Liberty Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Liberty Lake clear sky chart from 2005-11-06 to 2025-09-19.

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	9% 6% 2 5% 4 3 4 3 5% 7% 53%	126342
	Night	9% 5% 2 4 3 3 3 3 5% 7% 57%	122999
Transparency	Day	32% 3 9% 26% 23% 7%	130046
	Night	28% 2 9% 26% 26% 9%	127358
Seeing	Day	12% 9% 27% 30% 18% 4	16634
	Night	12% 9% 32% 35% 12% 1	26426

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	10% 7% 4 8% 4 4 3 3 4 5% 47%	4077
	11th to 20th	Day	6% 5% 2 6% 3 3 2 2 4 5% 62%	4080
	21st to end	Day	14% 9% 4 4 2 2 3 2 3 4 52%	4488
February	1st to 10th	Day	11% 10% 3 6% 4 3 3 3 4 6% 47%	1873
	11th to 20th	Day	10% 8% 2 6% 3 4 4 3 4 5% 51%	1949
	21st to end	Day	11% 9% 3 5% 3 3 3 3 4 5% 52%	1650
March	1st to 10th	Day	10% 6% 2 4 3 3 3 2 4 5% 58%	4842
	11th to 20th	Day	7% 6% 2 5% 4 3 4 3 4 5% 56%	4980
	21st to end	Day	10% 10% 3 7% 4 4 4 4 5% 7% 43%	5462
April	1st to 10th	Day	10% 5% 2 5% 3 4 4 4 5% 7% 52%	2200
	11th to 20th	Day	13% 6% 2 6% 4 4 4 3 5% 6% 48%	2381
	21st to end	Day	16% 6% 2 5% 3 3 3 4 5% 6% 46%	2600
May	1st to 10th	Day	17% 7% 2 6% 4 4 4 3 5% 6% 41%	5862
	11th to 20th	Day	8% 5% 2 6% 4 4 4 3 5% 7% 53%	5862
	21st to end	Day	12% 8% 3 7% 5% 5% 5% 4 5% 6% 41%	6434
June	1st to 10th	Day	6% 5% 2 6% 4 4 4 4 8% 9% 50%	2600
	11th to 20th	Day	6% 3 2 4 4 3 5% 4 7% 9% 53%	2600
	21st to end	Day	4 4 1 3 3 3 5% 4 5% 8% 60%	2600
July	1st to 10th	Day	7% 5% 2 7% 4 5% 6% 5% 7% 9% 43%	5900
	11th to 20th	Day	5% 4 2 5% 4 4 4 4 6% 9% 53%	5900
	21st to end	Day	3 3 1 3 3 3 4 4 7% 10% 60%	6422
August	1st to 10th	Day	5% 3 2 4 3 4 4 4 6% 10% 55%	4234
	11th to 20th	Day	6% 4 2 4 3 4 5% 4 7% 8% 54%	4171
	21st to end	Day	4 3 1 4 3 4 4 3 5% 8% 61%	4386
September	1st to 10th	Day	9% 4 2 4 3 3 4 3 4 7% 56%	2200
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 3 6% 6% 49%	2178
	21st to end	Day	7% 4 1 4 3 4 4 2 4 6% 59%	2090
October	1st to 10th	Day	7% 5% 1 4 4 3 3 2 4 6% 62%	2048
	11th to 20th	Day	9% 3 1 3 2 2 3 2 3 5% 68%	1900
	21st to end	Day	11% 5% 2 5% 3 2 3 2 3 4 59%	2090
November	1st to 10th	Day	9% 5% 1 3 2 2 2 3 5% 6% 61%	1864
	11th to 20th	Day	7% 5% 1 4 2 2 2 2 4 5% 65%	1800
	21st to end	Day	11% 5% 2 4 3 2 3 2 4 6% 58%	1800
December	1st to 10th	Day	6% 6% 2 5% 3 3 2 2 3 6% 62%	2940
	11th to 20th	Day	8% 5% 2 5% 3 3 3 3 4 6% 59%	3391
	21st to end	Day	15% 10% 3 6% 4 3 4 3 4 5% 43%	4488
January	1st to 10th	Night	13% 7% 2 7% 4 3 3 3 5% 5% 49%	5888
	11th to 20th	Night	4 3 1 4 3 3 3 3 5% 7% 63%	5900
	21st to end	Night	15% 7% 2 4 2 3 3 2 4 5% 52%	6490
February	1st to 10th	Night	13% 8% 3 5% 3 3 3 2 3 5% 51%	2545
	11th to 20th	Night	11% 7% 2 5% 3 3 3 3 5% 6% 53%	2338
	21st to end	Night	11% 7% 2 5% 3 3 3 3 4 5% 55%	1980
March	1st to 10th	Night	9% 6% 2 5% 3 3 3 2 4 6% 57%	5014
