Dauphin Island
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dauphin Island clear sky chart from 2005-11-06 to 2024-02-15.

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	10% 5% 2 5% 5% 3 5% 5% 6% 9% 45%	78936
	Night	10% 5% 2 5% 5% 3 4 5% 6% 9% 47%	80133
Transparency	Day	34% 9% 15% 20% 16% 6%	78680
	Night	34% 8% 14% 19% 18% 7%	79908
Seeing	Day	12% 2 10% 23% 32% 22%	13407
	Night	12% 3 14% 27% 30% 14%	23429

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	13% 6% 2 5% 5% 3 4 4 5% 7% 45%	3133
	11th to 20th	Day	10% 5% 2 4 4 2 3 4 6% 8% 51%	3160
	21st to end	Day	23% 8% 3 5% 4 3 4 4 4 6% 37%	3476
February	1st to 10th	Day	15% 7% 2 6% 6% 3 3 3 5% 6% 44%	1900
	11th to 20th	Day	14% 6% 2 6% 5% 3 4 4 5% 8% 44%	1788
	21st to end	Day	14% 8% 3 6% 4 3 5% 5% 6% 7% 39%	1480
March	1st to 10th	Day	10% 6% 3 5% 4 3 4 5% 5% 7% 48%	1800
	11th to 20th	Day	10% 5% 2 5% 5% 3 6% 5% 6% 7% 45%	1866
	21st to end	Day	9% 5% 2 5% 5% 3 4 3 5% 7% 50%	2376
April	1st to 10th	Day	11% 5% 2 4 4 3 5% 4 5% 8% 48%	2160
	11th to 20th	Day	11% 6% 3 5% 4 2 4 5% 6% 8% 46%	2134
	21st to end	Day	7% 3 2 4 4 2 4 5% 5% 7% 59%	2160
May	1st to 10th	Day	7% 3 2 3 4 2 4 4 5% 10% 55%	2160
	11th to 20th	Day	5% 4 2 4 5% 3 5% 6% 6% 10% 49%	2179
	21st to end	Day	5% 3 2 4 5% 3 5% 6% 7% 10% 50%	2531
June	1st to 10th	Day	7% 5% 2 5% 5% 3 6% 6% 9% 14% 38%	2340
	11th to 20th	Day	5% 2 2 4 4 3 6% 7% 10% 12% 45%	2340
	21st to end	Day	8% 5% 3 6% 5% 3 5% 6% 9% 14% 36%	2340
July	1st to 10th	Day	8% 5% 3 6% 7% 5% 7% 7% 8% 13% 31%	2278
	11th to 20th	Day	8% 5% 3 6% 7% 3 6% 7% 10% 13% 32%	2160
	21st to end	Day	6% 5% 3 6% 6% 3 7% 7% 10% 13% 36%	2350
August	1st to 10th	Day	7% 4 2 5% 4 4 7% 8% 10% 13% 37%	2148
	11th to 20th	Day	9% 4 2 5% 5% 3 7% 7% 10% 14% 34%	2125
	21st to end	Day	11% 5% 2 5% 6% 4 5% 7% 7% 10% 39%	2376
September	1st to 10th	Day	7% 4 2 5% 5% 4 6% 6% 8% 11% 42%	2160
	11th to 20th	Day	10% 4 2 6% 6% 3 4 6% 8% 8% 43%	1989
	21st to end	Day	8% 4 2 5% 5% 3 4 4 5% 8% 53%	1980
October	1st to 10th	Day	7% 3 2 3 4 2 3 5% 5% 9% 58%	1980
	11th to 20th	Day	7% 3 1 3 4 2 4 4 5% 8% 59%	1954
	21st to end	Day	9% 4 2 5% 5% 3 3 4 4 6% 54%	1980
November	1st to 10th	Day	8% 3 2 3 3 2 3 5% 4 5% 60%	1726
	11th to 20th	Day	9% 4 1 4 4 2 4 3 5% 8% 56%	1710
	21st to end	Day	10% 5% 2 5% 6% 3 4 4 5% 8% 47%	1710
December	1st to 10th	Day	11% 6% 3 7% 6% 3 4 4 5% 7% 45%	1710
	11th to 20th	Day	14% 7% 3 6% 5% 2 4 4 5% 7% 44%	2153
	21st to end	Day	15% 9% 4 7% 5% 2 4 3 4 6% 41%	3124
January	1st to 10th	Night	14% 6% 2 6% 5% 3 4 5% 5% 7% 43%	3793
	11th to 20th	Night	12% 6% 3 5% 4 3 3 4 4 6% 50%	3800
	21st to end	Night	19% 10% 3 5% 4 2 3 3 4 6% 40%	4180
February	1st to 10th	Night	14% 7% 3 5% 5% 3 4 4 4 7% 45%	2280
	11th to 20th	Night	16% 7% 2 4 4 2 4 4 6% 6% 45%	2153
	21st to end	Night	15% 7% 3 5% 6% 2 5% 5% 4 6% 41%	1776
