UF Campus Teaching Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the UF Campus Teaching Observatory 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	9% 6% 2 6% 5% 5% 5% 5% 7% 9% 40%	125947
	Night	9% 6% 2 6% 4 4 5% 4 6% 9% 43%	122777
Transparency	Day	37% 7% 16% 19% 14% 6%	129684
	Night	36% 7% 15% 19% 16% 7%	127109
Seeing	Day	11% 6% 21% 26% 22% 14%	16498
	Night	11% 6% 22% 32% 23% 6%	26512

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	10% 5% 2 5% 3 2 3 3 4 7% 56%	4056
	11th to 20th	Day	19% 10% 3 8% 4 3 3 3 4 6% 37%	4060
	21st to end	Day	11% 6% 2 5% 3 3 3 3 6% 9% 48%	4668
February	1st to 10th	Day	15% 6% 3 6% 4 4 4 4 5% 6% 44%	2000
	11th to 20th	Day	12% 5% 2 5% 3 4 4 3 5% 6% 50%	1948
	21st to end	Day	11% 6% 2 7% 5% 3 4 4 5% 6% 48%	1685
March	1st to 10th	Day	12% 7% 3 7% 4 4 4 4 6% 9% 41%	4935
	11th to 20th	Day	8% 4 2 4 3 3 3 3 6% 8% 57%	4980
	21st to end	Day	11% 5% 2 5% 4 4 3 4 5% 8% 49%	5465
April	1st to 10th	Day	8% 4 2 4 4 4 4 4 6% 9% 50%	2200
	11th to 20th	Day	9% 5% 2 7% 5% 5% 5% 4 5% 6% 47%	2181
	21st to end	Day	5% 3 2 5% 5% 4 5% 5% 5% 8% 53%	2493
May	1st to 10th	Day	5% 4 2 6% 5% 5% 5% 5% 7% 11% 46%	5862
	11th to 20th	Day	10% 6% 3 6% 4 4 5% 4 6% 9% 44%	5861
	21st to end	Day	4 4 2 5% 4 4 5% 5% 8% 12% 46%	6433
June	1st to 10th	Day	9% 7% 3 8% 6% 6% 8% 7% 8% 11% 28%	2600
	11th to 20th	Day	6% 5% 3 7% 8% 8% 9% 6% 9% 11% 28%	2600
	21st to end	Day	7% 7% 3 8% 8% 8% 7% 6% 8% 11% 27%	2600
July	1st to 10th	Day	7% 6% 3 10% 8% 9% 9% 8% 11% 13% 17%	5900
	11th to 20th	Day	4 4 2 6% 6% 7% 8% 7% 10% 15% 31%	5900
	21st to end	Day	5% 5% 2 7% 6% 7% 7% 7% 10% 13% 30%	6424
August	1st to 10th	Day	11% 5% 2 7% 5% 7% 8% 7% 9% 12% 26%	4234
	11th to 20th	Day	6% 5% 3 7% 6% 7% 8% 6% 9% 11% 32%	3982
	21st to end	Day	9% 6% 2 9% 7% 6% 7% 6% 8% 11% 27%	3987
September	1st to 10th	Day	10% 7% 3 8% 7% 7% 9% 7% 9% 9% 22%	2123
	11th to 20th	Day	12% 8% 3 10% 6% 7% 8% 6% 8% 9% 24%	2090
	21st to end	Day	10% 6% 3 9% 7% 6% 6% 4 7% 7% 36%	2090
October	1st to 10th	Day	11% 6% 2 8% 6% 6% 5% 4 6% 8% 37%	2090
	11th to 20th	Day	6% 5% 2 5% 4 3 4 4 5% 7% 54%	1914
	21st to end	Day	8% 4 2 5% 4 4 5% 4 7% 7% 51%	2090
November	1st to 10th	Day	9% 5% 2 6% 5% 4 4 4 5% 7% 49%	1957
	11th to 20th	Day	9% 7% 3 6% 5% 4 3 4 6% 6% 46%	1970
	21st to end	Day	11% 6% 2 6% 5% 4 4 3 4 7% 48%	1800
December	1st to 10th	Day	6% 4 2 5% 3 4 4 3 5% 8% 56%	2930
	11th to 20th	Day	11% 6% 3 6% 4 4 5% 3 6% 8% 43%	3373
	21st to end	Day	14% 9% 3 7% 4 4 3 3 4 7% 43%	4466
January	1st to 10th	Night	9% 6% 2 4 3 2 3 3 4 7% 58%	5889
	11th to 20th	Night	19% 8% 3 7% 5% 5% 5% 4 6% 7% 33%	5900
	21st to end	Night	15% 7% 2 6% 4 4 4 3 5% 7% 42%	6283
February	1st to 10th	Night	12% 6% 2 6% 5% 4 5% 3 4 6% 47%	2400
	11th to 20th	Night	11% 8% 3 6% 3 4 4 3 5% 6% 48%	2338
	21st to end	Night	10% 6% 3 6% 4 5% 3 3 5% 6% 50%	1942
