Bluefield Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bluefield Ranch clear sky chart from 2005-11-06 to 2026-04-02.

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 7% 6% 6% 6% 5% 8% 10% 38%	131129
	Night	7% 6% 2 6% 5% 5% 5% 4 7% 9% 44%	130701
Transparency	Day	37% 11% 18% 19% 12% 4	134796
	Night	34% 9% 19% 22% 12% 4	135104
Seeing	Day	7% 4 16% 26% 26% 21%	17748
	Night	8% 3 16% 32% 30% 11%	27905

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	6% 5% 2 5% 4 3 3 4 5% 9% 55%	5258
	11th to 20th	Day	15% 8% 3 8% 5% 5% 5% 5% 6% 9% 32%	5280
	21st to end	Day	14% 6% 2 7% 5% 5% 5% 4 6% 7% 40%	5836
February	1st to 10th	Day	9% 5% 2 5% 4 4 5% 4 7% 9% 47%	2100
	11th to 20th	Day	6% 4 2 4 4 4 5% 4 6% 9% 53%	2112
	21st to end	Day	7% 4 1 5% 4 4 4 4 6% 9% 51%	1903
March	1st to 10th	Day	5% 4 2 7% 6% 6% 6% 5% 6% 8% 43%	5045
	11th to 20th	Day	3 2 1 4 3 4 4 3 5% 8% 62%	5090
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 4 7% 9% 45%	5586
April	1st to 10th	Day	4 3 1 5% 5% 6% 6% 6% 8% 10% 45%	2211
	11th to 20th	Day	6% 4 2 5% 5% 5% 6% 5% 7% 11% 43%	2266
	21st to end	Day	4 4 2 5% 5% 5% 7% 5% 8% 8% 46%	2400
May	1st to 10th	Day	3 2 1 4 4 4 6% 5% 9% 13% 49%	5405
	11th to 20th	Day	6% 5% 2 6% 5% 5% 5% 5% 7% 10% 46%	5737
	21st to end	Day	4 4 2 6% 5% 5% 7% 6% 9% 13% 41%	6433
June	1st to 10th	Day	11% 8% 4 10% 9% 7% 7% 6% 9% 11% 20%	2600
	11th to 20th	Day	5% 7% 3 9% 9% 8% 9% 7% 9% 11% 24%	2600
	21st to end	Day	8% 6% 3 10% 9% 8% 9% 7% 9% 10% 22%	2600
July	1st to 10th	Day	7% 6% 3 9% 8% 7% 8% 7% 10% 12% 24%	5900
	11th to 20th	Day	6% 5% 2 9% 8% 8% 8% 7% 9% 12% 28%	5900
	21st to end	Day	4 5% 2 6% 6% 7% 8% 7% 10% 15% 30%	6424
August	1st to 10th	Day	5% 5% 3 10% 9% 9% 9% 7% 10% 13% 22%	4234
	11th to 20th	Day	4 3 2 7% 6% 8% 8% 7% 9% 12% 35%	3881
	21st to end	Day	5% 5% 2 8% 8% 9% 9% 7% 12% 14% 21%	4001
September	1st to 10th	Day	6% 6% 3 10% 7% 8% 9% 7% 11% 11% 21%	2200
	11th to 20th	Day	8% 7% 4 10% 7% 9% 8% 7% 8% 10% 22%	2200
	21st to end	Day	8% 7% 3 10% 8% 8% 7% 6% 9% 10% 23%	2200
October	1st to 10th	Day	9% 6% 3 9% 7% 6% 7% 5% 8% 9% 30%	2115
	11th to 20th	Day	7% 5% 2 8% 6% 6% 7% 5% 7% 10% 38%	2000
	21st to end	Day	7% 5% 2 6% 6% 5% 7% 5% 8% 10% 40%	2200
November	1st to 10th	Day	8% 5% 2 7% 6% 5% 7% 4 7% 8% 40%	2057
	11th to 20th	Day	8% 7% 2 8% 6% 5% 6% 4 6% 9% 40%	2100
	21st to end	Day	7% 6% 2 7% 5% 5% 5% 5% 7% 9% 43%	2100
December	1st to 10th	Day	7% 4 2 4 3 4 4 3 7% 7% 56%	3127
	11th to 20th	Day	9% 6% 2 7% 6% 5% 6% 6% 7% 9% 37%	3463
	21st to end	Day	10% 6% 2 8% 6% 6% 6% 5% 8% 9% 34%	4565
January	1st to 10th	Night	5% 4 2 5% 3 4 4 3 6% 8% 55%	7635
	11th to 20th	Night	12% 10% 3 10% 5% 5% 5% 4 6% 8% 32%	7680
	21st to end	Night	13% 7% 2 6% 4 4 4 3 5% 7% 45%	8341
February	1st to 10th	Night	8% 6% 3 6% 5% 4 5% 3 6% 7% 49%	2520
	11th to 20th	Night	7% 4 2 5% 4 4 4 3 6% 8% 53%	2390
