Coral Key Village Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Coral Key Village Observatory clear sky chart from 2005-11-06 to 2024-01-14.

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	6% 4 2 5% 5% 4 6% 7% 8% 12% 42%	74823
	Night	6% 5% 2 5% 6% 4 6% 6% 8% 11% 41%	74934
Transparency	Day	31% 11% 22% 23% 11% 2	74546
	Night	33% 10% 20% 22% 12% 2	74730
Seeing	Day	6% 2 7% 22% 38% 26%	14846
	Night	7% 2 9% 25% 37% 20%	25015

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	7% 4 1 4 5% 2 5% 6% 8% 13% 45%	1706
	11th to 20th	Day	6% 5% 2 5% 6% 3 6% 7% 7% 11% 42%	1647
	21st to end	Day	7% 5% 2 4 6% 3 6% 7% 8% 11% 41%	1917
February	1st to 10th	Day	6% 4 2 5% 4 3 5% 5% 7% 11% 49%	1800
	11th to 20th	Day	5% 3 2 3 3 3 4 5% 6% 10% 57%	1837
	21st to end	Day	3 2 1 3 2 3 4 4 7% 10% 61%	1628
March	1st to 10th	Day	3 2 1 3 4 2 4 6% 7% 10% 57%	1980
	11th to 20th	Day	4 3 1 3 3 3 5% 5% 7% 11% 55%	1980
	21st to end	Day	4 3 1 3 4 2 4 4 6% 9% 60%	2178
April	1st to 10th	Day	2 2 1 2 3 3 5% 4 7% 12% 60%	1980
	11th to 20th	Day	3 3 2 3 3 3 4 4 6% 11% 58%	1974
	21st to end	Day	5% 3 1 3 3 2 4 6% 7% 11% 56%	2160
May	1st to 10th	Day	4 2 1 2 3 2 3 3 6% 11% 64%	2160
	11th to 20th	Day	8% 5% 2 6% 5% 3 5% 6% 7% 11% 40%	2138
	21st to end	Day	7% 6% 2 5% 6% 4 6% 7% 7% 12% 38%	2531
June	1st to 10th	Day	10% 7% 4 8% 8% 4 7% 8% 9% 12% 24%	2340
	11th to 20th	Day	5% 4 3 6% 7% 5% 8% 7% 9% 16% 30%	2340
	21st to end	Day	4 5% 3 6% 6% 4 8% 8% 10% 13% 34%	2340
July	1st to 10th	Day	4 3 2 6% 5% 3 7% 7% 10% 17% 37%	2340
	11th to 20th	Day	4 3 3 6% 5% 4 7% 8% 11% 17% 33%	2340
	21st to end	Day	3 3 1 4 5% 4 8% 9% 10% 17% 36%	2547
August	1st to 10th	Day	3 4 2 6% 7% 4 7% 9% 12% 15% 31%	2293
	11th to 20th	Day	2 4 2 6% 6% 4 6% 8% 10% 17% 35%	2006
	21st to end	Day	6% 4 3 6% 7% 5% 7% 9% 10% 15% 28%	2178
September	1st to 10th	Day	5% 4 2 5% 8% 5% 7% 9% 11% 15% 28%	1980
	11th to 20th	Day	5% 6% 2 6% 7% 4 9% 8% 10% 14% 29%	1980
	21st to end	Day	7% 7% 3 7% 8% 5% 7% 8% 10% 12% 26%	1980
October	1st to 10th	Day	7% 4 3 6% 7% 5% 7% 7% 9% 15% 31%	1944
	11th to 20th	Day	8% 5% 2 5% 7% 5% 6% 7% 9% 12% 34%	1800
	21st to end	Day	9% 5% 2 5% 6% 4 5% 6% 7% 10% 40%	1980
November	1st to 10th	Day	8% 4 2 5% 4 4 5% 6% 6% 11% 48%	1857
	11th to 20th	Day	7% 4 3 5% 6% 3 6% 6% 7% 10% 43%	1900
	21st to end	Day	6% 4 2 5% 5% 4 5% 5% 7% 10% 48%	1900
December	1st to 10th	Day	6% 4 2 4 4 4 6% 5% 7% 11% 46%	1885
	11th to 20th	Day	6% 4 2 5% 5% 3 6% 6% 7% 11% 45%	2153
	21st to end	Day	11% 6% 3 6% 6% 4 6% 6% 8% 10% 35%	3124
January	1st to 10th	Night	6% 3 2 5% 5% 4 5% 6% 8% 11% 45%	2459
	11th to 20th	Night	7% 6% 3 7% 6% 3 5% 6% 7% 10% 41%	2391
	21st to end	Night	6% 5% 2 5% 6% 4 6% 6% 8% 10% 43%	2434
February	1st to 10th	Night	6% 4 2 5% 5% 4 5% 6% 6% 10% 46%	2160
	11th to 20th	Night	5% 4 2 4 5% 2 4 5% 6% 8% 54%	2005
