NR Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the NR 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	8% 5% 2 4 4 3 4 4 5% 7% 53%	74976
	Night	8% 4 2 4 4 2 3 4 5% 8% 57%	75099
Transparency	Day	30% 5% 10% 21% 22% 12%	74705
	Night	27% 5% 11% 21% 22% 14%	74891
Seeing	Day	10% 6% 23% 33% 23% 7%	13734
	Night	9% 6% 30% 39% 15% 1	23845

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	10% 5% 2 4 3 2 4 3 4 6% 58%	1707
	11th to 20th	Day	11% 5% 2 3 3 2 3 4 5% 6% 55%	1800
	21st to end	Day	10% 4 2 4 4 3 4 4 4 5% 57%	2040
February	1st to 10th	Day	10% 6% 2 5% 5% 2 3 3 4 5% 55%	1800
	11th to 20th	Day	11% 5% 2 4 3 2 4 3 6% 6% 52%	1749
	21st to end	Day	10% 5% 2 3 3 2 3 3 4 7% 58%	1480
March	1st to 10th	Day	12% 6% 3 4 5% 3 4 3 6% 6% 48%	1824
	11th to 20th	Day	11% 6% 3 5% 4 3 3 4 5% 6% 52%	1980
	21st to end	Day	8% 4 3 5% 4 2 3 4 5% 7% 55%	2178
April	1st to 10th	Day	8% 6% 2 5% 4 2 3 4 5% 7% 53%	2037
	11th to 20th	Day	10% 5% 3 4 5% 3 3 4 4 6% 53%	2134
	21st to end	Day	10% 6% 2 4 4 2 4 3 4 6% 56%	2160
May	1st to 10th	Day	10% 5% 2 5% 4 3 5% 4 5% 8% 48%	2330
	11th to 20th	Day	10% 6% 3 5% 4 3 5% 5% 6% 8% 46%	2302
	21st to end	Day	9% 5% 3 6% 5% 4 4 5% 5% 8% 44%	2531
June	1st to 10th	Day	3 3 1 4 5% 3 4 4 6% 8% 58%	2340
	11th to 20th	Day	4 3 2 4 4 3 5% 5% 6% 9% 55%	2340
	21st to end	Day	5% 3 3 5% 6% 3 6% 6% 7% 9% 48%	2340
July	1st to 10th	Day	8% 4 3 6% 7% 4 6% 6% 7% 9% 41%	2340
	11th to 20th	Day	4 2 2 3 4 3 5% 4 5% 9% 60%	2340
	21st to end	Day	4 2 2 3 4 3 5% 5% 6% 10% 57%	2492
August	1st to 10th	Day	1 2 1 3 4 2 4 5% 5% 8% 65%	2149
	11th to 20th	Day	6% 4 2 4 6% 4 4 6% 6% 8% 51%	2123
	21st to end	Day	5% 4 2 5% 6% 4 6% 6% 6% 9% 46%	2376
September	1st to 10th	Day	10% 5% 2 4 7% 4 5% 4 6% 7% 45%	2012
	11th to 20th	Day	10% 5% 2 7% 6% 3 4 6% 6% 9% 42%	1980
	21st to end	Day	8% 5% 2 4 5% 3 4 4 5% 7% 52%	1980
October	1st to 10th	Day	6% 4 2 3 5% 3 4 4 5% 8% 57%	1980
	11th to 20th	Day	11% 5% 2 4 4 2 4 4 3 6% 55%	1980
	21st to end	Day	10% 5% 1 4 3 2 3 2 3 5% 63%	1994
November	1st to 10th	Day	10% 6% 2 4 3 2 3 3 5% 8% 55%	1732
	11th to 20th	Day	8% 5% 1 4 4 2 4 5% 5% 6% 57%	1710
	21st to end	Day	11% 6% 3 5% 3 2 3 4 5% 6% 54%	1710
December	1st to 10th	Day	11% 6% 2 4 4 2 4 4 5% 7% 53%	1710
	11th to 20th	Day	11% 6% 3 5% 5% 2 4 3 5% 5% 51%	2161
	21st to end	Day	10% 6% 2 3 2 2 3 3 4 4 61%	3135
January	1st to 10th	Night	10% 5% 1 3 3 2 3 3 5% 7% 58%	2458
	11th to 20th	Night	10% 5% 2 4 3 2 3 3 4 7% 57%	2394
	21st to end	Night	11% 5% 3 4 4 3 4 4 4 6% 53%	2460
February	1st to 10th	Night	8% 6% 3 4 4 2 3 4 4 6% 57%	2160
	11th to 20th	Night	12% 5% 2 4 3 2 3 4 4 6% 54%	2098
	21st to end	Night	9% 5% 2 5% 3 2 4 4 5% 7% 55%	1776
March	1st to 10th	Night	9% 6% 2 4 4 3 4 4 5% 8% 51%	2135
