Show-Me-Stars Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Show-Me-Stars Observatory clear sky chart from 2005-11-06 to 2024-01-27.

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 5% 5% 3 4 5% 5% 7% 44%	74816
	Night	13% 6% 2 5% 4 3 4 4 5% 7% 48%	75246
Transparency	Day	39% 6% 11% 24% 17% 3	74533
	Night	36% 5% 11% 25% 19% 4	75051
Seeing	Day	17% 10% 25% 25% 17% 5%	14380
	Night	17% 10% 27% 28% 15% 2	24342

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% 7% 3 5% 4 2 3 3 3 6% 48%	1621
	11th to 20th	Day	16% 8% 3 6% 4 2 4 4 5% 6% 42%	1710
	21st to end	Day	16% 8% 3 5% 5% 2 3 4 4 6% 47%	1836
February	1st to 10th	Day	18% 7% 3 6% 5% 3 4 3 5% 5% 42%	1620
	11th to 20th	Day	17% 7% 3 6% 5% 3 3 4 5% 6% 41%	1716
	21st to end	Day	17% 9% 3 6% 6% 2 5% 5% 4 5% 38%	1480
March	1st to 10th	Day	17% 7% 3 4 4 2 2 3 4 6% 47%	1912
	11th to 20th	Day	21% 8% 3 5% 5% 2 4 4 4 6% 39%	1980
	21st to end	Day	20% 8% 3 6% 5% 3 4 5% 5% 8% 33%	2240
April	1st to 10th	Day	13% 7% 3 5% 5% 2 4 4 5% 6% 46%	2160
	11th to 20th	Day	17% 7% 3 5% 4 3 4 5% 5% 6% 40%	2134
	21st to end	Day	18% 6% 3 6% 6% 3 5% 4 5% 6% 38%	2160
May	1st to 10th	Day	15% 7% 3 6% 5% 3 5% 4 5% 8% 38%	2160
	11th to 20th	Day	14% 6% 2 4 6% 3 5% 5% 5% 8% 41%	2337
	21st to end	Day	10% 5% 3 7% 6% 4 6% 6% 8% 9% 36%	2725
June	1st to 10th	Day	8% 5% 2 6% 6% 4 5% 5% 6% 9% 44%	2520
	11th to 20th	Day	5% 3 2 4 5% 3 6% 6% 7% 10% 49%	2520
	21st to end	Day	4 3 2 4 4 3 6% 7% 7% 10% 50%	2520
July	1st to 10th	Day	8% 5% 2 6% 5% 4 5% 7% 7% 11% 40%	2520
	11th to 20th	Day	4 4 2 4 5% 3 5% 7% 6% 11% 49%	2376
	21st to end	Day	7% 4 2 5% 6% 4 7% 6% 7% 11% 42%	2546
August	1st to 10th	Day	7% 4 2 4 5% 4 6% 7% 8% 11% 41%	2324
	11th to 20th	Day	9% 6% 2 5% 5% 3 5% 6% 6% 9% 44%	2125
	21st to end	Day	7% 4 2 5% 5% 3 5% 6% 6% 10% 47%	2376
September	1st to 10th	Day	10% 5% 2 6% 4 3 4 5% 4 9% 48%	2160
	11th to 20th	Day	12% 5% 2 5% 4 3 4 4 5% 7% 49%	2160
	21st to end	Day	10% 4 1 5% 4 2 3 3 5% 8% 56%	1926
October	1st to 10th	Day	9% 5% 2 4 4 3 4 4 6% 6% 54%	1800
	11th to 20th	Day	14% 6% 2 4 4 2 2 3 4 4 55%	1800
	21st to end	Day	19% 6% 2 5% 4 2 3 4 3 6% 46%	1980
November	1st to 10th	Day	12% 5% 2 4 4 3 2 3 4 5% 56%	1778
	11th to 20th	Day	13% 5% 2 4 4 3 3 3 5% 6% 52%	1710
	21st to end	Day	20% 6% 3 5% 4 2 3 4 3 4 47%	1663
December	1st to 10th	Day	17% 8% 2 5% 5% 2 3 4 4 6% 44%	1520
	11th to 20th	Day	17% 8% 4 5% 5% 3 4 4 3 5% 43%	1918
	21st to end	Day	15% 14% 3 6% 5% 3 4 4 5% 6% 35%	2783
January	1st to 10th	Night	17% 5% 2 5% 3 3 4 4 5% 6% 46%	2539
	11th to 20th	Night	18% 6% 3 5% 3 2 4 3 5% 6% 46%	2470
	21st to end	Night	16% 8% 2 5% 5% 3 3 4 3 6% 45%	2665
February	1st to 10th	Night	18% 8% 3 6% 4 2 4 3 5% 5% 42%	2340
	11th to 20th	Night	17% 6% 3 5% 5% 2 3 3 3 6% 46%	2127
	21st to end	Night	18% 8% 2 4 4 3 3 3 4 6% 43%	1776
