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 2024-03-01.

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	14% 7% 3 6% 6% 3 5% 5% 6% 7% 38%	78842
	Night	15% 8% 3 6% 5% 3 4 4 5% 7% 40%	80574
Transparency	Day	45% 8% 12% 18% 15% 3	78565
	Night	44% 7% 12% 19% 16% 3	80370
Seeing	Day	18% 9% 20% 24% 20% 9%	13873
	Night	18% 7% 20% 31% 20% 3	24031

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% 10% 3 7% 7% 3 5% 4 7% 6% 30%	2836
	11th to 20th	Day	18% 10% 4 7% 6% 4 5% 5% 5% 6% 31%	2840
	21st to end	Day	23% 12% 3 6% 5% 3 4 3 4 6% 32%	3124
February	1st to 10th	Day	20% 8% 4 8% 5% 2 4 4 5% 6% 34%	1890
	11th to 20th	Day	21% 10% 4 7% 5% 3 3 3 4 6% 34%	1848
	21st to end	Day	21% 8% 3 5% 5% 3 5% 4 5% 6% 35%	1570
March	1st to 10th	Day	16% 8% 3 4 5% 3 4 4 6% 6% 40%	1856
	11th to 20th	Day	17% 8% 4 6% 6% 4 4 5% 6% 6% 34%	1980
	21st to end	Day	17% 8% 4 6% 5% 4 4 5% 5% 6% 35%	2178
April	1st to 10th	Day	11% 5% 2 6% 4 3 6% 6% 6% 8% 43%	2034
	11th to 20th	Day	14% 5% 2 5% 5% 3 4 5% 5% 6% 45%	2150
	21st to end	Day	14% 6% 2 6% 4 3 5% 5% 5% 7% 42%	2340
May	1st to 10th	Day	13% 5% 2 5% 5% 3 6% 5% 6% 7% 44%	2340
	11th to 20th	Day	13% 5% 3 6% 8% 4 6% 4 5% 7% 37%	2301
	21st to end	Day	11% 5% 3 6% 6% 4 6% 7% 7% 9% 37%	2531
June	1st to 10th	Day	9% 5% 3 6% 7% 4 6% 7% 7% 9% 38%	2340
	11th to 20th	Day	5% 5% 2 5% 6% 5% 7% 7% 8% 10% 41%	2340
	21st to end	Day	8% 4 2 5% 6% 4 6% 6% 7% 11% 38%	2340
July	1st to 10th	Day	9% 6% 3 6% 7% 4 7% 7% 8% 11% 31%	2340
	11th to 20th	Day	10% 5% 3 6% 7% 4 7% 7% 9% 10% 33%	2340
	21st to end	Day	8% 5% 3 6% 8% 4 7% 8% 9% 10% 31%	2547
August	1st to 10th	Day	10% 5% 3 7% 6% 5% 6% 8% 7% 11% 32%	2327
	11th to 20th	Day	10% 5% 2 7% 8% 4 5% 7% 7% 9% 35%	2256
	21st to end	Day	11% 7% 3 7% 6% 4 6% 6% 7% 9% 35%	2376
September	1st to 10th	Day	11% 6% 3 5% 6% 3 4 5% 5% 8% 43%	1990
	11th to 20th	Day	16% 6% 2 6% 5% 3 4 5% 5% 7% 41%	1980
	21st to end	Day	14% 5% 2 4 4 3 4 5% 6% 7% 47%	1980
October	1st to 10th	Day	12% 4 2 4 3 3 4 4 4 5% 54%	1980
	11th to 20th	Day	14% 5% 2 4 4 2 3 3 4 7% 51%	1842
	21st to end	Day	16% 5% 1 4 4 2 4 4 4 6% 49%	1967
November	1st to 10th	Day	12% 4 2 5% 3 2 3 3 5% 5% 55%	1672
	11th to 20th	Day	12% 6% 2 5% 5% 2 4 4 5% 7% 49%	1710
	21st to end	Day	14% 8% 3 5% 4 2 4 5% 4 7% 44%	1710
December	1st to 10th	Day	20% 9% 4 6% 5% 3 4 6% 5% 6% 33%	1710
	11th to 20th	Day	16% 12% 3 6% 4 3 4 5% 5% 6% 36%	2153
	21st to end	Day	17% 15% 3 6% 6% 3 4 4 5% 6% 31%	3124
January	1st to 10th	Night	20% 12% 4 7% 5% 3 3 4 4 6% 33%	4109
	11th to 20th	Night	22% 9% 3 5% 6% 3 3 3 4 5% 37%	4120
	21st to end	Night	23% 11% 4 6% 5% 2 3 4 3 4 34%	4532
February	1st to 10th	Night	17% 9% 4 6% 4 3 5% 5% 5% 7% 36%	2288
	11th to 20th	Night	23% 9% 4 5% 5% 3 4 4 4 4 35%	2218
	21st to end	Night	23% 9% 3 6% 5% 3 4 4 5% 6% 32%	1884
March	1st to 10th	Night	16% 9% 3 5% 5% 3 4 4 5% 6% 40%	2109
