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 2025-01-22.

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	14% 12% 4 10% 6% 5% 5% 4 6% 7% 29%	105272
	Night	13% 13% 5% 11% 6% 5% 5% 4 5% 5% 28%	104084
Transparency	Day	53% 8% 12% 19% 8% 1	108768
	Night	56% 8% 10% 17% 8% 1	108677
Seeing	Day	23% 21% 30% 17% 7% 2	14796
	Night	21% 20% 30% 21% 7% 1	24046

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	10% 21% 9% 20% 8% 5% 4 3 3 3 15%	2597
	11th to 20th	Day	10% 21% 8% 19% 13% 5% 4 3 4 3 11%	2600
	21st to end	Day	11% 21% 8% 15% 8% 8% 6% 4 5% 4 12%	2972
February	1st to 10th	Day	12% 17% 5% 17% 10% 7% 5% 4 4 4 15%	1710
	11th to 20th	Day	9% 17% 7% 15% 10% 6% 5% 2 4 3 22%	1712
	21st to end	Day	13% 18% 6% 14% 8% 4 4 3 4 5% 20%	1570
March	1st to 10th	Day	19% 15% 6% 11% 5% 4 3 3 4 6% 24%	3116
	11th to 20th	Day	9% 22% 7% 10% 5% 5% 4 3 4 5% 26%	3470
	21st to end	Day	12% 11% 5% 10% 7% 4 4 2 5% 5% 35%	4037
April	1st to 10th	Day	16% 16% 4 8% 5% 4 3 3 5% 5% 31%	2280
	11th to 20th	Day	15% 13% 3 7% 5% 4 4 4 5% 5% 34%	2254
	21st to end	Day	18% 13% 3 8% 5% 4 4 3 5% 7% 31%	2313
May	1st to 10th	Day	20% 11% 4 7% 4 5% 4 4 5% 6% 31%	4426
	11th to 20th	Day	14% 9% 4 8% 6% 6% 5% 4 7% 8% 30%	4398
	21st to end	Day	12% 7% 2 6% 5% 5% 6% 4 6% 8% 39%	4837
June	1st to 10th	Day	20% 8% 3 7% 5% 4 5% 5% 6% 8% 29%	2660
	11th to 20th	Day	16% 8% 3 6% 4 4 5% 5% 7% 8% 35%	2660
	21st to end	Day	17% 7% 3 7% 6% 5% 5% 4 6% 7% 32%	2660
July	1st to 10th	Day	11% 5% 2 6% 5% 5% 6% 4 8% 10% 38%	4440
	11th to 20th	Day	8% 5% 2 7% 5% 5% 6% 5% 8% 10% 37%	4440
	21st to end	Day	10% 6% 2 7% 5% 6% 5% 5% 8% 9% 38%	4814
August	1st to 10th	Day	15% 7% 3 6% 5% 5% 5% 4 6% 8% 37%	4278
	11th to 20th	Day	13% 7% 3 8% 5% 5% 6% 5% 7% 8% 34%	3902
	21st to end	Day	13% 7% 3 7% 5% 5% 4 4 6% 9% 38%	4180
September	1st to 10th	Day	13% 6% 2 6% 5% 4 6% 4 6% 8% 40%	2280
	11th to 20th	Day	13% 6% 3 8% 4 4 4 4 6% 7% 42%	2266
	21st to end	Day	17% 7% 2 6% 4 5% 5% 5% 6% 7% 36%	2053
October	1st to 10th	Day	20% 10% 4 7% 6% 4 4 3 5% 5% 32%	1900
	11th to 20th	Day	19% 12% 3 8% 4 4 6% 4 6% 6% 28%	1900
	21st to end	Day	23% 14% 3 7% 4 4 6% 4 4 6% 25%	1952
November	1st to 10th	Day	13% 15% 4 9% 7% 5% 4 4 5% 5% 29%	1761
	11th to 20th	Day	11% 16% 4 10% 6% 6% 5% 4 5% 6% 28%	1688
	21st to end	Day	14% 19% 7% 12% 7% 6% 4 3 4 5% 19%	1600
December	1st to 10th	Day	10% 20% 9% 21% 9% 5% 5% 3 4 4 10%	2600
	11th to 20th	Day	14% 19% 10% 15% 7% 5% 4 3 4 5% 14%	2986
	21st to end	Day	14% 15% 7% 14% 7% 4 5% 4 5% 6% 19%	3960
January	1st to 10th	Night	11% 20% 11% 18% 7% 5% 4 3 3 3 15%	4569
	11th to 20th	Night	8% 16% 10% 26% 10% 6% 4 3 3 3 10%	4580
	21st to end	Night	15% 18% 8% 18% 7% 7% 4 3 4 3 14%	4704
February	1st to 10th	Night	10% 18% 7% 17% 10% 7% 5% 3 5% 3 16%	2470
	11th to 20th	Night	9% 14% 8% 15% 9% 7% 5% 4 4 5% 21%	2353
