Little Ranch Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Little Ranch Observatory 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	7% 5% 2 4 4 3 4 4 5% 8% 54%	74830
	Night	7% 6% 2 5% 4 3 4 4 5% 7% 52%	74941
Transparency	Day	28% 6% 13% 27% 20% 6%	74534
	Night	30% 6% 13% 27% 19% 5%	74759
Seeing	Day	9% 7% 30% 30% 19% 5%	14581
	Night	9% 8% 38% 36% 9%	24688

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 6% 3 4 4 2 4 4 5% 6% 58%	1518
	11th to 20th	Day	4 5% 3 5% 5% 3 5% 5% 6% 7% 53%	1460
	21st to end	Day	5% 7% 2 5% 4 3 4 3 4 9% 54%	1641
February	1st to 10th	Day	4 7% 5% 7% 6% 3 6% 6% 5% 7% 45%	1680
	11th to 20th	Day	5% 7% 3 6% 5% 4 5% 4 5% 7% 49%	1749
	21st to end	Day	3 10% 4 5% 5% 3 4 4 4 7% 52%	1480
March	1st to 10th	Day	5% 7% 3 4 4 4 4 3 6% 7% 54%	1800
	11th to 20th	Day	7% 6% 3 5% 4 4 4 4 5% 7% 51%	1834
	21st to end	Day	9% 8% 3 5% 5% 4 4 5% 5% 8% 44%	2376
April	1st to 10th	Day	9% 7% 3 5% 4 3 4 4 5% 6% 50%	2160
	11th to 20th	Day	13% 6% 3 5% 5% 3 4 3 6% 8% 44%	2131
	21st to end	Day	11% 6% 2 6% 6% 3 4 4 5% 8% 44%	2252
May	1st to 10th	Day	14% 6% 2 4 5% 4 4 5% 5% 7% 45%	2340
	11th to 20th	Day	15% 7% 2 5% 4 3 4 4 6% 9% 42%	2388
	21st to end	Day	10% 6% 3 5% 5% 2 4 5% 7% 10% 44%	2724
June	1st to 10th	Day	7% 3 1 3 4 3 4 5% 6% 9% 55%	2520
	11th to 20th	Day	7% 3 2 4 4 3 4 5% 7% 7% 55%	2520
	21st to end	Day	3 3 1 3 3 2 4 4 5% 10% 61%	2520
July	1st to 10th	Day	7% 3 2 4 4 2 4 6% 6% 8% 54%	2520
	11th to 20th	Day	3 2 1 3 3 2 4 5% 6% 10% 61%	2520
	21st to end	Day	4 3 2 4 4 3 4 6% 7% 10% 53%	2742
August	1st to 10th	Day	5% 4 1 4 5% 3 4 7% 7% 11% 49%	2436
	11th to 20th	Day	4 2 1 3 4 2 3 5% 7% 10% 59%	2123
	21st to end	Day	5% 3 1 3 3 2 3 4 6% 8% 61%	2376
September	1st to 10th	Day	6% 4 2 4 4 2 3 4 5% 5% 62%	2160
	11th to 20th	Day	8% 3 1 3 3 2 3 4 4 6% 65%	2056
	21st to end	Day	9% 3 2 3 2 2 2 3 3 7% 63%	1980
October	1st to 10th	Day	11% 5% 2 3 3 2 3 3 5% 5% 58%	1945
	11th to 20th	Day	6% 5% 1 4 4 2 3 3 4 6% 62%	1792
	21st to end	Day	8% 5% 2 3 4 2 3 3 4 6% 60%	1782
November	1st to 10th	Day	4 4 2 3 3 2 4 4 6% 8% 61%	1673
	11th to 20th	Day	4 5% 2 3 3 3 3 3 5% 7% 62%	1710
	21st to end	Day	5% 6% 2 4 4 2 4 3 5% 6% 58%	1682
December	1st to 10th	Day	5% 6% 3 5% 4 2 4 5% 6% 8% 52%	1520
	11th to 20th	Day	3 5% 2 4 4 3 3 5% 4 8% 58%	1926
	21st to end	Day	5% 8% 3 6% 6% 4 5% 6% 4 6% 47%	2794
January	1st to 10th	Night	3 7% 2 4 5% 2 4 4 5% 7% 55%	2647
	11th to 20th	Night	4 5% 2 4 4 3 5% 4 5% 7% 56%	2562
	21st to end	Night	4 7% 3 7% 4 3 4 4 6% 8% 50%	2732
February	1st to 10th	Night	4 9% 5% 6% 5% 3 4 4 5% 7% 47%	2278
	11th to 20th	Night	4 7% 4 6% 6% 3 5% 4 6% 7% 48%	2098
	21st to end	Night	4 9% 4 6% 5% 3 4 4 5% 6% 51%	1776
March	1st to 10th	Night	7% 6% 3 5% 4 2 4 4 5% 6% 54%	2160
	11th to 20th	Night	8% 7% 3 5% 5% 2 4 4 4 7% 52%	2123
