The Shoals
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Shoals clear sky chart from 2005-11-06 to 2024-11-04.

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% 7% 2 6% 5% 4 5% 4 6% 8% 42%	101078
	Night	13% 7% 2 6% 4 4 4 3 5% 7% 45%	97903
Transparency	Day	38% 5% 11% 22% 19% 5%	104839
	Night	37% 5% 10% 22% 20% 6%	102281
Seeing	Day	13% 7% 20% 24% 22% 13%	15079
	Night	15% 5% 21% 32% 23% 4	24747

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	15% 12% 3 7% 5% 4 3 4 4 6% 37%	2527
	11th to 20th	Day	20% 7% 3 6% 4 5% 3 3 4 5% 40%	2762
	21st to end	Day	22% 10% 3 5% 3 3 3 3 5% 6% 38%	3476
February	1st to 10th	Day	19% 9% 4 6% 4 3 3 3 4 6% 39%	1900
	11th to 20th	Day	19% 9% 2 7% 5% 3 4 3 4 5% 39%	1848
	21st to end	Day	20% 9% 3 6% 4 3 4 3 4 5% 38%	1570
March	1st to 10th	Day	20% 10% 4 9% 4 4 4 3 5% 5% 31%	3120
	11th to 20th	Day	12% 7% 2 6% 4 3 3 3 5% 8% 45%	3249
	21st to end	Day	13% 7% 3 6% 5% 5% 5% 4 6% 7% 39%	4160
April	1st to 10th	Day	12% 6% 3 5% 4 4 4 4 6% 7% 45%	2280
	11th to 20th	Day	14% 6% 2 6% 4 4 4 3 5% 6% 45%	2254
	21st to end	Day	10% 5% 3 6% 4 4 4 4 6% 9% 45%	2280
May	1st to 10th	Day	12% 6% 3 7% 5% 5% 4 4 6% 9% 39%	3978
	11th to 20th	Day	14% 6% 3 7% 4 4 5% 4 7% 8% 37%	4081
	21st to end	Day	12% 6% 3 7% 5% 4 5% 4 7% 9% 40%	4476
June	1st to 10th	Day	8% 6% 2 6% 5% 5% 5% 5% 8% 9% 40%	2472
	11th to 20th	Day	4 4 2 5% 5% 5% 7% 5% 7% 10% 45%	2660
	21st to end	Day	5% 4 2 5% 5% 6% 5% 6% 7% 11% 43%	2660
July	1st to 10th	Day	6% 5% 2 7% 7% 7% 7% 6% 9% 11% 33%	4440
	11th to 20th	Day	8% 5% 2 6% 5% 6% 6% 6% 10% 12% 34%	4358
	21st to end	Day	13% 9% 4 9% 7% 6% 5% 5% 7% 8% 26%	4319
August	1st to 10th	Day	3 2 1 4 4 4 6% 4 7% 10% 55%	3785
	11th to 20th	Day	5% 5% 2 7% 5% 4 5% 4 6% 10% 47%	3729
	21st to end	Day	6% 4 2 6% 4 5% 5% 4 5% 7% 51%	4180
September	1st to 10th	Day	10% 5% 2 6% 6% 5% 6% 4 5% 8% 44%	2280
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 6% 7% 43%	2100
	21st to end	Day	10% 5% 2 4 4 4 4 4 5% 7% 51%	2090
October	1st to 10th	Day	9% 5% 2 5% 3 4 4 3 5% 6% 55%	2090
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 5% 6% 55%	2000
	21st to end	Day	14% 6% 2 5% 2 3 4 3 4 5% 51%	1981
November	1st to 10th	Day	11% 4 2 4 3 3 4 4 4 6% 55%	1699
	11th to 20th	Day	12% 6% 1 5% 4 4 3 3 4 5% 52%	1710
	21st to end	Day	15% 6% 2 6% 4 4 4 5% 5% 5% 43%	1710
December	1st to 10th	Day	20% 9% 2 7% 4 4 4 3 5% 5% 35%	1710
	11th to 20th	Day	16% 8% 2 7% 5% 4 4 3 4 5% 42%	2153
	21st to end	Day	14% 10% 3 9% 6% 5% 5% 4 6% 7% 33%	2991
January	1st to 10th	Night	19% 11% 3 6% 3 3 3 4 4 5% 39%	4428
	11th to 20th	Night	18% 9% 3 7% 4 3 3 2 4 6% 41%	4182
	21st to end	Night	20% 12% 2 6% 4 3 3 3 5% 4 39%	4180
February	1st to 10th	Night	17% 9% 3 7% 4 4 3 3 5% 5% 40%	2280
	11th to 20th	Night	20% 9% 3 6% 5% 4 4 3 4 4 40%	2218
	21st to end	Night	23% 7% 3 6% 4 3 4 3 4 5% 37%	1884
