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 2026-06-01.

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 5% 4 3 4 3 5% 7% 54%	132502
	Night	8% 5% 2 4 3 3 3 3 5% 7% 58%	130997
Transparency	Day	30% 5% 9% 21% 22% 14%	136374
	Night	26% 4 10% 21% 22% 16%	135190
Seeing	Day	10% 6% 24% 32% 22% 6%	16860
	Night	9% 6% 30% 39% 15% 1	26875

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	8% 3 2 4 3 3 3 2 4 6% 62%	5289
	11th to 20th	Day	8% 5% 2 3 2 2 3 3 4 5% 62%	5592
	21st to end	Day	16% 5% 2 5% 3 3 3 3 4 6% 49%	6468
February	1st to 10th	Day	9% 6% 2 5% 4 3 3 3 5% 5% 54%	2100
	11th to 20th	Day	10% 6% 2 4 3 3 3 3 6% 6% 54%	2049
	21st to end	Day	10% 5% 2 3 3 3 3 3 4 7% 58%	1730
March	1st to 10th	Day	8% 5% 2 5% 3 3 4 3 5% 6% 56%	4677
	11th to 20th	Day	10% 7% 2 5% 3 2 2 2 3 5% 57%	5090
	21st to end	Day	6% 6% 2 6% 3 3 4 3 5% 7% 54%	5583
April	1st to 10th	Day	8% 6% 2 5% 4 3 3 3 5% 7% 53%	2377
	11th to 20th	Day	11% 6% 3 6% 4 4 3 3 5% 6% 50%	2494
	21st to end	Day	9% 6% 2 4 4 3 4 3 5% 6% 54%	2520
May	1st to 10th	Day	11% 6% 3 7% 4 4 4 3 5% 7% 46%	5981
	11th to 20th	Day	8% 5% 2 5% 4 4 4 4 5% 7% 51%	5992
	21st to end	Day	9% 5% 2 6% 4 5% 5% 4 6% 9% 44%	6577
June	1st to 10th	Day	3 3 1 4 4 4 4 3 7% 9% 57%	2601
	11th to 20th	Day	4 4 2 4 3 4 5% 4 6% 9% 56%	2600
	21st to end	Day	4 5% 2 5% 5% 5% 5% 4 7% 9% 50%	2600
July	1st to 10th	Day	12% 6% 2 6% 5% 4 5% 4 6% 8% 42%	5900
	11th to 20th	Day	4 3 2 5% 4 4 5% 4 6% 9% 53%	5900
	21st to end	Day	5% 3 2 5% 5% 4 5% 3 6% 8% 55%	6273
August	1st to 10th	Day	1 2 1 3 3 3 3 3 5% 7% 71%	3905
	11th to 20th	Day	3 2 1 4 3 3 3 3 4 8% 65%	3846
	21st to end	Day	4 4 2 6% 5% 6% 6% 5% 6% 10% 49%	4312
September	1st to 10th	Day	11% 5% 2 6% 6% 5% 5% 3 6% 7% 45%	2235
	11th to 20th	Day	9% 5% 2 8% 5% 4 5% 4 6% 9% 43%	2200
	21st to end	Day	8% 5% 2 5% 4 5% 4 4 5% 7% 53%	2200
October	1st to 10th	Day	5% 4 2 4 4 3 4 3 5% 7% 59%	2200
	11th to 20th	Day	10% 5% 2 4 3 3 3 3 3 5% 57%	2200
	21st to end	Day	9% 5% 1 4 3 2 3 2 3 5% 64%	2215
November	1st to 10th	Day	10% 6% 2 4 3 3 3 2 5% 7% 56%	1918
	11th to 20th	Day	8% 5% 1 4 3 3 4 4 4 6% 59%	1890
	21st to end	Day	11% 7% 3 5% 3 2 3 3 5% 6% 53%	1890
December	1st to 10th	Day	18% 8% 3 6% 3 3 3 3 4 5% 45%	3030
	11th to 20th	Day	11% 7% 2 7% 4 4 4 3 5% 5% 49%	3481
	21st to end	Day	8% 7% 2 4 2 2 2 2 3 4 65%	4587
January	1st to 10th	Night	7% 4 2 5% 3 3 3 3 4 6% 63%	7634
	11th to 20th	Night	6% 4 1 3 2 2 2 2 4 5% 69%	7440
	21st to end	Night	21% 7% 2 4 3 3 3 2 3 5% 47%	7746
February	1st to 10th	Night	8% 7% 2 4 3 3 3 3 4 6% 58%	2520
	11th to 20th	Night	11% 5% 2 5% 3 3 3 3 5% 6% 54%	2458
	21st to end	Night	9% 5% 2 5% 3 3 3 3 6% 7% 55%	2076
March	1st to 10th	Night	6% 5% 1 4 3 3 3 3 5% 8% 58%	5412
	11th to 20th	Night	8% 6% 2 4 3 3 4 2 4 5% 59%	5090
