Tunnel Ridge Road
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tunnel Ridge Road clear sky chart from 2005-11-06 to 2026-01-02.

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	14% 9% 3 7% 5% 5% 5% 4 6% 7% 35%	127108
	Night	14% 9% 3 8% 4 4 4 3 5% 7% 37%	124285
Transparency	Day	46% 6% 11% 22% 14% 2	130808
	Night	45% 6% 10% 22% 16% 2	128653
Seeing	Day	21% 12% 25% 22% 14% 6%	16328
	Night	19% 10% 24% 29% 17% 2	26406

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% 18% 7% 14% 5% 3 4 3 4 5% 22%	4065
	11th to 20th	Day	15% 15% 7% 14% 4 5% 3 2 3 3 29%	4060
	21st to end	Day	19% 13% 5% 7% 5% 4 4 3 4 5% 31%	4466
February	1st to 10th	Day	19% 12% 5% 10% 4 4 4 3 4 5% 29%	1896
	11th to 20th	Day	22% 11% 5% 8% 5% 4 4 3 4 5% 30%	1948
	21st to end	Day	20% 13% 4 7% 4 4 4 3 4 4 33%	1650
March	1st to 10th	Day	18% 14% 4 7% 4 4 4 3 4 5% 34%	4636
	11th to 20th	Day	13% 8% 3 6% 4 4 4 3 6% 7% 42%	4980
	21st to end	Day	16% 8% 3 7% 4 5% 4 4 6% 7% 36%	5465
April	1st to 10th	Day	15% 10% 3 7% 4 4 4 4 5% 7% 37%	2270
	11th to 20th	Day	16% 8% 3 7% 4 5% 4 3 5% 7% 40%	2447
	21st to end	Day	17% 7% 3 7% 5% 5% 5% 4 5% 7% 35%	2600
May	1st to 10th	Day	19% 10% 3 8% 5% 6% 5% 5% 6% 7% 25%	5862
	11th to 20th	Day	18% 9% 3 8% 5% 5% 5% 4 6% 7% 30%	5861
	21st to end	Day	14% 7% 2 7% 5% 6% 7% 5% 8% 10% 30%	6433
June	1st to 10th	Day	11% 6% 3 6% 5% 5% 5% 5% 7% 9% 39%	2600
	11th to 20th	Day	8% 5% 3 7% 5% 5% 5% 7% 7% 9% 39%	2600
	21st to end	Day	10% 5% 2 6% 5% 6% 5% 5% 7% 10% 40%	2600
July	1st to 10th	Day	9% 6% 2 8% 5% 5% 5% 4 6% 9% 41%	5900
	11th to 20th	Day	10% 6% 3 7% 6% 6% 7% 6% 8% 11% 31%	5900
	21st to end	Day	15% 9% 3 9% 6% 6% 6% 4 7% 8% 27%	6424
August	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 4 6% 10% 40%	4234
	11th to 20th	Day	10% 7% 2 6% 5% 5% 5% 5% 8% 11% 36%	4174
	21st to end	Day	6% 4 2 4 4 5% 5% 4 6% 8% 53%	4385
September	1st to 10th	Day	13% 6% 3 5% 3 4 5% 3 5% 8% 44%	2220
	11th to 20th	Day	12% 5% 2 7% 4 4 4 4 6% 8% 45%	2200
	21st to end	Day	18% 5% 2 6% 4 3 4 3 4 7% 43%	2200
October	1st to 10th	Day	11% 4 2 5% 4 3 3 3 5% 8% 52%	2200
	11th to 20th	Day	14% 6% 2 5% 3 3 3 3 4 6% 50%	2005
	21st to end	Day	20% 8% 2 5% 3 3 3 2 4 6% 42%	2147
November	1st to 10th	Day	12% 6% 2 6% 4 4 3 4 4 5% 51%	1852
	11th to 20th	Day	15% 10% 3 7% 4 4 3 3 4 6% 42%	1890
	21st to end	Day	16% 11% 4 7% 4 4 4 3 5% 5% 37%	1890
December	1st to 10th	Day	18% 11% 3 7% 6% 4 4 3 4 5% 36%	3020
	11th to 20th	Day	21% 14% 4 8% 5% 4 3 3 5% 5% 27%	3463
	21st to end	Day	17% 15% 5% 10% 6% 5% 5% 4 5% 6% 22%	4565
January	1st to 10th	Night	15% 16% 6% 15% 6% 5% 4 3 4 5% 21%	5903
	11th to 20th	Night	18% 14% 5% 12% 6% 4 3 2 3 4 28%	5900
	21st to end	Night	19% 11% 4 7% 4 3 4 3 4 5% 37%	6490
February	1st to 10th	Night	19% 12% 4 9% 4 4 4 4 4 5% 29%	2500
	11th to 20th	Night	22% 11% 4 8% 4 4 4 3 4 5% 30%	2338