	21st to end	Night	12% 14% 5% 11% 8% 5% 5% 4 6% 7% 22%	1884
March	1st to 10th	Night	16% 11% 6% 11% 6% 5% 4 3 4 6% 27%	3724
	11th to 20th	Night	13% 20% 7% 10% 5% 4 4 4 5% 4 24%	3488
	21st to end	Night	14% 13% 5% 10% 5% 4 5% 3 4 5% 32%	3594
April	1st to 10th	Night	16% 14% 5% 9% 6% 4 4 3 4 5% 32%	1900
	11th to 20th	Night	16% 13% 4 7% 4 5% 4 3 6% 5% 33%	1875
	21st to end	Night	17% 11% 2 7% 4 4 5% 4 5% 6% 34%	1874
May	1st to 10th	Night	20% 12% 3 7% 4 5% 5% 4 6% 5% 28%	2520
	11th to 20th	Night	16% 11% 3 7% 5% 4 4 3 5% 6% 34%	2495
	21st to end	Night	12% 7% 3 7% 5% 5% 4 4 6% 8% 40%	2738
June	1st to 10th	Night	16% 7% 2 5% 4 4 5% 5% 6% 7% 37%	1520
	11th to 20th	Night	15% 5% 2 5% 5% 4 5% 5% 6% 8% 40%	1520
	21st to end	Night	13% 8% 3 7% 5% 5% 4 4 7% 8% 36%	1520
July	1st to 10th	Night	9% 6% 3 7% 5% 5% 6% 5% 6% 8% 41%	2520
	11th to 20th	Night	10% 5% 2 6% 5% 5% 4 5% 6% 8% 44%	2520
	21st to end	Night	9% 6% 3 7% 4 4 4 4 5% 8% 46%	2739
August	1st to 10th	Night	12% 8% 2 6% 5% 4 5% 4 5% 8% 41%	2648
	11th to 20th	Night	11% 6% 3 8% 5% 5% 5% 4 6% 8% 37%	2881
	21st to end	Night	8% 6% 2 7% 4 5% 5% 5% 7% 8% 44%	3476
September	1st to 10th	Night	13% 7% 2 6% 4 4 5% 4 5% 7% 44%	1900
	11th to 20th	Night	12% 6% 2 6% 4 4 3 3 4 7% 50%	1913
	21st to end	Night	15% 7% 3 7% 4 4 5% 4 6% 7% 40%	2123
October	1st to 10th	Night	19% 10% 3 8% 5% 5% 4 4 5% 6% 32%	2280
	11th to 20th	Night	18% 9% 3 8% 5% 5% 5% 3 6% 7% 33%	2280
	21st to end	Night	22% 13% 3 9% 6% 5% 5% 3 5% 5% 24%	2645
November	1st to 10th	Night	14% 14% 3 9% 6% 5% 5% 4 5% 5% 31%	2537
	11th to 20th	Night	13% 14% 4 10% 5% 5% 4 4 5% 7% 28%	2710
	21st to end	Night	13% 18% 7% 12% 7% 5% 5% 4 5% 5% 20%	2800
December	1st to 10th	Night	11% 20% 8% 19% 9% 7% 5% 4 4 4 10%	4580
	11th to 20th	Night	15% 18% 7% 15% 7% 5% 4 3 4 3 17%	5208
	21st to end	Night	15% 18% 7% 15% 6% 6% 5% 3 4 5% 17%	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	74% 6% 6% 10% 3	2598
	11th to 20th	Day	79% 6% 5% 5% 4 1	2600
	21st to end	Day	76% 7% 7% 6% 3 1	2972
February	1st to 10th	Day	74% 5% 6% 10% 3 1	1710
	11th to 20th	Day	68% 5% 7% 12% 7% 1	1721
	21st to end	Day	66% 7% 8% 12% 7%	1570
March	1st to 10th	Day	62% 5% 11% 12% 9% 1	3119
	11th to 20th	Day	60% 7% 13% 11% 7% 1	3470
	21st to end	Day	52% 4 9% 19% 13% 2	4037
April	1st to 10th	Day	57% 5% 8% 18% 11% 2	2280
	11th to 20th	Day	50% 8% 8% 20% 13% 1	2254
	21st to end	Day	54% 7% 9% 16% 11% 3	2313
May	1st to 10th	Day	53% 7% 10% 20% 10% 1	4440
	11th to 20th	Day	50% 10% 12% 20% 7% 1	4402
	21st to end	Day	40% 9% 14% 25% 11% 1	4837
June	1st to 10th	Day	52% 8% 12% 17% 11%	2660
	11th to 20th	Day	45% 8% 12% 23% 10% 1	2660
	21st to end	Day	49% 9% 13% 19% 9% 1	2660
July	1st to 10th	Day	37% 9% 16% 26% 11%	4370
	11th to 20th	Day	36% 12% 17% 27% 9%	4365
	21st to end	Day	40% 10% 15% 25% 9%	4661
August	1st to 10th	Day	43% 9% 15% 21% 11% 1	4264
