Mountain City
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mountain City clear sky chart from 2005-11-06 to 2026-02-16.

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% 10% 4 8% 5% 5% 5% 4 6% 7% 32%	131167
	Night	13% 11% 4 9% 5% 4 4 4 5% 7% 35%	129685
Transparency	Day	48% 6% 11% 18% 13% 3	134839
	Night	47% 6% 11% 19% 13% 4	134083
Seeing	Day	24% 16% 24% 19% 12% 6%	16771
	Night	22% 14% 20% 25% 16% 3	26909

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	13% 16% 6% 10% 5% 4 3 3 4 6% 31%	5258
	11th to 20th	Day	9% 15% 9% 13% 6% 5% 3 2 3 3 34%	5280
	21st to end	Day	13% 14% 6% 10% 6% 4 3 2 4 4 34%	5780
February	1st to 10th	Day	15% 13% 4 9% 6% 6% 4 3 4 6% 30%	1890
	11th to 20th	Day	20% 13% 5% 9% 4 4 3 2 4 5% 29%	1998
	21st to end	Day	20% 12% 4 8% 3 3 3 3 4 6% 34%	1650
March	1st to 10th	Day	15% 14% 7% 7% 4 4 4 3 4 5% 33%	4905
	11th to 20th	Day	11% 9% 4 7% 4 3 4 2 5% 7% 44%	4980
	21st to end	Day	15% 9% 3 6% 4 4 4 3 5% 7% 39%	5465
April	1st to 10th	Day	13% 11% 4 6% 5% 4 4 4 6% 7% 37%	2200
	11th to 20th	Day	15% 10% 3 5% 4 4 4 4 5% 6% 39%	2405
	21st to end	Day	16% 10% 3 7% 5% 5% 5% 4 5% 6% 36%	2600
May	1st to 10th	Day	16% 10% 4 10% 6% 6% 6% 5% 7% 8% 23%	5862
	11th to 20th	Day	17% 10% 4 10% 6% 6% 6% 5% 7% 8% 22%	5861
	21st to end	Day	15% 8% 3 8% 5% 5% 6% 5% 8% 10% 27%	6433
June	1st to 10th	Day	12% 8% 2 7% 6% 6% 6% 5% 7% 8% 32%	2600
	11th to 20th	Day	9% 7% 3 8% 7% 7% 7% 5% 8% 8% 31%	2600
	21st to end	Day	10% 7% 3 7% 7% 7% 7% 5% 8% 9% 32%	2600
July	1st to 10th	Day	8% 6% 3 7% 6% 6% 7% 6% 8% 10% 35%	5900
	11th to 20th	Day	10% 7% 3 9% 6% 7% 7% 5% 8% 10% 26%	5900
	21st to end	Day	15% 9% 4 10% 7% 7% 7% 6% 7% 8% 20%	6424
August	1st to 10th	Day	12% 8% 3 9% 6% 7% 7% 6% 9% 9% 23%	4234
	11th to 20th	Day	11% 7% 3 8% 6% 7% 7% 6% 8% 10% 28%	4174
	21st to end	Day	6% 5% 2 6% 5% 5% 6% 5% 7% 9% 46%	4436
September	1st to 10th	Day	11% 6% 3 6% 5% 6% 6% 5% 7% 8% 36%	2200
	11th to 20th	Day	13% 8% 4 8% 6% 5% 6% 5% 5% 7% 34%	2200
	21st to end	Day	15% 7% 3 8% 5% 5% 5% 4 7% 7% 33%	2200
October	1st to 10th	Day	13% 6% 2 6% 4 3 4 3 4 8% 45%	2115
	11th to 20th	Day	14% 7% 2 5% 3 3 4 3 4 6% 49%	2000
	21st to end	Day	15% 11% 2 6% 3 3 3 2 5% 6% 45%	2200
November	1st to 10th	Day	10% 9% 2 6% 3 3 4 4 5% 7% 48%	1989
	11th to 20th	Day	11% 11% 2 6% 4 4 4 4 5% 7% 42%	1890
	21st to end	Day	13% 11% 4 6% 4 3 4 3 6% 5% 40%	1890
December	1st to 10th	Day	12% 12% 4 11% 6% 5% 4 3 5% 5% 34%	3020
	11th to 20th	Day	16% 14% 6% 8% 4 4 4 4 5% 7% 29%	3463
	21st to end	Day	12% 12% 6% 11% 4 5% 6% 4 6% 6% 29%	4565
January	1st to 10th	Night	12% 17% 6% 14% 6% 5% 4 3 3 4 27%	7635
	11th to 20th	Night	11% 11% 6% 11% 7% 4 4 2 3 4 36%	7680
	21st to end	Night	13% 13% 5% 11% 5% 4 4 3 4 6% 33%	8401
February	1st to 10th	Night	14% 13% 4 9% 5% 4 4 3 6% 6% 33%	2725
	11th to 20th	Night	18% 13% 4 11% 5% 5% 5% 3 4 4 28%	2399
