Tallahassee
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tallahassee clear sky chart from 2005-11-06 to 2025-09-04.

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	10% 5% 2 6% 5% 5% 5% 5% 7% 9% 41%	125913
	Night	10% 6% 2 6% 4 4 4 4 6% 9% 45%	122792
Transparency	Day	37% 8% 14% 17% 16% 8%	129738
	Night	34% 7% 14% 18% 18% 9%	127036
Seeing	Day	12% 9% 24% 25% 20% 10%	16123
	Night	12% 7% 23% 30% 23% 5%	26083

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 4 2 5% 5% 55%	4056
	11th to 20th	Day	16% 7% 2 6% 4 3 4 3 5% 7% 44%	4082
	21st to end	Day	13% 6% 2 6% 4 4 4 3 6% 9% 44%	4972
February	1st to 10th	Day	15% 7% 2 6% 4 4 5% 3 5% 6% 42%	2000
	11th to 20th	Day	17% 6% 2 5% 3 3 4 3 4 6% 47%	1948
	21st to end	Day	15% 6% 2 5% 4 3 3 3 5% 6% 47%	1650
March	1st to 10th	Day	19% 7% 2 6% 4 3 3 3 5% 8% 39%	4682
	11th to 20th	Day	7% 4 2 5% 4 3 4 3 6% 8% 52%	4980
	21st to end	Day	14% 5% 2 4 3 3 4 3 5% 7% 49%	5465
April	1st to 10th	Day	9% 5% 2 6% 5% 4 4 5% 5% 7% 47%	2200
	11th to 20th	Day	11% 5% 2 5% 4 4 4 3 5% 6% 49%	2346
	21st to end	Day	6% 4 1 5% 5% 4 4 4 6% 8% 54%	2470
May	1st to 10th	Day	9% 6% 2 7% 5% 5% 5% 4 6% 8% 42%	5862
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 4 6% 10% 43%	5861
	21st to end	Day	3 3 2 6% 6% 5% 6% 5% 7% 12% 45%	6433
June	1st to 10th	Day	9% 7% 3 8% 6% 7% 8% 6% 8% 10% 27%	2600
	11th to 20th	Day	5% 4 2 8% 7% 9% 9% 7% 10% 10% 29%	2600
	21st to end	Day	7% 6% 2 8% 7% 8% 7% 6% 11% 10% 27%	2600
July	1st to 10th	Day	6% 7% 3 10% 9% 8% 10% 7% 11% 12% 18%	5900
	11th to 20th	Day	4 4 2 6% 6% 7% 8% 6% 10% 14% 35%	5900
	21st to end	Day	4 5% 2 8% 7% 8% 9% 8% 11% 14% 25%	6424
August	1st to 10th	Day	9% 5% 2 8% 7% 8% 8% 6% 9% 11% 27%	4009
	11th to 20th	Day	6% 5% 3 6% 5% 6% 7% 6% 8% 11% 37%	3849
	21st to end	Day	7% 6% 3 9% 7% 7% 7% 6% 8% 12% 29%	4232
September	1st to 10th	Day	9% 8% 3 10% 6% 7% 8% 5% 7% 11% 27%	2123
	11th to 20th	Day	11% 7% 3 8% 6% 7% 7% 6% 7% 9% 30%	2090
	21st to end	Day	11% 5% 3 6% 3 4 5% 5% 6% 8% 45%	2090
October	1st to 10th	Day	10% 6% 3 7% 4 5% 4 3 5% 6% 47%	2090
	11th to 20th	Day	6% 3 1 5% 3 3 3 3 4 6% 62%	2038
	21st to end	Day	7% 5% 2 6% 3 4 3 3 4 6% 55%	2090
November	1st to 10th	Day	9% 4 2 5% 4 3 3 3 5% 6% 56%	1902
	11th to 20th	Day	10% 5% 2 6% 3 3 3 4 5% 7% 53%	1800
	21st to end	Day	11% 6% 2 6% 5% 4 3 4 5% 5% 49%	1800
December	1st to 10th	Day	10% 6% 3 6% 4 3 3 3 4 6% 53%	2930
	11th to 20th	Day	12% 6% 2 6% 4 4 3 3 5% 7% 47%	3373
	21st to end	Day	19% 8% 2 5% 4 4 3 3 4 5% 43%	4466
January	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 5% 6% 52%	5889
	11th to 20th	Night	14% 8% 2 7% 4 4 5% 4 5% 7% 40%	5875
	21st to end	Night	16% 8% 2 5% 3 3 4 3 6% 7% 41%	5984
February	1st to 10th	Night	14% 8% 3 6% 5% 3 4 3 5% 6% 44%	2400
	11th to 20th	Night	16% 8% 2 5% 3 3 3 3 4 5% 47%	2338
	21st to end	Night	14% 8% 2 5% 4 3 4 3 4 5% 47%	1980
