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 2024-11-04.

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	7% 5% 2 7% 6% 6% 7% 6% 9% 11% 34%	100592
	Night	7% 6% 2 7% 5% 5% 6% 5% 8% 10% 39%	98364
Transparency	Day	20% 51% 13% 11% 4 1	104289
	Night	21% 50% 12% 12% 5% 1	102806
Seeing	Day	7% 3 13% 28% 30% 19%	16025
	Night	8% 2 14% 30% 32% 13%	26149

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% 8% 3 8% 5% 5% 5% 4 6% 10% 37%	2836
	11th to 20th	Day	16% 8% 3 10% 7% 5% 5% 5% 7% 9% 25%	2840
	21st to end	Day	6% 7% 4 9% 6% 6% 6% 5% 6% 7% 36%	3124
February	1st to 10th	Day	9% 6% 2 6% 5% 5% 5% 4 8% 10% 39%	1895
	11th to 20th	Day	7% 4 2 5% 4 4 4 5% 7% 10% 48%	1977
	21st to end	Day	6% 5% 2 5% 6% 5% 7% 5% 7% 9% 44%	1727
March	1st to 10th	Day	6% 6% 3 8% 6% 7% 8% 7% 10% 11% 29%	3435
	11th to 20th	Day	4 3 1 5% 4 4 4 5% 8% 12% 50%	3480
	21st to end	Day	9% 4 2 6% 4 4 5% 4 6% 10% 45%	3815
April	1st to 10th	Day	4 3 2 5% 4 4 6% 6% 8% 13% 45%	2090
	11th to 20th	Day	7% 5% 2 6% 4 5% 6% 6% 8% 11% 40%	2178
	21st to end	Day	6% 4 2 6% 5% 5% 6% 6% 9% 9% 43%	2280
May	1st to 10th	Day	2 2 1 4 3 4 4 5% 8% 10% 58%	3765
	11th to 20th	Day	6% 4 2 7% 5% 6% 7% 6% 9% 12% 34%	3781
	21st to end	Day	6% 5% 2 5% 5% 5% 6% 6% 8% 11% 42%	4476
June	1st to 10th	Day	12% 8% 4 11% 8% 7% 8% 7% 9% 9% 18%	2470
	11th to 20th	Day	7% 6% 3 10% 9% 8% 9% 7% 10% 10% 21%	2470
	21st to end	Day	7% 7% 2 9% 7% 6% 8% 8% 11% 12% 24%	2470
July	1st to 10th	Day	5% 5% 3 7% 6% 5% 6% 6% 9% 14% 34%	4120
	11th to 20th	Day	6% 6% 2 8% 6% 6% 7% 7% 9% 14% 29%	4120
	21st to end	Day	4 4 2 6% 6% 7% 6% 5% 10% 17% 33%	4466
August	1st to 10th	Day	5% 5% 3 10% 8% 8% 8% 8% 12% 13% 22%	3992
	11th to 20th	Day	4 4 2 7% 6% 6% 8% 7% 10% 16% 31%	3730
	21st to end	Day	5% 4 2 7% 6% 7% 8% 8% 12% 18% 22%	3971
September	1st to 10th	Day	7% 6% 2 10% 7% 7% 10% 7% 10% 12% 21%	2090
	11th to 20th	Day	7% 6% 3 8% 8% 8% 9% 7% 10% 11% 22%	2090
	21st to end	Day	11% 8% 3 10% 8% 8% 7% 7% 8% 9% 20%	2090
October	1st to 10th	Day	9% 6% 3 9% 6% 8% 8% 7% 10% 11% 22%	1979
	11th to 20th	Day	9% 6% 3 9% 6% 7% 8% 6% 9% 10% 27%	1900
	21st to end	Day	11% 6% 2 8% 6% 5% 6% 4 6% 10% 35%	2090
November	1st to 10th	Day	8% 6% 2 7% 5% 5% 6% 5% 9% 11% 36%	1887
	11th to 20th	Day	11% 6% 2 8% 7% 6% 7% 5% 8% 8% 31%	1900
	21st to end	Day	8% 5% 3 7% 7% 6% 8% 5% 7% 11% 35%	1900
December	1st to 10th	Day	8% 6% 3 8% 5% 5% 5% 5% 8% 8% 39%	1881
	11th to 20th	Day	9% 7% 3 8% 5% 4 5% 4 6% 9% 40%	2153
	21st to end	Day	12% 6% 3 8% 6% 6% 6% 6% 8% 11% 29%	3124
