Garland Mountain Trailhead
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Garland Mountain Trailhead clear sky chart from 2005-11-06 to 2024-11-02.

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	13% 7% 2 6% 5% 5% 5% 4 6% 8% 40%	100928
	Night	13% 7% 2 6% 4 4 4 4 5% 7% 42%	98002
Transparency	Day	42% 6% 11% 20% 17% 4	100738
	Night	40% 6% 11% 20% 19% 5%	97861
Seeing	Day	18% 11% 23% 23% 16% 8%	14811
	Night	17% 10% 23% 28% 19% 4	24808

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	18% 12% 4 6% 4 4 4 3 4 5% 37%	2836
	11th to 20th	Day	15% 8% 3 8% 4 4 3 3 3 4 45%	2840
	21st to end	Day	21% 13% 3 6% 3 3 3 2 4 5% 37%	3261
February	1st to 10th	Day	19% 10% 3 5% 5% 3 3 3 5% 7% 37%	1900
	11th to 20th	Day	24% 8% 2 6% 3 3 3 3 5% 5% 38%	1848
	21st to end	Day	22% 8% 3 7% 4 3 4 2 4 4 38%	1570
March	1st to 10th	Day	24% 9% 3 7% 4 3 4 3 4 6% 33%	3178
	11th to 20th	Day	14% 8% 3 6% 3 3 3 4 5% 6% 46%	3480
	21st to end	Day	16% 7% 2 8% 5% 4 4 3 5% 6% 38%	3815
April	1st to 10th	Day	13% 6% 2 6% 5% 4 4 4 6% 7% 42%	2185
	11th to 20th	Day	13% 6% 2 6% 5% 4 4 3 5% 6% 45%	2254
	21st to end	Day	11% 4 2 6% 5% 5% 5% 4 5% 8% 46%	2418
May	1st to 10th	Day	12% 7% 2 7% 4 5% 5% 4 6% 9% 40%	4082
	11th to 20th	Day	17% 9% 3 8% 4 5% 4 4 6% 7% 34%	4081
	21st to end	Day	9% 5% 2 6% 5% 5% 5% 4 7% 10% 42%	4476
June	1st to 10th	Day	10% 7% 3 7% 6% 6% 6% 5% 7% 10% 33%	2470
	11th to 20th	Day	5% 4 2 5% 5% 5% 7% 6% 10% 11% 40%	2470
	21st to end	Day	7% 6% 2 6% 5% 6% 7% 6% 8% 9% 37%	2470
July	1st to 10th	Day	7% 7% 2 7% 6% 6% 8% 6% 9% 12% 28%	4120
	11th to 20th	Day	8% 5% 2 7% 6% 6% 7% 6% 8% 10% 34%	4120
	21st to end	Day	14% 8% 4 11% 8% 8% 7% 6% 7% 8% 19%	4466
August	1st to 10th	Day	5% 4 2 7% 5% 6% 6% 5% 8% 11% 40%	4104
	11th to 20th	Day	8% 5% 2 6% 5% 5% 6% 5% 7% 11% 41%	3759
	21st to end	Day	7% 4 2 5% 5% 5% 6% 5% 5% 7% 48%	4180
September	1st to 10th	Day	10% 7% 3 6% 6% 4 5% 5% 7% 9% 39%	2120
	11th to 20th	Day	13% 8% 3 7% 5% 5% 5% 4 5% 7% 40%	2090
	21st to end	Day	12% 5% 2 6% 4 5% 4 3 4 7% 46%	2090
October	1st to 10th	Day	11% 4 1 5% 3 4 4 3 4 5% 55%	2090
	11th to 20th	Day	12% 5% 1 4 3 3 3 3 4 6% 55%	2001
	21st to end	Day	13% 6% 2 5% 3 3 3 3 4 5% 53%	2066
November	1st to 10th	Day	13% 5% 1 5% 3 3 3 3 5% 5% 55%	1681
	11th to 20th	Day	13% 6% 2 5% 3 4 4 3 4 5% 51%	1710
	21st to end	Day	15% 8% 2 5% 4 4 4 3 5% 6% 45%	1710
December	1st to 10th	Day	23% 8% 2 4 4 3 5% 3 5% 6% 36%	1710
	11th to 20th	Day	18% 7% 3 7% 5% 4 4 3 4 5% 41%	2153
	21st to end	Day	20% 8% 4 7% 4 4 4 4 5% 7% 33%	3124
January	1st to 10th	Night	17% 11% 2 5% 3 3 3 3 5% 6% 39%	4109
	11th to 20th	Night	16% 10% 4 6% 3 3 3 3 5% 5% 42%	4120
	21st to end	Night	22% 14% 3 6% 3 2 3 2 3 4 37%	4390
February	1st to 10th	Night	17% 8% 3 5% 4 4 4 3 5% 6% 42%	2280
	11th to 20th	Night	21% 8% 3 6% 4 4 3 3 3 5% 40%	2218
	21st to end	Night	23% 7% 2 6% 4 4 4 3 4 6% 37%	1884
