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 2024-05-13.

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% 7% 2 6% 4 4 4 4 6% 7% 42%	83779
	Night	14% 7% 2 5% 4 4 4 3 5% 7% 45%	85760
Transparency	Day	40% 7% 11% 21% 18% 4	83496
	Night	39% 6% 10% 21% 19% 5%	85564
Seeing	Day	16% 6% 19% 24% 22% 12%	14494
	Night	16% 6% 22% 32% 21% 3	24374

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	14% 14% 3 8% 4 4 4 2 4 5% 39%	2527
	11th to 20th	Day	21% 8% 2 7% 4 3 3 3 4 4 41%	2726
	21st to end	Day	23% 9% 2 4 3 3 3 3 4 5% 39%	3330
February	1st to 10th	Day	21% 10% 3 6% 3 3 2 2 4 6% 39%	1900
	11th to 20th	Day	20% 10% 3 6% 4 3 4 3 4 4 38%	1848
	21st to end	Day	22% 8% 3 7% 4 4 3 3 4 6% 36%	1570
March	1st to 10th	Day	19% 12% 3 8% 5% 5% 4 3 4 4 32%	3120
	11th to 20th	Day	13% 7% 3 6% 4 4 4 3 5% 6% 46%	3282
	21st to end	Day	13% 7% 2 6% 5% 5% 5% 3 6% 7% 41%	4165
April	1st to 10th	Day	15% 7% 2 5% 4 4 4 3 6% 5% 45%	2280
	11th to 20th	Day	15% 7% 3 6% 4 4 3 4 3 6% 46%	2254
	21st to end	Day	12% 6% 2 6% 5% 4 5% 4 6% 8% 44%	2280
May	1st to 10th	Day	15% 5% 2 6% 4 4 4 4 5% 7% 42%	2371
	11th to 20th	Day	11% 7% 2 7% 5% 4 5% 4 6% 8% 42%	2329
	21st to end	Day	8% 6% 3 7% 6% 5% 6% 4 7% 10% 38%	2531
June	1st to 10th	Day	9% 7% 2 6% 5% 4 5% 4 7% 10% 40%	2462
	11th to 20th	Day	5% 4 2 6% 4 4 6% 5% 7% 10% 48%	2520
	21st to end	Day	5% 3 2 6% 4 6% 5% 6% 7% 10% 45%	2520
July	1st to 10th	Day	8% 7% 2 7% 6% 6% 7% 6% 8% 10% 33%	2520
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 6% 8% 11% 38%	2520
	21st to end	Day	7% 4 2 7% 6% 6% 6% 5% 8% 10% 40%	2494
August	1st to 10th	Day	4 4 2 6% 7% 6% 6% 6% 8% 12% 39%	2148
	11th to 20th	Day	10% 5% 2 7% 5% 6% 5% 4 7% 11% 39%	2125
	21st to end	Day	10% 6% 2 7% 5% 5% 6% 4 6% 8% 41%	2376
September	1st to 10th	Day	10% 4 2 6% 6% 5% 4 5% 7% 7% 44%	2160
	11th to 20th	Day	12% 6% 2 6% 4 5% 5% 4 5% 7% 44%	2022
	21st to end	Day	10% 4 2 4 4 4 4 3 5% 8% 52%	1980
October	1st to 10th	Day	11% 4 2 4 4 3 4 3 4 6% 56%	1980
	11th to 20th	Day	10% 5% 2 5% 3 3 3 3 4 6% 54%	1836
	21st to end	Day	16% 6% 2 5% 3 3 3 3 4 5% 50%	1905
November	1st to 10th	Day	13% 5% 1 5% 2 2 2 3 4 6% 57%	1672
	11th to 20th	Day	14% 7% 2 5% 3 2 3 3 4 6% 50%	1710
	21st to end	Day	17% 9% 2 5% 4 4 3 3 5% 6% 43%	1710
December	1st to 10th	Day	22% 8% 3 6% 4 4 4 3 4 5% 36%	1710
	11th to 20th	Day	16% 8% 3 6% 5% 4 4 3 4 6% 42%	2113
	21st to end	Day	15% 12% 4 7% 5% 4 4 4 6% 5% 35%	2783
