Fort Leaton State Historic Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fort Leaton State Historic Site clear sky chart from 2005-11-06 to 2024-01-13.

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	3 3 1 3 3 2 3 4 5% 8% 63%	74539
	Night	4 3 1 3 4 2 4 5% 6% 8% 60%	75199
Transparency	Day	8% 62% 4 8% 10% 8%	74289
	Night	9% 61% 4 7% 10% 8%	74971
Seeing	Day	5% 4 13% 32% 31% 16%	13033
	Night	5% 3 21% 49% 21% 1	23539

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	7% 3 1 3 4 2 3 3 6% 8% 60%	1897
	11th to 20th	Day	6% 3 2 4 3 2 2 4 4 6% 64%	1825
	21st to end	Day	3 4 2 4 4 2 4 3 4 5% 64%	1980
February	1st to 10th	Day	3 3 1 3 4 3 4 4 5% 7% 64%	1800
	11th to 20th	Day	5% 4 2 4 3 3 3 3 5% 7% 62%	1749
	21st to end	Day	3 3 1 2 2 2 3 4 4 8% 69%	1480
March	1st to 10th	Day	4 4 1 3 4 2 3 4 5% 9% 62%	1800
	11th to 20th	Day	5% 4 2 3 4 2 4 5% 4 6% 62%	1966
	21st to end	Day	2 2 2 2 2 2 3 4 5% 7% 70%	2329
April	1st to 10th	Day	3 2 1 2 3 2 3 3 5% 6% 69%	2160
	11th to 20th	Day	1 2 1 2 2 1 3 3 4 6% 74%	2131
	21st to end	Day	3 2 1 2 2 1 2 3 4 6% 74%	2160
May	1st to 10th	Day	2 2 1 2 3 1 2 4 3 5% 74%	2160
	11th to 20th	Day	2 2 1 2 2 2 3 4 5% 6% 71%	2125
	21st to end	Day	1 2 1 2 1 1 2 4 5% 6% 75%	2337
June	1st to 10th	Day	1 1 1 2 2 3 4 4 9% 73%	2256
	11th to 20th	Day	1 2 1 2 3 2 3 4 6% 8% 69%	2250
	21st to end	Day	2 2 1 3 3 2 4 5% 6% 9% 64%	2160
July	1st to 10th	Day	4 3 2 4 5% 4 6% 7% 8% 9% 49%	2160
	11th to 20th	Day	4 2 2 3 3 2 4 4 7% 11% 59%	2160
	21st to end	Day	2 2 2 3 4 3 5% 6% 8% 13% 52%	2349
August	1st to 10th	Day	2 2 1 2 3 2 4 6% 7% 11% 61%	2149
	11th to 20th	Day	5% 3 2 4 5% 3 5% 7% 7% 12% 47%	2123
	21st to end	Day	3 3 2 4 4 4 5% 8% 8% 12% 47%	2376
September	1st to 10th	Day	6% 4 2 4 4 3 4 5% 7% 10% 51%	2160
	11th to 20th	Day	7% 5% 2 4 4 2 4 5% 6% 8% 53%	2071
	21st to end	Day	5% 3 1 4 3 2 3 5% 5% 7% 61%	1980
October	1st to 10th	Day	2 2 1 2 3 2 3 4 5% 7% 68%	1980
	11th to 20th	Day	5% 3 2 3 3 2 3 4 5% 6% 63%	1834
	21st to end	Day	3 3 1 2 3 1 2 2 3 5% 75%	1980
November	1st to 10th	Day	4 3 2 2 3 2 3 2 3 5% 71%	1859
	11th to 20th	Day	4 3 2 3 3 2 3 3 4 6% 68%	1753
	21st to end	Day	6% 4 2 4 3 3 3 3 4 6% 62%	1710
December	1st to 10th	Day	6% 3 2 4 3 2 4 4 6% 9% 58%	1710
	11th to 20th	Day	2 5% 2 5% 5% 3 5% 4 5% 8% 55%	2161
	21st to end	Day	3 2 1 3 3 3 3 4 7% 8% 62%	3459
January	1st to 10th	Night	4 3 1 3 3 2 3 3 5% 7% 65%	2268
	11th to 20th	Night	7% 2 1 3 3 2 3 3 5% 6% 66%	2196
	21st to end	Night	5% 3 2 4 4 2 4 4 6% 6% 60%	2376
February	1st to 10th	Night	4 3 1 3 3 2 3 3 5% 9% 65%	2160
	11th to 20th	Night	5% 4 2 4 4 2 4 4 5% 8% 58%	2098
	21st to end	Night	4 3 1 2 4 1 4 4 6% 7% 63%	1776
March	1st to 10th	Night	4 4 1 4 4 2 4 4 5% 8% 60%	2160
