Boca Raton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Boca Raton clear sky chart from 2005-11-06 to 2024-03-28.

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	8% 5% 3 7% 7% 4 7% 7% 8% 11% 32%	79172
	Night	7% 5% 3 6% 6% 4 6% 6% 7% 10% 38%	80821
Transparency	Day	31% 38% 10% 12% 7% 2	78895
	Night	28% 37% 12% 14% 8% 2	80617
Seeing	Day	7% 3 13% 27% 31% 19%	15141
	Night	8% 2 13% 30% 32% 13%	25342

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% 7% 3 7% 6% 3 5% 5% 6% 10% 37%	2836
	11th to 20th	Day	16% 7% 4 8% 8% 4 6% 6% 7% 9% 25%	2840
	21st to end	Day	6% 7% 4 8% 7% 5% 7% 6% 6% 7% 36%	3124
February	1st to 10th	Day	9% 5% 3 6% 6% 4 5% 5% 8% 10% 39%	1895
	11th to 20th	Day	7% 4 2 4 5% 3 5% 6% 7% 10% 48%	1977
	21st to end	Day	6% 4 3 4 6% 4 7% 6% 7% 9% 44%	1727
March	1st to 10th	Day	4 4 2 6% 6% 4 7% 7% 8% 11% 42%	2090
	11th to 20th	Day	6% 4 2 5% 5% 4 5% 6% 7% 12% 45%	2090
	21st to end	Day	5% 4 3 5% 6% 3 6% 6% 6% 10% 46%	2255
April	1st to 10th	Day	4 2 3 5% 5% 3 6% 7% 8% 13% 45%	1980
	11th to 20th	Day	8% 5% 3 6% 5% 4 6% 8% 8% 12% 37%	2062
	21st to end	Day	6% 4 2 5% 6% 3 6% 7% 9% 10% 42%	2160
May	1st to 10th	Day	4 2 1 5% 4 3 6% 7% 9% 11% 48%	2160
	11th to 20th	Day	9% 6% 3 8% 7% 5% 6% 7% 8% 11% 29%	2127
	21st to end	Day	10% 6% 4 7% 7% 5% 7% 8% 8% 10% 28%	2531
June	1st to 10th	Day	13% 8% 4 9% 10% 5% 8% 9% 8% 9% 17%	2340
	11th to 20th	Day	6% 5% 3 9% 10% 6% 9% 9% 10% 11% 21%	2340
	21st to end	Day	7% 6% 3 8% 8% 4 8% 9% 10% 12% 25%	2340
July	1st to 10th	Day	7% 6% 3 8% 8% 5% 8% 9% 11% 14% 22%	2340
	11th to 20th	Day	8% 5% 2 8% 7% 5% 8% 8% 9% 14% 25%	2340
	21st to end	Day	4 4 4 7% 9% 6% 8% 7% 10% 14% 26%	2547
August	1st to 10th	Day	6% 5% 3 7% 9% 5% 8% 8% 11% 13% 25%	2270
	11th to 20th	Day	4 5% 2 7% 8% 5% 8% 10% 9% 15% 26%	2126
	21st to end	Day	9% 5% 3 7% 9% 5% 8% 9% 10% 13% 20%	2265
September	1st to 10th	Day	8% 6% 2 8% 9% 5% 9% 10% 10% 12% 20%	1980
	11th to 20th	Day	7% 6% 4 6% 10% 6% 9% 9% 9% 11% 23%	1980
	21st to end	Day	11% 8% 3 9% 10% 6% 7% 9% 8% 9% 19%	1980
October	1st to 10th	Day	8% 6% 3 7% 7% 7% 8% 9% 10% 12% 22%	1875
	11th to 20th	Day	9% 6% 3 7% 7% 5% 8% 8% 9% 10% 28%	1800
	21st to end	Day	12% 6% 2 7% 7% 4 6% 6% 7% 9% 34%	1980
November	1st to 10th	Day	8% 5% 2 6% 6% 3 6% 6% 9% 11% 37%	1857
	11th to 20th	Day	12% 5% 3 7% 7% 4 8% 7% 7% 9% 31%	1900
	21st to end	Day	8% 5% 3 6% 7% 5% 8% 7% 7% 10% 35%	1900
December	1st to 10th	Day	8% 5% 3 7% 6% 3 6% 6% 8% 8% 39%	1881
	11th to 20th	Day	9% 6% 3 7% 6% 3 6% 5% 6% 9% 40%	2153
	21st to end	Day	12% 6% 3 7% 7% 5% 7% 7% 8% 11% 29%	3124
January	1st to 10th	Night	8% 7% 3 7% 7% 4 6% 7% 7% 9% 36%	4109
	11th to 20th	Night	15% 10% 4 7% 7% 4 6% 5% 6% 9% 27%	4120
	21st to end	Night	7% 7% 4 8% 8% 4 7% 6% 6% 8% 36%	4532
February	1st to 10th	Night	9% 5% 2 5% 5% 3 5% 5% 7% 10% 43%	2280