March	1st to 10th	Night	15% 9% 3 7% 4 3 4 3 4 6% 41%	4918
	11th to 20th	Night	6% 5% 2 4 3 3 4 3 6% 9% 54%	4980
	21st to end	Night	9% 6% 3 5% 3 3 4 4 6% 7% 50%	5467
April	1st to 10th	Night	9% 5% 2 5% 4 3 5% 5% 6% 8% 51%	2200
	11th to 20th	Night	8% 5% 2 5% 4 4 4 3 6% 8% 51%	2166
	21st to end	Night	6% 3 2 4 3 3 4 4 7% 8% 55%	1920
May	1st to 10th	Night	5% 5% 2 5% 4 4 5% 4 7% 10% 49%	4033
	11th to 20th	Night	9% 6% 2 5% 3 4 4 3 6% 10% 46%	4032
	21st to end	Night	3 3 1 4 3 4 5% 4 7% 11% 55%	4421
June	1st to 10th	Night	9% 7% 2 7% 5% 5% 5% 5% 7% 11% 36%	1800
	11th to 20th	Night	5% 5% 2 7% 6% 5% 7% 5% 11% 14% 32%	1800
	21st to end	Night	7% 5% 2 6% 6% 6% 5% 5% 9% 13% 36%	1800
July	1st to 10th	Night	8% 7% 4 10% 7% 8% 8% 6% 10% 12% 20%	4058
	11th to 20th	Night	3 5% 2 8% 5% 6% 7% 6% 9% 14% 35%	4057
	21st to end	Night	6% 6% 3 8% 7% 8% 7% 7% 9% 11% 29%	4427
August	1st to 10th	Night	10% 5% 2 7% 6% 5% 6% 6% 11% 11% 30%	2915
	11th to 20th	Night	4 4 2 6% 4 4 5% 5% 10% 14% 42%	3061
	21st to end	Night	7% 7% 3 9% 6% 6% 6% 6% 8% 11% 31%	3876
September	1st to 10th	Night	7% 7% 3 9% 6% 5% 7% 6% 11% 12% 28%	2124
	11th to 20th	Night	13% 7% 3 8% 6% 7% 7% 6% 6% 9% 29%	2090
	21st to end	Night	10% 7% 3 7% 4 5% 5% 3 7% 10% 39%	2090
October	1st to 10th	Night	11% 5% 3 7% 5% 5% 5% 3 6% 8% 42%	2090
	11th to 20th	Night	6% 4 2 5% 4 4 3 3 4 9% 56%	2264
	21st to end	Night	8% 6% 2 6% 4 4 4 3 4 7% 52%	2508
November	1st to 10th	Night	9% 4 2 5% 4 3 4 4 6% 8% 53%	2341
	11th to 20th	Night	10% 6% 2 5% 5% 4 3 4 6% 6% 49%	2425
	21st to end	Night	10% 7% 2 5% 4 4 4 3 5% 7% 48%	2600
December	1st to 10th	Night	9% 5% 1 5% 4 3 3 3 4 7% 55%	4250
	11th to 20th	Night	12% 7% 2 7% 4 4 3 3 4 5% 48%	4822
	21st to end	Night	14% 9% 3 7% 5% 4 4 3 5% 6% 40%	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% 3 8% 16% 27% 16%	4057
	11th to 20th	Day	51% 2 4 12% 19% 11%	4060
	21st to end	Day	33% 4 9% 25% 17% 12%	4668
February	1st to 10th	Day	39% 5% 9% 14% 21% 12%	2000
	11th to 20th	Day	34% 4 9% 17% 24% 12%	1958
	21st to end	Day	36% 5% 9% 17% 20% 13%	1685
March	1st to 10th	Day	39% 5% 10% 16% 20% 10%	4935
	11th to 20th	Day	25% 4 11% 19% 23% 19%	4980
	21st to end	Day	33% 4 9% 25% 19% 10%	5465
April	1st to 10th	Day	30% 5% 12% 21% 19% 12%	2200
	11th to 20th	Day	37% 5% 8% 18% 23% 9%	2181
	21st to end	Day	27% 6% 10% 26% 23% 9%	2493
May	1st to 10th	Day	30% 8% 18% 28% 13% 4	5897
	11th to 20th	Day	36% 6% 13% 32% 11% 2	5865
	21st to end	Day	27% 7% 18% 30% 16% 2	6447
June	1st to 10th	Day	46% 8% 19% 19% 8%	2600
	11th to 20th	Day	45% 11% 21% 19% 4	2600
	21st to end	Day	47% 10% 23% 15% 5% 1	2600
July	1st to 10th	Day	51% 14% 27% 7%	5835
	11th to 20th	Day	36% 14% 38% 11% 1	5831
	21st to end	Day	37% 13% 28% 19% 2	6240
August	1st to 10th	Day	44% 11% 29% 13% 2	4221
	11th to 20th	Day	40% 11% 23% 18% 7%	4021
	21st to end	Day	45% 11% 22% 19% 2	3987
