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 2026-03-18.

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	13% 6% 2 6% 4 5% 5% 4 6% 8% 42%	131342
	Night	13% 6% 2 6% 4 4 4 4 5% 7% 44%	130164
Transparency	Day	38% 7% 11% 19% 18% 6%	135143
	Night	37% 6% 10% 19% 20% 8%	134422
Seeing	Day	16% 9% 22% 25% 19% 9%	16403
	Night	15% 8% 22% 29% 21% 4	26475

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	18% 11% 4 6% 3 3 3 2 4 4 43%	5258
	11th to 20th	Day	11% 6% 3 4 3 2 3 2 5% 6% 55%	5400
	21st to end	Day	25% 9% 2 6% 4 3 3 3 4 4 37%	6436
February	1st to 10th	Day	17% 8% 3 5% 5% 5% 5% 4 4 5% 41%	2100
	11th to 20th	Day	23% 6% 2 5% 4 4 3 2 4 4 42%	2048
	21st to end	Day	17% 7% 3 7% 4 4 4 3 5% 6% 41%	1730
March	1st to 10th	Day	18% 8% 3 7% 4 4 5% 4 5% 6% 37%	4580
	11th to 20th	Day	12% 6% 2 5% 4 4 4 3 4 7% 48%	4963
	21st to end	Day	16% 6% 2 6% 5% 4 4 4 5% 6% 42%	5523
April	1st to 10th	Day	14% 5% 2 5% 4 5% 4 4 5% 6% 47%	2400
	11th to 20th	Day	11% 5% 2 6% 5% 4 3 4 5% 7% 48%	2374
	21st to end	Day	7% 5% 2 6% 4 4 4 4 6% 8% 51%	2405
May	1st to 10th	Day	12% 6% 3 8% 5% 5% 5% 4 7% 8% 37%	5862
	11th to 20th	Day	15% 7% 2 7% 5% 5% 5% 4 8% 9% 32%	5861
	21st to end	Day	10% 6% 2 6% 4 5% 4 4 7% 9% 42%	6433
June	1st to 10th	Day	11% 6% 3 7% 6% 7% 6% 6% 8% 9% 31%	2600
	11th to 20th	Day	7% 4 2 5% 5% 5% 6% 6% 9% 10% 41%	2600
	21st to end	Day	6% 5% 2 8% 6% 6% 6% 7% 9% 11% 35%	2600
July	1st to 10th	Day	7% 5% 3 7% 6% 6% 7% 7% 9% 11% 31%	5900
	11th to 20th	Day	5% 4 2 6% 5% 6% 7% 6% 9% 14% 35%	5900
	21st to end	Day	8% 6% 2 9% 6% 8% 8% 7% 10% 13% 24%	6410
August	1st to 10th	Day	5% 3 2 5% 4 6% 6% 6% 8% 12% 44%	3905
	11th to 20th	Day	8% 4 2 6% 4 5% 5% 4 6% 8% 48%	3849
	21st to end	Day	7% 4 1 6% 4 4 5% 5% 7% 10% 48%	4312
September	1st to 10th	Day	10% 6% 2 8% 7% 5% 5% 4 7% 7% 39%	2295
	11th to 20th	Day	14% 7% 2 5% 4 5% 5% 4 6% 7% 41%	2200
	21st to end	Day	12% 5% 2 6% 4 5% 4 4 5% 7% 48%	2200
October	1st to 10th	Day	11% 4 2 5% 3 3 4 3 5% 6% 54%	2200
	11th to 20th	Day	9% 4 2 5% 3 3 3 2 4 6% 59%	2200
	21st to end	Day	12% 5% 2 4 3 3 3 3 4 6% 55%	2118
November	1st to 10th	Day	10% 6% 2 6% 4 3 4 3 3 5% 53%	1852
	11th to 20th	Day	12% 4 2 5% 3 4 3 3 4 5% 54%	1890
	21st to end	Day	14% 5% 2 5% 4 3 4 3 5% 7% 47%	1890
December	1st to 10th	Day	20% 5% 2 4 3 4 4 3 4 6% 45%	3020
	11th to 20th	Day	15% 7% 3 6% 4 4 4 3 4 4 45%	3463
	21st to end	Day	22% 7% 2 5% 4 3 4 3 4 5% 42%	4565
January	1st to 10th	Night	18% 8% 3 5% 3 3 4 3 5% 5% 43%	7635
	11th to 20th	Night	14% 7% 3 7% 4 4 4 3 4 5% 47%	7542
	21st to end	Night	20% 9% 3 7% 3 3 3 2 4 5% 40%	7745
February	1st to 10th	Night	15% 8% 3 6% 5% 4 4 3 4 6% 43%	2520
	11th to 20th	Night	21% 8% 3 5% 4 3 3 2 4 4 42%	2458
	21st to end	Night	17% 7% 2 5% 4 4 4 3 6% 7% 42%	2076
March	1st to 10th	Night	22% 9% 3 7% 4 3 4 3 5% 7% 35%	5493