January	1st to 10th	Night	19% 13% 2 5% 3 3 3 3 4 4 40%	4428
	11th to 20th	Night	17% 10% 4 9% 4 3 3 2 3 4 41%	4239
	21st to end	Night	24% 11% 2 5% 3 3 3 2 4 4 41%	4327
February	1st to 10th	Night	20% 10% 3 6% 4 4 4 3 4 4 38%	2280
	11th to 20th	Night	20% 11% 3 6% 4 3 3 2 3 5% 39%	2218
	21st to end	Night	22% 7% 3 7% 4 4 4 2 4 5% 38%	1884
March	1st to 10th	Night	21% 10% 3 6% 4 3 3 3 4 5% 38%	3733
	11th to 20th	Night	14% 7% 2 5% 4 3 3 3 4 6% 48%	3706
	21st to end	Night	16% 7% 3 6% 5% 4 5% 4 4 6% 40%	3466
April	1st to 10th	Night	14% 6% 2 6% 4 3 4 4 4 7% 46%	1900
	11th to 20th	Night	15% 6% 2 4 3 3 4 3 5% 7% 48%	1875
	21st to end	Night	12% 6% 3 5% 4 3 5% 3 5% 7% 46%	1900
May	1st to 10th	Night	14% 6% 2 5% 4 4 4 3 5% 7% 47%	1805
	11th to 20th	Night	9% 6% 3 6% 4 4 4 4 6% 9% 44%	1619
	21st to end	Night	6% 5% 2 5% 4 5% 5% 4 8% 12% 45%	1744
June	1st to 10th	Night	8% 5% 2 5% 5% 5% 5% 4 7% 11% 44%	1493
	11th to 20th	Night	3 3 1 4 3 4 4 5% 7% 10% 56%	1440
	21st to end	Night	3 4 1 4 4 4 4 4 6% 10% 56%	1440
July	1st to 10th	Night	6% 5% 2 6% 5% 5% 4 6% 8% 12% 41%	1440
	11th to 20th	Night	7% 3 2 5% 4 5% 5% 4 7% 11% 47%	1440
	21st to end	Night	4 3 2 5% 4 4 5% 5% 8% 12% 47%	1818
August	1st to 10th	Night	4 2 2 5% 4 5% 6% 6% 8% 12% 46%	1790
	11th to 20th	Night	6% 4 1 5% 4 5% 6% 5% 7% 11% 45%	1776
	21st to end	Night	8% 5% 2 5% 4 4 4 5% 8% 9% 46%	1980
September	1st to 10th	Night	8% 5% 2 5% 3 4 4 4 7% 9% 50%	1800
	11th to 20th	Night	9% 5% 2 5% 5% 4 4 4 6% 8% 49%	1918
	21st to end	Night	8% 5% 2 3 3 4 4 3 5% 5% 59%	1980
October	1st to 10th	Night	9% 3 1 4 2 3 2 3 4 6% 62%	1980
	11th to 20th	Night	13% 5% 2 5% 3 3 4 3 4 6% 52%	2119
	21st to end	Night	16% 8% 2 4 3 3 3 3 3 5% 50%	2448
November	1st to 10th	Night	11% 5% 2 4 4 3 3 3 4 6% 55%	2406
	11th to 20th	Night	12% 5% 2 4 3 3 4 3 6% 7% 51%	2470
	21st to end	Night	17% 6% 2 3 4 4 3 3 4 6% 48%	2470
December	1st to 10th	Night	19% 9% 3 6% 4 4 4 3 4 6% 39%	2470
	11th to 20th	Night	16% 8% 2 5% 3 3 3 3 4 5% 48%	3074
	21st to end	Night	17% 10% 3 7% 5% 5% 5% 4 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	49% 3 8% 19% 19% 2	2528
	11th to 20th	Day	46% 5% 8% 20% 21% 1	2726
	21st to end	Day	47% 4 8% 21% 19% 2	3330
February	1st to 10th	Day	48% 3 8% 20% 18% 4	1900
	11th to 20th	Day	49% 4 5% 19% 17% 5%	1858
	21st to end	Day	50% 4 9% 15% 17% 7%	1570
March	1st to 10th	Day	55% 5% 6% 12% 14% 9%	3120
