Sumter
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sumter clear sky chart from 2005-11-06 to 2025-10-04.

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	12% 6% 2 6% 4 4 5% 4 6% 8% 42%	126430
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 44%	122962
Transparency	Day	37% 8% 13% 19% 18% 6%	130063
	Night	37% 8% 12% 17% 19% 7%	127398
Seeing	Day	13% 8% 22% 24% 21% 12%	16680
	Night	14% 7% 24% 33% 20% 2	26737

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	13% 5% 2 5% 3 3 3 3 4 6% 54%	4056
	11th to 20th	Day	11% 5% 2 5% 3 3 3 2 3 6% 57%	4060
	21st to end	Day	13% 7% 2 7% 5% 4 4 3 5% 5% 44%	4466
February	1st to 10th	Day	14% 7% 3 6% 5% 4 4 3 6% 6% 42%	1800
	11th to 20th	Day	20% 6% 2 6% 4 3 3 2 4 5% 45%	1908
	21st to end	Day	16% 6% 2 7% 4 3 4 5% 4 5% 44%	1762
March	1st to 10th	Day	20% 8% 3 7% 4 3 4 3 4 5% 39%	4935
	11th to 20th	Day	8% 4 2 5% 4 4 4 4 5% 7% 54%	4980
	21st to end	Day	13% 6% 2 6% 4 4 4 3 4 6% 47%	5465
April	1st to 10th	Day	9% 4 1 4 5% 4 5% 4 8% 8% 49%	2215
	11th to 20th	Day	10% 5% 2 4 4 4 3 4 6% 7% 51%	2374
	21st to end	Day	8% 4 1 5% 4 4 5% 3 6% 7% 52%	2440
May	1st to 10th	Day	9% 6% 2 7% 5% 5% 5% 4 7% 11% 38%	5862
	11th to 20th	Day	16% 7% 3 6% 5% 4 4 5% 7% 9% 34%	5861
	21st to end	Day	10% 5% 2 6% 4 5% 5% 4 7% 8% 44%	6433
June	1st to 10th	Day	9% 6% 2 7% 5% 5% 6% 5% 6% 11% 37%	2600
	11th to 20th	Day	7% 5% 2 5% 5% 6% 6% 6% 8% 10% 41%	2600
	21st to end	Day	5% 4 3 7% 6% 6% 7% 5% 8% 13% 37%	2600
July	1st to 10th	Day	11% 7% 3 9% 7% 7% 7% 6% 8% 10% 25%	5900
	11th to 20th	Day	5% 5% 2 7% 6% 6% 7% 6% 10% 15% 31%	5900
	21st to end	Day	8% 7% 3 8% 6% 6% 7% 6% 9% 13% 28%	6424
August	1st to 10th	Day	22% 7% 2 6% 6% 6% 6% 5% 8% 10% 20%	4234
	11th to 20th	Day	10% 6% 3 7% 5% 5% 6% 5% 7% 11% 35%	4123
	21st to end	Day	7% 4 2 6% 4 5% 5% 5% 8% 10% 43%	4312
September	1st to 10th	Day	7% 5% 2 7% 5% 5% 5% 6% 6% 10% 41%	2270
	11th to 20th	Day	13% 6% 2 6% 5% 4 5% 4 6% 7% 42%	2200
	21st to end	Day	17% 6% 3 6% 4 4 4 3 5% 7% 40%	2200
October	1st to 10th	Day	13% 6% 3 6% 3 4 3 3 5% 7% 49%	1979
	11th to 20th	Day	9% 5% 2 5% 4 3 3 3 4 6% 58%	1900
	21st to end	Day	10% 5% 2 5% 3 3 3 3 4 6% 57%	2090
November	1st to 10th	Day	13% 5% 1 4 4 3 3 3 4 7% 53%	1957
	11th to 20th	Day	14% 7% 2 5% 4 2 3 2 4 7% 50%	1955
	21st to end	Day	13% 6% 2 6% 4 3 4 3 5% 6% 50%	1800
December	1st to 10th	Day	10% 5% 2 6% 3 5% 4 4 5% 6% 52%	2930
	11th to 20th	Day	15% 6% 2 6% 4 3 3 3 5% 7% 46%	3373
	21st to end	Day	19% 7% 3 5% 3 3 3 3 4 6% 44%	4466
January	1st to 10th	Night	11% 4 2 5% 3 3 3 3 4 5% 57%	5889
	11th to 20th	Night	12% 5% 2 6% 4 4 4 3 5% 7% 48%	5900
	21st to end	Night	13% 8% 3 7% 4 3 4 2 4 5% 47%	6490
February	1st to 10th	Night	16% 6% 2 5% 4 4 3 4 5% 6% 45%	2600
	11th to 20th	Night	18% 8% 2 5% 4 4 4 3 5% 5% 43%	2375
	21st to end	Night	13% 6% 3 6% 5% 4 3 3 5% 6% 47%	1866
