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 2024-03-23.

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% 3 6% 6% 4 5% 6% 6% 8% 41%	79193
	Night	10% 6% 2 5% 5% 3 5% 5% 6% 8% 45%	80701
Transparency	Day	39% 9% 13% 16% 16% 8%	78916
	Night	35% 9% 13% 17% 18% 9%	80497
Seeing	Day	12% 9% 24% 25% 20% 10%	14122
	Night	12% 7% 22% 30% 23% 5%	24243

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% 6% 2 6% 5% 3 4 3 5% 6% 47%	2836
	11th to 20th	Day	12% 6% 2 5% 5% 3 4 5% 5% 9% 44%	2848
	21st to end	Day	19% 7% 2 5% 4 3 4 4 5% 7% 40%	3476
February	1st to 10th	Day	16% 6% 3 5% 5% 3 4 5% 4 6% 42%	1900
	11th to 20th	Day	16% 6% 3 4 4 2 4 4 4 6% 48%	1848
	21st to end	Day	15% 6% 2 5% 5% 3 4 3 5% 7% 46%	1570
March	1st to 10th	Day	10% 4 2 5% 5% 2 3 4 4 8% 51%	1981
	11th to 20th	Day	11% 4 2 5% 6% 2 4 4 6% 7% 47%	2090
	21st to end	Day	11% 5% 2 4 5% 3 4 4 5% 8% 50%	2200
April	1st to 10th	Day	10% 4 2 6% 5% 4 4 5% 5% 6% 48%	1980
	11th to 20th	Day	12% 6% 3 5% 6% 3 5% 4 5% 7% 46%	2108
	21st to end	Day	6% 3 1 4 5% 2 4 5% 6% 8% 55%	2222
May	1st to 10th	Day	6% 4 1 4 5% 3 4 4 6% 7% 56%	2340
	11th to 20th	Day	7% 5% 2 5% 6% 4 7% 6% 7% 10% 40%	2301
	21st to end	Day	6% 5% 2 7% 8% 5% 6% 7% 6% 9% 40%	2531
June	1st to 10th	Day	10% 7% 4 7% 7% 5% 8% 8% 8% 10% 27%	2340
	11th to 20th	Day	6% 3 2 6% 8% 7% 10% 9% 9% 10% 29%	2340
	21st to end	Day	8% 5% 3 8% 7% 5% 8% 8% 11% 10% 27%	2340
July	1st to 10th	Day	8% 6% 3 7% 8% 5% 9% 9% 9% 11% 23%	2340
	11th to 20th	Day	9% 6% 3 7% 9% 6% 8% 8% 9% 11% 24%	2340
	21st to end	Day	6% 5% 3 7% 8% 6% 8% 9% 9% 12% 27%	2547
August	1st to 10th	Day	8% 5% 3 8% 9% 6% 8% 9% 9% 10% 24%	2207
	11th to 20th	Day	10% 8% 4 8% 8% 5% 8% 9% 8% 11% 22%	2125
	21st to end	Day	10% 7% 3 9% 9% 6% 8% 8% 6% 9% 25%	2340
September	1st to 10th	Day	8% 7% 3 8% 7% 5% 8% 8% 8% 11% 27%	1980
	11th to 20th	Day	10% 6% 3 6% 8% 6% 7% 7% 7% 10% 31%	1980
	21st to end	Day	11% 5% 3 5% 4 3 4 6% 6% 8% 44%	1980
October	1st to 10th	Day	9% 6% 3 5% 5% 4 5% 4 5% 6% 48%	1980
	11th to 20th	Day	7% 3 1 5% 4 2 3 4 4 6% 60%	1931
	21st to end	Day	8% 5% 2 5% 4 3 4 5% 4 6% 53%	1980
November	1st to 10th	Day	8% 3 2 4 4 2 3 4 5% 7% 57%	1805
	11th to 20th	Day	10% 5% 2 5% 4 2 4 5% 5% 7% 54%	1710
	21st to end	Day	11% 5% 2 4 6% 3 4 5% 5% 5% 49%	1710
December	1st to 10th	Day	13% 6% 3 5% 5% 2 4 5% 4 7% 46%	1710
	11th to 20th	Day	16% 7% 2 5% 5% 3 4 4 5% 7% 41%	2153
	21st to end	Day	19% 8% 3 5% 5% 3 3 3 3 5% 42%	3124
January	1st to 10th	Night	16% 7% 2 6% 5% 2 4 4 5% 6% 43%	4109
	11th to 20th	Night	10% 7% 3 6% 5% 3 5% 5% 5% 7% 45%	4109
	21st to end	Night	19% 10% 3 5% 4 3 4 3 5% 6% 39%	4180
February	1st to 10th	Night	15% 6% 3 5% 5% 2 4 3 4 6% 45%	2280
	11th to 20th	Night	16% 7% 2 5% 4 2 3 3 3 5% 49%	2218
	21st to end	Night	14% 8% 2 4 5% 3 3 4 4 6% 47%	1884
March	1st to 10th	Night	12% 6% 2 4 4 2 4 3 5% 9% 49%	2197