	11th to 20th	Night	12% 6% 2 5% 4 4 4 3 5% 6% 51%	5152
	21st to end	Night	12% 6% 2 6% 5% 4 4 4 5% 6% 45%	5434
April	1st to 10th	Night	11% 6% 2 6% 4 4 4 4 5% 8% 45%	2000
	11th to 20th	Night	13% 5% 2 4 3 4 3 2 5% 9% 50%	1975
	21st to end	Night	8% 4 2 4 4 3 4 3 5% 8% 54%	1991
May	1st to 10th	Night	11% 6% 2 7% 5% 4 5% 5% 6% 9% 38%	4033
	11th to 20th	Night	16% 7% 3 7% 6% 4 5% 4 6% 8% 34%	4032
	21st to end	Night	9% 5% 2 5% 4 4 4 4 8% 12% 44%	4421
June	1st to 10th	Night	6% 6% 2 7% 5% 7% 7% 6% 8% 9% 37%	1800
	11th to 20th	Night	5% 5% 2 4 4 5% 4 4 7% 12% 48%	1800
	21st to end	Night	5% 5% 2 6% 5% 5% 5% 6% 7% 11% 44%	1800
July	1st to 10th	Night	8% 5% 3 8% 6% 6% 6% 6% 9% 11% 31%	4058
	11th to 20th	Night	5% 4 2 6% 6% 5% 6% 6% 10% 14% 36%	4057
	21st to end	Night	8% 8% 3 9% 6% 6% 7% 6% 8% 12% 28%	4427
August	1st to 10th	Night	4 3 1 5% 3 4 5% 6% 9% 14% 46%	3241
	11th to 20th	Night	5% 5% 2 5% 4 4 5% 4 6% 9% 51%	3200
	21st to end	Night	7% 5% 2 5% 4 4 5% 4 6% 10% 48%	3586
September	1st to 10th	Night	8% 5% 2 6% 5% 6% 5% 4 7% 9% 42%	2082
	11th to 20th	Night	13% 6% 2 6% 4 4 4 3 6% 8% 45%	2200
	21st to end	Night	10% 5% 2 6% 3 3 5% 4 5% 8% 49%	2200
October	1st to 10th	Night	9% 4 2 5% 3 3 3 3 5% 6% 58%	2200
	11th to 20th	Night	9% 5% 2 4 3 2 3 3 5% 5% 59%	2200
	21st to end	Night	11% 6% 1 6% 3 3 3 2 3 5% 57%	2715
November	1st to 10th	Night	11% 5% 2 5% 3 3 3 3 5% 5% 57%	2666
	11th to 20th	Night	11% 5% 2 4 4 3 3 3 3 5% 57%	2730
	21st to end	Night	14% 5% 2 5% 4 4 3 3 5% 6% 49%	2730
December	1st to 10th	Night	17% 6% 2 4 3 3 2 3 4 5% 51%	4380
	11th to 20th	Night	15% 6% 3 6% 3 3 3 3 4 6% 47%	4952
	21st to end	Night	21% 7% 2 5% 3 3 3 3 4 5% 42%	6633

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 5% 23% 19% 4	5259
	11th to 20th	Day	31% 2 5% 22% 31% 10%	5400
	21st to end	Day	52% 3 5% 11% 19% 10%	6436
February	1st to 10th	Day	45% 4 7% 16% 22% 6%	2100
	11th to 20th	Day	46% 3 5% 18% 21% 7%	2058
	21st to end	Day	44% 6% 7% 14% 21% 9%	1730
March	1st to 10th	Day	46% 5% 8% 13% 21% 6%	4580
	11th to 20th	Day	36% 4 7% 13% 22% 18%	4963
	21st to end	Day	42% 4 9% 18% 19% 8%	5525
April	1st to 10th	Day	38% 6% 9% 21% 18% 9%	2400
	11th to 20th	Day	36% 5% 7% 19% 25% 9%	2374
	21st to end	Day	31% 5% 12% 22% 26% 4	2405
May	1st to 10th	Day	42% 8% 12% 22% 15% 2	5897
	11th to 20th	Day	43% 9% 17% 21% 8% 1	5865
	21st to end	Day	36% 8% 13% 23% 18% 1	6447
June	1st to 10th	Day	44% 10% 14% 19% 12% 2	2600
	11th to 20th	Day	32% 11% 18% 24% 13% 2	2600
	21st to end	Day	37% 13% 17% 20% 10% 3	2600
July	1st to 10th	Day	38% 15% 21% 20% 5% 1	5835
	11th to 20th	Day	34% 16% 29% 17% 4	5831
	21st to end	Day	45% 16% 20% 16% 3	6226
August	1st to 10th	Day	29% 10% 14% 30% 16%	3893
	11th to 20th	Day	32% 9% 14% 27% 16% 2	3885
	21st to end	Day	29% 9% 18% 22% 18% 3	4311
September	1st to 10th	Day	42% 8% 12% 15% 18% 4	2295
