Anna Maria College
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Anna Maria College clear sky chart from 2005-11-06 to 2025-07-21.

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	17% 8% 3 6% 4 4 4 4 5% 7% 37%	119773
	Night	17% 8% 3 6% 4 4 4 3 5% 6% 39%	119343
Transparency	Day	44% 5% 12% 22% 14% 2	123351
	Night	44% 5% 12% 21% 16% 3	123926
Seeing	Day	24% 17% 32% 18% 7% 2	15884
	Night	22% 17% 34% 21% 6%	24808

By Month

Percentage Cloud Cover NE (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% 8% 3 10% 5% 4 5% 4 5% 6% 39%	3597
	11th to 20th	Day	13% 9% 3 6% 4 4 4 3 5% 5% 44%	3570
	21st to end	Day	16% 9% 3 6% 4 3 3 3 4 6% 42%	3960
February	1st to 10th	Day	17% 7% 3 6% 5% 5% 5% 5% 6% 6% 35%	1865
	11th to 20th	Day	13% 7% 2 7% 5% 6% 5% 4 6% 6% 39%	1948
	21st to end	Day	18% 10% 3 7% 4 4 4 2 3 5% 38%	1650
March	1st to 10th	Day	19% 12% 3 7% 4 4 4 3 5% 5% 35%	4476
	11th to 20th	Day	14% 8% 2 6% 4 5% 5% 4 6% 7% 38%	4704
	21st to end	Day	22% 11% 3 5% 4 4 4 3 6% 7% 32%	5868
April	1st to 10th	Day	18% 10% 3 6% 6% 5% 3 3 5% 6% 36%	2400
	11th to 20th	Day	18% 7% 2 5% 4 4 4 4 5% 7% 39%	2374
	21st to end	Day	21% 7% 3 7% 4 5% 4 3 4 7% 35%	2582
May	1st to 10th	Day	29% 10% 3 7% 4 4 4 3 5% 7% 24%	5886
	11th to 20th	Day	21% 9% 3 8% 5% 4 4 3 5% 6% 31%	6061
	21st to end	Day	19% 7% 3 7% 4 5% 4 4 6% 8% 34%	6949
June	1st to 10th	Day	18% 6% 2 6% 4 5% 5% 4 7% 8% 34%	2800
	11th to 20th	Day	17% 6% 3 6% 5% 4 4 4 7% 8% 36%	2800
	21st to end	Day	18% 6% 2 7% 5% 5% 4 4 6% 8% 34%	2800
July	1st to 10th	Day	13% 7% 2 6% 6% 6% 5% 5% 7% 9% 34%	4580
	11th to 20th	Day	12% 6% 2 6% 4 6% 5% 4 7% 11% 37%	4580
	21st to end	Day	18% 9% 3 6% 4 4 4 4 6% 7% 34%	4814
August	1st to 10th	Day	16% 7% 2 7% 5% 5% 5% 5% 7% 8% 32%	4209
	11th to 20th	Day	12% 6% 3 7% 5% 5% 6% 4 6% 7% 38%	3919
	21st to end	Day	8% 4 2 7% 4 5% 5% 4 6% 10% 45%	4180
September	1st to 10th	Day	13% 6% 3 5% 5% 4 4 4 6% 6% 44%	2280
	11th to 20th	Day	15% 6% 2 4 2 3 3 4 5% 6% 50%	2110
	21st to end	Day	17% 6% 3 5% 4 4 4 3 5% 7% 43%	2090
October	1st to 10th	Day	21% 7% 2 6% 3 4 4 3 4 5% 39%	2090
	11th to 20th	Day	14% 7% 2 5% 4 4 3 3 5% 7% 46%	1848
	21st to end	Day	20% 7% 3 6% 4 3 4 4 4 5% 40%	1881
November	1st to 10th	Day	13% 8% 3 6% 4 3 4 2 4 5% 48%	1761
	11th to 20th	Day	18% 7% 2 4 3 3 3 3 5% 6% 47%	1800