	11th to 20th	Night	7% 4 1 5% 4 3 3 5% 6% 9% 53%	2085
	21st to end	Night	6% 3 2 5% 5% 4 5% 6% 6% 10% 51%	1727
March	1st to 10th	Night	3 4 2 5% 5% 3 5% 6% 6% 9% 52%	2090
	11th to 20th	Night	6% 3 1 4 4 3 4 5% 6% 9% 54%	2090
	21st to end	Night	5% 3 2 4 5% 3 5% 5% 7% 9% 52%	2256
April	1st to 10th	Night	4 2 1 4 4 2 4 5% 7% 10% 56%	1980
	11th to 20th	Night	5% 3 2 5% 6% 3 6% 7% 8% 10% 45%	1845
	21st to end	Night	5% 4 2 5% 5% 3 4 6% 7% 10% 48%	1800
May	1st to 10th	Night	4 2 1 3 4 3 5% 6% 6% 11% 56%	1800
	11th to 20th	Night	7% 6% 3 6% 7% 4 6% 7% 7% 9% 38%	1770
	21st to end	Night	8% 5% 4 7% 6% 3 5% 8% 7% 11% 36%	1753
June	1st to 10th	Night	12% 6% 4 7% 8% 5% 7% 9% 8% 11% 23%	1620
	11th to 20th	Night	6% 5% 2 7% 7% 5% 7% 7% 9% 14% 32%	1620
	21st to end	Night	4 5% 3 6% 6% 4 8% 8% 10% 14% 31%	1620
July	1st to 10th	Night	5% 4 4 7% 6% 5% 7% 7% 9% 11% 34%	1620
	11th to 20th	Night	5% 5% 2 5% 6% 4 6% 7% 9% 13% 36%	1620
	21st to end	Night	3 3 3 5% 6% 4 9% 6% 9% 13% 38%	1771
August	1st to 10th	Night	6% 5% 2 5% 5% 4 7% 6% 9% 14% 38%	1647
	11th to 20th	Night	3 3 2 5% 6% 5% 6% 7% 9% 15% 39%	1774
	21st to end	Night	7% 5% 3 6% 8% 5% 8% 8% 9% 13% 27%	2084
September	1st to 10th	Night	6% 5% 3 7% 8% 5% 7% 10% 9% 13% 27%	1980
	11th to 20th	Night	8% 5% 3 8% 7% 5% 7% 8% 8% 12% 28%	1980
	21st to end	Night	9% 7% 3 8% 10% 6% 9% 8% 9% 10% 21%	1980
October	1st to 10th	Night	7% 6% 4 8% 8% 5% 7% 9% 9% 11% 28%	2083
	11th to 20th	Night	9% 5% 1 6% 6% 4 6% 6% 8% 12% 35%	2160
	21st to end	Night	11% 7% 3 6% 6% 4 6% 6% 6% 8% 38%	2376
November	1st to 10th	Night	9% 5% 3 6% 5% 3 5% 5% 7% 10% 41%	2221
	11th to 20th	Night	9% 6% 2 7% 8% 3 6% 7% 7% 10% 35%	2280
	21st to end	Night	9% 6% 3 5% 7% 3 6% 6% 6% 11% 38%	2280
December	1st to 10th	Night	8% 4 2 5% 5% 4 6% 6% 6% 10% 44%	2294
	11th to 20th	Night	12% 6% 4 6% 5% 3 5% 5% 6% 9% 41%	3042
	21st to end	Night	8% 8% 3 8% 8% 4 6% 7% 7% 9% 29%	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	33% 26% 6% 19% 14% 3	2837
	11th to 20th	Day	46% 27% 11% 9% 5% 2	2840
	21st to end	Day	36% 25% 6% 17% 11% 5%	3124
February	1st to 10th	Day	27% 36% 5% 16% 12% 4	1895
	11th to 20th	Day	22% 37% 7% 20% 10% 4	1987
	21st to end	Day	21% 35% 7% 13% 17% 6%	1727
March	1st to 10th	Day	23% 37% 8% 16% 12% 3	2090
	11th to 20th	Day	20% 37% 9% 20% 11% 3	2090
	21st to end	Day	22% 36% 8% 19% 12% 3	2255
April	1st to 10th	Day	21% 38% 11% 17% 11% 2	1980
	11th to 20th	Day	25% 38% 10% 15% 10% 1	2062
	21st to end	Day	24% 39% 7% 14% 13% 3	2160
May	1st to 10th	Day	16% 39% 10% 21% 14% 1	2160
	11th to 20th	Day	30% 40% 12% 14% 5%	2131
	21st to end	Day	35% 40% 11% 10% 5%	2531
June	1st to 10th	Day	41% 40% 10% 7% 3	2340
	11th to 20th	Day	35% 42% 11% 11% 1	2340
	21st to end	Day	37% 42% 14% 6% 1	2340
July	1st to 10th	Day	35% 45% 14% 5%	2275
	11th to 20th	Day	34% 44% 14% 8%	2271
	21st to end	Day	28% 46% 17% 8%	2405
