Dowdy Ranch Visitor Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dowdy Ranch Visitor Center clear sky chart from 2005-11-06 to 2025-11-18.

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	5% 3 1 3 3 3 3 3 5% 7% 65%	135243
	Night	6% 4 1 4 3 3 4 4 7% 9% 55%	132577
Transparency	Day	21% 4 8% 18% 25% 23%	130207
	Night	27% 7% 9% 17% 22% 18%	128595
Seeing	Day	8% 9% 27% 31% 19% 6%	16775
	Night	8% 4 17% 36% 28% 7%	26165

By Month

Percentage Cloud Cover SW (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% 6% 2 6% 4 3 4 3 5% 7% 53%	3800
	11th to 20th	Day	8% 4 2 7% 5% 5% 4 2 4 4 55%	4100
	21st to end	Day	14% 6% 2 7% 4 4 4 4 5% 6% 44%	4510
February	1st to 10th	Day	15% 6% 2 6% 4 3 4 3 4 6% 47%	1800
	11th to 20th	Day	9% 5% 2 6% 4 6% 5% 4 5% 7% 46%	1910
	21st to end	Day	10% 7% 2 6% 5% 4 4 4 5% 5% 47%	1650
March	1st to 10th	Day	9% 7% 3 7% 7% 7% 7% 6% 7% 7% 34%	4738
	11th to 20th	Day	9% 6% 2 5% 4 5% 5% 3 6% 8% 49%	5000
	21st to end	Day	10% 6% 2 7% 5% 5% 6% 5% 7% 9% 38%	5655
April	1st to 10th	Day	9% 6% 2 6% 5% 5% 4 4 5% 7% 48%	2400
	11th to 20th	Day	6% 5% 2 4 4 3 4 4 5% 7% 57%	2369
	21st to end	Day	5% 3 1 3 3 4 3 4 5% 8% 61%	2400
May	1st to 10th	Day	3 2 1 3 2 2 2 2 4 6% 74%	5440
	11th to 20th	Day	1 1 1 1 1 2 3 3 6% 8% 72%	6027
	21st to end	Day	1 1 1 2 2 2 3 6% 7% 76%	6902
June	1st to 10th	Day	2 2 1 2 3 2 4 3 6% 9% 67%	2800
	11th to 20th	Day	1 1 1 1 2 2 2 4 6% 79%	2800
	21st to end	Day	1 1 1 2 2 2 2 4 5% 80%	2800
July	1st to 10th	Day	1 1 1 1 3 5% 88%	6319
	11th to 20th	Day	1 1 1 1 1 1 2 3 5% 85%	6019
	21st to end	Day	1 1 1 2 5% 8% 81%	6402
August	1st to 10th	Day	1 1 1 1 1 2 2 3 7% 81%	5777
	11th to 20th	Day	1 1 2 4 6% 85%	5369
	21st to end	Day	1 1 2 2 2 3 6% 82%	5984
September	1st to 10th	Day	1 1 1 1 2 2 1 2 4 84%	2400
	11th to 20th	Day	1 1 1 1 2 2 4 4 5% 7% 73%	2400
	21st to end	Day	2 1 1 2 1 1 2 3 4 6% 77%	2155
October	1st to 10th	Day	1 2 1 2 2 2 3 3 4 6% 75%	3280
	11th to 20th	Day	2 1 1 3 2 2 3 2 4 5% 76%	3261
	21st to end	Day	2 3 1 3 3 4 4 3 5% 7% 64%	3558
November	1st to 10th	Day	6% 4 1 4 3 4 4 4 5% 9% 58%	1973
	11th to 20th	Day	7% 4 2 5% 3 4 4 4 6% 7% 54%	1863
	21st to end	Day	8% 5% 1 5% 3 3 3 4 5% 7% 56%	1730
December	1st to 10th	Day	6% 4 2 5% 4 4 4 3 5% 8% 55%	2620
	11th to 20th	Day	17% 7% 3 6% 5% 4 5% 4 6% 7% 37%	3028
	21st to end	Day	11% 8% 3 9% 7% 5% 5% 5% 6% 7% 33%	4004
January	1st to 10th	Night	8% 5% 2 4 3 4 3 4 6% 7% 55%	6149
	11th to 20th	Night	10% 6% 2 6% 4 4 3 3 4 5% 52%	5880
	21st to end	Night	12% 6% 2 7% 5% 5% 5% 4 5% 6% 44%	6468
February	1st to 10th	Night	14% 6% 2 5% 4 3 3 3 5% 6% 50%	2600
	11th to 20th	Night	9% 4 1 5% 5% 5% 5% 5% 5% 7% 50%	2377
	21st to end	Night	8% 5% 2 5% 4 4 4 3 5% 6% 54%	1980
March	1st to 10th	Night	11% 8% 2 8% 6% 6% 6% 5% 6% 6% 35%	5139