	11th to 20th	Night	7% 4 1 3 2 2 2 3 4 6% 66%	4980
	21st to end	Night	8% 6% 2 6% 3 4 4 4 6% 8% 49%	5467
April	1st to 10th	Night	10% 5% 1 4 4 3 3 3 5% 6% 57%	2200
	11th to 20th	Night	13% 4 1 4 4 3 3 3 4 7% 53%	1963
	21st to end	Night	14% 6% 1 4 3 3 3 3 5% 6% 52%	1800
May	1st to 10th	Night	16% 7% 2 5% 3 4 3 3 5% 5% 46%	4053
	11th to 20th	Night	9% 4 1 4 3 4 5% 4 6% 8% 52%	4053
	21st to end	Night	10% 5% 1 4 4 3 4 3 5% 7% 53%	4443
June	1st to 10th	Night	6% 4 2 3 3 4 4 3 6% 10% 57%	1800
	11th to 20th	Night	4 4 1 4 4 4 4 3 6% 11% 55%	1800
	21st to end	Night	3 2 1 3 3 2 3 3 6% 11% 64%	1800
July	1st to 10th	Night	5% 4 2 5% 4 5% 5% 4 7% 10% 48%	4078
	11th to 20th	Night	4 3 1 4 3 3 4 4 6% 10% 59%	4077
	21st to end	Night	3 2 1 3 3 2 3 3 6% 10% 64%	4449
August	1st to 10th	Night	2 2 1 4 2 4 4 4 7% 10% 62%	2926
	11th to 20th	Night	5% 3 1 4 4 5% 5% 4 6% 9% 54%	2888
	21st to end	Night	2 3 1 3 3 3 4 4 6% 9% 62%	3514
September	1st to 10th	Night	8% 4 2 4 3 3 3 2 5% 6% 60%	2200
	11th to 20th	Night	10% 4 2 5% 4 3 3 3 4 7% 55%	2178
	21st to end	Night	7% 3 1 4 2 3 4 3 5% 5% 62%	2090
October	1st to 10th	Night	6% 3 1 4 3 4 3 3 4 6% 62%	2111
	11th to 20th	Night	8% 4 2 3 3 3 2 2 4 4 65%	2280
	21st to end	Night	11% 4 2 3 2 2 3 2 4 4 63%	2508
November	1st to 10th	Night	8% 4 2 3 2 2 2 2 4 5% 65%	2430
	11th to 20th	Night	7% 5% 2 4 3 2 3 2 3 5% 63%	2600
	21st to end	Night	10% 6% 2 4 3 3 3 3 4 6% 57%	2600
December	1st to 10th	Night	6% 4 1 4 2 2 3 2 3 7% 64%	4250
	11th to 20th	Night	9% 5% 2 5% 3 3 3 2 4 4 59%	4816
	21st to end	Night	14% 9% 2 5% 3 3 3 2 3 5% 51%	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	41% 1 10% 25% 20% 3	4078
	11th to 20th	Day	27% 1 9% 22% 34% 7%	4080
	21st to end	Day	39% 1 4 21% 30% 5%	4488
February	1st to 10th	Day	41% 2 8% 24% 21% 5%	1873
	11th to 20th	Day	38% 2 7% 27% 21% 5%	1959
	21st to end	Day	35% 2 4 22% 26% 10%	1650
March	1st to 10th	Day	32% 1 4 17% 22% 24%	4842
	11th to 20th	Day	32% 1 7% 18% 24% 17%	4980
	21st to end	Day	42% 2 9% 29% 16% 3	5464
April	1st to 10th	Day	33% 4 10% 26% 21% 7%	2200
	11th to 20th	Day	38% 3 9% 23% 20% 8%	2381
	21st to end	Day	39% 3 9% 27% 19% 3	2600
May	1st to 10th	Day	45% 3 10% 21% 17% 3	5900
	11th to 20th	Day	33% 2 11% 24% 22% 8%	5866
	21st to end	Day	45% 3 10% 18% 18% 6%	6447
June	1st to 10th	Day	29% 4 17% 30% 16% 4	2600
	11th to 20th	Day	27% 4 14% 29% 21% 5%	2600
	21st to end	Day	22% 5% 14% 28% 25% 7%	2600
July	1st to 10th	Day	35% 7% 13% 23% 19% 3	5836
	11th to 20th	Day	27% 4 11% 30% 25% 3	5831
	21st to end	Day	19% 5% 16% 38% 21% 1	6240
August	1st to 10th	Day	25% 5% 10% 29% 24% 8%	4220
	11th to 20th	Day	27% 5% 15% 32% 18% 3	4210
	21st to end	Day	23% 4 11% 41% 17% 4	4385
September	1st to 10th	Day	30% 4 7% 24% 26% 10%	2200