March	1st to 10th	Night	21% 11% 3 7% 4 4 4 3 4 6% 33%	3674
	11th to 20th	Night	12% 6% 2 4 3 3 4 4 6% 7% 48%	3480
	21st to end	Night	16% 7% 3 7% 5% 4 4 4 4 6% 41%	3817
April	1st to 10th	Night	12% 4 2 5% 4 4 5% 4 6% 7% 47%	2009
	11th to 20th	Night	15% 6% 2 4 3 3 4 4 5% 7% 47%	1875
	21st to end	Night	8% 8% 2 6% 3 4 3 3 5% 7% 50%	1762
May	1st to 10th	Night	12% 7% 3 7% 5% 5% 5% 3 5% 8% 40%	2813
	11th to 20th	Night	18% 8% 2 6% 4 4 4 4 6% 7% 36%	2812
	21st to end	Night	6% 5% 2 6% 5% 5% 5% 5% 8% 10% 45%	3079
June	1st to 10th	Night	7% 6% 2 7% 6% 6% 6% 5% 8% 11% 36%	1710
	11th to 20th	Night	5% 4 1 5% 5% 5% 5% 6% 8% 11% 46%	1710
	21st to end	Night	5% 5% 3 6% 4 5% 6% 5% 7% 12% 42%	1710
July	1st to 10th	Night	9% 7% 3 7% 6% 5% 7% 5% 7% 12% 32%	2840
	11th to 20th	Night	8% 5% 2 6% 5% 5% 7% 6% 8% 12% 36%	2840
	21st to end	Night	13% 10% 4 11% 6% 6% 6% 5% 7% 9% 23%	3087
August	1st to 10th	Night	5% 4 2 7% 4 5% 6% 4 7% 13% 43%	2825
	11th to 20th	Night	8% 6% 2 6% 4 4 4 4 5% 9% 47%	3065
	21st to end	Night	7% 5% 2 5% 3 3 4 4 6% 7% 53%	3476
September	1st to 10th	Night	8% 5% 3 6% 6% 6% 4 4 6% 9% 43%	2039
	11th to 20th	Night	12% 6% 2 7% 4 4 4 4 6% 8% 43%	2090
	21st to end	Night	12% 5% 1 5% 3 3 4 3 5% 7% 51%	2090
October	1st to 10th	Night	10% 4 2 4 3 2 2 3 5% 6% 58%	2090
	11th to 20th	Night	11% 5% 2 4 3 3 3 2 4 5% 57%	2177
	21st to end	Night	12% 7% 2 5% 3 3 3 2 4 5% 55%	2527
November	1st to 10th	Night	11% 5% 2 5% 3 3 3 4 4 5% 55%	2420
	11th to 20th	Night	12% 6% 2 5% 3 3 3 3 4 6% 52%	2470
	21st to end	Night	15% 8% 2 5% 3 3 4 4 5% 5% 45%	2470
December	1st to 10th	Night	19% 8% 3 6% 4 4 3 3 4 7% 37%	2470
	11th to 20th	Night	16% 10% 3 6% 3 3 3 2 4 5% 45%	3042
	21st to end	Night	19% 10% 4 8% 4 4 4 3 5% 7% 32%	4532

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	49% 4 6% 15% 23% 3	2837
	11th to 20th	Day	43% 4 8% 19% 22% 5%	2840
	21st to end	Day	50% 3 5% 17% 20% 4	3261
February	1st to 10th	Day	47% 5% 6% 17% 21% 4	1900
	11th to 20th	Day	48% 4 6% 17% 19% 6%	1858
	21st to end	Day	50% 3 7% 14% 20% 6%	1570
March	1st to 10th	Day	52% 4 9% 12% 13% 10%	3178
	11th to 20th	Day	39% 4 8% 17% 23% 9%	3480
	21st to end	Day	45% 5% 8% 19% 19% 3	3815
April	1st to 10th	Day	39% 6% 10% 21% 19% 5%	2185
	11th to 20th	Day	39% 5% 7% 17% 24% 7%	2254
	21st to end	Day	34% 5% 11% 27% 19% 3	2418
May	1st to 10th	Day	39% 8% 12% 22% 17% 2	4120
	11th to 20th	Day	47% 8% 11% 23% 11% 1	4085
	21st to end	Day	35% 8% 13% 22% 20% 1	4489
June	1st to 10th	Day	42% 10% 17% 20% 10% 2	2470
	11th to 20th	Day	32% 11% 18% 26% 12% 1	2470
	21st to end	Day	38% 12% 16% 20% 12% 2	2470
July	1st to 10th	Day	44% 10% 21% 19% 6% 1	4055
	11th to 20th	Day	43% 8% 22% 20% 5% 2	4051
	21st to end	Day	60% 11% 13% 11% 5%	4324
August	1st to 10th	Day	34% 8% 14% 33% 10%	4091
	11th to 20th	Day	35% 7% 18% 24% 15% 2	3796
