Fossil Falls
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fossil Falls clear sky chart from 2005-11-06 to 2024-02-20.

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 2 1 2 2 1 2 3 4 6% 76%	78648
	Night	2 2 1 2 2 1 2 3 4 6% 76%	80576
Transparency	Day	11% 4 6% 16% 28% 34%	78362
	Night	12% 4 7% 19% 29% 29%	80383
Seeing	Day	5% 16% 36% 30% 10% 3	14313
	Night	3 9% 26% 35% 22% 6%	24127

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	3 2 1 1 2 2 3 3 5% 9% 71%	2539
	11th to 20th	Day	2 2 1 2 5% 2 4 4 5% 9% 65%	2608
	21st to end	Day	5% 4 1 3 3 2 3 4 6% 9% 61%	3341
February	1st to 10th	Day	4 2 1 2 2 2 3 2 4 8% 72%	1900
	11th to 20th	Day	3 2 1 2 2 1 3 3 4 10% 69%	1841
	21st to end	Day	4 2 1 2 3 1 2 3 5% 8% 71%	1480
March	1st to 10th	Day	2 2 1 2 3 2 2 3 5% 9% 68%	1800
	11th to 20th	Day	3 2 1 2 1 1 3 4 5% 10% 67%	1838
	21st to end	Day	2 1 1 1 2 2 3 3 5% 7% 74%	2376
April	1st to 10th	Day	2 2 1 2 2 1 3 3 4 7% 73%	2160
	11th to 20th	Day	1 2 1 2 2 1 2 3 4 5% 78%	2129
	21st to end	Day	1 1 1 1 2 1 2 3 5% 7% 77%	2160
May	1st to 10th	Day	1 1 1 1 2 1 2 3 3 6% 80%	2295
	11th to 20th	Day	1 1 2 2 2 2 3 4 7% 77%	2301
	21st to end	Day	1 2 1 2 2 1 3 4 5% 5% 75%	2530
June	1st to 10th	Day	1 1 1 1 2 1 2 2 4 6% 79%	2483
	11th to 20th	Day	1 1 2 1 1 2 3 5% 84%	2520
	21st to end	Day	1 1 1 1 1 2 1 2 3 86%	2520
July	1st to 10th	Day	1 1 1 2 2 2 2 3 5% 80%	2520
	11th to 20th	Day	2 2 1 2 2 2 3 3 4 5% 76%	2520
	21st to end	Day	2 2 1 3 3 2 3 4 3 7% 71%	2570
August	1st to 10th	Day	1 1 1 2 2 1 3 2 3 4 80%	2149
	11th to 20th	Day	1 1 1 1 2 2 2 5% 84%	2122
	21st to end	Day	1 1 1 1 1 1 2 3 4 85%	2376
September	1st to 10th	Day	1 1 1 1 1 1 2 2 3 5% 81%	2160
	11th to 20th	Day	1 1 1 1 1 2 3 89%	2026
	21st to end	Day	1 1 1 1 1 1 3 3 88%	1980
October	1st to 10th	Day	1 1 1 2 1 2 2 3 4 83%	1980
	11th to 20th	Day	2 1 1 1 1 2 2 2 4 83%	1850
	21st to end	Day	1 1 1 2 2 1 2 2 2 4 83%	1885
November	1st to 10th	Day	1 1 1 1 1 1 2 2 4 6% 80%	1674
	11th to 20th	Day	1 1 1 2 1 2 2 4 5% 80%	1710
	21st to end	Day	3 1 2 2 1 2 3 4 7% 75%	1710
December	1st to 10th	Day	2 2 1 3 2 2 2 3 5% 8% 71%	1710
	11th to 20th	Day	3 4 1 4 2 2 3 4 6% 9% 62%	2091
	21st to end	Day	6% 4 2 4 3 2 3 4 5% 9% 59%	2794
January	1st to 10th	Night	2 2 1 2 2 1 2 3 3 6% 74%	4406
	11th to 20th	Night	1 2 1 3 3 2 3 4 6% 10% 65%	4352
	21st to end	Night	4 4 2 3 4 3 3 4 5% 8% 62%	4329
February	1st to 10th	Night	2 3 1 2 2 2 3 4 5% 6% 70%	2280
	11th to 20th	Night	2 1 1 2 2 1 2 3 5% 6% 74%	2211
	21st to end	Night	4 2 1 1 2 1 2 3 4 6% 73%	1776
March	1st to 10th	Night	1 2 1 2 2 1 2 4 6% 8% 69%	2160
	11th to 20th	Night	2 2 1 2 3 2 3 3 5% 9% 69%	2119
	21st to end	Night	2 2 1 1 2 2 2 3 5% 8% 72%	1980
