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 2025-03-27.

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	19% 10% 3 8% 5% 5% 4 4 5% 6% 30%	113411
	Night	20% 11% 3 8% 5% 4 4 3 4 5% 31%	114558
Transparency	Day	53% 8% 12% 16% 9% 2	113169
	Night	53% 9% 13% 16% 8% 2	114446
Seeing	Day	24% 13% 23% 25% 13% 3	15528
	Night	27% 8% 18% 29% 17% 2	24073

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	33% 17% 4 13% 7% 6% 5% 3 4 3 6%	3381
	11th to 20th	Day	22% 13% 5% 11% 6% 5% 4 4 5% 6% 20%	3616
	21st to end	Day	25% 11% 4 10% 5% 6% 4 4 3 5% 23%	4295
February	1st to 10th	Day	28% 13% 3 11% 7% 5% 4 4 5% 6% 13%	1800
	11th to 20th	Day	29% 14% 5% 10% 6% 5% 4 3 4 4 16%	1755
	21st to end	Day	28% 16% 4 9% 5% 5% 4 4 4 5% 16%	1535
March	1st to 10th	Day	18% 17% 5% 12% 8% 6% 6% 4 5% 4 15%	3388
	11th to 20th	Day	20% 11% 4 9% 6% 5% 4 3 4 4 31%	3600
	21st to end	Day	23% 14% 4 12% 7% 6% 5% 4 5% 5% 14%	3975
April	1st to 10th	Day	28% 13% 4 9% 7% 5% 5% 4 5% 6% 15%	2280
	11th to 20th	Day	24% 12% 4 8% 5% 5% 5% 4 5% 5% 22%	2288
	21st to end	Day	21% 12% 4 10% 7% 5% 5% 4 5% 6% 21%	2470
May	1st to 10th	Day	19% 9% 3 7% 5% 3 4 4 5% 5% 36%	4406
	11th to 20th	Day	13% 9% 3 6% 5% 5% 5% 5% 7% 7% 34%	4377
	21st to end	Day	25% 10% 4 9% 6% 5% 6% 4 5% 6% 19%	4813
June	1st to 10th	Day	23% 10% 4 7% 5% 5% 4 4 5% 7% 26%	2669
	11th to 20th	Day	22% 11% 3 9% 7% 6% 5% 4 6% 6% 22%	2850
	21st to end	Day	13% 7% 3 8% 5% 5% 6% 4 5% 7% 38%	2850
July	1st to 10th	Day	8% 5% 2 5% 3 2 2 2 3 4 65%	4740
	11th to 20th	Day	7% 5% 1 3 3 3 3 2 4 5% 65%	4489
	21st to end	Day	11% 6% 2 5% 3 2 3 3 4 6% 55%	4790
August	1st to 10th	Day	6% 5% 2 4 3 3 3 3 4 7% 61%	4198
	11th to 20th	Day	9% 7% 3 8% 5% 5% 6% 4 6% 8% 39%	4026
	21st to end	Day	15% 8% 3 7% 3 4 4 3 4 6% 43%	4348
September	1st to 10th	Day	10% 7% 3 6% 4 4 4 3 5% 6% 48%	2280
	11th to 20th	Day	13% 8% 4 8% 6% 5% 4 4 5% 7% 37%	2275
	21st to end	Day	16% 7% 3 7% 5% 5% 4 4 6% 7% 37%	2000
October	1st to 10th	Day	15% 8% 3 7% 4 4 5% 4 6% 8% 36%	3180
	11th to 20th	Day	22% 9% 4 10% 5% 5% 4 3 6% 8% 24%	3161
	21st to end	Day	24% 10% 4 10% 5% 5% 6% 4 7% 6% 19%	3333
November	1st to 10th	Day	28% 13% 5% 9% 7% 5% 4 4 5% 5% 15%	1606
	11th to 20th	Day	33% 11% 3 9% 5% 5% 5% 3 5% 5% 15%	1600
	21st to end	Day	29% 13% 3 9% 6% 5% 5% 3 4 5% 18%	1600
December	1st to 10th	Day	21% 9% 3 9% 7% 7% 5% 4 5% 6% 24%	2620
	11th to 20th	Day	29% 14% 5% 12% 8% 6% 5% 4 5% 4 9%	3025
	21st to end	Day	31% 15% 5% 13% 6% 5% 5% 3 4 4 8%	3792
January	1st to 10th	Night	34% 16% 6% 13% 6% 5% 4 3 3 3 9%	6539
	11th to 20th	Night	19% 13% 3 10% 6% 5% 4 3 5% 7% 24%	6282
	21st to end	Night	25% 12% 3 8% 5% 4 4 4 5% 6% 24%	6671
February	1st to 10th	Night	28% 13% 4 9% 5% 5% 5% 3 5% 6% 17%	2600
	11th to 20th	Night	26% 13% 4 9% 6% 4 4 3 4 5% 22%	2532
	21st to end	Night	26% 14% 4 10% 5% 4 5% 3 5% 5% 19%	2093