January	1st to 10th	Night	8% 7% 3 8% 6% 5% 6% 5% 8% 9% 36%	4109
	11th to 20th	Night	15% 11% 4 8% 6% 5% 5% 4 6% 9% 26%	4120
	21st to end	Night	6% 8% 4 9% 6% 6% 6% 5% 6% 8% 36%	4532
February	1st to 10th	Night	9% 6% 2 5% 5% 5% 4 4 8% 10% 43%	2280
	11th to 20th	Night	7% 4 1 5% 4 4 4 4 7% 8% 53%	2085
	21st to end	Night	6% 3 1 5% 5% 4 5% 4 6% 9% 51%	1727
March	1st to 10th	Night	6% 7% 3 8% 6% 7% 6% 6% 7% 8% 37%	3418
	11th to 20th	Night	4 3 1 4 4 4 4 4 8% 11% 54%	3480
	21st to end	Night	7% 4 2 5% 4 4 5% 4 6% 9% 51%	3817
April	1st to 10th	Night	4 2 1 4 3 3 4 5% 7% 11% 55%	2090
	11th to 20th	Night	5% 4 2 5% 5% 5% 6% 6% 8% 9% 47%	1948
	21st to end	Night	5% 4 2 5% 5% 5% 4 6% 8% 9% 49%	1900
May	1st to 10th	Night	2 2 1 3 3 3 4 4 6% 11% 63%	3130
	11th to 20th	Night	5% 4 2 6% 5% 5% 5% 5% 7% 10% 46%	3130
	21st to end	Night	5% 5% 2 6% 4 4 5% 5% 7% 10% 45%	3088
June	1st to 10th	Night	11% 7% 4 8% 7% 7% 8% 6% 9% 11% 24%	1710
	11th to 20th	Night	7% 6% 2 7% 6% 7% 6% 5% 10% 13% 31%	1710
	21st to end	Night	4 6% 3 7% 6% 6% 7% 6% 10% 13% 31%	1710
July	1st to 10th	Night	4 5% 3 6% 5% 6% 5% 5% 8% 11% 41%	2840
	11th to 20th	Night	4 5% 2 7% 6% 5% 6% 6% 10% 13% 36%	2840
	21st to end	Night	2 3 2 6% 4 5% 7% 5% 9% 14% 42%	3087
August	1st to 10th	Night	4 5% 2 7% 5% 7% 8% 6% 9% 13% 34%	2903
	11th to 20th	Night	2 3 2 6% 5% 6% 7% 6% 9% 14% 41%	3097
	21st to end	Night	4 4 2 7% 6% 7% 8% 7% 12% 17% 25%	3664
September	1st to 10th	Night	6% 5% 3 8% 7% 8% 8% 8% 10% 12% 26%	2090
	11th to 20th	Night	8% 6% 3 9% 7% 7% 7% 6% 8% 12% 27%	2090
	21st to end	Night	8% 7% 3 9% 8% 8% 8% 6% 9% 10% 22%	2090
October	1st to 10th	Night	8% 7% 4 10% 6% 6% 7% 7% 9% 10% 27%	2199
	11th to 20th	Night	10% 6% 1 7% 6% 6% 6% 5% 9% 11% 34%	2280
	21st to end	Night	11% 7% 3 7% 5% 5% 5% 5% 7% 8% 38%	2508
November	1st to 10th	Night	9% 6% 3 6% 5% 5% 5% 4 7% 10% 41%	2264
	11th to 20th	Night	9% 7% 2 8% 7% 5% 6% 5% 8% 10% 35%	2280
	21st to end	Night	9% 7% 3 6% 6% 5% 5% 5% 6% 11% 38%	2280
December	1st to 10th	Night	8% 4 2 6% 5% 5% 5% 5% 7% 10% 44%	2294
	11th to 20th	Night	11% 7% 3 6% 5% 4 5% 4 5% 8% 41%	3042
	21st to end	Night	8% 9% 3 10% 6% 6% 6% 6% 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	30% 39% 6% 15% 10% 1	2837
	11th to 20th	Day	38% 39% 10% 8% 3	2840
	21st to end	Day	28% 42% 5% 12% 9% 4	3124
February	1st to 10th	Day	12% 67% 7% 10% 4 1	1895
	11th to 20th	Day	9% 64% 4 10% 10% 3	1987
	21st to end	Day	13% 66% 6% 7% 7% 2	1727
March	1st to 10th	Day	31% 45% 13% 8% 3 1	3435
	11th to 20th	Day	12% 42% 16% 25% 4 1	3480
