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 2024-03-06.

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% 7% 3 6% 5% 3 5% 5% 6% 7% 39%	78933
	Night	14% 7% 3 5% 5% 3 4 4 5% 7% 43%	80593
Transparency	Day	42% 7% 11% 18% 18% 4	78656
	Night	39% 6% 10% 19% 20% 5%	80389
Seeing	Day	19% 12% 22% 23% 16% 8%	13853
	Night	17% 10% 23% 28% 19% 4	23996

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% 11% 4 5% 5% 3 4 4 4 5% 37%	2836
	11th to 20th	Day	16% 7% 4 7% 5% 3 3 3 3 5% 45%	2840
	21st to end	Day	21% 13% 3 5% 4 2 3 3 3 5% 37%	3261
February	1st to 10th	Day	19% 10% 3 4 5% 3 3 4 4 7% 37%	1900
	11th to 20th	Day	24% 7% 2 6% 3 3 3 4 5% 5% 38%	1848
	21st to end	Day	23% 7% 3 6% 5% 2 5% 3 3 5% 38%	1570
March	1st to 10th	Day	17% 6% 2 5% 4 2 5% 5% 4 7% 43%	1880
	11th to 20th	Day	18% 8% 4 6% 4 3 5% 5% 5% 7% 36%	1980
	21st to end	Day	15% 7% 3 7% 6% 4 5% 4 5% 7% 38%	2178
April	1st to 10th	Day	13% 5% 2 5% 6% 3 5% 5% 6% 7% 43%	2070
	11th to 20th	Day	14% 6% 2 5% 6% 3 5% 4 4 6% 46%	2134
	21st to end	Day	11% 4 2 5% 5% 3 6% 5% 5% 8% 47%	2290
May	1st to 10th	Day	11% 5% 3 5% 5% 3 5% 4 5% 8% 46%	2340
	11th to 20th	Day	11% 6% 2 7% 6% 4 6% 6% 6% 7% 39%	2301
	21st to end	Day	8% 6% 3 6% 6% 4 6% 5% 7% 9% 41%	2531
June	1st to 10th	Day	10% 6% 3 6% 7% 4 6% 7% 7% 10% 34%	2340
	11th to 20th	Day	5% 4 2 5% 6% 4 7% 7% 10% 11% 39%	2340
	21st to end	Day	8% 5% 3 6% 6% 4 7% 7% 8% 9% 36%	2340
July	1st to 10th	Day	10% 6% 3 6% 6% 4 8% 7% 9% 13% 28%	2340
	11th to 20th	Day	8% 5% 2 6% 7% 5% 8% 9% 9% 12% 27%	2340
	21st to end	Day	7% 5% 3 8% 9% 5% 8% 8% 8% 10% 30%	2547
August	1st to 10th	Day	8% 5% 3 7% 7% 5% 8% 8% 9% 11% 29%	2327
	11th to 20th	Day	11% 6% 4 7% 7% 5% 8% 7% 6% 9% 31%	2142
	21st to end	Day	13% 6% 3 6% 9% 4 8% 8% 7% 7% 28%	2376
September	1st to 10th	Day	10% 7% 3 6% 6% 3 5% 6% 7% 10% 38%	2009
	11th to 20th	Day	13% 7% 3 6% 6% 3 5% 5% 5% 7% 41%	1980
	21st to end	Day	11% 5% 2 5% 5% 4 5% 4 4 7% 47%	1980
October	1st to 10th	Day	12% 5% 1 5% 4 3 4 4 4 5% 54%	1980
	11th to 20th	Day	12% 5% 2 4 4 3 3 4 4 6% 53%	1896
	21st to end	Day	14% 6% 2 4 4 2 4 3 4 5% 52%	1958
November	1st to 10th	Day	13% 4 2 4 3 2 3 4 4 5% 56%	1672
	11th to 20th	Day	13% 5% 3 4 3 3 4 4 4 5% 51%	1710
	21st to end	Day	15% 7% 2 5% 4 3 4 4 5% 7% 45%	1710
December	1st to 10th	Day	23% 7% 3 4 4 2 5% 4 5% 6% 37%	1710
	11th to 20th	Day	18% 7% 3 6% 6% 2 4 4 4 5% 41%	2153