	11th to 20th	Night	10% 5% 2 4 5% 3 4 4 5% 6% 52%	1980
	21st to end	Night	6% 4 2 4 4 2 3 4 5% 7% 59%	2178
April	1st to 10th	Night	6% 3 2 4 4 3 3 5% 5% 8% 57%	1918
	11th to 20th	Night	9% 5% 2 4 4 2 4 4 5% 7% 55%	1777
	21st to end	Night	9% 4 2 4 3 2 3 3 3 7% 61%	1800
May	1st to 10th	Night	7% 4 2 4 3 2 4 4 5% 8% 56%	1630
	11th to 20th	Night	8% 5% 2 4 4 2 4 4 6% 8% 51%	1593
	21st to end	Night	7% 4 3 5% 3 3 4 4 6% 10% 51%	1745
June	1st to 10th	Night	1 2 1 3 2 2 4 4 6% 12% 64%	1620
	11th to 20th	Night	2 1 1 2 3 3 4 4 6% 11% 64%	1620
	21st to end	Night	4 2 1 3 4 2 4 5% 5% 10% 59%	1620
July	1st to 10th	Night	5% 3 2 4 5% 2 4 5% 7% 13% 50%	1620
	11th to 20th	Night	2 2 1 3 2 2 3 4 5% 9% 68%	1620
	21st to end	Night	2 1 2 3 2 3 4 6% 12% 65%	1820
August	1st to 10th	Night	2 1 2 2 2 3 4 4 8% 74%	1790
	11th to 20th	Night	3 3 2 4 4 2 5% 5% 6% 10% 56%	1778
	21st to end	Night	5% 3 2 4 4 3 4 6% 6% 10% 53%	1980
September	1st to 10th	Night	7% 4 2 4 5% 3 4 5% 6% 8% 53%	1947
	11th to 20th	Night	8% 4 2 4 5% 2 5% 5% 5% 8% 50%	1980
	21st to end	Night	7% 3 2 4 4 2 4 5% 5% 8% 56%	1980
October	1st to 10th	Night	4 3 1 3 3 2 4 4 4 7% 65%	1980
	11th to 20th	Night	9% 5% 2 3 4 2 3 4 4 6% 59%	1980
	21st to end	Night	10% 4 1 3 3 2 2 3 3 4 64%	2343
November	1st to 10th	Night	9% 4 2 3 3 2 3 3 4 6% 61%	2341
	11th to 20th	Night	7% 4 1 3 3 2 4 3 4 7% 61%	2470
	21st to end	Night	11% 5% 2 4 4 2 3 4 5% 6% 53%	2470
December	1st to 10th	Night	10% 6% 2 3 3 2 4 4 4 7% 56%	2470
	11th to 20th	Night	10% 6% 3 5% 4 3 4 4 4 6% 51%	3036
	21st to end	Night	10% 6% 2 4 3 2 2 2 4 7% 58%	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	29% 3 5% 18% 28% 18%	1708
	11th to 20th	Day	30% 4 6% 17% 26% 17%	1800
	21st to end	Day	31% 4 7% 13% 28% 18%	2040
February	1st to 10th	Day	32% 3 7% 14% 23% 21%	1800
	11th to 20th	Day	33% 3 8% 18% 21% 17%	1759
	21st to end	Day	28% 3 8% 14% 26% 21%	1480
March	1st to 10th	Day	37% 4 7% 16% 20% 16%	1824
	11th to 20th	Day	34% 4 8% 16% 18% 20%	1980
	21st to end	Day	31% 4 9% 16% 22% 19%	2178
April	1st to 10th	Day	31% 4 8% 20% 21% 17%	2037
	11th to 20th	Day	32% 5% 7% 19% 21% 17%	2134
	21st to end	Day	31% 3 8% 21% 22% 14%	2160
May	1st to 10th	Day	33% 6% 11% 16% 24% 11%	2330
	11th to 20th	Day	35% 6% 11% 23% 20% 5%	2306
	21st to end	Day	37% 7% 10% 23% 18% 4	2531
June	1st to 10th	Day	22% 7% 13% 31% 22% 5%	2340
	11th to 20th	Day	24% 6% 12% 28% 23% 6%	2340
	21st to end	Day	31% 8% 12% 24% 19% 5%	2340
July	1st to 10th	Day	36% 9% 17% 27% 9% 1	2276
	11th to 20th	Day	22% 7% 15% 29% 24% 4	2271
	21st to end	Day	19% 8% 22% 36% 15% 1	2354
August	1st to 10th	Day	17% 6% 13% 39% 24% 2	2136
	11th to 20th	Day	31% 8% 14% 29% 15% 4	2123
	21st to end	Day	32% 9% 16% 25% 15% 4	2376
September	1st to 10th	Day	38% 7% 10% 20% 18% 7%	2012
