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 2024-11-06.

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%	100898
	Night	13% 7% 2 5% 4 4 4 3 5% 7% 45%	98180
Transparency	Day	38% 6% 11% 22% 19% 4	104631
	Night	37% 5% 10% 22% 20% 6%	102587
Seeing	Day	16% 6% 20% 25% 22% 12%	15227
	Night	16% 6% 21% 32% 21% 3	24959

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	16% 6% 2 6% 4 4 5% 4 6% 9% 37%	3921
	11th to 20th	Day	15% 7% 2 6% 4 4 4 5% 6% 8% 38%	4081
	21st to end	Day	12% 6% 3 7% 5% 5% 5% 4 7% 9% 38%	4476
June	1st to 10th	Day	9% 7% 2 6% 5% 5% 5% 4 7% 10% 40%	2599
	11th to 20th	Day	4 4 2 6% 4 5% 5% 5% 7% 9% 48%	2660
	21st to end	Day	5% 3 2 6% 4 6% 5% 6% 7% 11% 45%	2660
July	1st to 10th	Day	6% 6% 2 7% 5% 6% 6% 6% 8% 11% 37%	4440
	11th to 20th	Day	9% 5% 2 6% 5% 6% 6% 6% 8% 11% 35%	4440
	21st to end	Day	15% 10% 3 8% 6% 6% 5% 5% 6% 8% 28%	4360
August	1st to 10th	Day	3 3 1 4 4 4 4 4 7% 10% 56%	3785
	11th to 20th	Day	8% 4 2 6% 4 5% 5% 4 7% 10% 46%	3729
	21st to end	Day	6% 4 2 6% 4 4 5% 3 6% 8% 54%	4180
September	1st to 10th	Day	10% 5% 2 6% 6% 4 4 4 6% 8% 44%	2280
	11th to 20th	Day	12% 6% 2 6% 4 5% 5% 4 5% 7% 44%	2134
	21st to end	Day	11% 4 2 5% 4 5% 4 3 5% 7% 50%	2090
October	1st to 10th	Day	10% 4 2 4 3 2 3 3 4 6% 58%	2090
	11th to 20th	Day	10% 5% 2 5% 3 3 3 3 4 6% 56%	1938
	21st to end	Day	16% 6% 2 5% 3 3 3 3 4 4 52%	2010
November	1st to 10th	Day	13% 5% 1 5% 2 2 3 3 4 6% 56%	1717
	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	17% 7% 3 6% 4 4 4 3 5% 7% 41%	2970
	11th to 20th	Night	13% 8% 3 7% 5% 4 4 3 5% 8% 42%	2812
	21st to end	Night	9% 5% 2 6% 4 5% 5% 4 6% 10% 43%	3079
June	1st to 10th	Night	9% 5% 2 5% 5% 5% 5% 4 6% 11% 44%	1575
	11th to 20th	Night	3 3 1 4 3 3 4 4 7% 11% 55%	1520
	21st to end	Night	3 4 1 4 4 4 4 4 7% 10% 55%	1520
July	1st to 10th	Night	6% 5% 2 6% 6% 6% 5% 5% 8% 13% 39%	2530
	11th to 20th	Night	6% 4 2 5% 4 5% 4 4 7% 12% 48%	2530
	21st to end	Night	10% 8% 4 9% 6% 5% 5% 4 7% 9% 32%	3190
August	1st to 10th	Night	3 2 1 3 3 4 4 4 6% 9% 63%	3144
	11th to 20th	Night	4 3 1 4 4 4 5% 4 6% 11% 54%	3100
	21st to end	Night	5% 3 2 4 4 3 4 4 7% 9% 55%	3476
September	1st to 10th	Night	8% 5% 2 5% 3 4 4 4 7% 8% 49%	1900
	11th to 20th	Night	10% 5% 2 5% 5% 4 4 4 5% 8% 48%	2025
	21st to end	Night	9% 5% 2 4 3 4 4 3 5% 5% 57%	2090
October	1st to 10th	Night	9% 3 1 4 2 2 2 3 4 6% 63%	2090
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 4 6% 54%	2237
	21st to end	Night	15% 7% 2 4 3 3 3 3 4 5% 51%	2585
November	1st to 10th	Night	11% 5% 2 4 4 4 3 3 5% 6% 54%	2483
	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% 8% 11% 23% 15% 2	3956
	11th to 20th	Day	42% 8% 14% 22% 13% 1	4085
	21st to end	Day	40% 8% 12% 24% 15% 1	4489
June	1st to 10th	Day	37% 9% 13% 22% 17% 2	2599
	11th to 20th	Day	30% 8% 15% 27% 18% 2	2660
	21st to end	Day	31% 10% 16% 23% 18% 3	2660
July	1st to 10th	Day	37% 10% 18% 26% 7% 2	4371
	11th to 20th	Day	37% 9% 17% 29% 7% 1	4365
	21st to end	Day	53% 9% 11% 20% 7%	4221
August	1st to 10th	Day	22% 7% 16% 33% 21% 2	3773
	11th to 20th	Day	32% 8% 16% 25% 17% 3	3765
	21st to end	Day	28% 7% 11% 26% 25% 3	4179