March	1st to 10th	Night	18% 8% 3 7% 4 4 3 3 5% 6% 39%	4918
	11th to 20th	Night	10% 4 1 5% 3 3 3 3 5% 8% 54%	4980
	21st to end	Night	13% 5% 1 5% 4 4 3 3 5% 7% 50%	5467
April	1st to 10th	Night	10% 6% 2 5% 4 3 4 3 6% 8% 48%	2184
	11th to 20th	Night	10% 5% 2 5% 4 3 3 3 5% 7% 52%	1975
	21st to end	Night	8% 4 2 5% 4 4 4 4 6% 7% 52%	1975
May	1st to 10th	Night	8% 6% 2 6% 5% 5% 5% 4 7% 10% 42%	4033
	11th to 20th	Night	16% 6% 2 6% 4 5% 4 4 7% 10% 36%	4032
	21st to end	Night	11% 6% 2 7% 4 4 4 4 7% 9% 42%	4421
June	1st to 10th	Night	11% 6% 2 6% 5% 6% 6% 5% 9% 10% 35%	1800
	11th to 20th	Night	8% 6% 2 7% 6% 5% 5% 5% 7% 11% 39%	1800
	21st to end	Night	6% 5% 2 6% 5% 5% 8% 6% 10% 12% 36%	1800
July	1st to 10th	Night	12% 8% 3 8% 6% 7% 6% 6% 9% 11% 25%	4058
	11th to 20th	Night	7% 6% 3 8% 6% 6% 7% 6% 10% 14% 27%	4057
	21st to end	Night	10% 8% 3 10% 7% 7% 6% 6% 8% 10% 24%	4427
August	1st to 10th	Night	22% 7% 3 8% 5% 5% 6% 5% 8% 10% 23%	2915
	11th to 20th	Night	8% 7% 3 8% 6% 6% 6% 5% 7% 11% 34%	2891
	21st to end	Night	7% 4 2 5% 4 4 4 4 8% 11% 47%	3586
September	1st to 10th	Night	9% 5% 2 7% 6% 6% 5% 5% 7% 9% 39%	2125
	11th to 20th	Night	12% 6% 3 8% 5% 5% 5% 3 6% 7% 40%	2200
	21st to end	Night	17% 6% 3 6% 4 4 5% 4 5% 6% 41%	2200
October	1st to 10th	Night	13% 6% 2 5% 3 3 3 3 4 6% 52%	2267
	11th to 20th	Night	11% 4 2 5% 3 2 3 2 5% 6% 57%	2280
	21st to end	Night	9% 6% 2 4 3 3 3 3 5% 6% 57%	2508
November	1st to 10th	Night	13% 6% 2 5% 3 3 3 2 3 5% 55%	2341
	11th to 20th	Night	14% 6% 2 5% 3 3 3 3 5% 6% 50%	2440
	21st to end	Night	13% 5% 2 5% 4 4 4 3 5% 6% 49%	2600
December	1st to 10th	Night	12% 5% 2 6% 3 3 3 3 4 5% 55%	4250
	11th to 20th	Night	16% 7% 3 7% 4 3 3 3 4 6% 44%	4822
	21st to end	Night	17% 7% 3 5% 3 4 4 3 5% 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	30% 5% 7% 19% 32% 7%	4057
	11th to 20th	Day	30% 4 5% 16% 36% 9%	4060
	21st to end	Day	42% 5% 5% 16% 21% 12%	4466
February	1st to 10th	Day	40% 6% 10% 19% 19% 6%	1800
	11th to 20th	Day	43% 4 5% 17% 23% 6%	1918
	21st to end	Day	40% 7% 7% 16% 21% 9%	1762
March	1st to 10th	Day	48% 4 6% 12% 21% 9%	4935
	11th to 20th	Day	29% 6% 9% 15% 25% 17%	4980
	21st to end	Day	38% 5% 8% 17% 22% 10%	5465
April	1st to 10th	Day	30% 7% 11% 20% 25% 7%	2215
	11th to 20th	Day	31% 6% 12% 21% 20% 11%	2374
	21st to end	Day	29% 7% 12% 25% 23% 4	2440
May	1st to 10th	Day	37% 10% 17% 24% 11% 1	5897
	11th to 20th	Day	44% 9% 18% 18% 11%	5865
	21st to end	Day	34% 10% 14% 20% 20% 3	6447
June	1st to 10th	Day	39% 11% 18% 22% 10% 1	2600
	11th to 20th	Day	33% 11% 20% 23% 12% 1	2600
	21st to end	Day	33% 13% 21% 21% 11% 1	2600
July	1st to 10th	Day	49% 12% 17% 16% 4 1	5835
	11th to 20th	Day	35% 17% 34% 11% 3 1	5831
	21st to end	Day	42% 15% 17% 20% 6%	6240
August	1st to 10th	Day	54% 13% 19% 11% 3	4221
	11th to 20th	Day	39% 11% 16% 21% 12%	4162
	21st to end	Day	32% 9% 15% 29% 13% 1	4312