March	1st to 10th	Night	23% 8% 2 6% 4 4 4 3 4 6% 36%	3733
	11th to 20th	Night	13% 6% 2 5% 4 3 4 3 5% 7% 47%	3709
	21st to end	Night	16% 7% 3 7% 5% 5% 3 4 5% 5% 41%	3498
April	1st to 10th	Night	12% 5% 2 6% 4 4 4 4 5% 8% 47%	1900
	11th to 20th	Night	14% 5% 2 4 3 4 3 4 5% 7% 49%	1875
	21st to end	Night	11% 5% 3 5% 4 4 4 3 6% 8% 47%	1900
May	1st to 10th	Night	12% 8% 3 7% 4 3 4 3 6% 8% 43%	2917
	11th to 20th	Night	13% 7% 2 7% 5% 4 4 3 5% 8% 42%	2812
	21st to end	Night	6% 6% 2 6% 4 5% 5% 4 7% 10% 44%	3079
June	1st to 10th	Night	6% 5% 2 7% 5% 5% 5% 4 6% 10% 44%	1701
	11th to 20th	Night	3 2 2 3 4 4 5% 5% 7% 11% 54%	1520
	21st to end	Night	4 4 1 5% 5% 4 4 4 8% 11% 51%	1520
July	1st to 10th	Night	6% 4 2 7% 5% 6% 6% 5% 9% 12% 37%	2530
	11th to 20th	Night	8% 5% 2 5% 4 4 5% 4 8% 12% 42%	2592
	21st to end	Night	9% 10% 4 10% 7% 6% 6% 5% 6% 9% 27%	3230
August	1st to 10th	Night	2 2 1 4 4 4 4 4 6% 9% 60%	3144
	11th to 20th	Night	4 3 1 5% 4 4 5% 4 7% 10% 54%	3100
	21st to end	Night	5% 3 2 5% 4 4 4 3 6% 8% 57%	3476
September	1st to 10th	Night	9% 4 2 4 3 4 5% 3 6% 9% 50%	1900
	11th to 20th	Night	11% 6% 2 6% 4 4 4 4 5% 8% 46%	2060
	21st to end	Night	9% 5% 2 4 4 4 3 3 4 6% 56%	2090
October	1st to 10th	Night	8% 3 1 5% 3 3 3 3 4 5% 62%	2090
	11th to 20th	Night	11% 6% 2 6% 3 4 3 2 4 5% 55%	2175
	21st to end	Night	14% 6% 2 5% 3 3 3 2 4 5% 53%	2616
November	1st to 10th	Night	11% 4 2 5% 4 3 3 3 5% 6% 53%	2452
	11th to 20th	Night	11% 5% 2 5% 4 3 4 3 5% 6% 52%	2470
	21st to end	Night	16% 6% 3 5% 4 3 3 3 5% 5% 48%	2470
December	1st to 10th	Night	19% 8% 3 5% 3 4 4 3 5% 7% 39%	2470
	11th to 20th	Night	16% 6% 2 4 4 3 3 3 5% 6% 48%	3042
	21st to end	Night	15% 9% 3 8% 5% 5% 5% 4 6% 7% 32%	4660

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	48% 3 5% 20% 21% 3	2528
	11th to 20th	Day	46% 5% 6% 18% 22% 2	2762
	21st to end	Day	47% 4 7% 22% 19% 2	3476
February	1st to 10th	Day	47% 3 8% 19% 19% 4	1900
	11th to 20th	Day	49% 3 5% 20% 16% 5%	1858
	21st to end	Day	49% 2 8% 15% 19% 7%	1570
March	1st to 10th	Day	54% 4 7% 12% 14% 9%	3120
	11th to 20th	Day	38% 4 8% 26% 17% 7%	3249
	21st to end	Day	44% 5% 11% 21% 18% 2	4160
April	1st to 10th	Day	38% 4 10% 24% 18% 6%	2280
	11th to 20th	Day	38% 4 7% 21% 23% 7%	2254
	21st to end	Day	35% 5% 9% 29% 19% 2	2280
May	1st to 10th	Day	39% 6% 13% 25% 15% 2	4014
	11th to 20th	Day	43% 5% 15% 25% 12% 1	4085
	21st to end	Day	40% 5% 12% 25% 17% 1	4489
June	1st to 10th	Day	37% 6% 15% 22% 17% 3	2472
	11th to 20th	Day	30% 7% 15% 26% 20% 2	2660
	21st to end	Day	31% 9% 16% 23% 17% 4	2660
July	1st to 10th	Day	39% 9% 21% 23% 7% 2	4371
	11th to 20th	Day	38% 7% 21% 26% 6% 1	4283
	21st to end	Day	54% 7% 13% 19% 6%	4181
August	1st to 10th	Day	23% 7% 14% 36% 19% 1	3773
	11th to 20th	Day	32% 6% 16% 27% 16% 3	3765