	21st to end	Night	22% 13% 3 8% 4 4 3 3 5% 4 31%	1980
March	1st to 10th	Night	18% 14% 2 6% 4 4 4 3 4 5% 36%	5217
	11th to 20th	Night	12% 7% 2 5% 3 3 4 3 5% 6% 48%	4980
	21st to end	Night	14% 8% 4 8% 6% 5% 5% 4 6% 7% 34%	5467
April	1st to 10th	Night	14% 7% 3 7% 4 5% 4 3 6% 7% 41%	2145
	11th to 20th	Night	13% 7% 2 6% 4 4 4 4 5% 6% 45%	1902
	21st to end	Night	16% 8% 3 6% 4 4 3 4 5% 7% 39%	1800
May	1st to 10th	Night	19% 10% 3 9% 5% 5% 4 4 5% 8% 27%	4033
	11th to 20th	Night	16% 8% 3 8% 6% 4 5% 5% 6% 8% 31%	4032
	21st to end	Night	13% 7% 2 7% 5% 5% 5% 4 6% 9% 37%	4421
June	1st to 10th	Night	8% 5% 3 5% 4 4 4 5% 8% 10% 44%	1800
	11th to 20th	Night	6% 4 2 6% 4 5% 5% 4 9% 10% 45%	1800
	21st to end	Night	10% 4 1 5% 4 5% 5% 6% 8% 11% 41%	1800
July	1st to 10th	Night	6% 5% 3 7% 5% 6% 5% 4 8% 9% 43%	4058
	11th to 20th	Night	7% 5% 2 7% 5% 5% 6% 4 8% 11% 39%	4057
	21st to end	Night	11% 8% 3 8% 5% 6% 5% 5% 7% 10% 32%	4427
August	1st to 10th	Night	8% 5% 2 8% 5% 4 4 4 7% 9% 44%	2915
	11th to 20th	Night	9% 6% 3 7% 4 5% 5% 4 6% 9% 43%	2875
	21st to end	Night	5% 2 1 4 3 3 4 3 6% 8% 61%	3510
September	1st to 10th	Night	12% 4 2 5% 4 4 5% 4 5% 8% 48%	2160
	11th to 20th	Night	10% 6% 2 6% 4 4 4 4 5% 7% 50%	2200
	21st to end	Night	12% 7% 2 6% 3 4 3 3 4 6% 49%	2200
October	1st to 10th	Night	11% 5% 1 5% 4 3 4 3 4 7% 54%	2200
	11th to 20th	Night	14% 6% 2 5% 4 3 3 3 4 7% 50%	2394
	21st to end	Night	18% 8% 2 5% 3 3 3 3 4 6% 44%	2690
November	1st to 10th	Night	12% 7% 3 6% 3 3 3 3 4 6% 50%	2666
	11th to 20th	Night	15% 9% 3 5% 4 3 3 3 4 5% 44%	2730
	21st to end	Night	18% 11% 3 5% 4 3 4 4 4 5% 40%	2730
December	1st to 10th	Night	18% 13% 4 9% 4 4 3 2 4 4 36%	4380
	11th to 20th	Night	20% 13% 6% 9% 4 3 3 2 3 5% 31%	4952
	21st to end	Night	17% 15% 5% 10% 6% 5% 5% 4 5% 6% 20%	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	63% 5% 8% 17% 7% 1	4066
	11th to 20th	Day	61% 3 5% 16% 13% 2	4060
	21st to end	Day	56% 3 8% 21% 10% 1	4466
February	1st to 10th	Day	57% 5% 7% 19% 11% 1	1896
	11th to 20th	Day	57% 3 8% 19% 10% 2	1958
	21st to end	Day	55% 4 7% 18% 12% 3	1650
March	1st to 10th	Day	53% 4 6% 15% 16% 6%	4636
	11th to 20th	Day	39% 5% 9% 23% 22% 2	4980
	21st to end	Day	46% 5% 9% 27% 12% 1	5465
April	1st to 10th	Day	45% 6% 11% 22% 13% 3	2270
	11th to 20th	Day	44% 5% 8% 22% 16% 4	2447
	21st to end	Day	46% 7% 11% 22% 11% 2	2600
May	1st to 10th	Day	54% 8% 11% 18% 9% 1	5897
	11th to 20th	Day	53% 7% 11% 20% 9%	5865
	21st to end	Day	44% 9% 15% 18% 13% 2	6447
June	1st to 10th	Day	39% 9% 12% 24% 16% 1	2600
	11th to 20th	Day	37% 11% 14% 20% 17% 2	2600
	21st to end	Day	38% 10% 14% 19% 17% 3	2600
July	1st to 10th	Day	39% 7% 14% 23% 16% 1	5835
	11th to 20th	Day	43% 9% 15% 25% 6% 1	5831
	21st to end	Day	52% 7% 12% 19% 9% 1	6240
August	1st to 10th	Day	37% 8% 14% 30% 10%	4221
	11th to 20th	Day	38% 8% 12% 28% 12% 2	4213
