Woodland Trails
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Woodland Trails clear sky chart from 2005-11-06 to 2025-08-05.

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% 10% 4 9% 5% 5% 5% 4 5% 7% 31%	126193
	Night	14% 10% 4 9% 5% 5% 5% 4 6% 7% 32%	121793
Transparency	Day	49% 7% 12% 20% 11% 1	129786
	Night	48% 7% 12% 20% 12% 1	126287
Seeing	Day	20% 16% 31% 20% 9% 3	15512
	Night	20% 13% 32% 25% 9% 1	24686

By Month

Percentage Cloud Cover NE (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% 12% 4 11% 8% 6% 6% 4 5% 7% 25%	3597
	11th to 20th	Day	9% 17% 7% 19% 10% 7% 5% 4 4 4 13%	3862
	21st to end	Day	16% 17% 7% 15% 7% 5% 5% 3 4 5% 16%	4466
February	1st to 10th	Day	14% 17% 6% 13% 7% 6% 5% 3 6% 5% 19%	1800
	11th to 20th	Day	12% 16% 7% 13% 7% 5% 4 3 4 6% 23%	1753
	21st to end	Day	16% 16% 5% 10% 7% 5% 5% 3 5% 4 25%	1533
March	1st to 10th	Day	18% 11% 5% 10% 6% 5% 4 3 5% 5% 30%	4932
	11th to 20th	Day	11% 12% 5% 11% 6% 6% 5% 4 5% 7% 28%	4980
	21st to end	Day	18% 13% 4 8% 5% 4 4 3 4 5% 32%	5465
April	1st to 10th	Day	18% 14% 4 8% 5% 5% 4 3 5% 6% 27%	2370
	11th to 20th	Day	19% 11% 3 7% 4 3 4 3 5% 6% 34%	2447
	21st to end	Day	19% 10% 3 9% 5% 4 4 3 5% 6% 33%	2600
May	1st to 10th	Day	19% 9% 3 8% 5% 4 4 3 5% 7% 32%	5902
	11th to 20th	Day	14% 11% 4 8% 5% 5% 4 4 5% 7% 34%	6318
	21st to end	Day	18% 7% 2 7% 4 4 4 3 5% 7% 38%	6949
June	1st to 10th	Day	15% 8% 2 7% 5% 5% 5% 4 6% 7% 35%	2800
	11th to 20th	Day	13% 6% 2 6% 5% 4 5% 5% 7% 9% 38%	2800
	21st to end	Day	15% 7% 2 7% 5% 5% 5% 3 6% 9% 37%	2952
July	1st to 10th	Day	10% 7% 2 8% 5% 5% 6% 4 7% 9% 37%	6410
	11th to 20th	Day	8% 5% 2 6% 5% 5% 6% 4 6% 10% 43%	6360
	21st to end	Day	7% 5% 2 7% 5% 4 5% 4 7% 9% 45%	6529
August	1st to 10th	Day	15% 8% 3 6% 4 4 5% 4 6% 8% 36%	4156
	11th to 20th	Day	11% 8% 3 8% 5% 5% 6% 4 7% 9% 35%	4044
	21st to end	Day	9% 7% 3 6% 5% 5% 5% 4 6% 9% 42%	4351
September	1st to 10th	Day	13% 6% 2 7% 5% 4 5% 3 6% 6% 42%	2280
	11th to 20th	Day	11% 6% 2 5% 4 5% 5% 4 6% 8% 44%	2178
	21st to end	Day	14% 7% 3 8% 5% 5% 4 4 5% 6% 37%	2045
October	1st to 10th	Day	18% 9% 3 8% 5% 4 5% 3 5% 7% 34%	1900
	11th to 20th	Day	19% 10% 4 9% 5% 4 5% 4 5% 6% 28%	1900
	21st to end	Day	23% 14% 4 9% 5% 4 4 4 5% 6% 22%	2090
November	1st to 10th	Day	14% 12% 3 9% 5% 5% 5% 4 5% 7% 30%	1678
	11th to 20th	Day	15% 14% 4 10% 7% 5% 6% 5% 5% 6% 23%	1600