	21st to end	Night	17% 13% 5% 10% 4 3 4 3 5% 5% 31%	1980
March	1st to 10th	Night	19% 13% 4 7% 4 3 3 3 3 5% 36%	4946
	11th to 20th	Night	13% 8% 2 7% 3 3 4 3 5% 6% 48%	4980
	21st to end	Night	11% 10% 3 7% 5% 5% 5% 4 6% 6% 39%	5467
April	1st to 10th	Night	13% 13% 3 6% 4 3 4 4 6% 7% 37%	2200
	11th to 20th	Night	12% 10% 3 6% 3 3 5% 4 6% 8% 40%	1958
	21st to end	Night	13% 9% 2 7% 6% 4 4 3 6% 6% 39%	1800
May	1st to 10th	Night	17% 11% 3 8% 5% 5% 4 5% 7% 9% 26%	4033
	11th to 20th	Night	16% 11% 3 10% 7% 5% 5% 4 7% 8% 25%	4032
	21st to end	Night	17% 11% 3 8% 4 4 5% 4 6% 8% 29%	4421
June	1st to 10th	Night	10% 7% 2 7% 5% 6% 5% 5% 7% 11% 36%	1800
	11th to 20th	Night	7% 7% 2 7% 5% 5% 6% 6% 7% 10% 39%	1800
	21st to end	Night	9% 7% 3 6% 5% 5% 5% 4 8% 10% 38%	1800
July	1st to 10th	Night	10% 6% 2 7% 5% 4 6% 5% 8% 10% 36%	4058
	11th to 20th	Night	12% 8% 3 7% 5% 5% 5% 5% 8% 11% 32%	4057
	21st to end	Night	13% 10% 4 10% 7% 7% 7% 5% 8% 7% 23%	4427
August	1st to 10th	Night	13% 8% 3 8% 5% 6% 5% 6% 7% 10% 29%	2915
	11th to 20th	Night	12% 7% 2 8% 5% 6% 5% 5% 8% 8% 33%	2875
	21st to end	Night	5% 4 1 5% 4 4 5% 4 7% 10% 52%	3422
September	1st to 10th	Night	11% 7% 2 6% 5% 5% 4 4 6% 7% 43%	2200
	11th to 20th	Night	14% 7% 3 6% 4 4 4 4 6% 7% 42%	2200
	21st to end	Night	14% 8% 3 6% 4 4 4 5% 6% 6% 40%	2200
October	1st to 10th	Night	14% 6% 2 6% 3 3 4 4 5% 7% 47%	2285
	11th to 20th	Night	14% 9% 2 5% 4 3 4 3 5% 5% 47%	2400
	21st to end	Night	12% 12% 3 5% 3 4 3 2 4 6% 46%	2640
November	1st to 10th	Night	11% 9% 3 6% 3 3 4 3 5% 5% 47%	2524
	11th to 20th	Night	13% 10% 3 7% 3 3 3 3 5% 7% 42%	2730
	21st to end	Night	13% 11% 3 7% 4 4 4 3 5% 5% 42%	2730
December	1st to 10th	Night	12% 12% 4 12% 5% 4 4 3 4 5% 36%	4380
	11th to 20th	Night	17% 12% 7% 13% 4 4 4 2 4 5% 28%	4952
	21st to end	Night	13% 13% 8% 10% 4 4 5% 3 5% 7% 27%	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	54% 3 9% 16% 16% 2	5259
	11th to 20th	Day	56% 2 4 11% 22% 6%	5280
	21st to end	Day	54% 2 6% 19% 14% 4	5780
February	1st to 10th	Day	55% 5% 8% 15% 15% 2	1890
	11th to 20th	Day	58% 3 7% 15% 14% 3	2008
	21st to end	Day	51% 5% 9% 14% 16% 6%	1650
March	1st to 10th	Day	53% 4 6% 14% 16% 7%	4905
	11th to 20th	Day	41% 4 7% 20% 21% 9%	4980
	21st to end	Day	45% 5% 9% 24% 14% 3	5465
April	1st to 10th	Day	44% 6% 11% 21% 14% 3	2200
	11th to 20th	Day	44% 7% 9% 20% 16% 4	2405
	21st to end	Day	48% 8% 11% 21% 10% 2	2600
May	1st to 10th	Day	57% 7% 12% 18% 7%	5897
	11th to 20th	Day	56% 8% 15% 16% 4 1	5865
	21st to end	Day	47% 9% 14% 16% 11% 2	6447
June	1st to 10th	Day	47% 9% 15% 18% 11% 1	2600
	11th to 20th	Day	47% 11% 14% 16% 11% 1	2600
	21st to end	Day	44% 11% 15% 19% 11% 1	2600
July	1st to 10th	Day	42% 9% 19% 20% 10% 1	5835
	11th to 20th	Day	50% 8% 21% 16% 4 1	5831
	21st to end	Day	59% 8% 12% 13% 7%	6240
August	1st to 10th	Day	53% 8% 18% 17% 4	4221
	11th to 20th	Day	47% 9% 16% 19% 7% 1	4213
