Flying Horse Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Flying Horse Ranch clear sky chart from 2005-11-06 to 2025-05-26.

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	13% 7% 3 7% 4 4 4 4 5% 7% 41%	114085
	Night	14% 8% 3 7% 4 4 4 3 5% 7% 43%	115284
Transparency	Day	40% 6% 10% 23% 18% 3	117793
	Night	40% 5% 9% 23% 19% 4	119718
Seeing	Day	16% 8% 22% 24% 19% 10%	15973
	Night	17% 7% 24% 31% 19% 3	25815

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% 10% 7% 12% 5% 5% 4 3 5% 5% 30%	3617
	11th to 20th	Day	15% 9% 3 10% 5% 4 4 3 3 5% 40%	3620
	21st to end	Day	20% 9% 5% 5% 3 3 4 3 4 6% 39%	4809
February	1st to 10th	Day	18% 11% 3 8% 4 4 4 3 5% 6% 35%	2000
	11th to 20th	Day	21% 9% 4 7% 4 4 3 3 4 6% 34%	1948
	21st to end	Day	17% 10% 3 7% 4 4 4 3 5% 6% 37%	1650
March	1st to 10th	Day	16% 12% 5% 8% 4 4 4 3 4 4 36%	4480
	11th to 20th	Day	13% 9% 2 7% 3 4 3 2 4 6% 47%	4740
	21st to end	Day	12% 7% 3 7% 5% 4 4 3 5% 6% 43%	5819
April	1st to 10th	Day	14% 6% 2 7% 4 4 4 3 5% 7% 43%	2400
	11th to 20th	Day	14% 7% 3 7% 4 4 3 3 6% 6% 42%	2374
	21st to end	Day	15% 7% 3 6% 5% 5% 4 3 5% 7% 41%	2450
May	1st to 10th	Day	18% 8% 2 7% 5% 4 5% 4 7% 8% 33%	4212
	11th to 20th	Day	17% 7% 3 6% 4 4 4 4 6% 8% 37%	4211
	21st to end	Day	10% 6% 3 7% 5% 5% 5% 4 6% 8% 40%	4541
June	1st to 10th	Day	9% 6% 2 6% 4 4 5% 4 6% 9% 44%	2566
	11th to 20th	Day	5% 4 2 5% 4 5% 6% 5% 7% 10% 46%	2660
	21st to end	Day	5% 4 2 5% 5% 6% 6% 6% 8% 11% 43%	2660
July	1st to 10th	Day	8% 5% 3 7% 6% 6% 6% 4 7% 10% 38%	4440
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 4 7% 11% 42%	4440
	21st to end	Day	16% 10% 4 10% 5% 6% 6% 4 7% 8% 26%	4499
August	1st to 10th	Day	5% 4 2 4 3 4 5% 4 7% 8% 55%	3927
	11th to 20th	Day	8% 6% 2 7% 5% 5% 5% 5% 7% 10% 40%	3729
	21st to end	Day	5% 3 1 5% 4 4 5% 4 6% 9% 54%	4180
September	1st to 10th	Day	12% 6% 2 6% 5% 5% 5% 4 6% 8% 42%	2266
	11th to 20th	Day	12% 6% 3 6% 5% 4 4 3 5% 6% 46%	2090
	21st to end	Day	12% 5% 2 6% 3 4 4 3 4 7% 49%	2090
October	1st to 10th	Day	10% 5% 2 5% 3 3 4 3 4 6% 56%	2090
	11th to 20th	Day	13% 6% 2 5% 3 3 3 2 5% 6% 53%	2022
	21st to end	Day	18% 6% 2 6% 4 3 3 2 4 5% 47%	1891
November	1st to 10th	Day	13% 6% 2 5% 3 2 3 3 4 6% 54%	1762
	11th to 20th	Day	15% 8% 2 5% 3 3 3 3 5% 7% 47%	1800
	21st to end	Day	17% 8% 2 6% 4 4 4 3 5% 5% 44%	1800
December	1st to 10th	Day	17% 7% 2 6% 5% 3 4 3 4 5% 44%	2930
	11th to 20th	Day	18% 11% 4 7% 5% 4 5% 3 5% 6% 33%	3373
	21st to end	Day	18% 12% 5% 8% 5% 4 5% 4 4 7% 27%	3999
January	1st to 10th	Night	16% 12% 4 10% 4 3 3 3 5% 6% 34%	6348
	11th to 20th	Night	17% 11% 3 9% 5% 4 4 2 3 3 38%	6360
	21st to end	Night	19% 11% 4 7% 3 3 3 2 3 5% 40%	6129
February	1st to 10th	Night	22% 9% 4 8% 5% 4 3 3 4 5% 32%	2400
	11th to 20th	Night	22% 8% 4 8% 5% 3 4 3 3 5% 35%	2338
	21st to end	Night	20% 9% 4 7% 4 4 4 4 5% 5% 35%	1980