	11th to 20th	Night	7% 4 2 3 4 3 3 3 4 6% 62%	1990
	21st to end	Night	4 2 1 2 2 2 3 4 4 8% 69%	2026
April	1st to 10th	Night	4 3 1 3 4 2 4 3 5% 6% 66%	1800
	11th to 20th	Night	3 2 2 3 3 2 3 4 5% 7% 66%	1777
	21st to end	Night	3 3 1 2 3 2 3 3 3 6% 71%	1800
May	1st to 10th	Night	4 2 1 3 3 2 4 5% 5% 5% 67%	1800
	11th to 20th	Night	5% 3 2 4 4 2 4 5% 6% 6% 59%	1770
	21st to end	Night	3 3 1 3 3 3 4 5% 6% 8% 61%	1939
June	1st to 10th	Night	2 2 1 3 4 3 5% 6% 9% 11% 54%	1684
	11th to 20th	Night	3 2 2 4 6% 3 5% 6% 7% 12% 50%	1688
	21st to end	Night	3 3 2 3 4 3 5% 6% 8% 10% 54%	1800
July	1st to 10th	Night	4 4 2 4 5% 4 6% 7% 9% 12% 44%	1800
	11th to 20th	Night	3 1 1 3 4 3 5% 5% 7% 13% 54%	1800
	21st to end	Night	2 3 2 4 6% 4 6% 7% 8% 12% 46%	1969
August	1st to 10th	Night	3 2 2 3 5% 3 6% 7% 9% 11% 49%	1790
	11th to 20th	Night	4 4 2 4 5% 4 7% 9% 7% 12% 42%	1778
	21st to end	Night	4 4 3 5% 5% 4 7% 6% 9% 12% 41%	1980
September	1st to 10th	Night	4 5% 2 5% 5% 3 6% 6% 7% 9% 48%	1800
	11th to 20th	Night	5% 4 3 5% 6% 4 6% 8% 9% 9% 41%	1886
	21st to end	Night	4 3 2 4 7% 3 6% 6% 7% 9% 50%	1980
October	1st to 10th	Night	2 3 1 4 4 3 5% 5% 6% 9% 57%	1980
	11th to 20th	Night	6% 3 2 4 4 3 3 3 4 7% 61%	2121
	21st to end	Night	3 2 1 2 2 1 2 2 3 5% 75%	2376
November	1st to 10th	Night	5% 2 1 2 2 1 2 3 4 4 75%	2220
	11th to 20th	Night	3 3 1 2 3 2 3 3 5% 6% 69%	2403
	21st to end	Night	5% 3 2 3 3 2 3 4 4 6% 66%	2470
December	1st to 10th	Night	5% 3 1 3 3 2 3 3 5% 8% 63%	2470
	11th to 20th	Night	2 3 1 3 3 2 3 4 6% 9% 62%	3036
	21st to end	Night	3 3 1 3 3 2 4 4 6% 9% 62%	4232

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	12% 55% 3 8% 14% 8%	1898
	11th to 20th	Day	10% 57% 2 6% 16% 9%	1825
	21st to end	Day	9% 61% 2 5% 16% 6%	1980
February	1st to 10th	Day	9% 63% 2 5% 11% 10%	1800
	11th to 20th	Day	9% 62% 4 6% 7% 11%	1759
	21st to end	Day	7% 63% 2 4 9% 14%	1480
March	1st to 10th	Day	12% 64% 3 8% 9% 4	1800
	11th to 20th	Day	9% 68% 1 5% 7% 9%	1966
	21st to end	Day	6% 68% 1 3 9% 13%	2329
April	1st to 10th	Day	7% 67% 2 4 9% 11%	2160
	11th to 20th	Day	6% 69% 2 4 7% 12%	2134
	21st to end	Day	5% 68% 1 3 9% 13%	2160
May	1st to 10th	Day	3 67% 1 3 8% 18%	2160
	11th to 20th	Day	5% 67% 1 7% 9% 11%	2128
	21st to end	Day	4 67% 2 6% 9% 11%	2337
June	1st to 10th	Day	5% 68% 4 9% 9% 6%	2256
	11th to 20th	Day	5% 68% 3 7% 9% 8%	2250
	21st to end	Day	4 67% 5% 8% 8% 8%	2160
July	1st to 10th	Day	10% 63% 7% 10% 7% 3	2101
	11th to 20th	Day	6% 63% 6% 11% 8% 6%	2097
	21st to end	Day	5% 62% 6% 13% 12% 2	2219
August	1st to 10th	Day	6% 64% 5% 13% 9% 3	2136
	11th to 20th	Day	10% 67% 8% 9% 5% 2	2123
	21st to end	Day	8% 65% 7% 11% 5% 4	2376
September	1st to 10th	Day	9% 63% 6% 10% 7% 5%	2160