	11th to 20th	Night	8% 6% 2 6% 4 5% 4 4 6% 6% 49%	5000
	21st to end	Night	10% 7% 2 6% 6% 6% 6% 4 6% 7% 39%	5319
April	1st to 10th	Night	8% 4 1 5% 4 4 6% 5% 6% 7% 50%	2000
	11th to 20th	Night	5% 4 2 5% 4 4 4 5% 7% 7% 54%	1979
	21st to end	Night	3 3 1 3 3 4 4 5% 7% 9% 58%	2000
May	1st to 10th	Night	1 2 1 2 2 3 4 3 6% 10% 67%	4560
	11th to 20th	Night	1 1 1 1 2 4 5% 13% 16% 55%	3843
	21st to end	Night	1 1 1 1 2 3 4 10% 12% 65%	3972
June	1st to 10th	Night	1 2 1 3 3 4 5% 5% 8% 11% 58%	1600
	11th to 20th	Night	1 2 2 3 4 4 8% 8% 69%	1600
	21st to end	Night	1 1 2 2 4 4 7% 10% 69%	1600
July	1st to 10th	Night	1 2 2 6% 14% 74%	3640
	11th to 20th	Night	1 1 1 1 2 3 10% 19% 62%	3950
	21st to end	Night	1 1 2 2 3 6% 26% 21% 39%	4472
August	1st to 10th	Night	1 1 1 2 1 3 3 9% 15% 64%	4035
	11th to 20th	Night	1 1 1 2 2 10% 15% 67%	4501
	21st to end	Night	1 1 2 2 3 3 7% 10% 71%	5015
September	1st to 10th	Night	1 1 2 2 2 3 3 6% 8% 73%	2000
	11th to 20th	Night	2 1 1 2 2 4 5% 5% 8% 8% 63%	2000
	21st to end	Night	2 1 1 3 2 2 3 3 6% 6% 71%	2240
October	1st to 10th	Night	2 1 2 2 3 3 3 4 6% 75%	3920
	11th to 20th	Night	1 2 1 4 5% 5% 4 3 6% 8% 61%	3897
	21st to end	Night	3 2 1 3 3 3 4 4 6% 6% 66%	4253
November	1st to 10th	Night	4 2 1 4 3 3 4 3 5% 7% 63%	2544
	11th to 20th	Night	7% 4 2 5% 3 4 4 3 6% 8% 54%	2691
	21st to end	Night	6% 5% 2 4 4 4 4 4 4 7% 56%	2665
December	1st to 10th	Night	7% 3 1 4 3 3 4 3 5% 6% 59%	4560
	11th to 20th	Night	15% 7% 3 6% 5% 5% 6% 4 8% 8% 33%	5176
	21st to end	Night	15% 8% 3 9% 6% 6% 6% 4 5% 6% 32%	6952

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	31% 4 18% 25% 16% 6%	3800
	11th to 20th	Day	34% 4 8% 11% 22% 20%	4100
	21st to end	Day	40% 5% 9% 13% 20% 13%	4510
February	1st to 10th	Day	39% 4 6% 20% 19% 11%	1800
	11th to 20th	Day	38% 6% 9% 19% 21% 7%	1920
	21st to end	Day	39% 5% 8% 23% 18% 7%	1650
March	1st to 10th	Day	46% 8% 11% 14% 19% 2	4738
	11th to 20th	Day	33% 6% 14% 29% 11% 8%	5000
	21st to end	Day	38% 11% 17% 22% 11% 2	5655
April	1st to 10th	Day	34% 6% 12% 23% 19% 6%	2400
	11th to 20th	Day	28% 5% 12% 27% 21% 8%	2372
	21st to end	Day	23% 5% 13% 29% 24% 6%	2400
May	1st to 10th	Day	13% 4 9% 26% 33% 15%	5440
	11th to 20th	Day	10% 5% 10% 33% 34% 8%	6030
	21st to end	Day	10% 4 11% 29% 38% 8%	6904
June	1st to 10th	Day	17% 4 12% 26% 28% 13%	2800
	11th to 20th	Day	10% 2 7% 21% 36% 24%	2800
	21st to end	Day	11% 1 3 12% 33% 41%	2800
July	1st to 10th	Day	4 2 2 5% 21% 67%	6251
	11th to 20th	Day	6% 3 2 4 14% 71%	5946
	21st to end	Day	5% 6% 2 14% 30% 43%	6217
August	1st to 10th	Day	10% 2 2 8% 28% 50%	4206
	11th to 20th	Day	5% 2 2 8% 35% 48%	3885
	21st to end	Day	7% 2 2 10% 33% 45%	4311
September	1st to 10th	Day	8% 2 3 10% 30% 48%	2400
	11th to 20th	Day	12% 4 6% 21% 36% 21%	2400
