Alexander City
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Alexander City clear sky chart from 2005-11-06 to 2024-12-06.

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	12% 6% 2 6% 5% 5% 5% 4 6% 8% 42%	101131
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 44%	98552
Transparency	Day	38% 7% 11% 19% 19% 6%	104974
	Night	36% 6% 10% 19% 20% 8%	102835
Seeing	Day	16% 9% 22% 25% 19% 9%	14769
	Night	15% 8% 22% 29% 21% 5%	24769

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	17% 11% 3 6% 3 3 4 3 6% 5% 39%	2836
	11th to 20th	Day	13% 5% 2 5% 4 3 3 3 5% 6% 51%	2904
	21st to end	Day	25% 10% 2 4 3 3 2 2 3 4 41%	3476
February	1st to 10th	Day	18% 8% 3 5% 5% 5% 5% 4 4 5% 39%	1900
	11th to 20th	Day	23% 6% 2 4 4 4 3 2 4 4 42%	1848
	21st to end	Day	19% 8% 3 7% 4 4 4 3 4 6% 39%	1570
March	1st to 10th	Day	21% 10% 3 6% 3 3 4 4 5% 6% 35%	3120
	11th to 20th	Day	14% 7% 3 5% 5% 5% 4 3 5% 7% 43%	3416
	21st to end	Day	16% 5% 2 6% 4 5% 4 4 6% 7% 40%	3861
April	1st to 10th	Day	14% 5% 2 5% 4 4 4 4 5% 5% 47%	2280
	11th to 20th	Day	12% 6% 2 6% 5% 4 3 4 5% 7% 47%	2254
	21st to end	Day	7% 5% 2 5% 4 4 4 3 5% 8% 52%	2285
May	1st to 10th	Day	8% 5% 2 6% 5% 5% 5% 4 6% 9% 44%	4082
	11th to 20th	Day	15% 7% 2 6% 4 4 4 4 6% 8% 38%	4081
	21st to end	Day	9% 5% 2 7% 4 5% 4 4 6% 9% 44%	4476
June	1st to 10th	Day	11% 6% 3 7% 6% 7% 6% 6% 8% 9% 31%	2470
	11th to 20th	Day	7% 4 2 5% 5% 5% 6% 6% 9% 10% 42%	2470
	21st to end	Day	6% 5% 2 8% 7% 6% 6% 6% 8% 10% 35%	2470
July	1st to 10th	Day	9% 6% 3 8% 6% 7% 8% 7% 10% 12% 25%	4120
	11th to 20th	Day	7% 6% 3 7% 6% 7% 7% 6% 8% 11% 33%	4120
	21st to end	Day	9% 7% 3 10% 7% 8% 8% 8% 9% 11% 20%	4452
August	1st to 10th	Day	4 3 2 5% 4 6% 6% 6% 8% 12% 45%	3785
	11th to 20th	Day	8% 4 2 6% 4 5% 5% 4 5% 8% 48%	3729
	21st to end	Day	7% 4 1 5% 4 4 5% 5% 7% 10% 48%	4180
September	1st to 10th	Day	11% 6% 2 8% 7% 6% 5% 4 7% 7% 38%	2180
	11th to 20th	Day	14% 7% 2 5% 5% 5% 5% 4 6% 7% 40%	2090
	21st to end	Day	12% 5% 2 6% 4 5% 4 3 4 6% 48%	2090
October	1st to 10th	Day	11% 4 2 5% 3 3 3 2 5% 6% 55%	2090
	11th to 20th	Day	10% 4 2 5% 3 3 3 2 4 6% 58%	2090
	21st to end	Day	12% 5% 2 4 3 3 3 3 4 5% 56%	2012
November	1st to 10th	Day	11% 6% 2 6% 4 3 4 3 3 5% 52%	1762
	11th to 20th	Day	13% 4 2 5% 4 4 4 3 4 5% 53%	1800
	21st to end	Day	14% 6% 2 5% 5% 3 4 3 5% 7% 47%	1800
December	1st to 10th	Day	19% 6% 2 5% 3 5% 5% 4 5% 6% 41%	1755
	11th to 20th	Day	17% 7% 3 7% 4 4 4 2 4 4 43%	2153
	21st to end	Day	22% 8% 2 6% 4 3 4 3 5% 5% 37%	3124
January	1st to 10th	Night	19% 11% 3 5% 3 3 4 3 5% 5% 40%	4109
	11th to 20th	Night	13% 7% 3 6% 4 4 4 3 5% 6% 46%	4052
	21st to end	Night	22% 12% 3 6% 3 3 3 2 3 4 40%	4180
February	1st to 10th	Night	16% 8% 3 6% 5% 4 4 3 4 6% 41%	2280
	11th to 20th	Night	21% 8% 3 5% 4 3 3 2 4 4 44%	2218
	21st to end	Night	17% 7% 2 6% 5% 4 4 2 6% 7% 41%	1884
