Lewis County Fairgrounds
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lewis County Fairgrounds clear sky chart from 2005-11-06 to 2026-05-17.

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% 12% 4 10% 6% 5% 5% 4 5% 6% 29%	132183
	Night	13% 12% 5% 12% 7% 5% 5% 4 5% 6% 27%	130603
Transparency	Day	53% 8% 11% 18% 9% 1	135661
	Night	55% 8% 11% 16% 8% 1	135212
Seeing	Day	23% 21% 30% 16% 7% 2	16497
	Night	21% 20% 30% 21% 7% 1	25723

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	9% 17% 8% 25% 10% 6% 4 3 3 3 13%	4661
	11th to 20th	Day	7% 20% 9% 20% 13% 6% 5% 3 4 3 10%	4650
	21st to end	Day	8% 15% 7% 17% 11% 10% 7% 4 4 4 14%	5482
February	1st to 10th	Day	12% 16% 6% 17% 10% 7% 5% 4 4 4 15%	1890
	11th to 20th	Day	9% 17% 7% 15% 10% 6% 5% 2 4 3 21%	1898
	21st to end	Day	12% 19% 6% 14% 8% 5% 4 4 4 5% 19%	1730
March	1st to 10th	Day	16% 14% 6% 13% 6% 5% 4 3 4 5% 25%	4576
	11th to 20th	Day	8% 18% 6% 9% 6% 5% 5% 4 5% 5% 30%	5079
	21st to end	Day	12% 12% 5% 12% 7% 5% 4 3 4 4 31%	5913
April	1st to 10th	Day	16% 16% 4 8% 5% 4 4 2 5% 5% 30%	2520
	11th to 20th	Day	15% 13% 3 8% 5% 5% 4 4 5% 5% 33%	2494
	21st to end	Day	18% 13% 3 8% 5% 4 4 3 5% 7% 31%	2556
May	1st to 10th	Day	25% 12% 4 8% 5% 5% 4 3 4 5% 25%	6486
	11th to 20th	Day	14% 10% 4 9% 6% 6% 6% 4 6% 7% 29%	6402
	21st to end	Day	18% 10% 3 7% 5% 5% 5% 4 5% 7% 31%	6949
June	1st to 10th	Day	19% 8% 3 7% 5% 4 5% 5% 6% 8% 30%	2800
	11th to 20th	Day	15% 8% 3 6% 4 4 5% 5% 7% 8% 35%	2800
	21st to end	Day	16% 7% 3 7% 5% 5% 5% 4 6% 7% 33%	2800
July	1st to 10th	Day	10% 5% 3 7% 5% 5% 6% 4 8% 10% 37%	6360
	11th to 20th	Day	7% 5% 2 7% 5% 6% 7% 5% 8% 9% 38%	6360
	21st to end	Day	11% 5% 2 6% 4 5% 5% 5% 7% 8% 42%	6926
August	1st to 10th	Day	14% 7% 2 6% 5% 4 5% 4 6% 8% 38%	4413
	11th to 20th	Day	13% 7% 3 8% 5% 5% 6% 5% 7% 8% 34%	4028
	21st to end	Day	13% 7% 2 6% 5% 5% 4 4 6% 9% 38%	4312
September	1st to 10th	Day	13% 6% 2 6% 5% 4 6% 4 6% 8% 41%	2400
	11th to 20th	Day	12% 6% 2 7% 4 4 4 4 6% 7% 44%	2385
	21st to end	Day	17% 7% 2 6% 4 5% 5% 4 6% 7% 36%	2161
October	1st to 10th	Day	19% 10% 4 7% 5% 4 4 3 5% 5% 34%	2000
	11th to 20th	Day	19% 11% 3 8% 4 4 6% 4 6% 6% 28%	2000
	21st to end	Day	23% 14% 3 7% 4 4 6% 4 4 6% 25%	2055
November	1st to 10th	Day	13% 16% 4 10% 6% 5% 4 4 5% 5% 28%	1851
	11th to 20th	Day	11% 18% 4 10% 6% 6% 5% 4 5% 5% 28%	1772
	21st to end	Day	14% 19% 7% 12% 7% 6% 5% 3 4 4 19%	1680
December	1st to 10th	Day	10% 20% 9% 20% 8% 5% 5% 3 4 4 11%	2680
	11th to 20th	Day	14% 19% 10% 15% 7% 5% 4 3 4 5% 14%	3066
	21st to end	Day	14% 15% 8% 15% 7% 4 5% 4 5% 6% 19%	4048
January	1st to 10th	Night	9% 17% 10% 22% 9% 6% 4 3 3 3 15%	8234
	11th to 20th	Night	7% 17% 10% 27% 11% 7% 5% 3 3 3 7%	8235
	21st to end	Night	10% 13% 6% 17% 10% 9% 7% 4 5% 5% 14%	8682
February	1st to 10th	Night	10% 17% 7% 17% 9% 7% 5% 3 5% 4 17%	2730
