Maryville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Maryville clear sky chart from 2005-11-06 to 2026-08-30.

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% 7% 3 7% 5% 5% 5% 4 6% 8% 37%	143452
	Night	14% 8% 3 7% 4 4 4 4 6% 7% 38%	138787
Transparency	Day	44% 6% 13% 21% 14% 3	147202
	Night	44% 5% 12% 20% 15% 3	143108
Seeing	Day	17% 10% 21% 24% 19% 9%	17259
	Night	17% 7% 21% 31% 20% 3	27240

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% 3 8% 5% 4 4 4 6% 5% 33%	5258
	11th to 20th	Day	12% 9% 4 8% 4 4 4 3 4 5% 42%	5280
	21st to end	Day	20% 10% 3 9% 4 4 3 2 4 6% 34%	5780
February	1st to 10th	Day	18% 9% 4 9% 4 4 4 3 5% 6% 34%	2090
	11th to 20th	Day	22% 10% 3 8% 5% 3 3 2 4 6% 33%	2048
	21st to end	Day	20% 8% 3 6% 4 5% 5% 4 5% 5% 35%	1730
March	1st to 10th	Day	19% 9% 3 6% 5% 5% 4 3 6% 6% 34%	4737
	11th to 20th	Day	11% 6% 3 7% 4 4 4 3 5% 6% 47%	5090
	21st to end	Day	16% 7% 2 6% 4 4 4 3 5% 6% 43%	5586
April	1st to 10th	Day	12% 5% 2 6% 4 5% 6% 5% 7% 8% 42%	2373
	11th to 20th	Day	13% 6% 2 6% 4 4 4 4 5% 6% 46%	2513
	21st to end	Day	14% 6% 2 6% 4 4 4 4 5% 8% 42%	2730
May	1st to 10th	Day	15% 8% 3 7% 4 4 5% 4 6% 9% 33%	7616
	11th to 20th	Day	12% 7% 3 8% 6% 5% 6% 4 7% 7% 34%	7626
	21st to end	Day	15% 9% 3 10% 6% 6% 6% 5% 6% 7% 28%	8391
June	1st to 10th	Day	9% 6% 2 6% 6% 5% 6% 6% 7% 10% 37%	2730
	11th to 20th	Day	5% 5% 2 6% 6% 7% 7% 6% 8% 10% 40%	2730
	21st to end	Day	8% 5% 2 6% 6% 6% 6% 5% 8% 11% 38%	2730
July	1st to 10th	Day	5% 4 2 6% 5% 6% 6% 6% 9% 13% 38%	7680
	11th to 20th	Day	9% 7% 3 8% 6% 6% 7% 6% 8% 11% 31%	7680
	21st to end	Day	11% 9% 3 9% 6% 6% 7% 6% 9% 11% 23%	8340
August	1st to 10th	Day	7% 5% 3 8% 5% 5% 6% 5% 8% 12% 36%	4364
	11th to 20th	Day	7% 5% 2 7% 5% 5% 6% 5% 8% 11% 39%	4209
	21st to end	Day	6% 4 2 5% 4 4 5% 4 6% 8% 51%	4420
September	1st to 10th	Day	11% 6% 2 7% 5% 4 4 4 6% 8% 43%	2210
	11th to 20th	Day	15% 5% 2 6% 4 4 4 4 5% 8% 42%	2200
	21st to end	Day	14% 5% 2 5% 3 4 4 4 6% 7% 45%	2200
October	1st to 10th	Day	11% 4 2 5% 3 3 4 3 5% 5% 54%	2200
	11th to 20th	Day	13% 5% 2 5% 3 3 3 3 4 7% 53%	2046
	21st to end	Day	16% 5% 2 4 4 3 4 3 4 6% 49%	2185
November	1st to 10th	Day	12% 5% 2 5% 3 3 3 3 5% 5% 53%	1852
	11th to 20th	Day	11% 7% 2 5% 4 4 3 4 5% 7% 48%	1890
	21st to end	Day	13% 8% 3 7% 4 3 4 4 4 7% 42%	1890
December	1st to 10th	Day	14% 8% 3 7% 5% 5% 4 4 5% 6% 40%	3020
	11th to 20th	Day	16% 13% 4 10% 6% 5% 4 3 4 5% 29%	3463
	21st to end	Day	13% 14% 4 8% 5% 5% 4 4 6% 7% 31%	4565
January	1st to 10th	Night	17% 10% 3 8% 4 3 3 3 5% 6% 38%	7635
	11th to 20th	Night	18% 8% 2 6% 4 3 3 2 4 5% 44%	7680
	21st to end	Night	19% 11% 4 7% 4 3 4 3 4 5% 37%	8401
February	1st to 10th	Night	17% 10% 3 7% 4 4 4 4 5% 6% 36%	2528
	11th to 20th	Night	22% 10% 3 6% 4 4 4 3 4 4 34%	2458
	21st to end	Night	22% 9% 3 6% 4 4 4 3 5% 6% 33%	2076