	11th to 20th	Day	38% 7% 13% 20% 18% 5%	1980
	21st to end	Day	32% 6% 10% 20% 21% 11%	1980
October	1st to 10th	Day	26% 7% 9% 23% 26% 10%	1980
	11th to 20th	Day	32% 4 8% 14% 22% 19%	1980
	21st to end	Day	27% 3 5% 15% 29% 21%	1994
November	1st to 10th	Day	30% 4 9% 23% 21% 13%	1732
	11th to 20th	Day	28% 4 8% 19% 23% 18%	1710
	21st to end	Day	33% 4 6% 17% 24% 16%	1710
December	1st to 10th	Day	33% 3 8% 18% 27% 12%	1710
	11th to 20th	Day	35% 4 7% 12% 24% 18%	2159
	21st to end	Day	28% 3 4 15% 27% 22%	3135
January	1st to 10th	Night	28% 3 6% 14% 27% 22%	2458
	11th to 20th	Night	29% 2 6% 19% 24% 20%	2394
	21st to end	Night	33% 4 5% 13% 23% 21%	2460
February	1st to 10th	Night	29% 3 8% 14% 23% 22%	2160
	11th to 20th	Night	32% 3 7% 17% 23% 19%	2098
	21st to end	Night	30% 4 7% 13% 23% 23%	1776
March	1st to 10th	Night	32% 4 10% 17% 23% 14%	2135
	11th to 20th	Night	33% 5% 9% 15% 18% 20%	1980
	21st to end	Night	26% 4 12% 20% 19% 19%	2178
April	1st to 10th	Night	27% 5% 11% 21% 18% 19%	1918
	11th to 20th	Night	30% 5% 9% 18% 18% 19%	1777
	21st to end	Night	26% 5% 10% 24% 21% 14%	1800
May	1st to 10th	Night	27% 7% 10% 23% 22% 12%	1630
	11th to 20th	Night	31% 7% 12% 26% 19% 6%	1594
	21st to end	Night	30% 7% 16% 27% 18% 3	1746
June	1st to 10th	Night	14% 7% 17% 36% 22% 3	1620
	11th to 20th	Night	16% 6% 17% 32% 22% 7%	1620
	21st to end	Night	21% 6% 18% 29% 20% 6%	1620
July	1st to 10th	Night	25% 9% 25% 27% 13% 1	1575
	11th to 20th	Night	14% 7% 14% 33% 27% 4	1566
	21st to end	Night	9% 9% 25% 40% 17% 1	1719
August	1st to 10th	Night	10% 5% 18% 41% 24% 2	1779
	11th to 20th	Night	22% 9% 18% 31% 17% 3	1778
	21st to end	Night	25% 9% 19% 28% 16% 4	1980
September	1st to 10th	Night	28% 8% 13% 24% 20% 8%	1947
	11th to 20th	Night	31% 8% 16% 21% 19% 5%	1980
	21st to end	Night	24% 7% 13% 24% 19% 13%	1980
October	1st to 10th	Night	20% 5% 15% 25% 23% 12%	1980
	11th to 20th	Night	28% 4 9% 18% 24% 17%	1980
	21st to end	Night	26% 3 6% 17% 25% 24%	2343
November	1st to 10th	Night	26% 3 9% 20% 27% 15%	2341
	11th to 20th	Night	24% 5% 9% 21% 23% 19%	2470
	21st to end	Night	32% 4 8% 16% 23% 17%	2470
December	1st to 10th	Night	30% 4 9% 19% 24% 15%	2470
	11th to 20th	Night	35% 3 5% 15% 19% 22%	3037
	21st to end	Night	28% 3 5% 15% 29% 19%	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	13% 11% 41% 26% 8% 1	270
	11th to 20th	Day	16% 10% 33% 31% 9% 1	270
	21st to end	Day	12% 8% 41% 32% 6%	282
February	1st to 10th	Day	16% 11% 36% 25% 10% 1	240
	11th to 20th	Day	20% 10% 40% 23% 6%	240
	21st to end	Day	15% 13% 47% 23% 3	198
March	1st to 10th	Day	14% 12% 45% 23% 6%	240
	11th to 20th	Day	13% 13% 41% 22% 11% 1	240
	21st to end	Day	12% 13% 49% 19% 7% 1	264
April	1st to 10th	Day	12% 9% 44% 30% 5%	297
	11th to 20th	Day	9% 13% 44% 29% 5%	412