	21st to end	Day	20% 8% 4 6% 5% 3 4 5% 5% 7% 33%	3124
January	1st to 10th	Night	17% 11% 3 5% 4 2 4 4 5% 6% 39%	4109
	11th to 20th	Night	16% 9% 4 6% 4 3 3 4 5% 6% 42%	4120
	21st to end	Night	22% 13% 4 5% 4 2 3 3 3 4 37%	4390
February	1st to 10th	Night	17% 7% 3 5% 5% 2 4 4 5% 7% 42%	2280
	11th to 20th	Night	22% 7% 3 5% 4 3 4 4 3 5% 40%	2218
	21st to end	Night	23% 7% 2 5% 5% 3 4 4 4 7% 37%	1884
March	1st to 10th	Night	15% 7% 3 3 5% 2 4 4 5% 7% 45%	2196
	11th to 20th	Night	15% 7% 3 5% 5% 2 4 5% 6% 7% 41%	1980
	21st to end	Night	14% 6% 3 6% 5% 3 4 5% 4 6% 43%	2178
April	1st to 10th	Night	12% 4 2 3 4 3 6% 5% 6% 7% 48%	1904
	11th to 20th	Night	14% 6% 2 4 4 2 4 4 5% 7% 48%	1775
	21st to end	Night	9% 7% 2 5% 4 3 3 4 6% 7% 50%	1670
May	1st to 10th	Night	10% 4 3 4 5% 3 5% 4 4 8% 50%	1620
	11th to 20th	Night	11% 5% 2 6% 5% 3 5% 5% 7% 9% 40%	1592
	21st to end	Night	8% 5% 3 5% 6% 4 4 6% 7% 9% 44%	1744
June	1st to 10th	Night	6% 5% 3 6% 6% 5% 6% 6% 7% 12% 37%	1620
	11th to 20th	Night	5% 4 2 4 5% 3 5% 6% 7% 11% 47%	1620
	21st to end	Night	6% 4 3 5% 4 3 6% 6% 7% 12% 43%	1620
July	1st to 10th	Night	9% 5% 2 6% 6% 4 7% 7% 7% 13% 35%	1620
	11th to 20th	Night	7% 5% 2 5% 6% 3 7% 8% 8% 13% 36%	1620
	21st to end	Night	5% 6% 2 6% 7% 5% 6% 8% 8% 11% 36%	1771
August	1st to 10th	Night	6% 5% 2 7% 6% 3 7% 5% 8% 12% 39%	1611
	11th to 20th	Night	9% 6% 3 7% 5% 4 6% 6% 6% 10% 39%	1754
	21st to end	Night	12% 6% 4 6% 6% 4 5% 6% 8% 8% 36%	1980
September	1st to 10th	Night	8% 5% 3 6% 6% 4 5% 5% 6% 9% 43%	1931
	11th to 20th	Night	12% 5% 2 5% 5% 2 4 5% 6% 8% 45%	1980
	21st to end	Night	10% 5% 1 4 4 3 4 5% 5% 7% 53%	1980
October	1st to 10th	Night	11% 4 2 4 3 2 2 3 5% 6% 59%	1980
	11th to 20th	Night	12% 5% 2 4 4 3 2 3 4 5% 56%	2062
	21st to end	Night	12% 7% 2 4 4 2 3 3 4 5% 54%	2394
November	1st to 10th	Night	11% 5% 2 4 3 2 4 4 4 5% 56%	2406
	11th to 20th	Night	12% 5% 2 4 4 2 4 4 4 6% 52%	2470
	21st to end	Night	16% 8% 2 4 4 2 5% 5% 5% 5% 45%	2470
December	1st to 10th	Night	20% 7% 4 5% 5% 3 4 4 4 7% 37%	2470
	11th to 20th	Night	16% 10% 3 5% 3 2 3 3 4 6% 45%	3042
	21st to end	Night	19% 10% 4 6% 5% 3 4 4 5% 8% 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	41% 5% 10% 15% 21% 9%	1880
	11th to 20th	Day	47% 5% 10% 15% 17% 5%	1980
	21st to end	Day	46% 6% 9% 21% 16% 3	2178
