Red Rock Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Red Rock Ranch 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	12% 5% 2 4 4 3 4 4 5% 7% 49%	74968
	Night	11% 4 2 4 4 2 4 4 5% 7% 54%	75103
Transparency	Day	34% 4 10% 22% 19% 10%	74696
	Night	30% 4 11% 22% 19% 13%	74895
Seeing	Day	13% 3 17% 33% 27% 8%	13588
	Night	13% 4 23% 43% 16% 1	23706

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	15% 5% 2 3 3 2 2 3 4 6% 54%	1707
	11th to 20th	Day	17% 6% 2 4 4 2 3 3 4 6% 51%	1805
	21st to end	Day	14% 7% 1 5% 5% 2 4 3 5% 6% 48%	2040
February	1st to 10th	Day	17% 7% 3 5% 5% 2 3 4 4 4 48%	1800
	11th to 20th	Day	17% 6% 2 5% 4 2 4 3 4 6% 47%	1749
	21st to end	Day	15% 5% 2 4 4 2 2 3 5% 7% 51%	1480
March	1st to 10th	Day	19% 6% 3 4 4 1 4 3 4 6% 45%	1872
	11th to 20th	Day	15% 6% 3 5% 3 2 4 4 5% 7% 47%	1980
	21st to end	Day	16% 6% 2 5% 4 3 3 3 4 5% 50%	2178
April	1st to 10th	Day	13% 6% 2 5% 4 3 3 4 4 8% 47%	1980
	11th to 20th	Day	15% 5% 2 4 3 2 4 4 4 7% 48%	2084
	21st to end	Day	14% 5% 3 5% 4 2 4 4 4 6% 49%	2162
May	1st to 10th	Day	15% 5% 2 4 4 3 4 4 4 8% 46%	2340
	11th to 20th	Day	14% 6% 2 5% 5% 3 5% 5% 6% 7% 42%	2302
	21st to end	Day	12% 6% 3 7% 5% 4 5% 5% 6% 8% 39%	2531
June	1st to 10th	Day	5% 3 1 3 4 3 5% 5% 7% 10% 54%	2340
	11th to 20th	Day	6% 4 2 3 4 3 6% 5% 6% 9% 53%	2340
	21st to end	Day	6% 4 3 5% 5% 4 6% 7% 6% 9% 45%	2340
July	1st to 10th	Day	11% 6% 3 6% 6% 4 5% 4 5% 9% 41%	2340
	11th to 20th	Day	5% 2 1 3 4 2 5% 5% 6% 8% 58%	2340
	21st to end	Day	5% 2 2 3 4 2 5% 5% 5% 11% 56%	2495
August	1st to 10th	Day	2 2 1 2 3 2 4 3 5% 9% 66%	2149
	11th to 20th	Day	5% 3 1 3 3 4 4 6% 6% 8% 57%	2123
	21st to end	Day	7% 4 2 4 5% 3 5% 6% 7% 9% 49%	2354
September	1st to 10th	Day	11% 5% 2 6% 6% 4 6% 5% 7% 7% 41%	1980
	11th to 20th	Day	11% 6% 2 6% 6% 3 5% 5% 6% 8% 42%	1980
	21st to end	Day	8% 4 2 5% 5% 3 5% 5% 6% 7% 49%	1980
October	1st to 10th	Day	7% 4 2 4 4 3 4 5% 4 6% 56%	1980
	11th to 20th	Day	14% 4 2 5% 4 3 3 4 4 6% 51%	1972
	21st to end	Day	12% 4 2 3 3 1 2 3 5% 4 58%	1980
November	1st to 10th	Day	16% 7% 2 5% 4 2 3 3 4 6% 47%	1839
	11th to 20th	Day	15% 5% 2 4 4 3 4 4 4 5% 51%	1710
	21st to end	Day	17% 6% 3 5% 4 3 3 4 3 6% 47%	1710
December	1st to 10th	Day	19% 6% 3 5% 4 2 2 3 4 6% 47%	1710
	11th to 20th	Day	17% 6% 2 5% 5% 2 4 4 4 5% 44%	2161
	21st to end	Day	14% 6% 2 4 4 2 3 3 3 5% 54%	3135
January	1st to 10th	Night	15% 4 2 3 3 2 2 3 4 6% 56%	2458
	11th to 20th	Night	15% 5% 2 3 4 2 3 3 3 5% 54%	2390
	21st to end	Night	17% 5% 2 5% 3 2 3 4 4 6% 49%	2460
February	1st to 10th	Night	14% 5% 2 4 3 2 3 4 3 6% 55%	2160
	11th to 20th	Night	18% 5% 2 3 3 2 2 3 3 5% 53%	2098
	21st to end	Night	13% 5% 2 4 4 2 4 5% 5% 6% 50%	1776
March	1st to 10th	Night	15% 6% 2 4 3 3 3 4 4 7% 49%	2085