August	1st to 10th	Day	32% 42% 19% 6% 1	2257
	11th to 20th	Day	32% 42% 19% 7% 1	2126
	21st to end	Day	35% 45% 14% 6% 1	2265
September	1st to 10th	Day	34% 44% 14% 8% 1	1980
	11th to 20th	Day	36% 44% 12% 6% 2	1980
	21st to end	Day	41% 41% 9% 6% 3 1	1980
October	1st to 10th	Day	31% 43% 10% 11% 5% 1	1875
	11th to 20th	Day	31% 41% 8% 13% 6% 1	1800
	21st to end	Day	30% 39% 5% 12% 13% 1	1980
November	1st to 10th	Day	22% 42% 5% 11% 14% 6%	1857
	11th to 20th	Day	30% 41% 5% 12% 10% 2	1900
	21st to end	Day	26% 41% 8% 12% 12% 1	1900
December	1st to 10th	Day	24% 43% 8% 12% 11% 2	1881
	11th to 20th	Day	33% 34% 5% 11% 13% 4	2150
	21st to end	Day	36% 28% 11% 11% 12% 2	3124
January	1st to 10th	Night	33% 27% 10% 17% 12% 2	4109
	11th to 20th	Night	46% 25% 12% 10% 5% 2	4120
	21st to end	Night	35% 25% 8% 17% 9% 5%	4532
February	1st to 10th	Night	25% 35% 6% 17% 13% 4	2280
	11th to 20th	Night	20% 36% 9% 21% 11% 2	2086
	21st to end	Night	16% 35% 7% 17% 19% 5%	1727
March	1st to 10th	Night	19% 36% 9% 18% 15% 4	2090
	11th to 20th	Night	17% 35% 13% 21% 11% 3	2090
	21st to end	Night	17% 36% 10% 21% 13% 3	2256
April	1st to 10th	Night	16% 38% 14% 20% 10% 2	1980
	11th to 20th	Night	20% 38% 12% 16% 12% 1	1845
	21st to end	Night	21% 38% 10% 16% 13% 3	1800
May	1st to 10th	Night	13% 37% 10% 27% 13%	1800
	11th to 20th	Night	26% 39% 13% 16% 6%	1771
	21st to end	Night	30% 38% 13% 15% 4	1754
June	1st to 10th	Night	37% 41% 12% 8% 2	1620
	11th to 20th	Night	25% 42% 18% 13% 2	1620
	21st to end	Night	30% 44% 17% 8% 1	1620
July	1st to 10th	Night	32% 44% 17% 7% 1	1575
	11th to 20th	Night	29% 43% 20% 8%	1566
	21st to end	Night	22% 47% 20% 9% 2	1672
August	1st to 10th	Night	23% 43% 23% 10% 1	1636
	11th to 20th	Night	24% 44% 23% 9%	1774
	21st to end	Night	30% 45% 16% 6% 1	2084
September	1st to 10th	Night	29% 44% 17% 9% 1	1980
	11th to 20th	Night	33% 43% 15% 7% 1	1980
	21st to end	Night	39% 41% 10% 6% 4	1980
October	1st to 10th	Night	30% 40% 11% 12% 6% 1	2083
	11th to 20th	Night	26% 38% 13% 15% 7% 1	2160
	21st to end	Night	28% 37% 8% 14% 11% 2	2376
November	1st to 10th	Night	21% 41% 6% 12% 13% 6%	2221
	11th to 20th	Night	26% 40% 6% 17% 9% 2	2280
	21st to end	Night	24% 40% 9% 14% 10% 2	2280
December	1st to 10th	Night	21% 42% 9% 15% 10% 2	2294
	11th to 20th	Night	32% 34% 6% 12% 9% 7%	3044
	21st to end	Night	38% 28% 10% 11% 12% 2	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	8% 5% 29% 40% 17% 1	270
	11th to 20th	Day	13% 7% 26% 31% 19% 3	270
	21st to end	Day	9% 5% 35% 41% 9% 1	297
February	1st to 10th	Day	7% 7% 21% 40% 21% 3	270
	11th to 20th	Day	7% 5% 21% 38% 25% 5%	400
	21st to end	Day	6% 3 20% 38% 30% 2	382
March	1st to 10th	Day	3 5% 29% 44% 17% 2	460
	11th to 20th	Day	5% 3 23% 40% 27% 2	460
	21st to end	Day	5% 1 22% 40% 28% 4	490
April	1st to 10th	Day	3 2 23% 41% 25% 5%	420