	21st to end	Day	31% 6% 11% 22% 25% 4	4179
September	1st to 10th	Day	38% 7% 13% 19% 18% 4	2280
	11th to 20th	Day	39% 6% 12% 18% 22% 4	2100
	21st to end	Day	33% 5% 9% 25% 22% 7%	2090
October	1st to 10th	Day	20% 3 5% 16% 37% 18%	3480
	11th to 20th	Day	21% 2 5% 20% 34% 18%	3305
	21st to end	Day	26% 4 5% 22% 34% 9%	3245
November	1st to 10th	Day	31% 4 8% 19% 29% 8%	1699
	11th to 20th	Day	35% 4 6% 19% 28% 8%	1710
	21st to end	Day	42% 4 6% 21% 22% 5%	1710
December	1st to 10th	Day	50% 4 7% 18% 17% 4	1710
	11th to 20th	Day	45% 4 7% 22% 19% 4	2150
	21st to end	Day	47% 5% 10% 21% 14% 3	2991
January	1st to 10th	Night	48% 3 6% 19% 22% 2	4428
	11th to 20th	Night	46% 4 5% 21% 18% 6%	4182
	21st to end	Night	49% 4 5% 22% 18% 3	4180
February	1st to 10th	Night	48% 3 7% 19% 19% 4	2280
	11th to 20th	Night	49% 3 6% 17% 18% 6%	2219
	21st to end	Night	50% 4 6% 16% 18% 7%	1884
March	1st to 10th	Night	49% 5% 8% 14% 16% 8%	3733
	11th to 20th	Night	36% 4 9% 21% 20% 10%	3709
	21st to end	Night	45% 4 7% 20% 22% 2	3498
April	1st to 10th	Night	36% 4 11% 24% 20% 5%	1900
	11th to 20th	Night	34% 4 8% 21% 23% 10%	1875
	21st to end	Night	34% 4 12% 26% 21% 4	1900
May	1st to 10th	Night	39% 5% 12% 24% 18% 2	2946
	11th to 20th	Night	41% 6% 15% 24% 14% 1	2813
	21st to end	Night	32% 7% 15% 27% 17% 2	3087
June	1st to 10th	Night	34% 7% 15% 23% 19% 3	1701
	11th to 20th	Night	22% 7% 17% 30% 21% 3	1520
	21st to end	Night	26% 8% 15% 29% 19% 4	1520
July	1st to 10th	Night	36% 10% 22% 23% 7% 2	2490
	11th to 20th	Night	32% 7% 26% 27% 7% 2	2544
	21st to end	Night	51% 8% 15% 18% 8%	3127
August	1st to 10th	Night	18% 7% 13% 38% 22% 2	3132
	11th to 20th	Night	23% 7% 24% 27% 16% 2	3130
	21st to end	Night	25% 5% 15% 23% 27% 4	3476
September	1st to 10th	Night	31% 7% 14% 23% 19% 5%	1900
	11th to 20th	Night	36% 6% 13% 17% 24% 4	2060
	21st to end	Night	29% 4 8% 27% 22% 9%	2090
October	1st to 10th	Night	18% 4 5% 18% 36% 20%	3480
	11th to 20th	Night	20% 2 4 16% 35% 23%	3609
	21st to end	Night	24% 3 4 27% 27% 15%	4302
November	1st to 10th	Night	32% 4 7% 22% 24% 11%	2452
	11th to 20th	Night	34% 3 7% 19% 27% 10%	2470
	21st to end	Night	39% 3 7% 21% 24% 7%	2470
December	1st to 10th	Night	45% 4 8% 21% 19% 3	2470
	11th to 20th	Night	39% 3 6% 22% 26% 4	3044
	21st to end	Night	49% 5% 8% 20% 14% 3	4660

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	21% 16% 35% 21% 7%	270
	11th to 20th	Day	26% 14% 39% 14% 6% 3	270
	21st to end	Day	20% 13% 41% 20% 5%	297
February	1st to 10th	Day	21% 13% 34% 23% 7% 1	270
	11th to 20th	Day	31% 15% 31% 18% 3 2	270
	21st to end	Day	33% 13% 36% 12% 6%	225
March	1st to 10th	Day	23% 14% 31% 23% 8% 1	270
	11th to 20th	Day	19% 15% 35% 23% 7% 1	320
	21st to end	Day	21% 13% 30% 24% 11%	506
April	1st to 10th	Day	19% 12% 28% 27% 14% 1	460
	11th to 20th	Day	17% 12% 28% 26% 15% 2	452