	21st to end	Day	28% 7% 14% 32% 18% 2	4384
September	1st to 10th	Day	38% 7% 12% 21% 18% 5%	2220
	11th to 20th	Day	36% 6% 11% 24% 19% 3	2200
	21st to end	Day	41% 6% 10% 21% 20% 2	2200
October	1st to 10th	Day	24% 5% 8% 23% 38% 3	3590
	11th to 20th	Day	26% 3 9% 28% 31% 2	3245
	21st to end	Day	32% 3 9% 29% 19% 8%	3449
November	1st to 10th	Day	36% 5% 8% 25% 23% 4	1852
	11th to 20th	Day	44% 3 8% 23% 19% 4	1890
	21st to end	Day	48% 5% 8% 20% 16% 2	1890
December	1st to 10th	Day	51% 4 6% 23% 14% 1	3020
	11th to 20th	Day	59% 4 8% 16% 12% 1	3460
	21st to end	Day	62% 6% 11% 17% 5%	4565
January	1st to 10th	Night	65% 5% 7% 15% 7% 1	5903
	11th to 20th	Night	61% 3 5% 17% 11% 3	5900
	21st to end	Night	51% 3 7% 22% 14% 2	6490
February	1st to 10th	Night	57% 4 11% 18% 9% 1	2500
	11th to 20th	Night	57% 4 7% 18% 11% 2	2339
	21st to end	Night	56% 5% 9% 15% 12% 3	1980
March	1st to 10th	Night	50% 4 6% 22% 14% 4	5217
	11th to 20th	Night	35% 4 8% 28% 21% 3	4980
	21st to end	Night	48% 6% 8% 23% 15% 1	5467
April	1st to 10th	Night	41% 6% 12% 21% 17% 2	2145
	11th to 20th	Night	38% 7% 10% 22% 18% 6%	1902
	21st to end	Night	44% 6% 12% 22% 14% 2	1800
May	1st to 10th	Night	53% 8% 11% 19% 8% 2	4060
	11th to 20th	Night	50% 8% 14% 20% 8% 1	4033
	21st to end	Night	41% 8% 16% 20% 13% 2	4429
June	1st to 10th	Night	31% 10% 16% 23% 17% 3	1800
	11th to 20th	Night	31% 10% 17% 22% 19% 2	1800
	21st to end	Night	33% 10% 15% 20% 17% 4	1800
July	1st to 10th	Night	35% 9% 12% 25% 17% 2	4015
	11th to 20th	Night	37% 8% 19% 23% 11% 2	4006
	21st to end	Night	46% 8% 13% 21% 12%	4297
August	1st to 10th	Night	34% 7% 15% 28% 14% 1	2904
	11th to 20th	Night	36% 7% 13% 29% 14% 1	2902
	21st to end	Night	21% 6% 14% 33% 22% 4	3510
September	1st to 10th	Night	33% 8% 12% 21% 20% 7%	2160
	11th to 20th	Night	34% 7% 11% 22% 24% 3	2200
	21st to end	Night	36% 5% 10% 21% 24% 3	2200
October	1st to 10th	Night	26% 5% 8% 23% 36% 3	3590
	11th to 20th	Night	25% 3 7% 25% 34% 6%	3893
	21st to end	Night	30% 4 8% 22% 28% 8%	4338
November	1st to 10th	Night	36% 4 8% 25% 23% 4	2666
	11th to 20th	Night	42% 4 8% 20% 22% 5%	2730
	21st to end	Night	47% 3 8% 24% 16% 2	2730
December	1st to 10th	Night	53% 4 8% 21% 13% 1	4380
	11th to 20th	Night	56% 3 9% 20% 11% 1	4954
	21st to end	Night	62% 6% 10% 14% 7%	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	30% 24% 29% 13% 3 1	303
	11th to 20th	Day	37% 24% 27% 11% 2	300
	21st to end	Day	30% 26% 31% 12% 2	330
February	1st to 10th	Day	31% 23% 31% 11% 4	300
	11th to 20th	Day	43% 23% 26% 6% 1 1	300
	21st to end	Day	35% 22% 33% 8% 1	249
March	1st to 10th	Day	32% 22% 30% 12% 5%	365
	11th to 20th	Day	26% 23% 29% 18% 4	500
	21st to end	Day	31% 20% 28% 15% 5%	550
April	1st to 10th	Day	25% 19% 28% 18% 9% 1	500
	11th to 20th	Day	23% 17% 31% 17% 10% 2	492
	21st to end	Day	23% 16% 31% 20% 8% 3	500