	21st to end	Day	34% 8% 18% 29% 10% 1	4436
September	1st to 10th	Day	41% 11% 12% 17% 15% 4	2200
	11th to 20th	Day	47% 8% 9% 20% 14% 1	2200
	21st to end	Day	48% 8% 13% 16% 12% 3	2200
October	1st to 10th	Day	32% 5% 7% 19% 28% 9%	3440
	11th to 20th	Day	30% 3 7% 25% 15% 20%	3240
	21st to end	Day	31% 3 5% 30% 16% 15%	3538
November	1st to 10th	Day	36% 4 9% 19% 25% 6%	1989
	11th to 20th	Day	40% 4 8% 18% 23% 6%	1890
	21st to end	Day	45% 3 7% 22% 18% 4	1890
December	1st to 10th	Day	51% 4 7% 17% 19% 3	3020
	11th to 20th	Day	54% 3 10% 15% 15% 3	3460
	21st to end	Day	52% 4 12% 20% 10% 2	4565
January	1st to 10th	Night	60% 4 7% 17% 8% 4	7636
	11th to 20th	Night	51% 3 5% 14% 21% 6%	7680
	21st to end	Night	53% 3 7% 17% 16% 4	8401
February	1st to 10th	Night	51% 5% 10% 17% 15% 2	2725
	11th to 20th	Night	58% 5% 8% 14% 12% 4	2400
	21st to end	Night	54% 5% 8% 17% 11% 5%	1980
March	1st to 10th	Night	52% 5% 5% 18% 14% 6%	4946
	11th to 20th	Night	37% 4 8% 21% 20% 11%	4980
	21st to end	Night	45% 5% 11% 23% 13% 3	5467
April	1st to 10th	Night	44% 7% 13% 20% 13% 3	2200
	11th to 20th	Night	41% 7% 12% 20% 16% 4	1958
	21st to end	Night	43% 7% 13% 25% 11% 1	1800
May	1st to 10th	Night	52% 10% 14% 17% 6%	4060
	11th to 20th	Night	53% 10% 16% 17% 3	4033
	21st to end	Night	50% 9% 15% 17% 7% 1	4429
June	1st to 10th	Night	40% 13% 18% 19% 11%	1800
	11th to 20th	Night	36% 12% 20% 23% 8% 1	1800
	21st to end	Night	38% 11% 17% 20% 12% 2	1800
July	1st to 10th	Night	40% 8% 20% 24% 8%	4015
	11th to 20th	Night	44% 10% 26% 16% 3 1	4006
	21st to end	Night	56% 8% 15% 14% 7%	4297
August	1st to 10th	Night	48% 9% 21% 17% 5%	2904
	11th to 20th	Night	45% 9% 19% 20% 7%	2902
	21st to end	Night	27% 7% 19% 36% 10% 1	3422
September	1st to 10th	Night	38% 10% 16% 18% 14% 3	2200
	11th to 20th	Night	40% 7% 15% 21% 16% 1	2200
	21st to end	Night	43% 9% 12% 20% 14% 2	2200
October	1st to 10th	Night	36% 5% 7% 20% 21% 12%	3740
	11th to 20th	Night	32% 4 7% 20% 19% 19%	3899
	21st to end	Night	28% 3 6% 29% 19% 15%	4252
November	1st to 10th	Night	38% 5% 10% 20% 22% 5%	2524
	11th to 20th	Night	42% 4 7% 19% 21% 7%	2730
	21st to end	Night	44% 4 7% 21% 20% 5%	2730
December	1st to 10th	Night	50% 4 7% 21% 17% 2	4380
	11th to 20th	Night	59% 3 9% 14% 12% 3	4954
	21st to end	Night	55% 5% 11% 15% 12% 2	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	39% 31% 22% 6% 1 1	330
	11th to 20th	Day	44% 26% 23% 6% 1	330
	21st to end	Day	39% 35% 18% 7% 1	363
February	1st to 10th	Day	35% 31% 26% 6% 2	330
	11th to 20th	Day	54% 22% 21% 3	315
	21st to end	Day	45% 28% 22% 4	249
March	1st to 10th	Day	29% 28% 25% 13% 4 1	483
	11th to 20th	Day	35% 28% 22% 11% 3 1	500
	21st to end	Day	33% 25% 25% 13% 4	550
April	1st to 10th	Day	30% 23% 26% 13% 6% 1	500
	11th to 20th	Day	27% 23% 25% 14% 9% 2	492
	21st to end	Day	27% 18% 27% 16% 9% 4	500