	21st to end	Day	13% 9% 25% 31% 16% 5%	460
May	1st to 10th	Day	14% 10% 23% 29% 17% 7%	463
	11th to 20th	Day	11% 3 21% 30% 21% 14%	487
	21st to end	Day	10% 3 17% 26% 24% 19%	529
June	1st to 10th	Day	11% 3 13% 24% 25% 24%	492
	11th to 20th	Day	5% 2 13% 25% 31% 24%	680
	21st to end	Day	6% 2 14% 26% 33% 20%	680
July	1st to 10th	Day	7% 1 9% 27% 29% 25%	671
	11th to 20th	Day	8% 2 8% 21% 27% 33%	625
	21st to end	Day	8% 1 7% 21% 33% 30%	532
August	1st to 10th	Day	6% 2 8% 22% 36% 27%	486
	11th to 20th	Day	9% 1 9% 20% 42% 18%	479
	21st to end	Day	12% 2 7% 17% 35% 27%	539
September	1st to 10th	Day	9% 1 12% 18% 39% 21%	490
	11th to 20th	Day	12% 1 10% 21% 33% 23%	490
	21st to end	Day	13% 2 13% 25% 34% 13%	490
October	1st to 10th	Day	10% 1 14% 31% 30% 14%	490
	11th to 20th	Day	9% 7% 27% 34% 19% 5%	400
	21st to end	Day	18% 10% 22% 28% 18% 5%	330
November	1st to 10th	Day	16% 8% 24% 25% 20% 6%	279
	11th to 20th	Day	10% 10% 36% 32% 11% 1	270
	21st to end	Day	16% 13% 28% 23% 16% 4	270
December	1st to 10th	Day	24% 16% 29% 21% 9% 1	270
	11th to 20th	Day	17% 13% 34% 23% 11% 1	270
	21st to end	Day	21% 16% 35% 21% 8%	297
January	1st to 10th	Night	23% 9% 33% 29% 6%	950
	11th to 20th	Night	23% 10% 34% 26% 7%	891
	21st to end	Night	19% 8% 40% 31% 3	836
February	1st to 10th	Night	21% 9% 33% 32% 6%	760
	11th to 20th	Night	25% 11% 29% 31% 3	743
	21st to end	Night	26% 11% 35% 26% 2	628
March	1st to 10th	Night	20% 9% 31% 35% 5%	760
	11th to 20th	Night	20% 7% 34% 31% 8% 1	760
	21st to end	Night	16% 8% 33% 31% 12%	646
April	1st to 10th	Night	14% 8% 31% 34% 13%	570
	11th to 20th	Night	14% 6% 28% 37% 13% 2	563
	21st to end	Night	12% 6% 26% 39% 16% 1	570
May	1st to 10th	Night	11% 3 25% 38% 21% 2	570
	11th to 20th	Night	11% 3 16% 39% 26% 5%	561
	21st to end	Night	7% 1 11% 38% 36% 7%	617
June	1st to 10th	Night	7% 2 9% 37% 39% 7%	570
	11th to 20th	Night	4 8% 33% 47% 8%	570
	21st to end	Night	4 1 7% 34% 44% 11%	570
July	1st to 10th	Night	9% 1 6% 25% 45% 14%	555
	11th to 20th	Night	7% 1 4 25% 49% 14%	552
	21st to end	Night	7% 7% 26% 44% 16%	624
August	1st to 10th	Night	4 1 4 22% 55% 14%	567
	11th to 20th	Night	6% 1 4 29% 51% 9%	564
	21st to end	Night	10% 1 5% 23% 51% 10%	627
September	1st to 10th	Night	11% 2 8% 26% 46% 7%	570
	11th to 20th	Night	13% 2 10% 28% 40% 6%	730
	21st to end	Night	12% 2 12% 31% 39% 4	760
October	1st to 10th	Night	9% 2 12% 37% 35% 6%	760
	11th to 20th	Night	13% 4 19% 40% 21% 3	760
	21st to end	Night	17% 4 19% 37% 22% 2	836
November	1st to 10th	Night	12% 4 20% 40% 21% 2	755
	11th to 20th	Night	13% 5% 29% 38% 14% 1	760
	21st to end	Night	18% 8% 24% 37% 13% 1	760
December	1st to 10th	Night	21% 9% 28% 32% 9%	760
	11th to 20th	Night	21% 6% 30% 33% 10%	760
	21st to end	Night	25% 8% 29% 33% 5%	912

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