	21st to end	Day	34% 6% 13% 25% 20% 3	4179
September	1st to 10th	Day	40% 10% 12% 17% 18% 5%	2120
	11th to 20th	Day	43% 6% 11% 18% 20% 2	2090
	21st to end	Day	38% 5% 13% 15% 22% 7%	2090
October	1st to 10th	Day	32% 5% 8% 17% 28% 9%	2090
	11th to 20th	Day	31% 4 8% 22% 24% 12%	2001
	21st to end	Day	34% 3 6% 20% 27% 9%	2066
November	1st to 10th	Day	33% 3 6% 17% 32% 9%	1681
	11th to 20th	Day	35% 4 7% 18% 26% 10%	1710
	21st to end	Day	40% 5% 6% 17% 25% 6%	1710
December	1st to 10th	Day	47% 6% 7% 18% 18% 5%	1710
	11th to 20th	Day	46% 3 6% 16% 23% 6%	2150
	21st to end	Day	49% 4 11% 18% 16% 2	3124
January	1st to 10th	Night	44% 4 7% 16% 25% 4	4109
	11th to 20th	Night	43% 4 7% 21% 17% 8%	4120
	21st to end	Night	52% 2 5% 13% 22% 5%	4390
February	1st to 10th	Night	43% 5% 7% 18% 20% 7%	2280
	11th to 20th	Night	48% 4 5% 17% 20% 7%	2219
	21st to end	Night	48% 4 8% 15% 18% 8%	1884
March	1st to 10th	Night	51% 5% 9% 13% 14% 6%	3674
	11th to 20th	Night	33% 5% 9% 17% 25% 10%	3480
	21st to end	Night	43% 5% 7% 20% 20% 6%	3817
April	1st to 10th	Night	34% 7% 10% 18% 25% 6%	2009
	11th to 20th	Night	35% 5% 7% 21% 22% 9%	1875
	21st to end	Night	33% 6% 10% 28% 20% 4	1762
May	1st to 10th	Night	39% 9% 14% 21% 15% 2	2840
	11th to 20th	Night	44% 8% 15% 21% 12%	2813
	21st to end	Night	29% 10% 15% 26% 18% 2	3087
June	1st to 10th	Night	39% 11% 17% 20% 12% 2	1710
	11th to 20th	Night	28% 9% 23% 25% 14% 1	1710
	21st to end	Night	33% 11% 17% 21% 14% 4	1710
July	1st to 10th	Night	45% 9% 19% 19% 7% 1	2795
	11th to 20th	Night	38% 10% 22% 22% 6% 2	2786
	21st to end	Night	55% 12% 14% 13% 5% 1	2988
August	1st to 10th	Night	34% 8% 15% 33% 9%	2814
	11th to 20th	Night	35% 7% 14% 28% 16% 1	3094
	21st to end	Night	30% 6% 13% 22% 26% 3	3476
September	1st to 10th	Night	38% 8% 15% 18% 16% 5%	2039
	11th to 20th	Night	38% 8% 13% 20% 19% 2	2090
	21st to end	Night	33% 6% 11% 22% 20% 8%	2090
October	1st to 10th	Night	28% 4 11% 19% 31% 8%	2090
	11th to 20th	Night	31% 4 8% 21% 25% 11%	2177
	21st to end	Night	32% 3 5% 20% 29% 11%	2527
November	1st to 10th	Night	31% 4 7% 19% 27% 12%	2420
	11th to 20th	Night	33% 4 5% 19% 27% 11%	2470
	21st to end	Night	40% 5% 7% 19% 24% 6%	2470
December	1st to 10th	Night	47% 5% 7% 18% 18% 4	2470
	11th to 20th	Night	41% 5% 8% 15% 27% 5%	3044
	21st to end	Night	50% 4 9% 21% 15% 2	4532

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	31% 24% 34% 10% 1	270
	11th to 20th	Day	34% 23% 28% 13% 3	270
	21st to end	Day	25% 34% 29% 10% 3 1	297
February	1st to 10th	Day	30% 23% 35% 10% 2	270
	11th to 20th	Day	44% 24% 23% 8% 1	270
	21st to end	Day	38% 24% 31% 5% 2	225
March	1st to 10th	Day	30% 21% 28% 17% 4	302
	11th to 20th	Day	26% 21% 28% 19% 5%	460
	21st to end	Day	25% 20% 32% 18% 6%	506
April	1st to 10th	Day	26% 15% 28% 20% 10% 1	460
	11th to 20th	Day	18% 16% 32% 23% 10% 1	452