	11th to 20th	Day	44% 10% 17% 23% 6%	3941
	21st to end	Day	42% 9% 14% 28% 7% 1	4180
September	1st to 10th	Day	42% 8% 12% 25% 12% 1	2280
	11th to 20th	Day	41% 7% 11% 27% 14% 1	2266
	21st to end	Day	46% 8% 11% 23% 11% 1	2053
October	1st to 10th	Day	46% 8% 12% 26% 8%	3160
	11th to 20th	Day	47% 7% 14% 19% 12%	3140
	21st to end	Day	48% 7% 15% 23% 6% 1	3190
November	1st to 10th	Day	58% 7% 11% 15% 8% 1	1761
	11th to 20th	Day	57% 7% 11% 13% 9% 3	1688
	21st to end	Day	69% 7% 12% 8% 4	1600
December	1st to 10th	Day	74% 9% 9% 5% 2	2600
	11th to 20th	Day	71% 10% 6% 10% 2	2986
	21st to end	Day	66% 7% 9% 10% 9%	3960
January	1st to 10th	Night	75% 7% 6% 9% 4	4569
	11th to 20th	Night	80% 6% 5% 5% 3 1	4580
	21st to end	Night	75% 6% 6% 8% 5% 1	4704
February	1st to 10th	Night	73% 7% 7% 9% 4	2470
	11th to 20th	Night	66% 7% 7% 14% 6%	2355
	21st to end	Night	60% 7% 12% 14% 6% 1	1884
March	1st to 10th	Night	58% 7% 10% 15% 9% 1	3734
	11th to 20th	Night	62% 8% 10% 15% 6%	3489
	21st to end	Night	55% 4 7% 19% 12% 2	3594
April	1st to 10th	Night	55% 7% 10% 18% 9% 1	1900
	11th to 20th	Night	52% 8% 9% 18% 12% 1	1875
	21st to end	Night	50% 7% 10% 17% 13% 2	1874
May	1st to 10th	Night	55% 8% 10% 15% 10% 1	2526
	11th to 20th	Night	49% 8% 13% 20% 9% 1	2496
	21st to end	Night	41% 8% 13% 21% 16% 1	2739
June	1st to 10th	Night	45% 9% 14% 21% 9% 1	1520
	11th to 20th	Night	41% 9% 14% 22% 13% 2	1520
	21st to end	Night	44% 9% 13% 22% 11%	1520
July	1st to 10th	Night	39% 9% 15% 20% 16% 1	2480
	11th to 20th	Night	32% 12% 17% 27% 12%	2472
	21st to end	Night	36% 8% 13% 31% 11% 1	2651
August	1st to 10th	Night	38% 9% 17% 27% 9%	2638
	11th to 20th	Night	42% 10% 15% 27% 6%	2908
	21st to end	Night	33% 11% 14% 33% 8% 1	3476
September	1st to 10th	Night	37% 9% 13% 28% 11% 1	1900
	11th to 20th	Night	36% 6% 13% 31% 13% 1	1913
	21st to end	Night	43% 8% 12% 24% 12% 1	2123
October	1st to 10th	Night	45% 9% 11% 24% 10% 1	3800
	11th to 20th	Night	44% 7% 14% 22% 11% 2	3779
	21st to end	Night	49% 9% 13% 23% 5% 1	4357
November	1st to 10th	Night	53% 8% 11% 17% 9% 2	2537
	11th to 20th	Night	56% 8% 10% 15% 8% 2	2710
	21st to end	Night	67% 9% 9% 12% 3	2800
December	1st to 10th	Night	72% 10% 10% 7% 1	4580
	11th to 20th	Night	69% 8% 8% 11% 5%	5208
	21st to end	Night	70% 6% 7% 7% 8% 1	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	27% 26% 31% 12% 4 1	200
	11th to 20th	Day	30% 28% 33% 9% 1 1	200
	21st to end	Day	22% 28% 36% 12% 2	254
February	1st to 10th	Day	35% 30% 30% 6%	270
	11th to 20th	Day	30% 35% 31% 4	319
	21st to end	Day	35% 26% 31% 8% 1	382
March	1st to 10th	Day	27% 27% 32% 11% 4	460
	11th to 20th	Day	28% 27% 32% 11% 2	460
	21st to end	Day	32% 25% 27% 11% 4 1	506
April	1st to 10th	Day	34% 26% 22% 13% 4	460
	11th to 20th	Day	33% 24% 22% 13% 6% 3	452
	21st to end	Day	31% 23% 28% 12% 5% 2	460
