	36% 6% 9% 22% 22% 4	1710
	11th to 20th	Night	36% 8% 15% 22% 18% 2	1593
	21st to end	Night	30% 10% 14% 27% 16% 3	1745
June	1st to 10th	Night	33% 9% 13% 23% 20% 2	1493
	11th to 20th	Night	22% 8% 15% 32% 20% 4	1440
	21st to end	Night	23% 9% 17% 28% 19% 4	1440
July	1st to 10th	Night	30% 12% 20% 23% 12% 3	1400
	11th to 20th	Night	29% 9% 20% 26% 11% 5%	1392
	21st to end	Night	26% 11% 20% 30% 12% 1	1717
August	1st to 10th	Night	25% 12% 19% 30% 14% 1	1778
	11th to 20th	Night	29% 12% 19% 22% 15% 3	1776
	21st to end	Night	31% 10% 15% 25% 13% 5%	1980
September	1st to 10th	Night	29% 8% 12% 25% 20% 5%	1800
	11th to 20th	Night	33% 7% 12% 18% 26% 4	1918
	21st to end	Night	27% 6% 7% 27% 25% 8%	1980
October	1st to 10th	Night	24% 4 10% 24% 27% 10%	1980
	11th to 20th	Night	34% 5% 8% 19% 26% 9%	2119
	21st to end	Night	38% 3 7% 19% 25% 8%	2448
November	1st to 10th	Night	31% 4 7% 22% 27% 9%	2406
	11th to 20th	Night	32% 4 8% 20% 25% 10%	2470
	21st to end	Night	39% 4 7% 20% 24% 6%	2470
December	1st to 10th	Night	47% 4 8% 19% 18% 3	2470
	11th to 20th	Night	40% 4 5% 23% 24% 4	3076
	21st to end	Night	49% 5% 11% 19% 12% 4	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	25% 11% 36% 19% 7% 1	270
	11th to 20th	Day	29% 12% 36% 17% 4 3	243
	21st to end	Day	20% 14% 39% 22% 6%	264
February	1st to 10th	Day	23% 18% 33% 19% 6% 1	240
	11th to 20th	Day	37% 15% 31% 13% 4	240
	21st to end	Day	37% 10% 36% 11% 6% 1	198
March	1st to 10th	Day	26% 13% 32% 21% 8%	240
	11th to 20th	Day	22% 14% 36% 22% 6%	258
	21st to end	Day	22% 13% 31% 23% 10% 1	462
April	1st to 10th	Day	21% 13% 23% 27% 16%	420
	11th to 20th	Day	20% 10% 28% 25% 14% 2	412
	21st to end	Day	20% 8% 25% 28% 15% 3	420
May	1st to 10th	Day	18% 9% 22% 29% 16% 6%	423
	11th to 20th	Day	15% 3 23% 25% 19% 15%	447
	21st to end	Day	11% 3 16% 28% 24% 19%	485
June	1st to 10th	Day	12% 3 13% 23% 29% 20%	572
	11th to 20th	Day	6% 1 12% 29% 30% 21%	630
	21st to end	Day	7% 2 13% 30% 31% 17%	630
July	1st to 10th	Day	9% 2 6% 25% 31% 26%	621
	11th to 20th	Day	9% 2 7% 22% 33% 26%	618
	21st to end	Day	6% 2 7% 21% 39% 25%	550
August	1st to 10th	Day	6% 3 6% 23% 38% 24%	446
	11th to 20th	Day	13% 3 4 27% 36% 18%	439
	21st to end	Day	13% 2 4 20% 34% 27%	495
September	1st to 10th	Day	10% 2 7% 22% 39% 20%	450
	11th to 20th	Day	13% 3 6% 20% 36% 22%	450
	21st to end	Day	12% 4 11% 28% 30% 15%	450
October	1st to 10th	Day	11% 2 14% 30% 30% 13%	450
	11th to 20th	Day	11% 8% 28% 34% 14% 4	306
	21st to end	Day	22% 8% 28% 25% 14% 3	297
November	1st to 10th	Day	20% 4 22% 29% 20% 5%	270
	11th to 20th	Day	13% 9% 35% 29% 12% 2	270
	21st to end	Day	22% 9% 30% 19% 18% 3	270
December	1st to 10th	Day	29% 12% 28% 25% 5% 1	270
	11th to 20th	Day	21% 11% 31% 23% 12% 1	270
	21st to end	Day	25% 12% 34% 24% 5%	297
January	1st to 10th	Night	23% 11% 31% 29% 6%	950
	11th to 20th	Night	25% 12% 31% 27% 5%	908
	21st to end	Night	22% 9% 37% 30% 3	869
February	1st to 10th	Night	24% 10% 32% 29% 5%	720
	11th to 20th	Night	26% 15% 30% 27% 3	703
	21st to end	Night	27% 13% 33% 25% 2	592
March	1st to 10th	Night	21% 9% 33% 34% 4	720
	11th to 20th	Night	21% 9% 30% 32% 6% 1	686
	21st to end	Night	18% 7% 32% 31% 11% 1	594
April	1st to 10th	Night	15% 8% 34% 31% 12%	540
	11th to 20th	Night	18% 5% 30% 33% 14% 1	533
	21st to end	Night	15% 4 29% 35% 15% 1	540
May	1st to 10th	Night	16% 5% 23% 37% 17% 2	540
	11th to 20th	Night	11% 4 22% 34% 24% 4	531
	21st to end	Night	8% 2 11% 38% 32% 8%	584
June	1st to 10th	Night	9% 3 8% 40% 32% 8%	540
	11th to 20th	Night	4 1 9% 38% 43% 5%	540
	21st to end	Night	4 1 8% 35% 43% 9%	540
July	1st to 10th	Night	8% 2 6% 26% 47% 12%	525
	11th to 20th	Night	7% 1 6% 27% 43% 15%	522
	21st to end	Night	5% 1 5% 29% 46% 13%	591
August	1st to 10th	Night	5% 1 3 27% 53% 11%	537
	11th to 20th	Night	7% 2 4 36% 45% 6%	534
	21st to end	Night	9% 1 4 26% 50% 10%	594
September	1st to 10th	Night	8% 3 5% 33% 44% 7%	540
	11th to 20th	Night	9% 3 8% 31% 40% 8%	658
	21st to end	Night	11% 3 11% 33% 38% 5%	720
October	1st to 10th	Night	11% 3 12% 34% 35% 5%	720
	11th to 20th	Night	16% 3 21% 38% 20% 2	720
	21st to end	Night	20% 5% 22% 34% 18% 2	792
November	1st to 10th	Night	12% 6% 18% 42% 19% 2	740
	11th to 20th	Night	14% 7% 29% 36% 13% 1	760
	21st to end	Night	20% 8% 24% 33% 14% 1	760
December	1st to 10th	Night	25% 8% 28% 31% 7% 1	760
	11th to 20th	Night	22% 7% 28% 35% 8%	779
	21st to end	Night	27% 9% 29% 30% 6%	1045

Page generated at 2024-01-09 06:14:39. Version ac07

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