	11th to 20th	Day	10% 64% 6% 8% 9% 4	2071
	21st to end	Day	11% 64% 4 10% 10% 1	1980
October	1st to 10th	Day	7% 64% 6% 10% 8% 6%	1980
	11th to 20th	Day	9% 63% 3 6% 9% 10%	1834
	21st to end	Day	9% 61% 2 6% 12% 11%	1980
November	1st to 10th	Day	14% 56% 4 8% 10% 8%	1859
	11th to 20th	Day	11% 55% 5% 12% 11% 7%	1753
	21st to end	Day	11% 55% 3 8% 14% 10%	1710
December	1st to 10th	Day	11% 55% 4 13% 11% 6%	1710
	11th to 20th	Day	16% 45% 5% 11% 17% 6%	2159
	21st to end	Day	11% 35% 4 10% 22% 17%	3459
January	1st to 10th	Night	12% 53% 3 6% 16% 11%	2268
	11th to 20th	Night	9% 56% 3 6% 13% 14%	2196
	21st to end	Night	10% 61% 2 4 13% 10%	2376
February	1st to 10th	Night	7% 62% 2 7% 11% 10%	2160
	11th to 20th	Night	9% 62% 4 5% 8% 12%	2098
	21st to end	Night	10% 64% 3 5% 7% 12%	1776
March	1st to 10th	Night	13% 63% 3 8% 7% 6%	2160
	11th to 20th	Night	9% 68% 1 6% 8% 8%	1990
	21st to end	Night	6% 68% 2 4 8% 12%	2026
April	1st to 10th	Night	6% 68% 2 4 8% 12%	1800
	11th to 20th	Night	6% 69% 3 4 6% 12%	1777
	21st to end	Night	6% 68% 2 5% 9% 11%	1800
May	1st to 10th	Night	5% 68% 2 3 7% 15%	1800
	11th to 20th	Night	6% 68% 2 7% 6% 11%	1771
	21st to end	Night	6% 68% 4 7% 6% 9%	1940
June	1st to 10th	Night	8% 70% 4 7% 8% 3	1684
	11th to 20th	Night	10% 69% 3 5% 9% 4	1688
	21st to end	Night	5% 66% 6% 8% 7% 8%	1800
July	1st to 10th	Night	10% 65% 9% 9% 5% 2	1750
	11th to 20th	Night	8% 63% 5% 10% 9% 4	1740
	21st to end	Night	5% 61% 6% 14% 10% 3	1859
August	1st to 10th	Night	8% 65% 5% 11% 8% 2	1779
	11th to 20th	Night	12% 66% 9% 9% 3 1	1778
	21st to end	Night	12% 65% 5% 9% 6% 3	1980
September	1st to 10th	Night	10% 64% 6% 8% 6% 5%	1800
	11th to 20th	Night	13% 66% 4 6% 6% 3	1886
	21st to end	Night	12% 65% 5% 9% 7% 1	1980
October	1st to 10th	Night	11% 66% 6% 7% 7% 4	1980
	11th to 20th	Night	8% 62% 4 7% 10% 10%	2121
	21st to end	Night	8% 62% 2 6% 12% 10%	2376
November	1st to 10th	Night	11% 57% 5% 7% 11% 9%	2220
	11th to 20th	Night	11% 55% 3 11% 11% 8%	2403
	21st to end	Night	10% 54% 4 7% 12% 13%	2470
December	1st to 10th	Night	10% 55% 3 12% 11% 8%	2470
	11th to 20th	Night	11% 45% 5% 11% 18% 9%	3037
	21st to end	Night	11% 35% 4 9% 25% 15%	4232

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	8% 3 19% 41% 26% 4	270
	11th to 20th	Day	3 6% 14% 42% 29% 5%	248
	21st to end	Day	3 7% 23% 40% 22% 5%	264
February	1st to 10th	Day	8% 3 16% 34% 33% 7%	240
	11th to 20th	Day	10% 6% 18% 41% 22% 3	240
	21st to end	Day	6% 9% 22% 46% 16% 2	198
March	1st to 10th	Day	8% 5% 15% 47% 21% 4	240
	11th to 20th	Day	8% 10% 26% 30% 20% 6%	406
	21st to end	Day	4 13% 21% 39% 21% 2	462
April	1st to 10th	Day	5% 7% 25% 40% 20% 2	420
	11th to 20th	Day	2 12% 29% 36% 18% 3	412