March	1st to 10th	Night	25% 10% 3 6% 3 3 3 2 5% 6% 35%	3733
	11th to 20th	Night	11% 6% 2 4 4 4 4 4 5% 7% 48%	3544
	21st to end	Night	13% 6% 2 6% 5% 4 5% 4 6% 7% 42%	3798
April	1st to 10th	Night	11% 6% 2 6% 4 4 4 4 5% 8% 45%	1900
	11th to 20th	Night	14% 5% 2 4 4 3 3 2 5% 9% 49%	1875
	21st to end	Night	8% 4 2 4 4 3 5% 3 5% 8% 55%	1892
May	1st to 10th	Night	8% 5% 2 7% 5% 4 5% 5% 6% 10% 44%	2813
	11th to 20th	Night	15% 7% 2 7% 5% 4 4 4 5% 7% 40%	2812
	21st to end	Night	6% 3 1 4 4 4 5% 5% 8% 12% 49%	3079
June	1st to 10th	Night	6% 6% 2 7% 6% 7% 7% 6% 8% 10% 35%	1710
	11th to 20th	Night	5% 4 2 4 3 5% 4 4 7% 12% 49%	1710
	21st to end	Night	5% 5% 2 6% 6% 5% 5% 5% 7% 11% 43%	1710
July	1st to 10th	Night	9% 6% 3 8% 6% 7% 7% 6% 10% 12% 26%	2840
	11th to 20th	Night	6% 5% 2 6% 6% 5% 6% 6% 9% 14% 34%	2840
	21st to end	Night	9% 9% 3 10% 7% 6% 7% 6% 7% 11% 26%	3087
August	1st to 10th	Night	3 3 1 5% 4 5% 5% 6% 9% 14% 46%	3141
	11th to 20th	Night	5% 5% 2 5% 4 4 5% 4 6% 9% 51%	3100
	21st to end	Night	7% 4 2 5% 4 4 5% 4 6% 10% 49%	3476
September	1st to 10th	Night	8% 5% 3 6% 5% 6% 5% 3 7% 9% 42%	1978
	11th to 20th	Night	13% 6% 2 6% 4 4 4 3 6% 8% 44%	2090
	21st to end	Night	10% 5% 2 6% 3 3 5% 4 5% 8% 49%	2090
October	1st to 10th	Night	9% 4 2 5% 3 2 3 3 5% 6% 60%	2090
	11th to 20th	Night	10% 5% 2 4 3 3 3 3 5% 6% 58%	2090
	21st to end	Night	11% 5% 1 5% 3 3 3 2 3 5% 57%	2579
November	1st to 10th	Night	11% 5% 2 4 3 3 3 3 5% 5% 56%	2536
	11th to 20th	Night	12% 6% 2 4 4 3 3 3 4 5% 55%	2600
	21st to end	Night	14% 5% 2 5% 4 4 3 3 5% 6% 49%	2600
December	1st to 10th	Night	17% 6% 2 5% 4 3 3 3 5% 6% 45%	2542
	11th to 20th	Night	16% 7% 3 6% 3 4 3 3 4 5% 46%	3042
	21st to end	Night	19% 8% 3 7% 4 4 4 4 5% 6% 36%	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	45% 3 6% 16% 23% 6%	2837
	11th to 20th	Day	33% 3 6% 26% 24% 8%	2904
	21st to end	Day	49% 3 5% 14% 20% 10%	3476
February	1st to 10th	Day	46% 5% 7% 16% 21% 6%	1900
	11th to 20th	Day	46% 3 4 17% 22% 8%	1858
	21st to end	Day	46% 6% 7% 13% 21% 8%	1570
March	1st to 10th	Day	49% 6% 9% 13% 18% 7%	3120
	11th to 20th	Day	41% 5% 8% 16% 21% 10%	3416
	21st to end	Day	42% 5% 12% 17% 17% 8%	3861
April	1st to 10th	Day	38% 6% 9% 21% 18% 9%	2280
	11th to 20th	Day	37% 5% 7% 20% 23% 9%	2254
	21st to end	Day	30% 5% 11% 23% 27% 4	2285
May	1st to 10th	Day	33% 9% 11% 24% 19% 3	4120
	11th to 20th	Day	41% 7% 13% 27% 11% 2	4085
	21st to end	Day	33% 8% 14% 25% 18% 2	4489
June	1st to 10th	Day	44% 11% 13% 19% 12% 2	2470
	11th to 20th	Day	32% 11% 17% 25% 14% 2	2470
	21st to end	Day	38% 12% 17% 20% 10% 3	2470
July	1st to 10th	Day	43% 16% 22% 14% 4 1	4055
	11th to 20th	Day	40% 14% 19% 21% 6%	4051
	21st to end	Day	51% 16% 16% 13% 4	4310
August	1st to 10th	Day	28% 10% 14% 31% 17%	3773
	11th to 20th	Day	32% 8% 14% 27% 17% 2	3765
	21st to end	Day	28% 9% 18% 22% 19% 3	4179