March	1st to 10th	Night	19% 10% 3 7% 4 4 4 3 5% 6% 35%	5334
	11th to 20th	Night	13% 5% 2 5% 3 3 4 3 5% 8% 50%	5090
	21st to end	Night	12% 7% 3 6% 5% 5% 5% 4 5% 7% 42%	5588
April	1st to 10th	Night	12% 6% 2 5% 4 4 4 3 6% 8% 46%	2263
	11th to 20th	Night	12% 6% 2 6% 4 4 4 3 5% 7% 48%	2054
	21st to end	Night	13% 5% 2 7% 4 4 5% 4 5% 8% 43%	1890
May	1st to 10th	Night	15% 8% 3 8% 5% 4 5% 4 7% 9% 30%	5237
	11th to 20th	Night	15% 8% 3 8% 5% 4 4 4 6% 8% 35%	5234
	21st to end	Night	15% 9% 3 10% 6% 5% 5% 4 5% 7% 29%	5761
June	1st to 10th	Night	7% 6% 3 7% 5% 5% 6% 5% 8% 10% 38%	1890
	11th to 20th	Night	4 4 1 5% 4 5% 5% 5% 9% 13% 45%	1890
	21st to end	Night	7% 5% 2 7% 4 5% 6% 5% 7% 12% 40%	1890
July	1st to 10th	Night	8% 6% 2 7% 6% 6% 6% 6% 9% 12% 33%	5278
	11th to 20th	Night	9% 7% 3 8% 6% 6% 7% 5% 8% 11% 30%	5277
	21st to end	Night	11% 9% 4 10% 7% 6% 6% 5% 8% 11% 22%	5736
August	1st to 10th	Night	7% 6% 2 9% 5% 6% 6% 6% 6% 10% 37%	3005
	11th to 20th	Night	9% 6% 3 7% 5% 4 5% 5% 6% 10% 41%	3056
	21st to end	Night	6% 4 2 6% 4 4 5% 4 8% 11% 46%	3676
September	1st to 10th	Night	10% 6% 2 7% 5% 5% 4 4 6% 7% 42%	2168
	11th to 20th	Night	12% 6% 3 9% 4 4 6% 4 6% 7% 42%	2200
	21st to end	Night	12% 6% 2 5% 5% 5% 4 4 5% 7% 45%	2200
October	1st to 10th	Night	11% 6% 2 5% 4 3 3 3 5% 6% 53%	2200
	11th to 20th	Night	15% 5% 2 4 3 3 3 3 4 5% 53%	2351
	21st to end	Night	14% 6% 2 5% 3 3 3 3 4 6% 51%	2650
November	1st to 10th	Night	13% 7% 2 5% 4 3 3 3 4 6% 51%	2666
	11th to 20th	Night	14% 8% 2 5% 3 3 4 3 4 7% 47%	2730
	21st to end	Night	15% 7% 3 5% 4 4 4 3 5% 6% 44%	2730
December	1st to 10th	Night	16% 10% 3 8% 4 4 3 3 5% 5% 39%	4380
	11th to 20th	Night	19% 12% 4 8% 5% 4 4 3 4 6% 32%	4952
	21st to end	Night	16% 12% 3 8% 5% 5% 5% 4 5% 7% 30%	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	52% 3 12% 21% 12% 1	5259
	11th to 20th	Day	47% 3 5% 14% 27% 4	5280
	21st to end	Day	54% 2 7% 21% 13% 2	5780
February	1st to 10th	Day	52% 5% 9% 17% 15% 2	2090
	11th to 20th	Day	56% 4 7% 17% 14% 2	2058
	21st to end	Day	51% 4 7% 15% 17% 5%	1730
March	1st to 10th	Day	50% 4 7% 14% 17% 8%	4737
	11th to 20th	Day	39% 4 6% 17% 25% 10%	5090
	21st to end	Day	44% 3 8% 30% 13% 1	5586
April	1st to 10th	Day	39% 8% 12% 23% 16% 2	2373
	11th to 20th	Day	39% 5% 9% 19% 23% 4	2513
	21st to end	Day	42% 6% 11% 26% 13% 2	2730
May	1st to 10th	Day	48% 6% 13% 23% 10% 1	7651
	11th to 20th	Day	48% 5% 15% 21% 9% 1	7630
	21st to end	Day	55% 7% 11% 15% 11% 2	8405
June	1st to 10th	Day	42% 11% 15% 20% 11% 2	2730
	11th to 20th	Day	37% 11% 18% 21% 11% 2	2730
	21st to end	Day	38% 12% 17% 18% 13% 3	2730
July	1st to 10th	Day	35% 9% 26% 21% 9%	7615
	11th to 20th	Day	46% 7% 25% 17% 4 1	7611
	21st to end	Day	53% 7% 17% 16% 7%	8156
August	1st to 10th	Day	42% 7% 17% 26% 8%	4351
	11th to 20th	Day	38% 7% 21% 22% 11% 1	4248
	21st to end	Day	32% 6% 14% 35% 12% 2	4419