March	1st to 10th	Night	18% 6% 2 4 4 3 4 3 5% 6% 45%	2062
	11th to 20th	Night	19% 8% 3 5% 4 3 4 4 5% 7% 39%	1980
	21st to end	Night	19% 8% 4 6% 5% 3 5% 4 5% 6% 36%	2116
April	1st to 10th	Night	10% 5% 2 4 4 2 4 4 5% 7% 52%	1800
	11th to 20th	Night	14% 6% 2 4 5% 3 3 5% 5% 6% 47%	1775
	21st to end	Night	18% 6% 2 5% 5% 3 3 5% 6% 6% 42%	1800
May	1st to 10th	Night	14% 5% 2 5% 4 2 4 3 4 8% 49%	1800
	11th to 20th	Night	15% 6% 2 4 4 2 3 4 5% 6% 48%	1551
	21st to end	Night	9% 6% 3 7% 6% 3 5% 5% 6% 9% 41%	1551
June	1st to 10th	Night	8% 5% 3 4 4 3 4 4 5% 10% 51%	1440
	11th to 20th	Night	4 3 1 3 3 2 3 4 6% 11% 59%	1440
	21st to end	Night	4 3 1 3 3 3 4 4 6% 9% 60%	1440
July	1st to 10th	Night	5% 3 2 4 4 3 4 5% 7% 11% 52%	1440
	11th to 20th	Night	3 3 1 3 3 2 5% 5% 7% 9% 58%	1579
	21st to end	Night	5% 3 2 4 5% 3 5% 5% 6% 10% 52%	1772
August	1st to 10th	Night	5% 4 3 4 4 4 5% 4 6% 10% 52%	1612
	11th to 20th	Night	7% 4 2 4 4 3 5% 4 7% 8% 53%	1776
	21st to end	Night	7% 4 1 5% 4 2 5% 4 6% 10% 53%	1980
September	1st to 10th	Night	9% 5% 2 4 3 2 3 4 5% 9% 53%	1800
	11th to 20th	Night	8% 5% 2 5% 5% 2 4 5% 6% 8% 50%	1800
	21st to end	Night	8% 4 2 4 4 2 3 4 5% 7% 59%	2011
October	1st to 10th	Night	8% 4 2 4 3 2 3 3 4 6% 62%	2160
	11th to 20th	Night	13% 5% 1 4 3 2 3 3 3 6% 57%	2160
	21st to end	Night	19% 5% 2 5% 4 2 3 3 3 5% 49%	2376
November	1st to 10th	Night	12% 5% 2 3 3 2 2 3 4 5% 59%	2300
	11th to 20th	Night	14% 5% 2 4 3 2 3 4 5% 6% 54%	2470
	21st to end	Night	17% 6% 2 5% 4 2 4 3 3 6% 48%	2515
December	1st to 10th	Night	16% 8% 3 5% 4 2 3 3 4 6% 45%	2660
	11th to 20th	Night	17% 7% 3 6% 5% 3 3 4 4 6% 44%	3279
	21st to end	Night	18% 11% 3 7% 6% 4 5% 4 5% 6% 32%	4884

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	41% 3 8% 27% 16% 5%	1622
	11th to 20th	Day	44% 4 11% 24% 16% 2	1710
	21st to end	Day	40% 3 13% 24% 16% 4	1836
February	1st to 10th	Day	45% 4 10% 24% 14% 2	1620
	11th to 20th	Day	46% 4 10% 22% 15% 3	1726
	21st to end	Day	49% 4 8% 20% 13% 6%	1480
March	1st to 10th	Day	40% 4 9% 22% 19% 6%	1912
	11th to 20th	Day	49% 4 7% 20% 16% 4	1980
	21st to end	Day	50% 6% 11% 20% 11% 2	2240
April	1st to 10th	Day	39% 4 10% 26% 19% 2	2160
	11th to 20th	Day	44% 6% 10% 20% 16% 4	2134
	21st to end	Day	47% 6% 9% 21% 16% 1	2160
May	1st to 10th	Day	46% 6% 12% 21% 14% 1	2160
	11th to 20th	Day	40% 8% 13% 22% 14% 2	2341
	21st to end	Day	42% 9% 15% 21% 12% 2	2725
June	1st to 10th	Day	36% 9% 14% 25% 16% 1	2520
	11th to 20th	Day	29% 8% 14% 30% 16% 4	2520
	21st to end	Day	27% 8% 17% 25% 18% 4	2520
July	1st to 10th	Day	35% 10% 16% 22% 13% 4	2451
	11th to 20th	Day	28% 8% 15% 26% 18% 4	2305
	21st to end	Day	34% 9% 13% 31% 12% 1	2405
August	1st to 10th	Day	33% 9% 16% 27% 13% 1	2310
	11th to 20th	Day	36% 8% 13% 27% 14% 2	2125
	21st to end	Day	32% 8% 17% 22% 16% 6%	2376