	21st to end	Day	19% 12% 31% 23% 12% 3	460
May	1st to 10th	Day	17% 12% 30% 24% 13% 5%	463
	11th to 20th	Day	15% 7% 26% 27% 15% 9%	487
	21st to end	Day	13% 6% 20% 30% 20% 10%	529
June	1st to 10th	Day	14% 4 21% 28% 22% 11%	490
	11th to 20th	Day	7% 5% 18% 27% 23% 20%	490
	21st to end	Day	12% 4 19% 27% 22% 16%	490
July	1st to 10th	Day	12% 4 11% 26% 25% 22%	485
	11th to 20th	Day	8% 3 9% 24% 32% 24%	484
	21st to end	Day	10% 3 10% 27% 29% 20%	532
August	1st to 10th	Day	12% 3 16% 25% 24% 20%	486
	11th to 20th	Day	12% 2 14% 30% 27% 15%	479
	21st to end	Day	14% 4 9% 26% 31% 16%	539
September	1st to 10th	Day	9% 5% 17% 29% 26% 14%	490
	11th to 20th	Day	16% 7% 15% 25% 28% 9%	490
	21st to end	Day	14% 4 19% 29% 27% 6%	490
October	1st to 10th	Day	15% 6% 23% 32% 16% 7%	490
	11th to 20th	Day	14% 12% 24% 29% 18% 2	490
	21st to end	Day	18% 12% 26% 28% 14% 3	515
November	1st to 10th	Day	19% 15% 30% 23% 10% 3	273
	11th to 20th	Day	20% 20% 36% 19% 4 1	270
	21st to end	Day	21% 18% 35% 19% 6% 1	270
December	1st to 10th	Day	34% 22% 24% 14% 5% 1	270
	11th to 20th	Day	27% 21% 30% 19% 4	270
	21st to end	Day	30% 21% 33% 13% 3	297
January	1st to 10th	Night	26% 21% 29% 19% 5%	760
	11th to 20th	Night	25% 18% 29% 21% 6%	760
	21st to end	Night	23% 18% 32% 23% 3	836
February	1st to 10th	Night	22% 15% 32% 26% 5%	760
	11th to 20th	Night	28% 20% 30% 22% 1	743
	21st to end	Night	27% 19% 35% 17% 2	628
March	1st to 10th	Night	20% 17% 33% 26% 5%	760
	11th to 20th	Night	20% 17% 31% 23% 9%	760
	21st to end	Night	20% 14% 31% 27% 8%	836
April	1st to 10th	Night	16% 13% 31% 28% 12%	679
	11th to 20th	Night	19% 12% 28% 29% 12% 1	563
	21st to end	Night	13% 8% 26% 34% 18% 1	570
May	1st to 10th	Night	11% 9% 24% 35% 20% 1	570
	11th to 20th	Night	15% 6% 23% 30% 21% 5%	561
	21st to end	Night	9% 4 15% 35% 32% 6%	617
June	1st to 10th	Night	9% 4 12% 38% 33% 5%	570
	11th to 20th	Night	5% 3 13% 31% 34% 14%	570
	21st to end	Night	5% 2 10% 35% 40% 8%	570
July	1st to 10th	Night	10% 3 8% 25% 41% 14%	555
	11th to 20th	Night	10% 1 7% 25% 43% 14%	552
	21st to end	Night	7% 2 9% 27% 43% 12%	624
August	1st to 10th	Night	9% 1 7% 29% 41% 12%	567
	11th to 20th	Night	10% 2 10% 29% 40% 9%	564
	21st to end	Night	14% 3 10% 26% 37% 11%	627
September	1st to 10th	Night	10% 2 14% 28% 36% 9%	709
	11th to 20th	Night	14% 3 15% 30% 33% 4	760
	21st to end	Night	14% 4 16% 34% 30% 2	760
October	1st to 10th	Night	13% 5% 20% 33% 23% 6%	760
	11th to 20th	Night	14% 8% 26% 31% 20% 1	760
	21st to end	Night	14% 12% 22% 34% 17% 2	836
November	1st to 10th	Night	14% 10% 27% 30% 19% 2	745
	11th to 20th	Night	15% 15% 28% 30% 11% 1	760
	21st to end	Night	20% 14% 28% 26% 11% 1	760
December	1st to 10th	Night	23% 16% 29% 24% 8% 1	760
	11th to 20th	Night	25% 15% 26% 26% 7% 1	760
	21st to end	Night	28% 15% 27% 25% 6%	836

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