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 2024-10-24.

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% 5% 5% 5% 7% 9% 41%	100984
	Night	11% 6% 2 6% 4 4 5% 4 6% 8% 43%	97740
Transparency	Day	39% 5% 16% 20% 15% 5%	100797
	Night	39% 5% 14% 20% 16% 6%	97597
Seeing	Day	13% 6% 23% 28% 20% 10%	15392
	Night	13% 5% 21% 32% 24% 5%	25450

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	11% 5% 2 5% 4 4 5% 4 7% 7% 46%	2836
	11th to 20th	Day	12% 6% 2 6% 4 4 3 3 5% 9% 46%	2840
	21st to end	Day	13% 7% 2 6% 4 3 3 4 5% 6% 45%	3124
February	1st to 10th	Day	14% 8% 2 6% 5% 4 4 4 5% 7% 40%	1787
	11th to 20th	Day	18% 5% 2 5% 3 3 3 3 5% 5% 48%	1848
	21st to end	Day	13% 7% 3 5% 4 3 3 3 4 6% 48%	1655
March	1st to 10th	Day	20% 10% 3 7% 4 3 3 3 4 6% 37%	3435
	11th to 20th	Day	7% 5% 2 4 4 4 4 3 6% 8% 54%	3480
	21st to end	Day	16% 6% 2 4 4 4 4 3 5% 6% 45%	3815
April	1st to 10th	Day	9% 5% 1 4 4 4 3 4 6% 8% 51%	2090
	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	10% 5% 2 5% 4 3 3 3 5% 6% 54%	2010
November	1st to 10th	Day	11% 5% 2 4 4 3 4 3 5% 5% 55%	1857
	11th to 20th	Day	12% 6% 2 5% 4 4 4 2 4 6% 51%	1874
	21st to end	Day	13% 6% 2 5% 4 3 4 3 4 6% 50%	1710
December	1st to 10th	Day	11% 7% 3 5% 5% 4 4 4 4 7% 46%	1710
	11th to 20th	Day	15% 6% 2 4 3 3 3 4 4 5% 50%	2153
	21st to end	Day	16% 10% 3 6% 4 3 3 3 4 6% 42%	3124
January	1st to 10th	Night	15% 6% 2 5% 5% 4 5% 4 5% 6% 43%	4109
	11th to 20th	Night	10% 6% 2 6% 4 4 5% 4 6% 7% 44%	4120
	21st to end	Night	14% 8% 3 7% 4 4 4 3 4 5% 43%	4532
February	1st to 10th	Night	16% 6% 2 6% 5% 4 4 3 5% 6% 42%	2390
	11th to 20th	Night	16% 7% 3 5% 3 4 3 3 4 6% 47%	2218
	21st to end	Night	12% 5% 2 6% 5% 5% 5% 4 5% 7% 45%	1799
March	1st to 10th	Night	21% 12% 4 7% 3 3 2 2 4 5% 36%	3418
	11th to 20th	Night	10% 5% 2 6% 4 3 4 4 5% 8% 50%	3480
	21st to end	Night	15% 5% 2 6% 4 4 4 3 5% 7% 45%	3817
April	1st to 10th	Night	10% 4 2 4 4 4 5% 4 5% 8% 49%	2090
	11th to 20th	Night	12% 5% 2 6% 3 3 3 4 4 7% 52%	1931
	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% 55%	2413
November	1st to 10th	Night	10% 4 2 5% 3 3 4 3 4 5% 56%	2221
	11th to 20th	Night	13% 6% 2 5% 4 3 4 3 4 7% 49%	2303
	21st to end	Night	12% 7% 2 5% 4 5% 4 3 5% 6% 47%	2470
December	1st to 10th	Night	13% 5% 2 5% 4 4 4 4 6% 8% 44%	2470
	11th to 20th	Night	15% 6% 2 5% 4 3 3 3 4 5% 49%	3042
	21st to end	Night	17% 8% 2 6% 4 4 4 3 5% 6% 39%	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	37% 2 7% 20% 22% 11%	2837
	11th to 20th	Day	38% 1 6% 20% 25% 10%	2840
	21st to end	Day	41% 2 10% 14% 21% 11%	3124
February	1st to 10th	Day	43% 3 9% 19% 19% 8%	1787
	11th to 20th	Day	39% 3 8% 18% 24% 9%	1858
	21st to end	Day	39% 2 9% 18% 20% 12%	1655
March	1st to 10th	Day	51% 2 8% 18% 15% 6%	3435
	11th to 20th	Day	30% 3 13% 18% 22% 15%	3480
	21st to end	Day	42% 2 9% 20% 20% 6%	3815
April	1st to 10th	Day	31% 4 13% 22% 19% 10%	2090
	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	39% 3 8% 19% 20% 10%	2003
	11th to 20th	Day	27% 3 9% 22% 29% 10%	1900
	21st to end	Day	31% 3 7% 20% 25% 14%	2010
