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 2024-02-15.

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	22% 10% 4 7% 6% 3 5% 4 5% 6% 27%	78498
	Night	22% 10% 4 7% 6% 3 4 4 4 6% 29%	80495
Transparency	Day	57% 8% 12% 15% 7% 1	78217
	Night	56% 8% 12% 15% 7% 1	80356
Seeing	Day	24% 12% 23% 25% 13% 3	14087
	Night	27% 8% 17% 29% 17% 2	22665

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% 4 9% 8% 4 5% 4 4 3 8%	2351
	11th to 20th	Day	31% 13% 4 7% 6% 3 3 4 4 5% 19%	2516
	21st to end	Day	34% 14% 6% 9% 8% 4 4 4 3 4 10%	2987
February	1st to 10th	Day	30% 12% 4 10% 8% 4 4 4 5% 6% 13%	1710
	11th to 20th	Day	30% 13% 5% 8% 8% 3 4 4 4 5% 16%	1612
	21st to end	Day	28% 15% 5% 8% 6% 4 5% 5% 4 6% 16%	1376
March	1st to 10th	Day	26% 14% 5% 8% 8% 4 6% 5% 5% 4 15%	1880
	11th to 20th	Day	30% 12% 5% 9% 7% 4 5% 3 4 4 17%	1980
	21st to end	Day	27% 13% 5% 9% 8% 5% 6% 5% 5% 5% 10%	2222
April	1st to 10th	Day	29% 12% 4 8% 7% 4 5% 5% 5% 6% 15%	2160
	11th to 20th	Day	26% 12% 4 7% 6% 4 6% 5% 5% 5% 20%	2166
	21st to end	Day	21% 11% 4 9% 8% 4 5% 5% 5% 6% 22%	2340
May	1st to 10th	Day	17% 9% 4 7% 7% 3 5% 6% 5% 5% 32%	2506
	11th to 20th	Day	20% 9% 4 6% 7% 4 6% 6% 7% 6% 25%	2477
	21st to end	Day	23% 9% 5% 7% 7% 4 5% 5% 5% 6% 24%	2723
June	1st to 10th	Day	24% 10% 4 7% 6% 4 4 5% 5% 7% 25%	2528
	11th to 20th	Day	23% 10% 4 8% 7% 4 6% 6% 5% 6% 21%	2700
	21st to end	Day	13% 6% 4 7% 5% 4 6% 5% 5% 7% 39%	2700
July	1st to 10th	Day	11% 6% 3 5% 6% 3 3 4 4 6% 50%	2700
	11th to 20th	Day	12% 6% 3 4 4 2 4 3 5% 7% 50%	2561
	21st to end	Day	8% 5% 2 4 3 2 3 3 4 6% 59%	2741
August	1st to 10th	Day	11% 7% 3 5% 4 2 3 4 5% 7% 49%	2395
	11th to 20th	Day	8% 5% 2 4 4 2 4 4 5% 8% 54%	2298
	21st to end	Day	11% 6% 3 7% 5% 3 6% 4 5% 8% 42%	2479
September	1st to 10th	Day	10% 6% 3 5% 5% 3 4 4 5% 6% 48%	2160
	11th to 20th	Day	12% 7% 4 6% 6% 4 5% 5% 4 7% 38%	2156
	21st to end	Day	16% 7% 3 6% 5% 4 5% 4 5% 6% 37%	1895
October	1st to 10th	Day	21% 11% 3 8% 5% 3 5% 4 5% 6% 30%	1800
	11th to 20th	Day	22% 7% 4 9% 7% 4 5% 4 5% 7% 25%	1800
	21st to end	Day	28% 10% 4 8% 6% 3 4 4 5% 6% 22%	1918
November	1st to 10th	Day	29% 13% 5% 9% 7% 3 5% 4 5% 5% 16%	1524
	11th to 20th	Day	34% 10% 4 7% 6% 3 5% 4 4 6% 16%	1520
	21st to end	Day	30% 12% 4 8% 7% 3 5% 4 4 4 19%	1520
December	1st to 10th	Day	27% 11% 5% 9% 6% 4 5% 4 3 4 21%	1520
