Centralia
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Centralia clear sky chart from 2005-11-06 to 2026-07-31.

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% 10% 3 8% 5% 5% 5% 4 5% 6% 32%	143113
	Night	19% 11% 3 8% 5% 5% 4 3 5% 6% 31%	138583
Transparency	Day	51% 8% 13% 17% 9% 2	142830
	Night	52% 9% 14% 17% 8% 1	138448
Seeing	Day	23% 13% 23% 25% 12% 3	17352
	Night	26% 8% 18% 29% 17% 2	25626

By Month

Percentage Cloud Cover NW (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	30% 17% 5% 14% 7% 6% 5% 3 4 4 6%	4397
	11th to 20th	Day	19% 11% 5% 12% 7% 5% 4 4 5% 6% 22%	4716
	21st to end	Day	23% 11% 4 11% 6% 6% 5% 4 4 5% 22%	5558
February	1st to 10th	Day	28% 13% 3 11% 7% 6% 4 4 5% 6% 13%	1890
	11th to 20th	Day	28% 15% 5% 10% 6% 5% 4 3 4 5% 16%	1845
	21st to end	Day	28% 16% 4 9% 5% 5% 4 4 3 5% 15%	1610
March	1st to 10th	Day	18% 16% 5% 12% 7% 7% 6% 4 5% 4 15%	4833
	11th to 20th	Day	22% 15% 5% 10% 5% 5% 4 3 4 4 23%	5110
	21st to end	Day	24% 14% 4 13% 7% 7% 6% 5% 5% 5% 11%	5730
April	1st to 10th	Day	26% 13% 3 9% 7% 5% 5% 4 5% 6% 16%	2520
	11th to 20th	Day	23% 12% 4 8% 5% 5% 5% 4 5% 5% 24%	2532
	21st to end	Day	20% 12% 4 10% 7% 5% 5% 4 5% 6% 24%	2730
May	1st to 10th	Day	12% 7% 3 6% 5% 4 5% 4 6% 7% 41%	8155
	11th to 20th	Day	14% 11% 4 8% 6% 6% 6% 5% 7% 7% 26%	8160
	21st to end	Day	16% 8% 3 7% 5% 5% 5% 4 6% 8% 32%	8993
June	1st to 10th	Day	21% 10% 4 7% 5% 5% 4 4 5% 7% 28%	2950
	11th to 20th	Day	20% 10% 3 8% 6% 6% 5% 5% 6% 7% 24%	3150
	21st to end	Day	13% 7% 3 9% 5% 5% 5% 4 5% 7% 37%	3150
July	1st to 10th	Day	7% 5% 2 4 3 2 2 2 3 5% 64%	6930
	11th to 20th	Day	5% 4 1 3 2 2 3 2 3 5% 69%	6559
	21st to end	Day	8% 6% 2 5% 3 3 3 3 4 6% 57%	7015
August	1st to 10th	Day	6% 5% 2 5% 3 3 3 3 4 7% 60%	4331
	11th to 20th	Day	9% 7% 3 8% 5% 5% 6% 4 6% 8% 39%	4156
	21st to end	Day	15% 8% 3 7% 4 4 4 3 4 6% 43%	4485
September	1st to 10th	Day	10% 7% 3 6% 4 4 4 3 5% 7% 47%	2400
	11th to 20th	Day	12% 8% 4 7% 6% 5% 4 4 5% 7% 38%	2395
	21st to end	Day	16% 7% 3 7% 4 5% 4 4 5% 7% 38%	2105
October	1st to 10th	Day	15% 8% 3 7% 5% 4 4 4 6% 8% 36%	3280
	11th to 20th	Day	22% 9% 4 10% 5% 5% 4 3 6% 8% 24%	3261
	21st to end	Day	24% 10% 4 10% 5% 5% 6% 4 7% 6% 19%	3439
November	1st to 10th	Day	28% 13% 5% 9% 7% 5% 4 4 5% 5% 15%	1688
	11th to 20th	Day	33% 11% 3 10% 6% 5% 5% 3 4 5% 15%	1680