	11th to 20th	Night	9% 14% 8% 15% 9% 7% 5% 4 4 5% 21%	2607
	21st to end	Night	11% 14% 5% 13% 9% 5% 5% 4 6% 7% 21%	2076
March	1st to 10th	Night	14% 11% 5% 13% 8% 6% 5% 3 4 5% 25%	5484
	11th to 20th	Night	11% 15% 6% 9% 5% 4 4 4 5% 6% 30%	5098
	21st to end	Night	16% 13% 5% 12% 6% 5% 5% 3 4 4 26%	5260
April	1st to 10th	Night	16% 14% 5% 9% 5% 4 4 3 4 5% 32%	2100
	11th to 20th	Night	16% 13% 4 7% 4 4 4 3 5% 5% 34%	2075
	21st to end	Night	17% 10% 2 7% 4 4 5% 4 5% 6% 35%	2071
May	1st to 10th	Night	26% 13% 4 7% 5% 5% 4 3 5% 5% 22%	3680
	11th to 20th	Night	13% 10% 3 9% 5% 4 4 3 5% 7% 35%	3623
	21st to end	Night	16% 9% 3 9% 6% 6% 4 4 5% 6% 33%	3926
June	1st to 10th	Night	16% 8% 2 6% 4 4 5% 5% 6% 7% 37%	1600
	11th to 20th	Night	15% 5% 3 6% 5% 4 5% 5% 6% 8% 39%	1600
	21st to end	Night	13% 8% 3 7% 5% 5% 4 4 7% 8% 37%	1600
July	1st to 10th	Night	9% 6% 2 7% 5% 5% 6% 5% 6% 10% 41%	3600
	11th to 20th	Night	11% 5% 2 7% 5% 5% 4 5% 5% 8% 44%	3600
	21st to end	Night	8% 6% 2 7% 4 4 4 4 5% 8% 49%	3926
August	1st to 10th	Night	12% 8% 2 6% 5% 4 5% 4 5% 8% 42%	2732
	11th to 20th	Night	11% 6% 3 8% 5% 5% 5% 4 6% 8% 38%	2974
	21st to end	Night	8% 6% 2 7% 4 4 5% 5% 7% 8% 44%	3586
September	1st to 10th	Night	12% 6% 2 6% 4 4 5% 4 5% 7% 45%	2000
	11th to 20th	Night	11% 6% 2 5% 4 4 3 3 4 7% 50%	2014
	21st to end	Night	15% 7% 3 6% 4 4 4 3 6% 8% 40%	2235
October	1st to 10th	Night	19% 10% 3 7% 5% 4 4 3 5% 6% 34%	2400
	11th to 20th	Night	17% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	2400
	21st to end	Night	21% 13% 3 9% 6% 5% 5% 3 5% 5% 26%	2784
November	1st to 10th	Night	14% 14% 3 9% 6% 5% 5% 4 5% 5% 31%	2667
	11th to 20th	Night	13% 14% 5% 10% 6% 5% 4 4 5% 7% 28%	2846
	21st to end	Night	13% 18% 7% 12% 7% 6% 5% 3 5% 5% 19%	2940
December	1st to 10th	Night	10% 19% 8% 19% 9% 7% 5% 4 4 4 11%	4720
	11th to 20th	Night	15% 18% 7% 15% 8% 6% 4 3 4 3 17%	5348
	21st to end	Night	15% 18% 7% 15% 6% 6% 5% 3 4 5% 17%	7150

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	74% 7% 6% 9% 3	4662
	11th to 20th	Day	74% 8% 5% 5% 5% 2	4680
	21st to end	Day	68% 9% 9% 9% 4 1	5482
February	1st to 10th	Day	72% 6% 7% 11% 4 1	1890
	11th to 20th	Day	67% 6% 7% 12% 7% 1	1907
	21st to end	Day	66% 7% 9% 11% 6%	1730
March	1st to 10th	Day	59% 7% 11% 11% 10% 2	4579
	11th to 20th	Day	55% 7% 17% 12% 7% 2	5079
	21st to end	Day	55% 5% 8% 15% 15% 1	5913
April	1st to 10th	Day	57% 6% 8% 17% 11% 2	2520
	11th to 20th	Day	51% 8% 8% 19% 13% 1	2494
	21st to end	Day	54% 7% 9% 17% 12% 2	2556
May	1st to 10th	Day	60% 6% 8% 16% 8% 1	6497
	11th to 20th	Day	51% 10% 11% 18% 9% 1	6406
	21st to end	Day	50% 8% 12% 21% 8% 1	6949
June	1st to 10th	Day	51% 8% 11% 18% 11% 1	2800
	11th to 20th	Day	45% 8% 12% 23% 9% 1	2800
	21st to end	Day	48% 9% 13% 19% 10% 1	2800
July	1st to 10th	Day	37% 9% 17% 25% 12%	6290
	11th to 20th	Day	36% 12% 16% 25% 11%	6285
	21st to end	Day	36% 9% 14% 32% 9%	6728
