Woodland
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Woodland clear sky chart from 2005-11-06 to 2025-07-21.

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	20% 9% 3 7% 5% 4 4 3 5% 6% 34%	124813
	Night	23% 10% 3 7% 4 4 4 3 4 5% 34%	123054
Transparency	Day	51% 7% 11% 16% 12% 3	124579
	Night	52% 7% 11% 16% 10% 3	122931
Seeing	Day	26% 12% 26% 25% 10% 2	15768
	Night	30% 6% 19% 30% 13% 1	24360

By Month

Percentage Cloud Cover NW (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	41% 16% 4 8% 5% 3 4 3 4 4 9%	3639
	11th to 20th	Day	27% 10% 3 7% 6% 4 4 4 5% 5% 24%	3616
	21st to end	Day	31% 10% 3 7% 4 3 3 2 3 4 29%	4344
February	1st to 10th	Day	32% 15% 3 8% 4 4 5% 3 5% 6% 16%	1800
	11th to 20th	Day	32% 14% 5% 9% 5% 5% 4 2 5% 4 17%	1755
	21st to end	Day	33% 17% 3 7% 5% 5% 3 2 3 4 17%	1557
March	1st to 10th	Day	20% 16% 4 10% 6% 5% 5% 4 5% 7% 18%	4728
	11th to 20th	Day	27% 16% 4 9% 4 3 3 2 3 3 25%	5000
	21st to end	Day	29% 13% 4 11% 6% 5% 5% 4 5% 5% 11%	5611
April	1st to 10th	Day	30% 13% 4 10% 6% 4 4 3 5% 6% 16%	2400
	11th to 20th	Day	23% 14% 3 8% 5% 4 4 4 5% 4 26%	2378
	21st to end	Day	22% 11% 3 9% 6% 5% 5% 4 5% 7% 23%	2600
May	1st to 10th	Day	15% 8% 2 7% 4 4 4 3 5% 6% 42%	6266
	11th to 20th	Day	16% 9% 3 8% 6% 5% 6% 5% 7% 8% 29%	6277
	21st to end	Day	17% 7% 3 7% 6% 6% 5% 4 6% 8% 31%	6903
June	1st to 10th	Day	21% 9% 2 7% 5% 4 3 3 5% 7% 33%	2800
	11th to 20th	Day	18% 8% 3 8% 6% 5% 6% 5% 7% 7% 26%	2840
	21st to end	Day	10% 6% 2 6% 5% 5% 4 3 6% 7% 46%	3000
July	1st to 10th	Day	4 3 1 3 3 2 3 2 4 6% 67%	4701
	11th to 20th	Day	5% 2 1 3 2 3 2 2 4 4 72%	4560
	21st to end	Day	7% 3 1 3 2 2 3 3 4 7% 65%	4791
August	1st to 10th	Day	4 3 1 4 3 3 3 3 5% 7% 65%	4164
	11th to 20th	Day	6% 5% 2 6% 5% 5% 5% 4 6% 9% 48%	4026
	21st to end	Day	11% 7% 2 5% 3 4 4 3 5% 7% 49%	4314
September	1st to 10th	Day	9% 3 2 5% 3 4 4 3 6% 7% 55%	2280
	11th to 20th	Day	13% 7% 3 7% 5% 3 5% 4 5% 7% 41%	2280
	21st to end	Day	17% 6% 2 6% 4 4 3 3 5% 6% 43%	1999
October	1st to 10th	Day	17% 6% 2 5% 3 3 3 3 6% 8% 44%	3180
	11th to 20th	Day	21% 8% 3 8% 5% 5% 5% 4 6% 7% 28%	3161
	21st to end	Day	31% 9% 3 8% 4 4 4 3 5% 6% 23%	3355
November	1st to 10th	Day	33% 12% 4 8% 5% 5% 5% 5% 5% 5% 14%	1639
	11th to 20th	Day	38% 10% 4 7% 5% 4 3 3 5% 4 18%	1600
