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 2025-02-06.

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	9% 5% 2 5% 4 4 4 3 5% 7% 54%	109052
	Night	8% 5% 2 4 3 3 3 3 5% 7% 58%	109439
Transparency	Day	29% 5% 9% 22% 22% 13%	112963
	Night	26% 5% 10% 21% 22% 15%	113656
Seeing	Day	10% 6% 24% 32% 22% 7%	15098
	Night	9% 6% 30% 39% 15% 1	25192

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	11% 4 3 4 2 2 3 2 3 6% 60%	4077
	11th to 20th	Day	8% 5% 1 3 2 2 3 3 4 6% 62%	4292
	21st to end	Day	17% 4 1 5% 3 3 3 3 4 6% 51%	4994
February	1st to 10th	Day	9% 7% 2 6% 4 3 3 3 5% 5% 55%	1950
	11th to 20th	Day	11% 6% 2 4 3 3 3 3 6% 6% 53%	1849
	21st to end	Day	10% 5% 2 3 3 3 3 3 4 7% 58%	1570
March	1st to 10th	Day	11% 7% 3 6% 3 4 4 2 5% 6% 48%	3180
	11th to 20th	Day	15% 10% 3 8% 4 4 3 3 4 5% 41%	3480
	21st to end	Day	6% 6% 2 6% 4 4 4 4 6% 7% 51%	3814
April	1st to 10th	Day	8% 6% 2 5% 4 3 3 3 5% 7% 54%	2151
	11th to 20th	Day	10% 5% 2 5% 4 4 3 3 5% 6% 52%	2254
	21st to end	Day	9% 6% 2 4 4 3 4 2 5% 6% 56%	2280
May	1st to 10th	Day	11% 6% 3 7% 4 4 4 3 5% 7% 46%	4072
	11th to 20th	Day	11% 6% 2 5% 4 4 4 3 5% 6% 50%	4082
	21st to end	Day	7% 5% 2 5% 4 5% 4 4 6% 8% 49%	4477
June	1st to 10th	Day	3 3 1 4 4 4 4 3 6% 8% 58%	2470
	11th to 20th	Day	4 4 2 4 4 4 5% 4 6% 9% 55%	2470
	21st to end	Day	5% 5% 2 5% 5% 4 5% 4 7% 8% 49%	2470
July	1st to 10th	Day	5% 3 2 5% 4 4 5% 4 7% 7% 53%	4120
	11th to 20th	Day	3 2 1 4 4 4 5% 4 6% 9% 58%	4120
	21st to end	Day	7% 3 2 5% 5% 4 5% 4 6% 9% 50%	4358
August	1st to 10th	Day	1 2 1 3 3 3 3 3 5% 7% 70%	3785
	11th to 20th	Day	3 2 1 4 3 3 3 3 4 8% 65%	3726
	21st to end	Day	4 4 2 6% 5% 6% 6% 5% 6% 9% 48%	4180
September	1st to 10th	Day	11% 5% 2 6% 6% 5% 5% 3 6% 7% 45%	2123
	11th to 20th	Day	10% 6% 2 8% 5% 4 4 4 6% 8% 43%	2090
	21st to end	Day	8% 5% 2 5% 4 5% 4 4 5% 7% 53%	2090
October	1st to 10th	Day	5% 4 2 4 4 3 4 3 5% 7% 58%	2090
	11th to 20th	Day	11% 6% 2 4 3 3 4 3 3 5% 56%	2090
	21st to end	Day	9% 5% 1 4 3 2 3 2 3 5% 63%	2104
November	1st to 10th	Day	10% 6% 2 4 3 3 3 2 5% 7% 54%	1825
	11th to 20th	Day	8% 5% 1 4 3 3 4 4 5% 6% 59%	1800
	21st to end	Day	11% 7% 2 5% 3 2 3 3 5% 6% 54%	1800
December	1st to 10th	Day	19% 8% 3 6% 3 3 3 3 4 5% 44%	2940
	11th to 20th	Day	11% 7% 2 7% 4 4 4 3 5% 5% 48%	3391
	21st to end	Day	8% 7% 2 4 2 2 2 2 3 4 65%	4488
January	1st to 10th	Night	9% 5% 2 5% 3 3 3 2 4 6% 60%	5888
	11th to 20th	Night	6% 4 1 3 1 1 2 2 4 6% 69%	5716
	21st to end	Night	22% 6% 2 4 3 3 3 2 3 6% 47%	5984
February	1st to 10th	Night	8% 7% 2 5% 3 3 3 3 4 6% 57%	2340
	11th to 20th	Night	12% 6% 2 5% 3 3 3 3 4 6% 54%	2218
	21st to end	Night	9% 6% 2 5% 3 3 4 3 6% 7% 54%	1884
March	1st to 10th	Night	7% 5% 2 4 3 4 4 4 5% 8% 55%	3681
	11th to 20th	Night	12% 9% 2 6% 4 4 5% 3 5% 5% 45%	3480