	21st to end	Day	29% 13% 3 9% 6% 5% 5% 3 4 5% 18%	1680
December	1st to 10th	Day	22% 9% 3 9% 7% 7% 5% 4 5% 5% 23%	2700
	11th to 20th	Day	30% 14% 5% 12% 8% 6% 5% 4 5% 4 9%	3105
	21st to end	Day	31% 15% 5% 13% 6% 5% 5% 3 4 4 9%	3875
January	1st to 10th	Night	32% 16% 6% 13% 7% 5% 4 3 4 3 8%	8473
	11th to 20th	Night	18% 11% 3 10% 6% 6% 5% 4 5% 7% 25%	8182
	21st to end	Night	23% 13% 4 9% 6% 5% 5% 4 5% 6% 22%	8638
February	1st to 10th	Night	27% 13% 4 9% 5% 6% 5% 3 5% 6% 17%	2730
	11th to 20th	Night	25% 13% 4 9% 6% 4 4 3 5% 5% 22%	2662
	21st to end	Night	26% 14% 4 10% 5% 4 5% 3 5% 5% 19%	2194
March	1st to 10th	Night	16% 14% 4 11% 6% 7% 7% 4 6% 6% 19%	5276
	11th to 20th	Night	22% 13% 4 9% 4 4 5% 4 4 5% 27%	5109
	21st to end	Night	26% 15% 5% 12% 6% 5% 5% 3 4 4 13%	5487
April	1st to 10th	Night	22% 12% 4 9% 6% 5% 4 4 5% 5% 23%	2100
	11th to 20th	Night	18% 11% 3 9% 6% 5% 4 4 5% 6% 29%	2035
	21st to end	Night	20% 10% 3 7% 5% 4 4 3 5% 7% 33%	1890
May	1st to 10th	Night	11% 7% 2 5% 3 4 5% 3 5% 6% 49%	4752
	11th to 20th	Night	13% 13% 4 9% 4 4 5% 3 5% 7% 33%	4700
	21st to end	Night	9% 8% 3 7% 5% 5% 5% 4 6% 9% 39%	5178
June	1st to 10th	Night	14% 8% 3 7% 5% 5% 4 4 5% 7% 38%	1664
	11th to 20th	Night	16% 8% 2 8% 4 3 3 3 5% 8% 40%	1470
	21st to end	Night	8% 8% 2 5% 5% 4 4 3 4 6% 50%	1470
July	1st to 10th	Night	4 3 1 3 3 2 2 2 4 5% 71%	3250
	11th to 20th	Night	2 2 1 3 2 2 3 2 3 5% 75%	3616
	21st to end	Night	4 4 1 3 2 3 3 3 5% 6% 66%	4049
August	1st to 10th	Night	4 2 1 3 2 2 2 2 4 6% 71%	2823
	11th to 20th	Night	9% 6% 2 6% 4 3 4 3 5% 7% 51%	2902
	21st to end	Night	15% 5% 2 6% 3 4 3 2 3 5% 52%	3429
September	1st to 10th	Night	7% 4 1 5% 3 3 3 3 5% 7% 59%	2000
	11th to 20th	Night	12% 7% 3 6% 4 4 4 3 4 8% 44%	2003
	21st to end	Night	13% 7% 3 6% 4 4 5% 3 5% 7% 44%	2294
October	1st to 10th	Night	12% 7% 3 6% 6% 5% 5% 3 5% 7% 42%	3920
	11th to 20th	Night	20% 9% 3 8% 5% 4 3 3 5% 7% 33%	3897
	21st to end	Night	21% 10% 3 9% 6% 6% 4 4 5% 6% 26%	4367
November	1st to 10th	Night	31% 10% 3 9% 6% 6% 4 4 4 5% 19%	2829
	11th to 20th	Night	31% 12% 3 9% 5% 5% 5% 3 4 5% 18%	2940
	21st to end	Night	26% 11% 3 9% 7% 5% 5% 4 5% 5% 21%	2940
December	1st to 10th	Night	21% 11% 3 9% 6% 5% 6% 4 5% 5% 24%	4700
	11th to 20th	Night	31% 15% 6% 11% 6% 5% 5% 3 4 4 10%	5320
	21st to end	Night	28% 15% 6% 12% 6% 6% 5% 4 4 4 11%	7294