	21st to end	Night	9% 8% 3 5% 5% 3 5% 6% 7% 8% 41%	1980
April	1st to 10th	Night	11% 7% 3 5% 6% 3 4 4 6% 7% 46%	1800
	11th to 20th	Night	11% 7% 3 5% 5% 3 4 3 5% 6% 48%	1777
	21st to end	Night	14% 8% 3 5% 5% 3 4 5% 5% 7% 43%	1706
May	1st to 10th	Night	13% 6% 2 7% 4 3 5% 5% 6% 8% 42%	1620
	11th to 20th	Night	16% 6% 2 4 5% 3 4 5% 7% 6% 43%	1505
	21st to end	Night	13% 7% 2 6% 5% 3 4 6% 5% 8% 41%	1552
June	1st to 10th	Night	9% 4 2 3 5% 3 4 6% 6% 10% 49%	1440
	11th to 20th	Night	8% 3 2 4 3 3 5% 5% 7% 9% 51%	1440
	21st to end	Night	6% 3 2 5% 6% 3 5% 5% 7% 10% 48%	1440
July	1st to 10th	Night	7% 4 2 5% 5% 3 4 6% 6% 8% 48%	1440
	11th to 20th	Night	4 3 1 3 4 2 6% 5% 7% 9% 56%	1440
	21st to end	Night	5% 3 2 3 6% 4 5% 6% 7% 9% 50%	1576
August	1st to 10th	Night	5% 5% 2 5% 5% 4 5% 7% 6% 9% 48%	1503
	11th to 20th	Night	4 4 1 4 3 2 4 5% 6% 8% 58%	1773
	21st to end	Night	4 3 1 3 4 2 4 4 6% 8% 59%	1980
September	1st to 10th	Night	8% 4 1 4 4 3 4 3 5% 8% 58%	1800
	11th to 20th	Night	7% 4 2 3 4 2 4 3 5% 7% 59%	1903
	21st to end	Night	8% 4 2 4 3 2 4 3 4 6% 61%	1980
October	1st to 10th	Night	12% 5% 2 4 3 2 3 3 4 6% 57%	2011
	11th to 20th	Night	8% 4 2 3 4 2 3 3 4 5% 62%	2160
	21st to end	Night	8% 5% 2 4 3 2 3 4 5% 7% 57%	2564
November	1st to 10th	Night	5% 4 2 4 4 3 4 4 6% 7% 58%	2405
	11th to 20th	Night	5% 5% 2 4 4 3 4 3 5% 8% 58%	2470
	21st to end	Night	5% 6% 3 4 4 2 4 4 4 6% 57%	2496
December	1st to 10th	Night	5% 6% 3 6% 4 2 4 4 5% 7% 55%	2660
	11th to 20th	Night	4 4 2 4 4 2 4 5% 6% 9% 56%	3271
	21st to end	Night	6% 8% 4 7% 6% 3 4 3 5% 7% 47%	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	26% 5% 14% 33% 20% 2	1519
	11th to 20th	Day	29% 6% 16% 28% 19% 3	1460
	21st to end	Day	29% 4 17% 31% 16% 3	1641
February	1st to 10th	Day	37% 6% 15% 24% 15% 4	1680
	11th to 20th	Day	34% 5% 11% 26% 19% 5%	1759
	21st to end	Day	33% 5% 12% 26% 17% 6%	1480
March	1st to 10th	Day	30% 4 12% 29% 21% 4	1800
	11th to 20th	Day	34% 5% 13% 21% 23% 5%	1834
	21st to end	Day	38% 7% 15% 25% 13% 2	2376
April	1st to 10th	Day	35% 5% 14% 26% 15% 5%	2160
	11th to 20th	Day	37% 6% 14% 22% 16% 4	2134
	21st to end	Day	37% 5% 11% 26% 18% 2	2252
May	1st to 10th	Day	38% 6% 14% 29% 12% 1	2340
	11th to 20th	Day	39% 7% 17% 26% 10% 1	2392
	21st to end	Day	35% 9% 17% 23% 14% 2	2724
June	1st to 10th	Day	24% 8% 19% 32% 14% 4	2520
	11th to 20th	Day	26% 7% 11% 27% 22% 8%	2520
	21st to end	Day	19% 5% 12% 30% 26% 8%	2520
July	1st to 10th	Day	26% 7% 12% 25% 23% 7%	2451
	11th to 20th	Day	18% 6% 10% 28% 26% 12%	2445
	21st to end	Day	23% 8% 14% 27% 21% 7%	2590
August	1st to 10th	Day	27% 8% 16% 27% 15% 7%	2420
	11th to 20th	Day	20% 6% 13% 29% 24% 8%	2123
	21st to end	Day	20% 5% 10% 25% 27% 13%	2376
September	1st to 10th	Day	24% 4 8% 24% 26% 15%	2160