March	1st to 10th	Night	18% 11% 3 7% 4 4 3 3 4 6% 36%	5373
	11th to 20th	Night	11% 6% 2 6% 4 3 4 3 5% 6% 50%	5219
	21st to end	Night	13% 7% 3 8% 5% 5% 4 3 5% 6% 40%	5151
April	1st to 10th	Night	12% 6% 2 5% 4 3 4 4 5% 8% 46%	2000
	11th to 20th	Night	15% 6% 2 5% 3 4 3 3 5% 7% 46%	1975
	21st to end	Night	13% 7% 2 6% 5% 4 4 4 6% 9% 39%	1950
May	1st to 10th	Night	15% 9% 3 7% 4 4 4 4 5% 7% 38%	2903
	11th to 20th	Night	13% 7% 3 7% 4 5% 4 4 6% 8% 41%	2902
	21st to end	Night	7% 6% 2 6% 5% 5% 5% 5% 6% 10% 42%	3130
June	1st to 10th	Night	11% 7% 2 5% 4 4 4 3 6% 9% 46%	1609
	11th to 20th	Night	4 3 2 5% 4 3 4 4 7% 10% 56%	1520
	21st to end	Night	3 3 1 4 4 5% 4 6% 6% 12% 51%	1520
July	1st to 10th	Night	6% 4 2 5% 5% 5% 5% 4 8% 12% 44%	2530
	11th to 20th	Night	5% 4 3 5% 3 4 4 3 6% 10% 53%	2530
	21st to end	Night	10% 9% 3 10% 7% 6% 6% 5% 7% 8% 29%	3051
August	1st to 10th	Night	4 3 1 4 3 3 4 3 6% 7% 62%	2984
	11th to 20th	Night	4 3 2 6% 4 4 6% 5% 7% 11% 49%	3100
	21st to end	Night	4 3 1 4 3 4 4 4 6% 8% 59%	3476
September	1st to 10th	Night	10% 5% 2 6% 3 3 3 4 5% 8% 50%	1900
	11th to 20th	Night	10% 5% 2 6% 3 4 4 4 4 8% 50%	2085
	21st to end	Night	10% 5% 2 5% 3 3 4 3 4 6% 54%	2090
October	1st to 10th	Night	9% 5% 1 4 2 2 3 3 4 6% 62%	2090
	11th to 20th	Night	15% 6% 2 5% 3 3 2 3 3 5% 53%	2155
	21st to end	Night	15% 7% 2 5% 3 4 4 2 4 5% 48%	2705
November	1st to 10th	Night	13% 5% 1 4 4 4 4 2 5% 5% 52%	2536
	11th to 20th	Night	13% 7% 2 4 4 3 3 3 5% 8% 48%	2600
	21st to end	Night	16% 9% 3 5% 4 4 3 2 4 6% 47%	2600
December	1st to 10th	Night	19% 10% 3 7% 3 3 3 2 4 4 42%	4250
	11th to 20th	Night	20% 9% 3 6% 4 3 4 3 4 5% 39%	4822
	21st to end	Night	19% 12% 5% 10% 6% 5% 5% 3 4 5% 26%	6973

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	56% 4 10% 18% 10% 2	3618
	11th to 20th	Day	47% 4 6% 23% 19% 1	3620
	21st to end	Day	47% 4 7% 21% 17% 5%	4809
February	1st to 10th	Day	51% 4 8% 22% 13% 2	2000
	11th to 20th	Day	53% 3 7% 20% 13% 4	1958
	21st to end	Day	47% 4 9% 18% 16% 6%	1650
March	1st to 10th	Day	52% 3 4 17% 18% 6%	4480
	11th to 20th	Day	39% 4 8% 24% 19% 5%	4740
	21st to end	Day	41% 5% 9% 28% 15% 1	5821
April	1st to 10th	Day	40% 6% 11% 21% 20% 2	2400
	11th to 20th	Day	41% 5% 9% 22% 19% 3	2374
	21st to end	Day	43% 5% 10% 25% 14% 2	2450
May	1st to 10th	Day	46% 8% 14% 21% 11% 1	4250
	11th to 20th	Day	44% 9% 11% 24% 12% 1	4215
	21st to end	Day	39% 8% 12% 20% 20% 2	4554
June	1st to 10th	Day	36% 9% 11% 23% 18% 3	2566
	11th to 20th	Day	29% 10% 16% 23% 18% 3	2660
	21st to end	Day	30% 10% 16% 22% 17% 5%	2660
July	1st to 10th	Day	39% 7% 17% 25% 10% 2	4371
	11th to 20th	Day	34% 8% 14% 32% 10% 2	4365
	21st to end	Day	55% 7% 12% 17% 7% 2	4356
August	1st to 10th	Day	25% 7% 13% 34% 21%	3914
	11th to 20th	Day	37% 7% 12% 25% 18% 1	3765
	21st to end	Day	26% 8% 9% 34% 21% 2	4179