	21st to end	Day	5% 7% 23% 44% 21% 1	420
May	1st to 10th	Day	4 7% 20% 40% 24% 6%	423
	11th to 20th	Day	3 5% 20% 40% 26% 6%	448
	21st to end	Day	3 4 18% 37% 34% 4	485
June	1st to 10th	Day	2 1 11% 34% 40% 12%	546
	11th to 20th	Day	2 1 7% 30% 45% 15%	540
	21st to end	Day	2 1 7% 30% 38% 22%	450
July	1st to 10th	Day	5% 6% 22% 30% 36%	446
	11th to 20th	Day	3 2 22% 34% 39%	444
	21st to end	Day	2 1 2 25% 40% 30%	487
August	1st to 10th	Day	2 1 4 17% 35% 41%	447
	11th to 20th	Day	6% 1 5% 20% 32% 36%	437
	21st to end	Day	4 1 4 21% 32% 37%	495
September	1st to 10th	Day	6% 2 5% 26% 34% 28%	450
	11th to 20th	Day	7% 1 4 16% 39% 34%	361
	21st to end	Day	7% 5% 17% 37% 34%	270
October	1st to 10th	Day	4 2 6% 23% 36% 29%	270
	11th to 20th	Day	7% 2 8% 25% 35% 22%	270
	21st to end	Day	5% 4 10% 28% 31% 23%	297
November	1st to 10th	Day	4 3 7% 30% 41% 14%	270
	11th to 20th	Day	4 6% 10% 30% 33% 17%	270
	21st to end	Day	10% 5% 15% 36% 28% 7%	270
December	1st to 10th	Day	7% 3 8% 33% 38% 12%	270
	11th to 20th	Day	4 3 19% 42% 29% 4	270
	21st to end	Day	6% 3 15% 42% 30% 3	297
January	1st to 10th	Night	6% 2 22% 51% 17%	760
	11th to 20th	Night	9% 3 19% 50% 19%	732
	21st to end	Night	6% 4 27% 49% 13%	792
February	1st to 10th	Night	5% 5% 25% 47% 18%	720
	11th to 20th	Night	7% 5% 27% 50% 11%	704
	21st to end	Night	5% 7% 34% 49% 6%	592
March	1st to 10th	Night	9% 5% 33% 44% 9%	720
	11th to 20th	Night	9% 5% 33% 40% 12%	720
	21st to end	Night	5% 5% 36% 45% 9%	640
April	1st to 10th	Night	4 6% 38% 46% 6%	540
	11th to 20th	Night	3 9% 41% 41% 6%	533
	21st to end	Night	3 7% 38% 46% 6%	540
May	1st to 10th	Night	5% 6% 35% 45% 9%	540
	11th to 20th	Night	5% 5% 34% 47% 9% 1	531
	21st to end	Night	4 5% 30% 51% 10%	584
June	1st to 10th	Night	3 2 24% 56% 15%	540
	11th to 20th	Night	3 1 21% 53% 22%	540
	21st to end	Night	3 1 17% 58% 20% 1	540
July	1st to 10th	Night	3 1 12% 53% 29% 2	525
	11th to 20th	Night	4 2 7% 56% 31% 1	522
	21st to end	Night	3 2 6% 50% 36% 4	591
August	1st to 10th	Night	3 1 6% 42% 46% 3	537
	11th to 20th	Night	6% 1 5% 39% 44% 6%	534
	21st to end	Night	5% 1 6% 48% 38% 3	594
September	1st to 10th	Night	4 2 10% 48% 34% 2	540
	11th to 20th	Night	7% 1 10% 49% 32% 1	540
	21st to end	Night	5% 1 11% 51% 30% 2	540
October	1st to 10th	Night	4 1 13% 58% 24% 1	540
	11th to 20th	Night	7% 2 20% 46% 23% 2	681
	21st to end	Night	4 2 16% 44% 29% 4	792
November	1st to 10th	Night	6% 1 13% 46% 32% 2	740
	11th to 20th	Night	4 4 14% 52% 24% 1	883
	21st to end	Night	6% 2 21% 49% 20% 2	950
December	1st to 10th	Night	7% 2 14% 53% 23% 1	950
	11th to 20th	Night	4 3 22% 53% 19%	950
	21st to end	Night	5% 2 22% 53% 17% 1	862

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