	21st to end	Day	16% 9% 3 5% 4 4 4 4 5% 5% 42%	1795
December	1st to 10th	Day	13% 10% 3 5% 4 4 4 3 4 6% 44%	2600
	11th to 20th	Day	18% 8% 2 6% 3 3 4 2 4 5% 44%	2986
	21st to end	Day	18% 11% 4 6% 4 3 4 3 4 6% 36%	3960
January	1st to 10th	Night	14% 6% 2 6% 4 4 4 4 6% 7% 43%	6349
	11th to 20th	Night	13% 9% 3 8% 5% 4 4 4 5% 6% 40%	6315
	21st to end	Night	15% 10% 3 7% 5% 4 4 3 5% 6% 39%	6996
February	1st to 10th	Night	15% 9% 3 6% 4 4 5% 4 5% 6% 39%	2530
	11th to 20th	Night	13% 8% 3 7% 5% 5% 4 4 6% 6% 39%	2338
	21st to end	Night	16% 10% 3 7% 5% 5% 4 3 5% 5% 39%	1980
March	1st to 10th	Night	20% 10% 2 5% 3 4 3 3 5% 6% 38%	5364
	11th to 20th	Night	15% 9% 2 7% 4 4 4 3 5% 7% 39%	5255
	21st to end	Night	22% 10% 3 6% 4 4 3 3 5% 6% 34%	5059
April	1st to 10th	Night	18% 9% 2 7% 5% 5% 4 4 5% 6% 35%	2000
	11th to 20th	Night	19% 8% 2 6% 4 4 4 3 5% 6% 39%	1975
	21st to end	Night	20% 7% 3 7% 4 3 4 3 4 6% 40%	1816
May	1st to 10th	Night	32% 9% 3 6% 4 4 3 3 4 7% 25%	4054
	11th to 20th	Night	16% 11% 4 10% 6% 5% 4 4 5% 6% 30%	3862
	21st to end	Night	20% 9% 3 7% 5% 5% 4 3 5% 7% 33%	3926
June	1st to 10th	Night	17% 8% 3 7% 6% 5% 4 3 6% 6% 37%	1600
	11th to 20th	Night	18% 8% 3 6% 4 5% 4 3 6% 8% 37%	1600
	21st to end	Night	15% 6% 2 6% 4 4 4 3 7% 7% 41%	1600
July	1st to 10th	Night	13% 7% 3 7% 6% 5% 5% 5% 7% 9% 35%	2600
	11th to 20th	Night	15% 8% 2 6% 4 4 4 4 6% 8% 39%	2600
	21st to end	Night	16% 9% 3 7% 5% 4 4 4 5% 6% 37%	2739
August	1st to 10th	Night	21% 6% 3 8% 5% 5% 6% 3 5% 6% 31%	2688
	11th to 20th	Night	13% 8% 3 8% 6% 5% 5% 4 5% 7% 37%	2904
	21st to end	Night	9% 4 2 5% 3 3 3 3 5% 7% 58%	3476
September	1st to 10th	Night	13% 6% 2 7% 3 4 3 4 5% 6% 46%	1900
	11th to 20th	Night	12% 7% 2 5% 4 3 4 2 4 6% 52%	2069
	21st to end	Night	17% 7% 3 6% 3 3 4 3 5% 6% 44%	2090
October	1st to 10th	Night	20% 7% 2 5% 3 4 3 3 5% 6% 41%	2090
	11th to 20th	Night	15% 6% 2 5% 3 4 4 3 4 7% 47%	2328
	21st to end	Night	21% 8% 2 6% 4 4 3 3 4 6% 39%	2717
November	1st to 10th	Night	13% 7% 2 4 4 4 4 3 5% 5% 48%	2537
	11th to 20th	Night	17% 7% 2 5% 4 4 3 4 4 5% 46%	2600
	21st to end	Night	16% 8% 2 5% 4 4 4 4 5% 6% 43%	2602
December	1st to 10th	Night	15% 10% 3 6% 3 4 3 3 4 6% 42%	4580
	11th to 20th	Night	22% 8% 3 5% 3 3 3 3 5% 5% 40%	5208
	21st to end	Night	18% 10% 4 7% 3 3 3 2 5% 5% 39%	6996