	21st to end	Night	7% 4 1 4 4 4 4 4 5% 8% 55%	1903
March	1st to 10th	Night	7% 5% 3 6% 4 4 4 4 6% 7% 50%	5028
	11th to 20th	Night	5% 2 1 4 3 4 4 3 5% 10% 58%	5090
	21st to end	Night	7% 5% 2 6% 5% 4 5% 4 6% 7% 49%	5588
April	1st to 10th	Night	5% 3 1 4 4 3 4 4 6% 10% 56%	2212
	11th to 20th	Night	4 4 2 5% 4 4 4 4 7% 8% 53%	2080
	21st to end	Night	5% 3 2 4 3 4 5% 4 7% 9% 54%	2000
May	1st to 10th	Night	3 3 1 4 4 4 5% 4 7% 10% 56%	4490
	11th to 20th	Night	8% 4 2 5% 4 4 5% 4 7% 8% 48%	4183
	21st to end	Night	4 5% 2 7% 5% 5% 5% 5% 8% 11% 43%	4421
June	1st to 10th	Night	11% 8% 3 7% 6% 6% 6% 5% 8% 11% 29%	1800
	11th to 20th	Night	5% 6% 2 8% 6% 7% 7% 6% 10% 13% 29%	1800
	21st to end	Night	6% 6% 3 7% 6% 7% 6% 5% 8% 13% 34%	1800
July	1st to 10th	Night	7% 8% 3 8% 6% 6% 6% 4 8% 13% 31%	4058
	11th to 20th	Night	4 5% 3 7% 5% 5% 6% 6% 9% 13% 38%	4057
	21st to end	Night	4 5% 2 6% 5% 5% 6% 4 8% 12% 42%	4427
August	1st to 10th	Night	4 5% 2 9% 6% 5% 5% 5% 8% 14% 36%	2915
	11th to 20th	Night	5% 4 2 7% 5% 5% 6% 6% 8% 13% 39%	3130
	21st to end	Night	6% 5% 2 7% 6% 7% 8% 6% 11% 14% 29%	3877
September	1st to 10th	Night	6% 6% 2 8% 7% 8% 8% 5% 9% 12% 27%	2200
	11th to 20th	Night	9% 7% 4 10% 6% 6% 6% 5% 8% 10% 30%	2200
	21st to end	Night	10% 8% 3 8% 7% 6% 6% 5% 8% 10% 29%	2200
October	1st to 10th	Night	10% 7% 3 8% 5% 6% 6% 5% 8% 10% 33%	2282
	11th to 20th	Night	8% 6% 3 6% 4 5% 5% 4 7% 9% 43%	2400
	21st to end	Night	8% 5% 2 7% 5% 5% 5% 4 6% 10% 44%	2640
November	1st to 10th	Night	7% 5% 2 7% 4 5% 5% 4 6% 9% 47%	2461
	11th to 20th	Night	6% 6% 2 7% 6% 4 5% 4 6% 9% 46%	2520
	21st to end	Night	8% 6% 3 6% 6% 4 5% 4 6% 8% 46%	2520
December	1st to 10th	Night	6% 4 2 5% 3 3 3 3 5% 7% 58%	4268
	11th to 20th	Night	12% 7% 3 7% 5% 5% 4 4 6% 7% 41%	4952
	21st to end	Night	9% 9% 3 8% 5% 5% 5% 4 6% 9% 35%	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	27% 6% 10% 28% 23% 6%	5259
	11th to 20th	Day	47% 6% 12% 18% 13% 4	5280
	21st to end	Day	41% 7% 9% 23% 14% 6%	5836
February	1st to 10th	Day	33% 7% 12% 22% 19% 8%	2100
	11th to 20th	Day	25% 7% 13% 28% 18% 9%	2122
	21st to end	Day	28% 5% 14% 20% 24% 9%	1903
March	1st to 10th	Day	36% 7% 14% 19% 19% 5%	5045
	11th to 20th	Day	20% 5% 15% 24% 22% 14%	5090
	21st to end	Day	32% 7% 13% 26% 16% 7%	5586
April	1st to 10th	Day	28% 9% 16% 25% 19% 4	2211
	11th to 20th	Day	33% 7% 17% 19% 19% 5%	2266
	21st to end	Day	30% 7% 13% 21% 24% 5%	2400
May	1st to 10th	Day	20% 11% 21% 28% 16% 3	5437
	11th to 20th	Day	31% 7% 21% 27% 12% 2	5741
	21st to end	Day	28% 11% 22% 28% 10%	6447
June	1st to 10th	Day	53% 11% 20% 12% 3	2600
	11th to 20th	Day	46% 15% 21% 16% 2	2600
	21st to end	Day	48% 16% 23% 11% 2	2600
July	1st to 10th	Day	46% 17% 26% 9% 2	5835
	11th to 20th	Day	42% 17% 29% 11% 1	5831
	21st to end	Day	36% 17% 26% 20% 1	6240
August	1st to 10th	Day	46% 18% 27% 8% 1	4221