	11th to 20th	Day	35% 4 8% 24% 24% 6%	2178
	21st to end	Day	27% 3 7% 25% 31% 7%	2090
October	1st to 10th	Day	17% 1 6% 15% 46% 15%	3399
	11th to 20th	Day	16% 2 6% 24% 37% 16%	3140
	21st to end	Day	23% 2 6% 30% 31% 8%	3428
November	1st to 10th	Day	25% 3 7% 26% 28% 11%	1864
	11th to 20th	Day	24% 2 6% 29% 28% 11%	1800
	21st to end	Day	30% 1 6% 29% 26% 8%	1800
December	1st to 10th	Day	27% 1 7% 39% 24% 2	2940
	11th to 20th	Day	29% 1 5% 26% 32% 7%	3389
	21st to end	Day	45% 2 6% 25% 18% 5%	4488
January	1st to 10th	Night	39% 2 8% 28% 20% 3	5888
	11th to 20th	Night	23% 1 10% 22% 34% 9%	5900
	21st to end	Night	37% 1 6% 18% 31% 6%	6490
February	1st to 10th	Night	37% 2 8% 24% 22% 6%	2545
	11th to 20th	Night	34% 3 8% 26% 22% 7%	2338
	21st to end	Night	34% 2 4 20% 27% 12%	1980
March	1st to 10th	Night	31% 2 4 17% 26% 19%	5014
	11th to 20th	Night	23% 1 4 24% 22% 26%	4980
	21st to end	Night	34% 2 11% 30% 20% 3	5467
April	1st to 10th	Night	30% 2 10% 22% 24% 12%	2200
	11th to 20th	Night	32% 3 9% 26% 20% 11%	1963
	21st to end	Night	34% 3 10% 27% 22% 4	1800
May	1st to 10th	Night	41% 4 11% 19% 21% 4	4080
	11th to 20th	Night	30% 3 11% 24% 23% 9%	4054
	21st to end	Night	32% 4 13% 22% 20% 9%	4452
June	1st to 10th	Night	25% 4 19% 31% 18% 4	1800
	11th to 20th	Night	25% 3 13% 32% 21% 6%	1800
	21st to end	Night	17% 3 14% 33% 24% 9%	1800
July	1st to 10th	Night	30% 6% 18% 27% 16% 3	4035
	11th to 20th	Night	21% 4 10% 34% 27% 3	4026
	21st to end	Night	17% 3 15% 36% 26% 2	4320
August	1st to 10th	Night	17% 3 13% 31% 27% 8%	2916
	11th to 20th	Night	26% 3 12% 31% 22% 4	2915
	21st to end	Night	18% 5% 14% 37% 21% 5%	3514
September	1st to 10th	Night	26% 2 8% 27% 25% 12%	2200
	11th to 20th	Night	31% 3 8% 22% 26% 9%	2178
	21st to end	Night	25% 2 7% 24% 33% 9%	2090
October	1st to 10th	Night	16% 2 6% 13% 40% 23%	3527
	11th to 20th	Night	16% 1 4 21% 39% 19%	3779
	21st to end	Night	20% 2 5% 28% 35% 10%	4120
November	1st to 10th	Night	23% 2 9% 23% 31% 13%	2430
	11th to 20th	Night	27% 1 6% 24% 31% 11%	2600
	21st to end	Night	30% 2 7% 23% 29% 10%	2600
December	1st to 10th	Night	23% 2 8% 40% 24% 4	4250
	11th to 20th	Night	30% 2 5% 24% 31% 8%	4817
	21st to end	Night	39% 1 5% 27% 21% 6%	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	16% 14% 35% 26% 8%	300
	11th to 20th	Day	19% 19% 36% 23% 3 1	300
	21st to end	Day	13% 14% 44% 24% 4 1	330
February	1st to 10th	Day	18% 18% 40% 20% 5%	300
	11th to 20th	Day	19% 17% 47% 16% 2	300
	21st to end	Day	19% 22% 38% 16% 3	249
March	1st to 10th	Day	16% 20% 37% 22% 5%	300
	11th to 20th	Day	23% 20% 35% 18% 3	300
	21st to end	Day	18% 20% 39% 18% 5% 1	330
April	1st to 10th	Day	17% 18% 38% 20% 7%	300
	11th to 20th	Day	19% 19% 40% 19% 3	499
	21st to end	Day	21% 14% 35% 21% 8% 2	700
May	1st to 10th	Day	14% 13% 38% 27% 8% 1	703