September	1st to 10th	Day	43% 9% 12% 13% 18% 5%	2180
	11th to 20th	Day	42% 7% 11% 17% 20% 4	2090
	21st to end	Day	35% 6% 10% 20% 22% 7%	2090
October	1st to 10th	Day	25% 4 6% 12% 30% 22%	3480
	11th to 20th	Day	17% 2 4 16% 28% 32%	3458
	21st to end	Day	21% 3 6% 18% 39% 12%	3287
November	1st to 10th	Day	36% 3 6% 15% 28% 13%	1762
	11th to 20th	Day	33% 4 7% 15% 26% 15%	1800
	21st to end	Day	37% 5% 8% 16% 25% 8%	1800
December	1st to 10th	Day	44% 5% 8% 16% 21% 6%	1755
	11th to 20th	Day	45% 3 6% 16% 24% 7%	2150
	21st to end	Day	47% 5% 7% 19% 19% 3	3124
January	1st to 10th	Night	46% 4 5% 14% 24% 7%	4109
	11th to 20th	Night	39% 3 6% 21% 22% 9%	4052
	21st to end	Night	50% 3 3 13% 25% 6%	4180
February	1st to 10th	Night	44% 4 6% 18% 18% 10%	2280
	11th to 20th	Night	45% 4 5% 14% 21% 11%	2219
	21st to end	Night	43% 5% 9% 15% 18% 10%	1884
March	1st to 10th	Night	51% 4 8% 15% 14% 8%	3733
	11th to 20th	Night	35% 6% 10% 15% 22% 12%	3544
	21st to end	Night	40% 5% 7% 19% 22% 7%	3798
April	1st to 10th	Night	37% 5% 10% 17% 20% 10%	1900
	11th to 20th	Night	34% 5% 7% 20% 24% 10%	1875
	21st to end	Night	28% 5% 12% 24% 23% 8%	1892
May	1st to 10th	Night	32% 11% 14% 21% 20% 3	2840
	11th to 20th	Night	42% 8% 12% 23% 13% 2	2813
	21st to end	Night	24% 10% 15% 29% 19% 3	3087
June	1st to 10th	Night	39% 13% 17% 16% 15% 1	1710
	11th to 20th	Night	27% 9% 21% 26% 15% 2	1710
	21st to end	Night	33% 9% 19% 21% 14% 4	1710
July	1st to 10th	Night	44% 14% 23% 12% 5% 1	2795
	11th to 20th	Night	35% 15% 21% 23% 6% 1	2786
	21st to end	Night	51% 12% 17% 14% 5% 1	2988
August	1st to 10th	Night	24% 9% 16% 35% 14% 1	3130
	11th to 20th	Night	29% 8% 16% 30% 15% 3	3130
	21st to end	Night	29% 10% 15% 22% 21% 3	3476
September	1st to 10th	Night	37% 10% 15% 18% 14% 7%	1978
	11th to 20th	Night	38% 8% 11% 21% 17% 5%	2090
	21st to end	Night	32% 6% 10% 22% 21% 9%	2090
October	1st to 10th	Night	27% 4 7% 14% 28% 21%	3480
	11th to 20th	Night	17% 3 4 15% 30% 31%	3461
	21st to end	Night	21% 3 4 21% 35% 17%	4241
November	1st to 10th	Night	31% 4 8% 17% 25% 14%	2536
	11th to 20th	Night	32% 3 5% 17% 27% 15%	2600
	21st to end	Night	37% 3 8% 17% 23% 11%	2600
December	1st to 10th	Night	41% 5% 9% 18% 22% 6%	2542
	11th to 20th	Night	41% 3 7% 13% 29% 7%	3044
	21st to end	Night	47% 4 7% 20% 19% 3	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	27% 20% 35% 15% 3	270
	11th to 20th	Day	24% 22% 30% 18% 5% 1	270
	21st to end	Day	27% 24% 35% 12% 2 1	297
February	1st to 10th	Day	27% 21% 33% 15% 4 1	270
	11th to 20th	Day	36% 21% 30% 11% 1	270
	21st to end	Day	30% 21% 39% 9%	225
March	1st to 10th	Day	27% 19% 30% 20% 3 1	270
	11th to 20th	Day	23% 17% 32% 20% 6% 1	422
	21st to end	Day	22% 17% 31% 23% 8%	506
April	1st to 10th	Day	24% 15% 30% 20% 11% 1	460
	11th to 20th	Day	16% 13% 33% 24% 11% 3	452
	21st to end	Day	12% 10% 30% 33% 11% 3	460