	21st to end	Day	12% 12% 41% 28% 7%	420
May	1st to 10th	Day	11% 7% 42% 32% 8% 1	593
	11th to 20th	Day	14% 4 33% 33% 14% 2	625
	21st to end	Day	11% 5% 29% 37% 15% 2	679
June	1st to 10th	Day	4 3 14% 50% 25% 3	630
	11th to 20th	Day	3 1 19% 50% 21% 6%	630
	21st to end	Day	4 1 11% 45% 30% 8%	630
July	1st to 10th	Day	7% 1 6% 35% 39% 11%	621
	11th to 20th	Day	3 3 40% 45% 9%	618
	21st to end	Day	2 5% 34% 42% 17%	630
August	1st to 10th	Day	2 2 32% 44% 19%	447
	11th to 20th	Day	8% 3 29% 43% 17%	437
	21st to end	Day	6% 1 4 25% 42% 21%	495
September	1st to 10th	Day	11% 3 17% 47% 22%	302
	11th to 20th	Day	5% 1 3 23% 44% 23%	270
	21st to end	Day	13% 1 5% 27% 38% 16%	270
October	1st to 10th	Day	4 5% 13% 31% 36% 10%	270
	11th to 20th	Day	11% 4 17% 41% 23% 4	270
	21st to end	Day	15% 9% 25% 30% 16% 4	297
November	1st to 10th	Day	15% 6% 27% 34% 14% 3	270
	11th to 20th	Day	17% 11% 26% 25% 14% 7%	270
	21st to end	Day	18% 12% 36% 23% 8% 3	270
December	1st to 10th	Day	16% 7% 24% 35% 14% 4	270
	11th to 20th	Day	12% 15% 34% 29% 9% 1	270
	21st to end	Day	16% 10% 36% 27% 10%	297
January	1st to 10th	Night	12% 6% 38% 34% 9% 1	950
	11th to 20th	Night	13% 8% 37% 35% 7%	874
	21st to end	Night	14% 8% 39% 33% 6%	820
February	1st to 10th	Night	11% 10% 42% 31% 6%	720
	11th to 20th	Night	14% 8% 42% 31% 4	704
	21st to end	Night	13% 13% 49% 24% 2	592
March	1st to 10th	Night	13% 10% 46% 25% 5%	695
	11th to 20th	Night	11% 10% 39% 33% 6%	540
	21st to end	Night	7% 12% 51% 28% 3	594
April	1st to 10th	Night	7% 6% 55% 29% 4	540
	11th to 20th	Night	10% 10% 50% 28% 2	533
	21st to end	Night	8% 9% 54% 24% 6%	540
May	1st to 10th	Night	8% 8% 48% 33% 3	540
	11th to 20th	Night	11% 5% 39% 37% 8% 1	531
	21st to end	Night	8% 4 39% 40% 9% 1	584
June	1st to 10th	Night	2 1 24% 55% 16% 1	540
	11th to 20th	Night	1 1 29% 58% 10% 1	540
	21st to end	Night	4 2 18% 53% 22% 2	540
July	1st to 10th	Night	6% 2 6% 54% 31% 2	525
	11th to 20th	Night	2 6% 59% 32% 1	522
	21st to end	Night	2 1 6% 58% 33% 2	591
August	1st to 10th	Night	2 5% 54% 36% 2	537
	11th to 20th	Night	4 1 3 49% 39% 3	534
	21st to end	Night	5% 2 5% 41% 43% 4	594
September	1st to 10th	Night	6% 2 5% 45% 40% 3	540
	11th to 20th	Night	8% 1 6% 44% 39% 3	540
	21st to end	Night	7% 2 11% 46% 31% 2	540
October	1st to 10th	Night	4 1 17% 48% 28% 1	540
	11th to 20th	Night	11% 3 24% 44% 16% 1	540
	21st to end	Night	12% 6% 29% 34% 18% 1	759
November	1st to 10th	Night	12% 4 24% 40% 19% 1	861
	11th to 20th	Night	10% 5% 30% 37% 15% 2	950
	21st to end	Night	13% 8% 32% 34% 11% 1	950
December	1st to 10th	Night	13% 5% 29% 43% 9% 1	950
	11th to 20th	Night	15% 8% 34% 36% 7%	950
	21st to end	Night	11% 7% 39% 35% 7% 1	1045

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