April	1st to 10th	Night	2 1 1 2 2 2 3 3 3 7% 74%	1800
	11th to 20th	Night	1 1 1 1 2 1 2 2 3 5% 81%	1779
	21st to end	Night	1 1 2 1 1 2 4 5% 82%	1800
May	1st to 10th	Night	1 1 1 1 1 2 4 8% 80%	1661
	11th to 20th	Night	1 1 1 1 2 3 3 6% 83%	1594
	21st to end	Night	1 1 1 1 1 1 2 2 6% 84%	1746
June	1st to 10th	Night	1 1 1 1 1 2 2 3 5% 83%	1472
	11th to 20th	Night	1 1 1 1 1 1 1 2 2 2 87%	1440
	21st to end	Night	1 1 1 1 2 2 3 89%	1440
July	1st to 10th	Night	1 1 1 1 2 2 2 4 87%	1440
	11th to 20th	Night	1 1 1 2 1 1 3 3 4 81%	1440
	21st to end	Night	1 1 1 2 2 2 2 3 3 6% 76%	1742
August	1st to 10th	Night	2 1 1 2 1 2 2 3 4 81%	1790
	11th to 20th	Night	1 1 1 1 1 3 4 87%	1780
	21st to end	Night	1 1 1 1 1 2 2 3 87%	1980
September	1st to 10th	Night	1 1 1 1 1 1 2 2 4 86%	1800
	11th to 20th	Night	1 1 1 1 2 2 2 90%	1934
	21st to end	Night	1 1 2 3 4 88%	1980
October	1st to 10th	Night	1 1 1 1 1 1 2 3 4 85%	1980
	11th to 20th	Night	1 1 1 1 2 1 1 2 3 4 84%	2106
	21st to end	Night	1 1 1 1 1 2 3 5% 83%	2470
November	1st to 10th	Night	1 1 2 1 1 1 2 3 5% 82%	2405
	11th to 20th	Night	1 1 2 2 2 2 3 4 6% 79%	2470
	21st to end	Night	2 2 1 2 2 1 3 2 4 7% 75%	2470
December	1st to 10th	Night	2 2 1 3 3 2 3 3 4 7% 70%	2470
	11th to 20th	Night	2 4 2 3 3 2 4 4 6% 8% 62%	3112
	21st to end	Night	6% 3 1 3 4 2 4 5% 5% 8% 59%	4862

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% 5% 8% 25% 37% 12%	2539
	11th to 20th	Day	17% 7% 17% 24% 23% 12%	2608
	21st to end	Day	21% 7% 11% 25% 27% 10%	3341
February	1st to 10th	Day	15% 5% 7% 22% 30% 21%	1900
	11th to 20th	Day	13% 5% 8% 22% 32% 21%	1851
	21st to end	Day	14% 6% 10% 25% 30% 15%	1480
March	1st to 10th	Day	15% 5% 9% 25% 29% 17%	1800
	11th to 20th	Day	14% 6% 9% 25% 26% 20%	1838
	21st to end	Day	12% 5% 10% 27% 29% 17%	2376
April	1st to 10th	Day	14% 5% 9% 25% 29% 19%	2160
	11th to 20th	Day	10% 4 6% 21% 33% 25%	2132
	21st to end	Day	8% 4 8% 21% 39% 20%	2160
May	1st to 10th	Day	9% 4 6% 18% 33% 30%	2295
	11th to 20th	Day	9% 4 6% 16% 39% 26%	2304
	21st to end	Day	12% 5% 5% 16% 40% 22%	2530
June	1st to 10th	Day	9% 4 5% 12% 28% 42%	2483
	11th to 20th	Day	6% 2 4 9% 19% 60%	2520
	21st to end	Day	7% 1 2 4 18% 67%	2520
July	1st to 10th	Day	8% 3 3 6% 13% 67%	2451
	11th to 20th	Day	11% 3 4 10% 18% 52%	2445
	21st to end	Day	14% 4 6% 12% 22% 42%	2427
August	1st to 10th	Day	10% 2 3 7% 16% 63%	2135
	11th to 20th	Day	6% 3 3 5% 24% 59%	2122
	21st to end	Day	6% 2 2 7% 21% 61%	2376
September	1st to 10th	Day	9% 3 3 8% 18% 59%	2160
	11th to 20th	Day	4 2 3 7% 28% 56%	2026
	21st to end	Day	5% 1 2 7% 37% 47%	1980
October	1st to 10th	Day	8% 3 3 13% 31% 42%	1980
	11th to 20th	Day	8% 3 3 10% 36% 41%	1850
