Allison's Woods
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Allison's Woods 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	13% 6% 2 6% 4 4 4 4 6% 8% 43%	125765
	Night	14% 6% 2 6% 4 4 4 3 5% 7% 45%	122303
Transparency	Day	37% 7% 12% 21% 17% 6%	129411
	Night	38% 6% 11% 20% 20% 6%	126726
Seeing	Day	16% 7% 22% 25% 19% 11%	16258
	Night	16% 6% 24% 32% 19% 2	26324

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	15% 6% 2 4 2 2 2 2 3 4 58%	4056
	11th to 20th	Day	12% 6% 1 4 3 3 3 2 3 4 59%	4060
	21st to end	Day	18% 6% 2 6% 4 3 4 3 4 5% 47%	4466
February	1st to 10th	Day	15% 6% 2 5% 4 4 3 3 7% 7% 44%	1800
	11th to 20th	Day	20% 8% 1 5% 2 3 4 3 5% 4 45%	1889
	21st to end	Day	18% 7% 2 6% 4 4 4 3 4 6% 42%	1700
March	1st to 10th	Day	21% 7% 2 5% 3 3 3 3 4 6% 42%	4935
	11th to 20th	Day	9% 5% 2 5% 3 3 4 3 5% 6% 54%	4980
	21st to end	Day	17% 7% 2 5% 3 3 3 3 4 5% 47%	5465
April	1st to 10th	Day	12% 4 1 4 3 3 4 4 6% 8% 52%	2211
	11th to 20th	Day	13% 4 2 5% 4 3 4 3 5% 7% 49%	2374
	21st to end	Day	13% 6% 2 5% 4 4 5% 3 4 6% 47%	2560
May	1st to 10th	Day	9% 6% 3 7% 5% 6% 6% 4 8% 10% 34%	5862
	11th to 20th	Day	19% 7% 3 8% 5% 5% 5% 4 7% 8% 29%	5861
	21st to end	Day	12% 5% 2 6% 4 5% 5% 4 6% 8% 42%	6433
June	1st to 10th	Day	9% 5% 2 6% 4 4 5% 6% 8% 11% 39%	2600
	11th to 20th	Day	8% 5% 2 5% 6% 5% 6% 5% 8% 11% 40%	2600
	21st to end	Day	7% 4 2 5% 5% 5% 5% 6% 9% 11% 42%	2600
July	1st to 10th	Day	8% 5% 2 7% 6% 6% 6% 5% 8% 10% 39%	5900
	11th to 20th	Day	6% 6% 2 8% 6% 6% 7% 6% 9% 13% 32%	5900
	21st to end	Day	10% 7% 3 8% 5% 6% 7% 6% 8% 11% 29%	6424
August	1st to 10th	Day	17% 7% 3 7% 5% 6% 6% 5% 7% 10% 28%	4156
	11th to 20th	Day	8% 5% 2 8% 6% 6% 6% 5% 8% 11% 36%	4044
	21st to end	Day	5% 3 2 5% 4 4 4 4 6% 11% 53%	4250
September	1st to 10th	Day	10% 5% 2 5% 4 4 5% 5% 6% 8% 45%	2147
	11th to 20th	Day	15% 6% 2 6% 4 4 4 4 6% 8% 42%	2090
	21st to end	Day	20% 6% 2 7% 4 4 5% 3 5% 5% 38%	2090
October	1st to 10th	Day	14% 4 2 5% 3 3 2 3 4 5% 55%	1961
	11th to 20th	Day	13% 4 1 4 3 3 3 3 4 6% 57%	1900
	21st to end	Day	14% 5% 2 5% 2 3 3 3 3 5% 56%	2090
November	1st to 10th	Day	13% 6% 2 5% 3 3 2 3 5% 4 55%	1957
	11th to 20th	Day	13% 5% 2 3 4 3 3 4 5% 6% 53%	1835
	21st to end	Day	14% 5% 1 4 4 4 3 3 5% 6% 51%	1800
December	1st to 10th	Day	15% 5% 1 4 3 3 3 2 4 5% 53%	2930
	11th to 20th	Day	18% 7% 2 6% 4 3 4 3 5% 6% 43%	3373
	21st to end	Day	21% 6% 2 4 3 3 4 3 5% 7% 44%	4466
January	1st to 10th	Night	13% 5% 2 3 3 3 3 2 4 4 58%	5889
	11th to 20th	Night	13% 6% 2 4 3 2 2 2 3 4 58%	5900
	21st to end	Night	17% 7% 2 5% 3 3 3 2 4 5% 48%	6490
February	1st to 10th	Night	16% 5% 2 6% 4 4 4 4 5% 6% 45%	2600
	11th to 20th	Night	20% 8% 2 4 3 3 3 3 4 5% 44%	2392
	21st to end	Night	15% 6% 2 6% 4 3 4 3 4 6% 45%	1928
March	1st to 10th	Night	18% 7% 2 5% 3 3 3 3 4 5% 46%	4918