	21st to end	Night	6% 7% 2 5% 4 4 3 3 4 6% 56%	3817
April	1st to 10th	Night	6% 4 2 4 4 4 3 4 6% 7% 56%	2024
	11th to 20th	Night	9% 5% 2 5% 4 4 3 4 5% 7% 53%	1877
	21st to end	Night	9% 5% 1 4 3 3 2 3 3 7% 60%	1900
May	1st to 10th	Night	12% 8% 2 5% 3 3 3 3 5% 7% 50%	2833
	11th to 20th	Night	7% 6% 2 4 3 3 4 3 5% 6% 57%	2823
	21st to end	Night	7% 4 2 6% 2 3 4 4 6% 8% 54%	3090
June	1st to 10th	Night	2 2 3 2 3 4 3 6% 11% 63%	1710
	11th to 20th	Night	2 2 1 3 3 4 4 3 6% 10% 63%	1710
	21st to end	Night	4 2 1 3 4 3 3 4 5% 10% 60%	1710
July	1st to 10th	Night	4 3 1 3 4 3 4 3 7% 10% 60%	2850
	11th to 20th	Night	1 2 1 3 2 2 3 3 5% 9% 69%	2850
	21st to end	Night	5% 3 1 4 4 3 4 4 6% 10% 56%	3185
August	1st to 10th	Night	1 1 1 2 2 3 3 3 4 6% 74%	3155
	11th to 20th	Night	2 2 1 3 2 3 3 4 6% 9% 66%	3113
	21st to end	Night	4 3 2 4 3 3 4 4 6% 12% 54%	3487
September	1st to 10th	Night	7% 5% 2 5% 4 4 4 4 6% 7% 53%	2056
	11th to 20th	Night	7% 5% 2 5% 5% 3 5% 4 5% 8% 51%	2090
	21st to end	Night	7% 3 2 4 3 3 3 4 5% 8% 57%	2090
October	1st to 10th	Night	3 3 1 3 2 3 3 3 5% 6% 66%	2090
	11th to 20th	Night	8% 5% 2 4 3 3 3 2 4 6% 60%	2090
	21st to end	Night	10% 5% 1 4 3 2 2 2 3 4 65%	2474
November	1st to 10th	Night	9% 5% 2 4 3 3 2 2 4 6% 60%	2468
	11th to 20th	Night	7% 4 1 3 2 3 3 3 5% 7% 61%	2600
	21st to end	Night	11% 5% 2 4 4 3 3 3 5% 6% 55%	2600
December	1st to 10th	Night	20% 7% 2 4 3 3 3 3 4 5% 44%	4250
	11th to 20th	Night	11% 7% 2 5% 3 3 3 3 4 5% 53%	4816
	21st to end	Night	8% 6% 2 4 2 2 2 2 3 6% 63%	6490

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	28% 2 4 22% 24% 20%	4078
	11th to 20th	Day	25% 3 5% 19% 27% 22%	4292
	21st to end	Day	36% 3 5% 12% 28% 15%	4994
February	1st to 10th	Day	32% 3 7% 14% 23% 21%	1950
	11th to 20th	Day	32% 3 7% 18% 21% 18%	1859
	21st to end	Day	28% 3 7% 14% 27% 21%	1570
March	1st to 10th	Day	38% 4 6% 12% 21% 20%	3180
	11th to 20th	Day	45% 4 7% 12% 19% 13%	3480
	21st to end	Day	30% 5% 9% 14% 20% 21%	3814
April	1st to 10th	Day	30% 4 8% 19% 20% 18%	2151
	11th to 20th	Day	33% 5% 8% 18% 20% 17%	2254
	21st to end	Day	32% 3 8% 21% 22% 14%	2280
May	1st to 10th	Day	37% 6% 9% 14% 21% 13%	4110
	11th to 20th	Day	35% 5% 8% 18% 22% 12%	4086
	21st to end	Day	31% 7% 11% 26% 17% 7%	4489
June	1st to 10th	Day	22% 7% 13% 31% 22% 4	2470
	11th to 20th	Day	25% 6% 12% 27% 24% 6%	2470
	21st to end	Day	30% 8% 13% 24% 20% 5%	2470
July	1st to 10th	Day	26% 8% 17% 39% 9% 1	4056
	11th to 20th	Day	21% 7% 14% 35% 20% 3	4051
	21st to end	Day	27% 7% 15% 30% 19% 2	4221
August	1st to 10th	Day	13% 5% 11% 38% 32% 1	3772
	11th to 20th	Day	19% 5% 16% 43% 15% 2	3762
	21st to end	Day	30% 9% 16% 24% 20% 2	4179
September	1st to 10th	Day	38% 7% 10% 20% 18% 8%	2123
	11th to 20th	Day	37% 6% 12% 20% 19% 6%	2090