March	1st to 10th	Night	11% 5% 2 6% 5% 3 3 3 6% 8% 47%	2160
	11th to 20th	Night	11% 6% 3 5% 5% 2 5% 4 6% 10% 43%	2108
	21st to end	Night	9% 3 2 4 5% 2 5% 4 6% 7% 53%	1980
April	1st to 10th	Night	10% 5% 3 4 4 2 6% 5% 5% 7% 49%	1800
	11th to 20th	Night	10% 5% 2 4 4 3 3 5% 6% 8% 48%	1775
	21st to end	Night	4 3 2 3 4 2 4 4 5% 7% 63%	1800
May	1st to 10th	Night	7% 3 2 3 4 2 4 4 6% 9% 55%	1800
	11th to 20th	Night	4 4 2 6% 5% 4 6% 6% 6% 10% 47%	1711
	21st to end	Night	6% 2 2 4 4 3 5% 6% 7% 11% 50%	1744
June	1st to 10th	Night	7% 4 2 5% 4 4 5% 6% 6% 14% 42%	1620
	11th to 20th	Night	4 2 2 4 4 3 5% 5% 8% 13% 49%	1620
	21st to end	Night	6% 4 2 5% 6% 4 5% 5% 9% 13% 39%	1620
July	1st to 10th	Night	6% 5% 2 5% 6% 3 7% 7% 8% 13% 39%	1676
	11th to 20th	Night	4 4 2 5% 5% 4 6% 7% 10% 14% 40%	1800
	21st to end	Night	4 4 2 5% 6% 4 6% 6% 9% 15% 40%	1968
August	1st to 10th	Night	3 2 1 3 4 3 6% 6% 9% 15% 48%	1790
	11th to 20th	Night	7% 4 2 4 5% 4 5% 9% 8% 14% 38%	1776
	21st to end	Night	8% 5% 2 6% 6% 4 5% 6% 7% 11% 41%	1980
September	1st to 10th	Night	7% 5% 2 5% 5% 3 6% 6% 7% 13% 41%	1800
	11th to 20th	Night	9% 5% 3 6% 5% 3 4 5% 7% 10% 44%	1952
	21st to end	Night	8% 5% 2 4 4 3 4 5% 6% 9% 50%	1980
October	1st to 10th	Night	6% 4 2 4 5% 3 4 4 6% 7% 55%	1980
	11th to 20th	Night	7% 4 2 4 4 2 3 3 4 7% 61%	2002
	21st to end	Night	11% 5% 2 4 4 3 4 4 4 6% 54%	2376
November	1st to 10th	Night	9% 5% 2 4 4 2 3 3 4 7% 56%	2349
	11th to 20th	Night	10% 5% 2 4 4 3 4 3 4 7% 53%	2470
	21st to end	Night	10% 4 2 5% 4 3 4 5% 6% 7% 49%	2470
December	1st to 10th	Night	12% 5% 3 6% 5% 3 4 5% 5% 7% 46%	2470
	11th to 20th	Night	14% 6% 3 5% 5% 3 5% 4 5% 6% 45%	3042
	21st to end	Night	15% 9% 3 7% 6% 3 4 4 5% 6% 40%	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	37% 7% 9% 15% 21% 11%	3134
	11th to 20th	Day	30% 7% 8% 19% 29% 7%	3160
	21st to end	Day	49% 6% 4 16% 19% 7%	3476
February	1st to 10th	Day	42% 5% 10% 15% 19% 10%	1900
	11th to 20th	Day	39% 6% 10% 17% 20% 8%	1798
	21st to end	Day	41% 8% 12% 17% 15% 7%	1480
March	1st to 10th	Day	34% 7% 10% 22% 20% 6%	1800
	11th to 20th	Day	35% 8% 16% 14% 19% 6%	1866
	21st to end	Day	32% 8% 14% 22% 18% 6%	2376
April	1st to 10th	Day	34% 7% 13% 20% 18% 7%	2160
	11th to 20th	Day	34% 7% 10% 22% 19% 7%	2134
	21st to end	Day	25% 6% 13% 25% 23% 7%	2160
May	1st to 10th	Day	24% 7% 13% 27% 20% 8%	2160
	11th to 20th	Day	29% 9% 20% 22% 18% 2	2183
	21st to end	Day	26% 11% 18% 28% 15% 2	2531
June	1st to 10th	Day	33% 11% 22% 26% 9% 1	2340
	11th to 20th	Day	26% 12% 22% 29% 10% 2	2340
	21st to end	Day	35% 12% 26% 17% 9% 1	2340
July	1st to 10th	Day	42% 16% 23% 16% 3	2216
	11th to 20th	Day	38% 17% 27% 15% 3 1	2097
	21st to end	Day	34% 15% 26% 21% 4	2219
August	1st to 10th	Day	32% 15% 26% 22% 4	2136
	11th to 20th	Day	35% 17% 28% 15% 5%	2125