	21st to end	Day	10% 2 4 21% 36% 26%	2155
October	1st to 10th	Day	12% 3 5% 11% 24% 45%	3280
	11th to 20th	Day	13% 4 6% 22% 31% 24%	3261
	21st to end	Day	21% 4 6% 18% 33% 18%	3558
November	1st to 10th	Day	25% 6% 9% 20% 27% 13%	1973
	11th to 20th	Day	30% 5% 9% 22% 25% 8%	1863
	21st to end	Day	30% 3 9% 18% 30% 10%	1730
December	1st to 10th	Day	28% 4 8% 19% 35% 8%	2620
	11th to 20th	Day	45% 6% 9% 16% 17% 6%	3028
	21st to end	Day	50% 7% 13% 17% 10% 3	4004
January	1st to 10th	Night	29% 6% 18% 25% 18% 5%	6149
	11th to 20th	Night	34% 5% 11% 12% 24% 14%	5880
	21st to end	Night	42% 6% 9% 12% 16% 16%	6468
February	1st to 10th	Night	37% 3 8% 20% 19% 13%	2600
	11th to 20th	Night	35% 5% 10% 20% 21% 8%	2378
	21st to end	Night	32% 5% 11% 27% 17% 9%	1980
March	1st to 10th	Night	48% 8% 10% 12% 18% 3	5139
	11th to 20th	Night	36% 6% 13% 22% 16% 8%	5000
	21st to end	Night	41% 9% 15% 20% 12% 3	5319
April	1st to 10th	Night	34% 5% 13% 24% 18% 7%	2000
	11th to 20th	Night	29% 5% 13% 27% 19% 8%	1979
	21st to end	Night	23% 5% 11% 31% 23% 6%	2000
May	1st to 10th	Night	15% 9% 11% 22% 29% 15%	4557
	11th to 20th	Night	13% 7% 15% 28% 26% 11%	3843
	21st to end	Night	12% 8% 14% 25% 32% 10%	3972
June	1st to 10th	Night	21% 7% 9% 22% 28% 12%	1600
	11th to 20th	Night	16% 3 7% 16% 29% 28%	1600
	21st to end	Night	15% 2 5% 13% 27% 39%	1600
July	1st to 10th	Night	7% 10% 3 4 18% 58%	3600
	11th to 20th	Night	8% 19% 4 4 17% 48%	3900
	21st to end	Night	11% 40% 3 6% 18% 22%	4345
August	1st to 10th	Night	16% 3 3 8% 26% 44%	2929
	11th to 20th	Night	9% 8% 6% 9% 25% 44%	3251
	21st to end	Night	12% 6% 5% 9% 32% 36%	3608
September	1st to 10th	Night	13% 4 2 8% 26% 47%	2000
	11th to 20th	Night	18% 5% 6% 17% 32% 22%	2000
	21st to end	Night	15% 4 5% 15% 34% 27%	2240
October	1st to 10th	Night	13% 3 5% 11% 19% 50%	3920
	11th to 20th	Night	23% 8% 5% 17% 25% 22%	3897
	21st to end	Night	19% 5% 6% 18% 30% 22%	4253
November	1st to 10th	Night	22% 4 9% 23% 25% 16%	2544
	11th to 20th	Night	29% 4 11% 20% 28% 9%	2691
	21st to end	Night	29% 4 9% 19% 25% 14%	2665
December	1st to 10th	Night	26% 4 7% 21% 29% 14%	4560
	11th to 20th	Night	47% 6% 9% 14% 20% 4	5176
	21st to end	Night	53% 6% 14% 14% 8% 4	6952

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	25% 10% 27% 23% 13% 2	270
	11th to 20th	Day	14% 7% 27% 30% 19% 4	400
	21st to end	Day	15% 8% 23% 31% 19% 4	440
February	1st to 10th	Day	22% 13% 20% 26% 16% 5%	400
	11th to 20th	Day	16% 15% 25% 29% 15% 1	475
	21st to end	Day	13% 14% 27% 32% 13% 2	414
March	1st to 10th	Day	22% 15% 26% 24% 11% 2	500
	11th to 20th	Day	20% 13% 25% 21% 17% 4	500
	21st to end	Day	17% 15% 30% 24% 11% 2	550
April	1st to 10th	Day	14% 14% 30% 22% 15% 5%	500
	11th to 20th	Day	12% 17% 31% 24% 11% 5%	492
	21st to end	Day	6% 16% 35% 23% 13% 7%	500