May	1st to 10th	Day	26% 14% 30% 17% 9% 4	503
	11th to 20th	Day	19% 13% 25% 24% 13% 6%	527
	21st to end	Day	17% 8% 24% 24% 17% 10%	573
June	1st to 10th	Day	13% 7% 24% 27% 19% 9%	530
	11th to 20th	Day	10% 6% 21% 34% 21% 8%	530
	21st to end	Day	10% 6% 25% 28% 19% 13%	530
July	1st to 10th	Day	15% 4 17% 23% 23% 17%	525
	11th to 20th	Day	10% 4 18% 32% 22% 13%	524
	21st to end	Day	16% 4 16% 27% 25% 12%	576
August	1st to 10th	Day	15% 3 17% 27% 26% 13%	526
	11th to 20th	Day	14% 5% 18% 26% 24% 12%	519
	21st to end	Day	9% 4 13% 31% 26% 17%	583
September	1st to 10th	Day	13% 5% 17% 22% 31% 12%	530
	11th to 20th	Day	13% 4 11% 28% 30% 14%	530
	21st to end	Day	21% 8% 20% 24% 21% 6%	530
October	1st to 10th	Day	12% 6% 20% 31% 23% 7%	530
	11th to 20th	Day	14% 12% 28% 25% 15% 5%	530
	21st to end	Day	25% 12% 31% 23% 9% 1	530
November	1st to 10th	Day	19% 13% 35% 24% 8% 2	330
	11th to 20th	Day	25% 17% 34% 19% 5% 1	330
	21st to end	Day	26% 16% 35% 16% 5% 1	330
December	1st to 10th	Day	29% 21% 31% 15% 4	330
	11th to 20th	Day	25% 22% 34% 12% 7%	330
	21st to end	Day	30% 21% 34% 11% 3	363
January	1st to 10th	Night	26% 19% 30% 21% 4	805
	11th to 20th	Night	32% 15% 30% 19% 4	800
	21st to end	Night	23% 18% 35% 22% 2	880
February	1st to 10th	Night	27% 14% 34% 22% 3	800
	11th to 20th	Night	31% 17% 33% 18% 2	783
	21st to end	Night	30% 15% 34% 19% 1	660
March	1st to 10th	Night	26% 14% 30% 25% 5%	800
	11th to 20th	Night	25% 16% 31% 22% 7%	800
	21st to end	Night	21% 14% 32% 26% 7%	880
April	1st to 10th	Night	18% 16% 30% 28% 8%	745
	11th to 20th	Night	16% 14% 27% 30% 11% 1	593
	21st to end	Night	20% 8% 35% 28% 9% 1	600
May	1st to 10th	Night	19% 9% 27% 29% 15% 2	600
	11th to 20th	Night	17% 7% 21% 35% 18% 2	591
	21st to end	Night	10% 5% 18% 34% 28% 5%	650
June	1st to 10th	Night	9% 3 19% 40% 26% 3	600
	11th to 20th	Night	7% 3 15% 41% 31% 5%	600
	21st to end	Night	11% 3 16% 35% 33% 4	600
July	1st to 10th	Night	10% 2 12% 31% 37% 9%	585
	11th to 20th	Night	7% 1 12% 33% 44% 4	582
	21st to end	Night	11% 4 9% 31% 39% 5%	657
August	1st to 10th	Night	10% 2 9% 35% 38% 7%	597
	11th to 20th	Night	9% 3 9% 36% 35% 9%	594
	21st to end	Night	7% 3 8% 34% 40% 8%	660
September	1st to 10th	Night	12% 3 10% 33% 38% 5%	760
	11th to 20th	Night	10% 3 13% 29% 39% 6%	800
	21st to end	Night	16% 4 18% 33% 27% 2	800
October	1st to 10th	Night	13% 5% 17% 30% 31% 4	800
	11th to 20th	Night	17% 8% 23% 33% 17% 2	800
	21st to end	Night	21% 10% 26% 28% 13% 1	880
November	1st to 10th	Night	16% 8% 26% 32% 16% 2	820
	11th to 20th	Night	20% 13% 27% 30% 9%	840
	21st to end	Night	24% 11% 24% 31% 9%	840
December	1st to 10th	Night	29% 14% 28% 26% 4	840
	11th to 20th	Night	25% 13% 30% 26% 6% 1	840
	21st to end	Night	29% 14% 28% 25% 3	924

Page generated at 2025-12-30 01:14:09. Version ac07

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