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	79% 9% 6% 4 2	4397
	11th to 20th	Day	51% 12% 11% 14% 10% 2	4740
	21st to end	Day	59% 8% 7% 13% 11% 1	5559
February	1st to 10th	Day	69% 9% 9% 8% 4	1890
	11th to 20th	Day	69% 9% 7% 9% 4 1	1854
	21st to end	Day	70% 8% 8% 9% 5%	1610
March	1st to 10th	Day	64% 11% 13% 10% 2	4833
	11th to 20th	Day	64% 6% 10% 18% 1	5110
	21st to end	Day	71% 10% 11% 7%	5730
April	1st to 10th	Day	67% 10% 13% 9% 1	2520
	11th to 20th	Day	61% 8% 11% 12% 7% 1	2532
	21st to end	Day	62% 7% 12% 13% 5%	2730
May	1st to 10th	Day	40% 7% 17% 26% 10%	8155
	11th to 20th	Day	51% 12% 19% 15% 3	8163
	21st to end	Day	47% 10% 23% 17% 3	8994
June	1st to 10th	Day	55% 8% 16% 14% 7%	2950
	11th to 20th	Day	58% 9% 14% 14% 4	3150
	21st to end	Day	44% 9% 17% 20% 8% 1	3150
July	1st to 10th	Day	25% 5% 13% 24% 18% 15%	6856
	11th to 20th	Day	19% 4 10% 27% 35% 5%	6481
	21st to end	Day	27% 6% 17% 32% 15% 2	6822
August	1st to 10th	Day	24% 6% 11% 30% 24% 5%	4314
	11th to 20th	Day	39% 10% 18% 21% 9% 3	4195
	21st to end	Day	42% 6% 10% 25% 15% 2	4484
September	1st to 10th	Day	36% 8% 14% 23% 14% 5%	2400
	11th to 20th	Day	44% 9% 12% 18% 14% 2	2395
	21st to end	Day	45% 9% 15% 17% 12% 2	2105
October	1st to 10th	Day	41% 8% 13% 30% 8%	3280
	11th to 20th	Day	55% 8% 14% 14% 8%	3261
	21st to end	Day	59% 10% 12% 11% 8% 1	3439
November	1st to 10th	Day	70% 9% 10% 9% 2	1688
	11th to 20th	Day	70% 8% 9% 7% 5% 2	1680
	21st to end	Day	67% 8% 7% 10% 8%	1680
December	1st to 10th	Day	55% 10% 9% 13% 13%	2700
	11th to 20th	Day	72% 12% 8% 6% 1	3108
	21st to end	Day	74% 10% 10% 4 2	3875
January	1st to 10th	Night	77% 9% 7% 5% 1	8473
	11th to 20th	Night	47% 12% 13% 17% 10% 1	8220
	21st to end	Night	57% 8% 8% 16% 9%	8638
February	1st to 10th	Night	66% 9% 11% 10% 4 1	2730
	11th to 20th	Night	64% 8% 11% 9% 6% 1	2664
	21st to end	Night	66% 8% 11% 9% 5%	2194
March	1st to 10th	Night	60% 10% 14% 12% 4	5276
	11th to 20th	Night	57% 9% 14% 18% 2	5110
	21st to end	Night	71% 10% 12% 7%	5487
April	1st to 10th	Night	63% 10% 14% 12% 2	2100
	11th to 20th	Night	55% 8% 15% 13% 7% 1	2035
	21st to end	Night	53% 8% 16% 16% 6%	1890
May	1st to 10th	Night	35% 7% 18% 31% 9%	4749
	11th to 20th	Night	49% 10% 21% 14% 5%	4700
	21st to end	Night	41% 11% 26% 20% 1	5182
June	1st to 10th	Night	47% 7% 18% 22% 6%	1664
	11th to 20th	Night	44% 9% 21% 21% 5%	1470
	21st to end	Night	35% 8% 22% 25% 8% 2	1470
July	1st to 10th	Night	17% 6% 19% 28% 13% 17%	3215
	11th to 20th	Night	15% 3 10% 32% 36% 3	3571
	21st to end	Night	18% 7% 19% 37% 15% 3	3937
August	1st to 10th	Night	16% 5% 13% 33% 28% 4	2815
	11th to 20th	Night	31% 11% 23% 22% 10% 3	2929
	21st to end	Night	35% 7% 14% 29% 13% 1	3429
September	1st to 10th	Night	26% 7% 19% 26% 16% 6%	2000
	11th to 20th	Night	40% 8% 12% 20% 15% 5%	2003
	21st to end	Night	40% 7% 16% 21% 14% 2	2294
October	1st to 10th	Night	37% 9% 16% 32% 6% 1	3920
	11th to 20th	Night	51% 7% 14% 21% 6% 1	3897
	21st to end	Night	56% 9% 12% 15% 8%	4367
November	1st to 10th	Night	65% 8% 10% 11% 4	2829
	11th to 20th	Night	67% 9% 9% 9% 4 2	2940
	21st to end	Night	63% 10% 10% 8% 9% 1	2940
December	1st to 10th	Night	53% 11% 11% 17% 8%	4700
	11th to 20th	Night	73% 10% 9% 6% 2	5316
	21st to end	Night	71% 12% 9% 6% 1	7294