	11th to 20th	Day	40% 7% 11% 19% 20% 3	2200
	21st to end	Day	34% 6% 11% 20% 22% 7%	2200
October	1st to 10th	Day	26% 4 6% 13% 30% 22%	3590
	11th to 20th	Day	17% 2 4 16% 29% 32%	3568
	21st to end	Day	22% 3 6% 19% 39% 12%	3393
November	1st to 10th	Day	35% 3 6% 15% 28% 13%	1852
	11th to 20th	Day	32% 4 7% 16% 27% 14%	1890
	21st to end	Day	37% 5% 8% 17% 25% 8%	1890
December	1st to 10th	Day	41% 4 5% 18% 26% 6%	3020
	11th to 20th	Day	42% 3 7% 19% 22% 7%	3460
	21st to end	Day	45% 4 6% 23% 20% 2	4565
January	1st to 10th	Night	44% 4 6% 23% 19% 4	7636
	11th to 20th	Night	40% 3 5% 17% 26% 9%	7542
	21st to end	Night	48% 3 4 15% 23% 7%	7745
February	1st to 10th	Night	43% 4 5% 18% 19% 10%	2520
	11th to 20th	Night	46% 4 5% 15% 21% 10%	2459
	21st to end	Night	42% 5% 9% 16% 18% 11%	2076
March	1st to 10th	Night	49% 4 7% 15% 16% 9%	5493
	11th to 20th	Night	34% 5% 9% 13% 21% 19%	5152
	21st to end	Night	39% 4 6% 21% 21% 9%	5434
April	1st to 10th	Night	37% 5% 10% 17% 20% 10%	2000
	11th to 20th	Night	33% 4 7% 20% 26% 10%	1975
	21st to end	Night	29% 5% 12% 24% 22% 7%	1991
May	1st to 10th	Night	38% 11% 14% 20% 15% 2	4060
	11th to 20th	Night	46% 9% 15% 20% 9% 1	4033
	21st to end	Night	30% 8% 16% 25% 18% 2	4429
June	1st to 10th	Night	38% 12% 17% 15% 16% 1	1800
	11th to 20th	Night	28% 9% 21% 26% 14% 2	1800
	21st to end	Night	32% 10% 20% 21% 13% 4	1800
July	1st to 10th	Night	41% 13% 22% 17% 6% 1	4015
	11th to 20th	Night	33% 16% 28% 19% 4 1	4006
	21st to end	Night	46% 13% 22% 15% 4	4297
August	1st to 10th	Night	25% 9% 16% 35% 13% 1	3230
	11th to 20th	Night	29% 9% 16% 29% 14% 3	3230
	21st to end	Night	29% 10% 15% 22% 20% 3	3586
September	1st to 10th	Night	36% 9% 15% 19% 14% 7%	2082
	11th to 20th	Night	36% 8% 11% 22% 18% 5%	2200
	21st to end	Night	32% 6% 11% 21% 22% 8%	2200
October	1st to 10th	Night	27% 4 7% 14% 28% 20%	3590
	11th to 20th	Night	17% 3 4 16% 30% 31%	3571
	21st to end	Night	22% 3 4 20% 35% 17%	4377
November	1st to 10th	Night	30% 4 8% 17% 26% 15%	2666
	11th to 20th	Night	31% 3 6% 18% 28% 14%	2730
	21st to end	Night	37% 4 8% 17% 24% 11%	2730
December	1st to 10th	Night	38% 3 5% 21% 26% 7%	4380
	11th to 20th	Night	39% 4 10% 16% 25% 6%	4954
	21st to end	Night	44% 4 6% 23% 22% 2	6633

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% 21% 34% 15% 3	330
	11th to 20th	Day	24% 24% 30% 16% 5% 1	330
	21st to end	Day	29% 23% 33% 13% 2 1	363
February	1st to 10th	Day	24% 21% 35% 15% 4 1	330
	11th to 20th	Day	35% 21% 30% 12% 1	330
	21st to end	Day	29% 20% 38% 11% 2	273
March	1st to 10th	Day	25% 19% 30% 21% 3 1	330
	11th to 20th	Day	24% 18% 31% 20% 6% 1	486
	21st to end	Day	22% 17% 31% 23% 7%	550
April	1st to 10th	Day	24% 15% 31% 19% 10% 2	500
	11th to 20th	Day	15% 12% 35% 24% 11% 2	492
	21st to end	Day	12% 10% 30% 33% 12% 3	500
May	1st to 10th	Day	13% 10% 27% 29% 16% 5%	503