	21st to end	Day	33% 12% 3 9% 4 4 4 3 5% 4 20%	1600
December	1st to 10th	Day	23% 10% 3 6% 4 4 4 5% 4 6% 30%	2620
	11th to 20th	Day	38% 13% 5% 9% 5% 4 4 2 4 4 11%	3025
	21st to end	Day	37% 15% 5% 11% 5% 5% 4 3 3 3 10%	4004
January	1st to 10th	Night	38% 14% 4 9% 5% 4 4 3 3 3 13%	6306
	11th to 20th	Night	25% 12% 3 7% 4 4 4 4 4 5% 27%	6282
	21st to end	Night	30% 10% 3 6% 4 3 3 2 3 4 33%	6626
February	1st to 10th	Night	29% 14% 4 9% 5% 4 5% 4 5% 4 18%	2600
	11th to 20th	Night	29% 14% 3 7% 4 4 4 3 4 5% 23%	2532
	21st to end	Night	31% 13% 3 8% 5% 4 3 3 5% 6% 20%	2072
March	1st to 10th	Night	20% 15% 4 9% 6% 6% 6% 4 5% 6% 20%	5165
	11th to 20th	Night	27% 13% 3 8% 5% 4 4 3 4 4 26%	4999
	21st to end	Night	33% 14% 4 9% 5% 4 5% 3 5% 5% 13%	5363
April	1st to 10th	Night	25% 13% 4 9% 6% 5% 4 3 4 5% 23%	2000
	11th to 20th	Night	19% 12% 3 7% 5% 4 4 3 5% 5% 30%	1969
	21st to end	Night	22% 11% 3 7% 3 4 4 4 4 7% 31%	1800
May	1st to 10th	Night	17% 7% 2 5% 3 3 4 3 6% 6% 46%	3694
	11th to 20th	Night	14% 8% 3 6% 4 3 4 4 5% 7% 42%	3616
	21st to end	Night	10% 8% 3 7% 5% 4 5% 4 6% 8% 39%	3972
June	1st to 10th	Night	16% 9% 3 7% 6% 4 4 3 4 6% 40%	1600
	11th to 20th	Night	14% 7% 2 7% 4 3 3 3 5% 7% 44%	1550
	21st to end	Night	8% 4 1 5% 3 2 3 3 4 6% 59%	1400
July	1st to 10th	Night	2 1 1 1 2 1 2 2 3 5% 79%	2473
	11th to 20th	Night	3 2 1 3 2 1 2 2 2 4 77%	2620
	21st to end	Night	4 2 1 1 1 1 1 2 3 5% 79%	2762
August	1st to 10th	Night	2 2 1 2 1 2 2 1 4 6% 77%	2771
	11th to 20th	Night	6% 4 1 5% 2 3 3 3 4 7% 62%	2812
	21st to end	Night	11% 4 1 4 3 3 3 3 4 5% 59%	3360
September	1st to 10th	Night	7% 3 2 3 3 3 3 3 4 5% 66%	1900
	11th to 20th	Night	11% 5% 3 6% 5% 4 4 3 5% 6% 48%	1900
	21st to end	Night	12% 4 2 5% 4 4 4 3 5% 7% 49%	2175
October	1st to 10th	Night	13% 4 2 4 3 3 4 3 5% 8% 51%	3800
	11th to 20th	Night	20% 7% 3 6% 4 4 4 4 7% 7% 35%	3777
	21st to end	Night	27% 9% 4 7% 4 4 4 3 5% 6% 27%	4211
November	1st to 10th	Night	33% 10% 3 8% 5% 4 5% 3 4 5% 22%	2655
	11th to 20th	Night	37% 10% 3 7% 4 4 4 2 4 4 21%	2800
	21st to end	Night	29% 10% 3 7% 5% 4 5% 3 5% 4 24%	2800
December	1st to 10th	Night	22% 9% 3 6% 4 4 4 4 6% 6% 33%	4560
	11th to 20th	Night	38% 14% 4 9% 5% 4 3 3 4 4 12%	5180
	21st to end	Night	37% 16% 4 10% 4 4 4 3 3 3 11%	6952