	11th to 20th	Day	21% 5% 8% 23% 29% 13%	2056
	21st to end	Day	23% 4 7% 25% 33% 8%	1980
October	1st to 10th	Day	29% 4 10% 24% 26% 7%	1945
	11th to 20th	Day	25% 3 8% 29% 25% 10%	1792
	21st to end	Day	26% 3 12% 29% 22% 8%	1782
November	1st to 10th	Day	21% 5% 14% 28% 23% 9%	1673
	11th to 20th	Day	23% 3 11% 31% 28% 5%	1710
	21st to end	Day	26% 4 10% 30% 24% 6%	1682
December	1st to 10th	Day	29% 5% 14% 27% 21% 4	1520
	11th to 20th	Day	24% 5% 13% 34% 22% 2	1924
	21st to end	Day	36% 7% 9% 31% 15% 3	2794
January	1st to 10th	Night	28% 5% 14% 30% 20% 3	2647
	11th to 20th	Night	27% 4 13% 30% 22% 4	2562
	21st to end	Night	31% 6% 14% 31% 15% 2	2732
February	1st to 10th	Night	37% 5% 14% 24% 16% 3	2278
	11th to 20th	Night	34% 5% 14% 28% 16% 3	2098
	21st to end	Night	32% 4 12% 26% 20% 6%	1776
March	1st to 10th	Night	31% 5% 11% 26% 22% 6%	2160
	11th to 20th	Night	33% 4 12% 24% 23% 4	2123
	21st to end	Night	38% 7% 16% 22% 14% 2	1980
April	1st to 10th	Night	36% 8% 13% 20% 18% 6%	1800
	11th to 20th	Night	37% 5% 14% 25% 15% 4	1777
	21st to end	Night	40% 7% 8% 26% 16% 1	1706
May	1st to 10th	Night	38% 8% 16% 25% 12% 1	1620
	11th to 20th	Night	38% 10% 16% 25% 10% 1	1506
	21st to end	Night	39% 10% 18% 19% 10% 4	1552
June	1st to 10th	Night	29% 9% 23% 25% 11% 2	1440
	11th to 20th	Night	27% 9% 17% 25% 14% 7%	1440
	21st to end	Night	29% 8% 13% 25% 21% 4	1440
July	1st to 10th	Night	31% 8% 14% 25% 18% 4	1400
	11th to 20th	Night	23% 8% 12% 24% 22% 11%	1392
	21st to end	Night	27% 9% 17% 27% 17% 4	1488
August	1st to 10th	Night	30% 8% 22% 22% 13% 4	1495
	11th to 20th	Night	22% 7% 14% 27% 22% 8%	1773
	21st to end	Night	23% 6% 12% 24% 26% 10%	1980
September	1st to 10th	Night	26% 5% 10% 22% 26% 12%	1800
	11th to 20th	Night	25% 5% 9% 25% 23% 13%	1903
	21st to end	Night	25% 4 7% 28% 26% 10%	1980
October	1st to 10th	Night	30% 4 10% 23% 26% 6%	2011
	11th to 20th	Night	25% 4 9% 29% 22% 12%	2160
	21st to end	Night	26% 5% 12% 25% 23% 9%	2564
November	1st to 10th	Night	24% 4 14% 26% 24% 8%	2405
	11th to 20th	Night	26% 4 12% 28% 23% 8%	2470
	21st to end	Night	27% 5% 10% 28% 24% 7%	2496
December	1st to 10th	Night	29% 4 14% 29% 19% 5%	2660
	11th to 20th	Night	24% 4 14% 35% 20% 3	3272
	21st to end	Night	36% 5% 11% 31% 15% 2	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	7% 9% 39% 29% 15% 2	270
	11th to 20th	Day	9% 11% 40% 31% 8%	248
	21st to end	Day	9% 12% 55% 19% 4 1	264
February	1st to 10th	Day	7% 10% 59% 22% 2	240
	11th to 20th	Day	10% 13% 48% 21% 6% 2	240
	21st to end	Day	10% 19% 45% 21% 5% 1	198
March	1st to 10th	Day	8% 15% 37% 27% 13% 1	240
	11th to 20th	Day	10% 7% 34% 33% 13% 2	247
	21st to end	Day	14% 11% 40% 25% 8% 2	462
April	1st to 10th	Day	14% 16% 38% 25% 7%	420
	11th to 20th	Day	17% 14% 35% 23% 8% 2	412
	21st to end	Day	13% 12% 31% 27% 14% 2	512
