Woodland Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Woodland Observatory 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	18% 7% 2 6% 4 4 4 4 5% 7% 38%	119810
	Night	18% 8% 2 6% 4 4 4 3 5% 6% 40%	119321
Transparency	Day	44% 6% 11% 21% 15% 3	123362
	Night	43% 6% 12% 21% 15% 3	123917
Seeing	Day	24% 17% 31% 19% 8% 2	15844
	Night	22% 15% 32% 24% 7%	24736

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	12% 7% 3 9% 5% 5% 5% 4 6% 6% 38%	3597
	11th to 20th	Day	13% 7% 3 8% 3 3 4 4 5% 6% 44%	3570
	21st to end	Day	15% 10% 3 6% 4 3 3 3 5% 5% 44%	3960
February	1st to 10th	Day	17% 8% 3 7% 4 5% 4 4 5% 6% 35%	1830
	11th to 20th	Day	12% 8% 3 7% 5% 5% 4 5% 5% 7% 39%	1948
	21st to end	Day	17% 11% 3 8% 5% 4 4 4 4 5% 37%	1650
March	1st to 10th	Day	20% 10% 3 7% 4 4 4 3 4 5% 35%	4476
	11th to 20th	Day	16% 9% 3 5% 4 4 4 4 5% 6% 40%	4741
	21st to end	Day	25% 9% 2 6% 4 3 4 3 5% 7% 33%	5825
April	1st to 10th	Day	19% 10% 2 7% 5% 4 4 3 5% 6% 37%	2400
	11th to 20th	Day	17% 7% 2 6% 4 4 5% 4 6% 7% 39%	2384
	21st to end	Day	21% 8% 3 6% 5% 5% 4 3 4 6% 36%	2600
May	1st to 10th	Day	31% 10% 2 6% 4 4 4 3 5% 6% 25%	5886
	11th to 20th	Day	20% 7% 3 9% 5% 5% 5% 4 5% 6% 31%	6079
	21st to end	Day	20% 6% 2 6% 4 5% 4 4 5% 8% 35%	6949
June	1st to 10th	Day	19% 6% 2 6% 5% 5% 5% 4 6% 8% 34%	2800
	11th to 20th	Day	17% 5% 3 6% 5% 5% 4 5% 5% 8% 37%	2800
	21st to end	Day	18% 6% 3 6% 4 5% 4 4 6% 8% 36%	2800
July	1st to 10th	Day	13% 6% 2 6% 5% 5% 5% 5% 6% 9% 37%	4580
	11th to 20th	Day	10% 5% 2 6% 5% 5% 6% 5% 7% 10% 38%	4580
	21st to end	Day	17% 7% 3 7% 4 4 4 4 6% 7% 36%	4814
August	1st to 10th	Day	14% 6% 3 6% 5% 6% 5% 5% 6% 8% 35%	4211
	11th to 20th	Day	15% 7% 2 6% 5% 5% 5% 4 6% 7% 37%	3984
	21st to end	Day	8% 5% 2 6% 4 5% 5% 5% 8% 9% 43%	4180
September	1st to 10th	Day	14% 5% 1 5% 4 4 5% 4 5% 6% 47%	2280
	11th to 20th	Day	16% 5% 2 4 3 3 4 2 4 5% 52%	2100
	21st to end	Day	17% 5% 2 6% 4 4 4 3 4 7% 45%	2090
October	1st to 10th	Day	24% 6% 2 6% 4 4 4 3 4 5% 39%	2090
	11th to 20th	Day	15% 5% 2 6% 3 4 4 3 4 7% 46%	1833
	21st to end	Day	23% 6% 2 5% 3 4 4 4 4 5% 39%	1881
November	1st to 10th	Day	15% 6% 2 6% 4 3 3 3 4 5% 50%	1761
	11th to 20th	Day	18% 6% 2 4 3 4 3 3 4 5% 47%	1800
	21st to end	Day	19% 6% 2 5% 4 4 4 3 5% 5% 42%	1785
December	1st to 10th	Day	16% 7% 3 5% 4 3 4 3 6% 7% 42%	2600
	11th to 20th	Day	21% 5% 2 5% 4 3 3 4 4 5% 44%	2986
	21st to end	Day	19% 10% 3 6% 4 3 5% 3 4 5% 37%	3960
January	1st to 10th	Night	13% 6% 2 6% 4 4 5% 3 6% 7% 45%	6349
	11th to 20th	Night	12% 8% 4 8% 5% 4 4 4 5% 6% 39%	6315
	21st to end	Night	15% 10% 3 7% 4 4 4 3 5% 5% 39%	6996
February	1st to 10th	Night	15% 9% 3 6% 4 4 4 4 5% 6% 39%	2568
	11th to 20th	Night	13% 8% 2 6% 5% 5% 5% 4 6% 6% 40%	2338
	21st to end	Night	15% 9% 2 6% 4 4 5% 3 6% 6% 40%	1980