	11th to 20th	Night	11% 5% 2 4 4 3 4 4 6% 10% 46%	2090
	21st to end	Night	9% 5% 2 4 4 2 3 4 4 7% 54%	2201
April	1st to 10th	Night	9% 4 2 5% 5% 3 4 5% 5% 8% 49%	1980
	11th to 20th	Night	10% 4 2 6% 5% 3 4 5% 5% 7% 49%	1813
	21st to end	Night	6% 4 2 3 4 2 3 4 6% 7% 59%	1738
May	1st to 10th	Night	6% 3 2 4 3 3 3 4 5% 10% 57%	1620
	11th to 20th	Night	4 4 2 5% 5% 3 5% 6% 7% 10% 49%	1592
	21st to end	Night	5% 4 2 4 4 4 5% 6% 6% 10% 49%	1744
June	1st to 10th	Night	7% 4 2 5% 6% 3 6% 7% 7% 13% 40%	1620
	11th to 20th	Night	4 4 3 5% 6% 3 7% 6% 10% 13% 40%	1620
	21st to end	Night	6% 5% 3 5% 6% 4 6% 6% 9% 12% 37%	1620
July	1st to 10th	Night	6% 5% 2 5% 6% 4 5% 7% 9% 13% 36%	1620
	11th to 20th	Night	5% 5% 2 5% 6% 5% 7% 8% 10% 12% 35%	1620
	21st to end	Night	4 2 2 4 5% 3 7% 8% 10% 14% 41%	1771
August	1st to 10th	Night	6% 3 3 6% 6% 4 6% 8% 10% 14% 35%	1726
	11th to 20th	Night	5% 4 2 6% 6% 5% 6% 7% 10% 15% 33%	1776
	21st to end	Night	7% 6% 3 6% 6% 5% 7% 7% 8% 10% 34%	1998
September	1st to 10th	Night	7% 6% 3 7% 6% 5% 6% 9% 10% 12% 30%	1980
	11th to 20th	Night	8% 7% 3 6% 7% 4 6% 8% 9% 9% 34%	1980
	21st to end	Night	7% 6% 2 5% 5% 3 5% 7% 6% 10% 45%	1980
October	1st to 10th	Night	6% 5% 2 6% 6% 3 4 4 5% 8% 51%	1980
	11th to 20th	Night	7% 4 2 4 3 2 3 4 5% 7% 59%	2027
	21st to end	Night	7% 5% 3 5% 5% 3 4 5% 5% 6% 52%	2376
November	1st to 10th	Night	7% 4 2 5% 5% 3 4 4 4 7% 54%	2268
	11th to 20th	Night	10% 4 2 4 4 3 4 4 4 6% 55%	2470
	21st to end	Night	13% 5% 2 4 4 2 3 4 5% 7% 49%	2470
December	1st to 10th	Night	12% 6% 3 5% 5% 3 4 4 5% 7% 47%	2470
	11th to 20th	Night	15% 7% 3 4 4 2 4 3 4 6% 48%	3042
	21st to end	Night	19% 8% 3 6% 4 3 4 4 5% 5% 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	38% 5% 7% 16% 21% 13%	2837
	11th to 20th	Day	34% 8% 8% 15% 17% 18%	2848
	21st to end	Day	43% 6% 7% 13% 21% 11%	3476
February	1st to 10th	Day	42% 7% 7% 15% 18% 11%	1900
	11th to 20th	Day	38% 5% 7% 13% 24% 14%	1858
	21st to end	Day	37% 6% 10% 16% 19% 12%	1570
March	1st to 10th	Day	31% 7% 9% 18% 25% 11%	1981
	11th to 20th	Day	35% 6% 14% 16% 17% 12%	2090
	21st to end	Day	32% 7% 11% 21% 18% 10%	2200
April	1st to 10th	Day	35% 7% 11% 16% 17% 14%	1980
	11th to 20th	Day	36% 6% 9% 19% 19% 11%	2108
	21st to end	Day	25% 7% 11% 23% 23% 11%	2222
May	1st to 10th	Day	26% 7% 12% 19% 25% 11%	2340
	11th to 20th	Day	36% 12% 15% 17% 16% 4	2305
	21st to end	Day	38% 10% 13% 20% 17% 3	2531
June	1st to 10th	Day	46% 14% 17% 17% 6% 1	2340
	11th to 20th	Day	40% 16% 20% 16% 7% 1	2340
	21st to end	Day	44% 16% 21% 13% 5% 2	2340
July	1st to 10th	Day	48% 18% 21% 11% 2	2275
	11th to 20th	Day	49% 16% 21% 10% 4	2271
	21st to end	Day	42% 17% 24% 14% 2	2405
August	1st to 10th	Day	48% 17% 19% 13% 3	2194
	11th to 20th	Day	50% 17% 20% 10% 3	2125
	21st to end	Day	51% 15% 16% 12% 4 1	2340