March	1st to 10th	Night	18% 15% 5% 12% 6% 6% 5% 3 5% 6% 18%	3701
	11th to 20th	Night	19% 10% 3 7% 4 3 5% 4 4 5% 36%	3599
	21st to end	Night	27% 16% 5% 11% 6% 5% 4 3 4 4 16%	3816
April	1st to 10th	Night	24% 13% 4 9% 6% 4 4 4 5% 4 22%	1900
	11th to 20th	Night	19% 11% 3 9% 6% 5% 4 4 5% 6% 28%	1839
	21st to end	Night	21% 10% 3 8% 5% 4 4 3 5% 6% 31%	1710
May	1st to 10th	Night	19% 8% 2 6% 3 3 3 2 4 5% 43%	2554
	11th to 20th	Night	10% 10% 2 6% 3 3 4 4 5% 7% 46%	2516
	21st to end	Night	14% 10% 4 9% 6% 5% 5% 4 5% 6% 32%	2762
June	1st to 10th	Night	15% 8% 3 7% 5% 5% 4 4 5% 7% 37%	1506
	11th to 20th	Night	17% 9% 3 8% 4 3 4 3 5% 8% 36%	1330
	21st to end	Night	8% 7% 2 5% 5% 4 4 3 4 6% 52%	1330
July	1st to 10th	Night	4 3 1 4 3 2 2 2 3 4 71%	2220
	11th to 20th	Night	3 3 1 3 2 2 2 3 3 6% 72%	2466
	21st to end	Night	5% 4 1 3 2 2 2 2 4 5% 68%	2762
August	1st to 10th	Night	4 2 1 3 2 2 2 2 4 6% 72%	2737
	11th to 20th	Night	8% 6% 2 6% 4 3 4 3 5% 7% 51%	2812
	21st to end	Night	15% 5% 2 6% 3 4 3 2 3 5% 52%	3324
September	1st to 10th	Night	8% 4 1 4 3 3 3 3 5% 6% 60%	1900
	11th to 20th	Night	12% 7% 3 6% 4 4 4 3 5% 8% 43%	1903
	21st to end	Night	13% 7% 3 6% 4 4 6% 3 5% 7% 44%	2179
October	1st to 10th	Night	12% 7% 3 6% 6% 5% 5% 3 5% 7% 42%	3800
	11th to 20th	Night	20% 9% 3 8% 5% 4 3 3 5% 7% 33%	3777
	21st to end	Night	21% 10% 3 9% 6% 6% 4 4 5% 6% 26%	4231
November	1st to 10th	Night	31% 10% 3 9% 6% 6% 4 4 4 5% 20%	2691
	11th to 20th	Night	30% 12% 3 9% 6% 5% 5% 3 4 5% 19%	2800
	21st to end	Night	25% 11% 3 8% 7% 5% 5% 4 5% 5% 21%	2800
December	1st to 10th	Night	20% 10% 3 8% 6% 5% 6% 5% 5% 5% 25%	4560
	11th to 20th	Night	30% 15% 6% 12% 6% 5% 5% 3 4 4 10%	5180
	21st to end	Night	28% 15% 6% 12% 6% 6% 5% 4 4 4 11%	7136

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	78% 10% 6% 5% 2	3381
	11th to 20th	Day	58% 11% 10% 14% 6% 1	3640
	21st to end	Day	60% 8% 7% 14% 10% 1	4295
February	1st to 10th	Day	69% 10% 9% 8% 4	1800
	11th to 20th	Day	70% 9% 7% 9% 4 1	1764
	21st to end	Day	69% 7% 9% 9% 6%	1535
March	1st to 10th	Day	65% 11% 13% 9% 2	3388
	11th to 20th	Day	56% 6% 12% 24% 1 1	3600
	21st to end	Day	68% 10% 12% 9%	3975
April	1st to 10th	Day	69% 9% 13% 8% 1	2280
	11th to 20th	Day	63% 8% 11% 10% 7% 1	2288
	21st to end	Day	65% 7% 12% 11% 4	2470
May	1st to 10th	Day	48% 8% 16% 18% 10%	4406
	11th to 20th	Day	44% 12% 24% 16% 4	4380
	21st to end	Day	63% 11% 15% 9% 1	4814
June	1st to 10th	Day	59% 8% 16% 12% 6%	2669
	11th to 20th	Day	62% 10% 14% 11% 4	2850
	21st to end	Day	43% 9% 18% 20% 8% 2	2850
July	1st to 10th	Day	26% 5% 8% 18% 22% 22%	4666
	11th to 20th	Day	23% 5% 8% 24% 36% 6%	4411
	21st to end	Day	31% 5% 11% 30% 20% 3	4639
August	1st to 10th	Day	23% 6% 11% 30% 24% 5%	4181
	11th to 20th	Day	39% 10% 18% 21% 8% 3	4065
	21st to end	Day	42% 6% 10% 25% 15% 1	4347
