Lookout Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lookout Mountain Observatory clear sky chart from 2005-11-06 to 2024-01-12.

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	2 3 2 4 4 3 5% 5% 6% 9% 59%	74711
	Night	2 3 1 3 3 2 3 4 5% 8% 65%	75027
Transparency	Day	21% 7% 13% 26% 24% 9%	74427
	Night	17% 6% 13% 27% 27% 9%	74833
Seeing	Day	7% 11% 27% 30% 19% 6%	14186
	Night	3 6% 32% 39% 18% 2	24406

By Month

Percentage Cloud Cover SW (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	2 1 2 3 2 4 4 5% 10% 68%	1570
	11th to 20th	Day	1 2 1 2 3 2 3 4 5% 9% 68%	1633
	21st to end	Day	2 2 4 4 3 4 3 5% 8% 66%	1782
February	1st to 10th	Day	2 1 4 3 2 3 5% 6% 8% 66%	1620
	11th to 20th	Day	1 1 1 3 2 2 4 4 6% 10% 67%	1700
	21st to end	Day	3 2 4 4 3 4 5% 6% 8% 62%	1480
March	1st to 10th	Day	1 3 1 3 3 2 4 3 5% 9% 65%	1882
	11th to 20th	Day	3 5% 2 3 4 3 4 5% 5% 8% 58%	1980
	21st to end	Day	1 4 2 5% 4 2 4 5% 6% 9% 57%	2245
April	1st to 10th	Day	1 4 2 3 3 2 4 3 6% 10% 63%	2160
	11th to 20th	Day	2 5% 2 5% 4 3 4 5% 6% 8% 58%	2131
	21st to end	Day	3 4 2 4 4 3 4 6% 7% 11% 53%	2160
May	1st to 10th	Day	4 4 2 3 4 3 4 5% 7% 10% 55%	2162
	11th to 20th	Day	3 5% 2 4 5% 4 6% 7% 7% 9% 49%	2419
	21st to end	Day	2 3 2 4 4 3 5% 6% 6% 8% 58%	2724
June	1st to 10th	Day	2 2 1 4 4 3 5% 6% 7% 8% 58%	2520
	11th to 20th	Day	2 2 1 2 3 3 4 5% 6% 7% 66%	2520
	21st to end	Day	2 3 1 4 4 3 7% 7% 8% 9% 53%	2520
July	1st to 10th	Day	3 3 1 4 5% 4 7% 8% 8% 10% 46%	2520
	11th to 20th	Day	3 3 2 4 6% 5% 8% 8% 9% 12% 42%	2441
	21st to end	Day	4 4 2 5% 7% 6% 9% 9% 10% 11% 33%	2545
August	1st to 10th	Day	5% 5% 2 6% 7% 4 8% 8% 9% 10% 38%	2328
	11th to 20th	Day	4 4 2 4 6% 4 6% 7% 8% 10% 45%	2141
	21st to end	Day	3 4 2 5% 4 3 6% 7% 9% 9% 48%	2376
September	1st to 10th	Day	3 3 2 5% 4 4 6% 6% 8% 10% 50%	2160
	11th to 20th	Day	3 4 2 4 4 2 3 5% 7% 8% 59%	2160
	21st to end	Day	3 3 2 2 3 3 4 4 5% 6% 67%	1941
October	1st to 10th	Day	3 2 1 4 3 2 4 6% 5% 8% 61%	1800
	11th to 20th	Day	1 1 1 2 2 2 3 3 3 5% 76%	1800
	21st to end	Day	2 3 1 3 3 2 2 3 4 6% 72%	1980
November	1st to 10th	Day	2 1 1 1 1 3 3 5% 7% 76%	1742