	11th to 20th	Night	19% 7% 3 6% 5% 4 5% 4 4 7% 37%	1980
	21st to end	Night	16% 8% 3 6% 5% 3 5% 5% 4 7% 38%	2178
April	1st to 10th	Night	12% 6% 3 5% 4 3 4 4 5% 8% 48%	1940
	11th to 20th	Night	13% 7% 2 5% 4 3 4 3 5% 6% 47%	1757
	21st to end	Night	14% 5% 2 7% 4 3 4 5% 5% 8% 44%	1620
May	1st to 10th	Night	12% 5% 3 6% 4 4 5% 5% 7% 9% 41%	1620
	11th to 20th	Night	14% 6% 3 6% 5% 3 3 4 6% 11% 39%	1592
	21st to end	Night	7% 6% 3 7% 6% 4 6% 6% 5% 11% 40%	1744
June	1st to 10th	Night	7% 5% 3 6% 6% 4 6% 6% 9% 11% 37%	1620
	11th to 20th	Night	3 4 2 4 5% 3 5% 6% 8% 13% 46%	1620
	21st to end	Night	7% 4 3 6% 5% 4 5% 6% 6% 12% 41%	1620
July	1st to 10th	Night	10% 7% 2 6% 6% 4 7% 6% 8% 10% 33%	1620
	11th to 20th	Night	8% 4 3 5% 5% 4 6% 7% 8% 12% 38%	1620
	21st to end	Night	7% 5% 3 5% 7% 4 6% 7% 10% 12% 35%	1771
August	1st to 10th	Night	8% 5% 2 6% 5% 4 5% 7% 7% 10% 41%	1611
	11th to 20th	Night	9% 7% 4 7% 7% 4 6% 6% 6% 9% 37%	1642
	21st to end	Night	10% 6% 3 7% 6% 4 5% 6% 7% 11% 37%	1980
September	1st to 10th	Night	10% 6% 2 6% 5% 4 5% 5% 6% 8% 43%	1950
	11th to 20th	Night	12% 6% 3 7% 5% 3 5% 5% 5% 7% 42%	1980
	21st to end	Night	11% 5% 2 4 5% 4 4 5% 5% 7% 48%	1980
October	1st to 10th	Night	12% 6% 2 4 4 2 3 3 4 6% 54%	1980
	11th to 20th	Night	17% 4 2 4 4 2 3 4 4 5% 50%	2115
	21st to end	Night	14% 6% 2 4 4 2 3 3 4 6% 51%	2384
November	1st to 10th	Night	13% 7% 2 4 4 2 3 3 4 5% 52%	2406
	11th to 20th	Night	14% 8% 2 5% 4 2 4 3 4 7% 47%	2470
	21st to end	Night	15% 6% 3 4 5% 2 4 4 5% 6% 45%	2470
December	1st to 10th	Night	20% 9% 4 6% 5% 3 3 4 5% 6% 34%	2470
	11th to 20th	Night	18% 11% 4 6% 4 2 3 4 4 6% 38%	3042
	21st to end	Night	19% 12% 3 7% 5% 4 5% 5% 6% 7% 26%	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	51% 5% 10% 17% 15% 2	2837
	11th to 20th	Day	55% 5% 9% 13% 16% 1	2840
	21st to end	Day	54% 4 9% 19% 13% 1	3124
February	1st to 10th	Day	53% 5% 8% 16% 15% 2	1890
	11th to 20th	Day	55% 4 7% 17% 15% 2	1858
	21st to end	Day	52% 5% 8% 13% 17% 6%	1570
March	1st to 10th	Day	46% 5% 8% 18% 18% 5%	1856
	11th to 20th	Day	51% 7% 10% 16% 13% 3	1980
	21st to end	Day	50% 6% 11% 20% 11% 2	2178
April	1st to 10th	Day	38% 9% 11% 23% 17% 2	2034
	11th to 20th	Day	40% 6% 9% 17% 24% 4	2150
	21st to end	Day	42% 7% 11% 25% 13% 2	2340
May	1st to 10th	Day	41% 9% 12% 23% 13% 2	2340
	11th to 20th	Day	48% 9% 12% 18% 11% 1	2305
	21st to end	Day	43% 12% 13% 19% 12% 1	2531
June	1st to 10th	Day	42% 12% 14% 19% 11% 2	2340
	11th to 20th	Day	37% 13% 18% 19% 11% 2	2340
	21st to end	Day	39% 13% 16% 17% 12% 3	2340
July	1st to 10th	Day	44% 14% 16% 15% 10% 1	2275
	11th to 20th	Day	43% 13% 17% 12% 11% 4	2271
	21st to end	Day	44% 13% 17% 17% 8%	2405
August	1st to 10th	Day	44% 13% 17% 18% 7% 1	2314
	11th to 20th	Day	45% 13% 16% 14% 11% 1	2256
	21st to end	Day	45% 12% 15% 15% 10% 3	2376