	11th to 20th	Night	10% 3 2 4 3 3 3 3 4 7% 56%	4980
	21st to end	Night	15% 5% 1 5% 4 4 4 3 5% 7% 47%	5467
April	1st to 10th	Night	14% 5% 2 4 5% 3 3 3 5% 7% 49%	2186
	11th to 20th	Night	12% 6% 2 5% 4 3 3 3 5% 7% 48%	1975
	21st to end	Night	13% 5% 2 6% 4 4 5% 4 5% 7% 46%	1855
May	1st to 10th	Night	14% 7% 3 7% 4 4 4 4 5% 8% 39%	4033
	11th to 20th	Night	19% 7% 3 7% 5% 5% 4 4 5% 9% 32%	4032
	21st to end	Night	15% 5% 2 5% 3 4 4 4 6% 9% 43%	4421
June	1st to 10th	Night	10% 5% 2 6% 5% 5% 6% 5% 8% 11% 37%	1800
	11th to 20th	Night	10% 5% 3 6% 5% 5% 5% 6% 6% 11% 37%	1800
	21st to end	Night	7% 4 2 5% 6% 6% 6% 5% 8% 11% 40%	1800
July	1st to 10th	Night	10% 7% 3 8% 6% 6% 6% 6% 8% 10% 30%	4058
	11th to 20th	Night	10% 6% 3 9% 7% 6% 7% 6% 8% 11% 27%	4057
	21st to end	Night	10% 8% 4 9% 7% 6% 7% 6% 8% 11% 25%	4427
August	1st to 10th	Night	20% 8% 3 8% 5% 5% 5% 4 7% 8% 26%	2861
	11th to 20th	Night	9% 7% 3 8% 6% 5% 6% 6% 9% 10% 31%	2785
	21st to end	Night	5% 4 2 6% 5% 4 5% 4 7% 9% 49%	3372
September	1st to 10th	Night	10% 5% 2 6% 5% 5% 5% 4 6% 9% 44%	2028
	11th to 20th	Night	15% 7% 2 7% 4 4 5% 5% 5% 7% 39%	2090
	21st to end	Night	18% 7% 3 7% 3 4 5% 3 7% 7% 36%	2090
October	1st to 10th	Night	15% 5% 2 5% 4 3 4 2 5% 6% 49%	2218
	11th to 20th	Night	15% 5% 2 4 3 2 3 3 4 5% 54%	2280
	21st to end	Night	14% 4 2 5% 3 3 3 2 4 5% 57%	2508
November	1st to 10th	Night	16% 5% 2 4 4 2 2 3 4 5% 53%	2341
	11th to 20th	Night	14% 4 2 5% 3 4 4 3 5% 5% 52%	2560
	21st to end	Night	14% 4 2 4 3 3 4 3 6% 7% 52%	2600
December	1st to 10th	Night	15% 6% 2 5% 3 3 3 2 4 6% 52%	4250
	11th to 20th	Night	22% 7% 3 6% 4 3 3 3 4 5% 41%	4822
	21st to end	Night	20% 4 2 4 3 3 4 3 5% 6% 46%	6490

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	32% 2 5% 20% 31% 9%	4057
	11th to 20th	Day	31% 3 5% 17% 36% 9%	4060
	21st to end	Day	40% 3 6% 23% 23% 6%	4466
February	1st to 10th	Day	39% 5% 13% 19% 19% 5%	1800
	11th to 20th	Day	41% 4 8% 21% 19% 6%	1899
	21st to end	Day	44% 5% 9% 16% 19% 7%	1700
March	1st to 10th	Day	43% 4 7% 16% 18% 12%	4935
	11th to 20th	Day	31% 4 7% 18% 22% 18%	4980
	21st to end	Day	40% 4 8% 24% 19% 6%	5465
April	1st to 10th	Day	30% 6% 11% 23% 24% 6%	2211
	11th to 20th	Day	34% 6% 10% 21% 21% 8%	2374
	21st to end	Day	37% 7% 12% 24% 17% 3	2560
May	1st to 10th	Day	41% 9% 17% 19% 11% 2	5897
	11th to 20th	Day	50% 9% 11% 20% 9% 1	5865
	21st to end	Day	38% 8% 14% 20% 17% 4	6447
June	1st to 10th	Day	34% 11% 16% 24% 13% 1	2600
	11th to 20th	Day	34% 12% 17% 22% 13% 2	2600
	21st to end	Day	32% 12% 19% 21% 14% 2	2600
July	1st to 10th	Day	38% 10% 17% 21% 12% 2	5835
	11th to 20th	Day	39% 13% 26% 17% 4	5831
	21st to end	Day	44% 12% 15% 21% 7%	6240
August	1st to 10th	Day	49% 9% 17% 19% 5%	4143
	11th to 20th	Day	38% 11% 20% 20% 9% 2	4083
	21st to end	Day	26% 7% 16% 35% 14% 2	4250