	11th to 20th	Day	28% 14% 4 10% 9% 5% 5% 5% 5% 5% 11%	1925
	21st to end	Day	28% 13% 6% 11% 9% 4 6% 4 4 4 10%	2652
January	1st to 10th	Night	34% 17% 6% 10% 7% 3 4 3 3 3 10%	4569
	11th to 20th	Night	28% 14% 4 7% 6% 3 4 4 5% 7% 19%	4382
	21st to end	Night	33% 15% 5% 8% 7% 4 4 4 3 5% 12%	4672
February	1st to 10th	Night	29% 12% 5% 7% 6% 4 4 4 5% 6% 17%	2470
	11th to 20th	Night	26% 13% 4 8% 7% 3 4 3 4 6% 22%	2329
	21st to end	Night	26% 13% 5% 9% 6% 3 6% 4 5% 5% 20%	1878
March	1st to 10th	Night	26% 11% 4 7% 6% 4 5% 4 4 6% 23%	2075
	11th to 20th	Night	26% 11% 4 7% 6% 2 5% 6% 5% 5% 22%	1979
	21st to end	Night	26% 14% 5% 7% 7% 4 5% 5% 5% 5% 18%	2134
April	1st to 10th	Night	24% 12% 5% 8% 7% 3 5% 4 5% 5% 22%	1800
	11th to 20th	Night	20% 10% 4 8% 6% 4 5% 5% 5% 6% 27%	1742
	21st to end	Night	21% 9% 4 7% 5% 3 4 4 5% 7% 32%	1620
May	1st to 10th	Night	14% 8% 3 6% 6% 3 5% 4 5% 7% 39%	1454
	11th to 20th	Night	16% 9% 3 6% 5% 3 5% 7% 5% 7% 34%	1416
	21st to end	Night	15% 8% 4 6% 7% 4 5% 5% 5% 8% 34%	1552
June	1st to 10th	Night	15% 6% 4 6% 6% 4 4 5% 5% 7% 37%	1427
	11th to 20th	Night	18% 8% 3 8% 5% 2 4 4 5% 8% 35%	1260
	21st to end	Night	9% 7% 2 4 6% 3 4 3 4 6% 53%	1260
July	1st to 10th	Night	7% 4 2 4 4 3 4 3 5% 6% 59%	1260
	11th to 20th	Night	6% 5% 2 3 3 2 3 3 4 7% 63%	1394
	21st to end	Night	5% 3 1 2 2 1 2 2 3 5% 74%	1576
August	1st to 10th	Night	7% 2 2 4 3 2 3 3 4 8% 63%	1542
	11th to 20th	Night	5% 3 1 3 2 2 3 4 4 7% 66%	1602
	21st to end	Night	9% 4 2 5% 4 2 3 3 4 5% 58%	1876
September	1st to 10th	Night	8% 4 1 4 3 2 2 4 4 6% 61%	1800
	11th to 20th	Night	12% 6% 3 6% 5% 3 4 4 4 8% 44%	1802
	21st to end	Night	14% 7% 3 5% 5% 3 5% 5% 5% 7% 44%	2064
October	1st to 10th	Night	17% 7% 3 6% 5% 3 5% 4 4 5% 41%	2160
	11th to 20th	Night	21% 8% 3 6% 6% 3 4 4 4 6% 36%	2160
	21st to end	Night	25% 8% 3 7% 5% 4 4 4 4 5% 32%	2437
November	1st to 10th	Night	31% 9% 3 8% 6% 4 5% 4 4 5% 20%	2553
	11th to 20th	Night	30% 10% 4 8% 6% 4 5% 4 4 5% 20%	2660
	21st to end	Night	26% 10% 3 7% 7% 4 5% 5% 5% 5% 22%	2660
December	1st to 10th	Night	28% 10% 5% 7% 5% 3 6% 5% 5% 5% 23%	2660
	11th to 20th	Night	28% 12% 5% 9% 9% 4 5% 4 5% 5% 14%	3280
	21st to end	Night	27% 14% 6% 11% 7% 4 5% 5% 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	69% 9% 8% 9% 4 1	1621
	21st to end	Day	69% 8% 9% 9% 6%	1376