	11th to 20th	Day	34% 17% 29% 14% 6%	3918
	21st to end	Day	43% 20% 28% 7% 1	4001
September	1st to 10th	Day	50% 18% 22% 10% 1	2200
	11th to 20th	Day	50% 16% 20% 12% 2	2200
	21st to end	Day	51% 14% 17% 12% 6% 1	2200
October	1st to 10th	Day	52% 12% 16% 13% 6% 2	3440
	11th to 20th	Day	34% 9% 13% 24% 17% 3	3240
	21st to end	Day	32% 9% 11% 25% 18% 5%	3538
November	1st to 10th	Day	37% 8% 12% 18% 15% 9%	2057
	11th to 20th	Day	39% 6% 11% 21% 15% 7%	2100
	21st to end	Day	36% 6% 14% 20% 17% 6%	2100
December	1st to 10th	Day	26% 7% 17% 27% 15% 9%	3127
	11th to 20th	Day	39% 9% 13% 16% 17% 6%	3460
	21st to end	Day	42% 8% 15% 18% 14% 2	4565
January	1st to 10th	Night	25% 5% 12% 32% 18% 7%	7636
	11th to 20th	Night	48% 7% 13% 18% 11% 4	7680
	21st to end	Night	38% 6% 12% 25% 14% 6%	8341
February	1st to 10th	Night	32% 7% 12% 21% 19% 8%	2520
	11th to 20th	Night	27% 7% 12% 25% 23% 7%	2391
	21st to end	Night	25% 7% 12% 22% 26% 7%	1903
March	1st to 10th	Night	33% 5% 13% 23% 21% 5%	5028
	11th to 20th	Night	21% 6% 19% 26% 18% 11%	5090
	21st to end	Night	30% 8% 13% 25% 20% 4	5588
April	1st to 10th	Night	23% 7% 19% 29% 17% 6%	2212
	11th to 20th	Night	26% 7% 16% 23% 22% 5%	2080
	21st to end	Night	24% 8% 15% 27% 22% 4	2000
May	1st to 10th	Night	20% 9% 25% 30% 13% 3	4520
	11th to 20th	Night	29% 9% 22% 31% 10%	4184
	21st to end	Night	29% 12% 23% 27% 9%	4429
June	1st to 10th	Night	45% 12% 22% 17% 4	1800
	11th to 20th	Night	40% 14% 25% 18% 3	1800
	21st to end	Night	38% 16% 27% 16% 3	1800
July	1st to 10th	Night	42% 14% 30% 14% 1	4015
	11th to 20th	Night	34% 15% 40% 10% 1	4006
	21st to end	Night	29% 14% 31% 24% 2	4297
August	1st to 10th	Night	36% 15% 35% 12% 2	2904
	11th to 20th	Night	30% 16% 32% 16% 5%	3159
	21st to end	Night	41% 18% 33% 7% 1	3877
September	1st to 10th	Night	43% 19% 26% 10% 2	2200
	11th to 20th	Night	46% 16% 22% 13% 2	2200
	21st to end	Night	46% 13% 19% 15% 6%	2200
October	1st to 10th	Night	53% 13% 15% 12% 7% 1	3737
	11th to 20th	Night	35% 9% 13% 23% 18% 2	3899
	21st to end	Night	32% 7% 11% 26% 17% 6%	4252
November	1st to 10th	Night	34% 7% 14% 19% 18% 7%	2461
	11th to 20th	Night	33% 8% 12% 25% 16% 7%	2520
	21st to end	Night	34% 6% 14% 21% 19% 6%	2520
December	1st to 10th	Night	25% 7% 17% 30% 15% 7%	4268
	11th to 20th	Night	40% 8% 14% 17% 14% 7%	4954
	21st to end	Night	43% 8% 16% 17% 11% 4	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	5% 7% 34% 32% 18% 3	330
	11th to 20th	Day	12% 12% 28% 29% 15% 4	330
	21st to end	Day	14% 10% 37% 30% 9%	363
February	1st to 10th	Day	8% 9% 24% 33% 21% 5%	330
	11th to 20th	Day	7% 6% 26% 36% 21% 4	394
	21st to end	Day	5% 7% 25% 35% 24% 4	446
March	1st to 10th	Day	3 6% 30% 38% 20% 2	540
	11th to 20th	Day	8% 6% 25% 33% 24% 3	540
	21st to end	Day	4 4 23% 37% 27% 5%	594
April	1st to 10th	Day	3 6% 30% 36% 19% 6%	504
	11th to 20th	Day	5% 6% 21% 36% 24% 7%	492