	11th to 20th	Night	11% 6% 2 4 4 3 4 4 4 6% 51%	1980
	21st to end	Night	12% 4 2 2 4 2 3 3 5% 8% 55%	2178
April	1st to 10th	Night	9% 4 2 4 5% 2 4 5% 6% 9% 51%	1980
	11th to 20th	Night	15% 5% 1 4 4 2 3 5% 5% 7% 50%	1821
	21st to end	Night	14% 4 2 5% 4 2 4 3 3 6% 54%	1796
May	1st to 10th	Night	9% 4 2 5% 4 2 5% 4 6% 9% 51%	1620
	11th to 20th	Night	11% 4 2 4 4 2 4 5% 6% 9% 49%	1593
	21st to end	Night	8% 5% 3 4 5% 2 5% 4 6% 8% 50%	1745
June	1st to 10th	Night	3 2 2 3 2 2 4 4 4 10% 65%	1620
	11th to 20th	Night	3 2 1 3 4 2 4 5% 6% 10% 61%	1620
	21st to end	Night	5% 2 2 4 5% 3 5% 5% 6% 10% 53%	1620
July	1st to 10th	Night	7% 5% 2 5% 4 4 5% 4 4 11% 48%	1620
	11th to 20th	Night	2 2 1 2 3 2 4 4 5% 8% 65%	1620
	21st to end	Night	3 2 1 3 3 2 4 4 6% 13% 60%	1816
August	1st to 10th	Night	1 1 1 2 3 1 3 4 4 8% 71%	1790
	11th to 20th	Night	4 2 1 3 3 2 5% 4 7% 9% 59%	1778
	21st to end	Night	5% 4 2 5% 5% 3 4 5% 6% 9% 54%	2002
September	1st to 10th	Night	7% 4 2 5% 5% 3 6% 5% 7% 9% 46%	1980
	11th to 20th	Night	10% 6% 2 5% 5% 3 4 5% 6% 8% 45%	1980
	21st to end	Night	8% 4 2 4 4 3 4 4 7% 8% 53%	1980
October	1st to 10th	Night	6% 3 2 3 4 2 3 3 4 7% 64%	1980
	11th to 20th	Night	13% 3 2 3 3 2 4 3 4 6% 57%	1980
	21st to end	Night	12% 3 1 3 3 2 2 2 3 4 65%	2364
November	1st to 10th	Night	12% 5% 2 5% 3 1 3 3 4 6% 55%	2235
	11th to 20th	Night	11% 5% 2 4 4 2 3 4 4 6% 56%	2470
	21st to end	Night	16% 4 2 4 4 2 4 4 5% 6% 49%	2470
December	1st to 10th	Night	16% 5% 2 4 3 2 2 3 4 6% 53%	2470
	11th to 20th	Night	17% 5% 2 4 4 2 3 3 4 5% 50%	3036
	21st to end	Night	14% 5% 2 3 3 2 3 5% 5% 6% 52%	4532

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	34% 2 5% 18% 22% 19%	1708
	11th to 20th	Day	37% 2 6% 17% 20% 19%	1805
	21st to end	Day	38% 3 6% 14% 22% 17%	2040
February	1st to 10th	Day	42% 3 5% 13% 19% 19%	1800
	11th to 20th	Day	40% 2 6% 17% 21% 14%	1759
	21st to end	Day	34% 3 8% 17% 20% 17%	1480
March	1st to 10th	Day	40% 3 9% 18% 18% 12%	1872
	11th to 20th	Day	38% 4 8% 16% 15% 19%	1980
	21st to end	Day	37% 3 9% 17% 18% 16%	2178
April	1st to 10th	Day	37% 3 9% 19% 19% 13%	1980
	11th to 20th	Day	39% 3 7% 19% 17% 16%	2084
	21st to end	Day	36% 3 7% 20% 19% 14%	2162
May	1st to 10th	Day	37% 4 9% 23% 17% 10%	2340
	11th to 20th	Day	40% 4 9% 23% 19% 5%	2306
	21st to end	Day	41% 5% 9% 23% 18% 3	2531
June	1st to 10th	Day	23% 6% 14% 32% 20% 5%	2340
	11th to 20th	Day	27% 4 13% 30% 19% 6%	2340
	21st to end	Day	34% 5% 14% 27% 16% 4	2340
July	1st to 10th	Day	40% 5% 14% 25% 14% 2	2276
	11th to 20th	Day	23% 5% 17% 29% 22% 3	2271
	21st to end	Day	20% 5% 22% 36% 16% 1	2356
August	1st to 10th	Day	15% 4 18% 39% 22% 2	2136
	11th to 20th	Day	23% 6% 17% 34% 16% 3	2123
	21st to end	Day	30% 6% 17% 28% 16% 3	2354
September	1st to 10th	Day	40% 6% 12% 21% 15% 6%	1980