August	1st to 10th	Day	42% 9% 15% 21% 12% 1	4399
	11th to 20th	Day	43% 10% 17% 24% 6%	4067
	21st to end	Day	41% 9% 14% 28% 7% 1	4312
September	1st to 10th	Day	41% 8% 12% 27% 12% 1	2400
	11th to 20th	Day	39% 6% 11% 28% 14% 1	2385
	21st to end	Day	46% 8% 11% 23% 11% 1	2161
October	1st to 10th	Day	45% 7% 12% 27% 9%	3260
	11th to 20th	Day	47% 7% 14% 19% 12% 1	3240
	21st to end	Day	47% 7% 15% 23% 6% 1	3293
November	1st to 10th	Day	58% 7% 11% 15% 8%	1851
	11th to 20th	Day	58% 7% 11% 13% 9% 3	1772
	21st to end	Day	69% 7% 12% 8% 4	1680
December	1st to 10th	Day	74% 9% 9% 6% 2	2680
	11th to 20th	Day	70% 10% 7% 10% 2	3066
	21st to end	Day	66% 7% 9% 10% 9%	4048
January	1st to 10th	Night	71% 8% 8% 8% 4	8234
	11th to 20th	Night	77% 9% 6% 5% 3 1	8280
	21st to end	Night	63% 10% 11% 9% 6% 1	8682
February	1st to 10th	Night	71% 7% 7% 10% 5%	2730
	11th to 20th	Night	65% 7% 8% 13% 6%	2609
	21st to end	Night	60% 8% 12% 14% 6% 1	2076
March	1st to 10th	Night	58% 8% 10% 12% 10% 2	5494
	11th to 20th	Night	53% 8% 16% 15% 6% 3	5099
	21st to end	Night	58% 6% 7% 17% 9% 1	5260
April	1st to 10th	Night	55% 7% 10% 17% 9% 1	2100
	11th to 20th	Night	52% 8% 10% 18% 12% 1	2075
	21st to end	Night	49% 7% 10% 19% 14% 2	2071
May	1st to 10th	Night	63% 7% 8% 13% 8% 1	3686
	11th to 20th	Night	46% 9% 14% 21% 10% 1	3624
	21st to end	Night	49% 9% 12% 18% 12% 1	3927
June	1st to 10th	Night	45% 9% 14% 21% 10% 1	1600
	11th to 20th	Night	42% 9% 14% 21% 13% 2	1600
	21st to end	Night	43% 9% 13% 23% 12%	1600
July	1st to 10th	Night	37% 8% 18% 23% 14% 1	3560
	11th to 20th	Night	35% 10% 15% 24% 15% 1	3552
	21st to end	Night	32% 8% 13% 35% 11% 1	3809
August	1st to 10th	Night	38% 9% 17% 27% 9% 1	2722
	11th to 20th	Night	42% 9% 15% 27% 7%	3001
	21st to end	Night	33% 11% 14% 33% 8% 1	3586
September	1st to 10th	Night	36% 9% 13% 29% 11% 1	2000
	11th to 20th	Night	35% 6% 13% 32% 14% 1	2014
	21st to end	Night	43% 8% 12% 24% 13% 1	2235
October	1st to 10th	Night	44% 9% 11% 25% 11% 1	3920
	11th to 20th	Night	44% 7% 14% 22% 11% 2	3899
	21st to end	Night	49% 9% 13% 23% 6% 1	4496
November	1st to 10th	Night	53% 8% 11% 17% 8% 2	2667
	11th to 20th	Night	57% 8% 11% 15% 7% 2	2846
	21st to end	Night	67% 9% 9% 12% 3	2940
December	1st to 10th	Night	72% 10% 10% 7% 2	4720
	11th to 20th	Night	69% 8% 8% 11% 5%	5348
	21st to end	Night	70% 6% 7% 7% 8% 1	7150

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	26% 27% 31% 11% 3 1	220
	11th to 20th	Day	29% 31% 30% 8% 1 1	220
	21st to end	Day	24% 29% 33% 12% 2	308
February	1st to 10th	Day	35% 28% 32% 5% 1	330
	11th to 20th	Day	31% 34% 29% 5%	385
	21st to end	Day	33% 28% 32% 7% 1	446
March	1st to 10th	Day	27% 28% 31% 11% 3	540
	11th to 20th	Day	32% 26% 30% 10% 2	540
	21st to end	Day	32% 26% 27% 10% 4 1	594
April	1st to 10th	Day	36% 26% 22% 12% 4	540
	11th to 20th	Day	34% 24% 22% 12% 6% 2	532