March	1st to 10th	Night	17% 10% 3 6% 4 4 4 3 4 7% 38%	5155
	11th to 20th	Night	9% 4 2 4 3 3 3 3 6% 9% 52%	4980
	21st to end	Night	14% 6% 2 5% 4 3 3 3 4 6% 49%	5467
April	1st to 10th	Night	9% 5% 2 5% 4 4 4 4 6% 8% 48%	2200
	11th to 20th	Night	9% 4 2 6% 4 3 4 3 5% 7% 51%	2017
	21st to end	Night	5% 5% 2 5% 3 3 3 4 6% 8% 57%	1930
May	1st to 10th	Night	7% 5% 2 6% 4 4 5% 4 5% 10% 48%	4033
	11th to 20th	Night	11% 6% 2 6% 3 3 4 4 6% 10% 45%	4032
	21st to end	Night	3 3 1 5% 3 4 4 4 6% 12% 54%	4421
June	1st to 10th	Night	7% 4 2 6% 5% 5% 6% 6% 8% 12% 39%	1800
	11th to 20th	Night	4 4 3 5% 5% 5% 6% 5% 9% 14% 40%	1800
	21st to end	Night	6% 5% 3 6% 5% 5% 6% 5% 9% 12% 38%	1800
July	1st to 10th	Night	5% 7% 3 9% 7% 8% 9% 7% 11% 13% 21%	4058
	11th to 20th	Night	2 3 2 5% 4 6% 6% 6% 9% 15% 43%	4057
	21st to end	Night	4 4 3 7% 5% 6% 7% 7% 12% 14% 31%	4427
August	1st to 10th	Night	8% 4 2 6% 5% 5% 6% 6% 9% 14% 35%	3135
	11th to 20th	Night	4 3 1 5% 4 6% 5% 6% 10% 15% 41%	3200
	21st to end	Night	7% 7% 3 8% 6% 7% 6% 6% 10% 11% 30%	3619
September	1st to 10th	Night	8% 7% 3 8% 5% 6% 6% 7% 10% 11% 29%	2124
	11th to 20th	Night	9% 7% 3 7% 6% 6% 6% 7% 8% 9% 33%	2090
	21st to end	Night	8% 6% 2 5% 4 4 4 5% 5% 10% 46%	2090
October	1st to 10th	Night	6% 5% 2 6% 5% 5% 4 3 5% 8% 50%	2090
	11th to 20th	Night	6% 4 2 4 3 3 4 3 5% 6% 61%	2140
	21st to end	Night	7% 4 3 5% 4 4 4 3 5% 6% 54%	2508
November	1st to 10th	Night	7% 5% 2 6% 4 4 4 3 5% 7% 53%	2391
	11th to 20th	Night	11% 5% 2 5% 4 4 3 3 4 6% 54%	2600
	21st to end	Night	13% 6% 2 5% 4 3 3 3 5% 7% 50%	2600
December	1st to 10th	Night	10% 5% 2 5% 4 3 4 3 5% 5% 55%	4250
	11th to 20th	Night	14% 6% 2 4 3 3 3 3 4 6% 52%	4822
	21st to end	Night	16% 8% 2 6% 3 4 3 3 5% 6% 44%	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	32% 4 6% 15% 31% 13%	4057
	11th to 20th	Day	39% 6% 7% 13% 22% 14%	4082
	21st to end	Day	37% 5% 8% 19% 19% 12%	4972
February	1st to 10th	Day	41% 7% 7% 15% 19% 11%	2000
	11th to 20th	Day	38% 5% 7% 14% 23% 13%	1958
	21st to end	Day	37% 6% 10% 16% 19% 12%	1650
March	1st to 10th	Day	41% 6% 9% 15% 18% 11%	4682
	11th to 20th	Day	29% 6% 11% 14% 21% 21%	4980
	21st to end	Day	33% 6% 10% 23% 16% 12%	5465
April	1st to 10th	Day	34% 7% 11% 17% 17% 14%	2200
	11th to 20th	Day	34% 6% 8% 19% 20% 12%	2346
	21st to end	Day	26% 7% 12% 23% 21% 11%	2470
May	1st to 10th	Day	36% 8% 16% 20% 15% 5%	5897
	11th to 20th	Day	34% 8% 14% 27% 15% 2	5865
	21st to end	Day	29% 9% 19% 22% 19% 3	6447
June	1st to 10th	Day	45% 13% 17% 16% 8% 1	2600
	11th to 20th	Day	41% 15% 21% 15% 7% 1	2600
	21st to end	Day	44% 15% 21% 13% 6% 2	2600
July	1st to 10th	Day	54% 11% 27% 7% 1	5835
	11th to 20th	Day	37% 10% 36% 15% 2	5831
	21st to end	Day	43% 14% 24% 18% 1	6240
August	1st to 10th	Day	46% 11% 19% 15% 8% 1	3996
	11th to 20th	Day	36% 11% 19% 22% 12%	3885