	11th to 20th	Day	1 1 2 1 1 2 3 3 6% 80%	1710
	21st to end	Day	1 2 1 2 3 2 2 3 4 6% 73%	1619
December	1st to 10th	Day	2 2 3 2 2 3 3 4 7% 71%	1520
	11th to 20th	Day	1 2 1 2 2 1 3 5% 7% 10% 66%	1926
	21st to end	Day	1 2 1 4 3 2 3 4 5% 9% 67%	2794
January	1st to 10th	Night	2 1 2 3 1 2 2 4 7% 76%	2610
	11th to 20th	Night	4 1 3 2 1 3 2 3 6% 73%	2366
	21st to end	Night	2 1 3 3 2 2 3 5% 8% 71%	2574
February	1st to 10th	Night	3 2 4 2 2 2 3 4 8% 70%	2340
	11th to 20th	Night	1 2 1 3 3 2 4 3 5% 8% 68%	2147
	21st to end	Night	3 1 3 3 2 3 2 4 8% 70%	1776
March	1st to 10th	Night	3 2 2 2 1 3 4 4 7% 71%	2075
	11th to 20th	Night	2 4 2 4 3 2 3 3 4 7% 65%	1980
	21st to end	Night	2 3 1 2 3 2 4 4 5% 8% 66%	2109
April	1st to 10th	Night	2 2 1 2 2 2 3 3 5% 8% 72%	1800
	11th to 20th	Night	3 5% 2 5% 3 3 3 4 5% 6% 62%	1777
	21st to end	Night	2 4 2 3 4 2 3 4 5% 8% 63%	1800
May	1st to 10th	Night	3 4 2 3 4 3 4 4 6% 6% 62%	1794
	11th to 20th	Night	5% 6% 2 3 4 3 4 5% 6% 8% 55%	1472
	21st to end	Night	4 3 2 2 3 3 3 5% 5% 8% 63%	1552
June	1st to 10th	Night	2 1 1 2 4 2 3 5% 5% 8% 68%	1440
	11th to 20th	Night	1 2 1 2 3 2 2 4 5% 8% 71%	1440
	21st to end	Night	3 2 1 2 4 3 4 5% 6% 10% 60%	1440
July	1st to 10th	Night	3 3 1 5% 6% 4 8% 7% 8% 10% 45%	1440
	11th to 20th	Night	3 2 1 5% 5% 3 5% 8% 7% 10% 50%	1515
	21st to end	Night	3 3 2 4 6% 3 8% 8% 9% 13% 39%	1773
August	1st to 10th	Night	4 3 1 4 5% 4 6% 7% 7% 11% 48%	1611
	11th to 20th	Night	4 4 2 5% 5% 3 6% 5% 8% 12% 46%	1757
	21st to end	Night	4 4 2 5% 6% 4 5% 7% 8% 10% 47%	1980
September	1st to 10th	Night	5% 3 2 5% 5% 3 4 6% 6% 9% 52%	1800
	11th to 20th	Night	5% 3 1 3 3 2 4 4 5% 7% 63%	1800
	21st to end	Night	4 3 1 3 3 2 2 3 4 6% 68%	2015
October	1st to 10th	Night	3 3 1 2 2 2 3 4 5% 8% 67%	2160
	11th to 20th	Night	1 1 1 1 1 1 3 3 4 6% 78%	2160
	21st to end	Night	3 3 2 2 3 2 2 2 4 6% 72%	2376
November	1st to 10th	Night	1 2 1 1 1 3 3 4 7% 77%	2315
	11th to 20th	Night	1 1 2 2 1 2 2 4 6% 80%	2470
	21st to end	Night	1 4 1 3 2 2 2 3 4 6% 72%	2559
December	1st to 10th	Night	1 1 3 2 2 3 3 5% 6% 74%	2660
	11th to 20th	Night	1 3 2 3 3 2 3 4 6% 9% 64%	3271
	21st to end	Night	1 3 2 4 4 2 3 4 5% 7% 66%	4873