	21st to end	Night	4 3 2 3 5% 3 5% 4 5% 9% 58%	1628
March	1st to 10th	Night	3 3 2 4 4 4 6% 5% 7% 9% 53%	1980
	11th to 20th	Night	3 2 1 4 4 3 5% 6% 6% 10% 55%	1980
	21st to end	Night	4 3 2 3 5% 3 4 5% 6% 9% 56%	2178
April	1st to 10th	Night	3 3 1 4 3 3 5% 5% 7% 11% 55%	1980
	11th to 20th	Night	5% 3 2 5% 4 3 4 5% 7% 9% 52%	1934
	21st to end	Night	5% 3 3 4 4 3 5% 6% 6% 9% 52%	1800
May	1st to 10th	Night	3 2 1 2 2 2 3 4 6% 11% 63%	1800
	11th to 20th	Night	8% 6% 2 7% 6% 4 4 5% 7% 11% 40%	1768
	21st to end	Night	9% 5% 3 5% 6% 3 6% 6% 8% 9% 39%	1744
June	1st to 10th	Night	12% 10% 4 9% 8% 5% 5% 6% 9% 11% 21%	1620
	11th to 20th	Night	5% 4 3 6% 6% 4 6% 8% 9% 15% 34%	1620
	21st to end	Night	4 4 2 5% 8% 5% 8% 8% 9% 16% 32%	1620
July	1st to 10th	Night	3 2 2 4 6% 3 5% 7% 9% 16% 42%	1620
	11th to 20th	Night	3 4 2 5% 6% 3 6% 8% 10% 15% 38%	1620
	21st to end	Night	2 3 2 5% 6% 4 7% 7% 9% 15% 40%	1771
August	1st to 10th	Night	3 3 2 5% 6% 3 7% 9% 11% 16% 34%	1624
	11th to 20th	Night	2 4 2 5% 6% 4 7% 8% 8% 17% 39%	1887
	21st to end	Night	6% 5% 3 6% 7% 5% 7% 8% 9% 14% 30%	2178
September	1st to 10th	Night	5% 4 2 5% 7% 4 7% 9% 10% 14% 33%	1980
	11th to 20th	Night	4 6% 3 8% 8% 5% 9% 8% 11% 11% 28%	1980
	21st to end	Night	8% 7% 3 7% 8% 5% 8% 8% 8% 12% 26%	1980
October	1st to 10th	Night	7% 6% 3 7% 8% 4 7% 8% 10% 12% 29%	2013
	11th to 20th	Night	8% 5% 3 6% 7% 5% 6% 8% 9% 12% 32%	2160
	21st to end	Night	10% 6% 3 7% 7% 4 6% 7% 7% 9% 34%	2376
November	1st to 10th	Night	9% 5% 2 4 4 4 6% 6% 8% 10% 41%	2221
	11th to 20th	Night	8% 6% 3 6% 5% 3 6% 5% 7% 11% 39%	2280
	21st to end	Night	7% 4 2 6% 6% 4 6% 6% 8% 10% 43%	2280
December	1st to 10th	Night	7% 4 3 4 5% 4 5% 6% 7% 10% 44%	2289
	11th to 20th	Night	7% 5% 3 5% 5% 4 5% 5% 7% 10% 44%	3042
	21st to end	Night	9% 7% 3 8% 8% 5% 6% 6% 8% 9% 31%	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	29% 7% 18% 28% 13% 4	1707
	11th to 20th	Day	34% 9% 16% 25% 13% 4	1647
	21st to end	Day	34% 8% 14% 23% 17% 5%	1917
February	1st to 10th	Day	28% 6% 14% 32% 17% 3	1800
	11th to 20th	Day	22% 5% 14% 31% 22% 5%	1847
	21st to end	Day	17% 5% 11% 31% 30% 5%	1628
March	1st to 10th	Day	20% 6% 14% 33% 23% 3	1980
	11th to 20th	Day	21% 7% 14% 36% 18% 4	1980
	21st to end	Day	20% 5% 17% 32% 22% 4	2178
April	1st to 10th	Day	17% 6% 20% 42% 13% 2	1980
	11th to 20th	Day	20% 7% 20% 33% 17% 2	1974
	21st to end	Day	20% 7% 16% 34% 19% 3	2160
May	1st to 10th	Day	16% 5% 22% 33% 20% 5%	2160
	11th to 20th	Day	36% 9% 23% 24% 8%	2142
	21st to end	Day	36% 10% 18% 24% 10% 1	2531
June	1st to 10th	Day	49% 12% 22% 15% 3	2340
	11th to 20th	Day	38% 17% 32% 13% 1	2340
	21st to end	Day	35% 17% 35% 12%	2340
July	1st to 10th	Day	30% 18% 38% 14%	2275
	11th to 20th	Day	32% 16% 37% 15% 1	2271
	21st to end	Day	27% 18% 38% 15% 1	2405