September	1st to 10th	Day	34% 9% 13% 21% 18% 4	2147
	11th to 20th	Day	39% 8% 13% 18% 19% 3	2090
	21st to end	Day	47% 6% 9% 18% 17% 3	2090
October	1st to 10th	Day	28% 5% 7% 22% 28% 10%	3260
	11th to 20th	Day	21% 3 6% 21% 25% 25%	3140
	21st to end	Day	27% 4 7% 24% 22% 16%	3428
November	1st to 10th	Day	33% 4 8% 22% 26% 8%	1957
	11th to 20th	Day	31% 4 9% 23% 26% 7%	1835
	21st to end	Day	34% 4 10% 22% 25% 5%	1800
December	1st to 10th	Day	34% 4 7% 19% 28% 8%	2930
	11th to 20th	Day	43% 4 10% 15% 22% 6%	3370
	21st to end	Day	40% 4 11% 27% 16% 2	4466
January	1st to 10th	Night	30% 3 6% 19% 32% 10%	5889
	11th to 20th	Night	31% 3 5% 18% 34% 8%	5900
	21st to end	Night	38% 3 6% 20% 25% 7%	6490
February	1st to 10th	Night	40% 5% 10% 21% 19% 4	2600
	11th to 20th	Night	43% 5% 8% 17% 20% 7%	2393
	21st to end	Night	39% 5% 10% 17% 22% 7%	1928
March	1st to 10th	Night	39% 5% 7% 15% 25% 9%	4918
	11th to 20th	Night	29% 4 6% 18% 26% 18%	4980
	21st to end	Night	38% 5% 7% 25% 20% 6%	5467
April	1st to 10th	Night	35% 5% 11% 21% 22% 6%	2186
	11th to 20th	Night	34% 5% 10% 21% 21% 9%	1975
	21st to end	Night	37% 7% 12% 22% 19% 4	1855
May	1st to 10th	Night	43% 8% 15% 21% 13% 1	4060
	11th to 20th	Night	49% 8% 13% 17% 12% 1	4033
	21st to end	Night	36% 7% 13% 26% 15% 3	4429
June	1st to 10th	Night	38% 11% 16% 21% 13% 2	1800
	11th to 20th	Night	38% 11% 17% 20% 12% 1	1800
	21st to end	Night	35% 11% 17% 19% 14% 4	1800
July	1st to 10th	Night	45% 12% 15% 16% 10% 1	4015
	11th to 20th	Night	47% 13% 22% 14% 3 1	4006
	21st to end	Night	49% 11% 16% 19% 5%	4297
August	1st to 10th	Night	53% 10% 17% 15% 5%	2850
	11th to 20th	Night	41% 13% 20% 16% 9% 1	2812
	21st to end	Night	29% 9% 13% 31% 15% 3	3372
September	1st to 10th	Night	35% 10% 15% 20% 15% 5%	2028
	11th to 20th	Night	43% 9% 10% 17% 18% 2	2090
	21st to end	Night	45% 8% 11% 16% 16% 4	2090
October	1st to 10th	Night	36% 5% 7% 18% 25% 9%	3699
	11th to 20th	Night	23% 3 6% 23% 27% 18%	3779
	21st to end	Night	27% 3 6% 23% 27% 14%	4120
November	1st to 10th	Night	34% 4 8% 20% 24% 10%	2341
	11th to 20th	Night	34% 4 8% 18% 26% 10%	2560
	21st to end	Night	32% 4 8% 24% 26% 6%	2600
December	1st to 10th	Night	34% 4 7% 21% 29% 5%	4250
	11th to 20th	Night	47% 4 8% 15% 17% 9%	4824
	21st to end	Night	38% 4 14% 21% 21% 2	6490

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	22% 17% 35% 21% 5%	300
	11th to 20th	Day	22% 19% 33% 18% 7%	300
	21st to end	Day	21% 14% 41% 18% 6% 1	330
February	1st to 10th	Day	18% 17% 36% 20% 10%	300
	11th to 20th	Day	36% 13% 33% 14% 4	300
	21st to end	Day	25% 16% 32% 22% 5%	299
March	1st to 10th	Day	21% 11% 32% 26% 7% 1	500
	11th to 20th	Day	19% 11% 40% 24% 6% 1	500
	21st to end	Day	21% 14% 33% 25% 7%	550
April	1st to 10th	Day	17% 17% 30% 22% 12% 2	500
	11th to 20th	Day	15% 12% 28% 25% 16% 4	492
	21st to end	Day	14% 10% 27% 28% 16% 5%	500