	21st to end	Day	18% 15% 5% 12% 7% 6% 5% 4 5% 5% 19%	1600
December	1st to 10th	Day	17% 20% 6% 13% 7% 6% 6% 4 5% 6% 11%	2600
	11th to 20th	Day	17% 20% 5% 10% 6% 4 4 4 5% 6% 20%	2986
	21st to end	Day	22% 18% 6% 16% 6% 5% 4 3 3 5% 12%	3960
January	1st to 10th	Night	13% 12% 5% 12% 7% 6% 6% 4 7% 8% 20%	6349
	11th to 20th	Night	12% 13% 6% 17% 9% 7% 6% 5% 6% 6% 14%	6020
	21st to end	Night	14% 14% 6% 13% 6% 6% 5% 4 6% 6% 21%	6490
February	1st to 10th	Night	12% 16% 5% 10% 8% 6% 7% 4 5% 6% 22%	2600
	11th to 20th	Night	13% 14% 5% 12% 5% 6% 5% 4 7% 6% 24%	2533
	21st to end	Night	13% 12% 4 11% 5% 5% 5% 4 7% 6% 27%	2092
March	1st to 10th	Night	15% 11% 4 10% 6% 5% 5% 4 5% 6% 30%	4908
	11th to 20th	Night	9% 8% 3 9% 6% 5% 6% 5% 7% 7% 35%	4979
	21st to end	Night	19% 8% 3 9% 5% 4 4 3 5% 5% 34%	5467
April	1st to 10th	Night	18% 12% 3 7% 4 5% 4 4 6% 6% 30%	2030
	11th to 20th	Night	16% 9% 3 7% 5% 4 4 4 5% 5% 38%	1917
	21st to end	Night	14% 9% 3 9% 5% 4 5% 3 6% 7% 35%	1800
May	1st to 10th	Night	21% 8% 3 6% 4 4 4 3 6% 6% 35%	4036
	11th to 20th	Night	11% 7% 3 8% 5% 5% 5% 3 6% 7% 40%	3575
	21st to end	Night	18% 6% 2 6% 4 4 4 3 5% 7% 43%	3926
June	1st to 10th	Night	12% 7% 2 7% 5% 3 6% 4 6% 7% 41%	1600
	11th to 20th	Night	8% 6% 2 6% 5% 5% 5% 4 7% 8% 42%	1600
	21st to end	Night	13% 6% 3 6% 5% 5% 4 3 5% 8% 43%	1430
July	1st to 10th	Night	7% 6% 3 6% 5% 4 5% 4 6% 8% 46%	3512
	11th to 20th	Night	10% 5% 2 5% 4 4 4 3 5% 8% 50%	3600
	21st to end	Night	8% 5% 2 5% 3 4 4 3 6% 8% 51%	4306
August	1st to 10th	Night	9% 6% 3 6% 4 3 5% 4 6% 7% 48%	2861
	11th to 20th	Night	11% 6% 3 6% 3 3 3 3 5% 8% 49%	2785
	21st to end	Night	9% 7% 2 6% 4 4 4 3 6% 7% 48%	3272
September	1st to 10th	Night	9% 6% 2 6% 4 5% 3 4 6% 8% 46%	1900
	11th to 20th	Night	11% 5% 2 5% 4 3 3 3 6% 6% 53%	2000
	21st to end	Night	15% 7% 4 6% 4 4 4 3 5% 7% 41%	2134
October	1st to 10th	Night	15% 7% 3 9% 5% 4 5% 4 5% 6% 38%	2280
	11th to 20th	Night	18% 9% 3 9% 6% 4 4 4 5% 6% 32%	2280
	21st to end	Night	21% 10% 3 7% 6% 5% 5% 4 6% 6% 28%	2508
November	1st to 10th	Night	17% 10% 3 7% 5% 4 4 4 5% 6% 35%	2619
	11th to 20th	Night	16% 11% 4 9% 6% 6% 5% 4 5% 7% 27%	2800
	21st to end	Night	18% 14% 4 9% 5% 5% 6% 4 6% 7% 22%	2800
December	1st to 10th	Night	16% 16% 5% 12% 7% 7% 6% 5% 6% 7% 14%	4580
	11th to 20th	Night	14% 18% 6% 12% 6% 5% 5% 3 5% 5% 20%	5208
	21st to end	Night	22% 16% 5% 15% 6% 5% 4 3 5% 6% 12%	6996