May	1st to 10th	Day	27% 24% 29% 12% 7% 2	463
	11th to 20th	Day	20% 17% 34% 22% 6% 2	487
	21st to end	Day	18% 17% 34% 18% 11% 2	529
June	1st to 10th	Day	24% 18% 30% 21% 5% 1	490
	11th to 20th	Day	17% 19% 34% 19% 9% 2	490
	21st to end	Day	20% 20% 34% 20% 6% 1	490
July	1st to 10th	Day	12% 12% 36% 24% 13% 3	485
	11th to 20th	Day	12% 12% 33% 28% 13% 2	484
	21st to end	Day	13% 12% 39% 28% 8% 1	532
August	1st to 10th	Day	13% 13% 31% 27% 12% 5%	486
	11th to 20th	Day	15% 11% 29% 28% 13% 5%	479
	21st to end	Day	17% 14% 31% 21% 12% 4	539
September	1st to 10th	Day	14% 17% 28% 23% 12% 6%	490
	11th to 20th	Day	13% 13% 26% 19% 19% 11%	490
	21st to end	Day	18% 17% 29% 21% 11% 3	490
October	1st to 10th	Day	24% 18% 28% 16% 10% 3	490
	11th to 20th	Day	22% 28% 29% 14% 5% 1	490
	21st to end	Day	32% 22% 28% 16% 2	466
November	1st to 10th	Day	27% 24% 29% 15% 5%	395
	11th to 20th	Day	27% 30% 27% 13% 3 1	288
	21st to end	Day	32% 24% 37% 8%	200
December	1st to 10th	Day	36% 26% 25% 13% 2	200
	11th to 20th	Day	32% 32% 28% 7% 2	200
	21st to end	Day	27% 32% 30% 9% 1	220
January	1st to 10th	Night	25% 30% 32% 12% 2	800
	11th to 20th	Night	20% 32% 31% 13% 3	800
	21st to end	Night	16% 28% 36% 17% 3	841
February	1st to 10th	Night	22% 27% 36% 13% 1	760
	11th to 20th	Night	21% 30% 35% 13% 2	743
	21st to end	Night	25% 27% 31% 15% 2	628
March	1st to 10th	Night	24% 25% 34% 15% 2	760
	11th to 20th	Night	26% 26% 27% 18% 3	760
	21st to end	Night	23% 25% 30% 15% 6%	836
April	1st to 10th	Night	26% 22% 32% 19% 1	760
	11th to 20th	Night	24% 23% 30% 17% 5% 1	751
	21st to end	Night	26% 17% 29% 21% 6% 1	734
May	1st to 10th	Night	23% 14% 30% 27% 6% 1	386
	11th to 20th	Night	16% 17% 33% 28% 6% 1	374
	21st to end	Night	14% 9% 37% 29% 10% 1	411
June	1st to 10th	Night	18% 12% 29% 33% 7% 1	380
	11th to 20th	Night	17% 9% 29% 33% 12%	380
	21st to end	Night	17% 9% 33% 33% 7%	380
July	1st to 10th	Night	6% 8% 30% 43% 12% 1	370
	11th to 20th	Night	11% 6% 28% 36% 17% 1	368
	21st to end	Night	10% 6% 32% 39% 11% 1	416
August	1st to 10th	Night	14% 8% 25% 38% 15% 1	455
	11th to 20th	Night	14% 5% 25% 33% 21% 2	621
	21st to end	Night	12% 8% 28% 36% 15% 1	836
September	1st to 10th	Night	14% 11% 28% 30% 15% 2	760
	11th to 20th	Night	16% 7% 24% 29% 19% 4	760
	21st to end	Night	18% 13% 27% 24% 16% 1	760
October	1st to 10th	Night	24% 16% 26% 19% 13% 1	760
	11th to 20th	Night	23% 18% 28% 23% 7% 1	760
	21st to end	Night	29% 20% 31% 17% 2	836
November	1st to 10th	Night	25% 18% 32% 19% 5%	780
	11th to 20th	Night	24% 24% 30% 15% 6% 1	800
	21st to end	Night	26% 28% 27% 16% 3	800
December	1st to 10th	Night	26% 28% 31% 12% 2	800
	11th to 20th	Night	27% 28% 30% 13% 2 1	800
	21st to end	Night	28% 30% 29% 11% 2	880

Page generated at 2025-01-19 03:06:45. Version ac07

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