September	1st to 10th	Day	51% 13% 19% 11% 5% 1	2123
	11th to 20th	Day	53% 9% 17% 14% 6% 1	2090
	21st to end	Day	45% 7% 13% 18% 15% 3	2090
October	1st to 10th	Day	53% 7% 9% 13% 12% 7%	3480
	11th to 20th	Day	23% 5% 5% 19% 36% 12%	3154
	21st to end	Day	23% 5% 7% 24% 32% 8%	3428
November	1st to 10th	Day	34% 5% 9% 21% 18% 13%	1957
	11th to 20th	Day	37% 4 9% 18% 22% 11%	1970
	21st to end	Day	36% 4 8% 19% 25% 7%	1800
December	1st to 10th	Day	27% 3 13% 25% 21% 10%	2930
	11th to 20th	Day	38% 6% 9% 21% 17% 9%	3370
	21st to end	Day	42% 4 8% 19% 22% 5%	4466
January	1st to 10th	Night	29% 2 6% 16% 32% 15%	5889
	11th to 20th	Night	50% 4 6% 16% 18% 6%	5900
	21st to end	Night	41% 4 10% 18% 17% 10%	6283
February	1st to 10th	Night	38% 4 9% 17% 21% 12%	2400
	11th to 20th	Night	38% 4 7% 20% 19% 12%	2339
	21st to end	Night	35% 4 10% 18% 21% 11%	1942
March	1st to 10th	Night	45% 4 8% 15% 17% 10%	4918
	11th to 20th	Night	26% 5% 13% 18% 21% 18%	4980
	21st to end	Night	33% 5% 10% 23% 19% 11%	5467
April	1st to 10th	Night	30% 6% 14% 21% 19% 10%	2200
	11th to 20th	Night	31% 5% 10% 24% 21% 9%	2166
	21st to end	Night	25% 6% 14% 27% 19% 8%	1920
May	1st to 10th	Night	28% 9% 21% 27% 12% 3	4060
	11th to 20th	Night	33% 7% 16% 29% 14% 1	4033
	21st to end	Night	22% 6% 19% 33% 19% 1	4429
June	1st to 10th	Night	40% 7% 25% 22% 7%	1800
	11th to 20th	Night	36% 12% 28% 21% 3	1800
	21st to end	Night	35% 14% 26% 19% 5% 1	1800
July	1st to 10th	Night	52% 15% 26% 6% 1	4015
	11th to 20th	Night	35% 15% 37% 11% 1	4006
	21st to end	Night	43% 13% 24% 17% 2	4297
August	1st to 10th	Night	41% 12% 33% 11% 2	2904
	11th to 20th	Night	28% 13% 31% 21% 7%	3088
	21st to end	Night	43% 12% 24% 18% 3	3876
September	1st to 10th	Night	43% 15% 23% 13% 4 1	2124
	11th to 20th	Night	50% 10% 18% 16% 6% 1	2090
	21st to end	Night	40% 7% 18% 19% 13% 3	2090
October	1st to 10th	Night	51% 7% 11% 13% 11% 6%	3480
	11th to 20th	Night	24% 5% 7% 20% 35% 10%	3763
	21st to end	Night	24% 5% 6% 24% 34% 8%	4120
November	1st to 10th	Night	30% 4 12% 23% 20% 12%	2341
	11th to 20th	Night	35% 5% 9% 20% 20% 12%	2425
	21st to end	Night	36% 4 10% 18% 22% 10%	2600
December	1st to 10th	Night	30% 3 11% 22% 19% 15%	4250
	11th to 20th	Night	39% 5% 10% 20% 17% 10%	4824
	21st to end	Night	44% 4 10% 18% 18% 6%	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	11% 16% 53% 15% 5%	300
	11th to 20th	Day	14% 11% 45% 19% 8% 2	300
	21st to end	Day	18% 22% 41% 16% 2	330
February	1st to 10th	Day	15% 14% 36% 26% 8% 1	300
	11th to 20th	Day	16% 16% 40% 22% 6% 1	300
	21st to end	Day	13% 14% 36% 27% 10%	284
March	1st to 10th	Day	13% 16% 32% 28% 9% 1	500
	11th to 20th	Day	14% 12% 34% 24% 14% 2	500
	21st to end	Day	13% 11% 32% 28% 14% 2	550
April	1st to 10th	Day	14% 13% 28% 26% 17% 2	500
	11th to 20th	Day	13% 9% 29% 31% 15% 3	492