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	53% 8% 13% 16% 10%	3598
	11th to 20th	Day	72% 5% 10% 8% 4 1	3896
	21st to end	Day	69% 6% 9% 9% 7% 1	4466
February	1st to 10th	Day	65% 7% 9% 15% 4 1	1800
	11th to 20th	Day	60% 6% 10% 15% 7% 1	1762
	21st to end	Day	61% 6% 10% 15% 6% 1	1533
March	1st to 10th	Day	55% 5% 13% 15% 12% 1	4935
	11th to 20th	Day	51% 6% 15% 19% 7% 2	4980
	21st to end	Day	52% 4 10% 18% 14% 1	5465
April	1st to 10th	Day	56% 5% 12% 15% 11% 1	2370
	11th to 20th	Day	50% 5% 10% 20% 13% 1	2447
	21st to end	Day	51% 7% 11% 17% 12% 3	2600
May	1st to 10th	Day	49% 7% 12% 16% 11% 5%	5911
	11th to 20th	Day	49% 8% 10% 16% 17% 1	6322
	21st to end	Day	45% 5% 12% 21% 14% 3	6949
June	1st to 10th	Day	44% 8% 12% 19% 16% 1	2800
	11th to 20th	Day	40% 8% 13% 23% 15% 1	2800
	21st to end	Day	43% 7% 13% 23% 13% 1	2952
July	1st to 10th	Day	40% 7% 13% 24% 14% 2	6341
	11th to 20th	Day	33% 7% 13% 31% 15% 1	6285
	21st to end	Day	33% 7% 14% 30% 15%	6342
August	1st to 10th	Day	44% 7% 13% 22% 12% 1	4143
	11th to 20th	Day	41% 8% 14% 26% 10%	4083
	21st to end	Day	37% 7% 13% 33% 10% 1	4351
September	1st to 10th	Day	38% 9% 13% 27% 11% 1	2280
	11th to 20th	Day	36% 7% 13% 28% 14%	2178
	21st to end	Day	46% 7% 12% 25% 9%	2045
October	1st to 10th	Day	41% 5% 13% 26% 14% 1	3160
	11th to 20th	Day	42% 6% 15% 23% 14% 1	3140
	21st to end	Day	54% 7% 14% 19% 6%	3428
November	1st to 10th	Day	51% 8% 13% 19% 9% 1	1678
	11th to 20th	Day	56% 10% 12% 13% 8% 1	1600
	21st to end	Day	62% 8% 13% 14% 3	1600
December	1st to 10th	Day	70% 8% 12% 8% 3	2600
	11th to 20th	Day	63% 7% 11% 10% 8%	2986
	21st to end	Day	73% 6% 6% 8% 6% 1	3960
January	1st to 10th	Night	54% 7% 14% 18% 7%	6349
	11th to 20th	Night	65% 8% 10% 12% 4	6061
	21st to end	Night	60% 7% 11% 11% 10% 1	6490
February	1st to 10th	Night	59% 8% 10% 17% 6% 1	2600
	11th to 20th	Night	56% 7% 12% 16% 8% 1	2535
	21st to end	Night	53% 7% 13% 19% 8%	2092
March	1st to 10th	Night	53% 5% 10% 18% 11% 2	4918
	11th to 20th	Night	43% 6% 18% 21% 10% 2	4980
	21st to end	Night	47% 4 13% 18% 16% 2	5467
April	1st to 10th	Night	53% 5% 10% 18% 13% 1	2030
	11th to 20th	Night	48% 5% 9% 20% 16% 2	1917
	21st to end	Night	46% 7% 11% 18% 16% 2	1800
May	1st to 10th	Night	49% 6% 10% 15% 14% 6%	4043
	11th to 20th	Night	43% 8% 12% 21% 14% 2	3576
	21st to end	Night	40% 6% 13% 24% 15% 2	3927
June	1st to 10th	Night	39% 7% 10% 24% 17% 2	1600
	11th to 20th	Night	38% 6% 12% 23% 20% 2	1600
	21st to end	Night	38% 7% 14% 24% 16% 1	1430
July	1st to 10th	Night	33% 6% 15% 26% 18% 2	3472
	11th to 20th	Night	31% 6% 13% 32% 18% 1	3552
	21st to end	Night	30% 6% 12% 32% 20% 1	4178
August	1st to 10th	Night	36% 5% 13% 29% 15% 2	2850
	11th to 20th	Night	33% 6% 16% 31% 13% 1	2812
	21st to end	Night	34% 7% 12% 33% 14% 1	3272
September	1st to 10th	Night	35% 7% 16% 27% 15% 1	1900
	11th to 20th	Night	29% 6% 12% 33% 19% 1	2000
	21st to end	Night	41% 8% 12% 27% 12%	2134
October	1st to 10th	Night	33% 6% 8% 28% 24% 1	3800
	11th to 20th	Night	42% 6% 15% 25% 12%	3779
	21st to end	Night	41% 7% 15% 26% 10%	4120
November	1st to 10th	Night	47% 6% 13% 21% 12% 1	2619
	11th to 20th	Night	54% 8% 12% 15% 9% 1	2800
	21st to end	Night	57% 10% 17% 13% 3	2800
December	1st to 10th	Night	64% 9% 12% 11% 3	4580
	11th to 20th	Night	63% 8% 8% 11% 9%	5208
	21st to end	Night	70% 7% 10% 8% 5%	6996

