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 2024-10-20.

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	9% 5% 2 6% 4 4 5% 4 7% 9% 45%	100346
	Night	9% 6% 2 6% 4 4 4 4 6% 9% 46%	98301
Transparency	Day	33% 9% 17% 20% 15% 5%	100173
	Night	33% 9% 16% 20% 17% 6%	98143
Seeing	Day	12% 2 10% 24% 31% 22%	14365
	Night	12% 3 14% 27% 30% 14%	24244

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% 4 4 3 6% 7% 44%	3133
	11th to 20th	Day	10% 6% 2 5% 4 3 3 3 6% 7% 51%	3160
	21st to end	Day	23% 9% 3 6% 3 4 4 3 4 6% 37%	3476
February	1st to 10th	Day	15% 8% 2 7% 5% 3 3 3 5% 6% 44%	1900
	11th to 20th	Day	14% 6% 2 6% 4 4 4 3 6% 7% 44%	1848
	21st to end	Day	14% 8% 3 6% 4 4 4 4 6% 7% 39%	1570
March	1st to 10th	Day	18% 9% 4 8% 4 4 4 4 5% 6% 34%	3120
	11th to 20th	Day	9% 5% 2 6% 5% 4 5% 4 7% 9% 44%	3296
	21st to end	Day	13% 6% 2 6% 4 4 4 3 6% 6% 45%	4165
April	1st to 10th	Day	12% 6% 1 5% 4 5% 4 3 5% 7% 47%	2280
	11th to 20th	Day	10% 6% 3 5% 4 4 4 4 6% 8% 46%	2254
	21st to end	Day	7% 4 2 5% 3 3 3 4 5% 6% 58%	2280
May	1st to 10th	Day	8% 4 2 5% 4 4 5% 5% 8% 12% 44%	3765
	11th to 20th	Day	11% 5% 2 6% 5% 4 5% 4 5% 8% 45%	3875
	21st to end	Day	4 3 2 4 4 4 4 4 7% 11% 53%	4476
June	1st to 10th	Day	7% 5% 2 6% 4 4 6% 5% 10% 13% 39%	2470
	11th to 20th	Day	4 3 2 5% 4 4 5% 6% 10% 11% 45%	2470
	21st to end	Day	7% 6% 2 6% 4 4 5% 5% 9% 14% 36%	2470
July	1st to 10th	Day	5% 4 2 6% 6% 6% 5% 6% 10% 16% 33%	4002
	11th to 20th	Day	5% 5% 2 6% 5% 5% 6% 5% 9% 12% 40%	3800
	21st to end	Day	3 4 2 7% 6% 7% 8% 6% 11% 16% 31%	4118
August	1st to 10th	Day	4 3 1 3 3 4 5% 5% 9% 12% 51%	3785
	11th to 20th	Day	5% 3 1 5% 3 4 6% 5% 9% 12% 47%	3729
	21st to end	Day	6% 5% 2 9% 6% 6% 6% 5% 7% 10% 37%	4180
September	1st to 10th	Day	9% 5% 1 6% 4 5% 5% 5% 8% 11% 40%	2280
	11th to 20th	Day	10% 4 2 6% 5% 4 5% 5% 8% 8% 43%	2099
	21st to end	Day	8% 4 2 5% 4 3 4 3 5% 8% 55%	2090
October	1st to 10th	Day	7% 3 2 3 4 2 4 4 6% 8% 58%	2090
	11th to 20th	Day	6% 3 1 4 3 3 4 3 4 8% 61%	2052
	21st to end	Day	9% 4 2 6% 4 3 4 4 4 6% 54%	1980
November	1st to 10th	Day	8% 3 1 4 3 3 3 5% 5% 5% 60%	1726
	11th to 20th	Day	9% 4 1 4 3 3 4 3 5% 8% 56%	1710
	21st to end	Day	10% 5% 1 6% 5% 4 5% 3 6% 7% 47%	1710
December	1st to 10th	Day	10% 6% 3 8% 5% 4 4 3 5% 7% 44%	1710
	11th to 20th	Day	14% 8% 2 7% 4 3 4 3 5% 6% 44%	2153
	21st to end	Day	15% 9% 5% 8% 4 4 3 2 4 5% 41%	3124
January	1st to 10th	Night	14% 6% 2 6% 4 4 4 4 5% 7% 43%	3793
	11th to 20th	Night	12% 6% 3 6% 3 4 3 3 4 6% 50%	3800
	21st to end	Night	19% 11% 2 5% 4 3 3 3 4 6% 40%	4180
February	1st to 10th	Night	13% 8% 3 6% 4 4 3 3 4 7% 45%	2280
	11th to 20th	Night	16% 8% 2 5% 4 3 4 3 5% 6% 45%	2218
	21st to end	Night	14% 8% 2 6% 4 3 5% 4 5% 6% 42%	1884
March	1st to 10th	Night	20% 10% 3 9% 4 4 3 3 5% 6% 33%	3733
	11th to 20th	Night	10% 7% 2 6% 5% 5% 5% 4 7% 9% 42%	3692
	21st to end	Night	11% 6% 2 5% 4 4 4 4 5% 7% 47%	3466
April	1st to 10th	Night	10% 6% 2 5% 4 4 5% 4 5% 7% 48%	1900
	11th to 20th	Night	10% 5% 2 5% 3 4 4 4 6% 8% 48%	1875
	21st to end	Night	5% 4 2 4 3 2 4 4 5% 7% 62%	1900