	21st to end	Day	29% 25% 28% 11% 5% 1	540
May	1st to 10th	Day	29% 25% 28% 11% 6% 1	543
	11th to 20th	Day	21% 19% 33% 20% 5% 1	551
	21st to end	Day	20% 18% 33% 18% 10% 1	573
June	1st to 10th	Day	24% 19% 30% 22% 5% 1	530
	11th to 20th	Day	17% 19% 34% 19% 8% 2	530
	21st to end	Day	19% 20% 35% 20% 6% 1	530
July	1st to 10th	Day	11% 13% 37% 23% 13% 3	525
	11th to 20th	Day	11% 13% 34% 27% 13% 2	524
	21st to end	Day	13% 12% 40% 27% 7% 1	576
August	1st to 10th	Day	12% 12% 29% 30% 12% 5%	526
	11th to 20th	Day	15% 11% 29% 28% 13% 5%	519
	21st to end	Day	16% 15% 31% 22% 13% 4	583
September	1st to 10th	Day	15% 16% 27% 24% 12% 6%	530
	11th to 20th	Day	12% 12% 26% 21% 18% 11%	530
	21st to end	Day	18% 17% 30% 21% 11% 3	530
October	1st to 10th	Day	23% 18% 27% 17% 12% 3	530
	11th to 20th	Day	22% 28% 30% 14% 5% 1	530
	21st to end	Day	31% 22% 28% 17% 2	503
November	1st to 10th	Day	28% 25% 28% 14% 4	425
	11th to 20th	Day	27% 29% 27% 13% 3 1	312
	21st to end	Day	30% 26% 36% 7%	220
December	1st to 10th	Day	35% 28% 25% 11% 1	220
	11th to 20th	Day	32% 32% 28% 6% 1	220
	21st to end	Day	29% 33% 29% 8% 1	242
January	1st to 10th	Night	24% 30% 32% 12% 2	840
	11th to 20th	Night	21% 33% 30% 13% 3	840
	21st to end	Night	17% 29% 34% 17% 3	924
February	1st to 10th	Night	23% 26% 36% 15% 1	840
	11th to 20th	Night	22% 29% 34% 13% 2	823
	21st to end	Night	24% 27% 32% 15% 2	692
March	1st to 10th	Night	24% 25% 33% 15% 2	840
	11th to 20th	Night	27% 26% 27% 17% 2	840
	21st to end	Night	24% 25% 30% 15% 5%	924
April	1st to 10th	Night	26% 23% 31% 18% 1	840
	11th to 20th	Night	25% 23% 29% 17% 5% 1	831
	21st to end	Night	26% 18% 30% 21% 5%	811
May	1st to 10th	Night	26% 14% 29% 25% 6% 1	426
	11th to 20th	Night	16% 17% 33% 27% 6%	406
	21st to end	Night	15% 9% 36% 30% 10% 1	433
June	1st to 10th	Night	18% 12% 30% 32% 7% 1	400
	11th to 20th	Night	16% 11% 29% 33% 12%	400
	21st to end	Night	16% 10% 35% 32% 7%	400
July	1st to 10th	Night	7% 9% 30% 43% 12% 1	390
	11th to 20th	Night	11% 7% 28% 37% 17% 1	388
	21st to end	Night	10% 6% 32% 40% 11% 1	438
August	1st to 10th	Night	13% 8% 24% 39% 15% 1	479
	11th to 20th	Night	14% 5% 24% 33% 22% 2	654
	21st to end	Night	12% 8% 29% 36% 15% 1	880
September	1st to 10th	Night	14% 11% 28% 30% 16% 2	800
	11th to 20th	Night	15% 7% 23% 30% 20% 4	800
	21st to end	Night	18% 13% 27% 25% 16% 1	800
October	1st to 10th	Night	24% 15% 26% 21% 14% 1	800
	11th to 20th	Night	22% 19% 29% 23% 7% 1	800
	21st to end	Night	29% 20% 31% 18% 2	880
November	1st to 10th	Night	25% 19% 32% 19% 5%	820
	11th to 20th	Night	24% 24% 30% 16% 5% 1	840
	21st to end	Night	26% 29% 27% 16% 3	840
December	1st to 10th	Night	26% 28% 31% 12% 2	840
	11th to 20th	Night	27% 28% 30% 12% 2 1	840
	21st to end	Night	29% 29% 29% 11% 2	924

Page generated at 2026-05-14 01:59:00. Version ac07

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