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	13% 6% 15% 39% 24% 3	1571
	11th to 20th	Day	14% 5% 14% 34% 29% 3	1633
	21st to end	Day	17% 5% 12% 37% 22% 6%	1782
February	1st to 10th	Day	17% 6% 15% 33% 22% 8%	1620
	11th to 20th	Day	15% 6% 13% 33% 27% 6%	1710
	21st to end	Day	19% 5% 11% 25% 29% 11%	1480
March	1st to 10th	Day	16% 5% 14% 28% 31% 7%	1882
	11th to 20th	Day	23% 5% 10% 31% 26% 5%	1980
	21st to end	Day	22% 8% 11% 31% 23% 6%	2245
April	1st to 10th	Day	18% 6% 11% 28% 24% 12%	2160
	11th to 20th	Day	22% 6% 10% 27% 26% 9%	2134
	21st to end	Day	22% 7% 13% 27% 25% 6%	2160
May	1st to 10th	Day	23% 5% 11% 28% 25% 7%	2162
	11th to 20th	Day	28% 9% 16% 24% 18% 6%	2423
	21st to end	Day	21% 8% 12% 20% 26% 13%	2724
June	1st to 10th	Day	20% 8% 13% 23% 22% 14%	2520
	11th to 20th	Day	15% 6% 9% 19% 25% 26%	2520
	21st to end	Day	22% 8% 11% 21% 23% 15%	2520
July	1st to 10th	Day	29% 10% 15% 16% 18% 12%	2451
	11th to 20th	Day	28% 11% 20% 23% 11% 7%	2366
	21st to end	Day	38% 13% 27% 15% 7% 1	2404
August	1st to 10th	Day	37% 12% 18% 13% 12% 7%	2313
	11th to 20th	Day	30% 8% 17% 20% 17% 7%	2141
	21st to end	Day	27% 9% 17% 23% 19% 5%	2376
September	1st to 10th	Day	26% 7% 15% 20% 21% 10%	2160
	11th to 20th	Day	21% 6% 13% 20% 28% 12%	2160
	21st to end	Day	18% 4 8% 26% 35% 8%	1941
October	1st to 10th	Day	19% 8% 10% 26% 26% 10%	1800
	11th to 20th	Day	12% 4 6% 25% 40% 13%	1800
	21st to end	Day	16% 3 9% 32% 33% 8%	1980
November	1st to 10th	Day	9% 3 10% 30% 37% 10%	1742
	11th to 20th	Day	8% 3 11% 38% 34% 6%	1710
	21st to end	Day	13% 4 10% 32% 31% 10%	1619
December	1st to 10th	Day	14% 5% 17% 35% 20% 8%	1520
	11th to 20th	Day	13% 6% 19% 36% 23% 3	1924
	21st to end	Day	15% 7% 14% 25% 30% 9%	2794
January	1st to 10th	Night	10% 4 15% 37% 30% 4	2610
	11th to 20th	Night	14% 4 13% 32% 32% 4	2366
	21st to end	Night	14% 4 11% 37% 28% 5%	2574
February	1st to 10th	Night	15% 4 14% 34% 25% 8%	2340
	11th to 20th	Night	16% 6% 11% 33% 27% 7%	2147
	21st to end	Night	15% 5% 9% 25% 35% 10%	1776
March	1st to 10th	Night	13% 5% 11% 30% 33% 7%	2075
	11th to 20th	Night	19% 5% 9% 34% 26% 7%	1980
	21st to end	Night	17% 5% 12% 30% 32% 4	2109
April	1st to 10th	Night	13% 5% 10% 32% 27% 12%	1800
	11th to 20th	Night	21% 6% 10% 24% 28% 10%	1777
	21st to end	Night	19% 7% 11% 28% 27% 8%	1800
May	1st to 10th	Night	22% 6% 12% 25% 27% 10%	1794
	11th to 20th	Night	26% 8% 15% 23% 21% 7%	1473
	21st to end	Night	19% 7% 12% 23% 25% 14%	1552
June	1st to 10th	Night	15% 7% 15% 22% 24% 17%	1440
	11th to 20th	Night	12% 5% 8% 21% 25% 29%	1440
	21st to end	Night	19% 7% 14% 18% 24% 18%	1440
July	1st to 10th	Night	30% 12% 16% 14% 14% 14%	1400
	11th to 20th	Night	24% 11% 22% 22% 12% 8%	1467
	21st to end	Night	29% 18% 29% 18% 5% 1	1674
August	1st to 10th	Night	26% 15% 22% 15% 11% 10%	1602
	11th to 20th	Night	29% 9% 20% 19% 14% 8%	1757
	21st to end	Night	28% 11% 18% 19% 17% 5%	1980
September	1st to 10th	Night	26% 9% 17% 18% 19% 11%	1800
	11th to 20th	Night	21% 7% 13% 20% 26% 14%	1800
	21st to end	Night	18% 6% 7% 24% 36% 9%	2015
October	1st to 10th	Night	17% 7% 12% 23% 28% 13%	2160
	11th to 20th	Night	9% 4 8% 21% 44% 15%	2160
	21st to end	Night	15% 3 6% 32% 36% 9%	2376
November	1st to 10th	Night	8% 4 8% 34% 37% 9%	2315
	11th to 20th	Night	8% 4 8% 37% 36% 8%	2470
	21st to end	Night	16% 4 8% 30% 34% 9%	2559
December	1st to 10th	Night	12% 4 16% 36% 25% 7%	2660
	11th to 20th	Night	16% 6% 16% 31% 28% 3	3272
	21st to end	Night	17% 8% 14% 26% 29% 7%	4873