	11th to 20th	Day	7% 2 22% 39% 24% 6%	412
	21st to end	Day	4 2 14% 41% 33% 6%	420
May	1st to 10th	Day	3 1 8% 42% 36% 10%	423
	11th to 20th	Day	10% 2 10% 31% 34% 12%	447
	21st to end	Day	11% 2 7% 15% 40% 24%	485
June	1st to 10th	Day	10% 3 8% 18% 39% 21%	450
	11th to 20th	Day	7% 2 6% 14% 34% 39%	450
	21st to end	Day	2 2 2 10% 34% 50%	450
July	1st to 10th	Day	4 1 2 6% 33% 54%	445
	11th to 20th	Day	6% 3 7% 36% 48%	444
	21st to end	Day	5% 1 1 12% 34% 48%	488
August	1st to 10th	Day	6% 4 10% 36% 43%	446
	11th to 20th	Day	4 1 2 9% 37% 48%	439
	21st to end	Day	9% 1 6% 15% 35% 35%	495
September	1st to 10th	Day	9% 2 4 10% 36% 39%	450
	11th to 20th	Day	4 4 14% 35% 41%	450
	21st to end	Day	8% 3 7% 18% 34% 30%	450
October	1st to 10th	Day	10% 1 7% 30% 40% 11%	450
	11th to 20th	Day	10% 2 11% 31% 32% 13%	450
	21st to end	Day	10% 3 14% 31% 33% 9%	495
November	1st to 10th	Day	9% 5% 17% 33% 27% 9%	455
	11th to 20th	Day	11% 4 20% 33% 27% 4	460
	21st to end	Day	6% 2 20% 40% 30% 2	460
December	1st to 10th	Day	10% 3 17% 38% 28% 4	441
	11th to 20th	Day	10% 3 18% 35% 29% 5%	270
	21st to end	Day	8% 7% 22% 31% 26% 6%	297
January	1st to 10th	Night	10% 5% 20% 38% 25% 2	760
	11th to 20th	Night	10% 6% 24% 37% 21% 2	760
	21st to end	Night	8% 5% 27% 42% 16%	836
February	1st to 10th	Night	10% 6% 20% 41% 23% 1	760
	11th to 20th	Night	7% 4 24% 40% 24% 1	743
	21st to end	Night	6% 2 20% 44% 27%	628
March	1st to 10th	Night	5% 3 30% 41% 20% 2	760
	11th to 20th	Night	5% 3 21% 43% 26% 2	760
	21st to end	Night	6% 3 21% 46% 24% 1	821
April	1st to 10th	Night	4 2 13% 48% 29% 3	720
	11th to 20th	Night	5% 3 17% 45% 27% 2	711
	21st to end	Night	7% 1 16% 46% 28% 2	720
May	1st to 10th	Night	4 1 11% 42% 38% 3	720
	11th to 20th	Night	10% 2 10% 40% 34% 5%	709
	21st to end	Night	8% 2 8% 23% 46% 13%	593
June	1st to 10th	Night	11% 2 4 22% 44% 17%	540
	11th to 20th	Night	6% 1 3 13% 45% 31%	540
	21st to end	Night	5% 1 3 12% 37% 44%	540
July	1st to 10th	Night	6% 1 3 7% 37% 46%	525
	11th to 20th	Night	6% 1 1 7% 39% 46%	522
	21st to end	Night	3 1 2 7% 41% 47%	591
August	1st to 10th	Night	8% 1 1 8% 44% 37%	573
	11th to 20th	Night	4 2 9% 45% 40%	710
	21st to end	Night	9% 1 4 15% 38% 34%	792
September	1st to 10th	Night	7% 2 5% 12% 37% 37%	720
	11th to 20th	Night	9% 2 3 14% 38% 34%	720
	21st to end	Night	12% 2 6% 16% 35% 29%	720
October	1st to 10th	Night	10% 2 8% 29% 40% 11%	720
	11th to 20th	Night	9% 2 10% 25% 43% 10%	720
	21st to end	Night	16% 1 12% 34% 30% 8%	792
November	1st to 10th	Night	11% 3 19% 32% 30% 5%	740
	11th to 20th	Night	10% 2 20% 32% 33% 4	760
	21st to end	Night	10% 3 17% 41% 27% 2	760
December	1st to 10th	Night	9% 3 17% 36% 32% 4	760
	11th to 20th	Night	11% 5% 18% 33% 29% 4	760
	21st to end	Night	9% 4 20% 34% 29% 3	836

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