May	1st to 10th	Night	8% 5% 2 6% 4 4 5% 4 7% 8% 46%	3130
	11th to 20th	Night	9% 6% 3 7% 5% 5% 5% 4 5% 8% 44%	3015
	21st to end	Night	5% 3 1 4 3 4 4 4 7% 12% 53%	3079
June	1st to 10th	Night	6% 5% 2 6% 4 5% 5% 5% 6% 13% 42%	1710
	11th to 20th	Night	4 3 2 4 4 5% 5% 5% 8% 12% 48%	1710
	21st to end	Night	6% 5% 2 6% 6% 5% 5% 4 9% 13% 40%	1710
July	1st to 10th	Night	3 4 1 5% 5% 5% 7% 7% 9% 18% 35%	2952
	11th to 20th	Night	3 3 1 5% 4 4 5% 5% 9% 11% 51%	3160
	21st to end	Night	2 3 1 6% 6% 6% 6% 6% 12% 18% 33%	3435
August	1st to 10th	Night	2 2 1 3 4 5% 5% 5% 8% 15% 52%	3144
	11th to 20th	Night	4 3 1 4 3 4 5% 6% 7% 13% 51%	3100
	21st to end	Night	5% 4 2 6% 5% 6% 6% 5% 8% 12% 43%	3476
September	1st to 10th	Night	9% 6% 2 6% 4 4 6% 5% 7% 12% 39%	1900
	11th to 20th	Night	9% 5% 3 6% 5% 5% 4 4 7% 9% 43%	2061
	21st to end	Night	8% 5% 2 5% 3 4 4 4 6% 8% 52%	2090
October	1st to 10th	Night	7% 4 2 5% 4 3 4 3 6% 8% 54%	2090
	11th to 20th	Night	7% 4 2 4 3 3 2 3 4 7% 62%	2109
	21st to end	Night	11% 5% 2 5% 4 4 3 3 4 6% 54%	2376
November	1st to 10th	Night	9% 5% 2 5% 3 3 3 3 5% 7% 55%	2349
	11th to 20th	Night	10% 5% 2 5% 4 4 3 3 5% 6% 53%	2470
	21st to end	Night	10% 5% 2 5% 4 4 4 4 6% 7% 49%	2470
December	1st to 10th	Night	12% 6% 3 7% 4 4 4 4 5% 6% 46%	2470
	11th to 20th	Night	14% 6% 2 5% 4 4 4 3 6% 6% 45%	3042
	21st to end	Night	15% 9% 3 8% 5% 4 4 3 5% 6% 39%	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% 16% 20% 9%	1858
	21st to end	Day	40% 8% 12% 17% 15% 7%	1570
March	1st to 10th	Day	47% 8% 11% 18% 12% 4	3120
	11th to 20th	Day	33% 10% 15% 18% 20% 4	3296
	21st to end	Day	36% 8% 13% 18% 17% 8%	4165
April	1st to 10th	Day	35% 7% 12% 20% 18% 8%	2280
	11th to 20th	Day	34% 7% 10% 22% 19% 7%	2254
	21st to end	Day	25% 6% 13% 25% 23% 7%	2280
May	1st to 10th	Day	27% 12% 20% 23% 14% 4	3800
	11th to 20th	Day	36% 9% 15% 22% 18% 1	3879
	21st to end	Day	21% 10% 20% 35% 11% 1	4489
June	1st to 10th	Day	32% 11% 21% 25% 9% 1	2470
	11th to 20th	Day	26% 11% 22% 28% 11% 2	2470
	21st to end	Day	34% 12% 26% 18% 9% 1	2470
July	1st to 10th	Day	36% 12% 36% 14% 2	3940
	11th to 20th	Day	33% 13% 41% 9% 2	3737
	21st to end	Day	36% 17% 29% 15% 2	3987
August	1st to 10th	Day	23% 9% 20% 32% 16%	3773
	11th to 20th	Day	26% 10% 24% 29% 11%	3765
	21st to end	Day	40% 12% 19% 17% 10% 2	4179
September	1st to 10th	Day	35% 12% 22% 17% 11% 4	2280
	11th to 20th	Day	35% 12% 16% 17% 15% 5%	2099
	21st to end	Day	29% 7% 12% 25% 20% 7%	2090
October	1st to 10th	Day	24% 7% 14% 22% 20% 14%	2090
	11th to 20th	Day	22% 5% 10% 24% 25% 12%	2052
	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% 6% 8% 16% 20% 11%	2219
	21st to end	Night	41% 8% 10% 16% 14% 11%	1884
March	1st to 10th	Night	49% 8% 11% 14% 13% 5%	3733
	11th to 20th	Night	35% 10% 14% 18% 17% 7%	3692
	21st to end	Night	33% 8% 12% 21% 18% 9%	3466
April	1st to 10th	Night	34% 8% 12% 16% 19% 10%	1900
	11th to 20th	Night	33% 6% 11% 21% 20% 9%	1875
	21st to end	Night	21% 6% 12% 30% 24% 8%	1900
May	1st to 10th	Night	29% 12% 17% 20% 17% 4	3160
	11th to 20th	Night	36% 9% 14% 23% 17% 1	3016