September	1st to 10th	Day	35% 8% 14% 23% 15% 5%	2280
	11th to 20th	Day	45% 10% 12% 17% 13% 2	2275
	21st to end	Day	45% 10% 16% 16% 12% 2	2000
October	1st to 10th	Day	41% 8% 12% 30% 9% 1	3180
	11th to 20th	Day	56% 8% 15% 13% 8%	3161
	21st to end	Day	58% 10% 12% 11% 8% 1	3333
November	1st to 10th	Day	70% 8% 9% 9% 2	1606
	11th to 20th	Day	70% 8% 9% 7% 5% 2	1600
	21st to end	Day	67% 8% 6% 10% 8% 1	1600
December	1st to 10th	Day	54% 10% 9% 13% 13%	2620
	11th to 20th	Day	72% 13% 8% 6% 1	3028
	21st to end	Day	74% 10% 10% 4 2	3792
January	1st to 10th	Night	76% 10% 7% 5% 2 1	6539
	11th to 20th	Night	52% 12% 12% 17% 6% 1	6320
	21st to end	Night	58% 7% 8% 18% 9% 1	6671
February	1st to 10th	Night	67% 8% 10% 10% 4 1	2600
	11th to 20th	Night	64% 8% 11% 9% 6% 1	2534
	21st to end	Night	66% 8% 11% 9% 5%	2093
March	1st to 10th	Night	63% 8% 14% 12% 3	3701
	11th to 20th	Night	47% 10% 17% 23% 2 1	3600
	21st to end	Night	71% 9% 12% 8%	3816
April	1st to 10th	Night	65% 9% 13% 11% 2	1900
	11th to 20th	Night	57% 7% 15% 13% 7% 1	1839
	21st to end	Night	55% 8% 16% 14% 6% 1	1710
May	1st to 10th	Night	44% 7% 19% 24% 6% 1	2554
	11th to 20th	Night	36% 10% 26% 18% 9% 1	2516
	21st to end	Night	50% 15% 21% 12% 2	2762
June	1st to 10th	Night	49% 7% 17% 22% 5%	1506
	11th to 20th	Night	48% 9% 22% 18% 3	1330
	21st to end	Night	34% 8% 23% 25% 8% 3	1330
July	1st to 10th	Night	19% 5% 12% 25% 14% 24%	2185
	11th to 20th	Night	17% 3 10% 29% 38% 4	2421
	21st to end	Night	20% 5% 12% 36% 21% 5%	2674
August	1st to 10th	Night	16% 5% 12% 33% 29% 4	2729
	11th to 20th	Night	30% 11% 23% 23% 9% 3	2839
	21st to end	Night	35% 6% 14% 30% 13% 1	3324
September	1st to 10th	Night	26% 7% 18% 27% 16% 6%	1900
	11th to 20th	Night	41% 8% 12% 20% 15% 5%	1903
	21st to end	Night	40% 8% 15% 20% 15% 2	2179
October	1st to 10th	Night	37% 9% 15% 32% 6% 1	3800
	11th to 20th	Night	51% 7% 14% 21% 6% 1	3777
	21st to end	Night	56% 8% 12% 15% 9%	4231
November	1st to 10th	Night	65% 8% 11% 11% 5%	2691
	11th to 20th	Night	67% 9% 9% 9% 4 2	2800
	21st to end	Night	63% 10% 10% 8% 9% 1	2800
December	1st to 10th	Night	52% 11% 11% 18% 8%	4560
	11th to 20th	Night	73% 10% 9% 6% 2	5176
	21st to end	Night	72% 12% 9% 6% 1	7136

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	41% 12% 22% 16% 9% 2	200
	11th to 20th	Day	34% 16% 21% 14% 13% 3	200
	21st to end	Day	37% 13% 18% 18% 11% 4	342
February	1st to 10th	Day	41% 14% 18% 14% 11% 1	400
	11th to 20th	Day	39% 15% 23% 17% 6% 1	395
	21st to end	Day	37% 18% 21% 16% 7%	357
March	1st to 10th	Day	32% 16% 25% 19% 7% 1	500
	11th to 20th	Day	30% 19% 19% 17% 12% 3	500
	21st to end	Day	32% 18% 25% 17% 7% 2	531
April	1st to 10th	Day	35% 16% 21% 18% 8% 1	460
	11th to 20th	Day	30% 20% 24% 15% 6% 5%	452
	21st to end	Day	27% 18% 27% 17% 9% 1	460
May	1st to 10th	Day	19% 13% 29% 25% 12% 2	463