August	1st to 10th	Day	31% 19% 30% 17% 2	2280
	11th to 20th	Day	29% 18% 38% 14% 1	2006
	21st to end	Day	37% 20% 30% 11% 1	2178
September	1st to 10th	Day	37% 20% 28% 14% 1	1980
	11th to 20th	Day	38% 17% 29% 13% 2	1980
	21st to end	Day	42% 17% 23% 13% 4	1980
October	1st to 10th	Day	38% 14% 23% 18% 6% 2	1944
	11th to 20th	Day	38% 13% 18% 20% 10% 2	1800
	21st to end	Day	37% 9% 14% 22% 15% 4	1980
November	1st to 10th	Day	30% 7% 15% 24% 20% 4	1857
	11th to 20th	Day	35% 8% 13% 22% 18% 4	1900
	21st to end	Day	30% 8% 15% 23% 21% 3	1900
December	1st to 10th	Day	29% 9% 15% 29% 18% 1	1885
	11th to 20th	Day	31% 9% 11% 24% 19% 6%	2150
	21st to end	Day	41% 10% 16% 17% 15% 2	3124
January	1st to 10th	Night	30% 8% 16% 28% 14% 4	2459
	11th to 20th	Night	36% 7% 17% 23% 13% 3	2391
	21st to end	Night	34% 8% 13% 26% 15% 4	2434
February	1st to 10th	Night	32% 7% 13% 28% 18% 3	2160
	11th to 20th	Night	26% 5% 12% 26% 23% 7%	2006
	21st to end	Night	22% 6% 13% 22% 28% 8%	1628
March	1st to 10th	Night	26% 6% 12% 30% 23% 4	1980
	11th to 20th	Night	23% 6% 15% 33% 20% 3	1980
	21st to end	Night	24% 6% 13% 29% 23% 4	2178
April	1st to 10th	Night	22% 7% 17% 38% 15% 2	1980
	11th to 20th	Night	26% 7% 18% 28% 18% 2	1934
	21st to end	Night	27% 7% 13% 31% 20% 2	1800
May	1st to 10th	Night	16% 6% 18% 35% 21% 4	1800
	11th to 20th	Night	36% 10% 17% 25% 12%	1769
	21st to end	Night	37% 8% 18% 23% 12% 1	1745
June	1st to 10th	Night	53% 11% 19% 13% 3	1620
	11th to 20th	Night	35% 16% 31% 15% 2	1620
	21st to end	Night	35% 16% 35% 14%	1620
July	1st to 10th	Night	26% 16% 42% 16% 1	1575
	11th to 20th	Night	30% 14% 37% 18% 1	1566
	21st to end	Night	26% 14% 39% 17% 3	1672
August	1st to 10th	Night	30% 16% 34% 18% 2	1613
	11th to 20th	Night	28% 15% 39% 19% 1	1887
	21st to end	Night	39% 16% 31% 13% 1	2178
September	1st to 10th	Night	34% 19% 32% 14% 1	1980
	11th to 20th	Night	42% 16% 28% 12% 2	1980
	21st to end	Night	46% 15% 23% 13% 4	1980
October	1st to 10th	Night	41% 14% 20% 16% 7% 1	2013
	11th to 20th	Night	39% 13% 22% 17% 8% 2	2160
	21st to end	Night	44% 8% 10% 20% 15% 3	2376
November	1st to 10th	Night	33% 9% 14% 24% 16% 3	2221
	11th to 20th	Night	38% 6% 15% 23% 16% 3	2280
	21st to end	Night	34% 8% 13% 24% 19% 2	2280
December	1st to 10th	Night	32% 9% 16% 27% 16% 1	2289
	11th to 20th	Night	33% 7% 12% 26% 15% 7%	3044
	21st to end	Night	44% 10% 14% 18% 13% 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	9% 4 16% 31% 36% 4	270
	11th to 20th	Day	10% 4 15% 40% 24% 6%	249
	21st to end	Day	8% 6% 19% 39% 23% 4	264
February	1st to 10th	Day	4 3 10% 40% 40% 4	240
	11th to 20th	Day	4 2 10% 31% 46% 7%	329
	21st to end	Day	4 1 13% 29% 45% 8%	346
March	1st to 10th	Day	4 3 17% 41% 32% 4	420
	11th to 20th	Day	7% 14% 34% 40% 4	420
	21st to end	Day	3 1 13% 33% 45% 5%	462