May	1st to 10th	Day	17% 8% 31% 26% 15% 4	603
	11th to 20th	Day	20% 6% 25% 31% 15% 4	625
	21st to end	Day	13% 9% 27% 29% 19% 4	679
June	1st to 10th	Day	8% 5% 22% 30% 27% 9%	630
	11th to 20th	Day	6% 6% 32% 31% 20% 4	630
	21st to end	Day	4 4 28% 34% 24% 6%	630
July	1st to 10th	Day	8% 2 17% 38% 28% 7%	621
	11th to 20th	Day	4 2 16% 39% 32% 6%	618
	21st to end	Day	5% 2 15% 36% 34% 8%	684
August	1st to 10th	Day	7% 1 16% 37% 33% 6%	626
	11th to 20th	Day	4 4 22% 35% 26% 10%	437
	21st to end	Day	5% 2 21% 35% 27% 10%	495
September	1st to 10th	Day	7% 2 22% 35% 24% 10%	450
	11th to 20th	Day	5% 1 18% 32% 32% 12%	346
	21st to end	Day	11% 3 25% 27% 23% 10%	270
October	1st to 10th	Day	14% 6% 24% 24% 20% 11%	270
	11th to 20th	Day	8% 11% 35% 27% 12% 6%	270
	21st to end	Day	11% 13% 37% 24% 12% 3	297
November	1st to 10th	Day	4 9% 44% 27% 12% 4	270
	11th to 20th	Day	7% 12% 40% 27% 13% 1	270
	21st to end	Day	10% 7% 39% 31% 11% 1	270
December	1st to 10th	Day	7% 11% 45% 26% 11%	270
	11th to 20th	Day	8% 11% 47% 27% 7%	270
	21st to end	Day	11% 15% 48% 19% 6% 1	297
January	1st to 10th	Night	5% 12% 42% 31% 8% 1	950
	11th to 20th	Night	6% 14% 43% 31% 5%	915
	21st to end	Night	7% 12% 49% 28% 4	950
February	1st to 10th	Night	8% 11% 52% 25% 4	720
	11th to 20th	Night	7% 11% 52% 24% 6%	704
	21st to end	Night	8% 9% 51% 28% 3	592
March	1st to 10th	Night	10% 9% 44% 32% 5%	720
	11th to 20th	Night	11% 7% 42% 32% 8%	691
	21st to end	Night	12% 9% 39% 34% 5%	594
April	1st to 10th	Night	11% 12% 40% 32% 4	540
	11th to 20th	Night	15% 12% 40% 31% 3	533
	21st to end	Night	17% 13% 29% 35% 6%	540
May	1st to 10th	Night	16% 8% 33% 35% 8% 1	540
	11th to 20th	Night	19% 5% 29% 36% 11%	531
	21st to end	Night	15% 10% 34% 29% 11% 1	584
June	1st to 10th	Night	9% 5% 32% 38% 16% 1	540
	11th to 20th	Night	9% 6% 39% 40% 7%	540
	21st to end	Night	5% 4 28% 49% 12% 1	540
July	1st to 10th	Night	9% 3 26% 45% 17% 1	525
	11th to 20th	Night	5% 1 22% 56% 15%	522
	21st to end	Night	5% 2 23% 50% 20%	591
August	1st to 10th	Night	7% 2 18% 55% 18% 1	537
	11th to 20th	Night	6% 2 27% 51% 14%	534
	21st to end	Night	5% 2 23% 55% 15%	594
September	1st to 10th	Night	9% 4 29% 44% 14% 1	540
	11th to 20th	Night	9% 2 27% 43% 17% 2	540
	21st to end	Night	10% 4 29% 44% 13%	540
October	1st to 10th	Night	15% 7% 29% 35% 14% 1	571
	11th to 20th	Night	9% 8% 36% 35% 11%	720
	21st to end	Night	11% 8% 36% 36% 9% 1	980
November	1st to 10th	Night	7% 5% 41% 38% 8% 1	925
	11th to 20th	Night	8% 11% 42% 33% 6% 1	950
	21st to end	Night	8% 10% 38% 35% 8% 1	950
December	1st to 10th	Night	8% 11% 48% 27% 5% 1	950
	11th to 20th	Night	7% 8% 48% 30% 6%	950
	21st to end	Night	10% 13% 43% 30% 4	1045

Page generated at 2024-01-10 17:35:20. Version ac07

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