March	1st to 10th	Night	23% 9% 2 5% 4 4 4 3 4 6% 37%	5364
	11th to 20th	Night	16% 9% 3 6% 5% 4 4 3 5% 6% 38%	5217
	21st to end	Night	25% 8% 2 5% 3 3 4 3 6% 6% 34%	5105
April	1st to 10th	Night	19% 8% 3 7% 4 5% 5% 3 5% 6% 36%	2000
	11th to 20th	Night	20% 7% 2 5% 4 4 4 3 5% 6% 39%	1965
	21st to end	Night	21% 7% 3 5% 4 4 3 3 4 6% 40%	1800
May	1st to 10th	Night	34% 9% 2 6% 4 3 3 3 4 6% 25%	4054
	11th to 20th	Night	17% 8% 3 8% 5% 6% 5% 4 6% 8% 30%	3855
	21st to end	Night	21% 7% 3 8% 5% 4 4 3 5% 7% 33%	3926
June	1st to 10th	Night	18% 8% 3 7% 4 4 3 3 5% 7% 38%	1600
	11th to 20th	Night	19% 6% 2 5% 4 4 4 4 5% 8% 38%	1600
	21st to end	Night	18% 6% 3 5% 4 4 4 4 6% 8% 40%	1600
July	1st to 10th	Night	12% 5% 2 6% 5% 5% 6% 4 7% 9% 40%	2600
	11th to 20th	Night	13% 6% 2 6% 4 4 5% 4 5% 9% 42%	2600
	21st to end	Night	16% 7% 2 6% 4 4 4 3 6% 6% 41%	2739
August	1st to 10th	Night	21% 6% 2 7% 5% 4 5% 4 5% 6% 35%	2688
	11th to 20th	Night	12% 8% 3 7% 5% 5% 6% 4 6% 7% 38%	2839
	21st to end	Night	9% 4 1 3 3 4 3 3 5% 8% 56%	3476
September	1st to 10th	Night	14% 5% 1 5% 3 4 3 3 4 7% 50%	1900
	11th to 20th	Night	14% 5% 2 4 3 3 3 2 4 6% 53%	2078
	21st to end	Night	17% 4 2 6% 3 3 4 3 4 6% 47%	2090
October	1st to 10th	Night	22% 5% 2 6% 4 4 4 3 4 5% 41%	2090
	11th to 20th	Night	16% 4 2 4 3 3 5% 4 6% 7% 45%	2340
	21st to end	Night	22% 7% 2 5% 4 4 4 3 5% 5% 39%	2717
November	1st to 10th	Night	15% 6% 2 5% 4 3 4 4 4 6% 47%	2537
	11th to 20th	Night	17% 6% 3 5% 4 3 3 3 4 5% 47%	2600
	21st to end	Night	16% 7% 2 5% 4 3 4 3 5% 6% 44%	2611
December	1st to 10th	Night	17% 10% 2 6% 4 4 4 3 5% 6% 39%	4580
	11th to 20th	Night	22% 8% 2 5% 3 3 4 3 4 5% 41%	5208
	21st to end	Night	19% 10% 3 7% 4 4 4 3 4 6% 38%	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	45% 4 9% 25% 16% 1	3598
	11th to 20th	Day	40% 5% 11% 22% 18% 4	3600
	21st to end	Day	43% 4 8% 21% 19% 4	3960
February	1st to 10th	Day	47% 6% 12% 20% 12% 3	1830
	11th to 20th	Day	43% 7% 11% 21% 15% 4	1957
	21st to end	Day	49% 4 10% 19% 15% 3	1650
March	1st to 10th	Day	52% 4 9% 14% 11% 10%	4479
	11th to 20th	Day	42% 7% 14% 23% 12% 2	4741
	21st to end	Day	50% 4 7% 16% 17% 7%	5825
April	1st to 10th	Day	49% 5% 8% 18% 17% 4	2400
	11th to 20th	Day	44% 6% 11% 19% 17% 3	2384
	21st to end	Day	49% 6% 7% 17% 18% 4	2600
May	1st to 10th	Day	60% 7% 11% 13% 8% 1	5897
	11th to 20th	Day	52% 7% 13% 16% 10% 1	6083
	21st to end	Day	45% 7% 12% 22% 13% 1	6949
June	1st to 10th	Day	46% 8% 13% 21% 12% 1	2800
	11th to 20th	Day	43% 7% 13% 19% 15% 3	2800
	21st to end	Day	46% 8% 12% 20% 13% 1	2800
July	1st to 10th	Day	42% 7% 13% 20% 17% 1	4510
	11th to 20th	Day	37% 8% 16% 25% 12% 1	4505
	21st to end	Day	46% 6% 12% 21% 14% 2	4661
August	1st to 10th	Day	44% 8% 15% 22% 10%	4197
	11th to 20th	Day	43% 7% 14% 24% 10% 1	4023
	21st to end	Day	33% 8% 13% 28% 17% 2	4180