	11th to 20th	Day	26% 13% 23% 22% 12% 3	488
	21st to end	Day	22% 13% 26% 27% 10% 2	529
June	1st to 10th	Day	25% 12% 23% 26% 11% 3	499
	11th to 20th	Day	21% 19% 29% 24% 7% 1	680
	21st to end	Day	12% 11% 26% 33% 15% 2	680
July	1st to 10th	Day	12% 7% 26% 38% 15% 3	671
	11th to 20th	Day	10% 5% 26% 37% 19% 3	524
	21st to end	Day	7% 5% 21% 40% 22% 4	531
August	1st to 10th	Day	11% 5% 18% 41% 18% 6%	487
	11th to 20th	Day	6% 5% 17% 40% 23% 7%	477
	21st to end	Day	14% 10% 24% 31% 16% 6%	539
September	1st to 10th	Day	11% 8% 26% 36% 16% 4	490
	11th to 20th	Day	17% 7% 23% 34% 17% 3	490
	21st to end	Day	17% 13% 23% 27% 18% 1	490
October	1st to 10th	Day	24% 13% 22% 21% 17% 3	490
	11th to 20th	Day	26% 12% 21% 21% 15% 4	490
	21st to end	Day	30% 16% 21% 20% 10% 3	473
November	1st to 10th	Day	36% 20% 17% 14% 11% 1	220
	11th to 20th	Day	40% 14% 16% 15% 10% 6%	200
	21st to end	Day	30% 18% 23% 11% 11% 8%	200
December	1st to 10th	Day	33% 15% 17% 15% 15% 7%	200
	11th to 20th	Day	39% 17% 24% 13% 4 4	200
	21st to end	Day	43% 13% 20% 13% 9% 2	220
January	1st to 10th	Night	43% 12% 16% 17% 10% 2	851
	11th to 20th	Night	35% 10% 14% 24% 16% 1	800
	21st to end	Night	33% 7% 17% 24% 16% 2	880
February	1st to 10th	Night	36% 8% 18% 27% 9% 1	800
	11th to 20th	Night	33% 11% 19% 25% 11% 1	784
	21st to end	Night	37% 11% 19% 23% 9% 1	660
March	1st to 10th	Night	29% 13% 18% 27% 12% 2	800
	11th to 20th	Night	32% 12% 18% 25% 13% 1	800
	21st to end	Night	34% 11% 21% 24% 9% 1	862
April	1st to 10th	Night	31% 9% 20% 26% 13% 1	760
	11th to 20th	Night	23% 11% 24% 27% 13% 2	711
	21st to end	Night	26% 8% 18% 34% 13% 1	570
May	1st to 10th	Night	18% 7% 23% 33% 19%	394
	11th to 20th	Night	21% 5% 17% 34% 21% 2	374
	21st to end	Night	16% 6% 21% 36% 19% 1	411
June	1st to 10th	Night	18% 6% 20% 37% 19% 1	380
	11th to 20th	Night	21% 7% 23% 36% 14% 1	380
	21st to end	Night	13% 2 21% 42% 22% 1	380
July	1st to 10th	Night	8% 3 14% 47% 27%	370
	11th to 20th	Night	8% 2 14% 51% 23% 2	368
	21st to end	Night	6% 1 14% 44% 34% 1	416
August	1st to 10th	Night	10% 2 11% 37% 37% 4	495
	11th to 20th	Night	8% 2 6% 37% 41% 6%	564
	21st to end	Night	11% 3 15% 42% 27% 2	727
September	1st to 10th	Night	11% 3 15% 40% 28% 3	760
	11th to 20th	Night	15% 5% 15% 29% 32% 4	760
	21st to end	Night	16% 6% 17% 39% 20% 2	760
October	1st to 10th	Night	19% 6% 16% 31% 25% 2	760
	11th to 20th	Night	26% 8% 15% 28% 20% 4	760
	21st to end	Night	28% 9% 19% 26% 16% 2	836
November	1st to 10th	Night	35% 9% 18% 27% 10%	780
	11th to 20th	Night	38% 8% 20% 20% 13% 1	800
	21st to end	Night	31% 9% 20% 23% 14% 3	800
December	1st to 10th	Night	30% 8% 18% 27% 16% 2	800
	11th to 20th	Night	40% 10% 18% 22% 9% 1	800
	21st to end	Night	41% 15% 18% 19% 6% 1	920

Page generated at 2025-03-24 06:04:28. Version ac07

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