	11th to 20th	Day	14% 12% 31% 27% 13% 2	725
	21st to end	Day	15% 7% 32% 26% 16% 4	789
June	1st to 10th	Day	8% 5% 20% 38% 24% 6%	730
	11th to 20th	Day	7% 3 26% 43% 18% 3	730
	21st to end	Day	5% 2 24% 44% 22% 5%	730
July	1st to 10th	Day	6% 2 13% 34% 34% 10%	721
	11th to 20th	Day	3 1 13% 41% 35% 8%	718
	21st to end	Day	6% 1 8% 37% 37% 11%	794
August	1st to 10th	Day	6% 1 12% 46% 29% 7%	726
	11th to 20th	Day	7% 2 13% 36% 33% 9%	715
	21st to end	Day	7% 2 11% 34% 37% 10%	631
September	1st to 10th	Day	9% 2 12% 35% 32% 11%	330
	11th to 20th	Day	6% 4 13% 37% 33% 8%	324
	21st to end	Day	10% 5% 15% 40% 22% 8%	300
October	1st to 10th	Day	7% 4 29% 33% 17% 10%	300
	11th to 20th	Day	9% 11% 34% 32% 14% 1	300
	21st to end	Day	21% 9% 31% 25% 9% 4	330
November	1st to 10th	Day	13% 9% 37% 30% 9% 2	300
	11th to 20th	Day	13% 14% 37% 23% 12% 2	300
	21st to end	Day	15% 15% 41% 22% 6% 1	300
December	1st to 10th	Day	12% 11% 45% 20% 11% 1	300
	11th to 20th	Day	17% 12% 43% 19% 8% 1	300
	21st to end	Day	17% 21% 35% 23% 4	330
January	1st to 10th	Night	12% 11% 40% 30% 7%	1000
	11th to 20th	Night	13% 13% 38% 30% 5%	1000
	21st to end	Night	13% 11% 38% 33% 5%	1100
February	1st to 10th	Night	17% 12% 40% 27% 3	945
	11th to 20th	Night	16% 16% 39% 26% 3	784
	21st to end	Night	18% 14% 38% 27% 3	660
March	1st to 10th	Night	12% 13% 40% 31% 4	647
	11th to 20th	Night	19% 13% 37% 27% 4	600
	21st to end	Night	16% 15% 38% 25% 6%	660
April	1st to 10th	Night	14% 15% 42% 24% 5%	600
	11th to 20th	Night	15% 14% 42% 25% 4	593
	21st to end	Night	17% 12% 38% 27% 7% 1	600
May	1st to 10th	Night	12% 10% 42% 29% 7%	600
	11th to 20th	Night	12% 7% 35% 30% 14% 1	591
	21st to end	Night	10% 7% 33% 34% 16% 1	650
June	1st to 10th	Night	8% 3 23% 45% 19% 2	600
	11th to 20th	Night	6% 4 31% 46% 13% 1	600
	21st to end	Night	4 1 28% 47% 18% 3	600
July	1st to 10th	Night	5% 1 15% 47% 29% 2	585
	11th to 20th	Night	4 1 15% 50% 29% 2	582
	21st to end	Night	4 1 11% 51% 31% 2	657
August	1st to 10th	Night	3 1 14% 51% 29% 3	597
	11th to 20th	Night	6% 1 14% 46% 31% 2	594
	21st to end	Night	4 2 10% 45% 37% 3	660
September	1st to 10th	Night	9% 2 16% 46% 25% 2	600
	11th to 20th	Night	12% 2 21% 40% 23% 3	594
	21st to end	Night	9% 4 22% 44% 18% 4	570
October	1st to 10th	Night	8% 3 29% 37% 20% 3	591
	11th to 20th	Night	12% 6% 37% 35% 9% 1	760
	21st to end	Night	14% 11% 32% 30% 12% 1	836
November	1st to 10th	Night	11% 6% 38% 33% 11% 1	870
	11th to 20th	Night	10% 12% 37% 32% 8%	1000
	21st to end	Night	15% 11% 34% 31% 8%	1000
December	1st to 10th	Night	12% 10% 37% 34% 7%	1000
	11th to 20th	Night	16% 11% 39% 28% 6%	1000
	21st to end	Night	15% 14% 34% 32% 5%	1100

Page generated at 2025-09-16 00:49:16. Version ac07

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