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	4 9% 33% 36% 17% 1	270
	11th to 20th	Day	8% 9% 34% 36% 13%	245
	21st to end	Day	3 3 41% 41% 11%	264
February	1st to 10th	Day	5% 14% 40% 33% 7% 1	240
	11th to 20th	Day	8% 12% 40% 32% 9%	240
	21st to end	Day	12% 18% 37% 28% 4 1	198
March	1st to 10th	Day	9% 21% 36% 27% 7%	322
	11th to 20th	Day	10% 20% 33% 26% 10% 1	420
	21st to end	Day	15% 28% 34% 18% 5%	462
April	1st to 10th	Day	13% 25% 31% 20% 8% 2	420
	11th to 20th	Day	15% 29% 31% 17% 6% 2	412
	21st to end	Day	12% 26% 31% 21% 8% 1	420
May	1st to 10th	Day	9% 25% 34% 23% 9% 1	423
	11th to 20th	Day	9% 12% 28% 30% 15% 6%	566
	21st to end	Day	8% 12% 27% 33% 15% 4	679
June	1st to 10th	Day	4 9% 24% 33% 24% 5%	630
	11th to 20th	Day	3 10% 30% 32% 18% 6%	630
	21st to end	Day	3 8% 24% 31% 27% 7%	630
July	1st to 10th	Day	5% 5% 14% 32% 35% 9%	621
	11th to 20th	Day	4 3 10% 32% 36% 14%	539
	21st to end	Day	6% 4 10% 33% 28% 19%	487
August	1st to 10th	Day	5% 4 15% 32% 31% 13%	447
	11th to 20th	Day	7% 4 18% 34% 25% 12%	437
	21st to end	Day	5% 5% 18% 31% 29% 12%	495
September	1st to 10th	Day	5% 5% 18% 33% 28% 11%	450
	11th to 20th	Day	4 8% 25% 34% 22% 7%	450
	21st to end	Day	8% 6% 20% 30% 27% 9%	305
October	1st to 10th	Day	8% 9% 20% 30% 20% 13%	270
	11th to 20th	Day	4 10% 26% 30% 22% 8%	270
	21st to end	Day	9% 10% 28% 30% 19% 4	297
November	1st to 10th	Day	6% 11% 28% 33% 20% 2	270
	11th to 20th	Day	3 7% 30% 36% 21% 2	270
	21st to end	Day	4 6% 31% 37% 18% 3	270
December	1st to 10th	Day	3 10% 38% 33% 12% 3	270
	11th to 20th	Day	4 4 38% 37% 14% 3	270
	21st to end	Day	6% 11% 39% 32% 11% 1	297
January	1st to 10th	Night	1 6% 37% 41% 14% 1	913
	11th to 20th	Night	2 7% 41% 38% 12% 1	728
	21st to end	Night	1 3 43% 42% 9% 1	792
February	1st to 10th	Night	2 6% 48% 36% 7% 1	720
	11th to 20th	Night	2 7% 49% 35% 7%	704
	21st to end	Night	2 9% 53% 34% 4	592
March	1st to 10th	Night	3 12% 44% 35% 8%	720
	11th to 20th	Night	4 6% 39% 40% 10% 1	720
	21st to end	Night	3 12% 45% 36% 5%	723
April	1st to 10th	Night	3 15% 46% 31% 5%	540
	11th to 20th	Night	6% 14% 39% 34% 7%	533
	21st to end	Night	6% 11% 39% 35% 8% 1	540
May	1st to 10th	Night	6% 7% 35% 39% 12% 1	540
	11th to 20th	Night	9% 6% 24% 43% 16% 2	531
	21st to end	Night	5% 8% 30% 39% 17% 1	584
June	1st to 10th	Night	2 4 23% 45% 25% 1	540
	11th to 20th	Night	1 5% 28% 46% 19% 1	540
	21st to end	Night	2 3 19% 42% 31% 1	540
July	1st to 10th	Night	4 3 11% 40% 38% 4	525
	11th to 20th	Night	3 2 6% 34% 49% 6%	522
	21st to end	Night	6% 2 3 27% 54% 8%	591
August	1st to 10th	Night	4 3 9% 32% 47% 5%	537
	11th to 20th	Night	5% 2 9% 43% 38% 3	534
	21st to end	Night	5% 2 8% 43% 37% 5%	594
September	1st to 10th	Night	6% 2 13% 44% 31% 5%	540
	11th to 20th	Night	5% 1 18% 47% 25% 4	540
	21st to end	Night	5% 3 21% 44% 25% 2	611
October	1st to 10th	Night	4 2 28% 46% 18% 2	720
	11th to 20th	Night	1 3 39% 38% 16% 3	720
	21st to end	Night	4 6% 32% 39% 18% 2	792
November	1st to 10th	Night	2 5% 34% 44% 14%	835
	11th to 20th	Night	1 7% 35% 42% 13% 1	950
	21st to end	Night	3 7% 35% 40% 15% 1	950
December	1st to 10th	Night	1 7% 41% 40% 11% 1	950
	11th to 20th	Night	3 7% 38% 39% 12% 1	950
	21st to end	Night	2 10% 39% 40% 9%	1045

Page generated at 2024-01-09 14:24:27. Version ac07

Copyright 2024 Attilla Danko