September	1st to 10th	Day	45% 14% 17% 14% 7% 2	1980
	11th to 20th	Day	46% 12% 16% 13% 10% 2	1980
	21st to end	Day	37% 7% 15% 19% 15% 8%	1980
October	1st to 10th	Day	36% 8% 9% 15% 21% 11%	1980
	11th to 20th	Day	25% 5% 9% 21% 29% 11%	1931
	21st to end	Day	31% 6% 8% 14% 25% 17%	1980
November	1st to 10th	Day	27% 5% 9% 18% 24% 17%	1805
	11th to 20th	Day	30% 4 9% 16% 27% 14%	1710
	21st to end	Day	36% 6% 7% 19% 23% 10%	1710
December	1st to 10th	Day	38% 6% 12% 17% 19% 8%	1710
	11th to 20th	Day	41% 6% 8% 14% 20% 10%	2150
	21st to end	Day	46% 3 6% 18% 20% 7%	3124
January	1st to 10th	Night	41% 5% 7% 10% 20% 16%	4109
	11th to 20th	Night	37% 6% 7% 14% 25% 11%	4109
	21st to end	Night	45% 5% 7% 14% 20% 8%	4180
February	1st to 10th	Night	40% 5% 8% 15% 20% 12%	2280
	11th to 20th	Night	39% 5% 8% 13% 20% 15%	2219
	21st to end	Night	38% 6% 9% 17% 15% 15%	1884
March	1st to 10th	Night	33% 7% 9% 19% 21% 11%	2197
	11th to 20th	Night	33% 7% 12% 20% 18% 11%	2090
	21st to end	Night	30% 6% 13% 19% 22% 10%	2201
April	1st to 10th	Night	32% 7% 12% 16% 19% 13%	1980
	11th to 20th	Night	33% 6% 10% 18% 24% 9%	1813
	21st to end	Night	22% 7% 10% 26% 23% 11%	1738
May	1st to 10th	Night	23% 7% 11% 21% 26% 11%	1620
	11th to 20th	Night	26% 12% 18% 19% 19% 5%	1593
	21st to end	Night	27% 12% 16% 23% 18% 5%	1745
June	1st to 10th	Night	32% 13% 24% 21% 10% 1	1620
	11th to 20th	Night	31% 14% 25% 20% 9% 1	1620
	21st to end	Night	34% 15% 24% 19% 8% 1	1620
July	1st to 10th	Night	34% 18% 29% 16% 3	1575
	11th to 20th	Night	33% 20% 29% 13% 4	1566
	21st to end	Night	25% 20% 32% 19% 4	1672
August	1st to 10th	Night	32% 18% 28% 18% 4	1715
	11th to 20th	Night	34% 19% 29% 16% 3	1776
	21st to end	Night	40% 16% 21% 16% 5% 1	1998
September	1st to 10th	Night	40% 17% 20% 14% 8% 2	1980
	11th to 20th	Night	41% 14% 16% 15% 12% 2	1980
	21st to end	Night	32% 11% 16% 17% 16% 7%	1980
October	1st to 10th	Night	31% 9% 12% 17% 19% 13%	1980
	11th to 20th	Night	25% 5% 8% 24% 29% 10%	2027
	21st to end	Night	31% 6% 8% 13% 24% 17%	2376
November	1st to 10th	Night	30% 5% 8% 19% 20% 18%	2268
	11th to 20th	Night	31% 5% 7% 17% 25% 15%	2470
	21st to end	Night	34% 5% 11% 19% 20% 12%	2470
December	1st to 10th	Night	37% 7% 12% 17% 21% 7%	2470
	11th to 20th	Night	38% 6% 7% 15% 23% 12%	3044
	21st to end	Night	45% 5% 8% 16% 21% 5%	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	15% 23% 44% 14% 3	270
	11th to 20th	Day	14% 17% 38% 22% 6% 2	270
	21st to end	Day	28% 22% 39% 9% 2	297
February	1st to 10th	Day	22% 22% 36% 15% 5%	270
	11th to 20th	Day	24% 18% 39% 17% 2	270
	21st to end	Day	15% 26% 38% 19% 3	225
March	1st to 10th	Day	15% 20% 37% 21% 8%	351
	11th to 20th	Day	16% 16% 36% 20% 11% 1	460
	21st to end	Day	16% 19% 31% 23% 10% 1	470
April	1st to 10th	Day	13% 20% 30% 21% 15% 1	420
	11th to 20th	Day	12% 16% 31% 27% 13% 1	412