May	1st to 10th	Day	12% 10% 26% 30% 17% 5%	463
	11th to 20th	Day	10% 5% 24% 32% 21% 9%	487
	21st to end	Day	13% 5% 19% 32% 18% 13%	529
June	1st to 10th	Day	12% 3 15% 31% 26% 13%	490
	11th to 20th	Day	8% 2 14% 28% 31% 18%	490
	21st to end	Day	10% 3 13% 26% 30% 18%	490
July	1st to 10th	Day	8% 1 7% 26% 33% 25%	485
	11th to 20th	Day	7% 1 6% 21% 38% 27%	484
	21st to end	Day	8% 2 7% 23% 38% 23%	532
August	1st to 10th	Day	9% 2 9% 22% 34% 24%	486
	11th to 20th	Day	12% 3 10% 22% 35% 19%	479
	21st to end	Day	13% 4 8% 27% 30% 20%	539
September	1st to 10th	Day	12% 3 10% 27% 34% 14%	490
	11th to 20th	Day	15% 5% 10% 32% 28% 11%	490
	21st to end	Day	13% 4 16% 28% 30% 10%	490
October	1st to 10th	Day	12% 5% 24% 33% 19% 7%	490
	11th to 20th	Day	11% 7% 24% 33% 21% 3	490
	21st to end	Day	19% 8% 23% 30% 16% 4	441
November	1st to 10th	Day	19% 8% 33% 28% 10% 3	300
	11th to 20th	Day	15% 12% 44% 19% 9%	300
	21st to end	Day	14% 15% 38% 22% 10% 1	300
December	1st to 10th	Day	27% 18% 33% 20% 3 1	285
	11th to 20th	Day	28% 18% 30% 19% 5%	270
	21st to end	Day	31% 14% 28% 23% 4	297
January	1st to 10th	Night	25% 17% 32% 21% 5%	760
	11th to 20th	Night	22% 16% 28% 26% 8%	760
	21st to end	Night	22% 15% 34% 24% 4	836
February	1st to 10th	Night	22% 11% 33% 28% 5%	760
	11th to 20th	Night	25% 15% 31% 25% 4	743
	21st to end	Night	22% 16% 35% 24% 4	628
March	1st to 10th	Night	19% 15% 33% 28% 5%	760
	11th to 20th	Night	17% 14% 32% 26% 10%	760
	21st to end	Night	17% 14% 29% 29% 10%	829
April	1st to 10th	Night	14% 13% 32% 28% 13% 1	570
	11th to 20th	Night	16% 11% 30% 28% 14% 2	563
	21st to end	Night	9% 10% 25% 37% 18% 1	570
May	1st to 10th	Night	10% 6% 25% 32% 23% 3	570
	11th to 20th	Night	11% 5% 21% 33% 26% 4	561
	21st to end	Night	9% 1 12% 35% 35% 7%	617
June	1st to 10th	Night	9% 2 9% 38% 36% 6%	570
	11th to 20th	Night	5% 2 12% 30% 36% 16%	570
	21st to end	Night	7% 1 6% 29% 46% 11%	570
July	1st to 10th	Night	9% 3 5% 22% 44% 17%	555
	11th to 20th	Night	6% 1 4 20% 48% 22%	552
	21st to end	Night	8% 2 5% 23% 46% 15%	624
August	1st to 10th	Night	6% 1 4 25% 44% 19%	567
	11th to 20th	Night	10% 2 6% 24% 46% 11%	564
	21st to end	Night	14% 2 7% 28% 36% 13%	627
September	1st to 10th	Night	9% 1 10% 29% 38% 12%	648
	11th to 20th	Night	17% 3 12% 29% 34% 5%	760
	21st to end	Night	12% 3 15% 32% 34% 5%	760
October	1st to 10th	Night	10% 3 22% 35% 25% 4	760
	11th to 20th	Night	12% 6% 22% 34% 22% 4	760
	21st to end	Night	16% 7% 21% 34% 20% 2	836
November	1st to 10th	Night	13% 8% 23% 34% 20% 2	780
	11th to 20th	Night	15% 10% 30% 32% 13% 1	800
	21st to end	Night	17% 12% 27% 33% 10% 1	800
December	1st to 10th	Night	21% 11% 28% 30% 10% 1	783
	11th to 20th	Night	22% 10% 33% 26% 8% 1	760
	21st to end	Night	28% 11% 26% 29% 6%	836

Page generated at 2024-12-03 05:45:08. Version ac07

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