	21st to end	Day	20% 43% 7% 18% 9% 3	3815
April	1st to 10th	Day	8% 67% 9% 11% 5% 1	2090
	11th to 20th	Day	10% 68% 7% 7% 6% 2	2178
	21st to end	Day	9% 67% 5% 10% 8% 1	2280
May	1st to 10th	Day	9% 43% 8% 23% 14% 3	3800
	11th to 20th	Day	20% 43% 20% 14% 3	3785
	21st to end	Day	11% 43% 11% 26% 9%	4489
June	1st to 10th	Day	18% 71% 6% 5% 1	2470
	11th to 20th	Day	18% 71% 6% 4	2470
	21st to end	Day	11% 72% 13% 4	2470
July	1st to 10th	Day	17% 43% 25% 15%	4055
	11th to 20th	Day	23% 43% 27% 7%	4051
	21st to end	Day	17% 45% 26% 11%	4324
August	1st to 10th	Day	30% 46% 18% 6% 1	3979
	11th to 20th	Day	17% 46% 23% 14%	3766
	21st to end	Day	21% 47% 28% 4	3971
September	1st to 10th	Day	16% 68% 11% 6%	2090
	11th to 20th	Day	17% 65% 12% 5% 1	2090
	21st to end	Day	18% 66% 7% 6% 2	2090
October	1st to 10th	Day	30% 45% 13% 9% 3	3291
	11th to 20th	Day	29% 41% 12% 10% 7% 1	3140
	21st to end	Day	20% 39% 7% 22% 9% 2	3428
November	1st to 10th	Day	14% 62% 10% 9% 4 1	1887
	11th to 20th	Day	19% 63% 5% 7% 4 2	1900
	21st to end	Day	17% 61% 6% 8% 5% 2	1900
December	1st to 10th	Day	17% 61% 7% 9% 5%	1881
	11th to 20th	Day	18% 50% 6% 9% 12% 5%	2150
	21st to end	Day	34% 41% 11% 9% 5%	3124
January	1st to 10th	Night	32% 39% 8% 13% 7% 1	4109
	11th to 20th	Night	41% 38% 10% 8% 2	4120
	21st to end	Night	31% 42% 4 11% 8% 4	4532
February	1st to 10th	Night	11% 66% 8% 11% 4	2280
	11th to 20th	Night	8% 63% 4 10% 11% 4	2086
	21st to end	Night	11% 66% 5% 7% 8% 3	1727
March	1st to 10th	Night	33% 44% 11% 9% 3 1	3418
	11th to 20th	Night	12% 42% 21% 20% 5% 1	3480
	21st to end	Night	17% 42% 10% 14% 15% 2	3817
April	1st to 10th	Night	6% 66% 6% 15% 5% 1	2090
	11th to 20th	Night	9% 68% 6% 8% 8% 1	1948
	21st to end	Night	8% 67% 7% 11% 6% 1	1900
May	1st to 10th	Night	8% 42% 14% 26% 8% 3	3160
	11th to 20th	Night	16% 42% 17% 20% 5%	3131
	21st to end	Night	13% 43% 12% 26% 6%	3096
June	1st to 10th	Night	14% 69% 10% 6% 1	1710
	11th to 20th	Night	16% 71% 7% 6%	1710
	21st to end	Night	10% 69% 15% 5%	1710
July	1st to 10th	Night	18% 42% 25% 15%	2795
	11th to 20th	Night	19% 42% 32% 7%	2786
	21st to end	Night	18% 42% 28% 12%	2988
August	1st to 10th	Night	27% 44% 18% 10% 1	2892
	11th to 20th	Night	18% 43% 21% 18%	3127
	21st to end	Night	21% 48% 26% 4	3664
September	1st to 10th	Night	18% 67% 11% 5%	2090
	11th to 20th	Night	16% 66% 12% 5% 1	2090
	21st to end	Night	17% 67% 7% 7% 3	2090
October	1st to 10th	Night	33% 44% 12% 9% 1	3667
	11th to 20th	Night	32% 41% 9% 10% 7%	3779
	21st to end	Night	21% 40% 7% 20% 9% 3	4120