	21st to end	Night	7% 7% 2 4 3 3 3 3 5% 6% 57%	5588
April	1st to 10th	Night	7% 4 2 5% 4 3 3 4 6% 7% 56%	2237
	11th to 20th	Night	10% 6% 2 5% 4 4 3 4 5% 7% 52%	2077
	21st to end	Night	10% 5% 1 4 3 3 3 3 4 7% 56%	2100
May	1st to 10th	Night	13% 7% 2 5% 3 3 3 3 5% 7% 49%	4154
	11th to 20th	Night	5% 5% 2 5% 4 4 4 3 6% 7% 56%	4143
	21st to end	Night	9% 4 2 6% 3 4 5% 4 7% 10% 46%	4542
June	1st to 10th	Night	2 2 3 2 3 4 3 6% 12% 63%	1800
	11th to 20th	Night	2 2 1 3 3 4 4 3 6% 10% 63%	1800
	21st to end	Night	4 2 1 4 3 3 3 4 5% 10% 60%	1800
July	1st to 10th	Night	8% 5% 1 5% 5% 4 5% 4 7% 10% 47%	4078
	11th to 20th	Night	2 2 1 3 2 3 3 3 6% 10% 65%	4077
	21st to end	Night	4 3 1 4 4 3 4 4 6% 9% 59%	4578
August	1st to 10th	Night	1 1 1 2 2 3 3 3 4 6% 74%	3255
	11th to 20th	Night	2 2 1 3 2 3 3 4 6% 9% 65%	3213
	21st to end	Night	5% 3 2 5% 3 3 4 4 6% 12% 54%	3597
September	1st to 10th	Night	7% 5% 2 5% 4 4 4 3 6% 7% 52%	2164
	11th to 20th	Night	7% 5% 2 4 5% 4 5% 4 6% 9% 51%	2200
	21st to end	Night	7% 3 2 4 3 3 4 4 5% 8% 57%	2200
October	1st to 10th	Night	3 3 1 3 2 3 3 3 5% 6% 67%	2200
	11th to 20th	Night	8% 4 2 4 3 3 3 2 4 6% 61%	2200
	21st to end	Night	9% 4 1 4 3 2 3 2 3 4 65%	2604
November	1st to 10th	Night	9% 4 2 4 3 2 2 2 4 5% 62%	2595
	11th to 20th	Night	7% 4 1 3 2 3 3 3 5% 7% 62%	2730
	21st to end	Night	11% 5% 2 4 4 3 3 3 5% 6% 54%	2730
December	1st to 10th	Night	20% 7% 2 4 3 3 3 3 4 5% 45%	4380
	11th to 20th	Night	11% 7% 2 5% 3 3 3 3 4 5% 53%	4946
	21st to end	Night	8% 6% 2 4 2 2 2 2 3 5% 63%	6633

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	25% 2 5% 24% 26% 18%	5290
	11th to 20th	Day	26% 2 4 18% 27% 24%	5592
	21st to end	Day	37% 3 5% 14% 27% 14%	6468
February	1st to 10th	Day	32% 3 7% 14% 22% 22%	2100
	11th to 20th	Day	31% 3 8% 20% 21% 17%	2059
	21st to end	Day	27% 3 7% 14% 28% 21%	1730
March	1st to 10th	Day	30% 3 5% 15% 17% 30%	4677
	11th to 20th	Day	31% 3 5% 9% 18% 34%	5090
	21st to end	Day	30% 4 7% 17% 22% 20%	5585
April	1st to 10th	Day	31% 4 8% 19% 19% 18%	2377
	11th to 20th	Day	35% 5% 8% 17% 20% 16%	2494
	21st to end	Day	32% 4 9% 21% 20% 13%	2520
May	1st to 10th	Day	36% 6% 9% 16% 21% 13%	6019
	11th to 20th	Day	32% 5% 9% 16% 24% 15%	5996
	21st to end	Day	34% 7% 11% 26% 17% 5%	6590
June	1st to 10th	Day	22% 7% 13% 32% 22% 4	2601
	11th to 20th	Day	24% 6% 12% 27% 25% 6%	2600
	21st to end	Day	30% 7% 14% 25% 20% 5%	2600
July	1st to 10th	Day	39% 7% 16% 31% 7% 1	5836
	11th to 20th	Day	27% 7% 15% 34% 15% 2	5831
	21st to end	Day	25% 7% 17% 28% 20% 2	6094
August	1st to 10th	Day	13% 5% 11% 38% 32% 1	3892
	11th to 20th	Day	19% 5% 16% 43% 14% 2	3882
	21st to end	Day	29% 9% 16% 24% 20% 2	4311
September	1st to 10th	Day	38% 6% 10% 20% 18% 8%	2235
	11th to 20th	Day	36% 6% 13% 21% 18% 6%	2200