March	1st to 10th	Day	69% 9% 9% 10% 3	1880
	11th to 20th	Day	72% 5% 9% 11% 2 1	1980
	21st to end	Day	75% 9% 9% 7%	2222
April	1st to 10th	Day	70% 8% 12% 8% 1	2160
	11th to 20th	Day	66% 7% 10% 10% 6% 1	2166
	21st to end	Day	65% 7% 12% 11% 5%	2340
May	1st to 10th	Day	54% 8% 15% 17% 5%	2506
	11th to 20th	Day	57% 9% 16% 13% 4	2480
	21st to end	Day	61% 9% 14% 14% 2	2724
June	1st to 10th	Day	60% 8% 16% 11% 5%	2528
	11th to 20th	Day	63% 10% 15% 10% 3	2700
	21st to end	Day	43% 9% 18% 20% 8% 2	2700
July	1st to 10th	Day	38% 7% 13% 24% 16% 3	2626
	11th to 20th	Day	35% 6% 12% 27% 19% 2	2483
	21st to end	Day	26% 5% 12% 33% 20% 4	2589
August	1st to 10th	Day	34% 7% 15% 26% 15% 3	2378
	11th to 20th	Day	28% 8% 17% 29% 14% 5%	2298
	21st to end	Day	41% 7% 12% 28% 11% 1	2479
September	1st to 10th	Day	35% 8% 14% 24% 15% 5%	2160
	11th to 20th	Day	45% 10% 12% 18% 14% 3	2156
	21st to end	Day	46% 9% 15% 15% 13% 2	1895
October	1st to 10th	Day	53% 7% 11% 19% 8% 1	1800
	11th to 20th	Day	55% 10% 15% 14% 6% 1	1800
	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	2331
	21st to end	Night	67% 8% 10% 9% 6%	1878
March	1st to 10th	Night	63% 6% 13% 13% 4	2075
	11th to 20th	Night	64% 9% 10% 13% 3 1	1980
	21st to end	Night	69% 10% 13% 8% 1	2134
April	1st to 10th	Night	65% 9% 13% 11% 2	1800
	11th to 20th	Night	58% 7% 14% 13% 6% 1	1742
	21st to end	Night	54% 8% 17% 14% 7% 1	1620
May	1st to 10th	Night	46% 9% 18% 18% 8% 1	1454
	11th to 20th	Night	50% 9% 17% 17% 5% 2	1416
	21st to end	Night	50% 11% 19% 17% 4	1552
June	1st to 10th	Night	49% 7% 17% 22% 5%	1427
	11th to 20th	Night	49% 9% 23% 17% 3	1260
	21st to end	Night	34% 7% 23% 25% 8% 3	1260
July	1st to 10th	Night	28% 6% 19% 26% 15% 5%	1225
	11th to 20th	Night	25% 5% 15% 33% 21% 2	1349
	21st to end	Night	15% 4 13% 38% 22% 8%	1488
August	1st to 10th	Night	22% 7% 19% 28% 20% 5%	1534
	11th to 20th	Night	19% 6% 20% 33% 17% 5%	1602
	21st to end	Night	29% 5% 17% 33% 14% 1	1876
September	1st to 10th	Night	26% 7% 18% 27% 16% 6%	1800
	11th to 20th	Night	40% 8% 12% 20% 15% 5%	1802
	21st to end	Night	41% 7% 14% 20% 16% 2	2064
October	1st to 10th	Night	45% 8% 12% 24% 10% 1	2160
	11th to 20th	Night	50% 7% 13% 21% 7% 1	2160
	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	40% 16% 20% 19% 5% 1	348
	21st to end	Day	36% 20% 21% 15% 8%	300