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	79% 6% 4 6% 4	3639
	11th to 20th	Day	60% 5% 7% 18% 8% 1	3640
	21st to end	Day	58% 6% 5% 13% 15% 3	4344
February	1st to 10th	Day	70% 8% 9% 10% 4	1800
	11th to 20th	Day	72% 7% 6% 9% 4 1	1764
	21st to end	Day	72% 5% 8% 7% 7% 1	1557
March	1st to 10th	Day	62% 9% 15% 9% 5%	4728
	11th to 20th	Day	64% 6% 6% 19% 4	5000
	21st to end	Day	73% 9% 10% 6% 2	5611
April	1st to 10th	Day	69% 8% 11% 11% 2	2400
	11th to 20th	Day	61% 6% 11% 12% 8% 1	2378
	21st to end	Day	61% 9% 11% 12% 6% 1	2600
May	1st to 10th	Day	42% 8% 12% 22% 16% 1	6266
	11th to 20th	Day	48% 13% 18% 15% 5%	6280
	21st to end	Day	50% 11% 19% 16% 4	6904
June	1st to 10th	Day	52% 9% 17% 15% 8%	2800
	11th to 20th	Day	54% 12% 16% 14% 5%	2840
	21st to end	Day	36% 8% 17% 25% 10% 4	3000
July	1st to 10th	Day	19% 5% 9% 19% 21% 27%	4632
	11th to 20th	Day	16% 4 7% 21% 38% 14%	4485
	21st to end	Day	20% 4 13% 27% 31% 4	4640
August	1st to 10th	Day	20% 5% 11% 25% 29% 10%	4147
	11th to 20th	Day	31% 9% 18% 27% 12% 4	4065
	21st to end	Day	35% 6% 11% 23% 17% 8%	4313
September	1st to 10th	Day	27% 7% 15% 23% 18% 10%	2280
	11th to 20th	Day	43% 8% 14% 15% 14% 6%	2280
	21st to end	Day	42% 8% 13% 19% 14% 5%	1999
October	1st to 10th	Day	38% 5% 7% 26% 22% 2	3180
	11th to 20th	Day	53% 8% 12% 15% 11% 1	3161
	21st to end	Day	62% 5% 8% 15% 10%	3355
November	1st to 10th	Day	70% 9% 7% 10% 4	1639
	11th to 20th	Day	69% 8% 9% 8% 5% 2	1600
	21st to end	Day	66% 7% 6% 8% 12% 1	1600
December	1st to 10th	Day	54% 5% 7% 17% 17% 1	2620
	11th to 20th	Day	76% 6% 9% 8% 1	3028
	21st to end	Day	78% 8% 7% 5% 2	4004
January	1st to 10th	Night	76% 6% 6% 6% 4 1	6306
	11th to 20th	Night	56% 7% 7% 20% 8% 1	6320
	21st to end	Night	57% 4 5% 14% 14% 6%	6626
February	1st to 10th	Night	68% 9% 8% 11% 4	2600
	11th to 20th	Night	65% 7% 9% 10% 6% 2	2534
	21st to end	Night	66% 7% 10% 10% 7% 1	2072
March	1st to 10th	Night	62% 8% 12% 12% 6%	5165
	11th to 20th	Night	60% 9% 8% 17% 5%	5000
	21st to end	Night	72% 8% 11% 8% 1	5363
April	1st to 10th	Night	66% 7% 12% 12% 3	2000
	11th to 20th	Night	54% 9% 12% 13% 9% 2	1969
	21st to end	Night	54% 11% 14% 15% 5% 2	1800
May	1st to 10th	Night	38% 7% 12% 27% 15% 1	3691
	11th to 20th	Night	41% 8% 24% 20% 6% 1	3616
	21st to end	Night	41% 14% 26% 16% 4	3972
June	1st to 10th	Night	48% 6% 17% 22% 7% 1	1600
	11th to 20th	Night	41% 9% 20% 23% 6%	1550
	21st to end	Night	29% 5% 21% 31% 11% 4	1400
July	1st to 10th	Night	11% 5% 10% 25% 20% 28%	2433
	11th to 20th	Night	15% 3 8% 22% 37% 16%	2572
	21st to end	Night	11% 4 13% 32% 34% 6%	2674
August	1st to 10th	Night	11% 5% 12% 33% 32% 7%	2763
	11th to 20th	Night	23% 8% 28% 26% 10% 5%	2839
	21st to end	Night	28% 6% 16% 25% 19% 7%	3360
September	1st to 10th	Night	22% 6% 15% 27% 19% 10%	1900
	11th to 20th	Night	37% 8% 14% 20% 12% 9%	1900
	21st to end	Night	35% 8% 17% 18% 16% 6%	2175
October	1st to 10th	Night	32% 5% 11% 29% 22% 2	3800
	11th to 20th	Night	48% 7% 14% 19% 12% 1	3777
	21st to end	Night	59% 6% 8% 17% 9% 1	4211
November	1st to 10th	Night	67% 6% 9% 11% 6%	2655
	11th to 20th	Night	68% 7% 8% 9% 6% 2	2800
	21st to end	Night	62% 6% 9% 9% 12% 1	2800
December	1st to 10th	Night	50% 6% 8% 17% 19%	4560
	11th to 20th	Night	77% 6% 7% 7% 3	5176
	21st to end	Night	78% 9% 6% 6% 2	6952