	21st to end	Night	20% 10% 18% 35% 16% 1	3087
June	1st to 10th	Night	30% 12% 22% 26% 9% 1	1710
	11th to 20th	Night	25% 11% 25% 26% 12% 1	1710
	21st to end	Night	31% 12% 28% 18% 10% 1	1710
July	1st to 10th	Night	32% 12% 38% 15% 3	2904
	11th to 20th	Night	23% 14% 50% 11% 2	3100
	21st to end	Night	30% 21% 31% 15% 2	3325
August	1st to 10th	Night	20% 10% 27% 29% 14% 1	3132
	11th to 20th	Night	23% 11% 26% 34% 6%	3130
	21st to end	Night	33% 13% 23% 19% 11% 2	3476
September	1st to 10th	Night	34% 12% 22% 16% 12% 3	1900
	11th to 20th	Night	35% 10% 18% 18% 14% 5%	2061
	21st to end	Night	28% 9% 14% 23% 18% 8%	2090
October	1st to 10th	Night	28% 8% 11% 19% 21% 14%	2090
	11th to 20th	Night	24% 6% 9% 22% 25% 14%	2109
	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	22% 3 24% 33% 17% 1	270
	21st to end	Day	16% 2 21% 45% 15% 1	225
March	1st to 10th	Day	16% 2 22% 38% 20% 1	270
	11th to 20th	Day	15% 3 24% 35% 19% 4	298
	21st to end	Day	14% 1 22% 37% 23% 3	506
April	1st to 10th	Day	16% 2 18% 38% 21% 4	460
	11th to 20th	Day	15% 3 21% 33% 24% 6%	452
	21st to end	Day	7% 1 15% 34% 35% 7%	460
May	1st to 10th	Day	9% 1 10% 35% 35% 10%	463
	11th to 20th	Day	8% 1 6% 30% 40% 15%	487
	21st to end	Day	6% 1 3 22% 45% 22%	529
June	1st to 10th	Day	10% 1 2 16% 48% 24%	490
	11th to 20th	Day	8% 1 4 16% 42% 29%	490
	21st to end	Day	8% 1 1 17% 40% 33%	490
July	1st to 10th	Day	10% 7% 31% 52%	485
	11th to 20th	Day	8% 1 1 3 32% 55%	484
	21st to end	Day	8% 1 6% 36% 48%	532
August	1st to 10th	Day	5% 1 7% 36% 51%	486
	11th to 20th	Day	8% 1 4 33% 54%	479
	21st to end	Day	9% 2 2 11% 36% 40%	539
September	1st to 10th	Day	12% 1 3 8% 32% 44%	490
	11th to 20th	Day	14% 1 5% 12% 38% 28%	490
	21st to end	Day	9% 1 3 21% 39% 27%	490
October	1st to 10th	Day	9% 1 8% 32% 37% 13%	490
	11th to 20th	Day	8% 1 10% 23% 36% 21%	459
	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% 6% 26% 31% 17% 1	743
	21st to end	Night	17% 4 24% 38% 16%	628
March	1st to 10th	Night	15% 4 21% 39% 19% 2	760
	11th to 20th	Night	14% 2 22% 34% 23% 4	732
	21st to end	Night	11% 4 17% 40% 25% 3	627
April	1st to 10th	Night	14% 3 21% 37% 22% 4	570
	11th to 20th	Night	13% 2 19% 36% 26% 4	563
	21st to end	Night	7% 2 15% 34% 36% 6%	570
May	1st to 10th	Night	9% 2 11% 34% 36% 8%	570
	11th to 20th	Night	7% 1 9% 30% 43% 10%	561
	21st to end	Night	7% 1 3 22% 49% 18%	617
June	1st to 10th	Night	8% 1 1 22% 47% 21%	570
	11th to 20th	Night	5% 1 2 14% 49% 30%	570
	21st to end	Night	8% 1 1 12% 47% 31%	570
July	1st to 10th	Night	6% 1 7% 43% 42%	555
	11th to 20th	Night	5% 1 1 4 34% 57%	552
	21st to end	Night	4 1 1 5% 45% 44%	624
August	1st to 10th	Night	3 1 6% 38% 53%	567
	11th to 20th	Night	7% 1 5% 40% 46%	564
	21st to end	Night	10% 1 3 11% 39% 36%	627
September	1st to 10th	Night	11% 1 3 11% 39% 35%	570
	11th to 20th	Night	11% 1 4 17% 46% 21%	731
	21st to end	Night	10% 1 5% 23% 47% 15%	760
October	1st to 10th	Night	8% 1 10% 32% 38% 11%	760
	11th to 20th	Night	9% 3 12% 27% 35% 13%	759
	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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