	21st to end	Day	32% 5% 10% 20% 20% 13%	2090
October	1st to 10th	Day	16% 4 6% 13% 26% 35%	3480
	11th to 20th	Day	28% 4 6% 16% 20% 26%	3458
	21st to end	Day	22% 3 5% 18% 40% 13%	3442
November	1st to 10th	Day	30% 4 9% 22% 21% 13%	1825
	11th to 20th	Day	27% 4 7% 20% 22% 19%	1800
	21st to end	Day	32% 4 6% 19% 24% 16%	1800
December	1st to 10th	Day	44% 3 6% 16% 20% 11%	2940
	11th to 20th	Day	36% 5% 6% 14% 24% 15%	3389
	21st to end	Day	26% 2 3 17% 28% 24%	4488
January	1st to 10th	Night	27% 2 7% 15% 30% 18%	5888
	11th to 20th	Night	19% 1 4 20% 27% 28%	5716
	21st to end	Night	41% 3 4 11% 23% 18%	5984
February	1st to 10th	Night	29% 3 8% 14% 23% 22%	2340
	11th to 20th	Night	32% 3 7% 17% 23% 19%	2218
	21st to end	Night	30% 4 7% 13% 24% 22%	1884
March	1st to 10th	Night	27% 4 10% 16% 26% 16%	3681
	11th to 20th	Night	41% 5% 8% 14% 17% 14%	3480
	21st to end	Night	30% 4 9% 18% 17% 21%	3817
April	1st to 10th	Night	27% 5% 10% 20% 17% 21%	2024
	11th to 20th	Night	31% 6% 9% 17% 18% 19%	1877
	21st to end	Night	27% 5% 9% 24% 21% 14%	1900
May	1st to 10th	Night	35% 6% 10% 18% 19% 13%	2860
	11th to 20th	Night	27% 6% 12% 23% 21% 11%	2824
	21st to end	Night	27% 8% 14% 28% 13% 11%	3099
June	1st to 10th	Night	14% 7% 17% 37% 22% 3	1710
	11th to 20th	Night	17% 6% 16% 31% 23% 7%	1710
	21st to end	Night	21% 6% 17% 30% 20% 6%	1710
July	1st to 10th	Night	19% 7% 24% 38% 12% 1	2805
	11th to 20th	Night	12% 7% 17% 40% 22% 3	2796
	21st to end	Night	21% 8% 18% 34% 18% 1	3084
August	1st to 10th	Night	11% 5% 13% 38% 31% 1	3144
	11th to 20th	Night	15% 6% 22% 43% 13% 1	3143
	21st to end	Night	23% 9% 21% 26% 19% 2	3487
September	1st to 10th	Night	29% 8% 12% 23% 19% 9%	2056
	11th to 20th	Night	31% 8% 15% 21% 19% 6%	2090
	21st to end	Night	24% 7% 13% 24% 18% 14%	2090
October	1st to 10th	Night	13% 3 9% 15% 22% 37%	3480
	11th to 20th	Night	22% 3 8% 15% 26% 25%	3460
	21st to end	Night	21% 3 5% 20% 35% 17%	4074
November	1st to 10th	Night	27% 3 9% 20% 26% 16%	2468
	11th to 20th	Night	23% 4 9% 21% 22% 20%	2600
	21st to end	Night	31% 4 8% 17% 22% 18%	2600
December	1st to 10th	Night	43% 4 7% 16% 16% 14%	4250
	11th to 20th	Night	35% 3 6% 15% 22% 19%	4817
	21st to end	Night	25% 3 4 20% 29% 20%	6490

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% 42% 26% 8% 1	300
	11th to 20th	Day	15% 10% 36% 30% 8% 1	300
	21st to end	Day	14% 8% 42% 28% 8% 1	330
February	1st to 10th	Day	16% 12% 34% 25% 12% 1	285
	11th to 20th	Day	17% 11% 41% 25% 6%	270
	21st to end	Day	14% 13% 48% 23% 3	225
March	1st to 10th	Day	14% 13% 44% 24% 5%	270
	11th to 20th	Day	14% 13% 40% 23% 10% 1	270
	21st to end	Day	11% 13% 49% 19% 6% 1	297
April	1st to 10th	Day	11% 12% 43% 30% 5%	331
	11th to 20th	Day	9% 13% 44% 28% 5%	452
	21st to end	Day	12% 11% 41% 28% 7%	460