November	1st to 10th	Night	15% 60% 9% 10% 4 1	2264
	11th to 20th	Night	19% 62% 5% 8% 4 2	2280
	21st to end	Night	18% 61% 6% 7% 6% 2	2280
December	1st to 10th	Night	15% 63% 7% 9% 7%	2294
	11th to 20th	Night	18% 51% 4 11% 10% 7%	3044
	21st to end	Night	36% 41% 10% 8% 5% 1	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% 2 23% 40% 26% 4	506
April	1st to 10th	Day	3 2 24% 43% 23% 5%	460
	11th to 20th	Day	7% 3 22% 41% 22% 6%	452
	21st to end	Day	4 2 14% 43% 32% 6%	460
May	1st to 10th	Day	3 1 9% 41% 37% 10%	463
	11th to 20th	Day	9% 2 12% 33% 32% 11%	487
	21st to end	Day	10% 2 7% 17% 40% 24%	529
June	1st to 10th	Day	9% 3 8% 20% 39% 21%	490
	11th to 20th	Day	9% 2 8% 15% 31% 36%	490
	21st to end	Day	3 2 3 11% 34% 48%	490
July	1st to 10th	Day	4 1 3 9% 33% 50%	485
	11th to 20th	Day	5% 1 2 10% 37% 45%	484
	21st to end	Day	4 1 2 15% 34% 45%	532
August	1st to 10th	Day	6% 1 5% 12% 35% 40%	486
	11th to 20th	Day	4 1 2 11% 37% 46%	479
	21st to end	Day	8% 1 6% 17% 35% 33%	539
September	1st to 10th	Day	8% 2 3 12% 38% 37%	490
	11th to 20th	Day	5% 1 4 16% 34% 40%	490
	21st to end	Day	8% 3 8% 19% 33% 28%	490
October	1st to 10th	Day	11% 2 8% 30% 38% 11%	490
	11th to 20th	Day	11% 4 12% 32% 30% 12%	490
	21st to end	Day	10% 4 17% 30% 31% 8%	539
November	1st to 10th	Day	9% 5% 17% 34% 26% 9%	467
	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% 45% 24% 1	836
April	1st to 10th	Night	4 2 14% 49% 28% 3	760
	11th to 20th	Night	5% 3 18% 46% 26% 2	751
	21st to end	Night	7% 1 16% 47% 27% 2	760
May	1st to 10th	Night	4 1 11% 42% 39% 4	760
	11th to 20th	Night	9% 2 12% 41% 32% 5%	749
	21st to end	Night	8% 2 8% 24% 47% 12%	626
June	1st to 10th	Night	11% 2 4 23% 44% 16%	570
	11th to 20th	Night	7% 2 5% 14% 43% 30%	570
	21st to end	Night	5% 1 3 12% 37% 43%	570
July	1st to 10th	Night	6% 1 3 8% 39% 45%	555
	11th to 20th	Night	6% 1 1 7% 40% 44%	552
	21st to end	Night	3 1 2 7% 41% 45%	624
August	1st to 10th	Night	8% 1 2 10% 44% 35%	606
	11th to 20th	Night	4 2 9% 45% 40%	750
	21st to end	Night	9% 1 4 16% 38% 33%	836
September	1st to 10th	Night	7% 1 5% 13% 37% 36%	760
	11th to 20th	Night	9% 2 4 14% 38% 32%	760
	21st to end	Night	11% 2 7% 17% 35% 28%	760
October	1st to 10th	Night	10% 3 8% 29% 40% 11%	760
	11th to 20th	Night	10% 3 11% 26% 41% 9%	760
	21st to end	Night	15% 2 14% 33% 29% 7%	836
November	1st to 10th	Night	10% 3 18% 33% 30% 5%	755
	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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