	21st to end	Day	9% 3 3 11% 35% 39%	1885
November	1st to 10th	Day	9% 3 5% 15% 40% 28%	1674
	11th to 20th	Day	9% 3 7% 20% 35% 26%	1710
	21st to end	Day	12% 4 8% 19% 31% 27%	1710
December	1st to 10th	Day	14% 6% 9% 26% 25% 20%	1710
	11th to 20th	Day	21% 8% 9% 22% 26% 13%	2090
	21st to end	Day	24% 7% 13% 27% 20% 10%	2794
January	1st to 10th	Night	14% 4 7% 25% 37% 13%	4406
	11th to 20th	Night	16% 6% 13% 32% 22% 10%	4352
	21st to end	Night	21% 6% 13% 27% 25% 9%	4329
February	1st to 10th	Night	17% 4 8% 23% 28% 20%	2280
	11th to 20th	Night	13% 4 6% 22% 33% 23%	2212
	21st to end	Night	14% 3 8% 23% 34% 18%	1776
March	1st to 10th	Night	14% 6% 8% 25% 30% 18%	2160
	11th to 20th	Night	14% 7% 8% 21% 29% 20%	2119
	21st to end	Night	12% 6% 8% 31% 31% 13%	1980
April	1st to 10th	Night	13% 4 7% 27% 31% 18%	1800
	11th to 20th	Night	10% 3 6% 25% 31% 25%	1779
	21st to end	Night	7% 3 6% 24% 43% 18%	1800
May	1st to 10th	Night	6% 4 7% 20% 38% 24%	1661
	11th to 20th	Night	7% 3 5% 22% 38% 25%	1595
	21st to end	Night	6% 3 8% 22% 40% 21%	1746
June	1st to 10th	Night	7% 2 4 16% 33% 38%	1472
	11th to 20th	Night	6% 3 2 12% 25% 53%	1440
	21st to end	Night	5% 1 1 6% 20% 67%	1440
July	1st to 10th	Night	6% 2 2 6% 15% 70%	1400
	11th to 20th	Night	7% 4 5% 9% 21% 55%	1392
	21st to end	Night	12% 3 4 12% 23% 45%	1645
August	1st to 10th	Night	9% 2 3 8% 18% 60%	1780
	11th to 20th	Night	4 1 3 7% 26% 59%	1780
	21st to end	Night	6% 2 2 6% 25% 60%	1980
September	1st to 10th	Night	7% 2 3 6% 20% 63%	1800
	11th to 20th	Night	4 3 2 7% 28% 56%	1934
	21st to end	Night	4 2 2 8% 32% 53%	1980
October	1st to 10th	Night	7% 3 4 13% 30% 44%	1980
	11th to 20th	Night	8% 2 3 12% 36% 40%	2106
	21st to end	Night	7% 3 4 10% 36% 40%	2470
November	1st to 10th	Night	8% 3 5% 16% 40% 28%	2405
	11th to 20th	Night	9% 4 8% 18% 31% 30%	2470
	21st to end	Night	12% 3 6% 20% 31% 27%	2470
December	1st to 10th	Night	15% 6% 8% 22% 27% 21%	2470
	11th to 20th	Night	19% 9% 11% 24% 24% 13%	3112
	21st to end	Night	22% 8% 10% 26% 24% 10%	4862

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	9% 17% 42% 23% 9% 1	180
	11th to 20th	Day	9% 24% 27% 25% 12% 2	222
	21st to end	Day	11% 19% 31% 30% 8% 2	463
February	1st to 10th	Day	6% 26% 36% 23% 7% 2	460
	11th to 20th	Day	10% 24% 38% 21% 6% 1	452
	21st to end	Day	10% 25% 42% 18% 5%	346
March	1st to 10th	Day	10% 28% 36% 20% 5% 1	420
	11th to 20th	Day	9% 27% 41% 17% 5% 1	420
	21st to end	Day	10% 29% 41% 16% 3	462
April	1st to 10th	Day	10% 25% 37% 20% 6% 1	420
	11th to 20th	Day	9% 30% 36% 20% 4 1	412
	21st to end	Day	5% 26% 38% 21% 7% 3	420
May	1st to 10th	Day	7% 24% 42% 21% 4 3	423
	11th to 20th	Day	4 24% 37% 26% 7% 3	448
	21st to end	Day	5% 19% 37% 28% 9% 3	485