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	42% 4 10% 28% 15% 2	3598
	11th to 20th	Day	41% 5% 11% 21% 17% 6%	3600
	21st to end	Day	43% 4 10% 22% 19% 2	3960
February	1st to 10th	Day	47% 6% 13% 20% 13% 2	1865
	11th to 20th	Day	45% 6% 10% 22% 15% 3	1957
	21st to end	Day	49% 4 10% 20% 15% 2	1650
March	1st to 10th	Day	50% 3 12% 15% 11% 9%	4479
	11th to 20th	Day	41% 6% 15% 26% 9% 2	4704
	21st to end	Day	50% 3 6% 16% 18% 6%	5868
April	1st to 10th	Day	49% 4 10% 20% 15% 3	2400
	11th to 20th	Day	43% 5% 12% 20% 18% 3	2374
	21st to end	Day	48% 5% 8% 18% 17% 3	2582
May	1st to 10th	Day	59% 7% 13% 13% 8% 1	5897
	11th to 20th	Day	53% 6% 13% 17% 10% 1	6065
	21st to end	Day	47% 7% 11% 22% 12% 1	6949
June	1st to 10th	Day	46% 7% 12% 24% 11% 1	2800
	11th to 20th	Day	43% 7% 13% 21% 14% 2	2800
	21st to end	Day	45% 8% 12% 21% 13% 1	2800
July	1st to 10th	Day	45% 8% 11% 21% 14% 1	4510
	11th to 20th	Day	39% 7% 16% 25% 12% 1	4505
	21st to end	Day	48% 5% 13% 19% 13% 2	4661
August	1st to 10th	Day	48% 8% 15% 21% 8% 1	4195
	11th to 20th	Day	42% 7% 15% 26% 9% 1	3958
	21st to end	Day	34% 6% 11% 31% 17% 1	4180
September	1st to 10th	Day	39% 6% 11% 23% 19% 2	2280
	11th to 20th	Day	34% 4 9% 27% 23% 3	2110
	21st to end	Day	41% 5% 9% 23% 20% 2	2090
October	1st to 10th	Day	40% 5% 9% 23% 20% 3	3480
	11th to 20th	Day	32% 3 9% 27% 25% 4	3051
	21st to end	Day	34% 4 13% 28% 18% 3	3081
November	1st to 10th	Day	39% 4 12% 25% 17% 2	1761
	11th to 20th	Day	38% 5% 10% 22% 22% 3	1800
	21st to end	Day	43% 6% 12% 25% 12% 2	1795
December	1st to 10th	Day	41% 3 16% 28% 11% 1	2600
	11th to 20th	Day	42% 3 14% 18% 20% 3	2986
	21st to end	Day	49% 4 8% 19% 15% 5%	3960
January	1st to 10th	Night	37% 4 12% 31% 14% 2	6349
	11th to 20th	Night	45% 4 13% 20% 14% 4	6360
	21st to end	Night	47% 4 10% 16% 18% 5%	6996
February	1st to 10th	Night	45% 6% 13% 21% 13% 2	2530
	11th to 20th	Night	45% 5% 10% 20% 16% 4	2340
	21st to end	Night	47% 4 9% 22% 14% 4	1980
March	1st to 10th	Night	46% 4 10% 17% 16% 6%	5374
	11th to 20th	Night	44% 6% 17% 19% 11% 3	5256
	21st to end	Night	50% 3 6% 13% 22% 5%	5059
April	1st to 10th	Night	49% 5% 9% 19% 15% 3	2000
	11th to 20th	Night	45% 6% 10% 19% 18% 1	1975
	21st to end	Night	45% 5% 9% 20% 16% 5%	1816
May	1st to 10th	Night	58% 8% 13% 12% 8% 1	4060
	11th to 20th	Night	54% 8% 12% 16% 9% 2	3863
	21st to end	Night	50% 7% 13% 19% 11% 1	3927
June	1st to 10th	Night	47% 7% 10% 23% 12% 1	1600
	11th to 20th	Night	46% 7% 13% 22% 12% 1	1600
	21st to end	Night	39% 8% 15% 23% 15% 1	1600
July	1st to 10th	Night	43% 8% 14% 21% 14% 1	2560
	11th to 20th	Night	42% 7% 16% 23% 12%	2552
	21st to end	Night	47% 6% 12% 18% 16% 1	2651
August	1st to 10th	Night	52% 8% 12% 19% 9% 1	2678
	11th to 20th	Night	45% 8% 13% 25% 9%	2931
	21st to end	Night	26% 5% 16% 31% 20% 1	3476
September	1st to 10th	Night	39% 6% 11% 24% 19% 1	1900
	11th to 20th	Night	34% 5% 10% 24% 25% 2	2069
	21st to end	Night	41% 5% 8% 25% 18% 3	2090
October	1st to 10th	Night	38% 5% 14% 24% 16% 2	3480
	11th to 20th	Night	27% 4 12% 25% 28% 4	3864
	21st to end	Night	34% 4 12% 32% 16% 2	4467
November	1st to 10th	Night	37% 6% 11% 22% 21% 4	2537
	11th to 20th	Night	40% 4 11% 21% 20% 4	2600
	21st to end	Night	39% 5% 15% 26% 13% 1	2602
December	1st to 10th	Night	42% 3 13% 30% 10%	4580
	11th to 20th	Night	46% 4 14% 14% 20% 2	5208
	21st to end	Night	46% 5% 8% 21% 16% 4	6996

