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 2024-10-20.

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	20% 10% 3 8% 5% 4 4 3 5% 6% 31%	101888
	Night	20% 11% 3 8% 5% 4 4 3 4 5% 32%	96851
Transparency	Day	53% 8% 12% 16% 9% 2	101646
	Night	53% 8% 13% 16% 8% 2	96739
Seeing	Day	24% 13% 23% 25% 13% 3	15100
	Night	26% 8% 18% 29% 17% 2	23432

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	36% 16% 3 11% 6% 5% 5% 3 4 3 8%	2351
	11th to 20th	Day	31% 14% 4 8% 4 4 4 3 4 5% 19%	2516
	21st to end	Day	33% 15% 5% 11% 6% 6% 4 3 3 4 10%	2987
February	1st to 10th	Day	30% 14% 3 11% 7% 5% 4 3 5% 6% 13%	1710
	11th to 20th	Day	30% 14% 5% 9% 6% 5% 4 3 4 5% 15%	1665
	21st to end	Day	28% 17% 4 9% 5% 5% 5% 4 4 6% 15%	1460
March	1st to 10th	Day	19% 17% 5% 12% 8% 6% 6% 4 4 4 15%	3283
	11th to 20th	Day	20% 10% 4 8% 5% 5% 4 3 4 4 32%	3490
	21st to end	Day	23% 14% 4 12% 7% 6% 5% 4 5% 6% 15%	3907
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	20% 11% 3 9% 5% 4 4 4 4 6% 31%	1900
	11th to 20th	Day	22% 8% 4 10% 6% 5% 5% 3 6% 7% 25%	1891
	21st to end	Day	28% 11% 4 9% 5% 4 4 3 5% 5% 22%	1918
November	1st to 10th	Day	29% 14% 5% 10% 7% 5% 4 3 4 4 16%	1524
	11th to 20th	Day	34% 11% 3 9% 5% 4 5% 3 5% 5% 16%	1520
	21st to end	Day	30% 13% 3 9% 6% 5% 5% 2 4 4 19%	1520
December	1st to 10th	Day	27% 12% 5% 10% 5% 5% 5% 3 3 4 21%	1520
	11th to 20th	Day	27% 14% 4 12% 7% 6% 4 4 5% 5% 11%	1925
	21st to end	Day	28% 14% 5% 13% 7% 6% 5% 3 4 4 10%	2652
January	1st to 10th	Night	34% 17% 6% 11% 6% 4 4 2 3 3 10%	4569
	11th to 20th	Night	27% 14% 3 8% 5% 4 4 3 5% 7% 19%	4382
	21st to end	Night	33% 16% 4 10% 6% 5% 4 3 4 5% 12%	4672
February	1st to 10th	Night	29% 13% 4 9% 5% 5% 5% 3 5% 6% 17%	2470
	11th to 20th	Night	26% 13% 4 9% 6% 4 4 3 4 5% 22%	2402
	21st to end	Night	26% 14% 4 10% 5% 4 5% 3 5% 5% 19%	1992
March	1st to 10th	Night	18% 15% 5% 12% 6% 6% 5% 3 5% 6% 18%	3586
	11th to 20th	Night	19% 10% 3 7% 4 3 5% 4 4 5% 37%	3489
	21st to end	Night	27% 16% 5% 11% 6% 5% 4 3 4 4 16%	3746
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	17% 7% 3 6% 5% 4 5% 3 4 5% 41%	2280
	11th to 20th	Night	21% 8% 3 7% 4 4 3 4 4 6% 35%	2273
	21st to end	Night	25% 8% 3 7% 4 5% 3 3 5% 5% 32%	2437
November	1st to 10th	Night	31% 9% 3 9% 6% 5% 4 3 4 5% 20%	2553
	11th to 20th	Night	30% 12% 3 8% 6% 5% 5% 3 4 5% 20%	2660
	21st to end	Night	26% 11% 3 8% 7% 5% 5% 4 5% 5% 22%	2660
December	1st to 10th	Night	27% 12% 4 7% 5% 4 5% 4 5% 5% 23%	2660
	11th to 20th	Night	28% 13% 5% 11% 7% 5% 5% 3 5% 5% 14%	3280
	21st to end	Night	26% 15% 6% 12% 6% 5% 5% 4 4 4 14%	4990