March	1st to 10th	Day	34% 15% 25% 19% 7% 1	420
	11th to 20th	Day	31% 18% 20% 18% 11% 2	420
	21st to end	Day	33% 17% 24% 17% 6% 2	462
April	1st to 10th	Day	36% 16% 20% 18% 8% 1	420
	11th to 20th	Day	32% 19% 24% 14% 6% 5%	412
	21st to end	Day	26% 19% 27% 18% 10% 1	420
May	1st to 10th	Day	20% 12% 28% 26% 12% 2	423
	11th to 20th	Day	27% 12% 24% 22% 12% 3	448
	21st to end	Day	22% 11% 27% 27% 11% 2	485
June	1st to 10th	Day	25% 13% 23% 25% 11% 3	458
	11th to 20th	Day	21% 18% 29% 24% 7% 1	630
	21st to end	Day	12% 11% 26% 33% 15% 3	630
July	1st to 10th	Day	12% 7% 24% 39% 15% 3	621
	11th to 20th	Day	10% 5% 27% 37% 18% 2	482
	21st to end	Day	7% 4 20% 41% 23% 5%	487
August	1st to 10th	Day	13% 5% 18% 39% 20% 6%	447
	11th to 20th	Day	6% 4 17% 42% 24% 7%	437
	21st to end	Day	13% 9% 25% 32% 16% 5%	495
September	1st to 10th	Day	12% 9% 27% 35% 14% 3	450
	11th to 20th	Day	16% 7% 21% 35% 18% 3	450
	21st to end	Day	18% 13% 21% 27% 19% 1	450
October	1st to 10th	Day	25% 12% 22% 20% 17% 3	450
	11th to 20th	Day	26% 12% 20% 22% 16% 5%	450
	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% 13% 1	722
	21st to end	Night	36% 11% 19% 23% 10% 1	592
March	1st to 10th	Night	31% 12% 17% 25% 13% 2	720
	11th to 20th	Night	32% 12% 19% 24% 13% 1	720
	21st to end	Night	34% 10% 20% 26% 9% 1	792
April	1st to 10th	Night	32% 9% 19% 26% 13% 1	720
	11th to 20th	Night	24% 11% 23% 26% 14% 2	674
	21st to end	Night	26% 7% 18% 34% 14% 1	540
May	1st to 10th	Night	18% 7% 22% 33% 19%	374
	11th to 20th	Night	21% 5% 16% 34% 21% 2	354
	21st to end	Night	17% 6% 20% 36% 20% 1	389
June	1st to 10th	Night	18% 6% 19% 38% 20% 1	360
	11th to 20th	Night	21% 6% 21% 37% 14% 1	360
	21st to end	Night	13% 2 21% 42% 22% 1	360
July	1st to 10th	Night	9% 3 13% 46% 28%	350
	11th to 20th	Night	8% 2 14% 50% 24% 2	348
	21st to end	Night	6% 1 13% 45% 35% 1	394
August	1st to 10th	Night	10% 1 11% 36% 38% 4	468
	11th to 20th	Night	8% 2 6% 37% 42% 5%	534
	21st to end	Night	11% 3 15% 42% 27% 2	688
September	1st to 10th	Night	11% 3 16% 40% 27% 3	720
	11th to 20th	Night	14% 4 15% 29% 33% 4	720
	21st to end	Night	16% 6% 16% 40% 21% 2	720
October	1st to 10th	Night	20% 6% 16% 31% 25% 2	720
	11th to 20th	Night	26% 8% 14% 28% 20% 4	720
	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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