May	1st to 10th	Day	7% 14% 36% 26% 13% 4	503
	11th to 20th	Day	6% 12% 40% 28% 11% 3	528
	21st to end	Day	6% 11% 34% 33% 12% 4	573
June	1st to 10th	Day	3 9% 37% 31% 13% 6%	530
	11th to 20th	Day	2 12% 35% 32% 16% 3	530
	21st to end	Day	3 6% 31% 35% 19% 5%	530
July	1st to 10th	Day	1 3 29% 44% 18% 5%	526
	11th to 20th	Day	1 1 23% 44% 25% 6%	524
	21st to end	Day	1 2 24% 42% 21% 9%	575
August	1st to 10th	Day	3 4 30% 36% 20% 6%	527
	11th to 20th	Day	1 5% 26% 37% 22% 9%	517
	21st to end	Day	1 3 20% 43% 25% 10%	583
September	1st to 10th	Day	2 5% 21% 35% 24% 12%	530
	11th to 20th	Day	3 8% 29% 33% 19% 8%	530
	21st to end	Day	3 7% 22% 33% 25% 9%	530
October	1st to 10th	Day	4 9% 22% 29% 27% 9%	530
	11th to 20th	Day	5% 9% 21% 28% 29% 9%	530
	21st to end	Day	8% 6% 20% 31% 27% 8%	583
November	1st to 10th	Day	8% 7% 18% 28% 32% 8%	449
	11th to 20th	Day	10% 6% 18% 35% 25% 6%	321
	21st to end	Day	12% 5% 23% 32% 26% 2	265
December	1st to 10th	Day	15% 8% 23% 28% 24% 4	200
	11th to 20th	Day	15% 10% 24% 25% 22% 5%	200
	21st to end	Day	19% 10% 26% 25% 19% 2	220
January	1st to 10th	Night	16% 4 14% 35% 23% 8%	800
	11th to 20th	Night	11% 5% 13% 38% 26% 9%	800
	21st to end	Night	15% 4 12% 36% 27% 6%	880
February	1st to 10th	Night	18% 4 12% 35% 24% 7%	800
	11th to 20th	Night	13% 6% 16% 36% 22% 7%	784
	21st to end	Night	12% 7% 17% 43% 19% 3	660
March	1st to 10th	Night	15% 9% 18% 32% 21% 4	800
	11th to 20th	Night	13% 6% 20% 35% 21% 6%	800
	21st to end	Night	11% 10% 22% 34% 19% 4	880
April	1st to 10th	Night	12% 6% 20% 36% 22% 4	800
	11th to 20th	Night	8% 10% 28% 29% 20% 5%	791
	21st to end	Night	6% 9% 27% 31% 22% 6%	800
May	1st to 10th	Night	4 5% 27% 38% 21% 5%	800
	11th to 20th	Night	4 4 22% 42% 23% 4	504
	21st to end	Night	3 6% 27% 38% 23% 2	433
June	1st to 10th	Night	3 2 26% 42% 24% 3	400
	11th to 20th	Night	1 4 26% 43% 25% 2	400
	21st to end	Night	1 2 15% 44% 34% 4	400
July	1st to 10th	Night	2 2 15% 40% 38% 3	390
	11th to 20th	Night	1 8% 41% 41% 9%	514
	21st to end	Night	1 1 13% 39% 38% 9%	657
August	1st to 10th	Night	1 1 15% 40% 34% 9%	597
	11th to 20th	Night	2 19% 40% 31% 8%	787
	21st to end	Night	1 1 11% 37% 41% 9%	880
September	1st to 10th	Night	1 2 13% 33% 42% 9%	800
	11th to 20th	Night	3 3 18% 37% 31% 8%	800
	21st to end	Night	3 3 12% 36% 35% 11%	800
October	1st to 10th	Night	4 2 14% 38% 33% 10%	800
	11th to 20th	Night	5% 4 13% 34% 33% 12%	800
	21st to end	Night	5% 2 14% 33% 28% 18%	880
November	1st to 10th	Night	5% 4 14% 32% 34% 11%	820
	11th to 20th	Night	11% 2 12% 36% 32% 8%	828
	21st to end	Night	10% 4 13% 35% 30% 9%	800
December	1st to 10th	Night	14% 5% 11% 38% 25% 8%	800
	11th to 20th	Night	20% 3 13% 36% 24% 4	800
	21st to end	Night	16% 6% 18% 35% 21% 4	880

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