	11th to 20th	Day	39% 6% 11% 22% 18% 4	1980
	21st to end	Day	33% 4 10% 25% 18% 10%	1980
October	1st to 10th	Day	29% 3 9% 24% 26% 8%	1980
	11th to 20th	Day	34% 4 9% 18% 20% 14%	1972
	21st to end	Day	29% 3 4 18% 26% 20%	1980
November	1st to 10th	Day	39% 3 7% 21% 19% 11%	1839
	11th to 20th	Day	36% 2 7% 19% 21% 15%	1710
	21st to end	Day	41% 2 5% 19% 19% 15%	1710
December	1st to 10th	Day	41% 2 8% 17% 22% 11%	1710
	11th to 20th	Day	42% 2 8% 11% 20% 17%	2159
	21st to end	Day	35% 3 5% 16% 29% 13%	3135
January	1st to 10th	Night	31% 2 6% 16% 23% 21%	2458
	11th to 20th	Night	35% 2 6% 17% 20% 20%	2390
	21st to end	Night	38% 3 5% 15% 19% 20%	2460
February	1st to 10th	Night	32% 2 8% 16% 18% 23%	2160
	11th to 20th	Night	36% 2 6% 18% 20% 18%	2098
	21st to end	Night	36% 4 6% 16% 20% 19%	1776
March	1st to 10th	Night	36% 3 11% 17% 18% 14%	2085
	11th to 20th	Night	35% 5% 10% 14% 16% 20%	1980
	21st to end	Night	30% 3 14% 20% 16% 18%	2178
April	1st to 10th	Night	30% 4 12% 20% 20% 15%	1980
	11th to 20th	Night	35% 4 10% 17% 16% 18%	1821
	21st to end	Night	36% 3 9% 20% 17% 15%	1796
May	1st to 10th	Night	30% 6% 14% 21% 16% 13%	1620
	11th to 20th	Night	31% 6% 13% 25% 19% 6%	1594
	21st to end	Night	30% 6% 17% 29% 16% 2	1746
June	1st to 10th	Night	17% 4 17% 35% 24% 3	1620
	11th to 20th	Night	20% 5% 12% 32% 25% 6%	1620
	21st to end	Night	26% 7% 19% 27% 17% 4	1620
July	1st to 10th	Night	32% 7% 21% 26% 12% 2	1575
	11th to 20th	Night	17% 5% 19% 33% 24% 2	1566
	21st to end	Night	14% 6% 28% 37% 14% 2	1715
August	1st to 10th	Night	12% 5% 19% 43% 19% 1	1779
	11th to 20th	Night	21% 6% 21% 35% 14% 3	1778
	21st to end	Night	27% 6% 21% 29% 14% 3	2002
September	1st to 10th	Night	33% 7% 16% 21% 16% 7%	1980
	11th to 20th	Night	35% 7% 16% 21% 18% 4	1980
	21st to end	Night	27% 5% 12% 25% 19% 11%	1980
October	1st to 10th	Night	22% 4 11% 30% 21% 11%	1980
	11th to 20th	Night	29% 3 11% 21% 20% 16%	1980
	21st to end	Night	26% 2 6% 17% 25% 24%	2364
November	1st to 10th	Night	32% 3 6% 21% 24% 14%	2235
	11th to 20th	Night	30% 4 10% 20% 21% 16%	2470
	21st to end	Night	36% 3 8% 19% 18% 16%	2470
December	1st to 10th	Night	34% 3 8% 21% 20% 14%	2470
	11th to 20th	Night	39% 3 5% 17% 18% 19%	3037
	21st to end	Night	33% 3 7% 15% 25% 17%	4532

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	19% 7% 26% 34% 13%	270
	11th to 20th	Day	20% 6% 21% 39% 13% 1	270
	21st to end	Day	20% 4 30% 36% 10%	282
February	1st to 10th	Day	27% 5% 23% 24% 19% 3	240
	11th to 20th	Day	23% 6% 33% 27% 9% 3	240
	21st to end	Day	25% 5% 37% 25% 8%	198
March	1st to 10th	Day	22% 5% 35% 30% 8%	240
	11th to 20th	Day	14% 5% 36% 33% 12%	240
	21st to end	Day	16% 8% 35% 32% 7% 1	264
April	1st to 10th	Day	19% 5% 35% 33% 9%	240
	11th to 20th	Day	13% 8% 36% 32% 10% 1	362