September	1st to 10th	Day	35% 7% 12% 25% 19% 2	2280
	11th to 20th	Day	35% 5% 8% 26% 23% 2	2100
	21st to end	Day	40% 5% 10% 22% 21% 2	2090
October	1st to 10th	Day	44% 6% 9% 21% 18% 2	3480
	11th to 20th	Day	32% 5% 8% 29% 23% 4	3010
	21st to end	Day	34% 5% 9% 30% 19% 3	3081
November	1st to 10th	Day	38% 4 13% 26% 17% 2	1761
	11th to 20th	Day	38% 5% 10% 21% 22% 3	1800
	21st to end	Day	44% 4 16% 22% 12% 2	1785
December	1st to 10th	Day	42% 5% 14% 28% 10% 1	2600
	11th to 20th	Day	42% 4 12% 19% 19% 4	2986
	21st to end	Day	48% 6% 9% 18% 13% 5%	3960
January	1st to 10th	Night	38% 5% 12% 30% 14% 2	6349
	11th to 20th	Night	44% 5% 14% 20% 13% 4	6360
	21st to end	Night	48% 4 9% 17% 17% 5%	6996
February	1st to 10th	Night	44% 7% 13% 20% 13% 3	2568
	11th to 20th	Night	43% 5% 13% 20% 16% 3	2340
	21st to end	Night	44% 6% 9% 23% 14% 4	1980
March	1st to 10th	Night	48% 5% 9% 16% 15% 7%	5374
	11th to 20th	Night	45% 8% 15% 18% 12% 2	5218
	21st to end	Night	50% 4 6% 14% 21% 6%	5105
April	1st to 10th	Night	48% 5% 11% 18% 16% 3	2000
	11th to 20th	Night	45% 5% 10% 20% 18% 2	1965
	21st to end	Night	45% 5% 11% 18% 17% 4	1800
May	1st to 10th	Night	59% 6% 12% 13% 8% 1	4060
	11th to 20th	Night	50% 9% 14% 16% 9% 1	3856
	21st to end	Night	50% 7% 14% 18% 10% 1	3927
June	1st to 10th	Night	47% 6% 11% 24% 12% 1	1600
	11th to 20th	Night	44% 8% 13% 20% 13% 2	1600
	21st to end	Night	41% 9% 14% 22% 13% 2	1600
July	1st to 10th	Night	40% 8% 14% 23% 14% 1	2560
	11th to 20th	Night	39% 7% 16% 22% 15% 1	2552
	21st to end	Night	44% 6% 12% 23% 15% 1	2651
August	1st to 10th	Night	49% 7% 13% 20% 11% 1	2678
	11th to 20th	Night	44% 8% 14% 23% 10%	2866
	21st to end	Night	26% 6% 17% 30% 20% 1	3476
September	1st to 10th	Night	34% 6% 12% 27% 20% 1	1900
	11th to 20th	Night	32% 5% 11% 26% 24% 2	2078
	21st to end	Night	38% 6% 10% 27% 17% 2	2090
October	1st to 10th	Night	40% 5% 15% 23% 15% 2	3480
	11th to 20th	Night	28% 5% 11% 26% 27% 3	3889
	21st to end	Night	35% 4 12% 32% 14% 2	4467
November	1st to 10th	Night	38% 5% 11% 23% 20% 3	2537
	11th to 20th	Night	40% 4 11% 21% 21% 3	2600
	21st to end	Night	41% 5% 14% 26% 13% 1	2611
December	1st to 10th	Night	46% 5% 11% 27% 11% 1	4580
	11th to 20th	Night	46% 5% 13% 14% 20% 2	5208
	21st to end	Night	46% 6% 9% 22% 15% 3	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	34% 23% 27% 13% 4	200
	11th to 20th	Day	31% 23% 33% 11% 2 1	200
	21st to end	Day	30% 22% 32% 12% 4	220
February	1st to 10th	Day	30% 26% 30% 11% 2	368
	11th to 20th	Day	32% 28% 28% 11% 1	496
	21st to end	Day	29% 24% 30% 14% 3	414
March	1st to 10th	Day	32% 21% 32% 12% 3	500
	11th to 20th	Day	31% 25% 29% 10% 4 1	500
	21st to end	Day	33% 21% 30% 11% 4 1	550
April	1st to 10th	Day	33% 22% 27% 11% 5% 1	500
	11th to 20th	Day	32% 21% 28% 12% 5% 1	492
	21st to end	Day	29% 19% 31% 14% 6% 1	500