	21st to end	Day	45% 10% 22% 18% 4 1	4232
September	1st to 10th	Day	47% 13% 17% 14% 7% 2	2123
	11th to 20th	Day	47% 12% 15% 13% 10% 2	2090
	21st to end	Day	36% 7% 15% 20% 15% 8%	2090
October	1st to 10th	Day	44% 5% 6% 10% 18% 17%	3480
	11th to 20th	Day	15% 3 5% 18% 27% 31%	3369
	21st to end	Day	20% 4 5% 15% 38% 18%	3428
November	1st to 10th	Day	28% 5% 9% 19% 24% 16%	1902
	11th to 20th	Day	30% 4 9% 16% 26% 15%	1800
	21st to end	Day	35% 6% 7% 19% 24% 10%	1800
December	1st to 10th	Day	34% 4 8% 16% 26% 12%	2930
	11th to 20th	Day	36% 5% 8% 20% 22% 9%	3370
	21st to end	Day	44% 3 6% 17% 25% 5%	4466
January	1st to 10th	Night	32% 5% 7% 12% 30% 14%	5889
	11th to 20th	Night	43% 4 6% 14% 24% 8%	5875
	21st to end	Night	41% 4 8% 19% 20% 9%	5984
February	1st to 10th	Night	41% 5% 8% 15% 21% 11%	2400
	11th to 20th	Night	40% 5% 8% 13% 20% 14%	2339
	21st to end	Night	38% 6% 8% 17% 16% 15%	1980
March	1st to 10th	Night	45% 6% 8% 13% 18% 9%	5155
	11th to 20th	Night	26% 6% 11% 19% 19% 18%	4980
	21st to end	Night	36% 4 9% 19% 19% 12%	5467
April	1st to 10th	Night	33% 7% 12% 17% 18% 13%	2200
	11th to 20th	Night	31% 6% 10% 17% 23% 13%	2017
	21st to end	Night	24% 7% 11% 26% 22% 10%	1930
May	1st to 10th	Night	29% 10% 18% 25% 14% 5%	4060
	11th to 20th	Night	32% 8% 16% 27% 14% 2	4033
	21st to end	Night	22% 8% 20% 33% 15% 2	4429
June	1st to 10th	Night	33% 13% 23% 20% 10% 1	1800
	11th to 20th	Night	31% 14% 26% 19% 9% 2	1800
	21st to end	Night	33% 14% 24% 19% 9% 1	1800
July	1st to 10th	Night	52% 15% 25% 7% 1	4015
	11th to 20th	Night	28% 14% 41% 15% 2	4006
	21st to end	Night	37% 15% 31% 16% 1	4297
August	1st to 10th	Night	35% 11% 27% 19% 8%	3124
	11th to 20th	Night	28% 12% 27% 25% 7%	3230
	21st to end	Night	43% 11% 25% 16% 5% 1	3619
September	1st to 10th	Night	41% 16% 20% 14% 8% 2	2124
	11th to 20th	Night	42% 14% 15% 15% 12% 2	2090
	21st to end	Night	32% 10% 16% 19% 16% 8%	2090
October	1st to 10th	Night	41% 6% 9% 12% 18% 14%	3480
	11th to 20th	Night	16% 3 5% 17% 32% 27%	3548
	21st to end	Night	20% 4 5% 16% 38% 17%	4120
November	1st to 10th	Night	31% 5% 8% 19% 20% 17%	2391
	11th to 20th	Night	32% 5% 7% 16% 25% 15%	2600
	21st to end	Night	34% 5% 11% 18% 20% 13%	2600
December	1st to 10th	Night	32% 4 8% 17% 24% 16%	4250
	11th to 20th	Night	34% 5% 9% 20% 22% 10%	4824
	21st to end	Night	41% 4 8% 16% 25% 5%	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% 24% 44% 13% 3	300
	11th to 20th	Day	17% 17% 38% 21% 6% 2	300
	21st to end	Day	27% 21% 40% 11% 2	330
February	1st to 10th	Day	20% 20% 35% 19% 5%	300
	11th to 20th	Day	24% 19% 38% 16% 2	300
	21st to end	Day	15% 24% 39% 18% 3	249
March	1st to 10th	Day	17% 21% 36% 19% 7%	385
	11th to 20th	Day	17% 16% 35% 21% 10% 1	500
	21st to end	Day	16% 18% 32% 23% 9% 1	550
April	1st to 10th	Day	13% 20% 32% 21% 13% 1	500
	11th to 20th	Day	11% 15% 32% 29% 12% 1	492