September	1st to 10th	Day	36% 11% 15% 17% 17% 4	2270
	11th to 20th	Day	39% 8% 12% 18% 19% 4	2200
	21st to end	Day	42% 7% 10% 21% 16% 5%	2200
October	1st to 10th	Day	34% 5% 9% 18% 27% 7%	3265
	11th to 20th	Day	18% 3 6% 17% 28% 28%	3140
	21st to end	Day	24% 4 6% 20% 30% 16%	3428
November	1st to 10th	Day	32% 5% 8% 18% 26% 11%	1957
	11th to 20th	Day	35% 4 7% 19% 25% 10%	1955
	21st to end	Day	35% 5% 9% 18% 23% 9%	1800
December	1st to 10th	Day	33% 5% 8% 17% 27% 10%	2930
	11th to 20th	Day	37% 5% 11% 22% 19% 6%	3370
	21st to end	Day	41% 4 8% 21% 23% 2	4466
January	1st to 10th	Night	29% 5% 6% 17% 36% 7%	5889
	11th to 20th	Night	34% 5% 7% 15% 32% 7%	5900
	21st to end	Night	40% 5% 5% 12% 28% 9%	6490
February	1st to 10th	Night	39% 5% 8% 20% 20% 8%	2600
	11th to 20th	Night	43% 5% 8% 16% 19% 8%	2376
	21st to end	Night	37% 6% 8% 16% 19% 13%	1866
March	1st to 10th	Night	45% 6% 7% 11% 22% 9%	4918
	11th to 20th	Night	28% 5% 8% 12% 28% 19%	4980
	21st to end	Night	34% 5% 9% 21% 20% 12%	5467
April	1st to 10th	Night	33% 6% 12% 19% 21% 9%	2184
	11th to 20th	Night	30% 6% 10% 20% 22% 11%	1975
	21st to end	Night	29% 7% 13% 25% 21% 5%	1975
May	1st to 10th	Night	34% 11% 17% 24% 13% 2	4060
	11th to 20th	Night	41% 9% 20% 17% 12%	4033
	21st to end	Night	33% 11% 14% 22% 18% 2	4429
June	1st to 10th	Night	38% 12% 18% 20% 10% 2	1800
	11th to 20th	Night	37% 11% 20% 21% 10% 1	1800
	21st to end	Night	33% 15% 22% 20% 9% 2	1800
July	1st to 10th	Night	48% 14% 20% 14% 3 1	4015
	11th to 20th	Night	41% 18% 29% 9% 2	4006
	21st to end	Night	51% 12% 16% 16% 4	4297
August	1st to 10th	Night	55% 11% 21% 11% 2 1	2904
	11th to 20th	Night	41% 13% 21% 19% 6%	2918
	21st to end	Night	28% 9% 17% 33% 12% 1	3586
September	1st to 10th	Night	37% 11% 15% 19% 13% 5%	2125
	11th to 20th	Night	42% 8% 13% 18% 16% 4	2200
	21st to end	Night	42% 9% 13% 18% 14% 4	2200
October	1st to 10th	Night	33% 6% 9% 18% 26% 7%	3761
	11th to 20th	Night	19% 3 7% 14% 25% 33%	3779
	21st to end	Night	23% 5% 7% 20% 27% 18%	4120
November	1st to 10th	Night	33% 4 9% 15% 26% 14%	2341
	11th to 20th	Night	35% 4 7% 15% 26% 13%	2440
	21st to end	Night	35% 5% 8% 19% 23% 10%	2600
December	1st to 10th	Night	32% 5% 7% 15% 29% 11%	4250
	11th to 20th	Night	41% 5% 9% 17% 18% 9%	4824
	21st to end	Night	42% 5% 7% 20% 23% 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	16% 16% 45% 19% 4	300
	11th to 20th	Day	14% 20% 35% 24% 7% 1	300
	21st to end	Day	19% 19% 39% 18% 4	330
February	1st to 10th	Day	14% 18% 40% 20% 7%	300
	11th to 20th	Day	29% 16% 35% 18% 2	300
	21st to end	Day	18% 14% 38% 22% 6% 1	361
March	1st to 10th	Day	17% 15% 33% 22% 13% 1	500
	11th to 20th	Day	15% 13% 42% 23% 7%	500
	21st to end	Day	15% 13% 40% 21% 10% 1	550
April	1st to 10th	Day	12% 15% 32% 26% 13% 2	500
	11th to 20th	Day	9% 11% 27% 28% 20% 5%	492
	21st to end	Day	9% 8% 23% 26% 23% 11%	500
