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 2025-03-27.

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 6% 4 4 4 4 7% 9% 45%	109293
	Night	10% 6% 2 6% 4 4 4 4 6% 9% 46%	110065
Transparency	Day	33% 8% 16% 20% 17% 6%	113192
	Night	33% 8% 14% 19% 18% 7%	114304
Seeing	Day	12% 2 10% 24% 31% 21%	14847
	Night	12% 3 14% 27% 30% 14%	24867

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% 5% 2 5% 4 4 4 3 5% 8% 48%	4493
	11th to 20th	Day	13% 7% 2 5% 4 4 3 3 5% 7% 47%	4520
	21st to end	Day	19% 8% 2 6% 4 4 5% 3 5% 6% 37%	4972
February	1st to 10th	Day	15% 8% 2 7% 5% 4 3 3 5% 6% 43%	2000
	11th to 20th	Day	14% 6% 2 6% 4 4 4 3 6% 7% 44%	1948
	21st to end	Day	14% 8% 3 6% 4 4 4 4 6% 8% 40%	1650
March	1st to 10th	Day	17% 9% 3 8% 4 4 4 4 5% 6% 35%	3220
	11th to 20th	Day	9% 5% 2 6% 5% 4 5% 4 7% 9% 45%	3400
	21st to end	Day	13% 6% 2 6% 4 4 4 3 6% 6% 46%	4237
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%	2062
	21st to end	Day	9% 4 2 6% 4 3 4 3 4 5% 56%	2090
November	1st to 10th	Day	9% 4 2 4 3 3 3 5% 5% 5% 58%	1819
	11th to 20th	Day	10% 4 1 4 3 3 4 3 5% 8% 55%	1800
	21st to end	Day	10% 5% 2 6% 5% 4 5% 3 6% 7% 48%	1800
December	1st to 10th	Day	12% 6% 3 7% 4 4 3 3 5% 7% 46%	2930
	11th to 20th	Day	10% 6% 2 5% 4 3 4 3 5% 7% 52%	3373
	21st to end	Day	16% 8% 4 7% 4 3 3 2 4 5% 45%	4466
January	1st to 10th	Night	12% 6% 4 7% 4 4 4 4 5% 6% 45%	5433
	11th to 20th	Night	17% 9% 3 7% 3 3 3 3 4 6% 44%	5440
	21st to end	Night	16% 9% 2 6% 4 4 4 3 5% 8% 40%	5984
February	1st to 10th	Night	13% 8% 3 6% 4 4 4 4 4 7% 45%	2400
	11th to 20th	Night	16% 8% 2 5% 4 3 4 3 5% 6% 43%	2338
	21st to end	Night	14% 8% 2 6% 4 3 5% 4 4 6% 43%	1980
March	1st to 10th	Night	20% 10% 3 9% 4 4 3 3 5% 6% 33%	3853
	11th to 20th	Night	10% 7% 2 6% 4 5% 4 4 7% 9% 43%	3808
	21st to end	Night	11% 5% 2 5% 4 4 4 4 5% 7% 48%	3532
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 6% 62%	2114
	21st to end	Night	10% 5% 2 4 4 4 3 3 4 5% 56%	2508
November	1st to 10th	Night	9% 5% 2 5% 3 4 4 3 5% 7% 54%	2476
	11th to 20th	Night	11% 5% 2 5% 4 4 3 3 5% 6% 53%	2600
	21st to end	Night	10% 5% 2 5% 3 4 4 4 6% 7% 50%	2600
December	1st to 10th	Night	11% 5% 2 7% 4 4 4 4 5% 6% 47%	4250
	11th to 20th	Night	12% 5% 2 4 4 4 4 3 5% 6% 52%	4822
	21st to end	Night	15% 8% 3 7% 4 4 4 2 4 5% 44%	6490