September	1st to 10th	Day	41% 9% 13% 17% 16% 5%	1990
	11th to 20th	Day	44% 8% 11% 18% 16% 3	1980
	21st to end	Day	38% 7% 11% 20% 19% 5%	1980
October	1st to 10th	Day	33% 7% 11% 22% 22% 6%	1980
	11th to 20th	Day	34% 5% 9% 23% 23% 6%	1842
	21st to end	Day	36% 5% 7% 24% 23% 4	1967
November	1st to 10th	Day	33% 5% 9% 20% 28% 5%	1672
	11th to 20th	Day	37% 4 9% 22% 24% 5%	1710
	21st to end	Day	41% 5% 8% 21% 21% 4	1710
December	1st to 10th	Day	52% 8% 7% 19% 11% 2	1710
	11th to 20th	Day	50% 3 11% 17% 17% 2	2150
	21st to end	Day	53% 4 10% 23% 9% 1	3124
January	1st to 10th	Night	54% 4 9% 17% 14% 1	4109
	11th to 20th	Night	49% 4 11% 14% 18% 3	4120
	21st to end	Night	56% 4 9% 15% 15% 1	4532
February	1st to 10th	Night	49% 5% 9% 18% 16% 2	2288
	11th to 20th	Night	55% 5% 7% 16% 14% 4	2219
	21st to end	Night	53% 7% 8% 13% 15% 4	1884
March	1st to 10th	Night	47% 5% 9% 15% 19% 6%	2109
	11th to 20th	Night	49% 7% 8% 20% 14% 2	1980
	21st to end	Night	47% 6% 11% 21% 13% 2	2178
April	1st to 10th	Night	38% 6% 11% 23% 19% 3	1940
	11th to 20th	Night	38% 6% 10% 19% 21% 6%	1757
	21st to end	Night	40% 7% 11% 27% 14% 1	1620
May	1st to 10th	Night	40% 8% 15% 23% 13% 2	1620
	11th to 20th	Night	40% 10% 18% 20% 11% 1	1593
	21st to end	Night	40% 10% 14% 23% 11% 2	1745
June	1st to 10th	Night	38% 11% 17% 21% 11% 1	1620
	11th to 20th	Night	27% 12% 23% 25% 11% 1	1620
	21st to end	Night	37% 10% 15% 22% 11% 4	1620
July	1st to 10th	Night	43% 14% 15% 17% 11% 1	1575
	11th to 20th	Night	35% 13% 22% 16% 9% 4	1566
	21st to end	Night	37% 14% 20% 20% 8% 1	1672
August	1st to 10th	Night	36% 13% 19% 23% 10%	1600
	11th to 20th	Night	42% 12% 16% 16% 13% 1	1642
	21st to end	Night	40% 11% 17% 20% 11% 1	1980
September	1st to 10th	Night	39% 9% 15% 18% 15% 4	1950
	11th to 20th	Night	40% 10% 13% 16% 20% 1	1980
	21st to end	Night	36% 7% 11% 20% 20% 5%	1980
October	1st to 10th	Night	32% 6% 10% 20% 25% 6%	1980
	11th to 20th	Night	37% 5% 9% 21% 21% 6%	2115
	21st to end	Night	34% 4 8% 21% 25% 7%	2384
November	1st to 10th	Night	37% 5% 7% 20% 25% 7%	2406
	11th to 20th	Night	39% 4 7% 19% 23% 7%	2470
	21st to end	Night	41% 5% 8% 23% 20% 4	2470
December	1st to 10th	Night	54% 6% 10% 16% 12% 3	2470
	11th to 20th	Night	49% 4 9% 17% 19% 2	3044
	21st to end	Night	56% 6% 10% 17% 10% 1	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	22% 24% 28% 21% 4	270
	11th to 20th	Day	31% 22% 25% 16% 4 1	270
	21st to end	Day	23% 21% 37% 14% 5%	297
February	1st to 10th	Day	26% 18% 29% 19% 7%	270
	11th to 20th	Day	37% 20% 27% 14% 2	270
	21st to end	Day	37% 19% 30% 12% 1	225
March	1st to 10th	Day	24% 15% 34% 18% 8%	296
	11th to 20th	Day	22% 17% 36% 18% 7%	420
	21st to end	Day	26% 14% 31% 21% 8%	462
April	1st to 10th	Day	20% 17% 21% 29% 11% 2	420
	11th to 20th	Day	19% 13% 28% 22% 14% 3	412