September	1st to 10th	Day	40% 9% 12% 17% 17% 5%	2210
	11th to 20th	Day	42% 8% 11% 20% 16% 2	2200
	21st to end	Day	39% 6% 13% 19% 18% 5%	2200
October	1st to 10th	Day	26% 4 6% 22% 31% 11%	3590
	11th to 20th	Day	24% 3 6% 23% 30% 14%	3312
	21st to end	Day	28% 3 7% 30% 23% 9%	3511
November	1st to 10th	Day	34% 4 10% 20% 27% 5%	1852
	11th to 20th	Day	36% 3 9% 23% 24% 4	1890
	21st to end	Day	42% 5% 8% 22% 19% 4	1890
December	1st to 10th	Day	45% 4 6% 19% 23% 2	3020
	11th to 20th	Day	58% 2 9% 16% 13% 2	3460
	21st to end	Day	50% 3 13% 23% 9% 1	4565
January	1st to 10th	Night	49% 2 13% 23% 12% 1	7636
	11th to 20th	Night	46% 2 6% 17% 25% 4	7680
	21st to end	Night	53% 2 8% 17% 16% 4	8401
February	1st to 10th	Night	49% 5% 9% 19% 16% 2	2528
	11th to 20th	Night	56% 4 7% 16% 13% 3	2459
	21st to end	Night	53% 6% 7% 15% 15% 4	2076
March	1st to 10th	Night	50% 4 8% 16% 17% 4	5334
	11th to 20th	Night	33% 4 8% 22% 23% 11%	5090
	21st to end	Night	43% 4 11% 27% 14% 2	5588
April	1st to 10th	Night	38% 6% 13% 23% 18% 3	2263
	11th to 20th	Night	37% 5% 10% 21% 22% 5%	2054
	21st to end	Night	40% 7% 11% 26% 14% 1	1890
May	1st to 10th	Night	50% 6% 13% 22% 8% 1	5264
	11th to 20th	Night	47% 5% 15% 21% 12%	5235
	21st to end	Night	53% 7% 13% 17% 9% 1	5771
June	1st to 10th	Night	38% 11% 17% 21% 12% 1	1890
	11th to 20th	Night	29% 11% 22% 25% 12% 1	1890
	21st to end	Night	37% 9% 15% 22% 12% 4	1890
July	1st to 10th	Night	40% 8% 22% 23% 7%	5235
	11th to 20th	Night	46% 8% 24% 17% 3 1	5226
	21st to end	Night	54% 8% 19% 12% 6% 1	5606
August	1st to 10th	Night	41% 7% 17% 26% 9%	2994
	11th to 20th	Night	38% 6% 20% 24% 11%	3083
	21st to end	Night	32% 6% 13% 34% 13% 1	3676
September	1st to 10th	Night	40% 8% 15% 17% 16% 4	2168
	11th to 20th	Night	40% 9% 13% 18% 19% 1	2200
	21st to end	Night	39% 7% 12% 20% 19% 5%	2200
October	1st to 10th	Night	31% 3 6% 22% 28% 10%	3590
	11th to 20th	Night	26% 3 6% 23% 28% 15%	3824
	21st to end	Night	25% 2 5% 28% 26% 13%	4274
November	1st to 10th	Night	37% 4 8% 21% 23% 6%	2666
	11th to 20th	Night	39% 4 7% 20% 24% 6%	2730
	21st to end	Night	42% 4 8% 23% 19% 4	2730
December	1st to 10th	Night	51% 3 7% 16% 21% 2	4380
	11th to 20th	Night	54% 3 8% 18% 15% 1	4954
	21st to end	Night	52% 4 14% 18% 10% 1	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	24% 22% 29% 21% 4	330
	11th to 20th	Day	28% 22% 28% 16% 5% 1	330
	21st to end	Day	23% 21% 37% 14% 4	363
February	1st to 10th	Day	23% 19% 31% 20% 7%	330
	11th to 20th	Day	36% 22% 27% 13% 2	330
	21st to end	Day	34% 19% 31% 15% 2	273
March	1st to 10th	Day	26% 17% 32% 16% 8% 1	396
	11th to 20th	Day	22% 17% 35% 20% 6%	540
	21st to end	Day	25% 14% 33% 21% 7%	594
April	1st to 10th	Day	20% 16% 24% 28% 10% 2	540
	11th to 20th	Day	18% 14% 29% 23% 14% 2	532
	21st to end	Day	19% 13% 27% 25% 13% 4	540