September	1st to 10th	Day	35% 9% 10% 24% 17% 5%	2280
	11th to 20th	Day	39% 7% 9% 19% 21% 4	2134
	21st to end	Day	33% 6% 11% 22% 22% 7%	2090
October	1st to 10th	Day	19% 3 6% 15% 40% 16%	3480
	11th to 20th	Day	19% 2 5% 23% 34% 16%	3204
	21st to end	Day	27% 3 5% 24% 33% 8%	3287
November	1st to 10th	Day	32% 3 8% 21% 29% 7%	1717
	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	43% 7% 10% 23% 16% 2	3000
	11th to 20th	Night	39% 8% 16% 23% 14% 1	2813
	21st to end	Night	34% 9% 14% 26% 15% 2	3087
June	1st to 10th	Night	34% 9% 13% 23% 19% 2	1575
	11th to 20th	Night	22% 8% 15% 32% 21% 3	1520
	21st to end	Night	23% 8% 17% 28% 19% 4	1520
July	1st to 10th	Night	34% 10% 21% 25% 8% 2	2490
	11th to 20th	Night	27% 7% 20% 35% 7% 3	2482
	21st to end	Night	47% 9% 14% 21% 9% 1	3089
August	1st to 10th	Night	17% 7% 12% 38% 25% 1	3132
	11th to 20th	Night	22% 9% 22% 27% 18% 2	3130
	21st to end	Night	24% 7% 14% 25% 27% 4	3476
September	1st to 10th	Night	30% 8% 12% 25% 20% 6%	1900
	11th to 20th	Night	34% 7% 12% 18% 26% 4	2025
	21st to end	Night	28% 6% 8% 26% 24% 8%	2090
October	1st to 10th	Night	17% 3 7% 17% 38% 18%	3480
	11th to 20th	Night	20% 3 5% 16% 35% 22%	3710
	21st to end	Night	26% 2 6% 26% 24% 15%	4258
November	1st to 10th	Night	32% 5% 7% 21% 26% 9%	2483
	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% 26% 19% 14%	487
	21st to end	Day	11% 3 19% 27% 22% 17%	529
June	1st to 10th	Day	12% 3 15% 24% 27% 19%	619
	11th to 20th	Day	6% 2 12% 29% 30% 21%	680
	21st to end	Day	7% 2 13% 29% 32% 17%	680
July	1st to 10th	Day	9% 2 7% 26% 31% 25%	671
	11th to 20th	Day	10% 3 7% 23% 32% 25%	668
	21st to end	Day	9% 2 8% 20% 37% 24%	597
August	1st to 10th	Day	6% 3 7% 23% 38% 23%	486
	11th to 20th	Day	13% 3 6% 27% 35% 16%	479
	21st to end	Day	12% 1 5% 20% 33% 28%	539
September	1st to 10th	Day	9% 2 9% 23% 38% 19%	490
	11th to 20th	Day	14% 2 7% 21% 35% 20%	490
	21st to end	Day	13% 4 12% 28% 29% 14%	490
October	1st to 10th	Day	11% 2 14% 31% 30% 12%	490
	11th to 20th	Day	10% 7% 29% 33% 17% 5%	338
	21st to end	Day	20% 8% 28% 28% 14% 3	330
November	1st to 10th	Day	20% 5% 23% 28% 19% 5%	285
	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	12% 4 22% 34% 24% 4	561
	21st to end	Night	8% 2 13% 39% 30% 7%	617
June	1st to 10th	Night	10% 3 9% 40% 31% 7%	570
	11th to 20th	Night	4 1 9% 38% 43% 5%	570
	21st to end	Night	4 1 8% 35% 43% 9%	570
July	1st to 10th	Night	8% 2 6% 27% 46% 11%	555
	11th to 20th	Night	8% 1 6% 28% 43% 14%	552
	21st to end	Night	6% 2 5% 29% 45% 13%	624
August	1st to 10th	Night	5% 1 3 28% 53% 11%	567
	11th to 20th	Night	6% 2 5% 37% 44% 6%	564
	21st to end	Night	9% 1 4 26% 50% 11%	627
September	1st to 10th	Night	8% 3 6% 34% 43% 7%	570
	11th to 20th	Night	11% 3 8% 30% 40% 7%	695
	21st to end	Night	12% 3 11% 33% 37% 5%	760
October	1st to 10th	Night	11% 3 12% 34% 35% 5%	760
	11th to 20th	Night	15% 3 21% 38% 21% 2	760
	21st to end	Night	19% 5% 21% 35% 18% 2	836
November	1st to 10th	Night	13% 6% 19% 42% 18% 2	764
	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 2024-11-03 12:19:03. Version ac07

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