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	51% 12% 19% 12% 6% 1	200
	11th to 20th	Day	47% 12% 22% 9% 9% 2	200
	21st to end	Day	42% 9% 19% 18% 10% 2	365
February	1st to 10th	Day	46% 12% 18% 17% 6% 2	400
	11th to 20th	Day	45% 13% 24% 14% 4 1	395
	21st to end	Day	44% 13% 23% 15% 5%	369
March	1st to 10th	Day	37% 16% 25% 15% 6%	500
	11th to 20th	Day	37% 13% 24% 16% 7% 3	500
	21st to end	Day	40% 16% 22% 16% 6% 1	550
April	1st to 10th	Day	38% 13% 24% 16% 8% 2	500
	11th to 20th	Day	30% 19% 26% 17% 6% 2	492
	21st to end	Day	27% 18% 29% 18% 8% 1	500
May	1st to 10th	Day	19% 19% 27% 24% 9% 2	503
	11th to 20th	Day	28% 16% 23% 21% 9% 2	528
	21st to end	Day	24% 11% 26% 26% 10% 2	573
June	1st to 10th	Day	24% 10% 28% 25% 12% 1	530
	11th to 20th	Day	20% 18% 33% 22% 6% 1	570
	21st to end	Day	11% 11% 34% 32% 10% 2	730
July	1st to 10th	Day	10% 7% 36% 36% 10% 1	615
	11th to 20th	Day	6% 8% 31% 38% 14% 3	524
	21st to end	Day	5% 6% 31% 40% 16% 3	532
August	1st to 10th	Day	8% 5% 26% 43% 15% 3	487
	11th to 20th	Day	4 5% 25% 41% 21% 4	477
	21st to end	Day	11% 10% 30% 33% 14% 3	539
September	1st to 10th	Day	9% 7% 32% 37% 13% 2	490
	11th to 20th	Day	17% 9% 23% 35% 14% 2	490
	21st to end	Day	20% 11% 26% 30% 11% 1	490
October	1st to 10th	Day	25% 9% 26% 24% 14% 2	490
	11th to 20th	Day	28% 9% 22% 22% 17% 1	490
	21st to end	Day	35% 12% 23% 17% 9% 2	482
November	1st to 10th	Day	40% 16% 22% 16% 6%	237
	11th to 20th	Day	46% 10% 22% 14% 8% 2	200
	21st to end	Day	42% 11% 16% 19% 12%	200
December	1st to 10th	Day	43% 10% 19% 15% 12% 2	200
	11th to 20th	Day	51% 13% 19% 14% 4	200
	21st to end	Day	48% 13% 19% 15% 5%	220
January	1st to 10th	Night	48% 9% 16% 18% 9%	800
	11th to 20th	Night	44% 7% 15% 24% 11% 1	800
	21st to end	Night	39% 5% 17% 27% 11% 1	880
February	1st to 10th	Night	40% 8% 17% 26% 8% 1	800
	11th to 20th	Night	40% 8% 17% 25% 10%	784
	21st to end	Night	41% 8% 19% 24% 8%	660
March	1st to 10th	Night	37% 9% 19% 24% 11% 1	800
	11th to 20th	Night	37% 9% 18% 27% 10%	800
	21st to end	Night	40% 10% 17% 22% 10%	880
April	1st to 10th	Night	35% 9% 20% 24% 11% 1	800
	11th to 20th	Night	27% 10% 24% 27% 10% 1	781
	21st to end	Night	30% 5% 22% 30% 13% 1	600
May	1st to 10th	Night	19% 7% 28% 34% 12% 1	428
	11th to 20th	Night	21% 5% 22% 35% 16% 1	394
	21st to end	Night	18% 7% 22% 36% 17%	433
June	1st to 10th	Night	22% 4 24% 39% 11%	400
	11th to 20th	Night	20% 6% 28% 36% 10%	400
	21st to end	Night	11% 4 27% 48% 11%	400
July	1st to 10th	Night	6% 2 26% 51% 14% 1	390
	11th to 20th	Night	6% 3 31% 46% 14%	388
	21st to end	Night	4 4 25% 53% 14% 1	416
August	1st to 10th	Night	4 3 17% 48% 27% 2	516
	11th to 20th	Night	5% 2 12% 46% 32% 2	564
	21st to end	Night	10% 4 21% 43% 21% 1	750
September	1st to 10th	Night	9% 4 21% 46% 19% 1	760
	11th to 20th	Night	15% 4 17% 34% 27% 2	760
	21st to end	Night	16% 4 20% 42% 18% 1	760
October	1st to 10th	Night	22% 4 18% 36% 19% 2	760
	11th to 20th	Night	27% 4 15% 33% 18% 3	760
	21st to end	Night	36% 5% 18% 27% 13% 1	836
November	1st to 10th	Night	41% 8% 17% 27% 7%	780
	11th to 20th	Night	47% 7% 15% 22% 8% 1	800
	21st to end	Night	38% 8% 17% 27% 11% 1	800
December	1st to 10th	Night	37% 7% 20% 24% 12% 1	800
	11th to 20th	Night	48% 7% 17% 20% 7% 1	800
	21st to end	Night	52% 9% 17% 14% 6%	880

Page generated at 2025-07-17 22:10:02. Version ac07

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