September	1st to 10th	Day	38% 9% 10% 20% 19% 4	2266
	11th to 20th	Day	38% 7% 9% 22% 21% 3	2090
	21st to end	Day	34% 6% 10% 23% 22% 5%	2090
October	1st to 10th	Day	20% 3 6% 18% 46% 8%	3480
	11th to 20th	Day	24% 3 7% 25% 30% 10%	3340
	21st to end	Day	30% 3 6% 26% 28% 7%	3091
November	1st to 10th	Day	33% 4 8% 23% 27% 5%	1762
	11th to 20th	Day	37% 5% 8% 23% 22% 6%	1800
	21st to end	Day	42% 4 7% 25% 18% 4	1800
December	1st to 10th	Day	43% 3 7% 27% 19% 1	2930
	11th to 20th	Day	52% 4 8% 19% 15% 2	3370
	21st to end	Day	55% 6% 11% 21% 8%	3999
January	1st to 10th	Night	50% 4 10% 22% 13% 1	6348
	11th to 20th	Night	51% 4 4 19% 18% 3	6360
	21st to end	Night	49% 3 6% 21% 17% 4	6129
February	1st to 10th	Night	55% 4 9% 18% 14% 1	2400
	11th to 20th	Night	53% 4 6% 20% 14% 4	2339
	21st to end	Night	51% 6% 7% 17% 16% 3	1980
March	1st to 10th	Night	49% 4 6% 16% 19% 6%	5373
	11th to 20th	Night	35% 4 9% 21% 20% 11%	5219
	21st to end	Night	44% 4 9% 25% 15% 2	5151
April	1st to 10th	Night	36% 6% 11% 25% 19% 3	2000
	11th to 20th	Night	38% 5% 10% 19% 22% 6%	1975
	21st to end	Night	40% 7% 11% 24% 18% 1	1950
May	1st to 10th	Night	43% 9% 13% 22% 12% 1	2930
	11th to 20th	Night	40% 8% 15% 22% 15% 1	2903
	21st to end	Night	33% 11% 15% 22% 17% 2	3138
June	1st to 10th	Night	35% 7% 13% 25% 18% 3	1609
	11th to 20th	Night	22% 6% 19% 27% 23% 3	1520
	21st to end	Night	25% 9% 17% 29% 14% 6%	1520
July	1st to 10th	Night	31% 7% 17% 31% 12% 2	2490
	11th to 20th	Night	27% 6% 13% 37% 15% 2	2482
	21st to end	Night	50% 9% 13% 18% 8% 1	2954
August	1st to 10th	Night	21% 6% 11% 39% 23% 1	2973
	11th to 20th	Night	26% 8% 18% 29% 17% 1	3130
	21st to end	Night	21% 6% 12% 35% 24% 3	3476
September	1st to 10th	Night	32% 8% 9% 24% 21% 6%	1900
	11th to 20th	Night	32% 5% 9% 25% 24% 5%	2085
	21st to end	Night	30% 6% 8% 24% 25% 7%	2090
October	1st to 10th	Night	18% 3 5% 18% 46% 11%	3480
	11th to 20th	Night	21% 3 6% 23% 36% 11%	3576
	21st to end	Night	28% 3 7% 23% 27% 12%	4455
November	1st to 10th	Night	34% 4 7% 23% 25% 7%	2536
	11th to 20th	Night	35% 4 7% 23% 23% 8%	2600
	21st to end	Night	41% 4 7% 25% 19% 4	2600
December	1st to 10th	Night	47% 3 7% 21% 20% 1	4250
	11th to 20th	Night	47% 4 8% 22% 17% 2	4824
	21st to end	Night	58% 6% 8% 18% 8% 1	6973

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	24% 15% 33% 20% 7% 1	300
	11th to 20th	Day	27% 19% 34% 15% 4	300
	21st to end	Day	23% 12% 45% 16% 4	330
February	1st to 10th	Day	25% 15% 38% 17% 4 1	300
	11th to 20th	Day	31% 19% 35% 13% 2 1	300
	21st to end	Day	27% 16% 37% 16% 4	249
March	1st to 10th	Day	23% 17% 32% 22% 5% 1	300
	11th to 20th	Day	23% 13% 38% 20% 5% 1	390
	21st to end	Day	20% 15% 37% 20% 6% 1	550
April	1st to 10th	Day	20% 13% 29% 26% 11% 1	500
	11th to 20th	Day	17% 14% 27% 26% 13% 3	492
	21st to end	Day	19% 9% 30% 26% 12% 4	500