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	27% 30% 28% 14% 3	200
	11th to 20th	Day	31% 29% 32% 7% 3	200
	21st to end	Day	25% 28% 33% 11% 3	220
February	1st to 10th	Day	32% 25% 31% 11% 1	385
	11th to 20th	Day	29% 29% 32% 9% 1	496
	21st to end	Day	31% 18% 37% 10% 3	414
March	1st to 10th	Day	32% 22% 32% 11% 2	500
	11th to 20th	Day	28% 26% 29% 12% 3 1	500
	21st to end	Day	31% 22% 33% 9% 4 1	550
April	1st to 10th	Day	33% 24% 27% 9% 5% 1	500
	11th to 20th	Day	33% 19% 34% 10% 4	492
	21st to end	Day	31% 19% 32% 14% 3 1	500
May	1st to 10th	Day	33% 19% 28% 15% 4 1	503
	11th to 20th	Day	23% 18% 38% 16% 4 1	527
	21st to end	Day	21% 13% 37% 20% 9% 1	573
June	1st to 10th	Day	19% 11% 38% 22% 9% 2	530
	11th to 20th	Day	18% 15% 36% 23% 6% 2	530
	21st to end	Day	18% 14% 36% 21% 9% 2	530
July	1st to 10th	Day	18% 9% 32% 27% 10% 3	525
	11th to 20th	Day	15% 7% 31% 34% 11% 3	524
	21st to end	Day	13% 10% 37% 30% 8% 1	532
August	1st to 10th	Day	12% 9% 32% 35% 11% 2	486
	11th to 20th	Day	16% 7% 32% 29% 12% 3	479
	21st to end	Day	12% 12% 31% 27% 14% 3	539
September	1st to 10th	Day	18% 10% 29% 23% 14% 5%	490
	11th to 20th	Day	21% 9% 28% 19% 14% 9%	490
	21st to end	Day	22% 12% 32% 21% 9% 4	490
October	1st to 10th	Day	28% 13% 27% 19% 11% 3	490
	11th to 20th	Day	20% 20% 30% 22% 6% 2	450
	21st to end	Day	28% 16% 32% 17% 6% 1	429
November	1st to 10th	Day	23% 19% 33% 17% 7% 1	395
	11th to 20th	Day	28% 23% 29% 16% 3 1	400
	21st to end	Day	28% 24% 29% 15% 4	395
December	1st to 10th	Day	23% 31% 29% 15% 3	200
	11th to 20th	Day	37% 23% 32% 6% 3	200
	21st to end	Day	28% 25% 33% 9% 5%	220
January	1st to 10th	Night	24% 24% 38% 14% 1	800
	11th to 20th	Night	29% 23% 33% 14% 2	800
	21st to end	Night	22% 23% 35% 17% 2	880
February	1st to 10th	Night	25% 21% 37% 16% 1	800
	11th to 20th	Night	24% 27% 38% 10% 1	783
	21st to end	Night	26% 23% 35% 13% 2	660
March	1st to 10th	Night	26% 23% 34% 16% 2	800
	11th to 20th	Night	22% 25% 34% 17% 2	800
	21st to end	Night	26% 22% 31% 18% 3	880
April	1st to 10th	Night	26% 19% 36% 16% 2	800
	11th to 20th	Night	25% 21% 33% 17% 4	791
	21st to end	Night	24% 22% 34% 17% 2	616
May	1st to 10th	Night	31% 16% 31% 19% 3	600
	11th to 20th	Night	19% 18% 41% 18% 4	525
	21st to end	Night	22% 9% 37% 27% 5%	433
June	1st to 10th	Night	18% 9% 37% 29% 7%	400
	11th to 20th	Night	20% 8% 40% 26% 6%	400
	21st to end	Night	15% 6% 40% 32% 7%	400
July	1st to 10th	Night	15% 7% 33% 37% 8% 1	390
	11th to 20th	Night	18% 4 29% 36% 12% 1	388
	21st to end	Night	12% 6% 35% 38% 9%	416
August	1st to 10th	Night	12% 4 38% 36% 10%	482
	11th to 20th	Night	15% 6% 31% 33% 13% 1	632
	21st to end	Night	15% 6% 26% 37% 15% 2	836
September	1st to 10th	Night	16% 7% 34% 31% 11% 1	760
	11th to 20th	Night	16% 8% 27% 29% 17% 2	760
	21st to end	Night	20% 10% 29% 28% 11% 2	760
October	1st to 10th	Night	24% 13% 28% 24% 10% 2	760
	11th to 20th	Night	19% 15% 33% 21% 10% 1	760
	21st to end	Night	28% 16% 33% 18% 6%	836
November	1st to 10th	Night	19% 18% 36% 20% 7% 1	780
	11th to 20th	Night	24% 25% 29% 17% 5% 1	800
	21st to end	Night	23% 21% 36% 15% 4 1	800
December	1st to 10th	Night	27% 21% 34% 15% 4	800
	11th to 20th	Night	26% 22% 34% 16% 2	800
	21st to end	Night	25% 24% 34% 15% 2	880

Page generated at 2025-07-18 01:09:59. Version ac07

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