May	1st to 10th	Day	33% 20% 28% 14% 4 1	503
	11th to 20th	Day	22% 17% 37% 17% 5% 2	527
	21st to end	Day	19% 15% 35% 24% 6% 1	573
June	1st to 10th	Day	19% 15% 38% 17% 9% 2	530
	11th to 20th	Day	17% 16% 36% 21% 8% 2	530
	21st to end	Day	19% 13% 36% 21% 8% 3	530
July	1st to 10th	Day	18% 10% 30% 27% 12% 3	525
	11th to 20th	Day	11% 8% 34% 30% 13% 3	524
	21st to end	Day	13% 8% 36% 32% 10% 2	532
August	1st to 10th	Day	14% 9% 29% 31% 14% 3	486
	11th to 20th	Day	17% 9% 29% 25% 16% 4	479
	21st to end	Day	13% 10% 32% 27% 14% 5%	539
September	1st to 10th	Day	18% 11% 27% 22% 16% 6%	490
	11th to 20th	Day	20% 10% 27% 19% 14% 10%	490
	21st to end	Day	19% 13% 32% 21% 11% 5%	490
October	1st to 10th	Day	28% 13% 24% 20% 10% 4	490
	11th to 20th	Day	20% 15% 31% 21% 11% 2	437
	21st to end	Day	30% 14% 28% 21% 7% 1	429
November	1st to 10th	Day	21% 18% 28% 22% 8% 2	395
	11th to 20th	Day	33% 17% 25% 20% 5% 1	400
	21st to end	Day	31% 19% 28% 16% 5% 1	385
December	1st to 10th	Day	24% 28% 29% 14% 7%	200
	11th to 20th	Day	35% 23% 29% 11% 3	200
	21st to end	Day	27% 22% 29% 16% 4 1	220
January	1st to 10th	Night	23% 23% 35% 16% 3	800
	11th to 20th	Night	27% 20% 32% 18% 3	800
	21st to end	Night	21% 20% 38% 18% 3	880
February	1st to 10th	Night	22% 20% 37% 20% 1	800
	11th to 20th	Night	24% 23% 36% 15% 1	783
	21st to end	Night	24% 22% 34% 18% 2	660
March	1st to 10th	Night	26% 21% 33% 18% 2	800
	11th to 20th	Night	24% 21% 33% 19% 4	800
	21st to end	Night	27% 19% 33% 18% 4	880
April	1st to 10th	Night	26% 19% 33% 19% 4	800
	11th to 20th	Night	24% 21% 33% 18% 4	781
	21st to end	Night	25% 19% 33% 20% 3	600
May	1st to 10th	Night	26% 14% 35% 20% 4	600
	11th to 20th	Night	21% 15% 34% 25% 5%	518
	21st to end	Night	20% 8% 35% 30% 6%	433
June	1st to 10th	Night	19% 11% 34% 28% 9% 1	400
	11th to 20th	Night	19% 9% 31% 33% 7% 1	400
	21st to end	Night	18% 5% 35% 36% 8%	400
July	1st to 10th	Night	16% 7% 29% 38% 9% 1	390
	11th to 20th	Night	13% 4 28% 42% 12% 1	388
	21st to end	Night	13% 5% 29% 41% 12%	416
August	1st to 10th	Night	15% 4 30% 38% 14%	482
	11th to 20th	Night	14% 7% 29% 37% 12% 2	593
	21st to end	Night	15% 5% 24% 39% 16% 1	836
September	1st to 10th	Night	15% 6% 31% 32% 14% 1	760
	11th to 20th	Night	16% 8% 28% 27% 19% 2	760
	21st to end	Night	19% 8% 28% 29% 13% 2	760
October	1st to 10th	Night	25% 10% 24% 27% 12% 1	760
	11th to 20th	Night	19% 11% 33% 25% 11% 1	760
	21st to end	Night	26% 16% 29% 23% 6%	836
November	1st to 10th	Night	19% 14% 33% 27% 7% 1	780
	11th to 20th	Night	22% 18% 32% 20% 6% 1	800
	21st to end	Night	25% 18% 31% 20% 5% 1	800
December	1st to 10th	Night	26% 19% 36% 17% 4	800
	11th to 20th	Night	26% 21% 32% 18% 3	800
	21st to end	Night	25% 20% 34% 19% 3	880

Page generated at 2025-07-18 01:10:04. Version ac07

Copyright © 2025 Attilla Danko.