	21st to end	Day	8% 11% 31% 30% 16% 3	420
May	1st to 10th	Day	7% 9% 29% 31% 16% 8%	423
	11th to 20th	Day	7% 5% 24% 32% 22% 11%	447
	21st to end	Day	9% 3 19% 32% 24% 14%	485
June	1st to 10th	Day	12% 2 15% 30% 27% 13%	450
	11th to 20th	Day	6% 4 12% 28% 29% 21%	450
	21st to end	Day	8% 2 11% 28% 28% 22%	450
July	1st to 10th	Day	8% 5% 8% 18% 32% 30%	445
	11th to 20th	Day	6% 2 7% 20% 34% 29%	444
	21st to end	Day	5% 1 6% 25% 38% 26%	488
August	1st to 10th	Day	10% 2 7% 22% 35% 24%	446
	11th to 20th	Day	8% 1 6% 20% 38% 27%	439
	21st to end	Day	8% 4 10% 27% 32% 19%	495
September	1st to 10th	Day	10% 4 12% 26% 29% 21%	450
	11th to 20th	Day	11% 2 16% 31% 29% 10%	450
	21st to end	Day	12% 2 14% 24% 35% 14%	450
October	1st to 10th	Day	10% 6% 28% 33% 18% 5%	450
	11th to 20th	Day	6% 6% 22% 37% 23% 6%	450
	21st to end	Day	11% 9% 29% 31% 19% 2	495
November	1st to 10th	Day	14% 9% 27% 30% 17% 3	403
	11th to 20th	Day	13% 14% 45% 20% 6% 1	270
	21st to end	Day	12% 16% 39% 24% 9% 1	270
December	1st to 10th	Day	20% 14% 34% 20% 10% 2	270
	11th to 20th	Day	20% 14% 39% 24% 4	270
	21st to end	Day	23% 11% 32% 27% 6% 1	297
January	1st to 10th	Night	18% 14% 36% 23% 8% 1	760
	11th to 20th	Night	16% 13% 30% 30% 10% 1	760
	21st to end	Night	21% 14% 35% 24% 6%	836
February	1st to 10th	Night	18% 11% 31% 31% 9%	760
	11th to 20th	Night	19% 14% 30% 29% 7%	743
	21st to end	Night	17% 12% 35% 31% 4	628
March	1st to 10th	Night	15% 13% 29% 34% 9%	760
	11th to 20th	Night	14% 12% 30% 31% 13%	760
	21st to end	Night	12% 13% 32% 32% 11%	801
April	1st to 10th	Night	13% 9% 29% 35% 14%	720
	11th to 20th	Night	11% 9% 28% 36% 15% 1	571
	21st to end	Night	6% 6% 28% 37% 21% 1	540
May	1st to 10th	Night	6% 6% 24% 39% 23% 2	540
	11th to 20th	Night	5% 3 21% 37% 27% 6%	531
	21st to end	Night	6% 2 13% 38% 34% 6%	584
June	1st to 10th	Night	7% 2 10% 36% 39% 5%	540
	11th to 20th	Night	5% 2 7% 31% 41% 14%	540
	21st to end	Night	6% 2 7% 28% 43% 14%	540
July	1st to 10th	Night	5% 1 6% 20% 45% 22%	525
	11th to 20th	Night	6% 2 4 17% 46% 25%	522
	21st to end	Night	3 1 3 19% 54% 19%	591
August	1st to 10th	Night	6% 1 5% 20% 49% 18%	537
	11th to 20th	Night	7% 1 4 16% 50% 22%	534
	21st to end	Night	10% 1 9% 25% 38% 17%	612
September	1st to 10th	Night	9% 3 10% 26% 39% 13%	720
	11th to 20th	Night	9% 4 14% 33% 33% 7%	720
	21st to end	Night	8% 3 17% 31% 35% 6%	720
October	1st to 10th	Night	8% 4 25% 31% 28% 3	720
	11th to 20th	Night	8% 5% 23% 35% 26% 3	720
	21st to end	Night	11% 6% 23% 37% 22% 2	792
November	1st to 10th	Night	8% 8% 28% 37% 18% 2	740
	11th to 20th	Night	13% 10% 29% 33% 14% 1	760
	21st to end	Night	14% 9% 28% 36% 13% 1	760
December	1st to 10th	Night	14% 10% 30% 28% 17% 1	760
	11th to 20th	Night	16% 12% 29% 29% 14% 1	760
	21st to end	Night	22% 11% 27% 26% 12% 1	836

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