September	1st to 10th	Day	34% 6% 11% 26% 16% 6%	2160
	11th to 20th	Day	35% 5% 9% 22% 27% 2	2160
	21st to end	Day	29% 5% 8% 26% 29% 3	1926
October	1st to 10th	Day	29% 6% 10% 24% 25% 6%	1800
	11th to 20th	Day	34% 3 6% 24% 25% 7%	1800
	21st to end	Day	41% 4 7% 24% 18% 6%	1980
November	1st to 10th	Day	32% 4 10% 25% 23% 7%	1778
	11th to 20th	Day	34% 3 7% 24% 24% 7%	1710
	21st to end	Day	43% 3 8% 22% 22% 3	1663
December	1st to 10th	Day	42% 5% 9% 26% 15% 3	1520
	11th to 20th	Day	45% 5% 7% 21% 21% 2	1915
	21st to end	Day	50% 5% 11% 17% 13% 4	2783
January	1st to 10th	Night	40% 4 9% 24% 20% 3	2539
	11th to 20th	Night	41% 3 11% 26% 17% 3	2470
	21st to end	Night	41% 4 10% 26% 17% 3	2665
February	1st to 10th	Night	45% 4 9% 24% 16% 2	2340
	11th to 20th	Night	41% 3 10% 23% 19% 3	2128
	21st to end	Night	43% 3 9% 21% 17% 6%	1776
March	1st to 10th	Night	41% 3 9% 20% 19% 8%	2062
	11th to 20th	Night	45% 6% 11% 19% 16% 3	1980
	21st to end	Night	50% 5% 9% 21% 14% 1	2116
April	1st to 10th	Night	32% 5% 12% 25% 21% 4	1800
	11th to 20th	Night	37% 5% 10% 24% 18% 6%	1775
	21st to end	Night	42% 7% 10% 22% 18% 1	1800
May	1st to 10th	Night	37% 5% 14% 24% 18% 2	1800
	11th to 20th	Night	37% 8% 12% 23% 17% 3	1552
	21st to end	Night	40% 8% 15% 22% 14% 2	1552
June	1st to 10th	Night	29% 7% 14% 27% 21% 2	1440
	11th to 20th	Night	19% 5% 13% 37% 20% 5%	1440
	21st to end	Night	20% 6% 16% 30% 20% 8%	1440
July	1st to 10th	Night	25% 10% 18% 26% 19% 3	1400
	11th to 20th	Night	21% 8% 17% 31% 19% 5%	1528
	21st to end	Night	27% 7% 13% 35% 17% 1	1673
August	1st to 10th	Night	27% 8% 17% 33% 14% 1	1602
	11th to 20th	Night	28% 7% 15% 29% 19% 2	1776
	21st to end	Night	28% 7% 17% 24% 18% 6%	1980
September	1st to 10th	Night	28% 7% 11% 30% 19% 6%	1800
	11th to 20th	Night	30% 7% 11% 24% 24% 4	1800
	21st to end	Night	26% 5% 10% 23% 31% 5%	2011
October	1st to 10th	Night	24% 4 10% 27% 28% 7%	2160
	11th to 20th	Night	31% 3 8% 24% 28% 7%	2160
	21st to end	Night	39% 4 8% 22% 20% 7%	2376
November	1st to 10th	Night	28% 3 9% 28% 25% 7%	2300
	11th to 20th	Night	32% 4 8% 23% 25% 8%	2470
	21st to end	Night	39% 3 7% 24% 24% 3	2515
December	1st to 10th	Night	42% 4 10% 23% 19% 3	2660
	11th to 20th	Night	42% 4 9% 23% 20% 2	3281
	21st to end	Night	51% 6% 12% 18% 11% 2	4884

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	29% 18% 36% 14% 3	270
	11th to 20th	Day	33% 23% 29% 14% 1	270
	21st to end	Day	24% 23% 39% 10% 3	282
February	1st to 10th	Day	29% 21% 36% 11% 3	240
	11th to 20th	Day	34% 22% 31% 10% 3	240
	21st to end	Day	39% 17% 33% 9% 2 1	198
March	1st to 10th	Day	30% 20% 35% 12% 3	240
	11th to 20th	Day	38% 14% 32% 15% 1	240
	21st to end	Day	30% 23% 32% 10% 5%	326
April	1st to 10th	Day	24% 15% 36% 18% 7% 1	420
	11th to 20th	Day	29% 16% 29% 18% 7%	412
	21st to end	Day	21% 20% 30% 22% 5% 2	420