May	1st to 10th	Day	8% 11% 29% 26% 18% 8%	503
	11th to 20th	Day	16% 4 16% 26% 26% 12%	527
	21st to end	Day	12% 4 15% 25% 23% 21%	573
June	1st to 10th	Day	10% 3 13% 29% 29% 15%	530
	11th to 20th	Day	9% 3 12% 25% 30% 21%	530
	21st to end	Day	7% 2 10% 27% 30% 24%	530
July	1st to 10th	Day	6% 2 8% 22% 31% 31%	525
	11th to 20th	Day	7% 2 5% 21% 35% 30%	524
	21st to end	Day	5% 2 8% 23% 38% 24%	576
August	1st to 10th	Day	17% 2 11% 20% 29% 21%	526
	11th to 20th	Day	11% 4 8% 19% 33% 25%	519
	21st to end	Day	13% 2 9% 22% 31% 23%	583
September	1st to 10th	Day	8% 2 14% 26% 33% 18%	530
	11th to 20th	Day	15% 4 13% 25% 30% 13%	530
	21st to end	Day	19% 2 13% 28% 24% 13%	530
October	1st to 10th	Day	14% 5% 19% 30% 22% 10%	502
	11th to 20th	Day	9% 7% 23% 26% 25% 10%	490
	21st to end	Day	11% 5% 23% 28% 25% 7%	539
November	1st to 10th	Day	17% 6% 25% 28% 17% 7%	495
	11th to 20th	Day	20% 6% 32% 28% 11% 2	455
	21st to end	Day	10% 12% 31% 30% 14% 3	300
December	1st to 10th	Day	20% 12% 35% 24% 8%	300
	11th to 20th	Day	18% 10% 33% 27% 10% 2	300
	21st to end	Day	21% 15% 33% 20% 8% 3	330
January	1st to 10th	Night	17% 13% 36% 26% 7%	800
	11th to 20th	Night	17% 12% 33% 31% 8%	800
	21st to end	Night	18% 10% 39% 30% 3	880
February	1st to 10th	Night	19% 10% 34% 32% 5%	800
	11th to 20th	Night	19% 13% 39% 27% 1	783
	21st to end	Night	13% 13% 38% 30% 5%	660
March	1st to 10th	Night	17% 12% 33% 32% 7%	800
	11th to 20th	Night	15% 13% 36% 29% 8%	800
	21st to end	Night	15% 10% 39% 28% 8%	880
April	1st to 10th	Night	14% 15% 33% 30% 8%	800
	11th to 20th	Night	12% 11% 28% 36% 13% 1	791
	21st to end	Night	9% 9% 29% 42% 12%	775
May	1st to 10th	Night	10% 5% 30% 41% 13% 1	600
	11th to 20th	Night	12% 5% 26% 38% 17% 2	591
	21st to end	Night	11% 2 13% 38% 32% 4	650
June	1st to 10th	Night	12% 2 15% 44% 24% 3	600
	11th to 20th	Night	10% 2 14% 36% 31% 8%	600
	21st to end	Night	6% 3 10% 38% 37% 6%	600
July	1st to 10th	Night	9% 3 7% 35% 40% 6%	585
	11th to 20th	Night	7% 2 6% 28% 50% 7%	582
	21st to end	Night	7% 2 7% 37% 42% 5%	657
August	1st to 10th	Night	14% 2 6% 30% 41% 6%	597
	11th to 20th	Night	10% 3 7% 34% 38% 8%	597
	21st to end	Night	13% 2 8% 30% 40% 6%	880
September	1st to 10th	Night	11% 2 9% 33% 41% 5%	800
	11th to 20th	Night	14% 3 11% 32% 35% 6%	800
	21st to end	Night	19% 3 14% 33% 29% 3	800
October	1st to 10th	Night	14% 3 17% 32% 29% 4	773
	11th to 20th	Night	12% 4 25% 32% 24% 3	760
	21st to end	Night	12% 6% 23% 34% 24% 2	836
November	1st to 10th	Night	15% 6% 23% 35% 18% 4	780
	11th to 20th	Night	16% 9% 28% 33% 13% 1	800
	21st to end	Night	14% 8% 29% 32% 16% 1	800
December	1st to 10th	Night	18% 9% 30% 34% 9% 1	800
	11th to 20th	Night	19% 6% 28% 34% 12% 1	800
	21st to end	Night	23% 10% 25% 32% 9%	880

Page generated at 2025-10-01 01:39:01. Version ac07

Copyright © 2025 Attilla Danko.