April	1st to 10th	Day	39% 6% 10% 22% 19% 5%	2070
	11th to 20th	Day	40% 5% 7% 18% 24% 7%	2134
	21st to end	Day	34% 5% 11% 27% 19% 3	2290
May	1st to 10th	Day	35% 7% 12% 23% 20% 4	2340
	11th to 20th	Day	42% 9% 14% 21% 13% 2	2305
	21st to end	Day	38% 8% 13% 22% 16% 2	2531
June	1st to 10th	Day	42% 10% 16% 20% 11% 1	2340
	11th to 20th	Day	33% 11% 18% 25% 11% 2	2340
	21st to end	Day	38% 12% 16% 20% 11% 2	2340
July	1st to 10th	Day	42% 12% 19% 17% 9% 1	2275
	11th to 20th	Day	45% 11% 19% 14% 8% 3	2271
	21st to end	Day	44% 14% 16% 16% 9%	2405
August	1st to 10th	Day	43% 13% 18% 20% 5% 1	2314
	11th to 20th	Day	46% 10% 15% 17% 9% 2	2142
	21st to end	Day	49% 11% 14% 14% 9% 3	2376
September	1st to 10th	Day	40% 10% 12% 17% 17% 5%	2009
	11th to 20th	Day	41% 6% 11% 18% 21% 2	1980
	21st to end	Day	37% 5% 12% 16% 23% 7%	1980
October	1st to 10th	Day	33% 5% 9% 17% 28% 8%	1980
	11th to 20th	Day	32% 4 8% 22% 24% 10%	1896
	21st to end	Day	35% 3 6% 20% 28% 9%	1958
November	1st to 10th	Day	33% 3 6% 17% 32% 9%	1672
	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	39% 5% 8% 17% 20% 11%	2196
	11th to 20th	Night	42% 6% 10% 17% 19% 5%	1980
	21st to end	Night	42% 5% 8% 24% 19% 3	2178
April	1st to 10th	Night	34% 7% 11% 19% 25% 6%	1904
	11th to 20th	Night	35% 5% 7% 22% 22% 9%	1775
	21st to end	Night	32% 6% 10% 28% 20% 4	1670
May	1st to 10th	Night	32% 7% 12% 23% 22% 3	1620
	11th to 20th	Night	39% 8% 17% 21% 15% 1	1593
	21st to end	Night	35% 9% 12% 25% 16% 3	1745
June	1st to 10th	Night	38% 11% 17% 21% 12% 2	1620
	11th to 20th	Night	28% 9% 24% 25% 13% 1	1620
	21st to end	Night	33% 11% 18% 21% 13% 4	1620
July	1st to 10th	Night	38% 12% 19% 19% 12% 1	1575
	11th to 20th	Night	35% 12% 23% 17% 10% 3	1566
	21st to end	Night	37% 14% 19% 19% 9% 2	1672
August	1st to 10th	Night	36% 13% 18% 24% 8% 1	1600
	11th to 20th	Night	40% 10% 17% 18% 14% 1	1754
	21st to end	Night	42% 10% 15% 18% 12% 3	1980
September	1st to 10th	Night	37% 8% 16% 19% 16% 5%	1931
	11th to 20th	Night	36% 8% 13% 20% 20% 2	1980
	21st to end	Night	31% 7% 10% 23% 21% 8%	1980
October	1st to 10th	Night	28% 4 11% 19% 30% 7%	1980
	11th to 20th	Night	33% 4 8% 21% 24% 10%	2062
	21st to end	Night	33% 3 5% 19% 29% 11%	2394
November	1st to 10th	Night	31% 4 7% 19% 27% 12%	2406
	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	28% 21% 29% 18% 4	285
	11th to 20th	Day	28% 22% 25% 19% 6%	420