	21st to end	Day	38% 14% 22% 18% 7% 2	2376
September	1st to 10th	Day	32% 13% 22% 17% 12% 4	2160
	11th to 20th	Day	35% 12% 17% 16% 15% 5%	1989
	21st to end	Day	30% 8% 12% 25% 19% 6%	1980
October	1st to 10th	Day	23% 7% 14% 23% 21% 12%	1980
	11th to 20th	Day	24% 6% 11% 23% 26% 11%	1954
	21st to end	Day	31% 6% 7% 16% 24% 15%	1980
November	1st to 10th	Day	25% 6% 10% 23% 25% 11%	1726
	11th to 20th	Day	27% 6% 10% 19% 27% 11%	1710
	21st to end	Day	33% 8% 11% 20% 19% 9%	1710
December	1st to 10th	Day	38% 7% 13% 18% 18% 6%	1710
	11th to 20th	Day	41% 7% 8% 16% 19% 9%	2150
	21st to end	Day	45% 6% 9% 17% 20% 4	3124
January	1st to 10th	Night	40% 7% 7% 13% 23% 10%	3793
	11th to 20th	Night	34% 6% 6% 18% 29% 7%	3800
	21st to end	Night	46% 4 7% 14% 22% 8%	4180
February	1st to 10th	Night	39% 6% 7% 17% 21% 10%	2280
	11th to 20th	Night	39% 7% 8% 16% 20% 11%	2154
	21st to end	Night	42% 8% 10% 16% 13% 11%	1776
March	1st to 10th	Night	34% 7% 11% 18% 22% 8%	2160
	11th to 20th	Night	36% 7% 15% 18% 18% 7%	2108
	21st to end	Night	29% 6% 14% 21% 22% 7%	1980
April	1st to 10th	Night	34% 8% 13% 17% 19% 9%	1800
	11th to 20th	Night	33% 6% 11% 21% 21% 7%	1775
	21st to end	Night	20% 6% 11% 30% 25% 8%	1800
May	1st to 10th	Night	25% 6% 14% 24% 24% 7%	1800
	11th to 20th	Night	30% 10% 18% 21% 19% 2	1712
	21st to end	Night	25% 11% 17% 25% 20% 2	1745
June	1st to 10th	Night	30% 11% 22% 27% 8% 1	1620
	11th to 20th	Night	23% 11% 26% 27% 11%	1620
	21st to end	Night	31% 12% 28% 19% 10% 1	1620
July	1st to 10th	Night	34% 14% 26% 21% 5%	1628
	11th to 20th	Night	27% 20% 32% 18% 3 1	1740
	21st to end	Night	28% 14% 32% 22% 3	1858
August	1st to 10th	Night	22% 15% 35% 26% 3	1778
	11th to 20th	Night	32% 17% 30% 17% 4	1776
	21st to end	Night	36% 13% 23% 19% 6% 3	1980
September	1st to 10th	Night	32% 12% 23% 17% 13% 4	1800
	11th to 20th	Night	35% 10% 18% 17% 14% 6%	1952
	21st to end	Night	29% 9% 15% 22% 17% 8%	1980
October	1st to 10th	Night	27% 8% 11% 20% 21% 13%	1980
	11th to 20th	Night	25% 6% 10% 22% 25% 13%	2002
	21st to end	Night	33% 4 6% 15% 28% 14%	2376
November	1st to 10th	Night	29% 4 8% 19% 28% 12%	2349
	11th to 20th	Night	32% 4 7% 21% 26% 10%	2470
	21st to end	Night	32% 6% 10% 20% 21% 11%	2470
December	1st to 10th	Night	37% 7% 11% 20% 19% 5%	2470
	11th to 20th	Night	39% 5% 8% 17% 19% 12%	3044
	21st to end	Night	45% 6% 8% 19% 18% 4	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	16% 5% 24% 37% 16% 2	270
	11th to 20th	Day	11% 4 22% 39% 19% 5%	270
	21st to end	Day	25% 3 21% 36% 13% 1	297
February	1st to 10th	Day	21% 4 17% 40% 15% 3	270
	11th to 20th	Day	21% 3 24% 33% 18% 1	252
	21st to end	Day	16% 3 23% 43% 14% 1	198
March	1st to 10th	Day	13% 3 23% 39% 21% 2	240
	11th to 20th	Day	16% 3 23% 33% 20% 4	266
	21st to end	Day	14% 1 22% 36% 24% 3	462
April	1st to 10th	Day	15% 2 19% 37% 23% 4	420