May	1st to 10th	Day	22% 16% 33% 21% 7% 1	423
	11th to 20th	Day	19% 10% 29% 25% 14% 4	589
	21st to end	Day	12% 6% 30% 29% 17% 5%	679
June	1st to 10th	Day	9% 5% 21% 30% 25% 10%	630
	11th to 20th	Day	6% 3 22% 40% 25% 5%	630
	21st to end	Day	7% 4 28% 35% 22% 5%	630
July	1st to 10th	Day	9% 2 17% 31% 29% 11%	621
	11th to 20th	Day	6% 4 15% 33% 31% 11%	618
	21st to end	Day	9% 1 12% 33% 34% 11%	684
August	1st to 10th	Day	9% 3 12% 39% 30% 8%	622
	11th to 20th	Day	16% 3 15% 28% 30% 9%	439
	21st to end	Day	11% 1 11% 32% 30% 15%	495
September	1st to 10th	Day	9% 3 14% 36% 30% 8%	450
	11th to 20th	Day	9% 2 16% 32% 29% 13%	450
	21st to end	Day	12% 8% 22% 28% 21% 9%	378
October	1st to 10th	Day	11% 9% 30% 30% 16% 4	270
	11th to 20th	Day	19% 17% 34% 21% 8%	270
	21st to end	Day	30% 18% 27% 20% 5%	297
November	1st to 10th	Day	17% 13% 36% 23% 9% 1	270
	11th to 20th	Day	20% 17% 35% 16% 11% 1	270
	21st to end	Day	33% 13% 29% 16% 8% 1	270
December	1st to 10th	Day	22% 24% 29% 17% 7% 1	270
	11th to 20th	Day	28% 20% 30% 17% 5% 1	270
	21st to end	Day	30% 22% 34% 11% 4	297
January	1st to 10th	Night	23% 18% 34% 21% 4	950
	11th to 20th	Night	24% 19% 34% 18% 4	950
	21st to end	Night	23% 17% 36% 23% 2	1025
February	1st to 10th	Night	25% 16% 35% 22% 2	900
	11th to 20th	Night	24% 17% 40% 17% 2	732
	21st to end	Night	28% 18% 35% 16% 3	592
March	1st to 10th	Night	24% 15% 32% 26% 3	622
	11th to 20th	Night	24% 14% 31% 29% 3	540
	21st to end	Night	24% 12% 36% 23% 6%	594
April	1st to 10th	Night	15% 15% 40% 25% 6%	540
	11th to 20th	Night	17% 16% 31% 27% 9%	533
	21st to end	Night	21% 9% 38% 25% 6%	540
May	1st to 10th	Night	15% 6% 35% 31% 11% 1	540
	11th to 20th	Night	19% 6% 30% 27% 16% 2	531
	21st to end	Night	12% 5% 24% 37% 18% 4	584
June	1st to 10th	Night	10% 4 19% 32% 33% 2	540
	11th to 20th	Night	4 1 22% 44% 26% 3	540
	21st to end	Night	5% 2 19% 40% 30% 4	540
July	1st to 10th	Night	7% 1 10% 33% 41% 8%	525
	11th to 20th	Night	4 2 10% 36% 42% 7%	522
	21st to end	Night	5% 2 12% 36% 38% 7%	591
August	1st to 10th	Night	6% 1 10% 40% 39% 5%	537
	11th to 20th	Night	8% 1 13% 36% 38% 5%	534
	21st to end	Night	8% 1 10% 33% 41% 6%	594
September	1st to 10th	Night	11% 2 12% 34% 35% 5%	540
	11th to 20th	Night	10% 1 14% 31% 38% 6%	540
	21st to end	Night	10% 5% 22% 31% 29% 4	684
October	1st to 10th	Night	10% 5% 22% 34% 27% 3	720
	11th to 20th	Night	15% 10% 31% 29% 13% 1	720
	21st to end	Night	23% 10% 28% 29% 10% 1	792
November	1st to 10th	Night	14% 9% 32% 32% 13% 1	740
	11th to 20th	Night	18% 10% 33% 28% 10%	760
	21st to end	Night	23% 12% 28% 27% 9%	805
December	1st to 10th	Night	23% 12% 31% 27% 5%	950
	11th to 20th	Night	25% 12% 28% 29% 5%	950
	21st to end	Night	27% 14% 31% 24% 3	1045

Page generated at 2024-01-24 08:37:29. Version ac07

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