	21st to end	Day	7% 11% 30% 32% 16% 3	500
May	1st to 10th	Day	8% 9% 31% 30% 15% 7%	503
	11th to 20th	Day	8% 6% 27% 29% 20% 9%	527
	21st to end	Day	8% 3 21% 34% 22% 13%	573
June	1st to 10th	Day	11% 3 16% 32% 26% 12%	530
	11th to 20th	Day	6% 3 14% 29% 28% 20%	530
	21st to end	Day	8% 3 10% 28% 30% 22%	530
July	1st to 10th	Day	7% 4 7% 19% 32% 30%	525
	11th to 20th	Day	6% 2 6% 20% 36% 30%	524
	21st to end	Day	5% 2 6% 24% 37% 26%	576
August	1st to 10th	Day	11% 3 8% 22% 32% 24%	526
	11th to 20th	Day	7% 2 6% 19% 38% 28%	519
	21st to end	Day	8% 4 10% 29% 31% 18%	583
September	1st to 10th	Day	12% 3 13% 25% 27% 19%	502
	11th to 20th	Day	14% 2 16% 30% 28% 10%	490
	21st to end	Day	12% 2 15% 23% 34% 14%	490
October	1st to 10th	Day	12% 7% 27% 31% 18% 5%	490
	11th to 20th	Day	6% 6% 25% 36% 21% 6%	490
	21st to end	Day	10% 8% 29% 34% 18% 2	539
November	1st to 10th	Day	14% 8% 26% 31% 18% 3	440
	11th to 20th	Day	14% 14% 44% 20% 7% 2	300
	21st to end	Day	12% 18% 37% 23% 8% 1	300
December	1st to 10th	Day	20% 16% 34% 20% 9% 2	300
	11th to 20th	Day	18% 14% 39% 23% 5%	300
	21st to end	Day	22% 11% 33% 26% 6% 1	330
January	1st to 10th	Night	17% 15% 37% 23% 8% 1	800
	11th to 20th	Night	17% 13% 30% 30% 10% 1	800
	21st to end	Night	21% 13% 35% 25% 6%	880
February	1st to 10th	Night	18% 11% 30% 32% 9%	800
	11th to 20th	Night	20% 14% 31% 29% 7%	783
	21st to end	Night	18% 12% 36% 30% 4	660
March	1st to 10th	Night	16% 13% 30% 33% 9%	800
	11th to 20th	Night	14% 12% 31% 31% 12%	800
	21st to end	Night	13% 13% 32% 32% 10%	880
April	1st to 10th	Night	13% 9% 30% 34% 13%	800
	11th to 20th	Night	11% 9% 28% 38% 14% 1	635
	21st to end	Night	6% 6% 27% 37% 22% 1	600
May	1st to 10th	Night	8% 6% 24% 39% 23% 2	600
	11th to 20th	Night	7% 4 23% 37% 25% 5%	591
	21st to end	Night	6% 2 14% 39% 34% 5%	650
June	1st to 10th	Night	7% 2 12% 37% 38% 5%	600
	11th to 20th	Night	5% 2 8% 31% 42% 14%	600
	21st to end	Night	6% 2 7% 28% 44% 13%	600
July	1st to 10th	Night	6% 1 5% 20% 44% 22%	585
	11th to 20th	Night	6% 2 4 17% 47% 25%	582
	21st to end	Night	4 1 3 19% 54% 19%	657
August	1st to 10th	Night	7% 2 6% 20% 48% 17%	597
	11th to 20th	Night	6% 1 4 17% 50% 22%	594
	21st to end	Night	10% 2 9% 26% 38% 16%	680
September	1st to 10th	Night	10% 2 11% 26% 37% 13%	773
	11th to 20th	Night	11% 4 14% 32% 32% 7%	760
	21st to end	Night	8% 3 17% 30% 35% 6%	760
October	1st to 10th	Night	9% 4 25% 31% 28% 3	760
	11th to 20th	Night	7% 5% 24% 35% 25% 3	760
	21st to end	Night	10% 6% 23% 38% 21% 2	836
November	1st to 10th	Night	8% 8% 27% 37% 18% 2	780
	11th to 20th	Night	13% 10% 29% 33% 15% 1	800
	21st to end	Night	14% 10% 27% 35% 13% 1	800
December	1st to 10th	Night	14% 10% 31% 29% 16% 1	800
	11th to 20th	Night	15% 12% 30% 30% 13% 1	800
	21st to end	Night	22% 11% 28% 26% 12% 1	880

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