	21st to end	Day	6% 6% 26% 31% 23% 8%	500
May	1st to 10th	Day	6% 6% 27% 30% 21% 10%	503
	11th to 20th	Day	10% 5% 21% 31% 20% 14%	527
	21st to end	Day	9% 2 12% 28% 31% 17%	573
June	1st to 10th	Day	12% 2 12% 30% 26% 18%	530
	11th to 20th	Day	10% 2 10% 24% 31% 22%	530
	21st to end	Day	5% 7% 25% 34% 28%	530
July	1st to 10th	Day	8% 2 4 17% 31% 38%	525
	11th to 20th	Day	6% 2 16% 35% 41%	524
	21st to end	Day	8% 2 5% 18% 36% 32%	576
August	1st to 10th	Day	11% 2 5% 19% 30% 33%	526
	11th to 20th	Day	8% 1 4 17% 32% 39%	519
	21st to end	Day	11% 1 7% 20% 36% 25%	583
September	1st to 10th	Day	13% 3 8% 19% 31% 26%	502
	11th to 20th	Day	16% 3 6% 28% 28% 19%	490
	21st to end	Day	12% 2 9% 26% 33% 17%	490
October	1st to 10th	Day	16% 4 22% 30% 21% 6%	490
	11th to 20th	Day	6% 5% 22% 34% 27% 6%	490
	21st to end	Day	9% 4 24% 37% 22% 4	539
November	1st to 10th	Day	12% 5% 27% 29% 22% 4	495
	11th to 20th	Day	16% 6% 31% 30% 13% 4	470
	21st to end	Day	11% 9% 39% 30% 8% 2	300
December	1st to 10th	Day	10% 13% 38% 22% 13% 3	300
	11th to 20th	Day	16% 11% 36% 27% 9% 1	300
	21st to end	Day	14% 7% 38% 31% 8% 1	330
January	1st to 10th	Night	15% 12% 34% 29% 10% 1	800
	11th to 20th	Night	14% 11% 26% 37% 12% 1	800
	21st to end	Night	19% 11% 36% 28% 6%	880
February	1st to 10th	Night	17% 8% 31% 34% 10% 1	800
	11th to 20th	Night	15% 11% 32% 33% 9% 1	783
	21st to end	Night	11% 12% 33% 39% 5%	660
March	1st to 10th	Night	13% 10% 36% 31% 10%	800
	11th to 20th	Night	12% 12% 30% 33% 13%	800
	21st to end	Night	9% 9% 36% 35% 11%	880
April	1st to 10th	Night	10% 10% 32% 37% 12% 1	800
	11th to 20th	Night	10% 8% 33% 36% 12% 1	791
	21st to end	Night	8% 5% 28% 40% 18% 1	720
May	1st to 10th	Night	5% 3 23% 47% 21% 2	600
	11th to 20th	Night	8% 3 19% 39% 27% 4	591
	21st to end	Night	7% 1 11% 40% 35% 6%	650
June	1st to 10th	Night	13% 2 11% 34% 33% 8%	600
	11th to 20th	Night	6% 2 8% 27% 39% 19%	600
	21st to end	Night	9% 1 6% 22% 44% 19%	600
July	1st to 10th	Night	7% 1 4 18% 47% 23%	585
	11th to 20th	Night	4 2 2 15% 49% 28%	582
	21st to end	Night	6% 1 3 18% 51% 21%	657
August	1st to 10th	Night	10% 1 4 17% 47% 21%	597
	11th to 20th	Night	7% 2 3 14% 52% 22%	594
	21st to end	Night	12% 4 5% 25% 39% 15%	833
September	1st to 10th	Night	12% 2 7% 24% 41% 14%	773
	11th to 20th	Night	15% 3 9% 32% 33% 8%	760
	21st to end	Night	13% 3 10% 31% 36% 8%	760
October	1st to 10th	Night	14% 3 20% 34% 26% 3	760
	11th to 20th	Night	7% 4 22% 40% 25% 2	760
	21st to end	Night	10% 4 21% 42% 21% 2	836
November	1st to 10th	Night	11% 5% 28% 32% 22% 2	780
	11th to 20th	Night	12% 5% 28% 37% 17% 1	800
	21st to end	Night	15% 5% 30% 35% 14% 1	800
December	1st to 10th	Night	12% 8% 27% 34% 18% 1	800
	11th to 20th	Night	14% 8% 27% 36% 14% 1	800
	21st to end	Night	17% 8% 28% 34% 13% 1	880

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