	21st to end	Day	31% 5% 10% 20% 20% 13%	2200
October	1st to 10th	Day	15% 4 6% 14% 26% 34%	3590
	11th to 20th	Day	28% 4 6% 17% 20% 26%	3568
	21st to end	Day	22% 3 5% 17% 40% 14%	3553
November	1st to 10th	Day	29% 4 9% 21% 23% 15%	1918
	11th to 20th	Day	27% 4 7% 19% 23% 19%	1890
	21st to end	Day	33% 3 6% 18% 24% 15%	1890
December	1st to 10th	Day	43% 3 6% 16% 20% 12%	3030
	11th to 20th	Day	36% 5% 6% 13% 24% 15%	3479
	21st to end	Day	26% 2 3 17% 28% 24%	4587
January	1st to 10th	Night	25% 2 7% 18% 31% 17%	7635
	11th to 20th	Night	20% 1 4 18% 29% 29%	7440
	21st to end	Night	42% 3 4 11% 23% 18%	7746
February	1st to 10th	Night	28% 3 8% 15% 23% 23%	2520
	11th to 20th	Night	32% 3 7% 19% 22% 17%	2458
	21st to end	Night	29% 4 6% 13% 25% 22%	2076
March	1st to 10th	Night	24% 4 8% 19% 24% 21%	5412
	11th to 20th	Night	29% 3 6% 11% 18% 33%	5090
	21st to end	Night	29% 4 8% 17% 22% 21%	5588
April	1st to 10th	Night	28% 4 11% 20% 16% 20%	2237
	11th to 20th	Night	32% 5% 9% 18% 17% 18%	2077
	21st to end	Night	30% 5% 10% 23% 19% 13%	2100
May	1st to 10th	Night	36% 5% 9% 19% 17% 14%	4181
	11th to 20th	Night	27% 6% 11% 19% 22% 15%	4144
	21st to end	Night	32% 7% 15% 26% 13% 8%	4551
June	1st to 10th	Night	15% 7% 17% 38% 21% 3	1800
	11th to 20th	Night	18% 6% 16% 31% 23% 7%	1800
	21st to end	Night	21% 6% 18% 30% 20% 6%	1800
July	1st to 10th	Night	31% 8% 21% 30% 8% 1	4035
	11th to 20th	Night	15% 7% 19% 40% 17% 2	4026
	21st to end	Night	20% 8% 19% 30% 20% 2	4447
August	1st to 10th	Night	11% 5% 13% 38% 32% 1	3244
	11th to 20th	Night	15% 6% 22% 43% 13% 1	3243
	21st to end	Night	23% 9% 21% 26% 19% 2	3597
September	1st to 10th	Night	30% 7% 12% 23% 20% 9%	2164
	11th to 20th	Night	30% 8% 15% 22% 18% 6%	2200
	21st to end	Night	23% 7% 13% 25% 19% 14%	2200
October	1st to 10th	Night	13% 3 9% 15% 23% 36%	3590
	11th to 20th	Night	22% 3 8% 16% 25% 25%	3570
	21st to end	Night	20% 3 5% 19% 35% 18%	4204
November	1st to 10th	Night	25% 3 8% 19% 27% 17%	2595
	11th to 20th	Night	23% 4 9% 21% 22% 21%	2730
	21st to end	Night	31% 4 8% 16% 23% 17%	2730
December	1st to 10th	Night	42% 4 7% 16% 16% 15%	4380
	11th to 20th	Night	35% 3 5% 15% 22% 19%	4947
	21st to end	Night	25% 3 5% 19% 29% 20%	6633

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	330
	11th to 20th	Day	15% 10% 35% 31% 9% 1	330
	21st to end	Day	14% 8% 42% 26% 9% 1	363
February	1st to 10th	Day	17% 11% 35% 24% 12% 2	330
	11th to 20th	Day	15% 11% 42% 27% 5%	330
	21st to end	Day	14% 12% 47% 25% 3	273
March	1st to 10th	Day	15% 14% 42% 24% 5%	330
	11th to 20th	Day	13% 13% 41% 23% 9% 1	330
	21st to end	Day	10% 12% 45% 21% 10% 1	363
April	1st to 10th	Day	12% 11% 42% 29% 5%	397
	11th to 20th	Day	11% 14% 43% 26% 5% 1	532
	21st to end	Day	12% 11% 43% 27% 7%	540