May	1st to 10th	Day	12% 13% 28% 28% 15% 5%	503
	11th to 20th	Day	17% 5% 22% 26% 20% 11%	527
	21st to end	Day	18% 4 14% 23% 25% 16%	573
June	1st to 10th	Day	10% 4 16% 32% 26% 13%	530
	11th to 20th	Day	9% 4 15% 25% 26% 20%	530
	21st to end	Day	10% 2 9% 26% 34% 19%	530
July	1st to 10th	Day	10% 2 8% 23% 31% 26%	525
	11th to 20th	Day	6% 2 6% 23% 34% 30%	524
	21st to end	Day	10% 2 7% 24% 31% 25%	576
August	1st to 10th	Day	15% 2 12% 22% 28% 21%	502
	11th to 20th	Day	10% 2 12% 25% 28% 22%	479
	21st to end	Day	10% 1 9% 22% 31% 27%	539
September	1st to 10th	Day	12% 2 9% 23% 29% 25%	490
	11th to 20th	Day	17% 1 13% 20% 27% 22%	490
	21st to end	Day	21% 5% 20% 24% 22% 8%	490
October	1st to 10th	Day	18% 4 14% 29% 23% 11%	490
	11th to 20th	Day	13% 6% 23% 28% 23% 8%	490
	21st to end	Day	16% 7% 20% 30% 20% 7%	539
November	1st to 10th	Day	21% 4 25% 29% 16% 5%	495
	11th to 20th	Day	17% 9% 34% 23% 14% 4	335
	21st to end	Day	13% 10% 31% 27% 14% 5%	300
December	1st to 10th	Day	23% 12% 32% 25% 7% 1	300
	11th to 20th	Day	19% 10% 30% 29% 10% 2	300
	21st to end	Day	26% 10% 31% 23% 8% 2	330
January	1st to 10th	Night	18% 10% 37% 29% 6%	800
	11th to 20th	Night	20% 11% 34% 31% 4	800
	21st to end	Night	18% 8% 41% 30% 3	880
February	1st to 10th	Night	19% 9% 35% 35% 3	800
	11th to 20th	Night	23% 12% 38% 24% 2	783
	21st to end	Night	18% 11% 39% 29% 3	660
March	1st to 10th	Night	18% 10% 34% 35% 4	800
	11th to 20th	Night	18% 11% 35% 28% 8%	800
	21st to end	Night	18% 9% 35% 31% 6%	880
April	1st to 10th	Night	16% 10% 35% 30% 9%	800
	11th to 20th	Night	15% 10% 30% 32% 13%	791
	21st to end	Night	15% 6% 26% 38% 15%	655
May	1st to 10th	Night	13% 6% 29% 36% 16% 1	600
	11th to 20th	Night	16% 5% 22% 33% 22% 2	591
	21st to end	Night	17% 2 11% 34% 32% 4	650
June	1st to 10th	Night	10% 3 14% 35% 35% 4	600
	11th to 20th	Night	12% 2 13% 31% 35% 7%	600
	21st to end	Night	7% 2 10% 34% 43% 5%	600
July	1st to 10th	Night	11% 1 9% 30% 42% 6%	585
	11th to 20th	Night	10% 2 4 29% 48% 8%	582
	21st to end	Night	8% 1 9% 31% 42% 9%	657
August	1st to 10th	Night	16% 2 8% 27% 40% 7%	579
	11th to 20th	Night	13% 2 8% 33% 37% 8%	564
	21st to end	Night	9% 2 9% 27% 45% 7%	771
September	1st to 10th	Night	11% 3 9% 31% 40% 7%	760
	11th to 20th	Night	17% 2 12% 26% 37% 6%	760
	21st to end	Night	20% 3 17% 31% 26% 3	760
October	1st to 10th	Night	17% 3 17% 30% 27% 6%	760
	11th to 20th	Night	17% 6% 23% 34% 19% 2	760
	21st to end	Night	14% 6% 23% 36% 19% 2	836
November	1st to 10th	Night	18% 6% 20% 38% 16% 2	780
	11th to 20th	Night	16% 6% 27% 38% 12% 1	800
	21st to end	Night	15% 6% 29% 37% 13% 1	800
December	1st to 10th	Night	20% 8% 33% 31% 8%	800
	11th to 20th	Night	20% 6% 30% 36% 8% 1	800
	21st to end	Night	24% 6% 27% 35% 8%	880

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