May	1st to 10th	Day	17% 13% 30% 22% 14% 4	543
	11th to 20th	Day	13% 9% 25% 24% 21% 8%	567
	21st to end	Day	16% 6% 20% 24% 19% 13%	617
June	1st to 10th	Day	14% 5% 18% 31% 21% 11%	570
	11th to 20th	Day	8% 4 13% 31% 29% 15%	570
	21st to end	Day	10% 4 15% 27% 26% 18%	570
July	1st to 10th	Day	10% 4 11% 24% 29% 23%	565
	11th to 20th	Day	13% 2 8% 28% 28% 21%	564
	21st to end	Day	11% 4 10% 27% 30% 19%	620
August	1st to 10th	Day	16% 5% 10% 22% 29% 18%	566
	11th to 20th	Day	10% 3 11% 26% 33% 17%	559
	21st to end	Day	12% 1 9% 24% 32% 21%	619
September	1st to 10th	Day	11% 4 10% 27% 35% 14%	530
	11th to 20th	Day	15% 3 8% 24% 30% 20%	530
	21st to end	Day	15% 6% 15% 27% 30% 8%	530
October	1st to 10th	Day	13% 6% 16% 28% 26% 11%	530
	11th to 20th	Day	14% 9% 21% 32% 21% 4	530
	21st to end	Day	21% 8% 19% 30% 20% 3	568
November	1st to 10th	Day	17% 10% 27% 29% 13% 3	330
	11th to 20th	Day	14% 14% 31% 31% 9% 1	330
	21st to end	Day	16% 10% 33% 28% 12% 1	330
December	1st to 10th	Day	26% 17% 33% 20% 4	330
	11th to 20th	Day	22% 15% 31% 24% 8% 1	330
	21st to end	Day	24% 18% 28% 20% 9% 1	363
January	1st to 10th	Night	24% 13% 28% 30% 4	840
	11th to 20th	Night	25% 14% 31% 26% 4	840
	21st to end	Night	21% 13% 34% 30% 2	924
February	1st to 10th	Night	22% 11% 31% 33% 4	840
	11th to 20th	Night	28% 16% 33% 22% 1	823
	21st to end	Night	30% 14% 31% 23% 2	692
March	1st to 10th	Night	23% 13% 28% 31% 5%	840
	11th to 20th	Night	23% 11% 33% 27% 6% 1	840
	21st to end	Night	21% 10% 31% 29% 8%	924
April	1st to 10th	Night	17% 10% 30% 33% 10% 1	793
	11th to 20th	Night	16% 9% 31% 30% 14%	623
	21st to end	Night	15% 6% 25% 38% 14% 1	630
May	1st to 10th	Night	15% 6% 24% 36% 17% 3	630
	11th to 20th	Night	16% 5% 18% 34% 24% 3	621
	21st to end	Night	12% 3 13% 33% 36% 4	683
June	1st to 10th	Night	10% 2 13% 37% 33% 4	630
	11th to 20th	Night	5% 3 12% 35% 36% 9%	630
	21st to end	Night	8% 2 10% 33% 40% 7%	630
July	1st to 10th	Night	9% 2 6% 25% 46% 11%	615
	11th to 20th	Night	10% 3 4 26% 46% 12%	612
	21st to end	Night	11% 2 6% 28% 41% 11%	690
August	1st to 10th	Night	11% 2 6% 26% 46% 9%	627
	11th to 20th	Night	11% 3 6% 29% 45% 7%	624
	21st to end	Night	11% 2 6% 26% 44% 11%	687
September	1st to 10th	Night	11% 4 7% 30% 40% 9%	768
	11th to 20th	Night	14% 4 8% 30% 39% 6%	800
	21st to end	Night	14% 3 13% 34% 33% 3	800
October	1st to 10th	Night	14% 4 16% 26% 32% 8%	800
	11th to 20th	Night	17% 5% 20% 36% 20% 2	800
	21st to end	Night	17% 5% 21% 38% 17% 2	880
November	1st to 10th	Night	17% 5% 18% 38% 20% 2	820
	11th to 20th	Night	17% 10% 27% 34% 12% 1	840
	21st to end	Night	20% 9% 24% 35% 12%	840
December	1st to 10th	Night	26% 10% 25% 32% 7%	840
	11th to 20th	Night	22% 10% 25% 34% 9%	840
	21st to end	Night	24% 13% 22% 35% 6%	924

Page generated at 2026-08-27 04:07:15. Version ac07

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