April	1st to 10th	Day	3 8% 41% 45% 3	420
	11th to 20th	Day	2 1 10% 43% 39% 4	412
	21st to end	Day	6% 2 4 39% 44% 5%	420
May	1st to 10th	Day	4 1 4 29% 49% 13%	423
	11th to 20th	Day	9% 2 3 29% 45% 13%	447
	21st to end	Day	9% 1 5% 13% 48% 24%	485
June	1st to 10th	Day	14% 2 4 14% 38% 29%	450
	11th to 20th	Day	6% 1 2 12% 33% 46%	450
	21st to end	Day	3 2 4 29% 62%	450
July	1st to 10th	Day	3 2 2 27% 65%	445
	11th to 20th	Day	3 1 4 30% 61%	444
	21st to end	Day	6% 2 4 29% 59%	488
August	1st to 10th	Day	4 1 4 38% 53%	446
	11th to 20th	Day	3 2 4 34% 57%	439
	21st to end	Day	7% 1 3 8% 34% 48%	495
September	1st to 10th	Day	7% 1 2 6% 30% 55%	450
	11th to 20th	Day	6% 1 3 5% 26% 59%	450
	21st to end	Day	8% 2 4 9% 30% 47%	450
October	1st to 10th	Day	7% 1 4 18% 51% 20%	450
	11th to 20th	Day	10% 2 6% 20% 40% 22%	450
	21st to end	Day	8% 2 11% 23% 42% 14%	495
November	1st to 10th	Day	7% 2 11% 29% 41% 11%	455
	11th to 20th	Day	8% 3 13% 29% 37% 10%	460
	21st to end	Day	6% 2 13% 30% 38% 10%	460
December	1st to 10th	Day	9% 3 9% 29% 41% 9%	445
	11th to 20th	Day	8% 2 12% 25% 41% 11%	270
	21st to end	Day	8% 4 13% 29% 36% 9%	297
January	1st to 10th	Night	7% 3 15% 33% 36% 6%	760
	11th to 20th	Night	11% 3 18% 35% 29% 4	736
	21st to end	Night	7% 5% 20% 35% 30% 3	792
February	1st to 10th	Night	8% 3 14% 37% 36% 2	720
	11th to 20th	Night	5% 3 17% 34% 36% 5%	703
	21st to end	Night	4 2 9% 34% 44% 6%	592
March	1st to 10th	Night	4 2 18% 41% 33% 3	720
	11th to 20th	Night	4 2 14% 38% 39% 4	720
	21st to end	Night	4 2 14% 40% 36% 4	792
April	1st to 10th	Night	3 2 8% 42% 43% 3	720
	11th to 20th	Night	6% 2 11% 38% 39% 3	711
	21st to end	Night	6% 1 9% 41% 40% 3	720
May	1st to 10th	Night	4 7% 32% 46% 11%	720
	11th to 20th	Night	10% 1 7% 29% 45% 8%	707
	21st to end	Night	9% 1 6% 17% 51% 16%	584
June	1st to 10th	Night	16% 3 6% 16% 40% 19%	540
	11th to 20th	Night	4 1 4 10% 40% 41%	540
	21st to end	Night	4 1 1 7% 34% 53%	540
July	1st to 10th	Night	4 1 5% 30% 59%	525
	11th to 20th	Night	3 1 2 5% 34% 55%	522
	21st to end	Night	4 2 4 31% 59%	591
August	1st to 10th	Night	5% 2 4 40% 50%	550
	11th to 20th	Night	4 2 6% 33% 55%	710
	21st to end	Night	8% 1 4 9% 36% 42%	792
September	1st to 10th	Night	6% 1 2 7% 33% 51%	720
	11th to 20th	Night	7% 1 3 9% 29% 52%	720
	21st to end	Night	11% 1 5% 9% 34% 40%	720
October	1st to 10th	Night	8% 1 6% 19% 47% 19%	720
	11th to 20th	Night	10% 1 6% 20% 41% 23%	720
	21st to end	Night	14% 2 9% 27% 35% 14%	792
November	1st to 10th	Night	11% 3 15% 28% 36% 7%	740
	11th to 20th	Night	10% 2 9% 31% 39% 9%	760
	21st to end	Night	7% 2 14% 34% 36% 6%	760
December	1st to 10th	Night	8% 3 9% 34% 39% 7%	760
	11th to 20th	Night	9% 3 12% 32% 37% 7%	760
	21st to end	Night	8% 4 13% 32% 35% 9%	836

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