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	39% 13% 24% 15% 8% 1	220
	11th to 20th	Day	33% 15% 20% 13% 15% 5%	220
	21st to end	Day	36% 12% 19% 18% 11% 3	370
February	1st to 10th	Day	40% 14% 19% 15% 11% 1	430
	11th to 20th	Day	38% 16% 23% 17% 5%	425
	21st to end	Day	38% 19% 20% 15% 7%	384
March	1st to 10th	Day	33% 17% 24% 19% 6% 1	540
	11th to 20th	Day	34% 18% 19% 16% 11% 2	540
	21st to end	Day	32% 18% 25% 17% 6% 2	594
April	1st to 10th	Day	32% 16% 21% 21% 8% 2	540
	11th to 20th	Day	27% 20% 25% 16% 8% 5%	532
	21st to end	Day	25% 17% 27% 19% 10% 1	540
May	1st to 10th	Day	18% 13% 28% 25% 13% 2	543
	11th to 20th	Day	26% 15% 23% 22% 11% 3	568
	21st to end	Day	21% 12% 27% 27% 11% 3	617
June	1st to 10th	Day	22% 14% 24% 26% 11% 3	580
	11th to 20th	Day	19% 17% 32% 24% 7% 1	780
	21st to end	Day	12% 12% 26% 33% 14% 2	780
July	1st to 10th	Day	12% 7% 27% 37% 14% 2	771
	11th to 20th	Day	10% 6% 27% 38% 18% 2	608
	21st to end	Day	6% 6% 21% 39% 22% 5%	616
August	1st to 10th	Day	11% 6% 19% 41% 18% 5%	527
	11th to 20th	Day	6% 5% 19% 40% 22% 7%	517
	21st to end	Day	13% 9% 23% 32% 17% 5%	583
September	1st to 10th	Day	12% 8% 25% 35% 16% 4	530
	11th to 20th	Day	16% 8% 23% 34% 17% 3	530
	21st to end	Day	17% 13% 24% 26% 18% 2	530
October	1st to 10th	Day	23% 13% 23% 21% 17% 2	530
	11th to 20th	Day	27% 12% 21% 21% 15% 4	530
	21st to end	Day	30% 17% 21% 19% 10% 3	513
November	1st to 10th	Day	36% 20% 18% 15% 10% 1	242
	11th to 20th	Day	40% 13% 17% 16% 9% 5%	220
	21st to end	Day	30% 18% 24% 10% 11% 7%	220
December	1st to 10th	Day	35% 15% 17% 14% 13% 6%	220
	11th to 20th	Day	41% 17% 23% 12% 4 3	220
	21st to end	Day	42% 13% 19% 13% 9% 3	242
January	1st to 10th	Night	42% 12% 17% 17% 10% 2	896
	11th to 20th	Night	34% 10% 14% 24% 16% 2	840
	21st to end	Night	32% 7% 18% 25% 16% 2	924
February	1st to 10th	Night	35% 8% 18% 27% 10% 1	840
	11th to 20th	Night	33% 11% 19% 25% 12% 1	824
	21st to end	Night	36% 12% 20% 23% 9% 1	692
March	1st to 10th	Night	30% 13% 19% 26% 12% 2	840
	11th to 20th	Night	33% 12% 18% 24% 12% 1	840
	21st to end	Night	33% 11% 23% 24% 8% 1	924
April	1st to 10th	Night	29% 10% 20% 27% 13% 1	840
	11th to 20th	Night	22% 11% 24% 28% 13% 2	787
	21st to end	Night	25% 8% 18% 34% 13% 1	630
May	1st to 10th	Night	17% 7% 22% 35% 19% 1	435
	11th to 20th	Night	22% 5% 18% 34% 20% 2	414
	21st to end	Night	15% 6% 21% 37% 19% 1	455
June	1st to 10th	Night	17% 6% 20% 37% 19% 1	420
	11th to 20th	Night	19% 6% 23% 38% 14%	420
	21st to end	Night	13% 2 21% 43% 21%	420
July	1st to 10th	Night	8% 3 15% 46% 27%	410
	11th to 20th	Night	7% 3 17% 49% 23% 1	408
	21st to end	Night	5% 2 15% 44% 33% 2	458
August	1st to 10th	Night	10% 2 11% 38% 37% 4	521
	11th to 20th	Night	8% 3 7% 37% 40% 5%	594
	21st to end	Night	11% 4 15% 42% 27% 1	766
September	1st to 10th	Night	11% 4 16% 40% 28% 3	800
	11th to 20th	Night	14% 5% 16% 30% 31% 4	800
	21st to end	Night	16% 7% 17% 39% 20% 2	800
October	1st to 10th	Night	19% 7% 17% 31% 25% 2	800
	11th to 20th	Night	26% 9% 15% 27% 19% 4	800
	21st to end	Night	27% 10% 20% 27% 15% 2	880
November	1st to 10th	Night	35% 10% 18% 27% 10%	820
	11th to 20th	Night	39% 8% 20% 20% 12% 1	840
	21st to end	Night	31% 9% 20% 23% 13% 3	840
December	1st to 10th	Night	32% 7% 18% 26% 15% 2	840
	11th to 20th	Night	41% 10% 18% 21% 9% 1	840
	21st to end	Night	40% 15% 19% 19% 7% 1	968

Page generated at 2026-07-28 00:25:26. Version ac07

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