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 1	2351
	11th to 20th	Day	67% 7% 10% 11% 3 2	2540
	21st to end	Day	77% 8% 5% 7% 3	2987
February	1st to 10th	Day	71% 9% 9% 8% 4	1710
	11th to 20th	Day	70% 9% 8% 9% 4 1	1674
	21st to end	Day	69% 8% 9% 9% 5%	1460
March	1st to 10th	Day	65% 11% 13% 9% 2	3283
	11th to 20th	Day	55% 6% 12% 25% 1 1	3490
	21st to end	Day	68% 10% 12% 9%	3907
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	52% 7% 11% 20% 9% 1	1900
	11th to 20th	Day	55% 10% 15% 14% 6% 1	1891
	21st to end	Day	61% 8% 10% 13% 8%	1918
November	1st to 10th	Day	71% 8% 9% 9% 2	1524
	11th to 20th	Day	69% 8% 9% 7% 5% 2	1520
	21st to end	Day	67% 7% 6% 11% 9% 1	1520
December	1st to 10th	Day	65% 8% 7% 11% 8% 1	1520
	11th to 20th	Day	67% 15% 8% 8% 2	1928
	21st to end	Day	71% 11% 11% 5% 2	2652
January	1st to 10th	Night	78% 9% 6% 4 2 1	4569
	11th to 20th	Night	62% 8% 12% 14% 3 1	4420
	21st to end	Night	75% 7% 7% 7% 4 1	4672
February	1st to 10th	Night	67% 8% 10% 10% 4 1	2470
	11th to 20th	Night	64% 8% 12% 9% 6% 1	2404
	21st to end	Night	67% 8% 11% 9% 5%	1992
March	1st to 10th	Night	63% 8% 13% 12% 3	3586
	11th to 20th	Night	46% 10% 18% 24% 2 1	3490
	21st to end	Night	71% 9% 12% 8% 1	3746
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	44% 7% 13% 25% 10% 1	2280
	11th to 20th	Night	51% 7% 13% 21% 7% 1	2273
	21st to end	Night	54% 6% 12% 17% 11%	2437
November	1st to 10th	Night	64% 8% 11% 12% 5%	2553
	11th to 20th	Night	66% 9% 9% 9% 5% 2	2660
	21st to end	Night	62% 9% 10% 9% 9% 1	2660
December	1st to 10th	Night	63% 9% 9% 12% 6% 1	2660
	11th to 20th	Night	65% 13% 10% 8% 3	3276
	21st to end	Night	69% 13% 9% 7% 2	4990

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% 21% 16% 9% 2	180
	11th to 20th	Day	37% 15% 22% 13% 11% 2	180
	21st to end	Day	40% 13% 18% 18% 10% 2	313
February	1st to 10th	Day	43% 13% 18% 14% 11% 1	370
	11th to 20th	Day	39% 16% 22% 18% 5% 1	365
	21st to end	Day	36% 20% 21% 15% 8%	330
March	1st to 10th	Day	33% 15% 25% 19% 7% 1	460
	11th to 20th	Day	30% 17% 20% 18% 13% 3	460
	21st to end	Day	31% 18% 25% 17% 6% 2	506
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	25% 13% 21% 21% 15% 5%	487
	21st to end	Day	30% 15% 21% 20% 10% 3	433
November	1st to 10th	Day	37% 18% 17% 16% 11% 1	198
	11th to 20th	Day	39% 13% 16% 15% 11% 6%	180
	21st to end	Day	31% 19% 22% 11% 9% 9%	180
December	1st to 10th	Day	34% 16% 17% 15% 13% 4	180
	11th to 20th	Day	37% 18% 23% 14% 4 4	180
	21st to end	Day	41% 13% 21% 14% 9% 2	198
January	1st to 10th	Night	43% 11% 16% 17% 11% 2	806
	11th to 20th	Night	36% 10% 14% 23% 16% 1	760
	21st to end	Night	34% 8% 17% 24% 16% 2	836
February	1st to 10th	Night	37% 7% 17% 28% 10% 1	760
	11th to 20th	Night	34% 10% 18% 25% 12% 1	744
	21st to end	Night	36% 12% 19% 23% 10% 1	628
March	1st to 10th	Night	30% 13% 18% 25% 13% 2	760
	11th to 20th	Night	31% 11% 18% 25% 13% 1	760
	21st to end	Night	33% 11% 21% 25% 9% 1	836
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	27% 8% 14% 28% 20% 4	758
	21st to end	Night	29% 9% 19% 26% 16% 2	792
November	1st to 10th	Night	35% 9% 18% 28% 10%	740
	11th to 20th	Night	37% 8% 21% 21% 13% 1	760
	21st to end	Night	31% 9% 20% 23% 14% 3	760
December	1st to 10th	Night	31% 7% 19% 27% 15% 1	760
	11th to 20th	Night	40% 9% 18% 22% 9% 1	760
	21st to end	Night	41% 14% 19% 19% 7% 1	872

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