May	1st to 10th	Day	12% 7% 42% 32% 7% 1	643
	11th to 20th	Day	14% 5% 34% 33% 13% 2	675
	21st to end	Day	11% 5% 30% 37% 15% 2	734
June	1st to 10th	Day	4 3 15% 49% 25% 3	680
	11th to 20th	Day	4 1 19% 50% 20% 6%	680
	21st to end	Day	4 1 11% 45% 31% 8%	680
July	1st to 10th	Day	7% 1 7% 35% 38% 11%	671
	11th to 20th	Day	3 4 40% 44% 9%	668
	21st to end	Day	3 5% 36% 40% 16%	681
August	1st to 10th	Day	2 2 32% 44% 20%	487
	11th to 20th	Day	7% 4 30% 43% 16%	477
	21st to end	Day	6% 1 4 26% 42% 21%	539
September	1st to 10th	Day	11% 4 20% 45% 20%	333
	11th to 20th	Day	5% 1 4 23% 45% 22%	300
	21st to end	Day	12% 1 5% 28% 38% 16%	300
October	1st to 10th	Day	4 4 11% 31% 36% 13%	300
	11th to 20th	Day	11% 4 16% 43% 22% 4	300
	21st to end	Day	13% 9% 26% 30% 16% 6%	330
November	1st to 10th	Day	16% 7% 27% 33% 14% 3	300
	11th to 20th	Day	16% 11% 28% 23% 14% 8%	300
	21st to end	Day	16% 12% 38% 24% 8% 2	300
December	1st to 10th	Day	17% 8% 25% 33% 13% 3	300
	11th to 20th	Day	12% 15% 34% 27% 12% 1	300
	21st to end	Day	16% 11% 35% 26% 12%	330
January	1st to 10th	Night	12% 6% 39% 33% 9% 1	1000
	11th to 20th	Night	12% 8% 38% 35% 7%	920
	21st to end	Night	15% 8% 38% 33% 6%	880
February	1st to 10th	Night	11% 11% 41% 30% 7%	780
	11th to 20th	Night	14% 9% 42% 31% 4	744
	21st to end	Night	12% 13% 49% 24% 1	628
March	1st to 10th	Night	13% 10% 46% 26% 5%	733
	11th to 20th	Night	12% 10% 40% 32% 6%	570
	21st to end	Night	7% 12% 51% 27% 3	627
April	1st to 10th	Night	7% 7% 55% 28% 4	570
	11th to 20th	Night	10% 11% 51% 26% 2	563
	21st to end	Night	9% 9% 53% 24% 6%	570
May	1st to 10th	Night	9% 8% 48% 32% 3	570
	11th to 20th	Night	10% 6% 39% 37% 7% 1	561
	21st to end	Night	8% 5% 39% 39% 8% 1	617
June	1st to 10th	Night	2 1 24% 55% 16% 1	570
	11th to 20th	Night	2 1 29% 57% 10% 1	570
	21st to end	Night	4 2 18% 53% 22% 2	570
July	1st to 10th	Night	6% 1 6% 55% 30% 1	555
	11th to 20th	Night	2 7% 59% 32% 1	552
	21st to end	Night	2 1 6% 57% 32% 1	624
August	1st to 10th	Night	2 5% 54% 36% 2	567
	11th to 20th	Night	4 1 4 50% 38% 3	564
	21st to end	Night	5% 2 5% 41% 42% 4	627
September	1st to 10th	Night	7% 2 5% 45% 39% 3	570
	11th to 20th	Night	8% 1 6% 45% 38% 3	570
	21st to end	Night	7% 2 11% 47% 31% 2	570
October	1st to 10th	Night	4 1 16% 48% 29% 1	570
	11th to 20th	Night	11% 3 24% 45% 15% 1	570
	21st to end	Night	11% 6% 29% 35% 18% 1	802
November	1st to 10th	Night	12% 5% 25% 40% 18% 1	908
	11th to 20th	Night	10% 5% 31% 37% 15% 2	1000
	21st to end	Night	13% 8% 33% 34% 11% 1	1000
December	1st to 10th	Night	14% 5% 29% 42% 9% 1	1000
	11th to 20th	Night	15% 8% 33% 36% 8%	1000
	21st to end	Night	11% 7% 38% 36% 7% 1	1100

Page generated at 2025-02-03 02:05:51. Version ac07

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