	21st to end	Day	11% 7% 37% 36% 8%	422
May	1st to 10th	Day	16% 6% 31% 36% 10% 1	603
	11th to 20th	Day	17% 4 26% 38% 14% 1	625
	21st to end	Day	13% 4 22% 44% 16% 1	679
June	1st to 10th	Day	5% 1 13% 45% 30% 6%	630
	11th to 20th	Day	6% 1 11% 47% 30% 5%	630
	21st to end	Day	7% 1 8% 37% 37% 9%	630
July	1st to 10th	Day	12% 2 4 31% 41% 11%	621
	11th to 20th	Day	4 3 30% 51% 10%	618
	21st to end	Day	3 1 2 30% 50% 13%	633
August	1st to 10th	Day	2 2 29% 51% 15%	447
	11th to 20th	Day	4 1 2 28% 45% 20%	437
	21st to end	Day	7% 3 2 26% 36% 26%	473
September	1st to 10th	Day	12% 1 1 15% 44% 27%	270
	11th to 20th	Day	7% 1 2 14% 43% 32%	270
	21st to end	Day	9% 1 3 17% 47% 23%	270
October	1st to 10th	Day	9% 1 8% 29% 37% 16%	270
	11th to 20th	Day	15% 1 8% 35% 34% 8%	270
	21st to end	Day	18% 5% 20% 29% 22% 6%	297
November	1st to 10th	Day	21% 1 13% 36% 23% 6%	270
	11th to 20th	Day	23% 5% 16% 27% 23% 7%	270
	21st to end	Day	24% 5% 27% 31% 10% 3	270
December	1st to 10th	Day	22% 1 18% 33% 21% 4	270
	11th to 20th	Day	22% 4 24% 31% 18%	270
	21st to end	Day	18% 2 26% 34% 17% 4	297
January	1st to 10th	Night	18% 4 22% 42% 14% 1	950
	11th to 20th	Night	18% 4 25% 44% 9%	870
	21st to end	Night	19% 6% 25% 43% 8%	820
February	1st to 10th	Night	17% 7% 28% 38% 9% 1	720
	11th to 20th	Night	21% 5% 32% 35% 7%	704
	21st to end	Night	18% 6% 34% 39% 3	592
March	1st to 10th	Night	20% 7% 35% 33% 6%	645
	11th to 20th	Night	13% 6% 38% 39% 4	540
	21st to end	Night	12% 7% 42% 34% 5%	594
April	1st to 10th	Night	11% 6% 47% 32% 4	540
	11th to 20th	Night	16% 7% 44% 30% 3	533
	21st to end	Night	14% 8% 44% 30% 5% 1	540
May	1st to 10th	Night	10% 6% 45% 36% 3	540
	11th to 20th	Night	13% 4 37% 38% 8%	531
	21st to end	Night	8% 3 36% 45% 7%	584
June	1st to 10th	Night	3 1 25% 54% 16%	540
	11th to 20th	Night	2 1 32% 53% 11%	540
	21st to end	Night	4 3 16% 56% 20% 1	540
July	1st to 10th	Night	8% 2 7% 57% 23% 2	525
	11th to 20th	Night	3 1 9% 59% 27% 2	522
	21st to end	Night	3 2 8% 59% 27% 1	591
August	1st to 10th	Night	2 1 7% 55% 34% 1	537
	11th to 20th	Night	4 2 6% 57% 28% 3	534
	21st to end	Night	5% 2 7% 46% 37% 3	594
September	1st to 10th	Night	8% 1 4 47% 35% 4	540
	11th to 20th	Night	11% 1 5% 42% 38% 4	540
	21st to end	Night	9% 1 8% 43% 35% 4	540
October	1st to 10th	Night	6% 1 11% 49% 31% 2	540
	11th to 20th	Night	14% 2 15% 46% 21% 1	540
	21st to end	Night	13% 3 20% 39% 23% 2	780
November	1st to 10th	Night	14% 2 15% 42% 25% 2	755
	11th to 20th	Night	13% 3 19% 44% 21% 1	950
	21st to end	Night	18% 3 21% 41% 15% 1	950
December	1st to 10th	Night	19% 3 17% 43% 17% 1	950
	11th to 20th	Night	23% 4 20% 40% 13%	950
	21st to end	Night	16% 4 22% 46% 11% 1	1045

Page generated at 2024-01-24 08:37:25. Version ac07

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