June	1st to 10th	Day	4 12% 38% 33% 10% 4	450
	11th to 20th	Day	3 15% 35% 32% 12% 4	450
	21st to end	Day	1 13% 34% 36% 11% 5%	450
July	1st to 10th	Day	2 6% 35% 37% 15% 6%	446
	11th to 20th	Day	1 4 27% 43% 18% 8%	444
	21st to end	Day	2 2 29% 44% 15% 7%	487
August	1st to 10th	Day	2 8% 34% 35% 14% 6%	447
	11th to 20th	Day	2 5% 31% 39% 16% 8%	437
	21st to end	Day	1 4 36% 40% 15% 5%	495
September	1st to 10th	Day	2 9% 33% 38% 17% 2	450
	11th to 20th	Day	2 12% 36% 39% 11% 1	450
	21st to end	Day	3 10% 38% 33% 14% 1	450
October	1st to 10th	Day	3 16% 37% 34% 10%	450
	11th to 20th	Day	3 12% 36% 36% 12% 1	450
	21st to end	Day	4 15% 34% 33% 15% 1	400
November	1st to 10th	Day	7% 14% 27% 37% 12% 2	270
	11th to 20th	Day	3 16% 36% 27% 16% 3	270
	21st to end	Day	5% 12% 36% 30% 14% 2	270
December	1st to 10th	Day	6% 16% 38% 31% 9% 1	270
	11th to 20th	Day	4 18% 35% 27% 14% 2	246
	21st to end	Day	13% 22% 33% 23% 8% 2	198
January	1st to 10th	Night	4 12% 30% 26% 21% 7%	760
	11th to 20th	Night	3 10% 31% 35% 16% 4	760
	21st to end	Night	7% 12% 32% 29% 15% 5%	836
February	1st to 10th	Night	4 11% 32% 29% 18% 6%	760
	11th to 20th	Night	5% 11% 31% 32% 16% 5%	742
	21st to end	Night	6% 13% 35% 28% 14% 3	592
March	1st to 10th	Night	4 16% 35% 30% 13% 4	720
	11th to 20th	Night	5% 15% 31% 25% 17% 7%	720
	21st to end	Night	4 14% 37% 30% 13% 2	792
April	1st to 10th	Night	3 14% 35% 29% 14% 4	720
	11th to 20th	Night	2 17% 34% 27% 17% 3	711
	21st to end	Night	1 14% 33% 29% 18% 5%	720
May	1st to 10th	Night	1 13% 37% 33% 14% 2	581
	11th to 20th	Night	1 10% 30% 37% 20% 2	531
	21st to end	Night	2 12% 27% 40% 18% 1	584
June	1st to 10th	Night	1 6% 23% 46% 21% 2	392
	11th to 20th	Night	1 5% 26% 43% 22% 3	360
	21st to end	Night	1 3 23% 48% 23% 3	360
July	1st to 10th	Night	1 1 13% 50% 30% 5%	350
	11th to 20th	Night	1 8% 49% 39% 3	348
	21st to end	Night	1 1 11% 47% 37% 4	560
August	1st to 10th	Night	2 1 16% 44% 31% 6%	716
	11th to 20th	Night	1 1 12% 43% 35% 8%	712
	21st to end	Night	1 1 14% 39% 34% 10%	792
September	1st to 10th	Night	1 3 13% 36% 38% 9%	720
	11th to 20th	Night	4 20% 37% 30% 9%	720
	21st to end	Night	5% 19% 34% 30% 11%	720
October	1st to 10th	Night	1 7% 22% 45% 19% 6%	720
	11th to 20th	Night	3 6% 21% 38% 22% 11%	720
	21st to end	Night	2 9% 21% 30% 27% 11%	792
November	1st to 10th	Night	2 9% 21% 34% 24% 9%	740
	11th to 20th	Night	1 6% 24% 36% 24% 8%	760
	21st to end	Night	4 8% 30% 33% 19% 6%	760
December	1st to 10th	Night	4 9% 31% 31% 20% 5%	760
	11th to 20th	Night	4 8% 32% 35% 16% 5%	760
	21st to end	Night	4 15% 32% 28% 16% 5%	836

Page generated at 2024-02-17 03:28:37. Version ac07

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