	21st to end	Day	19% 12% 27% 25% 14% 4	420
May	1st to 10th	Day	17% 12% 29% 23% 15% 5%	423
	11th to 20th	Day	14% 7% 24% 22% 24% 9%	447
	21st to end	Day	16% 4 17% 24% 21% 17%	485
June	1st to 10th	Day	14% 4 16% 31% 23% 12%	450
	11th to 20th	Day	9% 3 12% 29% 30% 17%	450
	21st to end	Day	11% 3 16% 29% 26% 15%	450
July	1st to 10th	Day	11% 3 12% 22% 29% 23%	445
	11th to 20th	Day	13% 1 9% 30% 28% 20%	444
	21st to end	Day	10% 2 7% 28% 33% 20%	488
August	1st to 10th	Day	17% 4 9% 22% 30% 18%	446
	11th to 20th	Day	12% 3 10% 27% 34% 14%	439
	21st to end	Day	15% 1 8% 22% 33% 20%	495
September	1st to 10th	Day	10% 4 9% 25% 36% 15%	450
	11th to 20th	Day	16% 3 9% 23% 30% 19%	450
	21st to end	Day	14% 5% 13% 28% 32% 8%	450
October	1st to 10th	Day	14% 5% 17% 27% 26% 11%	450
	11th to 20th	Day	15% 10% 21% 30% 20% 5%	450
	21st to end	Day	22% 7% 18% 31% 19% 3	482
November	1st to 10th	Day	18% 9% 26% 30% 15% 3	270
	11th to 20th	Day	15% 13% 33% 31% 8% 1	270
	21st to end	Day	15% 9% 33% 29% 13% 1	270
December	1st to 10th	Day	27% 16% 30% 20% 5%	270
	11th to 20th	Day	24% 13% 29% 24% 10% 1	270
	21st to end	Day	26% 16% 29% 21% 7% 1	297
January	1st to 10th	Night	24% 13% 27% 30% 4	760
	11th to 20th	Night	25% 14% 30% 26% 5%	760
	21st to end	Night	22% 13% 32% 30% 2	836
February	1st to 10th	Night	22% 11% 31% 32% 4	760
	11th to 20th	Night	28% 15% 32% 23% 2	743
	21st to end	Night	30% 14% 31% 22% 2	628
March	1st to 10th	Night	23% 13% 29% 32% 4	723
	11th to 20th	Night	24% 10% 32% 26% 7% 1	720
	21st to end	Night	22% 10% 29% 29% 9%	792
April	1st to 10th	Night	17% 10% 29% 34% 10% 1	680
	11th to 20th	Night	17% 9% 31% 28% 15%	533
	21st to end	Night	16% 6% 26% 38% 14% 1	540
May	1st to 10th	Night	15% 5% 23% 36% 18% 3	540
	11th to 20th	Night	16% 4 19% 32% 26% 4	531
	21st to end	Night	8% 2 13% 31% 41% 4	584
June	1st to 10th	Night	9% 2 13% 36% 36% 4	540
	11th to 20th	Night	4 3 12% 34% 36% 10%	540
	21st to end	Night	8% 2 11% 34% 39% 7%	540
July	1st to 10th	Night	10% 2 6% 26% 46% 10%	525
	11th to 20th	Night	9% 3 5% 27% 45% 11%	522
	21st to end	Night	8% 2 6% 28% 44% 12%	591
August	1st to 10th	Night	9% 2 6% 26% 47% 10%	537
	11th to 20th	Night	11% 3 5% 30% 44% 6%	534
	21st to end	Night	12% 2 6% 25% 44% 11%	594
September	1st to 10th	Night	11% 4 7% 29% 41% 9%	690
	11th to 20th	Night	15% 4 8% 29% 38% 6%	720
	21st to end	Night	13% 2 13% 34% 34% 3	720
October	1st to 10th	Night	14% 4 17% 25% 32% 8%	720
	11th to 20th	Night	19% 5% 20% 34% 20% 2	720
	21st to end	Night	17% 5% 21% 37% 18% 2	792
November	1st to 10th	Night	17% 5% 18% 36% 21% 3	740
	11th to 20th	Night	16% 9% 27% 34% 13% 1	760
	21st to end	Night	20% 9% 23% 36% 13%	760
December	1st to 10th	Night	26% 10% 24% 32% 7%	760
	11th to 20th	Night	22% 10% 24% 34% 10%	760
	21st to end	Night	25% 13% 21% 35% 6%	836

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