May	1st to 10th	Day	27% 21% 28% 13% 8% 4	503
	11th to 20th	Day	24% 15% 24% 21% 10% 6%	527
	21st to end	Day	18% 13% 24% 20% 15% 11%	573
June	1st to 10th	Day	15% 10% 30% 23% 16% 7%	530
	11th to 20th	Day	13% 9% 25% 26% 18% 8%	530
	21st to end	Day	14% 10% 25% 27% 15% 8%	530
July	1st to 10th	Day	14% 6% 20% 28% 20% 13%	525
	11th to 20th	Day	12% 5% 18% 31% 23% 11%	524
	21st to end	Day	13% 6% 23% 25% 21% 13%	576
August	1st to 10th	Day	17% 6% 20% 27% 17% 13%	526
	11th to 20th	Day	15% 5% 21% 23% 25% 12%	519
	21st to end	Day	12% 5% 18% 29% 19% 17%	583
September	1st to 10th	Day	13% 4 19% 27% 25% 11%	530
	11th to 20th	Day	18% 5% 18% 25% 24% 11%	530
	21st to end	Day	19% 10% 25% 24% 17% 5%	530
October	1st to 10th	Day	19% 10% 22% 25% 18% 6%	530
	11th to 20th	Day	20% 18% 22% 23% 15% 2	530
	21st to end	Day	26% 15% 27% 20% 10% 4	583
November	1st to 10th	Day	19% 16% 32% 20% 9% 3	467
	11th to 20th	Day	29% 25% 25% 16% 5% 1	330
	21st to end	Day	30% 24% 29% 12% 5% 1	330
December	1st to 10th	Day	38% 22% 29% 8% 2	330
	11th to 20th	Day	35% 22% 28% 13% 2	330
	21st to end	Day	31% 28% 27% 9% 4 1	363
January	1st to 10th	Night	30% 27% 22% 17% 3	840
	11th to 20th	Night	33% 21% 24% 18% 3	840
	21st to end	Night	26% 29% 25% 17% 2	924
February	1st to 10th	Night	25% 23% 26% 22% 3	840
	11th to 20th	Night	34% 29% 23% 13% 1	804
	21st to end	Night	32% 26% 27% 13% 2	660
March	1st to 10th	Night	25% 24% 28% 19% 4	800
	11th to 20th	Night	29% 21% 25% 20% 6% 1	800
	21st to end	Night	24% 20% 31% 20% 5%	880
April	1st to 10th	Night	26% 19% 26% 22% 7% 1	800
	11th to 20th	Night	22% 18% 27% 22% 11% 1	738
	21st to end	Night	18% 17% 21% 34% 9% 1	600
May	1st to 10th	Night	22% 10% 27% 26% 14% 1	600
	11th to 20th	Night	18% 9% 21% 31% 18% 3	591
	21st to end	Night	14% 6% 18% 29% 27% 6%	650
June	1st to 10th	Night	11% 4 19% 34% 28% 4	600
	11th to 20th	Night	9% 5% 15% 33% 32% 6%	600
	21st to end	Night	11% 4 14% 35% 32% 4	600
July	1st to 10th	Night	14% 3 10% 28% 40% 4	585
	11th to 20th	Night	12% 3 7% 27% 45% 6%	582
	21st to end	Night	11% 3 9% 29% 40% 9%	657
August	1st to 10th	Night	15% 1 10% 32% 38% 5%	597
	11th to 20th	Night	14% 2 8% 32% 35% 8%	594
	21st to end	Night	10% 1 11% 31% 37% 9%	743
September	1st to 10th	Night	14% 4 12% 32% 32% 7%	800
	11th to 20th	Night	16% 5% 12% 29% 32% 5%	800
	21st to end	Night	19% 6% 17% 30% 25% 3	800
October	1st to 10th	Night	19% 10% 17% 26% 24% 6%	800
	11th to 20th	Night	19% 12% 23% 27% 16% 3	800
	21st to end	Night	22% 13% 23% 28% 12% 2	880
November	1st to 10th	Night	19% 12% 24% 28% 15% 2	820
	11th to 20th	Night	24% 18% 20% 29% 9% 1	840
	21st to end	Night	24% 18% 22% 25% 10% 1	840
December	1st to 10th	Night	30% 19% 26% 19% 6%	840
	11th to 20th	Night	27% 22% 22% 23% 5% 1	840
	21st to end	Night	31% 19% 23% 23% 4	924

Page generated at 2026-02-13 01:42:15. Version ac07

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