	11th to 20th	Day	11% 5% 25% 31% 20% 9%	527
	21st to end	Day	14% 5% 20% 32% 17% 12%	573
June	1st to 10th	Day	13% 4 15% 31% 25% 12%	530
	11th to 20th	Day	7% 2 13% 28% 31% 17%	530
	21st to end	Day	9% 3 13% 25% 32% 19%	530
July	1st to 10th	Day	7% 2 7% 26% 34% 25%	525
	11th to 20th	Day	6% 1 6% 20% 40% 27%	524
	21st to end	Day	8% 2 6% 24% 38% 22%	576
August	1st to 10th	Day	11% 2 8% 23% 33% 23%	526
	11th to 20th	Day	12% 3 10% 21% 35% 20%	519
	21st to end	Day	12% 4 9% 27% 29% 19%	583
September	1st to 10th	Day	11% 3 10% 30% 33% 13%	530
	11th to 20th	Day	14% 5% 9% 32% 29% 11%	530
	21st to end	Day	12% 4 16% 28% 30% 9%	530
October	1st to 10th	Day	12% 5% 24% 35% 18% 6%	530
	11th to 20th	Day	11% 7% 24% 33% 22% 3	530
	21st to end	Day	19% 9% 24% 30% 15% 3	480
November	1st to 10th	Day	18% 8% 33% 28% 10% 3	330
	11th to 20th	Day	14% 11% 44% 22% 10%	330
	21st to end	Day	15% 18% 37% 21% 9% 1	330
December	1st to 10th	Day	30% 17% 32% 18% 3 1	330
	11th to 20th	Day	25% 18% 30% 19% 6% 1	330
	21st to end	Day	29% 14% 28% 24% 5%	363
January	1st to 10th	Night	25% 17% 31% 22% 5%	840
	11th to 20th	Night	22% 16% 29% 25% 7%	840
	21st to end	Night	23% 15% 36% 24% 3	924
February	1st to 10th	Night	21% 11% 33% 29% 5%	840
	11th to 20th	Night	26% 16% 31% 24% 3	823
	21st to end	Night	22% 16% 35% 23% 4	692
March	1st to 10th	Night	19% 15% 33% 29% 5%	840
	11th to 20th	Night	17% 14% 31% 27% 10%	829
	21st to end	Night	17% 14% 30% 29% 10%	872
April	1st to 10th	Night	14% 14% 32% 28% 12% 1	600
	11th to 20th	Night	15% 10% 30% 29% 13% 2	593
	21st to end	Night	9% 11% 25% 37% 19% 1	600
May	1st to 10th	Night	10% 6% 25% 34% 23% 3	600
	11th to 20th	Night	10% 6% 21% 34% 25% 4	591
	21st to end	Night	10% 2 12% 35% 34% 7%	650
June	1st to 10th	Night	9% 2 9% 39% 36% 6%	600
	11th to 20th	Night	5% 2 12% 30% 36% 16%	600
	21st to end	Night	7% 1 6% 29% 47% 11%	600
July	1st to 10th	Night	9% 3 5% 22% 44% 17%	585
	11th to 20th	Night	6% 1 3 19% 49% 22%	582
	21st to end	Night	7% 2 6% 23% 47% 15%	657
August	1st to 10th	Night	7% 2 3 26% 43% 18%	597
	11th to 20th	Night	9% 2 6% 24% 47% 11%	594
	21st to end	Night	14% 2 8% 29% 35% 12%	660
September	1st to 10th	Night	9% 1 10% 31% 37% 11%	682
	11th to 20th	Night	16% 3 11% 30% 35% 5%	800
	21st to end	Night	12% 3 15% 32% 34% 4	800
October	1st to 10th	Night	10% 4 23% 35% 24% 4	800
	11th to 20th	Night	12% 6% 22% 35% 22% 4	800
	21st to end	Night	16% 7% 21% 34% 19% 2	880
November	1st to 10th	Night	13% 8% 23% 34% 20% 2	820
	11th to 20th	Night	15% 10% 29% 33% 13% 1	840
	21st to end	Night	17% 12% 27% 33% 10% 1	840
December	1st to 10th	Night	22% 11% 27% 30% 9% 1	840
	11th to 20th	Night	22% 11% 31% 27% 9% 1	840
	21st to end	Night	28% 11% 26% 28% 7%	924

Page generated at 2026-03-15 01:23:55. Version ac07

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