November	1st to 10th	Day	32% 3 10% 18% 24% 13%	1857
	11th to 20th	Day	36% 2 8% 20% 24% 10%	1874
	21st to end	Day	36% 3 8% 25% 20% 8%	1710
December	1st to 10th	Day	39% 4 13% 21% 16% 8%	1710
	11th to 20th	Day	37% 3 7% 22% 25% 6%	2150
	21st to end	Day	46% 1 6% 20% 22% 5%	3124
January	1st to 10th	Night	43% 2 6% 14% 23% 12%	4109
	11th to 20th	Night	39% 2 6% 18% 27% 8%	4120
	21st to end	Night	45% 2 6% 13% 23% 11%	4532
February	1st to 10th	Night	44% 2 7% 19% 20% 8%	2390
	11th to 20th	Night	41% 2 8% 15% 20% 13%	2219
	21st to end	Night	41% 3 9% 20% 15% 13%	1799
March	1st to 10th	Night	53% 2 10% 14% 13% 7%	3418
	11th to 20th	Night	34% 3 10% 18% 21% 14%	3480
	21st to end	Night	40% 2 10% 19% 20% 9%	3817
April	1st to 10th	Night	34% 4 12% 20% 20% 11%	2090
	11th to 20th	Night	34% 3 8% 24% 20% 11%	1931
	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	38% 5% 11% 21% 19% 8%	2175
	11th to 20th	Night	28% 4 6% 23% 26% 13%	2280
	21st to end	Night	32% 3 6% 18% 25% 15%	2413
November	1st to 10th	Night	33% 1 9% 18% 25% 13%	2221
	11th to 20th	Night	37% 2 7% 19% 23% 11%	2303
	21st to end	Night	38% 2 9% 20% 21% 9%	2470
December	1st to 10th	Night	39% 3 16% 18% 18% 6%	2470
	11th to 20th	Night	40% 2 7% 18% 26% 7%	3044
	21st to end	Night	48% 2 8% 20% 19% 4	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	13% 15% 46% 21% 4	270
	11th to 20th	Day	10% 13% 41% 25% 9% 3	270
	21st to end	Day	23% 19% 39% 15% 3	297
February	1st to 10th	Day	17% 14% 41% 22% 6%	270
	11th to 20th	Day	24% 11% 42% 20% 2	270
	21st to end	Day	15% 15% 42% 22% 6% 1	310
March	1st to 10th	Day	16% 11% 34% 26% 11% 1	460
	11th to 20th	Day	15% 10% 40% 23% 11% 2	460
	21st to end	Day	16% 10% 39% 25% 9% 1	506
April	1st to 10th	Day	15% 12% 37% 23% 12% 2	460
	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% 33% 19% 6%	507
November	1st to 10th	Day	16% 5% 25% 31% 18% 5%	455
	11th to 20th	Day	19% 5% 35% 29% 10% 1	434
	21st to end	Day	16% 8% 33% 32% 10% 2	270
December	1st to 10th	Day	16% 9% 39% 24% 10% 2	270
	11th to 20th	Day	19% 11% 33% 27% 9% 1	270
	21st to end	Day	24% 7% 32% 28% 8% 1	297
January	1st to 10th	Night	14% 11% 39% 28% 8%	760
	11th to 20th	Night	14% 10% 30% 34% 12% 1	760
	21st to end	Night	19% 9% 37% 30% 5%	836
February	1st to 10th	Night	20% 7% 34% 30% 9%	760
	11th to 20th	Night	20% 10% 31% 33% 6%	743
	21st to end	Night	16% 9% 34% 35% 7%	628
March	1st to 10th	Night	13% 8% 32% 37% 11%	760
	11th to 20th	Night	14% 8% 30% 35% 12% 1	760
	21st to end	Night	12% 9% 31% 34% 14% 1	836
April	1st to 10th	Night	13% 7% 32% 33% 14% 1	760
	11th to 20th	Night	14% 7% 29% 30% 19% 1	751
	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	12% 4 20% 35% 26% 3	805
November	1st to 10th	Night	13% 6% 21% 36% 22% 3	740
	11th to 20th	Night	17% 6% 26% 34% 16% 2	760
	21st to end	Night	15% 6% 29% 32% 17% 1	760
December	1st to 10th	Night	16% 7% 28% 33% 15% 1	760
	11th to 20th	Night	18% 7% 26% 33% 14% 2	760
	21st to end	Night	21% 7% 29% 30% 12%	836

Page generated at 2024-10-21 02:20:00. Version ac07

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