	11th to 20th	Day	38% 5% 8% 25% 17% 7%	3282
	21st to end	Day	42% 6% 11% 22% 19% 1	4165
April	1st to 10th	Day	39% 6% 9% 22% 20% 4	2280
	11th to 20th	Day	41% 5% 7% 20% 21% 6%	2254
	21st to end	Day	37% 7% 10% 27% 18% 2	2280
May	1st to 10th	Day	41% 7% 10% 24% 16% 3	2371
	11th to 20th	Day	40% 9% 13% 22% 15% 1	2333
	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	48% 4 6% 19% 21% 2	4428
	11th to 20th	Night	48% 4 6% 20% 17% 5%	4239
	21st to end	Night	49% 3 6% 22% 17% 3	4327
February	1st to 10th	Night	50% 4 9% 16% 18% 3	2280
	11th to 20th	Night	50% 3 6% 17% 18% 5%	2219
	21st to end	Night	51% 4 6% 16% 17% 6%	1884
March	1st to 10th	Night	48% 5% 10% 13% 16% 8%	3733
	11th to 20th	Night	38% 6% 8% 22% 18% 9%	3706
	21st to end	Night	44% 5% 10% 17% 23% 1	3466
April	1st to 10th	Night	38% 5% 12% 21% 21% 4	1900
	11th to 20th	Night	36% 4 8% 20% 24% 8%	1875
	21st to end	Night	37% 6% 11% 26% 18% 3	1900
May	1st to 10th	Night	37% 6% 9% 23% 21% 4	1805
	11th to 20th	Night	36% 8% 14% 23% 17% 2	1620
	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% 37% 19% 7% 1	270
	11th to 20th	Day	29% 14% 36% 15% 4 3	270
	21st to end	Day	23% 13% 37% 22% 6%	297
February	1st to 10th	Day	24% 16% 32% 20% 7% 1	270
	11th to 20th	Day	35% 14% 30% 15% 4 1	270
	21st to end	Day	36% 13% 36% 10% 5%	225
March	1st to 10th	Day	27% 13% 30% 21% 7% 1	270
	11th to 20th	Day	20% 13% 37% 24% 6%	289
	21st to end	Day	22% 12% 32% 24% 9% 1	506
April	1st to 10th	Day	22% 15% 23% 26% 14%	460
	11th to 20th	Day	21% 11% 30% 24% 13% 2	452
	21st to end	Day	19% 9% 26% 28% 14% 4	460
May	1st to 10th	Day	17% 9% 24% 29% 16% 6%	463
	11th to 20th	Day	15% 3 23% 25% 19% 15%	456
	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% 32% 26% 5%	950
	21st to end	Night	22% 8% 37% 30% 3	918
February	1st to 10th	Night	23% 10% 33% 29% 5%	760
	11th to 20th	Night	26% 14% 29% 27% 3	743
	21st to end	Night	27% 14% 33% 24% 2	628
March	1st to 10th	Night	22% 9% 33% 33% 4	760
	11th to 20th	Night	21% 9% 32% 32% 6% 1	724
	21st to end	Night	18% 7% 33% 31% 11%	627
April	1st to 10th	Night	16% 8% 34% 30% 12%	570
	11th to 20th	Night	18% 5% 31% 32% 13% 1	563
	21st to end	Night	16% 5% 30% 34% 15% 1	570
May	1st to 10th	Night	16% 5% 23% 36% 18% 2	570
	11th to 20th	Night	11% 4 22% 35% 24% 4	540
	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 2024-05-10 11:39:04. Version ac07

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