	21st to end	Day	5% 2 16% 36% 29% 11%	500
May	1st to 10th	Day	5% 2 14% 31% 35% 13%	503
	11th to 20th	Day	8% 4 13% 29% 30% 16%	527
	21st to end	Day	8% 2 7% 20% 36% 27%	573
June	1st to 10th	Day	11% 2 10% 19% 31% 27%	530
	11th to 20th	Day	7% 1 8% 16% 28% 40%	530
	21st to end	Day	4 2 5% 11% 28% 49%	530
July	1st to 10th	Day	6% 2 2 10% 26% 55%	525
	11th to 20th	Day	4 2 5% 9% 30% 51%	524
	21st to end	Day	6% 1 3 12% 29% 48%	576
August	1st to 10th	Day	5% 1 5% 11% 31% 47%	526
	11th to 20th	Day	2 3 12% 29% 54%	519
	21st to end	Day	7% 1 6% 18% 29% 39%	583
September	1st to 10th	Day	6% 3 5% 15% 24% 47%	530
	11th to 20th	Day	8% 2 10% 14% 30% 37%	530
	21st to end	Day	9% 3 10% 18% 28% 32%	530
October	1st to 10th	Day	12% 3 11% 28% 32% 14%	530
	11th to 20th	Day	6% 3 17% 33% 29% 12%	530
	21st to end	Day	7% 4 19% 32% 28% 10%	583
November	1st to 10th	Day	9% 5% 17% 32% 26% 10%	535
	11th to 20th	Day	11% 4 20% 35% 24% 6%	540
	21st to end	Day	6% 3 22% 34% 30% 4	540
December	1st to 10th	Day	8% 6% 25% 32% 23% 7%	398
	11th to 20th	Day	7% 6% 27% 35% 20% 5%	330
	21st to end	Day	7% 7% 23% 36% 20% 6%	363
January	1st to 10th	Night	10% 5% 25% 39% 20% 1	840
	11th to 20th	Night	8% 6% 30% 40% 15% 1	840
	21st to end	Night	12% 7% 30% 38% 13% 1	924
February	1st to 10th	Night	10% 7% 26% 39% 18% 1	840
	11th to 20th	Night	9% 5% 26% 41% 18% 1	823
	21st to end	Night	9% 4 24% 46% 18%	692
March	1st to 10th	Night	4 5% 31% 43% 16% 1	840
	11th to 20th	Night	7% 5% 23% 43% 21% 2	840
	21st to end	Night	6% 4 25% 45% 20% 1	924
April	1st to 10th	Night	5% 5% 20% 46% 21% 2	805
	11th to 20th	Night	5% 4 22% 46% 21% 2	791
	21st to end	Night	5% 2 21% 47% 23% 2	800
May	1st to 10th	Night	5% 1 18% 45% 29% 2	800
	11th to 20th	Night	8% 3 13% 39% 33% 4	664
	21st to end	Night	7% 1 7% 26% 46% 13%	650
June	1st to 10th	Night	13% 2 6% 21% 46% 13%	600
	11th to 20th	Night	6% 1 6% 16% 47% 24%	600
	21st to end	Night	8% 1 4 10% 46% 32%	600
July	1st to 10th	Night	7% 1 4 8% 46% 35%	585
	11th to 20th	Night	7% 2 8% 43% 40%	582
	21st to end	Night	3 1 2 7% 48% 39%	657
August	1st to 10th	Night	4 1 3 8% 45% 38%	597
	11th to 20th	Night	6% 3 9% 45% 36%	747
	21st to end	Night	11% 1 5% 17% 41% 25%	880
September	1st to 10th	Night	7% 2 5% 13% 44% 30%	800
	11th to 20th	Night	11% 2 7% 16% 43% 22%	800
	21st to end	Night	13% 2 8% 19% 40% 18%	800
October	1st to 10th	Night	12% 1 11% 32% 35% 9%	800
	11th to 20th	Night	10% 3 12% 29% 39% 8%	800
	21st to end	Night	10% 3 16% 35% 30% 5%	880
November	1st to 10th	Night	8% 3 19% 37% 28% 4	820
	11th to 20th	Night	7% 4 17% 42% 27% 3	840
	21st to end	Night	11% 2 20% 39% 27% 2	840
December	1st to 10th	Night	7% 4 21% 37% 27% 3	840
	11th to 20th	Night	10% 4 21% 37% 25% 3	840
	21st to end	Night	8% 4 21% 38% 26% 2	924

Page generated at 2026-03-30 02:18:45. Version ac07

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