	21st to end	Day	24% 20% 31% 18% 7%	462
April	1st to 10th	Day	25% 14% 28% 21% 10% 1	420
	11th to 20th	Day	18% 16% 31% 23% 11% 1	412
	21st to end	Day	19% 12% 29% 23% 13% 3	420
May	1st to 10th	Day	17% 11% 31% 23% 13% 4	423
	11th to 20th	Day	14% 7% 25% 28% 17% 10%	447
	21st to end	Day	14% 5% 18% 31% 21% 11%	485
June	1st to 10th	Day	14% 4 20% 27% 23% 12%	450
	11th to 20th	Day	8% 5% 16% 26% 24% 21%	450
	21st to end	Day	12% 4 19% 27% 22% 16%	450
July	1st to 10th	Day	13% 4 10% 26% 24% 23%	445
	11th to 20th	Day	8% 3 8% 24% 33% 25%	444
	21st to end	Day	8% 2 10% 26% 31% 22%	488
August	1st to 10th	Day	13% 4 14% 24% 25% 21%	446
	11th to 20th	Day	13% 2 12% 30% 28% 16%	439
	21st to end	Day	15% 4 10% 24% 31% 16%	495
September	1st to 10th	Day	9% 5% 14% 29% 27% 15%	450
	11th to 20th	Day	16% 6% 14% 24% 30% 10%	450
	21st to end	Day	12% 4 19% 30% 29% 6%	450
October	1st to 10th	Day	16% 6% 22% 32% 16% 8%	450
	11th to 20th	Day	16% 11% 24% 28% 18% 2	450
	21st to end	Day	19% 12% 26% 27% 12% 3	473
November	1st to 10th	Day	19% 15% 30% 23% 10% 3	270
	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%	743
	11th to 20th	Night	20% 17% 30% 23% 10%	720
	21st to end	Night	19% 14% 31% 27% 8%	792
April	1st to 10th	Night	16% 12% 30% 29% 12%	644
	11th to 20th	Night	19% 12% 28% 29% 12% 1	533
	21st to end	Night	14% 7% 26% 34% 18% 1	540
May	1st to 10th	Night	11% 9% 25% 35% 20% 1	540
	11th to 20th	Night	14% 5% 23% 30% 22% 5%	531
	21st to end	Night	9% 4 15% 33% 33% 6%	584
June	1st to 10th	Night	8% 3 12% 38% 34% 5%	540
	11th to 20th	Night	6% 3 12% 31% 35% 14%	540
	21st to end	Night	5% 2 10% 35% 41% 8%	540
July	1st to 10th	Night	10% 2 7% 25% 42% 14%	525
	11th to 20th	Night	9% 1 7% 26% 42% 14%	522
	21st to end	Night	6% 2 8% 28% 45% 13%	591
August	1st to 10th	Night	9% 1 7% 28% 42% 12%	537
	11th to 20th	Night	10% 2 9% 29% 41% 9%	534
	21st to end	Night	14% 3 9% 26% 37% 11%	594
September	1st to 10th	Night	10% 2 12% 28% 37% 10%	671
	11th to 20th	Night	14% 3 15% 30% 34% 4	720
	21st to end	Night	12% 4 17% 35% 30% 2	720
October	1st to 10th	Night	14% 6% 21% 31% 23% 6%	720
	11th to 20th	Night	14% 8% 27% 30% 20% 1	720
	21st to end	Night	14% 12% 22% 33% 16% 2	792
November	1st to 10th	Night	14% 10% 27% 29% 19% 2	740
	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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