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	20% 27% 31% 18% 5% 1	200
	11th to 20th	Day	25% 28% 26% 16% 3 2	265
	21st to end	Day	25% 25% 35% 12% 2	330
February	1st to 10th	Day	28% 26% 32% 11% 3	300
	11th to 20th	Day	27% 27% 38% 7% 1	300
	21st to end	Day	36% 21% 32% 10%	270
March	1st to 10th	Day	25% 22% 34% 15% 4	500
	11th to 20th	Day	23% 23% 34% 16% 3 1	500
	21st to end	Day	31% 20% 30% 14% 4 1	550
April	1st to 10th	Day	28% 20% 34% 12% 6%	500
	11th to 20th	Day	31% 20% 25% 16% 6% 3	492
	21st to end	Day	26% 18% 34% 14% 7% 2	500
May	1st to 10th	Day	22% 16% 31% 19% 7% 4	503
	11th to 20th	Day	17% 16% 32% 22% 10% 4	527
	21st to end	Day	18% 12% 28% 27% 12% 3	573
June	1st to 10th	Day	16% 16% 31% 27% 8% 1	530
	11th to 20th	Day	16% 12% 31% 27% 12% 2	530
	21st to end	Day	18% 10% 35% 26% 9% 2	682
July	1st to 10th	Day	10% 8% 29% 31% 19% 4	550
	11th to 20th	Day	13% 9% 26% 31% 16% 6%	524
	21st to end	Day	9% 8% 33% 32% 12% 6%	576
August	1st to 10th	Day	12% 9% 27% 29% 15% 8%	502
	11th to 20th	Day	12% 8% 24% 27% 22% 8%	479
	21st to end	Day	13% 8% 31% 26% 15% 7%	539
September	1st to 10th	Day	13% 9% 29% 25% 17% 8%	490
	11th to 20th	Day	9% 9% 25% 24% 21% 13%	490
	21st to end	Day	16% 12% 29% 24% 12% 7%	490
October	1st to 10th	Day	23% 11% 30% 18% 14% 4	490
	11th to 20th	Day	22% 20% 33% 17% 7% 2	490
	21st to end	Day	30% 18% 31% 17% 4	539
November	1st to 10th	Day	26% 21% 30% 15% 7%	281
	11th to 20th	Day	23% 28% 31% 15% 4 1	200
	21st to end	Day	25% 26% 38% 10% 2	200
December	1st to 10th	Day	27% 21% 35% 12% 5%	200
	11th to 20th	Day	32% 21% 31% 13% 3 1	200
	21st to end	Day	28% 22% 36% 12% 1 1	220
January	1st to 10th	Night	23% 21% 38% 13% 4 1	800
	11th to 20th	Night	27% 16% 33% 19% 4 1	800
	21st to end	Night	20% 14% 38% 21% 6%	880
February	1st to 10th	Night	22% 19% 38% 19% 2	800
	11th to 20th	Night	24% 18% 37% 19% 3	783
	21st to end	Night	21% 20% 37% 18% 4	660
March	1st to 10th	Night	21% 19% 36% 20% 4	800
	11th to 20th	Night	23% 19% 35% 18% 4 1	800
	21st to end	Night	21% 17% 33% 23% 6%	880
April	1st to 10th	Night	26% 16% 35% 20% 3	800
	11th to 20th	Night	19% 17% 35% 21% 8% 1	733
	21st to end	Night	21% 14% 32% 25% 8%	600
May	1st to 10th	Night	20% 8% 30% 30% 10% 1	596
	11th to 20th	Night	16% 7% 35% 29% 12% 1	394
	21st to end	Night	12% 8% 30% 34% 16% 1	433
June	1st to 10th	Night	15% 6% 33% 35% 11%	400
	11th to 20th	Night	11% 10% 29% 36% 13% 1	400
	21st to end	Night	15% 6% 30% 36% 13%	400
July	1st to 10th	Night	9% 5% 27% 41% 18% 1	390
	11th to 20th	Night	10% 5% 26% 39% 19% 1	388
	21st to end	Night	8% 4 28% 40% 19% 2	600
August	1st to 10th	Night	10% 3 21% 37% 28% 1	579
	11th to 20th	Night	8% 5% 19% 41% 24% 3	564
	21st to end	Night	13% 4 27% 34% 20% 3	710
September	1st to 10th	Night	12% 8% 26% 32% 19% 4	760
	11th to 20th	Night	14% 6% 23% 29% 24% 5%	760
	21st to end	Night	18% 8% 22% 32% 16% 4	760
October	1st to 10th	Night	20% 9% 28% 26% 15% 2	760
	11th to 20th	Night	22% 14% 33% 22% 9% 1	760
	21st to end	Night	26% 13% 33% 24% 4	836
November	1st to 10th	Night	25% 12% 33% 22% 8% 1	780
	11th to 20th	Night	23% 17% 32% 21% 6% 1	800
	21st to end	Night	25% 17% 31% 22% 4	800
December	1st to 10th	Night	28% 16% 37% 16% 4	800
	11th to 20th	Night	22% 19% 37% 18% 3 1	800
	21st to end	Night	30% 15% 36% 16% 2	880

Page generated at 2025-08-02 01:32:28. Version ac07

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