May	1st to 10th	Day	19% 12% 27% 26% 12% 4	503
	11th to 20th	Day	15% 8% 21% 28% 18% 10%	527
	21st to end	Day	10% 5% 19% 28% 22% 16%	549
June	1st to 10th	Day	12% 4 17% 25% 26% 17%	586
	11th to 20th	Day	5% 3 15% 28% 32% 18%	680
	21st to end	Day	5% 3 17% 32% 28% 14%	680
July	1st to 10th	Day	11% 2 11% 24% 28% 23%	671
	11th to 20th	Day	9% 3 10% 23% 34% 22%	668
	21st to end	Day	12% 2 9% 25% 29% 23%	552
August	1st to 10th	Day	10% 2 7% 25% 33% 22%	486
	11th to 20th	Day	11% 2 11% 29% 33% 14%	479
	21st to end	Day	8% 2 6% 23% 32% 29%	539
September	1st to 10th	Day	14% 2 10% 23% 33% 18%	490
	11th to 20th	Day	11% 2 9% 25% 36% 17%	490
	21st to end	Day	15% 5% 19% 22% 26% 13%	490
October	1st to 10th	Day	10% 2 16% 33% 27% 12%	490
	11th to 20th	Day	14% 8% 30% 27% 14% 6%	422
	21st to end	Day	24% 10% 25% 28% 12% 2	330
November	1st to 10th	Day	20% 6% 28% 27% 16% 3	300
	11th to 20th	Day	16% 16% 31% 28% 9% 1	300
	21st to end	Day	23% 10% 29% 22% 13% 2	300
December	1st to 10th	Day	21% 13% 34% 22% 8% 2	300
	11th to 20th	Day	21% 17% 29% 21% 11% 1	300
	21st to end	Day	25% 15% 32% 24% 4	330
January	1st to 10th	Night	21% 15% 32% 26% 5%	1000
	11th to 20th	Night	26% 12% 35% 22% 5%	1000
	21st to end	Night	24% 9% 41% 23% 3	899
February	1st to 10th	Night	26% 12% 34% 24% 4	800
	11th to 20th	Night	27% 14% 34% 22% 2	783
	21st to end	Night	26% 12% 37% 23% 2	660
March	1st to 10th	Night	22% 14% 30% 28% 6%	800
	11th to 20th	Night	20% 12% 34% 28% 6% 1	800
	21st to end	Night	20% 10% 32% 31% 7%	745
April	1st to 10th	Night	16% 10% 33% 33% 8% 1	600
	11th to 20th	Night	18% 8% 31% 31% 12%	593
	21st to end	Night	16% 8% 28% 35% 12% 2	600
May	1st to 10th	Night	17% 5% 29% 31% 16% 3	600
	11th to 20th	Night	13% 5% 21% 36% 20% 4	591
	21st to end	Night	8% 2 16% 39% 31% 5%	634
June	1st to 10th	Night	12% 3 13% 37% 30% 4	570
	11th to 20th	Night	5% 1 9% 42% 39% 4	570
	21st to end	Night	5% 1 11% 41% 37% 6%	570
July	1st to 10th	Night	8% 2 8% 30% 42% 11%	555
	11th to 20th	Night	10% 2 6% 30% 45% 7%	552
	21st to end	Night	9% 1 7% 33% 41% 8%	624
August	1st to 10th	Night	7% 1 4 35% 44% 9%	567
	11th to 20th	Night	7% 2 7% 39% 43% 4	564
	21st to end	Night	7% 1 7% 30% 47% 9%	627
September	1st to 10th	Night	12% 1 9% 30% 42% 6%	570
	11th to 20th	Night	12% 2 9% 30% 40% 6%	755
	21st to end	Night	12% 2 16% 32% 34% 4	760
October	1st to 10th	Night	11% 3 16% 36% 29% 5%	760
	11th to 20th	Night	17% 6% 22% 34% 19% 2	760
	21st to end	Night	17% 7% 29% 31% 15% 2	836
November	1st to 10th	Night	16% 5% 25% 35% 16% 3	780
	11th to 20th	Night	16% 9% 34% 31% 10% 1	800
	21st to end	Night	20% 10% 28% 32% 11% 1	800
December	1st to 10th	Night	26% 11% 27% 31% 6%	800
	11th to 20th	Night	24% 8% 31% 29% 8%	800
	21st to end	Night	26% 12% 30% 28% 4	1090

Page generated at 2025-05-23 08:21:01. Version ac07

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