	11th to 20th	Day	16% 2 21% 31% 24% 6%	412
	21st to end	Day	7% 1 15% 34% 35% 7%	420
May	1st to 10th	Day	8% 1 11% 34% 36% 9%	423
	11th to 20th	Day	6% 1 5% 30% 41% 17%	447
	21st to end	Day	6% 1 4 20% 46% 23%	485
June	1st to 10th	Day	10% 1 2 15% 47% 25%	450
	11th to 20th	Day	8% 1 4 15% 42% 30%	450
	21st to end	Day	9% 2 1 16% 39% 33%	450
July	1st to 10th	Day	10% 6% 31% 52%	445
	11th to 20th	Day	9% 1 1 3 32% 54%	444
	21st to end	Day	8% 1 7% 37% 47%	488
August	1st to 10th	Day	6% 2 7% 35% 51%	446
	11th to 20th	Day	8% 2 4 33% 53%	439
	21st to end	Day	9% 2 2 11% 34% 42%	495
September	1st to 10th	Day	9% 1 2 8% 34% 46%	450
	11th to 20th	Day	14% 1 4 12% 39% 30%	450
	21st to end	Day	10% 2 22% 39% 28%	450
October	1st to 10th	Day	8% 1 8% 32% 38% 14%	450
	11th to 20th	Day	9% 1 9% 21% 37% 23%	424
	21st to end	Day	15% 2 10% 23% 33% 18%	297
November	1st to 10th	Day	14% 1 7% 26% 39% 14%	270
	11th to 20th	Day	14% 1 17% 30% 29% 9%	270
	21st to end	Day	14% 1 17% 34% 24% 9%	270
December	1st to 10th	Day	15% 3 16% 33% 27% 7%	270
	11th to 20th	Day	18% 1 23% 37% 18% 3	270
	21st to end	Day	23% 2 15% 31% 24% 5%	297
January	1st to 10th	Night	17% 6% 28% 34% 14% 1	760
	11th to 20th	Night	14% 6% 24% 36% 18% 2	760
	21st to end	Night	20% 6% 28% 35% 10% 1	836
February	1st to 10th	Night	16% 6% 25% 38% 14% 1	760
	11th to 20th	Night	20% 5% 26% 30% 18% 1	722
	21st to end	Night	18% 4 24% 38% 16%	592
March	1st to 10th	Night	14% 4 22% 39% 19% 2	720
	11th to 20th	Night	14% 2 22% 34% 24% 5%	694
	21st to end	Night	10% 4 17% 40% 26% 3	594
April	1st to 10th	Night	14% 3 20% 37% 23% 4	540
	11th to 20th	Night	14% 2 19% 35% 26% 4	533
	21st to end	Night	6% 2 16% 34% 36% 6%	540
May	1st to 10th	Night	9% 2 11% 34% 36% 8%	540
	11th to 20th	Night	6% 1 8% 30% 45% 10%	531
	21st to end	Night	7% 1 3 20% 51% 19%	584
June	1st to 10th	Night	8% 1 1 21% 47% 22%	540
	11th to 20th	Night	5% 1 12% 50% 31%	540
	21st to end	Night	8% 1 1 11% 47% 32%	540
July	1st to 10th	Night	7% 1 6% 42% 43%	525
	11th to 20th	Night	5% 1 4 34% 57%	522
	21st to end	Night	4 1 1 5% 45% 44%	591
August	1st to 10th	Night	3 1 5% 38% 54%	537
	11th to 20th	Night	8% 1 5% 40% 45%	534
	21st to end	Night	10% 1 2 11% 39% 36%	594
September	1st to 10th	Night	9% 1 3 11% 40% 37%	540
	11th to 20th	Night	10% 1 4 16% 46% 22%	692
	21st to end	Night	10% 1 4 23% 48% 15%	720
October	1st to 10th	Night	7% 1 9% 32% 39% 11%	720
	11th to 20th	Night	9% 2 12% 26% 36% 14%	720
	21st to end	Night	13% 4 15% 31% 31% 8%	792
November	1st to 10th	Night	11% 4 14% 33% 31% 8%	740
	11th to 20th	Night	12% 5% 20% 33% 27% 3	760
	21st to end	Night	12% 2 23% 35% 23% 5%	760
December	1st to 10th	Night	13% 4 22% 33% 21% 7%	760
	11th to 20th	Night	18% 4 23% 32% 20% 3	760
	21st to end	Night	21% 5% 20% 38% 15% 2	836

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