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	35% 6% 8% 18% 25% 8%	4494
	11th to 20th	Day	36% 5% 6% 18% 28% 7%	4520
	21st to end	Day	48% 5% 7% 15% 16% 9%	4972
February	1st to 10th	Day	42% 5% 9% 15% 19% 10%	2000
	11th to 20th	Day	39% 6% 10% 17% 20% 8%	1958
	21st to end	Day	40% 7% 11% 18% 15% 8%	1650
March	1st to 10th	Day	46% 8% 11% 18% 13% 4	3220
	11th to 20th	Day	33% 9% 15% 18% 21% 5%	3400
	21st to end	Day	36% 8% 13% 18% 16% 8%	4237
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	28% 4 8% 14% 19% 27%	3480
	11th to 20th	Day	14% 3 7% 23% 24% 29%	3406
	21st to end	Day	21% 4 6% 14% 37% 18%	3428
November	1st to 10th	Day	26% 5% 11% 23% 24% 11%	1819
	11th to 20th	Day	28% 6% 9% 19% 26% 12%	1800
	21st to end	Day	33% 7% 11% 20% 20% 9%	1800
December	1st to 10th	Day	38% 5% 12% 18% 24% 5%	2930
	11th to 20th	Day	33% 5% 10% 23% 21% 9%	3370
	21st to end	Day	42% 5% 8% 16% 25% 3	4466
January	1st to 10th	Night	40% 5% 7% 14% 24% 9%	5433
	11th to 20th	Night	43% 4 4 16% 27% 5%	5440
	21st to end	Night	44% 4 9% 16% 18% 9%	5984
February	1st to 10th	Night	39% 6% 7% 17% 22% 10%	2400
	11th to 20th	Night	40% 6% 8% 15% 19% 11%	2339
	21st to end	Night	41% 8% 10% 17% 14% 11%	1980
March	1st to 10th	Night	49% 8% 10% 14% 13% 5%	3853
	11th to 20th	Night	35% 9% 13% 18% 17% 8%	3808
	21st to end	Night	33% 8% 12% 21% 18% 9%	3532
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	34% 6% 7% 13% 19% 21%	3480
	11th to 20th	Night	16% 3 6% 21% 27% 28%	3509
	21st to end	Night	20% 3 5% 11% 46% 15%	4120
November	1st to 10th	Night	30% 4 8% 19% 27% 11%	2476
	11th to 20th	Night	33% 4 6% 20% 26% 11%	2600
	21st to end	Night	32% 6% 11% 20% 21% 11%	2600
December	1st to 10th	Night	37% 5% 9% 18% 23% 8%	4250
	11th to 20th	Night	34% 4 8% 26% 19% 10%	4824
	21st to end	Night	42% 5% 7% 18% 24% 5%	6490

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% 26% 37% 14% 2	300
	11th to 20th	Day	11% 6% 23% 38% 17% 4	300
	21st to end	Day	25% 3 20% 38% 14% 1	330
February	1st to 10th	Day	20% 4 16% 40% 17% 2	300
	11th to 20th	Day	21% 3 27% 31% 16% 1	300
	21st to end	Day	15% 3 20% 44% 16% 1	249
March	1st to 10th	Day	15% 4 23% 39% 18% 1	300
	11th to 20th	Day	15% 3 26% 34% 18% 3	330
	21st to end	Day	14% 1 21% 37% 23% 3	530
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% 24% 36% 21%	462
	21st to end	Day	14% 2 9% 24% 34% 18%	330
November	1st to 10th	Day	14% 1 7% 27% 39% 12%	300
	11th to 20th	Day	17% 1 17% 28% 28% 9%	300
	21st to end	Day	13% 2 17% 34% 24% 9%	300
December	1st to 10th	Day	16% 3 16% 34% 25% 7%	300
	11th to 20th	Day	16% 2 22% 38% 20% 3	300
	21st to end	Day	22% 2 15% 33% 24% 5%	330
January	1st to 10th	Night	17% 6% 29% 34% 13% 1	800
	11th to 20th	Night	16% 6% 24% 36% 17% 2	800
	21st to end	Night	19% 6% 27% 37% 10% 1	880
February	1st to 10th	Night	16% 5% 24% 38% 16% 1	800
	11th to 20th	Night	20% 6% 26% 30% 17% 1	783
	21st to end	Night	17% 5% 24% 38% 16%	660
March	1st to 10th	Night	16% 4 21% 39% 19% 2	800
	11th to 20th	Night	13% 3 23% 35% 22% 4	770
	21st to end	Night	11% 4 17% 40% 26% 3	647
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% 28% 35% 13%	760
	21st to end	Night	12% 3 14% 32% 31% 7%	836
November	1st to 10th	Night	11% 4 13% 32% 31% 8%	780
	11th to 20th	Night	13% 5% 20% 33% 27% 3	800
	21st to end	Night	12% 3 24% 35% 23% 5%	800
December	1st to 10th	Night	13% 4 23% 34% 20% 6%	800
	11th to 20th	Night	17% 4 23% 32% 21% 3	800
	21st to end	Night	21% 5% 19% 38% 16% 2	880

Page generated at 2025-03-24 08:04:31. Version ac07

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