May	1st to 10th	Day	12% 8% 41% 31% 7% 1	742
	11th to 20th	Day	14% 5% 36% 31% 13% 1	775
	21st to end	Day	11% 5% 30% 37% 15% 2	844
June	1st to 10th	Day	4 3 17% 50% 24% 3	731
	11th to 20th	Day	4 1 20% 50% 20% 5%	730
	21st to end	Day	3 2 12% 43% 32% 8%	730
July	1st to 10th	Day	8% 2 7% 34% 38% 11%	721
	11th to 20th	Day	4 1 4 40% 43% 9%	718
	21st to end	Day	3 5% 36% 40% 15%	733
August	1st to 10th	Day	2 2 32% 44% 20%	527
	11th to 20th	Day	6% 3 31% 42% 17%	517
	21st to end	Day	5% 1 5% 26% 42% 21%	583
September	1st to 10th	Day	12% 4 20% 44% 20%	365
	11th to 20th	Day	5% 1 4 25% 45% 21%	330
	21st to end	Day	11% 1 5% 31% 38% 15%	330
October	1st to 10th	Day	4 4 10% 32% 36% 14%	330
	11th to 20th	Day	10% 4 17% 42% 24% 4	330
	21st to end	Day	12% 9% 26% 31% 15% 5%	363
November	1st to 10th	Day	14% 7% 25% 33% 17% 3	330
	11th to 20th	Day	16% 10% 27% 23% 16% 7%	330
	21st to end	Day	16% 12% 36% 25% 9% 2	330
December	1st to 10th	Day	16% 9% 28% 31% 13% 3	330
	11th to 20th	Day	11% 14% 33% 28% 12% 2	330
	21st to end	Day	16% 10% 33% 27% 13%	363
January	1st to 10th	Night	11% 6% 39% 33% 9%	1050
	11th to 20th	Night	12% 8% 38% 35% 7%	966
	21st to end	Night	15% 8% 38% 33% 6%	924
February	1st to 10th	Night	11% 10% 41% 31% 7%	840
	11th to 20th	Night	13% 11% 42% 31% 4	824
	21st to end	Night	12% 12% 49% 26% 2	692
March	1st to 10th	Night	13% 11% 45% 25% 5%	810
	11th to 20th	Night	12% 10% 40% 32% 6%	630
	21st to end	Night	7% 12% 49% 30% 2	693
April	1st to 10th	Night	8% 7% 53% 28% 4	630
	11th to 20th	Night	12% 11% 50% 25% 2	623
	21st to end	Night	10% 10% 52% 23% 5%	630
May	1st to 10th	Night	10% 8% 48% 32% 3	630
	11th to 20th	Night	10% 6% 40% 36% 7% 1	621
	21st to end	Night	8% 5% 39% 39% 8% 1	683
June	1st to 10th	Night	3 1 26% 54% 15% 1	600
	11th to 20th	Night	2 2 30% 56% 10% 1	600
	21st to end	Night	4 2 18% 54% 21% 2	600
July	1st to 10th	Night	6% 2 6% 55% 30% 1	585
	11th to 20th	Night	2 7% 59% 32% 1	582
	21st to end	Night	2 1 7% 57% 32% 2	657
August	1st to 10th	Night	2 4 55% 36% 2	597
	11th to 20th	Night	4 1 4 51% 38% 3	594
	21st to end	Night	5% 2 6% 41% 42% 4	660
September	1st to 10th	Night	7% 2 5% 44% 39% 3	600
	11th to 20th	Night	8% 1 6% 46% 37% 3	600
	21st to end	Night	7% 2 10% 48% 31% 2	600
October	1st to 10th	Night	4 2 15% 48% 30% 1	600
	11th to 20th	Night	10% 3 23% 47% 16% 1	600
	21st to end	Night	11% 6% 30% 35% 18% 1	844
November	1st to 10th	Night	11% 5% 25% 41% 18% 1	955
	11th to 20th	Night	10% 5% 30% 38% 15% 2	1050
	21st to end	Night	13% 8% 32% 34% 11% 1	1050
December	1st to 10th	Night	14% 5% 31% 41% 8% 1	1050
	11th to 20th	Night	14% 8% 33% 36% 9%	1050
	21st to end	Night	11% 7% 37% 36% 8% 1	1155

Page generated at 2026-05-29 00:53:25. Version ac07

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